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Accurately parameterizing human gait cycles is crucial for developing control systems for lower-limb wearable robots. Previous studies on characterizing human gait cycle investigated the use of human-inspired phase variables, but they lack robustness and adaptability to accommodate for transitions that occur between locomotor tasks. This paper proposes augmenting the traditional phase variables with a canonical dynamical system. This system considers the differences between the estimated and true thigh angular velocities, based on which the Fourier series coefficients and phase information will be dynamically updated via an adaptive frequency oscillator. Experiments with six able-bodied participants on level ground, inclines, and declines walking show that the augmented phase variable adapts to various locomotor tasks and transitions better than the traditional approach. 

Most current powered transfemoral prostheses are designed based on replicating normal anatomy with the inclusion of a revolute knee joint. Prosthesis users often have issues achieving proper leg length to maintain balance and perform push-off during stance, and to ensure sufficient toe clearance during swing. There is a clinical opportunity to develop a powered prosthesis that linearly shortens and lengthens during ambulation with a prismatic joint for improved leg length properties. To build on previous work, the research in this manuscript focuses on designing the physical device, the leg length actuation profile, and the control scheme. Based on gait analyses of two prosthesis users, the device provides an appropriate leg length actuation profile with sufficient shortening for toe clearance (exhibited by the greater prosthetic vs. intact side toe clearance) and lengthening for forward propulsion (exhibited by the ground reaction force peak in late stance). The device also has a motor torque and velocity capable of supporting up to a 90 kg user during normal ambulation, a control scheme with an adjustable actuation cycle based on gait cadence (matching within 2 ms), and a more compact mechanical system design (4.5 kg) less than anatomical weight requirements (5.5 kg). Additionally, the prosthesis users tested were highly encouraging of their stability, mobility, and safety while ambulating with the device.