Light weight ladder systems and methods

A method for manufacturing a rail for a ladder. The method may include pultruding in a longitudinal direction, a rail having a selected cross-sectional shape. The rail may then be cut to a predetermined length at a distal end. A force may be applied, in a lateral direction, to the rail to form a curvature therein. The curvature may be characterized by a flared portion, a straight portion, and a curved region providing the transition therebetween. The rail may be held at the desired curvature for a time selected for the rail to take on the curvature substantially permanently. The force may then be removed and the rail may be assembled into a ladder.

BACKGROUND

1. The Field of the Invention

This invention relates to ladders and, more particularly, to novel structures, systems, and methods for lightweight ladders.

2. The Background Art

Ladders are convenient for providing a user with access to locations that would otherwise be inaccessible. Ladders are typically available in several configurations, namely straight ladders, straight extension ladders, step ladders, and combination step and straight extension ladders (“combination ladders”). Each type of ladder may have particular situations for which it is best suited. Combination ladders are particularly useful because they provide, in a single ladder, most of the benefits of the other ladder designs. However, typical combination ladders are hampered by excessive weight, higher purchase costs, and safety concerns raised by the increased complexity of the ladder design.

In contrast to simpler ladder designs, combination ladders must support multiple load configurations. As a result, the structural elements of the ladder must be reinforced to support the loads. For example, the hinge of a combination ladder in a straight configuration must withstand larger moment loads than the hinge of a step ladder. Additionally, the hinge of a combination ladder must rigidly support the upper half of the ladder above the lower half. These load and rigidity requirements of a combination ladder hinge result in thicker components and more reinforcement material, both of which contribute to additional weight of the ladder.

Additionally, combination ladders are more expensive than traditional ladder designs. As stated above, combination ladders require additional reinforcement to compensate for the various loadings that may be applied. Stronger materials or simply additional materials increase the cost of the ladder. The greater complexity of combination ladders also increases assembly costs.

Furthermore, combination ladders present additional safety concerns. Due to the fact that combination ladders are by design collapsible, inadvertent release of the hinge may result in a total collapse of the ladder. For example, a hinge may contain a selective locking and releasing mechanism for maintaining the hinge in certain selected positions. A worker, through inadvertence or mistake, or even through stumbling or other physical imbalance, may, in some circumstances, strike a release mechanism, endangering the rigidity of the locking mechanism holding a hinge in a specific position. Typical combination ladders do not provide a remedy for such potential hazards.

Accordingly, what is needed is a combination ladder with components designed and arranged to provide the maximum strength without significantly increasing the over all weight of the ladder. Additionally, ladder components need to be designed to promote ease of manufacture and assembly, thus reducing the cost of the combination ladder. Moreover, what is needed is additional safety features such as an interlock that requires affirmative, intentional actions on behalf of a user, before a release mechanism actuates. It would be an advance in the art if the interlock and the release mechanism could both be operated by a single hand of a single user, simultaneously, but only intentionally.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION

In view of the foregoing, the present invention provides ladder componentry that maintains required strength while decreasing weight, is simplified to reduce manufacturing and assembly cost, and reduces the likelihood of potential hazards.

For certain applications, it may be desirable to widen the stance of the ladder rails (side rails) to increase stability of the ladder on the supporting surface. This may be accomplished by creating an outward flare in the rails, tapering above the supporting surface. The present invention may provide a method for manufacturing such a rail. The method may include pultruding in a longitudinal direction, a rail having a cross-sectional shape. The rail may then be cut to a predetermined length to receive rungs.

Before the rail material has cured or hardened, a force may be applied, in a lateral direction, to the rail to form a curvature therein. The curvature may be characterized by a flared portion, a straight portion, and a curved region providing the transition therebetween. The curved region may have a shape selected from a continuous arc substantially coincident with the flared portion, a series of angled bends spaced from one another along the curved region, and a single continuous bend connecting a straight portion to a flared portion.

The force may be maintained, holding the rail at the curvature, for a time selected for the rail to take on the curvature substantially permanently. The rail may then be assembled into a ladder. The rungs applied to the ladder may have a length selected to accommodate the flare.

Rails in accordance with the present invention may have any suitable cross-section. The cross-section may be selected for structural rigidity, strength, stiffness, ergonomics, ease of manufacturing, or some balance of other competing considerations. Rails may be formed with an open or closed cross-section. In certain selected embodiments, an extension ladder may comprise an open-cross-section exterior rail with a closed-cross-section interior rail sliding longitudinally within a portion thereof. If desired, glide pads or strips may be included at the interface between exterior and interior rails to decrease friction and wear during motion therebetween.

Rails and rungs in accordance with the present invention may be constructed of any suitable material. In certain embodiments, rails may be formed of a reinforcing fiber in a thermoset polymer matrix. A fiber reinforced thermoplastic polymer, metal, or metal alloy may also be used as the rail or rung material. The choice of material may influence the manufacturing process. For example, if aluminum were selected for the rail material, an extrusion process may be selected instead of a pultrusion process. If desired, portions or all of the interior of the rail or rung cross-sections may be filled with a filler material to increase structural performance such as resistance to buckling.

The present invention may provide a method for manufacturing a rung. The method may include monolithically forming a tube of a selected material. The tube may have a body portion comprising a closed cross-section with at least one substantially flat side wall. A first rib may extend in a first direction away from the body portion so as to be substantially co-planar with the flat side wall. If desired, a second rib may extend in a second direction away from the body portion so as to also be substantially co-planar with the flat side wall. The tube may be extruded, then cut to a desired length.

Depending on the application for which the rung is designed, ribs may be used for different purposes. For example, if the rung is to be used between interior rails, the ribs may form the tread surface. If the rung is to be used between exterior rails, the ribs may be used as securement locations for securing the rung to the rails. In such a case, portions of the ribs may be removed to expose the body portion for a tread surface.

The present invention may include various reinforcing methods and structures. These may maintain a required strength locally while permitting thinner wall thickness elsewhere, and thus reducing the weight of the ladder. For example, a collar may support the walls of a rail against crushing when swaging a rung thereto. In certain embodiments, a reinforcing plate may support the side wall of a rail against splitting forces under the load imposed thereon by an extension lock.

A hinge in accordance with the present invention may include a first armature pivotably connected to a second armature. A lock may connect to the first armature to be movable between a first, locked position fixing the first armature with respect to the second armature, and a second, unlocked position providing uninhibited pivoting of the armatures. If desired, additional locking positions may be added. Such locking positions may include a closed position, a step ladder position, and a straight position.

A pinch point may result when the end faces of corresponding armatures come in contact with one another. If a hand, finger, or the like of a user were to be caught in a pinch point, serious injury may result. Various hinge guards and armature designs and configurations may be applied to a hinge in accordance with the present invention in an effort to protect the user from being pinched.

Guards in accordance with the present invention may produce a barrier for preventing any part of a user from entering the pinch point, thus preventing injury. Additionally, the armature of a hinge may be shaped to provide spacing when in the straight position, thus greatly reducing the size of the pinch point, or in some embodiments, eliminating the pinch point entirely.

In certain embodiments, an interlock comprising an actuator may selectively resist the movement of the lock from a locked position to an unlocked position. The interlock may resist movement of the lock in any suitable manner. In selected embodiments, the interlock may pivot in and out of an interference position with respect to the lock, thus controlling the release of the lock.

The interlock may include a bias member to urge the interlock into the lock-secured (non-releasable) position. The lock and the interlock may be movable and positioned to be simultaneously actuated by a single hand of a user.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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 systems and methods of the present invention, as represented inFIGS. 1 through 48, is not intended to limit the scope of the invention, as claimed, but is merely representative of certain exemplary embodiments in accordance with the invention. The various preferred embodiments of the invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout.

Referring toFIGS. 1 and 2, ladders10typically comprise three main component groups, namely the rails12providing the vertical support, the rungs14providing the steps, and the hinges16providing pivoting of the rails12between open and closed positions. Step ladders10or combination ladders10may have components selected to meet the needs of the particular ladder design.

For example, while a step ladder10only requires a rung14with a single tread, a combination ladder10may require rungs14that provide a tread on two sides. Extension ladders10require rails12capable of extending or contracting in length. In one embodiment, an exterior rail18may house or engage an interior rail20in a telescoping relation to provide a ladder10of variable height.

Extension ladders10may have different rung14designs to accommodate extension of rails12. For example, exterior rungs22may be mounted on the outside of the exterior rails18to avoid interfering with the sliding motion of the interior rails20. Interior rungs24may extend between interior rails20. An extension lock26may provide a stop to releasably lock the exterior rails18with respect to the interior rails20at periodic locations of extension.

The intended use of a ladder10greatly affects the design of the hinges16. The hinges16used to lock a ladder10in a straight configuration must typically support much larger loads than the hinges16of a simple step ladder10. Moreover, the rigidity of a hinge16used in a straight configuration must be greater to securely and safely maintain the upper half of the ladder10above the lower half of the ladder10.

In the disclosure presented herein, each ladder10component group (i. e. rail12, rung14, hinge16), with illustrative alternative embodiments, will be addressed separately and in order. It should be understood that most of the designs of component12,14,16are compatible with one another and even interchangeable in many cases. Thus, for example, if a number of designs of rungs14are presented, the intended use of the ladder10may determine which rung14may be the most appropriate for the particular application.

Referring toFIG. 3, the rails12of a ladder10provide the vertical support for the user and the rest of the ladder10structure. Rails12may be constructed of any suitable material including metal, metal alloy, composite, reinforced polymer, wood, and the like. Commonly used materials may include aluminum alloys and fiber reinforced thermoset and thermoplastic polymers. The purpose for which the ladder10will be used may provide the information necessary to determine which rail12material may be best suited for the job. For example, a ladder10used by an electrician may have rails12made of a non-conducting material, thus reducing the risk of grounding the user through the ladder10and producing an electric shock.

In other ladder10applications, cost may be the driving factor when determining the best rail12material. The rail12configurations and manufacturing methods presented herein may be applied to rails12constructed of many suitable materials.

Exterior rails18may be shaped to improve the performance of the ladder10into which they are integrated. In certain embodiments, an exterior rail18may be divided into a straight portion28and a flared portion30. The transition from the straight portion28to the flared portion30may be accomplished by a curved region32. A length34of the curved region32may be of any suitable magnitude. For example, the length34of the curved region32may be comparatively short and simply provide the transition from the straight portion28to the flared portion30. In an alternative embodiment, the length34of the curved region32may be greater and make up a large part of the flared portion30. In such a case, the curved region32is increasing the flare throughout the flared portion30.

When assembled into a ladder10, the straight portions28of corresponding exterior rails18may be separated by a distance36corresponding to the width of a normal ladder10. The flared portions30of corresponding exterior rails18may begin with the same distance36of separation and then widen to produce a wider base stance38. The wide base stance38may improve overall stability of the ladder10.

The particular curved region32or flared portion30of an exterior rail18may be selected to improve stability of the ladder10. The curved region32may create any suitable curvature or flare in the flared portion30. For example, the curved region32may be a continuous arc substantially coincident with the flared portion30. In an alternative embodiment, the curved region32may be produced by a series of angled bends spaced from one another along the flared portion30. Additionally, the curved region32may be produced by a single continuous bend connecting the straight portion28and the flared portion30of the exterior rail18.

The exterior rails18may provide a location for the securement of the exterior rungs22. The length40of the exterior rungs22may be selected to fit the particular curvature of the exterior rails18. Several exterior rung22configurations are illustrated. These rung14embodiments will be presented hereinafter. Triangulation braces41are also illustrated. Triangulation braces41may be secured from the rails12to the rungs14to provide additional support and structural rigidity. Additionally, feet42may be applied to the lower extreme of selected rails12. The feet42may efficiently transfer the load from the rails12to a supporting surface44. The feet42may also resist slipping of the ladder10with respect to the supporting surface44, thus increasing safety.

Referring toFIG. 4, various methods may be used to shape a rail12. The rail12material may influence the choice of what shaping process may be most suitable. For example, with a fiber reinforced thermoset polymer, a pultrusion followed by a shaping process may be ideal. Such a process may include pultruding46, in a longitudinal direction, a rail12having a selected cross-sectional shape. The rail12may then be cut48to a pre-determined length at a distal end. While the pultruded rail12is yet uncured, a force may be applied50to the rail12in a lateral direction to form a selected curvature therein. The curvature may be characterized by a straight portion28, a flared portion30, and a curved region32providing the transition therebetween.

The applied force50may be held52or maintained52for a time selected for the thermoset material to fully cure and maintain the curvature substantially permanently. Once the desired curvature of the rail12is permanently fixed, the rail12may then be released54and assembled56into a ladder10.

Referring toFIG. 5, in an alternative embodiment, the pultrusion46of the rail12may be followed by applying a force50to the yet uncured rail12to generate a curvature therein. Once the rail12is held52at the desired curvature, it may be cut48to a proper length. Thus, the application of the force50and the cutting process48may be interchanged in the order in which they occur. Once the rail12has been held52or maintained52for a time period selected for the thermoset material to fully cure and maintain the curvature substantially permanently, the rail12may be released54and assembled56into a ladder10.

Referring toFIG. 6, in certain embodiments, fiber reinforced thermoplastic polymers may be used as the material for the rails12. In such a case, the rail12may be pultruded58, in a longitudinal direction, to have a selected cross-sectional shape. The rail12may then be cut60to a pre-determined length at a distal end. As mentioned hereinabove in conjunction with other embodiments, the particular order in which the cutting process60occurs in relation to the other steps may vary.

However, assuming that the cutting process60occurs immediately after the pultrusion58, the rail12may then follow one of two different paths. While the pultruded rail12is yet unhardened, a force may be applied62to the rail12in a lateral direction to form a selected curvature therein. Alternately, with the passage of time64, the rail12may be allowed to harden in its pultruded state. Then, when convenient, the rail12may be reheated66to near the glass transition temperature of the thermoplastic polymer.

While in this unhardened state, the force may then be applied62to the rail12in a lateral direction to form the selected curvature therein. The thermal and mechanical properties of thermoplastic polymers make this reheating and reshaping possible. Once the rail12has been held68or maintained68for a time period selected for the thermoplastic material to fully harden and maintain the curvature, the rail12may be released70and assembled72into a ladder10.

Referring toFIG. 7, when a metal or a metal alloy is selected as the material for the rail12, different processes may be employed. For example, a rail12may be extruded74, in a longitudinal direction, with a desired cross-sectional shape. The rail12may then be cut76to a desired length. The shape of the rail12may be controlled by applying a force78in a lateral direction to form a curvature therein. The force may be maintained until the rail12fully cools and permanently takes on the desired curvature.

In other embodiments, if the rail12has fully cooled by the time it is to be shaped, the shaping process may simply be a cold bending of the metal. In such a case, overcompensation in the application of the force78may be necessary to produce the desired curvature. That is, the rail12may need to be bent more than the desired curvature so when the force is released82, and the rail12springs back slightly, the resting position is actually the desired curvature. Once the rail12has been released82, it may be assembled84into a ladder10.

Referring toFIG. 8, rails12in accordance with the present invention may be shaped by any suitable force applicator86. In certain embodiments, a force applicator86amay have multiple actuators88for extending and retracting arms90. Once a rail12is formed and while it is still in an uncured, unhardened, or unbent state, a lateral force may be applied to the rail12by the actuators88extending arms90thereagainst to force the rail12against a mandrel92. The mandrel92may have the desired curvature already formed therein. Thus, when the rail12is forced against the mandrel92, it may conform to the curvature of the mandrel92.

In an alternative embodiment, a rail12may be shaped between a movable mandrel94and a rigid mandrel92. In such an embodiment, a rail12in an uncured, unhardened, or unbent state may be sandwiched between the movable mandrel94and the rigid mandrel92. An actuator88may manipulate an extending and retracting arm90to provide the impetus for forcing the movable mandrel94against the rigid mandrel92.

In another embodiment a rail12may be shaped by a series of roller pairs96. A roller pair96may consist of a first roller96aselectively rotated in a first direction98and one or more second rollers96bselectively rotatable in a second direction100. When actuated, the rollers96a,96brotate in a manner to pull the rail12along in a desired direction102. The roller pairs96may generate the curvature in the rail12by any suitable manner. In one embodiment, the roller pairs96may be spaced and positioned so that as a rail12is pulled between each successive roller pair96, it may be slightly redirected. Thus, when the rail12reaches the last roller pair96and rotation is stopped, the rail12is being held in the desired curvature. In an alternative embodiment, the roller pairs96may be linearly aligned as the rail12is received. Once the rail12reaches the last roller pair and stops, the roller pairs96may be repositioned, thus, forming the curvature in the rail12. Suitable retainers may hold the rails from distorting in other directions.

As mentioned hereinabove, the curvature of the rail12may have many different configurations. As stated, a rail12amay comprise a curved region32having continuous arc substantially coincident (tangent) between the straight portion28and the flared portion30. In such an embodiment, the curved region32extends substantially throughout the flared portion30.

In other embodiments, the curved region32of rail12bmay consist of a relatively short, single, continuous bend104connecting the straight portion28to the flared portion30. Additionally, the curved region32, as shown on rail12c, may consist of a series of small bends104a,104b,104c,104dperiodically dispersed throughout the flared portion30. Each forming method and resulting curvature may have certain benefits and disadvantages. For example, a series of slight bends104a,104b,104c,104ddoes not produce a stressed region or weakened region as large as that produced by a single, more dramatic bend104. This may be particularly true when the rail12is formed by bending an already hard material such as a metal.

Referring toFIGS. 9-15, the cross-sectional shapes of the exterior rails18and interior rails20may be selected to provide a desired strength, durability, rigidity, or some combination thereof. Naturally, cross-sections of greater rigidity allow for walls105a,105b(seeFIG. 9) of lesser thickness106a,106b, providing a more lightweight construction. The cross-sectional shapes embodied inFIGS. 9-15are illustrative only. Various cross-sectional shapes may be suitable. Other suitable cross-sections may be generally circular, elliptical, triangular, rectangular, or the like.

The particular cross-sectional shape selected may promote proper clearances between moving parts. For example, as will be discussed in more detail, an interior rung24may secure to an interior rail20by extending therethrough. Clearance107may exist on the far side of the interior rail20to accommodate the interior rung24securement.

In certain embodiments, the exterior rails18may be formed with an open cross-section. The open cross-section allows the exterior rails18to contain the interior rails20while still providing access for an interior rung24to secure to the interior rail20. The open cross-section of an exterior rail18may have a first retainer108and second retainer110connected by a web112. The first retainer108may engage or surround a first side114of an interior rail20. The second retainer110may engage or surround a second side116of the interior rail20. The web112may maintain the first and second retainers108,110in a substantially fixed relation to each other, thus containing the interior rail20within the exterior rail18to prevent motion therebetween in a lateral direction118b.

In certain embodiments, the retainers108,110of an exterior rail18may extend sufficiently around the sides114,116of an interior rail20to prevent motion therebetween in both a lateral direction118band a transverse direction118c. As a result, the interior rail20may only move in a longitudinal direction118awith respect to the exterior rail18.

In selected embodiments, it may be advantageous to incorporate glide strips119at the interface between certain exterior rail18and interior rail20surfaces. Glide strips119may be secured to either the exterior or the interior rail18,20. The glide strips119may be positioned to reduce the frictional forces resulting from the rails18,20sliding in a longitudinal direction118awith respect to each other.

The glide strips119may be constructed of any suitable friction-reducing material. In certain embodiments, the glide strips119are constructed of vinyl, Teflon®, high density polyethylene, or the like. The glide strips119may be integrally formed with the rail12or they may be applied with an adhesive or other fastening device during the assembly of the ladder10.

In other embodiments, instead of or in addition to surrounding the first side114of an interior rail20, a first retainer108may extend outward in the transverse direction118cto form a rib120along the length of the exterior rail18. This rib120may provide a location for an exterior rung22to secure to an exterior rail18without interfering with the motion of an interior rail20.

Referring specifically toFIG. 12, a retainer108,110need not surround a side114,116in order to resist motion between an exterior rail18and an interior rail20in a transverse direction118c. In selected embodiments, a retainer108may have a ridge122formed therein. A corresponding valley124may be formed in a side114of an interior rail20. Thus, when assembled, the ridge122and valley124engage and resist transverse motion of the exterior rail18with respect to the interior rail20.

Referring specifically toFIG. 13, and in view of the embodiments ofFIGS. 9-12, the clearance107for an interior rung24securement is incorporated as part of the interior rail20cross-sectional shape. However, the clearance107may also be incorporated as part of the cross-section of an exterior rail18. Specifically, the web112may have a contour126to provide the clearance107. In applications where no clearance107is needed, it may still be advantageous to form contours126in the web112. Such contours126may increase the rigidity (e.g. section modulus) of the exterior rail18.

Referring specifically toFIG. 14, the cross-section of an interior rail20may have internal webs128to increase the strength, rigidity, and the like. The number, positioning, and thickness of the internal webs128may be selected to provide optimum performance while minimally increasing the weight of the interior rail20.

Referring specifically toFIG. 15, a rib120may provide a location for an exterior rung22to secure to an exterior rail18without interfering with the motion of an interior rail20. Such a rib120may extend in a transverse direction118ctoward the inside of the ladder10(see FIGS.9-14). Additionally, the rib120may extend in a transverse direction118ctoward the outside of the ladder10.

Referring toFIGS. 16 and 17, either all or a portion of the interior rails20and either all or a portion of each exterior rail18may be filled with a lightweight material130to increase torsional rigidity and strength. The filling material130may be any material having the desired installation procedures, weight, and compression resistance. The filling material130may be sprayed, poured, or otherwise inserted inside the rail12. Once inserted, the filler130may expand and fill the interior of the rail12. In other embodiments, the filler130may occupy the interior of the rail12and only require a curing or drying time to achieve proper hardness. In certain embodiments, the filling material130may be an expanded polystyrene or other polymer.

Filling reinforcement may be advantageous because, with minimal increase in weight, the strength of rail12may be greatly increased. Unfilled rails12derive their strength by themselves. That is, the wall thickness106typically determines the strength of the rail12. An unfilled rail12is typically strengthened by increasing the thickness106of the rail12walls105. Varying wall thickness106along the length of the rail12may greatly increase manufacturing costs. Thus, the rails12are typically made with a uniform wall thickness106. In other words, the wall thickness106is determined by the maximum load that any portion of the rail12may experience. The thicker walls105at the locations of less loading result in dead weight. Filling a rail12allows for inexpensive reinforcement against buckling and distortion of strategic locations131that need the additional load carrying capacity without necessitating the thickening of walls105of the entire rail12. As a result, great weight savings may be had.

In selected embodiments, the interior rails20may be completely filled with foam. In other embodiments, a foam130or filling material130may be placed periodically within the rail12at strategic locations131. The strategic locations131may be any location requiring additional strength and rigidity. For example, in certain applications it may be advantageous to reinforce the regions where an interior rung24secures to the interior rail20. The ends132of a rail12or mid-span locations that are substantially laterally unsupported may also benefit from a reinforcing filling material130.

The filling material130may be applied to the rails12as part of their initial forming process. In other embodiments, the rails12may be filled at any suitable time prior to completion of assembly into a ladder10(e.g. before closure of tubular members). The rails12may be filled by inserting a wand134inside a closed cross-section of the rail12. The form in which the wand134delivers the filling material130may depend on the nature of the filler130.

For example, if the filling material130is an expanding foam, the material130may be deliver by the wand134in a liquid form or other form not fully expanded. Once released into the interior of the rail12, the liquid may finish foaming (expanding) and fill the interior. As the interior of the rail12is filled, the wand134may be continuously withdrawn, thus progressively filling the entire rail12. Periodic reinforcement may be accomplished in a similar manner differing only in that the wand134would apply the filling material134at the strategic locations131, but not continuously.

Referring toFIG. 18, rungs14may be constructed of any suitable material including metal, metal alloy, composite, reinforced polymer, wood, and the like. Commonly used materials may include aluminum alloys and fiber reinforced thermoset and thermoplastic polymers. A rung14may be formed by any suitable process. The material selected for the rung14may determine which process may be most appropriate. For example, if an aluminum alloy is selected for the rung14, an extruding process may be ideal. However, if a fiber-reinforced thermoset polymer is selected, a pultrusion process may be more appropriate.

The manufacture of multiple parts requiring many different tooling sets and assembly procedures will typically increase the cost of the final product. Thus, simple manufacturing methods requiring few assembly procedures are ideal. Constant cross-section parts lend themselves to less expensive manufacture. When the need for welding and other joining techniques is eliminated, costs can be reduced even further. Thus, a rung14of constant cross-section requiring no joining may be ideal or otherwise beneficial.

A rung14in accordance with the present invention may be manufactured by monolithically (or even homogeneously) forming a body portion136having a closed cross-section. In selected embodiments, one wall138of the body portion136may be substantially flat. The substantially flat side wall138may provide a surface140for securing the rung14against a rail12, or the surface140may act as a tread for the user. The surface140may more conveniently be used as an interface for exterior rungs22and as a tread for interior rungs24. A first rib142may extend in a first direction144away from the body portion136so as to be substantially co-planar with the flat wall side138. If desired, a second rib146may extend parallel to or co-planar with the flat side wall138in a second direction148substantially opposite the first direction144.

The purpose of the ribs142,146may depend on the application for which the rung14is intended. As stated hereinabove, exterior rungs22may secure to the outside of the exterior rails18to avoid interfering with the extension of the interior rails20and rungs24. In such an embodiment, the ribs142,146may provide securement tabs with sufficient access for riveting, bolting, screwing, or otherwise fastening the exterior rung22to the exterior rail18. The extension of the tabs away from the body portion136may increase the access and ease of securement while also providing increased torsion support when the exterior rung22is in use.

Referring toFIG. 19, as stated hereinabove, a single rib142may be provided if desired. When only one rib142is provided, one entire side149of the body portion136is exposed as a tread150for a user. The rib142may be sized and positioned to increase the rigidity and strength of the exterior rung22. Additionally, the rib142may provide securement access and torsional resistance. In certain embodiments, the end face152of the exterior rung22may be tapered back at an angle154to provide easy access to a securement aperture156placed in the flat side wall138. The angle154may be machined on the end of the exterior rung22once it has been cut to a proper length or as a part of the length cutting process.

Additional securement apertures158may be provided in the rib142as desired. A securement aperture158amay be placed near the end of the exterior rung22to permit securement to an exterior rail18. Another securement aperture158bmay be placed at a location spaced from the end of the exterior rung22to permit securement of a triangulation brace41.

Referring toFIGS. 3,20, and21, in certain embodiments, portions of the first or second ribs142,146may be removed from the exterior rung22. For example, the ribs142,146may be removed in a machining process along the center portion160to provide vertical clearance yet leave ribs142,146at both ends of the exterior rung22for securing the exterior rung22to an exterior rail18. Thus, while some of the ribs142,146may need to be removed to make the exterior rung22useful, forming the rib142,146initially as part of the exterior rung22allows for fast and inexpensive formation of a constant cross-section. Typically, it is simpler and less expensive to remove an unwanted rib142,146section than to attach the needed ribs142,146.

Apertures158may be formed in the ribs142,146to provide access for fasteners to secure the exterior rung22to a pair of ladder exterior rails18. The ribs142,146may extend along any selected length of the exterior rung22. For example, the ribs142,146may be relatively short to expose the great majority of the center portion160of the exterior rung22as a tread surface150. In other embodiments, the ribs142,146may extend a length sufficient to provide access for triangulation braces41to secure thereto.

The determination of what ribs142,146to include in the initial exterior rung22formation and the length and portions of the ribs142,146to remove once the exterior rung22has been formed, may be influenced by the intended use of the exterior rung22. For example, an exterior rung22for a combination ladder10must provide two tread surfaces150. As a result, the center portion of both ribs142,146corresponding with the center portion160of exterior rung22(seeFIG. 20) may be removed. When the exterior rung22only needs a tread surface150on one side, the rib142on the other side may extend along some portion or completely along the length of the exterior rung22.

In selected embodiments, the tread surfaces150have ridges162or other traction devices162formed to improve traction of the user's foot. In certain embodiments, the corners164and edges164of an exterior rung22(seeFIG. 21) in accordance with the present invention may be radiused to better distribute loadings and resist the formation of stress risers.

Referring toFIG. 22, when applied to an interior rung24, the ribs142,146may increase the width166of the tread150, thus, reducing user foot fatigue. In certain embodiments, an interior rung24may be monolithically (or even homogeneously) formed to have a body portion136having a closed cross-section. In selected embodiments, one wall138of the body portion136may be substantially flat. When applied to an interior rung24, the substantially flat side wall138may provide a surface140for supporting a tread150for the user.

A first rib142may extend in a first direction away from the body portion136so as to be substantially co-planar with the flat wall side138. If desired, a second rib146may extend co-planar with the flat side wall138in a second direction substantially opposite the first direction. In such an embodiment, the flat side wall138and first and second ribs142,146may make up the tread surface150. In certain embodiments, the tread surface150may have ridges162or other traction devices162formed therein to improve traction of the user.

Similar to an exterior rung22, portions of the ribs142,146of an interior rung24may be removed. While the ribs142,146are part of the tread150and therefore do not need to be removed to provide access for the foot of a user, it may be advantageous to remove a portion of the ribs142,146near the ends of the interior rung24to allow securement of the interior rung24to an interior rail20.

Referring toFIG. 23, the body section136of an interior rung24may have any suitable cross-section. For example, the body section136may be circular, elliptical, rectangular, triangular, another shape, or some combination thereof. InFIG. 23, a circular cross-section is illustrated. In such an embodiment, the flat side wall138has the first and second ribs142,146extending tangentially from the circular body section136. If desired, prongs169may be formed when unwanted rib142,146sections are removed. The prongs169may engage a corresponding interior rail20to resist rotation of the interior rung24with respect thereto about a central axis172.

Referring toFIG. 24, the interior rungs24of ladder10must be secured to the interior rails20in a manner to distribute the loads so as not to overload any particular point. One method for securing an interior rung24to an interior rail20involves inserting a tubular portion of an interior rung24through an aperture170a,170bin the interior rail20and then swaging the end168of the interior rung24to produce a rivet-like effect, maintaining the interior rung24securely against the interior rail20. As discussed hereinabove, thin side walls105a,105breduce the overall weight of the ladder10. However, bending forces in thin side walls105a,105bon an interior rail20complicate interior rung24securement. That is, with thin side walls105, the swaging may result in distortion, fracture, crushing, or breaking of the interior rail20.

A reinforcement method for reducing and substantially eliminating damage or fracture of the interior rail20is within the scope of the present invention. This method may first include providing an interior rung24defining an axial direction172aand a radial direction172b. The rung may comprise a body portion136or tube136having an end168with a stop174spaced therefrom in an axial direction172a. A collar176may be provided to fit radially around the tube136and rest axially against the stop174.

The interior rail20to which the interior rung24is to be secured may have a closed cross-section defining two walls105a,105b, each wall105having an aperture170formed therethrough. The first aperture170amay be sized to fit around the collar176and the second aperture170bmay be sized to fit around the tube136. Thus, the first aperture170ais larger than the second aperture170b. The interior rung24and interior rail20may be secured together by placing the collar176radially around the tube136and axially against the stop174.

The tube136may then be inserted with the collar176through the first aperture170ain the interior rail20. Once the collar176and tube136have passed through the first aperture170a,the tube136may be advanced through the second aperture170b. Due to the sizing of the second aperture170b, the collar176is unable to pass therethrough. Thus, the collar176may become pinched between the second aperture side wall105band the axial stop174of the interior rung24.

The tube136may have a length selected so that, when the collar176comes in contact with the internal side178of the second aperture170b, the tube136is still able to extend out a selected distance180. Thus, when the tube136is in proper alignment with the collar176and interior rail20, the end168of the tube136may be swaged to form a rivet head and maintain the interior rail20and collar176pressed snugly against the axial stop174on the rung24. In such a configuration, the collar176may support the swaging load and protect the interior rail20from crushing.

Referring toFIGS. 25 and 26, an extension lock26may secure an interior rail20with respect to an exterior rail18and resist motion in a longitudinal direction therebetween. Thus, when a load is applied to the interior rails20, the extension lock26must transfer that load to the exterior rails18, which, in turn, transfer the load to the supporting surface44(FIG.3). When the load applied to interior rails20is large, the extension lock26is sufficiently strong to support the load.

In certain embodiments, an extension lock26may include a shear pin184engaging both an interior rail20and an exterior rail18. Typically, the shear pin184passes through an aperture186in the exterior rail18and engages the tube136or body portion136of an interior rung24secured to an interior rail20.

Fiber-reinforced composites, and even metals, are susceptible to failure, such as by splitting, when loaded in a comparatively small area or effectively at a point. Thus, to resist the failure or splitting tendency, the loads applied by an extension lock26may be distributed by reinforcements. For example, the tube136of the interior rung24may house the shear pin184and distribute the loads applied thereto. A reinforcing plate188may be applied to the exterior rail18. The reinforcing plate188may be formed of any suitable material. In one embodiment, the plate188is formed of a metal or metal alloy such as aluminum, the more ductile steel, or the like.

In certain embodiments, the reinforcing plate188may be sized to withstand the entire load imparted by the shear pin184. In an alternative embodiment, the plate188may act to resist the splitting tendency of the exterior rail18rather than carry the load applied by the shear pin184. For example, a thin plate188may be secured to the exterior on an exterior rail18. Suitable machinery may punch an aperture186through both the plate188and the side wall105of the exterior rail18. The punch may be shaped and applied in a manner to also deform rather than simply cut the reinforcing plate188, thus, pulling or drawing a portion of the plate188through the aperture186.

The distorted surface or even edges190of the plate188around the aperture186may become the bearing surface192between the shear pin184and the aperture186in the exterior rail18. In such a manner, even a plate188that is not thick enough to alone withstand the loads applied by the shear pin184may carry or distribute to exterior the rail18enough of the load at the bearing surface192to prevent splitting of the exterior rail18and then let the rail18carry the rest of the load. A comparatively thinner reinforcement plate188may provide additional weight savings for the ladder10.

Referring toFIGS. 27-29, as discussed hereinabove, hinges16for step ladders10need not support the moment loads of hinges16designed for combination ladders10. Thus, a hinge16for a step ladder10may have a much lighter and simpler construction.

In certain embodiments, a hinge16for a step ladder10may include a first armature194connected to a second armature196by a pivot pin198. A lock200may provide two locking positions, a closed position (seeFIG. 27) and an open position (see FIG.29). The lock200may consist of a shear pin202occupying a locating aperture204(seeFIG. 30) in the first armature194.

When the locating aperture204is aligned with either an open aperture206or a closed aperture208of the second armature196, a biasing member210urges the shear pin202therethrough, thus locking the armatures194,196in a fixed relation (either open or closed) with respect to one another. The lock200may be released by pulling, a knob212secured to the shear pin202in a direction opposite to that urged by the biasing member210, thus removing the shear pin202from either the open aperture206or a closed aperture208and permitting relative motion between the armatures194,196.

Referring toFIGS. 30-32, hinges16for use with a combination ladder10may require a heavier construction to withstand the higher moment loads that may be imposed thereon. A hinge16for a combination ladder10may include a first armature194connected to a second armature196by a pivot pin198or axle198.

A hinge16in accordance with the present invention may be constructed of any suitable material. The particular weight and strength requirements of the ladder10design may influence the choice of material. In certain embodiments, the hinge16material is selected from the group including a metal, metal alloy, composite, polymer, fiber reinforced polymer, or the like. Hinge16components may likewise be selected of any suitable material. The loadings that the component must withstand may greatly influence the material selection. For example, components that must resist high shear loads may best be constructed of a metal or metal alloy, although other materials having adequate strength may be used as well.

In certain embodiments, a hinge16may have armatures194,196restricted in their respective pivotable motion by locking pins202or shear pins202. The pins202may be selectively engaged and disengaged by linearly maneuvering a knob212. The lock200operates by moving between a first, engaged, position (seeFIGS. 31 and 32) and a second, disengaged, position (see FIG.30). To engage the lock200, the knob212is pulled away from the armatures194,196with the aid of a biasing force, drawing therewith the locking pins202into properly aligned apertures in both the first armature194and in the second armature196.

Two locating apertures204are provided in the first armature194and three corresponding pairs of apertures are provided in the second armature196. The first pair of apertures is positioned to align with the locating apertures204of the first armature194in the straight configuration. The second pair of apertures is positioned to align with the locating apertures204of the first armature194in the step ladder configuration. The third pair of apertures is positioned to align with the locating apertures204of the first armature194in the closed configuration.

The second, or disengaged, position results from a user forcing the knob212to move against the biasing force, thus retracting the pins202from the apertures of the second armature196. A frame214may connect the pivot pin198to the pins202enabling the release knob212to move the locking pins202a,202bin unison.

The urging force tending to position the pins202in the engaged position, may be provided by a spring apparatus in a housing215. Suitable fasteners, spring mechanisms, and the like may be captured in the housing215for biasing the pins202toward the engaged position. One suitable embodiment for such a hinge16is described in U.S. Pat. No. 4,697,305, incorporated herein by reference.

To promote a stable connection between the armatures194,196and the interior rails20, spacers216may fit between or around plates194a,194b,196a,196bof the respective armatures194,196. The spacers216and armatures194,196may combine to provide a location for the interior rails20to secure thereto. In certain embodiments, the armatures194,196may have a relief218formed therein for fitting about interior rungs24or other structures. Thus, the length220of the armatures194,196may be increased, while avoiding interference with obstructing components.

In certain embodiments, an interlock222may provide an additional protection against inadvertent release of a hinge16. An interlock222may be a simple mechanism that can be operated simultaneously with actuation of the release knob212by a single hand of a user. Such one-handed operation, however, should not be readily executable by accident. An interlock222in accordance with the present invention may operate by resisting translation of the shear pins202. This may be accomplished in any suitable manner. For example, an interlock may engage the frame214to selectively prevent the shear pins202from being extracted. In another embodiment, an interlock222may be inserted in between the release knob212and the first armature194, thus, selectively preventing the lock200from opening. That is, if the release knob212is held away from the first armature194, the shear pins202cannot be extracted and the lock200will not release.

An interlock222may operate in a pivoting motion, a sliding motion, or any other rotary or translational motion. A post, a spring-loaded key, a cross-pin engaging the pivot pin198, or the like may be employed. In certain embodiments, an interlock222in accordance with the present invention may include a lever224with an actuator226at one end and a stop228at the other. The lever224may be constructed to pivot on a pivot pin230. A biasing member232, such as a coil spring, may urge the lever224in a selected direction234.

The direction234may be selected to urge the stop228in-between the release knob212and the first armature194whenever the lock200is in an engaged position. Thus, if the release knob212is accidentally hit, the stop228prevents the release knob212from translating and extracting the shear pins202. To release the lock200, a user may press the actuator226in a manner to counteract the biasing member232and produce a motion opposite that of the biasing direction234. Once the stop228is no longer obstructing the motion of the release knob212, the knob212may be urged to extract the shear pins202and disengage the lock200.

In certain embodiments, a support236or standoff236may provide spacing and strength for appropriately resisting motion of the release knob212. The support236may be built in as a monolithic, integral, or even homogeneous part of the stop228, or may be added as a separate material or appendage.

Referring toFIGS. 33 and 34, the armatures194,196illustrated inFIGS. 30-32are configured to be contained within the interior rails20to which they secure. In alternative embodiments, it may be advantageous to provide armatures194,196with a housing238to capture the end on the interior rail20to which the hinge16is to secure. The housing238may be shaped to snugly surround an end of the corresponding intrior rail20.

Recesses240may be formed at strategic locations throughout the housing238to provide for a better fit with the corresponding interior rail20. The housing238may provide for a distributed engagement, thus reducing the individual point loadings and accompanying stress risers that may result from the use of screws or other fasteners. The housing238may be bonded to the interior rail20to further promote an efficient load distribution. As discussed hereinabove, hinges16in accordance with the present invention may be constructed of any suitable material including metal, metal alloy, composite, polymer, fiber reinforced polymer, or the like.

In selected embodiments, the housings238of the armatures194,196may engage one another. In certain embodiments, a notch242may be formed in the first armature194. A corresponding extension244may be formed in the second armature196. The notch242may have a stop246formed therein. As the hinge16opens and reaches the straight configuration (seeFIG. 34) the stop246may engage the extension244and resist further rotation of the hinge16. Thus, the engagement between the first and second armatures194,196may reduce the shear loading of the shear pins202. Additionally, the engagement between the first and second armatures194,196may provide an additional safeguard against complete release of the hinge16.

While portions of the housings238of the first and second armatures194,196may meet (i.e. the notch242and extension244), the rest of the housings238need not meet. If desired, the housings238may be shaped to leave a gap247therebetween when the hinge16is in the straight configuration (see FIG.34). The gap247may reduce the likelihood of the user pinching a finger, hand, or the like therein while opening or closing the ladder10.

FIGS. 33 and 34do not illustrate the components and mechanisms necessary or contemplated to complete a functioning hinge16. Merely the locating apertures204and a pivot pin aperture248are shown. However, the components and methods discussed in connection withFIGS. 30-32may be applied to provide suitable pivoting and locking as desired. It should be noted that other hinge componentry may be applied as well and is contemplated within the scope of the present invention.

Referring toFIGS. 35-48, as mentioned hereinabove, hinges16may pinch a user's finger, hand, or the like, while opening or closing the ladder10. Such pinches may result in serious injury. Several methods and structures are available to protect the user from injury.

Referring toFIGS. 35 and 36, in certain embodiments, it may be advantageous to have a hinge16with no pinch point. This may be accomplished by spacing the pivot pin198a selected distance250away from the end face252a,252bof the interior rail20a,20b, which may comprise a housing238. Thus, in the embodiments where the armatures194,196include a housing238, the pivot pin198may be spaced a selected distance250away from an end face252of the housing238. The pivot pin198maybe spaced the same distance250from both end faces252a,252b. Thus, when the hinge16is in the straight configuration, the end faces252a,252bare separated a distance254substantially equivalent to twice the spacing of the pivot from one of the faces252a,252b. The separation distance254creates a gap247and removes any pinch point that may have been present had the end faces252a,252bmet with the hinge16in the open configuration.

In addition to creating a gap247and eliminating potential pinch points, other methods and structures are available to safeguard a user. For example, a shield256may provide a mechanical stop for preventing a user's fingers or the like from ever entering the pinch point. A pinch point results when the end faces252a,252bcome in contact with one another. A shield256may resist any part of a user from coming into the pinch point as the end faces252a,252bcome in contact with each other.

Referring toFIGS. 37 and 38, in selected embodiments, the shield may be a flexible band256. The band256may be constructed of any suitable material. In selected embodiments, the band256is made from either metal, metal alloy, composite, polymer, reinforced polymer, or the like. The band256may secure at one end257to an outside wall258bof the interior rail20b. The end257of the band256may be secured to the outside wall258bby any suitable method or structure.

In one embodiment, the band256is held in place by fasteners260. The other end264of the band256may be free to travel in a longitudinal direction118awithin a guide262or within multiple guides262. Thus, as the hinge16travels through its range of motion, the band256may adjust by sliding within the guides262to accommodate changes in arc length265. The free end264of the band256may be free to extend down the inside of the interior rail20a. In such a manner, the band256may be a mechanical barrier to prevent a user from placing fingers and the like in the pinch point area while still adjusting to compensate for the changing size of the pinch point area.

Referring toFIGS. 39 and 40, in certain embodiments, the flexible band256may be a densely wrapped coil spring256. Such a spring guard256may operate very similarly to the band guard256described hereinabove. The diameter of the spring256may be selected to fit within the interior of the interior rails20.

Referring toFIGS. 41 and 42, in selected embodiments, a shield256may be in the form of an extensible and retractable guard266. Such a guard266may have a first end267secured to a first interior rail20aand a second end268secured to a second interior rail20b. As the hinge16passes through its range of motion, the guard266may act as an accordion and extend to cover the varying arc length265. Such a guard266may be constructed of any suitable material. Possible materials may include a polymer, rubber or other elastomer, or the like.

If desired, the band256and spring256embodiments ofFIGS. 37-40may be applied to the guard266ofFIGS. 41 and 42. That is, the band256or spring256may support the guard266, holding it in an arced configuration spaced from the hinge16. As the hinge16pivots to the straight configuration, the band256or spring256may aid the collapsible guard266in properly gathering without being pinched between the end faces252a,252b.

Referring toFIGS. 43 and 44, in selected embodiments, a disk-like guard270may be employed to prevent a user from being caught in the pinch point of a hinge16. This guard270may act as a barrier to stop any part of a user from being introduced into the pinch point. In certain embodiments, the disk guard270may be generally circular. The guard270may be fixed by fasteners272to one of the interior rails20b. In embodiments where the armatures194,196include housings238, the guard270may secure directly to one of the housings238. Disk guards270may be constructed of any suitable material. Suitable materials may include metals, metal alloys, composites, polymers, woods, or the like.

Generally, the center of the disk guard270may be placed over the pivot pin198of the hinge16. The diameter of the disk guard270may be selected to correspond to the maximum distance274of separation between the first outer wall258aand the second outer wall258b. Thus, as the hinge16travels through its range of motion, the guard270stops anything from coming between the end faces252a,252b. If desired, disk guards270may be placed on both sides of both ladder hinges16, thus, preventing anything from entering the pinch point from either side.

In selected embodiments, an aperture276may be formed over the hinge16. The aperture276may provide the user with access to the components of the hinge16such as the release knob212, interlock222, and the like, which are needed for effective operation of the hinge16.

Referring toFIGS. 45 and 46, to be effective, a disk guard270need not extend in a complete circle around the hinge16. In certain embodiments, the guard270may be a half circle. Similar to a full circle disk guard270, a half circle disk guard270may be fixed by fasteners272to one of the interior rails20b. In embodiments where the armatures194,196include housings238, the guard270may secure directly to one of the housings238. A half circle disk guard270may also be constructed of any suitable material.

Similar to a full circle type of disk guard270, the center of the half circle disk guard270may be placed over the pivot pin198of the hinge16. The diameter of the half circle disk guard270may be selected to correspond to the maximum distance274of separation between the first outer wall258aand the second outer wall258b. Thus, as the hinge16travels through its range of motion, the guard270inhibits objects or bodily extremities from coming between the end faces252a,252b. If desired, disk guards270may be placed on both sides of both ladder hinges16, thus, preventing anything from entering the pinch point from either side.

A notch276may be formed over the hinge16. The notch276may provide the user with access to the components of the hinge16such as the release knob212, interlock222, and the like, which are needed for effective operation of the hinge16.

Referring toFIGS. 47 and 48, in certain embodiments, a smaller guard270may be advantageous. A guard270may be smaller than the maximum distance274between the outside walls258a,258bof the interior rails20a,20b. Thus, a length278of an end face252amay be exposed when the hinge16is in the closed position. As the hinge16transitions from the closed position to the straight position, a leading edge280of the guard270may be contoured to shorten the length278of the exposed end face252a. Thus, by the time the end faces252a,252bmeet, the guard270completely covers the interface and prevents a user from being pinched.

The leading edge280may form an angle282with respect to the end face252a. The angle282may change as the hinge16transitions from the closed position to the straight position. The contour of the leading edge280may be selected to consistently produce an acute angle282less than 90°. With the angle282less than 90°, the exposed length278will shorten as the hinge16transitions from the closed position to the straight position. Thus, the contour of the leading edge280and the corresponding angle282produced may be selected to gradually push the finger, hand, or other bodily member of the user out of the pinch point range before the hinge16ever reaches the straight configuration.

As discussed hereinabove, an aperture276may be formed over the hinge16. The aperture276may provide the user with access to the components of the hinge16such as the release knob212, interlock222, and the like, which are needed for effective operation of the hinge16.

From the above discussion, it will be appreciated that the present invention provides ladder componentry that maintains required strength while decreasing weight, is simplified to reduce manufacturing and assembly cost, and reduces the likelihood of potential hazards. The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, 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.