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This application claim benefit to provisional application No. 60/148,556 Aug. 12, 1999. 
    
    
     FIELD 
     The present invention applies to fence and barrier systems; more particularly, the present invention applies to gate or door opening systems typically used with fences or barriers. 
     BACKGROUND 
     For as long as fences or barriers have been used to enclose spaces, there has been a need to include in the fence or barrier system a portal for gaining access to the enclosed space. For security and for many other reasons, the portal to which access to the enclosed space may be gained typically includes a closure. Such portal closures may be opened in a variety of different directions to include both horizontal (parallel to the earth&#39;s surface) and vertical (perpendicular to the earth&#39;s surface). The present invention pertains to portal closures whose movement is substantially horizontal, such horizontal movement being along either a linear or an arcuate path with respect to the fence or barrier system. 
     Numerous systems have been used over the years to open gates or doors. One of the most common systems is a chain-drive system wherein the teeth on a rotating, stationary mounted, sprocket are used to engage the openings in a chain, which chain is mounted to a sliding gate. Such chain drive systems are slow, cumbersome, and prone to breakage. Such systems are also subject to the effects of weather; particularly the destructive effects of repeated exposure to moisture. Gates which open on an arcuate path typically use long arms—which long arms are prone to breakage. 
     There is therefore a need in the art to provide a system for opening a gate which will be fast operating, easy to use, and low in maintenance. 
     SUMMARY 
     A fast operating, easy to use, and relatively maintenance free system and method for moving a horizontally movable gate or door includes a stationary mounted linear induction motor or a magnetic stepper motor. A reaction piece, either a reaction plate or a reaction rod, is caused to move by the linear induction motor or the magnetic stepper motor. The movement of the reaction piece, which is mounted to the gate or door, is then used to control the opening and closing of the gate or door. When it is desired to open the gate or door, the linear induction motor is activated. The activation of the linear induction motor causes the reaction plate or reaction rod to move with respect to the position the linear induction motor. Because the reaction plate or reaction rod is mounted to the gate or door, the movement of the reaction plate or reaction rod causes the gate or door to move to an open position so that access to an enclosed space is allowed. Alternatively, the movement of the gate or door may be to a closed position so that the opening to the enclosed space is blocked. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     A better understanding of the system and method for moving a horizontally movable portal closure of the present invention will be had by reference to the drawing figures wherein: 
     FIG. 1 is a schematic front elevational view of the system of the present invention on a linearly horizontally moving portal closure; 
     FIG. 2 is a schematic front-elevational view of the system of the present invention on an arcuately horizontally movable portal closure; and 
     FIG. 3 is a schematic diagram of the electrical connection of the various parts of the system. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     As may be seen by reference to FIG.  1  and FIG. 2, the system and method of the present invention  10 ,  110  is described with reference to the opening and closing of a gate  20 ,  120  in a fence  100 . Those of ordinary skill in the art will understand that the present invention has applicability to any type of portal closure whose movement is substantially horizontal—either parallel or at an angle to the fence  100 . The portal may be formed in a gate, a wall, or any type of barrier which encloses a space. 
     In FIG. 1, the system and method of the present invention  10  is shown with a linear induction motor system  30  of the type that is frequently used on amusement park rides, particularly roller coasters. In a roller coaster, such linear induction motor systems initiate the motion of the string of passenger cars up an incline to begin the coasting motion of the ride. Specifically, the linear induction motor systems include a reaction plate on the passenger car. The reaction plate is constructed and arranged to be moved by a series of linear induction motors mounted between the rails on which the passenger cars roll. The reaction plates used in linear induction motor systems may be made of steel covered with a non-magnetic metal such as aluminum or copper, or they may be made from a solid non-magnetic metal such as aluminum or copper. Because of the magnetic fields applied by the linear induction motor to the reaction plate, the reaction plate is caused to be accelerated from a rest condition to a predetermined velocity past the linear induction motor. 
     In FIG. 1, the linear induction motor  35  imparts motion to the reaction plate  40  which causes the gate  20  to slide horizontally between open and closed positions. In FIG. 2, the linear induction motor  135  imparts motion to the reaction rod  145  which causes the gate  120  to swing on hinges  125  between open and closed positions. Alternatively, a magnetic stepper motor may be used instead of a linear induction motor. When a magnetic stepper motor is used the reaction plate may include a plurality of steel ridges formed on a steel plate. The steel ridges on the steel plate electrically interact with the permanent magnets within the magnetic stepper motor. When a reaction rod is used, the steel rod may include a plurality of steel rings. The steel rings electrically interact with the permanent magnets in the stepper motor. 
     As is commonly experienced with linear induction motors  35 ,  135 , the acceleration of the reaction plate or reaction rod past the linear induction motor  35  or through the linear induction motor  135  can be quite rapid. Such rapid acceleration is particularly desirable in a situation where it is necessary to open and close a portal closure in a minimum amount of time—as in prisons or incarceration facilities. 
     When it is desired to move the portal closure  20 ,  120  from a first closed or rest position, it is necessary to accelerate the portal closure  20 ,  120  to a predetermined linear or arcuate speed. As the portal closure  20 ,  120  nears the end of its travel path, it is then necessary to decelerate the portal closure  20 ,  120  from its linear or arcuate speed to a second nonmoving or rest position. Such acceleration and deceleration of the portal closure  20 ,  120  is easily governed by controlling the force and direction imparted on the reaction plate  40  or reaction rod  145  by the linear induction motor or the magnetic stepper motor  35 ,  135 . For particularly heavy gates a second linear induction motor or magnetic stepper motor may be placed alongside the first motor on the same side of the reaction plate or reaction rod or on the opposite side of the reaction plate or reaction rod. 
     While it is possible to program into the electronics  60  that control the linear induction motor or the magnetic stepper motor  35 ,  135 , the amount of time needed to accelerate the portal closure  20 ,  120  to its desired translational speed, then move the portal closure  20 ,  120  at this desired translational speed for a predetermined period of time or travel distance, and then decelerate the movement of the portal closure  20 ,  120  at the end at the end of its travel path according to a selected time or travel distance, some applications may require more precise control of the position of the portal closure  20 ,  120 . More precise control of the movement of the portal closure  20 ,  120  may be obtained by the use of a position sensing system  50  (FIG. 3) which provides a signal indicative of the position of the portal closure  20  along its travel path. Such position sensors may be inductive, rotary, magnetic, or photoelectric. Such inductive, rotary, magnetic, or photoelectric position sensors  50  are well known to those of ordinary skill in the art. 
     As shown in FIG. 3, the signals obtained from the position sensors  50  may be electronically transmitted or coupled to an electronic control means  60 . The electronic control means  60  governs the force applied by the induction motor or the magnetic stepper motor  35 ,  135  on the reaction plate  45  or the reaction rod  145  so that the termination of the period of acceleration of the travel of the portal closure  20 ,  120  to the translational speed may be governed by the actual position of the portal closure  20 ,  120 , and the initiation of the deceleration of the motion of the portal closure  20 ,  120  to the second or rest position may also be governed by the sensed position of the portal closure  20 ,  120 . 
     As shown in FIG. 1, the portal closure  20 , may include one or more pressure sensitive switches  70  on its ends to cut off power to the linear induction motor  35  when the position of the portal closure  20  matches the first or second rest position of the portal closure or when an object appears in the path of travel of the moving portal closure  20 . Power may be supplied to the system from commercially available sources of electrical energy, or a solar power unit may be used to provide the necessary electrical energy to operate the system. A similar array of pressure sensitive switches may also be used on the embodiment shown in FIG.  2 . 
     As shown in FIG. 2, the alternate embodiment of the system  110  of the present invention may be constructed so that it is operable with an arcuately pivotable gate or portal closure. Specifically, a reaction rod  140  is caused to pass through an induction motor or a magnetic stepper motor  135 . This will cause the portal closure  120  to swing open or closed, pivoting on a pair of hinges  125 . 
     As shown in FIG. 1, the construction of the system and method for moving a movable portal closure of the present invention horizontally includes simply mounting the reaction plate  40  on a gate  20  which is movable along a horizontal path. This motion is typically governed by a wheel and track assembly, guideways or other systems well known to those of ordinary skill in the art. 
     The linear induction motor or the magnetic stepper motor is located in close proximity to the travel path of the moving portal closure. Typically, the linear induction motor or the magnetic stepper motor is mounted in a stationary manner near the edge of the portal which is formed in the enclosure surrounding the space through which access through the portal is obtained. 
     While the foregoing disclosure enables those of ordinary skill in the art to make and use the disclosed invention, it will be understood that the foregoing disclosure will also enable those of ordinary skill in the art to make similar embodiments which include the principles of the disclosed invention. Such similar embodiments shall be included within the scope of the appended claims.

Summary:
A system and method for moving a horizontally sliding portal closure includes a linear induction or a magnetic stepper motor and a reaction piece. The reaction piece is attached to the portal closure such that activation of the stationary mounted linear induction or magnetic stepper motor causes movement of the reaction piece which, in turn, opens or closes the portal closure.