Abstract:
A self-climbing stage lighting system having a self-climbing apparatus and a light bar is disclosed. The self-climbing apparatus is hung from cables that extend approximately vertically from a fixed endpoint. The self-climbing apparatus includes an elongated support member and a linear actuator that drives travels sheaves along a portion support member. Responsive to the travel sheaves being driven in a first direction, the self-climbing apparatus climbs cables. Responsive to the travel sheaves being driven in the direction opposite the first direction, the self-climbing apparatus descends the cables.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority to copending U.S. provisional application entitled, “SELF-CLIMBING STAGE LIGHT SUPPORT,” having Ser. No. 60/523,191, filed Nov. 18, 2003, which is entirely incorporated herein by reference. 

   FIELD OF THE INVENTION 
   This invention concerns a support for light fixtures and other fixtures that are normally suspended above a stage of a theater or similar environment. More particularly, the invention concerns a light support that can be lowered to the level of the stage for adjustment and attachment of the fixtures that are carried by the light support and then raised to the proper height above the stage for illuminating the stage, etc. 
   BACKGROUND OF THE INVENTION 
   The support of overhead lighting systems in the environment of a theater stage is usually accomplished by mounting the light fixtures and other fixtures to an elongated horizontally oriented support beam. Usually, the light support beam can be lowered from above the stage down to the level where the technician can mount, adjust, replace, or otherwise maintain the lights and other fixtures. The support beam can then be raised to the desired elevated position for use in the stage production. Typically, the horizontal support beam is suspended at its ends by ropes or cables. In the older light supports the cables extended from the support beams upwardly to pulleys that were attached to the overhead structure of the building. In most cases, counterweights were attached to the cables to balance the load and the cables were controlled by a motor operated winch that is remotely positioned at the stage level. In many instances, the number of winches, cables, pulleys and other devices necessary to raise and lower the several light support beams was expensive and sometimes confusing to the technician, requiring the winches for each cable to be at the stage level, requiring a riser segment of the cable to extend upwardly from the stage to the overhead pulley, and then downwardly to the light support beam. 
   Another problem with the older stage light supports was that the pulleys that are attached to the overhead structure of the building are remote from the technician and from the operator, making inspection and replacement of the pulleys difficult. Yet another problem is the hazard of the sometimes heavy overhead equipment mounted on the stage light supports, and possibly overstressing the cables, pulleys, winches, or motors that are used to raise and lower the stage light supports. In some cases, these elements are positioned in remote locations, making it difficult for inspection, maintenance, repair, and replacement. 
   Later, stage light supports were constructed with motors and winches mounted directly to the light support, with each support cable requiring only one riser cable segment to extend from the ends of the light support to the overhead support structure. This eliminated the requirement for pulleys attached to the overhead structure and the segments of the riser cables that had to extend from the overhead pulleys down to the stage level and the previously required counterweights, etc. However, the newer light supports still had to include brakes for the cables to hold the light support in a fixed position, and the winch drums and brakes added weight to the assembly. 
   It would be desirable to provide a stage light support that has substantially all of its moving parts in one location, preferably on the stage light support itself, so that when the stage light support is lowered to stage level, its moving components can be inspected, maintained, etc. And, it would be desirable that the stage light support not be required to carry its own brakes and that a linear cable drive be employed for its cables to avoid the use of winches and their cable drums. It is to these features that this invention is directed. 
   SUMMARY OF THE INVENTION 
   Briefly described, the present invention comprises a self-climbing stage light support that includes an elongated support member or beam for mounting lights and other objects above a stage, and which includes it own motor, winch, and cables for raising and lowering the lights. 
   An embodiment of the invention includes a rectilinear tubular housing from which one or more light support beams are suspended for mounting the lights, etc. Cables are positioned at each end of the housing, with the upper ends or hanger portions of each cable being connected to the overhead structure of the stage, with the cables each extending downwardly to the opposed end portions of the tubular housing. The cables pass about stationary end sheaves mounted to the end portions of the tubular housing and extend along the length of the tubular housing to travel sheaves. The cable arrangement that extends about the travel sheaves is configured so that when the travel sheaves move along the length of the tubular housing, the cables at the opposed ends of the housing are simultaneously retracted back into the hosing or paid out of the housing, so as to raise or lower the tubular housing and the light fixtures, etc., mounted to the housing. The travel sheaves are controlled by a linear actuator, such as a travel screw. Upon rotation of the travel screw, the travel sheaves move along the length of the tubular housing, thereby paying out or retracting the cables from the opposite ends of the tubular housing. 
   In most instances, the configuration of the travel sheaves and the stationary end sheaves is such that several passes of the cable will pass about the sheaves so that a small movement of the travel sheaves results in greater movement of the cable paid out from or retracted into the ends of the tubular housing. For example, in a preferred embodiment of the invention, a one-foot movement of the travel sheaves results in four feet of movement of the cable being paid out of or retracted to the tubular housing. 
   In the embodiments illustrated, the motor that rotates the travel screw is mounted on one end portion of the tubular housing, known as the “motor end” and is connected to the transmission of the travel screw with a belt drive. The other end portion of the tubular housing has more returns of the cable an is known as the “fixed end.” 
   Another preferred embodiment of the invention includes two cables at each end of the elongated support member that are arranged about stationary end sheaves and extend to travel sheaves positioned intermediate the end sheaves. This places a total of four hanger segments of the cables at the ends of the elongated support member for stability purposes, to avoid tilting of the elongated support member in response to a light fixture being offset from the elongated support member. Moreover, the use of two cables at each end of the elongated support member provides a safety factor such that if a cable should somehow become disconnected from the overhead of the stage structure, the other cable at the same end of the elongated support member can maintain the stage light support suspended above the stage, avoiding the falling of the light fixtures, etc. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevation view of a self-climbing stage light system. 
       FIG. 2  is an exploded perspective view of a self-climbing apparatus with selected components of a self-climbing apparatus. 
       FIG. 3  is a perspective view of a double sheave block. 
       FIG. 4  is a perspective view of an end cap having a plurality double sheave blocks mounted thereon. 
       FIG. 5  is a perspective view of a travel member assembly. 
       FIG. 6  is a perspective view of a travel member frame of the travel member assembly. 
       FIG. 7A  is a side view of a first cable path for a first cable engaged by the self-claiming stage light system  10 . 
       FIG. 7B  is a top view of the first cable path for the first cable of  FIG. 7A . 
       FIG. 8A  is a side view of a second cable path for a second cable engaged by the self-claiming stage light system  10 . 
       FIG. 8B  is a top view of the second cable path for the second cable of  FIG. 8A . 
       FIG. 9  is a side elevation view of the self climbing stage light system, with the intermediate portion of the device being removed to shorten the length thereof for illustrative purposes. 
       FIG. 10  is a perspective view of cross mounted stationary double sheave blocks and travel double sheave blocks. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates a self-claiming stage light system  10 , which includes a self-climbing apparatus  12  having a longitudinal support member  36  in the form of a tubular housing and a light bar  14  suspended from the support member  36 . The self-climbing apparatus  12  climbs cables  16  and  18  at one end of the support member  36  and climbs cables  20  and  22  at the other end of the support member  36 . Each one of the cables  16 ,  18 ,  20 , and  22  has an upper end that is denoted by  24 ,  26 ,  28 , and  30 , respectively, which are affixed to a stationary support such as the joists of a roof structure. Typically the lengths of cables  16 ,  18 ,  20 , and  22  extending from the self-climbing apparatus  12  to their upper ends  24 ,  26 ,  28 , and  30 , respectively, are such that the self-climbing apparatus  12  is approximately horizontally aligned. However, as those skilled in the art would recognize, the lengths of the cables can be varied such that the self-climbing apparatus can be tilted with respect to horizontal. In addition, those skilled in the art would recognize that self-climbing apparatus can be adapted to climb fewer or more cables. 
   The light bar  14  is supported from the support member  36  of the self-climbing apparatus  12  and a plurality of stage lights  32  are attached to the light bar  14 . The light bar is connected to a power supply (not shown) via an electrical connector  34 . Those skilled in the art are familiar with lights bars, and consequently, it is not discussed in detail. 
   The self-climbing apparatus  12  includes the longitudinal support member  36 , which is typically of tubular shape, such cylindrically shaped or rectangularly shaped in cross-section. However, in alternative embodiments, the support member  36  can be of open shape such as L-shaped or C-shaped in cross-section. Those skilled in the art would recognize that the cross-sectional shape of the longitudinal support member can be varied and that the above-mentioned cross-sectional shapes were provided for non-limiting exemplary purposes only. An embodiment of the support member  36  will be described in detail as being tubular with a square cross-sectional shape, but this is done only for the sake of clarity and is a non-limiting example. In one embodiment, the support member  36  includes a top wall  38 , a bottom wall  40 , and a pair of opposed front and back sidewalls  42  and  44  (see  FIG. 2 ), respectively, extending therebetween. The support member  36  extends between a motor end  46  and opposed fixed end  48  of the support member  36 . 
   The front sidewall  42  includes a plurality of access openings  50  for providing access to the inside of the support member. The back sidewall  44  can also include access openings if so desired. Similarly, the top wall  38  and the bottom wall  40  can also have access openings if so desired. 
   As shown in  FIG. 1 , a motor  52  is affixed to the top wall  38 , proximal to the motor end  46  of the support member  36 . The motor  52  is connected to a power supply (not shown) and a controller (not shown) via an electrical connector  54 . A shaft  56  extends from the inside of the support member through a shaft opening  58  ( FIG. 2 ) formed through the front sidewall  42 . A pulley  60  is attached to the shaft  56 , and the pulley  60  is coupled to the motor  52  via a V-belt  62 . The shaft  56  is coupled to a drive mechanism that causes the self-climbing apparatus  12  to climb up and down the cables  16 ,  18 ,  20  and  22 . 
     FIG. 2  shows selected components of the self-climbing apparatus  12  in exploded perspective form. The top wall  38  of the support member  36  includes a motor end cable opening  64  and a fixed end cable opening  66 . Cables  16  and  18  ( FIG. 1 ) extend through the motor end cable opening  64  and engage a first redirectional sheave ( 166  in  FIG. 7A ) and a second redirectional sheave (not shown),repsectively, that direct cables  16  and  18  toward the fixed end  48 . Cables  20  and  22  ( FIG. 1 ) extend through the fixed end cable opening  66  and engage a first stationary sheave ( 180  in  FIG. 8A ) and a second stationary sheave (not shown), repsectively, coupled to the support member  36  proximal to the fixed end  48 . 
   The support member  36  also defines a hollow interior  68  ( FIGS. 2 and 9 ) that extends the longitudinal length of the support member from motor end  46  to fixed end  48 . The front sidewall  42  of the support member  36  defines a plurality of bolt openings  70 , which are used for receiving bolts (not shown) for coupling a first redirectional sheave  166  ( FIG. 7A ) to the front sidewall  42 . The back sidewall  44  also defines bolt openings for coupling a second redirectional sheave (not shown) to the back sidewall  44 . 
   As shown in  FIGS. 2 and 9 , the self-climbing apparatus  12  further includes a travel screw transmission  72  that is powered by the motor  52  via the V-belt  62 . The travel screw transmission  72  is coupled to a first end cap  73 , which is configured to removably mate with the motor end  46  of the support member  36  such that in operable position the end cap  73  holds the travel screw transmission fixed within the support member  36 . 
   As shown in  FIG. 9 , an externally threaded travel screw  74  extends from the travel screw transmission  72 . The travel screw  74  includes a right end portion  76  and a left end portion  78 . A travel member assembly  80  is coupled to the threads of the travel screw  74  and travels back and forth between the right and left end portion  76  and  78 , respectively, of the travel screw  74  in response to the rotation of the travel screw  74 . The travel screw transmission  72  is adapted to hold the travel screw  74  stationary when the travel screw transmission  72  is not being driven by the motor  52 . 
   In one preferred embodiment, the motor  52  is a 208-volt, 60-hertz, 1750-rpm, reversible three-phase motor. The motor can be of other specifications. The transmission reduces the speed of the motor as it is applied to the travel screw. As will be understood from the following disclosure, the motor and the transmission cooperate to power the travel member assembly  80  such that the self-climbing apparatus  12  can climb and descend the cables at a rate of 10 vertical feet per minute. 
   As shown in  FIGS. 2 and 4 , a second end cap  82  is adapted to couple to the support member  36  at the fixed end  48  of the support member. The end cap  82  has a plurality of double stationary or fixed sheave blocks of which  84 (A),  86 (A),  88 (A) and  90 (A) are visible. Similarly, the travel member assembly  80  includes a second plurality of double movable or travel sheave blocks of which  84 (B),  86 (B),  88 (B) and  90  B are visible. In one preferred embodiment, the number of sheaves coupled to the end cap  82  equals the number of sheaves coupled to the travel member assembly  80 . However, in alternative embodiments, the number of sheaves coupled to the end cap  82  and the number of sheaves coupled to the travel member assembly  80  may not be the same. 
   Before discussing the end cap  82  and the travel member assembly  80  in greater detail, a description of an exemplary double sheave block is provided. In one embodiment, the end cap  82  and travel member assembly  80  each include identical sheave blocks. (See  FIGS. 2 ,  4  and  5 .) However, in alternative embodiments, the sheave blocks coupled to the travel member assembly  80  can differ from the sheave blocks coupled to the end cap  82 . In one embodiment, the sheave blocks coupled to the travel member assembly  80  differ from the sheave blocks coupled to the end cap  82  such that the cables  16 ,  18 ,  20 , and  22  can be terminated on the travel member assembly. 
   Sheave Block 
     FIG. 3  is a perspective view of a double sheave block  84 . In this embodiment, the double sheave block  84  includes two sheaves  92  and  94  and three sidewalls  96 ,  98 , and  100 . The sheave  92  is sandwiched by sidewalls  96  and  98 , and the sheave  94  is sandwiched by sidewalls  98  and  100 . A base block  102  and a spacer  104  interpose the sidewalls  96  and  98  such that the sidewalls  96  and  98  do not bind the sheave  92 . Similarly, a second base block  106  and a second spacer  108  interpose the sidewalls  98  and  100  such that the sidewalls  98  and  100  do not bind the second sheave  94 . 
   The sidewalls  96 ,  98 , and  100  and the base blocks  102  and  106  each have a plurality of aligned holes (not shown) for receiving bolts  110 . The spacers  104  and  108  are open ended cylinders such that the bolts  110  can extend through them. The bolts  110  are fastened with nuts  112 . The sidewalls  96 ,  98 , and  100  also define aligned axle openings (not shown) for receiving an axle bolt  114  that extends through the assembly of sidewalls  96 ,  98 , and  100  and sheaves  92  and  94  such that the sheaves  92  and  94  can rotate about the axle bolt  114 . The axle bolt  114  is held in place by a nut  116 . 
   Each base block  102  and  106  also defines at least one internally threaded opening  118  for coupling with an externally threaded bolt. Typically, the internally threaded bolt openings  118  of base blocks  102  and  106  are juxtaposed. Thus, in the embodiment illustrated in  FIG. 3 , in the upper right hand portion hidden behind the sidewall  100 , there is an internally threaded bolt opening in base block  106 . The internally threaded openings  118  are used for coupling the double sheave block  84  to either the end cap  82  or to the travel member assembly  80 . It should be remembered the sheave block described hereinabove is an exemplary, non-limiting, sheave blocks. In some embodiments, a sheave block includes more than two sheaves. However, in other embodiments, a sheave block may comprise only one sheave. 
   End Cap with Plurality of Sheave Blocks 
   Referring to  FIG. 4 , end cap  82  includes an inner wall  120  to which the double sheave blocks  84 (A),  86 (A),  88 (A) and  90 (A) are coupled. The inner wall  120  is sized and dimensioned such that it fits within the hollow interior  68  of the support member  36 , and a circumambient flange  122  on the end cap  82  engages the end portions of the walls of the support member  36 . The end cap  82  also defines a plurality of cable termination holes  124  through which bolts (not shown) are inserted to couple to ends of the cables  16 ,  18 ,  20 , and  22  (not shown). 
   Double sheave blocks  84 (A) and  86 (A) are aligned approximately vertically and are disposed on the upper left hand side and upper right hand side (as viewed looking at the inner wall  120 ) of the interior wall  120 , respectively. Disposed on the bottom left hand side, (as viewed looking at the interior wall  120 ) is a double sheave block  88 (A); and disposed on the bottom right hand side (as viewed looking at the interior wall  120 ) is a double sheave block  90 (A). The double sheave block  88 (A) is tilted approximately 15° counter clockwise from vertical, and the double sheave block  90 (A) is tilted approximately 15° clockwise from vertical. 
   Travel Member Assembly with Plurality of Sheave Blocks 
   Referring to  FIG. 5 , the travel member assembly  80  includes a travel member frame  126 , a greaser  128 , and double sheave blocks  84 (B),  86 ( 3 ),  88 (B), and  90 (B). The greaser  128  carries grease and applies grease to the travel screw  74  as the travel member assembly  80  traverses portions of the travel screw  74 . 
     FIG. 6  illustrates the travel member frame  126  in greater detail. The travel member frame  126  includes two arms  130  and  132 . Each of the arms has opposed ends  134  and  136  and the arms are approximately L-shaped in cross-section having walls  138  and  140 . The lengths of the arms extending between the opposed ends  134  and  136  are such that the travel member frame  126  can fit within the interior  68  of the support member  36  with some free play. The walls  140  include holes  142  which are used to couple rollers  144  (see  FIG. 5 ) to the arms  130  and  132 . The rollers  144  engage the inside of the top wall  38  and the inside of the bottom wall  40  and prevent the travel member assembly  80  from rotating within the support member  36 . 
   Referring to  FIG. 6 , a cross member  146  extends between the arms  130  and  132  such that the cross member overlies at least a portion of the walls  138 (A) and  138 (B). The cross member  146  is approximately rectangularly C-shaped in cross section with the opening of the C directed towards the travel screw transmission  72 . The length of the cross member  146  is such that the width of the travel member frame  126  enables adequate clearance between arm  130  and front sidewall  42  for cables  16  and adequate clearance between arm  132  and back sidewall  44  for cable  18 . 
   The cross member  146  defines a travel screw opening  148  and bolt openings  150 . The travel screw  74  is adapted to fit through the travel screw opening  148 . The holes  150  are used for bolting a travel nut  152  (see  FIG. 5 ) to the cross member  146 . The travel nut  152  ( FIG. 5 ) is internally threaded and engages the external threads of travel screw  74 , thereby causing the travel member assembly  80  to traverse portions of the travel screw  74  in response to the turning of the travel screw  74  by the screw jack transmission  72 . 
   Referring to  FIG. 6 , arms  130  and  132  include bolt holes  154  and  156 . The cross member  146  includes bolt holes (not shown) that are aligned with bolt holes  154 . The bolt holes  154  and  156  are adapted to receive bolts (not shown) for bolting the double sheave blocks  84 (B) and  88 (B) to the arm  130  and the double sheave blocks  86 (B) and  90 (B) to arm  132 , as illustrated in  FIG. 5 . 
   A dashed line  158  (see  FIG. 5 ) represents the direction along which the travel member assembly  80  travels with arrows  160  and  162  pointing in the direction of the motor end  46  and opposed fixed end  48 , respectively. 
   The double sheave block  84 (B) is mounted to the arm  130  and is tilted approximately 15° clockwise (looking in the direction of arrow  160 ) from vertical. The double sheave block  86 (B) is mounted to the arm  132  and is tilted approximately 15° counterclockwise from vertical. The double sheave blocks  88 (B) and  90 (B) are mounted approximately vertically to arms  130  and  132 , respectively. 
   Cable Paths 
   As will become clear with the description of the cable paths in  FIGS. 7A ,  7 B,  8 A, and  8 B, the alignment of the sheaves provides a good fleet angle for the cables between pairs of sheave blocks 
   As shown in  FIG. 2 , double sheave blocks  88 (A) and  88 (B) are paired such that portions of cable  16  extend therebetween. Double sheave blocks  90 (A) and  90 (B) are paired such that portions of cable  18  extend therebetween. Double sheave blocks  84 (A) and  84 (B) are paired such that portions of cable  20  extend therebetween; and double sheave blocks  86 (A) and  86 (B) are paired such that portions of cable  22  extend therebetween. 
     FIGS. 7A and 7B  illustrate the cable path for cable  16  as viewed looking along the direction of arrow  164  (see  FIG. 2 ) and from above, respectively. Cable  16  enters the support member  36  at the motor end  46  and engages a redirectional sheave  166  proximal to the motor end  46 . A fixed length of cable  16 (A) extends from the redirectional sheave  166  to a fixed sheave  168 . A dashed line  170  represents the centerline of the support member  36 . The fixed sheave  168  is the outermost sheave, as measured from the centerline  170 , within the double sheave block  88 (A) (see  FIG. 4 ). The cable  16  wraps around the top of fixed sheave  168  to the bottom of fixed sheave  168 , and a variable length of cable  16 (B) extends from fixed sheave  168  to a travel sheave  172 , which is the outermost sheave of double sheave block  88 (B). The cable  16  wraps from the bottom to the top of travel sheave  172 , and a variable length of cable  16 (C) extends therefrom to the top of an inner fixed sheave  174  of double sheave block  88 (A). The cable wraps from the top to the bottom of inner fixed sheave  174 , and a variable length of cable  16 (D) extends therefrom to the bottom of an inner travel sheave  176  of the double sheave block  88 (B). The cable  16  then wraps from the bottom to the top of inner travel sheave  176 , and a variable length of cable  16 (E) extends to its termination point  178 , which is coupled to the end cap  82 . As the travel member assembly  80  traverses the travel screw  74 , the variable lengths of cable  16 (B),  16 (C),  16 (D), and  16 (E) change accordingly. The redirectional sheave  166  does not translate with respect to the fixed end  48 . Thus, the length of cable  16 (A) is fixed. As those skilled in the art will recognize, the tilting of the double sheave block  88 (A) with respect to the alignment of double sheave block  88 (B) provides for a better fleet angle for the lengths of cable extending between the double sheave blocks  88 (A) and  88 (B) than if the double sheave blocks were similarly aligned. 
     FIGS. 8A and 8B  illustrate the cable path for cable  20  as viewed looking along the direction of arrow  164  (see  FIG. 2 ) and from above, respectively. Cable  20  enters the support member  36  at the fixed end  48  and engages fixed outer sheave  180  of double sheave block  84 (A). Sheave  180  is the outermost sheave of double sheave block  84 (A), as measured from the centerline  170 . The cable  20  wraps around fixed outer sheave  180 , and a variable length of cable  20 (A) extends from fixed outer sheave  180  to an outer travel sheave  182 , which is the outermost sheave of double sheave block  84 (B). The cable  20  wraps from the bottom to the top of outer travel sheave  182 , and a variable length of cable  20 (B) extends therefrom to the top of an inner fixed sheave  184  of double sheave block  84 (A). The cable  20  wraps from the top to the bottom of inner fixed sheave  184 , and a variable length of cable  20 (C) extends therefrom to the bottom of an inner travel sheave  186  of the double sheave block  84 (B). The cable  20  then wraps from the bottom to the top of inner travel sheave  186 , and a variable length of cable  20 (D) extends to its termination point  179 , which is coupled to the end cap  82 . 
   Detailed descriptions of the cable paths for cables  18  and  22  are not provided. The cable paths for cables  18  and  22  mirror the cable paths for cables  16  and  18 , respectively, with the centerline  170  being the reflection plane. In one embodiment, the cable paths engage the outermost sheave and then work inward towards the centerline  170 . Those skilled in the art recognize that other cable paths such as working from the inner sheaves to the outer sheaves are also possible and/or terminating cables on the travel member assembly  80 . All such variations are intended to be within the embodiments of the invention. 
   When the distance between the travel member assembly  80  and the fixed end  48  is reduced, the lengths of the cables  16 ,  18 ,  20 , and  22  extending upwardly from the support member  36  is increased, thereby lowering the support member. Since the cables  16 ,  18 ,  20 , and  22  are simultaneously paid out or retracted by movement of the travel member assembly  80 , the support member  36  will remain in its fixed attitude, usually in a horizontal attitude as it is being raised and lowered. In the embodiment illustrated, the self-climbing apparatus  12  climbs (or descends) 4 feet for every 1 foot the travel member assembly  80  is moved away from (or towards) the fixed end  48 . Those skilled in the art recognize that other integer ratios of vertical displacement of the self-climbing apparatus  12  to the longitudinal displacement of the travel member assembly  80  are possible by changing the number of fixed and travel sheaves for each cable and by terminating the cables on the travel member assembly  80 . 
   Vertically Aligned Sheaves 
     FIG. 9  illustrates an embodiment of the self-climbing stage lighting system  10  having a support spider  192  disposed in the support member  36 . The spider support  190  is attached to the support member between the end cap  82  and the travel member assembly  80 . The support member  192  includes a radial bearing  194  that receives the left end portion  78  of the travel screw  74  and supports the travel screw  74 . 
   In addition, in this embodiment, sheaves are approximately vertically aligned, in that they rotate about horizontally extending axles. The motor end  46  of the support member  36  has two redirectional sheaves of which only  166  is shown. The redirectional sheaves are coupled to the support member  36  and extend partially outside of the support member  36  through an opening formed in the top wall  38 . The redirectional sheave  166  bends cable  16  such that the cable is directed approximately longitudinally within the support member to the double sheave block  88 (A) and approximately vertically from the support member  36 . The cable  16  engages the double sheave blocks  88 (A) and  88 (B) in the manner previously described. 
   The other redirectional sheave (not shown) bends cable  18  such that the cable is directed approximately longitudinally within the support member  36  to the double sheave block  90 (A) (not shown) and approximately vertically from the support member  36 . The cable  18  engages the double sheave blocks  90 (A) and  90 (B). 
   In this embodiment, an outer fixed sheave  188  is vertically offset from an inner fixed sheave  190  at the fixed end  48 . The outer fixed sheave  188  extends at least partially through the top wall  38  and directs the cable  20  towards the double sheave block  84 (B). Functionally, outer fixed sheave  188  and inner fixed sheave  190  operate identically to the sheaves  180  and  184  of the double sheave block  84 (A). Consequently, the sheaves  188  and  190  operate as an offset double sheave block in which cable  20  engages the double sheave block  84 (B). The cable path of cable  20  is such that it works from the outermost sheaves inward toward the centerline  170 . 
   Cross Mounted Sheaves 
     FIG. 10  illustrates another embodiment of the self-claiming stage light system  10  in which double sheave blocks are cross mounted and longitudinally offset. Proximal to the fixed end, a pair of fixed double sheave blocks  196 (A) and  198 (A) are mounted vertically. A matching pair of vertically mounted travel double sheave blocks  196 (B) and  198 (B) are mounted to the travel member assembly  80  (not shown). The vertical fixed double sheave blocks  196 (A) and  196 (B) engage the cable  20  (not shown) as previously described with respect to double sheave blocks  84 (A) and  84 (B); and the vertical fixed double sheave blocks  198 (A) and  198 (B) engage the cable  22  (not shown) as previously described with respect to double sheave blocks  86 (A) and  86 (B). 
   A pair of horizontally aligned fixed double sheave blocks  200 (A) and  202 (A) are mounted proximal to the vertically aligned fixed double sheave blocks  196 (A) and  198 (A) between the vertically aligned fixed double sheave blocks  196 (A) and  198 (A) and the travel member assembly  80  (not shown). A matching pair of horizontally aligned travel double sheave blocks  200 (B) and  202 (B) are mounted proximal to the vertically aligned travel double sheave blocks  196 (B) and  198 (B) between the vertically aligned travel double sheave blocks  196 (B) and  198 (B) and the fixed end  48 . The fixed double sheave blocks  200 (A) and  200 (B) each include an outer fixed sheave  204 (A) and  204 (B), respectively, and an inner fixed sheave  206 (A) and  206 (B), respectively. The travel double sheave blocks  202 (A) and  202 (B) are similarly configured to include an outer travel sheave  208 (A) and  210 (B), respectively, and an inner travel sheave  208 (A) and  210 (B), respectively. 
   In this embodiment, the redirectional sheave  166  (not shown) directs cable  16  (not shown) towards the horizontally fixed double sheave block  200 (A). The cable  16  (not shown) wraps around the outer fixed sheave  204 (A) and is directed towards the outer travel sheave  204 (B). The cable  16  wraps around outer travel sheave  204 (B) and is directed to inner fixed sheave  206 (A) where it is redirected to inner travel sheave  206 (B). After wrapping around inner travel sheave  206 (B), the cable terminates proximal the fixed end  48 . 
   Another motor end redirectional sheave (not shown) engages the cable  18  (not shown), and directs the cable to the horizontally aligned double sheave block  202 (A). The horizontally aligned double blocks sheaves  202 (A) and  202 (B) cooperate to engage cable  18  in a manner similar to which cable  16  is engaged by double sheave blocks  200 (A) and  200 (B). 
   As those skilled in the art will recognize, an advantage of having longitudinally offset and cross mounted sheave blocks is that each sheave can have a greater diameter than when the sheaves are not longitudinally offset and cross mounted. For example, in the embodiment where the double sheave blocks are vertically aligned, each sheave in the double sheave blocks must be less than one-half the height of the front and back sidewalls  42  and  44 , respectively. Thus, with longitudinally offset and cross mounted sheaves, it is possible to employ larger sheaves without increasing the cross sectional size of the support member  36 . As known by those skilled in the art, larger diameter sheaves are needed with increased cable diameter so as to maintain the diameter ratio of the sheave to cable within the desired range of 28-32:1. 
   Although preferred embodiments of the invention has been disclosed in detail herein, it will be obvious to those skilled in the art that variations and modifications of the disclosed embodiments can be made without departing from the spirit and scope of the invention as set forth in the following claims. For example, in another embodiment, stationary sheaves can be disposed between the screw jack transmission and the travel member assembly such that self-climbing apparatus will ascend the cables as the travel member assembly is moved away from the screw jack transmission