JPH02885A - Semiconductor laser unit - Google Patents

Abstract

PURPOSE:To eliminate the need for power adjusting operation at the time of the replacement of a semiconductor laser unit by a substrate including a comparator which compares the output of a monitor output amplifier with a reference voltage to control the driving circuit of a semiconductor laser. CONSTITUTION:The semiconductor laser unit 7 is equipped integrally with the gain adjustable monitor output amplifier 8, a reference voltage generating circuit 9, and the comparator 14. The output voltage Vm of the monitor output amplifier 8 is adjusted by individual units previously so that the output power of the semiconductor laser unit 7 matches an internal reference voltage Vref where a desired value (standard set power) is obtained on a photosensitive body. Consequently, no adjustment is required at a site when the semiconductor laser unit is replaced, the replacing operation is performed speedily, and the compatibility of the semiconductor laser unit is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser unit 1- which is detachably attached to an optical housing used in a laser printer, laser facsimile, digital copier, etc.

[Conventional technology]

As a light source for laser writing units such as laser printers,
Semiconductor laser units that are integrally equipped with a collimator lens that converts a diverging light beam from a semiconductor laser into a parallel light beam are often used.

The laser light emitted from this semiconductor laser unit is
The image is scanned onto the photoreceptor through the scanning means and the imaging means,
Images are recorded according to the principle of so-called electrostatic recording.

Here, the characteristics of laser light determined by the relationship between the output power of the semiconductor laser unit and the output voltage of the monitor output amplifier obtained by converting the high power of the monitor photodiode are determined by the variation in the divergence angle of the semiconductor laser. It is known that large variations occur due to factors such as variations in the arrangement and sensitivity of monitoring photodiodes, and variations in transmittance of collimator lenses.

If there is this variation, it is not possible to obtain a specific output power on the photoconductor for a specific input, so conventionally, the output power is measured with a power meter on the photoconductor, which is the final irradiation position. Light source unit 1 until the output power of
The above-mentioned variations were corrected by adjusting the gain with a gain adjustment unit such as a variable resistor on a board placed separately from the board.

[Problem to be solved by the invention]

However, with this method, there is the inconvenience of having to bring the power meter to the user's location where the laser printer etc. equipped with the semiconductor laser unit to be replaced is installed, and furthermore, the laser printer etc. is suspended during the on-site adjustment. There was also the problem of time.

Therefore, as seen in Japanese Patent Application Laid-Open No. 61-174.794, for example, the semiconductor laser unit 1 is equipped with means for adjusting the gain of the monitor output amplifier of the semiconductor laser.
There is also a device in which the above-mentioned variation can be corrected by increasing the gain of the monitor output amplifier by yAgi so that the output of the monitor output amplifier matches the standard setting voltage.

However, in this case as well, the standard setting voltage was supplied from an external board, so it was necessary to adjust the voltage.

For example, if the standard voltage is 2.50V, the voltage on each board will vary by 2.50V±10% without adjustment. In the power control (APC) of semiconductor lasers (laser diodes), this mark 7 (!! Lightning voltage same base $ 28
．． Since the voltage (V ref ) is feedback-controlled, the purpose cannot be achieved if the standard voltage is less than ±5%. Therefore, conventionally this standard lψ voltage was set to 2.50V±1
It was necessary to adjust U8 to about %.

By the way, the external boards 1~ that generate this standard voltage are installed in each printer, but in order to simplify the power adjustment, the power is usually adjusted using the standard voltage generated within the semiconductor laser unit adjustment jig. is being carried out.

In this way, conventionally, when adjusting the power when replacing the semiconductor laser unit 1, it was troublesome to adjust the standard voltage generated on the external board, and when using the standard voltage generated within the adjustment jig, it was difficult to adjust the power. (!!Not only does it require a jA adjustment jig that can generate lightning voltage, but the supply source of the standard voltage during power adjustment and the reference voltage during feedback control are different, so there is the problem that the accuracy of feedback control deteriorates. arise.

Furthermore, the internal substrate of the conventional semiconductor laser unit has
A comparator was not provided to compare the output of the monitor output amplifier with the above-mentioned standard voltage (reference voltage) to control one operating circuit of the semiconductor laser, and because it was provided on an external board, the semiconductor laser unit The wiring between the monitor output and the external board becomes long, and the i! ! ! There was also the risk that noise would be added to the quasi-voltage and cause malfunctions.

This invention has been made in view of the above points, and eliminates the need for power adjustment work when replacing a semiconductor laser unit.
Another purpose is to improve the accuracy of feedback control during use and to prevent malfunctions due to noise.

Another object of the present invention is to enable arbitrary power to be set between two points in a region where the current flowing through the semiconductor laser and the output of the semiconductor laser have a linear relationship.

[Means to solve problems]

In order to achieve the above object, the present invention provides a semiconductor laser unit as described above, including a monitor output amplifier with adjustable gain for amplifying the monitor output of the semiconductor laser, and a standard setting power for the output power from the semiconductor laser unit. a reference voltage generation circuit that generates an internal reference voltage corresponding to the output voltage of the monitor output amplifier at the time; and a reference voltage generation circuit that compares the output of the monitor output amplifier with the reference voltage to control a driving circuit of the semiconductor laser. It is equipped with a board including a comparator for.

Further, a first point corresponding to the output voltage of the monitor output amplifier at two points in a region where the current flowing through the semiconductor laser and the output of the semiconductor laser have a linear relationship. a first and second reference voltage generation circuit that generates a second reference voltage;
The output of the monitor output amplifier and the first output. The first voltage is compared with the second reference voltage to control the semiconductor laser drive circuit. A semiconductor laser unit including a substrate including a second comparator is also provided.

[For production]

According to this invention, even if there are variations in the characteristics of semiconductor lasers, the variations can be adjusted in advance as the characteristics of the entire semiconductor laser unit using internal standards and voltages. Unit replacement work can be easily and quickly performed without on-site adjustment.

In addition, power feedback control (AP
C) control accuracy is improved and resistance to noise is increased.

Furthermore, the first. Using the second internal reference voltage, it is also possible to set an arbitrary power between two points in a region where the current flowing through the semiconductor laser and the output of the semiconductor laser have a linear relationship.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view showing the structure of a semiconductor laser unit that is an embodiment of the present invention.

In this figure, 1 is a semiconductor laser (laser diode: LD), 2 is a base metal plate that supports this semiconductor laser 1, 3 is an electrical insulating material, and 4 is a parallel light beam that converts the diverging light beam from the semiconductor laser 1 into a parallel light beam. collimator lens, which converts into
Reference numeral 5 indicates an aperture for beam shaping, and reference numeral 6 indicates a printed circuit board (PCB), which are assembled into an integral unit by a plurality of screws 11 and 12 to constitute a semiconductor laser unit 1-7.

This semiconductor laser unit 7 is removably attached to a predetermined portion of a laser writing unit provided in a laser printer, which will be described later.

The printed circuit board 6 of this semiconductor laser unit 7 includes a monitor output amplifier 8 whose gain can be adjusted, and the output of the monitor output amplifier 8 when the output power from this semiconductor laser unit 7 is set to the standard setting power. a reference voltage generation circuit 9 that generates an internal reference voltage corresponding to the voltage;
The output of the monitor output amplification +a8 and the reference voltage generation circuit 9
A comparator 14 is provided for controlling an LD (I!j dynamic circuit 15 (FIG. 2)) that drives the semiconductor laser 1 by comparing the voltage with a reference voltage generated by the LD (I!j) circuit 15 (FIG. 2).

FIG. 2 is a block circuit diagram in which this semiconductor laser unit 7 is attached to a laser writing unit of a laser printer to form a feedback control loop.

In this figure, reference numeral 10 denotes a photodiode 1, which is provided in the same pack as the semiconductor laser 1 and for monitoring its light emission output, and inputs the monitor current to the monitor output amplifier 8.

Note that in FIG. 2, a portion surrounded by a dashed-dotted line is provided in the semiconductor laser unit 7.

The LDmTA dynamic circuit 15 is provided on the side of the laser printer body, and performs a comparison to compare the monitor voltage V m, which is the output of the monitor output amplifier 8, and the internal reference voltage V ref, which is output from the reference voltage generation circuit 9. The semiconductor laser 1 is controlled by the binary output of the device 14 so that both voltages match.
A driving current is applied to the device to cause it to emit light.

As shown in FIG. 3, the monitor output amplifier 8 includes an operational amplifier 81 and a gain adjustment variable resistor 8 that forms a feedback circuit for the operational amplifier 81.
It is planted by 2.

Also, base iLt! As shown in FIG. 4, the pressure generating circuit 9
It is composed of a resistor 91 and a Zener diode 92 connected in series between a power supply terminal to which a power supply voltage Vcc is supplied and the ground, and outputs the Zener voltage of the Zener diode 92 as an internal reference voltage V ref.

In this way, the gain! l! If the monitor output amplifier 8, the reference voltage generation circuit 9, and the comparator 14 that can be adjusted are provided, the output voltage Vm of the monitor output amplifier 8 and the output power of the semiconductor laser unit 7 can be determined in advance for each individual unit. It can be adjusted to match the internal reference voltage Vref, which is the voltage that gives the desired value (standard setting power) on the body, so there is no need to make adjustments on site when replacing the semiconductor laser unit. This eliminates the problem, allowing quick replacement work and improving the compatibility of the semiconductor laser unit.

Furthermore, since the monitor output amplifier 8, reference voltage generation circuit 9, and comparator 14 are connected within the printed circuit board 6 of the semiconductor laser unit 7, the wiring can be extremely short, and the monitor output and reference voltage Malfunctions caused by noise will no longer occur.

Next, the differences between this invention and the prior art will be explained with reference to FIG.

At the manufacturing stage, the following adjustments are made to each light source unit. That is, in FIG. 2, a part of the laser light emitted from the semiconductor laser 1 is also incident on the monitor photodiode 10, and the monitor current is input into the monitor output amplifier 8.

Here, a power meter 13 is also arranged to receive the laser light emitted from the semiconductor laser 1 on the photoreceptor.
While checking the measured value, the gain adjusting variable resistor 82 of the monitor output amplifier 8 is adjusted so that a predetermined standard setting power is obtained.

The Zener diode 92 is connected so that the reference voltage generation circuit 9 generates the same voltage as the monitor voltage Vm, which is the output of the monitor output amplification D8, as the internal reference voltage Vref.
Select the zener voltage.

In this way, if the semiconductor laser unit 7 is adjusted in advance, the semiconductor laser unit 7 can be simply connected to the LD power supply circuit 15 provided on the laser printer main body side without using the power meter 13 at the site. Then, according to the 211α output from the comparator 14, the selected sales current is applied from the LD drive circuit 15 to the semiconductor laser 1 so that the difference between the output voltage m of the monitor output amplifier 8 and the reference voltage Vref becomes zero. 4% Yi[t s constant power will be obtained.

Furthermore, a comparator 14 is located on the printer 1-circuit board 6,
Since the signal is binarized within the board, it becomes extremely resistant to noise on the wiring. Furthermore, since APC control is performed using the binarized output, the offset I-error of the comparator itself can also be canceled.

FIG. 5 is a sectional view showing a schematic configuration of a laser printer using the semiconductor laser unit according to the present invention described above.

This laser printer has a main body 100 and a paper feed tray 102.
is removably equipped, and the first paper output stacker IQ3 is installed on the top.
A second discharge stacker 104 is provided at the rear.

Of the two paper output stackers 103 and 104, the first paper output stacker 103 is normally selected, but in special cases, such as when using curly paper such as envelopes and postcards, the second paper output stacker 103 is selected. Stacker 104 is selected.

Note that the paper discharge to these two #1' paper stackers can be switched by a switching claw 105.

Further, inside the main body 100, a photoreceptor drum 106, a charger 107. Laser writing units 1-108, IJ
! Image unit 109. It is provided with a transfer charger 110, a fixing unit I-111, a paper feeding section including a paper feeding roller 112, a pair of registration rollers 113, etc., and a paper discharging transport section 114 including a transport roller, a paper guide plate, etc.

Furthermore, a printer controller control plate 115 for controlling the laser printer and an engine driver board 116 are mounted on the top of the printer.

When the print sequence is started by a command from the host, the paper feed roller 112
- Paper feeding starts from the tray 102 and is temporarily stopped at a position where the leading edge of the paper is held between the pair of registration rollers 113.

On the other hand, the photosensitive drum 106 rotates in the direction of the arrow, and the laser writing unit 108 directs a laser beam modulated in accordance with video data from the printer controller onto the surface charged by the charging unit charger 107 in the axial direction of the drum. It is irradiated and exposed while main scanning to form a latent image.

It is developed with the toner of the developing unit l-109, and the registration roller pair 11 is developed with the transfer charger 110.
3, the image is transferred onto a sheet of paper fed at a predetermined timing. Thereafter, the sheet on which the toner image has been heat-fixed by the fixing unit 111 is discharged to the first paper discharge stacker 103 via the second stray paper stacker 104 or the paper discharge transport section 114.

FIG. 6 is a plan view showing the internal configuration of the laser writing unit 108.

This laser writing unit 108 includes an optical housing 12
0, and a first cylindrical lens 122 attached near the center of the bottom surface. First mirror 123. Spherical lens 124 and polygon motor 12 attached to the rear of the bottom
5 rotates the polygon mirror 126 in the direction of the arrow.
, a second mirror 127 attached to the front side, a third mirror 130 attached to the bottom side, and a third cylindrical lens 131 and an optical fiber 132 attached to the side.

As explained with reference to FIGS. 1 and 2, the semiconductor laser unit 7 includes a semiconductor laser (laser diode) 1 inside and a collimator lens 4 that converts the diverging light beam emitted from the semiconductor laser 1 into a parallel light beam. and an automatic output control circuit (APC) that integrally incorporates an aperture 5 and the like that shapes the beam shape of the laser beam that has passed through it into a shape that is long in the scanning direction and short in the sub-scanning direction, and also controls the output of the semiconductor laser 1. A printed circuit board 6, which forms a part of the main body, is integrally attached with screws 12.

Further, the first cylindrical lens 122 directs the laser beam emitted from the semiconductor laser unit 7 to the photoreceptor drum 1.
06 in the sub-scanning direction.

The spherical lens 124 includes the first mirror 123 described above.
The laser beam reflected by the polygon mirror 12 is narrowed down to form a laser beam, and then refracted diagonally upward by about 5 degrees.
The light is incident on the mirror 126a of No. 6.

The polygon mirror 126 uses a rounded polygon mirror formed by curving each mirror 126a, and is a post-object optical deflector (concentrating a light beam) that does not use an fθ lens, which is conventionally arranged between the second mirror 127. This is a type of optical deflector in which a deflector is placed after converting the beam into a light beam.

The second mirror 127 reflects the laser beam (scanning beam) reflected by the polygon mirror 126 onto the photoreceptor drum 106 .

Further, the third mirror 130 is disposed outside the scanning area on the photosensitive drum 106 by the laser beam reflected by the polygon mirror 126, and reflects the incident laser beam toward the optical fiber 132 side.

The optical fiber 132 has its other end connected to a fiber connector mounted on the printer controller board 115 shown in FIG. , leads to a synchronization detection sensor consisting of a photodiode provided on the printer controller board Fills.

In the second laser writing unit 108, the laser beam emitted from the semiconductor laser 1 of the semiconductor laser unit 7 according to the writing information is collimated by the internal collimator lens 4, shaped by the aperture 5, and optically It is injected into the housing 120 (see FIG. 1).

The laser light passes through the first cylindrical lens 122, is reflected by the first mirror 123, is focused by the spherical lens 124, is refracted upward, and enters the mirror surface 126a of the polygon mirror 126.

The mirror surface 126a of this polygon mirror 126
The laser beam reflected by the second mirror 127
The light is reflected by the cylindrical lens 128 and irradiated onto the photoreceptor 106 (see also FIG. 5).

At this time, due to the rotation of the polygon mirror 126 in the direction of the arrow, the laser beam becomes a scanning beam that scans (main scan) the photoconductor 106 in the direction of the arrow B, and the scan (main scan) on the photoconductor 10B by this scanning beam. scanning) is repeated for each mirror 126a of the polygon mirror 126, and at the same time, the photoreceptor 106 rotates in the direction perpendicular to the main scanning direction (sub-scanning direction) as described above.
An electrostatic latent image corresponding to the written image is formed thereon.

In addition, the scanning beam reflected by the polygon mirror 126 (
(laser beam) is scanned over the photoreceptor for 10 days.
is incident on the mirror 130, and the third cylindrical lens 1
31 into the optical fiber 132 and guided to the synchronization detection sensor on the printer controller board 115.

The scan start timing is controlled based on this synchronization detection result.

In this manner, the laser writing unit 108 emits a laser beam from an oblique direction onto a line connecting the center position in the width direction of the photoreceptor drum 10 and the rotation center of the polygon mirror 126, and further emits the laser beam from an oblique direction onto the line connecting the center position in the width direction of the photoreceptor drum 10 and the rotation center of the polygon mirror 126. The laser beam is reflected toward the center of rotation of the polygon mirror 126 and refracted upward so that it enters the mirror 1268 surface of the polygon mirror 126 obliquely from below, and the reflected laser beam is guided onto the photoreceptor drum 106 via the mirror. Therefore, the laser beam incident on the polygon mirror 126 and the laser beam reflected from the polygon mirror 126 do not intersect in a three-dimensional manner, thereby reducing the size of the laser writing unit and improving writing accuracy. be able to.

Incidentally, since the emission intensity P of a semiconductor laser changes linearly with the drive current (2), the emission intensity P can be controlled by controlling this drive current (2).

Here, to explain with reference to FIG. 7, the straight lines X and Y in FIG. 7 (1) indicate the correspondence relationship between the emission intensity P of the semiconductor laser and the drive current ■, and the slope of the straight lines X and Y is the differential efficiency. It is known that this differential efficiency is not constant even in the same type of semiconductor laser, and varies statistically as shown in FIG. 7 (II).

In the case of a semiconductor laser having a P-I characteristic as shown by X in FIG. 7(+), in order to obtain the emission intensity P(B),
The drive current may be made smaller by ΔIX than the drive current when the emission intensity is r'(A), but in the case of a semiconductor laser whose P-1 characteristic is indicated by Y.

The light emission intensity P(B) cannot be achieved unless the drive current is made smaller by Δ■Y than the drive current when the light emission intensity is P(A).

FIG. 8 shows a block diagram of another embodiment of the present invention capable of solving this problem, in which - the portion surrounded by a dashed line is a semiconductor laser unit similar to that shown in FIG. 1; 7'.

In FIG. 8, 1 is a semiconductor laser, 10 is a photodiode for monitoring, and 8 is a monitor output amplifier, which are the same as in the previous embodiment.

17 is a first voltage generator that generates a first reference voltage V ref 1 .
reference voltage generation circuit 19, its first reference voltage V r
ef 1 and a monitor voltage Vm obtained by converting a current generated in proportion to the intensity of light received by the photodiode 10 into a voltage; 20 is an up/down counter (hereinafter simply referred to as a "counter"); ), the monitor voltage Vm from the first comparator and the first reference voltage V
An output signal that goes high or low depending on the magnitude of ref 1 is input to the U/D terminal to control the callan j mode and count up or down the clock pulse CP from the clock pulse generator 33.

21 is an edge detection circuit that detects the rising or falling edge of the first comparator 19; Reference numeral 22 denotes a flip-flop circuit which returns the counter 20 to the disabled state based on the detection output of the edge detection circuit 21. 23 is the third D/A
Converter, 24 is an adder, 25 is a semiconductor laser (LD) drive circuit, and the photodiode 10, amplifier 8, and first reference voltage generation circuits 17 and 19 to 25 generate the first voltage.
This constitutes an output intensity control circuit.

Further, 18 is a second reference voltage generation circuit that generates a second reference voltage V ref 2, and 26 is a monitor voltage Vm and a second reference voltage generation circuit that generates a second reference voltage V ref 2.
a second comparator for comparing the reference voltage V ref 2 of
27 is an up/down counter (
(hereinafter simply referred to as a "counter"), the second comparator 26
The output signal that becomes high or low level depending on the magnitude relationship between the monitor voltage Vm from U/D and the second reference voltage V ref 2 is
The count mode is controlled by inputting it to the terminal, and the clock pulse CP from the clock pulse generator 33 is turned up or down.

28 is an edge detection circuit which, like the edge detection circuit 21, detects the rising or falling edge of the second comparator 2B.

29 is a flip-flop circuit which, like the flip-flop circuit 22, returns the counter 27 to the disabled state by the detection output of the edge detection circuit 28.

30.51 are respectively the 1st. second D/A converter, 32
is an amplifier, and the photodiode 10 and the amplifier 8
．． Second reference voltage generation circuits 18 and 26-32. Adder 24. The LD drive circuit 25 constitutes a second output intensity control circuit.

34 is a power level setting circuit, and 35 is a digital value setting circuit, which outputs the digital value set in the power level setting circuit 34 by the flip-flop circuit 29 to the first D/A converter 30.

The operation of this device configured as described above will be described. First, generation of the reference value signal will be explained.

LDlli dynamic circuit 25 for driving the semiconductor laser 1
A constant drive signal (not shown) is applied to. Then, laser light of a constant intensity is emitted from the semiconductor laser 1 forward and backward.

Laser light emitted backward from the semiconductor laser 1 is received by the photodiode 10.

The photodiode 10 outputs a current proportional to the intensity of the received light, and this current is converted into a voltage by the amplifier 8. The monitor voltages Vm are applied to the second comparators 19 and 26, respectively, and compared with the first reference voltage Vref1 and the second reference voltage Vref2.

The output voltage of the first comparator 19 is equal to the monitor voltage Vm and the first
It becomes a high level or a low level depending on the magnitude relationship of the reference voltage Vref1, and controls the counting mode of the counter 20.

For example, when Vm<Vrefl, that is, the output intensity of the semiconductor laser 1 reaches the reference value P(A) shown in FIG. 7(1).
When the value has not been reached, the output of the first comparator 19 becomes a low level, and the counter 20 enters the count mode, that is, the up mode, in which it operates as an up counter.

Moreover, when Vm>Vrefx, it becomes a count mode in which it operates as a down counter, that is, a down mode.

The flip-flop circuit 22 is set by a power set signal PS to start controlling the light amount of the semiconductor laser 1, generates an output signal, and releases the disabled state of the counter 20.

Then, a digital value corresponding to the first reference value is output from the digital value setting circuit 35, and the first D/A converter 30
The signal is converted to analog and added to the adder 24.

Further, the counter 20 counts up or down the clock pulse CP from the clock pulse generator 33 according to the input from the first comparator 19 .

The count output of this counter 20 is converted into an analog signal by the third D/A converter 23, and is applied to the LD late drive circuit 25 via the adder 24 to change the drive signal. As a result, the emission intensity of the semiconductor device 1 changes.

That is, as the count value of the counter 20 gradually increases (or decreases), the intensity of the laser light from the semiconductor laser 1 gradually increases (or decreases), and the first comparator 19
The monitor voltage Vm applied to is gradually increased (or decreased).

In this way, when the monitor voltage Vm gradually changes and its magnitude relationship with the first reference voltage V ref 1 is reversed, the output of the first comparator also changes from a low level to a high level (or a high level). to low level).

At this time, the edge detection circuit 21 detects the rising (or falling) edge of the output of the comparator 19, resets the flip-flop circuit 22, and returns the counter 20 to the disabled state.

Therefore, the counter 20 holds the count value when the output of the first comparator 19 is inverted, thereby allowing the semiconductor laser 1
The magnitude of the drive current is maintained as is.

At this time, substantially Vm=Vrefl, and the output intensity of the semiconductor laser 1 is equal to the first reference voltage Vref 1
The first reference value P(A) is set through the first reference value P(A). In this manner, the digital signal outputted from the counter 20 in a state where the emission intensity of the semiconductor laser 1 is set to the first reference value P(A) is the reference value signal.

Note that the edge detection circuit 21 may be configured to disable the counter 20 only when the output of the first comparator 19 is inverted from a low level to a high level.

In this way, when the output level of the first comparator 19 is inverted from a low level to a high level, it is the same as the above case, but when the output level is inverted from a high level to a low level, It will look like this:

That is, when the output of the first comparator 1st is inverted from a high level to a low level, the counter 20 operates as an up counter with the disabled state released.

Then, the driving current of the semiconductor laser 1 increases.

When the output of the first comparator 19 inverts from a low level to a high level, the edge detection circuit 21 detects the rising edge and disables the counter 20 to hold its count value.

Further, the counter 20 operates as a down counter when the output of the first comparator 19 is at a low level, and operates as an up counter when the output is at a high level, and the count value and the driving current of the semiconductor laser 1 are inversely proportional to each other. You may also do so.

Note that what has been said here regarding the edge detection circuit 21 and the counter 20 applies to the edge detection circuit 28 and the counter 2.
The same applies to 7.

Further, when the flip-flop circuit 22 is reset, the counter 20 returns to the disabled state and the digital value setting circuit 35 outputs a digital value corresponding to the second reference value.

In this way, the digital values corresponding to the first and second reference values are converted into analog and output to the LD1gM output circuit 25.

Now, the output of the edge detection circuit 21 resets the flip-flop circuit 22 as described above, but at the same time sets the flip-flop circuit 29. This results in
Flip-flop circuit 2 produces an output and counter 27
Remove the disabled state.

Therefore, the emission intensity of the semiconductor laser 1 is set to the first reference value P(
At the same time as realizing A), the counter 27 counts up or down the clock pulse CP from the clock pulse generator 33 depending on whether the output of the second comparator 26 is at a low level or a high level.

The count output of the counter 27 is converted into an analog signal by the second D/A converter 31, and
．． First D/A converter 30. The signal is applied to the LD division circuit 25 via the adder 24.

In this way, as the count value of the counter 27 increases or decreases, the intensity of the laser light emitted from the semiconductor laser 1 also increases or decreases.

Then, the second reference value P(B
) is realized, the output level of the second comparator 26 is inverted and detected by the edge detection circuit 28, and the edge detection circuit 28 issues an output to reset the flip-flop circuit 29.

As a result, the counter 27 returns to the disabled state, and its output maintains the output value when the second reference value P(B) was realized. The output of the counter 27 at this time is the correction width control signal.

Further, based on the output of the flip-flop circuit 29, the digital value setting circuit 65 outputs the digital value set by the power level setting circuit 34 to the first D/A converter 30.

1st. The second reference values P(A) and P(B) are determined as the design conditions for the light amount variable width, and the drive current difference Δ■ which gives P(A)-P(B) as shown in FIG. 7(1) varies depending on the differential efficiency η of the semiconductor laser. Therefore, the magnitude of the correction width control signal is determined by the differential efficiency η of the semiconductor laser shown in the figure (■).
There is a correspondence relationship with.

The digital correction width control signal from the counter 27 obtained in this way is converted into an analog signal by the second D/A converter 31, and then sent to the first D/A converter via the amplifier 32.
is applied to converter 30 to change its gain in proportion to the magnitude of the correction width control signal.

The reference value signal and correction width control signal mentioned above may change each time a power set is performed, but once a power set has been performed, the next power cera setting signal may change.・It will not change until .

As is clear from the above description, the reference signal is determined based on the first reference value P(A) of the emission intensity of the semiconductor laser 1, and the setting signal is determined based on the power level setting value of the power level setting circuit 34. Therefore, neither the reference value signal nor the setting signal includes information regarding the differential efficiency η of the semiconductor laser.

Therefore, if the gain of the first D/A converter 30 is constant, the luminous intensity at the digital value that should output power corresponding to the second reference value will vary depending on variations in the differential efficiency η and changes over time. The intensity deviates from the predetermined intensity P(B). As a result, the emission intensity of the semiconductor laser 1 deviates from the digital value corresponding to the first reference value to the digital value corresponding to the second reference value.

However, in this embodiment, the gain of the first D/A converter 30 is adjusted according to the differential efficiency η using the correction width control signal (analog conversion output of the counter 27) that includes information regarding the differential efficiency η. Since the light emission intensity P(B) is achieved by using the light emission intensity P(B), it is possible to realize the desired light emission intensity from the first base value to the second reference value.

FIG. 9 shows an example of the digital value setting circuit 35 in FIG.
55B is a flip-flop circuit 22.2.
The decoder receives the output of No. 9 as an input, and the output thereof is input to the buffer 35A.

Further, a power set input from the power level setting circuit 34 is also input to this buffer 15A.

That is, the decoder 35B encodes the digital value corresponding to the first reference value or the digital value corresponding to the second reference value by the output of the flip-flop circuit 22.29, or the output value of the power level setting circuit 34 is encoded. It is selected by the buffer 35A and output to the first D/A converter 30.

In this embodiment, the auto power control (APC) is set to the first reference value every time the power set signal PS is generated.
L, the subsequent second reference value APC is the semiconductor laser 1
It is not necessary to do this every time if the temperature is stable.

Also, as a system, the first. If the second APC is performed, the second APC is performed as appropriate, but may be performed every time.

Note that the first reference value and the second reference value each satisfy P(A)<
It may be set to either P(B) or P(A)>P(B).

The power setting to the power level setting circuit 34 may be performed manually or automatically by a CPU or the like.

As explained above, according to this embodiment, each time the power set signal PS is input and set, the first reference value P(A) and the second reference value P(B) are set. Automatic power control is applied to the output, so the desired optical output is always adjusted from the first reference value to the second reference value.
Optical output up to the standard value can be obtained.

As a result, the light intensity can always be set accurately regardless of variations in the characteristics of the semiconductor laser element, temperature changes, etc.

By the way, modulated light from a semiconductor laser is transmitted through a rotating polygon mirror (
An optical scanning system in which the beam is deflected using a rotating deflector such as a polygon mirror (polygon mirror) or a holographic scanner is well known.

A rotary deflector generally deflects a light beam at a constant angular velocity, so in order to keep the scanning speed on the surface to be scanned constant,
Generally, an fθ lens is used.

However, since the f.theta. lens is a special lens and the manufacturing cost is high, there is also a desire to eliminate the use of the f.theta. lens if possible.

Furthermore, the polygon mirror used in the laser writing unit explained with reference to FIG.
020), the scanning angular velocity of the light beam is not constant, and in such a case, even if an fO lens is used, the scanning velocity will not be constant, so the fO lens cannot be used.

Therefore, an optical scanning method that performs optical scanning without using an fθ lens, as shown in the example shown in Fig. 6, has been adopted (for details, see, for example, Japanese Patent Application Laid-Open No. 62-32767). .

To briefly explain this scanning method with reference to FIG.
6, is reflected by one surface of the mirror surface 126a, and is incident on the photoconductive photoreceptor drum 10, and is reflected by the lens 1.
It is focused on the photoreceptor drum 10 days by the action of 24.

If the polygon mirror 126 is rotated at a constant speed in the direction of the arrow,
The light beam is deflected from left to right in FIG. 10, and optically scans the photosensitive drum 106 from left to right in the direction of its generatrix. In addition, 133 is a synchronization detection sensor (light receiving element)
The detection signal is used to synchronize the starting point of optical scanning.

As the polygon mirror 126 rotates, the mirror surface 126a that reflects the light flux is switched, and light scanning is periodically repeated.

Incidentally, in such optical scanning, a clock having a frequency fk given by 1/T is called an image scanning clock, where T is the time allocated to writing information for one pixel.

In such an optical scanning method that does not use an fθ lens, the first
As shown in Figure 1, the scanning speed of the scanned surface by the scanning light is not constant, so the frequency fk of the image scanning clock
If it is kept constant, the written information will be distorted.

In order to remove such distortion of information, it is necessary to change the -F frequency fk in accordance with changes in the scanning speed on the scanned surface. That is, where the scanning speed is high, the frequency fk of the image scanning clock must be increased accordingly, and where the scanning speed is low, the frequency fk must be decreased accordingly.

In this way, by changing the frequency f k of the image scanning clock according to the scanning speed, distortion of the written information image can be effectively reduced.

However, in this case as well, the semiconductor laser used as the light source has statistical variations in its differential efficiency, as described above, and therefore, adjustment is required for each laser writing unit according to the differential efficiency of the semiconductor laser. becomes.

Therefore, in such a case, an image clock frequency control circuit 40 as shown in FIG. 12 may be used in place of the power level setting circuit 34 in the embodiment shown in FIG.

In this image scanning clock frequency control circuit 40, a phase detection circuit 58, a low-pass filter 60°, a voltage controlled oscillator 62, and a frequency divider 64 constitute a phase locked loop circuit (hereinafter referred to as an rPLL circuit). Further, the up/down counter 68 substantially constitutes the digital value setting circuit 35 in FIG.

The operation of this image scanning clock frequency control circuit 40 will be briefly explained.

The reference clock of frequency fO emitted from the oscillator 54 is divided by the frequency divider 56 to become a position control clock of frequency fo/N, which is input to the control circuit 50 and the phase detection circuit 58 of the PLL circuit.

The phase detection circuit 58 compares the phases of this position control clock and the clock input from the frequency divider 64, and outputs the phase difference to the low-pass filter 60 as a pulse signal. When information on the phase difference is input to the voltage controlled oscillator 62 via this low-pass filter 60, this oscillator 6
2 outputs a clock having a frequency corresponding to the output voltage of the low-pass filter 60.

This clock becomes the image scanning clock. This image scanning clock is frequency-divided by a frequency divider 64, applied as a clock to the phase detection circuit 5, and compared in phase with the position control clock.

The frequency division ratio of the frequency divider 64 is a fixed value, if this is M, and the phase difference between the clock applied from the frequency divider 64 to the phase detection circuit 58 and the position control clock (frequency fo/N) changes When not, the frequency fk of the image scanning clock emitted from the voltage controlled oscillator 62 is fk=fo・M/
It is N.

In this state, when the frequency division ratio of the frequency divider 56 is switched from N to N1, the frequency of the position control clock becomes fo·1/N1.
The frequency fk of the 5-image scanning clock is fo−M/
It changes continuously and monotonically from N to fo.M/Nt.

Therefore, by switching the frequency division ratio of the frequency divider 56 stepwise, an image scanning clock whose frequency changes continuously can be obtained.

Now, the control circuit 50 includes a clock CK for outputting a preset value of the frequency division ratio in the frequency divider 56 from the up/down counter (hereinafter simply referred to as "counter") 52;
Signals EN to release the disabled state and UP/
Issues signal U/D to set down mode. In addition,
A synchronization signal obtained from the period detection sensor 133 shown in FIG. 10 is applied to the control circuit 50 and the frequency divider 56.

When the clock CK is input, the counter 52 updates the preset value and switches the frequency division ratio of the frequency divider 56. The switching width ΔN is constant.

Now, the scanning area where optical scanning is performed is made up of a plurality of blocks BLI, BL2, . ...,BLI.

It is divided into BLk, and each block BLi (i=l
-k), numerical values Mi and nl (i=1-k) are determined.

In the i-th block BLi, every time Mi pulses of the position control clock are input to the control circuit 50, the control circuit 50 generates the clock CK, thereby switching the frequency division ratio of the frequency divider 56 by ΔN.

In block BLi, clock CK is generated n i times. Therefore, block BLi has position control clock M
Corresponds to in i pieces. Then, while the block BLi is being optically scanned, the frequency division ratio changes by ni·ΔN.

The number of blocks and the values of Mi and ni are determined by the voltage controlled oscillator 6.
2, so that the frequency fk of the image scanning clock generated from 2 closely approximates the ideal frequency change as the scanning speed changes.
It is determined experimentally or theoretically depending on the design conditions of the optical scanning device.

An example is shown in FIG. In the figure, the curve a indicates the ideal image scanning clock fko, and the stepped broken line indicates the frequency f k1=(M/N)·fo. By switching the frequency divider N step by step, the frequency changes stepwise.

The numbers 5, 6, 10.16 below this broken line are Ml, M2, M3, respectively, with the right end of the figure as the scanning start side. M4
It corresponds to As is clear from the figure, n 1 = 6
, n 2 = 9, n 3 = 3, n
4. = 5.

This figure shows only half of the symmetrical figure, and as is clear from its symmetry, the number of blocks is 7°M5=10.
n5=3. M6=6. n6=9. M7=5, n7=6.

Further, the switching width ΔN of the frequency division ratio N is 1. As the frequency division ratio is switched stepwise, the image scanning clock changes continuously and closely approximates the ideal frequency change fko. By the way, the frequency division ratio N is 69. at both ends of the scanning area. It is 89 in the center.

Now, returning to FIG. 12 again, the generation of the correction signal will be explained.

Signals EN, CK, and U/D generated by the control circuit 50 are applied to the counter 52 and simultaneously applied to the digital value setting circuit 3.
5 up/down counter (hereinafter simply referred to as "r counter") 68.

Therefore, counter 68 and counter 52 are simultaneously released from the disabled state, perform a run 1-, and perform up mode/down mode switching. The counter 68 is activated and counted every time the frequency division ratio N for the base f<6 clock from the oscillator 54 in the image scanning clock frequency control circuit 40 is switched, and changes stepwise according to the counted amount. Outputs a digital signal. This signal is the correction signal shown in FIG.

In the above example, since the up/down modes of the counters 52 and 68 are the same, this correction signal is large at high scanning speeds, as shown in FIG.
Small at low scanning speeds.

This correction signal is converted into an analog (
3, and the reference value signal is subjected to additive calculation modulation in the adder 24 of FIG.

In this way, an analog signal that changes stepwise in proportion to the change in scanning speed is obtained. applied to).

By driving the semiconductor laser 1 in this way, the emission intensity of the semiconductor laser becomes large in areas where the scanning speed in the optical scanning area is high, and the emission intensity becomes small in areas where the scanning speed is low (however, the emission intensity changes in steps). Therefore, the non-uniformity of the exposure amount over the scanning direction is effectively reduced.

As is clear from the above description, the reference value signal is determined based on the reference value P(A) of the emission intensity of the semiconductor laser 1 (emission intensity at both ends of the main scanning line), and is
Since the reference value signal and the correction signal are determined according to changes in the optical scanning speed, neither the reference value signal nor the correction signal includes information regarding the differential efficiency η of the semiconductor laser.

Therefore, if the gain of the first D/A converter 30 is constant, the light emission intensity when scanning the central part of the main scanning line during optical writing scanning will vary depending on the variation in η and the fluctuation over time. It deviates from P(B). by this,
The emission intensity of the semiconductor laser deviates over the optical writing scanning region, with the maximum deviation occurring at the center of the main scanning line.

However, in this embodiment, when scanning the central portion, the gain of the first D/A converter 30 is adjusted according to the differential efficiency using the correction width control signal that includes information regarding the differential efficiency η. Since the light emission intensity P(B) is achieved, the desired light emission intensity can be achieved over the optical writing scanning area.

〔Effect of the invention〕

As explained above, according to the present invention, even if there are variations in the characteristics of semiconductor lasers, the variations can be adjusted in advance as the characteristics of the entire semiconductor laser unit. Replacement work can be performed easily and quickly without on-site adjustment.

In addition, not only does it eliminate the need for a standard voltage generator on the board that was conventionally installed in the laser printer body for power adjustment, but it also eliminates the need for a standard voltage generator on the board that was conventionally installed in the laser printer body for power adjustment. Since the reference voltage used during power adjustment is the same, variations in reference voltage during feedback control are eliminated, and control accuracy is improved.

Furthermore, according to the invention of claim 2, since the desired optical output can be obtained between the first reference value and the second reference value, regardless of variations in the characteristics of the semiconductor laser, temperature changes, etc.
You can always set the light intensity with high precision.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a semiconductor laser unit showing an embodiment of the present invention, and FIG. 2 is a block circuit diagram of the semiconductor laser unit installed in a laser printer to form a feedback control loop. FIG. 3 is a circuit diagram showing an example of the configuration of the monitor output amplifier in this embodiment, FIG. 4 is a circuit diagram showing an example of the configuration of the reference voltage generation circuit, and FIG. 5 is a circuit diagram showing an example of the configuration of the reference voltage generation circuit. FIG. 6 is a plan view showing the internal structure of the laser writing unit 108, and FIG. 7 (1) shows the emission intensity P and screen current of the semiconductor laser.
FIG. 8 is a block diagram of another embodiment of the present invention, and FIG. 9 is a diagram showing its digital value setting. A block diagram showing an example of the circuit 35, Fig. 10 is an explanatory diagram of an optical scanning method that does not use an fO lens, Fig. 11 is an explanatory diagram showing the correspondence between the scanning speed and correction signal, etc., and Fig. 12 is an explanatory diagram of the present invention. FIG. 13 is a block diagram of an image scanning clock frequency control circuit used in another embodiment of the present invention, and is also a diagram for explaining its operation. 1... Semiconductor laser 2... Base metal plate 3
...Electrical wAR material 4...Collimator lens 6...Printed circuit board 7.7'...Semiconductor laser unit 8...Monitor output amplifier 9...Reference voltage generation circuit 0...Monitor photo I-diode 5.25...LD drive circuit 7...First reference voltage generation circuit 8...Second reference voltage generation circuit 9...First comparator 2B...Second comparison Vessel 08
...Laser writing unit Fig. 1 m2 Fig. 4 Fig. 3 Fig. Q4 b → g5 Fig. 9 Fig. υ Fig. 11 Fig. 12 Fig. Image scanning chronograph

Claims (1)

[Scope of Claims] 1. A semiconductor laser unit that is equipped with a semiconductor laser and a collimator lens that converts a diverging light beam from the semiconductor laser into a parallel light beam, and is detachably attached to an optical housing of a laser writing unit, comprising: A monitor output amplifier with adjustable gain that amplifies the monitor output of a semiconductor laser, and a standard that generates an internal reference voltage that corresponds to the output voltage of the monitor output amplifier when the output power from this semiconductor laser unit is the standard setting power. A semiconductor laser unit comprising a substrate including a voltage generation circuit and a comparator for comparing the output of the monitor output amplifier and the reference voltage to control a drive circuit for the semiconductor laser. 2. In a semiconductor laser unit that is equipped with a semiconductor laser and a collimator lens that converts a diverging light beam from the semiconductor laser into a parallel light beam, and is detachably attached to an optical housing of a laser writing unit, the monitor output of the semiconductor laser is a monitor output amplifier to be amplified, and first and second reference voltages corresponding to the output voltage of the monitor output amplifier at two points in a region where the current flowing through the semiconductor laser and the output of the semiconductor laser have a linear relationship; first and second reference voltage generation circuits that generate
The present invention further includes a substrate including first and second comparators for comparing the output of the monitor output amplifier and the first and second reference voltages, respectively, to control the driving circuit of the semiconductor laser. Features of semiconductor laser unit.