JP2016085281A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device capable of forming an excellent image by preventing image banding, color shifting, etc., resulting from that an actual shape of a photoreceptor is different from a designed shape.SOLUTION: An image formation device comprises: a rotatable photoreceptor drum 100; an exposing device which exposes the photoreceptor drum 100 to form an electrostatic latent image; a developing device which develops the electrostatic latent image to form a toner image; an ITB to which the toner image formed on the photoreceptor is transferred as the ITB rotates abutting on the photoreceptor; a rotary encoder which detects an angular velocity of the photoreceptor: acquiring means of acquiring a radius R of the photoreceptor; correcting means of correcting the angular velocity of the photoreceptor drum 100 detected by the rotary encoder using the radius R of the photoreceptor; and control means of performing control so that the exposing device exposes the photoreceptor drum 100 in synchronism with the angular velocity having been corrected.SELECTED DRAWING: Figure 16

Description

  The present invention relates to an image forming apparatus capable of preventing image defects caused by fluctuations in the surface speed of a rotating photoconductor caused by the fact that the actual shape of the photoconductor is different from the designed shape.

  2. Description of the Related Art Image forming apparatuses such as an electrophotographic color copying machine and a color complex machine that include a plurality of photosensitive drums arranged in a tandem structure and transfer an image formed on each photosensitive drum to an intermediate transfer belt are known.

  In such an image forming apparatus, it is required to drive the photosensitive drum and the intermediate transfer body (ITB) so that the surface speeds are constant as a premise for preventing color misregistration of the image. As the first reason, when the exposure for drawing the electrostatic latent image on the photosensitive drum is time-synchronized exposure, the laser irradiation position is originally irradiated by the fluctuation of the surface speed of the photosensitive drum. It is possible to deviate from the position. 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 speeds of the photosensitive drum and the ITB, the toner transferred onto the ITB For example, the image may deviate from the position where it should originally be transferred.

  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 of arranging a rotary encoder on the drum shaft of the photosensitive drum and controlling the BLDC motor so that the rotation speed of the drum shaft is constant has been adopted. Yes.

  However, the speed feedback control described above detects the rotational speed of the drum shaft, but the surface speed of the drum is affected by the eccentricity of the drive gear shaft that transmits the drive of the photosensitive drum, drum motor, and motor to the drum, mounting tolerances, etc. It may not be a constant speed. The same applies to ITB, and similar problems occur due to eccentricity and mounting tolerances of the ITB drive roller, ITB motor, and drive gear shaft.

  On the other hand, the cause of image defects includes 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 the speed fluctuation generated 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 variation may cause a positional shift in the primary transfer. As described above, there are various causes for image defects, and it is very difficult to solve all of them.

  Therefore, 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) (see, for example, Patent Document 1). 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 drum and the image on the ITB is ensured. There is an advantage that image defects are hardly generated in transfer. However, in order to obtain the first merit, it is important to form an image based on the rotational position of the photosensitive drum. Therefore, a technique for performing exposure control in synchronization with the rotational movement amount of the drum has been developed (see, for example, Patent Document 2).

JP 2002-333752 A JP-A-8-99437

  The technique of Patent Document 2 performs exposure control in synchronization with the rotational movement amount of the photosensitive drum. According to this technique, there is no displacement on the drum even if the rotational movement amount of the drum varies. Since an electrostatic latent image can be drawn, fluctuations in the rotational movement amount of the photosensitive drum are allowed.

  However, if the drum shape is distorted due to the eccentricity of the photosensitive drum shaft, molding tolerance of the photosensitive drum, etc., the rotational movement amount does not represent the movement distance of the drum surface, and as a result, an equally spaced pitch is drawn on the drum. Banding may occur in the transferred image because the image cannot be printed. In addition, when the radii between the drums are different in the tandem structure, a difference in circumferential length occurs between the drums. Therefore, there is a problem in that a color shift based on the difference in circumferential length occurs every time the photosensitive drum makes one round.

  The present invention provides an image forming apparatus capable of forming a good image by preventing image banding, color misregistration, and the like caused by the actual shape of a photoconductor being different from a design shape. For the purpose.

  In order to achieve the above object, an image forming apparatus according to claim 1, a rotatable photoconductor, an exposure unit that exposes the photoconductor to form an electrostatic latent image, and develops the electrostatic latent image. Developing means for forming a toner image, an intermediate transfer member that rotates in contact with the photosensitive member and to which the toner image formed on the photosensitive member is transferred, and an angular velocity detector that detects the angular velocity of the photosensitive member. An acquisition unit that acquires the shape information of the photoconductor, an angular velocity correction unit that corrects the angular velocity of the photoconductor detected by the angular velocity detection unit using the shape information of the photoconductor acquired by the acquisition unit, and the exposure And means for controlling the photosensitive member to be exposed in synchronization with the corrected angular velocity obtained by correcting the angular velocity of the photosensitive member detected by the angular velocity detecting unit by the angular velocity correcting unit. Characterize

  According to the present invention, the exposure unit exposes the photosensitive member in synchronization with the corrected angular velocity obtained by correcting the angular velocity of the photosensitive member detected by the angular velocity detecting unit by the angular velocity correcting unit. As a result, exposure control can be performed in synchronization with the surface movement distance of the photoconductor, so that an equally spaced pitch can be drawn on the photoconductor, resulting in eliminating image banding and color misregistration on the recording paper. A good image can be formed.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an 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. It is a figure for demonstrating the driven drive system in which the photosensitive drum in FIG. 1 rotates following ITB. FIG. 6 is a diagram showing a change over time in load torque generated on the drum shaft of the photosensitive drum in FIG. 5. It is a figure which shows the state by which the load torque which arises in the drum axis | shaft in FIG. 5 was canceled by assist torque. FIG. 6 is a diagram showing the relationship between the sum of acceleration torque and fluctuating torque components in the photosensitive drum of FIG. 5 and the friction torque over time. 3 is a flowchart showing a procedure of assist torque derivation processing in the image forming apparatus of FIG. 1. FIG. 2 is a view showing an arrangement of exposure apparatuses in the image forming apparatus of FIG. 1. It is a figure which shows the structure of the LED head in the exposure apparatus of FIG. It is a block diagram which shows the control structure of exposure apparatus. It is a figure which shows the connection state of the LED element and LED driver circuit of the LED head in FIG. It is a figure which shows the structure of the rotary encoder applied in embodiment. It is a diagram for explaining the calculation process for obtaining the surface velocity (V _S) of the photosensitive drum based on the detected value of the rotary encoder. 6 is a flowchart illustrating a procedure of drum shape correction processing at sub-scan synchronized exposure timing during a printing operation. It is a timing chart of drum shape correction control. It is a figure which shows the distance L from the exposure irradiation position in each photosensitive drum to a primary transfer position, and the distance D between photosensitive drums. FIG. 6 is a diagram for explaining the start timing of exposure control for each photosensitive drum in a plurality of image forming units. FIG. 6 is a diagram illustrating an angle θ composed of an exposure irradiation position A and a primary transfer position B on the photosensitive drum. 6 is a timing chart showing a relationship between an image formation start signal and an exposure start timing in an image forming unit corresponding to each color. FIG. 4 is a diagram illustrating an image leading end position of a photosensitive drum in an image forming unit corresponding to each color. It is a flowchart which shows the procedure of the sub scanning exposure process in a printing process. 6 is a flowchart illustrating a procedure of a photosensitive drum and ITB control process in a print process.

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

  FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment. The image forming apparatus 300 is an electrophotographic color digital copying machine. In addition to the copying machine, the image forming apparatus 300 may be a multifunction machine or a facsimile, or may be a monochrome digital copying machine, a multifunction machine, or a facsimile instead of a color.

  In FIG. 1, an image forming apparatus 300 includes photosensitive drums 100Y, 100M, 100C, and 100K respectively corresponding to colors of yellow (Y), magenta (M), cyan (C), and black (K). An image forming unit is provided. The photosensitive drums 100Y to 100K as the photosensitive members are respectively rotatable, and are provided with encoders 7Y to 7K as angular velocity detecting means. Each of the photosensitive drums 100Y to 100K rotates 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. Yes. The developing devices 102Y to 102K include corresponding developing sleeves 103Y, 103M, 103C, and 103K. The image forming unit also includes cleaners 104Y, 104M, 104C, and 104K corresponding to the photosensitive drums 100Y to 100K, respectively.

  The primary charging devices 105Y to 105K uniformly charge the surfaces of the corresponding photosensitive drums 100Y to 100K, respectively. The exposure devices 101Y to 101K form electrostatic latent images by exposing the surfaces of the charged photosensitive drums 100Y to 100K based on image information. Further, the developing devices 102Y to 102K develop the electrostatic latent images formed on the surfaces of the corresponding photosensitive drums 100Y to 100K using developing sleeves (sleeve members) 103Y to 103K that respectively contain the corresponding chromatic toner. Thus, a toner image corresponding to each color is formed.

  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 provided 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 abuts 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 tension roller 110 is a driving roller that drives the ITB 108, and is provided with a rotary encoder 7ITB as an angular velocity detection means. The tension roller 110 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 in contact with the opposing secondary transfer outer roller 113. The toner image on the ITB 108 is transferred onto the sheet S at the contact portion between the inner and outer secondary transfer rollers 111 and 113, and the sheet S on which the toner image is transferred is carried into the fixing device 114 on the downstream side. The toner image is fixed on the paper S by 114. The sheet S on which the toner image is fixed is sent out from the fixing device 114 and discharged outside the image forming apparatus 300. 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 drum shaft 9 of the photosensitive drum 100 is mechanically connected to the reduction gear shaft 8 through a coupling 9a. The reduction gear shaft 8 is engaged with the motor shaft gear 11a via the reduction gear 10a. The reduction gear shaft 8 and the reduction gear 10a are fixed and connected by a joining mechanism (not shown). The reduction gear shaft 8 is provided with a rotary encoder 7DRM for detecting the angular velocity. The angular velocity detection value by the rotary encoder 7DRM is used, for example, to derive assist torque.

  The photosensitive drum 100 includes a host CPU 1, a controller 2, a motor driver IC 3a, a drive circuit 4a, a rotational position detector 6a, and a BLDC motor 5a as a photosensitive member driving unit as control components. The host CPU 1 collectively controls the start timing, stop timing, and various other set values of each process (charging, exposure, development, primary transfer, etc.) in the image forming process. In the assist torque derivation flow, the controller 2 includes a PID controller in order to perform angular velocity feedback control by the rotary encoder 7DRM. The controller 2 outputs a command signal from the host CPU 1, such as a drive on / off signal, a target speed signal, a register set value signal, a PWM value signal, and the like as control signals to the motor driver IC 3a. Further, the controller 2 performs a calculation for speed control based on the signal of the rotary encoder 7DRM.

  Based on the control signal from the controller 2 and the rotational position signal from the rotational position detector 6a, the motor driver IC 3a performs phase switching and adjustment of the amount of current flowing through the BLDC motor 5a of the drive circuit 4a. The BLDC motor 5a rotationally drives the drum shaft 8 via the motor shaft gear 11a and the reduction gear 10a. That is, the driving force from the BLDC motor 5a as the first driving source is transmitted to the reduction gear shaft 8 by the engagement of the motor shaft gear 11a and the reduction gear 10a, and the drum shaft 9 and the photosensitive drum 100 are coupled via the coupling 9a. Is transmitted to. The BLDC motor 5a is, for example, a low inertia type brushless DC motor.

  FIG. 3 is a diagram showing a drive 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 roller shaft 12 of the ITB drive roller 110 is engaged with the motor shaft gear 11b via the reduction gear 10b. The ITB roller shaft 12 and the reduction gear 10b are fixed and connected by a joining mechanism (not shown). The ITB roller shaft 12 is provided with a rotary encoder 7ITB for detecting the angular velocity.

  The ITB 108 includes a host CPU 1, a controller 2, a motor driver IC 3b, a drive circuit 4b, a rotational position detection unit 6b, and a BLDC motor 5b as an intermediate transfer member driving unit as control components. The ITB 108 is driven by the angular velocity feedback control of the detected value by the rotary encoder 7ITB. The angular velocity feedback control is performed by the controller 2 so that the difference between the target velocity commanded by the host CPU 1 (hereinafter referred to as “process velocity”) and the value detected by the rotary encoder 7ITB converted to the process velocity is small. Controlled by internal PID controller.

  The driving force from the BLDC motor 5b, which is the second driving source for driving the ITB 108, is decelerated by the meshing of the motor shaft gear 11b and the reduction gear 10b, via the roller shaft 12, as in the case of the photosensitive drum 100. Is transmitted to the ITB drive roller 110. The electrical configuration is the same as that of the photosensitive drum 100 of FIG.

  Next, the internal configuration of the controller 2 in FIGS. 2 and 3 will be described. FIG. 4 is a diagram showing an internal configuration of the controller in FIGS. 2 and 3.

  In FIG. 4, the controller 2 is mainly configured by a CPU 13 and a ROM 14 and a RAM 15 connected to the CPU 13, respectively. The CPU 13 that controls the driving of the photosensitive drum 100 is configured to perform angular velocity feedback control from a detection value of the rotary encoder 7DRM by a PID controller (not shown) when the assist torque is derived. Further, the CPU 13 is configured to output a PWM signal having a predetermined duty ratio corresponding to the derived assist torque to the motor driver IC 3 (a, b) during the image forming process.

  In the image forming apparatus of FIG. 1, the photosensitive drum 100 is configured to follow and drive the ITB 108. The driven drive means that the photosensitive drum 100 is driven and driven by the ITB 108 by using a 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. 5 is a diagram for explaining a driven drive system in which one photosensitive drum 100 in FIG. 1 is rotated by following ITB 108.

In FIG. 5, a load torque (T _L ) generated on the drum shaft 9 of the photosensitive drum 100 at a predetermined process speed and a transfer portion friction torque (T _F ) are visually shown. One surface of the ITB 108 contacts the photosensitive drum 100 to form a driven drive unit. A primary transfer roller 107 is disposed at a position facing the photosensitive drum 100 via the ITB 108.

The friction torque (T _F ) at the primary transfer portion where the ITB 108 and the photosensitive drum 100 abut is obtained by converting the friction force at the primary transfer portion into torque on the drum shaft 9 of the photosensitive drum 100. A load torque (T _L ) is always generated in the photosensitive drum 100 in a direction opposite to the rotation direction due to frictional forces of the blades of the cleaner 104 and the bearings of the rotating shaft. The load torque (T _L ) is a value obtained by adding together load torques generated due to, for example, the blades 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. The load torque (T _L ) does not include the friction torque (T _F ). Since the load torque (T _L ) is much larger _than the maximum value (T _FMAX ) of the friction torque (T _F ) (T _L >> T _FMAX ), only the friction torque (T _F ) is sensitive. The drum 100 cannot be driven and driven by the ITB 108.

FIG. 6 is a diagram showing a change with time of the load torque (T _L ) generated on the drum shaft 9 of the photosensitive drum 100 of FIG. The load torque (T _L ) is not always constant, and changes transiently depending on the timing at which a high voltage for charging is applied, the timing at which the transfer residual toner enters the blade of the cleaner 104, and the like. It is known that such a transient change component (hereinafter referred to as “torque fluctuation component”) is sufficiently small with respect to a constant load torque (T _L ). In order to rotate the photosensitive drum 100 following the ITB 108, it is effective to eliminate the load torque (T _L ).

In the present embodiment, the rotational torque generating means (for example, the BLDC motor 5a) applies the same amount of rotational torque as the DC component of the load torque (T _L ) to the photosensitive drum 100 in the opposite direction, so that the photosensitive drum 100 is reversed. The load torque (T _L ) generated above is canceled out. The rotational torque for canceling the load torque (T _L ) is called assist torque.

FIG. 7 is a diagram showing a state in which the load torque (T _L ) generated in the drum shaft 9 in FIG. 5 is offset by the assist torque. In FIG. 7, the steady component of the load torque (T _L ) is offset by the assist torque applied to the photosensitive drum 100, and only the fluctuating torque component (ΔT _L ) acts substantially.

By offsetting the steady component of the load torque (T _L ) with the assist torque (T _AS ), the fluctuation torque, which is the load torque component, compared to the friction torque (T _F ) acting on the contact surface between the photosensitive drum 100 and the ITB 108. The component (ΔT _L ) becomes smaller. As a result, the photosensitive drum 100 is driven in synchronization with the speed fluctuation of the ITB 108. That is, if the AC fluctuation torque component (the remaining component obtained by canceling the load torque with the assist torque) is equal to or less than the maximum value of the frictional torque (T _F ) of the transfer portion, the photosensitive drum 100 is driven to be driven by the ITB 108. become.

  However, it is necessary to ensure that the photosensitive drum 100 rotates following the AC speed fluctuation of the ITB 108. In this embodiment, the product of the drum inertia and acceleration on the drum shaft 9 of the photosensitive drum 100 is required. Is also taken into account.

That is, the sum of the acceleration torque and the fluctuation torque component on the photosensitive drum 100 and the friction torque (T _F ) between the photosensitive drum 100 and the ITB 108 always satisfy the following equations of motion (1) and (2): A driven drive in which the photosensitive drum 100 is driven by the ITB 108 is realized.

ここで、Ｔ_Ｆは転写部の最大摩擦トルク、Ｊは等価ドラムイナーシャ、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はトルク変動成分である。

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

The above formulas (1) and (2) are obtained by generating a rotational torque having the same amount as the DC component of the load torque (T _L ) as an assist torque (T _AS ) in the opposite direction to the load torque. This shows that the amount of torque that the friction torque ( _TF ) should bear is reduced.

  Here, the acceleration torque is expressed by multiplying the equivalent inertia on the drum shaft 9 (hereinafter referred to as “equivalent drum inertia”) and the angular acceleration of the photosensitive drum 100. Note that the angular acceleration of the photosensitive drum 100 is a value determined from the surface speed fluctuation component at the primary transfer portion of the ITB 108. The equivalent drum inertia represents the total rotating load as an inertia component on the drum shaft 9.

FIG. 8 is a graph showing the relationship between the fluctuation torque component and the friction torque in the photosensitive drum of FIG. 5 over time. In FIG. 8, the sum of the torque fluctuation component (ΔT _L ) and the acceleration torque is always smaller than the maximum value of the friction torque (T _F ) of the transfer portion.

Basically, the torque fluctuation component (ΔT _L ) is so small that it can be ignored. Therefore, in order to increase the followability in a portion other than the assist torque, it is conceivable to increase the maximum friction torque or decrease the acceleration torque. . The maximum friction torque is not easily changed because it is closely related to the toner transfer process in the primary transfer. On the other hand, lowering the acceleration torque can be realized relatively easily by reducing the equivalent drum inertia. The inertia component of the BLDC motor 5a added to the drum shaft 9 is greatly influenced by the gear ratio between the reduction gear 10 and the motor shaft gear 11, 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 5 a becomes much larger than the inertia component of the photosensitive drum 100 on the drum shaft 9. For this reason, the BLDC motor 5a in the present embodiment uses an inner rotor type low inertia type. As a result, the equivalent drum inertia can be greatly reduced, and the resulting acceleration torque is also greatly reduced.

In this way, the assist torque is applied to the drum shaft 9 to cancel the DC component of the load torque, and the motor having a low inertia component is selected, so that the photosensitive drum 100 is subjected to the friction torque (T _F ) of the transfer portion. Can be driven by the ITB 108. In the present embodiment, the BLDC motor 5a is used as an assist torque generation source. However, the assist torque generation source is not particularly limited to the BLDC motor as long as a constant torque can be generated.

  Hereinafter, a method for deriving the assist torque to be applied to the drum shaft 9 of the photosensitive drum 100 in order to drive the photosensitive drum 100 to follow the ITB 108 in the image forming apparatus 300 of FIG. 1 will be described.

  The image forming apparatus 300 first enters the 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 inclination correction, inter-color correction, and the like are performed.

  A sequence for deriving the assist torque is provided during the adjustment mode. The image forming apparatus 300 includes a plurality of process speeds because it can handle not only plain paper but also cardboard. Therefore, it is necessary to derive the assist torque according to each process speed.

  The assist torque is for canceling the load torque, and is obtained by measuring the load generated on the drum shaft 9. In the present embodiment, the load generated on the drum shaft 9 is obtained from the torque value generated in the BLDC motor 5a.

  As a motor driver IC 3a (see FIG. 2) that controls the BLDC motor 5a, a driver IC that determines the amount of phase current flowing through the BLDC motor 5a by using a PWM signal is used. Note that the PWM signal is a pulse width modulation signal, which is a rectangular wave signal with a fixed period, and a phase current based on a duty ratio determined by a high level time width (high level section divided by PWM period). 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. Here, 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 separated from the ITB 108. Second, since it is necessary to detect the load torque on the drum shaft 9 generated during the image forming process, the target process speed for actually executing the image forming process is controlled. It should be noted that the torque fluctuation component of the load in the image forming process is sufficiently small with respect to the load component that is constantly generated, and therefore, the idling torque may be idle when the assist torque is derived.

  In the assist torque deriving process during the adjustment mode, the host CPU 1 first issues a command to release the primary transfer roller 107 to a driver IC (not shown) of a stepping motor that moves the primary transfer roller up and down. Next, the host CPU 1 secondly controls various devices that execute the image forming process such as the exposure device 101, the primary charging device 105, and the developing sleeve 103, and thirdly issues a drive command for the photosensitive drum 100.

  FIG. 9 is a flowchart showing a procedure of assist torque derivation processing in the image forming apparatus of FIG. The assist torque deriving process is executed by the CPU 13 that has received a command from the host CPU 1 in accordance with an assist torque deriving procedure that is an assist torque deriving program.

  When the assist torque derivation process is started, the CPU 13 first receives a process speed set value, an assist derivation on command, etc. as an assist torque derivation command signal from the host CPU 1 (step S1). Next, the CPU 13 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 13 outputs a control signal to the motor driver IC 3a 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 13 that has started driving the photosensitive drum 100 stands by until a predetermined time (T1 time) has elapsed since the photosensitive drum 100 started driving (step S4). Then, after a predetermined time has elapsed, the CPU 13 starts sampling of the duty ratio of the PWM signal of the photosensitive drum 100 and stores the sampling value in the RAM 15 (step S5). Here, for example, the N-th sampled value and P _N.

  Next, the CPU 13 continues the sampling until the sampling number stored in the RAM 15 reaches the predetermined sampling number (N) (step S6), and stops the sampling after reaching the predetermined sampling number (N) (step S6). S7). After the sampling is completed, the upper CPU 1 stops the primary charging device 105, the exposure device 101, and the developing device 102.

  Next, the CPU 13 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 with the blade of the cleaner 104.

  Next, the CPU 13 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 13 stores the average value (P _ave ) in the RAM 15 (step S10). This completes the derivation of the assist torque at one process speed. Next, the CPU 13 determines whether or not the assist torque needs to be derived even at another process speed (step S11). If it is necessary to derive the assist torque (“YES” in step S11), the CPU 13 performs steps S2 to S2. The process of S10 is repeated. On the other hand, when it is not necessary to derive the assist torque at another process speed (“NO” in step S11), the CPU 13 ends the assist torque derivation process.

According to the process of FIG. 9, 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 (T _AS ) for canceling the load torque (T _L ) can be accurately derived.

  The assist torque derivation process in FIG. 9 is performed in a state where the contact between the photosensitive drum 100 and the ITB 108 is removed from the primary transfer portion, but the same amount of torque as the DC component of the load torque generated on the photosensitive drum 100 is derived. If possible, it is not limited to this state.

  Next, the exposure apparatus 101 that exposes the surface of the photosensitive drum 100 in the image forming apparatus 300 to form an electrostatic latent image on the surface of the photosensitive drum 100 will be described.

  FIG. 10 is a view showing an arrangement example of the exposure apparatus 101 in the image forming apparatus 300 of FIG. In FIG. 10, the LED head 101 a of the exposure apparatus 101 is supported and fixed by a support member (not shown) at a position facing the photosensitive drum 100 by a predetermined distance D. As shown in FIG. 11, the LED head 101 a is composed of minute LED element arrays (LED1 to N) arranged in parallel along the main scanning direction.

  12 is a block diagram showing a control configuration of the exposure apparatus 101, and FIG. 13 is a diagram showing a connection state between the LED elements and the LED driver circuit 101b in the LED head 101a of FIG. 12 and 13, the exposure apparatus 101 includes an LED head 101a, an LED driver circuit 101b that drives each LED element, and a light amount adjustment unit 101c. The light amount adjustment unit 101c is connected to the ASIC 50, and the ASIC 50 is connected to the host CPU 1, the rotary encoder 7DRM, the rotary encoder 7ITB, and the controller 60, respectively. An LED driver circuit 101b that drives LED1, which is an LED element, includes a transistor 101b_1 and a resistor 101b_2.

  Next, exposure control using the exposure apparatus 101 having such a configuration will be described.

  Exposure control in the sub-scanning direction in the exposure apparatus 101 in the image forming apparatus 300 is performed in synchronization with the angular velocity of the photosensitive drum 100 as a detection value of the rotary encoder 7DRM. This is because exposure control is performed in synchronization with the rotational speed of the photosensitive drum 100, thereby avoiding misalignment during exposure due to fluctuations in the surface speed as the angular speed of the photosensitive drum 100 that occurs in the case of time synchronization.

  In FIG. 12, the ASIC 50 divides the image data sent from the controller 60 into image data corresponding to each color of Y, M, C, and K, and is arranged from the image data in the main scanning direction of the LED head 101a. The amount of light emitted to each LED element is calculated. The amount of light emission is adjusted by the light emission time. The ASIC 50 starts and stops exposure by inputting an LED exposure start timing, an LED exposure stop timing, and an exposure enable signal from the host CPU 1. That is, light emission time information corresponding to each LED element is output from the ASIC 50 to the light amount adjustment unit 101c by the CLK signal and the PWM signal. The light amount adjusting unit 101c sequentially selects the base of the transistor 101b_1 constituting the LED driver circuit 101b from the LED 1 by the CLK signal. Then, an electrostatic latent image corresponding to the image data is formed in the main scanning direction by a PWM signal that determines the ON time of the base voltage of the selected LED.

Here, an exposure control method in the sub-scanning direction in the exposure apparatus 101 will be described. The image forming apparatus 300 is configured to form 600 dpi image data on a recording sheet, for example. Since the resolution is 600 dpi, the line-to-line distance (ΔL) in the sub-scanning direction is 2.54 cm divided by 600, that is, about 42.3 μm. This ΔL is defined as the target pitch interval of the distance between lines in the sub-scanning direction. On the other hand, the angular velocity of the photosensitive drum 100 is derived in a form converted from the detection value of the rotary encoder 7DRM into the surface velocity (V _S ), and the exposure timing (Δt) in the sub-scanning direction is calculated as ΔL / V _S. .

  FIG. 14 is a diagram showing a configuration of a rotary encoder applied in the present embodiment. In FIG. 14, the rotary encoder 7 faces the wheel 7a, the photosensors 7b and 7c arranged so as to face each other at the outer peripheral portion of the wheel 7a, and the side surface inside the outer peripheral portion of the wheel 7a. A photosensor 7d is provided. The photosensor 7b and the photosensor 7c are arranged so as to detect slits 7e formed at equal intervals around the outer circumference of the wheel 7a. Further, the photosensor 7d is configured to detect a slit 7f provided only at one place in the inner circumference of the wheel 7a.

The wheel 7a is fixed to a reduction gear shaft (reference numeral 8 in FIG. 2 and reference numeral 12 in FIG. 3), and the photosensor 7b, the photosensor 7c, and the photosensor 7d are fixed at predetermined positions by members that are not shown. ing. The number of slits of the wheel slit 7e is N _SLIT . The rotational speed detection by the rotary encoder 7 is processed by the controller 2 using the average value of the detection values of the photosensor 7b and the photosensor 7c.

Hereinafter, a calculation process for converting the detected value of the photosensor 7b and the photosensor 7c into the surface speed V _S will be described with reference to FIG.

FIG. 15 is a diagram for explaining a calculation process for obtaining the surface speed (V _S ) of the photosensitive drum 100 based on the detection value of the rotary encoder 7DRM.

In FIG. 15, when the drum 100 starts to rotate, a rectangular wave pulse is generated by the photosensor 7b and the photosensor 7c that detect the slit 7e. A signal output while the photosensors 7b and 7c detect the slit 7e is a HIGH signal, and a signal output while the slit 7e is not detected is a LOW signal. The HIGH signal and the LOW signal are output from the photosensor 7b and the photosensor 7c to the controller 2, respectively. The controller 2 detects the rising signal at which the detection signals in the photosensors 7b and 7c are switched from LOW to HIGH, and further calculates the time (T _ENC ) between the rising edges by counting the intervals of the rising signals. . In _{timing T ENC} photosensor 7b and the photo sensor 7c is established, the average value of _{T ENC} in both the photosensor _{(T ENCAVE)} is derived.

In FIG. 15, section A and section B are speed detection sections, and the controller 2 obtains times (T _ENC ) corresponding to the sections A ′ and B ′ in order to detect the surface speed of the photosensitive drum 100. In addition, when deriving the average value of detection values (detection time), the controller 2 calculates | requires as a result of having detected the rising of the output of the photosensor 7b previously. Such a _{T ENCAVE} calculated in the radius (design value) of the drum 100, and the slit number of the wheel slit 7e of the rotary encoder 7DRM based on _{(N SLIT),} the photosensitive drum 100 by the following equation (4) The surface speed V _S is calculated.

ここで、Ｒは、ドラムの半径（設計値）、Ｔ_{ＥＮＣＡＶＥ}は、ロータリーエンコーダ７ＤＲＭの検出値（時間）である。

Here, R is the radius of the drum (design value), and T _ENCAVE is the detection value (time) of the rotary encoder 7DRM.

As described above, the sub scanning exposure timing interval Δt in the exposure apparatus 101 is obtained by dividing ΔL, which is the target sub scanning direction pitch interval, by the obtained V _S.

ここで、Δｔは、副走査露光タイミング間隔、ΔＬは、目標副走査方向ピッチ間隔、Ｖ_Ｓは、ロータリーエンコーダ７ＤＲＭ検知値から求めた感光ドラム１００の表面速度である。

Here, Δt is the sub-scanning exposure timing interval, ΔL is the target sub-scanning direction pitch interval, and V _S is the surface speed of the photosensitive drum 100 obtained from the detected value of the rotary encoder 7DRM.

  Therefore, if the radius R of the photosensitive drum 100 is as designed, the image data is faithfully reproduced on the photosensitive drum by performing the exposure in the sub-scanning direction at the timing interval Δt obtained by the equation (5). An accurate latent image can be formed.

However, when calculating the surface speed V _S of the photosensitive drum 100, in the above (4), and using the radius R of the drum 100, the drum radius R, such as the tolerance at the time of eccentricity and the drum molding drum It depends, and does not necessarily match the design value. For example, when the actual drum radius is 1% larger than the design value R (0.3 mm when R = 30 mm), the target sub-scanning direction pitch interval ΔL is also 1%, for example, 0. It changes by 423 μm. When this is converted to A3 paper length (420 mm), a deviation of about 4.2 mm is obtained, which is a conspicuous large value as a color deviation. Accordingly, in order to correct such color misregistration, it is necessary to correct the drum shape.

  Hereinafter, drum shape correction control based on a shaping error using the drum radius R will be described.

  FIG. 16 is a flowchart illustrating a procedure of drum shape correction processing at sub-scan synchronized exposure timing during a printing operation. The drum shape correction process is executed by an ASIC (integrated circuit) that controls the exposure apparatus 101 in accordance with a drum shape correction process procedure in a drum shape correction program stored in a storage medium (not shown).

In FIG. 16, first, the ASIC 50 starts drum shape correction processing by receiving a drive start signal for the drum 100 from the host CPU 1 (step S21). Next, the ASIC 50 stands by until a reference position of one round of the drum is detected by a pulse signal input from the photosensor 7d of the rotary encoder 7DRM provided on the reduction gear shaft 8 of the photosensitive drum 100 (step S22). The ASIC 50 that has detected the reference position (HP) around the drum then initializes the pulse number count value m of the photosensors 7b and 7c to 0 (step S23). Here, m is used for numbering for determining the number of pulses counted from the HP of the pulse interval T _ENCAVE (m) of the currently detected rotary encoder.

Next, the ASIC 50 initializes the division number k to 1 (step S24). Here, k, which is used in the calculation of the correction coefficient to be described later, division when the number of slits N _SLIT wheel slit 7e of the rotary encoder 7DRM, the value n of the divided is divided by the number of divisions is an integral This indicates the number of the area. k is a value in the range of 1 to N _SLIT / n, and is used for numbering to correspond to the correction coefficient H (k) when correcting the pulse interval T _ENCAVE (m) of the currently detected rotary encoder. Used.

Next, the ASIC 50 determines whether or not a rising edge has been detected based on the pulse signal input by the photosensor 7b (step S25). If the rising edge is detected as a result of the determination in step S25, the ASIC 50 ends the timer count of the pulse interval T _ENCAVE (m) that has started counting before detecting HP in step S22 (step S26). Next, the ASIC 50 multiplies T _ENCAVE (m) by the correction coefficient H (k) (step S27).

  Here, a method of calculating the correction coefficient H (k) will be described. The correction coefficient H (k) is preferably calculated in advance.

First, divide by the division number as the value n obtained by dividing the number of slits N _SLIT drum one revolution of the wheel slit 7e of the rotary encoder 7DRM any block is an integer. Then, the radius R of the drum 100 is measured for every n pulses of the slit 7e with reference to the slit 7f which is the home position position of the rotary encoder 7DRM, and a lookup table R (k) for the radius R of the drum 100 is created. Obtain and save as information. The radius R is measured by a Kochi method. The measurement method is not particularly limited. In addition, as a counting method of the measurement timing, even if the value n obtained by dividing the number of divisions into a predetermined value becomes an arbitrary real number, n is adjusted by rounding off or the like each time so that the accumulated pulse number becomes N _SLIT around the drum. However, the method is not particularly limited.

なお、補正係数Ｈ（ｋ）におけるｋは、この補正係数が、ドラム一周分のスリット数Ｎ_ＳＬＩＴを分割した際のｋ番目のブロックに対応する補正係数であることを示す。 The correction coefficient H (k) can be expressed as equation (6) from equation (5).

Note that k in the correction coefficient H (k) indicates that this correction coefficient is a correction coefficient corresponding to the kth block when the slit number N _SLIT for one round of the drum is divided.

Returning to FIG. 16, the ASIC 50 that multiplies T _ENCAVE (m) by the correction coefficient H (k) increments m so as to sequentially count pulses based on HP (step S28). Next, the ASIC 50 starts a timer count of the pulse interval T _ENCAVE (m) (step S29). Then, ASIC 50 _uses the division value n obtained by dividing the _{N SLIT} in a predetermined number, m and n × k to determine whether the current pulse interval _{T ENCAVE} (m) is in the ordinal number of the divided area coincides Whether or not (step S30). If they do not match, the operations in steps S25 to S29 are repeated until they match.

As a result of the determination in step S30, if m and n × k match (“YES” in step S30), that is, if the slit to be counted newly enters the next division, the ASIC 50 increments the division number k. (Step S31). Next, the ASIC 50 determines whether k and N _SLIT / n (= number of divisions) match in order to determine whether or not the current division number has reached the final division, that is, whether or not the drum has completed one round. (Step S32). As a result of the determination in step S32, if k and the number of divisions do not match, the operations in steps S25 to S31 are repeated until they match. If k and the number of divisions match ("YES" in step S32), the ASCI 50 repeats S22 to S32 until a drive stop signal for the drum 100 is received from the host CPU 1 (step S33). When the driving stop signal for the drum 100 from the host CPU 1 is detected (“YES” in step S33), the ASCI 50 ends the drum shape correction process.

  Such drum shape correction processing is executed at the following timing, for example.

FIG. 17 is a timing chart of drum shape correction control. In FIG. 17, first, when the photosensitive drum 100 is driven, the rotary encoder 7DRM detects the rotational movement amount of the photosensitive drum 100. Specifically, a pulse signal is output from the photosensor 7 d for each rotation of the photosensitive drum 100, and a pulse signal is output from the photosensor 7 b for each predetermined phase (= n / N _SLIT ) of the drum 100. Using the output signal of the photosensor 7d as a trigger, the number of pulses m is counted each time the output signal of the photosensor 7b is detected, and the pulse interval T _ENCAVE (m) counted by the timer is numbered. Further, while counting the number of pulses m, the correction coefficient is sequentially read out from the look-up table of the correction coefficient H (k) corresponding to the count pulse number measured in advance for each predetermined pulse number n, and the pulse interval T _ENCAVE (m) The drum shape is corrected by multiplying by. H (k) changes the reading position (number) every n pulses. That is, the drum shape is sequentially corrected with drum shape information corresponding to a predetermined phase section within the drum circumference. Note that such drum shape correction processing is executed for each of the photosensitive drums 100Y to 100K in an exposure process (latent image forming process) of the photosensitive drum 100 by the exposure apparatus 101 described below.

  Next, an exposure timing adjustment process for the corrected photosensitive drums 100Y to 100K after the drum shape is corrected will be described.

FIG. 18 is a diagram showing the distance L from the exposure irradiation position to the primary transfer position on each photosensitive drum and the distance D between the photosensitive drums. 18, the distance from the photosensitive drum 100Y to the photosensitive drum 100M is _{D YM,} the distance from the photosensitive drum 100Y to the photosensitive drum 100C is _{D YC,} the distance from the photosensitive drum 100Y to the photosensitive drum 100K has a _{D YK.} Distance from the exposure irradiation position of the photosensitive drum 100Y to the primary transfer position L _Y, the distance from the exposure irradiation position of the photosensitive drum 100M until the primary transfer position is in the L _M. The distance from the exposure irradiation position of the photosensitive drum 100C to the primary transfer position L _C, the distance from the exposure irradiation position of the photosensitive drum 100K to the primary transfer position is in the L _K. The inter-drum distance D does not change unless the drum is displaced, and can be considered as a fixed value. However, if the inter-drum distance D fluctuates in the subsequent calculation, it can be calculated in the same manner in consideration of the fluctuating distance.

  In general, the distance L from the exposure irradiation position of the photosensitive drum 100 to the primary transfer position is determined by factors such as the molding accuracy of the photosensitive drum 100, the eccentricity of the drum shaft 9, and the distance from the rotation center of the photosensitive drum 100 to the drum surface. Is not constant. That is, the distance L from the exposure irradiation position of the photosensitive drum 100 to the primary transfer position has a different value for each photosensitive drum 100 and each surface position.

FIG. 19 is a diagram for explaining the start timing of exposure control for each photosensitive drum in a plurality of image forming units. In FIG. 19, the vertical axis represents distance and the horizontal axis represents time. The distances L _Y , L _M , L _C , and L _K from the exposure position to the primary transfer position are variables that vary with one rotation period of the drum. Accordingly, each of the curves L _Y , L _M , L _C and L _K becomes a graph like a sine wave having periodicity. However, since the drum shapes of the plurality of photosensitive drums 100 provided are not the same, the period, phase, and amplitude are different. The L _Y is changed dynamically by time from the exposure irradiation position on the photosensitive drum 100Y, the photosensitive drum 100M, 100C, and the distance to the primary transfer position of 100K, dynamically changing to the respective time Is shown. Further, L _M , L _C , and L _K dynamically change with time because the distance from the exposure irradiation position on the photosensitive drums 100M, 100C, and 100K to the primary transfer position of the photosensitive drums 100M, 100C, and 100K. Indicates that each changes dynamically. Therefore, in order to align the leading edge of the image formed on each photosensitive drum, it is necessary to adjust the exposure timing of each color according to dynamically changing L _Y , L _M , L _C , and L _K.

  A method for adjusting the exposure timing of each photosensitive drum in the image forming unit corresponding to each color will be described below.

When the CPU 13 (see FIG. 4) that controls the photosensitive drum receives the image formation start signal from the host CPU 1, the exposure device 101Y starts exposure to the photosensitive drum 100Y. At the same time, _LY is calculated. Further, after the start of exposure in the exposure apparatus 101Y, the distances L _M , L _C and L _K from the exposure irradiation position of the photosensitive drum 100 to the primary transfer position are continuously calculated.

  Here, the distance L from the exposure irradiation position to the primary transfer position is calculated as follows. FIG. 20 is a diagram illustrating an angle θ formed by the exposure irradiation position A and the primary transfer position B with respect to the rotary encoder 7DRM in the photosensitive drum 100. The angle θ is a design value and is a predetermined fixed value. The slits 7e of the rotary encoder 7DRM are installed at equal intervals with respect to the circumference of the wheel 7a. That is, when the number of slits is 800, for example, the interval between the slits is 360 ÷ 800 = 0.45 °. Therefore, the number of slits with respect to the angle θ is a fixed value S. For example, when θ = 135 °, the number of slits S = 135 ÷ 0.45 = 300.

Here, the angle θ on the photosensitive drum of the image forming unit corresponding to each color is set to the same design value. That is, the number of slits S is a value common to the photosensitive drums 100Y to 100K. Therefore, when the encoder pulse edge number at a certain timing is _n , a value obtained by adding the surface distance (hereinafter simply referred to as “surface distance”) z _n along the circumferential direction of the photosensitive drum from n to n + S is the distance. L. Note that the encoder pulse edge number n depends on the rotation angle state of each photosensitive drum 100, and therefore differs for each photosensitive drum 100. Further, since the shape of the photosensitive drum 100 is different for each individual, the surface distances L _Y , L _M , L _C , and L _{K of} the photosensitive drum 100 corresponding to the encoder pulse number n of the photosensitive drum 100 are also different for each photosensitive drum.

The CPU 13 continues to calculate the moving distance of the photosensitive drum 100Y from the start of exposure based on the pulse edge number at the start of exposure of the exposure apparatus 101Y and the pulse edge input thereafter. Even if the speed of the photosensitive drum 100 or the ITB 108 changes, only the time interval of pulse edge input changes, and the number of pulse edges with respect to the distance does not change. Therefore, it is possible to accurately measure the moving distance regardless of the speed fluctuation. . Then, the moving distance starts exposure of the exposure device 101M at the timing when reaching the N _M, the moving distance starts exposure of the exposure apparatus 101C at a timing reaches N _C, at a timing when the movement distance reaches N _K Exposure of the exposure apparatus 101K is started. _Hereinafter, a calculation method of _{N M, N C, N K} .

Here, each symbol is as follows.
w _y : encoder pulse number corresponding to the photosensitive drum 100Y when the exposure apparatus 101Y starts exposure
w _m : encoder pulse number corresponding to the photosensitive drum 100M at a certain timing
w _c: encoder pulse number corresponding to the photosensitive drum 100C at a certain timing
w _k : encoder pulse number corresponding to the photosensitive drum 100K at a certain timing
Z _Yp : surface distance of the photosensitive drum 100Y corresponding to the slit p of the encoder 7Y Z _Mp : surface distance of the photosensitive drum 100M corresponding to the slit p of the encoder 7M Z _Cp : surface of the photosensitive drum 100C corresponding to the slit p of the encoder 7C Distance Z _Kp : Surface distance L _Y of the photosensitive drum 100K corresponding to the slit p of the encoder 7K: Surface distance L _M from the exposure irradiation position of the photosensitive drum 100Y to the primary transfer position L _M : Primary from the exposure irradiation position of the photosensitive drum 100M Surface distance L _C to the transfer position: Surface distance L _K from the exposure irradiation position of the photosensitive drum 100C to the primary transfer position L _K : Surface distance from the exposure irradiation position of the photosensitive drum 100K to the primary transfer position D _YM : Photosensitive drum 100Y a photosensitive drum 100M of the primary transfer position distance _{D YC:} photosensitive drums 100Y Primary transfer position distance _{D YK} the photosensitive drum 100C: between the primary transfer position of the photosensitive drum 100Y and the photosensitive drum 100K distance

_{Z Yn, Z Mn, Z Cn} , Z Kn, D YM, D YC, D YK is previously stored in the ROM 14. L _Y is calculated by the CPU 13 every time an encoder pulse edge is input when L _M , L _C , L _K, N _M, N _{C, and} N _K are input when an image formation start signal is received.

FIG. 21 is a timing chart showing the relationship between the image formation start signal and the exposure start timing in the image forming unit corresponding to each color. In FIG. 21, the exposure ENB signal of the photosensitive drum 100Y is output after the ty time has elapsed after receiving the image formation start signal, and the exposure ENB signal of the photosensitive drum 100M is output after the lapse of tm time. Further, the exposure ENB signal of the photosensitive drum 100C is output after elapse of tc time after receiving the image formation start signal, and the photosensitive drum 100K exposure ENB signal is output after elapse of tk time. Here, tm is a timing when the photosensitive drum 100Y moves a distance N _M from the image formation start signal, and tc is a timing when the photosensitive drum 100Y moves a distance N _C from the image formation start signal. Further, tk is the time when the photosensitive drum 100Y is the distance N _K moves from the image formation start signal.

  FIG. 22 is a diagram illustrating the image leading edge position of the photosensitive drum in the image forming unit corresponding to each color. In FIG. 22, the image leading edge position of the photosensitive drum 100Y is represented by 200Y, and the image leading edge position of the photosensitive drum 100M is represented by 200M. FIG. 22A shows the image leading edge position after the ty time has elapsed after receiving the image formation start signal. The image leading end position 200Y of the photosensitive drum 100Y exists at the exposure irradiation position of the photosensitive drum 100Y. The image leading edge positions of the photosensitive drums 100M, 100C, and 100K do not exist because they are not exposed at this time.

FIG. 22B shows the position of the leading edge of the image after elapse of tm time after receiving the image formation start signal. The image leading end position 200M of the photosensitive drum 100M is present at the exposure irradiation position of the photosensitive drum 100M. Further, the image leading end position 200Y of the photosensitive drum 100Y exists on the intermediate transfer body, that is, on the ITB 108. The distance from the image tip position 200Y to the primary transfer position of the photosensitive drum 100M is equal to the distance _{L M} of the exposure start position of the photosensitive drum 100M until the primary transfer position. The image leading edge positions of the photosensitive drums 100C and 100K do not exist because they are not exposed at this time.

  FIG. 22C shows a state when the image leading end position 200Y of the photosensitive drum 100Y reaches the primary transfer position of the photosensitive drum 100M. The image leading edge position 200Y of the photosensitive drum 100Y and the image leading edge position 200M of the photosensitive drum 100M reach the primary transfer position of the photosensitive drum 100M at the same timing, and the image leading edge position of the photosensitive drum 100Y and the image leading edge position of 100M are the same. You can see that they overlap exactly. Note that the exposure timing of the image leading edge of the photosensitive drum 100C and the image leading edge of the photosensitive drum 100K is the same as that of the photosensitive drum 100M, and is omitted because only the coefficients of the calculation formula are different.

In Figure _{22, D YM, D MC,} D CK , respectively _{L M,} L C, has been described in case _{L K,} greater than, even if not, the formula (7), (8) If the image forming operation is performed based on the value calculated from the equation (9), the position of the leading edge of the image can be accurately adjusted.

  As described above, the sub-scanning image writing positions (image transfer start positions) in the ITB 108 of the photosensitive drums 100Y to 100K in the image forming units of the respective colors are aligned, and the sub-scanning writing position intervals of the respective colors vary with the speed of the photosensitive drum 100. Even if there is, it will always be constant. Accordingly, it is possible to eliminate color misregistration in a color image formed by transfer to the ITB 108, and as a result, it is possible to eliminate image color misregistration on the recording paper.

  Next, print processing by the image forming apparatus 300 in FIG. 1 including the above-described photosensitive drum shape correction and exposure timing adjustment processing will be described.

  FIG. 23 is a flowchart showing the sub-scanning exposure process in the printing process. This sub-scanning exposure process is executed by the ASIC 50 in FIG.

  In FIG. 23, as a premise of the sub-scanning exposure process, when the controller 60 receives a print operation command from the user, the controller 60 outputs various process control start command signals to the host CPU 1. At this time, the controller 60 transmits image data to the ASIC 50, and the ASIC 50 receives the image data from the controller 60 (step S41). Next, the ASIC 50 decomposes the image data into image data for controlling the exposure apparatuses 101Y to 101K corresponding to the Y, M, C, and K photosensitive drums 100Y to 100K (step S42).

  Next, the ASIC 50 stands by until an exposure start signal is received from the host CPU 1 (step S43). When the ASIC 50 receives the exposure start signal (“YES” in step S43), the ASIC 50 outputs a ΔCLK signal and a control signal of the PWM signal to the exposure apparatus 101Y to start image formation (step S44). Subsequent sub-scanning exposure timings follow Δt obtained by the above equation (5). As a result, exposure with the shape correction applied to the photosensitive drum 100Y is performed.

Next, the ASIC 50 counts the moving distance of the photosensitive drum 100Y at every rising edge of the pulse signal from the rotary encoder 7Y provided on the photosensitive drum 100Y (step S45). Then, ASIC 50 is moved a distance count value of the rotary encoder 7Y waits until the target count value _{N M} derived by Equation (7) (step S46). When the travel distance count value becomes _{N M} ( "YES" in step S46), ASIC 50 is, DerutaCLK signal to the exposure device 101M, and outputs a control signal of the PWM signal and starts image formation (step S47). Subsequent sub-scanning exposure timings follow Δt obtained by the above equation (5). As a result, exposure with the shape correction applied to the photosensitive drum 100M is performed.

Then, ASIC 50 is moved a distance count value of the drum rotary encoder 7Y waits until the target count value _{N C} derived by Equation (8) (step S48). When the movement distance count value becomes N _C (YES in step S48), the ASIC 50 outputs a ΔCLK signal and a PWM signal control signal to the exposure apparatus 101C and starts image formation (step S49). Subsequent sub-scanning exposure timings follow Δt obtained by the above equation (5). As a result, exposure with the shape correction applied to the photosensitive drum 100C is performed.

Then, ASIC 50 is moved a distance count value of the drum rotary encoder 7Y waits until the target count value _{N K} derived by Equation (9) (step S50). When the travel distance count value becomes _{N K} (YES at step S50), ASIC 50 is, DerutaCLK signal, and starts the image formation and outputs the control signal of the PWM signal to the exposure device 101K (step S51). Subsequent sub-scanning exposure timings follow Δt obtained by the above equation (5). As a result, exposure with the shape correction applied to the photosensitive drum 100K is performed.

  Next, the ASIC 50 waits until an exposure stop signal is received from the host CPU 1 (step S52). After receiving the exposure stop signal (YES in step S52), the control of the exposure apparatus 101 is stopped (step S53). The process ends.

  According to the processing of FIG. 23, the first distance from the exposure irradiation position to the transfer position on the photosensitive drum 100, the second distance between the rotation axis of the reference photosensitive member and the rotation shaft of the other photosensitive member, are detected by the rotary encoder 7. The timing of exposing each photoconductor is controlled by using the number of pulses. As a result, the transfer position of the latent image formed on the photoconductor corresponding to each color to the ITB 108 can be matched, so that a good image without color misregistration can be formed. The second distance is obtained based on the interval between the photoconductors.

  When the print process of FIG. 23 is executed, the photosensitive drum 100 and the ITB 108 are controlled as follows. FIG. 24 is a flowchart showing the procedure of the photosensitive drum and ITB control process in the printing process. This photosensitive drum and ITB control process is executed by the CPU 13 of the controller 2 in FIG.

  In FIG. 24, first, the CPU 13 receives various process control start command signals from the host CPU 1 to start print processing (step S61). Next, the CPU 13 feeds back the detected value input from the rotary encoder 7ITB to the angular velocity, and outputs various control signals to the ITB motor driver IC 3b so as to start driving the ITB 108 (step S62). Further, the CPU 13 outputs various control signals to the drum motor driver IC 3a so as to start driving the photosensitive drum 100 with the fixed PWM value obtained in the assist torque deriving sequence and stored in the RAM 15 (step S63).

  Next, the CPU 13 waits until a drive stop signal is received from the host CPU 1 (step S64). Then, after receiving the drive stop signal (YES in step S64), the CPU 13 outputs a drive stop signal to the drum motor driver IC3a and the ITB motor driver IC3b so as to stop driving the photosensitive drum 100 and the ITB 108 (step S64). S65). After outputting a drive stop signal to the drum motor driver IC3 and the ITB motor driver IC3b to stop the driving of the photosensitive drum 100 and the ITB 108, the CPU 13 ends this processing.

  24, the ITB 108 is feedback-controlled based on the detection value of the rotary encoder 7ITB, and the photosensitive drum 100 is driven by the ITB 108 by adding the assist force obtained in the assist force deriving sequence to the photosensitive drum 100. Accordingly, in combination with the effects obtained by the processing of FIG. 23, the images on the photoconductors 100Y to 100K corresponding to the respective colors can be transferred to the ITB 108 without causing color misregistration. Therefore, it is possible to form an image with no color misregistration.

In the present embodiment, the moving distances N _M , N _C , and N _K from the exposure start timing are calculated using the rotary encoder 7Y attached to the photosensitive drum 100Y. However, when the ITB 108 and the photosensitive drums 100 of the respective colors are driven, all the movement distances are always the same, and therefore the movement distances may be calculated using other photosensitive drums 100 or ITBs 108.

  In the present embodiment, the position accuracy can be further improved by selecting a rotary encoder having a higher resolution.

  In the present embodiment, the radius R of the drum 100 is used as a parameter for correcting the drum shape. However, a surface distance along the outer peripheral surface of the drum 100 can be applied instead of the drum radius R. Examples of the method for measuring the surface distance of the drum 100 include a method of directly measuring the drum surface distance using a laser distance meter, an ultrasonic distance sensor, or a three-dimensional distance image camera.

For example, the value n of the total number of slits N _SLIT divided by any integer wheel slit 7e of the rotary encoder 7DRM in FIG 14 is the division number such that the integer. Next, the surface distance of the drum 100 in the n-pulse section of the slit 7e is measured with reference to the slit 7f that is the home position of the rotary encoder 7DRM, and the lookup table S (k) of the surface distance of each section corresponding to the division number k. Create and save. Here, k is a division number and takes a value ranging from 1 to N _SLIT / n. In addition, as a counting method of the measurement timing, even if the value n obtained by dividing the number of divisions into a predetermined value becomes an arbitrary real number, n is adjusted by rounding off or the like each time so that the accumulated pulse number becomes N _SLIT around the drum. However, the method is not particularly limited. After measuring the surface shape of the drum 100, those values are converted into a correction coefficient H (k). The correction coefficient H (k) can be expressed as in Expression (10) from Expression (5) described above.

  Hereinafter, the drum shape may be corrected using the correction coefficient H (k) obtained by Expression (10) in accordance with the flowchart of the drum shape correction process of FIG.

1 Host CPU
2 Controller 3a, 3b Motor driver IC
4a, 4b Drive circuit 5a, 5b BLDC motor 6a, 6b Rotational position detector 7DRM Rotary encoder 7ITB Rotary encoder 8 Reduction gear shaft 9 Drum shaft 10a, 10b Reduction gear 11a, 11b Motor shaft gear 12 ITB roller shaft 13 CPU
50 ASIC
60 Controller 100 Drum 101 Exposure Device 108 Intermediate Transfer Belt (ITB)

Claims (8)

A rotatable photoreceptor,
Exposure means for exposing the photoreceptor to form an electrostatic latent image;
Developing means for developing the electrostatic latent image to form a toner image;
An intermediate transfer member to which the toner image formed on the photosensitive member is transferred by rotating in contact with the photosensitive member;
Angular velocity detection means for detecting the angular velocity of the photoreceptor;
Obtaining means for obtaining shape information of the photoreceptor;
Angular velocity correcting means for correcting the angular velocity of the photosensitive member detected by the angular velocity detecting means using the shape information of the photosensitive member acquired by the acquiring means;
Control means for controlling the exposure means to expose the photoconductor in synchronization with the corrected angular velocity obtained by correcting the angular velocity of the photoconductor detected by the angular velocity detection means by the angular velocity correction means;
An image forming apparatus comprising: The acquisition unit acquires the shape information of the photoconductor for each phase corresponding to a divided region obtained by dividing the outer peripheral portion of the photoconductor into a plurality of regions with a predetermined reference position as a reference,
2. The image forming apparatus according to claim 1, wherein the angular velocity correcting unit corrects the angular velocity detected by the angular velocity detecting unit using shape information for each phase acquired by the acquiring unit.   The image forming apparatus according to claim 1, wherein the shape information is information indicating a radius of the photosensitive member.   3. The image forming apparatus according to claim 1, wherein the shape information is information indicating a surface distance along an outer peripheral surface of the photoconductor. The photoreceptor is driven and driven by the intermediate transfer member,
5. The image forming apparatus according to claim 1, wherein the control unit applies an assist torque for canceling a load torque acting on the photoconductor to the photoconductor. 6. . Photoconductor driving means for rotating the photoconductor;
Intermediate transfer body driving means for rotating the intermediate transfer body,
6. The control unit according to claim 1, wherein the control unit feeds back a detection value of the angular velocity detection unit to the photoconductor driving unit and the intermediate transfer unit driving unit to perform feedback control. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the photosensitive member driving unit is a low inertia type DC motor. A plurality of the photoreceptors are provided corresponding to the image forming units for each color forming a color image,
The control means includes
The exposure means includes an exposure start position on the plurality of photoconductors, the photoconductor and the intermediate transfer body, such that leading positions of images formed on the plurality of photoconductors coincide on the intermediate transfer body. 8. Control is performed so that the plurality of photoconductors are exposed while being shifted by a predetermined timing obtained by using a distance from a transfer position where the photoconductors abut and a distance between the photoconductors. The image forming apparatus according to any one of the above.

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