Resolution evaluation of 6-degree-of-freedom precision positioning systems: Definitions and apparatus

Abstract

Resolution is a key criterion in 6 degrees of freedom (DOF) precision positioning systems such as Gough Stewart platforms. Nevertheless, there is no consensus on the definition of resolution and its evaluation. We propose a resolution characterisation method for the 6 DOF precision positioning systems based on users’ requirements (in telescope and synchrotron fields). The method is founded on two user-specific criteria: stability and increment motion length. A new measurement system based on capacitive sensor technology has been developed to assess resolution. The uncertainty of our measurement system was estimated by the Monte Carlo method. This system enables measurement of hexapod platform displacement along 6 DOF with nanometre uncertainty. This is a considerable advantage because it is possible to carry out all the measures of resolution along 6 DOF automatically and without setup modification. We evaluated the resolution of an hexapod specifically developed for the Eastern Anatolia Observatory. The 6 DOF contactless measuring system enabled us to demonstrate an hexapod resolution of 20 nm for translation and 0.25 µrad for rotation.