Real-time Perceptive Motion Control using Control Barrier Functions with Analytical Smoothing for Six-Wheeled-Telescopic-Legged Robot Tachyon 3

TL;DR

This study proposes a lightweight real-time perceptive motion control system for the newly developed six-wheeled-telescopic-legged robot, Tachyon 3 that satisfies joint limitations, environmental collision avoidance and safe convex foothold constraints.

Abstract

To achieve safe legged locomotion, it is important to generate motion in real-time considering various constraints in robots and environments. In this study, we propose a lightweight real-time perspective motion control system for the newly developed six-wheeled-telescopic-legged robot, Tachyon 3. In the proposed method, analytically smoothed constraints including Smooth Separating Axis Theorem (Smooth SAT) as a novel higher order differentiable collision detection for 3D shapes is applied to the Control Barrier Function (CBF). The proposed system integrating the CBF achieves online motion generation in a short control cycle of 1 ms that satisfies joint limitations, environmental collision avoidance and safe convex foothold constraints. The efficiency of Smooth SAT is shown from the collision detection time of 1 us or less and the CBF constraint computation time for Tachyon3 of several us. Furthermore, the effectiveness of the proposed system is verified through the stair-climbing motion, integrating online recognition in a simulation and a real machine.

Figures (10)

• Figure 1: Six-wheeled-telescopic-legged robot Tachyon 3 which has 6 legs and 4 actuated wheels and 2 omni passive wheels.
• Figure 2: (a) Tachyon 3 is equipped with three front legs (left-front (LF), middle-front (MF), and right-front (RF)) and three rear legs (left-rear (LR), middle-rear (MR) and right-rear (RR)). In total, it consists of 16 active joints including 6 prismatic joints, 6 hip joints and 4 drive wheels, and additional two passive omni wheels. (b) An example of static locomotion for climbing stairs. First, the three wheels, LR, RR and MF, swing to the next steps and the others move with the wheels. Second, MR, LF and RF next steps and the three other wheels move forward. Finally, each set of three wheels is located on the next steps. (c) The kinematic model for CBF consists of the ground moving origin using unicycle dynamics and origin-relative body and end-effector's wheel state.
• Figure 3: Overview of real-time perceptive motion control for the six-wheeled-telescopic-legged robot Tachyon 3.
• Figure 4: The six types of ECBF for Tachyon 3's geometric constraints.
• Figure 5: Separating axis theorem for collision detection between two oriented bounding boxes (2D).