The degree of passivation of the grinding wheel is gradually increased during the machining process, the friction between the grinding wheel and the workpiece is increased which causing the vibration and noise of the machine are changed. Therefore, the vibration and noise values could be obtained by using the vibration sensor and microphone. We use the spectrum analyzer to analyze the trend of the variation of vibration and noise signals. As the wear of the grinding wheel increases, the sound acoustic pressure in the range of 4.3 kHz to 5.3 kHz decreases. As the friction between the grinding wheel and the workpiece increases, high-frequency noise greater than 6 kHz are excited and the acoustic pressure increases. According to the experimental results, it is known that the wear state of the grinding wheel and the noise spectrum in generating process has a significant correlation. The cutting force of the grinding wheel can be observed by the noise spectrum of the spectrum analyzer to identify whether there is an abnormality in the processing process to optimize the grinding parameter immediately for avoiding the damage of the lens.
Optical metrology is a critical and complicated technique for the fabrication of precision optics which surface figure is better than RMS 1/30λ. The intrinsic systematic error of the experimental setup including the alignment error of the metrology tool and manufacturing error of the reference optics shall be calibrated carefully. Nevertheless, the measured consequence also includes the surface deformation caused by mounting supporter and gravity effect, which may result in a misleading judgment for surface figure correction, especially for mid- to-large optics. Besides the systematic error of experimental setup and deformation by an external condition of the optics, the environmental condition such as temperature drift, air turbulence, and vibration also affect the measured result. This paper proposes a method which adopts the magnitude and phase of each non-rotationally symmetrical Zernike coefficients grabbed from the multiple measurements from rotating the optics to analyze the absolute low-spatial frequency figures.