A New Approach to Achieve Variable Negative Stiffness by Using an Electromagnetic Asymmetric Tooth Structure

Abstract

Traditional passive nonlinear isolators have been paid much attention in recent literatures due to their excellent performance compared to linear vibration isolators. However, they are incapable of dealing with varying conditions such as changing excitation frequency due to the nonadjustable negative stiffness. To solve this drawback, a new approach to achieve variable negative stiffness is proposed in this paper. The negative stiffness is realized by an electromagnetic asymmetric magnetic tooth structure and can be changed by adjusting the magnitude of the input direct current. Analytical model of the electromagnetic force is built and simulations of magnetic field are conducted to validate the negative stiffness. Then the EATS is applied to vibration isolation and an electromagnetic vibration isolator is designed. Finally, a series of tests are conducted to measure the negative stiffness experimentally and confirm the effect of the EATS in vibration isolation.

An actuator with tuneable resonant frequency for active vibration damping

“…Due to the variation of applications and tuning methodologies, a direct comparison between the result of this study and other proposed solutions in the literature for extending the dynamic range of an actuator is not possible. However, a relatively similar percentage change in the resonance frequency of an electromagnetic actuator is presented by Han et al (2018) which showed that by tuning a variable negative stiffness, the resonance frequency of an asymmetric tooth actuator has been decreased from 23.25 to 17 Hz (26.8% reduction), when the control current is changed from 0 to 0.8 A. In that actuator applying the negative stiffness cause the reduction of the resonance frequency of the structure; however, for the presented AVTA in this paper, the tuning mechanism is designed to increase the resonance frequency of the actuator.…”

“…As a solution to the temperature sensitivity issue for electromagnetically tuneable stiffness in vibration isolators, Han et al (2018) proposed an electromagnetic asymmetric tooth structure wherein the absence of any permanent magnet material, the coil's current can be adjusted to tune the stiffness of the system. In this design, the stator and the moving part are both made of electrical steel and have the same number of teeth, which are arranged symmetrically.…”

Review of Passive Electromagnetic Devices for Vibration Damping and Isolation

“…Negative-stiffness elements have been identified as unique mechanisms for enhancing acoustical and vibrational damping. Examples of negative-stiffness mechanisms include mechanical systems with negative spring constants and materials with negative moduli [66][67][68][69]. Negative-stiffness elements contribute to damping behaviour because they tend to assist rather than resist deformation as a result of internally stored energy [70].…”

Improving Low Frequency Isolation Performance of Optical Platforms Using Electromagnetic Active-Negative-Stiffness Method

“…However, it is usually necessary to increase the stiffness of the isolator to maintain its stability when the mass of the payload increases. Negative-stiffness vibration isolators are isolators that use various kinds of restoring force, whether passive , semi-active [22][23][24][25][26][27][28], or active [29,30], to produce negative-stiffness characteristics, thus partially counteracting the positive stiffness within a micro-vibration stroke. And they have shown effective to produce high-static-low-dynamic stiffness characteristics.…”

“…Zhou [24] proposed a tunable negative-stiffness spring composed of a pair of electromagnets and a permanent magnet. Han [25] used an electromagnetic asymmetric tooth structure to obtain variable negative stiffness, which can be adjusted through tuning the magnitude of input current. Pu [26] proposed an electromagnetic negative stiffness vibration isolator composed of multilayer magnets and coils.…”