Study On Grating-based Phase-shifting Interference Differential Confocal Displacement Sensing Technology

With the development of microelectronics, micro-mechanical, micro-optics and other technologies, measurement resolution, range, working distance and other ultra-precision measurement indicators in the field of Geometric ultra-precision measurement has higher development needs, which contains structured surface topography high accuracy measurements, absolute displacement measurement of the height of projection and so on. With anti-vibration environments and high-resolution synchronization phase shifting interferometry technique is widely used in high-precision measurement, but the measurement range and measurement resolution limit each other, it is difficult compatible; Differential confocal microscopy with a bipolar and long working distance in three-dimensional scanning and imaging is widely used, it is vulnerable to environmental vibrations, system structure is complex, difficult to determine the position of the detection pinhole, to some extent, affect the overall measurement accuracy and reduce measurement synchronization. In order to overcome the influence of external environment vibration, to achieve a large measurement range, long working distance and absolute precision micro-displacement measurement, the subject put the synchronous phase shifting interferometry and confocal differential theory together, convert the displacement to a phase change, use differential confocal to achieve rough measurement of the absolute position, use synchronous phase shifting interferometry to accurate measurement of displacement.In order to solve the above-described ultra-precision displacement measurement problems, the project "study on grating-based phase-shifting interference differential confocal displacement sensing technology," the main work is below:(1) In order to solve the contradiction of measurement resolution and measurement range, put differential confocal theory into space synchronous phase shifting interferometry theory, establish phase shifting interferometry pupil differential confocal theoretical model, theoretical four-channel spatial phase shifting interferometry, the unlimited conjugate confocal system based on mirror, differential confocal principle based on pupil shift focus effect and four-channel spatial phase shifting interferometry differential confocal measuring properties.(2) In order to improve the ability of the system of anti-vibration environments, design phase type Ronchi grating, to achieve a total optical axis; design of polarization phase shift and phase pupil filter array such that four beams of light simultaneously coplanar probe, to achieve the purpose of stable measurement; use the microscope objective of reference surface and measuring surface to achieve pour lighting, detecting light intensity is no longer a fringe, but a uniform light spot, thereby improving the stability and synchronization system.(3) In order to expand the system working distance, combined with confocal differential system role in the overall device, in meeting the phase-shifting interferometry half cycle conditions appropriate to reduce the differential confocal resolution, select a smaller numerical aperture microscope objective, to improve the system working distance.Finally, use spectroscopic gratings, polarization phase shift array, phase pupil filter structures related optical test platform, analyze the operating characteristics, stability, repeatability and resolution of the optical system. The results showed that: a plane mirror as the test surface, using orthogonal Ronchi grating phase shifting interferometry displacement measurement device to test its resolution and stability, measurement range of 100μm, steady resolve small displacement 10 nm measured working distance up to 7mm.