Study On The Non-contact In-situ Measurement System For Free-form Surfaces

The appearance of optical free-form surface has injected new vitality to thedevelopment of optical technology, which not only simplifies the structure of theoptical system, but also makes the imaging quality improved, so it is widely applied.However, with the requirements of more complex and higher accuracy of opticalfree-form surface, its production has been a problem in the manufacturing areas,especially developing a suitable measurement system to detect the error of free-formsurface is even harder. Most of the present measurement methods are the off-linemeasurements with touch probe, although such measurements have got high precision,they need retighten the workpiece for the compensation machining and may hurt theworkpiece after measurement, which can bring new error, so these methods are notconducive to the production of optical free-form surface. An non-contact in-situmeasurement system based on the ultra-precision machine is proposed in this paperand design a non-contact probe system based on focused laser measurement. Themain research work is as follows:1. Based on the focus error signal detection principle, develop a focused opticalprobe, and build an effective signal processing system to ensure the highprecision of the output of the measurement signal, and a imaging system inthe optical system of the probe help adjust the probe to the center of spindlequickly and accurately;2. The overall in-situ measurement program is designed based on theultra-precision turning platform, and analyze the design method ofprocessing path of probe. At the same time, we develop a software to capturecoordinate position and error data synchronously, so the system complete theefficient measuring of the curved surface’s shape and error data;3. Because the optical probe can’t measure the workpiece with large curvature,this paper presents that with the help of high precision rotation, optical probecan measure the large curvature workpieces in the direction of normal vector,as a result, the effect of curvature to measurement is eliminated.The result of the final experiment shows that the focused laser probe achievemeasurement resolution of20nm and uncertainty of less than10nm, and can measure the plane and rotating surface with large curvature stably and reliably, in addition, itcomplete the in-situ measurement of double-sinusoidal free-form surface with thechange of curvature of less than10°.