This invention relates to a roller assembly, and to a track system comprising a track and a roller assembly for guided movement along the track. The invention has been devised particularly, although not necessarily solely, in relation to a door assembly comprising a track assembly and a sectional door movable between closed and open conditions along the track.

Background Art

The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application

Sectional doors are used in various commercial, industrial and residential applications to open and close access openings. In particular, sectional doors are commonly used as garage doors.

A sectional door comprises a series of adjacent panels hingedly connected one to another for movement between a closed condition in which the door closes an opening, and an open condition which is overhead and clear of the opening. The sectional door commonly moves along a track assembly which includes a main track comprising a generally vertical track section, a generally horizontal track section and a curved transition track section interconnecting the horizontal and vertical track sections. The vertical track section is typically defined by a track rail and the horizontal track section is defined by a track rail, with the two track rails commonly being of the same cross-sectional profile. The panels are typically mounted on rollers that fit in the track assembly, with the rollers and track assembly interacting to guide movement of the panels between the closed and open conditions. Movement of the door between the closed and open conditions is assisted by a counter-balance system coupled to the door.

The counter-balance system generally comprises a shaft (which is commonly known as a torsion pole) to which a counter-balance spring is connected. The counter-balance spring is typically a coil spring. The shaft is supported at its ends for rotation by support brackets. The shaft carries two cable drums, one adjacent each end of the sectional door. The cable drums are fixed to the shaft for rotation therewith, The counter-balance system further comprises two cables, each windingly received on one of the cable drums. The cables are connected to adjacent ends to the lowermost panel. With this arrangement, the spring is progressively tensioned as the sectional door moves towards the closed condition, thereby providing a counter-balancing effect during the closing action and also lifting assistance during the opening action.

In certain applications, particularly where there is restricted overhead space available, the track assembly may be configured to provide an auxiliary track section to receive and guide upper rollers on the top panel. The auxiliary track is referred to as a dub track. The auxiliary track is positioned above the transition track section and the horizontal track section and comprises an ramp section and an auxiliary horizontal section. The ramp section is adapted to interact with the respective upper roller of the top panel when the sectional door is in the closed condition and to guide the respective upper roller of the top panel towards the auxiliary horizontal section as the sectional door moves from the closed condition to the open condition. As the sectional door moves from the closed condition to the open condition, the rollers on the other panels sequentially move upwardly along the vertical track section, into engagement with the transition track section and ultimately into engagement with the horizontal track section. When the sectional door is in the open condition, the upper rollers on the top panel are on the auxiliary track and all other rollers are on the horizontal track section.

Typically, the auxiliary track is defined by componentry formed separately from the main track. In particular, the auxiliary horizontal section of the auxiliary track is defined by a track rail which is a different track rail from the track rail that defines the horizontal track section of the main track.

It would be advantageous to use a common track rail to provide both the horizontal track section of the main track and the auxiliary horizontal section of the auxiliary track.

This would necessitate a roller assembly configured to interact with that part of the common track rail which provides the auxiliary horizontal section of the auxiliary track.

It is against this background that the present invention has been developed. However, the roller assembly according to the invention need not necessarily be limited to use with sectional doors; it may be applicable to certain other arrangements involving movement of a roller along a track.

Disclosure of the Invention

According to a first aspect of the invention there is provided a roller assembly for movement along a track, the roller assembly comprising a support roller and a keeper, the support roller being adapted for guided rolling movement along the track, and the keeper being adapted to constrain the support roller for rolling movement along the track.

Preferably, the roller assembly further comprises a trolley having an axle on which the support roller is supported, the axle also supporting the keeper.

Preferably, the keeper is operable to restrain the trolley against derailment.

Preferably, the axle comprises an outer end portion on which the support roller is rotatably supported.

Preferably, the keeper is rotatably supported on the axle. Preferably, the keeper is disposed between the support roller and a stop on the axle.

Preferably, the outer end portion of the axle comprises an outer section on which a hub is rotatably mounted, and a shank section adjacent the hub Preferably, the support roller comprises a roller body mounted on the outer end portion of the axle.

Preferably, the roller body defines a rolling outer surface and a side surface.

Preferably, the roller body comprises a tyre mounted on the hub. Preferably, the tyre comprises a body formed of a plastics material.

Preferably, the keeper comprises a keeper sleeve, a keeper side and a keeper abutment.

Preferably the keeper sleeve, the keeper side and the keeper abutment are of integral construction and are defined by a body formed of a plastics material. Preferably, the keeper sleeve is mounted on the shank section of the axle to be freely rotatable with respect thereto.

Preferably, the keeper side is configured as a plate.

Preferably, the keeper abutment is configured as a skid.

According to a second aspect of the invention there is provided a track system comprising a track and a roller assembly for guided movement along the track, the roller assembly being in accordance with the first aspect of the invention.

In one arrangement, the track may comprise a track rail comprising an elongate track body configured to receive and guidingly supporting the support roller for rolling movement therealong. In such an arrangement, the elongate track body may be configured to define a longitudinal side presenting an outer longitudinal surface, an inner longitudinal surface and a free longitudinal edge, wherein the keeper side is disposed adjacent the free longitudinal edge and the keeper abutment is disposed adjacent the inner longitudinal surface. Preferably, the elongate track body comprises a longitudinal web and two opposed longitudinal sides which cooperate to define a channel interior, the longitudinal web being configured to define a supplementary track for receiving and guidingly supporting the support roller for movement along the track rail, wherein one of the two opposed longitudinal sides provides said longitudinal side presenting an outer longitudinal surface, an inner longitudinal surface and a free longitudinal edge. Preferably, the longitudinal web is configured to define a longitudinal rib providing the supplementary track for receiving and guidingly supporting the support roller for movement along the track rail.

In another arrangement, the track may be comprise a track formation in a radius bracket defining a curved transition track section interconnecting horizontal and vertical track sections.

In such an arrangement, the track formation comprise an upper track surface, a lower guide surface, an outer longitudinal edge, and a longitudinal groove adjacent the upper track surface on the opposed side thereof to the outer longitudinal edge, wherein roller assembly can travel along the track formation with the support roller accommodated in the longitudinal groove for guided rolling movement therealong, with the keeper side disposed adjacent the outer longitudinal edge, and the keeper abutment disposed adjacent the lower guide surface.

According to a third aspect of the invention there is provided a track assembly incorporating a track system according to the second aspect of the invention.

According to a fourth aspect of the invention there is provided a door assembly comprising a track assembly and a sectional door for movement along the track assembly between closed and open conditions, the track assembly being in accordance with the third aspect of the invention. Preferably, the sectional door comprises series of adjacent panels hingedly connected to one another, the panels including a top panel having opposed ends, each end being fitted with a respective roller assembly. Brief Description of the Drawings

The invention will be better understood with reference to the following description of one specific embodiment thereof as shown in the accompanying drawings in which: Figure 1 is a schematic fragmentary perspective view of an installed door assembly including a door track and a sectional door moveable along the door track, viewed from the exterior side of the door assembly;

Figure 2 is a view similar to Figure 1 except that it is viewed from the interior side of the door assembly; Figure 3 is a schematic fragmentary perspective view of the door assembly including the door track assembly according to the embodiment, viewed from the exterior side of the door assembly;

Figure is a view similar to Figure 3 except that it is viewed from the interior side of the door assembly; Figure 5 is a schematic fragmentary perspective view of the door assembly viewed from the interior side thereof;

Figure 6 is a further schematic fragmentary perspective view of the door assembly viewed from the interior side thereof;

Figure 7 is a view similar to Figure 6 except that it is viewed from the exterior side of the door assembly;

Figure 8 is a perspective view of a track rail incorporated in the door track according to the embodiment, the view being from one end and above;

Figure 9 is a view similar to Figure 8 except that it is from the underside;

Figure 10 is a perspective view of the track rail, the view being from the other end and above;

Figure 1 1 is a perspective view of a radius bracket which cooperates with two track rails to provide a main track and an auxiliary track; Figure 12 is a further perspective view of the radius bracket;

Figure 13 is a fragmentary perspective view of the junction between the radius bracket and a horizontal track rail;

Figure 14 is a fragmentary perspective view of the radius bracket illustrating in particular an end section thereof to provide a junction between the radius bracket and the horizontal track rail;

Figure 15 is a further fragmentary perspective view of the junction between the radius bracket and the horizontal track rail as shown in Figure 13;

Figure 16 is a front view of the radius bracket; Figure 17 is a sectional view of line 17-17 of Figure 16;

Figure 18 is a perspective view of the arrangement shown in Figure 17;

Figure 19 is a perspective view of an inset incorporated within the radius bracket;

Figure 20 is a side view of the inset incorporated within the radius bracket; Figure 21 is a perspective view of the radius bracket and the horizontal track rail, illustrating an upper roller assembly according to the embodiment movable therealong;

Figure 22 is a fragmentary perspective view of the roller assembly according to the embodiment and the track rail, viewed from the upper side thereof;

Figure 23 is a fragmentary perspective view of the roller assembly and the track rail, viewed from the lower side thereof;

Figure 24 is a view of the roller assembly and the track rail, depicting the interaction therebetween; and Figure 25 is a view similar to Figure 24 except that the roller assembly is shown in section. Best Mode(s) for Carrying Out the Invention

Referring to the drawings, there is shown a door assembly 10 for a structure such as a garage (not shown) having a wall 1 1 in hich there is an access opening 12 which is opened and closed by the door assembly. The door assembly 10 comprising a sectional door 13 mounted in a track assembly 14 for movement between closed and opened conditions.

The sectional door 13 comprises a series of adjacent panels 15 hingedly connected to one another in known manner for movement between the closed condition in which the sectional door 13 occupies the opening and an open condition in which the sectional door 13 is overhead and clear of the opening. The panels 15 include a top panel 15a and a bottom panel 15b, as well as various intervening panels 15c therebetween.

The track assembly 14 includes a main track 17 and an auxiliary track 19 (also known as a dub track) on each side of the sectional door 13. A counter-balance system 20 is provided to assist movement of the sectional door 13 between the open and closed conditions. The counter-balance system 20 is of known kind, comprising a torsion pole 23 to which a counter-balance spring (not shown) is connected. The counter-balance spring is typically a coil spring, with one end connected to the torsion pole 23 and the other end connected to a fixed support. The torsion pole 23 is supported at its ends for rotation by support brackets 25. The torsion pole 23 carries two cable drums 26, one adjacent each end of the sectional door 13. The cable drums 26 are fixed to the torsion pole 23 for rotation therewith. The counter-balance system 20 further comprises two cables (not shown), each windingly received on one of the cable drums 26. The cables are connected to adjacent ends to the bottom panel 15b. Specifically, each end of the bottom panel 15b is provided with a lug (not shown) to which the respective cable is connected in known manner. With this arrangement, the counter-balance spring is progressively tensioned as the sectional door 13 moves towards the closed condition, thereby providing a counterbalancing effect during the closing action. The tensioned counter-balance spring also provides lifting assistance during movement of the sectional door 13 from the closed condition to the open condition.

The panels 15 are provided with rollers 30 which are received in the track assembly 14. The rollers 30 and the track assembly 14 interact to guide movement of the sectional door 13 between the open and closed conditions,

The rollers 30 include an upper set of rollers 31 on the top panel 15a adjacent the upper edge thereof. The rollers 30 further includes a lower set of rollers 32 on the bottom panel 15b adjacent the lower edge thereof, and an intermediate sets of rollers 33operating between adjacent panels 5. The upper set of rollers 31 comprises two roller assemblies 35 according to the embodiment (as shown in detail in Figures 21 to 25), one adjacent each end of the top panel 15a. The rollers 32, 33 are typically rollers of known kind, as used with conventional sectional doors.

The two auxiliary tracks 19 are adapted to interact with the roller assemblies 35 on the top panel 15a during movement of the sectional door 13 between the closed and open conditions. All other rollers 30, including in particular the intermediate sets of rollers 33a operating between top panel 15a and the adjacent panel 15c, interact with the two main tracks 17 during movement of the sectional door 13 between the closed and open conditions. The main track 17 on each side of the sectional door 13 comprises a generally vertical track section 41 , a generally horizontal track section 43 and a curved transition track section 45 interconnecting the horizontal and vertical track sections.

The vertical track section 41 is defined by a track rail 46 and the horizontal track section 43 is defined by a track rail 47, with the two track rails 46, 47 commonly being of the same cross-sectional profile.

The auxiliary track 19 on each side of the sectional door 13 is positioned above , the transition track section 45 and the horizontal track section 43, and comprises a ramp section 51 and an auxiliary horizontal section 53. The ramp section 51 is adapted to interact with the respective upper roller assembly 35 of the top panel 15a when the sectional door 13 is in the closed condition and to guide the respective upper roller assembly of the top panel towards the auxiliary horizontal section 53 as the sectional door moves from the closed condition to the open condition. As the sectional door moves from the closed condition to the open condition, the rollers 32 33 sequentially move upwardly along the vertical track section 41 , into engagement with the transition track section 45 and ultimately into engagement with the horizontal track section. When the sectional door 13 is in the open condition, the upper roller assemblies 35 on the top panel 15a are on the auxiliary track 19 and all other rollers 32 33 are on the horizontal track section 43.

The track rail 47 which defines the horizontal track section 43 of the main track 17 also defines the auxiliary horizontal section 53 of the auxiliary track 19, as will be explained in more detail later.

The door assembly 10 further comprises two radius brackets 70 which are mounted on the wall 1 1 of the garage and which form part of the support structure for the sectional door 13. In the arrangement shown, each radius bracket 70 is mounted on the wall 1 1 by means of mounting brackets 71.

Each radius bracket 70 forms parts of the track assembly 14 and is installed above respective vertical track section 41. In particular, each radius bracket 70 is configured to define the respective curved transition track section 45 interconnecting the horizontal and vertical track sections 41 , 43 of the main track 17 and to also define the respective ramp section 51 of the auxiliary track 19.

In addition to forming parts of the track assembly 14, each radius bracket 70 also provides bracing for the track assembly 14. Each radius bracket 70 is also configured to provide the support bracket 25 for the respective end of the torsion pole 23.

The construction of the radius brackets 70 will be described in more detail later.

The track rail 46 and the track rail 47 are of a common profile which is depicted in Figures 8, 9 and 10. Each track rail 46, 47 comprises a longitudinal rail body 80 of channel cross-section. The rail body 80 comprises a longitudinal web 81 and two opposed longitudinal sides 82, 83 which cooperate to define a channel interior 84 and a longitudinal opening 85 opposite the web 81 . The two opposed longitudinal sides 82 and 83 will hereinafter be referred to as first longitudinal side 82 and second longitudinal side 83.

First longitudinal side 82 is configured to define a curved formation which provides a groove 86 to receive and guide the rollers 30 for rolling movement therealong.

The second longitudinal side 83 presents an outer longitudinal surface 87, an inner longitudinal surface 88, and a free longitudinal edge 89 in opposed relation to the longitudinal web 81.

The longitudinal web 81 incorporates a longitudinal rib 91 extending along the length thereof. The longitudinal rib 91 defines a longitudinal space 92 adjacent to, and opening onto, the channel interior 84. In the arrangement shown, the rib 91 is of channel formation comprising a rib base 93 and two rib sides 95, with the sides 95 being generally normal to the base 93 such that the space 92 is generally rectangular.

When the rail body 80 is used as the vertical track rail 46, second longitudinal side 83 cooperates with the longitudinal side 83 to constrain the rollers 30 as they move along the vertical track section 41 . When the rail body 80 is used as the horizontal track rail 47, the longitudinal web 81 and the second longitudinal side 83 cooperate to define the auxiliary horizontal section 53 of the auxiliary track 19, as will be described in more detail later.

The longitudinal rib 91 can serve a variety of functions, as described below.

One function is a strengthening function in that the rib 91 can serve as a strengthen rib for the rail body 80.

Another function is that the longitudinal space 92 can accommodate certain componentry of the door assembly 10. While note the case in this embodiment, the longitudinal space 92 may accommodate some of the componentry of the counter-balance system provided to assist movement of the sectional door 13 between the open and closed conditions. In particular, the longitudinal space 92 may accommodate the section of the cable (not shown) extending down from the elevated cable drum 26 to the bottom panel 15b and also the lug (not shown) on the bottom panel 15b to which the cable is connected. This may be advantageous as it could serve to conceal the downwardly extending section of the cable and also the lug.

In other embodiments, the longitudinal space 92 may also accommodate components of a power-operated drive system for automatically opening and closing the sectional door 13. For example, the longitudinal space 92 may accommodate a drive chain or belt forming part of a power-operated drive system.

Yet another function of the longitudinal rib 92 is that it can provide a facility for the mounting the rail body 80 in position, particularly when used as the horizontal track rail 47, without fixing elements intruding into the channel interior 84 and potentially impeding movement of the rollers 30. In particular, the rib base 93 can provide a mounting face for location against a mounting surface to which the rail body 80 is to be attached, with fasteners or other fixing elements extending through the rib base 93 to secure the rail body 80 to the mounting surface. With this arrangement, heads of the fasteners would be located again the rib base 93 within the confines of the longitudinal space 92 and thereby away for the channel interior 84 and the rollers 30 as they move therealong.

Still yet another function of the longitudinal rib 92 is that it may function as a spacer to space the second longitudinal side 83 of the rail body 80 away from a mounting surface to which the rail body 80 is to be attached when functioning as horizontal track rail 47, thereby providing clearance for the upper roller assembly 33 to move along the auxiliary horizontal section 53 of the auxiliary track 19.

Furthermore, in this embodiment/ the longitudinal rib 91 cooperates with an adjacent portion 81 a of the longitudinal web 81 to define a supplementary track 96 to facilitate guided movement of the respective upper roller assembly 35, as will be explained later. The radius brackets 70 form parts of the track assembly 14, provides bracing for the track assembly 14, and also supports the torsion pole 23.

Each radius bracket 70 comprises a body 101 formed of plastics material with internal reinforcement 102. The reinforcement 102 provides strengthening at locations where necessitated by loadings to which the bracket 70 is exposed, as will be explained in more detail later. In the arrangement shown, the internal reinforcement 102 comprises an insert 103 embedded within the plastic body 101. Typically, the insert 103 comprises a skeleton structure 105 formed of metal such as steel. The skeleton structure 105 is of unitary construction and includes integral first, second, and third portions. The first, second, and third portions are identified by reference numerals 105a, 105b and 105c respectively.

At least some of the mounting and fastening holes within the body 101 extend through the skeleton structure 105 so as to provide the radius bracket 70 with structural integrity and strength in order to withstand loadings imposed thereon during service.

The body 101 comprises a body portion 106 configured as a plate 107 having an upper edge 108, an inner edge 109 and a curved lower edge 1 10. The body portion 106 defines an outer end section 1 1 1 and a bottom end section 1 13, with the upper edge 108 extending to the outer end section 1 1 1 , the inner edge 109 extending to the bottom end section 1 13, and the curved lower edge 1 10 extending between the outer end section 1 1 1 and the bottom end section 1 13.

The plate 107 provides a mounting flange 1 14 which incorporates mounting holes 1 15 for mounting the radius bracket 70 in position. The mounting flange 1 14 is reinforced by the skeleton structure 105. In particular, the mounting flange 1 14 incorporates the first portion 105a of the skeleton structure 105 and the mounting holes 1 15 extend through the first portion to provide robust mounting points.

The upper edge 108 incorporates a formation 121 which provides a saddle 123 to receive and support the respective end of the torsion pole 23, as best seen in Figure 7. Mounting holes 124 are incorporated in the body 101 for securing an attachment fitting associated with the torsion pole 23 in position. The saddle 123 is configured to have a narrow entry opening 123a to snugly receive the respective end of the torsion pole 23. With this arrangement, the saddle 123 effectively functions as a clip to receive and captively retain the respective end of the torsion pole 23. The formation 121 is reinforced by the skeleton structure 105. In particular, the second portion 105b of the skeleton structure 105 incorporates a lateral flange arrangement 126 incorporated in the formation 121. Further, the mounting holes 124 extend through the second portion 105a of the skeleton structure 105 to provide robust mounting points. The outer end section 1 1 1 of the radius bracket 70 is adapted to be coupled to the adjacent end of the track rail 47. The outer end section 1 1 1 comprises a web portion 125 incorporating fastener holes 127 for receiving fasteners (not shown) for securing the coupled parts together. The web portion 125 is also reinforced by the skeleton structure 105. In particular, the web portion 125 incorporates the third portion 105c of the skeleton structure 105 and the fastener holes 127 extend through the third portion 105c of the skeleton structure 105 to provide robust attachment points.

Similarly, the bottom end section 1 13 of the radius bracket 70 is adapted to be coupled to the upper end section of the track rail 46 defining the vertical track section 41. The bottom end section 1 13 comprises a web portion 128 incorporating fastener holes 129 for receiving fasteners (not shown) for securing the coupled parts together.

While the internal reinforcement 102 has been described as being of metal, it should be appreciated that it may be of any other appropriate material suitable to provide the necessary reinforcement. The curved transition track section 45 interconnecting the horizontal and vertical track sections 41 , 43 of the main track 17 is defined by an arcuate rib formation 130 located along the curved lower edge 110. The rib formation 130 defines a groove 131 which is of a cross-sectional profile corresponding to the groove 86 in the track rails 46 and also the groove 86 in the track rail 47. Thus, the grooves 86 and the intervening groove 131 cooperate to provide a continuous track for the rollers 30 moving therealong as the sectional door 13 moves between the open and closed conditions. The outer end section 1 1 1 and the bottom end section 1 13 incorporate recesses 132 to accommodate the adjacent ends of the respective track rails 46, 47 to provide smooth transitions between the grooves 86, 131 and thereby establish the continuous track for the rollers. The arcuate rib formation 130 has integral lateral reinforcement webs 133 at intervals along the length thereof.

The radius bracket 70 also includes an integral rib 134 defining a guide wall 135 which cooperates with the groove formation 131 to provide the curved transition track section 45. The guide wall 135 assists in guiding the rollers 32, 33 around that part of the turn which has a predominant vertical component and retaining the rollers in the actuate groove formation 131 as the sectional door 13 moves between the open and closed conditions. The rib 134 has integral lateral reinforcement webs 137 at intervals along the length thereof on the side thereof opposite the guide wall 135. The radius bracket 70 also includes an integral rib 141 defining the ramp section 51 of the auxiliary track 19. The rib 141 forms a projecting flange 143 which defines an upper track surface 145 and a lower guide surface 147. The projecting flange 143 has an outer longitudinal edge 144. The rib 141 also incorporates lateral reinforcement webs 149 at intervals along the length thereof. The lateral reinforcement webs 149 are located inwardly of the lower guide surface 147 so as to avoid impeding roller movement therealong. The integral rib 141 incorporates a longitudinal groove 146 adjacent the upper track surface 145, the purpose of which will become apparent later. With this arrangement, the upper track surface 145 is defined between the outer longitudinal edge 144 and the longitudinal groove 146.

The integral rib 141 defining the ramp section 51 is profiled so that the path followed by the top panel 15a clears the cable drums 26 as the sectional door 13 moves between the open and closed conditions.

The integral rib 134 defining guide wall 135 terminates at upper end 136 which is below and spaced from the integral rib 141 defining the ramp section 51 of the auxiliary track 19. With this arrangement, a clearance space 138 is provided between the two integral ribs 134, 141 for passage of the roller assembly 35, as will be explained later.

As mentioned above, the panels 15 have rollers 30 which interact with the track assembly 14 to guide movement of the sectional door 13 between the open and closed conditions.

The roller assemblies 35 according to the embodiment are adapted to cooperate with the auxiliary tracks 19 during movement of the sectional door 13 between the closed and open conditions. All other rollers 30, including in particular intermediate sets of rollers 33a operating between top panel 15a and the adjacent panel 15c, interact with the two main tracks 17 during movement of the sectional door 13 between the closed and open conditions.

Each roller assembly 35, which is shown in Figures 21 to 25, comprises a trolley 150 having an axle 151 attached to the top panel 15a. The axle 151 has an outer end portion 153 on which a support roller 155 is rotatably supported. The outer end portion 153 also rotatably supports a keeper 157 operable to restrain the trolley 150 against derailment. The keeper 157 is disposed between the support roller 155 and a stop 159.

The outer end portion 153 of the axle 151 comprises an outer section 161 which is at the end of the axle and on which a hub 163 is rotatably mounted, and a shank section 164 adjacent the hub 163. In this embodiment, the hub 163 comprises a roller bearing mounted on the axle 151.

The support roller 155 comprises a roller body 165 mounted on the outer end portion 15 of the axle 151. The roller body 165 defines a rolling outer surface 166 and two opposed side surfaces 167. In the arrangement illustrated, the roller body 165 comprises a tyre 168 mounted on the rotatable hub 163. More particularly, the tyre 168 is configured to fit on the hub 163 to define the rolling surface 166. In this embodiment, the tyre 168 comprises a body 171 formed of a plastics material. The keeper 157 comprises a keeper sleeve 173, a keeper plate 175 and a keeper abutment 176 configured as a skid. In this embodiment, the keeper sleeve 173, the keeper plate 175 and the keeper abutment 176 are of integral construction and are defined by a body 177 formed of a plastics material. The keeper sleeve 173 is mounted on the shank section 164 of the axle 151 and is freely rotatable with respect thereto. With this arrangement, the keeper member 157 can pivot on the axle 151 about an axis of rotation corresponding to the central longitudinal axis of the axle.

The keeper plate 175 carries the keeper skid 176 which is arranged to travel along the underside of the second longitudinal side 83 adjacent the inner longitudinal surface 88. In the arrangement shown, the keeper skid 176 comprises two skid elements 179 configured as projecting pins.

With this arrangement, the roller assembly 35 can travel along the ramp section 51 of the auxiliary track 19 with the support roller 155 accommodated in the longitudinal groove 146 for guided rolling movement therealong, with the keeper plate 175 disposed adjacent the outer longitudinal edge 144, and the keeper skid 176 disposed adjacent the lower guide surface 147. The keeper plate 175 and the keeper skid 176 cooperate with the projecting flange 143 to retain the support roller 155 in rolling engagement with the ramp section 51 . In particular, the keeper skid 176 acts to constrain the support roller 155 for rolling movement along the ramp section 51 of the auxiliary track 19; that is, the keeper skid 176 prevents the support roller 155 from de-railing. With the keeper 157 able to pivot on the axle 151 , the orientation of the keeper can progressively vary as necessary during rolling movement of the roller assembly 35 along the arcuate ramp section 51 in order to maintain the keeper skid 176 positioned for sliding engagement with the lower guide surface 147.

Similarly, the roller assembly 35 can travel along the auxiliary horizontal section 53 of the auxiliary track 19, with the outer surface of the support roller 155 rolling along the longitudinal rib 91 and the side surface 167a disposed alongside portion 81 a of the longitudinal web 81 for guided movement therealong; that is, the support roller 155 travels along the supplementary track 96. Further, the keeper plate 175 is disposed adjacent the free longitudinal edge 89d of the second longitudinal side 83, and the and the keeper skid 176 disposed adjacent the inner longitudinal surface 88. The keeper plate 175 and the and the keeper skid 176 cooperate with the second longitudinal side 83 to retain the support roller 155 in rolling engagement with the auxiliary horizontal section 53 of the auxiliary track 19. In particular, the and the keeper skid 176 acts to constrain the support roller 155 for rolling movement along the horizontal section 53 of the auxiliary track 19; that is, the keeper skid 76 prevents the support roller 155 from de-railing.

The support roller 155 is adapted to travel along the auxiliary track 19, with the outer surface 166 rolling along the longitudinal rib 91 and the side surface 167a disposed alongside portion 81a of the longitudinal web 81 for guided movement therealong, as shown in Figure 24. The keeper plate 175 is disposed adjacent the free longitudinal edge 89d.

The clearance space 138 between the two integral ribs 134, 141 accommodates movement of the keeper skid 176 along the underside of the ramp section 51 without interference by the rib 134 which provides the guide wall 135 associated with the curved transition track section 45.

It should be appreciated that the scope of the invention is not limited to the scope of the embodiment described.

In the embodiment described, the ramp section 51 and the horizontal section 52 of the auxiliary track 19 are each configured for movement of the roller assembly 35 therealong, specifically by configuring the ramp section 51 to provide groove146 and by configuring the track rail 47 to provide the supplementary track 96. Other arrangements are of course possible. By way of example, the support roller 155 may be arranged for guided rolling movement along the upper track surface 145 of the ramp section and also arranged for guided rolling movement along the outer longitudinal surface 87 of the second longitudinal side 83.

Further, in the embodiment described, the keeper abutment 176 is configured as a skid. Other arrangements are, of course, possible. By way of example, the keeper abutment may comprise one or more keepers rollers mounted on the keeper plate 175 to be freely rotatable about axes of rotation which are mutually parallel and which are also parallel with the axis of rotation of the keeper 157 with respect to the axle 151.

Throughout the specification and claims, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.