JP2010079126A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of using a smaller stepping motor as a drive source. <P>SOLUTION: A cleaning blade 73 having resilience abuts against a photoreceptor drum 71. The photoreceptor drum 71 is rotated and driven by the stepping motor 81 and a decelerator 82. A control part 84 controlling the operation of the stepping motor 81 performs reverse rotation driving of the stepping motor 81 for a period of time corresponding to the backlash of the decelerator 82 so that the resilient repulsive force of the cleaning blade 73 against the photoreceptor drum 71 is canceled upon the rotation driving start of the photoreceptor drum 71, and then normally rotates and drives the stepping motor 81. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including a mechanism for rotating an image carrier with a stepping motor.

  A stepping motor may be used as a drive source of a drive device that drives a rotating body or a moving body. The stepping motor is advantageous in that it can be controlled with the number of drive pulses to be applied and that feedback control is unnecessary. In order to realize more precise pulse control, a reduction mechanism such as a reduction gear or a traction reducer is often interposed on the output shaft of the stepping motor. In such a drive device, it is known that when the stepping motor is started, the stepping motor is rotated in the reverse direction before being rotated in the normal rotation direction (for example, Patent Document 1 and Patent Document 2).

A driving device using a stepping motor is also used for driving a photosensitive drum of an image forming apparatus. The photosensitive drum is usually in contact with a cleaning blade for scraping off the toner remaining on the peripheral surface of the photosensitive drum after the toner image is transferred to a sheet or an intermediate transfer belt. This cleaning blade is not a rigid body but a plate-like member having a certain degree of elasticity, and generally its tip is in sliding contact with the peripheral surface of the photosensitive drum from the counter direction with respect to the normal rotation direction of the photosensitive drum. Is done. Accordingly, the contact resistance of the cleaning blade also becomes a driving load of the stepping motor.
Japanese Patent Laid-Open No. 2007-114042 Japanese Patent Laid-Open No. 11-127596

  In general, the stepping motor is more expensive as the output torque is larger. Therefore, when trying to reduce the cost of an image forming apparatus provided with a stepping motor as a driving source for a photosensitive drum or the like, the design is made so that the load of the stepping motor is not applied as much as possible, and a stepping motor with a small output torque (small size) can be supported. It is desirable to make it. However, since a contact load of the cleaning blade is applied to the photosensitive drum, it is difficult to use a small stepping motor.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an image forming apparatus in which a device capable of using a smaller stepping motor is provided and the cost can be reduced. And

  An image forming apparatus according to an aspect of the present invention includes a rotating image carrier, an elastic blade disposed so that a part of the image carrier is in contact with a peripheral surface of the image carrier, and a rotational driving force applied to the image carrier. And a control means for controlling the driving of the stepping motor, the control means driving the stepping motor in a normal rotation direction for rotating the image carrier in a normal rotation direction, and the image. It is controllable to perform reverse rotation driving for rotating the carrier in the direction opposite to the normal rotation direction, and when the image carrier starts to rotate, the elastic repulsion force of the elastic blade against the image carrier is After the reverse rotation drive is performed for a predetermined period so as to be eliminated, the forward rotation drive is performed (claim 1).

  According to this configuration, since a part of the elastic blade is in contact with the rotating image carrier, the elastic repulsive force of the elastic blade acts on the image carrier when the image carrier is stopped. It becomes. For this reason, the stepping motor at the time of starting the rotational drive requires the inertia acceleration torque of its own rotor and the load torque that cancels the elastic repulsion force of the elastic blade as the self-starting torque.

  However, in the present invention, the control means causes the image carrier to reversely rotate so that the elastic repulsive force of the elastic blade against the image carrier is eliminated at the start of the rotational drive, so that the inertia acceleration torque and the elastic repulsion load torque are simultaneously applied. There is no burden. That is, the elastic repulsion load torque can be substantially removed from the self-starting torque of the stepping motor. Therefore, it becomes possible to select a stepping motor having a smaller output torque than when both torques are simultaneously borne.

  In the above configuration, it is desirable that the tip of the elastic blade is in contact with the peripheral surface of the image carrier from the counter direction with respect to the normal rotation direction of the image carrier. Such a configuration is a configuration that is normally employed when the elastic blade is a cleaning blade. In this case, the elastic repulsion force of the elastic blade is increased. Therefore, by applying the present invention, a stepping motor having a smaller output torque can be selected.

  In any one of the above-described configurations, it is preferable that a reduction mechanism that further reduces the rotational driving force of the stepping motor to a predetermined rotational speed and transmits the reduction rotational force to the image carrier is preferable. In this case, it is desirable that the speed reduction mechanism has a backlash, and the control means performs the reverse rotation driving by an amount corresponding to the backlash.

  According to this configuration, the elastic repulsive force of the elastic blade is first released by the reverse rotation driving, and a state in which the stepping motor is substantially unloaded by the backlash can be created. And since the stepping motor can start itself in such a no-load state, a small stepping motor that can bear the inertia acceleration torque of its own rotor can be adopted.

  According to the present invention, even in an image forming apparatus having a structure in which an elastic blade is in contact with an image carrier, it is possible to suppress a self-starting torque of a stepping motor and select a stepping motor having a small output torque. Therefore, the cost of the image forming apparatus can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. As an image forming apparatus according to the present invention, a tandem color printer 1 is illustrated in the present embodiment. FIG. 1 is a schematic cross-sectional view showing the overall configuration of the color printer 1, and FIG. 2 is an enlarged view of a main part showing the configuration around the image forming unit of the color printer 1.

  The color printer 1 includes a box-type device main body 1a. Inside the apparatus main body 1a, a paper feeding unit 2 that feeds the paper P, an image forming unit 3 that transfers an image to the paper P while conveying the paper P fed from the paper feeding unit 2, and an image A fixing unit 4 that performs a fixing process on the image transferred to the paper P by the forming unit 3 is provided. Further, on the upper surface of the apparatus main body 1a, a paper discharge unit 5 for discharging the paper P subjected to the fixing process by the fixing unit 4 is provided.

  The paper feed unit 2 includes a paper feed cassette 21, a pickup roller 22, paper feed rollers 23, 24, 25, a registration roller 26, and a pickup roller 27. The paper feed cassette 21 is detachable from the apparatus main body 1a, and stores a plurality of sheets P having a predetermined size. The pickup roller 22 takes out the paper P stored in the paper feed cassette 21 one by one into the paper transport path. The paper feed rollers 23, 24, and 25 send out the paper P taken out by the pickup roller 22 to the paper transport path. The registration roller 26 temporarily waits for the paper P sent to the paper conveyance path, and then supplies the paper P to the image forming unit 3 at a predetermined timing. The pickup roller 27 takes out the paper P placed on a manual feed tray (not shown) attached to the right side surface shown in FIG. 1 of the apparatus main body 1a, and sends it out to the paper conveyance path.

  The image forming unit 3 includes an image forming unit 7, an intermediate transfer belt 11 on which a toner image is primarily transferred to the surface (contact surface) by the image forming unit 7, and a toner image on the intermediate transfer belt 11. 2 and a secondary transfer roller 12 for performing secondary transfer onto the paper P sent from 2.

  The image forming unit 7 includes a black unit 7K, a yellow unit 7Y, a cyan unit 7C, and a magenta unit 7M which are sequentially arranged from the upstream side (left side in FIG. 1) to the downstream side. At the central position of each unit 7K, 7Y, 7C, and 7M, a photosensitive drum 71 (image carrier) that carries a toner image of each color is arranged to be rotatable in the direction of an arrow (counterclockwise). . Around each photosensitive drum 71, a charger 75, an exposure device 76, a developing device 72, a cleaning blade 73 (elastic blade), and a static eliminator 74 are arranged in this order from the upstream side in the rotation direction.

  The charger 75 uniformly charges the peripheral surface of the photosensitive drum 71. For example, a scorotron charger is used. The exposure device 76 is a so-called laser scanning unit, which irradiates the peripheral surface of the photosensitive drum 71 uniformly charged by the charger 75 with laser light based on image data input from an external personal computer or the like. An electrostatic latent image is formed on the peripheral surface of the body drum 71. The developing device 72 supplies toner to the peripheral surface of the photosensitive drum 71 on which the electrostatic latent image is formed. The electrostatic latent image is developed with the toner, and a toner image is formed on the peripheral surface of the photosensitive drum 71. This toner image is primarily transferred to the intermediate transfer belt 11.

  The cleaning blade 73 cleans the toner remaining on the peripheral surface of the photosensitive drum 71 after the primary transfer of the toner image to the intermediate transfer belt 11 is completed. The cleaning blade 73 will be described in detail later with reference to FIG. The neutralizer 74 neutralizes the peripheral surface of the photosensitive drum 71 after the primary transfer is completed. The peripheral surface of the photosensitive drum 71 cleaned by the cleaning blade 73 and the charge eliminator 74 is directed to the charger 75 for a new charging process, and a new primary transfer is performed.

  The intermediate transfer belt 11 is an endless belt-like rotating body, and includes a driving roller 13, a belt support roller 14, a backup roller 15, and a backup roller 15 so that the surface (contact surface) side is in contact with the peripheral surface of each photosensitive drum 71. It is spanned across a plurality of rollers such as the primary transfer roller 16. The intermediate transfer belt 11 rotates endlessly while being pressed against the photosensitive drum 71 by the primary transfer roller 16 disposed opposite to the photosensitive drum 71.

  The driving roller 13 is rotationally driven by a driving source 18 such as a stepping motor, and gives a driving force for rotating the intermediate transfer belt 11 endlessly. The belt support roller 14, the backup roller 15, and the primary transfer roller 16 are driven rollers that rotate with the endless rotation of the intermediate transfer belt 11. The primary transfer roller 16 applies a primary transfer bias (a polarity opposite to the charging polarity of the toner) to the intermediate transfer belt 11. As a result, the toner image formed on each photoconductive drum 71 is transferred between each photoconductive drum 71 and the primary transfer roller 16 in the direction of the arrow (clockwise) by driving the drive roller 13. Primary transfer is sequentially performed on the belt 11 in an overcoated state.

  A cleaning brush 17 is provided at the upper left position of the belt support roller 14 in FIG. The toner remaining on the surface of the intermediate transfer belt 11 after the transfer process of the toner image onto the paper P is removed by the cleaning brush 17.

  The secondary transfer roller 12 applies a secondary transfer bias having a polarity opposite to that of the toner image to the paper P. The toner image primarily transferred onto the intermediate transfer belt 11 is transferred onto the paper P between the secondary transfer roller 12 and the backup roller 15 by the secondary transfer bias, whereby a color transfer image is transferred onto the paper P. It is formed.

  The fixing unit 4 performs a fixing process on the transfer image transferred to the paper P by the image forming unit 3. The fixing unit 4 is disposed opposite to the heating roller 41 heated by the energized heating element, and is disposed on the circumferential surface. Is provided with a pressure roller 42 pressed against and contacted with the peripheral surface of the heating roller 41. The transferred image transferred to the paper P is fixed on the paper P by a fixing process by heating when the paper P passes between the heating roller 41 and the pressure roller 42. The paper P on which the fixing process has been performed is discharged to the paper discharge unit 5 by a conveyance roller 6 disposed at an appropriate position between the fixing unit 4 and the paper discharge unit 5.

  Next, the drive mechanism 8 for the photosensitive drum 71 will be described. FIG. 3 is a schematic diagram showing one photosensitive drum 71 and its driving mechanism 8 in an extracted manner. The drive mechanism 8 is connected to a stepping motor 81 that generates a driving force for rotating the photosensitive drum 71 and an output shaft (not shown) of the stepping motor 81, and the rotational driving force of the stepping motor 81 is set to a predetermined number of rotations. A decelerator 82 (deceleration mechanism) that decelerates and transmits to the photosensitive drum 71 and a control unit 84 that controls driving of the stepping motor 81 are included.

  The stepping motor 81 includes a fixed stator and a rotor that rotates around a shaft (output shaft), and a rotation angle, a rotation speed, and a rotation direction are controlled by a drive pulse supplied from the control unit 84.

  The speed reducer 82 is provided to improve the control resolution of the stepping motor 81 or to make the index angle per pulse an integer. As the speed reducer 82, a gear speed reducer such as a parallel shaft gear speed reducer, a planetary gear speed reducer, a worm speed reducer, or a traction speed reducer can be employed. The speed reducer 82 has an inevitable backlash due to the gear mechanism. The output shaft 83 of the speed reducer 82 is connected to one end side of the rotating shaft 711 of the photosensitive drum 71 through a coupling 712. Thus, when the stepping motor 81 rotates, the rotational driving force is transmitted to the rotating shaft 711 via the output shaft 83 of the speed reducer 82, and the photosensitive drum 71 is rotated.

  The control unit 84 has a rotation control function for controlling the rotation angle, rotation speed, rotation direction, and the like of the stepping motor 81, and a function as a driver that generates a drive pulse corresponding to the rotation control and gives it to the stepping motor 81. . In other words, the control unit 84 controls the rotation angle and rotation speed of the photosensitive drum 71 via the stepping motor 81 and rotates the photosensitive drum 71 in the normal rotation direction (the above-described counterclockwise direction). (Forward rotation drive), it is possible to rotate in the direction opposite to the normal rotation (reverse rotation drive).

  Here, the tip 731 (a part) of the cleaning blade 73 is in contact with the peripheral surface 71 </ b> S of the photosensitive drum 71. The cleaning blade 73 is a plate-like member formed of a material such as urethane rubber and has a certain degree of elasticity. The tip 731 of the cleaning blade 73 is in sliding contact with the peripheral surface 71S of the photosensitive drum 71 from the counter direction with respect to the normal rotation direction of the photosensitive drum 71 (indicated by an arrow in FIG. 3). . Accordingly, the contact resistance of the cleaning blade 73 becomes a driving load of the stepping motor 81. Further, when the photosensitive drum 71 is shifted from the state of rotating in the normal rotation direction to the stopped state, a state in which the elastic repulsive force of the cleaning blade 73 is applied to the photosensitive drum 71 is formed. For this reason, when starting the rotation of the photosensitive drum 71 in the positive rotation direction, it is necessary to consider the elastic repulsion force as a driving load.

  In view of the above, the controller 84 reversely rotates the photosensitive drum 71 for a predetermined period in order to eliminate the elastic repulsion force of the cleaning blade 73 against the photosensitive drum 71 when the photosensitive drum 71 starts to rotate. Then, the stepping motor 81 is driven in reverse rotation and forward rotation so as to rotate forward. In the present embodiment, the stepping motor 81 is reversely driven by the amount of movement equivalent to the backlash of the speed reducer 82. Hereinafter, the control operation of the control unit 84 will be described based on the time charts shown in FIGS. 4 and 5.

  FIG. 4 is a time chart for explaining the self-starting torque of the stepping motor 81 in the case where the above-described reverse rotation drive is not performed, for comparison with the present invention, and FIG. 5 is reversed according to the present invention. It is a time chart for demonstrating the self-starting torque of the stepping motor 81 in the case of rotating. The upper part of these time charts shows the relationship between the angular velocity of the rotor of the stepping motor 81 and time, and the lower part shows the relationship between the torque borne on the rotor shaft (motor shaft) and time. FIG. 6 is a graph showing a general speed-torque characteristic curve of the stepping motor.

  First, in the time chart of the comparative technique shown in FIG. 4, until the time t1, the stepping motor 81 performs an operation (normal rotation drive) at a steady rotation speed that rotates the photosensitive drum 71 at a predetermined positive rotation speed. It shall be. At this time, the rotor shaft of the stepping motor 81 has a load torque for rotating the photosensitive drum 71 and a load torque associated with a frictional force caused by the tip 731 of the cleaning blade 73 being in contact with the peripheral surface 71S of the photosensitive drum 71. And bear. Even when the stop control is executed at time t1 and the stepping motor 81 is stopped at time t2, the rotor shaft of the stepping motor 81 is urged in the reverse rotation direction by the elastic repulsive force of the cleaning blade 73. An elastic repulsive load torque a1 is applied to the rotor shaft.

  Next, when the operation start control is executed at time t3, the stepping motor 81 is accelerated to a predetermined angular velocity in a self-starting region (region that can be started, stopped, and reversed in synchronization with the driving pulse; see FIG. 6). Subsequently, through-up is performed in the through region. Thereafter, at step t4, the stepping motor 81 is accelerated to the steady rotational speed. Here, as the load torque of the rotor shaft at time t3, that is, the self-starting torque a, first, the rotor inertia acceleration torque a2 for accelerating the rotor to the self-starting rotation speed is essential. In addition to this, it is necessary to bear the elastic repulsive load torque a1 due to the contact of the cleaning blade 73. Therefore, according to this comparative technique, it is necessary to select a stepping motor 81 having a large output torque having self-starting torque a = elastic repulsive load torque a1 + inertia acceleration torque a2 in order to prevent step-out. In this case, a relatively expensive stepping motor must be employed.

  On the other hand, when performing reverse rotation driving, as shown in the time chart of FIG. 5, the self-starting torque A can be substantially suppressed to only the rotor inertia acceleration torque a2. In FIG. 5, it is assumed that the stepping motor 81 is operating at a normal rotation speed (forward rotation drive) until time t11, and stop control is executed at time t12. In this case, the elastic repulsion load torque a <b> 1 is applied to the rotor shaft of the stepping motor 81 by the elastic repulsion force of the cleaning blade 73.

  Next, at the timing when the operation start control is executed at time t13, the control unit 84 drives the stepping motor 81 to rotate in the self-starting region so that the photosensitive drum 71 rotates in the reverse direction. This reverse rotation drive is continued until time t14 after a predetermined time. In the present embodiment, the time from time t13 to time t14 is a time during which the photosensitive drum 71 can move about the same amount as the backlash that the speed reducer 82 has. By such reverse rotation driving, the elastic repulsion load torque a1 applied to the rotor shaft of the stepping motor 81 is eliminated, and the rotor shaft is substantially in an unloaded state.

  When the operation start control is executed at time t14, the stepping motor 81 accelerates at a stroke to a predetermined angular velocity within the self-activation region. At this time, the stepping motor 81 can start itself in a no-load state due to the backlash of the speed reducer 82. That is, the self-starting torque A required for the stepping motor 81 is only an amount corresponding to the rotor inertia acceleration torque a2.

  Thereafter, when time t15 when the backlash of the speed reducer 82 is blocked elapses, load torque including elastic repulsion load torque a1 for rotating the photosensitive drum 71 is borne on the rotor shaft. At this time, since the stepping motor 81 has completed the acceleration up to the self-starting rotational speed, the load torque at the time t15 is an escape torque of the stepping motor 81 (a region exceeding the self-starting region and synchronized with the driving pulse). The torque can be generated within a range of the torque that can be generated without losing (see FIG. 6). Thereafter, at step t16, the stepping motor 81 is accelerated to the steady rotational speed.

As shown in FIG. 6, the escape torque of the stepping motor always shows a value larger than the pull-in torque that defines the self-activation region. Therefore, when selection of the stepping motor 81, and the load torque Tq1 of the rotor shaft at a constant rotational speed f _0, and the load torque Tq2 in the rotation start of the photosensitive drum 71 at time t15 is being borne by the through region, It is possible to select a stepping motor in which the load torque Tq3 (self-starting torque A) at time t14 when shifting from reverse rotation driving to forward rotation driving is borne within the self-starting region. Such a stepping motor naturally has a smaller output torque than that of the comparative technique. Therefore, a relatively inexpensive stepping motor can be employed.

  The color printer 1 according to the embodiment of the present invention has been described above, but the present invention is not limited to this, and for example, the following embodiment can be taken.

(1) In the above embodiment, the color printer 1 is exemplified as the image forming apparatus. The present invention can be applied to other than a color printer as long as it is an image forming apparatus provided with a rotating image carrier and an elastic blade in contact with the peripheral surface of the image carrier, for example, a monochrome printer, a copying machine, a facsimile machine. The present invention can also be applied to an apparatus or a multifunction machine of these.

(2) In the above embodiment, the photosensitive drum 71 is also in contact with the intermediate transfer belt 11. When the photosensitive drum 71 is reversely rotated, the control unit 84 may control the drive source 18 so that the intermediate transfer belt 11 is also reversely rotated by an amount corresponding to backlash.

(3) In the above embodiment, the photosensitive drum 71 is exemplified as an example of the image carrier. The image carrier may be an intermediate transfer belt to which a toner image is transferred. Although the cleaning blade 73 is illustrated as an example of the elastic blade, the elastic blade is not necessarily used for cleaning purposes, and may not be in contact with the image carrier from the counter direction.

1 is a schematic cross-sectional view illustrating an overall configuration of a color printer according to an embodiment of the present invention. FIG. 2 is an enlarged view of a main part illustrating a configuration around an image forming unit of a color printer. FIG. 2 is a schematic diagram illustrating one photosensitive drum and a driving mechanism thereof. It is a time chart for demonstrating the self-starting torque of a stepping motor when not performing reverse rotation drive. It is a time chart for demonstrating the self-starting torque of a stepping motor in the case of performing reverse rotation drive. It is a graph which shows the speed-torque characteristic curve of a stepping motor.

Explanation of symbols

1 Color printer (image forming device)
71 Photosensitive drum (image carrier)
73 Cleaning blade (elastic blade)
81 Stepping motor 82 Reducer (Deceleration mechanism)
84 Control unit (control means)

Claims (4)

A rotating image carrier;
An elastic blade disposed so that a part thereof contacts the peripheral surface of the image carrier;
A stepping motor for applying a rotational driving force to the image carrier;
Control means for controlling the driving of the stepping motor,
The control means causes the stepping motor to perform forward rotation driving for rotating the image carrier in a normal rotation direction and reverse rotation driving for rotating the image carrier in a rotation direction opposite to normal. Controllable, and at the start of rotational drive of the image carrier, the reverse rotational drive is performed for a predetermined period so that the elastic repulsion force of the elastic blade against the image carrier is eliminated, and then the forward rotational drive is performed. An image forming apparatus characterized by being performed.   The image forming apparatus according to claim 1, wherein a tip of the elastic blade is in contact with a peripheral surface of the image carrier from a counter direction with respect to a normal rotation direction of the image carrier.   The image forming apparatus according to claim 1, further comprising a speed reduction mechanism that reduces the rotational driving force of the stepping motor to a predetermined rotational speed and transmits the reduced speed to the image carrier. The speed reduction mechanism has a backlash,
The image forming apparatus according to claim 3, wherein the control unit performs the reverse rotation driving by an amount corresponding to the backlash.

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