Coordinate digitizer incremental system

Abstract

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.

Inventors

• 👤 W Cotter

Bibliographic Details