GB1237368A - Improvements in or relating to automatic steering systems - Google Patents

Abstract

1,237,368. Automatic steering. O. W. DUMPLETON. Aug. 1, 1968 [May 17, 1967], No.22854/67. Heading G3R. An automatic steering system comprises a magnetic compass 1 mounted on a steerable body e.g. a ship; a sensor e.g. photo-cells 15, 16, which gives an electric signal indicative of the orientation of the magnet system relative to the body and a controller 3 responsive to the electric signal to operate steering means e. g. motor 8 to correct any deviations of the body relative to a pre-set course on the compass, wherein the controller 3 produces a control signal for the steering means which contains a function of the difference between the sensor signal and a second signal which is a time-delayed opposite by polarized function of the sensor signal. In operation on deviation of the ship from a set course photo-cells 15, 16, which view the diametrically divided black-and-white card 10 through prisms 19, 18, feed an amplifer 20 to produce a signal proportional to the sense and magnitude of the error. This signal is fed via a potentiometer 21 and signal limiting amplifier 22 having a linear response over a restricted range of deviation to a terminal 24 whence part of the signal is fed to a potentiometer 25. A portion of the signal is applied to one end of potential divider 26, 27 directly and the remainder is applied to the other end through a degenerative inverter amplifier 29 which provides a time-delay adjustable by a switch 32 which inserts any one of three capacitors 33, 34, 35 into a capacitive feedback loop 31. The signal produced a junction 37 is proportional to the algebraic sum of the voltage from limiting amplifier 22 and the reverse polarity time delayed voltage from amplifier 29. This signal is fed through amplifier 50 to cause one or other of the power transistors 6, 7 to conduct and energize motor 8 in the correcting sense. Movement of the helm produces a feedback signal which is applied from potentiometer 9 and resister 60 to junction 41. If the rate of decrease of the course error remains constant a constant voltage is produced at junction 37 and a constant countering'helm is applied by motor 8 so that the voltage tapped off potentiometer 9 is equal to the voltage at 41. In practice as soon as the correcting helm is applied, the rate of change of the course error is reduced. As the ship commences to swing back on course, the voltage at junction 24 diminishes, but the delaying action of the analogue delay circuit amplifier 29 causes the controller to see an error which is less than exists and still diminishing. As the ship approaches the chosen course, the voltage at junction 37 reverses causing opposite helm to be applied. As the swing through the chosen course continues the voltage at junction 37 reduces so that a relatively decreasing corrective helm is applied. After the swing back to the chosen course commences the helm gradually reverses to counter the swing and apply a "meeting" helm. To compensate for a continuous error to port or starboard produced for example by windage a capacitor 44 is initially charged to the potential of junction 24 whilst the ship is on course, by adjusting the potentiometer slider 46 whilst switch 70, 71 is in position 1 or 2. When the switch is moved to position 3 corresponding to automatic steering, the capacitor charge slowly varies in response to deviation of the craft from the set course and the aggregate error signal is fed through a field effect transistor amplifier 42 to be added to control signal from junction 37. The compass card is illuminated by a lamp 13 which preferably flickers so that by means of circuitry not described the output of compass 1 will be influenced solely by variations in the flickering source of light and not by ambient light fluctuations.