Abstract:
A convertible tarp system provides an extendable and retractable enclosure especially suited for covering a flatbed trailer. The convertible tarp system includes a plurality of bows and trolleys that support a tarp structure. A guide track defines a longitudinal path of movement and supports the trolleys for movement along the longitudinal path. The guide track is configured to substantially restrict lateral movement of the trolleys along the longitudinal path.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates in general to convertible tarp systems, such as can be used to create an enclosed cargo area on a flatbed trailer or the like. In particular, this invention relates to a convertible tarp system having improved guide tracks and corresponding trolley assemblies. 
     Flatbed trailers are often used to haul loads that are bulky or heavy. These loads often have handling characteristics that rely on access to the open sides of the trailer for loading and unloading. Flatbed trailers provide open access for handling freight but lack a structure for conveniently covering the loads from the elements or for privacy. Tarps are often used to protect freight carried on a flatbed. Sometimes the tarps are applied directly over the loads to guard against the elements. Other flatbed covers rely on bows and other support structures to create a space over the trailer and support one or more tarp sheets. While these structures cover the flatbed trailer and create an enclosed freight hauling space, the structures are difficult or cumbersome to remove in order to gain side access of the trailer for freight handling. Thus, it would be desirable to provide an improved tarp system for protecting and accessing freight. 
     SUMMARY OF THE INVENTION 
     This invention relates to a convertible tarp system having improved guide tracks and corresponding trolley assemblies. 
     In one embodiment, a convertible tarp system has a guide track and a trolley assembly. The guide track is configured to be secured to a trailer. The trolley assembly is supported for movement along the guide track. The trolley assembly includes a pair of support rollers, an intermediate roller, and a pair of guide rollers. 
     In another embodiment, a convertible tarp system includes at least one bow for supporting a tarp of a trailer. The tarp and bow cooperate to provide an enclosure for cargo. A guide track has a having a channel that defines a path of movement of the bow. A trolley has a pair of spaced apart support wheels that engage the channel and support the bow for longitudinal movement relative to the trailer. The trolley also has at least one guide wheel that supports the bow perpendicular to the path of movement. 
     In yet another embodiment, a covered trailering system has a flatbed trailer defining a deck space configured to accommodate cargo. A tarp structure covers the deck space and is supported by a plurality of bows that support a covering. The covering defines an enclosed cargo space having a variable volume. The covering may be a flexible tarp sheet of a plurality of generally rigid panels that are arranged to telescope from an extended position to a position wherein the enclosed volume is reduced. A guide track is secured to the flatbed trailer. The guide track has a longitudinally extending channel that includes an outer wall. A plurality of trolleys engage the guide track. Each trolley supports at least one of the plurality of bows. The trolleys have a plurality of support wheels and at least one guide wheel. The plurality of support wheels engage the channel for longitudinal movement relative to the trailer. The at least one guide wheel engages the outer wall of the guide track for lateral support of the bows relative to the trailer. 
     Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a flatbed trailer with a convertible tarp system in accordance with this invention. 
         FIG. 2  is an enlarged perspective view of a portion of the flatbed trailer and convertible tarp system as shown in  FIG. 1 . 
         FIG. 3  is an enlarged perspective view of a portion of a guide track shown in  FIG. 2 . 
         FIG. 4A  is an end view of the guide track shown in  FIG. 3 . 
         FIG. 4B  is an end view of a second embodiment of a guide track, similar to the guide track of  FIG. 4A . 
         FIG. 5  is an enlarged perspective view of a first embodiment of a rear trolley assembly shown in  FIG. 2 . 
         FIG. 6  is a front view of the rear trolley assembly shown in  FIG. 5 . 
         FIG. 7  is a perspective view of an outer side of the rear trolley assembly shown in  FIG. 5 . 
         FIG. 8  is an end view of the rear trolley assembly shown in  FIG. 5 . 
         FIG. 9  is an enlarged perspective view of an intermediate trolley assembly shown in  FIG. 2 . 
         FIG. 10  is a front view of the intermediate trolley assembly shown in  FIG. 9 . 
         FIG. 11  is an end view of the intermediate trolley assembly shown in  FIG. 9 . 
         FIG. 12  is an enlarged end view of a portion of the convertible tarp system shown in  FIG. 2 . 
         FIG. 13A  is a second embodiment of a rear trolley assembly, similar to the rear trolley assembly of  FIG. 5 . 
         FIG. 13B  is an exploded view of the rear trolley assembly of  FIG. 13A  and a back bow connection. 
         FIG. 14  is a second embodiment of an intermediate trolley assembly similar to the intermediate trolley assembly of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIGS. 1 and 2 , there is illustrated a flatbed trailer  10  that is partially covered with a convertible tarp system, indicated generally at  20 . The illustrated convertible tarp system  20  includes a plurality of bows including a front bow  22 , a plurality of intermediate bows  24 , and a rear bow  26 . A tarp section  28  can be attached between the respective bows  22 ,  24 , and  26  or, alternatively, a single tarp can be stretched along a length of the flatbed trailer  10 . The ends of the bows  22 ,  24 , and  26  are supported on a rolling track system that is provided on opposite sides of the flatbed trailer  10 . Thus, the convertible tarp system  20  can be extended along a deck of the flatbed trailer  10  to create an enclosed cargo area or can be retracted when not in use. Although the convertible tarp system  20  is illustrated for use with a flatbed trailer  10 , it should be appreciated that the tarp system  20  can be used in any desired environment and for any desired purpose. For example, in addition to the trucking industry, the convertible tarp system  20  may also be used in the rail and shipping industries or any other industry. 
     Words used herein to describe the relative orientation of components, such as upper, lower, left, right, vertical, horizontal, inner, outer, front, rear, and the like are intended to assist the reader in interpreting the drawings and structures relative to how they are illustrated and conventionally observed. Such descriptions are not limited to an absolute coordinate system, unless specifically defined herein, and are merely descriptive aids to describe and define the various embodiments disclosed herein. 
     The illustrated convertible tarp system  20  includes a pair of guide tracks  30  that respectively extend along opposite sides of the flatbed trailer  10 . As shown in  FIGS. 4A and 4B , two embodiments of guide tracks  30  and  30 ′ are described. The same reference numbers are used to describe parts that are the same between the two embodiments. The guide tracks  30  and  30 ′ can be secured to the sides of the flatbed trailer  10  in any manner. For example, the guide tracks  30  can be removably supported on the flatbed trailer  10  using a plurality of threaded fasteners, support brackets, spacers, or any other support hardware. Alternatively, the guide tracks  30  can be permanently secured to the flatbed trailer  10  using welded connections or the like. The illustrated guide tracks  30  are preferably similar to one another, although such is not required. Therefore, only one of the guide tracks  30  will be described in further detail. 
     Referring now to  FIGS. 3 ,  4 A and  4 B, the illustrated guide tracks  30  and  30 ′ include a vertical back wall  31 . An upper wall  32  and a lower wall  33  horizontally extend outwardly from the back wall  31  so as to generally overlap one another. An outer wall  34  vertically extends downwardly from the upper wall  32  and is parallel with the back wall  31 . Thus, the back wall  31 , the upper and lower walls  32  and  33 , and the outer wall  34  define a channel  30   a  having a C-shape configuration. It should be appreciated, however, that the guide track  30  can define a channel having any cross-sectional shape or configuration. As will be explained below, the C-shaped channel  30   a  opens away from the flatbed trailer  10  when the guide track  30  is secured thereto. The C-shaped channel provides a track that permits selective longitudinal movement of the assembled tarp structure and restricts lateral (side to side) movement of the tarp structure relative to the trailer. 
     The illustrated guide track  30  also includes a recessed portion  31   a  that extends along an inner surface of the back wall  31  near the upper wall  32 , although such is not required. The recessed portion  31   a  increases the internal width W 1  of the channel between the back wall  31  and the outer wall  36  without increasing the overall width W of the guide track  30 . The internal width W 1  may provide clearance for guide rollers, associated with the various trolley assembly embodiments described herein, for free movement of the trolleys within the guide track  30 . This permits use of a larger guide wheels for added stability, durability, and reduced rolling resistance. The generally constant overall width W of the guide track  30  provides a generally flat surface of the back wall  31  for ease of mounting and leveling the guide track  30  relative to a side of the flat bed trailer  10 . The lower wall  33  defines a width W 2  that is less than the overall width W of the guide track  30 . This smaller width W 2  protects the lower wall from impacts such as from fork lifts during loading and unloading events. Thus, the width difference between the lower wall, which supports the support wheels of the trolleys, and the outer dimension W of the guide track shields the lower wall from damage to permit smooth operation of the trolleys during tarp movement. 
     Further, the illustrated lower wall  33  includes a groove  33   a  that extends along an upper surface thereof, although such is not required. The illustrated groove  33   a  has a dove-tail shape, when viewed in cross section, but may alternatively have any other shape or configuration. The groove  33   a  is configured to accept and retain a wear strip  33   b . In the illustrated embodiments of  FIGS. 3 and 4B , the wear strip has a mating dove-tail shape and may be a slip fit, press fit, or molded-in-place fit with the groove  33   a . The wear strip  33   b  may be retained by friction, fasteners, tape, adhesive, and the like. The wear strip  33   b  provides a surface for guide rollers to ride against during movement of the bows  22 ,  24 , and  26 . The wear strip  33   b  may be made of a hard metal or plastic material for wear resistance, reduced friction and/or corrosion resistance. In one embodiment, the wear strip  33   b  is a removable polymer strip, configured for replacement when excessively worn. 
     Referring to  FIG. 4A , the illustrated guide track  30  may also include a light bar  35 . The illustrated light bar  35  extends along a bottom portion of the guide track  30  and defines a housing-like structure having an opening along a back side thereof. The light bar  35  is configured to house lights, such as individual lights or a string of lights (not shown), along a length of the guide track  30 . The light bar  35  is not limited to the illustrated structure but can be alternatively configured in any suitable manner. The guide track  30  may also include one or more retaining grooves  36   a  and  37   a  to retain various protective coverings or splash guards, as will be explained below. As shown in  FIG. 4B , the guide track  30 ′ is formed without the light bar  35  and the retaining groove  37   a.  A lower flange  38  is an L-shaped flange that supports the optional retaining groove  36   a  and extends outwardly to further deflect debris and ice accumulation near where the trolley and guide track interface. The lower flange  38  and the lower wall  33  act together to form a sealing space  33   c  that acts as a dead air space. The sealing space  33   c  is configured such that a lip of the tarp covering (not shown) extends into the space to prevent or slow the progression of dirt, air and other road contaminants entering into the trailer. The light bar  35 , when provided, also acts to prevent debris and ice build up on the interface of the trolleys and the guide track  30 . 
     As shown in  FIG. 12 , the guide track  30  may optionally include a splash guard  36 . The splash guard  36  is a flexible member that is secured to the guide track  30  and extends therefrom for contact with the side of the flatbed trailer  10 . For example, the illustrated splash guard  36  includes an enlarged edge that is inserted and secured within the retaining groove  36   a  that is formed in the guide track  30 . Alternatively (or in addition), the splash guard  36  can be adhered to the guide track  30  or secured thereto in any other manner. The splash guard  36  can be made from any flexible material, such as a rubber or polymer-based material. 
     If the guide track  30  includes the light bar  35 , as shown in  FIG. 4A , then the guide track  30  may include a second splash guard  37  as shown in  FIG. 12 . The second splash guard  37  is also a flexible member that is configured to enclose the opening in the back side of the light bar  35 . For example, the illustrated second splash guard  37  includes an enlarged edge that is inserted and secured within the retaining groove  37   a  that is formed in an upper portion of the light bar  35 . An opposite edge of the second splash guard  37  is inserted into a retaining slot  37   b , that provides a space between spaced apart lips to retain the splash guard opposite end. As shown in  FIGS. 3 ,  4 , and  12 , the retaining slot may be provided along a lower portion of the light guard  35 . Alternatively (or in addition), the second splash guard  37  can be adhered to the light bar  35  or secured thereto in any other manner. Alternatively, the first and second splash guards  36  and  37  may formed as a single component if desired. The second splash guard  37  can be made from any flexible material, such as a rubber or polymer-based material. 
     As shown in  FIG. 2 , the rear bow  26  is supported on the guide track  30  by a rear trolley assembly  40 . Although not illustrated, it should be appreciated that the front bow  22  may also be supported on the guide track  30  by a front trolley assembly that, in one embodiment, is preferably similar to the illustrated rear trolley assembly  40 . Therefore, only the rear trolley assembly  40  will be further described and illustrated. 
     Referring now to  FIGS. 5 through 8 , the rear trolley assembly  40  includes a vertical base member  41 . The illustrated base member  41  includes a pair of support members  42   a  and  42   b  that vertically extend along opposite edges thereof. The illustrated support members  42   a  and  42   b  form an L-shape configuration but may alternatively define any shape or configuration such as a square or other polygonal shape. As shown in  FIG. 2 , the support members  42   a  and  42   b  are configured to support the ends of a pair of spaced apart bow members  26   a  and  26   b  that form part of the rear bow  26 , as shown in  FIG. 2 . The ends of the bow members  26   a  and  26   b  can be removably secured to the support members  42 A and  42 B using threaded fasteners, pins, or any other support hardware. Alternatively, the ends of the bow members may be permanently secured to the support members  42 A and  42 B using a welded connection or the like. 
     Referring back to  FIGS. 5 through 8 , the rear trolley assembly  40  further includes a pair of support rollers  43   a  and  43   b  that are vertically oriented and supported on an inner surface of the base member  41 , that may face the trailer  10 . The illustrated support rollers  43   a  and  43   b  are generally co-planar with one another and spaced apart along a lower edge  41   a  of the base member  41 . The lower edge  41   a  may include various offsets, bends, or ribs to provide mounting surfaces or increase stiffness of the trolley  40 . A portion of the outer circumference of the support rollers  43   a  and  43   b  extends below the lower edge of the base member  41  to movably support the rear trolley assembly  40  on the guide track  30  (see  FIG. 12 ). The support rollers  43   a  and  43   b  can be secured to the base member  41  by studs, threaded fasteners, or any other support hardware. The support rollers  43   a  and  43   b  can have any dimensions and may be made from any material, such as a rubber or a polymer-based material. 
     The illustrated rear trolley assembly  40  further includes an intermediate roller  44  that is vertically oriented and supported on the inner surface of the base member  41 . As shown, the intermediate roller  44  is located between the support rollers  43   a  and  43   b  along the base member  41 . Additionally, the illustrated intermediate roller  44  is also located a vertical distance above the support rollers  43   a  and  43   b.  The intermediate roller  44  may, alternatively, be aligned in the same vertical plane with the support rollers  43   a  and  43   b , or may extend any distance from the base member  41 . The illustrated intermediate roller  44  has the same diameter as the support rollers  43   a  and  43   b  and can be made from a similar material, although such is not required. The intermediate roller  44  provides stability for the trolley and attached bows, relative to the guide track  30 , as will be explained below. 
     The illustrated rear trolley assembly  40  further includes a pair of guide rollers  45   a  and  45   b  that extend from the inner surface of the base member  41 . In the illustrated embodiment, the guide rollers  45   a  and  45   b  are oriented along a horizontal plane. For example, the guide rollers  45   a  and  45   b  can each be supported on support brackets  45   c  and  45   d  that extend horizontally outwardly from the inner surface of the base member  41  toward the guide track  30 . Alternatively, the support brackets  45   c  and  45   d  may be a singular bracket, or a tab that is stamped out of and bent away from the base member  41 . The guide rollers  45   a  and  45   b  can be secured to the support brackets  45   c  and  45   d  using studs, threaded fasteners, or any other support hardware. As shown, the guide rollers  45   a  and  45   b  are located a vertical distance above the support rollers  43   a  and  43   b . The illustrated guide rollers  45   a  and  45   b  are smaller in diameter than the support rollers  43   a  and  43   b . However, the guide rollers  45   a  and  45   b  can have any dimensions or may be made from any desired material. 
     The illustrated rear trolley assembly  40  also includes a track stop assembly  46 , although such is not required. The illustrated track stop assembly  46  is illustrated to include locking member, such as a pin  46   a  or the like, that is movably supported relative to the base member  41  by a bracket  46   b  or the like. As shown in  FIG. 12 , an end portion of the pin  46   a  is biased into engagement with the upper wall  32  of the guide track  30  when the rear trolley assembly  40  is assembled therewith. The upper wall  36  may include a plurality of apertures, detents, or pockets (not shown) configured to accept the pin  46   a  and retain the location of the trolley  40  relative to the guide track  30 , though such is not required. The pin  46   a  may cooperate with a spring member (not shown), such as a coil spring, hairpin spring, Belleville washer or any other biasing member to bias the pin  46   a  into engagement with the guide track  30 . The spring (not shown) may react between the pin  46   a  and the bracket  46   b  to bias the pin  46   a  toward the guide track  30 . Thus, the pin  46   a  is configured to automatically extend into an aperture (not shown) that is provided in the upper wall  32  of the guide track  30  when the rear trolley assembly  40  reaches a desired position. The bracket  46   b  may be a generally C-shaped bracket or may be two cooperating tanks that are attached to or formed from the base member  41 . 
     As shown in  FIG. 2 , the intermediate bows  24  of the convertible tarp system  20  are each supported on the guide track  30  by an intermediate trolley assembly  50 . Referring now to  FIGS. 9 through 11 , the illustrated intermediate trolley assembly  50  includes a vertical base member  51 . A support member  52  extends upwardly from an upper surface of the base member  51  and may be generally, centrally located along a length thereof. As shown, a pair of angled support brackets or gussets  52   a  may be included to provide additional support for the support member  52 , although such is not required. The illustrated support member  52  defines a square or polygonal sleeve-like structure, but may alternatively define any shape or configuration. As shown in  FIG. 2 , the support member  52  is configured to support an end of the intermediate bow  24 . The end of the intermediate bow  24  can be removably secured to the support member  52  using threaded fasteners, pins, or any other support hardware. Alternatively, the end of the intermediate bow  24  may be permanently secured to the support member  52  using a welded connection or the like. 
     Referring back to  FIGS. 9 through 11 , the intermediate trolley assembly  50  further includes a pair of support rollers  53   a  and  53   b  that are vertically oriented and supported on an inner surface of the base member  51 . The illustrated support rollers  53   a  and  53   b  are generally co-planar with one another and spaced apart along a lower edge of the base member  51 . A portion of the outer circumference of the support rollers  53   a  and  53   b  extends below the lower edge of the base member  51  to movably support the intermediate trolley assembly  50  on the guide track  30  (see  FIG. 12 ). The support rollers  53   a  and  53   b  can be secured to the base member  51  by studs, threaded fasteners, or any other support hardware. The support rollers  53   a  and  53   b  can have any dimensions and may be made from any material, such as a rubber or a polymer-based material. 
     The illustrated intermediate trolley assembly  50  further includes an intermediate roller  54  that is vertically oriented and supported on the inner surface of the base member  51 . As shown, the intermediate roller  54  is located between the support rollers  53   a  and  53   b  along the base member  51 . Additionally, the illustrated intermediate roller  54  is located a vertical distance above the support rollers  53   a  and  53   b . Alternatively, the intermediate roller  54  can be aligned in the same vertical plane with the support rollers  53   a  and  53   b , or may extend any other distance from the base member  51 . The illustrated intermediate roller  54  has a smaller diameter than the support rollers  53   a  and  53   b  and can be made from a similar material, although such is not required. The intermediate roller  54  cooperates with the support rollers  53   a  and  53   b  and with the guide track  30  to provide stability, free movement, and support of the bows  24 , as will be explained below. 
     The illustrated intermediate trolley assembly  50  further includes a pair of guide rollers  55   a  and  55   b  that extend from the inner surface of the base member  51 . However, the illustrated guide rollers  55   a  and  55   b  are oriented along a horizontal plane. For example, the guide rollers  55   a  and  55   b  can each be supported on support brackets  55   c  and  55   d  that extend horizontally and outwardly from the inner surface of the base member  51 . Alternatively, the support brackets  55   c  and  55   d  may be a singular bracket, or a tab that is stamped out of and bent away from the base member  51 . The guide rollers  55   a  and  55   b  can be secured to the support brackets  55   c  and  55   d  using studs, threaded fasteners, or any other support hardware. As shown, the guide rollers  55   a  and  55   b  are located a vertical distance above the support rollers  53   a  and  53   b.  The illustrated guide rollers  55   a  and  55   b  are smaller in diameter than the support rollers  53   a  and  53   b . However, the guide rollers  55   a  and  55   b  can have any dimensions or may be made from any desired material. 
     Referring now to  FIG. 12 , the assembly of the convertible tarp system  20  will be explained in conjunction with the rear trolley assembly  40 . It should be understood that the other trolley embodiments described herein may cooperate with the guide track  30  in a similar manner. The guide track  30  is initially secured to the side of the flatbed trailer  10  as described above. The rollers on the rear trolley assembly  40  are inserted within the channel  30   a  of the guide track  30 . For example, the support rollers  43   a  and  43   b  (not shown) ride along the wear strip  33   a  of the lower wall  33  of the guide track  30  to support the weight of the rear trolley assembly  40  and the attached rear bow  26  (not shown). The intermediate roller  44  is configured to contact a surface of the upper wall  32  to prevent or reduce the rear roller assembly  40  from tilting relative to the guide track  40  as the convertible tarp system  20  is tightened. The guide rollers  45   a  and  45   b  (not shown) are positioned between the back wall  31  and the outer wall  34  to help guide the rear trolley assembly  40  along the guide track  30  and to facilitate alignment therebetween. The recessed portion  31   a  that is provided along the inner surface of the back wall  31  enables the guide rollers  45   a  and  45   b  to have increased diameters without increasing the overall dimensions of the guide track  30 . Also, the groove  33   a , formed in the lower wall  33 , secures the wear strip  33   b  and helps to maintain contact between the support rollers  43   a  and  43   b  and the lower wall  33  of the guide track  30 . It should be appreciated that the intermediate trolley assembly  50  (not shown) is similarly assembled with the guide track  30  and functions in generally the same manner as the illustrated rear trolley assembly  40 . 
     As shown in  FIGS. 1 and 2 , the bows  22 ,  24 , and  26  may be respectively secured to the trolley assemblies  40  and  50  either before or after the trolley assemblies  40  and  50  are assembled on the guide track  30 . Once the trolley assemblies  40  and  50  and the respective bows  22 ,  24 , and  26  are assembled to the guide track  30 , the tarps sections  28  can be attached to the respective bows  22 ,  24 , and  26  to complete the convertible tarp system  20 . 
     Referring now to  FIGS. 13A and 13B , there is illustrated a second embodiment of a front or rear trolley, shown generally at  60 . The trolley will be described in the context of a rear trolley  60 , and may share similar components to the rear trolley  40 , though such is not required. The rear trolley  60  includes a base member  61  and a pair of L-shaped support members  62   a  and  62   b , similar to the rear trolley  40  described above. The rear trolley  60  may also include a track stop assembly  66  having a locking member, such as a pin  66   a , and a bracket  66   b.  The support members  62   a  and  62   b  are configured to support the ends of bow members  26   a  and  26   b  and include cutouts  62   c  and  62   d . In the illustrated embodiment, the support members  62   a  and  62   b  are configured as mirror images, though such is not required. The characteristic of mirror-imaged support members  62   a  and  62   b  permits the trolleys to be reversed which provides economies since one part design may be mounted in each of the four corner positions of the trailer. The ends of the bow members  26   a  and  26   b  (not shown) may be removably or permanently secured thereto and may include a corresponding cutout  26   c  such that a space is formed in the assembled bow and trolley to accommodate a back bow  67 . The back bow  67  may provide an anchor point for a back tarp flap (not shown). 
     The rear trolley  60  further includes a pair of support rollers  63   a  and  63   b  and a pair of intermediate rollers  64   a  and  64   b . The support rollers  63   a  and  63   b  vertically oriented and supported on an inner surface of the base member  61 , that may face the trailer  10 . The illustrated support rollers  63   a  and  63   b  are generally co-planar with one another and spaced apart along a lower edge  41   a  of the base member  41 . The lower edge  61   a  may include various offsets, bends, or ribs to provide mounting surfaces or increase stiffness of the trolley  60 . A portion of the outer circumference of the support rollers  63   a  and  63   b  may extend below the lower edge of the base member  61  to movably support the rear trolley assembly  60  on the guide track  30 . Alternatively, the support rollers may extend above the base member  61  to accommodate a wear plate, similar to wear strip  33   b , described above. The spaced apart intermediate rollers  64   a  and  64   b  are located a vertical distance above the support rollers  63   a  and  63   b . The intermediate rollers  64   a  and  64   b  may, alternatively, be aligned in the same vertical plane with the support rollers  63   a  and  63   b , or may extend any distance from the base member  61 . The illustrated intermediate rollers  64   a  and  64   b  have the same diameter as the support rollers  63   a  and  63   b  and can be made from a similar material, although such is not required. The intermediate rollers  64   a  and  64   b  are illustrated in a spaced apart relationship from each other that is farther apart than their distance to the support rollers  63   a  and  63   b . The intermediate rollers  64   a,    64   b  and support rollers  63   a ,  63   b  cooperate to provide stability for the trolley  60  and attached bows  26   a  and  26   b , relative to the guide track  30 . The arrangement of the rollers provides a reactionary moment that resists bending of the bows  22  and  26  in a fore and aft direction relative to the trailer  10 , shown in  FIGS. 1 and 2 . The rear trolley  60  further includes guide rollers  65   a  and  65   b  supported on support brackets  65   c  and  65   d,  similar to the rear trolley  40 , described above. The guide rollers  65   a  and  65   b  and support brackets  65   c  and  65   d  extend from the inner surface of the base member  61  toward the guide track  30 . 
     Referring now to  FIG. 14 , there is illustrated a second embodiment of an intermediate trolley assembly  70 . The illustrated intermediate trolley assembly  70  includes a vertical base member  71 . A support member  72  extends upwardly from an upper surface of the base member  71  and may be generally, centrally located along a length thereof. As shown, a pair of angled support brackets or gussets  72   a  may be included to provide additional support for the support member  72 , although such is not required. The intermediate trolley  70  is configured to support an end of the intermediate bow  24 , similar to the intermediate trolley  50 , described above. 
     The intermediate trolley  70  further includes a pair of spaced-apart support rollers  73   a  and  73   b  that are arranged in a generally coplanar relationship and supported on the base member  71 . The support rollers  73   a  and  73   b  may be positioned relative to the base member  71  as described above in conjunction with the support rollers  53   a  and  53   b  and the base member  51 . The support rollers  73   a  and  73   b  can be secured to the base member  71  by welded studs, threaded fasteners, or any other support hardware. An intermediate roller  74  is supported on the base member  71 . As shown, the intermediate roller  74  is located between the support rollers  73   a  and  73   b  along the base member  71 . In the illustrated embodiment, the intermediate roller  74  is located a vertical distance above the support rollers  73   a  and  73   b  such that the distance between the rollers  73   a  and  74  is sufficient to engage the spaced-apart inner surfaces of the C-shaped section  31   a  of guide track  30 . Alternatively, the intermediate roller  74  can be aligned in the same vertical plane with the support rollers  73   a  and  73   b , or may extend any other distance from the base member  71 . The illustrated intermediate roller  74  has the same diameter as the support rollers  73   a  and  73   b  and can be made from a similar material. 
     The illustrated intermediate trolley assembly  70  further includes a pair of guide rollers  75   a  and  75   b  that are similar in function and layout to the guide rollers  55   a  and  55   b  of intermediate trolley assembly  50 . The illustrated guide rollers  75   a  and  75   b  are oriented along a horizontal plane and can each be supported on support brackets  75   c  and  75   d  that extend from the base member  71  toward the trailer  10 . Alternatively, the support brackets  75   c  and  75   d  may be a singular bracket, or a tab that is stamped out of and bent away from the base member  71 . The guide rollers  75   a  and  75   b  can be secured to the support brackets  75   c  and  75   d  using studs, threaded fasteners, or any other support hardware. As shown, the guide rollers  75   a  and  75   b  are located a vertical distance above the support rollers  73   a  and  73   b . The illustrated guide rollers  75   a  and  75   b  are smaller in diameter than the support rollers  73   a  and  73   b , and intermediate roller  74 . However, the guide rollers  75   a  and  75   b  can have any dimensions or may be made from any desired material. 
     The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope. It is further understood that any particular element of one embodiment may be applied in combination with other embodiments and remain within the scope of the invention.