# A Miniature Inductive Encoder for Linear Displacement Measurement

## TL;DR

This paper presents a small linear inductive encoder for measuring displacement in tight spaces with high accuracy and resolution.

## Contribution

The novelty lies in the miniaturized design of the encoder with high accuracy and resolution suitable for constrained environments.

## Key findings

- The encoder achieves a measurement accuracy of 12.8 μm within one pitch.
- It offers a resolution of 0.7 μm using a CORDIC algorithm for displacement calculation.
- The compact size (20 mm × 10 mm × 1 mm) allows installation in highly constrained mechanisms.

## Abstract

In order to satisfy the measurement of objects in compact settings, a miniaturized linear inductive encoder with a measurement range of 15 mm is investigated in this paper. The encoder structure integrates a movable part with conductive plates and a stationary part with planar excitation and inductive coils. When a high-frequency alternating current is applied to the excitation coils, a time-varying magnetic field will be generated. Meanwhile, the conductive plates on the movable element will produce an eddy current magnetic field to reduce or boost the magnetic field. As the movable part moves, two-channel amplitude-modulated electrical signals whose amplitudes vary with displacement are obtained. The CORDIC algorithm is utilized to calculate the displacement. The paper describes the structure and working principle of the encoder, presents corresponding finite element simulations of the magnetic field, and introduces a prototype fabricated by PCB technology. Experiments evaluating stability, resolution, and accuracy show that the encoder reaches the measurement accuracy of 12.8 μm within one pitch, and the resolution is 0.7 μm. Importantly, its minimal dimensions (20 mm × 10 mm × 1 mm) enable installation in highly constrained mechanisms.