JPH03247071A - Semiconductor laser drive method for optical writer - Google Patents

Abstract

PURPOSE:To improve the quality of an output picture by not immediately stimulating a write semiconductor laser even at application of power, sensing a non-write area, driving stimulation only in the non-write area and applying optical output control. CONSTITUTION:In the optical output control of a semiconductor laser 1, the semiconductor laser 1 is not immediately stimulated even after application of power of the writer and when a non-write area of a recording medium 5 is sensed, the laser is stimulated in the non-write area for the control. Then other semiconductor laser 6 is used for sensing the non-write area. Since the stimulation is driven in the non-write area and the optical output control is implemented, the stimulation at control is implemented at the on-write area and a cause to a dirt background in an output picture is avoided and the quality of an output picture is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser driving method for an optical writing device such as a laser printer, high-density laser plotter, etc., which uses a semiconductor laser as a writing light source.

BACKGROUND OF THE INVENTION In recent years, semiconductor lasers have been used as light sources for optical writing devices of this type because they can be directly modulated and the amount of light can be easily controlled. In general, the device configuration is as follows:
The light from the semiconductor laser is deflected and scanned by a rotating deflector such as a polygon mirror to form a scanning spot on the recording medium.

Here, as a light amount control method to perform stable optical writing, a drive circuit that supplies a drive current to the semiconductor laser, a detection voltage that is photoelectrically converted corresponding to the optical output of the semiconductor laser, and a predetermined optical output are used. A comparator that compares the magnitude with a corresponding reference voltage, an up/down counter that determines the up or down operation mode depending on the comparison result, and a D/A that converts the count value of this up/down counter into a current value. converter and a control circuit that controls the drive current by controlling a drive circuit according to the current value output from the D/A converter, and controls the semiconductor laser at a predetermined optical output corresponding to a reference voltage. I'm trying to make it emit light. In this case, conventionally, as shown in, for example, Japanese Patent Publication No. 63-308395, a semiconductor laser is caused to emit light at the same time as the power is turned on to perform the above-mentioned optical output control.

Problems to be Solved by the Invention Rolled films are used as recording media in high-density plotters and the like. Therefore, if the light output is controlled by causing the semiconductor laser to emit light at the same time the power is turned on as in the past (generally, when the power is turned on, the polygon mirror is also rotated and controlled to rotate at a constant speed), the light output The film is exposed to light due to the light emitted during control, resulting in background stains on the output image, which is undesirable.

Means for Solving the Problem When the device is powered on, an area detection means detects whether it is a write area or a non-write area of the recording medium, and when the non-write area is detected, a semiconductor laser for writing is emitted within this non-write area. The light output was controlled.

At this time, a semiconductor laser that does not irradiate the recording medium is provided separately from the semiconductor laser for writing, and this semiconductor laser is made to emit light after a certain period of time has elapsed from the time when the power of the apparatus is turned on to serve for area detection.

Even when the working power is turned on, the semiconductor laser is not driven to emit light immediately, but based on the detection of the non-written area, it is driven to emit light within the non-written area and its optical output is controlled, so that the light emission during control is in the non-written area. Therefore, the quality of the output image is improved without causing background stains on the output image.

In particular, we used light from a semiconductor laser different from the semiconductor laser for writing, and emitted light after a certain period of time from power-on to detect the non-written area. Area detection can be performed reliably without causing any negative effects such as background smearing.

Example An embodiment of the present invention will be described based on the drawings.

This embodiment is applied to an optical writing device using a multi-point synchronization method. This method is used, for example, in U.S. Pat.
9,403, etc., and based on this, JP-A-54-97050, JP-A-60
This is also disclosed in Japanese Patent No.-10667. Masu,
As shown in FIG. 2, a semiconductor laser l for writing is provided which emits a writing beam P1 modulated by image information (V 1deo signal). The writing beam P emitted from this semiconductor laser 1 is a polygon mirror 2.
After passing through the fθ lens 3, it is reflected by the mirror 4, and an image is formed on the recording medium S, where it is main-scanned. On the other hand, apart from the semiconductor laser 1, a semiconductor laser 6 for synchronization (for generating pixel clocks) is provided. The synchronized beam P3 emitted from the semiconductor laser 6 is incident on the same reflective surface of the polygon mirror 2 at a position separated by a certain distance from the writing beam P1 (same position in the main scanning direction), and is similar to the writing beam P1. The light enters the fθ lens 3. After passing through the fθ lens 3, the synchronous beam P is formed due to the different vertical positions.

passes over a mirror 4 and scans a grating 7 provided at an optically equivalent position to the recording medium 5. The synchronized beam P3 transmitted through the transparent portion of the grating 7 is transmitted to a plurality of light receiving elements 9a by a lens array 8, for example, five light receiving elements 9a.
The light is sequentially focused and imaged on the light receiving elements 9a to 9e.
A pulse train is generated from e. This pulse train is input to a PLL circuit (not shown), where predetermined processing is performed and a pixel clock is generated. The writing beam P1 is modulated synchronously with this pixel clock.

The semiconductor lasers 1 and 6 are driven and controlled by driving devices 10 and 11, respectively. Here, control of the optical output of the semiconductor laser I will be explained. This control is performed during APC (auto power control) operation. First, the optical output of the semiconductor laser 1 is received by a built-in photodiode, and a photovoltaic current proportional to the optical output is generated by a current-voltage converter. converted into a voltage signal. This detected voltage is compared with a reference voltage corresponding to a target predetermined light output in a comparator. Depending on the result of this comparison, it is determined whether the up/down counter operates up or down. This up/down counter counts up or down the system clock according to the comparator 8 output during APC operation, and this count output value is converted into a current value by a D/A converter. The drive current for the semiconductor laser I is controlled by this current value. Here, the detection voltage exceeds the reference voltage a specified number of times, in this example 4
Once crossed, the APC operation is completed, the up/down counter stops counting, and its output value is maintained until writing for one line is completed.

The above-mentioned contents are the basis of the multi-point synchronization method and the APC operation of the writing semiconductor laser.

Therefore, in this embodiment, regarding the optical power control of the semiconductor laser 1, even when the power of the device is turned on, the semiconductor laser 1 does not emit light immediately, and it is possible to ensure that the recording medium 5 is in a non-writing area. When detected, it is controlled by emitting light within this non-writing area. Another semiconductor laser 6 is used to detect this non-written area.

First, the emission timing of the semiconductor laser 6 will be explained with reference to FIG. When you turn on the device (power on),
The polygon motor starts. After a certain period of time L1 has elapsed after the input, the polygon motor is locked and the polygon mirror 2
rotates at a constant speed. After a certain period of time has elapsed after the power is turned on, the semiconductor laser 6 (control device 11
) is slowly raised by the slow starter, and the semiconductor laser 6 emits light. In this way, the semiconductor laser 6 emits light after the polygon mirror 2 becomes constant in velocity, so that the pulse train S! is generated.

This pulse train S3 is the semiconductor laser 1 (control device 10)
It is used for generating the light emission signal S7 for. FIG. 3 shows a circuit that detects whether it is a write area or a non-write area based on this pulse train S and generates a light emission signal S, and an example of its operation timing is shown in FIG. First, after the device is powered on, the synchronizing semiconductor laser 6 emits a pulse train S as described above.

When this occurs, the output S4 of the timer 13 becomes H level, and the first counter 14 starts counting the pulse train S and the signal, while the first to third flip-flops 15, 16, and 17 of the three stages are cleared. It is released and becomes the enabled state. Pulse train8. After the occurrence, when the first counter 14 measures 3 for a predetermined period of time, the pixel clock W, CLK
Gate signal (1 line write signal)
stands up. The second counter 18 outputs the pixel clock W, CLK.
When the Game width (the number of valid write data) is counted (for a predetermined period of time), the first flip-flop 15 is cleared, synchronized with the pixel clocks W and CLK, and the Gate signal falls.

This L', Gate signal is transmitted to the fourth flip-flop 19.
is input to the other flip-flops 15°16
．． 17, the signal S input to the clear terminal is
When the system clock of the device is started, it becomes H level, so the clearing is canceled, and the output S of the fourth flip-flop 19 is only at this point when the L and Gat6 signals fall.
, becomes L level. The signal S is a signal in which the falling edge of the Gate signal is delayed by a predetermined time, and this signal S
When , falls, the signal S becomes H level through NOR gate 20 processing with the signal S. This signal S, is the signal S,
It is also input to the AND gate 21.

This signal S is an APC signal for ending the APC operation of the semiconductor laser 1, and rises when the signal S falls, and when the APC operation ends (as mentioned above,
When the detection voltage crosses the reference voltage four times), it is generated by a circuit (not shown) at a timing such that it falls.

The output signal SII of this AND gate 21 is the APC
As a signal, it is sent from the host (not shown) and is ORed as a logical sum together with the Video signal synchronized with the Gate signal.
The light is input to the gate 22, and a light emission signal S is output. As a result, the APC operation, that is, the high-power control of the semiconductor laser 1 is performed in the non-writing area.

Furthermore, if the semiconductor laser 6 emits light in the middle of the writing area,
Even if the pulse train S is insufficiently generated, the Q output of the second flip-flop 16, and hence the L Gate signal, will not fall within the write area. Therefore, the signal S,
falls for the first time at the fall of the output signal S4 of the timer 13,
This makes APC operation permissible. Also, there is no output signal from the first counter 14 (there is no pulse train S3), and the L
, Gate signal does not rise, the APC operation is performed from the non-write area of the next line.

In this way, the signal S does not fall until the beam position reaches the non-writing area, prohibiting APC operation, and the APC operation is not performed until the beam position reaches the non-writing area and the signal S falls. A write operation that is not based on the V1deo signal is not performed in the area, and background smearing is prevented.

Effects of the Invention As described above, the present invention does not immediately drive the writing semiconductor laser to emit light even when the power is turned on, but detects that it is a non-writing area and drives the writing semiconductor laser to emit light only within this non-writing area. Since the light output control is performed, the light emission during the light output control is performed in the non-writing area.
The quality of the output image can be improved without causing background smudges on the output image. In particular, it is possible to improve the quality of the output image by using light from a semiconductor laser different from the writing semiconductor laser to detect non-written areas. In addition, since the light is emitted and detected after a certain period of time has elapsed since the power is turned on, the detection operation does not affect background stains, and reliable area detection can be performed.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention; FIG. 1 is a timing chart showing semiconductor laser emission control for synchronization, FIG. 2 is a schematic perspective view showing a multi-point synchronization type optical writing device,
Figure 3 is a block diagram showing a circuit for generating a light emission signal;
The figure is a timing chart showing the operation timing. l... Semiconductor laser for writing, 6... Another semiconductor laser

Claims (1)

[Claims] 1. A drive circuit that supplies a drive current to a semiconductor laser for writing, a detection voltage photoelectrically converted corresponding to the optical output of the semiconductor laser, and a reference voltage corresponding to a predetermined optical output. a comparator that compares the magnitude; an up/down counter that determines an up or down operation mode according to the comparison result;
A D/A converter that converts the count value of this up/down counter into a current value, and a control circuit that controls the drive circuit and controls the drive current according to the current value output from the D/A converter. In the semiconductor laser driving method for an optical writing device, the semiconductor laser is caused to emit light with a predetermined optical output corresponding to the reference voltage, and when the device is powered on, the area detection means determines whether the writing area of the recording medium is non-existent or not. A method for driving a semiconductor laser in an optical writing device, characterized in that a writing area is detected, and upon detection of a non-writing area, the semiconductor laser is caused to emit light within the non-writing area to perform the optical output control. 2. A semiconductor laser that does not irradiate the recording medium is provided separately from the semiconductor laser for writing, and this semiconductor laser is made to emit light after a certain period of time has elapsed from when the device is powered on to detect the area. 2. A semiconductor laser driving method for an optical writing device according to claim 1.