Dr. Masayuki Okugawa Profile

Dr. Masayuki Okugawa

Associate Professor at Aichi Institute of Technology

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Proceedings Article | 11 April 2007 Paper

Effect on detection sensitivity for smart washer configuration and ambient temperature characteristics on bolted joint

Masayuki Okugawa, Tohru Tanaka

Proceedings Volume 6532, 653213 (2007) https://doi.org/10.1117/12.715684

KEYWORDS: Capacitance, Inspection, Sensors, System identification, Temperature metrology, Amplifiers, Ferroelectric materials, Structural health monitoring, Numerical simulations, Data modeling

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The objective of this study is to apply the concept of structural health monitoring to the detection of bolted joints loosening without human involvement. This paper proposes a method of bolt loosening detection by adopting a smart washer with sub-space state space identification (4SID) algorithm. The smart washer is the cantilevered plate type washer bonded piezoelectric material. The feature is the self-sensing and actuation function. The principle of how to detect the loosening of a bolt is the basis that the natural frequency of a smart washer system vary depending on a bolt tightening axial tension. The natural frequency of the smart washer was identified by using the sub-space state space identification method. For practical use of the smart washer, it is necessary to investigate the problem of repeatability and data quality depending on the influence of the ambient temperature characteristics, and to improve the sensitivity at the initial state of the bolt tightening axial tension decreasing. This paper describes the results of experimental and analytical about the effect on the sensitivity for the smart washer configuration, and the ambient temperature characteristics on the bolted joint. The experimental results indicate the influence of the temperature variation to the bolt tightening axial tension. In order to the sensitivity of the improve bolt loosening detection, vibration-modal analysis of the smart washer system is performed for the configuration of the smart washer. The design parameters of the smart washer was discussed on the results of the numerical simulation.

Proceedings Article | 21 August 2001 Paper

System identification and controller design of a self-sensing piezoelectric cantilever structure

Masayuki Okugawa, Minoru Sasaki

Proceedings Volume 4326, (2001) https://doi.org/10.1117/12.436490

KEYWORDS: Bridges, System identification, Ferroelectric materials, Sensors, Smart structures, Vibration control, Systems modeling, Amplifiers, Feedback control, Control systems

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This paper addresses system identification and vibration control of a cantilever fabricated from piezoelectric materials (PZT), and shows how system identification and state estimation can be used to achieve self-maintenance of a self-sensing system. Currently, self-sensing systems that have concurrent actuation and sensing can be made by using a bridge circuit. However, hardware tuning is still needed due to the unstable nature of an imbalanced bridge circuit. This problem becomes serious in the space environment where human beings may not be available to perform the maintenance. A method of achieving self-sensing without a bridge circuit is proposed in this paper. Analysis of the system dynamics indicates that the subsystem corresponding to the bridge circuit for a self-sensing cantilever with PZT can be described as a direct transmission component in the state space expression of the system. This means that the problem of balancing the bridge circuit is equivalent to the system identification and state estimation problem. By performing a simple experiment, a model of the system was identified using the 4SID (SubSpace State Space Identification method). Observer theory can be used to estimate state vectors which include information about the mechanical dynamics. Thus, system stability depends on the estimated value of the state vectors. The system can be stabilized using a state feedback controller such as a LQ controller. The proposed method was verified with experimental results, demonstrating that smart structures can achieve self-maintenance.

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