JPH02197870A - Method for controlling emission intensity of semiconductor laser device - Google Patents

Abstract

PURPOSE:To control light emitting intensity in the line unit of a recording image light beam with accuracy by changing the command value of the light emitting intensity step by step, also calculating the deviation between a detection value and the set value of the light emitting intensity and setting the command value so that the smaller deviation may be kept in the relation between both. CONSTITUTION:In a control part 1, at the point of time of starting to control (t0), the command value CI is made to be '0' and the output intensity of a laser diode 2 is set '0' at an initial setting, since then, the command value CI is made to rise step by step with a fixed time cycle. And, when the output intensity exceeds a prescribed value LR at the point of time (t1), the command value CI is made to be stepped down by one step so as to become smaller than the prescribed value LR, then, the command value is made to be stepped up by one step so as to become larger than the prescribed value LR; the action is repeatedly performed by the prescribed number of times. When the action for reversing the relation between the sizes of the prescribed value LR and the command value CI by the prescribed number of times is finished, at the point of the time (t2) when the action is finished, the command value CI is set so that the state in which the smaller deviation is kept, the deviation ERp when the output intensity is larger than the prescribed value LR or the deviation EPm when the output intensity is smaller than the prescribed value LR may be secured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for controlling the emission intensity of a semiconductor laser element.

[Prior Art] In recent years, image forming apparatuses using electrophotographic technology have been used in, for example, plain paper facsimile machines, digital copying machines, and printers. A semiconductor laser element such as a laser diode is used as a means for generating the light.

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

The emission intensity control of this semiconductor laser element is performed by a control device using a microcomputer system, and conventionally, the control device disclosed in Japanese Patent Application Laid-Open No. 140482/1982 or the one disclosed in Japanese Patent Application Laid-Open No. 116570/1989 There are some that have been disclosed.

The former is a digital input of a D/A converter that compares the output of a light receiving element built into the laser diode for output monitoring with a reference voltage, and sets the laser diode drive current 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.

The latter similarly compares the monitor output with a reference value.

If the monitor output is small, the digital input value of the D/A converter is incremented, and if it is large, the digital input value is decremented for a predetermined period of time, and then the digital input value is fixed.

[Problems to be Solved by the Invention] However, the former method has the following two disadvantages.

(2) If the digital circuit malfunctions due to noise or the like, for example, if the value of the MSD bit of the counter changes from 0 to 1, the laser light output may be set to an excessive value.

■Since the laser light output takes discrete values, if the digital input value is fixed when the monitor output exceeds the reference value, the error with respect to the reference value will not necessarily be the minimum, resulting in poor control accuracy.

Moreover, although the latter can solve the problem (2) of the former mentioned above, it cannot solve the problem (2).

In this case, it is necessary to set the maximum value of the time expected for the laser light output to reach the target value as the set time for the control, resulting in a problem that the time required for the control becomes longer.

The present invention has been made to solve the problems of the prior art, and provides a method for controlling the emission intensity of a semiconductor laser device, which can control the output intensity of a semiconductor laser device to a specified value with high precision and in a short time. It is intended to. Furthermore, when controlling the light emission intensity on a page-by-page basis, it is not possible to eliminate fluctuations in the light emission intensity during the optical writing period.
There may be unevenness in recorded images, and this inconvenience can also be resolved.

[Means for Solving the Problems] The present invention changes the command value of the emission intensity step by step, calculates and holds the deviation between the detected value and the emission intensity setting value, and calculates and holds the deviation between the detected value and the emission intensity setting value. When the relationship changes, the command value is changed in a direction that reverses that relationship, and if this relationship is reversed a certain number of times, the deviation and the detected value when the previous detected value was greater than the emission intensity setting value becomes the emission intensity The deviation is compared when the deviation is smaller than the set value, and the command value is set to the relationship with the smaller deviation. Further, in the present invention, the emission intensity of the recorded image light is controlled line by line.

In addition, a microcomputer using a three-state output terminal is used as a control means, and an integrating circuit that integrates the output signal from the three-state output terminal and a drive current of a magnitude based on the output signal of this integrating circuit are applied to the semiconductor laser element. It is equipped with a current supply means for supplying the current.

[Operation] Therefore, the command value is controlled to a value with a smaller deviation, so that control accuracy is improved. Furthermore, since the light emission intensity is controlled line by line, unevenness in recorded images within one page can be eliminated. Further, since there is no need for a digital/analog converter for converting the digital output signal of the microcomputer used as the control means into an analog signal, the cost of the device can be reduced.

[Example] Hereinafter, an example 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 an 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 the figure, a control unit 1 performs control operations for this laser diode drive control device, and exchanges various control information with the main control device (shown in the diagram) of the laser printer, as well as controlling the emission intensity of the laser diode 2. A set value CI for setting is output to the digital/analog converter 3.

The digital/analog converter 3 converts the input setting value CI into a corresponding intensity setting signal AI, and the intensity setting signal AI is used to apply a driving current ID to the laser diode 2.
is added to the current control section 4 that supplies the current.

The current control unit 4 controls the drive current IO supplied to the laser diode 2 to a current value corresponding to the 1-intensity setting signal AI.

The photodiode 5 is housed in the same envelope as the laser diode 2, receives a part of the laser light output from the laser diode 2, and outputs an output signal P.
M is added to the analog-to-digital converter 6.

The analog/digital converter 6 converts the input signal 4 into a corresponding digital signal, and this digital signal is the output intensity monitor signal DF of the laser diode 2.
It is added to the control section 1 as a.

Further, the switching transistor 7 connected in parallel to the laser diode 2 is turned on and off by the recording data DT transferred from the main control device, and is used to modulate the output laser light from the laser diode 2 with the recording data DT. It is something.

Note that the number of bits of the digital/analog converter 3 is
The bit number of the analog/digital converter 6 is set to be larger, 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 l before starting recording of each page in order to control the emission intensity of the laser diode 2 to a specified value.

When the control unit l receives a laser intensity control command from the main control device, it first initializes the value of the counter CCI to rQJ (101), and sets the value of the counter CCI as the set value CI to the digital/analog converter 2. 102), thereby initializing the output level of the laser diode 2 to "0".

Next, the control system waits for a period of time until it settles to the state of the set value CI (process 103), and when it is finished, a flag is set for storing the magnitude relationship between the output intensity monitor signal DF and the specified value VR. FCH1 and output intensity monitor signal O
Process 10 to initialize the value of the counter CCH for storing the number of changes in the magnitude relationship between F and the specified value VR to rQJ.
4) A variable ERp for storing the deviation when the output intensity monitor signal DF is larger than the specified value VR, and a variable ERp for storing the deviation when the output intensity monitor signal DF is smaller than the specified value VR. Initialize variables ER+m to the maximum possible value MAX (process 105)
.

Then, the output monitor signal DF is input, and it is determined whether the value thereof is larger than the specified value VR (determination 106).

If the result of judgment 106 is No, process 107 to increment the counter CCI and increase its value by one step.
), a value obtained by subtracting the value of the output monitor signal DF from the specified value VR is assigned to the variable HRm (processing 108).

Then, it is checked whether the flag FCH is set to 1 (decision 109), and when the result of determination 109 becomes YES, it means that the output monitor signal DF has changed from a state larger than the specified VR to a state smaller than the specified VR.
When the result of the judgment 110)1 is NO, this means that there is no change in the state, so this process 110 is skipped, and the value of the flag FC)l is set to "0".
(processing 111).

Furthermore, when the result of the judgment 106 is YES, the counter CCI is decremented and its value is subtracted by one step (process 112), and the value obtained by subtracting the specified value VR from the value of the output monitor signal OF is assigned to the variable ER11 ( Processing 113)
.

Then, it is checked whether the flag FCH is 0 (judgment 114), and when the result of determination 114 is YES, it means that the output monitor signal DF has changed from a state smaller than the specified VR to a state larger than the specified VR, so the counter CCH
115), and when the result of judgment 114 is NO, there is no change in the state, so this process 115 is skipped and the value of flag FCJI is set to "1".
(processing 116).

When processing l11 and processing 116 are completed, counter C
Check whether the CH has exceeded the specified number of times Nc (
Judgment 117), when the result of judgment 117 is No, the value of counter CCI is output to the digital/analog converter 3 as set value CI. Return to

Further, when the result of judgment 117 is YES, the output intensity of the laser diode 2 is set to the specified value V for the specified number of times Nc.
Since this is a case where R is changed up and down between the two, in order to set the output intensity of laser diode 2, variable ERρ is changed to variable E
Check whether it is larger than Rm (Judgment 1
20).

When the result of decision 120 is '/ES, flag FCH
Check whether is rQJ (decision 121)
, when the result of judgment 121 is NO, the variable ER-
is smaller than the variable ERp, and the previous command value CI has a smaller error than the command value CI currently set in the digital/analog converter 3, so the counter C
Process 122) to output the value of CI to the digital/analog converter 3 as a command value CI, and after that, the command value C
I is held (process 123).

Further, when the result of judgment 121 is YES, the command value C currently set in the digital/analog converter 3
Since I is an appropriate value, processing 122 is skipped and processing 12 is performed.
Proceed to step 3.

On the other hand, when the result of judgment 120 is NO, it is checked whether the flag FCH is set to "1" (judgment 1
24). When the result of judgment 124 is NO, the process proceeds to process 122, and when the result of judgment 124 is YES, the process proceeds to process 123.

In this way, 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 initializes the output intensity of the laser diode 2 to "0" by setting the command value CI to "0" at the time t of starting control, and thereafter, The command value CI is increased one step at a time at a constant time period.

Then, when the output intensity exceeds the specified value LR at one point in time,
The operation of lowering the command value CI by one step to make it smaller than the specified value LR, and then raising it by one step to make it larger than the specified value LR is repeated a specified number of times.

In this way, the operation of reversing the magnitude relationship between the specified value LR and the command value CI by the specified number of times is completed.

As shown in FIG. 4, at the time t2 when the process ends, the deviation ERP when the output intensity is made larger than the specified value LR,
Deviation EP when the output intensity is made smaller than the specified value LR
The command value CI is set so as to take the smaller state of m.

First, since the output intensity is changed up and down near the specified value LR, even if the output of the digital/analog converter 3 becomes abnormal due to the incorporation of noise, etc., It is prevented that the output intensity is specified in the value.

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

Further, since the end of the control is determined depending on the state of the control system at that time, the time required for the output control process of the laser diode 2 is prevented from becoming unnecessarily long.

By the way, for example, at the time of starting recording of the second page, it is considered that the output intensity of the laser diode 2 has not changed significantly from the state set at the start of recording of the first page. It is also possible to start from process 104 in the figure.

In addition, when the process in FIG. 2 is performed at regular intervals, process 10
3,110 hours of waiting time can be omitted.

By the way, in the embodiment described above, since the emission intensity of the laser diode 2 is controlled on a page-by-page basis, it is not possible to deal with variations in the emission intensity of the laser diode 2 within the same page.

Although such fluctuations are very small, they become particularly noticeable when the environmental temperature of the laser diode 2 fluctuates (increases) significantly.

Next, another embodiment of the present invention that can solve this problem will be described.

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

As shown in FIG. 5, the laser beam LB modulated by the recording data DT output from the laser diode 2 is
The light is reflected by a polygon mirror 11 rotationally driven by a motor 10, and the belt-shaped photoreceptor 12 is scanned and exposed in the main scanning direction R3.

Immediately before the laser beam LB scans the photoreceptor 12, a line synchronization detection circuit 13 is provided at a position where the laser beam LB can be detected, and generates a line synchronization signal LS when receiving the laser beam LB.

Therefore, as shown in FIG. 6(a), in the immediate action period TA in which the laser diode 2 generates one line of recording image light, first, during the first period T1, the line synchronization detection circuit 13 outputs the laser beam LB. During the first period T2, the laser diode 2 stops emitting light because the laser beam LB is moving from the line synchronization detection circuit 13 to the photoreceptor 12, and during the subsequent period T3, the recording image light is turned on. is generated, and thereafter, light emission is stopped for a period T4 until the start of the next cycle.

As a result, during the period Tl, the period when the laser beam LB crosses the light receiving section of the line synchronization detection circuit 13,
), the line synchronization signal LS is generated from the line synchronization detection circuit 13.

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

Therefore, in this embodiment, the light emission intensity of the laser diode is controlled prior to page recording in the same manner as in the above-mentioned 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 generation timing of , thereby realizing light emission intensity control on a line-by-line basis.

FIG. 7 shows an example of such an embodiment.

In this figure, the same or corresponding parts as in FIG. 1 are given 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 is also applied to a main control device and a motor 1 that generate recording data DT.
The signal is output to an external device (not shown) such as a motor control means for controlling the rotation of the motor.

In this embodiment, the control section 1 executes the process shown in FIG. 2 before starting recording of each page, and when page recording starts, it sends a line synchronization signal and every time it inputs S, it executes the process shown in FIG. 8. Execute the specified processing.

That is, when the line synchronization signal LS is input, it is determined whether or not the optical writing mode for writing the recording image light modulated by the recording data DT onto the photoreceptor 12 is determined (201), and the result of determination 201 is YES. When the value of the counter CCI (see Figure 2) is changed to the set value C
It is output as I (process 202).

Then, input the output monitor signal DF at that time and compare the output monitor signal DF with the specified value VR to judge 203)
, when the value of the output monitor signal DF is smaller than the specified value VR, the counter CCI is incremented to increase the value by one (204), and when it is larger than the specified value VR, the counter CCI is decremented and the value is increased by one. Decrease process 205), this process ends.

Further, when the value of the output monitor signal DF is equal to the specified value VR, this process is ended while the value of the counter CCI is held.

As a result, the next time the line synchronization signal LS is generated, the value of the counter CC■ set at this time will be changed to the set value C.
As a result, the output monitor signal O
Emission intensity control of the laser diode 2 is performed line by line so that the value of F matches the specified value VR.

As a result, the emission intensity of the laser diode 2 is kept constant when one page of images is being recorded, so that it is possible to prevent problems such as density fluctuations from occurring in the recorded images.

In this embodiment, the output monitor signal DF and the specified value V
Although R is simply compared and the value of the counter CCI is adjusted based on the comparison result, other methods can be used to control the emission intensity of the laser diode 2.

Now, in recent years, a microcomputer device has been used as the above-mentioned control section 1, and an analog/
Since a one-chip type microcomputer device with a built-in digital converter 6 is in practical use, if these control section 1 and analog/digital conversion lI6 are realized by such a one-chip type microcomputer device, Equipment costs can be reduced.

However, since the set value CI output from the control section 1 is a digital signal, a digital-to-analog converter 3 is required to convert the digital signal into an analog signal that can be input to the current control section 4, which reduces device costs. It was becoming an obstacle.

FIG. 9 shows still another embodiment of the present invention that can eliminate such inconveniences. In this figure, the same or corresponding parts as in FIG. 1 are given the same reference numerals.

In the figure, a microcomputer device 20 is equipped with an analog/digital converter 6 as an input means, and a current control unit 20 outputted from a three-state input/output port of a data processing unit 21 that realizes various control processes. Signal IC is applied to an integrating circuit 22.

The integrating circuit 22 integrates the input current control signal IC to calculate the current command signal IN, and includes an operational amplifier OPI, an input resistor R1, voltage dividing resistors R2 and R3, and
It consists of a feedback capacitor C1. The output signal is output to the constant current circuit 23.

The constant current circuit 23 supplies the laser diode 2 with a driving current 0 corresponding to the current command signal IM outputted from the integrating circuit 22, and the operational amplifier OP2. It is composed of voltage dividing resistors R4 and R5, feedback resistor R6, and 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 this current/voltage conversion circuit 24 is input to the analog/digital converter 6 of the microcomputer device 20.

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

Therefore, since the integrating circuit 22 integrates the current control signal IC at the logic H level, the value of the current command signal knee output from the integrating circuit 22 decreases linearly with the time constant of the integrating circuit 22. do.

In this way, 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 the collector current of the transistor Tr increases and 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, so that the current output signal IN of the integrating circuit 22 is held at that point.

Further, 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, in order for the integrating circuit 22 to integrate the current control signal IC at the logical level, the value of the current command signal IN output from the integrating circuit 22 increases linearly with the time constant of the integrating circuit 22. do.

In this way, 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 the collector current of the transistor Tr decreases, and the drive current IO 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, so that the current output signal IN of the integrating circuit 22 is held at that point.

In this way, the data processing section 21 outputs the current control signal IC.
When the current control signal IC is raised to the logic H level, the drive current ID increases, and when the current control signal IC is lowered to the logic L level, the drive current IO is decreased, and the data processing section 21 outputs the current control signal IC. When an input/output port is set to a high impedance state, the value of the drive current ID is held at that point.

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

When the data processing unit 21 receives a laser intensity control command from the main control device, it first raises the input/output port outputting the current control signal IC to a logic H level for a certain period of time TV (processing 301 ), increases the drive current ID supplied to the laser diode 2, sets the input/output port to high impedance, and holds the drive current ID at the value at that time (process 302).

Next, the control system waits for a predetermined time TC, which is longer than the time it takes for the control system to stabilize to a state corresponding to the value of the drive current ID (process 303), and when that is finished, the output intensity monitor signal DF and the specified value Flag FCH1 for storing the magnitude relationship with VR, output strength monitor signal DF and specified value V
Counter C for storing the number of changes in the magnitude relationship with p
The value of CH is initialized to "0" (process 304).

Then, the output monitor signal DF is input, and it is determined whether the value thereof is larger than the specified value VR (determination 305).

If the result of the judgment 305 is NO, the light emission level of the laser diode 2 is lower than the specified value, so the input/output port is raised to the logic H level for a certain period of time Tl1l, and the current control signal IC at the logic H level is kept constant. Time TV is output to increase the drive current ID (process 306), and then the input/output port is set to a high impedance state to hold the value of the drive current ID (process 307).

Then, it is checked whether the flag FCH is set to 1 (judgment 308), and when the result of determination 308 becomes YES, it means that the output monitor signal OF has changed from a state larger than the specified VR to a smaller state, so the counter CCH
is incremented (process 309), and when the result of judgment 308 is No, there is no change in the state, so this process 309 is skipped, and the value of flag FCH is set to "0" (process 310).

Further, if the result of the judgment 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 a certain period of time Tll, and the current control signal at the logic L level is output. IC for a certain period of time Tw
is output to decrease the drive current ID (process 311), and then the input/output port is set to a high impedance state to maintain the value of the drive current ID (process 312).

Then, it is checked whether the flag FCH is set to O (judgment 313), and when the result of determination 313 becomes YES, it means that the output monitor signal DF has changed from a state smaller than the specified VR to a state larger than the specified VR, so the counter CCH
When the result of the judgment 313 is No, this process 314 is skipped because there is no change in the state, and the value of the flag FCH is set to "1" (process 315).

When processing 310 and processing 315 are completed, the counter C
Check whether CI( is greater than or equal to the specified number of times Nc (judgment 316), and wait for a certain period of time TC 317
After executing , the process returns to decision 305 .

Further, when the result of judgment 117 is YES, the output intensity of the laser diode 2 is set to the specified value V for the specified number of times Nc.
Since this is a case in which the output intensity of the laser diode 2 changes upward and downward with R in between, this process is terminated in order to maintain the output intensity of the laser diode 2 in that state.

In this way, 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, when the output intensity of the laser diode 2 is smaller than the specified value LR, the data processing unit 21 sets the current control signal IC to a logic H state that maintains the current control signal IC for a certain period of time T.
level, and the magnitude of the drive current IO is increased by one step.

Then, set the current control signal IC to the leap year operation state of TC for a certain period of time, wait until the control system stabilizes, and repeat this process at a certain period until the output intensity of the laser diode 2 exceeds the specified value LR. , the drive current IO is increased one step at a time at a constant time period.

When the output intensity exceeds the specified value LR, the current control signal IC is set to a logic level for a certain period of time TV, and the drive current I
The magnitude of D is decreased by one step, and the drive current IO is maintained 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, and then the drive current ID is decreased by one step to make the output intensity of the laser diode 2 larger than the specified value LR. Repeat the operation to reduce the size 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 a specified number of times is completed, the input/output port that outputs the current control signal IC is set to a high impedance state. , 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.

By the way, in the embodiment described above, the output intensity of the laser diode 2 is checked at fixed time intervals TC, and the value of the open current control signal IC of the fixed time TV is logically determined based on the magnitude relationship of the output intensity with the specified value LR. By setting the drive current ID to the H level or the logical L level, the drive current ID is raised or lowered by one step, but the drive current ID can also be controlled in the following manner.

That is, the output intensity of the laser diode 2 and the specified value LR
Check the deviation from To shorten the time required to set the logic H level or low logic level.

In addition, at this time, wait until the time for the control system to stabilize after the time for setting the value of the current control signal IC to the logic H level or logic L level has elapsed, and then start the next control. The output intensity of the laser diode 2 is sampled for this purpose.

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.

The rate of change when lowering the drive current ID can be set to an appropriate value.

For example, as the microcomputer device 20, 0MO8
When using this type of device, the logic H level of the input/output port approximately corresponds to the power supply voltage Vcc, and the logic L level approximately corresponds to the ground level.

Therefore, the voltage dividing resistor R2 of the integrating circuit 22 and the voltage dividing resistor R
When the resistance values of 3 are set to equal values, the operational adder OPI
The potentials of the non-inverting input terminal and the inverting input terminal of the are Vcc/2, therefore, the values of the current control signal IC flowing when the input/output port is set to output mode and output mode are +(Vcc/2RL), respectively. and -(Vcc
/2R1), so the rate of change when increasing the drive current ID is equal to the rate of change when decreasing it.

Further, if the resistance value of the voltage dividing resistor R2 is set to be 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.

In this way, in this embodiment, the output intensity of the laser diode 2 can be controlled very flexibly.

Further, compared to the case where current is controlled using a digital/analog converter, the number of signal lines between the microcomputer device W20 and the integrating circuit 22 is significantly reduced, and the output ports required for the microcomputer device 20 are significantly reduced. Since the number of devices can also be reduced, the cost of the device can be significantly reduced.

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

In the figure, the output signal of the current/voltage conversion circuit 24 is
It is added to a comparison circuit 25 for comparing the output intensity of the laser diode 2 with a specified value LR, and this comparison circuit 2
The comparison signal CP outputted from the microcomputer 30 is applied to a 1-bit data input terminal of the microcomputer 30.

Here, the comparison circuit 25 includes an operational amplifier OP4, a specified value L
The monitor signal PM (voltage value) output from the current/voltage converter 24 is the reference voltage. If the monitor signal PM (voltage value) is smaller than the reference voltage REF, the comparison signal CP is set to the logic L level, and if 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
controls the drive current ID of the laser diode 2 by performing the same process as in FIG.

In this way, in this embodiment, the drive current I is adjusted based on the magnitude relationship between the output intensity of the laser diode 2 and the specified value LR.
Since it is controlling D, the microcomputer device 30
does not require an analog/digital converter as an input means, thus further reducing device costs.

[Effects of the Invention] As described above, according to the present invention, the command value of the light emission intensity is changed step by step, and the deviation between the detected value and the set value of the light emission intensity is calculated and held.

When the relationship between the detected value and the emission intensity setting value changes, the command value is changed in a direction that reverses that relationship, and if this relationship is reversed a certain number of times, if the detected value was larger than the emission intensity setting value immediately before. Since the deviation is compared with the deviation when the detected value is smaller than the emission intensity setting value, and the command value is set in a relationship with the smaller deviation, control accuracy is improved. Furthermore, since the emission intensity of the recorded image light is controlled line by line, unevenness in recorded images within one page can be eliminated. Furthermore, a microcomputer with a three-state output terminal is used as a control means, and an integrating circuit that integrates the output signal from the three-state output terminal is used, and a driving current of a magnitude based on the output signal of this integrating circuit is applied to the semiconductor laser element. Since the device is equipped with a current supply means for supplying current to the device, a digital/analog converter is not required, and the device cost can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a laser diode drive control device according to an embodiment of the present invention, Fig. 2 is a flowchart showing an example of processing executed by the control section, and Fig. 3 shows how the output intensity of the laser diode is controlled. 4 is a schematic diagram for explaining the deviation, FIG. 5 is a schematic configuration diagram illustrating the optical system of a laser beam printer, and FIG. 6 is a diagram illustrating the writing period of the laser diode and the generation of the 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. 9 is a waveform diagram showing the relationship. FIG. 10 is a flowchart showing an example of processing of the data processing section; FIG. 11 is a graph diagram showing a mode of output intensity control of the laser diode by the apparatus shown in FIG. 9; FIG. FIG. 12 is a circuit diagram showing still another embodiment of the present invention. 1... Control unit, 2... Laser diode, 3...
Digital/analog converter, 4... Current control section, 5.
...Photodiode, 6...Analog/digital converter, 7...Switching transistor, 13...
Line synchronization detection circuit, 20, 30... microcomputer device. 21... Data processing section, 22... Integrating circuit, 23.
・・Constant current circuit, 24 ・・Current/voltage conversion circuit, 25
...Comparison circuit. Figure 3 Figure 6 Figure A Figure 8 Figure 1゜Figure

Claims (3)

[Claims] (1) A semiconductor laser that scans the photoreceptor and detects the emission intensity of the semiconductor laser element that exposes the recording image light before starting recording of each page, and controls and maintains the detected value at a constant value. In a method for controlling the emission intensity of an element, the command value of the emission intensity is changed step by step, and the deviation between the detected value and the emission intensity setting value is calculated and held, and the relationship between the detection value and the emission intensity setting value is determined. When the command value changes, the command value is changed in a direction that reverses the relationship, and when this relationship is reversed a certain number of times, the deviation from when the above detected value was larger than the light emission intensity setting value immediately before and the above detected value become the light emission intensity setting. A method for controlling the emission intensity of a semiconductor laser device, characterized in that the deviation is compared when the deviation is smaller than the specified value, and the command value is set in a relationship with the smaller deviation. (2) A semiconductor laser that scans the photoreceptor and detects the emission intensity of the semiconductor laser element that exposes the recording image light before starting recording of each page, and controls and maintains the detected value at a constant value. A method for controlling light emission intensity of an element includes a synchronization detection means for detecting a start timing when recording image light scans a photoreceptor in a main scanning direction, and during optical writing, a synchronization detection means is provided at a timing when a synchronization signal is output from the synchronization detection means. A method for controlling the emission intensity of a semiconductor laser device, comprising controlling the emission intensity of the semiconductor laser device line by line. (3) A semiconductor laser that scans the photoreceptor and detects the emission intensity of the semiconductor laser element that exposes the recording image light before starting recording of each page, and controls and maintains the detected value at a constant value. In the light emission intensity control device of the element, a microcomputer outputs a command value based on the detected value from the three-state output terminal, an integrating circuit integrates the output signal of the three-state output terminal, and an output signal of the integrating circuit. 1. A light emission intensity control device for a semiconductor laser device, comprising: current supply means for supplying a drive current of a predetermined magnitude to the semiconductor laser device.