Cordless digitizer using electromagnetic locating signals

A graphic digitizer for digitizing locations of a freely movable pointer on a work surface, said digitizer comprising:

• a coil carried by said pointer and energized signal;
• a first grid of spaced conductors defining said work surface and inductively coupled to said coil;
• a phase grid of spaced conductors inductively said coil, said phase grid comprising phase conductors forming overlapping elongated loops, said loops being formed in one direction only and spaced so that all locations on said work surface lie within loops formed by a minority of said phase grid conductors;
• selecting means for selecting from said phase grid conductors a conductor that forms a loop enclosing the center of said coil;
• phase reference output means for producing, in response to the signal induced by said coil in said selected phase grid conductor, a phase reference signal having a constant phase in relation to said ac signal;
• and
• detecting means connected to said first grid conductors and said phase reference output means for detecting signals inducted by said coil in selected ones of said first grid conductors and for determining the location of said pointer relative to said first grid conductors in response to said first grid induced signals and said phase reference signal.

A method for determining the position of a freely movable pointer including coil means relative to a base unit including a first grid of spaced conductors defining locations of a work surface on said base unit, said method comprising the steps of:

• a. forming a plurality of phase conductors in said base unit, said phase conductors being formed as overlapping, elongated loops that collectively span all locations of the work surface defined by said first grid conductors;
• b. inductively coupling a phase reference signal between said coil means in said pointer and one of said phase conductors;
• c. inductively coupling locating signals between said coil means and selected conductors of said first grid;
• and
• d. responsive to said inductively coupled locating signals and said inductively coupled phase reference signal, determining the location of said pointer relative to the work surface defined by said first grid.

A method for determining the position of a coil in relation to a work surface defined by a first grid of conductors and having a second, phase grid comprising a plurality of conductors, said method comprising the steps of:

• a. forming each of said phase grid conductors into at least one elongated loop, said loops overlapping and being spaced such that all locations on said work surface lie within loops formed by a minority of said phase grid conductors;
• b. exciting the coil to induce signals in the conductors of both grids, the induced signals having a magnitude and polarity depending upon the location of the coil relative to the conductors;
• c. using as a source of phase reference, a phase grid conductor having an induced signal magnitude greater than a predetermined magnitude, detecting the relative polarities of signals induced in all phase grid conductors;
• and
• d. using as a source of phase reference, a phase grid conductor having the induced signal relative polarity of the minority of phase grid conductors, detecting the magnitude and polarity of the signals induced in the first grid.

A method for determining the position of a coil in relation to a work surface defined by a first grid of conductors and having a second, phase grid comprising a plurality of conductors, said method comprising the steps of:

• a. forming each of said phase grid conductors into at least one elongated loop, said loops overlapping and being spaced such that all locations on said work surface lie within loops formed by a minority of said phase grid conductors;
• b. exciting the coil to induce signals in the conductors of both grids, the induced signals having a magnitude and polarity depending upon the location of the coil relative to the conductors;
• c. connecting a phase grid conductor having an induced signal magnitude greater than a predetermined magnitude to detecting means to serve as a phase reference source;
• d. connecting each of said phase grid connectors, one at a time to the detecting means to determine the relative polarities of the induced signals;
• e. connecting a phase grid conductor having the same induced signal relative polarity as the minority of phase grid conductors to the detecting means to serve as a phase reference source;
• and
• f. selectively connecting the first grid conductors to the detecting means to determine the magnitude and polarity of the induced signals.