JP2006267709A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a displacement in image pitch in a sub-scanning direction, which results from eccentricity or the like of a photoreceptor drum. <P>SOLUTION: A roller 44 is displaced according to an amount of periodic change in the surface velocity of the photoreceptor drum 12, thereby stretching or shrinking an elastic belt 52, and toner images in respective colors are transferred to the elastic belt 52 from the photoreceptor drum 12. Thus even where the circumferential length of the elastic belt 52 is not an integral multiple of the circumferential length of the photoreceptor drum 12, displacement of a toner image due to the periodic change in the surface velocity of the photoreceptor drum 12 can be prevented. In addition, by displacing the roller 44 extending the elastic belt 52 taut, the elastic belt 52 extended taut by the roller 44 is stretched or shrunk. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a laser printer, a laser copying machine, and a laser facsimile, and more particularly to an image forming apparatus that forms a color image by superimposing different color toner images on an intermediate transfer member.

Four color toners of Y (yellow), M (magenta), C (cyan), and K (black) are formed on the photosensitive drum, and the toner images are sequentially superimposed on the intermediate transfer member, so that color In an image forming apparatus for forming an image, if the peripheral speed of the photosensitive drum is constant, toner images of four colors are sequentially formed on the surface of the photosensitive drum, By matching the recording start position (transfer start position) of the toner image on the intermediate transfer member, no color shift occurs between the toner images of the respective colors.
However, the photosensitive drum is uneven due to eccentricity. Further, the rotation unevenness of the photosensitive drum is also caused by the eccentricity of the gear that transmits the rotational force to the photosensitive drum. As a result, the circumferential speed (speed in the sub-scanning direction) of the surface of the photosensitive drum is uneven at a constant cycle, and the pitch in the sub-scanning direction of the image formed on the surface of the photosensitive drum becomes non-uniform. End up. A color shift occurs when this pitch is different for each color.

Therefore, in order to avoid color misregistration due to uneven rotation of the photosensitive drum, it is generally performed that the circumference of the intermediate transfer member is an integral multiple of the circumference of the photosensitive drum (see Patent Document 1). ).
However, if the circumference of either the photoconductor drum or the intermediate transfer member is set under design constraints such as printable paper size, the other circumference is determined at the same time. There is a problem that there is no degree of freedom and leads to an increase in space.

In order to deal with this problem, it has been proposed to make the circumference of the intermediate transfer member (n + 0.5: n is an integer) times the circumference of the photosensitive drum (see Patent Document 2). For example, when an image is formed in the order of yellow, magenta, cyan, and black, it is possible to prevent only color misregistration between colors that are not adjacent to each other, that is, yellow and cyan, and magenta and black. A color shift between adjacent colors such as magenta or black cannot be prevented, and therefore a color shift between four colors cannot be prevented.
JP-A-61-083357 JP-A-11-002969

  In view of the above problems, an object of the present invention is to prevent a shift in the pitch of an image in the sub-scanning direction caused by eccentricity of a photosensitive drum.

  According to the first aspect of the present invention, an image carrier on which toner images of a plurality of colors are formed, a toner image is transferred following the image carrier, and the circumference is not the circumference of the image carrier. An image forming apparatus having an intermediate transfer body having an elasticity that is an integral multiple, characterized by having expansion / contraction means that expands and contracts the intermediate transfer body in accordance with a periodic fluctuation amount of a surface speed of the image carrier. Yes.

  According to the first aspect of the present invention, the toner image of each color is transferred from the image carrier to the intermediate transfer member by expanding / contracting the intermediate transfer member by the expansion / contraction means in accordance with the periodic fluctuation amount of the surface speed of the image carrier. To do.

  For example, when the surface speed of the image carrier is higher than a predetermined surface speed, the toner image formed when the pitch interval of the toner image formed on the surface of the image carrier rotates at the predetermined surface speed. It becomes larger than the pitch interval of the image. Therefore, when this toner image is transferred to the intermediate transfer member, the peripheral length of the intermediate transfer member is extended. As a result, the toner image formed on the stretched intermediate transfer member is simultaneously contracted when the intermediate transfer member contracts due to the elastic force, the pitch interval is reduced, and the toner image is formed when rotating at a predetermined surface speed. The toner image is transferred at the same interval as the pitch interval of the toner image.

  In addition, when the surface speed of the image carrier is lower than the predetermined surface speed, the toner image formed when the pitch interval of the toner image formed on the surface of the image carrier is rotating at the predetermined surface speed. It becomes smaller than the pitch interval of the image. Therefore, when the toner image is transferred to the intermediate transfer member, the circumference of the intermediate transfer member is contracted. As a result, the toner image formed on the contracted intermediate transfer member is simultaneously expanded when the intermediate transfer member expands due to the elastic force, the pitch interval is increased, and the toner image is formed when rotating at a predetermined surface speed. The toner image is transferred at the same interval as the pitch interval of the toner image.

  Therefore, even when the peripheral length of the intermediate transfer member is not an integral multiple of the peripheral length of the image carrier, it is possible to prevent the occurrence of positional deviation of the toner image due to the periodic fluctuation of the surface speed of the image carrier.

  According to a second aspect of the present invention, the intermediate transfer body is an elastic belt stretched around a plurality of rollers, and the expansion / contraction means displaces the position of the roller and moves the elastic belt. It is characterized by being.

  According to the second aspect of the present invention, the moving means displaces the position of the roller that stretches the intermediate transfer member, and expands and contracts the elastic belt that is stretched by the roller. Accordingly, the elastic belt can be expanded and contracted without separately providing a member for expanding and contracting the elastic belt, so that the number of parts does not increase.

  According to a third aspect of the present invention, the moving means displaces a first roller that is closest to a transfer position to which the toner image of the image carrier is transferred and is upstream in the moving direction of the elastic belt. It is characterized by letting.

  According to the third aspect of the present invention, the first roller located closest to the transfer position to which the toner image on the image carrier is transferred and located upstream in the moving direction of the elastic belt is displaced by the moving means to be elastic. Extend and retract the belt. As a result, the toner image is transferred to the elastic belt immediately after the elastic belt is expanded and contracted, so that the state of the elastic belt is accurately reflected at the transfer position.

  The invention according to claim 4 is characterized in that the expansion / contraction means is a pressing member that is disposed inside the elastic belt and presses the elastic belt from the inside.

  According to the invention described in claim 4, the elastic belt is expanded and contracted by pressing the elastic belt with the pressing member from the inside of the elastic belt. Thereby, even when the position of the roller for stretching the elastic belt cannot be displaced due to design constraints or the like, the elastic belt can be expanded and contracted.

  The present invention according to claim 5 is characterized in that the pressing member is provided between the first roller and the transfer position.

  According to the fifth aspect of the present invention, the elastic belt is expanded and contracted by providing the pressing member between the transfer position where the toner image on the image carrier is transferred and the first roller located upstream in the moving direction of the elastic belt. Let As a result, the toner image is transferred to the elastic belt immediately after the elastic belt is expanded and contracted, so that the state of the elastic belt is accurately reflected at the transfer position.

  According to a sixth aspect of the present invention, the expansion / contraction means is a load increasing / decreasing member that increases or decreases a load applied to the roller.

  According to the sixth aspect of the present invention, the load applied to the roller is increased or decreased by the load increasing / decreasing member. That is, when a load is applied to the roller, the rotation of the roller becomes slow, and the conveyance speed of the elastic belt stretched around the roller becomes slow. Thereby, the elastic belt expands on the downstream side in the rotation direction of the roller, and the elastic belt contracts on the upstream side in the rotation direction of the roller.

  Therefore, when the surface speed of the image carrier is higher than a predetermined surface speed, a load is applied to the roller on the upstream side of the image carrier and the circumferential length of the elastic belt is in contact with the image carrier (transfer portion). Stretch.

  According to a seventh aspect of the present invention, the expansion / contraction means expands / contracts the intermediate transfer body in accordance with a periodic variation of the image carrier detected by a detection device that detects a periodic variation of the surface speed of the image carrier. It is characterized by letting.

  According to the seventh aspect of the invention, the periodic fluctuation amount of the surface velocity of the image carrier is detected by the detection device, and the intermediate transfer member is expanded and contracted by the expansion / contraction means in accordance with the periodic fluctuation amount. The toner image of each color is transferred to the intermediate transfer member.

  Since the present invention has the above-described configuration, it is possible to prevent the shift of the image pitch in the sub-scanning direction caused by the eccentricity of the photosensitive drum.

The image forming apparatus 10 according to the first embodiment of the present invention will be described below. FIG. 1 is a schematic diagram illustrating a basic configuration of the image forming apparatus 10.
The image forming apparatus 10 is provided with a photosensitive drum 12. Around the photosensitive drum 12, a charging roller 14 that uniformly charges the peripheral surface of the photosensitive drum 12, an LPH 16 that forms an electrostatic latent image corresponding to each color on the photosensitive drum 12, and the photosensitive drum 12 The rotary developing device 18 that develops the electrostatic latent image formed on each toner image into a toner image of each color, the transfer roller 22 that transfers the toner image of each color onto an elastic belt 52 of an intermediate transfer member 20 described later, and the photosensitive drum 12. A cleaning blade 42 for removing the upper transfer residual toner is disposed in order along the rotation direction of the photosensitive drum 12 (the direction of arrow A in the figure).

  The developing device 18 includes developing devices 18a to 18d that store toners of each color of K (black), Y (yellow), M (magenta), and C (cyan). Is developed and visualized.

  Further, the sheet 24 is taken out from a paper feed tray 26 provided at the lower part of the main body of the image forming apparatus 10 by a pickup guide 28 and a pickup roller 30 and is conveyed along a predetermined path by a pair of conveying rollers 32 and 34 and the like. It is configured as follows. A secondary transfer roller 36 for transferring the toner images of the respective colors carried on the elastic belt 52 onto the paper 24 is disposed at a position facing the roller 48 of the intermediate transfer body 20. A fixing device 38 for fixing the unfixed toner image transferred to the sheet 24 is disposed downstream of the secondary transfer roller 36, and further, a sheet on which a fixed image is formed is disposed downstream of the secondary transfer roller 36. A discharge roller 40 is provided for discharging 24 to the outside of the machine.

  Next, a series of operations of the image forming apparatus 10 having the above configuration will be described. First, the peripheral surface of the photosensitive drum 12 is uniformly charged to a predetermined potential by the charging roller 14. Then, a light beam is irradiated from the LPH 16 onto the uniformly charged peripheral surface of the photosensitive drum 12. Then, the potential of the irradiated part is changed, thereby forming an electrostatic latent image.

  The electrostatic latent image is developed with toner of each color stored in the developing devices 18 a to 18 d of the developing device 18. That is, each time the photosensitive drum 12 rotates once, an electrostatic latent image corresponding to each color of K, Y, M, and C is sequentially formed on the circumferential surface of the photosensitive drum 12 one by one. The toner is electrostatically attracted and attached to the electrostatic latent image from the developing units 18a to 18d. Then, the toner images formed for the respective colors are sequentially transferred onto the elastic belt 52 by pressure contact and electrostatic attraction of the transfer roller 22 to the photosensitive drum 12, and a full-color multiple toner image in which the respective colors are superimposed is formed. It is formed.

  It should be noted that each time the toner image of each color is transferred to the elastic belt 52, the photosensitive drum 12 removes unnecessary toner particles by scraping off the peripheral surface thereof by the cleaning blade 42 and removing the charge (not shown). And is uniformly charged again by the charging roller 14 to prepare for the next electrostatic latent image forming step.

  Thus, the multiple toner images formed on the elastic belt 52 are pressed from the elastic belt 52 onto the paper 24 by the secondary transfer roller 36 being pressed against the roller 48 via the elastic belt 52 and the paper 24 being conveyed. The unfixed toner image is fixed by the fixing device 38 transferred and disposed downstream thereof. Then, the sheet 24 on which the toner image is fixed is discharged out of the apparatus by the discharge roller 40.

  Next, in the image forming apparatus 10 as described above, the intermediate transfer member 20 including the elastic belt 52 will be described in detail.

  As shown in FIGS. 1 and 2, the intermediate transfer member 20 includes rollers 44, 46, 48, and 50, and an elastic belt 52 having elasticity is stretched around these four rollers. The elastic belt 52 is configured to be driven to rotate in the direction of the arrow B shown in the figure by the rotation of the photosensitive drum 12 while contacting the peripheral surface of the photosensitive drum 12 between the roller 44 and the roller 46. Note that the circumferential length of the elastic belt 52 is a non-integer multiple of the circumferential length of the photosensitive drum 12.

  As shown in FIG. 3, the shaft 44 </ b> A of the roller 44 is inserted into a long hole 54 formed in a frame (not shown) of the image forming apparatus 10 (see FIG. 1). The outside of the frame of the shaft 44A (the side opposite to the side on which the roller 44 is disposed) is pivotally supported by a bearing 56. The bearing 56 is supported by a substantially U-shaped receiving portion 60 formed on the plate member 58. Is retained.

  On the other hand, both end portions of the plate member 58 are slidably attached to guide rails 59 fixed to the frame. A rack 65 is fixed to the plate material 58. A pinion 67 driven by a stepping motor 69 is engaged with the rack 65. The stepping motor 69 is connected to the control unit 74, and the drive amount of the pinion 67 is controlled by the control unit 74 counting the number of pulses of the stepping motor 69.

  On the other hand, the elastic belt 52 (see FIG. 2) is given a predetermined tension in the initial state. As a result, as shown in FIG. 4A, when the roller 44 is moved in the direction of the arrow D, the elastic belt 52 is extended. As shown in FIG. When moved in the direction of arrow C, the elastic belt 52 is contracted.

  Here, a method for detecting the periodic fluctuation of the photosensitive drum 12 will be described. First, an electrostatic latent image of a pattern is formed on the photosensitive drum 12 at regular intervals by the LPH 16. The electrostatic latent image having this pattern is developed by the rotary developing device 18 and transferred to the elastic belt 52.

  On the other hand, a reading sensor 76 is installed between the photosensitive drum 12 and the roller 44, and a pattern (color misregistration) of the photosensitive drum 12 formed on the elastic belt 52 by the reading sensor 76. For detecting misalignment).

  The reading sensor 76 is connected to a control unit 74 connected to the stepping motor 69, and the period fluctuation of the photosensitive drum 12 detected by the reading sensor 76 is stored in a storage unit (not shown).

  Here, a method for expanding and contracting the elastic belt 52 by the periodic fluctuation of the surface speed of the photosensitive drum 12 will be described.

  For example, when the surface speed of the photosensitive drum 12 is faster than a predetermined value, the pitch interval of the toner image becomes large. Therefore, the pinion 67 is driven by the stepping motor 69, and the plate material 58 moves substantially upward via the rack 65 meshed with the pinion 67. In this way, the roller 44 is moved in the direction of arrow D as shown in FIG. As a result, the elastic belt 52 expands, the toner image is transferred from the photosensitive drum 12 to the expanded elastic belt 52, and the toner image having a large pitch interval formed on the photosensitive drum 12 has a predetermined pitch interval. Is transferred to the elastic belt 52.

  Further, when the surface speed of the photosensitive drum 12 is low, the pitch interval of the toner image becomes small, so that the roller 44 is moved in the direction of arrow C as shown in FIG. As a result, the elastic belt 52 contracts, the toner image is transferred from the photosensitive drum 12 to the contracted elastic belt 52, and the toner image formed on the photosensitive drum 12 with a small pitch interval has a predetermined pitch interval. Is transferred to the elastic belt 52.

  Next, the operation of the first embodiment of the present invention will be described.

  The position of the roller 44 is displaced in accordance with the periodic fluctuation amount of the surface speed of the photosensitive drum 12, the elastic belt 52 is expanded and contracted, and the toner image of each color is transferred from the photosensitive drum 12 to the elastic belt 52.

  Thereby, even when the circumferential length of the elastic belt 52 is not an integral multiple of the circumferential length of the photosensitive drum 12, occurrence of positional deviation of the toner image due to the periodic fluctuation of the surface speed of the photosensitive drum 12 can be prevented.

  Further, by displacing the position of the roller 44 over which the elastic belt 52 is stretched, the elastic belt 52 stretched over the roller 44 is expanded and contracted. Accordingly, the elastic belt 52 can be expanded and contracted without separately providing a member for expanding and contracting the elastic belt 52, so that the number of parts does not increase.

  Further, the roller 44 closest to the transfer position (nip portion between the photoconductive drum 12 and the transfer roller 22) to which the toner image on the photoconductive drum 12 is transferred and upstream of the moving direction of the elastic belt 52 is displaced. By expanding and contracting the elastic belt 52, the toner image is transferred to the elastic belt 52 immediately after the elastic belt 52 is expanded and contracted, so that the state of the elastic belt 52 is accurately reflected at the transfer position.

  In the present embodiment, the elastic belt 52 is expanded and contracted by displacing the position of the roller 44, but other rollers (rollers 46, 48, The elastic belt 52 may be expanded and contracted by displacing the position (any of 50).

  Next, an image forming apparatus according to a second embodiment of the present invention will be described. In addition, the description about the part similar to 1st Embodiment is omitted.

  As shown in FIG. 5, a roller 78 is installed between the roller 44 and the transfer roller 22 so as to support the elastic belt 52 from the inside. The roller 78 is configured to expand and contract the elastic belt 52 by moving in the direction of the arrow E or the direction opposite to the direction of the arrow E by the same configuration as the roller 44 of the first embodiment.

  As described above, by providing the roller 78 supporting the elastic belt 52 separately from the rollers 44, 46, 48, and 50 supporting the elastic belt 52, the elastic belt 52 can be expanded and contracted. Even when the positions of the rollers 44, 46, 48, 50 cannot be displaced, the circumferential length of the elastic belt 52 can be expanded and contracted.

  Further, a roller 78 provided between a transfer position (a nip portion between the photosensitive drum 12 and the transfer roller 22) to which the toner image on the photosensitive drum 12 is transferred and the first roller on the upstream side in the moving direction of the elastic belt 52. When the elastic belt 52 is expanded and contracted, the toner image is transferred to the elastic belt 52 immediately after the elastic belt 52 is expanded and contracted, so that the state of the elastic belt 52 is accurately reflected at the transfer position.

  In the present embodiment, the pinion 67 is driven in accordance with the periodic fluctuation of the surface speed of one round of the photosensitive drum 12 detected by the reading sensor 76, thereby displacing the position of the roller 44 and elastic belt. As shown in FIG. 7, an eccentric cam 64 having the same periodic fluctuation as that of the photosensitive drum 12 is formed, and the eccentric cam 64 is used to position the roller 44 as shown in FIG. It is good also as a structure displaced according to the period fluctuation | variation of the drum 12. As a result, it is not necessary to rotate the motor forward and backward, and the control becomes simple.

  Next, an image forming apparatus according to a third embodiment of the present invention will be described. In addition, the description about the part similar to 1st Embodiment is omitted.

  As shown in FIG. 8, one end of the brake member 80 is in contact with the peripheral surface of the roller 44. A substantially central portion of the brake member 80 is rotatably attached to a frame (not shown) of the image forming apparatus 10. A cam 82 driven by a stepping motor (not shown) is in contact with the other end of the brake member 80. When the cam 82 is driven to press the other end of the brake member 80, one end of the brake member 80 is a roller. The force for pressing the peripheral surface of 44 is changed. A coil spring 84 is attached to one end of the brake member 80, and the brake member 80 is urged in the direction of arrow F.

  Accordingly, when a load is applied to the roller 44 by the brake member 80, the rotation of the roller 44 is slowed down, and the conveying speed of the elastic belt 52 stretched around the roller 44 is slowed down. Therefore, the elastic belt 52 extends on the downstream side in the rotation direction of the roller 44.

  In this case, the elastic belt 52 is stretched around the roller 44 in accordance with the case where the surface speed of the photosensitive drum 12 is the slowest. That is, when the surface speed of the photosensitive drum 12 is the slowest, the roller 44 is not loaded with the brake member 80. When the surface speed of the photosensitive drum 12 is higher than a predetermined speed, a load is applied to the roller 44 by the brake member 80 to extend the elastic belt 52 on the upstream side of the photosensitive drum 12.

  With such a configuration, the elastic belt 52 is extended to prevent the toner image from being misaligned due to the periodic fluctuation of the surface speed of the photosensitive drum 12.

  In this embodiment, the brake member 80 is moved by the cam 82. However, for example, a member that is displaced by applying a voltage is brought into contact with the brake member 80 to change the magnitude of the applied voltage. Thus, the force for pressing the brake member 80 may be changed.

1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic configuration diagram illustrating an intermediate transfer member and a photosensitive drum of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a roller of an intermediate transfer member of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a state in which a roller of an intermediate transfer member of the image forming apparatus according to the first exemplary embodiment of the present invention is displaced. FIG. 5 is a schematic configuration diagram illustrating an intermediate transfer unit of an image forming apparatus according to a second embodiment of the present invention. FIG. 6 is a schematic diagram illustrating a state in which a roller of an intermediate transfer member of an image forming apparatus according to a second embodiment of the present invention is displaced. It is the schematic which shows the roller of the intermediate transfer body of the image forming apparatus of the other form of this invention. FIG. 6 is a schematic diagram illustrating a relationship between a roller of an intermediate transfer member of an image forming apparatus according to a third embodiment of the present invention and a pressing member provided on the roller.

Explanation of symbols

10 Image forming apparatus 12 Photosensitive drum (image carrier)
20 Intermediate transfer member 44 Roller (first roller)
52 Elastic belt (intermediate transfer member)
65 racks (expandable means, moving means)
67 Pinion (expandable means, moving means)
76 Reading sensor (detection device)
78 roller (expandable means, pressing member)
80 Brake member (Expansion / contraction means, load increase / decrease member)

Claims (7)

An image carrier on which toner images of a plurality of colors are formed;
A toner image transferred following the image carrier, and an intermediate transfer member having elasticity whose circumference is a non-integer multiple of the circumference of the image carrier;
In an image forming apparatus having
An image forming apparatus comprising: an expansion / contraction means for expanding / contracting the intermediate transfer body in accordance with a periodic fluctuation amount of a surface speed of the image carrier.   2. The intermediate transfer member is an elastic belt stretched around a plurality of rollers, and the expansion / contraction means is a moving means that displaces the position of the roller and expands / contracts the elastic belt. The image forming apparatus described in 1.   3. The moving means displaces a first roller that is closest to a transfer position to which a toner image of the image carrier is transferred and is upstream in the moving direction of the elastic belt. The image forming apparatus described.   The image forming apparatus according to claim 2, wherein the expansion / contraction means is a pressing member that is disposed inside the elastic belt and presses the elastic belt from the inside.   The image forming apparatus according to claim 4, wherein the pressing member is provided between the first roller and the transfer position.   The image forming apparatus according to claim 1, wherein the expansion / contraction means is a load increasing / decreasing member that increases or decreases a load applied to the roller.   2. The expansion / contraction means expands / contracts the intermediate transfer body according to a periodic fluctuation of the image carrier detected by a detection device that detects a periodic fluctuation of a surface speed of the image carrier. The image forming apparatus according to claim 6.

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