The performance of a smart ball-and-socket actuator applied to upper-limb rehabilitation

Magnetorheological fluids are capable of providing continuously variable yield stresses in response to external magnetic fields. Greater potential application in rehabilitation may be realised if these fluids are utilised in controllable actuators offering multi-degree-of-freedom motions. This article presents the results of the comparative performance of a ball-and-socket actuator, employing magnetorheological fluids as the controllable medium, using theoretical and numerical approaches. The theoretical model combines the viscous friction and the controllable field-dependent characteristics of the magnetorheological fluid in which a Bingham plastic model is used to simulate the shear stress of the fluid under various input conditions. A special procedure to simulate the device performance using computational fluid dynamics techniques, which were performed using ANSYS CFX computer code, is detailed. Three commercial magnetorheological fluids (MRF241-ES, MRF132-AD and MRF122-2ED) were assessed and it was found that the simulated values of the device torque compared well with the theoretical values.