Recently, the import photographic film has not only risen in price but also has been out of stock. So, why do users not use cheap domestic films instead of import films? The reason is that, in addition to the quality and stability of the film itself, the light source used in the laser imagesetter is also one of them.
The domestic laser camera uses a helium-neon laser as the light source (wavelength 632.8 nm). Therefore, the domestic laser photocopies are mainly based on the shorter wavelength 6328 type. Its stable quality and large market share.
The domestic 6328 type Illumination film has a sensitized peak between 633-640nm. Therefore, a 620-640nm semiconductor laser should be used for exposure. If a 650-670 laser is used for exposure, problems such as insufficient blackness and halo will occur.
Now the laser with a wavelength of 633nm has matured. Therefore, replacing the 780nm infrared laser with a 633nm semiconductor red laser can make this type of imagesetter apply domestic 6328 Illumination film under the premise of ensuring the output quality, thereby reducing the production cost.
The replacement steps are as follows:
1. Changes in the laser drive circuit The 780 laser is a common cathode and the 633 laser is a common anode, so the laser-driven related circuit should be changed to inverting drive.
2. Changes in the photosensitive amplifier circuit In both lasers, there is a light-sensitive detection tube integrated with the light emitting tube. It is a closed-loop detection and control device to ensure that the laser light emitting tube operates stably under certain energy conditions when parameters such as temperature change. The relative sensitivity of the spectral response of the photodetector tube decreases with decreasing wavelength of the light wave. It was determined that the wavelength of the laser is 780nm. In the normal operating energy range, the photosensitive detection current is about 8mA: a laser with a 633 wavelength, and the photosensitive detection current is about 300mA. Therefore, the parameters of the photosensitive closed-loop detection circuit should be adjusted. At the same time, the parameters of the start detection circuit should also be adjusted.
3. Focusing 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 laser, it can be adjusted with the naked eye using an optical amplifying device.
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 Illumination Films to achieve the quality level of the original imported Type 780 film.