Development Of Magnetorheological Fluid Damper For Pathological Tremor Suppression

Pathological tremors, such as Parkinson’s disease, are common diseases thatseriously affect people’s normal life. Due to the lack of effective drug therapies, theso-called portable tremor suppression robot, which can provide damping force oractive force to suppress the tremor, is drawing more and more attention fromengineers and researchers across the world. Magnetorheological fluid damper (MRdamper), which can generate changeable and controllable damping force, is the keyelement in the semi-active rehabilitation robot system and plays important role intremor suppression.Aiming for design of light weight, compact size, suitable shape and enoughoutput torque, two MR dampers with new configuration are developed and used forelbow joint and wrist joint tremor suppression, respectively. They can be furtherassembled to a wearable tremor suppression robot existed.The design methodology of MR dampers is described as below. Firstly,research on the constitutive model, the operating model and the rheologicalproperties of magnetorheological fluid, as well as the computational model andtypical structures of MR damper in order to work out an overall design of MRdamper that suits for portable robot. Secondly, conduct design of structure andmagnetic circuit at the same time, investigate an approach to form serpentinemagnetic path by employing an offset electromagnetic coil and an asymmetric rotor,then apply electromagnetics to the determination of basic parameters andperformance evaluation of the proposed dampers. Thirdly, on the basis of finiteelement method, computational simulation and optimization are conducted toexplore the static and dynamic properties of the magnetic circuit. The design flawsin the above period are rectified then detailed design parameters are determined.Finally, the current-damping torque relation, the velocity-damping torque relationand the dynamic response performance of the optimized design are presented.Control algorithm of MR dampers to effectively suppress pathological tremoris studied after the design is done. Common control algorithms of MR dampers areonly designed to achieve desired output torque, while the algorithm proposed in thepaper is quite different since it aims for pathological tremor suppression and shouldfirstly separate pathological tremor from voluntary motion in real time and thenextract tremor features. An adaptive Butterworth band-pass filter, whose parametercan be changed by employing velocity feedback, is developed in this paper toachieve its self-adaption. Taking advantage of the frequency and the powerdifferences between pathological tremor and voluntary motion, the proposed filter can effectively extract pathological tremor from the whole motion signals andobtain the tremor features in real time.Experiments to verify the design of the two MR dampers are conducted. Thereal time motion separation algorithm and the control algorithm of MR dampers arealso tested using the tremor data from pathological tremor patients and a tremorsimulation setup.