Research On Variable Stiffness Control Of Virtual Leg For Biped Robot Based On SEA

Biped robot has sufficient joints and performs perfect movement flexibility. It has strong ability to adapt to the envrionment being able to walk on a flat road, stairs and crossing small obstacles ground. Spring-loaded inverted pendulum(SLIP) is a typical theoretical model to study stable walking for biped robot. SLIP model consists of two linear spring legs and upper body mass. The distinct feature is to regard legs of biped robot as two linear springs. Moreover the stiffness of spring leg can affect stability of walking for SLIP model. A necessary condition for SLIP model to walk stably is that the stiffness of spring leg must fall within the specified range. To use SLIP model to study the stability of the walking robot, we need to make the theoretical model realized with the aim to achieve variable stiffness characteristics of SLIP legs on a physical prototype. This paper focuses on virtual leg stiffness control for biped robot.We have completed the design of the biped robot lower limbs mechanism. Variable stiffness control method is proposed. Afterwards experiment is conducted to validate the feasibility of the control method. The main content is desrcibled as follow.Firstly, the paper analyzes typical structure and working principle of series elastic actuator(SEA). Then we design a new series elasticity module and complete the structural design of the lower limbs biped robot. Leg joints include knee and hip flexion freedom. Joint range of motion meets the requirements of walking. Later the paper processes joint kinematics analysis. Relationship among Joint angle, cylinder displacement and compression of the spring is obtained to facilitate angle control.Based on with robot leg structure, the article study variable stiffness virtual leg theory and variable stiffness control method. The influence of control variables on the stiffness of virtual equivalent legs is analyzed.We obtain three-dimensional equivalent stiffness figure of virtual leg by numerical computation. Torque Balance Control and Surface Fitting Method are proposed to implement virtual robot legs variable stiffness control. Finally, the variable stiffness experiment is made to verify the effectiveness of the two control methods. The experimental stffiness can achieve the expected range. By comparing the experimental error of two control methods, we obtain advatanges and disadvatanges of two control methods.Through the above work, the article achieves variable stiffness virtual leg control for biped robot on physical prototype. With the help of stiffness control in this paper, future work will include stabel walking by means of SLIP model.