Unit quaternion: a useful tool for inverse kinematics of robot manipulators

Kinematic control of robot manipulators requires the computation of reference trajectories for the joint servos, through an inverse kinematics, to execute a given end-effector trajectory. A key point is concerned with end-effector orientation description which may lead to the occurrence of the so-called representation singularities. To overcome this drawback, in this paper a closed-loop inverse kinematics algorithm is presented where the unit quaternion is conveniently adopted in lieu of the Euler angles. The implementation on an industrial robot manipulator in a number of case studies is described.