Reaserch Of Biped Robot With Variable-stiffness Ankle

In the field of biped walking robot research, researchers tend to refer to human characteristic. The comprehensive performance of robots can never surpass the human at present. Human lower limb has enough flexible, not only can make human realize smooth bipedal walking; energy saving; and can also protect the lower limb joints. The characteristics of human lower limbs are very meaningful to absorb the shock for biped robot.There have been some research results about flexible joints domestic and overseas. The structure of the flexible joint is very varied, but most of the existing flexible joints design is not well applied in a bipedal robot system. In order to study the influence of the flexible joint of bipedal robot walking, this paper designs a new kind of adjustable stiffness flexible joint. The robot consists of hip, knee, ankle ande foot. The flexible joint is on the ankle joint. An underactrated cycle walking controller is designed. The controller ensure the robot realize stable walking. Finally the correctness of the contro l strategy is verified by simulation and experiment. They confirmed the positive impact of flexible joints.First of all, according to the number of human lower limb joints, the degree of freedom distribution is determined of the robot. Analyse the positive and negative points of active robot and passive robot, determined the driving scheme. The 6 dof biped walking robot's overall mechanical structure is designed. Using the lever principle, the structure of the variable stiffness flexible joint is designed. The torque of the motor on the variable stiffness flexible joint is measured.Secondly, through the analysis of the foot structure of robot, ignored the problem of toe interference. The robot structure for "five-bar quad" structure model is simplified. Based on Lagrange energy principle, the dynamics model of single leg support is established in the state space. Based on the contact force for the Lagrange equation and the principle of virtual work, the dynamics model of double legs support is established in the state space.Thirdly, based on the calculation method of moment and virtual constraint principle, turn the robot's time- varying parameters to time- invariant parameters to track the reference trajectory. Based on the feedback linearization method, the robot's joint torque was isolated. Then the feedback controller is designed. Based on Bessel polynomial the time- invariant gait of underactuated robot is planed. Choosing limit cycle as the stability-verify method, the stability of robot is evaluated.Finally, a bipedal robot walking experiment platform is established. A bipedal robot prototype with flexible ankle is developed. The influence of variable stiffness ankle joint to robot walking is simulated in ADAMS. Two walking experiments are presented, one is chessboard type pavement continuous walking experiment, the other is single step experiment. The influence of variable stiffness mechanism to walking stability is shown by the results of the two experiments.