LAUSR

Abstract The determination of stances is of vital importance for legged robots that work in challenging environments where the terrain may be composed of uneven and slippery surfaces. However, the exploitation of uneven and slippery footholds has not received much research interest in the robotic community. This article proposes an efficient method to determine possible stances that may consist of uneven and slippery footholds by analyzing the degrees of freedom (DOFs) of the body of a legged robot and the capability of the legged robot to control these DOFs. The concept of the contact joint is proposed to describe the allowable foot motion considering the geometric foot-environment contacts. By adding a contact joint to each support foot, an equivalent parallel mechanism is formed by a legged robot and the ground. Subsequently, constraint-screw systems associated with the aforementioned equivalent parallel mechanism can be obtained. Based on that, the DOFs of the body of the legged robot and the capability of the legged robot to control these DOFs can be analyzed, and the possible stances can be determined. Case studies demonstrated the proposed approach.