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Hindi Research Article
Variable Impedance Control Based on Impedance Estimation Model with EMG Signals during Extension and Flexion Tasks for a Lower Limb Rehabilitation Robotic System
| Baoping Yuan1*, Masashi Sekine1, Jose Gonzalez1,2, Jose Gomez Tames1and Wenwei Yu1 | |
| 1Department of Medical System Engineering, Chiba University, Chiba, Japan | |
| 2Research Center for Frontier Medical Engineering, Chiba University, Chiba, Japan | |
| Corresponding Author : | Baoping Yuan Department of Medical System Engineering Graduate School of Engineering Chiba University, 1-33, Yayoicho, Inage Ku Chiba, 263-8522, Japan Tel: 81-43-290-3231 E-mail:yuanbaoping1981@gmail.com |
| Received July 23, 2013; Accepted August 23, 2013; Published August 26, 2013 | |
| Citation: Yuan B, Sekine M, Gonzalez J, Tames JG, Yu W (2013) Variable Impedance Control Based on Impedance Estimation Model with EMG Signals during Extension and Flexion Tasks for a Lower Limb Rehabilitation Robotic System. J Nov Physiother 3: 178. doi: 10.4172/2165-7025.1000178 | |
| Copyright: © 2013 Yuan B, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. | |
Abstract
Rehabilitation robotic devices could be used as an effective tool to restore impaired motion functionality. Due to the human-robot cooperative nature of rehabilitation, these systems are expected to be user-oriented i.e., they should be controlled considering users dynamic characteristics. In this article, we proposed a variable impedance control, in which desired impedance of a system was setup to match human joint stiffness estimated from Electromyogram (EMG) signals recorded. Two experiments were performed in this work. The objective of the first experiment (Experiment-1) was to study the relationship between EMG and changing impedance in knee joint extension and flexion tasks. Based on the recorded data, a nonlinear model was proposed to express the relationship between EMG and changing impedance. The results show that Root Mean Square of the EMG signals (RMS-EMG) of target muscles increases, as specified elastic modulus increases for both tasks, but there is a significant difference (p<0.01, t-test) between the extension and flexion task. The second experiment (Experiment-2) was to confirm the effectiveness of the variable impedance control with the motion-dependent models acquired in Experiment-1. Four different control policies were tested, i.e., NA: No Assist; FO: using EMG-impedance model from the Flexion Task; EO: using EMG-impedance graph from the Extension Task; FE: using two EMG-impedance models from Flexion and Extension task correspondently. Results indicate that the proposed control model (FE) achieved a smaller discrepancy (p<0.01, t-test) between desired angle and the reached angle than the control with EO or NA cases. Moreover, a small sum of RMS_EMG from the variable impedance control with motion- dependent models denoted less effort required than the NA (p<0.01, t-test) case or the control with FO (p<0.01, t-test). Results also indicate that the proposed nonlinear and motion-dependent variable impedance control method achieved a smaller angular discrepancy (P<0.05, t-test) than linear variable impedance control.
