Telegraphy – Systems – Position coordinate determination for writing
Patent
1978-12-13
1980-07-15
Robinson, Thomas A.
Telegraphy
Systems
Position coordinate determination for writing
178 19, G08C 2100
Patent
active
042130050
ABSTRACT:
A system for precisely determining the location of a cursor on a work surface with respect to a grid of coordinate conductors. The system is based on the time-distance relationship of current sheets caused to move sequentially along each axis of the work surface, and the detection of each current sheet as it approaches and passes an operator-movable sensor. A number of the grid wires are simultaneously energized with a fixed energization pattern which steps along the conductors, thereby generating the current sheet and consequent magnetic field which translate along the plane of the conductors parallel to the conductors. A preferred means responsive to the time of passage of the current sheet comprises an inductive pickup coil having a diameter approximately equal to the width of the current sheet and means for sensing current induced in the pickup coil. Preferably, the grid conductors are energized with substantially fixed constant currents. Among the important advantages of the invention are enhanced signal levels with improved signal to noise ratios, improved immunity to extraneous noise, relative insensitivity to minor inaccuracies in the placement of the grid wires in the manufacture of the tablet, excellent resolution, and a high degree of stability. Moreover, the system, through several discoveries, is characterized by a relative lack of undue complexity, while serving well its intended function.
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