Abstract:
A shock absorbing tow bar for connecting between a drive trolley and a load carrying trolley of a conveyor system. The tow bar includes a pair of tubes that reciprocate relative to each other. A plunger is located within a first of the tubes and attached to a second tube. Mounted on the plunger are a pair of brake surfaces that frictionally engage the first tube. The brake surfaces are biased toward the first tube by springs and the force applied to the brake surfaces is adjustable through an adjustment mechanism including a pair of wedges upon which the springs are located. An adjustment rod is joined with the adjustment mechanism and extends outwardly from the tow bar to allow an operator to adjust the friction produced by the brake surfaces without disassembly of the tow bar.

Description:
BACKGROUND OF THE INVENTION 
   The present invention is directed to a shock absorber for dampening the initial effect of relatively quick stopping and starting of a heavily loaded trolley or trolleys on a conveyor system, especially a power and free conveyor system. 
   Much of the assembly work done at various manufacturing plants and much of partially assembled or fully assembled transport of goods around a plant is by conveyor systems. In particular, partially completed goods or finished goods are placed on carriers with wheeled trolleys and conveyed about a plant on one type of conveyor system or another, especially the types of conveyor systems known as power and free conveyor systems. When the trolleys carrying a load come to a location where work is to be accomplished, or where the goods are simply to be accumulated, or where a moving trolley must stop because of a previously stopped trolley in front of it, etc., the trolleys and the loads on the trolleys must decelerate at a very high rate. Likewise, the drive units for such conveyors typically operate at a constant speed and loaded trolleys must almost instantly move at the speed of the driver, thereby placing stress on the conveyor parts and the goods being conveyed. 
   Because conveyor systems of the type described herein are utilized to transport many large and heavy items, such as washing machines, dishwashers, refrigerators, automobiles and trucks, sometimes weighing as much as 10,000 pounds each, almost instantaneous stopping and starting of the trolleys can cause damage to the loads as they try to continue in motion when stopping, or accelerate when starting. Over time this causes substantial damage to the conveyor system itself. Conveyor systems that utilize no dampening within the system very rapidly deteriorate, especially as the weight of the loads carried by the trolleys increases. Consequently, it has been recognized for some time by the conveyor industry that it is desirable to dampen the effect of the very rapid stops and starts required by many systems. This is normally accomplished by providing a lead or drive trolley which is in turn selectively driven by a driving mechanism such as a dog attached to a continuously moving chain. The drive trolley in turn is connected by a tow bar to one or more load carrying trolleys which actually support the goods being conveyed. The tow bar includes some type of dampening mechanism for reducing the stress applied to the load carrying trolleys and the load carried thereby during a quick stop or start. 
   The inventor of the present application has been the inventor or co-inventor of a number of different patents directed to shock absorbing devices of the type described herein, such as U.S. Pat. No. 3,330,953. Applicant has found that there is an ever increasing desire to provide a simple shock absorbing mechanism that is highly effective in dampening the effect of sudden stops and starts on the conveyor trolleys. 
   It has also been found that it is necessary to be able to adjust the strength of the dampening mechanism in correspondence to the weight of the load being carried by the trolleys. Where the dampening mechanism is the result of some type of resistance or friction producing mechanism, a very high resistence will result in effectively no dampening when used with very light loads, because the dampening system will never operate, whereas a light dampening resistence will have virtually no effect on dampening relatively heavy loads, because the weight of the load will overcome the resistance so easily that there will be no effective resistance, and consequently, no effective dampening. Therefore, it is also desirable to have a dampening mechanism in which the resistance can be relatively easily changed to adjust for the particular loads being carried by the trolleys. While certain prior art dampening systems for this type of device have allowed for adjustment, such adjustment has required disassembly of the dampening mechanism to such an extent that it has not been relatively easy to accomplish the change without essentially taking everything apart. Consequently, it is also desirable to have a dampening mechanism wherein adjustments can be made relatively easily when the conveyor is first placed in use, when loads on the system change, and after such a period of time when wear and tear reduces or increases resistance. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a shock absorbing tow bar for use in a conveyor system, so as to reduce the shock of stopping and starting load carriers, especially with very heavy loads. Without the shock absorbing tow bar, the required sudden stopping and starting can damage both the conveyor system and the loads being carried by the conveyor. 
   The tow bar has a pair of tubes reciprocally mounted with respect to each other along a common axis and with stops so as to limit maximum telescoping between the tubes. A plunger is attached to a first of the tubes by a shaft and the plunger is slidingly received in a second of the tubes. The plunger includes a pair of brake surfaces or shoes that are biased radially outward by springs so as to frictionally engage the second tube. 
   The pressure applied to the brake shoes can be varied in accordance with the load to apply the proper friction, so as to ensure proper operation of the shock absorber to dampen sudden stops and starts. The springs are mounted on spaced wedges for which spacing can be operably varied along an axis of the device which in turn varies the pressure applied to the springs and, consequently, the brake shoes. 
   An adjustment rod is threadably joined to the wedges such that rotation of the adjustment rod varies the spacing of the wedges and subsequently the pressure or force applied to the brake shoes through the springs. In this manner, the friction between the brake shoes and the second tube can be changed, so as to make relative movement between the tubes, along the axis easier or harder in accordance with the weight of the load. 
   The rod has a distal end that extends outward or externally relative to the remainder of the tow bar so as to allow an operator to be able to adjust the friction applied by the break shoes without disassembly of the tow bar. 
   OBJECTS AND ADVANTAGES OF THE INVENTION 
   Therefore, the objects of the present invention are: to provide a shock absorbing tow bar for use in conjunction with a conveyor system wherein the shock absorbing efficacy of the tow bar can be maintained even when the weight of the load changes by varying the resistance of the shock absorber in accordance with the weight of the load being carried; to provide such a tow bar having an adjustment mechanism that projects outwardly of a remainder of the tow bar to allow adjustment without disassembly of the tow bar; to provide such a tow bar that includes a pair of tubes with a plunger attached to a first tube and being slideable in a second tube and wherein the plunger has a pair of oppositely biased brake shoes extending radially outward from said plunger and frictionally engaging said second tube; to provide such a tow bar wherein the brake shoes are mounted on springs which in turn are mounted on wedges that can be operably varied in spacing so as to adjust the pressure applied to the shoes; to provide such a tow bar wherein the springs are captured in radially extending channels to prevent movement thereof along an axis of the tow bar; to provide such a tow bar wherein an adjustment rod threadedly engages the wedges so as to allow axial change in the spacing therebetween and thereby vary the force or pressure exerted by the brake shoes and wherein the rod extends axially outward of the tow bar so as to allow external adjustment of the force applied by the springs to the brake shoes and thereby adjustment of friction provided by the brake shoes; and to provide such a tow bar that functions extremely well in conjunction with a conveyor system, is easy to manufacture, is comparatively inexpensive to produce in view of the benefits provided and is especially well suited for the intended purpose thereof. 
   Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. 
   The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a fragmentary side elevational view of a power and free conveyor system including a lead trolley engaged by a drive chain and a pair of trailing trolleys supporting a load joined to the drive trolley by a tow bar incorporating a dampening device in accordance with the present invention. 
       FIG. 2  is an exploded view of the tow bar and dampening device. 
       FIG. 3  is an enlarged and side elevational view of the tow bar showing various components of the dampening device therein and illustrating internal parts thereof in phantom. 
       FIG. 4  is an exploded and enlarged perspective view of a portion of the dampening device that forms a reciprocating plunger when fully assembled. 
       FIG. 5  is an enlarged and fragmentary perspective view of the reciprocating plunger subsequent to assembly thereof. 
       FIG. 6  is an enlarged cross sectional view of the plunger, taken along line  6 — 6  of FIG.  5 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
     FIGS. 1 through 6  illustrate a dampening mechanism or device generally indicated by the reference number  1  incorporated in a conveyor system  2  in accordance with the present invention. 
   The conveyor system  2  of the illustrated embodiment is a type of conveyor that is generally referred to as power and free conveyor system. The conveyor system  2  includes a first track  5 , a second track  6 , a continuously driven chain  7  that follows the first track  5 , and trolleys  8  that follow the second track  6 . 
   As is best illustrated in  FIG. 1 , the chain  7  of the conveyor system  2  includes a continuous series of links  11  which are driven in a well known manner so as to continuously move about the first track  5  of the conveyor system  2 . The chain  7  is supported by a plurality of rollers  12  that are secured to the chain  7  and positioned there along so as to support the chain  7 . The rollers  12  roll on and follow the first track  5 . Extending upwardly from the chain  7  are a plurality of drive or chain dogs  15 . 
   The second track  6  generally parallels the first track  5  in the region where it is desirable for the chain  7  to drive the trolleys  8 . The trolleys  8  each include a body  20  and a plurality of trolley wheels  21  that are sized and shaped to roll along and follow the second track  6 . The trolleys  8  of the present embodiment include a lead or drive trolley  25  and a pair of load  26  supporting trolleys  27  and  28 . 
   The lead trolley  25  is connected to a first of the load supporting trolleys  27  by a tow bar  32 . The first load supporting trolley  27  is in turn connected to the second load supporting trolley  28  by a carrier  33 . It is foreseen with respect to certain installations that only single load supporting trolley or that a large number of load supporting trolleys might be necessary for particular loads. 
   The lead trolley  25  includes a dog engagement portion  36  that is pivotally joined to the lead trolley body  20  by a pivot  37 . The dog engagement portion  36  also has a forwardly projecting lever portion  38  and a lower projecting dog engaging arm  39  that includes a tooth  40  which during normal operation of the conveyor system  2  will engage the chain dog  15 , as shown in  FIG. 1 , in the region of the conveyor system  2  where it is desirable for the trolleys to be driven about the first track  5 . The lever portion  38  is located in a position so as to engage trailing cams  42  on load supporting trolleys or load stopping disengagement cams within the track system (not shown) that are well known in the art and designed to swing the dog engagement portion  36  in such a way so as to disengage from the chain dog  15  and thereby stop providing driving power to the drive trolley  25 . 
   The tow bar  32  includes a first inner member or tube  51 , a second outer member or tube  52  and a dampening or braking assembly  53 . The inner tube  51  is slideably received in the outer tube  52  and is able to reciprocate along a central axis A thereof within the limits described below and as braked by the braking assembly  53 , also as described below. 
   The outer tube  52  has a pair of axially projecting distal arms  55  and  56  and is pivotly secured to the lead trolley  25  by a bolt  57 . The inner tube  51  likewise has a pair of distal arms  58  and  59  that are pivotally secured by a bolt  57  to the load supporting trolley  27 . 
   The outer tube  52  includes a pair of diagonally spaced and diametrically opposed apertures  60  located therealong and somewhat near the end thereof opposite the arms  55  and  56 . The outer tube  52  has an inner bore  61  that is generally uniform along the length thereof and sized to snugly, but slideably receive the inner tube  51  except between the arms  55  and  56  whereat there is a restrictive throat  63  of reduced size having a central and axially aligned bore  64 . 
   The inner tube  51  has a pair of diametrically opposed slots  67  that are approximately four inches long in the present embodiment and which receive a bolt  62  which also passes through the apertures  60  and is thus held by a nut  65 , when the tubes  51  and  52  are fully assembled. The bolt  62  allows the inner tube to telescope when the tubes  51  and  52  are pulled axially apart and compress when the tubes  51  and  52  are urged toward each other axially to the extent of the length of the slots  67 . In this way opposite ends  68  and  69  of the slots  67  function as stops limiting comparative telescoping and compressing of the tubes  51  and  52  along the central axis A thereof. 
   The inner tube  51  has a first tube section  73  and an axially aligned second tube section  74  joined by a connecting spool  75 . Apertures  80  located near the end of the first section  73  align with similar apertures  81  on the spool and receive fasteners such as flat head bolts  83  to secure the spool  75  to the first section  73 . The second section  74  likewise has apertures  84  located at one end  85  thereof and aligned with apertures  87  of the spool  75  during assembly so as to receive flat head bolts  88  to secure the two together. A second end  90  of the second section  74  also has a series of apertures  91  for a purpose later described. 
   The dampening or braking assembly  53  is best seen in  FIGS. 2 and 4  to  6 . The breaking assembly  53  comprises a braking plunger  93 , a plunger connecting shaft  94  and a braking or friction adjustment rod  95 . 
   The braking plunger  93  is shown in the exploded view of FIG.  4 . The plunger  93  has a pair of body sections  98  and  99  that join together to form a generally cylindrically shaped body  100  having a generally cylindrical shaped outer surface  101 . Located at opposite ends of the body  100  are threaded bolt receiving apertures  102  that receive bolts  103  to secure the sections  98  and  99  together. 
   Axially aligned and located at one end  105  of the body  100  is a threaded bore  108 . A second bore  109  smaller than the bore  108  runs through a remainder of the body  100  along the axis A. The bore  109  is sized and shaped to receive the adjustment rod  95  therethrough and is threaded to rotate in the bore  109  in the manner described below. 
   An elongate slot  112  extends along a medial portion of the body  100  and extends diagonally from one side to the other side thereof. The slot  112  is generally rectangular in shape. A pair of guide channels or half bores  115  extend from the outer surface part way inward along each side of the slot  112  and from diagonally opposite directions from the surface  101 . 
   Located within the slot  112 , when assembled, is a pair of brakes  118  and  119  and a brake pressure or friction adjustment mechanism  120 . 
   Each of the brakes  118  and  119  has a triangular shaped body  121  with a brake shoe  122  mounted with a curved outer braking surface  123 . Opposite the surfaces  123  are a pair of spring engaging surfaces  125  and  126  that are angled with respect to each other so as to form a V-shaped under surface and come together at a ridge  124  that is directed away from the surface  123 . Each of the brakes  118  and  119  are sized and shaped to fit snugly, but slideably, in the slot  112  with side surfaces  128  and  129  engaging sides  130  and  131  respectively of the slot  112  and ends  134  and  135  of the brakes  118  and  119  respectively engaging ends  136  and  137  of the slot  112 . 
   Positioned between the brakes  118  and  119  are a pair of trapezoidal shaped pressure adjustment wedges  141  and  142 . Each of the wedges  141  and  142  are formed from a pair of sections  144  and  145  secured together by screws  147 . Located in each of the wedges  141  and  142  is an axially aligned and threaded bore  150  and  151  respectively. The bores  150  and  151  are oppositely threaded and are sized to receive the adjustment rod  95  therein. Each of the wedges  141  and  142  have opposed surfaces  153  and  154  that are sloped at angles that converge centrally and are respectively parallel to but spaced from the brake surfaces  125  and  126 . Located between each of the wedge surfaces  153  and  154  and the brake surfaces  125  and  126  is a spring  160 . It is foreseen that the springs can be many types of biasing devices. 
   The adjustment rod  95  is elongate and is sized and shaped to extend from the plunger  93  through the connecting shaft  94  and out thereof. The rod  95  is threaded in the region whereat the rod  95  engages the wedges  141  and  142  with opposed threads  161  and  162 , such that when the rod  95  is rotated in one direction, the wedges  141  and  142  move closer together, thus reducing the distance between opposed surfaces and exerting additional pressure on the brakes shoes  122  through the springs  160 , and such that when the rod  95  is rotated in an opposite direction, the wedges  141  and  142  move further apart, thus exerting less pressure on the brake shoes  122  through the springs  160 . In this manner, the tension, force or pressure applied to the brake shoes  122  can be varied depending on the expected load  26  to be carried by the trolleys  27  and  28 , so as to adjust the friction or resistance to movement of the brakes  118  and  119  relative to the tube  51 . When the load  26  is of greater weight, greater tension or pressure is necessary to produce greater friction, so that the brakes  118  and  119  can frictionally effectively resist comparative axial movement between the plunger  93  and the tube second section  74 . Whereas, when the load  26  is lighter, the pressure can be lessened, so that momentum of the load  26  can overcome the friction due to the brake shoes  122  and so that the brakes  118  and  119  will function to dampen a jarring stop. The same dampening occurs at startup. Further, the pressure applied to the brakes  118  and  119  must not be so great that as to produce more friction than can be overcome by initiating movement of the load  26 , as the dampening mechanism  1  must be reset in this way, each time, after coming to a stop. That is, the tubes  51  and  52  must be able to telescope relative to each other along the axis A under the dampening effect of the tow bar  32 , as the drive trolley  25  reengages the drive chain dog  15  and the load  26  begins to accelerate. 
   The rod  95  is sized and shaped such that an end  165  thereof opposite the plunger  93  extends axially outward from the tube  52 , either directly or alternative through extensions thereof. In the illustrated embodiment, the rod  95  is two part and has a first part  163  with an axially aligned hex shaped distal end  167 . Mounted on the rod end  167  is an extension  166  that has a hex shaped inner aperture  168 , extending the length thereof. The aperture  168  receives the rod first part  163  proceeded by a spring  169 . Mounted in the aperture  168  opposite the rod  95  is a hex extension  170 . The extension  170  is held in place by a pin  171  inserted through a radial bore  172  in the extension  166 . 
   An outer surface  173  of the extension  170  is sized and shaped to receive a hex head tool (not shown) or alternatively a wrench for operably rotating the rod  95  during adjustment, so as to move the wedges  141  and  142 , as desired, and thereby change the friction produced by the brake surfaces  123 . 
   A spacer sleeve  174  has a bore  175  sized to be slideably received on the connecting shaft  94  and an outer diameter sized to fit within the tube section  74 . A collar  177  is sized to have an inner bore  178  that slideably receives the shaft  94 . The collar  177  has a plurality of threaded radial bores  180 , that receive screws  181  that seat in the apertures  91  in tube section  74  to secure the collar  177  therein after receiving the plunger  93  and sleeve  174 . 
   A washer  182  and sleeve  183  are mounted on the shaft  94  on a forward neck  186  thereof. The washer  182  is sized to prevent passage through the tube throat  63 . A second washer  188  is located, so as to be received over the shaft neck  186  opposite the outer tube throat  63  and is bigger in diameter then the throat  63  so as to secure the shaft  94  therein when a nut  190  is secured on a threaded portion  191  of the shaft neck  186 . The shaft  94  has an inner bore  194  which is sized to slidingly receive the rod  95  and an outwardly threaded end  195  that is sized to be threadably received in and mate with the plunger bore  108 . 
   While the illustrated embodiment is sized and shaped such that the plunger  93  has a maximum travel of about four inches within the tube second section  74 , as determined by the stops  68  and  69 , this distance can be modified to satisfy the needs of a particular conveyor system. For example, the distance can be modified to six inches. 
   While the invention herein is illustrated in use with a power and free conveyor system, it is foreseen that it can be utilized with virtually any type of conveyor where it is desirable to dampen the effects of quick stops and starts, including overhead conveyors. 
   It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.