US2650014A

US2650014A - Stepladder

Info

Publication number: US2650014A
Application number: US204550A
Authority: US
Inventors: Harrison Henry
Original assignee: Individual
Current assignee: Individual
Priority date: 1951-01-05
Filing date: 1951-01-05
Publication date: 1953-08-25
Anticipated expiration: 1970-08-25

Description

H. HARRISON Aug. 25, 1953 STEPLADDER 3 Sheets-Sheet 1.

Filed Jan. 5. 1951 ATTORNEYS STEPLADDER 5 Sheets-Sheet 2 Filed Jan. 5, 1951 N mm. m mA H Y R N E .H

ATTORNEYS Aug. 25, 1953 H. HARRISON ,014

STEPLADDER Filed Jan. 5, 1951 w s Sheets-Sheet s INVENTOR. HENRY HARRISON ATTORNEYS Patented Aug. 25. 1953 UNITED- STATES PATENT OFFICE STEPLADDER Henry Harrison, Port Washington, N. Y.

Application January 5, 1951, Serial No. 204,550

7 Claims. (Cl. 228 -31) My invention relates generally to a step ladder construction having a main body portion, rearwardly extendable bracing legs, and operating linkage systems for controlling the folding movements of the same. In particular, I am concerned with such a step ladder construction wherein novel linkage systems are provided for simultaneously moving the bracing legs laterally and rearwardly with respect to the body portion of the structure so that the area of the base on which the ladder rests is substantially increased.

It is well known that step ladder of conventional design with bracing legs, whose base width is equal to the base width of the main body portion are unsafe for use on rough ground because they can so easily fall over sideways. Furthermore, when the ladder becomes worn, the joints et loose and it becomes unsafe for use on level supporting surfaces.

Therefore, the primary object of my invention is to improve the stability of step ladders by providing means for simultaneously and in a single motion extending the bracing legs laterally as Well as rearwardly of the main body portion so that the width of the base on which the ladder rests is substantially increased.

Another object of my invention is to provide a step ladder construction of the type described above, possessing increased stability over conventional forms of step ladder constructions which is strong and rigid in the vertical direction and having stiffness against torsional and shearing strains.

A further object of my invention is to provide operating linkage systems for ladders of this type including hinged frames defining substantially rigid planes adapted to positively control the motion of the bracing legs during ladder opening and folding movements and to maintain the bracing legs in a fixed position relative to the main ladder portion when the ladder is in open or operativ position.

Another object of my invention is to construct a ladder which may be efiiciently and safely employed either as a step ladder or as an ordinary ladder.

A still further object of my invention is to provide a step ladder construction of the type described above made of either wood or metal having operating linkage systems whereby the foot portions of the bracing legs fold to a position substantially above the plane of the ends of the uprights of the body portion of the structure, whereby the bracing legs do not engage the supporting surface as the ladder structure is leaned against an object to be scaled.

, Another object of my invention is to provide a step ladder construction including novel operating linkage systems which may be easily fabricated from either wood or metal, and which will be light in weight, strong and rigid in use and yet inexpensive in manufacture.

With these and other objects in view, the invention consists in certainnovel features of construction and combinations and arrangements of parts which will be more fully described and pointed out in the claims.

In the accompanying drawings:

Figure 1 is a perspective View of a metallic step ladder shown in the fully extended position and embodying my invention,

Figure 1a is a sectional view of a step element of my ladder structure.

Figure 2 is a perspective view of the same step ladder in a partially folded position illustrating the folding action of the operating linkage systems.

Figure 3 is a perspective view of the same ladder in the completely folded position.

Figure 4 is a diagram illustrating the essential steps of designing the operating linkage systems of my invention.

Figure 5 is a perspective view of a ladder utilizing wooden construction illustrating a modified form of operating linkage systems employed therewith.

Figure 6 is an isometric perspective view of the same ladder and linkage systems illustrated in part in Figure 5, illustrating the manner in which the modified linkage systems bring the bracing legs together with their lower ends somewhat above the plane of the ends of the uprights of the ladder position of the structure.

Figure 7 is a perspective view of a bracing leg hinge bracket suitable for use with wooden step ladder constructions.

Figure 8 is a view in elevation showing the bracket of Figure '7 in position.

The body portion of the step ladder of my invention as shown in Figure 1 may be of conventional design. Steps 5 of tubular construction are riveted or otherwise secured to channel uprights 2 and 2' forming a ladder portion which is strong and rigid in the vertical direction and stiff against torsional strains. To further increase the body portions stifiness in torsion and in shear, a platform 3 and a pivot hinge bracket are secured to the same. A corner of platform 3 has been broken away in this view so that part of the bracket l may be seen.

I have found that the substitution of extruded tubing of parallelogram section shown in Figure la for the extruded channel now in common use as steps in the body portions of step ladder construction, results in a very large increase in torsional rigidity. The addition of

web portions

50 and 5| to the

channel webs

52, 53 and 54 provide a step element, possessing great strength which substantially eliminates all twisting and warping of the body portion of my ladder structure.

Separate bracing legs 5, 5', shown in tubular form replace the conventional brace unit found in previous step ladder construction and are joined by hinge rivets 6. 6' to the bracket 4 shown in more detail in Figure 4 wherein the platform 3 has been removed.

Legs 5, 5' are further secured to the ladder portion uprights 2, 2' by two novel linkage systems, hereinafter described in detail. The first linkage system utilizes linkage frames D and E wherein the linkage frame D consisting of links I and 8 turns about pins 9 withrespect to links H} and H and cross brace l2 of a second linkage frame E. Linkage frame D joins leg 5' at hinge rivet 13, while linkage frame E joins upright 2 at hinge rivet I4. When the ladder is in extended position, the triangular linkage frames D and E, by hinge pin 9, positively control the relative motion between the main portion of the ladder and the bracing leg 5. On the opposite side of the ladder a triangular linkage frame F, similar to triangular frame D, is formed by links I, 8' and pin 9' and is also hinged to the operating frame E by the hinge pin 9. The frame E is formed of links H], Ill; H, H; and cross brace 12, and comprises an irregular shaped rigid plane member connected to the

body portion uprights

2 and 2 by angle brackets II, II and hinge rivets l4, l4.

Hinge pins 9 and 9' are provided with short collars l5, l5 and l6, it which prevent links I, l and 8, 8' from sliding together or apart along their

respective pins

9, 9. The cross brace l2, forming a strengthening member for frame B and shown of tubular construction, passes through suitable holes in the links II, II and is flattened, bent, and riveted to the links It, If! at its ends, as shown in Figure 1. This cross bar [2 maintains the links l0, l and l l, l l in a rigid plane and provides a convenient handle for closing the ladder. Angle brackets IT, II are interposed between links it, Iii and H, H and respective hinge rivets l4, I4, which pivotally connect operating frame E to the uprights 2 for reasons which will be subsequently explained.

In the extended position of the ladder structure, the operating linkage frames D, E and F lie in substantially the same plane and to insure this relationship, a cord or chain 18, joining the intersection of braces II, II and a hole H9 in the edge of one of the steps I is provided which prevents the linkage frame from bending downward and thus holds the frames substantially in a rigid plane when the ladder is open. It will be seen in referring to Figure 1, that the force of gravity operating on the linkage frames, securely locks and positively holds the bracing legs in their extended operative position.

In referring to Figure 2, the movements of the bracing legs is along

arcuate curves

20 and 2@ as the same pass to and from the open and closed positions of the ladder.

A desirable feature found on conventional step ladders is a shelf extension for holding paint cans or tools for convenient use, and this feature might be provided as shown in Figure 1 in which the fulcrum 2| of the shelf passes through holes 22 in the upper portion of the legs and 5', which holes are of sufficiently large diameter as to compensate for the angular changes between the bracing legs and the shelf fulcrum 2 i. In securing, the ends of the fulcrum 2i may be provided with any suitable means, as peening, to prevent the same from slipping through the holes 22 tobecome disarranged.

The shelf itself may be of conventional design having a substantially rectangular pan 23 and two brace extensions 24 extending under the edge of one of the steps I.

The effective base of this ladder is bounded by the dotted line 25, illustrated in Figure 1, wherein the base width of the bracing legs is much greater than the space between the uprights 2 of the ladder portion of the structure while the distances of bases 2% and 2! remain substantially equal. In this manner of construction, the step ladder is less inclined to tip over sideways than ladders of conventional design, and the precise proportions of the base are determined by the proportions of the linkage system frames D, E and F. I have found the proportions shown in Figure 1 to be very practical and to be sumciently stable for safe use on rough ground or other supporting surfaces.

In the folding of the ladder, the linkage frame members assume various positions as they turn about the hinge pins 9, 9' and the pivot pins l3, l3 and l4, [4. An intermediate position is illustrated in Figure 2.

The motion indicated in Figure 2 and continued to the position shown in Figure 3, is possible without deforming any of the parts if the extended axis of the hinge rivets 6', l3, and I4 and hinge pin d" all intersect at a common point, indicated at 28 and the extended axis of the hinge rivets 6, as, and E i and hinge pin 9, all intersect at a similar point 23 not shown in the drawing. The respective points of intersection of the axes S28 and 28' will be situated, as indicated, on opposite sides of the step ladder structure and must lie on a straight line 29 passing through the axes of the hinge rivets Hi and i4. Small deviations of the angular relation of the axis such as might exist because of necessary tolerances in manufacture, result only in small deformations of the parts and do not significantly affect the ease of operation or physical shape of the linkage elements. It will thus be seen that the main ladder portion, the bracing legs, and the linkage frames D, E, and F, constitute two separate linkage systems. The first link-age system consists of the ladder upright 2, the ladder bracing leg 5 and linkage frames D and pivoted at points B, is, I l and on hinge pin 9. The axes of the hinge rivets and pin of this system, when projected, intersect at the common point 28. The second operating system consists of the main ladder upright 2, bracing leg 5 and linkage frames E and F, pivoted at points 6, I3, I l and on hinge pin 9'. The axes of these pivot pins and hinge pin Q, when projected, intersect at the point 28', as indicated in Figures 2 and 4.

Figure 3 is a view of the ladder completely folded, wherein the bracing legs 5, 5' are drawn up against the

uprights

2, 2 and the linkage frame members D, E and F fold about the respective hinge pins 9, 9' and lie substantially flat against the plane of the uprights 2'. It is now clear that the angle brackets ll, ll permit links l0, IE and H, i! to turn up into this closed position while the hinge rivets i3 and I4 and hinge rivets I 3' and i4 remain separated so that the linkage frame does not accidentally become locked at dead center when the ladder is closed.

Figure 4 illustrates the geometrical method of laying out suitable frame systems for such a step ladder as illustrated and is in the plane of the linkage frame When the ladder is .in extended condition the linkage frame members D and F are also substantially in the plane of this figure. Points A and B illustrate the extended and folded positions respectively of the hinge rivet l3 and leg 5 and point C indicates the position of the hinge rivet I4 on the ladder upright. Of course, similar points A, B and C are utilized in determining the'geometrical lay-out of the linkage frame D and its operating relation to the linkage frame E.

As a first step, line 30 is drawn joining the points A and B, then a perpendicular bisector 3I of the line 30 is erected. This line 3| found by swinging arcs 32 about point A and B is the line about which the linkage frames must fold in order to carry hinge rivet I3 from point A to point B, and it is, therefore, the axis of hinge pin 9. The intersection of line 30 and a line 29 through the points 0, C is point 33, and the axis of hinge rivet I3 must be made to pass through this position. In locating the axis of hinge rivet 6 (see Figure 2) a plane determined by the hinge rivet and the axis of hinge rivet I3 and a plane determined by the hinge rivet 6 and the axis of hinge rivet I0 intersect and are formed to have two fixed points 0 and 28 in common. Therefore, these planes have a line in common about which they fold and this line should be made the axis of hinge rivet 0.

It is clear from the foregoing account how one can determine the axes of the various hinges of the linkage systems of this ladder, and it is to be understood that a similar procedure is employed in laying out both of the operating linkage systems.

The design of the linkage systems including the frames D, E and F, the

uprights

2 and 2 and bracing legs and 5 support these axes properly within the space limitations and can easily be carried out by anyone skilled in the art. However, it is necessary that the three separately cross hatched linkage frames D, E and F of Figure 4 be rigid surfaces hinged at 9 and 9.

In order to facilitate the use of the step ladder as an ordinary ladder and adapt the improved linkage systems to wooden ladder construction, certain modifications should be made in the linkage' frames D, E and F as Well as the pivotal connection of the bracing

legs

5, 5 with the main ladder portion.

In the modification shown in Figures 5, 6, and '7, metallic parts of the ladder structure of Figures 1, 2, and 3 have been replaced by wooden parts wherein the uprights I02, I02, steps I 0i, IN, the top step I03, I03 and bracing legs I05 and I05 are made of solid wood. Preferably, the linkage frames and the hinges are made of metal as it has superior properties for forming and machining and because it can be made strong and yet remain relatively light in weight. To further decrease Weight and yet retain strength, the links of the linkage frame members may be constructed of some suitable metal, such as Duralumin. Links I08, I08, as indicated in Figure 5, corresponding to links 8 and 8' of Figure 1, should be constructed with sufficient strength to resist bending forces as well a axial loads, because in this design, the links I01 and I01, corresponding to links I and I of Figure 1, are joined at intermediate points rather than at the hinge rivets H3 and H3. These links I08 and H18 should, therefore, be constructed of a solid bar, a deeply formed channel member or preferably a tube made of Duralumin. The primary purpose of these modified linkage frames D, E and F illustrated in Figures 5, 6, and 7 is to bring the bracing legs I05 and I05 together at their lower ends at a point substantially above the plane of the lower ends of the ladder uprights 6. I02 and I02 as the ladder is moved to its closed position, as shown in Figure 6. The particular configuration and proportions of the link elements used in the modified linkage frames D and F permit links I01, I01 and I08, I08 to fold about hinge pins I09, I09 and to lie substantially in the same plane as the link elements of linkage frame E as the ladder is folded to closed position. In addition, the bracing legs I05 and I05 may move inwardly Without binding against adjacent links of the linkage frames D, E" and F. The dotted line I40 represents the intersection of the plane of the bottoms of the uprights I02, I02 and the outer'surface of the legs I05 and I05. The clearance MI indicated in Figure 6, facilitates the use of the ladder as an ordinary ladder and prevents the bracing legs from engaging the floor or supporting surface as the ladder is leaned against an object to be scaled.

It will be seen that the linkage frame modification illustrated in Figures 5 and 6, does not depart from the general type of linkage frames illustrated in Figures 1-4 and these modified forms may be designed by the same method. It is only necessary that the frames D, E and F form rigid members supporting the axis of hinge rivet H3 in constant spaced and angular relation to the axis of hinge rod I00.

I In the modified form of the invention, the hinge connections of the bracing legs and body portion of the ladder have been altered in a manner suitable for wooden-type step ladder construction and only the pivot connection of brace leg I05 to upright 2 will be discussed in detail. Referring to Figures 6, 7, and 8, brace leg I05 is capped by a metal strap I50 attached to the same by rivets I5I. This strap is bent to a roof shape so that one oblique surface makes bearing contact with a plane surface I52 of a modified hinge bracket I04, illustrated in detail in Figure '7 and shown in position in Figure 8.

Hinge bracket I04 is constructed of a plane piece of sheet metal such as Duralumin or steel by simply bending a pre-cut blank. In this manner, a plane bearing surface I52 bent from the plane of the blank along the line I50 i made normal to the hinge axis I06 about which leg I05 swings. As explained in connection with the ladder of Figures 1, 2, and 3, this hinge axis must pass through the intersection of the axis of the hinge rivet I I4,'hinge pin I09 and hinge rivet I I3,

in order that the ladder may open or close without deformation of the structural parts. The portion of the bracket I04 which is turned back to form plane surface I 52 is continued and forms a brace I53 by a simple bend along the lines I55 and I51. Another bend along the line I56 serves to turn parts of the bracket I00 into the plane of the bottom of the top step I03 of the body portion of the ladder. In joining the bracket I04 to the cap strap I50 of the bracing leg I05 a hinge rivet I00 passes through holes in the corresponding oblique plate surfaces of these parts and is secured, as by peening, to hold the surfaces together. Rivets I58 passing through the holes I59 in the hinge bracket fasten the bracket I04 to the uprights member I02 and to the top step I03. Thus, the bracket I00, in addition to its function'as a hinge member, also serves as a bracket to join the top step I00 to the upright member I02.

A second hinge bracket I04, the mirror image of bracket I00, is also required for the pivotal connection of bracing leg I 05 to the upright I02.

7 A second cap strap liifi, similar in shape to cap strap 50 completes the pivotal connection.

The chain 18, disclosed in Figures 1, 2, and 3, has been omitted in the modified form of my step ladder construction, and in Figures 5 and 6 linkage frames D, E and F are maintained substantially within the same plane when the ladder is in its open position by links H0, H and HI and HI resting against the top of one of the adjacent steps Hit. It will thus be seen that the linkage frame members are positively prevented from passing downward to an inoperative position.

In this form of my step ladder construction, the shelf extension for holding paint cans or the like, may also be utilized. This feature has been omitted in Figures 5, 6, and 7. However, it may be conveniently installed, if provision is made in the bracing legs Hi and N35 for slidably and pivotally receiving the fulcrum pin M of the shelf structure.

In addition to the foregoing, I may modify my linkage frame systems so as to allow the bracing legs IE5 and N35 to actually cross. This arrangement of the bracing legs 505 and I55 would not depart from the substance of my invention, although it might then be desirable to attach the linkage frames to the outside of the bracing legs rather than the inside, as is shown in these drawings.

Metallic ladders of the type shown and described may be made of any light weight rigid metallic materials. However, I have found magnesium, magnesium alloys and Duralumin type metals are particularly adapted for light weight step ladder constructions.

I claim:

1. In a step ladder construction as herein described, a body portion comprising a pair of laterally spaced apart upright members having a plurality of vertically spaced horizontal step elements secured at their respective ends to the upright members, a pair of rearwardly disposed ladder bracing legs each pivotally fastened to the upper portion of one of said upright members, and means for simultaneously moving the bracing legs laterally and rearwardly of the body portion of the ladder and for securely holding the bracing legs fixed when the ladder is in its extended position comprising a plurality of rigid operating frames including a primaryframe element, a pair of secondary frame elements hinged to said primary frame element for folding movement with respect to the same, said primary frame having pivotal connection to the body portion of the step ladder and said secondary frames each having pivotal connection to a respective bracing leg.

2. A step ladder construction, as set forth in claim 1, wherein the primary frame engages a step element as the ladder is unfolded to its open position to maintain the operating frames substantially within a plane.

3. In a step ladder construction as herein described, a body portion comprising a pair of laterally spaced apart upright members having a plurality of vertically spaced horizontal step elements secured at their respective ends to the upright members, a pair of rearwardly disposed ladder bracing legs each pivotally fastened to the upper portion of one of said upright members, and means for simultaneousl controlling the rearward and lateral movement of said bracing legs comprising rigid operating frames composed of a plurality of link bars wherein a pair of secondary frame elements are hinged to a primary frame element along non-parallel lines for folding movement with respect to the same, said primary frame having pivotal connection to the body portion of the step ladder and said secondary frames each having pivotal connection to a respective bracing leg.

4. In a ladder construction as set forth in claim 3 wherein a plurality of hinged rigid frame elements controlling movements of the bracing legs with respect to the body portion of the step ladder lie substantially within a plane when the ladder is in extended position.

5. In a ladder construction as set forth in claim 3 wherein flexible means are provided for maintaining the rigid frame elements substantially within the same plane when the ladder is in its extended position.

6. In a step ladder construction as herein described, a body portion comprising a pair of laterally spaced apart upright members having a plurality of vertically spaced horizontal step elements secured at their respective ends to the upright members, a pair of rearwardly disposed ladder bracing legs each pivotally fastened to the upper portion of one of said upright members, and means for simultaneously controlling the rearward and lateral movements of said bracing legs comprising a pair of linkage systems, each of said systems including one of said ladder upright members, its respective bracing leg, a rigid triangular operating frame and a second operating frame common to said operating systems wherein the pivot axes of the elements of the systems when extended intersect at common points spaced laterally of the ladder body and on a line passing through the axes of the pivot connection of said second operating frame to the ladder upright members.

'7. In a step ladder construction as herein described, a body portion comprising a pair of laterally spaced apart upright members having a plurality of vertically spaced horizontal step elements secured at their respective ends to the upright members, a pair of rearwardly disposed ladder bracing legs each pivotally fastened to the upper portion of one of said upright members, and means for simultaneously controlling the rearward and lateral movements of said bracing legs comprising rigid operating frames composed of a plurality of link bars wherein a pair of secondary frame elements are hinged to a primary frame element along non-parallel lines for folding movement with respect to the same, said primary frame having pivotal connection to the body portion of the step ladder and said secondary frames each having a rigid link bar extending beyond the confines of its frame and pivotally connected to the respective bracing leg whereby the bracing legs in the ladder folded position come together toward their lower ends at a point above the plane of the ends of the upright members so that the bracing legs will clear a ladder supporting surface when the ladder is leaned against an object to be scaled.

HENRY HARRISON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 42,565 Curtis May 3, 1864 1,331,953 Brown Feb. 24, 1920 FOREIGN PATENTS Number Country Date 401,656 Great Britain Nov. 13, 1933