Novel capacitive displacement sensor based on interlocking stator electrodes with sequential commutating excitation

• We mark all the stator electrode units with sequentially opposite phase.
• We obtain quasi sine/cosine displacement incremental signals through double sensing channels.
• We balance the double sensing channels in a wide range of air gap size.
• We normalize the outputs of the double sensing channels in real-time.
• We achieve a continuous measurement uncertainty of 0.0017 mm through a PCB prototype.

A novel capacitive displacement sensor is proposed. The stator consists of a pair of interlocking comb-type electrodes, driven by two consistent high frequency voltage sources with opposite phase. The mover consists of double sensing channels with electrical orthogonal relationship. Through capacitive coupling, a relative displacement between the mover and the stator is converted to quasi sine/cosine signals, featured with direction identification and instantaneous displacement interpolation. Theoretical analysis indicates that the physical resolution of the studied sensor is the same as the electrode unit's width. And also, the interchannel's amplitude ratio and phase difference keep stable in a wide range of air gap size. Hence the performance of displacement detection can be enhanced by amplitude normalization and interpolation. Using a Printed Circuit Board (PCB) fabricated prototype, the proposed scheme was experimentally tested. Typical coupling statuses were captured. Main sensing characteristics and performance were investigated, such as the responding of air gap variation, the displacement sensitivity, and the measurement uncertainty.

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