Summary
This article introduced the principle and general method of changing the laser light source of semiconductor laser imagesetter laser machine from infrared laser light source (wavelength 780nm) to red laser light source (wavelength 633nm).
"Since September 98, with the continuous development of China's crackdown on smuggling activities, the most significant impact of the printing equipment industry is the rising price of imported photo film, the price of imported photo film has generally risen by 30% compared with the beginning of 1998, and the import phototype on the market. The inventory of films has been on a downward trend, and industry insiders estimate that there is room for further increase in the price of imported photo film.” (Extracted from “Printed Materials in China” 98/10), which makes the price of imported photo film that has a large disparity (50) -60 yuan / square meter) and domestic photo film price (34-38 yuan / square meter) further increase (import photo film price of about 65-70 yuan / square meter, domestic photo film price of about 38-40 yuan / square meter), more What disturbed some photocomposing users was that some import photo films were out of stock in the country. So why do these photo-composing users not use cheap domestic photo film instead of selecting imported films that are expensive and lack of supply? In addition to quality and stability, another important reason is the laser light source used in the laser imagesetter discussed in this paper.
First, the laser photosource laser light source
Table 1 List of Light Sources for Laser Phototypesetting Machines at Home and Abroad
He-Ne Laser (632.8nm) Semiconductor Infrared Laser (780nm) Semiconductor Red Laser (650-670nm) Semiconductor Red Laser (633nm) Agfa SelectSet SeriesAgfa Avantra Series Angels Dolve Series Hangzhou CBTX Series Changchun JZJ Series StudioSet2000
Ultre E/P/3000/4000
ECRM VR Series
F91 series (partially early) Herkules Pro
Accuset Series
Ultre vision series
Pather Pro Series
ECRM Knockout
ECRM VRL/HS Series
ECRM drumsetter
DotMate series
Crosfield Collection
F91 Series (Partial) SCREEN FT-R Series
F91 Series (Latest Type)
Table 1 shows the laser light sources used by laser imagesetters at home and abroad. Because the production process and technology of laser photodischarge film are more complex with the increase of the photosensitivity wavelength, and the production of domestic laser imagesetter is started from the He-Ne laser as the light source (wavelength 632.8nm), so the domestic laser phototype film is shorter. Wavelength 6328 film is the mainstream, its quality is stable, the market share is relatively large, until the recent domestic 670,780-type film was listed, but its quality and stability and imported films still have a certain gap. Domestic and foreign laser imagesetter manufacturers in order to adapt to this situation in the country, have to give up the infrared wavelength laser light source and use 6328-type helium laser light source or nearly 6328-type semiconductor laser light source (wavelength 650-670nm). It is worth noting that semiconductor lasers are used by many Phototypewriter manufacturers due to their simple control and optical systems, high light source efficiency, and long laser life (about 200,000 hours).
Second, domestic 6328 type photo film
The domestic 6328 phototype film sensitivity curve shown in Figure 1, can be seen from Figure 1 domestic 6328 phototype film sensitivity peak in the 633-640nm and the curve to the left of the peak flat, peak to the right curve steep, so the semiconductor laser light source It is appropriate to use the 620-640nm laser to expose the 6328 type film, and the use of the 650-670nm laser to expose the 6328 type film may cause problems such as insufficient blackness and halation.
Contrary to the effect of laser wavelength control row film production process and technology, the shorter the laser wavelength, the more complex the production process and technology of the laser, so most Phototypesetter manufacturers use 650-670nm laser, imported 670 film and domestic 6328 type This is the best compromise solution in the case of a small price difference between the photo film.
Lasers with a wavelength of 633 nm have now matured and have been applied by some foreign companies to their imagesetters. Therefore, by replacing the 780nm infrared laser with a 633nm semiconductor red laser, it is possible to solve the problem that this type of image-setter applies the domestic 6328 type photo film on the premise of guaranteeing the output quality, thereby reducing the production cost.
Third, the semiconductor laser
The semiconductor laser is a kind of laser similar to the crystal and triode process structure. It can be easily modulated in the range of up to several gigahertz. As the photosource light source, its output power can be selected from 3 to 10mW (its maximum exposure is 250-600W. Erg/cm2). The infrared semiconductor laser with a wavelength of 780 nm is a common cathode structure, as shown in FIG. The semiconductor laser with a wavelength of 633-670 nm is a common anode structure, as shown in FIG.
Semiconductor lasers are very fragile devices. Please pay attention to the following issues when using them: ● Prevent static electricity - Wear a grounding ring when handling, ensure that the soldering iron should be powered off and ensure that the soldering iron is well grounded; ● Prevent overvoltages. Its operating voltage should be less than 2.5V; ● prevent over-current - semiconductor laser's working energy is proportional to the current, adjust the current can adjust its luminous energy, but the current regulation should be less than 50mA.
Fourth, semiconductor laser change
1. Modification of the laser drive circuit: As mentioned before, since the 780 nm semiconductor laser is a common cathode and the 633 nm semiconductor laser is a common anode, the laser-driven related circuit should be changed to an inverting drive.
2. Changes of photosensitive amplifier circuit: As shown in Fig. 2 and Fig. 3, there are light-sensitive detection tubes integrated with the light-emitting tube in both lasers. It is a closed-loop detection and control device, which is to ensure that the laser light emitting tube works stably under a certain energy state when the temperature and other parameters are changed. The relative sensitivity of the spectral response characteristics of the photodetector tube decreases as the wavelength of the light wave decreases. It was determined that for a laser with a wavelength of 780 nm in the normal operating energy range, the photosensitive detection current is about 8 mA, and for a 633 nm wavelength laser, the photosensitive detection current is about 300 uA, so the parameters of the photosensitive closed-loop detection circuit should be adjusted. Similarly, the parameters for the start of line detection circuit should also be adjusted.
3. Focus: The 780nm laser is an invisible infrared laser, so the focus can only be adjusted by the instrument at the factory. After replacing the 633nm visible red laser, you can adjust the focus with the aid of an optical magnification instrument.
V. Summary
Using this method, we changed the light sources of dozens of ULTRE infrared laser imagesetters. After the replacement, we used Huaguang LP-6328II, III-type photostrips to achieve the quality level of the original imported 780 film.
Replacing the laser light source of the semiconductor laser image-setter is a very professional and complicated task. Without careful analysis of the machine, blindly moving the machine without the assistance of professionals, the consequences would be disastrous.
