ELECTRICAL PROBE-POSITION RESPONSIVE APPARATUS AND METHOD

• US 3,699,439 A
• Filed: 03/10/1970
• Issued: 10/17/1972
• Est. Priority Date: 03/13/1969
• Status: Expired due to Term

• Current Assignee: Frances B. Cuniberti, Scriptel Corporation, Walter T. Krumm
• Original Assignee: John A. Turner
• Inventors: Turner, John A.
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US05/018,174
• Time in Patent Office: 952 Days
• Field of Search: 324/71EB,62.65,71 178/18,19,20 33/1M
• US Class Current: 324/71.1
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact

Abstract

Position responsive apparatus is disclosed comprising a sheet of substantially uniform resistivity having first and second parallel, linear electrodes in electrical contact therewith. A movable, electrically conductive probe is energized from one pole of a current source whose other pole is connected to the two electrodes in parallel. Means are provided for comparing the current flowing through one electrode, when the probe is in contact with the surface, with the current flowing through the other electrode or with the total current. It is found that the ratio of the current through the first electrode to the current through the second electrode corresponds to the ratio of the distance of the probe contact point from the second electrode to the distance of the said point from the first electrode. A second pair of linear electrodes, arranged perpendicular to the first pair so as to form therewith the four sides of a square, may be provided. If the second pair of electrodes are energized, with respect to the probe, in the same manner as the first pair but alternately therewith, then x and y co-ordinates of the point of contact between the probe and the surface may be produced.

Claims

1. Position responsive apparatus, comprising means defining a rectangular surface having substantially uniform electrical resistivity, two electrode means each in electrical contact with the surface at points extending completely along a respective one of two opposite edges thereof so as to maintain each of the two said edges at a substantially uniform electrical potential, two further electrode means along said other two edges, movable probe means for making electrical connection with the surface at a point between the first-mentioned two electrode means, electrical connection means interconnecting the probe means and the electrode means so as to provide a pair of parallel circuit paths through the said point of connection between the probe means and the surface and to hold both of the electrode means at the same electricAl potential while maintaining the other two electrode means of the surface unconnected, each path including a respective one, only, of the first mentioned two electrode means, a single electrical current source connected to drive a current through the two circuit paths via the probe means and the said point of connection between the probe means and the surface so that the current divides between the first mentioned two electrode means in inverse proportion to the distance of that point from each of the first mentioned two electrode means, and output means connected to measure the current flowing in at least one of the paths.

2. Apparatus according to claim 1, in which the probe means comprises a member made of electrically conductive material.

3. Apparatus according to claim 1, in which the source is an a.c. source and including a layer of electrically insulating material over the said surface, the probe means making electrical connection with the surface by capacitive coupling through the layer.

4. Apparatus according to claim 1, in which each electrode means makes electrical contact with the said surface at discrete points along the respective said edge, the discrete points being sufficiently close that each of the said two edges is at substantially uniform electrical potential.

5. Apparatus according to claim 4, wherein said two further electrode means are each in contact with the said surface at points extending completely along a respective one of the said other two edges of the surface so as to maintain each of those other two edges at a substantially uniform electrical potential, further electrical connection means interconnecting the probe means and the two further electrode means so as to provide a further pair of parallel circuit paths through the said point of connection between the probe means and the surface and to hold both of the further electrode means at the same electrical potential, each further path including a respective one, only, of the further electrode means and excluding the first-mentioned electrode means, the said source being connected to drive current through the two further circuit paths via the probe means and the said point of connection thereof to the surface so that the current divides between the two further electrode means in inverse pro-portion to the distance of that point from each of the electrode means, means for rendering the two pairs of electrical connection means non-conductive successively whereby the two pairs of circuit paths are established alternately, and the output means being connected to measure the current in at least one of the further circuit paths.

6. Apparatus according to claim 5, in which the electrical connection means include first and second switch means respectively connected in circuit with the pairs of circuit paths, the said means for rendering the two pairs of electrical connection means non-conductive successively including means arranged to operate the first and second switch means alternately.

7. Apparatus according to claim 5, in which the means for rendering the two pairs of electrical connection means non-conductive successively comprises diode means connected in circuit with the respective circuit paths, and in which the polarity of the said current source periodically changes, the diode means being so poled that when the source has one polarity the diode means of the first mentioned pair of electrode means are forward-biased and the other diode means are back-biased and when the source has the opposite polarity the diode means of the further electrode means are forward-biased and the other diode means are back-biased.

8. Apparatus according to claim 5, including means operative to produce control signals indicative of a desired position of the said point, means responsive to the currents in the said circuit paths and to the control signals to compare the position of the said point with the desired position whereby to produce a correction sIgnal when the point diverges from the said desired position, and probe control means responsive to the control signal to automatically adjust the position of the probe means whereby to tend to maintain the point in the desired position.

9. Apparatus according to claim 8, in which the probe means comprises an electron beam of a cathode ray tube on whose screen the said surface is provided.

10. A method of determining the position of a movable point of electrical connection between probe means and a rectangular surface of substantially uniform electrical resistivity having two pairs of electrode means each said pair respectively making electrical contact with points extending completely along two opposite edges of the said surface so as to maintain each said opposite edge at a substantially uniform electrical potential, comprising the steps of connecting an electric current source between one pair of said electrode means on the one hand and the probe means on the other hand while holding said one pair of electrode means at the same electrical potential and maintaining the other pair of said electrode means along the edges of the rectangular surface unconnected, and measuring the current flowing through at least one of said one pair of electrode means whereby the ratio of the current through said one electrode means to the current through the other electrode means of said one pair corresponds to the ratio of the distance of the said movable point from said other electrode means to the distance of the said movable point from the said one electrode means.

11. A method of determining the position of a movable point of electrical connection between probe means and a rectangular surface of substantially uniform electrical resistivity having a pair of first electrode means respectively making electrical contact with points extending completely along two opposite edges of the rectangular surface so as to maintain each of those edges at substantially uniform electrical potential, and a further pair of electrode means respectively making electrical contact with points extending completely along the other two opposite edges of the rectangular surface so as to maintain each of those edges at substantially uniform electrical potential, said method comprising the steps of:

connecting an electric current source between the two first electrode means on the one hand and the probe means on the other hand while maintaining the two first electrode means at the same potential and maintaining the two further electrode means unconnected, connecting the said current source between the two further electrode means on the one hand and the probe means on the other hand while maintaining the two further electrode means at the same potential, this step being carried out after disconnection of the current source from the first electrode means, measuring the current flowing through at least one of each pair of electrode means when the said current source is connected thereto and the other pair of electrode means is unconnected, whereby the ratio of the current through one of these electrode means to the current through the other thereof corresponds to the ratio of the distance of the said movable point from the said other thereof to the distance of the said movable point from the said one thereof.

12. A method of determining the position of a movable point on a rectangular surface of substantially uniform electrical resistivity having electrode means along each edge of the rectangle, comprising the steps of injecting an electric current into the surface at the said movable point from a single current source, holding one pair of electrode means at opposite edges of the surface substantially completely at the same electrical potential, while holding the other pair of electrode means at opposite edges electrically unconnected, so that the injected current divides and flows to and through the two edges of the said one pair in inverse proportion to the distance of tHe said movable point from each edge of the said one pair, and comparing the currents flowing through each edge of the said one pair.