AU2006200945A1 - Steerable trolley or other vehicle - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "STEERABLE TROLLEY OR OTHER VEHICLE" The following statement is a full description of this invention, including the best method of performing it known to me: TITLE: STEERABLE TROLLEY OR OTHER VEHICLE BACKGROUND OF THE INVENTION 1. Field of the Invention THIS INVENTION relates to a steerable trolley or other vehicle.

The term "steerable trolley or other vehicle" shall be used throughout the specification to cover a wide range of vehicles, which may be hand-propelled, provided with steerable wheels. Examples include, but are not limited to: shopping trolleys; warehouse trolleys; hand trolleys; wheeled storage racks, wheeled tables or benches and wheeled storage bins; catering racks and bins; hospital and other beds; wheeled supports for medical and other equipment; baby or child strollers and perambulators.

While the invention is preferably applied to two pairs of steered wheels, it may also be applied to two or more groups of steered wheels, each group having two or more interconnected wheels which are selectively steered.

2. Prior Art The shopping trolley has not undergone any major improvement since its inception 50 years ago. Trying to control a shopping trolley can be a frustrating and difficult experience for many people.

The castor wheels on shopping trolleys are usually swivel castors, allowing the trolley to be moved in any direction. This can be very difficult to control in many situations and is particularly acute when the trolley is under heavy load and moving.

When trying to change direction, the user must overcome the ~2 0 0 inertia of the load and force the trolley around corners. This can take great energy and creates extreme torque on the spine.

IWhen navigating a sideways gradient, gravity will pull the trolley 0 sideways. The user must counteract this force by pushing the trolley at an angle to the gradient. This difficult task requires great strength to avoid olosing control and causing damage to property.

IThere have been attempts to move the steering point of the 0 0 N trolley away from the user to prevent potential injury to the user. These designs have included either fixing the back or front wheels. This moves the point around which the trolley steers to along the fixed axle.

One solution, proposed by Wanzl Metallwarenfabrik GmbH (Lapheim, Germany) is to arrange for the two front castor wheels of the shopping trolley to tilt backwards, as the load in the basket increases so that the loaded shopping trolley acts if fixed castor wheels were installed at the front of the shopping trolley.

An alternative solution has been to provide steering to at least a pair of the castor wheels. An example is disclosed in US Patent 5,964,471 (Copeland), where respective pairs of front and rear castor wheels can be selectively connected together to turn in unison, when that pair of wheels is the outer pair of wheels during a cornering manoeuvre. Each pair of wheels is connected via a bevel-gear and shaft assembly selectively controlled by a clutch which is operated when one of the wheels, usually the rear wheel, is turned. While this has some advantage over an unsteered trolley, only one of the pair of wheels is steered and only after a cornering or turning v.0 :3

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0 manoeuvre has commenced.

tSUMMARY OF THE INVENTION IIt is an object of the present invention to provide a steering

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mechanism for a steerable trolley or other vehicle, as hereinbefore defined, where the above problems are overcome, or at least minimised.

0It is a preferred object to provide such a steering mechanism ci Iwhere the wheels in a pair (or group) are substantially simultaneously aligned Cl substantially at right angles to a point about which the trolley or vehicle is being steered.

It is a further preferred object to provide such a mechanism where the wheels in a pair of groups can be spaced at different track widths from the longitudinal axis of the trolley or vehicle; and that the steering point can lie on a line extending transversely to the longitudinal axis of the trolley or vehicle parallel with the front and rear wheels), but not limited to being centred between the front and rear wheels.

It is a still further preferred object to provide such a steering mechanism which allows the trolley or other vehicle to be steered in any direction, eg., from an on-the-spot 3600 turn within its own length to a wide turn, in both the forward and reverse directions.

In a still further preferred object, the present invention resides in a trolley or other vehicle, as hereinbefore defined, provided with the steering mechanism.

In one aspect, the present invention resides in a steering mechanism for a steerable trolley or like vehicle, including: I4 0 at least two pairs of wheels pivotable about a respective substantially vertical axis, at least one pair of the wheels including a first Iwheel and a second wheel; 0 a first eccentric drive member operably connected to the first wheel of the one pair of the wheels; 0a second eccentric drive member operably connected to the 0 second wheel of the one pair of wheels; and N communication means interconnecting the first and second eccentric drive members; the communication means and first and second eccentric drive members being operable such that pivotal movement of the first wheel about a substantially vertical axis acts to provide pivotal movement of the second wheel, where both the first wheel and the second wheel are simultaneously aligned substantially at right angles to a steering point around which the steerable trolley or other vehicle is being steered.

In a second aspect, the present invention resides in a steering mechanism for a steerable trolley or like vehicle including: at least two groups of wheels pivotable about a respective substantially vertical axis, at least one group of the wheels including a first wheel and two or more second wheels; a first eccentric drive member operably connected to the first wheel of the one group of the wheels; respective eccentric drive members operably connected to the second wheels of the one group of the wheels; and IND

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o communication means interconnecting the first and respective eccentric drive members; IN the communication means and first and respective eccentric 0 drive members being operable such that pivotal movement of the first wheel 5 about a substantially vertical axis acts to provide pivotal movement of the osecond wheels, where the first wheel and the second wheels are IN simultaneously aligned substantially at right angles to a steering point around N which the steerable trolley or other vehicle is being steered.

In third and fourth aspects, the present invention resides in a steerable trolley or other vehicle, as hereinbefore defined, incorporating the steering mechanism of the first and second aspects, respectively.

The first wheel of the one pair or one group may be the rear wheel and the second wheel is the front wheel, or vice versa.

Preferably, the first and second eccentric drive members are connected to vertical steering shafts for the first and second wheels, the connection being preferably through right-angled gearboxes, bevel-gears or the like.

Preferably, the first and second eccentric drive members have an elliptical periphery, and may comprise gears, or sprockets, toothedpulleys, or drive-plates, arranged for (preferably) positive engagement with the communication means.

Alternatively, the drive members may have, substantially S-shaped, dumbbell-shaped, dogbone-shaped or other selectively shaped peripheries.

Ob o Preferably, the communication means may comprise a complementary chain, toothed belt or other flexible drive member a IN cable or cord) with protrusions/indentations thereon. While it is preferred 0 that the communication means is provided as a closed loop, it may have 5 respective ends anchored to the first and second eccentric drive members and have a single run therebetween, eg., in the manner of a Bowden-cable.

IN Preferably, the first and second eccentric drive members are 0 0 N rotated in the same direction by the communication means, the first eccentric drive member being arranged to rotate the first wheel in an opposite pivotal direction to the pivotal direction of the second wheel by the second eccentric drive member clockwise/anticlockwise or vice versa).

However, in an alternative embodiment, the communication means can rotate the first and second eccentric drive members in the opposite direction, to steer the first and second wheels in the opposite direction.

Preferably, the major axes of the first and second eccentric drive members are oppositely inclined, at an angle of 450 to the vertical, and at an included angle of 900, when the trolley or other vehicle is travelling parallel to its longitudinal axis.

Where the first and second wheels of the trolley or other vehicle have different tracks, ie., are at different spacings from the longitudinal axis, the relationship between the major and minor axes of the first and second eccentric drive member is varied, but the peripheral distance is identical, to cause the first and second wheels to pivot at different rates 0 o and so be maintained at an angle of substantially 900 to a line connecting the wheels to the point about which the trolley or other vehicle is steered. In Iaddition, the relationship between the major and minor axes can be varied so 0 that the steering point can lie on a line, transverse to the longitudinal axis parallel to the first and second wheels) either forward or rearward of the centre of the trolley or vehicle.

IN As the axes of the castor wheels normally trail the vertical 0 N steering axes of the castor wheels, one of the wheels will tend to "understeer" and the other "oversteer" the corner, as their respective axles are not aligned exactly with the steering point- although the actual error may be small. The shapes of the respective eccentric members can be modified to a slightly ogival shape, where on end is slightly thinner and elongated and the other end is slightly fatter and shorter, to provide a correction factor.

To enable the trolley or vehicle to be moved, eg., sideways, or in a free direction when nested with like trolleys, the eccentric drive member of one of the wheels may be selectively disengaged from the wheels. The disengagement may be affected by disengaging the eccentric drive member from its input shaft on the gearbox, or the disengagement of the output shaft of the gearbox from the vertical steering shaft of the wheel.

BRIEF DESCRIPTION OF THE DRAWINGS To enable the invention to be fully understood, preferred embodiments will now be described with reference to the accompanying drawings, in which: Fig. 1 is a perspective, underside, view of a shopping trolley 0 o incorporating a first embodiment of the steering mechanism of the present Sinvention; N Fig. 2 is a perspective top view of the steering mechanism; 0 Fig. 3 is a perspective bottom view thereof; Figs. 4 and 5 are perspective side views of respective ends of the steering mechanism; D Fig. 6 is a schematic side view of the two sprockets and chain 0 0 of the steering mechanism; Figs. 7 to 9 are schematic views demonstrating the steering of the wheels in three types of turn; Fig. 10 is a schematic side view showing the rotation of the rear wheels; Fig. 11 is a schematic drawing for the explanation of the relationship between the sprockets; Fig. 12 is a graphical illustration of the angles of the four wheels relative to a steering point; Fig. 13 is a perspective view of a second embodiment; and Fig. 14 is an exploded perspective view thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment will now be described with reference to Figs. 1 to 5, which illustrate the installation of the steering mechanism to a shopping trolley 10 of the type having a basket 11 (and handle 12) mounted on a substantially U-shaped frame 13, which has been modified to

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o incorporate the steering mechanism.

The frame 13 is arranged to enable the shopping trolley 10 to Ibe nested with like shopping trolleys and the frame 13 is arranged so that the 0 front or rear castor wheels are raised from contact with the ground or floor surface when the trolleys 10 are nested.

oThe steering mechanism 20, shown in more detail in Figs. 2 to 0 6, is effectively formed by a pair of steering systems for the left- and right- N side wheels, respectively, where the steering systems are "mirror-images" of each other.

In this embodiment, the rear castor wheels 21 are the "first" wheels and the front castor wheels 22 are the "second" wheels, it being assumed that a person controls the steering part of the shopping trolley from the rear via handle 12.

NB: If the shopping trolley 10 were, eg., a pulled hand trolley, the front wheels would be the "first" wheels and the rear wheels the "second" wheels.

Each rear castor wheel 21 has a housing 23 pivotally mounted relative to the frame 13 about a substantially vertical axis. Similarly, each front castor wheel 22 has a housing 24 pivotally mounted relative to the frame 13 about a substantially vertical axis.

The housings 23 incorporating braking mechanisms 25 for the rear castor wheels 21.

A right-angled gearbox 26 is provided for each rear castor wheel 21, with an input shaft (not shown) connected to the respective IN

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o housing 23 and an output shaft 27 fitted with an elliptical sprocket 30 (to be hereinafter described in more detail).

IA similar right-angled gearbox 28 is provided for each front 0 castor wheel 22, with its input shaft (not shown) connected to the respective housing 24 and an output shaft 29 fitted with an elliptical sprocket 31 (also to 0be hereinafter described in more detail).

IN The sprockets 30, 31 are connected by a chain 32.

0 0 Rotation of the rear castor wheels 21 about the vertical axis relative to the frame 13, when the shopping trolley 10 is steered, causes the rear gearboxes 26 to rotate their sprockets 30. This relation is transmitted by the chains 32 to the front sprockets 31, which cause the front gearboxes 28 to rotate the front castor wheels 22, about the vertical axes, relative to the frame 13.

The rear and front sprockets 30, 31 have the same peripheral distance and the same number of teeth 33, 34.

As shown in more detail in Fig. 6, the major axes Mr, Mf are both inclined at an angle of 450 to the vertical axis V, when the rear and front wheels 21 22 are parallel with the longitudinal axis of the shopping trolley and where the included angle between the major axes Mr, Mf is 900 The respective ratio of the major and minor axes Mr/mr and Mr/mf is selected so that the rear castor wheels 21 are turned at an exponential rate via the elliptical rear sprockets 30 and the chains 32 and front elliptical sprockets 31 transfer an inversely proportional turning rate to the front castor wheels 22 so that all of the wheels always remain Va 11 0 0 substantially at 900 to the steering point SP around which the shopping trolley 10 is steered, even as the rate of steering is changed. This is Iillustrated and hereinafter explained in more detail with reference to Figs. 7 0 to 12.

Because the front castor wheels 22 have a narrower track than 0the rear castor wheels 21, the rate of turn of the front castor wheels 22 is Idifferent than if the tracks between the front and rear castor wheels 22, 21 N were identical. This is allowed for in the different shape of the front and rear sprockets 31, 30. In this embodiment, the rear sprockets are "thinner" (ie., more elongate) than the front sprockets 31, ie., the ratio Mf/mf is greater than the ratio Mr/mr, where the front sprockets 31 are of a less apparently elliptical more circular) shape.

The operation of the steering mechanism 20 will now be described with reference to Figs. 7 to 9.

The steering mechanism 20 ensures the steering point SP, around which the trolley 10 is steered, falls along the centre line of the trolley where the centre line lies between and in parallel with the front and back wheels 22, 21 (see Fig. The steering mechanism 20 allows the user to steer the trolley 10 in any range of directions from an on the spot 3600 turn within its own length (Fig. through a sharp turn (Fig. to a wide turn with all four wheels simultaneously aligned at right angles to the point around which the trolley is being steered (Fig. As the steering point SP around which the trolley 10 is steered changes, the wheels 21, 22 remain perfectly aligned at right angles to that moving steering point SP (Fig. The D 12

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0 described motions are able to occur in either a forward or reverse direction.

The aligned wheels 21, 22 ensure the trolley 10 does not move sideways N when being navigated on a path with a sideways gradient.

0 Steering is controlled by moving the trolley handle 12 to the left 5 or right. The sideways motion from the handle 12, illustrated in FIG. translates to a rotation of the rear wheels 21 and an inversely proportional D turn in the front wheels 22 via the chain 32, and sprockets 30, 31. As the 0 N trolley 10 is turned more sharply as shown in Fig. 7 and Fig. 8, the back wheels 21 are turned at an exponential rate via the elliptical sprockets 30, 31 and chain 32 which transfer an inversely proportional exponential rate of change in the turning of the front wheels 22. This is achieved as the sprockets 30, 31 are positioned exactly 900 out of phase from one another, which additionally ensure the chain 32 connecting them remains evenly tensioned throughout the rotation. This system ensures all wheels 21, 22 always remain at 900 to the steering point SP around which the trolley 10 is steering, even when the rate of steering is changing.

The front and rear castor wheels 22, 21 require different shaped elliptical sprockets 31, 30 to ensure that both are pointing at a common point on the centre line, but both front castor wheels 22 use the same shape elliptical sprockets 31 and both rear castor wheels use the same shape elliptical shape 30. If the front and rear castor wheels have the same wheelbase (a rectangle or square), then the same shape elliptical sprockets will be required for all four castor wheels. The shape of the sprockets 30, 31 is directly related to the dimensions of the trolley they control (see Fig. 8).

o The shafts of the front castor wheels 22 equate to the foci of the elliptical sprockets 31 and a line from each focus to the centre point of the centre line IN equates to ri and r2. These dimensions can be used to calculate the ratio of

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the Mf axis to the Mr axis. The same procedure will determine the ratio of the Mr axis to the Mr axis of the sprocket 30 for the rear castors. Using these ratios, the front and rear sprockets must have the same circumference.

IND Referring to Fig. 11, the effect of the ellipse is to increase the N speed of the sprocket through the tight curve quadrants of the ellipse, and to slow the speed of the sprocket through the lesser curved quadrants. Looking at sprocket 30 in Fig. 11, quadrants 1 and 3 will generate faster rotation, while quadrants 2 and 4 will generate a slower rotation. The more elongated the ellipse, the greater the speed difference generated between quadrants 1 and 3, and quadrants 2 and 4.

To relate this to the trolley 10, when the rear sprocket moves through 2 quadrants, the attached rear castor wheel 21 moves 1800.

One full 3600 revolution of the rear sprocket 30 will turn the attached rear castor wheel 21 through 3600.

Throughout one full 3600 revolution of rear sprocket 30, front sprocket 31 will be perfectly aligned at the point of 1800 and 3600, but at all other points, it will be at a different degree of revolution from the (rear) sprocket By offsetting the sprockets 30, 31 by 900, a difference in shaft speed is generated. Note that quadrant 1 of rear sprocket 30 is a tight curve, which will produce faster rotation. Quadrant 1 of front sprocket 31 is a lesser IND 14

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0curve, which will produce a slower rotation.

Therefore, through the first quadrant, rear sprocket 30 will turn Ifaster than front sprocket 31. Through quadrant 2, rear sprocket 30 slows 0 down and front sprocket 31 speeds up. At the end of quadrant 2, both castor wheels 21,22 are perfectly aligned at 1800.

o At any stage of rotation, the chain 32 is in contact with Iapproximately 50% of the circumference of the sprockets 30, 31. Whether it 0 N is quadrants 1 and 2, 2 and 3, or 3 and 4, or 4 and 1, the periphery of the sprockets 30, 31 that is in contact with the chain 32 remains constant. This means that as long as the sprockets 30, 31 have the same periphery the same number of teeth 33, 34), the length of the chain 32 remains constant, even if the shape of the sprockets 30, 31 differs.

As hereinbefore described, in the case of a shopping trolley where the track of the front castor wheels 22 is narrower than the track of the rear castor wheels 21, two different shaped sprockets 30, 31 are required. The two front castor wheels 22 are closer together than the rear castor wheels 21, and therefore the front castor wheels 22 have a lesser difference of angle to the steering point SP than the rear castor wheels 21 (see Fig. As the rear castor wheels 21 have a greater difference of angle to the steering point SP, they, therefore, require a more elongated elliptical shape for rear sprockets 30 than the front sprockets 31 for the front castor wheels 22 to generate a greater difference to the rate at which the castor wheels 21 turn. The front castor wheels 22 require a rounder elliptical shape for front sprockets 31 which provides less difference to the rate at which the IN

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o front castor wheels 22 turn.

It will be noted that the steering direction of the front castor Iwheels 22 is counter opposite) to the steering direction of the rear castor 0 wheels 21.

In the present embodiment, this is effected by using identical right-angled gearboxes 26, 28 but rotating one through 1800 relative to the Iother.

N As an alternative, the gearboxes 26, 28 could be mounted identically but the internal gears is one of the pair arranged to drive oppositely to the other of the pair.

In the embodiment described and illustrated, the steering point SP lies on the centre line equally spaced from the front and rear wheels 22, 21. However, by selective variation of the ratios of the axes Mr/mr/Mf/mf, the shapes of the sprockets 30, 31 can be varied to enable the steering point SP to be forward of, or rearward of, the centre line, while still ensuring the front and rear wheels 32, 21 are always at right angles to the steering point SP.

With castor wheels, the axles of the wheels 21, 22 normally "trail" the vertical steering axes thereof (when travelling forward). This means that during a turn, the axles do not exactly point to the steering point, but one will be "advanced" and the other "retarded"; so that one wheel of a pair will tend to "understeer" the corner and the other "oversteer" the corner.

A correction factor can be designed into the elliptical driving members 30, 31, where one may be given a slightly ogival shape, with one end being slightly thinner and elongated and the other end slightly fatter and IN 16

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0 shorter.

As hereinbefore described, the steering mechanism 20 can be Ifitted to a wide range of trolleys or other vehicles, and the steering 0 mechanism may be used to control one or more groups of steerable wheels.

For example, a vehicle may have four wheels per side, where the first and second wheels are counter-steered, at different rate, to the third and Ifourth wheels. Or, eg., the third wheel could be fixed, and the first and N second wheels are counter-steered relative to the fourth wheel.

In these embodiments, the intermediate castor wheels, ie., the second and third, or the second, could have a pair of identical elliptical sprockets, on a common axle, each connected via a chain to the respective sprockets of the adjacent castor wheels. Alternatively, a single elliptical sprocket could be engaged by both runs of the chain passing around, eg., the sprockets for the first and fourth castor wheels.

While the preferred embodiment described and illustrated in Figs. 1 to 12 uses sprockets and chains, alternatives such as toothed pulleys and toothed bolts, or (ii) ropes or cables with protrusions/indentations engaging complementary gears, discs or like positive drive combinations can be employed.

Figs. 13 and 14 illustrate a second embodiment which enables one the rear) wheel of the pair to be disengaged to enable the trolley 110 to be moved, eg., sideways away from an obstruction, or when like trolleys are nested together for collection. The gearbox 126 has a pair of brackets 150, slidably mounted on posts 151 on the trolley body 152, and o engaged by compression springs 153 urging the gearbox 126 in a downward direction.

IND As shown in Fig. 14, the output shaft 160 of the gearbox 126 0 has a D-shaped distal end 161 operable to releasably engage a 5 complementary D-shaped slot or recess 170 in the top plate 171 of housing 123 of rear castor wheel 121.

IND The proximal end of the inner cable 181 of a Bowden cable c, 180 is attached to an anchor plate 162 on the gearbox 126, and the distal end is connected to an operating lever (not shown), eg., adjacent the trolley handle 12 or engageable by a like trolley when the trolleys are nested.

When the operating lever is operated, the gearbox 126 is raised relative to the trolley box 152, against the compression springs 153, to disengage the D-shaped distal end 161 of the output shaft 160 from the D-shaped slot or recess 170 in the top plate 170, allowing the castor wheel 121 to freely rotate about its vertical steering axis.

With both rear (or front) wheels disengaged, the trolley 110 can be steered in any direction.

When the operating lever is released, the output shaft 160 will re-engage the top plate 171 when the distal end 161 and D-shaped slot or recess 170 become re-aligned.

It will be noted in this embodiment that the chain 32 is replaced by a flexible plastics "chair" 132 having spaced protrusions 190 interconnected by connecting portions 191.

The complementary sprocket 130 has a central groove 192 IND 18 0 0 about its periphery and teeth 193 which engage the protrusions 190.

Various changes and modifications may be made to the IDembodiments described and illustrated without departing from the present invention.

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Claims (14)

1. A steering mechanism for a steerable trolley or like vehicle, Iincluding: 0 at least two pairs of wheels pivotable about a respective substantially vertical axis, at least one pair of the wheels including a first 0wheel and a second wheel; D a first eccentric drive member operably connected to the first 0 N wheel of the one pair of the wheels; a second eccentric drive member operably connected to the second wheel of the one pair of wheels; and communication means interconnecting the first and second eccentric drive members; the communication means and first and second eccentric drive members being operable such that pivotal movement of the first wheel about a substantially vertical axis acts to provide pivotal movement of the second wheel, where both the first wheel and the second wheel are simultaneously aligned substantially at right angles to a steering point around which the steerable trolley or other vehicle is being steered.

2. A steering mechanism for a steerable trolley or like vehicle including: at least two groups of wheels pivotable about a respective substantially vertical axis, at least one group of the wheels including a first wheel and two or more second wheels; a first eccentric drive member operably connected to the first IN O o wheel of the one group of the wheels; respective eccentric drive members operably connected to the Isecond wheels of the one group of the wheels; and 0 communication means interconnecting the first and respective eccentric drive members; othe communication means and first and respective eccentric I drive members being operable such that pivotal movement of the first wheel 0 N about a substantially vertical axis acts to provide pivotal movement of the second wheels, where the first wheel and the second wheels are simultaneously aligned substantially at right angles to a steering point around which the steerable trolley or other vehicle is being steered.

3. A steering mechanism as claimed in Claim 1 or Claim 2, wherein: the first wheel of the one pair or one group is a rear wheel and the second wheel is a front wheel, or vice versa.

4. A steering mechanism as claimed in any one of Claims 1 to 3 wherein: the first and second eccentric drive members are connected to vertical steering shafts for the first and second wheels, the connection being through right-angled gearboxes, bevel-gears or the like.

A steering mechanism as claimed in any one of Claims 1 to 4, wherein: the first and second eccentric drive members have an elliptical periphery, and comprise gears, or sprockets, toothed-pulleys, or drive-plates, IN 21 O o arranged for positive engagement with the communication means.

6. A steering mechanism as claimed in any one of Claims 1 to 4, wherein: 0 the drive members may have substantially S-shaped, dumbbell- 5 shaped, dogbone-shaped or other selectively shaped peripheries.

7. A steering mechanism as claimed in any one of Claims 1 to 6 wherein: N the communication means comprises a complementary chain, toothed belt or other flexible drive member with protrusions and/or indentations thereon.

8. A steering mechanism as claimed in Claim 7, wherein: the communication means is provided as a closed loop or has respective ends anchored to the first and second eccentric drive members and have a single run therebetween.

9. A steering mechanism as claimed in Claim 8, wherein: the first and second eccentric drive members are rotated in the same direction by the communication means, the first eccentric drive member being arranged to rotate the first wheel in an opposite pivotal direction to the pivotal direction of the second wheel by the second eccentric drive member.

A steering mechanism as claimed in Claim 8, wherein: the communication means rotates the first and second eccentric drive members in the opposite direction, to steer the first and second wheels in the opposite direction. o

11. A steering mechanism as claimed in any one of Claims 1 to Swherein: the major axes of the first and second eccentric drive members 0 are oppositely inclined, at an angle of 450 to the vertical, and at an included angle of 900, when the trolley or other vehicle is travelling parallel to its 0longitudinal axis.

S12. A steering mechanism as claimed in Claim 11, wherein: 0 0 when the first and second wheels of the trolley or other vehicle have different tracks or different spacings from the longitudinal axis, the relationship between the major and minor axes of the first and second eccentric drive member is varied, but the peripheral distance is identical, to cause the first and second wheels to pivot at different rates and so be maintained at an angle of substantially 900 to a line connecting the wheels to the point about which the trolley or other vehicle is steered; or the relationship between the major and minor axes is varied so that the steering point can lie on a line, transverse to the longitudinal axis, parallel to the first and second wheels, either forward or rearward of the centre of the trolley or vehicle.

13. A steering mechanism as claimed in any one of Claims 1 to 12, wherein: to enable the trolley or vehicle to be moved sideways, or in a free direction when nested with like trolleys, the eccentric drive member of one of the wheels is selectively disengaged from the wheels, the disengagement being affected by disengaging the eccentric drive member IN 23 O o from its input shaft on the gearbox, or the disengagement of the output shaft Sof the gearbox from the vertical steering shaft of the wheel.

14. A steering mechanism for a steerable trolley, or like vehicle 0 substantially as hereinbefore described with reference to the accompanying drawings. A steerable trolley or like vehicle incorporating the steering N mechanism as claimed in any one of Claims 1 to 14. 0 DATED this sixth day of March 2006. BRADLEY NEIL SMITH By his Patent Attorneys FISHER ADAMS KELLY