JP4965399B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus for transferring a visible image carried on an image carrier to an endless belt member that moves endlessly or a recording member held on the surface of the belt member.

  An image forming apparatus that forms an image using a belt member such as an intermediate transfer belt or a paper conveyance belt is known. In such an image forming apparatus, high-precision drive control of the belt member is essential to obtain a high-quality image. In order to drive the belt member with high accuracy, a drive control method for controlling the rotation of the drive roller so as to keep the rotation speed of the drive roller driving the belt member constant is known. In this drive control method, the rotational speed of the driving roller is made constant by maintaining the rotational angular speed of the motor that is the driving source and the rotational angular speed of the gear that transmits the rotational driving force generated by the motor to the driving roller. This is a drive control method. However, in the conventional belt member drive control method, when the belt member has a thickness variation, particularly in the direction along the belt moving direction, the belt moving speed is maintained even if the rotational angular velocity of the driving roller is constant. There was a problem that could not be made constant.

  The variation in the thickness of the belt member is caused by, for example, an uneven thickness in the belt moving direction seen in a belt member produced by a centrifugal firing method using a cylindrical mold. When such a belt member thickness variation is present in the belt member, the belt moving speed increases when a belt portion having a thick belt is wound around a driving roller that drives the belt member, and on the contrary, a belt portion having a thin belt thickness is formed. When it is wound, the belt moving speed becomes slow. As a result, the belt moving speed varies.

  Patent Document 1 describes an image forming apparatus that uses one of a plurality of driven rollers that are driven to rotate along with an endless movement of a belt member while providing an encoder as a rotation detecting means. . This image forming apparatus uses an encoder to move the belt member endlessly by driving the drive roller at a constant angular velocity at a predetermined timing such as during initial operation under the user or when the belt member is replaced. The rotational angular velocity signal or rotational angular displacement of the driven roller that is sent is acquired. As a result, a belt speed fluctuation pattern per one rotation of the belt member is detected, and the detected belt speed fluctuation pattern is stored in a storage unit such as a RAM. When forming an image, the belt drive motor, which is the drive source of the drive roller, is driven with a drive speed pattern opposite in phase to the belt speed change pattern, thereby suppressing the speed change of the belt member due to the thickness change. It is like that.

  However, in the image forming apparatus described in Patent Document 1, it is necessary to perform test driving for driving the driving roller at a constant angular velocity in order to acquire the rotational angular velocity signal or the rotational angular displacement of the driven roller. Therefore, there is a problem that during such test driving, image formation cannot be performed and the user waits until the test driving is completed.

  Therefore, Patent Document 2 describes an image forming apparatus in which a speed variation pattern per rotation of a belt member is detected and updated sequentially during an image forming operation. This Patent Document 2 describes that a belt speed fluctuation pattern can be detected even during an image forming operation for the following reason. That is, by subtracting the rotational angular velocity of the driving roller from the rotational angular velocity of the driven roller, the rotational angular velocity of the driven roller when the driving roller is driven at a constant angular velocity can be obtained, and the belt velocity per one rotation of the belt member A variation pattern can be detected. For this reason, even if the angular velocity of the driving roller fluctuates, the rotation of the driven roller when the driving roller is driven at a constant angular velocity is obtained by taking the difference value between the angular velocity fluctuation of the driven roller and the angular velocity fluctuation of the driving roller. Angular speed, that is, a belt speed fluctuation pattern per one rotation of the belt member can be detected. Therefore, the belt speed fluctuation pattern can be detected even during an image forming operation in which the drive roller is rotated at a constant speed to change the angular speed of the driving roller. Therefore, it is not necessary to perform a test drive for detecting the belt speed variation pattern, and the downtime of the apparatus can be reduced.

JP 2005-115398 A JP 2006-106642 A

  However, in Patent Document 2, for example, when an image is formed on a sheet having a short length in the transport direction, such as B5, the belt forming member may not rotate once and the image forming operation may end. In this case, it is not possible to detect a belt speed fluctuation pattern per one rotation of the belt member. Therefore, the drive speed pattern cannot be updated unless an image forming operation is performed in which the belt member rotates once. As a result, if the thickness of the belt member changes while the image forming operation is stopped for a long period of time, it is caused by fluctuations in the belt moving speed until the image forming operation is performed so that the belt member rotates once. The image will be disturbed.

  In addition, by setting an arbitrary position of the belt as a virtual reference position and grasping one cycle of the belt member based on the accumulated rotation angle of the motor, the speed of one rotation of the belt member based on the virtual reference position When detecting the fluctuation pattern and controlling the belt drive motor based on the speed fluctuation pattern based on the virtual reference position, the actual belt period and the belt period determined from the cumulative rotation angle of the motor, etc. There is an error. For this reason, when image formation in which the belt member makes one rotation is not performed for a long period of time, the virtual reference position when the speed fluctuation pattern is detected and the virtual reference position when the belt drive motor is controlled are set. The accumulated error increases, and the virtual reference position used as the reference when detecting the speed fluctuation pattern and the virtual reference position when controlling the belt drive motor are significantly different, making accurate belt drive motor control impossible. End up.

  The present invention has been made in view of the above problems, and the object of the present invention is to perform the speed fluctuation pattern update process even if the image forming operation is not performed such that the belt member rotates once. An image forming apparatus is provided.

In order to achieve the above object, an invention according to claim 1 is directed to an image carrier that carries a visible image, an image information obtaining unit that obtains image information of a visible image formed on the image carrier, and the image. Visible image forming means for forming a visible image based on information on the image carrier, and an endless belt member that is endlessly moved while being stretched on a driving roller and a driven roller, or held on the surface of the belt member A transfer means for transferring a visible image carried on the image carrier to a recording member, a driven roller rotation detection means for detecting a rotation angular velocity or a rotation angle displacement of the driven roller, and a rotation of the drive roller. Drive roller rotation detection means for detecting angular velocity or rotation angular displacement, detection results by the driven roller rotation detection means, and speed fluctuation pattern per one rotation of the belt member stored in the storage means The belt detected during an image forming operation for adjusting a driving angular velocity or a driving angular displacement of a driving source of the driving roller based on data or forming a visible image based on the image information The difference value between the detection result of the driven roller rotation detection means for one rotation of the member and the detection result of the drive roller rotation detection means is calculated, the speed fluctuation pattern is detected based on the calculated difference value, and the storage And an image forming apparatus including a control unit that performs a speed variation pattern update process for updating data stored in the unit based on a detection result. The belt member rotates once during the image forming operation time. If the time is shorter than the time, after the image forming operation is completed, the belt member is moved endlessly until the belt member makes one rotation to update the speed variation pattern. Treated to be carried out, it is characterized in that constitutes the control means.
According to a second aspect of the present invention, in the image forming apparatus of the second aspect, it is determined whether or not the requirements for execution of the speed fluctuation pattern update processing are satisfied before or at the end of the image forming operation. In this case, the control means is configured to move the belt member endlessly until the belt member makes one rotation even after the image forming operation is completed.
According to a third aspect of the present invention, in the image forming apparatus of the second aspect, a time measuring unit for measuring time is provided, and an elapsed time from the previous image forming operation has reached or exceeded a predetermined time. Based on the above, the control means is configured to determine that the implementation requirement is satisfied.
According to a fourth aspect of the present invention, in the image forming apparatus according to the second or third aspect, a time measuring unit for measuring time is provided, and an elapsed time from the previous execution of the speed fluctuation pattern update processing reaches a predetermined time. The control means is configured to determine that the implementation requirement is satisfied based on the fact that a predetermined time has been exceeded.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the second to fourth aspects, a counting unit that counts the number of rotations of the belt member is provided, and the number of rotations of the belt member reaches a predetermined number. The control means is configured to determine that the implementation requirement is satisfied based on exceeding a predetermined number.
According to a sixth aspect of the present invention, in the image forming apparatus of the fifth aspect, the number of rotations of the belt member has reached a predetermined number or exceeded a predetermined number since the previous execution of the speed fluctuation pattern update process. Based on this, the control means is configured to determine that the implementation requirement is satisfied.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the second to sixth aspects, a counting unit that counts the number of image forming operations is provided, and the speed change pattern update process from the previous execution is performed. The control means is configured to determine that the implementation requirement is satisfied based on an increase in the number of image forming operations reaching a predetermined number or exceeding a predetermined number. is there.
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the second to seventh aspects, an environmental detection unit that detects an environment is provided, and an environmental change from the previous execution of the speed variation pattern update process is provided. The control means is configured to determine that the implementation requirement is satisfied based on whether the amount reaches a predetermined amount or exceeds a predetermined amount.
According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the second to eighth aspects, an exchange detecting means for detecting the replacement of the belt member is provided, and the image forming operation is performed by replacing the belt member. In the first image forming operation after the replacement detection means detects that, the control means is configured to determine that the execution requirement is satisfied.
According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the second to ninth aspects, when the image forming operation is a first image forming operation after the apparatus is turned on, the implementation requirement is The control means is configured to determine that it is provided.
According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the first to tenth aspects, the length of the recording member in the transport direction, the number of recording members for recording a visible image, an image forming mode, and a paper type Based on the above, the control means is configured to determine whether or not the time of the image forming operation is shorter than the time for the belt member to make one rotation.
According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the first to eleventh aspects, the belt member has a thickness deviation of 3 [μm] or more in an environment where the thickness deviation in the circumferential direction is 25 [° C.]. , Is used.
The invention of claim 13 is the image forming apparatus according to any one of claims 1 to 12, wherein the belt member has a circumferential Young's modulus of 5000 [MPa] or less. To do.
The invention according to claim 14 is the image forming apparatus according to any one of claims 1 to 13, wherein the visible image forming means includes a plurality of the image carriers and forms visible images on the image carriers. And the transfer means is configured to superimpose and transfer the visible images respectively carried on the image carriers.
According to a fifteenth aspect of the present invention, in the image forming apparatus according to the fourteenth aspect, the plurality of image carriers are arranged side by side in the conveying direction of the belt member, and the transfer unit is supported on each image carrier. In a configuration in which a visible image is superimposed and transferred to the belt member and then transferred to a recording member at a time, the time for the image forming operation is determined based on the image carrier used during image formation. The control means is configured to determine whether or not the time is shorter than the time for one rotation.
According to a sixteenth aspect of the present invention, in the image forming apparatus according to any one of the first to fifteenth aspects, the belt member rotates once during the image forming operation based on the image information acquired by the image information acquiring means. The control means is configured to determine whether or not it is shorter than the time to be performed.

  According to the first to sixteenth aspects of the present invention, since the speed variation pattern update process can be performed even when the time of the image forming operation is shorter than the time for which the belt member makes one revolution, the image in which the belt member makes one revolution. Even if the forming operation is not performed, the speed variation pattern update process can be performed.

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 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, and the like in the drawing, 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 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 that is a transfer unit and is 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 is endlessly moved counterclockwise in the figure by the rotational drive of the driving roller 12 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 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 with 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. This time, the image transfer surface enters the secondary transfer nip while bringing the non-image-bearing surface into close contact with the intermediate transfer belt 8, and the second four-color toner image of the intermediate transfer belt 8 is collectively transferred to the non-image-bearing surface. Is done. 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 that is a drive source of a drive roller (12) that drives the intermediate transfer belt 8 (8), a temperature sensor 163 that detects an in-machine temperature, and the like. It is connected. 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 color misregistration correction process 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 K 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 smoothed potential data and toner adhesion amount data to perform linear approximation of the development 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 color misregistration correction processing in the image forming condition adjustment processing, a patch pattern for detecting misregistration 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 to each other, the detection intervals of the reference toner images are equal to each other. And the detection interval is also non-uniform. 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 gradation pattern image or patch pattern described above is formed, the secondary transfer bias roller 19 shown in FIG. 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 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 (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 8. 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.

  An encoder 170 as a driven roller rotation detecting means 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 photosensor 172, and a support. A plate 173, a cover 73, and the like are included.

  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. Specifically, when it is determined that the angular speed of the encoder roller 14 is slower than the control target value, the rotational speed of the belt drive motor 162 is increased accordingly. On the other hand, if it is determined that the angular velocity is faster than the control target value, the rotational speed of the belt drive motor 162 is delayed. By such feedback control, the movement speed of the intermediate transfer belt 8 is stabilized.

  More specifically, in a tandem system such as this printer, it is necessary to move the intermediate transfer belt 8 at a constant speed. However, actually, the belt moving speed varies due to the thickness variation in the circumferential direction of the belt. 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.

  Therefore, the configuration and operation for maintaining the intermediate transfer belt 8 at a constant speed with high accuracy will be described below. Note that the following description is not limited to the intermediate transfer belt 8, but is the same for a belt that is widely driven and controlled, and therefore will be described as a belt.

FIG. 12 is a schematic cross-sectional view showing the main part of the intermediate transfer belt 8. The intermediate transfer belt 8 is wound around the encoder roller 14 as a driven roller at a belt winding angle θ ₁ and is wound around the drive roller 12 at a belt winding angle θ ₂ . The intermediate transfer belt 8 moves endlessly in the direction of arrow A in the figure.

  The driving roller 12 is adapted to transmit a rotational driving force from a belt driving motor (162 in FIG. 3) via a transmission mechanism (not shown). The belt drive motor is also provided with a rotary encoder (not shown). As this encoder, the rotational angular velocity or angular displacement of the driving roller 12 is estimated from the rotational angle of the motor and the drive signal of the motor.

  The control unit 200 recognizes a fluctuation component generated in the rotation cycle of the intermediate transfer belt 8 based on a signal sent from the encoder 170 installed on the encoder roller 14, generates an appropriate target value, and performs feedback control. Do. As a recognition method, sampling of the rotational angular displacement or rotational angular velocity of the driving roller 12 and the rotational angular displacement or rotational angular velocity of the encoder roller 14 is performed. The amplitude and phase of the fluctuation component obtained from the difference between the rotational angular displacement or rotational velocity of the sampled drive roller 12 and the rotational angular displacement or rotational angular velocity of the encoder roller 14 are obtained. This is used as a fluctuation component that occurs in the belt rotation cycle, and feedback control is performed by setting a target value that does not cause a change in the conveyance speed in the belt rotation cycle.

Next, the relationship between the thickness of the belt and the moving speed of the belt will be described.
FIG. 13 is a graph showing an example of belt thickness variation (belt thickness deviation distribution) in the circumferential direction of a commonly used belt. The horizontal axis of this graph is obtained by replacing the length of one belt circumference (belt circumference) with an angle of 2π [rad]. The vertical axis represents a deviation value of the belt thickness based on the average belt thickness (100 μm) in the belt circumferential direction (reference value 0). The belt thickness variation shown in FIG. 13 shows only the basic (primary) component of the frequency components of the belt thickness variation. As will be described later, in the present embodiment, it is possible not only to control the belt drive from such a thickness variation of only the primary component, but also to take into account higher order components.

The belt moving speed on the drive roller 12 side is obtained as follows.
The belt moving speed on the side of the driving roller 12 is set such that the central portion of the intermediate transfer belt 8 on (1/2) of the belt winding angle θ ₂ of the driving roller 12 is temporarily set as the belt driving position X. Speed. When the thickness of the intermediate transfer belt 8 changes sinusoidally along the circumferential direction (sine wave), the belt effective thickness B _{t at the} driving position can be expressed by the following equation (1). In this equation, “B _t0 ” is the average thickness of the intermediate transfer belt 8, “B _ta ” is the amplitude value of thickness variation, “θb” is the belt thickness rotation angular velocity, and α is the initial phase. is there.

When the belt material is uniform and the absolute values of the degree of expansion / contraction between the inner peripheral surface and the outer peripheral surface of the intermediate transfer belt 8 are substantially equal, the effective thickness B _t is the center in the belt thickness direction and the belt inner peripheral surface. It corresponds to the distance. In a belt having a multilayer structure or the like, the stretchability differs between the hard layer and the soft layer. As a result, the distance between the position shifted from the center in the belt thickness direction and the belt inner peripheral surface becomes the belt effective thickness Bt. Sometimes. The belt effective thickness Bt may also change depending on the belt winding angle with respect to the drive roller 12. The belt effective thickness Bt can be expressed by the following equation 2 using the belt thickness effective coefficient κd. When the distance between the center in the belt thickness direction and the inner peripheral surface of the belt is exactly equal to the belt effective thickness Bt, the belt thickness effective coefficient κd is 0.5.

The belt conveyance speed V _b when the belt effective thickness Bt ′ is obtained is obtained from (drive roller radius R _d + belt effective thickness Bt ′) × drive roller rotation angular speed ω _{d, and} is expressed by the following equation (3). It can be expressed by a formula.

From Equation 3, it can be seen that if there is an amplitude “B _ta ” of the thickness variation, the belt conveyance speed at the drive position changes.

The belt moving speed on the encoder roller 14 side is obtained as follows. A central portion of the intermediate transfer belt 8 on (1/2) of the belt winding angle θ ₁ of the encoder roller 14 is temporarily set as a belt driven position Y, and the speed at this belt driven position is set. The distance from the belt driving position X to the belt driven position Y can be expressed as a phase difference τ radians when the length of one round of the belt is 2π radians. Then, the belt effective thickness Bt ″ at the driven position Y can be expressed by the following equation (4).

Here, κe is an effective belt thickness coefficient on the encoder roller 14 side, and a different belt winding amount is conceivable between the driving roller 12 and the encoder roller 14, so another coefficient was set. The belt conveyance speed _Vb at the driven position Y when the belt having such an effective belt thickness Bt ″ is wound can be expressed by the following equation (5). In this equation, “R _e ” is the driven roller radius, and ω _e is the driven roller rotation angular velocity.

Here, the relationship between the rotational angular velocity (ω) of the roller and the belt velocity (Vb) in the variation of the effective thickness (Bt) of the intermediate transfer belt 8 will be described with reference to FIG. FIG. 14A shows the relationship A between the belt speed (Vb) at each belt position when the roller rotates at a constant rotational angular velocity (ω = constant), and the belt has a constant speed (Vb = constant). FIG. 6 is a diagram showing a relationship B of the rotational angular velocity (ω) of the roller at each belt position when rotating at a position. Note that. Graph E shows the belt effective thickness (Bt). As can be seen from the graph A in FIG. 14A, when the roller is rotating at a constant rotational angular velocity (ω = constant), the belt speed (Vb) is the portion where the effective belt thickness (Bt) is maximum. The speed is maximum, and the speed is minimum at the portion where the belt thickness is minimum. On the other hand, when the belt speed is constant (Vb = constant), the rotational angular speed (ω) of the roller has a minimum speed at the portion where the belt effective thickness (Bt) is maximum, and the belt effective thickness (Bt) is The speed is maximum at the minimum portion (see B in FIG. 14A). As can be seen from Equation 3 and Equation 5, the rotational angular velocity (ω) of the roller, the belt velocity (V _b ), This is because a relationship of V _b = B _t × ω is established between the belt effective thickness (B _t ).

  The following can be said from the results of FIG. When the driving roller 12 is rotated at a constant angular velocity, the belt speed fluctuates as indicated by the waveform A in FIG. 14A due to the influence of the belt thickness. On the other hand, the rotational angular speed of the encoder roller 14 is affected by the speed fluctuation. If the influence of the thickness variation is not taken into consideration, the rotation angular velocity of the encoder roller 14 has a waveform similar to the above velocity variation. Actually, however, the rotational angular velocity of the encoder roller 14 is subject to fluctuation components such as the waveform B shown in FIG. 14A due to the influence of the thickness of the belt. That is, the rotation angle of the encoder roller 14 is a waveform in which the waveform A and the waveform B in FIG.

FIG. 14B shows the relationship between the speed of the driving roller 12 and the speed of the intermediate transfer belt 8 in the thickness fluctuation of the intermediate transfer belt 8 when the encoder roller 14 and the driving roller 12 are separated by τ as shown in FIG. FIG. 4 is a diagram showing the relationship between the speed of the encoder roller 14 and the speed of the intermediate transfer belt 8 when the thickness of the intermediate transfer belt 8 varies. A in FIG. 14B is a graph showing the belt conveyance speed when the driving roller 12 is rotated at a constant rotational angular speed. C is the rotational angular velocity of the encoder roller 14 when the drive roller 12 is rotated at a constant rotational angular velocity. B ′ is the rotational angular velocity of the encoder roller 14 when the belt is rotated at a constant conveyance speed. E _j is the effective thickness variation of the belt at the driven position Y shown in FIG. E _d is the effective thickness variation of the belt at the drive position X shown in FIG.

As can be seen from FIG. 14B, C, which is the rotational angular velocity of the encoder roller 14 when the driving roller 12 is rotated at a constant rotational angular velocity, is the rotation of the encoder roller 14 when the belt is rotated at a constant conveyance speed. The angular velocity fluctuation B ′ is superposed on the belt conveyance speed A when the driving roller 12 is rotated at a constant rotational angular speed. Here, R _e = R _d , κ _e = κ _d , α = 0, τ = 1.3 radians.

  As can be seen from FIG. 14B, when C, which is the rotational angular velocity, is detected by the encoder, if the phase difference τ is πrad (or an odd multiple of π), the waveform B ′ is the same curve as the waveform A. It becomes. As a result, the amplitude of the waveform C, which is a combined curve of the waveform B 'and the waveform A, is maximized (twice the amplitude of the curve A in the illustrated example). That is, if the distance between the driving roller 12 and the encoder roller 14 can be set to one half of the cycle of the belt thickness variation, the detection sensitivity of the rotational angular velocity of the encoder roller 14 is maximized. Similarly, when B is closer to π, the waveform B ′ and the waveform A are closer to the same curve, so that the detection sensitivity is increased. Accordingly, the encoder roller 14 for detecting the rotational angular velocity has a distance on the belt that is close to π with respect to the drive roller 12 (when the belt period component is one cycle of the belt, the encoder roller 14 is the most distant). Is preferably selected.

Actually, considering the belt conveyance path provided with functionality in the image forming apparatus, it is difficult to set τ to exactly one half of the belt thickness fluctuation period, but if it can be set as close as possible, the detection sensitivity Becomes higher. When there are two or more belt thickness fluctuations as a whole, the phase difference τ can be set to exactly π or an odd multiple of π in the fluctuation period, and high detection sensitivity can be obtained. To express this relationship by the length of the belt, the half belt length corresponding to the period T _b of the belt thickness fluctuation, or that its odd multiple possible.

  In the present embodiment, the rotational angular velocity of the drive roller 12 is adjusted so that the fluctuation of the rotational angular velocity of the encoder roller 14 becomes B ′. Specifically, the waveform B ′ is obtained from the waveform C in FIG. The period of both the waveform C and the waveform B 'is the period of the belt thickness variation and has the same period. If the waveform C is Ksin (θ + τ), the waveform B ′ can be expressed by ηKSin (θ + τ + T). If the amplitude correction coefficient η and the phase correction value Τ are known, the waveform B ′ is obtained from the waveform C. Can do.

  The rotational angular velocity (waveform B ′) of the encoder roller 14 when the belt is rotated at a constant conveyance speed is calculated from the rotational angular velocity (waveform C) of the encoder roller 14 when the driving roller is driven at a constant angular velocity. The calculation will be described.

First, the rotational angular velocity ω _e of the encoder roller 14 can be expressed by the following equation 6 from the above equations 3 and 5.

The belt thickness fluctuation B _ta can be expressed by the following equation 7 by approximating it as being sufficiently smaller than the roller diameter R.

Among the rotational angular velocities ω _e of the driven rollers expressed by Equation 7, the fluctuation component Δω _e can be expressed by the following equation (8).

  Δωe is a fluctuation component due to a fluctuation in the thickness of one circumference of the belt, and paying attention to two terms in {}. Represents belt fluctuation components at the driven position. In addition, it can be seen from the configuration of fractions outside {} that the detection sensitivity is increased by making the radius Rd of the drive roller 12 larger than the radius Re of the encoder roller 14.

Here, when the data component C is detected by the encoder roller 14 when the driving roller 12 is rotated at a constant angular velocity, it can be expressed by the following equation (11).

Since A and B are sine waves having the same period, the sum is synthesized into a single sine wave having the same period. Therefore, C can be expressed by a sine function, and when K and β are constants, It can be expressed by the formula shown below.

  Since A, B, and C all have the same rotation period as that of the belt, they can be expressed by phase vectors. FIG. 15 is a phase vector component diagram of A, B, and C. In FIG. 15, the vector A is set to 0 ° in a general sense, but even if the initial phase α is given to the vector A, the amplitude phase relationship of each vector is not affected.

The conversion coefficient η from the rotational angular speed fluctuation (vector C) of the encoder roller 14 when the driving roller 12 is rotated at a constant speed to the angular speed fluctuation (vector B) of the encoder roller 14 when the belt constant speed is the target value is corrected. It becomes a coefficient. Since both are sinusoidal functions, conversion from vector C to vector B is possible by applying a coefficient to the amplitude and performing phase operation. That is, as shown in FIG. 15, in order to convert the detected C vector component to the B vector component, the vector length (amplitude value) is converted by the correction coefficient, and the phase is changed by π−τ + β. Can be converted by delaying. Here, β is a phase difference between A and C.

また、位相に対する補正値Τは

となる。
つまり、駆動ローラ１２を一定回転させて検出されたベルト回転周期の変動データ（図１４（ｂ）の波形Ｃ）の変振幅及び位相数値に対して、振幅値は、補正係数ηをかけて、位相Ｔを加えた値が、ベルトが一定速度で回転させた場合のエンコーダローラ１４の回転角速度の変動データ（図１４（ｂ）の波形Ｂ’）となる。これがベルト厚み変動に対応したベルトを一定速度で回転させるためのエンコーダローラ１４の制御目標値となる。数１３〜１５は、ローラ径や位相差など、すべてベルト搬送機構の構成に関する数値で求められる。そのため、振幅の補正係数ηと位相補正値Ｔは、予め決定される定数である。ただし、ベルト厚み実効係数κは、ベルトの材質やベルトの巻付き角に応じて変化するものであり、駆動ローラ１２側とエンコーダローラ１４側のベルト厚み実効係数κを事前に把握する必要がある。このベルト厚み実効係数κは、ベルトの平均搬送速度と各ローラの平均回転角速度の関係を計測して求めることができる。ベルト厚み実効係数κは、ベルト材質やベルトの巻付き角が装置すべてに共通であれば、１つの装置において計測すれば他の装置に同じ数値を用いることができる。また、駆動ローラ１２とエンコーダローラ１４の半径Ｒを同一として、さらにベルト実効厚み係数κも同一となる構成にすることで、数１３、数１４が簡略化されることがわかる。そのことから、駆動側と従動側のκがほぼ同一となるように巻付き角を一致させるようにベルト搬送経路を設計することが好ましい。また、巻付き角がある角度を超える、つまり、駆動ローラ１２側とエンコーダローラ１４側の巻付き角を十分に持たせると、ベルト厚み実効係数κは、巻付き角に依らず、ベルト体の構造固有の値に安定することが実験から得られた。このことから、駆動と従動の両者の巻付き角を十分に持たせることで同様にκの比を１とすることが可能である。 The correction coefficient η for converting the fluctuation amplitude detected on the driven roller side when the driving roller 12 is rotated at a constant speed into the fluctuation amplitude on the driven roller side when the belt is conveyed at a constant speed is expressed by the following equation (15). It can be expressed by the formula shown.

The correction value 補正 for the phase is

It becomes.
That is, the amplitude value is multiplied by the correction coefficient η with respect to the variable amplitude and the phase value of the fluctuation data (waveform C in FIG. 14B) detected by rotating the driving roller 12 at a constant speed. The value obtained by adding the phase T is the fluctuation data of the rotational angular velocity of the encoder roller 14 (the waveform B ′ in FIG. 14B) when the belt is rotated at a constant speed. This is the control target value of the encoder roller 14 for rotating the belt corresponding to the belt thickness fluctuation at a constant speed. Expressions 13 to 15 are all obtained by numerical values relating to the configuration of the belt conveyance mechanism, such as a roller diameter and a phase difference. Therefore, the amplitude correction coefficient η and the phase correction value T are constants determined in advance. However, the belt thickness effective coefficient κ varies depending on the material of the belt and the winding angle of the belt, and it is necessary to grasp the belt thickness effective coefficient κ on the driving roller 12 side and the encoder roller 14 side in advance. . This belt thickness effective coefficient κ can be obtained by measuring the relationship between the average conveying speed of the belt and the average rotational angular speed of each roller. If the belt material and the belt wrap angle are common to all apparatuses, the belt thickness effective coefficient κ can be used for the other apparatuses by measuring in one apparatus. It can also be seen that Equations 13 and 14 are simplified by making the radius R of the drive roller 12 and the encoder roller 14 the same, and the belt effective thickness coefficient κ being the same. Therefore, it is preferable to design the belt conveyance path so that the wrapping angles coincide with each other so that κ on the driving side and the driven side are substantially the same. Further, when the winding angle exceeds a certain angle, that is, when the winding angle on the drive roller 12 side and the encoder roller 14 side is sufficiently provided, the belt thickness effective coefficient κ does not depend on the winding angle, and the belt body Experiments have shown that the values are stable to the specific values of the structure. From this, it is possible to set the ratio of κ to 1 in the same manner by providing sufficient wrapping angles for both driving and driven.

  So far, in order to facilitate understanding, the case where the rotational angular velocity of the driving roller 12 is constant has been described. However, the rotational angular velocity of the driving roller 12 does not need to be constant. The reason for this will be described below. In the following description, for the sake of easy understanding, the case where the angular velocity of the driving roller 12 is changed to make the belt velocity constant will be described. Assuming that the belt speed is constant, the rotational angular speed of the drive roller 12 is a waveform whose phase is shifted by π from the waveform A shown in FIG. At this time, the rotational angular velocity of the encoder roller 14 is a waveform B ′ shown in FIG. The difference between the rotational angular velocity (waveform A shifted by π from the waveform A) in the driving roller 12 and the rotational angular velocity (waveform B ′) in the encoder roller 14 is the waveform C in FIG. Rotation angular velocity of the encoder roller 14). In the above description, for the sake of simplicity, the case where the belt speed is assumed to be constant has been described. However, if the rotation angular velocity in the encoder roller 14 is subtracted from the rotation angular velocity in the drive roller 12 as described above, FIG. C waveform (rotational angular velocity of the encoder roller 14 when the driving roller 12 is rotated at a constant speed) is obtained. This is because the relationship between the fluctuation components caused by the belt thickness fluctuation expressed by the equations 9, 10, and 12 detected on the driven shaft side does not depend on the rotational angular velocity of the driving roller 12. In other words, even if the rotational angular velocity of the drive roller shaft fluctuates, subtracting the rotational angular velocity of the drive roller shaft from the rotational angular velocity of the encoder roller shaft results in fluctuations in the belt thickness as in the case where the drive roller shaft is rotated constant. The resulting fluctuation component can be obtained.

  As described above, the rotation angular velocity (angular displacement) variation of the encoder roller 14 due to the belt thickness variation is calculated from the data obtained by measuring the variation of the rotational angular velocity of the driven roller shaft and the rotation angular velocity (angular displacement) of the driving roller shaft. Then, a control target value (angular speed) of the driven roller at which the belt is at a constant conveyance speed is set from the calculated data, and drive control is performed by comparing the target value with the output value of the driven roller side rotary encoder. This controls belt speed fluctuations such as belt speed fluctuation due to rotation fluctuation of the drive system such as eccentricity of the drive roller, belt speed fluctuation due to belt thickness fluctuation, belt speed fluctuation due to thermal expansion of the belt and roller, belt speed fluctuation due to slip, etc. It becomes possible to do.

  Further, this principle obtained by approximating and developing the fluctuation component as a trigonometric function can be applied to any configuration regardless of the roller diameter, the belt circumferential length, or the like.

  Although the principle of controlling the periodic fluctuation of the belt by the rotational angular velocity of the driving roller 12 and the encoder roller 14 has been described, the same principle is applied not by the angular velocity but also by the rotational angular displacement (position). This is because the angular displacement is obtained by integrating the angular velocity. In the mathematical formula, the sin function is converted into a cos function, the amplitude changes, and a steady deviation occurs. However, an important point in this theory is the relationship between the amplitudes and phases of the waveforms A, B, and C, and the relationship between the amplitudes and phases of the waveforms A, B, and C does not change even at angular velocity or angular displacement. That is, even if the waveforms A, B, and C are angular displacements, the amplitude correction coefficient η and the phase correction value T expressed by the same mathematical expressions as described above are obtained.

  Also, here, the belt cycle variation is governed by the fundamental wave component of one belt cycle, the variation is approximated as a sine wave, and the target reference signal for one round of the belt is obtained as a sine wave from its amplitude and phase value. The principle of calculation is explained. However, in practice, there may be a large error in approximating the periodic fluctuation of the belt used as a fundamental wave. At that time, the second harmonic component having a half period of the fundamental wave or the nth harmonic component having a 1 / n period of the fundamental wave may be handled to approximate the belt period fluctuation. This is the same as the one in which the periodic function is expanded by Fourier series. Then, the same amplitude correction and phase correction may be performed for each harmonic component. However, the phase difference τ needs to be converted in accordance with the period of each harmonic component.

  Next, belt drive control of the printer will be described. FIG. 16 is a block diagram showing an electric circuit of a belt drive control system in the control unit 200 shown in FIG. In FIG. 3, the electric circuit is not shown for convenience, but the control unit 200 includes the electric circuit shown in FIG. 16. This electric circuit includes a motor drive unit 615 and a controller unit 614. The motor drive unit 615 is provided with an output control unit 604 including a servo amplifier 603, a loop filter, and a charge pump. The controller unit 614 includes a comparator 605, a target reference signal generation unit 606, a target function calculation unit 607, and a belt cycle variation detection unit 608.

  The controller unit 614 can appropriately select a part to be processed by software and a part to be processed by hardware based on the processing capability and cost of the CPU or DSP. For example, all of the controller unit 614 may be digitally processed by a CPU or DSP, and D / A conversion may be performed when output to the motor driving unit 615. Further, up to the target function calculation unit 607 is digitally processed by the CPU or DSP, and the target reference signal generation unit 606 is configured by a circuit that modulates the pulse output frequency in accordance with the signal from 607, and 605 is an output pulse of the encoder And a PLL control system that performs phase comparison. Further, all may be configured by a circuit. Increasing the digital processing area with a CPU or DSP or the like makes it less susceptible to the environment, changes over time, and noise, but causes high costs and quantization discretization noise. In consideration of the above, it is preferable to appropriately select a part for processing by software and a part for processing by hardware.

  The motor driving unit 615 performs control for rotating the driving roller 12 by the belt driving motor 162 so that the belt is conveyed at a stable speed. The motor drive unit 615 includes a known PLL control system using a servo amplifier 603 including a servo belt drive motor 162 and a loop filter + charge pump 604 as a phase comparator. The belt drive motor 162 is not limited to a servo motor, and may be a stepping motor or a vibration wave motor. When the belt drive motor 162 is a stepping motor or a vibration wave motor, the control block of the motor drive unit 615 is slightly changed accordingly. FIG. 17 is a block diagram of a control unit when the belt drive motor 162 is a stepping motor or a vibration wave motor. A motor driving unit 615 'shown in FIG. 17 has a configuration of a motor driver 603' and a driving pulse generation unit 604 'instead of the servo amplifier 603 and the loop filter + charge pump 604. In the motor drive unit 615 ′, a drive pulse train is output from the drive pulse generation unit 604 ′ in accordance with a signal output from the controller unit 614. This is received by the motor driver 603 'and a drive current is passed through each phase of the motor. The drive pulse generation unit 604 'has a function of converting the difference between the control target signal from the comparator 605 and the encoder output signal into a drive pulse. However, since the signal from the comparator 605 is a deviation from the target value, the drive pulse generator 604 'also has a function of driving the motor so that the deviation is reduced. Specifically, a drive pulse train is output after a PID controller or the like is incorporated in the drive pulse generation unit 604 ′ and the belt to be controlled is adjusted so that there is no deviation, overshoot, or oscillation with respect to the target speed. I am doing so.

  Further, the motor drive unit 615 transmits the rotational angular velocity information of the drive roller 12 to the controller unit 614 as a drive input signal. When the belt drive motor 162 is a stepping motor, a motor drive signal is transmitted to the controller unit 614 as a drive input signal. In the case of a stepping motor, step driving is performed according to a motor drive pulse train, so that the rotational angular velocity of the drive roller 12 can be easily estimated from the motor drive signal. When the belt drive motor 162 is a DC servo motor, an MR sensor signal for detecting the rotation speed of the motor shaft built in the servo motor is transmitted to the controller unit 614 as a drive input signal. The drive input signal is not limited to this. For example, a rotary encoder may be provided on the drive roller 12 and the output signal of the rotary encoder may be used as the drive input signal.

  The encoder 170 provided on the same axis as the encoder roller 14 outputs a waveform corresponding to the rotation angle of the encoder roller 14. The output waveform is sent to the controller unit 614 via the encoder rotation detection unit 610. When the controller unit 614 performs analog processing, the encoder output may be sent to the controller unit 614 as a pulse waveform. When the controller unit 614 performs digital processing, the encoder rotation detection unit 610 performs processing according to the detection content (rotation speed detection or rotation angular displacement detection) of the encoder. When the detected content of the encoder is rotation angular velocity detection, the period of the encoder output waveform is measured, the rotation angular velocity is calculated by the encoder rotation detection unit 610, and then a signal is transmitted to the controller unit 614. Further, the encoder output waveform (pulse wave) may be counted, the rotational angular velocity may be calculated from the pulse count value measured within an arbitrary time, and a signal may be transmitted to the controller unit 614.

  On the other hand, when the detected content of the encoder is rotation angle displacement detection, the encoder output waveform (pulse wave) is counted, the rotation angle displacement is calculated by the encoder rotation detection unit 610, and the drive output signal is transmitted to the controller unit 614. Alternatively, the rotation angular velocity result may be integrated by the encoder rotation detection unit 610 and a drive output signal may be transmitted to the controller unit 614.

  Whether the detection content of the encoder is angular velocity or angular displacement may be determined according to the cycle of the belt to be controlled. The rotation period of the endless belt such as the intermediate transfer belt 8 used in the image forming apparatus and the driving system components such as the belt driving motor 162, the transmission mechanism 18 and the driving roller 12 that drive the belt is 0.1 to 5 [Hz]. There are many. Since the intermediate transfer belt 8 of the image forming apparatus shown in FIG. 1 conveys an endless belt of about 800 [mm] at 160 [mm / sec], the rotation cycle is 0.2 [Hz]. When such a change in the belt rotation cycle is detected and appropriately controlled, the change in the angular displacement is larger than the detection of the angular velocity, and the control performance can be improved. This is because the angular velocity is to detect the fluctuation of the belt speed in one belt period, but the angular displacement is the amount of movement (rotation amount) of the roller per belt period. For example, the image forming apparatus shown in FIG. 1 often has a roller radius of 16 [mm], an average belt thickness of 100 [μm], and a belt thickness of ± 10 [μm]. When the case where the encoder roller 14 rotates at a constant speed and the case where the belt rotates at a constant speed are compared, the speed fluctuation rate is ± 0.16 [%], but the angular displacement is ± 20 [μm]. That's it. For this reason, it is more appropriate to detect rotational angle displacement information in the present embodiment. However, a speed feedback system may also be configured to control the drive system rotating body having a relatively high frequency with respect to the rotation of the belt with higher accuracy.

  In this way, the signal sent from the encoder rotation detection unit 610 to the controller unit 614 is sent to the belt cycle fluctuation detection unit 608 or the comparator 605. When it is a drive output signal described later, it is sent to the belt cycle fluctuation detecting unit 608, and when it is a signal detected for performing feedback control described later, it is sent to the comparator 605.

  The belt cycle variation detection unit 608 detects a belt cycle variation, which is a speed variation pattern per belt revolution, based on the virtual home position signal of the belt from the drive input signal and the drive output signal. The output value of the belt cycle fluctuation detection unit 608 is the amplitude and phase numerical value of the fundamental wave and the harmonic component of the belt rotation cycle fluctuation described above.

  The virtual home position signal is a signal set so as to be generated in one belt rotation cycle. The virtual home position signal sets the cumulative rotation angle of the motor corresponding to one rotation of the belt in consideration of, for example, the diameter of the drive roller 12 and the reduction ratio of the drive transmission system. Then, when the cumulative rotation angle of the motor reaches the set value, a virtual home position signal is generated. Further, in consideration of the diameter of the encoder roller 14, the cumulative rotation angle of the driven roller corresponding to one rotation of the belt is set. The rotation angle is detected by the encoder 170 installed on the encoder roller 14, and the virtual home position signal may be generated when the set cumulative rotation angle is reached. Further, when the belt is transported at the set average speed, a clock signal having a time interval corresponding to the belt rotation cycle may be set. By managing the cumulative rotation angle and the elapsed time based on this virtual home position signal, the current belt phase can be recognized.

  FIG. 18 is a block diagram illustrating a circuit configuration of the belt cycle variation detection unit 608. The belt cycle fluctuation detection unit 608 is also provided in the control unit 200 shown in FIG. The belt cycle variation detection unit 608 includes a conversion unit 803, a comparator 804, a cycle variation sample unit 805, and a variation amplitude / phase detection unit 806. The conversion unit 803 is a part that converts the drive input signal output from the belt drive motor 162 as the rotational angular velocity of the driven shaft. For example, when the drive input signal is a motor drive signal, when the motor is connected to the drive roller via a speed reducer, the motor drive signal is converted into a drive roller rotation angle in consideration of the reduction ratio. Further, in consideration of the diameter ratio between the driving roller and the driven roller, the rotation is converted to the driven shaft rotation angle. Also, if the drive input signal 802 and the output signal 807 are different information such as speed information and position information, respectively, an integrator or a differentiation is provided to the converter 803 so that the drive output signal matches the drive input signal. A vessel is added. The comparator 804 compares the drive output signal 807 and the drive input signal 802 converted by the conversion unit 803, and outputs the difference to the period variation sample unit 805. The difference information output to the periodic fluctuation sample unit 805 is a fluctuation component caused by the belt thickness fluctuation as described above. The period fluctuation sample unit 805 is a part that stores a fluctuation component resulting from the belt thickness fluctuation in one belt period in a memory. When the period variation sample unit 805 detects the belt virtual home position signal, the period variation sample unit 805 starts storing the variation component caused by the belt thickness variation in the memory. Then, when the belt virtual home position signal is detected again, storage of the fluctuation component due to the belt thickness fluctuation is stopped in the memory. As a result, the belt fluctuation component for one belt cycle is stored in the memory.

  The fluctuation amplitude / phase detection unit 806 is a part that detects the amplitude and phase of the fundamental wave and the harmonics from the fluctuation component for one period of the belt stored in the memory. As a fluctuation amplitude and phase detection method, there are a method of detecting the amplitude and phase of a fluctuation component of a predetermined cycle from a zero cross of a fluctuation value or a peak value, and a detection method of a predetermined cycle component by quadrature detection. These methods are selected from a hardware configuration such as a calculation load or memory of a CPU or DSP, a fluctuation amplitude, and an SN ratio of information input to the phase detection unit 806. The method of detecting from the zero cross or peak value has a small calculation load but is easily affected by noise. The method based on quadrature detection has a large calculation load but is not easily affected by noise. In this way, the amplitude and phase of the belt period component are detected.

  In the conveyance belt such as the intermediate transfer belt 8 used in the image forming apparatus shown in FIG. 1, various fluctuation components are superimposed on the data detected by the encoder in addition to the fluctuation (thickness) of the belt. For example, fluctuation components due to transmission errors due to eccentricity of drive system gears, accumulated pitch error of teeth, fluctuation components due to slip between drive roller and belt, eccentricity of drive roller, cleaning blade or roller in contact with belt, transfer material The fluctuation component due to the load fluctuation due to, and the fluctuation component due to the eccentricity of the encoder roller 14 or the encoder. When these fluctuation components cannot be ignored for detecting the belt cycle fluctuation component, the configuration shown in FIG. 18 is not sufficient. For this reason, a function for removing fluctuations other than the belt thickness fluctuation component is required.

  FIG. 19 shows a belt fluctuation detecting unit 809 including a filter unit 900 that can remove various fluctuation components in addition to the belt thickness fluctuation as described above and detect an AC component of the belt thickness fluctuation with high accuracy. It is a block diagram which shows a circuit structure. A belt cycle fluctuation detecting unit 809 indicated by a dotted line in the drawing has at least a function equivalent to that of the belt cycle fluctuation detecting unit 608 shown in FIG. The filter unit 900 includes a filter 1 (901), a filter 2 (902), and a DC removal unit 903. The belt fluctuation component output from the comparator 804 passes through the filter 1 (901), the filter 2 (902), and the DC removal unit 903, and is sent to the period fluctuation sample unit 805. The filter 1 (901) is designed for the purpose of removing high frequency noise components. The filter 1 (901) removes a signal of 100 Hz or higher when the belt rotational fluctuation is 0.1 to 5 Hz. At this time, it is desired that the folding component is not generated and that the signal around the belt rotation fluctuation is not changed. An example of a filter that satisfies such conditions is an FIR low-pass filter. Thus, by removing high-frequency noise by the filter 1 (901), a low-cost rotary encoder can be used. High-frequency noise includes quantization noise that occurs when the amount of rotation is detected using a rotary encoder. When high-speed rotary encoders with low resolution are used, high-frequency noise is noticeable, which can cause problems with belt cycle fluctuation detection. Become. However, in the present embodiment, high-frequency noise is removed by the filter 1 (901), so that detection by a rotary encoder with low resolution becomes possible, and low-cost and high-accuracy rotation detection can be realized.

  The filter 2 (902) is set for the purpose of removing the periodic fluctuation component of the rotating system. The filter 2 (902) is a low-pass filter for making a signal of only 0.2 Hz or less, which is a belt thickness variation, and an FIR low-pass filter is set. The fluctuations removed by the filter 2 (902) are mainly periodic fluctuations caused by the eccentricity of the driving roller 12, the rotating bodies (18a, 18b) of the transmission mechanism 18 and the encoder roller 14. When these periodic fluctuations are the same or have an integer ratio relationship, the filter 2 can be easily designed and can be removed more efficiently. In addition, when there is another roller on the transport path along which the belt is transported from the encoder roller 14 toward the drive roller 12, the rotary encoder also detects the fluctuation component generated in the rotation cycle due to the eccentricity of the roller. Is done. Similarly, when removing this fluctuation component by the filter 2, it is preferable that the rotation period is the same as the period fluctuation component of the drive roller 12 or an integer ratio.

  An example of the belt fluctuation component after passing through the filter 1 (901) and the filter 2 (902) is shown in FIG. The horizontal axis represents time, and the vertical axis represents the fluctuation value in rotation angle radians. Further, the belt conveyance speed is constant. Reference numeral 1001 denotes a belt fluctuation component that has not passed through the filter 1 (901) and the filter 2 (902). Reference numeral 1003 denotes the output timing (one belt cycle) of the belt virtual home position signal. As can be seen from FIG. 20, the belt fluctuation component 1002 that has passed through the filter 1 (901) and the filter 2 (902) has a smooth sine function from which noise has been removed.

  However, there are components that cannot be removed by the two filters. Examples of the component that cannot be removed include a DC component. As shown in FIG. 20, it can be seen that the belt fluctuation component 1002 that has passed through the two filters does not have a basic waveform with one cycle of the belt. That is, at the reference home position position 1003 (left side in FIG. 12), the belt fluctuation component 1002 removed by the two filters starts from 0 radians. However, the belt fluctuation component 1002 is not 0 radians at the next home position position (right side in FIG. 20) that is detected next and indicates one round of the belt. That is, this waveform shift amount (1004 in FIG. 20) is a DC component.

  This DC component is generated due to the difference in average speed due to steady slip and errors in the diameters of the drive roller 12 and encoder roller 14. The DC component is preferably removed because it affects subsequent amplitude and phase detection. The DC component removal 903 detects and removes this waveform shift amount.

  In addition, there are random fluctuation components such as random slips as fluctuation components that cannot be removed by the two filters. This random fluctuation component can be removed by a method generally called synchronous addition. Specifically, it is possible to remove the belt fluctuation component by sampling the belt fluctuation components for a plurality of belt rotations based on the belt home position and averaging the sampled data. That is, by adding and averaging the belt fluctuation components sampled for a plurality of rotations of the belt with the belt home position signal as a reference, the randomly generated fluctuation components are reduced, and the belt fluctuation components in one rotation cycle of the belt are emphasized. The This makes it possible to detect the amplitude and phase with higher accuracy. This synchronous addition process can be performed by the period variation sampler 805.

  The belt fluctuation component output from the comparator 804 passes through the filter unit 900, and fluctuation components other than the belt fluctuation component are removed and input to the periodic fluctuation sample unit 805. The belt fluctuation component of one belt cycle is stored in the memory. Is done.

  Further, the belt fluctuation component that has passed through the filter unit 900 may be downsampled and stored in the memory. Since the belt fluctuation component that has passed through the filter unit 900 is a smooth sine function, the amplitude and phase of the AC component corresponding to the belt thickness component can be accurately extracted even if downsampling is performed. In general, in order to detect a belt thickness period component per 0.2 Hz, sampling with a period of 10 times about 20 [Hz] is sufficient. Therefore, first, the output up to the output of the comparator is sampled with a short cycle of 100 [Hz] or more, and the detection is performed with high accuracy with little phase delay with respect to the fluctuation. Then, after filter processing is performed by the filter unit 900, the signal is downsampled to 20 [Hz] and output. Since the fluctuation component of the belt after passing through the filter unit 900 has a smooth sine waveform as shown in FIG. 20 from which other fluctuation components are removed, even if the data is saved by down-sampling, This waveform can be accurately reproduced. For this reason, the fluctuation amplitude / phase detection unit 806 can reduce the memory capacity used when detecting the amplitude and phase of the fundamental wave and harmonics of the belt cycle fluctuation component.

  In addition, as described above, sampling is performed with a short period of 100 [Hz] or more, and the belt fluctuation component sampled with this short period is filtered, so that even a low-resolution rotary encoder can perform periodic fluctuation with high accuracy. Can be detected. For example, even if the rotary encoder has a resolution of about 100 [μm] converted on the belt, sampling is performed at 500 [Hz] and the above filter processing is performed, thereby detecting a period variation with an accuracy of about several [μm]. It becomes possible.

  The filter 1 (901), filter 2 (902), and DC removal (903) of the filter unit 900 shown in FIG. 20 are processes added to detect angular velocity fluctuations and angular displacement fluctuations due to belt thickness fluctuations with high accuracy. It is possible to select which process to add depending on the relationship with the device used. Moreover, you may comprise by one filter which has the function of the filter 1 and the filter 2 together. Further, the filter is not limited to the FIR filter described above, and can be configured by a simple low-pass filter using a moving average.

  The target function calculation unit 607 includes the amplitude and phase numerical values of the fundamental and harmonic components of the belt thickness variation obtained by the belt cycle variation detection unit 608, the amplitude correction coefficient η of Equation 15 and the phase correction value T of Equation 16. Is used to calculate the target rotation fluctuation of the driven roller for keeping the belt conveyance speed constant. By changing the rotational angular velocity of the driven roller in the same manner as the target rotation variation calculated here, the belt conveyance speed can be made constant. This target rotation fluctuation is set every time a virtual home position signal is detected. In calculating the target rotation fluctuation, first, when a virtual home position signal is detected, time measurement is started. When the virtual home position signal is detected again, the time measurement is stopped. Using the measured time as one period (in the case of a fundamental wave) as a reference, the amplitude obtained by the belt period fluctuation detecting unit 608 is multiplied by an amplitude correction coefficient η to obtain a target rotation fluctuation (target function). Determine the amplitude value of. Further, with reference to a sine wave having the measured time as one period (in the case of a fundamental wave), a phase correction value T is added to the phase obtained by the belt period fluctuation detection unit 608 to obtain a target rotation fluctuation (target function). Determine the phase value of. Thereby, the target rotation fluctuation (target function) of the fundamental wave is generated. Similarly, with respect to the harmonic components, the amplitude obtained by the belt cycle fluctuation detection unit 608 is multiplied by the amplitude correction coefficient η based on the Sin wave having the measured time as n cycles, and the belt cycle fluctuation detection unit 608 is obtained. The phase correction value T is added to the phase obtained in (1) to generate a target rotation fluctuation (target function) of the harmonic component. Then, the target rotation fluctuation (target function) is generated by adding the target function of the fundamental wave and the target function of the harmonic component.

  So far, an example of calculating the target rotation fluctuation (target function) for each image formation has been described. Then, the numerical values may be stored in a table and read out every image formation.

The target reference signal generation unit 606 is a part that generates a reference signal, which is a control target value for comparison with an encoder output signal fed back by a comparator 605 to be described later, based on a target rotation fluctuation (target function). The reference signal generated by the target reference signal generation unit 606 differs depending on the output signal fed back from the encoder rotation detection unit 610.
FIG. 21 shows a target reference signal generation step when the encoder output signal fed back from the encoder rotation detection unit 610 to the comparator 605 is rotation angle displacement information. A graph 701 illustrated in FIG. 21 is a target rotation fluctuation (target function) of the encoder roller 14 output from the target function calculation unit 607. The target function is Expression 705. Expression 705 is the case of only the primary component (fundamental wave), and the amplitude is a1 and the phase is b1. ωb is the rotational angular velocity of the belt, and t represents the overtime after the belt virtual home position is detected. On the other hand, a graph 702 is an average target angular displacement and shows a desired movement of the belt. The slope of the graph 702 is the target average speed of the driven roller. Then, the target rotation fluctuation (target function) of the encoder roller 14 in the graph 701 and the average target angular displacement in the graph 702 are added by the adder 703, and a target reference signal shown in the graph 704 is generated. The vertical axis of each graph is displacement information, and here the rotation angle is radians. The horizontal axis is time. In the case of digital processing by the CPU or DSP, these are all handled as quantized discrete data, but are curved for explanation. If the target reference signal is only the average target angular displacement of the graph 702, it is not possible to appropriately control the amount of periodic fluctuation caused by belt thickness fluctuation. However, in the present embodiment, the target rotation fluctuation (target function) of the graph 701 calculated by the target function calculation unit 607 is combined with the average target angular displacement, and this combination is used as the target reference signal. Thereby, it is possible to control the belt to be conveyed at a constant speed even if the belt thickness varies. The same applies when the encoder output signal fed back from the encoder rotation detection unit 610 to the comparator 605 is rotation angular velocity information. That is, the average target angular displacement becomes the average target rotation angular velocity, and the target reference signal is generated by synthesizing the average target rotation angular velocity and the target rotation fluctuation (target function). At this time, the vertical axis of each graph is the speed information.

  The generation of the target signal as described above is also effective when the belt is intermittently fed as well as at a constant speed. If the target is to change the belt greatly instead of a constant speed (for example, acceleration or deceleration), the graph 702 indicating the average target angular displacement is not a straight line, but a graph in which the target motion is set is generated. Is done. By synthesizing the generated graph 702 and the target rotation fluctuation (target function) so as to coincide with each other, a target reference signal when the belt speed largely changes is generated.

  A difference between the target reference signal thus obtained and the encoder rotation detection signal fed back is calculated by the comparator 605, and the data is sent to the output control unit 604 of the motor driving unit 615. Then, the output is adjusted by the output control unit 604 according to the value, and the driving torque of the motor is adjusted. Thus, the belt can be conveyed at a desired speed.

  In the printer having the above basic configuration, the process units 6Y, M, C, and K for each color and the optical writing unit 7 are visible on the photoreceptors 1Y, 1M, 1C, and 1K for each color as an image carrier. It functions as a visible image forming means for forming Y, M, C, and K toner images. Further, the transfer unit 15 transfers a toner image carried on each of the plurality of photosensitive members by superimposing the toner image on an intermediate transfer belt 8 serving as a belt member that moves endlessly with the rotation of the driving roller 12. Is functioning.

  In this printer, when a monochrome image is output, image formation by the Y, M, and C process units 6Y, 6M, and 6C shown in FIG. 1 is not performed. Nevertheless, when they are driven, these members are wasted. In view of this, the printer supports three of 9Y, M, and C among the four primary transfer bias rollers 9Y, M, C, and K of the transfer unit 15 when outputting a monochrome image. The tension posture of the intermediate transfer belt 8 is changed by the swinging motion of the subframe. As a result, the intermediate transfer belt 8 is separated from the Y, M, and C photoconductors 1Y, 1M, and 1C. In such a configuration, the sub-frame swing mechanism and its drive system function as contact / separation means for contacting / separating the photoreceptors 1Y, 1M, and 1C, which are contact members that contact the intermediate transfer belt 8, with the intermediate transfer belt 8. is doing.

  In FIG. 3 shown above, the I / O unit 204 is connected to an image information input unit as image information acquisition means (not shown) for receiving image information sent from an external personal computer. The control unit 200 and the optical writing control circuit 205 drive the optical writing unit, process unit, transfer unit, and the like based on this image information to form an image. While forming an image in this manner, the control unit 200 grasps the timing of each rotation of the intermediate transfer belt 8 based on the above-described virtual home position, and at the same time per belt revolution. A speed fluctuation pattern update process for detecting the speed fluctuation pattern and updating the data of the speed fluctuation pattern in the periodic fluctuation sample unit 805 is performed.

Below, it demonstrates concretely based on FIG.
FIG. 22 is a sequence diagram when a color image is formed on four A3 sheets.
As shown in FIG. 22, when image information is sent from an external personal computer, the control unit 200 drives and rotates a rotating body in the process unit such as a photosensitive drum. Further, an encoder fed back with a target reference signal generated based on a target rotation fluctuation (target function) calculated from a speed fluctuation pattern detected during the previous image forming operation so that the intermediate transfer belt 8 rotates at a constant speed. The driving speed of the belt driving motor 162 is adjusted based on the output signal. Then, the motor (primary transfer contact / separation motor) of the contact / separation means is driven to swing the primary transfer bias rollers 9Y, 9M, 9C, thereby bringing the intermediate transfer belt 8 into contact with the photoreceptors 1Y, 1M, 1C. .

  When a color image is thus formed on the intermediate transfer belt 8, the optical writing unit, the process unit, etc. are driven based on this image information to start the image forming operation. At the same time, the speed variation pattern update process is performed. Specifically, a virtual home position signal is transmitted to detect a speed variation pattern per belt revolution. When the speed fluctuation pattern per belt revolution is detected, the speed fluctuation pattern data in the period fluctuation sample unit 805 is updated. When the speed fluctuation pattern data is updated, the speed fluctuation pattern update process is terminated, and a calculation process for calculating the target rotation fluctuation (the above graph 701) based on the updated speed fluctuation pattern is performed. Then, when the calculation process is executed and a new target rotation fluctuation is calculated, the drive speed is adjusted based on the target reference signal generated based on the newly calculated target rotation fluctuation.

  As shown in FIG. 22, when the image forming operation time is longer than the time required for the intermediate transfer belt 8 to make one revolution, the data of the speed variation pattern in the periodic variation sample unit 805 is updated during the image forming operation. A new target rotation fluctuation (target function) can be calculated. However, for example, when an image is formed on one sheet having a short length in the sheet conveyance direction, such as B5 sheet, the image forming operation time is shorter than the time for which the intermediate transfer belt 8 makes one turn. In such a case, since the speed fluctuation pattern per belt rotation cannot be detected, the speed fluctuation pattern data in the period fluctuation sample unit 805 is updated to obtain a new target rotation fluctuation (target function). It cannot be calculated. For this reason, when the image forming operation has been stopped for a long period of time, when the environment has changed significantly and the belt thickness has changed, only the operation in which the image forming operation time is short can be performed. The target rotation fluctuation (target function) is not updated, and the image disturbance caused by the fluctuation in the belt moving speed cannot be corrected.

  In particular, when the image forming operation time in the image forming operation for outputting only one A4 sheet of monochrome images that is frequently performed is shorter than the time for which the intermediate transfer belt 8 makes one turn, the target rotation fluctuation (target function) over a long period of time. May not be updated, and image distortion caused by fluctuations in the belt moving speed may not be corrected over a long period of time.

  Therefore, when the time for the image forming operation is shorter than the time for which the intermediate transfer belt 8 makes one rotation, the control unit 200 as the control unit performs an intermediate operation until the intermediate transfer belt 8 makes one rotation even after the image forming operation is completed. The transfer belt 8 is moved endlessly so that the speed variation pattern update process can be performed.

  FIG. 23 is a flowchart showing a control flow executed by the control unit 200. In the figure, when the control unit 200 receives image information sent from a personal computer or the like (YES in step 1; hereinafter, step is referred to as S), the image information (monochrome / color), the number of formed images, and the image The image forming time is calculated from the type of paper (size, paper thickness) forming the image, the image forming mode (high quality mode / speed priority mode performed at 1200 [dpi]), and the like, and the image forming operation time is calculated. As a result of the calculation, when the image forming operation time is longer than the time for which the intermediate transfer belt 8 makes one rotation (NO in S2), as described with reference to FIG. Perform update processing. When the image forming process is completed, the driving of each process such as the intermediate transfer belt 8 and the photosensitive member is stopped and the speed variation pattern update process is forcibly terminated (S3 to S5, S13).

  On the other hand, when the image forming operation time is shorter than the time for which the intermediate transfer belt 8 rotates once (YES in S2), the control unit 200 checks whether or not the requirement for executing the speed fluctuation pattern update process is provided. (S6). Specifically, if any one of requirement a to requirement g listed below is provided, control unit 200 determines that an implementation requirement for speed variation pattern update processing is provided.

[Requirement a]
As shown in FIG. 3, the printer has a temperature sensor 163 as environment detection means for detecting the in-machine temperature. Regarding the in-machine temperature obtained by the temperature sensor 163, if the temperature change amount from the previous speed fluctuation pattern update processing has reached a predetermined amount or exceeded the predetermined amount, the implementation requirement is satisfied. To be judged.

[Requirement b]
The control unit 200 has a timer circuit as a timer means (not shown) inside. When it is detected that the elapsed time from the previous speed fluctuation pattern update processing has reached a predetermined time or exceeds the predetermined time based on the time counting function of this time counting circuit, It is determined that

[Requirement c]
The control unit 200 increments the value of the counter for counting the number of rotations of the intermediate transfer belt stored in the RAM 200b by one each time the intermediate transfer belt makes one rotation. When it is detected that the value of the counter for counting the number of rotations of the intermediate transfer belt reaches a predetermined number (5 rotations in the present embodiment) or exceeds the predetermined number, the implementation requirement is satisfied. to decide. The count value is reset when it reaches a predetermined number. In addition, when the speed fluctuation pattern update process is performed, the control unit 200 is configured to reset the count value, and the number of intermediate transfer belt rotations reaches a predetermined number after the previous speed fluctuation pattern update process is performed. Or when it is detected that the predetermined number is exceeded, it may be determined that the implementation requirement is satisfied.

[Requirement d]
The control unit 200 increments the value of the counter for counting the number of image forming operations stored in the RAM 200b by one each time the image forming operation for one sheet of recording paper is completed. Further, when the speed fluctuation pattern update process is performed, the speed fluctuation pattern update process accumulated operation count stored in the RAM 200b is updated to the same value as the count value at that time. The difference between the counter value for counting the number of image forming operations and the accumulated number of times of speed fluctuation pattern update processing, that is, the number of increases in the number of image forming operations since the previous execution of the speed variation pattern update processing is predetermined. When it is detected that the number has reached or exceeded the predetermined number, it is determined that the implementation requirements are satisfied.

[Requirement e]
The control unit 200 sets a start flag when the apparatus is turned on, and when the start flag is set when determining whether or not the execution requirement of the speed variation pattern update process is satisfied, that is, If the image forming operation to be performed from now is the first image forming operation after the power of the apparatus is turned on, it is determined that the implementation requirements are satisfied. This activation flag is deleted after the first image forming process is completed after the apparatus is turned on.

[Requirement f]
The control unit 200 sets an exchange flag when the transfer unit including the intermediate transfer belt 8 is exchanged, and sets the exchange flag when determining whether or not the requirement for performing the speed variation pattern update process is satisfied. In this case, that is, when the image forming operation to be performed is the first image forming operation after the intermediate transfer belt 8 is replaced, it is determined that the implementation requirements are satisfied. The replacement flag is deleted after the first image forming process after the transfer unit is replaced. The replacement detection means for detecting whether or not the transfer unit has been replaced includes, for example, a push switch provided in the apparatus main body and a push means for pressing the switch provided in the transfer unit. When the transfer unit is mounted in the apparatus main body, the switch is turned on by pressing the switch with the push means. When the transfer unit is removed from the apparatus main body to replace the transfer unit, the push means is separated from the switch, the switch is turned off, and it is detected that the transfer unit has been replaced.

[Requirement g]
Based on the timing function of the timing circuit, the control unit 200 determines that the implementation requirement has been satisfied when it has detected that the elapsed time from the previous image forming operation has reached or exceeded the predetermined time. To do.

  If the control unit 200 does not have any of the requirements a to g (NO in S6), the control unit 200 performs only the image forming process without performing the speed variation pattern update process (S7). , S8, S13).

  On the other hand, if any one of the above requirements a to g is satisfied (YES in S6), as shown in the sequence diagram of FIG. Until the operation is completed, the photoconductor and the intermediate transfer belt 8 are driven without being stopped. Then, when the speed variation pattern update process is finished, the driving of each process is stopped and the process is finished (S9 to S13).

  As described above, even when the time for the image forming operation is shorter than the time for which the intermediate transfer belt 8 makes one rotation, the speed variation pattern update process can be performed, so that the image forming operation that makes the intermediate transfer belt 8 make one rotation can be performed. Even if it is not performed, the speed variation pattern update process can be performed. Therefore, it is possible to prevent the image from being disturbed due to the speed fluctuation of the intermediate transfer belt 8 over a long period of time without performing the speed fluctuation pattern update process over a long period of time despite the image forming operation being performed. . Further, only when the requirement for performing the speed fluctuation pattern update process is provided, even if the image forming process is completed, the intermediate transfer belt 8 is rotated to detect the speed fluctuation pattern around the intermediate transfer belt 81. By doing so, it is possible to always suppress wear of the photosensitive member and the intermediate transfer belt 8 as compared with the case where the speed fluctuation pattern update process is performed.

  In FIG. 23, before the image forming process, it is determined whether or not the image forming operation time is longer than the rotation time of the intermediate transfer belt 81 and whether or not the requirement for executing the speed variation pattern update process is provided. However, at least when the image forming process ends, the above-described process may be completed. Therefore, before the image forming process, it is determined whether the image forming operation time is longer than the rotation time of the intermediate transfer belt 81 and whether or not the speed fluctuation pattern update process execution requirement is satisfied. It may be done at the end.

FIG. 25 is a flowchart showing a control flow when it is determined whether or not the speed variation pattern update process execution requirement is provided at the end of the image forming process.
As shown in the figure, when image information sent from a personal computer or the like is received (YES in S21), an image forming process is started and a speed variation pattern update process is started (S22, S23). If belt speed fluctuation can be detected during the image forming process, an update flag is set, and at the end of image formation, it is detected whether or not this update flag is set, and the speed fluctuation pattern update process is performed at least once. It is detected whether it is executed (S25). If the update flag is set (YES in S25), the speed variation pattern update process has been executed at least once, so the update flag is turned off and the driving of each process is stopped (S27) and the process is terminated.

  On the other hand, when the update flag is not raised, that is, when the speed fluctuation pattern update process has never been completed (NO in S25), is the above-described requirement for executing the speed fluctuation pattern update process a to g satisfied? It is checked whether or not (S26). If the control unit 200 does not have any of the requirements a to g (NO in S26), the control unit 200 forcibly terminates the speed variation pattern update process and stops driving each process (S27).

  On the other hand, if any of the requirements a to g is satisfied (YES in S26), the process driving of the photosensitive member, the intermediate transfer belt 8, and the like is stopped until the speed variation pattern update process is completed. Drive without. Then, when the speed variation pattern update process is finished, the driving of each process is stopped and the process is finished.

  Further, in the above description, only when the execution requirements for the speed fluctuation pattern update process are satisfied, even if the image forming process is completed, the intermediate transfer belt 8 is rotated so that the speed fluctuation pattern per circumference of the intermediate transfer belt 81 is changed. Although the detection is performed, when the image forming process is performed, the speed variation pattern may be updated regardless of whether or not the requirement for performing the speed variation pattern update process is provided. . With this configuration, it is not necessary to determine whether or not the requirement for performing the speed variation pattern update process is provided, and the control can be simplified.

  In addition, when the execution requirement for the speed fluctuation pattern update process is not provided, the speed fluctuation pattern update process is not performed regardless of whether the image forming operation time is shorter than the rotation time of the intermediate transfer belt 81 or not. Also good.

  In this printer, as the intermediate transfer belt 8, an inexpensive one manufactured by a centrifugal molding method is used. In the centrifugal molding method, it is a limit that the thickness deviation in the circumferential direction of the belt is limited to about 3 [μm]. However, even with such an intermediate transfer belt 8, the belt is driven at a stable speed by feedback control of the belt drive motor. Can be moved.

  Further, in this printer, the Young's modulus of the intermediate transfer belt 8 is 5000 [MPa] or less for the purpose of improving the adhesion to the photoreceptor and the recording paper and realizing good primary transfer and secondary transfer. A relatively soft material is used. Such a belt has a relatively large amount of change in thickness due to temperature change. However, by detecting and updating the belt speed fluctuation pattern for each turn, the intermediate transfer belt 8 can be moved regardless of the belt thickness fluctuation. It can be moved at a stable speed.

  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, the image forming apparatus of the present embodiment includes a photoconductor that is an image carrier that carries a visible image, an image information input unit that is an image information acquisition unit that acquires image information of a visible image formed on the photoconductor, And an optical writing unit (7) for forming a visible image based on the image information on the photosensitive member, and an image forming device as a visible image forming means including process units (6Y, M, C, K) for each color. Yes. In addition, the intermediate transfer belt 8 that is an endless belt member that is endlessly moved while being stretched around a driving roller and a driven roller, or a recording sheet that is a recording member that is held on the surface of a paper conveyance belt that is a belt member is photosensitive. A transfer unit 15 serving as transfer means for transferring a visible image carried on the body is provided. Further, an encoder 170 as a driven roller rotation detecting means for detecting the rotation angular velocity or rotation angle displacement of the driven roller, a motor drive unit 615 or a rotary encoder as a driving roller rotation detecting means for detecting the rotation angular speed or rotation angle displacement of the driving roller, It has. Further, the driving angular velocity of the belt driving motor as the driving source of the driving roller based on the encoder rotation detection signal as the detection result by the encoder 170 and the data of the speed fluctuation pattern per one rotation of the belt member stored in the memory as the storing means. Or the control part 200 which is a control means which implements the drive adjustment process which adjusts a drive angular displacement is provided. The control unit 200 also detects an encoder rotation detection signal for one rotation of the belt member detected during the image forming operation for forming a visible image based on the image information, and a drive input signal as a detection result of the drive roller rotation detection unit. A speed fluctuation pattern update process is performed in which a speed fluctuation pattern is detected based on the calculated difference value, and data stored in the storage unit is updated based on the detection result. In addition, when the time for the image forming operation is shorter than the time for which the belt member makes one rotation, the control unit updates the speed fluctuation pattern by moving the belt member endlessly until the belt member makes one rotation even after the image forming operation is completed. Control so that processing can be performed. As a result, even when the time of the image forming operation is shorter than the time for which the belt member makes one rotation, the speed fluctuation pattern update process can be performed. Therefore, even if the image forming operation that makes the belt member make one rotation is not performed. The speed variation pattern update process can be performed. Further, since the speed variation pattern update process can be performed during the image forming operation, it is possible to prevent the user from waiting.

  Further, the control unit 200 determines whether or not the requirement for performing the speed fluctuation pattern update process is provided before the image forming operation is completed. Control is performed so that the intermediate transfer belt 8 is moved endlessly until the transfer belt 8 rotates once. As a result, when the speed fluctuation pattern update process is not necessary, the driving of the intermediate transfer belt 8 can be stopped when the image forming operation is completed, so that unnecessary driving of the intermediate transfer belt 8 can be prevented, and the intermediate transfer belt 8 can be prevented. Wear of the belt 8 and the photosensitive member can be suppressed.

  Further, when the control unit 200 detects that the elapsed time from the previous image forming operation has reached a predetermined time or exceeded the predetermined time based on the clocking function of the clocking circuit as the clocking means, Judge that the requirements are met. With this configuration, when there is a high possibility that the thickness of the intermediate transfer belt 8 has changed due to environmental changes or wrinkles on the belt due to the image forming operation being stopped for a long period of time, the speed fluctuation pattern update process is performed. It is possible to suppress the occurrence of image disturbance due to the speed fluctuation of the intermediate transfer belt 8 during the next image forming operation.

  In addition, when the control unit 200 detects that the elapsed time from the previous execution of the speed variation pattern update process has reached or exceeded the predetermined time based on the clocking function of the clocking circuit, Judge that the implementation requirements were met. In this configuration, when there is a high possibility that the thickness of the intermediate transfer belt 8 has changed due to environmental changes or the like, the speed fluctuation pattern update process can be performed, and image disturbance due to the speed fluctuation of the intermediate transfer belt 8 can be prevented from occurring in the next image. It is possible to suppress the occurrence during the forming operation.

  Further, based on a counter serving as a counting unit that counts the number of rotations of the intermediate transfer belt 8, the control unit 200 determines the speed when the number of rotations of the intermediate transfer belt 8 reaches a predetermined number or exceeds a predetermined number. It is determined that the implementation requirements for the variation pattern update process are provided. Even in such a configuration, when there is a high possibility that the thickness of the intermediate transfer belt 8 has changed with the extension of the intermediate transfer belt 8, the speed fluctuation pattern update process can be performed, and the image due to the speed fluctuation of the intermediate transfer belt 8 can be performed. Can be prevented from occurring during the next image forming operation.

  Further, as described above, the belt virtual home position signal obtains one cycle of the belt from the signal generated based on the cumulative rotation angle of the motor, the cumulative rotation angle of the rotary encoder, and the set belt rotation cycle clock. However, an error may occur between the actual belt period and the belt period obtained from the belt virtual home position signal due to component accuracy such as an error in the roller diameter. For example, when the virtual home position signal is output every 6 seconds while the actual belt rotates at a cycle of 6.1 seconds, an error of 0.1 seconds is accumulated for each lap. As a result, when feedback control is performed, the position of the reference virtual home position and the reference virtual home position when updating the speed fluctuation pattern are shifted every belt rotation cycle, and the above speed pattern is used. Accurate feedback control will not be possible. However, as described above, when the number of rotations of the intermediate transfer belt 8 reaches a predetermined number (5 rotations in the present embodiment) or exceeds the predetermined number, the speed fluctuation pattern update process is performed, whereby the belt It is possible to reset the accumulated phase shift every round.

  In particular, if the number of rotations of the intermediate transfer belt has reached a predetermined number or exceeded the predetermined number since the previous speed fluctuation pattern update process, it is determined that the requirements for executing the speed fluctuation pattern update process are satisfied. If the control unit 200 is configured as described above, it is possible to reduce the number of times the speed variation pattern update process is performed, and it is possible to suppress wear of the intermediate transfer belt 8 and the photoconductor.

  Further, the control unit 200 determines whether the number of image forming operations increased from the previous execution of the speed fluctuation pattern update process reaches a predetermined number based on a counter serving as a counting unit that counts the number of image forming operations. If the number exceeds the number, it is determined that the requirement for performing the speed variation pattern update process is satisfied. Even in such a configuration, when there is a high possibility that the thickness of the intermediate transfer belt 8 has changed with the extension of the intermediate transfer belt 8, the speed fluctuation pattern update process can be performed, and the image due to the speed fluctuation of the intermediate transfer belt 8 can be performed. Can be prevented from occurring during the next image forming operation.

  In addition, the control unit 200, based on the temperature sensor 163 serving as an environment detection unit for detecting the environment, has reached a predetermined amount or exceeded a predetermined amount since the previous speed variation pattern update process was performed. If this is detected, it is determined that the requirement for performing the speed variation pattern update process is provided. In such a configuration, when there is a high possibility that the thickness of the intermediate transfer belt 8 has changed due to a temperature change, the speed fluctuation pattern update process can be performed, and image disturbance due to the speed fluctuation of the intermediate transfer belt 8 can be prevented as follows. It is possible to suppress the occurrence of the image forming operation.

  In addition, when the replacement detection unit that detects replacement of the intermediate transfer belt 8 detects that the intermediate transfer belt 8 has been replaced, is the first image forming operation, the control unit 200 updates the speed variation pattern. It is judged that the implementation requirements are satisfied. In such a configuration, when the thickness of the intermediate transfer belt 8 changes as the intermediate transfer belt 8 is replaced, the speed fluctuation pattern update process can be performed. It is possible to suppress the occurrence of the image forming operation.

  In addition, when the image forming operation is the first image forming operation after the power of the apparatus is turned on, the control unit 200 determines that the implementation requirement is satisfied. Even in such a configuration, when there is a high possibility that the image forming operation is stopped for a long period of time and the environmental change or the intermediate transfer belt 8 is wrinkled and the thickness of the intermediate transfer belt 8 is changed, the speed fluctuation pattern update process is performed. It is possible to suppress the occurrence of image disturbance due to the speed fluctuation of the intermediate transfer belt 8 during the next image forming operation.

  In addition, the control unit 200 determines whether the time for the image forming operation is shorter than the time for which the intermediate transfer belt 8 rotates once based on the length of the recording paper in the conveyance direction and the number of recording papers on which the visible image is recorded. By determining whether or not, it is possible to accurately determine whether or not the time for the image forming operation is shorter than the time for which the intermediate transfer belt 8 rotates once.

  In the image forming apparatus according to the embodiment, an intermediate transfer belt 8 having a thickness deviation in the circumferential direction of 3 [μm] or more in an environment of 25 [° C.] is used. In such a configuration, even if an intermediate transfer belt 8 using an inexpensive centrifugal molding method is used, the belt can be moved at a stable speed.

  In the printer according to the embodiment, the intermediate transfer belt 8 having a circumferential Young's modulus of 5000 [MPa] or less is used. In such a configuration, the adhesion between each photoconductor and the belt and the adhesion between the recording paper and the belt are improved, and the intermediate transfer belt 8 is stabilized while forming a good image free from transfer omission and transfer failure. Can move at speed.

  In addition, a plurality of photoconductors are provided, an image forming device is configured to form a visible image on each of the photoconductors, and a transfer unit is configured to superimpose and transfer the visible images respectively carried on the photoconductors. Thus, a color image can be formed.

  Also, a plurality of photoconductors are arranged side by side in the conveyance direction of the intermediate transfer belt 8, and a transfer unit is transferred onto the intermediate transfer belt 8 by superimposing the visible images carried on the respective photoconductors, and then onto the recording paper. In the one configured to perform batch transfer, the control unit is configured to determine whether the time of the image forming operation is shorter than the time for one rotation of the intermediate transfer belt 8 based on the photosensitive member used at the time of image formation. Configured. The distance conveyed by the intermediate transfer belt 8 after the image formed on the photosensitive member is transferred to the intermediate transfer belt 8 until the image is secondarily transferred to the recording paper varies depending on the arrangement position of the photosensitive member. That is, the image formed by the photoconductor disposed on the upstream side in the moving direction of the intermediate transfer belt 8 has a longer time until the secondary transfer, and the image formation end time becomes longer. Accordingly, when an image is formed using the photoconductor disposed on the most upstream side in the moving direction of the intermediate transfer belt 8, the intermediate transfer belt 8 rotates once when the image forming operation is completed. When an image is formed using only the photoconductor disposed on the most downstream side in the moving direction of the belt 8, the intermediate transfer belt 8 may not be rotated once when the image forming operation is completed. Therefore, by configuring the control unit to determine whether the time of the image forming operation is shorter than the time for which the intermediate transfer belt 8 makes one rotation based on the photosensitive member used at the time of image formation, It is possible to accurately determine whether or not the time for the forming operation is shorter than the time for which the intermediate transfer belt 8 rotates once.

  Further, the control unit is configured to determine whether the time of the image forming operation is shorter than the time for which the intermediate transfer belt 8 rotates once based on the image information acquired by the image information input unit. For example, in the case of a color image, four color toner images of Y, M, C, and K are formed and superimposed on the recording paper, so that the image formation time is longer than that of a monochrome image such as a monochrome image. . Therefore, based on the image information acquired by the image information input unit, based on the image information such as a color image or a monochrome image, whether the time for the image forming operation is shorter than the time for which the intermediate transfer belt 8 makes one rotation. By configuring the control unit so as to determine whether or not, it is possible to accurately determine whether or not the time for the image forming operation is shorter than the time for which the intermediate transfer belt 8 rotates once.

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. 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. Timing chart showing generation timing of latent image writing clock when optical writing start timing is corrected in sub-scanning direction 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 schematic cross-sectional view showing a main part of the intermediate transfer belt. The graph which shows an example of the belt thickness fluctuation | variation (belt thickness deviation distribution) in the circumferential direction of a belt. (A) shows the belt speed relationship A at each belt position when the roller is rotating at a constant rotational angular speed, and the roller rotation at each belt position when the belt is rotating at a constant speed. The graph which showed the relationship B of angular velocity. (B) shows the relationship between the speed of the driving roller and the speed of the intermediate transfer belt when the encoder roller and the driving roller are separated by τ, and the speed of the encoder roller when the thickness of the intermediate transfer belt varies. And a graph showing the relationship between the speed of the intermediate transfer belt. The schematic diagram which shows the phase vector component of A, B, and C. FIG. The block diagram which shows the electric circuit of the belt drive control system in the control part. The block diagram which shows the same control part at the time of setting a belt drive motor as a stepping motor or a vibration wave motor. The block diagram which shows the circuit structure of the belt period fluctuation | variation detection part of the control part. The block diagram which shows the circuit structure of the belt fluctuation | variation detection part provided with the filter part. The graph which shows the fluctuation component of the belt after passing a filter part. The graph which shows the production | generation process of the target reference signal in case the encoder output signal fed back from an encoder rotation detection part to a comparator is rotation angle displacement information. FIG. 4 is a sequence diagram when forming a color image on four A3 sheets. The flowchart which shows the control flow implemented by the control part. FIG. 4 is a sequence diagram when a monochrome image is formed on one A4 sheet. 6 is a flowchart showing a control flow when it is determined whether or not a speed variation pattern update process execution requirement is provided at the end of the image forming process.

Explanation of symbols

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 means)
170: Encoder (Rotation speed detection means)
200: Control unit (control means)

Claims (16)

An image carrier for carrying a visible image;
Image information acquisition means for acquiring image information of a visible image formed on the image carrier;
Visible image forming means for forming a visible image based on the image information on the image carrier;
A visible image carried on the image carrier is transferred to an endless belt member that is endlessly moved while being stretched around a driving roller and a driven roller, or a recording member that is held on the surface of the belt member. Transcription means;
Driven roller rotation detecting means for detecting a rotation angular velocity or a rotation angle displacement of the driven roller;
Drive roller rotation detection means for detecting the rotation angular velocity or rotation angle displacement of the drive roller;
The drive angular velocity or the drive angular displacement of the drive source of the drive roller is adjusted based on the detection result by the driven roller rotation detection means and the data of the speed fluctuation pattern per circumference of the belt member stored in the storage means. The detection result of the driven roller rotation detecting means for one rotation of the belt member detected during the image forming operation for performing drive adjustment processing or forming a visible image based on the image information, and the driving roller rotation detection A speed fluctuation pattern update process that calculates a difference value with the detection result of the means, detects the speed fluctuation pattern based on the calculated difference value, and updates the data stored in the storage means based on the detection result In an image forming apparatus provided with a control means for performing
When the time of the image forming operation is shorter than the time of one rotation of the belt member, the belt member is moved endlessly until the belt member makes one rotation after the image forming operation is completed, and the speed variation pattern is updated. An image forming apparatus characterized in that the control means is configured so that processing can be performed. The image forming apparatus according to claim 2.
Before or at the end of the image forming operation, it is determined whether or not the requirements for execution of the speed variation pattern update process are satisfied. If it is included, the belt member after the image forming operation is completed. An image forming apparatus characterized in that the control means is configured to move the belt member endlessly until one rotation is made. The image forming apparatus according to claim 2.
The above control is provided so as to determine that the implementation requirement has been provided based on the fact that the time measuring means for measuring time is provided and the elapsed time from the previous image forming operation has reached or exceeded the predetermined time. An image forming apparatus comprising a means. The image forming apparatus according to claim 2 or 3,
It is determined that the implementation requirement has been provided based on the fact that a time measuring means for measuring time is provided and the elapsed time from the previous execution of the speed fluctuation pattern update processing has reached or exceeded the predetermined time. An image forming apparatus comprising the control unit as described above. The image forming apparatus according to claim 2,
A counting means for counting the number of rotations of the belt member is provided, and it is determined that the implementation requirement is satisfied based on whether the number of rotations of the belt member reaches a predetermined number or exceeds a predetermined number. An image forming apparatus comprising the control means. The image forming apparatus according to claim 5.
Based on the fact that the number of rotations of the belt member since the previous execution of the speed fluctuation pattern update process has reached a predetermined number or exceeded a predetermined number, it is determined that the execution requirement is provided, An image forming apparatus comprising a control means. The image forming apparatus according to any one of claims 2 to 6,
A counting means for counting the number of image forming operations is provided, and the increase in the number of image forming operations since the previous execution of the speed variation pattern update process has reached or exceeded a predetermined number. The image forming apparatus is characterized in that the control means is configured to determine that the implementation requirement is satisfied. The image forming apparatus according to any one of claims 2 to 7,
An environment detecting means for detecting the environment is provided, and the implementation requirement is based on whether the amount of change in the environment from the previous execution of the speed fluctuation pattern update process reaches a predetermined amount or exceeds a predetermined amount. An image forming apparatus, characterized in that the control means is configured to determine that it is provided. The image forming apparatus according to any one of claims 2 to 8,
When the replacement detection means for detecting replacement of the belt member is provided, and the image forming operation is the first image forming operation after the replacement detection means detects that the belt member has been replaced, An image forming apparatus, characterized in that the control means is configured to determine that the requirement is satisfied. The image forming apparatus according to any one of claims 2 to 9,
An image forming apparatus comprising: the control unit configured to determine that the execution requirement is satisfied when the image forming operation is an initial image forming operation after the apparatus is turned on. The image forming apparatus according to claim 1,
Based on the length of the recording member in the conveying direction and the number of recording members that record a visible image, the image forming mode, and the paper type, the time for the image forming operation is shorter than the time for the belt member to make one revolution. An image forming apparatus characterized in that the control means is configured to determine whether or not. The image forming apparatus according to claim 1,
An image forming apparatus using the belt member having a thickness deviation of 3 [μm] or more in an environment of 25 [° C.] in a circumferential direction. The image forming apparatus according to any one of claims 1 to 12,
An image forming apparatus using the belt member having a Young's modulus in the circumferential direction of 5000 [MPa] or less. The image forming apparatus according to claim 1.
A plurality of the image carrier,
The visible image forming means is configured to form a visible image on each of the image carriers,
An image forming apparatus, wherein the transfer means is configured to superimpose and transfer the visible images respectively carried on the image carriers. The image forming apparatus according to claim 14.
The plurality of image carriers are arranged side by side in the conveying direction of the belt member, and the transfer means superimposes the visible images carried on the respective image carriers and transfers them to the belt member, and then onto the recording member. In what is configured to batch transfer,
The control means is configured to determine whether or not the time for the image forming operation is shorter than the time for the belt member to make one rotation based on an image carrier used for image formation. Image forming apparatus. The image forming apparatus according to claim 1,
The control means is configured to determine whether the time of the image forming operation is shorter than the time for the belt member to make one rotation based on the image information acquired by the image information acquisition means. An image forming apparatus.

Images