An efficient algorithm for inverse kinematics of robots with non-spherical wrist

In this paper, 7 revolutions with 6 degrees of freedom (7R 6-DOF) robots having non-spherical wrist are widely used in automatic coating of automobiles and aircrafts. These robots do not follow the Pieper rule; thus, a large amount of time is spent using numerical algorithms to calculate the inverse kinematic (IK) solutions. Therefore, this paper attempts to propose an efficient algorithm to reduce the calculation time for the IK solutions. Analogous to robots with spherical wrist, the concepts of “inner wrist centre and “outer wrist centre are put forward after a detailed analysis on the structure of 7R 6-DOF robots with non-spherical wrist. Considering the relationship between the outer and inner wrist centre, the position of the inner wrist centre is estimated and taken as the decoupling point to update the IK solutions analytically. Besides, some special cases affecting the efficiency of the algorithm are also discussed. Finally, the algorithm was implemented on computer to test the efficiency and applicability. According to experimental results, the algorithm can reduce time consumption by 30% in comparison with traditional algorithm, indicating that the proposed calculation algorithm is significantly effective.