Abstract: There are no closed-form inverse displacement solutions for 6R robots with offset wrists. These robotic offset wrists are classified as side offset, top offset, and front offset. To solve the problem of inverse displacement analysis of 6R robots with front offset wrists, according to the geometric character of robotic mechanisms, the robotic kinematic chain is cut into two branches at the origin of the joint coordinate or at the intersection point of the axes of the adjacent coordinates. In this way, one component of degrees of freedom for the two branches becomes decoupled at the cutoff point, so the relationships among the joint variables can be easily deduced. The transcendental equations containing 6 variables are turned into a nonlinear equation containing 1 variable, and the numerical solution for the inverse displacement analysis is obtained by using one dimensional iterative search.

Key words: Inverse kinematics analysis, Offset wrist, Robotic manipulator