Control of a Transtibial Prosthesis with Monoarticular and Biarticular Actuators

Abstract

Common active ankle joint prostheses comprise monoarticular actuators mimicking the function of the human soleus and tibialis anterior muscles, but lack the function of the biarticular human gastrocnemius muscle. Although these devices can mimic human ankle biomechanics in the sagittal plane, persons with transtibial amputation still show compensatory movements and asymmetric gait patterns. The goal of our research is to investigate the benefits of a biarticular transtibial prosthesis comprising mono- and biarticular actuators. This contribution presents the hardware configuration, control design and bypass testing of a biarticular prosthesis prototype with two actuators. A control structure consisting of a model-based feedforward control and a feedback controller to control the actuator torque is introduced. Modeling of the actuators and identification of all relevant system parameters is demonstrated. A reference trajectory based on healthy human ankle biomechanics and a control allocation are introduced. The system’s capability to track desired torques is demonstrated in a walking experiment. It is able to generate human ankle torques and ankle angles with a variable distribution of torque between the mono- and biarticular actuator. Based on these results, further investigations on the torque allocation to improve the gait patterns of persons with transtibial amputation can be conducted.