Touch sensitive tablet using force detection

Hotta et al.

[45] Jun. 21,1983

[54] TOUCH SENSITIVE TABLET USING FORCE DETECTION

[75] Inventors: Masao Hotta, Hachioji; Yoshikazu Miyamoto, Kokubunji; Norio Yokozawa, Fuchu; Yoshimitsu Oshima, Tokyo, all of Japan

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

[21] Appl. No.: 177,058

[22] Filed: Aug. 11, 1980

[30] Foreign Application Priority Data

Aug. 17, 1979 [JP] Japan 54-104007

Sep. 19, 1979 [JP] Japan 54-119420

[51] Int. CU G08C 21/00

[52] U.S. CI 364/556; 73/1 B;

73/862.38; 178/18; 364/508; 364/731

[58] Field of Search 364/191-193,

364/474, 556, 508, 517, 522, 731, 506; 73/1 B, 862.38, 862.45, 862.54; 340/706, 384 E, 365 A, 365 C; 178/18; 177/211

[56] References Cited

U.S. PATENT DOCUMENTS

3,616,690 11/1971 Harden 177/211

3,657,475 4/1972 Peronneau et al 178/18

3,727,002 4/1973 Pear, Jr 178/18

3,875,331 4/1975 Hasenbalg 178/18

4,051,721 10/1977 Williams 73/862.38

4,094,192 6/1978 Watson et al 73/1 B

4,121,049 10/1978 Roeber 178/18

4,145,748 3/1979 Eichelberger et al 340/365 C

4,293,734 10/1981 Pepper, Jr 178/18

OTHER PUBLICATIONS

Lisk, "Electronic Keyboard"; IBM Tech. Disci. Bull.;
vol. 20, No. 1; Jun. 1977; p. 259.
Fajans, "Acoustical Touch Panel"; IBM Tech. Disci.
Bull.; vol. 20, No. 7; Dec. 1977; p. 2925.

Primary Examiner—Errol A. Krass

Attorney, Agent, or Firm—Antonelli, Terry and Wands

[57] ABSTRACT

A tablet comprising conversion means to convert component forces at three fulcra of an external force applied to one point on a faceplate into electric signals, sensing means to sense that no external force is applied, memory means to store the output signals of the conversion means at the respective fulcra as offset values at, at least, one point of time in the period in which no external force is applied, control means to control so as to execute writing into the memory means upon receiving an output of the sensing means, subtraction means to subtract outputs of the memory means from the outputs of the conversion means at the respective fulcra, and calculation means to execute calculations for evaluating coordinates of the point to which the external force has been applied, from outputs of the subtraction means in accordance with the output of the sensing means.

11 Claims, 12 Drawing Figures