Digitizer system with loopback conductor grid

A method for determining the position of a coil with respect to an active area defined by a grid of conductors, the grid including a first group of n parallel, spaced conductors oriented in an X direction, and a second group of m parallel spaced conductors oriented in a Y direction, each of the conductors having a predetermined unexcited polarity, said method comprising the steps of:

• (a) looping at least two adjacent conductors in each said group through a plurality of different sections of the active area such that the unexcited polarities of the adjacent conductors are different in each of the sections;
• (b) exciting either
• i. the coil to induce electrical signals in the conductors, or
• ii. selected ones of the conductors to induce electrical signals in the coil, the induced signals having a magnitude and polarity depending upon the position of the coil relative to the conductors;
• (c) selectively switching the conductors to either
• i. means for detecting the induced signals;
• or
• ii. means for exciting the conductors;
• and
• (d) selectively changing the polarities of the detected signals in accordance with the different unexcited polarities of the adjacent conductors in the sections.

Apparatus for determining the position of a coil with respect to an active area, comprising:

• (a) a grid of conductors defining said active area, said grid including a first group of parallel, spaced conductors oriented in an X direction and a second group of parallel, spaced conductors oriented in a Y direction, one end of each of said conductors in each of said groups being connected to ground, each of said conductors having a predetermined unexcited polarity defined by said grounded end;
• (b) each pair of adjacent conductors in each said group being looped through four different quarter sections of said active area such that the unexcited polarities of each said conductor pair are different in each one of said quarter sections;
• (c) a coil moveable relative to said grid;
• (d) means for exciting either
• i. said coil to induce electrical signals in said conductors, or
• ii. selected ones of said conductors to induce electrical signals in said coil, the induced signals having a magnitude and polarity depending upon the position of said coil in respect to said conductors;
• (e) means for detecting the magnitude and polarity of the induced signals;
• (f) multiplexer means for selectively switching the other ends of said conductors to either
• i. said detecting means;
• or
• ii. said exciting means;
• and
• (g) microprocessor means for controlling said detecting means and said multiplexer means and further including
• (1) means for selectively changing the polarities of said detected induced signals to account for the different unexcited polarities of said conductor pairs in each one of said quarter sections,
• (2) means for causing said multiplexer means to sample the polarities of said detected induced signals to coarsely locate said coil as being between two particular adjacent conductors, and
• (3) means for generating a ratio of the magnitudes of said detected induced signals for said two particular adjacent conductors to precisely locate said coil between said two particular adjacent conductors.