On a Novel Torque Detection Technique for Magnetorheological Actuators

This paper focuses on a new torque detection technique for magnetorheological (MR) actuators. An MR fluid consists of a suspension of ferromagnetic micrometer-sized particles in a carrier fluid. Under the action of a magnetic field, these particles form chain-like structures that interact with the magnetic poles. The torque detection technique is based on the assumption that a relative displacement of the poles stretches the chains, altering the magnetic reluctance of the fluid gap. This hypothesis is analytically developed using an elementary group of ferromagnetic particles placed in a nonmagnetic carrier liquid. A measure of the excitation coil impedance using a high precision demodulator, is used to verify this hypothesis. Experimental results show that when the poles are displaced before the rupture of the chains, the chains are stretched and the reluctance increases. A higher sensitivity system is subsequently proposed to detect the variation of an external torque. The experimental results demonstrate that the system is able to detect the application as well as the release of the torque and can successfully be employed to detect the chain rupture critical point.