Abstract:
Disclosed is an apparatus for a barrier gate designed to control vehicular travel through a passageway. The invention disclosed employs a barrier arm, a housing, a motor and transmission, a rotary encoder, and a torque limiter assembly. The torque limiter assembly comprises a hub, spindle, brake disk, rotor, and a gland nut. The torque limiter assembly is mounted to the motor and transmission as well as connected to the barrier arm. The torque limiter assembly provides sufficient friction to rotate the barrier arm and also protects the internal gears and linkages of the transmission and motor from costly repair/replacement by preventing any unwanted rotation. In the event an outside force rotates the barrier arm, the rotary encoder in cooperation with a controller instantly recognizes the position of the barrier arm and further acts as a limit switch to send a signal to the motor to stop when the barrier arm is in place.

Description:
FIELD OF THE INVENTION 
     This invention relates to barrier gates for roadways. In particular, this invention relates to an apparatus and method for preventing damage to the internal gears that move the barrier gate through the use of a torque limiter connected between the control arm of the gate and the transmission of the motor. 
     BACKGROUND OF THE INVENTION 
     Barrier gates that incorporate the use of a pivoting barrier arm are in widespread use. Typical uses of such devices include high occupancy freeway lane entrances, controlled parking lot entries and exits, toll booth lanes, airport entries and exits, railroad crossings, and drawbridges. Most often designs include some sort of actuator to initiate movement of the barrier arm such as a remote control, weight sensitive sensor, or an electronic card reader. Once a signal is received, a motor drives the internal mechanisms to rotate the barrier arm into the open or closed position. The motor and the transmission that convert the rotational motion into the proper orientation and speed are intricate components of the barrier gate system and are costly to repair or replace. Additionally the down time associated with the repair of a damaged motor or transmission prevents the use of the particular lane or passageway causing added expense and possibly traffic congestion. A motor or transmission can be easily damaged if a force from an unexpected direction occurs, moving the barrier. Such a force generally causes the internal gears and linkages of the motor and transmission to be damaged. 
     Prior art barrier gates have addressed this need in various ways. One way is to design the barrier arm itself to be of a breakaway nature. If an unexpected force is applied to the barrier arm, the barrier arm itself is designed to fail before the components are damaged. While this solution does indeed protect the internal components, the barrier arm itself requires replacement often and the barrier gate ceases to function as a traffic controlling passageway while the barrier arm is missing. 
     Other prior art barrier gates have designed the internal gears and mechanisms to withstand great pressure before failing by reinforcing them with high strength materials. Typical weather forces or the unwanted manual manipulation of the barrier arm will not be sufficient to move the barrier arm. A design such as this is costly and not marketable but in only the most heavy duty of applications. 
     Other traffic control devices known in the art such as U.S. Pat. No. 4,101,235 to Nelson employ an elongate series of tire engaging spikes extending transverse to an entering or exit lane of a parking lot or other controlled area. The spikes are carried by a shaft rotatably supported below the surface of the lane. The device discloses a drive means including a reversible electric motor to rotate the shaft between a normal and an actuated position. The device further includes an actuating switch means to cause the motor to rotate the shaft between a normal and an actuated position. Since there is not barrier arm available to lift, the gears of the motor are not in jeopardy from outside forces, but this type of warning lane system can cause expensive damage to the user&#39;s vehicle and subject the operator of the system to disgruntled users and possible litigation. 
     U.S. Pat. No. 4,227,344 to Poppke discloses an automatic parking lot gate with four-way flex connector. The flexible connector includes a first connection plate connected to the arm drive mechanism, a second connection plate connected to the gate arm, and first and second coil springs connected between the first and second connection plates. The coil springs are positioned essentially parallel to one another in a vertical plane. When exposed to outside forces such as a car, the barrier gate will continually flex back towards the starting point and continually apply pressure to the vehicle attempting to gain access. The resilient pressure of the barrier arm can cause damage to the vehicle in the form of dents and abrasions in the paint. 
     SUMMARY OF INVENTION 
     An apparatus for controlling vehicular travel through roadway passageways including a rotationally movable barrier arm is disclosed. The present invention addresses the need to safeguard the internal linkages and gears of the motor and transmission of the barrier gate from unwanted rotation due to outside forces and thus avoiding costly repairs and downtime. The barrier gate disclosed includes a barrier arm pivotally attached to a housing. The housing is anchored to the ground and includes a motor, a transmission, a torque limiter assembly, and a rotary encoder. The motor and transmission are pivotally connected to a horizontal axis torque limiter assembly. The torque limiter assembly is connected to an auxiliary crank which is ultimately connected to the shaft that provides the rotational axis for the barrier arm. The auxiliary crank is also connected to the rotary encoder to locate the angular position of the barrier arm at any time a controller is supplied, connected to the rotary encoder to provide input signals to the motor dependent on the position of the rotary encoder. One embodiment also provides a solid vertical axis torque limiter assembly allowing movement of the barrier gate in a horizontal plane. 
     The horizontal axis torque limiter assembly comprises a hub, a spindle, a brake caliper, and a brake disk. The brake caliper includes adjustable pressure bolts which create friction on the brake disk. The brake disk is rigidly connected to the hub which is further connected to the auxiliary crank. The motor and transmission rotate the torque limiter assembly and the friction created by the torque limiter assembly rotates the auxiliary crank and thus the barrier arm. The friction created by the torque limiter assembly is sufficient to move the barrier arm when a signal is received from the controller. But, in the event that an outside force acts on the barrier arm such as high winds or a vehicle driving under the barrier arm, the torque limiter assembly allows movement of the barrier arm in a vertical plane, but will not allow rotation of the spindle, thereby protecting the motor and transmission drive. In other words, the friction created by the torque limiter assembly is sufficiently balanced to move the barrier when the motor and transmission drive are activated, but not sufficient to damage the gears of the transmission. Further, a program is provided in the controller to reposition the barrier arm after movement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description of the preferred embodiments presented below, reference is made to the accompanying drawings. 
         FIG. 1  is an elevation view of a preferred embodiment of the present invention. 
         FIG. 2  is a plan view of the housing with the barrier arm and the top cover removed of a preferred embodiment of the present invention. 
         FIG. 3  is an elevation view of the housing along line  3 - 3  of  FIG. 2  of a preferred embodiment of the present invention. 
         FIG. 4  is an elevation view of the housing along line  4 - 4  of  FIG. 2  of a preferred embodiment of the present invention. 
         FIG. 5  is a sectional view of a preferred embodiment of a torque limiter assembly of the present invention. 
         FIG. 6  is an exploded isometric view of the components of a preferred embodiment of the torque limiter assembly of the present invention. 
         FIG. 7  is a schematic diagram showing the components of one preferred embodiment. 
         FIG. 8  a flow chart of a program run by a controller of one preferred embodiment. 
         FIG. 9   a  is a plan view of an alternate embodiment of the present invention having a second torque limiter assembly. 
         FIG. 9   b  is an elevation view of an alternate embodiment of the present invention having a second torque limiter assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the descriptions that follow, like parts are marked throughout the specification and drawings with the same numerals, respectively. The drawing figures are not necessarily drawn to scale and certain figures may be shown in exaggerated or generalized form in the interest of clarity and conciseness. 
     The present invention is a barrier gate for roadways that includes a rotating arm and a torque limiter. In the event the arm of the gate is moved out of position, the torque limiter prevents costly damage to the internal gears and linkages of the transmission and motor. The present invention can be installed at various vehicle passageways such as railroad crossings, high-occupancy lane entrances, draw bridges, parking lot entries and exits, etc. The specific dimensions of the present invention can be adjusted to accommodate smaller or larger applications as needed. 
       FIG. 1  shows a preferred embodiment of the present invention. Barrier arm  102  is connected to arm frame  106  by a plurality of bolts. Arm frame  106  is pivotally connected to housing  104  at two points on opposite sides of housing  104 . In an alternate embodiment, arm frame  106  is pivotally attached to housing  104  at one point on one side of housing  104 . Counterweight  108  is affixed to arm frame  106  to counter balance the moment arm produced by the weight of barrier arm  102 . Arm stop  110  prevents arm frame  106  from rotating past parallel to surface  112 . Housing  104  is secured to surface  112  via a plurality of anchors  114 . Depending on the application of the present invention, surface  112  may be any horizontal surface, such as a bridge truss or a roadbed. 
       FIGS. 2 ,  3 , and  4  show the internal components of a preferred embodiment without the attached arm frame  106  and barrier arm  102 . Housing  104  is a generally hollow rectangular structure constructed of ¼ inch carbon steel side walls and top cover. The preferred embodiment includes housing  104 . Housing  104  is weatherproof and corrosion resistant. 
     Bearings  214  and  215  are attached to opposite sides of housing  104  by a plurality of bolts and provide rotatable support for shaft  212 . In the preferred embodiment, shaft  212  is constructed of AISI 4150 steel and can range in diameter depending on the application between 1½ to 3 inches. Attachment hubs  210  and  211  are positioned on opposite ends of shaft  212  as shaft  212  extends beyond the exterior walls of housing  104  and provide mounting points for arm frame  106 . Crank  216  is affixed to shaft  212  with through belts  213 . Rod end  310  is affixed to connecting rod  308  by jam nut  340 . Rod end  310  is connected to crank  216  through eyelet  309  with bolt  325  and nut  326 . Rod end  312  is connected to connecting rod  308  by jam nut  342 . Rod end  312  is connected to auxiliary crank  220  and torque limiter assembly  206  through eyelet  313  by bolt  327  and nut  328 . Auxiliary crank  220  is an eccentric disk member that includes a protruding flange for attachment to connecting rod  308 . Crank  216 , connecting rod  308 , and auxiliary crank  220  form a mechanical 4-bar linkage defining a 360 degrees travel of auxiliary crank  220  and a 90 degrees travel of crank  216 . 
     Transmission sprocket  224  is a flat ring shaped  68  tooth sprocket. Transmission sprocket  224  defines a concentrically aligned sprocket hole  344 . Transmission sprocket  224  is concentrically aligned with and mounted to the circular section of auxiliary crank  220  by set of four bolts through a set of four sprocket spacers  322  spaced equidistant proximate the perimeter of transmission sprocket  224 . Auxiliary crank shaft  320  is integrally formed with or rigidly affixed to auxiliary crank  220  at the center point of auxiliary crank  220 . Auxiliary crank shaft  320  is rotatably supported by bearing  222  and provides a rotational axis for auxiliary crank  220 . Bearing  222  is attached to the interior surface of housing  104  by a plurality of bolts and includes a permanently lubricated bearing hub  246  which supports auxiliary crank shaft  320 . 
     Roller chain  314  is a series of connected links formed from high strength steel and constructed as is common in the art. In the preferred embodiment, the roller chain is ANSI 80 single pitch roller chain capable of transmitting about three horsepower. In an alternate embodiment, roller chain  314  is a notched timing belt and sprockets  224  and  226  are notched gears. Roller chain  314  is engaged with transmission sprocket  224  and sprocket  226 . Roller chain  314  transmits the rotational motion of transmission sprocket  224  to sprocket  226 . Sprocket  226  is the same diameter and contains the same number of teeth as transmission sprocket  224  thereby ensuring a 1:1 ratio as transmission sprocket  224  is rotated by motor  202 . Sprocket  226  rotates around shaft  240  located at the center of sprocket  226 . Shaft  240  is supported by brace  242  and rotary encoder  208 . Rotary encoder  208  is an electromechanical device common in the art used to convert the position of shaft  240  to an analog or digital code. Encoders such as BEI Industrial Encoders model H25 or H25X or Gurley Precision Instruments model 7700 are used in the preferred embodiment. Rotary encoder  208  determines and tracks the position of auxiliary crank shaft  320  and thus barrier arm  102  at all times. 
     Motor  202  is directly mounted to transmission  204 . Motor  202  is an electric motor where the voltage, phase and horsepower are determined by each specific application. Horsepower can range from ½ horsepower to up to 7½ horsepower for heavy duty applications. In the preferred embodiment, the motor is provided by Baldor Electric Company or Leeson Electric Motors and the transmission is provided by Peerless-Winsmith, Incorporated. Motor  202  includes manual crank  324 . Manual crank  324  facilitates manual operation of the barrier arm in case motor  202  malfunctions. Transmission  204  includes a drive shaft (not shown) that extends from transmission  204  and into drive shaft hole  530  of torque limiter assembly  206 . The drive shaft has a keyed cross-section that fits securely into drive shaft hole  530  and is locked in place with a cotter key (also not shown). Transmission  204  reduces the speed of motor  202  to the drive shaft and ultimately to torque limiter assembly  206  at a ratio of approximately 1000:1. Transmission  204  is mounted on platform  234  by a plurality of bolts. Platform  234  is a rectangular shaped support member approximately ¼ inch thick with a “C-shaped” cross section. In the preferred embodiment, platform  234  is constructed of high strength steel or cast iron and is capable of supporting the combined weight of motor  202  and transmission  204  or approximately 250 pounds. Platform  234  rests approximately at the midpoint of and perpendicular to base  232 . In the preferred embodiment, base  232  is constructed of high strength steel or cast iron approximately ¼ inch thick and rests adjacent to foundation  238 . Base  232  spans the width of housing  104 . Foundation  238  comprises four ¼ inch plate steel planks approximately four inches wide. The four planks of foundation  238  are attached to the bottom of the interior of housing  104  by a plurality of bolts or by spot welding. Support  236  is a ⅛ inch plate steel rectangle connected to platform  234  and brace  242 . Support  236  provides a level mounting surface for rotary encoder  208 . 
     As shown in  FIGS. 2 and 3 , the exterior of housing  104  includes doors  306  and  307 . Above door  306  is drip guard  230 . Above door  307  is drip guard  231 . Drip guards  230  and  231  are integrally formed angular protrusions constructed of ¼ inch carbon steel that run approximately the width of housing  104 . Doors  306  and  307  include gaskets  302  and  303  respectively. Gaskets  302  and  303  are neoprene bulb-type gaskets which seal the door openings. Latches  304  and  305  provide handles to open door  306  and also keep door  306  firmly closed. In the preferred embodiment, door  306  incorporates latches or handles and door  307  utilizes a plurality of screws to remain closed. In alternate embodiments, either door can utilize either fastening mechanisms to remain closed. In an additional alternate embodiment, a locakable strap can be used with heavy duty padlocks. 
     The components of torque limiter assembly  206  can be seen in  FIGS. 5 and 6 . Torque limiter assembly  206  includes hub  502 , spindle  504 , brake linings  506  and  510 , brake disk  508 , rotor plate  512 , and gland nut  514 . 
     The components of torque limiter assembly  206  are generally circular in shape and are concentrically aligned. Hub  502  is a circular dish shape constructed of ½ inch steel plate. Hub  502  includes mounting hole  544 , a plurality of brake disk mounting holes  602 , reinforcement  532 , and spacer  534 . Mounting hole  544  is located proximate the perimeter of hub  502  and is approximately ¾ to 1 inch in diameter. In the preferred embodiment, eight (8) brake disk mounting holes  602  are equally spaced in the perimeter wall of hub  502 . The axis of each brake disk mounting hole  602  is parallel to the center axis of hub  502 . Reinforcement  532  surrounds mounting hole  544  on the exterior of hub  502 . Reinforcement  532  can be integrally formed with hub  502  or can be a distinct part separate from hub  502  welded to hub  502  that fits into mounting hole  544  and extends from hub  502 . Spacer  534  is a flat circular shaped extension protruding approximately ½ inch from the interior of hub  502 . Spacer  534  has an approximate diameter of 2 inches and provides room for spindle  504  to rotate without interfering with the head of bolt  327  while further providing support for spindle  504 . 
     Spindle  504  is an axially symmetric construct whose longitudinal axis forms the axis of rotation for itself and the torque limiter assembly. Spindle  504  is comprised of threaded section  542  and base plate  540 . Threaded section  542  is a cylindrical stanchion, except for two opposing flat surfaces  604  and  605 . Adjacent the flat surfaces, threaded section  542  is threaded to receive gland nut  514 . Adjacent threaded section  542  is base plate  540 . Base plate  540  serves as one side of a cylindrical brake caliper. The surface of base plate  540  is machined flat to a tolerance of about 2 tenths of a mil to maximize the contact area with brake lining  506 . Spindle  504  further includes drive shaft hole  530 . Drive shaft hole  530  is a key-hole shaped hole approximately 1½ to 2 inches in diameter and is concentrically aligned with spindle  504 . Notch  528  interrupts the perimeter of drive shaft hole  530 . Notch  528  is a keyway that cooperates with a keyway in the drive shaft of transmission  204  and a cotter key (not shown) to ensure that the drive shaft does not slip while rotating spindle  504  of torque limiter assembly  206 . 
     Hub  502  is connected to brake disk  508  by a plurality of brake disk mounting bolts  520 . Lock washers inhibit the bolts from backing out during use. Brake disk  508  is a flat disk subject to the caliper action of the torque limiter assembly  206 . In the preferred embodiment, brake disk  508  is machined flat to a 2 tenths tolerance. Bushing  526  located between brake disc  508  and spindle  504  serves as a bearing between the two surfaces. The bushing of the preferred embodiment is a self lubricating brass composite impregnated with a lubricant as is known in the art. Brake disk  508  includes a concentric circular hole  606  that circumscribes spindle  504 . All of the components of torque limiter assembly  206  are constructed of steel or aluminum. 
     Rotor plate  512  is a circular disc that forms another side of a caliper on torque limiter assembly  206 . Rotor plate  512  includes rotor plate hole  608 , including two opposing flat sides  610  and  611 . Rotor plate  512  fits concentrically around spindle  504  and is axially movable. The opposing flat sides  610  and  611  conform to the flat surfaces  604  and  605  of spindle  504  and prevent rotation of the rotor plate with respect to the spindle. 
     Rotor plate  512  includes on its surface a plurality of spring seats  515 . Spring seats  515  are ⅛ inch deep circular indentions in the rotor plate. Spring seats  515  house spring washers  516 . Spring washers  516  are hemispherical shaped springs that, in use, maintain assembly tension and compensate for expansion or contraction of materials due to heat. In the preferred embodiment, spring washers  516  provide contact points for pressure bolts  518  on rotor plate  512  and distribute the axial force of each bolt over the surface of the rotor plate. Pressure bolts  518  cooperate with gland nut  514  to provide equally distributed and adjustable pressure on rotor plate  512 . In the preferred embodiment, there are eight (8) ¾ inch×1½ inch pressure bolts  518 , machine threaded. The eight pressure bolts are spaced in a regular circular pattern equidistant from each other and the edges of the gland nut flange. In the preferred embodiment, pressure bolts  518  are fine threaded and self-locking, eliminating the need for jam nuts. 
     Gland nut  514  includes gland nut flange  614  and gland nut collar  616 . Gland nut collar  616  includes hole  620 . Hole  620  is threaded to cooperate with the threads on threaded section  542  of spindle  504 . Gland nut flange  614  also includes eight threaded holes  618  for receipt of pressure bolts  518 . In the preferred embodiment, gland nut collar  616  is approximately 1 inch thick and gland nut flange  614  is approximately ½ inch thick. 
     In between brake disk  508  and base plate  540  is brake lining  506 . In between brake disk  508  and rotor plate  512  is brake lining  510 . In the preferred embodiment, both brake linings  506  and  510  are made of a composite fiberglass carbon fibers and asbestos fibers as is known in the art. Brake linings  506  and  510  may be bonded to brake disk  508  with a high temperature adhesive. In an alternate embodiment, the frictional surfaces of brake linings  506  and  510  are integrally formed with brake disk  508 . In another alternative embodiment, the brake linings are not connected to the brake disk and are free to rotate. 
     In use, housing  104  is mounted to surface  112  with a plurality of anchors  114 . Barrier arm  102  is attached to arm frame  106  which is pivotally mounted to housing  104  on shaft  212 . Door  306  is opened or removed to expose torque limiter assembly  206  and allow access to pressure bolts  518 . The torque on each pressure bolt is then adjusted to increase or decrease the friction force provided by the torque limiter assembly. The friction force of torque limiter assembly  206  is adjusted to be sufficient to ensure that the torque on the drive shaft from transmission  204  will rotate auxiliary crank  220  and thus shaft  212  and the connected barrier arm  102  without damaging the transmission in the preferred embodiment. The weight and resultant moment arm of barrier arm  102  is generally balanced by counterweight  108 , therefore the required friction force of the torque limiter assembly is relatively low and can range from 1,000 to 20,000 in-lbs depending on the specific application. A range of 0.6 to 12 ft-lbs of torque on each of the eight pressure bolts will result in the desired range of friction force. Table 1 approximates the ft-lbs of torque required on each pressure bolt to achieve the desired friction force of the torque limiter assembly. 
     
       
         
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Bolt Torque on each 
               
               
                   
                 Pressure Bolt (ft-lbs) 
               
             
          
           
               
                   
                 .6 
                 1.2 
                 3 
                 6 
                 9 
                 12 
               
               
                   
                   
               
             
          
           
               
                 Friction Force 
                 1,000 
                 2,000 
                 5,000 
                 10,000 
                 15,000 
                 20,000 
               
               
                 of Torque 
               
               
                 Limiter 
               
               
                 Assembly 
               
               
                 (in-lbs) 
               
               
                   
               
             
          
         
       
     
     Optimally, the desired friction force is sufficient to rotate the torque limiter assembly, the connecting parts, and the barrier arm. In the event that an outside force such as high winds, a vehicle forcing its way under the barrier arm, or a person lifting the barrier arm, the friction will be overcome and only barrier arm  102 , shaft  212 , auxiliary crank  220 , and hub  502  connected to brake disk  508  will rotate. Torque limiter assembly  206  allows brake disk  508  to rotate while spindle  504  and the drive shaft extending from transmission  204  remain stationary thus protecting the internal gears and linkages of transmission  204  and motor  202 . 
     Referring now to  FIGS. 2 ,  3  and  7 , operation of the system will be described. During operation, a control signal  705 , such as an electrical signal from a button or other control input device provides a “request” to move the barrier arm into a “raised” or “lowered” position to controller  701 . In the preferred embodiment, controller  701  is a microprocessor or personal computer having a Pentium class processor. Controller  701  receives the request and determines the current position of barrier arm  102  via sprocket  226  and rotary encoder  708  through a signal  710  from the rotary encoder. The controller uses the signal to generate an instruction signal  715  to send to the motor gearbox assembly  720 . The calculation is done by a program  725  which will be further described later. Instruction signal  715  causes the motor of the motor gearbox assembly to run until a signal is received from the rotary encoder that the relative position of gate arm  730  is correct. The position of the rotary encoder is related to the position of gate arm  730  because of a fixed mechanical linkage  735  between the gate arm and the motor gearbox assembly and the fixed mechanical linkage  740  between rotary encoder  708  and motor gearbox assembly  720 . If the barrier arm has been moved to a position other than 0 degrees (“lowered”) and 90 degrees (“raised”) by a force other than the motor gearbox assembly, the result is that hub  502 , brake disk  508 , auxiliary crank  220 , transmission sprocket  224 , sprocket  226 , and shaft  240  will have moved, thus moving the rotary encoder. But spindle  504  and thus the drive shaft extending from transmission  204  will not have moved. Corrective action is taken by the controller to move the barrier arm into either its raised or lowered position after a predetermined time period. 
     In operation, motor  202  and transmission  204  rotate drive shaft that extends into torque limiter assembly  206 . The drive shaft rotates spindle  504 . The friction force exerted by rotor plate  512  and base plate  540  on brake disk  508  causes brake disk  508  to rotate with the drive shaft. Hub  502 , connected to brake disk  508 , rotates simultaneously. The rotation of the drive shaft rotates the torque limiter assembly. As the torque limiter assembly rotates, auxiliary crank  220  rotates. As auxiliary crank  220  rotates, roller chain  314  rotates transmission sprocket  224 . As transmission sprocket  224  rotates, shaft  240  rotates and rotary encoder  208  tracks its position. Auxiliary crank  220 , connecting rod  308 , and crank  216  acting together rotate shaft  212 . As shaft  212  rotates, barrier arm  102  rotates into position. 
       FIG. 8  is a flow chart of program  725 , showing greater detail. At step  805 , the controller checks the position of the rotary encoder to determine the angular position of the sprocket. The angular position can be anywhere between 0 degrees and 359 degrees. At about 0 degrees (top dead center) the arm is in a lowered position. Between about 0 degrees and 180 degrees the arm is in transition from a lowered position to a raised position. At about 180 degrees (bottom dead center), the arm is in a raised position. At about 180 degrees to about 360 degrees the arm is in transition between being raised and being lowered. At step  810 , if the control input is “raise” or if there is no control input, the controller waits a predetermined period of time, in the preferred embodiment approximately 30 seconds. If the control input is “raise and hold”, the time delay is about five minutes. The controller then checks the sprocket to determine if it is between about 5 degrees and 355 degrees at step  815 . If not, the controller sends a signal to run the motor at  820  and check the rotary encoder at step  825  until the condition is met at loop  830 . Once met the controller issues a stop signal at step  835  and continues with step  840 . If the condition is met at step  815 , the controller continues at step  840  as well. At step  840 , the controller checks to see if an input has been delivered with a “raised” instruction. If a “raise” input has been delivered the controller moves to step  845  where it runs the motor and check the encoder at step  850  to determine if the condition is met at step  855 . At step  855 , the controller decides if the position of the encoder is between 175 degrees and 180 degrees. If it is, then at step  860  it stops the motor. If not, it returns to step  845  until the condition is met. If at step  840  the input is not a “raise” condition then the controller advances to step  865  to check if the control input is “raise and hold”. If it is, then the controller advances to step  845 . If not, the controller returns to step  805 . If the controller at step  860  determines the condition is met the motor is stopped and the controller returns to step  805 . 
       FIGS. 9   a  and  9   b  show an alternate embodiment of the present invention. Arm frame  906  is pivotally mounted to housing  904 . Counterweight  908  is affixed to one end of arm frame  906 . Torque limiter assembly  910  is mounted to the opposite end of arm frame  906 . Barrier arm  902  is mounted to torque limiter assembly  910 . The hub of torque limiter assembly  910  is rigidly connected to arm frame  906  by a set of mounting bolts  922 . Barrier arm  902  is rigidly connected to the gland nut of torque limiter assembly  910  by mounting bolts  920  and  921 . In the alternate embodiment shown, mounting bolts  920  and  921  occupy two axially opposed threaded holes of the gland nut previously used by pressure bolts. In operation, when a vehicle abuts barrier arm  902 , torque limiter assembly  910  allows the barrier arm to pivot horizontally about its vertical axis without breaking. The hub of torque limiter assembly  910  remains stationary as it is fixed to arm frame  906  and the barrier arm pivots with the spindle section of torque limiter assembly  910  against the braking force created by torque limiter assembly  910 . Torque limiter assembly  910  holds the barrier arm in the compromised position as the vehicle passes through thus reducing further damage to the vehicle. 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.