JP2641903B2 - Laser diode output control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output control device for a laser diode used in an optical scanning device, and more particularly to an output control device for a laser diode that changes its optical output according to a scanning speed.

2. Description of the Related Art An optical scanning device is a device for writing or reading image information by scanning a surface to be scanned with a laser spot, and FIG. 9 shows an example of an optical writing device as an example.

The laser beam output from the laser diode 1 which is excited by the drive current I _L is the power modulation or frequency modulation by the write signal, for example, by the polygon mirror 2 that rotates in the arrowed direction connexion is deflected, the optical system (not shown) As a result, the effective scanning surface 3a on the irradiation target 3 such as a photosensitive drum or a belt is scanned from left to right (main scanning) as a spot, and the sub-scanning is performed by the rotation of the irradiation target 3, A writing image is formed.

The laser beam irradiates the photodetector 4 immediately before scanning the effective scanning surface 3a, and a synchronizing signal DEPT is output from the photodetector 4, thereby determining the write start timing.

Here, since the laser beam is deflected at a constant angular velocity by the polygon mirror 2, the scanning speed of the spot on the main scanning line is not constant, but is slowest at the center and fastest at the right and left ends.

In order to keep the scanning speed constant, an fθ lens is generally used. However, this fθ lens is a special lens which is expensive and large in size.

Therefore, in order to prevent image distortion even when the scanning speed changes, the frequency of the write clock for turning on / off the laser beam is adjusted according to the scanning speed of the spot as shown in FIG. Changes are being made.

At this time, in order to obtain uniform irradiation energy over the entire effective scanning surface 3a, a laser diode (L
The light output P of D) also needs to be changed according to the spot scanning speed as shown in FIG. As apparent from the figure, the write clock frequency and the optical output P is the minimum value _B at each central portion takes the P _B, the maximum value _P in the left and right ends, so that the P _P.

FIG. 12 (a) is a light output characteristic diagram with respect to a drive current with temperature as a parameter for an example of a laser diode. FIG. 13B is a theoretical light output characteristic diagram of the laser diode with respect to the position on the main scanning line, which is the same as FIG. FIG. 12 (c) is a characteristic diagram of the laser diode driving current I _L (an example at 25 ° C.) with respect to the position on the main scanning line.

From this figure, it can be seen that when the temperature changes, the magnitude of the drive current of the laser diode for obtaining the same light output changes. Such characteristics vary among the elements of the laser diode.

Therefore, a laser for correcting such a change due to the temperature and a variation for each element so as to obtain an optical output corresponding to the scanning speed of the spot as shown in FIGS. 11 and 12 (b). As a method of controlling the output of a diode, for example, there is a method as disclosed in JP-A-62-30466.

According to this method, the light output is detected by the photodiode while changing the drive current of the laser diode, and the detected value is determined by the preset scanning speed of the light output shown in FIG. 12 (b). the magnitude of the drive current when a match with the minimum value P _B corresponding to the fixed part unchanged, is stored in the up-down counter, when the scanning of the surface to be scanned by Rezasupotsuto, the light output of the laser diode in accordance with the scanning speed A digital value corresponding to the change in the value is generated according to a preset function, converted into an analog value, amplified by an amplifier, and converted from the stored value of the up-down counter into an analog value. And the driving current of the laser diode is controlled.

Then, the gain of the amplifier is adjusted so that the intensity change of the optical output of the laser diode is optimized.

However, in such a method, not only must the gain of the amplifier be initialized manually, but the width of the change in the laser diode drive current (I _LD shown in FIG. 12 (c)) is fixed by the initial setting. Therefore, due to the change in the differential efficiency of the optical output with respect to the drive current due to the temperature drift of the laser diode and its drive circuit and the change over time (the slope of the linear portion shown in FIG. 12 (a)),
There is a possibility that the light output of the laser diode fluctuates and a predetermined writing or reading power corresponding to the scanning speed cannot be obtained.

Objective The present invention has been made in view of the above points, and in order to optimally control the light emitting output of a laser diode in accordance with a scanning speed, manual adjustment is not required, and temperature drift and changes over time are automatically performed. The purpose is to be compensated for.

In order to achieve the above object, the present invention provides a laser diode output control device for controlling a drive current so that the light output of a laser diode changes according to the scanning speed of a laser spot on the surface to be scanned. A first storage means for storing data corresponding to the maximum value of the drive current of the laser diode when the detected value of the light output coincides with the preset maximum value and minimum value of the light output, respectively; Second storage means for storing data corresponding to the difference between the maximum value and the minimum value, correction coefficient generation means for outputting correction coefficient data according to the scanning speed of the laser spot, and output from the correction coefficient generation means. Correction data synthesizing means for synthesizing correction coefficient data to be output and data corresponding to the difference between the maximum value and the minimum value output from the second storage means; Control signal synthesizing means for synthesizing the correction data output by the means and the data corresponding to the maximum value output by the first storage means, and controlling the drive current of the laser diode in accordance with the control signal output by the control signal synthesizing means. And a laser diode control means for controlling.

Hereinafter, a specific description will be given based on an embodiment of the present invention.

FIG. 1 is a circuit diagram showing an embodiment in which the present invention is applied to an optical writing device of a laser printer (hereinafter referred to as "printer").

A reference oscillator (OSC) 6 oscillates a synchronous clock CLK, which is a reference for the operation timing of the entire printer, and outputs it to each section of the printer.

The write clock control circuit 7 generates a write clock WCLK whose frequency changes as shown in FIG. 10 in response to a write start signal from a main controller (not shown) composed of a microcomputer, and not shown in synchronization with it. Video controller is intermittent depending on write data
Signals are sent to a laser diode drive circuit (hereinafter referred to as “LD driver”).
8).

With LD driver 8 is a laser diode control circuit generates a drive current I _L increases or decreases according to the control current I _C to be input from the control signal combining means which will be described later, the drive current
The a I _L during the write scanning the laser diode 1 is intermittently emitting light by by connexion intermittently to the VIDEO signal, the time of power adjust Yotsute laser diode 1 is continuously emitted to the drive current I _L.

Here, the drive current I _L, the control current decreases when the I _C is increased, the control current I _C is summer so increases when decreasing.

A photo diode (PD) 10 for detecting the optical output of the laser diode 1 is provided in a package that houses the laser diode 1 and forms a semiconductor laser.

The monitor current I _M output from the photo diode 10 according to the optical output of the laser diode 1 is amplified and converted by the monitor amplifier 11, and becomes the monitor voltage V _M to provide two comparators (CP). These are input to the-input terminals of each of 12 and 13.

On the other hand, the resistance of the power supply voltage _{+ V S R 1, R 2} , consisting of R ₃ divider 14
I pressed connexion min, the reference voltage V _P which correspond to the maximum value P _P and minimum value P _B of the predetermined light output, as shown in Figure 12 (b), to give a V _B, it The + input terminal of each of the comparators 12 and 13 is input as a reference value.

Comparator 12 compares the monitor voltage V _M with a reference voltage V _P, V _M <output if V _P to "H", V _M> to the output if V _P "L".

Similarly, the comparator 13 is a reference voltage V _B of the monitor voltage V _M
If V _M <V _B , the output is set to “H”, and if V _M > V _B , the output is set to “L”.

The outputs of the comparators 12 and 13 are output from a down edge (hereinafter referred to as “DE”) detection circuit 2 having the same circuit configuration.
Enter 1,31.

FIG. 2 is a circuit diagram showing an example of a DE detection circuit, and FIG. 3 is a timing chart showing an example of a level change of each section of the DE detection circuit.

As shown in FIG. 2, the DE detection circuit comprises two flip-flop circuits (hereinafter referred to as "F / F") 16, 17 and an AND circuit 18.
The synchronous clock CLK is input to the CK terminals of the F / Fs 16 and 17, respectively.

The output of the comparator 12 or 13 in the preceding stage is input to the D terminal of the F / F 16, the output Q ₁₆ of the F / F ₁₆ is input to the D terminal of the F / F 17, and the inverted output ₁₆ is input to one input terminal of the AND circuit 18. At the same time, it is output to the outside as a U / D signal.

The output Q ₁₇ of the F / F17 is input to the other input terminal of the AND circuit 18, AND circuit 18 connexion and an AND between ₁₆ and Q ₁₇ to enter, similarly output as DE detection signal.

FIG. 3 is a timing chart showing a level change of each part of the DE detection circuit.

When the input (comparator output) level changes from “H” to “L”, the F / F 16 latches the level of the D terminal at the first edge (hereinafter referred to as “UE”) of the subsequent (synchronous) clock CLK. , Output Q ₁₆ also changes from “H” to “L”, inverted output
_16, that is, the U / D signal is output from “L” to “H”,
At the UE following the clock CLK, the output Q ₁₇ of the F / F ₁₇ is also changed from “H” to “L”.
become.

The output of the AND circuit 18 is always "L", but the clock
Since the outputs ₁₆ and Q ₁₇ both become “H” at the first UE of CLK, the state changes from “L” to “H”, and since the output Q ₁₇ becomes “L” at the next UE, the state returns to “L” again. .

Next, when the input level changes from “L” to “H”, F / F16
Is the first UE of the clock CLK after that, the output Q ₁₆ is also “L” →
At “H”, the inverted output _16, that is, the U / D signal is output from “H” to “L”, and the output Q ₁₇ of the F / F ₁₇ is also changed from “L” to “H” at the next UE.
become.

At this time, the output of the AND circuit 18 becomes the output Q ₁₇ at the next UE after the output ₁₆ becomes “L” at the first UE of the clock CLK.
Becomes “H” and remains at “L”.

Accordingly, when the input level changes, the DE detection circuit outputs a U / D signal whose input level is inverted at the first UE of the subsequent clock CLK and changes the input level from “H” to “H”.
When the signal changes to "L", that is, according to the input level DE, a pulse-like DE detection signal (positive logic) having a width of one cycle of the clock CLK is output.

As shown in FIG. 1, the first storage means 20 and the second storage means 30 include the DE detection circuits 21 and 31 described above, respectively.
Up-down counter (hereinafter simply referred to as "counter")
22,32 and D / A converter (hereinafter "DAC") 23,33
And a set of F / F24, 25 or F / F34, 35.

The counters 22 and 32 are in the up mode when the U / D signal output from the DE detection circuits 21 and 31 is “H”, and in the down mode when the U / D signal is “L”. When the outputs ₂₅ and ₃₅ of the F / Fs ₂₅ and ₃₅ are "L", they are disabled and do not operate. When they are "H", they are enabled and the clock is set according to the mode indicated by the U / D signal. CLK is counted up or down.

The contents of the counters 22 and 32 are always output as analog current signals by the DACs 23 and 24, respectively.

A correction coefficient generating circuit 40, which is a correction coefficient generating means, normally inputs a write clock WCLK whose frequency f changes substantially in proportion to the scanning speed of the laser spot output from the write clock control circuit 7, and A correction coefficient that changes from a minimum value 0 to a maximum value F (hexadecimal number) in accordance with the input clock WCLK is output to the DAC 42 as digital data.

Although 0 is always output (at the time of non-writing), the maximum value F is output at the time of power setting according to the operation state.

Analog current signal DAC33 corresponding to the difference I _LD of the maximum value and the minimum value of the drive current I _L of the laser diode 1 to be output is current amplified by the amplifier 41 is input to DAC42 as a reference current.

The DAC 42, which is a correction data synthesizing means, is a current pull-in DAC, converts the digital correction coefficient data input from the correction coefficient generation circuit 40 into an analog current signal using the analog current input from the amplifier 41 as a reference current, and Output to 43.

That is, an analog current signal output of DAC42 the counter 32, the product of the correction coefficient data difference signal of the driving current I _L and the stored correction coefficient generating circuit 40 outputs,
The correction data changes in proportion to the correction coefficient data with the value corresponding to the width I _LD of the change in the drive current as the maximum width.

The arithmetic unit 43, which is a control signal synthesizing unit, inputs the content of the counter 22 output from the DAC 23, that is, the analog current signal corresponding to the maximum value I _LP of the drive current, and the analog current signal as the correction data, and adds them. , also output to the LD driver 8 as a control signal I _C is an analog current signal.

Here, since the LD driver 8 when the control current I _C is increased acts as the output of the laser diode 1 by reduction drive current I _L decreases, when the output of the correction coefficient is 0 or DAC42 is 0 the control current I _C is only the output of the DAC 23, the light output is maximum P _P.

As the correction coefficient is changed from 0 to the maximum value F, the control current I _C by the amount of the correction data current increases is increased,
The light output decreases.

That is, although the arithmetic unit 43 operates as a current adder, the amount of correction data is subtracted from the optical output of the laser diode 1, and the correction amount becomes maximum when the correction coefficient is the maximum value F. light output is minimum P _B.

Figure 4 shows an example of this in the case of the first connexion of each data by the power excisional signal from initials state in the embodiment to excisional the counter 22 and 32, the level of each section, the contents and the monitor voltage V _M of the counter change FIG.

 Hereinafter, description will be made with reference to FIG. 1 and FIG.

When the power of the printer is turned on, first, at the time of warm-up of the printer, the counter is activated by a reset signal ▲ ▼ output from a main controller (not shown).
22, 32 and F / Fs 24, 25, 34, 35 are initialized and wait for the power set signal ▲ ▼.

That is, the counter 22 is loaded with its maximum value, for example, FF (hexadecimal), and the counter 32 is loaded with 00 (that is, cleared). Also, the F / Fs 24, 25, 34, 35 are preset, and the respective outputs Q become "H" and "L". Therefore, the counter 22,
32 are both disabled.

DAC33 output current is zero, since the write clock control circuit 7 except when actually writing during the printing operation is being performed the writing clock frequency is oscillated at f _P, the correction coefficient generating circuit Since the correction coefficient output by 40 is also 0, DAC4
The correction data output from 2 is 0.

However, the output current is the maximum value of DAC 23, because they summer as it is the control current I _C, much less laser diode 1 than the drive current I _L is 0 or light emission threshold current output by the LD driver 8 does not emit light .

The power set signal ▲ ▼ is output from the main controller (not shown) at a cycle of, for example, about once every second except when the printer is performing a printing operation. It is adjusted so as to always keep the optimum value according to the rise or humidity.

Since the VIDEO signal is turned on from the output of the power set signal ▲ ▼ until the power set operation ends, the laser diode 1 is continuously lit.

When the power set signal ▲ ▼ is input, F / F24
There output Q ₂₄ is cleared becomes "L", and the next clock CLK
The F / F25 is also reset and the output ₂₅ becomes “H”.
The counter 22 starts counting when it is enabled.

However, since the monitor current I _{M of the} photodiode 10 and the monitor voltage V _M of the monitor amplifier 11 are 0, both outputs of the comparators 12 and 13 are “H”, and the DE detection circuits 21 and 31
Is also "L", the counters 22 and 32 are in the down mode.

Therefore, the counter 22 operates as a down counter,
Since the contents of slide into reduced from FF at the start, the control current I _C is also reduced, the drive current I _L is increased.

When the drive current I _L exceeds the light emission threshold current, because the laser diode 1 Yuku gaining increasingly light output to begin emission, also increases the monitor voltage V _M.

When the monitor voltage V _M is first exceeds the reference voltage V _B, the output comparator 13 is inverted becomes "H" → "L", DE detecting circuit
When the U / D signal output from the counter 31 becomes "H", the counter 32 is set to the up mode. However, since the counter 32 is in the disabled state, the content of the counter 32 does not change yet. Also, the DE detection circuit 31
The DE detection signal is output to the CK terminal of the F / F, but the F / F does not change because it is preset.

Then, for example, the contents of the counter 22 8C when reduced to (hexadecimal, hereinafter the same), when the monitor voltage V _M exceeds the reference voltage V _P, the output comparator 12 is inverted is "H" →
It becomes "L", and the DE detection circuit 21 makes the U / D signal "H" one clock later, and outputs the DE detection signal to the CK terminal of the F / F 24.

Reset by power set signal ▲ ▼
Since the D terminal of F / F 24 is always Puruatsupu, its output Q by the input of the CK pin ₂₄ is "H" becomes further 1 clock delay output of F / F25 ₂₅ is because becomes "L" Counter 2
2 becomes disabled.

During this two-clock delay, the content of the counter 22 changes from 8C to 8B, and when returning to 8C again in the up mode, the counter 22 is disabled and the next power set signal
The contents are held until ▼ is input.

That is, the data corresponding to the drive current I _LP is
2, and a current corresponding to the content is output from the DAC 23.

While the output Q ₂₄ becomes “H” and the output ₂₅ becomes “L” one clock delay later, both the output Q ₂₄ and the output ₂₅ become “H”, so the NAND circuit 26 outputs a negative pulse, This negative pulse serves as an operation start signal of the second storage means 30 and the C / F of the F / F 34
Input to the R terminal.

This negative pulse, F / F 34 is reset output Q ₃₄
Becomes "L", the F / F 35 is reset by the next clock CLK, and the output ₃₅ becomes "H".

The output ₃₅ is output to the correction coefficient generation circuit 40 and the EN terminal of the counter 32, and the correction coefficient generation circuit 40 deviates from the normal state (0 output) until the output ₃₅ returns to "L". And the counter 32 is enabled.

Since the counter 32 operates as an up-counter, its content starts from 00 and increases, and the
Since the second reference current and the correction data and the correction data and the control current I _C of the output data is added in DAC23 increases, the drive current I _L is also reduced light output of the laser diode 1 decreases.

When the counter 32 starts operating as an up counter,
Comparator 12 because the monitor voltage V _M is down than the reference voltage V _P
Is inverted and the output changes from “L” to “H”, and the DE detection circuit 21 outputs
The U / D signal changes from “H” to “L”, but the content of the counter 22 does not change because the counter 22 has already been disabled.

Under connexion comparator 13 is inverted from the monitor voltage is the reference voltage V _B, the output thereof becomes "L" → "H", DE detecting circuit 31
Connexion but such a U / D signal is "L" for output, the counter 32 is a down mode, the drive current I _L control current I _C is reduced to increase.

When the monitor voltage V _M exceeds the reference voltage again V _B, in a manner similar to that described counter 22, since the comparator 13 is inverted and outputted becomes "H" → "L", DE detecting circuit 31 that DE
And outputs a DE detection signal, F / F34 followed by F
/ F 35 and is excisional, counter 32 the output ₃₅ becomes "L" becomes Deisueburu state, data corresponding to the difference current I _LD is stored in the counter 32.

Further, when the output ₃₅ becomes "L", the correction coefficient generation circuit 40 returns to the normal state, and the power set ends.

Figure 4 and as is clear from the above description, the first storage unit 20 and the second storage means 30, given even including comparator 12 and 13 of the previous stage, respectively, the monitor voltage V _M is the reference, respectively When starting from a state lower than the voltages V _P and V _B , the counters 22 and 32 operate as down counters at first, and store the data returned one count further when the monitor voltage exceeds the reference voltage.

Conversely, when the monitor voltage starts from a state higher than the reference voltage, the counter operates as an up counter at first, and when the monitor voltage divides by the reference voltage, the counter further proceeds by one count, then becomes a down counter, and the monitor voltage is again increased. When the voltage exceeds the reference voltage, the data returned by proceeding one count further is stored.

FIG. 5 is a timing chart showing an example of the power setting operation by the input of the preset signal from the second time onward, and is denoted by the same reference numerals in the same arrangement as the timing chart shown in FIG.

The second and subsequent power set operations are different from the first initial power set operation in that they start from the state stored last time, and the change in the contents of the counter is zero or extremely small. Is short.

In the example shown in FIG. 5, the counter 2 corresponding to the maximum value I _LP
The counter corresponding to the difference I _LD with the content of 2 increased by 2 counts
This is a case where the content of 32 does not change, and detailed description is omitted.

As described above, the input power per excisional signal in this embodiment, the drive current I _LP in the first storage means 20 for outputting the maximum value P _P of the light output of the laser diode 1 is set in advance Corresponding data is stored in the second storage means 30 as data corresponding to the difference I _LD between the drive current I _LB and the drive current I _LP for outputting the preset minimum value P _B of the optical output. You.

During the printing operation, since the power set signal ▲ ▼ is not inputted, the data stored immediately before the power setting signal ▲ ▼ is held as it is, and the correction coefficient generation circuit 40 in the normal state is held.
Generates a coefficient from 0 to F and returns to 0 again in accordance with the write clock WCLK output from the write clock control circuit every time a scan line is written, and the scan line is properly exposed without unevenness.

The embodiment of the hardware control by the circuit has been described above, but the present invention can also be implemented by the software control by a controller including, for example, a microcomputer.

6 to 8 are flow charts showing an embodiment by software control. FIG. 6 shows a main routine, FIG. 7 shows a maximum value setting routine, and FIG. 8 shows a correction width setting routine.

When the power is turned on, the main routine starts,
During the warm-up operation of the printer, the reset signal ▲ ▼ of the departure control device of the laser diode is output, the counters 22 and 32 and the F / Fs 24, 25, 34 and 35 are initialized and the apparatus enters a standby state.

In the standby state, it is first determined whether or not a print command has been input. If the print instruction has been input, the process jumps to the print execution routine and prints.

If the print command has not been input, the presence or absence of the power set signal ▲ ▼ is determined, and if not, the process returns to the standby state.

If the power set signal ▲ ▼ is input, the process first jumps to the maximum value set routine.

The maximum value excisional routine, first, the first counter 22 by comparing the monitor voltage V _M and the reference voltage V _P After enabling, repeated up-count until not if V _M> V _P, as a result light output and V _M decreases.

If V _M > V _P is not satisfied, the down-counting is repeated until V _M <V _P is not satisfied, and as a result, the light output and V _M increase.

If V _M <V _P is not satisfied, the first counter 22 is disabled, and the process returns to the main routine.

 Next, the routine jumps to a correction width setting routine.

In the correction width setting routine, first, the correction coefficient generation circuit 40
Outputs of the the maximum value, after the second counter 32 is enabled, compares the monitor voltage V _M and reference voltage V _B, V _M>
Repeat up-count until not if V _B, resulting light output and V _M decreases.

If V _M > V _B is not satisfied, the down-counting is repeated until V _M <V _B is not satisfied, and as a result, the light output and V _M increase.

If V _M <V _B is not satisfied, the second counter 32 is disabled, the correction coefficient generation circuit 40 is set to the normal state, and the process returns to the main routine to return to the standby state.

As described above, according to this embodiment, manual adjustment requiring time and manual labor is not required. Moreover not only the control of the fixed part P _B of the light output which varies greatly depending on the temperature, variation of the accompanied light output P _P the change in the differential efficiency caused by temperature change or variation with time also has an effect of compensation.

In this embodiment, at the time of power setting, first, data corresponding to the maximum value I _LP of the drive current for obtaining the maximum light output value P _P of the laser diode is stored, and then the data corresponding to the correction width I _LD of the drive current is stored. Since the data is stored, the capacity of the second counter 32 can be small, or precise correction can be made.

When the laser diode deteriorates, the light conversion efficiency first decreases, but in this embodiment, the required maximum light output (constant value) is obtained by checking the data of the first counter 22. since the driving current I _LP can be known for, it is easy to (a correction by ambient temperature row of connexion if necessary) to monitor the decrease in light conversion efficiency, and advance warning of the laser diode replaced.

Further, in the present invention, when the change of the scanning speed is asymmetric with respect to the center of the main scanning line, that is, the minimum value of the write clock frequency and the light output of the laser diode corresponding to the scanning speed is reduced in the center of the main scanning line. However, it can also be applied to the case where there is a difference between the values at the left and right ends.

In the above embodiment, an example in which the present invention is applied to a printer, particularly an optical writing device of a laser printer, has been described. However, the present invention is similarly applied to a data reading device such as an image reader, or a display device using a laser beam. Can be implemented.

Effect As described above, according to the present invention, it is not necessary to manually adjust the light output of the laser diode so as to change in an optimum pattern according to the scanning speed of the laser spot, and it is automatically adjusted. In addition, temperature drift and aging are automatically compensated.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment in which the present invention is applied to a laser printer, FIG. 2 is a circuit diagram showing an example of a down-edge (DE) detection circuit thereof, and FIG. 4 and 5 are timing charts for explaining the first and second and subsequent operations of the embodiment, respectively. FIGS. 6 to 8 are flowcharts showing an embodiment controlled by software. FIG. 9 is an explanatory diagram showing an example of an optical writing device, FIG. 10 is a diagram showing a change in clock frequency depending on the position of the laser spot, and FIG. FIG. 12 is a diagram showing the relationship between the light output characteristics with respect to the drive current of the laser diode and the light output characteristics with respect to the position of the laser spot, and the drive current characteristics. 1 Laser diode (LD) 6 Reference oscillator (OSC) 7 Write clock control circuit 8 Laser diode drive circuit (LD driver: laser diode control means) 10 Photo diode, 11 Monitor Amplifiers 12, 13 Comparators (CP) 16, 17, 24, 25, 34, 35 Flip-flop circuits (F / F) 20, 30 (First and second) storage means 21, 31 Down-edge (DE) detection circuit 22, 32: Up-down counter (counter) 23, 33: D / A converter (DAC) 40: Correction coefficient generation circuit (correction coefficient generation means) 42: Current draw DAC ( Correction data synthesizing means) 43 ... Calculator (control signal synthesizing means)

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-26066 (JP, A) JP-A-63-53043 (JP, A) Jikai Sho 62-184522 (JP, U)

Claims (1)

(57) [Claims] 1. A laser diode output control device for controlling a driving current so that an optical output of the laser diode changes according to a scanning speed of a laser spot by the laser diode on a surface to be scanned. The optical output is detected while changing the drive current, and data corresponding to the maximum value of the drive current of the laser diode when the detected value matches the preset maximum value and minimum value of the optical output, respectively, is stored. First storage means, second storage means for storing data corresponding to a difference between the maximum value and the minimum value of the drive current, and a correction coefficient for outputting correction coefficient data according to the scanning speed of the laser spot. Generating means; data corresponding to the difference between the correction coefficient data output by the correction coefficient generating means and the maximum value and the minimum value output by the second storage means. Correction data synthesizing means for synthesizing the correction data, the correction data output by the correction data synthesizing means, and the first
Control signal combining means for combining data corresponding to the maximum value output by the storage means, and laser diode control means for controlling the drive current of the laser diode according to the control signal output by the control signal combining means. An output control device for a laser diode, comprising: