Design Of A Compliant Parallel Robotic Wrist Based On Serial Elastic Actuator

Robotic wrists play an important role in determining the position and the contact state of the end effector. The quality of a robotic wrist determines the performance of the whole robotic arm directly. For ensuring larger working space, higher positioning accuracy and response speed, traditional robotic wrist is mainly a serial rigid structure, which has poor adaptability to the environment. Rehabilitation robots, home service robots, industry collaboration robots are involving more and more human-robot interactions with uncertainties. Once wrong operations occur, the safety of people will in threats. Compliant design of a robotic arm is an important topic to solve the social application of the next generation service robot. In this paper, a three degrees of freedom compliant parallel robotic wrist-SoftWrist was designed. It's drive mechanism was designed based on serial elastic actuator. The main works are as follows:Referring to the human upper limb, a robotic wrist was design based on a 3SPS-1S parallel mechanism, which can achieve the rotations of roll, pitch and yaw. Three prismatic pairs were used as the driving pair of the robotic wrist.The kinematic model, the inverse kinematic and the Jacobi matrix was solved for the robotic wrist. The work space was calculated and its three-dimensional graphics was drawn using matlab. The influence of the structural parameters on the workspace was analyzed. Based on operation degree, singular configuration and flexibility was analyzed. Finally the size of SoftWrist prototype was determinded.The linear series elastic actuator(SEA) was designed by combining the spring group and the linear motor. The method of determining the spring stiffness of the SEA module was presented, and the spring parameters are calculated. Light-weight designing of the parallel wrist was achieved through material selection and structural optimization. Builting the prototype of SoftWrist was constructed, and the robotic wrist control system was built based on STM32.The comparative experiments of posture control of a rigid wrist and a compliant wrist were carried on. And the result showed that compliant robotic wrist has the similar positioning ability as its rigid counterpart. The static and dynamic experiments also showed that SoftWrist has the passive compliance and active compliance based on its SEA and force control approach.