Kinematic calibration methodology of hybrid manipulator containing parallel topology with main limb

There is a class of parallel kinematic mechanisms (PKMs) containing so-called "main limb", the kinematic characteristics of which are the same as those of their main limbs. This paper proposes a kinematic calibration method for hybrid manipulators containing parallel topology with main limb. We propose a kinematic equivalent limb (KEL) of the hybrid manipulator and then establish the error model of the KEL. After that, the calibration model of the entire manipulator is derived by integrating the differential error of the parallel part. Using the presented method, the calibration of a seven degrees-of-freedom (DOFs) hybrid manipulator is studied as an example. The error models of both the KEL and the entire hybrid robot are established. The calibration experiment for the hybrid manipulator is carried out. The kinematic parameter errors of the prototype are identified. The errors of the hybrid manipulator decreased by 85% after calibrating, which validates the calibration method. (C) 2019 Elsevier Ltd. All rights reserved.