6-DOF displacement and angle measurements using heterodyne laser encoder

Abstract

In this research, a novel heterodyne laser encoder for 6-DOF displacement and angle measurements is proposed. The technique combines the advantages of heterodyne interferometry, grating shearing interferometry, and Michelson interferometry. When a heterodyne light beam with two orthogonally polarized directions is used to focus on a semitransmission grating, two detection configurations for in-plane and out-of-plane will be obtained. By means of measuring the phase variations of the interfering signals from the moving grating, the in-plane displacement can be acquired. Besides, the out-of-plane displacement can be obtained by detecting the optical path difference between the reference beam and the reflection beam. Furthermore, 6-DOF displacement and angle information can be measured simultaneously by using the beam dividing method. According to the experimental results, the measurement resolution is about 2 nm. The experimental results show that our proposed method has the ability to measure 6-DOF displacement and angle information with high system stability. Comparing with other commercial measurement instructions, this laser encoder has the advantages of high resolution, high stability, and high flexibility.

Three-dimensional interferometric stage encoder using a single access port

“…Despite these drawbacks, optical interferometry remains an attractive technique for high-precision applications, and as such over the years numerous variations on standard interferometric setups have been developed for metrological purposes in single dimensions [17,18,19,20,21]. When extended to more than one spatial dimension, however, optical interferometers [22], 6 [26], 6 [27] Various optical elements: 10[22], 13 [26], 34 [27] Range-resolved Interferometer (This implementation) 1.3 nm Yes 3 3 mirrors, 2 beamsplitters…”

“…typically require multiple sensing heads or optical access ports. In addition, various designs using gratings to achieve multi-dimensional displacement measurements have been conceived [22,23,24,25,26,27,28].…”

Optical Sensors for Multi-Axis Angle and Displacement Measurement Using Grating Reflectors

“…In responding to the above requirements, two-axis optical angle sensors [46,47,48,49,50,51] based on the laser autocollimation [51], as well as the three-axis autocollimator [52], have been developed. The applications of planar encoders or surface encoders [53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79], which can carry out simultaneous detection of the position in a plane or in 3D space with the enhancement of a planar scale grating, is another possible solution. The planar encoders/surface encoders are expected to achieve multi-axis angle and/or displacement measurement, while complying with the Abbe principle and avoiding the increase of measurement uncertainty due to the increase of the degrees of freedom.…”

Ultraprecision Real-Time Displacements Calculation Algorithm for the Grating Interferometer System

“…One simple approach is establishing a linear readings–displacements model using various approximations and deriving its closed-form solutions. Although this method has high resolution and excellent real-time performance, its calculation precision degrades with an increase in the rotation range because its nonlinearities such as rotation–translation coupling and geometric errors are neglected [8,9,10]. To achieve ultraprecise displacements calculation, establishing a precise readings–displacements model is a prerequisite.…”