A gate operator in a first configuration opens and closes a gate that swings about an upstanding pivotal axis. In a second configuration the gate operator opens and closes a gate that extends and retracts along a straight line. A motor-driven wheel extends from the bottom of an open-bottomed enclosure and is perpendicular to the gate in the first configuration and parallel to the gate in the second configuration. The wheel is driven by a reversible DC motor. Turning a jack screw in a first direction increases the bias on an adjustable compression spring so that the weight of the gate is transferred to the wheel and rotation of the jack screw in an opposite direction shifts weight from the wheel to the gate.

CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of the inventor's U.S. Ser. No. 10/402,656, filed on Mar. 31, 2003 and abandoned on Sep. 20, 2004. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates, generally, to devices that open and close gates and other vertical panel closures. More particularly, it relates to a gate operator that operates gates of differing types. 
     2. Description of the Prior Art 
     Gates are commonly either pivotally mounted so that they swing open and closed about a vertical pivotal axis or longitudinally mounted so that they extend or withdraw along a straight line. A prior art operator for a swing gate is commonly different than the operator for a longitudinally-opening gate. In a property having both types of gates, the maintenance crew must store spare parts and learn how to maintain both types of gates. It would therefore be advantageous if one universal operator could be provided to operate both a swing gate and a longitudinally-mounted gate. 
     Many gates are mounted over an irregular surface that may comprise rough and uneven terrain such as a transition from a paved surface to a lawn, or over the ruts of a dirt road. Prior art operators have commonly avoided this problem by either providing a smooth flat surface adjacent the gate, or, in the case of a longitudinal gate or sliding closure, by providing tracks to carry the moving gate panel. 
     There is a clear need, then, for a gate operator of rugged construction that requires little maintenance, and for a gate operator designed so that the weight of the gate can easily be shifted onto the gate operator, or vice versa by means permitting the gate operator to traverse an irregular surface. 
     SUMMARY OF THE INVENTION 
     A preferred apparatus for opening and closing a gate of either the swinging or longitudinally mounted version comprises a wheel mounted within an enclosure for rotation about a horizontal axis. If the gate is of the type that swings about an upstanding pivotal axis, the enclosure of the preferred operator is attached to the gate so that the wheel is mounted for rotation in a plane substantially perpendicular to a plane of the gate. The same sort of structure may be employed to open and close a longitudinally-extending gate. The only difference is that the wheel is mounted for rotation in a plane parallel to the plane of the gate in that configuration. That is, the enclosure is simply rotated ninety degrees (90°) from its swinging gate orientation. Thus, one aspect of the invention is that it provides a universal gate operator for selectively operating either a swing gate or a longitudinally-opening gate. 
     As is known in the art of closure operators, various combinations of power sources, drive motors and speed reducers may be used to turn the wheel. In a preferred embodiment the drive train comprises a rechargeable battery; a reversible electric motor; a two-stage speed reducer comprising both a belt-and-pulley portion and a chain-driven portion; and a controller operable responsive to an input from a remote command device. Those skilled in the art will appreciate that some of these features can be dispensed with and, moreover, that there are many known equivalents for various of these components. For example, the preferred speed reducer could be replaced with one comprising a gear train, or with one having two belt-and-pulley or two drive chain portions. 
     The preferred apparatus also comprises a spring-supported lifting mechanism for shifting weight from the gate to the wheel and for shifting weight from the wheel to the gate. Thus, the invention provides a gate operator that does not add any weight to the gate and that can be adjusted to support at least some of the weight of a gate. In preferred embodiments the lifting mechanism is interposed between the wheel and the enclosure and comprises an elongated jack screw set in a vertical orientation. In some preferred embodiments an axis of the jack screw is directly above, and aligned to intersect, the axle upon which the wheel turns. In other embodiments, intended primarily for use with swinging gates, the axis of the jack screw may be positioned further from the enclosure wall that is attached to the gate than is the axle in order to null out any twisting effect on the gate. 
     Regardless of the choice of jack screw axis position, a coil spring is preferably disposed between a drive deck to which the axle is journaled and a jack screw-follower slidably and non-rotatably received within a vertically disposed tubular member fixedly attached to the drive deck. This arrangement may comprise the depicted combination of a square nut slidably movable within a tube having a square cross-section, hereinafter referred to a “square tube”. This spring biases the wheel into contact with a supporting surface and thus functions to allow the gate operator to move the gate over an irregular surface. 
     Accordingly, rotation of the elongate screw in a first direction causes the screw follower to travel downwardly along the extent of the elongate screw, thereby compressing the spring. By increasing the compressive force on the spring, an upward reactive force is imposed on the elongate screw, which in turn is transmitted to the housing and thereby to the gate. Rotation of the elongate screw in the opposite direction causes the screw-follower to travel upwardly along the extent of the elongate screw, thereby decompressing the spring. The closure is displaced upwardly when the elongate screw is rotated in the first direction, thereby transferring weight from the gate to the wheel. The closure is displaced downwardly when the elongate screw is rotated in the second direction, thereby transferring weight from the wheel to the gate. The jack screw may be turned far enough in the second direction to entirely lift the wheel off the ground, thus allowing the closure to be operated manually when the operator fails due to a low battery state or to some other operational condition. 
     Although it is believed that the foregoing rather broad recital of features and technical advantages may be of use to one who is skilled in the art and who wishes to learn how to practice the invention, it will be recognized that the foregoing recital is not intended to list all of the features and advantages. Those skilled in the art will appreciate that they may readily use both the underlying ideas and the specific embodiments disclosed herein as a basis for designing other arrangements for carrying out the same purposes of the present invention. Those skilled in the art will realize that such equivalent constructions are within the spirit and scope of the invention in its broadest form. Moreover, it may be noted that various embodiments of the invention may provide various combinations of the hereinbefore recited features and advantages of the invention, and that less than all of the recited features and advantages may be provided by some embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a perspective view depicting an operator of the invention connected to a swing gate where the swing gate is in a closed configuration; 
         FIG. 2  is a perspective view of the operator depicted in  FIG. 1  when the swing gate is in its open configuration; 
         FIG. 3  is a perspective view depicting the operator connected to a longitudinally-opening gate where the longitudinally-opening gate is in a closed configuration; 
         FIG. 4  is a largely schematic, broken away view depicting the interior of a preferred operator of the invention; 
         FIG. 5  is a perspective view of the parts depicted in  FIG. 4 , the view comprising additional parts broken away to reveal further structural details of the operator; 
         FIG. 6  is a sectional view depicting a mechanism for shifting the weight of a gate onto the gate operator. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In  FIG. 1  the reference numeral  10  denotes an illustrative embodiment of a gate operator of the present invention being used to operate a swinging gate  12  pivotally secured in a well-known way to a post  14  which is mounted in a post hole in a conventional manner. In this arrangement a pair of hinges  16   a ,  16   b  is secured to the post  14  at opposite ends thereof and a mating pair of hinges  18   a ,  18   b  is secured to a frame  20  of the swing gate  12 . A preferred weather-proof enclosure  22  is secured to the swing gate by any suitable clamping means. The method of such mounting is adapted to the particular structure of the swing gate to which the enclosure  22  is to be mounted. 
     As best understood in connection with  FIG. 2 , for a swing gate of the depicted type, a pair of links  24   a ,  24   b  is positioned behind upright frame members, collectively denoted as  26 , and these links are secured to the enclosure  22  by suitable clamping members. Those skilled in the art will recognize that many sorts of fixture hardware can be used to attach the operator to a gate. In the drawing these clamping members are depicted as bolts, collectively denoted as  28 , that engage threaded portions  29  of the housing  22 . Other attachment approaches include, but are not limited to brackets or housing portions directly welded to the gate. 
     The preferred weather-proof enclosure  22  is a generally rectangular, open-bottomed structure as depicted comprising a top closure member  30 , walls  32 , and a wheel  34 . In the embodiment of  FIGS. 1 and 2 , the wheel  34  is mounted for rotation about an axle  35  parallel to the plane of the gate  12 . Thus, the wheel  34  rotates in a plane perpendicular to the plane of the gate  12 . Counterclockwise rotation of the wheel  34 , when in the position depicted in  FIG. 1 , causes the gate  12  to swing about the post  14  toward the  FIG. 2  position, while clockwise rotation of the wheel  34 , when in the  FIG. 2  position, causes the gate  12  to swing about the post  14  toward the  FIG. 1  position as the wheel moves along an arc indicated by the curved double-headed arrow  36  in  FIG. 2 . 
     In the longitudinally-opening gate embodiment depicted in  FIG. 3 , the operator  10  is rotated ninety degrees about a vertical axis from swing gate mounting orientation depicted in  FIGS. 1 and 2 . This change in orientation is preferably provided for by having at least two mutually perpendicular clamping member receivers, such as the threaded fittings  29  for receiving clamping members, which may be the same links  24   a,b , and bolts  28 , used in the first-described mounting in substantially the same way as was done for the swing gate  12 . In the longitudinal-gate setting, the axle  35  upon which the wheel  34  is mounted is perpendicular to the plane of the longitudinally-opening gate  38  so that the wheel  34  rotates in a plane parallel to the plane of the gate. Counterclockwise rotation of the wheel  34  causes travel to the left in the depiction of  FIG. 3 , while clockwise rotation of the wheel causes travel to the right. This back-and-forth motion is indicated with the straight double-headed directional arrow  40  in  FIG. 3 . 
     Some of the preferred components housed within the weather-resistant enclosure  22  are depicted in the cut-away view of  FIG. 4 . A horizontally disposed drive deck  42  supports a battery  44 , a controller  46  for selecting the direction of motion, and a battery charger  48 . The drive deck  42  may be mounted in a cantilevered relation to the vertically disposed support plate  50  which, in turn is movably mounted for reciprocation in a vertical plane by any of a variety of known movable attachment arrangements which may comprise a pair of laterally spaced apart guide rails of the sort commonly used with large drawers, or upper  58   a ,  58   b  and lower  58   c ,  58   d  pairs of laterally spaced apart barn door trolleys housed within upstanding channel members  60   a ,  60   b  having respective slots (e.g.,  61   a ) for receiving the trolleys. Although the drawing depicts the vertical reciprocation mechanism disposed at one end of the drive deck  42 , those skilled in the arts will recognize that channels and rollers, or other suitable vertical reciprocation mechanisms, may be located elsewhere. 
     The preferred drive deck  42  is cut away in  FIG. 5  so that the parts housed therewithin may be seen. A reversible DC motor  62  has a power take-off shaft  64  to which is connected a belt  66  that wraps around a pulley  68 . The diameter of the pulley  68  is greater than the diameter of the power take-off shaft  64  so that the pulley rotates slower than the power take-off shaft by a ratio equal to the ratio of diameters. The pulley  68  is mounted for rotation about a hub  70  which is engaged by a sprocket chain  72  which also engages a second hub  74  which is mounted on the axle  35  of the wheel  34 . The diameter of the second hub  74  is greater than the diameter of the first hub  70  so that the second hub  74  rotates slower than does the first hub  70  by a ratio equal to the ratio of diameters. This particular speed reducer arrangement is not critical to the invention and those of ordinary skill in the mechanical arts may substitute other speed reducing methods without departing from the scope of this invention. For example, a gear-based speed reducer could also be employed. 
     In this way, the direction of rotation of wheel  34  is determined by the direction of operation of reversible motor  62 . 
     Flanges  76   a ,  76   b  extend from a bottom wall  42   a  of the drive deck  42  and their respective lower ends engage the axle  35  upon which wheel  34  is mounted. 
     As perhaps best understood in connection with the schematic depiction of  FIG. 6 , a spring suspension  53  comprising an adjustable compression spring  77  is preferably interposed between the wheel  34  and the enclosure  22  in order to allow the operator  10  to move a gate over uneven terrain. A preferred suspension  53  may comprise an elongate, partially externally threaded jack screw  80  having an unthreaded upper end thrust against and journaled for rotation within an upper closure member  30  of the enclosure  22  at a fixed axial position along the jack screw. This may be simply done using the arrangement shown in  FIG. 6  in which a lower washer  82   b  is welded to the upper portion of the jack screw  80  to rotate conjointly with it, leaving an upper end portion of the jack screw to stick up through an aperture in the top closure member  30 , which is fixedly attached to the walls  32  of the enclosure  22  by bolts, weldments, or other suitable attachment means (not shown). Those skilled in the art will recognize that the provision of an enclosure top  30  initially separate from the walls  32  is a matter of convenience and that one could choose to form the entire enclosure  22  from a single piece of material. An upper washer  82   a  can be used to cover the hole and a suitable crank handle  83  can be attached to the upper end of the screw. 
     The lower, threaded end of the jack screw  80  engages a screw-follower  81  arranged to press on an upper end of a coil spring  77 . In the depicted arrangement, the screw-follower  81  comprises a square nut housed within a square tube spring housing  78  fixedly attached in an upstanding relation to the drive deck  42 . Those skilled in the mechanical arts will recognize that there are many other functionally equivalent arrangements for providing an adjustably loaded suspension. For example, a different screw-follower arrangement, such as a nut having a lobe or ear projecting outwardly through a slot in a longitudinally slotted tube could be directly substituted. Other more extensive changes involving different sorts of springs and loading mechanisms will also come to the skilled artisan's mind. 
     In operating the suspension depicted in  FIG. 6 , turning the hand wheel  83  in a first direction rotates the screw  80  so as to drive the square nut  81  downward to compress the adjustable compression spring  77  against a lower spring seat  79 , thereby applying a downwardly directed force to the drive deck  42  and exerting an increased load on the drive wheel  34 . Because the wheel  34  is ground supported and cannot move downward, the support plate  50 , barn door trolleys  58 , and enclosure  22  are therefore displaced upward. Such upward displacement transfers weight from an operated gate to the drive wheel. 
     To reduce the weight on the wheel  34  and to transfer more load to the gate, the screw  80  is rotated in the opposite direction. When this happens, the screw-follower  81  travels upward, allowing expansion of the adjustable compression spring  77 , which thereby reduces the amount of bias exerted by the adjustable compression spring  77 , and allows the enclosure  22  to be lowered. Continuing to rotate the jack screw in this direction after the screw-follower  81  contacts an upper travel stop  84  will raise the wheel clear of the ground. 
     The depicted structure, which has the suspension  53  disposed immediately above the axle, is highly versatile and can be used on both kinds of common gates. Switching it from one type of gate to another is a very simple undertaking. An alternate embodiment of the invention, intended primarily for use with gates of the swinging variety, uses a vertically oriented suspension  53   a , depicted in phantom in  FIG. 6 , more distal from that wall of the enclosure  30  that is clamped to the gate  12  than is the axle  35 . This alternate embodiment can null out any twisting effects imposed on the gate by the operator. 
     Thus, the objects set forth above, and those made apparent from the foregoing description, are efficiently attained. Since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween. 
     Now that the invention has been described,