JP5203823B2 - Image forming apparatus, method for controlling image forming apparatus, program, and storage medium - Google Patents

Description

  The present invention relates to an image forming technique.

  FIGS. 15A and 15B show a schematic configuration of an image forming apparatus for forming a conventional color image. FIG. 15A shows a mechanical configuration of the image forming unit, and FIG. 15B shows a schematic control configuration of the image forming apparatus. As shown in FIG. 15A, the image forming unit forms, for example, four color images of Y (yellow), M (magenta), C (cyan), and K (black), respectively, by an electrophotographic method. It is composed of four sets of image forming units capable of. For example, an image forming unit that forms a Y (yellow) image includes a photosensitive drum 105, a developing device 106, a cleaner 107, a charger 108, a primary transfer roller 109, and a laser optical system 110. Each image forming unit forms a corresponding color image on the intermediate transfer belt 101.

  The image forming operation of the image forming unit is controlled by the system controller 120 shown in FIG. When color image data is supplied from the image reading device 121 or the image processing device 122, it is supplied to the image forming units of the respective colors via the system controller 120. On the photosensitive drum in each image forming unit, a photoconductive layer whose electrical characteristics are changed by light irradiation is formed. Each photosensitive drum rotates at a constant speed during an image forming operation, and the following processes (1) to (5) are performed in each image forming unit. In the following description, an image forming unit (Y image forming unit) for forming a Y (yellow) image will be described as an example.

  (1) Charging: The charger 108 uniformly charges the optical semiconductor layer of the photosensitive drum 105.

  (2) Laser exposure: The laser optical system 110 irradiates the photosensitive drum 105 with laser light to form an electrostatic latent image on the photosensitive drum 105.

  (3) Development: The developing unit 106 attaches toner to the electrostatic latent image on the photosensitive drum 105.

  (4) Primary transfer: The primary transfer roller 109 transfers the toner image on the photosensitive drum 105 to the intermediate transfer belt 101.

  (5) Cleaning: The cleaner 107 cleans the toner remaining on the photosensitive drum 105 without being completely transferred to the intermediate transfer belt 101.

  Next, by processing (6) and (7), the toner image transferred to the intermediate transfer belt 101 is transferred to a recording paper and fixed.

  (6) Secondary transfer: The secondary transfer device 111 transfers the toner image on the intermediate transfer belt 101 to a recording sheet.

  (7) Fixing: The fixing device 112 heats and presses the recording paper, fixes the toner on the recording paper, and discharges the recording paper out of the image forming unit.

  As described above, the toner images formed by the respective image forming units are sequentially transferred onto the intermediate transfer belt 101 at the same timing, and the respective toner images are overlapped. However, if the movement speed of the intermediate transfer belt 101 varies, the transfer position of each color toner image transferred to the intermediate transfer belt 101 is shifted from the original transfer position, and color shift (shift of the primary transfer position). ) And density unevenness occur.

  Here, as shown in FIG. 15A, the intermediate transfer belt 101 is driven to rotate in the direction of arrow A in the drawing in accordance with the rotational drive of the drive roller 104, and the drive roller 104 has a drive motor (stepping motor). 102) is transmitted via the drive gear 103.

  Next, the conveyance speed of the intermediate transfer belt 101 will be described below.

  The radius of the driving roller 104 is r, the thickness of the intermediate transfer belt 101 is 2d0, and the thickness of the intermediate transfer belt 101 to the center in the thickness direction is d0. When the angular velocity of the driving roller 104 is ω, the conveyance speed Vb of the intermediate transfer belt 101 can be obtained by Expression (1).

Vb = (r + d0) × ω (1)
Typical factors that cause the conveyance speed Vb of the intermediate transfer belt 101 to fluctuate include, for example, an eccentric component Δr of the driving roller 104 and a thickness unevenness Δd of the intermediate transfer belt 101 (occurred when the seamless belt is manufactured). Further, the angular speed fluctuation Δω of the driving roller 104 due to the eccentric component of the driving gear 103 is also considered as a fluctuation factor of the transport speed Vb. In consideration of such variation factors, the conveyance speed Vb is expressed by Expression (2).

Vb = (r + Δr + Δd) × (ω + Δω)
= Rω + Δrω + Δdω + (r + Δr + Δd) × Δω (2)
Therefore, the speed fluctuation component ΔVb (= Vb−rω) is expressed by Expression (3).

ΔVb = Δrω + Δdω + Δω × (r + Δr + Δd)
= ΔVr + ΔVd + ΔVω (3)
However, ΔVr = Δrω, ΔVd = Δdω, and ΔVω = Δω × (r + Δr + Δd).

  Here, ΔVr is the speed fluctuation due to the eccentric component Δr of the drive roller 104, ΔVd is the speed fluctuation due to the thickness unevenness Δd of the intermediate transfer belt 101, and ΔVω is the angular speed fluctuation Δω of the drive roller 104. This is the resulting speed fluctuation.

  The distance between the upper contact position P0 of the driving roller 104 with the intermediate transfer belt 101 and the transfer point P1 of the Y (yellow) photosensitive drum 105 is D1. The distances between the transfer points of the other photosensitive drums (between P1P2, P2P3, and P3P4) are distances D2, D3, and D4. The mechanical structure of the image forming unit is configured such that the circumferential length of the driving roller 104 coincides with the distance D1 and the total value of D2 to D4 is an integral multiple of the circumferential length of the driving roller 104. As a result, it is possible to reduce the influence of the speed fluctuation (ΔVr) due to the eccentric component Δr of the driving roller 104, which is the first term of the expression (3), on the color shift during the primary transfer.

  With respect to the speed fluctuation (ΔVd) caused by the thickness unevenness Δd of the intermediate transfer belt 101, which is the second term of the expression (3), a plurality of images of a predetermined pattern are formed on the intermediate transfer belt 101 at predetermined intervals. Each of the predetermined patterns formed on the intermediate transfer belt 101 is detected at one place along the circulation route of the intermediate transfer belt 101, and the thickness unevenness Δd of the intermediate transfer belt 101 is detected based on the time difference between the detection timings. A method for controlling the rotational speed of the driving roller 104 or a method for controlling the optical system writing position on each photosensitive drum has been proposed (Patent Document 1).

  Regarding the speed fluctuation (ΔVω) caused by the angular speed fluctuation Δω of the driving roller 104, which is the third term of the equation (3), an encoder is installed on the shaft of the driving roller 104, and the driving roller is based on the detection signal of the encoder. 104 drive frequency is calculated. A method of correcting the angular velocity fluctuation of the driving roller 104 by using this driving frequency is generally implemented.

  In the first term and the third term of the equation (3), the speed fluctuation due to the eccentric component Δr of the drive roller 104 (ΔVr) and the speed fluctuation due to the angular speed fluctuation Δω of the drive roller 104 (ΔVω). The following methods have been proposed for effect reduction. The mechanical structure of the drive transmission system can be adjusted, and the absolute angle and rotational speed of the load to be driven can be detected, and control is performed on the drive side in accordance with the phase of each load drive based on these values. Thus, a method for suppressing color misregistration and density unevenness has been proposed (Patent Document 2).

  The speed fluctuation component described above is due to machine components (eccentricity, thickness, roller diameter). Normally, a speed fluctuation element due to a torque change due to a disturbance factor generated during an image forming operation is further added as a speed fluctuation element in a motor drive device.

  Examples of disturbances that induce these load fluctuations include the passage of a sheet as a copying medium and the removal / attachment operation of the cleaner mechanism for the intermediate transfer belt 101. As a result, torque fluctuation due to this causes instantaneous fluctuation in the conveyance speed Vb of the intermediate transfer belt 101, resulting in color shift and density unevenness.

  Next, a pulse motor (stepping motor) on the drive side is a motor that can be driven by open-loop control without the need to detect the rotor position and feed it back to the control circuit. The command value can be controlled in position and speed according to the number and cycle of input pulses. In the operation synchronized with the input pulse, a rotating magnetic field is generated by sequentially switching the current flowing through each phase on the stator side (A, A *, B, B * in the case of a two-phase stepping motor) for each pulse input. .

  FIG. 13 is a diagram illustrating a drive circuit configuration of the stepping motor. In this circuit, each phase of A, A *, B, and B * is sequentially excited, and constant current control driving is performed by controlling the on / off ratio so that the winding current has a predetermined current value. PWM control is used to control the on / off ratio. Thereby, a rotating magnetic field proportional to the magnitude of the winding current is generated. By applying such control, the stepping motor is driven with the number of pulses of the command input signal as a position command and the pulse cycle as a speed command. This stepping motor belongs to the category of permanent magnet synchronous motors due to its structure, but the torque generated by this permanent magnet synchronous motor is as follows.

Torque = Magnetic flux of permanent magnet x Winding current x sin (phase difference φd) (4)
Phase difference φd: Angle between the magnetic flux generated by the permanent magnet and the magnetic flux generated by the motor winding current (= load angle)
When the winding current is controlled to a predetermined value by the constant current control, the magnetic flux generated by the winding current becomes a fixed value. Therefore, as shown in FIG. 14, the phase difference φd, that is, the load angle is automatically adjusted by driving the motor according to the load torque applied by the load connected to the motor shaft, and the motor torque is balanced with the load torque. Will rotate. This means that if a load greater than the maximum torque generated at the set current value is applied, the motor will not be able to drive synchronously, generally called a “step-out” state, and will be unable to drive. To do.

  As described above, the stepping motor has an advantage that positioning driving based on the number of pulses and speed control based on the pulse period can be performed without the position detecting means. On the other hand, it is necessary to design a torque that can be generated by the stepping motor by providing a torque margin so as not to step out of the load torque required for the product to be attached.

  Further, as described above, the balance position changes due to the change of the load, that is, the speed fluctuation occurs, which leads to the speed fluctuation of the driving load. While operating with a large torque margin has the advantage of suppressing speed fluctuations during load fluctuations, it also causes problems such as speed fluctuations, vibrations and noise caused by excess torque. There are more fault elements such as end.

  As a method for measuring the torque in a state where the stepping motor is mounted on the product against these current situations, there is a method of measuring the torque from the winding current or the winding current and encoder information (for example, Patent Document 3, Patent Document 4).

Also, as a stepping motor control device that avoids step-out and reduces vibration in response to fluctuations in load torque, an encoder is used to change the excitation timing from the positional relationship between the rotor and stator that is related to load torque. is there. Also, a device that changes the excitation timing by estimating the positional relationship between the rotor and the stator from the winding current value has been put into practical use. Further, there has been proposed a method in which the winding current set value is changed from the ratio between the winding current value and the input current value to the stepping motor (Patent Document 5).
JP-A-10-186787 JP 2003-29483 A JP-A-5-332857 JP 2001-255220 A JP 2004-260978 A

  However, the above-mentioned Patent Document 1 mainly proposes a means for detecting the speed fluctuation of the load to be driven (belt in the image forming apparatus), and no detailed explanation is given for feedback control for the speed fluctuation. . In addition, the image forming apparatus disclosed in Japanese Patent Laid-Open No. 2004-228561 has to be a high-cost configuration because it is a proposal for performing eccentricity / phase alignment of the drive system by the mechanical structure / adjustment of the transmission system.

  Further, in Patent Document 2, when a pulse motor (= stepping motor) is used as a drive motor, the feedback control with respect to the speed fluctuation is not clearly shown.

  Further, Patent Documents 3 to 5 disclose a method for measuring torque and a configuration for avoiding step-out and reducing vibration in response to fluctuations in load torque by an encoder. However, feedback control is described in detail. It has not been.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of obtaining an image of good image quality even when there is a load fluctuation of a mechanical element system during image formation and a fluctuation in the conveyance speed of an intermediate transfer belt due to a disturbance.

An image forming apparatus according to the present invention that achieves the above object is an image forming apparatus having a control unit for controlling a motor driven by a pulse, wherein the control unit includes:
Speed deviation calculating means for calculating the speed deviation of the motor from speed command drive pulses generated for driving the motor by speed control and detected speed information detected by the detecting means for detecting the speed of the motor. When,
Speed correction data generating means for generating speed correction data for correcting the speed deviation as a speed feedforward control command;
A speed deviation correction means for correcting a more the speed deviation to the speed feed forward control command,
Torque for calculating the torque for driving the motor from the current value input to the motor driver for driving the motor and the speed command drive pulse input to the motor driver for driving the motor A calculation means;
Torque fluctuation data calculating means for calculating torque fluctuation caused by rotation of the motor;
Torque correction data generating means for generating torque correction data for correcting fluctuations in the torque as a torque feedforward control command;
A torque correcting means for correcting the variation of more the torque on the torque feedforward control command,
The speed feed the speed deviation by the speed deviation correction means using forward control command is corrected, in a state where variation of the torque is corrected by the torque correcting means using the torque feed forward control command, the torque feed torque feedback control means for correcting the more the current value in the forward control command,
It is characterized by providing.

Alternatively, the image forming apparatus according to the present invention is an image forming apparatus having a control unit for controlling a motor driven by a pulse, and the control unit includes:
Speed deviation calculating means for calculating the speed deviation of the motor from speed command drive pulses generated for driving the motor by speed control and detected speed information detected by the detecting means for detecting the speed of the motor. When,
Speed correction data generating means for generating speed correction data for correcting the speed deviation;
A plurality of pattern images are formed at predetermined reference intervals on a belt to form a toner image, in accordance with the conveyance of the belt, and spacing of the pattern image by the image reading unit has read, from the reference interval Calculating means for calculating a speed deviation due to thickness unevenness for one round of conveyance of the belt;
Thickness unevenness correction data generating means for generating thickness unevenness correction data for correcting a speed deviation due to thickness unevenness of one round of conveyance of the belt calculated by the calculating means;
Generates a speed feedforward control command for correcting the speed deviation from the speed correction data generated by the speed correction data generation means and the thickness unevenness correction data generated by the thickness unevenness correction data generation means. Speed feedforward control command generating means for performing,
A speed deviation correction means for correcting a more the speed deviation to the speed feed forward control command,
In a state where the speed deviation by the speed deviation correction means using said speed feedforward control command is corrected, the more thickness irregularity correction data, the correction value of the current input to the motor driver to drive the motor A torque feedback control means for feedback controlling the driving torque of the motor;
It is characterized by providing.

  According to the present invention, it is possible to obtain an image having a good image quality even when there is a load variation of the machine element system during image formation and a conveyance speed variation of the intermediate transfer belt due to a disturbance.

  Alternatively, according to the present invention, by speed detection and load torque detection, speed fluctuation due to factors such as mechanical attachment error and shape error can be feedforward controlled as a speed command of the stepping motor. The steady load torque fluctuation factor can be corrected for the speed fluctuation factor by feedforward control to the motor current value.

  Further, according to the present invention, the motor current feedback control is performed by detecting the speed change with respect to the sudden load torque fluctuation factor, and the speed control stable with respect to the torque fluctuation becomes possible.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the constituent elements described in this embodiment are merely examples, and the technical scope of the present invention is determined by the scope of claims, and is limited by the following individual embodiments. is not.

  FIGS. 1A and 1B are diagrams illustrating a schematic configuration of an image forming apparatus according to the embodiment. The same components as those in FIGS. 15A and 15B are the same as those in FIG. Description is omitted by using reference numerals.

  Encoder 117 (Y, M, C, K) for detecting the rotational position / speed of the drum and a home position sensor for detecting the reference position of the encoder are arranged around the rotating shaft of each photosensitive drum (photosensitive body). 118 (Y, M, C, K).

  An encoder 113 is installed around the rotation shaft of the driving roller 104 of the intermediate transfer belt 101 in the same manner as the photosensitive drum. The encoder 113 can detect rotational position information and speed information (angular speed) of the driving roller 104.

  The drive roller home position sensor 114 is installed on the shaft of the drive roller 104 similarly to the encoder 113, and detects the reference position of the drive roller 104, thereby detecting the timing of the rotation period of one rotation of the drive roller 104.

  The belt home position sensor 115 detects a detection mark provided on the intermediate transfer belt 101. The image reading sensor 116 can detect a toner image or a predetermined pattern image formed on the surface of the intermediate transfer belt 101.

  FIG. 2 is a diagram illustrating a control block of the image forming apparatus according to the present embodiment. The image forming apparatus is comprehensively controlled by the system controller 120, and mainly plays a role of driving each unit constituting the image forming apparatus, collecting information detected by a sensor or an encoder, and analyzing collected information. Yes. A CPU 201 is mounted inside the system controller 120. The CPU 201 executes various sequences relating to a predetermined image forming sequence by a program stored in the ROM 202 mounted on the system controller 120. At that time, the RAM 203 is also mounted to store rewritable data that needs to be temporarily or permanently stored.

  The ASIC 301 controls the belt system that drives the intermediate transfer belt 101 by detecting the position / speed information of the intermediate transfer belt (ITB) 101, and the drum drive that drives the photosensitive drum 105 by detecting the position / speed of the photosensitive drum 105. Control the system.

(Belt drive system)
The ASIC 301 includes an AD converter 302, a position / speed detection counter 303, a belt drive roller position / speed information conversion unit 306, and a command value position / speed information conversion unit 307 as control of the belt drive system. The AD converter 302 AD converts the analog output signal read by the image reading sensor 116 provided above the intermediate transfer belt (ITB) 101.

  The position / speed detection counter 303 counts the output signal of the encoder 113 for detecting the position and rotation speed of the rotation shaft of the drive roller 104. The belt drive roller position / speed information conversion unit 306 converts the count value of the position / speed detection counter 303 into position / speed information of the drive roller 104 that drives the intermediate transfer belt 101. The command value position / speed information conversion unit 307 converts a counter 305 that counts drive pulses for driving the stepping motor 102b, and converts the count value in the counter 305 into position / speed information.

(Drum drive system)
The ASIC 301 controls the drum drive system as a position / speed detection counter 310, a counter 312, a drum shaft position / speed information converter 313, a command value position / speed information converter 314, an input current detector 206a, and an AD converter 315. And a load angle conversion unit 316. The position / speed detection counter 310 counts the output signal of the encoder 117 for detecting the position / speed of the drum drive shaft of the photosensitive drum 105. The drum shaft position / speed information conversion unit 313 converts the count value of the position / speed detection counter 310 into position / speed information. The counter 312 counts the driving pulse (command value information) of the stepping motor 102a. The command value position / speed information conversion unit 314 converts the count value of the counter 312 into position / speed information. The input current detection unit 206a detects an input current to the drive circuit (motor driver 205a) of the stepping motor 102a, and the AD converter 315 performs AD conversion on the value detected by the input current detection unit 206a. The load angle conversion unit 316 performs load angle conversion (calculation of phase angle) of the stepping motor based on the output of the command value position / speed information conversion unit 314 and the output of the AD converter 315.

  The values detected and converted by the above two systems are transmitted to the system controller 120. The ASIC 301 includes clock generators 304 and 311 as a belt driving system and a drum driving system, respectively. The clock generators 304 and 311 generate clocks for driving the intermediate transfer belt (ITB) 101 and the stepping motor 102a and the stepping motor 102b for rotationally driving the photosensitive drum 105. The clock generators 304 and 311 output drive clocks to the motor driver 205b and the motor driver 205a based on values (speed command and current command) set by the CPU 201. As a result, the motor drivers 205b and 205a drive the stepping motors b and 102a based on the frequency of the drive clock.

  In the above configuration, the speed control and current control of each stepping motor will be described.

(Drum drive system control)
The control of the drum drive system by the ASIC 301 will be described with reference to FIGS.

(Speed command control)
In FIG. 3, a control block 801 indicates a speed command control block for correcting the speed command of the stepping motor. The CPU 201 functions as a speed deviation calculation unit. The CPU 201 calculates a speed deviation based on the speed command drive pulse generated for driving the stepping motor by speed control and the detected speed information detected by the encoder 117 functioning as a detecting means for detecting the speed. The CPU 201 performs control for driving the stepping motor 102a for driving the photosensitive drum 105 based on the speed command driving pulse 350 at a predetermined driving frequency Vt set in advance. The driving pulse (command value information) of the stepping motor 102a counted by the counter 312 is converted into position / speed information by the command value position / speed information conversion unit 314. This conversion result corresponds to the speed command drive pulse 350. Based on the speed command drive pulse 350, the clock generator 311 generates a drive clock, and the motor driver 205a drives the stepping motor 102a based on the frequency of the drive clock.

  The position / speed detection counter 310 counts the number of pulses (output signal) output from the encoder 117 for detecting the position / speed of the drum drive shaft of the photosensitive drum 105. The position / velocity detection counter 310 operates based on the base clock of the ASIC 301 or the CPU 201 and can count at a sufficiently high speed to count the number of pulses (output signal) output from the encoder 117 one by one. Is possible.

  The position / speed detection counter 310 counts output signals based on the encoder resolution (angle deg / pls per pulse). Based on this count value (count value), the drum shaft position / speed information conversion unit 313 detects the position of the drive shaft of the photosensitive drum 105, and detects the speed from time conversion based on the base clock. The count value of the position / speed detection counter 310 is reset when the home position sensor 118 detects the reference position (home position position) of the encoder 117. The position / speed detection counter 310 starts counting to generate position / speed information from the home position.

  The output from the drum shaft position / speed information conversion unit 313 becomes detection position information and detection speed information 351 of the drive shaft of the photosensitive drum 105.

  The CPU 201 obtains a deviation between the detected speed information 351 output from the drum shaft position / speed information conversion unit 313 and the speed command drive pulse 350 that is a target value of the speed of the stepping motor 102a. Based on this deviation, the CPU 201 generates a speed deviation profile 3011 in which the eccentric component of the drive gear in one cycle of the rotational drive of the photosensitive drum 105 is extracted. The sinusoidal profile indicated by the speed deviation profile 3011 schematically shows the speed unevenness for one rotation of the photosensitive drum 105.

  The CPU 201 stores a speed deviation data table storing speed deviation data corresponding to the speed deviation profile 3011 in the RAM 203. The number of data in the speed deviation data table is equal to the encoder resolution, and corresponds to a frequency component that is sufficiently faster than the frequency component of the speed unevenness of the photosensitive drum 105.

  The CPU 201 can function as a speed correction data generation unit that generates speed correction data for correcting a speed deviation as a speed feedforward control command. The CPU 201 generates a speed correction profile 3021 for correcting the speed deviation component based on the speed deviation profile 3011. Then, the CPU 201 stores a speed correction data table storing speed correction data corresponding to the speed correction profile 3021 in the RAM 203. Drum_Encoder_HP in the speed deviation profile 3011 and the speed correction profile 3021 indicates the home position position of the encoder 117.

  The CPU 201 can obtain the speed correction profile 3021 so as to cancel the speed deviation profile 3011. In this case, the CPU 201 functions as a speed deviation correction unit that corrects the speed deviation based on the speed feedforward control command.

(Current command control)
A control block 901 shows a current command control block for correcting the current command of the stepping motor.

  A current command generated by the CPU 201 is input to the motor driver 205a. The input current (current command) to the motor driver 205a is synchronized with the drive pulse signal so that the stepping motor 102a operates at the drive frequency Vt. The input current to the motor driver 205a is detected by the input current detection unit 206a and sampled by the AD converter 315. The value sampled by the AD converter 315 is input to the load angle conversion unit 316.

  Further, the drive pulse (command value information) of the stepping motor 102a counted by the counter 312 is converted into position / speed information by the command value position / speed information conversion unit 314. This conversion result is input to the load angle conversion unit 316 as a speed command drive pulse 361.

  The CPU 201 functions as a torque calculation unit that calculates torque for driving the stepping motor 102a based on the current value input to the motor driver 205a and the speed command drive pulse input to the motor driver 205a.

  The load angle conversion unit 316 performs load angle conversion (calculation of phase angle) of the stepping motor 102a based on the speed command drive pulse 361 and the driver input current detection value 360 sampled by the AD converter 315. Based on this conversion result, the CPU 201 generates a load torque fluctuation profile 3031 from the drum home position. In this case, the CPU 201 functions as torque fluctuation data calculation means for calculating torque fluctuation caused by the rotation of the motor. Then, the CPU 201 stores a load torque fluctuation data table in which load torque fluctuation data corresponding to the load torque fluctuation profile 3031 is stored in the RAM 203.

  The CPU 201 generates a torque correction profile 3041 for the stepping motor based on the load torque fluctuation data table in the RAM 203 so as to correct the torque fluctuation for one cycle (one rotation) of the photosensitive drum. The CPU 201 functions as torque correction data generating means for generating torque correction data for correcting torque fluctuations as a torque feedforward control command.

  The CPU 201 stores a torque correction data table storing torque correction data corresponding to the torque correction profile 3041 in the RAM 203. Drum_Encoder_HP of the load torque fluctuation profile 3031 and the torque correction profile 3041 indicates the home position position of the encoder 117.

  The CPU 201 outputs the torque correction profile 3041 as a torque feedforward control command 353 for controlling the rotation of the photosensitive drum 105.

  The CPU 201 functions as a torque correction unit that corrects torque fluctuations based on the torque feedforward control command 353.

  The CPU 201 performs feedforward control of the stepping motor 102a based on the speed correction profile 3021 and the torque correction profile 3041. By performing feedforward control, it becomes possible to cancel the speed deviation due to mechanical factors (gear eccentricity, shaft eccentricity) and steady torque fluctuations due to the machine configuration.

(Torque feedback control)
At a node 610 of the torque feedback control block 601 shown in FIG. 3, the deviation between the speed command drive pulse 350 and the detected speed information 351 is obtained. At node 620, the speed feedforward control command is added to the deviation determined at node 610. This addition result is multiplied by the current correction gain Kp. At node 630, torque feedforward control command 353 is added.

  At node 650, a deviation between load torque fluctuation profile 3031 and torque feedforward control command 353 is obtained, and this deviation is multiplied by torque correction gain Ktp.

  At node 640, the multiplication result of torque correction gain Ktp and the addition result of torque feedforward control command 353 at node 630 are multiplied to generate torque feedback control command 660.

  The control of the torque feedback control block 601 is executed in a state where the speed deviation is corrected using the speed feedforward control command and the fluctuation of the torque is corrected based on the torque feedforward control command. The CPU 201 functions as a torque feedback control unit that corrects the current value input to the motor driver 205a based on the torque feedforward control command.

  A value obtained by multiplying the difference between the torque feedforward control command 353 and the detected torque value sequentially detected by the load angle conversion unit 316 by the correction proportional gain ktp is reflected in the torque feedback control command. This makes it possible to perform follow-up control against sudden torque fluctuations.

  As described above, by combining the feedforward control and the feedback control, it is possible to perform speed control with good responsiveness to load fluctuations.

(Control of belt drive system)
Control of the belt drive system by the ASIC 301 will be described with reference to FIGS.

  In FIG. 5, a control block 812 indicates a speed command control block for correcting the speed command of the stepping motor. The basic speed correction control is almost the same as the procedure performed in driving the photosensitive drum 105. The CPU 201 obtains a speed deviation profile 511 indicating the speed deviation of the belt driving roller for one rotation of the intermediate transfer belt 101 based on the deviation between the speed command driving pulse 550 and the detected speed information 551 regarding the rotation of the driving roller 104. The CPU 201 stores a speed deviation data table in which speed deviation data corresponding to the speed deviation profile 511 is stored in the RAM 203. The CPU 201 generates a speed correction profile 512 for correcting the speed deviation component based on the speed deviation profile 511. Then, the CPU 201 stores a speed correction data table storing speed correction data corresponding to the speed correction profile 512 in the RAM 203. ITB_HP of the speed deviation profile 511 and the speed correction profile 512 indicates the home position position of the encoder 113. The CPU 201 can obtain the speed correction profile 512 so as to cancel the speed deviation profile 511.

  The driving of the stepping motor 102b is corrected based on the speed correction profile 512 and the input of encoder data. In this state, the CPU 201 determines whether the encoder data is within a predetermined range set in advance. If the encoder data is outside the predetermined range, the CPU 201 acquires the speed correction profile again. If it is within the predetermined range, it is determined that the angular velocity of the driving roller 104 is stable, and a plurality of pattern images (N, N + 1, N + 2, N + 3,... As shown in FIG. 4 are formed on the intermediate transfer belt (ITB) 101.・) Is formed. Pattern images (N, N + 1, N + 2, N + 3...) Are formed by transferring a toner image formed on the photosensitive drum 105 to the intermediate transfer belt 101.

  FIG. 4A shows pattern images (N, N + 1, N + 2, N + 3...) Formed on the intermediate transfer belt 101. Pattern images (N, N + 1, N + 2, N + 3...) Are formed in a rectangular shape with a distance L and equally spaced.

  FIG. 4B shows a detection waveform when a rectangular pattern is detected by the image reading sensor 116 disposed above the intermediate transfer belt 101. If the speed of the intermediate transfer belt 101 is Vt, the pattern detection cycle is L / Vt = T0. When the speed of the intermediate transfer belt 101 in the conveyance direction does not vary, the detection cycle of each pattern is constant at T0. However, when the speed of the intermediate transfer belt in the conveyance direction fluctuates, the detection cycle becomes T0−Δt1, for example, between the patterns N + 1 and N + 2, and the cycle is shortened by Δt1 with respect to the reference cycle T0.

  When ΔT is the input interval time fluctuation and ΔV is the belt speed fluctuation, the relationship L / (T0 ± ΔT) = Vt ± ΔV is established.

  The cycle (T0 ± ΔT) between patterns can be acquired as the timer count value of the ASIC 301. The period (T0 ± ΔT) between the patterns acquired here becomes the patch interval data input 560 in FIG. The reference interval command value 561 is a command value corresponding to the reference cycle T0. Based on the deviation (± ΔT) between the patch interval data input 560 and the reference interval command value 561, the CPU 201 extracts the velocity unevenness due to the thickness unevenness of one rotation of the intermediate transfer belt 101 from which the thickness unevenness component of the intermediate transfer belt 101 is extracted. A profile 523 is obtained. Then, the CPU 201 stores a speed correction data table storing speed deviation data corresponding to the speed deviation profile 523 in the RAM 203. The number of data in the speed correction data table is equal to the number of formed patterns (N, N + 1, N + 2, N + 3,...), And is a frequency component that is sufficiently faster than the thickness unevenness frequency component of the intermediate transfer belt 101. It becomes a condition. The sinusoidal profile indicated by the speed deviation profile 523 schematically shows the speed unevenness for one round of the intermediate transfer belt. Then, the CPU 201 generates a thickness unevenness correction profile 524 that corrects the thickness unevenness based on the speed deviation profile 523. In this case, the CPU 201 functions as thickness unevenness correction data generating means for generating thickness unevenness correction data for correcting the speed deviation due to the thickness unevenness of the calculated conveyance of the intermediate transfer belt 101 for one round. ITB_HP of the speed deviation profile 523 and the thickness unevenness correction profile 524 indicates the home position position of the encoder 113.

  The CPU 201 functions as a speed feedforward control command generation unit that generates a speed feedforward control command for correcting a speed deviation based on the speed correction data and the thickness unevenness correction data. The CPU 201 calculates the motor drive frequency by multiplying the data of the speed correction profile 512 by the data of the thickness unevenness correction profile 524. This becomes the speed feedforward control command value 530. And CPU201 functions as a speed deviation correction means, and corrects a speed deviation based on a speed feedforward control command.

  Note that the speed extraction method of the intermediate transfer belt 101 is not limited to the above-described method. For example, the belt thickness unevenness is measured in advance with a measuring instrument and the profile is calculated based on the measurement result. Is possible. Further, instead of forming the pattern formed on the intermediate transfer belt as a toner image, for example, the belt itself may be marked in advance and the mark may be detected.

(Torque feedback control)
The CPU 201 functions as torque feedback control means, and corrects the current value input to the motor driver 205b based on the detected speed information 551 in a state where the speed deviation is corrected using the speed feedforward control command. Feedback control of the driving torque of the stepping motor 102b is executed by correcting the current value input to the motor driver 205b.

  In the node 670 of the feedback control block 611 shown in FIG. 5, the deviation between the speed command drive pulse 550 and the detected speed information 551 is obtained. At node 675, the speed feedforward control command is added to the deviation determined at node 670. This addition result is multiplied by the current correction gain Kp. In the node 680, based on the deviation between the patch interval data input 560 and the reference interval command value 561, the CPU 201 extracts the thickness unevenness component of the intermediate transfer belt 101 and the speed deviation profile due to the thickness unevenness of one turn of the intermediate transfer belt 101. 523 is obtained. The speed deviation profile 523 is multiplied by the torque correction gain Ktp.

  At node 690, the multiplication result of torque correction gain Ktp and the multiplication result of current correction gain kp are multiplied, and torque feedback control command 695 is generated.

(Load angle conversion)
Next, load angle conversion in the drive circuit of the stepping motor used in this embodiment will be described. As shown in FIG. 6, the drive circuit for the stepping motor includes a constant current control circuit 202 that performs torque control based on a torque feedback control command value, and an input current detection circuit 260a. The drum stepping motor drive circuit and the belt stepping motor drive circuit have the same configuration. As shown in FIG. 2, the drum driving circuit is provided with an AD converter 315 that is connected to the input current detection unit 206 a and is taken into the ASIC 301 as digital data. The drive circuit for the drum further includes a clock generator 311 for generating a drive pulse provided in the ASIC 301, and a load angle conversion unit to which a counter 312 for detecting the period of the generated drive pulse is connected. 316 is provided. The load angle conversion unit 316 is a circuit for calculating the load angle based on the position with respect to the stepping motor 102b, the speed command value, and the input current value to the driver.

  In accordance with a drive pulse signal input from a host device (clock generator 311 in the ASIC 301) such as a control device of the image forming apparatus, the phase excitation pattern generation circuit 300 determines a phase excitation pulse signal that determines the excitation order of the windings of the stepping motor. (A, A *, B, B *) is generated.

  For windings selected according to the phase excitation pulse signal from the phase excitation pattern generation circuit 300, the currents ia, ia *, ib, ib * flowing through the windings are A / A * current detection circuits 201A, B / B * is detected by the current detection circuit 201B. Then, the PWM control circuit 202A and the PWM control circuit 202B determine ON / OFF so that the current value is based on the constant current command value set by the torque control unit 202C, and the semiconductor switch element group (Q1 to Q4) is determined. Driven.

  Examples of torque characteristics of the stepping motor driven by the constant current control circuit 202 are shown in FIGS. FIG. 7 is a diagram showing the relationship between the input current and the drive frequency when the torque is constant. FIG. 8 is a graph showing the relationship between torque and input current when the speed is constant.

  As shown in FIG. 7, in the relationship between the drive frequency and the input current, the slope changes in the constant current region (drive frequency: low) and the constant voltage region (drive frequency: high). This is due to the influence of the induced voltage due to the magnetic flux of the permanent magnet of the motor rotor. However, as shown in FIG. 8, the relationship between the torque and the input current varies depending on the driving frequency, but each has a linear characteristic when the driving frequency is constant. In other words, it is only necessary to perform correction in consideration of the influence degree for each frequency. For this purpose, a configuration in which the clock generator 311 for detecting the drive pulse period is connected to the drive circuit of the stepping motor together with the input current detection unit 206a and the AD converter 315 for taking the detected value (analog amount) into the ASIC 301. It is said. In order to take into account the frequency factor from the relationship of the input current with respect to the torque based on the input values from these, the current amount per unit time [unit: A / s] is converted.

  The clock generator 311 for detecting the drive pulse period is configured using, for example, a timer counter that operates at a frequency sufficiently faster than the frequency of the drive pulse (here, CLK for ASIC 301 not shown). As shown in FIG. 9, the timer counter counts the pulse period using the rising or falling edge of the drive pulse as a base point.

  The current detected by the input current detection unit 206a is sampled by the AD converter 315 at an arbitrary period obtained by dividing the drive lock of the ASIC 301. However, sampling may be performed in synchronization with the drive pulse of the drive pulse period counter. However, when sampling is performed in synchronization with the driving pulse and the sampling period becomes extremely long, the current fluctuation is not taken into account, so that the sampling time is preferably short. When taking into account a decrease in detection accuracy due to such a long sampling cycle, the analog circuit unit of the input current detection unit 206a is configured to detect an effective value, and even when the sampling cycle is long, a short time is required. It is good also as a structure which can consider the electric current fluctuation part in. For example, as shown in FIG. 10, the output value of the input current detection unit 206a is output as an effective value of the current change, and further, the value of the clock generator 311 is converted into an analog value and compared with the output of the input current detection unit 206a. An A / D converter can also be configured by using a converter.

  The relationship between the motor torque and the input current can be grasped from the equation (4) and the following formula for calculating the supply current to the motor winding.

V = Ri + L · di / dt + eω (5)
(R: Winding resistance, L: Winding inductance, eω: Speed electromotive force)
More practically, the influence of various motor elements can be taken into account by determining from the current value at the maximum load angle based on the actually measured motor characteristics. Hereinafter, an example based on the actual measurement result will be described.

  The motor generated torque is expressed by equation (4). FIG. 11 shows the characteristics of speed and torque measured when the phase is changed with the amplitude of the winding current fixed. In FIG. 11, when the required drive speed (rotation speed: rpm) is taken on the vertical axis and the required load torque is taken on the horizontal axis, the change range of the phase = load angle during motor operation at the required speed depends on the load torque. You can see how it changes. When the load torque fluctuation time is taken into consideration, the maximum phase value that can ensure the required speed is extracted as the maximum load angle.

  Next, the relationship between the rotational speed and torque shown in FIG. 11 is shown in FIG. 12 as the relationship between input current and torque. In FIG. 12, the input current at the maximum load extracted as described above is extracted. Here, when the input current based on the torque fluctuation at the required speed is extracted, as shown in FIG. 8, the torque and the current change linearly when the speed is constant.

  If the load angle at the maximum drive speed and the required load torque value is set based on the values obtained from these characteristic diagrams, changes in the load angle within the drive range can be detected from the input current value obtained by frequency correction using the configuration described above. It becomes possible.

  As described above, according to the configuration described above, it is possible to detect the load torque in the stepping motor without using the position detection unit, and it is possible to detect the load torque in the stepping motor as in the case of the DC motor. . By combining the advantage of position / speed control with open loop control, which is a feature of stepping motors, it is possible to generate a profile for each position of torque change data.

  Accordingly, by continuing the rotation speed correction and the torque correction control during the image forming operation, it is possible to reduce density unevenness and color misregistration and to improve the image quality of the image forming apparatus.

  Here, the description has been made on the assumption that the stepping motor operates in a constant current region. In addition to this, a configuration that creates a power supply voltage correction profile based on the speed correction profile as a means to improve load tracking performance even when operated in a constant voltage range, allows control over a wider speed range. Can be secured.

  Further, the configuration of the position / velocity detection unit is simplified, and even when only the reference position is detected, it is possible to grasp the relative position from the reference position based on the position command value by the motor drive pulse. For this reason, by recording the load angle fluctuation at the relative position based on the machine reference position and the command value, it is possible to perform feedforward control corresponding to the load fluctuation at normal time and feedback control of the sequential load fluctuation.

  According to the present embodiment, it is possible to obtain an image with good image quality even if there is a load fluctuation of the machine element system during image formation and a fluctuation in the conveyance speed of the intermediate transfer belt due to a disturbance.

  Alternatively, according to the present embodiment, by speed detection and load torque detection, speed fluctuation due to factors such as mechanical attachment error and shape error can be feedforward controlled as a speed command of the stepping motor. The steady load torque fluctuation factor can be corrected for the speed fluctuation factor by feedforward control to the motor current value.

  Further, the feedback control of the motor current is performed by detecting the speed change with respect to the sudden load torque fluctuation factor, and the speed control stable with respect to the torque fluctuation becomes possible.

(Other embodiments)
Needless to say, the object of the present invention can also be achieved by supplying a system or apparatus with a computer-readable storage medium storing software program codes for realizing the functions of the above-described embodiments. Needless to say, this can also be achieved by the computer (or CPU or MPU) of the system or apparatus reading and executing the program code stored in the storage medium.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention.

  As a storage medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a nonvolatile memory card, a ROM, or the like can be used.

  Further, the functions of the above-described embodiment are realized by executing the program code read by the computer. In addition, an OS (operating system) running on a computer performs part or all of actual processing based on an instruction of a program code, and the above-described embodiment is realized by the processing. Needless to say.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a control block of the image forming apparatus according to the embodiment of the present invention. It is a figure explaining the production | generation process of a control command (speed Ford forward control command, torque feedforward control command, torque feedback control command). FIG. 4 is a diagram illustrating a predetermined pattern formed on an intermediate transfer belt and a detection signal when an image reading sensor detects the predetermined pattern. It is a figure explaining the production | generation process of a control command (speed Ford forward control command, torque feedback control command). It is a figure which shows the basic composition of the stepping motor drive circuit which concerns on embodiment of this invention. It is a figure which shows the input current-speed characteristic of the stepping motor at the time of constant current control. It is a figure which shows the input current-torque characteristic of the stepping motor at the time of constant current control. It is a figure which shows operation | movement at the time of comprising a drive pulse period detection with a counter. It is a figure which shows the drive pulse period detection counter operation | movement, and the sampling example of the input current in a pulse edge. It is a figure which shows the torque-speed-phase characteristic at the time of the constant current control by position reference | standard excitation. It is a figure which shows the torque-input current-phase characteristic at the time of the constant current control by position reference | standard excitation. It is the figure which illustrated the drive circuit structure of the conventional stepping motor. It is a figure explaining the load angle of a stepping motor. It is a figure which shows schematic structure of the conventional color image forming apparatus.

Explanation of symbols

101 Intermediate transfer belt 102a Stepping motor 102b Stepping motor 103 Driving gear 104 Driving roller 105 Photosensitive drum 113 Encoder 116 Image reading sensor

Claims (8)

An image forming apparatus having a control unit for controlling a motor driven by a pulse, wherein the control unit includes:
Speed deviation calculating means for calculating the speed deviation of the motor from speed command drive pulses generated for driving the motor by speed control and detected speed information detected by the detecting means for detecting the speed of the motor. When,
Speed correction data generating means for generating speed correction data for correcting the speed deviation as a speed feedforward control command;
A speed deviation correction means for correcting a more the speed deviation to the speed feed forward control command,
Torque for calculating the torque for driving the motor from the current value input to the motor driver for driving the motor and the speed command drive pulse input to the motor driver for driving the motor A calculation means;
Torque fluctuation data calculating means for calculating torque fluctuation caused by rotation of the motor;
Torque correction data generating means for generating torque correction data for correcting fluctuations in the torque as a torque feedforward control command;
A torque correcting means for correcting the variation of more the torque on the torque feedforward control command,
The speed feed the speed deviation by the speed deviation correction means using forward control command is corrected, in a state where variation of the torque is corrected by the torque correcting means using the torque feed forward control command, the torque feed torque feedback control means for correcting the more the current value in the forward control command,
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the motor is a stepping motor for driving a photosensitive member. An image forming apparatus having a control unit for controlling a motor driven by a pulse, the control unit comprising:
Speed deviation calculating means for calculating the speed deviation of the motor from speed command drive pulses generated for driving the motor by speed control and detected speed information detected by the detecting means for detecting the speed of the motor. When,
Speed correction data generating means for generating speed correction data for correcting the speed deviation;
A plurality of pattern images are formed at predetermined reference intervals on a belt to form a toner image, in accordance with the conveyance of the belt, and spacing of the pattern image by the image reading unit has read, from the reference interval a calculation means for calculating a speed deviation by one round of the thickness unevenness of conveyance of the belt,
Thickness unevenness correction data generating means for generating thickness unevenness correction data for correcting a speed deviation due to thickness unevenness of one round of conveyance of the belt calculated by the calculating means;
Generates a speed feedforward control command for correcting the speed deviation from the speed correction data generated by the speed correction data generation means and the thickness unevenness correction data generated by the thickness unevenness correction data generation means. Speed feedforward control command generating means for performing,
A speed deviation correction means for correcting a more the speed deviation to the speed feed forward control command,
In a state where the speed deviation by the speed deviation correction means using said speed feedforward control command is corrected, the more thickness irregularity correction data, the correction value of the current input to the motor driver to drive the motor A torque feedback control means for feedback controlling the driving torque of the motor;
An image forming apparatus comprising:   The image forming apparatus according to claim 3, wherein the motor is a stepping motor for driving the belt. A control method of an image forming apparatus having a control means for controlling a motor driven by a pulse,
From the speed deviation calculation means of said control means, a speed command driving pulse by the speed control is generated to drive the motor, and the detected velocity information detected by the detecting means for detecting the speed of the motor, the motor A speed deviation calculating step of calculating a speed deviation of
A speed correction data generating step in which the speed correction data generating means of the control means generates speed correction data for correcting the speed deviation as a speed feedforward control command;
Speed deviation correction means of said control means, and the speed deviation correction process for correcting the more the speed deviation to the speed feed forward control command,
Torque calculating means of the control means, a current value input to the motor driver to drive the motor, and a speed command driving pulse input to the motor driver for driving the motor, the motor A torque calculating step for calculating a torque for driving;
A torque fluctuation data calculating step in which the torque fluctuation data calculating means of the control means calculates a torque fluctuation caused by the rotation of the motor;
A torque correction data generating step in which the torque correction data generating means of the control means generates torque correction data for correcting fluctuations in the torque as a torque feedforward control command;
Torque correcting means of said control means, and the torque correction step for correcting the variation of more the torque on the torque feedforward control command,
Torque feedback control means of the control means, wherein said speed deviation by the speed deviation correction process using the speed feedforward control command is corrected, the variation of the torque by the torque correction process using the torque feed forward control command in a state but which it has been corrected, and torque feedback control step of correcting further the current value to the torque feedforward control command,
Method of controlling an image forming apparatus according to claim Rukoto to have a. A control method of an image forming apparatus having a control means for controlling a motor driven by a pulse,
From the speed deviation calculation means of said control means, a speed command driving pulse by the speed control is generated to drive the motor, and the detected velocity information detected by the detecting means for detecting the speed of the motor, the motor A speed deviation calculating step of calculating a speed deviation of
A speed correction data generating step in which the speed correction data generating means of the control means generates speed correction data for correcting the speed deviation;
The calculation means of the control means reads a plurality of pattern images formed at a predetermined reference interval on a belt for forming a toner image, according to the conveyance of the belt. and distance from the reference interval, a calculation step of calculating the speed deviation by one round of the thickness unevenness of conveyance of the belt,
Thickness unevenness correction data generation means for generating thickness unevenness correction data for correcting the speed deviation due to the thickness unevenness of one round of conveyance of the belt calculated by the calculating step. Process,
From the speed feedforward control command generating means of said control means, said said speed correction data generated by the velocity correction data generating step, and the thickness irregularity correction the thickness irregularity correction data generated by the data generating step, the rate A speed feedforward control command generating step for generating a speed feedforward control command for correcting the deviation;
Speed deviation correction means of said control means, and the speed deviation correction process for correcting the more the speed deviation to the speed feed forward control command,
Torque feedback control means of the control means, in a state where the speed deviation by the speed deviation correction process using the speed feedforward control command is corrected, and more to the thickness irregularity correction data, in order to drive the motor A torque feedback control step of correcting the current value input to the motor driver and performing feedback control of the driving torque of the motor;
Method of controlling an image forming apparatus according to claim Rukoto to have a.   A program for causing a computer to execute the control method for an image forming apparatus according to claim 5. A computer-readable storage medium storing the program according to claim 7.

Images