Variable Impedance Control for a Single Leg of a Quadruped Robot Based on Contact Force Estimation

A quadruped robot interacts with the ground during the stance phase. This interaction will have a great impact on the feet, torso and joints of the robot, thus affecting the stability of its movement and reducing its adaptability in complex environments with features such as uneven terrain. The contact between each foot of the quadruped robot and the ground should not only control the movement trajectory of the leg but also control the force between the leg and the ground to comply with the environmental constraints. In general, the environment is constantly changing, whereas the traditional impedance control parameters are fixed and thus impose fixed-point constraints. To improve the compliance of the feet of a robot and achieve flexible interactions with the ground in various complex environments, such as pipelines, ruins and forests, variable impedance control is proposed. Based on variable inertia, damping and stiffness parameters, a new Lyapunov function is selected to analyse the stability of the closed-loop system. Furthermore, a force estimator is applied to estimate the contact forces, thereby reducing the burden of structural design and the cost of the robot. The effectiveness of the proposed variable impedance control scheme and contact force estimator is verified through numerical simulations in MATLAB.