JP2008286923A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic image forming apparatus capable of reducing its cost and maintaining predetermined transfer performance against an environmental change or the like. <P>SOLUTION: The image forming apparatus has a plurality of image forming units including: a transfer belt 1 conveying a transfer medium in the direction of the arrow A while attracting it to its conveying face 1a; and photoreceptor drums 11 arranged opposite the transfer belt 1 so as to be parallel to one another in the direction of the arrow A. Transfer members 15 are disposed in firm contact with the internal face of the transfer belt 1 and downstream of the corresponding photoreceptor drums 11 in the direction of conveyance, and apply charges of opposite polarity to toner to the transfer medium via the transfer belt 1. Each of the transfer members 15 is made from a conductive material and is reciprocative so as to hold the distance L1, L2 between the corresponding photoreceptor drum 11 and the transfer member 15. When the environment has high humidity and regular paper is supplied, the transfer member 15 is set to the distance L1. When the environment has low humidity and cardboard paper is supplied, the transfer member 15 is set into the distance L2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms a toner image on a transfer medium by electrophotography.

  2. Description of the Related Art Conventionally, in an image forming apparatus that forms a toner image on a transfer medium such as paper by electrophotography such as a copying machine or a printer, the transfer medium is attracted to the transfer belt and conveyed, and the transfer belt is attached to the transfer medium. There is known a method of applying a charge having a polarity opposite to that of the toner and transferring the toner image formed on the photosensitive member to a transfer medium (see, for example, Patent Documents 1, 2, and 3).

In this type of transfer system, a rubber roller is generally used as a transfer member that applies a charge having a polarity opposite to that of toner to a transfer medium via a transfer belt. However, the rubber roller has a problem that it is expensive because a roller made of urethane foam having a resistance value of 1 × 10 ⁶ ohms or more is attached to the metal shaft. In addition, in the tandem method for forming a color image, a plurality of transfer members are installed. However, since each transfer member has a variation in electric resistance value, a high voltage power source is provided for each transfer member to set an applied voltage value. It has to be adjusted, and the cost of the power supply unit also increases.

On the other hand, when a transfer bias voltage is applied from the transfer member via the transfer belt by utilizing the electrical resistance of the semiconductive transfer belt, the transfer member has a nip portion between the photoreceptor and the transfer belt to stabilize the transfer discharge. On the other hand, the transfer belt is disposed at a predetermined distance in the vicinity of the upstream side or the downstream side in the moving direction. If the distance between the nip part and the transfer member is set to a constant value as in the transfer devices described in Patent Documents 2 and 3, the current value varies depending on changes in the environmental humidity, the thickness of the transfer medium, etc., and the transfer performance varies. Will occur. For example, at a distance determined from the stability of transfer discharge in a high humidity environment, if the environment changes to a low humidity environment, current will flow too much and transfer performance will deteriorate. In the opposite case, the amount of current decreases and the transfer performance deteriorates.
JP-A-10-228186 JP-A-11-249460 JP 9-21001 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus by electrophotography that can achieve cost reduction and can maintain a predetermined transfer performance against environmental changes.

In order to achieve the above object, an image forming apparatus according to the present invention includes:
A semiconductive transfer belt that is rotationally driven at a predetermined speed;
An image forming unit disposed to face the outer surface of the transfer belt;
A toner that is disposed in the vicinity of the upstream side or the downstream side of the transfer belt in the moving direction of the transfer belt with respect to the nip portion between the photoconductor included in the image forming unit and the transfer belt, and presses the inner surface of the transfer belt. A transfer member made of a conductive material that imparts a charge of opposite polarity to the transfer belt via a transfer belt;
Moving means for reciprocating the transfer member substantially along the moving direction of the transfer belt;
Control means for moving the transfer member by the moving means according to at least the environmental conditions or the type of transfer medium;
It is provided with.

  In the image forming apparatus according to the present invention, since the transfer member is made of a conductive material, the transfer member can be manufactured at a low cost using, for example, a metal roller. Since the transfer member is reciprocated substantially along the moving direction of the transfer belt by the moving means according to at least the environmental conditions or the type of transfer medium, an optimum transfer current corresponding to changes in environmental conditions is supplied. And a decrease in transfer performance can be eliminated.

  In the image forming apparatus according to the present invention, the transfer member may be a roller made of a conductive metal material or a roller made of a conductive resin material, or may be a conductive film in contact with the transfer belt.

  In the image forming apparatus according to the present invention, a plurality of image forming apparatuses that form toner images of the respective colors are juxtaposed along the moving direction of the transfer belt, and a plurality of transfer members are provided on the photoconductor included in each image forming unit. You may comprise so that a color image may be formed in what is called a tandem system arrange | positioned facing. In this case, the transfer belt attracts and holds the transfer medium on its outer surface, and the transfer member applies a transfer bias voltage to the transfer medium via the transfer belt.

  In the tandem image forming apparatus, it is only necessary to have one high-voltage power supply for applying a transfer bias voltage to each of the transfer members. Since the transfer member made of a conductive material has an electric resistance value of almost zero, it is not necessary to finely adjust the transfer bias voltage for each transfer member. If is applied, the cost of the power supply unit can be reduced.

  The moving unit may also serve as a belt contacting / separating unit that moves the transfer member to a position where the transfer belt is separated from the photosensitive member. In the tandem system, only the image forming unit that forms a black image is operated when a monochrome image is formed. In this case, contact / separation means for separating the transfer belt from the photoconductor of another image forming apparatus is provided, and the configuration is simplified by the moving means also serving as the contact / separation means.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the member which is common in each Example, and the overlapping description is abbreviate | omitted.

(Basic configuration of image forming apparatus, see FIG. 1)
FIG. 1 shows a main part of a basic configuration of an image forming apparatus according to the present invention. This image forming apparatus forms a color toner image by a tandem method using a well-known electrophotographic method and by a direct transfer method. Specifically, the transfer belt 1 wound and held endlessly around the driving roller 2 and the driven roller 3 and an image forming unit 10 (10Y) that forms toner images of four colors (Y, M, C, K). , 10M, 10C, 10K).

  The transfer belt 1 is driven to rotate at a constant speed in the direction of arrow A by a driving roller 2, and a transfer medium M such as paper is supplied one by one from the direction of arrow B and statically applied to the lower surface by an electric field applied from the suction roller 4. It is electrically attracted and held and conveyed in the direction of arrow A. Hereinafter, this lower side surface is referred to as a suction conveyance surface 1a for the transfer medium M. Further, the transfer belt 1 maintains a constant tension by the driven roller 3 being elastically biased by the coil spring 5.

  Each image forming unit 10 includes a photosensitive drum 11, a charger, a developing device, an image exposure unit (optical scanning unit) (not shown), and the like, and Y, M, C, and K on the surface of each photosensitive drum 11. A toner image is formed. The process of forming a toner image is well known and will not be described.

  On the inner side of the suction conveyance surface 1 a of the transfer belt 1, a transfer member 15 is elastically pressed to a position almost opposite to each photosensitive drum 11. The transfer member 15 is made of a conductive material having a configuration described in detail below, and is near the downstream side of the transfer belt 1 in the moving direction (arrow A direction) with respect to the nip portion between the photosensitive drum 11 and the transfer belt 1. Is arranged. A transfer bias voltage of a predetermined value is applied to each transfer member 15 by one high-voltage power supply 20.

  The toner image formed on the surface of each photosensitive drum 11 is transferred from the transfer member 15 to the transfer medium that is attracted to and transported by the suction transport surface 1a of the transfer belt 1. It is transcribed by being applied via. As described above, the toner images formed on the respective photoconductive drums 11 are transferred to the surface of the transfer medium, synthesized, and heated and fixed by the fixing unit 21 installed in the subsequent stage.

  The transfer belt 1 includes a roller 2 and 3 and a transfer member 15 and is attached to a frame (not shown) to form a unit. Can be opened. Therefore, when the transfer medium is jammed during conveyance, the jammed transfer medium can be easily removed by opening the conveyance path by rotating the transfer unit in the direction of arrow C.

  The transfer member 15 is made of a conductive material, and can be manufactured at low cost if it is made of, for example, a metal roller as described below. Further, since the electric resistance value of the transfer member 15 is almost zero, it is not necessary to finely adjust the transfer bias voltage for each transfer member 15, and a constant voltage may be applied from one high-voltage power supply 20. The cost of the power supply unit can be reduced.

(Specific examples of transfer member, see FIGS. 2 to 5)
FIG. 2 shows a first example of the transfer member. This transfer member is constructed by using the metal shaft 16 as a transfer roller as it is, and can be manufactured at a very low cost. As the metal material, stainless steel and aluminum are suitable. A thin solid shaft having a diameter of about 8 mm is preferable in terms of strength and cost. If the pipe is made of metal, the weight can be reduced.

  In the case of a thin transfer roller, creep may occur in the transfer belt at a portion where the transfer belt 1 is wound around the transfer roller, which may cause transfer failure (image noise). However, if the large-diameter transfer roller shown in FIGS. 3 and 4 is used, it is possible to avoid such a problem.

  The second example of the transfer member shown in FIG. 3 is obtained by attaching metal flanges 17b to both ends of a metal pipe 17a, and the diameter of the pipe 17a is 12 mm or more. A third example of the transfer member shown in FIG. 4 is a roller body in which a plurality of conductive resin sleeves 18a made of conductive polyacetal or the like are covered with a metal shaft 18b, and the diameter of the sleeve 18a is 12 mm or more. It is. If the electrical resistance value of the conductive resin sleeve 18a is 1 kΩ or less, variation in resistance between the sleeves constituting the roller body can be ignored, and each roller disposed opposite to each photosensitive drum 11 can be ignored. Variations in resistance between bodies can be ignored, and a predetermined charge can be applied to the transfer medium by applying a constant voltage from one high-voltage power supply 20.

  FIG. 5 shows an image forming apparatus provided with a fourth example of a transfer member. The transfer member shown in FIG. 5 uses a conductive film 19. For example, it is made of a fluorine resin or a polyamide resin having a surface resistivity of about 100Ω. The leading end portion of the conductive film 19 is pressed against the inner surface of the transfer belt 1 on the downstream side in the conveying direction indicated by the arrow A from the nip portion between the photosensitive drum 11 and the transfer belt 1. Thus, the transfer belt 1 is bent, and the transfer belt 1 is brought into contact with the photosensitive drum 11 in the circumferential direction by about 1 to 2 mm.

  Note that the conductive film 19 such as a fluorine-based resin has a thickness of about 100 μm and low rigidity. Therefore, in order to obtain the required nip width by bending the transfer belt 1, it is necessary to back up the film 19 with polyphenylene sulfide resin or the like.

(Arrangement and transfer of transfer member, see FIG. 6)
Incidentally, since the transfer member 15 made of the conductive material described above has a small electric resistance, the electric resistance component (surface resistivity of about 1 × 10 ⁸ to 1 ×) of the semiconductive transfer belt 1 itself. It is necessary to form a transfer electric field using 10 ¹⁰ Ω). Specifically, the transfer member 15 is disposed about 2 to 6 mm downstream in the conveyance direction with respect to the nip portion between the photosensitive drum 11 and the transfer belt 1, and the electric resistance of the transfer belt 1 corresponding to the distance is used. It will be.

  Note that the transfer member 15 may be disposed on the upstream side in the transport direction by about 2 to 6 mm with respect to the nip portion between the photosensitive drum 11 and the transfer belt 1. However, if the transfer member 15 is arranged on the upstream side, electric discharge is likely to occur before the transfer of the toner image, so that there are cases where sufficient transfer performance cannot be exhibited.

  As described above, when the transfer member 15 made of a conductive material is used, as shown in FIGS. 6A and 6B, the transfer member 15 and the transfer belt 1 from the nip portion between the photosensitive drum 11 and the transfer belt 1 are used. The transfer current flowing through the transfer medium is changed by the transfer bias voltage applied from the high-voltage power supply 20 in accordance with the distances L1 and L2 to the nip portion.

  On the other hand, even if the distances L1 and L2 are the same, a large transfer current flows in a high humidity environment such as a humidity of 85%, and a transfer current decreases in a low humidity environment such as a humidity of 15%. If it is determined that the distance L1 is optimal from the stability of transfer discharge in a high humidity environment, if the distance L1 is changed to a low humidity environment, current flows too much at the same distance L1 and transfer performance deteriorates. Therefore, when the environment changes to a low humidity environment, the transfer member 15 is slightly moved to the upstream side in the transport direction A to correct the distance L2. Thus, good transfer performance can be maintained even in a low humidity environment.

  When the transfer belt 1 has an electrical resistance that changes not only with humidity but also with temperature, it is preferable to correct the distances L1 and L2 in consideration of temperature changes. Specifically, an ion conductive belt tends to have a high resistance at a low temperature (10 ° C. or lower) and tends to have a low resistance at a high temperature (30 ° C. or higher).

  Also, the transfer current varies depending on the type of transfer medium. For example, a transfer current is more likely to flow with thick paper than with plain paper. Therefore, when the thick paper is supplied, it is preferable to shorten the distance L1. In consideration of the environmental humidity and the type of transfer medium, in the first and second examples described below, the distance is set so that an optimum transfer current can be obtained assuming that plain paper is supplied in a high humidity environment. L1 was set. On the other hand, when thick paper is supplied in a low humidity environment, the transfer member 15 is moved to change the distance L2.

(Refer to FIG. 7 as a first example of moving means)
FIG. 7 shows a first example of moving means for the transfer member 15. 7 shows the moving means 30 of the transfer member 15 with respect to one image forming unit, the similar moving means 30 is also provided in the transfer member 15 with respect to other image forming units.

  This moving means 30 has a transfer member 15 attached to a lower portion of a lever 31 that is rotatably provided with a pin 32 as a fulcrum. The upper portion of the lever 31 is elastically biased in the direction of arrow D by a coil spring 33. In addition, the slider 35 is in contact with the inner wall surface 36 a of the recess 36. One end of the slider 35 is elastically biased in the direction of arrow D by a coil spring 37, and the outer peripheral surface of the cam 38 is in contact with the other end. The cam 38 is rotationally driven by a motor 40 with the support shaft 39 as a fulcrum.

  The motor 40 is controlled by the control unit 41. The controller 41 receives environmental humidity information from a sensor (not shown) and also inputs the type of transfer medium to be supplied, that is, plain paper and cardboard (including postcards, envelopes, and the like).

  In the above configuration, when the small diameter portion of the cam 38 is in contact with the other end of the slider 35, the slider 35 is moved in the direction of arrow D by the spring force of the coil spring 37, and the upper portion of the lever 31 is the coil spring 33. The spring 31 is pressed against the inner wall surface 36a, and the lever 31 rotates counterclockwise with the pin 32 as a fulcrum. Thereby, the transfer member 15 is set to the distance L1 shown in FIG.

  On the other hand, the control unit 41 drives the motor 40 to rotate the cam 38 by 180 ° when the environmental humidity information has changed to low humidity and when thick paper is supplied as the transfer medium. As a result, the large diameter portion of the cam 38 abuts against the other end of the slider 35, the slider 35 moves in the direction opposite to the arrow D against the spring force of the coil spring 37, and the inner wall surface 36 a moves to the lever 31. Move the top of in the same direction. As a result, the lever 31 rotates clockwise with the pin 32 as a fulcrum, and the transfer member 15 is set to the distance L2 shown in FIG. 6B.

  It should be noted that the movement amount of the transfer member 15 can be adjusted in a plurality of stages by controlling the rotation angle of the cam 38. Further, by expanding the rotation range of the lever 31 in the counterclockwise direction, it also serves as a belt contacting / separating means for releasing the pressure on the transfer belt 1 by the transfer member 15 and separating the transfer belt 1 from the photosensitive drum 11. You can also.

(Refer to the second example of moving means, FIG. 8)
FIG. 8 shows a second example of moving means for the transfer member 15. 8 shows the moving means 45 of the transfer member 15 with respect to one image forming unit, the same moving means 45 is also provided in the transfer member 15 with respect to other image forming units.

  The moving means 45 places the support shaft 22 of the transfer member 15 on the inclined surfaces 46a and 46b of the guide 46 so as to be freely rollable, and elastically presses the support shaft 22 downward by a coil spring 47. This is in contact with the regulating surface 48 a of the slider 48. One end of the slider 48 is elastically biased in the direction of arrow E by a coil spring 49, and the outer peripheral surface of the cam 50 is in contact with the other end. The cam 50 is rotationally driven by the motor 40 with the support shaft 51 as a fulcrum. The motor 40 is controlled by the control unit 41, and the configuration and operation of the control unit 41 are as described in the first example.

  In the above configuration, when the small diameter portion of the cam 50 is in contact with the other end of the slider 45, the slider 48 moves in the direction of arrow E by the spring force of the coil spring 49, and the support shaft 22 moves to the coil spring 47. It is pressed by the restricting surface 48 a by the spring force and is positioned below the inclined surface 46 a of the guide 46. Thereby, the transfer member 15 is set to the distance L1 shown in FIG.

  On the other hand, the control unit 41 drives the motor 40 to rotate the cam 50 by approximately 90 ° when the environmental humidity information has changed to low humidity and when thick paper is supplied as a transfer medium. As a result, the abdomen of the cam 50 abuts against the other end of the slider 48, the slider 48 moves in the direction opposite to the arrow E against the spring force of the coil spring 49, and the regulating surface 48 a moves the support shaft 22. Move in the same direction. The support shaft 22 slightly moves along the inclined surface 46a, and the transfer member 15 is set to the distance L2 shown in FIG.

  By making the inclination angle of the inclined surface 46a coincide with the angle at which the transfer belt 1 is wound around the photosensitive drum 11, even if the transfer member 15 is reciprocated to the distances L1 and L2, the photosensitive drum of the transfer belt 1 is used. 11 can be kept constant.

  Further, when the cam 50 is rotated 90 ° (180 ° from the state shown in FIG. 8), the large diameter portion of the cam 50 contacts the other end of the slider 48, and the slider 48 is in the direction opposite to the arrow E. Move the maximum distance to. As a result, the support shaft 22 rides on the inclined surface 46 b, the pressure on the transfer belt 1 by the transfer member 15 is released, and the transfer belt 1 is separated from the photosensitive drum 11. That is, the second example is configured to also serve as a belt contacting / separating means.

(Other examples)
The image forming apparatus according to the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the gist thereof.

  For example, the present invention can also be applied to an indirect transfer type primary transfer portion in which a toner image is primarily transferred and synthesized on a transfer belt and then secondarily transferred onto a transfer medium. The present invention can also be applied to a monochrome image forming apparatus having a single image forming unit. Alternatively, not only the type in which the adsorption surface of the transfer medium faces downward but also the type in which the suction surface faces upward may be used.

  Moreover, in the said Example, although the transfer member was installed so that a movement to two positions was carried out according to environmental humidity or the kind of transfer medium, you may install so that a movement to three or more multiple positions is possible.

1 is a schematic configuration diagram illustrating a basic configuration of an image forming apparatus according to the present invention. It is a front view which shows the 1st example of a transfer member. It is sectional drawing which shows the 2nd example of a transfer member. It is sectional drawing which shows the 3rd example of a transfer member. It is a schematic block diagram which shows the image forming apparatus provided with the 4th example of the transfer member. It is explanatory drawing which shows the movement aspect of a transfer member. It is a schematic block diagram which shows the 1st example of a transfer member moving means. It is a schematic block diagram which shows the 2nd example of a transfer member moving means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transfer belt 10 (10Y, 10M, 10C, 10K) ... Image forming unit 11 ... Photoconductor drum 15 ... Transfer member 20 ... High voltage power supply 30, 45 ... Moving means 41 ... Control part

Claims (7)

A semiconductive transfer belt that is rotationally driven at a predetermined speed;
An image forming unit disposed to face the outer surface of the transfer belt;
A toner that is disposed in the vicinity of the upstream side or the downstream side of the transfer belt in the moving direction of the transfer belt with respect to the nip portion between the photoconductor included in the image forming unit and the transfer belt, and presses the inner surface of the transfer belt. A transfer member made of a conductive material that imparts a charge of opposite polarity to the transfer belt via a transfer belt;
Moving means for reciprocating the transfer member substantially along the moving direction of the transfer belt;
Control means for moving the transfer member by the moving means according to at least the environmental conditions or the type of transfer medium;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the transfer member includes a roller in contact with the transfer belt, and the roller is made of a conductive metal material or a conductive resin material.   The image forming apparatus according to claim 1, wherein the transfer member includes a conductive film that contacts the transfer belt. A plurality of image forming apparatuses that form toner images of the respective colors are juxtaposed along the moving direction of the transfer belt,
A plurality of transfer members are arranged to face the photoconductor included in each image forming unit;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The transfer belt sucks and holds the transfer medium on its outer surface, and conveys it,
The transfer member applies a transfer bias voltage to the transfer medium via the transfer belt;
The image forming apparatus according to claim 4.   6. The image forming apparatus according to claim 4, further comprising one high-voltage power supply that applies a transfer bias voltage to each of the transfer members.   7. The image according to claim 4, wherein the moving unit also serves as a belt contacting / separating unit that moves the transfer member to a position where the transfer belt is separated from the photosensitive member. Forming equipment.

Images