Design Of Mechanical Leg Actuated By Pneumatic Muscles And Computed Torque Control Of The Leg In Swing Phase

The joint actuated by an antagonistic pair of pneumatic muscles(PMs)has good capability to imitate motion of joints of animals.And it is with intrinsic flexibility,which can strengthen ability to adapt quadruped robots to environment.However,the range of rotation for joints with PMs is small,and its torque is difficult to be measured and controlled,which limit motion capacity for quadruped robots.The specific work is carried out as follows.The relationship between ground reaction force(GRF)and the height of jumping for mechanical leg is derived.And joints torque formula is established with jumping height and initial angel of joints.Based on the formula,a two degree-of-freedom mechanical leg actuated by PMs is designed.Characteristics of pneumatic regulating proportional valve and PMs is tested.Output air pressure model of the valve and PM contraction force model are established.Kinematics model from PMs displacement to joints position angle is established,and the inverse solution of PMs displacement is solved.Furthermore,joints torque model is established.And the relationship from joints torque to PMs contraction force is designed.Finally,a Lagrangian dynamic model of mechanical leg is established in swing phase.Cascade control strategy with the position loop outside the inner contraction force loop for mechanical leg is designed by using computed torque control method.Joint position loop controller is PD control with dynamics of mechanical leg for feedback compensation,and PM contraction force loop controller is PI control with inverse PM contraction force model for feedforward control.In Matlab/Simulink,control of mechanical leg in swing phase is simulated,which realizes sinusoidal tracking of joints position,and joint torque and PM contraction force also achieve stable tracking.Simulation proves the correctness of joints kinematic model and torque model,and control strategy is effective.In experiments,feedback signals are offered by position encoder,load cell and pressure sensor,respectively.Experiments of control of swing and jumping for mechanical leg are carried out,and data of joints position angle,torque and GRF under foot are analyzed.The correctness of dynamic model of mechanical leg can be further confirmed by swing experimental results.And the validity of cascade computed torque control is also demonstrated.Tracking control of position and torque of joints can be realized.Jumping experimental results show that designed joints of mechanical leg can meet the requirements of range of angle position and torque of rotation.