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

Abstract

The invention provides a two-degree-of-freedom heterodyne grating interferometer displacement measurement method. A measurement system adopted by the measurement method comprises a reading head, a measurement grating and an electronic signal processing part. The two-degree-of-freedom measurement method comprises the steps that the reading head gives two beams of measurement light to be incident to the measurement grating at the Littrow angle and two beams of diffracted light is generated to return along the original path, the reading head gives a heterodyne reference electric signal and two heterodyne measurement electric signals to be inputted to the electronic signal processing part, and two-degree-of-freedom displacement output is realized through resolving. According to the measurement method, polarization aliasing can be avoided, nano and even higher level of resolution and precision can be realized, and the two-degree-of-freedom large stroke displacement can be simultaneously measured. The measurement system applying the measurement method has the advantages of being insensitive to environment, compact in structure, small in size and low in mass and is suitable for the occasions of multi-degree-of-freedom precision displacement measurement like a photoetching machine ultra-precision workbench and a precision machine tool.

Description

technical field [0001] The invention relates to a grating measurement method, in particular to a two-degree-of-freedom heterodyne grating interferometer measurement method, which 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] Ultra-precision displacement measurement technology ha...

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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 uses a two-dimensional grating with specific readings The head realizes displacement measurement, which can simultaneously measure horizontal and vertical displacements, but the cost of large-scale two-dimensional gratings is extremely expensive; Japanese CANON company US Patent Publication No. US2011 / 0096334 A1 (publication date April 28, 2011) disclosed A heterodyne interferometer, which uses a grating as the objective mirror, but the interferometer can only achieve 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

Chinese Patent Publication No. CN103759657A (disclosure date: April 30, 2014) and CN103759656A (disclosure date: April 30, 2014) respectively disclose a heterodyne grating interferometer measurement system, and the readings in the two interferometer measurement systems The head structure makes its travel very small when measuring the vertical direction, and it is impossible to measure a larger stroke of the vertical movement, and the application range is limited.

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