Design Of Three-dimensional Micro-displacement Measuring System Using Photoelectric Stylus

Micro-nano-measurement has become a hot and cutting-edge research in measurement technology field all over the world and it is also one of the high-tech technologies which are being supported by government. With the development of micro and nano technologies, various micro-nano-level measurement instruments are coming out such as Nano Coordinate Measuring machines, Optical Microscopy, Electron Microscopy, Scanning Tunneling Microscopy (STM), Atomic Force Microscopy (AFM), ect which are widely used in research and are very expensive and not suitable for experiments teaching for undergraduates. A low-cost stylus micro-displacement measuring system is proposed in this paper, which can be used in undergraduate teaching of micro-nano detection experiments. On the base of the guaranteed accuracy, it illustrates the measuring principle of the micro-displacement and helps the undergraduates understand the frontier of knowledge during the experiments.In the system, the beam emitted by the laser projects onto the small mirror fixed on the back of the cantilever and projects onto the PSD sensor after reflected by the small mirror. When the probe had sensed ups and downs of the measured surface, it drives the cantilever beam bending and change the light path, and then position of the light spot on PSD changes. The distance of spot movement and the distance of probe movement have a one-one correspondence. Measuring the distance of spot movement, the distance of probe movement can be calculated through the geometrical optics method. The micro-displacement was got by cantilever. By measuring a number of sampling points, we can get the tested surface morphology.The mathematical model of the micro-displacement measurement system is established based on the optical path and calibration methods of the system parameters in the mathematical model are analyzed. In this article, the design of the beryllium bronze cantilever with low elasticity and the wear-resistant probe are completed, finally built the experimental platform. Using LabVIEW to filter, operate, display and save the system's output data. On the base of system soft and hardware, the assessment of stability and accuracy, error analysis, system parameters calibration experiments and sample measuring experiment are completed. Experiments show that the system could achieve the micro-nano measurement tasks in undergraduate experimental teaching.