Bolt Loosening Monitoring Using Thin Plate Sensor (Natural Frequency Evaluation Using Oscillator Circuit)

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  • NAKAHARA Takeshi
    Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology
  • OHYA Yuusuke
    Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology
  • OKUMA Masaaki
    Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology

Bibliographic Information

Other Title
  • 薄板形センサによるボルトゆるみモニタリング（発振回路を用いた固有振動数評価）
  • Natural Frequency Evaluation Using Oscillator Circuit
  • 発振回路を用いた固有振動数評価

Abstract

Bolted joints are commonly used for many machines and structures. They sometimes suffer from bolt loosening and may sometimes induce accidents. Therefore, bolt loosening detection techniques are essential for many machines and structures having bolted joints. Authors have proposed a new bolt loosening detection sensor using a specific natural frequency of a thin plate and named it thin plate sensor. The natural frequency of the sensor is identified by admittance of piezoelectric elements attached to the plate without human commitments. However, this method requires a complicated setup consisting of a function generator, a voltage-current measurement circuit, A/D converters and a computer with data processing software. In this paper we propose a method to evaluate the natural frequency using an oscillator circuit as an easier means. The oscillator circuit consists of an amplifer and a feedback circuit. The feedback circust consists of a capacitor, piezoelectric elements of the thin-plate sensor and CR low-pass filters. The oscillating frequency of the circuit is automatically synchronized with the natural frequency of the plate. Experiments are conducted to measure the relation between axial tension of the bolt and the oscillating frequency and the validity of the present method is confirmed.

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