WO2010043391A4

WO2010043391A4 - Capacitive null-mode displacement measurement technology

Info

Publication number: WO2010043391A4
Application number: PCT/EP2009/007386
Authority: WO
Inventors: Jose A Carrasco; Francisco Garcia De Quiros
Original assignee: Embedded Instruments And Systems Sl
Priority date: 2008-10-14
Filing date: 2009-01-12
Publication date: 2010-12-23
Also published as: NL1036070C2; WO2010043391A2; WO2010043391A3

Abstract

Technique for sensing the absolute position of an object, in linear or rotary displacement, relative to a stationary object or the speed of displacement, is formed, in one embodiment, by two stationary elements and a moving element able to have a linear or rotary displacement when located between the stationary elements. The stationary elements have metallic coatings on their confronted sides to form eight capacitances whose value change when the moving element is displaced between them. Four pairs of sinusoidal waveforms are injected in the metallic tracks of one stationary element by the processing electronics whose amplitude is controlled to cancel each other in the metallic tracks of the confronted stationary element. The generation of the four pairs of sinusoidal waveforms occurs in a close loop that generates coarse and fine information of the position of the moving object. Such information is offered to a user as analog or digital.

Claims

AMENDED CLAIMS received by the International Bureau on 12 October 2010 (12.10.2010)What is claimed as new and asked to be protected is:

1. A capacitive null-mode displacement measurement technology for absolute sensing and control of angular displacements or velocities of objects formed by two circular or ring-shaped opposed static plates, made of an insulating material, defining a space in between where a moving plate is positioned attached to the object to control, one of the static opposed plates presenting multiple concentric metallic coatings or tracks on the confronted side and the other presenting concentric ring-shaped metallic coatings or tracks right confronted to the multiple concentric metallic coatings on the other plate to form and add up the capacitance between the multiple coatings and the rihg-shaped metallic coatings or tracks, the total capacitance of which varies with the position of the moving plate, the moving plate formed by a dielectric material with holes that cover or uncover some of the multiple concentric metallic coatings or tracks, the plates are arranged so as a set of injected voltage signals on the multiple concentric metallic coatings or tracks are added or subtracted on the ring-shaped metallic coatings or tracks directly confronted to the formers,

2. A capacitive null-mode displacement measurement technology according to claim 1, characterised by presenting one, two or more concentric sets of multiple metallic coatings on one of the static plates, the number of elements on each set multiple of four, confronted each tα a concentric ring-shaped metallic coating or track on the other static plate, the number of sets defining the accuracy in which the displacement or velocity is measured. Where one of the concentric multiple sets of metallic coatings has a number of metallic coatings or tracks bigger than four then they are interconnected in four sets in a symmetric structure that connects each metallic coating or track with the one at four positions in a row at each side of it.

3. A capacitive null-mode displacement measurement technology according to claim 1 and 2, wherein a coarse angular displacement measurement is performed by the capacitance formed by one inner set of concentric multiple metallic coatings or tracks, on one of the static plates, and its confronted ring-shaped metallic coating or track, on the second static plate, and a fine angular displacement measurement is performed by another outer set of concentric multiple metallic coatings or tracks, on the former static plate, and its confronted ring-shaped metallic coating or track, on the second, whose variation in the added capacitance with the moving object being produced by two sets of holes in the moving plate directly in between the set of multiple metallic coatings or tracks and the ring-shaped metallic coatings of the coarse measurement and the fine measurement.

4. A capacitive null-mode displacement measurement technology that makes equal to 0 Volts the voltage on each concentric ring-shaped metallic coating or track of one of the static plates by injecting appropriate AC voltages in each set of the multiple metallic coatings or tracks on the confronted static plate with independence of the position of the moving plate, the amplitude of the AC signals injected being proportional to the position of the moving plate.

5. A capacitive null-mode displacement measurement technology according to claim 4, that implements an electronic circuit that by means of negative feedback continuously generates the amplitudes of four AC voltages to be injected in each set of four concentric multiple metallic coatings or tracks on one static plate and measures and amplifies the voltage at each ring-shaped metal coating of the confronted static plate to exactly null it either if the moving plate is moving or stationary. The negative feedback of the circuit varies the amplitude of an AC generator and diverts it in a way that produces four AC signals whose values are a multiple of the maximum gain produced by the AC generator, its inverse, the subtract of the maximum gain and the previous multiple of the maximum gain and its inverse. The four signals naturally result proportional to the angular position of the moving plate.

6. A capacitive null-mode displacement measurement technology according to claim 4, that may implement an electronic circuitry that offers two digital outputs: one directly proportional to the amplitude of the AC signals multiple of the maximum gain produced by the AC generator and the other the subtract of the maximum gain and the multiple of the maximum gain. The analog to digital conversion made by any well-known conversion technique.

7. A capacitive null-mode displacement measurement technology wherein the static plates are produced from an insulating material and the metallic coatings or tracks, on top of them, from a conductive material and connected among them with conductive tracks.

8. A capacitive null-mode displacement measurement technology wherein the electronic circuitry needed to provide the output is implemented over one, or both, of the static plates following present state of the art printed circuit board technology.

9. A capacitive null-mode displacement measurement technology according to claim 1, wherein the moving plate is produced from a dielectric material with a high dielectric constant and its holes are directly above one of each four in a row coatings or tracks of the multiple concentric metallic coatings or tracks on one of the static plates.

10. A capacitive null-mode displacement measurement technology that may be used to sense linear displacements or velocities by implementing the embodiment in a linear form, that is to say by implementing the plates in rectangular shape and the metallic coatings on top of them also in rectangular shape as if the circular structure of claim 1 is stretched to a rectangular linear shape. The multiple metallic coatings over one of the confronted plates are confronted to a metallic rectangular strip over the other static plate. The moving plate is rectangular and with the same size of the static plates and has rectangular holes over one of each four of the multiple metallic plates. The electronic circuit is unchanged and may be implemented over one, or both, static plates.