JP5273579B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of favorably suppressing both overlapping misalignment of each color toner image on an intermediate transfer belt 8 resulting from a change in latent image write-in position and overlapping misalignment of each color toner image resulting from a change in speed of the intermediate transfer belt 8. <P>SOLUTION: The image forming device includes: a drive roller 12 which is rotatably driven; an intermediate transfer belt 8 stretched by a driven roller which can be driven and rotated; and an optical sensor unit 150 which detects a predetermined pattern image formed on the surface of the intermediate transfer belt 8. The device overlaps and transfers Y, C, M and K toner images formed on photoreceptors for Y, C, M and K (not shown), respectively, onto the surface of the intermediate transfer belt 8. The optical sensor unit 150 is arranged so as to face a region of a winding and rotating position for an encoder roller 14 as the driven roller, of an entire peripheral region of the intermediate transfer belt 8, and an encoder for detecting a rotating speed of the encoder roller 14 is provided. <P>COPYRIGHT: (C)2013,JPO&amp;INPIT

Description

  The present invention relates to a transfer device that transfers a visible image carried on each of a plurality of image carriers in an overlapping manner on an endless belt member that moves endlessly or on a recording member held on the surface of the belt member. Is. The present invention also relates to an image forming apparatus that forms an image using such a transfer apparatus.

  Conventionally, as this type of image forming apparatus, the one described in Patent Document 1 is known. This image forming apparatus has a transfer unit that moves an endless paper conveying belt as a belt member endlessly while being stretched by a driving roller and a plurality of driven rollers. Then, toner images of different colors respectively formed on a plurality of photoconductors as image carriers are transferred onto the recording paper on the paper conveying belt by the transfer unit described above to obtain a full color image. Instead of directly superimposing and transferring each color toner image carried on each of the plurality of photoconductors on a recording paper as a recording member, the toner images are superposed on the surface of an intermediate transfer belt as a belt member and are primarily transferred to the recording paper. One that performs batch secondary transfer is also known. As described above, the method of transferring the toner images formed on the plurality of image carriers in a superimposed manner on the surface of the belt member or the recording paper on the belt member is called a tandem method.

  In a tandem image forming apparatus, if an optical system component such as a lens or a mirror of a latent image writing device slightly changes the optical path with a temperature change, the latent image writing device uses a latent image writing device between each image carrier. The image writing start position is relatively shifted. Then, the toner images of the respective colors are transferred while being superimposed on the belt member or the recording paper in a state where they are displaced from each other, so that a so-called overlay shift occurs and the image of the full color image is disturbed.

  Therefore, the image forming apparatus described in Patent Document 1 periodically measures the relative positional deviation amount of each color toner image, and adjusts the latent image writing start timing and the tilt of the optical system parts as necessary. Thus, the positional deviation of each color toner image is corrected. Specifically, a predetermined toner image formed on each of the plurality of image carriers is transferred to the belt member while shifting the positions thereof, thereby obtaining a positional deviation detection pattern image on the belt member. Then, based on the timing at which each color toner image in the positional deviation detection pattern image is detected by an optical sensor as an image detecting means, the relative positional deviation of each color toner image is detected. Next, the latent image writing start timing for each image carrier is adjusted based on the detection result, and the inclination of the lens and mirror is adjusted, so that the relative toner images between the image carriers are relative to each other. Reduce misalignment.

  However, as a factor causing the misalignment of the toner images of the respective colors, the speed fluctuation of the belt member can be cited in addition to the fluctuation of the latent image writing position with respect to the image carrier. If the belt member speed fluctuates during superimposing transfer, even if the relative positions of the toner images are matched between the image carriers, the toner images of the respective colors are transferred out of alignment with each other. . Factors that cause the speed fluctuation of the belt member include uneven thickness in the circumferential direction of the belt member, eccentricity of a driving roller that drives the belt member, and the like.

  The occurrence of the registration error of each color toner image due to the speed fluctuation of the belt member cannot be suppressed by adjusting the latent image writing start timing and adjusting the tilt of the optical system components as described above. Specifically, the positional deviation of each color toner image due to the above-described change in the latent image writing position is such that the position of the entire image is shifted between the colors, and the relative positions of the dots in the image are almost the same for each color. does not change. For this reason, by adjusting the latent image writing start timing or adjusting the tilt of the optical system parts, it is possible to suppress the positional deviation of each dot together with the entire image between the respective colors. On the other hand, in the positional deviation caused by the speed fluctuation of the belt member, the relative positional relationship between the dots in the image changes between the colors. For this reason, even if the latent image writing start timing and the tilt of the mirror are adjusted, the positional deviation cannot be suppressed.

  Further, if the belt member speed fluctuation occurs while the above-described misregistration detection pattern image is detected by the optical sensor, the misregistration pattern of each color toner image in the misregistration detection pattern image cannot be detected correctly. . For this reason, when the belt member speed fluctuation occurs, not only the overlay deviation due to the speed fluctuation occurs but also the positional deviation of each color toner image due to the fluctuation of the latent image writing position is suppressed satisfactorily. I can't do that either.

  Up to now, the problem that occurs in the tandem image forming apparatus has been described. However, the same problem may occur in the following image forming apparatus. That is, the image forming apparatus employs a system in which the visible image on the image bearing member is superimposed and transferred onto the belt member or the recording member on the belt member while moving the belt member over a plurality of turns.

  The present invention has been made in view of the above background, and an object thereof is to provide the following transfer device and an image forming apparatus using the same. That is, with a transfer device or the like that can satisfactorily suppress both the overlay deviation of the visible image due to the fluctuation in the latent image writing position and the overlay deviation of the visible image due to the speed fluctuation of the belt member. is there.

In order to achieve the above object, the invention of claim 1 is directed to an image carrier that carries a visible image, a visible image forming means that forms a visible image on the image carrier, and a carrier that is carried on the image carrier. And a transfer unit that transfers the visible image onto an endless belt member that is moved endlessly as the drive roller rotates, or a recording member that is held on the front surface of the belt member. together, the drive roller that is driven to rotate, and an endless belt member that is stretched by the driven rotatable driven roller, covering the front surface of the belt member in almost all regions in the width direction of the belt member A covering member that is arranged in such a manner that a visible image on the front surface of the belt member can be detected by an optical sensor that is an image detecting means through an opening provided on itself or a window made of a light transmitting member. When, for detecting the rotational speed of the driven roller A rolling speed detecting means an image forming apparatus for chromatic in the transfer unit, the opening or the window of the covering member, of the entire area in the circumferential direction of the belt member, the over-turning position with respect to the driven roller The optical sensor is fixed to the image forming apparatus main body, and includes the belt member, the covering member, and the rotation speed detecting means. The transfer unit is detachable from the main body of the image forming apparatus without the optical sensor .
The invention of claim 2 is the feature in the image forming apparatus according to claim 1, as the cover member, that the opening or the window used was disposed side by side a plurality in the direction of the rotation axis of the driven roller To do .
Also, the invention of claim 3, the image forming apparatus according to claim 1 or 2, a plurality provision of the image carrier, the belt member or the belt member a visible image to be respectively supported on their image carrier The transfer device is configured to transfer the image on the upper recording member in a superimposed manner.
According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the third aspect , wherein each of the plurality of image carriers is composed of a plurality of visible images having different image densities formed on the surface of the image carrier. The pattern image is transferred to the belt member, the image density of each visible image in the gradation pattern image on the belt member is detected by the optical sensor, and the visible image forming means is configured based on the detection result. An image forming condition adjusting unit for adjusting an image condition and a driving speed adjusting unit for adjusting a driving speed of a driving source of the driving roller based on a detection result by the rotation speed detecting unit are provided. is there.
According to a fifth aspect of the present invention, in the image forming apparatus according to the third aspect , the predetermined visible images respectively formed on the plurality of image carriers are transferred to the belt member so as not to overlap each other, and the belt Based on the result of detecting the visible images on the member by the optical sensor , the relative position shift of the visible images is grasped, and the image forming condition of the visible image forming means is adjusted based on the result. The image forming condition adjusting means and drive speed adjusting means for adjusting the drive speed of the drive source of the drive roller based on the detection result by the rotation speed detecting means are provided.
The invention according to claim 6 is the image forming apparatus according to any one of claims 1 to 5, wherein the optical sensor faces the front surface of the belt member from below. It is a thing fixed to the main body, It is characterized by the above-mentioned.

  In these inventions, it is possible to detect the speed fluctuation of the belt member based on the rotational speed of the driven roller. And based on this detection result, the speed fluctuation of a belt member can be suppressed by adjusting the driving speed of a driving roller with the pattern which cancels the speed fluctuation of a belt member with the fluctuation | variation of the rotational speed of a driving roller. If the speed fluctuation of the belt member is suppressed in this way, each visible image in the position deviation detection pattern image transferred onto the belt member does not include the position deviation due to the speed fluctuation of the belt member. Therefore, it is possible to cause the image detection means to detect only the positional deviation of the visible image due to the change in the latent image writing position. In addition, since the belt member is stabilized in the moving speed by stabilizing the rotational speed of the driven roller at the position facing the image detecting means for detecting the visible image, the belt member is out of the entire circumferential region of the belt member. The belt moving speed in the area at the position facing the image detecting means is most stabilized. Accordingly, the position detection pattern image on the belt member is moved at a stable speed at a position facing the image detection means, and the position shift of the visible image caused by the fluctuation of the latent image writing position is transferred to the image detection means. It can be detected accurately. As a result of the above, it is possible to satisfactorily suppress both the overlay deviation of the visible image due to the fluctuation in the latent image writing position and the overlay deviation of the visible image due to the speed fluctuation of the belt member.

1 is a schematic configuration diagram showing a printer according to a reference form. FIG. 3 is an enlarged configuration diagram showing a process unit for Y of the printer and its surroundings. FIG. 2 is a block diagram showing a part of an electric circuit in the printer. FIG. 3 is a perspective view showing a gradation pattern image formed on an intermediate transfer belt of the printer. The graph which plotted the relationship between the electric potential of the photoconductor of the printer, and the toner adhesion amount on the xy coordinates. FIG. 3 is a perspective view showing a patch pattern formed on the intermediate transfer belt. 6 is a timing chart showing generation timings of various signals when optical writing start timing in the sub-scanning direction is corrected. 4 is a timing chart showing the generation timing of a latent image writing clock when the optical writing start timing in the sub-scanning direction is corrected. FIG. 3 is an enlarged configuration diagram illustrating an encoder roller disposed in a loop of the intermediate transfer belt together with an encoder disposed on one end side thereof. The expansion perspective view which shows the code wheel of the encoder with a transmission type photosensor. The graph which shows the output voltage characteristic from the transmission type photosensor. FIG. 3 is a partially enlarged perspective view showing one end of the transfer unit of the printer in the belt moving direction together with the optical sensor unit. FIG. 4 is a partially enlarged perspective view showing one end of the transfer unit in the belt width direction in the printer according to the embodiment .

Hereinafter, as an image forming apparatus to which the present invention is applied , before describing an embodiment of an electrophotographic printer (hereinafter simply referred to as a printer), a printer according to a reference embodiment that is helpful in understanding the present invention will be described. Explain .
First, the basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram showing the printer. In this figure, this printer includes four process units 6Y, 6M, 6C, and 6K for generating toner images of yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K). Yes. These use Y, M, C, and K toners of different colors as the image forming material, but the other configurations are the same and are replaced when the lifetime is reached. Taking a process unit 6Y for generating a Y toner image as an example, as shown in FIG. 2, a drum-shaped photosensitive member 1Y as a latent image carrier, a drum cleaning device 2Y, a charge eliminating device (not shown), and a charging device 4Y. And a developing unit 5Y. The process unit 6Y, which is an image forming unit, can be attached to and detached from the printer body, so that consumable parts can be replaced at a time.

  The charging device 4Y uniformly charges the surface of the photoreceptor 1Y as an image carrier that is rotated clockwise in the drawing by a driving unit (not shown). The uniformly charged surface of the photoreceptor 1 </ b> Y is exposed and scanned by the laser beam L to carry a Y electrostatic latent image. The electrostatic latent image of Y is developed into a Y toner image by a developing device 5Y using a Y developer containing Y toner and a magnetic carrier. Then, intermediate transfer is performed on an intermediate transfer belt 8 described later. The drum cleaning device 2Y removes the toner remaining on the surface of the photoreceptor 1Y after the intermediate transfer process. The static eliminator neutralizes residual charges on the photoreceptor 1Y after cleaning. By this charge removal, the surface of the photoreceptor 1Y is initialized and prepared for the next image formation. Similarly, in the other color process units (6M, C, K), an (M, C, K) toner image is formed on the photoreceptor (1M, C, K), and an intermediate transfer belt as a belt member is formed. 8 is intermediately transferred.

  The developing device 5Y has a developing roll 51Y disposed so as to be partially exposed from the opening of the casing. Further, it also includes two conveying screws 55Y, a doctor blade 52Y, a toner density sensor (hereinafter referred to as T sensor) 56Y, and the like that are arranged in parallel to each other.

  In the casing of the developing device 5Y, a Y developer (not shown) including a magnetic carrier and Y toner is accommodated. The Y developer is frictionally charged while being agitated and conveyed by the two conveying screws 55Y, and is then carried on the surface of the developing roll 51Y. Then, after the layer thickness is regulated by the doctor blade 52Y, the layer is transported to the developing region facing the Y photoreceptor 1Y, where Y toner is attached to the electrostatic latent image on the photoreceptor 1Y. This adhesion forms a Y toner image on the photoreceptor 1Y. In the developing unit 5Y, the Y developer that has consumed Y toner by the development is returned into the casing as the developing roll 51Y rotates.

  A partition wall is provided between the two transport screws 55Y. By this partition wall, the first supply unit 53Y that accommodates the developing roll 51Y, the right conveyance screw 55Y in the drawing, and the like, and the second supply unit 54Y that accommodates the left conveyance screw 55Y in the drawing are separated in the casing. . The right conveying screw 55Y in the drawing is driven to rotate by a driving means (not shown), and supplies the Y developer in the first supply unit 53Y to the developing roll 51Y while being conveyed from the near side to the far side in the drawing. The Y developer conveyed to the vicinity of the end of the first supply unit 53Y by the right conveyance screw 55Y in the drawing enters the second supply unit 54Y through an opening (not shown) provided in the partition wall. In the second supply unit 54Y, the left conveyance screw 55Y in the drawing is driven to rotate by a driving means (not shown), and the Y developer sent from the first supply unit 53Y is the right conveyance screw 55Y in the drawing. Transport in the reverse direction. The Y developer transported to the vicinity of the end of the second supply unit 54Y by the transport screw 55Y on the left side in the drawing passes through the other opening (not shown) provided in the partition wall, and the first supply unit. Return to 53Y.

  The above-described T sensor 56Y composed of a magnetic permeability sensor is provided on the bottom wall of the second supply unit 54Y and outputs a voltage having a value corresponding to the magnetic permeability of the Y developer passing therethrough. Since the magnetic permeability of the two-component developer containing toner and magnetic carrier shows a good correlation with the toner concentration, the T sensor 56Y outputs a voltage corresponding to the Y toner concentration. This output voltage value is sent to a control unit (not shown). This control unit includes a RAM that stores a Vtref for Y that is a target value of an output voltage from the T sensor 56Y. The RAM also stores M Vtref, C Vtref, and K Vtref data, which are target values of output voltages from a T sensor (not shown) mounted in another developing device. The Y Vtref is used for driving control of a Y toner conveying device to be described later. Specifically, the control unit drives and controls a Y toner conveying device (not shown) so that the value of the output voltage from the T sensor 56Y is close to the Y Vtref, and the Y toner in the second supply unit 54Y. To replenish. By this replenishment, the Y toner concentration in the Y developer in the developing device 5Y is maintained within a predetermined range. The same toner replenishment control using the M, C, and K toner conveying devices is performed for the developing units of the other process units.

  In FIG. 1 described above, an optical writing unit 7 as a latent image writing device is disposed below the process units 6Y, 6M, 6C, and 6K in the drawing. The optical writing unit 7 irradiates the respective photosensitive members in the process units 6Y, 6M, 6C, and 6K with the laser light L emitted based on the image information and exposes it. By this exposure, electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 1Y, 1M, 1C, and 1K. The optical writing unit 7 irradiates the photosensitive member through a plurality of optical lenses and mirrors while scanning laser light (L) emitted from a light source with a polygon mirror rotated by a motor.

  On the lower side of the optical writing unit 7 in the figure, a paper storage means having a paper storage cassette 26, a paper feed roller 27 incorporated therein, and the like is disposed. The paper storage cassette 26 stores a plurality of transfer papers P, which are sheet-like recording bodies, and a paper feed roller 27 is brought into contact with each uppermost transfer paper P. When the paper feeding roller 27 is rotated counterclockwise in the drawing by a driving means (not shown), the uppermost transfer paper P is sent out toward the paper feeding path 70.

  A registration roller pair 28 is disposed near the end of the paper feed path 70. The registration roller pair 28 rotates both rollers so as to sandwich the transfer paper P, but temporarily stops rotating immediately after sandwiching. Then, the transfer paper P is sent out toward a later-described secondary transfer nip at an appropriate timing.

  Above the process units 6Y, 6M, 6C, and 6K, a transfer unit 15 that moves the endless intermediate transfer belt 8 as an endless moving body while stretching is disposed. The transfer unit 15, which is a transfer unit and an endless moving body unit, includes a secondary transfer bias roller 19 and a cleaning device 10 in addition to the intermediate transfer belt 8. Also provided are four primary transfer bias rollers 9Y, 9M, 9C, 9K, a driving roller 12, a cleaning backup roller 13, an encoder roller 14, and the like. The intermediate transfer belt 8 has a multilayer structure, and the base layer is made of, for example, a fluororesin, PVDF sheet, polyimide resin, or the like that has little elongation. On this base layer, a surface layer made of a material having excellent toner releasability such as a fluorine resin is coated. The intermediate transfer belt 8 having such a configuration is endlessly moved counterclockwise in the figure by the rotational driving of the driving roller 12 while being stretched by a plurality of rollers.

  The primary transfer bias rollers 9Y, M, C, and K sandwich the intermediate transfer belt 8 moved endlessly in this manner from the photoreceptors 1Y, M, C, and K to form primary transfer nips, respectively. Yes. In these methods, a transfer bias having a polarity opposite to that of toner (for example, plus) is applied to the back surface (loop inner peripheral surface) of the intermediate transfer belt 8. All of the rollers except the primary transfer bias rollers 9Y, 9M, 9C, and 9K are electrically grounded. The intermediate transfer belt 8 sequentially passes through the primary transfer nips for Y, M, C, and K along with the endless movement thereof, and Y, M, and C on the photoreceptors 1Y, M, C, and K are sequentially transferred. , K toner images are superimposed and primarily transferred. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 8.

  The drive roller 12 sandwiches the intermediate transfer belt 8 between the secondary transfer roller 19 and forms a secondary transfer nip. The visible four-color toner image formed on the intermediate transfer belt 8 is transferred to the transfer paper P at the secondary transfer nip. Then, combined with the white color of the transfer paper P, a full color toner image is obtained. Untransferred toner that has not been transferred onto the transfer paper P adheres to the intermediate transfer belt 8 after passing through the secondary transfer nip. This is cleaned by the cleaning device 10. The transfer paper P on which the four-color toner images are collectively transferred at the secondary transfer nip is sent to the fixing device 20 via the post-transfer conveyance path 71.

  The fixing device 20 forms a fixing nip by a fixing roller 20a having a heat source such as a halogen lamp inside, and a pressure roller 20b that rotates while contacting the roller with a predetermined pressure. The transfer paper P fed into the fixing device 20 is sandwiched between the fixing nips so that the unfixed toner image carrying surface is in close contact with the fixing roller 20a. Then, the toner in the toner image is softened by the influence of heating and pressurization, and the full color image is fixed.

  The transfer sheet P on which the full-color image is fixed in the fixing device 20 exits the fixing device 20 and then reaches a branch point between the paper discharge path 72 and the pre-reversal conveyance path 73. At this branch point, a first switching claw 75 is swingably disposed, and the path of the transfer paper P is switched by the swing. Specifically, by moving the tip of the claw in the direction approaching the pre-reverse feed path 73, the path of the transfer paper P is changed to the direction toward the paper discharge path 72. Further, by moving the tip of the claw in a direction away from the pre-reversal conveyance path 73, the path of the transfer paper P is changed to the direction toward the pre-reversal conveyance path 73.

  When the path to the paper discharge path 72 is selected by the first switching claw 75, the transfer paper P is disposed outside the apparatus after passing through the paper discharge roller pair 100 from the paper discharge path 72. Are stacked on a stack 50a provided on the upper surface of the printer housing. On the other hand, when the path toward the conveyance path 73 before reversal is selected by the first switching claw 75, the transfer paper P enters the nip of the reversing roller pair 21 via the conveyance path 73 before reversal. The reversing roller pair 21 conveys the transfer paper P sandwiched between the rollers toward the stack portion 50a, but reversely rotates the rollers immediately before the rear end of the transfer paper P enters the nip. Due to this reverse rotation, the transfer paper P is transported in the opposite direction, and the rear end side of the transfer paper P enters the reverse transport path 74.

  The reverse conveyance path 74 has a shape extending while curving from the upper side to the lower side in the vertical direction, and the first reverse conveyance roller pair 22, the second reverse conveyance roller pair 23, and the third reverse conveyance in the path. A roller pair 24 is provided. The transfer paper P is transported while sequentially passing through the nips of these roller pairs, so that the upper and lower sides thereof are reversed. After the transfer paper P is turned upside down, it is returned to the paper feed path 70 and then reaches the secondary transfer nip again. Then, this time, the image transfer surface enters the secondary transfer nip while bringing the non-image carrying surface into close contact with the intermediate transfer belt 8, and the second four-color toner image of the intermediate transfer belt is collectively transferred to the non-image carrying surface. The Thereafter, the sheet is stacked on the stack unit 50a outside the apparatus via the post-transfer conveyance path 71, the fixing device 20, the paper discharge path 72, and the paper discharge roller pair 100. A full color image is formed on both sides of the transfer paper P by such reverse conveyance.

  A bottle support portion 31 is disposed between the transfer unit 15 and the stack portion 50a located above the transfer unit 15. The bottle support portion 31 has toner bottles 32Y, 32M, 32C, 32K serving as toner storage portions for storing Y, M, C, and K toners. The toner bottles 32Y, 32M, 32C, and 32K are arranged so as to be arranged at an angle slightly inclined from the horizontal, and the arrangement positions are higher in the order of Y, M, C, and K. The Y, M, C, and K toners in the toner bottles 32Y, 32M, 32C, and 32K are appropriately replenished to the developing units of the process units 6Y, 6M, 6C, and 6K, respectively, by a toner conveyance device described later. These toner bottles 32Y, 32M, 32C, and 32K are detachable from the printer body independently of the process units 6Y, 6M, 6C, and 6K.

  FIG. 3 is a block diagram showing a part of an electric circuit in the printer. In the figure, a control unit 200 that is a calculation means includes a CPU 201, a ROM 202 that stores a control program and various data, and a RAM 203 that temporarily stores various data. The control unit 200 includes an optical writing unit 7, T sensors 56 Y, M, C, and K via an I / O interface 204 for transmitting and receiving signals to and from each peripheral control unit. 7 is connected to an optical writing control circuit 205, a power supply circuit 206, a toner replenishing circuit 207, and the like. In addition, a rotary encoder (hereinafter simply referred to as an encoder) 170, a belt drive motor 162 serving as a drive source for a drive roller (12) for driving the intermediate transfer belt (8), a temperature sensor 163 for detecting the temperature inside the apparatus, and the like are also connected. Has been. Furthermore, the optical sensor unit 150 includes a first end photosensor 151, a center photosensor 152, a second end photosensor 153, a Y photosensor 154Y, an M photosensor 154M, a C photosensor 154C, a K photosensor 154K, and the like. Is also connected. Each of these photosensors is a reflection type photosensor that reflects light emitted from a light emitting means (not shown) on a surface to be examined and detects the reflected light by a light receiving means (not shown).

  The optical writing control circuit 205 controls the optical writing unit 7 based on a command input from the control unit 200 via the I / O interface 204. Further, the power supply circuit 206 applies a high voltage to the charging device of each process unit based on a command input from the control unit 200 via the I / O interface 204, and develops a developing bias to each developing roller of each developing device. Apply.

  The toner replenishing circuit 207 controls a toner conveying device (not shown) for each color based on a command input from the control unit 200 via the I / O interface 204. As a result, toner supply from the toner bottles (32Y, M, C, K in FIG. 1) (not shown) to the two-component developer in each developing device is controlled.

  Based on the output values of the T sensors 56Y, M, C, and K for each color, the control unit 200 issues a command to set the toner concentration of the two-component developer in the developing device to a reference level via the I / O interface 204. Output to the toner supply circuit 207.

  This printer has an image forming condition for adjusting the image forming condition of an image forming apparatus as a visible image forming unit comprising an optical writing unit (7) and process units (6Y, M, C, K) of respective colors. The adjustment process is performed at a predetermined timing such as every predetermined time. In this image forming condition adjustment process, a process control process and a positional deviation correction process which will be described later are performed. In these processes, the optical writing control circuit 205 controls the optical writing unit 7 or the like based on a command input from the control unit 200 via the I / O interface 204, or the control unit 200 performs each process. Control the drive of the unit and transfer unit. As a result, a gradation pattern image for image formation performance detection and a patch pattern made up of a plurality of toner images are formed on the intermediate transfer belt 8.

  More specifically, in the process control process in the image forming condition adjustment process, a gradation pattern image for image forming performance detection is formed on the intermediate transfer belt 8. As the gradation pattern images for detecting the imaging performance, four gradation pattern images of Y, M, C, and K are formed. Each gradation pattern image is composed of 14 Y, M, C, and K reference toner images each having a predetermined pixel pattern. Each of the 14 Y, M, C, and K reference toner images is formed to have a different toner adhesion amount.

  For example, taking a K gradation pattern image SK as an example, this is referred to as Y reference toner images SK1, SK2,... SK13, SK14 in which the toner adhesion amount gradually increases as shown in FIG. It consists of 14 K reference toner images. These K reference toner images are formed on the front surface of the belt so as to be arranged at a predetermined interval in the traveling direction of the intermediate transfer belt 8, and the toner adhesion amount per unit area with respect to these K reference toner images is determined by an optical sensor. Detected by the K photo sensor 154K of the unit 150. This detection result is sent to the RAM 203 via the I / O interface 204 as an output value Vpi (i = 1 to 14).

  In the optical sensor unit 150, the photosensors (153, 154K, C, 152, 154M, Y, 151) are arranged in a straight line in the belt width direction (the rotation axis direction of the roller). The K reference toner image described above is formed at the same position as the installation position of the K photo sensor 154K in the belt width direction of the front surface of the intermediate transfer belt 8, and is thus detected by the K photo sensor 154K. Similarly to K, for Y, M, and C, the 14 Y, M, and C reference toner images are the same as the installation positions of the Y, M, and C photosensors 154Y, M, and C in the belt width direction. And detected by the Y, M, C photosensors 154Y, M, C. Then, output values Vp 1 to 14 of Y, M, and C photosensors 154 Y, M, and C, which are detection results of the toner adhesion amounts with respect to the Y, M, and C reference toner images, are stored in the RAM 203.

  Based on these output values stored in the RAM 203 and the data table stored in the ROM 202, the control unit 200 converts each output value into a toner adhesion amount per unit area, as toner adhesion amount data. Stored in the RAM 203.

FIG. 5 is a graph in which the relationship between the potential of the photoreceptor and the toner adhesion amount is plotted on the xy coordinates. In the figure, the development potential (difference between the development bias voltage at the time of gradation pattern image formation and the surface potential of the photoreceptors 1K, Y, M, and C: unit V) is assigned to the x-axis, and the unit is assigned to the y-axis. The toner adhesion amount per area (mg / cm ² ) is allocated.

  The control unit 200 selects, from the potential data and toner adhesion amount data stored in the RAM 203, a region in which the relationship (development characteristics) between the potential data and the toner adhesion amount data is a straight line for each color, These data are smoothed. The least square method is applied to the potential data and the toner adhesion amount data after the smoothing process to perform linear approximation of the developing characteristics of each developing device. Further, after obtaining the linear equation y = ax + b of the developing characteristics of each developing device for each color, the image forming conditions in each process unit (6K, Y, M, C) are adjusted based on the slope a in this linear equation. . Examples of the method for adjusting the image forming conditions include a method for adjusting the uniform charging potential of the photosensitive member and the developing bias as described in JP-A-9-211191. Further, the toner concentration of the two-component developer may be adjusted.

  As shown in FIG. 4, in the process control process, the image forming apparatus includes 14 K reference toner images SK1, SK2,... SK13, SK14 arranged at a predetermined pitch in the moving direction (sub-scanning direction) of the intermediate transfer belt 8. A K gradation pattern image SK is formed. Further, 14 Y reference toner images SY1, SY2 arranged at a predetermined pitch in the sub-scanning direction (belt traveling direction) so as to be adjacent to the K gradation pattern image SK in the main scanning direction (belt width direction). ... A Y gradation pattern image SY composed of SY13 and SY14 is formed. Further, an M-th floor composed of 14 M reference toner images SM1, SM2,... SM13, SM14 arranged at a predetermined pitch in the sub-scanning direction so as to be adjacent to the Y gradation pattern image SY in the main scanning direction. A tone pattern image SM is formed. Further, the M-th floor composed of 14 C reference toner images SC1, SC2,... SC13, SC14 arranged at a predetermined pitch in the sub scanning direction so as to be adjacent to the M gradation pattern image SM in the main scanning direction. A tone pattern image SC is formed.

  Further, in the misregistration correction process in the image forming condition adjustment process, a misregistration detection patch pattern as shown in FIG. 6 is formed near both ends and the center of the intermediate transfer belt 8 in the width direction. These three patch patterns formed near both ends and near the center are composed of four Y, M, C, and K reference toner images Sy, Sm, Sc, and Sk arranged at predetermined intervals in the sub-scanning direction. The reference toner images are formed so as to be aligned in the main scanning direction.

  In the drawing, each reference toner image in the patch pattern formed near the front side end in the belt width direction is detected by the first end photosensor 151. Each reference toner image in the patch pattern formed near the center in the belt width direction is detected by the center photosensor 152. Further, each reference toner image in the patch pattern formed near the back end in the belt width direction is detected by the second end photosensor 153. If the formation timings of the reference toner images of the respective colors are appropriate, the detection intervals of the reference toner images are equal to each other, but if they are inappropriate, the formation intervals of the reference toner images of the respective colors are not equal. Also, the detection intervals are not equal. If there is no optical writing skew in the optical system, the reference toner images of the same color are detected at the same timing between the three patch patterns. However, if the skew is generated, the detection timing is different. come. The control unit 200 adjusts the optical writing start timing and the optical system for each photoconductor on the basis of the detection interval and detection timing of each color toner image in the main scanning direction and the sub-scanning direction, and determines the position of each color toner image. Reduce the deviation.

  When the above-described gradation pattern image or patch pattern is formed, the secondary transfer bias roller 19 shown in FIG. 1 is separated from the intermediate transfer belt 8 to perform secondary transfer of the gradation pattern image or patch pattern. Dislocation to the bias roller 19 is avoided.

  The skew deviation is corrected by adjusting the tilt of the mirror for turning back each color laser beam in the optical writing unit 7 by a driving mechanism (not shown). A stepping motor is used as a drive source for biasing the mirror.

  Further, the correction of the positional deviation of each color toner image in the sub-scanning direction (belt moving direction) is performed by adjusting the optical writing start timing for each photoconductor. FIG. 7 is a timing chart showing generation timings of various signals when the optical writing start timing in the sub-scanning direction is corrected. In the figure, ON / OFF (rise and fall) of the latent image write enable signal, which is an image area signal in the sub-scanning direction, is adjusted in units of time corresponding to one dot of the image. That is, the correction resolution of the latent image writing enable signal is a time corresponding to one dot. This latent image write enable signal is written near the edge of the scanning area in the main scanning direction by writing laser light reciprocally scanned in the main scanning direction (rotation axis direction of the photosensitive member) by reflection on the reflecting surface of the polygon mirror. It adjusts based on the synchronous detection signal emitted by having detected by. For example, the optical writing start timing for the photosensitive member is advanced by one dot in the sub-scanning direction, and the falling timing of the latent image write enable signal is advanced by one synchronization detection signal as shown in FIG. .

  FIG. 8 is a timing chart showing the generation timing of various signals when the optical writing start timing in the sub-scanning direction is corrected. Also in the timing chart of the figure, the correction resolution of each signal is 1 dot. In this timing chart, the latent image writing clock is determined so as to obtain a clock in which each line is accurately in phase by the falling edge of the synchronization detection signal. Optical writing is started in synchronization with the latent image writing clock, and a latent image writing enable signal in the main scanning direction is also generated in synchronization with this clock. If the optical writing start timing is advanced by one dot time in the sub-scanning direction based on the detection timing of each reference toner image in the patch pattern, as shown in FIG. The write enable signal may be activated early.

  Further, when the magnification in the main scanning direction of each reference toner image in the Y, M, and C patch patterns is deviated from the reference color K, the clock that can change the signal frequency in very small steps. The magnification is corrected by a device such as a generator.

  FIG. 9 is an enlarged configuration diagram showing the encoder roller 14 as a driven roller disposed in the loop of the intermediate transfer belt (8 in FIG. 6) together with the encoder 170 disposed on one end side thereof. The encoder roller 14 is made of stainless steel or the like, and is rotated following the endless movement of the intermediate transfer belt. One of the shaft portions (15a) protruding from the both ends of the roller portion so as to be rich in the axis line has a structure that becomes thinner in three steps toward the outside as shown in the figure. The shaft portions at both ends are rotatably supported by bearings 169 provided on the support plate of the transfer unit.

  The encoder 170 covering the shaft portion 14a of the encoder roller 14 includes a disk-shaped code wheel 171 fixed to the shaft portion 14a so as to rotate together with the shaft portion 14a, a transmission type photo sensor 172, a support plate 173, a cover 73, and the like. have.

  The support plate 173 is made of a resin material such as polyacetal, and is press-fitted (lightly press-fitted) into the base side portion of the shaft portion 14 a of the encoder roller 14. The code wheel 171 is fixed to one end face (end face opposite to the press-fitting direction) of the support plate 173 via a double-sided tape (not shown). The tip end portion of the shaft portion 14a is also rotatably supported by a bearing, thereby improving the positioning accuracy of the support plate 173 on which the code wheel 171 is fixed.

  The code wheel 171 is made of PET (polyethylene terephthalate) having a thickness of about 0.2 mm, and as shown in FIG. 10, radial slits 171a are formed on the outer edge portion thereof. The slit 171a is formed by, for example, a pattern drawing technique using a photoresist.

  The transmissive photosensor 172 has its light emitting element 172a and light receiving element 172b facing each other through a slit forming portion of the code wheel 171. As the code wheel 171 rotates, each slit 171a of the slit forming portion is positioned between the light receiving element 172a and the light emitting element 172b so that light can be transmitted and received. It is repeated in a short cycle that transmission / reception is not made. More specifically, when a slit 171a (a black portion in the figure) is interposed between the two elements, the light emitted from the light emitting element 172a is received by the light receiving element 172b and the output voltage from the transmission type photosensor 172 is output. Becomes Hi level. On the other hand, when the slit 171a is not interposed, the light from the light emitting element 172a is blocked at a position between the slits, and the output voltage from the reflective photosensor 172 becomes a low level. Therefore, for example, based on the frequency of the encoder output signal as shown in FIG. 11, the rotational angular velocity (hereinafter simply referred to as angular velocity) of the encoder roller 14 is grasped. This grasp is performed by the control unit 200 shown in FIG. The control unit 200 feeds back the detection result of the angular speed of the encoder roller 14 obtained based on the output from the encoder 170 to the driving speed of the belt driving motor 162.

  In the tandem system like this printer, it is necessary to move the intermediate transfer belt 8 at a constant speed. In practice, however, the belt moving speed varies due to uneven thickness in the circumferential direction of the belt, eccentricity of the driving roller 12, and the like. When the belt moving speed of the intermediate transfer belt 8 fluctuates, the actual belt moving position deviates from the target belt moving position, and the leading end position of each toner image on the photoreceptors 1Y, 1M, 1C, and 1K in the belt moving direction. Is shifted on the intermediate transfer belt 8 to cause overlay shift (color shift). Further, when the belt moving speed is relatively high, the toner image portion transferred onto the intermediate transfer belt 8 has a shape extended in the belt circumferential direction rather than the original shape, and conversely, the belt moving speed is relatively high. At a later time, the toner image portion transferred onto the intermediate transfer belt 8 has a shape reduced in the belt circumferential direction from the original shape. In this case, in the image finally formed on the recording paper, a periodic change in image density (banding) appears in a direction corresponding to the belt circumferential direction.

  The relationship between the uneven thickness of the belt and the speed fluctuation is as follows. That is, when a relatively thick portion of the belt is wound around the driving roller 12 that drives the intermediate transfer belt 8, the belt moving speed is increased. On the other hand, when a relatively thin portion of the belt is wound, the belt moving speed becomes slow. This causes a speed fluctuation while the intermediate transfer belt 8 moves one round. In the belt member molded by the centrifugal molding method, the maximum thickness portion and the minimum thickness portion have a phase difference of 180 ° per belt circumference due to the eccentricity of the mold for molding the belt. It is easy to cause uneven thickness. In such a belt member, the speed fluctuation per belt circumference has a characteristic of drawing a sine curve for one cycle.

  Even when the driving roller 12 is eccentric, the speed of the intermediate transfer belt 8 is changed. In many cases, the circumferential length of the drive roller 12 is smaller than the belt circumferential length, so that a plurality of sinusoidal fluctuation characteristics due to the eccentricity of the drive roller 12 appear per belt circumference. The eccentricity of the drive roller 12 is mainly caused by an elastic layer made of rubber or the like on the surface. Specifically, in the case of a roller made only of metal, it is relatively easy to manufacture a roller having almost no eccentricity by lathe processing or the like. However, for the purpose of preventing the belt from slipping on the surface of the driving roller 12, it is common to use a metal cored bar whose surface is covered with an elastic layer. In the drive roller 12, even if a metal cored bar having almost no eccentricity due to lathe processing or the like is used, eccentricity is inevitably generated due to uneven thickness of the elastic layer.

  Therefore, in this printer, the detection result of the angular speed of the encoder roller 14 obtained based on the output from the encoder 170, that is, the speed fluctuation of the intermediate transfer belt 8 is fed back to the driving speed of the belt driving motor 162. Yes. Specifically, when it is determined that the angular velocity is slower than the control target value, the number of clock pulses to the belt drive motor 162 is increased accordingly to increase the rotational speed of the motor. On the other hand, if it is determined that the angular velocity is faster than the control target value, the number of clock pulses to the belt drive motor 162 is decreased to slow the motor rotation speed. By such feedback control, the movement speed of the intermediate transfer belt 8 is stabilized.

Next, a characteristic configuration of the printer will be described.
As described above, in this printer, the speed fluctuation of the intermediate transfer belt 8 is suppressed by controlling the driving speed of the belt driving motor 162 based on the detection result of the angular speed of the encoder roller 14. As a result, the registration error due to the fluctuation in the speed of the belt when transferring the toner images on the photosensitive members of the respective colors on the intermediate transfer belt 8 is suppressed. In such a configuration, the patch pattern for detecting misregistration formed on the intermediate transfer belt 8 by transfer from the photoconductor of each color does not include misregistration due to the speed fluctuation of the intermediate transfer belt 8. For this reason, the optical sensor unit 150 is caused to detect only the positional deviation of each reference toner image due to the optical path variation of the optical writing unit.

As shown in FIGS. 4 and 6, in this printer, the optical sensor unit 150 including a plurality of photosensors as image detection means is hung on the encoder roller 14 in the entire circumferential region of the intermediate transfer belt 8. It arrange | positions facing the area | region in a rotation position. The intermediate transfer belt 8, because the stabilization of the travel speed is achieved by the stabilization of the rotational angle velocity of the encoder roller 150 in a position facing the optical sensor unit 150, a belt of a region of a position facing the optical sensor unit 150 The movement speed is most stabilized. Therefore, the positional deviation detection patch pattern on the intermediate transfer belt 8 is moved at a stable speed at a position facing the optical sensor unit 150. Thereby, the optical sensor unit 150 can accurately detect the positional deviation of each reference toner image due to the optical path variation of the optical writing unit.

  As a result of the above, it is possible to satisfactorily suppress both the toner image overlay deviation caused by the optical path fluctuation of the optical writing unit and the toner image overlay deviation caused by the speed fluctuation of the intermediate transfer belt 8.

  The alignment accuracy in the above-described misalignment correction processing is required to be on the micron order. Such high-accuracy alignment requires a patch pattern having high detection accuracy by the optical sensor unit 150 shown in FIG. However, if the roller around the intermediate transfer belt 8 swings, bends, or rotates eccentrically at a position facing the optical sensor unit 150, the photosensors of the optical sensor unit 150 become out of focus. The desired detection accuracy cannot be obtained. The allowable range of vibration required for a general driven roller is 0.3 mm or less to 0.5 mm or less. However, if such a vibration is present, sufficient detection accuracy cannot be obtained.

  In order to cope with the recent increase in functionality, the allowable range of deflection of the driven roller disposed at a position facing the optical sensor unit 150 becomes particularly small. Specifically, in the old days, one photosensor sequentially detects gradation patterns for four colors and performs process control, or one photosensor detects a patch pattern and corrects misalignment (in this case) , Only position correction in the sub-scanning direction is performed). In such a configuration, a long time is required for processing by sequentially forming and detecting a gradation pattern and a patch pattern for each color. Therefore, in recent years, as shown in FIG. 4, a plurality of photosensors are arranged along the roller axial direction. As a result, it is possible to shorten the process control process and the positional deviation correction process by forming gradation patterns and patch patterns of the respective colors in parallel or detecting them in parallel. However, in such a configuration, since it is necessary to maintain the detection accuracy of each photosensor high, it is necessary to suppress the shake in the entire region in the roller axis direction, and as a result, the allowable range of the shake becomes very small. is there.

  The encoder roller 14 shown in FIGS. 4 and 6 is a driven roller, but unlike a general driven roller, it plays a role of detecting the rotational angular velocity of the intermediate transfer belt 8. If the encoder roller 14 is bent, shakes, or rotates eccentrically, even if the intermediate transfer belt 8 moves at a constant speed, the rotational angular speed of the encoder roller 14 changes. As a result, the rotational angular velocity of the intermediate transfer belt 8 cannot be accurately detected. For this reason, conventionally, the encoder roller 14 has a high rigidity that does not cause bending or deflection, and is obtained by removing eccentricity and distortion by high-precision machining. In general, the allowable deflection range is set to 0.05 mm or less to 0.1 mm or less.

  In this printer, the optical sensor unit 150 is opposed to the encoder roller 14 having high rigidity and no eccentricity or distortion via the intermediate transfer belt 8. As a result, if the encoder roller 14 having the same allowable vibration range as that of the conventional one is used for the purpose of accurate rotation speed, the positional deviation detection accuracy is deteriorated due to the roller vibration at the position facing the optical sensor unit 150. It can be suppressed at the same time. In such a configuration, by using the encoder roller 14 having the same high rigidity as that of the prior art and having no eccentricity or distortion, it is possible to improve the detection accuracy of the rotational speed of the roller and improve the accuracy of detecting the displacement.

  FIG. 12 is a partially enlarged perspective view showing one end portion of the transfer unit 15 in the belt moving direction together with the optical sensor unit 150. As shown in the figure, the optical sensor unit 150 holds each photosensor on a long plate-like support plate 155 taking a posture extending in the belt width direction (roller axis direction). In the figure, only the center photosensor 152, the second end photosensor 153, the Y photosensor 154Y, the M photosensor 154M, the C photosensor 154C, and the K photosensor 154K are shown. A first end photosensor (151) not shown is also held by the support plate 155 in a region not shown.

  Positioning angle members 156 are fixed to both ends of the support plate 155 in the longitudinal direction. The round hole provided in the angle member 156 is fitted to the outer peripheral surface of the bearing 169 that rotatably supports the shaft portion 14 a of the encoder roller 14, so that the optical sensor unit 150 is in contact with the encoder roller 14. Is positioned. Accordingly, the optical sensor unit 150 is positioned with respect to the intermediate transfer belt 8 with reference to the encoder roller 14. With this configuration, the front surface of the intermediate transfer belt 8 can be positioned with high accuracy with respect to the focal position of each photosensor of the optical sensor unit 150. Thereby, compared with the case where the optical sensor unit 150 is positioned on the basis of another member, the detection accuracy of each photosensor can be improved.

Next, the printer according to the embodiment will be described. Unless otherwise specified below, the configuration of the printer according to the embodiment is the same as that of the reference embodiment.
As shown in FIG. 12, in the printer according to the reference embodiment, the optical sensor unit 150 is fixed to the transfer unit 15 and is attached to and detached from the printer main body together with the transfer unit 15. On the other hand, in the printer according to the embodiment , the optical sensor unit is fixed to the printer main body, and the transfer unit 15 is attached to and detached from the printer main body without the optical sensor unit. .

FIG. 13 is a partially enlarged perspective view showing one end of the transfer unit 15 in the belt width direction in the printer according to the embodiment . The transfer unit 15 includes a cover member 180 that covers the intermediate transfer belt 8 from the front surface side over almost the entire region in the width direction at a position facing the encoder roller 14. The cover member 180 as a cover member is provided with seven openings 181 arranged in the belt width direction (roller axis direction). Seven photosensors of an optical sensor unit (not shown) fixed to the printer main body detect a gradation pattern image and a patch pattern on the intermediate transfer belt 8 through any of the openings 181.

  Even in such a configuration, the encoder roller 14 having high rigidity and having no eccentricity or distortion is also used as a driven roller that wraps around the intermediate transfer belt 8 at a position facing the optical sensor unit. Thus, unlike a case where a driven roller other than the encoder roller 14 is disposed at a position facing the optical sensor unit and the driven roller is also used with high rigidity and no eccentricity or distortion, high detection is achieved at low cost. Accuracy can be achieved.

  Note that a window made of a light-transmitting material such as glass or transparent resin may be provided on the support plate 180 instead of the opening 181.

  Up to this point, a description has been given of a printer in which each color toner image formed on each photoconductor is primary-transferred on the intermediate transfer belt 8 as a belt member and then secondarily transferred to a recording sheet. Instead of such a configuration, the present invention also relates to an image forming apparatus having a configuration in which each color toner image formed on each photoconductor is directly superimposed and transferred onto a recording sheet held on the surface of a paper conveyance belt as a belt member. Can be applied.

As described above, in the printer according to the reference embodiment, the optical sensor unit 150 serving as the image detecting unit is positioned with respect to the intermediate transfer belt 8 serving as the belt member with the encoder roller 14 serving as the driven roller serving as a reference. In such a configuration, as described above, the detection accuracy of each photosensor can be improved as compared with the case where the optical sensor unit 150 is positioned with reference to another member.

In the printer according to the reference embodiment, a plurality of photosensors in the optical sensor unit 150 serving as image detection means are arranged side by side in the rotation axis direction of the encoder roller 14. In such a configuration, a plurality of gradation patterns and patch patterns formed in parallel with each other are detected in parallel by one of the plurality of photo sensors, respectively, so that one photo sensor can sequentially detect the patterns. Thus, it is possible to shorten the process control process and the misalignment correction process.

Further, in the printer according to the embodiment, the reference toner image on the surface of the intermediate transfer belt 8 is transferred to the optical sensor unit through the opening 181 provided on the intermediate transfer belt 8 so as to cover the front surface of the intermediate transfer belt 8. The opening 181 of the cover member 180 serving as a cover member to be detected is disposed so as to face the region in the circumferential position of the intermediate transfer belt 8 in the position where the intermediate transfer belt 8 is wound around the encoder roller 14. Even in such a configuration, unlike a case where a driven roller different from the encoder roller 14 is disposed at a position facing the optical sensor unit and the driven roller is also used with high rigidity and no eccentricity or distortion, the cost is low. High detection accuracy can be realized.

In the printer according to the embodiment, a cover member 180 in which a plurality of openings 181 are arranged in the direction of the rotation axis of the encoder roller 14 is used. Even in such a configuration, as in the printer according to the reference embodiment , one photosensor can be obtained by causing each of a plurality of photosensors to detect a plurality of gradation patterns and patch patterns formed in parallel with each other. Compared with the case where these patterns are sequentially detected, the process control process and the positional deviation correction process can be shortened.

Further, in the printer according to the reference embodiment or the embodiment, for each of the plurality of photosensitive members, the gradation pattern image formed of the plurality of reference toner images having different image densities formed on the surface is transferred to the intermediate transfer belt 8. The image density of each reference toner image in the gradation pattern image on the intermediate transfer belt 8 is detected by the photo sensor of the optical sensor unit 150, and based on the detection result, the optical writing unit 7, each color process unit, etc. The driving speed of the belt driving motor 162 that is the driving source of the driving roller 12 is adjusted based on the detection result by the image forming condition adjusting means that adjusts the image forming condition of the visible image forming means and the encoder 170 that is the rotational speed detecting means. The control unit 200 is configured to function as drive speed adjusting means. In such a configuration, the gradation pattern image is detected while the belt speed fluctuation is suppressed by feeding back the detection result of the encoder 170 to the driving speed of the belt driving motor 162, thereby forming an image caused by the belt speed fluctuation. It is possible to appropriately adjust the image forming conditions while suppressing the deterioration of the performance detection accuracy. Specifically, as described above, when the belt speed fluctuates during the transfer of the toner image from the photosensitive member to the intermediate transfer belt 8, the toner image is expanded and contracted in the belt moving direction more than originally. Is done. Accordingly, the image density of the toner image changes from the state before transfer. For this reason, in the process control process described above, when the speed fluctuation of the intermediate transfer belt 8 occurs during the transfer of the gradation pattern image, the image density of the gradation pattern image changes from the state before the transfer. Then, the gradation pattern image on the intermediate transfer belt 8 does not accurately reflect the image forming performance (image forming density) of the optical writing unit or process unit. In contrast, in the printer according to the reference embodiment or the embodiment , the gradation pattern image is transferred to the intermediate transfer belt 8 while suppressing the speed variation of the intermediate transfer belt 8 by the feedback control described above, thereby causing the belt speed variation. The deterioration of the detection accuracy of the image forming performance can be suppressed.

In the printer according to the reference embodiment or the embodiment , predetermined reference toner images respectively formed on a plurality of photoconductors are transferred to the intermediate transfer belt 8 so as not to overlap each other, and the reference toners on the intermediate transfer belt are transferred. Image formation for grasping relative positional deviations of the reference toner images based on the results of detecting the images by the optical sensor unit 150 and adjusting the image forming conditions of the optical writing unit and the process units of the respective colors based on the results. The control unit 200 is configured to function as a condition adjusting means or a driving speed adjusting means for adjusting the driving speed of the belt driving motor 162 based on the detection result by the encoder 170. In such a configuration, by detecting the patch pattern while suppressing the belt speed fluctuation by adjusting the driving speed of the belt driving motor 162, the positional deviation detection error caused by the belt speed fluctuation is suppressed, and the position of each color toner image is suppressed. Deviation correction can be performed appropriately.

1Y, M, C, K: photoconductor (image carrier)
6Y, M, C, K: Process unit (part of visible image forming means)
7: Optical writing unit (part of visible image forming means)
8: Intermediate transfer belt (belt member)
12: Driving roller 14: Encoder roller (driven roller)
15: Transfer unit (transfer device)
150: Optical sensor unit (image detection means)
151: First end photosensor (image detection means)
152: Central photosensor (image detection means)
153: Second end photosensor (image detection means)
154Y, M, C, K: Y, M, C, K photosensor (image detection means)
170: Encoder (Rotation speed detection means)
180: Cover member (cover member)
181: Opening

JP 2007-077941 A

Claims (6)

An image carrier for carrying a visible image;
Visible image forming means for forming a visible image on the image carrier;
The visible image carried on the image carrier is transferred to an endless belt member that is moved endlessly as the drive roller rotates, or a recording member that is held on the front surface of the belt member. And a transfer unit that
An endless belt member that is stretched by the driving roller, and a driven rotatable driven roller which is driven to rotate,
The front surface of the belt member is disposed so as to cover almost entire area in the width direction of the belt member, the front surface of the belt member through a window consisting of open or light transmitting member provided on its own an image forming apparatus for chromatic and cover member capable of detecting the visible image on the image sensing means serving optical sensor, and a rotation speed detecting means for detecting a rotational speed of the driven roller in the transfer unit ,
The opening or the window of the covering member, of the entire area in the circumferential direction of the belt member, which is configured to face the region of the hanging turning position with respect to the driven roller,
The optical sensor is fixed to the image forming apparatus main body,
And, an image, wherein the transfer unit having the above-described belt member and the covering member and the rotational speed detection means is intended to be detachably attached to the image forming apparatus main body in a state that does not have the optical sensor Forming equipment . The image forming apparatus according to claim 1 .
A transfer apparatus using the cover member in which a plurality of the openings or windows are arranged in the rotational axis direction of the driven roller. The image forming apparatus according to claim 1 or 2 ,
A plurality of the image carriers are provided, and the transfer device is configured to transfer the visible images respectively carried on the image carriers on the belt member or the recording member on the belt member. An image forming apparatus. The image forming apparatus according to claim 3 .
For each of the plurality of image carriers, a gradation pattern image composed of a plurality of visible images having different image densities formed on the surface of the image carrier is transferred to the belt member, and the gradation on the belt member is transferred. An image forming condition adjusting means for causing the optical sensor to detect the image density of each visible image in a pattern image and adjusting the image forming condition of the visible image forming means based on the detection result;
An image forming apparatus comprising: a drive speed adjusting means for adjusting a drive speed of a drive source of the drive roller based on a detection result by the rotation speed detecting means. The image forming apparatus according to claim 3 .
The predetermined visible images respectively formed on the plurality of image carriers are transferred to the belt member so as not to overlap each other, and the visible images on the belt member are respectively detected by the optical sensors. Based on the relative position shift of the visible images based on the image forming condition adjusting means for adjusting the image forming conditions of the visible image forming means based on the results;
An image forming apparatus comprising: a drive speed adjusting means for adjusting a drive speed of a drive source of the drive roller based on a detection result by the rotation speed detecting means.   The image forming apparatus according to claim 1,
An image forming apparatus, wherein the optical sensor is fixed to the main body of the image forming apparatus so as to face the front surface of the belt member from below.

Images