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Tablet with improved pen height compensation

  • US 4,009,338 A
  • Filed: 12/22/1975
  • Issued: 02/22/1977
  • Est. Priority Date: 12/22/1975
  • Status: Expired due to Term
First Claim
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1. A method for operating a graphic tablet having X dimension wires and Y dimension wires, means for selecting one of said sets of wires to be given a pattern of activation in which a wire is given a fixed potential (designated 0) or is given an alternating voltage of a predetermined amplitude (designated 1), said wires being individually activatable to produce a 0-1 transition in the region of a selected pair of adjacent wires, and a pen for capacitively receiving a position signal from wires of the dimension selected for activation, the pen position signal for a predetermined height of the pen above the tablet surface being related to the position of the pen between said two adjacent wires by a characteristic curve that is closely linear in the region between said two adjacent wires and a portion of the space outside of said two adjacent wires, comprising,producing a first activation pattern having said 0-1 transition in the region of the wires adjacent to the pen position and sampling a first pen position signal, said first pen position signal representing a locus on the pen characteristic curve at said pen position,producing a second activation pattern in which said 0-1 transition is shifted from the position of said first activation pattern by the pitch, P, between wires and sampling a second pen position signal, said second pen position signal representing a locus on said pen characteristic curve at a second position shifted from said pen position by the value of said pitch between wires,producing a third activation pattern and sampling a third pen position signal, said third pen position signal representing a locus on said pen characteristic curve at a third position on said pen characteristic curve, andforming an address identifying the position of said pen with respect to one of said adjacent wires according to said value P and said first, second and third pen position signals.

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