Output Torque Modeling of a Magneto-Rheological Based Actuator

Recent research intended to integrate robots into the anthropic domains has introduced a new set of challenges with regard to design and control of such robots. Among these challenges, human safety is perhaps one the most predominant issues. While, existing solution relies on highly specialized and high cost actuation mechanisms, a new generation of intrinsically safe robots (manipulators) that use alternative technologies is yet to prevail. There is however a general consensus that the conventional actuation mechanisms are not capable of providing intrinsic safety while maintaining the high performance of the robot. On these premisses, a new Magneto-Rheological (MR) based actuation mechanism was developed in our research group. The actuator uses a magnetic field to precisely control its output torque delivery. The actuator demonstrates remarkable mass to torque ratio and low output inertia, at the same time, its bandwidth is comparable, if not better, than current leading actuators. The output torque of the actuator however, is hysterically related to its input current which makes its control challenging. The objective of the current work is to obtain a precise open-loop model that relates the output torque to the applied input current. The advantages of the obtained model are twofold. While such a model enables accurate control of the actuator, hence the actuated mechanism; in our case a robotic arm, it also eliminates the need for a force/torque sensor for performing high fidelity force/torque control tasks. To validate the accuracy of the constructed model simulation results for the output torques are presented and compared to those measured experimentally using the prototyped actuation mechanism. Results agreements attest to the validity of the presented model.