Patent GB-1179824-A (GB)
Title: Navigational beacon
IPC: G01S13/933
Filed: 1968-05-21
Abstract: 1,179,824. Light-wave navigation. INTERNATIONAL BUSINESS MACHINES CORP. 21 May, 1968 [11 July, 1967], No. 24080/68. Heading H4D. Specification describes an optical navigation system wherein at a transmitter site 10 fan beams 18, 20, Fig. 4, of laser radiation are scanned through sectors of space, the laser radiation being pulsed at a repetition frequency which varies as a function of the direction of the beam. Thus at a co-operating receiver site 12, the angular position of said site with respect to the transmitter site can be determined from the repetition frequencies of the received beams. Beam 18 rotates in azimuth and gives bearing information and beam 20 rotates in azimuth and also scans in elevation 21, thus giving altitude information. By providing the receiver with a retro-reflector 112 the range of the receiver may be determined at the transmitter site from interval between the transmission of a pulse and the reception of its echo, said range being transmitted to the receiver site by pulse modulating the bearing beam 18 with pulse pairs, the spacing thereof representing said range. At the transmitter site, Fig. 5A, a crystal oscillator 117 synchronizes all operations. The laser beam transmitters 100 and 104 are rotated by rotator 124 powered by oscillator 117 via power amplifier 120. Rotator 124 produces a signal indicating the bearings of the beams and this is fed into angle sensor 146 together with a signal on line 148 representing the flight direction &c. of the transmitter site. Output 150 thus indicates the relative bearings of the beams and is used via means 152, 156 and 168 to control the repetition rate of the laser pulses from bearing beam transmitter 100. The variation of the repetition frequency with angular displacement of the beam may be as shown in Fig. 2B or as in Fig. 2C. Rotation 124 also drives a nodding drive 116 whereby the altitude beam transmitter 104 is caused to nod in elevation. The scan angle of elevation relative to the flight direction of the transmitter site is determined by sensor 128 and the resultant output used to control the repetition rate of the laser pulses from altitude beam transmitter 104. When the two beams intercept the receiver station, Fig. 5B, they are reflected by the retro-reflector thereof and the echoes 18<SP>1</SP>, 20<SP>1</SP> are received back at 110, the repetition frequencies thereof giving the relative bearing and altitude of the receiver site respectively. Such repetition frequencies are detected by detectors 160 and 142 respectively using the outputs of the angle sensors 146 and 128 as references, and the bearing and altitude indicated on display 196. The time of the reception of a bearing pulse echo is compared in counter 186 with its transmission time on line 187, and the resultant range information is fed for display at 196 and also to control the spacing of pulse pairs generated at 190. These pulse pairs then modulate the output of the bearing beam transmitter 100. At the receiver station, Fig. 5B, the beams 18 and 20 are received at optical means 114 to provide two signals on lines 212 and 250. The difference of these two signals is formed at output 254 of signal combiner 253 and is used to control a servo amplifier 200 powering retroreflector and receiver optics direction motor 204, whereby said retro-reflector and optics track the transmitter station. The same signal output of combiner 253 is detected and the altitude and bearing components separated out to give bearing and altitude from counter 229 (using the output from clock 222 to determine the repetition frequencies) and the range from counter 227. Since beams 18 and 20 are directed in opposite directions they are received alternately and a simple switch 236 directs the bearing and altitude results to inputs 238 and 240 of display 230. If the beams are in the same direction, i.e. as in Fig. 1, they may be distinguished by polarization or carrier frequency.