Patent GB-184882-A (GB)
Title: Improvements in or relating to apparatus for indicating and recording the direction and distance of travel of a vehicle
IPC: B63B9/00
Filed: 1921-05-21
Abstract: 184,882. Brewerton, A. E. May 21, 1921. Course-recording apparatus. -The course of a vessel is plotted on a chart by an electromagnetic recording-device which walks over the chart a step at a time. The length of each step is constant, being determined by the throw of an eccentric ; the rapidity of the steps is proportional to the speed of the vessel, the eccentric being rotated through 180‹ every time an impulse is received from a Forbes log; the direction of each step is determined by a gyro-compass, which controls the direction of throw of the eccentric. The plotter comprises two pairs of electromagnets, 5, 6, Fig. 5, which are alternately energized. The energized pair clamps itself to the chart table, which is covered with an iron sheet, and the unenergized or floating pair is then displaced ready to clamp itself in a fresh position. The connection between the two pairs of magnets is by means of a shaft 7, Fig. 6, which has a concentric part which runs in bearings carried by one pair of magnets and an eccentric part which runs in bearings carried by the other pair of magnets. The shaft 7 is connected by gearing 9 and a flexible shaft 8 to a motor 17, Fig. 9, which drives a wheel 15 through worm gear, the gearing being such that the shaft 7 copies the angular movements of the wheel 15. The wheel 15 carries a split contact plate 16 engaged by brushes 18, 19 on a secondary compass wheel 14, which is controlled in known manner from a gyro compass. The wheel 15 and eccentric shaft 7 are normally maintained by a hunting action in angular positions corresponding to the secondary compass 14. but every time an impulse arrives from the log the wheel 15 and shaft 7 are given a half-revolutinn. The impulses from the Forbes log alternately energize and de-energize a relay 20, so as to supply current to one of the brushes 18, 19 and to short-circuit one of the pairs of magnets 5, 6. Suppose that at a given moment the relay 20 is de-energized, so that the magnets 6 are energized. The arrival of the next impulse energizes the relay 20, which de-energizes the magnets 6, energizes the magnets 5, and supplies current through the brush 19 and one or other half of the contact plate 16 to the motor 17, which rotates the wheel 15, 180‹ until the brush 19 arrives on the insulating gap between the two half rings of the plate 16. The eccentric shaft 7 is turned to the same extent as the wheel 15, so that the magnets 6, which are now the floating pair, are displaced on the chart relatively to the magnets 5, which are now the fixed pair, At the next impulse the magnets 5 become the floating pair and are displaced relatively to the magnets 6, which are then the fixed pair, and so on. As long as a straight course is steered the plotter walks in a straight line. When a change of course occurs between two impulses the angular change of the gyro compass is repeated to the eccentric shaft 7, so that the next impulse clamps the floating pair of magnets at an angle which is correspondingly greater or less than 180‹ from their last position, and the pencil carried by the plotter traces a corresponding change of course on the chart. In the modification shown in Fig. 10, the impulses from the Forbes log alternately energize and de-energize a magnet 35, which controls an escapement device 31, 34, 32 to allow the motor 29 to give the wheel 15 a half -revolution. The alternate energization of the magnets 5, 6 is controlled by the brush 38 on the secondary compass 14 engaging the divided contact plates 36, 37 on the wheel 15. The division between the plates 36, 37 is unsymmetrical, so that one pair of magnets is short-circuited for a longer period than the other; this disparity may be varied by adjusting the brush 38 radially in the wheel 14, whereby the scale plotting may be altered. The gyro-compass error dependent on the speed, course, and latitude of the vessel may be corrected on the secondary compass wheel 14 by the device shown in Fig. 7<A>. The driving-worm of the wheel 14 is slidably feathered on its motor shaft and is formed with a series of grooves 14a engaging a pinion 14<b> attached to the knurled head 14<c>. When this head is turned the grooves 14<a> act like a rack and move the worm on its shaft, thus superimposing a correction on the wheel 14. Correction for tide is made by fitting the plotter with a threaded drift-bar 43, Fig. 12, which can be angularly adjusted by a protractor 45. The bar is rotated at definite intervals by an electromagnetic ratchet 48 and advances a nut 44 carrying the plotting pencil 11. The throw of the armature 47 can be adjusted by a screw-stop so that it turns the ratchet from one to five teeth every time according to the rate of the tide. For marking intervals of time on the plotted course, the pencil 11 may be mounted eccentrically in a pinion 50, Fig. 13, which is rotated every 15 minutes by an electromagnetically operated rack 54, to draw a circle on the chart. Instead of covering the chart table with an iron sheet, the magnets of the plotter may be provided with armatures attached to the rubber diaphragms of suction cups, as shown in Fig. 14.