Force Free Add-on Position Measurement Device for the TCP of Parallel Kinematic Manipulators

The position of the tool center point (TCP) of a parallel kinematic manipulator (PKM) is traditionally being measured indirectly by means of the position measurement of the drives. Cutting forces and acceleration forces cause displacements of the TCP, which cannot be detected from the position measurement of the drives. To improve the position accuracy of the TCP a force free add-on position measurement device is suggested. The kinematic design of such a measurement device, the calibration and its application for feedback control and improved TCP positioning in the presence of external forces is described. Experimental results are presented to illustrate the expected improvements in TCP positioning.