Development of Linear Absolute Type Magnetic Scale
|School||Harbin Institute of Technology|
|Course||Mechanical Design and Theory|
|Keywords||magnetic field analyses successive displacement code magnetic scale absolute displacement measurement|
Magnetic scale becomes used more and more widely, due to its low-cost, simple structure. Our magnetic scales measure relative displacement mainly, and have great gap with western countries in technologies. As the development of automation, the high precise linear absolute displacement measurement becomes significant. We must develop researches on the precision and absolute measurement of magnetic displacement sensor no time to delay.Relative displacement sensor measured multiple-periods by counting pulses. There are two defects. First, every meterage must be started at the beginning, and need zero-adjustment; second, the measuring dates can not be stored without electricity. So aimed at improving those problems, I proposed a successive displacement binary code. I marked every period with this code, the processor can recognise every periods. In this way, the absolute displacement can be measured. By using switch hall, the successive displacement binary code was converted into magnetic-pole arrangement. And the binary code was fulfilled conveniently.The signal generating and processing parts of traditional magnetic scale are very complicated. For simpleness, I used alnicos arrays and magnetic sense hall combination. The movement of hall on top of alnicos generated sinusoidal voltage. Using single-chip as the main processor reduced peripheral hardware greatly. The arithmetic of sinusoidal signals processing is piecewise linear interpolation. This is a kind of high precision, real-time Digital Signal Processing. The magnetic scale was calibrated by using a higher resolution optical grating off-line: displacement output from optical grating and sinusoidal signals from magnetic scale were sampled at the same time and transmitted to computer, their relation can be get and stored in MCU for looking-up. The displacement was looked up according the Hall signals in different regions while in working state. For better quality of original signals, I do lots of magnetic field analyses to establish positional relation between alnicos and positional relation between hall and alnicos.The experiment results indicated that: The magnetic scale fulfilled absolute displacement measurement in 2048 millimeter; compared with high precise Optical Grating, whose resolution is 0.5μm, the magnetic scale’s resolution reached 0.75μm; the magnetic scale has small sizes, low-cost, simple structure.For micromation of magnetic sensor, I improved two line-up alnicos design, and proposed one line-up alnicos design. In some special fields as aviation and spaceflight, it will have important application.