Sujatha Srinivasan

A prosthetic swing-phase control mechanism simulates the action of the upper leg musculature to aid in increased gait function. More specifically, swing-phase control mechanisms limit the maximum knee flexion and allow the shank to smoothly decelerate into full knee extension, without excessive impact. In this work, a magnetorheological (MR) damper is designed with the objective of controlling swing-phase damping in an above-knee prosthesis. A parametric model, the modified Bouc-Wen model, is used to represent the highly nonlinear dynamic properties of the MR damper. Based on this model, twelve control parameters that govern the hysteretic force and displacement of the damper have been identified. The parameters of the damper are determined through optimization of the prosthesis knee angle with a desired knee angle trajectory obtained from experimental data in normal level walking. Experimental data of thigh and hip motions are introduced as input into a dynamic system to find out a set of control parameters. A computer simulation is carried out. Comparison of the desired knee angle with the knee angle obtained from control parameters of the designed MR damper shows the effectiveness of the present design. Also, using the optimal control parameters, knee angle trajectories at zero and at lowered input currents, representing circumstances when the battery turns off and the power supply is reduced respectively, have been shown. Moreover, conditions of knee angle and shank velocity at the end of swing phase have been checked. The results obtained show a satisfactory performance of the system.

In this work, a magnetorheological (MR) damper valve is designed with the primary objective of controlling swing-phase damping in an above-knee prosthesis. Initially, a swing phase model of the desired single axis knee incorporating MR damper was modelled. The control parameters that govern damping force and displacement of the damper were identified and optimized to enable the prosthetic knee to produce near normal swing phase trajectory for ground walking as obtained from experimental data. Then, the MR damper valve is optimally designed by selecting typical performance indices of the damper for the intended application. A multi-objective optimization problem is formulated where the MR damper valve is constrained in a desired cylindrical volume defined by its radius and height. Effects of the geometrical design variables of the valve are analytically investigated by mapping finite element analysis (FEA) numerical responses with response surface method (RSM). The results show that the MR damper with designed damper valve enables the prosthetic knee to achieve near to normal swing phase trajectory, and compare to the existed MR damper, up to 71 % reduction by weight has been achieved.

A prosthetic swing-phase control mechanism simulates the action of the upper leg musculature to aid in increased gait function. More specifically, swing-phase control mechanisms limit the maximum knee flexion and allow the shank to smoothly decelerate into full knee extension without excessive impact. In this work, a hydraulic damper is designed with the objective of controlling swing-phase damping in an above-knee prosthesis. A linear spring and damper model is used to represent the dynamic properties of the damper. Based on this model, three control parameters that govern the damping force and displacement of the damper have been identified. The parameters of the damper are determined through optimization of the prosthesis knee angle with a desired knee angle trajectory obtained from experimental data in normal level walking. Experimental data of thigh and hip motions are introduced as inputs into a dynamic system to find out a set of control parameters. A computer simulation is carried out. Comparison of the desired knee angle with that of the knee angle obtained from control parameters shows the effectiveness of the present design. Moreover, conditions of knee angle and shank velocity at the end of swing phase have been checked. The results obtained show a satisfactory performance of the system.

A prosthetic swing-phase control mechanism simulates the action of thigh musculature to aid in increased gait function. In this work, a hydraulic damper and a magnetorheological (MR) damper are designed as controllers with an objective of evaluating their performance in controlling swing-phase damping in an above-knee prosthesis. Parametric models are utilized to represent dynamic properties of the dampers. Based on the models, control parameters that govern damping force and displacement of the dampers are identified. Parameters of the dampers are determined through optimization that minimizes the error between the prosthesis knee angle trajectories and a desired knee angle trajectory for normal level ground walking from experimental data. Experimental data of thigh and hip motions are introduced as inputs into a dynamic system to determine sets of control parameters. Furthermore, input thigh motion is also deviated to evaluate robustness of the controllers in real application. Comparison of the desired knee angle trajectory with those of the knee angle trajectories obtained from control parameters is done with respect to maximum achievable knee flexion angle, duration of swing phase, shank velocity at the end of swing phase and mean angle difference. Evaluation results of the dampers show a better competence of MR damper over hydraulic damper.