What is modal analysis?Modal analysis is the dynamic characteristic of object structure under vibration excitation. Structural engineers can extract modal parameters (dynamic characteristics) of a structure through modal analysis. Modal parameters can help structural engineers understand the response of a structure to environmental conditions for design validation.The modal analysis of the optical discWith the increase of the data transmission rate of the optical disc drive, the speed of the spindle motor also increases. Today, it has reached about 12,000 revolutions per minute, and if the disc has a little eccentric mass, the vibration caused by the unbalance will be intensified, causing great difficulties for the focus and circulation of the optical head. The modal analysis of the optical disc is carried out to obtain its natural frequency and modal changes, which can be used as a theoretical basis for evaluating the characteristics of the optical disc and to determine whether the strength of the optical disc meets the design requirements.Optical disc modal test analysis challenge1) The quality of the disc is small, and the contact sensor has a large impact on the test of the disc;2) The mode mode needs to collect multi-point data from the disc, and the traditional method needs to be measured several times, which is low efficiency;3) Optical disc modal analysis is in urgent need of an efficient measurement method without mass addition.Optical disc modal test analysis solutionScanning laser vibrometer LV-SC400 & modal test systemThe laser Doppler vibrometer can achieve the amplitude resolution of nanometer and picmeter-level. The system uses laser as a means of detection, has no additional mass effect, and can be measured on extremely small and lightweight structures.System features: The galvanometer can achieve deflection Angle change of 40°×50°. The camera can achieve 30x optical zoom and 12x digital zoom. Velocity resolution is better than 0.01μm/√Hz, displacement resolution is better than 0.31pm.Test environment construction1) The signal generator generates the sweep frequency signal, and the optical disc vibration is stimulated by the piezoelectric plate.2) The scanning laser vibrometer equipment is built3) The model is laid out on the software, and the laser point is scanned point by point and the data is collectedData analysis1) The software can be time domain analysis, spectrum analysis, frequency response amplitude analysis and frequency response phase analysis2) Modal analysis is carried out by modal algorithm, and the frequency and damping ratio are obtainedMode display50Hz105Hz265Hz487HzTest conclusionThe natural frequency and modal modes of the optical disc are obtained by scanning laser vibrometer, which provides a favorable theoretical basis for evaluating the characteristics of the optical disc and can be used to interpret the strength of the optical disc. Under the high-speed operation of the disc, the natural frequency is avoided, and the structure is optimized under a specific frequency. The "Modal artifact" can perform modal testing quickly and efficiently, which has a great advantage over traditional chip sensors. "Modal artifact" not only can be used for optical disk modal testing, but also can be widely used in various structural analysis, ultrasonic piezoelectric testing, and research of new materials.