US3737007A - Adjustable scaffold - Google Patents

Abstract

An adjustable scaffold has movable ladder sections and a base with a fixed ladder portion. Cable and pulley assemblies in conjunction with a counterweight permit raising and lowering of the movable ladder sections. Guide means are mounted on the fixed ladder portion to guide movement of the counterweight. A locking device has dogs which selectively engage a plurality of vertically spaced openings in a movable ladder section to lock the movable sections in desired positions.

Description

United States Patent 1 Herrell 1451 June 5, N73

54 ADJUSTABLE SCAFFOLD 2,616,769 11 1952 Rector ..l82/146 Inventor: Robert C. Herrell, Indianapolis, 3,323,616 6/1967 Best ..l82/l46 FORElGN PATENTS OR APPLICATIONS Assignee: s,'ln Indianap is, Ind. 851,279 10/1960 Great Britain ..l82/l03 Filed: y 0, 1971 Primary ExaminerReinaldo P. Machado [21] Appl 145,281 Attorney-Trask, Jenkins & Hanley [57] ABSTRACT [52] US. Cl. ..l82/2l0,l82/103, 182/118, I

132/127 182/14] An ad ustable scaffold has movable ladder sections 151 int. Cl. ..E06c 5/04 and a base with a fixed ladder P Cable and P [581 Field ofSearch.... ..182/146, 145, 209, 16y assemblies in Conjunction with a counterweight 132/210 132 15 103 141 127 1 permit raising and lowering of the movable ladder sec- 243/407 423 tions. Guide means are mounted on the fixed ladder portion to guide movement of the counterweight. A [56] References Cited locking device has dogs which selectively engage a plurality of vertically spaced openings in a movable UNITED STATES PATENTS ladder section to lock the movable sections in desired 3,232,377 2/1966 Smith ..-l82/l7 Positimls- 2,636,659 4/1953 Salisbury t ..182/210 856,875 6/1907 Hughes et al..... ..l82/2l0 8 Clams 6 Drawmg F'gures 2,798,652 7/1957 Easton ..i82/l5 Patented June 5, 1973 3,737,007

2 Sheets-Sheet 1 INVENTOR l ROBERT C. HERRELL ail, kWh/ ATTORNE Patented June 5, 1973 2 Sheets-Sheet 2 l NVENTOR ROBERT C. HERRELL ADJUSTABLE SCAFFOLD BACKGROUND OF THE INVENTION This invention relates to adjustable scaffolds, and more particularly to the type of scaffold in which vertically extensible means are supported from a portable base structure. Such a scaffold will provide a substan-. tial range of vertical adjustment for an operators platform which may be attached thereto and will support the platform stably throughout that range.

A caster-supported base frame is provided adjacent each of its corners with an upright or corner post. Two of the corner posts at one end of the base frame extend vertically upwardly. The other two corner posts at the other end of the base frame extend upwardly and obliquely toward the vertical corner posts. Rungs extending between the obliquely extending corner posts provide a fixed ladder portion by which a workman may reach a fixed platform supported at or near the tops of the corner posts. The two vertical corner posts constitute guides slidably receiving the lower one of two telescopically associated ladder sections. The upper ladder section may carry near its top a second platform which is desirably arranged for ready attachment to or removal from that section. Cross braces, including the aforesaid rungs, extend between and rigidly interconnect the corner posts so that the corner posts and base frame form a rigid truck-like structure portably supported on casters. For convenient reference, that side of such truck-like structure in which the telescopically associated ladder sections are supported will be called the front, and the opposite side will be called the rear. The truck-like structure may be provided with outrigger braces adjustable to engage the floor or other supporting surface outwardly beyond the scaffoldsupporting casters to increase the stability of the scaffold when the ladder sections are extended.

To facilitate extension of the movable ladder sections they are counterbalanced by a counterweight slidably supported by a guide or sleeve carried by the fixed ladder section for movement within the truck-like structure. Desirably, the movable lower ladder section is connected to the counterweight while the movable upper ladder section is supported from the lower section by a cable which runs over a pulley at the top of the lower ladder section and has its ends connected respectively to the truck-like structure and to the bottom of the upper ladder section. Such cable functions to carry the weight of the upper ladder section and also serves to coordinate relative movements of the two ladder sections and the truck-like structure in such a way that movement of the upper ladder section relative to the lower ladder section will be substantially equal to movement of the lower section relative to the trucklike structure.

Locking means mounted on the truck-like structure cooperate with the front corner posts and the lower ladder section to lock the movable ladders in any desired degree of extension.

BRIEF DESCRIPTION OF THE DRAWING The invention is illustrated in the accompanying drawing in which:

FIG. 1 is a side elevation of a scaffold in accordance with this invention with the movable ladder sections in a retracted position;

FIG. 2 is a top view of the scaffold of FIG. 1;

FIG. 3 is a side elevation of the scaffold of FIG. 1 with the movable ladder sections partially extended and with a platform attached thereto;

FIG. 4 shows the cable and pulleys which interconnect the movable ladder sections and the base;

FIG. 5 is a partial sectional view taken along the line 55 in FIG. 1; and

FIG. 6 is a partial sectional view taken along the line 6-6 in FIG. 4.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The scaffold shown in the drawings comprises a truck-like structure, designated in its entirety by the reference numeral 15, including a generally rectangular base frame 16, and rear corner posts 17 which extend upwardly and obliquely toward the front corner posts 18. Corner posts 18 extend vertically upwardly from the base frame 16. Horizontal cross-members 19 extend between the rear corner posts 17 in vertically spaced relation to provide a fixed ladder affording access to a platform 20 located near the upper ends of the four corner posts. The two front corner posts 18 slidably support a movable lower ladder section 24 which in turn slidably supports a movable upper ladder section 25.

As shown in FIGS. 2 and 6, the front corner posts 18 are conveniently standard channels arranged with their open sides facing toward each other and receiving smaller channels which constitute the uprights of the lower ladder section 24. Ladder section 24 also includes rungs 28 extending between and secured to its channels, desirably near the rear edge thereof. Rungs 33 extend between and are secured to the channels of the upper ladder section 25, desirably near the forward edge thereof.

To provide for free sliding of the ladder sections 24 and 25 while at the same time reducing lost motion, the opposed faces of the several upright channel members may be provided with rubbing elements.

To facilitate extension of the ladder sections 24 and 25, a pair of cables 48 secured to the lower end of lower ladder section 24 extend over pulleys 49 on the cross-member 23 to a counterweight 50 arranged for movement in the truck-like structure. The counterweight 50 is provided at opposite ends with pairs of rollers 51 running in channel-like sleeves or guides 52. The sleeves or guides 52 are carried by the rear corner posts 17 and extend downwardly and rearwardly from their upper ends. By reason of this arrangement, that portion of each cable 48 extending between a pulley 49 and the counterweight 50 will be generally parallel to the guides 52, and the counterweight will be near the rear of the truck-like structure when it is in its lowermost position and the ladder sections are fully extended. In order that the counterweight may be effective on the upper ladder section 25 as well as on the lower section 24, a cable 54 extends from the lower end of the upper ladder section 25 around a pulley 55 at the upper end of the lower ladder section to the crossmember 22 of the truck-like structure. The cable 54 not only transfers the weight of the upper ladder section 25 to the lower ladder section 24 but also coordinates the movements of the two ladder sections in such a way that movement of the lower section 24 relative to the corner posts 18 will be accompanied by an equal relative movement of the upper ladder section 25.

The counterweight 50 may be conveniently constructed as a tank adapted to be filled with sand or other material to provide the mass necessary to balance the combined weight of the upper and lower ladder sections 24 and 25.

A locking device 56 (FIGS. 1, 2, and 6), accessible from platform 20, secures the movable ladder sections 24 and 25 in any desired position of extension. The locking device 56 comprises a sleeve 58 mounted on the cross member 23 at the frontupper corners of the structure 15. A rod member 60 is rotatably carried in sleeve 58 and extends beyond each end of the sleeve. A relatively heavy handle 62, such as a 3 inch steel bar of inch diameter, is attached to each end of rod member 60. A dog 64, such as 1% inch steel rod of '54: inch diameter, is attached to the rod member 60 adjacent each end of sleeve 58. Handles 62 and dogs 64 are angularly offset from the another about 45, as well as being longitudinally spaced from one another. In the normal or locking position, handles 62 are lower than the dogs 64. The two handles 62 are coplanar, as are the two dogs 64.

The rear flanges of the channels of the lower ladder section 24 are provided with a plurality of vertically spaced openings 68 therethrough (see FIG. 6). Openings 68 are adapted to receive dogs 64 so that dogs 64 protrude therethrough to lock the movable ladder in any desired position. Openings 68 must be of such size that dogs 64 may be completely removed when handles 62 are physically lifted in an upward and rearward direction as indicated by the arrow in FIG. 1. Such movement of the handles removes the dogs from the openings and thus completely unlocks" the movable ladder portions 24 and 25.

In the fully retracted position illustrated in FIG. 1, the relatively heavy handles 62 are in their normal low position with respect to dogs 64. An upward force may be applied to either of the movable ladder sections to cause them to rise. As the ladder sections 24 and 25 rise, successive openings 68 come into proximity with the dogs 64. The heavy, angularly offset handles 62 hold the dogs in position to successively engage the openings 68. Thus as the ladder sections 24 and 25 are raised, there is a ratchet-like action between dogs 64 and openings 68. The movable ladder sections may thus be raised to any desired extent and locked into position.

When it is desired to lower the ladder sections, the handles 62 may be physically moved in the direction illustrated in FIG. 1, thus removing the dogs 64 from operable proximity to ladder section 24. In this manner the ladder sections may be lowered. When lowered to the extent desired, the handles may be returned to their normal positions and the dogs will engage adjacent openings 68 and lock the ladder sections in that positron.

The upper ladder section 25 is adapted to have an upper platform 70 mounted thereon. Platform 70 may be secured to ladder section 25 in any convenient manner and at any desired elevation thereon. The trucklike structure is desirably provided with retractable outrigger braces 72 in order to provide stability for the scaffold. When the Outriggers are not in use they may be swung inwardly into overlapping relation at the front of the structure 15.

The scaffold is most conveniently operated from the lower platform which is accessible from the fixed ladder 17, 19. An operator standing on the platform 20 can readily operate the locking device 56 and, by applying a vertical force to either of the movable ladder sections, extend or retract them as desired. When the ladder sections are near their retracted positions, it will usually be most convenient for the operator to apply the lifting effort to the upper section 25. However,

when the ladder sections are near fully extended posi-' tions, it will probably be more convenient for the vertical effort to be applied to the lower section 24, since application of the effort to the upper section might require the operator to reach through the spaces between the rungs of the lower section. The interconnection of the ladder sections by the cable 54, coupled with the counterbalancing of both sections by the single counterweight 50 makes it possible to effect movement of both sections by a force applied to either.

I claim:

1. In an adjustable scaffold having a base and a movable ladder section, a locking device comprising a sleeve, a rod member rotatably carried in said sleeve and extending beyond an end of said sleeve, a dog attached to said rod member adjacent an end of said sleeve, a handle attached to said rod member adjacent and end thereof, said handle being angularly offset and longitudinally spaced from said dog, said dog being adapted to selectively engage a plurality of vertically spaced openings in the movable ladder section to lock said ladder section in a plurality of fixed positions.

2. A locking device as set forth in claim 1 with the addition ofa second dog attached to said rod member adjacent the other end of said sleeve and a second handle attached to said rod member adjacent the other end of said rod, said second handle being angularly offset and longitudinally spaced from said dogs.

3. A locking device as set forth in claim 2 wherein said dogs are coplanar and said handles are coplanar.

4. A locking device as set forth in claim 2 wherein said handles are of sufficient weight to cause said dogs to successively engage said openings while the movable ladder section is being extended.

5. A locking device as set forth in claim 4 wherein said handles are normally in a position lower than said dogs and said handles are movable upwardly to remove said dogs from operative association with said openings in order to permit free movement of the movable ladder section.

6. An adjustable scaffold comprising, a base having a fixed ladder portion, a plurality of movable ladder sections interconnected to each other and to said base, said fixed ladder portion extending obliquely upwardly toward said movable ladder sections, a first cable and pulley assembly interconnecting said base and said movable ladder sections, a second cable and pulley assembly interconnecting said movable ladder sections and a counterweight, a guide mounted on said fixed ladder portion, a roller received in said guide, said roller being connected to said counterweight so as to guide movement of the counterweight in a path parallel to the fixed ladder portion and between said fixed ladder portion and said movable ladder sections during extension and retraction of the movable ladder sections.

7. The invention set forth in claim 6 wherein said guide extends along at least a substantial portion of the length of the fixed ladder portion.

8. The invention set forth in claim 6 with the addition of a second guide carried by the fixed ladder portion, a second roller received in said second guide, said second roller also being connected to said counterweight. l l=

Claims (8)

1. In an adjustable scaffold having a base and a movable ladder section, a locking device comprising a sleeve, a rod member rotatably carried in said sleeve and extending beyond an end of said sleeve, a dog attached to said rod member adjacent an end of said sleeve, a handle attached to said rod member adjacent and end thereof, said handle being angularly offset and longitudinally spaced from said dog, said dog being adapted to selectively engage a plurality of vertically spaced openings in the movable ladder section to lock said ladder section in a plurality of fixed positions.

2. A locking device as set forth in claim 1 with the addition of a second dog attached to said rod member adjacent the other end of said sleeve and a second handle attached to said rod member adjacent the other end of said rod, said second handle being angularly offset and longitudinally spaced from said dogs.

3. A locking device as set forth in claim 2 wherein said dogs are coplanar and said handles are coplanar.

4. A locking device as set forth in claim 2 wherein said handles are of sufficient weight to cause said dogs to successively engage said openings while the movable ladder section is being extended.

5. A locking device as set forth in claim 4 wherein said handles are normally in a position lower than said dogs and said handles are movable upwardly to remove said dogs from operative association with said openings in order to permit free movement of the movable ladder section.

6. An adjustable scaffold comprising, a base having a fixed ladder portion, a plurality of movable ladder sections interconnected to each other and to said base, said fixed ladder portion extending obliquely upwardly toward said movable ladder sections, a first cable and pulley assembly interconnecting said base and said movable ladder sections, a second cable and pulley assembly interconnecting said movable ladder sections and a counterweight, a guide mounted on said fixed ladder portion, a roller received in said guide, said roller being connected to said counterweight so as to guide movement of the counterweight in a path parallel to the fixed ladder portion and between said fixed ladder portion and said movable ladder sections during extension and retraction of the movable ladder sections.

7. The invention set forth in claim 6 wherein said guide extends along at least a substantial portion of the length of the fixed ladder portion.

8. The invention set forth in claim 6 with the addition of a second guide carried by the fixed ladder portion, a second roller received in said second guide, said second roller also being connected to said counterweight.

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