| 摘要 |
<p>A digitizing system includes a plurality of spaced parallel grid conductors embedded beneath a support surface. A movable pen coil powered by an amplifier induces AC signals in the grid conductors. The grid conductors are scanned at a first rate from a reference point to detect the approximate location of the pen coil. The grid conductors are then "up scanned" at a second rate toward the pen coil. As the scan counter is incremented, a pen position counter is simultaneously incremented at a third rate which is substantially greater than the second rate to effect interpolation between grid conductors. The up scanning is halted when a rectified and integrated waveform resulting from the up scanning operation undergoes a phase change. A first digital number contained in the pen position counter then is stored. The polarity of the signal driving the pen coil then is reversed. The grid conductors are then "down scanned" at the second rate toward the pen coil. The scan counter is decremented from a preset value at the second rate to effect the down scanning. The pen position counter is simultaneously decremented at the third rate from a preset value. The down scanning is halted when a rectified and integrated waveform resulting from the down scanning undergoes a phase change. A second digital number contained in the pen position counter is averaged with the first digital number to provide an accurate interpolated number representing the location of the pen coil.</p> |
