GB1173442A - Improvements in or relating to the Positional Control of Water Borne Vessels - Google Patents

Abstract

1,173,442. Radio navigation. DECCA Ltd 17 May, 1968 [19 May, 1967], No. 23348/67. Heading H4D. [Also in Division G3] A floating vessel is maintained in a desired position and heading, or on a predetermined course and heading, by automatic control of two vertical axes, variable pitch propellers positioned respectively at the bow and stern, the error signals of position and heading being obtained respectively from a radio position fixing system between the vessel and the shore and from the magnetic or gyroscopic compass of the vessel. A transmitter and receiver unit 4 carried by the vessel transmits continuous wave constant frequency radio signals to shore-based stations 6, 8 which re-radiate signals synchronized in phase with the transmitted signals for phase comparison in the receiver of unit 4 with the transmitted signals, thus providing positional output signals which are converted by a digital computer 20 to geographical positional co-ordinates. The latter are compared in comparator 24 with fixed or time-varying signals from a generator 26 respectively representative of the desired position or course and the two-error signals so produced are fed to a resolver 28 controlled by the compass 16 to produce output signals 32 representing the positional error in axes defined by the heading direction (X) and transversely thereto (Y). The signals 32 are fed to respective control amplifiers 34 whose frequency characteristics are suitably chosen to provide overall stability of the complete closed loop system. The outputs of amplifiers 34 are fed via a change-over switch 38 to coefficient and summing devices 60, 62, 64, 66 of which 62 and 66 also receive heading error signals for combination with the Y components of the positional error signals. Members 60-66 respectively control units 68, 70, 72, 74 forming control pairs for the bow and stern propellers 10, 12 to vary the thrust in the X and Y directions. The heading error signals are obtained from a circuit comprising the compass 16, comparator 44 fed with a desired heading signal manually adjustable by member 46, amplifier 50, change-over switch 54 and inverter 59. Switches 38, 54 permit manual control of the position and heading by members 40, 42 and 56, 58 respectively. The computer may be omitted if shore stations 6, 8 are suitably located to provide ranges for use directly as geographical cartesian co-ordinates. An additional transmitter and receiver 84 and additional shore stations 80, 82 may be provided to insure against failure of the system comprising members 4, 6, 8. If the vessel is to be moved continuously or in steps along a predetermined path, e.g. in a dredging operation, by time varying the position signals from generator 26 to define the required track, such variation may be produced by an electromechanical timing device or by suitable programming of the computer 20.