Error motion of a kinematic spindle

A prototype spindle for low-force, low-speed applications that is kinematically constrained in accordance with the principles of exact constraint was designed, fabricated, and tested. In the prototype spindle, the position and orientation of the shaft (rotor) are constrained at five contact points; four constraints are arranged radially around the rotor, and one constraint is located at the end of the rotor. This paper describes the design of the prototype spindle and presents a study of its error motion for the hardened steel rotor sliding on brass and UHMW-PE bonded to ceramic. The error motion is observed to be highly repeatable with less than 100nm asynchronous errors, and a simple analytical model enables the prediction of the synchronous error motion using measurements of the rotor's roundness profiles.