WO2002099540A1

WO2002099540A1 - Image forming apparatus

Info

Publication number: WO2002099540A1
Application number: PCT/JP2001/004619
Authority: WO
Inventors: Satoshi Seino; Susumu Imado; Mitsuo Shimura; Morihisa Kawahara; Tetsuya Takei; Hisashi Hanzawa; Yutaka Sato; Katsuei Asano; Yoshihiro Watanabe
Original assignee: Fuji Xerox Co., Ltd.
Priority date: 2001-05-31
Filing date: 2001-05-31
Publication date: 2002-12-12

Abstract

An image forming apparatus comprising: an electronic photography process mechanism for transferring an image, as developed in an image forming unit, primarily to an intermediate transfer belt and then transferring the transferred image secondarily to a sheet of paper; a detector for detecting a change in the belt length from the motion of a tension roller disposed at the intermediate transfer belt; and a timing regulating unit for vegulating the control timing of the electronic photography process mechanism on the basis of the change in the belt length by the detector. The image forming apparatus detects the change in the belt length in real time and keeps the precision for each sheet of paper with respect to the change in the belt length.

Description

Technical field

The present invention relates to an image forming apparatus such as a printer or a copier that forms a color image by an electrophotographic process, and in particular, transfers toner images of different colors formed on a plurality of photosensitive drums to an intermediate transfer belt. The present invention relates to a fine image forming apparatus provided with an intermediate transfer process for finally transferring onto a sheet after superimposing. Background art

Conventionally, a tandem type is known as an image forming apparatus for forming a color image using an electrophotographic process, such as a printing machine.

FIG. 1 shows a conventional electrophotographic process (Japanese Patent Application Laid-Open No. 11-249452). In the evening dem type, image forming units 112-1 to 1 12-4 are arranged in a row for each color of yellow (Y), magenta (Μ), cyan (C), and black (Κ). That is, the image forming unit 112-1 to 112-4 has a photosensitive drum 1141-1 to 114-14, around which a cleaning blade, a charger, an LED exposure unit and a developing device are arranged. Forming units 1 12—1 to 1 12—4 form images of each color. The image of each color formed on the photoreceptor drum 114_1-1_114_14 is placed on the intermediate transfer belt 116 that moves in contact with the photoreceptor drum 114_1-1_114_14 of each color. When the primary transfer voltage is applied by the transfer rollers 118-1 to 118-4, they are sequentially superposed and electrostatically transferred. The toner image transferred onto the intermediate transfer belt 1 16 is collectively transferred onto paper by applying a secondary transfer voltage by the secondary transfer roller 120, and is fixed on the paper by the fixing device 122 to form a color image. Has been obtained. In the case of such a tandem type, since a color image can be formed in one pass, there is an advantage that the printing speed can be increased.

The electrophotographic process will be described in more detail as follows. yellow

(Y), magenta (M), cyan (C) and black (K) imaging units When image data for printing is input in the order of 1 1 2—1 to 1 1 2—4, the toner image of each color is written to the photosensitive drum 1 1 4 1 to 1 1 4—4, and When the primary transfer voltage is applied by the transfer ports — 1 1 8 — 1 to 1 1 8 — 4, the toner images of each color are primarily transferred onto the intermediate transfer belt 1 16 in a superimposed manner. After that, the transferred image is conveyed by the intermediate transfer belt 116, and a certain time T has passed since the last toner image was transferred on the black (K) image forming unit 112-4. When the position 1 2 4 is reached, the printer 1 2 6 is activated and the recording paper 1 3 0 stopped at the registration roller 1 2 8 is sent out to the secondary transfer roller 1 2 0, and the intermediate transfer is performed. Belt 1 16 Images on the sheet are transferred to recording paper at once.

Here, the intermediate transfer belt 116 is made of a resin material such as, for example, a polycarbonate resin, and has relatively large expansion and contraction with respect to the operating temperature. Particularly in the electrophotographic process, a fixing device 122 is installed in front of the secondary transfer roller 120, and the temperature is increased by heat from the fixing device 122. When the temperature rises and the intermediate transfer belt 1 16 extends, the image does not reach the position 1 24 where it should have arrived even after a certain time T has elapsed since the image was transferred onto the belt. Therefore, the image is shifted below the original position on the recording paper where batch transfer is to be performed. Conversely, if the intermediate transfer belt 1 16 contracts, the image will be shifted above the original position on the recording paper where batch transfer is to be performed.

In order to solve the shift of the transfer position on the recording paper due to the change in the belt length, in a conventional image forming apparatus, a mark is transferred onto an intermediate transfer belt, and the time required to pass between the marks is optically determined based on the mark. The belt length is calculated by detecting with a sensor, and, for example, the conveying speed is adjusted so that the time to the position 124 is maintained at a constant time T (Japanese Patent Application Laid-Open No. H11-194564).

However, in such a method of transferring marks on a belt and optically detecting the marks, it is necessary to drive the belt at least by a distance corresponding to at least the mark in order to calculate the belt length. Change in length cannot be detected. Also, since it is necessary to transfer the mark on the belt, an operation for measuring the belt length is required separately from the printing operation, and there is a problem that it is not possible to cope with a change in the belt length during printing. Optical sensor for detecting marks transferred onto the belt Is required, the cost is increased by the optical system, and toner is wasted in measuring the belt length.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of detecting a change in belt length in real time and appropriately adjusting the timing of an electrophotographic process. Disclosure of the invention

The image forming apparatus of the present invention includes an electrophotographic process mechanism for performing primary transfer of an image developed by an image forming unit to an intermediate transfer belt and then secondary transfer onto paper, and movement of a tension roller provided on the intermediate transfer belt. And a timing adjustment unit that adjusts the timing of the electrophotographic process mechanism based on the change in the belt length by the detector.

Therefore, according to the present invention, the amount of change in the belt length can be known in real time, and the sheet transfer position corresponding to the change in the belt length is adjusted for each sheet to maintain high printing accuracy. In addition, by using a detector with a simple structure that mechanically detects the change in the belt length and converts the change in the tension roller into a change in resistance, the cost of the optical detector can be reduced, and the mark on the mark can be reduced. Since no belt transfer is required, toner consumption other than for printing can be eliminated.

Here, the detector supports the tension roller at the end of the frame and attaches a rotary potentiometer to the base of the frame. Detected as a change in resistance value overnight.

The timing adjustment unit adjusts the timing of writing an image on the photosensitive drum in the electrophotographic process according to a change in the belt length by the detector. That is, the timing adjustment unit adjusts the writing timing according to the amount of elongation when the intermediate transfer belt is stretched, and adjusts the writing timing according to the amount of shrinkage when the intermediate transfer belt is shrunk. Adjust to delay.

Further, the timing adjusting section may adjust the sheet pull-in timing of the registrar in the electrophotographic process according to the change in the belt length by the detector. That is, when the intermediate transfer belt is stretched, the timing adjustment unit Adjust the roller pull-in timing according to the amount of elongation. If the intermediate transfer belt shrinks, adjust the registrar roller's paper pull-in timing according to the amount of contraction.

The electrophotographic process mechanism of the image forming apparatus includes a plurality of image forming units for electrostatically attaching developers of different colors to an image carrier to form visible images of each color, and an image forming unit for each image. It has a primary transfer unit that transfers the developer adhering to the carrier onto the intermediate transfer belt in an electrostatically superimposed manner, and a secondary transfer unit that transfers the visible image transferred to the intermediate transfer belt to paper. For example, in the case of a plurality of image forming units, four image forming units using black, cyan, magenta, and yellow developers are arranged in tandem along the intermediate transfer belt. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is an illustration of a conventional electrophotographic process;

FIG. 2 is an explanatory diagram of an embodiment of the image forming apparatus of the present invention applied to a color printer; FIG. 3 is a block diagram of the left half in the hardware configuration of the control unit in FIG. 2;

Fig. 4 is a block diagram of the right half of the hardware configuration of the control unit of Fig. 2;

FIG. 5 is an explanatory view of the mechanism structure of the intermediate transfer belt of FIG. 2;

Fig. 6 is an explanatory drawing of the detector of Fig. 5;

FIG. 7 is an explanatory view of the movement of the detector of FIG. 6 with respect to a change in the belt length;

Fig. 8 is an illustration of the displacement of the tension roller with the detector attached to the belt length.

Fig. 9 is a characteristic diagram of the resistance value Z against the rotation angle Θ of the potentiometer;

Figure 10 is a characteristic diagram of the belt length change with respect to the resistance change Δ Δ;

FIG. 11 is an explanatory diagram of a process for adjusting the writing timing with respect to the elongation of the belt length; FIG. 12 is an explanatory diagram of a process for adjusting the writing timing with the contraction of the belt length; FIG. The flow of the process for adjusting the write timing for h; FIG. 14 is an explanatory diagram of a process for adjusting the paper pull-in timing with respect to the elongation of the belt length; FIG. 15 is an explanatory diagram of a process for adjusting the paper retraction timing with the contraction of the belt length; FIG. Flow chart of a process for adjusting the start timing of a registrar; Best Mode for Carrying Out the Invention

FIG. 2 shows an embodiment of an image forming apparatus according to the present invention, and exemplifies a case in which the present invention is applied to a printing system. In FIG. 2, an intermediate transfer belt 24 is arranged in the color printer 10, and the intermediate transfer belt 24 is wrapped around a drive roller 26, a tension roller 28, and a backup roller 32 functioning as a driven roller. The rotation of the drive roller 26 rotates counterclockwise in the illustrated case. From the upstream side (right side) of the intermediate transfer belt 24 to the downstream side (left side) of the belt, images are formed in the order of yellow (Y), magenta (Μ), cyan (C), and black (Κ). Units 12-1 and 12-2, 12-3 and 12-4 are arranged. The image forming units 12-1 to 12-4 are provided with photosensitive drums 14-1, 14-2, 14-3, 14-14 as image carriers. Photoconductor drum 14 :! Around ~ 14-4, there are a charger 16_1 ~ 16-4, an LED array 18-1 ~ 18-4, and a developing unit 22-1 ~ 22-4 with a toner cartridge 20-1 ~ 20-4. Be placed. Charger 16— :! Cleaning blades, static eliminators, etc. are arranged in front of ~ 16-4. Image forming units 12-1 to 12-4 photoconductor drums 14-1! 14 to 14 are in contact with the intermediate transfer belt 24 at the lower end, and apply a primary transfer voltage to a position opposite to the belt contact point (ep) via the intermediate transfer belt 24. 38-1, 1, 38-2, 38-3, 38-4 are arranged. In this embodiment, the primary transfer rollers 38-1 to 38-3 are arranged upstream of the belt contact point of the photosensitive drums 141-1 to 14-13, and the primary transfer rollers 38-4 Is located downstream of the belt contact point of the photosensitive drums 14-14. Of course, the primary transfer rollers 38-1 to 38-4 may be arranged on the side opposite to the photosensitive drums 141-1 to 14-14. Not shown for primary transfer rollers 38-1 to 38-4 A predetermined voltage set within the range of +500 to 1000 ports from the power supply is applied at the timing of the primary transfer. At a position of the intermediate transfer belt 24 opposite to the drive roller 26, a secondary transfer roller 45 is disposed so as to face the backup roller 32. A specified bias voltage is applied to the secondary transfer roller 45 from a constant current power supply (not shown) at the time of secondary transfer, and the paper 50 fed from the hopper 48 by the pickup roller 52 and the registration roller 54 is applied. Then, the toner image formed on the intermediate transfer belt 24 is transferred onto the paper.

Here, the paper 50 pulled out of the hopper 48 by the pickup roller 52 stops the paper at the position of the register roller 54 and is in a standby state, and the image forming unit 1 is placed on the intermediate transfer belt 24. When the transfer start position of the toner images sequentially superimposed and transferred according to 2 _ 1 to 12 _ 4 reaches the paper drawing start position 68 indicated by a predetermined arrow, the motor 56 is activated, The paper 50, which has been stopped by the register roller 54, is sent to the secondary transfer roller 48, and the secondary transfer of the toner image onto the paper from the belt is performed. The LED array 18-1 to 1-1 for the photosensitive drums 141-1 to 14-4 in each image forming unit 12-1 to 12-4 until the toner image reaches the paper drawing start position 68 The time from the start of writing by 8-4 is the predetermined length L of the intermediate transfer belt 24. The fixed time T is set in the adjustment state according to. Here, the fixed time T is, of course, a different time for each of the image forming units 12-1 to 12-4. For this reason, if the intermediate transfer belt 24 does not expand or contract, a certain document corresponding to a certain time T until the paper forming position 68 of each of the image forming units 12-1 to 12-4 is reached. By sequentially writing and transferring the Y, Μ, C, and 画像 images at the transfer timing, the toner image on the belt can always be accurately transferred to the predetermined paper position by the secondary transfer roller 45.

The paper on which the image transfer has been performed by the secondary transfer roller 45 in this manner is heated and fixed by the fixing device 58, and then discharged to the scanning force 64. The fixing device 58 is provided with a heat port 60 and a backup roller 62. In addition, a cleaning blade 42 is disposed between the backup roller 32 on the upstream side of the intermediate transfer belt 24 and the image forming unit 12-1 using the first yellow (Υ) toner. An earth roller 44 electrically connected to the ground is provided on the opposite side of the cleaning blade 42 with the intermediate transfer belt 24 interposed therebetween.

The tension roller 28 applies a specified tension to the intermediate transfer belt 24. In the present invention, a belt length detector 30 for detecting the movement of the tension roller 28 provided on the intermediate transfer belt 24 is provided. The belt length detector 30 detects the movement of the tension roller 28 due to elongation or contraction due to the temperature change of the intermediate transfer belt 24, and sends a detection signal to the controller unit 66 so that the intermediate transfer belt 24. The timing adjustment in the electrophotographic process is performed so that the image transfer position on the paper by the secondary transfer roller 48 becomes a constant position with respect to the expansion and contraction of the image.

FIGS. 3 and 4 are block diagrams of the hardware configuration of the controller unit 66 in FIG. 2, and also show the main part of the electrophotographic process mechanism. The control unit 66 of the present invention includes an engine 70 and a controller 72. The engine 70 is provided with an 80 converter 74, a sensor processing MPU 76, a nonvolatile memory 78, a mechanical controller 82 and an engine connector 84. For the MPU 76 for sensor processing, the detection signal (detection voltage) from the belt length detector 30 provided on the tension roller 28 of the intermediate transfer belt 24 is converted to digital data by the AD converter 74. Has been entered. A non-volatile memory 8 is connected to the MPU 76 for sensor processing, and the non-volatile memory 78 has a reference length L of the intermediate transfer belt 24. Reference voltage data V corresponding to the detection voltage of the belt length detector 30 corresponding to. Is stored in advance. The function of the timing adjustment unit 80 is provided in the MPU 76 for sensor processing. The timing adjustment section 80 adjusts the control timing of the electrophotographic process mechanism based on a change in the belt length by the belt length detector 30. The control timing of the electrophotographic process mechanism may be adjusted by adjusting the timing of writing an image on the photosensitive drum in the electrophotographic process according to a change in the belt length by the belt length detector 30, or by adjusting the belt length. Either adjust the paper pull-in timing of the registration roller 54 in the electrophotographic process according to the change. In addition to the control timing adjustment for the belt length change, the sensor processing MPU 76 The toner mark is transferred onto the image 4, and is optically read by a sensor (not shown), and the color matching processing including the color misregistration adjustment and the mode adjustment is performed together. The mechanical controller 82 is connected to the controller 72 via an engine connector 84. The controller 72 is provided with a controller MPU 86. For example, a personal computer 102 as a higher-level device is connected to the controller MPU 86 via an interface processing unit 88 and a controller connector 90. The personal computer 102 has a driver 106 for printing color image data provided from the arbitrary application program 104, and the driver 106 is connected to the controller via the personal computer connector 108. 7 2 Connected to controller connector 4 6 For the controller MPU 86 of the controller 72, the image data of Y, M, C, and K transferred from the personal computer 102 are expanded into pixel data (dot data) and stored. There are provided image memories 94_1 to 94-4. The controller MPU 86 is further connected to an engine 70 via an interface processing unit 90 and a controller connector 92, and receives positional deviation information and toner density information detected by the engine 70, The color matching processing including the correction of the positional deviation and the correction of the toner density is performed on the image data of each toner developed in the image memories 941-1 to 944-1. The controller MPU 86 is further connected to an address designating section 96, which designates an address when each color image is developed in the image memories 941-1 to 944-1. The address designating section 96 additionally has a function of performing address conversion for positional deviation correction based on positional deviation information provided from the engine 70 side. In addition, an operation panel 110 provided in the color printer is connected to the interface processing section 8 8 so that the operator can perform manual setting for print processing, and the operation panel 11 1 Various displays can be performed on the liquid crystal display provided at 0.

FIG. 5 shows a transport mechanism provided with the intermediate transfer belt provided in the color printer 10 of FIG. 2 together with the photosensitive drum. In FIG. 5, a belt length detector 30 is attached to a tension roller 28 provided below the intermediate transfer belt 24. The belt length detector 30 has a structure enlarged in FIG. In FIG. 6, the tension roller 28 is rotatably mounted on the tension frame 120 from the shaft 122, and can move along the guide groove 125 formed on the fixed plate side. I have. The left end of the tension frame 120 fixes the main body 1 16 of the potentiometer 114 provided on the belt length detector 30. The potentiometer 1 14 has a ring-shaped sliding resistance and a contact terminal that makes rotational contact with the ring-shaped sliding resistance inside the main body 1 16. It has a structure as a well-known potentiometer fixed at Since the body 1 1 6 of the potentiometer 1 1 4 is fixed to the tension frame 120, the stud 1 1 8 of the potentiometer 1 1 4 is fixed to the fixing plate 1 1 2 side. ing. The fixing plate 1 12 on which the potentiometer 1 1 4 is mounted is fixed to the fixing plate side of the color pudding by fixing screws 1 30. For this reason, a tension frame 120 provided with a tension roller 28 at the tip thereof has a stud 1 18 serving as a fixed side fixed to the fixed plate 1 12 as a fixed portion, and the main body 1 16 side thereof has a tension frame 1. It rotates according to the expansion and contraction of the intermediate transfer belt together with 20. Tension frame 1

At the upper part on the rotation side of 20 is provided a locking hole 124 on which the left end of the tension spring 126 is engaged and the opposite side is fixed to the fixed plate side. Locked to 8. For this reason, the tension frame 120 urges the tension roller 28 at the tip thereof clockwise (clockwise) around the stud 118 to apply tension to the intermediate transfer belt 24. The reference length L that the intermediate transfer belt 24 has predetermined. At this time, the tension roller 28 is located at the position shown in the figure. On the other hand, when the temperature rises and the belt is extended, the tension of the tension roller 28 is moved to the position of the intermediate transfer belt 24-1, for example. Displaced by receiving. When the temperature of the intermediate transfer belt 24 decreases and the intermediate transfer belt 24 shrinks, the tension roller 28 moves to the position of the intermediate transfer belt 24-2.

FIG. 7 shows the movement of the tension roller and the belt length detector with respect to the expansion and contraction of the intermediate transfer belt. FIG. 7A shows the reference length L of the intermediate transfer belt. In this case, the center line 1 connecting the center of the stud 1 1 4 and the center of the tension roller 28

3 2 and the center line 1 3 4 of the belt length detector 30 themselves match, and in this state The angle S of the frame 120 is set to 0 = 0 °, and the resistance value of the potentiometer 114 is a predetermined resistance value Z 0 (Ω) corresponding to the belt reference length L 0. FIG. 7 (B) shows the case where the intermediate transfer belt is extended, the tension roller 28 moves downward by the amount of the extension of the intermediate transfer belt, and the tension frame 120 rotates clockwise around the stud 114. The center line 134 of the tension frame 120 rotates downward with respect to the sensor center line 132, for example, to a rotation angle of 0 °. Corresponding to the rotation angle S i, the resistance value of the potentiometer 114 is, for example, Z in FIG. 7A in this embodiment. Increases from to. FIG. 7C shows a case where the intermediate transfer belt is contracted, and the tension roller 28 moves upward in response to the contraction of the belt. Move. Rotation angle of the tension frame center line 134 with respect to the sensor center line 132 at this time is the rotation angle of + 0 _2, for example. In response to the rotation angle of + 0 _2, the resistance value of potentiometer 1 14 increases to Z _2.

FIG. 8 also shows a case where the intermediate transfer belt 24 is elongated and a case where the intermediate transfer belt 24 is contracted as shown in FIGS. When the tension roller 28 is extended, it moves to the position of the tension roller 28-1 when the tension roller 28 expands, and when the tension roller 28 contracts, it moves to the position of the tension roller 28-2. With the movement of the tension frame 120 to the position 120-1 or 120-2 associated with the movement of the tension roller 28, the resistance value of the belt length detector 30 and the resistance of the potentiometer 1-14 of the belt length detector increases. It changes according to shrinkage. Here, a predetermined reference voltage is applied to the potentiometer 114 of the belt length detector 30 from the controller side, and a detection voltage V proportional to the resistance value Z accompanying the change in the rotation angle Θ is output. I do.

FIG. 9 is a characteristic diagram of a change in the resistance value Z of the potentiometer 114 with respect to a change in the rotation angle 0 according to the belt expansion and contraction of the tension roller 28 in the belt length detector 30 in FIG. Is taken as an example. That is, when the rotation angle 0 is 0 ° in the state of the belt reference length L 0 in FIG. 7A, the resistance value of the potentiometer 114 is the reference resistance value Z. It has become. In this state, as shown in FIG. 7B, when the intermediate transfer belt is stretched and the rotation angle ø changes to, for example, 1Θi, the resistance value changes to. Become Also as shown in FIG. 7 (C), the the rotation angle 0 shrinks intermediate transfer belt is changed to S = + 0 _2, the resistance value changes in Z _2. The change in the resistance value Z of the potentiometer due to the change in the rotation angle 6> is actually output as the voltage value V, and the reference resistance value

Z. Is the reference voltage value V. And the resistance Z when the belt is stretched! Is the voltage value V! The resistance value Z ₂ when the belt is contracted becomes the voltage value V ₂ .

FIG. 10 shows the characteristic of the belt length L with respect to the resistance value Z from the potentiometer 114 provided in the belt length detector 30. An example in which the characteristic is linear is shown. First, as shown in Fig. 7 (A), the belt has no expansion and contraction, and the resistance value Z of the potentiometer is 1 1 4. In the case of, the belt length L is a predetermined reference length L. It has become. When the intermediate transfer belt is stretched as shown in Fig. 7 (B), the resistance value is Z. From Z to Z, and the belt length at this time is 1 ^. When the intermediate transfer belt shrinks as shown in Fig. 7 (C), the resistance value Z is Z in Fig. 10. Increased Z ₂ from the order belt length L is L. From L to ₂ . Here, since the resistance value Z corresponds to the voltage value V, the detection signal from the actual belt length detector 30 is the voltage value V, and the reference belt length L. Is the reference voltage value V. And the reference voltage value V. From the voltage value V! When the belt length is reduced to L, the belt length is L. From 1 ^ to the reference voltage V. Belt length Increasing the V ₂ from L. From L to ₂ . Therefore, in the actual processing, the reference voltage V at the reference belt length L0. And the reference belt length L corresponding to the detected voltage change Δ ν V ₂ of the detection voltage V ₂ . The belt length change ALAL ₂ of the belt length L _{2 with} respect to. Such a change in the belt length of the intermediate transfer belt 24 is because the time required for the leading position of the transfer image in FIG. 2 to reach the paper pull-in start position 68 is shifted from the predetermined time T. According to the present invention, in accordance with the present invention, the writing timing in the image forming unit 12-1 to 12-4 is adjusted, or the paper pull-in timing by starting the register roller 54 is adjusted. Will be.

FIG. 11 is an explanatory diagram for adjusting the writing timing of the photosensitive drum according to a change in the belt length. Fig. 11 (A) shows the write timing t1 and the paper pull-in timing t2 when the reference belt length L0 is adjusted. The writing start timing of the photosensitive drums 14 to 14 in the black (K) image forming unit 12-4 arranged on the side is set to t1. In this case, the time from the start of image writing to the photoconductor drums 14 to 14 by the LED array 18_4 to the time when the image transferred to the intermediate transfer belt 24 reaches the predetermined paper drawing start position 68 is set. , A fixed time T. Here, assuming that the intermediate transfer belt 24 is extended, if the extension amount ΔΙ ^ of the intermediate transfer belt can be calculated as shown in FIG. 11 (B), the belt transport speed V is constant, so that time

△ T \ = AL no V

However, when the write timing t1 is used as a reference, the paper pull-in timing is extended by the time change ΔΤ \ until time t3. Therefore, with respect to the delay of the writing time t1 due to such belt elongation, in the timing adjustment unit 80 of the present invention, the writing timing t1 is set to the time ΔΤ \ calculated according to the belt elongation amount. Adjust to the writing timing t10 so that it is accelerated.

FIG. 12 shows the case where the intermediate transfer belt 24 is contracted, and the reference belt length L in FIG. 12 (A). As shown in Fig. 12 (B), due to the contraction of the belt, the fixed time T from the writing timing t1 of the

ΑΎ ₂ = AL ₂ / V

However, the paper pull-in timing is advanced as at time t20. Therefore, when the belt contracts, the write timing t1 is adjusted to the write timing t11, which is the write timing t1 delayed by the calculated change time ΔΤ2, as shown in FIG. 10 (C).

FIG. 13 is a flowchart of a timing adjustment process for adjusting the writing timing on the photosensitive drum with respect to the expansion and contraction of the belt length of the intermediate transfer belt 24 as shown in FIGS. First, in step S1, the detection voltage V of the belt length detector 30 is fetched, and the reference belt length L stored in the nonvolatile memory 78 in advance. Reference voltage V corresponding to. And in step S3, a differential voltage AV corresponding to the change in the belt length is obtained.

AV = VV ₀

Is calculated as Here, it is checked in step S4 whether or not the difference voltage Δν is zero. If the difference voltage is zero, the process ends because the belt length has not changed. Step S If Δν is not 0 at 3, the belt length has changed, so the process proceeds to step S 5, and it is determined whether the belt is extended or contracted based on the difference voltage Δν is equal to or greater than zero or less. If the differential voltage ΔV is equal to or greater than the width, the intermediate transfer belt is extended, and the process proceeds to step S6, where the photosensitive drum is moved for a time ΔΤ corresponding to the differential voltage Δν as shown in FIG. 11C. Advance the writing timing. On the other hand, if the difference voltage Δν is less than zero, that is, negative in step S5, the intermediate transfer belt is contracted, and the process proceeds to step S7, where the difference voltage ΔV is reduced as shown in FIG. The writing timing of the photosensitive drum is advanced by the time {} corresponding to. Equations may be used to calculate the relationship between and in steps S6 and S7. Alternatively, table information in which the relationship between the two is set may be prepared in advance, and the corresponding Δ 求め may be obtained by referring to the table using Δν . By performing the evening adjustment for the change in the belt length shown in FIG. 13, a change in the belt length of the intermediate transfer belt 24 during printing is output in real time from the belt length detector 30 to a detection voltage corresponding to the change in the belt length. The change in the belt length AL is detected in real time at that time, and when the leading edge of the image transferred to the paper drawing start position 68 from the timing of writing to the photosensitive drum reaches the leading end, the register roller by the motor 56 is used. Feeding of paper is started by the start of 54, and the image transfer by the secondary transfer roller 48 can always be performed accurately from a predetermined position on the paper even if the belt length changes.

FIG. 14 is an explanatory diagram of a case where the paper pull-in timing is adjusted in response to a change in the belt length by the belt length detector 30. That is, FIG. 14 shows the case where the intermediate transfer belt 24 is extended, and the reference belt length L in FIG. On the other hand, if the belt elongates and the amount of elongation becomes ΔΙ ^, for example,

AT ^ AL ^ V

Then, as shown in Fig. 14 (Β), the paper pull-in timing t2 is adjusted to the timing t21 which is delayed by the change time ΔΊ \ corresponding to the belt elongation.

Fig. 15 shows the case where the intermediate transfer belt 24 is contracted. In this case, the paper pull-in timing t2 for the reference belt length 1 ^ in Fig. 15 (A) is shown in Fig. 15 (B). Change in belt shrinkage

AT ₂ = AL ₂ / y The timing is adjusted to t 20 just earlier.

FIG. 16 is a flowchart for adjusting the paper pull-in timing with respect to the change in the belt length in FIGS. 14 and 15. In this flowchart, steps S1 to S5 are the same as the adjustment of the write timing in FIG. 13, but if the differential voltage is zero or more, that is, if belt elongation is detected in step S5, In step S6, as shown in FIG. 14 (口), the activation timing of the register port 54 is delayed by the time ΔΤ corresponding to the difference voltage Δν. On the other hand, if the differential voltage △ V becomes less than zero and negative in step S5, the register is closed for a time △ 対応 corresponding to the differential voltage Δ V in step S7 as shown in Fig. 15 (Β). La 54 is quicker to start. A calculation formula may be used for the relationship between mm V and ΔΤ in steps S 6 and S 7. Table information in which the relationship between the two is set is prepared in advance, and the corresponding Δ Δ is determined by referring to the table using ΔV. You may ask.

In the present invention, whether the writing timing or the paper pull-in timing is adjusted, a change in the belt length is detected by the belt length detector 30 in real time, and the belt length is adjusted for each sheet. The timing can be adjusted to keep the secondary transfer position at a constant value with respect to changes, and even if the belt length changes, the position of the image transferred to the paper does not shift, and accurate printing operation is stable. Can be maintained.

In the above embodiment, as shown in FIG. 9, a case where the rotation angle の and the resistance value の of the potentiometer have a linear relationship with a change in the belt length is taken as an example. Of course, it is also good. In the above embodiment, the application to the power printer is taken as an example. However, a copy using paper as a recording medium may be used, or an appropriate apparatus for forming an image on another recording medium is included. . Further, the present invention includes appropriate modifications that do not impair the objects and advantages thereof, and is not limited by the numerical values shown in the above embodiments. Industrial applicability

As described above, according to the present invention, a change in the belt length can be detected in real time by detecting the movement of the tension roller with respect to the change in the belt length. This makes it possible to make adjustments so as to eliminate the influence of the change in the belt length for each sheet, and to maintain accurate alignment of the secondary transfer image with respect to the sheet. In addition, by using a detector with a simple structure that mechanically detects the change in the belt length and detects the displacement of the tension roller and converts it into a change in the resistor, the cost can be reduced compared to an optical detector. Since there is no need to transfer the mark to the belt length, toner consumption other than printing can be suppressed.

Claims

The scope of the claims

1. An electrophotographic process mechanism that first transfers the image developed by the image forming unit to the intermediate transfer belt and then secondary transfers it to paper.

A detector that detects a change in belt length from the movement of a tension roller provided on the intermediate transfer belt;

A timing adjustment unit that adjusts the timing of the electrophotographic process mechanism based on a change in the belt length by the detector;

An image forming apparatus comprising:

2. The image forming apparatus according to claim 1, wherein the detector pivotally supports the tension port at a frame tip and mounts a rotary potentiometer on a frame base to extend or contract the intermediate transfer belt. An image forming apparatus comprising: detecting a change in the rotation angle of the frame corresponding to a change in the resistance value during the potentiometer.

3. The image forming apparatus according to claim 1, wherein the timing adjustment unit adjusts a timing of writing an image to a photoconductor drum in the electrophotographic process according to a change in a belt length by the detector. Characteristic image forming apparatus.

4. The image forming apparatus according to claim 3, wherein, when the intermediate transfer belt is extended, the timing adjustment unit adjusts the writing timing so as to be advanced in accordance with the amount of extension, and The image forming apparatus is characterized in that when shrinking, the writing timing is adjusted so as to be delayed according to the shrinkage amount.

5. The image forming apparatus according to claim 1, wherein the timing adjustment unit adjusts a sheet pull-in timing of a registration roller in the electrophotographic process according to a change in a belt length by the detector. Image forming device.

6. The image forming apparatus according to claim 5, wherein, when the intermediate transfer belt is extended, the timing adjustment unit adjusts the registration roller to delay the drawing-in timing of the registration roller according to the amount of extension. An image forming apparatus, wherein when the intermediate transfer belt shrinks, the timing for drawing in the registration rollers is adjusted so as to be advanced according to the amount of shrinkage.

7. The image forming apparatus according to claim 1, wherein the electrophotographic process mechanism includes a plurality of image forming units configured to form a visible image of each color by electrostatically attaching a developer of a different color to an image carrier. When,

A primary transfer unit that electrostatically sequentially overlaps and transfers the developer adhered on each image carrier of the image forming unit to the intermediate transfer belt;

An image forming apparatus, comprising: a secondary transfer unit configured to transfer a visible image transferred to the intermediate transfer belt to a sheet.

8. The image forming apparatus according to claim 7, wherein the plurality of image forming units include four image forming units using black, cyan, magenta, and yellow developers along the intermediate transfer belt. An image forming apparatus characterized by being arranged in tandem.