An Analysis of the Focus Variation Microscope and Its Application in the Measurement of Tool Parameter

Ultra-precision manufacturing is essential to the production of workpieces of the highest quality in terms of form accuracy, surface accuracy, and integrity. Compared with physical and chemical material removal methods, it has the advantages of high efficiency, high flexibility, and low cost. Because of the direct interaction between the workpiece and the tool during the process of ultra-precision manufacturing, the geometrical parameters of the tool directly affect the surface quality of the workpiece and need to be measured accurately and comprehensively. However, due to the large surface slopes of some tools, some three-dimensional measurement methods cannot measure their geometrical parameters because of limited maximum measurement angle. In this work, we build a focus variation system to make three-dimensional measurements of tools and extract their geometrical parameters. The data processing procedures and the selection of experimental parameters are analyzed in detail using simulations and experiments. Furthermore, we use a step height standard to verify the high accuracy of the measurement system and a roughened flat surface to evaluate the measurement noise and vertical resolution. Measurements of the parameters of a round nose cutting tool and the surface texture parameters of a grinding tool are conducted and indicate that the focus variation system is suitable for measuring the geometrical parameters of tools for ultra-precision manufacturing.