Patent Description:
The manufacture of a vehicle tire commonly includes the steps of forming a tire carcass, forming a toroid-shaped belt and tread "package" of the tire separately from the carcass, and thereafter marrying the belt and tread package to the tire carcass to form a "green" tire. The green tire is thereafter treated to form the tread and various other features of a finished tire. Other supplementary steps, such as bonding the belt and tread package to the tire carcass (often referred to as "stitching" the belt and tread package), may be performed during the course of, or following, one or more of the aforementioned steps.

Formation of a belt and tread package of a tire is typically accomplished using a belt and tread drum, of the type disclosed in <CIT>. Such a belt and tread drum typically has an outer cylindrical surface, or circumference, about which one or more layers of the tire belt material (comprising, for example, reinforcement cords embedded in a polymeric binder) are laid to define the belt and tread package. The circumference of the belt and tread drum is preferably capable of expanding and contracting to allow, for example, removal of a completed belt and tread package from the drum. A completed belt and tread package is typically essentially nonexpandable radially. However, a completed belt and tread package is typically flexible to the extent that, when unsupported, the toroid-shaped belt and tread package will deform and sag under the influence of gravity. Also, desirably, the adjustable circumference of the belt and tread drum enables a single drum to be used to form belt and tread packages of alternative diameters.

In the manufacture of vehicle tires, a tire carcass is typically fabricated using a tire building drum, of the type described in <CIT>. Such a tire building drum typically defines a radially expandable and contractible cylindrical working surface, similar to the above-discussed belt and tread drum, upon which a tire carcass is formed. Subsequent to the formation of the tire carcass on the cylindrical working surface, such tire carcass typically is transferred to an expansion drum, of the type discussed in <CIT>. The tire carcass is positioned surrounding the expansion drum, and a portion of the tire carcass is overlaid with the belt and tread package. The tire carcass is then inflated to a toroid shape resembling, though often not identical to, the shape of a finished tire. While the tire carcass is inflated, the belt and tread package is stitched to the tire carcass.

In the above-described process, the steps of transferring a tire carcass from a tire building drum to an expansion drum and transferring a belt and tread package to a tire carcass for stitching are typically both accomplished using one or more transfer rings, of the type described in <CIT>. Such a transfer ring typically includes a plurality of "shoe" segments having arced interior surfaces which collectively form a segmented, radially-inwardly-facing cylindrical surface suitable for grasping and holding a tire carcass and/or a belt and tread package. Each shoe segment is mounted on an appropriate linkage such that the shoes are collectively radially expandable and contractible with respect to one another, such that the diameter of the segmented, radially-inwardly-facing cylindrical surface can be expanded to fit over a tire carcass and/or belt and tread package, contracted to grasp the tire carcass or belt and tread package for transfer, and then re-expanded to release the tire carcass or belt and tread package following transfer.

When a transfer ring is used as described above to transfer a tire carcass and/or belt and tread package (hereinafter, collectively, "tire component"), it is not uncommon for the shoes and associated linkages of the transfer ring to be configured such that, as the transfer ring is contracted to bring the shoes radially inward around the tire component to grip the tire component, the linkages move each of the shoes along an arced path both radially inwardly and circumferentially around the central axis of the transfer ring. This type of motion is sometimes referred to as an "iris" motion pattern. In certain prior art transfer rings employing an iris motion pattern of the shoes, movement of the shoes both radially inwardly and circumferentially around the central axis of the transfer ring can, in some instances, result in the shoes imparting "twisting" forces to the tire component in a direction along a circumference of the tire component. These "twisting" forces can, in certain instances, be undesirable, and in some instances, can hinder efforts in maintaining structural integrity and a uniform shape of the tire component during transfer.

In light of the above, it would be desirable to transfer tire components with a tire transfer ring which allows expansion and contraction of the shoes in a radial direction while inhibiting circumferential travel, and which maintains the alignment and stability of the shoes in the aforementioned segmented cylindrical shape in relation to one another.

<CIT> discloses a bearing axle adapted to rotatably secure a mounting ring between opposing interior surfaces of respective spaced apart first and second housing rings of a tire transfer ring and to allow removal of the bearing axle from between the housing rings absent additional separation of the housing rings.

<CIT> discloses gripping bodies which are moved in radial directions by rocking a pair of outer links separated from each other as they go toward a radial direction inner side and a pair of inner links coming close to each other as they go toward the radial direction inner side, which constitute respective moving unit, by a driving unit while holding line symmetrical relation relative to each radial line.

<CIT> discloses a transfer ring assembly for supporting a belt and tread package during a tire manufacturing process. A method of assembling tire components in a tire production facility is also provided that incorporates at least one transfer ring assembly as disclosed.

<CIT> discloses a device for holding and transporting a tire belt for the production of a vehicle tire, with an annular base frame on which segment units with segment nests are arranged, which have segment supports for holding the tire belt on its outside, wherein the segment supports can be moved in the radial direction of the base frame and can be fixed in at least two different segment positions which correspond to different diameter ranges for holding tire belts for different tire dimensions.

Another transfer ring for holding an unvulcanized tire is disclosed in <CIT>.

According to an aspect of the invention, there is provided a system according to claim <NUM>. Further features according to embodiments of the invention are defined in the dependent claims.

According to various example embodiments of the present general inventive concept, a transfer ring is provided that is equipped with a plurality of shoes arranged in a substantially circular configuration to define an inwardly- facing segmented cylindrical gripping surface, wherein each of the shoes is actuated by a plurality of linkages that allow for movement of the shoe in a linear direction radially inwardly and outwardly in relation to a central axis of the segmented cylindrical gripping surface.

Additional aspects and advantages of the present general inventive concept will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the present general inventive concept.

The foregoing and/or other aspects and advantages of the present general inventive concept may be achieved by providing a transfer ring to use in the manufacture of vehicle tires, the transfer ring including a circular frame, a plurality of driven linkages coupled to the circular frame and configured to be movable between a contracted position and an expanded position, a drive member disposed along the circular frame, the drive member being coupled to the driven linkages and configured to drive the driven linkages between the contracted position and the expanded position, and a plurality of shoes having arcuate interior surfaces facing substantially radially inwardly toward a central axis to collectively define a substantially cylindrical segmented gripping surface, each of the shoes being coupled to at least one of the driven linkages so as to be selectively move toward and away from the central axis, wherein each of the driven linkages includes a first member coupled to the circular frame, a second member coupled to the drive member and the first member, a third member coupled to a corresponding one of the shoes and to the first member, and a block-and-rail cam follower configured such that a rail portion is fixed to the circular frame, and a block portion is coupled to the third member, wherein the driven linkages are configured to limit movement of the arcuate surface to linear movement radially toward and away from the central axis.

Other features and aspects may be apparent from the following detailed description, the drawings, and the claims.

The following example embodiments are representative of example techniques and structures designed to carry out the objects of the present general inventive concept, but the present general inventive concept is not limited to these example embodiments. In the accompanying drawings and illustrations, the sizes and relative sizes, shapes, and qualities of lines, entities, and regions may be exaggerated for clarity. A wide variety of additional embodiments will be more readily understood and appreciated through the following detailed description of the example embodiments, with reference to the accompanying drawings in which:.

Reference will now be made to the example embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings and illustrations. The example embodiments are described herein in order to explain the present general inventive concept by referring to the figures.

The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the structures and fabrication techniques described herein. Accordingly, various changes, modification, and equivalents of the structures and fabrication techniques described herein will be suggested to those of ordinary skill in the art. The progression of fabrication operations described are merely examples, however, and the sequence type of operations is not limited to that set forth herein and may be changed as is known in the art, with the exception of operations necessarily occurring in a certain order. Also, description of well-known functions and constructions may be simplified and/or omitted for increased clarity and conciseness.

Note that spatially relative terms, such as "up," "down," "right," "left," "beneath," "below," "lower," "above," "upper" and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over or rotated, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features.

According to various example embodiments of the present general inventive concept, a transfer ring is provided that is equipped with a plurality of shoes arranged in a substantially circular configuration to define an inwardly- facing segmented cylindrical gripping surface, wherein each of the shoes is actuated by a plurality of linkages that allow for movement of the shoe in a linear direction radially inwardly and outwardly in relation to a central axis of the segmented cylindrical gripping surface. In various example embodiments the inward and outward movement of the shoes is guided by driven linkage sets including a block-and-rail cam follower that limits the movement of the shoes to radial movement relative to the central axis, inhibiting any circumferential travel about the central axis by the shoe.

<FIG> illustrates a perspective view of a transfer ring in an expanded position according to an example embodiment of the present general inventive concept, and <FIG> illustrates a front view of the transfer ring of <FIG> in the expanded position. In this example embodiment the transfer ring <NUM> includes a plurality of shoes <NUM> that are movable from an expanded to a contracted position, and vice versa, to grip an outer surface of a desired tire component for transfer to another location and/or device. It is understood that various example embodiments of the present general inventive concept may include more or fewer components than those illustrated in these figures, and/or of different configurations, without departing from the scope of the present general inventive concept. Also, some components may be omitted from these figures and descriptions for the sake of clarity. The transfer ring <NUM> includes first and second circular frame members <NUM>,<NUM> disposed in a fixed, registered, side-by-side, parallel, and space apart relationship to one another. The first and second circular frame members <NUM>,<NUM> may be configured with substantially the same inner and outer diameters, and each may have a generally rectangular cross-section having respective inner and outer opposite flat side surfaces <NUM>,<NUM> and <NUM>,<NUM>, respectively.

A plurality of hinge pin connectors <NUM> extend between the first and second circular frame members <NUM>,<NUM> at spaced apart locations about the respective perimetral margins of the first and second circular frame members <NUM>,<NUM> to rigidly retain the side-by-side, parallel, registered, and spaced apart relationship of the first and second circular frame members <NUM>,<NUM>, thereby defining a skeletal cage <NUM> having an open space <NUM> between the first and second circular frame members <NUM>,<NUM>.

Within the open space <NUM> of the skeletal cage <NUM>, there is disposed a circular drive member <NUM> mounted in side-by-side, parallel, and coaxial relationship to the first and second circular frame members <NUM>,<NUM>, via a plurality of rollers <NUM> extending between the first and second circular frame members <NUM>,<NUM>, such that the drive member <NUM> is disposed between the first and second circular frame member <NUM>,<NUM> and rotatable about a central axis of the drive member <NUM> with respect to the skeletal cage <NUM>. The components and mechanisms between the first and second circular frame members <NUM>,<NUM> may be more easily seen in <FIG>, which illustrates a front view of the transfer ring <NUM> as depicted in <FIG> without the front, or first, frame member <NUM>. A plurality of sets of driven linkages <NUM> are provided within the open space <NUM> of the skeletal cage <NUM>. Each of the driven linkage sets <NUM> includes a first member <NUM> configured with an elongated geometry, and having a first end <NUM> which is pivotably coupled to a respective hinge pin connector <NUM> extending between the first and second circular frame members <NUM>,<NUM>, and a second end <NUM> which extends generally inwardly of the skeletal cage <NUM>. Each of the driven linkage sets <NUM> also includes a second member <NUM> configured with an elongated geometry, and having a first end <NUM> which is pivotably coupled to a portion of the circular drive member <NUM>, and a second end <NUM> which is pivotably coupled to a portion of a corresponding first member <NUM>, between the first end <NUM> and the second end <NUM> of the first member <NUM>. Each of the driven linkage sets <NUM> also includes a third member <NUM> configured with an elongated geometry, and having a first end <NUM> which is pivotably coupled to a block portion <NUM> of a block-and-rail cam follower <NUM>, and a second end <NUM> which is pivotably coupled to a corresponding shoe <NUM>. Each second end <NUM> of each first member <NUM> is pivotably coupled to the third member <NUM> proximate a central portion of the third member <NUM>. Each block portion <NUM> is configured to slidably follow a rail portion <NUM> of the block-and-rail cam follower <NUM>, for example via an appropriate tongue-and-groove fitting, rollers, or the like. In the illustrated embodiments, each respective rail portion <NUM> of the block-and-rail cam follower <NUM> is mounted along a portion of the inner surfaces <NUM>,<NUM> of the first and second frame members <NUM>,<NUM>. In various example embodiments, grooves may be formed in the inner surfaces <NUM>,<NUM> of the first and second frame members <NUM>,<NUM> to receive the respective rail portions <NUM> of the block-and-rail cam followers <NUM>, so as to provide a more secure fitting.

As previously described, a plurality of articulating shoes <NUM> are provided, with each shoe <NUM> being pivotably coupled to a corresponding second end <NUM> of the third member <NUM> of the driven linkage sets <NUM> along a dimension parallel to the central axis of the skeletal cage <NUM>. Each shoe <NUM> includes a plate <NUM> having an arcuate interior surface <NUM> facing substantially radially inwardly of the skeletal cage <NUM> and an outer surface <NUM> facing substantially radially outwardly of the skeletal cage <NUM>. Each plate <NUM> defines first and second arcuate side edges <NUM>,<NUM>, respectively, as well as first and second end edges <NUM>,<NUM>, respectively, which extend at opposite ends of the arcuate plate <NUM> between the first and second side edges <NUM>,<NUM>. The various shoes <NUM> are arranged in an end-to-end configuration with each first end edge <NUM> of each plate <NUM> extending generally along a second end edge <NUM> of an adjacent plate <NUM>, such that the various arcuate interior surfaces <NUM> of the plates <NUM> of the shoes <NUM> cooperate to collectively establish a segmented cylindrical surface which, as will be further discussed below, is adapted to surround and grasp an object, such as, for example, a tire component.

Each shoe further includes at least one wall <NUM> extending outwardly from the plate <NUM> generally perpendicular to the outer surface <NUM>. In the illustrated embodiment, a pair of walls <NUM> extend outwardly from the plate <NUM> at a parallel, spaced apart orientation to one another along an arcuate dimension of the plate <NUM>.

The walls <NUM> are spaced apart from one another a suitable distance to allow the second end <NUM> of the third member <NUM> of a corresponding one of the driven linkage sets <NUM> to be inserted therebetween, so as to be pivotably coupled to the inner surface of at least one of the walls <NUM>. Suitable fastening means, such as, for example, a plurality of axially-aligned through openings <NUM>, may be provided along the walls <NUM> and through each corresponding third member <NUM> second end <NUM> to allow receipt therein of a pin, bolt, or other such rotatable connector, so as to allow each shoe <NUM> to be pivotably connected to the corresponding third member <NUM> second end <NUM>. In the illustrated embodiment, an internally-threaded set screw opening is provided opening perpendicular to an axial dimension of one of the through openings <NUM>, such that upon receipt of a pin connector through the through openings <NUM> in the walls <NUM> and the third member <NUM> second end <NUM>, a set screw (not shown) may be received within the set screw opening to secure the pin connector through the through openings <NUM>. However, it will be understood that other suitable configurations exist which may be used to achieve a rotatable connection between each shoe <NUM> and a corresponding driven third member <NUM> second end <NUM>, and such other configurations may be used without departing from the scope of the present general inventive concept.

First and second grooves <NUM>,<NUM> may be defined along each wall <NUM> of each shoe <NUM>, with each first groove <NUM> having at least one open end which opens toward an adjacent shoe <NUM>, and with each second groove <NUM> having at least one open end which opens toward an opposite adjacent shoe <NUM>. The first groove <NUM> is adapted to receive therein a first end <NUM> of a rigid guide rod <NUM> of sufficient length to span two adjacent ones of the shoes <NUM>. The first end <NUM> of each guide rod <NUM> is anchored within its respective first groove <NUM> by a suitable fastener, such as for example a screw, bolt, weld, adhesive, or other fastener, or by an integral connection. An opposite second end <NUM> of each guide rod <NUM> extends into and is slidably received within the second groove <NUM> of an adjacent shoe <NUM>.

A power source <NUM>, such as a piston/cylinder device, may be provided for effecting controlled rotation of the circular drive member <NUM> in relation to the skeletal cage <NUM>. Thus, actuation of the power source <NUM> results in rotational movement of the circular drive member <NUM> in relation to the skeletal cage <NUM>, which in turn rotates each driven linkage set <NUM> about its respective hinge connectors <NUM> between a contracted position, in which each second end <NUM> of each first member <NUM> of the respective driven linkage sets <NUM> is moved inwardly and thus causes the second end <NUM> of the third member <NUM> to move the corresponding shoe <NUM> inwardly toward the central axis of the circular drive member <NUM> and the first and second circular frame members <NUM>,<NUM>, and an expanded position in which the driven linkage sets <NUM> are collapsed to bring the corresponding shoes <NUM> outwardly from the central axis of the circular drive member <NUM> and the first and second circular frame members <NUM>,<NUM>. <FIG> illustrates a front view of the transfer ring of <FIG> in a contracted position, and <FIG> illustrates a front view of the transfer ring as depicted in <FIG> without the front frame member. Due to the linear movement action of the block-and-rail cam follower <NUM> controlling the first end <NUM> of the third member <NUM>, which is linked to the first member <NUM>, and to the second member <NUM> through the connection with the first member <NUM>, the arcuate interior surface <NUM> of the shoe <NUM> moves toward the central axis of the circular drive member <NUM> and the first and second circular frame members <NUM>,<NUM> without circumferential movement about that central axis.

<FIG> illustrate different positions of a transfer ring shoe according to an example embodiment of the present general inventive concept as the shoe moves from the expanded position to the contracted position. <FIG> illustrates one of the shoes <NUM> in a fully expanded position, <FIG> illustrates the shoe <NUM> being moved toward the central axis as the circular drive member <NUM> is rotated relative to the first and second frame members <NUM>,<NUM>, and <FIG> illustrates the shoe <NUM> moved to the fully contracted position. As the first end <NUM> of the first member <NUM> is pivotably coupled to the inner flat surface <NUM> of the first frame member <NUM> (which has been omitted from this drawing for clarity), and the first end <NUM> of the second member <NUM> is pivotably coupled to the circular drive member <NUM>, when the circular drive member is rotated (in a clockwise fashion in the views of <FIG>) the first ends <NUM>,<NUM> of the first and second members <NUM>,<NUM> are brought in closer to proximity to one another. This forces the pivotable coupling of the second end <NUM> of the second member and the first member <NUM> to move generally inward toward the central axis, which in turn causes the second end <NUM> of the third member <NUM> to also move generally inward toward the central axis. This movement is guided by the sliding of the block portion <NUM> along the rail portion <NUM> of the block-and-rail cam follower <NUM>, the rail portion <NUM> being fixed to the inner flat surface <NUM> of the first frame member <NUM> (again, removed for this drawing), to move the shoe <NUM> inwardly and directly toward the central axis of the circular drive member <NUM> and the first and second frame members <NUM>,<NUM>. As illustrated, the angle Δ remains relatively constant, as circumferential movement of the shoe <NUM> is inhibited by the driven linkage set <NUM> with the block-and-rail cam follower <NUM>. Thus, the driven linkages <NUM> are configured to rotate between the expanded position and the collapsed position upon appropriate rotation of the circular drive member <NUM> in relation to the skeletal cage. Thus, upon rotation of the circular drive member <NUM> to the expanded position, the shoes <NUM> are carried by the second ends <NUM> of the third members <NUM> radially outwardly from a central axis of the transfer ring <NUM> to an expanded configuration, wherein the interior surfaces <NUM> of the shoes <NUM> are separated from one another to increase the overall diameter of the segmented cylindrical surface used to grip the tire component. Conversely, upon rotation of the circular drive member <NUM> to the contracted position, the shoes <NUM> are carried by the second ends <NUM> of the third members <NUM> radially inwardly toward a central axis of the transfer ring <NUM> to a contracted configuration, wherein the interior surfaces <NUM> of the shoes <NUM> are brought closer to one another to decrease the overall diameter of the segmented cylindrical surface. To this end, each of the first and second grooves <NUM>,<NUM> is oriented with respect to one another such that each of the guide rods <NUM> slide along its respective second groove <NUM> to cooperatively maintain the interior surfaces <NUM> of the shoes <NUM> with respect to one another in a generally cylindrical configuration throughout the above-discussed expansion and contraction of the shoes <NUM> between the expanded configuration and the contracted or collapsed configuration. Likewise, each of the rail portions <NUM> of the block-and-rail cam follower <NUM> is oriented with respect to one another such that each of the driven linkages <NUM> limits its corresponding shoe <NUM> to linear movement radially inwardly and outwardly, toward and away from the central axis of the transfer ring <NUM>, throughout contraction and expansion of the shoes <NUM> between the expanded configuration and the collapsed configuration. It is understood that while single driven linkage sets <NUM> are illustrated in <FIG>, in various example embodiments, such as that illustrated in <FIG>, pairs of these driven linkage sets are provided side by side so as to be connected to both respective inner flat surfaces <NUM>,<NUM> of the first and second frame members <NUM>,<NUM>, while also being connected to both respective sides of the circular drive member <NUM>.

Various example embodiments of the present general inventive concept may provide a transfer ring to use in the manufacture of vehicle tires, the transfer ring including a circular frame, a plurality of driven linkages coupled to the circular frame and configured to be movable between a contracted position and an expanded position, a drive member disposed along the circular frame, the drive member being coupled to the driven linkages and configured to drive the driven linkages between the contracted position and the expanded position, and a plurality of shoes having arcuate interior surfaces facing substantially radially inwardly toward a central axis to collectively define a substantially cylindrical segmented gripping surface, each of the shoes being coupled to at least one of the driven linkages so as to be selectively move toward and away from the central axis, wherein each of the driven linkages includes a first member coupled to the circular frame, a second member coupled to the drive member and the first member, a third member coupled to a corresponding one of the shoes and to the first member, and a block-and-rail cam follower configured such that a rail portion is fixed to the circular frame, and a block portion is coupled to the third member, wherein the driven linkages are configured to limit movement of the arcuate surface to linear movement radially toward and away from the central axis. The first member may have a first end pivotably coupled to the circular frame, and a second end pivotably coupled to a portion of the third member. The second end of the first member may be pivotably coupled to third member proximate a central portion of the third member. The second member may have a first end pivotably coupled to the drive member, and a second end pivotably coupled to a portion of the first member. The second end of the second member may be pivotably coupled to the first member at a point closer to the second end of the first member than the first end of the first member. The third member may have a first end pivotably coupled to the block portion of the block-and-rail cam follower, and a second end pivotably coupled to the shoe. The transfer ring may further include a plurality of grooves formed in the circular frame to receive the respective rail portions of the bock-and-rail cam followers of each of the driven linkages. A pair of driven linkages may be provided for each of the respective shoes. Each pair of driven linkages may be configured to be respectively coupled to opposite inner surfaces of the circular frame. The drive member may be configured as a circular drive member disposed between the inner surfaces of the circular frame.

Numerous variations, modifications, and additional embodiments are possible, and accordingly, all such variations, modifications, and embodiments are to be regarded as being within the scope of the present general inventive concept. For example, regardless of the content of any portion of this application, unless clearly specified to the contrary, there is no requirement for the inclusion in any claim herein or of any application claiming priority hereto of any particular described or illustrated activity or element, any particular sequence of such activities, or any particular interrelationship of such elements. Moreover, any activity can be repeated, any activity can be performed by multiple entities, and/or any element can be duplicated.

It is noted that the simplified diagrams and drawings included in the present application do not illustrate all the various connections and assemblies of the various components, however, those skilled in the art will understand how to implement such connections and assemblies, based on the illustrated components, figures, and descriptions provided herein, using sound engineering judgment. Numerous variations, modification, and additional embodiments are possible, and, accordingly, all such variations, modifications, and embodiments are to be regarded as being within the scope of the present general inventive concept.

Claim 1:
A transfer ring (<NUM>) to use in the manufacture of vehicle tires, the transfer ring (<NUM>) comprising:
a circular frame (<NUM>, <NUM>);
a plurality of driven linkages (<NUM>) coupled to the circular frame (<NUM>, <NUM>) and configured to be movable between a contracted position and an expanded position;
a drive member (<NUM>) disposed along the circular frame (<NUM>, <NUM>), the drive member (<NUM>) being coupled to the driven linkages (<NUM>) and configured to drive the driven linkages (<NUM>) between the contracted position and the expanded position; and
a plurality of shoes (<NUM>) having arcuate interior surfaces (<NUM>) facing substantially radially inwardly toward a central axis to collectively define a substantially cylindrical segmented gripping surface, each of the shoes (<NUM>) being coupled to at least one of the driven linkages (<NUM>) so as to be selectively move toward and away from the central axis;
wherein each of the driven linkages (<NUM>) comprises:
a first member (<NUM>) coupled to the circular frame (<NUM>, <NUM>),
a second member (<NUM>) coupled to the drive member (<NUM>) and the first member (<NUM>), a third member (<NUM>) coupled to a corresponding one of the shoes (<NUM>) and to the first member (<NUM>), and
a block-and-rail cam follower (<NUM>) configured such that a rail portion (<NUM>) is fixed to the circular frame (<NUM>, <NUM>), and a block portion (<NUM>) is coupled to the third member (<NUM>);
wherein the driven linkages (<NUM>) are configured to limit movement of the arcuate surface (<NUM>) to linear movement radially toward and away from the central axis.