Abstract:
A seesaw includes a manually rotatable actuator for adjusting the balance of the seesaw to accommodate a weight differential between two riders. After adjusting the seesaw, the actuator automatically locks the adjustment mechanism in place. A rack-and-pinion assembly provides fine adjustment, and a protective cover avoids creating a pinching hazard.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The subject invention generally pertains to playground equipment and more specifically to a seesaw. 
   2. Description of Related Art 
   A seesaw is a well-known piece of playground equipment that comprises a pivotal beam balanced on a fulcrum. Two children typically sit at opposite ends of the beam to teeter up and down. 
   When the two children are of equal weight, they can sit the same distance away from the fulcrum, and the seesaw will be balanced. If there is a weight difference between the children, the seesaw may be imbalanced. 
   To compensate for such an imbalance, some seesaws include a feature for adjusting the location of the fulcrum relative to the beam, thereby adjusting the relative distance that each child sits away from the fulcrum. U.S. Pat. No. 2,431,138, for example, discloses a seesaw whose balance can be adjusted by selectively setting the beam upon a fulcrum at different points along the beam. Another seesaw, disclosed in U.S. Pat. No. 5,951,406, is balanced by way of an adjustable telescopic beam. Although such adjustable seesaws are effective, they do have their drawbacks. 
   For the seesaw of the &#39;138 patent, the adjustment mechanism appears to pose a finger pinching hazard as the plank needs to be lifted and set back down in order to adjust its balance. Moreover, two people may be needed at opposite ends of the plank to lift and reposition it. If just one person adjusts the plank, that person would likely lift the plank near its center of gravity, but that is where the potential pinching hazard exists. In operation, if a child “pushes off” especially hard, the child might dislodge the plank from its adjusted position. 
   For the seesaw of the &#39;406 patent, shot pins help hold the telescopic beam at its adjusted position. If someone fails to install those pins, the seats could unexpectedly slide all the way in or fall out entirely. This could suddenly create a drastic and dangerous imbalance. 
   Consequently, a need exists for a seesaw that is easier and safer to adjust. 
   SUMMARY OF THE INVENTION 
   To provide a seesaw that is easier and safer to adjust, an object of the invention to adjust the balance of a seesaw beam by using a rack-and-pinion assembly. 
   Another object of some embodiments is to adjust the balance of a seesaw beam without having to lift the beam off its fulcrum. 
   Another object of some embodiments is to provide a single dual-purpose mechanism that provides a seesaw with both an adjustment feature and a locking feature 
   Another object of some embodiments is to provide an adjustable seesaw with a locking mechanism that automatically locks the beam in position after it has been adjusted. 
   Another object of some embodiments is to provide a seesaw with an adjustment mechanism whose rotational movement adjusts the seesaw&#39;s balance and whose axial translation holds the beam at its adjusted position. 
   Another object of some embodiments is to provide a seesaw with a locking mechanism that selectively engages and disengages a portion a track follower to selectively inhibit and permit the adjustment of the seesaw. 
   Another object of some embodiments is to provide an adjustable seesaw with a protective cover that permits the adjustment of the seesaw yet avoids creating a pinching hazard. 
   Another object of some embodiments is to provide a seesaw with an adjustment mechanism that can easily be adjusted and subsequently locked with a simple hand motion. 
   One or more of these and/or other objects of the invention are provided by a seesaw that includes a rack-and-pinion assembly for adjusting the balance of the seesaw. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a side view of a seesaw according to one embodiment of the invention. 
       FIG. 2  is a cross-sectional view taken along line  2 — 2  of  FIG. 1 , wherein the actuator is in a lock position. 
       FIG. 3  is a cross-sectional view similar to  FIG. 2  but showing the actuator in an unlock position. 
       FIG. 4  is a bottom view of a central section of the seesaw, wherein the actuator is in the lock position and the protective cover is omitted to show components that would otherwise be hidden. 
       FIG. 5  is a bottom view similar to  FIG. 4  but showing the actuator in the unlock position. 
       FIG. 6  is a cross-sectional side view of the seesaw at one adjusted position. 
       FIG. 7  is a cross-sectional side view of the seesaw at another adjusted position. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A seesaw  10  shown in  FIGS. 1–7  includes a beam  12 , such as a plank, mounted for pivotal motion upon a fulcrum. The fulcrum comprises a base  14  with a pivotal coupling  16  that pivotally couples beam  12  to base  14  so that the beam can pivot about a pivotal axis  18 . To carry two riders, beam  12  includes a first seat  20  with a first handle  22  for supporting a first person  24  and a second seat  26  with a second handle  28  for supporting a second person  30 . 
   To accommodate a weight differential of the riders, seesaw  10  can be adjusted so that person  24  can sit a first adjustable distance  32  away from axis  18 , and person  30  can sit a second adjustable distance  34  away from axis  18 . This is done by installing a track follower  36  that can slide along a track  38 , which is attached to beam  12 . Track follower  36  includes one or more bearing blocks  40  with a first bore  42  that supports a shaft  44  and defines pivotal axis  18 . Shaft  44  helps pivotally couple beam  12  to base  14  such that the position of beam  12  relative to axis  18  can be varied by sliding track follower  36  along track  38 . Actually track  38  is what moves, and track follower  36  remains generally stationary. 
   Bearing block  40  also includes a second bore  46  within which a rotatable actuator  48  rotates about its longitudinal centerline  50 . Actuator  48  is coupled to a rack-and-pinion assembly  52 , which in turn is coupled to beam  12  and base  14 . Rotatable actuator  48  is what controls rack-and-pinion assembly  52 . 
   In a currently preferred embodiment, rack-and-pinion  52  includes a gear rack  54  coupled to beam  12  and a pinion gear  56  coupled to and rotatable with actuator  48 . Rack  54  is any elongate member with a series of gear teeth, protrusions, discontinuities, elements, holes, voids, detents, etc. Pinion  56  is any rotatable member having a mating series of gear teeth, protrusions, discontinuities, elements, holes, voids, detents, etc. For the illustrated embodiment, pinion  56  has a series of gear teeth  58  that mesh with a series of gear teeth  60  on rack  54 . Rack  54 , track  38  and beam  12  are substantially parallel to each other. 
   When rotational actuator  48  is in the position shown in  FIGS. 3 and 5 , actuator  48  can be manually rotated to rotate pinion  56 . Arrow  62  represents the step of manually rotating pinion  56 . With pinion  56  being engaged with rack  54 , this forces relative sliding motion between track  38  and track follower  36 , whereby track  38 , rack  54  and beam  12  translate as a unit relative to track follower  36 , shaft  44  and pivotal axis  18 . As a result, rotating actuator  48  varies the first adjustable distance  32  and the second adjustable distance  34 , thereby providing a means for balancing the seesaw. The rotational direction of actuator  48  determines in which direction beam  12  shifts relative to pivotal axis  18 . 
   After balancing seesaw  10 , a locking mechanism  64  can be used to help hold beam  12  at its properly adjusted position. Although the structural design of locking mechanism  64  can vary widely, in a currently preferred embodiment, mechanism  64  is coupled to or is part of rotatable actuator  48 . Locking mechanism  64 , for instance, may comprise a locking portion  66  that is selectively movable between a lock position ( FIGS. 3 and 5 ) and an unlock position ( FIGS. 2 and 4 ) by sliding actuator  48  along centerline  50 . In this example, locking portion  66  is one or more of the pinion&#39;s gear teeth  58 , which in the lock position engages a tab  68  on track follower  36  and disengages tab  68  in the unlock position. In the lock position, tab  68  inhibits the rotation of pinion  56  and thus inhibits the translation of rack  54  and beam  12 . In the unlock position, pinion  56  is free to rotate within an opening  70  of track follower  36  to adjust the position of rack  54  and beam  12 . A spring  72  can be used to urge locking mechanism  64  to the normally locked position, and pins  74  or some other type of stopping element can be used to limit the axial travel distance of actuator  48 . 
   To avoid creating a pinching hazard with rack-and-pinion assembly  52  or between track  38  and track follower  36 , a protective cover  76  can be attached to track follower  36 . 
   Although the invention is described with reference to a preferred embodiment, it should be appreciated by those of ordinary skill in the art that various modifications are well within the scope of the invention. Many of the various component parts, for instance, are shown assembled by way of threaded fasteners; however, the parts could instead be assembled or manufactured by other means. Bearing blocks  40 , for example, could be press-fitted into a mating hole or cavity in track follower  36  as opposed to be held together by screws. Or, various assembled components could be combined as a unitary piece. Therefore, the scope of the invention is to be determined by reference to the following claims.