JP2001230485A - Automatic luminous quantity controller and automatic luminous quantity control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain optimum automatic luminous quantity control for an automatic luminous quantity controller. SOLUTION: When a laser beam is scanned for an area other than a photoreceptor, charging/discharging a capacitor C1 generates a feedback voltage to bring a luminous quantity of the laser beam output from a laser diode 120 close to a reference luminous quantity. In the case that a voltage change rate of the capacitor C1 per unit time at charging/discharging is smaller than a reference voltage change rate, the capacitor C1 is replaced with a capacitor C2 so as to reduce the current capacitance thereby quickly conducting charging/ discharging.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an automatic light amount control device and an automatic light amount control method suitable for an image forming apparatus for forming an electrostatic latent image on a photosensitive member by scanning a laser beam.

[0002]

2. Description of the Related Art At present, an image forming apparatus such as a printer, a facsimile, a copying machine, etc., which forms an image by using a semiconductor laser, is widely used. Since the light intensity characteristics of a semiconductor laser change sensitively in response to changes in the surrounding temperature, even if the semiconductor laser is driven at a constant current, the amount of emitted light varies greatly due to changes in the surrounding temperature or self-heating. I do.

In order to deal with the temperature dependence of the light emission amount of the semiconductor laser, a photodiode called a photodetector for monitoring the light emission amount of the semiconductor laser is generally incorporated in the package of the semiconductor laser. The light emission amount of the semiconductor laser is monitored by the photodiode, and the drive current of the semiconductor laser is controlled by a signal output from the photodiode, so that the light emission amount of the semiconductor laser is always kept constant. A drive circuit of a semiconductor laser having a feedback mechanism using a photodiode is called an automatic light amount control device.

In an image forming apparatus such as a printer, a facsimile, or a copying machine that forms an image by applying a semiconductor laser, a drive circuit that turns on / off the semiconductor laser in accordance with image data has an irregular laser emission time. Therefore, generally, laser light is emitted outside the image area of the photoconductor for a certain period of time to perform automatic light amount control.

[0005]

However, such conventional automatic light amount control is performed based on the voltage of a capacitor which is charged and discharged within a predetermined time while a laser beam is scanned outside the image area of the photosensitive member. ing. Since the automatic light amount control is performed in a very short time, if the capacitance of the capacitor is not appropriate, it takes time until the voltage value of the capacitor reaches a desired voltage value. If it takes time to charge and discharge the capacitor, the laser beam is scanned on the photoconductor without sufficient automatic light amount control. That is, an electrostatic latent image is formed on the photoconductor without the amount of laser light reaching the desired amount, and there is a problem that an image having an expected density cannot be obtained.

In some cases, the linear velocity is reduced to half, the amount of laser light emitted is reduced to half, and the pixel density is switched to form an electrostatic latent image on the photoreceptor. Switching is performed by the program of the CPU, it is necessary to perform very complicated control.

The present invention has been made in order to solve such a conventional problem. By changing the capacity of a capacitor used for automatic light quantity control in accordance with the state of charge and discharge of the capacitor, It is an object of the present invention to provide an automatic light amount control device and an automatic light amount control method that enable optimal automatic light amount control and can easily switch the pixel density.

[0008]

[MEANS FOR SOLVING THE PROBLEMS] To solve the above-mentioned problems,
In order to achieve the object, an automatic light amount control device according to claim 1 is an automatic light amount control device of an image forming apparatus that scans a laser beam to form an electrostatic latent image on a photosensitive member, A laser diode that outputs laser light, a photodiode that monitors the amount of laser light output from the laser diode, and a capacitor that provides a feedback voltage for bringing the amount of laser light output from the laser diode closer to a reference amount. A feedback voltage generating means for generating, and charging a capacitor of the feedback voltage generating means if the light quantity of the laser light monitored by the photodiode is smaller than a reference light quantity, and charging the feedback if the light quantity of the laser light is larger than the reference light quantity. Capacitor charging / discharging to discharge the capacitor of voltage generation means Means, and the capacitance of the capacitor of the feedback voltage generation means is smaller than the reference voltage fluctuation rate if the voltage fluctuation rate per unit time of the capacitor of the feedback voltage generation means charged and discharged by the capacitor charging / discharging means is smaller than the reference voltage fluctuation rate. And a drive current supply for supplying a drive current for outputting laser light to the laser diode in accordance with the feedback voltage generated by the feedback voltage generation means to the laser diode. Means.

According to the first aspect of the present invention, the feedback voltage generation means generates the feedback voltage for bringing the light amount of the laser light output from the laser diode closer to the reference light amount by the capacitor. The capacitor charging / discharging means charges the capacitor of the feedback voltage generating means if the light amount of the laser light monitored by the photodiode is smaller than the reference light amount, and charges the feedback voltage generating means if the light amount of the laser light is larger than the reference light amount. Discharge the capacitor. Capacitance adjusting means, if the voltage fluctuation rate per unit time of the capacitor of the feedback voltage generation means charged and discharged by the capacitor charging / discharging means is smaller than a reference voltage fluctuation rate, the capacitor of the feedback voltage generation means Is made smaller than the current capacitance. The drive current supply unit supplies a drive current for outputting a laser beam to the laser diode according to the feedback voltage generated by the feedback voltage generation unit.

When the voltage fluctuation rate per unit time of the capacitor of the feedback voltage generating means is smaller than the reference voltage fluctuation rate, since the capacitance of the capacitor is reduced, the voltage value of the capacitor is maintained within a predetermined time. Thus, it is possible to reliably reach the desired voltage value, and it is possible to prevent the photosensitive member from being scanned without sufficient automatic light amount control of the laser beam.

According to a second aspect of the present invention, in the automatic light amount control device according to the first aspect, the feedback voltage generation means includes a plurality of capacitors each having a different capacitance. The capacitance adjustment unit includes a selection unit that selects one of the plurality of capacitors of the feedback voltage generation unit, and the capacitor currently selected by the selection unit is changed to a capacitor having a small capacitance. By switching, the capacitance of the capacitor of the feedback voltage generation means is made smaller than the current capacitance.

According to the second aspect of the present invention, when the rate of voltage change per unit time of the capacitor of the feedback voltage generation means is smaller than a reference voltage change rate, the plurality of capacitors of the feedback voltage generation means are controlled. Of the above, the capacitor currently selected by the selection means is switched to a capacitor having a small capacitance.

When the voltage fluctuation rate per unit time of the capacitor of the feedback voltage generating means is smaller than the reference voltage fluctuation rate, the capacitance of the capacitor is switched by switching the capacitor to a capacitor having a smaller capacitance. Since the voltage of the capacitor is reduced, the voltage value of the capacitor can surely reach a desired voltage value within a certain period of time, and the photosensitive member can be scanned without sufficient automatic light amount control of laser light. Can be prevented.

According to a third aspect of the present invention, in the automatic light amount control device according to the first or second aspect, further, it is detected that the laser beam is scanned on the photosensitive member. And a capacitor charging / discharging unit configured to charge / discharge the feedback voltage generating unit to / from the capacitor when the laser beam detecting unit detects that the laser beam is being scanned on the photoconductor. And stopping the feedback voltage output from the feedback voltage generating means.

According to the third aspect of the present invention, the laser beam detecting means detects that the laser beam is being scanned on the photosensitive member. The capacitor charge / discharge means stops charging / discharging the capacitor of the feedback voltage generation means when the laser light detection means detects that laser light is being scanned on the photoconductor, and the feedback voltage generation means Hold the feedback voltage output from.

Therefore, the feedback voltage output from the feedback voltage generating means is held when the laser beam is being scanned on the photoconductor, that is, when an electrostatic latent image is formed on the photoconductor. . For this reason, the laser beam is scanned on the photoconductor with the light amount after the automatic exposure control.

According to a fourth aspect of the present invention, in the automatic light quantity control device according to any one of the first to third aspects, the capacitor charging / discharging means includes a step of: By switching the resistance value of the resistor according to the pixel density when forming an electrostatic latent image,
A reference light amount switching means for switching a reference light amount of the laser light is provided.

According to the fourth aspect of the present invention, the reference light amount switching means changes the resistance value of the resistor in accordance with the pixel density when the laser light forms an electrostatic latent image on the photosensitive member. By switching, the reference light amount of the laser light is switched.

Therefore, the pixel density can be switched simply by switching the resistance value of the resistor and does not require complicated control by the CPU, so that the pixel density can be easily switched.

An automatic light amount control method according to a fifth aspect of the present invention is an automatic light amount control method for an image forming apparatus for forming an electrostatic latent image on a photosensitive member by scanning a laser beam. A capacitor charging / discharging step of charging a capacitor for generating a feedback voltage for bringing the light amount of the laser light closer to the reference light amount if the light amount is smaller than the reference light amount, and discharging the capacitor if the light amount of the laser light is larger than the reference light amount; If the voltage fluctuation rate per unit time of the capacitor charged / discharged in the capacitor charging / discharging step is smaller than a reference voltage fluctuation rate, the electrostatic capacity of the capacitor is made smaller than the current capacitance. Outputting a laser beam according to a feedback voltage generated in the capacitance adjusting step, the capacitor charging / discharging step, and the capacitance adjusting step. And wherein the driving current of the order that it contained, and driving current supply step of supplying to said laser diode.

According to the fifth aspect of the present invention, in the capacitor charging / discharging step, if the light quantity of the laser light is smaller than the reference light quantity, a capacitor for generating a feedback voltage for bringing the light quantity of the laser light closer to the reference light quantity. And discharges the capacitor when the light amount of the laser light is larger than the reference light amount. In the capacitance adjusting step, if a voltage fluctuation rate per unit time of the capacitor charged and discharged in the capacitor charging / discharging step is smaller than a reference voltage fluctuation rate, the capacitance of the capacitor is changed to a current capacitance. Smaller than In the drive current supply step, a drive current for outputting a laser beam is supplied to the laser diode in accordance with the feedback voltage generated in the capacitor charge / discharge step and the capacitance adjustment step.

When the voltage fluctuation rate per unit time of the capacitor is smaller than the reference voltage fluctuation rate, since the capacitance of the capacitor is reduced, the voltage value of the capacitor can be reliably set within a predetermined time. It is possible to reach the voltage value, and it is possible to prevent the photosensitive member from being scanned without sufficient automatic light amount control of the laser beam.

According to a sixth aspect of the present invention, in the automatic light amount control method according to the fifth aspect, in the capacitance adjusting step, a plurality of capacitors having different capacitances are used. By switching the currently selected capacitor to a capacitor having a smaller capacitance, the capacitance of the capacitor is made smaller than the current capacitance.

According to the present invention, when the voltage fluctuation rate per unit time of the capacitor is smaller than the reference voltage fluctuation rate, the currently selected capacitor is switched to a capacitor having a small capacitance. .

When the voltage fluctuation rate per unit time of the capacitor is smaller than the reference voltage fluctuation rate, the capacitance of the capacitor is reduced by switching the capacitor to a capacitor having a smaller capacitance. The voltage value of the capacitor can surely reach a desired voltage value within a certain period of time, and it is possible to prevent the photosensitive member from being scanned without sufficient automatic control of the amount of laser light.

According to a seventh aspect of the present invention, in the automatic light amount control method according to the fifth or sixth aspect, in the capacitor charging / discharging step, a laser beam is scanned on the photosensitive member. At times, charging and discharging of the capacitor is stopped, and the feedback voltage is held.

According to the seventh aspect of the present invention, the feedback voltage is held when the laser beam is scanned on the photoconductor, that is, when an electrostatic latent image is formed on the photoconductor. Is done. For this reason, the laser beam is scanned on the photoconductor with the light amount after the automatic exposure control.

According to an eighth aspect of the present invention, in the automatic light amount control method according to any one of the fifth to seventh aspects, the reference light amount is such that the laser light is applied to the photosensitive member. The switching is performed by switching the resistance value of the resistor in accordance with the pixel density at the time of forming the electrostatic latent image.

According to the eighth aspect of the invention, the switching of the pixel density only requires switching the resistance value of the resistor, and does not require complicated control by the CPU.
The pixel density can be easily switched.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an automatic light amount control device and an automatic light amount control method according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram of a laser diode (hereinafter, referred to as LD) scanning optical system in which an automatic light amount control device according to the present invention is mounted or an automatic light amount control method according to the present invention is applied. It is.

As shown in FIG. 1, the LD scanning optical system 100
Are LD control plate 110, LD 120, collimating lens 130, polygon scanner 140, fθ lens 150,
A photoconductor 160 and a synchronization detecting element 170 are provided.

The LD control plate 110 is a substrate on which a control circuit for controlling light emission of the LD 120 is formed. The automatic light amount control device according to the present invention is formed in a part of the control circuit. The LD 120 is a diode that outputs a laser, and the amount of light emission and the timing of the light emission are controlled by the control circuit of the LD control plate 110. LD1
20 is directly attached to the LD control plate 110. The collimating lens 130 converts the laser light output from the LD 120 into parallel light.

The polygon scanner 140 scans the parallel light output from the collimating lens 130 by rotating the polygon scanner 140. Polygon scanner 1
Reference numeral 40 is rotated at high speed by a drive motor (not shown). lens 150 is a polygon scanner 14
This lens corrects the curvature of both ends of the scanning surface of the parallel light in order to form the parallel light scanned by 0 on the photoconductor 160 without distortion.

The photoreceptor 160 forms an electrostatic latent image by the parallel light emitted through the fθ lens 150. The synchronization detecting element 170 is disposed outside the image area of the photoconductor 160, and synchronizes the rotation of the polygon scanner 140 and the rotation of the photoconductor 160 from the irradiated parallel light, or the automatic light amount according to the present invention. This is a photo sensor provided to set the control device to a sampling mode or a hold mode. These modes will be described later in detail. When the parallel light applied to the photoconductor 160 departs from the image area and is applied to the synchronization detection element 170, a synchronization detection signal is output from the synchronization detection element 170.

The laser light output from the LD 120 is converted into parallel light by the collimating lens 130, and the converted laser light is scanned by the polygon scanner 140. The scanned parallel light is reflected by the fθ lens 1
Irradiated linearly in the longitudinal direction of the photoconductor 160 via 50, an electrostatic latent image is formed on the photoconductor 160 by the irradiated parallel light. The illuminated parallel light is transmitted to the synchronization detecting element 170.
Is output from the synchronization detection element 170, and the automatic light quantity control device according to the present invention is set to the sampling mode.

FIG. 2 is a schematic configuration diagram of a synchronization detection signal generation circuit for generating a synchronization detection signal when parallel light is detected by the synchronization detection element 170. The synchronization detection signal generation circuit 200 includes a synchronization detection element 170, a resistor R
1 and a comparator 210.

The synchronization detecting element 170 is turned on when parallel light is received, and connects the resistor R1 to a power supply. Resistor R
1 applies the same voltage as the voltage of the power supply to the comparator 210 when connected to the power supply. Comparator 210
Compares the voltage VR1 applied by the resistor R1 with the reference voltage Vref, and determines whether the voltage VR1 is equal to the reference voltage Vref.
If it is larger than the threshold value, an "L" synchronization detection signal XDETP is output. Therefore, the "L" synchronization detection signal XDET
P is output when the parallel light is received by the synchronization detecting element 170.

The synchronization detection signal XDETP is transmitted to a later-described CP.
U, the CPU detects the synchronization detection signal XDET
An S / H signal is output based on P. When the “L” synchronization detection signal XDETP is input to the CPU, the CPU outputs an “L” S / H signal. Conversely, when the “H” synchronization detection signal XDETP is input to the CPU, the CPU outputs an “H” S / H signal.

The automatic light amount control device according to the present invention comprises a CP
When the S / H signal of “L” is output from U, that is, when parallel light is received by the synchronization detecting element 170, the sampling mode is set, and the S / H signal of “H” is output from the CPU.
/ H signal is output, that is, the synchronization detecting element 17
0 when no parallel light is received (photosensitive member 16
When parallel light is irradiated to 0), the hold mode is set.

For example, as shown in FIG. 3, assuming that the scanning period for one line is T2 seconds and the light receiving time of the parallel light by the synchronization detecting element 170 is T1 seconds, every 1 second T2 seconds. The "L" synchronization detection signal XDETP having a time width of "L" is output once, and the "L" S / H signal is output from the CPU. Further, during the remaining time of T2 seconds−T1 seconds, the “H” synchronization detection signal XDETP is output, and the “H” S / H signal is output from the CPU. Therefore, the automatic light quantity control device according to the present invention is set in the sampling mode for a time of T1 second every T2 seconds, and is set in the hold mode for a time of T2 seconds−T1 seconds.

FIG. 4 is a block diagram showing a schematic configuration of an automatic light amount control device according to the present invention. The automatic light amount control device 400 includes an LD 120, a photodetector (hereinafter, referred to as a PD) 410, and light emitting amount setting variable resistors 420 and 43.
0, a light emission amount setting switch 440, a reference voltage setting switch 450, and a comparator 460.

The PD 410 is a photodiode for monitoring the amount of laser light output from the LD 120, and has a monitor current I according to the amount of light emitted from the LD 120.
generate m. Variable resistors 420 and 430 for setting the light emission amount
Is a variable resistor for adjusting the amount of laser light output from the LD 120, and the variable resistor 4 for setting the light emission amount.
20 and the variable resistor 430 for setting the light emission amount have different set resistance values.

For example, to switch the pixel density,
In the case of adopting a method in which the linear velocity is reduced to half and the light emission amount of the LD 120 is reduced to half, the value of the set resistance value VR1 of the light emission amount setting variable resistor 420 is changed to the light emission amount setting variable resistor. Is set to 1/2 of the value of the set resistance value VR2 of the detector 430. With this setting, the required pixel density can be switched by switching the light emission amount setting switch 440.

The light emission amount setting switch 440 is connected to the PD 41
0 and the connection between the light emission amount setting variable resistor 420 or P
These switches are used to switch the connection between the D410 and the light emission amount setting variable resistor 430, respectively. The light emission amount setting switch 440 is switched by an I-output from the CPU.
This is performed by the N1 signal. Light emission amount setting switch 44
0 connects the PD 410 to the light emission amount setting variable resistor 420 when the IN1 signal is “L”, and connects the PD 410 and the light emission amount setting variable resistor 4 when the IN1 signal is “H”.
30 is connected.

For example, the variable resistor 420 for setting the light emission amount
Of the light emitting amount setting variable resistor 43
In the case where the resistance value of the LD 120 is set to twice the value of the set resistance value VR2 of 0 and the light emission amount of the LD 120 at the pixel density of 1200 dpi is reduced to half of that at the pixel density of 600 dpi, the IN1 signal is set to “H”. To connect the PD 410 and the light emitting amount setting variable resistor 430. This allows LD
The light emission amount of the light emitting unit 120 can be reduced to １ ／ of that when the light emission amount setting variable resistor 420 is connected.

The reference voltage setting switch 450 changes the voltage value of the reference voltage V1 applied to the comparator 460 to Vre.
Switch to either f1 or Vref2. Switching of the reference voltage setting switch 450 is performed by an IN2 signal output from the CPU. The reference voltage setting switch 450 applies Vref2 to the comparator 460 as the voltage value of the reference voltage V1 when the IN2 signal is “L”, and applies the comparator 46 when the IN2 signal is “H”.
Vref1 is applied to 0 as the voltage value of the reference voltage V1. As described above, the reference light amount of the LD 120 can also be switched by switching the voltage value of the reference voltage V1 applied to the comparator 460.

For example, voltage value Vref of reference voltage V1
1 is set to 1/2 of Vref2,
As described above, LD1 at a pixel density of 1200 dpi
In order to reduce the light emission amount of the pixel 20 to half of the pixel density of 600 dpi, the IN2 signal is set to “H” and the comparator 4
60 is applied with Vref1 as the voltage value of the reference voltage V1. As a result, the amount of light emitted from the LD 120 can be reduced to half that when Vref2 is applied.

The comparator 460 receives the reference voltage V applied by switching the reference voltage setting switch 450.
1 is compared with a monitor voltage V2 generated from a monitor current Im corresponding to the light emission amount of the LD 120. Comparator 4
60 outputs an "H" output voltage V3 if the monitor voltage V2 is smaller than the reference voltage V1. When the monitor voltage V2 is higher than the reference voltage V1, the comparator 460 outputs an output voltage V3 of "L".

The light emission amount setting switch 440 sets the PD
410 and the light emitting amount setting variable resistor 420 are connected,
Assuming that the resistance value of the light emitting amount setting variable resistor 420 is set to VR1, if a monitor current of Im1 amp is output from the PD 410, a voltage of Im1 × VR1 volts is output to the comparator 460 as the monitor voltage V2. Applied. The light emitting amount setting switch 440 connects the PD 410 to the light emitting amount setting variable resistor 430, and the resistance value of the light emitting amount setting variable resistor 430 is VR2.
If the monitor current of Im2 amp is output from the PD 410, the comparator 46
A voltage of Im2 × VR2 volts is applied to 0 as the monitor voltage V2. Further, the comparator 460 sets the reference voltage V1 as Vref1 or Vref2 selected by switching the reference voltage setting switch 450.
Is applied.

The comparator 460 compares the reference voltage V1 with the monitor voltage V2, and compares the monitor voltage V2 with the reference voltage V2.
If it is smaller than 1, the output voltage V3 of "H" is output. That is, if the comparator 460 determines that the light emission amount of the LD 120 is smaller than the reference light amount (the LD 120 is darker than the reference light amount), the comparator 460 outputs the “H” output voltage V3. When the monitor voltage V2 is higher than the reference voltage V1, the comparator 460 outputs an output voltage V3 of "L". That is, the comparator 460 controls the LD 120
Is determined to be larger than the reference light amount (the LD 120 is brighter than the reference light amount), the “L” output voltage V3
Is output.

The automatic light amount control device 400 further includes a control circuit 470, a constant current source 480 for charging, a constant current source 490 for discharging, capacitors C1 and C2, and a switch 5
00, 510, and a capacitor changeover switch 520.

The control circuit 470 switches between the sampling mode and the hold mode according to the S / H signal. As described above, this S / H signal is output by the CPU based on the synchronization detection signal XDETP output from the comparator 210 in FIG. The CPU detects the synchronization detection signal X
When DETP is “H” (parallel light is the photoconductor 160 in FIG. 1)
During scanning, the S / H signal of “H” is output to set the control circuit 470 to the hold mode.
On the other hand, when the synchronization detection signal XDETP is “L” (when parallel light is received by the synchronization detection element 170), the CPU outputs the S / H signal of “L” and sets the control circuit 470 to the sampled mode. Set to.

When control circuit 470 is set to the sampling mode, control circuit 4
When the output voltage V3 is “H”, only the changeover switch 500 is turned on (closed) and the charging constant current source
0 and the capacitor switch 520 are connected. The control circuit 470 determines that the output voltage V3 is “L”.
At this time, only the changeover switch 510 is turned on to connect the discharging constant current source 490 and the capacitor changeover switch 520.

When control circuit 470 is set to the hold mode, control circuit 470
Turns off (opens) both the changeover switches 500 and 510 regardless of whether the output voltage V3 is "H" or "L".

The charging constant current source 480 includes a capacitor C1
Or supply a constant current to C2 to provide a capacitor C1 or C2.
2 is a power source for charging 2. Discharge constant current source 490
Is a power supply for discharging a constant current from the capacitor C1 or C2 to discharge the capacitor C1 or C2. The capacitor switch 520 is connected to the capacitor C1
Or a switch for selecting C2. Switching of the capacitor changeover switch 520 is performed by the IN3 signal output from the CPU. The capacitor changeover switch 520 connects the capacitor C1 when the IN3 signal is “L”, and connects the capacitor C2 when the IN3 signal is “H”.

The capacitance of the capacitor C1 is
If the capacitance is larger than the capacitance of the capacitor C2, charging and discharging can be performed more quickly when the capacitor is connected to the capacitor C2 than when the capacitor is connected to the capacitor C1. However, discharge of the capacitor in the hold mode is smaller when the capacitor is connected to the capacitor C1 having a large capacitance than when the capacitor is connected to the capacitor C2. Therefore, in the present invention, the capacitor is connected to a capacitor having a large capacitance as much as possible, and is connected to a capacitor having a small capacitance in a special case where automatic light amount control cannot be performed in time.

The automatic light quantity control device 400 further includes A /
It includes a D converter 530, an error amplifier 540, a transistor 550, a resistor 560, a bias current source 570, and a resistor 580.

The A / D converter 530 includes a capacitor C
1 or the feedback voltage V formed by C2
4 is converted into a digital value and output to the CPU.
Error amplifier 540 applies an error voltage obtained by amplifying a difference voltage between the voltage value of reference voltage Vref3 and the voltage value of feedback voltage V4 to the base of transistor 550. The transistor 550 allows the collector current Ic to flow to the LD 120 via the resistor 560 according to the magnitude of the error voltage output from the error amplifier 540. The bias current source 570 supplies a bias current Ib to the LD 120.
The value of the bias current Ib can be changed according to the resistance value of the resistor 580. The modulation speed of the LD 120 can be increased by flowing a bias current.

Therefore, a current obtained by adding the bias current Ib determined by the resistance value of the resistor 580 and the collector current Ic determined by the error voltage is supplied to the LD 120, and the LD 120 outputs the bias current Ib and the collector current Ic.
Light emission is performed at a current value equal to the sum of c and c. When the voltage value of the error voltage changes, the current flowing through the LD 120 also changes, and the light emission amount of the LD 120 changes.

The automatic light amount control device 400 increases the supply current of the LD 120 when the light emission amount of the LD 120 is smaller than the reference light amount, and decreases the supply current of the LD 120 when the light emission amount of the LD 120 is larger than the reference light amount.
Automatic control is performed so that the light emission amount of the LD 120 becomes the reference light amount.

The error amplifier 540 receives the video data XDATA from the CPU and outputs the video data XDAT.
Only when A is "L", the error voltage is
Is applied. That is, when XDATA is "L", L
A current obtained by adding the bias current Ib and the collector current Ic is supplied to D120, and the LD120 emits light with the current. On the other hand, when the video data XDATA is “H”, only the bias current Ib is supplied to the LD 120 and the LD 1
20 emits offset light (no electrostatic latent image is formed on the photoconductor 160).

FIG. 5 is a block diagram showing a schematic configuration of CPU 600. The CPU 600 includes a storage unit 610, a timer 620, a calculation unit 630, and a signal output unit 640. Storage unit 610 stores feedback voltage V4 output from A / D converter 530 shown in FIG. The storage unit 610 stores the capacitor C1 or C2
Voltage Vs for comparing the charging or discharging speed of the battery
Is stored in advance. The timer 620 outputs a sample signal to the storage unit 610 at regular time intervals, and A / D
The current feedback voltage V4a output from the converter 530 and the immediately preceding feedback voltage V4b are updated and stored in the storage unit 610.

The operation section 630 extracts the current feedback voltage V4a and the immediately preceding feedback voltage V4b stored in the storage section 610 and obtains the difference V4b-V between the two voltages.
4a, and further obtains the set voltage Vs stored in the storage unit 610 and obtains the difference V4b-V4a between the two voltages.
And the set voltage Vs. The difference between the two voltages V4b-V4
If “a” is smaller than the set voltage Vs, the response speed switching signal of “H” is output, and if the difference V4b−V4a between the two voltages is larger than the set voltage Vs, the response speed switch signal of “L” is output.

The signal output unit 640 includes a synchronization detection signal XDETP output from the comparator 210 in FIG. 2, a pixel density switching signal output from a not-shown pixel, a light emission amount switching signal for switching the light emission amount of the LD, and an arithmetic unit 630. Input the response speed switching signal output from the S / H signal, IN
1 signal, IN2 signal, IN3 signal, video data XDA
Output TA.

The signal output section 640 outputs an “L” S / H signal when the “L” synchronization detection signal XDETP is input, and outputs “S” when the “H” synchronization detection signal XDETP is input. H ”is output. In addition, the signal output unit 640 outputs the “L” IN1 signal when the “L” pixel density switching signal is input from the pixel density switching switch to switch the pixel density, and outputs the “H” pixel density switching signal. , The "H" IN1 signal is output. Further, the signal output unit 640 outputs the “L” IN2 signal when the “L” light emission amount switching signal for switching the light emission amount of the LD 120 is input, and receives the “H” light emission amount switching signal. If so, an IN2 signal of "H" is output. Further, the signal output unit 640 outputs the “L” IN3 signal when the “L” response speed switching signal is output from the arithmetic unit 630, and outputs the “H” response speed switching signal when the “H” response speed switching signal is output. An "H" IN3 signal is output. And
If there is no video data for exposing the photoconductor 160 of FIG. 1 to the signal output unit 640, the video data X of “L” is output.
DATA is output, and if there is video data, "H" video data XDATA is output.

Next, the operation of the automatic light quantity control device 400 according to the present invention will be described with reference to the flowchart shown in FIG. First, the CPU 600 inputs to the signal output unit 640 whether the “H” synchronization detection signal XDETP or the “L” synchronization detection signal XDETP is output from the comparator 210 in FIG. The determination is made based on the signal (S610).

If the synchronization detection signal XDETP of “H” is output from the comparator 210 (while the parallel light scans the photoconductor 160 in FIG. 1), the CPU 600 controls the control circuit via the signal output unit 640. "H" to 470
Is output (S620). "H" S / H
The control circuit 470 to which the signal is input is set to the hold mode to hold the feedback voltage. When the hold mode is set, the control circuit 470 turns off (opens) both the changeover switches 500 and 510 (S630).

The current voltage of the capacitor (C1 in FIG. 4) connected by the capacitor switch 520 is applied to the error amplifier 540 as a feedback voltage V4. The error amplifier 540 amplifies the difference voltage between the voltage value of the reference voltage Vref3 and the voltage value of the feedback voltage V4 and applies the amplified voltage to the base of the transistor 550 (S6).
40).

The transistor 550 supplies the collector current Ic to the LD 120 via the resistor 560 according to the magnitude of the amplified difference voltage.
Supplies a bias current Ib to the LD 120. LD1
20 emits light with the current value of the sum of the bias current Ib and the collector current Ic (S650).

When the laser beam scans the photosensitive member, the laser beam is emitted based on the held feedback voltage V4 as described above. The discharge of the capacitor in the hold mode is smaller for a capacitor having a larger capacitance, and the voltage fluctuation of the feedback voltage V4 is smaller. Therefore, when the capacitance of the capacitor is large, the voltage of the feedback voltage V4 does not change for a long time. Considering that an image is formed with as uniform a density as possible, it is advantageous that the capacitance of the capacitor is large. However, if the capacitance of the capacitor is large, appropriate automatic light amount control may not be performed. In the present invention, the following processing is further performed to perform appropriate automatic light amount control.

If the comparator 210 outputs the “L” synchronization detection signal XDETP (the synchronization detection element 17
0 when parallel light is received).
Is connected to the control circuit 470 via the signal output unit 640.
Then, an S / H signal of "L" is output (S660). "L"
The control circuit 470 to which the S / H signal is input is set to the sampling mode in order to generate an appropriate feedback voltage in preparation for the next scan on the photoconductor.

When the sampling mode is set, the control circuit 470 turns on (closes) only the changeover switch 500 when the output voltage V3 is “H”, and sets the constant current source 480 for charge and the capacitor changeover switch 520 Connect. When the output voltage V3 is “L”, the control circuit 470 turns on only the changeover switch 510 to connect the discharge constant current source 490 and the capacitor changeover switch 520. Both the changeover switches 500 and 510 are turned off (open) (S670).

Hereinafter, the control of the step S670 will be specifically described. The comparator 460 compares the reference voltage V1 with the monitor voltage V2, and outputs an “H” output voltage V3 if the monitor voltage V2 is smaller than the reference voltage V1. That is, if the light emission amount of the LD 120 is smaller than the reference light amount (the LD 120 is darker than the reference light amount), the comparator 460 outputs the output voltage V3 of “H”.

The control circuit 470 connects only the changeover switch 500 to connect the constant current source 480 for charging and the capacitor changeover switch 520 in order to bring the light emission amount of the LD 120 closer to the reference light amount. Capacitor changeover switch 5
Since the capacitor 20 selects the capacitor C1, a constant current is supplied from the charging constant current source 480 to the selected capacitor C1. Therefore, the feedback voltage V
4 increases in accordance with the capacitance of the capacitor C1.

On the other hand, if the monitor voltage V2 is higher than the reference voltage V1, the comparator 460 outputs an "L" output voltage V3. That is, the comparator 460 sets L
If the light emission amount of D120 is larger than the reference value (LD12
0 is brighter than the set light amount), and outputs an output voltage V3 of “L”.

The control circuit 470 turns on only the changeover switch 510 to connect the discharge constant current source 490 and the capacitor changeover switch 520 in order to bring the light emission amount of the LD 120 closer to the reference light amount. Capacitor changeover switch 5
Since the capacitor 20 has selected the capacitor C1, the constant current is discharged from the selected capacitor C1 to the constant current source 480 for discharge. Therefore, the voltage of the feedback voltage V4 decreases according to the capacitance of the capacitor C1.

As described above, the key to ensuring that the LD 120 can always emit light with the reference light amount is how quickly the feedback voltage V4 finally used for error amplification is increased or decreased. Since the feedback voltage V4 is generated by the capacitor C1 or C2, if the value of the capacitor C1 or C2 is large, the rising speed and the falling speed of the feedback voltage V4 become slow, and as a result, the light emission amount of the LD 120 always becomes the reference light amount. It becomes difficult to maintain.

For example, if the light emission amount of the LD 120 is smaller than the reference light amount, the capacitor C1 or C2 is charged. However, if the value of the capacitor C1 or C2 is large, it takes a long time to charge the capacitor C1 or C2. The voltage value does not rise easily, and the light emission amount of the LD 120 does not increase to an appropriate light emission amount. Conversely, LD12
If the light emission amount of 0 is larger than the set light amount, the capacitor C1
Alternatively, the discharge of C2 is performed. If the value of the capacitor C1 or C2 is large, the discharge takes a long time, the voltage value of the feedback voltage V4 does not readily decrease, and the light emission amount of the LD 120 reaches the appropriate light emission amount. Does not decrease.

In the automatic light quantity control device 400 of the present invention, in order to prevent such a problem from occurring, the voltage value of the feedback voltage V4 is converted into a digital value by the A / D converter 530, and the digital value is output to the CPU 600. Looking at the voltage fluctuation rate of the voltage V4, the capacitor C1 or C2
Is switching.

The CPU 600 has an A / D converter 530
The current feedback voltage V4 output from the A / D converter 530 is input after the voltage value of the current feedback voltage V4 output from the A / D converter 530 is checked after a predetermined time is checked by the timer 620 in the CPU 600 after the input. Is input as V4b.

CPU 600 calculates V4b-V4a and determines whether or not the voltage value has reached a preset set voltage value. That is, the CPU 60
0 determines whether the voltage rise value or the voltage fall value is equal to or greater than a preset value as the voltage fluctuation rate per unit time (S680).

CPU 600 determines IN based on this determination.
The three signals are output to the capacitor switch 520 to switch the connected capacitor (S690). The switching operation of the capacitor by the capacitor changeover switch 520 will be described in detail separately for a case where the capacitor is charged and a case where the capacitor is discharged.

When the capacitor is charged When the capacitor is charged by the charging constant current source 480 and the capacitor selected by the capacitor changeover switch 520 is C1, the voltage of V4b-V4a that increases by charging If the value has not reached the preset voltage value, the CPU 6
00 outputs the “H” IN3 signal to the capacitor switch 520 via the signal output unit 640. The capacitor changeover switch 520 switches the connected capacitor from the capacitor C1 having a large capacitance to the capacitor C2 having a small capacitance.

Since the switching is switched from the capacitor C1 having a large capacitance to the capacitor C2 having a small capacitance by this switching, the voltage rise value per unit time of the current feedback voltage V4 is increased, and the feedback voltage V4 is set earlier than the set voltage. Value can be reached. As described above, when the voltage value of V4b-V4a does not reach the preset voltage value, connecting to a capacitor having a small capacity requires a long time to charge the capacitor if the capacity of the capacitor is too large. This is because the light emission amount of the LD 120 cannot maintain an appropriate light emission amount.

When the capacitor is discharged When the capacitor is discharged by the discharging constant current source 490 and the capacitor selected by the capacitor changeover switch 520 is C1, the voltage of V4b-V4a falling by the discharge is assumed. If the value has not reached the preset voltage value, the CPU 6
00 outputs the “H” IN3 signal to the capacitor switch 520 via the signal output unit 640. The capacitor changeover switch 520 switches the connected capacitor from C1 to C
Switch to 2.

As the switching is switched from the large-capacitance capacitor C1 to the small-capacity capacitor C2, the voltage drop value of the current feedback voltage V4 per unit time increases, and the feedback voltage V4 reaches the set voltage value earlier. Will be able to
As described above, when the voltage value of V4b-V4a does not reach the preset voltage value, connecting to a capacitor having a small capacity requires a long time to discharge the capacitor if the capacity of the capacitor is too large. This is because the light emission amount of the LD 120 cannot maintain an appropriate light emission amount.

As described above, in the automatic light amount control device 400 according to the present invention, when the photosensitive member 160 is scanned with the laser beam, the LD 120 is caused to emit light by the held feedback voltage, and When a laser beam is scanned over the deviated region, the capacitance of the capacitor for generating the feedback voltage is switched as needed in order to quickly obtain an appropriate feedback voltage. Normally, the capacitance of the capacitor is increased. This is because if the capacitance is increased, it is possible to prevent the held feedback voltage from decreasing in a short time. Then, the connection is switched to a capacitor having a small capacitance only in a special case where the automatic light quantity control cannot keep up.

FIG. 7 is a flowchart showing the operation of the CPU 600 when the pixel density is switched by the automatic light amount control device 400 according to the present invention. When a pixel density switch (not shown) is turned on, a pixel density switch signal is input to the signal output unit 640 of the CPU 600. When the pixel density switching signal is input (S710), the signal output unit 6
Reference numeral 40 denotes an output of the IN1 signal to the light emission amount setting switch 440 to connect the PD 410 to the light emission amount setting variable resistor 420, or to connect the PD 410 and the light emission amount setting variable resistor 430.
The connection with each is switched (S720).

For example, the variable resistor 420 for setting the light emission amount
Is set for the pixel density of 1200 dpi, and the set resistance value V of the light emission amount setting variable resistor 430 is set.
This is a case where the value of R2 is set for a pixel density of 600 dpi.
When a pixel density switching signal for switching to dpi is input to the signal output unit 640, the signal output unit 640 outputs an IN1 signal of “H” to the light emission amount setting switch 440, and the PD 410 and the light emission amount setting variable. The resistor 430 is connected. As a result, the amount of light emitted from the LD 120 can be reduced to half that when the variable resistor 420 for setting the amount of light is connected.

As described above, in the automatic light amount control device 400 according to the present invention, the pixel density can be easily switched by switching to the light emitting amount setting variable resistor having a different resistance value. Note that the pixel density can be switched by switching the reference voltage setting switch 450. When switching the reference voltage setting switch 450, the signal output unit 640 outputs an IN2 signal to the light emission amount setting switch 440.

[0092]

As described above, according to the first aspect of the present invention, when the voltage fluctuation rate per unit time of the capacitor of the feedback voltage generation means is smaller than the reference voltage fluctuation rate, Because the capacitance is small, the voltage value of the capacitor can reach the desired voltage value within a certain period of time, and the photosensitive member is scanned without sufficient automatic light intensity control of the laser beam. Can be prevented. As a result, there is an effect that a high-quality image can always be obtained.

According to the second aspect of the present invention, when the voltage fluctuation rate per unit time of the capacitor of the feedback voltage generation means is smaller than the reference voltage fluctuation rate, the capacitor is replaced with a capacitor having a smaller capacitance. By switching, the capacitance of the capacitor is reduced, so that the voltage value of the capacitor can surely reach a desired voltage value within a certain period of time, and the automatic light amount control of the laser beam is sufficiently performed. It is possible to prevent the photosensitive member from being scanned without being scanned. As a result, there is an effect that a high-quality image can always be obtained.

According to the third aspect of the present invention, the feedback voltage output from the feedback voltage generating means is such that when the laser beam is scanned on the photosensitive member,
That is, since the laser beam is held when the electrostatic latent image is formed on the photoconductor, the laser beam can scan the photoconductor with the light amount after the automatic exposure control. As a result, there is an effect that a high-quality image with little density fluctuation can be obtained.

According to the fourth aspect of the present invention, the reference light amount switching means switches the resistance value of the resistor according to the pixel density when the laser light forms an electrostatic latent image on the photosensitive member. Thus, since the reference light amount of the laser beam is switched, the switching of the pixel density need only be performed by switching the resistance value of the resistor, and complicated control by the CPU is not required, so that the switching of the pixel density becomes easy. As a result, there is an effect that a high quality image can be obtained.

According to the fifth aspect of the present invention, when the voltage fluctuation rate per unit time of the capacitor is smaller than the reference voltage fluctuation rate, the capacitance of the capacitor is reduced. The voltage value can surely reach a desired voltage value within a certain period of time, and it is possible to prevent the photosensitive member from being scanned without sufficient automatic light amount control of the laser beam. As a result, there is an effect that a high-quality image can always be obtained.

According to the invention described in claim 6, when the voltage fluctuation rate per unit time of the capacitor is smaller than the reference voltage fluctuation rate, the capacitor is switched to a capacitor having a smaller capacitance, whereby Since the capacitance of the capacitor is reduced, the voltage value of the capacitor can surely reach a desired voltage value within a certain period of time, and the photoconductor is not sufficiently controlled while the automatic light amount control of the laser beam is not sufficiently performed. Scanning can be prevented. As a result, there is an effect that a high-quality image can always be obtained.

According to the seventh aspect of the present invention, the feedback voltage is held when the laser beam is scanned on the photoconductor, that is, when an electrostatic latent image is formed on the photoconductor. Therefore, the laser beam can scan the photosensitive member with the light amount after the automatic exposure control.
As a result, there is an effect that a high-quality image with little density fluctuation can be obtained.

According to the eighth aspect of the present invention, the switching of the pixel density only requires switching the resistance value of the resistor, and does not require complicated control by the CPU. Therefore, the switching of the pixel density is easily performed. be able to. As a result, there is an effect that a high quality image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a laser diode scanning optical system in which an automatic light amount control device according to the present invention is mounted or an automatic light amount control method according to the present invention is applied.

FIG. 2 is a schematic configuration diagram of a synchronization detection signal generation circuit for generating a synchronization detection signal when parallel light is detected by a synchronization detection element.

FIG. 3 is a waveform diagram of a synchronization detection signal XDETP used in the automatic light quantity control device according to the present invention.

FIG. 4 is a block diagram showing a schematic configuration of an automatic light amount control device according to the present invention.

FIG. 5 is a block diagram illustrating a schematic configuration of a CPU.

FIG. 6 is a flowchart showing the operation of the automatic light amount control device according to the present invention.

FIG. 7 is a flowchart showing the operation of the automatic light quantity control device according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 LD scanning optical system 110 LD control plate 120 Laser diode 130 Collimating lens 140 Polygon scanner 150 fθ lens 160 Photoconductor 170 Synchronous detection element 200 Synchronous detection signal generation circuit 210 Comparator 400 Automatic light amount control device 410 Photodetector 420 Variable light emission amount setting resistor Unit 430 Variable resistor for setting light emission amount 440 Switch for setting light emission 450 Switch for setting reference voltage 460 Comparator 470 Control circuit 480 Constant current source for charging 490 Constant current source for discharging 500 Changeover switch 510 Changeover switch 520 Capacitor changeover switch 530 A / D converter 540 Error amplifier 550 Transistor 560 Resistor 570 Bias current source 580 Resistor 600 CPU 610 Storage unit 620 Thailand Over 630 arithmetic unit 640 signal output unit

Claims (8)

[Claims] 1. An automatic light amount control device of an image forming apparatus for forming an electrostatic latent image on a photosensitive member by scanning a laser beam, comprising: a laser diode for outputting the laser beam; and an output from the laser diode. A photodiode that monitors the amount of laser light; feedback voltage generation means that generates a feedback voltage for bringing the amount of laser light output from the laser diode closer to a reference amount by a capacitor; and a laser that is monitored by the photodiode. A capacitor charging / discharging means for charging the capacitor of the feedback voltage generating means if the light quantity of light is smaller than the reference light quantity, and discharging the capacitor of the feedback voltage generating means if the light quantity of the laser light is larger than the reference light quantity; Charged and discharged by charging and discharging means It is smaller than the voltage variation rate of the feedback voltage voltage regulation reference per unit time of the capacitor of the generator,
Capacitance adjusting means for reducing the capacitance of the capacitor of the feedback voltage generating means to be smaller than the current capacitance; and driving for outputting a laser beam according to the feedback voltage generated by the feedback voltage generating means. An automatic light amount control device comprising: a drive current supply unit that supplies a current to the laser diode. 2. The feedback voltage generation means includes a plurality of capacitors having different capacitances, and the capacitance adjustment means selects one of the plurality of capacitors of the feedback voltage generation means. Selecting means for selecting, and switching the capacitor currently selected by the selecting means to a capacitor having a small capacitance so as to make the capacitance of the capacitor of the feedback voltage generating means smaller than the current capacitance. The automatic light amount control device according to claim 1, wherein: 3. The apparatus according to claim 1, further comprising: a laser beam detecting unit configured to detect that the laser beam is being scanned on the photoconductor. 3. The method according to claim 1, wherein when the scanning is detected, charging and discharging of the feedback voltage generating means to the capacitor are stopped, and the feedback voltage output from the feedback voltage generating means is held. 3. The automatic light amount control device according to 1. 4. The method according to claim 1, wherein the capacitor charge / discharge unit switches a resistance value of a resistor in accordance with a pixel density when the laser light forms an electrostatic latent image on the photoconductor, thereby setting a reference value of the laser light. The automatic light amount control device according to any one of claims 1 to 3, further comprising a reference light amount switching unit that switches a light amount. 5. An automatic light amount control method for an image forming apparatus for forming an electrostatic latent image on a photosensitive member by scanning a laser light, wherein the light amount of the laser light is reduced if the light amount of the laser light is smaller than a reference light amount. A capacitor charging / discharging step of charging a capacitor for generating a feedback voltage for approaching the reference light amount and discharging the capacitor if the light amount of the laser beam is larger than the reference light amount, and the capacitor charged and discharged in the capacitor charging / discharging step If the voltage fluctuation rate per unit time is smaller than a reference voltage fluctuation rate, a capacitance adjusting step of making the capacitance of the capacitor smaller than a current capacitance; Supplying a drive current for outputting a laser beam to the laser diode according to the feedback voltage generated in the capacitance adjustment step An automatic light amount control method, comprising: a driving current supply step. 6. In the capacitance adjusting step, among the plurality of capacitors having different capacitances, the currently selected capacitor is switched to a capacitor having a smaller capacitance to thereby reduce the capacitance of the capacitor. 6. The automatic light amount control method according to claim 5, wherein the capacitance is set to be smaller than the capacitance. 7. In the capacitor charging / discharging step, when a laser beam is being scanned on the photoconductor, charging / discharging of the capacitor generating the feedback voltage is stopped.
7. The automatic light amount control method according to claim 5, wherein the feedback voltage is held. 8. The method according to claim 1, wherein the reference light quantity is switched by switching a resistance value of a resistor according to a pixel density when the laser light forms an electrostatic latent image on the photoconductor. 8. The automatic light amount control method according to any one of 5 to 7.