JP2006058344A - Drive control unit of endless belt - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drive control unit of an endless belt in an image forming apparatus with which the control to stabilize a speed fluctuation generated by a belt thickness can be appropriately performed by an inexpensive technique. <P>SOLUTION: The drive control unit of the endless belt is equipped with a mark 304 which is a reference position of the endless belt 60, a detecting means 305 for detecting the mark, a nonvolatile memory for storing the phase, maximum, amplitude and period of the mark which are the reference position of the thickness profile of the endless belt, and a means for developing and generating the thickness profile of the endless belt based on the value stored in the nonvolatile memory, and storing the data in the nonvolatile memory. The speed fluctuation due to the belt thickness is stabilized by referring to the profile data stored in the nonvolatile memory according to the distance from the belt mark when driving the belt and adding the data to a control target value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an apparatus capable of forming a color image and an endless belt drive control apparatus that can be used in a transfer device used in the image forming apparatus.

  In an image forming apparatus, for example, in Patent Document 1, when a driving roller is driven at a constant pulse rate, it is generated by a known thickness profile over the entire circumference of a transfer belt with reference to a position detected by a belt mark. A speed profile that cancels out the speed fluctuation Vh that would occur is measured in advance, a drive motor control signal is generated at a modulated pulse rate, and the motor is driven on the basis of the drive motor control signal. A technique is disclosed in which the final transfer belt speed Vb does not vary by driving the transfer belt.

JP 2000-310897 A

Representative methods of color image formation include a direct transfer method in which toner images of different colors formed on a plurality of photoconductors are transferred while being superimposed directly on a transfer sheet, and toners of different colors formed on a plurality of photoconductors. There is an intermediate transfer method in which an image is transferred while being superimposed on an intermediate transfer member, and then transferred onto a transfer sheet at once. Since a plurality of photoconductors are arranged side by side facing a transfer paper or intermediate transfer body, this is called a tandem method, and yellow (Y), magenta (M), cyan (C), and black (K) for each photoconductor. For each color, an electrophotographic process such as formation and development of an electrostatic latent image is performed, and the image is transferred onto a running transfer sheet in the direct transfer method, or onto a running intermediate transfer member in the intermediate transfer method.

  In the tandem color image forming apparatus using each of these methods, the direct transfer method receives an endless belt that runs while supporting transfer paper, and the intermediate transfer method receives an image from a photoconductor. Generally, an endless belt to be carried is employed. Then, an image forming unit including four photoconductors is arranged side by side on one running side of the belt.

  In the tandem color image forming apparatus, it is important to prevent the occurrence of color misregistration by accurately superimposing the toner images of the respective colors. For this reason, in any transfer system, in order to avoid color misregistration due to transfer belt speed fluctuation, an encoder is attached to one of the driven shafts composed of a plurality of transfer units, and the transfer speed varies depending on the encoder rotation speed fluctuation. Thus, feedback control of the rotational speed of the drive roller is an effective means.

  The most common method for realizing feedback control is proportional control (PI control). This detects a difference e (i) between the target angular displacement Ref (i) of the encoder and the detected angular displacement P (i-1) of the encoder, and applies a low-pass filter to the detection result to remove high frequency noise. By controlling the drive pulse frequency of the drive motor connected to the drive roller by adding a constant standard drive pulse frequency by applying a control gain, the encoder output is always controlled to be driven at the target angular displacement. Is the method.

  As actual control, a counter that counts the rising edge of the A-phase output of the encoder pulse and a counter that counts every control cycle (for example, 1 ms) are used, and the target angular displacement moving during the control cycle (1 ms) is detected. The position deviation can be acquired from the difference between the calculation result and the detected angular displacement obtained by acquiring the encoder count value for each control period.

  The specific calculation is as follows when the roller diameter of the driven shaft to which the encoder is attached is φ15.615.

  Here, for example, assuming that the control resolution is 300 ms and the encoder resolution is 300 pulses per revolution, and the feedback control is performed so that the transfer belt operates at 162 mm / s, the following is assumed.

  A position deviation is acquired by performing the above calculation for every control period, and feedback control is performed.

  However, in this method, the transfer speed of the transfer paper changes depending on the thickness of the minute transport belt, and the image quality deteriorates that the image deviates from the ideal position. There is a problem that the reproducibility of the repetitive position between recording sheets deteriorates.

  Assuming that the conveyance speed is determined at the center of the belt thickness at the belt drive position, the belt conveyance speed V is expressed by the following equation (1).

  However, when the belt thickness B varies, the position of the belt thickness effective line shown in FIG. 20 changes. This is because the belt driving effective radius is changed, and (R + B / 2) in the equation (1) is changed, so that it is understood that the belt conveying speed is changed even when the driving roller angular velocity ω is constant. That is, even if the driving roller is rotated at a constant angular velocity, the belt conveyance speed changes if there is a belt thickness variation.

  FIG. 21 shows a model of the belt drive conveyance system.

  First, FIG. 22 conceptually shows belt thickness fluctuations and belt conveyance speed fluctuations over one round of the belt when the drive shaft is rotated at a constant angular velocity.

  When a thick portion of the belt is wound around the drive shaft, the belt drive effective radius shown in FIG. 20 increases and the belt conveyance speed increases. On the contrary, when the thin part of the belt is wound around the drive shaft, the belt conveyance speed is reduced.

  Next, FIG. 23 shows the belt thickness fluctuation on the driven shaft and the belt conveyance speed fluctuation detected on the driven shaft when the belt is being conveyed at a constant conveyance speed. Even if the belt is conveyed ideally without speed fluctuation, if the thick part of the belt is wound around the driven shaft, the effective driven radius of the belt increases and the rotational angular velocity of the driven shaft decreases. This is detected as a decrease in belt conveyance speed. When the thin part of the belt is wound, the rotational angular velocity of the driven shaft increases and is detected as an increase in the belt conveyance speed.

  In this way, when there is a belt thickness variation, if the belt conveyance speed (position) is detected by the rotational angular velocity (displacement) of the driven shaft with an encoder or the like, a false detection component occurs. Therefore, even if the belt is conveyed at a constant speed, the rotational angular speed detection of the driven shaft is detected as if the belt is fluctuating due to fluctuations in the belt thickness. For this reason, belt thickness variation cannot be controlled by conventional driven shaft feedback control.

  A technique for solving such belt thickness fluctuation is described in Patent Document 1 described above. The feature of Patent Document 1 is that the speed that would be generated by a known thickness profile over the entire circumference of the transfer belt with reference to the position detected by the belt mark when driving the drive roller at a constant pulse rate. A speed profile that cancels the fluctuation Vh is measured in advance, and a drive motor control signal is generated at a modulated pulse rate. The motor is driven based on this, and the transfer belt is driven via the drive roller. By doing so, the final transfer belt speed Vb does not fluctuate.

  However, at this time, since the speed profile data requires data for each control cycle, a large-capacity memory is required when the control cycle is performed in a short cycle, and when the control cycle is set to a long cycle, feedback control itself is performed. There is a problem that a sufficient effect cannot be obtained. For example, when the belt circumferential length is 815 mm, the belt driving speed is 125 mm / s, and the control cycle is 1 ms, the control is executed 6520 times per belt circumference as follows.

815mm / (125mm / s × 1ms) = 6520 times Also, if the data size of the belt thickness per point is expressed in 16 bits, a memory of 100 Kbit or more is required as shown below.

6520 times × 16bit = 104320 bit
Therefore, when performing the above control with an actual machine, it is necessary to newly prepare a memory for storing the belt thickness profile as a non-volatile memory. Even if it is stored as compressed data and decompressed to a volatile memory when the power is turned on, A large capacity memory is required. Therefore, in addition to the memory used as a normal work area, a separate memory is required, which greatly increases the cost and is not realistic.

  The present invention has been made paying attention to the above circumstances, and the object of the present invention is to appropriately perform control for stabilizing speed fluctuations caused by the belt thickness by an inexpensive method and according to image quality. Another object of the present invention is to provide an endless belt drive control device in an image forming apparatus.

  In order to solve the above-mentioned problem, the invention described in claim 1 is an endless belt, a driving roller for driving the endless belt, a driving motor for driving the driving roller, and a plurality of driven rollers driven by the endless belt. In an endless belt drive control device that attaches an encoder to one of the driven rollers and feedback-controls the endless belt based on the signal, a mark serving as a reference position of the endless belt, and for detecting the mark Mark detecting means, a non-volatile memory for storing a phase, a maximum amplitude and a period at the mark serving as the reference position of the thickness profile of the endless belt, and an endless belt based on a value stored in the non-volatile memory. Develop thickness profile and store the data in volatile memory Step speed is stabilized by referring to profile data stored in the volatile memory according to the distance from the belt mark when driving the endless belt, and adding it to the control target value. It is characterized by becoming.

  According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the phase, amplitude, and period values stored in the nonvolatile memory are developed in the volatile memory. It is executed at the time of turning on the power source or starting the driving of the endless belt.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the belt uses a Sin function from the phase, amplitude, and period values stored in the nonvolatile memory. It is characterized by calculating data according to the arrival position.

  According to a fourth aspect of the present invention, when the thickness profile of the endless belt is developed and stored in the volatile memory in the first aspect of the present invention described in any one of the first to third aspects, The memory capacity of the volatile memory is reduced by thinning and storing the data.

  Further, the invention described in claim 5 is the invention described in claim 4, wherein the volatile memory has a plurality of storage areas, and the thickness profile data of the endless belt having different thinning-out numbers is stored in each area. It is characterized by that.

  The invention described in claim 6 is stored in the volatile memory according to the distance from the belt mark when driving the endless belt in the invention described in claim 4 or 5. When referring to the profile data, the reference area of the volatile memory is switched according to the image quality.

  According to the drive control device for an endless belt of the present invention, it is possible to appropriately perform the control for stabilizing the speed fluctuation caused by the belt thickness by an inexpensive method and according to the image quality.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  First, an embodiment in which the present invention is applied to an electrophotographic direct color transfer color laser printer (hereinafter referred to as “laser printer”) as an image forming apparatus will be described with reference to FIGS.

  FIG. 1 is a schematic configuration diagram of a laser printer according to the present embodiment. This laser printer includes four toner image forming units 1Y, 1M, 1C, and 1K (hereinafter referred to as “yellow” (Y), magenta (M), cyan (C), and black (K)). The subscripts Y, M, C, and K of the reference numerals indicate yellow, magenta, cyan, and black members, respectively, and the direction of movement of the transfer paper 100 (the belt 60 along the arrow A in the figure). In the traveling direction) from the upstream side. Each of the toner image forming units 1Y, 1M, 1C, and 1K includes photosensitive drums 11Y, 11M, 11C, and 11K as image carriers and a developing unit. In addition, the arrangement of the toner image forming units 1Y, 1M, 1C, and 1K is set so that the rotation axes of the photosensitive drums are parallel and arranged at a predetermined pitch in the transfer paper moving direction. .

  In addition to the toner image forming units 1Y, 1M, 1C, and 1K, the laser printer carries the optical writing unit 2, the paper feed cassettes 3 and 4, the registration roller pair 5, and the transfer paper 100, and each toner image forming unit. A transfer unit 6 as a belt driving device having a transfer conveyance belt 60 as a transfer conveyance member that conveys the sheet so as to pass through the transfer position, a belt fixing type fixing unit 7, a paper discharge tray 8, and the like. In addition, a manual feed tray MF and a toner supply container TC are provided, and a waste toner bottle, a duplex / reversing unit, a power supply unit, and the like (not shown) are also provided in a space S indicated by a two-dot chain line.

  The optical writing unit 2 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each of the photosensitive drums 11Y, 11M, 11C, and 11K while scanning the laser beam based on the image data. To do.

FIG. 2 is an enlarged view showing a schematic configuration of the transfer unit 6. The transfer conveyance belt 60 used in the transfer unit 6 is a high-resistance endless single-layer belt having a volume resistivity of 10 ⁹ to 10 ¹¹ Ωcm, and the material thereof is PVDF (polyvinylidene fluoride). The transfer conveyance belt 60 is wound around support rollers 61 to 68 so as to pass through the transfer positions that are in contact with and face the photosensitive drums 11Y, 11M, 11C, and 11K of the toner image forming units.

  Among these support rollers, the entrance roller 61 on the upstream side in the transfer sheet moving direction is disposed on the outer peripheral surface of the transfer conveyance belt 60 so that the electrostatic adsorption roller 80 to which a predetermined voltage is applied from the power source 65a is opposed. Yes. The transfer paper 100 that has passed between the two rollers 61 and 65 is electrostatically attracted onto the transfer conveyance belt 60.

  A roller 63 is a drive roller that frictionally drives the transfer conveyance belt 60, and is connected to a drive source (not shown) and rotates in the direction of the arrow.

  As a transfer electric field forming means for forming a transfer electric field at each transfer position, transfer bias applying members 67Y, 67M, 67C, and 67K are provided at positions facing the photosensitive drum so as to be in contact with the back surface of the transfer conveyance belt 60. ing. These are bias rollers provided with a sponge or the like on the outer periphery, and a transfer bias is applied to the roller core from each transfer bias power source 9Y, 9M, 9C, 9K. Due to the action of the applied transfer bias, a transfer charge is applied to the transfer conveyance belt 60, and a transfer electric field having a predetermined strength is formed between the transfer conveyance belt 60 and the surface of the photosensitive drum at each transfer position. In addition, a backup roller 68 is provided to keep the contact between the transfer paper and the photoconductor in the area where the transfer is performed, and to obtain the best transfer nip.

  The transfer bias applying members 67Y, 67M, and 67C and the backup roller 68 disposed in the vicinity thereof are integrally held by the swing bracket 93 so as to be rotatable, and can be rotated around a rotation shaft 94. This rotation is clockwise when the cam 96 fixed to the cam shaft 97 is rotated in the direction of the arrow.

The entrance roller 61 and the suction roller 80 are integrally supported by the entrance roller bracket 90, and can be rotated clockwise from the state shown in FIG. A hole 95 provided in the swing bracket 93 and a pin 92 fixed to the entrance roller bracket 90 are engaged with each other, and rotate in conjunction with the rotation of the swing bracket 93. By the clockwise rotation of these brackets 90, 93, the bias applying members 67Y, 67M, 67C and the backup roller 68 disposed in the vicinity thereof are separated from the photoreceptors 11Y, 11M, 11C, and the entrance roller 61 and the suction roller 80 also moves downward. It is possible to avoid contact between the photoconductors 11Y, 11M, and 11C and the transfer conveyance belt 60 when forming a black-only image.
On the other hand, the transfer bias applying member 67K and the backup roller 68 adjacent to the transfer bias applying member 67K are rotatably supported by the outlet bracket 98, and are rotatable about a shaft 99 coaxial with the outlet roller 62. When attaching / detaching the transfer unit 6 to / from the main body, the transfer unit 6K is rotated clockwise by operating a handle (not shown), and the transfer bias applying member 67K and the backup roller 68 adjacent thereto are moved from the black image forming photosensitive member 11K. They are separated.

  A cleaning device 85 composed of a brush roller and a cleaning blade is disposed on the outer peripheral surface of the transfer conveyance belt 60 wound around the driving roller 63. The cleaning device 85 removes foreign matters such as toner adhering to the transfer conveyance belt 60.

  A roller 64 is provided downstream of the driving roller 63 in the traveling direction of the transfer conveyance belt 60 in a direction to push the outer peripheral surface of the transfer conveyance belt, and a winding angle around the drive roller 83 is ensured. A tension roller 65 that applies tension to the belt with a pressing member (spring) 69 is provided in the loop of the transfer conveyance belt 60 further downstream from the roller 64.

  The one-dot chain line in FIG. 1 shown above indicates the conveyance path of the transfer paper 100. The transfer paper 100 fed from the paper feed cassettes 3 and 4 or the manual feed tray MF is transported by transport rollers while being guided by a transport guide (not shown), and is transported to a temporary stop position where the registration roller pair 5 is provided. The transfer paper 100 delivered at a predetermined timing by the registration roller pair 5 is carried on the transfer conveyance belt 60, conveyed toward the toner image forming units 1Y, 1M, 1C, and 1K, and passes through the transfer nips. .

  The toner images developed on the toner drums 11Y, 11M, 11C, and 11K of the toner image forming units 1Y, 1M, 1C, and 1K are superimposed on the transfer paper 100 at the transfer nips, respectively. It is transferred onto the transfer paper 100 under the action of pressure. By this superposition transfer, a full-color toner image is formed on the transfer paper 100.

  The surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K after the toner image transfer are cleaned by a cleaning device, and are further discharged to prepare for the formation of the next electrostatic latent image.

  On the other hand, the transfer paper 100 on which the full-color toner image is formed is fixed in the first paper discharge direction B or the second in accordance with the rotation posture of the switching guide G after the full-color toner image is fixed by the fixing unit 7. In the paper discharge direction C. When the paper is discharged from the first paper discharge direction B onto the paper discharge tray 8, it is stacked in a so-called face-down state with the image surface down. On the other hand, when the paper is discharged in the second paper discharge direction C, it is conveyed toward another post-processing device (such as a sorter or a binding device) (not shown), or is registered again for double-sided printing via a switchback unit. It is conveyed to the roller pair 5.

  With the above configuration, a full color image is formed on the transfer paper 100. In the tandem color image forming apparatus, it is important to prevent the occurrence of color misregistration by accurately superimposing the toner images of the respective colors. However, the drive roller 63, the entrance roller 61, the exit roller 99, and the transfer belt 60 used in the transfer unit 6 are subject to a manufacturing error of several tens of μm when manufacturing parts. The fluctuation component generated when each part makes one rotation due to this error is transmitted onto the transfer belt 60, and the conveyance speed of the paper fluctuates, so that the toner on each of the photosensitive drums 11Y, 11M, 11C, and 11K is transferred to the transfer paper 100. A slight shift occurs in the timing of transfer to the image, and a color shift occurs in the sub-scanning direction. In particular, in an apparatus that forms an image with minute dots of 1200 × 1200 dpi or the like as in the present embodiment, a timing shift of several μm becomes conspicuous as a color shift. In this embodiment, an encoder is provided on the shaft of the lower right roller 66, the rotation speed of the encoder is detected, and the rotation of the drive roller 63 is feedback-controlled so that the transfer belt 60 travels constant.

  FIG. 3 shows a configuration diagram of main components of the transfer unit 6. The transfer drive roller 63 is connected to the drive gear of the transfer drive motor 302 through the timing belt 303, and is rotated in proportion to the drive speed of the drive motor 302 by rotating the drive motor 302. When the transfer driving roller 63 rotates, the transfer belt 60 is driven, and when the transfer belt 60 is driven, the lower right roller 66 rotates. In this embodiment, the encoder 301 is arranged on the axis of the lower right roller 66, and the speed of the drive motor 302 is controlled by detecting the rotational speed of the lower right roller 66 by the encoder 301. This is performed in order to minimize the speed fluctuation because the color shift occurs due to the speed fluctuation of the transfer belt 60 as described above. A mark 304 for managing the reference position of the transfer belt is attached to the non-image forming area on the surface of the transfer belt 60, and a sensor 305 attached in the vicinity thereof detects ON / OFF of the mark. Is going. As will be described later, the effective driving radius of the lower right roller 66 changes due to the uneven thickness of the transfer belt 60, and the speed of the encoder 301 changes even though the speed of the transfer belt 66 is actually constant. In order to prevent such detection, the control target value is variably controlled according to the thickness profile data measured in advance, so that erroneous detection due to the belt thickness is canceled and the belt is moved at a constant speed. Transport. A mark is attached to match the actual belt position at this time with the position of the thickness profile data.

  FIG. 4 shows a detailed view of the lower right roller 66 and the encoder 301. The encoder 301 includes a disk 401, a light emitting element 402, a light receiving element 403, and press-fit bushings 404 and 405. The disc 401 is fixed by press-fitting press-fitting bushes 404 and 405 on the shaft of the lower right roller 66, and rotates simultaneously with the rotation of the lower right roller 66. Further, the disk 401 has slits that transmit light with a resolution of several hundred units in the circumferential direction, and the rotation amount of the lower right roller 66 is provided by arranging the light emitting element 402 and the light receiving element 403 on both sides thereof. A pulsed ON / OFF signal is obtained according to the above. The drive amount of the drive motor 302 is controlled by detecting the movement angle (hereinafter referred to as the displacement angle) of the lower right roller 66 using this pulse-like ON / OFF signal.

  FIG. 5 is a block diagram of a drive control apparatus for carrying out the drive control method according to the embodiment of the present invention. Hereinafter, the case where the drive control apparatus of this embodiment is applied to the rotating body drive apparatus of the said embodiment is demonstrated.

  In FIG. 5, the difference e (i) between the target angular displacement Ref (i) of the encoder 301 and the detected angular displacement P (i−1) of the encoder 301 is input to the control controller unit 501. The control controller unit 501 includes a low-pass filter 502 for removing high frequency noise and a proportional element (gain Kp) 503. In the control controller unit 501, a correction amount for the standard drive pulse frequency used for driving the transfer drive motor 302 is obtained and provided to the calculation unit 504. In the calculation unit 504, the correction amount is added to the constant standard drive pulse frequency Refp_c to determine the drive pulse frequency u (i).

  Further, a control target profile corresponding to the variation in the thickness of the transfer belt is added to the target angular displacement Ref (i), and a difference e (i) from the detected angular displacement P (i−1) of the encoder 301 is obtained. Then, the difference displacement amount is calculated. The addition of the control target profile corresponding to the variation in the thickness of the transfer belt is added so as to be repeated periodically according to the timing of the mark sensor output detected by the rotation of the transfer belt.

  FIG. 6 is a block diagram illustrating a hardware configuration of a control system and a control target of the transfer driving motor 302 according to the first embodiment. This control system is a control system that digitally controls the angular displacement of the transfer drive motor 302 based on the output signal of the encoder 301. This control system includes a CPU 601, a RAM 602, a ROM 603, an IO control unit 604, a transfer motor drive I / F unit 606, a driver 607, and a detection IO 608.

  The CPU 601 controls the entire image forming apparatus including the reception of image data input from the external apparatus 610 and the transmission / reception control of control commands. A RAM 601 used for work, a ROM 603 for storing a program, and an IO control unit 604 are connected to each other via a bus, read / write processing of data and a motor / clutch / solenoid driving each load according to instructions from the CPU 601, Perform various operations such as sensors.

  The transfer motor drive motor IF 606 outputs a command signal for commanding the drive frequency of the drive pulse signal to the transfer motor 302 via the driver 607 in response to a drive command from the CPU 601. Since the transfer motor 302 is rotationally driven according to this frequency, the drive speed control can be varied.

  The output signal of the encoder 305 is input to the detection IO unit 608. The detection IO unit 608 processes the output pulse of the encoder 305 and converts it into a digital numerical value. Further, the detection IO unit 608 includes a counter that counts the output pulses of the encoder 305. Then, the numerical value counted by the counter is multiplied by a predetermined conversion constant of the pulse number diagonal displacement to convert it into a digital numerical value corresponding to the angular displacement of the motor shaft. A digital numerical signal corresponding to the angular displacement of the disk is sent to the CPU 601 through the bus.

  The transfer motor driving IF unit 606 generates a pulse-shaped control signal having the driving frequency based on the driving frequency command signal sent from the CPU 601. The driver 607 includes a power semiconductor element (for example, a transistor). The driver 607 operates based on the pulsed control signal output from the transfer motor driving IF unit 606 and applies a pulsed driving voltage to the transfer driving motor 302. As a result, the transfer drive motor 302 is driven and controlled at a predetermined drive frequency output from the CPU 601. Thus, the additional value is controlled so that the angular displacement of the disk 401 follows the target angular displacement, and the lower right roller 66 rotates at a constant angular velocity at a predetermined angular velocity. The angular displacement of the disk 401 is detected by the encoder 301 and the detection IO unit 608 and is taken into the CPU 601 and the control is repeated.

  In addition to the function used as a work area when executing the program stored in the ROM 603, the RAM 602 is a belt from the belt mark 304 corresponding to the thickness variation of the transfer belt measured in advance. Data of the control target profile for one round is stored. Since the RAM 602 is a volatile memory, profile data is stored in a volatile memory such as an EEPROM (not shown) such as the phase / amplitude / period parameters of the belt as shown in FIG. Data for one belt period is developed on the RAM 602 using the Sin function.

  The actual belt thickness profile depends largely on the manufacturing process, but in most cases it is a sine-like profile, and it is not particularly necessary to have all the data for one belt revolution. Even if the phase, amplitude, and period from the reference position are sometimes calculated and profile data is calculated from this data, it can be handled as sufficiently equivalent profile data.

  Therefore, it is not necessary to store the belt thickness profile data for each control cycle in the nonvolatile memory, and the belt thickness profile data is generated using only the phase, amplitude, and cycle parameters. Control is possible only by preparing. Profile data is generated by the following arithmetic expression when the power is turned on or the transfer motor is started.

Δθ [rad]: Rotational angular velocity fluctuation value of driven shaft [= b × sin (2 × π × ft + τ)]
The above Δθ is calculated according to the control time from the belt mark, and sequentially stored in the RAM 602 which is a volatile memory.

  When the transfer motor 302 is actually driven, data is read by switching the reference address of the RAM 602 according to the timing when the belt mark detection sensor 305 detects the belt mark. By adding the read data to the aforementioned control target angular displacement, control is performed to cancel the erroneous detection by the belt thickness.

  Further, when only the peak value of the speed fluctuation due to the belt thickness is lowered, the profile data of the belt thickness for each control cycle is not necessary. Therefore, in order to reduce the memory area, for example, as shown in FIG. 17, profile data of about 50 points per belt rotation is generated, and the thickness profile data is updated when the transfer belt reaches each point. It is possible to reduce it sufficiently.

  However, if the number of locations to be updated per one rotation of the belt is decreased, the smaller the number of update locations, the more the value immediately before the update has an error from the ideal value as shown in FIG. Therefore, at least this error is output as a belt speed fluctuation.

  For this reason, in this embodiment, control is performed to vary the number of updates per belt revolution in accordance with the image quality for image formation. When printing high-quality images, increasing the number of updates reduces errors and minimizes belt speed fluctuations. Conversely, when printing low-quality images, the number of updates is reduced to reduce the control load. . At this time, an allowable number of times is selected even if the error slightly increases and the speed fluctuation occurs.

  In the above operation, the control is switched depending on the image quality, for example, when the print resolution is high and low resolution such as 1200/600 dpi, or when the image is a natural image and a text image.

  When the image quality is high as shown in FIG. 18, the belt thickness profile data is 100 times per belt revolution, and when the image quality is low as shown in FIG. 19, the belt thickness profile data is 20 times per belt circumference. For example, the control is switched according to the image quality. This is effective in reducing the memory capacity and shortening the time for developing the profile data in the memory.

  Also, if you do not have the time to develop data before starting printing, prepare multiple memory areas to store the above-mentioned several types of profile data, and use them when developing images and forming images collectively when the power is turned on. The same effect can be obtained when the memory area to be selected is selected.

  8 and 9 are timing charts for realizing this control.

  First, the count value of the encoder pulse counter 1 is incremented by the rising edge of the A-phase output of the encoder pulse. The control cycle of this control is 1 ms, and the count value of the control cycle timer counter is incremented every time the microcomputer is interrupted by the control cycle timer. The timer is started when the rising edge of the encoder pulse is detected for the first time after the drive motor has been slewed up and settled, and the count value of the control cycle timer counter is reset.

  Each time the microcomputer is interrupted by the control cycle timer, the count value: ne of the encoder pulse counter 1 is acquired and the count value: q of the control cycle timer counter is acquired and incremented.

  Similarly to the encoder pulse counter 1, the encoder pulse counter 2 is incremented by the rising edge of the A-phase output of the encoder pulse, and is reset at the rising edge of the first encoder pulse when the belt mark sensor 305 is input. Therefore, the encoder pulse counter 2 substantially counts the moving distance from the belt mark, and switches the reference address of the RAM 602 in which the data of the control target profile for one round of the belt is stored according to this value.

  Based on each count value, the position deviation is calculated as follows.

  In this embodiment, the diameter of the driven roller to which the encoder is attached is φ15.515 [mm], and the belt thickness is 0.1 [mm]. The driven roller is driven to rotate by friction with the belt, and assuming that a thickness of about ½ of the belt thickness is a core wire for rotating the driven roller, the lower right roller diameter L = 15.515 + 0.1 = 15.615 [ mm]. In this embodiment, the resolution p of the encoder is 300 pulses per rotation.

  Next, in order to avoid responding to a sudden position change, a filter calculation with the following specifications is performed on the calculated deviation. Filter type: Butterworth IIR Low-pass filter Sampling frequency: 1KHz (= equal to control period) Passband ripple (Rp): 0.01dB Stopband end attenuation (Rs): 2dB Passband end frequency (Fp): 50Hz Stopband end frequency (Fs): 100 Hz A block diagram of this filter calculation is shown in FIG. 10, and a list of filter coefficients is shown in Table 1 below.

Here, a two-stage cascade connection is used, and the intermediate nodes at each stage are u1 (n), u1 (n-1), u1 (n-2) and u2 (n), u2 (n-1), u2 (n -2). Here, the meaning of the index is as follows. (n): Current sampling (n-1): Previous sampling (n-2): Previous sampling
The following program calculation is performed each time a control timer interrupt occurs during feedback execution.

  FIG. 11 shows the amplitude characteristics of this filter, and FIG. 12 shows the phase characteristics.

  Next, the control amount for the controlled object is obtained. In the control block diagram 5, when considering PID control as a position controller,

  The above equation (3) is represented as a block diagram as shown in FIG. Here, e ′ (n) and f (n) indicate that E ′ (S) and F (S) are treated as discrete data, respectively. In FIG. 13, when w (n), w (n-1), and w (n-2) are respectively determined as intermediate nodes, the difference equation is as follows (general expression for PID control). Here, the meaning of the index is as follows.

(n): Current sampling
(n-1): Previous sampling
(n-2): Two previous samplings

  Considering proportional control as a position controller, the integral gain and derivative gain are zero. Therefore, each coefficient in FIG. 13 is as follows, and the equations (4) and (5) are simplified as the equation (6).

  FIG. 14 shows a flowchart when interrupt processing by encoder pulses is performed.

  First, it is determined whether or not it is the first interrupt after through-up and settling (step S1). If YES, the encoder pulse counter 1 is cleared to zero (step S2), the control period counter is cleared to zero (step S3), and the control period The interruption by the timer is permitted (step S4), the control cycle timer is started (step S5), and RETURN is performed. If NO in step S1, the encoder pulse counter is incremented (step S6) and RETURN is performed.

  FIG. 15 shows a flowchart of processing of the encoder pulse counter 2.

  First, when an encoder pulse interrupt is input, the state of the belt mark sensor is determined (step S1). If YES, the encoder pulse counter 2 is cleared to zero (step S2). If NO in step S1, the encoder pulse counter 2 is incremented (step S3) and RETURN is performed.

  FIG. 16 shows a flowchart of interrupt processing by the control cycle timer.

  First, the control cycle timer counter is incremented (step S1), and then the encoder pulse count value: ne is acquired (step S2). Further, the value of Δθ is acquired with reference to the table data (step S3), and the table reference address is incremented (step S4). Using these values, position deviation calculation is performed (step S5), filter calculation is performed on the obtained position deviation (step S6), and control amount calculation (proportional calculation) is performed based on the result of the filter calculation. In step S7, the frequency of the driving pulse of the stepping motor is actually changed (step S8), and RETURN is performed.

  With the above control, the control for stabilizing the speed fluctuation caused by the belt thickness can be performed with an inexpensive method and according to the image quality.

  In the above embodiment, the present invention is applied to the transfer unit 6 in the tandem printer in which a plurality of the photosensitive drums 11Y, 11M, 11C, and 11K are arranged on the transfer conveyance belt 60. However, the present invention is applied. Possible printers and belt drives are not limited to this configuration. The present invention can be applied to any belt driving device in a printer having a belt driving device that rotationally drives an endless belt stretched around a plurality of rollers by at least one of the rollers. In this embodiment, the exposure light source is a laser beam, but is not limited to this. For example, an LED array may be used. Furthermore, the speed and position of the belt are detected by a rotary encoder attached to the driven roller shaft. However, the present invention is not limited to this. For example, a scale or toner mark formed on the front or back surface of the belt may be detected. good. Furthermore, the control calculation performed by the control controller is PI control, but is not limited to this, and P control, PID control, H∞ control, or the like may be used.

  As described above, according to the present invention, when the endless belt is controlled by the encoder attached to the driven roller, the control for stabilizing the speed fluctuation caused by the belt thickness is performed by an inexpensive method and according to the image quality. And appropriate processing can be performed. Good feedback control can be performed.

1 is a schematic configuration diagram of a laser printer according to an embodiment. It is an enlarged view showing a schematic configuration of a transfer unit. It is a block diagram of the main components of a transfer unit. It is detail drawing of a lower right roller and an encoder. 1 is a block diagram of a drive control device for implementing a drive control method according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a control system of a transfer drive motor and a hardware configuration to be controlled in an embodiment of the present invention. It is a figure which shows the phase, amplitude, and period parameter of the belt stored in a volatile memory. It is a timing chart in implement | achieving control which concerns on one Embodiment of this invention. It is a timing chart in implement | achieving control which concerns on one Embodiment of this invention. It is a block diagram of filter calculation. It is an amplitude characteristic figure of a filter. It is a phase characteristic figure of a filter. It is the figure which represented PID control as a block diagram. It is a flowchart at the time of performing the interruption process by an encoder pulse. It is a flowchart of a process of an encoder pulse counter. It is a flowchart of the interruption process by a control period timer. It is a figure which shows the profile data of about 50 points per belt circumference. It is a figure which shows the belt thickness profile data of 100 times per belt circumference. It is a figure which shows the belt thickness profile data of 20 times per belt circumference. It is a figure which shows the relationship between a drive roller and a transfer belt. It is a model figure of a belt drive conveyance system. FIG. 6 is a diagram conceptually showing belt thickness fluctuation and belt conveyance speed fluctuation over one belt rotation when a drive shaft is rotated at a constant angular velocity. It is the figure which showed the belt thickness fluctuation | variation in a driven shaft when the belt was conveyed with the fixed conveyance speed, and the belt conveyance speed fluctuation | variation detected by the driven shaft.

Explanation of symbols

60 Transfer conveyor belt (endless belt)
63 Drive roller 301 Encoder 304 Mark 305 Sensor (mark detection means)

Claims (6)

It has an endless belt, a driving roller for driving the endless belt, a driving motor for driving the driving roller, and a plurality of driven rollers driven by the endless belt, and an encoder is attached to one of the driven rollers, In an endless belt drive control device that feedback-controls an endless belt based on
The mark that is the reference position of the endless belt,
Mark detection means for detecting the mark;
A non-volatile memory for storing a phase, a maximum amplitude, and a period at a mark serving as the reference position of the thickness profile of the endless belt;
Means for developing and generating an endless belt thickness profile based on the value stored in the non-volatile memory and storing the data in a volatile memory;
With
When driving the endless belt, the profile data stored in the volatile memory is referred to according to the distance from the belt mark and added to the control target value to stabilize the speed fluctuation due to the belt thickness. An endless belt drive control device.   The timing for developing the phase, amplitude, and period values stored in the nonvolatile memory in the volatile memory is executed when the image forming apparatus is turned on or when the endless belt is started. The endless belt drive control device described.   3. The endless belt according to claim 1, wherein data corresponding to a belt arrival position is calculated from a phase, amplitude, and period value stored in a nonvolatile memory using a Sin function. Drive control device.   4. The memory capacity of the volatile memory is reduced by thinning and storing the data when the endless belt thickness profile is expanded and generated and stored in the volatile memory. An endless belt drive control device according to claim 1.   5. The drive control apparatus for an endless belt according to claim 4, wherein a plurality of volatile memory storage areas are provided, and the endless belt thickness profile data having different thinning-out numbers is stored in each area. The reference area of the volatile memory is switched according to the image quality when the profile data stored in the volatile memory is referred to according to the distance from the belt mark when driving the endless belt. The drive control device for an endless belt according to claim 4 or 5.

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