A SIMPLE OPTICAL SENSOR FOR THE STRAIGHTNESS ERROR MEASUREMENT OF A MOVING STAGE

Chu-shik Kang, Jong-ahn Kim, Jonghan Jin, Tae Bong Eom, Ho Suhng Suh, Jae Wan Kim

Abstract

The watt balance, a metrological instrument that might provide the new definition of the kilogram, consists of a moving coil which has a tight tolerance for its straight motion. Normal straightness sensors cannot be used for the watt balance because any electronic device might disturb the magnetic field around the coil. We propose a simple optical sensor to measure out-of-straightness of a moving coil. The sensor is comprised of a cube-corner prism and a reflector having a sharp edge. When a laser beam is incident on the cube-corner prism which is located on the moving coil, any out-of-straightness movement of the coil shifts the outcoming beam. The shifted beam is partly reflected by the edge reflector and the rest of the beam transmitted. Each beam is collected into an optical fiber and sent to a balanced photo detector. The lock-in detection is used for measuring the difference of the reflected beam intensities. After obtaining the relation between the amount of beam-shift and the lock-in output signal by using the knife edge scanning method, the straightness error of a moving stage could be measured with high accuracy. In our preliminary experiment which was performed in air, the sensitivity of the sensor was 2.457 mV/nm, and the nonlinearity of the sensor turned out to be about 0.7 % for the straightness error range of ±7 mm.

Keywords

straightness sensor, watt balance, edge reflector

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IMEKO TC

TC14 - Measurement of Geometrical Quantities

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