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This paper describes a single degree-of-freedom active-knee transfemoral prosthesis to be used as a test bed for the development of architectures for myoelectric control. The development of an active-knee transfemoral prosthesis is motivated by the inability of passive commercial prostheses to provide the joint power required at the knee for many activities of daily living such as reciprocal stair ascent, which requires knee power outputs of up to 4 W/kg. Study of myoelectric control based on surface electromyogram (EMG) measurements of muscles in the residual limb is motivated by the desire to restore direct volitional control of the knee using a minimally-invasive neuromuscular control interface. The presented work describes the design of a transfemoral prosthesis prototype including the structure, actuation, instrumentation, electronics, and real-time control architecture. The performance characteristics of the prototype are discussed in the context of the requisite knee energetics for a variety of common locomotive functions. This paper additionally describes the development of a single-subject diagnostic socket with wall-embedded surface EMG electrodes and the implementation of a control architecture for myoelectric modulation of knee impedance. Experimental results of level walking for a single subject with unilateral transfemoral amputation demonstrate the potential for direct EMG-based control of locomotive function.

This paper presents the development of a torque-based myoelectric impedance controller for an active-knee transfemoral prosthesis. An anthropomorphically inspired agonist-antagonist impedance controller studied in a myoelectric elbow prosthesis is adapted for the knee joint. To parameterize the controller, regression analysis was applied to a recently updated lower-extremity neuromuscular simulation model that provides estimates of knee torque as a function of knee angle and neural activation. Initial results using a constant moment arm suggest physically unreasonable parameters and poor model performance, but the inclusion of an angle-dependent moment arm in the reduced-order muscle model enables good correlation with the high-order neuromuscular model. The resulting limb controller is tested using a 1-DOF active knee prosthesis donned by a non-amputee subject with an able-bodied adapter. Initial treadmill walking tests demonstrate the potential of this controller to enable effective myoelectric control of the prosthetic limb.

This paper presents the development and preliminary validation of a control interface for a transfemoral prosthesis that enables EMG-based control of a powered knee during stair ascent. The approach uses results from non-amputee gait studies of stair ascent in the design of a control architecture that enables EMG modulation of knee torque in a manner biomechanically similar to that exhibited by non-amputee subjects. The myoelectric torque controller is formulated with a finite-state linear impedance model in stance and swing. The stance phase is modulated by surface EMG signals co-activated by antagonist residuum muscles. Preliminary results with a sound-limb subject using a knee immobilizer indicate that the EMG-based control architecture has the potential to enable the amputee to directly generate torque commands appropriate for stair ascent using an actively powered artificial limb.

Commercial prosthetic limb development for transfemoral amputees has historically focused on legged locomotive function with energetically dissipative or conservative limbs. While such passive devices are effective at approximating the mechanics of the knee during level walking and stair/slope descent, the inability of these limbs to impose net positive power prevents amputees from executing a number of activities of daily living. Activities such as ascending slopes, ascending stairs, and jumping require net positive power outputs that are not fully realizable with current prosthetic leg technology [1–3]. While functionality has improved with microprocessor-based passive limbs [4], amputees continue to exhibit increased metabolic demands and non-anthropomorphic asymmetric gait [5].