Capacitive sensor for measuring displacement or position

Claim 2

Scale reading apparatus comprising, two relatively movable parts, respective electrically conductive scalar reading patterns on said parts the relative positions of which patterns determine a reading, said reading patterns being electrically unconnected but at a spacing that provides a capacitive effect between them, electrical supply means and sensing means connected to said patterns to generate signals indicative of said capacitance effect and to detect variations in said capacitive effect with relative movement between the parts, the apparatus further comprising a further electrically conducting scalar pattern arranged on one of said parts to be electrically insulated from said two scalar reading patterns, the further scalar pattern having a pattern pitch corresponding to that of the scalar reading pattern on said one of said parts and being disposed 180* out of phase thereto, means holding said further pattern at a predetermined electrical potential for operation of said further pattern as an electrical screen for the stray capacitances set up between said scalar patterns.

Claim 3

Apparatus according to claim 1 wherein said supply means is in the form of a voltage source and said sensing means is in the form of an evaluating circuit sensitive to voltage amplitude, the voltage source and the evaluating circuit being connected to the respective scalar reading patterns whereby said variations are detected by the evaluating circuit as voltage signals.

Claim 4

Apparatus according to claim 2 wherein said voltage source is a constant-frequency alternating voltage generator and said evaluating circuit is a voltage amplitude demodulation circuit having high input impedance for the measurement of the voltage signal amplitude-modulated by the capacitance change, with relative movement between said parts.

Claim 5

Apparatus according to claim 1 wherein said supply means is in the form of a current source and said sensing means is in the form of an evaluating circuit sensitive to current amplitude, the current source and the evaluating circuit being connected to the respective scalar reading patterns whereby said variations are detected by the evaluating circuit as current signals.

Claim 6

Apparatus according to claim 4 wherein said current source is a constant-frequency generator and said evaluating circuit is a current amplitude demodulation circuit having low input impedance for the measurement of the current signaL amplitude-modulated by the capacitance change with relative movement between said parts.

Claim 7

Apparatus according to claim 1 wherein at least one of said relatively movable parts comprises a base or support substrate on which the screen is disposed between said substrate and said scalar reading pattern on said part.

Claim 8

Apparatus according to claim 1 wherein said scalar patterns are formed as thin vapor-deposited layers on their relatively movable parts and there is an additional thin vapor-deposited electrically insulating layer between said further electrically conducting scalar pattern and the scalar reading pattern of its relatively movable part to insulate said reading and further patterns from each other.

Claim 9

Scale reading apparatus comprising, in combination, two relatively movable parts, respective first layers of electrically conductive material on said parts, said first layers being in the form of respective scalar patterns the relative positions of which patterns determine a reading, said layers being electrically unconnected but at a spacing that provides a capacitive effect between them, electrical supply means and sensing means connected to said first conductive layers to generate signals indicative of said capacitance effect and to detect variations in said capacitive effect with relative movement between the parts, the apparatus further comprising an electrically insulating layer upon said first layer of at least one of said parts and a further electrically conductive layer disposed upon said insulating layer to be electrically insulated but close to the scalar pattern layer of said one part, and means to hold said further conductive layer at a predetermined electrical potential whereby said further layer acts as an electrical screen for the stray capacitances set up between said scalar patterns of the respective parts.

Claim 10

Scale reading apparatus comprising, in combination, two relatively movable parts, respective first layers of electrically conductive material on said parts, said first layers being in the form of respective scalar patterns the relative positions of which patterns determine a reading, said layers being electrically unconnected but at a spacing that provides a capacitive effect between them, electrical supply means and sensing means connected to said first conductive layers to generate signals indicative of said capacitance effect and to detect variations in said capacitive effect with relative movement between the parts, the apparatus further comprising an electrically insulating layer upon said first layer of at least one of said parts and a further electrically conductive layer disposed upon said insulating layer to be electrically insulated but close to the scalar pattern layer of said one part, and means to hold said further conductive layer at a predetermined electrical potential whereby said further layer acts as an electrical screen for the stray capacitances set up between said scalar patterns of the respective parts.

Claim 11

Apparatus according to claim 8 wherein each of the relatively movable parts is provided with an aforesaid insulating layer and further conductive layer, each said further conductive layer being in the form of a scalar pattern having the same pitch as the scalar reading pattern of its associated relatively movable part but being positioned 180* out of phase thereto.

Claim 12

Apparatus according to claim 8 wherein said screen is also formed as a scalar pattern.

Claim 13

Apparatus according to claim 10 wherein said screen pattern has a pitch corresponding to that of said scalar reading pattern on the associated relatively movable part and is disposed 180* out of phase thereto.

Claim 14

Apparatus according to claim 11 wherein the screen is formed in the same plane as said scalar reading pattern and the elements of the respective patterns on said part are interposed in alternation to each other but are spaced from each other.