Capacitive transducer

• US 4,177,421 A
• Filed: 02/27/1978
• Issued: 12/04/1979
• Est. Priority Date: 02/27/1978
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Thornburg, David D.
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US05/881,287
• Time in Patent Office: 645 Days
• Field of Search: 324/61 R, 324/61 P, 340/166 R, 340/200, 340/324 M, 340/365 C, 200/DIG. 1, 200/DIG. 2, 307/116
• US Class Current: 324/725
• CPC Class Codes: G01D 5/2415 adapted for encoders
• CPC Class Codes: G06F 3/0442 using active external devices, e.g. active pens, for transmitting changes in electrical potential to be received by the digitiser
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer

Abstract

A capacitive transducer comprises two plate electrodes positioned in juxtaposed relationship on one surface of a dielectric substrate and an array of segmented electrodes provided on the opposite side of the substrate. Capacitive coupling is achieved between the segmented electrode array and the two plate electrodes. The geometrics of the transducer are such that increasing capacitive coupling is obtained along the main axis of the transducer. An AC signal supplied to one of the plate electrodes of the transducer can be attenuated by physically touching the segmented electrode array. Attenuation can be varied by moving such physical contact along the main axis of the transducer. One or more transducer can be used in a coordinate arrangement to provide an X-Y position indicating device.

Claims

1. A capacitive transducer comprising at least two plate electrodes aligned along a main axis in spaced juxtaposed relation, a substantially parallel array of segmented electrodes each of smaller dimensional width than said plate electrodes and aligned in a direction transverse to said main axis overly said plate electrodes but separated therefrom by dielectric means, said segmented electrodes capacitively coupled to said plate electrodes in an increasing capacitive and monotonic manner from one end of the transducer to the other along said main axis.

2. The transducer of claim 1 wherein said plate electrodes are of triangular shaped configuration.

3. The transducer of claim 2 wherein said segmented electrode array has the configuration of said plate electrodes.

4. The transducer of claim 1 wherein one of said plate electrodes is an input terminal, a varying signal source connected to said input terminal to provide an input signal, means engageable with one or more of said segment electrodes and movable thereacross to shunt a portion of said input signal.

5. The transducer of claim 4 wherein a detection means connected to the other said plate electrodes, said attenuated input signal being detected by said detection means.

6. The transducer of claim 5 wherein said detection means is a load resistor.

7. The transducer of claim 1 wherein said plate electrodes are provided with a taper along one edge thereof.

8. The transducer of claim 7 wherein said taper is parabolic.

9. The transducer of claim 7 wherein said taper is a step function.

10. The transducer of claim 7 wherein said taper is linear and is disposed at an acute angle relative to said main axis.

11. The transducer of claim 1 wherein the segments comprising said electrode array are elongated stripes having narrow and identical widths.

12. The transducer of claim 11 wherein the width of said segments is greater than the distance of separation of said segments.

13. The transducer of claim 1 wherein the segments comprising said electrode array are elongated stripes having narrow widths, the widths of said segments of increasing magnitude from one end of the array to the other.

14. The transducer of claim 1 wherein the thickness of said dielectric means is of increasiong magnitude from one end of the transducer to the other along said main axis.

15. The transducer as claimed in claim 1 for use as an X-Y position indicator, at least two of said transducers being employed, the main axis of one of said transducers parallel to the X axis of a coordinate system and the other of said transducers parallel to the Y axis of the same coordinate system.

16. A capacitive transducer for varying the amplitude of an input signal comprising a pair of tapered conductive plate electrodes in a juxtaposed relation, a signal source connected to one of said plate electrodes to provide an input signal, a detection means connected to the other of said plate electrodes, an array of segmented conductive electrodes each of smaller dimensional width than said plate electrodes and in substantially parallel alignment positioned over both of said plates and separated therefrom by a dielectric layer, each of said segment electrodes being capacitively coupled to both of said plate.

17. The transducer as claimed in claim 16 for use as an X-Y position indicator, at least two of said transducers being employed, the main axis of one of said transducers parallel to the X axis of a coordinate system and the other of said transducers parallel to the Y axis of the same coordinate systems.

18. The transducers of claim 17 wherein a signal source for each of said at least two transducers has a different frequency.

19. The transducers of claim 17 wherein each of said at least two transducers have a triangular configuration.

20. The transducers of claim 17 wherein four of said transducers are used as said X-Y position indicator, the main axis of pairs of oppositely disposed transducers being, respectively, parallel to the X of Y axis of said coordinate system.