The design of exactly constrained walking robots

This paper discusses the design of legged walking robots that are exactly constrained during the stance phase of locomotion. Legged robots with a large number of actuated degrees of freedom, while allowing for the widest range of controllable foot placements, often end up with overconstrained kinematics when in contact with the ground, requiring complex redundant control schemes for effective locomotion. Exactly-constrained robots would be capable of full body mobility while avoiding the weight and complexity costs of fully actuating each joint and would also allow for simpler control schemes. We discuss the constraints and degrees of freedom of a common legged robot kinematic structure and describe strategies for removing redundant constraints. Two major design considerations — architectural singularities and the uniqueness of the ground reaction forces — are discussed along with potential solutions. Finally, a prototype exactly-constrained walking robot is presented as a validation of this design strategy.