COORDINATE DIGITIZER INCREMENTAL SYSTEM

• US 3,818,133 A
• Filed: 04/06/1973
• Issued: 06/18/1974
• Est. Priority Date: 04/05/1971
• Status: Expired due to Term

• Current Assignee: William L. Cotter
• Original Assignee: William L. Cotter
• Inventors: Cotter, William L.
• Primary Examiner(s): Robinson, Thomas A.
• Application Number:
  US05/348,688
• Time in Patent Office: 438 Days
• Field of Search: 178/18,19,20 340/347AD,347SY,347P 33/1M
• US Class Current: 178/19.03
• CPC Class Codes: G06F 3/0442 using active external devices, e.g. active pens, for transmitting changes in electrical potential to be received by the digitiser

Abstract

A system provides digital information of the incremental changes of the position of a stylus that is freely movable on a platen having a grid constituted by groups of parallel wires. Along each coordinate axis, wires of each group are interleaved with parallel wires of the other groups to form repetitively recurring sets of wires. Each set may, for example, have four wires, each wire being of a different group. To digitize the position of the stylus on one coordinate axis, the coordinate axis is scanned by exciting all wires of a group simultaneously with an electrical signal that couples by capacitance to an electrical conductor at the tip of the stylus. the electrical signal impressed on a group of wires may, for example, have a characteristic modulation or the signal may occur in an exclusive time interval. The signal coupled to the stylus can thus be identified as originating from a specific wire group. The stylus signals are combined to derive '"'"''"'"''"'"''"'"'sine'"'"''"'"''"'"''"'"' and '"'"''"'"''"'"''"'"'cosine'"'"''"'"''"'"''"'"' signals. The '"'"''"'"''"'"''"'"'sine'"'"''"'"''"'"''"'"' and '"'"''"'"''"'"''"'"'cosine'"'"''"'"''"'"''"'"' signals are periodic waveforms which are generated when the stylus is moved along the coordinate axis. The periodic waveforms divide the platen into divisions and subdivisions. The ratio of the '"'"''"'"''"'"''"'"'sine'"'"''"'"''"'"''"'"' signal to the '"'"''"'"''"'"''"'"'cosine'"'"''"'"''"'"''"'"' signal gives the position of the stylus on the coordinate axis. However, that position recurs periodically along the axis. As the stylus moves along the platen, each crossing of a subdivision causes the generation of a pulse which is emitted at one output for one direction of stylus movement along the axis and is emitted at a different output for movement of the stylus in the opposite direction. The pulses are accumulated in an up-down (viz., reversible) counter which keeps track of the stylus position along one coordinate axis. The position of the stylus along the other (i.e., second) coordinate axis is obtained by scanning the second axis in a similar manner and accumulating the pulses in a second up-down counter. The information in the up-down counters is continually up-dated by alternately scanning the two coordinate axis at a rapid rate to permit the track of the stylus to be accurately reconstructed.

Claims

1. In a system for locating the position of a stylus movable along a coordinate axis, the system being of the type having a platen having groups of parallel wires, the wires of each group being interleaved with and parallel to the wires of the other groups whereby the wires of the groups repetitively occur in the same successive order along the coordinate axis, the stylus having an electrical conductor providing capacitive coupling to the wires of the platen, means for simultaneously energizing all the wires of a group with an electrical signal, each group of wires being characterized by its own identifying signal, means connected to the output of the stylus for deriving from each group of wirEs a signal whose amplitude is dependent upon the strength of the signal capacitively coupled to the stylus by that group of wires, the improvement of signal combining means responsive to the ratio of the amplitudes of the derived signals, the signal combining means providing a basic signal which varies periodically in amplitude as the stylus is moved at a uniform ratio along the coordinate axis.

2. The improved system according to claim 1 for locating the position of the stylus, including the further improvement of means for deriving pulse signals from the basic signal as the stylus is moved along the coordinate axis, and means responsive to the derived pulse signals for maintaining a count related to the position of the stylus.

3. The improved system according to claim 2, further including the improvement of logic gating means responsive to the derived pulse signals and to gating signals derived from the basic signal, the logic gating means providing output signals related to the direction of movement along the coordinate axis.

4. The improved system according to claim 3, wherein the logic gating means causes the derived pulse signals to appear at different outputs in dependence upon the direction of movement of the stylus and wherein the means maintaining a count related to the position of the stylus is a reversible counter having as inputs the different outputs of the logic gating means.