JPH0460558A - Semiconductor laser protection device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus (laser beam printer) using a semiconductor laser as a light source, and particularly to a semiconductor laser protection device.

[Conventional technology]

A semiconductor laser, a photodetector that detects the optical output of this semiconductor laser, a comparator that compares the output signal of this photodetector with a reference signal, and a counter that increases or decreases a count value according to the output signal of this comparator. A D/A converter converts the count output of this counter into an analog quantity, and an amplifier amplifies the output signal of this D/A converter, and a current corresponding to the output signal of this amplifier is applied to the semiconductor laser. Laser control circuits equipped with semiconductor laser drive circuits that allow light to flow are widely known.

FIG. 7 shows an example of a semiconductor laser drive circuit.

In the figure, 100 and 101 are FETs, 102 is an inverter, 103 is a bias circuit, and 104 is a semiconductor laser. In this way, by using a so-called differential amplifier type, on/off of the semiconductor laser can be modulated at high speed.

[Problem to be solved by the invention]

In the above circuit, if the laser Kawagiri S (+5V■) is turned on before the power is turned on to the laser drive section,
Since the amount of current flowing through the semiconductor laser 104 is not controlled, an excessive current flows through the semiconductor laser 104 and destroys it. In addition, if the power to the power control unit is turned on before both of the above power supplies are turned on, the APC circuit operates because the output signal of the photodetector is still 0, and the D/A output increases, causing the semiconductor laser to It operates automatically to increase the current injected into 104. After this, when the power to the laser driving section is turned on, an excessive current flows through the semiconductor laser 104.

If the above-mentioned condition occurs even if there is a slight difference in the power-on timing, the semiconductor laser 104
There is a risk of excessive current flowing.

In other words, the APC circuit that controls the light output from the semiconductor laser 104 to be constant malfunctions when the power of the main body is turned on and off, or when the interlock is turned on and off when opening and closing the door to handle errors such as jams. Otherwise, an unexpected excessive current may flow through the semiconductor laser 104 due to the effects of chattering, noise, etc. when the power supplies are turned on and off, and the semiconductor laser 104 may be destroyed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor laser protection device that can prevent a semiconductor laser from being destroyed due to excessive current flowing through the semiconductor laser.

[Means to solve the problem]

The above purpose consists of a semiconductor laser, a photodetector that detects the optical output of this semiconductor laser, a comparator that compares the output signal of this photodetector with a reference signal, and a count value that is calculated according to the output signal of this comparator. A counter that increases or decreases, a D/A converter that converts the count output of this counter into an analog quantity, and an amplifier that amplifies the output signal of this D/A converter to generate a current that corresponds to the output signal of this amplifier. A semiconductor laser protection device for a laser control circuit comprising a semiconductor laser drive circuit that supplies power to the semiconductor laser, a constant current power supply that is manually input to the laser drive system, a control system power supply that is also input to the laser drive system, and a direct current power supply that is input to the laser drive system. The laser power supplies connected to the semiconductor laser are turned on in the order in which they are turned on, and when they are turned off, they are turned on in the reverse order, and further,
This is achieved by providing a power supply control means for resetting the counter of the APC circuit when the laser type a is cut off.

[Function] By regulating the rise and fall order of each power supply and resetting the APC circuit in the case of a transient state, excessive current is prevented from flowing into the semiconductor laser.

〔Example〕

FIG. 1 is a schematic diagram of a digital color image forming apparatus to which the present invention is applied.

FIG. 1 shows a color copying machine as an example of an image recording device. The copying machine includes a scanner section 1 for reading originals, an image processing section 2 that electrically processes image signals output as digital signals from the scanner section 1, and image recording of each color from the image processing section 2. It has a printer section 3 that forms an image on copy paper based on the information. The scanner part 1 includes a lamp 5 that scans and illuminates the document on the document table 4.
, with, for example, fluorescent lights. The reflected light from the document when illuminated by the fluorescent lamp 5 is reflected by the mirror 6.7.8 and enters the imaging lens 9. The image light is imaged onto a dichroic prism 10 by the imaging lens 9, and separated into light of three different wavelengths, for example, R, green G, and blue B. The light is input to CCD11R for green, CCDIIG for green, and CCDIIB for blue. Each CCDIIR, II
G.

11B converts the incident light into a digital signal and outputs it, and the output is subjected to necessary processing in the image processing unit 2 to record color information of each color, such as black (hereinafter abbreviated as Bk), yellow (Y), etc. The signals are converted into signals for recording of each color: magenta (abbreviated as M), and cyan (abbreviated as C).

Although FIG. 1 shows an example of forming four colors, Bk, Y, M, and C, it is also possible to form a color image using only three colors. In that case, the number of recording devices can be reduced by one compared to the example shown in FIG.

The signal from the image processing section 2 is input to the printer section 3,
Laser light emitting devices 12Bk, 12C, 1 for each color
, 2M, and 12Y.

In the example shown in the figure, the printer section includes a 4Mi recording device 13Y,
13M, 13C, and 13Bk are arranged side by side. Since each recording device 13 is made of the same constituent members, in order to simplify the explanation, the recording device for C will be explained, and the explanations for other colors will be omitted. Furthermore, for each color layer,
Identical parts are given the same reference numerals, and in order to distinguish the composition of each color, a subscript indicating each color is added to the reference numerals.

The recording device 13C has a photoreceptor 14C1, for example, a photoreceptor drum, outside the laser beam emitting device 12C.

A charger 15C, an exposure device using a laser beam emitting device 12C, a developing device 16C, a potential sensor SC1, a transfer charger 17C, and the like are attached to the photoreceptor 14C in the same manner as in a known copying apparatus.

Photoreceptor 1 uniformly charged by charger 15C
4C forms a latent image of the Soane light image by exposure by the laser beam emitting device 12C, and develops it by the developing device 16C to form a developed image. Copy paper is fed by a paper feed roller 18 from a paper feed unit 19, for example, one of two paper feed force centers, and the leading edge of the copy paper is aligned by a registration roller 20 and sent to a transfer belt 21 at the same timing. Transcription help) 2
The copy paper conveyed by 1 is sequentially sent to photoreceptors 14Bk, 14C, 14M, and 14Y on which developed images are formed, and the developed images are transferred under the action of a transfer charger 17. The transferred copy paper is fixed by a fixing roller 22 and discharged by a paper discharge roller 23.

By being electrostatically attracted to the transfer heald 21, the copy paper can be conveyed accurately at the speed of the transfer heald.

FIG. 2 is a front view of the transfer heald section. Transfer Held 21
is supported by a heald drive roller 24 and a driven roller 25, and moves in the input direction to convey the transfer paper. Further, the cleaning unit 26 removes toner adhering to the heald. A reflective sensor 27 is provided as a pattern image detection means on the downstream side of the photoreceptor I4 in the direction of heald movement.

The detection means is provided at the drive roller portion of the transfer belt to prevent the influence of flapping of the transfer heald and to maintain a constant distance from the transfer heald 21 at all times. The pattern on each photoreceptor, which is imaged in a shifted manner on the transfer heald 21, is read by this detection means to prevent positional shift during overlapping transfer.

FIG. 3 is a system block diagram according to the embodiment.

The system controller 30 controls each module of the scanner 1, image processing section 2, and printer 3. The control contents include display control on the operation panel 31, manual key processing, and according to the mode set on the operation panel 31.
Sending start signals and scaling ratio designation signals to the scanner 1 and printer 3; image processing mode designation signals to the image processing unit 2 (color conversion, masking, trimming, mirroring, etc.)
transmission, abnormal signals from each module, operating status status signals (Wait, Ready, Busy, 5t
OP, etc.) to control the entire system.

Scanner 1 is 1. The original is scanned at a scanning speed that matches the magnification specified by the start signal from the system controller 30, the original image is read by a reading element such as a CCD, and the image is processed into an image processing unit as image data of 8 bits each for R, G, and B. 5-LSYNC (horizontal synchronization signal) from 2,
S-3TPOBE (image clock) and FGATE
(vertical synchronization signal) and sends it to the image processing section 2.

The image processing unit 2 processes 8 each of R and CB sent from the scanner 1.
The bit image data is subjected to image processing such as T correction, UCR (undercolor removal), and color correction, and converted into 3-bit image data for each of Y, M, and CBk, and sent to the printer 3. It also performs editing processing such as scaling processing, masking, trimming, color conversion, mirroring, etc. according to commands from the system controller 30. It also has a buffer memory for outputting Y, M, C, and Bk image data shifted by the distance between the photoreceptor drums of the printer 3.

The printer 3 operates a laser beam emitting device according to image data of 3 bits each of Y, M, C, and Bk sent from the image processing section 2 in synchronization with P-LSYNC (horizontal synchronization signal) and P-5TPOBE (image clock). is modulated, and a copy image is obtained on transfer paper using an electrophotographic process.

Image recording modes in this embodiment include the following.

○: Use ×: Do not use FIG. 4 is a control block diagram of the printer section 3.

The main control unit 70 has a CPU as its center and a ROMRAM.
It consists of an I10 interface, etc. On the input side, there is a paper ejection sensor 71 for detecting transfer paper being ejected outside the machine, a paper end sensor 72 for detecting the presence or absence of transfer paper in the cassette, and a paper end sensor 72 for controlling paper feeding to the registration rollers. registration sensor 73, cassette size sensor 74 for detecting the size of the cassette, Bk,
A toner sensor 75 (Bk, C, M, Y) for detecting the concentration of each developer of CM and Y, a thermistor 76 for detecting the temperature of the fixing heater 79, and a potential sensor for detecting the surface potential of the photoreceptor. There are S etc.

On the output side, there is a high voltage power supply 77 for supplying high voltage to various chargers and developing sections, a heater control section 78 for controlling the temperature of the fixing heater 79, and a toner replenishment clutch 80 for replenishing toner to the developing device. , a motor driver 81 for controlling various motors.

Furthermore, there is a polygon mortar driver 82 for controlling the polygon motor, a video control unit 84 for receiving image data from the image processing device and controlling the LD driver 83 for each hue, and an interface with the system controller.

FIG. 5 is a circuit diagram of a semiconductor laser protection device according to an embodiment of the present invention, in which 104 is a semiconductor laser, 105 is a semiconductor laser drive circuit, 106 is a photodetector for detecting the optical output of the semiconductor laser, and 107 is a photodetector for detecting the optical output of the semiconductor laser. An amplifier 108 is a comparator that compares the amplified output signal of the photodetector 106 with a reference signal, and constitutes a laser driving section 109.

Further, 110 is a counter whose count value increases or decreases according to the output signal of the comparator 108, and 111 is a counter that converts the count output of this counter 110 into a D/A and drives the semiconductor laser drive circuit 105.
112 is an oscillator, 113 is an edge detector, and these constitute an APC circuit 114. Further, 115 is a reset circuit, and 116 is a power supply control section.

In this embodiment, the control photoelectric voltage # (+5V■) and the constant current power supply (±12V) input to the laser drive unit 109 are
and a laser beam directly connected to the semiconductor laser 104.
(+sv■), and the power supply control unit 116 supplies or cuts off each power supply depending on the state of each power supply. Further, when the laser power supply is cut off, the counter 110 is reset by the reset circuit 115.

Figure 6 is a timing chart for turning on and off the power of each part.As shown in the figure, the constant current power supply, control system power supply, and laser power supply are turned on (turned on) and then turned off (off).
The time is the opposite.

〔Effect of the invention〕

As described above, according to the present invention, destruction of the semiconductor laser can be prevented by regulating the order in which each power source rises and falls, and by resetting the APC circuit in the case of a transient state.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a digital color image forming apparatus to which the present invention is applied, Fig. 2 is a block diagram of the transfer belt section, Fig. 3 is a system block diagram of the entire apparatus, and Fig. 4 is a control diagram of the printer section. 5 is a circuit diagram of a semiconductor laser protection device according to an embodiment of the present invention, FIG. 6 is a timing chart of turning on and off the power of each part, and FIG. 7 is a semiconductor laser drive circuit diagram. . 104... Semiconductor laser, 105... Semiconductor laser drive circuit, 106... Photodetector, 108... Comparator, 110... Counter, 111... D/A converter,
115... Reset circuit, 116... Power supply control unit. Agent: Patent attorney Kenjibu Take (1 other person) Figure 2

Claims (1)

[Claims] A semiconductor laser, a photodetector that detects the optical output of this semiconductor laser, a comparator that compares the output signal of this photodetector with a reference signal, and a counter that increases or decreases a count value according to the output signal of this comparator. A D/A converter converts the count output of this counter into an analog quantity, and an amplifier amplifies the output signal of this D/A converter, and a current corresponding to the output signal of this amplifier is applied to the semiconductor laser. This is a semiconductor laser protection device for a laser control circuit that is equipped with a semiconductor laser drive circuit that allows current to flow, and includes a constant current power supply that is input to the laser drive system, a control system power supply that is also input to the laser drive system, and a semiconductor laser drive circuit that is directly connected to the semiconductor laser. A semiconductor laser protection device characterized in that it is equipped with a power supply control means that turns on the laser power supplies in the order in which the laser power supplies are turned on, and in the reverse order when the laser power supply is turned off, and further resets the counter of the APC circuit when the laser power supply is cut off. .