Offline Teaching Algorithm to Pass Through the Singularity for Robot Machining

This study proposes an algorithm to change the type of inverse kinematics solution for a 6-Degrees of Freedom (DOF) manipulator to pass through the vicinity of a singularity, where the inverse kinematics solution is not determined. Some joints rotate rapidly when passing through the singularity and its vicinity. A general 6-DOF manipulator has eight different inverse kinematics solutions. The proposed algorithm suppressed the rapid rotation by changing the type of inverse kinematics solution when passing through the singularity. However, in the vicinity of the singularity, the joint rotates rapidly because of the connection between different types of discontinuous solutions. Therefore, we defined an interpolation area in the vicinity of the singularity where the rotational speed of the joint is k (0 < k ≦ 1) times or more than the maximum rotational speed of the servomotor and linearly interpolated the joint angles. This algorithm generated a pitch angle error, which was used to determine whether solution type for each Tool Center Point (TCP) speed was to be changed or maintained. The algorithm was verified on a large industrial robot with a 6-DOF manipulator. The rapid rotation of joints passing through the vicinity of the singularity was suppressed depending on the TCP speed and distance from the singularity.