阅读说明：本技术 纸张位置检测装置、纸张输送装置以及图像形成装置 (Paper position detection device, paper conveying device and image forming device ) 是由 佐藤正幸 峰村太辅 吉川彰一 十都善行 于 2019-05-28 设计创作，主要内容包括：本发明提供一种能够不依赖于纸张状态地高精度地检测纸张位置的纸张位置检测装置、纸张输送装置以及图像形成装置。纸张位置检测装置具有：第一输送辊和第二输送辊,夹着被输送的纸张对置地配置,并且夹持纸张；以及检测部,检测纸张的端部位置,检测部具有配置于第一输送辊侧的发光部以及受光部,发光部以及受光部被配置成从发光部射出的光被第二输送辊的反射面反射并入射至受光部,检测部基于从发光部射出的光被纸张遮挡而入射至受光部的光的量发生变化,来检测纸张的端部的通过。(The invention provides a paper position detection device, a paper conveying device and an image forming device, which can detect the position of paper with high precision without depending on the state of the paper. The paper position detection device includes: a first transport roller and a second transport roller which are arranged to face each other with a conveyed sheet therebetween and which sandwich the sheet therebetween; and a detection unit that detects a position of an end portion of the sheet, the detection unit including a light emitting portion and a light receiving portion that are disposed on a side of the first transport roller, the light emitting portion and the light receiving portion being disposed such that light emitted from the light emitting portion is reflected by a reflection surface of the second transport roller and enters the light receiving portion, the detection unit detecting passage of the end portion of the sheet based on a change in an amount of light entering the light receiving portion due to the light emitted from the light emitting portion being blocked by the sheet.)

1. A paper position detecting device includes:

A first transport roller and a second transport roller which are arranged to face each other with a sheet being transported therebetween and which sandwich the sheet therebetween; and

A detection section that detects an end position of the paper,

The detection part is provided with a light-emitting part and a light-receiving part which are arranged on the first conveying roller side,

The light emitting section and the light receiving section are configured such that light emitted from the light emitting section is reflected by a reflection surface of the second conveying roller and is incident on the light receiving section,

The detection unit detects passage of an end of the sheet based on a change in the amount of light that is incident on the light receiving unit as a result of the light emitted from the light emitting unit being blocked by the sheet.

2. The paper position detecting device according to claim 1,

The reflecting surface is formed by a cylindrical portion of the second conveying roller.

3. The paper position detecting device according to claim 2,

The cylindrical portion is a roller shaft of the second conveying roller.

4. The paper position detecting device according to claim 2,

The light emitting section and the light receiving section are arranged so as to be separated from each other in an axial direction of the first transport roller, and the reflecting surface has an inclined shape or a curved shape.

5. The paper position detecting device according to claim 4,

The light receiving unit is positioned such that a direction of incident light is orthogonal to a conveying direction of the sheet.

6. The paper position detecting device according to claim 2,

The light receiving unit is disposed on a downstream side in a conveying direction of the sheet with respect to a center position of a nip portion between the first conveying roller and the second conveying roller,

The light emitting unit is disposed downstream of the light receiving unit in a conveying direction of the sheet.

7. The paper position detecting device according to claim 6,

The light receiving unit is positioned such that a direction of incident light is orthogonal to a conveying direction of the sheet.

8. The paper position detecting device according to claim 1,

The second transport roller has a mirror surface portion subjected to mirror surface processing, and the reflection surface is formed by the mirror surface portion.

9. The paper position detecting device according to claim 1,

And a cleaning member for cleaning the reflecting surface.

10. the paper position detecting device according to claim 1,

The first transport roller side is located above the sheet in the vertical direction.

11. a sheet conveying apparatus having the sheet position detecting apparatus according to claim 1.

12. The paper conveying apparatus according to claim 11,

A positioning mechanism of a steering type for correcting the inclination of the paper,

The detection unit of the paper position detection device is provided in plurality so as to be separated in the axial direction of the first transport roller and can detect the inclination of the paper,

The alignment mechanism corrects the inclination of the paper sheet based on the inclination of the paper sheet detected by the detection unit.

13. An image forming apparatus includes:

The paper conveying device of claim 11; and

And an image forming unit configured to form an image on the sheet conveyed by the sheet conveying device.

14. the image forming apparatus according to claim 13,

The paper conveying device is provided with a contraposition mechanism of a steering mode, the contraposition mechanism corrects the inclination of the paper,

A plurality of detection units of the paper position detection device are arranged so as to be separated in the axial direction of the first transport roller, and can detect the inclination of the paper,

The alignment mechanism corrects the inclination of the paper sheet based on the inclination of the paper sheet detected by the detection unit.

15. The image forming apparatus according to claim 13,

The image forming section has a secondary transfer roller that transfers the toner image to the sheet,

The detection portion of the paper position detection device detects the passage of the end of the paper to adjust the timing at which the paper reaches the secondary transfer roller.

Technical Field

The invention relates to a paper position detection device, a paper conveying device and an image forming device.

background

An image forming apparatus such as a copying machine is required to form an image with good positional accuracy. However, the sheet may be inclined due to the type of sheet on which an image is formed, the temperature and humidity during sheet conveyance, the characteristics of members such as conveyance rollers, and the like, and when an image is formed in this state, the positional accuracy of image formation is lowered.

Therefore, the sheet conveying apparatus provided in the image forming apparatus includes a sheet positioning mechanism of a reversing type for correcting the inclination of the sheet. The paper sheet positioning mechanism corrects the inclination of the paper sheet based on the detection of the paper sheet position. In other words, in order to correct the inclination of the sheet with high accuracy, it is necessary to detect the sheet position with high accuracy.

However, depending on the state of the paper, the paper floats (bends) due to curling or the like, and it is difficult to detect the position of the paper with high accuracy.

On the other hand, the detection means for detecting the position of the sheet includes a non-contact sensor having a light emitting section and a light receiving section. Unlike the contact sensor, the non-contact sensor is preferable because the sheet is not folded or scratched when detecting the sheet position.

For example, japanese patent application laid-open No. 2014-112138 discloses a configuration in which a light emitting section and a light receiving section of a non-contact sensor are arranged above and below a sheet to be conveyed.

However, when the arrangement structure of the light emitting section and the light receiving section of the non-contact sensor described in japanese patent application laid-open No. 2014-112138 is applied to the detection of the paper position, there is a problem that the improvement of the detection accuracy is limited.

For example, since the floating is eliminated in a state where the sheet is nipped by the conveying rollers, it is preferable to detect the position of the sheet in the vicinity of the nip portion. On the other hand, the light emitting section and the light receiving section are arranged so as to sandwich the transported sheet. Therefore, the light emitted from the light emitting section passes through the vicinity of the nip section and is separated from the conveying roller at a position where it is not blocked (disturbed) by the conveying roller. In other words, the distance between the light emitting section and the light receiving section needs to be increased. Therefore, although it is possible to suppress a decrease in detection accuracy due to the floating of the sheet, the increase in distance between the light emitting section and the light receiving section causes a decrease in detection accuracy, and thus the improvement in detection accuracy is insufficient.

On the other hand, in the configuration in which the light emitted from the light emitting section does not pass through the vicinity of the nip portion, the distance between the light emitting section and the light receiving section can be shortened, but the decrease in detection accuracy due to the floating of the sheet cannot be suppressed, so that it is difficult to detect the position of the sheet with high accuracy.

Disclosure of Invention

The present invention has been made to solve the problems associated with the conventional techniques described above, and an object thereof is to provide a paper position detecting device, a paper conveying device, and an image forming apparatus capable of detecting the position of paper with high accuracy without depending on the state of the paper.

(technical means 1)

To achieve at least one of the above objects, a sheet position detecting device reflecting one side of the present invention includes: a first transport roller and a second transport roller which are arranged to face each other with a sheet being transported therebetween and which sandwich the sheet therebetween; and a detection unit that detects the position of the end of the paper. The detection unit includes a light emitting unit and a light receiving unit arranged on a first transport roller side, the light emitting unit and the light receiving unit being arranged such that light emitted from the light emitting unit is reflected by a reflection surface of the second transport roller and incident on the light receiving unit, and the detection unit detects passage of an end portion of the sheet based on a change in an amount of light incident on the light receiving unit due to the light emitted from the light emitting unit being blocked by the sheet.

Drawings

fig. 1 is a front view for explaining a paper position detection device according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view for explaining a paper position detection device according to an embodiment of the present invention.

Fig. 3 is a plan view for explaining the first conveying roller shown in fig. 1.

Fig. 4 is a plan view for explaining the second conveying roller shown in fig. 1.

Fig. 5 is a schematic diagram for explaining an image forming apparatus and a sheet conveying apparatus according to an embodiment of the present invention.

Fig. 6 is a schematic diagram for explaining the aligning mechanism in which the paper position detecting device shown in fig. 5 is incorporated.

Fig. 7A is a flowchart for explaining the tilt correction and the offset correction in the positioning mechanism shown in fig. 6.

Fig. 7B is a flowchart following fig. 7A.

Fig. 8A is a schematic diagram for explaining an example of the rotation of the registration rollers in step S109 shown in fig. 7A.

Fig. 8B is a schematic diagram for explaining another example of the rotation of the registration rollers in step S109 shown in fig. 7A.

fig. 9 is a schematic diagram for explaining modification 1 of the embodiment of the present invention.

Fig. 10 is a schematic diagram for explaining modification 2 of the embodiment of the present invention.

Fig. 11 is a schematic diagram for explaining modification 3 of the embodiment of the present invention.

fig. 12 is a schematic diagram for explaining modification 4 of the embodiment of the present invention.

Fig. 13 is a schematic diagram for explaining modification 5 of the embodiment of the present invention.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. For convenience of explanation, the dimensional ratio of the drawings may be exaggerated and may be different from the actual ratio.

Fig. 1 and 2 are a front view and a cross-sectional view for explaining a paper position detection device according to an embodiment of the present invention, and fig. 3 and 4 are plan views for explaining a first conveyance roller and a second conveyance roller shown in fig. 1.

The paper position detection apparatus 100 shown in fig. 1 includes a conveying roller pair 110 and a transmission sensor 150.

The conveying roller pair 110 is composed of a first conveying roller 120 and a second conveying roller 130 which are arranged to face each other with the conveyed paper P therebetween, and is arranged in a direction (hereinafter, referred to as a paper width direction) orthogonal to the paper conveying direction.

The first transport roller 120 is positioned vertically above the sheet P. The first conveying roller 120 is a driven roller, and as shown in fig. 3, includes cylindrical roller portions 121, 124, 127, shafts 122, 125, 128, and a support portion (not shown).

The roller portions 121, 124, 127 are arranged apart in the sheet width direction. Shafts 122, 125, and 128 are axes of the roller portions 121, 124, and 127, and have a short shaft shape. The support portion rotatably supports the shafts 122, 125, 128, and the roller portions 121, 124, 127 are rotatably driven.

the second transport roller 130 is positioned vertically below the sheet P. The second transport roller 130 is a drive roller, and as shown in fig. 4, includes cylindrical roller portions 131, 134, 137, a shaft 132, and a reflection surface 140.

The roller portions 131, 134, 137 are arranged separately in the sheet width direction. The shaft 132 is a shaft (roller shaft) common to the roller portions 121, 124, 127, has a long shaft shape, and is rotationally driven by a drive source (not shown). In other words, the roller portions 131, 134, 137 are rotationally driven. As shown in fig. 2, the roller portions 131, 134, and 137 and the roller portions 121, 124, and 127 of the first conveying roller 120 are positioned so as to form a nip 115 (capable of nipping the paper P) between the paper P.

The reflecting surface 140 is formed by a portion of the shaft 132 located between the roller portion 131 and the roller portion 134 and a portion of the shaft 132 located between the roller portion 134 and the roller portion 137. The reflecting surface 140 is not limited to the form of being constituted by the shaft 132, and may be constituted by the roller portions 131, 134, and 137, for example. The reflecting surface 140 is not limited to the form of the cylindrical portion (the roller portions 131, 134, 137 and the shaft 132) of the second conveying roller 130.

The transmission sensor 150 is a detection unit that detects the end position of the sheet P, and is disposed between the roller portion 121 and the roller portion 124 and between the roller portion 124 and the roller portion 127 on the first transport roller 120 side. The transmissive sensor 150 includes a light emitting portion 152 and a light receiving portion 154. In the present embodiment, the end of the sheet P is the sheet leading end in the sheet conveying direction.

The light emitting unit 152 incorporates a light source and emits light as a medium for detecting the position of the edge of the sheet P. The light receiving unit 154 incorporates a photoelectric conversion element and converts the light emitted from the light emitting unit 152 into an electrical signal. The light emitting section 152 and the light receiving section 154 are arranged apart in the axial direction of the first transport roller 120 such that light emitted from the light emitting section 152 is reflected by the reflective surface 140 of the second transport roller 130 and enters the light receiving section 154.

therefore, when the sheet P passing between the first conveying roller 120 and the second conveying roller 130 (the nip portion 115) blocks the light emitted from the light emitting portion 152, the amount of light reflected by the reflection surface 140 of the second conveying roller 130 and incident on the light receiving portion 154 decreases, and the electrical characteristics of the photoelectric conversion element of the light receiving portion 154 change. In other words, the passage of the edge of the sheet P can be detected based on the change in the amount of incident light to the light receiving unit 154 due to the light emitted from the light emitting unit 152 being blocked by the sheet P.

As described above, in the sheet position detection apparatus 100, one of the pair of transport rollers (the second transport roller 130) that sandwiches the sheet P is used as a reflection surface, and the light emitting portion 152 and the light receiving portion 154 of the transmission sensor 150 are disposed on the other side (the first transport roller 120 side). Therefore, even when the distance between the light emitting section 152 and the light receiving section 154 is shortened, the light emitted from the light emitting section 152 can be configured to pass through the vicinity of the nip section 115 (above the nip section). Therefore, it is possible to suppress a decrease in detection accuracy of the paper position due to the floating of the paper P and a decrease in detection accuracy due to a large distance between the light emitting section 152 and the light receiving section 154.

since the reflective surface 140 of the second conveyor roller 130 is the cylindrical portion of the second conveyor roller 130 (the cylindrical surface of the shaft 132), the point of reflection at which the light emitted from the light-emitting portion 152 returns to the light-receiving portion 154 is limited to a point on the ridge line of the cylindrical portion (see fig. 2 and 4), and the light (reflected light) returning to the light-receiving portion 154 has directivity. Therefore, even if no slit is provided between the reflection surface 140 and the light receiving portion 154, the detection performance of the light returned to the light receiving portion 154 can be improved. Further, the ridge line corresponds to the center of the nip.

The light emitting portion 152 and the light receiving portion 154 of the transmission sensor 150 are located on the first conveying roller 120 side above the sheet P in the vertical direction. Therefore, contamination by paper dust originating from the paper P can be avoided. Further, the first conveying roller 120 may be disposed vertically downward and the second conveying roller 130 may be disposed vertically upward, as necessary.

The plurality of transmissive sensors 150 are arranged separately in the sheet width direction. Therefore, the inclination amount of the sheet P with respect to the sheet width direction can be detected (calculated) based on the difference (time difference) in the detection timing of the sheet end portion of the transmissive sensor 150.

the reflecting surface 140 is preferably formed of a mirror surface portion having a mirror surface finish. In this case, the detection accuracy can be improved by suppressing a decrease in the amount of reflected light (increasing the specular reflection component and reducing the diffuse reflection component). The mirror finishing is preferably performed only on the reflecting surface 140. In this case, the surface treatment cost can be reduced.

The transmissive sensor 150 is not limited to the configuration of a plurality. Further, if necessary, the transmission sensor 150 may be disposed on the second conveying roller side positioned below in the vertical direction, and the reflection surface 140 may be provided on the first conveying roller 120 positioned above in the vertical direction.

The number of roller portions of the first conveying roller 120 and the second conveying roller 130 is not limited to 3, and can be set appropriately according to the paper width, for example. The first transport roller 120 may be configured to have a single common shaft. The roller portions 131, 134, and 137 of the second conveying roller 130 may have separate shafts.

Next, an example of an apparatus incorporating the paper position detection apparatus 100 will be described.

Fig. 5 is a schematic diagram for explaining an image forming apparatus and a sheet conveying apparatus according to an embodiment of the present invention.

The image forming apparatus 200 shown in fig. 5 is, for example, an MFP (Multi-Function Peripheral) having a copy Function, a printer Function, and a scan Function, and includes a control unit 210, a storage unit 215, an image reading unit 220, an operation display unit 230, an image forming unit 240, a transfer unit 250, a fixing unit 260, a paper conveying unit 270, and a communication interface 290. As will be described later, the paper position detection device 100 is incorporated in the positioning mechanism 280 of the paper conveying unit 270.

the control Unit 210 is a control Circuit including a microprocessor (CPU) or an ASIC (Application Specific Integrated Circuit) that executes control of each Unit and various arithmetic processes according to a program, and the functions of the image forming apparatus 200 are exhibited by the control Unit 210 executing the corresponding program.

the storage unit 215 is configured by appropriately combining a ROM (Read Only Memory), a RAM (Random Access Memory), and an HDD (Hard Disk Drive), for example. The ROM is a read-only storage device that stores various programs and various data. The RAM is a high-speed random access storage device that temporarily stores programs and data as a work area. The HDD is a large-capacity random access storage device that stores various programs and various data.

The image reading unit 220 is used to generate image data of a document, and includes a light source 222, an optical system 224, and an image pickup device 226. The light source 222 irradiates light on the document placed on the reading surface 228, and the reflected light is imaged on the image pickup device 226 moved to the reading position via the optical system 224. The imaging element 226 is formed of, for example, a line image sensor, and generates an electric signal (photoelectric conversion) from the intensity of reflected light. The generated electric signal is subjected to image processing and then input to the image forming unit 240. The image processing is a/D conversion, shading correction, filter processing, image compression processing, or the like. The image reading unit 220 may also include an ADF (Auto Document Feeder), for example.

The operation display unit 230 is composed of, for example, a touch panel and a physical keyboard, and has both an output unit and an input unit. The touch panel can be used to notify a user of a device configuration, a status of progress of a print job, a status of occurrence of a jam, currently changeable settings, and the like. The physical keyboard is used for a user to perform various instructions (inputs) such as character input, various settings, and start instruction.

The image forming section 240 is provided in plural to form an image on the sheet P, corresponding to each color of Y (yellow), M (magenta), C (cyan), and K (black) in this order from the top. The image forming unit 240 includes a photosensitive drum 242, a charging unit 244, an optical writing unit 246, and a developing device 248.

The photosensitive drum 242 is an image bearing member having a photosensitive layer made of a resin such as polycarbonate containing an Organic Photoconductor (OPC) and is configured to rotate at a predetermined speed. The charging section 244 is constituted by a corona discharge electrode disposed around the photoreceptor drum 242, and the surface of the photoreceptor drum 242 is charged by the generated ions.

the optical writing section 246 incorporates a scanning optical device, and exposes the charged photosensitive drum 242 based on raster image data to lower the potential of the exposed portion, thereby forming a charge pattern (electrostatic latent image) corresponding to the image data.

The developing device 248 transfers the stored developer to the photosensitive drum 242 to develop the electrostatic latent image formed on the photosensitive drum 242. The developer is formed by mixing carriers and toners corresponding to respective colors, and the electrostatic latent image is visualized by the toners.

The transfer section 250 includes an intermediate transfer belt 252, a primary transfer roller 254, and a secondary transfer roller 256. The intermediate transfer belt 252 is wound around the primary transfer roller 254 and a plurality of rollers, and is supported so as to be able to travel. The primary transfer rollers 254 are provided in plural numbers, and correspond to respective colors of Y (yellow), M (magenta), C (cyan), and K (black) in this order from top to bottom. The secondary transfer roller 256 is disposed outside the intermediate transfer belt 252, and is configured to allow the sheet P to pass through between the intermediate transfer belt 252 and the secondary transfer roller 256.

The toner images of the respective colors formed in the image forming unit 240 are sequentially transferred onto the intermediate transfer belt 252 by the primary transfer roller 254, and color toner images of yellow, magenta, cyan, and black are formed in an overlapping manner. The formed toner image is transferred to the conveyed paper P by the secondary transfer roller 256.

The fixing unit 260 is for fixing the color image transferred to the paper P, and includes a fixing roller (heat roller) 262 and a pressure roller 264. When the paper P passes through a nip between the fixing roller 262 and the pressure roller 264, the paper P is pressed and heated, and the toner is melted, whereby the color image is fixed.

the paper transport unit 270 is a paper transport device including a paper feed unit 272, a registration mechanism 280, a fixing transport roller 285, a paper discharge roller 286, and a paper reversing unit 288.

The paper feed unit 272 includes paper feed trays 273 to 275 for storing the paper P, a conveying roller 276, and a separation roller 277. The conveying roller 276 and the separation roller 277 convey the sheets one by one from the sheet feed trays 273 to 275 to the conveying path 271 of the sheet conveying unit 270.

the alignment mechanism 280 conveys the paper P from the paper feed unit 272 to the secondary transfer roller 256, and at this time, performs skew correction and offset correction of the paper P. Further, reference numerals 281, 282, and 283 are a registration roller, a shift detection sensor, and a leading end timing detection sensor.

The fixing conveying roller 285 conveys the sheet P passing through the secondary transfer roller 256 and the fixing unit 260 toward the sheet discharge roller 286. The sheet discharge roller 286 discharges the conveyed sheet P to the outside of the apparatus.

the paper reversing unit 288 is used to guide the paper P having passed through the fixing conveying roller 285 to a conveying path between the paper feed trays 273 to 275 and the paper discharge roller 286, without being guided to the conveying path toward the paper discharge roller 286. This enables the front and back sides of the sheet P to be reversed and discharged, or images to be formed on both sides of the sheet P.

the communication interface 290 is, for example, an expansion device (LAN port) that adds a communication function for connecting to a computer that transmits data such as a print job via a network to the image forming apparatus 200. The Network is constituted by various networks such as a Local Area Network (LAN), a Wide Area Network (WAN) in which LANs are connected by a dedicated line, the internet, and a combination thereof.

next, the positioning mechanism 280 of the paper conveying unit 270 will be described.

Fig. 6 is a schematic diagram for explaining the paper position detecting device and the aligning mechanism shown in fig. 5.

The registration mechanism 280 is of a reverse type, and includes the paper position detection device 100, a registration roller 281, a shift detection sensor 282, and a leading end timing detection sensor 283, as shown in fig. 6.

As described above, the paper position detection apparatus 100 includes 2 transmissive sensors 150, and can detect the amount of inclination of the paper P with respect to the paper width direction orthogonal to the paper conveyance direction. Therefore, the paper position detection device 100 is disposed upstream of the registration rollers 281 in the paper conveyance direction, and is used as a skew detection sensor. In the following, one of the transmissive sensors 150 is referred to as a near sensor 150A and a far sensor 150B as appropriate, respectively.

The registration roller 281 is a turn roller (correction roller) configured to be rotatable (swingable) about one end thereof and to be movable in the sheet width direction. The rotation of the registration rollers 281 is performed to correct the inclination of the sheet P based on the inclination detection of the sheet position detection device 100. The movement of the registration rollers 281 is performed to correct the deviation of the paper P.

The shift detection sensor 282 is, for example, a line sensor in which photoelectric conversion elements are arranged along the sheet width direction. The offset detection sensor 282 is disposed downstream of the registration roller 281 in the sheet conveying direction, and is configured to detect an offset amount of the sheet P in the sheet width direction after the skew correction. The detected shift amount is used to calculate the movement amount of the registration roller 281.

The leading end timing detection sensor 283 is disposed between the deviation detection sensor 282 and the secondary transfer roller 256, and is configured to detect the leading end of the paper P and to be able to adjust the timing at which the paper P reaches the secondary transfer roller 256. The front end timing detection sensor 283 is not limited to the arrangement between the displacement detection sensor 282 and the secondary transfer roller 256.

next, the tilt correction and the offset correction will be described in detail.

fig. 7A and 7B are flowcharts for explaining the tilt correction and the offset correction in the registration mechanism shown in fig. 6, and fig. 8A and 8B are schematic diagrams for explaining one example and another example of the rotation of the registration roller in step S109 shown in fig. 7A. The algorithm represented by the flowcharts shown in fig. 7A and 7B is stored as a program in the storage unit 215 and executed by the control unit 210.

First, as shown in fig. 7A, driving of paper conveying rollers such as conveying roller 276 and separation roller 277 is started (step S101), and feeding of paper P is started (step S102).

Then, it is determined whether or not the front end of the sheet P is detected by the near side sensor 150A (see fig. 6) which is one of the transmissive sensors 150 (step S103).

When it is determined that the front end of the sheet P is detected by the near-side sensor 150A (yes in step S103), it is determined whether or not the front end of the sheet P is detected by the rear-side sensor 150B (see fig. 6) which is the other of the transmissive sensors 150 (step S104). If it is determined that the front end of the sheet P is detected by the back side sensor 150B (yes in step S104), the process proceeds to step S107.

When it is determined that the front end of the sheet P is not detected by the near side sensor 150A (no in step S103), it is determined whether or not the front end of the sheet P is detected by the far side sensor 150B (step S105). If it is determined that the front end of the sheet P is not detected by the back sensor 150B (no in step S105), the process returns to step S103. When it is determined that the front end of the sheet P is detected by the back side sensor 150B (YES in step S105), it is determined whether or not the front end of the sheet P is detected by the front side sensor 150A (step S106). If it is determined that the front end of the sheet P is detected by the near-side sensor 150A (yes in step S104), the process proceeds to step S107.

In step S107, the amount of inclination of the sheet P with respect to the sheet width direction is detected (calculated) based on the difference (time difference) between the timing of detecting the sheet end by the near side sensor 150A and the timing of detecting the sheet end by the far side sensor 150B.

Then, based on the inclination amount of the paper P, the rotation amount of the registration roller 281 for correcting the inclination of the paper P is calculated (step S108), and the registration roller 281 rotates based on the rotation amount (step S109).

For example, when the front end of the sheet P is detected earlier by the front sensor 150A (step S103 and step S104), the registration roller 281 rotates downstream in the sheet conveying direction as shown in fig. 8A. On the other hand, when the front end of the sheet P is detected earlier by the back side sensor 150B (step S105 and step S106), the registration roller 281 rotates upstream in the sheet conveying direction as shown in fig. 8B.

After that, after the leading end of the paper P passes through the registration rollers 281, the registration rollers 281 are rotated to a fixed position (home position), whereby the inclination of the paper P is corrected (step S110).

Next, it is determined whether or not the leading end of the sheet P is detected by the offset detection sensor 282 (step S111).

when the leading edge of the sheet P reaches the offset detection sensor 282 and the leading edge of the sheet P is detected by the offset detection sensor 282 (YES in step S111), the amount of offset of the sheet P is detected (step S112).

then, the amount of movement of the registration roller 281 for correcting the displacement of the paper P is calculated based on the amount of displacement of the paper P (step S113), and the registration roller 281 is moved in the paper width direction based on the amount of movement to perform the displacement correction of the paper P (step S114).

Then, it is determined whether or not the leading edge of the sheet P is detected by the leading edge timing detection sensor 283 (step S115).

When the leading edge of the paper P reaches the leading edge timing detection sensor 283 and the leading edge of the paper P is detected by the leading edge timing detection sensor 283 (yes in step S115), the registration roller 281 moves to perform offset correction of the paper P (step S116). In other words, in the present embodiment, the offset correction of the sheet P is performed in 2 times.

Then, the timing at which the sheet P reaches the secondary transfer roller 256 is adjusted, and then, when the sheet P reaches the secondary transfer roller 256, the toner image is transferred (step S117).

As described above, in the paper transport section 270, the paper position detection device 100 capable of accurately detecting the paper position without depending on the paper state is used as the inclination detection of the paper aligning mechanism of the switchback system, and therefore, the inclination of the paper can be accurately corrected. Further, since the image forming apparatus 200 includes the sheet conveying device capable of correcting the inclination of the sheet with high accuracy, the image can be formed with good positional accuracy.

The number of transmissive sensors 150 is not limited to 2, and can be set as appropriate according to the width of the paper P. The paper position detection device 100 is not limited to the type applied to the inclination detection sensor of the alignment mechanism 280 of the paper conveying unit 270.

Next, modifications 1 to 5 of the embodiment of the present invention will be explained in order.

fig. 9 and 10 are schematic diagrams for explaining modifications 1 and 2 of the embodiment of the present invention.

As in modification 1 shown in fig. 9, the shaft 132 of the second conveyor roller 130 may have a profiled portion 133.

The special-shaped portion 133 includes a first frustum portion 133A, a second frustum portion 133C, and a reduced-diameter portion 133B connecting the first frustum portion 133A and the second frustum portion 133C. The first frustum portion 133A is tapered toward one end of the reduced diameter portion 133B. The second frustum portion 133C is tapered toward the other end of the reduced diameter portion 133B. The reflecting surface 140 that reflects the light emitted from the light emitting section 152 of the transmissive sensor 150 disposed on the first conveying roller 120 side is formed by the first frustum 133A and has an inclined shape.

In this case, the light receiving portion 154 of the transmission sensor 150 can be positioned so that the direction of the incident light is orthogonal to the sheet conveying direction. In this case, the degree of freedom in the arrangement of the light-receiving unit 154 and the light-emitting unit 152 is increased, and the light-emitting unit 152 and the light-receiving unit 154 can be further brought closer to each other. The direction orthogonal to the sheet conveying direction is a direction parallel to the thickness direction of the sheet P.

The first frustum portion 133A constituting the reflection surface 140 is not limited to the inclined shape, and may be curved as in modification 2 shown in fig. 10, for example. In this case, the degree of freedom in the arrangement of the light-receiving unit 154 and the light-emitting unit 152 is increased, and the light-emitting unit 152 and the light-receiving unit 154 can be further brought closer to each other.

Fig. 11 is a schematic diagram for explaining modification 3 of the embodiment of the present invention.

The transmission sensor 150 may include a light receiving unit 154 and a light emitting unit 152 arranged as in modification 3 of fig. 11. Specifically, the light receiving unit 154 is disposed downstream of the center position of the nip 115 in the sheet conveying direction, and is positioned so that the direction of the incident light is orthogonal to the sheet conveying direction, and the light emitting unit 152 is disposed downstream of the light receiving unit 154 in the sheet conveying direction. In this case, the degree of freedom in the arrangement of the light-receiving unit 154 and the light-emitting unit 152 is increased, and the light-emitting unit 152 and the light-receiving unit 154 can be further brought closer to each other.

Fig. 12 is a schematic diagram for explaining modification 4 of the embodiment of the present invention.

As in modification 4 shown in fig. 12, the paper position detection apparatus 100 may also include a cleaning member 160. Cleaning member 160 is in the form of a brush, and is configured to scrape off dirt on reflecting surface 140 to clean reflecting surface 140. In this case, since the cleaning property of the reflection surface 140 is maintained (dirt is removed), the detection accuracy of the edge portion of the sheet P can be maintained while suppressing a decrease in the amount of reflected light.

The cleaning member 160 is not limited to a brush shape, and may be a sponge shape, for example. The cleaning member 160 is made of MYLAR (registered trademark) or other material, and can remove dirt on the reflecting surface 140.

Fig. 13 is a schematic diagram for explaining modification 5 of the embodiment of the present invention.

As in modification 5 shown in fig. 13, the paper conveying unit 270 may include a second paper position detecting device 100A. The paper position detection device 100A is used as a leading end timing detection sensor 283 (fig. 6), is disposed between the displacement detection sensor 282 and the secondary transfer roller 256, detects the leading end of the paper P, and adjusts the timing at which the paper P reaches the secondary transfer roller 256.

The paper position detection apparatus 100A has a single transmissive sensor 150 because it does not detect the inclination of the paper P, but is not particularly limited to this embodiment, and may have a plurality of transmissive sensors 150. The paper position detection device 100A is not limited to the one used together with the paper position detection device 100 for detecting the inclination of the paper P, and may be used independently.

As described above, the present embodiment can provide a paper position detection device, a paper transport device, and an image forming apparatus capable of detecting the position of paper with high accuracy regardless of the state of the paper.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of protection. For example, modifications 1 to 5 can be combined as appropriate. The form of application of the sheet position detection device to the sheet conveying unit (sheet conveying device) of the image forming apparatus is not limited. In addition, the image forming apparatus is not limited to the MFP type.