Features of Capacitive Displacement Sensing That Provide High-Accuracy Measurements with Reduced Manufacturing Precision

The capacitive displacement sensing method based on time grating employs a set of movable induction electrodes suspended with some gap width above a set of fixed excitation electrodes, and signals are obtained through electric field coupling. In this paper, we consider three features of time-grating capacitive displacement sensors that reduce the required manufacturing precision while maintaining high-accuracy measurements. First, the effect of edge roughness of the induction electrodes is suppressed by the filtering effect of the overlapping area integral method. Second, the effect of edge roughness of the excitation electrodes can be suppressed by the smoothing effect of the electric field. Third, the averaging effect of multiple induction electrodes is adopted to reduce the effect of geometric errors in the excitation electrodes. Printed circuit board manufacturing technology with a manufacturing accuracy on the order of 10 μm is selected to fabricate a prototype time-grating capacitive sensor, and a linearity of 0.005% is obtained for a single-period range of 0.8 mm. The measurement accuracy is largely independent of the manufacturing precision owing to the three aforementioned smoothing effects, which is promising for transforming the presently challenging technology of long-range displacement measurements with nanometer-scale accuracy into a conventional technology.