JP4719043B2 - Drive control apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a drive control device that drives and controls a drive roller that rotates an endless moving member such as a transfer conveyance belt used in a transfer device and the like, and image formation such as a color printer and a color copier equipped with the drive control device. Relates to the device.

  As a general method of forming a color image in a color image forming apparatus, a direct transfer method in which toner images formed in different colors on a plurality of photosensitive members are transferred while being directly superimposed on a transfer sheet, and toners having the same color 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. These methods are commonly called a tandem method because a plurality of photosensitive members are arranged side by side facing a transfer paper or intermediate transfer member. For each photosensitive member, yellow (Y), magenta (M), cyan (C ), An electrophotographic process such as formation and development of an electrostatic latent image is executed for each color of black (K), and on the transfer paper in the direct transfer method, the intermediate transfer in the intermediate transfer method Transfer on the body.

  In a tandem color image forming apparatus using each of these methods, an endless belt (endless belt) that runs while supporting transfer paper is used in the direct transfer method, and a photoconductor in the intermediate transfer method. It is common to employ an endless belt that receives and carries an image. Image forming units each including four photoconductors are arranged side by side along one running side of the endless 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. Therefore, in any transfer system, an encoder is attached to one of the plurality of driven shafts constituting the transfer unit in order to avoid color misregistration due to the speed fluctuation of the transfer belt, and according to the rotational speed fluctuation of the encoder. Thus, feedback control of the rotational speed of the drive roller is an effective means.

  The most common method for realizing such feedback control is proportional control (PI control). First, the position deviation e (n) is calculated from the difference between the target angular displacement Ref (n) of the encoder and the detected angular displacement P (n-1) of the encoder. Then, a low-pass filter is applied to the position deviation e (n) of the calculation result to remove high frequency noise, a control gain is applied, and a certain standard drive pulse frequency is added. By controlling the drive motor that drives the drive roller based on the obtained drive pulse frequency, the encoder output can be controlled to always be driven at the target angular displacement.

As actual control, a counter that counts the rising edge of the output of the encoder pulse and a counter that counts every control cycle (for example, 1 ms) are used, and the calculation result of the target angular displacement that moves during the control cycle (1 ms) The position deviation can be acquired from the difference from the detected angular displacement obtained by acquiring the encoder count value for each control cycle.
A specific calculation is as follows when the roller diameter of the driven shaft to which the encoder is attached is φ15.615.

e (n) = θ0 × q−θ1 × ne [rad]
The meaning of each symbol in this formula is as follows.
e (n) [rad]: Position deviation calculated in the current sampling θ0 [rad]: Movement angle per control cycle (= 2π × V × 10 ⁻³ /15.615π [rad])
θ1 [rad]: Movement angle per pulse of encoder (= 2π / p [rad], where p is the slit pitch of the encoder)
q: Count value of control cycle timer ne: Encoder count value V: Belt linear velocity [mm / s]

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.
θ0 = 2π × 162 × 10 ⁻³ /15.615π=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.

  In a general encoder configuration, a disk having a radial slit that transmits light with a resolution of several hundred units in the circumferential direction is press-fitted into a driven roller shaft. This disk rotates at the same time as the driven roller, and a pulse signal (pulsed ON / OFF signal) corresponding to the amount of rotation of the driven roller can be obtained by detecting the slit with a sensor. The rotational speed of the driving roller is controlled by detecting the moving angle of the driven roller using this pulse signal.

  However, due to the influence of the concentricity processing accuracy of the disk of the encoder, when the disk is mounted on the driven roller, it may be mounted in a state shifted from each other. When rotating in this state, the driven roller is rotated at a constant speed, but the disk is rotated in an eccentric state. When this is read by a sensor (light receiver), one rotation component of the disk is output to the sensor output, that is, a pulse signal. Further, since one rotation component is amplified by feedback control to rotate the driving roller, the transfer belt speed fluctuates every time the disk rotates, and color misregistration occurs.

  Originally, in feedback control, we would like to improve the response to load fluctuations by increasing the control gain. However, if the control gain is increased, one rotation component of the disk increases, resulting in increased color misregistration. Had to perform feedback control with a low control gain. For this reason, the removal of other variable components that are originally desired to be controlled has not been sufficiently performed.

  As a method for controlling the speed fluctuation of the transfer belt caused by the eccentricity of the disk attached to the driven roller described above, for example, there is one described in Patent Document 1. This is because the driving roller is rotated at a constant speed, the angular velocity information obtained from the encoder output is acquired for at least one driving roller cycle, and the first half portion and the latter half portion are added by dividing the driving roller by one-half cycle. The offset speed fluctuation component caused by the drive roller is canceled out, and only the speed fluctuation caused by the driven roller is extracted. Further, at the time of image formation, the speed running of the belt is made constant by taking the difference between the angular velocity information detected from the driven roller and the speed fluctuation.

Alternatively, as a control method that is not affected by the eccentricity of the disk attached to the driven roller, for example, there is a method described in Patent Document 2. This is because a linear scale is partially formed along the circumferential direction of the endless belt or drum, and a plurality of timing marks printed on the linear scale are displayed on the linear sensor while the endless belt or drum rotates once. At least two sensors detect, output a pulse signal as a speed signal from the encoder based on the output pulse of each sensor, and a controller generates a control signal for making the difference between the pulse signal and the command pulse signal zero. The surface speed of the endless belt or drum is controlled to be constant by generating and driving the drive motor in accordance with this control signal.
JP 2000-47547 A JP 2004-69933 A

  The control method described in Patent Document 1 measures the encoder pulse interval with a constant clock, and subtracts the encoder speed fluctuation when the drive roller is rotated at a constant speed from the encoder speed when feedback control is performed, The speed control is performed to cancel the speed fluctuation caused by the disk eccentricity and to keep the speed of the encoder constant. To achieve this control, at least a clock rate that can sufficiently sample the influence of the eccentric component of the disk from the pulse interval of the encoder, high-speed hardware that can process it, and measurements such as high-resolution counters and timers Means are required, resulting in an expensive system, which is disadvantageous in terms of cost.

  Further, as described above, the position deviation e (n) is calculated from the difference between the target angular displacement Ref (ni) of the encoder and the detected angular displacement P (n−1) of the encoder, and the drive pulse of the drive motor is calculated from the calculation result. In the case of position control for controlling the frequency, the methods described in Patent Documents 1 and 2 cannot be applied in the first place.

  The present invention has been made to solve such a problem, and is a target roller in an image forming apparatus or the like (for example, a driving roller for rotating an endless moving member such as a transfer conveying belt or the rotation of the endless moving member) In the drive control device that drives and controls the drive roller based on the output signal of the encoder that detects the circumferential motion of the driven roller that is driven and rotated by the rotation of the endless moving member that is caused by the eccentricity of the disk of the encoder, The purpose is to ensure that the configuration can be used.

In order to achieve the above object, the present invention provides the following drive control device and an image forming apparatus including the same.
The drive control apparatus according to the first aspect of the present invention includes a drive roller that rotates the endless moving member or an encoder that detects the peripheral movement of the driven roller that rotates following the rotation of the endless moving member, and outputs an output signal of the encoder. A drive control device for driving and controlling the drive roller based on the encoder, wherein the encoder includes a disk having a plurality of marks or slits arranged at predetermined intervals in the circumferential direction and a pair for detecting each mark or slit. Each of which is mounted at a position shifted by 180 degrees, a combining means for combining the output signals of the pair of sensors, and a multiplication for multiplying the combined signal from the combining means by 1/2 Means, a counting means for counting the half-multiplied composite signal from the multiplication means, and a count value obtained by the means at a predetermined timing. A sampling means for controlling the driving roller based on a count value sampled by the sampling means, a feedback control means for controlling the driving roller, and an output signal of the pair of sensors. A drive control device comprising delay means for delaying input timing of one output signal to the synthesis means.

A drive control apparatus according to a second aspect of the present invention is the drive control apparatus according to the first aspect, further comprising delay amount input means for inputting an arbitrary delay amount as the delay amount of the input timing.
According to a third aspect of the present invention, there is provided a drive control apparatus according to the first aspect, wherein the output timing detection means for detecting the output timings of the pair of sensors and the detection result of the output timing by the output timing detection detection means. Accordingly, delay amount calculation means for calculating the delay amount of the input timing is provided.

A drive control apparatus according to a fourth aspect of the present invention is the drive control apparatus according to the third aspect, further comprising operation instruction means for operating the output timing detection means at predetermined time intervals .

A drive control device according to a fifth aspect of the present invention is the drive control device according to any one of the first to fourth aspects, wherein the feedback control means is configured such that when one of the pair of sensors becomes unusable, The feedback control is performed using only the output signal of the other sensor.
A drive control device according to a sixth aspect of the present invention provides the drive control device according to any one of the first to fifth aspects, wherein the feedback control means performs the feedback control when both of the pair of sensors become unusable. It will be canceled.

An image forming apparatus according to a seventh aspect of the invention includes the drive control device according to any one of the first to sixth aspects, and an endless moving member for image formation that is driven and controlled by the drive control device.
An image forming apparatus according to an eighth aspect of the present invention is the image forming apparatus according to the seventh aspect , wherein the endless moving member is any one of a photosensitive belt, a transfer belt, an intermediate transfer belt, and an image recording medium conveying belt. That's it.

  According to the drive control device of the present invention, the encoder that detects the circumferential movement of the target roller (the driving roller that rotates the endless moving member or the driven roller that rotates following the rotation of the endless moving member) includes a plurality of marks or The disc includes slits arranged at predetermined intervals in the circumferential direction and a pair of sensors for detecting the marks or slits, and the sensors are mounted at positions shifted by 180 degrees. The synthesizing means synthesizes the output signal of the sensor, the multiplication means multiplies the synthesized signal by 1/2, the counting means counts the synthesized signal multiplied by 1/2, and the count value is sampled at a predetermined timing. And the feedback control means performs feedback control for the control target value based on the sampled count value. Drives and controls the driving roller by. At this time, of the output signals of the pair of sensors, the input timing of one output signal to the synthesizing unit is delayed by the delay unit as necessary.

Therefore, stabilization of the speed fluctuation of the endless moving member caused by the disk eccentricity of the encoder can be reliably performed with a simple configuration.
According to the image forming apparatus of the present invention, it is possible to perform appropriate processing according to the image quality at a low cost by including the drive control device.

Hereinafter, the best mode for carrying out the present invention will be specifically described with reference to the drawings.
[First embodiment]
First, a configuration example of an image forming apparatus provided with a drive control apparatus according to the present invention will be described with reference to FIGS. This image forming apparatus is a color laser printer (hereinafter referred to as “laser printer”) that forms a color image by an electrophotographic method of a direct transfer method, and FIG. 2 is a schematic configuration diagram of the entire laser printer.

As shown in FIG. 2, the laser printer includes four sets of toner image forming units 1 (1Y) for forming images of each color of Y (yellow), M (magenta), C (cyan), and K (black). , 1M, 1C, 1K) are arranged in order from the upstream side (lower right side in the figure) in the direction in which the transfer paper P moves as the transfer conveyance belt 60 travels along the arrow A in the figure.
Each toner image forming unit 1 includes a photosensitive drum 11 (11Y, 11M, 11C, 11K) as an image carrier and a developing unit 12. The arrangement of the toner image forming units 1 is set so that the rotation axes of the photosensitive drums 11 are parallel to each other and arranged at a predetermined pitch in the transfer paper moving direction.

  In addition to the toner image forming unit 1, this laser printer carries an optical writing unit 2, paper feed cassettes 3 and 4, a registration roller pair 5, and a transfer paper (image recording medium) P to form each toner image. Belt driving device 6 equipped with a transfer conveyance belt (which combines the functions of a transfer belt and an image recording medium conveyance belt) 60 as an endless moving member that conveys the paper so as to pass through the transfer position of the belt, belt fixing type fixing A unit 7 and a paper discharge tray 8 are provided. The belt drive device 6 is a combination of a control system (drive control device) described later, and also functions as a transfer unit.

The laser printer further includes a manual feed tray 14 and a toner replenishing container 22, 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 (outer peripheral surface) of each photosensitive drum 11 while scanning with laser light based on image data. .

FIG. 3 is an enlarged view showing a schematic configuration of the belt driving device 6 described above.
The transfer conveying belt 60 used in the belt driving device 6 is a high-resistance endless single-layer endless belt (endless belt member) having a volume resistivity of 10 ⁹ to 10 ¹¹ Ωcm, and the material thereof is, for example, PVDF (Polyvinylidene fluoride). The transfer conveyance belt 60 is stretched around support rollers 61 to 66 so as to pass through the transfer positions that are in contact with and face the photosensitive drum 11 of the toner image forming units 1.

  An electrostatic attraction roller 80 is provided so as to face the entrance roller 61 located upstream of the support rollers 61 to 66 in the transfer paper moving direction on the outer peripheral surface side of the transfer conveyance belt 60. Yes. A predetermined voltage is applied to the electrostatic attraction roller 80 by the power supply 18, and the transfer paper P that has passed between the two rollers 61 and 80 is charged and electrostatically adsorbed onto the transfer conveyance belt 60. The driving roller 63 is a driving roller that frictionally drives the transfer conveyance belt 60, and is rotated in the direction of arrow D by a driving motor (described later).

  The transfer bias applying member 27 (27Y, 27M, 27C, 27K) as transfer electric field forming means for forming a transfer electric field is brought into contact with the back surface of the transfer conveyance belt 60 at each transfer position facing each photoconductor drum 11. Is provided. These transfer bias applying members 27 are bias rollers provided with a sponge or the like on the outer periphery, and a transfer bias voltage is applied to the roller core from each transfer bias power source 9 (9Y, 9M, 9C, 9K). By the action of the applied transfer bias voltage, a transfer charge is applied to the transfer conveyance belt 60, and a transfer electric field having a predetermined intensity is generated between the surface of the transfer conveyance belt 60 and the surface of the photosensitive drum 11 at each transfer position. It is formed. In addition, a backup roller 68 is provided in order to keep the contact between the transfer sheet and the photosensitive drum 11 in an area where the transfer is performed, and to obtain the best transfer nip.

  Each transfer bias applying member 27 and the backup roller 68 disposed in the vicinity thereof are respectively integrally held by a 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 arrow E.

  The entrance roller 61 and the electrostatic attraction roller 80 described above are integrally supported by the entrance roller bracket 90, and can be rotated clockwise from the state of FIG. A pin 92 projecting from the entrance roller bracket 90 is fitted into a hole 95 provided in the swing bracket 93, and the entrance roller bracket 90 also rotates in conjunction with the rotation of the swing bracket 93. . By rotating the brackets 90 and 93 in the clockwise direction, the respective transfer bias applying members 27 and the backup rollers 68 disposed in the vicinity thereof are separated from the photosensitive drum 11, and the entrance roller 61 and the electrostatic adsorption roller 80. Also move downwards. This makes it possible to avoid contact between the photosensitive drums 11Y, 11M, and 11C and the transfer conveyance belt 60 when an image is formed using only black toner.

  On the other hand, the transfer bias applying member 27K and the backup roller 68 adjacent to the transfer bias applying member 27K are rotatably supported by the outlet bracket 98, and are rotatable about a shaft 99 coaxial with the outlet roller 62. When the belt driving device 6 is attached to or detached from the laser printer main body, the exit bracket 98 is rotated clockwise by the operation of a handle (not shown), and the transfer conveying belt 60 is moved together with the transfer bias applying member 27K and the backup roller 68. It can be separated from the photosensitive drum 11K for black image formation.

As shown in FIG. 2, a cleaning device 85 including a brush roller and a cleaning blade is disposed on the outer peripheral surface of the portion of the transfer conveyance belt 60 wound around the driving roller 63. The cleaning device 85 removes foreign matters such as residual toner adhering to the transfer / conveying belt 60.
A roller 64 is provided so as to push the outer peripheral surface of the transfer conveyance belt 60 immediately downstream of the drive roller 63 in the traveling direction of the transfer conveyance belt 60, and a large winding angle of the transfer conveyance belt 60 with respect to the drive roller 63 is ensured. Yes. A tension roller 65 that is in contact with the inner peripheral surface of the transfer conveyance belt 60 and is pressed outward by the biasing force of a spring 69 that is a pressing member to apply tension to the transfer conveyance belt 60 is provided immediately downstream of the roller 64. It is arranged.

Next, an image forming operation by this laser printer will be described.
At the time of image formation by this laser printer, the transfer paper P is fed from one of the paper feed cassettes 3 and 4 and the manual feed tray 14 shown in FIG. 2, and is guided along a dashed line while being guided by a conveyance guide (not shown). And is conveyed to a temporary stop position where the registration roller pair 5 is provided.

  On the other hand, at the time of color image formation, the photosensitive drums 11 (11Y, 11M, 11C, 11K) of the four sets of toner image forming units 1 (1Y, 1M, 1C, 1K) are rotated clockwise in FIG. After the surface is uniformly charged by a charging member (not shown), the optical writing unit 2 irradiates and scans the surface with laser light modulated by data of each color of the image to be formed, A latent image is written. Thereafter, the toner is developed with toner of each color by the developing unit, and a toner image of each color is formed on the surface of each photoconductive drum 11.

The transfer paper P sandwiched between the registration roller pair 5 and temporarily stopped as described above is sent out at a predetermined timing by the registration roller pair 5 and is carried on the transfer conveyance belt 60 toward each toner image forming unit 1. It is sequentially conveyed and passes through each transfer nip. The toner images of the respective colors formed on the photosensitive drums 11 of the respective toner image forming units 1 are formed at sequentially shifted image forming timings so as to be superimposed on the transfer paper P at the respective transfer nips. When the transfer paper P passes through each transfer nip, it is transferred onto the transfer paper P under the action of the transfer electric field and nip pressure. A full color toner image is formed on the transfer paper P by this superposition transfer.
The surface of each photosensitive drum 11 after the toner image transfer is cleaned by a cleaning device 13 and is further discharged to prepare for the formation of the next electrostatic latent image.

  On the other hand, the transfer paper P 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 21 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 (not shown) (such as a sorter or a binding device) or printed on both sides via a switchback unit. It is again conveyed to the registration roller pair 5.

As described above, this laser printer forms a full-color image on the transfer paper P.
In such a tandem image forming apparatus, it is important to prevent the occurrence of color misregistration by superimposing toner images of respective colors with high positional accuracy. However, the drive roller 63, the entrance roller 61, the exit roller 62, and the transfer / conveying belt 60 used in the belt drive device 6 are subject to a manufacturing error 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 to the transfer conveyance belt 60, and the transfer paper conveyance speed fluctuates.

Due to the change in the transfer paper conveyance speed (the rotation speed of the transfer conveyance belt 60), when the toner image on each photoconductive drum 11 is transferred to the transfer paper P, a subtle shift occurs in the timing. Color misregistration occurs in the direction (transfer paper transport direction). In particular, in an apparatus that forms an image with minute dots such as 1200 × 1200 DPI, a timing shift of several μm is conspicuous as a color shift.
Therefore, in the belt driving device 6 (including the drive control device) in the first embodiment, the detection signal (output) of the encoder provided on the shaft of the lower right driven roller (referred to as “lower right roller”) 66 in FIG. The rotation speed of the lower right roller 66 is detected by a pulse signal), and the rotation of the driving roller 63 is feedback-controlled, so that the transfer conveyance belt 60 is driven at a constant speed.

FIG. 4 is a perspective view illustrating the entire configuration of the belt driving device 6 through the transfer conveyance belt 60.
The drive roller 63 is connected to the drive motor 32 via the timing belt 33 and is driven to rotate in proportion to the rotational speed of the drive motor 32. The transfer conveyance belt 60 is frictionally rotated by the rotation of the driving roller 63, and the lower right roller 66 is frictionally rotated by the rotation of the transfer conveyance belt 60. As described above, in the first embodiment, the encoder 31 is provided on the shaft of the lower right roller 66 (target roller), and based on the rotational speed of the lower right roller 66 detected from the detection signal of the encoder 31. The speed control of the drive motor 32 is performed. As described above, this is performed in order to suppress color misregistration due to positional variation (rotational variation) of the transfer conveyance belt 60.

FIG. 5 is a perspective view showing a configuration example of the lower right roller 66 and the encoder 31 of FIG.
6A and 6B are diagrams showing a configuration example of the disk 311 and the sensor in the encoder 31. FIG. 6A is a front view of only the disk 311 and FIG. 6B is a side view of the disk 311 and the sensor.
FIG. 7 is a diagram showing different examples of sampling results when the drive motor 32 of FIG. 4 is driven at a constant speed and the count value of the output pulse of the encoder 31 is sampled at a constant timing (predetermined timing).

For example, as shown in FIGS. 5 and 6, the encoder 31 includes a disk 311, two light emitting elements 312 and 316, two light receiving elements 313 and 317, and press-fit bushings 314 and 315.
The disk 311 is fixed by press-fitting press-fitting bushes 314 and 315 onto the shaft of the lower right roller 66, and rotates simultaneously with the rotation of the lower right roller 66.
Further, the disk 311 is formed with radial slits that transmit light with a resolution of several hundred units in the circumferential direction, and a light emitting element 312 that constitutes a pair, that is, two encoder sensors, on both sides thereof. The element 313, the light emitting element 316, and the light receiving element 317 are arranged at positions shifted by 180 degrees, and the light receiving elements 313, 317 cause the number of pulse signals (pulse-like ON / OFF) corresponding to the rotation angle of the lower right roller 66 OFF signal) is generated. The drive amount of the drive motor 32 is controlled by detecting the movement angle (hereinafter referred to as “angular displacement”) of the lower right roller 66 using the pulse signal.

  By the way, an error of several μm occurs in the machining of the coaxial hole when the disk 311 is press-fitted into the lower right roller 66, and it is practically impossible to make it zero. Therefore, when the disk 311 is attached to the lower right roller 66, the disk 311 may be attached so as to be displaced from each other. When the disk 311 is rotated in this state, the disk 311 is rotated at a constant speed even though the lower right roller 66 is rotating at a constant speed. 311 is rotated in an eccentric state. When this is read by the encoder sensor (light receiving elements 313, 317), angular displacement fluctuations occur every cycle (one rotation) of the disk 311.

In FIG. 7, (a) shows the sampling result when there is no eccentricity of the disk 311 and (b) shows the sampling result when there is eccentricity. Usually, when there is no eccentricity of the disk 311, a sampling result that rises to the right is obtained, but when there is eccentricity, a sine wave sampling result is obtained.
Since the sampling result indicates the detected angular displacement of the encoder 31, the fact that the sampling result is sinusoidal indicates that the detection position error is large accordingly. When the machining accuracy error of the coaxial hole of the disk 311 is large, the amplitude of the sine wave is detected to be larger.

  Since the two light receiving elements 313 and 317 are arranged at positions shifted by 180 degrees, the phase of the sine wave of the sampling result is shifted by 180 degrees. Therefore, by combining these two sampling results, it is possible to cancel the angular displacement fluctuation due to the eccentricity of the disk 311. In the first embodiment, the two sampling results are synthesized by an output synthesis circuit, which will be described later, so that a proportional control calculation that is not affected by the eccentricity of the disk 311 is performed and the rotation speed of the transfer conveyance belt 60 is kept constant. It is characterized by doing.

FIG. 8 is a block diagram illustrating a hardware configuration example of a control unit including the drive motor control unit (drive control device) of the belt drive device 6 described above in the laser printer. In FIG. 8, only one encoder sensor is shown for convenience of illustration, but it is assumed that there are actually two encoder sensors.
The drive motor control unit of the belt drive device 6 digitally controls the drive pulse of the drive motor 32 based on the output pulse signal of each encoder sensor 331 (each composed of a light emitting element and a light receiving element).

The control unit 600 including the drive motor control unit includes a CPU 601, a RAM 602, a ROM 603, an IO control unit 604, a drive motor IF 606, a driver 607, a detection IO unit 608, and a bus 609.
The CPU 601 controls the entire laser printer based on the program in the ROM 603, including receiving image data from an external device 38 such as a personal computer and control of transmission / reception of control commands to / from the external device 38. Central processing unit.

The CPU 601 operates in accordance with a program in the ROM 603 and uses the encoder sensor 331 and the like, so that each means according to the present invention, that is, sampling means, feedback control means, output timing detection means, delay amount input means, delay amount calculation means. , And an operation instruction means.
A RAM 602, a ROM 603, an IO control unit 604, a drive motor IF 606, and a detection IO unit 608 are connected to the CPU 601 via a bus 609.
A RAM 602 is a readable / writable memory (storage means) used as a work memory used when the CPU 601 performs control (processing) or an image memory when developing image data.

The ROM 603 is a read-only memory that stores fixed data such as programs executed by the CPU 601 (for the CPU 601 to operate).
The IO control unit 604 controls input / output of signals to / from each load 39 such as a motor, a clutch, a solenoid, and a sensor in accordance with an instruction from the CPU 601.
The drive motor IF 606 outputs a drive pulse signal to the drive motor 32 (drive roller 63) for rotating the transfer conveyance belt 60 via the driver 607 in response to a drive command from the CPU 601, thereby rotating the drive motor 32. Control the drive. Since this rotation driving is performed according to the frequency of the drive pulse signal, the rotation speed of the transfer conveyance belt 60 can be variably controlled.

An output pulse signal (encoder pulse) of the encoder sensor 331 is input to the detection IO unit 608.
The detection IO unit 608 processes the output pulse of the encoder sensor 331 and converts it into a digital value. The detection IO unit 608 includes a plurality of counters including a counter (counting unit) that counts (counts) the output pulses of the encoder sensor 331. Then, a digital value corresponding to the angular displacement of the shaft of the lower right roller 66 (FIG. 5) is obtained by multiplying the counter value (the number of output pulses of the encoder sensor 331) by a predetermined pulse number diagonal displacement conversion constant. Convert to A digital value signal corresponding to the angular displacement of the disk 311 of the encoder 31 is sent to the CPU 601 via the bus 609.

Here, the drive motor IF 606, the driver 607, and the RAM 602 will be described in a little more detail.
When the drive motor IF 606 receives a drive command (including a drive frequency instruction) from the CPU 601 via the bus 609, the drive motor IF 606 generates a pulse-like control signal having a drive frequency instructed based on the drive command. Output to the driver 607.

  The driver 607 is configured by a power semiconductor element (for example, a transistor) or the like. The driver 607 operates based on a pulsed control signal input from the drive motor IF 606 and outputs a drive pulse signal to the drive motor 32. That is, a pulsed drive voltage is applied. As a result, the drive motor 32 is driven and controlled at a speed proportional to the drive frequency instructed by the drive command of the CPU 601. As a result, the additional value is controlled so that the angular displacement of the disk 311 of the encoder 31 becomes 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 311 is detected by the encoder sensor 331 and the detection IO unit 608 and is taken in by the CPU 601 and the control is repeated.

In addition to functions used as a work memory and an image memory when the CPU 601 controls (executes a program in the ROM 603), the RAM 602 controls the drive motor 32 at a constant speed without executing an image forming process in advance. It has a function as a data memory for storing detected angular displacement error data for one rotation of the disk corresponding to the disk eccentricity of the encoder 31 measured by driving, that is, data sampled at regular intervals. .
Since the RAM 602 is a volatile memory, the detected angular displacement error data is stored in a nonvolatile memory such as an EEPROM (not shown), and the detected angular displacement error is detected when the power is turned on or the drive motor 32 is started. Data can also be expanded on the RAM 602.

  By the way, in the proportional control calculation generally used for the feedback control of the drive motor, 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 drive speed of the drive motor. If the detected angular displacement error due to the disk eccentricity of the encoder is large, it will be further amplified and drive the drive motor. For this reason, the position of the transfer / conveyance belt 60 varies every rotation of the disk, and color misregistration occurs.

Further, as described above, FIG. 7B shows the behavior when the drive motor 32 is driven at a constant speed. In other words, the count value of the pulse number of the encoder 31 is sampled at a constant timing. If the result is as shown in FIG. 7B, the lower right roller 66 is rotating at a constant speed.
Therefore, in the first embodiment, as shown in FIG. 7B, the target angular displacement for each control cycle (actually, the control target value that makes the angular displacement per unit time of the encoder 31 constant). Is obtained by adding the detected angular displacement error to the target angular displacement), the angular displacement of the encoder 31 corresponding to the target angular displacement is detected by the encoder sensor 331, and the proportional control is not affected by the eccentricity of the disk 311. By calculating and controlling the drive motor 32, the rotation speed of the transfer conveyance belt 60 is made constant.

FIG. 1 is a schematic functional block diagram showing a configuration for explaining functions of an embodiment of a drive control apparatus according to the present invention. This embodiment shows an example when the present invention is applied to the control of the belt driving device 6 described above.
In FIG. 1, the controller section 40 includes a subtracting circuit 41, a low-pass filter 42 for removing high-frequency noise, a proportional calculation section (gain Kp) 43, a steady drive pulse frequency setting section 44, and an adding circuit. 45. The control controller unit 40, the target angular displacement generation unit 30, and the pulse output unit 37 are realized by the CPU 601 in FIG. 8 executing the program in the ROM 603 and using the drive motor IF 606, the driver 607, and the detection IO unit 608. can do.

  The target angular displacement generation unit 30 drives the drive motor 32 at a constant speed without executing the image forming process, and the detected angular displacement error caused by the disk eccentricity of the encoder 31 measured in advance is used as a characteristic value in the memory 301 (FIG. 8). (Corresponding to a data memory in the RAM 602). Then, during the image forming process, a reference mark on the disk 311 indicating the reference position is detected by a mark sensor (not shown), for example, and a mark detection signal output from the mark sensor is input from the memory 301 at a predetermined timing. Read characteristic values sequentially. This is performed by sequentially switching the memory reference address from the detection timing of the reference position of the disk 311. Thereafter, the read characteristic value is added to the target angular displacement which is the control target value to obtain a new target angular displacement Ref (n), which is input to the control controller unit 40.

Here, for adding the characteristic value (detection angular displacement error) and the target angular displacement, for example, the mark sensor detects the reference mark every rotation of the disk 311 and the mark detection signal output from the mark sensor is input. It is performed so as to be repeated periodically according to the timing.
Note that the target angular displacement generation unit 30 holds the target angular displacement Ref (n) obtained by adding the detected angular displacement error (characteristic value) measured in advance in the memory 301, and the predetermined timing ( For example, the target angular displacement Ref (n) may be read out by sequentially switching the reference address of the memory from the detection timing of the reference position of the disk 311 and input to the control controller unit 40.

The control controller 40 receives the target angular displacement Ref (n), which is a control target value input from the target angular displacement generator 30, and the detected angular displacement P () received from the encoder sensor 331 of the encoder 31 via the output synthesis circuit 700. n-1) is input to the subtraction circuit 41 and the difference e (n) is obtained. That is, the difference displacement amount is calculated. The detected angular displacement P (n−1) is actually calculated based on the output pulse signal of the encoder sensor 331, which will be described in detail later.
The difference e (n) is input to the proportional calculation unit 43 after high frequency noise is removed by passing through the low-pass filter 42.

The proportional calculation unit 43 proportionally amplifies the difference e (n) from the low-pass filter 42 with the gain Kp, and supplies the result to the addition circuit 45 as a correction amount (rad) Hz.
The adder circuit 45 determines the drive pulse frequency f (n) by adding the correction amount (rad) Hz from the proportional calculation unit 43 to the constant steady drive pulse frequency (Refpc) Hz from the steady drive pulse frequency setting unit 44. Then, it is output to the pulse output device 37.
The pulse output unit 37 generates a drive pulse signal having the drive pulse frequency f (n) received from the adder circuit 45 and outputs it to the drive motor 32.

FIG. 9 is a block diagram illustrating a first configuration example of the output synthesis circuit 700 of FIG.
The output synthesis circuit 700 includes a delay circuit 701, a synthesis circuit 702, and a multiplication circuit 703.
Output pulse signals of the light receiving elements 313 and 317 of the two encoder sensors 331 in the encoder 31 are input to the synthesis circuit 702.
The synthesizing circuit 702 is a synthesizing unit, synthesizes the input output pulse signals, and outputs the synthesized output pulse signal to the multiplication circuit 703.

The multiplication circuit 703 is a multiplication means, which synchronizes the output pulse signal from the synthesis circuit 702 with a reference clock from a reference clock generation circuit (not shown), and multiplies the output pulse signal to ½ frequency for output.
1 performs feedback control on the control target value based on the output pulse signal from the output synthesis circuit 700 (actually, the count value of the output pulse signal sampled at a predetermined timing), and the drive The drive of the motor 32, that is, the transfer / conveying belt 60 is controlled.

  However, in order to exert this effect, the two light receiving elements 313 and 317 need to be accurately displaced by 180 degrees. In practice, however, the manufacturing variation of the encoder 31, particularly each encoder sensor in the encoder 31 Actually, the accuracy of 180 degrees is not always obtained due to the variation in the attachment of 331. If this accuracy is not achieved, the sampling result of the two light receiving elements 313 and 317 when the count value of the output pulse signal of the encoder 31 is sampled at a constant timing is not limited to being a sine wave. The deviation is not 180 degrees, and even if synthesized, the angular displacement fluctuation due to the eccentricity of the disk 311 cannot be canceled.

  In the example shown in FIG. 10, the positional relationship between the two encoder sensors 331 (light emitting element 312, light receiving element 313 and light emitting element 316, light receiving element 317) is 180 degrees with respect to the disk 311 of the encoder 31. When there is not, a characteristic obtained by subtracting the characteristic shown in (b) from the characteristic shown in (a) of FIG. 7, that is, a displacement error count value caused by the eccentricity of the disk 311 is as shown in FIG. This is a characteristic of a phase difference α (not 180 degrees) with respect to the positional relationship α. Therefore, it can be seen that even if these two characteristics are combined, the angular displacement fluctuation due to the eccentricity of the disk 311 cannot be canceled.

  Therefore, in the first embodiment, correction is performed by the delay circuit 701 in FIG. 9 in order to correct this phase shift. Specifically, for example, in FIG. 10, when α = 175 degrees, the phase difference is 5 degrees earlier, and the delay circuit 701 delays transmission for the phase difference of 5 degrees. Become. Thereby, when the output pulse signals of the two encoder sensors 331 are combined, it is possible to cancel the angular displacement fluctuation due to the eccentricity of the disk 311.

In the first embodiment, the case where the accuracy of 180 degrees is not obtained due to the manufacturing variation of the encoder 31, particularly the mounting variation of the two encoder sensors 331 in the encoder 31, has been taken as an example. Depending on the delay amount prepared in the above, it is effective when the positional relationship between the two encoder sensors 331 is intentionally arranged at an angle other than 180 degrees, and the mechanical layout of the light receiving elements 313 and 317 and the light emitting elements 312 and 316 is effective. Even if it is arranged at a position of 90 degrees for the convenience of the above, it is possible to cancel the angular displacement fluctuation by the output pulse signals of the two encoder sensors 331.
With the above operation, the detected angular displacement of the encoder 31 is set to P (n−1) as a value obtained via the synthesis circuit 702 and the multiplication circuit 703.

  FIG. 12 shows an example of a timing chart for realizing the drive control according to the present invention. Although not shown in FIG. 8, it is assumed that the control unit 600 is provided with a control cycle timer for measuring time. The detection IO unit 608 is provided with an encoder pulse counter and a control cycle timer counter, which will be described later. Further, the output pulse of the encoder 31 below is actually an output pulse of the output synthesis circuit 700.

  First, in FIG. 12, the count value of the encoder pulse counter that counts the encoder pulse that is the output pulse of the encoder 31 is incremented (+1) by the rising edge of the encoder pulse output. The control cycle of this control is 1 ms, and the count value of the control cycle timer counter is incremented (+1) every time the CPU 601 is interrupted by the control cycle timer.

The time measurement of the control cycle timer is started when the rising edge of the encoder pulse is detected for the first time after the through-up and settling of the drive motor 32 is completed, and the count value of the control cycle timer counter is reset to “0”. .
Each time the CPU 601 is interrupted by the control cycle timer, the encoder pulse counter count value: ne is acquired, and the control cycle timer counter count value: q is acquired and incremented (+1).

Based on these count values, the position deviation is calculated as follows.
P (n−1) = θ1 × ne
Ref (n) = θ0 × q
e (n) = Ref (n) -P (n-1) (unit: rad)

Here, the meaning of each symbol in the above formula is as follows.
e (n) [rad]: Position deviation (calculated in this sampling) θ0 [rad]: Movement angle per control period 1 [ms] (= 2π × V × 10 ⁻³ / Lπ [rad])

θ1 [rad]: Movement angle per encoder pulse (= 2π / p [rad])
q: Count value of control cycle timer V: Belt linear velocity [mm / s]
L: Lower right roller diameter [mm]
f: Disk rotation period [Hz]

In the first embodiment, the diameter of the lower right roller, which is a driven roller to which the encoder 31 is attached, is φ15.515 [mm]. The resolution p of the encoder 31 is assumed to be 300 pulses per revolution.
Next, in order to avoid responding to a sudden position change, it is preferable to perform a filter calculation with the following specifications on the calculated deviation.

Filter type: Butterworth IIR low-pass filter Sampling frequency: 1 KHz (= equal to control period)
Passband ripple (Rp): 0.01 dB
Stop band end attenuation (Rs): 2 dB
Passband edge frequency (Fp): 50Hz
Stopband edge frequency (Fs): 100Hz

A block diagram of the filter operation is shown in FIG. 13, and a list of filter coefficients is shown in FIG. Two stages of filters having the same configuration are cascade-connected, and intermediate nodes in each stage are u1 (n), u1 (n-1), u1 (n-2) and u2 (n), u2 (n-1), u2 respectively. (N-2). Here, the meaning of the index is as follows.
(N): Current sampling (n-1): Previous sampling (n-2): Second previous sampling

The following program calculation is performed each time a control timer interrupt occurs during feedback execution.
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. 15 shows the amplitude characteristics of this filter, and FIG. 16 shows the phase characteristics.

Next, the control amount for the controlled object is obtained. In the control block diagram, first, considering PID control as a position controller,
F (S) = G (S) × E ′ (S) = Kp × E ′ (S) + Ki × E ′ (S) / S + Kd × S × E ′ (S)
However, Kp: proportional gain, Ki: integral gain, Kd: differential gain.
G (S) = F (S) / E ′ (S) = Kp + Ki / S + Kd × S (1)

Here, when the bilinear transformation (S = (2 / T) × (1-Z ⁻¹ ) / (1 + Z ⁻¹ )) is performed on the equation (1), the following equation is obtained.
G (Z) = (b0 + b1 * Z- ¹ + b2 * Z- ² ) / (1-a1 * Z- ^1- a2 * Z- ² ) (2)
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 (2) 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. 15, when w (n), w (n-1), and w (n-2) are defined as intermediate nodes, the difference equation is as follows (general expression of PID control).
w (n) = a1 * w (n-1) + a2 * w (n-2) + e '(n) (3)
f (n) = b0 * w (n) + b1 * w (n-1) + b2 * w (n-2) (4)
Here, the meaning of the index is as follows.
(N): Current sampling (n-1): Previous sampling (n-2): Second previous sampling

Now, considering proportional control as a position controller, the integral gain and derivative gain are zero. Accordingly, the coefficients in FIG. 17 are as follows, and the expressions (3) and (4) are simplified as the following expression (5).
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) (5)

Also, the discrete data f0 (n) corresponding to F0 (S) is constant in the case of the first embodiment,
f0 (n) = 6105 [Hz]
It is. Therefore, the pulse frequency set in the drive motor 32 is finally calculated by the following equation (6).
f ′ (n) = f (n) + f0 (n) = Kp × e ′ (n) +6105 [Hz] (6)

FIG. 18 shows an operation flowchart of the encoder pulse counter described above. In the flowchart of FIG. 18 and the flowchart described below, each step is abbreviated as “S”.
First, it is determined whether or not it is the first pulse input after the through-up and settling of the drive motor 32 (S1). If YES, the encoder pulse counter is reset (S2), the control cycle timer counter is reset (S3), The interrupt by the control cycle timer is permitted (S4), the control cycle timer is started (S5), and the process returns to the main routine (not shown). If the determination in step 1 is NO, the encoder pulse counter is incremented (S6), and the process returns to the main routine.

FIG. 19 shows a flowchart of interrupt processing by the control cycle timer.
First, the control cycle timer counter is incremented (S21), and then the encoder pulse count value ne is acquired (S22). Furthermore, the value of Δθ is acquired by referring to the table data (S23), and the table data reference address is incremented (S24). Next, a position deviation calculation is performed using these values (S25), a filter calculation is performed on the obtained position deviation (S26), and a control amount calculation (proportional calculation) is performed based on the result of the filter calculation. (S27). Then, the frequency of the drive pulse of the drive motor 32 (stepping motor) is actually changed (S28), and the process returns to the main routine.

  With the above control, it is possible to appropriately perform the control for stabilizing the rotational speed of the transfer conveyance belt 60 generated by the disk eccentricity of the encoder 31 in the position control at a low cost and according to the image quality.

[Second Embodiment]
Next, a second embodiment will be described. That is, in the above description, the timing for determining the delay amount of the input timing to one of the synthesis circuits 702 of the output pulse signals of the two encoder sensors 331, which is the delay amount necessary for the delay circuit 701 in FIG. The timing will be described as a second embodiment.
The phase difference between the output pulse signals of the two encoder sensors 331 in the encoder 31 is determined by the mechanical positional relationship. Therefore, once it is decided to use the encoder 31, it can be said that the phase difference between the output pulse signals of the two encoder sensors 331 is substantially the same.

In the second embodiment, in view of this feature, before the encoder 31 is incorporated into a machine, first, the generation timings of the output pulse signals of the two encoder sensors 331 are examined by a single component. Accordingly, the delay amount necessary for the delay circuit 701 is calculated, and the relationship between one component and one characteristic value (delay amount) is clarified.
After that, when the encoder 31 is assembled to the machine body at the factory, the delay circuit 701 inputs a necessary delay amount by an operation on an external device such as a personal computer or an operation unit, which is stored in a memory (shown in the CPU 601 in FIG. 8). In this case, the delay amount is always applied when the encoder 31 is operated.

As a result, one of the output pulse signals of the two encoder sensors 331 is delayed by the delay circuit 701 by the necessary delay amount (optimum delay amount), and then input to the synthesis circuit 702. As a result, there is no error. Thus, a frequency signal is obtained.
Since this method can be handled by a serviceman in the market not only at the time of factory assembly but also by operation on an external device or an operation unit, it is necessary for the delay circuit 701 even if the parts of the encoder 31 are replaced. Re-entering the delay amount will not cause any problems.

[Third embodiment]
Next, a third embodiment will be described. Since only the first embodiment or the second embodiment is slightly different, only the different portions will be described.
In the third embodiment, the output synthesis circuit 700 shown in FIG. 20 is used instead of the output synthesis circuit 700 shown in FIG.
FIG. 20 is a block diagram showing a second configuration example of the output synthesis circuit 700 in FIG. 1, and parts corresponding to those in FIG. 9 are given the same reference numerals.

In the second embodiment, it has been described that the phase difference between the output pulse signals of the two encoder sensors 331 is determined by the mechanical positional relationship. However, in fact, there are factors other than the encoder 31 such as signal path differences and changes over time. Actually exists.
Therefore, in the third embodiment, a necessary delay amount as a mechanical system is calculated so that a more accurate frequency can be obtained.
Specifically, as shown in FIG. 20, the CPU 601 directly detects the output pulse signals of the two encoder sensors 331 in a state where it is incorporated as a mechanical system, checks the generation timing thereof, and is required by the delay circuit 701. A delay amount, that is, an optimum delay amount is calculated.

Then, the delay circuit 701 requires only the output pulse signal of one encoder sensor 331 for the delay amount so that the phase relationship cancels the angular displacement fluctuation due to the eccentricity of the disk 311 between the output pulse signals of the two encoder sensors 331. The signal is input to the synthesizing circuit 702 after being delayed by a certain amount.
As a result, an optimum delay as a mechanical system is applied, and as a result, a target frequency signal with less error is obtained.

Further, in the third embodiment, it is also assumed that the amount of delay is reconsidered not only at the time of incorporation into the machine but also every certain time (predetermined time) assuming a change with time. The value of “certain fixed time” varies depending on the mechanical system to be assembled.
For example, in a system having a characteristic in which the generation timing of the output pulse signal of the encoder sensor 331 changes in a long cycle, it is always performed once a day as long as the copying machine or printer is used. If it goes to, it will not be a problem.
Also, if the generation timing of the output pulse signal of the encoder sensor 331 changes in a short cycle, which changes in the daily usage situation, such as changes due to the temperature in the machine, the temperature in the machine is detected, It can be said that it is optimal to detect the output pulse signal according to the temperature change and reexamine the generation timing.

In any case, the “certain fixed time” differs depending on the system to be assembled, but the third embodiment makes it possible to cope with the mechanical system.
As described above, even when the mechanical positional relationship between the two encoder sensors 331 in the encoder 31 is not 180 degrees, it is possible to suppress angular displacement fluctuations caused by the eccentricity of the disk 311 in the encoder 31.

[Fourth embodiment]
Next, a fourth embodiment will be described. In addition, since it is only slightly different from any of the first embodiment to the third embodiment, only the different portions will be described.
In the fourth embodiment, the synthesis circuit 702 is improved.
The synthesis of the output pulse signals by the synthesis circuit 702 is generally easy to perform OR synthesis. However, if the pulses of the output pulse signals of the light receiving elements 313 and 317 of the two encoder sensors 331 overlap, the clocks are simply clocked. One pulse is reduced, and an error occurs in the resulting frequency. In order to cope with this, in the fourth embodiment, the output synthesis circuit 700 shown in FIG. 21 is used instead of the output synthesis circuit 700 shown in FIG.

FIG. 21 is a block diagram showing a third configuration example of the output synthesis circuit 700 of FIG. 1, and portions corresponding to those in FIGS. 9 and 20 are denoted by the same reference numerals.
In the fourth embodiment, the delay circuit 701 used in the first to third embodiments is a delay circuit 705, and a delay circuit 706 is further provided.
Specifically, this corresponds to the phenomenon shown in FIG. 22, and a control unit such as the CPU 601 can intentionally delay the generation timing of the output pulse signal of one encoder sensor 331.

As a result, the input timing of the output pulse signals of the two encoder sensors 331 to the synthesis circuit 702 can be shifted and the frequency remains the same, so that the output pulse signals that have passed through the synthesis circuit 702 and the multiplication circuit 703 are accurate. Frequency synthesized.
Although there may be a plurality of drive frequencies in this system, the frequency to be feedback-controlled is basically determined, and the first to third embodiments, that is, the mechanical functions of the two encoder sensors 331 are determined. By correcting the positional relationship, it is possible to manage the overlap of pulses of the output pulse signals of the two encoder sensors 331 in a state where the delay amount required by the delay circuit 705 is determined.

In the fourth embodiment, due to this characteristic, the output pulse signal of one encoder sensor 331 is always delayed by a certain amount by the delay circuit 705. This eliminates the need to make a determination when the pulses of the output pulse signals of the two encoder sensors 331 described above overlap, thereby reducing the circuit and the load on the CPU 601.
As described above, when the delay circuit 706 is operated, only when the pulses overlap or when a predetermined delay amount is set in advance, the number of pulses is not lost, but the frequency of one pulse per pulse is In order to eliminate such sudden fluctuations, it is necessary to suppress the fluctuations by providing a function (filter calculation means) for performing a filter calculation in the feedback control system.

[Fifth embodiment]
Next, a fifth embodiment will be described. Since only the fourth embodiment is slightly different, only the different parts will be described.
As described above, since the phase difference between the output pulse signals of the two encoder sensors 331 is determined by the mechanical positional relationship, a delay amount required by the delay circuit 705 in FIG. 21 can be determined as a mechanical system. If the delay amount required by the delay circuit 705 is determined, the delay amount required by the delay circuit 706 can also be determined.

In the fifth embodiment, in view of this feature, the generation timings of the output pulse signals of the two encoder sensors 331 are first checked with a single component before being incorporated in the machine. Accordingly, two necessary delay amounts are calculated by the delay circuits 705 and 706, respectively, and the relationship between one component and one characteristic value (delay amount) is clarified.
Thereafter, when the encoder 31 is assembled to the machine body at the factory, two delay amounts necessary for the delay circuits 705 and 706 are input by an external device such as a personal computer or an operation on the operation unit, and the CPU 601 in FIG. It is stored in an internal memory (which may be a non-volatile memory (not shown)), and the two delay amounts are always applied when the encoder 31 operates.

As a result, one of the output pulse signals of the two encoder sensors 331 is delayed by two necessary delay amounts by the delay circuits 705 and 706, and then input to the synthesis circuit 702, resulting in a target frequency without error. A signal will be obtained.
Since this method can be handled by a serviceman in the market not only at the time of factory assembly but also by operation on an external device or operation unit, even if the parts of the encoder 31 are replaced, the delay circuits 705 and 706 There is no problem by re-entering the two required delay amounts.

[Sixth embodiment]
Next, a sixth embodiment will be described. Since only the fourth embodiment or the fifth embodiment is slightly different, only the different portions will be described.
In the sixth embodiment, the output synthesis circuit 700 shown in FIG. 23 is used instead of the output synthesis circuit 700 shown in FIG.
FIG. 23 is a block diagram showing a fourth configuration example of the output synthesis circuit 700 in FIG. 1, and parts corresponding to those in FIG.

In the fifth embodiment, it has been described that the phase difference between the output pulse signals of the two encoder sensors 331 is determined by the mechanical positional relationship. However, in fact, there are factors other than the encoder 31 such as signal path differences and changes with time. Exists.
Therefore, in the sixth embodiment, a necessary delay amount as a mechanical system is calculated so that a more accurate frequency can be obtained.
Specifically, as shown in FIG. 23, the CPU 601 directly detects the output pulse signals of the two encoder sensors 331 in a state where it is incorporated as a mechanical system, checks the generation timing thereof, and is required by the delay circuit 705. Calculate the amount of delay.

In addition, when the delay amount required by the delay circuit 705 is determined, the CPU 601 directly detects the output pulse signal of the delay circuit 705, checks the generation timing thereof, and calculates the necessary delay amount by the delay circuit 706.
The output pulse signals of the two encoder sensors 331 have a phase relationship that cancels out the angular displacement fluctuation caused by the eccentricity of the disk 311, and there is no frequency mismatch after passing through the synthesis circuit 702 due to the overlap of pulses. Only the output pulse signal of the encoder sensor 331 is delayed by the required delay amounts by the delay circuits 705 and 706 and then input to the synthesis circuit 702.

As a result, an optimum delay as a mechanical system is applied, and as a result, a target frequency signal with less error is obtained.
Furthermore, in the sixth embodiment, it is also assumed that the amount of delay is reconsidered not only at the time of incorporation in the machine but also at certain time intervals, assuming a change with time. The value of “certain fixed time” varies depending on the mechanical system to be assembled.
For example, in a system having a characteristic in which the generation timing of the output pulse signal of the encoder sensor 331 changes in a long cycle, it is always performed once a day as long as the copying machine or printer is used. If it goes to, it will not be a problem.

Also, if the generation timing of the output pulse signal of the encoder sensor 331 changes in a short cycle, which changes in the daily usage situation, such as changes due to the temperature in the machine, the temperature in the machine is detected, It can be said that it is optimal to detect the output pulse signal according to the temperature change and reexamine the generation timing.
In any case, the “certain fixed time” varies depending on the system to be assembled, but this sixth embodiment makes it possible to cope with the mechanical system.

[Seventh embodiment]
Next, a seventh embodiment will be described. Note that only new control is added to the same control as in any of the first to sixth embodiments, and only the new control will be described.
In the first to sixth embodiments described above, if there is an abnormality in the output of the encoder sensor 331, the drive system may be damaged in order to perform the feedback control. It is.

  Therefore, in the seventh embodiment, when one of the light receiving elements 313 and 317 of the two encoder sensors 331 becomes unusable, the output pulse signal of the other light receiving element is the combined signal. Is output from the output combining circuit 700, and the feedback control is performed using the combined signal. At this time, the multiplication circuit 703 does not multiply the combined signal by 1/2. Further, when both of the light receiving elements 313 and 317 become unusable, the feedback control is stopped. Specifically, the value of the difference e (n) between the target angular displacement Ref (n) and the detected angular displacement P (n−1) of the encoder 31 is always set to “0”. Actually, this can be realized by monitoring whether a normal pulse is coming in step S1 of FIG.

  In the first to seventh embodiments described above, the lower right roller 66 among the driven rollers that are driven to rotate by the rotation of the transfer / conveyance belt is the target roller to which the encoder is attached. A driving roller that rotates the belt may be a target roller. Also, as an encoder, there are a disk on which a radial mark that reflects light with a resolution of several hundred units in the circumferential direction is formed, and a pair of sensors arranged so as to face the mark portion at a position shifted by 180 degrees. A sensor provided with two sensors (each consisting of a light emitting element and a light receiving element) can also be used.

  As described above, the embodiment in which the present invention is applied to the drive control device (belt drive device) for driving and controlling the transfer conveyance belt has been described. However, the present invention is not limited to this, and other endless moving members (photosensitive members) for image formation. The present invention can also be applied to a drive control device that drives and controls a body belt, a transfer belt, an intermediate transfer belt, or an image recording medium conveyance belt.

That is, an example in which the present invention is applied to a belt driving device in a tandem type laser printer in which a plurality of photosensitive drums 11Y, 11M, 11C, and 11K are arranged on the transfer conveyance belt 60 has been described. Possible image forming apparatuses and belt driving apparatuses are not limited to this configuration.
As long as the image forming apparatus has a belt driving device that rotationally drives an endless belt stretched around a plurality of rollers by at least one of the rollers (target roller), any of the belt driving devices Is also applicable.

In each of the above-described embodiments, the present invention is applied to a direct transfer type color printer in which transfer paper is transported by the transfer transport belt 60 and four color toner images from the photosensitive drum are sequentially transferred onto the transfer paper. However, the present invention is also applied to an intermediate transfer belt driving device in an indirect transfer type color printer or the like that transfers four color toner images onto an intermediate transfer belt, superimposes the four colors, and transfers them onto a transfer sheet at once. Applicable.
Further, in each of the embodiments described above, laser light is used as the exposure light source. However, the present invention is not limited to this. For example, an LED array or the like may be used as the light source.

As is apparent from the above description, according to the drive control device of the present invention, it is possible to perform control that stabilizes the rotational speed fluctuation of the endless moving member caused by the disk eccentricity of the encoder at a low cost, Good feedback control can be performed. Therefore, if this invention is utilized, the drive control apparatus which can implement | achieve stabilization of the rotational speed of an endless moving member at low cost can be provided.
According to the image forming apparatus of the present invention, an endless moving member (photosensitive belt, transfer belt, intermediate transfer belt, or image recording medium conveying belt) generated by the disk eccentricity of the encoder is obtained by using the drive control device. Control for stabilizing the fluctuation of the rotation speed can be appropriately performed at low cost according to the image quality. Therefore, if this invention is used, an image forming apparatus capable of acquiring a high-quality image at a low cost can be provided.

It is a typical functional block diagram which shows the structure for demonstrating the function of one Embodiment of the drive control apparatus by this invention. 1 is a schematic configuration diagram of an entire laser printer showing an example of an image forming apparatus including a drive control device according to the present invention. FIG. 3 is an enlarged view showing a schematic configuration of a belt driving device 6 shown in FIG. 2. FIG. 6 is a perspective view showing the configuration of the transfer conveying belt 60 in the belt driving device 6 as seen through.

FIG. 5 is a perspective view illustrating a configuration example of a lower right roller 66 and an encoder 31 illustrated in FIG. 4. It is a figure which shows the example of a structure of the disk 311 in the encoder 31, and a sensor. FIG. 5 is a diagram showing different examples of sampling results when the drive motor 32 of FIG. 4 is driven at a constant speed and the count value of the output pulse of the encoder 31 is sampled at a constant timing. It is a block diagram which shows the hardware structural example of the control part containing the drive motor control part of the belt drive device 6 in the laser printer shown in FIG.

FIG. 2 is a block diagram illustrating a first configuration example of an output synthesis circuit 700 in FIG. 1. FIG. 5 is a diagram for explaining a positional shift between the light emitting element 312 and the light receiving element 313 and the light emitting element 316 and the light receiving element 317 in the disk 311 in FIG. 4. FIG. 11 is a diagram for explaining a displacement error count value when the positional relationship between the light emitting element 312 and the light receiving element 313 and the light emitting element 316 and the light receiving element 317 in the disk 311 in FIG. 4 is shifted as shown in FIG. It is a timing chart for demonstrating the belt drive control by this invention.

It is a block diagram which shows the structure of the filter calculation used for this invention. It is a table figure which similarly shows the filter coefficient list.

It is a diagram which similarly shows the amplitude characteristic of the filter. It is a diagram which similarly shows the phase characteristic of the filter. FIG. 14 is a block diagram illustrating a configuration of one-stage filter calculation in FIG. 13.

It is an operation | movement flowchart of an encoder pulse counter. It is a flowchart of a control cycle timer interrupt process. FIG. 6 is a block diagram illustrating a second configuration example of the output synthesis circuit 700 in FIG. 1. FIG. 10 is a block diagram showing a third configuration example of the output synthesis circuit 700 in the same manner. FIG. 22 is a diagram showing the relationship between the output pulse signals of the light receiving elements 313 and 317 of FIG. 21 and the output pulse signals of the combining circuit 702 when those pulses overlap. FIG. 8 is a block diagram illustrating a fourth configuration example of the output synthesis circuit 700 in FIG. 1.

Explanation of symbols

1Y, 1M, 1C, 1K: toner image forming unit 6: belt driving device 30: target angular displacement generating unit 31: encoder 32: driving motor 37: pulse output device 40: control controller unit 60: transfer conveyance belt 63: driving roller 66: Lower right roller (driven roller) 311: Disk 331: Encoder sensor 600: Control unit 601: CPU 602: RAM
603: ROM 604: IO control unit 606: Drive motor IF
607: Driver 608: Detection IO unit 609: Bus 700: Output synthesis circuit 701, 705, 706: Delay circuit 702: Synthesis circuit 703: Multiplication circuit

Claims (8)

Drive control for driving and controlling the drive roller based on an output signal of the encoder, the drive roller for rotating the endless moving member or the encoder for detecting the peripheral movement of the driven roller rotated by the rotation of the endless moving member A device,
The encoder has a disk in which a plurality of marks or slits are arranged at predetermined intervals in the circumferential direction, and a pair of sensors for detecting the marks or slits, and the sensors are shifted by 180 degrees. It has a configuration attached to
Combining means for combining the output signals of the pair of sensors;
A multiplying means for multiplying the combined signal from the combining means by 1/2;
Counting means for counting the half multiplied composite signal from the multiplication means;
Sampling means for sampling the count value by the means at a predetermined timing;
Feedback control means for driving and controlling the drive roller by performing feedback control on the control target value based on the count value sampled by the sampling means;
A drive control device comprising: delay means for delaying input timing of one output signal to the combining means among the output signals of the pair of sensors. The drive control device according to claim 1,
A drive control device comprising delay amount input means for inputting an arbitrary delay amount as the delay amount of the input timing. The drive control device according to claim 1,
Output timing detecting means for detecting the output timing of the pair of sensors;
A drive control apparatus comprising delay amount calculating means for calculating a delay amount of the input timing in accordance with a detection result of the output timing by the output timing detecting means. The drive control device according to claim 3, wherein
A drive control device comprising operation instruction means for operating the output timing detection means at predetermined time intervals. In the drive control device according to any one of claims 1 to 4 ,
The drive control device, wherein the feedback control means performs the feedback control using only the output signal of the other sensor when one of the pair of sensors becomes unusable. In the drive control device according to any one of claims 1 to 5 ,
The drive control device, wherein the feedback control unit stops the feedback control when both of the pair of sensors become unusable. And a drive control apparatus according to any one of claims 1 to 6, the image forming apparatus characterized by comprising an endless moving member for image forming which is driven and controlled by the drive control unit. The image forming apparatus according to claim 7 .
The image forming apparatus, wherein the endless moving member is at least one of a photosensitive belt, a transfer belt, an intermediate transfer belt, and an image recording medium conveyance belt.

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