JP2014178570A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which prevents image defects, such as color misregistration, without reducing productivity.SOLUTION: An image forming apparatus includes: correction means which corrects assist torque derived by assist torque deriving means; and control means which controls a BLDC motor for driving a photoreceptor drum 100 and a BLDC motor for driving an ITB 108. The control means applies the assist torque corrected by the correction means to the photoreceptor drum 100, to control the photoreceptor drum 100 to be driven by the ITB 108. The assist torque deriving means derives the assist torque within a predetermined period immediately after a main power source is turned on. The correction means corrects the assist torque before the start of printing operation.

Description

  The present invention relates to an image forming apparatus including a photosensitive drum and an intermediate transfer belt.

  In an electrophotographic image forming apparatus used as a copying machine or a multifunction machine, the surface speed of a photosensitive drum and an intermediate transfer belt (hereinafter referred to as “ITB”) that carry a toner image is constant. There is a need to drive. As the first reason, when the laser exposure for forming an electrostatic latent image on the photosensitive drum is time-synchronized exposure, when the surface speed of the photosensitive drum fluctuates, the laser irradiation position is changed from the originally irradiated position. It is possible to shift. Also, as a second reason, in the primary transfer process in which the toner image formed on the photosensitive drum is transferred to the ITB, if there is an alternating speed difference between the surface speed of the photosensitive drum and the ITB, the toner transferred onto the ITB For example, the position of the image fluctuates from the position to be originally transferred. That is, if the surface speeds of the photosensitive drum and ITB are not constant, the image finally formed on the recording paper is called banding, which is color misregistration (position misalignment between colors) or periodic position misalignment. There is a problem that an image defect occurs.

  For this reason, the driving of the photosensitive drum and ITB ensures high-precision constant speed by performing speed feedback control of a motor as a driving source using various speed detection sensors. As a motor, a brushless DC motor (hereinafter referred to as “BLDC motor”) is frequently used because it is inexpensive, quiet, and highly efficient. Recently, as a speed feedback control using a BLDC motor, a method in which a rotary encoder is arranged on the drum shaft and the motor is controlled so that the rotation speed of the drum shaft is constant is widely used.

  However, since the speed feedback control detects the rotational speed of the drum shaft, it does not detect the surface speed of the photosensitive drum, so the drum shaft is decentered, the drum diameter is inaccurate, etc. There is a problem that the surface speed does not become constant. The same problem occurs in the ITB, and the same problem occurs due to the eccentricity of the ITB driving roller shaft that drives the ITB, poor accuracy of the roller diameter, uneven thickness of the ITB, and the like.

  On the other hand, the cause of image defects is the mutual interference caused by friction between the photosensitive drum and the transfer surface of the ITB. That is, there is a problem that the influence of speed fluctuation occurring in one of the photosensitive drum and the ITB is transmitted to the other. In addition, when the toner image carried on the ITB is secondarily transferred onto the recording paper, if the recording paper is a thick paper, a sudden load fluctuation occurs on the ITB, resulting in a high-speed speed fluctuation. However, this speed fluctuation causes a positional shift in the primary transfer. As described above, there are various causes of image defects, and it is very difficult to solve all of them.

  Therefore, as described in Patent Document 1, a technique has been developed in which an image cylinder (equivalent to a photosensitive drum) is driven by friction with an image transfer cylinder (equivalent to ITB). This technique has the following advantages. That is, first, since the image on the photosensitive drum becomes an image on the ITB, if the image is formed based on the position on the photosensitive drum, the influence of the uneven rotation of the photosensitive drum is eliminated. Second, even if the ITB speed fluctuates due to a shock when the recording paper enters the ITB secondary transfer section, the consistency between the image on the photosensitive drum and the image on the ITB is ensured. There is a merit that image defects hardly occur in primary transfer. However, such a driving method in which the image cylinder is moved by friction with the image transfer cylinder has to increase the frictional force at the contact portion, which greatly affects the transferability of the toner. As a result, the technology is not necessarily highly practical depending on the type of toner constituting the image forming apparatus, the transfer process specifications, and the like.

JP 2002-333752 A

  However, as described in Patent Document 1, in order to drive the photosensitive drum by ITB by friction, the transfer pressure of the primary transfer portion must be increased. Here, the reason why the transfer pressure of the primary transfer portion is increased is that the rotation torque corresponding to the load torque generated on the photosensitive drum is rotated between the photosensitive drum and the ITB when the photosensitive drum is rotationally driven in the image forming process. This is because it needs to be generated by the frictional force on the contact surface.

  However, when the transfer pressure is increased, the load amount generated on the photosensitive drum and the ITB increases, and the torque amount of the motor increases. In addition, the transferability of the toner is affected. On the other hand, in order to drive the surface speed of the photosensitive drum and the surface speed of the ITB to coincide with each other without increasing the transfer pressure, it is necessary to reduce the force exerted by the frictional force on the contact surface between the photosensitive drum and the ITB. . Specifically, it is necessary to separately prepare a drive source that applies a rotational force to the rotation shaft of the photosensitive drum. An example of the drive source is a BLDC motor. In this case, the torque generated by the BLDC motor is a torque corresponding to a load torque other than the friction torque in the primary transfer portion when the photosensitive drum rotates at a predetermined target speed. The target speed corresponds to the recording paper production speed, for example, 50 ppm. Thereby, the force that the friction force bears can be limited only to the acceleration force due to the AC speed fluctuation component of the photosensitive drum or ITB.

  However, when such a driving method is adopted, it is required to accurately measure the load torque generated when the photosensitive drum rotates at a predetermined target speed. Ideally, the load torque is always the same, but in reality, it is the same due to the effects of aging deterioration of the surface of the photosensitive drum, aging of the cleaner blade, ambient temperature of the photosensitive drum, changes in humidity, and the like. It will not be. Therefore, it is necessary to change and adjust the appropriate torque to be generated by the motor that is the drive source of the photosensitive drum each time, and as a result, it is necessary to frequently prepare the adjustment mode by frequently measuring the load torque. The problem of reduced productivity occurs.

  An object of the present invention is to provide an image forming apparatus capable of preventing the occurrence of image defects such as color misregistration without reducing productivity.

  In order to achieve the above object, an image forming apparatus of the present invention includes a rotatable image carrier, an intermediate transfer member that rotates in contact with the image carrier, and a first that rotates the image carrier. A driving means; a second driving means for rotationally driving the intermediate transfer member; and an assist torque for causing the first driving means to cancel a load torque acting on the image carrier with respect to the image carrier. An assist torque deriving unit for deriving; a correcting unit for correcting the assist torque derived by the assist torque deriving unit; a control unit for controlling the first driving unit and the second driving unit; The control unit controls the first driving unit to apply the corrected assist torque to the image carrier so that the image carrier is driven by the intermediate transfer member. And butterflies.

  Further, the image forming apparatus of the present invention includes a rotatable intermediate transfer member, an image carrier that rotates in contact with the intermediate transfer member, a second drive unit that rotationally drives the intermediate transfer member, and the image. A first driving means for rotating the carrier; and an assist torque deriving means for deriving an assist torque for the second driving means to cancel the load torque acting on the intermediate transfer body with respect to the intermediate transfer body. And correction means for correcting the assist torque derived by the assist torque deriving means, and control means for controlling the second drive means and the first drive means, wherein the control means comprises the first The assisting torque corrected by the correcting unit is applied to the driving unit 2 so that the intermediate transferring member is driven by the image bearing member. It is characterized in.

  According to the present invention, the assist torque to be applied to the photosensitive drum 100 is corrected to the optimum assist torque after starting the printing process, not in the adjustment mode immediately after the main power source of the image forming apparatus is turned on. As a result, the optimum assist torque can be applied without frequently preparing the adjustment mode, so that the surface speed difference between the photosensitive drum and the ITB is eliminated, and the image defect such as color misregistration is reduced without reducing the productivity. Occurrence can be prevented.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment. It is a figure which shows the drive structure of the photosensitive drum in FIG. FIG. 2 is a diagram illustrating a driving configuration of an intermediate transfer belt (ITB) in FIG. 1. It is a figure which shows the internal structure of the controller in FIG.2 and FIG.3. FIG. 2 is a diagram for explaining a driven drive system in which the photosensitive drum in FIG. 1 is rotated by following an intermediate transfer belt. FIG. 6 is a diagram for explaining a load torque generated on the photosensitive drum in FIG. 5 and a friction torque generated on a contact surface between the photosensitive drum and the intermediate transfer belt. It is a figure which shows the time-dependent change of the load torque which arises in the photosensitive drum in FIG. FIG. 7 is a diagram illustrating a state where a load torque generated in the photosensitive drum in FIG. 6 is offset by an assist torque. FIG. 7 is a diagram showing the relationship between the sum of acceleration torque and fluctuating torque components and the friction torque in the photosensitive drum of FIG. 6 over time. FIG. 10 is a diagram showing a relationship between a torque command value when rotating the photosensitive drum and a surface speed of the photosensitive drum during printing, and FIG. 10A shows a driven state when an appropriate assist torque is derived. FIG. FIG. 10B is a diagram showing a driven state when an inappropriate assist torque is derived, and FIG. 10C is a diagram showing a driven state when torque fluctuations are not symmetrical. FIG. 6 is a diagram illustrating a rotation speed from the start of driving of the photosensitive drum and ITB to the stop of driving through an image forming period. FIG. 11 (a) shows the behavior when starting with the torque command value 524, and FIG. 11 (b) shows the behavior with the torque command value 522 derived by the optimum assist torque derivation method. It shows the behavior at the time. FIG. 11C shows the behavior when starting with the torque command value 525. FIGS. 12A and 12B are diagrams for explaining a surface speed deriving process of the photosensitive drum in the image forming apparatus of FIG. 1, FIG. 12A is a flowchart illustrating a procedure of the surface speed deriving process, and FIG. It is a flowchart which shows the procedure of Duty ratio UP measurement process performed by step S1131 of a). FIG. 12C is a diagram for explaining the surface speed deriving process of the photosensitive drum in the image forming apparatus of FIG. 1, and FIG. 12C illustrates the procedure of the duty ratio DOWN measurement process executed in step S1151 of FIG. FIG. 12D is a flowchart showing the procedure of the surface speed (ω _S ) derivation process at the predetermined process speed executed in step S1181 of FIG. It is a figure for demonstrating Duty ratio UP process (a) and Duty ratio DOWN process (b). FIGS. 14A and 14B are diagrams for explaining print processing using the image forming apparatus of FIG. 1, FIG. 14A is a flowchart showing the procedure of print processing, and FIG. 14B is step S <b> 2141 of FIG. 7 is a flowchart showing a procedure of assist torque correction value derivation processing executed in step S2. FIG. 3 is a schematic diagram illustrating a positional relationship between a surface of a photosensitive drum and a surface position detection unit that detects the position of the surface. It is a figure which shows schematic structure of the image forming apparatus which concerns on 2nd Embodiment.

  Hereinafter, embodiments will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a schematic configuration of the image forming apparatus according to the first embodiment. The image forming apparatus 200 is an electrophotographic color digital copying machine. Note that the image forming apparatus 200 may be a multifunction machine or a facsimile in addition to a copying machine, and may be a monochrome digital copying machine, a multifunction machine, or a facsimile in addition to a color.

  In FIG. 1, a plurality of, for example, four image forming units each having a photosensitive drum 100Y, 100M, 100C, and 100K corresponding to each of yellow (Y), magenta (M), cyan (C), and black (K) are substantially omitted. It is arranged along the horizontal direction. The photosensitive drums 100Y to 100K as image bearing members are rotatable and rotate in the direction of arrow A in FIG.

  In addition to the corresponding photosensitive drums 100Y to 100K, the image forming units include primary charging devices 105Y, 105M, 105C, and 105K, exposure devices 101Y, 101M, 101C, and 101K, and developing devices 102Y, 102M, 102C, and 102K. ing. The developing devices 102Y to 102K include corresponding developing sleeves 103Y, 103M, 103C, and 103K. Further, the image forming unit includes cleaners 104Y, 104M, 104C, and 104K corresponding to the photosensitive drums 100Y to 100K and surface position detecting means 106Y, 106M, 106C, and 106K that detect the surface positions of the photosensitive drums 100Y to 100K. Yes.

  The primary charging devices 105Y to 105K uniformly charge the surfaces of the corresponding photosensitive drums 100Y to 100K, respectively. The exposure apparatuses 101Y to 101K expose the surfaces of the charged photosensitive drums 100Y to 100K based on image information to form electrostatic latent images.

  The developing devices 102Y to 102K form toner images by developing the electrostatic latent images formed on the surfaces of the corresponding photosensitive drums 100Y to 100K using the developing sleeves 103Y to 103K containing the corresponding chromatic toner, respectively. .

  Primary transfer rollers 107Y, 107M, 107C, and 107K are disposed to face the photosensitive drums 100Y to 100K, respectively. An endless intermediate transfer belt (ITB) 108 as an intermediate transfer member is stretched so as to be conveyed between the photosensitive drums 100Y to 100K and the primary transfer rollers 107Y to 107K.

  The ITB 108 is stretched by a plurality of stretching rollers 110 to 112, and rotates so as to come into contact with the surfaces of the photosensitive drums 100Y to 100K. The ITB 108 rotates in the direction of arrow B in FIG. The toner images of the respective colors formed on the surfaces of the photosensitive drums 100Y to 100K are sequentially transferred and superimposed on the ITB 108 to form a color image.

  The tension roller 110 is a drive roller that drives the ITB 108, and also functions as a tension roller that controls the tension of the ITB 108 to be constant. The tension roller 111 is a secondary transfer inner roller that forms a nip portion at a contact portion with the opposing secondary transfer outer roller 113.

  The toner image on the ITB 108 is transferred to the paper P by the action of the internal and external secondary transfer rollers, and the paper P on which the toner image has been transferred is carried into the downstream fixing device 114, and the toner image is transferred to the paper by the fixing device 114. It is fixed to P and then discharged outside the apparatus. On the other hand, the ITB 108 after the secondary transfer is subjected to repeated image forming processes after the transfer residual toner, paper dust and the like are cleaned by the cleaning device 109.

  FIG. 2 is a diagram showing a driving configuration of the photosensitive drum in FIG. 1, and shows an electrical and mechanical configuration for driving the photosensitive drum 100.

  In FIG. 2, the photosensitive drum 100 is mechanically connected to the drum shaft 50 via a coupling 52. A motor shaft gear 32a is engaged with the drum shaft 50 via a reduction gear 51a, and a rotary encoder 40a for detecting the rotational speed of the drum shaft 50 is provided. A driving force from a BLDC motor 30a serving as a first driving source for driving the photosensitive drum 100 is transmitted to the drum shaft 50 by the engagement of the motor shaft gear 32a and the reduction gear 51a. Above the photosensitive drum 100, a surface position detecting means 106 for detecting the surface position of the photosensitive drum 100 is provided.

  The controller 20 outputs a command signal from the host CPU 10, such as a drive on / off signal, a target speed signal, a register setting value signal, a PWM value signal, and the like as a control signal to the motor driver IC 24. Note that the PWM signal is a pulse width modulation signal, and is obtained by dividing a section in which the signal is at a high level by one period of the signal as a duty ratio, and its magnitude is expressed in percent. The duty ratio is proportional to the rotational torque of the BLDC motor 30a. Hereinafter, although details will be described later, the photosensitive drum 100 does not perform the conventionally used speed feedback control of adjusting the duty ratio so that the surface speed becomes the target speed. Here, it is driven by inputting a predetermined duty ratio to the motor driver IC 24.

  Based on the control signal from the controller 20 and the rotational position signal from the rotational position detector 31a, the motor driver IC 24 performs phase switching of the phase current that flows to the BLDC motor 30a of the drive circuit 25 and adjustment of the current amount. The BLDC motor 30a rotationally drives the drum shaft 50 through the motor shaft gear 32a and the reduction gear 51a. The BLDC motor 30a is, for example, a low inertia type brushless DC motor.

  In this embodiment, the rotary encoder 40a is used to detect the rotational speed. However, the rotary encoder 40a is not particularly limited as long as the rotational speed or the surface speed of the photosensitive drum 100 can be detected. Absent.

  On the other hand, FIG. 3 is a diagram showing a driving configuration of the intermediate transfer belt (ITB) in FIG. 1, and shows an electrical and mechanical configuration for driving the ITB 108.

  In FIG. 3, the ITB 108 is driven by rotationally driving an ITB drive roller 110 installed so as to contact the inside of the ITB 108. The motor shaft gear 32b is engaged with the roller shaft 70 of the ITB drive roller 110 via a reduction gear 51b, and a rotary encoder 40b for detecting the rotational speed of the ITB drive roller shaft 70 is provided. Yes. The driving force from the BLDC motor 30b as the second driving source for driving the ITB 108 is decelerated by the meshing of the motor shaft gear 32b and the reduction gear 51b as in the case of the photosensitive drum 100, and the ITB driving roller 110 is driven. Is transmitted to. The ITB controller 20 outputs a command signal from the host CPU 10, such as a drive on / off signal, a target speed signal, a register set value signal, a PWM value signal, etc., to the motor driver IC 21 as a control signal. Further, the controller 20 performs a calculation for speed control based on the signal of the rotary encoder 40. Unlike the photosensitive drum 100, the ITB 108 is speed-feedback controlled so that the surface speed becomes the target speed. The surface position detection unit 106 as an electrical configuration is not provided on the ITB side.

  Next, the internal configuration of the controller 20 will be described.

  FIG. 4 is a diagram showing an internal configuration of the controller 20 in FIGS. 2 and 3. In FIG. 4, the controller 20 is mainly configured by a CPU 21, a ROM 22, and a RAM 23. The CPU 21 calculates the surface speed from the speed detection signal from the rotary encoder 40. In the ROM 22, optimum assist torque (details will be described later) at the time of shipment is derived, and the duty ratio is written. After shipment, the CPU 21 reads the duty ratio from the ROM 22, inputs it to the motor driver IC 24 as the duty ratio of the PWM signal, and outputs a constant assist torque by the BLDC motor 30a. When the optimum assist torque is newly derived by the adjustment, the duty ratio is written in the RAM 23. If the duty ratio is written in the RAM 23, reading from the ROM 22 is not performed.

  In the image forming apparatus 200 having such a configuration, for example, when the host CPU 10 that controls the entire apparatus receives an image formation command for the paper P from the user, the photosensitive drums 100Y to 100K start rotating. Further, the CPU 10 activates the primary charging devices 105Y to 105K, the developing devices 102Y to 102K, the primary transfer rollers 107Y to 107K, the ITB driving roller 110, the secondary transfer inner roller 111, the fixing device 114, and the like.

  A high voltage power supply (not shown) is connected to the primary charging devices 105Y to 105K, and a DC voltage or a high voltage obtained by superimposing a sine wave voltage on the DC voltage is applied. As a result, the surfaces of the photosensitive drums 100Y to 100K with which the primary charging devices 105Y to 105K are in contact are uniformly charged to the same potential as the DC voltage supplied from the high-voltage power supply. The charged photosensitive drums 100Y to 100K rotate to the laser irradiation positions of the exposure devices 101Y to 101K, and are exposed by the corresponding exposure devices 101Y to 101K according to the image signal, thereby forming an electrostatic latent image. A high voltage obtained by superimposing a rectangular wave voltage on a direct current is applied to the developing sleeves 103Y to 103K of the developing devices 102Y to 102K by a high voltage power source (not shown). The negatively charged toner is supplied by the developing sleeves 103Y to 103K to the electrostatic latent images on the photosensitive drums 100Y to 100K having a positive potential with respect to the developing sleeve and a negative potential with respect to GND. Form. The toner images on the four photosensitive drums 100Y to 100K are sequentially transferred to the ITB 108 by corresponding primary transfer rollers 107Y to 107K, and are superimposed to form a color image. The color image on the ITB 108 is transferred onto the paper P by the secondary transfer inner roller 111 and the secondary transfer outer roller 113. A DC high voltage for transferring the toner image is applied to the primary transfer rollers 107Y to 107K and the secondary transfer inner roller 111 from a high voltage power supply (not shown).

  The toner image transferred to the paper P is fixed on the paper P by applying pressure and temperature by the downstream fixing device 114 to form a color image. The untransferred toner remaining on the photosensitive drums 100Y to 100K is scraped and collected by the cleaners 104Y to 104K. On the other hand, transfer residual toner or the like remaining on the ITB 108 is scraped and collected by the ITB cleaner 109.

  In the image forming apparatus 200, the photosensitive drums 100Y to 100K are driven and driven by the ITB 108, and the surface speed of the photosensitive drums 100Y to 100K and the surface speed of the ITB 108 are controlled to be always the same.

  Hereinafter, the driven drive in which the photosensitive drums 100Y to 100K rotate in accordance with the rotation of the ITB 108 will be described using an arbitrary photosensitive drum 100.

  FIG. 5 is a diagram for explaining a driven drive system in which the photosensitive drum 100 in FIG. 1 is rotated by following ITB.

  In FIG. 5, the ITB 108 is disposed so as to contact the photosensitive drum 100 in the image forming apparatus 200, and the primary transfer roller 107 is disposed so as to contact the photosensitive drum 100 via the ITB 108 at the contact portion, and is driven. The part is formed. A surface position detecting means 106 as a surface position detecting unit is provided facing the photosensitive drum 100, and a sub-scanning synchronous exposure unit is formed by the ASIC 60 that receives a signal from the host CPU 10, the laser driver 61, and the exposure device 101. Is formed.

  The exposure apparatus 101 is controlled to form an electrostatic latent image on the photosensitive drum 100 by performing exposure (sub-scanning synchronous exposure) in synchronization with the surface position of the photosensitive drum 100 detected by the surface position detection unit 106. Is done. The same applies to other photosensitive drums.

  The exposure control method uses time-synchronized exposure. In this method, it is assumed that the surface speed of the photosensitive drum 100 is constant. If the speed fluctuation is not constant, the irradiated electrostatic latent image is originally irradiated from the position to be irradiated. The image quality is deteriorated due to deviation. However, in the present embodiment, a driving state in which the surface speeds of the photosensitive drum 100 and the ITB 108 are the same is realized. As a result, exposure can be controlled in synchronization with the surface position of the photosensitive drum 100, and image quality such as misalignment does not occur in the image transferred to the ITB 108, so that the image quality is improved.

  In this embodiment, the driven drive means that the photosensitive drum 100 is rotated by the ITB 108 using the frictional force between the ITB 108 and the photosensitive drum 100. More precisely, it means that the surface speed of the ITB 108 and the surface speed of the photosensitive drum 100 are always driven to be the same by rotating the photosensitive drum 100 with the ITB 108.

  Hereinafter, the driven drive, the surface position detection unit, and the sub-scanning synchronous exposure unit will be described. First, the driven drive will be described in detail.

  At the time of driven driving, the ITB 108 is driven at a constant speed by speed feedback control, and the photosensitive drum 100 is driven at a predetermined duty ratio.

  The duty ratio has a linearity with respect to the magnitude of torque when rotating stably, and is uniquely determined. This is because the duty ratio represents a period during which the applied voltage is turned on, and the motor driver IC passes a current through the motor during that period, so the duty ratio and the current are proportional. Note that, depending on the motor driver IC, there is an OFF period.

  In addition, the BLDC motor and the brush DC motor have good linearity between current and torque, and the duty ratio and torque are also linear. That is, the driven drive can be realized by adjusting a predetermined torque for rotating the photosensitive drum 100, and this predetermined torque is hereinafter defined as assist torque. That is, as described above, the assist torque is rotational torque applied to the drum shaft 50 in order to cancel out a certain component of the load torque acting on the drum shaft 50 of the photosensitive drum 100, for example.

  In the present embodiment, the assist torque is a design parameter, and the size of this parameter can be changed according to the duty ratio.

  Hereinafter, technical means for realizing the driven drive will be described.

  FIG. 6 is a diagram for explaining the load torque generated on the photosensitive drum 100 in FIG. 5 and the friction torque generated on the contact surface between the photosensitive drum and the ITB.

  In FIG. 6, the load torque in the photosensitive drum 100 is a value obtained by adding the load torque generated by the cleaner blade 104, the drum bearing portion, and the like in the rotation operation during image formation, and the friction torque is not included in the load torque.

  FIG. 7 is a view showing a change with time of the load torque generated in the photosensitive drum of FIG.

  In FIG. 7, the load torque is not always constant, and changes depending on the timing of applying the charging high voltage and the timing of the toner remaining without being transferred completely entering the cleaner blade 104. However, it is known that such a transient change component (hereinafter referred to as “fluctuating torque component”) is sufficiently small with respect to a constant generated load torque.

  Further, since the steady component of the load torque is very large with respect to the friction torque, it is usually difficult to drive the photosensitive drum 100 by the ITB 108 using the friction torque.

  Therefore, in the present embodiment, the BLDC motor 30a applies a rotational torque equivalent to the steady component of the load torque to the photosensitive drum 100 as an assist torque so as to cancel (cancel) the constant component of the load torque.

  FIG. 8 is a diagram illustrating a state where the load torque generated in the photosensitive drum in FIG. 6 is offset by the assist torque.

  In FIG. 8, the steady component of the load torque is canceled out by the assist torque applied to the photosensitive drum 100, and only the fluctuation torque acts substantially.

  In this way, by offsetting the steady component of the load torque with the assist torque, the fluctuation torque, which is the load torque component, becomes smaller than the friction torque acting on the contact surface between the photosensitive drum 100 and the ITB 108. As a result, the photosensitive drum 100 is driven in synchronization with the rotational speed of the ITB 108.

  In order to improve the followability of the photosensitive drum 100 with respect to the speed variation of the ITB 108, it is preferable to consider an acceleration torque represented by the product of the drum inertia and acceleration on the drum shaft 50 of the photosensitive drum 100.

  That is, if the sum of the acceleration torque and the fluctuation torque component on the photosensitive drum 100 is equal to or less than the friction torque between the photosensitive drum 100 and the ITB 108, the photosensitive drum 100 is effectively driven by the ITB 108.

  FIG. 9 is a graph showing the relationship between the sum of the acceleration torque and the fluctuation torque component in the photosensitive drum of FIG. 6 and the friction torque over time.

  As for the friction torque, when the surface speeds of the photosensitive drum 100 and the ITB 108 match, the static friction coefficient becomes dominant. The friction torque has a force so that there is no difference between the surface speeds of the photosensitive drum 100 and the ITB 108, and its magnitude varies. At that time, the maximum frictional torque that works so as not to cause a difference in the surface speed is the maximum static frictional torque.

  The relationship in FIG. 9, that is, the relationship when the assist torque that cancels the constant component of the load torque is generated from the BLDC motor 30 a is shown using the equation of motion as follows.

Here, _{T F} is the friction torque, J is a drum inertia, d [omega / dt is the angular acceleration of the photosensitive drum, the _{T L} the load _{torque, T AS} is the assist torque, the [Delta] T _L is a torque fluctuation component.

The above equation (1) indicates that the photosensitive drum 100 follows the ITB 108 when the friction torque (T _F ) is larger than the sum of the acceleration torque in the first term on the right side and the variable torque component in the second term on the right side. Yes.

That is, in the present embodiment, as described above, the steady component of the load torque (T _L ) is canceled by the assist torque (T _AS ), and the load torque component including the fluctuation torque ΔT _L is made small enough to be ignored. Then, the photosensitive drum 100 is driven and driven by the ITB 108. Then, in order to improve the followability at a portion other than the assist torque, it can be seen from the above formula (2) that it is effective to increase the friction torque or decrease the acceleration torque.

Basically, when ΔT _L is made so small that it can be ignored, in order to improve the followability in a portion other than the assist torque, it is conceivable to increase the friction torque or decrease the acceleration torque from the above equation (2). .

  Here, it is difficult to change the friction torque because it is closely related to the toner transfer process in the primary transfer, but it is relatively easy to reduce the acceleration torque by reducing the equivalent drum inertia. is there. The equivalent drum inertia represents the total rotating load as an inertia component on the drum shaft 50.

  The inertia component of the BLDC motor 30a that appears on the drum shaft 50 is greatly influenced by the gear ratio between the reduction gear 51a and the motor shaft gear 32a, and is a value obtained by multiplying the motor shaft inertia by the square of the gear ratio. As a result, the rotor inertia of the BLDC motor 30a may be much larger on the drum shaft 50 than the inertia component of the photosensitive drum 100. Therefore, in the present embodiment, the inner rotor type low inertia type is used as the BLDC motor 30a. As a result, an assist torque is applied to cancel a constant component of the equivalent load torque on the photosensitive drum shaft, and a motor having a low inertia component is selected, so that the photosensitive drum 100 is effectively driven by the ITB 108 by the friction torque. Can be expanded. In the present embodiment, the BLDC motor 30a is used as an assist torque generating source. However, the present invention is not particularly limited to the BLDC motor as long as a constant torque can be generated.

  By the way, the method for obtaining the assist torque based on the equations of motion (1) and (2) has the following problems.

  That is, the assist torque is equivalent to the load torque, and the necessary assist torque can be obtained by measuring the load torque. However, since the measurement state is different from the actual printing operation state, a measurement error is likely to occur. The load torque is a torque generated by the motor at the time when the photosensitive drum 100 is driven to be the same as the surface speed of the ITB 108. Although the actual printing operation is in a state where the photosensitive drum 100 and the ITB 108 are in contact with each other, the load torque and the friction torque cannot be distinguished unless the measurement is performed in a separated state. Therefore, the measurement is performed with the photosensitive drum 100 and the ITB 108 separated. At this time, if there is a steady difference between the surface speeds of the photosensitive drum 100 and the ITB 108, the friction torque is steadily generated at the time of printing in which both are in contact. In this case, there is a possibility that the follower is likely to come off. The steady speed difference is caused by an error in the diameter of the photosensitive drum 100, an error in the diameter of the ITB drive roller 107, an error in the belt thickness of the ITB 108, and the like.

  An optimum assist torque for realizing stable follow-up control is a torque command that falls within a positive / negative range of maximum static friction torque (hereinafter referred to as “follow-up region”) with respect to any torque fluctuation of the photosensitive drum 100. Value.

  A method for obtaining the optimum assist torque will be described below.

  FIGS. 10A to 10C are diagrams showing the relationship between the torque command value when rotating the photosensitive drum and the surface speed of the photosensitive drum during printing, and FIG. 10A shows an appropriate assist. It is a figure which shows the driven drive state at the time of deriving | reducing torque. FIG. 10B is a diagram showing a driven state when an inappropriate assist torque is derived, and FIG. 10C is a diagram showing a driven state when torque fluctuations are not symmetrical.

  In FIG. 10A, a torque command value that is a predetermined assist torque is given each time during printing, and the average value of the surface speed 511 at that time is plotted. Normally, when the torque command value applied to the photosensitive drum 100 is increased, the surface speed 511 naturally increases. However, there is a region 505 where the surface speed 511 does not change even when the torque command value is increased. This area is a driven area 505. At this time, the minimum torque command value 524 and the maximum torque command value 525 in the driven region 505 are the maximum static friction torque.

  The torque command value 522 is a point at which the maximum static friction torque is divided into two, positive and negative, and is a point at which the friction torque becomes zero. That is, the magnitude of the friction torque increases as it approaches the torque command value 524 or 525 with the torque command value 522 at which the friction torque is zero as the center. Further, if the driven region 505 is sandwiched between the torque command values 524 and 525, the non-driven region 506 is obtained, the dynamic friction coefficient becomes dominant, and the friction torque decreases. Accordingly, the median value of values 524 and 525 at which the surface speed of the photosensitive drum 100 starts to change with respect to the torque command value is the optimum assist torque. However, since the torque fluctuation may be asymmetric as shown in FIG. 10C, the optimum assist torque is not necessarily the median value in the driven region.

  Here, when the assist torque is not properly obtained, the result is as shown in FIG. That is, in FIG. 10B, the assist torque 525 is within the range of the driven region 505, but may deviate from the driven region 505. Further, the torque fluctuation may become larger than expected due to the influence of the high pressure of the primary transfer that could not be seen when the photosensitive drum 100 and the ITB 108 were separated from each other, and the torque may deviate from the driven area 505. In this case, the surface speed of the photosensitive drum 100 appears as a speed fluctuation 571, and color misregistration and banding become conspicuous.

  The assist torque derivation method described above is based on the assumption that torque fluctuations are symmetric, and the assist torque derived by the above method is a method adapted to a state in which the value of the load torque is constant. is there. In such a case, for example, once the assist torque is derived in the adjustment mode performed immediately after the main power supply of the image forming apparatus is turned on, no problem occurs. Generally, the image forming apparatus first enters a state called an adjustment mode when the main power supply is turned on. In the adjustment mode, temperature adjustment of the fixing roller of the fixing device 114, main scanning tilt correction, color correction, and the like are performed. Only when the adjustment mode is finished, the printing operation is possible.

  However, the load torque varies depending on the amount of toner loaded on the cleaner blade 104 in contact with the photosensitive drum 100, the ambient temperature and humidity of the photosensitive drum 100, the aging of the surface of the photosensitive drum 100, and the like. For this reason, in order to cope with the above assist torque deriving method, it is necessary to frequently derive an appropriate assist torque, which also increases the adjustment mode state and causes a decrease in productivity. Become.

  Therefore, in the present embodiment, the application timing of the assist torque derivation method according to the above method is limited to a predetermined period in the adjustment mode immediately after the main power is turned on, and before the start of the actual image forming operation, We decided to correct the assist torque to the optimum value.

  That is, the inventor starts driving the photosensitive drum 100 at a predetermined time earlier than the driving start timing of the ITB 108 by a predetermined time, that is, earlier by ΔT531, and from the start of driving through the image forming process to the stop of driving. The operation up to is verified in detail. As a result, the speed at which the photosensitive drum stabilizes (hereinafter referred to as “drum”) between the torque command value (FIG. 10A) when the magnitude of the torque fluctuation is symmetric and ΔT 531 after the photosensitive drum 100 starts to be driven. It was found that there was a correlation between the startup speed 526 "and the like.)

  FIG. 11 is a diagram showing the rotational speed from the start of driving of the photosensitive drum 100 and the ITB 108 to the stop of driving through the image forming period 532, and FIG. 11A shows a torque command value 524 (see FIG. 10). ) Shows the behavior when the photosensitive drum is activated. FIG. 11B shows the behavior when the photosensitive drum is started with the torque command value 522 (see FIG. 10) derived by the optimum assist torque deriving method. FIG. 11C shows the behavior when the photosensitive drum is activated with a torque command value 525 (see FIG. 10).

  In FIG. 10, ΔT531 is provided between the drum activation time 529 and the ITB activation time 530 for any torque command value. ΔT 531 is set to be longer than, for example, a time for one rotation after the photosensitive drum 100 has reached a certain rotation speed when rotating only by the assist torque.

  Immediately after the start of drum activation, the photosensitive drum 100 does not receive a driving force from the ITB 108 in the rotational direction. Within this ΔT531, the rotational speed of the photosensitive drum 100 (hereinafter referred to as “drum rotational speed 527”) is higher than the rotational speed of the ITB 108 (hereinafter referred to as “ITB rotational speed 528”). At that time, it receives a driving force from the ITB 108 and is accelerated toward a target speed 523 which is a constant rotational speed. 11A, the drum rotation speed 527 in the image formation period 532 is different from the drum rotation speed 527 before the image formation period. This is because in the image forming section 532, the toner transfer process and load torque due to toner entering the cleaner blade 104 are reduced. When the image forming period 532 ends, the magnitude of the load torque changes again, and the drum rotation speed 527 decreases.

  11A to 11C, the magnitude of the drum activation speed 526 is proportional to the magnitude of the assist torque. This is because the rotational speed of the motor is proportional to the magnitude of the torque. Of course, the drum starting speed 526 at the torque command value 522 which is the optimum assist torque is also uniquely determined. That is, the torque command value 522 and the drum activation speed 526 have a one-to-one relationship. Therefore, using this relationship, the optimum value of the assist torque when the constant value (DC component) of the load torque on the photosensitive drum 100 changes is adjusted.

  That is, even if the photosensitive drum 100 is activated with the torque command value 522, the drum activation speed may be slowed down by repeatedly performing print jobs, for example, when the load torque increases. This is the same behavior as the behavior shown in FIG. 11A when the assist torque is activated at 524. That is, the torque command value before the load torque is increased is 522 which is the optimum assist torque. However, since the optimum assist torque is changed to a larger value due to the increase of the load torque, the drum starting speed is increased. Becomes slower. This indicates that the optimum assist torque 522 can be corrected based on the detected value by detecting the drum activation speed 526.

  Therefore, in the present embodiment, the torque command value is corrected to an optimum value based on the drum starting speed. That is, a predetermined correction coefficient is calculated by the following formulas (3) and (4), and the torque command value after correction is derived by multiplying the torque command value by the calculated correction coefficient.

D = ω _B / ωs (3)
Duty_C = D × Duty_D (4)
Here, D is a correction coefficient, ω _B is a drum starting speed when driving is started with the assist torque before correction before the load torque is changed, and ω _S is started driving with the assist torque before correction after the load torque is changed. This is the drum start speed when Further, Duty_C is a duty ratio corresponding to the corrected assist torque, and Duty_D is a duty ratio corresponding to the pre-correction assist torque.

  The corrected assist torque (hereinafter referred to as “Duty_C”) from the drum activation speed 526 is output as assist torque from the controller 20 to the motor driver IC 24 before the image formation period 532, thereby forming an image. It is possible to set an optimum value as the torque command value in the period 532.

  Such assist torque correction is performed in a timely manner when the drum activation speed 526 varies. The above-described assist torque correction calculation is merely an example, and the present invention is not limited to this.

  Hereinafter, a specific flow for deriving the surface speed of the photosensitive drum 100m, correcting the assist torque to the optimum assist torque using the derived surface speed, and forming an image using the corrected assist torque will be described.

12A is a diagram for explaining the surface speed processing of the photosensitive drum in the image forming apparatus of FIG. FIG. 12A is a flowchart showing the procedure of the surface velocity deriving process, and FIG. 12B is a flowchart showing the procedure of the duty ratio UP measurement process executed in step S1131 of FIG. FIG. 12B is a diagram for explaining surface speed processing of the photosensitive drum in the image forming apparatus of FIG. FIG. 12C is a flowchart showing the procedure of the duty ratio DOWN measurement process executed in step S1151 of FIG. FIG. 12D is a flowchart showing the procedure of the surface speed (ω _S ) deriving process at the predetermined process speed executed in step S1181 of FIG.

  The surface speed deriving process is executed by the CPU 21 of the controller 20 that has received a command from the host CPU 10 in accordance with a surface speed deriving procedure that is a surface speed deriving program stored in the ROM 22, for example.

  In FIG. 12A, when the surface speed deriving process is started, first, the CPU 21 receives a surface speed deriving command signal from the host CPU 10 (step S1111). Next, the CPU 21 selects a process speed (step S1121). In general, an image forming apparatus has a plurality of process speeds so as to cope with cardboard. Therefore, it is necessary to derive the assist torque according to each process speed.

  Next, the CPU 21 starts a duty ratio UP measurement process in FIG. 12B described later (step S1131). That is, the average value of the surface speed of the photosensitive drum 100 when the duty ratio is increased from the driven area is measured. By this sequence, a duty ratio T2 that yields a positive maximum static friction torque 525 as shown in FIG. 13A is derived.

  Next, the CPU 21 records the duty ratio obtained in the duty ratio UP measurement process as T2 in the RAM 23 (step S1141).

  Next, the CPU 21 starts a duty ratio DOWN measurement process in FIG. 12C described later (step S1151). By this sequence, a duty ratio T1 that is a negative maximum static friction torque as shown in FIG. 13A is derived. Next, the CPU 21 records the duty ratio obtained in the duty ratio DOWN measurement process as T1 in the RAM 23 (step S1161).

  Next, as shown in FIG. 13B, the CPU 21 records the median value (T1 + T2) / 2 between T1 and T2 in the RAM 23 as a new set duty ratio (step S1171). Note that the assist torque in step S1171 is an assist torque having an optimum value of torque fluctuation during image formation as described above, and is not necessarily a median value. For example, (αT1 + T2) / 2 or (T1 + αT2) / 2 is obtained by multiplying by a weight coefficient α larger than 0.

  After recording the new duty ratio, the CPU 21 starts ωs derivation processing at a predetermined process speed, which is the process speed of FIG. 12D described later (step S1181).

  Next, the CPU 21 repeats the processing from step S1111 to step S1181 even at other process speeds (step S1191), and thereafter ends the assist torque derivation processing.

  According to the process of FIG. 12A, the surface speed of the photosensitive drum 100 is obtained based on the average value of the duty ratio obtained by the duty ratio UP measurement process and the duty ratio DOWN measurement process. It is possible to derive a more accurate surface velocity in consideration of

  Here, the duty ratio UP measurement process, the duty ratio DOWN measurement process, and the ωs derivation process at a predetermined process speed will be described.

  FIG. 12B is a flowchart showing the procedure of the duty ratio UP measurement process executed in step S1131 of FIG.

  In FIG. 12B, the CPU 21 first inputs the fixed duty ratio read from the RAM 23 or the ROM 22 to the motor driver IC 24 and drives the BLDC motor 30 (step S3111). At this time, the ITB 108 is controlled by speed control so that the surface speed of the ITB 108 becomes the set process speed, and this state is maintained during the assist torque derivation period.

  Next, the CPU 21 waits for a predetermined period during which the surface speed of the photosensitive drum 100 is stabilized, for example, 0.2 seconds (step S3121). Next, the CPU 21 samples the surface speed of the photosensitive drum 100 at a predetermined interval, for example, every 10 milliseconds, and obtains an average value (step S3131). Next, the CPU 21 determines whether or not the average value of the surface speed of the photosensitive drum 100 is larger than, for example, 103% of the speed setting value that is the target speed (step S3141). At this time, the target speed may be an average value of the actual surface speed of the ITB 108. If the result of determination in step S3141 is not greater than 103% (“NO” in step S3141), the CPU 21 sets a value obtained by adding + 1% to the current duty ratio as a new set duty ratio. This new set duty ratio is input to the motor driver IC 24 and reflected as the newly set assist torque (step S3151). Thereafter, the CPU 21 returns the processing to S3121 and repeats the same processing thereafter.

  On the other hand, if the result of determination in step S3141 is greater than 103% (“YES” in step S3141), the CPU 21 causes the process to exit the sequence of step S1131 and shifts to step S1141 of FIG.

  FIG. 12C is a flowchart showing the procedure of the duty ratio DOWN measurement process executed in step S1151 of FIG.

  In FIG. 12C, the CPU 21 first inputs the duty ratio read from the RAM 23 or the ROM 22 to the motor driver IC 24 to drive the BLDC motor 30a (step S3611). At this time, the ITB 108 is controlled by speed control so that the surface speed of the ITB 108 becomes the set process speed, and this state is maintained during the assist torque derivation period.

  Next, the CPU 21 waits for a predetermined period during which the surface speed of the photosensitive drum 100 is stabilized, for example, 0.2 seconds (step S3621). Next, the CPU 21 samples the surface speed of the photosensitive drum 100 at a predetermined interval, for example, every 10 milliseconds, and obtains an average value (step S3631). Next, the CPU 21 determines whether or not the average value of the surface speed of the photosensitive drum 100 is smaller than, for example, 97 (100-3)% of the speed setting value that is the target speed (step S3641). At this time, the target speed may be an average value of the actual surface speed of the ITB 108. If the result of determination in step S3641 is not smaller than 97%, that is, equal to or larger than 97% (“NO” in step S3641), the CPU 21 subtracts 1% from the current duty ratio. Is set as a new duty ratio. Next, the CPU 21 inputs the set new duty ratio to the motor driver IC 24 and reflects it as the newly set assist torque (step S3651). Thereafter, the processing returns to step S3621, and the same processing is repeated thereafter.

  On the other hand, if the result of determination in step S3641 is smaller than 97% (“YES” in step S3641), the CPU 21 causes the process to exit the sequence of step S1151 and shifts to step S1161 of FIG.

  On the other hand, FIG. 12D is a flowchart showing the procedure of the ωs derivation process at the predetermined process speed executed in step S1181 of FIG.

In FIG. 12D, the CPU 21 starts driving the photosensitive drum 100 with the duty ratio derived in S1171 (step S1181A). Next, the CPU 21 waits for a predetermined time during which the speed of the photosensitive drum 100 is stabilized, for example, 0.2 seconds (step S1181B). Next, the CPU 21 samples the surface speed of the photosensitive drum 100 for a predetermined time, for example, 0.5 seconds, and derives the average value (step S1181C). Note that the average value corresponds to the drum activation speed 526 as described above. Next, the CPU 21 stores ω _S in the RAM 23 (step S1181D). The CPU 21 storing ω _S in the RAM 23 stops driving the photosensitive drum 100 (step S1181E), ends the ω _S derivation process, and returns the process to FIG.

  The above is the process associated with the surface velocity derivation process in FIG.

Next, a description will be given of a printing process that is executed using the corrected assist torque after correcting the assist torque using ω _S obtained in FIG.

  The print process is executed when a print command from the user interface (UI) or PC is input to the host CPU 10 and the CPU 300 of the controller 20 is executed by the CPU 21 receiving the control command from the host CPU 10.

  FIG. 14 is a diagram for explaining print processing using the image forming apparatus of FIG. 1, and FIG. 14A is a flowchart showing the procedure of print processing. FIG. 14B is a flowchart showing the procedure of the assist torque correction value derivation process executed in step S2141 in FIG. These processes are executed by the CPU 21 of the controller 20 in accordance with the print processing procedure in the print processing program.

  In FIG. 14A, when the printing process is started, the CPU 21 receives drive command signals for the photosensitive drum 100 and the ITB 108 from the host CPU 10 (step S2111). The drive command signal is, for example, a process speed, a drive on signal, or the like. Next, the CPU 21 reads the assist torque as the fixed duty ratio from the RAM 23 or the ROM 22 in accordance with the process speed (step S2121). The assist torque is obtained by performing an image forming process similarly to the printing operation and measuring the surface speed of the photosensitive drum 100, and the surface speed is detected by the rotary encoder 40a. In order to rotate the photosensitive drum 100, a current is passed through the BLDC motor 30a. The motor driver IC 24 is a driver IC that determines a phase current flowing through the BLDC motor 30a based on the PWM signal. The magnitude of torque generated by the motor is determined by the duty ratio of the PWM signal. Accordingly, the duty ratio of the assist torque generated during the image forming process is adjusted so that the surface speed of the photosensitive drum 100 becomes a target process speed.

  Next, the CPU 21 outputs the fixed duty to the motor driver IC 24 as Duty_D, and starts driving the photosensitive drum 100 (step S2131). After driving the photosensitive drum 100, the CPU 21 starts an assist torque correction value derivation process in FIG. 14B described later (step S2141).

  After executing the assist torque correction value deriving process, the CPU 21 starts driving the ITB 108 by speed feedback control (step S2151), and drives the photosensitive drum 100 to follow the ITB 108 to execute an image forming process.

  At this time, the surface position detection unit detects the position of the surface of the photosensitive drum 100, and the sub-scanning synchronous exposure unit forms an electrostatic latent image on the surface of the photosensitive drum 100 based on the detected position. That is, in the image forming process, the surface position of each photosensitive drum 100 is detected by using a reflective photoelectric sensor as the surface position detection unit 106.

  FIG. 15 is a schematic diagram illustrating a positional relationship between the surface of the photosensitive drum 100 and a surface position detection unit that detects the position of the surface.

  In FIG. 15, mark patterns are formed at equal intervals in advance on the surface of the photosensitive drum 100 which is the surface of the image carrier. The mark pattern is formed in the non-image forming area of the photosensitive drum 100 and is not formed in the image forming area. The reflection type photoelectric sensor detects a mark pattern by detecting reflection of incident light by a photoelectric sensor. Accordingly, the sensor output is switched between the place with the mark and the place without the mark. Then, by setting a threshold value to an appropriate voltage, the output waveform of the photoelectric sensor becomes a rectangular wave. In order to specify the position on the surface of the photosensitive drum 100, a reference position is determined, and a rectangular wave number is counted from the reference position, thereby detecting the surface position on the photosensitive drum 100 with an accuracy determined by the resolution of the mark pattern. be able to.

  By performing exposure control in synchronization with the surface position of the photosensitive drum 100 detected in this manner, an electrostatic latent image having no positional deviation is formed on the photosensitive drum 100.

  That is, in FIG. 5 described above, the surface position detection unit 106 detects the surface position on the photosensitive drum 100 at a certain time with the accuracy of the resolution of the mark pattern. Since the ASIC 60 controls the timing of the exposure signal for forming the electrostatic latent image, the surface position detection signal is input to the ASIC 60, so that there is no electrostatic displacement corresponding to the surface position of the photosensitive drum 100. A latent image is formed. The electrostatic latent image formed on the photosensitive drum 100 is developed by a corresponding developing device to become a toner image, and then sequentially transferred and superimposed on the ITB 108 to become a color image. The color image on the ITB 108 is transferred to the paper P and fixed. The paper P on which the color image is fixed is discharged out of the image forming apparatus by a paper discharge roller (not shown).

  Next, the CPU 21 determines whether or not a drive stop signal is input from the host CPU 10 (step S2161). If the drive stop signal is input, the CPU 21 stops driving the photosensitive drum 100 and the ITB 108 (step S2171). The process ends. If the result of determination in step S2161 is that there is no drive stop signal input (“NO” in step S2161), processing continues until a drive stop signal is input.

  According to the processing in FIG. 15, the assist torque to be applied to the photosensitive drum 100 is corrected to the optimum assist torque after the print processing is started, not in the adjustment mode in which the main power source of the image forming apparatus is turned on. As a result, the assist torque can be corrected to the optimum assist torque, so that it is possible to prevent the occurrence of image defects such as color misregistration by eliminating the surface speed difference between the photosensitive drum and the ITB without reducing the productivity. it can. In addition, since the assist torque can be corrected before shifting to the actual printing operation, it is possible to continuously form good images without image defects by correcting the assist torque at appropriate times during the printing process as necessary. .

  Here, the assist torque correction value derivation process will be described.

  FIG. 14B is a flowchart showing the procedure of the assist torque correction value derivation process executed in step S2141 in FIG.

In FIG. 14B, when the assist torque correction value derivation process is started, the CPU 21 starts driving the photosensitive drum 100 and then waits for a predetermined time, for example, 0.2 seconds (step S2141A). Next, the CPU 21 samples the surface speed of the photosensitive drum 100 for 0.5 seconds, for example, and obtains an average value (step S2141B). This average value corresponds to the drum activation speed 526 in FIG. Note that ω _S obtained in FIG. 12D can also be used as the average value.

Next, the CPU 21 reads ω _S (hereinafter referred to as “ω _B ”) measured last time from the RAM 23 (step S2141C). The CPU 21 that has read ω _S then calculates ω _B / ω s as a correction coefficient, and multiplies the correction request by the duty ratio (Duty_D) at the time of startup to obtain a corrected duty ratio (Duty_C). (Step SS2141D). Next, the CPU 21 stores Duty_C and ω _S in the RAM 23 (step S2141E). Next, the CPU 21 changes the duty ratio of the PWM signal output to the motor driver IC 24 to Duty_C (step S2141F), and ends the assist torque correction value derivation process.

  The case where the assist torque is corrected based on the drum rotation speed when the drive start timing of the photosensitive drum 100 is started earlier by a predetermined time (ΔT531) than the drive start timing of the ITB 108 has been described. However, in the present embodiment, the drive stop timing of the photosensitive drum 100 can be delayed by a predetermined time with respect to the ITB 108 drive stop timing. That is, the assist torque is corrected based on the surface speed of the photosensitive drum 100 when the photosensitive drum 100 is rotationally driven only by the assist torque when the photosensitive drum 100 is stopped by being delayed by ΔT531. You can also.

  The second embodiment will be described below.

  FIG. 16 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to the second embodiment. The image forming apparatus 400 is an electrophotographic black-and-white digital copying machine or a multifunction machine.

  In FIG. 16, an image forming apparatus 400 is a one-drum image forming apparatus, and the configuration thereof is the same as that of the image forming apparatus according to the first embodiment except that four drums are changed to one drum. is there. Further, the drive configurations of the photosensitive drum 300 and the ITB 308 are the same as those shown in FIGS. This embodiment is different from the first embodiment in that the first embodiment drives the photosensitive drum 100 to be driven by the ITB 108, whereas the present embodiment does not use the ITB 108. This is the point that the photosensitive drum 100 is driven. Such a driven drive system can be realized by using one drum.

  In the present embodiment, the method for realizing the driven drive is the same as the method described in the first embodiment. That is, in the case of the present embodiment, the assist torque is applied to the BLDC motor 30b so that the constant component of the load generated on the ITB 108 drive roller 310 is canceled by the assist torque. The method for deriving the assist torque can be realized by performing the method performed on the photosensitive drum 100 in the same manner with respect to the ITB 108 in the first embodiment. The assist torque correction method is the same as the method performed in the first embodiment, and can be realized by performing the method performed on the photosensitive drum 100 on the ITB 108.

  According to the present embodiment, the assist torque to be applied to the ITB 108 is corrected to the optimum assist torque after the print processing is started, not in the adjustment mode in which the main power source of the image forming apparatus is turned on. As a result, it is possible to prevent the occurrence of image defects such as color misregistration by eliminating the surface speed difference between the photosensitive drum and the ITB without reducing productivity.

100 Photosensitive drum 106 Surface position detector 108 Intermediate transfer belt (ITB)
10 Host CPU
20 Controller 21 CPU
22 ROM
23 RAM
24 Motor driver IC
25 Drive circuit 30 Brushless DC motor (BLDC motor)
31 Rotation position detection unit 32 Motor gear 40 Rotary encoder 50 Drum shaft 51 Reduction gear 60 ASIC
61 Laser driver 70 Roller shaft 505 Driven area 506 Non-driven area 522 Assist torque 532 Image formation period

Claims (22)

A rotatable image carrier;
An intermediate transfer member rotating in contact with the image carrier;
First driving means for rotationally driving the image carrier;
Second driving means for rotationally driving the intermediate transfer member;
Assist torque deriving means for deriving an assist torque for causing the first driving means to cancel the load torque acting on the image carrier with respect to the image carrier;
Correction means for correcting the assist torque derived by the assist torque deriving means;
Control means for controlling the first drive means and the second drive means,
The control unit applies the assist torque corrected by the correction unit to the first driving unit, so that the image supporting unit is driven by the intermediate transfer unit. An image forming apparatus that controls the image forming apparatus.   2. The assist torque deriving unit derives the assist torque within a predetermined period immediately after the main power is turned on, and the correction unit corrects the assist torque before starting a printing operation. Image forming apparatus. Exposure means for forming an electrostatic latent image on the image carrier;
Surface position detecting means for detecting the surface position of the image carrier;
Have
3. The image forming apparatus according to claim 1, wherein the exposure unit forms the electrostatic latent image on the surface of the image carrier in synchronization with the surface position of the image carrier by the surface position detection unit. apparatus. The assist torque deriving means includes
The predetermined torque in a region where the surface speed of the image carrier does not change even if the assist torque applied to the image carrier during image formation is changed is derived as the assist torque. The image forming apparatus according to claim 1. The assist torque deriving means includes
5. The image forming apparatus according to claim 4, wherein a median value in a region where the surface speed of the image carrier does not change is derived as the assist torque. The assist torque correction means includes
The drive start timing of the image carrier is made a predetermined time earlier than the drive start timing of the intermediate transfer member, and immediately after the image carrier starts to rotate, the rotation speed of the image carrier is rotated only by the driving force of the assist torque. 6. The image forming apparatus according to claim 1, wherein the assist torque is corrected based on a detection value.   7. The predetermined time is longer than a time for which the image carrier rotates at least once after reaching a constant rotational speed when the image carrier rotates only by the assist torque. The image forming apparatus described in 1. The assist torque correction means includes
The drive stop timing of the image carrier is delayed by a predetermined time from the drive stop timing of the intermediate transfer member, and after the intermediate transfer member stops rotating, the image carrier is only driven by the driving force by the assist torque. The image forming apparatus according to claim 1, wherein the assist torque is corrected based on a detection value of a rotation speed when rotating.   The predetermined time is longer than the time at which the image carrier is rotated at least once after the image carrier is not driven in the rotational direction by the intermediate transfer member from the drive stop timing of the intermediate transfer member. The image forming apparatus according to claim 8.   The image forming apparatus according to claim 6, wherein the rotation speed of the image carrier is derived from an average value of values sampled at a predetermined interval within the predetermined period. A rotatable intermediate transfer member;
An image carrier that rotates in contact with the intermediate transfer member;
Second driving means for rotationally driving the intermediate transfer member;
First driving means for rotationally driving the image carrier;
Assist torque deriving means for deriving assist torque for causing the second drive means to cancel load torque acting on the intermediate transfer member with respect to the intermediate transfer member;
Correction means for correcting the assist torque derived by the assist torque deriving means;
Control means for controlling the second drive means and the first drive means,
The control unit applies the assist torque corrected by the correction unit to the second transfer unit, so that the intermediate transfer unit is driven by the image carrier. An image forming apparatus that controls the image forming apparatus.   12. The assist torque deriving unit derives the assist torque within a predetermined period immediately after the main power is turned on, and the correcting unit corrects the assist torque before starting a printing operation. Image forming apparatus. Exposure means for forming an electrostatic latent image on the image carrier;
Surface position detecting means for detecting the surface position of the image carrier;
Have
13. The image forming apparatus according to claim 11, wherein the exposure unit forms the electrostatic latent image on the surface of the image carrier in synchronization with the surface position of the image carrier by the surface position detection unit. apparatus. The assist torque deriving means includes
14. The predetermined torque in a region where the surface speed of the image carrier does not change even if the assist torque applied to the image carrier during image formation is changed is derived as the assist torque. The image forming apparatus according to claim 1. The assist torque deriving means includes
The image forming apparatus according to claim 14, wherein a median value in a region where the surface speed of the image carrier does not change is derived as the assist torque. The assist torque correction means includes
The drive start timing of the intermediate transfer member is made a predetermined time earlier than the drive start timing of the image carrier, and immediately after the intermediate transfer member starts rotating, the rotation speed of the intermediate transfer member is rotated only by the driving force of the assist torque. The image forming apparatus according to claim 11, wherein the assist torque is corrected based on a detection value.   17. The predetermined time is longer than a time during which the intermediate transfer member rotates at least once after reaching a constant rotational speed when the intermediate transfer member rotates only by the assist torque. The image forming apparatus described in 1. The assist torque correction means includes
After the drive stop timing of the intermediate transfer member is delayed by a predetermined time from the drive stop timing of the image carrier, and after the image carrier stops rotating, the intermediate transfer member is driven only by the driving force by the assist torque. The image forming apparatus according to claim 11, wherein the assist torque is corrected based on a detection value of a rotation speed at the time of rotation.   The predetermined time is longer than the time at which the intermediate transfer member rotates at least once after the intermediate transfer member does not receive the driving force in the rotation direction by the image carrier from the drive stop timing of the image carrier. The image forming apparatus according to claim 18.   20. The image forming apparatus according to claim 16, wherein the rotation speed of the intermediate transfer member is derived from an average value of values sampled at predetermined intervals within the predetermined period. ROM that records the assist torque at the time of shipment;
A RAM for recording the assist torque derived after shipment;
21. The correction unit according to claim 1, wherein when the assist torque is not recorded in the RAM, the correction unit performs the correction using the assist torque recorded in the ROM. The image forming apparatus described in 1.   The image forming apparatus according to any one of claims 1 to 21, wherein each of the first drive unit and the second drive unit is a low inertia type DC motor.