US 2809603 A
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Oct. 15, 1957 J. BELL APPARATUS FOR THE STABILIZATION OF SHIPS 2 Sheets-Sheet 1 Filed March '7, 1952 %/A/vPL/F/El? 2 771 15 GYQOSCOPE f/A w/va H25 SP/NDLE AX/S MOUNTED ATHWAQTISH/P Z 7 vaoc/ry SEA/SA alum/1365 1,
Oct. 15, 1957 J. BELL APPARATUS FOR THE STABILIZATION OF SHIPS Filed March 7, 1952 2 Sheets-Sheet 2 lVlET/JDYNE Unite APPARATUS FOR THE STABILIZATION OF SHIPS John Bell, Beckenham, England, assigior to Mnirhead & Company Limited, Beckenham, England This invention relates to the stabilization of ships, which may be carried out in known ways as, for example, by means of movable fins or hydroplanes, water jets or the like. The invention is adapted for use with any of these means but is particularly suited to the control of movable fins or hydroplanes and is described in relation thereto.
The fins are structures which project from the sides of the ship, usually on the curve of the hull between the upright portion and the bottom, and are mounted upon shafts so that they may be tilted in order to impose a torque upon the ship to counter the roll.
The natural rolling motion of a ship is harmonic in character but this motion is, in the practical case, dis turbed by Wave motion, wind and other factors. Nevertheless the roll tends to have a periodic time approximating to the natural periodic time of the ship, so that large and small roll cycles tend to occupy the same time period but the roll velocity varies. In known ship stabilisation arrangements two gyroscopes are employed, one being a vertical keeping or pendulous gyro and the other a velocity sensitive gyro. Signals derived from these gyros are applied in any desired combination to control gear which, in turn, governs the movement of the heavy torque-producing means.
The sensing means must be of high sensitivity in order to provide effective stabilisation against small degrees of roll and they must also provide correct signals under conditions of heavy rolling without manual adjustment, to ensure that the stabiliser is fully automatic. It is also important that the changeover time of the stabilising means from port to starboard torque or vice versa be kept short since two changes are required in each roll cycle; desirably the two changes should not occupy much more than 20% of the roll cycle time. The size of the stabilising means is subject to certain practical limitations including considerations for the stability of the ship and, in general, is not adequate to supply a torque sufficient to counter the heaviest degree of roll. Under such conditions the stabilising means can effect a large reduction in the roll amplitude but cannot provide full stabilisation.
Sensing apparatus of high sensitivity and quick response is incapable of producing large mechanical forces to initiate control signals and if the control gear imposes an appreciable load or reaction back, the sensing means may be prevented from following the ships movement freely and the control signal will therefore contain errors. To avoid this difiiculty, elaborate systems have been devised in which the control gear is incapable of reacting back on the sensing means.
An object of the invention is to provide a simplified control system for the stabilisation of ships employing a velocity sensitive gyroscope only (omitting the vertical keeping gyro) arranged so that the fin deflection from the zero torque position is related to roll velocity up to the maximum deflection or torque of the stabilising means and for all roll velocities above this maximum the sta- States Patent ice bilising means remain in the maximum position, but reaction back on the gyro whilst the stabilising means are in the maximum position does not cause an error in subsequent movements of the gyro.
According to the invention, a control arrangement for the stabilisation of ships comprises one gyroscope only, of the velocity-sensitive type, together with means by which the torque-producing means are controlled in a proportional or graduated manner up to a maximum torque value over a relay mechanism having a limited travel and allowing reaction back on the gyro when the said relay mechanism reaches the limit of its travel. Such reaction back affects the movement of the gyroscope whilst the stabilising means are in the maximum position but causes no error in its subsequent movements within the proportional range.
The relay may consist of an electronic, magnetic or hydraulic amplifier and may include synchro or magslip systems and hydraulic servo motors.
The invention will be further described with reference to the accompanying drawings in which:
Figure l is a diagrammatic layout of one arrangement in accordance with the invention.
Figure 2 shows a modification of Figure 1.
Figure 3 is a further arrangement.
Figure 3a is an end view of a part of Figure 3.
Figure 4 shows a modified form of Figure 3.
Figure 5 shows a modified form of Figure 1.
In a practical construction according to the invention a velocity sensitive gyroscope 1 is employed, mounted in known manner with its spindle athwartships, so that the wheel spins in a vertical plane parallel to the fore and aft axis of the vessel. The gyro is mounted according to the known art in such a manner that it has one degree of freedom only, that is to say, the gyro in its casing may be rotated about an axis 20 substantially normal to the deck plane of the ship. An arm 21 is attached to the casings of gyro 1 and is linked to the junction of two springs 22 and 22' and the remote ends of the springs are anchored to a part of the fixed structure. The springs urge the gyro into its normal position in which its axis is athwartships. When the ship rolls, the spin axis of the gyro is forced to tilt with it and the gyro tends to turn about the axis in which it is free, i. e. it develops a precessional torque which is proportional to the velocity with which the spin axis is moved out of its original plane. This torque is opposed by the centralising springs so that the actual movement of the gyro against the springs is proportional to velocity. This is a Well-known arrangement and is referred to as a velocity sensitive gyroscope.
The gyroscpoe may be coupled to control gear directly by mechanical linkage or may conveniently be coupled by the use of synchronous transmission units known as synchros or magslips, which are similar in character. Thus the movement of gyro 1 causes a corresponding rotation of the rotor of transmit synchro or magslip 2 through the medium of the gear and lever system shown.
synchro is a generic term covering data transmission units, including magslips, and these are of a form akin to small electric motors comprising a stator having three equally spaced windings similar to those of a three-phase induction motor and a rotor which may have one or more windings. If the stator windings of two such units are connected together line-to-line and single rotor windings in the two units are connected to an A. C. supply, then the alternating field due to each rotor will, by transformer action, induce voltages in its respective stator windings having magnitudes depending upon their positions with respect to the axis of the rotor winding. If the two rotors are in different angular positions, the respective stator voltages will not balance and out-of-balance currents flow between the two stators. These cur- 3 rents set up additional fields which cause equal torque to be exerted on the two rotors to move them into coincident positions, in which the stator voltages balance and no torque is exerted on either rotor. If one rotor is used as a master and is moved, then the second rotor will act as a slave and will follow.
The movement of the rotor of transmit synchro 2 is reproduced by the rotor of receive synchro 3. The rotor of synchro 3 operates a sensitive hydraulic valve 4 which in turn controls the movement of a pair of hydraulic pistons 5 and 5 actuating an appropriate lever system 6. The structure of valve 4 is old and well known in the art of hydraulic power systems. The force available at synchro 3, which is of the order of a few grams, is thus increased in value to a force which may lie between 10 and 160 pounds and the stroke is likewise increased to a travel of the order of one-inch. This larger control force is used to operate a powerful hydraulic system which directs the torque-producing means.
In operation, gyro 1 precesses in one direction or the other according to the direction of the ships movement and to an extent depending upon the roll velocity. Its movement is transmitted mechanically to transmit synchro 2 and thence over the transmission lines to receiver synchro 3 The movement of this arm operates sensitive hydraulic valve 4.
The length of the valve 4 will be such that when the proportional range of operation is exceeded, there will be a reaction back on the gyro, which, however, as previously mentioned, will introduce no error in the control system.
In a practical case it may, for example, be found desirable that the maximum stabilising torque shall be applied when the angular roll velocity reaches 2 per secnd, and the fins are then tilted to their maximum angles. For roll velocities lower than 2 per second, the fin angles are proportionately smaller but when the roll velocity exceeds 2 per second by any amount, the fins remain tilted to their maximum angles. Operation of the control under conditions of heavy rolling is thus discontinuous to the extent that during that part of each roll in which the roll velocity exceeds 2 per second, the torque-producing means remain in full operation in the desired sense, but when the roll velocity falls below this predetermined figure, the torque-producing means are controlled in a proportional or graduated manner.
When the roll velocity reaches the predetermined maximum, the movement of the arm coupled to the spindle of transmit synchro 2 is such that arm 23 of synchro 3 comes into contact with stops 9. Any movement of arm 24 beyond the position at which arm 23 is held by the stops encounters extra resistance due to the nature of the synchro transmission system. This increased resistance is communicated to gyro 1 and is added to the resistance offered by springs 22 and 22 and the movement of gyro 1 is restricted just as would be the case if stronger springs were used. This, however, causes no error in later movements of the gyro since it remains in the precessed position until the roll velocity drops below the maximum when it begins to move back to its central position and arm 23 moves away from the stop. When arm 23 reaches one of the stops 9, the movement of valve 4 is stopped and the torque-producing means are also stopped in the corresponding position.
Piston 5 operates lever system 6 through a lever 25. A pivoted lever 26, in conjunction with a link 27, forms a parallel lever system. The lower piston 5 bears against lever 26, and, in this way, the separation between the pistons is constant but the pistons are, nevertheless, free to move in unison.
A further pivoted lever 23 which pivots about a pin 29 is carried in a block attached to the ships structure. Lever 28 is linked to the body of sensitive valve 4 by a link 30 engaging lever 28 at an intermediate point 31.
When synchro arm 23 moves in either direction from its central position, valve 4 is opened in one direction or the other. This allows hydraulic liquid to flow into one or the other of the closed chambers below pistons 5 and 5. The piston which is energized begins to move and actuates the lever 6. It also causes lever 28 to move the body of valve 4 in such a direction as to close the valve. This will be recognized as a normal servo follow-up which ensures that the controlled mechanism follows the movement of the controlling mechanism exactly.
Alternatively, other forms of electro-mechanical relay may be used to operate the hydraulic control.
Thus, Figure 2 shows the transmit synchro supplying a rectifier circuit 7 (connections are taken from two of the three stator phases), to provide a circuit for operating an electro-magnetic relay 8 which in turn operates the sensitive hydraulic valve 4.
A further alternative shown in Figures 3 and 3a would be to use a transmitter 2 of the synchro type, again as the control link, but in this case supplying a coincidence transmitter or synchro control transformer 10 giving an ele trical output instead of a mechanical output which would be used as a receiving instrument feeding to a relay or other force-producing means 12. Thus the signal to the control transformer 10 will endeavour to cause the shaft connecting the control transformer to the fin 16 to turn. In so far as it is unable to do so, a signal will be transmitted to relay 12. The relay or other force-producing means is followed up by a hydraulic system; alternatively, as shown, the output may be applied to an electrical generator system such as a metadyne (a dynamo-electric amplifier) 12 (Fig. 3), or alternatively, an amplidyne or a Ward-Leonard system; such a system operating a powerful motor 13 whose duty it is to operate the torque-producing means for stabilisation of the ship. In such a system the torque reaction on the transmitter is generally not large but again by the method of control used, namely, a velocity sensitive gyro, no error in the control is introduced.
A further feature, however, which is desirable for electrical control is to restrain or suitably control the torque of the main power motor when the fin or other torqueproducing means has been moved to the end of its travel. With the electrical link urging further movement of the motor, a maximum torque effort would be produced and, further, the inertia of the motor is required to be arrested at the end of the travel in order to avoid over-stressing of the motor, the gears and the other parts of the mechanism. A method of achieving this is, as shown, to introduce electrical control elements 14' which may be-of a potentiometer type or, alternatively, inductive type such as synchro, etc. located at the torque-producing means in such a way that they come into operation only as the limits of movement are approached.
Thus the motor 13 drives a wheel 15 operating the fin 16 and a radius arm 17 on the wheel 15 towards its desired limits of travel engages one or other of the radius arms 18 respectively on the shafts of the control elements 14. In the last few degrees of movement the rotation of the control elements produces a progressively increasing voltage which may be fed back to the amplifier 11 or to the metadyne system 12 in such a way as to oppose the signal from the magslip or synchro control transformer 10. Such a synchro control transformer is one whose primary is supplied with electrical angular information from the transmit synchro 2 and whose secondary transmits or supplies electrical information or furnishes output impulses dependent upon the impulse signals or information received from the transmit synchro and the position of the fin means 16. In this way a balance will be achieved in which the torque output generated by the motor will be just sufficient to keep the fin or other torque-producing means in the desired position substantially at the limit of movement.
The limiting device may be applied in duplicate, as shown, or alternatively one limit device with appropriate mechanical connecting levers may be employed to provide limits for each direction of motion.
In a further arrangement of remote control, linear inductive devices, transducers, or potentiometers may be used instead of magslips or synchros, the system operating on a balance of voltage between the potentiometer or other device controlled by the gyro and the corresponding instruments coupled to the fin or torque-producing means.
Following known technique, a resetting transmitter of whatever type may be mechanically coupmd to the motor with precise gearing, the purpose of this re-arrangement being to avoid hunting due to possible back-lash in the main drive to the torque-producing means.
The operation by the velocity sensitive gyro of a suitable relay by a mechanical linkage is shown in Figure 5 which is the same as Figure 1 but with the synchro transmission system taken out.
Various other modifications may be made within the scope of the invention.
1. A control apparatus for a stabilizing system for vessels and which system is of the type in which movable fin means projecting from the hull of the vessel constitute torque producing means for stabilizing purposes, said control apparatus including in combination with a vessel including a hull, a movable fin means, a single gyroscope comprising a velocity sensitive gyroscope mounted with its spindle axis athwartship so as to spin in a vertical plane parallel with the fore and aft axis of the vessel, said gyroscope having only one degree of freedom about a vertical axis and being rotatable about an axis substantially normal to the deck plane of the vessel whereby the angular velocity of rolling of the vessel will cause a precessional torque to be exerted by the gyroscope deflecting from zero up to a predetermined maximum that is proportional to the velocity with which the spindle axis is moved, spring means operatively associated with the gyroscope to oppose the torque and urge the gyroscope into normal position with its axis athwartship whereby the torque is converted into movement that is proportional to the rolling velocity, a transmit synchro, coupling means between said gyroscope and said transmit synchro so that the latter furnishes impulse signals responsive to gyroscope deflection, a synchro control transformer means connected to said fin means, means coupling said transmit synchro to said synchro control transformer means so that the latter is responsive to said gyroscope deflection and furnishes output impulses dependent upon the impulse signals received from the transmit synchro and the position of the fin means, power imparting means for actuating the fin means, coupling means between the synchro control transformer means and the power imparting means and actuated by the impulses from the synchro control transformer means to actuate the power imparting means to correspondingly actuate the fin means between zero deflection position and predetermined maximum positions in opposite stabilizing movements and means limiting the travel of the fin means in opposite stabilizing movements at least as the fin means approach a maximum position in said movement so as to allow reaction back on said gyroscope at least when said fin means are in a maximum position to restrict further movement of said gyroscope until roll velocity falls below maximum.
2. A control apparatus as claimed in claim 1 in which the power imparting means comprises an electric motor and the coupling means between said synchro control transformer means and said motor comprises an electrical generating system operable in response to output signal impulses from said synchro control transformer means to correspondingly actuate said motor.
3. A control apparatus as claimed in claim 2 and the means limiting the extent of travel of the fin means including electrical control means actuated in response to the fin means approaching the limit of travel and operably associated with the electrical generating system between the synchro control transformer means and the motor to furnish impulses to said system operative to reduce the torque output of the motor so as to keep the fin means in a position substantially at the limit of travel until the rolling velocity falls below maximum.
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