JP2006321234A - Ld control device and method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide LD control device and method which prevent an LD light emission amount from being set to a value different from a set value, and prevent LD deterioration even when timing of sampling signals is shifted. <P>SOLUTION: When a lighting signal and a sampling signal are to be generated and output based on a synchronization detection signal input from a light receiving element, an image processing unit 12 performs control so that the sending time of the sampling signal is shorter than either one of the sending time of the LD lighting signal or the sending time of a channel switching signal, and the sending period of the sampling signal is included in the sending period of each of the sampling signal and the channel switching signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an LD control device for controlling the amount of laser light emitted from a laser diode and a method for controlling the amount of laser light, and in particular, an LD for writing an image with a light beam in a digital copying machine, a laser beam printer, a facsimile, or the like. The present invention relates to a control device and an LD control method.

  A laser diode (LD) that is used in digital copying machines, laser printers, facsimile machines, and the like that are currently on the market and emits a light beam for writing 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. FIG. 12 shows an example of the configuration of a conventional light source control circuit that controls the light emission amount of the LD.

  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 power 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.

  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.

  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.

  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.

  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.

  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.

  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.

  The present invention has been made in view of the above problems, and in a multi-beam laser printer in which image writing is performed simultaneously with a plurality of laser beams, the timing of sample signals is shifted and all LDs are turned off. Sampling to prevent the LD emission amount from being set larger than the set value or sampling during the period when a plurality of LDs are lit to prevent the LD emission amount from being set to a small value, so that the correct LD emission amount can be controlled. Another object of the present invention is to provide an LD control apparatus and method capable of preventing LD degradation.

  In order to achieve this object, the present invention, as a first aspect, detects the end of an image writing period, which is a period during which a laser beam irradiated from a plurality of light emitting sources scans a photosensitive member in the main scanning direction. Detection means for outputting a detection signal, an LD lighting signal (LDON signal) as an image data signal for lighting a plurality of light emission sources, and automatic power control based on the light emission amount of the light emission source turned on by the LD lighting signal A sample signal (S / H signal) for executing (APC) and a channel switching signal (SW signal) for controlling switching between channels of a plurality of light emitting sources in order to select a channel to be subjected to automatic power control. An image processing means for outputting based on the detection signal and an LD lighting signal, a channel switching signal provided for each channel. And an LD control device having driving means for driving a plurality of light emission sources based on the sample signal, wherein the image processing means sends the sample signal sending time at the timing of executing APC and the LD lighting signal sending time and Provided is an LD control device characterized in that it is shorter than any of the channel switching signal transmission times and is controlled so that the sample signal transmission period is included in each of the sample signal and channel switching signal transmission periods. It is.

  In the first aspect of the present invention, the image processing means is such that the transmission time of the channel switching signal is shorter than the transmission time of the LD lighting signal, and the transmission period of the channel switching signal is included in the transmission period of the LD lighting signal. It is preferable to control.

  In any of the above-described configurations of the first aspect of the present invention, the image processing means does not send the LD lighting signal sent to each channel, and the channel switching signal and the sample signal of those channels are not sent. During the period, it is preferable to control so that they are output at the same time partially overlapping in time. In addition, the image processing means includes a sample signal transmission time shorter than an LD lighting signal transmission time, a sample signal transmission period included in the LD lighting signal transmission period, and at least two of each channel. The sample signal is transmitted so as not to overlap with a predetermined time interval from the period in which the LD lighting signal is output at the same time, or the image processing means sends the sample signal shorter than the channel switching signal. The sample signal transmission period is included in the channel switching signal transmission period, and the sample signals are transmitted so as not to overlap each other at a predetermined time interval from the period in which at least two LD lighting signals of each channel are simultaneously output. More preferably.

  In order to achieve the above object, as a second aspect, the present invention detects the end of an image writing period, which is a period during which a laser beam irradiated from a plurality of light emitting sources scans the photosensitive member in the main scanning direction. Detecting means for outputting a detection signal, an LD lighting signal (LDON signal) as an image data signal for lighting a plurality of light emitting sources, and automatic power based on the light emission amount of the light emitting source turned on by the LD lighting signal Sample signal (S / H signal) for executing control (APC), and channel switching signal (SW signal) for controlling switching between channels of a plurality of light emitting sources in order to select a channel to be subjected to automatic power control. Image processing means for outputting the signal based on the detection signal, and for each channel, LD lighting signal, channel switching And an LD control method using an LD control device having a driving means for driving a plurality of light emission sources based on the sample signal, wherein the image processing means sends the sample signal at a timing for executing APC. It is shorter than both the transmission time of the LD lighting signal and the transmission time of the channel switching signal, and is controlled so that the transmission period of the sample signal is included in each of the transmission periods of the sample signal and the channel switching signal. An LD control method is provided.

  In the second aspect of the present invention, the image processing means is such that the transmission time of the channel switching signal is shorter than the transmission time of the LD lighting signal, and the transmission period of the channel switching signal is included in the transmission period of the LD lighting signal. It is preferable to control.

  In any of the above-described configurations of the second aspect of the present invention, the image processing means transmits the LD lighting signal transmitted to each channel, and the channel switching signal and sample signal of each channel are transmitted. It is preferable to perform control so that the signals are output at the same time during a period that does not overlap during some period. In addition, the image processing means includes a sample signal transmission time shorter than an LD lighting signal transmission time, a sample signal transmission period included in the LD lighting signal transmission period, and at least two of each channel. Transmitting the sample signal so as not to overlap with a predetermined time interval from the period in which the LD lighting signal is simultaneously output, or the image processing means sends the sample signal shorter than the channel switching signal. The sample signal transmission period is included in the channel switching signal transmission period, and the sample signals are transmitted so as not to overlap each other at a predetermined time interval from the period in which at least two LD lighting signals of each channel are simultaneously output. More preferably.

  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.

  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, so the APC circuit determines that the LD is not lit and the LD emission amount is lower 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.

  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, it is possible to prevent the LD light emission amount from being set larger than the set value even when the timing of the sample signal is slightly shifted. In addition, it is possible to prevent LD degradation due to over-emission.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  First, a first embodiment of the present invention will be described in detail with reference to FIGS. 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, the laser beam emitted from the laser diode (LD) inside the laser diode unit (LDU) 21 becomes parallel rays by the collimating lens inside the LDU 21, and is deflected and scanned by the rotating polygon mirror (hereinafter referred to as 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.

  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.

  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.

  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.

  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.

  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.

  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.

  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.

  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 writing is repeated.

  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 transmission period of the LD lighting signal, and FIG. 5 shows a time chart of the sample signal and LD lighting signal output from this circuit.

  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.

  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.

  Next, a second embodiment of the present invention will be described in detail with reference to FIGS. 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.

  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.

  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.

  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.

  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.

  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.

  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.

  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.

  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.

  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.

  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.

  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.

  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.

  In the third embodiment, as a method of generating a plurality of laser beams, a plurality of light sources that can be individually controlled on one chip are arranged in an array rather than 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.

  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 where only one built-in PD 101 is used as described above will be described, particularly 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.

  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 configured 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.

  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 of 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.

  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. Further, it can be seen from FIG. 8 that the lighting times of the LDs 1 and 2 overlap.

FIG. 2 is a block diagram of a write control system circuit in the first embodiment of the present invention. 1 is a diagram illustrating a configuration example of an optical system of a laser beam printer as an image forming apparatus. It is a circuit block diagram showing an example of composition of an APC circuit in an embodiment of the present invention. It is a time chart to LD lighting signal and S / H signal at the time of performing APC operation in a 1st embodiment of the present invention. It is the circuit block diagram for producing | generating the LD lighting signal and S / H signal in the 1st Embodiment of this invention, and its time chart. It is a conceptual diagram of the synthetic | combination method of the laser beam in the 2nd Embodiment of this invention. It is the block diagram which showed the circuit structural example of the write-control part in the 2nd Embodiment of this invention. It is a time chart of the LD lighting signal in the 2nd Embodiment of this invention, S / H signal, and a monitor current switching signal. It is a circuit block diagram for producing | generating the LD lighting signal, S / H signal, and monitor current switching signal in the 2nd Embodiment of this invention. It is a conceptual diagram which shows the generation method of the laser beam when using the LDA chip | tip in the 3rd Embodiment of this invention. It is the block diagram which showed the circuit structure of the write-control part in the 3rd Embodiment of this invention. It is the block diagram which showed an example of the conventional LD control circuit. It is a time chart for demonstrating the conventional APC control operation. It is the time chart which showed the normal state and abnormal state of the 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 Generation Circuit 35 Switch Circuit 36 I / V Conversion Circuit 61 Beam Synthesis Prism 62 Collimator Lens 102 LDA Chip

Claims (10)

Detection means for detecting the end of an image writing period, which is a period during which the laser beams emitted from a plurality of light emitting sources scan the photosensitive member in the main scanning direction, and outputting a detection signal;
An LD lighting signal (LDON signal) as an image data signal for lighting the plurality of light emitting sources, and a sample signal for executing automatic power control (APC) based on the light emission amount of the light emitting source turned on by the LD lighting signal (S / H signal), and a channel switching signal (SW signal) for controlling switching between the channels of the plurality of light emitting sources in order to select a channel to be subjected to automatic power control based on the detection signal Image processing means,
An LD control device provided for each of the channels, and having a driving means for driving the plurality of light emission sources based on the LD lighting signal, the channel switching signal, and the sample signal,
In the image processing means, the transmission time of the sample signal at the timing of executing APC is shorter than both the transmission time of the LD lighting signal and the transmission time of the channel switching signal, and the transmission period of the sample signal is An LD control device that performs control so as to be included in a transmission period of each of a sample signal and the channel switching signal.   The image processing means performs control so that a transmission time of the channel switching signal is shorter than a transmission time of the LD lighting signal, and a transmission period of the channel switching signal is included in the transmission period of the LD lighting signal. The LD control device according to claim 1, wherein   In the image processing means, the LD lighting signal transmitted to each of the channels is partly temporally during a period in which the channel switching signal and the sample signal of those channels are not transmitted. The LD control device according to claim 1 or 2, wherein the control is performed so that the signals are output simultaneously.   The image processing means includes a transmission time of the sample signal shorter than a transmission time of the LD lighting signal, a transmission period of the sample signal included in the transmission period of the LD lighting signal, and at least two of each channel. 4. The LD control device according to claim 3, wherein the sample signals are transmitted so as not to overlap each other at a predetermined time interval from a period in which two LD lighting signals are simultaneously output.   The image processing means has a transmission time of the sample signal shorter than a transmission time of the channel switching signal, a transmission period of the sample signal is included in the transmission period of the channel switching signal, and at least two of each channel. 4. The LD control device according to claim 3, wherein the sample signals are transmitted so as not to overlap each other at a predetermined time interval from a period in which two LD lighting signals are simultaneously output. Detection means for detecting the end of an image writing period, which is a period during which the laser beams emitted from a plurality of light emitting sources scan the photosensitive member in the main scanning direction, and outputting a detection signal;
An LD lighting signal (LDON signal) as an image data signal for lighting the plurality of light emitting sources, and a sample signal for executing automatic power control (APC) based on the light emission amount of the light emitting source turned on by the LD lighting signal (S / H signal), and a channel switching signal (SW signal) for controlling switching between the channels of the plurality of light emitting sources in order to select a channel to be subjected to automatic power control based on the detection signal Image processing means,
An LD control method using an LD control device provided for each of the channels and having a drive means for driving the plurality of light emission sources based on the LD lighting signal, the channel switching signal, and the sample signal. ,
In the image processing means, the transmission time of the sample signal at the timing of executing APC is shorter than both the transmission time of the LD lighting signal and the transmission time of the channel switching signal, and the transmission period of the sample signal is An LD control method, wherein control is performed so as to be included in a transmission period of each of a sample signal and the channel switching signal.   The image processing means performs control so that a transmission time of the channel switching signal is shorter than a transmission time of the LD lighting signal, and a transmission period of the channel switching signal is included in the transmission period of the LD lighting signal. The LD control method according to claim 6, wherein:   In the image processing means, the LD lighting signal transmitted to each of the channels is partly temporally during a period in which the channel switching signal and the sample signal of those channels are not transmitted. 8. The LD control method according to claim 6, wherein control is performed so that the signals are output simultaneously when they overlap.   The image processing means includes a transmission time of the sample signal shorter than a transmission time of the LD lighting signal, a transmission period of the sample signal included in the transmission period of the LD lighting signal, and at least two of each channel. 9. The LD control method according to claim 8, wherein the sample signals are transmitted so as not to overlap each other at a predetermined time interval from a period in which two LD lighting signals are simultaneously output.   The image processing means has a transmission time of the sample signal shorter than a transmission time of the channel switching signal, a transmission period of the sample signal is included in the transmission period of the channel switching signal, and at least two of each channel. 9. The LD control method according to claim 8, wherein the sample signals are transmitted so as not to overlap each other at a predetermined time interval from a period in which two LD lighting signals are simultaneously output.

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