Patent GB-805820-A (GB)
Title: Improvements in or relating to measuring devices
Inventor: WUERTH JOHN M
IPC: G01P15/08
Filed: 1954-07-20
Abstract: 805,820. Electric analogue calculating systems. NORTH AMERICAN AVIATION Inc. July 20, 1954, No. 21192/54. Class 37. [Also in Group XIX] The invention relates to the use of the inertia forces of a rotating flywheel for integration and differentiation and provides apparatus which may be used as an integrating accelerometer. When a torque is applied to a flywheel, the angular velocity of the wheel is proportional to the first integral of the torque, and the angular position is proportional to the second integral of the torque. Alternatively, by controlling the position or velocity of the flywheel the reaction torque, due to changing motion of the flywheel, is proportional to the second or first derivative of the controlling signal respectively. Apparatus.-As shown, a pivoted platform or "stator" la houses a combined motor/ flywheel unit 4 and generator 15a, giving a signal proportional to the angular velocity. The end face 36 of the motor has strobe markings enabling the angular position to be detected by a photo-electric system 34, 35, operating a counter 37, and a potentiometer 20 driven by the motor provides signals proportional to the angular position. Movement of the stator is detected by a differential capacitor 8, 9, 10 connected in a bridge circuit 11, or alternatively by a photo-electric detector, Fig. 6, not shown. An electromagnet 19 may be used to apply a balancing torque to the stator. Operation : integration.-When a torque is applied to the platform tending to rotate it, the movement signal from the capacitor pick-off circuit passes through an R.C. network 12 which introduces a differential signal to prevent hunting and is amplified at 14 and fed to the motor 4 causing it to exert a substantially equal and opposite torque on the stator. Then the velocity signal from the generator 15a is proportional to the integral of the applied torque, and the displacement measured by the revolution counter 37 is proportional the double integral of the applied torque. Differentiation.-A voltage signal to be differentiated is applied to a comparator 17 and compared with the output of the generator 15a and the difference signal is amplified at 18 to drive the motor 4 so that its speed varies with time according to the function to be differentiated. The reaction torque on the stator is opposed by the electromagnet 19 energized from the amplifier 14 to. maintain the stator stationary. Movement of the stator is detected by the capacitor pick-off as before, and the output of discriminator as indicated by a voltmeter 16 or the current supplied the electromagnet as indicated by an ammeter 21 are measures of the reaction torque, i.e. the first derivative of the voltage signal applied to the comparator. Alternatively, if the input signal is compared with the output of the potentiometer 20 so that the angular position of the motor varies with time according to the function to be differentiated, the reaction torque is a measure of the second derivative of the input signal. Measurement of acceleration.-If the stator is unbalanced, as by a weight 33, movement of the whole apparatus (vertically, as shown) produces a torque proportional to acceleration of the apparatus which acts in the same manner as the externally applied torque described above (see integration). Thus the acceleration (torque) and its first and second integrals may be measured as described above.