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

With the rapid development of defense, aerospace and other areas, optical free-form surface, which is a key part of their core, is becoming more and more important, and the various applications need also demand higher surface accuracy. The in-situ measurement is an important means to improve the form accuracy of optical free-form surface, because it not only can avoid the repeat installation error, but also can improve the machining efficiency and achieve process automation. However, it is difficult to conduct the in-situ measurement for optical free-form surface due to the shape complexity. An in-situ measurement system of optical free-form based on the ultra-precision machine is developed in this paper, whose probe head is composed of air bearing and laser interferometer,and it can realize the synchronous acquisition of the machine coordinates and surface measurement data quickly and accurately.The core contents of the paper involve two parts: one is the development of in -situ measurement system, and the other is the research of measuring path algorithm and data acquisition software. Main innovation and improvement of the dissertation are as follows:(1) A new type of probe head is developed which adjusts measuring force through the air pressure,and a minimum measuring force of about 80mgf is achieved. Besides,it can make the measuring force maintain a constant value,so the measuring force will not vary with the measuring position;(2) The spiral measurement path is proposed,which is the same as processing path. Therefore,the surface reconstruction is avoided, and the compensation process becomes easier. The compensation of probe radius is also studied in depth;(3) The special software for data acquisition is developed. It can achieve the synchronous output of measurement data and coordinates data, and is capable of measuring the profile of non-reversible free-form surface;(4) The entire in-situ measurement system for free-form surface is completed, which is smaller and is convenient to install.In conclusion, the in-situ measurement system for free-form surface can achieve the measurement of non-reversible surface, and a measurement range of 3.5mm and a sub-micro accuracy are achieved. Besides, it has many advantages, such as linear output, constant measuring force, and small drift. In this paper, double-sinusoidal free-form surface is measured by the in-situ measurement system to verify its accuracy and practicality.