Preliminary Study On Vibration Measurement Based On Self-mixing Interference For Ultrasonic Numerical Control Machine Tools

The Ultrasonic numerical control machining technology is an effective way formachining all kinds of complex shapes, such as high-precision plane surfaces,high-precision curved surfaces. More importantly, it plays an important part inmachining many optical elements. It is especially important to measure and select thebest operation frequency for improving the surface quality and reducing rejection rateduring the machining process. In this paper, the self-mixing interference technique isused to measuring the operation frequency on the basis of comparing several commonlyused measurement methods. The self-mixing interference technique has manyadvantages such as good usability, compactness, easy alignment, contact free,high-precision and low cost, so it is a promising way for measuring vibration.Based on Lang-Kobayashi rate equations and three-mirror Fabry Perot cavity model,the theoretical model of the self-mixing interference is established, and the principle andcharacteristics of fringe counting method and reconstruction measurement method areintroduced. In order to quantitatively study the self-mixing phenomena and measure themicorvibration, an experimental installation is set up to measure the microvibration ofpiezoelectric ceramics. The relationship between the electrostrictive rate and the drivingfrequency of piezoelectric ceramics has been got and there are three resonance points ofpiezoelectric ceramics in the frequency zone of0~4kHz. And the response times ofpiezoelectric ceramics are also measured. Through detailed analysis, the reason of thedifferences of linewidth enchancement factor at different frequencies has been shown tobe that the optical feedback strength factor changes with the driving frequency ofpiezoelectric ceramics.At last, the experimental installation has been set up in situ for measuring themicrovibration of machining tools of a certain ultrasonic numerical control machine. Ithas been shown that the vibration mode of the machining tools are satisfied with sinefunction, and frequencies of self-mixing signal are in accordance with the ultrasonicdriving frequency. Based on reconstruction measurement method, the vibration picturesof3kinds of machining tools are obtained. By analyzing the relationships betweenamplitudes of machining tool vibration and ultrasonic driving frequency, the resonancepoints of3kinds of machining tools are picked out. Finally, the experimental errors areanalyzed. It has been shown that different machining tools have different resonantcharacteristics even if the ultrasonic coupling coils are the same, which will be muchhelpful in selecting the driving frequency of ultrasonic machining tools.