GB2278773A

GB2278773A - Steerable mobile load carrier: swivel castor

Info

Publication number: GB2278773A
Application number: GB9312105A
Authority: GB
Inventors: Philip Stuart Michael; David Michael Abbott
Original assignee: CLARES EQUIP Ltd
Current assignee: CLARES EQUIP Ltd
Priority date: 1993-06-11
Filing date: 1993-06-11
Publication date: 1994-12-14
Anticipated expiration: 2013-06-11
Also published as: DE4420375A1; GB2278773B; FR2706367B1; GB9312105D0; FR2706367A1

Description

r 2278773 1 STEERABLE MOBILE LOAD CARRIER AND SWIVEL CASTOR-THEREFOR The

present invention relates to a steerable mobile load carrier and to an arrangement for improving steerability thereof, and is concerned particularly, though not exclusively, with a shopping trolley. The invention also relates to a swivel castor f or such a load carrier, the castor being adapted so as to improve steerability of the carrier.

Fig. 1 of.the accompanying drawings illustrates schematically in side elevation, a conventional form of shopping trolley as used in large shops or supermarkets. It comprises a base chassis 1 supporting an upwardly open wire mesh shopping basket 2, an elongate transverse handle 3 being fixed to the rear portion of the basket to permit the shopper to push the trolley from the rear. Mobility is provided by a set (commonly f our) of castors 5 located at corners of the base chassis; this set normally comprises two rear castors and two f ront castors.

Normally, all four castors are freely rotatable about vertical axes to provide manoeuvrability.

As used herein, the "wheel plane" of a swivel castor is the plane which is perpendicular to the a 2 rotational axis of the castor wheel, and which passes generally centrally through the wheel. The location of this plane A is best illustrated in Fig. 2 of the accompanying drawings; Figs. 2 and 3 illustrate schematically a typical conventional construction and mounting of a swivel castor on a trolley as seen respectively from the front and side of the trolley with the castor swivelled for forward travel.

With reference to Figs. 2 and 3, a swivel castor 5 basically comprises a castor housing 10 in which a castor wheel 12 is mounted for rotation about a wheel axis W, and a cylindrical support spigot 14 to which the castor housing is swivelably attached. The spigot carries a central bolt (not shown) which defines the swivel axis S about which the castor housing swivels. This axis S is generally perpendicular to, and laterally spaced from the wheel axis W. As can be seen from Fig. 2, the conventional castor is constructed so that the swivel axis S lies in the wheel plane A (which is parallel to the plane of the drawing of Fig. 3).

With reference to Fig. 3, the conventional mounting of a swivel castor on the chassis of a shopping trolley is shown in side view. The castor is illustrated with its spigot 14 secured (e.g. welded) to two generally horizontal chassis frame members 16.

3 The swivel axis S is vertical when the trolley is supported on a horizontal surface H.

Although, it may be thought that in the conventional arrangement the freedom of all f our castors to swivel about their vertical axes should af f ord maximum freedom of steerability f or the user, it is f ound in practice that such shopping trolleys are somewhat difficult to steer. For example, the large momentum of a heavily laden trolley in motion tends to make steering, particularly around sharp corners such as at the ends of shelf gondolas in supermarkets, and on sloping surfaces such as in car parks, rather difficult. Also, imperfections in the construction of the castors, or in the mounting of the castors on the trolley chassis within normal manufacturing tolerances, can result in a tendency for the trolley to steer in a direction which is not in the straight-ahead travel direction. In such cases, the ef fort which needs to be applied by the user to keep the trolley travelling straight-ahead can be very tiring, particularly when the trolley is heavily laden.

Various attempts have been made in the past to provide a construction which inhibits this tendency of shopping trolleys to "wander". More particularly, it is known to mount at least some of the castors (e.g.

is 4 each of the front pair of castors) on the chassis 1 with their swivel axes S being, instead of upright, inclined forwardly relative to the vertical V. This arrangement is shown schematically for one castor 51 in Fig. 4 of the accompanying drawings. References herein to a "forward" inclination of the swivel axis of a castor are to be interpreted with reference to Fig. 4.

Although such an arrangement provided a degree of improvement, it has been found that the magnitude of the forward inclination (i.e. the size of the angle a in Fig. 4) necessary to achieve the required inhibition of trolley wander and bias to straightahead travel, results in deterioration in manoeuvrability, the trolley becoming very hard to turn.

The present invention addresses this problem and provides, in one aspect, a steerable mobile load carrier having a set of ground-contacting wheel elements, at least one of which is a swivel castor which is able to swivel about a swivel axis which is generally perpendicular to and displaced from the axis of rotation of the wheel, wherein the wheel plane, as herein defined, is offset in the direction of said axis of rotation, relative to said swivel axis.

This lateral offset of the wheel plane has been is found to alleviate the above-mentioned problem of poor manoeuvrability where the swivel axis is forwardly inclined.

Accordingly, the invention also provides a steerable mobile load carrier comprising a set of ground-contacting wheel elements, at least one of which is a swivel castor which is able to swivel about a swivel axis which is generally perpendicular to and displaced from the axis of rotation of the wheel, wherein said swivel axis is inclined forwardly relative to the vertical when the carrier is on a horizontal support surface, and wherein the wheel is mounted so that the wheel plane, as herein defined, is offset in the direction of said axis of rotation, relative to said swivel axis.

This combination of forward inclination of the swivel axis, and lateral offset of the wheel plane can thus afford the combined advantages of ease in maintaining straight-ahead travel, and trolley manoeuvrability and control.

Where the load carrier is a trolley having a f ront pair and a rear pair of swivel castors, the wheel plane offset is preferably included in each of the front castors or in each of the rear castors. It is, however, possible to include the wheel plane offset in all four swivel castors.

6 The magnitude of the inclination of the swivel axis preferably is between 20 and 100, and ideally is from 40 to 50. The offset is preferably from 2 mm to 10 mm, and ideally approximately 5 mm.

The invention also provides a swivel castor for a steerable mobile load carrier, said castor having a wheel which is able to swivel about a swivel axis which is generally perpendicular to and displaced from the axis of rotation of the wheel, wherein the wheel is mounted so that the wheel plane, as herein defined, is offset in the direction of said axis of rotation, relative to said swivel axis.

A preferred embodiment of the invention will now be described by way of example with reference to Figs. 5 and 6 of the accompanying drawings. In the drawings:- Fig. 1 is a schematic side view illustrating the essential components of a conventional shopping trolley; Fig. 2 illustrates schematically the basic components of a conventional swivel castor as mounted on a trolley chassis, as seen f rom the front of the trolley; Fig. 3 is a schematic side view illustrating the swivel castor mounting of Fig. 2; Fig. 4 is a schematic side view illustrating an 7 is inclined mounting of a swivel castor in accordance with a prior proposal; and Fig. 5 is a schematic illustration of a swivel castor as provided on a steerable mobile load carrier in accordance with the invention, as seen from the front of the carrier; and Fig. 6 is a schematic side view illustrating the manner in which the castor shown in Fig. 5 is mounted on the carrier.

For the sake of clarity, similar components to those referred to earlier in connection with the known arrangements will be indicated by like reference numerals in the following description.

With reference to Figs. 5 and 6, a castor 8 having a castor housing 10 in which a castor wheel 12 is rotatably mounted is again swivelable about a swivel axis S relative to a spigot 14. However, the swivel interconnection between the spigot and the castor housing is such that the wheel plane A is offset by a spacing d relative to the swivel axis S. Line C-C in Fig. 5 represents the vertical centre line of the trolley on which the castor is mounted, and it will be seen that the of f set of the wheel plane is toward the centre line C-C. A similar effect can be achieved by making the of f set away from the centre line.

8 With reference to Fig. 6, the swivel axis S is inclined relative to the vertical V in a forward sense in relation to the f orward direction of travel F of the trolley.

The forward inclination by the angle a illustrated in Fig. 6 provides the required stability of straight ahead travel, and inhibits trolley wander, in a manner known Der se. This angle a can lie between 20 and 100, but more preferable is from 40 to 51'.

The lateral offset d of the wheel plane A alleviates the above-mentioned problem, introduced by the forward inclination of the swivel axis S, of poor manoeuvrability.

The optimum magnitude of the wheel axis offset is determined by a number of factors, such as the swivel axis inclination, wheel diameter, separation of swivel axis from wheel axis, lateral and longitudinal spacing of the castors, etc. However, as a result of experimental testing, it has been determined that for a swivel castor with a wheel diameter of 125 mm and a separation between swivel axis and wheel axis (known as "trail") of 104 mm, and a swivel axis forward inclination of approximately 511, an improvement in manoeuvrability is achieved for an offset of between 2 and 10 mm, this improvement being particularly 9 marked at approximately 5 mm.

The advantageous ef f ect on manoeuvrability of the lateral of f set d has been observed in experimental test. A full mathematical analysis of the reason for this advantageous effect and of its dependence on the above factors, though derivable, is not considered essential to the understanding of the present invention.

Although a particular kind of swivel castor has been described above, it will be appreciated that the present invention is not limited to such a construction. It will also be appreciated that many kinds of mounting arrangement on a trolley chassis other than that illustrated in the accompanying drawings are possible.

In the embodiment described, the lateral offset of the wheel plane A is a constructional f eature of the swivel castor and the forward inclination a is a f eature of the mounting of the swivel castor on the trolley chassis. However, it will be understood that both features may be incorporated in the swivel castor itself. This could be particularly advantageous where the trolley chassis is specifically designed for a particular mounting arrangement of a castor and modification of such mounting arrangement would be inconvenient. In this case, the combined features of a the forward swivel axis inclination and lateral wheel plane offset, both incorporated in the castor construction, can be applied without modification to the chassis structure.

a is 11

Claims

CLAIMS:. A steerable mobile load carrier having a set of ground-contacting wheel elements, at least one of which is a swivel castor which is able to swivel about a swivel axis which is generally perpendicular to and displaced from the axis of rotation of the wheel, wherein the wheel plane, as herein defined, is offset in the direction of said axis of rotation, relative to said swivel axis. 2. A steerable mobile load carrier comprising a set of ground-contacting wheel elements, at least one of which is a swivel castor which is able to swivel about a swivel axis which is generally perpendicular to and displaced from the axis of rotation of the wheel, wherein said swivel axis is inclined forwardly relative to the vertical when the carrier is on a horizontal support surface, and wherein the wheel is mounted so that the wheel plane, as herein defined, is offset in the direction of said axis of rotation, relative to said swivel axis. 3. A load carrier according to claim 1 or claim 2 having a front pair and a rear pair of said swivel castorsf wherein each castor of at least one of said A is 12 pairs of castors has its said wheel plane offset. 4. A load carrier according to claim 3 wherein said at least one pair comprises said front pair of castors. 5. A load carrier according to claim 3 wherein said at least one pair comprises said rear pair of castors. 6. A load carrier according to any of claims 3 to 5 wherein each castor of said at least one pair, when in a swivel position for forward movement of the carrier, has its wheel plane offset relative to the swivel axis toward the centre line of said carrier. 7. A load carrier according to any of claims 3 to 5 wherein each castor of said at least one pair, when in a swivel position for forward movement of the carrier, has its wheel plane offset relative to the swivel axis away from the centre line of said carrier. 8. A load carrier according to any preceding claim wherein the offset in the at least one castor is from 2 mm to 10 mm. a is 13 9. A load carrier according to claim 8 wherein said offset is approximately 5 mm. 10. A load carrier according to claim 2 or any claim dependent thereon, wherein the magnitude of the inclination of the swivel axis in said at least one castor is between 20 and 100. 11. A load carrier according to claim 10 wherein said inclination is from 40 to 50. 12. A load carrier according to any preceding claim in the form of a shopping trolley having a base chassis on which said set of wheel elements is mounted, and an upwardly open basket supported on said chassis. 13. A swivel castor for a steerable mobile load carrier, said castor having a wheel which is able to swivel about a swivel axis which is generally perpendicular to and displaced from the axis of rotation of the wheel, wherein the wheel is mounted so that the wheel plane, as herein defined, is offset in the direction of said axis of rotation, relative to said swivel axis. 14 14. A swivel castor according to claim 13 wherein the of f set of said wheel plane relative to said swivel axis is from 2 mm to 10 mm. 15. A swivel castor according to claim 14 wherein the offset is approximately 5 mm. 16. A shopping trolley substantially as hereinbefore described with reference to Figures 1, 5 and 6 of the accompanying drawings. 17. A swivel castor from a steerable mobile load carrier, substantially as hereinbefore described with reference to Figures 5 and 6 of the accompanying drawings. v 5 so Amendments to the claims have been filed as follows CLAIMS:

1. A steerable mobile load carrier comprising a set of ground-contacting wheel elements. at least one of which is a swivel castor which is able to swivel about a swivel axis which is generally perpendicular to and displaced from the axis of rotation of the wheel, wherein said swivel axis is inclined forwardly relative to the vertical when the carrier is on a horizontal support surface, and wherein the wheel is mounted so that the wheel plane, as herein defined, is offset in the direction of said axis of rotation, relative to said swivel axis.

2. A load carrier according to claim 1 having a front pair and a rear pair of said swivel castors, wherein each castor of at least one of said pairs of castors has its said wheel plane offset.

3. A load carrier according to claim 2 wherein said at least one pair comprises said front pair of castors.

4. A load carrier according to claim 2 wherein said at least one pair comprises said rear pair of castors.

5. A load carrier according to any of claims 2 to 4 wherein each castor of said at least one pair, when in a swivel position for forward movement of the carrier, has its wheel plane offset relative to the swivel axis AP toward the centre line of said carrier.

6. A load carrier according to any of claims 2 to 4 wherein each castor of said at least one pair, when in a swivel position for forward movement of the carrier, has its wheel plane offset relative to the swivel axis away from the centre line of said carrier.

7. A load carrier according to any preceding claim wherein the offset in the at least one castor is from 2 mm to 10 mm.

8. A load carrier according to claim 7 wherein said offset is approximately 5 mm.

9. A load carrier according to any preceding claim, wherein the magnitude of the inclination of the swivel axis in said at least one castor is between 20 and 100.

10. A load carrier according to claim 9 wherein said inclination is from 40 to 50.

11. A load carrier according to any preceding claim in the form of a shopping trolley having a base chassis on which said set of wheel elements is mounted, and an upwardly open basket supported on said chassis.

12. A swivel castor for a steerable mobile load 1-7 carrier, said castor having a support member and a wheel which is rotatably mounted on said support member and is able to swivel about a swivel axis which is generally perpendicular to and displaced from the axis of rotation of the wheel, wherein the wheel is mounted so that the wheel plane, as herein defined, is offset in the direction of said axis of rotation, relative to said swivel axis, and the support member is arranged so that the swivel axis is inclined forwardly relative to the vertical when the castor is mounted on the load carrier.

13. A swivel castor according to claim 12 wherein the offset of said wheel plane relative to said swivel axis is from 2 mm to 10 mm.

14. A swivel castor according to claim 13 wherein the offset is approximately 5 mm.

15. A swivel castor according to any one of claims 12 to 14, wherein the magnitude of the inclination of the swivel axis is between 20 and 100, when the castor is mounted on the load carrier.

16. A swivel castor according to claim 15, wherein said inclination is from 40 to 50.

17. A shopping trolley substantially as hereinbef ore described with reference to Figures 1, 5 and 6 of the 1,3 accompanying drawings.

18. A swivel caster from a steerable mobile load carrier, substantially as hereinbef ore described with reference to the Figures 5 and 6 of the accompanying drawings.