GB2470961A

GB2470961A - Gyroscopic controllable moment generator adapted for use onboard a marine vessel

Info

Publication number: GB2470961A
Application number: GB0910191A
Authority: GB
Inventors: Alan John Murphy; Ramanand Ajit Shenoi; Nicholas Charles Townsend
Original assignee: University of Southampton
Current assignee: University of Southampton
Priority date: 2009-06-12
Filing date: 2009-06-12
Publication date: 2010-12-15
Anticipated expiration: 2029-06-12
Also published as: GB0910191D0; GB2470961B

Abstract

A gyrostabiliser system is provided comprising: at least two flywheels 14,14', each having a respective spin axis; a first drive system 18,18', adapted to rotate the at least two flywheels 14,14', about their respective spin axes; at least two gimbal supports 10,10' each being arranged, in use, to mount a respective flywheel 14,14', to a fixed base 4, each flywheel 14,14' being rotatably mounted in a respective gimbal support 10,10', each gimbal support 10,10', being rotatably mountable to the fixed base 4 for rotation about a nutation axis which is orthogonal to the spin axis of the respective flywheel 14,14'; a second drive system 20 adapted to rotate the gimbal supports 10,10', and the respective flywheel 14,14' mounted therein; and a control system for controlling the second drive system 20 and adapted selectively to switch it between an oscillatory mode, for causing oscillatory nutation of the gimbal supports 10,10', and a continuous mode, for causing continuous nutation of the gimbal supports 10,10'. The system is particularly suited to improving the motion characteristics of a marine vessel subject to uncontrolled and undesirable movements resulting from wave and/or wind forces.

Description

CONTROLLABLE MOMENT GENERATOR

The present invention relates to a controllable moment generator, in particular a gyroscopic controllable moment generator. More particularly, the gyroscopic controllable moment generator may be adapted to be used as a motion control device for incorporation into a vehicle, for example a marine vessel such as a boat or ship.

The present invention further relates to a marine vessel having mounted therein a controllable moment generator device according to the invention. The present invention yet further relates to a method of controlling the motion of an object.

Vehicle motion can cause uncontrolled and undesirable movements. This is a particular problem for marine vessels, which, due to wave and/or wind forces, may be subjected to angular movements such as pitch and/or roll and/or yaw and translational movements such as heave and/or sway and/or surge. Such motions of a marine vessel, such as a ship, can cause undesirable phenomena including: motion sickness of the crew, loss of vessel stability potentially resulting in capsize of the vessel, loss of steering, shipping water into the vessel, slamming, cargo damage and decreased propulsion efficiency. These phenomena can affect the resistance, safety and economic viability of marine operations.

There is a need in the art for systems or apparatus to control or improve the motion characteristics of a vehicle, in particular marine vessels, subjected to such uncontrolled and undesirable movements. Such systems or apparatus are highly sought after.

Motion control systems have been fitted to a variety of marine structures and vessels, and can be classified as either external or internal.

External systems are exemplified by fins, bilge keels, foils, jet flaps, rudder control devices, trim tabs or interceptors which extend outwardly from the hull of the vessel into the water. Such external devices are typically used on passenger ships, and rely on hydrodynamic principles. External devices often have the advantage of being lightweight. However, such external systems are vulnerable to inadvertent damage, from slamming, grounding, submerged objects, debris or wildlife, for example,, are ineffective when the vessel is stationary and or moving at slow speeds, and can create hydrodynamic drag.

A first type of internal system is exemplified by a moving weight system, the weight being liquid or solid. Such a system is typically used on deadweight carriers e.g. offshore supply vessels. These systems have the advantage, compared to external systems, of avoiding the addition of hydrodynamic drag. Internal systems are less liable to inadvertent damage as compared to external systems. Internal systems are usually also effective at zero forward speed. However, such internal systems utilise otherwise exploitable space and weight within a ship, which limits the load carrying capacity of the ship.

Another known internal system comprises a gyrostabiliser. Gyrostabiliser systems generate stabilising moments entirely within the hull of a vessel without simply relying on providing sufficient movable weight. Such gyrostabiliser systems are becoming of increased interest in the marine vessel art, and are a re-emerging solution.

Gyrostabiliser systems are effective at zero forward speed. Such gyrostabilisers also have the advantage as compared to external systems in that they do not add additional hydrodynamic drag, are not prone to damage from submerged objects, do not require a vessel to be dry docked for maintenance, can generate artificial ship motions, and have low locational dependency and, as compared to current internal moving weight systems, represent a weight and volume saving.

However, current gyrostabiliser systems suffer from the problem that they are limited in their stabilisation capability, for example providing a limited duration of stabilising moments, providing a limited stabilisation time, or reaching a stabilisation saturation, or having a limited stabilisation capacity relative to the size (i.e. weight or internal space) of the vessel.

Currently available gyrostabilisers have a limited application to particular vessels, which is determined by the maximum threshold of the magnitude of the stabilising moments which the gyrostabiliser is capable of generating.

A gyrostabiliser uses the inertial property of a rotating body or flywheel to apply moments to a vehicle (or other object) to alter the amplitude of oscillatory motions that a vehicle suffers when subject to external excitation (e.g. the wave excitation of a ship).

Referring to Figure 1, the moments acting around each orthogonal axis of a gyroscope, assuming the xyz axes are chosen to coincide with the principal axes of inertia of the body, rotating with the body but not spinning with the body, and a symmetrical rotating body or flywheel in x and y axes, (i.e. II,=I and IxyIIxzIzxIyz=IzyO), can be expressed as; (1) M = i ( + ) - (a + (2) = (o. +) (3) where: M, M and M are, respectively, the moment acting about the x, y or z axis, I is the mass moment of inertia of the rotating body or flywheel, about the x or y axis, I is the mass moment of inertia about the z axis, w &, and a, are, respectively, the rate of rotation of the gyroscope about the x, y or z axis, th ó, and d are, respectively, the angular acceleration of the gyroscope about the x, yorz axis, is the spin rate of the rotating body or flywheel, and is the angular acceleration of the rotating body or flywheel.

When operating, the rotating body or flywheel within the gyroscope rotates about an axis, which itself is free to rotate. Therefore, in addition to the usual terms that account for moments when the rotating body or flywheel is not spinning, Equations.

(2) and (3) indicate the existence of additional gyroscopic moments, that act around the x and y axes (i.e. M = Jv and M = -Jwfr). These gyroscopic moments are used to apply stabilising moments in gyrostabilisers.

In a gyrostabiliser, one of the gyroscopic axes is fixed to the axis of the vessel about which the undesirable (target) motion occurs. The other axis of the gyroscope is permitted to rotate independently of the vessel.

In one particular arrangement, known as a passive gyrostabiliser system, the moment causing the undesirable motion is reacted by the gyroscope and results in a rotation of the gyroscope about its free axis, which rotation may be damped by the provision of damping elements.

In another particular arrangement, known as active gyrostabiliser system, the gyroscope is forced to rotate about its free axis, such rotation herein being known as nutation, resulting in a motion-controlling moment being generated about the ship-fixed axis of the gyroscope.

For both passive and active gyrostabilisers the stabilising effect is dependent on; * The mass-moment-of-inertia of the rotating body or flywheel about the spin axis, i, which is dependent on both the magnitude and distribution of the weight within the body or flywheel, * The spin rate of the body or flywheel about the spin axis (i) and, * The rate of rotation of the gyroscope about its free axis, (w or at,, depending on axis definition).

The rate of rotation of the rotating body or flywheel of the gyroscope about its free axis (u or &,,). in a gyrostahiliser, must retain a phase relationship to the excitation.

In an active gyrostabiliser, where this rotation (a or o) is forced by nutation, a greater magnitude of rotation can be generated (for a given excitation), compared to an equivalent passive system, providing a greater stabilising effect. However in currently commercialised active gyrostabiliser systems, the gyroscopic moments act solely about the desired ship-fixed axis of rotation when the plane of the flywheel is oriented in one axis (dependent on the arrangement and orientation of the system).

Thus, the gyroscopic moments act around the desired ship-axis of rotation in proportion to the cosine of its angular displacement from this axis but also (undesirably) about another axis of the ship in proportion to the corresponding sine function. To limit the action of the undesirable moments, currently used gyrostabiliser systems only perform small perturbations (for example, a maximum perturbation of 60 degrees is known for one such system) of the gyroscope about the desired mean position, with the effect of limiting the stabilising moments that can be achieved.

An improved active gyrostabiliser system is to utilise two gyroscopes, spinning at the same rate with forced oscillatory nutation in opposing directions, often referred to as a scissor or v-arrangement control moment gyroscope (herein referred to as a control moment gyroscope or CMG) to provide a moment about a single body-fixed axis, eliminating the undesirable gyroscopic moments. However for such CMG units, the maximum motion-controlling moments provided by the gyroscopes are still restricted because only oscillatory rotations of the gyroscopes are forced (i.e. w or are relatively small, oscillatory variables).

A paper by Townsend, N.C.; Murphy, A. J.; Shenoi, R. A. entitled "A new active gyrostabiliser system for ride control of marine vehicles", published in Ocean Engineering, vol. 34 (2007), Issues 11 -12, p. 1607-1617, discloses a gyrostabiliser in which the gyroscopes of the gyrostabiliser are operated by rotating them continuously by whole revolutions, rather than by oscillatory motion. This can provide a greater stabilising moment under certain operating circumstances.

However, even such a gyrostabiliser system does not readily provide effective stabilising effects over wide range of operation conditions, or a control system coupled to the gyrostabiliser system for achieving such effective stabilising effects over wide range of operation conditions.

The present invention aims to provide a greater stabilising effect and range of effective operation compared to existing gyroscopic systems.

Accordingly, the present invention provides a controllable moment generator device comprising: at least two flywheels, each having a respective spin axis, a first drive system adapted to rotate the at least two flywheels about their respective spin axes, at least two gimbal supports, each being arranged, in use, to mount a respective flywheel to a fixed base, each flywheel being rotatably mounted in a respective gimbal support, each gimbal support being rotatably mountable to the fixed base for rotation about a nutation axis which is orthogonal to the spin axis of the respective flywheel, a second drive system adapted to rotate the gimbal supports, and the respective flywheel mounted therein, and a control system for controlling the second drive system and adapted selectively to switch the second drive system between an oscillatory mode, for causing oscillatory nutation of the gimbal supports, and a continuous mode, for causing continuous nutation of the gimbal supports.

In this specification, the term "flywheel" is intended to refer to any rotatable body suitable for incorporation into a gyroscope, as well as such a body formed as a flywheel.

In use, when two flywheels are present, the first drive system spins the flywheels in opposite angular directions and, when subjected to nutation, the respective gimbals are continuously rotated, or precessed with oscillatory motion, by the second drive system in opposite angular directions. The same relationship applies to any additional pairs of flywheel/gimbal assemblies.

The controllable moment generator device may further comprise at least one external sensor for sensing at least one motion parameter external of the controllable moment generator device and providing first input data for the control system, and at least one internal sensor for sensing at least one motion parameter of the flywheels and providing second input data for the control system Preferably, the control system comprises a mode selector for selecting, based on the first and second input data, a respective mode for operating the second drive system, and a calculator adapted to calculate, from the first and second input data, control parameters for the first and second drive systems.

Preferably, the calculator is adapted to calculate control parameters comprising the nutation angular velocity and the spin angular velocity for each flywheel.

Typically, the internal sensors are adapted to sense the gyroscope motion parameters, such as angle, rate and spin rates, relative to a given axis such as a ship fixed axis.

More preferably, the control system comprises a means to acquire and perform signal conditioning processes, such as filtering and a control selector, based on the at least one motion parameter andlor gyro motion parameters to select a suitable control law to implement, in an autonomous, continuous or continual manner, or by manual selection. Yet more preferably, the control system is adapted to control the first and second drive systems to minimise the resultant moment.

The mode selector may be adapted to select between the oscillatory mode, the continuous mode or an OFF mode for the second drive system.

Preferably, the mode selector is operable automatically by the control system to minimise the resultant moment.

The controllable moment generator device may further comprise at least one damping device for selectively damping oscillatory motion of the gimbal supports, and wherein the mode selector is operable automatically by the control system to activate or deactivate the at least one damping device. Optionally, the controllable moment generator device may further comprise a controller for the at least one damping device for actively damping the oscillatory motion of the gimbal supports.

The controllable moment generator device may further comprise an electrical generator system coupled to at least one of the first and second drive systems.

The first drive system may be optionally configured to act as an electrical generator by drawing power from the stored energy within the rotating flywheels. The second drive system may be optionally configured to act as an electrical generator by drawing power from the precessional motion of the gimbal structures and flywheels.

The present invention additionally provides a marine vessel having mounted therein a controllable moment generator device according to the present invention, the fixed base being fixed to the vessel.

The present invention further provides method of controlling the motion of an object, the method comprising the steps of: (a) mounting a gyroscopic device on the object, the gyroscopic device having at least two flywheels, each having a respective spin axis, a first drive system adapted to rotate the at least two flywheels about their respective spin axes, at least two gimbal supports, each mounting a respective flywheel to the object, each flywheel being rotatably mounted in a respective gimbal support, each gimbal support being rotatably mountable to the object for rotation about a nutation axis which is orthogonal to the spin axis of the respective flywheel, and a second drive system adapted to rotate the gimbal supports, and the respective flywheel mounted therein, (b) controlling the second drive system by selectively switching the second drive system between an oscillatory mode, for causing oscillatory nutation of the gimbal supports, and a continuous mode, for causing continuous nutation of the gimbal supports.

In the method, when two flywheels are present, the flywheels spin in opposite angular directions and, when subjected to nutation, the respective gimbals are continuously rotated, or precessed with oscillatory motion, in opposite angular directions. The same relationship applies to any additional pairs of flywheel/gimbal assemblies.

Preferably, the method further comprises the steps of: (c) sensing at least one motion parameter external of the gyroscopic device to provide first input data for the controlling step; and (d) sensing at least one motion parameter of the flywheels to provide second input data for the controlling step.

More preferably, the method further comprises the steps of: (e) selecting, based on the first and second input data, a respective mode for operating the second drive system; (f) calculating, from the first and second input data, control parameters for the first and second drive systems; and (g) controlling the first and second drive systems by said control parameters to provide a desired resultant moment or to minimise the resultant moment.

Preferably, the control parameters comprise the nutation angular velocity and the spin angular velocity for each flywheel.

The first input data may comprise motion parameters such as angle, rate and spin rate of the flywheels within the gyro scopic device The control mode may be selected from the operating parameters of the flywheels and their respective gimbal supports; and the least one motion parameter external of the gyroscopic device.

Optionally, the controlling step (b) further selectively switches between the oscillatory mode, the continuous mode or an OFF mode for the second drive system.

The controlling step (b) may be effected automatically to minimise the resultant moment.

The method may further comprise the step of: (h) selectively damping oscillatory motion of the gimbal supports.

Optionally, the damping actively damps the oscillatory motion of the gimbal supports.

The method may further comprise the step of: (h) generating an electrical output from at least one of the first and second drive systems.

In a preferred method, the object is a marine vessel.

Accordingly, in accordance with a particular aspect of the present invention, a controllable moment generator device comprises two or more flywheels, supported within gimbal structures, surrounding a portion or all of the flywheel, with flywheel drive motors configured to spin said flywheels about their spin axis. The gimbal structures and flywheels are, at least in use, supported on or within a base body, which permits the rotation around one axis orthogonal to the flywheel spin axis and restricting the rotation about the other axis. A drive motor is configured to rotate the gimbal structures and enclosed flywheels, independently or together, in an oscillatory and/or continuous fashion, with a desired rotational rate and direction. The base body is, in use, secured in or to a portion to the object/vehicle/structure to which the generated moments are to be applied. There may be provided a means to monitor and control/adjust the spin rates of said flywheels, individually and automatically, and/or a means to monitor and controlladjust the rotation of the gimbal structures and flywheels, individually and automatically, in an oscillatory and/or continuous fashion, with a desired rotational rate and direction. The drive motor may be able to act as a generator, and/or the flywheel motors may be able to act as generators.

Through control of flywheel spin rates and directions, and flywheel rotation rates and directions, desirable motion effects can be generated on the object/vehicle/structure to which the device is attached, including: motion damping of the object/vehicle/structure which the device is attached, by allowing oscillatory (damped and/or non-damped) motion of said flywheels and gimballed structures within the secured base structure; energy generation and motion damping of the object/vehicle/structure which the device is attached by allowing motion of said flywheels and gimballed structures within the secured base structure, with rotational drive motor and/or flywheel spin motors acting as generators; providing a desirable motion response/effect through forced oscillatory rotation of the flywheels within said gimbal structures that generates moments which act on the object/vehicle/structure the device is secured to; and/or providing a desirable motion response/effect through forced continuous rotations of the flywheels within said gimbal structures that generates moments which act on the object/vehicle/structure the device is secured to. Any number of possible combinations of each control method can be implemented over a period of time, automatically and continuously to maintain or create a desirable motion response/effect of the object/vehicle/structure the device is secured to. Multiple units can be secured to an object/vehicle/structure to achieve desirable motion responses/effects, arranged in any number of orientations and controlled in combination and/or independently, in any number of possible combinations of each control method over a period of time in an automatic and continuous fashion. The alignment of flywheel spin axes and orthogonal axes are not necessarily restricted to coincide with the object/vehicle/structures presumed' axis system, and/or the axis of each flywheel within the device is not necessarily restricted to being orthogonal and parallel to one another.

The preferred embodiments of the present invention can provide an improved gyrostabiliser which is capable of generating greater stabilising moments than known gyrostabiliser systems. The gyrostabiliser of the preferred embodiments of the present invention can improve the revenue generating capability of a vessel by, for example: reducing any undesirable motions of the vessel; reducing the incidences of sea sickness and improving habitability; reducing the physical and mental fatigue (and human errors) of crew and/or passengers; and reducing drag, improving speed and/or fuel consumption.

The preferred embodiments of the present invention can provide a gyrostabiliser system which is capable of maintaining levels of ride control comparable and greater than existing stabilising systems, as discussed above.

The gyrostabiliser systems of the preferred embodiments of the present invention have particular application as a motion control device for marine craft, though other motion control or vehicular stabilising applications will be apparent to those skilled in the art. The moment generator may be used or adapted to provide a desired motion control by preventing or reducing undesired motions of a moving vehicle or object or by causing desired motions of an otherwise stationary, in at least the direction of imparted motion, of a stationary vehicle or object.

Embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings, in which:-Figure 1 schematically illustrates the moments acting around each orthogonal axis of a gyroscope; Figure 2(a) and (b) schematically illustrate two gyroscopic stabiliser system embodiments of the present invention; Figure 3 is a schematic diagram of a control system for the gyroscopic stabiliser system of Figure 2; Figures 4(a) and (b) respectively illustrate the relationship between the induced roll motion and the spin and rotation rates of the flywheels, induced by a (model, roll) gyrostabiliser system operated as a conventional active system and by a gyrostabiliser system according to Figure 2(a); Figure 5, illustrates the relationship between the non-dimensional pitch response and the non-dimensional encounter frequency, as experimental values and theoretical estimates, of a (model, pitch) gyrostabiliser system according to Figure 2 and for a vessel not incorporating such a system; and Figure 6 illustrates the relationship, determined by calculation, between the stabilising moment and the roll excitation frequency, for a gyrostabiliser of the present invention and a commercially available gyrostabiliser, each when used as a roll motion control system.

Referring to Figure 2(a), there is shown schematically a gyrostabiliser system in accordance with a first embodiment of the present invention. The gyrostabiliser system, designated generally as 2, comprises a base body 4 which is in use affixed to a vehicle 6, such as a hull of a ship. The base body 4, together with two spaced frames 8 (in the embodiment illustrated in Figure 2(a)) mounted to the vehicle 6 on opposite sides of the base body 4, rotatably supports a respective gimbal support structure 10, 10' which can each rotate about a common, typically horizontal, axis H, typically corresponding to a transverse axis of the vessel. The gimbal structures 10, 10' are fixedly mounted on respective shafts 12, 12' so that the gimbal structures 10, 10' and the respective shaft 12, 12' can independently, and oppositely, rotate about the horizontal axis H. In use, the horizontal axis H is typically oriented orthogonal to the direction of ship travel F, orthogonal to the plane of the drawing, direction F corresponding to a longitudinal axis of the vessel -that is, when the stabiliser system is oriented principally for roll stabilisation.

Each gimbal structure 10, 10' supports a respective flywheel 14, 14' therein, with a shaft 16, 16' of the flywheel 14, 14' being rotationally mounted in the respective gimbal structure 10, 10'. A spin motor 18, 18' is mounted to the shaft 16, 16' of each flywheel 14, 14'. The spin motor 18, 18' is adapted to spin the respective flywheel 14, 14' in a respective angular rotational direction about an axis which is orthogonal to the horizontal axis H about which the respective gimbal structure 10, 10' rotates, and with the two flywheels 14, 14' being arranged, together with their respective spin motors 18, 18', to spin in opposite rotational directions D, D'. The spin motors 18, 18' together comprise a first drive system for rotating the flywheels 14, 14', with the flywheels 14, 14' preferably being independently and autonomously driven at a selected respective spin rate and/or acceleration. The first drive system may be optionally configured to act as an electrical generator by drawing power from the stored energy within the rotating flywheels 14, 14'.

A nutation motor 20 is mounted on shaft 12 and is adapted to rotate the gimbal structures 10, 10' and their supported rotating flywheels 14, 14' about the horizontal axis H. The nutation motor 20 comprises a second drive system for rotating the gimbal structures 10, 10' and their supported rotating flywheels 14, 14' about a nutation axis H. The second drive system may be optionally configured to precess the gimbal structures 10, 10' and their supported rotating flywheels 14, 14' about the nutation axis H thereby to act as an electrical generator by drawing power from the stored energy within the rotating gimbal structures 10, 10' and flywheels 14, 14'.

A switchable damper mechanism 22 is selectively couplable to the gimbal structures 10, 10' and/or the shafts 12, 12' controllably to damp, by a variable damping force, any rotational motion of those mutually coupled elements. The damper mechanism 22 may be incorporated into the nutation motor 20 or a controller therefor, for example by electromagnetic damping, and may be adapted to provide regenerative braking, or energy retrieval. The damper may be actively driven, or passive.

Figure 2(b) shows an alternative embodiment in which the oppositely rotating flywheels 14, 14' are mounted on respective gimbal structures 10, 10' mounted to a common base body 4 which is in use affixed to a vehicle 6, such as a hull of a ship.

in alternative embodiments, the gimbal structures 10, 10' and associated flywheels 14, 14' may be mounted along the longitudinal axis of the vessel rather than along the transverse axis of the vessel, as for Figure 2. Furthermore, each gimbal structure 10, 10' may be provided with a dedicated nutation motor 22. More than two gimbal structurelO, 10' /flywheel 14, 14' assemblies may be provided, for example as two or more pairs thereof, located in the same or different parts of the vessel.

As described further below, a control system is provided to control the nutation motor 20, and the damper mechanism 22, so that it can selectively be operated in one of five operating modes: Undamped OFF to provide an undamped passive gyrostabiliser; Passive damped OFF -to provide a passive gyrostabiliser, with passive damping; Semi-passive damped OFF -to provide a passive gyrostabiliser, with active damping; Intermittently ON -to provide oscillatory nutation; or Continuously ON -to provide continuous nutation for an active gyrostabiliser.

Furthermore, the spin rate (i.e. the angular velocity) of both the nutation motor 20, on the one hand, and the spin motors 16, 16', on the other hand, may be independently controlled by the control system.

Active control of marine gyrostabiliser systems (and motion control systems in genera!) can provide improved performance compared to an equivalent passive system. In a passive system with no damping control, the gyrostabiliser flywheel(s) precess as the vessels rolls, with the precessional axis having a fixed damping characteristic. In a passive system with semi-passive damping, the gyrostabiliser flywheel(s) precess as the vessel rolls, with the precessional axis having a controlled variable damping characteristic. In an active system with active nutation control, the gyrostabiliser flywheel(s) are oscillatory nutated in a maimer to produce opposing moments to the roll motion excitation moments.

The orientation of the flywheel(s) defines the direction of the applied moment on the gyrostabiliser frame. The angular velocity of nutation of the gyrostabiliser flywheel(s) defines the magnitude of the applied moment.

The preferred embodiments of the present invention provide a gyrostabiliser system in which not only are all of these modes possible, by manual selection or automatic control, but also a further active continuous nutation mode is possible in which the gyrostabiliser flywheel(s) are rotationally nutated in a continuous manner to produce opposing moments to the roll motion excitation moments. The orientation of the flywheel(s) defines the direction of the applied moment on the gyrostabiliser frame.

The angular velocity of nutation of the gyrostabiliser flywheel(s) defines the magnitude of the applied moment.

To provide the optimum stabilising effect (of an active gyrostabiliser system) the angular velocity of nutation (whether oscillatory or rotational) in most cases should be greatest when the orientation of the gyrostabiliser flywheel(s) is such that it provides a moment counter to the targeted axis, which furthermore is required to occur in phase to that of the excitation moment(s), to provide the most suitable change in motion of the stabilised object.

The control system for the gyrostabiliser system of Figure 2 is illustrated schematically in Figure 3.

The control system 50 comprises a mode selector 52 for selecting one of the five operating modes, Undamped OFF -to provide an undamped passive gyrostabiliser; Passive damped OFF -to provide a passive gyrostabiliser, with passive damping; Semi-passive damped OFF -to provide a passive gyrostabiliser, with active damping; Intermittently ON -to provide oscillatory nutation for an active gyrostabiliser; or Continuously ON -to provide continuous nutation for an active gyro stabiliser.

The nutation motor 22 is provided with a nutation angular velocity control 54. The spin motors 18, 18' are provided with a respective or a common spin angular velocity control 56. An external sensing apparatus 58, which is adapted to sense one or more position and motion parameters of the vehicle, is provided. In particular, for a marine vessel the one or more position and motion parameters represent parameters such as the angle of the vessel relative to a given axis, usually an inertial reference system that is oriented with an earth-fixed system and moves with the vessel's average velocity, indicating roll, pitch and/or yaw, and corresponding values of angular velocity and/or angular acceleration, which may be sensed by the sensing apparatus. Such sensing apparatus 58, in particular for marine vessels, are well known in the art (e.g. potentiometers, accelerometers, rate gyroscopes etc.).

A control processor 60 is connected to the external sensing apparatus 58 and to an internal sensing apparatus 61 which senses the internal motion parameters of the gyroscopic system, including the nutation angular velocity and the spin angular velocity, and optionally additionally the corresponding accelerations and/or angular positions. The control processor 60 includes a data receiver 63, which therefore receives data from the external sensing apparatus 58 representing the one or more position and motion parameters of the vehicle, and data from the internal sensing apparatus 61 representing motion parameters such as angle, nutation rate and spin rate of the flywheels within the gyroscopic device. The mode selector 52 of the control processor 60 enables selection of an appropriate mode, i.e. an appropriate control law to follow, based on the received external and internal data signals. A calculator portion 64 calculates the necessary motion of the gyros and required voltage signal required to provide that particular selected mode of motion, in particular the nutation angular velocity (A) and the spin angular velocity (B).

The control processor 60 includes an amplifier 66, to provide output control voltages for the drive systems. Accordingly, particular values of the nutation angular velocity (A) and the spin angular velocity (B) calculated and selected to minimise the excitation moment, by establishment of a gyroscopic moment accordingly matched, as closely as possible, to the excitation moment.

The control processor 60 therefore calculates and determines output control parameters, and outputs those parameters as output signals, to control the nutation angular velocity control 54 and the spin angular velocity control 56 so that the nutation motor 22 rotates at the desired nutation angular velocity (A) and the spin motors 16, 16' rotate, in respective opposite rotational directions, at the desired spin angular velocities (B). This in turn causes the required stabilisation by applying the calculated gyrostabiliser moment determined to minimise the excitation moment.

The determination of the output control parameters and to generate control signals therefrom may additionally control the mode selector 52 to select a particular mode which has been determined to provide the minimum excitation moment. The control system is adapted to receive input data continually or continuously and correspondingly to output control signals continually or continuously. This provides a constant motion control of the vehicle.

A sequence of control steps to be employed by the control system in a method of operating the controllable motion generator device of the preferred embodiment is disclosed below.

In a first step, boat motions are sensed using the sensing apparatus 58. In particular, boat motions such as the angle of the boat relative to a given axis, such as to indicate roll, pitch and/or yaw, and corresponding values of angular velocity andlor angular acceleration, may be sensed. These input parameters define the position and motion of the boat which are desired to be controlled by the gyrostabiliser system 2. The boat motions are the result of input forces and moments, for example from wind and/or waves, impacting on the vessel which can create undesirable motions.

A control type of operation for the gyrostabiliser system is selected. The control type may be selected from a passive control system, a passive damped system, a semi-passive actively damped system; an oscillatory active system or a constant rotational active system. The control type may be set by the user, and/or may be set automatically by the control system, as described below. Such control type in turn sets the nutation of the gyroscopes, and a corresponding angular velocity A. A spin rate of the gyroscopes, at an angular velocity B is set. Again, both angular velocities A and B may be set by the user, and/or may be set by the control system, as described below.

The gyroscopic motions of spin and nutation are sensed. The motions of the boat are sensed. From such motions a control law is selected and particular values of the nutation angular velocity A and the spin rate angular velocity B to achieve the technical effect to minimise the resultant moments, which would have the net effect of causing boat excitation, are created.

From such selected values of the angular velocities A and B, control signals are calculated which are applied (e.g. as voltage signals) to the nutation motor 22 and spin motors 18, 18' of the gyrostabiliser system 2. Such signals then effect stabilisation of the vessel by the applied gyrostabiliser moment.

The overall effect on the vessel is a combination of the applied gyrostabiliser moments and the input wave and input forces and movements on the boats which can create undesirable motions indicated at 100 in Figure 3. Such combined moments provide composite resultant excitation forces and moments applied to the boat. This provides an output represented by new boat motion. This process flow may be repeated intermittently or continuously to provide a constant motion control of the vehicle.

By switching between the different control types, the performance of the gyrostabiliser system can be significantly improved, increasing its range, efficiency, effectiveness and smoothness.

The gyro stabiliser system can provide a reduced degree of undesirable motion of the vessel, resulting in a lower incidence of sea sickness and improved safety. This can also provide a potential for fuel savings.

Yet further, the gyroscopes may function as an electrical generator system. In particular, each flywheel may be coupled to an electromagnetic generator so that the device can function as an emergency power source for example in a regenerative or energy capture mode.

Although the motion control device incorporating the gyroscopic system has a primary application to reduce or eliminate undesirable motion of a vehicle, in contrast the motion control device may be employed to create desired motion in an otherwise stationary vehicle, for example for use by an ice breaker or as an anti-boarding system for a vessel.

The operation of the gyrostabiliser system of the preferred embodiment of the present invention permits a selected operating mode which sets constant (continuous) rotation of the gyroscopes (in opposing directions) rather than restricting the nutation to an oscillatory motion. This operation, with each gyroscope undergoing a complete revolution in the oscillatory excitation period, equates to a greater magnitude of rotation (a or cog), compared to oscillating the gyroscopes through fractions of a revolution, providing a greater stabilising effect, in addition to simplif'ing the mechanical actuation.

The preferred embodiments of the present invention can provide a gyroscopic controllable moment generator, with singular paired and/or multiple paired gyroscopic stabiliser units, with the gyroscopes having one axis of rotation fixed to the body of the vehicle, with multiple operational control modes of the gyroscopes of the gyroscopic units including: 1. Free andlor damped precessional motion of gyroscopes under external disturbance, i.e. as a passive system, such damped motion including regenerative braking, or energy retrieval.

2. Active damping of the precessional motion of the gyroscopes under external disturbance, i.e. as a semi-passive system, where damped motion includes regenerative braking, or energy retrieval.

3. Active oscillatory nutation of the gyroscopes, i.e. as an oscillatory nutation active system.

4. Active continuous rotational nutation of the gyroscopes, i.e. as a continuous nutation active system.

The damping affects and/or nutation rates, for active control, are maintained in a controllable phase relationship to the external disturbing moments and forces. In addition, the spin rates, under each of the above mentioned operational control modes, of variable control are maintained in a controlled relationship to the magnitude and frequency of the external disturbing moments and forces. The operational control may be actively controlled, according to which mode is in operation, with each mode being able to be implemented in a continuous fashion, i.e. without being reset, from each of the other modes.

In other words, the mode selection can be controlled by manual input and/or automatically by the control system by measuring arid reacting to the magnitude and frequency of the external disturbing moments and forces. This provides the significant advantage that the controllable moment generator device of the preferred embodiments can generate greater stabilising moments than existing systems.

The preferred embodiments of the present invention may provide gyrostabiliser systems which can deliver, as compared to existing available systems, greater performance, in particular with regard to the effective range of external input conditions to be controlled and the consequential stabilising effect), reduced weight and volume penalty for a similar stabilising performance, great flexibility by delivering several selectable control strategies, some capable of mimicking another dedicated gyrostabiliser system. The gyrostabiliser systems may be employed in a variety of vehicle, but in particular marine vessels such as fishing vessels, rescue craft, pilot boats, cruise ships, ferries, military craft, bulk carriers, container ships and moored marine structures.

The system may provide one or more of the following advantages: to control the motion characteristics of ships, improving the revenue generating capability of a vessel by; reducing the imdesirable motions; reducing the incidences of sea sickness and improving habitability; reducing crew fatigue and human errors; reducing drag, reducing journey time and/or fuel consumption.

The present invention will now be illustrated in greater detail with reference to the following non-limiting Examples. It should be noted that the principal focus of the examples vary and the undesirable motion and ship-fixed axis of rotation about which the motion principally occurs (such as roll, pitch or yaw), targeted using the gyrostabiliser system, is arbitrary. Examples I and 3 illustrate the present invention as a means of controlling the undesirable rolling motions of marine craft. Example 2 illustrates the present invention as a means of controlling the pitching motion of marine craft.

Example 1

A model gyrostabiliser system having the structure shown in Figure 2(a) was developed and tested as a roll motion control system. The system was tested as a roll ride control system on a scale model boat representative of a luxury monohull motor boat. The experiments were conducted in a water tank. The water was calm, and the experiments induced roll motion in the boat, the induced motion being related to the roll motion which could be eliminated in rough water andlor wind conditions.

Figures 4(a) and (b) respectively illustrate the relationship between roll motion (measured by the RMS roll angle in degrees) induced by a gyrostabiliser system operated as a conventional active system and system according to Figure 2(a) with spin rates of(a) 3000rpm and (b) 2500rpm over a range of motion frequencies (Hz).

In calm water the gyrostabiliser system of the present invention induced the greater motion, for a given spin rate, over a majority of the investigated range. A direct comparison to full-scale commercial gyrostabiliser systems cannot be made as the nutation angles and rates are unknown for those commercial systems. However the significant, and enhanced, motion induced by the modelled gyrostabiliser system of the present invention clearly shows an advantage in the amount of motion that can be induced (and hence eliminated).

Example 2

A model gyrostabiliser system having a similar structure as shown in Figure 2(a) was developed and tested as a pitch motion control system on a scale model catamaran ferry. Again the experiments were conducted in a water tank.

A comparison between the experimental results and theoretical estimates of the model gyrostabilised vessel is given in Figure 6, which shows the relationship between the non-dimensional pitch response and the non-dimensional encounter frequency. Figure 5 also shows corresponding experimental results and theoretical estimates for a conventional actively controlled gyrostabiliser system. Figure 5 shows that the theoretical estimates of the effectiveness of the gyrostabiliser system of the present invention are reasonably consistent (in trend) with those found experimentally, and the motion (pitch) reductions range from 40 to 70%, which is comparable to current external pitch control systems. The results are also improved as compared to the conventional system.

Example 3

In this example, the stabilising moments that can be generated by the gyrostabiliser system of the present invention under typical operating conditions were calculated for a range of roll excitation frequencies, and compared to the corresponding stabilising moment/roll excitation frequency relationship for a two gyroscope active gyrostabiliser system available in commerce from Seakeeper, Inc., U.S.A., which can be considered as representative of current commercially available gyroscopic systems.

The results, illustrated in Figure 6 which indicates the relationship between the stabilising moment and the roll excitation frequency, shows that when used as a roll motion control system, the gyrostabiliser of the present invention may be capable of inducing a greater motion, or eliminating a greater motion, over a wider range of frequencies, than existing systems.

Comparative Example 1 In regular waves, model test results showed that a passive gyrostabiliser system can reduce the motion except at lower frequencies. This is consistent with theoretical expectations, similar to passive roll tank stabiliser systems. However the Examples show that the gyrostabiliser system of the present invention can provide roll and pitch control at low frequencies.

The proposed operation of the gyrostabiliser of the preferred embodiments of the present invention can provide (in addition to better performance) greater flexibility in design, by judicious selection of nutation control, spin rate and flywheel mass-moment of inertia.

Existing gyroscopic stabiliser systems range in mass from 0.5 tonne to 60 tonne and are available for vessels ranging in length from lOm to lOOm with powering requirements ranging from 0.5 to 200kW. The gyrostabiliser of the preferred embodiments of the present invention provides the advantages of potentially reducing the spin rates andlor size of the system required for a similar performance or enabling larger vessels to be stabilised. Typical applications are luxury motorboats, less than 50m in length, where gyroscopic stabiliser systems have a mass in the order of tonnes, with powering requirements of around 1-10kW. The gyrostabiliser of the preferred embodiments of the present invention is not vulnerable to damage from submerged objects, can provide stabilisation at low (loiter) and zero speeds and has a low locational dependency.

The gyrostabiliser of the preferred embodiments of the present invention can provide any or all of: * Greater magnitudes and range of motion induction/reduction than other gyrostabiliser systems.

* Greater flexibility in design (i.e. sizing/potential product ranges) of the gyrostabiliser than other gyrostabiliser systems.

* Reduced spin rates and/or size for the same performance compared to other gyrostabiliser systems, reducing start-up/ready time, or utilised space (volume and weight).

* Capability to stabilise ships to a greater degree than other gyrostabiliser systems.

* Capability to stabilise larger ships than current gyrostabiliser systems.

In addition, the gyrostabiliser of the preferred embodiments of the present invention can provide all the benefits associated with existing gyrostabiliser systems, including; * Low locational dependency.

* Capability of providing stabilisation at low (loiter) and zero speeds.

* Elimination of system vulnerability from damage from submerged objects.

However, to provide improved performance (over other gyrostabiliser systems) the system requires additional power. In addition, as the excitation moments required to stabilise a vessel, increase at a greater proportional rate than the gyroscopic effect provided by larger flywheels, the system, although capable of providing greater stabilising moments than equivalent gyrostabiliser systems (enabling larger vessels to be stabilised), is likely to favour small to medium sized vessels.

The proposed gyrostabiliser system is an attractive stabilisation system for small to medium sized vessels, that require stabilisation specifically at low/no speed, for example research vessels, rescue, military and leisure craft.

Claims

CLAIMS; 1 A controllable moment generator device comprising: at least two flywheels, each having a respective spin axis, a first drive system adapted to rotate the at least two flywheels about their respective spin axes, at least two gimbal supports, each being arranged, in use, to mount a respective flywheel to a fixed base, each flywheel being rotatably mounted in a respective gimbal support, each gimbal support being rotatably mountable to the fixed base for rotation about a nutation axis which is orthogonal to the spin axis of the respective flywheel, a second drive system adapted to rotate the gimbal supports, and the respective flywheel mounted therein, and a control system for controlling the second drive system and adapted selectively to switch the second drive system between an oscillatory mode, for causing oscillatory nutation of the gimbal supports, and a continuous mode, for causing continuous nutation of the gimbal supports.
2. A controllable moment generator device according to claim 1 further comprising at least one external sensor for sensing at least one motion parameter external of the controllable moment generator device and providing first input data for the control system, and at least one internal sensor for sensing at least one motion parameter of the flywheels and providing second input data for the control system.
3. A controllable moment generator device according to claim 2 wherein the control system comprises a mode selector for selecting, based on the first and second input data, a respective mode for operating the second drive system, and a calculator adapted to calculate, from the first and second input data, control parameters for the first and second drive systems.
4. A controllable moment generator device according to claim 3 wherein the calculator is adapted to calculate control parameters comprising the nutation angular velocity and the spin angular velocity for each flywheel..
5. A controllable moment generator device according to claim 4 wherein the control system is adapted to control the first and second drive systems to provide a desired resultant moment or to minimise the resultant moment.
6. A controllable moment generator device according to any one of claims 3 to wherein the mode selector is adapted to selecting between the oscillatory mode, the continuous mode or an OFF mode for the second drive system.
7. A controllable moment generator device according to claim 6 wherein the mode selector is operable automatically by the control system to minimise the resultant moment.
8. A controllable moment generator device according to any foregoing claim further comprising at least one damping device for selectively damping oscillatory motion of the gimbal supports, and wherein the mode selector is operable automatically by the control system to activate or deactivate the at least one damping device.
9. A controllable moment generator device according to claim 8 further comprising a controller for the at least one damping device for actively damping the oscillatory motion of the gimbal supports.
10. A controllable moment generator device according to any foregoing claim further comprising an electrical generator system coupled to at least one of the first and for second drive systems.
11. A marine vessel having mounted therein a controllable moment generator device according to any foregoing claim, the fixed base being fixed to the vessel.
12. A method of controlling the motion of an object, the method comprising the steps of: (a) mounting a gyroscopic device on the object, the gyroscopic device having at least two flywheels, each having a respective spin axis, a first drive system adapted to rotate the at least two flywheels about their respective spin axes, at least two gimbal supports, each mounting a respective flywheel to the object, each flywheel being rotatably mounted in a respective gimbal support, each gimbal support being rotatably mountable to the object for rotation about a nutation axis which is orthogonal to the spin axis of the respective flywheel, and a second drive system adapted to rotate the gimbal supports, and the respective flywheel mounted therein, (b) controlling the second drive system by selectively switching the second drive system between an oscillatory mode, for causing oscillatory nutation of the gimbal supports, and a continuous mode, for causing continuous nutation of the gimbal supports.
13. A method according to claim 12 further comprising the steps of: (c) sensing at least one motion parameter external of the gyro scopic device to provide first input data for the controlling step; and (d) sensing at least one motion parameter of the flywheels to provide second input data for the controlling step.
14. A method according to claim 13 further comprising the steps of: (e) selecting, based on the first and second input data, a respective mode for operating the second drive system; (f) calculating, from the first and second input data, control parameters for the first and second drive systems; and (g) controlling the first and second drive systems by said control parameters to provide a desired resultant moment or to minimise the resultant moment.
15. A method according to claim 14 wherein the control parameters comprise the nutation angular velocity and the spin angular velocity for each flywheel.
16. A method according to any one of claims 12 to 15 wherein the controlling step (b) further selectively switches between the oscillatory mode, the continuous mode or an OFF mode for the second drive system.
17. A method according to any one of claims 14 to 16 wherein the controlling step (b) is effected automatically by the control system to minimise the resultant moment.
18. A method according to any one of claims 12 to 17 further comprising the step of: (h) selectively damping oscillatory motion of the gimbal supports.
19. A method according to claim 18 wherein the damping actively damps the oscillatory motion of the gimbal supports.
20. A method according to any one of claims 12 to 19 further comprising the step of: (h) generating an electrical output from at least one of the first and second drive systems.
21. A method according to any one of claims 12 to 20 wherein the object is a marine vessel.