Personalized Control Method of Lower Limb Prosthesis with Variable Speeds

The active knee-ankle prosthesis is an important auxiliary device to protect the daily life of the knee amputees. The tight human-interaction coupling makes its control face many challenges, which results in poor continuity and low degree of individuation. This paper presents a personalized control method for the active knee-ankle prosthesis which can adapt to different walking speeds and users' height. According to the height and speed of the subject, the current appropriate knee and ankle joint trajectory can be planned adaptively. The specific method is to design the phase variable based on thigh angle to achieve continuous control of the whole gait cycle. And then, build the task function and basis function based on the speed, height and phase variable separately. By introducing the proportional weight coefficient, the parameters to be estimated are reduced by doubling because of the 2 influence factors (speed and height), and the calculation amount and difficulty are reduced. The convex optimization is used to fit the function of gait surface with respect to height and walking speed. The result of gait trajectory planning is taken as the reference input of impedance control to complete the compliant control of the prosthesis. The algorithm is verified by simulation experiments, which can ensure the stable and smooth walking.