The Research Of Grating Light Valve Based Thermal CTP Technology

Thermal CTP technology which has advantages including bright room operation, good environmental performance, high plate-making quality and speed etc, has become the mainstream of current computer-to-plate technology. In thermal CTP system, the research and development of infrared laser devices and thermal plates has been mature, and the main technical difficulties lie in the design and improvement of laser scanning imaging system. The Grating Light Valve(GLV) is a kind of diffractive spatial light modulators. It uses the modulation effect on laser beams to form laser scanning imaging system, and it has been successfully applied in the thermal CTP system. Special structure design of the GLV device makes it have properties such as fast modulation speed, strong capability to withstanding high power laser, digital working states, precise control of beam shape and so on. Therefore, it plays an important role in improving plate-making speed and imaging quality of thermal CTP system. The GLV-based thermal CTP system forms square exposure spots on the plate, so it does not exist dot enlargement in the process of exposure imaging and gives full rein to its advantage in outputting fine dots and controlling dot size accurately. As a result, the GLV-based thermal CTP system is more suitable for high resolution FM screening printing than traditional diodes array scanning imaging system.This paper first introduces the structure, working principle and excellent properties of Grating Light Valve. The electromechanical characteristic of GLV is analyzed by the spring-capacitor model, and calculation formula of the GLV ribbon’s displacement is deduced according to differential equation of the GLV ribbon’s bending. A simplified Grating Light Valve optical model is put forward, and calculation formula of the GLV device’s diffraction light intensity is deduced according to Fraunhofer single-slit diffraction theory and multiple beam interference theory. Secondly, the effect of the GLV device’s structural parameters on its working efficiency is expounded. The electromechanical characteristic of GLV is simulated using ANSYS software, and light modulation effect of GLV is analyzed by way of the data and charts. Thirdly, the structure and imaging principle of GLV-based thermal CTP scanning imaging system is studied in detail. The GLV-based thermal CTP digital imaging process is presented in summary. At last, the plate-making speed and imaging quality of GLV-based thermal CTP system is analyzed by analyzing properties of the GLV device. The dot enlargement rate of 0% ~ 100% FM dots composed by square spots and circular spots is separately calculated, and the dot enlargement rate curves are drawn out using MATLAB software. Exposure imaging quality of GLV-based thermal CTP system is compared with that of diodes array scanning imaging system by analyzing these two dot enlargement rate curves.