Abstract:
Apparatus for tensioning torsion spring, shaft-mounted in association with a spring cone, has a central ratchet assembly with two spaced, cogged ratchet wheels, slotted to allow the assembly to be rotatably positioned over the shaft. The ratchet assembly is connectable to the spring cone so that the spring cone will rotate with the ratchet assembly. The ratchet wheel slots are closed off by cogged bridging elements that create a continuous cogged perimeter around each ratchet wheel. Pawl-equipped levers are positioned over the ratchet wheels with the pawls engageably aligned with the ratchet wheel cogs, and then operated in alternating fashion to rotate the ratchet assembly and spring cone, thus tensioning the spring. Upon achieving a desired spring tension, the spring cone may be secured to the shaft, whereupon the bridging elements may be retracted from the ratchet wheel slots to permit removal of the apparatus from the shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part of application Ser. No. 10/662,366 filed Sep. 16, 2003, and the disclosure of said earlier application is fully incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to apparatus for tensioning shaft-mounted helical springs, and in particular for tensioning shaft-mounted torsion springs of overhead doors. 
   BACKGROUND OF THE INVENTION 
   Sectional overhead doors for residential and commercial garages typically have a number of hinged horizontal sections with rollers at each end that run inside tracks extending vertically on each side of the door opening. The tracks continue either vertically or, perhaps most commonly, horizontally inward above the door opening to accommodate the door when in its open position. These doors commonly incorporate a counterweighting system to reduce the effective door weight that must be lifted by a manual or motorized door-opening mechanism. 
   The components of a typical counterweighting system include an elongate round shaft with a pulley at each end, and at least one helical torsion spring mounted generally concentrically on the shaft. The shaft is rotatably mounted to the building structure above and parallel to the door opening. Each pulley has a door-lifting cable attached to the door at a selected point, typically near the bottom of the door. One end of the spring is non-rotatably fixed to the building structure, and the other end is fixed to a spring cone which in turn is lockably mounted onto the shaft (typically by means of set screws). The spring may be tensioned by rotating the spring cone around the shaft and then locking the spring cone on the shaft. The tensioned spring exerts a rotational force on the shaft, inducing tension forces in the cables, which in turn exert upward forces on the door. These upward forces effectively counteract and reduce the weight that needs to be lifted when operating the door. 
   There are many known types of spring cones, most of which incorporate a number of radial sockets (typically four) into which steel winding rods can be inserted for purposes of winding the spring cone around the shaft to tension the spring. With the spring cone loose on the shaft, a first rod is inserted into one socket and manual force is applied to the rod to rotate the spring cone and one end of the spring a partial turn, thus increasing spring tension. With the first rod being firmly held (to restrain spring tension), a second rod is inserted into another socket and used to turn the cone further. With the second rod being firmly held, the first rod may be withdrawn and moved to a new socket. This alternating process is continued until a desired spring tension has been achieved, whereupon the spring cone is tightened onto the shaft and the rods are removed from the sockets. 
   This well-known procedure is effective but potentially dangerous. If the rods are accidentally let go of while the spring cone is loose on the shaft, the tensioned spring will quickly unwind, causing the spring cone to spin on the shaft. If one or both rods are still engaged in spring cone sockets, they will spin rapidly with the spring cone and thus may injure a person standing too close. In fact, the rods may even fly out of the spring cone and thus become dangerous projectiles that can seriously injure or even kill a bystander. The danger inherent in such situations is greater for larger and heavier doors, which typically have heavier springs that store greater potential energy when tensioned. 
   These risks are particularly great when spring tensioning is being attempted by a single worker. Muscle fatigue and momentary inattention or distraction are only two factors that could cause the worker to lose hold of the winding rods. In view of these concerns, it is less dangerous if the spring tensioning procedure is performed by two workers, each operating only one winding rod. Then if one worker becomes unexpectedly tired or inattentive and loses control of one rod, the other worker will in most cases be holding the other rod safely, and preventing the spring from unwinding. An obvious disadvantage of this safer alternative procedure, however, is that the need for two workers results in higher cost for the spring tensioning operation. 
   For the foregoing reasons, it is desirable to have spring tensioning methods and means that do not use loose winding rods that can cause injury in case of inadvertent and uncontrolled unwinding of a tensioned spring, and, further, that can be safely by only one worker. The prior art discloses a number of attempts to address this problem. U.S. Pat. No. 2,718,282 (Davis), discloses spring tensioning apparatus having a splined cylindrical member with a longitudinal slot to permit mounting of the member over a spring shaft. The slot is then closed off using a secondary member that slides into longitudinal keyways in the cylindrical member on either side of the slot. The secondary member is also splined so as to create an effectively continuous splined perimeter around the cylindrical member when the secondary member has been positioned in the slot. The cylindrical member has means for connecting to a spring cone so that the spring cone will rotate when the cylindrical member is rotated. Also provided is a pair of pawl-equipped ratchet levers, each having a cylindrical inner surface and an opening to allow positioning over the shaft. The levers are placed over the shaft and slid over the splined cylindrical member, whereupon they may be operated in alternating fashion, with the pawls of the levers engaging the splines of the cylindrical member and causing it to rotate, thus rotating the spring cone and tightening the spring. Because the shaft openings in the levers are smaller than the diameter of the cylindrical member, the levers cannot come free of the cylindrical member without sliding them laterally off of the cylindrical member. 
   Although being a useful device, the Davis apparatus has several disadvantages. For example, it requires precise machining for splining of the cylindrical and secondary members, as well as for the keyways in the cylindrical member and the corresponding keys of the secondary member. Indeed, if the keyways are not machined to close tolerances, the secondary member will either fit too tightly (thus being difficult to install and remove) or it will be too loose (thus being prone to sliding out of the cylindrical member, making the apparatus inoperable. Even when these parts have been machined to provide an optimal fit, their mating surfaces can become damaged or covered with grime, paint, or other contaminants, in each case making insertion and/or removal of the secondary member difficult or impossible. Furthermore, the secondary member is of necessity a loose component that could be accidentally lost, again making the apparatus unusable. 
   U.S. Pat. No. 3,651,719 (Wessel) discloses another spring tensioning apparatus that operates on the ratchet principle. This apparatus features an hinged split collar assembly releasably mountable around a spring cone, with a rigid pin that goes into one of the spring cone sockets so that rotation of the collar will cause rotation of the spring cone. The split collar has rounded ratchet teeth around its perimeter, the teeth extending across the full width of the inner collar. The apparatus includes a pair of pawled ratchet handles, each with a hinged split collar section approximately half the width of the toothed inner collar. The Wessel apparatus is operated by opening the inner collar and mounting it to the spring cone, closing the inner collar and locking its hinged sections with an anchor pin, opening the ratchet handle collars of the ratchet handles and placing them over the inner collar, closing the ratchet handle collars and locking their hinged sections together with anchor pins, and, finally, operating the handles in alternating fashion to tighten the spring. 
   The Wessel apparatus also has disadvantages and drawbacks. Its installation requires the use of three anchor pins, and the loss of even one of these loose components may make the apparatus unusable. It also has several hinges that are prone to wear and breakage that could make efficient use of the apparatus difficult or impossible. Furthermore, installation of the Wessel apparatus on the spring shaft involves a number of steps before it is ready to operate, and these steps must also be performed in reverse in order to remove the apparatus from the shaft after the spring has been tensioned. This comparatively labour-intensive procedure increases the cost of spring tensioning. 
   Another ratchet-type spring tensioning device is found in U.S. Pat. No. 5,605,079 (Way). This apparatus has a split housing, which is separable for installation onto the shaft and the spring cone, with a bore for receiving the shaft and a number of pins for engaging holes in the winding cone. A split sprocket is integrally mounted to the housing and an annular groove on each side of the sprocket receives a ratchet tool. The ratchet tools are locked into the groove using bolts to prevent disengagement, and are operated in alternating fashion to rotate the sprocket, thus rotating the spring cone to adjust the tension in the spring. Disadvantages of this system include the number of loose components and the higher degree of assembly and disassembly required (i.e. assembly of the split housing and sprocket, attachment of the ratchet tools, and the corresponding disassembly once the adjustment is completed). 
   In view of the disadvantages of the prior art devices described above, there is a need for an improved apparatus for adjusting the tension of a helically wound torsion spring that has minimal or no small loose components prone to being misplaced, that has minimal hinged components prone to wear and disrepair, and that is simple to attach to and remove from a spring shaft, while being safely operable by a single worker. The present invention is directed to these needs. 
   BRIEF SUMMARY OF THE INVENTION 
   In general terms, the invention is an apparatus for safely tensioning a torsion spring, without need for spring cone tightening rods that may pose an injury hazard in the event of an inadvertent release of spring tension during the tensioning operation. The apparatus features a central ratchet assembly with cogged ratchet wheels at each end, slotted to allow the assembly to be placed over the spring shaft adjacent to the spring cone. The ratchet assembly includes sub-apparatus connectable to the spring cone so that the spring cone (and therefore the spring) will rotate when the ratchet assembly is rotated. The slots in the ratchet wheels are closed by cogged bridging elements to create a continuously cogged perimeter around the ratchet wheels. The apparatus includes a pair of pawl-equipped operating levers that may be positioned over the ratchet wheels so that the pawls can engage the ratchet wheel cogs. The levers may then be operated in alternating fashion to rotate the ratchet assembly, thus tensioning the spring. 
   Accordingly, in one aspect the present invention is an apparatus for tensioning a helical spring mounted generally concentrically on an elongate round shaft having a shaft diameter, said spring having a first end fixed to a building support and a second end anchored to a spring cone lockably mounted on the shaft, said apparatus comprising:
         (a) a ratchet wheel assembly comprising:
           a.1 a trunnion having a substantially semi-cylindrical inner surface with a diameter slightly greater than the shaft diameter, and having a concentrically semi-cylindrical outer surface defining an open side; and   a.2 a pair of primary ratchet wheels, each having a centroidal opening, plus a radial slot contiguous with the centroidal opening and having two slot edges, said radial slot extending radially from the centroidal opening to the wheel&#39;s perimeter so as to intersect with and define a gap in said perimeter;   wherein:   a.3 the centroidal opening of each primary ratchet wheel is large enough to allow the shaft to be disposed therewithin, and concentrically with the primary ratchet wheel;   a.4 the width of each radial slot is at least slightly greater than the shaft diameter;   a.5 the perimeter of each primary ratchet wheel defines a continuous plurality of uniformly-spaced cogs between the edges of the primary ratchet wheel&#39;s perimeter gap; and   a.6 the primary ratchet wheels are spaced apart and coaxially mounted to the trunnion with their radial slots aligned with the open side of the trunnion, such that the ratchet wheel assembly can be positioned substantially coaxially over the shaft;   
           (b) a pair of bridging elements, each bridging element being associated with a corresponding one of the primary ratchet wheels; each bridging element having an arcuate-edged section defining a plurality of cogs configured and spaced to match the cogs of the corresponding primary ratchet wheel; wherein each bridging element is selectively operable between:
           b.1 an open position, in which the arcuate-edged section is substantially clear of the perimeter gap and radial slot of the corresponding primary ratchet wheel so as to permit positioning of the ratchet wheel assembly coaxially over the shaft; and   b.2 an engaged position, in which the arcuate-edged section bridges the perimeter gap of the bridging element&#39;s corresponding primary ratchet wheel such that the cogs of the bridging element and the corresponding primary ratchet wheel combine to form a continuous and uniformly-spaced series of cogs;   
           (c) locking means, for releasably locking the bridging elements in the engaged position;   (d) spring cone engagement means, for releasably engaging the spring cone such that the spring cone will rotate with the ratchet wheel assembly; and   (e) a pair of levers, each lever having a hub section rotatably mountable around the outer surface of the trunnion in association with one of the primary ratchet wheels, each lever having a pawl member with an inner end and an outer end, said inner end defining a cog-engaging surface and a non-engaging surface, each pawl member being mounted to its corresponding lever such that the pawl member may be retractably extended such that the cog-engaging surface may engage the cogs of one of the primary ratchet wheels and its corresponding bridging element;
 
wherein said apparatus may be substantially coaxially mounted over the shaft when the bridging elements are in the open position, whereupon:
   (f) the bridging elements may be moved to, and releasably locked in, the engaged position, thereby to prevent disengagement of the apparatus from the spring shaft;   (g) the spring cone engagement means may be releasably engaged with the spring cone;   (h) the pawl members may be positioned to engage the cogs of the primary ratchet wheels in a desired orientation; and   (i) with the spring cone free to rotate about the spring shaft, the levers may be cooperatively manipulated to rotate the spring cone in a desired direction around the shaft, thereby tensioning or alternatively relaxing the tension in the torsion spring, until a desired degree of tensioning has been achieved, whereupon the spring cone may be locked in position relative to the shaft, the bridging elements may be moved to the open position, and the apparatus may be disengaged from the shaft.       

   In the preferred embodiment, the trunnion is a semi-cylindrical sleeve. In an alternative embodiment, the trunnion may be an elongate member having separate cylindrical outer surfaces for rotatably receiving the levers. 
   Also in the preferred embodiment, the primary ratchet wheels are mounted at opposite ends of the trunnion. In operation of the apparatus in this embodiment, the levers are mounted onto the trunnion inboard of the primary ratchet wheels. In an alternative embodiment, the primary ratchet wheels are mounted inboard of the ends of the trunnion, such that the levers are mounted onto the trunnion outboard of the primary ratchet wheels. In a variant of this alternative embodiment, the levers may be mounted either inboard or outboard of the primary ratchet wheels. 
   In the preferred embodiment, each bridging element is an auxiliary ratchet wheel having substantially the same configuration and features of the primary ratchet wheels. Each auxiliary ratchet wheel is rotatably and coaxially mounted to its corresponding primary ratchet wheel, such that it is rotatable relative to the primary ratchet wheel between the open and engaged position. Unlike the primary ratchet wheels, the auxiliary ratchet wheels need not have cogs around their full perimeter, although that might be convenient or advantageous in some situations. What is important is for the auxiliary ratchet wheels to have sufficient cogs positioned so as to provide a substantially continuous series of cogs around the periphery of the combined primary/auxiliary ratchet wheel combination when in the engaged position. The cogs of the two wheels will necessarily lie in closely adjacent parallel planes, such that the cogs of both wheels are readily engageable by the pawl member of one of the levers. 
   Alternatively, each bridging element may be a cogged element smaller than its corresponding primary ratchet wheel, mountable thereto in either hinged or swivelling fashion so that it can either swing or swivel between the open and engaged positions. Where the bridging element is a cogged element hinged to the primary wheel, it may be adapted such that when in the engaged position its cogs will lie in the same plane as the primary wheel cogs. Alternatively, and in embodiments where the bridging element is a swivelling cogged element, its cogs will typically lie in a plane parallel to and closely adjacent to the plane of the primary wheel cogs, as in the case where the bridging elements are auxiliary ratchet wheels. 
   In the preferred embodiment, each lever includes pawl biasing means, for biasing the lever&#39;s pawl member inwardly toward the primary ratchet wheel on which the lever may be mounted. The pawl biasing means may comprise a spring. Also in the preferred embodiment, each lever includes pawl orientation means, for selectively orienting the cog-engaging surface of the lever&#39;s pawl member to accommodate rotation of the ratchet wheel assembly in either direction. The pawl orientation means may be a handle associated with the outer end of the pawl member. 
   Each lever preferably includes pawl alignment means, to facilitate positioning of the lever on the trunnion with the lever&#39;s pawl member in optimal alignment with the cogs of the corresponding primary ratchet wheel and bridging element. The pawl alignment means may comprise a guide member mounted to the hub section of the lever, with the guide member being rotatable against a rub plate mounted to the trunnion. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described with reference to the accompanying figures, in which numerical references denote like parts, and in which: 
       FIG. 1A  is an exploded isometric view of the ratchet wheel assembly of the preferred embodiment of the invention, in which the bridging elements are auxiliary ratchet wheels. 
       FIG. 1B  is an isometric view of a pair of ratchet levers for use in association with the ratchet wheel assembly of the invention. 
       FIG. 1C  is a side view of a primary ratchet wheel of the preferred embodiment, illustrating the centroidal opening and radial slot thereof. 
       FIG. 2  is a side view of the preferred embodiment, with the auxiliary ratchet wheels in the open position, ready for mounting of the apparatus on a spring shaft. 
       FIG. 3  is a side view of the preferred embodiment, mounted on a spring shaft with the auxiliary ratchet wheels in the open position. 
       FIG. 4  is a side view of the preferred embodiment, mounted on a spring shaft with the auxiliary ratchet wheels in the engaged position. 
       FIG. 5  is a partially-sectional elevation of the preferred embodiment, mounted on a spring shaft preparatory to engagement with the spring cone of a torsion spring. 
       FIG. 6  is an isometric view of the fully-assembled preferred embodiment, with the auxiliary ratchet wheels in the open position and ready for mounting on a spring shaft. 
       FIG. 7  is a side view of a primary ratchet wheel and bridging element in accordance with a first alternative embodiment of the invention. 
       FIG. 8  is an end view of the primary ratchet wheel and bridging element shown in  FIG. 7 . 
       FIG. 9  is a side view of a primary ratchet wheel and bridging element in accordance with a second alternative embodiment of the invention. 
       FIG. 10  is an end view of the primary ratchet wheel and bridging element shown in  FIG. 9 . 
       FIG. 11  is a side view of a primary ratchet wheel and bridging element in accordance with a third alternative embodiment of the invention. 
       FIG. 12  is an end view of the primary ratchet wheel and bridging element shown in  FIG. 11 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The preferred embodiment of the invention, generally represented by reference numeral  10 , is shown fully assembled in  FIG. 6 . To assist in understanding the construction of the preferred embodiment, reference may be made to  FIGS. 1-A ,  1 -B, and  1 -C, which illustrate separate components and sub-assemblies forming part of the invention  10  when fully assembled, as will be described later herein. Referring to  FIG. 1-A , a ratchet wheel assembly  20  is made up of two primary ratchet wheels  30  mounted to a trunnion  22 . The trunnion  22  has a semi-cylindrical inner surface  23  slightly larger in diameter than the torsion spring shaft  90  (see  FIG. 6 ) on which it is intended to use the apparatus, such that the trunnion  22  can rotate substantially coaxially around the shaft  90 . The trunnion  22  has an open side  24  of a width greater than the diameter D of the shaft  90  so as to allow the trunnion  22  to be removably positioned coaxially over the shaft  90  (as conceptually indicated in  FIGS. 2 and 3 ). The trunnion  22  also has a cylindrical outer surface  25 , for purposes that will soon be apparent. In the preferred embodiment, the trunnion  22  is a semi-cylindrical sleeve as shown in the Figures. 
   A pair of primary ratchet wheels  30  are fixedly and coaxially mounted to the trunnion  22  in spaced relation. In the preferred embodiment shown in  FIG. 1-A , the primary ratchet wheels  30  are mounted at opposite ends of the trunnion  22 ; however, in alternative embodiments, either or both of the primary ratchet wheels  30  may be mounted a distance inboard from the ends of the trunnion  22 . 
   As best understood by reference to  FIG. 1-C , each primary ratchet wheel  30  has a centroidal opening  34 A and a radial slot  34 B, with the latter extending outward to the perimeter  31  of the primary ratchet wheel  30  and creating a perimeter gap  31 A therein. As used in reference to centroidal opening  34 A, the term “centroidal” indicates that centroidal opening  34 A is disposed in the region of the geometric center of primary ratchet wheel  30 . The perimeter of each primary ratchet wheel  30  defines a plurality of uniformly-spaced ratchet teeth, or “cogs”  32 , disposed continuously around the perimeter  31  of the primary ratchet wheel  30  between the edges  31 B of the perimeter gap  31 A. 
   In the illustrated embodiments, the portion of centroidal opening  34 A farthest from perimeter gap  31 A is shown as having a semi-circular portion (which is concentric with the primary ratchet wheel); however, this is not essential. What is important regarding the geometrical configuration of centroidal opening  34 A is that it is large enough to enclose a circular shape having a diameter equal to that of inner surface  23  of trunnion  22  (and thus will be at least slightly larger than the cross-section of shaft  90 ), such that there will be no interference when the assembled apparatus  10  is positioned over shaft  90 . It may be preferable or convenient to fashion centroidal opening  34 A with a semi-circular portion to facilitate mounting of the primary ratchet wheel  30  onto trunnion  22 , particularly in embodiments where one or both of the primary ratchet wheels  30  are mounted inboard of the ends of trunnion  22 . It will be appreciated, however, that centroidal opening  34 A could take a different shape, subject to suitable adaptation for concentrically mounting trunnion  22  to primary ratchet wheels  30 . 
   As will be appreciated from  FIG. 1-C  in particular, centroidal opening  34 A and radial slot  34 B are necessarily contiguous, but they are given separate reference numerals herein for ease of understanding. The radial slot  34 B is shown as being of essentially constant width W, but this is not essential; what is essential is for the minimum slot width W to be greater than the diameter D of the shaft  90 , so as to allow the assembly  10  to be removably positioned coaxially over shaft  90 . 
   Also provided, in association with each primary ratchet wheel  30 , is a bridging element with a cogged, arcuate-edged section, for closing off the perimeter gap in the primary ratchet wheel  30 . Each bridging element is operable between:
         an “open” position, in which the radial slot  34 B of the associated primary ratchet wheel  30  is clear, so as to permit mounting of the assembled apparatus  10  over the spring shaft  90 , and   an “engaged” position in which at least a portion of the bridging element spans the perimeter gap  31 A of its associated primary ratchet wheel  30 , such that there will be a continuous series of cogs around the full perimeter of the primary ratchet wheel  30 , with the cogs of the bridging element providing the effective continuity of cogs across perimeter gap  31 A.       

   It will be appreciated by persons skilled in the art that it is not necessary for the bridging element or any portion thereof to be disposed within perimeter gap  31 A of primary ratchet wheel  30  when the bridging element is in the engaged position. In some embodiments (such as those illustrated in  FIGS. 9–10 ), the bridging element may be at least partially disposed within the perimeter gap, such that the cogs of the bridging element are substantially aligned with (i.e., co-planar with) the cogs of primary ratchet wheel  30  when the bridging element is in the engaged position. In other embodiments (such as those illustrated in  FIGS. 1-A ,  7 ,  8 ,  11 , and  12 ), the bridging element will lie adjacent to rather than in alignment with primary ratchet wheel  30  when the bridging element is in the engaged position, such that the bridging element cogs lie in a plane substantially parallel to and slightly offset from the plane of primary ratchet wheel  30 . 
   Accordingly, the term “bridging” and related forms of this term, as used herein in association with a bridging element of the apparatus, are to be construed as denoting that the bridging element spans (i.e., bridges) perimeter gap  31 A of its associated primary ratchet wheel  30  when in the engaged position, with the cogs of the bridging element being either in a substantially co-planar relationship with the cogs of the primary ratchet wheel  30 , or lying in a plane parallel to and offset from the plane of the primary ratchet wheel  30 . 
   As illustrated in  FIG. 1-A  and other Figures, the bridging elements in the preferred embodiment will be in the form of auxiliary ratchet wheels  40  similar in construction to the primary ratchet wheels  30 , with each auxiliary ratchet wheels  40  having a corresponding centroidal opening  44 A, radial slot  44 B, and cogs  42 . Each auxiliary ratchet wheel  40  is rotatably mounted (using suitable mounting means) to its corresponding primary ratchet wheel  30  so as to be rotatably operable between the open and engaged positions. 
   In the preferred embodiment, as particularly illustrated in  FIGS. 2 ,  3 , and  4 , the mounting means will comprise a pair of arcuate slots  46  in each auxiliary ratchet wheel  40 , plus a pair of stop posts, with each stop post projecting through an associated arcuate slot  46  and anchored to the corresponding primary ratchet wheel  30 . As illustrated in  FIG. 1-A , the stop post may be a machine bolt  54  (with or without washer  56 ) which engages a mating threaded opening  36  in the corresponding primary ratchet wheel  30 . However, it will be readily apparent that the stop post could take any of several other forms. 
   The arcuate slots  46  and stop posts are configured such that when an auxiliary ratchet wheel  40  is rotated in one direction until the stop posts hit the ends of their respective arcuate slots  46 , the auxiliary ratchet wheel  40  will be in the open position, and when the auxiliary ratchet wheel  40  is rotated in the other direction until the stop posts hit the other ends of their arcuate slots  46 , the auxiliary ratchet wheel  40  will be in the engaged position, with the spacing of the cogs  42  of the auxiliary ratchet wheel  40  conforming as desired with the spacing of the cogs  32  of the corresponding primary ratchet wheel  30 . 
   Although the bridging elements of the embodiments shown in  FIGS. 1-A ,  2 ,  3 , and  4  (i.e., in the form of auxiliary ratchet wheels) are shown with cogs spaced around their full perimeter, persons skilled in the field will appreciate that this is not essential. Each bridging element need only have enough cogs to span or bridge the perimeter gap  31 A of its associated primary ratchet wheel  30  when the bridging element is in the engaged position. Accordingly, a bridging element in the form of an auxiliary ratchet wheel could have un-cogged perimeter except in a cogged region intended to bridge perimeter gap  31 A in the engaged position. In fact, a bridging element in the form of an auxiliary ratchet wheel, in alternative embodiments, need not form a complete circular shape, provided that it has an arcuate cogged region adapted to bridge perimeter gap  31 A in the corresponding primary ratchet wheel  30 . 
   The apparatus of the invention also includes locking means, for releasably securing each bridging element in the engaged position such that cogs of the bridging element cannot be displaced relative to the cogs of the associated primary ratchet wheel  30 . In the preferred embodiment, and as particularly illustrated in  FIGS. 2 ,  3 , and  4 , the locking means is provided by way of a releasable pin  52  or other fastener that may be inserted through an opening  48 B in the auxiliary ratchet wheel  40  into a mating opening  38  in the corresponding primary ratchet wheel  30 . The pin  52  may be loose or, preferably, mounted to the auxiliary ratchet wheel  40  in spring-loaded fashion such that it will be biased to stay engaged in opening  38  when inserted therein, but may be conveniently withdrawn therefrom as desired. Although not essential to the invention, an additional opening  48 A may be provided in the auxiliary ratchet wheel  40  for holding the auxiliary ratchet wheel  40  in the open position, with said opening  48 A being located so as to align with opening  38  when the auxiliary ratchet wheel  40  is in the open position. It will be readily appreciated by those skilled in the art that various other locking means may be used without departing from the fundamental concept or scope of the present invention. 
   In alternative embodiments, the bridging element may be a comparatively small member with a cogged, arcuate-edged section just large enough to span the perimeter gap of the corresponding primary ratchet wheel  30 . In a first alternative embodiment, shown in  FIGS. 7 and 8 , bridging element  140 , with cogs  132 , is attached to modified corresponding primary ratchet wheel  130  by means of hinge  142  adjacent one edge of the radial slot  34 B, such that it can swing between the engaged position (in which it will lie adjacent to the primary ratchet wheel  130 ) and the open position). 
   In a second alternative embodiment, shown in  FIGS. 9 and 10 , the bridging element  240 , with cogs  242 , is attached to modified corresponding primary ratchet wheel  230  by means of hinge  242  adjacent one edge of the radial slot  34 B, such that it will lie in substantially co-planar relation with primary ratchet wheel  230  when in the engaged position, as indicated by the solid lines in  FIG. 10  (in which dotted lines also illustrate bridging element  240  in the open position). 
   In a third alternative embodiment, shown in  FIGS. 11 and 12 , the bridging element  340 , with cogs  342 , is swivellingly mounted to modified corresponding primary ratchet wheel  330  so that it swivels between the open and engaged positions about an axis parallel to the axis of the primary ratchet wheel  330  (for example, about a pivot pin  350  as illustrated). In this third embodiment, bridging element  340  may be secured in the engaged position by means analogous to the securing means previously described for the embodiment illustrated in  FIG. 1-A ; i.e., by providing holes  336  and  346  in primary ratchet wheel  330  and bridging element  340  respectively, through which a suitable bolt or pin may be inserted so as to releasably lock bridging element  340  in the engaged position. 
   In a yet further embodiment, the bridging element could take the form of a segment of an auxiliary ratchet wheel  40  as illustrated in  FIGS. 3 and 4 , with an arcuate slot  46  having a pair of stop posts extending therethrough, so as to allow the bridging element to rotate concentrically relative to its corresponding primary ratchet wheel  30 . 
   The invention  10  also includes spring cone engagement means  60 , which may take a variety of forms well known in the art of the invention. In the preferred embodiment illustrated in  FIGS. 1-A ,  5 , and  6 , the spring cone engagement means  60  has a central hub  62  and at least one outwardly-extending bracket  64  having mounted thereto a radially-oriented sleeve  66  which slidingly receives a cone-engaging pin  68  adapted to be insertable into a socket  96  of a spring cone  94 . The pin  68  may be spring-loaded to bias it radially inward, such that it will tend to stay engaged in the socket  96  when engaged therein. Alternatively, and as illustrated in  FIG. 5 , the pin  68  may have an operating wand  69  that extends through an L-shaped slot  67  in sleeve  66 , such that the pin  68  can slide within the sleeve  66  by moving the wand  69  within one leg  67 A of the L-shaped slot  67  for purposes of inserting the pin  68  into the socket  96  or retracting it therefrom, and such that the pin  68  can be releasably locked in position inside the socket  96  by moving the wand  69  into the other leg  67 B of the L-shaped slot  67 . 
   The spring cone engagement means  60  is mounted to other components of the invention  10  such that it will rotate with the ratchet wheel assembly  20 . In the preferred embodiment, and as particularly illustrated in  FIGS. 1-A ,  5 , and  6 , this is accomplished by rigidly connecting the spring cone engagement means  60  to one of the auxiliary ratchet wheels  40 , such as by welding. In other embodiments, however, such as where the bridging elements are comparatively small and do not cover the entire surface of their associated primary ratchet wheels  30 , the spring cone engagement means  60  may be mounted directly to one of the primary ratchet wheels  30 . 
   The invention  10  also comprises a pair of ratchet levers  70 , as illustrated in  FIG. 1-B . Each lever  70  has a hub assembly  74  adapted to be rotatably mounted around the outer surface  25  of the trunnion  22 , and for that purpose will preferably have a bushing element  72  with an inner diameter slightly greater than the diameter of the outer surface  25  of the trunnion  22 . The configuration of the hub assemblies  74  as shown in the Figures is merely representative; various other hub configurations could be used without departing from the scope of the invention. 
   Each lever  70  also has a pawl assembly  80  comprising a pawl member  82  with an inner end  82 A and an outer end  82 B, with the inner end  82 A defining a cog-engaging surface  83 A and a non-engaging surface  83 B. The pawl member  82  is mounted to the lever  70  in any suitable fashion such that its inner end  82 A can be retractably extended inward toward the hub  74 . In the particular embodiment shown in  FIG. 1-B  and  FIGS. 2 through 6 , the outer end  82 B of the pawl member  82  passes slidably through a bracket  86  mounted to the lever  70 , and the inner end  82 A of the pawl member  82  passes slidably through an opening in the hub  74 . In the preferred embodiment, the pawl member  82  is provided with a spring  84  (with spring retainer means  84 A) or other biasing means, for biasing the pawl member  82  inward toward the hub  74 . 
   Preferably, the pawl member  82  is also provided with pawl-orientation means, for orienting the cog-engaging surface  83 A as desired, depending on the direction in which the lever  70  is to be operated. As illustrated in the Figures, the pawl-orientation means can be provided by way of a handle  88  associated with the outer end  82 B of the pawl member  82 . However, this is merely one example, and those skilled in the art of the invention will understand that various other pawl-orientation means could be used without departing from the concept or scope of the invention. 
   Assembly of the preferred embodiment of the invention  10  may now be readily understood having reference to  FIGS. 5 and 6  in particular. The levers  70  are positioned between the primary ratchet wheels  30  so as to be rotatable around the outer surface  25  of the trunnion  22 , with the pawl member  82  of each lever  70  aligned so as to be able to engage the cogs  32  of one of the primary ratchet wheels  30  as well as the cogs  42  of the associated auxiliary ratchet wheel  40  (or other form of bridging element) as the case may be. In the illustrated embodiment, the required alignment of the pawl members  82  is accomplished by providing rub plates  26  on the trunnion  22  and providing a guide member (typically a flat plate)  76  in association with each hub  74 , with these components being configured and positioned such that the pawl members  82  will be properly aligned when the levers  70  are rotated with their guide members  76  closely adjacent their corresponding rub plates  26 . Persons skilled in the art of the invention will readily appreciate that other suitable alignment means may be devised without departing from the scope of the invention. 
   In the illustrated embodiment, the levers  70  cannot be readily removed from the ratchet wheel assembly  20  because of the geometry of the assembly, and in particular the fact that the hubs  74  in the illustrated embodiment closely enshroud their corresponding primary ratchet wheels  30 . In this arrangement, the invention  10  has no loose components that might be inadvertently misplaced. More significantly, perhaps, this arrangement prevents the levers  70  from flying loosely away from the ratchet wheel assembly in the event of an unexpected unwinding of a torsion spring being tensioned with the apparatus. However, there may be circumstances in which it will be desirable for the levers  70  to be removable, which can be easily accomplished by modifying the configuration of the hubs  74  (e.g., by making them essentially semi-circular or smaller) so that they can be mounted directly over their corresponding primary ratchet wheels  30 . 
   The operation of the present invention may now be easily understood having particular reference to  FIGS. 5 and 6 . With the bridging elements in the open position, the apparatus of the invention  10  is coaxially mounted over a torsion spring shaft  90  adjacent a spring cone  94  on the side opposite the torsion spring  92  anchored thereto. The apparatus is then moved laterally as required such that the spring cone engagement means  60  can engage the spring cone  94 . The bridging elements are moved to their engaged positions and locked; as preferred or convenient, this step may be taken either before or after engagement of the spring cone  94 . With the spring cone  94  free to rotate about the shaft  90 , with the pawl members  82  oriented as desired, and with the pawl-engaging surfaces  83 A aligned to engage cogs  32  and/or  42  as the case may be, the two levers  70  may be operated with one lever  70  being used to restrain the spring  92  from unwinding while the other lever  70  is operated in typical ratchet fashion so as to rotate the spring cone engaging means  60 , in turn tensioning (or relaxing the tension in) the spring  92 , depending on the direction of rotation. When the spring  92  has reached the desired level of tension, the spring cone  94  may be anchored to the shaft  90  (typically by means of set screws  98  as shown in  FIG. 5 ), whereupon the spring cone engaging means  60  may be disengaged, the bridging elements may be moved to the open position, and the apparatus may be removed from the shaft  90 . 
   It will be readily appreciated by those skilled in the art that various modifications of the present invention may be devised without departing from the essential concept of the invention, and all such modifications are intended to be included in the scope of the claims appended hereto. 
   In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following that word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one such element.