High precision, high resolution and absolute position are the key characteristics for linear displacement measurement.This paper proposes an absolute linear displacement sensor which is suitable for harsh environment. The sensor has a primary coil and a secondary coil.The primary coil is composed of two arrays of spiral coils which are arranged orthogonally.The primary coil is supplied with 4 kHz alternating current to generate two arrays of magnetic field that travel orthogonally. Meanwhile, the spatial periods of the magnetic fields are N and (N+1). The secondary coil consists of two sets of spiral coils, and every set of spiral coils induce only one array of magnetic field.With the motion of the secondary coil, two roads of signals are induced. According to the phase comparison, the absolute position is determined.The structure and working principle of the sensor is proposed. The sensor model is simulated by finite element analysis software. A sensor prototype is fabricated to be verified by experiment. The experimental results show that the measurement range is 61.5mm with the linearity 0.54%.
The precision measurement of two-dimensional displacements is needed in many domains, such as precision fabrication and detection. This paper presents a novel inductive position sensor with the capability of measuring displacements in x- and y- directions simultaneously. The sensor consists of two parts: a ferromagnetic plate with primary windings which are composed of four layers of planar coils, a ferromagnetic plate with secondary windings which are composed of four layers of planar coils. Primary windings are supplied with two orthogonal 20KHz alternating current to generate traveling wave magnetic field along x- and y- directions separately. Secondary windings output two signals whose phases are proportional to linear displacements of X and Y directions respectively. The structure and working principles of the sensor are proposed. Meanwhile, a sensor model is simulated to verify the feasibility of the working principle and a sensor prototype is fabricated for physical experiment. According to the analysis of experiment results, the measurement range is 140mm×140mm, and the maximum linearity in one pitch is 1%. The performance of sensor may be improved by optimizing the layout of primary and secondary windings and signal processing circuit.