Position sensing device and method using self-capacitance

Abstract

The invention provides a position sensing device and method using self-capacitance. A capacitive position sensing system has a pickup electrode, a shield electrode partially enclosing the pickup electrode, and an essentially grounded relatively movable target near the pickup electrodes; a capacitance-to-digital converter, and switching means for connecting each electrode in turn to the converter input or to ground. Aiming at different switch arrangement, the input self-capacitance of the converter is measured, mutual capacitance between the pickup electrode and the target is calculated according to the measurement, and the position of the target is obtained according to the mutual capacitance. The mutual capacitance between electrodes can be obtained through calculation according to the measurement. Perferably, a capacitive position sensing device uses an incremental position sensing device's scale as a target in order to detect the position through the movement of the scale, thereby enabling an absolute position determination over a range larger than the incremental sensor's pitch.

Description

[0001] Cross References to Related Applications [0002] This application claims priority to US Provisional Patent Application No. 61 / 968,456, filed March 21, 2014, the entire disclosure of which is incorporated herein by reference. technical field [0003] The present invention relates to capacitive position sensing devices and methods based on the measurement of self-capacitance of electrodes. Background technique [0004] Existing capacitive position sensors directly measure the mutual capacitance between relatively movable electrodes to avoid or at least reduce the influence of parasitic capacitance. ASICs (Application Specific Integrated Circuits) have been the only way to implement such sensors, but only some applications (such as digital calipers and spirit levels) have a market large enough to bear the high R&D costs of ASICs. [0005] More recently, mass-produced microcontrollers have emerged that integrate capacitive touch sensing electronics. They can also be us...

AI Technical Summary

Problems solved by technology

[0009] Finally, a common drawback of capacitive position sensors is that it is difficult to monitor contamination (which in most cases can only be detected when the measured electrofusion or its changes exceed a certain threshold)

The warning will be too late as the sensor will most likely become unreliable long before the threshold is reached

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