3D-Printed All-Dielectric Electromagnetic Encoders with Synchronous Reading for Measuring Displacements and Velocities

Abstract

In this paper, 3D-printed electromagnetic (or microwave) encoders with synchronous reading based on permittivity contrast, and devoted to the measurement of displacements and velocities, are reported for the first time. The considered encoders are based on two chains of linearly shaped apertures made on a 3D-printed high-permittivity dielectric material. One such aperture chain contains the identification (ID) code, whereas the other chain provides the clock signal. Synchronous reading is necessary in order to determine the absolute position if the velocity between the encoder and the sensitive part of the reader is not constant. Such absolute position can be determined as long as the whole encoder is encoded with the so-called de Bruijn sequence. For encoder reading, a splitter/combiner structure with each branch loaded with a series gap and a slot resonator (each one tuned to a different frequency) is considered. Such a structure is able to detect the presence of the apertures when the encoder is displaced, at short distance, over the slots. Thus, by injecting two harmonic signals, conveniently tuned, at the input port of the splitter/combiner structure, two amplitude modulated (AM) signals are generated by tag motion at the output port of the sensitive part of the reader. One of the AM envelope functions provides the absolute position, whereas the other one provides the clock signal and the velocity of the encoder. These synchronous 3D-printed all-dielectric encoders based on permittivity contrast are a good alternative to microwave encoders based on metallic inclusions in those applications where low cost as well as major robustness against mechanical wearing and aging effects are the main concerns.

Position Sensors for Industrial Applications Based on Electromagnetic Encoders

“…The working principle of electromagnetic encoders is amplitude modulation (AM) of a harmonic signal injected to the stator, and caused by encoder motion [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. Figure 1 depicts a sketch of this working principle, where (without loss of generality) the encoder consists of a single (linear) chain of linear inclusions.…”

“…In applications where high accuracy is required, the solution is the encoder system reported in [ 25 ], where the dielectric inclusions have a shape similar to the one of the linear strips of the encoders of the previous subsection. In [ 25 ], the reported encoders are incremental, whereas the absolute position encoder counterparts are reported in [ 27 ]. Let us review these encoders next.…”

“…However, for that purpose, the reader must be modified, and equipped with, at least, two resonant elements (slot resonators). This new reader and absolute encoder based on apertures are depicted in Figure 18 [ 27 ]. Actually, the encoder was 3D-printed using the RS Pro MT-copper as filament, whereas the reader was implemented on the substrate RO4003C (with dimensions, dielectric constant and loss tangent mentioned before).…”

“… 3D-printed quasi-absolute all-dielectric permittivity contrast position encoder and reader based on a pair of slot resonators [ 27 ]. …”

“… Measured envelope functions for the clock and ID code signals tuned to f 0 l = 3.155 GHz and f 0 u = 4.229 GHz [ 27 ]. …”