Design of twin-rod flow mode magneto rheological damper for prosthetic knee application

Abstract

In the present study, a twin-rod magneto rheological (MR) damper working in flow mode is designed. The piston core, annular fluid gap, outer sleeve, and the outer cylinder forms the magnetic flow path. A nonlinear constrained optimization problem is formulated to obtain the geometric dimensions of the piston assembly. The flow mode equations of the damper and the electromagnetic circuit design equations, assuming constant magnetic field links are coupled together to form an optimization problem. The design torque and angular velocity requirements of the normal human knee are converted to damping forces and linear velocity using the knee and damper geometry based on the previous study. The damping force design constraints and the constraints related to current requirements and magnetic field saturation are imposed. The obtained optimum dimensions of the piston assembly yielded an off state damping force of 56.8 N and a maximum on-state damping force of 1582 N at a current of 1.6 A for a design velocity of 0.1 m/s. Magnetostatic analysis of the piston assembly using the optimized dimensions is performed which showed that the annular gap is exposed to a field of 0.6 T, as assumed and the piston core is subjected to a field of 1.8 T which is below the saturation limit of the core material. � 2019 Author(s).