Two-degree-of-freedom heterodyne grating interferometer displacement measurement system and method

Abstract

The invention provides a two-degree-of-freedom heterodyne grating interferometer displacement measurement system and method. The system comprises a double-frequency laser device, a grating interferometer, a measuring grating, a receiver and a signal processing unit. The grating interferometer comprises a lateral displacement light splitting prism, a polarization light splitting prism, a 1 / 4 wave plate, a reflecting mirror and an optical fiber coupler. The method realizes displacement measurement based on grating diffraction, the optical Doppler effect and the optical-beat frequency principle. Laser of the double-frequency laser device is incident to the interferometer and the measuring grating and then optical signals are outputted to the signal processing unit. When the interferometer and the measuring grating perform two-degree-of-freedom linear relative movement, the system can output two linear displacements; the measurement system adopts Littrow incident conditions, a measurement target has large passive movement tolerance and two linear displacements can be measured simultaneously so that precision can reach the nanoscale and higher scale; and the measurement system has advantages of short light path, small size, compact structure, low weight and low requirement for the measuring grating and is suitable for two-degree-of-freedom high-precision long-stroke displacement measurement.

Description

Technical field [0001] The invention relates to a two-degree-of-freedom heterodyne grating interferometer measurement system and method, in particular to the displacement measurement of an ultra-precision workpiece stage, belonging to the technical field of displacement measurement. Background technique [0002] As a typical displacement sensor, the grating measurement system is widely used in many electromechanical equipment. The measurement principle of the grating measurement system is mainly based on the principle of Moiré fringe and the principle of diffraction interference. As a mature displacement sensor, the grating measurement system based on the moiré fringe principle has become the first choice for displacement measurement of many electromechanical equipment due to its many advantages such as long distance measurement, low cost, and easy installation. However, the accuracy is usually on the order of micrometers. For general industrial applications. [0003] Ultra-preci...

AI Technical Summary

Problems solved by technology

Netherlands ASML company US patent US7,102,729B2 (disclosure date August 4, 2005), US7,483,120B2 (disclosure date November 15, 2007), US7,,940,392B2 (disclosure date December 24, 2009) , Publication No. US2010 / 0321665A1 (publication date: December 23, 2010) discloses a planar grating measurement system and layout scheme applied to ultra-precision workpiece tables of lithography machines. The measurement system mainly uses a one-dimensional or two-dimensional plane The grating cooperates with the reading head to measure the horizontal large-stroke displacement of the workpiece table, and height sensors such as eddy currents or interferometers are used to measure the displacement in the height direction, but the application of various sensors limits the measurement accuracy of the workpiece table

U.S. Patent Publication No. US2011 / 0255096A1 (published on October 20, 2011) of ZYGO Corporation of the United States discloses a grating measurement system applied to ultra-precision workpiece tables of lithography machines. The measurement system also uses two-dimensional gratings with specific readings The head realizes the displacement measurement, which can simultaneously measure the horizontal and vertical displacements, but the structure is complicated, and the cost of the two-dimensional grating is extremely expensive; the Japanese CANON company US Patent Publication No. US2011 / 0096334A1 (publication date April 28, 2011) discloses A heterodyne interferometer, which uses a grating as the objective mirror, but the interferometer can only achieve one-dimensional measurement

Japanese scholar GAOWEI proposed a single-frequency two-dimensional grating measurement system using the principle of diffraction interference in the research paper "Design and construction of two-degree-of-freedom linear encoder for nanometric measurement of stage position and straightness. Precision Engineering 34 (2010) 145-155". Vertical displacement measurement, but due to the use of single-frequency laser, the measurement signal is susceptible to interference, and the accuracy is difficult to guarantee

In addition, Chinese Patent Literature Publication Nos. CN103759657A (publication date: April 30, 2014) and CN103759656A (publication date: April 30, 2014) respectively disclose a heterodyne grating interferometer measurement system. The structure of the reading head makes its travel very small when measuring the vertical direction, and it cannot measure the larger stroke of the vertical movement, so the application range is limited.

Images