Capacitive position encoder

Claim 2

The encoder of claim 1 wherein the first and second input signals are Asin t and - Asin t, respectively.

Claim 3

The encoder of claim 1 or 2 wherein the input and output areas are copper.

Claim 4

A high resolution rotary capacitive encoder, comprising: a first plate having first and second circular concentric equally spaced conductive input areas formed thereon, wherein the input areas are separated by a gap having a cyclic waveform which corresponds to a square wave; a second plate whose surface is spaced a predetermined distance from the first plate, wherein the plates are rotatable with respect to each other, said second plate including a plurality of 65 ii i GB 2 139 359A 5 conductive output areas Which are arranged in a circle in overlapping relation to the gap wherein each output area corresponds in shape and area to one half of a wavelength of the gap, whereby as the plates rotate with respect to each other the amount of overlap between each output area and the two input areas will vary linearly; means for providing a first periodic input signal to the first input area; means for providing a second periodic input signal to the second input area, wherein the second periodic input signal in the inverse of the first periodic input signal, wherein the input signals will be capacitively coupled to the output areas and wherein each output area will provide a null output when it overlaps the first and second input areas equally.

Claim 5

The encoder of claim 4, wherein the gap wavelength is equal to C P and the output areas 10 are separated by a distance CP/N where N is an integral, wherein each Nth output area is connected together and wherein the number of output areas is equal to an integer multiple of N.

Claim 6

A high resolution capacitance encoder, comprising: a first plate having first and second conductive input areas formed thereon, wherein the input areas are separated by a gap having a cyclic wave form; a second plate whose surface is spaced a predetermined distance from the first plate, said plates being movable with respect to each other, said second plate including a series of conductive output areas formed thereon, wherein the output areas are arranged serially in facing relation to the gap and are spaced from each other by a predetermined amount; wherein the gap and output areas are configured so that the portion of each output area 20 which overlaps each respective input area varies linearly between a minimum and maximum as the plates move with respect to each other and wherein when the portion of any output area overlapping the first input area is at a maximum the portion overlapping the second input area is at a minimum; means for providing a first periodic input signal to the first input area; means for providing a second periodic input signal to the second input area, wherein the second signal is the inverse of the first signal; whereby as the plates move with respect to each other the input signals will be capacitively coupled to the output areas in proportion to the overlap between each output area and the respective input areas, each output area providing a null signal when it overlaps the first and 30 second input areas equally.

Claim 7

The encoder of claim 6 wherein the input areas and output areas are arranged in a circular fashion.

Claim 8

The encoder of claim 6 or 7 wherein the input areas and output areas are copper.

Claim 9

The encoder of claim 6, 7 or 8 wherein the gap is in the shape of a square wave and the 35 output areas are square, wherein the length of each output area is equal to one half of the wavelength of the gap.

Claim 10

The encoder of claim 6, 7, 8 or 9 wherein the waveform has a wavelength of Cp and the output areas are separated by a distance of Cp/N where N is an integer, wherein each Nth output area is connected together, whereby the encoder will provide null outputs corresponding 40 to N different positions of the plates with respect ot each other.

Claim 11

A capactive encoder substantially as hereinbefore described with reference to the accompanying drawings. Printed in the United Kingdom for Her Majesty's Stationery Office, Dd 8818935, 1984, 4235.. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 'I AY, from which copies may be obtained.