Citation: Lu, X.; Kilikeviˇcius, A.;
Yang, F.; Gurauskis, D. A Method to
Improve Mounting Tolerance of
Open-Type Optical Linear Encoder.
Sensors 2023, 23, 1987. https://
doi.org/10.3390/s23041987
Academic Editors: Fang Cheng,
Tegoeh Tjahjowidodo, Qian Wang
and Ziran Chen
Received: 15 December 2022
Revised: 31 January 2023
Accepted: 7 February 2023
Published: 10 February 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Article
A Method to Improve Mounting Tolerance of Open-Type
Optical Linear Encoder
Xinji Lu
1
, Art
¯
uras Kilikeviˇcius
1
, Fan Yang
2,3,
* and Donatas Gurauskis
1,
*
1
Institute of Mechanical Science, Vilnius Gediminas Technical University, LT-03224 Vilnius, Lithuania
2
Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences,
Changchun 130033, China
3
University of Chinese Academy of Sciences, Beijing 100049, China
* Correspondence: yangfan@ciomp.ac.cn (F.Y.); donatas.gurauskis@vilniustech.lt (D.G.);
Tel.: +370-(672)-30668 (D.G.)
Abstract:
Accuracy becomes progressively important in the wake of development in advanced
industrial equipment. A key position sensor to such a quest is the optical linear encoder. Occasionally,
inappropriate mounting can cause errors greater than the accuracy grade of the optical linear encoder
itself, especially for open-type optical linear encoders, where the mounting distance between the
reading head and main scale must be accurately controlled. This paper analyzes the diffraction
fields of a traditional scanning reticle made by amplitude grating and a newly designed combined
grating; the latter shows a more stable phase in mathematical calculation and simulations. The
proposed combined gratings are fabricated in a laboratory and assembled into the reading heads.
The experimental results indicate that the mounting tolerance between the reading head and the
main scale of the optical linear encoder can be improved.
Keywords: open-type optical linear encoder; scanning reticle; gratings
1. Introduction
The finest approach for sensors to measure displacement with high accuracy is pos-
sibly through optical technology [
1
]. Back in the 1950s, optical linear encoders began to
be adopted in machine tools for direct position feedback [
2
]. Today, optical encoders are
widely used in numerous applications where position measurements are vital to controls,
from printers in households [
3
] to industrial robot arms [
4
], high-end 3D printers [
5
], ac-
celerometers [
6
], high-end medical instruments, such as MRI [
7
], and wafer scanners in
the semiconductor industry [
8
]. The resolutions of optical linear encoders should be at
least 10 times finer than the accuracy of the designed machines so that control accuracy
can be ensured [
9
]. Consequently, the resolution and accuracy of optical linear encoders
have a strong demand for improvement to keep pace with the development of advanced
equipment. Over the last decades, the resolution and accuracy of optical linear encoders
have been enhanced significantly owing to innovations in electronics and optical technolo-
gies. Nevertheless, these achievements can be easily offset by external or unintentional
man-made errors, such as temperature variations [
10
], mechanical vibrations [
11
], surface
pollution [
12
], imperfect mounting, etc. The errors caused by linear encoders not only re-
duce the accuracy of equipment but also put restrictions on the operation speed or increase
the amount of computational work for machines [
13
]. In worst-case scenarios, incorrect
displacement feedback from optical linear encoders could lead to a decrease in the stability
of the machine and have a negative impact on the dynamic controls [
14
]. Multitudinous
research and experiments have been performed to diminish these errors. Some works
designed special tools or techniques to keep the linear encoder apart from the source of
vibration [
15
], while others focused on developing algorithms to compensate for the errors
Sensors 2023, 23, 1987. https://doi.org/10.3390/s23041987 https://www.mdpi.com/journal/sensors
