The IMGC calibration setup for microdisplacement actuators

For the calibration of piezo-capacitive displacement actuators, we use an i nterferometric setup with subnanometric resolution. In order to minimize th e periodic nonlinearity effect of the laser interferometer, the optical pat h difference is changed in steps of lambda, obtained from a computer-based loop control of the out-of-phase difference between the reference and the m easuring signal of the interferometer. Experimental results show an expande d uncertainty of about 0.7 nm + 0.1 x 10(-3) L. The calibrated actuator is then used as a transfer standard at the nanometer level, both for testing t he nonlinearity of the laser interferometer and for calibrating the linear variable differential transformer (LVDT) probe of the Istituto di Metrologi a "G, Colonnetti," (IMGC) Torino, Italy, roundness instrument (used for mea suring silicon spheres for the Avogadro constant).