Abstract:
A rim assembly for a roller assembly and method of forming a rim assembly for cargo mover systems are disclosed. Various steps and construction details are developed for affecting the response of the rim assembly to operative conditions. In one detailed embodiment, the roller assembly has a rim assembly having a rolling surface whose operative surface characteristics are set by the material of the surface material; and structure is disposed inwardly of the rolling surface which affects the bulk behavior of the roller assembly. In one particular embodiment, the roller assembly is adapted for use with moving doors or wall panels in elevator systems.

Description:
TECHNICAL FIELD 
     This invention relates to a roller assembly which passes through predetermined points in its travel for use in the field of cargo mover systems, such as in elevators, escalators, and moving walkway systems. More particularly, this invention relates to a rim assembly for the roller assembly of such a system. This invention was developed for lightweight roller assemblies used with elevator doors as the doors are moved between the open and closed positions and has application to other roller assemblies following a defined path used for cargo mover systems. 
     BACKGROUND OF THE INVENTION 
     Roller assemblies used in escalator systems and elevator systems typically pass through predetermined points that form a defined path. These systems are of the type that are typically self-propelled or driven externally. The systems that are driven externally may be driven by a cable, belt or chain of both the open or endless type, or by a mechanical mechanism utilizing screw drives or lever arm actuation. In these systems, the roller assembly and the rail on which the roller assembly moves are a defined portion of the system. For example, the shape and the surface characteristics of the rail surface are defined. Since the rail surface is well-defined, expectations for life, low noise and other characteristics are greater than expectations for roller assemblies used on undefined surfaces, such as might be experienced by bicycles, automobiles and moving carts. 
     Roller assemblies used in escalators and elevators typically have a rim assembly which includes a rim and a ring in solid form that is positioned from the rim. The ring in solid form has requirements for operative characteristics that are very different from the operative requirements for a ring which is in part supported by gas under pressure, such as automobile tires and the like. In particular, roller assemblies used for elevator doors especially have significant requirements for operative characteristics that can be in conflict. Such roller assemblies may be driven or nondriven. 
     In contrast, roller assemblies used for guiding elevators or used for escalator systems do not have as many demanding operative characteristics even though the roller assembly follows a defined path. Escalator systems typically use nondriven roller assemblies. For example, the nondriven roller assembly may be attached to an operating element for guiding the element, such as a step chain in the escalator system. One example is shown in U.S. Pat. No. 5,137,135 entitled “Escalator Step-Chain Roller” issued to Pietsch et alia. The roller assembly includes a rim assembly having a rim. The rim has a groove bounded by a surface which faces outwardly. A flexible outer ring in solid form is disposed in the groove and is spaced axially from the sides of the groove. The ring has a rolling surface for rolling contact with a second element. In Pietsch, the cooperating second element is an escalator track. 
     Elevator systems employ both nondriven roller assemblies and driven roller assemblies that have a ring in solid form. Nondriven roller assemblies may be used for guiding movement of an elevator car as the car moves vertically between predetermined locations. These guide roller assemblies are similar to the roller assembly shown in Pietsch and have somewhat similar operating requirements. The guide roller assemblies are distinguished by the need for the roller assembly to rotate at relatively high speeds in comparison to the escalator roller assembly to accommodate the speed of the elevator car. 
     As discussed earlier, elevator systems also employ door roller assemblies for guiding elevator doors on the car as the doors are opened and closed. The roller assemblies rotate at a lower rotational speed than do guide rollers for guiding the elevator car. The door roller assemblies are lightweight and may be non-driven, rolling as the door is moved; or may be driven, rotating to drive the door. 
     A nondriven roller assembly may be attached to the door and may roll on a track as the door is moved by another device between the open and dosed positions. A driven roller assembly engages the track and might be attached to the door. These driven roller assemblies, or traction roller assemblies, are driven about an axis of rotation to move the door between the open and closed positions. An example of such a motorized roller assembly is shown in U.S. Pat. No. 5,852,897 entitled “Door Drive” issued to Sukale. 
     FIG. 1 is a simplified side elevation view of a roller assembly, such as a lightweight roller assembly  10  for elevator doors, and of a rail  12  on which the roller assembly moves. The rail has a plurality of predetermined location points P which form a defined path  13  for the roller assembly 
     The roller assembly has an axis of rotation A. FIG. 2 is a cross-sectional view taken through the simplified roller assembly and the rail along the lines  2 — 2  of FIG.  1 . The cross-sectioning plane contains the axis A and passes through the circumferential location L. The circumferential location L is the location at which the maximum force is transmitted from the rail to the roller assembly as the rail reacts to the load imposed by the roller assembly on the rail. 
     As shown in FIG.  1  and in FIG. 2, the roller assembly  10  has a rim assembly  14 . The rim assembly is usable with both a driven and a nondriven roller assembly. The rim assembly has a freestanding rim  16  and a groove  18  bounded by a radially outwardly facing surface  20 . A flexible ring  22  in solid form is disposed in the groove. The ring extends circumferentially and axially about the rim. 
     The ring  22  has an outwardly facing surface  24 . The outwardly facing surface includes the rolling first surface  26  which adapts the roller assembly to engage the rail. The rolling first surface has an axial width Rs. The rolling first surface under a particular operative condition of the roller assembly is limited to that portion of the outwardly facing surface, which contacts the rail. 
     A first element, as represented for example by a shaft  28 , is attached to one of the doors. The shaft is disposed about an axis of rotation A. In alternate embodiments the shaft might be part of the roller assembly and attached to another portion of the first element. The rail  12  is a second element and is engaged by the roller assembly  10 . The roller assembly includes a bearing, as represented for example by a sleeve bearing  32  or a roller bearing as shown in Pietsch. The bearing is disposed between the shaft and the rim assembly to enable movement of the rolling first surface  26  of the ring on the rail. 
     The rim  16  positions and supports the rolling surface of the flexible ring  22  under operative conditions through a support region R against loads acting on the rolling surface. The ring  22  forms the support region R for the rolling surface in the operative condition. The support region extends radially from the rolling surface to the rim and across the width Rs of the rolling surface. In the embodiment shown, the lightweight roller assembly is not absolutely constrained against movement except for the engagement between the ring and the rail. In one sense, it is a self-guiding roller assembly. 
     The above art notwithstanding, scientists and engineers are working under the direction of applicants assignee to develop new materials or to develop alternative designs and methods for forming a rim assembly having a flexible ring in solid form which would enhance one or more operative characteristics of the rim assembly under different operative conditions. 
     SUMMARY OF INVENTION 
     This invention is in part predicated on the realization that cargo mover systems use different kinds of roller assemblies for following a defined path with a flexible ring in solid form. The roller assemblies have operative characteristics which may markedly differ depending on the application chosen for the roller assembly or, in a particular application, may change as operative conditions of the cargo mover system change. 
     A flexible ring is considered to be in solid form where the material of the flexible ring does not rapidly assume the shape of a container in which it is disposed as does a gas or a low viscosity liquid; and, where the average radial height A of the ring is at least sixty (60) percent of the radial distance from the rolling surface of the ring to the support rim. The term “ring” means annular constructions of flexible material of one or more annular parts that have surfaces in faying contact over at least a portion of the circumference of the ring. The ring provides a radial load path from the rolling surface to the rim and may have continuous circumferential elements or one or more circumferential elements having relatively small circumferential gaps which present the appearance of a ring shape, such as might be used if there is a need for “noise” under operative conditions. 
     Typically, the flexible ring is circumferentially continuous. One example of such a roller assembly is a lightweight roller assembly used with elevator doors. The roller assembly may require a ring having acceptable load bearing and rolling characteristics that are supplemented with a need for a noise-damping characteristic (vibrational energy damping characteristic). In a driven roller assembly system, the friction or traction characteristic is more important because slipping between the ring and the rail directly effects operation of the doors. 
     Many flexible materials provide a mix of these operative characteristics. This frequently requires using flexible materials having many operative characteristics that are desirable when used with elevator door systems but also requires accepting some operative characteristics that are less than ideal. 
     For example, a material providing an acceptable service life and rolling characteristic might have a less than ideal friction characteristic and damping characteristic. This may cause elevator passengers to notice slow door speed or elevator door noise by having these annoyances intrude into their consciousness. On the other hand, providing an adequate damping characteristic might require using a material having a poor rolling characteristic, causing a flat spot to form on the rolling surface which results in noisy operation. Still another compromise might result in using a material having better friction characteristics but which is less durable. Then, noise might result from wear on the surface of the ring. The significance of these concerns increases for door roller assemblies because of the close proximity of the roller assembly to passengers as the doors open and close. 
     This invention is also in part predicated on the recognition that improved operative characteristics may result from using a roller assembly having special features for any of the preceding applications, and particularly for a door roller assembly. The special features include having a ring in solid form backed with a radial cavity, having a ring in solid form that has more than one part or more than one material, or having a ring in solid form which provides a combination of these features. This permits selecting a material for the surface based on operative characteristics related to surface behavior. These include, for example, cut characteristics, tear characteristics, wear resistance characteristics, resistance to fluid exposure characteristics and friction or traction characteristics. The special features permit modifying operative characteristics of the rim assembly relating to bulk behavior from the bulk behavior characteristics expected from use of the material selected for the rolling surface. Characteristics relating to bulk behavior include rolling resistance characteristics, deformation under load characteristics, damping characteristics and hysterisis heating characteristics. As a result, the bulk behavior of the rim assembly could differ from that which might normally be expected when using the material of the surface as taught by prior art constructions. 
     According to the present invention, a method for forming a rim assembly for a roller assembly includes disposing a ring in solid form about the rim, forming the rolling surface with a first layer of first material selected for an operative characteristic related to surface behavior; and, providing structure inwardly of at least a portion of the rolling surface which changes an operative characteristic relating to bulk behavior from the operative characteristic that an identical rim assembly would have when entirely filled with the first material in the radial direction. 
     According to the present invention, the flexible ring is in solid form, has at least a first layer of material which forms the rolling surface to effect the interaction of the flexible ring with the environment; and has a support region for the rolling surface which is defined by the location of the ring radially inward of the rolling surface under operative conditions; and, in the uninstalled condition, the layer of first material is located such that the layer does not entirely fill the space of the support region that exists over the axial width of the rolling surface under operative conditions either because the outer layer of first material deforms under operative loads into a cavity which exists radially below the outer layer in the uninstalled condition or because the support region includes both the material of the first layer and another, different material. 
     In accordance with one detailed embodiment of the present invention, a rim assembly for a door roller assembly has a first material selected for the rolling surface of the rim assembly and has a stiffness characteristic which is less than about ninety (90) percent of the stiffness characteristic of a rim assembly having a ring having the same contour for the rolling surface with the ring and any portion of a cavity radially between the ring and the rim filled entirely with the first material. 
     In accordance with one detailed embodiment of the present invention, the ring is formed of a first layer of material having the rolling surface and at least one layer of a different material disposed radially inwardly of the first layer of material. 
     In accordance with another detailed embodiment of the present invention, the first layer of material has discrete cavities disposed within the layer and filled with a different flexible material. 
     A primary feature of the present invention is a roller assembly having a rim assembly. The rim assembly has a rim and a flexible ring in solid form. The flexible ring has a rolling surface. A primary feature of one embodiment of the present invention is a rim assembly having an operative characteristic relating to rolling behavior at the rolling surface established in part by the material of the rolling surface and a bulk behavior characteristic for the rim assembly which differs from the expected bulk behavior characteristic of a rim assembly having no cavities and having a flexible ring in solid form which is formed entirely of the material used for the rolling surface. In one detailed embodiment, the rolling surface is concave. In one embodiment, the flexible ring has a first layer of a first material. A feature is a groove which adapts the rim assembly to receive the ring. In one detailed embodiment, the first material is disposed in the groove and spaced radially from the rim. In another detailed embodiment, a second layer of material is disposed radially inwardly of the first layer of material. 
     A principal advantage of the present invention is the performance of a roller assembly which results from establishing the rolling characteristic of the rim assembly (and thus the roller assembly) with a first material and modifying the bulk behavior characteristic of a roller assembly from that which is expected from using the first material throughout the rim assembly. Another advantage is the rolling characteristic which results from being able to tailor the response of the rolling surface to exterior loads by varying in the axial direction the radial stiffness of the flexible ring which forms the rolling surface. Still another advantage of the present invention is the design and manufacturing flexibility for forming a roller assembly which results from combining, for example, a single material or at least two different materials and a cavity for forming the rim assembly. Another advantage is the ability to tailor the response of the rim assembly to different applications or to retrofit changes to an existing application without changing the external contour of the rim assembly. In one embodiment, a principal advantage is the noise for a given amount of traction which results from using a relatively soft material for the inner layer as compared to the outer rolling layer or which results from disposing a cavity beneath an outer layer to decrease the effective stiffness of the structure. 
     The foregoing and other features and advantages of the present invention will become more apparent in light of the following detailed description of preferred embodiments thereof as discussed and as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified side elevation view of a prior art lightweight roller assembly for a door assembly of an elevator and a rail or track upon which the roller assembly moves; 
     FIG. 2 is a cross-sectional view of the roller assembly and rail shown in FIG. 1 taken along the line  2 — 2  of FIG. 1; 
     FIG. 3 is a cross-sectional view of an alternate embodiment of the roller assembly shown in FIG. 2 in the uninstalled condition showing one embodiment of the present invention; 
     FIG. 4 is a schematic, cross-sectional, side elevation view of the roller assembly shown in FIG. 3 in exploded form illustrating the method of assembling the roller assembly; 
     FIG. 5 is a schematic cross-sectional view of an alternate embodiment of the roller assembly shown in FIG. 3 at the location L, the embodiment being a reference roller assembly for comparison with the embodiment shown in FIG. 3; 
     FIG. 6 is a schematic cross-sectional view of the roller assembly shown in FIG. 3 at the location L showing in full the installed or operative position of the ring and its local deformation and showing with dotted lines the uninstalled position of the ring; 
     FIGS. 7A-7F are alternate embodiments of the roller assembly shown in FIG.  3  and of each other with each having a cavity disposed between the ring and the rim; 
     FIGS. 8A-8C are alternate embodiments of the roller assembly shown in FIG. 3 having a second material disposed inwardly of the rolling surface either as a second layer (FIG. 8A, FIG. 8B) or disposed as discrete portions in the first layer (FIG.  8 C). 
    
    
     DETAILED DESCRIPTION 
     FIG. 3 is a cross-sectional view showing one embodiment of a roller assembly  10   a  of the present invention in the uninstalled condition. The rail  12  is in phantom. FIG. 3 shows the relationship of the rail to the undeformed concave rolling surface  26   a  which is part of the outwardly facing surface  24   a  of the ring  22   a . The ring is in solid form. The ring is disposed in the groove  18   a  of the rim  16   a . The ring is constructed of a preformed insert made of a layer of first material  42   a . In one embodiment, the first material is a fluoroelastomer material having a first radial stiffness characteristic under operative conditions. 
     The ring  22   a  engages the outwardly facing surface  20   a  of the rim  16   a . The rim surface  20   a  extends radially inwardly away from the ring. This spaces the ring radially from a portion of the rim surface  20   a  leaving an annular cavity  34   a  therebetween. In one particular embodiment, the ring has an average radial height Rr which is at least twenty (20) percent of the radial height Ra of the rim assembly and in the embodiment shown, about forty (40) percent. 
     FIG. 4 is a schematic, cross-sectional, side elevation view of the roller assembly  10   a  shown in FIG.  3 . The roller assembly is shown in exploded fashion, illustrating one method of assembling a roller assembly. This method forms the rim into a first half  36   a  and a second half  38   a  which are joined by bonding, bolting or the like. This enables using a preformed insert for the ring. 
     The rim  16   a  is formed of a material, such as steel, having a second radial stiffness characteristic under operative conditions. The second radial stiffness characteristic of the material of the rim is greater than the first radial stiffness characteristic of the ring. Each half  36   a ,  38   a  of the rim has a portion of the radially facing surface  20   a  which bounds the groove. A surface is a radially facing surface if the surface is viewable from a direction perpendicular to the axis of the roller assembly. In the embodiment shown, a radially outwardly facing surface is shown which is viewed radially inwardly. The ring may be circumferentially discontinuous, circumferentially continuous, preformed or molded in place. 
     FIG. 5 is a schematic cross-sectional view at the location L of a reference roller assembly  10   b  for comparison with the roller assembly  10   a  shown in FIG.  3 . The first material fills the entire radial volume between the rolling surface  26   b  and the surface  20   b  of the rim  16   b . This filled volume includes the space corresponding to the open cavity  34   a . Accordingly, the first material of the ring  22   b  has no volume to deform into in the radial direction and the compressibility of the material becomes a significant factor. This increases the stiffness of the ring as compared to the FIG. 3 construction which does have a cavity. 
     FIG. 6 is a schematic cross-sectional view of the roller assembly  10   a  shown in FIG. 3 at the location L. FIG. 6 shows in full the installed or operative contour of the ring  22   a  with the rail  12  broken away for clarity and represented by lines of force F. The ring is locally deformed by contact with the rail. The ring has a support region Rs formed by part of the ring for the rolling surface  26   a  at each operative condition of the roller assembly including the at rest operative condition. Accordingly, this part of the ring in the operative condition is radially inwardly of the rolling surface with radial boundaries aligned with the span lines associated with the dimension line for the region Rs. This part of the ring entirely occupies the support region for the rolling surface. The space occupied by that part of the ring (i.e. the support region) at a particular operative condition, provides a reference space that corresponds to the support region for that condition. 
     As shown in FIG. 6, the ring  22   a  of FIG. 3 under at least one operative condition extends into faying contact with the second surface  20  of the rim over at least a portion of the axial width of the rim. Accordingly, the support region extends radially from the rolling (first) surface toward and to the second surface  20  or face of the rim over at least a portion of the axial width of the rim. The contact is represented by the faying contact in FIG. 6 of the ring with the two portions Rsa of the axial length of the rim such that it engages the rim on either side of the annular cavity  34   a . The support region also extends into the cavity  34   a  and includes that portion of the cavity which is occupied by the ring but, as shown, does pot include that portion of cavity  34   a  into which the ring does not extend. 
     FIG. 6 also shows with dotted lines the contour of the ring  22   a  in the uninstalled condition of the roller assembly  10   a  of FIG.  3 . In the uninstalled condition, the first material comprises a first layer of material  42   a  forming the ring. The layer of material in the uninstalled condition is not deflected into a portion of the cavity  34   a . Accordingly, the layer of first material fills a larger portion of the reference space corresponding to the support region under operative conditions than does that layer in the uninstalled condition. In other embodiments, the ring may have more than one layer of material. 
     This provides an advantage in forming a roller assembly  10  by permitting use of a material having at least one operative characteristic selected for use with the roller assembly which is different from the operative characteristic that the reference roller assembly  10   b  would have with the same material. For example, an elevator door does not move as the elevator car moves between floors. As a result, the roller assembly develops a flat spot on the rolling surface at the location L. The cavity  34   a  behind the ring  22   a  allows the ring to bend into the cavity and to deform radially into the cavity. This reduces the effective radial stiffness of the rim assembly  10   a  by reducing the effect that the compressibility of the material has on the stiffness of the rim assembly (by reason of the ability of material to deform into the cavity). This increases the effect that the elastic modulus of the material has on the stiffness of the system. The roller assembly recovers more quickly from a flat spot than a stiffer structure and the material radially re-forms into a symmetrical shape as it rolls along the track. Therefore, quieter operation results than would result from the roller assembly  10   b  having the entire radial volume between the rolling surface  26   b  and the surface  20   b  of the rim filled with the first material. 
     In one embodiment, the rim assembly  14   a  has a stiffness characteristic which is less than about ninety (90) percent of the stiffness characteristic of the rim assembly  14   b  of the reference roller assembly shown in FIG.  5 . As discussed earlier, the FIG. 5 embodiment has a ring having the same contour for the rolling surface with the ring and any portion of a cavity radially between the rolling surface  26   b  of the ring and the rim  16   b  filled entirely with the first material. 
     Another advantage that results from deforming or bending the ring  22   a  inwardly is the tracking characteristic of the rim assembly  14   a  on the rail  12  as compared to the FIG. 5 reference roller assembly  10   b . The rail exerts a restoring axial force on the ring  22   a  which increases as the roller assembly moves axially away from an axially centered position on the rail. The restoring force results from the axial component of force which grows larger with deflection of the ring because the surface of the ring assumes a more radially directed slope as the ring deflects more in the less radially stiff region (thinner region) at the axial central portion of the ring. Thus, as the roller assembly tends to move away from an axially centered location on the rail, the rail exerts a larger component of restoring force in the axial direction because of the deflection of the ring. 
     FIG. 7A is an alternate embodiment  10   c  of the roller assembly  10   a  shown in FIG.  3 . The roller assembly  10   c  is shown in the uninstalled condition. The roller assembly has an annular cavity  34   c . The annular cavity is formed in part by the inner surface  46   c  of the ring which extends radially outwardly away from the rim  16   c  to form an annular concavity in the ring  22   c . The ring may be made of a preformed insert because the rim assembly  14   c  has a rim  16   c  formed in two halves  36   c ,  38   c . In this embodiment, the decreased thickness of the ring in the axial center of the ring permits the roller assembly to better track the rail by centering the flexible ring on the rail in the axial direction. 
     FIG. 7B is an alternate embodiment  10   d  of the roller assembly  10   a  shown in FIG.  7 A. The roller assembly  10   d  is shown in the uninstalled condition. The roller assembly has a rim assembly having a rim  22   d  formed of two parts or layers as represented by the preformed layers  42   d ,  44   d . The layers are shown partially in cross-section and partially in full by the shading lines. The layers are interrupted circumferentially by a small gap at the location where the layers are shown in full. The first layer  42   d  has an annular cavity  34   d  formed by a concavity in the first layer. The second layer  44   d  is an elliptical core which is disposed in the annular cavity. The second layer has a first portion which is spaced from the first layer and a second portion which is in faying contact with the first layer. The second part or layer deforms under load in both the radial and axial directions. The first part or layer deforms in the radial direction over at least a portion of the axial width of the rim assembly. This permits both parts to bend radially and to deform axially and radially, reducing the effect that compressibility has on stiffness. Stiffness becomes more a function of the modulus of elasticity of both materials, with the inner material of the second part  44   d  having a smaller modulus of elasticity than the outer material of the first part  42   d . This decreased stiffness or increased softness speeds recovery of the rim assembly from a flat spot. In an alternate embodiment, the first layer of the ring might be spaced from the second part over the entire extent of the ring in the uninstalled condition and in faying contact under operative conditions. The first and second layers might have a circumferential gap which extends entirely through the first layer and the second layer. 
     FIG. 7C is a split cross-sectional view of an alternate embodiment  10   e  of the roller assemblies  10   a ,  10   d  shown in FIG.  3  and FIG. 7B; and, shows the uninstalled position of the ring  22   e  on the left one-half of FIG.  7 C and the installed position of the ring on the right half FIG.  7 C. The ring is spaced radially from the axially central portion of the surface  20   e  of the rim  16   e  leaving a cavity  34   e  therebetween. As with the FIG. 7A roller assembly  10   c , the cavity allows the ring  22   e  to deflect more than if the cavity were filled. 
     The ring  22   e  has a second layer  44   e  of flexible material or flexible foam material disposed inwardly of the first layer  42   e  of material. The second layer of material may be an insert and is in faying contact with the first layer of flexible material. The second layer of material has an outhardly oriented surface  54   e  having a first axially facing side  56   e , a second axially facing side  58   e . The second layer has a third face  62   e  which faces radially outwardly and which extends between the first axially facing side and the second axially facing side. The first layer  42   e  of material may be molded over the second layer  44   e  of material such that it partially encapsulates the second layer of material on the axially facing surfaces  56   e ,  58   e  or sides and on the third, outermost surface  62   e  of the second layer. The first layer of material protects the second layer of material from contact with harmful contaminants, such as corrosive liquids or grease. 
     FIG. 7D is an alternate embodiment  10   f  of the roller assemblies  10   c ,  10   e  shown in FIG.  7 A and FIG.  7 C. The roller assembly  10   f  has a ring  22   f  which includes a concave-concave first layer  42   f  of flexible material and a convex-concave second layer  44   f  of a second flexible material. The convex portion of the second layer nests with the concave portion of the first layer. The second layer extends axially across the concave portion of the first layer. The concave portion of the second layer is spaced radially from the rim  16   f  leaving an annular cavity  34   f  therebetween. The second layer of material might be a flexible foam or flexible material with properties which differ from the properties of the first layer. For example, the second material might have a smaller radial stiffness characteristic than the first; and, the second layer in combination with the cavity  34   f  might then allow a greater deflection of the ring under operative conditions than does the embodiment shown in FIG.  7 A. 
     FIG. 7E is an alternate embodiment  10   g  of the roller assembly shown in FIG.  7 C. The rim assembly  14   g  has a ring  22   g  having a relatively thin first layer  42   g  of flexible material that forms a flexible skin for the ring. The skin has a substantially constant cross-sectional thickness as measured along a line perpendicular to the inner surface  46   g  and to the outer surface  48   g  of the first layer. The first layer extends into a faying relationship with the second layer  44   g  to encapsulate the thicker second layer on two sides and the face. The second layer forms a flexible core and is spaced radially from the rim  16   g  leaving an open cavity  34   g  therebetween. The core is made from a dissimilar material or foam. A preformed flexible ring  22   g  might be used because the rim assembly is formed in two halves  36   g ,  38   g . For example, the ring might have a flexible skin molded over a preformed core. Alternatively, another way of forming the ring is molding the skin over an existing core on the rim assembly or making the ring using a two shot or coinjection molding process 
     FIG. 7F is an alternate embodiment  10   h  of the roller assembly  10   e  shown in FIG.  7 C. The flexible second layer  44   h  extends across substantially the entire axial width of the surface  20   h  of the rim  16   h . The surface  20   h  has a concavity that spaces the rim from the second layer  44   h  leaving the cavity  34   h  therebetween. The flexible second layer  44   h  extends into a faying relationship with the first layer  42   h ; and, into a faying relationship with the rim surface  20   h  on either side of the concavity in the rim. 
     FIG. 8A is an alternate embodiment  10   k  of the roller assembly  10   e  shown in FIG.  7 C. The ring  22   k  includes a first layer  42   k  of flexible material. The first layer of material is disposed outwardly of a second layer  44   k  of material. The second layer is bounded by the first layer on three sides. The first layer of material is spaced from the rim leaving an opening  34   k  for the second layer therebetween. The second layer of material extends axially across the opening; and, extends into a faying relationship with the rim  16   k  and with the flexible first layer of material. The second layer may be a flexible material such as a foam material or other material which compresses as a result of operative forces acting on the first layer of the ring. The first layer may be molded over the second layer. 
     FIG. 8B is an alternate embodiment  10   m  of the roller assembly  10   k  shown in FIG. 8A having a ring  22   m . The ring  22   m  includes an annular second layer  44   m  which has a convex outer surface  54   m  which faces outwardly and a convex inner surface  52 m which faces inwardly. Each of the surfaces is in faying relationship with and is bounded by the adjacent surface, that is, by the rim  16   m  on the inwardly facing surface and by the first layer  42   m  of material on the outwardly facing surface. The second layer may be a flexible material such as a foam material or other material which compresses as a result of operative forces acting on the first layer of the ring. 
     FIG. 8C is an alternate embodiment  10   n  of the roller assembly  10   k  shown in FIG. 8A having a first layer  42   n  of material disposed in the rim  16   n . The first layer of material has a plurality of cavities  34   n  disposed radially inwardly of the rolling surface  26   n  on the first layer of material. Each cavity is entirely filled with a discrete portion of a second flexible material  44   n . Under operative loads, the first layer of material is deflected inwardly, compressing the second material  44   n . The second material may have a lesser or greater radial stiffness characteristic than the first material in this embodiment and in the other embodiments. The radial stiffness characteristic will affect the amount of compression of the second material which occurs for a given operative condition. The disposition of the discrete portions of material may also be tailored for the type of application in which the roller assembly is used. 
     In each of these embodiments, the new embodiments of the roller assembly  10  may have improved operative characteristics by using a multipart or multimaterial layer construction. For example, the performance of the outer skin or shell  42  may be tailored by using materials with characteristics matched to the requirements of the outer surface. In a particular system, changes in operating requirements with time may change and may be accomodated with the same external contour of the roller assembly by adjusting the operative characteristics of the rim assembly. These requirements include but are not limited to rolling surface characteristics such as cut, tear, wear, friction or traction, and resistance to fluid exposure characteristics. The overall bulk behavior of the new embodiment of the roller assembly may be tailored using core materials which match the bulk requirements. These bulk requirements include but are not limited to the rolling resistance, deformation under load, damping and hysterisis heating characteristics discussed earlier. Materials acceptable for the outer shell include, but are not limited to, polyurethane elastomers, polyester elastomers, Viton® material or other fluoroelastomers, and vulcanized synthetic rubbers. Examples of these materials and their availability are: castable polyurethane elastomer materials, such as Adiprene® material and Vibrathane® materials, available from Uniroyal Chemical Co., Inc., Southbury, Conn.; thermoplastic polyurethane elastomer materials, such as Pellethane® material, available from The Dow Chemical Co., Midland, Mich.; thermoplastic polyester elastomers, such as Hytrel® material, available from the E.I. du Pont de Nemours and Company, Newark, Del.: fluoroelastomer materials, such as Viton® material, available from Dupont Dow Elastomers LLC, Wilmington, Del. 19880 and Fluorel™ material available from Dyneon LLC, St. Paul, Minn.; and, synthetic rubber, available from Goodyear Chemicals, Goodyear Tire and Rubber Company, Akron, Ohio. 
     Materials for the core or second layer  44  include, but are not limited to, polyurethane elastomers, polyolefin elastomers, silicones, fluorosilicones, and synthetic or natural rubbers. Core materials also include foams of these materials and may include metal, plastic or rubber springs depending on the application. Examples of these materials are: castable polyurethane elastomer materials, such as Adiprene® material and Vibrathane® materials, available from Uniroyal Chemical Co., Inc., Southbury, Conn.; thermoplastic polyurethane elastomer materials, such as Pellethane® material, available from The Dow Chemical Co., Midland, Mich.; polyolefin elastomer materials, such as Santoprene® material, available from Advanced Elastomer Systems LP, Akron, Ohio; silicone materials, such as GE Silicone materials, available from GE Plastics, General Electric Company, Pittsfield, Mass. 01201; fluorosilicone materials, such as NuSil materials, available from NuSil Technology, Carpinteria, Calif. 93013; synthetic rubber available from Goodyear Chemicals, Akron, Ohio; and, natural rubber, available from General Latex, Boston, Mass. 
     Although the invention has been shown and described with respect to detailed embodiments thereof, it should be understood by those in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.