Capacitive position sensor

Claim 2

A capacitive sensor for measuring a position of an object adjacent a homogeneous resistive sensing layer, the presence of the object changing an electric capacitance to a ground, the sensor comprising: a predetermined number, greater than one, of electrodes spaced apart around a periphery of the sensing layer, the electrodes conterminous with the sensing layer, the sensing layer disposed in a planar configuration beneath the tops of a plurality of keys of a keyboard operatively connected to a computer, the sensing layer further comprising an upstanding portion between two adjacent ones of the keys; the predetermined 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 predetermined 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 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.

Claim 3

In a pointing device connected to a computer, wherein a position of an object is detected by means for measuring an electrical capacitance to a ground, wherein a cursor on a display operatively connected to the computer moves responsive to a change in the detected position, 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 voltage source; means for selectively connecting the voltage source to at least one of a second predetermined number, greater than one, of electrodes spaced out along a periphery of a resistive layer disposed beneath a selected portion of the active typing area, the resistive layer comprising a plurality of throughholes, each of the throughholes accommodating a portion of a respective one of those keys disposed within the selected portion of the active typing area; wherein each of the electrodes is separately electrically connected to a respective charge transferring switch having a dosed state and an open state, each charge transferring switch electrically connecting the electrode associated therewith to a respective charge detector when in the closed state, each charge transferring switch, when in the open state, not connecting the electrode associated therewith to the respective charge detector, each of the charge detectors having a respective output representative of the electrical capacitance to the ground; and a calculation means for calculating the position of the object from a ratio of the outputs.

Claim 4

In a pointing device connected to a computer, wherein a position of an object is detected by means for measuring an electrical capacitance to a ground, wherein a cursor on a display operatively connected to the computer moves responsive to a change in the detected position, 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 voltage source; means for selectively connecting the voltage source to at least one of a second predetermined number, greater than one, of electrodes spaced out along a periphery of a resistive layer disposed beneath a selected portion of the active typing area, the resistive layer comprising a plurality of throughholes, each of the throughholes accommodating a portion of a respective one of those keys disposed within the selected portion of the active typing area; wherein each of the electrodes is separately electrically connected to a respective charge transferring switch having a dosed state and an open state, each charge transferring switch electrically connecting the electrode associated therewith to a respective charge detector when in the closed state, each charge transferring switch, when in the open state, not connecting the electrode associated therewith to the respective charge detector, each of the charge detectors having a respective output representative of the electrical capacitance to the ground; and a calculation means for calculating the position of the object from a ratio of the outputs.

Claim 5

The pointing device of claim 2 wherein each key comprises a keycap movable perpendicular to a fixed support between an uppermost and a lowermost position, and wherein each key provides a respective output when the keycap associated therewith is in its lowermost position.

Claim 6

The pointing device of claim 2 wherein the resistive layer comprises an upstanding portion between two adjacent ones of the keys disposed within the selected portion of the active typing area.

Claim 7

The pointing device of claim 4 wherein the upstanding portion comprises a ridge.

Claim 8

The pointing device of claim 4 wherein the upstanding portion surrounds one of the keys.

Claim 9

The pointing device of claim 2 wherein the resistive layer has a sheet resistivity greater than ten Ohms per square and less than one million Ohms per square.

Claim 10

The pointing device of claim 2 wherein the second predetermined number is four.

Claim 11

The pointing device of claim 2 further comprising an analog multiplexer having a respective input from each of the charge detectors and wherein the calculation means comprises a microprocessor having an input from the analog multiplexer.

Claim 12

The pointing device of claim 2 further comprising means for closing all the charge transferring switches simultaneously.

Claim 13

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, wherein the resistive layer comprises a plurality of throughholes, each of the throughholes accommodating a portion of a respective one of those keys within the selected portion of the active typing area; 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.

Claim 14

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, wherein the resistive layer comprises a plurality of throughholes, each of the throughholes accommodating a portion of a respective one of those keys within the selected portion of the active typing area; 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.

Claim 15

The pointing device of claim 11 wherein the resistive layer comprises a plurality of throughholes, each of the throughholes accommodating a portion of a respective one of those keys within the selected portion of the active typing area.

Claim 16

The pointing device of claim 12 wherein the upstanding portion comprises a ridge.

Claim 17

The pointing device of claim 12 wherein the upstanding portion comprises a wall surrounding one of the keys.

Claim 18

The pointing device of claim 11 wherein the resistive layer has a sheet resistivity greater than ten ohms per square and less than one million ohms per square.