JPH08258334A - Controlling device for quantity of light - Google Patents

Abstract

PURPOSE: To obtain reference quantity of light in a short time by providing a means for outputting a quantity-of-light-setting control signal in order to energize a voltage control means in non-image area in the horizontal scanning direction, after the elapse of predetermined time. CONSTITUTION: A quantity-of-light control signal outputted from a CPU and an S/H timing signal S2 outputted from a timing control circuit 19 are inputted to an AND circuit 21. The output signal of the AND circuit 21 is supplied to an invertor as a sample-holding signal S/H and also supplied to an one-sided input side of the AND circuit 20. The quantity-of-light control signal is a high signal at a time for writing of an image, but is maintained low for a certain time from the start of the feeding until the preset timer value comes to a time-up in CPU for the control of the quantity of light. As a result, a lighting signal V and the S/H signal being output of the AND circuits 20, 21 become the low signal, and an APC becomes a sample mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam light amount control device, and more particularly to a laser beam light amount control device for irradiating an object to be scanned for image formation.

[0002]

2. Description of the Related Art A circuit configuration of a general laser beam light quantity control device will be described with reference to FIG. In the figure,
The switching circuit 1 is turned on / off at high speed based on the lighting signal v. The lighting signal v is a light amount control signal for setting the light amount in the non-image area, a control signal forcibly generated for detecting the synchronization signal, or a write signal generated based on video data. Or For example, when a high level signal (hereinafter referred to as “high signal”) is supplied to the switch circuit 1, it is turned off, and when a low level signal (hereinafter referred to as “low signal”) is supplied, the switch circuit 1 is turned on. It is a switching circuit. The laser diode LD is driven by a current flowing when the switching circuit 1 is on, and the magnitude of the current is set by the drive current control circuit 2.

Further, in order to control the current to a constant value, the following constitution is adopted. The photodiode PD receives the back beam of the laser beam output from the laser diode LD, and as a result, a current proportional to the light amount of the laser beam flows through the photodiode PD. A resistor R1 is connected between the photodiode PD and the ground, and the connection point is connected to the positive input terminal of the comparator 3. That is, the current flowing through the photodiode PD is converted into the monitor voltage Vmon and input to the comparator 3. Comparator 3
A light amount setting signal Vref serving as a reference value for obtaining a desired light amount is input to the minus input terminal of the.

The output signal of the comparator 3 is the OR gate 4.
Also, the sample / hold signal S / H is input to the AND gate 5 as the other input signal of the OR gate 4, and the sample / hold signal S / H is input to the inverter 6 as the other input signal of the AND gate 5. It is inverted and input. The output signal of the OR gate 4 is a P channel CMOS switch (hereinafter referred to as "P switch").
7 and the output signal of the AND gate 5 is an N channel CMOS switch (hereinafter referred to as "N switch").
8 is input. Further, the P switch 7 and N
The drain of the switch 8 is connected to the hold capacitor 9 and the operational amplifier 10. The output side of the operational amplifier 10 is connected to the drive current control circuit 2.

With the above configuration, when the sample / hold signal S / H is a low signal, that is, in the sample mode, the monitor voltage Vmon is the light amount setting signal Vr.
When it is smaller than ef, the P switch is conductive and the N switch is non-conductive. Therefore, the holding voltage of the hold capacitor 9 rises, and as a result, the voltage supplied to the drive current control circuit 2 also rises and the light quantity of the laser diode LD increases. When the light amount of the laser diode LD increases and the light receiving amount of the photodiode PD increases, the monitor voltage V
mon rises, and when this reaches the light amount setting signal Vref, the output of the comparator 3 is inverted to a high signal. When the output of the comparator 3 is inverted to a high signal, when the sample / hold signal S / H is a low signal, the N switch 8 becomes conductive and the P switch 7 becomes non-conductive. Therefore, the holding potential of the hold capacitor 9 drops, and as a result, the voltage applied to the drive current control circuit 2 drops and the light quantity of the laser diode LD decreases.

As described above, the light quantity control device operates so as to make the current of the photodiode PD, that is, the received light quantity constant, and therefore, the sample / hold signal S / H and the lighting signal v at the timing outside the image area before the start of printing. Is set to be a low signal and the above control is performed so that the laser diode LD outputs a laser beam having a reference light amount. At the time of printing, if the sample / hold signal S / H is set to a high signal and switched to the hold mode, the voltage held by the hold capacitor 9 causes the desired light quantity to be changed in accordance with the lighting signal v, that is, the writing signal being turned on / off. A laser beam is output, and an image with uniform density is formed on a photoconductor (not shown).

The amount of light thus set changes due to heat generation of the laser diode LD and leakage of the holding voltage of the hold capacitor 9 due to use. Therefore, the above control is performed as needed in a predetermined area outside the image area to keep the light amount constant and maintain the print quality.

[0008]

An analog type light quantity control circuit (APC) using the above sample and hold circuit.
Then, when the potential is increased to increase the light amount from the time when the hold capacitor 9 is in the reset state, it is difficult to accurately end the light amount control when the light amount of the laser beam reaches the reference light amount. That is, even when the hold mode is switched to when the light amount reaches the reference light amount, for example, when the charge speed for the hold capacitor 9 is high, overshoot may occur and a light amount larger than the reference light amount may be set. . On the contrary, if the charging speed is low, it takes time to reach the reference light amount.

The following method is conceivable as a means for solving such problems and setting the light quantity accurately. For example, a light quantity adjusting device for a laser beam is disclosed in which the quantity of light is digitally controlled by the processing of a CPU (Japanese Patent Laid-Open No. 63-301075). The operation timing of this device is shown in FIG. In the figure,
The light quantity of the laser diode is continuously increased stepwise according to the adjustment timing. When the light detection device that detects the laser beam output from the laser diode and emits the synchronization signal reaches the light amount at which the detection signal is first obtained, the operation of continuously increasing the light amount, that is, the mode 1 is terminated. . After that, the mode is shifted to mode 2, and the light amount is gradually increased in response to the synchronization signal, and finally the reference light amount is obtained.

In this device, the light amount is increased stepwise in response to the synchronizing signal, so that the correct light amount is reached eventually. However, since the amount of light from which the synchronizing signal is obtained is extremely lower than the reference amount of light finally necessary for image formation, it is possible that the amount of light is gradually increased in response to the synchronizing signal after shifting to mode 2. There is a problem that it takes a very long time to reach the reference light amount. If it takes time to obtain the reference amount of light as described above, for example, in a copying apparatus, it takes a long time from the image forming instruction operation until the actual print operation becomes possible, which lowers efficiency. Appears as dots.

An object of the present invention is to solve the above problems and to provide a light quantity control device capable of obtaining a reference light quantity in a short time.

[0012]

SUMMARY OF THE INVENTION To solve the above problems and to achieve the object, the present invention compares a monitor voltage and a reference voltage with a means for detecting a light quantity of a laser beam to generate a monitor voltage. Comparing means, voltage control means for accumulating a potential in the capacitor when the monitor voltage is lower than the reference voltage, and lowering the potential of the capacitor when the monitor voltage is higher than the reference voltage, and a laser according to the potential of the capacitor. From the initial state of the drive current control means for controlling the drive current of the light source and the capacitor, until the lapse of a scheduled time in consideration of the characteristics of the laser light source, the voltage control means is continuously energized, After the lapse of time, the first feature is that it further comprises a control signal output means for outputting a light amount setting control signal for energizing the voltage control means in the non-image area in the main scanning direction. A.

Further, according to the present invention, the voltage control means is continuously energized from the initial state of the capacitor until the monitor voltage reaches a limit value which is set lower than the reference voltage in anticipation of overshoot. The second feature is that it further comprises control signal output means for outputting a light amount setting control signal for energizing the voltage control means in the non-image area in the main scanning direction after reaching the limit value. is there.

Further, according to the present invention, the rate of change detecting means for detecting the rate of change of the monitor voltage, and the rate of change detected by the rate of change detecting means from the initial state of the capacitor until the predetermined lower limit value is reached. Control signal output means for continuously energizing the voltage control means and, after reaching the lower limit value, outputting a light amount setting control signal for energizing the voltage control means in the non-image area in the main scanning direction. The third feature lies in that

[0015]

According to the first feature, the voltage control means controls the accumulation of the potential in the capacitor so that the reference light quantity and the laser light quantity match. And
The light quantity of the laser beam is determined based on the potential accumulated in the capacitor. The light amount control operation that accumulates the potential in the capacitor from the initial state of the capacitor is continuously executed until the lapse of the scheduled time determined in consideration of the characteristics of the laser light source, and then the light amount control is performed in the non-image area in the main scanning direction. Is done.

According to the second feature, the transition from the continuous light amount control operation to the timing of executing the light amount control in the non-image area in the main scanning direction is performed by setting the monitor voltage lower than the reference voltage. Since the process is performed when the limit value is reached, there is no influence of overshoot and the light amount of the laser beam almost reaches the reference light amount, so that the reference light amount can be obtained early.

Further, according to the third feature, when it is detected that the rate of change of the monitor voltage has dropped below a predetermined value,
Since it can be determined that the light amount is near the reference light amount, it is considered that the light amount has reached the reference light amount based on this determination, and the light amount setting control is once terminated.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 9 is a plan view showing a main configuration of an image forming apparatus to which the light quantity control device according to the embodiment of the present invention is applied. In the figure, a laser diode LD is provided as a laser light source. The laser beam Lt emitted from the laser diode LD passes through the collimator lens 11 and the cylinder lens 12 and reaches the rotating polyhedron 13.
The rotating polyhedron 13 has eight reflecting surfaces, and is rotated in the direction of arrow D1 by a driving source (not shown). As a result, the laser beam Lt reaching the reflecting surface of the rotating polyhedron 13
Is scanned on the medium to be scanned, that is, the photoconductor 14 in the direction of arrow D2, that is, the main scanning direction. Here, an example in which the laser beam Lt is scanned on the drum-shaped photoconductor 14 as the medium to be scanned has been described, but the same applies to a planar photoconductor.

An f.theta. Lens 15 and a cylinder lens 16 are provided between the rotating polyhedron 13 and the photoconductor 14 in order to scan the photoconductor 14 at a constant speed with the laser beam Lt. The optical position detector 17, which is composed of a photoelectric conversion element such as a photodiode, detects the laser beam Lt reflected by the mirror 17a, and a horizontal synchronization signal () necessary for synchronizing the laser beam generation position with the modulation signal. SOS). By starting the printing after the scheduled time elapses after the generation of the horizontal synchronizing signal SOS, the deviation (jitter) of the printing position in the main scanning direction may occur even when the surface accuracy of the rotating polyhedron 13 varies. You can prevent it from happening.

The drum-shaped photosensitive member 14 is rotatably supported by, for example, a housing (not shown) of the image forming apparatus, and is rotated at a predetermined speed in the direction of arrow D3 by a drive source (not shown). Around the photoconductor 14, a charging device, an exposing device, a developing device, a transfer device, and the like for uniformly charging the surface layer of the photoconductor 5 are provided, but they are not essential parts of the present embodiment. Therefore, the illustration is omitted.

Next, a first embodiment of the light quantity control device for the laser diode LD in the image forming apparatus will be described. In the first embodiment, the circuit described with reference to FIG. 10 is used as it is, and is characterized by the generation means of the control signal to be input to the circuit. Therefore, FIG. 10 and its description will be used here.

FIG. 1 is an example of a circuit for generating the sample / hold signal S / H and the lighting signal v of the light quantity control device described with reference to FIG. In the figure, the timing control circuit 19 uses the SOS lighting signal s1 and S / H.
The timing signal s2 is output. That is, the synchronization signal S
When detecting the OS, the SOS lighting signal s1 is set to a low signal. Further, the signal s2 is set to a low signal when the APC is set to the sample mode, and the signal s2 is set to a high signal when the APC is set to the hold mode.

The AND circuit 18 receives video data from an image processing unit (not shown) and the SOS lighting signal s1. The SOS lighting signal s1 is a high signal during image writing, and the output of the AND circuit 18 changes according to ON / OFF of video data. As a result, the output of the AND circuit 20, which is supplied with a signal from the AND circuit 18, that is, the lighting signal v changes, the switching circuit 1 (FIG. 10) is turned on / off, and the laser diode LD is turned on or off. On the other hand, when the synchronization signal SOS is obtained, the SOS
Since the lighting signal s1 becomes a low signal, at this time, the output of the AND circuit 18 outputs a low signal regardless of whether the video data is on or off to light the laser diode LD.

The AND circuit 21 has a C (not shown).
The light amount control signal output from PU and the S / H timing signal s2 output from the timing control circuit 19 are input. The output signal of the AND circuit 21 is converted into the sample / hold signal S / H by the inverter 6 (see FIG. 1).
0) and also to one input side of the AND circuit 20.

The light amount control signal is a high signal at the time of writing an image, but is kept at a low signal until the preset timer value expires in the CPU since the light amount control is performed during the scheduled period from the startup. As a result, the outputs of the AND circuits 20 and 21, that is, the lighting signal v and the S / H signal are low signals, and the APC is in the sampling mode. During the period, the light amount control is continuously performed. The function of measuring the scheduled time using the CPU and outputting the time-up signal can be realized by a known program.

On the other hand, since the light amount control is not performed during image writing, the light amount control signal and the S / H timing signal s2 are both set so that a hold signal, that is, a high signal is output from the AND circuit 21 at this time. It is a high signal. Further, since the light amount control is performed outside the image area after the image writing is started, the S / H timing signal s2 output from the timing control circuit 19 is a low signal.

In this way, the timing control circuit 19
Clocks are counted with the synchronization signal SOS supplied from the optical position detector 17 as a reference, and the SOS lighting signal s1 is output (to a low signal) at a planned writing position, or the S / H timing is set in a non-image area. The circuit configuration is such that the signal s2 is output (to a low signal). Further, in order to obtain the synchronization signal SOS, it is necessary to turn on the laser diode LD at the position of the optical position detector 17, and therefore, the position where the laser beam is irradiated to the optical position detector 17 is planned to be included. It includes a circuit configuration for setting the SOS lighting signal s1 to a low signal in a range. As the circuit configuration described above, there are provided a clock counting means, a counter which sets a predetermined count value for obtaining the SOS lighting signal s1 and the S / H timing s signal 2 based on the count value of the clock. .

FIG. 2 shows the sample hold signal S / H.
3 is a timing chart showing changes in the output timing of the lighting signal v and the light amount (output light amount) of the laser beam output from the laser diode LD. In the figure, when the lighting signal v and the sample / hold signal S / H are set to low signals at the timing t1, a current flows through the laser diode LD to gradually increase the light quantity, and at the timing t2, a reference represented by the light quantity setting signal Vref. Reach the light intensity. Even after the light amount reaches the reference light amount, the sample hold signal S / H and the lighting signal v are kept at low signals according to the light amount control signal until the timer period of the timer value set by the CPU ends. The light amount control is continued. Then, after the elapse of the period T, at timing t3, the lighting signal v is inverted to a high signal, the switching circuit 1 is turned off, the laser diode LD is extinguished, and the light amount becomes “0”.
However, during this period, the sample / hold signal S / H is still a high signal.
The potential corresponding to the reference light amount is held. The period T
Can be determined based on the time required to reach the reference light amount, that is, the time calculated based on the threshold current of the laser diode LD, the differential efficiency, and the like.

Subsequently, in order to obtain the synchronizing signal SOS, the sample hold signal S / H and the lighting signal v are changed to the low signal from the timing t4 to the timing t5, and the laser diode LD is lit. Similarly, at timing t6 in the next non-image area, the laser diode LD is turned on to obtain the synchronization signal SOS. Then, after the synchronization signal SOS is obtained, the main scanning timing signal s1 for image writing is output at a scheduled timing t7. That is, assuming that the synchronization signal SOS is obtained at the timing ts, the image writing is started after the lapse of the scheduled time Tw.

Next, the operation in the non-image area will be described in detail with reference to FIG. This figure corresponds to the portion after the timing t6 in FIG. 2, for example. In the figure, the number of dots described in the lowermost row is the count value of the image clock counted based on the falling edge of the synchronization signal SOS. At the 5300th dot from the detection of the sync signal SOS (not shown), the SOS
The lighting signal changes to a low signal, and accordingly, the lighting signal v also changes to a low signal, and the laser diode LD is turned on. Next, the S / H timing signal s2 is changed to a low signal between the 5400th dot and the 5470th dot to set the APC to the sample mode, and the light amount is set to the light amount setting signal vr.
Control to be ef. After this, the synchronization signal SOS is detected at the timing tss, and the counter for counting the synchronization signal SOS is cleared at the fall tse. Then, when the newly counted number of dots reaches the third dot, the SOS lighting signal s1 is changed to a high signal. As a result, the lighting signal v also changes to a high signal, and the laser diode LD is turned off. Next, at the 200th dot, the video data output permission signal becomes a high signal, the video data is read to the AND circuit 18, and the laser diode LD is turned on / off according to the video data.
The video data output permission signal is kept high until the 4877th dot. The video data output permission signal is generated by the timing control circuit 19 based on the preset set value and the synchronization signal SOS, and is supplied to the image processing unit (not shown) to read the video data.

As described above, according to the first embodiment, the light amount setting control is performed by continuously turning on the light for a period T determined in anticipation of the time until the reference light amount is reached, and thereafter, the light amount control is performed in the non-image area. Is done. According to this first embodiment,
For example, even if the light amount is overshooting or has not yet reached the reference light amount due to variations in elements, etc., it is considered that the reference light amount is almost reached after the period T. The subsequent control in the non-image area makes it possible to reach the correct reference light amount in a short time.

Next, the second embodiment will be described. FIG.
1 is a circuit diagram of a light quantity control device according to a second embodiment.
The same symbols as 0 indicate the same or equivalent parts. In the second embodiment, in addition to the configuration shown in FIG. 10, a second comparator 22 that outputs a signal when the output of the photodiode PD reaches a predetermined value (limit value) VLMT lower than the light amount setting signal Vref is provided. Provided. Then, the output signal of the second comparator 22 is used as a light amount setting control end signal, and in response to this signal, the continuous light amount setting control that has been executed from the reset state of the hold capacitor 9 is ended, and thereafter, non- By controlling the light amount in the image area, the light amount corresponding to the light amount setting signal Vref is gradually reached. The limit value VLMT is set to a voltage lower than the light amount setting voltage calculated by the threshold current of the laser diode LD and the differential efficiency by an amount that allows for overshoot and the like. In this way, the light quantity is continuously increased up to the preset limit value VLMT, and thereafter, the light quantity of the laser beam can reach the reference light quantity by a relatively small number of light quantity control in the non-image area. it can.

FIG. 5 shows a sample / hold signal S / H and a lighting signal v in the light quantity control device according to the second embodiment.
Is an example of a circuit for generating the same, and the same reference numerals as those in FIG. 1 indicate the same or equivalent portions. In the figure, when the hold capacitor 9 is reset and, for example, a start instruction is issued by a copying machine including the light amount control device, the light amount setting control start signal input from the CPU to the set terminal S of the latch 23 becomes a high signal. , The latch 23 is set, and the output Q bar of the latch 23 becomes a low signal. As a result, the lighting signal v and the sample / hold signal S / H become low level signals, the laser diode LD is lit, and the light amount control is started.

When the monitor voltage Vmon exceeds the limit value VLMT, the light amount setting control end signal is sent to the latch 23.
Is input to the reset terminal R of the latch 23, the latch 23 is reset, and the output Q-bar becomes a high signal. As a result, the light amount control by continuous lighting is completed. After that, in response to the output signal from the timing control circuit 19, lighting for light amount control is performed in the non-image area, and lighting for image writing is performed at print timing.

FIG. 6 shows a lighting signal v and a sample / hold signal S / H in the light quantity control device according to the second embodiment.
7 is a timing chart showing the relationship between the above and the change in the light amount. As shown in the figure, at the timing t1, the output light quantity, that is, the monitor voltage Vmon reaches the limit value VLMT, the lighting signal v and the sample / hold signal S / H become high signals, and the continuous light quantity setting control ends. Then, between timings t2 and t3, and between timings t4 and t
During 5th, lighting for light amount control is performed in the non-image area, and the light amount is finally set to the reference light amount. Then, at the print timing t6 determined based on the synchronization signal SOS, the image writing is performed, so that the lighting is performed according to the video data.

Next, a third embodiment will be described. Figure 7
4 is a circuit diagram of a light quantity control device according to a third embodiment, and FIG.
The same reference numerals as in the above indicate the same or equivalent portions. In the figure,
Output of photodiode PD, that is, monitor voltage Vmon
Is input to the third comparator 25 via the differentiating circuit 24. That is, the differentiating circuit 24 monitors the monitor voltage Vmon.
Of the third comparator 2 is detected.
In step 5, it is compared with the lower limit value VdLMT of the rate of change.

The monitor voltage Vmon increases at a constant rate of change as the light amount increases, and is controlled so that the light amount becomes constant after reaching the reference light amount. Therefore, the change rate of the monitor voltage Vmon also decreases after the light amount reaches the reference light amount, and finally becomes “0”. Therefore, by setting a value close to “0” as the lower limit value VdLMT, the output signal of the third comparator 25 is reached when the light amount has almost reached the reference light amount, that is, when the rate of change has decreased to the lower limit value VdLMT. Is reversed. Therefore, the light amount setting control end signal may be output based on this output signal to end the light amount setting control. The output signal of the third comparator 25 is input to the AND circuit 28 via the delay circuit 26 that functions as a low-pass filter and the inverter 27 for edge detection. The inverter 27 has a Schmitt trigger function. Further, the output signal of the third comparator 25 is directly input to the other input terminal of the AND circuit 28. In the third embodiment, as the circuit for generating the lighting signal v and the sample / hold signal S / H, the same circuit as that of the second embodiment shown in FIG. 5 can be used.

Next, the operation timing of the third embodiment will be described. FIG. 8 is a timing chart showing the relationship between the lighting signal v and the sample / hold signal S / H and the change in the light quantity in the light quantity control device according to the third embodiment. As shown in the figure, when the light quantity increases from the reset state of the hold capacitor 9 and the output signal of the differentiating circuit 24 becomes equal to or higher than the lower limit value VdLMT, the output of the third comparator 25 is inverted to the low signal at the timing t1, and The output of the inverter 27 changes to a high signal at the timing t2 with a delay of the scheduled time set by the delay circuit 26.

After that, when the light quantity increases at a constant light quantity change rate and reaches, for example, the reference light quantity, the change rate becomes the lower limit value VdLM.
When it becomes T or less (timing t3), the output of the third comparator 25 is inverted to a high signal, and further, the output of the inverter 27 is changed to a low signal at a timing t4 with a delay of the preset time set by the delay circuit 26. . The output signal of the AND circuit 28, that is, the light amount setting control end signal becomes a high signal when the outputs of the comparator 25 and the inverter 27 are both high signals, that is, between timings t3 and t4. This light amount setting control end signal is sent to the latch 23.
Is supplied to the reset terminal of the light quantity setting control, that is, the light quantity control at the time of startup is completed.

As described above, according to the third embodiment, it is possible to accurately detect that the light quantity approaches the reference light quantity based on the rate of change of the monitor voltage Vmon.

[0041]

As is apparent from the above description, according to the first aspect of the invention, the light amount control is not continued until the light amount converges to the reference light amount, but it can be considered that the light amount has almost reached the reference light amount. Since the light amount can be controlled step by step in the non-image area in the main scanning direction by performing only for the scheduled time, it is possible to reach the reference light amount in a short time.

According to the second aspect of the invention, the transition from the continuous light amount control operation to the timing for executing the light amount control in the non-image area in the main scanning direction is performed when the monitor voltage reaches the limit value. Done. This limit value is determined in consideration of the influence of overshoot, and is set slightly lower than the reference light amount, so that the reference light amount can be obtained early.

Further, according to the third aspect of the invention, it can be judged that the light quantity is near the reference light quantity based on the rate of change of the monitor voltage. Then, based on this determination, the light amount control is continuously performed until it is considered that the light amount has reached the reference light amount, so that the reference light amount can be obtained early.

As described above, according to the light quantity control device of the present invention, it is possible to shorten the time from the start of printing to the acquisition of a printed image.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a light quantity control signal generator according to a first embodiment of the present invention.

FIG. 2 is a timing chart of a light amount control operation according to the first example.

FIG. 3 is a timing chart showing a detailed operation of a light amount control operation.

FIG. 4 is a circuit diagram of a light quantity control device according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram of a light quantity control signal generator according to a second embodiment of the present invention.

FIG. 6 is a timing chart of a light amount control operation according to the second embodiment of the present invention.

FIG. 7 is a circuit diagram of a light quantity control device according to a third embodiment of the present invention.

FIG. 8 is a timing chart of a light quantity control operation according to the third embodiment of the present invention.

FIG. 9 is a plan view showing a main configuration of an image forming apparatus to which the light amount control device according to the embodiment of the present invention is applied.

FIG. 10 is a circuit diagram of a general light amount control device.

FIG. 11 is a timing chart of a light amount control operation of a general light amount control device.

[Explanation of symbols]

1 ... Switching circuit, 2 ... Drive current control circuit, 9
… Hold capacitor, 19… Timing control circuit,
22 ... 2nd comparator, 23 ... Latch, 25 ... 3rd
Comparator, LD ... Laser diode, PD ... Photo diode

Claims (3)

[Claims] 1. A means for detecting a light amount of a laser beam output from a laser light source to generate a monitor voltage, a comparing means for comparing the monitor voltage and a reference voltage, and a result of the comparison by the comparing means, a monitor voltage. Is lower than the reference voltage, the potential is stored in the capacitor, and when the monitor voltage is higher than the reference voltage, the voltage control means for lowering the potential of the capacitor, and the drive current of the laser light source is controlled according to the potential of the capacitor. Drive current control means, from the initial state of the capacitor, until the lapse of a scheduled time considering the characteristics of the laser light source, continuously energize the voltage control means, after the lapse of the scheduled time, the main scanning direction Light amount control means for outputting a light amount setting control signal for energizing the voltage control means in the non-image area of Apparatus. 2. A means for generating a monitor voltage by detecting a light quantity of a laser beam outputted from a laser light source, a comparing means for comparing the monitor voltage and a reference voltage, and a monitor voltage as a result of the comparison by the comparing means. Is lower than the reference voltage, the potential is stored in the capacitor, and when the monitor voltage is higher than the reference voltage, the voltage control means for lowering the potential of the capacitor, and the drive current of the laser light source is controlled according to the potential of the capacitor. Drive current control means, and continuously activating the voltage control means from the initial state of the capacitor until the monitor voltage reaches a limit value preset lower than the reference voltage in anticipation of overshoot, After reaching the limit value, control for outputting a light amount setting control signal for energizing the voltage control means in the non-image area in the main scanning direction Light amount control apparatus, characterized by comprising a signal output means. 3. A means for detecting a light quantity of a laser beam output from a laser light source to generate a monitor voltage, a comparing means for comparing the monitor voltage and a reference voltage, and a monitor voltage as a result of the comparison by the comparing means. Is lower than the reference voltage, the potential is stored in the capacitor, and when the monitor voltage is higher than the reference voltage, the voltage control means for lowering the potential of the capacitor, and the drive current of the laser light source is controlled according to the potential of the capacitor. Drive current control means, change rate detection means for detecting the change rate of the monitor voltage, and until the change rate detected by the change rate detection means reaches a predetermined lower limit value, continuously from the initial state of the capacitor. After the voltage control means is energized to reach the lower limit value, the light amount setting control for energizing the voltage control means in the non-image area in the main scanning direction is performed. Light amount control apparatus, characterized by comprising a control signal outputting means for outputting the issue.