JPH0247746B2 - REEZAAKIROKUSOCHI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser recording device using a semiconductor laser as a light source.

FIG. 1 shows an optical system in an example of a laser recording device. The laser beam emitted from the semiconductor laser 1 passes through a coupling lens 2, a beam shaping optical system 3, mirrors 4 and 5, and a correction optical system 6, and is deflected at equal angles by an optical deflector 7 such as a rotating polygon mirror. - The speed is changed to constant speed by the θ lens 8, and the rotating photoconductor 9 is main scanned, and information is written by exposing it to light. As is well known, this information is developed in a copy processing section and transferred onto recording paper. A photodetector 10 for detecting information writing timing is placed near the photosensitive drum 9 and detects the laser beam from the f-θ lens 8.
The signal from 0 is binarized, and in synchronization with the binarized signal, the semiconductor laser 1 is modulated by a modulation circuit with an information signal for one main scanning line.

FIG. 2 shows a general output control circuit that controls the optical output of a semiconductor laser. Monitor light emitted from the rear of the semiconductor laser 1 is detected by a photodetector 11, and its output signal is amplified by an amplifier 12 and compared with a reference voltage by an error amplifier 13. The output signal of this error amplifier 13 is passed through the low pass filter 1.
4, high-frequency components are removed and input to the drive circuit 15, forming a negative feedback loop. The semiconductor laser 1 is driven by the drive circuit 15 and the amplifier 1
The optical output is controlled so that the output of No. 2 is always equal to the reference voltage.

In the above-mentioned laser recording apparatus, optical parts such as mirrors and lenses are cleaned periodically or when it is determined that the amount of light is insufficient based on the actual recorded image quality. However, when determining insufficient light intensity rather than recorded image quality, for example, a decrease in the density of a recorded image is caused not only by a decrease in light intensity but also due to a malfunction in the copy processing unit.
It is difficult to judge whether the amount of light is insufficient. Furthermore, if the light intensity of the semiconductor laser is increased unnecessarily to obtain a normal image when the light intensity to the photoreceptor drum is reduced due to dirt in the optical system, there is a risk of destroying the semiconductor laser. Furthermore, if the reflectance of only one surface of the rotating polygon mirror decreases due to dirt, etc., the output of the photodetector 10 will decrease, and the timing of rising to the threshold level for binarization will be delayed, causing a delay in the timing of information writing and recording. The image will contain jitter. This jitter is also caused by uneven rotation of the rotating polygon mirror, so it is difficult to determine the cause.

In view of the above circumstances, it is an object of the present invention to provide a laser recording apparatus that detects and displays defects in the optical system, thereby making it possible to easily and accurately handle the defects.

The present invention will be described below by way of examples with reference to the drawings.

An embodiment of the present invention is such that the laser recording apparatus detects and displays when the output difference between the photodetectors 10 and 11 exceeds a predetermined value due to contamination of the optical system or the like. FIG. 3 shows a light output control circuit, an information write timing detection circuit, and an optical system failure detection and display circuit in this embodiment. The monitor light emitted from the rear of the semiconductor laser is directly incident on the photodetector 11, and the photodetector 11 outputs a signal as shown in FIG. 4. This signal is amplified by an amplifier 12, and a peak hold circuit 16 detects and holds the maximum value. The output signal of this peak hold circuit 16 has a waveform as shown in FIG.
It is compared with a reference voltage and the difference is amplified. The output signal of the error amplifier 13 has high frequency components removed by a low-pass filter 14 and is fed back to a drive circuit 15 to control the power supply of the semiconductor laser 1. Therefore, the optical output of the semiconductor laser 1 is controlled so that the output of the peak hold circuit 16 and the reference voltage are always equal.

On the other hand, a laser beam is incident on the photodetector 10 for detecting information writing timing every time the laser beam is scanned by the optical deflector 7, and the output signal is amplified by the amplifier 17, as shown in FIG. Become. The output signal of the amplifier 17 is sent to the binarization circuit 18
The signal is binarized into a synchronization signal as shown in FIG. 4, and in synchronization with this synchronization signal, the semiconductor laser 1 is modulated by the information signal for one main scanning line in a modulation circuit. Further, the output signal of the binarization circuit 18 is waveform-shaped by the waveform shaping circuit 19 to become a pulse as shown in FIG.
The waveforms shown in FIG. 4 are obtained by sampling and holding the pulses from . The output signal of the sampling hold circuit 20 is compared with the output signal of the peak hold circuit 16 in a comparator 21 . The display section operates when the output signal of the comparator 21 exceeds a predetermined value, and indicates a defect due to dirt or the like in the optical system.

As described above, according to the present invention, when the difference between the output signal of the photodetector for information write timing detection and the output signal of the photodetector for controlling optical output exceeds a predetermined value in a laser recording device, the optical system is activated. Since defects such as dirt are displayed, defects caused by dirt and the like in the optical system can be clearly recognized and dealt with easily, and damage caused by increased output of the semiconductor laser can also be prevented.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an example of an optical system in a conventional laser recording device, Fig. 2 is a block diagram showing an optical output control circuit of the same device, and Fig. 3 shows a circuit section in an embodiment of the present invention. The block diagram, FIG. 4, is a timing chart of the same circuit section. 10...Photodetector for information write timing detection, 11...Photodetector for controlling optical output, 21...Comparator.

Claims (1)

[Claims] 1. Information writing timing detection that uses a semiconductor laser as a light source, modulates it with an information signal, main scans the photoconductor with the laser beam from this semiconductor laser to write information, and detects the laser beam near the photoconductor. and a second photodetector for controlling light output that detects light emitted from the rear of the semiconductor laser.
The output signal of the second photodetector is compared with the output signal of the second photodetector, and when the difference between the two output signals exceeds a predetermined value, a defect in the optical system is indicated. Features a laser recording device.