Toward Controlling Transtibial Prostheses Using a Single Degree of Freedom Inertial Sensor System

Abstract

Control strategies for lower limb prostheses have made multiple significant advancements over the years. In this work, we investigate the scope and capabilities of a controller for ankle-foot prostheses that relies only on a one-degree-of-freedom inertial sensor, supplemented with a control algorithm that can perform a real time update of actuation parameters using gait information available from past gait cycles. The updated actuation parameters are applied to the subsequent gait cycle and the cycle repeats itself. The idea behind this controller is to allow a user to have infinite possible variations in gait speeds (within the allowable limits of actuation) while keeping the required sensory inputs to a minimum. As a consequence of this controller design, the user is not forced to choose discrete speeds of walking (slow, medium, fast) and is capable of freely varying his gait speeds on each step, while utilizing only a single-degree-of-freedom sensor. We implement the controller on an actuated transtibial prosthesis prototype based on a series-elastic spring configuration, and conduct tests for level ground walking at a self-selected walking speed, to explore the achievable range of response pertaining to daily living tasks. The pilot tests on a healthy participant, conducting level ground walking with turns and remotely controlling the prosthesis, suggest that it is possible to control a transtibial prosthesis using a simple uni-sensor framework, with a maximum angular deviation of 5°, and maximum deviation in angular velocity of $20^{\circ} /s$ compared to that of healthy humans.

Keywords

• Prosthetics
• rehabilitation robotics
• control design