JPS635317A - Abnormality detecting circuit in laser writing device - Google Patents

Abstract

PURPOSE:To eliminate the necessity of intervention of software at the time of rising of a laser writing device, by checking synchronizing signals only when a scanning device makes stable rotation and generating an abnormal signal when the synchronizing signal of a photodetector is not produced for a prescribed time. CONSTITUTION:While a stable signal RD is low (nonstable), the output of a D.F/F24 stays low at the rise of pulses P0 and no ERR signal is produced regardless of the presence/absence of synchronizing signals BD. When the stable signal RD becomes high, the D.F/F24 is latched at the rise of the pulses P0 and its outputs S1 becomes high. However, since the synchronizing signals BD are generated in a period shorter than that of the pulses P0, the D.F/F24 is cleared in the next period and, when the pulses P0 become low thereafter, the signal S1 of the D.F/F24 becomes low and, therefore, no ERR signal is generated. In case where the synchronizing signals BD are not generated for a prescribed time, the abnormal signal ERR is generated from the inverted signal of the pulses P0 and output S1 of the D.F/F24 when the next pulses P0 become low.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a laser writing device that deflects a laser driven by a laser drive circuit using a scanning device to write on a photoreceptor, and particularly relates to a laser writing device that writes on a photoconductor by deflecting a laser driven by a laser drive circuit, and particularly relates to a laser writing device that writes on a photoconductor by deflecting a laser driven by a laser drive circuit. The present invention relates to a detection circuit that detects.

(Prior Art) In a laser writing device, it is necessary to accurately perform horizontal and vertical synchronization to obtain a stable image at a predetermined position on a photoreceptor.

By the way, in the past, a camera that creates a stable image by detecting the stable rotation speed of a rotating polygon mirror (polygon mirror) that constitutes a part of a scanning device, and processing the signal after stabilization. There are devices that check the stability signal and synchronization signal using software processing to detect abnormalities, but in writing devices with fast scanning speeds and synchronization, it is not reliable to detect only the stable state of the rotation speed. In addition, in those that perform software processing, the burden of software processing for abnormality detection becomes large, which is inconvenient for the software processing for system control, which is the original purpose.

(Purpose) The present invention was made based on this background,
The object of the present invention is to provide an abnormality detection circuit with high reliability.

(1) For this purpose, the present invention checks the synchronization signal only when the rotation of the scanning device is stable, i.e. the synchronization of the photodetector.
If No. 1 does not occur for a predetermined period of time, an abnormality signal is generated.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows the configuration of a laser writing device. 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 then deflected by an fθ lens 4. When an image is formed on the charged surface of the photoreceptor drum 5 and the imaged spot moves repeatedly in the direction of arrow X by the rotation of the rotating polygon mirror 3, the photoreceptor drum 5 rotates at the same time. A photodetector 6 is provided outside the information writing area, detects the laser beam deflected by the rotating polygon mirror 3, and generates a synchronizing signal BD. The signal processing circuit 7 adds qJ of information signals to the semiconductor laser drive circuit 8, but the timing is determined by the synchronization signal B from the photodetector 6.
Control 8 by D. The semiconductor laser drive circuit 8 drives the semiconductor laser 1 in accordance with the information signal from the signal processing circuit 7, and therefore, the laser beam modulated by the fJ information signal is irradiated onto the photoreceptor drum 5 to generate an electrostatic 1 sweet image. is formed. This electrostatic latent image is developed by a developing device and transferred onto paper or the like by a transfer device. Further, the laser beam emitted backward from the semiconductor laser 1 enters the photodetector 9 and its light intensity is detected, and the control circuit 10 controls the semiconductor laser drive circuit 8 according to the output signal of the photodetector 9. is controlled to keep the output light amount of the semiconductor laser l constant.

Note that 3' is a device that drives the rotating polygon mirror, and 3 and 3'
constitute the entire scanning device.

FIG. 2 shows an example of the circuit of the scanning device 3', using the PLL control method. In the figure, 11 is a reference oscillator, and this output and
A phase comparator 14 outputs the output of the encoder 12, which generates an output by the rotation of the motor, and the output amplified by the amplifier 13.
The speed controller 1 compares the voltage according to the output of the comparison result.
5 to the power transistor 16, the power is amplified by the power amplifier 17, and the power is applied to the motor coils 18, 19, 20.
is supplying electricity to. At the same time, the phase sensor 21 detects the position of the motor rotor and the motor coils 18 to 2
The power supply to 0 is sequentially switched.

The stability detector 22 compares the output of the phase comparator 14 with a predetermined value, and when the output is determined to be the predetermined value, generates a stability signal RD.

FIG. 3 shows an embodiment of an abnormality detection circuit, in which a pulse P having a period t1 longer than a predetermined period t0 of the synchronization signal BD. The rise of the pulse circuit 23 that generates the pulse P causes the D-F/F (D flip-flop) 24 that latches the stable signal RD and the pulse P of the pulse circuit 23 to latch the stable signal RD. an inverter 25 for inverting the A
It consists of an ND circuit 26.

Now, when the stable signal RD is LOW (unstable state),
At the rising edge of the pulse P0, the output of the DF/F 24 remains low, that is, the ERR signal is not generated regardless of the presence or absence of the synchronization signal BD, which is a clear signal for the DF/F 24.

Next, when the stable signal RD becomes H4gh, the next pulse P
At the rising edge of 0, the D-F/F 24 is latched and the output Sl becomes Hlgh. However, since the synchronization signal BD is generated at a shorter period than Po, the next D -F/F 2
4 is cleared, then pulse P. When becomes LOW, the signal Sl of the D-F/F 24 is (,ow, so no ERR signal is generated.

By the way, if the stable signal RD is latched by the pulse P0 and the D-F/F 24 is at H4gh, if the laser does not emit light due to an abnormality in the laser drive circuit 8 or the laser itself, and if the laser fixing part or synchronization detection etc. For example, if the positional relationship changes due to temperature changes, etc., the synchronization signal B
If D is not generated, when the next pulse P0 becomes LOW, an abnormal signal ERR is generated by its inverted signal and the output S of the D-F/F 24.

By this abnormal signal ERR: D-F/F 27 is set, ERR' is output and held, and indicator 28 is turned on. Note that this D-F/F 27 is held until the reset signal R3T generated after abnormality processing is input.

As above, the synchronization signal BD of synchronization t0, the pulse P0 of synchronization t,
, the stability signal RD, the output S8 of the DF/F 24, and the error signals ERR and ERR' are shown in FIG.

(Effects) The present invention is as described above, and according to the abnormality detection circuit in the laser writing device according to the present invention, by checking the synchronization signal, the device can always be kept in a stable state, and the scanning device By limiting the check period to only when the rotation is stable, there is no need for software intervention when starting up the device, and by performing these steps in hardware, it is effective even in devices with fast scanning speeds and scanning cycles. It is.

4゜

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of the laser writing device, Figure 2 is a block diagram showing the configuration of the laser writing device.
The figure is a circuit diagram showing an example of a scanning device related to PLL control 8-way, and FIG. 3 is an abnormality detection circuit diagram according to an embodiment of the present invention.
FIG. 4 is a timing chart of each signal. 3.3'...Scanning device, 6...Photodetector, 8...
Laser drive circuit, 24.25.26... Abnormality detection circuit component. Figure 1 Figure 2

Claims (3)

[Claims] (1) A laser drive circuit, a scanning device that scans laser light, a photodetector that is provided outside the information writing area and that detects the laser light and generates a synchronization signal BD, and a laser drive circuit that provides information to the laser drive circuit. A laser writing device comprising a signal processing unit that provides a signal according to An abnormality detection circuit in a laser writing device characterized in that the abnormality detection circuit includes an abnormality detection circuit that generates an abnormality signal ERR when a synchronization signal BD of a photodetector is not generated for a predetermined period of time. (2) The scanning device controls the rotation speed by PLL control, and the stability signal RD is the lock of the PLL control circuit.
An abnormality detection circuit in a laser writing device according to claim 1, wherein the abnormality detection circuit is a signal. (3) The abnormality detection circuit latches and outputs the stable signal RD with a pulse P_0 having a cycle longer than the predetermined cycle of the synchronization signal BD, and has a D flip-flop that uses the synchronization signal BD as a clear signal. An abnormality detection circuit in a laser writing device according to claim 1, characterized in that the circuit outputs the logical product of the output of the flip-flop and the inverted signal of the pulse P_0.