Graphical input apparatus for electrical equipment

• US 4,149,029 A
• Filed: 03/08/1978
• Issued: 04/10/1979
• Est. Priority Date: 03/09/1977
• Status: Expired due to Term

• Current Assignee: National Research Development Corporation
• Original Assignee: National Research Development Corporation
• Inventors: Pobgee, Peter J.
• Primary Examiner(s): Robinson, Thomas A.
• Application Number:
  US05/884,550
• Time in Patent Office: 398 Days
• Field of Search: 178/18, 178/19, 178/20, 340/365 C, 340/347 AD, 338/90, 33/1 M, 200/46, 323/63
• US Class Current: 178/18.06
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact

Abstract

A graphical input tablet is disclosed in which the lower surface of a sheet is spaced from the upper surface of a fixed member. Each or both surfaces are formed by parallel conductors but where only one surface is formed in this way the other surface is resistive. Currents are passed alternately through the surfaces to provide voltage gradients, and when a stylus is used to indicate a point, alternate co-ordinate signals for the point are obtained.

Claims

1. Apparatus for obtaining signals representative of the co-ordinates of a point indicated in a working area, including a sheet having a first surface and a fixed member having a second surface facing the first surface, one of the surfaces being partially formed by a plurality of parallel conductors spaced apart from one another, the other surface being a substantially homogeneous resistive surface or being formed by parallel conductors at right angles to those in the said one surface, the sheet being held in tension across, and adjacent to, the fixed member with the first and second surface out of contact, and the sheet being of such material and/or so mounted that the first and second surfaces are able to make contact temporarily with one another when the sheet is pressed towards the fixed member by means for indicating the position of a point, the apparatus also including resistive means for each surface which has parallel conductors so connected to the conductors that when a current is passed between two terminals of the resistive means a voltage gradient is set up from conductor to conductor of that surface in a direction at right angles to the conductors, changeover means for causing current supplied to the apparatus to flow alternately in two paths, a first path in which the current sets up a voltage gradient in one direction in the first surface, and a second path in which the current sets up a voltage gradient in a direction at right angles to the said one direction in the second surface, and means for deriving first and second signals when the sheet is pressed at a relatively small area towards the fixed member so that the first and second surfaces make contact, the first signal being dependent on the voltage of the first surface when current flows in the second surface and the second signal being dependent on the voltage of the second surface when the current flows in the first surface, and the first and second signals being representative of first and second co-ordinates of the said small area, respectively.

2. Apparatus according to claim 1 wherein only one surface is partially formed by parallel conductors and it is the first surface which is so formed.

3. Apparatus according to claim 1 wherein the said resistive means for each surface which has parallel conductors comprises two elongated resistive members positioned at opposite edges of the surface at right angles to the conductors thereof and in contact therewith.