A robotic hoof to enhance slip resistance

Abstract

Slippage occurs when the tangential reaction forces cannot counteract the transverse force at the contact point. Slip is a critical challenge in robotic locomotion because it affects the stability and energy efficiency of the robots. To solve this problem, some approaches detect slip by using sensors near or at the bottom of the feet to measure the ground reaction forces or kinematic variables. Nevertheless, the control complexity, the low robustness to noise, and the price of sensors limit the application of these approaches.

Recently, bio-inspired designs have shown that the natural dynamics of the body can be used to simplify the control complexity of robots, increment its robustness to perturbations, and improve its energy efficiency. Therefore, this thesis studies how the natural dynamics of a bio-inspired robotic hoof enhance slip resistance. The first analysis comprises designing the robotic hoof and evaluating its slip resistance against that of the conventional approach in robotic feet. Since the robotic hoof exhibits a significantly higher slip resistance than that of the conventional robotic foot, the anisotropy of its slip resistance is analyzed. The results reveal that the slip resistance of the hoof is maximum when the external force and the forward direction of the symmetry axis of the hoof are aligned. Then, by running numerical analysis and experiments, it was found that compliant yaw and pitch and stiff roll are essential for the emergence of the Anti-lock braking system-like behavior and the energy absorbing behavior of the hoof. Depending on the compliance level at the joints, the hoof can store part of the kinematic energy as potential energy. Therefore, these behaviors contribute to improving slip resistance. These findings reveal the importance of the natural dynamics of the body for solving challenging problems such as slippage in robotics.