Linearized Torque Actuation Using FPGA-Controlled Magnetorheological Actuators

In recent years, magnetorheological (MR) clutches have been increasingly used for realizing compliant actuation. One difficulty in using MR clutches is the existence of nonlinear hysteretic behaviors between the input current and output torque of an MR clutch. In this paper, a new closed-loop, field-programable-gate-array (FPGA)-based control scheme to linearize an MR clutch's input-output relationship is presented. The feedback signal used in this control scheme is the magnetic field acquired from hall sensors within the MR clutch. The FPGA board uses this feedback signal to compensate for the nonlinear behavior of the MR clutch using an estimated model of the clutch magnetic field. The local use of an FPGA board will dramatically simplify the use of MR clutches for torque actuation. The effectiveness of the proposed technique is validated using an experimental platform that includes an MR clutch as part of a compliant actuation mechanism. The results clearly demonstrate that the use of the proposed FPGA-based closed-loop control scheme can effectively eliminate hysteretic behaviors of the MR clutch, allowing to have linear actuators with predictable behaviors.