Study On Motion Control For Underactuated Biped Robot

Underactuated biped robot is a kind of biped robot which possesses the property of underactuation,brought forward to research dynamic walking.The robot has pointed feet such that there is obviously no drive torque between the feet and the ground,which forms an underactuated system.Because of this property,the robot isn't able to stand still,which means that it can only achieve dynamic balance by keeping walking.Then,it becomes more difficult for the stable control of the robot;on the other hand,by taking advantage of its natural underactuation,the robot can achieve stable dynamic walking by gravity.In fact,dynamic walking has several advantages over static walking,such as high efficience,high speed,low energy consumption and natural gait.Hence,the underactuated biped robot with the ability of dynamic walking points out an important research aspect in the field of biped robot.Firstly,the phenomenon of underactuation in the process of walking of human and passive biped robot is analyzed.With some simplifications and assumptions,the research object of the underactuated biped robot is introduced,which is a planar five-link robot with two telescopic legs.Secondly,the forward kinematics model of the robot is obtained by using the screw method;the inverse kinematics model is derived by the method of solving the subproblems of kinematics model.The bipedal walking of the underactuated biped robot consists of the two phases of single-leg support and double-leg support which succeeds each other circularly.Consequently,the complete dynamic model,which contains two parts,of the robot is hybrid:the first part is a continuous dynamic model of the phase of single-leg support,which is established by Lagrange's equation;the second part is an algebraic model of the impact in the phase of double-leg support.In consideration of the underactuation of the robot,the time-invariance-based control strategy is adopted,and the design of the complete virtual constraint is finished;then,for the design of the feedback controller,the computed torque method is used.At last,after the parameters of the links of the robot is given,the bipedal walking motion of the underactuated biped robot is simulated in the MATLAB software.