JP2002052755A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which is superior in the operability and can form a high quality image without color shift. SOLUTION: This image forming apparatus comprises a plurality of rotatable photosensitive bodies 6Y, 6M, 6C, 6K, an exposing device 8 for scanning and exposing an electrostatic latent image on the photosensitive bodies 6Y, 6M, 6C, 6K and sensors 50, 51 for detecting synchronization of the exposing device 8. The image forming apparatus further comprises a reference selecting circuit 106 and a controller 100 that control each exposing timing of the exposing device 8 by a scanning synchronism detection signal from the sensors 50, 51 based on a paper supply starting signal of a transferring paper 1 to which an image is transferred.

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 which is applied to a copying machine, a printer, a facsimile, a printing machine, etc. and forms an image using a light beam scanning device having a plurality of light beams.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer, a facsimile, and a printing machine, an image is exposed on a photosensitive member by a plurality of light beams such as a semiconductor laser.
Conventionally, an image is formed on a transfer sheet by transferring an image on a photoreceptor to a transfer sheet.
When the image formation is color, four sets of image forming units are provided for forming a color image by superimposing images of four colors of yellow, magenta, cyan, and black, and these four sets of image forming units are provided. Is equipped with a laser beam scanning device that exposes images of each color.

[0003]

An image of each color is exposed on a photoreceptor in the form of an electrostatic latent image by the laser beam scanning apparatus. In this case, in order to transfer a color image to a transfer paper without color shift, In addition, it is necessary to perform exposure of each color on the photoreceptor in a timely manner in accordance with the feeding of transfer paper.

The present invention has been made in view of such a demand, and an object thereof is to provide a high quality image forming apparatus which is excellent in operability and does not cause color shift.

[0005]

In order to achieve the above-mentioned object, the present invention provides a method for scanning one or more photoconductors,
In an image forming apparatus including a plurality of exposure means for forming an electrostatic latent image on a photoreceptor and a synchronization detection means for detecting the synchronization of the exposure means, a feed start signal of a transfer paper on which an image is transferred is based on a signal. And control means for controlling each exposure timing of the exposure means with a scan synchronization detection signal from the synchronization detection means. In this case, the control unit temporarily delays the paper feed start signal that is not synchronized with the scan synchronization detection signal in which each of the exposure units is asynchronous until a period in which the scan synchronization detection signal in which each of the exposure units is not asserted. And a reference signal generating means for generating a reference signal, the reference signal generating means arbitrarily selecting from the scanning synchronization signals of the exposure means, and performing a delay based on the signal. Further, the reference signal generation means may be arbitrarily selected from the scanning synchronization signals of the exposure means, and the delay amount may be changed based on the signal.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings by taking as an example a case where the present invention is applied to a tandem type color image forming apparatus in which image forming units are arranged along a conveyor belt. I do. FIG. 1 is a schematic diagram showing a configuration of an image forming apparatus according to an embodiment, FIG. 2 is a schematic diagram showing a configuration of an optical unit in an exposure unit in FIG. 1 viewed from above, and FIG. FIG. 4 is a block diagram showing a control circuit of the image forming apparatus, and FIG. 4 is a timing chart showing the timing of the control circuit of FIG.

In this embodiment, four sets of image forming sections for forming a color image by superimposing images of four colors (yellow: Y, magenta: M, cyan: C, black: K) are provided. The transfer papers 1 are arranged in a line along a transport belt 2 that transports the transfer paper 1. The transport belt 2 is bridged by drive rollers, one of which is driven and rotated, and the transport rollers 3, 4 which are driven rollers which are driven and rotated, and is driven to rotate in the direction of the arrow by the rotation of the transport rollers 3, 4. A paper feed tray 5 in which the transfer paper 1 is stored is provided below the conveyor belt 2. The transfer paper 1 at the uppermost position among the stored transfer papers 1 is fed at the time of image formation, is timed with each image forming unit by a registration sensor 14 in the middle, and is placed on the transport belt 2 by electrostatic attraction. Adsorbed. The attracted transfer paper 1 is conveyed to a first image forming unit, where a yellow image is formed, then a magenta image is formed in a second image forming unit, and a third image is formed. A cyan image is formed in the forming section, and finally a black image is formed in the fourth image forming section. In this way, a color image in which the four color images are superimposed is formed on the transfer paper 1. be able to.

The first image forming section (yellow) includes a photosensitive drum 6Y, a charger 7Y, an exposing unit 8, a developing unit 9Y, and a photosensitive cleaner 10Y disposed around the photosensitive drum 6Y. Have been. The exposing device 8 is constituted by a laser beam scanning device as described later, and is shared with the remaining three image forming units. After the surface of the photosensitive drum 6Y is uniformly charged by the charger 7Y, the laser beam 11Y corresponding to the yellow image is
To form an electrostatic latent image. The formed electrostatic latent image is developed by the developing device 9Y, and a toner image is formed on the photosensitive drum 6Y. The toner image is transferred by the transfer device 12Y at a position (transfer position) where the toner image is in contact with the photosensitive drum 6Y and the transfer paper 1 on the conveyor belt 2, and a single color (yellow) image is formed on the transfer paper. The unrequired toner remaining on the drum surface of the photoreceptor drum 6Y after the transfer is cleaned by the photoreceptor cleaner 10Y to prepare for the next image formation. The transfer paper 1 on which the single color (yellow) has been transferred in the first image forming unit is transported by the transport belt 2
To the second image forming section (magenta).

The second image forming section, like the first image forming section, includes a photosensitive drum 6M, a charger 7M, a developing unit 9M, a photosensitive cleaner 10M, and a transfer unit 12M. Toner image (magenta) formed on top
Is transferred onto the transfer paper 1 in a superimposed manner. The transfer paper 1 is further conveyed to a third image forming section (cyan) and a fourth image forming section (black), and a toner image formed in the same manner is transferred to form a color image. I will do it. The third and fourth image forming apparatuses are also the first image forming apparatuses described above.
And the same configuration as the second image forming apparatus,
C and K representing colors are added after the reference numbers, respectively, and the description is omitted. The transfer paper 1 on which the color image has been formed after passing through the fourth image forming unit is peeled off from the transport belt 2, fixed by the fixing device 13, and then discharged. The exposing device 8 is composed of a laser beam scanning device as shown in FIG. In the following description, Y for yellow, M for magenta, C for cyan, and K for black will be referred to. LD (laser diode) unit for K3
The light beams from the 1 and Y LD units 32 pass through the CYL (cylinder lens) 33 for K and the CYL 34 for Y,
The light is incident on the lower surface of the polygon mirror 37 by the K reflection mirror 35 and the Y reflection mirror 36, and the polygon mirror 37 rotates to deflect the light beam. The light passes through the fθ lens 39 which is also used for M, and is folded by the first mirror 40 for K and the first mirror 41 for Y.

On the other hand, the LD unit 42 for C and the L unit for M
The light beam from the D unit 43 passes through the CYL 44 for C and the CYL 45 for M, and is incident on the upper surface of the polygon mirror 37. The polygon mirror 37 rotates to deflect the light beam, and is used for both K and C. Fθ lens 38
Then, the light passes through the fθ lens YM39 which is used for both Y and M, and is folded back by the first mirror 46 for C and the first mirror 47 for M.

B is located upstream of the writing position in the main scanning direction.
A cylinder mirror 48 for dual use and KC, a cylinder mirror 49 for dual use for Y and M, a sensor 50 for dual use for K and C, and a sensor 51 for dual use for Y and M, The light beams passing through the fθ lens 38 and the fθ lens 39 are reflected by the cylinder mirrors 48 and 4
9 and reflected and collected by the sensor 50 and the sensor 5
1. These sensors are synchronization detection sensors for synchronizing in the main scanning direction.

Thus, the LD units 31 and 42
From the cylinder mirror 48 and the sensor 5
0, the LD unit 32 and the LD unit 43
Uses a cylinder mirror 48 and a sensor 50. As a result, light beams of two colors are incident on the same sensor.
By changing the angle of incidence on the sensor, the timing at which each light beam enters the sensor is changed, and the light beam is output as a pulse train in time series. As can be seen from FIG. 2, K and C and Y and M are scanned in opposite directions. Note that a method of separating the output from the common synchronous detection sensor for two colors into each color component is omitted in the description of the present embodiment since various methods have been published conventionally.

Next, the control circuit will be described with reference to FIG. FIG.
The controller 100 converts the image data to be printed by the image forming apparatus into a timing_Y generation circuit 10 for each color.
2. Transfer to the timing_M generation circuit 103, the timing_C generation circuit 104, and the timing_K generation circuit 105. A synchronization separation (Y) circuit 107 and a synchronization separation (M) circuit 108 separate the output of the sensor 51 in FIG. 2 into respective synchronization signals. Similarly, the synchronization separation (C) circuit 109 and the synchronization separation (K) The circuit 110 is a circuit that separates the output of the sensor 50 into each synchronization signal. Furthermore, LDB (Y) 1
11 is built in the LD unit 32, and
The DB (M) 112 stores the LDB (C) in the LD unit 43.
113 is the LD unit 42 and LDB (K) 11
4 is built in the LD unit 31. Reference numeral 106 denotes a reference selection circuit, and LDB (Y) 111 and LDB (M) 11
2, a signal from LDB (C) 113 and LDB (K) 114 is arbitrarily selected to generate a reference signal, and a timing_Y generation circuit 102, a timing_M generation circuit 103,
This is applied to the timing_C generation circuit 104 and the timing_K generation circuit 105.

The operation of the control circuit will be described with reference to the timing chart of FIG. DETP_Y from the sync separation (Y) circuit 107, and D from the sync separation (M) circuit 108
TP_M, the synchronization separation (C) circuit 109 outputs DETP_
C, and from the sync separation (K) circuit 110, DETP_
K are respectively output. Output DETP_Y, DETP
_M, DETP_C, and DETP_K are asynchronous signals, respectively. This is because the same mirror surface is not used on the YM side and the CK side, and the position of the laser light emitted from each LD unit is different. However, FIG.
Of each output DETP_Y, DETP_
There is a period during which the Sart edge of M, DETP_C, and DETP_K does not come, and it can be derived from the precision of the components of the optical system. LDB (Y) 111 outputs DETP_
The signal DPSYNC_Y synchronized with the write clock of the LD unit 32 from Y to Y is output to the reference selection circuit 106. Similarly, the LDB (M) 112 outputs the output DETP_M
, The signal DPSYNC_M synchronized with the write clock of the LD unit 43 of the M
A signal DPSYNC_C synchronized with the write clock of the LD unit 42 of C from ETP_C is output to the LDB
(K) 114 is the LD unit 4 of DETP_K to K
The signal DPSYNC_K synchronized with the write clock of No. 8
Are output to the reference selection circuit 106, respectively.

The reference selection circuit 106 has four types of signals DPS.
YNC_Y, DPSYNC_M, DPSYNC_C, and DPSYNC_K are arbitrarily selected, and the reference signal CNT_LD is generated during an arbitrary period of the selected signals. On the other hand, the timing_Y generation circuit 102 converts the signal XSTART output from the registration sensor 14 into the reference signal CNT.
_LD, and counts with the signal DPSYNC_Y for the set number of lines of the signal PFGDLY_Y applied to the timing_Y generation circuit 102, and the signal PFGAT
Assert E_Y and transfer the image data PD for the transfer paper size.
ATA_Y is synchronized with the main scanning synchronization signal PLSYNC_Y, and reading is performed from the controller 100. The timing_C generation circuit 103 delays the signal XSTART from the resist sensor 14 to the reference signal CNT_LD, and the signal PFGD applied to the timing_C generation circuit 103
Counting is performed by the signal DPSYNC_C for the number of set lines of LY_C, and the signal PFGATE_C is asserted.
The image data PDATA_C for the transfer paper size is synchronized with the main scanning synchronization signal PLSYNC_C, and the controller 10
Read from 0. Similarly, the timing_M generation circuit 104 outputs the signal XST from the registration sensor 14
The signal ART is delayed until the reference signal CNT_LD, and the signal PFGDLY_M applied to the timing_M generation circuit 104.
Is counted by the signal DPSYNC_M for the set number of lines, the signal PFGATE_M is asserted, and the image data PDATA_M for the transfer paper size is transferred to the main scanning synchronization signal P.
In synchronization with LSYNC_M, reading is performed from the controller 100 to obtain image data PDATA_M. The remaining timing_K generation circuit 105 is also the resist sensor 1
4 is delayed until the reference signal CNT_LD, and the signal DPSY is set by the number of lines set by the signal PFGLY_K applied to the timing_K generation circuit 105.
The counting is performed by NC_K, the signal PFGATE_K is asserted, the image data PDATA_K is synchronized with the main scanning synchronization signal PLSYNC_K, and read from the controller 100 to obtain the image data PDATA_K.

As described above, by the control circuit of FIG. 3, the signals PFGATE_Y and PFGATE_ for starting the lighting of the LDs of yellow, magenta, cyan, and black with reference to the signal XSTART which is the sheet feeding start signal.
M, PFGATE_C, and PFGATE_K are generated, and the LD can be turned on independently for each color. As a result, even if a failure occurs in an LD of one color, the L of another color
D can be turned on independently for printing. Also,
The signal XSTART is latched at a position where the synchronization detection signal of each color cannot be asserted, and the LD signal of each color is obtained from the reference signal.
Signals PFGATE_Y, PFGAT for starting lighting
Since E_M, PFGATE_C, and PFGATE_K are generated, an image free from color shift can be obtained.

In the above-described embodiment, a full-color image formation has been described. However, when forming an image in a monochrome mode or a mono-color mode, control for synchronizing LDs of unnecessary colors is omitted. Accordingly, the image forming operation can be performed only with the necessary colors, and even if the rotation speed of the polygon motor for driving the polygon mirror 37 changes by switching the print mode, the LD of each color can be always kept in a stable area. Lighting signal PFGATE_
Y, PFGATE_M, PFGATE_C, PFGAT
E_K can be generated.

[0018]

As is apparent from the above description, according to the first aspect of the present invention, the scanning synchronization detection signal from the synchronization detecting means is based on the paper feeding start signal of the transfer paper on which the image is transferred. Since each exposure timing of the exposure means is controlled, it is possible to control the lighting of each color LD based on the paper feed start signal. As a result, even if a failure occurs in a certain color LD,
It can also be controlled to print in other colors.

According to the second aspect of the present invention, the paper feed start signal which is not synchronized with the scanning synchronization detection signal in which each of the exposure means is asynchronous is used for a period in which the scanning synchronization detection signal which is asynchronous is not asserted. Since the reference signal is generated by delaying once, the sheet feed start signal is latched at a position where the synchronization detection signal of each color cannot be asserted, and a signal for starting the lighting of the LD of each color is generated from the reference signal. As a result, an image free from color shift can be obtained.

According to the third aspect of the present invention, the scanning synchronization signal of the exposure means is arbitrarily selected, and the delay is performed based on the signal. The image forming can be performed with the LD of only the necessary color, omitting the control for generating the synchronizing.

According to the fourth aspect of the present invention, since the delay amount can be arbitrarily selected from the scanning synchronization signal of the exposure means and the delay amount can be changed based on the signal, the polygon motor in the scanning device can be changed by switching the printing mode. Even if the rotation speed of the driving means changes, a signal for lighting the LD of each color can be generated in a stable region by adjusting the amount of delay.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram showing a configuration of an optical unit of the exposure device in FIG. 1 as viewed from above.

FIG. 3 is a block diagram illustrating a control circuit of the image forming apparatus according to the embodiment.

FIG. 4 is a timing chart showing the timing of the control circuit of FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transfer paper 2 Conveyor belt 14 Registration sensor 6Y, 6M, 6C, 6K Photoreceptor drum 8 Exposure unit 9Y, 9M, 9C, 9K Developing unit 12Y, 12M, 12C, 12K Transfer unit 31K LD unit 32Y LD unit 37 Polygon mirror 42 LD unit for C 43 LD unit for M 50, 51 Sensor 100 Controller 102 Timing_Y generation circuit 103 Timing_M generation circuit 104 Timing_C generation circuit 105 Timing_K generation circuit 107 Synchronization separation (Y) circuit 108 Synchronization separation ( M) circuit 109 Sync separation (C) circuit 110 Sync separation (K) circuit 111 LDB (Y) 112 LDB (M) 113 LDB (C) 114 LDB (K) 106 Reference selection circuit

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H04N 1/113 H04N 1/04 104A 1/29 (72) Inventor Koji Oshikiri 1-3-6 Nakamagome, Ota-ku, Tokyo No. F-term in Ricoh Co., Ltd. (Reference) 2C362 BA52 BA69 BA70 BB37 BB38 CA22 CA39 CB47 2H027 ED04 EE01 EE02 2H076 AB02 AB16 AB33 AB67 AB68 DA41 5C072 AA03 BA19 HA02 HB11 HB13 NA04 QA14 QA17 UA18 XA03 DD05 FF15 GG09 GG15 HH02 HH04

Claims (4)

[Claims] 1. An image forming apparatus comprising: one or more photoconductors; a plurality of exposure units that expose the photoconductors to form an electrostatic latent image; and a synchronization detection unit that detects synchronization of the exposure units. An image forming apparatus comprising: a control unit that controls each exposure timing of the exposure unit based on a scan synchronization detection signal from the synchronization detection unit based on a feed start signal of a transfer medium onto which an image is transferred. . 2. The control device according to claim 1, wherein the control unit controls the sheet feeding start signal, which is not synchronized with the scan synchronization detection signal in which each of the exposure units is asynchronous, until the scan synchronization detection signal in which each of the exposure units is not asserted. 2. The image forming apparatus according to claim 1, further comprising a reference signal generating unit that generates a reference signal by temporarily delaying the reference signal. 3. The image forming apparatus according to claim 2, wherein the reference signal generation unit arbitrarily selects a scan synchronization signal of the exposure unit and performs delay based on the signal. 4. The image forming apparatus according to claim 2, wherein the reference signal generation unit arbitrarily selects a scan synchronization signal of the exposure unit and changes the delay amount based on the signal.