1. Field of the Invention
The present invention relates generally to the field of 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 installing, maintaining and operating sectional doors which utilize spring mechanisms to facilitate door movement.
2. 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 or metal panels which are joined by metal hinges and hung from metal 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 where they are found in one and two car sizes.
The size of sectional doors and the weight of their materials make them relatively heavy and, therefore, difficult to lift. Many doors also contain insulation and other materials which further add to the door""s weight. Even an average-sized residential garage door can weigh several hundred pounds, making it impossible for the average person to lift.
As a consequence of the weight of sectional doors, mechanisms have been invented to counteract the door""s weight thereby allowing manual operation of the door. One common method of counteracting a door""s weight is accomplished with a counterspring mechanism using 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 slows the fall of the door during closing and aids significantly in lifting the door; in effect, the door weight is balanced.
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 FIG. 1, one or more coil springs 2 are wound around a shaft 4 near the top of the door 6. One end of each coil spring 2 is attached to a mounting bracket 8 which is connected by screws 12 to the building structure which is typically a wooden beam 14 across the door opening. The other end of the spring is attached to a cable drum pulley 16 around which a cable 18 is wound. The cable 18 extends to the bottom of the door where it is attached with a bracket 20. These coil springs are pre-wound or pre-tensioned to increase lifting potential and ensure that the door is lifted to a fully opened position.
As the door closes, the cable unwinds from the cable drum pulley 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 holds 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. Under proper operating conditions, this mechanism results in a smoothly operating door, but when poorly or improperly maintained or installed this force can be instantly unleashed in an injurious and even deadly fury.
One problem area where serious injuries can occur is at the location where the spring mounting bracket 8 attaches to the building. The spring mounting bracket is usually attached to a wood header or beam spanning across the doorway opening or vertical wood stud members.
These beams, headers or studs are typically wood members that sometimes have a relatively high moisture content at the time of construction. Over time the wood loses its natural moisture, causing shrinkage, warping or bowing of the framing members as the shrinkage pattern encounters natural inconsistencies in the grain of the wood. Cracking also results from this natural moisture loss leaving large voids in what was once solid lumber. As a result of this drying process, holes drilled for screws and mounting hardware may expand, crack and otherwise deform leaving the screws or other connectors loose and structurally weakened.
The connection to the wood support is typically made with lag screws which penetrate holes in the bracket and thread into drilled holes in the wood. This type of connection generally appears structurally sound over the short term, but problems may arise with wood shrinkage and installation problems. As the wood shrinks, the screw holes expand and the grip on the screw threads decreases and fails. Problems may also arise from installation error or misjudgment. Holes for lag screws should be drilled to an exact size to provide optimal screw capacity. When holes are over-bored to a diameter that is larger than the optimal size for the screw, the screw""s holding capacity is greatly diminished. Similarly, a hole may be drilled too small or not at all which may cause the wood to crack when the lag screw is installed or a screw is inserted. Likewise, a lag screw or other fastener maybe over-tightened, causing the screw thread to twist within the hole, thereby removing some of the wood material within the hole and effectively stripping the hole interior. This also weakens the screw""s holding capacity.
Often, siding material is applied to the interior face of the doorway structure to which the spring mounting bracket is attached. Generally, this siding is a gypsum-based xe2x80x9cdrywallxe2x80x9d or xe2x80x9csheetrockxe2x80x9d material that provides fire-proofing and aesthetic benefits but has very little structural strength. Screws and other fasteners which must penetrate this layer have considerably lower holding capacity due to the decreased fastener penetration into the sound structural wood below. Sometimes a piece of 2xc3x974 or 2xc3x976 is nailed through the sheetrock to the structure below, to which the spring mounting brackets are fastened. In this situation, the spring""s torsional force is now contained only by the nails.
The problem is exacerbated by the repetitive vibration the connection must endure. The vibration and stress caused by the repeated opening and closing of the door, especially when performed by high-speed electric openers, can be an additional and significant factor in connection failure. Screw connections that are already weakened by the above-mentioned factors can vibrate loose and screws can even wiggle right out of their holes.
When the mounting bracket connection fails, the entirety of the stored torsional energy of the door spring is instantaneously unleashed, typically through uncontrolled, high-velocity spinning of the sharp-edged metal mounting bracket. When this failure occurs, any person or thing in close proximity to the bracket will be injured or destroyed. The energy of the spring mechanism is sufficient to cause severe injury and can easily maim, dismember or kill a person who is near the unit at the time of failure.
A dangerous situation often presents itself when an unwary homeowner or repairman observes loose or missing fasteners on the spring mounting bracket. Generally, the observer""s reaction is to tighten the loose fasteners. This typically requires the xe2x80x9crepairmanxe2x80x9d to climb a ladder, putting himself in very close proximity to the spring mounting bracket while tightening the loose fastener with a wrench. If the holes have expanded due to drying or have been stripped out or otherwise weakened, the attempted xe2x80x9ctighteningxe2x80x9d will generally cause further weakening of the connection which is under spring force load often causing complete connector failure. When complete connector failure occurs, the spring force is instantly released by the wildly spinning mounting bracket immediately adjacent to the unwary, surprised and potentially badly injured xe2x80x9crepairman.xe2x80x9d
Another safety problem occurs at the location where the cable 18 attaches to the door. This connection is typically made with a bracket 20 which is attached to the door with sheet metal screws. Like the rest of the spring mechanism, an enormous amount of energy is stored in the connection between the cable and the door. While this connection is not as prone to failure from wood deterioration or installer error, it can fail as a consequence of fatigue, improper installation, collision damage or corrosion. Common sheet metal screws are typically installed with power tools which can over-tighten and strip the metal parts they connect, leaving a weakened connection. Fatigue due to repeated stress cycles as the door opens and closes also takes a toll on the connection, especially with light gauge materials. Even when the connection is not seriously compromised, for example, in a light collision which slightly bends or breaks a bracket, an observer will have a desire to replace the damaged part, thereby exposing himself to danger. Most commonly, this danger presents itself when untrained repairmen or unsuspecting homeowners try to adjust or disconnect any part of the lift cable, bottom bracket or spring mechanism. When the majority of the cable bracket screws are removed, the lift cable can instantly fly from the door, slicing or shredding most objects in its path. Again, the full energy required to lift the heavy door around above the opening is instantly unleashed with the potential to maim or kill. Typical lift cable brackets are stamped light-gauge metal with sharp edges, further increasing the hazard.
Set screws on the spring fixtures, such as winding and stationary cones, can also be inadvertently released by a repairman or unsuspecting home owner, resulting in a similar instantaneous release of the dangerous spring energy.
The present invention reduces or eliminates the safety hazards of the prior art through the use of side mounted springs attached to lock-on side bearing brackets, tamper-resistant set screws and fasteners and lock-on bottom roller brackets which attach the lift cable to the door frame.
The problematic connection of the prior art between the mounting bracket and the building structure is eliminated by moving the coil springs to the sides of the torsion shaft above the door and attaching the springs to a bracket which is bolted to the metal track structure of the door. The track structure is screwed into the building framework, but through a much more expansive connection which avoids the concentrated, high-stress, high-torsion connection of the prior art. The preferred embodiments of the present invention incorporate multiple safety features that serve as additional safety back-ups for the systems of the present invention. Among these redundant safety features is a lock-on side bearing bracket with an inventive locking device that prevents the spring mechanism from releasing its energy even when the track and spring mechanism are entirely disconnected from the wall. Additionally, the spring mechanism energy will be retained even when the bolts holding the lock-on bearing bracket are removed. This redundant safety feature is accomplished by the use of a novel lock-on hook device which is an integral part of the bearing bracket. Many prior art side-mounted springs totally ignore safety concerns. Many of them utilize very dangerous outside lift cables which can entrap and strangle children playing with the door.
The present invention also eliminates the dangerous and problematic connection between the spring mechanism cable and the sectional door. This problem is eliminated by the use of a lock-on bottom roller bracket which is attached to the door frame with screws in a conventional manner, but which also incorporates redundant safety features. One safety feature is a lock-on bracket mechanism which hooks below the door frame, but which does not lock onto the door frame unless the attachment screws are removed or fail while tension is on the lift cable. Another safety feature is a curl located at the bottom of the lift cable which prevents the lift cable from straightening and coming off the cable drum.
The lock-on bottom roller bracket comprises a lift cable connection which uses a cable loop and clevis pin assembly. Additionally, the lock-on bottom roller bracket comprises a hook device which wraps around the bottom of the door frame and with the slightest movement prevents the bracket from being removed from the door frame while there is tension on the lift cable. The lock-on feature fastens solid only when the screws are removed while there is tension on the lift cable. The lock-on hook is designed to be free from the vertical part of the door frame unless the fasteners are removed while there is tension on the lift cable. At that point, the bottom lock-on roller bracket locks on. Further, the lock-on bottom roller bracket comprises a bottom plate which attaches below the door frame, thereby strengthening the attachment to the door and helping to prevent the bracket from instantaneously separating from the door in the case of conventional fastener failure or removal. The lock-on bottom roller bracket is designed for safer interior lift cables and may not be used as an option for dangerous outside lift cables used in some prior art designs.