An integrated fringe counting and interpolation laser heterodyne interferometer for micro-robot position measurement /

This thesis describes a laser heterodyne interferometer for measuring the displacement of a high performance micro-robot limb. The limb movements must be measured over a range of 10 mm, with a resolution of 1 nm SD (standard deviation), in experiments lasting less than 1 second. The maximum displacement speed of the limbs is 2 m/s.To fulfil the design requirements, the approach taken here is to consider that the full measurement resolution is only needed when the limb is approaching its target at low speed.The interferometer described in this thesis is capable of high accuracy fringe interpolation measurements over a range of 10 mm, with a resolution of 0.1 nm SD, in a bandwidth of 100 kHz, in a 1 second time period. For low resolution measurements when the limb is moving at high speed, the interferometer measures displacements by fringe counting.Experimental results are presented which demonstrate that the accuracy of the interferometer actually exceeds the high resolution design objective by an order of magnitude. Also, results of experiments which study the effect of noise sources (both inherent to the interferometer and from the environment) on the accuracy of the measurements are presented.Finally, results of an experiment where the interferometer was used in a practical application to demonstrate its usefulness are presented: the interferometer was used in the closed-loop control of a non-linear micro-actuator