JP3842004B2 - LD controller - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser diode. (LD) The amount of laser light emitted from the LD Concerning control devices, especially for writing images with light beams in digital copying machines, laser beam printers, facsimiles, etc. LD The present invention relates to a control device.
[0002]
[Prior art]
Used in digital copiers, laser printers, and facsimile machines that are currently on the market, and emits a light beam for writing. laser A diode (LD) is desired to have a constant light emission amount. However, it is known that the amount of emitted light varies depending on the environment where the LD is placed or the temperature variation caused by the heat generated by the LD itself. For this reason, control is generally performed in which the control unit adjusts the light emission amount to the LD to be constant by detecting the light emission amount of the LD with a photodiode (PD) attached to the LD and feeding back to the control unit. It has been broken. An example of the configuration of a conventional light source control circuit for controlling the light emission amount of such an LD is shown in FIG. 2 Show.
[0003]
In the light emission source control circuit shown in FIG. 12, as shown in the timing chart of FIG. 13, the sample and hold signal (S / H signal) is intermittently synchronized with the sample state (indicated by high level in the figure). There is a period of automatic control (hereinafter referred to as APC). In this control method, in the standby state outside the image signal output period, the sample mode is shifted to the sample mode based on the sample-and-hold signal (hereinafter referred to as the sample signal) in the sample state, and the light amount adjustment by APC is performed. Based on the sample & hold signal in the hold state (hereinafter referred to as the hold signal), the mode shifts to the hold mode, and constant current drive is performed to fix the LD drive current to the same current value as in the sample mode.
[0004]
In this type of conventional technology, an LD lighting signal is sent simultaneously with a sample signal as a control signal from the LD control device during APC operation. The sample signal switches ON / OFF of the S / H switch 122 in FIG. 12, and the LD lighting signal switches ON / OFF of the switch circuit 125 to light the LD. The PD current value proportional to the light intensity of the LD is converted into a voltage by the I / V conversion circuit 126, and the voltage is compared with the reference voltage by the comparator 121. Based on the comparison result, the hold capacitor 123 is charged or discharged to change the voltage value, the output current of the current generation circuit 124 is controlled, and the LD light quantity is controlled to be constant.
[0005]
[Problems to be solved by the invention]
However, in the above prior art, when the control signal is disturbed for some reason and the timing of the sample signal and the LD lighting signal is shifted, the APC operation is performed even though the LD is not lit as shown in FIG. The situation that you do occurs. Under such circumstances, since no LD light is incident on the PD, the APC circuit determines that the LD is not lit, and sets the current setting value flowing through the LD, that is, the voltage of the hold capacitor to an infinitely large value. There is a possibility.
[0006]
As a result, when shifting from the sample mode to the hold mode, the first problem is that the light emission amount of the LD becomes larger than the set value, or in some cases, a non-standard current flows through the LD to induce the deterioration of the LD. This is a problem.
[0007]
Further, in this type of conventional technology, since there is only one light receiving element for each LD control device, the APC operation is sequentially performed with the timing slightly shifted for each LD control device during the APC operation. However, in the above-described technique, if the timing of the sample signal and the LD lighting signal is shifted when the control signal is disturbed for some reason, the light emission amount of the LD becomes larger than the set value in the same process as above, Inducing degradation can occur as a second problem. As a third problem, if the lighting timings of the LD control devices overlap, the APC circuit determines that the LD is emitting too much light, and the light emission amount of the LD is set smaller than the set value. It can happen.
[0008]
Further, when configuring an actual circuit, for example, when using an LD driver with an APC circuit built in as a component, current-voltage conversion is often built into the driver. For this reason, the switch may be switched based on the control signal to feed back the light receiving element output to the APC circuit inside the driver.
[0009]
However, in the above-described technique, when the control signal is disturbed for some reason and the timings of the sample signal and the switch switching signal are shifted, a situation occurs in which the APC operation is performed even though the feedback signal does not return. Under such a situation, there is a possibility that the APC circuit determines that the LD is not lit, and the current value flowing through the LD is set to an infinitely large value. As a result, when shifting from the sample mode to the hold mode, the light emission amount of the LD becomes larger than the set value, or in some cases, a non-standard current flows through the LD, which may induce the deterioration of the LD. This can be cited as the fourth problem.
[0010]
The present invention has been made in view of the above problems, and in a multi-beam laser printer that performs image writing simultaneously with a plurality of laser beams, the timing of sample signals. And light receiving element output switching signal Sampling during the period when all the LDs are extinguished and the LD emission amount is set to be larger than the set value, or sampling is performed during periods when a plurality of LDs are lit and the LD emission amount is set to be small. Can be controlled to the correct amount of LD light emission, and can also prevent LD degradation LD An object is to provide a control device.
[0011]
[Means for Solving the Problems]
In order to achieve this object, the invention according to claim 1 includes a plurality of Channel The laser beam emitted from the LD is received by one light receiving element, and each APC period Channel LD According to LD lighting signal Lights up sequentially and in sync with the lights A channel switching signal for switching each channel and a sample signal for sampling the light emission amount of the LD are sequentially sent. APC is performed by feeding back the signal from the light receiving element LD In the control device, when APC is performed, the sample signal is transmitted in each channel. time But More than the transmission time of the channel switching signal whose transmission time is shorter than the LD lighting signal Short and Sending those signals Within the period, at least two LD lighting signals for each channel are output simultaneously. Simultaneous transmission Sample signal at a predetermined time from the period And channel switching signal But Both during the simultaneous transmission period It is characterized by being sent out so as not to overlap.
[0012]
According to the second aspect of the present invention, the laser beam irradiated from the plurality of light emitting sources In the main scanning direction scanning It is a period to Image writing period Among Detection means for detecting the end and outputting a detection signal, and an image data signal for lighting a plurality of light sources LD Lighting signal, the LD For lighting signal Depending on Perform automatic power control (APC) based on the amount of light emitted from the light source sample Controls switching between multiple light source channels to select signals and channels for automatic power control execution Channel Switching signal Based on detection signal Image processing means to output, provided for each channel, Channel When selected by the switching signal, LD Lighting signal and sample Driving means for driving a plurality of light emitting sources based on the signal. In the LD control device The image processing means The transmission time of the sample signal in each channel is further longer than the transmission time of the channel switching signal whose transmission time is shorter than the LD lighting signal. Short and Within the lighting period of those signals And at least two of each channel LD Lighting signal is output at the same time Simultaneous transmission A predetermined time from the period Sample signal and channel switching signal But Both during the simultaneous transmission period It is characterized by being sent out so as not to overlap.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0014]
First, a first embodiment of the present invention will be described with reference to FIGS. 5 Details will be described with reference to FIG. FIG. 2 is a diagram illustrating a configuration example of an optical system of a laser printer as an image forming apparatus. In FIG. 2, a laser beam emitted from a laser diode (LD) inside a laser diode unit (LDU) 21 is converted into parallel rays by a collimating lens inside the LDU 21, and is deflected and scanned by a rotating polygon mirror (hereinafter referred to as a polygon mirror) 22. After that, an image is formed on the charged surface of the drum-shaped photosensitive member (photosensitive drum) 25 by an imaging lens including the F-θ lens 23 and the like.
[0015]
At this time, the laser beam is modulated based on the image signal, repeatedly turned on and off, and repeatedly moved in the main scanning direction indicated by the arrow in the drawing according to the rotation of the polygon mirror 22, and at the same time, the photosensitive drum 25 is rotated. An electrostatic latent image is formed on the photosensitive drum 25 by performing sub-scanning. The formed electrostatic latent image is developed with a charged developer (toner), and a transfer material such as transfer paper to which a charge opposite to that of the developer is applied is brought into intimate contact with the photosensitive drum 25, thereby developing the developer. Is transferred to the transfer material. Then, after the transfer material is separated from the photosensitive drum 25, the developer is fused on the transfer material by being heated, and fixing is performed.
[0016]
Here, the light receiving element 26 disposed outside the scanning region on the photosensitive drum 25 detects a laser beam incident through an imaging lens formed of an F-θ lens or the like, and the LD control unit Based on the detection signal obtained by the light receiving element 26, an effective scanning period, which is a period during which an image is written on the photosensitive drum 25, is determined.
[0017]
FIG. 1 is a block diagram showing a circuit configuration of the write control unit. In FIG. 1, a central processing unit (CPU) 111 controls the entire laser printer. The image processing unit (IPU) 12 electrically processes the image data, and in parallel with the writing unit constituted by the LD driver 14 and the like, the pixel clock and the image data (collectively DATA in the figure), and the sample & hold signal Is sending. The image data transmitted to the writing unit is modulated by the pulse width modulation (PWM) unit 13 and transmitted to the LD driver 14.
[0018]
The LD driver 14 drives the LD based on the transmitted signal. Then, the image processing unit 12 sends an LD lighting signal to the PWM unit 13 outside the effective scanning period based on the detection signal obtained by the light receiving element, and lights the LD for APC control. In addition, the image processing unit 12 sends a sample signal to the LD driver 14 during the sending period of the LD lighting signal, so that the monitor current generated by the photodiode (PD) built in the LD package can be converted into the built-in APC circuit. APC is performed by feeding back to the LD driver 14. During the effective scanning period, the image processing unit 12 fixes the output current of the LD driver 14 to a constant value by sending a hold signal.
[0019]
Next, a circuit block diagram of an APC circuit built in the LD driver 14 is shown in FIG. The operation of the APC circuit will be described in detail with reference to this figure. During the APC operation, an LD lighting signal and a sample signal are transmitted as control signals from the image processing unit 12 which is an LD control device. The LD lighting signal switches the switch circuit 35 of FIG. 3 to ON, and the sample signal switches the S / H switch 32 to ON. As a result, a current based on the voltage value of the hold capacitor 33 flows from the current generation circuit 34 into the LD through the switch circuit 35, the LD emits light, and a current proportional to the light intensity of the LD flows into the PD.
[0020]
Then, the current value flowing through the PD is converted into a voltage in the I / V conversion circuit 36, and the converted voltage and the reference voltage are compared by the comparator 31. Based on this result, the hold capacitor 33 is charged or discharged to change the voltage value, the output current of the current generation circuit 34 is controlled, and the LD light quantity is controlled to be constant.
[0021]
At the time of image writing, the S / H signal changes to a hold signal, and the S / H switch 32 is switched to OFF. As a result, since the value of the hold capacitor 33 is fixed to a constant value, the current flowing from the current generation circuit 34 to the LD is fixed to a constant value. Based on the image data signal sent from the pulse width modulation (PWM) unit 13, the switch circuit 35 is switched, and the LD light source is modulated to write an image on the photosensitive drum 25.
[0022]
After that, when the laser beam scans the photosensitive drum 25 once in the seed scanning direction and the image writing period ends, that is, outside the effective scanning period, the APC operation is performed again, and the LD is controlled to a prescribed light amount value. When APC is completed, an effective scanning period is reached, and the operation in which the laser beam scans the photosensitive drum 25 in the main scanning direction again and performs writing is repeated.
[0023]
FIG. 4 shows a time chart of the LD lighting signal and the S / H signal (sample signal) when performing the APC operation. As is apparent from FIG. 4, when performing APC, control is performed so that the sample period based on the sample signal is shorter than the LD lighting period and included in the LD lighting period. As described above, the circuit block configuration example for generating the sample signal and the LD lighting signal such that the sample signal transmission time is shorter than the LD lighting signal transmission time and included in the LD lighting signal transmission period, and FIG. 5 shows a time chart of the sample signal and LD lighting signal output from this circuit.
[0024]
First, when the image processing unit (IPU) 12 turns on the LD for synchronization detection after the write signal is sent in FIG. 1, the laser beam scanned along with the rotation of the polygon mirror as shown in FIG. Is incident on a light-receiving element 26 for synchronization detection, etc., and is converted into a synchronization detection signal and sent to an image processing unit (IPU) 12. The image processing unit (IPU) 12 detects the end of the image writing period based on the synchronization detection signal, and generates an APC start signal.
[0025]
Then, inside the image processing unit (IPU) 12, as shown in FIG. 5, signals D1 and D2 shifted by a predetermined time are generated by a delay circuit (delay line) based on the APC start signal D0. A logical sum of these signals, that is, D0 + D1 + D2 is used as the LD lighting signal for APC operation, while D2 which is a signal delayed from the APC start signal by a certain time is used as a sample signal. Control signal operation can be achieved.
[0026]
Next, a second embodiment of the present invention will be described with reference to FIGS. 9 Details will be described with reference to FIG. Here, as in the first embodiment, a laser printer is used as the image forming apparatus of the second embodiment. For this reason, the description overlapping with the first embodiment is omitted as much as possible.
[0027]
The second embodiment shows an embodiment of a multi-beam laser printer that performs image writing simultaneously with a plurality of laser beams, among laser printers. In the multi-beam laser printer, an image is formed on the photosensitive drum 25 by individually controlling a plurality of laser beams that are close to each other and simultaneously scanning with the same polygon mirror. For this reason, the multi-beam laser printer is exactly the same as the one-beam laser printer described in the first embodiment except for simultaneous writing with a plurality of laser beams. For this reason, in the second embodiment, the description is omitted assuming that the optical system described in the first embodiment and the equivalent of the development process are used.
[0028]
The difference between a multi-beam laser printer and a single-beam laser printer is that multiple LDs are used as a light source for writing and the laser beams are bundled together or can be individually controlled on a single chip. A laser diode array (LDA) in which a plurality of light emitting sources are arranged in an array is used. Therefore, in the second embodiment, a method of using a plurality of LDs and bundling laser beams into one is taken up, and in particular, a case of using two LDs will be described. In addition, as a method for detecting the light amount of the LD, a common light receiving element 26 is used for the two LDs.
[0029]
Here, it is assumed that a single photodiode (PD) 64 is used as the light receiving element 26 as shown in FIG. A conceptual diagram of a laser beam synthesis method is shown in FIG. The laser beams emitted from the LDs 1 and 2 pass through the collimator lens 61 to become parallel light beams, and enter the beam combining prism 62 to become two adjacent laser beams. Similar to the first embodiment, these two laser beams are simultaneously scanned by a rotary polygon mirror (polygon mirror) 63, reach the photosensitive drum 25, and are adjacent to each other in the sub-scanning direction. At the same time, the image for two lines is written.
[0030]
FIG. 7 is a block diagram illustrating a circuit configuration of the write control unit. In FIG. 7, a central processing unit (CPU) 71 controls the entire laser printer. An image processing unit (IPU) 72 electrically processes image data, and in parallel with a writing unit constituted by an LD driver 74 and the like, a pixel clock signal and an image data signal (DATA collectively in the figure), sample and hold A signal and a monitor current switching signal are transmitted. The image data signal transmitted to the writing unit is modulated by the pulse width modulation (PWM) unit 73 and transmitted to the LD driver 74.
[0031]
The LD driver 74 drives the LD 1 and 2 based on the transmitted signal. Then, APC is performed on each of the LDs 1 and 2 sequentially in time within the ineffective scanning period. First, from an image processing unit (IPU) 72, which is an LD control device, an LD lighting signal of LD1 is sent as an image data signal, and a sample signal and a monitor current switching signal are sent as control signals. The monitor current switching signal forms an APC closed loop circuit for ch1 as in the first embodiment, and APC control of LD1 is performed in the same manner as in the first embodiment.
[0032]
Next, the LD lighting signal, sample signal, and monitor current switching signal of LD1 are turned off, and the LD lighting signal, sample signal, and monitor current switching signal of LD2 are sent out. As a result, the monitor current switching signal forms an APC closed loop circuit for ch2 as in the first embodiment, and APC control of LD2 is performed in the same manner as in the first embodiment.
[0033]
During the effective scanning period, the S / H signal sent to each LD driver 74 is held, that is, the hold signal is used to fix the output current of each LD driver 74. Here, FIG. 8 shows a time chart of the ch1 and ch2 LD lighting signals, the S / H signal, and the monitor current switching signal when the APC operation is performed.
[0034]
As is apparent from FIG. 8, when APC is performed, control is performed so that the transmission time of the sample signal is shorter than the LD lighting period for each channel and is included in the LD lighting period. Further, the control is performed so that the transmission time of the sample signal is shorter than the transmission period of the monitor current switching signal for each channel and is included in the transmission period of the monitor current switching signal. Furthermore, it can be seen from FIG. 8 that the lighting times of the LDs 1 and 2 overlap.
[0035]
As described above, (1) the sample signal transmission time within the APC operation period is shorter than the LD lighting time period and is included in the LD lighting period, and (2) the sample signal transmission time is monitored for each channel. An example of a circuit block configuration for transmitting a signal that is shorter than the transmission period of the current switching signal and included in the monitor current switching signal period, and (3) the lighting times of the LDs overlap each other. As shown in FIG.
[0036]
First, after the write signal is sent, the image processing unit (IPU) 72 lights one or both of the LDs 1 and 2 for synchronization detection, and an APC start signal is generated by the same process as in the first embodiment. Then, in the image processing unit (IPU) 72, as shown in FIG. 9, signals D0 to D5 shifted by a predetermined time by a delay circuit (delay line) are generated based on the APC start signal. However, the delay amount is assumed to be large in the order of numbers from D0.
[0037]
Of these, a logical sum of five signals D0 to D4 is used as a 1ch LD lighting signal, and a logical sum of three signals D1 to D3 is a 1ch monitor current switching signal. In addition, the signal D2 delayed further to the middle is used as a sample signal. Further, the control signal operation of the time chart of FIG. 8 can be achieved by using the most delayed signal D5 and generating and using the control signal for ch2 by the delay circuit in the same manner as ch1.
[0038]
Next, a third embodiment will be described in detail with reference to FIGS. Here, as in the second embodiment, an embodiment of a multi-beam laser printer that simultaneously writes images with a plurality of laser beams is shown. For this reason, the description overlapping with the second embodiment will be omitted as much as possible.
[0039]
In the third embodiment, as a method for generating a plurality of laser beams, a plurality of light sources that can be individually controlled on a single chip are used instead of using a plurality of LDs as in the second embodiment. It is assumed that a laser diode array chip (LDA chip) 102 arranged in an array is used. FIG. 10 shows a conceptual diagram when an LDA chip is used as a method for generating a plurality of laser beams.
[0040]
In the laser beam generation method according to the present embodiment, since a plurality of light emitting sources are close to each other on one LDA chip 102, there is usually only one LD light amount detection photodiode (PD) built in the LD. Many have only one built-in package. In the third embodiment, a case in which only one internal PD 101 is used as described above will be described, in particular, one having two light emitting points. A plurality of laser beams emitted from the LDA chip 102 are converted into parallel rays by a collimator lens, and simultaneously scanned by a rotating polygon mirror (polygon mirror) 22 as in the first and second embodiments. When the light reaches the photosensitive drum 25, the two laser beams are close to each other in the sub-scanning direction, and two lines of images are simultaneously written. The main scanning direction and the sub scanning direction shown in FIG. 10 indicate the positional relationship of a plurality of laser beams when the laser beam reaches the photosensitive drum 25.
[0041]
FIG. 11 is a block diagram illustrating a circuit configuration of the write control unit. In FIG. 11, a central processing unit (CPU) 111 controls the entire laser printer. An image processing unit (IPU) 112 electrically processes image data, and in parallel with a writing unit constituted by an LD driver 114 and the like, a pixel clock and image data (collectively DATA in the figure), a sample & hold signal, And a monitor current switching signal. The image data signal transmitted to the writing unit is modulated by the pulse width modulation (PWM) unit 113 and transmitted to the LD driver 114. The LD driver 114 drives the LDA based on the transmitted signal.
[0042]
The third embodiment is different from the second embodiment in that the LDA chip 102 is used as a light source of a plurality of laser beams, and thus the light is emitted from separate LDs as in the second embodiment. The laser beams do not need to be bundled together later by the combining prism 91 or the like. In addition, what has been described in the second embodiment is a type that uses a common photodiode (PD) for two LDs as a method of detecting the amount of light of the LDs. In the third embodiment, the same control can be performed by simply replacing the PD and the two LDs in the second embodiment with LDA. For this reason, the control method of the third embodiment is based on the second embodiment, and a detailed description of the control method is omitted. However, in order to clarify the control method of the third embodiment, the description will be given again in the same manner as the second embodiment based on the time chart of FIG.
[0043]
As apparent from FIG. 8, when APC is performed, control is performed so that the transmission time of the sample signal is shorter than the LD lighting time for each channel and is included in the LD lighting period. Further, control is performed so that the sample signal transmission time is shorter than the monitor current switching signal transmission time for each channel and is included in the monitoring current switching signal transmission period. Furthermore, it can be seen from FIG. 8 that the lighting times of the LDs 1 and 2 overlap.
[0044]
【The invention's effect】
As is apparent from the above description, in the present invention, control is performed so that the LD lighting signal is transmitted for a period longer than the sample signal within the APC period. For this reason, even when the timings of the LD lighting signal and the sample signal are slightly shifted, it is possible to prevent the LD emission amount from being set larger or smaller than the set value. In addition, it is possible to prevent LD degradation due to over-emission.
[0045]
In addition, the LD lighting signals sequentially sent to the LD control devices within the APC period overlap each other little by little in time, and control is performed so as to send the sample signal while avoiding the overlapping portions of the LD lighting of each channel. ing. For this reason, even if the timing of the LD lighting signal and the sample signal slightly deviates, one of the LDs always emits light. Therefore, the APC circuit determines that the LD is not lit and the LD emission amount is larger than the set value. It is possible to prevent a large value from being set. In addition, it is possible to prevent LD degradation due to over-emission.
[0046]
Further, control is performed so that the light receiving element output switching signal sequentially transmitted to each channel within the APC period is transmitted for a period longer than the sample signal. For this reason, even when the timing of the sample signal is slightly deviated, it is possible to prevent the LD light emission amount from being set larger than the set value. In addition, it is possible to prevent LD degradation due to over-emission.
[Brief description of the drawings]
FIG. 1 is a block diagram of a write control system circuit according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration example of an optical system of a laser beam printer as an image forming apparatus.
FIG. 3 is a circuit block diagram showing a configuration example of an APC circuit in the embodiment of the present invention.
FIG. 4 is a time chart showing an LD lighting signal and an S / H signal when performing an APC operation in the first embodiment of the present invention.
FIG. 5 is a circuit configuration diagram and a time chart for generating an LD lighting signal and an S / H signal in the first embodiment of the present invention.
FIG. 6 is a conceptual diagram of a laser beam combining method according to a second embodiment of the present invention.
FIG. 7 is a block diagram illustrating a circuit configuration example of a write control unit according to a second embodiment of the present invention.
FIG. 8 is a time chart of an LD lighting signal, an S / H signal, and a monitor current switching signal according to the second embodiment of the present invention.
FIG. 9 is a circuit configuration diagram for generating an LD lighting signal, an S / H signal, and a monitor current switching signal according to the second embodiment of the present invention.
FIG. 10 is a conceptual diagram showing a method for generating a laser beam when using an LDA chip in a third embodiment of the present invention.
FIG. 11 is a block diagram showing a circuit configuration of a write control unit according to a third embodiment of the present invention.
FIG. 12 is a block diagram showing an example of a conventional LD control circuit.
FIG. 13 is a time chart for explaining a conventional APC control operation;
FIG. 14 is a time chart showing a normal state and an abnormal state of a conventional APC control operation.
[Explanation of symbols]
11, 71, 111 Central processing unit (CPU)
12, 72, 112 Image processing unit (IPU)
13, 73, 113 Pulse width modulation section (PWM section)
14, 74, 114 LD driver
21 LD unit
22, 63 Polygon mirror
23 F-θ lens
24 reflection mirror
25 Photosensitive drum
26, 64, 101 Light-receiving element (PD)
31 Comparator
32 S / H switch
33 Hold capacitor
34 Current generator
35 Switch circuit
36 I / V conversion circuit
61 Beam synthesis prism
62 Collimating lens
102 LDA chip

Claims (2)

Receives the laser light emitted from the plurality of channels LD at one light receiving element, wherein in the APC period LD of each channel lights sequentially independently in accordance with the LD lighting signal, the synchronization with the lighting each channel in LD controller for APC signal by feeding back the from the light receiving element by leaving sequentially feeding a sample signal for sampling the emission amount of the channel switching signal and the LD for switching,
When performing the APC, the delivery time of the sample signal for each channel, the shorter than transmission time of the channel switching signal is shorter transmission time than the LD lighting signal, and in the delivery period of the signals as would fall, sends such that the do not overlap on at least two LD lighting signal the sample signal and the channel switching signal are both the simultaneous delivery period at a predetermined time from the simultaneous delivery period to be outputted simultaneously in each channel LD control device characterized by the above. A detection means for the laser beam emitted from a plurality of light emitting sources for outputting a detected detection signal the end of the inter-image writing period is a period for scanning the photosensitive member in the main scanning direction,
An LD lighting signal as an image data signal for lighting the plurality of light emitting sources, a sample signal for executing automatic power control (APC) based on the light emission amount of the light emitting source turned on in response to the LD lighting signal, and Image processing means for outputting a channel switching signal for controlling switching between the channels of the plurality of light emitting sources based on the detection signal in order to select a channel to be subjected to automatic power control.
Wherein provided in each channel, when selected by the channel switching signal, the LD controller that have a driving means for driving the plurality of light emitting sources on the basis of the LD lighting signal and the sample signal,
In the image processing means, the transmission time of the sample signal in each channel is shorter than the transmission time of the channel switching signal whose transmission time is shorter than that of the LD lighting signal , and is included in the lighting period of those signals. In addition, the sample signal and the channel switching signal are transmitted so as not to overlap in the simultaneous transmission period after a predetermined time from the simultaneous transmission period in which at least two LD lighting signals of each channel are simultaneously output. An LD control device.

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