Research On Miniature Robotic Arm Based On Shape Memory Alloy Wire Actuator

As robots are developed in the direction of light-weight and intelligence,higher demands are placed on the size and weight of drives.Shape Memory Alloys(SMAs)are well suited for intelligent drives,with its integrated sensing and driving,high power-toweight ratio,and easy compactness.A miniature drive based on SMA wires is proposed to replace the traditional joint motor actuator to achieve the miniaturization of robotic arm in this thesis.This thesis develops a miniature actuator based on SMA theory,and a three-degreeof-freedom micro-compact robotic arm is designed.The structural design of the SMAdriven robotic arm system is completed,and the parameters are optimized based on the offset spring stiffness and preload force.The 3D models of the actuator and robotic arm are established.The size of the SMA actuator is 41.5mm×32mm×18mm,and the maximum rotation angle is 90°.The maximum rotation angle of the single side jaw of the SMA robot arm is about 15°,and the minimum object diameter to grip is 10.6mm.The coupled kinematic equations and coupled static equations of the system are established based on the rotational volume theory.The influence of the self-weight of the parts on the load capacity is analyzed.The kinematic simulation of the overall model is completed.Compared with the theoretical calculation results,the maximum position error is 2.09% and the maximum velocity error is 6.18%.The coupled kinetic equations of the system and the heat transfer equations of SMA wire in the process of electric heating and air cooling are obtained based on the Lagrangian dynamics and heat transfer principles.The thermal-force-electric coupling motion control model of the three-degree-of-freedom SMA robotic arm is established by combining SMA intrinsic structure model,system dynamics equation and heat transfer equation.The open-loop circuit design of the motion control system is completed.The solution of heating voltage,temperature,strain,and martensite fraction of SMA wire during the motion of the three-degree-of-freedom SMA robot arm is obtained.The SMA wire is subjected to differential scanning calorimetry experiments and tensile tests,and some thermodynamic and material parameters of the SMA wire are determined according to the test results.The development and assembly of the SMA actuator and the micro-compact robotic arm prototype are completed,and the rotational performance of the actuator and robotic arm are tested.The results show that the SMA actuator can achieve bidirectional rotation,and the maximum rotation angle is about 70°when the load is zero and the driving voltage is 4V.The maximum rotation range of the robot arm is about 21° for the shoulder joint and 60° for the elbow joint,and the maximum weight lifted is 12 g.