A Splicing Technique and Structure for Long-Range Absolute-Type Capacitive Displacement Sensors

Abstract

This study presents a novel capacitive sensor and a new technique for splicing multiple sensor segments to extend measurement ranges. Single segments adopting a vernier structure were used for absolute measurements with a range of 600 mm. Two independent groups of induction electrodes, with fixed distances between two groups, were included to smooth the transition of signals near the joint and eliminate splicing errors introduced by installation and manufacturing flaws. The passive design of the mover simultaneously reduced limitations caused by increased cable length, achieved using several groups of emission electrodes (EMs) and reception electrodes (REs). The corresponding induction signal provided both displacement measurements and position determinations. A single-segment prototype of the proposed sensor was manufactured using a PCB process, in which each segment achieved an absolute-type measurement accuracy of ± 3 μm. A series of experiments were used to validate the proposed technique, applied to two-segment rulers. Results revealed that the measurement precision, peak value of repeatability, and 3-sigma value were ± 3 μm, less than 0.6 μm, and approximately 1.62 μm, respectively, over a measurement range expanded to 1140 mm after splicing. Thus, absolute-type displacement measurements are viable over the entire range.