A thin-film magnetorheological fluid damper/lock

Abstract

This paper presents the design, testing, and application of a thin-film magnetorheological(MR) fluid damper/lock. This MR damper/lock is designed for the use in a model adaptivefan nozzle system actuated by shape memory alloy wires. The MR damper/lock (a total ofeight in the fan nozzle system) will lock the opening size of the fan nozzle and providesdamping when the system vibrates. For this purpose, the MR damper/lock hasto have the following characteristics: (1) The device is in the locking positionwhen the power is off. (2) The device has a small static friction force (less than1 lbf) when the power is on. (3) The device generates a small kinetic friction forcewhen it slides during the power-on period. (4) Its damping coefficient can beadjusted. (5) It must be compact. To meet these requirements, a new designof a damper/lock using thin MR fluid film is employed. The device consists offive major components: two soft steel bars, two stacks of permanent magnets,two groups of magnetic wires, a soft steel slider, and MR fluids. Utilizing thepermanent magnets, the MR fluid is trapped and the device is always in thelocked position. When the device is powered on, the flux of the electromagnetspartially cancels and re-directs the rest of the flux from the permanent magnets, andthen the slider is free to move. In this design, MR fluid reduces the air gap andincreases the locking force when it is powered off. On the other hand, it alsofunctions as a lubricant to reduce the kinetic friction forces when electromagnets arepowered on. Extensive tests of the MR damper/lock are conducted to reveal itsforce–displacement curves and force–velocity curves under different applied voltages.Utilizing these testing results, the MR damper/lock is applied to the model adaptivefan nozzle system to perform both locking and damping tasks with a feedbackcontrol. Experimental results show that these tasks are successfully accomplished.