Abstract
Optical and magnetic linear/rotary encoders are well-known systems traditionally used in industry for the accurate measurement of linear/angular displacements and velocities. Recently, a different approach for the implementation of linear/rotary encoders has been proposed. Such an approach uses electromagnetic signals, and the working principle of these electromagnetic encoders is very similar to the one of optical encoders, i.e., pulse counting. Specifically, a transmission line based structure fed by a harmonic signal tuned to a certain frequency, the stator, is perturbed by encoder motion. Such encoder consists in a linear or circular chain (or chains) of inclusions (metallic, dielectric, or apertures) on a dielectric substrate, rigid or flexible, and made of different materials, including plastics, organic materials, rubber, etc. The harmonic signal is amplitude modulated by the encoder chain, and the envelope function contains the information relative to the position and velocity. The paper mainly focuses on linear encoders based on metallic and dielectric inclusions. Moreover, it is shown that synchronous electromagnetic encoders, able to provide the quasi-absolute position (plus the velocity and direction of motion in some cases), can be implemented. Several prototype examples are reviewed in the paper, including encoders implemented by means of additive process, such as 3D printed and screen-printed encoders.
Highlights
This review paper has been focused on the design and applications of electromagnetic encoders, of interest as position and velocity sensors
Operating at microwaves, electromagnetic encoders are robust against harsh environments, e.g., subjected to pollution, dirtiness, or grease
As compared to magnetic encoder systems, typically based on magnets or inductive elements, the reviewed electromagnetic encoder systems are very simple, since the reader consists merely on a transmission line loaded with a planar resonator, the sensitive element, whereas the encoder is a chain of metallic or dielectric inclusions in a host dielectric substrate
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. A new type of encoder systems operating at microwaves has been reported [15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32] These encoders, designated as electromagnetic (or microwave) encoders, are the subject of this review paper. As the inclusions are in relative motion with regard to the sensitive element of the stator (the resonator), the transmission coefficient of the line at the frequency/ies of the feeding harmonic signal/s is modulated. Several materials and inclusion types for the encoders, as well as different design strategies for the transmission line based stator, have been reported.
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