A Novel Eddy Current Sensor for Displacement Measurement With High Accuracy and Long Range

To enlarge the measurement range of traditional eddy current displacement sensors, a novel eddy current linear sensor for displacement measurement with high accuracy and long range is proposed in this article. The sensor consists of a stationary component with metal reflection conductors and a movable component with spiral coils. The metal reflection conductors below the movable component will generate an eddy current and radiate an eddy current magnetic field after the high-frequency alternating excitation signal is applied to field spiral coils. The inductive electromotive forces (EMFs) will be generated in inductive spiral coils. The measurement of displacement relies on the inductive EMFs variation of inductive spiral coils caused by the change of coupling areas between the spiral coils and the metal reflection conductors. The absolute positioning is realized by the combination of a coarse measurement channel and a fine measurement channel. The structure and measurement principle are described in detail. A sensor prototype is fabricated by printed circuit board (PCB) technology, and the experiments are carried out. Based on the experimental results, some error sources are analyzed and the sensor is optimized. The experimental results show that the sensor can achieve absolute positioning, and the worst-case error is 6.75 $\mu \text{m}$ within the measurement range of 500 mm.

I. Introduction

Measurement of wide-range linear displacement with nanometer resolution and micrometer accuracy is vital for various fields, such as precision manufacturing, aerospace industry, and military application [1], [2], [3], [4]. Unlike incremental sensors, absolute sensors can measure the absolute position of a target without calibration and more than 60% of linear displacement sensors currently belong to the absolute types [5], [6], [7], [8]. The main evaluation performance criteria of displacement sensors used are: non-linearity, resolution, sensitivity, compactness, long-term stability, and so on [2], and [9].