Automatic self-calibration of piezo systems in phase shifting Fizeau interferometers

A digital piezo system comprises a PZT and a capacitive sensor combined in a single unit. The desired displacement can be achieved by simply inputting the displacement value into the software. However, when target value of /spl lambda//8 was input to the three PZT´s, the Fizeau plate did not show parallel movement, resulting in tilt to the linear fringes of the interferogram, In order to measure the length of the gauge block with high accuracy, this non-parallel movement of the Fizeau plate should be corrected precisely. This could be accomplished by multiplying correction factors to the target values of the piezo systems, which are self-measured by the phase shifting Fizeau interferometer.