Experimental results of a 1D passive magnetic spring approaching quasi-zero stiffness and using active skyhook damping

Abstract

The use of permanent magnets has been investigated in recent years to provide load bearing forces for vibration isolation. Using two pairs of magnets in both repulsion and attraction, it is possible to generate a force-displacement characteristic that has an inflection point at zero stiffness, known as the quasi-zero stiffness location. Since vibration isolation performance is known to improve with lower resonance frequencies and therefore isolator stiffnesses, the quasi-zero stiffness location is considered the point at which vibration isolation is best achieved. However, since this location is only marginally stable, for passive operation it is only possible in practice for the equilibrium position of the system to asymptotically approach the quasi-zero stiffness point. The proximity to this point that can be achieved depends on the loads to be borne and the amplitude of vibration to be isolated. In previous works, this particular magnetic system has seen theoretical treatment. A prototype of the magnetic system will be presented that uses magnet pairs mounted on a rigid lever arm to constrain their motion to a single degree of freedom. Experimental results are presented that demonstrate the quasi-zero stiffness behaviour of the practical system. Finally, a novel electromagnetic actuator is incorporated into the design to attenuate the resonance peak via active skyhook damping using accelerometer measurements. The limits of this feedback are shown to be caused by the filter poles of the accelerometers used to measure the vibration.