US3726361A

US3726361A - Foldable ladder

Info

Publication number: US3726361A
Application number: US00213469A
Authority: US
Inventors: G Emmons
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-12-29
Filing date: 1971-12-29
Publication date: 1973-04-10
Anticipated expiration: 1990-04-10

Abstract

A step ladder structure having a foldable three legged tripod supporting frame. The ladder component utilizes one of the tripod legs as a side piece and a second ladder side piece is secured at one end to the ground engaging end of the other side piece from which it extends upwardly in a suitable spaced relationship with spaced steps connected to the two side pieces in a ladder relationship. Bracing is provided between the second side piece and the other two tripod legs.

Description

United States Patent 1 I i I 3,726,361

Emmons 1 Apr. MD, 1973 [541 FOLDABLE LADDER 590,335 9/1897 Price ..1s2 171 [761 Invem George Harvey Emmons, 11 South 5122533. 31132? 52.21;;......................:::::::::1351132 12th St., Marshalltown, Iowa 50158 22 Filed; D 29, 1971 Primary Examiner-Reinaldo P. Machado Attorney-Morton S. Adler [2i] Appl. No.: 213,469

Related US. Application Data [57] ABS CT A step ladder structure having a foldable three legged [63] fgimuation-m-pan of Ser. No. 57,484, July 23, tripod pp g frame The ladder component util izes one of the tripod legs as a side piece and a second ladder side piece is secured at one end to the ground [52] US. Cl ..182/170, l82/1l7i engaging end of the other side piece from which it 1?: tends upwardly in a suitable spaced relationship with e 0 re spaced steps connected to the two side pieces in a ladder relationship. Bracing is provided between the second side piece and the other two tripod legs.

11 Clains, 9 Drawing Figures [56] References Cited UNITED STATES PATENTS 419,821 l/1890 Burrows ..l82/l70 FOLDABLE LADDER This invention is an improvement of the foldable ladder disclosed in my U.S. Pat. No. 3,540,549 and is a continuation-in-part of my co-pending application under the same title, Ser. No. 57,484, filed July 23, 1970 and now U.S. Pat. No. 3,637,046.

2. Description of the Prior Art Foldable ladders, or step ladders as they are commonly referred to, are old and well known and include the conventional ladder structure having substantially parallel side pieces with connecting steps or rungs to which some form of a foldable brace means of lesser sturdiness than the side pieces is hingedly attached to the top portion of the respective side pieces of the ladder so that it can be swung out into ground engaging position. So far as is known, all such step ladders except the ones disclosed in my patent and co-pending application identified above, aredesigned so that the bottom ends of both step supporting side pieces are load hearing members and must engage the ground or supporting surface at all times to properly support the weight load. While the brace'leg components on the commonly used step ladder are generally a pair of closely spaced legs, U.S. Pat. Nos. 5,451 and 46,105 disclose the concept of the two rear supporting brace legs converging to form a single ground engaging means although in addition to such means, there appears to be used additional side leg supports.

The use of a swingable or foldable support leg for a step ladder whether having a single ground engaging arrangement or a plural ground engaging arrangement does not overcome the difficulty of using the ladder in a rigid and stable condition when both of the ladders side rails must engage the ground or support. By virtue of the relative closeness of the side rails and brace legs at the ground or support level on the commonly used step ladder, such ladders are quite susceptible to lateral tipping even when on a level surface and this susceptibility materially increases as the weight forces on the ladder are extended to its upper extremities. Also, the traditional step ladder has many disadvantages when the ground level is uneven or sloping and while it is well known that shims or blocks are frequently placed under one of these side rails in such a situation, this does not appear to satisfactorily correct the inherent instability of ladders of this type;

The present invention provides improved efficiency and strength in a tripod frame supported step ladder for which the principle thereof, so far as is known, was first disclosed in my U.S. Pat. No. 3,540,549 and in which other improvements have been disclosed in my copending application above referred to.

The present invention utilizes the principle of a tripod type supporting structure wherein three ground i pieces for the ladder component and has associated therewith a second side piece which is not an independent ground engaging member but is converged at its lower end for attachment to the lower end of the first side piece to form a unitary ground engaging end and also serves with the first side piece to support a series of steps in a ladder relationship that in turn is functionally related to the other tripod legs by appropriate bracing.

SUMMARY This invention is directed to foldable ladders or step ladders and the primary object herein is to materially improve the rigidity of the ladder supporting structure and to substantially increase the stability of the ladder while it is being used. This ladder incorporates a ladder component with a foldable tripod supporting structure that provides a highly stable three point ground engaging support frame.

One leg of the tripod frame is utilized as one of the side pieces or side rails of the ladder. A second side rail or side piece is utilized to complement the first side piece in providing the ladder component for the'support of the steps or rungs but such second side piece is not an independent ground engaging member in the traditional manner of ladder construction but has its lower end converged towards and connected to the ground engaging end of the first side piece to form a unitary ground engaging end. Appropriate bracing is connected between the other two tripod legs and the second side piece so that when the ladder is in open or operable position, any weight forces on the ladder component are adequately transferred to the tripod frame. By the expedient of connecting the lower end of the second side piece to the ground engaging end of the first side piece, the relative width of the lower steps from bottom to top becomes progressively greater so that weight forces applied to the relatively narrow lower steps are transmitted directly to the first ground engaging side piece to eliminate any twisting or tilting as the ladder is initially mounted and as weight forces are continued to the higher steps, the appropriate bracing between the second side piece and the other tripod legs effectively transmits such weight forces throughout the frame structure.

The objects of this invention together with details of the operation outlined and the advantages of the same will be more fully described and developed in relation to the more detailed description of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective front view of this new ladder in open position,

FIG. 2 is a perspective rear view of this ladder in open position,

FIG. 3 is a side elevational view of this ladder in open position,

FIG. 4 is a perspective view thereof showing the ladder in closed or folded position,

FIG. 5 is a schematic view of the shape of the ladder component of FIGS. 1-4,

FIGS. 6, 7 and 8 are respective schematic elevational views of the ladder component showing modifications for the configuration thereof as compared with FIG. 5, and

FIG. 9 is a fragmentary perspective view of the upper end of this ladder showing a modified form of attaching the third leg to the ladder component.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, this new ladder is designated generally by the numeral as best seen in FIGS. 1 and 2. The ladder component of this invention is designated generally by the numeral 12 and comprises one of the important improvements in the overall ladder structure using the principle of a tripod-type supporting frame disclosed in my prior patent and copending application referred to above. Certain modifications of the ladder component 12 may be utilized to advantage under varying circumstances as will be later referred to and are identified in FIGS. 6, 7 and 8 by the respective numerals 12a, 12b, and 120.

The ladder component 12 comprises what is believed to be an entirely new and novel ladder construction which includes an elongated rigid first side piece 14 having an upper end 16 and a ground engaging lower end 18. A second side piece 20 having the respective upper end 22 and lower end 24 is connected at end 24 to the ground engaging end 18 of the first side piece 14 by any suitable means such as a bolted clamp 26 so that in effect, end 24 of side piece 20 and end 18 of side piece 14 form a single or unitary ground engaging extremity of the ladder component 12. From clamp 26, side piece 20 extends upwardly in an appropriate spaced relationship to side piece 14 to end 22 as seen in FIGS. 1 and 4 and intermediate clamp 26 and the

upper ends

22 and 16 of

side pieces

20 and 14, said side pieces are connected by a plurality of spaced steps 28 in a ladder relationship. In the embodiment'shown in the several figures except FIG. 7, the configuration of the second side piece 20 between

ends

24 and 22 defines a slight radius having advantages as will later appear. Because of the angular relationship of side piece 20 to side piece 14 in the lower end portion thereof, it will be seen that the lowermost step 28 has a relatively short length as compared to the next succeeding step and those above it and the advantage and purpose of this arrangement will become apparent as this description proceeds.

Side piece 14 in addition to serving as a component part of the ladder component 12, also serves as a first support leg of a tripod frame structure. A second ground engaging support leg 30 is pivotally attached in any suitable manner at its upper end to the upper end portion of the first side piece or leg 14 to form an apex area. While such pivot connection may be in any suitable form, I have preferably secured a pair of rigid straps 32 to opposite sides of leg 14 so that they project rearwardly therefrom whereby the upper end of leg 30 is pivotally attached between said projections by means of a pin 34. A hinged brace means 36 connects

legs

14 and 30 and permits leg 30 to be swung outwardly on pivot pin 34 to a predetermined position whereby brace 36 has an over-the-center locking component 38 in a well known manner.

A third ground engaging support leg 40 is pivotally secured near and spaced from its upper end to a suitable support 42 (FIG. 2) which is preferably attached to the underside of the top step 28 being generally the next step below a top plate 44 connecting the top ends 22 of side piece 20 and end 16 of side piece 14. By connecting the upper extremity of leg 40 as shown in FIG. 2, the out ward movement of the ground engaging lower end of said leg will cause the upper end thereof to move into engagement with the upper end of the first leg 14 to complement the apex area of the tripod structure formed by

legs

14, 30 and 40.

With reference now more particularly to FIGS. 1 and 2, I will now describe the bracing arrangement between my

tripod legs

14, 30 and 40. Such bracing structure as will appear follows the principle disclosed in my prior patent and co-pending application referred to above but includes certain improvements and refinements as follows.

An elongated rigid arm member 46 is pivotally attached at one end to leg 14 preferably just below the second step from the bottom by any suitable means designated generally by the numeral 48. The other end of arm 46 is adapted to be movably attached to leg 40 so as to bear against the same and be longitudinally slidable thereon. For this purpose, a ring member 50 is secured to end 52 of arm 46 so that such ring is slidably disposed on leg 40 and its downward position of travel is limited by a stop 54 secured to leg 40. Projecting outwardly from end 52 of arm 46 are the

spaced tongues

56 and 58 which straddle leg 40 as best seen in FIG. 2 and serve to keep arm 46 in a desired alignment with leg 40 so that when the ladder is moved to closed position as seen in FIG. 4, arm 46 and leg 40 will be in juxtaposition in a direction between

side pieces

14 and 20 whereby for purposes of transportation and storage, there are only two thicknesses of arts at this point.

A second elongated rigid arm 60 is pivotally connected to the lower end portion of leg 30 by any suitable pivot means designated generally by the numeral 62 and at the other end arm 60 is pivotally connected as by pin 64 near but spaced slightly inwardly from end 52 of .arm 46. On the rear side of the ladder component 12 there is provided a projecting abutment or brace member 66 which is preferably of a U-shape as best seen in FIG. 2. Brace 66 is secured at one end to side piece 20 just above the second step 28 from the bottom and extends in a U-shaped path rearwardly and diagonally with the other end being secured to approximately the longitudinal center of the next ascending step 28. The arrangement of brace 66 is such that when this ladder is opened or extended for use as seen in FIGS. 1 and 2, it will bear directly against arm 46 and by virtue of the connecting points of brace 66 relative to side piece 20, any weight forces imparted to side piece 20 are transmitted directly to the tripod frame and particularly as such forces are applied to steps 28 above the bottom step. By virtue of the narrowness of the lower step 28 as a result of the converging lower end portion of side piece 20, it will be appreciated that weight forces imposed upon the lowermost step 28 will be transmitted directly to leg 14 and thus while side piece 20, though serving in the support of steps 28 in a ladder relationship, is not an independent ground engaging leg as with conventional step ladders, the design and arrangement of the lowermost step 28 effectively transmits weight forces to the solid support afforded by leg 14 as the ladder is mounted, without any twisting, tilting or unsteadiness. As such weight forces are applied at successively higher steps and begin to bear against side piece 20, the stability of this ladder is assured by the relationship of brace 66 to the tripod frame through

arms

46 and 60 as described above.

At the top portion of this ladder between the uppermost step 28 and the top plate 44 a diagonal rod 68 is provided at the front side of the ladder extending between leg 14 and side piece and on the rear side of the ladder a second diagonal rod 70 is provided at a different angle extending between the top step and the top plate 44 whereby as the ladder is opened, the upper end of leg 40 will move between

rods

68 and 70 in its path of travel toward leg 14. By this bracketing the upper end of arm 40 by

rods

68 and 70, such rods serve as a lateral guide and limit means to assure that the upper end of leg 40 will not for any reason become disaligned in its path of movement for engagement with leg 14 to provide the apex engagement with leg 14 and leg 30.

With reference to FIG. 9, there is shown a slight modification for the attachment of the third leg, here designated as 40. In this arrangement, support 42 is secured to the side piece 20 just above the plane of step 28. Leg 40' is pivotally secured near its upper end to support 42' as previously described whereby it can be swung out in a direction substantially perpendicular to the plane of

legs

14 and 30. When this'is done, theupper end of leg 40' above support 42' will engage the stop or support 72 secured to the underside of the top plate 44 and complement

legs

14 and 30 in forming an apex area for the tripod frame. By this arrangement, leg 40' is effective in transmitting weight forces to the apex area of this ladder even though the upper end of such leg does not actually engage leg 14 as in FIG. ll. In other aspects, the construction of the ladder in FIG. 9 is as previously described. I

The extreme stability and rigidity of support of this ladder adds materially to its safety of use and also its utility particularly in situations where it may be desirable to place scaffolding between two of such ladders such as might be used by painters or carpenters in work on a building wall. While such scaffolding can be solidly supported on the traditional type top plate 44 as seen in FIGS. 4 and 6, I have illustrated a slight modification in the ladder component identified as 12c in FIG. 8 to provide an added feature of safety for this ladder when it will customarily be used for supporting such scaffolding. In FIG. 8, the top plate 44in its conventional concept is not utilized and the upper extremities of leg 14 and the side piece 20c in the variation of the ladder component 120 projects slightly above the top step 28 so as to in effect provide stops or curbs 80 and 82 at respective ends of the upper step 28. With this arrangement, a scaffolding board can be placed upon the top step 28 and thus be protected from accidental lateral displacement by the upper projecting curbs or stops as described.

The generally curved configuration of side piece 20 of ladder component 12 as seen in FIGS. l, 2, 4 and 5 and side piece 200 of modification 120 as seen in FIG. 8 provide in effect a truss-like supporting structure which can be utilized to advantage in the transfer of weight forces to the three main supporting

legs

14, 30 and 40 and particularly to leg 14 in the present environment where the second side piece 20 is not a separate ground engaging member and side piece 20a in ladder component 12a (FIG. 6).illustrates a more complete truss arrangement by connecting the upper end of side piece 20a to the upper end 16 of leg 14 similarly as end 24a is connected to end 18 of leg 14. While such a truss-like arrangement for the second side piece 20 is quite effective in the distribution of weight forces on this tripod frame support, it perhaps can be more economically utilized on relatively short ladders on the order of 6 to 8 feet since on ladders of considerably longer lengths which are frequently used in commercial buildings, for example, the use of the general design shown in FIGS. 5, 6, and 8 in order to provide conveniently usable steps at the upper and lower end portions of the ladder component could very likely require a relatively wide spacing between the two side pieces throughout the centerportion of the ladder component so as to make it bulky and possibly less easy to manipulate. Accordingly, utilizing my tripod frame principle and support as described, a further modification is disclosed in FIG. 7 where the ladder component 12b illustrates a substantially parallel relationship between the leg 14 and the second side piece 20b from the upper extremities thereof to point 84 where the second side piece 20b converges to its point of attachment 24b with the bottom of leg 14. Thus, with the arrangement in FIG. 7, a

. step ladder of any desirable and practical height can be constructed on the tripod frame disclosed to provide the stability and rigidity of support which is inherent in this ladder structure.

Iclaim:

1. A foldable latter structure, comprising:

a ladder component including:

first and second elongated side pieces having respective upper and lower ends,

a plurality of longitudinally spaced step members disposed intermediate said side pieces and secured thereto in a ladder relationship,

the lower end portion of said second side piece converged towards the corresponding end portion of said first side piece with the respective lower ends of said side pieces being secured together to form a unitary ground engaging end,

a pair of elongated ground engaging support legs each having respective upper and lower ends and each operatively pivotally arranged at their upper ends relative to the upper end of said ladder component,

foldable brace means interconnecting said first side piece and said pair of legs, and

means on said second side piece for engaging said brace means.

2. A ladder structure as defined in claim 1 including:

one of said pair of legs being pivotally secured at its upper end to the upper end of said first side piece to forman apex area, and

the other of said pair of legs being pivotally secured near its upper end to the upper end of said ladder component so that when the lower end of said leg is moved outwardly, the upper end of said other pair of legs is cooperatively related to said apex area.

3. A ladder structure as defined in claim 1 including said step members in the lower end portion of said ladder component below the plane where said second side piece begins to converge towards said first side piece and to said unitary ground engaging endbeing progressively shorter in lateral length whereby weight forces applied to step members in said lower portion of said ladder component are transmitted to said unitary ground engaging end.

4. A ladder structure as defined in claim 1 including said means on said second side piece for engaging said brace means being an abutment member on said ladder component disposed intermediate the upper and lower ends thereof.

5. A ladder structure as defined in claim 1 wherein said second side piece defines a radius between the respective upper and lower ends thereof.

6. A ladder structure as defined in claim 1 including the respective upper ends of said first and second side pieces extending upwardly from the plane of the uppermost step member to define opposed guard stops for any scaffolding placed upon said uppermost step member.

7. A ladder structure as defined in claim 1 including a top plate connected to the respective upper ends of said first and second side pieces.

8. A ladder structure as defined in claim 7 wherein said second side piece defines a radius between said top plate and said unitary ground engaging end.

9. A ladder structure as defined in claim 1 including said first and second side pieces being in substantially parallel relationship from their respective upper ends 7 to the point where said second side piece converges to said first side piece.

10. A ladder structure as defined in claim 1 including the upper end portion of said second side piece converged toward the corresponding end of said first side

Claims

1. A foldable latter structure, comprising: a ladder component including: first and second elongated side pieces having respective upper and lower ends, a plurality of longitudinally spaced step members disposed intermediate said side pieces and secured thereto in a ladder relationship, the lower end portion of said second side piece converged towards the corresponding end portion of said first side piece with the respective lower ends of said side pieces being secured together to form a unitary ground engaging end, a pair of elongated ground engaging support legs each having respective upper and lower ends and each operatively pivotally arranged at their upper ends relative to the upper end of said ladder component, foldable brace means interconnecting said first side piece and said pair of legs, and means on said second side piece for engaging said brace means.

2. A ladder structure as defined in claim 1 including: one of said pair of legs being pivotally secured at its upper end to the upper end of said first side piece to form an apex area, and the other of said pair of legs being pivotally secured near its upper end to the upper end of said ladder component so that when the lower end of said leg is moved outwardly, the upper end of said other pair of legs is cooperatively related to said apex area.

3. A ladder structure as defined in claim 1 including said step members in the lower end portion of said ladder component below the plane where said second side piece begins to converge towards said first side piece and to said unitary ground engaging end being progressively shorter in lateral length whereby weight forces applied to step members in said lower portion of said ladder component are transmitted to said unitary ground engaging end.

9. A ladder structure as defined in claim 1 including said first and second side pieces being in substantially parallel relationship from their respective upper ends to the point where said second side piece converges to said first side piece.

10. A ladder structure as defined in claim 1 including the upper end portion of said second side piece converged toward the corresponding end of said first side piece with the respective upper ends of said side pieces being secured together to form a unitary end.

11. A ladder structure as defined in claim 10 wherein said second side piece defines a radius between said unitary end at the upper end of said ladder component and the unitary ground engaging end at the lower end thereof.