A laser measurement system for automatic calibration of a height-setting micrometer

We have constructed a laser measurement system for automatic calibration of a height-setting micrometer (HSM). The automation is accomplished by an interactive software tool which performs essential calibration functions. The instrument incorporates a double-frequency-stabilized laser whose operation is based on the heterodyne measurement technique. Positioning of the HSM is undertaken by using an X - Y stage driven by servo motors and calibration is performed by combining laser and electronic probe readings. Abbe offset error is eliminated by using a double-path interferometer scheme. The instrument has measurement range 0 - 350 mm, resolution 40 nm and expanded uncertainty of height measurement better than at the 95% confidence level over the full range. The whole calibration procedure can be completed in 2 h, making it much more efficient than the conventional method of gauge-block comparison. The instrument can also be applied to various linear measurements with high accuracy to reduce the measuring time.