Research On Liquid Crystal Encoder Measurement System

An absolute linear encoder, as a tool for linear measurement, is widely used in the fields of automation industry and the scientific research. With the national emphasis on manufacturing automation, absolute linear encoders have become a hot research.Absolute liquid crystal encoder measurement system belongs to the absolute linear encoder measurement system. It has the advantages of high positioning precision, large measurement range, low cost, simple operation without returning to zero and programmable. As the manufacturing process of the liquid crystal panels is getting mature, high-resolution and large-size liquid crystal panels have been ubiquitous in the market. Since the LCD screen of the liquid crystal pixel array has a high spatial uniformity, the entire LCD screen can be regarded as a huge encoder.Based on the Gray code and the positioning principles of the system, we design a new code called "Deformed Gray Code", "Deformed Gray Code" can greatly reduce the BER caused by the mechanical errors. Each pixel on the LCD screen is controllable, and any graphics can be displayed on the LCD screen, when the "Deformed Gray Code" diagram is displayed on the LCD screen, LCD screen will become an absolute linear encoder, which can be called absolute liquid crystal encoder.The maximum range of the absolute liquid crystal encoder measurement system is 256000μm, the maximum pixel level resolution is 2.4μm, the measurement accuracy can be achieved ±2.1μm when eliminating the rail mechanical fluctuations. For the absolute liquid crystal encoder, the key technology to achieve high-precision positioning is subdivision technology. Combines CMOS microscopic subdivision technology, this system can further subdivide the byte of absolute liquid crystal encoder. And the edge base point positioning algorithm or central peak base point positioning algorithm can be used to compute the subdivision distance, however, the experimental results show that the edge base point method requires an image of high quality, while the center base point algorithm can cope with the relative low quality images. We adopt the system with the low-cost Logitech C270 cameras and zoom lenses, since the quality of the acquired image is not very high, our system finally adopts center base point positioning algorithm to calculate the subdivided distance.The software part of the absolute liquid crystal encoder measurement system is based on the Android platform, which reduces the volume of the system and provides a friendly interactive interface.