JP2798410B2 - Method for controlling emission intensity of semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention detects a light emission intensity of a semiconductor laser element that scans a photoconductor and exposes recording image light before starting recording of each page, and detects the light emission intensity. The present invention relates to a method for controlling the light emission intensity of a semiconductor laser device that controls and holds a value to be a constant value.

[Related Art] In recent years, an image forming apparatus using an electrophotographic technique has been used in, for example, a plain paper facsimile apparatus, a digital copying machine, or a printer. A semiconductor laser device such as a laser diode is used as a generating means.

In this image forming apparatus, in order to record a recorded image at a constant density, it is necessary to control the light emission intensity of the semiconductor laser element to a specified value, and this control is usually performed immediately before starting recording of each page. This is carried out, and is held during the image recording of one page.

The emission intensity control of this semiconductor laser device is performed by a control device using a microcomputer system, and is conventionally disclosed in JP-A-62-140482 or JP-A-62-116570. Are disclosed.

The former compares the output of the light-receiving element for output monitoring built into the laser diode with a reference voltage, and sets the drive current of the laser diode if the monitor output is smaller than the reference voltage. The value is incremented from the minimum value, and the drive current value is fixed when the monitor output exceeds the reference voltage.

In the latter case, the monitor output is compared with the reference value, and if the monitor output is small, the digital input value of the D / A converter is incremented. Is what you do.

[Problems to be Solved by the Invention] However, in the former case, the following two problems have occurred.

If the digital circuit malfunctions due to noise or the like, for example, the value of the MSD (most significant digit) bit of the counter becomes 0 to 1
, The laser light output may be set to an excessive value.

Since the laser light output takes a discrete value, if the digital input value is fixed when the monitor output exceeds the reference value, the error with respect to the reference value is not always minimum and the control accuracy is poor.

The latter can solve the former problem described above, but cannot solve the problem. Also, in this case, the maximum value of the time predicted to be required until the laser beam output reaches the target value needs to be set as the control setting time, and the time required for the control becomes longer.

The present invention has been made in order to solve the problems of the related art, and provides a method for controlling the emission intensity of a semiconductor laser device that can accurately control the output intensity of the semiconductor laser device to a specified value in a short time. It is intended to be. Further, when the light emission intensity is controlled on a page basis, fluctuations in the light emission intensity during the optical writing period cannot be eliminated, so that the recorded image may be uneven, but such disadvantages are also eliminated.

[Means for Solving the Problems] The present invention detects a light emission intensity of a semiconductor laser element that scans a photoconductor and exposes recording image light before starting recording of each page, and the detected value is set to a constant value. In the method for controlling the light emission intensity of a semiconductor laser device, the command value of the light emission intensity is changed one step at a time, and the deviation between the detected value and the light emission intensity set value is calculated and held. When the relationship between the value and the emission intensity set value changes, the command value changes in a direction that reverses the relationship, and when this relationship is repeated a certain number of times, immediately before the detected value is greater than the emission intensity set value Is compared with the deviation when the detected value is smaller than the emission intensity setting value, and the command value is set to have a smaller deviation.

[Operation] Therefore, since the command value is controlled to a value having a smaller deviation, the accuracy of the emission intensity control of the semiconductor laser device is improved.

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

FIG. 1 shows a laser diode drive control device according to one embodiment of the present invention. This laser diode drive control device controls, for example, the emission intensity of a laser diode of a laser printer.

In FIG. 1, a control unit 1 performs a control operation of the laser diode drive control device, exchanges various control information with a main control device (not shown) of a laser printer, and emits light of a laser diode 2. Is output to the digital / analog converter 3.

The digital / analog converter 3 converts the input set value CI into a corresponding intensity setting signal AI. The intensity setting signal AI is applied to a current control unit 4 that supplies a driving current ID to the laser diode 2. ing.

The current control unit 4 controls the drive current ID supplied to the laser diode 2 to a current value corresponding to the intensity setting signal AI.

The photodiode 5 is housed in the same envelope as the laser diode 2 and receives a part of the laser light output from the laser diode 2, and the output signal
PM is applied to the analog / digital converter 6.

The analog / digital converter 6 converts the input signal PM into a corresponding digital signal. This digital signal is output from the output intensity monitor signal DF of the laser diode 2.
Is added to the control unit 1.

The switching transistor 7 connected in parallel to the laser diode 2 is turned on / off by the recording data DT transferred from the main control device, and modulates the output laser light from the laser diode 2 with the recording data DT. Things.

The number of bits of the analog / digital converter 6 is set to be larger than the number of bits of the digital / analog converter 3 so that the output intensity of the laser diode 2 can be monitored in finer steps. .

FIG. 2 shows an example of processing executed by the control unit 1 before the start of recording of each page in order to control the light emission intensity of the laser diode 2 to a specified value.

When a laser intensity control command is input from the main control device, the control unit 1 first initializes the value of the counter CCI to “0” (process 101), and sets the value of the counter CCI to digital / analog as the set value CI. Output to the converter 2 (process 102),
Thus, the output level of the laser diode 2 is initialized to “0”.

Next, the control system performs the wait time until the settling to the state of the setting values CI (process 103), the end it, for storing the magnitude relationship between the output intensity monitor signal DF and the specified value V _R Flag FCH, output intensity monitor signal DF and specified value V
Counter CCH for storing the number of changes in magnitude relationship with _R
Initialize the value to "0" setting (processing 104), the output intensity monitor signal DF is variable ERp for storing the deviation of the time was greater than the predetermined value V _R, and the output intensity monitor signal DF is defined value V _R is initially set to the maximum value MAX that can take a variable ERm for storing the deviation of the time smaller respectively than (process 105).

Then, input the output monitor signal DF and set the value to the specified value.
Determine if it is greater than V _R (decision 106).

If the result of the determination 106 is NO, the counter CCI is incremented and its value is increased by one step (processing 107), and the variable E
Assigns a value obtained by subtracting the value of the output monitor signal DF from the specified value V _R to rm (processing 108).

Then, the flag FCH is checked whether it is 1 (decision 109). If the result of step 109 is YES, because if the output monitor signal DF is changed to a small state from a large state than the specified V _R, the counter When CCH is incremented (process 110) and the result of decision 109 becomes NO,
Since there is no state change, this process 110 is skipped,
The value of the flag FCH is set to “0” (process 111).

When the result of the determination 106 is YES, the counter
Decrement CCI and reduce its value by one step (Process 1
12), it assigns a value obtained by subtracting the prescribed value V _R from the value of the output monitor signal DF variable ERm (process 113).

Then, it is checked whether the flag FCH is set to 0 (decision 114). If the result of step 114 is YES, because if the output monitor signal DF is changed to a large shifts from being smaller than the prescribed V _R, the counter When CCH is incremented (process 115) and the result of determination 114 is NO,
Since there is no state change, this process 115 is skipped,
The value of the flag FCH is set to "1" (process 116).

When the processing 111 and the processing 116 are completed, it is checked whether or not the counter CCH is equal to or more than a specified number Nc (determination 11).
7) If the result of decision 117 is NO, the counter CCI
Is output to the digital / analog converter 3 as the set value CI (process 118), and after performing a time waiting process 119, the process returns to the determination 106.

If the result of the determination 117 is YES, the specified number of times Nc
Only, since if the output intensity of the laser diode 2 changes vertically across the prescribed value V _R, to set the output intensity of the laser diode 2, the variable ERp determine whether is greater than the variable ERm ( Judgment 120).

When the result of the determination 120 is YES, the flag FCH is set to “0”.
A check is made to determine whether or not it is (decision 121). When the result of the determination 121 is NO, the value of the variable ERm is smaller than the variable ERp, and the error of the previous command value CI is smaller than the command value CI currently set in the digital / analog converter 3. In this case, the value of the counter CCI is output as the command value CI to the digital / analog converter 3 (process 122), and thereafter, the command value CI is held (process 123).

When the result of the determination 121 is YES, the command value CI currently set in the digital / analog converter 3 is an appropriate value, and thus the process 122 is skipped and the process proceeds to the process 123.

On the other hand, when the result of the determination 120 is NO, the flag FCH
It is checked whether or not is "1" (decision 124).
When the result of the determination 124 is NO, the process proceeds to a process 122, and when the result of the determination 124 is YES, the process proceeds to a process 123.

Thus, the control unit 1 controls the output intensity of the laser diode 2 to the specified value LR.

That is, as shown in FIG. 3, the control unit 1 sets the command value CI to “0” at the time point t ₀ of the control start, initializes the output intensity of the laser diode 2 to “0”, and thereafter, The command value CI is increased one step at a time.

When the output intensity at time t ₁ is greater than a specified value LR, lower the command value CI 1 step smaller than the prescribed value LR, then the specified number of times the operation to be larger than the prescribed value LR raised one step Repeat.

In this way, when the operation ends to reverse the magnitude relationship between the specified value LR of a command value CI only specified number, at its exit point in time t _2, as shown in FIG. 4, than the specified value LR output intensity The command value CI is set so as to take a state in which the deviation ERp when the value is increased and the deviation EPm when the output intensity is smaller than the specified value LR are smaller.

Accordingly, first, since the output intensity is changed up and down in the vicinity of the specified value LR, even if the output of the digital / analog converter 3 becomes abnormal due to the incorporation of noise or the like, the output intensity is changed. This prevents the value from defining the output intensity.

Further, based on the magnitude relationship between the deviations ERp and ERm, the command value CI
Is set, the output intensity of the laser diode 2 can be adjusted to a value with a smaller error.

In addition, since the end of the control is defined by the state of the control system at that time, the time required for the output control processing of the laser diode 2 is prevented from being unnecessarily long.

By the way, for example, when the recording of the second page starts,
Since it is considered that the output intensity of the laser diode 2 has not significantly changed from the state set at the time of starting the recording of the first page, the second processing 104 can be started on the second and subsequent pages.

In the case where the processing of FIG.
3,110 time waiting processing can be omitted.

In the above-described embodiment, since the light emission intensity of the laser diode 2 is controlled on a page basis, it is not possible to cope with a change in the light emission intensity of the laser diode 2 within the same page. Such a change is very small, but becomes remarkable particularly when the ambient temperature of the laser diode 2 largely changes (rises).

Next, another embodiment of the present invention which can solve such a disadvantage will be described.

First, an optical system such as a laser beam printer will be described.

As shown in FIG. 5, the laser beam LB output from the laser diode 2 and modulated by the recording data DT is reflected by a polygon mirror 11 which is driven to rotate by a motor 10 and passes through a belt-shaped photoconductor 12. The exposure is performed by scanning in the main scanning direction RS.

Immediately before the laser beam LB scans the photoconductor 12, the laser beam LB is moved to a position where the laser beam LB can be detected.
A line synchronization detection circuit 13 that generates a line synchronization signal LS when receiving LB is provided.

Therefore, as shown in FIG. 6A, in the drive period TA in which one line of recording image light is generated by the laser diode 2, first, in the first period T1, the laser beam LB is supplied to the line synchronization detection circuit 13. Lights continuously to detect,
In the next period T2, the laser beam LB is
Laser diode 2 because it is moving from photoconductor 12 to photoconductor 12
Is stopped, and the recording image light is generated in a subsequent period T3. Thereafter, the light emission is stopped in a period T4 until the start of the next cycle.

Thus, during the period T1, during the period when the laser beam LB crosses the light receiving portion of the line synchronization detection circuit 13, the line synchronization signal LS is generated from the line synchronization detection circuit 13 as shown in FIG.

The line synchronization detection circuit 13 is conventionally used to synchronize the rotation of the motor 10 and the transfer timing of the recording data DT.

Therefore, in this embodiment, the emission intensity of the laser diode is controlled prior to page recording in the same manner as in the above-described embodiment, and the line synchronization signal LS is used during page recording.
The light emission intensity of the laser diode 2 is controlled in synchronization with the occurrence timing of the laser light, thereby realizing the light emission intensity control for each line.

FIG. 7 shows an example of such an embodiment. In addition,
In the figure, the same parts as those in FIG. 1 and corresponding parts are denoted by the same reference numerals.

In the figure, a line synchronization signal LS output from a line synchronization detection circuit 13 is applied to a control unit 1 and
The data is output to an external device (not shown) such as a main control device for generating the recording data DT and a motor control means for controlling the rotation of the motor 10.

In this embodiment, the control unit 1 executes the processing of FIG. 2 before the recording of each page is started, and when the page recording is started, each time the line synchronization signal LS is input, the control unit 1 shown in FIG. Execute the process.

That is, when the line synchronizing signal LS is input, it is determined whether or not the optical writing mode in which the recording image light modulated by the recording data DT is written to the photoconductor 12 at this time (decision 201). , The value of the counter CCI (see FIG. 2) is output as the set value CI (process 202).

Then, enter the output monitor signal DF at that time, compares the specified value V _R and the output monitor signal DF (decision 203), when the value of the output monitor signal DF is smaller than the set value V _R is the counter CCI Increment and increase one value (Process 2
04), when greater than the specified value V _R decrements the counter CCI reduce one value (processing 205), the processing ends.

Further, when the value of the output monitor signal DF is equal to the specified value V _R is kept essentially stationary holding a value of the counter CCI, the processing ends.

Thus, the next time the line synchronization signal LS is generated, the value of the counter CCI set at this time is output as the set value CI, consequently, the value of the output monitor signal DF matches the specified value V _R As a result, the emission intensity control of the laser diode 2 is executed for each line.

Thus, the emission intensity of the laser diode 2 when recording an image of one page is kept constant, so that it is possible to prevent a problem such as a density change from occurring in the recorded image.

In this embodiment, the output monitor signal DF and the specified value V _R
Are simply compared, and the value of the counter CCI is adjusted based on the comparison result. However, the emission intensity of the laser diode 2 can be controlled by other methods.

In recent years, a microcomputer device has been used as the control unit 1 described above, and a one-chip microcomputer device having a built-in analog / digital converter 6 has been put into practical use. If the control unit 1 and the analog / digital converter 6 are realized by such a one-chip microcomputer device, the device cost can be reduced.

However, since the set value CI output from the control unit 1 is a digital signal, a digital / analog converter 3 for converting the digital signal into an analog signal that can be input to the current control unit 4 is required, thereby reducing the apparatus cost. Was an obstacle to doing so.

FIG. 9 shows still another embodiment of the present invention which can solve such a disadvantage. In the figure, the same parts as those in FIG. 1 and corresponding parts are denoted by the same reference numerals.

In the figure, a microcomputer device 20 has an analog / digital converter 6 as an input means, and controls a current output from a three-state input / output port of a data processing unit 21 for implementing various control processes. The signal IC is added to the integration circuit 22.

The integration circuit 22 integrates the input current control signal IC to calculate a current command signal IM, and includes an operational amplifier OP
1. It is composed of an input resistor R1, voltage dividing resistors R2 and R3, and a feedback capacitor C1. Its output signal is
It is output to the constant current circuit 23.

The constant current circuit 23 outputs a drive current ID corresponding to the current command signal IM output from the integration circuit 22 to the laser diode 2.
The operational amplifier OP2, the voltage dividing resistors R4 and R
5. It is composed of a feedback resistor R6 and an output transistor Tr.

The current / voltage conversion circuit 24 converts the output signal PM from the photodiode 5 into a corresponding voltage signal, and includes an operational amplifier OP3, resistors R7, R8, and a feedback resistor R9. The output signal of the current / voltage conversion circuit 24 is input to the analog / digital converter 6 of the microcomputer device 20.

When the data processing unit 21 of the microcomputer device 20 sets the input / output port to the output mode, the level of the input / output port rises to the logic H level, and the current control signal IC rises to the logic H level.

Therefore, the value of the current command signal IM output from the integration circuit 22 decreases linearly with the time constant of the integration circuit 22 in order for the integration circuit 22 to integrate the current control signal IC at the logic H level. I do.

In this manner, when the value of the current command signal IM decreases, the base voltage of the transistor Tr of the constant current circuit 23 decreases, so that the collector current of the transistor Tr increases,
The drive current ID increases.

In this state, when the data processing unit 21 sets the input / output port to high impedance, the current control signal IC is stopped, thereby the current output signal IM of the integration circuit 22 is stopped.
Is retained at that time.

When the data processing unit 21 sets the input / output port to the input mode, the level of the input / output port falls to the logic L level, and the current control signal IC falls to the logic L level.

Therefore, the value of the current command signal IM output from the integration circuit 22 increases linearly with the time constant of the integration circuit 22 so that the integration circuit 22 integrates the current control signal IC at the logic L level. I do.

In this manner, when the value of the current command signal IM increases, the base voltage of the transistor Tr of the constant current circuit 23 increases, so that the collector current of the transistor Tr decreases,
The drive current ID decreases.

In this state, when the data processing unit 21 sets the input / output port to high impedance, the current control signal IC is stopped, thereby the current output signal IM of the integration circuit 22 is stopped.
Is retained at that time.

In this manner, when the data processing unit 21 raises the current control signal IC to the logic H level, the drive current ID increases, and when the current control signal IC falls to the logic L level, the drive current ID changes.
When the ID decreases and the data processing unit 21 sets the input / output port outputting the current control signal IC to the high impedance state, the value of the drive current ID is held at that time.

FIG. 10 shows a processing example executed by the data processing unit 21 before the start of recording of each page in order to control the emission intensity of the laser diode 2 to a specified value. Note that in FIG.
The same reference numerals are used for the same elements as in the figure.

When the laser intensity control command is input from the main control device, the data processing unit 21 first raises the input / output port outputting the current control signal IC to a logic H level for a predetermined time TW (step 301). Then, after increasing the drive current ID supplied to the laser diode 2, the input / output port is set to high impedance to hold the drive current ID at the value at that time (process 302).

Next, the control system waits for a predetermined time TC longer than the time required to settle to the state corresponding to the value of the drive current ID (process 303).
Flag FCH for storing the magnitude relationship between the F a specified value V _R,
And the value of the counter CCH for storing the number of changes in the magnitude relationship between the output intensity monitor signal DF and the specified value V _R "0"
(Step 304).

Then, input the output monitor signal DF and set the value to the specified value.
Determine if it is greater than V _R (decision 305).

If the result of the determination 305 is NO, since the light emission level of the laser diode 2 is smaller than the specified value, the input / output port is raised to the logic H level for a certain time TW, and the logic H level current control signal IC is kept constant. The drive current ID is increased by outputting the time TW (process 306), and then the input / output port is set to the high impedance state to hold the value of the drive current ID (process 307).

Then, the flag FCH is checked whether it is 1 (decision 308). If the result of step 308 is YES, because if the output monitor signal DF is changed to a small state from a large state than the specified V _R, the counter When CCH is incremented (process 309) and the result of decision 308 is NO,
Since there is no state change, this processing 309 is skipped,
The value of the flag FCH is set to “0” (process 310).

If the result of determination 305 is YES, since the light emission level of the laser diode 2 is higher than the specified value, the input / output port is lowered to the logic L level for the predetermined time TW, and the current control signal of the logic L level is set. The IC outputs TW for a certain period of time to reduce the drive current ID (process 311), and then sets the input / output port to a high impedance state to hold the value of the drive current ID (process 312).

Then, it is checked whether the flag FCH is set to 0 (decision 313). If the result of step 313 is YES, because if the output monitor signal DF is changed to a large shifts from being smaller than the prescribed V _R, the counter When CCH is incremented (process 314) and the result of the determination 313 is NO,
Since there is no state change, this process 314 is skipped,
The value of the flag FCH is set to “1” (process 315).

When the processing 310 and the processing 315 are completed, it is checked whether or not the counter CCH is equal to or more than a specified number Nc (determination 31).
6) After performing the process 317 of waiting for a certain time TC, the process returns to the determination 305.

If the result of the determination 117 is YES, the specified number of times Nc
Only, since if the output intensity of the laser diode 2 changes vertically across the prescribed value V _R, in order to keep the output intensity of the laser diode 2 in this state, the process ends.

Thus, the data processing unit 21 controls the output intensity of the laser diode 2 to the specified value LR.

That is, as shown in FIG. 11, the data processing unit 21
When the output intensity of the laser diode 2 is smaller than the specified value LR, the current control signal IC is set to the TW logic H level for a certain time, and the magnitude of the drive current ID is increased by one step.

Then, the current control signal IC is set to a non-operation state for a certain time TC, and the control system waits until the control system is settled.
The process is repeated at a constant cycle until the output intensity of the laser diode 2 exceeds the specified value LR, and the drive current ID is increased one step at a time interval.

When the output intensity exceeds the specified value LR, the current control signal IC is set to the logic L level for the fixed time TW, the magnitude of the drive current ID is reduced by one step, and the drive current ID is held in that state. .

Then, the drive current ID is increased by one step to make the output intensity of the laser diode 2 larger than the specified value LR.
The operation of lowering the drive current ID by one step and making the output intensity of the laser diode 2 smaller than the specified value LR is repeated a specified number of times.

In this way, when the operation of reversing the magnitude relationship between the specified value LR and the output intensity by the specified number of times is completed, the input / output port outputting the current control signal IC is set to the high impedance state at the time of the completion. , The value of the drive current ID is held at the value at that time.

Thereby, the output intensity of the laser diode 2 can be reliably set to the specified value LR.

In the above-described embodiment, the output intensity of the laser diode 2 is checked at regular time intervals TC, and the value of the current control signal IC is logically determined for the constant time TW based on the magnitude relationship between the output intensity and the specified value LR. The drive current ID is raised or lowered by one step by setting the drive current ID to the H level or the logic L level. However, the drive current ID can be controlled in the following manner.

That is, the output intensity of the laser diode 2 and the specified value LR
If the deviation is large, the time for setting the value of the current control signal IC to the logic H level or the logic L level is extended, and if the deviation is small, the value of the current control signal IC is changed. The time for setting the logic H level or the logic L level is shortened.

At this time, after the time for setting the value of the current control signal IC to the logical H level or the logical L level ends and the time until the control system stabilizes, the next control is started. Sampling of the output intensity of the laser diode 2 is performed.

By doing so, the drive current ID can be controlled steplessly, so that the accuracy of controlling the output intensity of the laser diode 2 can be further improved.

Also, the rate of change when increasing the drive current ID and the rate of change when decreasing the drive current ID can be set to appropriate values.

For example, when a CMOS-type device is used as the microcomputer device 20, the logic H level of the input / output port substantially matches the power supply voltage Vcc, and the logic L level substantially matches the ground level.

Therefore, when the resistance values of the voltage dividing resistor R2 and the voltage dividing resistor R3 of the integrating circuit 22 are set to the same value, the potential of the non-inverting input terminal and the inverting input terminal of the operational amplifier OP1 becomes Vcc / 2, and therefore, the input / output port Is set to the output mode and the output mode, the value of the current control signal IC flowing is + (Vcc / 2R1) and − (Vcc / 2R1), respectively.
The rate of change when the drive current ID increases is equal to the rate of change when the drive current ID decreases.

Further, when the resistance value of the voltage dividing resistor R2 is set smaller than the resistance value of the voltage dividing resistor R3, the rate of change when the drive current ID increases is smaller than the rate of change when the drive current ID decreases.

Thus, in this embodiment, the laser diode 2
Can be very flexibly controlled.

In addition, the number of signal lines between the microcomputer device 20 and the integrating circuit 22 is greatly reduced as compared with the case where current control is performed using a digital / analog converter, and the output port required for the microcomputer device 20 is reduced. Can also be reduced, so that the apparatus cost can be significantly reduced.

FIG. 12 shows still another embodiment of the present invention. In this figure, the same parts as those in FIG. 9 and corresponding parts are denoted by the same reference numerals.

In the figure, the output signal of the current / voltage conversion circuit 24 is
A comparison circuit 25 for comparing the output intensity of the laser diode 2 with a prescribed value LR is added to a comparison signal CP.
Is applied to the 1-bit data input terminal.

Here, the comparison circuit 25 includes an operational amplifier OP4 and voltage dividing resistors R10 and R1 for generating a reference voltage REF corresponding to the specified value LR.
1 and a feedback resistor R12. When the monitor signal PM (voltage value) output from the current / voltage converter 24 is larger than the reference voltage REF, the comparison signal CP is set to logic L.
Level, and when the monitor signal PM (voltage value) is smaller than the reference voltage REF, the comparison signal CP is set to the logic H level.

Therefore, in this case, the microcomputer device 30
Performs the same processing as in FIG. 10 to control the drive current ID of the laser diode 2.

Thus, in this embodiment, the laser diode 2
Drive current ID based on the magnitude relationship between the output intensity of
Since the microcomputer 30 is controlled, the microcomputer device 30 does not require an analog / digital converter as an input means, so that the device cost can be further reduced.

[Effects of the Invention] As described above, according to the present invention, before starting recording of each page, the light emission intensity of the semiconductor laser element that scans the photosensitive member and exposes the recording image light is detected, and the detected value is obtained. In the method for controlling the emission intensity of a semiconductor laser device, the emission intensity command value is changed one step at a time, and the deviation between the detected value and the emission intensity set value is calculated and held. When the relationship between the detected value and the emission intensity setting value changes, the command value changes in a direction that reverses the relationship, and when this relationship is reversed a certain number of times, the detected value immediately exceeds the emission intensity setting value. The deviation when it was large and the deviation when the detection value was smaller than the emission intensity setting value were compared, and the command value was set to a relationship having a smaller deviation. Command value Is controlled, and as a result, the effect of improving the accuracy of the emission intensity control of the semiconductor laser device is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a laser diode drive control device according to one embodiment of the present invention, FIG. 2 is a flowchart showing an example of processing executed by a control unit, and FIG. FIG. 4 is a schematic diagram for explaining the deviation, FIG. 5 is a schematic configuration diagram illustrating an optical system of the laser beam printer, and FIG. 6 is a writing period of a laser diode and generation of a line synchronization signal. FIG. 7 is a block diagram showing a laser diode drive control device according to another embodiment of the present invention, FIG. 8 is a flowchart showing an example of processing performed when a line synchronization signal is generated, and FIG. FIG. 10 is a circuit diagram showing still another embodiment of the invention, FIG. 10 is a flowchart showing a processing example of a data processing unit, and FIG. 11 is a diagram showing a mode of laser diode output intensity control by the apparatus of FIG. FIG. 12 is a circuit diagram showing still another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... Control part, 2 ... Laser diode, 3 ... Digital / analog converter, 4 ... Current control part, 5 ... Photodiode, 6 ... Analog / digital converter, 7 ...
Switching transistor, 13 ... Line synchronization detection circuit, 20, 30 ... Microcomputer device, 21 ... Data processing unit, 22 ... Integration circuit, 23 ... Constant current circuit, 24 ...
Current / voltage conversion circuit, 25 comparison circuit.

Claims (1)

(57) [Claims] 1. Before starting recording of each page, a photoconductor is scanned to detect the light emission intensity of a semiconductor laser element for exposing a recording image light, and the detected value is controlled and held so as to be a constant value. In the emission intensity control method for a semiconductor laser device, the emission intensity command value is changed one step at a time, and the deviation between the detected value and the emission intensity set value is calculated and held,
When the relationship between the detected value and the emission intensity set value changes, the command value changes in a direction that reverses the relationship. And comparing the deviation when the detected value is smaller than the emission intensity setting value and setting the command value in a relationship having a smaller deviation.