Coordinate determining device employing a slowly varying difference signal to determine approximate cursor position

Claim 3

The device of claim 1 in which: said first signal providing means includes means defining a first set of substantially equal, adjacent measuring intervals along a selected dimension, and said first signal shifting instantaneously to said predetermined value at the beginning of each interval and varying monotonically as the cursor is moved in one direction through an interval to indicate the relative position of said cursor within said interval; said means providing said second signal includes means defining a second set of substantially equal, adjacent measuring intervals along said selected dimension, said intervals of said second set being slightly larger than said intervals of said first set, and said second signal shifting instantaneously to said predetermined value at the beginning of each interval of said second set and varying monotonically as the cursor is moved in said one direction through a second set interval to indicate the relative position of said cursor within said second set interval; and said difference is directly proportional to the distance along said selected dimension between a reference position and said cursor.

Claim 4

The device of claim 2 wherein said means for providing an output indicating cursor position include: means for using said difference to identify the number of complete intervals of cursor displacement from the reference position, said number of interVals being an indication of approximate cursor position; and means for using one of said cyclic signals to identify cursor position within an interval, said indication of approximate cursor position and said identified position within an interval together providing a precise indication of cursor position.

Claim 5

The device of claim 2 wherein said first signal comprises a sawtooth signal that has a first value whenever said cursor is positioned at one edge of a measuring interval of said first set of measuring intervals, that has a second value whenever said cursor is positioned at an opposite edge of a measuring interval of said first set, and that varies linearly in response to cursor movement from said one edge to said opposite edge of a measuring interval of said first set of measuring intervals; and said second signal comprises a sawtooth signal that has a first value whenever said cursor is positioned at one edge of a measuring interval of said second set, and that has a second value whenever said cursor is positioned at the opposite edge of a measuring interval of said second set, and that varies linearly in response to cursor displacement from said one edge to said opposite edge of a measuring interval of said second set of measuring intervals.

Claim 6

The device of claim 2 wherein the lengths of said intervals of said first and second sets satisfy the equation: Delta d < or = (D2/Y) where: Delta d the difference between the length of a measuring interval of said first set and the length of a measuring interval of said second set; D the length of a measuring interval of said first set; and Y the length of said first and second sets along which measurements are to be made; said dimensions of said intervals thereby preventing said difference signal from having the same value for different cursor positions along said selected dimension that are separated by a substantial distance.

Claim 7

The device of claim 5 wherein said means defining said first and said second sets of measuring intervals comprise electrically conductive grid means.

Claim 8

The device of claim 2 further including means for compensating for any error in said determined difference between said first and second signals comprising: means for determining each value that said difference may have for each value of said first signal in the absence of any error; means for comparing said determined difference with each of said permitted differences to determine the permitted difference value closest to said determined difference; means for utilizing said closest permitted difference value to provide a readout signal indicating cursor position, said readout signal being unaffected by errors in said difference signal smaller than the change in said difference signal caused by cursor displacement of one-half of one of said measuring intervals.

Claim 9

The device of claim 7 wherein said utilization means includes: means providing a third signal indicating the cursor position represented by said closest permitted difference value; and means for combining said first and third signals to provide said readout signal, said readout signal thereby being a precise indication of cursor position.