GB2301085A - Method of Making a Drive for a Telscopic Mast - Google Patents

Abstract

A method of constructing an expandable and collapsible drive member for extending and retracting a plurality of interconnected mast sections of a telescoping mast assembly, which method comprises: bending a metal sheet strip (160, Fig.1) inwardly adjacent each longitudinal edge to form outer flange portions 161, 162 between the ends; bending the sheet longitudinally on opposite sides of its centreline to form an inner flange portion 167 between the ends and a middle portion 168, 169 between the inner flange portion and each of the outer flange portions; folding the inner flange portion along the centreline to provide inner flange portions 167a, 167b on laterally opposite sides of the centreline and abutting the inner flange portions; abutting the outer flange portions 161, 162; and joining the outer flange portions together, preferably by spot welding. Preferably, the inner flange portions 167a, 167b are also spot welded. Preferably the collapsible tube so formed is heat treated by placing a rod (172) down its centre and placing in a furnace for e.g. 8 hours. In use, the drive will wind-up flat on a reel (Fig 5) and expand to form a rigid drive member when payed out.

Description

TELESCOPING MAST ASSEMBLY BACKGROUND OF THE INVENTION The present invention relates to the art of telescoping masts and more particularly to a telescoping mast having a drive assembly for translation of the mast sections to a fully retracted position, a fully extended position or any position therebetween.

The present invention is particularly applicable for use with mobile land and sea vehicles and to provide a lighting system used to illuminate areas under bridges or over sharp drop-offs such as cliffs and mountain roads.

Telescoping masts are used for many applications. Generally such telescoping masts may be adapted to fit on the roof of a vehicle such as a military or emergency type vehicle. Such mast is usually outfitted with a top mounted fixture such as a light or antenna fixed at the top of the mast.

Generally, a mast to be placed on the roof of a vehicle must be of relatively light weight, durable, compact in size, capable of withstanding all kinds of weather and relatively maintenance free.

A common mast used for such applications is a pneumatically actuated telescoping mast. 'However, such a mast is subject to damage during operation which can affect its operability. In this respect, the mast must remain airtight for proper operation. A hole or fracture formed in a section of the mast may allow the escape of air and thus affect operation and prevent proper inflation. Pneumatic masts also lack rigidity and may be subject to damage in high winds or from impact with adjacent objects.

Further, pneumatic masts are not generally adaptable to be partially extended in those instances where a certain desired elevation of a light fixture or other top mounted fixture is desired. Additionally, pneumatic masts are typically only extendable in a vertical or horizontal direction. This prevents use of such masts under bridges or over cliff sides where it would be desirable to extend the mast at an angle to project a light away from its mounting. One attempt to overcome the latter disadvantage of pneumatic masts is disclosed in commonly owned, copending application Serial No. 286,269, filed August 5, 1994, the disclosure of which is hereby incorporated by reference. While overcoming the bi-directional problem, the invention disclosed in application Serial No. 286,269 does not overcome the other disadvantages of pneumatic masts described hereinabove.

An alternative to pneumatically actuated telescoping masts is a tubular type of mast assembly comprising a plurality of telescoping mast sections and a rigid drive assembly operable to displace the mast sections to any position between a fully retracted position and a fully extended position. Such telescoping mast assemblies are disclosed, for example, in United States Patents 5,102,375, 5,107,672, 5,168,679 to Featherstone and U.S.

Patents 5,139,464 and 5,203,746 to Lehnert. In the latter patents, the drive assembly comprises a plurality of interengaging chain members, and such chain driven masts typically require a large number of moving parts including a plurality of sprocket and chain arrangements, a drive mechanism or mechanisms and special structural arrangements to interlock the chain members. In order to obtain positive extension and retraction, such a rigid drive mechanism must be used to raise and lower the mast sections.

Typically, as shown in the foregoing art, it is necessary to provide at least two sprockets or reels to store the chain while the mast is in the retracted position and pay-out the chain to extend the mast. A significant amount of space is therefore required to store such chain due to the cross-sectional size of each chain link and the plurality of reels required. Additionally, a drive unit is often required for each of the reels. Even in those masts where the number of reels has been reduced, at least two chains are still required. Accordingly, masts using such drive arrangements are undesirably expensive to manufacture and to maintain. Moreover, such mast arrangements are heavy and cumbersome and are not readily capable of being mounted on the rooftop of a vehicle without adding special structural support to the rooftop.

A further type of extension-retraction mechanism is disclosed in United States Patent . 5,056,278 to Atsukawa. The latter discloses band-like plates having an accurate cross-sectional shape and which pass through corresponding contoured guide slits in support elements in the mast sections to extend and retract the telescoping mast sections. Atsukawa '278 requires the use of at least two arcuate bands driven and retracted from separate reels.

Additionally, Atsukawa requires the use of guide slits formed in a bottom plate of each of the mast sections and located within the telescoping sections to maintain rigidity. Further, the arcuate band plates are not effective against vertical and lateral loads except when the unsupported length of the bands is relatively small. Further, as mentioned above, at least two storage reels are required, one for the storage of each band whereby Atsukawa requires additional space for each of the storage reels. Moreover, Atsukawa requires plural drive roll arrangements and corresponding drive motors for operation. All of these requirements result in the mast being uneconomical to make and operate and, due to the number of parts, expensive to maintain.

SUMMARY OF THE INVENTION An extendable and retractable mast is provided in accordance with the present invention which overcomes the foregoing and other disadvantages of the prior art. More particularly, a telescoping mast assembly and drive assembly according to the invention reduces the space requirements for a mast relative to that of prior art masts, reduces the overall weight for a rigid telescoping mast, and provides the ability to use such a mast on the rooftop of a vehicle without the prior art disadvantages of having to reinforce the vehicle roof.More particularly in this respect, a telescoping mast according to the invention is capable of positive extension and retraction of the mast sections by means of a single tubular drive member utilizing a single take up reel or drum for storing the drive member when the mast is in a retracted position and a single drive motor for the reel or drum. Preferably, the drive member is expandable and collapsible and, upon extension from the take-up reel, the drive member expands from a flattened storage condition to a laterally expanded hollow condition giving the drive member rigidity in both its longitudinal and lateral directions.

The present invention advantageously provides an improved telescoping mast assembly which can extend the mast components and thus a utility light or other electrical device on a mast at any desired angle to horizontal and thus directly at or over a site at which it is required. The improved drive arrangement provides a less complex and less expensive mechanical drive arrangement than heretofore available. In this respect, the expandable and collapsible drive member can be reduced to a relatively flat crosssectional shape, against an inherent bias, and is capable of being wound on a take-up reel in the flat cross sectional shape. In this flat state, the drive member has a flexibility and elasticity which enables the drive member to be wound a number of times about the take-up reel.When unwound from the reel, the drive member's inherent bias expands the drive member from its flat cross section to its expanded configuration which, preferably, is that of a tube having opposed arcuate walls providing a somewhat elliptical contour in cross-section. In this expanded state, the drive member is rigid in both its longitudinal and lateral directions. The rigidity allows positive extension and retraction of the sections of a telescoping mast. The rigidity also provides a skeletal structure within a hollow tubular telescoping mast to provide additional rigidity to such a mast in order that the mast may support larger loads at the mast tip. A mast according to the invention also enables reducing the number of component parts required and also enables reducing the size of the drive assembly in contrast to link and chain or dual drive systems in that a single reel, single expandable and collapsible drive member and a single drive motor is all that is required to operate the mast assembly in the extending and retracting modes.

In accordance with another aspect of the invention, the expandable and collapsible drive member is preferably comprised of a single metal sheet having two concave portions, the sheet being folded for the two concave portions to face one another.

Preferably, the expandable and collapsible drive member is formed from a thin metal drive member sheet having opposite longitudinal edges parallel to a longitudinally extending centerline. Outer flange portions are initially formed by bending the metal foil adjacent each of the longitudinal edges. The foil is then bent longitudinally adjacent the centerline at two bendlines equidistant from and on opposite sides of the centerline to form two inner flange portions. The drive member is then folded along the centerline to abut the inner flange portions, and the inner flange portions are fastened together. The outer flange portions are then abutted together and joined to form a folded metal drive member having flanges on the opposite longitudinal edges and an unfastened area between the flanges and in which the opposed portions of the foil between the flanges are of concave contour.A longitudinally extending rod is placed between the concave portions, forcing the latter to remain in a preferred elliptical cross-sectional shape.

The metal drive member sheet is then heat treated so that the expandable and collapsible drive member inherently assumes the elliptical shape while in a relaxed or expanded state. After heat treating the rod is removed. When the drive member is wound onto a cylindrical drum or take up reel it collapses against the inherent spring bias to assume a flat cross sectional shape on the drum.

In accordance with another aspect of the present invention, the telescoping mast assembly is constructed of polygonal tube mast sections. The polygonal tubes provide a lightweight, rigid mast, and when in combination with the collapsible drive member, provide an especially rigid mast structure. The mast sections include bearing supports. The polygonal construction of the mast allows the use of simple bearings. Thus, the mast is easier to displace between extended and retracted positions and a smaller motor for driving the mast may be used.

It is thus an outstanding object of the invention to provide an improved drive assembly for actuating a telescoping mast.

It is yet another object of the invention to provide an improved drive assembly for a telescoping mast which provides positive extension and retraction of the mast with the use of a single expandable and collapsible drive member.

Still another object of the invention is to provide an improved telescoping mast assembly which is light weight and is compact in size.

Yet another object of the invention is to provide an improved telescoping mast assembly in which the drive member provides added rigidity for withstanding longitudinal and lateral loads while promoting lightness in weight of the mast assembly.

Still a further object of the invention is to provide an improved telescoping mast assembly which is less expensive to manufacture and is easier and less expensive to maintain than alternative telescoping mast drive assemblies.

Yet a further another object of the invention is to provide an improved telescoping mast assembly which reduces the number of component parts required for operation.

Still another object of the invention is to provide an improved drive member assembly for displacing a plurality of mast sections which is tubular and has an inherent bias for assuming an expanded state for extension and retraction and a collapsed state for storage.

Yet another object of the invention is to provide a method of constructing an expandable and collapsible tubular drive member according to the invention.

Still a further object of the invention is to provide an improved telescoping mast assembly comprised of polygonal tube mast sections with bearing supports which reduces the driving face required to extend and retract the mast.

These and other objects of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description of the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS The invention may take physical form in certain parts and arrangement of parts, preferred embodiments of which will be described in detail herein and are illustrated in the accompanying drawings wherein: FIGURE 1 is an elevation view illustrating use of a telescoping mast assembly of the present invention; FIGURE 2 is a plan view showing the telescoping mast assembly mounting arrangement as seen along line 2-2 in FIGURE 1; FIGURE 3 is a side elevation view of the telescoping mast of FIGURE 2; FIGURE 4 is a plan view, partially in section of a drive assembly according to the invention taken along line 4-4 in FIGURE 3; FIGURE 5 is a sectional elevation view of the drive assembly taken along line 5-5 in FIGURE 4; FIGURE 6 is a sectional elevation view of the drive assembly taken along line 6-6 in FIGURE 4;; FIGURE 7 is a cross-sectional view of the telescoping mast assembly taken along line 7-7 of FIGURE 5; FIGURE 8 is a cross-sectional view of the telescoping mast assembly taken along line 8-8 of FIGURE 5; FIGURE 9 is an exploded view showing the coupling between the mast sections and drive member of the mast assembly; FIGURE 10 ista cross-sectional view of the outer end of the telescoping mast assembly taken along line 10-10 of FIGURE 3; FIGURE 11 is a cross-sectional view taken along line 11-11 of FIGURE 10; and FIGURES. 12A-12H are pictorial views showing the sequence of steps in making the expandable and collapsible drive member according to the invention.

PREFERRED EMBODIMENT Referring to the drawings, wherein the showings are for the purpose of illustrating preferred embodiments of the invention only and not for the purpose of limiting same, FIGURE 1 shows a telescoping mast assembly 10 mounted on the roof 11 of a transporting vehicle 12. As shown in phantom, telescoping mast 10 is capable of being displaced from a retracted, solid line position to an extended, broken line position and is capable of pivoting about an axis C from a generally horizontal position to an upwardly inclined position. Telescoping mast assembly 10 is shown with a utility light 14 at the upper end thereof. Mast 10 thus has the capability of providing illumination to areas under bridges or over sharp drop-offs such as cliffs and mountain roads. It can also be used to light the underside of an overpass or bridge.It will be appreciated that mast 10 may be outfitted with any desired electrical fixture, or with a multiple light configuration, depending on customer requirements. Similarly, mast 10 may be mounted on any suitable support vehicle including, for example, emergency or military vehicles as well as watercraft for use in search and rescue operations.

FIGURES 2 and 3 show mast assembly 10 mounted on a base plate 21, which can be permanently or removably attached to transporting vehicle 12. Mounted on base plate 21 is a swivel plate 22. Swivel plate 22 is generally capable of rotating through 3600 in order to place the mast in any rotational position desired. Swivel plate 22 is rotatably supported on base plate 21 by L-shaped brackets 23 welded to base plate 21. In the preferred embodiment, swivel plate 22 is manually rotated. Mounted on swivel plate 22 are trunnion mounts 13a and 13b with mast assembly 10 pivotably disposed therebetween. Mast assembly 10 is pivotably mounted on trunnion mounts 13a and 13b by means of journals 24 and 25, respectively, which are welded to the exterior of mast section 10a and rotatably received within openings 26a and 26b in trunnion mounts 13a and 13b, respectively. Journals 24 and 25 provide pivot axis C and, in the preferred embodiment, axis C of the journals is six inches above the top of base plate 21. This allows for 15 of vertical elevation for mast 10 from the solid line to the first position shown in phantom in FIGURE 1. It is contemplated that the elevation of axis C may be eight inches such that the mast can be elevated to 240 as shown by the second position in phantom in FIGURE 1. While not shown, it is also contemplated that the trunnion mounts and journals can provide for mast 10 to be elevated to a vertical position relative to base plate 21.

Mast 10 is adapted to be pivoted from a generally horizontal position by an air actuated piston-cylinder unit 31 pivotally mounted to swivel plate 22 by a support 32. The piston cylinder unit 31 includes a piston rod 33 pivotally attached to mast section 10a by a cylinder collar 34, whereby outward displacement of the piston rod 33 from the cylinder causes pivoting movement of mast 10 from the generally horizontal solid line position to the position shown in phantom in FIGURE 3. A hydraulic, electrical or other suitable drive may be used to cause the pivoting movement. In its horizontal position, mast 10 rests on and is supported by a Ushaped storage support 35 mounted on base plate 21.

In the preferred embodiment, mast 10 is constructed of three telescoping sections 10a, 10b and 10c of square aluminum tubing.

However., it will be appreciated that the mast sections can be of a material other than metal or of a metal other than aluminum and that the cross-sectional configuration can be of any one of a number of polygonal profiles such as rectangular, triangular diamond and the like. Tubes 10a, 10b and 10c are axially slidably interengaged for translation between retracted and extended positions relative to trunnion mounts 13a and 13b. As mentioned above, tube 10a is pivotally mounted on trunnion mounts 13a and 13b via journals 24 and 25. In the preferred embodiment, tube 10a is 2.5 inches square and 68.25 inches long. Tube 10b is slidable within tube 10a and is 2.0 inches square and 67 inches long, and tube 10c is slidable within tube lOb and is 1.5 inches square and 66 inches long.These dimensions provide for the mast to have an extension capability of about 14 feet from the trunnion mounts.

Square mast assembly 10 is preferably mounted diagonally with respect to base plate 21 such that imaginary lines drawn between opposite corners of the tubing are parallel and perpendicular to base plate 21 when mast 10 is in its horizontal position. Tubes 10a, 1Db and 10c include corresponding outboard ends 40a, 40b and 40c, respectively, and tubes 10a and 10b also include outboard collars 41a and 41b, respectively, welded to the outboard ends thereof. Tubes 10a, 10b and lOc also include inboard ends 42a, 42b and 42c, respectively, and tubes 10b and 10c include inboard collars 43b and 43c, respectively, welded to the inboard ends thereof.

FIGURES 10 and 11 best show the structure of outboard collars 4lb and 41a which are virtually identical, except in size.

Outboard collar 41b includes lower outer surfaces 44 and 45 and lower inner surfaces 46 and 47. A rectangular opening 51 is provided between outer surface 44 and inner surface 46 and a rectangular opening 52 is provided between outer surface 45 and inner surface 47. As seen in FIGURE 11, outboard collar 41a also includes two rectangular openings 54 and 55, identical to rectangular openings 51 and 52 of outboard collar 4lb. Roller bearings 56, 57, 58 and 59 are supported in rectangular opening 51, 52, 54 and 55, respectively. Roller bearings 56 and 57 are rotatably mounted for the outer surfaces thereof to extend beyond inner surfaces 46 and 47 of tube 4lb in order that the lower adjacent surfaces 61 and 62 of tube 10c are in contact with the roller bearings. Roller bearings 58 and 59 are mounted in a like manner.Roller bearings 56-59 are adapted to rotate about a corresponding support shaft 63 provided, in the preferred embodiment, by a shoulder bolt having a threaded end 63a received in a threaded opening therefor, not designated numerically.

Inboard collars 43b and 43c are respectively welded to the inboard ends 42b and 42c of tubes 10b and 10c, as best shown in FIGURES 5, 7 and 8. Inboard collars 43b and 43c have inner ends located within tubes 10b and 10c, respectively, and the outer ends of the collars extend radially outwardly such that the outer surface of inboard collar 43b is adjacent the inside surface 64 of tube 10a and inboard collar 43c is adjacent the inside surface 65 of tube 10b. As shown in FIGURE 7 two rectangular openings 67 and 68 are provided within inboard collar 43b. Rectangular opening 67 is between the upper inner surface 71, and upper outer surface 73, and rectangular opening 68 is between the upper inner surface 72 and the upper outer surface 74 of inboard collar 43b.Roller bearings 75 and 76 are supported within rectangular openings 67 and 68, respectively, and are mounted to rotate about a corresponding support shaft 77 such as a shoulder bolt having an outer threaded end 77a received in a threaded opening therefor in the collar. As mounted, roller bearings 75 and 76 contact upper inside surface 64 of tube 10a. As best seen in FIGURES 8 and 9, inboard collar 43c is a solid stub having an inner end 78 fitted onto end 42c of tube 10c and an outer end 79. Pockets 81 and 82 are machined into the upper outer surfaces 83 and 84 of outer end 79, respectively, and roller bearings 85 and 86 are respectively mounted in pockets 81 and 82 and supported for rotation by corresponding shafts 87 provided by shoulder bolts as described herein with respect to roller bearings 75 and 76.The outer surfaces of roller bearings 85 and 86 extend above upper outer surfaces 83 and 84 to contact upper inside surfaces 65 of tube 10b. Mast assembly 10 is adapted to be extended and retracted in the horizontal direction and when inclined relative to horizontal. The orientation of roller bearings 75, 76, 85 and 86 on the upper outer surfaces of inboard collars 43b and 43c together with the orientation of roller bearings 56, 57, 58 and 59 on the lower outer surfaces of outboard collars 41a and 4nb support the load of the mast sections during extension and retraction and restrain downward deflection when mast assembly 10 is in an extended position. Further, friction between adjacent tubes 10a, 10b and 10c during extension and retraction is significantly reduced by the roller bearing arrangement whereby extension and retraction can be achieved with a minimal driving force, and the diagonal orientation of the mast tubes optimizes the rigidity thereof against vertical deflection when the mast is extended. It will be appreciated that additional roller bearings may be added or the orientation of the existing roller bearings may be changed as the use and potential vertical elevation requirements of mast 10 change. Furthermore, it will be appreciated that while not shown, outboard collars 41a and 41b coact with inboard collars 43b and 43c during extension of mast 10 to prevent separation of tubes 10b and 10c from tube 10a or from one another.As is well known in this respect, for example, each of the collars 41a and 41b can include a shoulder portion extending radially into tubes 10a and 10b, respectively, to coact with shoulder portions on collars 43b and 43c, respectively, extending radially outward of tubes 10b and 10c. During extension, the abutment of corresponding shoulder portions prevents tubes 10b and lOc from separating from tube 10a or from one another.

As best shown in FIGURE 9, inboard collar 43c includes a boss 91 extending axially outwardly from outer end 79 thereof. Boss 91 includes an elliptical portion 92 and a solid cylindrical portion 93. Collar end 79 also includes mounting tabs 94 and 95 which extend radially inwardly and axially outwardly from opposite corners thereof. Elliptical portion 92 and solid cylindrical portion 93 are coaxial and centered on outer surface 96 of inboard collar 43c, and tabs 94 and 95 extend forwardly from outer surface 96 and have upper surfaces 102 and 103, respectively, in a plane located directly below a line connecting the corresponding opposite corners of inboard collar 43c. Cylindrical portion 93 includes two diametrically opposite tapped holes 97 for receiving hex head bolts 98.Tabs 94 and 95 are tapped at the upper flat surfaces 102 and 103 to provide threaded holes 104 and 105, respectively for receiving two cap screws 106 and 107. Boss 91 provides the interconnection point between the tubes of mast 10 and the drive assembly for extending and retracting mast 10 which is now described hereinafter.

As best seen in FIGURES 4-9 an expandable and collapsible drive member 110 is provided for extending and retracting mast 10.

Drive member 110 has an axis A, is of sheet metal construction and comprises longitudinally extending upper and lower portions 111 and 112, respectively, which are of opposed concave contour relative to one another in the expanded condition of the drive member. Drive member 110 further includes opposite longitudinally extending flange portions 113 and 114 extending laterally outwardly from the corresponding juncture between portions 111 and 112. Specifically, as shown in the cross-section of FIGURE 7, drive member 110 includes an elliptically shaped opening 115 between concave portions 111 and 112 in the expanded condition, and this elliptical cross-section provides strength and rigidity to the drive member 110 when expanded and subjected to both lateral and longitudinal forces. As will be appreciated from FIGURE 9, drive member 110 is attached to mast 10 using boss 91.In this respect, end 110a of the drive member in its expanded condition is placed over cylindrical portion 93 and elliptical portion 92, each of which have dimensions slightly less than or generally equal to the corresponding diameter dimensions of opening 115. Inner surface 116 of concave portion 111 and inner surface 117 of concave portion 112 facially contact the outer surfaces of elliptical portion 92 and cylindrical portion 93. Drive member 110 is rigidly fastened to boss 91 and, for this purpose holes 122 are provided in concave portions 111 and 112 for registry with tapped holes 97 in portion 93, thus to receive hex head bolts 98, and openings 124 and 125 are respectfully provided in flange portions 113 and 114 for respective registry with threaded holes 104 and 105 in mounting tabs 94 and 95, thus to receive cap screws 106 and 107.Preferably, drive member 110 is fabricated such that the distance between the laterally outermost tips of flanges 113 and 114 is generally equal to the distance between the opposite inside corners of inside surface 65 of tube 10b, as shown in FIGURE 7. Therefore, the laterally outermost tips of flanges 113 and 114 are nested in the opposite inside corners and work to prevent rotation of drive member 110 about axis A. This provides added rigidity to mast 10 by providing a relatively stable internal skeletal structure.

Further, in this position, the size of drive member 110 is maximized within mast 10 to its largest possible dimensions, thus maximizing the rigidity to be obtained from drive member 110.

Drive member 110 is adapted to be extended and retracted by a drive unit D and relative to drive unit enclosure 131 in connection with extending and retracting the mast tubes. As will become apparent hereinafter, the drive member is adapted to be collapsed and stored on a storage drum when retracted. When payed from the drum, drive member 110 is biased to its expanded condition by the inherent resiliency of members 111 and 112. As shown in FIGURES 46, drive unit D includes a rubber covered drive wheel 132 and storage or take up drum 133 mounted on storage drum shaft 134 in drive unit enclosure 131. The opposite ends of storage drum shaft 134 are supported in floating bearing blocks 135 and 136. Floating bearing blocks 135 and 136 are vertically slidable in bearing block supports 137 and 138, respectfully, and are biased downwardly therein by springs 140 and 141.Springs 140 and 141 force floating bearing blocks 135 and 136 and thus drum 133 downward for drive member 110 on the drum to engage the outer rubber surface 143 of drive reel 132. The inner end 110b of drive member 110 is fixed to take up drum 133 by a mounting block 144.

Drive unit D further includes a drive motor 151 and gear box 152 mounted outside drive unit enclosure 131. Preferably, drive motor 151 is electric or air powered. Advantageously in accordance with the invention, the ease with which the mast can be extended and retracted enables motor 151 to be a small motor such as an automobile power window motor. Drive motor 151 is coupled to the drive wheel shaft 153 through gear box 152, and shaft 153 is rotatably supported by bearing blocks 154 and 155 which are mounted on drive unit enclosure 131. As shown in FIGURE 5, storage drum shaft 134 is located in a vertical plane E and preferably, drive wheel shaft 153 is located in a vertical plane F. For the reasons set forth hereinafter, plane E and plane F are offset slightly, plane F being slightly forward of plane E toward'mast assembly 10.

Rotation of drive wheel 132 by drive motor 151 causes rubber surface 143 to displace drive member 110, thus to rotate take-up drum 133.

In order to retract mast assembly 10 to a retracted position relative to drive unit D, drive member 110 is drawn into drive unit enclosure 131 and about take up drum 133. More particularly in this respect, drive motor 151 is energized to rotate drive wheel 132 in a counter clockwise direction in FIGURE 5, whereby drive member 110 moves from right to left and is pinched between take up drum 133 and drive wheel 132 by the bias of springs 140 and 141 against floating bearing blocks 135 and 136. Counter clockwise rotation of drive wheel 132 causes clockwise rotation of take up drum 133 to wind drive member 110 onto the drum, and the offset by which plane F is located forward of plane E, preferably 0.125 to 0.25 inch, promotes frictional engagement between rubber surface 143 of drive wheel 132 and the drive member to assure a positive drive with respect to drum 133.The pinching action between drive wheel 132 and take up drum 133 forces expandable and collapsible drive member 110 to collapse against its inherent spring bias to a flat configuration in cross-section. Thus, inner surfaces 116 and 117 are flat and in abutting contact. As the drive member is wound onto the drum, the floating bearing blocks and springs 140 and 141 exert a constant force as the radial dimensions of the drum and drive member thereon progressively increase. This advantageously promotes use of a small drive motor. Take up drum 133 thus stores drive member 110 in its collapsed condition. Advantageously, very little space is required to store drive member 110 in the collapsed condition thereof.

When it is desired to extend mast 10, the direction of drive motor 151 is reversed causing drive wheel 132 to rotate in a clockwise direction in FIGURE 5 and drum 133 counterclockwise, whereby drive member 110 is payed out from take up drum 133. As the drive member moves into end 42a of mast tube 10a which extends into opening 154 therefor in drive unit enclosure 131, the inherent bias of portions 111 and 112 of drive member 110 causes the latter to expand to the elliptical shape creating a rigid drive ribbon which pushes outward on tube 10c through boss 91. Once tube 10c is fully extended out of tube 10b, tube 10b is pulled outward from within tube 10a.Thus, the present invention provides a single metal band drive member capable of assuming a rigid tubular condition for extension and retraction of the mast, and a space saving collapsed condition which is advantageous for storing the drive member flat on a reel. This provides a space saving system over prior art chains and multiple drive systems while retaining positive extension and retraction characteristics. Further, when the mast is extended additional rigidity is provided within each of telescoping sections 10a-lOc by the rigid skeletal structure provided by the drive member 110.

A preferred method of making expandable and collapsible drive member 110 is shown in FIGURES 12A-12B. Preferably, drive member 110 is fabricated from a flat sheet 160 of Custom 455 stainless steel foil which is 0.010 inch thick, 5.5 inches wide and 12 to 14 feet long in the direction of arrow 160a in FIGURE 12A. As shown in FIGURE 12B, outer flanges 161 and 162, each having a width of 0.375 inches are formed by bending the laterally outer edges of sheet 160 upwardly at approximately 45 angles along fold lines 163 and 164 which extend the entire length of sheet 160. All bends referred to hereinafter extend the entire length of sheet 160. As shown ip FIGURE 12C, sheet 160 is then bent upwardly, at 450 angles along fold lines 165 and 166 which are equidistant from and on opposite sides of the longitudinal centerline of sheet 160.These folds form an inner flange portion 167 having a width of 0.750 inches and two panel portions 168 and 169, respectively between flange portion 167 and outer flanges 161 and 162. Panels 168 and 169 each have a width of 2.0 inches. As shown in FIGURE 12D, sheet 160 is then folded along foldline 170 which is the centerline of sheet 160. This fold divides inner flange portion 167 into laterally adjacent inner flange portions respectively extending upwardly at a 450 angle to panels 168 and 169. Adjacent inner flange portions are then further folded to the positions shown in FIGURE 12E in which the inner flange portions are in abutting contact and panels 168 and 169 are at an angle of 900 to one another. Inner flange portions 173a and 173b are then welded together generally along the centerline of the flange portions using a spot welder 171.As shown in FIGURE 12F, outer flanges 161 and 162 are then brought together and spot welded in a like manner.

As thus formed, drive member 110 will assume its expanded condition in which opposed panels 168 and 169 are in concave relative to one another and have a generally elliptical contour. Upon collapsing the drive member to a flat condition, the inherent resiliency of the sheet metal tends to bias the drive member toward the expanded condition whereby the drive member returns to the latter condition upon release of the force holding it in the collapsed condition.

Preferably, in order to optimize the spring and strength characteristics of drive member 110, a 0.75 inch O.D. support cylinder 172 having a length corresponding to the length of the drive member is inserted between panels 168 and 169 and, as depicted in FIGURE 12G, the drive member is heat treated in a furnace or the like 173 at about 10500F for eight hours. After heat treating, tube 172 is removed and, as depicted in FIGURE 12H, end 110b of the drive member is attached to mounting block 144 on take up drum 133, and the drive member is collapsed and wound onto take up drum 133 for installation in a telescoping mast assembly 10.As will be appreciated from the description herein regarding mast assembly 10 and drive member 110, and with further reference to FIGURE 12H, it will be appreciated that flanges 161 and 162 correspond to flange 113 as shown, for example, in FIGURE 9, that flanges 167a and 167b correspond to flange 114, and that panels 168 and 169 correspond respectively to concave portions 111 and 112 of the drive member.

While considerable emphasis has been placed herein on a specific embodiment of the invention, it will be appreciated that other embodiments as well as modifications of the embodiment disclosed will be suggested or apparent and can be made without departing from the principles of the invention. For example, insofar as the drive member is concerned the mast sections are not limited to being of polygonal shape and may be of any shape.

Likewise, insofar as the polygonal mast sections are concerned, the drive member can be other than the tubular drive member disclosed herein. Additionally, the tubular drive member may be of any closed curve or polygonal shape including round, oval or diamond shaped. While it is preferred that the tubular drive member be collapsible, the desired rigidity and strength for extending and retracting the mast are obtained by a tubular contour. Thus, though a non-collapsible tube would require more space when wound on a storage reel, it would operate as in the preferred embodiment to extend and retract a mast. Finally, a collapsible drive member in accordance with the invention may be filled with a compressible filling, such as foam rubber, or could be inflatable and thus be biased from the collapsed to the expanded position. Accordingly, it is to be distinctly understood that the foregoing descriptive matter is to interpreted merely as an illustration of the present invention and not as a limitation of same.

Claims (7)

Claims:

1. A method of constructing an expandable and collapsible drive member for extending and retracting a plurality of interconnected mast sections of a mast assembly, which method comprises: providing a metal sheet having opposite ends and longitudinal edges between said ends and parallel to a centreline between said ends; bending said sheet inwardly adjacent each said longitudinal edge to form outer flange portions between said ends; bending said sheet longitudinally on opposite sides of said centreline to form an inner flange portion between said ends and a middle portion between said inner flange portion and each of said outer flange portions; folding said inner flange portion along said centreline to provide inner flange portions on laterally opposite sides of said centreline and abutting said inner flange portions; abutting said outer flange portions; and joining said outer flange portions together.

2. A method according to claim 1, further including joining said inner flange portions together.

3. A method according to claim 1 or 2, further including inserting a longitudinally extending rod between said middle portions, heat treating said foil and removing said rod.

4. A method according to any of claims 1 to 3, wherein said bending of said sheet inwardly adjacent each said longitudinal edge is at a substantially 45 angle.

5. A method according to claim 4, wherein said bending adjacent said centreline includes bending generally at a 450 angle.

6. A method according to claim 5, wherein said joining of said outer flange portions is by spot welding, and joining said inner flange portions by spot welding.

7. A method according to claim 7, wherein said joining of said outer fange portions is by spot welding.