GB986318A - Improvements relating to navigational intertial platforms - Google Patents

Abstract

986,318. Inertial navigation systems. FERRANTI Ltd. Feb. 4, 1964 [Feb. 6, 1963], No. 4800/63. Heading G1C. An inertial platform of the kind having X and Y-axis gyros 4, 5 for stabilizing the platform about the X and Y-axis in accordance with signals derived from Y and X-axis accelerometers 7, 8 respectively, and a Z-axis gyro 6 for stabilizing the platform about the Z-axis, includes means for aligning the X-axis of the platform with the East-West direction, comprising an integrator for integrating the output signal from the Y-axis accelerometer 7 in the X-axis gyro loop, means for dividing the said output by a signal representing the product of the earth's rotation rate and the cosine of the lattitude at which the platform is located to determine the deviation of the X-axis from the East-West direction and means for applying a precession signal to the Z-axis gyro 6 for a time proportional to this deviation, the signal being such as to cause the Z- axis gyro to rotate the platform to remove the deviation. Prior to use the platform is approximately aligned with the X-axis disposed East- West by reference to e.g. a gyro-magnetic compass and the following procedure is then adopted using the circuit of Fig. 2. Switches 12, 16, 18 are opened and the switch 20 closed, and the switch 29 is moved to the position 2a for a set time e.g. ten minutes, the switch 37 remaining open. The signal from the Y-axis accelerometer is applied to the integrator formed by an amplifier 32, motor 33 and tachometer generator 34 and causes rotation of the shaft of the motor 33 from a zero position. The switch 29 is then moved to position 3 and the switch 37 closed. For all positions of the switch 35 other than the zero position one or other of its segments makes contact with the infer according as to whether the deviation of the X axis from East-West is positive or negative. Thus a constant current source 36 is connected to the precession coil of the 2-axis gyro 6, and the output signal from the Y- axis gyro (proportional to the cosine of the latitude) is applied to run the output shaft of the motor 33 back to zero. In this way the X-axis is aligned with the East-West direction, the theory being discussed in the Specification. The use of the apparatus in normal operation with the switches 12, 16, 18 closed switches 20 and 37 open and with the switch 29 in position 1 is also described in the Specification, the Z-axis gyro being then precessed only by a signal from a source 39 which signal represents the product of the earth's rotation rate and the sine of the latitude.