Abstract:
Hardware that improves the safety of operating sectional doors that use torsional coil springs to facilitate door movement. A rotor assembly with centrifugally activated throw-out latches is affixed to the rotating shaft that bears the torsional coil springs. When a spring breaks, the shaft rotates rapidly as cables supporting the door unwind. Rapid rotation causes centrifugal force to bias the latches to an outer position in which they strike a trigger plate, allowing a pawl to move into a position in which the pawl blocks further rotation of the rotor, thus halting the descent of the sectional door. Raising the sectional door manually moves the latches, trigger plate, and pawl to their original position, disengaging the present invention and permitting the door to be lowered slowly without danger of injury.

Description:
BACKGROUND OF THE INVENTION 
     1. Related Applications 
     This application claims priority to U.S. provisional application Ser. No. 60/672,763, filed Apr. 19, 2005. 
    
    
     2. Field of the Invention 
     The present invention relates to sectional doors and related safety devices. More particularly, the present invention relates to novel hardware devices designed to improve safety and minimize the risk involved in operating sectional doors that utilize spring mechanisms to facilitate door movement. 
     3. Background 
     Large doorways in garages, shops, stores, warehouses and other buildings often use sectional doors to enclose the doorway opening. These doors are generally constructed of wood, vinyl, fiberglass, or metal panels which are joined by hinges and hung from rollers which travel along a fixed track at each side of the door. Sectional doors typically range in size from small storage unit models of just a few feet wide to very large models which accommodate trucks and heavy equipment. Sectional doors are used for residential garages in sizes sufficient to accommodate either one or two vehicles. 
     The size of sectional doors and the weight of their materials make them relatively heavy and, therefore, difficult to lift without assistance. Many doors also contain insulation and other materials which further add to the door&#39;s weight. Even an average-sized residential garage door can weigh several hundred pounds, making it impossible for the average person to lift without assistance. 
     As a consequence of the weight of sectional doors, mechanisms have been invented to counteract the door&#39;s weight, thereby allowing manual operation of the door. The most common method of counteracting a door&#39;s weight is accomplished with a counter-spring mechanism using a spring or springs which are displaced elastically as the door is shut, thereby exerting a lifting force on the door as it is closed. This spring force keeps the weight of the door in balance during movement. 
     Coil springs, in a torsion spring configuration, are often used for these mechanisms. In a torsion spring configuration, the coil spring is deflected or wound around the axis of its helix. In a typical coil spring configuration, as shown in  FIGS. 1 and 2 , one or more coil springs are wound around a shaft near the top of the door. One end of each coil spring is attached to a mounting bracket which is affixed to the building structure or to the metal frame in which the sectional door is mounted. The other end of the spring is attached to a torsion shaft. A cable drum is likewise mounted on the shaft. A cable is wound around the cable drum. The cable extends to the bottom of the door where it attaches to a bracket. These coil springs are sized and pre-wound or pre-tensioned to ensure that the door remains in balance through the entire path of movement of the door, between closed and open, or open and closed positions. 
     As the door closes, the cable unwinds from the cable drum thereby twisting the spring and increasing the torsion on the spring and the energy stored within the spring. A properly adjusted spring mechanism will exert a force on a door that is about the same as the weight of the door, allowing a user to open the door with the slightest of lifting effort. This means that the ideal spring mechanism, on an average door, will need to store an amount of energy that is approximately equal to the weight of the door. In terms of force and considering the lever arm of the cable drum, the spring exerts a force of at least twice the weight of the door. Consequently, these spring mechanisms store a great deal of energy that is unleashed as a twisting force. Because of the tremendous forces involved, even well-maintained coil springs will eventually weaken or break. When a spring weakens, the door is no longer in balance. When a spring breaks, it unwinds around its helical axis and releases the stored energy that was balancing the weight of the door. 
     The coil springs are most likely to break when a door is closed, because that is the point in the traverse of the door when the force stored in the coil spring is greatest—the coil spring is at that point ready to assist in lifting the door. Breakage can occur, however, at any point. This is particularly true in many modern residential and industrial applications where an electric garage door opener is in use. The majority of doors in such situations use more than one coil spring, but the power of an electric garage door opener enables that device to lift the door in many cases when one of the coil springs is weakened or broken, unbeknownst to the user of the door. 
     When a single remaining coil spring breaks, the only counter-balancing force to the full weight of the door is found in any electric garage door opener that may be attached to the door. These openers are not designed to bear the weight of the door without any assistance from the coil springs. In any case where all the coil springs break, the door will effectively be without a force to counter its full weight. If the coil springs break when the door is fully closed, the door will likely be impossible for an individual to lift without assistance. More troubling, if the coil springs break when the door is not fully closed, the full weight of the door will force it to a closed position, posing a threat of serious injury or even death to any person or animal that lies in its path as it falls. A particular danger may be that of residential homeowners or their children who, unaware that a spring is weakened or broken, release the door&#39;s connection to a garage door opener, and then attempt to block the path of a falling door without the benefit of the counterbalancing effect of one or more broken or weakened coil springs. 
     Inventions in the prior art have used a number of techniques to stop the instantaneous free-fall of a door in a situation where either the coil springs break or are weakened. 
     In some industrial applications, a hydraulic mechanism is used that restricts the speed of rotation of a cam or drive wheel associated with the door lift mechanism. In these devices, a fluid flows through chambers as the door is raised or lowered. By controlling the size of chambers and the viscosity of the fluid, the amount of force needed to rotate the drive wheel can be changed. Manufacturers select specifications in which the weight of a free-falling door does not provide a sufficient force to rotate the drive wheel at greater than a safe speed, thus controlling the speed of descent for the door. Unfortunately, these hydraulic devices are expensive to manufacture and maintain, and thus inappropriate for many small industrial and residential sectional garage doors. 
     Solutions used for sectional doors have most often used a mechanical tensioning device to detect a slackening of the tension in a coil spring mechanism. Such a slackening indicates that the coil spring no longer provides a balancing force to the weight of the door. When tension is released in the coil spring, these prior art devices use various techniques to stop the movement of the door. 
     Although these prior art inventions are effective when a coil spring breaks, they are much less helpful when a coil weakens or is installed incorrectly. A spring that has weakened or that has been incorrectly adjusted or installed generally provides enough tension that a prior art safety device will not detect that a spring is now exerting a much-reduced lifting force on the door. If one or both springs become weakened, the door may drop unexpectedly without triggering a prior art safety device. Such an event might also occur if a user releases a door having a weakened spring from a garage door opener that was preventing the door from falling. 
     Prior art safety devices pose another potentially serious problem when coil springs break, triggering these devices. Prior art safety devices are typically designed to stop all downward movement of the door, rather than simply the overly rapid descent that poses a danger to users. Because the breakage of a coil spring is most likely to occur when a door is at or near a closed position, the contents of the garage or building are likely to be “locked inside” by these prior art safety devices until a qualified repair technician can arrive on site. Given human nature and the pressures of modern life, an unwary home or business owner is highly likely to attempt to disable or disengage the safety device in order to remove a vehicle, secure a dwelling, or for similar purposes. Individuals who do not understand the mechanisms and forces involved will assume they can manually manipulate the door. Serious injury may result from an attempt to disable or disengage prior art safety devices in order to permit such manual operation. 
     It is evident, then, that what is needed is a safety device that will prevent the rapid and dangerous descent of a door but not prevent all downward door movement. Such a device would protect against injury by a heavy, falling door. It would also allow a user to disengage the safety device, raise a door with assistance, then carefully lower it to a closed position, or otherwise operate it manually, all the while being protected from grave injury by a safety device that stops a rapid and perilous falling door. Ideally, the invention would allow intuitive use, where a user who has not read an operator&#39;s manual can “figure out” how to operate a disabled sectional door manually without risking injury. 
     SUMMARY OF THE INVENTION 
     The present invention reduces or eliminates the safety hazards posed by broken or weakened coil springs in a sectional door lift mechanism. It also reduces or eliminates the limitations and safety hazards of prior art devices as they relate to stopping a falling door. 
     Unlike devices in the prior art that detect only a broken spring, the present invention detects overly rapid descent based upon the speed of rotation of the shaft on which the coil spring mechanism is mounted. If the shaft rotates at too high a speed, the device in the present invention is activated and stops the descent of the door. If a user then raises the door a few inches, the mechanism of the present invention resets, allowing the user to lower the door at a slow rate of speed. If the user slips or moves the door too rapidly, the device reengages to prevent injury. The device may be reset and reengaged repeatedly to allow manual operation while protecting against the dangerous and overly rapid descent of a falling door. 
     A preferred embodiment of the present invention relies on centrifugal force to activate a means for stopping the descent of a sectional door when the coil-bearing shaft rotates at an excessive rate of speed. In one embodiment, a rotor assembly is mounted about the coil-bearing shaft. This assembly includes at least one elongate latch attached by one end near the perimeter of the rotor. During normal operation of a sectional door, the coil-bearing shaft rotates at an acceptable rate of speed. As the rotor rotates, the latch rotates freely, under the influence of gravity, between a position substantially parallel to the perimeter of the rotor and a position extended from the rotor. When the coil-bearing shaft rotates rapidly, as when a sectional door begins a dangerous free-fall, the latch is thrown by centrifugal force into an outer position. In that outer position, the latch engages a trigger plate. The trigger plate rotates around the coil-bearing shaft and releases a catch that holds back a pawl. The pawl is pulled upwards toward the rotating rotor by a spring attached to the trigger plate. The rotor contains at least one protrusion, which strikes the pawl and halts the rotation of the rotor, and thus the rotation of the coil-bearing shaft. Because the coil-bearing shaft is connected to the descending door by one or more cables, when the shaft ceases to rotate, the descent of the door also ceases. 
     If a user thereafter lifts the door manually, the rotor will be rotated in a direction opposite to the direction of when the door was falling. The pawl will be pushed out of the path of the rotating rotor and the trigger plate will be pulled back to its original position. The latch, which was thrown into an outer position by centrifugal force, will fall back to an inner position because of the slow rotation of the rotor and coil-bearing shaft. The user could continue to raise the door manually, or could lower the door at a slow rate of speed. If the weight of the door caused the user to inadvertently release the door, the rotor assembly would again spin rapidly, and centrifugal force would throw the latch to the outer position, once again hitting the trigger plate, permitting the pawl to be pulled into a position that again stopped the free-falling door. 
     The maximum distance that the door could descend in free-fall is determined in this embodiment by the number of protrusions on the rotor and the circumference of the cable drum on which the door lift cable was mounted. For example, if the cable drum has a circumference of 12 inches and the rotor contains three protrusions, the maximum distance that the door can free-fall before a protrusion strikes the pawl is 120 degrees of arc around the 12 inches of circumference—about 4 inches. 
     While the methods and processes of the present invention have proven to be particularly useful in the area of sectional doors, those skilled in the art can appreciate that the methods and processes may be useful in a variety of different applications and in a variety of different areas of manufacture where they have not heretofore been used, and where such use would yield improved safety or control of mechanical devices. Any number of devices that include a rotating shaft or disc might benefit from the present invention as a way to halt overly rapid movement of component parts. 
     These and other features and advantages of the present invention will be set forth or will become more fully apparent in the description that follows and in the appended claims. The features and advantages may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. Furthermore, the features and advantages of the invention may be learned by the practice of the invention or will be obvious from the description, as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the manner in which the above recited and other features and advantages of the present invention are obtained, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. Understanding that the drawings depict only typical embodiments of the present invention and are not, therefore, to be considered as limiting the scope of the invention, the present invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  illustrates a representative system in the prior art that provides a suitable operating environment for use of the present invention; 
         FIG. 2  illustrates a shaft and torsion spring assembly in the prior art, on which the present invention is typically installed; 
         FIG. 3  illustrates one end of the shaft and torsion spring assembly shown in  FIG. 2 , as they exist in the prior art; 
         FIG. 4  shows a view of a preferred embodiment of the present invention; 
         FIG. 5  shows an alternate embodiment of the present invention; 
         FIG. 6   a  shows the rotor assembly used in a preferred embodiment of the present invention; 
         FIG. 6   b  shows the rear side of the rotor assembly used in a preferred embodiment of the present invention; 
         FIG. 7   a  shows the present invention during normal operation of a sectional door; 
         FIG. 7   b  shows the present invention during engagement caused by overly rapid descent of a sectional door; 
         FIG. 7   c  shows the present invention fully engaged, as caused by overly rapid descent of a sectional door. 
         FIG. 8  shows an embodiment of the present invention, without all of its components, in the general position it would be found when placed at the center of a torsion shaft. 
         FIG. 9  shows an embodiment of the present invention in which the rotor and cable drum are fashioned as a single component. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The figures listed above are expressly incorporated as part of this detailed description. 
     It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but is merely representative of the presently preferred embodiments of the invention. 
     The presently disclosed embodiments of the invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. 
     The term “conventional fasteners” as used in this document refers to fasteners for connecting metal, wood, plastic and other materials common in sectional door construction. By way of example and not limitation, these fasteners comprise screws, bolts, nuts, washers, rivets, cotter pins, clevis pins, studs, threaded rods and other mechanical fasteners as well as adhesives such as epoxy, welding joints such as spot welds and conventional fillet and butt joint welds. 
     A “non-fastener structure” is a device that does not hold the items of its connection in a fixed physical relationship without other support, force or torque. A non-limiting example of a non-fastener structure is a hook, such as a hook which engages an element but only remains in contact with that element while a force acts on the hook, pulling it against the element. 
     A “torsion spring” is an element which is elastically deformed by a torque or rotational force and which counteracts against that torque with an equal, but opposite, torque. The torsion spring may provide the counteracting torque directly by virtue of its shape and configuration or it may counteract the torque indirectly through a mechanism which converts spring force into torque. By way of non-limiting example, a torsion spring may be a helically wound coil spring which is elastically deformed by a rotational motion about its helical axis, or a torsion bar or a leaf spring connected to a lever and gear mechanism which creates torque. 
     The term “static structure” shall refer to any structure that is substantially static or immovable in response to the forces exerted by a typical sectional door. Examples of static structures, given by way of example and not limitation, are roller tracks, mounting brackets, and residential or commercial building frames including framing elements such as studs, posts, columns, beams, headers, lintels, stem walls, foundation structures and other elements that are assembled into a building frame. Other non-limiting examples of static structures are posts, fences, retaining walls and garden walls. These elements may be constructed of concrete, masonry, lumber, steel, plastic, fiberglass, aluminum or other materials. 
     The term “counter-spring” shall refer to any type of mechanism which uses elastic deformation of an element&#39;s shape to counteract a force or weight. By way of example and not limitation, a counter-spring may take the form of a coil spring which stretches along its helical axis and exerts a force as it is stretched. Also, by way of non-limiting example, a coil spring may be connected coaxially, in a torsion spring configuration, to a pulley or drum so that the spring rotates with the pulley or drum such that a cable wound around the pulley or drum from which an object is suspended would exert a counter-force against gravity, thereby allowing the object to be lifted with a force lesser than the weight of the object. 
     A specific embodiment of the present invention comprises a novel safety feature for use with a spring-based system of pivotally connected sectional doors, as shown in  FIG. 1 . This embodiment utilizes a torsion assembly comprising a coil spring  100  and cable drum  110  mounted on a shaft  120 . The torsion assembly is connected by cable  130  to sectional door  140 . The roll-up door rides on rollers  150  which engage and travel within tracks  160  at each side of the door  140 . 
     When a force such as a garage door opener moves the sectional door  140  downward, cable  130  unwinds from the cable drum  110 , causing the shaft  120  to rotate and increasing tension in coil spring  100 . When a force moves the sectional door  140  upward, cable  130  winds onto the cable drum  110 , causing the shaft  120  to rotate and decreasing the tension in coil spring  100 . Importantly, in this system, the shaft  120  and the cable  130  are connected in such a way that whenever the door  140  moves in its track  160 , the shaft  120  rotates, and if the shaft  120  cannot rotate, the door  140  cannot move downward. 
     Structure of a Preferred Embodiment 
     In a preferred embodiment of the present invention, a rotor assembly  10 , shown in  FIG. 6   a , is fixedly, coaxially mounted on the shaft  120 , so that when the shaft  120  rotates, the rotor assembly  10  also rotates; if rotation of the rotor assembly  10  is halted, the rotation of the shaft  120  is also halted. The rotor assembly  10  is attached securely to the shaft  120  so as to withstand significant torque forces during stoppage of a falling sectional door  140 , as hereinafter described. One preferred method of securely attaching the rotor assembly  10  to the shaft  120  comprises using one or more set screws that are inserted through a set screw tapped hole  11  and that extend to engage the shaft  120  at the set screw hole  12  in the inner perimeter of the rotor assembly  10 . Three set screws are used in a preferred embodiment. The rotor assembly  10  may also be attached securely to the shaft  120  by means of a fastener that extends through at least a portion of the rotor assembly  10  and substantially into or through the shaft  120 . The rotor assembly  10  can be retrofitted onto a variety of pre-existing installed sectional door assemblies to provide an added measure of safety as herein disclosed. 
     In one embodiment, intended primarily for newly installed sectional doors, the cable drum  110  and the rotor assembly  10  as herein disclosed are manufactured as a single component, as illustrated in  FIG. 9 . This embodiment saves manufacturing costs compared to creating two separate components. It also may make installation easier. Finally, using a single component for cable drum  110  and rotor assembly  10  eliminates the need to transfer torque from the rotor  20 , through the set screws, to the cable drum  110 , in order to halt a falling sectional door  140 . 
     The rotor assembly  10  comprises a rotor  20  and latches  30 . The rotor  20  in a preferred embodiment has a width of approximately 0.75 inches along the longitudinal axis of the shaft  120  and includes, in a preferred embodiment, three protrusions  21  that extend beyond the perimeter of the rotor  20 . The width of each protrusion  21  along the longitudinal axis of the shaft  120  is not as great as that of the main body of the rotor  20 , leaving a portion  22  of the perimeter of the rotor that is not extended by a protrusion. In a typical sectional door configuration, the cable  130  as described herein is wound on the cable drum  110  so that the rotor  20  rotates clockwise when the sectional door  140  is rising and counter-clockwise when the sectional door  140  is descending. The descriptions that follow assume this configuration, though reversed or altered configurations and viewpoints can easily be imagined using the same principles by those skilled in the art. 
     Each protrusion  21  on the rotor  20  is configured to include a substantially flat surface  23  on the leading edge of the protrusion during counter-clockwise rotation. This is evident in  FIG. 6   a . Each protrusion  21  is further configured to include a substantially sloped surface  24 , smoothly connecting the non-protruding perimeter of the rotor  20  with the extended perimeter of the protrusion  21 . This sloped surface  24  is located on the trailing edge of the protrusion  21  during counter-clockwise rotation, as seen in  FIG. 6   a . Similar embodiments having a rotor  20  of varying shapes can be envisioned by those skilled in the art. 
     The rotor  20  may be constructed of a variety of materials. In this embodiment, cast or machined aluminum is used. The center portion of the rotor may be designed to include a thinner area and spokes  25 , so as to reduce the amount of metal used for casting operations. The rotor  20  may also be constructed by a process of metal stamping of a hub section followed by welding multiple protrusions onto the hub; or by forming the rotor  20  from UHMWPE or nylon 66, or a variety of other plastics, composites, or metals. 
     The rotor assembly  10  in this embodiment further includes one or more latches  30 . In this preferred embodiment, three latches  30  are used, each located adjacent to a protrusion  21 ; these latches  30  are made of a substantially planar piece of material. In this embodiment, 12 gauge galvanized steel is used, though any other material known in the art that can be formed with sufficient precision, via stamping or otherwise, may also be used. The latches  30  are substantially elongate and trapezoidal in shape, having a notch  31  in one end. The un-notched end of each latch is attached to the rotor  20 , near the perimeter of the rotor  20 , using a fastener  32  that permits the latch  30  to rotate freely about the fastener  32 . The latch  30  is constrained in its rotational movement by the shape of the rotor  20  and the trapezoidal shape  33  of the ends of the latch  30 , so that it moves freely only between a first position that is substantially parallel to the perimeter of the rotor  20 , and a second position that is extended from the perimeter of the rotor as the trapezoidal shape  33  presses against the edge  22  of the rotor  20 . 
     During normal, slow rotation of the rotor  20 , the latches  30  move back and forth between the first latch position and the second latch position. When a latch  30  is rotated to the bottom part of the rotor  20 , the latch  30  falls to the second latch position in which the latch  30  is extended to the limit of its free movement. When the latch  30  is rotated to the top part of the rotor  20 , the latch  30  falls into the first latch position in which it lies substantially parallel to the perimeter of the rotor  20 . If, however, the rotor  20  spins rapidly, centrifugal force will cause the latch  30  to remain in the second latch position even when the latch  30  is rotated to the top part of the rotor  20  where gravity would otherwise cause the latch  30  to fall back to the first latch position. A similar result could be obtained by relying on latch mechanisms that were biased with springs on a rotor oriented in a non-vertical plane. 
     This preferred embodiment, as shown in  FIGS. 7   a  through  7   c , includes a plate  40  that is typically mounted in the vicinity of rotor assembly  10 . In a preferred embodiment, plate  40  is made from 12-gauge galvanized steel and is mounted on the shaft  120 , adjacent to the rotor assembly  10 . The mounting hole in the plate  40  is large enough to permit the plate  40  to fit over the bearing  122  in which the shaft  120  rotates. The rotor  20  has a space  27  formed near its inner diameter so that during rotation, the rotor  20  does not contact the body of the bearing  122  in which the shaft  120  rotates, but only contacts the bearing race. A ridge  26  protrudes from the rotor  20  outside the perimeter of the bearing  122  so that it touches the plate  40 .  FIG. 6   b  shows the back side of the rotor  20  where it is assembled against the plate  40 . The plate  40  is not fixed to the shaft  120  or rotor  20 , but can remain stationary as the shaft  120 , rotor  20 , and cable drum  110  rotate. Though a variety of materials can be used for the rotor  20  and plate  40 , two different metals are used in this embodiment. As the rotor  20  rotates against the stationary plate  40 , the softer aluminum of the rotor  20  in this embodiment is polished to form a smooth surface, permitting quieter operation. 
     The plate  40  includes a flange  41  near its top portion. The flange  41  extends over the top of the rotor assembly  10 . The plate  40  in this embodiment also includes a means for attaching a spring to plate  40 . Typically, this means is a second flange  42  with a hole drilled through it or a small hook to which spring  60  or other means can be attached for biasing the movement of plate  40 . In a preferred embodiment, a hook is used to permit easy attachment of spring  60 . 
     Plate  40  further includes a means for restraining the movement of the pawl  50 . This means is typically a notch  43  in the planar surface of plate  40 . Both the second flange  42  and the notch  43  are typically located in the bottom portion of plate  40 . 
     A preferred embodiment also includes a pawl  50 . Pawl  50  is not mounted coaxially with the rotor assembly  10  in a preferred embodiment. One end of pawl  50  is mounted so that when the pawl  50  rotates about its mounting point, pawl  50  engages a flat surface  23  of rotor  20  when rotor  20  rotates in a counter-clockwise direction. Pawl  50  is typically mounted near rotor  20  on a static structure such as the bracket  170  that holds the shaft  120 . The rotor  20  and pawl  50  are configured so that when the rotor  20  rotates in a clockwise direction as the sectional door  140  is raised, the pawl  50  does not engage flat surface  23  or otherwise interfere with the free rotation of the rotor  20 . 
     Pawl  50  can be made of any suitable material, including a variety of metals or plastics. In the preferred embodiment, cast or machined aluminum is used. 
     In a preferred embodiment, pawl  50  includes a means for holding the pawl in position, which maintains the position of pawl  50  when plate  40  is in its first position. A preferred means for holding pawl  50  in position is a pin  51  positioned near the free end of pawl  50 . In a preferred embodiment, a small hole  171  is formed into bracket  170  on which pawl  50  is mounted to prevent any binding or interference with the movement of pawl  50  caused by scraping against bracket  170  or other static structures. When the plate  40  is in a first position, pin  51  engages notch  43  on plate  40 . In this position, pawl  50  cannot move. Pawl  50  also comprises a means for attaching coil spring  60  or other means for biasing the movement of pawl  50 . In a preferred embodiment, the means for attaching coil spring  60  may be a pin  52  extending horizontally from pawl  50 , formed such that coil spring  60  or other means for biasing the movement of pawl  50  can be attached to pawl  50 . 
     Operation of a Preferred Embodiment 
     This section describes the functioning of the present invention in a preferred embodiment as just described and as illustrated in  FIGS. 7   a  to  7   c.    
     During normal operation of the sectional door  140 , rotor  20  rotates about its axis and latches  30  move cyclically under the influence of gravity from a first latch position to a second latch position and back as the rotor  20  rotates. Plate  40  does not move; pawl  50  does not move. This is shown in  FIG. 7   a.    
     Imagining now that sectional door  140  begins a dangerously rapid descent, shaft  120  rotates rapidly in a counter-clockwise direction as the falling sectional door causes cable  130  to unwind rapidly from cable drum  110 . Rotor assembly  10 , which is securely attached to shaft  120 , also rotates rapidly. As rotor assembly  10  rotates rapidly, centrifugal force causes latches  30  to remain in a second latch position in which they extend beyond the protrusions  21  in the rotor  20  during their entire rotational circuit, even when positioned at the top of the rotor  20  where gravity would otherwise cause them to fall into a first latch position. 
     In the second latch position, the latch  30  nearest the top of the rotor  20  engages flange  41  on plate  40 , as shown in  FIG. 7   b . The rotation of rotor  20  causes plate  40  to rotate in a counter-clockwise direction. The shape of the notch  31  in the extended end of latch  30  is such that if latch  30  is sufficiently extended to engage a very small portion of flange  41 , the rotation of rotor  20  will cause latch  30  to rotate fully to the second latch position. In the second latch position, latch  30  is fully engaged with flange  41 . This design ensures that it will never occur that only a very small edge of latch  30  will be in contact with flange  41  and attempt to rotate plate  40 . 
     As plate  40  rotates, notch  43  disengages pin  51 , permitting pawl  50  to rotate towards rotor assembly  10 , as biased by coil spring  60 . Once plate  40  has moved sufficiently that notch  43  permits pin  51  to allow pawl  50  to move towards rotor assembly  10 , the biasing force of coil spring  60  pulls pawl  50  upwards and into the path of the flat surface  23  of protrusion  21 . This is shown in  FIG. 7   c . The rotation of the rotor assembly  10  is halted by pawl  50 . When rotor assembly  10  stops rotating, shaft  120  also stops rotating. This halts the rotation of cable drum  110 . Because cable drum  110  is fixedly connected to the sectional door  140  by means of one or more cables  130 , sectional door  140  halts its rapid downward movement. 
     In an embodiment in which the rotor assembly  10  and the cable drum  110  are formed as a single component, as shown in  FIG. 9 , cable drum  110  obviously halts its rotation as rotor assembly  10  rotation is halted by pawl  50 . 
     After sectional door  140  movement has been halted by the present invention, a user may wish to secure sectional door  140  in a closed position, or may need to lift sectional door  140  in order to remove an item located within the space enclosed by the sectional door  140 . One example would be a car or other vehicle. With the help of others, as required, an individual can lift the weight of sectional door  140  without the assistance of broken or weakened springs  100 . 
     As the user lifts the sectional door  140 , cable drum  110 , shaft  120 , and attached rotor assembly  10  rotate in a clockwise direction. As rotor assembly  10  rotates clockwise, the sloped side  24  of protrusion  21  contacts pawl  50 , biasing it away from rotor  20  as the rotation continues. At the same time, latch  30  that engaged flange  41  at the top of plate  40  is rotating clockwise as part of the rotor assembly  10 . As latch  30  disengages flange  41  on plate  40 , latch  30  falls back to the first latch position. Coil spring  60  biases plate  40  back to its first position. As pawl  50  is pushed away from rotor assembly  10  and plate  40  rotates clockwise to its first position, notch  43  re-engages pin  51 . This prevents pawl  50  from moving towards rotor assembly  10  after protrusion  21  has passed and would no longer inhibit the movement of pawl  50  towards rotor  20 . The device has thus been disengaged by manually lifting the door a short distance. 
     In a preferred embodiment, the shape of notch  43  formed in plate  40  determines the timing of the interaction between pawl  50  and flat surface  23  as the present invention engages to halt the movement of sectional door  140 . Notch  43  includes two seating points that restrain all movement of pawl  50 . During normal operation of the sectional door  140 , pawl  50  is positioned away from rotor  20 , and is locked in a position so it cannot move towards rotor  20 . As plate  40  begins to rotate, pawl  50 , as biased by coil spring  60 , moves towards rotor assembly  10 . Once plate  40  has rotated sufficiently to permit pin  51  to slip into the second area of notch  43 , pawl  50  is held firmly in place in a position where it will engage with the flat surface  23  of rotor  20 . In this position, “bouncing” action of latch  30  or plate  40  will not suffice to permit pawl  50  to move out of the path of rotor  20 . When pawl  50  is forced downward by the clockwise rotation of rotor  20 , this force will cause plate  40  to rotate slightly, permitting pin  51  to move out of the second area of notch  43 . 
     If at any time the manual lifting force is removed from the sectional door  140 , so that sectional door  140  again begins a rapid and dangerous descent, the present invention will re-engage as described previously. In this manner, a user can, by trial-and-error, realize that the sectional door  140  is not functioning normally; rapid downward motion is blocked; but upward motion is possible, and slow downward motion is possible. If a sectional door  140  held up by a manual force is released, it falls a short distance until the present invention re-engages. By repeated efforts, therefore, a user can easily discover how to raise or lower an unbalanced sectional door  140  that includes the present invention without the risk of serious injury or death that accompanies inventions in the prior art. 
     Other Embodiments 
     The present invention may be embodied in numerous other specific forms without departing from its spirit or essential characteristic of sensing the overly rapid descent of a sectional door and halting that descent. The herein described non-limiting embodiments are therefore to be considered in all respects only as illustrative, and not restrictive. 
     Other methods and positions for mounting a sensing component such as rotor assembly  10  are also included within the scope of this invention, so long as the rotation of shaft  120  is coupled to the rotation of rotor  20 . This coupling may be achieved through means that include, but are not limited to, mechanical means such as gearing or friction, electrical, optical, electro-optical, and magnetic means. 
     When mounted directly on shaft  120 , rotor assembly  10  can be positioned in various ways depending on manufacturing requirements. In one embodiment, rotor assembly  10  is mounted on shaft  120  in the center  121 , rather than at one of the ends where a cable drum  110  is typically located. A partial illustration of the present invention as used for this embodiment is shown in  FIG. 8 , with pawl  50  and plate  40  rotated somewhat to permit free movement of sectional door  140  directly beneath the center  121  of shaft  120  where the device is mounted. This embodiment is particularly effective for retrofitting a pre-existing sectional door  140  with the safety advantages of the present invention. Depending on the shape and configuration of the pre-existing sectional door  140 , a retro-fitting may also be accomplished by placing the present invention at either end of shaft  120 , adjacent to a cable drum  110 . 
     In one embodiment, cable drum  110  and rotor assembly  10  of the present invention are formed as a single component to obtain efficiencies in cost, manufacturing, installation, and effectiveness of the stopping force. This embodiment has the advantage that cable drum  110  is halted implicitly when rotor assembly  10  halts, as they are a single component, without the need for rotor assembly  10  to transfer a large impulse through a very short length of shaft  120 , exerting great strain on set screws or similar components fastening rotor assembly  10  and cable drum  110  to shaft  120 . 
     Other shapes and configurations for rotor assembly  10  are also included within the scope of this invention. The rotor  20  may be formed in various polygonal shapes that include a stopping surface that a member can engage to halt rotation of rotor assembly  10 . In one alternative embodiment, shown in  FIG. 5 , rotor  70  includes pins  71  that slide in and out under the force of gravity during normal operation of a sectional door  140 . If sectional door  140  begins an overly rapid decent, centrifugal force causes pins  71  to move to an outer position where a pin  71  strikes a stationary plate  72  that halts movement of rotor  70 , thus halting the movement of the cable drum and the movement of sectional door  140 . 
     Numerous methods are encompassed within the present invention for coupling a rotor to a moveable member that moves to a second position when the angular velocity of the rotor exceeds a threshold value. Latches  30  described previously are merely one preferred embodiment of this component of the present invention. Other mechanical, electrical, optical, or other technological means may be used to sense the angular velocity of the rotor and cause another component of the invention to change to a second position in which the components of the invention engage to halt rotation of the rotor. 
     The scope of the present invention is indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.