JP2012058285A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing the generation of an abnormal image by changing the secondary transfer pressure of a secondary transfer roller (contact transfer body) with respect to an intermediate transfer body, thereby suppressing impact when a sheet-like recording medium such as paper rushes into a secondary transfer part, when switching from a full color mode to a color reduction mode is performed, or the like.SOLUTION: An image forming apparatus 50 capable of executing the full color mode for forming an image by a plurality of photoreceptors 15K, 15C, 15M and 15Y and the color reduction mode for separating an intermediate transfer belt 13 and bias rollers 16C, 16M and 16Y from the plurality of photoreceptors 15C, 15M and 15Y and forming the image by the remaining photoreceptor 15K includes a secondary transfer pressure reduction mechanism 2 or 2A for making the secondary transfer pressure of a secondary transfer roller 10 with respect to the intermediate transfer belt 13 when the color reduction mode is executed smaller than that when the full color mode is executed.

Description

  The present invention relates to an image forming apparatus. More specifically, the present invention relates to a color mode and a subtractive color in an electrophotographic system or an electrostatic recording system, such as a copying machine, a printer, a facsimile machine, a plotter, or a multifunction machine having two or more functions. The present invention relates to a technique for reducing so-called shock jitter in an image forming apparatus capable of executing a mode.

Conventionally, in a tandem type image forming apparatus such as a copying machine or a printer that employs an intermediate transfer method, when switching from a full color mode to a subtractive color mode, considering the life of unused photoconductors and developers, A technique having a mechanism for separating the primary transfer roller facing the photoreceptor of the image forming unit that does not function via the intermediate transfer belt or a mechanism for separating the intermediate transfer belt and the primary transfer roller is already known (for example, Patent Documents 1 and 2).
Here, the “full color mode” means an operation of functioning a plurality of photoconductors (image forming units) for all colors to form a full color image, and the “subtractive color mode” means a plurality of photoconductors. It means an operation of forming a single color image (usually monochrome) by causing a part (usually one for black) to function.

  In the conventional technology configuration in which the primary transfer roller facing the photosensitive member of a color not used in the color reduction mode is separated, the support force of the intermediate transfer belt becomes unstable due to weakening of the binding force of the intermediate transfer belt at the time of separation, and the sheet-like recording medium It is already known that the speed of the intermediate transfer belt fluctuates due to an impact when a sheet or the like enters the secondary transfer portion, and abnormal images such as streaks or white spots are generated in the image (so-called shock jitter). (For example, refer to Patent Document 2).

  Japanese Patent Application Laid-Open No. 2005-228867 discloses a technique for detecting the color used in the color reduction mode for the purpose of suppressing image defects caused by a reduction in the binding force of the intermediate transfer belt when the full color mode is switched to the color reduction mode. A technique for increasing the pressing force of the primary transfer roller facing the body and increasing the nip amount (clamping area) is disclosed.

  However, in the technique described in Patent Document 2, since the primary transfer pressure is increased and the nip amount is increased, the charge amount of the toner is changed. Will occur.

  The present invention has been made in view of the above-described problems and circumstances. When switching from the full color mode to the subtractive color mode or the like, the impact when a sheet-like recording medium such as paper enters the secondary transfer portion is applied. The main object is to suppress the occurrence of abnormal images by suppressing the secondary transfer pressure of the secondary transfer roller (contact transfer body) with respect to the intermediate transfer body.

In order to solve the above-described problems and achieve the above-mentioned object, the invention according to each claim employs the following characteristic means / invention-specific matters (hereinafter referred to as “configuration”).
The invention according to claim 1 is provided for each of the plurality of image carriers, a plurality of image carriers on which toner images are formed, an intermediate transfer member that is movable while contacting the plurality of image carriers, A primary transfer means for transferring a toner image formed on the image carrier to the intermediate transfer member; and a sandwiching portion provided so as to be in contact with the intermediate transfer member and for conveying a sheet-like recording medium together with the intermediate transfer member. A voltage for secondary transfer of the toner image primary-transferred on the intermediate transfer member onto the sheet-like recording medium is applied to the contact transfer member to be formed and the sheet-like recording medium conveyed through the sandwiching portion. A color mode in which an image is formed by the plurality of image carriers, and a part of the plurality of image carriers and the intermediate transfer member are relatively separated from each other and an image is formed by the remaining part of the image carriers. Image formation capable of forming color reduction mode And a secondary transfer pressure reducing mechanism that reduces the secondary transfer pressure of the contact transfer body with respect to the intermediate transfer body more than that during the color mode when the color reduction mode is executed. .

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the secondary transfer pressure reducing mechanism includes an elastic body and an eccentric cam.
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the secondary transfer pressure reducing mechanism includes an elastic body and a crank mechanism.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the secondary transfer pressure reducing mechanism is also used as another drive source constituting the image forming apparatus. It is characterized by being performed.

According to the present invention, a novel image forming apparatus can be realized and provided by solving the above-described problems. The effects of the invention for each claim are as follows.
According to the first aspect of the present invention, the secondary transfer pressure reducing mechanism that reduces the secondary transfer pressure of the contact transfer body with respect to the intermediate transfer body when executing the subtractive color mode than that when executing the color mode is provided. The occurrence of abnormal images can be suppressed by suppressing the impact when the sheet-like recording medium enters the secondary transfer portion when the color mode is switched to the subtractive color mode by the secondary transfer pressure reducing mechanism. it can.

  According to the second and third aspects of the invention, the configuration can reduce the secondary transfer pressure applied to the contact transfer body (for example, the secondary transfer roller).

  According to the fourth aspect of the present invention, the number of parts and the cost can be reduced by the configuration.

1 is a schematic front sectional view of a conventional image forming apparatus to which the present invention is applied together with an image forming apparatus showing a first embodiment of the present invention. (A) is a schematic explanatory view for explaining the position and contact relationship between the intermediate transfer belt, the bias (primary transfer) roller and the photoconductor when the full color mode is executed, and (b) is the above-mentioned when the subtractive color mode is executed. It is typical explanatory drawing explaining the position and contact relationship of each member, shock jitter, and image defect. It is a simplified front view showing the secondary transfer pressure reduction mechanism of the first embodiment. FIG. 9 is a simplified front view showing a secondary transfer pressure reducing mechanism of Modification 1; FIG. 10 is a perspective view showing a main part of Modification 2.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, modes for carrying out the present invention including examples (hereinafter referred to as “embodiments”) will be described in detail with reference to the drawings. In each embodiment and modification, etc., components (members, components, etc.) having the same function, shape, etc. will be described by giving the same reference numerals after having been described once unless there is a possibility of confusion. Omitted. In order to simplify the drawings and the description, even if the components are to be represented in the drawings, the components that do not need to be specifically described in the drawings may be omitted as appropriate. When quoting and explaining constituent elements such as published patent gazettes, the reference numerals are shown in parentheses to distinguish them from those of the embodiments.

FIG. 1 shows an image forming apparatus of this embodiment together with a conventional image forming apparatus to which the present invention is applied. In the figure, reference numeral 100 with parentheses indicates a conventional image forming apparatus to which the present invention is applied, and reference numeral 50 indicates an image forming apparatus of the present embodiment. First, an overall configuration and operation of a conventional image forming apparatus 100 will be described with reference to FIG.
The conventional image forming apparatus 100 has a secondary transfer pressure reduction mechanism 2 or 2A shown by a broken line in the same drawing as compared to the image forming apparatus of the first embodiment and the first modification described later. Only the difference is not.

  The image forming apparatus 100 has a tandem apparatus configuration that forms a full-color image. That is, in the image forming apparatus 100, the first to fourth process cartridges 1K, 1C, 1M, and 1Y are arranged in this order from right to left. The image forming apparatus 100 includes first to fourth process cartridges 1K, 1C, 1M, and 1Y that are mounted and disposed in the apparatus main body 49, and an intermediate transfer member that is disposed to face these process cartridges. A transfer belt 13. The intermediate transfer belt 13 is an endless belt and is wound around the driving roller 11, the driven roller 12 and the tension roller 14.

The process cartridges 1K, 1C, 1M, and 1Y have drum-shaped photoreceptors 15K, 15C, 15M, and 15Y as image carriers. Specifically, the process cartridge 1K is a black photoconductor 15K, the process cartridge 1C is a cyan photoconductor 15C, the process cartridge 1M is a magenta photoconductor 15M, and the process cartridge 1Y is yellow. Each having a photosensitive member 15Y. Different color toner images are formed on the photoreceptors 15K, 15C, 15M, and 15Y, and the toner images are sequentially transferred to the intermediate transfer belt 13.
Each of the process cartridges 1K to 1Y is also called an image forming unit, and is configured to be detachable from the apparatus main body 49.

  The configuration of the first to fourth process cartridges 1K to 1Y and the configuration of transferring the toner images formed on the photosensitive members 15K to 15Y to the intermediate transfer belt 13 are substantially different only in the colors of the toner images. Therefore, the configuration of the fourth process cartridge 1Y and the configuration of transferring the toner image on the photoconductor 15Y to the intermediate transfer belt 13 will be described as a representative, and the description of the rest will be omitted. Further, in FIG. 1, for the same components, European characters representing colors are attached only to the process cartridge, the photosensitive member, and the developing device to simplify the drawing, and omit the components to other components. And

  The fourth process cartridge 1Y includes a charging device 20Y having a charging roller 8Y and the like disposed around the photoreceptor 15Y, a developing device 18Y having a developing roller 17Y and the like, and a cleaning device 21Y having a cleaning blade and the like. It has. The cases of these devices 20Y, 18Y, and 21Y are integrally disposed in a cartridge case that is a common unit case.

  When the image forming operation is started, the photoreceptor 15Y is rotationally driven in the clockwise direction in FIG. 1, and the intermediate transfer belt 13 is rotationally driven in the arrow A direction. At this time, the charging roller of the charging device 20Y rotates while contacting the surface of the photoconductor 15Y, and the photoconductor 15Y is uniformly charged to a predetermined polarity by the action of the charging roller. The charged photoconductor 15Y is irradiated with a light-modulated exposure beam 19Y emitted from the exposure device 22 shown in FIG. 1 which is separate from the process cartridge 1Y, whereby an electrostatic latent image is formed on the photoconductor 15Y. It is formed.

  The developing roller 17Y of the developing device 18Y is driven to rotate counterclockwise in FIG. 1, and a dry developer is carried and conveyed on the developing roller 17Y, and yellow toner in the developer is formed on the photoreceptor 15Y. The electrostatic latent image is transferred and attached to the electrostatic latent image, and the electrostatic latent image is visualized as a yellow toner image. A bias roller 16Y, also called a primary transfer roller, serving as a primary transfer means is disposed on the opposite side of the process cartridge 1K across the intermediate transfer belt 13, and is formed on the photoreceptor 15Y by the action of the bias roller 16Y. The toner image is transferred onto the intermediate transfer belt 13. The transfer residual toner adhering to the photoreceptor 15Y after the toner image transfer is scraped and removed from the surface of the photoreceptor 15Y by the cleaning blade of the cleaning device 21Y.

  In exactly the same manner as described above, a black toner image, a cyan toner image, and a magenta toner image are formed on the photosensitive members 6K, 6C, and 6M of the first to third process cartridges 1K, 1C, and 1M shown in FIG. These toner images are formed, and these toner images are sequentially transferred onto the intermediate transfer belt 13 onto which the yellow toner image has been transferred.

  On the other hand, as shown in FIG. 1, a paper feed cassette 23 containing a sheet P as an example of a sheet-like recording medium is disposed in a paper feed unit disposed at a lower portion in the apparatus main body 49. Sheet P is fed in the direction of arrow B by the cooperation of the rotation of the sheet feed roller 24 and a separation member (not shown). The fed paper P is abutted against the pair of registration rollers 25, stopped once, corrected for oblique displacement, etc., and sent in time with the toner image on the intermediate transfer belt 13. Then, the toner is conveyed to a secondary transfer portion formed by a drive roller 11, an intermediate transfer belt 13, and a secondary transfer roller 10 as a contact transfer member disposed opposite thereto. The toner image on the intermediate transfer belt 13 is transferred to the paper P by the secondary transfer bias applied from the driving roller 11 and the action of the secondary transfer roller 10 in the secondary transfer portion. The sheet P on which the toner image has been transferred is further conveyed upward and passes through a fixing unit 26 as a fixing device. At this time, the toner image on the sheet P is fixed by the action of heat and pressure. The paper P that has passed through the fixing unit 26 is discharged onto a paper discharge unit 27 at the top of the apparatus main body 49. Further, the transfer residual toner adhering to the intermediate transfer belt 13 after the toner image is transferred is removed by the cleaning unit 28 for the intermediate transfer belt 13.

  The secondary transfer roller 10 is urged by an urging means 29 made of an elastic body such as a compression coil spring in a direction to be pressed against the intermediate transfer belt 13 facing the drive roller 11 with a predetermined pressure. A transfer portion is formed. An electrode (not shown) that can apply a voltage (secondary transfer bias) for secondary transfer of the toner image primarily transferred on the intermediate transfer belt 13 onto the paper P is applied to the driving roller 11 of this example. Is provided. A secondary transfer bias is applied to the electrode provided on the driving roller 11 from a secondary transfer voltage applying means (not shown).

  Here, the mechanism of the shock jitter that occurs when the paper enters the secondary transfer portion will be described. The paper P once hits the intermediate transfer belt 13 and then is conveyed upward along the intermediate transfer belt 13 and inserted into a secondary transfer portion formed by the drive roller 11, the intermediate transfer belt 13 and the secondary transfer roller 10. The At this time, since the secondary transfer roller 10 is pushed down in the direction of the arrow C in the figure, the sheet P is applied by the action of the urging means 29 that urges the secondary transfer roller 10 in the direction in pressure contact with the intermediate transfer belt 13. As a result, the pressing force (pressing force) against the secondary transfer roller 10 increases, and the load increases instantaneously. As a result, the speed of the intermediate transfer belt 13 is decreased. As a result of the speed fluctuation (position fluctuation) occurring in the intermediate transfer belt 13 in this way, the toner transfer position from each photoconductor 15 to the intermediate transfer belt 13 in the primary transfer portion is deviated from the target position, so-called density. Unevenness occurs. Normally, the toner image becomes thinner (extends) when the intermediate transfer belt 13 becomes faster, and becomes darker (shrinks) when it becomes slower.

  The so-called shock jitter described above appears prominently in the subtractive color mode. FIG. 2B shows the position state / mechanism of the intermediate transfer belt 13, the photoconductor 15, and the bias roller 16 in the color reduction mode. The subtractive color mode is a mode in which a pair of any one or more colors (photosensitive member 15 and bias roller 16 (primary transfer roller)) is separated from all the colors to be used. In the monochrome mode, bias rollers 16Y, 16M, which are opposed to the yellow photoconductor 15Y, the magenta photoconductor 15M, and the cyan photoconductor 15C, which are not used, are shown. 16C is separated.

  In the full color mode, the intermediate transfer belt 13 is supported by a driving roller 11, a driven roller 12, a tension roller 14, and four pairs of photoconductors 15 and a bias roller 16. In the monochrome mode, the photoconductors 15Y and 15M are supported. , 15C and the bias rollers 16Y, 16M, and 16C opposed thereto are separated from each other, and the support from the three pairs is free. Therefore, the stability of the intermediate transfer belt 13 is lowered, the speed fluctuation of the intermediate transfer belt 13 when the paper P enters the secondary transfer portion becomes significant, and shock jitter occurs. The mechanism for switching between the full color mode and the subtractive color mode shown in FIG. 2 may be the same as the mechanism disclosed in Patent Documents 1 and 2 or the like.

  Here, in the monochrome mode (color reduction mode), the toner that is primarily transferred onto the intermediate transfer belt 13 is a single black layer. Since the bias voltage applied by the driving roller 11 of the secondary transfer unit is not different from that in the full color mode, an image with a reduced number of layers can be easily moved to a sheet P or a recording medium P. Thus, even if the required pressure by the driving roller 11 and the secondary transfer roller 10 in the secondary transfer portion is set lower than that in the full color mode, the transferability is not adversely affected. By setting the pressure low, it is possible to suppress the impact caused when the sheet P enters the secondary transfer portion, so that the shock jitter that occurs when the intermediate transfer belt 13 becomes unstable is reduced.

(First embodiment)
Based on the above-described phenomenon and the obtained knowledge, a first embodiment of the present invention will be described with reference to FIG. Compared with the conventional image forming apparatus 100 shown in FIGS. 1 and 2, the first embodiment is surrounded by a broken line in FIG. 1 and has a secondary transfer pressure reducing mechanism 2 shown in FIG. (Refer to the image forming apparatus 50 of FIG. 1 showing the first embodiment). Except for this difference, the first embodiment is the same as the image forming apparatus 100 of FIG.

In FIG. 3, the secondary transfer pressure reduction mechanism 2 has a function of reducing the secondary transfer pressure of the secondary transfer roller 10 with respect to the intermediate transfer belt 13 when executing the color reduction mode as compared with that when executing the color mode.
The secondary transfer pressure reduction mechanism 2 is mainly composed of a motor 3 as a drive source / drive means, an eccentric cam 5, a support member 6, an elastic body 9, a slide member 7, and a roller support member 8. ing.

The motor 3 is composed of a stepping motor, for example. The eccentric cam 5 is fixed to a cam shaft 4 connected to the motor 3 via a driving force transmission means such as a gear (not shown). The eccentric cam 5 is supported by a side plate (not shown) of the apparatus main body (not shown) via the cam shaft 4 so as to be rotatable in the arrow direction in the figure.
The elastic body 9 is made of, for example, a compression coil spring, but can be replaced with another member as long as it exhibits an equivalent function and durability.

The support member 6 is provided such that one end surface on the right side in the drawing can come into contact with the eccentric cam 5, and the other end surface on the left side in the drawing is connected to the elastic body 9. The support member 6 is a guide member (not shown) similar to the guide member 30 fixed to the side plate of the apparatus main body (not shown) so as to be movable in the arrow D direction (horizontal direction in the figure) and the opposite direction in the figure. It is supported by.
The slide member 7 has a triangular thick plate shape when viewed from the front, and smoothly slides in the direction of arrow D (horizontal direction in the figure) on the guide member 30 whose bottom surface is fixed to the side plate of the apparatus body (not shown). It is supported to guide. The slide member 7 has a right end face connected to the elastic body 9 in the drawing, and a slanting face on the left side in FIG. The slide member 7 moves in the direction of arrow D in the figure (horizontal direction in the figure), and the inclined surface comes into contact with the roller support member 8, thereby applying a secondary transfer pressure load on the intermediate transfer belt 13 to the secondary transfer roller 10. It functions as a motion direction conversion member that converts in the direction of arrow C. The guide member 30 is a member having a cross-sectional shape having a U-shape when viewed from the right side in the drawing.

The roller support member 8 has a fan shape, and is supported by the shaft end portions 10a on the front side and the back side of the secondary transfer roller 10 so as to be rotatable within a predetermined angle range. The roller support member 8 is illustrated in an elongated hole (not shown) in which each shaft end portion 10a protruding outward from the roller support member 8 is opened in parallel with the side plate of the apparatus main body (not shown) along the arrow C direction. It is supported so that it can be moved minutely through a non-bearing bearing.
The eccentric cam 5, the support member 6, the slide member 7, and the roller support member 8 are formed of a material that can be regarded as a substantially rigid body. It is preferable that the support member 6, the slide member 7, and the roller support member 8 are formed of a resin having good slidability and durability in terms of their functions to reduce the weight.

  The operation of the secondary transfer pressure reducing mechanism 2 will be described. For example, when the eccentric cam 5 of the secondary transfer pressure reduction mechanism 2 occupies the initial position indicated by the solid line in the drawing when the full color mode is set, the secondary transfer pressure similar to that shown in FIG. It is set to the state. When the eccentric cam 5 is rotated 180 ° from the initial position by driving the motor 3 during execution of the color reduction mode (for example, monochrome mode), the eccentric cam 5 occupies the rotational position indicated by the broken line. Accordingly, the support member 6 connected to the elastic body 9 also slides in the direction of arrow D in the figure and moves to the position indicated by the broken line. At this time, the elastic body 9 is stretched along with the support member 6, and its compression length changes long. As a result, the pressure (secondary pressure) applied to the roller support member 8 of the secondary transfer roller 10 and the secondary transfer roller 10 through the slide of the support member 7 connected to the elastic body 9 in the direction of arrow D in the figure. The transfer pressure is reduced by the amount of movement of the elastic body 9 by Δx.

(Modification 1)
With reference to FIG. 4, the modification 1 of 1st Embodiment is demonstrated. Modification 1 differs from the first embodiment only in that a secondary transfer pressure reduction mechanism 2A shown in FIG. 4 is used instead of the secondary transfer pressure reduction mechanism 2 shown in FIGS. To do. Except for this difference, the first modification is the same as the first embodiment.

The secondary transfer pressure reduction mechanism 2A has the same function as the secondary transfer pressure reduction mechanism 2 of the first embodiment.
The secondary transfer pressure reducing mechanism 2A includes an elastic body 9 and a slider crank mechanism, and includes a motor 3 as a driving source, a crank rotating plate 31 as a crank, a crankshaft 32 as a connecting node, and a guide. The member 33, the piston 36, the elastic body 9, the slide member 7, and the roller support member 8 are mainly configured. Hereinafter, components different from the secondary transfer pressure reduction mechanism 2 of the first embodiment will be mainly described.

  The crank rotation plate 31 is fixed to a crank rotation shaft 35 connected to the motor 3 via driving force transmission means such as a gear (not shown). The crank rotation plate 31 is supported by a side plate (not shown) of the apparatus main body (not shown) via a crank rotation shaft 35 so as to be rotatable in the arrow direction in the figure.

  The guide member 33 is composed of one plate-like member fixed to the side plate of the apparatus main body (not shown). In the upper and lower wall surfaces of the guide member 33, the piston 34 is guided and supported so as to slide smoothly. A crankshaft 32 is connected between a piston pin 36 planted on the piston 34 and a crankpin 37 planted on the outer peripheral side surface of the crank rotation plate 31. The left end face of the piston 34 is connected to the elastic body 9.

  The operation of the secondary transfer pressure reducing mechanism 2A will be described. For example, when the full color mode is set, when the crank pin 37 of the crank rotation plate 31 of the secondary transfer pressure reducing mechanism 2A is at the position E and the crankshaft 32 occupies the initial position, the same as shown in FIG. The secondary transfer pressure is set to be applied by the elastic body 9. When the subtractive color mode (for example, the monochrome mode) is executed, when the crank rotating plate 31 is rotated 180 ° from the initial position in the direction of the arrow in the drawing by driving the motor 3, the crankshaft 32 is displaced as indicated by a broken line. The piston 36 slides along the direction of arrow D in the figure while being guided by the guide member 33. At this time, the elastic body 9 is stretched along with the piston 36, and the compression length thereof changes long. As a result, the pressure (secondary pressure) applied to the roller support member 8 of the secondary transfer roller 10 and the secondary transfer roller 10 through the slide of the support member 7 connected to the elastic body 9 in the direction of arrow D in the figure. The transfer pressure is reduced by the amount of movement of the elastic body 9 by Δx.

(Modification 2)
With reference to FIG. 5, a first embodiment and a second modification of the first modification will be described. The operation of the secondary transfer pressure reduction mechanisms 2 and 2A (which can also be expressed as a secondary transfer pressure variable means or a secondary transfer pressure variable mechanism) as shown in FIGS. 3 and 4 is performed when switching between the full color mode and the color reduction mode. Therefore, in order to reduce the cost and the like, it is possible to perform this by controlling the driving force connecting / disconnecting means for connecting / disconnecting the driving force of another driving source constituting the image forming apparatus 50.
That is, the modification 2 is configured such that the driving force of another driving source constituting the image forming apparatus 50 is also used instead of the motor 3 as the driving source of the secondary transfer pressure reducing mechanisms 2 and 2A. Mainly different. As another drive source, a secondary transfer contact / separation mechanism as a secondary transfer contact / separation unit similar to those disclosed in Patent Documents 1 and 2, a primary transfer contact / separation mechanism as a primary transfer contact / separation unit, It is also used by using a drive source of a mechanism existing around the secondary transfer roller such as an intermediate transfer member or a sheet conveyance drive mechanism.

  As shown in FIG. 5, in the second modification, the electromagnetic clutch 43 as a driving force connecting / disconnecting means for connecting / disconnecting the driving force of another driving source and the full color mode in the secondary transfer pressure reducing mechanism 2 or 2A to the subtractive color mode. A timing sensor 41 serving as a mode switching detection unit that detects the switching state of the motor, and a control unit 40 that controls on / off of the electromagnetic clutch 43 based on a signal from the timing sensor 41.

  At the time of mode switching, the control means 40 controls the potential clutch 43 to be in a connected state based on a signal output at this time, so that one end of the idler gear 45 is connected to the idler gear 45 via the meshing idler gears 44 and 45. The cam shaft 4 or the crank rotating shaft 35 shown in FIGS. 3 and 4 is fixedly rotated. In the configuration shown in FIGS. 3 and 4, the cam shaft 4 or the crank rotation shaft 35 is controlled to rotate 180 °, so that the semicircular shape fixed to the other end of the cam shaft 4 or the crank rotation shaft 35 is used. The control means 40 performs control for switching on / off of the electromagnetic clutch 43 based on a signal generated based on whether light transmitted from the timing sensor 42 is transmitted (ON / OFF) using the light shielding plate 41. It will be. With this configuration, the secondary transfer pressure in the full color mode and the subtractive color mode can be controlled using the same drive source as the other mechanisms.

  As described above, the present invention has been described with respect to specific embodiments and modifications. However, the scope disclosed by the present invention is limited to those exemplified in the embodiments and modifications including the above-described embodiments. However, those skilled in the art can configure various embodiments, modifications, and examples in accordance with the necessity and application within the scope of the present invention. If so, it is clear.

  The mechanism for switching between the full color mode and the subtractive color mode using the primary transfer contact / separation mechanism as the primary transfer contact / separation means is not limited to that described with reference to FIG. The mechanism is applicable.

1 Process cartridge 2, 2A Secondary transfer pressure reduction mechanism (secondary transfer pressure reduction means, secondary transfer pressure variable means)
3 Motor (drive source)
4 cam shaft 5 eccentric cam 6 support member 7 slide member 8 roller support member 9 elastic body (biasing means)
10 Secondary transfer roller (contact transfer body)
11 Drive roller 12 Driven roller 13 Intermediate transfer belt (intermediate transfer member)
14 Tension roller 15 Photoconductor (image carrier)
16 Bias roller (primary transfer means)
30 Guide member 31 Crank rotating plate (crank)
32 Crankshaft (joint joint)
33 Guide member 34 Piston 35 Crank rotating shaft 40 Control means 41 Light shielding plate 42 Timing sensor (mode switching detection means)
43 Electromagnetic clutch (drive force connection / disconnection means)
49 apparatus main body 50 image forming apparatus

JP 2001-242680 A JP 2007-33938 A

Claims (4)

A plurality of image carriers on which toner images are formed, an intermediate transfer member that can move while contacting the plurality of image carriers, and each of the plurality of image carriers is provided on the image carrier. A primary transfer unit that transfers a toner image to the intermediate transfer member; a contact transfer member that is provided so as to be in contact with the intermediate transfer member and forms a sandwiching portion that conveys a sheet-like recording medium together with the intermediate transfer member; An electrode capable of applying a voltage for secondary transfer of the toner image primarily transferred on the intermediate transfer member onto the sheet-like recording medium conveyed to the sheet-like recording medium conveyed through the sandwiching portion;
A color mode in which an image is formed by the plurality of image carriers, and a subtractive mode in which a part of the plurality of image carriers and the intermediate transfer member are relatively spaced apart and an image is formed by the remaining part of the image carrier. In an executable image forming apparatus,
An image forming apparatus comprising: a secondary transfer pressure reducing mechanism that reduces a secondary transfer pressure of the contact transfer body with respect to the intermediate transfer body when executing the subtractive color mode than that when executing the color mode. . The image forming apparatus according to claim 1.
The secondary transfer pressure reduction mechanism includes an elastic body and an eccentric cam. The image forming apparatus according to claim 1.
The secondary transfer pressure reducing mechanism includes an elastic body and a crank mechanism. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus, wherein the secondary transfer pressure reducing mechanism is driven by using another drive source constituting the image forming apparatus.

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