JP3677915B2 - Light control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light amount control device for controlling the amount of laser light emitted from a plurality of semiconductor lasers provided in a semiconductor laser array.
[0002]
[Prior art]
Conventionally, a semiconductor laser array is used as a light source in an image recording apparatus such as a copying machine or a laser printer. By using this semiconductor laser array as a light source of an image recording apparatus, optical recording of a plurality of scanning lines can be performed simultaneously, and thus there is an advantage that high-speed printing is possible. However, the semiconductor laser has output characteristics, and the output characteristics differ for each semiconductor laser. For this reason, the output characteristics of the semiconductor lasers vary, and there is a problem that a light amount difference occurs between the laser beams emitted from the respective semiconductor lasers.
[0003]
In order to solve this problem, there is a light quantity control device that controls the quantity of light so as to suppress the difference in quantity of laser light emitted from a plurality of semiconductor lasers. As shown in FIG. 4, the light quantity control device includes a light quantity detector 56 that detects a back beam of laser light emitted from the semiconductor lasers 52 and 54 and outputs a current proportional to the detected light quantity of the laser light. The amplifier 58 converts the output current of the light amount detector 56 into a voltage and distributes the converted voltage to the error amplifiers 60 and 62, and the light amounts of the output characteristics 78 and 80 (see FIG. 5) of the semiconductor lasers 52 and 54, respectively. Error amplifiers 60 and 62 that perform offset adjustment and gain adjustment to correct variations in sensitivity, comparators 64 and 66 that compare an output voltage of the error amplifiers 60 and 62 and a preset reference voltage 68, and comparison S / H control circuits 70 and 72 for controlling the drive currents for driving the semiconductor lasers 52 and 54 based on the comparison results by the devices 64 and 66, and the drive currents for the semiconductor lasers 52 and 54, respectively. And a laser driving circuit 74 for controlling the lighting of each of the semiconductor lasers 52 and 54 output.
[0004]
In the light quantity control device 50 having such a configuration, the output current of the light quantity detector 56 is converted into a voltage by the amplifier 58 and distributed to the error amplifiers 60 and 62, and then the light quantity sensitivity offset adjustment and gain adjustment are performed to perform the semiconductor laser. Variations in the output characteristics 78 and 80 of 52 and 54 are corrected, and the drive current for driving the semiconductor lasers 52 and 54 is controlled. As a result, the difference in the amount of laser light emitted from each of the semiconductor lasers 52 and 54 is suppressed.
[0005]
[Problems to be solved by the invention]
However, when the output current of the light quantity detector 56 is converted into a voltage and then distributed to the error amplifiers 60 and 62 for light quantity control, variations in the light quantity sensitivity of the output characteristics 78 and 80 of the semiconductor lasers 52 and 54 are detected. In order to correct the error, a circuit configuration such as an inverting amplifier circuit and a differential amplifier circuit is required, and therefore it is necessary to perform offset adjustment and gain adjustment. As described above, when the offset adjustment and the gain adjustment of the light amount sensitivity are performed to correct the variations in the output characteristics 78 and 80 of the semiconductor lasers 52 and 54, it is difficult to make the output characteristics 78 and 80 coincide with each other. There is a problem that it is difficult to suppress the light quantity difference between 52 and 54.
[0006]
In addition, when the circuit configuration in which the output current of the light quantity detector 56 is converted into voltage and distributed to each light quantity control unit as shown in FIG. 4 is taken, the output characteristics 78 and 80 of the respective semiconductor lasers 52 and 54 are completely set. Since many adjustment mechanisms are required for matching, there is a problem that the circuit configuration becomes complicated and complicated adjustment processing is required.
[0007]
In view of the above-described facts, an object of the present invention is to provide a light quantity control device capable of controlling light quantity differences between a plurality of semiconductor lasers with a simple circuit configuration and performing stable and accurate light quantity control.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 is a light quantity control device for controlling the quantity of laser light emitted from a plurality of semiconductor lasers provided in a semiconductor laser array, wherein the plurality of semiconductor lasers A light amount detecting means for detecting the light amount of the laser light emitted from the light source and outputting a current corresponding to the detected light amount; and an output current of the light amount detecting means is equally distributed according to the number of the plurality of semiconductor lasers and current distribution means, a plurality of conversion means for converting each voltage corresponding to a current that is distributed to the gain of the light amount sensitivity of each of the plurality of semiconductor laser by the current distribution means, the output voltage of said plurality of conversion means and a plurality of comparing means for comparing each of the semiconductor lasers on a common preset reference voltage, respectively, the semiconductor laser corresponding to on the basis of a comparison result of said plurality of comparing means It has a plurality of current control means for controlling a drive current for driving the THE and.
[0009]
According to the first aspect of the present invention, the light quantity control device detects laser light emitted from a plurality of semiconductor lasers provided in the semiconductor laser array and outputs a current corresponding to the detected light quantity of the laser light. A light quantity detection means is provided. This light quantity detection means is constituted by, for example, a photodiode. In addition, the light quantity control device is provided with current distribution means, and distributes the output current of the light quantity detection means corresponding to the number of semiconductor lasers provided in the semiconductor laser array. By this current distribution means, the output current of the light quantity detection means can be evenly distributed. Further, the light quantity control device is provided with a plurality of conversion means for converting each current into a voltage. Each conversion means, for the variable resistor can be set a plurality of semiconductor lasers each of the light amount sensitivity of the resistance value corresponding to a gain, respectively are provided, respectively, each conversion means is a gain adjustment of the light amount sensitivity Output voltage. That is, by the gain adjustment of the light amount sensitivity is performed respectively in each conversion means, it is possible to correct variations in light intensity sensitivity of the output characteristics of a plurality of semiconductor lasers.
[0010]
Output voltage of each converter is compared common predetermined reference voltage to the semiconductor laser by the respective comparing means. The reference voltage at this time is a voltage when the laser light emitted from the semiconductor laser has a desired light amount. Further, the current control means controls the drive current for driving each semiconductor laser so that the reference voltage and the output of each conversion means become the same based on the comparison result by each comparison means. For example, when the output voltage of the conversion means is lower than the reference voltage, control is performed so that the drive current for driving the semiconductor laser increases. On the other hand, when the output voltage of the conversion means is higher than the reference voltage, control is performed so that the drive current for driving the semiconductor laser decreases. In this way, by controlling the drive current for driving the semiconductor laser by the current control means, the reference voltage and the output of the conversion means become the same, so that the light quantity difference between the semiconductor lasers can be suppressed.
[0011]
Therefore, by converting them voltage after evenly distribute the output current of the light intensity detection means with the current distribution means, is corrected for variations in output characteristics in performing only the gain adjustment of the light amount sensitivity this time each of the semiconductor lasers, a simple The light quantity of each semiconductor laser can be controlled by the circuit configuration.
[0012]
The invention described in claim 2 is characterized in that a rectifying means is provided on the downstream side of the current distribution means, and prevents a reverse flow of the current distributed by the current distribution means.
[0013]
As described above, the output current of the light quantity detection means provided in the light quantity control device is evenly distributed according to the number of semiconductor lasers by the current distribution means, and each is input to the conversion means and converted into a voltage. However, if the difference between the voltage generated between the conversion means may reverse current flow to the current distributing means. Therefore, according to the second aspect of the present invention, the light quantity control device is provided with the rectifying means for preventing the backflow of the current distributed by the current distributing means. As this rectifying means, there is a rectifying element such as a diode, for example, which is disposed downstream of the current distributing means. Therefore, by connecting the output terminal of the current distribution means to the input terminal of the conversion means via the rectification means, the output current of the light quantity detection means is always evenly distributed and the light quantity of each semiconductor laser is accurately controlled. can do.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing a configuration of a light amount control apparatus 10 according to the present embodiment.
[0015]
As shown in FIG. 1, a plurality of semiconductor lasers 12 and 14 (only two are shown in the present embodiment) provided in the semiconductor laser array are arranged on a substrate (not shown) at a predetermined interval. These semiconductor lasers 12 and 14 are connected to output terminals of laser drive circuits 34 and 36, respectively, and the amount of light is controlled by the drive current output from the laser drive circuits 34 and 36. The amount of light of the semiconductor laser 12 is controlled by the drive current output from the laser drive circuit 34, and the front beam is emitted forward and the back beam is emitted backward. The front beam is used for optical recording of scanning lines in an image recording apparatus such as a copying machine or a laser printer provided with the light quantity control device 10 according to the present embodiment. On the other hand, the back beam is emitted at the same time as the front beam. At this time, the back beam is emitted with a light amount that is proportional to the light amount of the front beam and less than the front beam. Similarly to the semiconductor laser 12, the amount of light of the semiconductor laser 14 is controlled by the drive current output from the laser drive circuit 36, and the front beam is emitted forward and simultaneously the back beam is emitted backward.
[0016]
A light amount detector 16 is disposed in the vicinity of the semiconductor lasers 12 and 14. The light amount detector 16 is configured by, for example, a photodiode, detects the back beam of the laser light emitted from the semiconductor lasers 12 and 14, and outputs a current corresponding to the detected light amount. The output terminal of the light quantity detector 16 is connected to the input terminal of the current distributor 18. Accordingly, the output current of the light quantity detector 16 is input to the current distributor 18. The current distributor 18 evenly distributes the input output current of the light quantity detector 16 to the amplifiers 20 and 22. The amplifiers 20 and 22 are provided corresponding to the number of the semiconductor lasers 12 and 14, and convert the current distributed by the current distributor 18 into a voltage. At this time, the amplifiers 20 and 22 are provided with the variable resistors RV1 and RV2 (see FIG. 2), thereby correcting variations in the light amount sensitivity of the output characteristics 47 and 49 (see FIG. 3) of the semiconductor lasers 12 and 14, respectively. Gain adjustment can be performed. Accordingly, the amplifiers 20 and 22 output a voltage in which the light amount sensitivity is adjusted.
[0017]
Detailed circuit configurations of the current distributor 18 and the amplifiers 20 and 22 will be described later.
[0018]
The output terminals of the amplifiers 20 and 22 are connected to the input terminals of the comparators 24 and 26, and the output voltages of the amplifiers 20 and 22 are input to the comparators 24 and 26. The comparators 24 and 26 are supplied with a preset reference voltage 28. Accordingly, the comparators 24 and 26 compare the magnitude relationship between the output voltages of the amplifiers 20 and 22 and the preset reference voltage 28, and when the S / H control circuits 30 and 32 described later are in an enabled state. Output high or low voltage. On the other hand, when the S / H control circuits 30 and 32 are in a disabled state, the drive current for driving the semiconductor lasers 12 and 14 is maintained as it is, and current control described later is not performed.
[0019]
The output terminals of the comparators 24 and 26 are connected to the input terminals of the S / H control circuits 30 and 32. The output terminals of the S / H control circuits 30 and 32 are connected to the input terminals of the laser drive circuits 34 and 36. It is connected. Based on the output voltages of the comparators 24 and 26, the S / H control circuits 30 and 32 drive currents output from the laser drive circuits 34 and 36 so that the output of the reference voltage 28 and the light amount detector 16 are the same. To control.
[0020]
FIG. 2 shows the light quantity control device 10 in which the circuit configuration of the current distributor 18 and the amplifiers 20 and 22 is shown.
[0021]
The anode of the light amount detector 16 is connected to the collector terminal of the transistor 38 provided in the current distributor 18, and is connected to the base terminal of the transistor 38, the base terminals of the transistor 40 and the transistor 42. The emitter terminal of the transistor 38 is connected to the constant voltage power supply line 19 via the resistor R1. Further, the constant voltage power line 19 is connected to the emitter terminal of the transistor 40 via the resistor R2, and is connected to the emitter terminal of the transistor 42 via the resistor R3.
[0022]
The collector terminal of the transistor 40 is connected to the amplifier 20, and is connected to the negative side input terminal of the operational amplifier 44 provided in the amplifier 20 via the resistor R5, and is connected to the operational amplifier 44 via the variable resistor RV1. Is connected to the positive input terminal. The variable resistor RV1 can set a resistance value corresponding to the gain of the light amount sensitivity of the semiconductor laser 12. The positive input terminal of the operational amplifier 44 is grounded via a resistor R4. On the other hand, the negative input terminal of the operational amplifier 44 is connected to the positive input terminal of the comparator 24 via the resistor R6, and the output terminal of the operational amplifier 44 is connected to the positive input terminal of the comparator 24. . Accordingly, the output voltage of the operational amplifier 44, that is, the voltage whose gain sensitivity is adjusted by the amplifier 20 is input to the comparator 24.
[0023]
The collector terminal of the transistor 42 provided in the current distributor 18 is connected to the amplifier 22. Since the configuration of the amplifier 22 is substantially the same as that of the amplifier 20 described above, the same parts are denoted by the same reference numerals and description thereof is omitted. The variable resistor RV2 provided in the amplifier 22 is set to a resistance value corresponding to the gain of the light quantity sensitivity of the semiconductor laser 14.
[0024]
Next, the operation of the embodiment of the present invention will be described.
When laser light is emitted from the semiconductor lasers 12 and 14, the light amount detector 16 detects the back beam of the laser light. The light amount detector 16 outputs a current corresponding to the detected light amount of the back beam to the current distributor 18. A current proportional to the output current of the light quantity detector 16 flows through the transistor 38 provided in the current distributor 18. Further, a current proportional to the current flowing through the transistor 38 flows through the transistors 40 and 42. The transistors 40 and 42 are connected to the resistors R2 and R3 having the same resistance value. That is, the currents output from the transistor 40 and the transistor 42 have the same value. As described above, the output current of the light amount detector 16 is evenly distributed to the plurality of amplifiers 20 and 22 by the current distributor 18.
[0025]
Here, the light amount control in the semiconductor laser 12 will be described.
The amplifier 20 converts the current distributed by the current distributor 18 into a voltage and outputs the voltage. At this time, the gain is adjusted by setting the variable resistor RV1 provided in the amplifier 20 to a resistance value corresponding to the gain of the light amount sensitivity of the semiconductor laser 12. That is, the variation in the output characteristics 47 and 49 (see FIG. 3) can be corrected by adjusting the gain of the light amount sensitivity corresponding to each of the semiconductor lasers 12 and 14 provided in the semiconductor laser array.
[0026]
The comparator 24 is supplied with the output voltage of the amplifier 20 (the voltage with which the light intensity sensitivity is adjusted) and a preset reference voltage 28, and compares the magnitude relationship between these voltages.
[0027]
When the S / H control circuit 30 connected to the comparator 24 is enabled by the timing signal T1, the comparator 24 outputs a high-level or low-level voltage. The count mode of an up / down counter (not shown) provided in the S / H control circuit 30 is controlled by this output voltage. For example, when the output voltage of the amplifier 20 is lower than the reference voltage 28, the output voltage of the comparator 28 is at a low level, and the up / down counter operates as an up counter. On the other hand, when the output voltage of the amplifier 20 is higher than the reference voltage 28, the output voltage of the comparator 24 is at a high level, and the up / down counter operates as a down counter. In this way, an up / down counter operation is performed based on the output voltage of the comparator 28, and the drive current for driving the semiconductor laser 12 output from the laser drive circuit 34 so that the reference voltage 28 and the output of the amplifier 20 are the same. To control.
[0028]
On the other hand, when the S / H control circuit 30 is disabled by the timing signal T1, the drive current for driving the semiconductor laser 12 is maintained as it is, and the above-described current control is not performed.
[0029]
As described above, the output current of the light quantity detector 16 is evenly distributed by the current distributor 18 and then converted into a voltage. At this time, the resistance value corresponding to the gain of the light quantity sensitivity of each of the semiconductor lasers 12 and 14 is obtained. By adjusting the gain using the variable resistors RV1 and RV2 that can be set, variations in the light amount sensitivity of the output characteristics 47 and 49 of the semiconductor lasers 12 and 14 can be corrected. Therefore, it is possible to stably and accurately control the light amount by suppressing the light amount difference between the laser beams emitted from the plurality of semiconductor lasers 12 and 14 provided in the semiconductor laser array with a simple circuit configuration.
[0030]
Although the light amount control in the semiconductor laser 12 has been described in the present embodiment, the same applies to the light amount control in the semiconductor laser 14. However, the operation of the S / H control circuit 32 is controlled by the timing signal T2.
[0031]
Further, the output terminal of the current distributor 18 may be connected to the input terminals of the amplifiers 20 and 22 via diodes 46 and 48 (see FIG. 2) which are rectifying elements. In this way, by connecting the current distributor 18 to the amplifiers 20 and 22 via the diodes 46 and 48, it is possible to prevent the current from flowing back to the current distributor 18 when a voltage difference occurs in the amplifiers 20 and 22. Can be prevented.
[0032]
Furthermore, the current distributor 18 is not limited to the circuit configuration shown in the present embodiment, and any circuit configuration may be used as long as the output current of the light amount detector 16 is evenly distributed to the amplifiers 20 and 22.
[0033]
【The invention's effect】
As described above, according to the present invention, the output current of the light quantity detection means is evenly distributed by the current distribution means and then converted into a voltage. At this time, the gain adjustment of the light quantity sensitivity is performed by the variable resistor to Since the variation in the output characteristics is corrected, the light amount can be stably and accurately controlled with a simple circuit configuration.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a light amount control apparatus according to an embodiment.
FIG. 2 is a detailed diagram showing a circuit configuration of a current distributor and an amplifier of the light quantity control device according to the embodiment of the present invention.
FIG. 3 is a graph showing output characteristics of the semiconductor laser in the light amount control apparatus according to the embodiment of the present invention.
FIG. 4 is a block diagram showing a configuration of a conventional light quantity control device.
FIG. 5 is a graph showing output characteristics of a semiconductor laser in a conventional light quantity control device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Light quantity control apparatus 12, 14 Semiconductor laser 16 Light quantity detector (light quantity detection means)
18 Current distributor (current distribution means)
20, 22 Amplifier (conversion means)
24, 26 comparator (comparison means)
30, 32 S / H control circuit (current control means)
34, 36 Laser drive circuit (current control means)
46, 48 Diode (rectifying means)

Claims (2)

A light quantity control device for controlling the quantity of laser light emitted from a plurality of semiconductor lasers provided in a semiconductor laser array,
A light amount detecting means for detecting a light amount of laser light emitted from the plurality of semiconductor lasers and outputting a current corresponding to the detected light amount;
Current distribution means for evenly distributing the output current of the light amount detection means corresponding to the number of the plurality of semiconductor lasers;
A plurality of conversion means for converting each current distributed by the current distributing means to the voltage corresponding to the gain of the light amount sensitivity of each of the plurality of semiconductor lasers,
A plurality of comparison means for respectively comparing output voltages of the plurality of conversion means and a preset reference voltage common to each semiconductor laser ;
A plurality of current control means for controlling a drive current for driving the corresponding semiconductor laser based on a comparison result of the plurality of comparison means;
A light quantity control device.   2. The light quantity control device according to claim 1, further comprising a rectifying unit provided on a downstream side of the current distribution unit and preventing a reverse flow of the current distributed by the current distribution unit.

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