Self-calibration of redundantly actuated PKM based on motion reversal points

Abstract

In this paper a novel self-calibration method for redundantly actuated parallel manipulators (RA-PKM) is proposed. It does not require external measurements or encoders in passive joints but only uses actuator joint measurements. The method uses motion reversal points (MRP) as calibration landmarks. MRP are characterized by vanishing velocity of one actuator while the RA-PKM performs a continuous motion. In other word the MRP are the input-singularities of an associated non-redundantly actuated PKM. The general calibration concept is introduced in the paper and applied to a planar 4RPR RA-PKM. Numerical simulation results are presented that confirm the feasibility of this method. The selection of appropriate MRP is briefly discussed.