Graphical input apparatus for electrical apparatus

• US 3,885,097 A
• Filed: 08/11/1972
• Issued: 05/20/1975
• Est. Priority Date: 08/11/1972
• Status: Expired due to Term

• Current Assignee: British Technology Group Ltd.
• Original Assignee: Peter John Pobgee
• Inventors: Pobgee, Peter John
• Primary Examiner(s): Robinson, Thomas A.
• Application Number:
  US05/279,774
• Time in Patent Office: 1,012 Days
• Field of Search: 178/18,19,20,21,87 1/19 33/1M 35/9C 340/146.3E,146.3SY 346/139C
• US Class Current: 178/18.05
• 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 device for electrical apparatus such as a computer or a cathode ray tube display is described. The device comprises two spaced apart sheets of resistive material one over the other and includes means for applying voltage alternately to the two sheets between electrodes along opposite edges thereof. A stylus is used to write or draw on the top sheet and in so doing it is deformed to contact the lower sheet. When a sheet is not connected to the applied voltage, it is used to pick off a voltage corresponding to one co-ordinate of the point of contact. The voltage is applied in directions which are at right angles to one another in the two sheets so that the X and Y co-ordinates of the point of contact are provided alternately. In order to suppress lines in a display which would occur between consecutive points when the stylus was lifted, a contact detector is provided to suppress co-ordinates produced under these conditions. To overcome the extraneous contacts which occur when an operator rests his hand on the top sheet, a separator such as an insulating mesh is positioned between the sheets.

Claims

1. Apparatus for obtaining signals indicative of the coordinates of a point indicated on a surface, including a continuous sheet held parallel and adjacent to, but not in contact with the continuous planar surface of a member, the sheet and the member comprising electrically resistive material, the sheet being of such material and so mounted that it is able to make contact temporarily with the planar surface over a relatively small area when pressed towards the surface by means for indicating the position of a point, means positioned between the sheet and the planar surface to prevent contact between the sheet and the surface over relatively large areas, change-over means for causing current supplied to the apparatus to flow alternately in two paths;

a first path in which the current flows in a substantially single direction through the sheet, and a second path in which the current flows in a substantially single direction, at an angle to the other current direction, through the resistive member, and means for deriving a first signal giving the value of the voltage of the resistive member when current flows in the sheet and a second signal giving the value of the voltage of the sheet when current flows through the resistive member, the first and second signals being representative of first and second co-ordinates of the point, respectively.

2. Apparatus according to claim 1 including suppression means for detecting good contact between the sheet and the member and for suppressing the output of the apparatus unless a good contact exists.

3. Apparatus for obtaining the co-ordinates of a point indicated on a surface, including a sheet of electrically resistive material held parallel and adjacent to, but not in contact with the planar surface of an electrically resistive member, the sheet being sufficiently resilient to deform temporarily and make contact with the planar surface over a relative small area, when pressed by means for indicating the position of a point, change-over means for coupling current-supply means to pass a current in a substantially single direction through the sheet, and for coupling measuring means to the resistive member, and for subsequently coupling the current-supply means to pass a current in a substantially single direction, at an angle to the other current direction, through the resistive member, and for coupling the measuring means to the sheet, the measuring means being so adapted to measure voltage when the sheet and the member are in contact at the said area that the voltages at the area due to the said currents are provided one after another, and suppression means for detecting good contact between the sheet and the member and for suppressing the output of the apparatus unless a good contact exists.

4. Apparatus according to claim 3 including means positioned between the sheet and the planar surface to prevent contact between the sheet and the surface over relatively large areas.

5. Apparatus according to claim 4 wherein the sheet extends over a rectangular area between first and second parallel electrodes of conducting material and the resistive member extends over a rectangular area between third and fourth parallel electrodes of conducting material, the first and second electrodes being at right angles to the third and fourth electrodes, the sheet being connected to the change-over means by way of the first and second electrodes, and the resistive member being connected to the change-over means by way of the third and fourth electrodes.

6. Apparatus according to claim 5 wherein the sheet of electrically resistive material is a sheet of resilient resistive material.

7. Apparatus according to claim 5 wherein the sheet of electrically resistive material is a layer of resistive material which is mounted on a sheet of resilient insulating material.

8. Apparatus according to claim 7 wherein the sheet is made of carbon loaded plastics material.

9. Apparatus according to claim 7 wherein the sheet is made of conducting silicone rubber and is mounted on glass cloth.

10. Apparatus according to claim 5 wherein the resistive member is a layer of resistive material which is mounted on insulating material.

11. Apparatus according to claim 5 wherein the change-over means includes first and second change-over switches, each having a common terminal, and first and second terminals either of which can be connected by operating the switch to the common terminal, the common terminals of the switches being connected to the terminals of direct-current supply means, the sheet being connected between the first terminals of the switches, and the resistive member being connected between the second terminals of the switches.

12. Apparatus according to claim 5 wherein the change-over means includes means for applying an alternating current to a first series circuit comprising the sheet and first rectifier means, and a second series circuit comprising the member and second rectifier means, the first and second rectifier means being oppositely poled with the result that the sheet and the member pass current for alternate half cycles of the alternating current.

13. Apparatus according to claim 5 wherein the change-over means includes a first switching circuit comprising first and second transistors with their emitter-collector paths connected in series with the sheet, and a second switching circuit comprising third and fourth transistors with their emitter-collector paths connected in series with the resistive member, and control means for causing the first and second transistors to conduct together and alternately with the third and fourth transistors conducting together.

14. Apparatus according to claim 5 wherein the measuring means includes first and second peak detector circuits which are connected to the sheet and the resistive member respectively.

15. Apparatus according to claim 5 wherein the suppression means includes switching means for periodically connecting a part of the sheet or resistive member to a reference-potential source of potential outside the potential limits of the current supply means, when current is not being passed through the sheet or resistive member, respectively, and means for comparing the potential at the said part with the potential of the reference source tO indicate that the sheet and resistive member are out of contact if the potential difference between the part and the reference source is less than a predetermined value.

16. Apparatus according to claim 15 wherein one end of the sheet or the resistive member is connected to a pair of transistors, one transistor forming part of the change-over means and when conducting connecting the said end to a terminal of a current supply, and the other transistor when conducting connecting the said end to a terminal of a reference-voltage source whose voltage is of the same polarity but greater than that of the current supply terminal, the transistors of the pair being arranged to conduct at different times, and the means for comparing potentials being connected to the said one end.

17. Apparatus according to claim 15 for providing voltages for an oscilloscope to allow a display corresponding to movement of the point indicated, wherein the change-over means includes a first switching circuit comprising first and second transistors with their emitter-collector paths connected in series with the sheet, and a second switching circuit comprising third and fourth transistors with their emitter-collector paths connected in series with the resistive member, and control means for causing the first and second transistors to conduct together and alternately with the third and fourth transistors conducting together the measuring means includes first and second peak detector circuits which are connected to the sheet and the resistive member respectively, means for providing a signal when the oscilloscope trace is to be visible, and means for clamping the outputs of the peak detectors to zero are provided, and the control means provides a cycle of operation in which firstly the outputs of the peak detectors are released from clamping, secondly current is passed through whichever of the sheet or the resistive member includes the said part, thirdly the said part and the reference potential source are disconnected while current is passed through whichever of the sheet or the resistive member did not pass current, fourthly the said part is reconnected to the reference-potential source, and fifthly if there is contact between the sheet and the resistive member the signal indicating that the oscilloscope trace is to be brightened is provided.

18. Apparatus according to claim 5 wherein the means for preventing contact between the sheet and the surface over relatively large areas include a liquid or a liquid gel contained between the sheet and the surface.

19. Apparatus according to claim 5 wherein the means for preventing contact between the sheet and the surface over relatively large areas include a grid of insulating material between the sheet and the surface.

20. Apparatus according to claim 5 wherein the means for preventing contact between the sheet and the surface over relatively large areas include a matrix of islands of insulating material between the sheet and the surface.

21. Apparatus according to claim 5 wherein the measuring means includes first and second peak detector circuits which are connected to the sheet and the resistive member, respectively, and the apparatus includes integrator means, comparator means for indicating when the content of the integrator means has reached a predetermined value during readout, means for allowing clock pulses from a generator to reach a counter only while the integrator content is being reduced and before the comparator indicates that the integrator content has reached the predetermined value, and selection means for connecting the integrator means to carry out the following sequence of operation cyclically, firstly, connect that peak rectifier circuit connected to the resistive member to the input of the integrator means, secondly, connect the integrator means to means for reducing its content at a constant predetermined rate, thirdly, connect that peak rectifier connected to the sheet to the integrator means, and fourthly connect the iNtegrator means to the means for reducing its content, whereby the counter receives pairs of trains of pulses, the value represented by the pulses of one train in each pair being the current value of one co-ordinate, and the value represented by the pulses of the other train in each pair being the current value of the other co-ordinate.

22. Apparatus according to claim 21 including means for adding a marker signal to each pair of pulses indicating whether the sheet and resistive member are in good contact with one another.

23. Apparatus according to claim 22 including second and third counters for holding the current and preceding values of one co-ordinate, respectively, fourth and fifth counters for holding the current and preceding values of the other co-ordinate, respectively, first and second difference means for finding the differences between the current and preceding values of the said one and the said other co-ordinates, respectively, logic means for activating the first and second difference means only if the said marker signal indicates that the sheet and resistive member were in contact when the current co-ordinates were generated, means for updating the third and fifth counters in accordance with output signals from the difference means, and first and second digital to analogue converters for providing analogue output signals representative of the contents of the third and fifth counters, respectively.

24. An apparatus for obtaining signals representative of the co-ordinates of a point indicated on a surface, including a continuous sheet held parallel and adjacent to, but not in contact with the continuous planar surface of a member, the sheet and the member comprising electrically resistive material, the sheet being sufficiently resilient to deform temporarily and make contact with the planar surface over a relatively small area, when pressed by means for indicating the position of a point, means positioned between the sheet and the planar surface to prevent contact between the sheet and the surface over relatively large areas, change-over means for coupling current-supply means to pass a current in a substantially single direction through the sheet without substantial current being passed through the resistive member, and for subsequently coupling the current-supply means to pass a current in a substantially single direction, at right angles to the other current direction, through the resistive member without substantial current being passed through the sheet, and means for deriving a first signal giving the value of the voltage of the resistive member when current flows in the sheet and a second signal giving the value of the voltage of the sheet when current flows through the resistive member, the first and second signals being representative of first and second co-ordinates of the point, respectively.