A pressing challenge in the design of actuated knee prostheses is the ability to address the high variation of speed and torque requirements for the different types and phases of locomotion. This manuscript presents a novel over-actuated knee prosthesis which makes use of a dual motor actuation architecture to address this issue. It utilizes a high speed/low torque motor to enable natural and highly dynamical motion, as required for swing phases of walking, which is permanently engaged. In addition to this motor, a clutchable uni-directional low dynamics high torque motor is present to assist during the execution of tasks which demand active torque. Preliminary experimental validations have been performed on a healthy subject provided with an able-bodied adapter to demonstrate natural walk patterns and power-assisted sit-to-stand activities.

This paper presents the first practical demonstration of a recently developed theory of balance control that aims to achieve high performance in the sense of allowing a robot to make large, fast movements while maintaining its balance on a narrow support. This theory includes a simple method of leaning in anticipation of future motion commands, which is largely responsible for the high performance. The experiments reported here use a robot acting as a reaction wheel pendulum, and they test only the 2-D version of the theory. The results show that the balance controller's performance in practice closely resembles its theoretical performance. This paper also presents a simple yet accurate balance offset observer that measures the difference between true and estimated balanced configurations.

This paper first presents a formula to predict the largest balance disturbance from which a legged robot can recover without taking a step. It then presents an actuator design criterion derived from this formula that maximizes the robot's ability to recover. In this study, it is assumed that the robot is using a single major joint (e.g, a hip joint) to perform its balance recovery movement, and that the actuator consists of an electric motor and reduction gear. It is also assumed that the robot's support polygon is sufficiently small that it can be approximated as a point, and that the balance recovery motion is essentially planar, so that a 2-D analysis remains valid in 3-D. Finally, it is assumed that, for the purpose of studying balance recovery motion, the robot can be approximated by a reaction wheel pendulum. The theory has been tested experimentally on a robot designed to be good at balancing, and was found to agree closely with experimental results.