This paper deals with a novel self-adaptive magneto-rheological (MR) damper in shear-mode which can control vibrations of washing machines more effectively than commercial passive dampers. The damper comprises a shaft and a housing sliding relatively on a gap filled with MR fluid (MRF). Permanent magnets are fastened on the two shaft ends leaving a middle plain shaft part. The greater the vibration the more magnets enter the MRF region, which results in a higher damping force to attenuate the vibration. Compared with conventional and self-powered MR dampers, the proposed damper has much lower cost for commercial ability since it can itself adjust damping levels corresponding to external vibratory excitations without any control equipment or power unit. It also has simple and compact structure (no magnetic coils), which facilitate manufacturing and maintenance. Another remarkableness of the proposed MR damper is its displacement-dependent damping characteristic which extremely conforms to operation of washing machines. After an overview of the state of the art of vibration control for washing machines, the proposed self-adaptive MR damper is configured. Major geometry of the proposed damper is then optimized to satisfy production cost, size, installation space, off-state force and desired damping force. Based on the obtained optimal solutions, detailed design of the damper is performed and two damper prototypes are manufactured. The dampers are then installed in a prototype washing machine for testing and their experimental performances are compared with conventional passive dampers.

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This paper studies a semi-active control system for magneto-rheological (MR) damper-based suspension of front-loaded washing machines. In this system, a permanent magnet is fastened to the shaft end of a shear-mode MR damper and an induction coil is wound directly on the slots of damper housing. Vibration of the washing machine tube leads to the relative reciprocal movement between the magnet and induction coil, which results in an induction voltage. The induced voltage is then served as an input signal to control the damping force of the MR damper. Because of the MR fluid hysteresis, a phase-lead compensator and an amplifier are employed in the controller of the MR damper. After the controller design, simulations and experiments are performed to evaluate the control system effectiveness. From the experimental results, performance characteristics of the proposed control system are discussed and compared with those of constant current and uncontrolled states.