JP3384211B2 - Light control device for semiconductor laser - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light quantity control device for controlling a light quantity of a semiconductor laser, which is provided in a laser printer for a copying machine, a facsimile machine or the like.

[0002]

2. Description of the Related Art Conventionally, electrophotographic laser printers using semiconductor laser diodes have been widely used in copying machines, facsimile machines and the like. In these laser printers, it is possible to appropriately control the light quantity of the semiconductor laser. is necessary. In recent digital copiers and the like, automatic light amount control (hereinafter referred to as APC (Automatic Power Control)) processing is performed in real time in order to print with multiple gradations, but the circuit becomes large and complicated, and There is a problem that the control method becomes complicated and the manufacturing cost becomes high.

In order to solve this problem, in a low-cost laser printer, just before the page to be printed,
APC processing is executed between pages, such as outside the image area during image writing on the photosensitive drum. As shown in FIG. 3, the mirror scannable area MS of the polygon mirror
Of the above, the portion excluding the image region IR is the APC possible region, and the APC process can be executed outside the image region during image writing on the photosensitive drum. For example,
With only APC processing before the page or between pages, when the amount of light emitted from the semiconductor laser diode changes due to fluctuations in the power supply voltage during image writing on the photoconductor drum, that portion appears as uneven print density, so the image APC outside the area
You need to perform some processing.

FIG. 12 is a flowchart showing APC processing outside the image area in the conventional laser printer.
In the process, first, the light amount control value DA (corresponding to the constant current value supplied to the semiconductor laser) DA set in the immediately preceding line in step # 81 is set as the light amount control value DAA of the line, and then step # 82. To turn on the laser diode to emit light. Then, after detecting the light quantity of the laser diode, the comparison means composed of an operational amplifier compares it with a predetermined threshold light quantity to obtain a comparison signal CO indicating whether the light quantity is equal to or more than the threshold light quantity. Here, when the detected light amount is equal to or more than the threshold light amount, the comparison signal CO becomes H level, while when the detected light amount is less than the threshold light amount,
The comparison signal CO becomes L level. By the operation of this operational amplifier, it is possible to obtain the comparison signal CO after 20 microseconds have passed from step # 82. In step # 83, it is judged whether or not the comparison signal CO is at L level,
If it is the level, in step # 86, the light amount control value DA
Is incremented by 1 and after waiting 20 microseconds for the operating time of the operational amplifier, it is determined in step # 87 whether the comparison signal CO is at the L level. In FIG. 12, "waiting time 20 microseconds" between steps means that the CPU of the copying machine waits for 20 microseconds between those steps. Then, the processes of steps # 86 and # 87 are repeated until the comparison signal CO becomes H level. Here, a waiting time of 20 microseconds is required every time the light amount control value DA is incremented. When the comparison signal CO becomes H level in step # 87, the light amount control value DA is decremented by 1 in step # 88, the processing is ended, and the process returns to the main routine. On the other hand, when the comparison signal CO is at H level in step # 83,
In steps # 84 and # 85, the above steps # 86,
The reverse process of # 87 is executed.

[0005]

As described above, FIG.
In the processing of the conventional example, the laser diode is turned on with the light amount control value DA of the previous line, and then the line is compared with a predetermined threshold value (target value). , The light quantity control value DA is incremented or decremented each time, and the light quantity control value DA is set until the comparison signal CO switches from the H level to the L level or from the L level to the H level.
The control process of is repeated. With such a method, the target light intensity of the laser diode can be set accurately, but since the above-described control processing is repeatedly executed, a waiting time of 20 microseconds occurs many times, and the APC processing is performed. There is a problem that it takes time.
As a result, the number of pages printed per minute [ppm], which represents the printing speed of the printer, could not be increased.

Further, if the waiting time of the CPU is not inserted or the waiting time is shortened, it is not possible to obtain the correct light quantity of the laser diode based on the light quantity control amount DA, and for example, overexposure or exposure is performed. There is a problem that the print density becomes short and the print density becomes uneven.

An object of the present invention is to solve the above problems, overexposure and underexposure are without arise in a short time as compared with the conventional example, to set the amount of some accuracy semiconductor laser An object of the present invention is to provide a light quantity control device for a semiconductor laser.

[0008]

A light quantity control device for a semiconductor laser according to claim 1 of the present invention is a laser for a photosensitive member.
Equipped with a semiconductor laser for irradiation, 1 in the main scanning direction
Scan the laser beam line by line and
A device that scans multiple lines in the sub-scanning direction by rotating
In the light quantity control device used, light quantity detecting means for detecting the light quantity of the semiconductor laser, and comparing means for comparing the light quantity detected by the light quantity detecting means with a predetermined threshold light quantity and outputting a comparison signal indicating a comparison result. When, determining means for determining a control amount of current supplied to the semiconductor laser based on the comparison signal outputted from said comparing means, said determining
Based on the control amount determined by the means.
Control means for controlling the light emission of the laser, the control means preliminarily sets the control amount used for controlling the light emission of the semiconductor laser in the previous line before the light amount detection by the light amount detection means. After changing, if the emission of the semiconductor laser of the line to be processed is controlled using the changed control amount
Both are characterized in that the light amount is detected by the light amount detecting means.

According to a second aspect of the present invention, there is provided a semiconductor laser light amount control apparatus according to the first aspect, wherein the control means is such that two adjacent scan-on signals indicate the start of print scanning. Between the signals, in the area other than the image area, the control amount used in the previous line
It is characterized in that it is changed in advance .

Further, a light quantity control device for a semiconductor laser according to a third aspect is the light quantity control device for a semiconductor laser according to the first aspect, further comprising a light quantity detection means for detecting the light quantity.
Before emitting the laser beam from the laser diode in the previous printed line.
Predict the amount of control used in the previous line based on the light time.
It is characterized in that it is changed .

[0011]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a main control board and a laser diode board of a copying machine according to an embodiment of the present invention, and FIG. 2 shows a device arrangement from a laser diode to a photosensitive drum in the copying machine of FIG. It is a perspective view shown. The copying machine according to the present embodiment includes an electrophotographic laser printer including a semiconductor laser diode (hereinafter, referred to as a laser diode) 20 that exposes a photosensitive drum 37 for printing. The laser printer is a laser diode. The light quantity control means for controlling the light quantity of 20 is provided with the CPU 10, and the light quantity detecting means for detecting the light quantity of the laser diode 20 is compared with the photodiode 21, and the detected light quantity is compared with a predetermined threshold light quantity. Based on the comparison signal CO output from the operational amplifier 23, which is the comparison means that outputs the comparison signal CO indicating the comparison result, the laser diode 20 is generated.
And a determination unit 11 that determines the control amount of the supply current of the constant current source 22 that supplies the current to the determination unit 11 in the CPU 10.
Is characterized in that the light amount control value DA of the line to be printed is changed before the light amount detection based on the light amount control value DA of the line immediately before being printed.

As shown in FIG. 1, the laser printer of the copying machine of this embodiment comprises a main control board 101 and a laser diode board 102. The image reading unit 103 reads the original image, converts it into an image signal, and outputs the image signal to the image signal processing unit 104. After performing the predetermined image processing, the image signal processing unit 104 drives the laser diode 20 with a video signal, which is a binary laser diode drive signal, for example, as a drive switch SW1.
And output to the counter 12 in the CPU 10.

The CPU 10 includes a judgment unit 11 and a counter 12
, Signal receiving unit 13, CO register 14, RAM 15 and D
A / A converter 16 is provided. The counter 12 counts the ON time per video signal and outputs the count result to the determination unit 11. The comparison signal CO output from the operational amplifier 23, which operates as a comparator described later, is temporarily stored in the CO register 14 and then output to the determination unit 11. Vertical sync signal VSYNC, EOL signal indicating the end of each line and / SOS (Scan On
Signal) signal is input to the determination unit 11 via the signal reception unit 13. The former two signals are the signals output from the image signal processing unit 104, and the latter / SOS signal is the SOS signal.
This is the signal output from the signal detector 38. RAM15
Is a work area which is connected to the determination unit 11 and stores data necessary for executing the processing described later. When controlling the drive current of the laser diode 20, the determination unit 11 outputs digital data of the light amount control value DA to the D / A conversion unit 16, and the analog signal after A / D conversion is used as the drive current control value. It is input to the constant current source 22.

In the laser diode substrate 102,
The drive switch SW1 is connected in parallel with the laser diode 20, and the anode of the laser diode 20 is connected to the positive DC voltage V _DD , while the cathode of the laser diode 20 is connected to the constant current source 22 whose one end is grounded. At the same time, the cathode of a photodiode 21 provided near the laser diode 20 for detecting the light quantity of the laser diode 20 is connected. The anode of the photodiode 21 is connected to the non-inverting input terminal of the operational amplifier 23. The non-inverting input terminal of the operational amplifier 23 is grounded via a variable resistor VR for adjusting the light amount detection sensitivity. The DC voltage V _DD is applied to the resistor R1 and the Zener diode 24.
The reference voltage Vr divided by and is input to the inverting input terminal via the resistor R2. Further, a feedback resistor R3 is connected between the inverting input terminal and the output terminal of the operational amplifier 23. The operational amplifier 23 thus configured operates as a comparator.

In the laser diode substrate 102 configured as described above, the drive switch SW1 is turned off in response to an H level video signal, and a drive current is supplied to the laser diode 20 from the constant current source 22 to emit light. To do. The light amount is increased / decreased according to the supply current value of the constant current source 22 controlled by the light amount control value DA from the CPU 10, while the signal voltage Vd corresponding to the detected light amount is detected by the photodiode 21. It is input to the non-inverting input terminal of the operational amplifier 23. On the other hand, the reference voltage Vr corresponding to the target value (threshold value) of the emitted light amount is input to the inverting input terminal. At this time, when Vd ≧ Vr, the operational amplifier 23 outputs the H-level comparison signal CO to the determination unit 11 via the CO register 14, while when Vd <Vr, the operational amplifier 23 outputs the L-level comparison signal CO.
It is output to the determination unit 11 via the register 14.

Further, as shown in FIG. 2, during the printing operation processing, for example, a quadrangular polygon mirror 32 having four sides is used.
Is rotated in the rotation direction indicated by the arrow 200, and the photosensitive drum 37 is rotated in the rotation direction indicated by the arrow 202 (sub-scanning direction). The laser light emitted from the laser diode 20 is reflected by the collimator lens 20 a, the folding mirror 31, one surface of the polygon mirror 32, the cylindrical lens 33, the folding mirrors 34 and 35, and the free-form surface mirror 36, and then is reflected on the photosensitive drum 37. Is irradiated. Here, the irradiation of the laser beam onto the photosensitive drum 37 is performed by the arrow 2 caused by the rotation of the polygon mirror 32.
A line of laser light for printing is scanned in the 01 direction (main scanning direction), and the photosensitive drum 37 is moved to the arrow 2
Scanning is performed so that a plurality of lines are scanned in the sub-scanning direction by rotating in the 02 direction. Here, irradiation for printing one page is performed by sub-scanning a predetermined number of lines.

The laser light output from the laser diode 20 before being irradiated on the photosensitive drum 37 is SOS.
The signal is input to the signal detector 38, and the SOS signal detector 38
Is an L-level / SOS signal that indicates the start of scan-on.
The signal is output to the signal receiving unit 10 in the PU 10. Since a charger, a transfer charger, and the like around the photosensitive drum 37 in the laser printer are conventional techniques, the description thereof will be omitted here. Here, “/” indicates a low-enable signal, and so on.

Further, as shown in FIG. 3, in the mirror scannable area MS, an area other than the image area IR in which the photosensitive drum 37 can be irradiated to scan the laser light,
It becomes an APC possible area in which the APC process can be executed. An APC area signal indicative of the APC possible area is generated, as shown in FIG. 4, to substantially prevent diffuse reflection. That is, the APC area signal, which is low enable, rises from the L level to the H level at the rising edge of the image area signal, and then the APC area signal falls from the H level to the L level at the rising edge of the / SOS signal. That is, the APC area is an area other than the image area between two adjacent / SOS signals each indicating the start of print scanning, and the light amount control value DA is set as will be described later in detail in the APC area. To change.

In this embodiment, the polygon mirror 32 is used.
Shows the case of four faces, but the present invention is not limited to this, and may be six faces or eight faces. The reflection angle of the polygon mirror 32 is 180 ° for four surfaces, 120 ° for six surfaces, 90 ° for eight surfaces, and becomes smaller as the number of surfaces increases.

FIG. 5 is a flow chart showing the main routine of the printing process executed by the CPU of FIG. In FIG. 5, first, when the print command is received in step # 1, the pre-page APC process (see FIG. 7) is executed in step # 2, and then it is checked in step # 3 whether or not the vertical synchronization signal VSYNC is received. Judgment, wait until reception, and when received, in step # 4 outside image area A
The PC process (see FIG. 8) is executed. Next, in step # 5, it is determined whether or not the / SOS signal has been received, and the process waits until the signal is received.
The print operation process of is executed. Next, in step # 7, it is determined whether or not the next page is printed. If yes, the process proceeds to step # 8, and if not, the printing process ends. In step # 8, the inter-page APC process is executed similarly to the above-described pre-page APC process, and then the process returns to step # 3.

FIG. 6 shows the print operation process (step #
6 is a flowchart showing a subroutine of 6). Figure 6
First, in step # 11, the laser diode 2
After 0 is driven to perform the printing process by irradiating the laser light of the main scanning direction of one line, at step # 12, the EOL
Whether or not a signal has been received is determined. If no signal has been received, the process returns to step # 11 to continue scanning the laser beam in the sub-scanning direction. When the EOL signal is received in step # 12, the AP outside the image area is received in step # 13.
After the C process (see FIG. 8) is executed, it is judged in step # 14 whether or not the printing for one page is completed. When it is completed, the printing operation process is completed and the process returns to the main routine. . If not completed in step # 14, it is determined in step # 15 whether or not the / SOS signal is received, and the process waits until it is received. When it is received, the process returns to step # 11.

FIG. 7 is a flowchart showing a subroutine of the APC process before page (step # 2) of FIG. In FIGS. 7 and 8 to 11, the “waiting time 20 microseconds” between steps means that
During those steps, the CPU 10 of the copying machine 2
Indicates to wait for 0 microseconds.

In FIG. 7, in step # 21, the light amount control value DA is set to a predetermined initial value which is, for example, 0, and in step # 22 the drive switch SW1 is turned off to turn on the laser diode 20 and emit light. Let CP
The U10 waits for 20 microseconds in order to generate the accurate comparison signal CO by the operational amplifier 23 as described above, and then in Step # 23, it is determined whether or not the comparison signal CO is at the L level, and at the H level. In some cases, since it is in an abnormal state, error processing of the laser diode is executed in step # 28, the APC processing is terminated, and the process returns to the main routine. On the other hand, when the comparison signal CO is at the L level in step # 23, the CPU 10 waits for 20 microseconds after incrementing the light amount control value DA by 1 in step # 24. Then, in step # 25, it is determined whether or not the comparison signal CO is at the L level, and if it is at the L level, step # 2 is performed to increase the light amount control value DA.
On the other hand, when the H level is returned to 4, it is determined that the target light amount control value DA is reached, and the light amount control value DA is decremented by 1 in step # 26, and then step # 2 is performed.
7, the light quantity control value DA is set to the light quantity control value DA of the line.
After setting as A and outputting to the constant current source 22 via the D / A conversion unit 16, the APC process is finished. As a result, the constant current source 22 causes the light amount control value DA
The laser diode 20 will be driven by the drive current corresponding to.

Step # 2 of the APC process before page
4, the light amount control value DA is incremented by 1, but the present invention is not limited to this and may be incremented by a predetermined value of 2 or more in order to shorten the APC process.

FIG. 8 shows the APC outside the image area of FIGS. 5 and 6.
It is a flowchart which shows the subroutine of a process (step # 4, # 13). In FIG. 8, first, step #
If it is the printing of the first line in step 31, if it is the printing of the first line, the light amount control value DA in the immediately preceding page APC process or the inter-page APC process is set to the light amount control of the line in step # 32. After setting the value DAA, the laser diode 20 is turned on in step # 33. Then, after waiting for 20 microseconds, the CPU 10 determines whether or not the comparison signal CO is at L level in step # 34. If the L level is set in step # 34, the end code flag ECFF is set to 2 in step # 37, and then the process returns to the main routine. on the other hand,
If it is H level in step # 34, step # 3
In step 5, the light amount control value DA is decremented by 1, and in step # 36, the end code flag ECFF is set to 1. Then, the process returns to the main routine.

In the above processing from step # 31 to step # 37, since the first line is printed, the AP before page
There is no light emission of the laser diode 20 between the C processing or the APC processing between pages and the APC processing of the first line,
It is considered that the value at which the amount of emitted light changes as the temperature of the laser diode 20 changes is small. On the other hand, when the laser diode 20 continues to emit light, the temperature of the laser diode 20 rises and the amount of light output decreases even with the same drive current value.
Therefore, since the laser diode 20 is not turned on between the APC process before page and the APC process of the first line, the temperature of the laser diode 20 decreases and
In many cases, the amount of light is slightly increased in the APC processing on the line. Therefore, when the comparison signal CO is at the L level in step # 34, the light amount does not change much, but even if the L level is detected, it is considered that the range of change from the target value of the light amount is small, and therefore the first line is kept as it is. It is used as the light intensity control value of. On the other hand, when the H level is set in step # 34, which is a naturally conceivable result, there is no temperature change that affects the light amount due to the off time of the laser diode 20 between the inter-page APC process and the APC process of the first line. Since it is considered to be small, in step # 35 the light amount control value D
Only by incrementing A by 1, the amount of light is not detected again, the APC process is terminated, and the process returns to the main routine.

In the case of printing the second and subsequent lines, the process proceeds from step # 31 to step # 38, and it is determined whether the printing is one of the following two. (A) Comparison signal CO in the APC processing of the immediately preceding line
Ends at the L level without changing the light amount control value DA (at this time, the end code flag ECFF is 2). (B) Comparison signal CO in the APC processing of the immediately preceding line
Is decremented by 1 at the H level and the light intensity control value DA is decremented (at this time, the end code flag ECFF
Is 1. ).

At step # 38, the end code flag ECF
When F is 1, the laser diode 20 is turned on with the light amount control value as it is in step # 39, and after waiting for 20 microseconds, the comparison signal CO at that time is detected in step # 40. If it is at the level, it means that the light amount control value was decremented by 1 at the H level in the immediately preceding line and switched to the L level, so the end code flag ECFF is set to 2 at step # 43, and the light amount is kept as it is. Return to the main routine with the control value. On the other hand, if it is determined in step # 40 that the comparison signal CO is at the H level, it is determined that the light intensity of the laser diode 20 is still strong. Therefore, in step # 41, the light intensity control value DA is decremented by 1 and In step # 42, the end code flag ECFF is set to 1 and the process returns to the main routine.

When the end code flag ECFF in the immediately preceding APC process is 2 in step # 38, that is, when the comparison signal CO is printed at the L level in the immediately preceding line, the laser diode 2 is output in steps # 44 and # 45.
Before turning 0 on, the light quantity control value DA is incremented by 1. Thereafter, the processing from step # 46 to step # 49 is executed in the same manner as step # 40 to step # 43, as shown in FIG. That is, as in steps # 44 and # 45, the light quantity control value DA is incremented by 1 before turning on the laser diode 20 to change the light quantity control value DA after turning on the laser diode 20. Compared to the case, the difference between the light amount and the target value can be reduced. Further, since the difference between the light amount and the target value is small, the number of times the laser diode 20 is turned on and the comparison signal CO is detected can be reduced,
As a result, the overall standby time of the CPU 10 can be reduced. Further, in the out-of-image-area APC process of FIG. 8, the number of times the CPU 10 waits is limited to one, and the time of the APC process can be shortened compared to the conventional example.

9 to 11 are flowcharts showing a subroutine of a modified example of the APC processing outside the image area (steps # 4 and # 13) of FIGS. 5 and 6. The dashed-dotted line in FIG. 8 shows the characteristic point in the said modification. In FIG. 9, when the first line is printed, the processing is exactly the same as the processing from step # 31 to step # 37 in FIG. When it is determined in step # 31 that the second and subsequent lines are to be printed, the end code flag E is determined in step # 50.
Branch according to CFF. The process when the end code flag ECFF is 1 or 2 is the same as the process when the end code flag ECFF is 1 or 2 in the process of FIG. That is, the end code flag ECF
The processing from step # 51 to step # 55 when F = 1 is the same as the processing from step # 39 to step # 43, and from step # 62 to step # 66 when the end code flag ECFF = 2. Is the same as the processing from step # 44 to step # 49. However, in step # 65, the end code flag ECFF is set to 3.

When the end code flag ECFF is 3, that is, when the immediately preceding line is printed with the comparison signal CO at the L level, the duty ratio of the immediately preceding line is 50% or more in step # 71. It is determined whether or not. Here, the duty ratio of the immediately preceding line is the value [%] of the ratio of the ON time to the time of the video signal in the immediately preceding line, and is counted by the counter 12. In step # 71, the duty ratio of the immediately preceding line is 5
If it is less than 0%, the light amount control value D is determined in step # 72.
Decrement A by 1. This is because when the duty ratio of the immediately preceding line is less than 50%, it is determined that the temperature of the laser diode 20 has not risen so much, so the laser diode 20 is turned on in step # 73 and waits for 20 microseconds. Then, it is determined whether the comparison signal CO is at L level. If it is not the L level in step # 74, the light amount control value DA is decremented by 1 in step # 75, and the end code flag ECF is decremented in step # 76.
Set F to 1 and return to the main routine. On the other hand, when the H level is set in step # 74, the process proceeds to step # 76, the end code flag ECFF is set to 1, and the process returns to the main routine.

On the other hand, when the duty ratio of the immediately preceding line is 50% or more in step # 71, it is expected that the temperature of the laser diode 20 will rise and the light quantity of the laser diode 20 will fall. At 61, the light amount control value DA is incremented by 1, and thereafter, the processes of step # 62 and thereafter are executed.

In the modification described above, the CPU 1
In the light amount control by 0, the light amount control value DA of the line to be printed is changed based on the light emission time of the laser diode 20 in the line before being printed.

As described above, according to the present embodiment, during the APC processing of the line to be printed, the light amount is previously detected before the light amount detection of the laser diode 20 based on the light amount control value DA of the immediately preceding line. since changing the control value DA, it is possible to reduce the number of light quantity detection and light intensity control (light amount adjustment), as a result, overexposure or underexposure without the arising this <br/>, compared with the conventional example In a short time, the light quantity of the semiconductor laser can be set to a certain degree. Therefore,
Without the density unevenness raw Jill, it can be printed. Further, since the light quantity control value of the line is determined based on the light quantity control value of the immediately preceding line, the laser diode 2
Since the light amount control value of 0 can be set to a value substantially close to the target value, there is an advantage that the accuracy of the APC process does not decrease.

Although the copying machine has been described in the above embodiments, the present invention is not limited to this, and can be applied to a so-called electrophotographic laser printer and a device such as a facsimile machine using the laser printer.

[0036]

As described in detail above, according to the light quantity control device for a semiconductor laser according to the first aspect of the present invention, a photoconductor is provided.
Equipped with a semiconductor laser that irradiates the
Scan the laser light line by line and
Scan multiple lines in the sub-scanning direction by rotating the photoconductor
In the light amount control device used for the device, the light amount detecting means for detecting the light amount of the semiconductor laser, and the light amount detected by the light amount detecting means is compared with a predetermined threshold light amount to output a comparison signal indicating a comparison result. comparison means for, determining means for determining a control amount of current supplied to the semiconductor laser based on the comparison signal outputted from said comparing means, based on the control amount determined by said determining means
And a control means for controlling the emission of the semiconductor laser,
The control means controls the emission of the semiconductor laser on the previous line before the light amount detection by the light amount detection means .
After pre-change control amount used in order, the light emitting semiconductor laser of the line to be processed using the control amount and the change
Is controlled, and the light amount is detected by the light amount detecting means. That is, during the APC processing of the line to be printed, the light amount control amount DA of the line is previously detected before the light amount detection of the semiconductor laser based on the control amount of the previous line, that is, the light amount control value DA of the previous line. Since it is changed, the number of times of light amount detection and light amount control (light amount adjustment) can be reduced, and as a result, overexposure or underexposure does not occur, and a semiconductor laser with a certain degree of accuracy can be obtained in a shorter time than the conventional example. The amount of light can be set. Therefore, printing can be performed without causing density unevenness. Also,
Since the light quantity control value of the line is determined based on the light quantity control value of the previous line, the light quantity control value of the semiconductor laser can be set to a value substantially close to the target value. There is an advantage that the accuracy does not decrease.

According to a second aspect of the present invention, there is provided a semiconductor laser light amount control apparatus according to the first aspect of the present invention, wherein the control means includes two adjacent scans each indicating the start of print scanning. Used in the previous line in the area other than the image area during the ON signal
Change the control amount in advance. As a result, in the optical system from the semiconductor laser to the photoconductor, it is possible to substantially prevent irregular reflection and the like, and it is possible to more stably scan the laser beam for printing.

Further, the light quantity control device for a semiconductor laser according to a third aspect is the light quantity control device for a semiconductor laser according to the first aspect, further comprising a light quantity detection means for detecting the light quantity.
Before emitting the laser beam from the laser diode in the previous printed line.
Predict the amount of control used in the previous line based on the light time.
To change. Thus, the light amount detection and the light quantity control can reduce the number of (light amount adjustment), as a result, overexposure and underexposure are without arise in a short time as compared with the conventional example, some accuracy semiconductor laser The light intensity of can be set. Therefore, without the density unevenness arising, it can be printed. Further, in this case, there is an advantage that the accuracy of the APC process can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram of a main control board and a laser diode board of a copying machine according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a device arrangement from a laser diode to a photosensitive drum in the copying machine of FIG.

[3] and a plan view showing the positional relationship between the polygon mirror and the photosensitive drum in the copying machine 1 is a timing chart showing the relationship between the mirror scannable area and image area and APC region.

4 is a diagram showing an image area signal / in the copying machine of FIG.
6 is a timing chart showing a relationship between an SOS signal and an APC area signal.

5 is a flowchart showing a main routine of a printing process executed by the CPU of FIG.

FIG. 6 is a flowchart showing a subroutine of the print operation process of FIG.

FIG. 7 is a flowchart showing a subroutine of pre-page APC processing of FIG.

FIG. 8 is a flowchart showing a subroutine of APC processing outside the image area of FIGS. 5 and 6;

9 is a flowchart showing a first part of a subroutine of a modified example of the out-of-image-area APC process of FIGS. 5 and 6. FIG.

10 is a flowchart showing a second part of a subroutine of a modified example of the out-of-image-area APC processing of FIGS. 5 and 6. FIG.

FIG. 11 is a flowchart showing a third part of a subroutine of a modified example of the out-of-image-area APC process of FIGS. 5 and 6.

FIG. 12: Outside area A in a conventional laser printer
It is a flow chart which shows PC processing.

[Explanation of symbols]

10 ... CPU, 11 ... Judgment section, 12 ... Counter, 13 ... signal receiving unit, 14 ... CO register, 15 ... RAM, 16 ... D / A converter, 20 ... laser diode, 20a ... Collimator lens, 21 ... Photodiode, 22 ... Constant current source, 23 ... operational amplifier, 24 ... Zener diode, 31, 34, 35 ... Folding mirror, 32 ... Polygon mirror, 33 ... Cylindrical lens, 36 ... Free-form surface mirror, 37 ... Photosensitive drum, 38 ... SOS signal detector, 101 ... Main control board, 102 ... laser diode substrate, 103 ... Image reading unit, 104 ... Image signal processing unit, SW1 ... Drive switch, VR ... Variable resistance, R1, R2, R3 ... Resistance.

Claims (3)

(57) [Claims] 1. A semiconductor laser for irradiating a laser on a photoconductor.
The laser beam is provided for each line in the main scanning direction.
While scanning, the sub-scanning direction due to the rotation of the photoconductor
In a light quantity control device used in a device for scanning a plurality of lines, a light quantity detecting means for detecting the light quantity of the semiconductor laser, and a light quantity detected by the light quantity detecting means are compared with a predetermined threshold light quantity, and a comparison result is obtained. comparison means for outputting a comparison signal indicating a determination means for determining a control amount of current supplied to the semiconductor laser based on the comparison signal outputted from the comparing means, the control amount determined by said determining means Based on the above
A control means for controlling the light emission of the semiconductor laser, wherein the control means controls the light emission of the semiconductor laser on the previous line before the light quantity detection by the light quantity detection means .
After pre-change control amount used in order, the light emitting semiconductor laser of the line to be processed using the control amount and the change
Controls the semiconductor laser light quantity control device, characterized in that the light quantity detected by the light quantity detecting means. 2. The control means is provided between two adjacent scan-on signals each indicating the start of print scanning,
2. The semiconductor laser light amount control device according to claim 1, wherein the control amount used in the previous line is changed in an area other than the image area. 3. The control means further preliminarily determines the control amount used in the previous line based on the light emission time of the semiconductor laser in the previous line printed before the light amount detection by the light amount detection means. The light quantity control device for a semiconductor laser according to claim 1, wherein the light quantity control device is changed.