JPS6367962A - Defect detecting circuit for optical system in laser printer - Google Patents

Abstract

PURPOSE:To easily investigate a defect generating position by comparing the output voltage of a detecting circuit with a threshold during a time band sending a BMON signal. CONSTITUTION:Since a control circuit 11 is led after sending a video signal and trailed synchronously with a scanning start signal, the circuit 11 modulates a laser beam for a fixed period and forms a signal to be sent to a rotary mirror 5 as primary light. A laser beam sent from a laser unit 1 is inputted to an optical modulator 2, and when the modulator 2 is not driven, sent to a detector 9 through a slit of a shielding plate 4. A comparator 10 compares the output Vi of the detector 9 with the threshold during the period of a BMON signal based on a clock formed synchronously with the scanning start signal and detects a state that >=80% light, e.g., is inputted to the detector as 0-order light and a state that the laser beam from the laser unit 1 is instantaneously interrputed as if the laser beam is not temporarily sent is detected.

Description

[Detailed Description of the Invention] [Summary] In the optical system of a laser printer, a defect in the laser unit, a defect in the optical modulator and its drive circuit, a defect in other rotary mirror drive motors, etc. are detected separately. This makes it easier to locate the fault, especially in the case of faults that occur intermittently and need to be recovered.

[Industrial application field]

The present invention relates to a circuit for detecting defects in the optical system of a laser printer, and more particularly, a circuit for detecting defects in the optical system of a laser printer that distinguishes and detects defects in a laser unit, an optical modulator and its drive circuit, and other defects. Regarding.

The optical system of a laser printer generally includes a laser unit that emits laser light, an optical modulator that splits the laser light into 0-order light and 1st-order light, a drive circuit that drives the optical modulator, and 1-order light. A rotating mirror that receives light and reflects it in the scanning direction, a lens that uniformly images the primary light reflected by the rotating mirror on a photosensitive drum, and a scanning start signal of the primary light by the rotating mirror, It is equipped with a detector that detects light that has passed through the lens, and defects in the optical system are detected by the detector.

By the way, some defects in the optical system occur intermittently and can be recovered from, and in this case, it is necessary to be able to easily detect the defective location.

[Conventional technology]

FIG. 6 is a block diagram illustrating a conventional optical system.

The laser unit 1 constantly emits laser light, and this laser light is manually input to the optical modulator 2.

When the optical modulator 2 is not driven, it sends out this laser light with almost no attenuation.

When the optical modulator 2 is driven by the drive circuit 3, approximately 40
% is sent out as zero-order light, and the remaining approximately 60% is sent out as first-order light in a direction different from the sending direction of the zero-order light. This primary light passes through the slit of the shielding plate 4 provided with a slit,
It is reflected by the mirror and sent to the rotating mirror 5.

The rotating mirror 5 is a polygon mirror rotated by a motor, reflects the primary light in the scanning direction, and sends it to the lens 6. The lens 6 uniformly images this reflected primary light onto the photosensitive drum.

A detector 7 detects the reflected primary light by a mirror 8 that reflects the light that first passed through the lens 6, and sends it out as a scanning start signal.

[Problem that the invention seeks to solve]

A laser printer scans a beam of laser light on a photosensitive drum, and the position where this beam hits becomes exposed to light.
Dots are formed, and a collection of these dots constitutes characters. Driven by the drive circuit 3, the optical modulator 2 sends primary light that forms this dot to the rotating mirror 5, but the video signal sent to the drive circuit 3 is synchronized with the scan start signal detected by the detector 7. Sent synchronously.

Since this scan start signal is an important signal that is also used to check the power of the laser unit 1, the cycle of this scan start signal is checked.

However, this scanning start signal is caused by fluctuations in the rotational speed of the rotating mirror 5.
Detection may not be possible due to a defect in the laser unit 1, a defect in the optical modulator 2, a defect in the drive circuit 3, or the like. Therefore, when a cycle abnormality in the scan start signal is detected, there are many factors that cause the abnormality, making it difficult to identify the defective location. In particular, a momentary interruption of the laser beam occurs suddenly, and when it is restored, it is even more difficult to investigate the defect.

[Means for solving problems]

FIG. 1 is a block diagram of the principle of the present invention, and FIG. 2 is a time chart explaining the operation of FIG. 1.

FIG. 1 shows a detection circuit 9 and a comparator circuit 10 added to FIG. 6. As shown in FIG. By falling in synchronization with the start signal, the laser beam is modulated for a certain period of time to create a signal that is sent to the rotating mirror 5 as −5=first-order light.

This BMON signal is combined with the video signal by an OR circuit,
It is sent to the drive circuit 3 as an AOMON signal.

Laser light emitted by the laser unit 1 enters the optical modulator 2, and when the optical modulator 2 is not driven, it is transmitted to the detector 9 through a slit in the shielding plate 4. Since approximately 100% of the power is input to the detector 9 as described above, the output (1) is input to the comparator circuit 10 as the maximum voltage as shown by Vloo in (i) in FIG.

When the AOMON signal is input to the drive circuit 3, the optical modulator 2 is driven and the laser beam is divided into zero-order light and first-order light, so that the power input to the detector 9 is approximately 40%.

Therefore, the output Vi of the detector 9 is as shown in FIG. As shown in FIG.

The comparison circuit 10 compares the output Vi of the detector 9 with a threshold value during the BMON signal using a clock generated in synchronization with the scanning start signal, and 60% of the primary light is sent out and 40% of the 0.
Where the secondary light should be input to the detector 9, the optical modulator 2 and/or the drive circuit 3 are defective, and sufficient primary light is not sent out, resulting in zero
The structure is configured to detect a state in which, for example, 80% or more of the secondary light is input to the detector 9, and a state in which the laser unit 1 generates a momentary interruption and temporarily does not send out laser light.

[Effect]

With the above configuration, the comparison circuit 10 compares the voltage of the output Vi of the detector 9 with a threshold value, and detects that the detection circuit 9 detects, for example, 80% or more of the zero-order light during the time period when the BMON signal is sent. When it is determined that the optical modulator 2 and drive circuit 3 are defective, and when less than 20% of the zero-order light is detected, it is possible to determine that the laser unit 1 is defective, making it easy to identify the location of the defect. You can.

〔Example〕

FIG. 3 is a block diagram of a circuit showing one embodiment of the present invention.

FIG. 3 is a detailed block diagram of the comparator circuit 10 of FIG. 0 of 0.
Apply 8 times the voltage ■1 to the child terminal of the operational amplifier circuit 13,
For example, a voltage 2 which is 0°2 times the voltage V100 is applied. The operational amplifier circuit 12 outputs “0” when the input voltage Vi is larger than ■1.
”, the NOT circuit 14 sends “1” to the flip-flop 15.

Therefore, the flip-flop 15 is clocked by the clock CL and the AOM signal indicates a failure of the optical modulator and drive circuit.
Sends an NG signal.

At this time, since Vi is larger than V2, the operational amplifier circuit 13
0'' and the flip-flop 16 is not sent.

FIG. 4 is a time chart explaining AOMNG signal detection.

As described above, the control circuit 11 shown in FIG. 1 generates the BMON signal in synchronization with the scan start signal, and also generates the clock CL in synchronization with the scan start signal. The output Vi of the detector 9 is (2) when the optical modulator 2 is not driven as described above. When the optical modulator 2 is modulating the video signal, it sends out VB.
O and V2O are sent out in response to the video signal.

If the optical modulator 2 and/or the drive circuit 3 become defective and the laser beam cannot be converted into primary light, the BMON
When modulated by a signal, the voltage input to one terminal of the operational amplifier circuit 12 becomes larger than ■1. Therefore, the flip-flop 15 is set by the clock CL and the AOMNG signal is sent out.

FIG. 5 is a time chart illustrating defect detection of the laser unit 1.

If the laser unit 1 temporarily stops transmitting the laser beam while modulating the video signal, for example, the output Vi of the detector 9 becomes O volts as shown in FIG. Therefore,
Since the primary light is not sent out, the scanning start signal is not detected either. Therefore, the BM falling in synchronization with this scan start signal
The ON signal remains sent.

The operational amplifier circuit 12 sends out "1" because Vi is O-halt and lower than the threshold value (1), and the NOT circuit 14 sends out "θ'. Therefore, the flip-flop 15 is not set even if the clock CL is input.

Since Vi is 0 volts and lower than the threshold value V2, the operational amplifier circuit 13 sends out 1", and the flip-flop 16 outputs the clock C.
When L is input, it is set and sends out a LASNG signal indicating that the laser unit 1 is defective.

〔Effect of the invention〕

As explained above, the present invention distinguishes between defects in the laser unit that could not be identified by detecting period abnormalities in the scanning start signal, defects in the optical modulator and its drive circuit, and defects in the motor of the rotating mirror, etc. In particular, it is possible to easily search for failures that occur intermittently and recover from them.

=10-

[Brief explanation of drawings]

Figure 1 is a block diagram of the principle of the present invention, Figure 2 is a time chart explaining the operation of Figure 1, and Figure 3 is a block diagram of the principle of the present invention.
The figure is a block diagram of a circuit showing an embodiment of the present invention, Figure 4 is a time chart explaining AOMNG signal detection, Figure 5 is a time chart explaining laser Unisoto defect detection, and Figure 6 is a diagram showing a conventional optical system. FIG. 2 is a block diagram for explanation. In the figure, 1 is a laser unit, 2 is an optical modulator, 3 is a drive circuit,
4 is a shielding plate, 5 is a rotating mirror, 6 is a lens, 7.9 is a detector, 8 is a mirror, 10 is a comparison circuit, 11 is a control circuit, 12 and 13 are operational amplifier circuits, 14 is an N07 circuit,

Claims (1)

[Claims] A laser unit (1) that emits laser light, an optical modulator (2) that divides the laser light into zero-order light and first-order light,
A drive circuit (3) that drives the optical modulator (2) and a drive signal that rises after sending the video signal and falls in synchronization with a scan start signal obtained from the primary light are sent to the drive circuit (3). A laser printer equipped with a control circuit (11), a detector (9) that detects zero-order light transmitted by the optical modulator (2), and an output of the detector (9) that is transmitted by the drive signal. A comparison circuit (10) is provided to compare the optical modulator (2) with a predetermined threshold value while the optical modulator (2) is being operated.
and an optical system defect detection circuit for a laser printer, characterized in that a defect in the drive circuit (3) and a defect in the laser unit (1) are separately determined.