US 6,535,200 B2 · Capacitive position sensor

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.

Claims22

Dependent claims

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 more elements

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.

3 more elements

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.

2 more elements

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.

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.

6 more elements

Dependencies are inferred from the claim text.

Capacitive position sensor

Life of this patent

Capacitive position sensor

Life of this patent

Abstract

Claims22