A displacement measurement system and method of a two-degree-of-freedom heterodyne grating interferometer

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 measurement system and method of a two-degree-of-freedom heterodyne grating interferometer, in particular to the displacement measurement of an ultra-precision workpiece table, and belongs 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 Moiré fringe principle and the diffraction interference principle. As a well-developed 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 long measuring range, low cost, and easy installation and adjustment, but the accuracy is usually on the order of microns, which is common for general industrial applications. [0003] Ul...

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Netherlands ASML company US patent US7,102,729 B2 (disclosure date August 4, 2005), US7,483,120 B2 (disclosure date November 15, 2007), US7,940,392 B2 (disclosure date December 24, 2009) , Publication No. US2010 / 0321665 A1 (published on 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 one-dimensional or two-dimensional The planar grating cooperates with the reading head to measure the horizontal large-stroke displacement of the workpiece table, and the displacement measurement in the height direction uses height sensors such as eddy currents or interferometers, but the application of various sensors limits the measurement accuracy of the workpiece table

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

In the research paper "Design and construction of a two-degree-of-freedom linear encoder for nanometric measurement of stage position and straightness. Precision Engineering 34 (2010) 145-155", Japanese scholar GAOWEI proposed a single encoder using the principle of diffraction interference. Frequency two-dimensional grating measurement system, which can realize horizontal and vertical displacement measurement at the same time, 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.

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