Electromyography-based control of active above-knee prostheses

Abstract This paper presents a new electromyography (EMG)-based control approach for above-knee (AK) prostheses, which enables the user to control the prosthesis motion directly with his or her muscle activating neural signals. Furthermore, the unique ‘active–reactive’ control structure mimics the actuation mechanism of a human biological joint, and thus provides the user an experience similar to that of a biological lower limb in the control process. In the proposed control approach, surface EMG is utilized to provide a non-intrusive interface to the user's central nervous system, through which the muscle-activating signals can be obtained. With the EMG signals as inputs, an ‘active–reactive’ control algorithm is developed based on the analysis on a simplified musculoskeletal structure of human biological joint. This control algorithm incorporates an ‘active’ component, which reflects the user's active effort to actuate the joint, and a ‘reactive’ component, which models the reaction of the joint to the motion as a result of the controllable impedance displayed on the joint. With this unique structure, the controller enables the active control of the joint motion, while at the same time achieves a natural interaction with the environment through the modulation of the joint impedance. The effectiveness of the proposed control approach was demonstrated through a set of free swing experiments, in which the user was able to control the prosthesis to follow arbitrary motion commands, and a set of level walking experiments, in which the user achieved natural walking gait similar to the typical walking gait of healthy subjects.