A miniaturized capacitive absolute angular positioning sensor based on a dual two-stage secondary re-modulation Scheme with time-division multiplexing

Abstract

This paper proposes a new capacitive absolute angular positioning sensor based on time grating that adopts two capacitor arrays, each employing a two-stage secondary re-modulation scheme, where the output signals from the first-stage induction electrodes are applied as the excitation signals to the second-stage excitation electrodes to generate second-stage induction electrode outputs with respective periodicities of N+1 and N+2. This enables the capture of high precision absolute angular measurements according the principle of Vernier calipers, where the N+2 period output signal is employed for obtaining fine measurements, while the phase difference between the output signals is employed for absolute positioning. Sensor miniaturization is facilitated by sharing the outputs of the first-stage capacitor arrays with a single second-stage capacitor array using time division multiplexing, which eliminates the need for a second second-stage capacitor array by alternately applying the excitation signals to the two sets of first-stage electrodes. Measurement performance is evaluated experimentally by testing a prototype sensor fabricated by printed circuit board processing with an outer diameter of 83 mm and an inner diameter of 24 mm. The experimental results demonstrate a peak-to-peak measurement error of about 30″ over the 360° measurement range.