Inverse Kinematics of a 7-DOF Spraying Robot with 4R 3-DOF Non-spherical Wrist

In this paper, an Inverse Kinematics (IK) algorithm combining the analytical method and the numerical one is proposed to solve the IK problem of a 7-DOF spraying robot with 4R 3-DOF non-spherical wrist. Firstly, the 7-DOF spraying robot is transformed into a 7-DOF robot with 3R spherical wrist and the arm angle is used as the redundancy parameter. The approximate IK solution is calculated analytically using offset angle method by means of approximation. Secondly, the approximate solution is taken as the initial value of the iterative algorithm and by updating the joint angles through the damped least-square method with augmented Jacobian matrix, the final exact solution is obtained after a few iterations. Three simulation experiments show that the proposed algorithm not only has high computational efficiency and accuracy, but also can obtain multiple solutions and show the self-motion characteristics of the 7-DOF robot. The novel algorithm may be implemented in real-time control of the 7-DOF spraying robot.