Design And Experimental Study Of Robot Soft Joint Based On Magneto-rheological Fluid

Aiming at solving the problems of insufficient on security and adaptability for the traditional robot rigid joints and insufficient on accuracy for the soft robots,a joint which combines rigid with flexible is worthy of developing.Magneto-rheological fluid is a kind of smart material which has phase transition in magnetic field.It is in liquid phase when the magnetic field intensity is zero and it changes to solid phase when the magnetic field intensity is large enough.The phase change process is continuously controllable,reversible and the response frequency is high.The magneto-rheological transmission mechanism was embedded into the traditional joint to study the soft joint which was variable and controllable.A soft joint based on magneto-rheological fluid was proposed in this paper:(1)A new principle of robot soft joint based on magneto-rheological technology was proposed.The magneto-rheological transmission mechanism was embedded in the traditional joint.The rigidity and flexibility were combined in the new joint.Thus,the accuracy of the operation can be kept,and the flexibility and the safety can be ensured.(2)A magneto-rheological fluid transmission device was designed.The electro-magnetic simulation software MAXWELL was applied to analyze the initial magneto-rheological transmission device.The optimal parameters were adopted to make the prototype.The optimal parameters for the model were as follows: the work gap was 2 mm and the excitation coil was 300 turns.And the overall structure of magneto-rheological fluid soft joint was designed.(3)The variable stiffness model of the soft joint for the robot that based on the macro and micro behaviors was established.The relationship between the control current and the transmission torque,and the relationship between the control current and the rotation angle were analyzed.The kinematic model was established and the theoretical model was verified by software MATLAB.The results indicated that the angle approximately increased linearly as the electric current increased.The rotation angle increased when the electric current increased and the angle increased faster when the work time increased.(4)The control mechanism of the magneto-rheological soft joint was studied.Fuzzy logic control was adopted as the control method for the soft joint.Rules for soft joint control were made.A fuzzy controller for magneto-rheological soft joint was designed.(5)The magneto-rheological soft joint prototype was made.The experimental platform for the performance test of the magneto-rheological soft joint was established.The torque output experiment of the magneto-rheological transmission device and the experiment of the angle output and force output of the passive bar were operated.The experimental results showed that the output torque of the magneto-rheological device had a linear relationship with the coil current.It could effectively guarantee the accuracy of joint operation.It could be seen from the results of the experiment of passive bar that the response time of the device was very short,and it could reach 200 ms.The first generation of magneto-rheological soft joint was designed and manufactured in this paper.The external dimensions were 120 mm×125 mm×400 mm.And the maximum output force was 0.2 N.The prototype could basically realize the dynamic transfer function of the magneto-rheological fluid soft joint,which had guiding significance for the following research.