Transmission Analysis And Structure Design Of Tendon-driven Dexterous Finger

With the continuous development of space technology and the increase of space activities,astronauts will face more dangerous missions.The installation of a multi-functional dexterous manipulation tool such as a space dexterous hand at the end of the robotic arm can replace and assist the astronauts in performing many dangerous tasks.Therefore,many countries have begun to develop space dexterous hand.This paper presents the transmission analysis and structure design of a tendon-driven dexterous finger for space operation environment.Firstly,the research status and characteristics of tendon-driven dexterous hand are analyzed.The development history and research status of tendon-driven dexterous hand at home and abroad are presented.The design ideas and difficulties of tendon-driven dexterous hand are summarized,including joint decoupling,path design,tendon pre-tightening and friction control.Secondly,the tendon transmission system is analyzed.The overall design of the finger is completed.The modular finger consists of four joints and three degrees of freedom,driven by three motors through N tendon transmission mode.The finger kinematics is calculated.The joint torque produced by different kinds of external loads and the internal force of tendon which balances the joint torque are obtained.The influence of the tendon path on the internal force of the tendon and the power of the motor is analyzed.The guiding principle of the design of the tendon-driven finger is put forward,and the best transmission path scheme is obtained.Then,the finger structure design is completed.The finger is functionally divided into four parts: finger joints,tendon transmission system,motor module and sensor system.The finger joint consists of two parts: the interphalangeal coupling joint and the base joint.The coupling joint is coupled by tendons.The base joint is composed of a vertical staggered cross axis and a pulley group,which can realize two-degree-of-freedom coupled motion.Tendon transmission system consists of material selection,pre-tightening,fixing,guiding and path design of tendon.The unique design of the motor module allows the tendon to be introduced from the middle of the finger to the end of the joint,making the finger symmetrical,which is conducive to the subsequent design of the dexterous hand.The sensor system consists of position sensor,torque sensor and tension sensor.The position sensor consists of Hall sensor in the motor module and joint end Hall sensor.The two-dimensional torque of the base joint and the torque of the distal interphalangeal joint can be measured by the torque sensor disposed in front of the base joint.Necessity and location of tension sensor are analyzed.Finally,the finger transmission relationship is analyzed and the finger performance is verified by experiments.The influence of tendon friction and extension on finger transmission relationship is analyzed and the mapping relationship between motor space and joint space is obtained.A finger is assembled for motion experiment.The rationality and reliability of finger structure is verified,which lays a foundation for the design of control system.