Direct kinematic analysis of a heavy-payload forging manipulator in the grasping stage

Purpose - The purpose of this paper is to present the direct kinematic analysis of a heavy-payload forging manipulator. In the grasping stage, the manipulator is equivalent to a 3-DOF under-actuated mechanism. In order to deal with the direct position kinematics of the under-actuated mechanism, the analysis is performed in two steps. Design/methodology/approach - The paper analyzes the direct position kinematics of the 3-DOF under-actuated mechanism as follows: first, the authors add a virtual constraint on the mechanism, convert it to a 2-DOF fully actuated mechanism and calculate the direct kinematics of the constrained mechanism. Then, the constraint is applied to many different positions and the corresponding direct kinematics of the constrained mechanism are calculated, respectively. Finally, the mechanism with lower gravitational potential energy than any other constrained mechanism is chosen, and its direct position is what is needed for the 3-DOF underactuated mechanism. Findings - The paper provides a solution for the direct kinematic analysis of a heavy-payload forging manipulator in the grasping stage. Furthermore, the simulation and experiment results confirm the effectiveness of the solution. Originality/value - The paper proposes a methodology to deal with the direct position kinematics of the 3-DOF under-actuated mechanism in two steps.