Design, Testing and Control of a Magnetorheological Damper for Knee Prostheses

Abstract

This study aims to develop a magnetorheological (MR) damper for semi-active knee prostheses to restore the walking ability of transfemoral amputees. The core dimensions of the MR damper were determined via theoretical magnetic field calculations, and the theoretical relationship between current and joint torque was derived through electromagnetic simulation. Then, a physical prototype of the semi-active prosthetic knee equipped with the MR damper was manufactured. Based on the data obtained from angle sensor, pressure sensor (loadcell), and inertial measurement unit (IMU) on the prosthesis, a matching control algorithm is developed. The joint torque of the MR damper can be adaptively adjusted according to the walking speed of the amputee, allowing the amputee to realize a natural gait. The effectiveness of the control program was verified by the ADAMS and MATLAB co-simulation. The results of the test and simulation show that the MR damper can provide sufficient torque needed for normal human activities.

Appendix

Spindle magnetoresistance $R_{1}$:

$$R_{1} = \frac{{l_{1} }}{{\mu_{1} A_{1} }} = \frac{{l_{1} }}{{\mu_{1}\uppi r_{1}^{2} }}$$

(15)

Endcap magnetoresistance $R_{2}$:

$$R_{2} = \frac{{r_{3} - r_{1} }}{{\mu_{1} A_{2} }} = \frac{{r_{3} - r_{1} }}{{\mu_{1}\uppi (r_{3} + r_{1} )l_{3} }}$$

(16)

MR fluid magnetoresistance $R_{3}$:

$$R_{3} = \frac{{l_{2} - 2Ne}}{{\mu_{2} A_{3} }} = \frac{{l_{2} - 2Ne}}{{\mu_{2}\uppi (r_{4}^{2} - r_{2}^{2} )}}$$

(17)

Stator disc magnetoresistance $R_{4}$:

$$R_{4} = \frac{e}{{\mu_{1} A_{4} }} = \frac{e}{{\mu_{1}\uppi (r_{0}^{2} - r_{2}^{2} )}}$$

(18)

Rotor disc magnetoresistance $R_{5}$:

$$R_{5} = \frac{e}{{\mu_{1} A_{5} }} = \frac{e}{{\mu_{1}\uppi (r_{4}^{2} - r_{i}^{2} )}}$$

(19)

where $e$ is the thickness of the stator and rotor discs.