It is well known that a number of designs of shopping and stock trolleys have been published which seek to have a load platform which can move downwards as load is added and move upwards as load is removed.

Patent GB 2214470 A filed in 1988 by Aldo-Manta Limited uses spring supports above the platform plus rollers in guide channels to determine the movement of the platform.

GB Patent Application 2292712 of Karl Adrian James, entitled"Shopping trolley with self levelling base for goods"uses a base supported from below by springs.

The design of J H Worley in GB 2290756 A has vertical slide assemblies with a bag container supported and movable vertically by gas struts.

These designs and others, incorporating slidable members, expandable guide columns, scissors-type lifting mechanisms, provide a platform which can move as the loading varies. However the use of vertically mounted springs requires a specific increase in load for a given lowering of the platform. Shopping items vary considerably in density and these platforms may not move

sufficiently to allow the trolley to accommodate large lightweight items.

The above designs do not address the primary requirement of the supermarket or store owner that shopping trolleys should be nestable to conserve floor space.

Therefore any commercially viable design of movable platform which can be retro-fitted to an existing shopping trolley or any design of trolley incorporating a movable platform, should be nestable, should allow the carriage of young children and carry shoppers goods generally as trolleys presently in use. Ideally they should provide increasing volume of trolley with increasing bulk of shoppers goods.

The present invention provides a movable platform for a trolley comprising, an upper platform spaced apart from a base by means of a collapsible support linkage and resisting means arranged to resist collapse of said collapsible support as the spacing between said upper platform and said base decreases, said resisting means being arranged such that resisting forces generated by said resisting means remain balanced against one another as the spacing between said upper platform and said base changes.

According to the present invention such a movable platform can be realised either as a separate, self supporting, platform apparatus which can be easily fitted to an existing shopping trolley or the platform apparatus can be incorporated as part of the trolley during manufacture.

The separate, self supporting, platform apparatus comprises an upper platform, a base, four collapsible support linkages between base and upper platform, means of resisting the collapsing of each of the support linkages as the load on the upper platform increases and means of retaining said resisting means such that the resisting forces are balanced against one another.

The collapsible support linkages are each constrained such that each will collapse in one vertical plane only. The four collapsible support linkages are arranged (in plan view) to be across the 4 corners of a substantially square formation (i. e. as diagonally opposing pairs). As the upper platform moves towards the base the four collapsible supports bend inwards such that their centres move equally towards the opposite collapsing support.

Four resisting means are held in a X formation such that each resisting means acts between the centre of one collapsible support linkage and the centre of the X. The four resisting means provide equally balanced resisting forces on the centre of the collapsible support linkages.

The lateral force exerted by each resisting means on the centre of each collapsible support linkage increases as the resisting means is compressed. However, as the upper platform approaches the base the greater is the bend of each collapsible support linkage and the internal angle of the upper and lower parts of each collapsible support linkage decreases. This reduces the vertically resolved component of the lateral resisting force thereby reducing the uplift.

As the platform moves towards the base under load it reaches a level (the transition level) where a small increase in load produces an abrupt fall of the platform to the base.

The advantages of this apparatus are: the platform moves towards the base with increasing load without tilt or lateral shift; for equal increments of loading, the platform will move down in increasing increments so providing increased volume within the trolley for bulky lightweight items ; the strength of the resisting means can be varied to set the load at which the transition level occurs ; the ratio of the unloaded to loaded height of the platform can be set by the length of the support linkages; the fully collapsed platform has minimal restoring force and so can be easily retained as a compact unit attached to the front of the trolley; the compact unit so attached does not prevent the nesting of trolleys; there are no guide rails or other attachments which need to be fixed to the trolley A preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:- Figure 1 shows in plan the unloaded platform apparatus Figure 2 shows in elevation the unloaded platform apparatus Figure 3 shows in elevation a partly loaded platform apparatus

Figure 4 shows in elevation a fully loaded platform apparatus Figure 5 shows in elevation a platform incorporated in a trolley Figure 6 shows in elevation an alternative platform incorporated in a trolley Referring to figures 1 and 2 Figure 1 shows a plan view of the base 2 with the four lower parts 4b of the four collapsible support linkages 3 rotatably attached.

The top 1 is similar to the base 2 and has the four upper parts 4a of the four collapsible support linkages 3 similarly rotatably attached.

Figure 2 shows two of the four collapsible support linkages 3, each of which consists of identical upper and lower members 4a, 4b and a central linking box 5.

The lower and upper parts 4a, 4b of the collapsible support linkages 3 are identical and are preferably made from round steel wire, bent into the desired U shape and given rigidity by welded cross members of the same material.

The outwardly bent ends 6 of each of the eight linkages 4a, 4b pass through holes 8a in angled brackets 8 in both base 2 and top 1. This enables the linkages 4a, 4b to rotate but only in the planes of the diagonals.

The central sections 7a, 7b of the four upper and four lower linkage arms 4a, 4b pass through upper and lower pairs of holes 5a, 5b in the opposite sides of linkage box 5. If desired, friction reducing bushings 10 can be fitted to holes 5a, 5b, 5c and 8a in linkage box 5 and angled brackets 8 respectively.

Four rods lla, llb, llc, lld pass through pairs of holes 5c in each linkage box 5. The four rods 11 are demountably attached at one extremity to a central boss 12. Each rod 11 carries a compressible resisting means 13a, 13b, 13c, 13d which provides a resisting force between the central boss 12 and linkage box 5. The holes 5c through which each rod 11 passes serve to keep the linkage box 5 perpendicular to rod 11 as the compressible resisting means 13 is compressed.

The underside of the base 2 has a hook 14 which allows the fully compressed platform to be hung onto the wired frame front of the trolley and also to be positioned on the base of the trolley at a point which allows the side panels 15, 16 to be extended on hinges 17 to rest against the trolley front and rear panels.

Figure 3 shows a partially loaded, partially compressed platform. Upper and lower linkage arms 4a, 4b have hinge closer together pushing the linking boxes 5 closer to each other. Resisting means 13 have been compressed somewhat on rods 11 to provide a resisting force between opposing linking boxes 5 via boss 12. This outward force provides an upward force on arms 4a, 4b to balance the downward force imposed by the load on the platform.

Hinged side panels 15,16 continue to rest against the sloping sides of the front and rear panels of the trolley as the platform moves down.

Figure 4 shows the platform in its fully compressed position in normal use. Note that it is possible to compress the platform further but this is prevented by the stop arms 18 which hold the top 1 away from the base 2.

In this position the link arms 4a, 4b are still held at an angle to each other which enables the force exerted by the compressible resisting means 13 to generate an uplifting force. This will raise the top 1 from the base 2 if the load on the platform reduces.

The stop arms 18 can swivel in holes la so that they can be manually moved parallel to the undersurface of the top 1 and so allow the top 1 to further approach the base 2.

In this position the linkage arms 4a, 4b are almost parallel, so that the lateral force exerted by the compressible resisting means 13 provides almost no uplifting force to move the top 1 away from the base 2. Engaging swing clips 20 on the top 1 with the studs 19 on the base 2 holds the top and base close together. In this position the platform assembly, with side panels 15,16 folded back onto the top 1 can be hooked onto the front panel of the trolley. In this position trolleys can be nested.

Referring to figure 5 the platform apparatus has been incorporated into a trolley by discarding the base 2, fitting the base of the trolley with the necessary angled brackets 8 to engage with the ends 6 of the link arms 4b and replacing the top 1 and side panels 15,16 with one

platform 21. When platform 21 is held against the trolley base, with stop arms 18 moved out of the way and swing clips 20 engaged with studs 19 on the platform 21, trolleys can be nested.

An alternative arrangement for fitting the self supporting platform apparatus to an existing trolley will now be described. In this alternative arrangement the platform apparatus can be pushed in its uncollapsed state to the front of the trolley by the action of the trolley tailgate as it swivels upwards as a second trolley is nested within.

With reference to figure 6, the movable platform system remains substantially unchanged. The top 1, bottom 2 and collapsible support linkages 3-13 remain unchanged. Hook 14, clips 20 and studs 19 are no longer required. Side panels 15,16 are not hinged but slide in channels 22,23 on either side of top 1.

Pivot pins 24 at the edge of the base 2 co-operate with brackets 25 which are fixed to the trolley to enable the base 2 to rotate about the axis between said brackets.

A lifting bracket 26 fixed to the tailgate of the trolley pushes up on the lower surface of the base 2 as the tailgate swivels. Bracket 26 therefore causes the movable platform assembly to lift and rotate from its normal operating position into the front of the trolley. Side panels 15,16 slide closer together as the platform assembly rotates. The rearward side panel 15 slides downwards as it approaches a vertical position, the

forward side panel 16 slides upwards as it presses against the front of the trolley.

When a nesting trolley is withdrawn the tailgate swivels downwards. A flexible linking member 27 connecting the front of bracket 26 with the base 2 causes the movable platform assembly to rotate rearwards as the tailgate swivels downwards. The movable platform assembly comes to rest in its original operating position.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment (s). The invention extend to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.