JP2001005310A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably feed a transfer material to a transfer nip part between a transfer roller and a photoreceptive drum, to prevent the void of a toner image transferred to the transfer material and to prolong the service life of the photoreceptive drum. SOLUTION: One end side of a holder 22 holding a transfer drum 5 via a pressure spring 20 is pressed and moved by a change-over lever 24 by a rotating the changeover lever 24 by turning on a solenoid 25, only when the thickness of the transfer material is set to be that of a post card and thick paper or the like, so that a transfer gear 28 provided at the rotary shaft 5a of the transfer roller 5 is meshed with a drum gear part 27a formed at the flange 27 of the photoreceptive drum 1 by a specified gear ratio. Thus, a circumferential speed difference is caused in the rotation of the transfer roller 5, and the photoreceptive drum 1 when the transfer roller 5 is rotated and driven according to the rotation and driving of the photoreceptive drum 1, so that the transfer material is fed stably to a transfer nip part N, and also the void of the toner image transferred to the transfer material is prevented and the service life of the photoreceptive drum 1 is prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a copying machine or a printer for forming an image by an electrophotographic system or an electrostatic recording system.

[0002]

2. Description of the Related Art An image forming apparatus of this type irradiates an image exposure corresponding to an original image or an image signal input from a computer onto a photosensitive drum surface as an image carrier uniformly charged by a charging means. An electrostatic latent image is formed on the photosensitive drum, the electrostatic latent image is developed into a toner image by a developing unit, and the toner image is transferred to a transfer material by a transfer unit (for example, a transfer roller). There are electrophotographic copiers and printers that thermally fix the toner image to the transfer material and output it.

As the fixing means, for example, a heat-resistant fixing film is slid in contact with a heat-generating member, and a pressure member is pressed in contact with the heat-generating member via the fixing film. A so-called film-fixing type fixing device is used in which heat energy is applied from a heat-generating member to a transfer material such as paper that is pinched and conveyed at a pressure contact portion with a pressure member through a fixing film to thermally fix a toner image.

In this fixing device of the film fixing system, the transfer material is conveyed by a pressing roller as the pressing member, and the pressing roller has a certain or more holding portion (nip).
Since it requires a width, it is formed of an elastic rubber layer, and therefore expands due to heat. As a result, the transfer speed of the transfer material changes by several percent (about 3%).

Therefore, in order to absorb the change in the transfer speed of the transfer material, conventionally, when the transfer means is a transfer roller,
The transfer roller is configured so that the pressing force at which the transfer roller presses the photosensitive drum at the transfer nip portion is strong (total pressure is about 800 g to 1500 g).

[0006] Further, in the so-called heat roller type fixing device which applies thermal energy to the transfer material while nipping and transporting the transfer material by two cylindrical roller pairs as the fixing means, the transfer material is similarly stabilized. In some cases, the pressing force of the transfer roller against the photosensitive drum is set high for traveling.

[0007]

By the way, as described above, when the transfer roller is pressed against the photosensitive drum at a high pressure, if the thickness of the transfer material is large (for example, thick paper such as a postcard), In addition, a phenomenon in which a part of the toner image on the transfer material is re-transferred to the photosensitive drum and a part of the toner image on the transfer material is lost (hereinafter, referred to as “hollow”) is likely to occur.

For this reason, conventionally, as a countermeasure against this dropout, for example, a rotation driving means is provided on the transfer roller, and the transfer roller is rotated slightly faster than the rotation of the photosensitive drum to make a difference in peripheral speed, thereby making it possible to reduce the transfer speed on the transfer material. The toner image is rubbed with the toner image to prevent the void.

However, if there is always a peripheral speed difference between the photosensitive drum and the transfer roller, the rubbing resistance at the transfer nip portion on the photosensitive drum increases, so that the photosensitive layer on the surface of the photosensitive drum is easily shaved, and There is a disadvantage that the life of the device is shortened.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of preventing a toner image from dropping out and prolonging the life of a photosensitive drum while maintaining good conveyance of a transfer material. I do.

[0011]

In order to achieve the above object, the present invention provides an image carrier having a surface on which a toner image is formed;
A transfer roller that is in pressure contact with the image carrier, and a transfer bias is applied by passing a transfer material through a transfer nip portion between the image carrier and the transfer roller that rotates in a pressure-contact state by rotation of the image carrier. In an image forming apparatus that transfers the toner image onto the transfer material by the transfer roller, a detection unit that detects a type of the transfer material, and a rotation speed of the transfer roller with respect to a rotation speed of the image carrier, the detection unit And a rotation speed adjusting means for adjusting the rotation speed in accordance with the type information of the transfer material input from the printer.

The rotation speed adjusting means includes a first mode in which the transfer roller is driven to rotate by rotating the image carrier in accordance with the type information of the transfer material input from the detection means; The transfer roller can be freely switched between a second mode in which the rotational driving force of the image carrier is inputted and the image carrier is rotationally driven in accordance with the rotational drive of the image carrier. In the second mode, the rotation speed of the transfer roller is adjusted so as to be different from the rotation speed of the image carrier, so that the transfer roller and the image are rotated at the same speed as the image carrier. It is characterized in that a peripheral speed difference is generated in the rotation of the carrier.

Further, in the second mode, the rotational driving force of the image carrier is transmitted to the transfer roller side by meshing of a gear, and the transfer roller is rotationally driven.

In the second mode, the rotation speed of the transfer roller is adjusted so as to be faster than the rotation speed of the image carrier.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic sectional view showing an image forming apparatus according to the present embodiment.

This image forming apparatus comprises a photosensitive drum 1 as an image carrier, a charging roller 2, an exposure device 3,
Developing device 4, transfer roller 5, cleaning blade 14
Is provided, and a fixing device 15 is provided downstream of the transfer roller 5 in the transport direction of the transfer material P.

In the present embodiment, the photosensitive drum 1 is a negatively charged organic photosensitive member and has a photosensitive layer on an aluminum drum base. The photosensitive drum 1 is driven to rotate at a predetermined process speed in the direction of arrow a. In the process, the charging roller 2 receives a uniform charging process of negative polarity.

The charging roller 2 rotates while being in contact with the surface of the photosensitive drum 1 with a predetermined pressing force, and applies a predetermined charging bias to the charging roller 2 from a charging bias power source 7.
The photosensitive drum is charged to a predetermined polarity and potential.

The exposure device 3 has a scanning optical system (not shown) using a semiconductor laser. The exposure L by laser light is charged through a reflection mirror 8 in accordance with an input image signal. The operation is performed on the photosensitive drum 1 to form an electrostatic latent image.

In the present embodiment, the developing device 4 is a non-contact type
The toner 11 is a non-magnetic one-component toner. As a developing bias applied to the developing sleeve 10, a bias obtained by superimposing an AC bias on a DC bias was used.

The transfer roller 5 is brought into contact with the surface of the photosensitive drum 1 with a predetermined pressing force at the transfer nip N, and
Is rotated by the drive of the transfer bias power supply (not shown).
, A predetermined transfer bias is applied.

In this embodiment, the rotation of the transfer roller 5 can be controlled in accordance with the type (thickness) of the transfer material P to which the toner image is transferred (detailed structure of the transfer roller 5). Will be described later).

The fixing device 15 is a film-fixing type fixing device, in which a heat-resistant fixing film 15a is slidably brought into contact with a heating element 15c provided inside, and a pressure roller 15b is contacted with the heating element 15c via the fixing film 15a. By pressing the heating element 15c with the movement of the fixing film 15a.
A transfer member P such as a paper pinched and conveyed by a pressure contact portion (fixing nip portion) with a pressure roller 15b is supplied with heat energy from a heating element 15c via a fixing film 15a to thermally fix the toner image.

Next, the image forming operation of the above-described image forming apparatus will be described.

At the time of image formation, the photosensitive drum 1 is driven to rotate in the direction of arrow a by a driving device (not shown), and the surface thereof is uniformly charged by the charging roller 2 rotating while contacting the photosensitive drum 1. Then, an exposure L is given from the exposure device 3 to the charged photosensitive drum 1 via the reflection mirror 8,
An electrostatic latent image corresponding to the input image information is formed. The toner 11 in the toner container 9 is supplied onto the photosensitive drum 1 after an appropriate amount of the toner 11 receives an appropriate charge with the rotation of the developing sleeve 10 to which the developing bias is applied. 11 adheres to the electrostatic latent image on the photosensitive drum 1 and the electrostatic latent image is developed and visualized as a toner image.

When the toner image on the photosensitive drum 1 reaches the transfer nip portion N between the photosensitive drum 1 and the transfer roller 5, the transfer material P such as paper in the sheet cassette 16 is fed at this timing. The sheet is conveyed after being separated one by one by the roller 17 and the separation pad 18, a transfer bias is applied, and a charge having a polarity opposite to that of the toner is applied to the back side of the transfer material P by the transfer roller 5. The toner image is transferred.

The transfer material P onto which the toner image has been transferred is conveyed to the fixing device 15, and the toner image is transferred onto the surface of the transfer material P by heating and pressing between the fixing film 15a and the pressure roller 15b of the fixing device 15. The sheet is thermally fixed, and is discharged to the outside by a discharge roller 19. The untransferred toner remaining on the photosensitive drum 1 without being transferred is a cleaning blade 14.
The photosensitive drum 1 that has been removed and collected in the cleaning device 6 and the surface of which has been cleaned is repeatedly used for the next image formation.

Next, the structure of the transfer roller 5 which is a feature of the present invention will be described.

As shown in FIG. 2, the transfer roller 5 is attached to the photosensitive drum 1 by a pressure spring 20 whose one end is connected to a holder 22 via bearings 21 fitted to both ends of the rotating shaft 5a. It is being rushed. Rotary shaft 5a of transfer roller 5
A transfer gear 28 is fitted to the other end (right side in FIG. 2). A drum gear 27a and a groove 27b are formed on a flange 27 fitted to the other end (right side in FIG. 2) of the photosensitive drum 1 to which a rotation driving means (not shown) is connected. Reference numeral 27a is free to mesh with the transfer gear 28. The flange 27 is rotatably supported by a support member 30.

The front wall portion 22a on one end side (left side in FIG. 2) of the holder 22 is urged by a holder spring 23 connected to a holding member 29 to urge the holder 22 rightward in FIG. .

A lever end portion 24 of the switching lever 24 is provided on a back wall portion 22b on the other end side (right side in FIG. 2) of the holder 22.
a is in contact. The switching lever 24 has its rotating shaft 24b
The rotation (clockwise rotation) of the switching lever 24 is restricted by a stopper plate 26 provided on the front side of the lever rear end 24c (in FIG. 2, the transfer roller 5 side of the lever rear end 24c). ing. A solenoid 25 is connected to a surface of the lever rear end 24c opposite to the stopper plate 26.

The solenoid 25 has a detection sensor 40 for detecting the type (thickness) of the transfer material P, and a control device 41 for controlling ON / OFF of the drive of the solenoid 25 based on detection information input from the detection sensor 40. It is connected.
The detection sensor 40 is arranged, for example, in the transfer path of the transfer material P.

When the solenoid 25 is in the OFF state, FIG.
, The solenoid 25 is not driven and the switching lever 2
4 is the lever end portion 24a of the holder 22 at the back wall portion 22b.
With almost zero pressure. When the solenoid 25 is ON, as shown in FIG. 3, the solenoid 25 is driven to rotate the switching lever 24 counterclockwise about the rotation shaft 24b by a predetermined angle, and the lever tip 24a is moved to the inner wall of the holder 22. The holder 22 is pressed against the portion 22b to urge the holder 22 leftward in FIG. 3 to move the holder 22 by a predetermined distance. At this time, the transfer gear 28 meshes with the drum gear 27a by the movement of the holder 22.

Next, the operation of the transfer roller 5 will be described.

First, a description will be given of a transfer mode (first mode) in which a toner image is transferred to a general paper sheet having a small thickness, such as a postcard or a thick paper, at the time of image formation.

In the transfer mode in this case, as shown in FIG. 2, the transfer roller 5 has bearings 21 fitted at both ends thereof.
And is urged against the photosensitive drum 1 by the pressure spring 20 via the.

In this case, the type of the transfer material P (normal thin paper in this case) is detected by the detection sensor 40, so that the control device 41 controls the solenoid 25 based on the detection information from the detection sensor 40. Outputs an OFF signal.
As a result, the solenoid 25 is in the OFF state, and the solenoid 25 is not driven, and the lever tip 24a of the switching lever 24 is in contact with the inner wall portion 22b of the holder 22 with almost no pressure. Therefore, since the transfer roller 5 is biased by the holder spring 23 in the rightward direction in FIG. 2, the transfer gear 28 is located in the groove 27 b of the flange 27, and the transfer roller 5 drives the photosensitive drum 1 to rotate. It is driven to rotate.

During the image forming operation, the photosensitive drum 1 is rotationally driven by a driving device (not shown), so that the transfer roller 5 which comes into pressure contact with the photosensitive drum 1 is driven to rotate.
And the paper (transfer material P) as described above.
The toner image is transferred thereon, and is thermally fixed by the fixing device 15 and then discharged onto a paper discharge tray.

In this transfer operation, the total pressure of the transfer roller 5 against the photosensitive drum 1 at the transfer nip N is about 5
00 g.

According to the experimental results of the present inventor, when a toner image is transferred onto a general paper having a small thickness such as a postcard or a thick paper as described above, the transfer material P No void phenomenon occurred in the transferred toner image.

Further, even if the conveying speed slightly changes due to the expansion of the pressure roller 15a of the fixing device 15, the toner image is not disturbed, and the circumferential distance between the transfer roller 5 and the photosensitive drum 1 does not occur. Since there is no difference in speed, the photosensitive layer on the surface of the photosensitive drum 1 is not cut away more than necessary, and the life of the photosensitive drum 1 can be extended.

Next, a description will be given of a case of a transfer mode (second mode) in which a toner image is transferred to a thick paper such as a postcard or a thick paper in which the thickness of the transfer material P is formed at the time of forming the image.

In the transfer mode in this case, as shown in FIG. 3, the transfer roller 5 has bearings 21 fitted at both ends thereof.
And is urged against the photosensitive drum 1 by the pressure spring 20 via the.

In this case, the type of the transfer material P (thick paper in this case) is detected by the detection sensor 40, and the control device 41 turns on the solenoid 25 based on the detection information from the detection sensor 40. Output a signal. As a result, the solenoid 25 is turned on, and the solenoid 2
5 is driven, the switching lever 24 is rotated counterclockwise about the rotation shaft 24b by a predetermined angle, and the lever tip 24a is
The holder 22 is pressed against the rear wall portion 22b of FIG. 2 and presses the holder 22 leftward in FIG. 3 to move a predetermined distance against the urging force of the holder spring 23 in the rightward direction in FIG. As a result, the holder 22 moves to the left in the drawing, and the transfer gear 28 meshes with the drum gear 27a.

Thus, with the rotation of the photosensitive drum 1, the transfer roller 5 also moves the drum gear 27 a and the transfer gear 28.
Are driven to rotate by the meshing of. At this time, since the gear ratio between the drum gear portion 27a and the transfer gear 28 is set to a predetermined value, the transfer roller 5 rotates slightly faster than the photosensitive drum 1 (peripheral speed difference about + 1% to + 6%). Then, the toner image is transferred onto the transfer material P.

In this way, the transfer roller 5 is rotated slightly faster than the rotation of the photosensitive drum 1 to make a difference in peripheral speed, so that the toner image is rubbed on the transfer material P during the transfer to prevent the hollowing out. can do.

When a toner image is to be transferred from this transfer mode to a general non-thick paper such as a postcard or a thick paper, the solenoid 25 is turned off and the lever tip 24a of the switching lever 24 is turned off. Is holder 2
2 is released from the pressure contact with the back wall portion 22b,
The engagement between the drum gear portion 27a and the transfer gear 28 is released by the urging force of the holder spring 23 against the front wall portion 22a of the holder 22.

As a result, the state returns to the state shown in FIG. 2, and the transfer roller 5 is driven to rotate by the driving of the photosensitive drum 1, whereby the photosensitive drum 1 and the transfer roller 5 are rotated at the same peripheral speed.

As described above, in the present embodiment, when the transfer material P is thick paper such as a postcard or a thick paper, the solenoid 25 is turned on and the drum gear 27a and the transfer gear 2 are turned on.
8, the transfer roller 5 is driven to rotate in accordance with the driving rotation of the photosensitive drum 1, and the transfer roller 5 is rotated slightly faster than the rotation of the photosensitive drum 1 to make a difference in peripheral speed. While the P is stably conveyed, the toner image can be rubbed on the transfer material P to prevent the dropout.

The operation of rotating the transfer roller 5 with a peripheral speed difference relative to the rotation of the photosensitive drum 1 is limited to only the case where the transfer material P is a thick paper such as a postcard or a thick paper. By doing so, it is possible to minimize the scraping of the photosensitive layer on the surface of the photosensitive drum 1 and prolong the life of the photosensitive drum 1.

In the present embodiment, the fixing film 1
The fixing device 15 of the film fixing type in which the pressing roller 15b is pressed against the heating element 15c via the heating member 15a is used, but the transfer material is conveyed between the heating roller and the pressing roller that are pressed against and heat-fixed. The same effect can be obtained in a fixing device of a heat roller type.

<Embodiment 2> FIG. 4 is a diagram showing a configuration of a transfer roller of an image forming apparatus according to the present embodiment. The same members as those of the first embodiment shown in FIGS. 2 and 3 are denoted by the same reference numerals and described.

In this embodiment, the transfer roller 5 has a bearing 21 and a holder 22 fitted to both ends of the rotating shaft 5a.
Are biased to the photosensitive drum 1 by a spring force of a pressure spring 20 connected to the photosensitive drum 1. A transfer gear 28 is fitted on the other end (right side in FIG. 4) of the rotation shaft 5a of the transfer roller 5. A groove 28 is provided outside the transfer gear 28 of the rotating shaft 5a.
a, a regulating plate 28b is formed, and the transfer gear 28, the groove 28a, and the regulating plate 28b formed integrally are movably fitted along the axial direction of the rotating shaft 5a.

A drum gear 27a and a groove 27b are formed on a flange 27 fitted to the other end (right side in FIG. 4) of the photosensitive drum 1 to which a driving means (not shown) is connected. The drum gear 27a is freely meshable with the transfer gear 28. The flange 27 is rotatably supported by the support member 30.

The groove 2 formed outside the transfer gear 28
A lever distal end portion 32a of the switching lever 32 is fitted between the control lever 8a and the regulating plate 28b, and a stopper plate 26 is provided on the outer surface (opposite to the transfer roller 5) of the lever rear end portion 32b of the switching lever 32. Is installed so that it can be freely contacted.

A solenoid 25 is connected to a connecting portion 32c formed on the inner side (toward the transfer roller 5) near the lever rear end portion 32b of the switching lever 32, and a surface of the connecting portion 32c opposite to the solenoid 25 is A stopper spring 31 for connecting the lever rear end portion 32b of the switching lever 32 to the stopper plate 26 with a predetermined urging force is connected.

The solenoid 25 has a detection sensor 40 for detecting the type (thickness) of the transfer material P, and a solenoid 25 based on detection information input from the detection sensor 40 for detecting.
A control device 41 that controls ON and OFF of the drive of the LM is connected. The detection sensor 40 is arranged, for example, in the transfer path of the transfer material P.

In the state where the solenoid 25 is OFF, FIG.
, The solenoid 25 is not driven and the switching lever 3
The second lever rear end 32b is in contact with the stopper plate 26 by the urging force of the stopper spring 31. In this state, the transfer gear 28 is located in the groove 27b without engaging with the drum gear 27a. Also, the solenoid 25
5, the solenoid 25 is driven and the switching lever 32 moves toward the transfer roller 5 against the urging force of the stopper spring 31, as shown in FIG. Switching lever 32
5 is fitted between the groove 28a and the regulating plate 28b, the transfer roller 5 moves to the left in FIG. 5 with the transfer roller 5 pressed against the photosensitive drum 1 with the movement of the switching lever 32. The transfer gear 28 meshes with the drum gear 27a.

Next, the operation of the transfer roller 5 will be described.

First, a description will be given of a transfer mode (first mode) in which a toner image is transferred onto a general paper sheet having a small thickness, such as a postcard or a thick paper, at the time of forming the image.

In the transfer mode in this case, as shown in FIG. 4, the transfer roller 5 has bearings 21 fitted at both ends thereof.
And is urged against the photosensitive drum 1 by the pressure spring 20 via the.

In this case, the type of the transfer material P (normal thin paper in this case) is detected by the detection sensor 40, so that the control device 41 controls the solenoid 25 based on the detection information from the detection sensor 40. Outputs an OFF signal.
Thus, the solenoid 25 is in the OFF state, and the solenoid 25 is not driven, and the lever rear end portion 32 b of the switching lever 32 is in contact with the stopper plate 26 by the urging force of the stopper spring 31. Therefore, the transfer gear 28 is located in the groove 27 b of the flange 27, and the transfer roller 5 is driven to rotate by the rotation of the photosensitive drum 1.

During the image forming operation, the photosensitive drum 1 is rotationally driven by a driving device (not shown), so that the transfer roller 5 which comes into pressure contact with the photosensitive drum 1 is driven.
And the paper (transfer material P) as described above.
The toner image is transferred thereon, and is thermally fixed by the fixing device 15 and then discharged onto a paper discharge tray.

In this transfer operation, the total pressure of the transfer roller 5 against the photosensitive drum 1 at the transfer nip N is about 5
00 g.

Next, a description will be given of a case of a transfer mode (second mode) in which a toner image is transferred to a thick paper such as a postcard or a thick paper in which the thickness of the transfer material P is formed at the time of forming the image.

In the transfer mode in this case, as shown in FIG. 5, the transfer roller 5 has bearings 21 fitted at both ends thereof.
And is urged against the photosensitive drum 1 by the pressure spring 20 via the.

In this case, the type of the transfer material P (thick paper in this case) is detected by the detection sensor 40, and the control device 41 turns on the solenoid 25 based on the detection information from the detection sensor 40. Output a signal. As a result, the solenoid 25 is turned on, and the solenoid 2
5 is driven to move the switching lever 32 to the transfer roller 5 side against the urging force of the stopper spring 31. As a result, the lever tip 32a of the switching lever 32 is
5, the transfer roller 5 moves to the left in FIG. 5 with the transfer lever 5 pressed against the photosensitive drum 1 with the movement of the switching lever 32, and the transfer gear 28 meshes with the drum gear 27a.

As a result, as the photosensitive drum 1 is driven and rotated, the transfer roller 5 also moves the drum gear 27a and the transfer gear 28.
Are driven to rotate by the meshing of. At this time, since the number of teeth of the drum gear portion 27a and the transfer gear 28 is set to a predetermined value, the transfer roller 5 rotates slightly faster than the photosensitive drum 1 (peripheral speed difference about + 1% to + 6%). As a result, the toner image is transferred onto the transfer material P.

In this way, the transfer roller 5 is rotated slightly faster than the rotation of the photosensitive drum 1 to make a difference in peripheral speed, so that the toner image is rubbed on the transfer material P during the transfer to prevent the dropout. can do.

When the toner image is transferred from the transfer mode to general non-thick paper such as a postcard or thick paper, the switching lever 32 is turned off by turning off the solenoid 25 as described above. The engagement between the drum gear 27a and the transfer gear 28 is released by the spring force of the stopper spring 31.

As a result, the state returns to the state shown in FIG. 4, and the transfer roller 5 is driven to rotate by the driving of the photosensitive drum 1, whereby the photosensitive drum 1 and the transfer roller 5 are rotated at the same peripheral speed.

As described above, also in the present embodiment, when the transfer material P is a thick paper such as a postcard or a thick paper, the solenoid 25 is turned on to engage the drum gear 27a with the transfer gear 28. The transfer roller 5 is driven to rotate in accordance with the rotation of the photosensitive drum 1, and the transfer roller 5 is rotated slightly faster than the rotation of the photosensitive drum 1 to make a peripheral speed difference, so that the transfer material P is stably conveyed. However, the toner image can be rubbed on the transfer material P to prevent the void.

The operation of rotating the transfer roller 5 with a difference in peripheral speed with respect to the rotation of the photosensitive drum 1 is limited to only the case where the transfer material P is a thick paper such as a postcard or a thick paper. Since it can be performed, the scraping of the photosensitive layer on the surface of the photosensitive drum 1 can be minimized, and the life of the photosensitive drum 1 can be extended.

In this embodiment, the switching lever 3
With the configuration in which the transfer gear 28 is directly moved in Step 2, the load can be reduced, and a small and inexpensive solenoid 25 can be used, so that the cost can be reduced.

Further, in this embodiment, the switching lever 3
2, the transfer roller 5 itself does not move even if the transfer gear 28 moves, so that no extra space is required for the transfer roller 5 to move, and the size of the image forming apparatus can be reduced.

In each of the above embodiments, the transfer gear 28 is a single gear, but may be a gear train in which a plurality of gears are engaged.

Further, in each of the above-described embodiments, the detection sensor 40 for detecting the type of the transfer material P is arranged in the conveyance path of the transfer material P. A switch for setting the type of the transfer material P may be provided in the operation unit, and an operator may operate this switch to input an input signal of the type of the transfer material to the control device 41.

[0079]

As described above, according to the present invention, the rotation speed adjusting means adjusts the rotation speed of the transfer roller with respect to the rotation speed of the image carrier in accordance with the type information of the transfer material inputted from the detection means. For example, when the transfer material is thick paper such as a postcard or thick paper, the transfer roller is rotated at a different speed from the image carrier so that the transfer roller and the image carrier are rotated. By generating a peripheral speed difference in the rotation of, it is possible to prevent hollowing out while maintaining the conveyance stability of the transfer material and obtain a good image.

Also, the life of the photosensitive drum can be extended by generating a peripheral speed difference between the rotation of the transfer roller and the image carrier only when the transfer material is thick paper such as postcard or thick paper. it can.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to Embodiments 1 and 2 of the present invention.

FIG. 2 is a side view showing a photosensitive drum and a transfer roller of the image forming apparatus according to the first embodiment.

FIG. 3 is a side view showing a photosensitive drum and a transfer roller of the image forming apparatus according to the first embodiment.

FIG. 4 is a side view showing a photosensitive drum and a transfer roller of the image forming apparatus according to the second embodiment.

FIG. 5 is a side view showing a photosensitive drum and a transfer roller of the image forming apparatus according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Exposure device 4 Developing device 5 Transfer roller 15 Fixing device 20 Pressure spring 21 Bearing 22 Holder 23 Holder spring 24, 32 Switching lever 25 Solenoid 27 Flange 27a Drum gear 27b Groove 28 Transfer gear 31 Stopper spring 40 Sensor 41 Controller

Claims (4)

[Claims] An image bearing member having a surface on which a toner image is formed; and a transfer roller pressed against the image bearing member, wherein the transfer roller rotates in a pressed state by rotating the image bearing member. An image forming apparatus that passes the transfer material through the transfer nip portion and transfers the toner image onto the transfer material by the transfer roller to which a transfer bias is applied; a detection unit configured to detect a type of the transfer material; Image-forming means for adjusting the rotation speed of the transfer roller with respect to the rotation speed of the image carrier in accordance with the type information of the transfer material input from the detection unit. apparatus. 2. The image forming apparatus according to claim 1, wherein the rotation speed adjustment unit is configured to rotate the transfer roller in accordance with the type information of the transfer material input from the detection unit, the rotation mode being driven by the rotation of the image carrier. The transfer roller can be freely switched between a second mode in which the rotational driving force of the image carrier is inputted and the image carrier is rotationally driven in accordance with the rotational drive of the image carrier. In the second mode, the rotation speed of the transfer roller is adjusted so as to be different from the rotation speed of the image carrier, so that the transfer roller and the image are rotated at the same speed as the image carrier. The image forming apparatus according to claim 1, wherein a peripheral speed difference is generated in rotation of the carrier. 3. The image forming apparatus according to claim 2, wherein in the second mode, a rotational driving force of the image carrier is transmitted to the transfer roller side by meshing of a gear to rotate the transfer roller. 4. The image forming apparatus according to claim 2, wherein in the second mode, the rotation speed of the transfer roller is adjusted to be higher than the rotation speed of the image carrier.