Graphical input apparatus for electrical equipment
First Claim
1. Apparatus for generating signals representing the co-ordinates of a point, including a sheet of electrically resistive material held in tension across, and adjacent to, but not in contact with, the smooth surface of an electrically resistive member, the sheet being of such material and/or so mounted that it is able to make contact temporarily with the said surface of the resistive member over a relatively small area when pressed towards the said surface by means for indicating the position of a point, change-over means for causing current supplied to the apparatus to flow alternately in two paths, a first path in which current flows in a substantially single direction through the sheet, and a second path in which current flows in a substantially single direction, at an angle to the other current direction through the resistive member, and means for deriving first and second signals, when the sheet is pressed at a relatively small area into contact with the resistive member, the first signal being dependent upon the voltage of the sheet when current flows through the resistive member, the second signal being dependent upon the voltage of the resistive member when current flows through the sheet, and the first and second signals being representative of first and second co-ordinates of the said small area, respectively, wherein the sheet and/or the resistive member are divided into regions by spaced apart narrow elongated low resistance strips traversing the sheet or resistive member, and means for providing a signal indicating, when the sheet is pressed into contact with the resistive member, in which region of the sheet and/or the resistive member the contact is made.
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Accused Products
Abstract
Two improvements are disclosed for a known graphical input tablet employing a resistive sheet stretched across, but spaced from, a resistive member, wherein the co-ordinates of a point are indicated by pressing the sheet into contact with the member at the point: firstly the resolution of the tablet is increased by the addition of conducting strips dividing the sheet and/or the member into regions, and a circuit for indicating in which region the contact occurs; and secondly by the addition of a circuit for indicating when two such contacts are made at the same time.
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Citations
14 Claims
- 1. Apparatus for generating signals representing the co-ordinates of a point, including a sheet of electrically resistive material held in tension across, and adjacent to, but not in contact with, the smooth surface of an electrically resistive member, the sheet being of such material and/or so mounted that it is able to make contact temporarily with the said surface of the resistive member over a relatively small area when pressed towards the said surface by means for indicating the position of a point, change-over means for causing current supplied to the apparatus to flow alternately in two paths, a first path in which current flows in a substantially single direction through the sheet, and a second path in which current flows in a substantially single direction, at an angle to the other current direction through the resistive member, and means for deriving first and second signals, when the sheet is pressed at a relatively small area into contact with the resistive member, the first signal being dependent upon the voltage of the sheet when current flows through the resistive member, the second signal being dependent upon the voltage of the resistive member when current flows through the sheet, and the first and second signals being representative of first and second co-ordinates of the said small area, respectively, wherein the sheet and/or the resistive member are divided into regions by spaced apart narrow elongated low resistance strips traversing the sheet or resistive member, and means for providing a signal indicating, when the sheet is pressed into contact with the resistive member, in which region of the sheet and/or the resistive member the contact is made.
- 10. Apparatus for generating signals representing the co-ordinates of a point including a sheet of electrically resistive material held in tension across, and adjacent to, but not in contact with, the smooth surface of an electrically resistive member, the sheet being of such material and/or so mounted that it is able to make contact temporarily with the said surface of the resistive member over a relatively small area when pressed towards the said surface by means for indicating the position of a point, change-over means for causing current supplied to the apparatus to flow alternately in two paths, a first path in which current flows in a substantially single direction through the sheet, and a second path in which current flows in a substantially single direction, at an angle to the other current direction through the resistive member, means for deriving first and second signals, when the sheet is pressed at a relatively small area into contact with the resistive member, the first signal being dependent upon the voltage of the sheet when current flows through the resistive member, the second signal being dependent upon the voltage of the resistive member when current flows through the sheet, and the first and second signals being representative of first and second co-ordinates of the said small area, respectively, and means for generating a predetermined signal when the sheet is pressed into contact with the resistive member in two separate areas.
Specification