JPH05116370A - Laser beam printer - Google Patents

Abstract

PURPOSE:To suppress the density irregularity of a recording image at every predetermined output by storing the reference range of a light output level being a range larger than predetermined width and controlling the light output level of semiconductor laser so that a detection level becomes the value within the reference range. CONSTITUTION:The photocurrent Im outputted from a photodiode 3b is converted to a voltage signal Vm by a resistor 23 and converted to a digital signal by the A/D conversion part 11 of a microcomputer 11 to be applied to a CPU 12. The CPU 12 receives the laser output signal APC and printing completion signal PES from an image control circuit through an input and output control part 13. The CPU 12 executes the programs stored in an ROM 14 and an RAM 15 on the basis of various signals to control the driving of semiconductor laser 3a to control the output of the semiconductor laser 3a so that a detection level becomes the value within a reference range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam printer using a semiconductor laser.

[0002]

2. Description of the Related Art A laser beam printer using a laser beam which is an optical output oscillated from a semiconductor laser performs recording by a laser beam which is directly modulated based on image information. Therefore, in order to perform recording faithful to the image information, it is necessary to always control the output of the semiconductor laser stably. Since the output of the semiconductor laser is easily affected by temperature, conventionally, in order to stably control the output of the laser beam, the intensity of the oscillated laser beam is detected, and the laser beam of the laser beam is detected based on the detection result. Feedback control has been performed to control the output level of the semiconductor laser so that the intensity has a constant value.

In the feedback control, a reference value of the intensity of the laser beam is set in advance, and the output level of the semiconductor laser is digitally stepped by a predetermined width so that the detected value of the laser beam intensity substantially matches the reference value. It is controlled, for example, every time one line is output or every page is output. In this control, before the output of each line or each page, the output level of the semiconductor laser is step by step when the detected value is lower than the reference value so that the detected value matches the reference value. When the detected value is increased and the detected value is higher than the reference value, the output level of the semiconductor laser is decreased by one step, and the output is adjusted a predetermined number of times.
After that, the output level is held at the final adjustment value (value higher or lower than the reference value), and recording with the laser beam is performed at the output level of the final adjustment value.

[0004]

However, in the conventional control method as described above, for example, the initial deviation between the detected value and the reference value slightly exceeds the output adjustment width for one step of the semiconductor laser. In the state, the final adjustment value of the output of the semiconductor laser is the first value obtained by performing the output adjustment of one step from the detected value, and the output of the other step from the first value exceeding the reference value. If the detected value of the second value is higher than the reference value or lower than the reference value in the initial state, the value becomes either the adjusted second value or the second value. There is an output difference corresponding to approximately two steps of the output adjustment width between the upper limit value and the lower limit value that the final adjustment value can take. Therefore, for each predetermined output of the semiconductor laser (one line or one line). Significant unevenness in the density of the recorded image (for each page) There is a problem that Jill.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a laser beam printer which suppresses unevenness in recorded image density for each predetermined output of a semiconductor laser.

[0006]

A laser beam printer according to the present invention detects the optical output level of a semiconductor laser for forming an electrostatic latent image, and based on this detection result, the optical output level of the semiconductor laser is detected. In a laser beam printer that controls a predetermined width stepwise, a means for storing a reference range of a light output level that is a range wider than the predetermined width, and a detection level of the light output to be a value within the reference range. And means for controlling the optical output level of the semiconductor laser.

[0007]

According to the present invention, the light output level of the semiconductor laser is controlled so that the detection level of the light output is within a predetermined reference range. The reference range is the light output level. Since the control value is set to a range wider than the one-step optical output width, the hunting phenomenon of the control value of the optical output level does not occur. It is controlled to a substantially constant value,
The unevenness of the recorded image density is suppressed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a schematic configuration diagram of a laser beam printer according to the present invention.

Image information to be recorded is read from the image memory 1a in the image control circuit 1 and input to the laser driving device 2. The laser driving device 2 outputs an excitation current based on the image information to the semiconductor laser 3a in the laser head 3. From the semiconductor laser 3a,
The laser beam B directly modulated by this excitation current is oscillated.

The laser beam B is collimated by a collimator lens 4 and reflected by a reflecting surface 5a having a polygon mirror 5 rotating at a high speed. The reflected laser beam B is converged by the fθ lens 6 and imaged on the photosensitive drum 7 whose surface is uniformly charged, and the charging potential at the imaging position is attenuated according to its intensity.

The rotation of the polygon mirror 5 changes the inclination of each reflecting surface 5a with respect to the laser beam B which is incident as parallel light. Thereby, the reflected laser beam B is
Scanning is performed in the longitudinal direction of the photosensitive drum 7 (this direction is the main scanning direction). On the other hand, the photosensitive drum 7 is configured to rotate at a constant speed in synchronization with the rotation of the polygon mirror 5 (this rotation direction is the sub-scanning direction).

By repeating the scanning of the laser beam B as the photosensitive drum 7 rotates, an electrostatic latent image corresponding to image information is formed on the photosensitive drum 7.

After that, although not shown in the drawing, toner, which is a color pigment, is selectively adhered to the electrostatic latent image and developed. Then, the output paper is brought into close contact with the toner adhering surface to transfer the toner onto the paper surface. Further, the toner is melted by heating and fixed on the output paper to obtain an output image.

A photo sensor 8 is provided on the scanning side of the photoconductor drum 7. This photo sensor 8
Is the laser beam B after being reflected by the polygon mirror 5.
Outputs a photocurrent when scanned by. This photocurrent is shaped by the waveform shaping circuit 9, and after a certain time,
That is, the laser beam B to be scanned is input to the image control circuit 1 as the synchronizing signal SOS after a time corresponding to the time when the laser beam B to be scanned reaches the recording start position of the photosensitive drum 7 from the position of the photo sensor 8. A print request signal PDS and a print end signal PES are input to the image control circuit 1 from a host computer (not shown).

In response to the synchronizing signal SOS, the image control circuit 1 starts reading one row of image information from the built-in image memory 1a. Then, the laser driving device 2 includes the image memory 1a.
The image information for one line is received, and the output of the excitation current I to the semiconductor laser 3a based on the image information is started.

The synchronizing signal SOS is for aligning the start position of the electrostatic latent image formed by the repeated scanning of the laser beam B with respect to the rotation direction of the photosensitive drum 7, that is, the sub-scanning direction. is there. That is, the polygon mirror 5
There is a slight manufacturing error in the angle division accuracy of each reflecting surface 5a. Further, there is uneven rotation of the polygon mirror 5 and vibration associated with the rotation. Therefore, the scanning direction of the laser beam B may not always be aligned with the sub-scanning direction, which causes recording jitter.

Therefore, the start of modulation of the laser beam B scanned on the photosensitive drum 7 is controlled on the basis of the time when the laser beam B is received by the photo sensor 8 to avoid the occurrence of recording jitter. I am trying to do it.

On the other hand, in the laser head 3, a photodiode 3b for receiving the laser beam B oscillated from the semiconductor laser 3a is provided. The output signal from the photodiode 3 is input to the laser driving device 2.
Then, the excitation current I to the semiconductor laser 3a is controlled so that the power of the laser beam B oscillated using the output signal from the photodiode 3b is always constant regardless of the temperature.
Is configured to control.

Next, the structure and operation of the laser oscillator including the laser driver 2 and the laser head 3 will be described. FIG. 2 is a circuit diagram showing the configuration of the laser oscillator.

The image information read from the image memory 1a is given to the base of the switching transistor 22 via the inversion buffer 21 as the drive control signal DCS. The switching transistor 22 is adapted to be turned on / off in response to the inverted signal of the drive control signal DCS, and when the drive control signal DCS becomes high level, the inverted signal given to the base of the switching transistor 22 becomes low. Switching transistor 22
Is turned off, an excitation current I from a driving transistor 27 described later flows to the semiconductor laser 3a, the laser beam B is oscillated from the semiconductor laser 3a, and when the control signal DCS becomes low level, the switching transistor 22 is turned on. The inversion signal applied to the base of the transistor becomes high level, the switching transistor 22 is turned on, the excitation current I does not flow to the semiconductor laser 3a, and the laser beam B is not oscillated from the semiconductor laser 3a.

On the other hand, switching is performed from the image control circuit 1 via the inversion buffer 21 so as to oscillate the laser beam B in the vicinity of the photosensor 8 in the portion other than the electrostatic latent image forming area on the photosensitive drum 7. The inverted signal of the drive control signal DCS is applied to the base of the transistor 22 for use. While the laser beam B is oscillated in a portion other than the electrostatic latent image forming area by the inversion signal of the drive control signal DCS, the intensity of the laser beam B is monitored by using the photodiode 3b of the laser head 3.

The photocurrent I _m output from the photodiode 3b is converted into a voltage signal V _m by the resistor 23, and this voltage signal V _m is A / A in the microcomputer 10.
A / D conversion is performed by the D conversion unit 11 and the result is given to the CPU 12. In addition to this, the CPU 12 is supplied with the laser output control signal APC and the print end signal PES from the image control circuit 1 through the input / output control unit 13. CPU 12
R0 is based on the various signals given to it.
The semiconductor laser 3a is driven and controlled by executing the program stored in the M 14 and the RAM 15, and the output of the semiconductor laser 3a is controlled by the control method described later.

The output of the CPU 12 is output to the D / A converter 16 by the D / A converter 16.
It is converted and applied to the non-inverting input terminal (+) of the comparison amplifier 24. In addition, the inverting input terminal (-) of the comparison amplifier 24,
The collector voltage of the driving transistor 27, whose collector is connected to the power supply 26 via the resistor 25, is applied, and from the comparison amplifier 24, the output voltage of the CPU 12 and
An output corresponding to the difference from the collector voltage is given to the base of the driving transistor 27 via the resistor 28. With such a configuration, the excitation current I corresponding to the output of the D / A conversion unit 16 flows from the driving transistor 27 to the semiconductor laser 3a.

Next, a method of controlling the output of the semiconductor laser 3a in the CPU 12 will be described. FIG. 3 is a flowchart showing the content of output control of the semiconductor laser.

First, the count value K of the loop counter for managing the loop of the program is initialized (K = 0) (step S1). Then, the detected laser beam B
Is within the reference range of the laser beam intensity (the intensity P of the laser beam B is lower limit value P _min and upper limit value P _max).
It is determined whether or not) (step S2). However, the reference range is a value larger than the control width ΔP for one step of the output of the laser beam B.

If it is determined in step S2 that the intensity detection value P of the laser beam B is within the reference range of the laser beam intensity, the process returns.

On the other hand, when it is determined in step S2 that the intensity detection value P of the laser beam B is not within the reference range of the laser beam intensity, the count value K of the loop counter
Is incremented by 1 count (K = K + 1) (step S3), and it is determined whether the count value K is equal to or _larger than a preset set count value K _set (step S3).
S4).

If it is determined in step S4 that the count value K of the loop counter is greater than or equal to the set count value K _set , it means that the loop of the program has been repeated more than necessary. It is determined that the error has occurred, and predetermined error processing is performed. That is, since this control program is a program that does not require repetition of a large number of loops, loop control of the program is performed by comparing the set count value K _set with the count value K.

On the other hand, if it is determined in step S4 that the count value K of the loop counter is not equal to or greater than the set count value K _set , it means that the program is operating normally. Intensity detection value P
Is smaller than the lower limit P _min (step S5).

If it is determined in step S5 that the intensity detection value P is smaller than the lower limit value P _min , it means that the intensity of the laser beam B is below the reference range. Therefore, the output of the semiconductor laser 3a 1 step (ΔP)
The number is increased (step S6), the process returns to step S2, and the above-described processing is repeated.

On the other hand, in step S5, the intensity detection value P
Is not smaller than the lower limit value P _min , it means that the intensity of the laser beam B is above the reference range. Therefore, the output of the semiconductor laser 3a is decreased by one step (ΔP) (step S7) and returns to the step S2 to repeat the above-mentioned processing.

When the above processing is performed, the intensity detection value P is controlled within the reference range. In this control, the output of the semiconductor laser 3a is controlled by increasing / decreasing the output step by step. However, since the target value of the control is the reference range having a width larger than 1 step as described above, the output Since the control value of 1 does not cause a hunting phenomenon and is kept within the reference range, the output of the semiconductor laser 3a is always controlled within the reference range and stabilized.

Next, the control timing of the above laser beam printer will be described. FIG. 4 is a time chart showing the control timing of the laser beam printer.

When the print request signal PDS is input from the host computer to the image control circuit 1, the drive control signal DCS is supplied for a predetermined time T to obtain the synchronizing signal SOS.
₁ becomes high level H, and the laser driving device 2 is driven. After the drive control signal DCS changes from the low level L to the high level H, the laser output control signal APC becomes the high level H for the predetermined time T _{3 with a} delay of the predetermined time T ₂ . During the predetermined time T ₃ when the laser output control signal APC is at the high level H, the output P of the semiconductor laser 3a is controlled as described above, and after the predetermined time T _{3 has} passed, the laser output control signal
When APC becomes low level L, the level of the output P of the semiconductor laser 3a is maintained at the value at that time. And
After that, the drive control signal DCS corresponding to the image information is intermittently maintained at the high level H (A in the drawing), so that the recording at the held output level is performed line by line. The output of the semiconductor laser 3a has a temperature dependency, and when the temperature rises due to continuous driving of the laser driving device 2, the level of the output P gradually decreases. The level of is stably maintained at a substantially constant level.

[0035]

As described in detail above, in the laser beam printer according to the present invention, the light output level of the semiconductor laser is controlled so that the detection level of the light output becomes a value within a predetermined reference range. However, since the reference range is set to a range wider than the light output width of one step in the control of the light output level, the hunting phenomenon of the control value of the light output level does not occur, and the width that the control value can take is small. For,
The control value of the light output level is controlled to a substantially constant value, and the unevenness of the recorded image density for each predetermined output of the light output can be suppressed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a laser beam printer according to the present invention.

FIG. 2 is a circuit diagram showing a configuration of a laser oscillator.

FIG. 3 is a flowchart showing the content of output control of a semiconductor laser.

FIG. 4 is a time chart showing the control timing of the laser beam printer.

[Explanation of Codes] 2 Laser driving device 3a Semiconductor laser 3b Photodiode 10 Microcomputer 12 CPU 14 R0M 15 RAM

Claims (1)

[Claims] 1. A laser beam printer for detecting the optical output level of a semiconductor laser for forming an electrostatic latent image, and controlling the optical output level of the semiconductor laser stepwise by a predetermined width based on the detection result. Means for storing a reference range of the light output level which is a range wider than the predetermined width; and means for controlling the light output level of the semiconductor laser so that the detection level of the light output becomes a value within the reference range. A laser beam printer comprising: