| Low-frequency vibration has a destructive impact on high-precision measurement,which is difficult to be reduced effectively by passive isolation.High precision measurement for low-frequency vibration is the first step of active isolation.For the accurate measurement of low frequency micro-vibration,a low-frequency high-sensitivity optical accelerometer is proposed.The following tasks are mainly completed in this paper:1.An optical accelerometer based on the four-quadrant photodetector was designed.This optical accelerometer mainly comprises two components:a seismic structure consisting of seismic mass and leaf spring,and a sensing component based on a four-quadrant photodetector(QPD).2.Optimized parameters of key components of optical accelerometers.The resonant frequencies and elastic coefficients of various seismic structures are simulated.According to the output of QPD,I/V conversion circuit,addition and subtraction operation circuit and low-pass filter circuit are designed.3.For the calibration of low-frequency and high-sensitivity optical accelerometers,a low–cost and high–precision vibration generator was developed.A piezoelectric actuator is used as vibration exciter,a leaf spring made of beryllium copper is used as elastic support.An appropriate amplifier PA92 was selected and a large current capacitive load amplifying circuit was designed.4.Experimental results demonstrate that the vibration generator can achieve steady output displacement with frequency range from 0.6 Hz to 50 Hz,an analytical displacement resolution of 3.1 nm and an acceleration range from 3.72 mm/s2 to 1.9 m/s2 with the relative standard deviation less than 1.79%.5.The developed accelerometer is calibrated with a vibration generator and a high-precision eddy current sensor as the reference sensor.And the calibration and error analysis experimental results demonstrate that the sensitivity of the optical accelerometer is 1.74V/(m·s-2),the measurement range of the accelerometer is 0.003–7.29 m/s2,the operating frequencies range of 0.4–12 Hz,the indication residual error is lower than 2×10-3 m/s2,and the standard deviation from ten measurements is under 7.9×10-4 m/s2.The efficacy of the optical accelerometer in measuring low-frequency,low-amplitude dynamic responses is verified. |
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