Planar Two-Dimensional Capacitive Displacement Sensor Based on Time Grating

Efforts to meet the demand for planar 2-D displacement measurement systems are limited by the difficulties of manufacturing 2-D diffraction gratings with high precision over a large area. The present work addresses this issue by capitalizing on the high-precision of 1-D capacitive displacement sensors based on time-grating to develop a planar 2-D capacitive displacement sensor technology composed of a large-area array of excitation electrodes positioned on a fixed ruler and a small-area array of induction electrodes assembled on a coplanar moving ruler that travels over the fixed ruler at a fixed separation gap. First, the individual traveling wave signals of the induction electrodes on the moving ruler are analyzed theoretically to develop a method for decoupling information pertaining to the separate displacements in the x- and y-directions. Then, the feasibility of the proposed decoupling method is verified by simulations based on a 3-D electric field model. Finally, the proposed measurement technology is validated experimentally based on tests conducted using a prototype sensor manufactured using standard printed circuit board technology. The experimental results demonstrate that the prototype sensor achieves measurement errors of +/- 8.2 mu m and +/- 6.8 mu m in the x- and y-directions, respectively, over the full 200 mm x 200 mm measurement range of the sensor.