JP4975539B2 - Image forming apparatus - Google Patents

Description

  The present invention includes a plurality of rollers in an image forming apparatus including a copying machine, a printer, and a multi-function machine that includes a plurality of image carriers, forms a plurality of color images, and prints on a medium such as paper. The present invention relates to a transfer apparatus having a contact / separation mechanism for bringing a belt into contact with an image carrier from the inside of the belt that is mounted.

  In recent years, the surface of an intermediate transfer belt using an intermediate transfer system, which has an image forming unit of each color of yellow, magenta, cyan, and black using an electrophotographic system, and formed on each image carrier surface There is known an image forming apparatus in which a primary transfer is sequentially performed, and then a toner image on a belt surface is transferred to a medium by a secondary transfer unit such as a transfer roller.

  Among them, there is an image forming apparatus using a system in which the intermediate transfer belt and the image carrier are brought into contact with and separated from each other in order to provide durability of the intermediate transfer belt. Yes. In addition, in order to prevent the intermediate transfer belt from moving in one direction and, in the worst case, misalignment in the superimposed image of multiple colors and breaking from the end of the belt, a protrusion (rib) on the back side of the belt Measures are taken by providing a belt, winding a reinforcing tape around the belt end, or providing a regulating member. This is disclosed in Patent Documents 2 and 3, for example.

JP 2005-266269 A JP 05-333707 A JP 2005-107033 A

  In general, the intermediate transfer belt has uneven thickness, and the lengths (peripheral lengths) of both ends along the running direction are slightly different. For this reason, it is known that the intermediate transfer belt is shifted to either end during traveling. This tendency is also affected by individual differences in belts, differences in the thickness of the rollers that stretch the belt, the running direction between the belts that stretch the belt and the parallelism in the axial direction, etc. It is a town. In any case, if the intermediate transfer belt travels greatly deviating in one direction, the positional deviation of the image in which the toners of a plurality of colors are superimposed is imitated.

  In addition, the intermediate transfer belt is slightly uneven at the end due to its manufacture. When the belt is driven while being displaced in one direction, the convex portion comes into strong contact with the end of the restricting member in a timely manner, and the belt weak in strength rises. When the belt rises, the function of the cleaning mechanism that cleans the toner remaining without being transferred to the belt surface is hindered. Furthermore, if a force that moves toward the belt continues to be applied, the belt will crack and break from the concentrated point in the long term.

  It is an object of the present invention to provide an image forming apparatus that solves these problems. In addition, the present invention can be applied to many types of machine parts having a belt stretched by rollers, and mechanical parts that push up both ends of the belt are provided, and the axial direction in which the belt approaches during idling is periodically determined. It is possible to correct the deviation of the belt by lifting or periodically lowering the opposite side.

  The image forming apparatus according to claim 1 of the present invention forms an electrostatic latent image on a uniformly charged image carrier by light emitted from an optical system, and visualizes the electrostatic latent image. For this purpose, a plurality of process units for developing toner are provided on the surface of the image carrier, and the movable endlessly stretched by at least two or more rotating bodies under the image carriers of the plurality of process units. A belt is provided, and a first transfer rotator capable of applying a bias is provided so as to face each of the image carriers across the endless belt, and the toner image on the surface of the image carrier is transferred to the endless belt. The toner image on the surface of the endless belt is transferred to a transfer medium sandwiched between second transfer rotators that can apply a bias opposite to the rotator over which the endless belt is stretched. Toner image In the image forming apparatus to be fixed by the attaching device, the endless belt is separated from the image carrier without being stretched by the first transfer rotator when not in operation, and the image forming operation on the transfer medium is started. And a contact / separation drive means for performing an operation of shifting the contact timing when the endless belt is brought into contact with the image carrier before the endless belt is rotationally driven in the axial direction of the first transfer rotator. And

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the endless belt is brought into contact with the image carrier using the first transfer rotator before the endless belt is rotationally driven. The timing at the time of the contact is such that when the endless belt is rotated, the direction in which the endless belt approaches in the axial direction of the rotating body on which the endless belt is stretched is the direction in which the endless belt approaches. It is characterized by performing an operation in which the opposite direction comes into contact later.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the endless belt is brought into contact with the image carrier using the first transfer rotator before the endless belt is rotationally driven. The timing is such that when the endless belt is rotated, the endless belt is first brought into contact with the image carrier in the axial direction of the rotating body on which the endless belt is stretched, and the endless belt is moved in this state. It is characterized in that it is driven to rotate, and after that, an operation is made so as to contact the direction opposite to the direction in which the endless belt approaches.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the endless belt is brought into contact with the image carrier using the first transfer rotator before the endless belt is rotationally driven. When the endless belt is rotated, the timing is such that the endless belt is first brought into contact with the image carrier in the axial direction of the rotating body around which the endless belt is stretched, and the endless belt is moved in this state. In an operation in which the endless belt is brought into contact with the direction opposite to the direction in which the endless belt approaches, the endless belt is driven to rotate within two revolutions of the endless belt.

  The process cartridge according to claim 5 is the image forming apparatus according to claim 3, wherein the endless belt is brought into contact with the image carrier using the first transfer rotator before the endless belt is rotationally driven. The timing of the endless belt is such that when the endless belt is rotated, the direction in which the endless belt approaches in the axial direction of the rotating body around which the endless belt is stretched is brought close to the image carrier first, and in this state the endless belt Is driven to rotate, and then the belt is brought into contact with the direction opposite to the direction in which the belt approaches.

  The replacement part for an image forming apparatus according to claim 6 is the image forming apparatus according to claim 5, wherein the endless belt is moved to the image carrier using the first transfer rotator before the endless belt is rotationally driven. When the endless belt is rotated, when the endless belt is rotated, the direction in which the endless belt approaches in the axial direction of the rotating body on which the endless belt is stretched is first brought close to the image carrier. In the operation in which the endless belt is driven to rotate, and then the endless belt is brought into contact with the direction opposite to the direction in which the endless belt approaches, the endless belt is driven to rotate within two revolutions of the endless belt. To do.

  According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the contact / separation driving unit uses a plurality of elliptical cams and utilizes the first transfer rotator. The endless belt is brought into contact with and separated from the image carrier.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the contact / separation driving means uses a plurality of elliptical cams facing each other, and the first transfer rotator is used. The endless belt is used to contact and separate from the image carrier.

  According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the contact / separation driving means uses a plurality of elliptical cams whose center of gravity is shifted, and the first transfer rotating body. The endless belt is brought into contact with and separated from the image bearing member by utilizing the above.

  According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the contact / separation driving unit uses a plurality of elliptical cams whose center of gravity is shifted facing each other, and the first A driving method for contacting and separating the endless belt from and to the image carrier using a transfer rotator is provided.

  According to the eleventh aspect of the present invention, an electrostatic latent image is formed on a uniformly charged image carrier by light emitted from an optical system, and the surface of the image carrier is used to visualize the electrostatic latent image. A plurality of process units for developing toner, and a movable endless belt stretched by at least two or more rotating members is provided below each of the image carriers of the plurality of process units; A transfer rotator capable of applying a bias is provided so as to face each of the image carriers so as to sandwich the toner image from the image carrier by the image carrier and the endless belt. In an image forming apparatus in which a toner image is transferred to a transfer medium that is sandwiched and biased and the transferred toner image is fixed by a fixing device, the endless belt is stretched around the transfer rotator when not operating. The contact rotation timing is determined when the endless belt is brought into contact with the image carrier before the endless belt is rotationally driven in an operation of starting image formation on the transfer medium, separated from the image carrier. It has the contact / separation drive means which performs the operation | movement shifted in the axial direction of a body.

  According to a twelfth aspect of the present invention, in the image forming apparatus according to the eleventh aspect, the endless belt is brought into contact with the image carrier using the transfer rotator before the endless belt is rotationally driven. The timing at the time of contact is such that when the endless belt is rotated, the direction in which the endless belt approaches in the axial direction of the rotating body on which the endless belt is stretched is opposite to the direction in which the endless belt approaches. This is characterized in that it performs an operation of touching later.

  According to a thirteenth aspect of the present invention, in the image forming apparatus according to the twelfth aspect, the timing when the endless belt is brought into contact with the image carrier using the transfer rotator before the endless belt is rotationally driven. If the endless belt is rotated, the endless belt is first brought into contact with the image carrier in the axial direction of the rotating body around which the endless belt is stretched, and the endless belt is rotationally driven in this state. Then, an operation is performed in which the endless belt is brought into contact with the direction opposite to the direction in which the endless belt approaches.

  According to a fourteenth aspect of the present invention, in the image forming apparatus according to the thirteenth aspect, the timing when the endless belt is brought into contact with the image carrier using the transfer rotator before the endless belt is rotationally driven. If the endless belt is rotated, the endless belt is first brought into contact with the image carrier in the axial direction of the rotating body on which the endless belt is stretched, and the endless belt is driven to rotate in this state. In the operation in which the endless belt comes in contact with the direction opposite to the direction in which the endless belt approaches, the endless belt is driven to rotate within two revolutions of the endless belt.

  According to a fifteenth aspect of the present invention, in the image forming apparatus according to the thirteenth aspect, the timing when the endless belt is brought into contact with the image carrier using the transfer rotator before the endless belt is rotationally driven. If the endless belt is rotated, the direction in which the endless belt approaches in the axial direction of the rotating body on which the endless belt is stretched is first brought close to the image carrier, and the endless belt is driven to rotate in this state. Then, after that, an operation is performed in which the direction in which the belt approaches and the opposite direction are brought into contact with each other.

  According to a sixteenth aspect of the present invention, in the image forming apparatus according to the fifteenth aspect, the timing when the endless belt is brought into contact with the image carrier using the transfer rotator before the endless belt is rotationally driven. If the endless belt is rotated, the direction in which the endless belt approaches in the axial direction of the rotating body on which the endless belt is stretched is first brought close to the image carrier, and the endless belt is driven to rotate in this state. Then, in an operation in which the endless belt is brought into contact with the direction opposite to the direction in which the endless belt approaches, the rotational drive of the endless belt is within two revolutions of the endless belt.

  According to a seventeenth aspect of the present invention, in the image forming apparatus according to any one of the eleventh to sixteenth aspects, the contact / separation driving unit uses a plurality of elliptical cams and the endless rotation using the transfer rotator. A belt is brought into contact with and separated from the image carrier.

  According to an eighteenth aspect of the present invention, in the image forming apparatus according to any one of the eleventh to sixteenth aspects, the contact / separation driving unit uses a plurality of elliptical cams facing each other and uses the transfer rotator. The endless belt is brought into contact with and separated from the image carrier.

  According to a nineteenth aspect of the present invention, in the image forming apparatus according to any one of the eleventh to sixteenth aspects, the contact / separation driving unit uses a plurality of elliptical cams whose centers of gravity are shifted and uses the transfer rotator. Then, the endless belt is brought into contact with and separated from the image carrier.

  According to a twentieth aspect of the present invention, in the image forming apparatus according to any one of the eleventh to sixteenth aspects, the contact / separation driving means uses a plurality of elliptical cams whose center of gravity is shifted facing each other, and the transfer rotation A driving method for bringing the endless belt into and out of contact with the image carrier using a body is provided.

  According to the present invention, when the endless belt is rotationally driven, it is possible to eliminate the problem of being always offset in one direction, so that the belt is prevented from rising, and the function of the belt cleaning mechanism is not hindered. Therefore, it is possible to prevent smearing of the printed image related to this. Furthermore, it is possible to prevent cracking and breakage of the belt, which can contribute to extending the life of the image forming apparatus including the belt, and to provide a long-life image forming apparatus including the intermediate transfer unit. It becomes.

  The best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings.

  FIG. 1 is a schematic sectional view of a so-called tandem indirect transfer type image forming apparatus to which the present invention is applied. In the figure, reference numeral 1 denotes a photosensitive drum, which is an image carrier having a diameter of 24 mm, and rotates clockwise at a peripheral speed of 120 mm / s. A roller-shaped charger 2 serving as charging means is pressed against the surface of the photosensitive drum 1 and is driven to rotate by the rotation of the photosensitive drum 1, and is about -1000 V from a high-voltage power source (not shown). By applying a bias, the photosensitive drum 1 is uniformly charged.

  Subsequently, an electrostatic latent image of image information is formed on the photosensitive drum 1 by the exposure unit 3. In this embodiment, an optical system using a laser diode is employed as the exposure means 3, but an LED may be substituted.

  The electrostatic latent image formed by the exposure unit 3 passes through the developing device 4 and is visualized as a toner image. The developing device 4 contains non-magnetic single component toner. The toner charged in contact with the inside is visualized as an electrostatic latent image on the photosensitive drum 1 as a toner image by a developing roller supplied with a developing bias from a high voltage power source. In the image forming apparatus of this embodiment, the photosensitive drum 1, the charger 2, and the developing unit 4 are integrated as a process unit 10, and are arranged in the order of black, magenta, cyan, and yellow from the right side of the figure. .

  The toner images visualized on the surface of the photosensitive drum 1 are sequentially superimposed on the intermediate transfer belt 15 and transferred to form a full-color image. The toner remaining without being transferred to the intermediate transfer belt 15 is scraped off by the cleaning blade A and collected in the waste toner portion 6. The intermediate transfer belt 15 is separated from the photosensitive drum 1 except during driving. The intermediate transfer belt 15 is stretched by a tension roller 20 and a drive / secondary transfer counter roller 21, and is driven at the same speed as the photosensitive drum 1 by a drive motor attached in the extending direction of the drive / secondary transfer counter roller 21. , Operate with left rotation.

  In order to describe the present invention in more detail, the intermediate transfer belt 15 from the image forming apparatus used in this embodiment, a tension roller 20 that supports and stretches the intermediate transfer belt 15, a driving and secondary transfer counter roller 21, A configuration including the primary transfer roller 5 is referred to as an intermediate transfer unit.

When the intermediate transfer belt 15 is brought into contact with the photosensitive drum 1, the primary transfer roller 5 also contributes to the tension of the intermediate transfer belt 15. The intermediate transfer belt 15 is always separated from the photosensitive drum 1, and when forming an electrostatic latent image and developing the image, the primary transfer roller 5 is in contact with the photosensitive drum 1 by a contact / separation mechanism described later. The intermediate transfer belt 15 is brought into contact with the photosensitive drum 1 by being lifted in the direction of. The intermediate transfer belt 15 used in this example has a volume resistivity of 10 ⁷ to 10 ¹¹ Ω · cm and a surface resistivity of 10 ⁷ to 10 ¹¹ Ω / mm ² (both measured and applied with Hiresta HT450 manufactured by Mitsubishi Chemical Corporation). A thermoplastic elastomer having a voltage of 500 V / 10 seconds was used. The primary transfer roller 5 is shifted 8 mm in the movement (running) direction of the intermediate transfer belt 15 and 1 mm in the vertical upward direction with respect to the photosensitive drum 1, and is wound around the photosensitive drum 1 when the intermediate transfer belt 15 is in contact. Thus, the toner image is effectively transferred. Further, the primary transfer roller 5 applies a bias voltage +500 to +1000 V to each color to form a transfer electric field via the intermediate transfer belt 15, and transfers the toner image on the photosensitive drum 1 to the intermediate transfer belt 15. The tension roller 20 was a roller having a diameter of 20 mm, and the driving roller 21 was a 20 mm roller having a roller surface coated with 50 μm polyurethane.

  In the figure, reference numeral 17 denotes a sensor used to adjust the image density and alignment by measuring the amount of toner transferred on the intermediate transfer belt 15 and the position of each color, and combines regular reflection and diffuse reflection. . In the figure, reference numeral 32 denotes a cleaning unit for cleaning the toner remaining on the surface of the intermediate transfer belt. The cleaning blade 31 is in contact with the belt moving direction so as to be a counter, and is made of a metal cleaning so as to face the belt. A counter roller 16 is provided. The toner conveyed from the cleaning unit is stored in the waste toner storage unit 33.

The secondary transfer roller 25 is formed by coating an elastic body of polyurethane adjusted to a resistance value of 10 ⁶ to 10 ¹⁰ Ω with a conductive material on a metal core having a diameter of 20 mm with a hardness of 35 to 50 ° (Asker C). I use it.

  The transfer material 22 is fed by a paper feeding / conveying roller 23 and a registration roller pair 24 so that the front end portion of the toner image on the surface of the intermediate transfer belt 15 reaches a secondary transfer position composed of a driving / secondary transfer counter roller 21 and a secondary transfer roller 25. The toner image on the intermediate transfer belt 15 is transferred to the transfer material 22 by applying a predetermined transfer bias from a metal cored bar of the secondary transfer roller 25 that is sent in time. Thereafter, the toner image transferred to the transfer material 22 is heated and pressed by the fixing device 58 and then discharged.

  In the present embodiment, the intermediate transfer belt 15 is offset in the present embodiment in order to prepare for an emergency situation where the intermediate transfer belt 15 moves too far in one direction and comes off the tension roller 20. It is attached. As a result of actually driving the intermediate transfer unit, it was found that almost all of the intermediate transfer belt 15 approaches the direction in which the motor for driving and driving the secondary transfer counter roller 21 exists. Although the motor is not shown, it corresponds to the front side of FIG. If a force that keeps the intermediate transfer belt 15 moving in one direction is applied, the end of the intermediate transfer belt 15 extends, cracks occur without being able to withstand the force, the end widens and climbs over the detent member, etc. A problem occurs. In order to solve this problem, it is sufficient to apply a force that moves in the direction opposite to the direction in which the intermediate transfer belt 15 approaches. What is considered here is that a means for moving the intermediate transfer belt 15 in the reverse direction is performed at the beginning of a series of printing steps.

  More specifically, based on the contact / separation mechanism of the intermediate transfer belt 15 provided in the intermediate transfer unit, the primary transfer roller 5 is not lifted simultaneously, but the lifting timing is shifted. That is, since the intermediate transfer belt 15 approaches the front side of the figure, the front side of the primary transfer roller 5 is operated and lifted first, and the back side is operated and lifted later. As a result, the intermediate transfer belt 15 that has continued to move toward the front of the drawing at the time of printing can be once moved closer to the back side, thereby preventing the belt surface from rising due to the intermediate transfer belt 15 continuing to move toward one side. Thus, the function of the cleaning mechanism portion of the intermediate transfer belt 15 is not hindered, and it is possible to prevent stains on the printed image related thereto. Further, it effectively works against cracks and breaks in the intermediate transfer belt 15 and is useful for extending the life.

  In the first embodiment, the intermediate transfer unit requires two types of drive mechanisms for contacting and separating the intermediate transfer belt 15 on the front side and the back side. In the present embodiment, an examination was made so that the contact / separation driving mechanism is shared as a new means for lifting the intermediate transfer belt 15.

  In order to explain the means for lifting the primary transfer roller 5, an excerpt is shown in FIG. 2. FIG. 2 shows a state when the intermediate transfer belt 15 contacts the photosensitive drum 1. The cam shown by the solid line in FIG. 2 is the front side (the side with the motor that drives the intermediate transfer unit), and the dotted line is the back side. The mark ● shown on the inner side of the cam 100 indicates the shaft 101 to which the drive unit for driving the cam 100 is connected. The cam 100 has a shape that is inverted between the near side and the far side. The shaft 101 is fixed while being shifted from the center of the cam 100, and the cam 100 is aligned so that the cam 100 lifts the primary transfer roller 5 most at a position farthest from the center of the shaft 101. When the cam 100 is actually driven, the primary transfer roller 5 is lifted from the back side, the intermediate transfer belt 15 is brought into contact with the photosensitive drum 1, and then the front side is brought into contact.

  Of course, if the cam shape is changed between the front side and the back side, the shaft can be fixed at the center of the cam and the timing can be shifted to contact the photosensitive drum. It may be preferable to make the shape shifted.

  Alternatively, the same effect can be obtained by increasing the curvature of one side by changing the shape of the cam 100 from an ellipse to a minor axis as shown in FIG. As a result of using this example, the intermediate transfer belt 15 that had been kept close to the front side in FIG. 2 at the time of printing could be once moved to the back side. As a result, the belt surface is prevented from rising due to the intermediate transfer belt 15 being always deviated toward one side, the function of the cleaning mechanism of the intermediate transfer belt 15 is not hindered, and the stain on the print image related thereto is prevented. Was able to prevent. Furthermore, it effectively works against cracks and breaks in the intermediate transfer belt 15 and helps to extend the life.

  In the present invention, the cam is applied as the contact / separation mechanism, but it is needless to say that it may be driven up and down by a solenoid or the like.

  As Example 3 of the present invention, in order to move the intermediate transfer belt 15 to the opposite side more effectively, the primary transfer roller 5 which is the approaching side is first operated and lifted, and one side is separated from the photosensitive drum 1. In this state, the intermediate transfer belt 15 was once driven, and the other side was operated later and lifted up. As a result, the intermediate transfer belt 15 that had been kept close to the front side in the drawing at the time of printing could be brought closer to the back side. For this operation, it was sufficient to bring the intermediate transfer belt 15 closer to the photosensitive drum 1 and to drive the intermediate transfer belt 15 once. Of course, if it is difficult to move close, there is no problem even if they are brought into contact with each other, and the intermediate transfer belt 15 may be driven twice with a margin. According to the third embodiment, the belt surface is prevented from rising due to the intermediate transfer belt 15 being constantly deviated toward one side, and the function of the cleaning mechanism portion of the intermediate transfer belt 15 is not hindered. Dirt was prevented. Further, it effectively works against cracks and breaks in the intermediate transfer belt 15 and is useful for extending the life.

  FIG. 4 is a schematic sectional view of a so-called tandem type direct transfer type image forming apparatus to which the present invention is applicable. The difference from the apparatus of the first embodiment is a configuration in which a transfer material 63 passes between a photosensitive drum 61 as an image carrier and a transfer belt 62. Since the operation is almost the same as in the first embodiment, only the outline is given.

  The photosensitive drum 61 of this embodiment rotates rightward in the figure. By applying a bias from a charger 64 in contact with the surface of the photosensitive drum 61, the photosensitive drum 61 is uniformly charged. Subsequently, an electrostatic latent image of image information is formed on the photosensitive drum 61 by the exposure unit 65. The electrostatic latent image formed by the exposure unit 65 passes through the developing unit 67 of the process unit 66 and is visualized as a toner image. The visualized toner image is sequentially transferred onto the transfer material 63 in accordance with the passing timing of the transfer material 63. The transfer belt 62 is always separated from the photosensitive drum 61, and comes into contact with the photosensitive drum 61 when the opposing roller 68 is lifted upon receiving input of image information. The opposing roller 68 applies a bias having a polarity opposite to that of the toner image. The transfer material 63 having a toner image is conveyed by the transfer belt 62, heated and pressed by the fixing device 69, and discharged as an image. It should be noted that dirt such as residual toner and paper dust adhering to the surface of the transfer belt 62 is removed using the cleaning unit 70.

  Regarding the shift of the transfer belt 62, as a result of actually driving the transfer unit, it has been found that almost all of the transfer belt 62 approaches the direction in which the motor attached to the roller for driving the belt exists. Although the motor is not shown, it corresponds to the back direction of the figure. As in the first embodiment, means for moving the transfer belt 62 in the reverse direction at the beginning of the printing process is performed.

  That is, since the transfer belt 62 approaches the back side in the figure, before the transfer material 63 passes through the transfer belt 63, the back side of the plurality of opposed rollers 68 is first operated and lifted, and the opposite side is operated and lifted later. As a result of the operation, the transfer belt 62 that had continued to move toward the back side of the drawing during printing could be once moved toward the front side. As a result, the belt surface is prevented from rising due to the transfer belt 62 being continuously moved to one side, the function of the cleaning mechanism of the transfer belt 62 is not hindered, and the print image related to this is prevented from being stained. I was able to. Further, it effectively works against cracks and breaks of the transfer belt 62 and is useful for extending the life.

  In Example 4 described above, two types of driving on the front side and the back side of the transfer belt 62 are required. Therefore, as in Example 1, as a result of attaching the cams as shown in FIGS. 2 and 3, the transfer belt 62 that had continued to move toward the back side in FIG. 4 at the time of printing could be once moved toward the front side. As a result, the belt surface is prevented from rising due to the transfer belt 62 always moving to one side, the function of the cleaning mechanism of the transfer belt 62 is not hindered, and the print image related to this is prevented from being stained. And helped to extend the service life. Although the cam is applied as the contact / separation mechanism of the present invention, it may be driven up and down by a solenoid or the like.

  Further, as a result of operating and lifting the back side of the opposing roller 68 first, driving the transfer belt 62 once with one side separated, and operating and lifting the opposite side later, FIG. The transfer belt 62 that continued to approach the back side could be effectively moved to the near side once. In this operation, it was sufficient to bring the transfer belt 62 closer to the photosensitive drum 61 and to drive the transfer belt 62 once. Of course, if it is difficult to move close, there is no problem even if they are brought into contact with each other, and the intermediate transfer belt 15 may be driven twice with a margin. According to the fifth embodiment, the belt surface is prevented from rising due to the transfer belt 62 always moving to one side, the function of the cleaning mechanism portion of the transfer belt 62 is not hindered, and the stain on the print image related to this is prevented. This is also useful for extending the life of the transfer belt 62.

Schematic sectional view of a so-called tandem type indirect transfer image forming apparatus to which the present invention is applied The figure which shows the example contact | abutted in the counter direction with respect to the movement of a photoconductive drum. Diagram showing cam shape example Schematic sectional view showing another example of a so-called tandem type direct transfer type image forming apparatus to which the present invention is applicable

Explanation of symbols

1: Photosensitive drum 2: Charger 3: Exposure means 4: Developing unit 5: Primary transfer roller 6: Waste toner unit 10: Process unit 15: Intermediate transfer belt 16: Cleaning counter roller 20: Tension roller 21: Driving and driving Secondary transfer counter roller 22: Transfer material 23: Paper feed roller 24: Registration roller pair 25: Secondary transfer roller 31: Cleaning blade 32: Cleaning unit 33: Waste toner storage unit 58: Fixing device 61: Photosensitive drum 62: Transfer belt 63: Transfer material 64: Charger 65: Exposure means 66: Process unit 67: Developer 68: Opposing roller 69: Fixing unit 70: Cleaning unit 100: Cam 101: Shaft of cam A: Cleaning blade

Claims (20)

A plurality of processes in which an electrostatic latent image is formed on a uniformly charged image carrier by light emitted from an optical system, and toner is developed on the surface of the image carrier in order to visualize the electrostatic latent image And a movable endless belt stretched by at least two or more rotating bodies is provided below the image carriers of the plurality of process units, and the image carriers are sandwiched between the endless belts. A first transfer rotator capable of applying a bias is provided so as to face each other, the toner image on the surface of the image carrier is transferred to the endless belt, and the toner image on the surface of the endless belt is stretched over the endless belt. In an image forming apparatus in which a toner image is transferred to a transfer medium sandwiched between second transfer rotators capable of applying a bias facing the rotator, and the transferred toner image is fixed by a fixing device.
The endless belt is kept away from the image carrier without being stretched by the first transfer rotator when not operating, and before the endless belt is driven to rotate in the image forming start operation on the transfer medium. An image forming apparatus comprising contact / separation drive means for performing an operation of shifting the contact timing when the endless belt is brought into contact with the image carrier in the axial direction of the first transfer rotator.   2. The image forming apparatus according to claim 1, wherein the endless belt is brought into contact with the image carrier using the first transfer rotator before the endless belt is rotationally driven. If the endless belt is rotated, the direction in which the endless belt approaches in the axial direction of the rotating body on which the endless belt is stretched first, and the direction opposite to the direction in which the endless belt approaches comes into contact later. What is claimed is: 1. An image forming apparatus comprising:   3. The image forming apparatus according to claim 2, wherein the timing when the endless belt is brought into contact with the image carrier using the first transfer rotator before the endless belt is rotationally driven is temporarily set to the endless belt. When the endless belt is rotated, the endless belt is first brought into contact with the image carrier in the axial direction of the rotating body on which the endless belt is stretched, and the endless belt is driven to rotate in that state, and then the endless belt is rotated. An image forming apparatus that performs an operation of contacting a direction opposite to a direction in which the belt approaches.   4. The image forming apparatus according to claim 3, wherein the timing when the endless belt is brought into contact with the image carrier using the first transfer rotating body before the endless belt is rotationally driven is temporarily set to the endless belt. When the endless belt is rotated, the direction in which the endless belt approaches in the axial direction of the rotating body on which the endless belt is stretched is first brought into contact with the image carrier, and in this state, the endless belt is rotated and driven. The image forming apparatus according to claim 1, wherein the rotation of the endless belt is within two rotations of the endless belt in an operation in which the opposite direction of the belt is brought into contact.   4. The image forming apparatus according to claim 3, wherein the timing when the endless belt is brought into contact with the image carrier using the first transfer rotating body before the endless belt is rotationally driven is temporarily set to the endless belt. When the endless belt is rotated, the direction in which the endless belt approaches in the axial direction of the rotating body on which the endless belt is stretched is first brought close to the image carrier, and in this state, the endless belt is rotated and driven. An image forming apparatus that performs an operation of making contact in a direction opposite to a direction in which the lens approaches.   6. The image forming apparatus according to claim 5, wherein the timing when the endless belt is brought into contact with the image carrier using the first transfer rotator before the endless belt is rotationally driven is temporarily set to the endless belt. When the endless belt is rotated, the direction in which the endless belt approaches in the axial direction of the rotating body on which the endless belt is stretched is first brought close to the image carrier, and in this state, the endless belt is rotated and driven. The image forming apparatus according to claim 1, wherein the rotation of the endless belt is within two revolutions of the endless belt in an operation in which the opposite direction of the belt is brought into contact with the opposite direction.   7. The image forming apparatus according to claim 1, wherein the contact / separation driving unit uses a plurality of elliptical cams, and uses the first transfer rotator to attach the endless belt to the image carrier. An image forming apparatus characterized in that it is brought into contact with and separated from the image.   7. The image forming apparatus according to claim 1, wherein the contact / separation driving unit uses a plurality of elliptical cams facing each other and uses the first transfer rotator to attach the endless belt to the image forming apparatus. An image forming apparatus which is brought into contact with and separated from an image carrier.   7. The image forming apparatus according to claim 1, wherein the contact / separation driving unit uses a plurality of elliptical cams whose centers of gravity are shifted, and uses the first transfer rotator to rotate the endless belt. An image forming apparatus, wherein the image forming apparatus is brought into contact with or separated from the image carrier.   7. The image forming apparatus according to claim 1, wherein the contact / separation driving unit uses a plurality of elliptical cams whose center of gravity is shifted facing each other, and uses the first transfer rotator. An image forming apparatus, characterized in that a driving method for bringing an endless belt into and out of contact with the image carrier is provided. A plurality of processes for forming an electrostatic latent image on a uniformly charged image carrier by light emitted from an optical system and developing toner on the surface of the image carrier to visualize the electrostatic latent image A unit is provided, and a movable endless belt stretched by at least two rotating bodies is provided below each of the image carriers of the plurality of process units, and each of the image carriers is sandwiched between the endless belts. A transfer rotating body capable of applying a bias is provided so as to face each other, and the toner image from the image carrier is sandwiched between the image carrier and the endless belt through the medium path, and the bias is applied. In an image forming apparatus for transferring to a transfer medium and fixing the transferred toner image by a fixing device,
The endless belt is separated from the image carrier without being stretched by the transfer rotator during non-operation, and the endless belt is rotated before the endless belt is driven to rotate in the image formation start operation on the transfer medium. An image forming apparatus comprising contact / separation drive means for performing an operation of shifting a contact timing when the belt is brought into contact with the image carrier in an axial direction of the transfer rotator.   12. The image forming apparatus according to claim 11, wherein the endless belt is brought into contact with the image carrier using the transfer rotator before the endless belt is rotationally driven. If the endless belt is rotated, the direction in which the endless belt approaches in the axial direction of the rotating body on which the endless belt is stretched, and the direction opposite to the direction in which the endless belt approaches comes into contact with the endless belt. An image forming apparatus.   13. The image forming apparatus according to claim 12, wherein the timing when the endless belt is brought into contact with the image carrier using the transfer rotator before the endless belt is rotationally driven is temporarily rotated. The endless belt is first brought into contact with the image carrier in the axial direction of the rotating body on which the endless belt is stretched, and the endless belt is driven to rotate in this state. An image forming apparatus, which performs an operation of contacting a direction opposite to the approaching direction.   14. The image forming apparatus according to claim 13, wherein the timing when the endless belt is brought into contact with the image carrier using the transfer rotator before the endless belt is rotationally driven is temporarily rotated. The endless belt is first brought into contact with the image carrier in the axial direction of the rotating body on which the endless belt is stretched, and the endless belt is driven to rotate in this state. The image forming apparatus according to claim 1, wherein the endless belt is driven to rotate within two rotations of the endless belt in an operation in which the direction opposite to the approaching direction is brought into contact.   14. The image forming apparatus according to claim 13, wherein the timing when the endless belt is brought into contact with the image carrier using the transfer rotator before the endless belt is rotationally driven is temporarily rotated. In this case, the direction in which the endless belt approaches in the axial direction of the rotating body on which the endless belt is stretched is first brought close to the image carrier, and in this state, the endless belt is driven to rotate, and then the belt approaches. An image forming apparatus that performs an operation of making contact in a direction opposite to a direction.   16. The image forming apparatus according to claim 15, wherein the timing when the endless belt is brought into contact with the image carrier using the transfer rotator before the endless belt is rotationally driven is temporarily rotated. When the endless belt is stretched, the axial direction of the endless belt is moved closer to the image carrier first, and the endless belt is driven to rotate in this state. An image forming apparatus characterized in that, in an operation in which the opposite direction and the opposite direction are brought into contact with each other, the rotation of the endless belt is within two revolutions of the endless belt.   17. The image forming apparatus according to claim 11, wherein the contact / separation driving unit uses a plurality of elliptical cams and contacts the endless belt to the image carrier using the transfer rotator. An image forming apparatus characterized by being separated.   17. The image forming apparatus according to claim 11, wherein the contact / separation driving unit uses a plurality of elliptical cams facing each other, and uses the transfer rotator to support the endless belt as the image carrier. An image forming apparatus which is brought into contact with or separated from a body.   17. The image forming apparatus according to claim 11, wherein the contact / separation driving unit uses a plurality of elliptical cams whose centers of gravity are shifted, and uses the transfer rotating body to display the endless belt. An image forming apparatus which is brought into contact with and separated from a carrier. 17. The image forming apparatus according to claim 11, wherein the contact / separation driving unit uses a plurality of elliptical cams whose center of gravity is shifted facing each other, and the endless belt using the transfer rotator. An image forming apparatus, characterized in that a driving method for contacting and separating the image carrier from the image carrier is provided.