Abstract
In this paper, a semi-absolute interpolation method to improve the resolution of a monofrequency laser interferometer is proposed. The displacement of the moving device which corresponds to λ/2 is measured by an up-down counter. The location within a λ/2 movement is detected using an absolute encoding technique which is referred to as the phase encoding method. The system becomes immune from the error caused by mechanical, optical and/or electrical noise. The analysis and experiments indicate that the combination of 6 bit A-D converters and 4 kbyte ROM is enough to obtain 5nm resolution.
A circuit scheme to provide with the velocity information in analogue voltage is also presented for the convenience of constructing servo-systems. As the measuring interval of the system varies according to the object speed, the method is applicable to a system where the object speed varies widely.
