Faculty Publications

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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.
Design of bypass rotary vane magnetorheological damper for prosthetic knee application
(SAGE Publications Ltd, 2021) Saini, R.S.T.; Chandramohan, S.; Sujatha, S.; Kumar, H.
Semi-active systems using magnetorheological fluids have been realized in many novel devices such as linear dampers, rotary dampers, brakes, and so on. Rotary vane-type magnetorheological damper is one such device that uses magnetorheological fluid as a hydraulic medium and a controllable magnetorheological valve to generate variable resistance. This device, due to its limited angle motion, lends itself to a natural application for prosthetic knee joint. In this article, a bypass rotary vane-type magnetorheological damper suitable for prosthetic knee device is designed. In the proposed design, the rotary vane chamber and the bypass magnetorheological valve are connected using hydraulic cables and ports. The design of rotary cylinder is implemented based on the largest possible dimensions within the envelope of a healthy human knee, while the magnetorheological valve is designed optimally using a multi-objective genetic algorithm optimization. Off-state braking torque, induced on-state braking torque and mass of the valve are selected as three objectives. The torque and angular velocity requirements of the normal human knee are used as design limits. The optimal solution is chosen from the obtained Pareto fronts by prioritizing the objective of weight reduction of magnetorheological valve. The optimal solution is capable of producing a damping torque of 73 Nm at a design speed of 8.4 rpm and current supply of 1.9 A. Potential benefits offered by this design when compared with multi-plate magnetorheological brake are flow mode operation, large clearance gap, and fewer design components, thus reducing the manufacturing complexity. © The Author(s) 2020.

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