This paper presents the development and experimental evaluation of a volitional control architecture for a powered-knee transfemoral prosthesis that affords the amputee user with direct control of knee impedance using measured electromyogram (EMG) potentials of antagonist muscles in the residual limb. The control methodology incorporates a calibration procedure performed with each donning of the prosthesis that characterizes the co-contraction levels as the user performs volitional phantom-knee flexor and extensor contractions. The performance envelope for EMG control of impedance is then automatically shaped based on the flexor and extensor calibration datasets. The result is a control architecture that is optimized to the user's current co-contraction activity, providing performance robustness to variation in sensor placement or physiological changes in the residual-limb musculature. Experimental results with a single unilateral transfemoral amputee user demonstrate consistent and repeatable control performance for level walking at self-selected speed over a multi-week, multi-session period of evaluation.

Control of prosthetic limbs using myoelectric muscle potentials from the wearer’s residual limb enables direct control of artificial limb behavior. The typical approach entails the integration of surface electromyogram (sEMG) electrodes within the inner wall of the socket interface, located to target specific superficial muscles in the amputee’s residual limb. While myoelectric upper-limb control is commonplace in prosthetic practice, its use in lower-extremity devices has been slow to follow suit. Various research efforts have studied approaches to implementing myoelectric control of artificial leg behavior [1–4], but the need for myoelectric control in lower-limb prostheses has been limited by the lack of commercial prototypes with the capability of net power generation.