阅读说明：本技术 带单元、图像形成装置以及标记形成方法 (Belt unit, image forming apparatus, and mark forming method ) 是由 高泽贵之 于 2019-07-19 设计创作，主要内容包括：本发明的一种带单元具备：带,为环形且具有外周面、内周面以及标记部,外周面形成为平坦状,内周面位于外周面的相反侧,标记部形成在外周面上且从外周面向内周面凹陷；驱动辊,与内周面抵接,并且使带在第一方向上运行；以及从动辊,与内周面抵接。标记部具有多个槽,多个槽沿着第一方向延伸。多个槽中的2个以上的槽各自包括中央部和缘部,中央部远离2个以上的槽的各个槽与外周面的交界,缘部连接中央部与交界。在2个以上的槽的各个槽中,中央部到外周面的深度比缘部到外周面的深度深,最深部形成在从交界向中央部移动0.2mm以上的位置。(A belt unit of the present invention includes: a belt which is annular and has an outer peripheral surface, an inner peripheral surface and a mark portion, wherein the outer peripheral surface is formed in a flat shape, the inner peripheral surface is positioned on the opposite side of the outer peripheral surface, and the mark portion is formed on the outer peripheral surface and is recessed from the outer peripheral surface to the inner peripheral surface; a drive roller that abuts the inner peripheral surface and moves the belt in a first direction; and a driven roller which abuts against the inner peripheral surface. The marking portion has a plurality of grooves extending in a first direction. Each of the 2 or more grooves of the plurality of grooves includes a central portion and an edge portion, the central portion being distant from a boundary between each of the 2 or more grooves and the outer peripheral surface, and the edge portion connecting the central portion and the boundary. In each of the 2 or more grooves, a depth from the central portion to the outer peripheral surface is deeper than a depth from the edge portion to the outer peripheral surface, and a deepest portion is formed at a position shifted from the boundary to the central portion by 0.2mm or more.)

1. A belt unit is provided with:

a belt having a ring shape and an outer peripheral surface formed in a flat shape, an inner peripheral surface located on the opposite side of the outer peripheral surface, and a mark portion formed on the outer peripheral surface and recessed from the outer peripheral surface toward the inner peripheral surface;

a drive roller that abuts the inner peripheral surface and moves the belt in a first direction; and

a driven roller abutting against the inner peripheral surface,

the marking portion has a plurality of grooves extending along the first direction,

each of 2 or more of the plurality of grooves includes a central portion that is distant from a boundary between each of the 2 or more grooves and the outer peripheral surface, and an edge portion that connects the central portion and the boundary,

in each of the 2 or more grooves, a depth from the central portion to the outer peripheral surface is deeper than a depth from the edge portion to the outer peripheral surface, and a deepest portion is formed at a position shifted from the boundary toward the central portion by 0.2mm or more.

2. The belt unit according to claim 1,

the edge of the mark portion forms a slope, and the depth of the slope to the outer peripheral surface gradually increases from the boundary toward the central portion.

3. The belt unit according to claim 1 or claim 2,

in each of the 2 or more grooves, a depth from a position shifted by 0.2mm from the boundary toward the central portion to the outer peripheral surface is equal to or less than half of a depth from the deepest portion to the outer peripheral surface.

4. The belt unit according to any one of claims 1 to 3,

in each of the 2 or more grooves, a depth from the deepest portion to the outer peripheral surface is 2[ μm ] or more and 11[ μm ] or less.

5. The belt unit according to any one of claims 1 to 4,

the length of the mark portion in the first direction is within a range in which the periphery of the mark portion on the tape is not deformed by the formation of the mark portion.

6. The belt unit according to any one of claims 1 to 5,

the length of the mark portion in the first direction is 5mm or more and 15mm or less.

7. An image forming apparatus includes:

the belt unit of any one of claim 1 to claim 6;

an image forming unit that forms a developer image with a developer and transfers the developer image onto the belt or a medium conveyed by the belt; and

a sensor that irradiates irradiation light on the outer peripheral surface and detects the mark portion from reflected light reflected by the belt.

8. An image forming apparatus includes:

a belt unit that runs a belt in a first direction, the belt being annular and having an outer peripheral surface, an inner peripheral surface, and a mark portion, the outer peripheral surface being formed in a flat shape, the inner peripheral surface being located on an opposite side of the outer peripheral surface, the mark portion being formed on the outer peripheral surface and recessed from the outer peripheral surface toward the inner peripheral surface, and being wound around a plurality of rollers, the mark portion being formed on the outer peripheral surface and recessed from the outer peripheral surface toward the inner peripheral surface

A sensor that irradiates irradiation light on the outer peripheral surface and detects the mark portion from reflected light reflected by the belt,

the marking portion has a plurality of grooves extending in the first direction,

the at least 2 grooves of the plurality of grooves include a deepest portion in a central portion, the central portion being provided at a position away from a boundary between each of the at least 2 grooves and the outer peripheral surface and being detectable by the sensor as the mark portion, the deepest portion having a maximum depth to the outer peripheral surface.

9. The image forming apparatus according to claim 8,

each of 2 or more of the plurality of grooves includes a central portion that is distant from a boundary between each of the 2 or more grooves and the outer peripheral surface, and an edge portion that connects the central portion and the boundary,

in each of the 2 or more grooves, a depth from the central portion to the outer peripheral surface is deeper than a depth from the edge portion to the outer peripheral surface.

10. The image forming apparatus according to claim 8 or claim 9,

the sensor generates a light reception signal having a signal level corresponding to the intensity of the reflected light,

the difference between the signal level of the central portion and the signal level of the outer peripheral surface is equal to or greater than a predetermined threshold value.

11. The image forming apparatus according to any one of claim 8 to claim 10,

the length of the central portion in the first direction is longer than the diameter of a spot formed on the outer peripheral surface by the irradiation light.

12. The image forming apparatus according to any one of claim 8 to claim 11,

the belt unit forms a winding mark on the belt by the roller,

the sensor detects a position where the winding mark is formed,

the marker portion is selected as: when the length of the central portion in the first direction is detected by the sensor, the length is not equal to the length of the lap mark.

13. The image forming apparatus according to any one of claim 8 to claim 12,

further comprises a cleaning part which is provided with a cleaning part,

the cleaning portion has a blade that abuts the outer peripheral surface only by a prescribed nip width in the first direction, the cleaning portion scrapes the developer from the outer peripheral surface running in the first direction,

in each of the 2 or more grooves, a length of an edge portion in the first direction, which is adjacent to a boundary between each of the 2 or more grooves and the outer peripheral surface, is equal to or greater than the nip width.

14. The image forming apparatus according to claim 13,

in each of the 2 or more grooves, a depth from the deepest portion to the outer peripheral surface is set to a range in which the developer entering the groove can be scraped off by the scraper.

15. A method for forming a mark, comprising the steps of,

forming a mark portion on an outer peripheral surface of a belt, the belt being annular and having an inner peripheral surface, the outer peripheral surface being formed flat, the inner peripheral surface being located on an opposite side of the outer peripheral surface, the mark portion being recessed from the outer peripheral surface toward the inner peripheral surface,

the mark forming method includes:

a first irradiation step of irradiating the outer peripheral surface with laser light in a first irradiation range from a first start point to a first end point substantially in parallel with a first direction within a formation range that is a range in which the mark portion is to be formed; and

a second irradiation step of irradiating the outer peripheral surface with laser light in a second irradiation range from a second start point different from the first start point to a second end point different from the first end point in a direction substantially parallel to the first direction at a portion where a part of the formation range overlaps the first irradiation range,

in the mark portion, a depth from a central portion of a boundary between the mark portion and the outer peripheral surface is formed larger than a depth from an edge portion adjacent to the boundary between the mark portion and the outer peripheral surface within the formation range.

Technical Field

The present invention relates to a belt unit, an image forming apparatus, and a mark forming method, and is suitably applied to an electrophotographic image forming apparatus (so-called printer), for example.

Background

Heretofore, as an image forming apparatus, for example, there is an apparatus that prints an image by: toner images are respectively generated with toners of respective colors (i.e., developers) by a plurality of developing units, the toner images are transferred onto a belt running by a belt unit, the toner images are transferred from the belt onto a medium (e.g., a printing paper) conveyed by a conveying section, and the printing paper is heated and pressed to be fixed.

In addition, among the image forming apparatuses, there are the following types of apparatuses: a mark portion for detecting a position (hereinafter, referred to as a position detection mark) is formed in advance at an end portion of the belt where the toner image is not transferred, and the position detection mark is detected by an optical sensor. In this image forming apparatus, the position detection mark is detected by the sensor, and thus, for example, when toner images of respective colors transferred onto the belt are superimposed, the registration position and the running speed of the belt can be controlled.

The position detection mark is formed, for example, by the following method: the surface of the tape is modified by irradiating the tape with a laser beam at a position where the position detection mark is to be formed, so that the light reflectance at the position is lower than that of the surroundings (see, for example, patent document 1).

For example, when a laser beam having a spot diameter of 0.1 mm is irradiated onto a belt and the irradiation position is moved in the running direction of the belt, a linear groove having a width of 0.1 mm is formed. Then, the linear grooves are formed in the belt in the order of 0.1 mm in position shifted in the width direction orthogonal to the running direction, thereby forming position detection marks having, for example, a square shape with each side of 7 mm and a depth to the surface of about 10[ mu ] m.

Disclosure of Invention

A belt unit according to an embodiment of the present invention includes: a belt which is annular and has an outer peripheral surface, an inner peripheral surface and a mark portion, wherein the outer peripheral surface is formed in a flat shape, the inner peripheral surface is positioned on the opposite side of the outer peripheral surface, and the mark portion is formed on the outer peripheral surface and is recessed from the outer peripheral surface to the inner peripheral surface; a drive roller that abuts the inner peripheral surface and moves the belt in a first direction; and a driven roller which abuts against the inner peripheral surface. The marking portion has a plurality of grooves extending in a first direction. Each of the 2 or more grooves of the plurality of grooves includes a central portion and an edge portion, the central portion being distant from a boundary between each of the 2 or more grooves and the outer peripheral surface, and the edge portion connecting the central portion and the boundary. In each of the 2 or more grooves, a depth from the central portion to the outer peripheral surface is deeper than a depth from the edge portion to the outer peripheral surface, and a deepest portion is formed at a position shifted from the boundary to the central portion by 0.2mm or more.

An image forming apparatus according to an embodiment of the present invention includes: the belt unit, make the belt move along the first direction, the belt is annular and has outer peripheral surface, inner peripheral surface and marking part and winds around a plurality of rollers, the outer peripheral surface is formed into the flat shape, the inner peripheral surface is located the opposite side of outer peripheral surface, the marking part is formed on the outer peripheral surface and is sunken to the inner peripheral surface from the outer peripheral surface, and the sensor, illuminate the illumination light on the outer peripheral surface of the belt, and detect the marking part according to the reflected light reflected by the belt. The marking portion has a plurality of grooves extending in a first direction. The at least 2 grooves of the plurality of grooves include a deepest portion in a central portion, the central portion is provided at a position away from a boundary between each of the at least 2 grooves and the outer peripheral surface and is detectable by a sensor as a mark portion, and the depth from the deepest portion to the outer peripheral surface is the largest.

In the mark forming method according to one embodiment of the present invention, the mark portion is formed on the outer peripheral surface of the belt, the belt is annular and has an inner peripheral surface, the outer peripheral surface is formed flat, the inner peripheral surface is located on the opposite side of the outer peripheral surface, and the mark portion is recessed from the outer peripheral surface toward the inner peripheral surface. The mark forming method includes: a first irradiation step of irradiating the outer peripheral surface with laser light in a first irradiation range from a first start point to a first end point substantially in parallel with a first direction within a formation range that is a range in which a mark portion is to be formed; and a second irradiation step of irradiating the outer peripheral surface with laser light in a second irradiation range from a second start point different from the first start point to a second end point different from the first end point substantially in parallel with the first direction at a portion where a part of the formation range overlaps the first irradiation range. In the mark portion, a depth from a central portion of a boundary between the mark portion and the outer peripheral surface is formed larger than that from an edge portion adjacent to the boundary between the mark portion and the outer peripheral surface within the formation range.

Drawings

Fig. 1 is a schematic diagram illustrating the structure of an image forming apparatus.

Fig. 2 is a schematic diagram showing the structure of the belt and the layout of the position detection marks.

Fig. 3 is a schematic view showing the structure of the cleaning portion.

Fig. 4 is a schematic diagram showing the structure of the sensor.

Fig. 5 is a schematic diagram showing the structure of the position detection mark.

Fig. 6 is a schematic cross-sectional view showing a cross-sectional shape of the position detection mark.

Fig. 7 is a schematic diagram showing the lengths of the respective portions of the position detection mark and the light reception signal.

Fig. 8 is a table showing values of respective portions and evaluation results in the first evaluation test.

Fig. 9 is a table showing evaluation levels in the first evaluation test.

Fig. 10 is a table showing the edge depth ratio and the edge length ratio in the first evaluation test.

Fig. 11 is a table showing values and evaluations of each part in the second evaluation test.

Fig. 12 is a table showing evaluation levels in the second evaluation test.

Description of the symbols

1 image forming apparatus

4 control part

11 image forming unit

12-belt unit

16 cleaning part

18 sensor

31 drive roller

32. 33,34 follower rollers

35. 36 support roller

37 belt

40 belt surface

41 position detection mark

61 scraper

71 light emitting part

72 light receiving part

81 end portion

82 central part

83 edge part

84 deepest part

AR1 first irradiation Range

AR2 second irradiation Range

E belt running direction

Width of N press area

Effective length of La mark

Local concave part of PH

QS1 first starting point

QE1 first end point

QS2 second starting point

QE2 second end point

SD light receiving signal

T1 irradiating light

T2 reflected light

VS reference voltage

Delta V differential voltage

α spot diameter

Detailed Description

Embodiments for carrying out the present invention will be described in detail below with reference to the accompanying drawings. The embodiments described below all represent preferred specific examples of the present invention. Therefore, the numerical values, shapes, materials, constituent elements, arrangement positions of constituent elements, connection forms, and the like shown in the following embodiments are merely examples, and are not intended to limit the present invention. Therefore, among the components of the following embodiments, components that are not recited in the independent claims indicating the uppermost concept of the present invention will be described as arbitrary components. Each drawing is a schematic diagram, and the illustration is not necessarily strict. In the drawings, substantially the same components are denoted by the same reference numerals, and redundant description is omitted or simplified.

On the other hand, in an image forming apparatus, a cleaning section is provided to clean the surface of a belt after a toner image is transferred from the belt onto a medium (e.g., printing paper). In the cleaning portion, for example, a plate-like member made of resin called a blade is brought into contact with the surface of the belt, and the blade is slid on the belt along with the running of the belt, whereby the toner remaining on the surface of the belt can be scraped off.

However, the position detection mark is formed on the belt outside the range in which the toner image is to be transferred in the width direction. Therefore, in the image forming apparatus, toner does not originally enter the position detection mark, and even if toner enters the position detection mark for some reason, it can be easily scraped off by the blade.

However, if the linear grooves are formed in the belt, the moving speed of the spot is slower at the start and end of irradiation than when the irradiation position of the laser beam is moving in the middle. As a result, in the position detection mark, a larger amount of heat is generated at the position where the laser light starts to be irradiated and at the position where the laser light ends to be irradiated, that is, in the vicinity of the outer edge, and a locally deep recess (hereinafter, referred to as a local recess) is formed.

In the image forming apparatus, when the toner enters the partial concave portion of the position detection mark, the toner cannot be completely scraped off by the scraper, and a part of the toner remains in the position detection mark. In this case, the following problems may occur in the image forming apparatus: the position detection mark cannot be accurately detected by the sensor to cause the toner image to have a positional shift or the like; when the printing paper is tilted, the end portion of the printing paper enters the position detection mark and toner is attached, so that the printing paper is stained, that is, the printing quality is degraded.

Accordingly, it is desirable to provide a belt unit, an image forming apparatus, and a mark forming method that can maintain a high-quality print state well.

[1. Structure of image Forming apparatus ]

As shown in fig. 1, the image forming apparatus 1 of the present embodiment is configured as an electrophotographic printer, and is used to print a desired color image on a long medium such as a long printing sheet P, for example. The image forming apparatus 1 is generally composed of a main body 2 that performs a printing process and a printing paper supply section 3 that supplies printing paper P. Further, a control unit 4 for comprehensively controlling the entire system is provided inside the main body 2.

The control Unit 4 is configured mainly with a CPU (Central Processing Unit), not shown, and performs various processes related to printing by reading and executing a predetermined program from a ROM (Read Only Memory), a flash Memory, or the like, not shown. The control unit 4 has a Memory unit, such as a RAM (Random Access Memory), a hard disk drive, and a flash Memory, and stores various information in the Memory unit.

The control unit 4 is connected to a host device (not shown) such as a personal computer by wireless or wired connection via a communication processing unit (not shown). When the host device transmits image data representing an image to be printed to the control unit 4 and issues an instruction to print the image data, the control unit 4 starts a printing process of forming an image on the surface of the printing paper P.

For convenience of explanation, the printing paper supply section 3 side is defined as the front side, the main body section 2 side as the rear side, the front side of the paper surface in fig. 1 as the left side, the rear side as the right side, and the upper and lower sides are defined, and the following explanation is made based on the above definitions.

The printing paper P as a medium is wound in a roll shape around the peripheral side surface of a core extending in the left-right direction. The core member is rotatably supported by the paper supply section 3, and the paper supply section 3 sequentially feeds the paper P to the rear main body section 2 by lifting one end of the paper P from the outermost periphery of the rolled portion.

The main body 2 is formed in a cubic shape as a whole, and 5 image forming units 11(11Y, 11M, 11C, 11K, and 11CL) are sequentially provided at positions on the inside thereof in a row from the front side to the rear side. Incidentally, the image forming units 11Y, 11M, 11C, 11K, and 11CL form toner images of respective colors using respective toners of yellow (Y), magenta (M), cyan (C), black (K), and transparent (CL), respectively. The transparent toner is a colorless transparent toner, and is used when it is necessary to give a glossy feeling to a surface by being superimposed on a toner of another color, for example.

The image forming unit 11 is generally constituted by a toner cartridge 21, a developing unit 22, and an LED (Light emitting diode) printhead 23. The toner cartridge 21 accommodates toner as a developer therein and supplies the toner to the developing unit 22. The LED print head 23 is formed by a plurality of LEDs arranged linearly in the left-right direction, which is the main scanning direction, and sequentially emits light from the LEDs in accordance with a light emission pattern based on data from the control unit 4.

The developing unit 22 incorporates a plurality of rollers such as a photosensitive drum 24 and a charging roller 25. The developing unit 22 appropriately applies a predetermined voltage to each roller, appropriately rotates each roller together with the photosensitive drum 24, charges the surface of the photosensitive drum 24 with the charging roller 25, and irradiates the circumferential surface of the photosensitive drum 24 with light emitted from the LED head 23, thereby forming an electrostatic latent image.

The developing unit 22 then attaches the toner supplied from the toner cartridge 21 to the peripheral side surface of the photosensitive drum 24, thereby forming a toner image based on the electrostatic latent image (hereinafter also referred to as a developer image), which reaches the vicinity of the lower end of the peripheral side surface of the photosensitive drum 24 by the rotation of the photosensitive drum 24.

A belt unit 12 is disposed below each image forming unit 11. The belt unit 12 is constituted by a driving roller 31, driven rollers 32,33,34, supporting rollers 35,36, a belt 37, and the like. The rollers other than the belt 37, i.e., the driving roller 31, the driven rollers 32,33,34, and the support rollers 35,36, are each formed in an elongated cylindrical shape having a central axis extending in the left-right direction, and are rotatably supported by the main body 2.

The drive roller 31 is disposed on the front lower side of the image forming unit 11Y, and when a belt drive motor, not shown, supplies a driving force to the drive roller 31, the drive roller 31 rotates in the direction of arrow R1 clockwise in the figure. The driven roller 32 is disposed on the lower rear side of the image forming unit 11 CL. The driven roller 33 is disposed behind and below the driving roller 31 and in front of and below the driven roller 32. The driven roller 34 is disposed on the rear upper side of the driven roller 33 and on the front lower side of the driven roller 32. The support roller 35 is disposed on the rear upper side of the drive roller 31 and in the vicinity of the drive roller 31. The backup roller 36 is disposed on the front upper side of the driven roller 33 and in the vicinity of the driven roller 33.

The belt 37 is made of, for example, polyamide-imide (PAI) resin to which carbon black as a conductive agent is added, and is formed into a flexible endless belt (that is, an endless belt). Incidentally, the length of the belt 37 in the left-right direction (hereinafter also referred to as the main scanning direction or the width direction) is about 350[ mm ].

As shown in the schematic plan view of fig. 2, a plurality of position detection marks 41 are provided on the belt 37 in the vicinity of the right end of the belt surface 40. On the belt 37, a surface layer of high material density is formed at and near the belt surface 40, so that the belt surface 40 is smooth. Thus, the belt 37 can transfer the toner image onto the printing paper P while maintaining the image quality of the toner image transferred onto the belt surface 40 as much as possible. Accordingly, the light reflectance is high on the belt surface 40.

On the other hand, a large number of fine holes are formed in the inside of the belt 37, which is slightly away from the belt surface 40, whereby the belt 37 itself can be easily deformed in accordance with the shape of the running path. When the position detection mark 41 is formed, as will be described later, the surface layer formed on the belt surface 40 and its vicinity is removed by irradiating the belt surface 40 with laser light, and the internal voids are exposed, so that the surface of the position detection mark 41 is rough. That is, the light reflectance of the position detection mark 41 is lower than the light reflectance of the tape surface 40.

Specifically, the position detection mark 41 is formed in a small square or rectangular shape, and is disposed at a position shifted by 0.5[ mm ] from the right end to the left side (i.e., the inner side) on the outer surface of the belt 37. The period (pitch) at which the position detection marks 41 are arranged in the running direction of the belt 37 is 78[ mm ]. This cycle is the same as the cycle of arrangement of the image forming units 11 in the front-rear direction in the main body 2 (fig. 1).

The belt 37 (fig. 1) is wound around the drive roller 31, the driven rollers 32 and 33, and the support rollers 35 and 36, i.e., with the inner peripheral surfaces thereof abutting against the drive roller 31, the driven rollers 32 and 33, and the support rollers 35 and 36, and the driven roller 34 presses the outer peripheral surface of the belt 37 between the driven rollers 32 and 33. Thereby, the belt 37 is in a tensioned state between, for example, the upper side of the drive roller 31 and the upper side of the driven roller 32.

In the belt unit 12, primary transfer rollers 38 are disposed below the belt 37 between the driving roller 31 and the driven roller 32 and below the photosensitive drums 24 of the respective image forming units 11. The primary transfer roller 38 is formed in a cylindrical shape having a central axis extending in the left-right direction, is rotatably supported by the main body 2, and is applied with a predetermined voltage, similarly to the rollers of the image forming unit 11.

Incidentally, each image forming unit 11 is biased downward by a biasing means not shown. Therefore, the photosensitive drum 24 of each image forming unit 11 presses the primary transfer roller 38 across the belt 37.

When the driving roller 31 supplies a driving force to the belt unit 12, the driving roller 31 is rotated in the direction of the arrow R1, and the belt 37 is moved clockwise in the drawing around the driving roller 31, the driven roller 32, and the like. For convenience of explanation, the direction in which the belt 37 runs is also referred to as a belt running direction E hereinafter.

At this time, if a toner image is formed on the peripheral side surface of the photosensitive drum 24, the image forming unit 11 transfers the toner image from the photosensitive drum 24 onto the belt surface 40 (fig. 2) which is the surface on the outer peripheral side of the belt 37. The toner image is transferred from each image forming unit 11 onto the outer peripheral surface of the belt 37 while the belt 37 is run by the belt unit 12, whereby a toner image of a color in which toner images of the respective colors are superimposed is formed on the outer peripheral surface of the belt 37.

Further, a transport path CP for transporting the printing paper P from the front to the rear by a plurality of rollers, transport guides, and the like (not shown) is formed below the belt unit 12, and the lower end of the driven roller 33 of the belt unit 12 abuts on the transport path CP. A secondary transfer roller 51 is disposed directly below the driven roller 33. The secondary transfer roller 51 is formed in a cylindrical shape having a central axis extending in the left-right direction, is rotatably supported by the main body 2, and is applied with a predetermined voltage, similarly to the primary transfer roller 38. For convenience of description, the secondary transfer roller 51 and the driven roller 33 are also collectively referred to as a secondary transfer portion 13 hereinafter.

When the portion of the belt 37 on which the toner image is transferred moves from the drive roller 31 side and the printing paper P is conveyed backward from the printing paper supply section 3 along the conveyance path CP, the secondary transfer section 13 transfers the toner image from the belt 37 to the printing paper P and continues to feed the printing paper P backward along the conveyance path CP.

A fixing unit 14 is provided behind the secondary transfer unit 13. The fixing section 14 is provided with rollers, one of which includes a heater, on the upper side and the lower side of the conveyance path CP, respectively. The fixing section 14 heats the rollers by heating the rollers by the heaters while rotating the rollers appropriately, thereby heating and pressurizing the printing paper P conveyed along the conveyance path CP, fixing the toner image on the printing paper P, and then feeding the printing paper P backward.

Then, the image forming apparatus 1 conveys the printing paper P to the rear of the fixing unit 14 and discharges the paper P to the rear, and the paper P is placed on the discharge tray 15. In this manner, the image forming apparatus 1 can form an image on the printing paper P, that is, can print an image on the printing paper P.

Further, between the driven rollers 32 and 34 of the belt unit 12, a cleaning portion 16 is provided. As shown in the enlarged view of fig. 3, in the cleaning portion 16, a blade 61 is provided so as to be in contact with the belt surface 40 which is the outer peripheral surface of the belt 37, and a roller 62 is provided above the blade 61, i.e., on the opposite side across the belt 37. That is, in the cleaning section 16, the outer peripheral surface of the belt 37 is pressed near the end portion on the front upper side of the blade 61, and the roller 62 receives the urging force from the blade 61 on the opposite side across the belt 37. A box-shaped cleaning tank 63 having an open upper side is provided below the scraper 61.

The cleaning portion 16 causes the blade 61 to slide on the outer surface of the belt 37, i.e., the belt surface 40, when the belt 37 runs. Thus, when toner adheres to the belt surface 40, the cleaning section 16 can scrape the toner off and perform cleaning. The toner scraped off at this time is accommodated in the cleaning tank 63.

The scraper 61 is formed in a plate shape having a plate thickness of 2.0[ mm ], for example, and is supported from below by a support member 64 having sufficient rigidity and fixed to the main body 2. Incidentally, the lengths of the doctor blade 61 and the supporting member 64 in the left-right direction (main scanning direction or width direction) are about 350[ mm ], and are substantially equal to the length of the belt 37.

The blade 61 is made of, for example, urethane rubber having a rubber hardness of 78 ° according to JIS a. The urethane rubber has high hardness and sufficient elasticity in the rubber material, and is excellent in properties such as abrasion resistance, mechanical strength, oil resistance, and ozone resistance, and therefore is used as the material of the blade 61. The doctor blade 61 is not limited to urethane rubber having a rubber hardness of JIS a78 °, and for example, an elastic material having a rubber hardness in the range of JIS a 65 ° to 100 ° can be used.

In the cleaning section 16, the length of the portion of the blade 61 in contact with the belt 37 in the running direction of the belt 37 (i.e., the length in the substantially front-rear direction), i.e., the nip width N, is adjusted to 0.2[ mm ], and the line pressure of the blade 61 is adjusted to 4.3[ g/mm ]. In other words, in the cleaning portion 16, the blade 61 is substantially in line contact with the belt 37. Thus, in the cleaning section 16, the blade 61 can be brought into good close contact with the belt 37 to perform appropriate cleaning, and the blade 61 can be brought into surface contact with the belt 37 to prevent excessive frictional resistance.

In the cleaning section 16, the contact angle θ of the blade 61 with the belt 37, that is, the angle formed by the plane extending along the outer surface of the belt 37 and the tangent line H at the rear upper end of the blade 61 is set to 21 °. The abutment angle θ is not limited to 21 °, preferably 20 ° to 30 °, and more preferably 20 ° to 25 °.

Further, a sensor 18 is provided near the right end of the belt 37, i.e., at a position corresponding to the position detection mark 41 (fig. 2), on the rear side of the driven roller 32 of the image forming apparatus 1 (fig. 1). The sensor 18 is a so-called reflective sensor, and as shown in fig. 4, the sensor 18 has a structure in which a light emitting section 71 that emits light and a light receiving section 72 that receives light are held by a base 73.

The light emitting unit 71 emits the irradiation light T1 of a predetermined wavelength forward and irradiates the belt surface 40 of the belt 37 with the irradiation light T1. the light emitting unit 71 is adjusted so that the spot diameter α (i.e., the diameter) of the irradiation light T1 formed on the belt surface 40 at this time is 2[ mm ], and for convenience of explanation, the position on the belt 37 irradiated with the irradiation light T1 will be referred to as an irradiation position S hereinafter.

The irradiation light T1 is reflected by the belt surface 40 or the like to form reflected light T2, and the light receiving unit 72 receives the reflected light T2, generates a light receiving signal SD having a signal level (i.e., voltage) according to the intensity of the reflected light T2, and transmits the light receiving signal SD to the control unit 4 (fig. 1). In response to this, the control unit 4 can determine whether the irradiation position S is the belt surface 40, the position detection mark 41 (fig. 2), or the like, based on the received light reception signal SD. Further, the control section 4 measures, for example, the time interval (i.e., the period) at which each position detection mark 41 is detected, and adjusts the running speed of the belt 37 so that the time interval reaches a predetermined value, thereby making it possible to align the position of the toner image transferred onto the belt 37 with high accuracy.

Specifically, in the sensor 18, the respective portions are adjusted to: when the light emitting unit 71 irradiates the belt surface 40 with the irradiation light T1 and the light receiving unit 72 receives the reflected light T2, the voltage of the light receiving signal SD generated by the light receiving unit 72 (hereinafter referred to as the non-mark voltage) is 2.7V. In this case, it is assumed that the belt surface 40 is not attached with foreign matter and is not damaged, and the belt 37 itself is not bent, that is, is in a normal state. The non-mark voltage is the highest voltage among the voltages of the light reception signal SD generated by the light reception unit 72.

On the other hand, in the sensor 18, when the light emitting unit 71 irradiates the position detection mark 41, which is a portion having low light reflectance, with the irradiation light T1 and the light receiving unit 72 receives the reflected light T2, the voltage of the light receiving signal SD generated by the light receiving unit 72 is lower than the non-mark voltage.

In the sensor 18, if a foreign substance adheres to or a flaw exists on the belt surface 40 of the belt 37, the light reflectance of the belt surface 40 is slightly lower than that in a normal state where no foreign substance or flaw exists, and therefore the light amount of the reflected light T2 slightly decreases, and the voltage of the light reception signal also slightly decreases.

Then, the control unit 4 determines that the position detection mark 41 is formed at the irradiation position S when the differential voltage Δ V, which is the difference between the non-mark voltage and the voltage of the light reception signal SD, is 1.0[ V ] or more, in consideration of an error due to individual difference of the sensor 18, on the premise that the belt 37 is operated at a speed of 6ips (inch/sec). Specifically, in the control unit 4, 1.7[ V ] lower than the non-marker voltage 2.7[ V ] by 1.0[ V ] is set as the reference voltage VS as the threshold. When the voltage of the light receiving signal SD is lower than the reference voltage VS, the control unit 4 determines whether or not the position detection mark 41 is formed at the irradiation position S, taking into consideration the time length and the like.

Thus, the control unit 4 can distinguish the change of the light reception signal SD when foreign matter adheres to or is damaged on the outer surface of the belt 37, recognize the change of the light reception signal SD due to the presence of the position detection mark 41, and detect the position detection mark 41 with high accuracy.

[2. formation of position detecting Mark ]

Next, the structure of the position detection mark 41 will be described. As enlarged in fig. 5, the position detection mark 41 is formed in a square or rectangular shape as a whole, and the side length of the side extending in the belt running direction E (hereinafter also referred to as the first direction) is L and the side length of the side extending in the left-right direction (width direction) is W.

When the position detection mark 41 is formed, the tape surface 40 of the tape 37 is irradiated with laser light by a predetermined laser marking device (not shown), so that the tape surface 40 and a surface layer portion in the vicinity thereof are removed, and as a result, a region recessed from the periphery and having a lower light reflectance is formed.

Specifically, for example, MD-V9900A manufactured by Keyence corporation is used as a laser marking device, and a laser beam having a spot diameter of about 0.1 mm is irradiated onto the belt surface 40 of the belt 37 to form a concave shape having a spot shape. A plurality of the concave shapes are arranged in the belt 37 in a continuous and adjacent manner as square or rectangular position detection marks 41.

Further, on the belt 37, a linear groove having a groove width of about 0.1[ mm ] and extending substantially in parallel to the belt running direction E is formed by linearly moving the spot of the laser light in the belt running direction E. The grooves are formed in the belt 37 at positions shifted by 0.1[ mm ] in the horizontal direction (main scanning direction) in sequence, and finally, the flat position detection marks 41 are formed.

Incidentally, on the belt 37, by adjusting the laser irradiation intensity of the laser marking device, the depth of the concave formed, that is, the distance of the concave in the thickness direction to the belt surface 40 can be adjusted. For example, on the belt 37, if the laser irradiation intensity of the laser marking device becomes large, the depth of the concave to the belt surface 40 becomes large, and conversely, if the irradiation intensity becomes small, the depth also becomes small.

In addition, in the belt 37, a mark corner 41C corresponding to each vertex of the square or rectangle of the position detection mark 41 is formed in a curved shape having an arc shape with a radius of about 0.1[ mm ]. This can prevent the belt 37 from being broken due to stress concentration in the belt 37, prevent the boundary between the belt surface 40 and the position detection mark 41 from being chipped or curled, and prevent the blade 61 from being damaged due to the above.

However, when the laser marking device irradiates the laser beam to linearly move the spot in the tape running direction E on the tape 37, the moving speed of the spot is slower in the vicinity of the start point and the end point than in the case of moving the other portions, and therefore the irradiation time of the laser beam is relatively long. Thus, on the belt 37, the vicinities of both ends of the groove are heated more than other portions.

Thus, as shown in FIG. 6(A), in a cross section A1-A2 of FIG. 5, i.e., a schematic cross section extending in the belt running direction E, the depth of the groove formed in the belt 37 is locally increased in the vicinity of both ends, and a local concave portion PH is formed. In this case, in the position detection mark 41 formed on the belt 37, the toner cannot be scraped off by the scraper 61 when it enters the partial recessed portion PH, and the toner remains inside the position detection mark 41. In this case, as described above, the following problems may occur in the image forming apparatus 1: the accuracy of detection of the position detection mark 41 by the sensor 18 is lowered, and the toner image is shifted in position, or toner adheres to the end of the printing paper P, or the like.

In the present embodiment, when one groove is formed as a part of the position detection mark 41, the laser marking device linearly moves the spot of the laser light in a state where the irradiation intensity is low, and this operation is performed twice, and the positions of the start point and the end point of the first time and the second time are made different from each other.

For example, as shown in the cross-sectional view corresponding to fig. 6a in fig. 6B, when the position detection mark 41 is formed, the laser light is linearly irradiated as the first laser light irradiation in the first irradiation range AR1 from the first start point QS1 to the first end point QE1, that is, in the range of the length L (fig. 5) corresponding to the entire length of the position detection mark 41, so that a shallow groove is formed. When the position detection mark 41 is continuously formed, the laser beam is linearly irradiated in the second irradiation range AR2 from the second start point QS2 to the second end point QE2, that is, in the narrow range of the entire length L of the position detection mark 41 excluding the vicinity of both ends, as the second laser irradiation for the same groove, so that a part of the groove is formed deeper.

As a result, the position detection mark 41 has a slope gradually deepening from the vicinity of both ends toward the center, and the center portion excluding the vicinity of both ends has a flat and sufficiently deep shape.

Incidentally, in the position detection mark 41, as described above, a plurality of grooves extending in the belt running direction E are formed so as to be arranged in the width direction (left-right direction). Therefore, in the position detection mark 41, a ridge portion extending in the belt running direction E, that is, a portion that is raised from the periphery and is connected in a linear shape is formed at the boundary portion between the respective concave grooves.

[3. conditions to be provided for position detection marks ]

Next, the length of each part of the position detection mark 41 will be described with reference to fig. 7(a), and fig. 7(a) is a simplified diagram of the cross-sectional shape of fig. 6 (B). When the position detection mark 41 on the belt 37 and the belt surface 40 around the mark are set as the irradiation position S, the voltage of the light reception signal obtained by the sensor 18 is shown in fig. 7(B), and fig. 7(B) is a schematic waveform diagram corresponding to fig. 7 (a). Incidentally, the horizontal axis of fig. 7(B) directly represents time, but since the running speed of the belt 37 is a fixed value of 6ips, it can also be regarded as a position extending in the belt running direction E.

First, in fig. 7(a), a position corresponding to the boundary line between the belt surface 40 and the position detection mark 41, that is, the outer end position of the position detection mark 41 is defined as an end portion 81. The end portion 81 corresponds to the outer wire of the position detection mark 41 in fig. 2 and 5. In fig. 7(a), a portion sandwiched by both end portions 81 in the belt running direction E is the position detection mark 41, and a distance between both the end portions 81 is a length L of the position detection mark 41. In other words, the range of the length L sandwiched by the both end portions 81 is a formation range in which the position detection mark 41 should be formed.

In fig. 7B, the range in which the voltage of the light receiving signal SD is lower than the reference voltage VS is defined as the central portion 82 of the position detection mark 41 (fig. 7 a), and the portion of the position detection mark 41 excluding the central portion 82, that is, the portion near the end portion 81 is defined as the edge portion 83. Hereinafter, the lengths of the central portion 82 and the edge portion 83 in the belt running direction E are defined as a central length La and an edge length Lb, respectively. As is apparent from fig. 7, in the position detection mark 41, the following relationship holds with respect to the length in the belt running direction E: l ═ La + (Lb × 2).

Since the central portion 82 is a portion where the voltage of the light receiving signal SD is lower than the reference voltage VS, the central portion 82 is an area that is substantially a range of the position detection mark 41 and can be effectively detected by the sensor 18. Therefore, hereinafter, the central portion 82 is also referred to as a mark effective portion or a mark effective region, and the central length La is also referred to as a mark effective length La.

Incidentally, in addition to the case where the position detection mark 41 is formed, for example, when a foreign substance adheres to or a damage is present on the belt surface 40, similarly, the light reflectance is lowered, and therefore the voltage of the light reception signal SD may be lower than the reference voltage VS. Therefore, regardless of the cause, hereinafter, a portion of the light reception signal SD whose voltage is lower than the reference voltage VS is referred to as an effective portion, and a length of a portion of the band surface 40 corresponding to the effective portion is referred to as an effective length.

On the other hand, although the edge 83 is formed together with the central portion 82 by irradiating the belt 37 with the laser light, the edge 83 is an area that is not detected by the sensor 18 as the position detection mark 41 because the edge 83 corresponds to a range in which the voltage of the light reception signal SD is higher than the reference voltage VS.

As is clear from fig. 7(a), in the position detection mark 41, there is a sufficiently large difference between the belt surface 40 and the central portion 82 in the depth direction, and a slope connecting the both is formed on the edge portion 83. The ramp extends at a gradually tapering angle (i.e., a decreasing angle relative to the belt surface 40) toward the center portion 82 adjacent the edge portion 83. In other words, in the position detection mark 41, the deepest portion 84, which is the position where the depth to the belt surface 40 is the largest, is not formed on the edge portion 83, but is formed at a certain position within the central portion 82.

The depth from the deepest portion 84 of the position detection mark 41 to the belt surface 40 is hereinafter set to the maximum depth Da. The depth near the end 81 in the position detection mark 41 is defined as the outer circumferential depth Db, specifically, the depth from the position where the end 81 moves 0.2[ mm ] toward the center of the position detection mark 41 to the belt surface 40.

However, in the image forming apparatus 1, when the toner enters the position detection mark 41 of the belt 37, it needs to be scraped or scraped by the blade 61 of the cleaning section 16, as with the toner adhering to the belt surface 40. As described above, since the blade 61 is made of urethane rubber and has sufficient elasticity, the surface following the position detection mark 41 may be deformed depending on the shape of the position detection mark 41.

For example, if the depth of the center portion 82 of the position detection mark 41 is small, the blade 61 can scrape out the toner entering the inside of the position detection mark 41 satisfactorily by elastic deformation. However, if the depth of the central portion 82 is sufficiently large, the blade 61 may not completely scrape the toner entering the inside of the position detection mark 41, leaving a portion.

Further, if the inclination angle of the edge portion 83 of the position detection mark 41, that is, the angle formed by the edge portion 83 with respect to the belt surface 40 is small, the doctor blade 61 can deform to follow the slope of the edge portion 83 well, and toner can be scraped off without fail. However, if the inclination angle of the edge portion 83 is large, the blade 61 may not be able to completely follow the slope of the edge portion 83 and deform, and thus the toner may not be scraped off completely and some toner may be missed.

Further, in the position detection mark 41, a plurality of restrictions are also generated with respect to the length L in the belt running direction E. For example, in the image forming apparatus 1, when the power supply is turned off for a long period of time, a part of the belt 37 is continuously in a partially bent state by the driving roller 31, the supporting roller 35, and the like, and therefore the belt 37 may be bent. When the light is irradiated with the irradiation light T1 emitted from the light emitting portion 71 of the sensor 18, the portion of the belt 37 where the bending mark is formed is bent to spread the irradiation light T1, and thus the light amount of the reflected light T2 received by the light receiving portion 72 is reduced. Accordingly, in the light reception signal SD generated by the light receiving unit 72 of the sensor 18, the signal level (i.e., voltage) of the portion where the bending mark is formed decreases, and this portion becomes an effective portion. At this time, the control unit 4 may erroneously recognize the bending mark of the tape 37 as the position detection mark 41.

Thus, on the belt 37, one can consider: the mark effective length La, which is the length of the position detection mark 41 in the belt running direction E of the portion that can be detected by the sensor 18 (i.e., the central portion 82), is set to a value different from or easily distinguishable from the effective length due to the bending mark. In this case, the control unit 4 (fig. 1) of the image forming apparatus 1 can determine whether the position detection mark 41 is a bend mark or not, based on the time length (or the length in the belt running direction E) of the effective portion lower than the reference voltage VS (fig. 7B) in the received light signal SD.

Further, if the length L of the position detection mark 41 in the tape running direction E is too long in the tape 37, the amount of modification of the tape surface 40 by the laser irradiation becomes too large, and the tape 37 itself is deformed in the vicinity of the position detection mark 41, and is locally displaced to the outer and inner peripheral sides, that is, so-called moire occurs. If the waviness occurs in the vicinity of the right end where the position detection mark 41 is formed, the belt 37 runs off to a rim (not shown) provided in the main body 2 to restrict meandering of the belt 37, and the mechanical durability of the belt 37 is significantly reduced.

In this manner, in the position detection mark 41 formed on the belt 37, the length of each portion needs to be set to an appropriate value that satisfies various conditions: toner can be appropriately scraped off by the blade 61 of the cleaning section 16; the bending mark of the strip 37 can be distinguished from the light reception signal SD; the strip 37 is not corrugated.

[4. evaluation of position detection marker ]

Next, in order to examine the conditions to be satisfied by the position detection marks 41 formed on the belt 37, a first evaluation test in which a value relating to the depth is mainly changed and a second evaluation test in which a value relating to the length in the belt running direction E is mainly changed were performed.

[4-1. first evaluation test ]

As shown in fig. 8, in the first evaluation test, position detection marks 41 of various shapes were formed as examples and comparative examples. In the first evaluation test, the values of the maximum depth Da, the outer peripheral depth Db, and the edge length Lb were varied while setting the length L of the position detection mark 41 in the belt running direction E and the length W in the width direction (left-right direction) to fixed values of 7.0[ mm ]. Incidentally, the maximum depth Da and the peripheral depth Db in FIG. 8 were measured with a laser microscope VK 8500.

When the position detection mark 41 is formed, specifically, the laser marking device adjusts the laser intensity to change the shape of each part. However, when the groove is formed with a constant laser intensity, as described above, the moving speed of the spot is slow in the vicinity of the start point and the end point, the irradiation time is long, and a locally deep pit is formed. Comparative example 1 was formed in this manner.

In the other comparative examples and examples, when the laser was irradiated to the vicinity of the starting point and the ending point of the groove, the laser intensity was locally decreased, thereby avoiding the formation of a locally deep concave portion. In the comparative examples and examples, as described above with reference to fig. 6(B), the weak laser light is irradiated twice, and the positions of the start point and the end point of the first and second irradiation are made different from each other. Further, in the above-described comparative examples and embodiments, the shape of the position detection mark 41 is changed by variously changing the time and position at which the laser irradiation intensity is decreased in the vicinity of the start point and the end point of the groove.

In the first evaluation test, as shown in fig. 9, each comparative example and each example were evaluated with attention paid to the following two points: whether or not the toner entering the position detection mark 41 can be scraped off by the blade 61 of the cleaning section 16; and whether it can be detected as the position detection mark 41 by the sensor 18.

Here, regarding the first point, that is, the point of scraping toner from the position detection mark 41 by the blade 61, the case where toner remains in the position detection mark 41 after the blade 61 is slid once on the belt 37 is referred to as "omission", and evaluation is made as to whether or not the omission occurs and the occurrence position when the omission occurs. This evaluation is also referred to as missing evaluation hereinafter. In the omission evaluation, it is judged as "OK" if omission does not occur, and judged as "NG" if omission occurs.

In addition, at the second point, that is, at the point where the position detection mark 41 is detected by the sensor 18, an evaluation is made as to whether or not the voltage of the light reception signal SD generated by the light reception unit 72 has dropped below the reference voltage VS, that is, whether or not the differential voltage Δ V between the voltage of the light reception signal SD and the reference voltage VS is 1.0[ V ] or more. This evaluation is also referred to as detection evaluation hereinafter. In this detection evaluation, the differential voltage Δ V is determined to be "OK" if it is 1.0[ V ] or more, and is determined to be "NG" if it is less than 1.0[ V ].

In the first evaluation test, the results of the judgment of the missing evaluation and the results of the judgment of the detection evaluation are combined, and a comprehensive evaluation is made at five levels of an evaluation level 1 to an evaluation level 5.

Specifically, the case where the omission occurs in the entire position detection mark 41 and the differential voltage Δ V is 1.0[ V ] or more is defined as the evaluation level 1, and the case where the omission occurs only in the central portion 82 and the differential voltage Δ V is 1.0[ V ] or more is defined as the evaluation level 2. Further, the case where the omission is present only in the edge portion 83 and the differential voltage Δ V is 1.0[ V ] or more is defined as evaluation level 3, and the case where the omission is not present and the differential voltage Δ V is less than 1.0[ V ] is defined as evaluation level 4. Further, the case where no omission occurs and the differential voltage Δ V is 1.0[ V ] or more, that is, the case where neither omission evaluation nor detection evaluation has a problem is set as the evaluation level 5. In the first evaluation test, the position detection marks 41 that reached the evaluation level of 5 among the formed position detection marks 41 were used as examples, and the remaining position detection marks 41 were used as comparative examples.

In the first evaluation test, although a specific value is not shown in fig. 8, the magnitude of the differential voltage Δ V tends to be proportional to the magnitude of the maximum depth Da as a whole. In particular, as is clear from comparison of comparative example 6 with other comparative examples and examples, when the maximum depth Da is 2.0[ μm ] or more, the differential voltage Δ V is 1.0[ V ] or more, and the position detection mark 41 can be normally detected by the sensor 18.

When the position detection mark 41 is formed, as described above, the laser beam is irradiated to sufficiently eliminate the surface layer of the belt surface 40 and the vicinity thereof, thereby exposing the pores inside to roughen the surface and lowering the light reflectance, and the voltage of the light reception signal SD is sufficiently lowered, whereby the position detection mark 41 can be detected by the sensor 18. In comparative example 6, it is considered that: since the maximum depth Da is small, the surface layer does not sufficiently disappear, and the light reflectance of the surface remains high, resulting in insufficient drop in the voltage of the light reception signal SD.

In comparative example 7, although the maximum depth Da is 5.3[ μm ] and larger than 2.0[ μm, the length La of the central portion 82 is extremely small, only 1.0[ mm ], and even smaller than the spot diameter α (2[ mm ]) of the irradiation light T1, and therefore the differential voltage Δ V is smaller than 1.0[ V ], and the determination of the detection evaluation is ng.

On the other hand, when the maximum depth Da is large as in comparative examples 1, 2, and 3, although the differential voltage Δ V is 1.0[ V ] or more, there is no problem in detection evaluation, but toner cannot be scraped sufficiently by the scraper 61, that is, cleaning cannot be performed normally, and omission occurs. In comparative examples 1, 2 and 3, it can be considered that: since the maximum depth Da is sufficiently larger than the particle diameter of the toner (for example, about 5 to 7 μm), the toner particles are buried in the position detection mark 41, and the blade 61 cannot sufficiently follow the position detection mark 41 by elastic deformation, so that the blade 61 cannot sufficiently scrape the toner by only one pass.

Further, as in comparative examples 4 and 5, although the maximum depth Da is as large as 10.6[ μm ] or so, the length Lb of the edge portion 83 is too short to be as short as 0.1[ mm ] or the edge portion 83 is not substantially formed, and in this case, although the omission does not occur in the central portion 82, the omission occurs in the edge portion 83 (that is, in the vicinity of the end portion 81). In comparative examples 4 and 5, it is considered that: since the inclination angle of the edge portion 83 of the position detection mark 41 is steep, the blade 61 sliding on the belt 37 cannot completely follow the edge portion 83 to be deformed, and thus cannot completely scrape the toner.

On the other hand, as in example 1, when the maximum depth Da was 11.0[ μm ] and the length Lb of the edge portion 83 was 0.2[ mm ], no omission occurred in the edge portion 83, and the evaluation was judged as "OK". In this example 1, it can be considered that: since the nip width N of the blade 61 of the cleaning section 16 (fig. 3) is 0.2[ mm ], the blade 61 is easily deformed following the slope of the edge portion 83. In examples 2,3, 4 and 5, both the detection evaluation and the omission evaluation were "OK", and an evaluation level of 5 was reached.

By analogy with the above examples and comparative examples, it can be considered that: in the edge portion 83 of the position detection mark 41, omission occurs or does not occur in accordance with the inclination angle of the edge portion 83.

Then, the quotient of the peripheral depth Db of the position detection mark 41 divided by the maximum depth Da is defined as the rim depth ratio Db/Da. The rim depth ratio Db/Da is a depth ratio of two positions apart from each other in the belt running direction E within the position detection mark 41. Therefore, the rim depth ratio Db/Da can be regarded as a value representing the position shifted 0.2[ mm ] inward from the end 81 of the position detection mark 41, that is, the approximate magnitude of the inclination angle of the rim 83 or its vicinity.

As shown in FIG. 10, in examples 1 to 5 in which no omission occurred, the ratio Db/Da of the edge depth was approximately in the range of 0.4 to 0.5. In addition, it can be inferred that: even if the value of the rim depth ratio Db/Da is less than 0.4 and the inclination angle of the rim 83 or its vicinity is smaller than that in examples 1 to 5, the toner can be scraped well at the rim 83 by the scraper 61. On the other hand, in comparative examples 4 and 5 in which omission occurred in the edge portion 83, the edge portion depth ratio Db/Da was approximately in the range of 0.8 to 0.9. In summary, it can be considered that: if at least the rim depth ratio Db/Da is 0.5 or less, that is, the outer peripheral depth Db is not more than half the maximum depth Da, particularly, in the range of 0.4 to 0.5, there is high reliability without missing at the rim 83 of the position detection mark 41.

Further, a quotient obtained by dividing the edge length Lb of the position detection mark 41 by the maximum depth Da is defined as an edge length ratio Lb/Da. The maximum depth Da is correlated to a depth De (fig. 7 a) of a boundary portion between the central portion 82 and the edge portion 83 of the position detection mark 41 to some extent. Therefore, the edge length ratio Lb/Da is an approximate value of the cotangent (cot) of the inclination angle of the edge 83.

In examples 1 to 5 in which no omission occurred, the rim length ratio Lb/Da was approximately in the range of 0.018 to 0.100. In addition, it can be inferred that: even if the value of the rim length ratio Lb/Da is larger than 0.100 and the inclination angle of the rim 83 or its vicinity is smaller, the toner can be scraped off well in the rim 83 by the doctor blade 61. On the other hand, in comparative examples 4 and 5 in which omission of the edge portion 83 occurred, the edge length ratio Lb/Da was in the range of 0 to 0.009. In summary, it can be considered that: as long as at least the rim length ratio Lb/Da is 0.018 or more, especially in the range of 0.018 to 0.100, omission does not occur in the rim 83 of the position detection mark 41.

Based on the results of the first evaluation test, the depth-related conditions that the position detection marks 41 need to have are summarized as follows.

(1-1) the maximum depth Da is 2.0[ mu ] m or more and 11.0[ mu ] m or less.

(1-2) the depth ratio Db/Da of the edge portion is 0.5 or less, preferably 0.4 to 0.5.

(1-3) the ratio of the length of the rim Lb/Da is 0.018 or more, preferably 0.018 to 0.100.

[4-2 ] second evaluation test ]

In the second evaluation test, as shown in fig. 11, position detection marks 41 having various shapes were formed by variously changing the length L in the belt running direction E within a range of 1 to 20[ mm ] as examples and comparative examples. However, the length W in the width direction (left-right direction) of the position detection mark 41 is set to a fixed value of 7.0[ mm ], and the maximum depth Da of the position detection mark 41 is set to a range of 5[ μm ] to 8[ μm ].

In the second evaluation test, the belt 37 was run at a running speed of 6ips, and the position detection mark 41 was irradiated with the irradiation light T1 and received the reflected light T2 by the sensor 18, and the light reception signal SD of a voltage based on the light amount of the reflected light T2 was generated. Next, in a second evaluation test, a differential voltage Δ V, which is a difference between the light reception signal SD and the reference voltage VS, is measured, and a portion (i.e., an effective portion) where the differential voltage Δ V is 1.0[ V ] or more is regarded as the central portion 82 of the position detection mark 41, and a central length La (i.e., a mark effective length La) is obtained. The mark effective length La can be easily calculated by multiplying the time length of the effective portion by the running speed of the belt 37.

Incidentally, in the second evaluation test, when the groove extending in the belt running direction E was formed for forming the position detection mark 41, the local concave portion PH (fig. 6(a)) was formed without adjusting the laser irradiation intensity, and the edge portion 83 was not formed. Thus, in the second evaluation test, the influence of the edge portion 83 on the waveform of the light reception signal SD is eliminated as much as possible.

In the second evaluation test, as in the detection evaluation in the first evaluation test, the evaluation is made for each of the comparative examples and examples with a view to whether or not the position detection mark 41 can be appropriately detected from the light reception signal SD generated by the sensor 18.

Specifically, an evaluation is made as to whether or not the voltage of the light receiving signal SD generated by the light receiving unit 72 has dropped below the reference voltage VS, that is, whether or not the difference voltage Δ V between the voltage of the light receiving signal SD and the reference voltage VS is 1.0[ V ] or more (i.e., a detection evaluation in the first evaluation test). In this second evaluation test, basically, as in the case of the first evaluation test, if the differential voltage Δ V is 1.0[ V ] or more, it is determined as "OK", and if the differential voltage Δ V is less than 1.0[ V ], it is determined as "NG".

In the second evaluation test, the mark effective length La generated in the light reception signal SD by the position detection mark 41 is also evaluated. Specifically, "NG" is determined if there is the following possibility, and "OK" is determined if there is no following possibility: the mark effective length La is approximate to the effective length of an effective portion formed in the light reception signal SD due to a factor other than the position detection mark 41; the running of the belt 37 is problematic due to the size of the effective length La of the mark.

In the second evaluation test, the total evaluation was made on the basis of the above-described judgment results in five grades of evaluation grade 1 to evaluation grade 5, as in the first evaluation test.

Specifically, the evaluation level 1 is set to the case where the position detection mark 41 cannot be detected because the differential voltage Δ V is less than 1.0[ V ], and the evaluation level 2 is set to the case where the ripple is generated in the belt 37 although the differential voltage Δ V is 1.0[ V ] or more. In addition, the evaluation level 3 was set to a value in which the mark effective length La of the position detection mark 41 is similar to the effective length due to the flaw formed on the belt surface 40 even though the differential voltage Δ V was 1.0[ V ] or more. The evaluation level 4 was set to the case where the effective length La of the mark was similar to the effective length due to the winding mark of the tape 37 even though the differential voltage Δ V was 1.0[ V ] or more. Then, the case where the differential voltage Δ V is 1.0[ V ] or more and the mark effective length La of the position detection mark 41 is not similar to the effective length due to other causes is set as evaluation level 5. In the second evaluation test, as in the first evaluation test, the position detection mark 41 that reached the evaluation level of 5 among the formed position detection marks 41 was used as an example, and the remaining position detection marks 41 were used as comparative examples.

In this second evaluation test, it was found that: in general, when the length L of the position detection mark 41 is 2[ mm ] or more, an effective portion where the differential voltage Δ V is 1.0[ V ] or more is formed in the light reception signal SD, and therefore, at least the presence or absence of the position detection mark 41 can be determined. On the other hand, in comparative example 8 having a length L of 1[ mm ], the differential voltage Δ V is less than 1.0[ V ] and 0.7[ V ], and an effective potential difference cannot be obtained with respect to the voltage of the light reception signal SD (i.e., the non-mark voltage) obtained on the belt surface 40.

The reason for this is considered to be that the spot diameter α of the irradiation light T1 emitted from the light emitting section 71 in the sensor 18 is 2[ mm ], that is, in the case of the comparative example 8, the length L of the position detection mark 41 is smaller than the spot diameter α, and therefore, although a part of the irradiation light T1 is irradiated on the position detection mark 41 and reflected with low reflectance, the remaining part of the irradiation light T1 is beyond the range of the position detection mark 41 and irradiated on the surrounding belt surface 40 and reflected with high reflectance, and it is inferred that the light quantity of the reflected light T2 returned to the light receiving section 72 is large in the sensor 18 and the voltage of the light receiving signal SD is high, and incidentally, in the comparative example 7 of the first evaluation test described above, it is considered that the differential voltage Δ V is smaller than 1.0[ V ] for the same reason.

In comparative example 9, the length L is equal to the spot diameter α and 2[ mm ], and the differential voltage Δ V is 1.0[ V ] or more, and thus the presence or absence of the position detection mark 41 can be determined, however, if the mark effective length La in this comparative example 9 has a value of 1.3[ mm ], and if the tape surface 40 is damaged by contact with an end portion of the printing paper P or the like, the length of 1.3[ mm ] is similar to the effective length of the effective portion generated in the light receiving signal SD due to the damage.

In comparative example 10, the length L was 3[ mm ], and the mark effective length La was 2.2[ mm ]. If the tape 37 generates a curl mark at the backup roller 36 (fig. 1) due to a long-time stop of the operation, the length of 2.2[ mm ] will be similar to the effective length of the effective portion generated in the light reception signal SD due to the curl mark.

In comparative example 11, the length L was 4[ mm ], and the mark effective length La was 3.2[ mm ]. If the tape 37 generates a curl mark at the backup roller 35 (fig. 1) due to a long-time stop of the operation, the length of 3.2[ mm ] will be similar to the effective length of the effective portion generated in the light reception signal SD due to the curl mark.

In comparative example 12, the length L was 20[ mm ], and the mark effective length La was 15.7[ mm ]. If the tape 37 generates a roll mark at the drive roller 31 (fig. 1) due to a long-time stop of operation, the length of 15.7 mm will be similar to the effective length of the effective portion generated in the light reception signal SD due to the roll mark.

When the length L of the position detection mark 41 is selected in comparative examples 9 to 12, it is preferable to exclude 2[ mm ], 3[ mm ], 4[ mm ] and 20[ mm ] so that the effective length of the effective portion generated in the light reception signal SD due to other reasons is not close to the mark effective length La.

In comparative example 12, when the position detection mark 41 is formed, the amount of modification of the tape 37 by laser irradiation is excessively large, and therefore the periphery of the position detection mark 41 on the tape 37 is deformed to generate a moire. On the belt 37, it can be considered that: if the length L of the position detection mark 41 is set to 20[ mm ] or more, the moire is similarly generated.

On the other hand, as in examples 6, 7 and 8, in the case where the lengths L are 5[ mm ], 10[ mm ] and 15[ mm ], the differential voltage Δ V is 1.0[ V ] or more. In the above case, the mark effective lengths La are 4.3[ mm ], 7.3[ mm ] and 11.9[ mm ], respectively, and there is a sufficient difference in the effective lengths of the various effective portions generated in the received light signal SD due to other reasons to distinguish them.

Based on the results of the second evaluation test, the conditions relating to the length L that the position detection mark 41 needs to have are summarized as follows.

(2-1) the length L is equal to or larger than the spot diameter α of the irradiation light T1.

(2-2) the length L is 5[ mm ] or more and 15[ mm ] or less.

[5. Effect and the like ]

In the above configuration, in the image forming apparatus 1 of the present embodiment, the position detection mark 41 is formed by irradiating the tape 37 with laser light using the laser marking device to modify a part of the tape surface 40. In the present embodiment, a plurality of grooves extending in the belt running direction E are arranged in the width direction, whereby a rectangular or square position detection mark 41 (fig. 2 and 5) is formed.

In the present embodiment, when forming each groove of the position detection mark 41, the laser beam is irradiated at a weak intensity to linearly move the spot, and this operation is performed twice, and the start point and the end point are different in position each time (fig. 6 (B)).

Further, in the position detection mark 41, the length of each portion is defined as a condition relating to the depth from the result of the first evaluation test: the maximum depth Da is set to be not less than 2.0[ mu ] m and not more than 11.0[ mu ] m, the rim depth ratio Db/Da is set to be within a range of 0.4-0.5, and the rim length ratio Lb/Da is set to be within a range of 0.018-0.100 (FIGS. 7-10).

In the position detection mark 41 (fig. 7), the deepest portion 84 that is the deepest portion is positioned at the central portion 82, and the edge portion 83 can be formed with a shallower slope than the deepest portion 84, by satisfying the above-described conditions. That is, in the position detection mark 41, it is possible to reliably avoid the formation of the local concave portions PH in the vicinity of both ends as in the case where the laser spot is moved only once in a straight line (fig. 6 a).

Therefore, in the image forming apparatus 1 in which the position detection mark 41 is formed on the belt 37, it is possible to prevent: the toner enters the partial concave section PH; the toner cannot be scraped off completely by the blade 61 of the cleaning section 16 to cause toner residue (i.e., omission). As a result, the image forming apparatus 1 can avoid the following situations, such as: the detection accuracy of the position detection mark 41 by the sensor 18 is lowered to cause the toner images of the respective colors to be shifted in position, resulting in a color registration error; the end of the printing paper P enters the position detection mark 41 and is stained.

In the position detection mark 41, the length L is set to be not less than α (2 mm) and not more than 5mm and not more than 15mm (fig. 11 and 12) in the spot diameter of the irradiation light T1, in other words, the effective length of the effective portion appearing due to the position detection mark 41 in the light reception signal SD (i.e., the mark effective length La) is set to be in the range of 4.3 mm to 11.9 mm, based on the result of the second evaluation test.

Accordingly, in the image forming apparatus 1 in which the position detection mark 41 is formed on the belt 37, the effective length of the effective portion (the portion where the differential voltage Δ V is 1.0[ V ] or more) generated in the light reception signal SD generated by the sensor 18 can be clearly differentiated between the case where the effective length is caused by the position detection mark 41 and the case where the effective length is caused by other causes.

For example, when the control unit 4 of the image forming apparatus 1 detects a valid portion from the light reception signal SD transmitted from the sensor 18, if the valid length is within a range of 4.3[ mm ] to 11.9[ mm ], it can be determined that the valid portion is caused by the position detection mark 41, and if the valid length is outside the range, it can be determined that the valid portion is caused by another cause. Therefore, in the image forming apparatus 1, the position detection mark 41 can be detected with extremely high accuracy from the light reception signal SD generated by the sensor 18, and therefore, based on this, the position, the running speed, and the like of the belt 37 can be controlled with high accuracy, and finally, printing processing of extremely high quality can be performed on the printing paper P.

However, it is also conceivable that, in the position detection mark 41, the groove is formed not in the belt running direction E but in other directions, such as the width direction (i.e., the left-right direction). In this case, however, in the image forming apparatus 1 in which the position detection mark 41 is formed on the belt 37, when the blade 61 of the cleaning section 16 is slid on the belt 37, the blade 61 repeatedly passes over the ridge portion formed at the boundary portion between the concave grooves. In this case, in the image forming apparatus 1, a load may be applied to the driving roller 31 of the belt unit 12 and the blade 61 may be vibrated or curled.

In view of the above, in the position detection mark 41, a method of forming a groove in the belt running direction E is adopted. Therefore, in the image forming apparatus 1, when the blade 61 of the cleaning portion 16 is slid on the belt 37, the blade can be smoothly slid along the groove in the position detection mark 41, and occurrence of a load on the drive roller 31 and the like and vibration of the blade 61 can be suppressed.

However, in the image forming apparatus 1, if the variation width of the film thickness is large in one rotation of the belt 37, the running speed of the belt surface 40 may locally vary depending on the variation of the film thickness. That is, in the belt unit 12, in a portion where the film thickness of the belt 37 is large (thick), the running speed of the belt 37 becomes large (fast) when the driving force is transmitted from the driving roller 31. In the belt unit 12, in a portion where the film thickness of the belt 37 is small (thin), the running speed of the belt 37 is reduced (slow) when the driving force is transmitted from the driving roller 31. In the image forming apparatus 1, if such a change occurs in the running speed of the belt 37, the toner images of the respective colors transferred from the image forming units 11 to the belt 37, respectively, are displaced, resulting in a so-called color register error.

In the image forming apparatus 1, in order to suppress the occurrence of such a color registration error, it is conceivable to reduce the variation width of the film thickness of the belt 37. However, since the belt 37 is made of an elastomer such as a polyamide-imide resin and has a sufficient thickness, it is difficult to suppress the variation width (step) of the film thickness.

In view of the above, in the image forming apparatus 1, the arrangement period of the position detection marks 41 in the belt running direction E is made to coincide with the arrangement period of the image forming units 11 of the main body portion 2 (fig. 1) in the front-rear direction. Thus, in the image forming apparatus 1, it is possible to suppress occurrence of a color misregistration due to a variation in the film thickness of the belt 37, and it is also possible to improve the feedback accuracy of the control relating to the running speed of the belt 37.

According to the above configuration, in the image forming apparatus 1, the maximum depth Da of the position detection mark 41 formed on the belt 37 is set to be 2.0[ mu ] m or more and 11.0[ mu ] m or less, the rim depth ratio Db/Da is set to be in the range of 0.4 to 0.5, the rim length ratio Lb/Da is set to be in the range of 0.018 to 0.100, and the length L is set to be 5[ mm ] or more and 15[ mm ] or less. Thus, in the position detection mark 41, the deepest portion 84 can be positioned at the central portion 82, and the edge portion 83 can be formed with a shallower slope than the deepest portion 84, thereby avoiding the formation of the local concave portion PH. As a result, in the image forming apparatus 1, the toner in the position detection mark 41 can be reliably scraped off by the blade 61 of the cleaning section 16, and the position detection mark 41 can be detected with high accuracy by the sensor 18.

[6 ] other embodiments ]

In the above embodiment, the following case is explained: the outer peripheral depth Db of the position detection mark 41 is set to a depth from the position shifted 0.2[ mm ] toward the center side from the end 81 to the belt surface 40. However, the present invention is not limited to this, and the outer peripheral depth Db may be defined as a depth at a position shifted from the end 81 toward the center by various distances such as 2.5 mm and 1.8 mm. In short, the outer circumferential depth Db may be a value indicating the depth of the edge 83.

In the above embodiment, the following case is explained: the voltage (non-mark voltage) of the portion corresponding to the belt surface 40 in the light reception signal SD generated by the sensor 18 is set to 2.7V, and the reference voltage VS is set to 1.7V lower than 1.0V (FIG. 7). However, the present invention is not limited to this, and the non-marker voltage may be set to various voltages such as 3.3[ V ] and 2.5[ V ], or the reference voltage VS may be set to various values such as 0.8[ V ] and 1.4[ V ] in difference from the non-marker voltage. When the operating speed of the belt 37 affects the signal level of the light reception signal SD, each value may be set according to the operating speed of the belt 37. In short, the position detection mark 41 may be detected with high accuracy from the effective portion of the light reception signal SD lower than the reference voltage VS.

In the above embodiment, the following case is explained: when forming each groove of the position detection mark 41, the laser beam is irradiated at a weak intensity to linearly move the spot, and this operation is performed twice, and the start point and the end point of each operation are made to be different in position (fig. 6). However, the present invention is not limited to this, and the operation of linearly moving the laser spot may be performed once or three times or more, for example, when one groove is formed. For example, the laser intensity may be finely controlled in the vicinity of the start point or the end point, or the above may be appropriately combined. In short, the partial recess PH is not formed in the edge portion 83 of the position detection mark 41, and the edge portion 83 is inclined so as to gradually become deeper from the end portion 81 toward the center side, and finally the deepest portion 84 is located in the center portion 82.

In the above embodiment, the following case is explained: from the results of the first evaluation test, the depth-related condition that the position detection mark 41 needs to have is defined as the range of the edge depth ratio Db/Da and the edge length ratio Lb/Da (fig. 10). However, the present invention is not limited to this, and for example, the depth at the boundary between the central portion 82 and the edge portion 83 may be defined as the boundary depth De (fig. 7), and the condition regarding the depth that the position detection mark 41 needs to have may be defined as the range of the boundary depth ratio De/Da using the boundary depth De.

In the above embodiment, the following case is explained: when the condition relating to the length L that the position detection mark 41 needs to have is set based on the result of the second evaluation test, since the effective length of the effective portion due to the curl mark generated on the tape 37 is similar to the mark effective length La, 3 mm, 4 mm, and 20 mm are excluded from the length L at the time of setting (fig. 11). However, the present invention is not limited to this, and for example, when the effective length of the effective portion due to the curl mark or other various causes generated on the tape 37 is similar to the mark effective length La of the other length L, the length L may be excluded.

In the above embodiment, the spot diameter α of the irradiation light T1 of the irradiation belt 37 in the sensor 18 was described as 2mm, however, the present invention is not limited to this, and the spot diameter α may be set to other various values such as 1.6 mm, 3 mm, and the like.

In the above embodiment, the following case is explained: the nip width N of the blade 61 is set to 0.2[ mm ] in the cleaning section 16 (fig. 3). However, the present invention is not limited thereto, and the nip width N may be set to other values such as 0.1 mm, 0.3 mm, and the like.

In the above embodiment, the following case is explained: the belt 37 is formed using a polyamide-imide resin as a material. However, the present invention is not limited thereto, and various resin materials having a Young's modulus of 2000[ MPa ] or more, preferably 3000[ MPa ] or more, may be used. Specifically, resins such as Polyimide (PI), Polyetherimide (PEI), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyvinylidene fluoride (PVDF), Polyamide (PA), Polycarbonate (PC), and polybutylene terephthalate (PBT), or resin materials in which these resins are mixed can be used.

In the above embodiment, the following case is explained: carbon black is added as a conductive agent to the belt 37. For example, furnace Black, channel Black, Ketjen Black (Ketjen Black carbon), acetylene Black, and the like may be added. One of the above carbon blacks may be used alone, or a plurality of carbon blacks may be used in combination.

The kind of the carbon black is appropriately selected according to the desired conductivity. For example, when the belt 37 is formed, a predetermined resistance can be obtained by selecting a channel black and a furnace black in particular. In addition, according to the use, there can be adopted: carbon black subjected to oxidation degradation prevention treatment such as oxidation treatment and graft treatment; carbon black having improved dispersibility in solvents. In the belt 37, the carbon black content may be, for example, 3 to 40% by weight, and more preferably 3 to 30% by weight, based on the solid content of the resin, from the viewpoint of mechanical strength and the like. The method of imparting conductivity to the belt 37 is not limited to an electron conduction method using carbon black or the like, and may be, for example, a method of imparting predetermined conductivity to the belt 37 by adding an ion conductive agent.

In the above embodiment, the following case is explained: in the image forming apparatus 1, in the case where the position detection mark 41 is formed on the belt 37, the image forming apparatus 1 employs a so-called indirect transfer method (secondary transfer method) in which a toner image formed in the image forming unit 11 is transferred onto the belt 37 of the belt unit 12, and the toner image is transferred from the belt 37 onto the printing paper P. However, the present invention is not limited to this, and for example, the position detection mark 41 may be formed on various belts such as a transfer belt that transfers the printing paper P on a transfer path in an image forming apparatus that employs a direct transfer method, that is, transfers the toner image formed in the image forming unit 11 onto the printing paper P on the transfer path.

In the above embodiment, the following case is explained: the present invention is applied to the image forming apparatus 1 as a single-function printer. However, the present invention is not limited thereto, and may be applied to, for example, the following devices: an MFP (Multi Function Printer) having a scanning Function, a communication Function, and the like and also functioning as a copier and a facsimile machine; various devices that perform printing processing by electrophotography, such as copying machines and facsimile devices.

The present invention is not limited to the above-described embodiments and other embodiments. That is, the application range of the present invention also covers: an embodiment in which a part or all of the above embodiment and the other embodiments are arbitrarily combined, or an embodiment in which a part is extracted.

In the above embodiment, the following case is explained: the belt unit 12 as a belt unit is constituted by a belt 37 as a belt, a position detection mark 41 as a mark portion, driven rollers 32,33, and 34 as driven rollers, and a drive roller 31 as a drive roller. However, the present invention is not limited to this, and the belt unit may be configured by a belt, a marking portion, a driven roller, and a driving roller of other various configurations.

The marking portion of the present invention may further include a groove other than the grooves shown in fig. 6(B) and 7. For example, the marking portion of the present invention may further include a groove other than the groove satisfying the following conditions. The conditions are as follows: the groove extends along a first direction and includes a central portion and an edge portion, the central portion is spaced apart from a boundary between the groove and the outer peripheral surface, the edge portion connects the central portion and the boundary, a depth from the central portion to the outer peripheral surface is deeper than a depth from the edge portion to the outer peripheral surface, and a deepest portion is formed at a position shifted from the boundary to the central portion by 0.2mm or more. However, among the grooves provided in the mark portion, more grooves are preferable to satisfy the above condition.

The present invention can be used for an image forming apparatus that transfers a toner image onto a printing paper via a belt by, for example, an indirect transfer method.

In the present invention, the deepest portion is located at the center of the marking portion, and the edge portion is formed shallower than the deepest portion, so that when the toner entering the marking portion is scraped off by sliding the scraper, no toner is left. Thus, in the present invention, when the sensor detects the mark portion based on the reflected light from the surface of the belt, the mark portion can be detected with high accuracy without being affected by the toner, and the position of the toner image transferred onto the belt can be controlled with high accuracy.

According to the present invention, a belt unit, an image forming apparatus, and a mark forming method capable of maintaining a high-quality print state can be realized.

Further, the present technology can also adopt the following configuration.

(1)

A belt unit is provided with:

a belt having a ring shape and an outer peripheral surface formed in a flat shape, an inner peripheral surface located on the opposite side of the outer peripheral surface, and a mark portion formed on the outer peripheral surface and recessed from the outer peripheral surface toward the inner peripheral surface;

a drive roller that abuts the inner peripheral surface and moves the belt in a first direction; and

a driven roller abutting against the inner peripheral surface,

the marking portion has a plurality of grooves extending along the first direction,

each of 2 or more of the plurality of grooves includes a central portion that is distant from a boundary between each of the 2 or more grooves and the outer peripheral surface, and an edge portion that connects the central portion and the boundary,

in each of the 2 or more grooves, a depth from the central portion to the outer peripheral surface is deeper than a depth from the edge portion to the outer peripheral surface, and a deepest portion is formed at a position shifted by 0.2[ mm ] or more from the boundary to the central portion.

(2)

The belt unit of (1) above, wherein,

the edge of the mark portion forms a slope, and the depth of the slope to the outer peripheral surface gradually increases from the boundary toward the central portion.

(3)

The belt unit of the above (1) or (2), wherein,

in each of the 2 or more grooves, a depth from a position shifted by 0.2[ mm ] from the boundary toward the central portion to the outer peripheral surface is not more than half of a depth from the deepest portion to the outer peripheral surface.

(4)

The belt unit according to any one of the (1) to (3), wherein,

in each of the 2 or more grooves, a depth from the deepest portion to the outer peripheral surface is 2[ μm ] or more and 11[ μm ] or less.

(5)

The belt unit according to any one of the (1) to (4), wherein,

the length of the mark portion in the first direction is within a range in which the periphery of the mark portion on the tape is not deformed by the formation of the mark portion.

(6)

The belt unit according to any one of the (1) to (5), wherein,

the length of the mark portion in the first direction is 5[ mm ] or more and 15[ mm ] or less.

(7)

An image forming apparatus includes:

the belt unit of any one of claim 1 to claim 6;

an image forming unit that forms a developer image with a developer and transfers the developer image onto the belt or a medium conveyed by the belt; and

a sensor that irradiates irradiation light on the outer peripheral surface and detects the mark portion from reflected light reflected by the belt.

(8)

An image forming apparatus includes:

a belt unit that runs a belt in a first direction, the belt being annular and having an outer peripheral surface, an inner peripheral surface, and a mark portion, the outer peripheral surface being formed in a flat shape, the inner peripheral surface being located on an opposite side of the outer peripheral surface, the mark portion being formed on the outer peripheral surface and recessed from the outer peripheral surface toward the inner peripheral surface, and being wound around a plurality of rollers, the mark portion being formed on the outer peripheral surface and recessed from the outer peripheral surface toward the inner peripheral surface

A sensor that irradiates irradiation light on the outer peripheral surface and detects the mark portion from reflected light reflected by the belt,

the marking portion has a plurality of grooves extending in the first direction,

the at least 2 grooves of the plurality of grooves include a deepest portion in a central portion, the central portion being provided at a position away from a boundary between each of the at least 2 grooves and the outer peripheral surface and being detectable by the sensor as the mark portion, the deepest portion having a maximum depth to the outer peripheral surface.

(9)

The image forming apparatus according to the above (8), wherein,

each of 2 or more of the plurality of grooves includes a central portion that is distant from a boundary between each of the 2 or more grooves and the outer peripheral surface, and an edge portion that connects the central portion and the boundary,

in each of the 2 or more grooves, a depth from the central portion to the outer peripheral surface is deeper than a depth from the edge portion to the outer peripheral surface.

(10)

The image forming apparatus of the (8) or the (9), wherein,

the sensor generates a light reception signal having a signal level corresponding to the intensity of the reflected light,

the difference between the signal level of the central portion and the signal level of the outer peripheral surface is equal to or greater than a predetermined threshold value.

(11)

The image forming apparatus of any one of the (8) to (10), wherein,

the length of the central portion in the first direction is longer than the diameter of a spot formed on the outer peripheral surface by the irradiation light.

(12)

The image forming apparatus of any one of the (8) to (11), wherein,

the belt unit forms a winding mark on the belt by the roller,

the sensor detects a position where the winding mark is formed,

the marker portion is selected as: when the length of the central portion in the first direction is detected by the sensor, the length is not equal to the length of the lap mark.

(13)

The image forming apparatus of any one of the (8) to (12), wherein,

further comprises a cleaning part which is provided with a cleaning part,

the cleaning portion has a blade that abuts the outer peripheral surface only by a prescribed nip width in the first direction, the cleaning portion scrapes the developer from the outer peripheral surface running in the first direction,

in each of the 2 or more grooves, a length of an edge portion in the first direction, which is adjacent to a boundary between each of the 2 or more grooves and the outer peripheral surface, is equal to or greater than the nip width.

(14)

The image forming apparatus of (13) above, wherein,

in each of the 2 or more grooves, a depth from the deepest portion to the outer peripheral surface is set to a range in which the developer entering the groove can be scraped off by the scraper.

(15)

A method for forming a mark, comprising the steps of,

forming a mark portion on an outer peripheral surface of a belt, the belt being annular and having an inner peripheral surface, the outer peripheral surface being formed flat, the inner peripheral surface being located on an opposite side of the outer peripheral surface, the mark portion being recessed from the outer peripheral surface toward the inner peripheral surface,

the mark forming method includes:

a first irradiation step of irradiating the outer peripheral surface with laser light in a first irradiation range from a first start point to a first end point substantially in parallel with a first direction within a formation range that is a range in which the mark portion is to be formed; and

a second irradiation step of irradiating the outer peripheral surface with laser light in a second irradiation range from a second start point different from the first start point to a second end point different from the first end point in a direction substantially parallel to the first direction at a portion where a part of the formation range overlaps the first irradiation range,

in the mark portion, a depth from a central portion of a boundary between the mark portion and the outer peripheral surface is formed larger than a depth from an edge portion adjacent to the boundary between the mark portion and the outer peripheral surface within the formation range.

This disclosure contains subject matter relating to the disclosure in japanese priority patent application JP2018-160635 filed at the japanese patent office at 29.8.2018, the entire contents of which are incorporated herein by reference.

It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alternatives are possible in light of design requirements and other factors, but are intended to be included within the scope of the appended claims or their equivalents.