JP2002137441A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve noise resistances of an imaging apparatus and reduce costs of the imaging apparatus which exposes each of a plurality of photoreceptors set for each of mutually different colors by light beams outputted from a plurality of light sources. SOLUTION: Light quantity-setting signals Vref for generating light quantity- setting signals Vref-K, Vref-C, Vref-M and Vref-Y for each of colors in time series are sent out as an equal signal to all laser drive circuits 54, so that a light quantity control signal is made common (equal) among colors. Each of the laser drive circuits 54K, 54C, 54M and 54Y adjusts a quantity of light when a value of the light quantity-setting signal Vref is the Vref-K, Vref-C, Vref-M, Vref-Y respectively. Accordingly, sharing a member for transmitting the light quantity control signal to each of the laser drive circuits 54 from a control part 58, e.g. connecting the control part 58 and each of the laser drive circuits 54 by the same wiring cable 56, setting one connector 60 for the control part 58, or the like is enabled.

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, and more particularly, to an image forming apparatus that exposes a plurality of photosensitive members provided for different colors to corresponding light beams output from a plurality of light sources. About.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses such as an electrophotographic copying machine and a laser printer, which form (print) a color image by scanning and exposing a photosensitive drum with a light beam using an optical scanning apparatus, have rapidly spread. ing. An image forming apparatus generally includes photoconductor drums for different colors such as black (K), cyan (C), magenta (M), and yellow (Y), and a corresponding color is provided on each photoconductor drum. A color image is formed by forming a toner image and transferring the formed toner images of the respective colors sequentially on a sheet or a transfer medium.

[0003] Such image forming apparatuses are classified into two types according to the form of the optical scanning apparatus. One of them is
A total of four optical scanning devices are arranged side by side for each of the colors K, C, M, and Y, and a light beam modulated based on image data of the corresponding color is output from each optical scanning device, and each corresponding optical scanning device is output. This is a mode in which the photosensitive drum is irradiated (hereinafter, referred to as a “four-tandem system”). The feature of this quadruple tandem system is that a semiconductor laser (LD: Laser Diode) is used as a light source for each color.
ode) and a deflecting means such as a polygon mirror, so that the light beams of each color can be independently controlled.

Another one is provided with only one optical scanning device,
In this embodiment, a plurality of light beams corresponding to the respective colors of K, C, M, and Y are output from the single optical scanning device and irradiated onto the corresponding photosensitive drums (hereinafter, referred to as “spray paint method”). . The main feature of this spray paint method is that although the LD is provided for each color, the LD is provided in common, and the scanning position of the light beam of each color is related.

As described above, in each of the systems, the LD is provided for each color, and the LD of each color is turned on by a laser driving circuit (LDD: LD Driver) as shown in FIG. It was supposed to be.

The laser driving circuits 200K, 200K,
Since 00C, 200M, and 200Y have the same configuration,
FIG. 13 shows the detailed configuration of only the laser drive circuit 200K for K color, and omits the other colors. In the following description, a symbol (K / C / M / Y) indicating a color added to the end of the code is omitted unless the color is particularly distinguished. Also,
For each signal of each color, a symbol (K / C / M / Y) indicating the color is added to the end of the code indicating the signal together with “−”. In the following description, unless the color is particularly distinguished, the code suffix is used. The symbol “−” and the symbol attached to “.

Each laser drive circuit 200 includes a bias current source 204 and a switching (SW) current source 206 as current sources for driving the LD 202, and outputs from the bias current source 204 and the switching current source 206. The currents are added by adder 208 to produce L
D202. The LD 202 is turned on when a current obtained by adding the two currents is supplied, and outputs a light beam having a light amount corresponding to the magnitude of the supplied current.

At this time, the drive of the bias current source 204 and the switching current source 206 is permitted by the laser lighting permission signal nENB, and the bias current source 204
202 outputs a current equal to or lower than a predetermined threshold value for outputting light, and the switching current source 206 outputs an image signal nV for each color.
The switching current output of the specified current value is
By turning on / off, each LD 202 is turned on / off.

A part of the light beam output from the LD 202 is received by a PD (PhotoDiode) 210 as monitor light, and a current proportional to the output light amount is output. This current is converted into a monitor voltage by voltage conversion by a current / voltage converter 212, and a comparator 214 sets a light amount setting signal Vref
Is compared to In the sample hold (S / H) circuit 216, when a sample is instructed by the light amount adjustment signal nS / H, the LD 202 is turned on and the output current of the switching current source 206 is determined based on the comparison result of the comparator 214. The light amount is adjusted so that a predetermined amount of light beam is output from the LD 202 by adjusting the value, and when the hold is instructed, the adjustment result is held.

At this time, various control signals (laser lighting permission signal nEN) for controlling the output light quantity of LD 202 of each color.
B, a light amount adjustment signal nS / H and a light amount setting signal Vref) are a control unit (MCU: Main Control Unit) that controls the operation of the image forming apparatus.
From 220 (see FIG. 15), it is input to each laser drive circuit 200. Each laser drive circuit 200 controls the light amount of the LD 202 based on the input control signal.

This light amount control will be specifically described with reference to a timing chart of FIG. FIG. 14 shows an example of the light amount control executed in the spray paint type image forming apparatus.

Generally, the light quantity control is performed outside the image forming area for each scanning line. Further, in the image forming apparatus, the amount of light when exposing the photoconductor drum differs for each color due to the reproducibility of the intermediate length and the variation in the sensitivity of each photoconductor drum. , A light amount setting signal set in advance for each color is supplied. FIG. 14 shows an example in which the light quantity setting signal Vref-K for K color is 2.
The light amount setting signal Vref-C for 0 V and C color is 1.6 V, the light amount setting signal Vref-M for M color is 1.8 V, and the light amount setting signal Vref-Y for Y color is
The case where it is set to 1.4V is shown.

First, in the state E1, the control unit 220
Outputs a light amount adjustment signal nS / HK for K color and a light amount adjustment signal nS / HM for M color. In response to this signal, the laser driving circuits 200K and 200M respectively turn on the LD 202 and change the monitor voltage to the light amount setting signal Vref for K color.
The output current value of each switching current source 206 is adjusted so as to be a value corresponding to the light intensity setting signal Vref-M for -K, M colors, and the output light intensity of the LD 202 is adjusted (K
Color, M light amount adjustment).

In the next state E2, the image signal nV for K color
DATA-K and an image signal nVDATA-M for M color are output, and the laser drive circuits 200K and 200M output the SOS signal (nSOS-
K, nSOS-M) is obtained and L
D202 is turned on (K-color and M-color pre-SOS lighting).

At the same time, the light amount adjustment signal nS / H-
A light amount adjustment signal nS / HY for C and Y colors is output. In response to this signal, the laser drive circuits 200C and 200Y
Similarly to the above, L is set to a value corresponding to the light quantity setting signal Vref-C for C color and the light quantity setting signal Vref-Y for Y color.
The output light amount of D202 is adjusted (light amount adjustment of C color and Y color).

In the next state E3, the SOS signal nSOS-K for K color and the SOS signal for M color acquired in the above state E2.
In synchronization with nSOS-M, an image signal nVDATA-K for K color and an image signal nVDATA-M for M color based on the image data are output,
In the laser driving circuits 200K and 200M, the lighting of the LD 202 based on the image data is started (K color,
M-color image writing). Image signal nVDATA based on image data
-K, output of nVDATA-M ends, and SOS signal nSOS-
After a lapse of a predetermined time from K and nSOS-M, the light amount control timing comes again, and the same control as in the state E1 is performed.

Further, an image signal nVDATA-C for C color and an image signal nVDATA-Y for Y color are output, and in response to these signals, the laser driving circuits 200C and 200Y output the SOS signal (nS
In order to obtain OS-C and nSOS-Y), the LD 202 is lit with the output after the light amount adjustment (C-color and Y-color SOS pre-lighting).

In the next state E4, the SOS signal nSOS-C for C color and the SOS for Y color obtained in the above state E3.
In synchronization with the signal nSOS-Y, an image signal nVDATA-C for C color based on the image data and an image signal nVDATA-Y for Y color are output, and the laser drive circuits 200C and 200Y output the LD 202 based on the image data. Lighting is started respectively (C
Color, Y color image). Image signal nV based on image data
The output of DATA-C and nVDATA-Y ends, and the SOS signal nSO
When a predetermined time has elapsed from SC and nSOS-Y, the light amount control timing comes again, and the same control as in the state E2 is performed.

As described above, in the image forming apparatus, the light amount setting signals Vref are supplied with different values to the respective laser driving circuits 200, and the light amount adjustment signals Vref are supplied at different timings.
nS / H must be supplied.

For this reason, the control unit 220 is disclosed in
As shown in Japanese Patent No. 18737, the laser drive circuits 200 were connected to each other by independent wiring cables 222 (see FIG. 15). In this case, in order to transmit the signal output from the control unit 220 to each wiring cable 222, as shown in Table 1, the laser lighting permission signal
nENB, a light amount adjustment signal nS / H, a light amount setting signal Vref, and a signal line for supplying a driving power supply of 5 V, each of which is four in total, and a total of four ground lines for each signal line are added. A total of eight signal lines are required.

[0021]

[Table 1]

[0022]

However, according to the prior art, as can be seen from FIG. 15, the wiring cable 222 for supplying a control signal from the control unit 220 to the laser drive circuit 200 is provided by the number of laser drive circuits 200. The distance between the control unit 220 and the laser drive circuit 200 is increased in total, and the wiring cable is inevitably lengthened. Further, in the control unit 220, a space for installing the connector 224 for all the laser driving circuits 200 is required, and a space for passing the wiring cable 222 must be secured in the vicinity thereof.

For this reason, there is a problem that the cost of parts such as a wiring cable and a connector is high, and the apparatus cannot be miniaturized. In addition, there is a problem in that the wiring is liable to be affected by noise due to the routing of the wiring cable and the like, and the assembling operation is complicated, which further increases the cost.

The present invention has been made to solve the above problems, and has as its object to provide an image forming apparatus capable of improving noise resistance and reducing costs.

[0025]

In order to achieve the above object, according to the present invention, a plurality of photoconductors provided for different colors are provided by light beams output from a plurality of light sources. An image forming apparatus for exposing each of the light sources, the light source driving means being provided for each of the light sources for lighting the light sources at a predetermined output light quantity, and controlling the output light quantity of the light sources to the light source drive means. And a control unit for outputting a light amount control signal and an image signal for instructing lighting of the light source, wherein at least the light amount control signal sent from the control unit to each light source control unit is the same.

According to the first aspect of the present invention, a light source driving means is provided for each light source, and each light source driving means controls a predetermined output light amount and a predetermined output light amount based on a light amount control signal from the control unit. The amount of output light of the light source is controlled so that the light source is turned on based on the image signal. At this time, the light amount control signal is sent to the respective light source driving units in the same (common) manner from the control unit. Thereby, a member for transmitting the light amount control signal from the control unit to each light source driving unit can be shared, for example, the total number of signal lines for all colors and the light amount control required for the control unit. The number of connectors and the like for outputting signals can be reduced, the space for passing wiring cables can be reduced, and the number of work steps during assembly can be reduced.

As described in claim 2,
The control unit may output a light quantity setting signal for setting the output light quantity of each of the plurality of light sources in time series as the light quantity control signal.

Further, as described in claim 3,
The control unit outputs, as the light amount control signal, a light amount adjustment permission signal that permits execution of light amount adjustment for adjusting the output light amount to the predetermined output light amount. May be instructed to execute the light amount adjustment, or as described in claim 4, the control unit controls the light amount adjustment to adjust the predetermined output light amount as the light amount control signal. May be output, and a designation signal for designating a light source driving unit for performing the light quantity adjustment may be output.

Further, as described in claim 5,
The control unit and the plurality of light source driving units may be connected by a common harness, or, as described in claim 6, the control unit and the plurality of light source driving units, Daisy chain connection may be used.

[0030] As described in claim 7, the light quantity control of all the light sources may be performed in the same scanning line, or as described in claim 8,
The light amount control of the light sources may be performed on different scanning lines for each group obtained by dividing the plurality of light sources.

According to a ninth aspect of the present invention, when a photoconductor corresponding to at least black is provided, a light beam is applied to the photoconductor corresponding to the black among the plurality of light source driving units. Preferably, the plurality of light source driving units are connected to the control unit, with the light source driving unit that drives the light source that outputs the image data being the uppermost stage.

[0032]

Next, an example of an embodiment according to the present invention will be described in detail with reference to the drawings.

(Overall Configuration) FIG. 1 shows a schematic configuration of an image forming apparatus according to the present invention. Image forming apparatus 10
Is provided with a transfer belt 14 in the form of an endless belt wound around a plurality of winding rollers 12 and conveyed in the direction of arrow A. Above the transfer belt 14, a photosensitive drum 16K for forming a black (K) image and a cyan (C)
A photosensitive drum 16C for forming an image, a photosensitive drum 16M for forming a magenta (M) image, and a photosensitive drum 16Y for forming a yellow (Y) image are arranged at substantially equal intervals.

In the following, for the portions provided for each of the colors K, C, M, and Y, the symbols of K / C / M / Y are added to the end of the code of each portion in the same manner as described above. However, when the colors are not particularly distinguished, the symbols at the end of the reference numerals are omitted.

The axis of each photosensitive drum 16 is the transfer belt 1
4 are arranged so as to be orthogonal to the movement direction. Each of the photosensitive drums 16 is rotated at a predetermined speed in the direction of arrow B by a motor (not shown).

Above each photosensitive drum 16, K, C,
An optical scanning device 18 (details will be described later) that irradiates a plurality of light beams modulated based on the image data of each of the M and Y colors while scanning them toward the corresponding photosensitive drum 16 is arranged.

In order to uniformly charge the photosensitive drum 16 around each of the photosensitive drums 16 and on the downstream side in the rotation direction of the photosensitive drum 16 from the light beam irradiation position by the optical scanning device 18. Chargers 20 are arranged. Each of the photoconductor drums 16 is charged by a charger 20 by rotating, and then is rotated by an optical scanning device 18.
Thus, the light beams modulated based on the image data of the corresponding colors are scanned and exposed to form an electrostatic latent image.

Around the photosensitive drum 16, an electrostatic latent image formed on the photosensitive drum 16 is provided at a predetermined position downstream of the light beam irradiation position along the rotation direction of the photosensitive drum 16. A developing unit 22 for developing a toner image by developing with color (K or C or M or Y) toner, a first transfer unit 24 for transferring the toner image formed on the photosensitive drum 16 to the transfer belt 14, A cleaner 26 for removing the toner remaining on the body drum 16 is sequentially arranged.

The toner images of different colors formed on the photosensitive drums 16 are transferred to the transfer belt 14 so as to overlap each other on the belt surface of the transfer belt 14. As a result, a color toner image is formed on the transfer belt 14, and the formed color toner image is taken out one by one from a paper tray (not shown) by the second transfer unit 28 and conveyed. The image is transferred to the paper 30.
Then, the paper 30 is sent to a fixing device (not shown),
The transferred toner image is fixed. Thereby, the paper 3
A color image is formed on 0.

(Detailed Configuration of Optical Scanning Apparatus) Next, the optical scanning apparatus 18 will be described with reference to FIGS. Each of the photoconductor drums 16K, 16C, 1
LDs 50K, 50C, 50M, and 50Y as light sources for outputting light beams for irradiation to 6M and 16Y, and each LD 5
The light beams output from 0K, 50C, 50M, and 50Y are deflected to form photosensitive drums 16K, 16C, 16M, 1M.
And a polygon mirror 52 for scanning on 6Y.

Each LD 50 is connected to a laser driving circuit (LDD) 54 (described later in detail) as a light source driving means. Each laser drive circuit 54 is connected to a control unit (MCU) 58 that controls the operation of the image forming apparatus 10 via a common wiring cable 56 such as a ribbon cable. The light amount control signal thus transmitted is transmitted to each laser drive circuit 54.

More specifically, the connection cables 56 are provided on the distribution cable 56 at a total of five places, namely, at both ends and three places therebetween.
0 is provided. The connector 60 at one end is connected to the control unit 5.
8 and the remaining four connectors 60 are sequentially connected to the laser drive circuits 54K, 54K
C, 54M, and 54Y. Wiring cable 5
Reference numeral 6 includes a signal line for transmitting a laser lighting permission signal nENB, a light quantity adjustment permission signal nPCONT, a light quantity setting signal Vref, and the like as light quantity control signals commonly used by all the laser drive circuits 54.

Each laser drive circuit 54 receives various light amount control signals output from the control unit 58 and transmitted by the wiring cable 56 via the connector 60. Each laser drive circuit 54, based on the received signal,
The output light quantity of each corresponding LD 50 is adjusted, and each LD 50 is adjusted.
Output a predetermined amount of light beam.

The light beams output from the respective LDs 50 are converted into substantially parallel lights via collimator lenses 62 provided for the respective colors, and then are incident on the polygon mirror 52.

The polygon mirror 52 is formed in a regular polygonal shape (a regular octagon in the present embodiment) having a plurality of reflecting surfaces 52A on the side surfaces. The light beams output from the LDs 54K and 54C are incident on the same reflection surface 52A,
The light beams output from the LDs 54M and 54Y are incident on the opposite reflection surface 52A different from the reflection surface 52A by 180 degrees.

The polygon mirror 52 includes a motor 64
The motor 64 drives the motor 64 to rotate at a predetermined rotation speed (a predetermined speed) in the direction of arrow C. Due to this rotation, the light beam and the incident angle of the light beam on each reflection surface 52A are continuously changed, and are reflected and deflected. Thus, the light beam scans on the corresponding photosensitive drum 16.

LD 54K, 5 by polygon mirror 52
A condensing optical system 66A including an fθ lens or the like is arranged in the reflection direction of the light beam output from 4C. LD
The light beams output from 54K and 54C and reflected by the reflecting surface 52A of the polygon mirror 52 are condensed by a focusing optical system 66A.
The light is condensed in the main scanning direction and the sub-scanning direction. At this time, the respective light beams are incident on the reflection surface 52A of the polygon mirror 52 at different incident angles along the sub-scanning direction, and the light beams transmitted through the condensing optical system 66A are separated by different reflection mirrors. 68K and 68C.

The light beam incident on the reflecting mirror 68K is
After being reflected by the reflection mirror 68K, the reflection mirror 70K,
The light is reflected by 72K and output from the optical scanning device 18 while scanning toward the photosensitive drum 16K. The light beam incident on the reflection mirror 68C is reflected by the reflection mirror 68C.
After being reflected by C, the light is reflected by the reflection mirrors 70C and 72C, and is output from the optical scanning device 18 while scanning toward the photosensitive drum 16C.

On the other hand, the LD 50 by the polygon mirror 52
In the reflection direction of the light beam output from M and 50Y, f
A condensing optical system 66B including a θ lens and the like is arranged. The light beams output from the LDs 50M and 50Y and reflected by the reflection surface 52A of the polygon mirror 52 are condensed by the condensing optical system 66B in the main scanning direction and the sub-scanning direction. At this time, the respective light beams are incident on the reflection surface 52A of the polygon mirror 52 at different incident angles along the sub-scanning direction, and the light beams transmitted through the condensing optical system 66B are separated by different reflection mirrors. 68M and 68Y.

The light beam incident on the reflecting mirror 68M is
After being reflected by the reflection mirror 68M, the reflection mirror 70M,
The light is reflected by 72M, and is output from the optical scanning device 18 while scanning toward the photosensitive drum 16M. The light beam incident on the reflection mirror 68Y is reflected by the reflection mirror 68Y.
After being reflected by Y, the light is reflected by the reflection mirrors 70Y and 72Y, and is output from the optical scanning device 18 while scanning toward the photosensitive drum 16Y.

As described above, the light beams output from the LDs 50K and 50C and the light beams output from the LDs 50M and 50Y correspond to the reflecting surfaces 5 of the polygon mirror 52.
2A, as shown by arrows in FIG.
Scanning is performed in the reverse direction.

In the optical scanning device 18, a pickup mirror is provided near the output portion of the light beam toward the photosensitive drum 16 so as to cross the scanning locus of the light beam reflected by each of the reflection mirrors 72K and 72C. (Flat mirror) 74A is arranged. Similarly, the reflection mirror 72
The pickup mirror (plane mirror) 7 crosses the scanning locus of the light beam reflected by each of the M and 72Y.
4B are arranged.

The pickup mirrors 74A and 74B are arranged near the scanning start side end (SOS: Start Of Scan) outside the image forming area in the scanning locus of each light beam.

In the direction of reflection of each light beam by the pickup mirror 74A and at a position substantially equivalent to the photosensitive drums 16K and 16C with respect to the pickup mirror 74A,
SOS sensor 76K composed of PD (Photo Diode), etc.
76C is arranged. SOS sensors 76K, 76C
Each time each light beam scans the photosensitive drums 16K and 16C in the axial direction, the pickup mirror 74A
Thereby, the light beam at the scanning start side end outside the image forming area is guided. That is, the SOS sensors 76K, 76C
Then, the photosensitive drums 16K, 16
C detects the scan start timing for each scan,
The result is output as SOS signals (nSOS-K, nSOS-C).

Similarly, in the direction of reflection of each light beam by the pickup mirror 74B,
SOS sensors 76M and 76Y made of PD and the like are arranged at positions substantially equivalent to the photosensitive drums 16M and 16Y with respect to 4B. Each time the light beam scans the photosensitive drums 16M, 16Y in the axial direction thereof, the light beam at the scanning start side end outside the image forming area is guided to the SOS sensors 76M, 76Y by the pickup mirror 74B. . That is, in the SOS sensors 76M and 76Y,
The scanning start timing of each scanning of the photosensitive drums 16M and 16Y by the optical scanning device 18 is detected, and the result is output as SOS signals (nSOS-M, nSOS-Y).

In the following, as for the signal for each color, similarly to the SOS signal, a symbol (K / C / M / Y) indicating the color is added to the end of the code indicating the signal together with "-". However, unless otherwise specified, the symbol “−” and the symbol added to the end of the code are omitted.

(Generation Unit of Light Amount Setting Signal) Next, the generation unit of the light amount setting signal Vref in the control unit 58 will be described with reference to FIG.
This will be described with reference to FIG. The control unit 58 controls the light amount setting signal Vref
, A delay pulse generator 80 and a one-shot pulse generator 82 are provided for each color, and an analog switching circuit 84 is provided.

The delay pulse generators 80 each have a corresponding S
The SOS sensor 7 is connected to the OS sensor 76.
The SOS signal acquired at 6 is input. The output of each delay pulse generator 80 is input to a corresponding one-shot pulse generator 82. Each one-shot pulse generator 82
Is input to the analog switching circuit 84. The analog switching circuit 84 includes light amount setting signals Vref-K, Vref-C, Vref-M, and Vref set in advance for each color.
-Y has been entered. Analog switching circuit 84
Selects one of the light quantity setting signals Vref-K, Vref-C, Vref-M, and Vref-Y based on the signal from the one-shot pulse generator 82, and sends the same light quantity to all the laser drive circuits 54. Output as setting signal Vref.

(Operation) Next, the operation of the present embodiment will be described. FIG. 5 is a timing chart of various signals when the control unit 58 generates the light amount setting signal Vref.

As shown in FIG. 5, an SOS signal acquired by the SOS sensor 76 for each color is input to the control unit 58. In each delay pulse generator 80 provided for each color, the SOS signals nSOS-K, nSOS-C, nSOS generated for each color are generated.
The delay pulses SOST-K, SOST-C, SOST-M, and SOST-Y are generated at timings based on the falling edges of -M and nSOS-Y, respectively. The width of the delay pulse is set for each color in accordance with the timing at which the light amount control is performed.

The delay pulses SOST-K, SOST-C, SOST-M,
SOST-Y is input to the corresponding one-shot pulse generator 82. Each one-shot pulse generator 82 generates a pulse signal SOSP-K having a pulse width for a time necessary for light amount adjustment based on the input delayed pulses SOST-K, SOST-C, SOST-M, and SOST-Y. Generate SOSP-C, SOSP-M, and SOSP-Y.

The pulse signals SOSP-K, SOSP-C, SOSP-M,
SOSP-Y is input to the analog switching circuit 84. The analog switching circuit 84 includes light amount setting signals Vref-K, Vref-C, Vref-M, and Vref set in advance for each color.
-Y has been entered. In the present embodiment, as an example, the light amount setting signal Vref-K for K color is 2.0 V, the light amount setting signal Vref-C for C color is 1.6 V, and the light amount setting signal Vref-M for M color.
Is set to 1.8V, and the light amount setting signal Vref-Y for Y color is set to 1.4V.

The analog switching circuit 84 uses the pulse signals SOSP-K, SOSP-C, SOSP-M, and SOSP-Y as triggers, and sets the light quantity setting signals Vref-K, Vref that are preset for each color. Any one of -C, Vref-M, and Vref-Y is sequentially switched and output as the light amount setting signal Vref. That is, from the analog switching circuit 84, the light amount setting signals Vref generated by switching the light amount setting signals Vref-K, Vref-C, Vref-M, and Vref-Y for each color in time series are output from the laser driving circuits 54K, 54C, It is sent to 54M and 54Y.

The light amount setting signals Vref-K, Vref-C, Vref-M, Vr for each color are time-sequentially changed using a D / A converter or the like.
The light amount setting signal Vref that generates ef-Y may be generated.

As described above, in the present embodiment, in the light amount setting signal Vref transmitted as the same signal to the laser driving circuits 54K, 54C, 54M, 54Y, the light amount setting signals Vref-K, Vref-C, Vref-M, and Vref-Y are generated, and a common light amount control signal can be used between colors. Specifically, the laser drive circuit 54
K, 54C, 54M, and 54Y are light quantity control signals common to the colors if light quantity adjustment is performed when the value of the light quantity setting signal Vref is Vref-K, Vref-C, Vref-M, and Vref-Y, respectively. Even if there is, the output of each of the LDs 50K, 50C, 50M, and 50Y can be adjusted to an appropriate value.

Next, an example of light quantity control for adjusting the light quantity of each color using a specific laser drive circuit 54 will be described.

<First Embodiment> FIG. 6 shows an example of the laser drive circuit 54. Since the laser driving circuits for the respective colors have the same configuration, FIG. 6 shows only the detailed configuration of the laser driving circuit for the K color and omits the other colors.

As shown in FIG. 6, each laser drive circuit 54
Are supplied with a common laser lighting permission signal nENB, a light quantity adjustment permission signal nPCONT, and a light quantity setting signal Vref as light quantity control signals from the control unit 58. Further, the image signals nVDATA (nVDATA-K, nVDATA -C, nVDATA-M, nVDATA-
Y) is supplied.

Each laser drive circuit 54 includes a bias current source 100 and a switching current source 102 as current sources for driving the LD 50. The currents output from the bias current source 100 and the switching current source 102 are added. Are added by the detector 104 and supplied to the LD 50. The LD 50 is turned on when a current obtained by adding the two currents is supplied, and outputs a light beam having an amount of light corresponding to the magnitude of the supplied current.

At this time, the drive of the bias current source 100 and the switching current source 102 is permitted by the laser lighting permission signal nENB, and the bias current source 100
50 outputs a current equal to or less than a predetermined threshold value for outputting light, and the switching current source 102 outputs an image signal nV for each color.
The switching current output of the specified current value is
By turning on / off, each LD 50 is turned on / off.

A part of the light beam output from the LD 50 is received by the PD 106 as monitor light, and a current proportional to the output light amount is output. This current is voltage-converted by the current-voltage converter 108 and compared with the light quantity setting signal Vref in the comparator 110. The result of this comparison is input to the sample and hold (S / H) circuit 112.

The S / H circuit 112 is connected to the OR circuit 114. The OR circuit 114 receives the image signal nVDATA of the corresponding color and the light amount adjustment permission signal nPCO from the control unit 58.
NT is input, and the result of OR operation of these input signals is output as a light amount adjustment signal nS / H.

That is, each of the laser drive circuits 54K, 54K
In C, 54M, and 54Y, a common light amount adjustment permission signal nPCO
NT and each image signal nVDATA-K, nVDATA-C, nVDATA-M,
Based on nVDATA-Y, light intensity adjustment signals nS / HK, nS / HC,
nS / HM and nS / HY are respectively generated.

The output signal from the OR circuit 114, that is, the light amount adjustment signal nS / H is input to the S / H circuit 112. When a sample is specified in the light amount adjustment signal nS / H, the LD 50 is turned off. By turning on the light and adjusting the output current value of the switching current source 102 based on the comparison result in the comparator 110, the light amount is adjusted so that a predetermined amount of light beam is output from the LD 50. If so, the adjustment result is held.

With such a configuration of the laser driving circuit 54, the control unit 58 can control the common light amount adjustment permission signal.
The execution of the light amount adjustment is permitted to all the laser drive circuits 54 by nPCONT, and the laser drive circuit 54 that actually executes the light amount adjustment is instructed by the image signal nVDATA transmitted for each laser drive circuit 54.

Next, the light amount control when the laser drive circuit 54 having the above configuration is used will be described with reference to the timing chart of FIG. Hereinafter, the states A1 to A7 indicated by arrows in FIG. 7 will be described in order. LD5
In driving 0, the control unit 58 controls the laser lighting permission signal.
nENB is turned on in advance.

In the state A1, the light quantity setting signal Vref has the value of the light quantity setting signal Vref-K for K color. At this time,
The control unit 58 first turns on the light amount adjustment permission signal nPCONT.
Then, the image signal nVDATA-K for K color is turned on for a predetermined period. Note that this timing is the same as the K color SO during the previous scan.
The SOS signal nSOS-K for K color, for example, when a predetermined time has elapsed from the SOS signal nSOS-K acquired by the S sensor 76K.
Is set so as to be performed when the scanning light beam is outside the image forming area.

Thus, in the laser driving circuit 54K, the light amount adjustment permission signal nPCO input to the OR circuit 114 is output.
The light amount adjustment signal nS / HK is output from the OR circuit 114 based on NT and the image signal nVDATA-K. That is, during the period when the image signal nVDATA-K for K color is in the ON state, both of the input signals to the OR circuit 114 are turned ON.
The light intensity adjustment signal nS / HK is output from the
/ HK is ON). When the light amount adjustment signal nS / HK turns ON, the laser drive circuit 54K adjusts the light amount so that the output light amount of the LD 50K becomes the value indicated by the light amount setting signal Vref, that is, the same value as Vref-K (K color). Light intensity adjustment).

In the next state A2, the light amount setting signal Vref becomes
It is the value of the light quantity setting signal Vref-C for C color. The control unit 58 turns on the image signal nVDATA-C for C color for a predetermined period. Note that this timing is also the same as the SOS signal for C color.
Based on nSOS-C, it is set to be performed when the scanning light beam is outside the image forming area.

Thus, similarly, the laser driving circuit 54
At C, while the image signal nVDATA-C for C color is in the ON state, both of the input signals to the OR circuit 114 are turned ON, the light amount adjustment signal nS / HC is output from the OR circuit 114, and the LD 50C The light amount is adjusted so that the output light amount becomes the value indicated by the light amount setting signal Vref, that is, the same value as Vref-C (light amount adjustment of C color).

In the next state A3, the light amount setting signal Vref is
It is the value of the light amount setting signal Vref-M for M color. The control unit 58 turns on the image signal nVDATA-M for M color for a predetermined period. This timing is also the same for the SOS signal for M color.
Based on nSOS-M, it is set to be performed when the scanning light beam is outside the image forming area.

As a result, in the laser drive circuit 54M, while the image signal nVDATA-M for M color is in the ON state, O
When both input signals to the R circuit 114 are turned on,
The light amount adjustment signal nS / HM is output from the R circuit 114 and the LD
The light amount is adjusted so that the output light amount of 50M becomes the value indicated by the light amount setting signal Vref, that is, the same value as Vref-M (light amount adjustment of M color).

In the next state A4, the light amount setting signal Vref becomes
It is the value of the light amount setting signal Vref-Y for the Y color. The control unit 58 turns on the Y-color image signal nVDATA-Y for a predetermined period. Note that this timing is also the same as the SOS signal for the Y color.
Based on nSOS-Y, it is set to be performed when the scanning light beam is outside the image forming area.

As a result, in the laser driving circuit 54Y, while the Y-color image signal nVDATA-Y is in the ON state,
When both input signals to the R circuit 114 are turned on,
The light amount adjustment signal nS / HY is output from the R circuit 114, and the LD
The output light quantity of 50Y is adjusted so that the output light quantity becomes the value indicated by the light quantity setting signal Vref, that is, the same value as Vref-Y (light quantity adjustment of Y color).

After that, the O of the image signal for detecting the SOS signal is
N (light before SOS), the light amount adjustment permission signal nPCONT
Is turned off. In states A5 and A6, the LD 50 is turned on (before SOS lighting) with the adjusted output light amount in order to detect the SOS signal.

More specifically, first, in the state A5, the image signal nVDATA-K for K color is turned on. As a result, in the laser drive circuit 54K, the LD 50K is turned on with the adjusted output light quantity (K-color SOS pre-lighting). By this lighting, S
The light beam output from the LD 50K is incident on the OS sensor 76K, and the SOS signal nSOS-K for K color is output.

When the SOS signal nSOS-K for K color is output, the image signal nVDATA-K for K color is turned off, and the state is changed to state A6. In synchronization with the SOS signal nSOS-K, an image signal nVDATA-K for K color based on the image data is output.
As a result, in the laser drive circuit 54K, the LD 50K is turned on based on the image signal with the adjusted output light amount, and the photosensitive drum 16K is irradiated with a light beam based on the image data to write an image (K color image book). Included).

In the state A5, the M-color image signal nV
DATA-M is turned ON, and similarly, SOS pre-lighting is performed for the M color. When the SOS signal nSOS-M for M color is output, M
The color image signal nVDATA-M is turned off. And the S
In state A6 after a predetermined period has elapsed since the OS signal output,
An M color image signal nVDATA-M based on the image data is output in synchronization with the M color SOS signal nSOS-M (M color image writing).

In the next state A6, the image signal for C color
The image signals nVDATA-Y for nVDATA-C and Y colors are turned on, and the SOS pre-lighting is similarly performed for C and Y colors.
SOS signal nSOS-C for C color, SOS signal nSOS-Y for Y color
Is output, the image signal nVDATA-C for C color and the image signal nVDATA-Y for Y color are turned off.

Then, in state A7 after a lapse of a predetermined period from the output of the SOS signal, the SOS signal nS for the C color
The C-color image signal nVDATA-C and the Y-color image signal nVDATA-Y based on the image data are output in synchronization with the SOS signals nSOS-Y for the OS-C and Y colors (C color, Y Color image writing).

Thereafter, the image signal nVDA of each color for one line
When the output of the TA ends and a predetermined time has elapsed from the output of the SOS signal, the light amount control timing comes again, and the control from the state A1 is repeated.

As described above, the value of the light amount setting signal Vref is switched in time series, and each light amount adjusting signal nS / H is generated at a timing corresponding to the light amount setting signal for each color, so that a common color is used between colors. Even with the light amount control signal, the light amount can be adjusted to an appropriate value. Further, since the light amount adjustment of all the LDs 50 is performed on the same scanning line, the holding period (hold period) after the light amount adjustment can be shortened, and the LD 50
Can quickly respond to the fluctuation of the output light quantity.

<Second Embodiment> In the second embodiment, a case will be described in which the light quantity adjustment of all colors cannot be performed within one scan as in the first embodiment. Note that the configuration of the laser driving circuit 54 may be the same as that of the first embodiment described above, and thus the description thereof is omitted here.

FIG. 8 is a timing chart in the case where the light amount is adjusted for each of two colors for each interval scan. The adjustment of the light amount of each color is performed when the scanning light beam is outside the image forming area. Hereinafter, the states B1 to B7 indicated by arrows in FIG. 8 will be described in order.

In the state B1, the light quantity setting signal Vref has the value of the light quantity setting signal Vref-K for K color.
Turns on the light amount adjustment permission signal nPCONT as the light amount control for the scanning of the Nth line. And the image signal for K color
By turning on nVDATA-K for a predetermined period, the light amount adjustment signal nS / HK is output from the OR circuit 114 of the laser drive circuit 54K.
Is output to the laser driving circuit 54K.
The output light amount of K is adjusted so that it becomes the value indicated by the light amount setting signal Vref, that is, the same value as Vref-K.

In the state B2, the light quantity setting signal Vref has the value of the light quantity setting signal Vref-C for C color.
Similarly, by turning on the image signal nVDATA-C for C color for a predetermined period, the LD 50
The light intensity of the output C is adjusted so that it becomes the value indicated by the light intensity setting signal Vref, that is, the same value as Vref-C.

In the state B3, the image signal nVDATA-
By turning on the image signals nVDATA-M for the K and M colors, respectively,
Pre-SOS lighting is performed for the M color. SOS signal for K color
nSOS-K, When the SOS signal nSOS-M for M color is output, K
The color image signal nVDATA-K and the M color image signal nVDATA-M are turned off. Then, in a state B4 after a lapse of a predetermined period from the output of the SOS signal, the SOS signal nSOS-K for the K color and the SOS signal nSOS-M for the M color are synchronized with each other,
The image signal nVDATA-K for K color and the image signal nVDATA-M for M color based on the image data are output (K and M color image writing).

In the state B4, the image signal nVDATA-
The image signals nVDATA-Y for the C and Y colors are turned on, and the SOS pre-lighting is similarly performed for the C and Y colors. S for C color
When the OS signal nSOS-C and the SOS signal nSOS-Y for the Y color are output, the image signal nVDATA-C for the C color and the image signal nV for the Y color
Turn off DATA-Y. Then, in the state B5 after a lapse of a predetermined period from the output of the SOS signal, the SOS for the C color
In synchronization with the signal nSOS-C and the Y-color SOS signal nSOS-Y, the C-color image signals nVDATA-C and Y based on the image data, respectively.
The image signal nVDATA-Y for color is output (image writing of C color and Y color).

In the next state B6, the light amount setting signal Vref is
The value of the light amount setting signal Vref-M for M color is N + 1
As the light amount control for the scanning of the line, the same control as in the state B1 described above is performed for the M color, and the laser driving circuit 54M
Then, the light amount is adjusted so that the output light amount of the LD 50M becomes the value indicated by the light amount setting signal Vref, that is, the same value as Vref-M.

In the state B7, the light amount setting signal Vref has the value of the light amount setting signal Vref-Y for the Y color, and the same control as in the above state B2 is performed for the Y color, and the laser drive circuit 54Y , The output light amount of the LD 50Y to the light amount setting signal Vref
, Ie, the light amount is adjusted to be the same value as Vref-Y.

In states B8, B9, and B10, the same control as in the above states B3, B4, and B5 is performed, and
Lighting before SOS of color, M color, lighting before SOS of C color, Y color,
And writing of an image of each color.

As described above, even when the light quantity adjustment of all colors cannot be performed within one scan, the scanning lines for which the light quantity adjustment is performed are different, so that the period which can be occupied by the light quantity adjustment due to the lack of the effective scanning area is insufficient. Even in this case, the light amount can be adjusted to an appropriate value.

<Third Embodiment> In a third embodiment, a case will be described in which the light amount adjustment signal nS / H is generated without using the image signal nVDATA. FIG. 9 shows an example of the laser drive circuit 54 in this case.

Since the laser driving circuits of the respective colors have the same configuration, FIG. 9 shows only the detailed configuration of the laser driving circuit of the K color and omits the other colors. In FIG. 9, the same members as those in FIG. 6 are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 9, the laser drive circuit 54 includes a gate circuit 120 instead of the OR circuit 114. Further, the control unit 58 newly supplies select signals SL1 and SL2 to the respective laser drive circuits 54.

The gate circuit 120 is supplied with select signals SL1 and SL2 as designating signals together with a light amount adjustment permission signal nPCONT from the control unit 58, and based on these input signals, a light amount adjustment signal nS / H. Is output. Specifically, the gate circuit 120 of each laser drive circuit 54 can be driven when the two-bit value indicated by the select signals SL1 and SL2 is a predetermined value that is different from each other for each color, Light intensity adjustment permission signal
When nPCONT is turned on, a light amount adjustment signal nS / H is output.

With such a configuration of the laser drive circuit 54, the control unit 58 can control the common light amount adjustment permission signal.
The execution of light amount adjustment is permitted to all the laser drive circuits 54 by nPCONT, and the laser drive circuit 54 that actually performs light amount adjustment is instructed by the common select signals SL1 and SL2.

Next, the light amount control when the laser drive circuit 54 having the above configuration is used will be described with reference to the timing chart of FIG. Hereinafter, the states C1 to C6 indicated by arrows in FIG. 10 will be described in order. Note that L
At the time of driving D50, the control unit 58 previously sets the laser lighting permission signal nENB to the ON state. The adjustment of the light amount of each color is performed when the scanning light beam is outside the image forming area.

In the state C1, the light amount setting signal Vref has the value of the light amount setting signal Vref-K for K color. At this time,
The control unit 58 sets the select signals SL1 and SL2 to the Low level, sets the gate circuit 120 of the laser drive circuit 54K to a drivable state, and sets the light amount adjustment permission signal nPCONT to a predetermined time O.
N.

As a result, in the laser driving circuit 54K,
The light amount adjustment signal nS / HK is output from the gate circuit 120,
The amount of light output from the LD 50K is adjusted so as to be a value indicated by the light amount setting signal Vref, that is, the same value as Vref-K.

In the next state C2, the light amount setting signal Vref is
It is the value of the light quantity setting signal Vref-C for C color. At this time, the control unit 58 sets the select signal SL1 to Hi level and sets SL2 to
At the low level, the gate circuit 120 of the laser drive circuit 54C is driven, and the light amount adjustment permission signal nPCONT is turned on for a predetermined time.

As a result, in the laser driving circuit 54C,
The light amount adjustment signal nS / HC is output from the gate circuit 120,
The light intensity of the output light of the LD 50C is adjusted so as to be the value indicated by the light intensity setting signal Vref, that is, the same value as Vref-C.

In the state C2, the image signal nV for K color
When DATA-K is turned on and the K-color SOS pre-lighting is performed and the K-color SOS signal nSOS-K is output, the K-color image signal is output.
Turn off nVDATA-K. Then, in state C3 after a lapse of a predetermined period from the output of the SOS signal, the K color S
An image signal nVDATA-K for K color based on image data is output in synchronization with the OS signal nSOS-K (K color image writing).

In the next state C3, the light amount setting signal Vref is
It is the value of the light amount setting signal Vref-M for M color. At this time, the control unit 58 sets the select signal SL1 to the low level,
Is set to the Hi level, the gate circuit 120 of the laser drive circuit 54M is driven, and the light amount adjustment permission signal nPCONT is turned on for a predetermined time.

As a result, in the laser driving circuit 54M,
The light amount adjustment signal nS / HM is output from the gate circuit 120,
The light amount is adjusted so that the output light amount of the LD 50M becomes the value indicated by the light amount setting signal Vref, that is, the same value as Vref-M.

In the state C3, the C-color image signal nV
When the C-color SOS signal nSOS-C is output by turning on the DATA-C and performing the SOS pre-SOS lighting, the C-color image signal nVDATA-C is turned off. Then, in state C4 after a lapse of a predetermined period from the output of the SOS signal, an image signal nVDATA-C for C color based on image data is output in synchronization with the SOS signal nSOS-C for C color (C). Color image writing).

That is, in the state C3, the adjustment of the light amount of the color M, the pre-SOS lighting of the color C, and the writing of the image of the color K are simultaneously executed.

In the next state 4, the light amount setting signal Vref becomes Y
It is the value of the light amount setting signal Vref-Y for color. At this time, the control unit 58 sets both of the select signals SL1 and SL2 to the Hi level and sets the gate circuit 120 of the laser drive circuit 54Y.
Is set in a drivable state, and the light amount adjustment permission signal nPCONT is turned on for a predetermined time.

As a result, in the laser driving circuit 54Y,
The light amount adjustment signal nS / HY is output from the gate circuit 120,
The light amount is adjusted so that the output light amount of the LD 50Y becomes the value indicated by the light amount setting signal Vref, that is, the same value as Vref-Y.

In the state C4, the M-color image signal nV
When the M-color SOS signal nSOS-M is output, the M-color SOS signal nSDATA-M is turned off, and the M-color image signal nVDATA-M is turned off. Then, in state C5 after a lapse of a predetermined period from the output of the SOS signal, the M-color image signal nVDATA-M based on the image data is output in synchronization with the M-color SOS signal nSOS-M (M Color image writing).

That is, in the state C4, the light amount adjustment of the Y color
M-color SOS pre-lighting-K and C-color image writing are performed simultaneously.

In the next state C5, the image signal nVDA for Y color
When TA-Y is turned ON, the SOS pre-lighting of the Y color is performed, and when the SOS signal nSOS-Y for the Y color is output, the image signal for the Y color is output.
Turn off nVDATA-Y. That is, in the state C5, the Y-SOS pre-lighting-K-CM color image writing is simultaneously executed.

Then, in state C6 after a lapse of a predetermined period from the output of the SOS signal, the SOS signal nS for the Y color
The image signal nVDATA-Y for Y color based on the image data is output in synchronization with the OS-Y (Y color image writing).

As described above, the value of the light quantity setting signal Vref is switched in time series, and the select signals SL1 and SL2 and the light quantity adjustment permission signal nPCO are switched at the timing corresponding to the light quantity setting signal for each color.
By generating the light amount adjustment signal nS / H by the NT, it is possible to adjust the light amount to an appropriate value even if the light amount control signal is common to the colors.

Further, in the third embodiment, unlike the first and second embodiments, since the image signal nVDATA is not required for generating the light quantity adjustment signal nS / H, the SOS pre-lighting is performed when the light quantity of another color is adjusted. This eliminates the restriction that it cannot be performed, and the light amount can be independently adjusted for each color. This is especially true for SOS for each color.
It is particularly effective for a quadruple tandem type image forming apparatus in which it is difficult to synchronize signals and the timing of light quantity control is not fixed.

In summary, in the present embodiment, the light amount setting signals Vref-K, Vref-C, Vref-M,
Even if the light amount setting signal Vref for generating Vref-Y is transmitted to all the laser drive circuits 54 as the same signal, and the light amount control signal is shared between the colors, as described specifically in the first to third embodiments. In each of the laser driving circuits 54, the light amount can be adjusted at the timing when the value of the light amount setting signal Vref corresponds to each color.

In other words, by making the light quantity control signal common (identical) between the colors, it becomes possible to use a common member for transmitting the light quantity control signal from the control unit 58 to each laser drive circuit 54. As shown in FIG. 2, the control unit 58 and each laser drive circuit 54 are connected to the same wiring cable 5.
6 and the number of connectors 60 of the control unit 58 can be reduced to one.

As a result, the total number of signal lines for all colors for supplying signals to each laser drive circuit 54 and the total number of connectors can be reduced as compared with the related art, and the cost can be reduced.

For example, in the case of the first embodiment, the distribution cable 56 may include a total of eight signal lines for transmitting signals from the control unit 58. As shown in Table 2, the signal lines for supplying the laser lighting permission signal nENB, the light quantity adjustment permission signal nPCONT, the light quantity setting signal Vref, and the driving power supply 5V commonly used in all the laser driving circuits 54 are provided. 1 each
4 lines each, and 4 ground lines for each signal line
It is a book.

[0130]

[Table 2]

As can be seen from the comparison between Table 1 and FIG. 15 and Table 2 and FIG. 2, the total number of signal lines is 32 → 8
The total number of connectors can be changed from eight to five. Table 3 shows the cost of the conventional wiring cable.
2 shows the cost of the distribution cable according to the present embodiment, and the cost of the distribution cable can be reduced by 16% as compared with the related art.

[0132]

[Table 3]

[0133]

[Table 4]

As can be seen from a comparison between FIG. 15 and FIG. 2, the number of connectors of the control unit 58 can be changed from four to one. Thereby, the space required for passing the wiring cable near the control unit 58 can be reduced as compared with the related art,
The size of the device can be reduced, and the work at the time of assembly can be simplified. Also, than before,
The amount of routing of the distribution cable can be reduced, and the influence of noise can be reduced.

In this embodiment, an example is shown in which the control unit 58 and each laser drive circuit 54 are connected by one wiring cable 56, but the present invention is not limited to this. For example, as shown in FIG. 11, the control unit 58 and each of the laser drive circuits 54 may be connected in a daisy chain using a distribution cable 56 having connectors 60 at both ends. In this case, the total number of connectors is the same as the conventional one, but the number of internal signal lines and the
Can be reduced in the same manner as in the above embodiment. Further, the total length of the distribution cable can be further reduced as compared with the above embodiment.

Further, by connecting the laser driving circuit 54K for K color in the laser driving circuit 54 in the order closest to the control unit 58, the laser driving circuit for K color is set to the upstream side, Even when the supply of the light amount control signal is stopped halfway due to an abnormality in the wiring cable downstream of the circuit 54 or the laser drive circuit 54, multicolor printing cannot be executed, black and white printing can be executed.

In this embodiment, when the values of the light quantity setting signals Vref-K, Vref-C, Vref-M, and Vref-Y of each color are different, that is, the value of the light quantity setting signal is set for each color, The case where high-quality image formation is enabled has been described as an example, but the present invention is not limited to this. The value of the light amount setting signal may be the same for all colors.

In this case, it is possible to omit the means for generating the light quantity setting signal whose value changes in a time series as shown in FIG. 4 of the control unit 58, so that the light quantity can be adjusted with a simpler configuration and the cost can be reduced. Can be achieved.

With respect to a specific embodiment, using the timing chart of FIG. 12, the state D indicated by an arrow in the figure will be described.
Description will be made in the order of 1 to D4. The configuration of the laser drive circuit 54 is the same as that of the first embodiment. The light amount adjustment is performed when the scanning light beam is outside the image forming area.

In the state D1, the light quantity setting signal Vref has the same value for all colors, and the control unit 58 first turns on the light quantity adjustment permission signal nPCONT. Then, the image signals nVDATA-K, nVDATA-C, nVDATA-M, and nVDATA-Y for each color are turned on for a predetermined period. Thereby, the laser driving circuit 54K,
Light amount adjustment signals nS / HK, nS / HC, nS / HM, and nS / HY are output from OR circuits 114 of 54C, 54M, and 54Y, respectively, and laser drive circuits 54K, 54C, 54M, and
In 4Y, the light amount is adjusted so that the output light amounts of the LDs 50K, 50C, 50M, and 50Y have the same value as the light amount setting signal Vref which is the same value for all colors (K color, C color, M color,
Adjustment of light amount of Y color).

In the state D2, the image signal nVDATA-
Turn on the image signals nVDATA-M for the K and M colors, respectively,
Pre-SOS lighting is performed for the colors M and M. SOS for K color
When the signal nSOS-K and the SOS signal nSOS-M for M color are output, the image signal nVDATA-K for K color and the image signal nVDA for M color
Turn off TA-M. Then, in the state D3 after a lapse of a predetermined period from the output of the SOS signal, the S color S
The image signal nVDATA-K for K color based on the image data is synchronized with the OS signal nSOS-K and the SOS signal nSOS-M for M color, respectively.
An image signal nVDATA-M for M color is output (K and M color image writing).

In the state D3, similarly, the image signal for C color
The nVDATA-C and nVDATA-Y image signals for Y color are each turned on, and pre-SOS lighting is performed for C and Y colors. When the SOS signal nSOS-C for C color and the SOS signal nSOS-Y for Y color are output, the image signal nVDATA-C for C color and the image signal for Y color
Turn off nVDATA-Y.

In the state D4 after a lapse of a predetermined period from the output of the SOS signal, the C-color SOS signal nSOS
-Output the C-color image signal nVDATA-C and the Y-color image signal nVDATA-Y based on the image data in synchronization with the C and Y-color SOS signals nSOS-Y, respectively. Image writing).

As described above, when the value of the light amount setting signal is the same for all colors, the light amount can be adjusted more easily.

Further, in the present embodiment, an image forming apparatus of a spray paint system has been described as an example, but the present invention may be applied to an image forming apparatus of a quadruple tandem system.

[0146]

As described above, the present invention has an excellent effect that noise resistance can be improved and cost can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a top view of the optical scanning device according to the embodiment.

FIG. 3 is a side view of the optical scanning device according to the embodiment.

FIG. 4 is provided in a control unit according to the present embodiment;
FIG. 4 is a block diagram illustrating a detailed configuration of a unit that generates a light amount setting signal whose value changes in a time series.

FIG. 5 is a timing chart of various signals when generating a light amount setting signal according to the present embodiment.

FIG. 6 is a block diagram showing a detailed configuration of a laser drive circuit in the first and second embodiments.

FIG. 7 is a timing chart for explaining light amount control in the first embodiment.

FIG. 8 is a timing chart for explaining light amount control in a second embodiment.

FIG. 9 is a block diagram illustrating a detailed configuration of a laser drive circuit according to a third embodiment.

FIG. 10 is a timing chart for explaining light amount control in a third embodiment.

FIG. 11 is a diagram illustrating connection between a control unit and a laser drive circuit according to another embodiment.

FIG. 12 is a timing chart for explaining light amount control in another embodiment.

FIG. 13 is a block diagram showing a detailed configuration of a conventional laser drive circuit.

FIG. 14 is a timing chart for explaining conventional light quantity control.

FIG. 15 is a diagram showing a connection between a conventional control unit and a laser drive circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image forming apparatus 16K, 16C, 16M, 16Y Photoconductor drum 18 Optical scanning apparatus 50K, 50C, 50M, 50Y Semiconductor laser 52 Polygon mirror 54K, 54C, 54M, 54Y Laser drive circuit 56 Wiring cable 58 Control part 60 Connector 76K, 76C, 76M, 76Y SOS sensor 110 Comparator 112 Sample hold circuit 114 OR circuit 120 Gate circuit Vref light quantity setting signal nENB laser lighting permission signal nPCONT light quantity adjustment permission signal nS / HK, nS / HC, nS / HM, nS / HY light quantity Adjustment signal nVDATA-K, nVDATA-C, nVDATA-M, nVDATA-Y Image signal nSOS-K, nSOS-C, nSOS-M, nSOS-Y, SOS signal SL1, SL2 Select signal

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 2C362 AA12 AA16 AA52 AA54 AA55 AA56 AA61 AA63 BA51 BA67 CA18 CA31 CA39 CB74 DA09 2H030 AB02 AD11 AD17 BB02 BB13 BB16 BB71 2H076 AB02 AB06 AB11 AB16 AB58 AB66 DA03 DA19 DA01 DA22

Claims (9)

[Claims] An image forming apparatus that exposes a plurality of photoconductors provided for different colors with light beams output from a plurality of light sources, wherein the plurality of photoconductors are provided for each of the light sources. A light source driving unit for lighting with a predetermined output light amount, and a control unit for outputting a light amount control signal for controlling an output light amount of the light source to the light source driving unit and an image signal for instructing lighting of the light source. An image forming apparatus, wherein at least the light amount control signal transmitted from the control unit to each light source control unit is the same. 2. The control unit according to claim 1, wherein the control unit outputs a light amount setting signal for setting an output light amount of each of the plurality of light sources in a time series as the light amount control signal. Image forming device. 3. The control unit outputs, as the light amount control signal, a light amount adjustment permission signal for permitting execution of light amount adjustment for adjusting to the predetermined output light amount, based on an image signal transmitted to each light source driving unit. The image forming apparatus according to claim 1, wherein the light source driving unit is instructed to execute the light amount adjustment. 4. The light quantity control signal, wherein the light quantity control permission signal for permitting execution of light quantity adjustment for adjusting to the predetermined output light quantity, and a designation for designating a light source driving means for executing the light quantity adjustment, as the light quantity control signal. The image forming apparatus according to claim 1, wherein a signal is output. 5. The image forming apparatus according to claim 1, wherein the control unit and the plurality of light source driving units are connected by a common connection cable. 6. The image forming apparatus according to claim 1, wherein the control unit and the plurality of light source driving units are connected in a daisy chain. 7. The image forming apparatus according to claim 1, wherein light amount control of all of the light sources is performed on the same scanning line. 8. The image according to claim 1, wherein light amount control of the light sources is performed on scanning lines different from each other for each of the plurality of light sources. Forming equipment. 9. When at least a photoconductor corresponding to black is provided, the light source driving unit outputs the light beam to the photoconductor corresponding to black among the plurality of light source driving units. 9. The image forming apparatus according to claim 1, wherein the plurality of light source driving units are connected to the control unit, with the light source driving unit being the uppermost stage. 10.