Position sensing with variable capacitance transducers
AssigneeGenetic Microsystems, Inc.
InventorsJean I. Montagu, Peter Honkanen, Nathan K. Weiner
Life of this patent
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Abstract
For enabling precise operation of an oscillating device, such as a galvanometric optical scanner, a capacitive position transducer is provided with strategically located internal capacitive fiducial features that interact with the armature of the transducer beyond the central range of excursion of the transducer, typically beyond the normal operating range of the device. Electric pulses obtained at instants of interaction with the fiducials enable determination of position drift caused e.g. by change in environmental conditions. The pulses can be detected by simple circuits to produce recalibration of the amplitude and null position of the instrument on an automatic or elective basis.
Claims39
A capacitive position detector comprising a fixed structure comprising an energizing plate and opposed thereto, separated by a gap, at least one sensing plate, and an armature movable in the gap dependently with the motion of an element the position of which is to be sensed, the armature constructed to alter the capacitive coupling between the energizing and sensing plates dependently with its change in position, and at least one capacitive fiducial feature located in a known position substantially opposed to the energizing plate, the position being disposed at a predetermined point along the path of travel of the armature, the fiducial feature so arranged to produce a discrete signal at the time when the armature reaches and interacts with it, thereby to signal a precise location of the armature relative to the fixed structure.
The position detector of any of the preceding claims in which the fiducial feature comprises a discrete capacitor fiducial plate, arranged to produce a position signal which is independent of signal derived from said sensing plate.
The position detector of claim 14 in which the sensing plates and the fiducial plate are supported on isotropic material in the manner that the angular location of the fiducial plate and the sensing plates do not change with respect to each other with change in ambient conditions.
A position transducer comprising a fixed and a movable structure constructed to provide to a measurement circuit an electrical signal corresponding to a position of the movable structure with respect to the fixed structure;
- said position transducer including at least one internal fiducial calibration feature causing an electrical perturbation signal at a selected position of the movable structure with respect to the fixed structure.
A method of determining a center position of a transducer comprising the acts of:
- providing a fixed and a movable structure constructed to provide to a measurement circuit an electrical signal corresponding to a position of said movable structure relative to said fixed structure;
- said fixed structure including two internal fiducial calibration features causing, with respect to said movable structure, electrical perturbation signals received by the measurement circuit;
- displacing said movable structure;
- determining position signals based on said electrical signal corresponding to a position of said movable structure relative to said fixed structure;
- detecting said electrical perturbation signals caused by said two internal fiducial calibration features;
- and
- defining the center or null position, the position being defined with reference to positions of said two internal fiducial features.
A method of calibrating a position transducer comprising the acts of:
- providing a fixed and a movable structure constructed to provide to a measurement circuit an electrical signal corresponding to a position of said movable structure;
- said position transducer including at least one internal fiducial calibration feature causing an electrical perturbation signal at a selected position of the movable structure with respect to the fixed structure;
- displacing said movable structure;
- determining position signals based on said electrical signal corresponding to a position of said movable structure relative to said fixed structure;
- detecting said electrical perturbation signal caused by said at least one internal fiducial calibration feature;
- and
- calibrating said position transducer.
Dependencies are inferred from the claim text.