JP2006018518A - Drive control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent generation of banding and displacement due to characteristics of a drive transmission mechanism and to prevent deterioration of image quality due to a low resonance frequency in a one-step timing belt type transmission mechanism when control for accurate follow-up on a target position is carried out for driving a drive object such as a photosensitive drum or an intermediate transfer belt in an image forming apparatus. <P>SOLUTION: A brushless motor 111 drives the photosensitive drum 101 via a motor shaft timing pulley 109, a timing belt 108, a relay shaft large timing pulley 107, a relay shaft small timing pulley 105, a timing belt 104, and a drum shaft timing pulley 103. Each of components for a two-step timing belt transmission mechanism is constructed with an equal deceleration ratio, and a contact angle of the timing belt with the timing pulley is constructed to be equal to that constructed in a first-step timing belt transmission mechanism. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a copying machine, a printer, a plotter, a facsimile, and a printing apparatus, and more particularly, to a driving unit that drives a driving object such as an image carrier, an intermediate transfer member, and a paper transfer member.

  In an electrophotographic image forming apparatus such as a copying machine or a printer, there is a proposal for reducing banding and misalignment related to a drive control system and a drive transmission system (see, for example, Patent Document 1). According to the proposal, in an image forming apparatus including a plurality of drive units that have a plurality of motors and a transmission mechanism, and a plurality of drive targets that are respectively driven by the plurality of motors and the transmission mechanism are driven in contact with each other. The plurality of drive units are a plurality of drive units that connect a drive shaft timing pulley to be driven and a motor shaft timing pulley through a timing belt, respectively, and rotate the plurality of drive targets by driving each motor. The frequency is determined by the relationship between the surface speed of the driving target, the pitch circle diameter of the driving shaft timing pulley, the diameter of the driving target, the pitch of the driving shaft timing pulley, and the image quality speed fluctuation allowable value. However, this prior art corresponds to the case where the drive is transmitted from the motor drive shaft to the drive target shaft by only one stage of deceleration.

FIG. 15 is a configuration diagram of an image forming apparatus in which the transmission system is a one-stage deceleration system.
In the figure, reference numeral 81 is a photosensitive drum, 82 is a drum driving shaft, 83 is a drum shaft timing pulley, 84 is a timing belt, 85 is a motor shaft timing pulley, 86 is a drum driving motor, 87 is a rotary encoder, and 88 is an intermediate. The transfer belt 89 is a belt drive shaft, 90 is a belt drive shaft timing pulley, 91 is a timing belt, 92 is a motor shaft timing pulley, 93 is a belt drive motor, 94 is an encoder scale provided outside the image area, and 95 is a signal. The optical head 96 reads a paper transfer roller.
The photosensitive member 81 that is one of the driving targets is connected to a drum driving motor 86 that is a driving source through a transmission system such as a drum driving shaft 82, a drum shaft timing pulley 83, a timing belt 84, and a motor shaft timing pulley 85. And driven. A sensor by a rotary encoder 87 is attached to the drum drive shaft 82.

The second transfer target intermediate transfer belt 88 is transferred to a belt driving motor 93 which is a driving source through a transmission system such as a belt driving shaft 89, a driving shaft timing pulley 90, a timing belt 91, and a motor shaft timing pulley 92. Connected and driven. The intermediate transfer belt device includes an intermediate transfer belt 88 and an encoder scale (slit) 94 provided outside the image area. Further, an optical head (belt sensor) 95 for reading the signal is attached on the facing surface. A sensor based on a rotary encoder (not shown) may be attached to the belt drive shaft 89 instead of the slit and the optical head.
The third paper transfer roller 96 to be driven is also a drive source through a transmission system such as a drive shaft timing pulley (not shown), a timing belt (not shown), a motor shaft timing pulley (not shown). It is connected to and driven by a motor (not shown).
The intermediate transfer belt 88 and the photosensitive drum 81 rotate in contact with each other. Further, the intermediate transfer belt 88 and the paper transfer roller 96 rotate in contact with each other through the paper.
Further, the intermediate transfer belt and the photosensitive member are adjacent to a charging roller (not shown) and a cleaning blade (not shown).
This figure shows an indirect transfer type image forming apparatus using an intermediate transfer belt, but the so-called direct transfer system, which does not use an intermediate transfer belt, but directly transfers from a photosensitive drum to paper fed by a conveyor belt. In general, the image forming apparatus of FIG.
The photosensitive drum and its peripheral device including the transfer mechanism are collectively referred to as an image forming unit.

FIG. 16 is a diagram for explaining the hardware of the drive system.
First, a microcomputer 150 that is responsible for overall control is provided. In the microcomputer 150, a microprocessor (CPU) 151, a read only memory (ROM) 152, and a random access memory (RAM) 153 are connected via a bus 154. The output of the encoder scale (slit) 94 through the optical head (belt sensor) 95 or the output of the sensor (95 ′) from the rotary encoder 87 is sent via the state detection interfaces 155 and 155 ′ and the bus 154. Are input to the microcomputer 150. The state detection interfaces 155 and 155 ′ process encoder outputs and convert them into digital numerical values, and include a counter (not shown) for counting the number of encoder pulses. At this time, the state detection interfaces 155 and 155 ′ use the origin information of the encoders 87 and 94 to associate (correlate) with the movement positions of the photosensitive drum 81 and the intermediate transfer belt 88. It has a function.
Further, the motors 93 and 86 are connected to the microcomputer 150 via the bus 154, driving interfaces 156 and 156 ′, and drivers 157 and 157 ′. The driving interfaces 156 and 156 ′ convert the digital signal of the calculation result in the microcomputer 150 into an analog signal, and supply the analog signal to the motor driving drivers 157 and 157 ′ that are driving devices. To control. As a result, the intermediate transfer belt 88 and the photosensitive drum 81 are driven so as to follow a predetermined target position. The positions of the intermediate transfer belt 88 and the photosensitive drum 81 at this time are detected by the state detection interfaces 155 and 155 ′ from the sensor output by the rotary encoder or the output of the encoder scale (slit). It is captured.

FIG. 17 is a diagram for explaining the relationship between the drive pulley and the driven pulley when the reduction ratio is changed. The figure (a) is a diagram of the pulley when the first stage reduction of 1:16 is performed, and the figure (b) is the first stage when the reduction ratio of 1:16 is reduced to two stages of 1: 4. Pulley diagrams are shown respectively.
In the figure, reference numeral 161 denotes a motor pulley as a driving pulley, 162 denotes a driven pulley, and 163 denotes a timing belt.
The prior art described above corresponds to the case where the drive is transmitted from the motor drive shaft to the drive target shaft by only one stage of deceleration. However, since there is a limit on the minimum diameter of the drive pulley 161, if the required reduction ratio is large, the diameter of the driven pulley 162 will inevitably increase when attempting to reduce the speed by only one stage. When this is a two-stage deceleration, the winding angle of the timing belt 163 in the driven pulley 162 is configured to be equal to each other as shown in FIGS. However, in the case of two-stage deceleration, another set of combinations shown in FIG.

  The resonance frequency of the transmission system is determined by the values of the spring constant and the moment of inertia. The spring frequency is small, and the resonance frequency is low when the moment of inertia is large. The spring constant is inversely proportional to the rigidity of the timing belt and the length of the portion not in contact with the pulley (the thick black line portion in the figure). The moment of inertia is proportional to the fourth power of the radius when the material of the pulley is the same. Therefore, the first-stage timing belt transmission mechanism is clearly disadvantageous to banding because the spring constant is small and the moment of inertia is larger than the two-stage timing belt transmission mechanism, and the resonance frequency is low.

JP 2002-351280 A

  Provided is an image forming apparatus in which a resonance frequency of a drive transmission mechanism can be set high, and a high-quality image wrinkle with less banding can be obtained.

According to the first aspect of the present invention, the driving object having at least a driving object having a position sensor, a position control means, a motor for driving the driving object, and a driving means for driving the motor is included in the driving object. A transmission mechanism that decelerates and transmits torque, feedbacks a signal from the position sensor, drives the driving unit, and causes the position control unit to follow the target to be driven by the position control unit; The transmission mechanism is constituted by at least a two-stage timing belt system transmission mechanism, the open loop crossing frequency of the position control means is Fcm, the belt transmission angle is the same as that of the drive transmission system and has the same reduction ratio. When the open loop crossing frequency of the position control means constituted by the timing belt transmission mechanism is Fc1,
Fcm> Fc1
The drive target is made to follow a target position with an Fcm such that
In the invention according to claim 2, in the drive control device according to claim 1, when the transmission mechanism resonance frequency of the at least two-stage timing belt transmission mechanism is Frm,
Frm> Fcm
Frm is set such that

According to a third aspect of the present invention, in the drive control device according to the first or second aspect, when the torque ripple frequency of the motor is Ftr, the Ftr is set so as not to be equal to either Fcm or Frm. It is characterized by that.
According to a fourth aspect of the present invention, in the drive control device according to any one of the first to third aspects, when the pitch frequency of the timing belt is Ftp, the Ftp is in any of the Fcm and Frm. It is characterized by being set not to be equal.
According to a fifth aspect of the present invention, in the drive control device according to any one of the first to fourth aspects, the position control means drives the motor with a smooth start-up.
According to a sixth aspect of the present invention, in the drive control device according to any one of the first to fifth aspects, the drive target is an intermediate transfer belt or a paper transport belt.

According to a seventh aspect of the present invention, in the drive control device according to any one of the first to sixth aspects, the drive target is a photosensitive drum.
According to an eighth aspect of the present invention, in the drive control device according to the seventh aspect of the present invention, the photosensitive drum constitutes a one-drum type image forming unit that uses only one photosensitive drum.
According to a ninth aspect of the present invention, in the drive control apparatus according to the seventh aspect of the present invention, the photosensitive drum constitutes a tandem-type image forming unit that uses a plurality of the photosensitive drums.
According to a tenth aspect of the present invention, in the drive control device according to the eighth or ninth aspect, the image forming unit is a direct transfer type image forming unit.
According to an eleventh aspect of the present invention, in the drive control device according to the eighth or ninth aspect, the image forming unit is an indirect transfer type image forming unit.

The present invention
1: The target to be driven can be tracked with high accuracy by the target position, and noise is lower than that of gear drive 2; a stable position control means can be realized, so that 3 is highly reliable; vibration due to torque fluctuation can be suppressed. Speed fluctuation is small 4; disturbance vibration due to contact and separation of timing belt and timing pulley teeth can be suppressed, so speed fluctuation is small 5; Tracking error due to delay in feedback system and excitation of vibration due to overshoot are suppressed Therefore, it is possible to provide a high-quality image forming apparatus with small banding and suppressed positional deviation.

FIG. 1 is a configuration diagram of a photosensitive drum driving device to which the present invention is applied.
In the figure, reference numeral 101 is a photosensitive drum, 102 is a drum shaft, 103 is a drum shaft timing pulley, 104 is a timing belt, 105 is a relay shaft small timing pulley, 106 is a relay shaft, 107 is a relay shaft large timing pulley, and 108 is A timing belt, 109 is a motor shaft timing pulley, 110 is a motor shaft, 111 is a brushless motor, 112 is a rotary encoder, and 113 is a drive control circuit.
The point that the photosensitive drum 101 is rotationally driven from the brushless motor 111 is basically the same as the configuration shown in the prior art. However, the brushless motor 111 rotates the drum via a two-stage timing belt transmission mechanism. The ratio of the timing pulley is 1: 4 for both the first stage and the second stage.
In the position sensor, an incremental encoder 112 is attached to the drum shaft. The drive control circuit 113 feeds a current to the brushless motor 111 based on a result calculated by the position control means by feeding back a signal from the position sensor.

FIG. 2 is a Bode diagram of transmission characteristics of a certain timing belt transmission mechanism. FIG. 4A is a diagram of a two-stage transmission system, and FIG. 4B is a diagram of a one-stage transmission system.
One method for indicating the performance of a drive transmission system is a frequency transfer function. This shows the change of the output signal with respect to the input signal of the sine wave by the change of the gain and the phase, and a graph showing these relations is called a Bode diagram. When the gain increases locally, the peak position is called the resonance frequency. Depending on the combination of conditions, the system may be stable or unstable.
This figure shows the frequency characteristics from the torque generated by the motor to the drive shaft angle to be controlled through the drive transmission system.
The resonance frequency (referred to as Fr1) in the one-stage transmission system in FIG. 2B is approximately 1440 Hz, whereas the resonance frequency (referred to as Frm) in the two-stage transmission system in FIG. The resonance frequency of the two-stage transmission system is nearly twice that of the one-stage transmission system.
Generally, the resonance frequency Frm of the two-stage timing belt transmission mechanism determined as described above is higher than the resonance frequency Fr1 of the first-stage timing belt transmission mechanism.

FIG. 3 is a block diagram focusing on the drive control system.
In the figure, reference numeral 131 denotes a control object such as a photosensitive drum, 132 a reference signal generator, 133 a target value transfer function, 134 a correction transfer function, and 135 a position control means.
Since this transmission system gives an initial speed of 0 and an initial acceleration of 0, smooth start-up is obtained, the target position trajectory at the start of the drive target is smoothed, and the motor current required at that time is given in feedforward . The reference signal from the reference signal generator 132 becomes the following ramp function when the target angular velocity ωref and time t are given.
refo = ωref × t
The target position becomes a smooth target position trajectory by the target value transfer function 133. The feedforward current is given by a correction transfer function 34 that multiplies the target value transfer function by the inverse of the transfer function to be controlled. The flow shown by the solid line in FIG.

FIG. 4 is a Bode diagram of the control drive system shown in FIG. FIG. 4A is a diagram of a two-stage transmission system, and FIG. 4B is a diagram of a one-stage transmission system.
In the figure, the crossing point with 0 dB is the open loop crossing frequency. In FIG. 4A, the open loop crossing frequency of the position control means of the two-stage timing belt transmission mechanism is Fcm, and in FIG. If the frequency is Fc1,
Fcm = Fc1≈250 Hz
The phase is delayed by 180 ° in the vicinity of the resonance frequency Frm. At this time, since the gain is smaller than 0 dB, the system is in a stable state, but the phase is delayed by 180 ° in the vicinity of the resonance frequency Fr1. Since the gain is greater than 0 dB, the one-stage timing belt transmission mechanism drive system becomes unstable.

FIG. 5 is a diagram showing the response of the two-stage timing belt system transmission mechanism drive system.
FIG. 6 is a diagram showing the response of the first stage timing belt transmission mechanism drive system. FIG. 4A shows the state from the start of driving to 2 seconds later, and FIG. 4B shows the state from 1.9 seconds to 2 seconds later.
The vertical axis in both figures indicates the tracking error from the target position to the detected position.
In FIG. 5, the positional deviation is within a few μm after 1.1 seconds.
In FIG. 6, the tracking error increases with time and vibrates. In order to drive stably, it is necessary to satisfy Fcm> Fc1. In other words, the position control means must be adjusted (gain reduced) to reduce Fc1 to a smaller value. In other words, Fcm can be set to a frequency higher than Fc1 in order to stably drive both the first-stage timing belt system transmission mechanism drive system and the second-stage timing belt system transmission mechanism drive system.

Assuming that a three-phase 15-pole brushless motor is used, the torque ripple of one rotation of the motor is 30 times. When the photosensitive drum 1 is rotated at 30 rpm, the brushless motor 11 has a total pulley ratio of 16, and thus becomes 480 rpm. Therefore, the torque ripple frequency Ftr is
Ftr = 480 × 30/60 = 240 Hz
become.
From FIG. 4, the open loop crossing frequency Fcm of the position control means of the two-stage timing belt transmission mechanism is
Fcm = 240 [rad / s] = 38.2 [Hz]
The resonance frequency Frm is
Frm = 2520 [rad / s] = 401 [Hz]
Thus, since Ftr can be brought to a frequency region away from Fcm and Frm, stable control can be realized.

The drum of FIG. 1 is rotated at 30 rpm. The number of teeth of the motor shaft timing pulley 9 and the relay shaft small timing pulley 5 is 60, and the number of teeth of the relay shaft large timing pulley 7 and the drum shaft timing pulley 3 is 240.
The pitch frequency Ftp1 of the timing belt 8 spanned between the motor shaft tamming pulley 9 and the relay shaft large timing pulley 7 is based on the motor rotation speed 480 rpm and the number of teeth 60 of the motor shaft tamming pulley 9.
Ftp1 = 480/60 × 60 = 480 Hz
The pitch frequency Ftp2 of the timing belt 4 spanned between the relay shaft small timing pulley 5 and the drum shaft timing pulley 3 is based on the drum rotation speed of 30 rpm and the number of teeth 240 of the drum shaft timing pulley 3.
Ftp2 = 30/60 × 240 = 120 Hz
It becomes. Since both Fcm = 38.2 [Hz] and Frm = 401 [Hz] in FIG. 4 can be brought to a frequency region distant from each other, stable control can be realized. Ftp1 and Ftp2 are separated from the aforementioned torque ripple frequency Ftr = 240 Hz.

FIG. 7 is a diagram showing an embodiment of a drum drive control device in which a timing belt transmission mechanism and a gear transmission mechanism are combined.
In the figure, reference numeral 114 denotes a large gear, and 115 denotes a small gear.
In the position sensor, an incremental encoder 112 is attached to the drum drive shaft 102. The drive control circuit 113 feeds back the position sensor signal and the result calculated by the position control means to the motor 111 as a current. The motor 111 rotates the drum via a gear transmission mechanism and a timing belt transmission mechanism. The gear ratio is 1: 4, and the timing pulley ratio is 1: 4. Since the gear transmission mechanism has high rigidity, the resonance frequency can be made higher than that of the timing belt transmission mechanism. Since the disturbance due to the meshing of the gear is the timing belt transmission mechanism at the second stage, the disturbance is not easily transmitted to the drum 101, so that the speed fluctuation can be suppressed as compared with a simple gear transmission mechanism.

FIG. 8 is a diagram showing an embodiment of an intermediate transfer belt drive control device using a two-stage timing belt system transmission mechanism drive system.
In the same figure, 116 is an intermediate transfer belt, 117 is a driving roller, 118 is a driven pulley, 119 is a timing belt, 120 is a relay shaft small timing pulley, 121 is a relay shaft, 122 is a relay shaft large timing pulley, and 123 is a timing. A belt, 124 is a motor shaft timing pulley, 125 is a motor shaft, 126 is a brushless motor, 127 is an encoder slit, 128 is a pickup, and 129 is a drive control circuit.
The position sensor has an encoder slit 127 formed on the front surface or the back surface of the intermediate transfer belt 116. A signal is read by the pickup 128. The drive control circuit 129 feeds back the position sensor signal and the result calculated by the position control means to the motor 126 as a current. The motor 126 rotates the driving roller 117 via the two-stage timing belt transmission mechanism to move the intermediate transfer belt 116. The ratio of the timing pulley is 1: 4 for both the first stage and the second stage.

The position control method of the belt conveyance device of the present embodiment is executed by an arithmetic processing function in the microcomputer. It is obvious that a DSP (digital signal processor) having a high numerical processing capability may be used instead of the microcomputer.
Next, an image forming apparatus to which the present invention is applied will be described.

FIG. 9 is a schematic configuration diagram of a one-drum type image forming unit.
In the figure, reference numeral 200 denotes a photosensitive drum, 400 denotes a developing unit, 500 denotes an intermediate transfer unit, 600 denotes a secondary transfer unit, and 700 denotes a fixing unit 700. Other symbols will be cited sequentially in the following description.
An image forming unit that can be used in a color copying machine, a color printer, and the like includes a photosensitive drum 200 as an image carrier, a charging charger 201 as a charging unit, a photosensitive member cleaning device 210 including a cleaning blade and a fur brush, and an exposure unit. A writing optical unit (not shown), a revolver developing unit 400 as developing means, an intermediate transfer unit 500, a secondary transfer unit 600, a fixing unit 700 using a fixing roller pair 701, and the like are included.
In the case of a color copier, in addition to the image forming unit shown in the figure, a color image reading unit (hereinafter referred to as a “color scanner”), a paper feeding unit, and a control unit that drives and controls these are included. .
The color scanner reads color image information of a document for each color separation light of, for example, red, green, and blue (hereinafter referred to as “R”, “G”, and “B”) and converts them into electrical image signals. To do. Then, based on the intensity levels of the R, G, and B color separation image signals obtained by this color scanner, color conversion processing is performed by an image processing unit (not shown), and black, cyan, magenta, yellow (hereinafter, respectively) Image data “Bk”, “C”, “M”, and “Y”) is obtained.

The photosensitive drum 200 rotates in a counterclockwise direction as indicated by an arrow A in the drawing, and a charging charger 201, a photosensitive member cleaning device 210, a selected developing device of the revolver developing unit 400, and an intermediate transfer unit are disposed around the photosensitive drum 200. An intermediate transfer belt 501 as an intermediate transfer member 500 is disposed. Further, the writing optical unit converts the color image data from the color scanner into an optical signal, and applies the laser beam L corresponding to the image of the document to the surface of the photosensitive drum 200 uniformly charged by the charging charger 201. Irradiation and optical writing are performed to form an electrostatic latent image on the surface of the photosensitive drum 200. This writing optical unit can be constituted by, for example, a semiconductor laser as a light source, a laser emission drive control unit, a polygon mirror and its rotation motor, an f / θ lens, a reflection mirror, and the like.
The revolver developing unit 400 includes a Bk developing unit 401 that uses Bk toner, a C developing unit 402 that uses C toner, an M developing unit 403 that uses M toner, a Y developing unit 404 that uses Y toner, and a half of the entire unit. A developing revolver driving unit (not shown) that rotates clockwise is configured.
Each of the developing devices 401 to 404 installed in the revolver developing unit 400 is a developing sleeve as a developer carrying member that rotates by bringing the ears of the developer into contact with the surface of the photosensitive drum 200 in order to develop the electrostatic latent image. And a developer paddle that rotates to draw up and stir the developer, and a developing sleeve drive section (not shown) that rotates the developing sleeve clockwise as indicated by an arrow.

In this embodiment, the toner in each of the developing machines 401 to 404 is negatively charged by stirring with the ferrite carrier, and each developing sleeve is negatively charged with a negative DC voltage by a developing bias power source as a developing bias applying means (not shown). A developing bias voltage in which an AC voltage Vac (AC component) is superimposed on Vdc (DC component) is applied, and each developing sleeve is biased to a predetermined voltage with respect to the metal substrate layer of the photosensitive drum 200. In the standby state of the color copying machine main body, the revolver developing unit 400 is stopped at the home position where the Bk developing machine 401 is located at the developing position. When the copy start key is pressed, reading of the original image data is started. Based on the color image data, light writing by the laser beam L, that is, formation of an electrostatic latent image is started (hereinafter, an electrostatic latent image by Bk image data is referred to as “Bk electrostatic latent image”. The same).
In order to enable development from the leading edge of the Bk electrostatic latent image, before the leading edge of the electrostatic latent image reaches the Bk development position, the rotation of the Bk developing sleeve is started and the Bk electrostatic latent image is cleaned with Bk toner. develop. Thereafter, the developing operation of the Bk electrostatic latent image is continued. When the rear end portion of the Bk electrostatic latent image passes the Bk developing position, the revolver is promptly moved until the next color developing device comes to the developing position. The developing unit 400 rotates. This is completed at least before the leading edge of the electrostatic latent image based on the next image data reaches the developing position.

The intermediate transfer unit 500 includes an intermediate transfer belt 501 that is an intermediate transfer member stretched around a plurality of rollers to be described later. Around the intermediate transfer belt 501 are a secondary transfer belt 601 that is a transfer material carrier of the secondary transfer unit 600, a secondary transfer bias roller 605 that is a secondary transfer charge applying unit, and an intermediate transfer member cleaning unit. A belt cleaning blade 504, a lubricant application brush 505 that is a lubricant application means, and the like are arranged to face each other.
The intermediate transfer belt 501 is stretched around a primary transfer bias roller 507, a belt driving roller 508, a belt tension roller 509, a secondary transfer counter roller 510, a cleaning counter roller 511, and a ground roller 512 serving as a primary transfer charge applying unit. It is built. Each roller is formed of a conductive material, and each roller other than the primary transfer bias roller 507 is grounded.
The primary transfer bias roller 507 is applied with a transfer bias controlled to a predetermined current or voltage according to the number of superimposed toner images by a primary transfer power source 801 controlled at a constant current or voltage. ing. The intermediate transfer belt 501 is driven in the arrow direction by a belt driving roller 508 that is driven to rotate in the arrow B direction by a drive motor (not shown).
The intermediate transfer belt 501 is formed of a semiconductor or an insulator and has a single layer or a multilayer structure.

In a transfer portion (hereinafter referred to as “primary transfer portion”) that transfers the toner image on the photosensitive drum 200 to the intermediate transfer belt 501, the intermediate transfer belt 501 is moved to the photosensitive drum by the primary transfer bias roller 507 and the earth roller 512. A nip portion having a predetermined width is formed between the photosensitive drum 200 and the intermediate transfer belt 501 by being stretched so as to be pressed against the side 200.
The lubricant application brush 505 polishes zinc stearate 506 as a lubricant formed in a plate shape and applies the polished fine particles to the intermediate transfer belt 501. The lubricant application brush 505 is also configured to be adjacent to the intermediate transfer belt 501 and is controlled to contact the intermediate transfer belt 501 at a predetermined timing.

The secondary transfer unit 600 includes a secondary transfer belt 601 stretched between three support rollers 602, 603, and 604, and the stretched portion between the support rollers 602 and 603 of the secondary transfer belt 601 is a secondary. It can be pressed against the transfer facing roller 510. One of the three support rollers 602, 603, and 604 is a drive roller that is rotationally driven by a drive unit (not shown), and the secondary transfer belt 601 is driven in the direction indicated by an arrow C in the drawing. .
The secondary transfer bias roller 605 is a secondary transfer unit, and is disposed so as to sandwich the intermediate transfer belt 501 and the secondary transfer belt 601 between the secondary transfer counter roller 510 and is subjected to constant current control. A transfer bias having a predetermined current is applied by the next transfer power source 802. Further, the support roller 602 and the secondary transfer bias are set so that the secondary transfer belt 601 and the secondary transfer bias roller 605 can take a position where they are pressed against and separate from the secondary transfer counter roller 510. A separation mechanism (not shown) for driving the roller 605 in the direction of the arrow is provided. The secondary transfer belt 601 and the support roller 602 at the separated positions are indicated by a two-dot chain line in FIG.

Reference numeral 650 denotes a registration roller pair, which is a transfer sheet that is a transfer material at a predetermined timing between the intermediate transfer belt 501 and the secondary transfer belt 601 sandwiched between the secondary transfer bias roller 605 and the secondary transfer counter roller 510. P is sent.
The portions of the secondary transfer belt 601 that are stretched by the support roller 603 on the fixing roller pair 701 side are provided with a transfer sheet neutralization charger 606 that is a transfer material neutralization unit and a belt neutralization charger 607 that is a transfer material carrier neutralization unit. Are facing each other. Further, a cleaning blade 608 serving as a transfer material carrier cleaning means is in contact with a portion of the secondary transfer belt 601 that is stretched around a lower support roller 604 in the drawing.
The transfer paper neutralization charger 606 neutralizes the charge held on the transfer paper so that the transfer paper can be satisfactorily separated from the secondary transfer belt 601 with the strength of the transfer paper itself. The belt neutralization charger 607 neutralizes the charge remaining on the secondary transfer belt 601. Further, the cleaning blade 608 is for removing the adhering matter adhering to the surface of the secondary transfer belt 601 for cleaning.

  In the color copying machine configured as described above, when the image forming cycle is started, the photosensitive drum 200 is rotated in the counterclockwise direction indicated by the arrow A by a driving motor (not shown), and the intermediate transfer belt 501 is driven by the belt driving roller 508. Is rotated clockwise as indicated by an arrow. As the intermediate transfer belt 501 rotates, Bk toner image formation, C toner image formation, M toner image formation, and Y toner image formation are performed by the transfer bias by the voltage applied to the primary transfer bias roller 507. Finally, a toner image is formed on the intermediate transfer belt 501 in the order of Bk, C, M, and Y.

For example, Bk toner image formation is performed as follows. The charging charger 201 uniformly charges the surface of the photosensitive drum 200 to a predetermined potential with a negative charge by corona discharge. Then, raster exposure with laser light is performed based on the Bk color image signal by a writing optical unit (not shown). When this raster image is exposed, the charge proportional to the exposure light amount disappears in the exposed portion of the surface of the photosensitive drum 200 that is initially uniformly charged, and a bk electrostatic latent image is formed.
When the negatively charged Bk toner on the Bk developing roller of the Bk developing machine 401 comes into contact with this Bk electrostatic latent image, the toner does not adhere to the remaining portion of the photosensitive drum 200, and the charge is charged. Toner is adsorbed on the portion without exposure, that is, the exposed portion, and a Bk toner image similar to the electrostatic latent image is formed. The Bk toner image formed on the photosensitive drum 200 is transferred to the surface of the intermediate transfer belt 501 that is driven at a constant speed in contact with the photosensitive drum 200. Hereinafter, the transfer of the toner image from the photosensitive drum 200 to the intermediate transfer belt 501 is referred to as “belt transfer”.
Some untransferred residual toner remaining on the surface of the photosensitive drum 200 after the belt transfer is cleaned by the photosensitive member cleaning device 210 in preparation for the reuse of the photosensitive drum 200.

On the photosensitive drum 200 side, the process proceeds to the C image forming process after the Bk image forming process, and reading of the C image data by the color scanner starts at a predetermined timing. A C electrostatic latent image is formed on the surface.
Then, after the rear end portion of the previous Bk electrostatic latent image passes and before the front end portion of the C electrostatic latent image arrives, the revolver developing unit 400 is rotated, and the C developing device 402 is developed. The C electrostatic latent image is developed with C toner.
Thereafter, the development of the C electrostatic latent image area is continued. When the rear end of the C electrostatic latent image passes, the revolver developing unit is rotated in the same manner as in the case of the Bk developing machine 401, and the next The M developing machine 403 is moved to the developing position. This is also completed before the leading edge of the next M electrostatic latent image reaches the developing position.
Note that the M and Y image forming steps are the same as the Bk and C steps described above because the operations of reading color image data, forming an electrostatic latent image, and developing are the same as those described above.
On the intermediate transfer belt 501, Bk, C, M, and Y toner images sequentially formed on the photosensitive drum 100 are sequentially aligned and transferred on the same surface. As a result, a toner image in which a maximum of four colors are superimposed is formed on the intermediate transfer belt 501.
Depending on the configuration of the color scanner, there is a system in which three colors are simultaneously read by one reading scan, image data is stored in a memory, and transferred to an image forming unit as necessary. The present invention can be similarly applied. .

At the time when the image forming operation is started, the transfer paper P is fed from a paper feed unit such as a transfer paper cassette or a manual feed tray (not shown) and is waiting at the nip of the registration roller pair 650. When the leading edge of the toner image on the intermediate transfer belt 501 approaches the secondary transfer portion where the nip is formed by the secondary transfer counter roller 510 and the secondary transfer bias roller, the leading edge of the transfer paper P is just the leading edge of the toner image. The registration roller pair 650 is driven so as to match the above, and registration of the transfer paper P and the toner image is performed.
Then, the transfer paper P is superimposed on the toner image on the intermediate transfer belt 501 and passes through the secondary transfer portion. At this time, the four-color superimposed toner image on the intermediate transfer belt 501 is collectively transferred onto the transfer paper by a transfer bias by a voltage applied to the secondary transfer bias roller 605 by the secondary transfer power source 802.
The transfer paper P is neutralized and separated from the secondary transfer belt 601 when it passes through a portion facing the transfer paper neutralization charger 606 disposed downstream of the secondary transfer portion in the moving direction of the secondary transfer belt 601. To the fixing roller pair 701.
The toner image is melted and fixed at the nip portion of the fixing roller pair 701, sent out of the apparatus main body by a pair of discharge rollers (not shown), and stacked on a copy tray (not shown) so as to obtain a full color copy.

On the other hand, the surface of the photosensitive drum 200 after the belt transfer is cleaned by the photosensitive member cleaning device 210 and is uniformly discharged by the discharging lamp 202.
Further, the toner remaining on the surface of the intermediate transfer belt 501 after the toner image is transferred to the transfer paper P is cleaned by a belt cleaning blade 504 pressed against the intermediate transfer belt 501 by a not-shown separation / contact mechanism.
Here, at the time of repeat copy, the operation of the color scanner and the image formation on the photosensitive drum 200 are performed at a predetermined timing following the first color (Y) image formation process of the first sheet and the first color of the second sheet. The process proceeds to the image forming process (Bk). Further, the intermediate transfer belt 501 has a second Bk toner in the area cleaned by the belt cleaning blade 504 on the surface following the batch transfer process of the first four-color superimposed toner image to the transfer paper. The image is transferred to the belt. After that, the operation is the same as the first sheet.

The above is a copy mode for obtaining a four-color full-color copy. In the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times.
In the single color copy mode, only the predetermined color developing machine of the revolver developing unit 400 is in the developing operation state until the predetermined number of sheets is completed, and the belt cleaning blade 504 is pressed against the intermediate transfer belt 501. The copy operation is performed at the same position.
The figure shows an indirect transfer type image forming unit, but there is also a so-called direct transfer method in which the image is directly transferred onto a sheet a plurality of times.

10 and 11 are schematic configuration diagrams of an image forming unit using a plurality of photosensitive drums.
FIG. 10 shows a direct transfer method, and FIG. 11 shows an indirect transfer method.
In both figures, reference numeral 141 denotes a photoconductor, 142 denotes a transfer device, 143 denotes a sheet conveying belt, 144 denotes an intermediate transfer belt, 145 denotes a secondary transfer belt, 146 denotes a paper feeding device, 147 denotes a fixing device, and 148 denotes a photoconductor cleaning device. Reference numeral 149 denotes a belt cleaning device.
FIG. 9 shows the one-drum type image forming unit. However, when image forming speed is required, a so-called tandem type image forming apparatus using a plurality of photosensitive drums is used.
As shown in FIG. 10, the tandem type electrophotographic apparatus includes a direct transfer system in which an image on each photoconductor 141 is directly transferred onto a sheet s conveyed by a sheet conveying belt 143 by a transfer device 142. As shown in FIG. 11, the image on each photoconductor 141 is sequentially transferred to the intermediate transfer member 144 once by the primary transfer device 142, and then the image on the intermediate transfer member 144 is transferred to the sheet s by the secondary transfer device 145. There are indirect transfer systems that batch transfer. The secondary transfer device 145 is a transfer conveyance belt, but there is also a roller-shaped method.

Comparing the direct transfer type and the indirect transfer type, the former arranges the paper feeding device 146 on the upstream side of the tandem image forming apparatus T on which the photoconductors 141 are arranged, and the fixing device 147 on the downstream side. There is a drawback in that the size increases in the sheet conveying direction.
On the other hand, the latter can set the secondary transfer position 145 relatively freely.
The sheet feeding device 146 and the fixing device 147 can be arranged so as to overlap with the tandem image forming apparatus T, and there is an advantage that downsizing is possible.
In the former, in order not to increase the size in the sheet conveying direction, the fixing device 147 is disposed close to the tandem type image forming apparatus T. Therefore, the fixing device 147 cannot be disposed with a sufficient margin that the sheet s can bend, and an impact (particularly with a thick sheet) when the leading edge of the sheet s enters the fixing device 7 or fixing. There is a problem that the fixing device 147 tends to affect the image formation on the upstream side due to the speed difference between the sheet conveyance speed when passing through the apparatus 147 and the sheet conveyance speed by the transfer conveyance belt.
On the other hand, in the latter case, the fixing device 147 can be disposed with a sufficient margin that the sheet s can be bent, so that the fixing device 147 hardly affects the image formation.

In view of the above, in recent years, indirect transfer type among tandem type electrophotographic apparatuses has been attracting attention.
In this type of color electrophotographic apparatus, as shown in FIG. 11, the transfer residual toner remaining on the photoconductor 141 after the primary transfer is removed by the photoconductor cleaning device 148 to clean the surface of the photoconductor 141. In preparation for another image formation. Further, the transfer residual toner remaining on the intermediate transfer member 144 after the secondary transfer is removed by the intermediate transfer member cleaning device 149 to clean the surface of the intermediate transfer member 144 to prepare for the image formation again.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 12 is a view showing a tandem indirect transfer type electrophotographic apparatus according to an embodiment of the present invention.
In the figure, reference numeral 1100 denotes a copying apparatus main body, 1200 denotes a paper feed table on which the copying apparatus is mounted, 1300 denotes a scanner mounted on the copying apparatus main body 1100, and 1400 denotes an automatic document feeder (ADF) mounted thereon.
FIG. 13 is a diagram illustrating a configuration example of the intermediate transfer member. In the figure, reference numeral 10 denotes an intermediate transfer member, 11 denotes a base layer, 12 denotes an elastic layer, and 13 denotes a coat layer.
The copying machine main body 1100 is provided with an endless belt-shaped intermediate transfer member 10 in the center. As shown in FIG. 13, in the intermediate transfer member 10, a base layer 11 is made of a base layer made of a material that hardly stretches, such as a fluorine resin having a small elongation or a rubber material having a large elongation, and an elastic layer thereon. 12 is provided. The elastic layer 12 is made of, for example, fluorine-based rubber or acrylonitrile-butadiene copolymer rubber.
The surface of the elastic layer 12 is coated with, for example, a coating layer 13 having good smoothness by coating a fluorine resin.

Then, as shown in FIG. 12, in the illustrated example, it is wound around three support rollers 14, 15, and 16 so that it can be rotated and conveyed clockwise in the figure.
In this illustrated example, an intermediate transfer body cleaning device 17 for removing residual toner remaining on the intermediate transfer body 10 after image transfer is provided on the left of the second support roller 15 among the three.
Further, among the three images, four images of yellow, cyan, magenta, and black are arranged on the intermediate transfer member 10 stretched between the first support roller 14 and the second support roller 15 along the conveyance direction. The tandem image forming apparatus 20 is configured by arranging the forming units 18 side by side.
An exposure device 21 is further provided on the tandem image forming apparatus 20 as shown in FIG.

On the other hand, a secondary transfer device 22 is provided on the side opposite to the tandem image forming apparatus 20 with the intermediate transfer body 10 interposed therebetween. In the illustrated example, the secondary transfer device 22 is configured by spanning a secondary transfer belt 24, which is an endless belt, between two rollers 23, and is pressed against the third support roller 16 via the intermediate transfer body 10. The image on the intermediate transfer body 10 is transferred to a sheet.
A fixing device 25 for fixing the transfer image on the sheet is provided beside the secondary transfer device 22. The fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 that is an endless belt.
The secondary transfer device 22 described above is also provided with a sheet transport function for transporting the sheet after image transfer to the fixing device 25. Of course, a transfer roller or a non-contact charger may be arranged as the secondary transfer device 22, and in such a case, it is difficult to provide this sheet conveying function together.
In the illustrated example, under such a secondary transfer device 22 and a fixing device 25, a sheet reversing device 28 for reversing the sheet to record images on both sides of the sheet in parallel with the tandem image forming device 20 described above. Is provided.

Now, when making a copy using this color electrophotographic apparatus, a document is set on the document table 30 of the automatic document feeder 1400. Alternatively, the automatic document feeder 1400 is opened, a document is set on the contact glass 32 of the scanner 1300, and the automatic document feeder 1400 is closed and pressed by it.
When a start switch (not shown) is pressed, when the document is set on the automatic document feeder 1400, the document is transported and moved onto the contact glass 32, and then the document is set on the other contact glass 32. At that time, the scanner 1300 is immediately driven to travel the first traveling body 33 and the second traveling body 34. Then, the first traveling body 33 emits light from the light source and further reflects the reflected light from the document surface toward the second traveling body 34 and is reflected by the mirror of the second traveling body 34 and passes through the imaging lens 35. The document is placed in the reading sensor 36 and the original content is read.
When a start switch (not shown) is pressed, one of the support rollers 14, 15 and 16 is rotationally driven by a drive motor (not shown), the other two support rollers are driven to rotate, and the intermediate transfer body 10 is rotated and conveyed. To do. At the same time, the individual image forming means 18 rotates the photoconductor 40 to form black, yellow, magenta, and cyan monochrome images on each photoconductor 40. Then, along with the conveyance of the intermediate transfer member 10, the single color images are sequentially transferred to form a composite color image on the intermediate transfer member 10.

On the other hand, when a start switch (not shown) is pressed, one of the paper feed rollers 42 of the paper feed table 1200 is selectively rotated, the sheet is fed out from one of the paper feed cassettes 44 provided in the paper bank 43 in multiple stages, and the separation roller 45 Then, the sheets are separated one by one and put into the paper feed path 46, transported by the transport roller 47, guided to the paper feed path 48 in the copying machine main body 1100, and abutted against the registration roller 49 and stopped.
Alternatively, the sheet feed roller 50 is rotated to feed out the sheets on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual feed path 53, and abutted against the registration roller 49 and stopped.
Then, the registration roller 49 is rotated in synchronization with the composite color image on the intermediate transfer member 10, the sheet is fed between the intermediate transfer member 10 and the secondary transfer device 22, and transferred by the secondary transfer device 22. A color image is recorded on the sheet.
The sheet after the image transfer is conveyed by the secondary transfer device 22 and sent to the fixing device 25, and heat and pressure are applied to the fixing device 25 to fix the transferred image. The paper is discharged at 56 and stacked on the paper discharge tray 57. Alternatively, it is switched by the switching claw 55 and put into the sheet reversing device 28, where it is reversed and guided again to the transfer position, and the image is recorded also on the back surface, and then discharged onto the discharge tray 57 by the discharge roller 56.

On the other hand, the intermediate transfer body 10 after the image transfer is removed by the intermediate transfer body cleaning device 17 to remove residual toner remaining on the intermediate transfer body 10 after the image transfer, so that the tandem image forming apparatus 20 can prepare for another image formation.
Here, the registration roller 49 is generally used while being grounded, but it is also possible to apply a bias for removing paper dust from the sheet.
FIG. 14 is a partial view for explaining details of the image forming means.
In the figure, reference numeral 60 denotes a charging device, 61 denotes a developing device, 62 denotes a primary transfer device, 63 denotes a photosensitive member cleaning device, and 64 denotes a charge eliminating device.
In the tandem image forming apparatus 20 described above, the individual image forming means 18 includes, for example, a charging device 60, a developing device 61, and a primary device around a drum-shaped photoconductor 40 as shown in FIG. The image forming apparatus includes a transfer device 62, a photoconductor cleaning device 63, a charge removal device 64, and the like.

  In the one-drum type image forming unit shown in FIG. 9, the direct type tandem type image forming unit shown in FIG. 10, and the indirect type tandem type image forming unit shown in FIG. By using the two-stage reduction mechanism of the present invention for the drive transmission mechanism such as the photosensitive drum, the primary or secondary transfer belt, an image forming apparatus with less banding and high image quality can be obtained.

It is a block diagram of a photosensitive drum driving device to which the present invention is applied. It is a Bode diagram of transmission characteristics of a certain timing belt system transmission mechanism. It is a block diagram which paid its attention to the drive control system. FIG. 4 is a Bode diagram of the control drive system shown in FIG. 3. It is a figure which shows the response of a 2 step | paragraph timing belt type transmission mechanism drive system. It is a figure which shows the response of a 1 step | paragraph timing belt type transmission mechanism drive system. It is a figure which shows the Example of the drum drive control apparatus which combined the timing belt type | system | group transmission mechanism and the gear transmission mechanism. It is a figure which shows the Example of the intermediate transfer belt drive control apparatus by a 2 step | paragraph timing belt type transmission mechanism drive system. FIG. 2 is a schematic configuration diagram of a one-drum type image forming unit. It is a schematic block diagram of an image forming unit using a plurality of photosensitive drums. It is a schematic block diagram of an image forming unit using a plurality of photosensitive drums. 1 is a diagram showing an electrophotographic apparatus of a tandem type indirect transfer system according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a configuration example of an intermediate transfer member. It is a partial view for explaining details of an image forming unit. 1 is a configuration diagram of an image forming apparatus in which a transmission system is a one-stage deceleration system. It is a figure for demonstrating the hardware of a drive system. It is a figure for demonstrating the relationship between a drive pulley and a driven pulley at the time of changing a reduction ratio.

Explanation of symbols

101 Photosensitive drum 103 Drum shaft timing pulley 104 Timing belt 105 Relay shaft small timing pulley 107 Relay shaft large timing pulley 108 Timing belt 109 Motor shaft timing pulley 111 Brushless motor 113 Drive control circuit 116 Intermediate transfer belt

Claims (11)

A transmission mechanism for decelerating and transmitting the torque of the motor to the drive target having at least a drive target having a position sensor, a position control means, a motor for driving the drive target, and a drive means for driving the motor. In the drive control device that feeds back a signal from the position sensor, drives the drive means, and causes the drive target to follow the target position by the position control means, the transmission mechanism has at least two timings. It is composed of a belt system transmission mechanism, and is composed of a one-stage timing belt system transmission mechanism in which the open loop crossing frequency of the position control means is Fcm, the belt winding angle is equal to that of the drive transmission system, and has the same reduction ratio. When the open loop crossing frequency of the position control means is Fc1,
Fcm> Fc1
A drive control device that causes the drive target to follow a target position with an Fcm such that In the drive control device according to claim 1, when the transmission mechanism resonance frequency of the at least two-stage timing belt transmission mechanism is Frm,
Frm> Fcm
A drive control device characterized by setting Frm such that   3. The drive control device according to claim 1, wherein when the torque ripple frequency of the motor is Ftr, the Ftr is set not equal to either Fcm or Frm. .   4. The drive control device according to claim 1, wherein when the pitch frequency of the timing belt is Ftp, the Ftp is set so as not to be equal to either Fcm or Frm. 5. A drive control device.   5. The drive control apparatus according to claim 1, wherein the position control unit drives the motor with a smooth start-up. 6.   6. The drive control apparatus according to claim 1, wherein the drive target is an intermediate transfer belt or a paper transport belt.   7. The drive control apparatus according to claim 1, wherein the drive target is a photosensitive drum.   8. The drive control apparatus according to claim 7, wherein the photosensitive drum constitutes a one-drum type image forming unit in which only one photosensitive drum is used.   8. The drive control apparatus according to claim 7, wherein the photosensitive drum constitutes a tandem type image forming unit using a plurality of photosensitive drums.   10. The drive control device according to claim 8, wherein the image forming unit is a direct transfer type image forming unit.   10. The drive control apparatus according to claim 8, wherein the image forming unit is an indirect transfer image forming unit.

Images