| 摘要 |
PROBLEM TO BE SOLVED: To obtain a method and an apparatus in which the tension of a membrane can be measured quickly and in a noncontact manner by a method wherein sound waves are given to the membrane which is stretched at a uniform tension, the membrane is vibrated and its vibration is measured optically. SOLUTION: A membrane ring 10 is fixed, and a membrane 9 is vibrated by the sound waves of a loudspeaker 105. The surface of the membrane 9 is irradiated with a laser beam from a laser Doppler vibrometer 101. A change in the displacement due to the vibration of the membrane 9 is captured by the laser beam, and the wavelength of a reflected laser beam is measured. The reflected laser beam is sensed by the sensing part of the Doppler vibrometer 101, and the fundamental frequency of the fixed vibration of the membrane 9 is measured. The fundamental frequency is measured by an FFT servoanalyzer 102 in a sound region, and the intensity of respective sound waves in every frequency is analyzed and output. A frequency in a point in which a peak is obtained is the fundamental frequency, and a computer 120 computes and outputs the tension of the membrane 9 on the basis of the fundamental frequency. Data and a computing program regarding the fundamental frequency are stored in advance in the computer 120.
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