Calibration of non-contact incremental linear encoders using a macro–micro dual-drive high-precision comparator

Abstract

The accuracy of a linear encoder is determined by encoder-specific errors, which consist of both long-range and cyclic errors. Generally, it is difficult to measure the two errors of a non-contact incremental linear encoder with a large measuring range and small signal period in one measurement because of the contradiction between long travel range and high resolution. To resolve this issue, a prototype high-precision interferometric comparator with a macro–micro dual-drive system is presented. The measurement and motion resolution of the comparator are 1 nm and 3 nm, respectively. A measuring range of 320 mm is realized and the theoretical maximum range of the comparator is 2 m. The comparator mainly includes a high-accuracy aerostatic linear-motion stage, a constant displacement ratio piezoelectric-driven stage, two laser interferometers, a 6-DOF grating pair position adjustment devices and a PC-based data processor. The measurable linear movement is afforded, respectively, by the long-stroke stage and the piezoelectric-driven stage for the long-range error and cyclic error measurement. The movement can be measured by the encoder and then be calibrated by the corresponding laser interferometer. In the experiment, the accuracy of a non-contact incremental linear encoder with a 20 μm-long signal period and 320 mm measuring range proposed by our team was calibrated after proper mounting. The long-range error is measured to be 3.123 μm, and the cyclic error is within ±0.159 μm, which matches well with the theoretical estimation given by ±0.145 μm. The measurement uncertainties are estimated and the results confirm the effectiveness and feasibility of the proposed scheme and instruments.

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

“…For such a purpose, optical diffractometers can be employed; by detecting the diffraction angle of the diffracted beams from the scale grating in the Littrow configurations, the grating pitch can be obtained based on the grating equation [141,142]. Another candidate for the evaluation of planar scale gratings is the linear scale comparator [143,144,145]. In the linear scale comparator, an edge of each grating pattern structure is detected by using focused light, while the displacement of the grating pattern structure is measured by using a laser interferometer.…”

A review of interferometry for geometric measurement

“…Most of the commercial laser interferometers are heterodyne interferometers [59][60][61], also called dual-frequency interferometers, in which the frequency difference can be generated by the Zeeman effect [62] or an acousto-optical modulator [63,64], as shown in figure 5(a). It overcomes the shortcomings of the DC drift of the single-frequency laser, and has the advantages of low noise and strong anti-interference ability.…”

Error Analysis of an Economical On-Site Calibration System for Linear Optical Encoders

“…Yu et al designed a high-precision comparator with a macro-micro dual drive for calibrating non-contact incremental linear encoders. The measurement and motion resolution of the comparator are 1 nm and 3 nm, respectively [13]. Gurauskis et al developed a thermal and geometric error compensation system for a linear optical encoder [14].…”