The design and performance of a smart ball-and-socket actuator

In this paper, the design and performance of a multi-degree-of-freedom smart ball-and-socket actuator and its application to rehabilitation training systems are investigated. A key feature of this actuator is the use of magnetorheological fluids which can exhibit dramatic changes in their rheological properties, including yield stress, when subjected to external magnetic fields. These fast and reversible fluid rheological changes permit the smart actuator to provide the required impedance at orthotic arm joints aimed for upper-limb rehabilitation

Electromagnetic finite element analyses using ANSYS software were carried out to design the electromagnetic circuit of the actuator and important design factors affecting the efficiency of the generated magnetic field and its best delivery to the MR fluid, were examined. These factors included the relative permeability of the magnetic material and the electromagnetic coil properties such as its shape, size and location. In addition, the utilisation of non-magnetic materials in the electromagnetic circuit design was investigated with the aim to optimise the performance of the smart actuator.

Finally, the performance of the smart actuator was assessed theoretically and numerically under various input conditions in which Bingham plastic fluid characteristics were assumed, and the results determined by the two techniques were found to compare well.