JPS6397060A - Laser recorder - Google Patents

Abstract

PURPOSE:To prevent the errorneous output of a maintenance signal by providing a counting means consisting of a programmable timer circuit and a temperature detecting means and the like, and setting a maximum current value which can be caused to flow to a laser diode at that time variable. CONSTITUTION:If an APC signal which is a start signal for controlling the strength of a laser beam projected on a photoconductive sensitive drum from a control circuit 28 is outputted, the illumination of the laser beam projected on the photoconductive sensitive drum changes with a prescribed value as a boundary. In such a case, the resistant value of a thermister 28a provided in the circuit 28 changes according to the change in temperature, and the change appears as a change in the value of an analogue signal outputted from an operational amplifier 28e. Namely, the thermister 28 decides time of a digital counter in the programmable timer circuit 29 until time over(time corresponding to the maximum value which is caused to flow to the laser diode 21 in the peripheral temperature at that time). Thus, the errorneous output of the maintenance signal can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a laser recording device used as a copying machine, a printer, or the like.

Conventional technology Conventionally, laser recording devices using electrophotography using a laser diode form an electrostatic latent image on the surface of a photoconductive photosensitive drum using laser light generated from a laser diode, and then develop the electrostatic latent image. In many cases, the resulting toner image is transferred to ordinary recording paper, and then the transferred toner image is fixed to obtain a recorded matter.

As shown in FIG. 4, this type of laser recording device rotates a photoconductive photosensitive drum 1o at a constant speed for image formation, and attaches a laser beam output from a laser diode 1 to a polygon motor 11. polyhedral mirror 1
2, and further corrects errors such as beam diameter using an fθ lens 13, and repeatedly scans the photoconductive photosensitive drum 10 in its axial direction to form an electrostatic latent image on the photoconductive photosensitive drum 10. That's what I do.

Furthermore, during scanning with the laser beam, the photoelectric conversion element 14 for position detection, which is arranged near the photoconductive photosensitive drum and outside the image forming area, is also irradiated with the laser beam for each scan.
Under time management from the time when the light passes through the photoelectric conversion element 14, the drive current of the laser diode 1 is switched on and off based on the modulation signal, and the laser light is modulated.

In such a laser recording apparatus, in order to obtain a high-quality recorded image, it is necessary to maintain the intensity of the laser light irradiated onto the surface of the photoconductive photosensitive drum to a substantially constant value.

The configuration of the main parts of a conventional laser recording apparatus will be explained below with reference to the block diagram of FIG.

In the figure, 1 is a laser diode, 2 is placed near the photoconductive drum, and converts the intensity of the irradiated laser light output from the laser diode 1 and irradiated onto the photoconductive drum via an fθ lens etc. into an analog signal. 3 is a comparison circuit that compares the analog signal output from the pin photodiode 2 with a preset reference electric signal and outputs the result as a binary code. , 4 is a digital counter circuit that is switched between count-up mode and count-down mode by the binary numbering, 5 is a digital-analog conversion circuit that converts the digital signal of the digital counter circuit 4 into an analog signal, and 6 is the digital-analog converter circuit. a current control circuit 7 that controls the drive current flowing to the laser diode 1 according to the analog signal output from the conversion circuit;
8 is a modulation circuit that intermittents the driving current of the laser diode 1 according to a modulation signal, and 8 is a control circuit that controls the digital counter circuit 4. FIG. 6 is a circuit diagram showing the detailed configuration of the digital counter circuit 4 and the digital-to-analog converter circuit 5 described above. A down counter is constructed, and the 8-bit digital signal is input to a digital-to-analog conversion circuit 5 having 8-bit resolution. Further, the 8-bit digital signal is input in parallel to an 8-manufactured NAND gate 9.

In the conventional laser recording device configured as described above,
First, the control circuit 8 generates a start signal (
The following APC signal (AUTOPOWERC0NTR0L)
) is output to the reset terminals (R) of the digital counters 4a, 4b. Then digital counter 4a
, 4b become operational, and the data input terminals D1 to D
The minimum value 'OJ set to 4 is loaded.

Therefore, the digital signals output from the digital counters 4a and 4b have the minimum value, and the set current of the current control circuit 6 also has the minimum value. Therefore, the emission intensity of the laser diode 1 is also at its minimum value, and the value of the analog signal output from the pin photodiode 2 is less than the reference electric signal. Therefore, the 2M signal output from the comparator circuit 3 is at a high level, and this binary value is The numbers are input to the up/down terminals (hereinafter referred to as U/D terminals) of the digital counters 4a and 4b,
In the count-up mode, the digital counter counts up by "1" according to the sample clock, the set current of the current control circuit 6 gradually increases, the laser emission intensity also increases, and the analog signal from the pin photodiode 2 increases. The value of the signal also becomes thick (becomes). Then, when the value of the analog signal exceeds the reference electric signal, the binary sign output from the comparator circuit 3 becomes low level and is sent to the U/D terminals of the digital counters 4a and 4b. input, each digital counter enters countdown mode and counts down by 'IJ' according to the sample clock.Then, the set current of the current control circuit 6 decreases, the emission intensity of the laser diode 1 also decreases, and the analog signal of the pin photodiode 2 decreases. Since the voltage is less than the base r!! electric signal, the binary code from the comparator circuit 3 becomes high level again, and the digital counters 4a and 4b enter the count-up mode.

By repeating the above operations, the intensity of the laser light irradiated to the photoconductive drum can be adjusted to ±
It fluctuates within a one-step fluctuation range.

Here, if the intensity of the laser light irradiated to the photoconductive photosensitive drum decreases due to deterioration of the laser diode 1, etc., the value of the analog signal from the pin photodiode will become smaller, compared to when it is not deteriorated. The count-up period becomes longer, and therefore the boundary value between the count-up mode and the count-down mode becomes thicker (as the drive current of the laser diode 1 increases, the intensity of the laser light irradiated to the photoconductive photosensitive drum increases). be compensated.

Then, as the deterioration of the laser diode gradually increases, the value of the digital signal output from the digital counters 4a and 4b gradually increases, and the value finally reaches rFF.
(Hex)'', and all the inputs of the 8-man power NAND gate 9 become high level, so the output from the NAND gate 9 becomes low level rather than high level, and a maintenance signal is output.

This maintenance signal drives an abnormality display circuit (not shown) and causes, for example, a light emitting diode to shine, thereby informing the operator that the laser diode is abnormal.

Problems to be Solved by the Invention Incidentally, it is known that the relationship between the drive current of a laser diode and the emission intensity varies considerably depending on the ambient temperature under the conditions of use, as shown in FIG.

From this figure, it can be seen that in order to obtain the same emission intensity, the higher the ambient temperature, the larger the value of the drive current must be.

For this reason, in the conventional device, if the ambient temperature at which the laser recording device can be used is, for example, 0 to 50°C, the maximum current value flowing through the laser diode must be set at 0°C. This is because of the following reasons.

In other words, when the maximum current value is determined at, for example, 50°C, if the intensity of the laser light reaching the photoconductive photosensitive drum decreases due to dirt on the optical system such as the fθ lens, the analog signal output from the pin photodiode will change. The value also decreases, so the comparator circuit 3, digital counter circuit 4,
The value of the current flowing to the laser diode 1 via the digital-to-analog conversion circuit 5 and the current control circuit 6 is gradually increased toward the maximum current value. At that time, if the ambient temperature when this laser recording device is used is 0°C, the laser diode 1 will have a maximum output value Pm at 0°C.
This is because a current exceeding ax (0° C.) is caused to flow, which causes a problem that the laser diode is destroyed.

However, the maximum current value flowing to the laser diode is 0.
Even if it is set at ℃, the following problems will occur.

That is, if the current ambient temperature of this laser recording device is 25°C, which is higher than 0°C, then at 25°C, the seventh
Imax(
25°C), the current value is
This causes a malfunction in which a maintenance signal is output when the temperature reaches max (0°C).

Means for Solving the Problems Accordingly, the laser recording device of the present invention
The configuration is such that the maximum current value that can be passed through the laser diode at that time is variable.

Function: With this configuration, it is possible to increase the current flowing through the laser diode up to the maximum current value depending on the ambient temperature at that time.

EXAMPLE Hereinafter, an explanation of an example of the laser recording apparatus of the present invention will be given in the first example.
Do this referring to the diagram.

In FIG. 1, 21 is a laser diode, 22 is placed near the photoconductive drum, and is an analog signal that measures the intensity of the laser light output from the laser diode 21 and irradiated onto the photoconductive drum via an fθ lens, etc. A pin photodiode 23, which is an example of a photoelectric conversion element that converts into a signal, compares the analog signal output from the pin photodiode 22 with a preset reference electric signal, and assigns a binary value to the result. 24 is a digital counter circuit that is switched between count-up mode and count-down mode by the binary code; 25 is a digital-to-analog conversion circuit that converts the digital signal of the digital counter circuit 24 into an analog signal; 26 is a current control circuit that controls the drive current flowing to the laser diode 21 according to the analog signal output from the digital-to-analog conversion circuit; 27 is a modulation circuit that intermittents the drive current to the laser diode 21 according to a modulation signal; 29
28 is a programmable timer circuit that is reset by the binary code output from the comparator circuit 23; 28 is an M control circuit that controls the digital counter circuit 24 and the programmable timer circuit 29; There is.

FIG. 2 is a circuit diagram showing the detailed configuration of the digital counter circuit 24 and the digital-to-analog converter circuit 25 described above. A down counter is constructed, and the 8-bit digital signal is input to a digital-to-analog conversion circuit 25 having 8-bit resolution. Also, inside the programmable timer circuit are 4-bit digital counters 29a and 29a.
9b, and when the carrier of 29b becomes high level, it is latched by the flip-flop 29C and a maintenance signal is generated.

29d is a two-man AND gate, 29e is an inverter, 2
9f is a flip-flop.

FIG. 3 is a circuit diagram showing a part of the internal configuration of the control circuit 28. In the figure, 28a is a thermistor whose resistance value changes depending on the temperature, 28b, 28c, and 28d are resistors, and 28e is the thermistor 28a. An operational amplifier 28f amplifies the difference between the voltage divided by the resistor 28b and the resistor 28C and the resistor 28d, and the operational amplifier 28f converts the analog temperature signal output from the operational amplifier 28e into a digital temperature signal. It is an analog-to-digital conversion circuit.

In the laser recording apparatus of this embodiment configured as described above, when the APC signal is output from the control circuit 28, the signal is input to the R terminals of the digital counters 24a and 24b, and both counters become ready for operation. As in the conventional example, the digital counters 24a and 24b alternately switch between count-up mode and count-down mode, and the intensity of the laser light irradiated to the photoconductive photosensitive drum fluctuates within a range of ±1 step from a predetermined value. do.

Furthermore, as shown in FIG.
This occurs as a change in the value of the analog signal output from e, and is input to the analog-to-digital conversion circuit 28f, where it becomes a change in the digital temperature signal.

Then, as shown in FIG. 2, the signals are input to terminals D1 to D4 of digital counters 29a and 29b of the programmable timer circuit.

When the APC signal becomes high level, the digital counters 29a and 29b of the programmable timer circuit also become operable. Next, the control circuit 28 inputs a load signal to the Load terminals of the digital counters 29a and 29b, and the digital temperature signals D1 to D4 are loaded and timed according to the sample clock. When the binary code from the comparison circuit 23 becomes low level, it is latched by the flip-flop 29f, and the digital counters 29a and 29b of the programmable timer circuit are reset.

Here, if the emission intensity of the laser diode 210 does not increase due to deterioration or destruction of the laser diode 21, and the intensity of the laser light irradiated to the pin photodiode 22 does not reach a predetermined value, the 2 Since the value sign remains at high level, the digital counter circuit 29a
, 29b continue to count up until the drive current reaches the maximum allowable value. At this time, the digital counters 29a and 29b of the programmable timer circuit 29 time out, and the carrier from the digital counter 29b is latched into the flip-flop 29c, thereby generating a maintenance signal.

In addition, if the intensity of the laser beam irradiated to the pin photodiode 22 decreases due to dirt in the optical system such as the fθ lens, the output from the comparator circuit 23 will not reach the low level easily, so the digital counters 29a and 29b will not count. If it continues to increase and the time is over, the carrier from the digital counter 29b is latched into the flip-flop 29c and a maintenance signal is generated, as in the case described above. Furthermore, if the intensity of the laser light irradiated to the pin photodiode 22 reaches a predetermined value before this time-out, the comparator circuit 23 becomes low level, so it fluctuates within a range of ±1 step from that value. As a result, it behaves the same as usual.

According to this embodiment, the time until the digital counters 29a and 29b time out (this time corresponds to the maximum current value flowing to the laser diode 21 at the ambient temperature at that time) is determined by the thermistor according to the ambient temperature at that time. This eliminates the malfunctions that previously occurred.

Effects of the Invention As explained above, the laser recording device of the present invention is configured such that the maximum current value that can be passed through the laser diode at that time is variable depending on the ambient temperature during use, so that the maintenance signal can be adjusted. There is no erroneous output, and it is practically effective.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the main parts of a laser recording device according to an embodiment of the present invention, and FIG. 2 shows the detailed configuration of the digital counter circuit 24 and digital-to-analog conversion circuit 25 in FIG. 1. FIG. 3 is a circuit diagram showing a part of the internal configuration of the control circuit 28 in FIG.
The figure is a perspective view showing the main components of a laser recording device, FIG. 5 is a block diagram showing the structure of the main parts of a conventional laser recording device, and FIG. 6 shows the digital counter circuit 4 and digital/analog circuit in FIG. FIG. 7 is a circuit diagram showing the detailed configuration of the conversion circuit 5, and a characteristic curve diagram showing the relationship between the driving current of the laser diode and the emission intensity. 21... Laser diode, 22... Pin photodiode, 23...
...Comparison circuit, 24...Digital counter circuit, 24a, 24
b...Digital counter, 25...Digital-to-analog conversion circuit, 26...Current control circuit, 27...Modulation circuit, 28...・Control circuit, 28a...Thermistor, 28b, 28
c, 28d--Resistor, 28e--Operational amplifier, 28f--Analog-to-digital conversion circuit, 29
...Programmable timer circuit, 29a, 29
b...Digital counter, 29c...
Flip-flop, 29d... 2-person AND gate, 29e... Inverter, 29f... Flip 70 Tsubu Name of agent Patent attorney Toshio Nakao 1 person N
Portrait N
〜＝Fumi Pillar Facilitation −+Contest Participation−−Contest−−−−ψ+−−− , (%J rQ + LQ<1. ”' ” Figure 7 Procedural Amendment Document February 2, 1988 Roro 62 Hirobi 1 Indication of the case Patent application No. 242513 of 1985 2 Name of the invention Laser recording device 3 Person making the amendment Relationship to the case Patent application Person 1006 Kadoma, Kadoma City, Osaka Prefecture Name Name
(5B2) Representative of Matsushita Electric Industrial Co., Ltd.
Akio Tanii 4 agents 〒5
71 Address 1006-5 Kadoma, Kadoma City, Osaka Prefecture Specifications to be amended Document 1, Name of the invention Laser recording device 2, Claims (1) Laser diode and intensity of laser light output from the laser diode a photoelectric conversion element that converts the signal into an electrical signal; a comparison circuit that compares the output signal from the charging conversion element with a preset reference signal and outputs a comparison result; a counter circuit that can be switched between a mode and a countdown mode, a current control circuit that controls the magnitude of a drive current flowing through the laser diode according to an output signal of the counter circuit, and a counter circuit that can set a time until a time-out in advance; 1. A laser recording device characterized by comprising a timer for measuring the count-up time of a circuit and outputting a maintenance signal when the time is over. (2) The laser recording device according to paragraph 2, wherein the timekeeping means is a programmable timer circuit. (3) The timekeeping means is started at the same time as the counter circuit, and is reset by the output from the comparison circuit. The laser recording device according to item 1 or 2. (4) The time until time-out in the timing means corresponds to the maximum allowable current value of the laser diode. 3. Detailed description of the invention Industrial application field Book The present invention relates to a laser recording device used as a copying machine, a printer, etc. Conventional technology Conventionally, a laser recording device using an electrophotographic method using a laser diode uses laser light generated from a laser diode. An electrostatic latent image is formed on the surface of the photoconductive photosensitive drum, and a seven-toner image obtained by developing the electrostatic latent image is transferred to ordinary recording paper, and then the transferred toner image is fixed to form a recorded matter. As shown in FIG. 4, this type of laser recording device rotates a photoconductive photosensitive drum 10 at a constant speed for image formation, and uses a laser beam output from a laser diode 1. Polygon mirror 1 attached to polygon motor 11
2, and further corrects errors such as beam diameter using an fθ lens 13, and repeatedly scans the photoconductive photosensitive drum 10 in its axial direction to form an electrostatic latent image on the photoconductive photosensitive drum 10. That's what I do. Furthermore, during scanning with the laser beam, the photoelectric conversion element 14 for position detection, which is arranged near the photoconductive photosensitive drum and outside the image forming area, is also irradiated with the laser beam for each scan.
Under time management from the time when the light passes through the photoelectric conversion element 14, the drive current of the laser diode 1 is switched on and off based on the modulation signal, and the laser light is modulated. In such a laser recording apparatus, in order to obtain a high-quality -a quasi-image, it is necessary to keep the intensity of the laser light irradiated onto the surface of the photoconductive photosensitive drum to a substantially constant value. The configuration of the main parts of a conventional laser recording apparatus will be explained below with reference to the block diagram of FIG. In the figure, 1 is a laser diode, 2 is placed near the photoconductive drum, and converts the intensity of the irradiated laser light output from the laser diode 1 and irradiated onto the photoconductive drum via an fθ lens etc. into an analog signal. 3 is a comparison circuit that compares the analog signal output from the pin photodiode 2 with a preset reference electric signal and outputs the result as a binary code. , 4 is a digital counter circuit that is switched between count-up mode and count-down mode by the binary numbering, 5 is a digital-analog conversion circuit that converts the digital signal of the digital counter circuit 4 into an analog signal, and 6 is the digital-analog converter circuit. a current control circuit 7 that controls the drive current flowing to the laser diode 1 according to the analog signal output from the conversion circuit;
8 is a modulation circuit that intermittents the driving current of the laser diode 1 according to a modulation signal, and 8 is a control circuit that controls the digital counter circuit 4. FIG. 6 is a circuit diagram showing the detailed configuration of the digital counter circuit 4 and the digital-to-analog converter circuit 5 described above. A down counter is constructed, and an 8-bit digital signal is input to a digital-to-analog conversion circuit 5 having an 8-bit resolution. Further, the 8-bit digital signal is input in parallel to an 8-manufactured NAND gate 9. In the conventional laser recording device configured as described above,
First, the i\ill ia circuit 8 outputs a start signal (hereinafter referred to as an APC signal) for controlling the intensity of the laser beam irradiated onto the photoconductive drum at a constant level.
TR0L) is output to the reset terminals (R) of the digital counters 4a and 4b. Then, the digital counters 4a and 4b become operational, and the minimum value rOJ set to the data input terminals D1 to D4 is loaded. Therefore, the digital signals output from the digital counters 4a and 4b have the minimum value, and the set current of the current control circuit 6 also has the minimum value. Therefore, the emission intensity of the laser diode 1 becomes the minimum value, and the value of the analog signal output from the pin photodiode 2 becomes less than the reference electric signal. Therefore, the binary code output from the comparator circuit 3 becomes a high level. The binary numbers are input to the up/down terminals (hereinafter referred to as U/D terminals) of the digital counters 4a and 4b,
In the count-up mode, the digital counter counts up by rl in accordance with the sample clock, the set current of the current control circuit 6 gradually increases, the laser emission intensity also increases, and the analog signal from the pin photodiode 2 increases. The value of will also increase. When the value of the analog signal exceeds the reference electric signal, the binary sign output from the comparator circuit 3 becomes low level and is input to the U/DP and W terminals of the digital counters 4a and 4b, causing each digital counter to count down. mode, sample,
Counts down by rl according to the clock. Then, the set current of the current control circuit 6 decreases, the emission intensity of the laser diode 1 also decreases, and the analog signal of the pin photodiode 2 also becomes less than the reference electric signal, and the two from the comparison circuit 3
The price tag becomes high level again, and the digital counter 4a
, 4b enter count-up mode. By repeating the above operations, the intensity of the laser light irradiated to the photoconductive drum can be adjusted to ±
It fluctuates within a one-step fluctuation range. Here, if the intensity of the laser light irradiated to the photoconductive photosensitive drum decreases due to deterioration of the laser diode l, the value of the analog signal from the pin photodiode becomes smaller, compared to when it is not deteriorated. The count-up period becomes longer, and therefore the boundary value between the count-up mode and the count-down mode becomes thicker (as the drive current of the laser diode 1 increases, the intensity of the laser light irradiated to the photoconductive photosensitive drum increases). Then, as the deterioration of the laser diode gradually increases, the value of the digital signal output from the digital counters 4a and 4b gradually increases, and the value finally reaches rFF.
(Hex)'', and all inputs of the 8-man power NAND gate 9 become high level, so the output from the NAND gate 9 becomes low level rather than high level, and a maintenance signal is output. This maintenance signal drives an abnormality display circuit (not shown) and causes, for example, a light emitting diode to shine, thereby notifying the operation sound that the laser diode is abnormal. Problems to be Solved by the Invention Incidentally, it is known that the relationship between the drive current of a laser diode and the emission intensity varies considerably depending on the ambient temperature under the conditions of use, as shown in FIG. From this figure, in order to obtain the same emission intensity, the ambient temperature must be high (
It can be seen that the more the value of the drive current increases, the more the value of the drive current must be increased. For this reason, in the conventional device, if the ambient temperature at which the laser recording device can be used is, for example, 0 to 50°C, the maximum current value flowing through the laser diode must be set at 0°C. This is because of the following reasons. In other words, when the maximum current value is determined at, for example, 50°C, if the intensity of the laser light reaching the photoconductive photosensitive drum decreases due to dirt on the optical system such as the fθ lens, the analog signal output from the pin photodiode will change. The value also decreases, so the comparator circuit 3, digital counter circuit 4,
The value of the current flowing to the laser diode 1 via the digital-to-analog conversion circuit 5 and the current control circuit 6 is gradually increased toward the maximum current value. At that time, if the ambient temperature when this laser recording device is used is 0°C, the laser diode 1 will have a maximum output value Pm at 0°C.
This is because a current exceeding ax (0° C.) is caused to flow, which causes a problem that the laser diode is destroyed. However, the maximum current value flowing to the laser diode is 0.
Even if it is set at ℃, the following problems will occur. That is, if the current ambient temperature of this laser recording device is 25°C, which is higher than 0°C, then at 25°C, the seventh
Imax, which is a value greater than or equal to Imax (0°C) shown in the figure
Although the current can flow up to (25℃), the current value is r
This causes a malfunction in which a maintenance signal is output when the temperature reaches max (0° C.). In addition to the characteristic changes due to temperature as described above, the characteristics of laser diodes vary widely between products, so the maintenance signal is
If the output is fixed so that it is output when the output becomes ``(hex)'', it also has the disadvantage that it cannot deal with this variation between products. Means for Solving the Problems Therefore, the laser recording device of the present invention measures the count-up time of a counter circuit in which the time until time-out can be set in advance and can be switched between count-up mode and count-down mode by the output from the comparator circuit. and a timer for outputting a maintenance signal when the timer is out of time. Function: With this configuration, the current flowing through the laser diode can be increased to a maximum current value depending on, for example, the ambient temperature at that time or the laser diode used. EXAMPLE Hereinafter, an explanation of an example of the laser recording apparatus of the present invention will be given in the first example.
Do this referring to the diagram. In FIG. 1, 21 is a laser diode, 22 is placed near the photoconductive drum, and is an analog signal that measures the intensity of the laser light output from the laser diode 21 and irradiated onto the photoconductive drum via an fθ lens, etc. A pin photodiode 23, which is an example of a photoelectric conversion element that converts into a signal, compares the analog signal output from the pin photodiode 22 with a preset reference electric signal, and assigns a binary value to the result. 24 is a digital counter circuit which can be switched between the power C Kun add-up mode and the countdown mode by the binary number; 25;
26 is a digital-to-analog conversion circuit that converts the digital signal of the digital counter circuit 24 into an analog signal;
27 is a current control circuit that controls the drive current flowing to the laser diode 21 in accordance with the analog signal output from the digital-to-analog conversion circuit; 27 is a modulation circuit that intermittents the drive current to the laser diode 21 according to a modulation signal;
9 is a programmable timer circuit that is reset by the binary code output from the comparator circuit 23; 28 is a control circuit that controls the digital counter circuit 24 and the programmable timer circuit 29; It is growing. FIG. 2 is a circuit diagram showing the detailed configuration of the digital counter circuit 24 and the digital-to-analog converter circuit 25 described above. A down counter is constructed, and the 8-bit digital signal is input to a digital-to-analog conversion circuit 25 having 8-bit resolution. Also, inside the programmable timer circuit are 4-bit digital counters 29a and 29.
When the two carriers b become high level, they are latched by the flip-flop 29C and a maintenance signal is generated. 29d is a two-man AND gate, 29e is an inverter, 2
9f is a flip-flop. FIG. 3 is a circuit diagram showing a part of the internal configuration of the control circuit 28. In the figure, 28a is a thermistor whose resistance value changes depending on the temperature, 28b, 28c, and 28d are resistors, and 28e is the thermistor 28a. An operational amplifier 28f amplifies the difference between the voltage divided by the resistor 28b and the resistor 28C and the resistor 28d, and the operational amplifier 28f converts the analog temperature signal output from the operational amplifier 28e into a digital temperature signal. It is an analog-to-digital conversion circuit. In the laser recording apparatus of this embodiment configured as described above, when the APC signal is output from the control circuit 28, the signal is input to the R:4J terminals of the digital counters 24a and 24b, and both counters are in an operable state. As in the conventional example, the digital counters 24a and 24b alternately switch between the count-up mode and the count-down mode, and the intensity of the laser light irradiated onto the photoconductive photosensitive drum is within a range of ±1 step from a predetermined value. It fluctuates. Further, as shown in FIG. 3, the resistance value of the thermistor 28a changes depending on the temperature change, and this change is caused by the change in the resistance value of the operational amplifier 28e.
This occurs as a change in the value of the analog signal outputted from the converter circuit 28f, and is input to the analog-to-digital conversion circuit 28f, where it becomes a change in the digital temperature signal. Then, as shown in FIG. 2, the signals are input to terminals D1 to D4 of digital counters 29a and 29b of the programmable timer circuit. When the APC signal becomes high level, the digital counters 29a and 29b of the programmable timer circuit become operational. Next, the control circuit 28 inputs a load signal to the Load terminals of the digital counters 29a and 29b, and the digital temperature signals D1 to D4 are loaded and timed according to the sample clock. When the binary code from the comparison circuit 23 becomes low level, it is latched by the flip-flop 29f, and the digital counters 29a and 29b of the programmable timer circuit are reset. Here, if the emission intensity of the laser diode 21 does not increase due to deterioration or destruction of the laser diode 21, and the intensity of the laser light irradiated to the pin photodiode 22 does not reach a predetermined value, the Since the binary code remains at high level, the digital counter circuit 29a
, 29b continue to count up until the drive current reaches the maximum allowable value. At this time, the digital counters 29a and 29b of the programmable timer circuit 29 time out, and the carrier from the digital counter 29b is latched into the flip-flop 29c, thereby generating a maintenance signal. In addition, if the intensity of the laser beam irradiated to the bin photodiode 22 decreases due to dirt on the optical system such as the fO lens, the output from the comparator circuit 23 will not reach the low level easily, so the digital counters 29a and 29b will not count. If it continues to increase and the time is over, the carrier from the digital counter 29b is latched into the flip-flop 29c and a maintenance signal is generated, as in the case described above. Furthermore, if the intensity of the laser light irradiated to the pin photodiode 22 reaches a predetermined value before this time-out, the comparator circuit 23 becomes low level, so it fluctuates within a range of ±1 step from that value. As a result, it behaves the same as usual. According to this embodiment, the time until the digital counters 29a and 29b time out (this time corresponds to the maximum current value flowing to the laser diode 21 at the ambient temperature at that time) is determined by the thermistor according to the ambient temperature at that time. This eliminates the malfunctions that previously occurred. Furthermore, in this embodiment, data corresponding to the operating temperature at that time was used as the 8-bit data loaded into the digital counters 29a and 29b, but as this data, different characteristic data for each laser diode was used. Needless to say, it's a good thing. Effects of the Invention As explained above, the laser recording device of the present invention has a structure in which the maximum current value that can be passed through the laser diode at that time is variable depending on, for example, the ambient temperature during use and the laser diode used. This configuration prevents maintenance signals from being output erroneously (,
It is practically effective. 4. Brief description of the drawings Fig. 1 is a block diagram showing the configuration of the main parts of a laser recording device according to an embodiment of the present invention, and Fig. 2 shows the digital counter circuit 24 and digital-to-analog conversion circuit in Fig. 1. 3 is a circuit diagram showing a detailed configuration of the control circuit 25, FIG. 3 is a circuit diagram showing a part of the internal configuration of the control circuit 28 in FIG.
The figure is a perspective view showing the main components of a laser recording device, and FIG. 5 is a conventional laser recording device 1. A block diagram showing the configuration of the main parts of the I device, FIG. 6 is a circuit diagram showing the detailed configuration of the digital counter circuit 4 and digital-to-analog converter circuit 5 in FIG. 5, and FIG. FIG. 3 is a characteristic curve diagram showing the relationship between current and luminescence intensity. 21... Laser diode, 22... Pin photodiode, 23...
...Comparison circuit, 24...Digital counter circuit, 24a, 24
b...Digital counter, 25...Digital-to-analog conversion circuit, 26...Current control circuit, 27...Modulation circuit, 28...・Control circuit, 28a...Thermistor, 28b, 28
c, 28d...-Resistor, 28e...Operational amplifier, 28f...Analog-to-digital conversion circuit, 29
...Programmable timer circuit, 29a, 29
b...Digital counter, 29c...
Flip-flop, 29d...Two-man AND gate, 29e...Inverter,

Claims (4)

[Claims] (1) A laser diode, a photoelectric conversion element that converts the intensity of laser light output from the laser diode into an electrical signal, and a comparison between the output signal from the photoelectric conversion element and a preset reference signal. A comparison circuit that outputs a comparison result, a counter circuit that is switched between a count-up mode and a count-down mode according to the output from the comparison circuit, and a magnitude of a drive current flowing to the laser diode is controlled in accordance with an output signal of the counter circuit. a current control circuit that measures the count-up time of the counter circuit and outputs a maintenance signal when the time is over; a temperature detection device that detects the ambient temperature of the laser diode; 1. A laser recording device comprising: a control circuit that sets a time until a timeout of the clock means based on the output. (2) The laser recording device according to claim 1, wherein the time measuring means is constituted by a programmable timer circuit. (3) The laser recording device according to claim 1 or 2, wherein the timer is started at the same time as the counter circuit and is reset by an output from the comparator circuit. (4) The laser recording device according to any one of claims 1 to 3, wherein the time until time-out in the timer is set to a value corresponding to the maximum allowable current value of the laser diode. Device.