Maximum Dorsiflexion Detection Based on an On-Board Adaptive Algorithm for Transtibial Amputees With Robotic Prostheses

Abstract

Maximum dorsiflexion (MDF) is an important gait event corresponding to the maximum ankle dorsiflexion angle in each gait cycle. MDF timing plays an important role in the control of robotic prosthesis. This article puts forward an on-board adaptive algorithm to detect MDF timing of robotic transtibial prosthesis in different walking conditions (at different speeds and on different ramps) and for different users. Based on the adaptive algorithm, we can get a time-variant detection model. The framework of the adaptive algorithm is composed of: 1) training data collecting and labeling; 2) model training and real-time detection; and 3) model updating according to the detection results. Based on the adaptive algorithm, we conducted speed and ramp experiments to detect MDF timings at slow, normal, and fast speeds, and on ramps with different inclination angles (10°, 5°, 0°, -5°, and -10°). Three transtibial amputee participated in the experiments. The model training/updating time ranges from 3.6 to 4.1 s and the detection time ranges from 0.95 to 1.17 ms for different speeds and ramps. In real-time detection, there is false detection (1.67%) at normal walking speed. In addition, all MDF timings are detected correctly (accuracy: 100%) based on the adaptive algorithm. The mean detection delays are 7.23, 18.27, and 7.5 ms corresponding to slow, normal and fast speeds and 10.60, 10.30, 18.27, 10.27, and 15.63 ms for ramps of different inclination angles (10°, 5°, 0°, -5°, and -10°). Compared with the proposed adaptive algorithm, both the nonadaptive and adaptive threshold decision methods cause more false detections. The results show that the proposed approach for MDF timing detection has adaptations to different walking conditions (speeds and ramps) and prosthesis users, which indicates that the adaptive algorithm is effective and shows the potential in robotic prosthesis control in the future. Note to Practitioners-This article proposes an on-board adaptive algorithm to detect the maximum dorsiflexion (MDF) timing based on inertial measurement unit (IMU) and ankle angle sensor for robotic transtibial prosthesis users in each gait cycle. IMU and angle sensor are integrated in the prosthesis, and the adaptive algorithm is embedded in the control circuit of prosthesis. The adaptive algorithm can realize the model updating continuously for real-time MDF timing detection with collected and labeled training data. The proposed adaptive algorithm shows satisfactory adaptation for MDF timing detection in different walking speed and ramp conditions. In addition, the adaptive algorithm also shows some generalizations for prosthesis users, which are useful to improve prosthesis control.