Abstract:
The limit switch uses a rolling sprocket mounted on an offset pivot point mounted in a housing in combination with inserts into individual links of the chain. The sprocket engages the chain using spring tension on the pivot point and rolls along the chain as the chain moves with the teeth of the sprocket inserting into the chain link spaces. An insert is attached in a chain link and positioned such that when the curtain reaches the desired terminal position, the inserts are at the point where the sprocket contact the insert. The insert blocks the cog of the sprocket which pushes the sprocket away from the chain and inwardly into the interior of the housing. Inside the housing the limit switch that is activated—either by contact or other means. The activation of the kill switch stops the motor and thus the movement of the curtains.

Description:
[0001]    This application is based upon and claims priority from U.S. Provisional application Ser. No. 62/290,663, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    Applicants&#39; invention relates to a device for shutting off motorized rigging. More particularly, it relates to a limit switch that confines the motion of a stage curtain to a predetermined position by deactivating the motor that drives the rigging. 
         [0004]    Background Information 
         [0005]    Theater drapes and stage curtains are large pieces of cloth that are designed to mask backstage areas of a theater from spectators or change acoustic values of a room. They are designed for a variety of specific purposes and come in several types. 
         [0006]    There are several parts typically used in the curtain assemblies, generally including:
       Cable Drum: Helically grooved drums that neatly wrap the cable lifting battens. Multiple drums may be used, and supported by a line shaft assembly. They are spaced to properly support the batten or load.   Chain Track: Chain and supported track combination used to move curtains or scenery.   Computerized Control Systems: Control systems that allow precise position of battens for each scene. They can also track speed, height, and travel of the battens, allowing the changes between scenes to be recorded into memory, and repeated in the exactly the same manner.   Drum Winches: Motorized winch with a single drum long enough to accommodate all of the lift lines required to support a batten. The helically grooved drum wraps the cable neatly in a single layer, to avoid damage to the cable and to keep all lines lifting equally. Winches can be located on the grid, catwalks, or in a separate motor platform. Head and loft blocks may be used to direct the lift lines to the batten.   Gear Motor: The combined gearbox, motor and brake provide speed reduction, power, and mechanical braking in the smallest space.   Limit Switch: Rotary switch geared to rotation of the shaft of the motor. When the switch turns to the appointed spot, it cuts power to the motor. Limit switches can have a number of positions to allow for high trim, low trim, or over travel.   Line Shaft Winch: An assembly consisting of the gear motor, and cable drums connected with a steel shaft. Each lift line uses a separate cable drum. The entire load is transferred through the winch frame assembly to the structure, eliminating horizontal loads, and the need for head blocks and loft blocks. The line shaft winch is ideal for situations where there is not much space nor structure to accommodate the horizontal loads.   Manual Controls: Simple push button controls to allow visual positioning of battens with motorized systems. All buttons release when they are not being pushed. All controls include an emergency stop that kills power to the motors.   Point Hoists: When great flexibility is required, a set of spot lines, or point hoists work together to support and operate a batten or load. Small portable point hoists can be attached to a grid. Larger units can be used with loft blocks to position the lift line appropriately.   The rigging assemblies also have several standard components, generally including:   Batten: A metal pipe, generally 1½″ in diameter attached to the onstage lines from a rigging system. Scenery, draperies, or lighting equipment is attached to the batten.   Counterweight Arbor: A metal carriage that holds the counterbalancing weights used in a counterweight rigging system.   Counterweight Arbor Guides: A device that attaches to a counterweight arbor and engages the guide rails to control the movement of the arbor. Guides employ low friction sliding materials or roller elements. Arbors are generally guided by a fixed (Tee-Bar or JBar) guides, but can also be guided with wire rope.   Hand Line: The rope pulled by the rigging operator to raise and lower the counterweight rigging battens.   Headblock: A multisheave block with two or more pulley wheels, used to change the direction of all the cables that support the batten. It is located directly above the arbor, pin rail, or hoist.   Lift Lines: Cables or ropes attached to the counterweight arbor at the offstage end, reeved through head blocks, and loft blocks and are terminated to the batten or load over the stage.   Loading Bridge: A catwalk or walkway that is suspended just below the grid where the counterweights are loaded onto or removed off from the arbor.   Loft Block: A grooved pulley mounted on top of the grid, used to change the direction in which the cable travels from the head block to the batten.   Mule Block: A grooved pulley mounted on top of the grid, used to redirect the lift line in another direction.   Outrigger Batten: A batten mounted in a fixed position to support locking rail work lights and protect the counterweight rigging equipment from contact with scenic elements.   Rope Lock: A positioning device, located on the locking rail, which grips or releases the hand line of a counterweight set.   Tension/Floor Block: A grooved pulley mounted at the floor level of the counterweight set. The floor block removes slack from the hand line and prevents it from twisting in its travel.   Trim Chain: Short chain used to attach the lift lines to the battens. The chain is attached to the lift line, wraps around the batten, and then is attached back to itself or the lift line with a shackle.       
 
         [0030]    The curtains are hung from battens or tracks. Often, it is desirable to have the curtains move outwardly along the battens. Heavyweight velour is the current industry standard for these types of curtains. Due to the heavyweight material and the size of the curtains, they tend to be extremely heavy. In order to move the curtains, they are generally hung on a chain or cable suspended by pulleys, while the chain is moved by an electric motor. The chain moves in a circuit so at the terminal ends it generally takes a tight turn about a terminal sprocket or pulley and then follows the batten back along the track of the curtain. It can be extremely important that the curtain stop before getting into a position that causes excessive torque on the motor and damage to the motor, curtains, battens, or chains. Therefore, it&#39;s important that the curtain motor to have a stop system that limits movement of the curtains at a desired or necessary point. Likewise, there may be a point at which the users wish the curtains to be stopped for use, aesthetic, or other purposes. 
         [0031]    Stopping the massive theater drapes has generally been done using a limit switch with a rotational counter, a limit switch that the curtain contacts to activate, or simply a person as a spotter to hit a stop button. 
       SUMMARY OF THE INVENTION 
       [0032]    The present invention is a new design of a kill switch for stopping the motor on a stage curtains rigging system. 
         [0033]    The present invention uses a rolling sprocket mounted on an offset pivot point mounted in a housing in combination with inserts into individual links of the chain. The sprocket engages the chain using spring tension on the pivot point and rolls along the chain as the chain moves with the teeth of the sprocket inserting into the chain link spaces. Users place the inserts into the chain links and position them such that when the curtain reaches the desired terminal position that inserts are at the point where the rolling sprocket is engaging the chain. When the sprocket contact the inserts, the teeth of the sprocket are not allowed to engage into the interstitial portion of the chain links. Thus, the sprocket is pushed on the offset pivot against the spring tension and inwardly into the interior of the housing. Inside the housing is a kill switch that is activated upon the inward movement of the sprocket—either by contact or other means. The activation of the kill switch stops the motor and thus the movement of the curtains. 
         [0034]    This works particularly well when the chain is a double chain. When a double chain is used, the track pulleys and motor engage with a first row of chain links while the curtain is hung from a second row of chain links. It is generally intended that the inserts and rolling sprocket will engage with the second row of chain links such that the track pulleys and motor will not damage or contact the inserts. 
         [0035]    Because of the weight of the curtains and the resulting momentum, the chain and curtains may continue to move for a short distance after the kill switch is activated upon the contact sprocket with the inserts. It is conceivable that, after the insert has passed the sprocket, that the kill switch would be deactivated and the motor restarted starting movement of the curtains forward again and possibly causing damage. Therefore, it may be advantageous to have multiple inserts such that the sprocket and consequently the kill switch remains in the activated position long enough for the curtain to come to a complete stop. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]      FIG. 1  is a perspective view of the limit switch. 
           [0037]      FIG. 2  is a perspective view of the limit switch with sprocket extended. 
           [0038]      FIG. 3  is a perspective view of the interior of the limit switch housing with rotatable sprocket. 
           [0039]      FIG. 4  is a perspective view of the double chain with inserts and limit switch and sprocket positioned on the chain. 
           [0040]      FIG. 5  is a perspective view of an insert. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0041]    Referring to the figures, references are labeled as: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 10 
                 Limit Switch 
               
               
                   
                 12 
                 Housing 
               
               
                   
                 12a 
                 Housing End 
               
               
                   
                 12b 
                 Housing Side 
               
               
                   
                 12c 
                 Housing Bottom 
               
               
                   
                 14 
                 Sprocket 
               
               
                   
                 16 
                 Cog 
               
               
                   
                 18 
                 Sprocket Aperture 
               
               
                   
                 20 
                 Sprocket Connector 
               
               
                   
                 22 
                 Sprocket Axle 
               
               
                   
                 24 
                 Swingarm 
               
               
                   
                 24a 
                 Swingarm Sprocket End 
               
               
                   
                 24b 
                 Swingarm Attachment End 
               
               
                   
                 24c 
                 Swingarm Midportion 
               
               
                   
                 26 
                 Swingarm Axle 
               
               
                   
                 28 
                 Swingarm Connector 
               
               
                   
                 30 
                 Attachment Aperture 
               
               
                   
                 32 
                 Switch 
               
               
                   
                 34 
                 Spring 
               
               
                   
                 36 
                 Spring Attachment Point 
               
               
                   
                 38 
                 Switch Actuator 
               
               
                   
                 40 
                 Spring Base 
               
               
                   
                 42 
                 Switch Connector 
               
               
                   
                 44 
                 Contacts 
               
               
                   
                 46 
                 Insert 
               
               
                   
                 48 
                 Insert Connector 
               
               
                   
                 50 
                 Double Chain 
               
               
                   
                 50a 
                 Drive Chain 
               
               
                   
                 50b 
                 Hanging Chain 
               
               
                   
                 52 
                 Track 
               
               
                   
                 54 
                 Pulley 
               
               
                   
                 56 
                 Sprocket Assembly 
               
               
                   
                 58 
                 Bearing 
               
               
                   
                 60 
                 Insert 
               
               
                   
                 62 
                 Insert Back 
               
               
                   
                 64 
                 Finger 
               
               
                   
                 66 
                 Pocket 
               
               
                   
                 68 
                 Shoulder 
               
               
                   
                 70 
                 Flex Slot 
               
               
                   
                 72 
                 Terminal Pulley 
               
               
                   
                   
               
             
          
         
       
     
         [0042]      FIG. 1  illustrates the limit switch  10 . The limit switch  10  has a housing  12  with a hollow interior. It is generally anticipated that the housing  12  will be rectangular in shape with two housing ends  12   a , two housing sides  12   b , a housing bottom  12   c , and an open side opposite the housing bottom  12   c . Attached to the housing, generally near one of the housing ends  12   a , is a swingarm axle  26 . The swingarm axle  26  may be connected to the housing  12  by a swingarm connector  28  or by other means such as welding, adhesive, or friction. A swingarm  24  is rotatably connected to the swingarm axle  26  at the swingarm&#39;s  24  swingarm attachment end  24   b . The swingarm attachment end  24   b  has an aperture through which the swingarm axle  26  is inserted. This allows the remainder of the swingarm  24  to rotate in and out of the interior of the housing  12 . 
         [0043]    At the swingarm sprocket end  24   a , a sprocket axle  22  is attached. A sprocket  14  having a centrally located aperture  18  is rotatably connected to the sprocket axle  22  such that the sprocket  14  rotates about the sprocket axle  22 . Thus, the rotatable sprocket  14  is in mechanical cooperation with the sprocket assembly  56 . The sprocket assembly  56  is comprised of the swingarm  24 , the sprocket axle  22 , the sprocket  14 , and other parts attached to said swingarm  24 . The rotatable sprocket  14  is offset from the rotational point of the swingarm  24 . It is anticipated that the sprocket  14  will be attached on the sprocket axle  22  by a sprocket connector  20 . The swingarm  24  acts as a hinged lever. The swingarm attachment end  24   b  rotates about the swingarm axle  26  like a lever. The amount of plunger  38  movement is increased at the end of the lever  24   a  by the lever ratio. The swingarm axle  26  acts as a fulcrum about which the swingarm  24  rotates. 
         [0044]    It is anticipated that the sprocket  14  may simply have an aperture in its center through which the sprocket axle  22  is inserted, or a bearing  58  may be inserted between the axle  22  an the sprocket  14  in order to ease rotation and reduce friction and wear of the sprocket  14 . Likewise, a bearing  58  may be inserted between the swingarm attachment end  24   b  aperture and the swingarm axle  26  also to ease rotation and reduce friction and wear of the swingarm  24 . 
         [0045]    The housing  12  may have attachment apertures  30  through any portion of the housing  12 . Connectors may be inserted through the housing apertures  30  so that the limit switch  10  may be connected to a track  52  or adjacent to a track  52 . 
         [0046]      FIG. 2  illustrates the limit switch  10  with sprocket  14  extended. This figure shows the limiting switch housing  12  with the rotatable sprocket  14  attached to the centered sprocket axle  22 . The sprocket  14  rotates about the sprocket axle  22 . The sprocket assembly  56  rotates at the swingarm attachment end  24   b  on the offset pivot, swingarm axle  26 . In use, the rotation of the swingarm assembly  56  would be minimal. The movement being from a position wherein the cogs  16  are engaging with and inserting into the chain  50  to a position where the apex of the cog  16  is abutted against an insert  60 . Tension spring  34  is attached to the swingarm  24  at the spring attachment point  36 . Inside the housing  12  is the switch  32 . 
         [0047]      FIG. 3  illustrates the interior of the limit switch housing  12  with rotatable sprocket  14 . This figure shows the interior of the limiting switch housing  12  with the sprocket  14  assembly pivoted out on the offset pivot, swingarm axle  26 . When the sprocket  14  assembly is in its working position, the tension spring  34  engages the swingarm  24  at the spring attachment point  36  to urge the sprocket  14  against the chain  50 . Inside the housing  12  is spring base  40 . The end of spring  34  opposite the spring attachment point  36  urges against the spring base  40 . 
         [0048]    The swingarm  24  is a fulcrum that pivots about swingarm axle  26 . The swingarm axle  26  will generally be attached to the housing  12 , however it could be secured with in the housing  12  without being directly attached to the housing  12 . It is anticipated that the sprocket  14  and swingarm  24  will comprise a sprocket assembly  56 . The sprocket assembly  56  rotates about the swingarm axle  26  and the sprocket  14  is engaged with the chain  50 . In a first embodiment the swingarm  24  is sized at its widest to substantially fill the width of the interior of the housing  12  with enough space between the swingarm  24  and the interior of the housing  12  so that the swingarm  24  is movable within the housing  12 . In this first embodiment, the swingarm  24  would have a narrowed swingarm midportion  24   c  and swingarm sprocket end  24   a . The narrowing of this portion of the swingarm  24  allows the sprocket axle  22  to be inserted through the sprocket aperture  18  and the sprocket  14  to be rotatably connected to the sprocket axle  24  in the interior of the housing  12  such that the sprocket assembly  56  is still movably rotatable inside the interior of the housing  12 . It is anticipated that in separate embodiments, the swingarm  24  may be narrowed throughout its entire length such that the sprocket axle  22  may be inserted through the sprocket aperture  18  and the sprocket  14  to be rotatably connected to the sprocket axle  24  in the interior of the housing  12  such that the sprocket assembly  56  is still movably rotatable inside the interior of the housing  12 . 
         [0049]    Also shown in this figure is the switch  32  attached via a switch connector  42 . The swingarm sprocket end  24   a  acts as a “dog,” and is used to activate the switch actuator  38 . The swingarm sprocket end  24   a  may be thus swingarm  24  in itself, a cam, or an object attached to the swingarm  24  that is able to contact the switch actuator  38 . When the sprocket  14  engages the chain inserts  60  the sprocket assembly is pushed inwardly and activates the switch  32  which is in operative communication with the curtain motor (not shown), and when the switch actuator  38  is depressed, the switch  32  sends a signal that turns off the curtain motor (not shown). It is anticipated that the signal will be via electrical communication from the switch  32  and communicated via contacts  44  to a wire (not shown) that is connected either directly or indirectly to the curtain motor (not shown). 
         [0050]    It is anticipated that the switch actuator  38  will be a plunger type such that when the cogs  16  engage the inserts  60  rather than inserting into the chain  50  interstitial spaces, the swingarm  24  is moved inwardly into the housing  12  and the swingarm sprocket end  24   a  pushes the switch actuator  38  so that it depresses—activating the switch  32  and turning off the curtain motor (not shown). When the sprocket cogs  16  are engaged with the chain  50  and not urged against an insert  60  then the spring  34  acts to insert the cogs  16  into the chain and away from the switch actuator  38 . When the swingarm  24  is not urged against the switch activator  38 , the switch activator  38  resets and the curtain motor (not shown) may be turned on and drive movement of the curtain (not shown). It is anticipated that there may be various types of switches  32  and switch actuators  38 . For example, the switch actuator  38  may be a plunger type or contact type wherein the swingarm  24  completes an electrical circuit in the switch  32 . 
         [0051]    Attached at or near the housing bottom  12   c  in the interior of the housing  12  may be an insert  46  within which the switch  32  may be connected via an insert connectors  48 . It is anticipated that the insert  46  may be insulated in order to electrically isolate the switch  32  from the housing  12 . 
         [0052]      FIG. 4  illustrates the inserts  60 , limit switch  10 , and sprocket  14  positioned in mechanical communication with a chain  50 . This picture illustrates a portion of a curtain track  52  with pulleys  54 , terminal pulleys  72 , and a double chain  50 . The track pulleys  54  and  72  and curtain motor (not shown) engage the double chain  50  on its first row, or drive chain,  50   a  of links. The curtains (not shown) are hung from the second row, or hanging chain,  50   b  of links. Inserts  60  are placed in the interstitial space between links of the second row  50   b  of the chain  50  at a position where the user wishes movement of the curtain (not shown) to always be stopped. The limiting switch  10  is shown in place with the sprocket  14  engaged with the second row  50   b  of the chain  50 . Depending upon the configuration of the track  52 , the limit switch  10  may be positioned using the attachment apertures  30  and connectors in a variety of positions or orientations. It is anticipated that a single row chain  50  could be used with the limit switch  10  and inserts  60 , the majority of chains  50  used in the industry are double rowed. 
         [0053]      FIG. 5  illustrates an insert  60 . The insert  60  is shaped and sized to be inserted and held in the interstitial space of a chain  50  link. In a first embodiment of the insert  60 , the insert  60  has two or more fingers  64  that insert into the chain  50  link interstitial space. The multiplicity of fingers  64  creates a flex slot  70 . The flex slot  70  allows the fingers  64  to slightly flex inwardly while the elasticity of the insert  60  causes the fingers  60  to resist the distorting influence or stress and to return to its original shape. This elasticity causes the fingers  64  to continually urge themselves against the chain  50  links. It is further anticipated that the pockets  66  of the fingers  64  that are urged against the chain  50  links will be shaped to be complementary with the shape of the chain  50  links. Shoulders  68  of the insert  60  will extend outwardly from the chain  50  links and are connected by an insert back  62  which is designed to contact the cogs  16 . When the cogs  16  come in contact with the insert back  62 , the cogs  16  are not able to insert into the interstitial space of a chain  50  link because it is filled with the insert  60 . Thus, the sprocket  14  is pushed away from the chain  50  and inwardly to the interior of the housing  12  against the resistance of the spring  34  and causing the swingarm  24  to contact and activate the switch actuator  38 , which in turn communicates with the curtain motor to deactivate and stop movement of the curtains. 
         [0054]    Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limited sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the inventions will become apparent to persons skilled in the art upon the reference to the description of the invention. It is, therefore, contemplated that the appended claims will cover such modifications that fall within the scope of the invention.