JPH0588501A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device which automatically matches the phase of the speed variation of an image carrier, prevents color slippage, performs the phase matching operation without damaging the image carrier, etc., and prolongs the life of the image carrier, etc. CONSTITUTION:When an operator turns on a power source which is not shown in a figure to revolve a motor 75, its revolving force is transmitted to a cam 61 through gears 66, 64, and 63 and also transmitted to a cam 74, as well through gears 67, 68, 69, 70, and 71. An upper frame 30 and a lower frame 31 are rotated around a shaft part 27 through the operation of those cams 61 and 72 to be moved inwards respectively (toward center frame 29). Consequently, the tension of an intermediate transfer belt 12 is reduced and the intermediate transfer belt 12 and all photosensitive drums 19Y-19B are separated. In this state, the respective photosensitive drums 19Y-19B are automatically set at reference positions (home position) and their phases are matched.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image using an intermediate transfer member composed of an endless belt,
In particular, the present invention relates to an image forming apparatus that includes a plurality of image carriers for image formation to form a color image.

[0002]

2. Description of the Related Art Heretofore, an image forming apparatus for forming a color image of this type has a transfer belt (conveying belt) on which yellow, magenta, and yellow are formed, as disclosed in, for example, JP-A-63-75759. The configuration is such that the photosensitive drums (image bearing members) for forming images of cyan are arranged in a line. In such an image forming apparatus, since the photosensitive drums are installed for the respective colors, the speed can be increased.

[0003]

By the way, in such an image forming apparatus, the three photoconductor drums are rotationally driven by the drive motors via the reduction gear trains, respectively. A speed error occurs between the photoconductor drums due to the meshing error of the rows. This speed error causes speed fluctuations on the surface of the photosensitive drum. As a result, when an image is formed on the photoconductor drum by the exposure unit, a position shift of the image writing position occurs, and this position shift appears as a color shift or a hue change.

As a means for preventing such a color shift or a change in phase, there is a method of driving each photosensitive drum with a direct drive motor without using a gear train. According to this method, the speed fluctuation due to the gear train can be prevented, but such a motor is currently very expensive, and it is costly to use it. Then, JP-A-6
In Japanese Patent Laid-Open No. 3-75759, eccentricity and meshing of gears reproduced by one rotation of the photoconductor drum by rotating the photoconductor drum by a stepping motor through a reduction gear train having an integer ratio. The pulse generation pattern that cancels the rotation fluctuation due to the error is stored in the memory, and the pulse is generated based on the pulse generation pattern to drive the stepping motor and rotate the photosensitive drum, thereby canceling the rotation fluctuation and eliminating the color misregistration. A method of prevention is disclosed. Also, JP-A-62-59
Japanese Laid-Open Patent Publication No. 977 discloses a method for detecting color fluctuations by detecting speed fluctuations on the surface of the photosensitive drum and matching the phase angles of the respective speed fluctuation cycles.

However, in the conventional image forming apparatus, the positional relationship between the transfer belt and the plurality of photosensitive drums is fixed. Therefore, there is a problem in that the photosensitive drum and the transfer belt are damaged when the phases of the photosensitive drums are aligned, the life of these is shortened, and the image quality is deteriorated.

The present invention has been made in view of the above problems, and an object thereof is to automatically adjust the phase of the speed fluctuation of the image carrier, prevent the occurrence of color misregistration, and adjust the phase. An object of the present invention is to provide an image forming apparatus capable of performing work without damaging the image bearing member or the like and extending the life of the image bearing member or the like.

[0007]

SUMMARY OF THE INVENTION An image forming apparatus according to the present invention comprises an intermediate transfer member composed of an endless belt, a rotary drive unit for applying a predetermined tension to the intermediate transfer member to rotate the intermediate transfer member, and the intermediate transfer member. A plurality of image carriers arranged around the transfer body, a plurality of rotation driving means for driving these image carriers respectively via rotation transmitting members, and a tension of the intermediate transfer body is relaxed to reduce the intermediate Tension releasing means for separating the transfer body from the image carrier, and phase adjusting means for automatically adjusting the phase of the speed fluctuation of each of the plurality of image carriers after the intermediate transfer body is separated from the image carrier. It is equipped with.

[0008] Specifically, the phase aligning means has a reference position detecting means for detecting a reference position preset for each of the image carriers according to a speed variation factor of the rotation transmitting member. After the intermediate transfer member is separated from the carrier,
Each of the plurality of rotation drive means is driven, the rotational force of these rotation drive means is transmitted to the image carrier, and the drive of the rotation drive means is stopped when the reference position detection means detects the reference position. It is composed.

In the image forming apparatus of the present invention having such a structure, after the intermediate transfer member is separated from the plurality of image carriers, the plurality of rotation driving means are respectively driven, and the rotational force thereof is transferred to the image through the transmission member. The image carrier is transmitted to the image carrier, and each image carrier is rotated. Then, when each image carrier reaches a predetermined reference position, the driving of the rotation driving means is stopped and each image carrier is positioned at the reference position, whereby the phase matching is automatically completed. Therefore, color misregistration of a color image can be prevented without particularly improving the processing accuracy of the rotation transmitting member, and the image carrier and the intermediate transfer body are not damaged during the phase alignment.

[0010]

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

FIG. 1 shows the configuration of an image forming apparatus according to an embodiment of the present invention. This image forming apparatus 11 uses an intermediate transfer method to perform 4
A color color image is formed, and the intermediate transfer belt 12 is arranged at the center thereof. The intermediate transfer belt 12 is formed by an endless belt, and is stretched in a substantially isosceles triangular shape with the right side in the figure as the apex and the left side in the figure as the base. Two image forming portions 13 and 14 are arranged in parallel on the upper inclined surface 12a of the intermediate transfer belt 12, while two image forming portions 15 and 16 are arranged on the lower inclined surface 12b.
Are installed side by side. The image forming unit 13 forms a yellow color image, the image forming unit 14 forms a magenta image, the image forming unit 15 forms a cyan image, and the image forming unit 16 forms a black color image.

The image forming units 13 to 16 respectively have
The photoconductor drums 19Y, 19M, 19C and 19B are rotatably attached to a housing (not shown). These photosensitive drums 19Y, 19M, 19C, 19
Each of B's rotates in a direction indicated by an arrow at a predetermined speed, and around each of them, the charging corotrons 20Y, 20M, 20C, 20B are rotated counterclockwise in the drawing.
Image writing unit 21Y, 21M, 21C, 21B, developing device 2
2Y, 22M, 22C, 22B, transfer corotron 23
Y, 23M, 23C, 23B, cleaning device 24
Y, 24M, 24C and 24B are arranged.

Charging corotrons 20Y, 20M, 20C,
20B are photosensitive drums 19Y, 19M, and 19 respectively.
The surface of C and 19B is uniformly charged. The image writing units 21Y, 21M, 21C and 21B are composed of, for example, an image bar, an image scanner, etc., and are disposed on the surfaces of the photosensitive drums 19Y, 19M, 19C and 19B charged by the charging corotrons 20Y, 20M, 20C and 20B. It is designed to form a latent image. Developing device 22Y, 22
M, 22C and 22B are image writing units 21Y, 21M and 21.
The electrostatic latent image formed by C and 21B is developed with toner to form a visible image. Transfer Corotron 23
Y, 23M, 23C and 23B are the developing devices 22Y and 22
The image visualized by M, 22C and 22B is electrostatically transferred to the intermediate transfer belt 12. The cleaning devices 24Y, 24M, 24C and 24B remove the toner remaining on the surfaces of the photoconductor drums 19Y, 19M, 19C and 19B after the transfer.

The upper image forming portions 13 and 14 are supported by the frame 17 except the transfer corotrons 23Y and 23M, and the image forming portions 15 and 16 are supported by the frame 18 except the transfer corotrons 23C and 23B, which are unitized respectively. Has been done. The frames 17 and 18 can be pulled out to the right side (direction of arrow A) in the figure along rails 25 and 26 provided on the main body.

The intermediate transfer belt 12 is rotated at a constant speed in the clockwise direction in the figure by a drive roll 28 that rotates about a shaft portion 27 connected to a drive motor (not shown). The shaft portion 27 further supports the ends of the three frames 29 to 31. The position of the central frame 29 is fixed by shafts 54 and 55. Ends of the upper frame 30 and the lower frame 31 are supported by shafts 27 via bearings and are rotatable. Rolls 32, 3 on the frame 30
4, 35 are attached. Rolls 33, 36, and 37 are attached to the frame 31. A roll 38 is attached to the tip of the central frame 29. The intermediate transfer belt 12 is stretched between the rolls 32 to 38 and the drive roll 28. Further, the intermediate transfer belt tensioner 39 is provided inside the intermediate transfer belt 12.
Is provided, so that an appropriate tension is applied to the intermediate transfer belt 12.

Intermediate transfer belt tensioner 39 and roll 3
A belt meandering correction section 40 is provided between the belt 2 and the belt 2, and the meandering state of the intermediate transfer belt 12 caused by the rotation is corrected. Further, an intermediate transfer belt cleaning unit 41 is arranged outside the intermediate transfer belt 12 so as to face the roll 38, and cleans the surface of the intermediate transfer belt 12 after transfer. It should be noted that the transfer corotrons 23Y and 23M are attached to the upper frame 30 so as to correspond to the positions when the above-described photosensitive drums 19Y and 19M are attached. On the other hand, transfer corotrons 23C and 23B are attached to the lower frame 31 so as to correspond to the positions when the above-described photosensitive drums 19C and 19B are attached.

The frames 30 and 31 are rotated inward (center frame 29 side) about the shaft portion 27 by the tension release mechanism 60 shown in FIG. 1, whereby the tension of the intermediate transfer belt 12 is relaxed, and at the same time, the image is formed. Forming parts 13 to 16
The intermediate transfer belt 12 is separated from.

A paper feed tray 42 is disposed below the image forming units 15 and 16, and recording paper 43 is stacked. The paper 43 is taken out one by one by the paper feed roll 44, and then conveyed by the conveyance roll 46 along the conveyance path 45. When the paper 43 transported by the transport roll 46 reaches the position of the registration roll 47, its progress is temporarily stopped and the transport timing is adjusted so as to be synchronized with the rotation of the intermediate transfer belt 12. A transfer corotron 48 is arranged at the lower end of the intermediate transfer belt 12 so as to face the roll 33. The paper 43 is fed between the transfer corotron 48 and the intermediate transfer belt 12. Then, the photosensitive drums 19Y, 19M, 19
The image transferred to the intermediate transfer belt 12 by C and 19B is transferred by the transfer corotron 48.

The sheet 43 on which the image is transferred is sent to the fixing section 50 by the conveying section 49. The fixing unit 50 includes a heating roll 51 and a pressing roll 52, and heats the transferred image on the paper 43. The paper 43 on which the image is fixed is discharged by a discharge roll 53 to a discharge unit (not shown).

Next, the operation of the image forming apparatus 11 will be described.

In the image forming apparatus 11, the drive roll 28 is rotated by the rotational force of a drive motor (not shown), and the intermediate transfer belt 12 is rotated in the clockwise direction in the figure at a predetermined speed. On the other hand, the image forming unit 13
, The image writing unit 21Y causes the photosensitive drum 19
An image is formed on the surface of Y, and this image is developed by the yellow toner in the developing device 22Y, and then this developed image is transferred to the intermediate transfer belt 12 by the transfer corotron 22Y. Thereafter, similarly, images of magenta in the image forming unit 14, cyan in the image forming unit 15, and black in the image forming unit 16 are sequentially transferred to the intermediate transfer belt 12.

In parallel with the transfer of the image on the intermediate transfer belt 12, the paper feed roll 44 is fed from the paper feed tray 42.
Thus, the paper 43 is sent to the conveyance path 45, and the registration roll 47 adjusts the arrival timing at the transfer portion. The paper 43, the timing of which is adjusted, is fed between the transfer corotron 48 and the intermediate transfer belt 12, and the above-described four color images are transferred. The paper 43 to which the image is transferred is conveyed to the fixing unit 50 by the conveying device 49, and the image is thermally fixed by passing between the heating roll 51 and the pressing roll 52 in the fixing unit 50. The paper 43 on which the image is fixed is discharged by a discharge roll 53 to a discharge tray (not shown). On the other hand, the intermediate transfer belt 12 after the image has been transferred onto the paper 43 is cleaned by the intermediate transfer belt cleaning unit 40 by scraping off the residual toner on the surface.

[Tension release mechanism 60]

FIG. 1 shows a specific structure of the tension release mechanism 60. The tension release mechanism 60 includes cams 61 and 72 supported by the central frame 29, a cam follower 62 that is rotatably supported by the upper frame 30 and that drives the upper frame 30 by following the cam 61.
The cam follower 73 is rotatably supported by the lower frame 31 and is driven by the cam 72 to drive the lower frame 31. The cam follower 62 comes into contact with and follows the cam 61 by the weight of the upper frame 30. On the other hand, the cam follower 73 is urged upward in the drawing by the elastic force of the spring 74 stretched between the central frame 29 and the lower frame 31, so that the cam follower 73 comes into contact with the cam 72 and is driven thereby. It has become. Each of the cams 61 and 72 is adapted to be automatically rotated by a motor 75.

A gear 66 is attached to the shaft portion of the motor 75, and the rotational force of the gear 66 is transmitted via the gear 64 to the cam 6
1 is transmitted to a gear 63 coaxial with 1 and the gear 6
7. It is adapted to be transmitted to a gear 71 coaxial with the cam 72 via gears 68, 69, 70 coaxial with the gear 67.

FIG. 3 shows the configuration of the cam positioning device 80 for the cams 61 and 72. A disk 81 is coaxially attached to each of the cams 61 and 72.
A slit 82 for position detection is formed in the peripheral portion of 1. The slit 82 is detected by a photo interrupter 83 arranged so as to face the disk 81. The slit 82 is formed by the photo interrupter 83.
When the position of is detected, the rotation of the motor 75 is stopped by the CPU 100 described later, and the rotation of the cams 61 and 72 is stopped. The stop positions of the cams 61 and 72 are the top dead center or the bottom dead center.

That is, in the tension release mechanism 60, when the operator turns on a power source (not shown) to rotate the motor 75, the rotational force is transmitted to the cam 61 via the gears 66, 64 and 63, and the gear 67, 68, 69, 7
It is transmitted to the cam 72 via 0 and 71. These cams 6
The positions 1 and 72 are positioned by the cam positioning device 80, whereby the cam followers 62 and 73 move from the top dead center to the bottom dead center. As a result, the upper frame 30 and the lower frame 31 rotate around the shaft portion 27 and move inward (toward the central frame 29). Therefore, the upper frame 30 and the lower frame 31
The tension rolls 32 and 33 provided at the tips of the respective rollers move from the first position shown by the solid line in FIG. 1 to the second position shown by the chain double-dashed line in the figure. As a result, the tension of the intermediate transfer belt 12 is relaxed, and the intermediate transfer belt 12 and all the photoconductor drums 19Y to 19B are separated from each other. FIG. 2 partially shows the state. In this state,
Phase matching described later is performed.

The motor 75 is further rotated, and the cams 61, 7
When 2 rotates, the tension rolls 32 and 33 return to the state of the solid line position in FIG. As a result, the intermediate transfer belt 12
While the tension is applied to the intermediate transfer belt 12, the intermediate transfer belt 12 is brought into contact with the photosensitive drums 19Y to 19B. In this state, the above-mentioned image formation is performed.

[Phase alignment device]

Next, the structure of the phase aligning device for aligning the phases of the photosensitive drums 19Y to 19B will be described. FIG. 4 shows, as an example, the structure of the rotating mechanism of the photosensitive drum 19Y. Shaft 92 of photoconductor drum 19Y
Are supported by the frames 90 and 91 via bearings 93. A gear 96 is attached to one end of the shaft 92. A gear 95 formed on the shaft of the photoconductor motor 94 ₁ meshes with the gear 96. The gear 96 has a detection hole 97 for determining the reference position (home position) of the photoconductor drum 19Y.
The detection hole 97 is detected by the photo interrupter 98 ₁ .

Here, each of the gears 95 and 96 generally has a meshing error and eccentricity as described above. When the tooth number ratio is an integer ratio, the photosensitive drum 19
When Y is rotated once, the amount of deviation from the normal position of the photosensitive drum 19Y due to the speed variation becomes a periodic function having a cycle of one rotation of the photosensitive drum 19Y as shown in FIG. Here, the x-axis represents time, and the y-axis represents the positional deviation from the normal position on the surface of the photosensitive drum 19Y. The y-axis is the product of the radius (D / 2) of the photosensitive drum 19Y and its angular velocity fluctuation dω, D · dω / 2, integrated with respect to time. Therefore, in the image forming apparatus having a plurality of photoconductor drums 19Y to 19B as in this embodiment, if the waveforms of the position shift functions of the photoconductor drums 19Y to 19B are overlapped, the color shift caused by the phase shift is caused. Can be eliminated. Therefore, in this embodiment, first, as shown in FIG. 1, the transfer positional relationship between the photoconductor drums 19Y to 19B is set according to the following equation.

[0032]

[Formula 1] πD = πd = l ₁ = l ₂ = l ₃ (D: radius of photosensitive drum, d: radius of drive roll 28)

Further, in order to match the phase of the position shift waveform, the meshing error and eccentricity of the gears 95 and 96 are measured in advance to determine the reference position of the photosensitive drum 19Y.
Then, in correspondence with the position, the detection hole 97 is formed in the gear 96.
Is formed and is read at a position determined by, for example, the photo interrupter 98, the photosensitive drum 1
Align 9Y. Here, the gears 95 and 96 are
If it is a molded product, it can be formed with the same precision, and the periodic functions are in a state of being completely matched between the photoconductor drums 19Y to 19B, which is more desirable. This structure is the same for the other photosensitive drums 19M to 19B.

This phase adjustment may be performed, for example, during the first warm-up in the morning, and an alignment command for a service person is prepared and executed at the end of maintenance. Further, when a paper jam occurs, it is automatically executed after the processing. The circuit configuration of this automatic phase aligner is shown in FIG.

In this automatic phasing device, the motor 75 of the tension release mechanism 60 and the photo interrupter 82 are electrically connected to the CPU (central processing unit) 100, and the photosensitive drums 19Y to 19B are driven. The photoconductor motors 94 _{1 to} 94 ₄ and the photo interrupters 98 _{1 to} 98 ₄ for detecting the reference position are connected. C
The PU 100 has a ROM (Read Only Memory) 10
1 is connected. The ROM 101 stores the program shown in FIG.
100 controls the automatic phase adjustment.

Assuming that the operation is performed during warm-up, the CPU 100 rotates the motor 75 of the tension release mechanism 60 when the power is turned on (step S).
101). Then, the photo interrupter 8 shown in FIG.
2 detects the slit 81, and when the detection signal is input (step S102), the motor 75 is stopped (step S103). As a result, the tension release mechanism 60 operates as described above, the upper frame 30 and the lower frame 31 pivotally move toward the central frame 29, and the intermediate transfer belt 12 and all the photoconductor drums 19Y to 19B are separated from each other. Becomes In this state, the CPU 100 rotates each of the photoconductor motors 94 _{1 to} 94 ₄ (step S
104-107). Then, each photo interrupter 98
_{When 1 to} 98 ₄ detect the respective detection holes 97 and the detection signal is input (steps S108 to 111), the photoconductor motors 94 _{1 to} 94 ₄ are stopped (step S11).
2-115). As a result, each of the photosensitive drums 19Y-1
9B is set to the reference position (home position), and the phase matching is completed.

When this phase adjustment is completed, CP
U100 rotates the motor 75 again, and the upper frame 3
0 and the lower frame 31 are returned to their original positions, so that the intermediate transfer belt 12 and the photosensitive drums 19Y to 19Y-1.
Contact with 9B. As a result, the image forming preparation state is set.

As described above, in the image forming apparatus 11 of this embodiment, the phase adjustment of the respective photosensitive drums 19Y to 19B is automatically performed. Therefore, the occurrence of color misregistration of the color image can be prevented without particularly improving the processing accuracy of the gears 96 and 97. Further, since the phase adjustment is automatically performed after the intermediate transfer belt 12 is separated from the photoconductor drums 19Y to 19B, the photoconductor drums 19Y to 19B and the intermediate transfer belt 12 may be damaged by the phase adjustment work. Disappears. Therefore, the life of the photoconductor drums 19Y to 19B and the intermediate transfer belt 12 can be extended.

The present invention has been described with reference to the examples.
The present invention is not limited to the above embodiments, but can be variously modified without departing from the scope of the invention. For example, in the above embodiment, the gear trains of the gears 96 and 97 are used as means for transmitting the rotational force from the photoconductor motors 94 _{1 to} 94 ₄ to the photoconductor drums 19Y to 19B. May be used.

[0040]

As described above, according to the image forming apparatus of the first and second aspects, after the intermediate transfer member is separated from the image carrier, the speed fluctuation of each of the plurality of image carriers is suppressed. Since the phase is automatically adjusted, it is possible to prevent the occurrence of color misregistration of the color image without particularly improving the processing accuracy of the transmission member, and it is possible to damage the image carrier and the intermediate transfer member. Disappear. Therefore, there is an effect that the life of the image carrier and the intermediate transfer member can be extended.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the operation of a tension release mechanism according to an embodiment of the present invention, and is a vertical cross-sectional view showing a state where tension is applied to an intermediate transfer belt.

FIG. 2 is a vertical cross-sectional view partially showing the state of the tension release mechanism of FIG. 1 when releasing the tension.

FIG. 3 is a diagram showing a configuration of a cam alignment device in the tension release mechanism of FIG.

FIG. 4 is a diagram showing a mechanical configuration of a phase matching device according to an embodiment of the present invention.

5 is a view as seen from the direction of arrow AA in FIG.

FIG. 6 is a diagram showing a positional deviation amount from a regular position on the surface of the photosensitive drum.

7 is a block diagram showing a circuit configuration of the phase matching device in FIG.

FIG. 8 is a flowchart for explaining the operation of the phase matching device in FIG.

FIG. 9 is a vertical sectional view showing the overall configuration of an image forming apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 11 ... Image forming apparatus, 12 ... Intermediate transfer belt, 13-1
6 ... Image forming unit, 19Y, 19M, 19C, 19B ...
Optical drum (image carrier), 24Y, 24M, 24C, 2
4B ... Cleaning device, 60 ... Tension release mechanism, 61,
72 ... cam, 62,73 ... cam follower, 75 ... mo
Ta, 94₁~ 94_Four… Photosensitive motor, 98 ₁~ 98_Four…
Photo interrupter, 100 ... CPU 100, 101 ...
ROM (Read Only Memory)

Claims (2)

[Claims] 1. An intermediate transfer member composed of an endless belt, a rotation driving means for rotating the intermediate transfer member by applying a predetermined tension to the intermediate transfer member, and a plurality of images arranged around the intermediate transfer member. A carrier, a plurality of rotation driving means for driving each of the image carriers via a rotation transmission member, and a tension release for relaxing the tension of the intermediate transfer body and separating the intermediate transfer body from the image carrier. An image forming apparatus comprising: a unit and a phase adjusting unit that automatically adjusts the phase of the speed fluctuation of each of the plurality of image carriers after the intermediate transfer member is separated from the image carrier. 2. The phase adjusting means has a reference position detecting means for detecting a reference position preset for each of the image carriers according to a speed variation factor of the rotation transmitting member,
After the intermediate transfer member is separated from the image carrier, each of the plurality of rotation driving units is driven, the rotational force of these rotation driving units is transmitted to the image carrier, and the reference position detecting unit sets the reference position. The image forming apparatus according to claim 1, wherein the driving of the rotation driving unit is stopped at the time of detection.