US2868426A - Stepladder - Google Patents

Description

Jan. 13, 1959 H. T. GROVES STEPLADDER Filed June 16, 1954 INVENTOR HOWARD T. Graovzs ATTORNEYS STEPLADDER Howard T. Groves, Parsons, Kane.

Application June 16, 1954, fierial No. 437,035

1 Claim. ((Il. 228-411) This invention relates to step ladders and particularly to V-type or straddle type ladders.

As is well known in the art, straddle type ladders comprise two basic structural members, namely a stile having a desired number of steps and a backbrace or prop for supporting the stile. These two members are usually hingedly connected at the top to form an inverted V when the feet of the ladder are spread in erecting the ladder. Conventionally, means are provided to limit the spread between the stile and backbrace.

Because ladders of this type have four point support, there being two feet each on the stile and the backbrace, it is essential to the'stability and safety of known forms of these ladders that they be erected on a perfectly level surface. Even small irregularities, particularly on a hard surface, result in one leg of the ladder failing to make contact so that the ladder tends to wobble when the user shifts his weight, "which can cause him to lose his balance and fall from or capsize the ladder. In addition to the dangerous lack of stability which results when such ladders are set up on an uneven surface, a severe wrench or twisting stress is imposed on the ladder structure when a weight is placed on it, which stress eventually so loosens the steps or rungs, the brace members and joints that the ladder becomes too wobbly and insecure for use even on perfectly smooth and level surfaces.

Efforts have been made in the past to eliminate these difficulties as shown, for example, by the patents to Call, Patent No. 2,397,468 and to Ruse, Patent No. 1,928,158. These efforts, however, have been at best only partially successful.

For example, ladders of the type shown by Gail are limited to a fixed number of relative lateral angular positions between stile and backbrace and therefore unless one of these positions conveniently suits the particular irregularities encountered on the support surface, the lad der will not be steady. Furthermore, in any position of adjustment of the ladder, the stile and backbrace are so connected that the deleterious efiects of twisting stresses on the structure are not eliminated.

The ladder disclosed by Ruse provides for adjustment of the feet of the stile without definite limiting positions but the manner in which adjustment is accomplished makes it necessary that both of the legs of the backbrace be independently adjustable in length. The result is a relatively complex and unwieldy structure requiring trial and error levelling involving manual adjustment of the length of either or both legs of the backbrace.

The present invention in its broadest aspects contemplates a straddle type ladder in which the foregoing disadvantages of prior art ladders are completely eliminated by means of a ladder structure wherein the backbrace and stile are adapted for relative pivotal movement about an axis normal to the plane of the bacltbrace.

It is a further general object of the present invention to provide improved straddle type step ladders adapted to provide stable support on uneven surface.

it is another object of the invention to provide a novel straddle-type step ladder which automatically adjusts itself to irregularities small or large in the surface on which it is supported thus invariably and inherently assuming a stable, steady position when erected.

Still another object is the provision of an improved straddle type step ladder characterized by the absence of wrenching or twisting stresses in its structure regardless of the irregularity of the surfaces on which it is erected and mounted.

A further object of the invention is the provision of an improved straddle type step ladder in which the supporting force provided by the backbrace for the stile is transmitted through laterally extended contacting surfaces.

A. still further object of the invention is the provision of an improved straddle-type step ladder as characterized by the preceding objects which is simple, durable, and inexpensive to manufacture.

These and other objects as well as the many important advantages of the present invention will be apparent to those skilled in the art from the followingdescription and subjoined claim to be read in conjunction with the annexed drawings, in which:

Figure l is a perspective elevation of a straddle-type ladder embodying the present invention;

Figure 2 is a rear elevation of the ladder shown in Figure l; and

Figure 3 is a fragmental sectional view on line 3-3 of Figure 2, showing details of the toggle brace connection between the stile and backbrace.

Referring now to the drawings in which like parts are identified by like reference numerals throughout the several views, 10 indicates, in its entirety, a straddle-type step ladder embodying the present invention.

Ladder 10 comprises two primary structural components: a stile l2 and a backbrace or prop l4. Stile 12 is made up of a pair of side rails 16 which are secured together by a number of transversely extending steps or rungs 18a, ltib, 18c, and Mid. Side rails 16 are preferably disposed in downwardly diverging relation so as to provide a relative broad base and therefore, steps ltia liid are progressively shorter in length. They are secured to the side rails in any suitable manner, for example, in the disclosed embodiment the ends of the steps are disposed in shallow grooves provided on the inner surfaces of the side rails. Transverse tie rods 26 running under each step and through the side rails, tie the ladder together. Nut and washer assemblies 22 on at least one end of tie rods 20 allow the tie rods to be tightened to suflicient tension to eliminate any play or looseness in the parts of stile 12. It will be understood that if only one end of the tie rods 2t] is provided with a nut and washer assembly, the opposite end has a suitable head or enlargement to prevent its being pulled through the respective side rail.

As clearly shown in Figure 1, a spreader block 24- is provided between the underside of each step 18a-l8d and corresponding tie rod 24 Spreader blocks 24 are located substantially midway between the ends of the steps and contain a suitable groove 26 for the reception of the tie rods.. By virtue of this construction, a substantial part of the weight placed on the steps is transmitted through blocks 24 to the tie rods 24 causing them to flex downwardly and pull the respective side rails together. This action not only reduces flexing of the steps but allows a large part of the weight placed on steps to be absorbed as compressive forces on the ends of the steps instead of as bending or flexing moments.

The structure of the stile 12 is further reinforced by means of corner braces 23 between the ends of the lowermost step 18a and the respective side rails 16.

A top step or platform 3d of. the ladder is secured to the upper ends of side rails 16 by a pair of brackets 32, bolted, riveted or otherwise securely fastened to the rails and'p'latform. Brackets 32 serve to hingedly connect the stile l2 and backbrace Mas willhereinaft'er be explained.

Backbrace 1.4- consists of? apair' of legs '34 secured to- 'gether in downwardly diverg ent' relation by anycoir venient number of cross braceiiasseinblies 36 and'36r1, preferably in the following manner. Each braceassembly 36 and 36a consists of a brace member 38 extending substantially horizontally between legs 34- and having grooves 46 in its upper and lower longitudinal edges. Brace members are retained and 'th'eoppo'sing, legs 34 tied together by a pair ofparallel, horizontal tie rods .42 disposed in the upper and. lower grooves respectively of the brace members. The ends of tie rods 42pass through suitable holes in legs 34 and at least one end of each is threaded and provided with a nut and washer assembly 44 for tightening up the rods. It: will beunderstood, of course, that if the nut and washer assemblies are provided at one end of the tie rods only, the opposite end is provided with a head or othersuitable enlargement to prevent its being pulled through the respective leg,

As clearly shown in Figure l, the upper ends of legs 34 are bifurcated as at 46 to receive and support a quadrant block 48 secured therein by suitable fasteners t).

Quadrant block 4% consists of a flat plate of wood or other suitable material and may be of one piece or multiple piece construction, the latter type being illustrated. The upper edge 52 of quadrant block 43 extends upwardly out of bifurcations 46 and is curved in a relatively long radius circular are having its center located somewhat below the lower portion of the quadrant block and midway between legs 34.

The lower edge of quadrant block 48 is provided with a relatively deep notch 53 midway between legs 34. The arcuate edge 52 of quadrant block 48 preferably is covered with a strip 54 of high friction wear resisting material secured thereto in any suitable manner for a purpose hereinafter appearing. I

Brackets 32 are formed with cars 56 containing Icoaxially aligned holes receiving and freely rotatably supporting the opposite ends of a horizontal hinge rod 58 (see Figure 3) eitending therebetween. Hinge rod 58 is retained against axial displacement from ears 56 by cotter keys 6%) or other convenient means.

A sheet metal yoke 62 having a pair of parallel generally V-shaped dependent legs 64 straddles hinge rod .58.. A crest block 66, having a straight upper edge is block 48 and overlie notch 53. I A nut and bolt assembly .76 or equivalent fastening means extends between and connects the lower ends of legs 64, approximate center of notch 53. I

From the structure described it will be und rstood that quadrant block 48 is retained between the legs 64 of yoke 62 by the cooperation of bolt assembly '70 and notch 53 with sufficient play so that the quadrant block can move laterally, or toward and away from crest block 66 and can pivot about the center of curvature of arcuate passing through the edge 52. Thus it will be seen that bolt assembly 76 has free play in notch. 53 and therefore, the bolt and notch serve only to maintain the assembly of the backbrace with the remainder of the ladder when the ladder is being carried or erected. j

To limit the spread or separation between stile 16 and backbrace 14, a toggle brace 72 is provided which '4 consists of a pair of links 75% and 76, pivotally connected as at 78. The opposite ends of brace 72 are connected to the rear edge'of step 180 and to cross brace 36a in such a manner as to allow relative pendulous or lateral angular movement of the stile and backbrace. For example, in the disclosed embodiment a nut and bolt assembly 86 extends vertically through step 18c. An ogee-shaped link 82 has one end looped around bolt 80 and its other end hooked through an aperture 84 in brace link 74. The'other end of toggle brace 72 is connected to brace member 36a by means of a swivel hook 86 having its bight portion hooked through an aperture 88 inbrace link 76 and its stem or shaft'extended through a suitable aperture in brace member 36a and secured by means of a nut 90.

From the foregoing description, it will be understood that the functioning of the invention is as follows':' The ladder folds and is erected in the conventional manner and when erected, if the supporting surface is perfectly level, assumes the solid line position shown in Figure 2.

In the event that the supporting surface is not level the stile 21 and backbrace 14 are free to pivot angularly with respect to each about the center of curvature of arcuate surface 52, the coacting surfaces 52 and 69 sliding on each other until the ladder components 12 and 14 spontaneously assume a position in which all four feet are firmly implanted on the supporting surface. In Figure 2 the backbrace 14 is shown in'phantom lines representing one of an almost infinite number of relative positions which can exist between the stile 16 and the backbrace. An extreme case is shown in Figure 1 wherein a block is used to represent a high spot on the supporting surface. While in most instances, the ladder would not have to compensate for such a great difference in height (block 92 is about four inches high in the scale of the drawing) it is fully capable of doing so, the ladder as shown in Figure 1 being entirely stable and susceptible of being mounted with complete safety. The action of the ladder in compensating for an unlevel supporting surface is the same regardless of which of the four feet encounter high or low spots.

It is important to note that, when the ladder is mounted, the load is transmitted from the stile to the backbrace by and is substantially equally distributed over the contacting arcuate surfaces 52 and 69. A vertical projection of the center of mass of the ladder falls within the central portion of the base rectangle having the feet of the ladder as its corners, regardless of the relative angular positions of the stile and backbrace.

The friction strip 54 prevents accidental slippage between the quadrant block 48 and crest block 66 when a weight is placed on the ladder and therefore, it'will be appreciated that this strip may be located onthe arcuate surface of either the crest block or quadrant block.

The invention may be embodied in other'specific forms without departing from the spirit or'essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claim rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claim are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

A straddle type step ladder comprising a stile including a pair of side rails rigid with respect to each other and a number of steps extending transversely therebetween, a backbrace having a pair of spaced legs. rigid with respect to each other and at least one cross brace extending between said legs, a transverse hinge rod securedto saids'tile adjacent the upper end thereof, a yokeswingabl'y straddling said hingerod and having a pair of "spaced parallel planardepending legs, a fiat crest'bloc'k --rigidlysecured to said yoke between the upper portions of the depending legs thereof, a flat quadrant block on the upper end of said backbrace slidably disposed between the lower portions of the depending legs of said yoke, complementary arcuate surfaces on the upper edge of said quadrant block and lower edge of said crest block, respectively, said surfaces being in the form of relatively long radius circular arcs having a common center in the plane of said quadrant block and crest block and in the vertical plane of symmetry of said ladder, said yoke legs acting as aguide for said quadrant block, and a pin and slot connection between said quadrant block and the legs of said yoke allowing relative rotational and translational movement of said quadrant block and crest block whereby said arcuate surfaces are in abutment at least when the ladder is erected, said surfaces carrying the load transmitted between said stile and backbrace and allowingsaid stile and backbrace to assume relative angular positions about said common center to compensate for irregularities in the surface upon which the ladder is erected.

, References Cited the file of this patent UNITED STATES PATENTS Staring Mar. 8, McCormick Oct. 6, McKinney Sept. 6, Franklin Feb. 17, Osterhoudt Feb. 24, Mitchell Apr. 6, Patterson Aug. 8, Blosser Aug. 23, Trowbridge Feb. 14, Thrasher Jan. 9, Gail Apr. 2, Fowler Oct. 15, Young Mar. 14, Pierce May 26,

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