Faculty Publications
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Item Semi-active control of a swing phase dynamic model of transfemoral prosthetic device based on inverse dynamic model(Springer, 2020) Saini, R.S.T.; Kumar, H.; Chandramohan, S.Improving the gait of transfemoral amputees and making it biomimetic and stable has always been a major effort. A dynamic model of the prosthetic device can predict the kinetic and kinematic performances, when incorporated with a musculoskeletal model. In this regard, a dynamic model of a recent trend of variable damping technology will help a great deal in evaluating the performance of the prosthetic device and also in studying the effect of various parameters on the prostheses. The current paper presents the dynamic model of a single axis two segmental prosthetic knee implemented with a magneto-rheological (MR) damper as a variable damping element. The MR damper is modeled mathematically using Bouc–Wen model with model parameters evaluated by minimizing the error norms for time, displacement and velocity between the experimental and the model-generated results using a genetic algorithm. Two different experimental data sets are used, one for mathematical modeling and other to assess the accuracy of the fit model. A Proportional Derivative plus Controlled Torque controller is employed, and the parameters are tuned to minimize the error between the desired and control input torques. Further, an inverse dynamic model using Bouc–Wen model variables is assumed and validated later. This model predicts the current directly and avoids the necessity of solving any quadratic equation, which is required in the case of inverse models based on modified Bouc–Wen. The dynamic model of the prosthesis is analyzed for the swing phase alone, and the results show that the model traces the desired knee angle and also the shank reaches full knee extension at the end of this phase with terminal velocity small enough to be handled by an extension stop. © 2020, The Brazilian Society of Mechanical Sciences and Engineering.Item Optimal design of ow mode semi-active prosthetic knee dampers(Sharif University of Technology, 2022) Saini, R.S.T.; Kumar, H.; Chandramohan, S.Magnetorheological (MR) fluid devices operate in four modes: ow, shear, squeeze, and pinch. Among these, the flow mode is the most efficient one and results in large field-induced pressure differences. Despite being the least efficient, shear mode is the most commonly used in numerous applications, including prosthetic knees, due to its ease of construction. Additionally, shear mode designs require larger shear areas and reduced fluid gap tolerance compared to their ow mode counterparts, resulting in a complex design such as the commercially available multi-plate MR brake. Therefore, in this study, two ow mode designs, twin-rod and rotary vane MR dampers, are optimally designed for prosthetic knee application. The optimal designs obtained from solving a multi-objective particle swarm optimization problem are fabricated and experimentally characterized for various harmonic excitations of varying amplitudes, frequencies, and currents. The optimal designs are compared with many MR fluid-based prosthetic knee design configurations. Based on the results, a twin-rod MR damper with a mass of 0.71 kg and a damping force of 1020 N at 1 A is identified as the optimal design configuration for prosthetic knee application. © 2022 Sharif University of Technology. All rights reserved.