04991148 is referenced by 83 patents and cites 16 patents.

An acoustic position sensing apparatus is described which determines the position of an indicator in relation to a datum surface or volume. The apparatus comprises an acoustic point source transmission device mounted on the indicator for transmitting a sequence of periodic acoustic oscillations, and a plurality of acoustic point receivers positioned about the datum surface for receiving the acoustic oscillations. Comparators are connected to each acoustic receiver for converting the received acoustic oscillations to squared waves having logical up and down levels. A register or other time determining circuit is coupled to each comparator and receives at least a leading portion of a squared wave and determines that the squared wave has resulted from an acoustic oscillation generated by said acoustic point source transmission device. It provides an output upon making such a determination, which is indicative of an occurrence of a step transition of the squared wave. A processor is responsive to the outputs from the registers to find the position of the indicator. The acoustic point source transmission device is configured both as a linear stylus and as a planar "puck", both having at least a pair of acoustic transmitters. The apparatus employs, for two dimensional position detection, at least three acoustic receivers arranged in a non-linear fashion. A three dimensional position detector system is described which employs four receivers, three of which are oriented in one plane and a fourth in another plane.

Title
Acoustic digitizing system
Application Number
7/412885
Publication Number
4991148
Application Date
September 26, 1989
Publication Date
February 5, 1991
Inventor
Ian R Gilchrist
2318 Springlake Dr., Timonium, 21093
MD, US
Agent
Perman & Green
IPC
G08C 21/00
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