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FIELD OF THE INVENTION  
         [0001]    The present invention relates to a chain drive assembly, and, more specifically, to a chain drive assembly for directing a force both in a pull direction and push direction such as for moving a garage door or movable barrier.  
         BACKGROUND OF THE INVENTION  
         [0002]    Typically, a chain is operable in only a pull direction. A chain, by definition, is a series of interlinked sections, or links, which are free to move relative to each other, at least to some degree. Accordingly, when one end of a chain is pulled in a direction, the links aligned in a linear path and provide a tension force on that which an second end of the chain is attached. Chains are often desirable in many uses as a chain provides the strength, wear, and environmental properties of steel, while also being able to be stored compactly in a coil, for example.  
           [0003]    Because of the links being movable relative to each other, the links are unable to provide a force in compression. That is, when a force is applied towards the chain, the links tend to deviate from their alignment and, as such, are unable to provide a force in a push direction. In addition, the links of a chain may be deflected in a direction lateral to their alignment. A transverse force applied to the chain will cause the links to deviate from their alignment. In order to prevent the links from deviating, the chain must be located within a closely-aligned track (or transmission rail) to constrain the links, a track which results in considerable friction and may cause seizing of the chain within the track.  
           [0004]    As an example, conventional drive systems for automatically raising and lowering movable barriers, such as a garage door or a gate, often involve relatively large and cumbersome components. Specifically, many conventional automatic garage door systems include a garage door, a head unit mounted to the garage ceiling in a position for pulling a chain attached to the center of the garage door, a motor, door rails along which the sides of a garage door are moved, and a controller located in the head unit that is operative to energize the motor to raise and lower the door. Many garage door operator systems also include a hand-held transmitter unit adapted to send signals to an antenna positioned on the head unit and a wall control connected to the head unit. Furthermore, many garage door systems include a transmission rail for the chain, or transmission means, for raising and lowering the garage door.  
           [0005]    A number of disadvantages are present in the use of garage door systems of this type. For instance, the head unit is usually installed on the ceiling aligned with the center of the garage door, extending down from the ceiling into the interior of the garage. If a garage ceiling is particularly low, a garage door systems of this type cannot be installed because the system may create an obstruction to vehicles or other items which require clearance in the garage. In addition, if the ceiling is particularly high, a rigid support structure must be attached to the ceiling for placing the head unit in the proper alignment with the direction of the pull on the garage door. Often times, this requires a custom installation of the head unit to the support structure.  
           [0006]    Another disadvantage is that many conventional systems include a transmission rail for supporting the chain. The transmission rail is typically made of hardened metal and is relatively lengthy, approximately eight feel long. Accordingly, the transmission rail is expensive and cumbersome to install.  
           [0007]    Due to the components of a typical chain-type garage door system, the systems are typically difficult to remove once installed and are not easily transferable. As the height of the ceiling in which the system is installed determines the mounting of the head unit, the system is not easily removed and re-installed in a different garage. Furthermore, the door rails and transmission rail are not easily transferred to a different garage due to their length, weight, and installation into a concrete floor, into the walls surrounding the garage door, and into the ceiling.  
           [0008]    These facts may discourage people from purchasing and installing a garage door system. The systems require expensive, heavy components, often require custom installation by a professional, and are difficult to remove and transfer. At times, these systems are simply unable to be utilized in some garages.  
           [0009]    An alternative to a chain-type garage door system is a screw-type system. In a screw-type, all the components detailed above are required. However, instead of utilizing a chain which is operable only in a pull direction, a screw is utilized which may provide operate in a push direction, as well as a pull direction. However, the screw must extend at least a distance equal to the length of travel of the door from a closed position to an open position. This requires a screw of a length often eight feet or more made of steel with hardened threads for wear and strength. Accordingly, the screw is somewhat expensive, as well as requiring the transmission rail or other means for support.  
           [0010]    A single chain which may be utilized in a push direction, which may be referred to as a push-pull chain, are known in the art. However, these chains must consider transverse forces that would otherwise cause a chain to deflect or deviate from a linear alignment. For example, a chain may be made such that it may deflect only in one particular direction, and the portion of the chain being utilized in a push direction may rest against a flat surface such that the direction of deflection of the chain is against the flat surface. Such a chain is disclosed for example, in U.S. Pat. No. 6,173,352 to Beausoleil.  
         SUMMARY OF THE INVENTION  
         [0011]    In accordance with the present invention, a chain drive assembly is provided which may be utilized to transmit a force in both a push and pull direction. In conjunction with a garage door system, the chain drive assembly of the present invention does not require a support rail, and does not require mounting on the ceiling of the garage. The chain drive assembly includes at least two chains (multi-chain, or multi-strand) with pivotally-connected links. The links of each strand have interfering portions such that the links of one chain cooperate with interfering portions of the links of another chain to inhibit the of the links relative to each other. The result is a rigid chain drive assembly that may be directed in both a push and pull directions, and also resists transverse forces applied to the chain. In addition, the interfering links may be easily separated so that each chain may be coiled or otherwise stored compactly.  
           [0012]    As used in the system, the multi-strand rigid chain drive includes at least two chains engaged and disengaged like a zipper. During operation, interfering portions of the first chain links are alternately engaged with interfering portions of the second chain links so as to inhibit the chains from separating and from being deflected from a linear alignment. This engagement may be referred to as “zipping.” In addition, during operation, interfering portions of the first chain and second chain are alternately disengaged to separate the two chains from each other, this being referred to as “unzipping.” The chain drive assembly may include a pair of sprockets and a pair of storage guides for the individual strands. The sprockets may be positioned so that the chains are deflected and guided around the sprockets, and the interfering portions are engaged or disengaged by the sprockets as the chain links transition between a linear alignment and a deflected alignment.  
           [0013]    The chain drive assembly may be utilized with a number of components conventionally used in a garage door system. More specifically, when a movable barrier, such as a garage door, is to be raised, a motor may be energized in a forward direction and the chain drive assembly is lengthened. A first end of the chain drive includes the engaged ends of two or more chains and is coupled directly or with an apparatus to the top of the garage door. When the motor is energized in one direction, sprockets of a head unit may be used to engage the interfering portions of the two chains to lengthen the rigid length of the chain drive and advance the first end of the chain drive into the interior of the garage, thereby raising the door with the chain drive in a push direction. When the motor is energized in a second direction, sprockets may be used to disengage the interfering portions of the two chains to shorten the rigid length of the chain drive. Accordingly, the first end of the chain drive is drawn towards the head unit, and the door is lowered. Once the interfering portions of the links are disengaged from each other, the disengaged chains may be coiled, or otherwise stored, in respective compact storage guides for efficient storage.  
           [0014]    A system utilizing the chain drive of the present invention provides a number of benefits. The head unit, or any other component, need not be located on the ceiling. Instead, a garage door system utilizing the chain drive assembly may have a head unit located and mounted in any position where the chain may be connected to the garage door as to provide a force in a push direction. For instance, the head unit may be located on the outer wall that includes the garage door. Although a head unit may be located in a similar orientation when used with a screw-type system, the screw itself would still be required, as well as a mount for the distal end of the screw, the mount requiring the same considerations as the above-discussed chain drive systems.  
           [0015]    In addition, this chain drive assembly does not require a transmission rail. The chain drive is able to maintain a linear alignment under compression, and resists transverse forces that would otherwise cause a single chain to deflect from a linear alignment.  
           [0016]    A garage door system utilizing a chain drive of the present invention simplifies installation or removal. As discussed above, no component need be mounted to ceilings which may vary in height, a fact reduces the time and complexity of installing or removing the system compared to a conventional system. In addition, no transmission rail, or screw, need be mounted. As a result, a system incorporating the present invention is less expensive, more easily installed, and more easily transferred and reinstalled than a typical system. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    In the drawings, FIG. 1 is a fragmentary side elevation view in partial cross-section of a garage door system incorporating a chain drive assembly of the present invention;  
         [0018]    [0018]FIG. 2 is a fragmentary side elevation view in partial cross-section of the garage door system of FIG. 1;  
         [0019]    [0019]FIG. 3 is a perspective view of a first embodiment of a chain drive of the present invention;  
         [0020]    [0020]FIG. 4 is a perspective view of a second embodiment of a chain drive of the present invention;  
         [0021]    [0021]FIG. 5A is a perspective view of a third embodiment of a chain drive of the present invention;  
         [0022]    [0022]FIG. 5B is a side elevation view of an interfering link of the chain drive of FIG. 5A;  
         [0023]    [0023]FIG. 5C is a top plan view of the interfering link of FIG. 5B;  
         [0024]    [0024]FIG. 6A is a perspective view of a fourth embodiment of a chain drive of the present invention;  
         [0025]    [0025]FIG. 6B is a front elevation view of an interfering link of the chain drive of FIG. 6A;  
         [0026]    [0026]FIG. 6C is a side elevation view of the interfering link of FIG. 6B; and  
         [0027]    [0027]FIG. 6D is a top plan vie of the interfering link of FIG. 6B. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]    Referring initially to FIGS. 1 and 2, a head unit  10  of a garage door system  11  is shown attached to an outer wall  12  of a structure, such as a garage, and attached to a movable barrier such as a garage door  14 . As depicted in FIG. 1, the garage door  14  is in a closed position. In FIG. 2, the garage door  14  is in an intermediate (partially open) position. The garage door  14  includes a plurality of door sections  16  which span vertically from a ground level (not shown) to a point below the outer wall  12 . Each door section  16  is connected to any abutting door section with a hinge  17 . A rubber seal  18  is provided attached to the outer wall  12  or, preferably, to the top of the garage door  14 . When the garage door  14  is in a closed position, the seal  18  is deflected so as to press against the outer wall  12  and closes the space between the top of the garage door  14  and the outer wall  12 . The seal  18 , for instance, minimizes the air or other environmental passage between an inside region  1  within the garage and an outdoor region  0  outside of the garage. When the garage door  14  is not in a closed position, the seal  18  straightens to a natural position (FIG. 2).  
         [0029]    As is known in the art, the garage door system  11  may include garage door rails (not shown) along which the sides of the garage door  14  are moved, and a controller (not shown) located in the head unit  10  that is operative to energize a motor (not shown) to raise and lower the garage door  14 . Many garage door systems  11  also include a hand-held transmitter unit (not shown) adapted to send signals to an antenna (not shown) positioned on the head unit  10 , and a wall control (not shown) connected to the head unit  10 .  
         [0030]    The head unit  10  operates to direct the chain drive  40  in a horizontal, linear direction. To raise the garage door  14 , the chain drive  40  is operated in a push direction, represented by the arrow U. To lower the garage door  14 , the chain drive  40  is operated in a reverse direction, represented by the arrow D.  
         [0031]    The head unit  10  is coupled to the garage door  14  with a bracket system  20 . The bracket system  20  includes a first bracket  22 , a second bracket  24 , and an arm  26  and is aligned with a path of travel of a chain drive  40  of the garage door system  11 . The first bracket  22  is attached to the garage door  14  and is rotatably secured to the arm  26 . The arm  26  is rotatably secured to the second bracket  24 , which is, in turn, in secured communication with a distal end of the chain drive  40 . The natural position of the seal  18  (FIG. 2) is such that the seal does not interfere with the operation of the bracket system  20 . The chain drive  40  is preferably directed in a horizontal direction generally parallel with the position of the garage door  14  in an open position. The bracket system  20  is configured such that the path of travel of the chain drive  40  is as close to the path of travel of the garage door  14 . In other words, a gap G exists between the chain drive  40  and the garage door  14  when the door is in an intermediate position: in order to minimize the stress upon the bracket system  20  and the chain drive  40 , the gap G should be minimized while not eliminated. In the event the gap G were eliminated, the chain drive  40  would contact and may mar an outer surface  30  of the garage door  14 . As the garage door  14  is raised or lowered, the arm  26  rotates so that the force directed by the chain drive  40  remains aligned with the path of travel of the top of the garage door  14  to insure smooth travel of the garage door  14  along garage door rails (not shown).  
         [0032]    The head unit  10  provides locomotive force to the chain drive  40 . The motor (not shown) within the head unit  10  is an electrical motor providing force in two directions, each corresponding to a direction of travel (U, D) of the garage door  14 . The motor (not shown) is in communication with a first sprocket  42  and a second sprocket  44  (FIG. 3) and provides rotational power to the sprockets  42 ,  44 . Referring to FIGS.  3 - 6 , the chain drive  40  includes a first chain  46  and a second chain  48 . The first sprocket  42  is in sprocket-chain mating relationship with the first chain  46 , while the second sprocket  44  is in sprocket-chain mating relationship with the second chain  48 . A portion of the chain drive  40  is an engaged relationship E, and a portion is a disengaged relationship F.  
         [0033]    Each chain  46 ,  48  includes pivotally connected links including interfering links  50  and coupling links  52 . Other than the ends of each chain  46 ,  48 , each interfering link  50  is connected at each end to a coupling link  52  by a pivot formed by a cylindrical rivet  54 , as is known in the field of the art, and the sprockets  42 ,  44  mate with the cylindrical rivet  52 , as is known in the field of the art. In the present embodiment, each interfering link  50  includes an interfering portion, specifically a top and a bottom trapezoidal flange  60  where the greatest portion of each trapezoid extends away from the cylindrical rivets  54 . When the interfering links  50  are engaged, the sides of the flanges  60  of the first chain  46  are in a mating relationship with the opposing flanges  60  of the second chain. As the sprockets  42 ,  44  rotate to extend the chain, the chains  46 ,  48  are fed between the sprockets  42 ,  44 , and the interfering links  50  are mated in an interlocking position that prevents the chains  46 ,  48  from being pulled apart and that prevents the chains  46 ,  48  from being deflected in a direction transverse the direction of the feeding of the chains  46 ,  48 . As the sprockets  42  in the opposite direction to retract the chain, the chains  46 ,  48  are unmated, or disengaged such that the interfering links  50  and coupling links  52  are free to rotate relative to each other. In the engaged relationship E, the chain drive  40  is able to receive and transmit a force in a push direction. In the disengaged relationship F, the chains  46 ,  48  of the chain drive  40  are able to be coiled in a manner common to chains linked by cylindrical rivets for mating with a sprocket.  
         [0034]    Referring now to FIG. 4, a second embodiment of the chain drive  40  is depicted. The chain drive  40  includes a first and second chain  72 ,  74  with interfering links  76 , and coupling links  78  connected by cylindrical rivets  80  for mating with respective first and second sprockets  82 ,  84 . As discussed above, the interfering links  76  of the first chain  72  have an interfering portion, specifically a top and a bottom trapezoidal flange  86  for mating with trapezoidal flanges of the interfering links  76  of the second chain  74 . In the present embodiment, the interfering links  76  have a identical trapezoidal flanges  86  on the non-engaging sides of each interfering link  76 . By manufacturing the interfering links  76  in this manner, the assembling each chain  72 ,  74  is simplified, and the assembly of the chain drive within the head unit  10  is simplified, as the possible orientations for each interfering link  76  and each chain  72 ,  74  is reduced.  
         [0035]    Referring now to FIGS.  5 A-C, a third embodiment of the chain drive  40  is depicted. The chain drive  40  includes a first and second chain  90 ,  92  with interfering links  94  and coupling links  96  connected by cylindrical rivets  98  for mating with respective first and second sprockets  100 ,  102 . Referring to FIG. 5B, the interfering links  94 , when viewed from a top plan view or bottom plan view, have a profile including a trapezoid as in the previous two embodiments. However, referring to FIG. 5C, while the previous two embodiments include a pair of trapezoidal flanges, the interfering portion of present embodiment includes a single piece  104  that mates with the rivets  98  at the top and at the bottom, the single piece  104  being viewed in cross-section as a U-shape. As discussed above, the interfering links  94  of the first chain  90  mate with the interfering links  94  of the second chain  92 .  
         [0036]    Referring now to FIGS.  6 A-D, a fourth embodiment of the chain drive  40  is depicted. The chain drive  40  includes a first and second chain  110 ,  112  with interfering links  114  and coupling links  116  connected by cylindrical rivets  118  for mating with respective first and second sprockets (not shown). Referring to FIG. 6B, the interfering links  114  have a profile of three sides generally at right angles, the corners  124  of which are slightly rounded. Referring to FIG. 6C, when viewed from a top plan view or bottom plan view, the interfering links  114  have a top and bottom base portion  126  with generally straight shoulders  128  which abut straight shoulders  128  of the opposing chain when in an engaged position. The base portion  126  further includes peripheral sides  130  which are generally straight and at least a contact portion of which forms a right angle with the shoulders  128 . Each peripheral side  130  abuts a peripheral side  130  of another interfering link (FIG. 6A). Due to the shape of the base portions  124  of the interfering links  114 , each chain  110 ,  112  is itself a push/pull chain that is deflectable in one direction. That is, each chain  110 ,  112  may be deflected in the direction as depicted. However, neither chain  110 ,  112  may be deflected in an opposite direction. Therefore, when the chains  110 ,  112  are engaged, each provides a constraint against for the other by virtue of the configuration and mating of the base portions  124  to base portions  124  of opposing as well as abutting interfering links  114 .  
         [0037]    Referring to FIG. 6D, the interfering links  114  have an interfering portion, specifically a lateral prong  140 . As can be seen in FIG. 6E, when the chains  110 ,  112  are engaged, each lateral prong  140  is mated with an opposing interfering link  114  by abutting an interior portion  142  (FIG. 6B). As discussed above, the interfering links  114  of the first chain  110  mate with the interfering links  114  of the second chain  112 . In the present embodiment, it is preferred that each interfering link  114  includes only a single lateral prong  140  which is located on the interfering link  114  in a direction in the direction of travel of the chains  110 ,  112  when the chains are being engaged, represented by arrow Z. Although, as an alternative, each interfering link  114  may include a lateral prong  140  on an opposite side as well, such would cause undesirable interference when the chains  110 ,  112  are disengaged.  
         [0038]    It is clear that a number of embodiments and configurations may be fashioned whereby links of a first chain may engage and interfere with links of a second chain in order to prevent the links from being deflected from a linear orientation. It is also clear that a number of chains may be employed. For instance, a central chain (not shown) may be provided wherein two chains (not shown) laterally disposed of the central chain both include interfering links in order to prohibit the engaged chains from deflecting from a linear orientation. Furthermore, although the present invention has been discussed with reference to a conventional garage door that raises and lowers, the present invention may be utilized with a garage door that moves laterally. In this case, the push/pull ability of the chain drive would be utilized where the head unit is located at one side of the door, and the is required to provide a force without the benefit of gravity. For example, doors of an aircraft hangar or of a barn are often moved laterally without any place other than an outer wall to mount a door system. While there have been illustrated and described particular embodiments of the present invention, it will be appreciated that numerous changes and modifications will occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention.

Summary:
A multi-strand chain forms a chain drive including at least two chains so that the chain drive may communicate a force when the chain is pushed or pulled. The chains may be separated or disengage so as to be stored compactly. The chains may be engaged to form the chain drive so that the chain drive is substantially rigid and in a linear orientation, and pivotally connected chain links may not substantially rotate relative to each other and may not be deflected substantially from the linear orientation. The chains may be engaged and disengaged by rotating around sprockets which deliver the force to the chain drive. The chain drive may be utilized as a garage door system for raising or moving laterally a garage door or movable barrier with the chain drive in compression.