Variable-Stiffness Mechanisms of a Spatial 5-DOF Compliant Robot Wrist

The errors of position and attitude of robot operations can be rectified by configuring a robot with a compliant wrist and applying a compliance control method. So as to satisfy the requirements of pose adjustment and stiffness modulation of the robot operations in a three-dimensional space, a spatial 5-DOF robot wrist with a significant range of stiffness change is proposed. The flexibility of the wrist can be greatly changed during a compliance operation according to different processes and workpieces. The rigid localization of the robot can be achieved, and the positional inaccuracies of robot operations can be rectified by applying the compliance control method. The mechanisms for adjusting the stiffness of the wrist by modulating a spring tension to change a stiffness is researched, and the model of the wrist stiffness varying with rotating angles during the pose variation of the wrist is established. The stiffness of wrist joints rises proportionally with the increase in spring tension. It is confirmed that the stiffness changes with the wrist pose is less by applying feedback control on the wrist stiffness. The assembly-clamping experiment shows that the compliance operation of the robot can be accomplished by the feedback control of wrist stiffness.