JP2006259173A - Drive controller and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a such problem that absolute velocity of belt conveyance velocity is varied by variation in belt thickness, and thermal expansion and thermal contraction of a driven roller. <P>SOLUTION: A drive controller is provided which stabilizes velocity variation by thickness of a belt 60 by referring to correction data stored in a volatile memory and adding the correction data to a control object value to perform drive control of a drive means when driving the belt 60, the drive controller is provided with a subscanning magnification correction means for detecting subscanning magnification error of a transfer conveyance device based on velocity information of the transfer conveyance device, calculating an amount of correction of the detected subscanning magnification error and performing drive control of the transfer conveyance device so as to reduce the subscanning magnification error based on the calculated amount of correction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a drive control device that drives and controls an endless belt of an image forming apparatus, and an image forming apparatus such as a copying machine, a printer, and a facsimile.

  In an image forming apparatus, for example, Patent Document 1 discloses that a position detected by a belt mark on a transfer conveyance belt when a driving roller is driven at a constant pulse rate to rotate an endless transfer conveyance belt is used as a reference. Measure the speed profile in advance to cancel the speed fluctuation Vh that would be generated by the known thickness profile over the entire circumference of the transfer conveyance belt, and send the drive motor control signal at a modulated pulse rate. It is described that the final transfer / conveyance belt speed Vb is not changed by driving the motor based on this and driving the transfer / conveyance belt via a driving roller.

  Patent Document 2 aims to reduce color misregistration due to belt thickness deviation. A resist pattern is formed on the belt, and the thickness of the belt measured based on the read result of the resist pattern. There is described a technique in which a speed fluctuation amount of a belt one-round component generated due to unevenness is extracted, and belt driving control is performed based on the speed fluctuation amount when an image is output. In Patent Document 3, the rotational angular displacement or rotational angular velocity of the driven roller is detected, and the AC component of the rotational angular velocity having a frequency corresponding to the periodic thickness fluctuation in the circumferential direction of the belt is extracted from the detection result. A device that controls the rotation of the drive roller based on the amplitude and phase of the AC component is described.

  In Patent Document 4, the rotational angle of the driving roller and the driven roller is detected by a rotary encoder, and the difference between the rotational speeds of both rollers is obtained by an up / down counter, and this rotational speed difference is superimposed on the rotational speed control system of the motor. Thus, what performs the FESO back control is described. In Patent Document 5, when assembling a copying machine, three reference patterns printed in advance on the surface of a transfer belt are detected to correct magnification misalignment in the sub-scanning direction. Is output to the belt surface, and these test patterns are detected and compared with a reference pattern to correct parallel displacement in the sub-scanning direction, parallel displacement in the main scanning direction, and magnification displacement in the main scanning direction of each color image. Things are listed.

JP2000-310897 Japanese Patent Laid-Open No. 10-186787 (Japanese Patent No. 3564953) JP 2004-123383 A JP 2000-330353 A Japanese Patent Laid-Open No. 11-352,737

  A typical method for forming a color image includes a direct transfer method in which a plurality of toner images having different colors formed on a plurality of photoconductors are transferred while being directly superimposed on a transfer sheet, and a color image formed on a plurality of photoconductors. There is an intermediate transfer system in which a plurality of different toner images are transferred while being superimposed on an intermediate transfer member such as an intermediate transfer belt, and then transferred onto a transfer sheet at once. Since a plurality of photoconductors are arranged side by side facing the transfer paper or intermediate transfer body, this is called a tandem system, and yellow (hereinafter referred to as Y), magenta (hereinafter referred to as M), cyan (hereinafter referred to as C) for each photoconductor. , Black (hereinafter referred to as “K”) is subjected to an electrophotographic process such as electrostatic latent image formation and development to form a toner image of each color, and the toner image of each color is being transferred in the direct transfer system. On the transfer paper, in the intermediate transfer method, the image is transferred onto the running intermediate transfer member.

  In the tandem color image forming apparatus using each of these methods, in the direct transfer method, an endless belt that travels while supporting transfer paper is adopted as the direct transfer conveyance belt, which is suitable for the intermediate transfer method. In general, an endless belt that receives and carries an image from a photoreceptor is generally used as the intermediate transfer conveyance belt. Then, an image forming unit including four photoconductors is arranged side by side on one side in the running direction of the endless belt.

  In the tandem color image forming apparatus, it is important to prevent the occurrence of color misregistration by accurately transferring toner images of respective colors onto a transfer sheet or an intermediate transfer conveying belt as a recording member by a transfer unit. . Therefore, in any of the transfer methods, in order to avoid color misregistration due to speed fluctuation of the transfer conveyance belt, an encoder is provided on one of the plurality of driven shafts driven by the direct transfer conveyance belt or the intermediate transfer conveyance belt of the transfer unit. It is an effective means to feedback-control the rotational speed of the driving roller that directly drives the transfer transfer belt or the intermediate transfer transport belt in accordance with fluctuations in the rotational speed of the encoder.

  The most common method for realizing feedback control is proportional control (PI control). This calculates the position deviation e (n) from the difference between the target angular displacement Ref (n) of the encoder and the detected angular displacement P (n−1) of the encoder, and applies a low-pass filter to the calculation result to generate high frequency noise. By applying a control gain, adding a constant standard drive pulse frequency signal and controlling the drive pulse frequency of the drive motor connected to the drive roller based on the result, the encoder output is always at the target angle. This is a method of controlling to be driven by displacement.

  For actual feedback control, an encoder pulse counter that counts the rising edge of the output pulse of the encoder and a control period counter that counts every control period (for example, 1 ms), and a target that moves during the control period (1 ms) The position deviation can be acquired from the difference between the calculation result of the angular displacement and the detected angular displacement obtained by acquiring the count value of the encoder pulse counter for each control cycle.

As a specific calculation, assuming that the roller diameter of the driven shaft to which the encoder is attached is 15.615, the following is obtained.
e (n) = θ0 * q-θ1 * ne Unit: rad
e (n) [rad]: Position deviation calculated by this sampling θ0 [rad]: Movement angle per control cycle (= 2π * V * E-3 / l5.565π [rad])
θ1 [rad]: Movement angle per encoder pulse (= 2π / p [rad])
q: Count value of control cycle timer V: Belt linear velocity [mm / s]
ne: Count value of the encoder pulse counter Here, for example, a control cycle of 1 ms with a resolution of 300 pulses per revolution is used, and feedback is performed so that the endless belt (transfer conveyance belt) operates at 162 mm / s. Assuming the case where control is applied, it is as follows.

θ0 = 2π * 162 * E-3 / l5.615π = 0.0207487 [rad]
θ1 = 2π / p = 2π / 300 = 0.0209439 [rad]
A position deviation is acquired by performing the above calculation for every control period, and feedback control is performed.

However, with this method, the transfer speed of the transfer paper changes depending on the thickness of the minute transfer transport belt, and the image quality shifts from the ideal position. There has been a problem that the reproducibility of the repetitive image position between recording sheets deteriorates.
This is because, assuming that the belt conveyance speed is determined at the center of the belt in the thickness direction at the belt driving position, the belt conveyance speed V is
V = (R + B / 2) × ω (1)
R: radius of the driving roller, B: thickness of the belt, ω: angular velocity of the driving roller. However, when the belt thickness B varies, the position of the effective thickness line of the endless belt 701 driven by the driving roller 702 changes as shown in FIG. This is because the effective belt driving radius changes, and (R + B / 2) in equation (1) changes, so that the conveying speed of the belt 701 changes even if the angular velocity ω of the driving roller 702 is constant. I understand. That is, even if the driving roller 702 is rotated at a constant angular velocity, if the thickness of the belt 701 varies, the conveying speed of the belt 701 changes.

FIG. 21 shows a model of the belt drive conveyance system. The belt 701 is stretched around a driving roller 702 and driven rollers 703 and 704.
First, FIG. 22 conceptually shows the thickness fluctuation and the conveyance speed fluctuation over one circumference of the belt 701 when the driving shaft of the driving roller 702 is rotated at a constant angular velocity. When the thick portion of the belt 701 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 701 is wound around the drive shaft, the belt conveyance speed is lowered.

  Next, FIG. 23 shows the belt thickness variation on the driven shaft when the belt 701 is conveyed at a constant conveyance speed, and the belt conveyance speed variation detected on the driven shaft of the driven roller 703. Even if the belt 701 is conveyed ideally without speed fluctuation, if the thick portion of the belt 701 is wound around the driven roller 703, the driven effective radius of the belt 701 increases and the rotational angular speed of the driven roller 703 decreases. This is detected as a decrease in the conveyance speed of the belt 701. When a thin portion of the belt 701 is wound around the driven roller 703, the rotational angular speed of the driven roller 703 increases and is detected as an increase in belt conveyance speed.

  In this way, when there is a belt thickness variation, if the belt conveyance speed is detected by the rotational angular displacement of the driven shaft with an encoder or the like, a false detection component is generated. For this reason, even if the belt 701 is conveyed at a constant speed, the rotation angle displacement of the driven shaft is detected as if the belt 701 fluctuates due to the thickness fluctuation of the belt 701. For this reason, in the conventional feedback control in which the belt conveyance speed is detected by the rotational angular displacement of the driven shaft, it is impossible to control the belt thickness variation.

  Patent Document 1 describes a technique for solving such belt speed fluctuation due to belt thickness fluctuation. The feature of the method described in Patent Document 1 is generated by a known thickness profile over the entire circumference of the belt with reference to the position detected by the belt mark on the belt when driving the driving roller at a constant pulse rate. 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. By driving the belt, the final belt speed Vb does not fluctuate.

However, in the method described in Patent Document 1, since the speed profile data requires data for each control cycle, a large-capacity memory is required when the control cycle is short, and when the control cycle is long. There is a problem that the feedback control itself cannot obtain a sufficient effect. For example, when the belt circumference 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 x 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 = 104320bit
Therefore, when the above control is performed on an actual machine, it is necessary to prepare a new memory for storing the belt thickness profile as a nonvolatile memory, and temporarily store the belt thickness profile data as compressed data in the nonvolatile memory, Even if decompressed to volatile memory at the time of 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.

Furthermore, in the method described in Patent Document 1, it is necessary to measure the thickness of the belt itself as belt thickness profile data, and as a means for that purpose, the thickness of the belt is measured with a laser displacement meter. The measured data is input from an input unit such as an operation panel at the time of product shipment, or input from an input unit such as an operation panel by a service person.
However, in order to measure the thickness variation of a belt of several um, a high-precision measuring means is required, and since there is a large amount of data management and data amount of the measurement result, an input error may occur.

  Further, in the color image forming apparatus, driving the belt so that the absolute speed of the belt conveyance speed is always the target speed is an extremely important item for maintaining the permanent image quality. This is because when the absolute speed of the belt conveyance speed is different from the target speed, it appears as an error in the on-image sub-scanning magnification. The cause of the change in the absolute speed of the belt conveyance speed is that the outer diameter of the roller that determines the transfer conveyance speed varies depending on the environment due to thermal expansion and contraction of the roller. Such a problem cannot be solved by a method of forming a resist pattern on a belt as described in Patent Document 2. For example, when the transfer conveyance speed is 1% faster than the target, the pitch of the resist pattern formed on the belt is 1% longer than the target. However, when this resist pattern is read by a sensor, the transfer conveyance speed is 1% faster, and as a result, it is impossible to know the change in absolute speed by outputting at the desired interval.

  The object of the present invention is to control the speed fluctuation caused by the belt thickness by an inexpensive method and to change the absolute speed of the transfer conveyance speed in a short time without adding new parts. Another object of the present invention is to provide a drive control device and an image forming apparatus capable of correcting a sub-scanning magnification error caused by the above.

  In order to achieve the above object, an invention according to claim 1 is directed to an endless belt that conveys a recording member and transfers an image onto the recording member, a driving roller that drives the belt, and a driving that drives the driving roller. An encoder attached to one of the plurality of driven rollers in a transfer conveying apparatus having a motor, drive means for driving the drive motor, and a plurality of driven rollers driven by the belt; The control target value is set so that the angular displacement amount of the encoder per hit is constant, and the speed of the belt is controlled by controlling the driving means so that the angular displacement amount of the encoder becomes the same as the control target value. A drive control device that performs control, comprising: a mark detection unit that detects a mark that is a reference position of the belt; and an encoder that is generated by a variation in the thickness of the belt. Detection angular displacement error detection means for detecting an output angular displacement error; first means for calculating a phase and amplitude at the mark in the detected angular displacement error of the encoder obtained from the detection angular displacement error detection means; A non-volatile memory for storing a calculation result of the first means; a second means for calculating correction data according to a distance from the mark of the belt based on a value stored in the non-volatile memory; A volatile memory for storing correction data; when driving the belt, the correction means stored in the volatile memory is referred to, and the correction data is added to the control target value. In the drive control device that stabilizes the speed fluctuation due to the belt thickness, the sub-scanning magnification error of the transfer transport device is detected based on the speed information of the transfer transport device. And a sub-scanning magnification correction unit that calculates a correction amount of the detected sub-scanning magnification error and performs drive control of the transfer conveyance device so as to reduce the sub-scanning magnification error based on the calculated correction amount. Is.

  According to a second aspect of the present invention, an endless belt that conveys a recording member and transfers an image onto the recording member, a driving roller that drives the belt, a driving motor that drives the driving roller, and this driving motor A driving means for driving; a plurality of driven rollers driven by the belt; and an encoder attached to one of the driven rollers, wherein the angular displacement of the encoder per unit time is constant. An image forming apparatus that controls the speed of the belt by setting a control target value so that the angular displacement amount of the encoder is the same as the control target value, and controlling the belt speed, Mark detection means for detecting a mark serving as a reference position of the belt, and detection angular displacement error detection means for detecting a detection angular displacement error of the encoder caused by a variation in the thickness of the belt; First means for calculating the phase and amplitude at the mark in the detected angular displacement error of the encoder obtained from the detected angular displacement error detecting means; and a non-volatile memory for storing the calculation result of the first means; A second means for calculating correction data in accordance with a distance of the belt from the mark based on a value stored in the nonvolatile memory; and a volatile memory for storing the correction data. When the drive unit is driven, the correction data stored in the volatile memory is referred to, the correction data is added to the control target value, and the drive unit is driven to control the speed variation due to the thickness of the belt. In an image forming apparatus having a transfer transfer device to be stabilized, a sub-scan magnification error of the transfer transfer device is detected based on speed information of the transfer transfer device, and the detected sub-scan magnification error is detected. It calculates a correction amount, those having a sub-scanning magnification correction means for controlling the driving of the transfer conveying device so as to reduce the sub scanning magnification error based on the correction amount thus calculated.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the speed information of the transfer / conveyance device is an output signal from the mark detection means.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the second aspect, the speed information of the transfer / conveyance device is a drive pulse of the drive motor.

  A fifth aspect of the present invention is the image forming apparatus according to the third aspect, wherein a plurality of the marks are provided.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the second to fifth aspects, the timing for correcting the sub-scanning magnification error is other than during the conveyance of the recording member.

  According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the second to fifth aspects, the timing for correcting the sub-scanning magnification error is immediately before the conveying operation of the recording member.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the second to fifth aspects, an image formation number counting unit that counts the number of image formations during image formation, and the image formation number counting unit. When the counted number of image formations exceeds a preset reference number, the recording member interval for sending the recording member from the recording member supply means to the transfer conveying device is changed to a recording member interval that is a predetermined amount longer than the recording member interval. The sub-scanning magnification error is corrected between the recording members at the changed recording member interval.

  According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the second to fifth aspects, the image forming apparatus includes a measuring unit that measures the temperature of the driven roller to which the encoder is attached. When the set temperature exceeds a preset reference temperature, the recording member interval for sending the recording member from the recording member supply means to the transfer conveying device is changed to a recording member interval that is longer than the recording member interval by a predetermined amount. The sub-scanning magnification error is corrected between the recording members at the changed recording member interval.

  According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the second to ninth aspects, the timing of developing the phase and amplitude values stored in the nonvolatile memory in the volatile memory is When the power of the drive control device is turned on or when the belt starts to be driven.

  According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the second to tenth aspects, a sine wave function or an approximate expression is used from the phase and amplitude values stored in the nonvolatile memory. Thus, correction data corresponding to the position of the belt from the mark is calculated.

  According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the second to eleventh aspects, the correction data according to the distance from the belt mark from the phase / amplitude value stored in the nonvolatile memory. Is calculated and stored in the volatile memory, the memory capacity of the volatile memory is reduced by thinning and storing the data.

  According to a thirteenth aspect of the present invention, in the image forming apparatus according to any one of the second to twelfth aspects, the correction data stored in the volatile memory is referred to when the belt is driven, and the correction is performed. When the data is added to the control target value to drive the drive unit, the correction data is started from zero at the start of control.

  According to a fourteenth aspect of the present invention, in the image forming apparatus according to any one of the second to thirteenth aspects, the phase and amplitude values stored in the non-volatile memory are input from an operation panel.

  An invention according to a fifteenth aspect is the image forming apparatus according to any one of the second to fourteenth aspects, which is a quadruple tandem system.

  According to a sixteenth aspect of the present invention, in the image forming apparatus according to any one of the second to fifteenth aspects, the belt is an intermediate transfer belt or a direct transfer belt.

  According to the present invention, it is possible to perform control that stabilizes the speed fluctuation caused by the thickness of the endless belt by an inexpensive method and an appropriate process according to the image quality, and performs good feedback control. be able to. Furthermore, it is possible to correct the sub-scanning magnification error that occurs when the outer diameter of the driven roller to which the encoder is attached changes according to the environment, and the correction can always be kept in a good state.

An embodiment in which the present invention is applied to an electrophotographic direct color transfer color laser printer (hereinafter referred to as a laser printer) as an image forming apparatus will be described.
FIG. 1 shows a laser printer of this embodiment. In this laser printer, four sets of toner image forming units 1Y, 1M, 1C, and 1K (hereinafter referred to as subscripts Y, M, C, and K) are used to form images of colors Y, M, C, and K. , Indicating the members for yellow, magenta, cyan, and black, respectively. The moving direction of the transfer paper 100 as a recording member (the endless belt 60 as a direct transfer conveyance belt 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 13. The toner image forming units 1Y, 1M, 1C, and 1K are arranged so that the rotation axes of the photosensitive drums 11Y, 11M, 11C, and 11K are parallel to each other and at a predetermined pitch in the transfer sheet moving direction. Is set to

This laser printer carries an optical writing unit 2 as an exposure unit, paper feed cassettes 3 and 4, a registration roller pair 5 and a transfer paper 100 in addition to the toner image forming units 1Y, 1M, 1C and 1K. A transfer unit 6 as a transfer conveyance device having a direct transfer conveyance belt 60 that conveys the toner image forming units 1Y, 1M, 1C, and 1K so as to pass through the transfer positions, a belt fixing type fixing unit 7, and a paper discharge tray 8 Etc. 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.
In each of the toner image forming units 1Y, 1M, 1C, and 1K, the photosensitive drums 11Y, 11M, 11C, and 11K are rotationally driven by a rotation driving unit (not shown) and are uniformly charged by a charging roller 12 as a charging unit. Thereafter, an electrostatic latent image is formed by exposure with a plurality of laser beams respectively modulated by image data of each color of Y, M, C, and K by the optical writing unit 2.

  The optical writing unit 2 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and a plurality of laser beams modulated by image data of each color of Y, M, C, and K, respectively, for each photosensitive drum 11Y. , 11M, 11C, and 11K are irradiated while scanning. The electrostatic latent images on the photosensitive drums 11Y, 11M, 11C, and 11K are developed by the developing device 13 and become toner images of Y, M, C, and K colors. The toner images of the respective colors on the photosensitive drums 11Y, 11M, 11C, and 11K are transferred to the transfer paper 100 on the transfer conveyance belt 60 by the transfer electric field by the transfer unit 6 at each transfer position, and then the photosensitive drums 11Y, 11M. , 11C and 11K are cleaned by the cleaning device 14 and further discharged by the charge eliminator to prepare for the formation of the next electrostatic latent image.

FIG. 2 shows the 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 / conveying belt 60 is wound around support rollers 61 to 68 so as to pass through the transfer positions in contact with and opposed to the photosensitive drums 11Y, 11M, 11C, and 11K of the toner image forming portions 1Y, 1M, 1C, and 1K. Has been.

  Of these support rollers 61 to 68, the inlet roller 61 on the upstream side in the transfer paper moving direction is formed on the inner peripheral surface of the transfer conveyance belt 60 so as to face the electrostatic adsorption roller 80 to which a predetermined voltage is applied from the power source 80a. They are placed in contact. The transfer paper 100 charged between the two rollers 61 and 80 is electrostatically attracted onto the transfer conveyance belt 60. The roller 63 is a driving roller that frictionally drives the transfer / conveying belt 60, and is connected to a driving source (not shown) and is driven to rotate in the arrow direction.

  As a transfer electric field forming means for forming a transfer electric field at each transfer position of the toner image forming portions 1Y, 1M, 1C, and 1K, the photosensitive drums 11Y, 11M, 11C, and 11K are opposed to the back surface of the transfer conveyance belt 60. As described above, transfer bias applying members 67Y, 67M, 67C, and 67K are provided. These transfer bias applying members 67Y, 67M, 67C, and 67K are bias rollers provided with a sponge or the like on the outer periphery, and transfer bias is applied to the roller core from each of the transfer bias power supplies 9Y, 9M, 9C, and 9K. Due to the applied transfer bias, a transfer charge is imparted to the transfer / conveying belt 60, and a transfer with a predetermined strength is made between the transfer / conveying belt 60 and the surface of the photosensitive drums 11Y, 11M, 11C, and 11K at each transfer position. An electric field is formed. A plurality of backup rollers 68 are provided in order to keep the transfer paper and the photosensitive drums 11Y, 11M, 11C, and 11K in contact with each other in an area where 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 about a rotation shaft 94. The transfer bias applying members 67Y, 67M, and 67C and the backup roller 68 are rotated 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 of FIG. A hole 95 provided in the swing bracket 93 and a pin 92 fixed to the entrance roller bracket 90 are engaged, and the entrance roller 61 and the suction roller 80 rotate in conjunction with the rotation of the swing bracket 93. To do. By rotating the brackets 90 and 93 in the clockwise direction, the bias applying members 67Y, 67M and 67C and the plurality of backup rollers 68 disposed in the vicinity thereof are separated from the photosensitive drums 11Y, 11M and 11C, and the entrance roller 61 The suction roller 80 also moves downward. This makes it 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 the transfer unit 6 is attached to or detached from the main body of the laser printer, the transfer bias applying member 67K and the backup roller 68 adjacent thereto are rotated clockwise by the operation of a handle (not shown) for black image formation. The photosensitive member 11K is separated from the photosensitive member 11K.

  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, and the toner adhered on the transfer conveyance belt 60 by the cleaning device 85. Etc. are removed.

  A roller 64 is provided downstream of the drive 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 60, and a winding angle of the transfer conveyance belt 60 around the drive roller 63 is secured. . A tension roller 65 that applies tension to the belt 60 by a spring 69 as a pressing member is provided further downstream from the roller 64 in the loop of the transfer conveyance belt 60.

  A one-dot chain line in FIG. 1 indicates a 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 sent out by the registration roller pair 5 at a predetermined timing is carried by the transfer conveyance belt 60 and conveyed toward the toner image forming units 1Y, 1M, 1C, and 1K, and the toner image forming unit 1Y, It passes through each transfer nip of 1M, 1C and 1K.

  The toner images of the respective colors formed on the photosensitive 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, The image is transferred onto the transfer paper 100 under the action of the nip pressure. A full color toner image is formed on the transfer paper 100 by superimposing and transferring the color toner images. The surface of the photosensitive drums 11Y, 11M, 11C, and 11K after the toner image transfer is cleaned by the cleaning device 14, and is further neutralized by a static eliminator (not shown) 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. Heading in the paper discharge direction C. When the transfer paper 100 is discharged onto the paper discharge tray 8 from the first paper discharge direction B, the transfer paper 100 is stacked on the paper discharge tray 8 in a so-called face-down state with the image surface down. On the other hand, when the transfer paper 100 is discharged in the second paper discharge direction C, the transfer paper 100 is conveyed toward another post-processing device (not shown) (sorter, binding device, etc.), or both sides through a switchback unit. It is again conveyed to the registration roller pair 5 for printing.

  In this tandem laser printer, it is important to prevent the occurrence of color misregistration by accurately superimposing toner images of respective colors. However, the drive roller 63, the entrance roller 61, the exit roller 99, and the transfer / conveying belt 60 used in the transfer unit 6 are subject to manufacturing errors of several tens of μm when parts are manufactured. Due to this error, a fluctuation component generated when each part makes one rotation is transmitted onto the transfer conveyance belt 60, and the conveyance speed of the transfer paper 100 varies, so that the toner on each of the photosensitive drums 11Y, 11M, 11C, and 11K is transferred. A slight shift occurs in the timing of transfer to the transfer paper 100, 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 this embodiment, a timing shift of several μm becomes conspicuous as a color shift.

In the present embodiment, an encoder is mounted 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 conveyance belt 60 travels at a constant speed. Yes.
FIG. 3 shows a configuration of main parts of the transfer unit 6. The drive roller 63 is connected to the drive gear of the transfer drive motor 302 through the timing belt 303, and rotates at a speed proportional to the drive speed of the drive motor 302 when the drive motor 302 is driven to rotate. When the driving roller 63 rotates, the transfer conveyance belt 60 is driven, and when the transfer conveyance belt 60 is driven, the lower right roller 66 rotates following the transfer conveyance belt 60. In the present embodiment, the encoder 301 is disposed on the shaft 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 of the transfer / conveyance belt 60 because the color shift occurs due to the speed fluctuation of the transfer / conveyance belt 60 as described above.

  FIG. 4 shows details 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 is rotated 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 a light emitting element 402 and a light receiving element 403 are disposed on both sides thereof, and light from the light emitting element 402 is passed through the slits of the disk 401. Is received by the light receiving element 403, and a pulse-like on / off signal is obtained according to the amount of rotation of the lower right roller 66. The driving amount of the driving motor 302 is controlled by detecting the moving angle (hereinafter referred to as angular displacement) of the lower right roller 66 using this pulse-like on / off signal.

  A mark 304 for managing the reference position of the transfer / conveyance belt 60 is attached to the non-image forming area on the surface of the transfer / conveyance belt 60. The presence or absence of 304 is detected. This is because, as will be described later, the effective driving radius of the lower right roller 66 changes due to uneven thickness of the transfer conveyance belt 60, and the speed of the encoder 301 is in spite of the fact that the speed of the transfer conveyance belt 66 is actually constant. In order to prevent the detection from being detected as fluctuating, the detected angular displacement error caused by the fluctuation of the belt thickness of the transfer conveyance belt 60 that has been measured in advance is added to the control target value, and the addition result is obtained. By performing feedback control of the transfer conveyance motor 302 as a control target value, the belt 60 is conveyed at a constant speed. A mark 304 is attached to associate the actual position of the belt 60 with the detected angular displacement error. The control target value is set so that the angular displacement amount of the encoder 301 per unit time is constant.

  In the proportional control calculation of the feedback control, as described above, the control gain is applied to the difference between the target angular displacement and the detected angular displacement for each control cycle to control the driving speed of the driving motor 302. If the displacement error is large, the drive motor 302 is driven after further amplification. Therefore, the speed variation of the transfer / conveyance belt 60 is generated depending on the thickness of the belt 60, and color misregistration occurs.

  In other words, as described above, when the drive motor is driven at a constant speed, even if the transfer conveyance belt is ideally conveyed without fluctuations in speed, if the thick part of the belt is wound around the driven shaft, As the radius increases, the rotational angular displacement of the driven shaft per fixed time decreases, and this is detected as a decrease in belt conveyance speed. Further, when the thin portion of the belt is wound around the driven shaft, the amount of rotational angular displacement of the driven shaft increases, and this is detected as an increase in the belt conveyance speed.

  This shows the behavior when the drive motor 302 is driven at a constant speed. In other words, when the count value obtained by counting the pulses of the encoder 301 is sampled at a constant timing, as shown in FIG. The lower roller 66 is rotating at a constant speed. Therefore, in the present embodiment, as shown in FIG. 24, a target angular displacement is generated for each control cycle, and the encoder 301 is controlled like the target angular displacement, so that the speed of the belt 60 is made constant.

This is not to measure the actual thickness of the transfer / conveying belt 60 in μm and use it as a control parameter, but to control the detected angular displacement error of the encoder 301 in rad generated due to the influence of the thickness of the belt 60. It is said.
Since the control parameter is generated from the output result of the encoder 301 when the drive motor 302 is driven at a constant speed as described above, it is possible to generate the control parameter even with an actual machine, so that the thickness of the belt 60 is measured. Therefore, it is possible to configure the apparatus at a very low cost.

  As will be described later, since the thickness of the belt 60 has a sinusoidal characteristic in most cases, when high-resolution measurement is possible with an external jig or the like, the belt mark 304 is obtained from the measurement result with the external jig. It is also possible to realize feedback control of the drive motor 302 by calculating the phase and the maximum amplitude of the motor and inputting them as the control parameters from the operation panel on the actual machine.

  In addition, not only the detected angular displacement error due to the thickness of the belt 60 but also the fluctuation / rotation eccentric component of the driving roller 63 and other components are superimposed and output on the actual output result of the encoder 301. Therefore, a process for extracting only the influence component of the driven roller 66 is performed, and the extracted result is used as a control parameter for the detected angular displacement error.

FIG.5 (b) shows the drive control apparatus as a rotary body drive device for implementing the belt drive control method as a rotary body drive method in embodiment of this invention. Hereinafter, the drive control apparatus of this embodiment will be described.
In FIG. 5, the difference e (n) between the target angular displacement Ref (n) of the encoder 301 and the detected angular displacement P (n−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 (steady 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 a certain standard drive pulse frequency Refp_c (Rfpc) to determine the drive pulse frequency f (n).

  Further, as shown in FIG. 5C, the CPU 601 (see FIG. 6) generates a control target value by adding the detected angular displacement error caused by the thickness variation of the transfer conveyance belt 60 to the target angular displacement Ref (n). Then, by calculating the difference e (n) between this control target value and the detected angular displacement P (n−1) of the encoder 301, the displacement amount of the difference is calculated. The CPU 601 periodically repeats the addition of the detected angular displacement error caused by the thickness variation of the transfer conveyance belt 60 according to the output timing of the mark sensor 305 detected by the rotation of the transfer conveyance belt 60. To do. The pulse output unit 505 operates based on the pulsed control signal output from the calculation unit 504, applies a pulsed drive voltage to the transfer drive motor 302, and outputs the transfer drive motor 302 from the calculation unit 504. Drive control is performed at a predetermined drive frequency.

  FIG. 6 shows a control system of the transfer drive motor 302 and a hardware configuration to be controlled in the present embodiment. This control system is a control system that digitally controls the drive pulse 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 unit 608.

  The CPU 601 performs overall control of the laser printer, including reception of image data input from the external device 610 and transmission / reception control of control commands. A RAM 602 used for work, a ROM 603 for storing a program, and an IO control unit 604 are connected to each other via a bus, and according to instructions from the CPU 601, read / write processing of data and motors, clutches, solenoids, Various operations such as sensors are executed.

  The transfer drive motor IF unit 606 outputs a command signal for instructing the drive frequency of the drive pulse signal to the transfer drive motor 302 via a driver 607 (corresponding to the pulse output unit 505) 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 of the transfer drive motor 302 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. The detection IO unit 608 includes a counter that counts the output pulses of the encoder 305, and the numerical value counted by the counter is multiplied by a predetermined conversion constant of the diagonal displacement of the number of pulses, and the lower right roller 66 (disk 401). Convert to a digital value corresponding to the angular displacement of the axis. A digital numerical signal corresponding to the angular displacement of the disk 401 is sent to the CPU 601 via the bus.

  The transfer drive motor IF unit 606 generates a pulse-like control signal having the drive frequency based on the drive frequency command signal sent from the CPU 601 (control signal from the calculation unit 504). The driver 607 is composed of a power semiconductor element (for example, a transistor). The driver 607 operates based on the pulsed control signal output from the transfer drive motor IF unit 606 and applies a pulsed drive voltage to the transfer drive motor 302. As a result, the transfer drive motor 302 is driven and controlled at a predetermined drive frequency output from the CPU 601. As a result, the transfer drive motor 302 is subjected to additional value control so that the angular displacement of the disk 401 follows the target angular displacement, and the lower right roller 66 rotates at a predetermined constant 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 above 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 transfer conveyance that has been measured in advance by the CPU 601 based on the outputs of the mark sensor 305 and the encoder 301. Stored is the detected angular displacement error data for one round of the belt from the belt mark 304 corresponding to the thickness variation of the belt 60. Since the RAM 602 is a volatile memory, the CPU 601 detects in a non-volatile memory such as an EEPROM (not shown) corresponding to the thickness variation of the belt 60 as shown in FIG. 7 obtained from the outputs of the mark sensor 305 and the encoder 301. Stores the phase and amplitude parameters (phase and maximum amplitude data up to the detected angular displacement error mark 304) of angular displacement error (or detected angular displacement error input from the operation panel), and power-on or transfer drive The detected angular displacement error data corresponding to the thickness variation of one cycle of the belt 60 is calculated from this phase / amplitude parameter using the SIN (sinusoidal) function or approximate expression when the motor 302 is started, and is stored in the RAM 602. expand.

  The actual thickness of the belt 60 largely depends on the manufacturing process, but in most cases, it is a SIN shape, and it is not necessary to have all detected angular displacement error data for one belt revolution. The CPU 601 calculates the phase and amplitude from the reference position (the position of the mark 304) of the detected angular displacement error corresponding to the thickness variation of the belt 60 during measurement, and calculates the detected angular displacement error data of the encoder 305 from this data. However, it can be handled as sufficiently equivalent data.

  Therefore, it is not necessary to store the detected angular displacement error data for each control cycle in the nonvolatile memory, and the detected angular displacement error data based on the belt thickness is generated using only the phase / amplitude parameters. Control is possible only by preparing. Generation of detected angular displacement error data by the thickness of the belt 60 by the CPU 601 is performed by the following arithmetic expression when the power is turned on or when the transfer driving motor 302 is activated.

Δθ [rad]: rotational angular velocity fluctuation value of the driven shaft of the lower right roller 66 [= b * sin (2 * π * ft + τ)]
The CPU 601 calculates Δθ from the value of the nonvolatile memory according to the control time from the belt mark 304, and sequentially stores it in the RAM 602, which is a volatile memory.

  When the transfer motor 302 is actually driven, the CPU 601 reads the detected angular displacement error data from the RAM 602 by switching the reference address of the RAM 602 according to the timing when the belt mark detection sensor 305 detects the belt mark 304. The CPU 601 performs feedback control without being affected by the belt thickness by adding the read data to the control target angular displacement.

  Further, when only the peak value of the speed fluctuation due to the thickness of the belt 60 is lowered, the detected angular displacement error data based on the thickness of the belt 60 for each control cycle is not necessary. Therefore, in order to reduce the memory area, the CPU 601 thins out the value of the non-volatile memory and, for example, about 50 (or 100 or 20) points per revolution of the belt 60 as shown in FIG. 18 (or FIG. 19). By generating control target profile data and updating the thickness profile data when the transfer / conveying belt 60 reaches each point, the peak value of the speed fluctuation due to the thickness of the belt 60 can be sufficiently reduced.

  8 and 9 are timing charts for realizing this control. First, the detection IO unit 608 increments the count value of the encoder pulse counter 1 by the rising edge of the A-phase output of the output pulse of the encoder 301. Further, the control cycle of this control is 1 ms, and the detection IO unit 608 increments the count value of the control cycle timer counter every time the control cycle timer interrupts the CPU 601. The detection IO unit 608 starts the control cycle timer when the rising edge of the output pulse of the encoder 301 is detected for the first time after the through-up and settling of the drive motor 302 is completed, and resets the count value of the control cycle timer counter. .

  The detection IO unit 608 obtains and increments the count value: ne of the encoder pulse counter 1 and the count value: q of the control period timer counter each time an interruption is made to the CPU 601 by the control period timer. Similarly to the encoder pulse counter 1, the detection IO unit 608 increments the encoder pulse counter 2 at the rising edge of the A-phase output of the output pulse of the encoder 301, and when the mark detection signal is input from the belt mark sensor 305. Reset at the rising edge of the output pulse of the first encoder 301. Therefore, the encoder pulse counter 2 substantially counts the moving distance from the mark 304 on the belt 60, and switches the reference address of the RAM 602 in which the control target profile data for one round of the belt 60 is stored according to the count value. .

The CPU 601 calculates the positional deviation of the belt 60 based on the count value of each counter of the detection IO unit 608 as follows.
e (n) = θ0 * q + (Δθ−Δθ ₀ ) −θ1 * ne Unit: rad
here,
e (n) [rad]: Position deviation (calculated in this sampling) θ0 [rad]: Movement angle per control cycle 1 [ms] (= 2π * V * E-3 / lπ [rad])
Δθ [rad]: Rotational angular velocity fluctuation value of driven shaft of lower right roller 66 [= b * sin (2 * π * ft + τ)] (table reference value)
Δθ ₀ [rad]: Δθ value acquired first after driving motor 302 is started θ1 [rad]: Movement angle per pulse of encoder 301 (= 2π / p [rad])
q: Count value of control cycle timer V: Linear velocity of belt 60 [mm / s]
l: Diameter of lower right roller 66 [mm]
b: Amplitude fluctuating with the thickness of the belt 60 [rad]
τ: phase at the belt mark 304 of the belt 60 thickness variation [rad]
f: Period of thickness variation of belt 60 [Hz]
In this embodiment, the diameter of the driven roller 66 to which the encoder 301 is attached is 15.515 [mm], and the thickness of the belt 60 is 0.1 [mm]. The driven roller 66 is rotationally driven by the friction of the belt 60. If the thickness of the belt 60 is substantially a half of the thickness of the belt 60, the driven roller 66 is rotated.
l = 15.515 + 0.1 = 15.615 [mm]
It becomes. In this embodiment, the resolution p of the encoder 301 is assumed to be 300 pulses per rotation of the encoder 301.

In this embodiment, the CPU 601 obtains the first Δθ value obtained after the drive motor 302 is started as Δθ _0, and obtains the first value after the drive motor 302 is started from Δθ using the calculation formula “(Δθ−Δθ ₀ )”. By subtracting Δθ ₀ , the rapid speed fluctuation at the start of the feedback control is reduced as shown in FIG. The CPU 601 uses the same value as Δθ ₀ during the rotation of the transfer motor 302 and updates it every time the transfer motor 302 is activated.

Next, the CPU 601 performs a filter calculation of the following specifications with respect to the calculated position deviation with the filter 502 of the position controller unit 501 shown in FIG. 5 in order to avoid a response to a sudden position change of the belt 60. .
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 edge frequency (Fp): 50Hz
Stopband edge frequency (Fs): 100Hz
FIG. 10 shows a block diagram of this filter calculation, and FIG. 11 shows a list of the filter coefficients. This filter has a two-stage cascade connection, and the intermediate nodes in 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): Second previous sampling The CPU 601 performs the following program calculation every time an interrupt is generated by the control cycle timer during execution of feedback control.

u1 (n) = a11 * u1 (n−1) + a21 * u1 (n−2) + e (n) * ISF
e1 (n) = b01 * u1 (n) + b11 * u1 (n−1) + b21 * u1 (n−2)
u1 (n−2) = u1 (n−1)
u1 (n−1) = u1 (n)

u2 (n) = a12 * u2 (n−1) + a22 * u2 (n−2) + e1 (n)
e '(n) = b02 * u2 (n) + b12 ** u2 (n-1) + b22 * u2 (n-2)
u2 (n−2) = u2 (n−1)
u2 (n−1) = u2 (n)
FIG. 12 shows the amplitude characteristics of this filter, and FIG. 13 shows the phase characteristics of this filter.

Next, the CPU 601 obtains a control amount for the control target. As shown in FIG. 5, the CPU 601 first performs PID control in the proportional element 503 of the position controller unit 501.
F (S) = G (S) * E '(S) = Kp * E' (S) + Ki * E '(S) / S + Kd * S * E' (S)
Where Kp: proportional gain, Ki: integral gain, Kd: derivative gain
G (S) = F (S) / E '(S) = Kp + Ki / S + Kd * S (2)
Here, when the equation (2) is bilinearly converted (S = (2 / T) * (1−Z ⁻¹ ) / (1 + Z ⁻¹ )), the following equation is obtained.

G (Z) = (b0 + b1 * Z- ¹ + b2 * Z- ² ) / (1-a1 * Z- ^1- a2 * Z- ² ) (3)
However, a1 = 0
a2 = 1
b0 = Kp + T * Ki / 2 + 2 * Kd / T
b1 = T * Ki-4 * Kd / T
b2 = −Kp + T * Ki / 2 + 2 * Kd / T
Expression (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. 14, when w (n), w (n-1), and w (n-2) are respectively determined as intermediate nodes, the difference equation is expressed by the following equation (general equation for PID control). Here, the meaning of the index is as follows.

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

w (n) = a1 * w (n-1) + a2 * w (n-2) + e '(n) (4)
f (n) = b0 * w (n) + b1 * w (n−1) + b2 * w (n−2) (5)
Now, considering the proportional control with the proportional element 503 of the position controller 501, the integral gain and the differential gain are zero. Accordingly, the coefficients in FIG. 14 are as follows, and the equations (4) and (5) are simplified as the equation (6).
a1 = 0
a2 = 1
b0 = Kp
b1 = 0
b2 = −Kp
w (n) = w (n−2) + e ′ (n)
f (n) = Kp * w (n) -Kp * w (n-2)
→ ∴ f (n) ＝ Kp ＊ e '(n) (6)
Also, discrete data corresponding to F0 (S): f0 (n) is constant in the present embodiment,
f0 (n) = 6105 [Hz]
It is. Therefore, the pulse frequency set for the transfer drive motor 302 is finally calculated by the following equation.

F ′ (n) = f (n) + f0 (n) = Kp * e ′ (n) +6105 [Hz] (7)
FIG. 15 shows an operation flowchart of the encoder pulse counter 1.
First, the detection IO unit 608 determines whether or not the pulse input from the encoder 301 is the first pulse input after through-up and settling of the transfer drive motor 302 (step: STEP1), and a positive determination (step 1). If YES, the encoder pulse counter 1 is cleared to zero (STEP 2), the control cycle counter is cleared to zero (STEP 3), the interrupt by the control cycle timer is permitted (STEP 4), and the control cycle timer is started (STEP 5). ), Return. If the determination in STEP 1 is negative (NO), the detection IO unit 608 increments the encoder pulse counter 1 (STEP 6) and returns.

FIG. 16 shows an operation flowchart of the encoder pulse counter 2.
First, the detection IO unit 608 determines whether or not the output of the belt mark sensor 305 has changed from the high level H to the low level L when a pulse from the encoder 301 is input (STEP 1). 2 is cleared to zero (STEP 2). If the determination at STEP 1 is NO, the detection IO unit 608 increments the encoder pulse counter 2 (STEP 3) and returns.

FIG. 17 shows a flowchart of interrupt processing by the control cycle timer.
The CPU 601 first increments the control cycle timer counter (STEP 1), and then acquires the encoder pulse count value: ne (STEP 2). The CPU 601 further refers to the table data with the encoder pulse count value: ne, acquires the value of Δθ (STEP 3), and increments the table reference address (STEP 4). Using these values, the CPU 601 performs the calculation for obtaining the position deviation as described above (STEP 5), performs the filter calculation for the position deviation obtained by this calculation as described above (STEP 6), and performs the filter calculation. Based on the result, the control amount calculation (proportional calculation) is performed as described above (STEP 7), the frequency of the drive pulse of the stepping motor as the transfer drive motor 302 is actually changed (STEP 8), and the process returns.
By the above control, it is possible to perform the control for stabilizing the speed fluctuation caused by the belt thickness by an inexpensive method and an appropriate process according to the image quality. In other words, the speed fluctuation caused by the thickness fluctuation of the belt 60 is stabilized, so that the speed fluctuation of the belt 60 as shown in FIG. 26 is stabilized as shown in FIG. However, for example, when the speed of the belt 60 is constantly higher than the target speed as shown in FIG. 28 due to the expansion of the encoder 301, the on-image sub-scanning magnification increases and the image is stretched. This is corrected by a sub-scanning magnification correcting means described later.

  Next, a sub-scanning magnification error caused by a change in the absolute speed of the conveyance speed of the belt 60 in this embodiment will be described. From the above equation (1), the conveyance speed V of the belt 60 is normally determined by the radius R of the driving roller 63, the thickness B of the belt 60, and the angular speed ω of the driving roller 63. When the radius R of the drive roller 63 undergoes thermal expansion or contraction depending on the usage environment, the conveyance speed V of the belt 60 changes.

  However, when the driven shaft feedback control is performed, the expansion / contraction of the radius R of the driving roller 63 does not contribute to the conveyance speed V of the belt 60, and the belt conveyance speed by the expansion / contraction of the lower right roller 66 to which the encoder 301 is attached. V changes. As described above, the driven shaft feedback controls the drive pulse of the drive roller 63 so as to follow the control target value (target angular displacement amount of the encoder) shown in FIG. This is because the conveyance speed V of the belt 60 is corrected by feedback control. However, when the lower right roller 66 itself to which the encoder 301 is attached expands and contracts, the belt driven effective radius increases and decreases to cause the same phenomenon as the erroneous detection of the change in the rotational angular velocity of the driven shaft. When the belt expands, the belt conveyance speed becomes faster than the target speed, and when the lower right roller 66 contracts, the belt conveyance speed becomes slower than the target speed.

Further, since the change in the belt conveyance speed is a change in speed due to the expansion and contraction of the diameter of the lower right roller 66, it is not a periodic change like the speed change due to the thickness of the belt 60, and always increases or decreases constantly. Therefore, it appears as a sub-scanning magnification error on the actual image. In the present embodiment, as described above, sub-scanning that corrects the sub-scanning magnification error that occurs when the outer diameter of the lower right roller 66 undergoes thermal expansion and contraction depending on the environment in a short time without adding new parts. The magnification correction unit will be described.
FIG. 29 shows a drive control apparatus having sub-scanning magnification correcting means for performing sub-scanning magnification error correction. The sub-scanning magnification correction unit includes a target value, calculation units 506 and 508, and a proportional element (gain Kq) 507. Since the configuration of the drive control device other than the sub-scanning magnification correction unit is the same as that shown in FIG. 5, detailed description thereof is omitted.

In FIG. 29, the target value is information relating to the belt conveyance speed. This target value is obtained from the output signal of the sensor 305 for the belt mark 304. For example, when the circumference of the belt 60 is 815 mm and the driving speed of the belt 60 is 125 mm / s, the timing of the output signal of the sensor 305 with respect to the belt mark 304 is
815 (mm) / 125 (mm / s) = 6.52 (s)
It becomes. In the sub-scanning magnification correcting means, the timing of the output signal of the sensor 305 is set as a target value.

For example, when the diameter of the lower right roller 66 is thermally expanded and the diameter becomes 0.1% thick, the belt conveyance speed is also increased by 0.1%, so the target value is
125 (mm / s) x (100.1 / 100) = 125.125 (mm / s)
It becomes. At this time, the sub-scanning magnification is also increased by 0.1%, and the timing of the output signal of the sensor 305 with respect to the belt mark 304 is
815 (mm) / 125.125 (mm / s) = 6.51 (s)
It becomes.

  The calculation unit 506 compares the output signal of the sensor 305 with the target value to calculate a timing deviation 0.01 (s) from the target value 6.52 (s) of the output signal of the sensor 305, and a proportional element In 507, the gain Kq is applied, and the calculation unit 508 subtracts the output of the proportional element 507 from the output of the calculation unit 504 to determine the number of drive pulses Y (n) to the pulse output device 505 (driver 607). Correct the scanning magnification error.

Normally, to accurately detect the absolute speed of the belt conveyance speed, information for several belt revolutions is necessary. During that time, printing (image formation) is interrupted, or the image during that time remains in the sub-scan magnification ratio. However, if the sub-scanning magnification correction is performed after stabilizing the speed fluctuation caused by the thickness of the belt 60, it is possible to correct the sub-scanning magnification error in the time of one round of the belt.
As described above, according to the first embodiment, it is possible to correct the sub-scanning magnification error that occurs when the outer diameter of the driven roller 66 to which the encoder 301 is attached changes depending on the environment, and the correction is always in a good state. Can be kept in.

  In Embodiment 2 of the present invention, in the above embodiment (hereinafter referred to as Embodiment 1), the marks 304 are a plurality of marks provided on the belt 60 at equal intervals. The plurality of marks are detected by the sensor 605, and an output signal of the sensor 305 is input to the calculation unit 506. As a result, it is possible to further reduce the time required to detect a timing shift from the target value of the output signal of the sensor 305.

  In the third embodiment of the present invention, the target value input to the calculation unit 506 in the first embodiment is used as the drive pulse of the drive motor 302. A driving pulse per unit time is set as a target value, a deviation from the target value of the output signal of the sensor 305 is calculated by the calculation unit 506, and the gain Kq is multiplied by the proportional element 507 to the calculation unit 508. By subtracting the output of the proportional element 507 from the output of the calculation unit 504, the drive pulse Y (n) subjected to the sub-scanning magnification correction is determined.

In each of the above embodiments, the information related to the belt conveyance speed as the target value is normally calculated at the time of factory shipment and stored in the nonvolatile memory, and the target value is generated from the information in the nonvolatile memory at the time of correcting the sub-scanning magnification error. And input to the calculation unit 506.
In Embodiment 4 of the present invention, in each of the above embodiments, if the correction of the sub-scanning magnification error is performed while the paper is being passed (while the transfer paper is being conveyed), the lower right roller 66 expands and contracts in the middle of the image. The sub-scanning magnification correcting unit does not correct the sub-scanning magnification error while passing the paper.

Embodiment 5 of the present invention is such that, in each of the above embodiments, the sub-scanning magnification correction unit performs correction of the sub-scanning magnification error immediately before the sheet passing (transfer paper transfer) operation. Can be kept in a good state.
In Embodiment 6 of the present invention, in Embodiments 1 to 3, the internal temperature (internal temperature of Embodiment 6) rises during printing, the diameter of the lower right roller 66 expands, and the conveying speed of the belt 60 increases. Therefore, the image forming number counting means (not shown) counts the number of image forming sheets by counting the number of passing sheets, and compares the counted number with a preset reference number by the comparing means. When the number exceeds a preset reference number, the sub-scanning magnification correcting means corrects the sub-scanning magnification. As a result, it is possible to perform sub-scanning magnification error correction as the temperature inside the apparatus increases. Further, if the sub-scanning magnification correction is performed while the paper is passing, the image is expanded and contracted as described above. Therefore, the transfer paper conveyance interval is widened without performing the paper passing during the sub-scanning magnification correction.

  In Embodiment 7 of the present invention, in Embodiments 1 to 3, the temperature in the apparatus rises during mass printing, the diameter of the lower right roller 66 expands, and the conveying speed of the belt 60 increases, so the lower right roller The temperature of 66 is constantly measured and monitored by the temperature sensor, and when the output value of the temperature sensor exceeds the preset temperature by comparing the output value of the temperature sensor with the preset temperature by the comparison means. The sub-scanning magnification correction means performs sub-scanning magnification correction, and printing can be performed without changing the sub-scanning magnification during mass printing. Similarly to the sixth embodiment, when the sub-scanning magnification correction unit performs sub-scanning magnification correction when passing paper, the transfer paper conveyance interval is set to be longer than the sub-scanning magnification correction time.

  In each of the embodiments described above, the present invention is applied to a tandem type printer in which a plurality of photosensitive drums 11Y, 11M, 11C, and 11K are arranged on the transfer conveyance belt 60 and includes the transfer unit 6. However, the image forming apparatus and the drive control apparatus to which the present invention can be applied are not limited to the configuration of the above embodiment. The present invention is applied to a printer, a copying machine, a facsimile, or the like having a drive control device that rotationally drives an endless belt stretched around a plurality of rollers by at least one of the plurality of rollers, and the drive control device. It is possible to apply.

  In the above embodiment, the transfer belt 60 is used to transfer the transfer paper, and the toner of each color on the photosensitive drums 1111Y, 11M, 11C, and 11K is transferred onto the transfer paper. The present invention can also be applied to an intermediate transfer system in which four color toners are superimposed and transferred to form a four-color superimposed image and then transferred onto a transfer sheet. In the above embodiment, the exposure light source is a laser light source, but the present invention is not limited to this, and the exposure light source may be, for example, an LED array.

It is sectional drawing which shows the laser printer which is one Embodiment of this invention. It is a front view which shows the structure of the transfer unit in the embodiment. It is a perspective view which shows the structure of the main components of the transfer unit in the embodiment. It is a perspective view which shows the detail of the lower right roller and encoder in the same embodiment. FIG. 3 is a block diagram showing a belt drive control device in the same embodiment, a detected angular displacement error caused by a change in the belt thickness of the encoder, a control target value, and a sum thereof. FIG. 2 is a block diagram illustrating a control system of a transfer drive motor and a hardware configuration to be controlled in the embodiment. It is a figure which shows the detection angular displacement error corresponding to the thickness variation of the belt in the same embodiment. It is a timing chart which shows the control timing of the embodiment. It is a timing chart which shows the control timing of the embodiment. It is a block diagram which shows the filter calculation of the same embodiment. It is a figure which shows the filter coefficient list | wrist of the embodiment. It is a characteristic view which shows the amplitude characteristic of the filter of the embodiment. It is a characteristic view which shows the phase characteristic of the filter of the embodiment. It is a figure which shows the formula of PID control in the same embodiment. It is a flowchart which shows the operation | movement flow of the encoder pulse counter 1 in the same embodiment. It is a flowchart which shows the operation | movement flow of the encoder pulse counter 2 in the same embodiment. It is a flowchart which shows the interruption processing flow by the control period timer in the embodiment. It is a figure which shows the example of the profile data in the same embodiment. It is a figure which shows the other example of the profile data in the same embodiment. It is a front view which shows a part of endless belt and the example of a driving roller. It is a front view which shows the model of a belt drive conveyance system. It is a figure which shows notionally the belt thickness fluctuation | variation and belt conveyance speed fluctuation | variation over 1 round of a belt when the drive shaft of a drive roller is rotated at a fixed angular velocity. It is a figure which shows the belt thickness fluctuation | variation by the driven shaft when the belt is conveyed by the fixed conveyance speed, and the belt conveyance speed fluctuation | variation detected by the driven shaft of the driven roller. It is a figure which shows the example of the target angular displacement for every control period. It is a figure which shows a mode that the rapid speed fluctuation | variation at the time of the feedback control start of the said embodiment is eased. It is a figure which shows the speed fluctuation of a belt. It is a figure which shows a mode that the belt speed fluctuation | variation of the said embodiment is stabilized. It is a figure which shows the state by which the speed of the belt became constant and faster than the target speed by the expansion | swelling of the encoder. It is a block diagram which shows the drive control apparatus which has the subscanning magnification correction | amendment means of the said embodiment.

Explanation of symbols

2 Writing unit 11Y, 11M, 11C, 11K Photosensitive drum 12 Charging roller 13 Developing unit 63 Drive roller 60 Transfer conveyance belt 67Y, 67M, 67C, 67K Transfer device 65 Tension roller 66 Driven roller 301 Encoder 302 Transfer conveyance motor 305 Mark sensor 501 Control controller unit 506, 508 Calculation unit 507 Proportional element 601 CPU

Claims (16)

An endless belt that conveys the recording member and transfers an image onto the recording member, a driving roller that drives the belt, a driving motor that drives the driving roller, driving means that drives the driving motor, and the belt A transfer conveyance device having a plurality of driven rollers, and having an encoder attached to one of the plurality of driven rollers, and controlling the angular displacement of the encoder per unit time to be constant A drive control device configured to control a speed of the belt by setting a target value and controlling the driving means so that an angular displacement amount of the encoder is equal to the control target value;
Mark detection means for detecting a mark serving as a reference position of the belt;
A detection angular displacement error detecting means for detecting a detection angular displacement error of the encoder that occurs due to a thickness variation of the belt;
First means for calculating the phase and amplitude at the mark in the detected angular displacement error of the encoder obtained from the detected angular displacement error detecting means;
A nonvolatile memory for storing the calculation result of the first means;
Second means for calculating correction data according to a distance from the mark of the belt based on a value stored in the nonvolatile memory;
A volatile memory for storing the correction data;
When the belt is driven, the correction data stored in the volatile memory is referred to, the correction data is added to the control target value, and the driving means is driven to control the speed according to the thickness of the belt. In the drive control device that stabilizes fluctuations,
A sub-scan magnification error of the transfer / conveyance device is detected based on the speed information of the transfer / conveyance device, a correction amount of the detected sub-scan magnification error is calculated, and a sub-scan magnification error is calculated based on the calculated correction amount. A drive control apparatus comprising: a sub-scanning magnification correction unit that performs drive control of the transfer / conveyance device so as to reduce the amount. An endless belt that conveys the recording member and transfers an image onto the recording member, a driving roller that drives the belt, a driving motor that drives the driving roller, driving means that drives the driving motor, and the belt The control target value is set so that the angular displacement of the encoder per unit time is constant, having a plurality of driven rollers that are driven and an encoder attached to one of the driven rollers. An image forming apparatus that controls the speed of the belt by controlling the driving unit so that the angular displacement amount of the encoder is equal to the control target value,
Mark detection means for detecting a mark serving as a reference position of the belt;
A detection angular displacement error detecting means for detecting a detection angular displacement error of the encoder that occurs due to a thickness variation of the belt;
First means for calculating the phase and amplitude at the mark in the detected angular displacement error of the encoder obtained from the detected angular displacement error detecting means;
A nonvolatile memory for storing the calculation result of the first means;
Second means for calculating correction data according to a distance from the mark of the belt based on a value stored in the nonvolatile memory;
A volatile memory for storing the correction data;
When the belt is driven, the correction data stored in the volatile memory is referred to, the correction data is added to the control target value, and the driving means is driven to control the speed according to the thickness of the belt. In an image forming apparatus having a transfer conveyance device that stabilizes fluctuations,
A sub-scan magnification error of the transfer / conveyance device is detected based on the speed information of the transfer / conveyance device, a correction amount of the detected sub-scan magnification error is calculated, and a sub-scan magnification error is calculated based on the calculated correction amount. An image forming apparatus, comprising: a sub-scanning magnification correction unit that performs drive control of the transfer / conveyance device so as to reduce the amount.   3. The image forming apparatus according to claim 2, wherein the speed information of the transfer / conveyance device is an output signal from the mark detection means.   3. The image forming apparatus according to claim 2, wherein the speed information of the transfer / conveyance device is a drive pulse of the drive motor.   4. The image forming apparatus according to claim 3, wherein a plurality of the marks are provided.   6. The image forming apparatus according to claim 2, wherein the timing for correcting the sub-scanning magnification error is other than during conveyance of the recording member.   6. The image forming apparatus according to claim 2, wherein the timing of correcting the sub-scanning magnification error is immediately before the recording member is transported.   6. The image forming apparatus according to claim 2, wherein an image forming number counting unit that counts the number of formed images during image formation and an image forming number counted by the image forming number counting unit are set in advance. When the set reference number is exceeded, the recording member interval for sending the recording member from the recording member supply means to the transfer conveying device is changed to a recording member interval that is longer than the recording member interval by a predetermined amount, and the changed recording member An image forming apparatus that corrects the sub-scanning magnification error between recording members at intervals.   6. The image forming apparatus according to claim 2, further comprising a measuring unit that measures a temperature of a driven roller to which the encoder is attached, and the temperature measured by the measuring unit is set in advance. When the reference temperature is exceeded, the recording member interval for sending the recording member from the recording member supply means to the transfer conveying device is changed to a recording member interval that is a predetermined amount longer than the recording member interval, and each of the changed recording member intervals is changed. An image forming apparatus that corrects the sub-scanning magnification error between recording members.   10. The image forming apparatus according to claim 2, wherein the phase and amplitude values stored in the non-volatile memory are developed in the volatile memory at a timing when the drive control device is turned on. Or an image forming apparatus, wherein the belt starts to be driven.   11. The image forming apparatus according to claim 2, wherein the phase and amplitude values stored in the non-volatile memory are used to calculate from the mark of the belt using a sine wave function or an approximate expression. An image forming apparatus that calculates correction data corresponding to the position of the image.   12. The volatile memory according to claim 2, wherein correction data is calculated according to a distance from a belt mark from a phase / amplitude value stored in the nonvolatile memory. A drive control device characterized by reducing the memory capacity of the volatile memory by thinning and storing data when storing in the storage.   13. The image forming apparatus according to claim 2, wherein when the belt is driven, the correction data stored in the volatile memory is referred to and the correction data is added to the control target value. Then, when controlling the driving unit, the correction data is started from zero at the start of the control.   14. The image forming apparatus according to claim 2, wherein the phase and amplitude values stored in the nonvolatile memory are input from an operation panel.   15. The image forming apparatus according to claim 2, wherein the image forming apparatus is a quadruple tandem system. 16. The image forming apparatus according to claim 2, wherein the belt is an intermediate transfer belt or a direct transfer belt.

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