A Small-Size Linear Encoder Based on Eddy Current Effect

In this paper, a small-size eddy current linear displacement encoder is introduced for the purpose of achieving linear displacement measurements in confined spaces. The encoder is made up of two parts: a movable part featuring metallic reflective conductors and a stationary part consisting of spiral coils, which include both excitation and induction coils. The reflected magnetic field generated by the metal reflecting conductor on the movable part is produced by passing a high frequency current through the excitation coils. The displacement will be calculated through the change of the output voltage signal in the induction coils, as the movement of the metal reflecting conductors. This article describes the structure and principle of the encoder. The feasibility of the encoder was analyzed through Finite Element Method simulation, and a prototype of encoder is fabricated by PCB technology. The encoder has been experimentally verified to be capable of achieving an accuracy of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{17.8 \mu \mathrm{m}}$</tex> within a range of 2 mm (one pitch).