Stylus position digitizer using acoustic waves

United States Patent m

Kriewall et al.

[li] Patent Number: [45] Date of Patent:

5,691,959 Nov. 25, 1997

[54] STYLUS POSITION DIGITIZER USING
ACOUSTIC WAVES

[75] Inventors: James A. Kriewall, Saratoga; Edwin F.
Johnson, Sunnyvale; Alan R.
Selfridge, Los Gatos; John P.
Fairbanks, Sunnyvale; Verne H.
Wilson, Belmont; Robert W. Parry,
Santa Cruz; James D. Cummins, Union
City, all of Calif.

[73] Assignee: Fujitsu, Ltd., Tokyo, Japan

[21] Appl. No.: 223,897
[22] Filed: Apr. 6, 1994

[51] IntCl.6 G08C 21/00

[52] U.S. CI 367/129; 367/127; 367/907;

178/18

[58] Field of Search 367/907, 129,

367/127; 178/18; 327/68, 60, 90, 91

[56] References Cited

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OTHER PUBLICATIONS

E. Dieulesaint, et al., "Saw Graphic Sensor", 1978 Ultrasonics Symposium Proceedings, IEEE Cat #78H1344— ISU, 1978, pp.198-200.

Primary Examiner—Ian J. Lobo

Attorney, Agent, or Firm—Skjerven, Morrill, MacPherson, Franklin & Friel; David E. Steuber

[57] ABSTRACT

A digitizer uses acoustic waves originating from a stylus to determine the position of the stylus on a plate. The acoustic waves are introduced into the plate from the tip of the stylus and are detected by a plurality of detectors positioned at various points along the periphery of the plate. By sensing differences in the arrival times of the acoustic waves at the detectors, a microprocessor calculates the position of the stylus. In a preferred embodiment using a non-tethered stylus, four detectors are positioned at the corners of a rectangle, and the time differences are used as addresses in a lookup table, which is programmed to contain x and y coordinates corresponding to the time differences, Different embodiments may detect only the "fast" symmetrical waves or only the "slow" antisymmetrical waves generated in the plate, or may use the arrival times of both types of waves to determine the stylus position.

44 Claims, 29 Drawing Sheets