Patent GB-994896-A (GB)
Title: Improvements in arrangements for inertial navigation
IPC: G01C21/18
Filed: 1962-02-05
Abstract: 994,896. Inertial navigation. AGA A. B. Feb. 5, 1962 [Feb. 5, 1961], No. 4314/62. Heading G1C. A horizontal platform carries one or more gyroscopes 21 which are made to presess at a constant rate with reference to the horizontal, such as the type described in Specification 972, 762, and one or more accelerometers responding to asselerations in the plane of the platform, and, if the platform deviates from the horizontal, signals from the or each gyroscope are used to restore the horizontality of the platform, and whilst this is occurring, also supply corrections to the output of the or each accelerometer. As shown the accelerometer is of the type described in Specification 980, 492 in which a continuously revolving disc 20 carries weights eccentrically suspended between springs, the radial position of the weights being sensed by pickoffs supplying a sine-cosine resolver 22. The phase and amplitude of the modulating frequency in each output 23, 32, thus indicates the vector components of direction and magnitude of the linear acceleration in two perpendicular directions e.g. north-south and eastwest. As the output in each coil 23, 32 is further processed in a similar manner only one of them, viz that from coil 23, will be described. An oscillator 25 controlled by crystal 26 generates a frequency of 98, 304 e/s. which is stepped down in the ratio 1: 32 in divider 29 so that a frequency of 3, 072 c/s is supplied through amplifier 30 to lines 27, 28, 34. That in line 27 supplies the carrier frequency for the pick-ups of the accelerometer and line 28 supplies a reference with which the output from coil 23 is compared in phase detector 24. A device 33 is supplied with pulses, from 24, whose widths correspond to the magnitude of the component of acceleration in the one coordinate direction and also with pulses derived from the frequency in lines 27, 28, through line 34. The device 33 compares the tur sets of pulses and supplies them at 35 to further devices, not shown, supplied with similar outputs derived from coil 32, so that a digital indication of direction and magnitude of the acceleration and, though integration of speed and distance travelled is furnished. Two gyroscopes, such as 21, maintain the platform horizontal in the two coordinate directions. Each has its rotor speed controlled by a 384 c/s current in line 47, derived from divider 38, having a demultiplying ratio of 1: 8, after amplification at 61. A light source 45 and photo-cell 46 form a scanner associated withthe rotating disc 44 having alternate opaque and transparent segments so that 3 c/s pulses are supplied through line 50 to phase detector 43 for comparison with the 3 c/s reference frequency in line 42 derived from divider 40 having a ratio of 1: 128. When the platform is level no signal appears in the output of phase detector 43, but when it is not, a signal is delivered through line 51 to a modulator 52 supplied with 384 c/s carrier frequency through line 53, and the modulated signal is resolved at 54 into its sine and cosine components which appear at coils 55, 56. These coils are connected by lines 57, 58 to the two torques 59, 60, associated with the accelerometer platform to restore it to the horizontal. Simultaneously the output of photo-cell 46 is fed to an electronic gate 37 also supplied with the reference 3 c/s frequency through line 41. So long as the two frequencies are equal, i.e. the platform is horizontal, no pulses appear in the output of gate 37, but when the frequencies differ due to platform inclination, the gate 37 supplies a number of pulses which are added to, or subtracted from, those at 33 so that the output at 35 is corrected from platform inclination.