Control of contact forces in wheeled and legged off-road vehicles

Abstract

The use of variable configuration vehicles creates the possibility of direct control of the contact forces between the foot or wheel of a vehicle and the ground. That control is an important element of the coordination of practical walking machines. Control of the contact forces at each wheel is also attractive for wheeled vehicles. For example, the power consumed in driving such a vehicle is quite sensitive to wheel-ground conditions. In conditions of strict power budgets, as in planetary roving vehicles, it becomes attractive to attempt to minimize power consumption by optimizing the wheel-ground contact forces. Unfortunately, control of contact forces in a wheeled vehicle is very complex because of the non-holonomic nature of the system.In this paper we will review the allocation of contact forces in legged systems and examine the attempts that have been made to apply similar principles to the guidance and propulsion of wheeled systems on uneven terrain. The Adaptive Suspension Vehicle (ASV) and Wheeled Actively Articulated Vehicle (WAAV) from the authors' laboratory will be used as examples, and as sources of experimental validation of theoretical and numerical results. The former is a six-legged walking machine with each leg having three actively controlled degrees of freedom relative to the vehicle body. The latter is a six-wheeled variable configuration vehicle with three-axis, actively controlled, spherical articulations between successive axles.

Control allocation—A survey

“…Traction control for mobile robots that operate off-road is considered in (Waldron & Hubert 1999, Waldron & Abdallah 2007. Based on the geometry of the problem, several simple (unconstrained) closed-form computationally efficient control allocation strategies for wheeled and legged mobile robots with active suspension are derived and compared in (Waldron & Abdallah 2007), while pseudo-inverse type control allocation strategies are studied in (Waldron & Hubert 1999, An & Kwon 2010.…”

“…Based on the geometry of the problem, several simple (unconstrained) closed-form computationally efficient control allocation strategies for wheeled and legged mobile robots with active suspension are derived and compared in (Waldron & Abdallah 2007), while pseudo-inverse type control allocation strategies are studied in (Waldron & Hubert 1999, An & Kwon 2010. A linear programming solution to control allocation for wheeled mobile robots is presented in (Feng, Xu, Li & Sun 2010).…”

Curvature based point stabilization for compliant framed wheeled modular mobile robots

“…As the author states, the system provides high levels of mobility, but since the axle units are coupled by a relatively non conforming rigid frame, its ability to maneuver in confined environments will be limited [15]. Other flexible robots use actuated articulated joints to provide similar relative motion between axles, as in the case of the Marsokhod rover [I61 and other six wheeled research rovers with high relative DOF provided bemeen axles modules [17].…”

Internal posture sensing for a flexible frame modular mobile robot

“…Other flexible robots use actuated articulated joints to provide similar relative motion between axles, as in the case of the Marsokhod rover [14] and other six wheeled research rovers with high relative DOF provided between axles modules [15].…”