Capacitive position sensor

• US 6,535,200 B2
• Filed: 08/27/2001
• Issued: 03/18/2003
• Est. Priority Date: 01/25/1999
• Status: Expired due to Term

• Current Assignee: Neodrón Limited (Atlantic IP Services Limited)
• Original Assignee: Harald Philipp
• Inventors: Philipp, Harald
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): Eisen, Alexander
• Application Number:
  US09/940,006
• Publication Number:
  US 20020030666A1
• Time in Patent Office: 568 Days
• Field of Search: 178/18-1-, 178/19-1-, 245/168-172, 245/173-179
• US Class Current: 345/168
• CPC Class Codes: G06F 3/0213 Arrangements providing an integrated pointing device in a keyboard, e.g. trackball, mini-joystick for pointing devices integrated in a laptop computer G06F1/169; joysticks G05G9/047; constructional details of pointing devices G06F3/033
• CPC Class Codes: G06F 3/03547 Touch pads, in which fingers can move on a surface
• CPC Class Codes: G06F 3/041 Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes

Abstract

A multi-electrode capacitive position sensor functions as part of a computer pointing device that can be integrated with the computer'"'"'s keyboard and that employs ratiometric capacitive sensing techniques. This approach allows a computer user to move a cursor about on a display by skimming his or her fingers over the keyboard without actually depressing any of the keys. The preferred sensing arrangement comprises a circuit for first charging a resistive layer disposed on an active portion of the keyboard and then discharging the layer by simultaneously connecting each of several spaced-apart electrodes to respective inputs of a multi-channel charge detection circuit. For a one-dimensional pointing device, two or more charge transferring switches and electrodes are required, with two being the preferred number. For a two-dimensional pointing device, three or more charge transferring switches and electrodes are required, with four being a preferred number.

Claims

1. A capacitive sensor for sensing a position of an object adjacent a sensing region comprising a portion of a resistive layer having a sheet resistivity of at least ten Ohms per square, the sensor comprising:

a selected number, greater than one, of electrodes contacting the resistive layer and spaced apart about a periphery of the sensing region so that none of the electrodes extend within the sensing region;

the selected number of charge detectors, each charge detector respectively associated with one of the electrodes;

means for transferring electrical charge from a voltage source to at least one of the electrodes so as to charge the resistive layer to a selected voltage; and

the selected number of charge transferring switches, each of the charge transferring switches respectively associated with one of the electrodes, each of the charge transferring switches having a closed state in which it electrically connects the electrode associated therewith to a respective charge detector, each of the charge transferring switches having an open state in which it does not connect the electrode associated therewith to the respective charge detector associated therewith, and wherein each of the charge detectors has a respective output.

2. The sensor of claim 1 wherein the sensing region comprises an active typing portion of a computer keyboard and wherein the sensor supplies an output representative of the position of the object to a computer pointing means, the computer pointing means determining a position of a cursor on a display responsive to the position of the object.

3. A capacitive sensor for measuring a position of an object adjacent a sensing portion of a homogeneous resistive layer, the presence of the object changing an electric capacitance to a ground, the sensor comprising:

a selected number, greater than one, of electrodes contacting the resistive layer and spaced apart around a periphery of the sensing portion so that none of the electrodes extend within the sensing portion;

the selected number of charge detectors, each of the charge detectors respectively associated with one of the electrodes;

means for selectively connecting at least one of the electrodes to a voltage source;

the selected number of charge transferring switches, each having only an open state and a closed state, each charge transferring switch, when in its closed state, respectively electrically connecting the electrode associated therewith to the charge detector associated therewith, each charge transferring switch, when in its open state, respectively electrically disconnecting the electrode associated therewith from the charge detector associated therewith; and

means for closing all the charge transferring switches simultaneously.

4. The sensor of claim 3 further comprising multiplexing means having a separate input from each of the charge detectors, the multiplexing means having an output for sequentially supplying respective values representative of each of the inputs to a calculational means.

5. The sensor of claim 4 wherein the calculational means comprises means for calculating the position of the object from ratios of ones of the values representative of the inputs.

6. The sensor of claim 3 wherein the means for connecting the voltage source to the at least one of the electrodes comprises a charging switch having an open state and a closed state, the charging switch connecting the at least one of the electrodes to the voltage source when in the closed state, the charging switch disconnecting the at least one of the electrodes from the voltage source when in the open state.

7. The sensor of claim 6 further comprising the selected number of charging switches, each of the charging switches respectively connected to a separate one of the electrodes.

8. A method of measuring a position of an object adjacent a sensing portion of a homogeneous resistive sensing layer having a sheet resistivity of at least ten Ohms per square and no more than one million Ohms per square, the layer having a selected number of electrodes, greater than one, disposed thereupon about a periphery of the sensing portion so that none of the electrodes extends within the sensing portion, each of the electrodes respectively associated with one of the selected number of charge transferring switches, each of the charge transferring switches having exactly two states, one of the states being a closed state wherein it electrically connects the electrode associated therewith to a respective charge detector, the other state of each of the charge transferring switches being an open state wherein it does not connect the electrode associated therewith to the respective charge detector, the method comprising the steps of:

a) charging a layer of resistive material by connecting a voltage source to at least one of the electrodes;

b) simultaneously closing all the charge transferring switches;

c) reading, from each of the charge detectors, a respective output representative of an associated value of a capacitance to an electric ground; and

d) calculating, from the selected number of capacitance values, the position of the object.

9. The method of claim 8 wherein step d) comprises calculating the position from ratios of the capacitance values.

10. The method of claim 8 wherein each of the charge detectors is separately connected to a respective input to an analog multiplexer and wherein step c) comprises supplying, from the multiplexer to a microprocessor, a sequence of values respectively representative of the inputs.

11. The method of claim 8 wherein step a) is carried out by closing a charging switch electrically connected between the voltage source and the at least one of the electrodes, the method further comprising steps intermediate steps a) and b) of:

a1) holding the charging switch in its closed position for a first selected interval;

a2) opening the charging switch for a second selected interval and thereby disconnecting the at least one of the electrodes from the voltage source.

12. The method of claim 8 comprising an additional step after step d) of:

e) using the position of the object to determine a position of a cursor on a computer display.

13. In a computer apparatus comprising a keyboard having an active typing area comprising a plurality of keys, each of the plurality of keys comprising a respective moveable portion moveable along a line perpendicular to a fixed support between an uppermost position and a lowermost position, each of the keys providing a respective output when the moveable portion of the key is at the respective lowermost position, an improvement comprising a capacitive means for supplying the computer apparatus an input representative of a position of an object above a selected portion of the active typing area when the moveable portions of all of the keys are in their respective uppermost positions, the capacitive means comprising a selected number of electrodes disposed on a resistive layer parallel to the fixed support and disposed below the uppermost position, the selected number of electrodes spaced out along the periphery of the selected portion so that none of the electrodes extends thereinto.

14. The apparatus of claim 13 wherein the resistive layer has a sheet resistivity greater than ten Ohms per square and less than one million Ohms per square.

15. The apparatus of claim 13 wherein the capacitive means comprises:

at least one charging switch having an open state and a dosed state, the at least one charging switch connecting a respective at least one of the electrodes to a voltage source when in the closed state, the at least one charging switch disconnecting the respective one of the electrodes from the voltage source when in the open state;

the selected number of charge transferring switches, each having an open state and a closed state, each charge transferring switch, when in its closed state, respectively electrically connecting the electrode associated therewith to a respective charge detector, each charge transferring switch, when in its open state, respectively electrically disconnecting the electrode associated therewith from the respective charge detector; and

means for closing all of the charge transferring switches simultaneously.

16. The apparatus of claim 13 wherein each of the electrodes is separately electrically connected to a respective charge detector having a respective output and wherein the capacitive means further comprises a calculation means for calculating the position of the object from a ratio of the outputs.

17. In a pointing device connected to a computer, wherein a position of an object is detected by electrical capacitance measurement means having an output representative of a capacitance to an electrical ground, wherein a cursor on a display operatively connected to the computer moves responsive to a change in the detected position of the object, and wherein a keyboard operatively connected to the computer comprises an active typing area comprising a first predetermined number of keys, an improvement comprising:

a second predetermined number, greater than one, of electrodes spaced apart upon a homogeneous resistive layer disposed in a planar configuration beneath the tops of those keys within a selected portion of the active typing area so that none of the electrodes extends into the selected portion; and

wherein the capacitance measurement means comprises;

a voltage source;

means connecting the voltage source to at least one of the electrodes; and

the second predetermined number of charge transferring switches, each charge transferring switch having a closed state and an open state, each charge transferring switch, when in its closed state respectively electrically connecting that one of the electrodes uniquely associated therewith to a respective charge detector having a respective output, each charge transferring switch, when in its open state, not connecting the electrode associated therewith to the respective charge detector; and

calculation means for calculating the position of the object from a ratio of the outputs of the charge detectors.

18. The computer pointing device of claim 17 wherein each key comprises a keycap moveable perpendicular to a fixed support between an uppermost and a lowermost position, and wherein each key provides an output when the respective keycap is at its lowermost position.

19. The pointing device of claim 17 wherein the second predetermined number is four.

20. The pointing device of claim 17, further comprising means for closing all the second predetermined number of charge transferring switches simultaneously.

21. The pointing device of claim 17 wherein the means connecting the voltage source to the one of the electrodes comprises a charging switch.

22. The pointing device of claim 17 wherein the means connecting the voltage source to the one of the electrodes comprises a pull-up resistor.