AbstractThere are several ways in which a disability can occur. Strokes are a leading cause, affecting older people in particular, with an estimated annual incidence rate of 180, 125, 200, and 280 per 100,000 citizens in the USA, Europe, England, and Scotland, respectively.
Muscle strengthening through resistance training has been reported to have a positive effect on the recovery of normal physiological functions after the occurrence of a neurological or traumatic injury. A number of studies have shown that resistance training results in improved mobility, a reduction in pain, and improved stability. Several rehabilitation devices have been developed and introduced for use in the healthcare sector, but a new generation of intelligent therapy-assisted machines is needed if there is to be a significant impact on the numbers of patients that can be treated under current staffing level.
In this project, the design and performance of multi-degree-of-freedom smart balland-socket dampers and their application to fully-controllable rehabilitation training systems were investigated. A key feature of these dampers is the use of magnetorheological (MR) fluids which can exhibit dramatic changes in their rheological properties, such as yield stress, when subjected to external magnetic fields. These fast and reversible fluid rheological changes would permit the smart damper to provide the required impedance at orthotic arm joints, which are aimed for upper-limb rehabilitations and in accord with the exercise specifications prescribed by the physiotherapist.
An exemplar upper-limb orthotic arm incorporating smart ball-and-socket dampers at its joints was assessed using SolidWorks software and the results confirmed the response of the dampers to variable excitation inputs under an input simulating a wheelchair driving motion. This study also enabled the estimation of the orthotic arm reach envelope, task performance and limitations in which important device design factors such as the angle of rotation of the smart dampers were taken into account.
Although, three smart dampers with variable torque resistance capability are required at the shoulder, elbow and wrist joints of upper-limb rehabilitation orthoses, this project was focused on the development of a smart ball-and-socket damper aimed for the shoulder joint only. The target was to produce a compact smart electromagnetic damper that is capable to deliver the required torque resistance with the least power consumption. The efficient excitation of MR fluids requires a magnetic circuit, which consists of a source of magnetic flux and a path to deliver it to the fluid. Electromagnetic finite element analysis using Ansys software were carried out to achieve the optimum design of the damper’s electromagnetic circuit. The effects of the relative permeability of the damper’s materials on the generation of the magnetic field and its delivery to the MR fluid were examined. Other factors such as the coil shape, size, orientation and location in addition to the utilisation of non-magnetic materials in the electromagnetic circuit design were also investigated with the aim to optimise the performance of the smart damper. Furthermore, 3-D electromagnetic analyses were conducted, which confirmed the validity of the 2-D magnetic trials. Accordingly, the size of the MR fluid ball-and-socket damper was estimated with a ball diameter of 100 mm, which was found to produce a braking torque of about 50 N.m when the MR fluid is energised by about 1 Tesla.
The performance of the ball-and-socket damper was estimated using theoretical, and numerical approaches. The theoretical model combines the viscous-friction and the controllable field-dependent characteristics of the MR fluid in which a Bingham plastic model was used to simulate the shear stress of the fluid under various input conditions.The numerical approach involved a special procedure to simulate the device performance using computational fluid dynamics techniques, which were performed using Ansys CFX code. Three commercial MR fluids were assessed and it was found that the simulated device torque compared well with the theoretical values. The mechanical design of the optimised ball-and-socket damper was accomplished using SolidWorks software when several important design and manufacturing factors were taken into account. These factors included the assembly of the ball and socket parts, the sealing of the MR fluid inside its designated gap, winding of the coil inside the socket part, maintaining a uniform MR fluid gap, and insertion of the nonmagnetic rings at their predesigned locations.
Finally, a dedicated experimental rig was constructed which facilitated the assessment of the smart damper under both static and dynamic testing conditions. It was found that agreement between model predictions and experimental observations was excellent. Furthermore, this device performance was found to meet torque requirements expected in most upper-limb rehabilitation regimes.
|Date of Award
|Ali El-Wahed (Supervisor)
- Magnetorheological (MR)