GB1308548A - Position indicating system - Google Patents

Abstract

1308548 Co-ordinate determining arrangement THOMSON - CFS VISUALISATION ET TRAITEMENT DES INFORMATIONS 18 March 1970 [19 March 1969; 31 March 1969] 13129/70 Heading G1N [Also in Divisions G4 and H4] The co-ordinates of the position M on a rigid plate at which a force is applied (for example by a finger) is determined from the signals derived from transducers supporting the plate. As shown for piezo-electric transducers C 1 - C 4 are disposed in a square and the sides C 2 C 1 and C 2 C 3 represent the X and Y axes respectively. If X and Y represent the co-ordinates of the point M on the plate 8 at which the force is applied and F 1 , F 2 , F 3 , F 4 represent the reaction forces sensed by the transducers then, F 1 +F 2 +F 3 +F 4 = F, and by taking moments X = K(F 1 +F 4 )/F and Y = K(F 3 +F 4 )/F Signals G 1 , G 2 , G 3 , G 4 Fig. 2 (not shown) proportional to the respective forces are derived from the transducers and integrated, G 1 and G 4 being added at 51, 63 and G 4 being added at 53, and all four being added at 52, division circuits 61, 62 then being provided so that output signals H 1 , H 2 representative of X and Y are derived. To overcome the effect of extraneous signals due to vibration an OR gate 2 and a threshold circuit 3 are provided to control gates 41 ..... 44 upstream of the adders. If A-D converters are provided after the integrators 11 ..... 14, the circuit may be designed thereafter in a digital form. In a modification Fig. 3 (not shown), the sensors are piezo-electric devices are of a type that resonate and have a Q factor dependent on the applied pressure. These devices are fed with a signal at their resonate frequency, the amplitude of the output obtained (which is dependent on the Q factor and hence the forces) being utilized in a circuit similar to that of Fig. 2 (not shown). If the plate 8 is of glass and disposed above a cathode ray tube screen the signals H 1 H 2 obtained by pressing on the plate may be utilized to trace curves on the screen. The plate 8 may be suspended by extensionresponsive transducers.