The Research On Mechanism Of Ultra-low Frequency Vibration Sensor Mechanism Based On DVD Pickup

In order to guarantee the normal work of precision instruments and measurement accuracy, the requirements of environmental factors such as temperature, humidity, cleanliness and vibration parameters are stringent. A design of optical sensor for low-frequency vibration measurement is introduced in this paper.The sensor makes use of focus error signal (FES) of DVD pickup, which is sensitive to displacement variation, to detect relative movement of vibration-pickup of sensor. It is just necessary to put the sensor vertically on the surface of vibration object to be measured, and so noted for simple structure, high sensitivity, low cost. The sensor's structure is mainly made up of two parts: DVD pickup and cantilever beam vibration-pickup. One end of cantilever is fixed at the metal base, the other end hangs freely with a mirror mounted on the opposite side. In the static state, DVD pickup's output light reaches the surface of mirror and is reflected back to pickup, the value of DVD pickup's FES is zero. When there is vibration outside, the base will be synchronized with the outside vibration, and the overhang end of cantilever beam will vibrates relatively under the inertia force, and the corresponding FES is linear proportional to the displacement variation. Further according to the function relationship between the cantilever beam's relative vibration and external vibration, outside vibration value comes out from the FES signal through the following calculation.With the analysis of design principle of vibration displacement sensor and accelerometer, and the characteristics of the DVD pickup's FES: high sensitivity, small linear range, the design scheme is firstly introduced in this paper. It is concluded that using DVD pickup for accelerometer can meet practical requirements. Fatherly, the mechanical structures of sensor and vibration pickup structure are introduced, particularly elaboration on influence of cantilever beam's dimension to sensor's performance (natural frequency).The natural frequency of cantilever beam will affect frequency response range and sensitivity. Because the optical sensor's transfer function is a low-pass filter, increasing the natural frequency will improve the frequency response at high-end while simultaneously reduce the sensitivity, and vice versa. The appropriate natural frequency, namely, cantilever beam geometry should lie on actual vibration characteristics. Modal analysis of cantilever beam using ANSYS software has verified theoretical analysis. Finally, the design of an embedded measurement systems based on microprocessor MSP130F149 is implemented, including signal pre-processing, computing, as well as frequency, voltage measurement. The result of frequency and acceleration can be displayed on the LCD, so that the sensor can handle and display signal real time to facilitate the operation of the sensor.