Abstract:
A rope lock is disclosed, suitably adapted for use in theatrical applications that use counterweight rigging systems. The rope lock includes an indicator to show if the counterweight rigging system is in- or out-of-balance. The rope lock also includes an automatic lockout that prevents the rope lock from being unlocked if there is an out-of-balance condition.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to rope locks that are used to secure control ropes for raising or lowering scenery sets and other equipment on theatrical stages.  
         [0003]     2. Description of Prior Art  
         [0004]     The theater industry uses, among others, counterweight rigging systems to raise, lower and suspend scenery sets, lighting equipment (“loads”) and other equipment that is used in theatrical productions and events. A typical counterweight rigging set consists of a balanced system of weights and pulleys by which loads can be raised and lowered. Each set is comprised of a load batten suspended from pickup cables which pass over loft block sheaves, then over a head block at one side of the stage, and finally down to a counterweight arbor. The arbor holds weights that are adjusted by the user to balance (or counterweight) the load. Movement of the load is controlled by a rope hand line that passes from the top of the arbor over the head block, down through a rope block mounted on the locking rail, around a tensioning floor block and back to the bottom of the arbor.  
         [0005]     Rope locks used in such counterweight rigging systems fix the rope hand line in position while a load is suspended or while a load and/or counterweight is being added to or removed from the system. As a result, the rope lock must be able to fix the rope in position not only when the load and counterweight are balanced (“in-balance condition”), but also when the load and counterweight are out-of-balance (“out-of-balance condition”).  
         [0006]     Under normal operation of the counterweight system, the rope lock can be released while the system is in balance, allowing the operator to move the load up or down by moving the rope hand line. If the rope lock is released when the system is out of balance, either the load or the counterweight may fall, potentially causing damage to equipment and injury to individuals in the area. It is therefore important that the rope lock be released only when the system is in balance.  
         [0007]     It is known to manufacturer rope locks that include means of retaining a rope in position when a counterweight system is out of balance. Such rope locks, however, allow the handle of the rope lock to move to a release position even if the counterweight system is out of balance. Furthermore, it is difficult for an operator of such a system to determine when the system has been brought back into balance.  
         [0008]     3. Objects and Advantages  
         [0009]     It is therefore a principal object and advantage of the present invention to provide a rope lock with a release handle that cannot be opened when it is locking a counterweight system that is out of balance.  
         [0010]     It is a further object and advantage of the present invention to provide a rope lock that displays an indicator when a counterweight system is out of balance.  
       SUMMARY OF THE INVENTION  
       [0011]     In accordance with the foregoing objects and advantages, the present invention provides a rope lock that comprises two jaws mounted in a jaw block that may be selectively activated to grip a rope using a release handle pivotally attached to the jaw block. The jaw block is mounted in a housing and slides on guide rails mounted within the housing. The guide rails have springs that bias the jaw block toward a central position on the guide rails. The front of the housing contains a slot into which the release handle can rotate when selectively gripping the rope. When the rope has been locked and experiences an out of balance condition that exceeds the springs&#39; preset threshold, the jaw block moves relative to the housing and against one set of springs, which causes a locking pin to be secured behind the face of the housing. This locking pin prevents the release handle from being pivoted to the unlocked position while the system is out of balance. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:  
         [0013]      FIG. 1  is a front perspective view of the present invention.  
         [0014]      FIG. 2  is a partial side perspective view of the present invention.  
         [0015]      FIG. 3A  is a side elevation view of an embodiment of the present invention.  
         [0016]      FIG. 3B  is another side elevation view of an embodiment of the present invention.  
         [0017]      FIG. 4  is a partial front elevation view of an embodiment of the present invention.  
         [0018]      FIG. 5  is a rear side perspective view of an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0019]     Referring now to the drawings, wherein like reference numerals refer to like parts throughout, there is seen in  FIG. 1 a  rope lock assembly  10 , comprising a housing  12 , which has a housing face  14 , a housing upper plate  16  and a housing lower plate  18 . The housing is preferably made of ductile iron, but other materials of sufficient rigidity and durability are also acceptable.  
         [0020]     The rope lock assembly  10  also comprises a mounting bracket  20 , an upper rope aperture  22  in the housing upper plate  16 , a lower rope aperture  24  in the housing lower plate  18 , and an outer cover  26 . The mounting bracket  20  is shaped so that it can be secured (e.g., by bolts or clamps) to a mounting rail (not shown) in a counterweight rigging assembly. The upper rope aperture  22  and lower rope aperture  24  are sized to allow unrestricted passage of a rope (not shown) that is part of a counterweight rigging assembly. Preferably, upper rope aperture  22  and lower rope aperture  24  have rounded edges to minimize friction as the rope passes through. The outer cover  26  may be removable for maintenance and repair.  
         [0021]     The rope lock assembly  10  also comprises a release handle  28  that is pivotally attached to a jaw block  30 . Preferably, the release handle  28  is made of ductile iron, but other materials of sufficient rigidity and durability are also acceptable. In the preferred embodiment, when pivoted to a locked position the release handle  28  fits into a release handle slot  29  in the housing face  14 . When pivoted to an unlocked position, the release handle  28  is generally perpendicular to the housing face  14 .  
         [0022]     Referring now to  FIG. 2 , the rope lock assembly  10  grips the rope (not shown) by means of a first jaw  32  and a second jaw  34 . Preferably, first jaw  32  and second jaw  34  are pivotally mounted within the jaw block  30  (the jaw block  30  is not shown in  FIG. 2  to provide an unobstructed view of the jaws). Alternatively, first jaw  32  and second jaw  34  may be slidably mounted within the jaw block  30  in such a way that they can slide perpendicular to the rope&#39;s direction of travel. The jaws  32 ,  34  have a smooth clamping surface to minimize wear on the rope as it passes between the jaws when the lock is open. Preferably, jaws  32 ,  34  are made of ductile iron. The jaws  32 ,  34  have a concave clamping surface to provide maximum contact between the jaws  32 ,  34  when the lock is closed.  
         [0023]     The jaw block  30  slides on guide rails  36  that are mounted in the housing  12  and are oriented parallel to the path of the rope through the rope lock assembly  10 . Preferably, jaw block  30  is made of aluminum, but other materials of sufficient rigidity and durability are also acceptable. Guide rails  36  are preferably made of stainless steel, but other materials that are durable and that will allow the jaw block  30  to slide freely on the rails are also acceptable. A portion of the jaw block  30  extends through the release handle slot  29  in the housing face  14  and slides within the release handle slot  29  as the jaw block  30  slides along the guide rails  36 . The release handle  28  is pivotally attached to the jaw block  30 , preferably to the portion of the jaw block  30  that extends through the release handle slot  29  in the housing face  14 .  
         [0024]     The first jaw  32  and second jaw  34  grip the rope when the second jaw  34  is forced toward the first jaw  32  by a cam portion of release handle  28 . Preferably, the cam portion of release handle  28  exerts pressure on second jaw  34  when the release handle  28  is pivoted to a locked position. In the locked position the release handle  28  is positioned in the release handle slot  29  on the housing face  12 . When the release handle  28  is pivoted to an unlocked position, it exerts no pressure on second jaw  34  and second jaw  34  is not forced toward first jaw  32 . In the unlocked position, the rope is free to pass between the jaws  32 ,  34 .  
         [0025]     In the preferred embodiment, the gap between first jaw  32  and second jaw  34  when the release handle  28  is in an unlocked position can be adjusted by means of a tension adjuster  38 . The tension adjuster  38  also controls the degree of pressure exerted on the rope by jaws  32 ,  34  when the release handle  28  is in the locked position. In the preferred embodiment, the tension adjuster  38  comprises a bolt that passes through threads in jaw block  30  to set a rearward limit for first jaw  32 . Preferably, tension adjuster  38  also includes means for fixing such a bolt in position, for example a jam nut.  
         [0026]     Referring now to  FIGS. 3A and 3B , there is shown a side elevation view of rope lock assembly  10 , with outer cover  26  removed for clarity. As described above, jaw block  30  slides on guide rails  36 . As shown in  FIG. 3A , when the release handle  28  is in the locked position and the counterweight rigging system is in-balance (i.e., the load and counterweight are equal), the jaw block  30  is centrally positioned on the guide rails  36 . The central position of the jaw block  30  is maintained by upper spring  40  and lower spring  42 . In an in-balance condition, jaw block  30  rests between upper spring  40  and lower spring  42  and upper spring  40  and lower spring  42  do not exert any force on jaw block  30 . According to the preferred embodiment, upper spring  40  is stopped by upper spring washer  44 , which in turn is stopped by upper retaining pin  48 . Lower spring  42  is stopped by lower spring washer  46 , which in turn is stopped by lower retaining pin  50 . Jaw block  30  fits closely between upper spring washer  44  and lower spring washer  46 , and is not free to slide along guide rails  36  without contacting one of upper spring washer  44  or lower spring washer  46 . Alternatively, upper spring  40  and lower spring  42  may be stopped by upper retaining pin  48  and lower retaining pin  50 , respectively, without use of intervening upper spring washer  44  and lower spring washer  46 . In this alternate embodiment, upper spring  40  and lower spring  42  would act directly on jaw block  30 .  
         [0027]     As shown in  FIG. 3B , when release handle  28  is in the locked position and the counterweight rigging system is out-of-balance (i.e., the load and counterweight are not equal), the out-of-balance condition moves the jaw block  30  from the central position on guide rails  36 . When the jaw block  30  moves from the central position, it is forced against one of the upper spring washer  44  or lower spring washer  46 , compressing the respective upper spring  40  or lower spring  42 . The direction of displacement of the jaw block  30  depends on the type of out-of-balance condition: in the preferred embodiment, a counterweight rigging system out-of-balance with a heavy load will force the jaw block  30  against the upper spring washer  44 ; out-of-balance with a light load will force jaw block  30  against the lower spring wisher  46 . The magnitude of displacement of the jaw block  30  from the central position is determined by the degree to which the counterweight rigging system is out of balance and the bias strength of the spring  42 ,  44  being compressed.  
         [0028]     Preferably, upper spring  40  and lower spring  42  are compression springs having an approximately equal resistance to compression. Preferably, upper spring  40  and lower spring  42  are preloaded. That is, upper spring  40  is compressed between the housing upper plate  16  and the upper spring washer  44  and lower spring  42  is compressed between housing lower plate  18  and lower hosing spring  46 . In the preferred embodiment, each of upper spring  40  and lower spring  42  are preloaded to 25 lbs. Thus, a minor out-of-balance condition (i.e., one in which the difference between the counterweight and load is less than 50 lbs.) will not displace the jaw block  30  away from a central position on the guide rails  36 . The magnitude of preloading of the upper spring  40  and lower spring  42  can be chosen to set a threshold imbalance at which the automatic lockout feature of the rope lock assembly  10  will be engaged.  
         [0029]     The compression resistance of upper spring  40  and lower spring  42  must be such that in an out-of-balance condition jaw block  30  will move sufficiently from the central position on guide rails  36  to engage the automatic lockout described below. Preferably, upper spring  40  and lower spring  42  are made of steel, but other materials are also acceptable and fall within the scope of this invention.  
         [0030]     Upper retaining pin  48  and lower retaining pin  50  protrude from the surface of guide rails  36 . In the preferred embodiment, therefore, jaw block  30  comprises slots for receiving the retaining pin  48  and lower retaining pin  50  when the jaw block  30  is compressed against one of upper spring washer  44  or lower spring washer  46 .  
         [0031]     Referring now to  FIG. 4 , the automatic lockout feature of the preferred embodiment is depicted. Release handle  28  comprises a locking pin  52 , which preferably extends from the sides of release handle  28 . When the rope lock assembly  10  is attached to a rope in a counterweight rigging system that is in-balance, locking pin  52  is aligned with and freely passes through locking pin slot  54  on housing face  14  and release handle  28  is free to pivot with respect to jaw block  30 . After release handle  28  is pivoted to a locked position, if the counterweight rigging system to which rope lock assembly  10  is attached experiences an out-of-balance condition, locking pin  52  is no longer aligned with locking pin slot  54 . Locking pin  52  is thus retained behind housing face  14  when the rope lock assembly  10  is locked in an out-of-balance counterweight rigging system. This prevents release handle  28  from being pivoted to an unlocked position until the counterweight rigging system is brought into balance (e.g., by adjusting the relative weights of the counterweight and load), at which time the jaw block  30  will be forced back to a central position on the guide rails  36  and locking pin  52  will align with locking pin slot  54  to allow release handle  28  to pivot to an unlocked position.  
         [0032]     A rope lock assembly  10  according to the present invention also comprises an indicator to give a visual display that shows if a locked counterweight rigging system is in or out-of-balance and shows whether such an out-of-balance system has a heavy or light load. According to the preferred embodiment, rope lock assembly  10  comprises an indicator  56  that moves with jaw block  30  and shows its position relative to an indicator scale  58 . In one embodiment, indicator  56  is a needle or pin that is attached to release handle  28 . Alternatively, indicator  56  may be attached to jaw block  30 . In another embodiment, indicator  56  is a visible line on jaw block  30 . Alternatively, indicator  56  may be a line on release handle  28 . Preferably, indicator  56  is clearly distinguishable from its background surrounding to allow an operator of rope lock assembly  10  to determine easily if the associated counterweight rigging system is in or out-of-balance. If indicator  56  is a pin attached to release handle  28 , it must have a width that is less than the width of the release handle slot  29 , so that it can pass through the release handle slot  29  when release handle  28  is pivoted in and out of the locked position. In a preferred embodiment, indicator scale  58  is printed or etched on the surface of housing face  14 .  
         [0033]     If desired, housing  12  may be constructed with locking ears  60  on housing face  14  on both sides of release handle slot  29 . If it is necessary to prevent the rope lock from being unlocked, a padlock or bar can be passed through locking ears  60  after release handle  28  has been pivoted into the locked position to prevent release handle  28  from being pivoted out of the locked position. In a similar fashion, a padlock or bar can be passed through locking ears  60  when release handle  28  is in the unlocked position to prevent the release handle  28  from being pivoted into the locked position.  
         [0034]     While there has been illustrated and described what are at present considered to be preferred and alternate embodiments of the present invention, it should be understood and appreciated that modifications may be made by those skilled in the art, and that the appended claims encompass all such modifications that fall within the full spirit and scope of the present invention.