JP4599199B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, or the like that obtains a superimposed image by superimposing and transferring visible images formed on a plurality of image carriers.

  Conventionally, as this type of image forming apparatus, the one described in Patent Document 1 is known. This image forming apparatus includes a plurality of photosensitive members as image carriers and a belt member as an endless moving member that can be moved endlessly so as to sequentially pass through transfer positions facing the respective photosensitive members. Then, toner images having different colors formed on the surface of each photoconductor are formed by an electrophotographic process. These toner images are transferred while being superimposed on the surface of the recording paper sequentially passing through the transfer positions while being held on the surface of the belt member. By this superposition transfer, a multicolor toner image is formed on the surface of the recording paper.

  In such a configuration, the position of the toner image formed on each photoconductor is relatively shifted due to a change in the optical path due to a temperature change of the optical system that optically scans each photoconductor or a backlash of each photoconductor that can be attached and detached. It may end up. When such a shift occurs, a registration shift of each color toner image with respect to the recording paper occurs, and the image quality deteriorates.

  Therefore, in the image forming apparatus described in Patent Document 1, a speed setting process for individually setting the driving speed of each photoconductor is performed to suppress the misalignment of the color toner images. In this speed setting process, first, a predetermined reference toner image is formed on each photoconductor at a predetermined timing and transferred to the surface of the belt member. Next, based on the timing at which the respective reference toner images are detected by the photosensors, the relative positional shift amounts of the respective reference toner images are calculated. Based on the calculation result, the driving speed of each photoconductor is individually set. As a result, each photoconductor is driven at a speed difference corresponding to the amount of positional deviation, and the toner image on the photoconductor can be superimposed on the toner image on the recording paper without deviation.

  On the other hand, the misalignment of the toner image includes not only the deviation of the optical path of the optical system and the backlash of the photoreceptor, but also the eccentricity of the photoreceptor gear fixed to the rotating shaft of the photoreceptor. This overlay deviation occurs as follows. That is, in the photosensitive member gear, when the portion having the longest radius due to the eccentricity meshes with the driving side gear, the linear velocity of the photosensitive member becomes the slowest. On the other hand, when the portion having the shortest radius meshes with the driving gear, the linear velocity of the photosensitive member becomes the fastest. Since the former part and the latter part of the photoconductor gear are in a point-symmetrical position of 180 ° with respect to the center of rotation, the linear velocity of the photoconductor is a sine curve for one cycle per one rotation of the gear. Fluctuation characteristics appear. When the photoconductor is rotating at a linear velocity around the upper limit of the sine curve, the surface of the photoconductor passes through the transfer position at the fastest speed, so the toner image has a shape extending in the surface movement direction than the original. Transferred to recording paper. On the other hand, when the photoconductor is rotating at a linear velocity around the lower limit of the sine curve, the surface of the photoconductor passes through the transfer position at the slowest speed, so that the toner image is shrunk in the surface movement direction than the original. It is transferred to the recording paper in the shape. In the superimposing transfer process, if a toner image having a contracted shape is transferred onto a toner image having a shape extending more than the original on the recording paper, a registration error occurs. On the other hand, even if the toner having a shape extended more than the original is transferred onto the toner image having a shape smaller than the original, an overlay error occurs.

  In recent years, in order to avoid such misalignment, control of so-called phase alignment that synchronizes the rotational phases of a plurality of photoconductor gears has been introduced. This phase alignment is performed as follows, for example. That is, first, a mark is attached to the maximum radius portion or the minimum radius portion of a photoconductor gear (hereinafter simply referred to as “gear”) fixed to the rotation shaft of each photoconductor, and this is detected by a photo sensor or the like. . Based on the detection result, the rotation angle of each photoconductor gear is grasped. Based on this grasp, if each photoconductor is individually stopped at the same rotational angle position at the end of the image forming operation, the rotational phase of each gear can be synchronized in the next image forming operation. At the start of the image forming operation, the rotational speeds of the gears are adjusted by temporarily varying the drive speeds of the drive sources of the photoconductors based on the rotational phase shift amount determined based on the detection result by the photosensor. You may do it.

Japanese Patent Laid-Open No. 10-20607

  However, even if the rotational phases of the respective gears are adjusted in this way, in the configuration in which each photoconductor has a linear velocity difference as in the image forming apparatus described in Patent Document 1, the rotational phase that has been adjusted is linearly changed. It will be mad by the difference. As the linear velocity difference is increased, the rotational phase shift of the gear becomes more serious, and the overlay shift due to the phase shift is likely to occur. In particular, in a continuous print mode (continuous image forming operation) in which images are continuously printed out on a plurality of recording sheets, the phase shift is increased every time printing is performed, and the overlay shift becomes noticeable.

  The present invention has been made in view of the above background, and an object thereof is to provide the following image forming apparatus. That is, a situation in which the overlay shift due to the rotational phase shift of the gear becomes conspicuous in the continuous image forming operation while suppressing the overlay shift due to the relative shift of the formation position of the visible image by the plurality of image carriers. It is an image forming apparatus that can suppress the above.

In order to achieve the above object, the invention of claim 1 is characterized in that a black image carrier that carries a black visible image on a moving surface, and a visible image of a color different from black is carried on the moving surface. A plurality of image carriers including a non-black image carrier, a plurality of gears for transmitting rotational driving force to the respective image carriers while individually rotating on the rotation axis of each image carrier, and Driving means for individually rotating and driving each image carrier by a plurality of motors that individually exhibit rotational driving forces for transmission to a plurality of gears, and a visible means for forming a visible image on each image carrier An endless moving body that moves the surface endlessly so as to sequentially pass through the opposing positions of the image forming means and each image carrier, and a visible image formed on the surface of each image carrier. Or transfer to a recording medium held on the surface of A transfer unit for transferring the recording medium after transferring to the surface of the endless moving member, an image detecting means for detecting a visible image borne on the surface of the endless moving member, each of the image bearing member at a predetermined timing A predetermined reference image is formed on each image carrier while being driven at a standard speed and transferred to the surface of the endless moving body, and then the above non- referenced image is detected based on the timing detected by the image detection means. For the black image carrier, the reference image detection deviation time from the black image carrier is calculated, and the speed setting for individually setting the driving speed of the non-black image carrier based on the calculation result Control means for performing processing, and during the image forming operation, the black image carrier is rotated at the standard speed, while the non-black image carrier is driven at the driving speed set by the speed setting process. By rotating and driving with Between the use image bearing member and said non-black for image bearing member, in by generating a linear velocity difference corresponding to the detection deviation time the image forming apparatus for reducing relative displacement of the visible image, said plurality In addition to providing a mark at a predetermined position in the rotation direction for each of the gears, a plurality of mark detection sensors are provided for detecting the mark of each gear at a predetermined rotation angle position of the gear, and the detection deviation time and drive A data table that associates the speed difference value and associates the upper limit value of the detection deviation time with the driving speed difference value is stored in the data storage means, and the marks of the plurality of gears are stopped at the same rotation angle position. By stopping the driving of the plurality of motors at the timing, or by temporarily varying the driving speeds of the plurality of motors when the driving of the plurality of motors is started. The control means is configured to perform a phase matching process for matching the rotational phases of a plurality of gears, and when the calculation result of the detection deviation time is less than the upper limit value in the speed setting process. The drive speed difference value corresponding to the calculation result is specified from the data table, and the value obtained by adding or subtracting the specified result to the standard speed is used to drive the non-black image carrier during the image forming operation. On the other hand, if the calculation result is not less than the upper limit value while setting as a speed, the drive speed difference value corresponding to the upper limit value is specified from the data table, and the specified result is compared with the standard speed. The control means is configured to perform a process of setting the added or subtracted value as the driving speed of the non-black image carrier during the image forming operation .
Also, the invention of claim 2, the image forming apparatus according to claim 1, in a continuous image forming operation for continuously forming an image on a plurality of recording medium, for forming an image on the recording material prior to The image forming operation for setting the drive speed of each image carrier while forming the reference image is performed between the image forming operation of the image forming operation and the image forming operation for forming an image on the subsequent recording member. In this case, each image forming operation is continuously performed without being stopped .
Also, the invention of claim 3, claim 1 or the second image forming apparatus, and a low-speed image forming operation for forming an image while the surface of each image bearing member is relatively slow moving, each of the image bearing The control means is configured such that the upper limit value is different for each of the high-speed image forming operation for forming an image while moving the surface of the body at a relatively high speed.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, each image carrier disposed in the housing of the image forming apparatus is attached and detached through an opening provided in the housing. It is characterized by being made possible.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the image carrier and the charging means for uniformly charging the surface thereof are supported by a common support to constitute one unit. The plurality of units provided in the housing of the image forming apparatus are detachable through openings provided in the housing.

In these inventions, the driving speed of each image carrier is based on the relative displacement amount of the visible image transferred from the plurality of image carriers to the surface of an endless moving body such as an intermediate transfer belt or a paper transport belt. Are set individually. By setting the linear velocity difference corresponding to the positional deviation amount to each image carrier by this setting, it is possible to suppress the overlay deviation due to the relative displacement of the formation position of the visible image by the plurality of image carriers. it can.
At this time, the difference in rotational speed between a plurality of gears individually corresponding to each latent image carrier is kept within a predetermined range by keeping the drive speed difference in each image carrier within a predetermined upper limit. . As a result, it is possible to reduce the rotational phase deviation due to the difference in rotational speed between the gears, and to suppress a situation in which the overlay shift caused by the rotational phase shift of the gear becomes significant in the continuous image forming operation.

Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of an electrophotographic printer (hereinafter simply referred to as a printer) will be described.
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 photoreceptor 1Y, a drum cleaning device 2Y, a charge eliminating device (not shown), a charging device 4Y, a developing device 5Y, and the like. It has. 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 that is rotated clockwise in the drawing by a driving unit (not shown). The uniformly charged surface of the photoreceptor 1 </ b> Y as an image carrier is exposed and scanned by the laser beam L to carry an electrostatic latent image for Y. 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. In the other color process units (6M, C, K), (M, C, K) toner images are similarly formed on the photoreceptors (1M, C, K), and the intermediate transfer belt 8 is subjected to an intermediate process. Transcribed.

  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 shown above, an optical writing unit 7 is disposed below the process units 6Y, 6M, 6C, and 6K in the drawing. The optical writing unit 7 serving as a latent image forming unit scans the respective photosensitive members in the process units 6Y, 6M, 6C, and 6K with the laser light L emitted based on the image information. By this scanning, electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 1Y, 1M, 1C, and 1K. The optical writing unit 7 passes through a plurality of optical lenses and mirrors while deflecting laser light (L) emitted from the light source in the main scanning direction by reflection on a polygon mirror that is rotationally driven by a motor. Irradiates the photoconductor.

  On the lower side of the optical writing unit 7 in the figure, paper storage means having a paper feed cassette 26, a paper feed roller 27 incorporated therein, and the like are disposed. The paper feed cassette 26 stores a plurality of transfer papers P, which are sheet-like recording media, 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, there is disposed a transfer unit 15 that is an endless moving body that allows the intermediate transfer belt 8 that is an intermediate transfer body to move endlessly while stretching. This transfer unit 15 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 secondary transfer backup roller 12, a cleaning backup roller 13, a tension roller 14, and the like. The intermediate transfer belt 8 is endlessly moved in the counterclockwise direction in the figure by the rotational drive of at least one of the rollers while being stretched around these seven 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 secondary transfer backup 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 the electric circuit of the printer. In the figure, the control unit 150 includes a process unit 6Y, M, C, K, an optical writing unit 8, a paper feed cassette 26, a registration roller pair 28, a transfer unit 15, a toner image detection sensor 69, a data input port 68, and the like. It is connected. Further, Y, M, C, and K photoconductor motors 90Y, M, C, and K, and Y, M, C, and K gear sensors 91Y, M, C, and K are also connected. The toner image detection sensor 69 detects a later-described reference toner image transferred on the intermediate transfer belt (8). The Y, M, C, and K photoconductor motors 90Y, M, C, and K rotate the Y, M, C, and K photoconductors (1Y, M, C, and K). The Y, M, C, K gear sensors 91Y, M, C, K detect the marks attached to the gears fixed to the rotary shaft members of the Y, M, C, K photoconductors.

  The control unit 150 includes a CPU 150a that performs arithmetic processing and a RAM 150b that stores data. The speed setting process is performed each time a predetermined timing arrives. In this speed setting process, first, the photoconductors 1Y, 1M, 1C, 1C shown in FIG. Charge K uniformly while rotating K. Then, electrostatic latent images for forming Y, M, C, and K reference toner images each having a predetermined pixel pattern are formed on the four photoconductors 1Y, 1M, 1C, and 1K, respectively, by scanning with laser light. . The Y, M, C, and K reference toner images obtained on the photoreceptors 1Y, 1M, 1C, and 1K by these developments are transferred onto the intermediate transfer belt 8, respectively.

Next, a characteristic configuration of the printer will be described.
As shown in FIG. 4, the optical scanning for the reference toner images on the photoreceptors 1Y, 1M, 1C, and 1K is performed by moving the Y, M, C, and K reference toner images on the intermediate transfer belt 8 in the belt moving direction. It starts at a timing such that the images are transferred at regular intervals. The Y, M, C, and K reference toner images Ty, Tm, Tc, and Tk transferred so as to be arranged at equal intervals on the intermediate transfer belt 8 are sequentially detected by a toner image detection sensor 69 including a reflective photosensor. . Normally, the detection intervals of the Y, M, C, and K reference toner images by the toner image detection sensor 69 are equal. However, if the optical path of the laser beam in the optical writing unit fluctuates due to a temperature change or the process units 6Y, 6M, 6C, 6K rattle, the optical writing position for the photoreceptors 1Y, 1M, 1C, 1K Are relatively displaced from each other, and Y, M, C, and K reference toner images are not formed at equal intervals. Then, the detection intervals of the Y, M, C, and K reference toner images by the toner image detection sensor 69 are not equal. In such a state, an overlay error occurs in each color toner image at the time of printout. Therefore, the control unit 150 determines the Y, M, C, K photoconductor motors 90Y, M, C, K based on the variation in the detection interval of the Y, M, C, K reference toner image by the toner image detection sensor 69. Set the drive speed individually. With this setting, if necessary, a linear velocity difference is given to each photoconductor during a printing operation so that each color toner image is accurately superimposed at each primary transfer nip.

  FIG. 5 is a flowchart illustrating an example of a control flow of the speed setting process performed by the control unit 150. This speed setting process is performed immediately after the main power of a printer (not shown) is turned on or whenever a predetermined time elapses with the main power turned on. In this speed setting process, first, after the driving of each photoconductor and the intermediate transfer belt is started, optical writing for forming a Y, M, C, K reference toner image is performed on each photoconductor. (Step 1: Hereinafter, step is denoted as S). The electrostatic latent images obtained by the optical writing are developed by corresponding developing units to become Y, M, C, and K reference toner images (S2), and then transferred onto the intermediate transfer belt. (S3). The Y, M, C, and K reference toner images transferred onto the intermediate transfer belt are sequentially detected by the toner image detection sensor (S4). In this detection process, the control unit is the YK detection interval, which is the time from the Y reference toner image detection time to the K reference toner image detection time, and the time from the M reference toner image detection time to the K reference toner image detection time. Each MK detection interval is measured (S5). Also, the CK detection interval, which is the time from the C reference toner image detection time to the K reference toner image detection time, is measured (S5). Then, YK transfer deviation time T1, CK transfer deviation time T2, and MK transfer deviation time T3 are respectively calculated by subtracting predetermined values X1, X2, and X3 from the YK detection interval, MK detection interval, and CK detection interval, respectively (S6). , S7, S8). When these transfer deviation times are “zero”, there is no transfer deviation between the K reference toner image and the Y, M, and C reference toner images.

  In the RAM (150b) of the control unit, for each transfer deviation time T1, T2, and T3, a deviation that associates the value of the transfer deviation time with an appropriate driving speed difference correction value that has been confirmed by a preliminary test. A correction data table is stored. These drive speed difference correction values are such that a drive speed difference corresponding to that value is provided between the K photoconductor and the Y, M, C photoconductor, so that the Y, M, C toner image is perfect for the K toner image. It can be overlapped with. After calculating the transfer deviation times T1, T2, and T3, the control unit next determines whether or not the transfer deviation time T1 is below a predetermined upper limit value (S9). This is whether or not the drive speed difference between the Y photoconductor (1Y) and the K photoconductor (1K) to be set corresponding to the transfer deviation time T1 is below a predetermined upper limit value. Judgment is made. If it is lower (Y in S9), the drive speed difference corresponding to the transfer deviation time T1 is specified from the YK correction data table (S10), and the value is increased or decreased from the standard speed by that amount. The driving speed of the Y photoconductor is set (S11). If it exceeds (N in S9), the drive speed difference corresponding to the upper limit value is specified from the YK data table (S12), and the Y photosensitivity is increased or decreased from the standard speed accordingly. The body driving speed is set (S11). As a result, the drive speed difference between the Y photoconductor and the K photoconductor is kept within a predetermined upper limit. For the transfer deviation times T2 and T3, the same processing as S11 to S12 described above is performed (S13 to S19), and the drive speed difference corresponding to the drive times of the M photoconductor and C photoconductor is specified. Set to a value that is increased or decreased only. In the next print job, the K photoconductor is driven at a predetermined standard speed, and the Y, M, and C photoconductors are driven at the drive speeds set in the illustrated speed setting process. Thus, a toner image of each color is formed.

  FIG. 7 is an enlarged configuration diagram showing the four photoconductors 1Y, 1M, 1C, and 1K, the transfer unit, and the surrounding configuration thereof. In the figure, photoconductors 1Y, 1M, 1C, and 1K are each supported by a bearing (not shown) so as to be rotatable about its rotation axis. At one end of each rotation shaft, photosensitive gears 101Y, 101M, 101C, 101K, which are much larger than the photoreceptors 1Y, 1M, 1C, 1K, are fixed. The K driving gear 103K fixed to the motor shaft of the K photosensitive motor 102Y is engaged with the K photosensitive gear 101K. The C driving gear 103C fixed to the motor shaft of the C photoconductor motor 102C is engaged with the C photoconductor gear 101C. Further, the M driving gear 103M fixed to the motor shaft of the M photoconductor motor 102M meshes with the M photoconductor gear 101M. Further, the Y driving gear 103Y fixed to the motor shaft of the Y photoconductor motor 102Y is engaged with the Y photoconductor gear 101Y.

  Each photoconductor gear 103Y, M, C, K is provided with marks 104Y, M, C, K made of a light-reflective material at its maximum eccentricity, and this is a gear sensor 105Y made of a reflective photosensor. , M, C, and K are detected at a predetermined rotation angle.

  In monochrome printing, which is more demanding than color printing, only the photoconductor 1K for K is driven, so that consumption of other photoconductors 1Y, 1M, 1C, and motors can be suppressed and energy saving can be achieved. Or At this time, the transfer unit 15 takes a posture in which the intermediate transfer belt 8 is brought into contact with only the K photoconductor 1K among the four photoconductors 1Y, 1M, 1C, and 1K.

  In monochrome printing, only the K photoconductor 1K is rotationally driven in this way, and therefore the phase of the maximum eccentricity between the K photoconductor gear 103K and the other photoconductor gears 103Y, 103, and 103C. Once combined, it will inevitably differ afterwards. Therefore, in this printer, at the end of the printing operation, each photoconductor motor is individually stopped so that the rotational phase of each photoconductor gear is matched based on the detection result from each gear sensor.

  Next, a printer according to an example in which a more characteristic configuration is added to the printer according to the embodiment will be described. Unless otherwise specified, the basic configuration of the printer according to the example is the same as that of the printer according to the embodiment.

  FIG. 6 is a schematic diagram showing the relative positional relationship of the optical scanning start position in the sub-scanning direction with respect to the photoreceptors 1Y, 1M, 1C, and 1K. In the drawing, the alphabets Y, M, C, and K surrounded by circles indicate the first-dot laser irradiation spots for the photoreceptors 1Y, 1M, 1C, and 1K, respectively. Further, in the same figure, C surrounded by a dotted line ◯ indicates a laser irradiation scheduled position of the first dot on the C photoconductor 1C. At the same time, L1 indicates the length of one dot in the sub-scanning direction. Needless to say, L1 / 2 indicates half the length of L1. As described above, in this printer, the driving speed of the Y, M, and C photoconductors 1Y, 1M, and 1C is based on the K photoconductor 1K that is driven at the standard speed. Each is set.

  In the figure, if the laser spot irradiation position of the first dot on the C photoconductor 1C is a C position surrounded by a dotted line in the figure, the C toner image and the K toner image are L1 in the sub-scanning direction. / 2 or more, that is, an overlay error that is more than half of the size of one dot occurs. In order to eliminate such a shift in the sub-scanning direction, it is not possible to simply shift the irradiation time of the laser beam by that amount. Since the laser beam moves in the main scanning direction, if the irradiation is started slightly shifted from the scheduled irradiation start timing, optical writing corresponding to the end is performed from the center rather than the end in the main scanning direction. Because it will end up. In order to shift the irradiation start timing, it is necessary to shift at least one dot (one line). Here, it is assumed that the irradiation start timing for the C photoconductor 1C is delayed by one dot from the original schedule. Then, the optical writing start position for the C photoconductor 1C is shifted from the position C surrounded by a dotted line ◯ in the drawing to the position C surrounded by a solid line ◯. Then, the overlay deviation between the C toner image and the K toner image is shorter than L1 / 2. That is, the overlay deviation is reduced. By shifting the irradiation start timing in this way, the overlay deviation amount can be kept to L1 / 2 or less without causing a linear velocity difference between the photoconductors. Similarly, in the relationship between the M toner image and the K toner image, and the C toner image and the K toner image, the overlay deviation amount can be kept to L1 / 2 or less without causing a linear velocity difference between the photoconductors. it can.

  Therefore, in the printer according to the present embodiment, in the speed setting process described above, the overlay deviation with K among the three colors Y, M, and C is L1 / 2 based on the detection timing of each reference toner image. The following processing is performed for the calculation result as described above. That is, first, as shown in FIG. 7, the irradiation start timing is set to be advanced or delayed by one dot from the scheduled irradiation start timing. As a result, the overlay deviation amount that should have occurred at a length of L1 / 2 or more without changing the driving speed of the photosensitive member is set to be able to remain at L1 / 2 or less.

  However, even if such a setting is made, an overlay error occurs with a length of L1 / 2 or less. Therefore, with respect to the overlay deviation with a length of L1 / 2 or less, the setting of the driving speed of the Y, M, or C photoconductor 1Y, 1M, or 1C is changed, and the driving speed of the K photoconductor 1K ( The linear speed difference is given to the standard speed. Therefore, the upper limit values in S9, S13, and S17 in FIG. 5 are values smaller than half of one pixel.

  In such a configuration, as compared with the case where the overlay deviation of L1 / 2 or more is suppressed only by the linear velocity difference of the photosensitive member, the overlay deviation is suppressed only by the linear velocity of the photosensitive member while reducing the linear velocity difference. It is possible to suppress misalignment.

  In addition, when performing the speed setting process described above, this printer sets the Y, M, and C photoconductors 1Y, M, and C (hereinafter referred to as color photoconductors) to the driving speeds set in the previous speed setting process. These are also driven at a standard speed in the same manner as the K photoconductor 1K. In such a configuration, it is possible to avoid complication of calculation processing and deterioration of accuracy due to accumulation of correction values of driving speeds by driving each color photoconductor at the driving speed set in the previous speed setting process. .

  As described above, the speed setting process is performed every time a predetermined time elapses with the main power supply (not shown) turned on (for example, every time a predetermined number of printouts are performed). The timing for performing the speed setting process may come during a continuous printing operation, which is a continuous image forming operation in which images are continuously printed out on a plurality of transfer sheets P. When such arrival has occurred, the speed setting process is executed at the timing between the printing operation corresponding to the preceding transfer paper P and the printing operation corresponding to the subsequent transfer paper P (hereinafter referred to as “inter-paper timing”). In this case, if a long time is required for the speed setting process, the waiting time of the user is extended. Therefore, in this printer, when the speed setting process is performed at the sheet interval timing, the preceding print operation, the speed setting process operation, and the subsequent print operation are continuously performed without stopping. ing. With such a configuration, it is possible to shorten the waiting time of the user as compared with the case where any printing operation is stopped.

  By the way, even in a printer just completed, the detection sensitivity of the above-described toner image detection sensor, the driving load on each photoconductor, etc. are greatly different from the standard one due to differences in production lots. Thus, the relationship of the above-described deviation correction data table cannot be obtained. As a result, when the speed setting process is performed as usual, a situation occurs in which the overlay deviation is not reduced well. However, in this case, generally, the overlay displacement amount after the speed setting process is almost constant. Therefore, in this printer, in such a case, correction is performed by adding a predetermined numerical value to the YK transfer deviation time T1, CK transfer deviation time T2, or MK transfer deviation time T3, which is the amount of positional deviation. It is supposed to be. Adding a predetermined numerical value to these deviation times is the same as adding a predetermined numerical value to the driving speed. In such a configuration, even when there is an error for each product in the detection sensitivity of the toner image detection sensor and the driving load for each photoconductor, it is possible to satisfactorily suppress the misalignment of the toner images of each color. A specific method for adding a predetermined numerical value is as follows. That is, in the flowchart of FIG. 5 shown above, a predetermined numerical value is added to the YK transfer deviation time T1, the CK transfer deviation time T2, or the MK transfer deviation time T3 after the process of S8.

  The printer also operates in the high-speed print mode that prioritizes the print speed over the high-quality image, and on the contrary, the operation in the image-quality priority mode that achieves higher image quality by lowering the print speed than the high-speed print mode. Switching is performed based on an input to a display unit or the like. Then, different values are used in both modes as the upper limit values previously shown in S9, S13, and S17 of FIG. In such a configuration, even when switching between two or more modes having different driving speeds, the overlay error amount of each color toner image can be kept below a predetermined value in each mode. Of course, the above-described deviation correction data tables are also different from each other in each mode.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 3 is an enlarged configuration diagram showing a process unit for Y of the printer and its surroundings. FIG. 3 is an enlarged configuration diagram illustrating a reverse conveyance unit and a casing of the printer with a side cover opened. FIG. 2 is a perspective view showing a transfer unit of the printer. 6 is a flowchart illustrating an example of a control flow of speed setting processing performed by the control unit of the printer. FIG. 3 is a schematic diagram showing a relative positional relationship of optical scanning start positions in the sub scanning direction with respect to Y, M, C, and K photoconductors of the printer. FIG. 3 is an enlarged configuration diagram showing four photoconductors, a transfer unit, and a peripheral configuration thereof.

Explanation of symbols

1Y, M, C, K photoconductor (image carrier)
4Y charging device (electrical resistance means)
6Y, M, C, K Process unit (unit)
8 Intermediate transfer belt (endless moving body)
15 Transfer unit (transfer means)
101Y, M, C, K photoconductor gear (part of drive means)
102Y, M, C, K Photoconductor motor (part of drive means)
103Y, M, C, K Driving gear (part of driving means)
150 Control unit (control means)
P Transfer paper (recording medium)

Claims (5)

The black image bearing member configured to bear a visible image of black on a moving surface, and a plurality of image bearing members include non-black for image bearing member, a bearing a color visible image which is different from the black moving surface When,
A plurality of gears for transmitting rotational driving force to each image carrier while individually rotating on the rotation axis of each image carrier;
Driving means for individually rotating and driving the respective image carriers by a plurality of motors that individually exhibit the rotational driving force for transmission to the plurality of gears ;
Visible image forming means for forming a visible image on each image carrier;
An endless moving body that moves the surface endlessly so as to sequentially pass a position facing each image carrier;
Transfer the visible image formed on the surface of each image carrier to a recording body held on the surface of the endless moving body, or transfer to the recording body after transferring it to the surface of the endless moving body Means,
Image detecting means for detecting a visible image carried on the surface of the endless moving body;
While driving each image carrier at a standard speed at a predetermined timing, a predetermined reference image is formed on each image carrier and transferred to the surface of the endless moving body, and then each reference image is transferred to the image detection means. For the non-black image carrier, the reference image detection deviation time between the non-black image carrier and the non-black image carrier is calculated, and the non-black image carrier is calculated based on the calculation result. and control means for performing the speed setting processing for setting individual drive speed of
During the image forming operation, the black image carrier is rotated at the standard speed, while the non-black image carrier is rotated at the driving speed set in the speed setting process. In an image forming apparatus that reduces a relative positional shift of a visible image by generating a linear velocity difference corresponding to the detection shift time between the image carrier and the non-black image carrier .
While providing a mark at a predetermined position in the rotational direction for each of the plurality of gears,
Provided with a plurality of mark detection sensors for detecting the mark of each gear at a predetermined rotation angle position in each gear,
A data table that associates the detection deviation time with the driving speed difference value and associates the upper limit value of the detection deviation time with the driving speed difference value is stored in the data storage means,
The driving of the plurality of motors is stopped at the timing at which the marks of the plurality of gears are stopped at the same rotational angle position, or the driving speeds of the plurality of motors are temporarily set at the start of driving the plurality of motors. By configuring the control means to implement a phase matching process for matching the rotational phases of a plurality of gears,
In the speed setting process, when the calculation result of the detection deviation time is less than the upper limit value, the drive speed difference value corresponding to the calculation result is specified from the data table, and the specification result is determined as the standard result. A value obtained by adding or subtracting to the speed is set as the driving speed of the non-black image carrier during the image forming operation, and when the calculation result is not lower than the upper limit value, the upper limit value is set. Is determined from the data table, and a value obtained by adding or subtracting the specified result to the standard speed is set as the driving speed of the non-black image carrier during the image forming operation. process to implement the image forming apparatus being characterized in that constitute the control means. The image forming apparatus 請 Motomeko 1,
An image forming operation for forming an image on a preceding recording body and an image forming for forming an image on a succeeding recording body in a continuous image forming operation for continuously forming images on a plurality of recording bodies. When performing an image forming operation for setting the driving speed of each image carrier while forming the reference image between the operations, the respective image forming operations are continuously performed without being stopped. An image forming apparatus characterized by being configured as described above. The image forming apparatus according to claim 1 or 2 ,
A low-speed image forming operation for forming an image while moving the surface of each image carrier at a relatively low speed, and a high-speed image forming operation for forming an image while moving the surface of each image carrier at a relatively high speed. The image forming apparatus is characterized in that the control means is configured to vary the upper limit value. The image forming apparatus according to claim 1 to 3,
An image forming apparatus, wherein each image carrier disposed in a housing of the image forming apparatus is detachable through an opening provided in the housing. The image forming apparatus according to claim 1 to 4,
The image carrier and the charging means for uniformly charging the surface thereof are supported on a common support to constitute one unit, and each of the plurality of units disposed in the housing of the image forming apparatus is provided. An image forming apparatus, wherein the image forming apparatus is detachable through an opening provided in the housing.

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