Detachment avoidance of joint elements of a robotic manipulator with clearances based on trajectory planning

The positioning accuracy and dynamic performance of robotic manipulators are significant for achieving robotic tasks such as maintenance and assembly. However, the joint clearances decrease the positioning accuracy, bring the impact between joint elements, and produce much noise. This paper presents a novel method based on trajectory planning to avoid the detachment of joint elements of a manipulator with clearances. An improved detachment criterion for the revolute and spherical joints is proposed. The angular displacements and velocities of virtual links are approximately solved through the directions of joint forces and their time rates of the corresponding ideal mechanism, but the accelerations of virtual links need not be approximately solved. The polynomial function is adopted to perform the trajectory planning, enabling joint forces to be expressed as functions of the motion parameters of active joints and virtual links. By taking the time interval of each trajectory segment as the adjustable parameter, the dynamic response spectrums of joint forces are obtained, which can be used to facilitate the selection of the adjustable trajectory parameters so as to avoid the detachment between joint elements.