Sectional door cable tensioner

A cable tensioner (20) for a sectional overhead door (D) having a motor-driven counterbalance system (30) including, a spring-loaded axle (31), cable drums (24) carried by the axle, cables (C) attached to and interconnecting the cable drums and the door and forming and releasing cable wraps (29) on the cable drums upon raising and lowering of the door, the cable tensioner having, a tension spring (31) adapted to be mounted on the sectional door having a first end (34) and a second end (35), the first end being adapted to engage the door and the second end being adapted to slidingly engage the cable, wherein the tension spring urges the second end to take up any slack in the cable.

TECHNICAL FIELD

In general, the present invention relates to upwardly acting sectional doors. More particularly, the present invention relates to an upwardly acting sectional door system employing a motor-driven counterbalance system having a shaft, a torsional spring and cable to counterbalance the weight of the door. Most particularly, the present invention relates to a cable tensioner for maintaining the proper tension on the cable of such a door system.

BACKGROUND ART

Counterbalancing systems for sectional overhead doors have commonly employed torsion spring arrangements. The use of torsion springs in such sectional overhead doors is, in significant part, because the linear tension characteristics of a torsion spring can be closely matched to the substantially linear effective door weight as a sectional door moves from the open, horizontal position, where the door is largely track supported, to the closed, vertical position or vice versa. In this manner, the sum of the forces acting on such a sectional garage door may be maintained relatively small except for momentum forces generated by movement of the door by the application of manual or mechanical forces. In this respect, sectional overhead doors have been provided with lift cables or similar flexible elements attached to the bottom of the door and to cable storage drums mounted in spaced relation on a drive tube, which rotate when the drive tube is actuated.

In many cases, these cable storage drums have surface grooves that guide the lift cables on and off of the cable storage drum to prevent the coils or cable wraps from rubbing against each other and chafing which would occur if positioned in side-by-side engaging relationship or if coiled on top of each other. Lift cables sized to meet operational requirements for sectional overhead door applications are commonly constructed of multiple strand steel filaments that have a pronounced resistance to bending when stored on the circumference of the cable drums and, thus, require tension to remain systematically coiled or wrapped about the cable drums in the surface grooves therein.

A problem arises if tension is removed from one or both of the lift cables of a sectional overhead door in that the lift cables tend to unwrap or separate from the cable drums; thereafter, when tension is restored, the lift cables may not relocate in the appropriate grooves or in appropriate relation to adjacent cable wraps. In some instances, a cable wrap will locate on a groove further axially inboard of the door from its original position so that as the door moves to the fully opened position, the cable drum runs out of grooves for cable wraps, such that the lift cable coils about parts of the drum that are not designed for cable storage. In this instance, if the lift cable dislodges from the cable storage drum and engage the smaller radius of the counterbalance system drive tube, the leverage affected by the springs through the cable drum and cable is reduced such that the door will be extremely difficult or impossible to move. This is because the linear force between the door and the counterbalance springs relies on the leverage against the counterbalance spring being applied by the weight of the door operating through the radius of the cable storage drum grooves rather than a reduced radius portion of the cable drum or the drive tube for the counterbalance system

In other instances, the removal of tension from the lift cables can result in cable wraps or coils being axially displaced from the proper groove on the cable drum to overlie existing cable wraps stored on the cable drum, which may cause the length of cable between the cable drums at opposite ends of a door to assume a different effective operating length. In such case, the door may be shifted angularly in the door opening, with the bottom edge of the door no longer paralleling the ground and the ends of the door sections moving out of a perpendicular orientation to the ground. When thus angularly oriented, continued movement of the door can readily result in the door binding or jamming in the track system and, thus, being rendered inoperative.

In the instance of either of these operating anomalies occasioned by loss of tension in the lift cables, it is probable that the resultant tangling of the lift cables and/or jamming of the doors will prevent the door from further automatic or manual operation, leave the door in a partially open condition, and require qualified service personnel to repair or replace damaged components and reassemble and realign the door and counterbalance system components before the door is restored to normal operating condition.

There are a number of possible operating circumstances wherein tension in the lift cables of a counterbalance system for a sectional overhead door becomes reduced to such an extent that the lift cables may become mispositioned on or relative to the cable storage drums, thereby producing the problems discussed above. One example is when a door is rapidly raised from the closed to the open position at a velocity that is faster than the cable storage drums can rotationally react, such that slack is created in the lift cables. Another example is in the utilization of a motorized unit, such as a jackshaft type operator, that turns the counterbalance system shaft to open and close a sectional overhead door. A jack-shaft may create cable slack when the operator turns the cable storage drums without the door moving. Many jackshaft operators have motor controls and sensors that will determine if the operator is turning the counterbalance tube without the door moving to minimize cable slack which will result in the cables becoming entangled. However these methods are not exact nor are they instantaneous such that the operator could rotate the drive tube and cable drums through one or more revolutions before the sensors signal the motor controls to shut the motor off. During this time the cable is slack and if this occurs when the door is in the fully open position, the cables can become tangled preventing further movement of the door.

One approach to preventing cable mispositioning has involved utilization of grooves in the circumference of the cable storage drums, which are otherwise present for positioning and spacing cable as it is taken up during the raising of a garage door. In some instances, exaggerated or deep grooves have been employed in the cable storage drums in an effort to maintain the lift cables appropriately positioned during a loss of tension on the lift cables. While the use of grooves so configured may be helpful in preventing lift cable mispositioning in minor losses of tension, this approach does not solve the commonly encountered problem of appreciable slack being created in the lift cables.

Another approach to preventing cable mispositioning has involved utilization of retainers in the form of a hood, shroud or snubber associated with the cable drums. With these devices capturing the cable between the drum and the retainer, the proper cable positioning can be maintained for a particular size drum and system components. However, these retainers do not permit utilization on other than a particular one of the many different drum sizes and configurations employed by different manufactures for different door systems.

Thus, no solution to substantial cable slack in sectional overhead door systems having motor driven counterbalance systems, for cable drums of different designs and sizes, has been recognized in the industry.

DISCLOSURE OF THE INVENTION

Therefore, an object of the present invention is to provide a cable tensioner for a motor driven counterbalance system for a sectional overhead door that accommodates slack developed in a lift cable without attendant mispositioning of the lift cable on the cable storage drums when tension in the lift cables is restored. Another object of the present invention is to provide such a cable tensioner which is operative independent of the style, shape, or size of the cable storage drums of the counterbalance system of the door. A further object of the present invention is to provide such a cable tensioner wherein cable tension and thus, cable positioning on the cable drums, is maintained even in the event of the development of several feet of slack in the cable due to the cable drums being driven without attendant movement of the door.

Another object of the present invention is to provide a cable tensioner for a motor driven counterbalance system for a sectional overhead door which consists of springs, a cable engaging clip and mounting brackets for positioning the springs on the door. Yet another object of the invention is to provide such a cable tensioner that does not mount over or adjacent to the cable storage drums and does not require pulleys or other components to manage even substantial amounts of cable slack. Still a further object of the invention is to provide such a cable tensioner that employs a flexible wand, which may be formed unitary with the spring, that can deflect to maintain cable alignment with the cable drum grooves even when substantial slack is being taken up by the tensioner when the door is in the fully open position.

Still another object of the present invention is to provide a cable tensioner for a motor driven counterbalance system for a sectional overhead door that may employ cable storage drums having conventional guide grooves. A still further object of the present invention is to provide such a cable tensioner that does not affect the counterbalance system or alter its operational performance in a manner that could produce adverse effects on the operation of the door. A still further object of the present invention is to provide such a cable tensioner which mounts to the lower panel of the door and therefore does not require a ladder or special tools to install. A still further object of the present invention is to provide such a cable tensioner that is relatively inexpensive, requires no service, and can readily be retrofitted to existing motor driven counterbalance systems.

In general, the present invention contemplates a cable tensioner for a sectional overhead door having a motor-driven counterbalance system including, a spring-loaded axle, cable drums carried by the axle, cables attached to and interconnecting the cable drums and the door and forming and releasing cable wraps on the cable drums upon raising and lowering of the door, the cable tensioner having, a tension spring adapted to be mounted on the sectional door having a first end and a second end, the first end being adapted to engage the door and the second end being adapted to slidingly engage the cable, wherein the tension spring urges the second end to take up any slack in the cable.

BEST MODE FOR CARRYING OUT THE INVENTION

A door system, generally indicated by the numeral10, is shown in the accompanying drawings. Door system10generally includes an upwardly acting door D, such as a rolling door or a sectional door, as shown. Door system10is located within an opening defined by a framework11which may include a pair of vertically oriented jambs12that are horizontally spaced from each other and connected by a header13near their upper vertical extremity. Track assemblies, generally indicated by the numeral15, may be supported on the framework11, as by flag angles14that extend rearwardly from the jambs12. Track assemblies15may include a generally vertical track section16and a generally horizontal track section17interconnected by an arcuate transition section18. The track assemblies15may include channel-like track sections16,17,18that receive guide rollers19mounted on the door D. The rollers19and track assemblies15interact to guide the door from a generally vertical closed position (FIG. 1) to a generally horizontal open position (FIG. 3).

To aid in the lifting of the door D, a counterbalance assembly, generally indicated by the numeral20, is provided. The counterbalance assembly20generally includes an axle21, a counterbalance spring22, which may be a coil spring30, as shown, and a cable C (FIG. 3), which may be windingly received on a cable drum24located at either end of the axle21. The axle21is supported by a support bracket25and freely rotatable therein. In turn, the cable drum24is rotatably fixed to the axle21, such that it rotates therewith to wind and unwind the cable C to raise and lower the door D. The opposite end of the cable C is attached to the door D, as by a lug26extending from an edge27of the door D. As best shown inFIG. 4, the lug26may be located at the approximate lower extremity of the door D. It will be appreciated that cables C are located at both ends of the door D, but for sake of simplicity, the description will proceed with reference to a single cable C.

With reference toFIGS. 1 and 2, as the door D assumes a closed position, the cable C is paid out from the cable drum24and is held taut by the force of the counterbalance spring22acting through the axle21and cable drums24. Turning toFIG. 3, as the door D is raised to the open position, force from the counterbalance spring22is applied to the door D by cable C to help offset the weight of the door D and allow it to be opened with little effort. To automatically operate the door D, an operator28, for example, a jack shaft operator as shown, may be provided and may interact with the counterbalance assembly20in a manner well know in the art to raise and lower the door D. As the door D is raised, the cable C is wound on the cable drum24forming successive cable wraps29. To ensure proper winding of the cable C and avoid any slack in either of the cables C that might skew the door D or cause the door D to bind, tension must be maintained on the cables C throughout the winding and unwinding process.

To that end, a cable tensioner, generally indicated by the numeral30in the drawings, is provided. With reference toFIG. 2, the cable tensioner30generally includes a tension spring31, which may be a coil spring, as shown, and a clip32that couples the tension spring31to the cable C. In the example shown, tension spring31has a coiled body33, a first end34that engages the door D, and a second end35that attaches to the clip32. As shown, the second end35of tension spring31may be relatively long in comparison to the first end34to constitute a wand-like member. It will be appreciated that the length of the second end35may be adjusted to take up a selected amount of slack within the cable C. It is preferable that the second end35have a degree of flexibility, such that the second end35may bend to maintain the cable C in proper alignment with the cable drum24as successive cable wraps29are formed around the cable drum24and to cushion the take-up and release of excess cable when that occurs. The length and thickness of the second end35may be used to create sufficient flexibility for this task or an otherwise rigid second end35may be provided with a suitably flexible attachment (not shown).

Aside from maintaining alignment of the cable C as it is wound, the length of the second end35may be limited by other operating conditions. For instance, in a sectional door D, as shown in the drawings, the height of a door section36on which the cable tensioner30is mounted may limit the length of the second end35as the second end35might interfere with the movement of the door section36, as by contacting a roller19, as it travels through the transition section18of the track assembly15. While the length of second end35will vary depending on the type of door D used, in the example shown, a second end length of approximately one half the height H of the door section36was found to be suitable.

The cable tensioner30may be mounted on a bracket, generally indicated by the numeral40, which may, in the example of a coil spring, include a pair of tabs41spaced sufficiently to receive the tension spring31therebetween. A shaft42, which may be formed by a bolt, as shown, extends between the tabs41and may pass through the body33of the tension spring31to secure the tension spring31to the tabs41. Tabs41are, in turn, secured to the door D as by a crosspiece43that is mounted flush against the door D as by screws (not shown).

With reference toFIGS. 5-7, the clip32includes a pair of walls46that may be connected at a first end47and open at a second end49to form a U-shaped channel48. To facilitate attachment of the clip32to the second end35of spring31, a pair of dog ears50may extend outwardly from the second ends49. As depicted inFIG. 7, the dog ears50may extend from the center of the walls46in parallel fashion, such that the dog ears50are laterally spaced from each other. To help hold the clip32on the cable C, the dog ears50may initially extend inward to at least narrow the gap between the dog ears50and neck over the channel48to reduce the likelihood of the clip32falling from the cable C. To that end, the dog ears50may be somewhat flexible to allow the cable C to at least initially be forced through the gap between the dog ears50and into the channel48. After the cable C passes, the flexible dog ears50retract to close the cable C within the channel48.

In the example shown in the drawings, dog ears50each define an opening51through which the second end35of spring31may pass in securing the second end35of spring31to the clip32. For example, as shown inFIG. 2, the hook37of second end35may pass through the openings51and then bend back upon the second end35to secure the clip32to the second end35of spring31during operation. The cable C fits within the channel48between the second end35of tension spring31and the first end47of the clip32. A channel48defined by the clip32is sufficiently sized to allow the clip32to slide along the cable C as necessary as the cable tensioner30moves with the door section36. As best depicted inFIG. 7, the channel48may be curved within the plane of the cable C, giving the lower surface53of the clip32, a generally semicircular profile. While the clip32is sliding on cable C, the curved configuration of clip32allows the clip32and cable C allowing the clip32to slide more freely and thus reduce the wear on the cable C. As best shown inFIG. 4, when the clip32engages the cable C to take up slack, the curved channel48enlarges the contact area of the clip32with the cable C to apply the force of spring31over a substantial area of the cable at all times.

It will be appreciated, however, that a less elaborate clip may be suitable for connecting the second end35of spring31to the cable C. In an alternate embodiment depicted inFIGS. 8 and 9, an alternative clip132is shown. Since the alternate embodiment, depicted inFIGS. 8 and 9, shares similar components with the embodiment depicted inFIGS. 1-7, like numerals will be used to refer to like components. As in the previous embodiment, the clip132attaches to the second end135of the tension spring131. In this example, the clip132defines a generally circular channel148through which the cable C passes. The second ends149are brought into close proximity to each other with the dog ears150extending outward therefrom in very close parallel relationship, such that the dog ears150are in contact with each other. As in the previous embodiment, the second end135may pass through openings151formed in the dog ears150. Like the previous embodiment, the channel148is sized larger than the cable C, such that the clip132may slide along the cable C during operation of the door D. As best shown inFIG. 9, as the door D is operated, the clip132maintains its contact with the cable C to provide the necessary tension to the cable C if any slack is formed. Otherwise, the tension on the cable C created by the counterbalance spring22offsets the force created by the cable tensioner130, such that the cable tensioner130does not cause any deflection of the cable C that might cause damage to the cable C or binding of the door D.

With reference toFIGS. 2-4, operation of the cable tensioner30will now be described. The alternate cable tensioner130, depicted inFIGS. 8 and 9, operates in a similar fashion as cable tensioner30, and thus this description will apply to both embodiments. Any distinctions between the two embodiments will be noted herein.

Starting with the door D in a closed position (FIG. 2), the cable tensioner30is shown with the cable clip32in contact with the cable C and attached to the second end35of the tension spring31. The tension spring31applies a tension to the cable C by contact of the clip32on the cable C. In the position shown inFIGS. 2, it may be seen that the tension on the cable C, generated by the counterbalance spring22, maintains the cable C in a taut condition without any slack. This tension in the cable C also overcomes any tension created by the tension spring31and thus, the cable clip32is held in an upright position.

Similarly, as the door D reaches an open position (FIG. 3), tension within the cable C may operate to hold the second end35of tension spring31and cause it to rotate relative to the position shown inFIG. 2. As can be seen by comparingFIGS. 2 and 3, the second end35of tension spring31rotates counterclockwise from an upright position, where the second end35extends upwardly from the bracket40to a rotated position, shown inFIG. 3, where the second end35extends downwardly toward the bottom of the door D. It will be appreciated that this rotation occurs gradually as the door section36, on which the cable tensioner30is mounted, moves through the transition section18of track assembly15.

In the event that slack is created in the cable C, as shown inFIG. 4, the second end35of the cable tensioner30may be urged outwardly by tension spring31, relative to the cable drum24, to take up any slack within the cable C. In the example shown, the second end35of spring31rotates in a clockwise direction under the urging of the tension spring31to draw the slack in cable C outward from the cable drum and maintain the appropriate tension in the cable C and maintains proper alignment axially of cable drum24. As can be seen from a comparison ofFIGS. 3 and 4, the second end35rotates in a clockwise direction urging the clip32upward relative to the door section36toward its uppermost extremity. The degree of clip movement will, of course, be proportional to the amount of slack within the cable C. In the example shown, the cable tensioner30may gather up cable equal to four times the length of second end35of spring31.

To reduce the stress on the cable tensioner30as it is urged toward the open position (FIG. 3), it may be beneficial to position the cable tensioner30closer to the point where the cable C is attached to the door D, for example, near lug26. In other words, in considering a single panel36, the cable tensioner30,130is mounted to the side of the panel's midpoint M closest to the cable's point of attachment. In the example shown, the cable tensioner30,130is mounted below the midpoint of panel36. In this way, the second end35undergoes a lesser degree of rotation in moving from the closed position (FIG. 2) to the open position (FIG. 3).

As shown in the depicted embodiments, cable tensioner30,130is mounted on the lowermost panel making it accessible in either the closed (FIG. 2) or open (FIG. 3) positions. Thus, the cable tensioner30,130is easily accessed for installation or maintenance without the need for a step ladder.

The second end35of tension spring31may be attached in any manner including the clips32,132shown. The clips32,132are preferable in that they are less likely to damage the cable C over extended use. Clips32,132may be constructed of any material including metallic and nonmetallic materials, preferably providing low friction engagement with the cable C to prevent wear and fraying of the cable C.

Thus, it should be evident that the sectional door cable tensioner disclosed herein carries out one or more of the objects of the present invention set forth above and otherwise constitutes an advantageous contribution to the art. As will be apparent to persons skilled in the art, modifications can be made to the preferred embodiments disclosed herein without departing from the spirit of the invention, the scope of the invention herein being limited solely by the scope of the attached claims.