Identification and compensation for offset errors on the rotary axes of a multi-axis Magnetorheological Finishing machine tool

In this paper, offset errors in rotary axes of a multi-axis Magnetorheological Finishing (MRF) machine tool are identified using a “trial cut” method and compensated in postprocessor for MRF figuring process. Kinematic model considering the offset errors of the multi-axis MRF machine tool UPF700-7 is built, utilizing homogenous transformation matrices theory. Then, a trial cut method by acquiring removal functions (RFs) in given positions of a sphere workpiece is proposed to identify the offset errors, in which only one rotary axis and two translational axes move simultaneously to obtain a circular trajectory. The maximum material removal position of the RFs is defined as the actual tool tip position in MRF process. The difference between ideal and actual tip tool position is applied to determine the relation between actual tool tip position and offset errors. The relations between them are derived with a linear equation, and offset errors are calculated using the least squares method. Finally, figuring correction experiments are performed on an off-axis aspheric mirror to validate the feasibility of the improved technology in an integrated MRF figuring process, in which offset errors are compensated in a postprocessor.