Abstract:
The trailing, load supporting component of a product conveyor is connected to a powered, leading component by a shock absorbing tow bar that employs relatively movable friction elements in a sandwich configuration to absorb the shock by sliding engagement at internal wear surfaces. A brake tongue slides between opposed brake pads of the sandwich which are placed under pressure against the tongue. A two-piece, telescoping tubular housing shields the brake assembly from contaminants and enhances the structural integrity of the unit.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to improvements in tow bars for product conveyor systems and, in particular, to a shock-absorbing tow bar that utilizes a bidirectional friction brake to couple a load-supporting carrier to a powered component of the movable conveyor.  
           [0002]    As a product travels through a conveyor path, there are stations at which the product and carrier must halt and later resume travel. Stopping a load travelling at full conveyor speed, or restarting a load by engaging the carrier with a power source operating at full conveyor speed, can cause significant impact forces or shocks to be transmitted to both the conveyor apparatus and the product itself. These impacts can cause excessive noise in the work environment and damage to the conveyor and product. The load may shift or become dislodged causing an unsafe work environment. Shocks to the conveyor and product can cause attachment devices to fail and increase faults such as stress fractures in the product.  
           [0003]    Industrial conveyor systems, including those of the power and free type disclosed herein, typically utilize tow bars between the powered component of the moving conveyor and one or more trailing, load-supporting carriers. Referring particularly to power and free conveyor systems, the powered component is the accumulating trolley on the free track and, when driven, is engaged by a pusher dog projecting from the conveyor chain on the power track. The accumulating trolley is the lead trolley and is connected to a trailing load trolley (or trollies) with a tow bar. Due to the rigidity of the trolley train and carrier assembly, the impact of a pusher dog engaging the accumulating trolley, or the impact of the accumulating trolley striking a stop, is imparted directly to the carrier under tow and may cause the load to shift, damage to the product, or excessive fatigue and wear on the components of the conveyor system.  
           [0004]    To alleviate this excessive shock loading, a shock-absorbing link between the driven and towed components of industrial conveyor systems is highly desirable in order to provide a means of controlling the rapid acceleration and deceleration inherent in normal operation of the systems. One such device is an air-type shock absorber utilizing a piston that operates in a pneumatic chamber, an orifice through the piston permitting movement thereof only at a controlled rate. Also, similar devices have been employed of the hydraulic type and have the advantage of improved control due to the incompressibility of hydraulic fluid. An example of the air-type shock absorber is shown and described in U.S. Pat. No. 3,720,172 to Clarence A. Dehne, issued Mar. 13, 1973.  
           [0005]    Furthermore, as the hydraulic-type shock absorber is subject to eventual leakage problems which render it totally inoperable and can cause contamination of the plant area occupied by the conveyor, a shock absorber utilizing metallic balls has been employed in an attempt to avoid the disadvantages of air and hydraulic-type shock absorbers. Such a metallic ball device is disclosed in U.S. Pat. No. 5,027,715 to Archie S. Moore et al, issued Jul. 2, 1991 where particulate damping material such as a quantity of ball bearings is positioned in a damping chamber. Acceleration and deceleration cause the bearings to be drawn past a piston through an annular space between the piston and the surrounding wall of the damping chamber. As the bearings become crowded on one side of the piston or the other, the resistance to movement increases. A disadvantage, however, is that over a period of time the piston abrades the surfaces of the balls and can cause them to fracture, thus their ability to roll lessens and the shock absorbing ability is degraded.  
           [0006]    More recently, a shock absorbing tow bar has been developed and utilized in power and free conveyors and is disclosed in U.S. Pat. No. 5,511,486 to Pollard et al, issued Apr. 30, 1996, owned by the assignee hereof. A dampener tube is employed in which an oversized plunger moves against the resistance of a sleeve of resilient material thereby causing compression and displacement of the material as the plunger head shifts in response to rapid acceleration or deceleration of the conveyor. Although successful, the useful life of the tow bar can be a limitation along with its inability to withstand harsh operating conditions such as elevated heat and exposure to paint and paint solvents.  
         SUMMARY OF THE INVENTION  
         [0007]    It is, therefore, the primary object of the present invention to provide a tow bar for a product conveyor- which controls acceleration and deceleration and absorbs the shock that would otherwise be applied to the conveyor and the product, but accomplishes these results without the use of compressed air, hydraulic fluid, resilient materials or parts requiring close machining tolerances.  
           [0008]    As a corollary to the foregoing object, it is an important aim of this invention to provide a tow bar for a conveyor in which relatively movable friction elements in a sandwich configuration respond to rapid acceleration and deceleration and absorb the shock by sliding engagement at internal wear surfaces.  
           [0009]    Another important object is provide a tow bar as aforesaid in which the two friction elements comprise a rigid tongue slidably sandwiched between opposing wear surfaces.  
           [0010]    Another important object is to provide a tow bar as aforesaid wherein pressure exerted by the wear surfaces on the tongue is adjustable to increase or decrease resistance to said relative movement.  
           [0011]    Another important object is to provide a tow bar that can operate in a dynamic environment where it is repetitively subjected to high axial forces in response to acceleration and deceleration of associated conveyor components.  
           [0012]    Another important object is to provide a tow bar for conveyors having an extended life and which can operate in a dynamic environment to dampen or absorb repetitive impacts.  
           [0013]    Another important object is to provide a tow bar for conveyors that can provide shock absorption through multiple consecutive compressing impacts or multiple consecutive extending impacts.  
           [0014]    Still another important objective is to provide such a tow bar that is able to withstand harsh operating conditions such as elevated heat and exposure to paint and paint solvents.  
           [0015]    Another important object of the invention is to provide a tow bar construction of this type having an outer, protective sleeve which shields the friction elements from contaminants and enhances the structural integrity of the tow bar assembly.  
           [0016]    Yet another important object of the invention is to provide a tow bar for conveyors of sufficient durability to undergo repetitive compression and extension hundreds of thousands of times during the life of the tow bar, and which is fail-safe in the event of a failure in response to an extending shock.  
           [0017]    Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawings, wherein is set forth by way of illustration and example, a now preferred embodiment of this invention. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a fragmentary, side elevational view of an inverted power and free conveyor system showing a carrier joined to a powered trolley by the tow bar of the present invention.  
         [0019]    [0019]FIG. 2 is an enlarged, elevational view of the tow bar alone.  
         [0020]    [0020]FIG. 3 is a longitudinal cross-sectional view of the tow bar of FIG. 2, but in an extended condition, some parts being shown in elevation for clarity.  
         [0021]    [0021]FIG. 4 is a view of the dampener shaft and tongue assembly of the tow bar of FIG. 3 separated from the brake assembly to reveal details of construction.  
         [0022]    [0022]FIG. 5 is a view of the brake assembly of the tow bar of FIG. 3 separated from the dampener shaft and tongue assembly to reveal details of construction.  
         [0023]    [0023]FIG. 6 is a fragmentary exploded side view of the dampener shaft/tongue assembly and the brake assembly.  
         [0024]    [0024]FIG. 7 is an enlarged plan view of the dampener shaft and brake tongue.  
         [0025]    [0025]FIG. 8 is a side elevational view of the dampener shaft and brake tongue on the same scale as FIG. 7.  
         [0026]    [0026]FIG. 9 is a cross-sectional view, as in FIG. 3, but with the tow bar in a partially compressed condition.  
         [0027]    [0027]FIG. 10 is a cross-sectional view, as in FIGS. 3 and 9, with the tow bar in a fully compressed condition.  
         [0028]    [0028]FIG. 11 is a detail in longitudinal cross section of the dampener sleeve.  
         [0029]    [0029]FIG. 12 is a detail in longitudinal cross section of the front shaft cover.  
         [0030]    [0030]FIG. 13 is a detail in longitudinal cross section of the shaft cover.  
         [0031]    [0031]FIG. 14 is a detail in longitudinal cross section of the shaft bearing support.  
         [0032]    [0032]FIG. 15 is a plan view of the end connection adapter showing the hole used for securing the adapter to the dampener sleeve and the slot provided to accept the extension bar.  
         [0033]    [0033]FIG. 16 is a plan view of the front end lug.  
         [0034]    [0034]FIG. 17 is a side elevational view of the front end lug.  
         [0035]    [0035]FIG. 18 is a side elevational view of the shaft seat showing the counter sunk screw hole used to fix the shaft seat and front shaft cover in position.  
         [0036]    [0036]FIG. 19 is a plan view of the top plate of the brake assembly.  
         [0037]    [0037]FIG. 20 is a plan view of a brake pad.  
         [0038]    [0038]FIG. 21 is a plan view of a brake shoe.  
         [0039]    [0039]FIG. 22 is a plan view of the bottom plate of the brake assembly.  
         [0040]    [0040]FIG. 23 is an enlarged, plan view of the brake assembly alone.  
         [0041]    [0041]FIG. 24 is an enlarged, exploded, perspective view of the brake assembly.  
         [0042]    [0042]FIG. 25 is a side elevational view showing the tow bar of the present invention joined to the extension bar.  
     
    
     DETAILED DESCRIPTION  
       [0043]    [0043]FIG. 1 illustrates a portion of an inverted power and free conveyor system having the usual power track  20  disposed below and extending in parallelism with the free track  22 . The tracks are rigidly interconnected by longitudinally spaced yoke plates  24  secured to a floor or other horizontal surface at spaced locations  26  along the span of the system. Typically, each of the tracks  20  and  22  is formed by a pair of spaced, opposed channel members within which the trolley rollers ride.  
         [0044]    The trolley train shown in FIG. 1 has a leading (accumulating) trolley  28  to which a carrier  30  is connected by a tow bar  32 . The carrier  30  includes a platform  34  which bears a product under assembly on a production line, such as an automotive vehicle illustrated at  36 . The platform  34  is supported by a front pedestal  38  borne by an intermediate load trolley  40 , and a rear pedestal  42  carried by a trailing load trolley  44 . During movement, the leading trolley  28  is powered by a conveyor chain  46  on spaced power trollies which ride in the power track  20 . As is conventional, the conveyor chain  46  is provided with spaced, upwardly projecting pusher dogs  48 , each engageable with a driving dog  50  depending from the lead trolley  28  of each train and spaced forwardly from a holdback dog  52 . One of the pusher dogs is designated  48 a for clarity and is shown in engagement with the driving dog  50  of trolley  28  of the train illustrated in FIG. 1. The front and rear ends of the tow bar  32  are connected to the leading trolley  28  and the intermediate trolley  40  by clevis and pin connections  54  and  56 .  
         [0045]    An enlarged, side elevational view of the tow bar of the present invention is shown in FIG. 2. The tow bar  32  of FIG. 2 is shown in cross-sectional detail in FIG. 3. Major components of the tow bar  32  are shown in FIGS.  3 - 5  and comprise a dampener sleeve  60  within which a brake assembly  100  is secured, a front shaft cover  68  coaxial with and attached to a dampener shaft  62 , a brake tongue  74  affixed to and extending axially from the shaft  62 , and a shaft cover  64  providing a tubular link extending coaxially from the inner end of sleeve  60 . The dampener sleeve  60  and shaft cover  64 , and front shaft cover  68  are formed from elongated tubular members that cooperate to present a two-piece, telescoping tubular housing for the tow bar  32 . An end connection adapter  70  projecting from the outer end of dampener sleeve  60  (as viewed in FIGS. 2 and 3) presents the rear end of tow bar  32  that is connected to the intermediate trolley  40  at connection  56  (FIG. 1). Similarly, a lug  72  projecting from the outer end of the front shaft cover  68  presents the front end of the tow bar  32  that is attached to the leading trolley  28  at connection  54  (FIG. 1).  
         [0046]    Referring to FIGS.  3 - 8 , it may be appreciated that the tongue  74  is a flat, substantially rectangular plate having an elongated central slot  75  (FIG. 7) disposed along a substantial portion of the longitudinal center thereof. The tongue  74  is welded or otherwise attached to the dampener shaft  62 , which secures the tongue  74  to a shaft seat  88 . As is particularly clear in FIG. 6, a number of parts fit over the dampener shaft  62  including a two-piece metal shaft collar  76  secured within circumferential recess  77  (FIG. 6), an annular rear compression ring  82  preferably composed of Viton and which provides a safety impact absorbing bumper at maximum travel (FIG. 3), a cylindrical shaft bearing support  66  having a rearward threaded end, and a forward compression ring  80  serving the same function as ring  82  but at the opposite end of travel (FIG. 10). The forward, threaded end of the dampener shaft  62  screws into a threaded, axial bore in the shaft seat  88 . The shaft seat  88  also has a circumferential threaded male portion that screws into a threaded female portion of the forward end of the front shaft cover  68 .  
         [0047]    The tongue  74  is received between spaced friction elements presented by brake pads  105  of the brake assembly  100 . FIGS. 6 and 24 show exploded views of the brake assembly  100  and tongue  74  to clarify the relative location of individual parts. The brake assembly  100  is comprised of a flat rectangular top plate  101  having a top surface and a bottom surface (FIGS. 6 and 19). Two spaced-apart holes  110  are provided in the top plate  101  that penetrate the top surface through to the bottom surface. Surrounding each hole  110  is a larger recess  109  in the top surface that does not penetrate the bottom surface. The holes  110  are provided to allow passage of bolts  107 , the heads of the bolts  107  being set into the respective recesses  109  (FIG. 23). The brake assembly also comprises a flat rectangular bottom plate  102  having holes  111  therein positioned to align with the holes  110  in the top plate  101  (FIG. 22).  
         [0048]    Spring washers  106 , brake shoes  103  and brake pads  105  are positioned between the top  101  and bottom  102  plates to provide wear surfaces at the opposed faces of pads  105  that can be tightened against the slidable tongue  74  (FIG. 24). A first set of spring washers  106  are positioned underneath the top plate  101  to provide compression between the top plate  101  and a brake shoe  103  beneath the washers  106 . The brake shoe  103  is a rectangular, relatively flat block with two holes  113  aligned with the holes  110 ,  111  in the top  101  and bottom  102  plates (see FIGS.  19 - 22  and  24 ). In the preferred embodiment, the brake shoe  103  has two elongated recesses  114  located on either side of the holes  113  as shown in FIGS. 21 and 23. The brake shoe  103  is positioned with the recesses  114  facing downward (FIG. 23). Brake pads  105  thus project downwardly from the brake shoe  103  and are received by and held within the recesses  114 . This structure forms the top part of the brake assembly  100  that contacts the top surface of the positioned tongue  74 .  
         [0049]    Below the tongue  74  is a second set of brake pads  105 ′ held within a second brake shoe  103 ′ (see FIGS. 6 and 24). This second brake shoe  103 ′ is typically identical to the first, upper brake shoe  103 , however, it is oriented with the recesses  114 ′ facing upward to hold the lower, second set of brake pads  105 ′. A set of spring washers  106  is positioned below the second brake shoe  103 ′ to separate it from the bottom plate  102 , which is positioned below these washers. The bottom plate  102  differs from the top plate  101  in that it is not provided with recessed areas surrounding the holes  111 . Locknuts  108  are threaded onto bolts  107 , which are inserted into the top plate  101  and pass through the entire brake assembly  100 . By tightening the locknuts  108 , the top and bottom portions of the brake assembly  100  are squeezed against the positioned tongue  74 .  
         [0050]    The components of the brake assembly  100  are typically composed of a rigid, durable material such as steel or other metal. In the preferred embodiment the brake pads are rectangular blocks, approximately 5 inches long, ¾ inches wide, and ¼ inch thick. The brake pads may be composed of materials similar to those for automobile brake pads and may include constituents such as carbon fiber, fiberglass, and polytetrafluoroethylene or other heat and chemical resistant plastics. Preferably, the material selected to form the brake pads should be capable of withstanding temperatures in excess of 450° F. as may be experienced along a conveyor line in an automobile assembly plant. The currently preferred material is glass-filled polytetrafluoroethylene.  
         [0051]    [0051]FIGS. 3, 6,  9  and  10  show the tongue  74  received within the longitudinal passage presented by the brake assembly  100  between the brake pads  105  and  105 ′. The tongue  74  and brake assembly  100  are movable relative to each other longitudinally (axially) of tubular housing members  60 ,  64  and  68 , such movement occurring in response to rapid acceleration or deceleration of the conveyor as will be discussed in detail below. The tongue  74  in FIG. 3 is shown at nearly the limit of its movement relative to brake assembly  100  when the tow bar  32  is in an extended position. FIGS. 9 and 10 show the tow bar  32  in partially compressed and fully compressed positions, respectively.  
         [0052]    Assembly of the tow bar  32  may be appreciated from viewing FIGS.  3  to  6  collectively. Turning first to FIG. 6, the top and bottom portions of the shaft collar  76  are fitted over the dampener shaft  62  and tightened together using bolts on either side. The Viton compression ring  82  slides on the dampener shaft  62  and is positioned against the shaft collar  76 . The shaft bearing support  66  is also positioned on the dampener shaft  62 , threads facing rearward. The shaft cover  64  is then threaded onto the shaft bearing support  66 . A set screw is installed in a tapped hole at the joint between the shaft cover and the shaft bearing support to fix the two pieces in place relative to each other (i.e. to prevent the threaded union from loosening). The second Viton ring  80  is then positioned on the dampener shaft  62  forward of the shaft bearing support  66 . The front shaft cover  68  is placed over the shaft bearing support  66  with the internal threads of the cover oriented forward. The shaft seat  88  is threaded onto the dampener shaft  62  via the central shaft seat hole  92 . The front shaft cover  68  is then threaded onto the shaft seat  88 . A set screw is installed to fix the cover  68  and seat  88  in position and prevent loosening of the attachment.  
         [0053]    Turning to the brake assembly  100 , the brake pads  105  are installed in the recesses  114  provided in the brake shoes  103 . Pads  105  are typically held in place by pressure fit without need for adhesive. Hex head bolts  107  are then placed through holes  110  in top plate  101  and three washer springs  106  are placed over the end of each bolt  107 . The brake shoe  103 , with installed pads  105  facing downward, is placed over the bolt ends and the resulting upper brake assembly is fitted over the tongue  74  by placing the bolt ends  107  through the brake tongue slot  75 . The second brake shoe  103 ′ (installed pads facing upward) is placed through the bolts  107  below the tongue  74 , washer springs  106  are installed, and the bottom plate  102  is placed over the bolts  107 . A lock nut  108  is threaded onto the end of each bolt  107  to secure the brake assembly  100 . The nuts  108  are tightened sufficiently to hold tongue  74  between pads  105  and the bolt heads are checked to make sure that they are within the top plate recesses  109 .  
         [0054]    The end connection adapter  70  is placed into the rearward end of the dampener sleeve  60  and and secured with a bolt  78  and locknut  79 . The dampener sleeve  60  is then threaded onto the shaft cover  64  and tightened. At this point it is important to assure that the adjustment holes  94  in the dampener sleeve  60  are positioned in line with the locknuts  108  on the brake assembly  100  so that the nuts  108  may be externally accessed for adjustment. When said positioning is attained, a hole is drilled and tapped through the dampener sleeve  60  into the shaft cover  64  and a set screw installed therein to secure the threaded joint from loosening and to maintain positioning of the adjustment holes  94 .  
         [0055]    Opposite the end connection adapter  70 , the end lug  72  is threaded into the shaft seat hole  92  at the outside end of the shaft seat  88 . It is important that the connection hole  90  in the lug  72  is positioned parallel to the adjustment holes  94  in the dampener sleeve  60  so that adjustment holes  94  can be positioned facing downward upon installation of the tow bar  32  on a conveyor. The lug  72  is preferably secured in position by welding a fillet around the juncture with the shaft seat  88 .  
         [0056]    Extension of the tow bar  32  to the necessary length to reach from the leading trolley  28  to the intermediate trolley  40  in FIG. 1 is accomplished by welding an extension bar  147  onto the end connection adapter  70 . See FIG. 25. The extension bar  117  may be cut, or otherwise formed, to any length that is appropriate.  
         [0057]    Due to the adjustable design of this shock absorbing tow bar  32 , resistance may be selected such that the tow bar  32  can absorb multiple consecutive shocks or impacts in the same direction. Preferably, the device is set so that the tongue  74  slides approximately one inch upon each impact. A device with a five-inch slot  75  in the tongue  74  could thereby absorb five compressing impacts from a fully extended starting position, or five extending shocks from a fully compressed position. In use, a compressing impact such as caused by collision with another trolley is typically followed by an extending shock delivered when the lead trolley is reengaged by a conveyor pusher dog. In the unlikely event of a total failure of the brake in response to an extending shock, collar  76  abuts compression ring  82  (held by bearing  66 ) to preclude separation (FIG. 3) and provide a fail-safe design.  
         [0058]    In summary, relative movement of the tongue  74  within the brake pad assembly  100  requires that the resistance or friction caused by contact between the pads  105 ,  105 ′ and tongue  74  be overcome, and thus energy is absorbed in the course of moving the tongue  74  from an initial to a final, rest position. This absorption of the energy of impact isolates the carrier  30  in FIG. 1 from sudden, high forces that would otherwise be applied to the carrier by rapid acceleration or deceleration.