JP2011013240A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to more highly accurately perform a color shift correction control by promptly stabilizing a frictional coefficient of each portion of an intermediate transfer belt and suppressing speed fluctuation, through the use of existing configuration.SOLUTION: When the color shift correction control starts, toner is discharged from a belt cleaning device 116 to the intermediate transfer belt 9 to level the uneven toner deposition amounts among respective portions of the intermediate transfer belt 9. After the toner discharged from the belt cleaning device 116 goes round and passes through a secondary transfer part T2, toner images as a positional index are formed on photoreceptor drums 1Y and 1M, then, the formed toner images are primarily transferred to the intermediate transfer belt 9. The toner images as the positional index on the intermediate transfer belt 9 are detected by color shift sensors S1 and S2, and the exposure start timing of an exposure device 1Y is adjusted by taking the exposure start timing of the exposure device 1M as a reference.

Description

  The present invention relates to an image forming apparatus that adjusts a toner image forming position on a photoreceptor using a toner image of a position index during non-image formation, and more specifically, adjustment of a toner image forming position by suppressing speed fluctuation during adjustment. It relates to control that increases accuracy.

  A tandem type full-color image forming apparatus in which a plurality of image forming units having different development colors are arranged along an intermediate transfer member or a recording material transport member is widely used. In a tandem type full-color image forming apparatus, color misregistration correction control is executed prior to image formation to adjust the position in the main scanning direction of the toner image formed on each photoconductor of a plurality of image forming units. The accuracy of superimposing toner images of each color is improved (Patent Document 1).

  In the color misregistration correction control disclosed in Patent Document 1, as shown in FIG. 1, during non-image formation, a toner image with a linear position index in the main scanning direction is formed on the photosensitive drums 1Y, 1M, 1C, and 1K. Then, primary transfer is performed on both ends of the intermediate transfer belt 9. Then, the toner image of the position index on the intermediate transfer belt 9 is detected by the optical sensors S1, S2, and the exposure start timing on the photosensitive drums 1Y, 1M, 1C, 1K is adjusted according to the detection result.

  Incidentally, as shown in FIG. 1, an image forming apparatus including an electrostatic cleaning device (116) that removes transfer residual toner from the intermediate transfer belt 9 by contacting a fur brush to which a voltage is applied has been put into practical use. (Patent Document 2).

  In Patent Document 2, the polarity of the DC voltage applied to the fur brush is reversed from that at the time of image formation, whereby the toner accumulated in the fur brush 31 at the time of image formation is discharged to the intermediate transfer belt 9 to clean the fur brush 31. The performance is restored.

JP 2002-014507 A JP 2006-30520 A

  Immediately after the start of the image forming apparatus, the coefficient of friction varies for each portion of the intermediate transfer belt 9, and it has been found that if the color misregistration correction control is performed as it is, the alignment accuracy of the toner images of the respective colors deteriorates.

  Since the frictional load of the secondary transfer portion T2 differs between the case where the color misregistration correction control images P1 and P2 shown in FIG. 4 do not pass through the secondary transfer portion T2, the tension on the intermediate transfer belt 9 is different. Cause fluctuations. It has been found that an error occurs in the color misregistration correction between the first time and the second time because the formation positions of the color misregistration correction control images P1 and P2 on the intermediate transfer belt 9 are shifted due to the tension fluctuation.

  In particular, when the transfer efficiency is increased by setting a peripheral speed difference between the intermediate transfer belt 9 and the secondary transfer roller 23 in the secondary transfer portion T2, the driving torque of the intermediate transfer belt 9 depending on the presence or absence of toner adhesion. The fluctuation of becomes large. It was also found that the color misregistration correction error increases as the driving torque fluctuation increases.

  Therefore, it has been proposed to perform the color misregistration correction control after continuing the pre-rotation until the friction coefficient of the entire intermediate transfer belt 9 is stabilized after the image forming apparatus is started. In this case, the time of the pre-rotation is extended. The start of image formation is delayed.

  The present invention provides an image forming apparatus that can perform highly accurate color misregistration correction control by quickly stabilizing the friction coefficient for each portion of the intermediate transfer belt and suppressing speed fluctuations using an existing configuration. It is an object.

  An image forming apparatus according to the present invention includes an intermediate transfer member, an image forming unit that transfers a toner image formed on a photosensitive member to the intermediate transfer member at a primary transfer unit, and a secondary transfer for transferring the toner image to a recording material. A transfer member that contacts the intermediate transfer member so as to form a portion, and a detection unit that detects a toner image of a position index formed by the image forming unit and transferred to the intermediate transfer member by the primary transfer unit; An electrostatic cleaning device that contacts a brush member to which a voltage is applied and collects transfer residual toner of the intermediate transfer member. And at the time of non-image formation, the detection means detects the toner image of the position index transferred to the intermediate transfer member, and has a registration mode for adjusting the toner image formation position on the photosensitive member, In the alignment mode, the electrostatic cleaning device is controlled so that the amount of toner that adheres to the intermediate transfer member and increases is increased.

  In the image forming apparatus of the present invention, the cleaning performance of the electrostatic cleaning device is lowered, or toner is positively discharged from the brush member to the intermediate transfer member, thereby increasing the amount of toner attached to the intermediate transfer member. As a result, the variation in the friction coefficient for each portion of the intermediate transfer member is leveled, and the variation in the friction load when the intermediate transfer member passes through the primary transfer portion and the secondary transfer portion is reduced.

  Therefore, by utilizing the existing configuration, the friction coefficient for each portion of the intermediate transfer belt is stabilized to suppress the speed fluctuation, thereby enabling highly accurate color misregistration correction control.

1 is an explanatory diagram of a configuration of an image forming apparatus. It is explanatory drawing of a structure of a belt cleaning apparatus. 2 is a block diagram of a control system of the image forming apparatus. FIG. It is explanatory drawing of the detection of a color shift correction control image. FIG. 10 is an explanatory diagram of a driving state of a developing sleeve in color misregistration correction control. 3 is a flowchart of color misregistration correction control according to the first exemplary embodiment. It is explanatory drawing of the effect of reducing the rotation speed of a fur brush. It is explanatory drawing of a structure of the belt cleaning apparatus in Example 2. FIG. 10 is a flowchart of color misregistration correction control according to the second exemplary embodiment. It is explanatory drawing of the effect which switches a DC voltage to an AC voltage. FIG. 6 is an explanatory diagram of a change in toner charge amount when a DC voltage and an AC voltage are switched. FIG. 6 is an explanatory diagram of a configuration of a belt cleaning device in Embodiment 3. 10 is a flowchart of color misregistration correction control according to a third exemplary embodiment. It is explanatory drawing of the effect which reverses the polarity of DC voltage. It is explanatory drawing of the change of the charge amount of the toner at the time of switching polarity. FIG. 6 is a comparison diagram of tension fluctuation of an intermediate transfer belt in Examples 1, 2, and 3. FIG. 6 is an explanatory diagram of a change in the toner accumulation amount of the fur brush accompanying continuous image formation. 10 is a flowchart of control according to the fourth embodiment. FIG. 10 is an explanatory diagram of a configuration of an image forming apparatus according to Embodiment 5.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is another implementation in which part or all of the configuration of the embodiment is replaced with the alternative configuration as long as the discharge of the toner accumulated in the brush member before the start of the color misregistration correction control is started. It can also be implemented in the form.

  Therefore, as long as the toner image forming position on the photosensitive member is adjusted by transferring and detecting the toner image of the position index to the intermediate transfer member or the recording material conveying member, the tandem type / 1 drum type, the intermediate transfer type / This can be done without distinction between the recording material conveyance type.

  In the present embodiment, only the main part of the image forming apparatus related to toner image formation / transfer will be described. However, the present invention adds printers, various printing machines, and copiers in addition to necessary equipment, equipment, and housing structure. , FAX, multi-function machine, etc.

  In addition, about the general matter of the image forming apparatus shown by patent document 1, 2, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus. As shown in FIG. 1, the image forming apparatus 100 is a tandem intermediate transfer type full-color printer in which yellow, magenta, cyan, and black image forming portions PY, PM, PC, and PK are arranged along an intermediate transfer belt 9. is there.

  In the image forming unit PY, a yellow toner image is formed on the photosensitive drum 1Y and is primarily transferred to the intermediate transfer belt 9. That is, the image forming unit (PY) transfers the toner image formed on the photoreceptor (1Y) to the intermediate transfer member (9) by the primary transfer unit TY. In the image forming unit PM, a magenta toner image is formed on the photosensitive drum 1M, and is primarily transferred onto the yellow toner image on the intermediate transfer belt 9. In the image forming units PC and PK, a cyan toner image and a black toner image are formed on the photosensitive drums 1C and 1K, respectively, and are sequentially transferred onto the intermediate transfer belt 9 in order.

  The four-color toner images primarily transferred to the intermediate transfer belt 9 are transported to the secondary transfer portion T2 and collectively transferred to the recording material P. The recording material P on which the four-color toner images are secondarily transferred is heated and pressurized by the fixing device 28 to fix the toner images on the surface, and then discharged to the outside of the machine body.

  The intermediate transfer belt 9 is supported around a tension roller 22, a driving roller 20, and a counter roller 21, and is driven by the driving roller 20 to rotate in the direction of arrow R2 at a process speed of 300 mm / sec. The intermediate transfer belt 9 has an elastic layer formed on a base layer having a thickness of 100 μm, has a total thickness of 300 μm, and a circumferential length of 2400 mm.

  The recording material P drawn from the recording material cassette 25 is separated one by one by the separation roller 26 and sent to the registration roller 27. The registration roller 27 receives and waits for the recording material P in the stopped state, and sends the recording material P to the secondary transfer portion T2 in time with the toner image on the intermediate transfer belt 9.

  The secondary transfer roller 23 abuts on the intermediate transfer belt 9 whose inner surface is supported by the counter roller 21 to form a secondary transfer portion T2. That is, the transfer member (23) contacts the intermediate transfer member (9) so as to form a secondary transfer portion T2 for transferring the toner image to the recording material. By applying a positive DC voltage from the power source D2 to the secondary transfer roller 23, the toner image charged to the negative polarity and carried on the intermediate transfer belt 9 is secondarily transferred to the recording material P.

  The belt cleaning device 116 rubs the intermediate transfer belt 9 with a fur brush, escapes the transfer onto the recording material P, passes through the secondary transfer portion T2, and collects the transfer residual toner remaining on the intermediate transfer belt 9. .

  The image forming units PY, PM, PC, and PK are configured substantially the same except that the color of toner used in the developing devices 4Y, 4M, 4C, and 4K is different from yellow, magenta, cyan, and black. Hereinafter, the yellow image forming unit PY will be described, and the other image forming units PM, PC, and PK will be described by replacing Y at the end of the reference numerals attached to the constituent members being described as M, C, and K. Shall be.

  In the image forming unit PY, a charging roller 2Y, an exposure device 3Y, a developing device 4Y, a primary transfer roller 5Y, and a cleaning device 6Y are arranged around the photosensitive drum 1Y.

  The photosensitive drum 1Y is configured by applying an organic photoconductor layer (OPC) to the outer peripheral surface of an aluminum cylinder having a diameter of 80 mm. Both ends of the photosensitive drum 1Y are rotatably supported by flanges, and a driving force is transmitted to one end from a driving motor (not shown) to rotate in the direction of arrow R1 at a process speed of 300 mm / sec.

  The charging roller 2Y rotates in contact with the photosensitive drum 1Y and applies a vibration voltage obtained by superimposing an AC voltage on a DC voltage, thereby charging the surface of the photosensitive drum 1Y to a uniform negative potential VD. To do.

  The exposure apparatus 3Y scans the scanning line image data obtained by developing the yellow separated color image with a rotating mirror, and writes an electrostatic image of the image on the surface of the charged photosensitive drum 1Y.

  The developing device 4Y stirs the two-component developer to charge the toner negatively and the carrier positively. The charged two-component developer is carried on the developing sleeve 4a that rotates around a fixed magnet roller and rubs against the photosensitive drum 1Y. By applying an oscillating voltage in which an AC voltage is superimposed on a negative DC voltage Vdc to the developing sleeve 4a, the toner is transferred from the developing sleeve 4a to the exposed portion of the photosensitive drum 1Y, and the electrostatic image is reversely developed.

  The cleaning device 6Y slides a cleaning blade on the photosensitive drum 1Y to collect the transfer residual toner remaining on the photosensitive drum 1Y by escaping from the transfer to the intermediate transfer belt 9.

<Electrostatic cleaning device>
FIG. 2 is an explanatory diagram of the configuration of the belt cleaning device.

  In recent years, in an image forming apparatus using an electrostatic process, an intermediate transfer belt has been adopted because of the need to form a high quality image with a wide variety of recording materials. As the intermediate transfer belt, a resin belt using a resin is generally used, but in response to the demand for high image quality, an elastic intermediate transfer belt having an elastic layer and excellent in transferability to paper is used. It is becoming mainstream. Also, various materials are coated on the surface of the intermediate transfer belt in order to increase the releasability from the toner and increase the transfer efficiency.

  In order to deal with such a diversified intermediate transfer belt, a belt cleaning apparatus is generally an electrostatic cleaning system that electrically collects toner instead of a conventional mechanical cleaning blade system.

  As an example of the electrostatic cleaning method, there is a fur brush method in which a conductive fur brush to which a voltage having a polarity opposite to that of the toner to be collected is applied is rubbed against the intermediate transfer belt in a rotating state. The fur brush method has a relatively high degree of freedom in the material and shape of the intermediate transfer belt that is the member to be cleaned, the surface is soft, and it has stable cleaning characteristics even for elastic intermediate transfer belts that are difficult to clean with the cleaning blade method. Can demonstrate.

  The voltage applied to the fur brush is generally a DC voltage having a polarity opposite to the charging polarity with the toner, but there is also a case where an oscillating voltage in which an AC voltage is superimposed on the DC voltage is applied. In the fur brush, toner accumulates in the fur brush as image formation is accumulated. If the toner is excessively accumulated, the resistance of the fur brush increases or the cleaning performance decreases. Therefore, during non-image formation, by applying a DC voltage with the opposite polarity to the normal cleaning bias to the fur brush, the toner accumulated in the fur brush is discharged to the intermediate transfer belt to restore the fur brush cleaning performance. (Patent Document 2).

  As shown in FIG. 2, the belt cleaning device 116 is an electrostatic cleaning device that electrically collects transfer residual toner remaining on the intermediate transfer belt 9 that has passed through the secondary transfer portion T2. That is, the electrostatic cleaning device (116) contacts the brush member (118) to which a voltage is applied, and collects the transfer residual toner on the intermediate transfer member (9).

  The belt cleaning device 116 includes a fur brush 118, a bias roller 119, and a cleaning blade 120 inside an apparatus housing 117 disposed in the vicinity of the intermediate transfer belt 9. The fur brush 118 and the bias roller 119 are driven by a motor 121 attached to the belt cleaning device 116 and rotate in the direction of the arrow, respectively. The cleaning blade 120 is fixed to the apparatus housing 117 with its tip abutting against the bias roller 119.

The fur brush 118 has a volume resistivity of 0.3 M (Ω / cm) and a carbon dispersion type nylon fiber having a fiber thickness of 6 denier and is planted on a central metal roller at a rate of 500,000 / inch ² of planting density. This is a conductive fur brush formed. The bias roller 119 is an aluminum metal roller having a mirror finished surface. The cleaning blade 120 is a urethane rubber blade.

  The fur brush 118 is disposed with an intrusion amount of about 1.0 mm with respect to the intermediate transfer belt 9, and the bias roller 119 is disposed with an intrusion amount of about 1.0 mm with respect to the fur brush 118. The bias roller 119 rotates in the arrow direction at a rotation angular velocity equal to that of the fur brush 118. The cleaning blade 120 is disposed with an intrusion amount of 1.0 mm with respect to the bias roller 119.

  A positive polarity DC voltage is applied to the bias roller 119 of the belt cleaning device 116 by a DC power supply 131. Specifically, a voltage of +1500 V was applied to the bias roller 119, and the current value at this time was +20 μA as measured by an ammeter (not shown).

  By applying a positive polarity DC voltage to the bias roller 119, a potential difference is generated between the intermediate transfer belt 9 and the fur brush 118 that are in contact with the backup roller 115 connected to the ground potential. Driven by this potential difference, the toner having the (−) polarity in the transfer residual toner on the intermediate transfer belt 9 is transferred to the fur brush 118 side. The toner adsorbed on the fur brush 118 is driven by a potential difference between the fur brush 118 and the bias roller 119 and is transferred from the fur brush 118 to the bias roller 119. The toner adsorbed on the bias roller 119 is scraped off by the cleaning blade 120 and collected in the apparatus housing 117.

  By the way, even if the belt transfer device 116 cleans the transfer residual toner having the (−) polarity on the intermediate transfer belt 9, the intermediate transfer belt 9 has a non-polar toner or (+) polarity. Toner remains. As shown in FIG. 1, these toners are retransferred onto the photosensitive drums 1Y, 1M, 1C, and 1K by the image forming units PY, PM, PC, and PK, and then cleaned by the cleaning devices 6Y, 6M, 6C, and 6K. Removed.

<Color misregistration correction control>
FIG. 3 is a block diagram of a control system of the image forming apparatus. FIG. 4 is an explanatory diagram of detection of a color misregistration correction control image. FIG. 5 is an explanatory diagram of a driving state of the developing sleeve in the color misregistration correction control.

  In a full-color image forming apparatus, full-color images are formed by sequentially superimposing toner images of different colors. Therefore, it is necessary to form a plurality of images having different colors at correct positions without relatively shifting.

  In an image forming apparatus using an intermediate transfer belt, toner images of different colors may be relatively displaced due to various factors. For example, when the belt circumferential length changes due to the thermal expansion of the intermediate transfer belt due to the temperature rise in the apparatus during image formation, the image expands and contracts and the overlay is displaced. A registration error occurs due to an attachment position error of the image forming unit of each color and a slight movement of the primary transfer unit of each color. When a deviation occurs in the superposition of the toner images of the respective colors, a color deviation occurs in the image and the image quality is deteriorated.

  A typical method of color misregistration correction control for correcting such color misregistration is a color misregistration corrected image sampling method. The color misregistration corrected image sampling method forms a toner image (color misregistration correction control image) as a position index at a plurality of positions on the intermediate transfer belt in order to correct the color misregistration by canceling the influence of image expansion and contraction. Then, by reading a plurality of color misregistration correction control images formed on the intermediate transfer belt, data on the relative misregistration amount of each color is obtained, and an average of the misregistration amounts is obtained from the obtained plurality of misregistration amount data. The value is obtained and the color shift of each color is corrected. Since the average value obtained from the color misregistration corrected image sampling method is a value in which the influence of image expansion / contraction is offset, if correction processing is performed using the average value, the accuracy of color misregistration correction is improved.

  Further, the positional deviation of the toner images of the respective colors is also affected by the frictional force at the contact portion with the photosensitive drum, the transfer roller, the stretching roller, etc. that are in contact with the intermediate transfer belt. Further, at the contact portion with the photosensitive drum and the contact portion with the secondary transfer roller, the frictional load during passage varies depending on the amount of toner attached to the surface of the intermediate transfer belt, so that the toner adheres to the intermediate transfer belt. The amount is also affected. When non-image formation is performed, color misregistration correction control using a color misregistration correction image sampling method with a large friction load at these abutting portions reduces the frictional force at the abutting portions during image formation with a high image ratio. There is a concern that the amount of color misregistration increases.

  Similarly, there is a concern that the amount of color misregistration changes when an image with a high image ratio is formed and when an image with a low image ratio is formed. However, it has been confirmed that when the image ratio is simply low, the developing sleeve rotates and the fog toner continues to adhere to the photosensitive drum, so that the frictional force is reduced and the color misregistration amount does not change much.

  As shown in FIG. 3 with reference to FIG. 1, the controller 35 of the control unit 11 controls the tandem type image forming apparatus 100 to control the image forming operation, the detection of the color shift and the density shift, the correction operation, and the like. To do.

  The image processing unit 33 converts image information to be formed into a digital image signal based on a command from the controller 35. The image output unit 34 outputs the digital image signal generated by the image processing unit 33 under the control of the controller 35 at an appropriate timing. These functions in the control unit 11 are realized by, for example, a program-controlled CPU (Central Processing Unit). The image output unit 34 outputs digital image signals (color misregistration correction control) to the exposure devices 3Y, 3M, 3C, and 3K of the image forming units PY, PM, PC, and PK that form images of Y, M, C, and K colors. Output).

  The control unit 11 includes a nonvolatile ROM 32 and a readable / writable RAM 31 as memories. The ROM 32 stores a software program for controlling image forming operations, color misregistration detection and correction operations, and the like executed by the controller 35. The pattern information of the color misregistration correction control image is also stored in the ROM 32.

  In the RAM 31, the count value of the cumulative number of image formations by the number counter 32, the temperature / humidity value by the environmental sensor 22, the count value of the cumulative number of image formations by the cleaning life counter 24, etc. are acquired along with the operation of the image forming apparatus 100. Various types of information are stored. The color misregistration amount of the color misregistration correction control image detected by the color misregistration sensors S1 and S2, the elapsed time information after the previous color misregistration detection process, and the like are also stored.

  As shown in FIG. 4A, in the color misregistration correction control, a position index toner image (color misregistration correction control images P1 and P2) is formed on the photosensitive drum, and both end portions in the width direction of the intermediate transfer belt 9 are formed. The primary transfer. In order to detect the color misregistration correction control images P1 and P2, color misregistration sensors S1 and S2 are attached so as to face both ends of the intermediate transfer belt 9 in the width direction. The color misregistration sensors S1 and S2 are reflection type LED sensors, and detect regular reflection light by irradiating the surface of the intermediate transfer belt 9 with a spot of infrared light. That is, the detection means (S1, S2) detects the toner image of the position index formed by the image forming unit and transferred to the intermediate transfer member (9) by the primary transfer unit T1.

  Since the specularly reflected light from the intermediate transfer belt 9 is scattered and absorbed by the color misregistration correction control images P1 and P2, the moment the spot passes through the color misregistration correction control images P1 and P2, the output of the color misregistration sensors S1 and S2 Depressed. The controller 35 detects the fall timing of the outputs of the color misregistration sensors S1 and S2, and measures the relative positions of the color misregistration correction control images P1 and P2.

  The color misregistration correction control image P1 is a line-shaped toner image that is inclined at an angle of 45 degrees with respect to the rotation direction composed of a magenta color as a reference color. The color misregistration correction control image P2 is a line-shaped toner image inclined at an angle of 45 degrees with respect to the rotation direction composed of one of yellow, cyan, and black. The exposure start timing is set so that the color misregistration correction control image P1 and the color misregistration correction control image P2 are primarily transferred on the intermediate transfer belt 9 at a predetermined distance in the rotation direction.

  As shown in FIG. 4B, the case where the yellow color misregistration correction control image P2 of the adjustment color is formed aiming at the broken line position in the center of the interval of the reference color magenta color misregistration correction control image P1 will be described. To do. Since the image forming unit PY and the image forming unit PM have color misregistration in the width direction and the rotation direction of the intermediate transfer belt 9, the yellow color misregistration correction control image P2 is deviated from the position of the broken line.

  When the color misregistration sensor S1 detects the color misregistration correction control images P1 and P2 along the detection line, the controller 35 captures the detection timings of the color misregistration correction control images P1 and P2 and measures the distances A1, A2, B1, and B2. To do.

At this time, the color shift amount ΔV in the main scanning direction and the color shift amount ΔH in the sub-scanning (rotating) direction are calculated as follows.
ΔV = [(B2-B1) / 2- (A2-A1) / 2] / 2
ΔH = [(B2-B1) / 2 + (A2-A1) / 2] / 2

  In this way, the controller 35 measures the color misregistration amount between the magenta color misregistration correction control image P1 and the yellow color misregistration correction control image P2. The color shift amounts ΔV and ΔH correspond to the relative shift Δx in the main scanning direction and the shift y in the sub-scanning (rotation) direction in the exposure apparatuses 3Y and 3M.

  The controller 35 obtains an adjustment amount of the image writing start timing by the exposure apparatus 3Y so that y becomes a standard value so that Δx becomes zero. The controller 35 feeds back the adjustment amount to the image output unit 34. Thereby, the writing position and timing of data on the photosensitive drum 1Y by the exposure device 3Y are optimized in the main scanning direction and the sub-scanning direction, respectively, and the color shift is eliminated. That is, the alignment mode is executed during non-image formation, and the toner image of the position index transferred to the intermediate transfer member (9) is detected by the detection means (S1, S2), and the toner image on the photosensitive member (1Y) is detected. Adjust the formation position.

  Similar color misregistration correction control is repeated for cyan and black with respect to magenta of the reference color, so that color misregistration in the image forming units PY, PM, PC, and PK is eliminated, and a high-quality image is obtained.

  By the way, in the color misregistration correction control, the color misregistration correction control images P1, P2 formed on the photosensitive drums 1Y, 1M, 1C, 1K are transferred onto the intermediate transfer belt 9 and detected by the color misregistration sensors S1, S2. For this reason, when the speed of the intermediate transfer belt 9 fluctuates, the transfer positions of the correction control images P1 and P2 are shifted, and the amount of color shift cannot be obtained accurately. If the color misregistration correction control is performed with the apparent color misregistration amount due to the speed fluctuation, the color misregistration may be increased.

  That is, in the image forming apparatus 100, the color misregistration correction control is executed at the start of the start immediately after turning on the main power of the image forming apparatus 100 in the morning and when the cumulative number of image formations from the previous control reaches a predetermined number. To do. When the color misregistration correction control images P1 and P2 are formed on the intermediate transfer belt 9 in the morning, the driving load of the intermediate transfer belt 9 greatly fluctuates during the formation, causing the intermediate transfer belt 9 to vary in speed. End up.

  In recent high-speed machines, as the size of the intermediate transfer belt increases, the peripheral length of the intermediate transfer belt is often long. Color misregistration correction control images P1 and P2 are formed repeatedly at a plurality of positions. Since the color misregistration correction control is performed for each of the reference color and the adjustment color, the developing sleeve is stopped in the developing device that is not used in order to prevent deterioration of the two-component developer.

  As shown in FIG. 5, when the color misregistration correction control is performed a total of six times over two rotations of the intermediate transfer belt 9, the developing sleeve of the reference color magenta rotates every time. However, in the other adjustment colors yellow, cyan, and black, the developing sleeve is stopped at a ratio of two times, and the fog toner is supplied to the photosensitive drums 1Y, 1C, and 1K while the developing sleeve is stopped. Not. For example, while the M and Y color misregistration correction control images P1 and P2 are formed, the C and K color developing sleeves are stopped.

  For this reason, during the color misregistration correction control, fog toner is applied to the intermediate transfer belt 9 in a mottled manner, and unevenness of the friction coefficient occurs in each portion of the intermediate transfer belt 9. In the primary transfer portion and the secondary transfer portion, the portion where the color misregistration correction control image of the intermediate transfer belt 9 is formed is reduced in frictional force by the fog toner, but the portion where the color misregistration correction control image is not formed is Since there is no fog toner, the frictional force increases.

  Then, when the intermediate transfer belt 9 having a large unevenness of the friction coefficient for each part passes through the secondary transfer portion T2, speed fluctuation occurs in the intermediate transfer belt 9, and the transfer positions of the color misregistration correction control images P1 and P2 are set. It will shift. The intermediate transfer belt 9 in which the presence of toner is not uniform has a frictional force that changes in the primary transfer portion and the secondary transfer portion. Therefore, the speed of the intermediate transfer belt 9 is uneven, and the accuracy of color misregistration correction control is reduced. End up.

  Therefore, in the following embodiments, prior to color misregistration correction control, toner is applied to the intermediate transfer belt 9 using the fur brush 118 of the belt cleaning device 116, and the friction coefficient does not increase even in a portion where there is no fog toner. I am doing so.

  That is, in the color misregistration correction control, the electrostatic cleaning device (116) is controlled so that the toner adhering to the intermediate transfer member (9) increases. Thereby, at the time of color misregistration correction control, the toner can uniformly exist on the intermediate transfer belt 9, and the speed of the intermediate transfer belt 9 can be stabilized. As a result, it is possible to improve the accuracy during color misregistration correction control and obtain a good image with little color misregistration.

  In the color misregistration correction control, after the toner discharged from the brush member (119) to the intermediate transfer member (9) arrives at the secondary transfer portion T2, the toner image of the position index is transferred to the intermediate transfer member (primary transfer portion T1). 9) Primary transfer. As a result, the variation in the frictional load caused by the unevenness of the toner adhesion amount on the intermediate transfer belt 9 at the secondary transfer portion T2 does not affect the primary transfer of the toner image of the position index.

  In the color misregistration correction control, after the toner discharged from the brush member (118) to the intermediate transfer member (9) arrives at the secondary transfer portion T2, a toner image of a position index is formed at the image forming portion (PY). . As a result, the variation in the frictional load caused by the unevenness in the toner adhesion amount of the intermediate transfer belt 9 at the secondary transfer portion T2 does not affect the toner image forming position of the position index on the photosensitive drum 1Y.

<Example 1>
FIG. 6 is a flowchart of color misregistration correction control according to the first embodiment. FIG. 7 is an explanatory diagram of the effect of reducing the rotation speed of the fur brush. In the first exemplary embodiment, the toner accumulated in the fur brush 118 is discharged to the intermediate transfer belt 9 by lowering the rotation speed of the fur brush 118 than that during image formation.

  As shown in FIG. 6, after the main switch is turned on (S11), image formation is started (S12). Whether the color misregistration correction control is possible or not is determined by detecting the temperature rise in the machine from the environmental sensor in the machine (S13). If it is determined that color misregistration correction control is necessary (YES in S13), even when the image forming apparatus 100 forms an image, the process proceeds to a down sequence, and the peripheral speed of the fur brush 118 is higher than that at the time of image formation. (S14).

  After the peripheral speed of the fur brush 118 decreases, color misregistration correction control is started (S15), a correction value is calculated (S16), and the correction value is fed back to the exposure apparatuses 3Y, 3M, 3C, and 3K (S17). . Thereafter, the peripheral speed of the fur brush 118 is switched to the same rotational speed as that at the time of image formation (S18), and the color misregistration correction control is completed (S19).

  As shown in FIG. 2, the rotation speed of the fur brush 118 is controlled by a motor 121 connected to the control unit 11, and rotates in the arrow direction at a rotation speed of 50 rpm during normal image formation. On the other hand, during the color misregistration correction control, the rotation speed of the fur brush 118 is reduced to an arbitrary speed by the control of the control unit 11. The voltage applied to the bias roller 119 is −1500 V both during normal image formation and during color misregistration correction control.

  By making the rotation speed of the fur brush 118 slower than that during normal image formation, the cleaning ability of the fur brush 118 is lowered. When the cleaning capability decreases, the amount of toner having a charge amount of (−) that adheres to the intermediate transfer belt 9 and increases is increased. On the other hand, the toner holding the (+) charge amount is transferred to the photosensitive drums 1Y to 1K by the voltage of the (+) polarity applied to the primary transfer rollers 5Y to 5K, and the cleaning devices 6Y to 6K. Continue to be cleaned by.

  As shown in FIG. 7, the fog toner density on the intermediate transfer belt 9 increases as the rotation speed of the fur brush 118 decreases. Here, the fog toner density was measured in the state where the developing sleeve 4a shown in FIG. 1 is rotating and the state where it is not rotating. In the measurement method, with the image forming apparatus 100 stopped, a transparent seal tape is applied to the intermediate transfer belt 9 to collect the fog toner, and the seal is measured with a reflection densitometer manufactured by X-RITE, and quantified. did.

  Here, when the fog toner density on the intermediate transfer belt 9 becomes 0.13 or more, the specularly reflected light from the surface of the intermediate transfer belt 9 illuminated by the color misregistration sensors S1 and S2 is insufficient, and the color misregistration sensors S1 and S1. The reading accuracy of the color misregistration correction control image in S2 is lowered. Therefore, in the first embodiment, the fur brush 118 at the time of color misregistration correction control is controlled to a rotation speed of 10 rpm.

  In the first exemplary embodiment, by reducing the rotation speed of the fur brush 118, the amount of fog toner on the intermediate transfer belt 9 is made uniform during color misregistration correction control. The difference in fog toner amount between the state where the developing sleeve of the intermediate transfer belt 9 is rotating and the state where the developing sleeve is stopped is reduced, and the difference in friction load between the primary transfer portion T1 and the secondary transfer portion T2 is also small. Become. By uniformizing the fog toner amount over the entire circumference of the intermediate transfer belt 9, the frictional load unevenness when the intermediate transfer belt 9 passes through the primary transfer portion T1 and the secondary transfer portion T2 is reduced. The speed fluctuation of the intermediate transfer belt 9 during the color misregistration correction control is suppressed. For this reason, the accuracy of the color misregistration correction control is improved, and the color misregistration amount of each color toner image is reduced.

<Example 2>
FIG. 8 is an explanatory diagram of the configuration of the belt cleaning device according to the second embodiment. FIG. 9 is a flowchart of color misregistration correction control according to the second embodiment. FIG. 10 is an explanatory diagram of the effect of switching the DC voltage to the AC voltage. FIG. 11 is an explanatory diagram of the change in the charge amount of the toner when the DC voltage and the AC voltage are switched. In the second embodiment, the toner applied to the fur brush 118 is discharged to the intermediate transfer belt 9 by switching the voltage applied to the fur brush 118 from the DC voltage to the AC voltage.

  As shown in FIG. 8, a DC power supply 131 and an AC power supply 132 connected to the control unit 11 are connected to the fur brush 118 so as to be switchable with a switch. The switch is controlled by the control unit 11.

  A positive polarity DC voltage (+1500 V) is applied to the fur brush 118 during normal image formation by the DC power supply 131 and a current of 20 μA flows. As a result, the transfer residual toner having the polarity of (−) that has not been transferred to the recording material P is transferred to the fur brush 118 and collected by the bias roller 119.

  Further, even when the fur brush 118 cleans the transfer residual toner having the (−) polarity on the intermediate transfer belt 9, the intermediate transfer belt 9 has a non-polar toner or a (+) polarity. Toner is left. These toners are transferred again to the photosensitive drums 1Y, 1M, 1C, and 1K at the primary transfer portions TY, TM, TC, and TK shown in FIG. 1, and then removed by the cleaning devices 6Y, 6M, 6C, and 6K.

  As shown in FIG. 9, image formation is started (S22) after the main switch is turned on (S21). Thereafter, a temperature rise in the machine is detected from the environmental sensor in the machine, and whether or not color misregistration correction control is possible is determined (S23). If it is determined that the color misregistration correction control is necessary (YES in S23), even if the image forming apparatus 100 is forming an image, the process proceeds to a down sequence, and the power source connected to the fur brush 118 is changed from the DC power source 131. Switching to the AC power source 132 is performed (S24).

  After switching to the AC voltage, the color misregistration correction control is started (S25), the color misregistration amount correction value is calculated (S26), and the correction value of each color is fed back to the exposure devices 3Y, 3M, 3C (S27). ). Thereafter, the power source connected to the fur brush 118 is switched again from the AC power source 132 to the DC power source 131 (S28), and the color misregistration correction control is completed (S29).

  In the second embodiment, an AC voltage is applied to the fur brush 118 from the AC power source 132 under the control of the control unit 11 during the color misregistration correction control. The AC voltage is a sine wave having a frequency of 1 kHz. When the peak-to-peak voltage Vpp of the AC voltage is changed, the adhesion amount of the fog toner on the intermediate transfer belt 9 changes as shown in FIG.

  As shown in FIG. 10, as the AC voltage peak-to-peak voltage Vpp increases, the toner adhesion amount on the intermediate transfer belt 9 increases, and if the AC voltage peak-to-peak voltage Vpp is 1500 V or more, the toner adhesion. The amount is saturated. This is because by switching the voltage applied to the fur brush 118 from the DC voltage to the AC voltage, the charge amount of the toner stored in the fur brush 118 is neutralized and converged to near zero.

  FIG. 11A shows the toner charge amount distribution in the fur brush 118 when a DC voltage of 1500 V is applied to the bias roller 119. FIG. 11B shows a toner charge amount distribution in the fur brush 118 when an AC voltage having a peak-to-peak voltage Vpp of 1500 V is applied to the bias roller 119. The charge amount distribution was measured using an E-spert EST3 manufactured by Hosokawa Micron.

  As shown in FIG. 11A, when a DC voltage of 1500 V was applied, the average charge amount in the fur brush 118 was −15 μC / g. On the other hand, as shown in FIG. 11B, the average charge amount in the fur brush 118 when the AC voltage with the peak-to-peak voltage Vpp of 1500 V is applied is −2 μC / g, which converges to almost zero. It was. When the charge amount is in the vicinity of 0, the toner binding force in the fur brush 118 is weakened, and the toner is transferred to the intermediate transfer belt 9, thereby increasing the fog toner amount of the intermediate transfer belt 9.

  In the second embodiment, during the color misregistration correction control, the voltage applied to the fur brush 118 is switched from the DC voltage to the AC voltage, so that the distribution state of the fog toner on the intermediate transfer belt 9 is made uniform. As a result, the difference in the amount of fog toner adhesion between the portion of the intermediate transfer belt 9 that contacts the photosensitive drum when the developing sleeve rotates and the portion that contacts the photosensitive drum when the developing sleeve stops. Get smaller. Thereby, unevenness of the frictional force when each portion of the intermediate transfer belt 9 passes through the primary transfer portion T1 and the secondary transfer portion T2 is reduced, and the speed fluctuation is suppressed. As a result, the accuracy of the color misregistration correction control is improved, and a high quality output image with a small amount of color misregistration can be obtained.

<Example 3>
FIG. 12 is an explanatory diagram of a configuration of the belt cleaning device according to the third embodiment. FIG. 13 is a flowchart of color misregistration correction control according to the third embodiment. FIG. 14 is an explanatory diagram of the effect of reversing the polarity of the DC voltage. FIG. 15 is an explanatory diagram of changes in the toner charge amount when the polarity is switched. In Embodiment 3, the toner accumulated in the fur brush 138 is discharged to the intermediate transfer belt 9 by switching the polarity of the DC voltage applied to the fur brush 138.

  As shown in FIG. 12, the second belt cleaning device 116B disposed on the downstream side in the rotation direction of the intermediate transfer belt 9 is configured in the same manner as in the second embodiment, and includes the fur brush 118, the bias roller 119, and the cleaning blade 120. Including. Connected to the bias roller 119 are a DC power supply 131 and an AC power supply 132 that are controlled by the control unit 11 and can be switched in connection.

  The first belt cleaning device 116A disposed on the upstream side in the rotation direction of the intermediate transfer belt 9 includes a fur brush 138, a bias roller 139, and a cleaning blade 140. A DC power supply 133 that outputs a positive DC voltage and a DC power supply 134 that outputs a negative DC voltage are connected to the bias roller 139 via a switch. The control unit 11 controls this switch to switch the DC voltage applied to the bias roller 139 between positive polarity and negative polarity.

  In the first and second embodiments, during normal image formation, the belt cleaning device 116 collects only the transfer residual toner having the (−) polarity, and the transfer residual toner having the (+) polarity is the photosensitive drum. Re-transferred and recovered.

  In contrast, in the third embodiment, during normal image formation, the first belt cleaning device 116A and the second belt cleaning device 116B collect all the transfer residual toner and do not reach the photosensitive drum.

  During normal image formation, a positive polarity DC voltage (1500 V) is applied from the DC power supply 133 to the fur brush 138 of the first belt cleaning device 116A, and a current of 20 μA flows. As a result, the fur brush 138 sucks the transfer residual toner having the (−) polarity on the intermediate transfer belt 9.

  During normal image formation, a negative polarity DC voltage (−1500 V) is applied to the fur brush 118 of the second belt cleaning device 116 </ b> B from the DC power supply 131, and a current of −20 μA flows. As a result, the fur brush 118 adsorbs the transfer residual toner having the (+) polarity on the intermediate transfer belt 9.

  On the other hand, at the time of color misregistration correction control, a switch for switching the power applied to the fur brush 138 is operated under the control of the control unit 11. As a result, the output from the positive DC power supply 133 is switched to the output from the negative DC power supply 134, and the output voltage changes from positive to negative.

  At the time of normal image formation, a plus bias is applied to the fur brush 138 to selectively collect the transfer residual toner having a minus charge amount on the intermediate transfer belt 9. At the time of color misregistration correction control, a minus bias is applied to the fur brush 138, and the accumulated transfer residual toner having a minus charge amount is discharged from the fur brush 138 onto the intermediate transfer belt 9.

  As shown in FIG. 13, image formation is started (S32) after the main switch is turned on (S31). Thereafter, a temperature rise in the machine is detected from the environmental sensor in the machine, and whether or not color misregistration correction control is possible is determined (S33). If it is determined that color misregistration correction control is necessary (YES in S33), even when the image forming apparatus 100 is forming an image, the process proceeds to a down sequence, and the power source connected to the fur brush 138 is switched from the DC power source 133. Switching to the DC power supply 134 is performed (S34). Then, the power source connected to the fur brush 118 is switched from the DC power source 131 to the AC power source 132 (S35).

  After the power is switched in the first belt cleaning device 116A and the second belt cleaning device 116B, the color misregistration correction control is started (S36). Then, the correction value of the color misregistration amount is calculated (S37), and the correction value of each color is fed back to the exposure devices 3Y, 3M, and 3C (S38).

  Thereafter, the power source connected to the fur brush 138 of the first belt cleaning device 116A is switched again from the DC power source 134 to the DC power source 133 (S39). Then, the power source connected to the fur brush 118 of the second belt cleaning device 116B is switched from the AC power source 132 to the DC power source 131 (S40), and the color misregistration correction control ends (S41).

  FIG. 14 shows how the DC toner voltage is inverted by applying a DC voltage of +1500 V to the fur brush 138 and then the polarity of the DC voltage is reversed, and how the fog toner adhesion amount on the intermediate transfer belt 9 changes depending on the voltage. It is the result of having investigated. As shown in FIG. 14, as the switched DC voltage having the opposite polarity is increased, the amount of fog toner attached to the intermediate transfer belt 9 tends to increase, and tends to be saturated at −1000 V or more. Therefore, in Example 3, the DC voltage applied to the fur brush 138 at the time of color misregistration correction control was set to −1500V.

  The toner discharged from the first belt cleaning device 116A by reversing the polarity of the DC voltage moves to the second belt cleaning device 116B as the intermediate transfer belt 9 rotates. At this time, the control unit 11 switches the connection of the second belt cleaning device 116B to the fur brush 118 from the negative polarity DC power supply 131 to the AC power supply 132 that outputs a sine wave having a frequency of 1 kHz. As a result, the fur brush 118 loses its ability to collect transfer residual toner having a (+) polarity during normal image formation, and functions as a toner neutralizing device on the intermediate transfer belt 9.

  FIG. 14 shows the result of examining the fog toner adhesion amount on the intermediate transfer belt 9 after passing through the second belt cleaning device 116B by changing the peak-to-peak voltage Vpp of the AC voltage applied to the fur brush 118 by the AC power source 132. It is. As shown in FIG. 14, as the AC voltage peak-to-peak voltage Vpp increases, the amount of fog toner adhesion on the intermediate transfer belt 9 increases. However, if the AC voltage peak-to-peak voltage Vpp is 1500 V or higher, It was confirmed that the adhesion amount was saturated. This is because, as described in the second embodiment, by changing the voltage applied to the fur brush 118 from the DC voltage to the AC voltage, the charge amount of the toner stored in the fur brush 118 is converged to near zero.

  FIG. 15 shows the result of measuring the charge amount distribution of the toner collected on the intermediate transfer belt 9 before and after passing through the second cleaning device 116B, with the peak-to-peak voltage Vpp of the AC voltage set to 1500V. The charge amount distribution was measured using an E-spert EST3 manufactured by Hosokawa Micron. As shown in FIG. 15A, the average charge amount of the toner collected on the intermediate transfer belt 9 immediately after passing through the first belt cleaning device 116A was +15 μC / g. On the other hand, as shown in FIG. 15B, the average charge amount of the toner on the intermediate transfer belt 9 immediately after passing through the second belt cleaning device 116B is -1 μC / g, which is converged to almost zero. This is because when the charge amount is close to 0, the toner binding force in the fur brush 118 is weakened, and the toner is transferred onto the intermediate transfer belt 9 and reattached.

  In the third embodiment, the second fur brush (118) is disposed on the downstream side of the first fur brush (138) in the rotation direction of the intermediate transfer member. During image formation, a DC voltage is applied to the first fur brush (138), and a DC voltage having a polarity opposite to that of the first fur brush (138) is applied to the second fur brush (118). On the other hand, in the color misregistration control mode (alignment mode), the polarity of the DC voltage applied to the first fur brush (138) is reversed and the AC voltage is applied to the second fur brush (118).

  That is, at the time of color misregistration correction control, the polarity of the DC voltage applied to the first belt cleaning device 116A is reversed, and the toner accumulated in the fur brush 138 is reattached on the intermediate transfer belt 9. Further, the DC voltage is switched to the AC voltage by the second belt cleaning device 116B, and the toner reattached by the first belt cleaning device 116A is converged to a charge amount near 0 and stayed on the intermediate transfer belt 9.

  Even if the developing sleeve is controlled as shown in FIG. 5, the amount of fog toner for each portion of the intermediate transfer belt 9 at the time of color misregistration correction control is made uniform, so that the intermediate transfer belt 9 is moved to the primary transfer portion T1 and the secondary transfer. Unevenness of the friction load when passing through the portion T2 is reduced. As a result, the speed fluctuation of the intermediate transfer belt 9 is suppressed, the accuracy of color misregistration correction control is improved, and a high quality image with a small amount of color misregistration can be output.

<Comparison of Examples 1, 2, and 3>
FIG. 16 is an explanatory diagram for comparing torque fluctuations of the driving roller of the intermediate transfer belt in the first, second, and third embodiments. The frictional load unevenness when the intermediate transfer belt 9 passes through the primary transfer portions TY, TM, TC, TK and the secondary transfer portion T2 during the color misregistration correction control was measured as the torque fluctuation of the driving roller 20. The torque fluctuation was measured by monitoring the driving torque of a driving motor (not shown) connected to the driving roller 20 of the intermediate transfer belt 9 with a memory scope. At the time of color misregistration correction, the average value of the driving torque is measured when the developing sleeve 4a is stopped and when rotated, and (torque difference amount between stopped and rotated) / (torque during rotation) = torque variation ratio, The frictional load unevenness on the intermediate transfer belt 9 was quantified.

  As shown in FIG. 16, the smaller the unevenness of the friction load (torque fluctuation ratio), the smaller the color misregistration amount of the output image after the color misregistration correction control. The amount of color misregistration that allows the user to recognize color misregistration is approximately 150 μm. When the belt cleaning device 116 is operated in the same way as during image formation during color misregistration correction control (conventional example), the torque fluctuation ratio increases and the color misregistration amount is located in the NG region (outside the allowable range).

  On the other hand, in the first embodiment in which the rotational speed of the fur brush 118 is reduced to 10 rpm during the color misregistration correction control, the color misregistration amount is located in the OK region (within the allowable range) due to the decrease in the torque fluctuation ratio. .

  On the other hand, in the second embodiment in which the voltage applied to the fur brush 118 is switched from the DC voltage to the AC voltage during the color misregistration correction control, the color misregistration amount is further shifted to the OK region due to the decrease in the torque fluctuation ratio. .

  In contrast, in the third embodiment in which the polarity of the DC voltage applied to the fur brush 138 is switched during color misregistration correction control, and the voltage applied to the fur brush 118 is switched from the DC voltage to the AC voltage, the amount of color misregistration is increased. Furthermore, it has shifted to the OK region.

<Example 4>
FIG. 17 is an explanatory diagram of changes in the toner accumulation amount of the fur brush accompanying the accumulation of image formation. FIG. 18 is a flowchart of control according to the fourth embodiment.

  In the fourth exemplary embodiment, the supply toner image (toner band) is supplied to the fur brush 118 to temporarily accumulate the toner during color misregistration correction control until the amount of toner that can be discharged is accumulated on the fur brush 118. Let me.

  In the second and third embodiments, the toner accumulated in the fur brush 118 at the time of image formation is used to reattach the toner to the intermediate transfer belt 9. However, the amount of toner accumulated in the fur brush 118 varies depending on the cumulative number of images formed and the print image of the user.

  As shown in FIG. 17, when image formation is accumulated in the image forming apparatus 100, the weight of toner accumulated in the fur brush 118 increases as the accumulated number increases. The weight of the toner accumulated in the fur brush 118 was obtained by measuring the weight of the fur brush 118 at each accumulated number of times and subtracting the new product weight.

  At the initial stage of the cumulative number of sheets, the amount of toner accumulated in the fur brush 118 is small and tends to increase with the cumulative number of sheets. Therefore, if the cumulative number is 5000 or more, the toner in the fur brush 118 can be discharged to the intermediate transfer belt 118 by applying the control of Embodiments 1 to 3, but if it is 5000 or less, the toner in the fur brush 118 is discharged. The toner amount is insufficient and cannot be discharged sufficiently. For this reason, it is not possible to sufficiently obtain the effect of leveling the friction load unevenness and suppressing the speed fluctuation.

  Therefore, in Example 4, when the durable number is 5000 sheets, a replenishing toner image (hereinafter referred to as a toner band) is supplied to the fur brush 118 at the time of color misregistration correction control. The toner band is formed in parallel by the image forming portions PY, PM, PC, and PK, and is primarily transferred to the intermediate transfer belt 9. The power source D2 applies a DC voltage (which may be −several hundred volts) having a polarity opposite to that at the time of image formation to the secondary transfer portion T2 so that the toner band is not transferred to the secondary transfer roller 23.

  In the belt cleaning device 116, a positive polarity DC voltage (+1500 V) is applied to the fur brush 118 to wait for the toner band. The toner band that has passed through the secondary transfer portion T2 is attracted and accumulated on the fur brush 118 of the belt cleaning device 116.

  As shown in FIG. 18, the control unit 11 stores the time when the user turns on the main power supply (S51). When image formation starts (S52), the control unit 11 estimates the thermal expansion amount of the intermediate transfer belt 9 from the value of an in-machine thermometer (not shown) and the operating time of the machine, and determines whether or not color misregistration correction control is necessary. (S53). When it is determined that the color misregistration correction control is necessary (YES in S53), the control unit 11 reads the accumulated number of fur brushes 118 from the RAM (31: FIG. 3) storing the counted number (S54). ). Then, it is determined whether or not the band toner needs to be formed before the color misregistration correction control (S55).

When it is necessary to form a belt toner on less than 5000 sheets (YES in S55), a toner band having a width of 300 mm, a length of 10 mm, and a toner applied amount of 0.30 mg / cm ^{2 at} the image forming portions PY, PM, PC, and PK, respectively. Is formed (S56), and is primarily transferred to the intermediate transfer belt 9.

  About 10 seconds after the toner band passes through the secondary transfer portion T2 and is supplied to the belt cleaning device 116, the voltage applied to the fur brush 118 is switched from a DC voltage to an AC voltage to start color misregistration correction control. (S57).

  At each stage of the cumulative number of sheets, color misregistration correction control is executed depending on whether the toner band is supplied to the belt cleaning device 116 or not, and whether or not color misregistration occurs in the output image immediately after the color misregistration correction control. evaluated.

  As shown in Table 1, it was found that when the color misregistration correction control is executed without supplying the toner band until the cumulative number reaches 5000, a color misregistration image is output. It can be seen that the level of color misregistration is improved by supplying the belt toner in the initial use of the fur brush 118.

  In the color misregistration correction control (positioning mode) according to the fourth exemplary embodiment, when the cumulative usage amount of the brush member (118) is less than a predetermined level, the toner band (replenishment toner image) is supplied to the brush member (118). To do. Before the toner accumulated in the brush member (118) is discharged to the intermediate transfer member (9), a replenishment toner image is formed on the photosensitive member (1Y) and transferred to the intermediate transfer member (9) to be transferred to the secondary transfer portion. Let T2 pass. Thereby, even when the fur brush 118 is in a new state, the speed fluctuation of the intermediate transfer belt 9 can be suppressed and the color misregistration correction control can be executed precisely.

<Example 5>
FIG. 19 is an explanatory diagram of a configuration of the image forming apparatus according to the fifth embodiment.

  As shown in FIG. 19, the color misregistration correction control of the first to fourth embodiments can be performed also in the image forming apparatus 200 using the recording material conveyance belt 9H. The image forming apparatus 200 is a recording material conveyance type full color printer in which image forming portions PY, PM, PC, and PK of yellow, magenta, cyan, and black are arranged along the recording material conveyance belt 9H. In FIG. 19, the same components as those described in the first embodiment are denoted by the same reference numerals as those in FIG.

  In the image forming apparatus 200 according to the fifth exemplary embodiment, the image forming unit (PY) transfers the toner image formed on the photoconductor (1Y) to the recording material carried on the recording material conveyance body (9H) by the transfer unit. The detection means (S1, S2) detects the toner image of the position index formed by the image forming unit and transferred to the recording material conveyance body by the transfer unit. The electrostatic cleaning device (116) contacts the brush member to which a voltage is applied, and collects the toner adhering to the recording material conveyance body.

  The control unit 11 executes the alignment mode during non-image formation, detects the toner image of the position index transferred to the recording material conveyance body, and adjusts the formation position of the toner image on the photoconductor. In the alignment mode, the electrostatic cleaning device is controlled so that the toner adhering to the recording material conveyance body is increased.

  Thereby, the toner adhesion amount for each portion of the recording material conveyance belt 9H at the time of color misregistration correction control is leveled, so that speed fluctuation is suppressed and the accuracy of color misregistration correction control is increased.

<Example 6>
In the first embodiment, the embodiment has been described in which the color misregistration correction control images P1 and P2 are formed in parallel by the two image forming portions PY and PM at a time, and transferred to the intermediate transfer belt 9 in parallel.

  On the other hand, in Example 6, one color misregistration correction control image P1 is a fixed pattern formed in advance on the belt member by printing or the like. For the four image forming units PY, PM, PC, and PK, color misregistration correction control similar to that in the first embodiment is performed in order. The color misregistration correction control image P <b> 2 is formed by one image forming unit and transferred to the interval of the color misregistration correction control image P <b> 1 fixed to the intermediate transfer belt 9. By repeating such an operation four times, the four image forming portions PY, PM, PC, and PK are individually positioned with respect to the intermediate transfer belt 9.

  Prior to the color misregistration correction control, toner is discharged from the belt cleaning device 116 to the intermediate transfer belt 9, and after the discharged toner has passed through the secondary transfer portion T2, a color misregistration correction control image P2 is formed.

1Y, 1M, 1C, 1K photoconductor (photosensitive drum)
2Y, 2M, 2C, 2K Charging member (charging roller)
3Y, 3M, 3C, 3K Exposure devices 4Y, 4M, 4C, 4K Developing devices 5Y, 5M, 5C, 5K Primary transfer roller 9 Intermediate transfer belt, 11 Control unit, 21 Opposing roller, 23 Secondary transfer roller 115 Backup roller, 116 Belt cleaning device 117 Device housing, 118 Fur brush, 119 Bias roller 131 DC power source, 132 AC power source P1, P2 Color misregistration correction control images S1, S2 Color misregistration sensor

Claims (7)

The intermediate transfer member, the image forming portion for transferring the toner image formed on the photosensitive member to the intermediate transfer member at the primary transfer portion, and the intermediate transfer portion for forming the secondary transfer portion for transferring the toner image onto the recording material. A transfer member that contacts the transfer member, a detection unit that detects a toner image of a position index formed by the image forming unit and transferred to the intermediate transfer member by the primary transfer unit, and a brush member to which a voltage is applied In an image forming apparatus comprising: an electrostatic cleaning device that contacts and collects transfer residual toner of the intermediate transfer member;
The non-image formation includes a registration mode in which a toner image of the position index transferred to the intermediate transfer member is detected by the detection unit, and a toner image formation position on the photosensitive member is adjusted. In the mode, the electrostatic cleaning device is controlled so that the toner that adheres to the intermediate transfer member and rotates increases.   In the alignment mode, after the toner discharged from the brush member to the intermediate transfer member arrives at the secondary transfer unit, the toner image of the position index is transferred to the intermediate transfer member at the primary transfer unit. The image forming apparatus according to claim 1, wherein:   The toner image of the position index is formed in the image forming unit after the toner discharged from the brush member to the intermediate transfer member has arrived at the secondary transfer unit in the alignment mode. 2. The image forming apparatus according to 2.   4. The image formation according to claim 1, wherein in the alignment mode, the toner accumulated in the brush member is discharged to the intermediate transfer member by applying an AC voltage to the brush member. 5. apparatus. The brush member is disposed on the downstream side of the first fur brush to which a DC voltage is applied during image formation and the first fur brush in the rotation direction of the intermediate transfer member, and the first fur brush is formed during image formation. A second fur brush to which a DC voltage having a polarity opposite to that of the brush is applied,
5. The image forming apparatus according to claim 4, wherein in the alignment mode, the polarity of a DC voltage applied to the first fur brush is reversed and an AC voltage is applied to the second fur brush.   If the cumulative amount of use of the brush member is less than a predetermined level, a replenishment toner image is formed on the photosensitive member before the toner accumulated on the brush member is discharged to the intermediate transfer member. The image forming apparatus according to claim 1, wherein the brush member is replenished with the replenishing toner image that has been transferred to a body and passed through the secondary transfer portion. A recording material conveying member; an image forming portion for transferring a toner image formed on the photosensitive member to a recording material carried on the recording material conveying member by a transfer portion; and the recording portion formed by the image forming portion and the recording portion A detecting unit that detects a toner image of a position index transferred to the material conveying member, and an electrostatic cleaning device that recovers toner adhering to the recording material conveying member by contacting a brush member to which a voltage is applied. In the image forming apparatus,
A position adjustment mode for adjusting a toner image formation position on the photosensitive member by detecting the toner image of the position index transferred to the recording material conveyance body by the detection unit during non-image formation; In the alignment mode, the electrostatic cleaning device is controlled so that the toner adhering to the recording material conveyance body is increased.

Images