JPS60169179A - Abnormality processing device for semiconductor laser - Google Patents

Abstract

PURPOSE:To protect a semiconductor laser, in an output control circuit for the semiconductor laser using a counter, by making the current of the semiconductor laser zero when the counted value of the counter reaches a specified value, and displaying abnormality. CONSTITUTION:A gate circuit 17 detects the specified preset value when the counted value of an up and down counter 13 becomes said preset value. The output signal of a gate circuit 17 is generated when a driving current for a semiconductor laser 1 is not increased for any reason and the counted value of the up and down counter 13 reaches the preset value. The output signal of the gate circuit 17 is held by a holding circuit 18 and resets the up and down counter 13. Then the counted value is made to be zero. The driving current for the semiconductor laser 1 is also made to be zero and the laser 1 is protected. A display device 19 is provided in an operating panel of a laser printer or in a printed wiring board in the machine. The display device 19 is driven by a driving circuit 20 based on the output signal of the holding circuit 18 and abnormality is displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an abnormality processing device that protects a semiconductor laser and displays an abnormality.

(Prior art) Since the output intensity of a semiconductor laser is extremely unstable with respect to temperature, it is necessary to stabilize the output intensity of the semiconductor laser using a semiconductor laser output control device, etc. in an environment where the ambient temperature of the semiconductor laser changes. It is necessary to do so. A semiconductor laser output control device generally uses a counter, and FIG. 1 shows an example of a laser printer employing this method.

A laser beam generated by a semiconductor laser 1 is collimated by a collimator lens 2, deflected by an optical scanning device 3 consisting of a rotating polygon mirror, and imaged by an fθ lens 4 on the charged surface of a photoreceptor drum 5 to form an image spot. is repeatedly moved in the direction of arrow X by the rotation of the rotating polygon mirror 3, and at the same time, the photosensitive drum 5 rotates. A photodetector 6 is provided outside the information writing area, and detects the laser beam deflected by the rotating polygon mirror 3 to generate a synchronizing signal. The signal processing circuit 7 applies an information signal to the semiconductor laser drive circuit 8, and its dimming is controlled by a synchronization signal from the photodetector 6. The semiconductor laser drive circuit 8 drives the semiconductor laser 1 according to the information signal from the signal processing circuit 7, and therefore, one laser beam modulated by the information signal is irradiated onto the photoreceptor drum 5 to form an electrostatic latent image. be done. This electrostatic latent image is leveled by a developing device and transferred onto paper or the like by a transfer device. The laser beam still emitted backward from the semiconductor laser 1 is detected by the photodetector 9.
The light intensity is detected by the control circuit 10, which controls the semiconductor laser drive circuit 8 in accordance with the output signal of the photodetector 9 to keep the output light amount of the semiconductor laser 1 constant.

FIG. 2 shows the semiconductor laser drive circuit 8 and control circuit 10.
is shown in detail.

A laser beam emitted backward from the semiconductor laser 1 is incident on a photodetector 9 such as a photodiode, and the photodiode 9 outputs a current proportional to the intensity of the laser beam. This current is converted into a spot pressure by an amplifier 11, and compared with a reference voltage Vref by a comparator 12. The output voltage of the comparator 12 is controlled to be a high level or a low level depending on the magnitude relationship between both input voltages of the comparator 12, and the count mode of the shunt down counter 13 is controlled. For example, when the intensity of the laser beam from the semiconductor laser 1 is weaker than the reference value, the output of the comparator 12 is at a low level, and the up/down counter 13 operates as an up counter. When the edge detection circuit 14 releases the enable signal to the up/down counter 13 in response to the timing signal Tl, the count value of the up/down counter 13 increases in response to the clock signal from the oscillator 15. The count output of this up/down counter 13 is sent to the digital/analog converter 1.
6, the signal is converted into an analog quantity and input to the semiconductor laser drive circuit 8.

The semiconductor laser drive circuit drives the semiconductor laser I based on the information signal from the signal processing circuit 7, and changes its drive current in accordance with the output of the digital/analog converter 16. Therefore, as the count value of the up/down counter 13 gradually increases, the intensity of the laser beam from the semiconductor laser 1 gradually increases, and the output of the amplifier 11 increases. Then, when the output of the comparator 12 is inverted from low level to high level.

An edge detection circuit 14 detects the rising edges and edges of the output of the comparator 12 and applies an enable signal to the up/down counter 13. Therefore, the up/down counter 13 is enabled and holds its count value, so that the magnitude of the driving current of the semiconductor laser 1 is maintained as it is. Next, when the edge detection circuit 14 releases the enable state of the up-down counter 13 by the timing signal TI, if the output of the comparator 12 is at a high level (if the output intensity of the semiconductor laser is strong), the up-down counter 13 will be activated. It operates as a down counter and the count value decreases in response to the clock signal from the oscillator 15. Therefore, the output of the digital/analog converter 16 decreases, the drive current of the semiconductor laser 1 decreases, and the output of the amplifier 11 decreases.

Then, when the output of the amplifier 11 becomes smaller than the reference voltage Vref and the output of the comparator 12 is inverted from high level to low level, the edge detection circuit 14 detects the falling edge of the output of the comparator 12 and converts it into an up/down counter. 13 is enabled. Therefore up/down counter 1
3 holds the count value 9, and the magnitude of the driving current of the semiconductor 1 nose 1 is held as it is. Here, the edge detection circuit 14 enables the shrapdown counter 13 according to the timing signal T1.

If the configuration is such that the active counter 13 is enabled only when the output of the comparator 12 is reversed from a low level to a high level after the comparator 12
When the output of the comparator 12 is inverted from a low level to a high level when the output of the comparator 12 is at a low level and the enable of the up/down counter 13 is canceled by the timing signal T+,
The up/down counter 13 is enabled and holds the count value.

When the output of the comparator 12 is at a high level, the timing signal T is generated.

If the output of the comparator 12 goes from a high level to a low level while the enable of the up-down counter 13 is released by I will do it. When the drive current of the semiconductor laser 1 increases and the output of the comparator 12 is reversed from high level to low level, the edge detection circuit 14 detects the falling level.

When the up/down counter 13 is detected, the up/down counter 13 is enabled and its counted value is held. In a laser printer, the environmental temperature changes slowly, and the output fluctuations of the semiconductor laser can be ignored in a short period of time due to the heat capacity of the semiconductor laser and its mounting hardware. For this reason, by using, for example, a print start signal at each start of recording or a power-on reset signal at power-on as the timing signal Tl, fluctuations in the amount of light output from the semiconductor laser can be suppressed and high-quality recorded images 1 can be obtained.
You can get an elephant.

However, in the semiconductor laser output control device of this laser printer, if the output intensity of the semiconductor laser does not increase for some reason, the count value of the up/down counter 13 increases rapidly, and the driving current of the semiconductor laser 1 increases accordingly. There is a risk that the semiconductor laser l will be destroyed.

(Objective) An object of the present invention is to provide an abnormality processing device that protects a semiconductor laser and displays an abnormality in a semiconductor laser output control device using a counter.

(Structure) The present invention will be described below based on examples with reference to the drawings.

FIG. 3 shows an embodiment in which the present invention is implemented on the semiconductor laser output side of the laser printer.

The gate circuit 17 detects when the count value of the up/down counter 13 reaches a predetermined set value.

The above set value is the count value of the up-down counter 13 when the drive current of the semiconductor laser 1 reaches a constant value H [which does not cause the risk of damage to the semiconductor laser 1, and in a normal state, the count value of the up-down counter 13 reaches It is set to a large value so that it does not occur. Therefore, the output signal of the gate circuit 17 is generated when the drive current of the semiconductor laser 1 does not increase for some reason and the count value of the up/down counter 13 reaches the above set value. The output signal of this gate circuit 17 is held by a holding circuit 18 and is sent to an up/down counter 1.
By resetting 3 and making the count value zero, the drive current of the semiconductor laser l is set to zero, and the semiconductor laser l'f
! r: protect. Further, the display device 19 is provided on the operation panel of the laser printer or the printed wiring board inside the machine, and is driven by the drive circuit 20 based on the output signal of the holding circuit 18 to display an abnormality. The operator or service person can learn from the abnormality display that the driving current of the semiconductor laser does not increase for some reason, and can take countermeasures against the abnormality.

Note that the overflow signal of the up/down counter 13 may be used to detect that the count value of the up/down counter 13 has reached the set value. Furthermore, the present invention is not limited to the above-mentioned embodiments, but is a semiconductor laser output control device using a counter, in which the counter is controlled by the output signal of the comparator, and a current proportional to the count value of the counter is controlled by the output signal of the comparator. It can be implemented in a device where the current is passed through a semiconductor laser.

(Effects) As described above, according to the present invention, in a semiconductor laser output control device using a counter, when the count value of the counter reaches a predetermined value, the current of the semiconductor laser is made zero and an abnormality is displayed. In addition, the semiconductor laser can be protected, and an operator or a service person can be notified of an abnormality and can deal with it.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of a laser printer, FIG. 2 is a block diagram showing a part of the same laser printer, and FIG. 3 is a block diagram showing an example of a semiconductor laser output control device to which the present invention is applied. . 17...Gate circuit %18...Holding circuit, 19...
- Display device, 20... drive circuit.

Claims (1)

[Claims] A photodetection means for detecting the first output of the semiconductor laser, a comparator for comparing the output signal of the photodetection means with a reference signal, a counter controlled by the output signal of the comparator, and an output of the counter. A tental/analog converter that converts into an analog quantity, a semiconductor laser drive circuit that flows a current proportional to the output signal of the tental/analog converter to the semiconductor laser, and both input signals of the comparator are always zero. In the semiconductor laser output control device having means for controlling and holding the current of the semiconductor laser, when the count value of the counter reaches a predetermined value, the current of the semiconductor laser is made zero and an abnormality is detected. A semiconductor laser abnormality processing device characterized by displaying information.