GB1528581A - Position sensors for displays - Google Patents

Abstract

1528581 Position co-ordinates sensor DEFENCE SECRETARY OF STATE FOR 4 Feb 1967 [4 Feb 1975] 4776/75 Heading G1N Apparatus for generating co-ordinate signals X, Y to represent the co-ordinates of any selected point on a display device includes a substantially rigid sheet 5 mounted on four force-sensing transducers in the form of strain gauge bridges 1, 2, 3, 4 and providing signals representative of the force applied to them to a computing circuit, 7. Taking the co-ordinates of the transducers as (O, M) (L, M) (O, O) and (L, O) respectively and the force applied at the selected point as F z where F z = F 1 + F 2 + F 3 + F 4 and F 1-4 are the forces sensed at the transducers then X = L(F 2 + F 4 )/F z and Y = M(F 1 + F 2 )/F z . The circuit shown in Fig. 2 calculates these co-ordinates. If F z is below a given threshold represented by reference voltage source 23 then comparator 22 acts with relay 24 to earth the output lines 8, 9 and to signal "no point indicated" via line 25. This is because if the dividers 19, 21 receive denominators below a given value they give incorrect results. In an alternative embodiment only three force-sensing transducers are used, at co-ordinates (O, M) (O,-M) and (L, O) when X = F 3 L/F z ' and Y = M(F 1 -F 2 )/F z ' where F z ' = F 1 + F 2 + F 3 , the sum of the signals from the three transducers.