JP2014123037A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of a difference in surface speed between a photoreceptor drum and an ITB without increasing transfer pressure on a primary transfer unit so as to prevent the occurrence of image defects such as color shift.SOLUTION: A color digital copier 200 includes: rotatable photoreceptor drums 100Y to 100K; an ITB 108 that rotates in contact with the respective photoreceptor drums 100Y to 100K; a BLDC motor 30a that drives the photoreceptor drums and a BLDC motor 30b that drives the ITB 108; and a control unit 20 that controls the BLDC motor. The control unit 20 provides the BLDC motor 30a with assist torque for cancelling load torque acting on the BLDC motor 30a, so that the photoreceptor drums 100 are driven to be rotated by the rotation of the ITB 108.

Description

  The present invention relates to an electrophotographic image forming apparatus.

  In electrophotographic image forming apparatuses such as copying machines, multifunction machines, and facsimiles, the photosensitive drum and the intermediate transfer belt (ITB) that carry the toner image can be driven so that the surface speed is constant. It has been demanded. As a first reason, when the laser exposure for drawing an electrostatic latent image on the photosensitive drum is time-synchronized exposure, the laser irradiation position is deviated from the original irradiation position due to fluctuations in the surface speed of the photosensitive drum. Can be mentioned. The second reason is that in the primary transfer process of transferring the toner image formed on the photosensitive drum to the ITB, if there is an AC difference between the surface speeds of the photosensitive drum and the ITB, the toner transferred onto the ITB. For example, the image may be shifted from the position where the image should be transferred. That is, when the surface speeds of the photosensitive drum and ITB are not constant, the image finally formed on the recording paper has a periodic position called image misalignment, for example, color misregistration or banding caused by misregistration between colors. There is a problem that deviation occurs.

  For this reason, the driving of the photosensitive drum and the ITB is secured at high constant speed by performing speed feedback control of a motor as a driving source using various speed detection sensors. As the drive 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, for example, a method in which a rotary encoder is arranged on the drum shaft and the BLDC motor is controlled so that the rotation speed of the drum shaft is constant is adopted.

  However, although 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 applies to ITB, and similar problems occur due to the eccentricity of the ITB drive roller shaft that drives the ITB, poor accuracy of the roller diameter, uneven ITB thickness, and the like.

  On the other hand, the cause of image defects is mutual interference due to 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 recording paper is a thick paper during the secondary transfer to transfer the toner image carried on the ITB onto the recording paper, a sudden load fluctuation occurs on the ITB, resulting in a high-speed speed fluctuation. However, this speed fluctuation may cause a position 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.

  Accordingly, 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 an intermediate transfer belt). 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 on the basis of the position on the photosensitive drum, the influence of 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.

JP 2002-333752 A

  However, as described in Patent Document 1, in order to drive the photosensitive drum appropriately (without slipping) by the intermediate transfer belt by friction, the transfer pressure of the primary transfer portion must be increased. When the transfer pressure at the primary transfer portion is increased, the load generated on the photosensitive drum and ITB increases and the driving torque increases, and the surface speed between the photosensitive drum and ITB tends to be different, resulting in image defects such as color misregistration. There's a problem.

  Therefore, the present invention prevents image defects such as color misregistration and the like by preventing a difference in surface speed between the photosensitive drum and ITB without increasing the transfer pressure of the primary transfer portion. An object is to provide an apparatus.

  In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention includes a rotatable image carrier, an intermediate transfer member that rotates in contact with the image carrier, and a rotary drive for driving the image carrier. 1 drive means, second drive means for rotationally driving the intermediate transfer member, and control means for controlling the first drive means and the second drive means, wherein the control means comprises: The first driving means controls the image carrier so as to apply a torque for canceling a load torque acting on the image carrier.

  According to a second aspect of the present invention, there is provided an image forming apparatus comprising: a rotatable image carrier; an intermediate transfer member that rotates in contact with the image carrier; and a first driving unit that rotationally drives the image carrier. A second drive unit that rotates the intermediate transfer member; and a control unit that controls the first drive unit and the second drive unit. The control unit is configured by the second drive unit. Control is performed such that torque for canceling load torque acting on the intermediate transfer member is applied to the intermediate transfer member.

  According to the present invention, it is possible to prevent a difference between the surface speeds of the photosensitive drum and the ITB without increasing the transfer pressure of the primary transfer portion, and to prevent the occurrence of image defects such as color misregistration.

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. 3 is a flowchart of assist torque derivation processing using the image forming apparatus of FIG. 1. 3 is a flowchart illustrating print processing using the image forming apparatus of FIG. 1. It is an enlarged view showing the positional relationship between the surface position detecting means and the photosensitive drum. It is sectional drawing 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 (hereinafter referred to as “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 rollers 110 to 112 and rotates so as to abut on 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 roller 110 is a driving 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 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 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 P by the fixing device 114. It is fixed and discharged out of the device. 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 24a. Further, the controller 20 performs a calculation for speed control based on the signal of the rotary encoder 40a. The motor driver IC 24a performs phase switching of the phase current flowing through the BLDC motor 30a of the drive circuit 25a and adjustment of the amount of current based on the control signal from the controller 20 and the rotational position signal from the rotational position detection means 31a. 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.

  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.

  The ITB 108 is driven by rotationally driving an ITB drive roller 110 installed so as to be in contact with the inside of the ITB 108. A motor shaft gear 32b is engaged with the ITB drive roller shaft 70 via a reduction gear 51b, and a rotary encoder 40b for detecting the rotational speed of the ITB drive roller shaft 70 is provided. 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 electrical configuration is the same as that of the photosensitive drum 100 of FIG. The ITB 108 is not provided with a surface position detection means.

  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 speed from the speed detection signal from the rotary encoder 40 (40a, 40b). Further, the controller 20 performs general control calculations such as proportional control, differential control, and integral control written in the ROM 22 based on the comparison between the calculated speed and the target process speed, and the corresponding photosensitive drum 100 or ITB 108. Speed feedback control is 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. Also, the primary charging devices 105Y to 105K, the developing devices 102Y to 102K, the primary transfer rollers 107Y to 107K, the ITB drive roller 110, the secondary transfer inner roller 111, the fixing device 114, and the like are activated.

  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 onto the ITB 108 by corresponding primary transfer rollers 107Y to 107K 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 such an image forming apparatus 200, the photosensitive drums 100 </ b> Y to 100 </ b> K are driven by the ITB 108 to control the surface speed of the photosensitive drums 100 </ b> Y to 100 </ b> K and the surface speed of the ITB 108 to be always the same.

  Hereinafter, the driven drive will be described.

  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, a primary transfer roller 107 is disposed so as to come into contact with an arbitrary photosensitive drum 100 among the plurality of photosensitive drums in the image forming apparatus 200 via the ITB 108, and a driven drive unit is formed. Further, a surface position detecting means 106 is provided so as to face the photosensitive drum 100.

  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 coincide with each other by rotating the photosensitive drum 100 with the ITB 108.

  FIG. 6 is a diagram for explaining the load torque generated in the photosensitive drum 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 refers to a value obtained by adding together the load torque generated by, for example, the blade of the cleaner 104, the drum bearing portion, and the like in the rotation operation of the photosensitive drum 100 during the image forming process. On the other hand, a friction torque between the drum and ITB (hereinafter simply referred to as “friction torque”) is generated on the contact surface between the photosensitive drum 100 and the ITB 108. 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, the timing of the remaining toner entering the blade of the cleaner 104, and the like. 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.

  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 steady 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 speed fluctuation 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.

  The relationship of FIG. 9 is shown as follows using the equation of motion.

ここで、Ｔ_Ｆは摩擦トルク、Ｊはドラムイナーシャ、ｄω／ｄｔは角加速度、Ｔ_Ｌは負荷トルク、Ｔ_ＡＳはアシストトルク、ΔＴ_Ｌは変動トルク成分である。

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

The above equation (2) indicates that the photosensitive drum 100 follows the ITB 108 if the friction torque (T _F ) is larger than the sum of the acceleration torque of the first term on the right side and the fluctuation torque of the second term on the right side. .

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.

  Here, although the friction torque is closely related to the toner transfer process in the primary transfer, it is difficult to change the friction torque, but it is relatively easy to reduce the acceleration torque by reducing the drum inertia. . The drum inertia represents the total load that rotates 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. At this time, the rotor inertia of the BLDC motor 30 a may be much larger than the inertia component of the photosensitive drum 100 on the drum shaft 50. Therefore, an inner rotor type low inertia type is used as the BLDC motor 30a. As a result, an increase in the rotor inertia can be prevented and the photosensitive drum 100 can be effectively driven by the ITB 108. That is, it is preferable to apply a low inertia type brushless DC motor as a driving source of the photosensitive drum 100. In addition, as long as it is a low inertia type and can generate a constant torque, it is not particularly limited to a BLDC motor.

  Hereinafter, a method for deriving the assist torque in the driven drive system will be described.

  The load torque in the photosensitive drum 100 varies according to a plurality of process speeds such as handling thick paper in the image forming apparatus. Therefore, it is preferable that the assist torque for canceling the load torque is derived in advance according to the process speed.

  Generally, when the main power supply is turned on to the image forming apparatus, the state is first called an adjustment mode. In the adjustment mode, temperature adjustment of the fixing roller of the fixing device, main scanning tilt correction, color correction, and the like are performed. Then, when the adjustment mode is completed, the state shifts to a print mode state in which a print operation is possible.

  In the present embodiment, a sequence for deriving the assist torque is provided in the adjustment mode. In the assist torque deriving sequence in the adjustment mode, the host CPU 10 issues a command to remove the primary transfer roller 107 by controlling a driver IC (not shown) of a stepping motor that moves the primary transfer roller up and down. This is to eliminate the influence of friction at the primary transfer portion. The host CPU 10 controls various devices that perform an image forming process, such as the exposure device 101, the primary charging device 105, and the developing device 102, and issues a drive command for the photosensitive drum 100.

  The assist torque is for canceling the load torque, and is obtained from the torque value generated in the BLDC motor 30a. As a motor driver IC 24a (see FIG. 2) that controls the BLDC motor 30a, a driver IC that determines a phase current flowing through the BLDC motor 30a by a PWM signal is applied. The PWM signal is a pulse width modulation signal, which is a rectangular wave signal with a fixed period, and the ratio between the high level section and the low level section (duty ratio: the high level section divided by the low level section). The phase current is adjusted. When the duty ratio is large, the amount of current flowing through the phase increases. Conversely, when the duty ratio is small, the amount of current flowing through the phase decreases. The magnitude of the phase current is equivalent to the torque generated in the motor, and the magnitude of the phase current is proportional to the duty ratio. Therefore, the duty ratio can be considered as torque generated in the motor.

  As a premise for deriving the assist torque, first, the primary transfer roller 107 is in a state of being detached from the intermediate transfer belt 108. Further, the assist torque is derived during the image forming process in which there is an influence of the interference between the primary charging device 105, the developing device 102, and the toner and the blade of the cleaner 104. Since the load torque component in the image forming process is sufficiently smaller than the load component that is constantly generated, the image forming apparatus may be in an idling state when the assist torque is derived.

  FIG. 10 is a flowchart showing assist torque derivation processing in the image forming apparatus of FIG. The assist torque derivation process is executed by the CPU 21 that has received a command from the host CPU 10 according to an assist torque derivation procedure that is an assist torque derivation program.

  When the assist torque derivation process is started, the CPU 21 first inputs a process speed set value, an assist derivation on command, etc. as an assist torque derivation command signal from the host CPU 10 (step S1). Next, the CPU 21 selects a process speed for deriving the assist torque according to the thickness of the corresponding paper P or the like (step S2).

  After selecting the process speed, the CPU 21 outputs a control signal to the motor driver IC 24 to perform speed feedback control of the photosensitive drum 100 at a predetermined process speed, thereby starting driving of the photosensitive drum 100 (step S3). .

The CPU 21 that has started driving the photosensitive drum 100 stands by until a predetermined time (time T1) has elapsed since the photosensitive drum 100 started driving (step S4). After the predetermined time has elapsed, the CPU 21 starts sampling the duty ratio of the PWM signal of the photosensitive drum 100 and stores the sampling value in the RAM 23 (step S5). Here, the N-th sampled value and P _N.

  Next, the CPU 21 continues the sampling until the sampling number stored in the RAM 23 reaches the predetermined sampling number (= N) (step S6), and stops the sampling after reaching the predetermined sampling number (= N). (Step S7). After the sampling is completed, the upper CPU 10 stops the primary charging device 105, the exposure device 101, and the developing device 102.

  Next, the CPU 21 rotates each photosensitive drum 100 once or twice, outputs a drive stop command, and stops driving (step S8). The reason why each photosensitive drum 100 is rotated once or twice is to remove the toner on the photosensitive drum 100 by the cleaner blade 104.

  Next, the CPU 21 calculates the average value of the sampled duty ratio (P) based on the following equation (3) (step S9).

ここで、Ｐ_ａｖｅは、ＰＷＭデューティの平均値、Ｐ_Ｎは、Ｎ個目のサンプリングデータ、Ｎは、サンプリング数である。

Here, P _ave is the average value of the PWM duty, _PN is the Nth sampling data, and N is the number of samplings.

Next, the CPU 21 stores the average value (P _ave ) in the RAM 23 (step S10). Thereby, the derivation of the assist torque at one process speed is completed.

  Next, the CPU 21 determines whether or not the assist torque needs to be derived even at another process speed (step S11). If the assist torque needs to be derived ("YES" in step S11), the CPU 21 performs steps S2 to S2. The process of S10 is repeated. On the other hand, when the derivation of the assist torque for all the process speeds is completed and the derivation of the assist torque at another process speed is unnecessary (“NO” in step S11), the CPU 21 ends the assist torque derivation process.

  According to the process of FIG. 10, the duty ratio (P) at a predetermined process speed is sampled a plurality of times, and the average value is taken. Thereby, the duty ratio (P) at the process speed, that is, the assist torque for canceling the load torque can be accurately derived.

  Next, the operation of the CPU 21 during the printing operation will be described.

  When a print command from a user interface (UI) or a PC is input to the upper CPU 10, each device constituting the image forming apparatus is controlled by the upper CPU 10. The operation of the CPU 21 that has received a control command from the host CPU 10 will be described with reference to FIG.

  FIG. 11 is a flowchart showing print processing using the image forming apparatus of FIG. This print processing is executed by the CPU 21 that has received a command from the host CPU 10 in accordance with a print processing procedure that is a print processing program.

  In FIG. 11, when the printing process is started, the CPU 21 inputs drive command signals for the photosensitive drum 100 and the ITB 108 from the host CPU 10 (step S101). Examples of the drive command signal include a process speed signal and a drive on signal.

  Next, the CPU 21 selects a fixed PWM corresponding to the process speed in the print process from a plurality of duty ratios (hereinafter referred to as “fixed PWM”) derived in the assist torque deriving process of FIG. 10 (step S102). ).

  Next, the CPU 21 outputs a drive-on signal and a fixed PWM signal to the motor driver IC 24a, and starts driving the photosensitive drum 100 while applying an assist torque corresponding to the fixed PWM to the photosensitive drum 100. Further, the CPU 21 starts driving the ITB 108 by the speed feedback control by the rotary encoder 40a and performs the printing process (step S103). In this printing process, the load torque acting on the photosensitive drum 100 in the printing process can be canceled, and a printing operation in which the photosensitive drum 100 rotates following the rotation of the ITB 108 by the friction torque is realized. When the photosensitive drum 100 is driven by the ITB 108, occurrence of misregistration, color misregistration associated with the misregistration, and banding, which is a periodic misregistration, can be avoided, and favorable image formation can be performed.

  Here, the operation of the surface position detecting means in the printing operation will be described.

  The surface position detecting means 106 is provided so as to face the surface of the photosensitive drum 100 as shown in FIG.

  FIG. 12 is an enlarged view showing the positional relationship between the surface position detecting means and the photosensitive drum.

  In FIG. 12, mark patterns are formed on the surface of the photosensitive drum 100 at equal intervals in advance. The mark pattern is formed outside the image forming area of the photosensitive drum 100. The surface position detecting means 106 includes a reflective photoelectric sensor, which irradiates light toward the surface of the photosensitive drum 100 and detects the reflected light reflected by the mark pattern. Detect mark patterns. Accordingly, the sensor output is switched between the place with the mark pattern and the place without the mark pattern. Then, by providing a threshold value for an appropriate voltage, the output waveform becomes a rectangular wave. Therefore, by determining a reference position on the surface of the photosensitive drum 100 and counting the rectangular wave number from the reference position, the surface position on the photosensitive drum 100 can be specified and detected with an accuracy determined by the resolution of the mark pattern. .

  The surface position detector 106 detects the surface position of the photosensitive drum 100 and outputs the detection result to the ASIC 60 (see FIG. 5). The ASIC 60 adjusts the exposure timing in the laser driver 61 in response to a command from the upper CPU 10 and a detection result from the surface position detection means 106. The exposure apparatus 101 irradiates the photosensitive drum 100 with laser light generated at a predetermined timing by the laser driver 61 to form an electrostatic latent image.

  By performing exposure control (sub-scanning synchronized exposure) in synchronization with the surface position of the photosensitive drum 100 based on the detection result of the surface position detecting means 106, accurate exposure according to the surface position of the drum can be performed. Accordingly, an electrostatic latent image having no positional deviation is formed on the photosensitive drum 100. The formed electrostatic latent image becomes a toner image by the developing device, and a plurality of toner images are superimposed on the ITB 108 to become a color image. The color image is transferred to the paper P and fixed on the paper P by the downstream fixing device 114.

  Returning to FIG. 11, the CPU 21 that has finished a certain printing operation (step S <b> 103) determines whether or not a stop signal is input from the host CPU 10 (step S <b> 104), and prints until the stop signal is input from the host CPU 10. To continue. On the other hand, when a stop signal is input from the host CPU 10, the CPU 21 stops driving the photosensitive drum 100 and the ITB 108 (step S105) and ends the printing process.

  According to the process of FIG. 11, when executing the print process, the load torque corresponding to the process speed in the print process can be canceled by the assist torque, so that the photosensitive drum 100 is driven and driven by the intermediate transfer belt 108. Can do. As a result, it is possible to prevent the occurrence of banding, which is color misregistration and periodic misregistration due to misregistration, and to execute good print processing.

  In the present embodiment, the rotary encoder 40 is used for deriving the assist torque. However, as long as the rotational speed or surface speed of the photosensitive drum 100 can be detected, a rotary encoder other than the rotary encoder may be applied.

  Next, a second embodiment will be described.

  FIG. 13 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 a monochrome digital copying machine using an electrophotographic system, and is a one-drum apparatus.

  In FIG. 13, the configuration of the image forming apparatus 400 is the same as that of the image forming apparatus of FIG. Accordingly, the driving configuration of the photosensitive drum 300 and the ITB 308 is the same as that of the image forming apparatus 200 of FIG.

  The image forming apparatus 400 is different from the image forming apparatus 200 in FIG. 1 in that the driven drive system, that is, the apparatus in FIG. 1 drives the photosensitive drum 100 in accordance with the ITB 108, whereas the apparatus in FIG. Are different in that they are driven by the photosensitive drum 300. Such a driven drive system can be realized when the image forming apparatus 300 has one drum.

  In the present embodiment, the method for realizing the driven drive is essentially the same as in the first embodiment described above. That is, in the present embodiment, assist torque (assist force) is applied to a corresponding BLDC motor (not shown) so that the steady component of the load torque generated on the ITB 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 first embodiment in the same manner on the ITB 308. During image formation, the ITB 308 is driven by a fixed PWM signal, and the photosensitive drum 300 is driven by speed feedback control based on a speed detection signal from a corresponding rotary encoder. As a result, it is possible to realize driving in which the surface speed of the ITB 308 follows the surface speed of the photosensitive drum 300.

  According to the present embodiment, the ITB drive roller 310 is provided with assist torque for canceling the load torque acting on the ITB drive roller 310. Accordingly, the ITB 308 can be driven and driven by the photosensitive drum 300 by the friction torque between the photosensitive drum 300 and the ITB 308. Accordingly, the surface speeds of the photosensitive drum 300 and the ITB 308 can be always controlled to be the same, and a good image can be formed by preventing the occurrence of misregistration, color misregistration due to misregistration, and banding that is periodic misregistration. can do.

100, 300 Photosensitive drum 101, 301 Exposure device 102, 302 Developing device 103, 303 Developing sleeve 104, 304 Cleaner 105, 305 Charging device 106 Surface position detecting means 107, 307 Primary transfer roller 108, 308 Intermediate transfer belt (ITB)
109, 309 ITB cleaners 110, 310 ITB drive rollers 111, 311 Secondary transfer inner rollers 113, 313 Secondary transfer outer rollers 114, 314 Fixing device 10 Upper CPU
20 Controller 21 CPU
22 ROM
23 RAM
24a, 24b Motor driver IC
25a, 25b Drive circuits 30a, 30b Brushless DC motor (BLDC motor)
31 Rotation position detection means

Claims (7)

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;
Control means for controlling the first drive means and the second drive means,
The control means applies the torque for the first driving means to cancel the load torque acting on the image carrier to the image carrier, so that the image carrier is moved by the intermediate transfer member. An image forming apparatus that is controlled to be driven. 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;
Control means for controlling the first drive means and the second drive means,
The control unit applies the torque for the second driving unit to cancel the load torque acting on the intermediate transfer member, so that the intermediate transfer member is moved by the image carrier. An image forming apparatus that is controlled to be driven. Surface position detecting means for detecting the position of the surface of the image carrier, and exposure means for forming an electrostatic latent image on the surface of the image carrier,
3. The image forming apparatus according to claim 1, wherein the exposure unit exposes the surface of the image carrier in synchronization with the surface position of the image carrier by the surface position detection unit.   4. The load torque according to claim 1, wherein the load torque is an average value of a load torque generated in the first driving unit for rotating the image carrier during image formation. Image forming apparatus.   The image forming apparatus according to claim 4, wherein the load torque does not include a friction torque generated on a contact surface between the image carrier and the intermediate transfer member during image formation.   The image forming apparatus according to claim 1, wherein the first driving unit is a low inertia type DC motor.   3. The image forming apparatus according to claim 2, wherein the second driving unit is a low inertia type DC motor.

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