A Planar Laser Diffraction Encoder in Littrow Configuration for 2D Nanometric Positioning

Abstract

This paper presents a novel design of a planar encoder based on the principle of diffractive interferometry. The system is capable of measuring the two-dimensional displacement of the planar grating of any size. It adopts a specially designed optical path that can increase the alignment tolerance between the optical head and the grating. Given the merits of its simple optical configuration and compact size, it can effectively reduce the environmental disturbance and allow higher stability. The signal processing circuit and waveform subdivision software were also developed to effectively compensate for the waveform errors and count the position to 1nm resolution. Experimental results showed that even in the normal laboratory environment the standard deviation of measured values can be controlled to within 15 nm for a long stroke up to 25 mm on both axes.

An Inductive Sensor for Two-Dimensional Displacement Measurement

“…Then, the digital filtering is employed to reduce the noise jamming. In the module of signal synthesis, e1~ e4 are computed as Equation (8) and S1~S4 are outputted.…”

“…Taking the simulation results of FEA as the input, the flowchart of the resolving process of x and y is shown in Figure 7. Firstly, the outputs of Sc1~Sc4 are processed by Equation (8), and S1~S4 are obtained. Secondly, the FFT algorithm is utilized to acquire the amplitudes and phases of the signals.…”

“…The optical planar encoders have been developed for the 2D displacement measurement. The study shown in [8] described a kind of planar laser diffraction encoder with Littrow configuration. Using the Doppler Effect, 2D displacements were obtained.…”

An FPGA Platform for Next-Generation Grating Encoders

“…So far, many researchers have provided effective methods, spanning from two-axes to six-axes [7][8][9][10][11][12][13][14][15][16][17]. For multi-axes measurement, a combination of translational with rotational motion measurement is used.…”

“…For multi-axes measurement, a combination of translational with rotational motion measurement is used. For multi-axes translational measurement, a two-axis scale grating with a micrometer-order grating period is employed and the X-and Y-direction diffraction beams interference with each other, allowing simultaneous measurement of two-axes translational motion [6,7,9,[11][12][13][14]. The incident direction of the two orthogonal beams can be along the grating normal or in a Littrow configuration [10,15,16].…”