Improvement of JTS200 laser image-setter

JTS200 type laser phototypesetting machine is an early old model, has a certain amount in the printing industry, the machine scanning method is a line scan, accuracy is 742DPI and 1016DPI two. During the initial use, it was found that the stability of the aircraft is not good, and there are many problems encountered. Although the after-sales service of the manufacturer is very good, it is due to a long way to go. It takes a certain period to solve the problem, and the failure phenomenon is frequent. So as to affect the normal production schedule. In view of this, we began to conduct a comprehensive analysis of the imagesetter and found that it is only necessary to improve and debug the part of the circuit of the rower, which can greatly enhance the stability of the aircraft. After the improvement, good economic benefits have been achieved since 1992. Summarize some points and have this model or the same type of phototype mechanism peers to discuss, the text of the deficiencies, please enlighten.
As the manufacturer did not provide the schematics and technical parameters of the image-setter, after analysis, a schematic block diagram of the structural principle of the JTS200 laser image-setter is depicted, as shown in FIG. 1 .
The photocard is installed in the computer. It is the interface between the computer and the photo machine. It is used to process the large file format into the data stream format that the photo machine can recognize. In the processing of large samples, the processing is performed in pages, and the data of the page is sent to the image processing circuit of the imagesetter (abbreviated as the large control board), which coordinates the laser modulator and the mechanical operation control circuit (abbreviated as Small control board). The small control board is also responsible for shaping and amplifying the received raster lock signal, and sends the processed raster lock signal to the large board. After a page is completed, the data processing circuit and mechanical operation circuit of the imagesetter are Waiting for the status and issuing an interrupt request command at the same time, request to receive the data of the next page. Throughout the operation, a series of components must be closely matched to operate properly. During the use of the imagesetter, the most common problems are the phase-locked grating generators and the small control boards. The following describes the fault phenomena and improvement methods as follows:
First, the improvement of the lock-in grating generator The structure of the lock-in grating generator is shown in Fig. 2. It can be seen from Fig. 2 that the design of the light source circuit lacks safety and reliability. In the photocopying, the extinguishing of any small light bulb is unknowable, causing serious waste of the film. Because, at the time of scanning, the light bulb does not shine, the photosensitive diode does not receive the grating signal, the large and small control boards will be in the waiting state, and the small control board does not interrupt the movement of the transmission parts (this is also the deficiency of the imagesetter). ) It is difficult for the operator to notice if he is not paying special attention. The film will be finished in vain and cause waste. In order to keep track of the operation of the imagesetter at all times, we designed a simple and easy-to-use light source control circuit (see Figure 3). As can be seen from FIG. 3, when W1 and W2 emit light normally, T1 is saturated and turned on, T2 is cut off, and relay J is not actuated. When either W1 or W2 is damaged, T1 is turned off and T2 is saturated and the relay is connected in series with its positive electrode loop. J action, start the alarm device.
W1, W2 use 6.3V, 0.5A ~ 6.3V, 0.8A small light bulbs, R1 use 10Ω, 5W power negative voltage from the role of negative pressure, so that the pressure drop on W1 and W2 is controlled at about 5V, slightly less than the rated 6.3V, extend lamp life, and its brightness can still meet the needs, R2-R5 are selected 0.25W, resistance values ​​were 7.0kΩ, 3.5KΩ, 15KΩ, 50KΩ, diodes used IN4004, transistor selection 2SV9014, relay selection JRX -13F, filter capacitor is generally 100μF/50V. The original 6V AC is no longer applicable. Fortunately, the original transformer has 15V AC output. It can be easily found with a multimeter. After full-wave rectification, a DC voltage of about 20V can be obtained. After the 7581 three-terminal regulator, Circuit power supply, because this circuit's power consumption is not very large, so you can not consider the transformer load problem.
Second, the debugging of the small control panel Another failure phenomenon of the JST200 Typesetter is the poor stability, sometimes the text on the film appears to be divided into two sides, and sometimes the text image density is not enough, there is a point, especially the ambient temperature. When it's too high, it's particularly serious. After analysis, the reason is on the small control board. Due to the mechanical stability of the contrast rower and the dust protection of the optical components, the manufacturer of the imagesetter uses an extremely thick cast aluminum and is almost closed. Although there is ventilation, it is not enough to make the machine All the heat is discharged outside the machine, the temperature inside the machine gradually increases, so that the resistance of the LM318 peripheral circuit changes, resulting in changes in the working status of the LM318, resulting in non-linear distortion, making the amplifier circuit can not work. Because the grating signal received by the photodiode is very weak, it must be amplified by the LM318, and the unstable power amplifier circuit causes the phase-locked signal to become weaker and weaker. This causes the above-mentioned fault phenomenon.
Through experiments, there is an RP12 trimming potential circuit on the peripheral circuit of the LM318. By adjusting it and combining the oscilloscope, the static operating point of the LM318 can be adjusted to an appropriate position in the amplification region. If you don't have an oscilloscope, you can adjust it in one way and it works well. That is, the imagesetter is operated in a self-test state, and then the hair dryer is kept at a certain distance from the small control board and the hot air is blown, so that the surface of the small control board has a temperature of about 45°C. At this time, if the stability of the small control board is not good, the self-check signal will be disordered, and then the RP12 potentiometer will be trimmed until the self-check signal is normal. There are two points to note in the debugging process. First, do not look at the laser directly to avoid damaging the eyes. Second, do not touch the high-voltage components that generate the laser power to avoid electric shock.
The improvement and debugging of the JTS200 laser image-setter solves the main problem of the model. After nearly 6 years of use, the image-setter has been operated with an average of 15 volumes per month (30m/volume) and has not occurred. The passive situation when the photo attendance machine enters the factory

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