JPH1184800A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image without color slippage by controlling an image forming unit by a signal outputted from a means detecting the rush-in of a transfer material at the next image forming time and deciding the writing time of the image with respect to an image carrier. SOLUTION: It is detected by the respective means 7b-7d detecting the rush-in of the transfer material that the transfer material rushes in an abutting part between the image carrier 3b and a carrying transfer means 6b, an abutting part between the image carrier 3c and a carrying transfer means 6c and an abutting part between the image carrier 3d and a carrying transfer means 6d. Then, the rush-in detection signals are transmitted to a writing time decision means 8. By the decision means 8, the toner image forming time on the respective carriers 3a-3d and the rush-in time of the transfer material P at the first image forming time are compared based on the signals outputted from the detection means 7b-7d. Besides, the compared result is fed back to an image forming control means 9. Then, the image writing time of the latent image writing means 4 of the image forming unit 2 is controlled by a control means 9 based on the decided result of the decision means 8 at the second image forming time. Thus, the image writing time is set so that the image is written at the optimum time.

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 employing an electrophotographic system or the like, and more particularly, to disposing a plurality of image forming units along a transfer material transport path and moving the transfer material transport path. The present invention relates to an improvement of an image forming apparatus for sequentially transferring a toner image from a plurality of image forming units to a transfer material to be transferred.

[0002]

2. Description of the Related Art As a conventional color image forming apparatus, for example, a plurality of image forming units (for example, adopting an electrophotographic system) are arranged on a paper transporting path along a horizontal direction, and move along the paper transporting path. A so-called tandem type in which a toner image is sequentially transferred from each of the image forming units to a sheet to be formed and a color image is formed on the sheet is known. As a paper transport system of this type of color image forming apparatus, there is provided a paper transport belt circulating along a paper transport path, and a belt transport system in which paper is electrostatically attracted to the paper transport belt, or A transfer roll transport system has been proposed in which each image forming unit is provided with a transfer roll in contact with a photoconductor for carrying an image, and the photoconductor and the transfer roll perform a paper transport operation.

[0003]

However, in the belt conveying method, it is difficult to keep the speed of the conveying belt constant due to the accuracy of the peripheral parts and the environment. Easy to occur. In order to solve such a technical problem, there has been proposed an apparatus that calculates the surface speed of the conveyor belt using a test patch provided on the conveyor belt, and feeds the result back to an image writing timing ( JP-A-63-4317
No. 2). However, in this type of belt transport system, it is necessary to drive the transport belt, control the walk of the transport belt, adsorb paper to the transport belt, and the like, as compared with the transfer roll transport system. There is a technical problem of becoming.

On the other hand, in the transfer roll transport system, unlike the belt transport system, the paper orientation cannot be controlled between the transfer rolls of each color, and the paper speed cannot be directly detected using a test patch or the like. For this reason, there is a technical problem that the arrival time of each color to the transfer position becomes unstable, and a color shift occurs because the image writing timing of each color does not match.

As a solution to this, for example, it is conceivable to provide a sensor for detecting the leading edge of the sheet on the front side of each transfer roll, and adjust the image writing timing by detecting the entry of the sheet with this sensor. However, from the viewpoint of preventing interference between the sensor and the transfer roll, the sensor cannot be arranged close to the nip area between the image carrier such as a photosensitive drum and the transfer roll. For this reason, it is still difficult to accurately detect the timing at which a sheet enters the nip area, and it is still insufficient to solve the technical problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above technical problem, and is based on the premise that the image forming unit is provided with a separate transfer / conveying means for each image forming unit. It is an object of the present invention to provide an image forming apparatus capable of preventing a color shift of a color image.

[0007]

That is, according to the present invention, as shown in FIG. 1, a plurality of image forming units 2 (for example, 2a to 2d) are arranged in parallel along a transfer material conveying path 1,
An image carrier 3 (e.g., 3a to 3d) that is at least rotatably disposed on each image forming unit 2 and carries an image;
Latent image writing means 4 for writing a latent image on the image carrier 3
(For example, 4a to 4d) and developing means 5 (for example, 5a to 5d) for developing the latent image written on the image carrier 3.
And a plurality of transfer means 6 (for example, 6a to 6d) for transferring the transfer material P in contact with each image carrier 3 and transferring the toner image on the image carrier 3 to the transfer material P. An image forming apparatus for sequentially transferring a toner image from the plurality of image forming units 2 to a transfer material P moving on the transfer material transport path 1, wherein the plurality of image carriers are attached to the plurality of transport transfer means 6. A plurality of transfer material intrusion detection means 7 (for example, 7a to 7d) for detecting the intrusion of the transfer material P into the respective contact portions of the transfer material 3 and the plurality of transfer transfer means 6; At the time of the next image formation,
An image writing time determining means for controlling the latent image writing means to determine an image writing time on the image carrier; and controlling an image forming operation based on a determination result of the image writing time determining means. And an image forming control unit 9 for performing the operation.

In such technical means, the image forming unit 2 (2a to 2d) may be appropriately selected as long as it forms a toner image of each color component and carries it on the image carrier 3. However, in consideration of the mounting workability and the like, it is preferable that the peripheral components of the image carrier 3 be formed into a cartridge as much as possible.

The image forming unit 2 (2a to 2d)
May be appropriately selected depending on the arrangement relationship of the transfer material transport path 1. For example, transfer material transport path 1
Are arranged in a substantially horizontal direction, it is necessary to arrange the image forming units 2 in the horizontal direction.
If the transfer material conveying path 1 is arranged in a substantially vertical direction, it is necessary to arrange the image forming units 2 in the vertical direction. In this case, in consideration of downsizing of the apparatus, it is preferable that the transfer material conveying path 1 is arranged substantially vertically and the image forming units are vertically arranged.

Here, the arrangement order of the image forming units 2 may be appropriately selected. However, from the viewpoint of maintaining good image quality in the frequently used monochromatic black mode, the most downstream image forming unit 2d may be arranged in black. It is preferable to form a toner image.

The image carrier 3 (3a to 3d) may be any as long as it can carry at least a toner image, and an appropriate material such as a photoconductor or a dielectric is selected according to the type of the latent image forming means. The shape may be a drum shape or a belt shape.

Further, latent image writing means 4 (4a to 4d)
As long as it writes a latent image on the image carrier 3, it may be appropriately selected from those that write with light and those that write with ion current.

The developing means 5 (5a to 5d) may be appropriately selected as long as it develops and visualizes the electrostatic latent image formed on the image carrier 3.

Further, the transfer members 6 (6a to 6d) are provided so as to be in contact with the image carriers 3 (3a to 3d), respectively. Any form may be used as long as the toner image can be transferred thereon, but from the viewpoint of simplification and miniaturization of the apparatus, it is preferable to use a transfer roll to which a transfer electric field is applied. Further, in such an embodiment, from the viewpoint of more stably conveying the transfer material P, before each image forming unit 2 (2a to 2d),
It is preferable to provide a transfer material guide that guides the transfer material P to a nip portion between the image carrier 3 and the transfer unit 6 of each image forming unit 2. Further, the transport transfer unit 6 may be driven by a motor or the like, or may be driven by the rotation of the image carrier 3 that comes into contact with itself without having a drive source.

The transfer material rush detecting means 7 (7a to 7a)
d) is appropriately selected as long as it can detect the intrusion of the transfer material P into the respective abutting portions (for example, the image carrier 3a and the transfer member 6a) between the image carrier 3 and the transfer member 6. I don't mind. However, from the viewpoint of easily detecting the entry of the transfer material P, the transfer means 6 (6a to 6
d) It is preferable to provide an encoder for each and detect a temporary decrease in the transport speed that occurs when the transfer material enters. Further, in a mode in which a transfer roll to which a transfer bias is applied is used as the transfer unit 6, a transfer bias fluctuation detection unit is provided for each of the transfer units 6 (6a to 6d), and the transfer bias generated when the transfer material enters the transfer material. Is preferably detected by detecting a temporary change in

Further, the image writing time determining means 8 controls the image forming unit 2 at the time of the next image formation based on the detection result of the transfer material intrusion detecting means 7 and controls the image carrier 3.
Any one may be selected as long as it determines the timing of image writing for. The determination of the image writing time at the time of the next image formation by the image writing time determination means 8 may be performed for each image formation. However, from the viewpoint of simplification of control and reduction of practical problems. Then, when the power is turned on for the first time, when the type of the transfer material P is changed, when the environment is changed, the image writing timing is determined for the first sheet, and after the next image formation, the first one is determined. It is preferable to use the image writing time determined for a sheet as it is. After that, the image writing timing may be determined again every predetermined number of sheets, for example, every ten sheets.

The image forming control means 9 transmits an image forming signal obtained from an exposure device (not shown) to each latent image writing means 4 of each image forming unit 2 to transfer each color image on each image carrier 3. When the determination result of the writing time is transmitted from the image writing time determining means 8 to each image carrier 3 of each image forming unit 2 based on the result. Any one may be selected as long as it controls the writing timing of.

Next, the operation of the present invention will be described. When the image forming operation is started and the first image forming signal is output from the image forming control means 9, the image forming units 2a to 2d of the respective colors correspond to the latent image writing means 4a to 4d. To form a latent image on each of the image carriers 3a to 3d, and thereafter, a toner image is formed by each of the developing units 5a to 5d. On the other hand, the first transfer material P moves along the transfer material transport path 1 and reaches the first contact portion between the image carrier 3a and the transport transfer means 6a. At this time, the image carrier 3
The toner image on the transfer material P is transferred onto the transfer material P by the transfer operation of the transfer material transfer device 6a, while the transfer material P enters the abutting portion by the transfer material transfer detecting device 6a. 7a, and this rush detection signal is transmitted to the image writing timing determining means 8. Thereafter, the transfer material P
While the toner image of each color is transferred to the transfer material P along with the conveyance, the contact portion between the image carrier 3b and the transfer device 6b, the contact portion between the image carrier 3c and the transfer device 6c, Carrier 3
Each of the transfer material rush detecting means 7b, 7c, 7d detects the rush of the transfer member 6d into the contact portion between the transfer material 6d and the transfer transfer means 6d.
These intrusion detection signals are transmitted to the image writing time determination means 8. At this time, the image writing time determining means 8
According to signals from the transfer material intrusion detection means 7a to 7d, 1
The timing of forming the toner image on each of the image carriers 3a to 3d during the image formation of the first sheet is compared with the time of entry of the transfer material P, and the result is fed back to the image forming control means 9. Then, at the time of forming the second image, the image forming control means 9 controls the image writing time of the latent image writing means 4 of the image forming unit 2 based on the determination result from the image writing time determining means 8. Make settings to write the image at the optimal time.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 2 shows a first embodiment of a color image forming apparatus to which the present invention is applied. In the figure, a color image forming apparatus
Image forming units 22 (specifically, 22a to 22d) of four colors (in this embodiment, yellow, magenta, cyan, and black) are vertically arranged in a housing 21,
Below this, a paper feed cassette 2 for storing paper for supply
3 and a paper transport path 24 serving as a transport path for the paper from the paper feed cassette 23 is vertically disposed at a position corresponding to each image forming unit 22.

In the present embodiment, the image forming units 22 (22a to 22d) form yellow, magenta, cyan, and black toner images in order from the upstream side of the paper transport path 24. , A photoreceptor cartridge 30, a laser exposure device 40, and a transfer roll 50. Here, the photoconductor cartridge 30 is
In particular, as shown in FIG. 3, a drum-shaped photosensitive drum 31 and a charging roll 32 for charging the photosensitive drum 31 in advance.
A developing unit 33 for developing an electrostatic latent image formed on the charged photosensitive drum 31 by exposure by the laser exposure device 40 with a corresponding color toner; and a cleaner for removing residual toner on the photosensitive drum 31 34 is integrated into a cartridge.

In the present embodiment, the developing device 33 is provided below the photosensitive drum 31 and has a developing housing 331 extending in the lateral direction.
1 accommodates a developer containing a predetermined color toner (one-component developer composed of a non-magnetic developer or a magnetic developer), and a pair of developer agitating members 332 is provided in a developing housing 331. Further, a developing roll 333 is provided at an opening of the developing housing 331 facing the photosensitive drum 31.
, A developer supply member 334 for supplying the developer in the developing housing 331 to the developing roll 333 side is disposed near the developing roll 333, and further, the developer is supplied onto the developing roll 333. Is provided with a developer layer thickness regulating member 335 whose layer thickness is regulated. On the other hand, the cleaner 34 is disposed above the photosensitive drum 31 and has a cleaner housing 341 extending in the lateral direction. The cleaner housing 341 is provided at a position facing the photosensitive drum 31 for scraping residual toner. A blade 342 is provided.

The laser exposure device 40 includes a case 41
A semiconductor laser (not shown), a polygon mirror 42, an imaging lens 43, and mirrors 44 and 45 are stored therein, and light from the semiconductor laser (not shown) is deflected and scanned by the polygon mirror 42. The optical image is guided to an exposure point on the photosensitive drum 31 via the light source 45.

Further, in the present embodiment, the transfer roll 50
The photoreceptor cartridge 30 is provided separately from the photoreceptor cartridge 30, abuts on the photoreceptor drum 31 of the photoreceptor cartridge 30, and rotates following the rotation of the photoreceptor drum 31. An encoder 51 is provided on the rotation shaft of the transfer roll 50. Here, the encoder 51 detects the leading edge of the sheet by detecting the rotation speed of the transfer roll 50. In the present embodiment, as shown in FIG. 4, in particular, each of the transfer rolls 50a to 50d and The encoders 51a to 51d are defined by the respective rotation shafts 52a to 52d of the transfer rolls 50a to 50d.
1d. Then, the timing of writing the electrostatic latent image of the laser exposure device 40 of each image forming unit 22 is controlled based on the rush detection signal of each encoder 51. In addition, a predetermined transfer electric field is applied to the transfer roll 50, so that a transfer force to the transfer roll 50 side is applied to the toner image on the photosensitive drum 31. The transfer roll 50 may be integrated into the photoreceptor cartridge 30.

In the present embodiment, the sheet cassette 2
3 is provided with a feed roll 61 for sending out the paper at a predetermined timing, and the paper feed path 24 located between the feed roll 61 and the transfer portion of the uppermost stream image forming unit 22a has an entrance side. A nip roll 62 is provided.

Further, a fixing device 64 is provided in the sheet transport path 24 located on the downstream side of the most downstream image forming unit 22d. At the downstream side of the fixing device 64, a discharge roll 66 for carrying out the paper is provided.
A discharge sheet is stored in a storage tray 67 formed in the upper part of the tray 1.

In this embodiment, each of the image forming units 22a is located in front of the most upstream image forming unit 22a.
The paper guides 71 that regulate the movement trajectory of the paper are respectively provided between the image forming unit 22d and the rearmost image forming unit 22d.
To 75 are provided.

FIG. 5 shows a drive control system of the color image forming apparatus used in the present embodiment. In the figure, a drive control system of the color image forming apparatus is provided for each of the transfer rolls 50 and is provided with a photosensitive drum 31 (31a to 31) of the paper 25.
d) and the next and subsequent image writing timings are optimally set and stored based on the rush detection signals from the encoders 51 (51a to 51d) for detecting the rush of the transfer rolls 50 (50a to 50d) into the abutting portions. Image writing timing control device 101
An image forming operation control device 111 for controlling an image forming operation based on a signal from the image writing timing control device 101; and a laser exposure device 40 (40a to 40d) based on a signal from the image forming operation control device 111. ) To output an image signal.

Next, the operation of the color image forming apparatus according to the present embodiment will be described. For example, when forming the first image, such as when the power is turned on, a start switch (not shown) is pressed (the first image may be automatically operated).
Then, the paper 25 in the paper feed cassette 23 is sent out by the feed roll 61, and the leading end of the paper 25 reaches the nip transport roll 62 on the entrance side. Thereafter, the paper 25 is sequentially transferred to each of the image forming units 22a to 22d of the paper transport path 24.
To the transfer site.

Here, the operation of detecting the speed of the transfer roll 50 by the encoder 51 will be described in detail. 6 and 7 show the relationship between the entry of the sheet 25 into the contact portion between the photosensitive drum 31 and the transfer roll 50 and the entry signal output from the encoder 51 at this time. In FIG. 6, the photosensitive drum 31 whose leading end of the paper 25 is the transfer position of each color
(31a-31d) and the transfer roll 50 (51a-51d)
d), the speed of each transfer roll 50 slightly changes. The speed fluctuation of the transfer roll 50 is detected by encoders 51 (51a to 51d) attached to the respective ends of the transfer roll 50. For example, as shown in FIG. 6A, when the paper 25 enters a transfer portion (nip area) between the photosensitive drum 31a and the transfer roll 50a at time t1, an encoder 51a attached to the transfer roll 50a.
Of the transfer roller 50a is detected by the encoder 51a attached to the transfer roll 50a and output as an output signal of the encoder 51a as shown in FIG. The same applies to the entry of the sheet 25 into the nip area between the other photosensitive drums 31b to 31d and the transfer rolls 50b to 50d. The profile of the speed fluctuation detected in this manner is input to the image writing timing control device 101 as an inrush signal.

Thereafter, the photosensitive drum 31 and the transfer roll 5
The leading end of the sheet 25 that has passed through the contact portion with the sheet No. 0 and on which an image has been formed reaches the fixing device 64 (the exit side nip transport roll 65) and is nipped. And the paper 25
When the sheet 25 has passed through the fixing device 64, the sheet 25 on which the unfixed toner image is fixed is discharged to a storage tray 67 through a discharge roller 66.

On the other hand, in the image writing timing control device 101, the feeding timing of the sheet 25 by the feed roll 61, the rush times t1 to t4 of the rush signal at each input transfer position, and the rush time difference Δt calculated from this.
The arrival time of the leading end of the sheet 25 to each transfer position is derived from 1 to Δt3, and the optimum time for the next image writing is determined from this value and stored. During the subsequent image formation, a signal is output to the image forming operation control device 111 so that an image signal is output at the determined image writing time.
A signal is output to an image signal output control device 121 that outputs an image signal to (40a to 40d). Therefore, after the second image formation, the image formation is performed at the optimum image writing time for each color, and an image without color shift is obtained.

Second Embodiment FIG. 8 shows a second embodiment of a color image forming apparatus to which the present invention is applied. In the present embodiment, the color image forming apparatus includes image forming units 22 (22a to 22d) of four colors in substantially the same manner as in the first embodiment. Are denoted by the same reference numerals as in Embodiment 1 and detailed description thereof is omitted here.)
However, unlike the first embodiment, the detection of the entry of the paper 25 into the contact portion between the photosensitive drum 31 and the transfer roll 50 is performed by detecting the voltage fluctuation of the transfer bias applied to the transfer roll 50. It was made. Further, in such an embodiment, the transfer roll 50 is used in the first embodiment.
Similarly to the above, the photosensitive drum 3
The transfer roller 50 may be driven to rotate by one rotation, or the transfer roll 50 may be independently driven by providing a drive source.

In particular, in the present embodiment, the transfer roll 50
Is applied by the constant current sources 131 (131a to 131d) provided on each transfer roll 50, and each charging bias voltage at this time is measured by each voltmeter 141 (141a to 141d). , To the image writing timing control device 101.
This focuses on the fact that when a charging bias is applied to the transfer roll by, for example, constant current control, the voltage value of the charging bias changes when the sheet enters the transfer position.

Next, the operation of the color image forming apparatus according to this embodiment will be described. In FIG. 8, the photosensitive drums 31 (31a to 31a) where the leading end of the paper 25 is the transfer position of each color.
31d) and the transfer rolls 50 (50a to 50d) enter the respective transfer positions, the constant current sources 131 (131a to 131d).
By 1d), the transfer voltage value applied to each transfer roll 50 slightly changes. This transfer voltage value is applied to the constant current source 1
The voltmeters 141 (141a to 141a)
d), and the profile is input to the image writing timing control device 101. On the other hand, the image writing timing control device 101 calculates the arrival time of the leading end of the sheet 25 to each transfer position from each of the input sheet entry signals, and determines and stores the optimal time for the next image writing from this value. Then, in the subsequent image formation, the image forming operation control device 1 outputs an image signal at the determined image writing time.
11 to the image forming unit 22 (22a to 22d).
A signal is output to an image signal output control device 121 that outputs an image signal to the image signal output control device 121. Therefore, after the second image formation, the image formation is performed at the optimum image writing time for each color, and an image without color shift is obtained as in the first embodiment.

[0035]

As described above, according to the present invention,
A transfer transfer unit that contacts the image carrier is provided for each image forming unit, and a transfer material intrusion detection unit that detects that the transfer material has entered a contact portion between each image carrier and each transfer transfer unit is provided. The image transfer unit controls the image forming unit at the time of the next image formation by the signal from the transfer material intrusion detection unit so that the image writing time on the image carrier is determined by the image writing time determination unit. The instability of the transfer material attitude between the respective color transfer positions, which has been a problem in the transport method, can be solved, and image formation can be performed at the optimal image writing time of each color at the time of the next image formation. A stable image without deviation can be obtained. Also, compared to the method of detecting the position of the transfer material with a sensor, the timing of passing the transfer material to the transfer point is directly detected, enabling more accurate detection of the transfer material entry timing. Thus, a stable image without color shift can be obtained.
Further, even when the type of the transfer material changes, the image formation can be performed at the optimal image writing timing by adjusting the image writing timing again. Further, in an embodiment in which an encoder is used as the transfer material intrusion detecting means, the apparatus can be configured without unnecessarily complicating the configuration of the image forming apparatus.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a configuration of an image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram illustrating an outline of Embodiment 1 of the image forming apparatus to which the present invention has been applied.

FIG. 3 is an explanatory diagram illustrating details of an image forming unit used in the first embodiment.

FIG. 4 is an explanatory diagram showing a configuration of a transfer roll and an encoder used in the first embodiment.

FIG. 5 is an explanatory diagram showing details of a control system according to the first embodiment.

FIG. 6 is an explanatory diagram illustrating an operation state according to the first embodiment.

FIG. 7 is a timing chart showing an operation state according to the first embodiment.

FIG. 8 is an explanatory diagram showing details of a control system according to the second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transfer material conveyance path, 2 ... Image forming unit, 3 ... Image carrier, 4 ... Latent image writing means, 5 ... Developing means, 6 ... Conveyance transfer means, 7 ... Transfer material intrusion detection means, 8 ... Image writing time Determining means, 9 ... image forming control means, 21 ... housing,
25: paper, 30: photoconductor cartridge, 31: photoconductor drum, 333: developing roll, 40: laser exposure device,
Reference numeral 50: transfer roll, 51: encoder, 61: feed roll, 101: image writing timing control device, 111: image forming operation control device, 121: image signal output control device,
131: constant current source, 141: voltmeter, P: transfer material

Claims (3)

[Claims] 1. An image carrier having a plurality of image forming units arranged in parallel along a transfer material conveying path, each image forming unit being arranged at least rotatably to carry an image,
A latent image writing unit for writing a latent image on the image carrier, a developing unit for developing the latent image written on the image carrier, a transfer material for transporting a transfer material in contact with each image carrier, and And a plurality of transport transfer means for transferring the toner image on the image carrier, the image forming apparatus for sequentially transferring the toner image from the plurality of image forming units to a transfer material moving in the transfer material transport path, A plurality of transfer material intrusion detecting means attached to the plurality of transport transfer means for detecting the intrusion of the transfer material into respective contact portions between the plurality of image carriers and the plurality of transport transfer means; An image writing time determining unit that controls the latent image writing unit to determine an image writing time on the image carrier when the next image is formed, based on a detection result of the material rush detection unit; Determination of means Based on the result, the image forming apparatus, comprising an image forming control means for controlling the image forming operation. 2. The image forming apparatus according to claim 1, wherein the transfer material intrusion detecting means is an encoder provided in each of the plurality of transfer means for detecting a speed change of the transfer means. Image forming apparatus. 3. The image forming apparatus according to claim 1, wherein the transfer material intrusion detection unit is provided in each of the plurality of transfer units and detects a transfer bias change applied to the transfer unit. An image forming apparatus, which is a detection unit.