Patent Description:
Ductwork is often used for conveying conditioned air (e.g., heated, cooled, filtered, etc.) discharged from a fan and distributing the air to a room or other areas within a building. Ducts are typically formed of rigid metal, such as steel, aluminum, or stainless steel. In many installations, ducts are hidden above suspended ceilings for convenience and aesthetics. But in warehouses, manufacturing plants and many other buildings, the ducts are suspended from the roof of the building and are thus exposed. In those warehouse or manufacturing environments where prevention of air-borne contamination of the inventory is critical, metal ducts can create problems.

For instance, temperature variations in the building or temperature differentials between the ducts and the air being conveyed can create condensation on both the interior and exterior of the ducts. The presence of condensed moisture on the interior of the duct may form mold or bacteria that the duct then passes onto the room or other areas being supplied with the conditioned air. In the case of exposed ducts, condensation on the exterior of the duct can drip onto the inventory or personnel below. The consequences of the dripping can range anywhere from a minor irritation to a dangerously slippery floor or complete destruction of products underneath the duct (particularly in food-processing facilities).

Further, metal ducts with localized discharge registers have been known to create uncomfortable drafts and unbalanced localized heating or cooling within the building. In many food-processing facilities where the target temperature is <NUM> degrees Fahrenheit, a cold draft can be especially uncomfortable and perhaps unhealthy.

Many of the above problems associated with metal ducts are overcome by the use of flexible fabric ducts, such as DUCTSOX from DuctSox Corporation of Dubuque, Iowa. Such ducts typically have a pliable fabric wall (often porous) that inflates to a generally cylindrical shape by the pressure of the air being conveyed by the duct. Fabric ducts seem to inhibit the formation of condensation on its exterior wall, possibly due to the fabric having a lower thermal conductivity than that of metal ducts. In addition, the fabric's porosity and/or additional holes distributed along the length of the fabric duct broadly and evenly disperse the air into the room being conditioned or ventilated. The even distribution of airflow also effectively ventilates the walls of the duct itself, thereby further inhibiting the formation of mold and bacteria.

In many cases, however, once the room's conditioning demand has been met, the air supply fan is turned off or down until needed again. When the fan is off, the resulting loss of air pressure in the duct deflates the fabric tube, causing it to sag. Depending on the application and material of the fabric, in some cases, the sagging creates a less than optimal appearance or may interfere with whatever might be directly beneath the duct. Moreover, when the duct is re-inflated, the duct can produce a loud popping sound as the duct's fabric again becomes taut from the air pressure.

<CIT> pertains to a telescopic suction duct. A sliding ring is slidably fitted to a guide bar formed of a vinyl chloride pipe installed by being extended in the axial direction of this suction duct, and the sliding ring is allowed to slide only along the guide bar. A shape-keeping ring integrated with the sliding ring can be moved only in the axial direction of the suction duct. <CIT> describes a soft duct composed of a hollow body made of thin cloth and detachably engaged with a wall of a building by means of a supporting wire. The soft duct comprising a framework with a plurality of radial support members each comprising a hub connected to first and second spokes which in turn position a ring-shaped rib inside the soft duct. The radial support members are arranged on a rod inside the soft duct. Tension is applied to the duct by the wire in axial direction.

In order to solve the drawbacks of the prior art there is proposed, according to the present invention, a framework for use with a duct system according to claim <NUM> and an air duct system comprising said framework according to claim <NUM>.

Certain examples are shown in the above-identified figures and described in detail below. In describing these examples, like or identical reference numbers are used to identify same or similar elements. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic for clarity and/or conciseness. Additionally, several examples have been described throughout this specification. Any features from any example may be included with, a replacement for, or otherwise combined with other features from other examples.

Example air ducts comprising pliable tubular sidewalls are provided with example internal frameworks that hold the duct in a generally expanded shape even when the duct is depressurized. The framework tensions the pliable sidewall material along the length of the ducts to keep the material taut. In some examples, the framework is restrained within the duct such that the duct's sidewall, being in tension, holds the framework in compression longitudinally. Thus, in the longitudinal direction, the duct is in tension and the framework is in compression. To prevent the framework from buckling under the compressive force, some example frameworks comprise a central longitudinal shaft with a plurality of radial spokes and rings that help hold the shaft straight. In some examples, the rings also help hold the duct radially expanded. In some examples, the framework is spring loaded.

<FIG> show example air duct systems <NUM> and <NUM> for conveying air <NUM> discharged from a blower <NUM> and for dispersing or otherwise delivering air <NUM> to a room or other areas of a building. Duct system <NUM> of <FIG> will be explained first, and the differences between duct systems <NUM> and <NUM> being explained later.

To convey air <NUM>, duct system <NUM> includes an air duct <NUM> comprising a tubular sidewall <NUM> made of a pliable material. As used herein, the term, "sidewall" will refer to the full circumferential extent of the fabric tube, even if the portion of the sidewall runs along the top or bottom of the tube or anywhere in between. Some examples of pliable sidewall materials include, but are not limited to, a polymer coated or impregnated cloth fabric, an uncoated fabric, a polyester sheet, other polymer or non metallic sheets, and various combinations thereof. To release air <NUM> from within duct <NUM> to the room or area it serves, sidewall <NUM> and/or an end cap <NUM> of duct <NUM> includes one or more discharge openings such as, for example, cut-out openings, plastic or metal discharge registers, and/or porosity in the sidewall material itself.

In some examples, duct system <NUM> is mounted underneath a ceiling <NUM> with a plurality of hangers <NUM> suspending duct system <NUM> from an overhead support structure <NUM> (e.g. a cable, track, channel, beam, ceiling, etc.). An example framework <NUM> comprising a shaft <NUM> and a plurality of ribs <NUM> installed inside duct <NUM>, and being of a relatively rigid material (e.g., rigid plastic, fiberglass, steel, aluminum, etc.) that is stiffer and less flexible than sidewall <NUM>, holds duct <NUM> in a generally expanded shape, regardless of whether blower <NUM> is energized or inactive. Thus, framework <NUM> helps prevent or minimize the pneumatic shock and resulting popping noise of a pliable air duct being suddenly inflated as blower <NUM> turns on, which can suddenly increase the air pressure within duct <NUM> from an inactive ambient air pressure to an active positive air pressure. Framework <NUM> also eliminates or minimizes the extent to which duct <NUM> sags or otherwise suffers degradation in appearance when blower <NUM> is de-energized. In some installations of the frameworks and/or shaft assemblies disclosed herein, such structures also help hold duct <NUM> open when duct <NUM> is used as a return air duct conveying subatmospheric air to the suction inlet of a blower.

Framework <NUM> is contained within duct <NUM> in such a way that framework <NUM> exerts a tensile force <NUM> that tensions duct <NUM> in a generally longitudinal direction <NUM> so that at least sidewall <NUM> is maintained at a minimum level of tautness whether blower <NUM> is activated or not. In some examples, the frame work <NUM> tensions the full and/or substantially the full circumference of the duct <NUM>. Tensioning duct <NUM> lengthwise subjects shaft <NUM> of framework <NUM> to a reactive longitudinal compressive force <NUM>. To prevent compressive force <NUM> from buckling shaft <NUM> and to help hold duct <NUM> in a radially expanded shape, ribs <NUM> are sized to hold duct <NUM> open and are spaced along the duct's <NUM> length to limit the radial deflection of shaft <NUM>.

Although the framework's <NUM> specific design details and means for mounting within a pliable air duct may vary, some examples are illustrated in the referenced figures. In <FIG>, for example, framework <NUM> includes a radial support member <NUM> comprising a plurality of spokes <NUM> that connect rib <NUM> to a hub <NUM>. In this example, rib <NUM> is a complete <NUM>-degree ring, but in other examples, rib <NUM> is a curved rod that extends less than <NUM>-degrees around the inner diameter of duct <NUM>. Also in this example, rib <NUM>, spokes <NUM> and hub <NUM>, which make up radial support member <NUM> in this case, comprise a single construction or fabricated member such as a weldment.

Radial support member <NUM> can be installed at various locations along the length of shaft <NUM>, as shown in <FIG>. When radial support member <NUM> is installed at one end <NUM> of duct <NUM>, as shown in <FIG>, a retainer <NUM> holds rib <NUM> substantially fixed relative to the adjacent sidewall <NUM> of duct <NUM> so that this particular radial support member <NUM> can resist compressive force <NUM> and transmit the corresponding reactive force as tensile force <NUM>, which tensions sidewall <NUM>. Retainer <NUM> can be any means for holding a rib or radial support member generally fixed relative to an adjacent sidewall of a duct. Examples of such a retainer include, but are not limited to, a clip (rigid or spring loaded), a strap (elastic or rigid), an axial brace between rib <NUM> and the blower's housing, a constricting band-style hose clamp (e.g., retainer <NUM> of <FIG>, <FIG> and <FIG>), a screw, rivet, fastener, etc..

In examples where retainer <NUM> is in the form of an elastic strap or spring loaded clip, the retainer's <NUM> elasticity can help compensate for permanent longitudinal stretching of duct <NUM>, which may slowly occur over time, depending on the material of sidewall <NUM>. In addition or alternatively, elastic compensation of permanent longitudinal duct stretching may be incorporated within the framework <NUM> itself at almost any other location along the length of framework <NUM>.

When radial support member <NUM> is installed at various intermediate locations within the length of duct <NUM>, retainer <NUM> at those locations may be omitted. Without retainer <NUM>, rib <NUM>, or actually an imaginary plane <NUM> defined by rib <NUM>, can still be maintained substantially perpendicular to a longitudinal centerline <NUM> of duct <NUM> by spokes <NUM> connecting rib <NUM> to hub <NUM> in combination with a telescopic connection <NUM> (or comparably stiff connection) between hub <NUM> and an adjoining shaft segment 32a. Shaft segment 32a is one of a plurality of segments that when connected to a plurality of hubs <NUM> provide an assembled shaft (shaft <NUM>) that lies generally along centerline <NUM>. The rib's <NUM> perpendicular orientation within duct <NUM> is further ensured by virtue of spokes <NUM> being tilted (e.g., spokes <NUM> lie at an angle <NUM> not perpendicular to the shaft <NUM>) as shown in <FIG>. Such an arrangement creates an axially offset arrangement where spokes <NUM> connect to hub <NUM> (e.g., spokes <NUM> are attached to hub <NUM> at a plurality of points <NUM> and <NUM> that are distributed and spaced apart lengthwise along hub <NUM>), thereby making spokes <NUM> an effective angled brace.

In the example shown in <FIG>, hub <NUM> is a solid rod and shaft segment 32a is a tube with the rod fitting telescopically within the tube. In other examples, hub <NUM> is a tube and shaft segment 32a is a solid rod, wherein the solid rod of the shaft segment fits telescopically within the tubular hub. In some examples, both the hub and the shaft segment are tubes of different diameters with the smaller diameter tube fitting telescopically within the larger one. In some examples, hubs <NUM> provide a coupling that interconnects a plurality of shaft segments 32a, and in other examples, the hub and the "shaft segments" are a unitary piece or a single weldment. In other examples, the hub and shaft segments are joined by some other means for attachment. In still other examples, as shown in <FIG>, a framework <NUM>' comprises ribs <NUM> being interconnected by one or more shafts <NUM>' at the rib's periphery, thereby eliminating the need for spokes <NUM> and hub <NUM>.

<FIG> shows an example where one end <NUM> of hub <NUM> fits within a shaft segment 32b with a fastener <NUM> (e.g., a screw, pin, spring loaded button, etc.) holding the two together. In addition or alternatively, hub <NUM> includes a spring loaded button <NUM> that protrudes selectively into one of several holes <NUM> in a shaft segment 32c to provide discrete axial adjustment between hub <NUM> and shaft segment 32c. Such axial adjustment can be used for adjusting the overall length of framework <NUM>.

<FIG> shows an example where solid shaft segments 32d and 32e fit within a tubular hub 46a. A self-tapping screw <NUM> fastens shaft segment 32d to one end of hub 46a. To provide the framework with an adjustable length, a pin <NUM> is inserted selectively in one of a series of holes <NUM>. Once inserted, pin <NUM> holds the chosen fixed axial relationship between hub 46a and shaft segment 32e.

<FIG> shows an example where a radial support member 30a has a tubular hub 46b that can telescopically slide along a continuous shaft 32f, rather than a segmented one. When inserted within duct <NUM>, in some examples, rib <NUM> is attached to sidewall <NUM> and hub 46b is left with limited freedom to slide relative to shaft 32f, but in other examples, hub 46b is fastened to shaft 32f to hold it in place axially along shaft 32f.

<FIG> shows an example where a radial support member 30c includes a ring <NUM>' that may be formed from a flat bar, which might make radial support member 30c more suitable for clamping with a band-style hose clamp such as retainer <NUM> of <FIG>, <FIG> and <FIG>.

In the illustrated example shown in <FIG> and <FIG>, end cap <NUM> comprises a pliable end sheet <NUM> with a fastener <NUM> for connecting end cap <NUM> to the end of duct <NUM>. Radial support member 44a comprises a plurality of spokes <NUM> connecting rib <NUM> to a hub 46c. Some examples of fastener <NUM> include, but are not limited to, a zipper, a touch-and-hold fastener, snaps, clips, etc. To ensure framework <NUM> is sufficiently long to tension duct <NUM> when end cap <NUM> is installed, a telescopic connection <NUM> between hub 46c and a shaft segment <NUM> enables a total length of framework <NUM> to be increased adequately by sliding radial support member 44a out to phantom line <NUM>, as shown in <FIG>. When framework <NUM> is adjusted to the proper length, that length is held fixed by fastening hub 46c to shaft segment <NUM> by way of screw <NUM>, for instance. In addition or alternatively, a pin <NUM> selectively insertable in one of a series of holes <NUM> can be used for setting a minimum length of framework <NUM>, which can be a helpful feature during installation of duct system <NUM>.

After framework <NUM> is set at the proper length, duct <NUM> and its end cap <NUM> are forcibly pulled together over rib <NUM> and fastener <NUM> is closed, as shown in <FIG>. In some examples, the proper length of framework <NUM> is determined based on the anticipated pressure of air <NUM> that blower <NUM> discharges into duct <NUM>. In some examples, the length of framework <NUM> is sized such that the mechanical force exerted by framework <NUM> in longitudinal direction <NUM> is greater than the pneumatic force applied to the duct's end cap <NUM> so that the application of the pneumatic force does not expand or "pop" duct <NUM> beyond the end of framework <NUM>. In other words, air duct <NUM> is at a first magnitude of tension in longitudinal direction <NUM> when the air inside air duct <NUM> is at the inactive ambient air pressure, air duct <NUM> is at a second magnitude of tension in longitudinal direction <NUM> when the air inside duct <NUM> is at the active positive air pressure, and the first magnitude of tension is greater than a difference between the first and second magnitudes of tension. Also, the first magnitude of tension is less than the second magnitude of tension. Furthermore, framework <NUM> is at a first magnitude of compression in longitudinal direction <NUM> when the air inside duct <NUM> is at the inactive ambient air pressure, framework <NUM> is at a second magnitude of compression in longitudinal direction <NUM> when the air inside duct <NUM> is at the active positive air pressure, and the first magnitude of compression is greater than a difference between the first and second magnitudes of compression. Also, the first magnitude of compression is greater than the second magnitude of compression.

Once contained within duct <NUM>, framework <NUM> requires no additional support because duct <NUM>, which may be independently suspended from overhead support structure <NUM>, carries most if not all the framework's total weight. In some examples, however, as shown in <FIG>, backup hangers <NUM> extending through sidewall <NUM> fasten framework <NUM> directly to some overhead support (e.g., support structure <NUM>) so that framework <NUM> has a redundant source of support if frame support provided by duct <NUM> fails.

<FIG> show an example end cap <NUM> that can be used instead of end cap <NUM> and can be used in a wide variety of pliable or inflatable air ducts, regardless of whether or not the air duct has any other internal framework. End cap <NUM>, in this example, comprises an end piece <NUM> over which a pliable sheet <NUM> is stretched or tightly held. In the illustrated example, end piece <NUM> is provided by rib <NUM> with an optional hub <NUM> and optional set of spokes <NUM>. Hub <NUM> and spokes <NUM> can be useful when end cap <NUM> is used in conjunction with a framework, such as the frameworks shown in <FIG>. Moreover, while the example shown here uses rib <NUM>, any member with a complementary shape to end cap <NUM> can be used. In the case of a round duct, such a complementary shape would be circular. Accordingly, in addition to a ring, a circular plate or similar structure could also be used. It may not even be necessary for the structure to be continuous circumferentially.

In some examples, end cap <NUM> also includes a hem <NUM>, fastener <NUM>, an extension <NUM>, and a constricting member <NUM>. Sheet <NUM> with hem <NUM> has an outer peripheral portion <NUM> and overlies an outer periphery <NUM> of rib <NUM>. In some examples, hem <NUM> is sewn to the outer peripheral portion of sheet <NUM>. In other examples, hem <NUM> is an integral extension of sheet <NUM>. Fastener <NUM> is illustrated to represent any means for connecting hem <NUM> to the end of a tubular pliable air duct, such as duct <NUM>. In some examples, extension <NUM> extends from a virtual circular line <NUM> (<FIG>) at the general vicinity where both hem <NUM> meets sheet <NUM> and where sheet <NUM> overlies rib <NUM>.

In this example, constricting member <NUM> is connected to extension <NUM> and is used for tightening sheet <NUM> in an outward radial direction, thereby avoiding a loose-fitting appearance of sheet <NUM>. In some examples, constricting member <NUM> is a drawstring and extension <NUM> is a circular web having an inner sleeve <NUM> through which the drawstring (member <NUM>) is threaded. In other examples, extension <NUM> comprises a plurality of fabric tabs circumferentially spaced apart and distributed along circular line <NUM>. In either case, manually pulling the ends 104a and 104b of the drawstring pulls extension <NUM> radially inward toward a central point <NUM> of rib <NUM>, thereby tightening sheet <NUM> in a radially outward direction. The drawstring is then tied, clamped or otherwise fixed to maintain sheet <NUM> in a taut state.

In more general terms, constricting member <NUM> has a tight state (<FIG>, <FIG> and <FIG>) and a loose state (<FIG> and <FIG>), wherein pliable sheet <NUM> is more taut when constricting member <NUM> is in the tight state than when constricting member <NUM> is in the loose state, and extension <NUM> is closer to central point <NUM> when constricting member <NUM> is in the tight state than when constricting member <NUM> is in the loose state. After sheet <NUM> is taut, fastener <NUM> connects end cap <NUM> to tubular pliable air duct <NUM>, as shown in <FIG>.

Regardless of the shape and other design features of end piece <NUM>, constricting member <NUM> pulling extension <NUM> radially inward toward central point <NUM> pulls pliable sheet <NUM> over outer periphery <NUM> of end piece <NUM> and pulls pliable sheet <NUM> radially outward. The resulting radial tension in pliable sheet <NUM> provides end cap <NUM> with a neat appearance with minimal, if any, wrinkles.

Various additional features and benefits of the aforementioned examples are illustrated in <FIG>. <FIG> is a top view of an example L-shaped air duct system <NUM> comprising a pliable elbow duct <NUM> connecting two pliable air ducts 18a and 18b. To keep substantially the entire L-shaped duct appearing inflated, a first framework 30a is disposed within duct 18a to create longitudinal tension and/or tensile force <NUM> in that duct, wherein radial support members <NUM> and 44a are circumferentially clamped or otherwise held to duct 18a by any suitable means including, but not limited to, strap clamps <NUM>. In addition or as an alternative to strap clamp <NUM> in some examples, a short pliable air duct segment with one or more retainers <NUM> holds radial support members <NUM> and/or 44a in place while circumferential zippers at either end of the duct segment connects the duct segment to the rest of air duct 18a. Likewise, a second framework 30b is disposed within duct 18b to create longitudinal tension or tensile force <NUM> in that duct, wherein one or more radial support members <NUM> are circumferentially clamped to duct 18b by any suitable means including, but not limited to, strap clamps <NUM>. One or more radial support members <NUM> are disposed within elbow <NUM> to keep elbow <NUM> appearing generally inflated. In some examples, a curved shaft interconnecting radial support members <NUM> within elbow <NUM> helps hold radial support members <NUM> in place. The curved shaft is not shown because not all examples of an elbow with radial support members include such a shaft.

<FIG> shows an example flow restrictor <NUM> attached to radial support member <NUM>. Flow restrictor <NUM>, in some examples, is a fabric cone with a reduced airflow outlet <NUM>. In some examples, outlet <NUM> is a fixed opening, and in other examples the downstream opening of outlet <NUM> is adjustable by way of a constricting drawstring <NUM>.

<FIG> shows how a plurality of radial support members <NUM> can be stacked in a compact transportable arrangement. Such a nested arrangement is possible due to the offset between spoke connecting points <NUM> and <NUM>, wherein points <NUM> and <NUM> are longitudinally offset (dimension <NUM>) and are on opposite sides of hub <NUM>. In more specific terms, the example illustrated apparatus/assembly <NUM> comprises a plurality of ribs <NUM>, wherein each rib <NUM> lies along an imaginary plane <NUM> to define a plurality of imaginary planes <NUM>. Apparatus/assembly <NUM> also includes a hub <NUM> attached to each rib <NUM> to create a plurality of hubs <NUM>. Rings <NUM> are in a transportable stacked arrangement with rings <NUM> lying adjacent each other so that the plurality of imaginary planes <NUM> are substantially parallel to each other. The plurality of hubs <NUM> are radially offset to each other (dimension <NUM>), and the plurality of ribs <NUM> are radially offset to each other. In the illustrated example, at least one hub <NUM> extends through more than one imaginary plane <NUM>.

<FIG> illustrate an example method for taking an existing, previously functional air duct system <NUM> that includes an inflatable air duct <NUM> and retrofitting system <NUM> with framework <NUM> or one similar to it. In some examples, the method involves accessing the interior volume of duct <NUM> by opening the duct at some point, for example, at the duct's end cap <NUM>, as shown in <FIG> shows installing framework <NUM> inside duct <NUM>. In some examples, alternate styles of frameworks are installed instead, such as framework <NUM>'. In some examples, framework <NUM> is assembled progressively as it is inserted in duct <NUM>. <FIG> shows framework <NUM> inside duct <NUM> with example retainer <NUM> holding one radial support member <NUM> in place. <FIG> show how a longitudinal length <NUM> of framework <NUM> is adjustable, where framework <NUM> is longer in <FIG> than in <FIG>. Arrow <NUM> of <FIG> represents closing end cap <NUM>, thereby enclosing framework <NUM> within the internal volume of duct <NUM>. Forcibly enclosing framework <NUM> within duct <NUM>, as shown in <FIG>, results in compressing framework <NUM> and tensioning inflatable air duct <NUM> in longitudinal direction <NUM>.

With previous air ducts having pliable tubular sidewalls and an internal framework, the sidewall material still tends to sag with the loss of internal air pressure and/or as the sidewall material stretches over time. An example of an air duct, which is able to keep continuous tension on the sidewall material, and thus maintain tautness of the duct, uses the stored compression in a spring, which supplies continuous force on the end cap in the lengthwise direction of the duct. With this example, the stored compression in the spring can be released when the duct is deflated, resulting in the lengthening of the duct. The stored compression is drawn upon due to the internal framework having a variable overall length and the spring providing the actual force to change the length. <FIG> and <FIG> illustrate an example air duct system <NUM> with features that facilitate installation and ensure tautness of the system's air duct <NUM> even when duct <NUM> is deflated. In this example, air duct <NUM> includes tubular pliable sidewall <NUM> (<FIG>) and attached end cap <NUM>. Sidewall <NUM> being tubular is suitable for conveying air <NUM> in a longitudinal direction <NUM> through duct <NUM> and eventually releasing air <NUM> in a radial and/or axial direction through pores or other outlets in duct <NUM>.

To keep sidewall <NUM> taut so duct <NUM> appears inflated when duct <NUM> is actually deflated (unpressurized), an example spring loaded framework <NUM> is installed within duct <NUM>, as shown in <FIG>. Framework <NUM>, in this example, comprises a shaft <NUM> supporting a plurality of ribs <NUM>. Ribs <NUM> engage an inner surface <NUM> of sidewall <NUM> to maintain duct <NUM> in a radially expanded shape. To keep sidewall taut in longitudinal direction <NUM>, shaft <NUM> comprises a first shaft segment <NUM>, a second shaft segment 46d, a spring or biasing element <NUM>, and a telescopic connection <NUM> between shaft segments <NUM> and 46d (e.g., first and second shaft segment examples include, but are not limited to, previously mentioned hubs <NUM>, 46a, 46b, 46c and <NUM>); wherein the various shaft components and other elements of system <NUM> are designed to hold duct <NUM> in longitudinal tension in reaction to shaft <NUM> being in longitudinal compression.

Lengthwise adjustment of the internal structure is provided by a pin engaging a helical spring which makes the length continuously (opposed to by discreet increments) adjustable. For instance, in some examples, spring <NUM> is a helical compression spring with one end <NUM> attached to a fixed point <NUM> on second shaft segment 46d. An intermediate section <NUM> of spring <NUM> threadingly engages a pin <NUM> or comparable feature at a point <NUM> fixed on first shaft segment <NUM>. The distance between points <NUM> and <NUM>, in addition to other physical dimensions of system <NUM>, determines the overall length of shaft <NUM> and/or the compression of spring <NUM>.

To adjust shaft length and/or spring compression, a first rotational joint <NUM> at telescopic connection <NUM> enables second shaft segment 46d to be rotated relative to first shaft segment <NUM>. Depending on the direction of rotation, manually turning second shaft segment 46d relative to first shaft segment <NUM>, as shown in <FIG>, effectively screws the two shaft segments <NUM> and 46d together or apart due to the two shaft segments <NUM> and 46d being threadingly coupled to each other by way of spring section <NUM> engaging pin <NUM>. Thus, spring <NUM> serves as an adjustment screw for adjusting the overall length of shaft <NUM> when shaft <NUM> is unrestrained lengthwise by duct <NUM> (unrestrained, for example, when end cap <NUM> is removed or when shaft <NUM> is appreciably shorter than duct <NUM>). When the length of shaft <NUM> is restrained by the finite length of duct <NUM> with end cap <NUM> installed, spring <NUM> serves as an adjustment screw for adjusting the compression of spring <NUM> and thus serves as a means for adjusting the longitudinal compression of shaft <NUM>. Adjusting the longitudinal compression of shaft <NUM>, in turn, adjusts the longitudinal tension in duct <NUM> accordingly.

In some examples, the adjustment of shaft <NUM> is carried out as follows: First, the length of framework <NUM> is set as shown in <FIG>, wherein the framework's relatively short, uncompressed length allows a portion <NUM> of end cap <NUM> to be readily zipped or otherwise attached to sidewall <NUM>. With another portion <NUM> of the end cap's periphery unzipped or otherwise unattached to sidewall <NUM>, as shown in <FIG>, a person can reach their arm <NUM> through the unzipped opening <NUM> into the duct's interior to manually rotate second shaft segment 46d relative to first shaft segment <NUM> so that the shaft's relaxed, uncompressed length becomes greater than the length of duct <NUM> and sidewall <NUM>. However, with end cap <NUM> restricting the shaft's ability to fully extend to its relaxed, uncompressed length, spring <NUM> and shaft <NUM> become compressed within the confines of duct <NUM>. Next, the person withdraws their arm <NUM> and closes opening <NUM>. End cap <NUM> now fully attached to sidewall <NUM> holds spring <NUM> and shaft <NUM> in compression. Shaft <NUM> being compressed subjects sidewall <NUM> to longitudinal tension <NUM>, as shown in <FIG>.

To make it easier to manually rotate second shaft segment 46d relative to first shaft segment <NUM> without rib <NUM> tending to rotate end cap <NUM> in the process, some example shafts, such as shaft <NUM> of <FIG>, includes a second rotatable joint <NUM> between a second shaft segment 46e and a hub 46f that renders second shaft segment 46e further rotatable relative to end cap <NUM>.

In some examples, as shown in <FIG> and <FIG>, a shaft <NUM> includes a releasable lock <NUM> at telescopic connection <NUM>. The function of the releasable lock is to temporarily store some of the adjustable length/spring compression and release it only when the end cap is in place to react to the force. Releasable lock <NUM> can make it easier to close the connection between sidewall <NUM> and end cap <NUM> while spring <NUM> and shaft <NUM> are under compression. For instance, lock <NUM> in its holding position of <FIG> holds shaft <NUM> at a retracted length that easily fits within duct <NUM>. Just before completely closing the closure between end cap <NUM> and sidewall <NUM>, a person can reach into duct <NUM> to move lock <NUM> to its release position of <FIG>. This allows spring <NUM> to extend shaft <NUM> to the length shown in <FIG>, whereby spring <NUM> still under some compression provides the axial force to place sidewall <NUM> in longitudinal tension. After releasing lock <NUM>, the person can complete the closure between end cap <NUM> and sidewall <NUM>.

Although the actual structure of lock <NUM> may vary, in some examples, lock <NUM> is a thumb screw threadingly engaging a second shaft segment <NUM> with an axial end <NUM> selectively abutting first shaft segment <NUM>. In the holding position, axial end <NUM> presses firmly against first shaft segment <NUM> to hold segment <NUM> fixed relative to second shaft segment <NUM>. In the release position, axial end <NUM> is spaced apart from first shaft segment <NUM> to permit relative movement between shaft segments <NUM> and <NUM>.

In some examples, as shown in <FIG> and <FIG>, an air duct system <NUM> includes a novel elbow particularly suited for redirecting a current of air <NUM> through a tubular pliable sidewall <NUM> of an air duct <NUM>. In <FIG>, air duct <NUM> defines a nonlinear airflow path <NUM> from an inlet <NUM> to an outlet <NUM> of duct <NUM>. To hold air duct <NUM> in a radially expanded shape, the illustrated example includes a plurality of ribs <NUM> supported by a shaft <NUM> that is selectively configurable to a removed configuration and an installed configuration.

In the removed configuration, shaft <NUM> is removed out from within duct <NUM> and has a first shape that in some examples is relatively or somewhat straight (e.g., straighter than a <NUM>-degree elbow), as shown in <FIG>. In the installed configuration, shaft <NUM> is installed within duct <NUM> with ribs <NUM> engaging an inner surface <NUM> of sidewall <NUM>, as shown in <FIG>. In the installed configuration, shown in <FIG>, shaft <NUM> has a second shape that is distinguishable from its first shape shown in <FIG>. In the illustrated example, shaft <NUM> has a longitudinal centerline <NUM> that is straighter in <FIG> than in <FIG>. In <FIG>, centerline <NUM> lies along a nonlinear line. <FIG> shows centerline <NUM> lying along a substantially linear line or at least along a line that deviates from the nonlinear line shown in <FIG>. The variable shape of shaft <NUM> can be beneficial in the installation, shipping, and/or manufacturing of shaft <NUM>. The variable shape of shaft <NUM> can also be useful in fitting shaft <NUM> to duct elbows of various shapes.

In some examples, the variable shape of shaft <NUM> is achieved by having shaft <NUM> be comprised of a plurality of shaft segments <NUM> interconnected by at least one articulation joint <NUM>, wherein joint <NUM> renders the plurality of shaft segments <NUM> angularly movable relative to each other when shaft <NUM> is in the removed configuration. In some examples, articulation joint <NUM> is a helical spring that is more flexible than the plurality of shaft segments <NUM>. In other examples, as shown in <FIG> and <FIG>, an example articulation joint <NUM> is a tube made of a resiliently bendable polymer (e.g., rubber, polyurethane, etc.). In still other examples, as shown in <FIG>, an example articulation joint <NUM> is a pivotal link such as, for example, two interconnected eyelets (e.g., two interconnected eyebolts or disconnectable clasp).

In the examples shown in <FIG>, air duct <NUM> is selectively inflated and deflated. Air duct <NUM> has an internal deflated volume <NUM> that when air duct <NUM> is deflated, the internal deflated volume is greater when shaft <NUM>, 196a or 196b is in the installed configuration (<FIG>, <FIG> and <FIG>, respectively) than when the shaft is in the removed configuration.

In some examples, as shown in <FIG>, an air duct <NUM> in the shape of an elbow has a tubular pliable sidewall <NUM> with at least some elastic material <NUM> that helps control the puckering of sidewall <NUM> to evenly distribute a plurality of wrinkles or puckers <NUM>. In some examples, material <NUM> is an elastic strip intermittently sewn or otherwise attached to an inner radius <NUM> of tubular sidewall <NUM>. In other examples, most if not all of sidewall <NUM> is comprised of elastic material.

With previous air ducts having pliable tubular sidewalls and an internal framework which could be adjustable in the lengthwise direction, the adjustment could only be made in discreet increments. Also, adjusting the length of the internal framework of the previous duct, to achieve adequate tension of the sidewall was difficult, do the relatively high tension forces required. In an example of an air duct having adjustable length internal framework, a linear clutch device not only provides for continuous (non-discreet) length adjustment, it also utilizes mechanical advantage to achieve the required tension in the sidewall. In this example, the sidewall material can be pre-stressed taut enough so that it does not sag even when deflated. In some examples, as shown in <FIG>, an air duct system <NUM> includes an example shaft assembly <NUM> with an example linear clutch <NUM> for holding air duct <NUM> in tension <NUM> (<FIG>) longitudinally in response to shaft assembly <NUM> being in longitudinal compression <NUM>. The term, "linear clutch" means any mechanism that has at least one configuration in which the mechanism facilitates longitudinal extension of an elongate assembly (e.g., shaft assembly <NUM>) while resisting longitudinal retraction of the elongate assembly. Examples of linear clutch <NUM> and other linear clutches include, but are not limited to, a Lever Action Cargo Bar, P/N-<NUM>, provided by Erickson Manufacturing LTD. of Marine City, MI; a Pro Grip Cargo Control Cargo Bar, PIN <NUM>, provided by USA Products Group, Inc. of Lodi, CA; a Ratcheting Cargo Bar, PIN <NUM> (<CIT> of North Windham, CT; a Haul-Master <NUM>-in-<NUM> Support Cargo Bar, PIN <NUM>, provided by various distributors (e.g., Harbor Freight of Camarillo, CA; Amazon. of Seattle, WA; and Sears Holdings Corp. of Hoffman Estates, IL).

In the illustrated example, to extend shaft assembly <NUM> from its length of <FIG> to that of <FIG>, a person reaches their arm <NUM> through opening <NUM> to repeatedly move or cycle a reciprocator <NUM> extending from linear clutch <NUM>. The term, "reciprocator" means any member that is operated by repeated back and forth movement. Repeatedly moving reciprocator <NUM> between its relaxed position (<FIG>) and its stressed position (<FIG>) and doing so for a plurality of cycles <NUM> (<FIG>) during a given period <NUM> extending between a start <NUM> and an end <NUM>, lengthens shaft assembly <NUM>. Thus, an adjustable length <NUM> of shaft assembly <NUM> is longer at the period's end <NUM> than at the period's start <NUM>, and length <NUM> increases incrementally with each cycle, as shown in the example of <FIG>.

Once linear clutch <NUM> extends shaft assembly <NUM> to a desired length that places air duct <NUM> in tension and shaft assembly in compression, zipper <NUM> is closed, as shown in <FIG>, and air duct system <NUM> is ready for use. To minimize airflow resistance in duct <NUM>, in some examples, reciprocator <NUM> and a handle <NUM> are moved to a stored position, as shown in <FIG>. If, for any reason, one wants to relieve the air duct's tension and the shaft assembly's compression by shorting shaft assembly <NUM>, a person can reach arm <NUM> into duct <NUM>, as shown in <FIG>, and actuate <NUM> a release lever <NUM> that allows linear clutch <NUM> to retract <NUM> shaft assembly <NUM>.

Although the actual design and operation of linear clutch <NUM> may vary, <FIG> illustrate one example, wherein linear clutch <NUM> is selectively moveable to a hold configuration (<FIG>) and a release configuration (<FIG> shows linear clutch <NUM> in another hold configuration but with linear clutch <NUM> having incrementally lengthened shaft assembly <NUM>. In this illustrated example, linear clutch <NUM> comprises a housing <NUM>, handle <NUM> attached to housing <NUM>, reciprocator <NUM> pinned to housing <NUM>, a shaft segment <NUM> slidingly disposed within housing <NUM>, a first annular binding member <NUM> encircling shaft segment <NUM>, a second annular binding member <NUM> encircling shaft segment <NUM>, release lever <NUM> integrally extending from second annular binding member <NUM>, a first compression spring <NUM> urging first annular binding member <NUM> to its free position (shown in <FIG>), and a second compression spring <NUM> urging second annular binding member <NUM> to its grip position (shown in <FIG>).

In this example, pivotally moving reciprocator <NUM> from its relaxed position (<FIG>) to its stressed position (<FIG>) tilts first annular binding member <NUM> from its free position (<FIG>) to its grip position (<FIG>) such that first annular binding member <NUM> grips shaft segment <NUM>. While first annular binding member <NUM> grips shaft segment <NUM>, moving reciprocator <NUM> from its relaxed position (<FIG>) to its stressed position (<FIG>) pushes first annular binding member <NUM> and shaft segment <NUM> to the left <NUM> one increment <NUM> (<FIG> and <FIG>), thereby extending shaft assembly <NUM>. Second annular binding member <NUM> allows such movement because as shaft segment <NUM> moves leftward, axial friction between shaft segment <NUM> and second annular binding member <NUM> is in a direction that diminishes the frictional holding force between shaft segment <NUM> and second annular binding member <NUM>. Subsequently releasing reciprocator <NUM> from its stressed position (<FIG>) to its relaxed position (<FIG>) allows first spring <NUM> to push first annular binding member <NUM> back to its free position of <FIG> while second spring <NUM> urging annular binding member <NUM> to its grip position (<FIG>) prevents shaft segment <NUM> from retracting rightward back to where it was previously in <FIG>. This cycle is repeated to incrementally extend shaft assembly <NUM>.

To later retract shaft assembly <NUM>, in this example, release lever <NUM> is tilted from its normal binding position of <FIG> to a release position of <FIG>. In the release position, second annular binding member <NUM> releases its binding grip on shaft segment <NUM>. With both annular binding members <NUM> and <NUM> in their release positions, as shown in <FIG>, linear clutch <NUM> allows shaft assembly <NUM> to retract.

In the example shown in <FIG>, an air duct system <NUM> includes a shaft assembly <NUM> with another example linear clutch <NUM>. Linear clutch <NUM> includes a ratchet mechanism <NUM> comprising a pawl <NUM> engaging a rack <NUM> having a plurality of discontinuities <NUM>. The term, "pawl" means any movable element selectively engaging one or more discontinuities in a rack. Examples of a pawl include, but are not limited to, a pivotal bar or lever engaging one or more teeth or other discontinuities on a rack, and a partial or full pinion gear (e.g., pawl <NUM>) with teeth mating with one or more teeth or other discontinuities on a rack. The term, "rack" means a generally linear elongate member with a plurality of discontinuities (e.g., teeth, protrusions, holes, detents, etc.) distributed along its length. Examples of a rack include, but are not limited to, a tube with a plurality of holes distributed along the tube's length, a tube with a plurality of detents distributed along the tube's length, and an elongate bar with a plurality of gear teeth distributed along the bar's length. A specific example of linear clutch <NUM> is a Ratcheting Cargo Bar, PIN <NUM> (<CIT> of North Windham, CT.

In the example illustrated in <FIG>, repeatedly moving (in a cyclical manner <NUM>) a reciprocator <NUM> of linear clutch <NUM> lengthens shaft assembly <NUM>. Shaft assembly <NUM> can be shortened by manually actuating a release lever <NUM> to disengage lever <NUM> from pawl <NUM>, wherein arrow <NUM> represents the actuation of release lever <NUM>. <FIG> is similar to <FIG> in that linear clutch <NUM> is shown having extended shaft assembly <NUM> to place duct <NUM> in tension <NUM> and shaft assembly <NUM> in compression <NUM>. An example of an air duct capable of automatic tension adjustment of the pliable sidewall material in the length direction of the duct, is shown in <FIG>.

In another example, shown in <FIG>, an air duct system <NUM> includes an example screw-style linear clutch <NUM> for placing duct <NUM> in tension <NUM> in reaction to a shaft assembly <NUM> being in compression <NUM>. To adjust the length of shaft assembly <NUM> and/or to adjust the tension in duct <NUM>, a head <NUM> of linear clutch <NUM> is rotated by a tool <NUM> in a cyclical manner (e.g., rotating tool <NUM> a plurality of continuous revolutions <NUM>, or rotating tool <NUM> a plurality of partial revolutions <NUM>). Such action varies the extent to which a rotatable screw <NUM> (helically threaded member) extends into a shaft tube <NUM> of shaft assembly <NUM>.

In some examples, linear clutch <NUM> comprises screw <NUM> screwed into an internally threaded member <NUM> affixed to shaft tube <NUM> (e.g., a nut welded to the end of tube <NUM>, or tube <NUM> being internally threaded), a shank <NUM> affixed to screw <NUM> such that shank <NUM> and screw <NUM> rotate as a unit, a tubular hub <NUM> radially supporting shank <NUM>, and head <NUM> on shank <NUM>. In some examples, tool <NUM> is a crank extending generally permanently from head <NUM>. In some examples, tool <NUM> is a dedicated crank removably attached to head <NUM>. In some examples, tool <NUM> is a general purpose wrench, such as a ratchet wrench with a socket that fits head <NUM>. The direction and amount that tool <NUM> and screw <NUM> are rotated relative to internally threaded member <NUM> determine the extent to which screw <NUM> extends into shaft tube <NUM> and thus determines the adjusted length of shaft assembly <NUM>. The adjusted length of shaft assembly <NUM>, in turn, determines the tension and compression of duct <NUM> and shaft assembly <NUM>, respectively.

In some examples, as shown in <FIG>, a linear clutch <NUM> allows the extension of a shaft assembly <NUM> (framework example) by inflating air duct <NUM> from a deflated state of <FIG> to an inflated state of <FIG> while a retainer <NUM> (e.g., strap, clip, clamp, pocket, loop, etc.) couples a distal end <NUM> of shaft assembly <NUM> to the air duct's end cap (e.g., end cap <NUM>). In addition to retainer <NUM> and/or alternatively, in some examples, distal end <NUM> is attached to the duct's end cap in the manner illustrated in <FIG>.

As inflation naturally extends the length of duct <NUM>, the air duct's resulting elongation lengthens shaft assembly <NUM> because the shaft assembly's distal end <NUM> is coupled to the duct's end cap. Once shaft assembly <NUM> is extended from its shorter length of <FIG> to its longer length of <FIG>, the unidirectional gripping action of linear clutch <NUM> holds shaft assembly <NUM> at its extended length even after duct <NUM> is subsequently deflated, as shown in <FIG>.

In some examples, linear clutch <NUM> used in shaft assembly <NUM> is identical to linear clutch <NUM>; however, many parts of linear clutch <NUM> can be left unused. Eliminating the unused parts renders example linear clutch <NUM>, as shown in <FIG>. <FIG> shows the elimination of handle <NUM>, reciprocator <NUM>, first annular binding member <NUM> and first compression spring <NUM>. Thus, linear clutch <NUM> is left comprising housing <NUM>, shaft segment <NUM>, annular binding member <NUM> encircling shaft segment <NUM>, release lever <NUM> integrally extending from annular binding member <NUM> and compression spring <NUM>. The function of the parts included in linear clutch <NUM> function as those same parts which were described with reference to linear clutch <NUM>.

<FIG> illustrates an example linear clutch <NUM> that is functionally similar or identical to linear clutch <NUM> and in some examples is used as a substitute for linear clutch <NUM> in the air duct system illustrated in <FIG>. Structurally, linear clutch <NUM> includes a housing <NUM> instead of housing <NUM> and a tension spring <NUM> instead of compression spring <NUM>. Tension spring <NUM> urges annular binding member <NUM> to its grip position shown in <FIG>.

As for various methods pertaining to the examples illustrated in <FIG>, <FIG> provides at least one example that illustrates inserting a shaft assembly into an air duct. An arrow <NUM> of <FIG> and <FIG> provides at least one example that illustrates manipulating the actuator in a cyclical manner that involves a plurality of cycles. An arrow <NUM> of <FIG> provides at least one example that illustrates lengthening the shaft assembly in a plurality of increments corresponding to the plurality of cycles. <FIG> provides at least one example that illustrates, as a consequence of lengthening the shaft assembly, subjecting the air duct to tension (arrow <NUM>) in the longitudinal direction and subjecting the shaft assembly to compression (arrow <NUM>) in the longitudinal direction. Arrow <NUM> of <FIG> and <FIG> provides at least one example that illustrates manipulating the actuator in a reciprocating motion. Arrow <NUM> of <FIG> provides at least one example that illustrates turning a helically threaded member a plurality of revolutions. Arrow <NUM> of <FIG> and arrow <NUM> of <FIG> provide at least one example that illustrates manipulating a ratchet mechanism in a reciprocating motion. The current of air <NUM> in <FIG> and comparing the relatively limp air duct in <FIG> (deflated with no appreciable current of air <NUM>) to the inflated taut air duct in <FIG> provides at least one example of inflating the air duct. Comparing a dimension <NUM> in <FIG> to a longer dimension <NUM> in <FIG> provides at least one example that illustrates as a consequence of inflating the air duct, lengthening the framework longitudinally to an extended length (e.g., L2 in <FIG>). <FIG> without arrow <NUM> provides at least one example that illustrates deflating the air duct to a deflated state. Arrow <NUM> in <FIG> provides at least one example that illustrates subjecting the air duct to at least some longitudinal tension while the air duct is in the deflated state. Arrow <NUM> of <FIG> provides at least one example that illustrates subjecting the air duct to at least some longitudinal compression while the air duct is in the deflated state. Arrows <NUM> and <NUM> and shaft assembly <NUM> (example of a framework) in <FIG> provide at least one example that illustrates the framework holding the air duct in longitudinal tension while the air duct is in the deflated state and holding the framework in longitudinal compression while the air duct is in the deflated state.

In some examples, as shown in <FIG>, air duct <NUM> of an air duct system <NUM> is held in tension longitudinally by a compression spring <NUM> that is adjustably compressed between a collar <NUM> and a tubular hub 46i. In the illustrated example, spokes <NUM> and rib <NUM> couple end cap <NUM> to hub 46i, and collar <NUM> encircles a tubular shaft 32i such that the collar's axial position on shaft 32i can be changed to adjust and set the tension of air duct <NUM>.

<FIG>, for instance, shows collar <NUM> at a less-stress position on shaft 32i to place spring <NUM> in a less-compressed state. Spring <NUM> being compressed between collar <NUM> and a shoulder <NUM> on hub 46i subjects air duct <NUM> to tension <NUM> and shaft 32i to compression <NUM>. <FIG> shows collar <NUM> at a more-stress position that places spring <NUM> in a more-compressed state, which subjects air duct <NUM> to more tension <NUM> and shaft 32i to more compression <NUM>.

To adjust the position of collar <NUM> on shaft 32i, collar <NUM> and/or shaft 32i includes a collar holding mechanism for selectively holding and releasing collar <NUM> relative to shaft 32i. Releasing collar <NUM> allows collar <NUM> to be manually slid axially to another position along shaft 32i. In the illustrated example, the holding mechanism is a thumbscrew <NUM> that screws into a threaded hole in collar <NUM> to selectively engage or release shaft 32i.

<FIG> and <FIG> show thumbscrew <NUM> engaging shaft 32i to place collar <NUM> in a locked condition such that collar <NUM> remains axially fixed relative to shaft 32i. <FIG> shows thumbscrew <NUM> partially unscrewed from within the collar's threaded hole to release collar <NUM> from shaft 32i, thereby placing collar <NUM> in an unlocked condition. In the unlocked condition, collar <NUM> is free to be slid axially along shaft 32i for adjusting the compression of spring <NUM>, which determines the tension in duct <NUM>. In the unlocked condition, collar <NUM> can also be moved to completely release the compression of spring <NUM>, as shown in <FIG>.

In some examples, a pin <NUM> affixed to shaft 32i protrudes through one or more slots <NUM> that extend longitudinally along hub 46i. This limits the range of axial adjustment or relative movement between hub 46i and shaft 32i. In some cases, if end cap <NUM> is removed, the limited range of movement of pin <NUM> along slot <NUM> prevents a compressed spring <NUM> from pushing hub 46i completely off of shaft 32i.

In some examples, as shown in <FIG> and <FIG>, an air duct system <NUM> comprises a shaft assembly <NUM> from which spokes <NUM> extend radially outward to support a plurality of ribs <NUM>, which in turn support air duct <NUM>. The length of shaft assembly <NUM> is adjustable to hold duct <NUM> in longitudinal tension <NUM>, which places shaft assembly <NUM> in longitudinal compression <NUM>. In this example, the adjustment of shaft assembly <NUM> is by virtue of a telescopic connection <NUM> between a first shaft segment <NUM> and a second shaft segment <NUM> in combination with an adjustable threaded connection <NUM> between a screw <NUM> (e.g., threaded rod, bolt, etc.) and an internally threaded member <NUM> (e.g., a conventional nut, block with a tapped hole, plate with a tapped hole, etc.). Shaft assembly <NUM> is shown more extended in <FIG> than in <FIG>, so the air duct's tension is greater in <FIG> than in <FIG>.

To increase the shaft assembly's length and thus increase the tension in duct <NUM>, head <NUM> on screw <NUM> is rotated in one direction relative to threaded member <NUM> such that threaded member <NUM> travels axially along the length of screw <NUM>, away from head <NUM>, to push first shaft segment <NUM> partially out from within second shaft segment <NUM>. As shaft assembly <NUM> lengthens, a shaft retainer <NUM> abutting a plate <NUM> on end cap <NUM> prevents the head-end <NUM> of screw <NUM> from being forced axially outward from within duct <NUM>. Examples of retainer <NUM> include, but are not limited to, a nut, washer or pin welded to screw <NUM>; a shoulder on screw <NUM>; an E-clip or C-clip on screw <NUM>, etc. Examples of plate <NUM> include, but are not limited to, a washer, a disc, a grommet, etc. Rotating head <NUM> in the opposite direction moves threaded member <NUM> toward head <NUM>, which allows first shaft segment <NUM> to retract into second shaft segment <NUM> and thus shorten shaft assembly <NUM> to reduce the duct's tension.

Relative rotation of screw <NUM> and threaded member <NUM> is achieved, in some examples, by an anti-rotation feature between threaded member <NUM> and a longitudinal slot <NUM> in second shaft segment <NUM>. In some examples, the anti-rotation feature is a disc <NUM> attached to threaded member <NUM> and encircling screw <NUM>, wherein disc <NUM> has a radial protrusion <NUM> extending into slot <NUM>. Protrusion <NUM> extending into slot <NUM> inhibits relative rotation between disc <NUM> and second shaft segment <NUM>. Since disc <NUM> is attached to threaded member <NUM>, protrusion <NUM> extending into slot <NUM> also inhibits relative rotation between threaded member <NUM> and second shaft segment <NUM>. In other words, protrusion <NUM> extending into slot <NUM> provides limited relative rotation between internally threaded member <NUM> and second shaft segment <NUM>, wherein the term, "limited relative rotation," means that in reference to second shaft segment <NUM>, threaded member <NUM> is rotatable less than <NUM> degrees and in some examples the threaded member's relative rotation is limited to zero degrees. Disc <NUM> also provides a bearing surface for pushing against an axial end of first shaft segment <NUM>.

It should be noted that as head <NUM> is rotated to extend or retract shaft assembly <NUM>, screw <NUM> has a substantially fixed longitudinal position relative to second shaft segment <NUM>, and internally threaded member <NUM> has a substantially fixed axial position relative to first shaft segment <NUM>.

Claim 1:
A framework (<NUM>) for use with an air duct system (<NUM>, <NUM>, <NUM>, <NUM>) having an air duct (<NUM>), the framework (<NUM>) comprising:
a shaft (<NUM>); and
a plurality of radial support members (<NUM>),
each radial support member (<NUM>) comprising:
a hub (<NUM>) to be coupled to the shaft (<NUM>),
a rib (<NUM>) at least partially encircling the hub (<NUM>), the rib (<NUM>) to be positioned adjacent an inner surface of the air duct (<NUM>) to substantially maintain the air duct (<NUM>) in an open position;
a first spoke (<NUM>) coupling the rib (<NUM>) to a first side of the hub (<NUM>); and
a second spoke (<NUM>) coupling the rib to a second side of the hub (<NUM>), the first side being opposite the second side,
the framework (<NUM>) having a variable length between first and second ends corresponding to a first and a second radial support member (<NUM>), positioned within the air duct (<NUM>), the first and second ends of the framework (<NUM>) being configured to tension the pliable sidewall material along a length of the air duct (<NUM>) as the variable length of the framework (<NUM>) is increased, such that the tension in the pliable sidewall material is maintained to keep the pliable sidewall material taut.