Abstract:
An anti-reversing pawl mechanism is claimed that includes a pawl that is engaged by a flexible coupling but that is also biased toward a driven member such that when the engagement of the flexible coupling is removed, the pawl engages the driven member and stops it from moving.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims benefit of U.S. Provisional application Ser. No. 60/742,837 filed on Dec. 6, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Cable pullers are used by electrical contractors to pull cables through pipe or conduit so that the cables can be terminated at either end. Once terminated, these cables can be used to supply power or data between locations. In particular, cables that supply power can require significant forces in order to be pulled. For this reason, cable pullers are used that typically comprise a motor that powers a drive sprocket, which then transmits torque to a capstan around which a pulling rope can be wound. It is often the case that a drive chain is the means used to connect the capstan to the drive sprocket so that the torque from the motor can be transmitted to the capstan. The capstan is configured to rotate in a primary direction during which the pulling rope is wrapped around the capstan, causing the wire or cable to be pulled through the conduit.  
         [0003]     In use, the pulling rope is fished through the conduit by means commonly known in the art after it has been attached to the cable that is to be pulled. Once the cable puller is turned on, the motor causes the drive sprocket to rotate, which transmits its torque to another sprocket to which the capstan is connected by the drive chain. As the capstan begins to rotate, the pulling rope is wound around it such that the user can pull onto its tail end. This arrangement creates a great amount of mechanical advantage, aiding in pulling the cable through the conduit. During a cable pull, great amounts of force in the order of magnitude of thousands of pounds can be exerted on the components of the cable puller. Consequently, these parts can become stressed and can be damaged or broken, including the drive chain. If the drive chain should break, it is very undesirable that the capstan should rotate in a direction that is opposite to the primary direction for a host of reasons including safety.  
         [0004]     For this reason, an anti-reversing pawl is often employed such that if the capstan should rotate in the wrong direction, the pawl will engage the capstan and stop it from moving. Pawl mechanisms that have been previously employed are needlessly complex and require too much time to assemble, making them costly. In addition, they often continuously engage the teeth that are part of the sprocket that drives the capstan, which is an ineffective method for pulling rope when the capstan is operating at high speeds because of the drag it creates on the sprocket. Another drawback of this design is that it creates a significant amount of noise as the pawl engages each individual tooth of the sprocket. Yet another drawback is that there is wear on the part of the pawl that engages the sprocket, which could adversely affect the manner in which the pawl engages the sprocket when it needs to prevent the capstan from reversing its direction. Accordingly, there exists a need for an anti-reversing pawl mechanism that is simpler, cheaper, quieter, more robust, and that will work effectively at high speeds without creating unnecessary drag.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention includes an anti-reversing pawl mechanism that includes a pawl, a drive member, a driven member, and a flexible coupling that is in communication with the drive member and driven member. The pawl is in contact with the flexible coupling and is biased toward the driven member such that if the pawl&#39;s engagement with the flexible coupling is removed, then the pawl will engage the driven member. This engagement may prevent the driven member from reversing its direction.  
         [0006]     The present invention may also take the form of a cable pulling device with a capstan anti-reversing pawl mechanism. This mechanism comprises a frame, a motor that is attached to the frame, a drive member that is powered by the motor, a driven member, a flexible coupling that is in communication with the drive and driven members, and a capstan that is attached to the driven member. It further includes a pawl which is in contact with the flexible coupling and which is biased to engage the driven member if contact with the flexible coupling is removed. Preferably, this engagement will prevent the driven member from reversing its direction.  
         [0007]     This invention also encompasses the following method for providing an anti-reversing pawl mechanism. One step is to provide a drive member, a driven member, and a flexible coupling that is in communication with both the drive member and driven member. Another step is to provide a pawl that is engaged by the flexible coupling and is capable of engaging the driven member. Yet another possible step is to bias the pawl toward engaging the driven member. The last possible step would be to remove the engagement between the flexible coupling and the pawl, allowing the pawl to engage the driven member.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a perspective view of a cable puller employing the capstan anti-reversing pawl mechanism with a pulling rope wrapped around the capstan;  
         [0009]      FIG. 2  is a perspective view of the cable puller of  FIG. 1  with the pulling rope and chain guard removed;  
         [0010]      FIG. 3  is a side elevational view of the cable puller of  FIG. 2  showing the capstan anti-reversing pawl mechanism with an unbroken chain;  
         [0011]      FIG. 4  is a side elevational view of the cable puller of  FIG. 2  showing the capstan anti-reversing pawl mechanism with a broken chain;  
         [0012]      FIG. 5  is a perspective view of the pawl of the capstan anti-reversing pawl mechanism; and  
         [0013]      FIG. 6  is a perspective view of the torsion spring of the capstan anti-reversing pawl mechanism.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]     Looking at  FIGS. 1 and 2 , there is shown the preferred embodiment of a cable pulling device  10  with a capstan anti-reversing pawl mechanism that satisfies the aforementioned need. It comprises, in part, a frame (only partially shown)  12 , an electric plug  14 , an electric motor  16 , a capstan  18 , and a pulling rope  20 . In use, the electric plug  14  of the cable pulling device  10  is plugged into an electric outlet (not shown) and the activation switch (not shown) is placed into the “on” position. This causes the electric motor  16  to produce power, which is conveyed by a gear box  30  to a drive shaft  22  that has a first sprocket  24  attached to its end, both of which begin to rotate. A drive chain  26  connects the first sprocket  24  to a second sprocket  28 , to which the capstan  18  is attached, such that both the capstan  18  and second sprocket  28  begin to rotate in a primary direction to aid in pulling a cable through conduit. The user wraps the pulling rope  20 , whose front end  32  has been attached to the cable that needs to be pulled, around the rotating capstan  18  and pulls on its rear end  34 , creating mechanical advantage in addition to that created within the internal workings of the cable pulling device  10 , helping to create the force necessary to pull the cable through the conduit.  
         [0015]     Closer inspection of the capstan  18  reveals the following structure. It includes a first cylindrical portion  36  that is next to the frame  12  and a second cylindrical portion  38  that extends from the first cylindrical portion  36  and that is concentric therewith. The first cylindrical portion  36  has a land length for wrapping the pulling rope around it that is less than the land length of the second cylindrical portion  38 . Initially, the user will wrap the pulling rope  20  around the first cylindrical portion  36  to effectuate the pulling of the cable as quickly as possible. If the user feels that more torque is necessary to pull the cable, the user can simply wind the pulling rope over the second cylindrical portion  38 , whose diameter is less than the diameter of the first cylindrical portion  36 , to provide the additional mechanical advantage that is needed. Also, the increased land length of the second cylindrical portion  38  also allows the pulling rope  20  to be wrapped around it more, which also increases the mechanical advantage for pulling the cable.  
         [0016]     As the cable is being pulled through the conduit, the pulling rope  20  will tend to stretch, storing great amounts of energy. The force required to perform the pull can cause the drive chain  26  to break or malfunction, allowing the capstan  18  to reverse its direction and release the energy stored in the pulling rope  20 . This is undesirable as it could pose a safety hazard. Consequently, two safety precautions are provided to reduce this hazard if the drive chain  26  should break. First, a chain guard  40  is secured to the frame  12  of the pulling device  10  by screws  42  to keep the chain  26  restrained within the frame  12  of the cable pulling device  10 . This prevents the chain  26  from catapulting and striking an object that is within the vicinity of the cable pulling device  10  if the chain  26  should break or malfunction. Second, a capstan anti-reversing pawl mechanism is employed to prevent the energy stored within the pulling rope  20  from being released. This mechanism is shown in  FIG. 2 , where the chain guard  40 , screws  42  , and pulling rope  20  have been removed to more clearly show this mechanism and its relation to the cable pulling device  10  as a whole.  
         [0017]     The construction and operation of the capstan anti-reversing pawl mechanism can be best seen in  FIGS. 3 and 4 . It includes, in part, a drive shaft  22 , a first sprocket  24 , a drive chain  26 , a second sprocket  28 , a capstan  18  that is attached to the second sprocket  28 , a torsion spring  74 , and a pawl  44 . The drive shaft extends through an aperture in the frame  12  of the cable pulling device  10 . The first sprocket  24  has a central passageway  46  and a plurality of teeth  48  along its periphery. The first sprocket  24  is positioned such that its central passageway  46  is slid over the end of the drive shaft  22 , and is secured to the drive shaft  22  by a washer  50  and screw  52 .  
         [0018]     The second sprocket  28  is freely rotatably mounted to the outside of the frame  12  such that the first and second sprocket members  24 ,  28  are co-planar. The second sprocket  28  has a plurality of teeth  54  around its periphery. The second sprocket  28  preferably has a larger diameter than the first sprocket  24  and more teeth along its periphery than the first sprocket  24 . Preferably, the ratio of the diameter of the second sprocket  28  as compared to the first sprocket  24  is four and a half to one. This ensures that the capstan  18  can supply the mechanical advantage needed to pull the cable during a cable pull.  
         [0019]     The drive chain  26  is a continuous chain member that is configured with gaps between its rollers, which allow the teeth  48  of the first sprocket  24  and the teeth  54  of the second sprocket  28  to fit therebetween. Thus, the first and second sprockets  24 ,  28  are positioned at a distance away from the outside of the frame  12  such that the drive chain  26  is able to fit around and engage the teeth  48 ,  54  of the first and second sprockets  24 ,  28 , respectively. It is preferable to use a chain instead of a belt due to the speeds and forces necessary to effectuate the cable pull.  
         [0020]     A pawl  44  is pivotally mounted to the outside of the frame  12  and is coplanar with the first and second sprockets  24 ,  28 . The pawl  44  is positioned between the first and second sprockets  24 ,  28  but is close enough to the second sprocket  28  such that it can engage second sprocket  28  when appropriate. Looking at  FIG. 5 , the pawl  44  is a generally triangular block such that the pawl  44  has first, second and third corners  56 ,  58 ,  60  and first, second and third edges  62 ,  64 ,  66 . The first side edge  62  extends between the first and second corners  56 ,  58 . The second side edge  64  extends between the second and third corners  58 ,  60 . Finally, the third side edge  66  extends between the first and third corners  58 ,  60 . Each of the corners is generally rounded. The first side edge  62  is also preferably slightly rounded. The third corner  60  is configured such that the third corner  60  looks like a finger that can engage the teeth  54  of the second sprocket  28 , as will be discussed in further detail below. The pawl  44  also includes a central hole  68  so that it can be slid onto a pin  70  and held into place by a c-clip  72 . There is also a small hole  75  located along the second edge  64  proximate to the third corner  60  for receiving part of the torsion spring  74 , which will be described in detail next.  
         [0021]     The torsion spring  74  is mounted to the outside of the frame  12  and is positioned between the pawl  44  and first sprocket  24 , but is proximate to the pawl  44 . The torsion spring  74  is formed of wire that is coiled along its length such that it has a first arm  76  and a second arm  78 , which are perpendicular to each other (see  FIG. 6 ). A first hook  80  extends down from the first arm  76  and is configured to engage a hole found on the frame  12  of the pulling device  10 . A second hook extends from the second arm  78  and is coplanar with the hole  75  found on the second edge  64  of the pawl  44  such that it can be placed therein. The center  84  of the torsion spring  74  can be slid over a pin  86 , thereby holding the spring  74  in place during operation of the capstan anti-reversal mechanism. When the spring  74  is in its normal position, with only a small preload force biasing the spring member, the spring  74  acts on the second side edge  64  of the pawl  44  such that the third corner  60  of the pawl  44  can engage the teeth  54  of the second sprocket  28 .  
         [0022]     During normal operation when the drive chain  26  is not malfunctioning or is unbroken, the capstan anti-reversing mechanism operates in the following manner as best seen in  FIG. 3 . The drive chain  26  is positioned such that drive chain  26  engages the first side edge  62  of the pawl  44 , such that the force created by this contact overcomes the spring force exerted by the torsion spring  74 , which is in a deflected state, ensuring that the third corner  60  of the pawl  44  is disengaged from the teeth  54  of the second sprocket  28 . This, in turn, allows the capstan  18  and second sprocket  28  to rotate as powered by the motor  16  and first sprocket  24  in a primary or clockwise direction as shown. During this operation, the drive chain  26  maintains engagement with the first side edge  62  of the pawl  44 , whose rounded configuration ensures that contact with the drive chain  26  is kept to a minimum, reducing friction. This helps to reduce the noise and drag that is created during a cable pull.  
         [0023]     However, should the drive chain  26  break or somehow malfunction, as best illustrated in  FIG. 4 , the drive chain  26  would disengage from the first side edge  62  of the pawl  44 , allowing the spring force of the torsion spring  74  to rotate the pawl  44  until its third corner  60  comes into contact with the teeth  54  of the second sprocket  28 . At this point, the second sprocket  28  and capstan  18  become locked, ensuring that any energy stored in the pulling rope  20  will not be released when the capstan  18  rotates in a non-primary or counter clockwise direction. In this way, the cable pulling device  10  uses chain tension to prevent the pawl  44  from engaging the teeth  54  of the second sprocket  28 . If the drive chain breaks  26 , the pawl  44  is biased to engage the teeth  54  of the second sprocket  28  and stop it from reversing its direction.  
         [0024]     As can be seen, this capstan anti-reversing pawl mechanism is configured such that reverse rotation of the capstan  18  (because of tension in the pulling rope  20 ) is prevented if the drive chain  26  breaks or malfunctions. The preferred embodiment is especially useful for high-speed cable pullers that operate at speeds that are too fast for mechanisms that employ pawls that are always in contact with the teeth of a sprocket member. It also provides for a reduction in noise over the prior art where high pulling speeds are desired, and further provides for reduced wear on the pawl in the area critical for preventing the reverse rotation of the capstan. Of course, those with ordinary skill in the art will be able to make modifications to this preferred embodiment. For example, it is possible to substitute a belt, a first sheave with a groove on its rim for engaging the belt, and a second sheave with a groove on its rim for engaging the belt instead of using the chain, first sprocket, and second sprocket of the preferred embodiment. Therefore, the scope of this invention should be interpreted in view of the attached claims.