Experimental Evaluation of a ‘Self-Sensing’ Capability of an Electromagnetic Induction System Designed for MR Dampers

Abstract

This article presents a sensing capability of an electromagnetic induction (EMI) system that is incorporated in a vibration control system based on an MR fluid damper. The EMI system, consisting of permanent magnets and coils, converts reciprocal motions (kinetic energy) of the MR damper into electrical energy (electromotive force or emf). The EMI system was previously studied as an alternative power source for the MR damper control system, eliminating the need of external power sources, such as a battery. The primary goal of the current study, however, is to study a sensing capability of the EMI with an aim to eliminate a conventional velocity sensor being used to implement control policies for MR damper based vibration control systems. According to the Faraday’s law of electromagnetic induction, the emf signal, produced from the EMI, is an alternating voltage signal, and it is proportional to the velocity of the motion. As such, the induced voltage (emf) signal of the EMI can sufficiently provide necessary measurement information (i.e., relative velocity across the damper) to some of the well-known control methods designed for MR damper systems (such as skyhook and maximum energy dissipation algorithm). This is because such control methods only require the sign change of the velocity signal (or phase of the velocity), rather than the exact magnitude and phase of the velocity signal. In order to evaluate the proposed concept of the EMI sensor, an EMI system was constructed. The EMI was designed to be augmented to a large-scale MR damper system (MR-EMI). The MR-EMI system was then mounted on a hydraulic servo controlled shaking table. Both harmonic and scaled historic earthquake inputs were used in a series of shaking table tests. The emf signals generated by the EMI were compared with the velocity signals (derivative of the reference input displacements). The results show that the induced emf voltage signal coincided with the phase of the velocity signal, indicating that the EMI can act as a relative velocity sensor for common control methods for MR damper systems.