Proximity sensor

• US 5,801,340 A
• Filed: 06/29/1995
• Issued: 09/01/1998
• Est. Priority Date: 06/29/1995
• Status: Expired due to Term

• Current Assignee: Flextronics Automotive Inc
• Original Assignee: Invotronics Manufacturing (Flex, Ltd.)
• Inventors: Peter, Walter H.
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): LOOMIS, PAUL A
• Application Number:
  US08/496,561
• Time in Patent Office: 1,160 Days
• Field of Search: 178/18, 178/19, 178/20, 345/173, 345/174, 341/33, 364/709.1, 364/709.11, 340/562, 340/679, 324/688
• US Class Current: 178/20.04
• CPC Class Codes: E05F 15/46 responsive to changes in electrical capacitance
• CPC Class Codes: E05Y 2900/132 Doors
• CPC Class Codes: E05Y 2900/148 Windows
• CPC Class Codes: G01S 13/04 Systems determining presence of a target based on relative movement of target G01S13/56
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2217/96072 Phase comparison, i.e. where a phase comparator receives at one input the signal directly from the oscillator, at a second input the same signal but delayed, with a delay depending on a sensing capacitance
• CPC Class Codes: H03K 2217/960765 Details of shielding arrangements

Abstract

An improved capacitive sensor for detecting the presence of objects in a sensing region. The sensor is a multilayer structure with alternating layer of condutive and insulating materials. The sensor structure has three electrodes: a touch plate, a guard layer, a ground plane, each of which are separated from each other by insulating layers. The sensor is operated by detection electronic circuitry which function in a either a self excited mode or an externally excited mode. This sensor is capable of detecting objects in a sensing region several feet away from the sensing surface and is particularly suitable for automobile applications, such as detecting potentially jamming objects in power (auto-closing) windows, doors, and the like.

Claims

1. A capacitive sensor for detecting the presence of an object in a sensing region comprising:

a ground plane;

a first insulating layer disposed on said ground plane;

a guard layer disposed on said first insulating layer;

a second insulating layer disposed on said guard layer;

a touch plate disposed on said second insulating layer;

an oscillator means for supplying an excitation signal to said touch plate; and

a driving means for supplying an excitation signal to said guard layer such that the capacitance between said guard layer and said ground plane substantially cancels the capacitance between said touch plate and said ground plane.

2. The sensor as defined in claim 1 wherein said driving means comprises a buffer amplifier which electrically isolates said touch plate from said guard layer.

3. The sensor as defined in claim 1 further comprising means for measuring the change in amplitude of the output voltage from said sensor and wherein the presence of an object in the sensing region is detected using said means for measuring.

4. The sensor as defined in claim 1 further comprising means for measuring the change in amplitude of the output voltage from said sensor and means for measuring the change in phase of the output voltage from said sensor and wherein the presence of an object in the sensing region is detected using said means for measuring the change in amplitude and said means for measuring the change in phase.

5. The sensor as defined in claim 1 wherein said ground plane is at least as large as said guard layer and extends beyond it in all dimensions.

6. The sensor as defined in claim 1 wherein said first insulating layer is at least as large as said guard layer.

7. The sensor as defined in claim 1 wherein said guard layer is substantially the same size as said touch plate.

8. The sensor as defined in claim 1 wherein said touch plate and said guard layer are conducting and have a thickness between 0.1-10 mils.

9. The sensor as defined in claim 1 wherein said oscillator means generates a sinusoidal, square, or ramp waveform with a frequency of 10 kHz-10 MHz.

10. A capacitive sensor for detecting the presence of an object in a sensing region comprising:

a ground plane;

a first insulating layer disposed on said ground plane;

a guard layer disposed on said first insulating layer;

a second insulating layer disposed on said guard layer;

a touch plate disposed on said second insulating layer; and

an inductor in parallel to said sensor, said inductor and said sensor forming an oscillator means to excite said sensor.

11. The sensor as defined in claim 10 further comprising means for measuring the change in amplitude of the output voltage from said sensor and wherein the presence of an object in the sensing region is detected using said means for measuring.

12. The sensor as defined in claim 10 further comprising means for measuring the change in frequency of the output voltage from said sensor and wherein the presence of an object in the sensing region is detected using said means for measuring.

13. The sensor as defined in claim 12 wherein said means measuring the change in frequency of the output voltage from said sensor comprises a microprocessor.

14. The sensor as defined in claim 10 wherein said ground plane is at least as large as said guard layer and extends beyond it in all dimensions.

15. The sensor as defined in claim 10 wherein said first insulating layer is at least as large as said guard layer.

16. The sensor as defined in claim 10 wherein said guard layer is substantially the same size as said touch plate.

17. The sensor as defined in claim 10 wherein said touch plate and said guard layer are conducting and have a thickness between 0.1-10 mils.

18. A method for detecting the presence of an object in a sensing region comprising:

providing a ground plane;

providing a first insulating layer on said ground plane;

providing a guard layer on said first insulating layer;

providing a second insulating layer on said guard layer;

providing a touch plate on said second insulating layer;

exciting said touch plate by an oscillator means;

exciting said guard layer by a driving means such that the capacitance between said guard layer and said ground plane substantially cancels the capacitance between said touch plate and said ground plane.

19. The method as defined in claim 18 further comprising choosing said driving means to be a buffer amplifier that electrically isolates said touch plate from said guard layer.

20. The method as defined in claim 18 further comprising the step of measuring the change in amplitude of the output voltage from said sensor in order to determine the presence of an object in the sensing region.

21. The method as defined in claim 18 further comprising the step of measuring the change in amplitude and phase of the output voltage from said sensor in order to determine the presence of an object in the sensing region.

22. A method for detecting the presence of an object in a sensing region comprising:

providing a ground plane;

providing a first insulating layer on said ground plane;

providing a guard layer on said first insulating layer;

providing a second insulating layer on said guard layer;

providing a touch plate on said second insulating layer;

placing an inductor in parallel to said sensor, and exciting said sensor by an oscillator means formed by said inductor and said sensor.

23. The method as defined in claim 22 further comprising the step of measuring the change in amplitude of the output voltage from said sensor in order to determine the presence of an object in the sensing region.

24. The method as defined in claim 22 further comprising the step of measuring the change in frequency of the output voltage from said sensor in order to determine the presence of an object in the sensing region.

25. The method as defined in claim 24 wherein said step of measuring the change in frequency of the output voltage from said sensor is performed using a microprocessor.