Image forming apparatus with a plurality of image forming units
阅读说明:本技术 成像装置 (Image forming apparatus with a plurality of image forming units ) 是由 辻村宗士 筑岛悠 金子健佑 于 2020-04-21 设计创作,主要内容包括:一种成像装置,包括:图像承载部件;转印部件;在片材输送方向上布置在转印部分的上游的输送单元;布置在输送单元上游的上游输送单元;驱动输送单元的驱动单元;以及控制器,所述控制器构造成控制驱动单元以改变输送单元的输送速度,使得在片材在片材输送方向上的前缘已经进入转印部分之后片材的后缘通过上游输送单元的情况下,在片材的后缘通过上游输送单元之前输送单元以第一速度输送片材,并且在片材的后缘已经通过上游输送单元后输送单元以比第一速度更快的第二速度输送片材。(An image forming apparatus comprising: an image bearing member; a transfer member; a conveying unit arranged upstream of the transfer portion in a sheet conveying direction; an upstream conveying unit arranged upstream of the conveying unit; a drive unit that drives the conveying unit; and a controller configured to control the drive unit to change a conveying speed of the conveying unit such that, in a case where a trailing edge of the sheet passes through the upstream conveying unit after a leading edge of the sheet in a sheet conveying direction has entered the transfer portion, the conveying unit conveys the sheet at a first speed before the trailing edge of the sheet passes through the upstream conveying unit, and the conveying unit conveys the sheet at a second speed faster than the first speed after the trailing edge of the sheet has passed through the upstream conveying unit.)
1. An image forming apparatus comprising:
an image bearing member configured to bear a toner image and rotate;
a transfer member configured to form a transfer portion between the transfer member and the image bearing member and to transfer a toner image from the image bearing member to a sheet at the transfer portion;
a conveying unit disposed upstream of the transfer portion in a sheet conveying direction and configured to convey the sheet toward the transfer portion;
An upstream conveying unit that is arranged upstream of the conveying unit in a sheet conveying direction and configured to convey the sheet to the conveying unit;
a driving unit configured to drive the conveying unit; and
a controller configured to control the drive unit to change a conveying speed of the conveying unit such that, in a case where a trailing edge of the sheet in the sheet conveying direction passes through the upstream conveying unit after a leading edge of the sheet in the sheet conveying direction has entered the transfer portion, the conveying unit conveys the sheet at a first speed before the trailing edge of the sheet passes through the upstream conveying unit, and the conveying unit conveys the sheet at a second speed faster than the first speed after the trailing edge of the sheet has passed through the upstream conveying unit.
2. The image forming apparatus as set forth in claim 1,
wherein the controller is configured to:
executing a first mode in which the conveying speed of the conveying unit is not changed before and after a trailing edge of the sheet having the first grammage has passed through the upstream conveying unit, in a case where the sheet having the first grammage is conveyed, and
Executing a second mode in which the conveying speed of the conveying unit is changed such that the conveying unit conveys the sheet with the second grammage at the first speed before a trailing edge of the sheet with the second grammage passes through the upstream conveying unit, and the conveying unit conveys the sheet with the second grammage at the second speed after the trailing edge of the sheet with the second grammage has passed through the upstream conveying unit, in a case where the sheet with the second grammage which is larger than the first grammage is conveyed.
3. An image forming apparatus according to claim 1, wherein said controller is configured to set a conveying speed after a trailing edge of said sheet has passed through said upstream conveying unit to one of different speeds in accordance with a sheet type of said sheet.
4. An image forming apparatus according to claim 1, further comprising a conveying guide configured to form a curved conveying path between said upstream conveying unit and said conveying unit in said sheet conveying direction.
5. An image forming apparatus according to claim 1, wherein said conveying unit is a registration roller pair configured to correct skew of the sheet and then convey the sheet to said transfer portion based on a timing to start forming a toner image to be carried on said image carrying member.
6. The imaging device of claim 1, wherein the controller is configured to: changing the driving unit from a state in which the conveying unit is driven at the first speed to a state in which the conveying unit is driven at the second speed at a timing corresponding to a trailing edge of the sheet passing through the upstream conveying unit.
7. The imaging device of claim 1, wherein the controller is configured to: if the leading edge of the sheet passes through a conveying unit arranged downstream of the transfer portion in the sheet conveying direction before the trailing edge of the sheet passes through the conveying unitThe conveying unitThen, a process of changing the conveying speed of the conveying unit is performed at a timing corresponding to the leading edge of the sheet passing through the conveying unit disposed downstream of the transfer portion.
8. The image forming apparatus according to claim 7, wherein the conveying unit arranged downstream of the transfer portion is a fixing portion configured to fix the toner image transferred to the sheet at the transfer portion onto the sheet.
9. The imaging device of claim 1, wherein the controller is configured to: if the trailing edge of the sheet passes through a conveying unit arranged further upstream of the upstream conveying unit after the leading edge of the sheet has entered the transfer portion, a process of changing the conveying speed of the conveying unit is performed at a timing corresponding to the trailing edge of the sheet passing through a conveying unit arranged further upstream of the upstream conveying unit.
10. The imaging device of claim 1, wherein the controller is configured to: changing the conveying speed of the conveying unit from the first speed to the second speed at a timing corresponding to a leading edge of the sheet in the sheet conveying direction entering the transfer portion.
11. The imaging apparatus according to any one of claims 1 to 10, further comprising:
a support portion configured to support the sheet; and
a feeding unit configured to feed the sheet supported on the support portion,
wherein the upstream conveying unit is a conveying roller pair that is arranged between the feeding unit and the conveying unit in the sheet conveying direction and is configured to convey the sheet fed by the feeding unit toward the conveying unit.
12. The image forming apparatus according to any one of claims 1 to 10, further comprising a supporting portion configured to support the sheet;
wherein the upstream conveying unit is a feed roller configured to feed the sheet supported on the supporting portion toward the conveying unit.
13. The imaging apparatus according to any one of claims 1 to 10, further comprising:
a reverse conveying unit that is arranged downstream of the transfer portion in the sheet conveying direction and is configured to reverse a conveying direction of the sheet to which the image has been transferred on the first side of the sheet in the transfer portion; and
a re-conveying path configured to guide the sheet reversed by the reverse conveying unit toward the conveying unit;
wherein the upstream conveying unit is a conveying roller pair that is arranged on the re-conveying path and is configured to convey the sheet reversed by the reverse conveying unit toward the conveying unit with an image being formed on a second side of the sheet, the second side being opposite to the first side.
14. The imaging apparatus according to any one of claims 1 to 10, further comprising: a plurality of image forming units each including a photosensitive member, each image forming unit being configured to develop a latent image formed on the photosensitive member into a toner image,
wherein the image bearing member is an intermediate transfer body configured to bear a toner image transferred from each of the photosensitive members of the plurality of image forming units and convey the toner image to the transfer portion.
Technical Field
The present invention relates to an image forming apparatus for forming an image on a sheet.
Background
In an image forming apparatus employing an electrophotographic system, a toner image carried on an image bearing member such as a photosensitive drum or an intermediate transfer belt is transferred onto a sheet as a recording medium at a transfer portion, and then fixed onto the sheet by a fixing unit. Along a sheet conveying path passing through the transfer portion and the fixing unit, a plurality of conveying members for nipping and conveying the sheet are arranged, including registration roller pairs that feed the sheet to the transfer portion.
The speed at which the sheet is conveyed by such a registration roller pair may be changed in the middle of the conveyance operation of the sheet. Japanese patent application laid-open publication No.2014-202983 discloses reducing the conveying speed before the trailing edge of the sheet passes through the registration roller pair, thereby reducing the deflection of the sheet between the registration roller pair and the transfer portion and alleviating the influence occurring when the trailing edge of the sheet passes through the registration roller pair. Japanese patent application laid-open publication No.2017-37097 discloses increasing the conveying speed of the registration roller pair after the leading edge of the sheet enters the fixing nip so that the influence of the deflection of the sheet from the transfer portion to the fixing nip is offset by the deflection of the sheet from the registration roller pair to the transfer portion.
The above document indicates that the deflection of the sheet in the range from the registration roller pair passing through the secondary transfer portion to the fixing portion affects the transfer of the toner image at the secondary transfer portion. However, the inventors of the present invention found through studies that the image transferred onto the sheet is disturbed by a cause related to the behavior of the sheet due to a problem other than the deflection of the sheet in this range.
Disclosure of Invention
The invention provides an imaging device capable of reducing image distortion.
According to an aspect of the present invention, an image forming apparatus includes: an image bearing member configured to bear a toner image and rotate; a transfer member configured to form a transfer portion between the transfer member and the image bearing member and transfer the toner image at the transfer portion from the image bearing member to a sheet; a conveying unit arranged upstream of the transfer portion in a sheet conveying direction and configured to convey the sheet toward the transfer portion; an upstream conveying unit arranged upstream of the conveying unit in a sheet conveying direction and configured to convey the sheet to the conveying unit; a driving unit configured to drive the conveying unit; and a controller configured to control the drive unit to change a conveying speed of the conveying unit such that, in a case where a trailing edge of the sheet in the sheet conveying direction passes through the upstream conveying unit after a leading edge of the sheet in the sheet conveying direction has entered the transfer portion, the conveying unit conveys the sheet at a first speed before the trailing edge of the sheet passes through the upstream conveying unit, and the conveying unit conveys the sheet at a second speed faster than the first speed after the trailing edge of the sheet has passed through the upstream conveying unit.
Other features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Drawings
Fig. 1 is a schematic view of an image forming apparatus according to a first embodiment.
Fig. 2 is a view illustrating an example of a sheet conveying path according to the first embodiment.
FIG. 3A is an illustration of color misalignment.
FIG. 3B is an illustration of color misalignment.
Fig. 4 is a graph illustrating color misalignment caused by a sheet in the case of using plain paper.
Fig. 5 is a graph illustrating color misalignment caused by a sheet in the case of using thick paper.
Fig. 6 is a view illustrating misalignment of the transfer position of the toner image that has been primarily transferred.
Fig. 7 shows an example of color misalignment of a toner image that has been secondarily transferred onto a sheet, with reference to yellow.
Fig. 8 is a graph illustrating a fluctuation in driving torque of the image forming motor while the sheet is passing through the secondary transfer portion.
Fig. 9 is a schematic diagram illustrating a force acting on the secondary transfer portion from the sheet.
Fig. 10 is a view showing a correspondence relationship between a driving torque fluctuation and a position of a sheet on a conveying path.
Fig. 11 is a view showing an example of the speed control sequence according to the first embodiment in the case of No. 1 thick paper.
Fig. 12 shows a color misalignment waveform in the case where the speed control according to the first embodiment is not performed in the case of No. 1 thick paper.
Fig. 13 is a color misalignment waveform in the case where the speed control according to the first embodiment is performed in the case of No. 1 thick paper.
Fig. 14 is a view showing another example of the speed control sequence according to the first embodiment in the case of No. 2 thick paper.
Fig. 15 is a color misalignment waveform in the case where the speed control according to the first embodiment is not performed in the case of No. 2 thick paper.
Fig. 16 is a color misalignment waveform in the case where the speed control according to the first embodiment is performed in the case of No. 2 thick paper.
Fig. 17 is a block diagram showing a control structure of the image forming apparatus according to the first embodiment.
Fig. 18 is a flowchart illustrating a control method of the image forming apparatus according to the first embodiment.
Fig. 19 is a diagram showing a data structure of a speed control sequence according to the first embodiment.
Fig. 20 is a diagram illustrating a change in position of a sheet on the conveying path according to the second embodiment in the case where an a 3-size sheet is fed from the second feeding portion.
Fig. 21 is a diagram showing a data structure of a speed control sequence according to the second embodiment.
Fig. 22 is a view showing a relationship between the conveying direction length of the sheet fed from the second feeding portion and the conveying timing size correlation (i.e., the correlation of the event timing) according to the second embodiment.
Fig. 23 is a view showing an example of a speed control sequence according to the second embodiment in the case where a sheet of a3 size is fed from the second feeding portion.
Fig. 24 is a flowchart illustrating a control method of an image forming apparatus according to a second embodiment.
Fig. 25 is a graph illustrating a difference in driving torque fluctuation of the image forming motor according to different sheet sizes.
Fig. 26 is a diagram illustrating a change in position of a sheet on a conveying path according to the second embodiment in a case where a sheet having a length of 300mm is fed from the second feeding portion.
Fig. 27 is a diagram illustrating a change in position of a sheet on the conveying path according to the second embodiment in the case where an a3 size sheet is fed from the third feeding portion.
Fig. 28 is a view showing a relationship between the conveying direction length of the sheet fed from the third feeding portion and the conveying timing size correlation (i.e., the correlation of the event timing) according to the second embodiment.
Detailed Description
Exemplary embodiments for implementing the present invention will now be described with reference to the accompanying drawings.
First embodiment
Fig. 1 is a schematic diagram of an imaging apparatus 201 according to a first embodiment. The image forming apparatus 201 is a laser printer equipped with an image forming portion 201B employing an electrophotographic system. The image reading apparatus 202 is mounted substantially horizontally on an upper portion of an image forming apparatus main body (hereinafter referred to as an apparatus main body) 201A. A sheet discharge space S, into which a sheet is discharged, is formed between the image reading apparatus 202 and the apparatus main body 201A.
The image forming portion 201B as an example of the image forming portion is a four-drum full-color electrophotographic unit. That is, the image forming portion 201B is equipped with a laser scanner 210 and four process cartridges PY, PM, PC, and PK which form toner images of four colors of yellow (Y), magenta (M), cyan (C), and black (K). The process cartridges PY to PK are image forming units each equipped with a photosensitive drum 212 as a photosensitive member, a charger 213 as a charging unit, and a developer 214 as a developing portion. Further, the image forming portion 201B is provided with a
The intermediate transfer unit 201C is equipped with an
A
An imaging operation of the imaging section 201B will be described. The image information of the document is read by the image reading device 202, and is subjected to image processing by the control unit 280, and thereafter converted into an electric signal and conveyed to the laser scanner 210 of the imaging portion 201B. In the image forming portion 201B, a laser beam is irradiated from the laser scanner 210 to the photosensitive drum 212, the surface of the photosensitive drum 212 has been uniformly charged to a predetermined polarity and potential by the charger 213, and the photosensitive drum surface is exposed with the rotation of the photosensitive drum. Thus, an electrostatic latent image corresponding to monochrome images of yellow, magenta, cyan, and black is formed on the surface of the photosensitive drum 212 of each of the process cartridges PY to PK. The electrostatic latent image is developed and visualized by the toners of the respective colors supplied from the developers 214, and the image is primarily transferred from the photosensitive drum 212 to the
The image forming apparatus 201 includes a sheet feeding unit 201E for feeding the sheet P. The sheet feeding unit 201E according to the present embodiment includes a first feeding portion 231, a second feeding portion 232, a third feeding portion 233, and a fourth feeding portion 234 for feeding the sheets P stored in each
Each of the
Each of the feed roller pairs 251 to 254 includes: a feed roller 257 that feeds the sheet P from the
The sheet P fed from the
Further, the sheet feeding unit 201E of the present embodiment includes a manual sheet feeding portion 230 (i.e., a multi-purpose feeding portion) to which a user can set sheets as desired. The sheets set on the manual feed tray 240 are conveyed one by one toward the
After the skew correction of the sheet P, the
Thereafter, the sheet P is placed on the sheet discharge portion 223 arranged on the bottom of the sheet discharge space S by the first sheet
The above-described image forming portion 201B is an example of an image forming portion, and a direct transfer image forming portion in which a toner image formed on a photosensitive member is directly transferred onto a sheet may also be used. An inkjet or offset type imaging section may also be used instead of the electrophotographic system.
Conveying path
Next, the conveying path of the sheet P will be described in detail. Fig. 2 is a schematic diagram illustrating a conveying path of the sheet P in a case where the sheet P is fed from the second feeding portion 232 to be imaged thereon and then discharged from the first sheet discharging
As described above, the second
The second
The
The
The fixing
In such a conveying path, a conveying guide for guiding the sheet P is arranged between nip portions of conveying members arranged adjacent to each other in the conveying direction. The conveying guide guides a leading edge (i.e., a downstream edge in the sheet conveying direction) of the sheet P sent from the nip portion of the upstream conveying member to the nip portion of the downstream conveying member. As shown in the drawing, the sheet conveying path is curved in a plurality of regions, and the sheet P is conveyed in a curved shape along the conveying path formed by the conveying guide. Further, a certain space margin is provided between the conveying guides opposed to each other, the conveying path is interposed between the conveying guides, and the sheet P may warp in the thickness direction. The degree of deflection of the sheet P can be adjusted by the difference between the conveying speeds (i.e., peripheral speeds) of the conveying members arranged adjacent to each other in the conveying direction.
Sheet induced color misalignment
Fig. 3A and 3B are schematic diagrams illustrating color misalignment of an image formed on a sheet P in the conveying direction (i.e., the sub-scanning direction) of the sheet P. In the figure, Y1, M1, C1, and K1 are images of respective colors of yellow, magenta, cyan, and black, which are formed by the image forming portion 201B based on image information specifying equivalent positions on the sheet P with respect to the conveying direction, as are Y2, M2, C2, and K2. Fig. 3A shows a case where no color misalignment is generated in the conveying direction, and fig. 3B shows a case where color misalignment is generated in the conveying direction.
Images of respective colors formed based on image information of designated pixels at the same position in the sub-scanning direction will be aligned as in fig. 3A at respective positions on the sheet in the conveying direction if under ideal conditions. However, due to fluctuation in the conveying speed of the
Fig. 4 and 5 are graphs (i.e., color misalignment waveform diagrams) showing fluctuation in color misalignment occurring when image forming is performed on a sheet, in which fig. 4 shows a case of image forming on plain paper, and fig. 5 shows a case of image forming on one thick paper having a grammage greater than that of plain paper (which will be referred to as "thick paper No. 1" in the following description). To obtain the color misalignment waveform, first, an image forming operation is performed by the image forming portion 201B to form images of respective colors at a plurality of positions at intervals in the conveying direction of the sheet. Thereafter, a color-misregistration waveform is obtained by sequentially observing the output images in order from one line on the downstream side in the conveying direction, and plotting the original target position of each line as the horizontal-axis position and the image displacement of each color corresponding to the image of the color set as the reference for each line as the vertical-axis position. Fig. 4 and 5 respectively show color misalignment waveforms in a state where an a 3-size sheet P having a length of 420mm is fed from the second feeding portion 232 in the conveying direction and discharged from the first sheet discharging
By comparing the waveforms of fig. 4 and 5, it can be seen that the color misalignment of thick paper is greater than that of plain paper, indicating that they are affected by the type of sheet.
Next, the principle of how sheet-induced color misalignment occurs will be described. First, in a state where the sheet is nipped and conveyed by the
Generally, the driving
If the conveyance speed of the
Such a displacement occurs in the transfer position of the toner image for each of the toner images of the respective colors, and the positions of the primary transfer portions of the respective process cartridges PY to PK are spaced from each other by a substantially constant interval in the rotational direction of the
In the view of fig. 6, the displacement of the toner image with respect to the target position is plotted on the vertical axis with respect to the timing at which the toner image of each color on the horizontal axis is transferred to the sheet at the
Fig. 7 shows a color misalignment waveform in the case where the amount of displacement from the target position shown in fig. 6 is converted into a color misalignment with the yellow image as a setting reference. The peak positions pm ', pc ', and pk ' of the color misalignment waveform correspond to the peak positions pm, pc, and pk of the displacement amounts of magenta, cyan, and black shown in fig. 6. As shown in fig. 7, it can be appreciated that the color misalignment waveform becomes apparent from the color sequence starting from the color in which the primary transfer position is disposed most downstream in the conveying direction of the
By determining the color misalignment waveform of fig. 5 in the case of image formation on a sheet of No. 1 thick paper, it can be recognized that the peak of the color misalignment appears in a specified order of black, cyan, and magenta. Therefore, it can be presumed that, in the case of using a sheet of thick paper No. 1 having a higher hardness than that of plain paper, color misalignment occurs due to "the conveying speed of the
By measuring the fluctuation in the driving torque of the image forming motor M4 (fig. 17) that drives the driving
Fig. 8 shows the driving torque fluctuation in the case where the sheet conveying operation is performed for the case of conveying plain paper and the case of conveying thick paper No. 1 under the same conditions as fig. 4 and 5. Here, a section from the leading edge of the sheet entering the
Next, a force acting on the
The following are examples of external forces and internal stresses acting on the sheet P during conveyance:
A force F1, i.e., a conveying force received from rotational driving of a conveying member that nips the sheet P and applies a force in a conveying direction, wherein the conveying member refers to the
a reaction force F2, caused by the stiffness (i.e., elasticity) of the sheet P, caused by the buckling (i.e., elastic deformation) of the sheet P at the nip portions of the conveying members arranged adjacent to each other in the conveying direction; and
the resultant F3 of the normal force and the frictional force that occurs when the sheet P contacts or slides against the conveying guide forming the conveying path.
In a state where the sheet P subjected to such a force is in contact with the
Note that the configuration that affects the force acting on the
Therefore, in order to investigate the force fluctuation acting on the
Now, fig. 10 is a graph in which a section in which each conveying member nips a sheet is added to the driving torque fluctuation graph shown in fig. 8. According to this condition, the leading edge of the sheet enters the
In fig. 10, when focusing on the relationship between the waveform of the driving torque fluctuation of the thick paper and the section in which each conveying member nips the sheet, it can be recognized that the driving torque fluctuation tendency is changed before and after the leading edge of the sheet enters each conveying member or before and after the trailing edge of the sheet passes therethrough. Specifically, after the leading edge of the sheet enters the
A description will be made of a main phenomenon that has occurred in the example of fig. 10. First, in a state where the leading edge of the sheet enters the fixing
In a state where the trailing edge of the sheet passes through the second pulling
As described above, the force acting on the
Transport speed control
Next, a method for controlling the conveying speed at which the
As described above, in order to reduce the color misalignment caused by the sheet, it is considered effective to reduce the force fluctuation acting on the
Therefore, according to the present embodiment, in the passing section of the secondary transfer portion, the conveying speed of the
Further according to the present embodiment, the conveying speed of the
From the above-described viewpoint, the result of performing the speed control of the
Fig. 11 shows the relationship between the drive torque fluctuation (upper portion) and the speed control sequence (lower portion) of the
In the control example illustrated in fig. 11, when the leading edge of the sheet enters the
The upper part of fig. 11 shows by a thick solid line the fluctuation of the driving torque of the imaging motor M4 in the case where such speed control (control is performed). Further, it shows by a thin solid line that the conveying speed V is set to V at the passing section of the secondary transfer portion similarly to the case of "thick paper" in fig. 10 0In the state of (fixed value), the driving torque fluctuates without speed control (no control). As can be seen from the graph, by performing the speed control of the
The fluctuation is suppressed if the average value of the absolute value of the difference between the driving torque at the passing section of the secondary transfer portion and the average value of the driving torque in a state where the sheet does not pass through the secondary transfer portion is small.
The evaluation criterion as to whether the fluctuation in the driving torque of the imaging motor M4 has been suppressed is not limited to the above-described example, and for example, the above-described "average value" may be replaced by a "maximum value". As described later, an evaluation criterion for evaluating whether the driving torque fluctuation of the image forming motor M4 has been suppressed is necessary for determining an appropriate speed control sequence according to the size and type of the sheet.
Fig. 12 shows a color misalignment waveform in the case where speed control is not performed, and fig. 13 shows a color misalignment waveform in the case where speed control is performed. Both figures show the color misalignment waveforms obtained using sheets of the same size and grammage (i.e., No. 1 thick paper). By comparing fig. 12 and 13, it can be appreciated that color misalignment has been reduced by performing speed control of the
Next, fig. 14 shows the relationship between the fluctuation of the driving torque of the image forming motor M4 (upper portion) and the speed control sequence of the registration roller pair 270 (lower portion) in the state where "thick paper No. 2" is similarly fed from the second feeding portion 232. The gram weight of the No. 2 thick paper is smaller than that of the No. 1 thick paper and larger than that of the common paper. In this example, the driving torque fluctuation and the speed control sequence of the sheet of No. 2 thick paper having an a3 size with a length of 420mm in the conveying direction are shown.
In the speed control sequence for the No. 2 thick paper, when the trailing edge of the sheet passes through the second
The speed control sequence for thick paper No. 2 (fig. 14) differs from the speed control sequence for thick paper No. 1 (fig. 11) because the force acting on the
If the sheet of No. 2 thick paper is conveyed without speed control of the
Fig. 15 shows a color misalignment waveform in the case where speed control is not performed, and fig. 16 shows a color misalignment waveform in the case where speed control is performed. Both figures show the color misalignment waveforms obtained using sheets of the same size and grammage (i.e., thick paper No. 2). Although the sheet of thick paper No. 2 results in a lower level of color misalignment than thick paper No. 1, by comparing fig. 15 and 16, it can be appreciated that color misalignment has been reduced by performing speed control of the
As described above, by changing the conveying speed of the
The order in which the leading edge and the trailing edge of the sheet pass through the respective conveying members in the conveying path differs depending on, for example, the sheet size (particularly, the length of the sheet in the conveying direction) and the position of a sheet feeding portion as a feeding source. Therefore, the speed control sequence should preferably be changed according to these conditions.
Control method
Next, a control method of the imaging apparatus 201 according to the present embodiment will be described. Fig. 17 is a block diagram showing a control structure of the imaging apparatus 201. A control unit 280 as a controller according to the present embodiment is provided in the apparatus main body of the image forming apparatus 201. The control unit 280 includes a Central Processing Unit (CPU)281, a memory 282, and a timer 283. The CPU 281 reads and executes a program stored in the memory 282, and controls the operation of the image forming apparatus 201. Memory 282 includes volatile and nonvolatile memory devices and serves as both a storage location for programs and data and as a workspace for CPU 281 to execute the programs. The memory 282 is an example of a non-transitory computer-readable storage medium storing a program for controlling the imaging apparatus 201 by a control method described below. The timer 283 may utilize the function of a hardware timer such as a real-time clock or the function of an interval timer included in a program or a combination thereof.
The control unit 280 sends command signals to the drive circuits of the various motors (M1-M5) described above, and issues commands to start or stop the rotation of the various motors or to specify the rotational speeds thereof. Further, the control unit 280 is connected to the conveyance sensor 129 or the operation portion 130 provided in the imaging apparatus 201, and may also be connected to external devices such as a personal computer and a portable information device through a network interface (I/F) 131. For example, if job information including image information is received from an external apparatus, the control unit 280 performs a series of operations, such as a print job, feeding a sheet from one of the sheet feeding portions, and forming an image on the sheet by the image forming portion.
The conveyance sensor 129 is a sensor for monitoring sheet conveyance in the image forming apparatus 201. The conveyance sensors 129 are arranged at a plurality of positions on the sheet conveyance path, and are designed to output different detection signals depending on whether or not a sheet is detected. As the conveyance sensor 129, a photo interrupter that detects a mark that contacts and swings with the sheet or a photo reflector that detects reflected light from the sheet may be used. The control unit 280 refers to the detection signal of the conveyance sensor 129 to confirm whether the leading edge or the trailing edge of the sheet has passed the detection position of each sensor, and specifies the current positional relationship between the sheet and each conveying member on the conveyance path. For example, based on a detection signal from the conveyance sensor 129 provided in the vicinity of the upstream side in the sheet conveyance direction of the
The operation section 130 is a user interface of the image forming apparatus 201, and it includes a display device such as a liquid crystal panel and input devices such as a numeric keypad, a print start button, and a touch panel function unit on the liquid crystal panel. The operation section 130 provides setting information such as the size and type of sheets stored in each cassette to a user through a display device, and receives an operation from the user through an input device. The control unit 280 instructs the display contents on the operation section 130, changes the setting information based on the user's operation, and stores the changed setting information in the memory 282.
In other words, the control unit 280 can acquire information on the sheet size and the sheet type used to form the image based on the operation of the user using the operation portion 130. However, the unit by which the control unit 280 acquires the sheet-related information is not limited to the operation portion 130, and for example, the sheet size may be automatically detected using a sensor provided on the cassette. Further, if information specifying a sheet type is included in job information received from an external apparatus, the control unit 280 may analyze the job information and store the specified sheet type as a sheet type for a current print job.
Next, a control method of the imaging apparatus according to the present embodiment will be described using a flowchart shown in fig. 18. Each process of the flowchart is realized by the CPU 281 of the control unit 280 executing a program.
First, in a state where the control unit 280 receives a print job (S1), the control unit 280 checks the setting of the sheet designated in the received job (S2). The setting of the sheet is a setting value indicating a type of the sheet set by the user, such as a grammage classification of the sheet (e.g., "the number of grams is 64 to 75 g/m)2") and information specifying the feeding section as the feeding source (e.g.,"
The grammage classification of the sheet is used as a setting value indicating the sheet type because, in many cases, the grammage classification of the sheet is clearly indicated on the sheet package, and the grammage classification of the sheet is widely used as a setting relating to the sheet type in the image forming apparatus. Further, the grammage classification of the sheet is a set value related to the force acting on the
After checking the setting of the sheet, the control unit 280 refers to a speed control sequence corresponding to the acquired sheet setting from among the speed control sequences stored in the memory 282 (S3), starts an image forming operation by the image forming portion 201B and starts a sheet feeding operation (S4).
Fig. 19 is a diagram showing a data structure of the speed control sequence stored in the memory 282. In the present embodiment, speed control sequences for various combinations of the following three conditions are prepared in advance and stored in the memory 282: a sheet feeding portion as a feeding source, a size or a conveying direction length of the sheet, and a grammage classification. The content of the speed control sequence should be determined in advance by testing for each combination of conditions so as to effectively suppress the driving torque fluctuation of the imaging motor M4. Further, such data of the speed control sequence may be stored in the memory 282, for example, in the form of a hash table, with the condition combination set as a key and the speed control sequence set as a numerical value.
If the leading edge of the sheet fed from the feeding portion as the feeding source reaches the
In S6, driving of the
Summary of the present examples
According to the present embodiment, as described above, after the leading edge of the sheet has entered the
In the case where the sheet is fed from the second feeding portion 232, the configuration of the present embodiment is particularly effective in the case where the driving torque fluctuation of the image forming motor M4 is large when the trailing edge of the sheet passes through the conveying member (e.g., the second pull roller pair 262) upstream of the
In other words, the conveying unit conveys the sheet at a first speed before the trailing edge of the sheet passes through the upstream conveying unit, and the conveying speed of the conveying unit is changed after the trailing edge of the sheet passes through the upstream conveying unit, so that the conveying unit conveys the sheet at a second speed faster than the first speed. For example, in the case of the speed control sequence shown in fig. 14, an example of the upstream conveying unit is the second
The timing of changing the conveying speed may be a timing at which the trailing edge of the sheet has passed through the upstream conveying unit, but the timing may be different from the timing at which the trailing edge of the sheet passes through the upstream conveying unit. For example, according to the speed control sequence shown in fig. 11, an example of the upstream conveying unit is the second
The second speed is a speed faster than a processing speed that is a conveyance speed of the sheet at the transfer portion. The first speed may be a speed equal to or less than the processing speed, or greater than the processing speed.
Further, according to the present embodiment, the content of the speed control sequence of the
In other words, according to the present embodiment, the first mode is performed when conveying a sheet having the first grammage in which the driving unit does not change the driving speed of the conveying unit before and after the trailing edge of the sheet passes through the upstream conveying unit. Further according to the present embodiment, the second mode is executed when conveying a sheet having a second grammage greater than the first grammage, in which the conveying speed of the conveying unit is changed between the first speed and the second speed before and after the trailing edge of the sheet passes through the upstream conveying unit. Thus, unnecessary changes in the conveying speed of the conveying unit can be prevented under conditions in which color misalignment caused by the sheet is not likely to occur, so that the possibility of pulling the sheet between the conveying unit and the upstream conveying unit can be minimized.
Further, according to the present embodiment, at the timing when the leading edge of the sheet enters the transfer portion, the conveying speed at which the sheet is conveyed by the conveying unit is changed to a speed faster than the speed before the leading edge of the sheet enters the transfer portion (refer to fig. 11). Thus, the drive torque of the image forming motor M4, which is increased due to the increase in the speed of the
An advantage of performing such a speed change at the timing when the leading edge of the sheet enters the transfer portion is that the rotation speed fluctuation of the
Therefore, if the conveying speed of the
A method of performing speed control of the
Second embodiment
Next, an image forming apparatus according to a second embodiment will be described. In the present embodiment, a method for preparing a speed control sequence of the
According to the present embodiment, instead of determining and storing the speed control sequence in advance in the memory 282 for each sheet size as in the first embodiment, the speed control sequence is generated based on the sheet size or the like each time. According to the present method, even according to a mode for feeding sheets having a size not corresponding to a normal sheet size, speed control for effectively reducing color misalignment can be performed according to the sheet size.
In the present embodiment, the timing at which the leading edge or the trailing edge of a sheet passes through each conveying member on the conveying path (hereinafter referred to as conveying timing) is calculated from the size of the sheet used in a print job (i.e., the conveying direction length) and the position of the feeding portion of the feeding source. Based on the conveyance timing and a set value indicating a sheet type used in the print job, a speed control sequence is generated.
Hereinafter, as a specific example, a description will be made of a method of how to determine the speed control sequence in the case of feeding the thick paper No. 1 of a3 size having a conveying direction length of 420mm from the second feeding portion 232. For simplicity, the length of time that the leading edge of the sheet waits at the
First, the conveyance timing according to the above conditions is calculated. As shown in fig. 2, the conveying path for feeding the sheet from the second feeding portion 232 is constituted by the fixing
Fig. 20 is a diagram showing the position of a sheet in the conveying path in the case where a sheet of a3 size is fed from the second feeding portion 232, in which the vertical axis represents the position in the conveying path and the horizontal axis represents time. The thick solid line in the figure indicates the position of the sheet leading edge at this time, the thick broken line indicates the position of the trailing edge thereof, and the filled area indicates the sheet passing area. FIG. 20 shows Ti1<To5bAnd it can be recognized that the trailing edge of the sheet has passed through the second
Now, the time at which the force acting on the
Next, a speed control sequence is generated by referring to the speed set value stored in the memory in addition to the calculated conveyance timing. The speed set value is a set value of the conveyance speed of the
As shown in
Further, the number of values selectable as the speed setting value and the level of the values are not necessarily limited to those shown in the present embodiment. This is because the speed set value is determined according to the actual configuration of the conveying path provided by the image forming apparatus, thereby suppressing the force fluctuation acting on the
As shown in fig. 21, the number of speed setting values stored in the memory corresponds to the number of combinations of the sheet feeding portion of the feeding source, the classification of the conveying direction length of the sheet, and the grammage classification of the sheet set by the user. The conveying path changes with a change in the feeding portion of the feeding source, and in a state where the grammage classification has changed, the magnitude of the force acting on the
Fig. 22 shows the correspondence of the sheet length classification with the conveyance timing size correlation (i.e., the correlation of the timing order) for the sheets fed from the second feeding portion 232. In the present embodiment, if the sheet lengths are sorted so that the order of the conveyance timings becomes the same for the conveyance paths of the sheets fed from the second feeding portion 232, there are eight kinds of sheet length sorting as shown in fig. 22. For example, the conveyance direction length L of the a3 size sheet is 420mm, so that the speed setting No. 1 of fig. 22 is referred to. The speed control sequence determined in the above process is shown in fig. 23.
By generating the speed control sequence according to the above-described procedure, an appropriate speed control sequence can be applied to a sheet that does not correspond to the standard sheet size.
Hereinafter, a control method of the imaging apparatus according to the present embodiment is explained with reference to a flowchart shown in fig. 24. The process of the steps of the flowchart is executed by the CPU 281 of the control unit 280 executing a program. The present flowchart differs from the flowchart of the first embodiment shown in fig. 18 in that S3 is replaced with S3a and S3 b.
First, in a state where the control unit 280 receives a print job (S1), the control unit 280 checks the setting of the sheet designated in the received job (S2). After checking the sheet setting, the control unit 280 uses the acquired sheet setting (in particular, information about the conveying direction length L of the sheet and the feeding portion of the feeding source), and calculates the conveying timing based on
The following steps S4 to S8 are similar to the steps in the process described in the first embodiment (fig. 18). That is, after the image forming operation by the image forming portion 201B is started and the sheet feeding operation is started (S4), the control unit 280 waits the sheet at the registration roller pair 270 (S5). Next, at a timing matching the image writing at the imaging section 201B, the control unit 280 starts driving the
As described above, the speed control sequence according to the present embodiment depends on the conveying direction length L of the sheet, the grammage classification of the sheet, and the feeding portion of the feeding source. A practical example of a speed control sequence is described below.
The first practical example considers the case of feeding No. 1 thick paper from the second feeding portion 232, which has an irregular size and a length of 300mm (i.e., a width of 297mm and a length of 300 mm). Fig. 25 shows a graph of fluctuation in driving torque of the in-section image forming motor M4 of the secondary transfer portion under the present conditions, and fig. 26 shows a graph representing the sheet position in the conveying path.
As can be seen from fig. 25, even if the sheets are fed from the same feeding portion, if the conveying direction lengths of the sheets are different, the transition of the driving torque is changed. Further based on fig. 26, it can be seen that if the lengths of the sheets are different, the timing at which the leading edge of the sheet enters each conveying member is not changed, but the timing at which the trailing edge passes therethrough is changed. At Ti3<To5b<Ti2In fig. 26, it can be appreciated that after the leading edge of the sheet enters the
In this example, the conveying direction length L of the sheet is 300mm so that the length classification shown in fig. 22 corresponds to No. 4, and the speed control sequence is generated based on the corresponding speed set value. Therefore, in the case where the sheet length is 300mm, an optimum control sequence corresponding to the driving torque fluctuation (fig. 25) is applied, and the speed fluctuation of the
The second practical example considers the case of feeding thick paper No. 1 from the third feeding portion 233, whichHas a size of A3 and a length in the conveying direction of 420 mm. Fig. 27 shows a diagram representing the sheet position in the conveyance path under the current condition. The positions of the third pull roller pair 263 and the third feed roller pair 253 in the conveying path of the sheet fed from the third feeding portion 233 are respectively referred to as Y6aAnd Y6b. Further, timings at which the leading edge of the sheet enters the roller pairs are respectively referred to as Ti6aAnd Ti6bThe time at which the trailing edge of the sheet passes therethrough is referred to as To6aAnd To6b。
By comparing fig. 27 with the diagram of fig. 20 showing a case where sheets are fed from the second feeding portion 232, if the feeding portions as the feeding sources are different, even if the sheet lengths L are the same, the appearance order of the conveyance timings and the intervals thereof are changed. If the feeding portions as the feeding sources are different, the tendency of fluctuation of the driving force of the image forming motor M4 caused by the force acting on the
As shown in fig. 28, when the sheet lengths are sorted such that the conveying timing order is the same with respect to the conveying path of the sheet fed from the third feeding portion 233, the lengths of the sheets are classified into ten types. For example, the length of a sheet of a3 size in the conveying direction is 420mm, and reference should be made to the speed setting value classified as No. 3 in fig. 28.
As described above, according to the present embodiment, for a sheet having an arbitrary length L in the conveying direction, a speed control sequence is generated according to the feeding portion as the feeding source, the classification of the length of the sheet in the conveying direction, and the grammage classification of the sheet. The speed control of the
Modified example 1
In the first embodiment described above, the speed control sequence determined in advance is read when the print job is executed, and in the second embodiment, the speed control sequence is generated during execution of the print job. The embodiments are not mutually exclusive and both methods may be implemented in one imaging device. For example, for sheets having regular sizes such as "a 4-sized sheet having a length of 210mm in the conveying direction" and "A3-sized sheet having a length of 420mm in the conveying direction", the method of the first embodiment may be adopted, and for sheets not corresponding to the regular sizes, the method of the second embodiment may be adopted.
Modified example 2
Further, according to the first embodiment and the second embodiment, in the configuration in which the full-color toner image is transferred onto the sheet by the image bearing member and the
Modified example 3
Further, according to the first and second embodiments, the speed control sequence of the sheets fed from the
Other embodiments
Embodiments of the invention may also be implemented by a computer of a system or apparatus that reads and executes computer-executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a "non-transitory computer-readable storage medium") to thereby perform one or more of the functions of the above-described embodiments; and/or the computer includes one or more circuits (e.g., Application Specific Integrated Circuits (ASICs)) for performing one or more of the functions of the one or more embodiments described above, e.g., by reading and executing computer-executable instructions from a storage medium to perform the functions of the one or more embodiments described above and/or controlling one or more circuits to perform the functions of the one or more embodiments described above. The computer may include one or more processors (e.g., Central Processing Unit (CPU), Micro Processing Unit (MPU)) and may include a separate computer or a network of separate processors to read and execute computer-executable instructions. The computer-executable instructions may be provided to the computer from a network or from a storage medium, for example. The storage medium may include, for example, a hard disk, Random Access Memory (RAM), Read Only Memory (ROM), memory of a distributed computing system, an optical disk (e.g., Compact Disk (CD), Digital Versatile Disk (DVD), or blu-ray disk (BD) TM) One or more of a flash memory device, a memory card, etc.
OTHER EMBODIMENTS
The embodiments of the present invention can also be realized by a method in which software (programs) that perform the functions of the above-described embodiments are supplied to a system or an apparatus through a network or various storage media, and a computer or a Central Processing Unit (CPU), a Micro Processing Unit (MPU) of the system or the apparatus reads out and executes the methods of the programs.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
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