Patent Publication Number: US-10767418-B2

Title: Tripod stepladder

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not applicable. 
     INCORPORATION-BY-REFERENCE OF MATERIALS SUBMITTED ON A COMPACT DISC 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to stepladders. More particularly, the present invention relates to tripod or three-legged stepladders. More particularly, the present invention relates to frames that secure the single leg of the tripod stepladder to the front section of the stepladder. 
     2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98. 
     Stepladders allow an individual to climb to a height for manipulating objects or performing work where the latter is essentially pre-standing. In other words, the ladder depends solely upon its construction and erection to ensure its stability, in comparison to standard extension ladders which are braced against a structure to be climbed. 
     A typical stepladder is designed to be folded into a convenient size for storage and carrying. This requirement that the stepladder be portable is a further constraint on the weight of the ladder. Thus, a typical stepladder will be found to weigh thirty pounds or less in order to ensure that it may be easily handled. It is typically designed to be folded into an essentially flat package. 
     The classic stepladder has a front ladder portion having two vertically ascending parallel members with angled steps periodically interposed therebetween to permit climbing. At an upper end, a rear leg section is pivotally attached. A folding brace member is used to extend the ladder to an expanded climb-aboard configuration. 
     The stability of the ladder is totally dependent upon the user&#39;s movement upon the ladder during use. The requirement that the ladder be portable tends to reduce the static weight of the ladder to as low of a level as is consistent with minimal structural strength. When considering that a typical user will weigh 150 pounds or more, practically all of the weight involved in the dynamic couple of the stepladder and user will be concentrated in the user. 
     There are two forces that affect the stability of the ladder. The first is static stability. In other words, static stability extending downward from the combined center-of-gravity of the user and the ladder to a point outside the area demarked by the legs of the ladder. This is a classic condition of static instability. Since the ladder has such little weight relative to the user, the actual location of the center-of=ravity of the user pre-determines the stability. A second dynamic condition relating to stability exist because the user at the top of the ladder, normal conditions, is exerting a reactive force across a moment couple essentially equal to the distance from the foot of the ladder to the point of contact with the user. This can often be a six-foot moment couple. Since this is a dynamic condition, induced by the motions of the user during work, the resisting couple is the weight of the ladder and the user. 
     The motion of the user also creates a torsional stress, twisting the ladder. The torsional stresses, in the form of twisting about the vertical axis of the ladder, is the most common cause of dynamic unloading of one or more ladder legs in response the user&#39;s motion. The result is an alternative loading and unloading of the legs of the ladder which produces an effect called “walking” where the ladder moves or creeps along the floor as the individual shifts his or her weight. 
     Since tripods are known to be inherently stable structures, especially on uneven ground, various attempts have been made to create stepladders of a triangular structure with an independent rear leg. In the past, various patents have issued with respect to said tripod stepladders. For example, U.S. Pat. No. 2,440,831, issued on May 4, 1948 to L. R. Pease, teaches a tripod stepladder having rails, step rungs, and a platform at the upper end of the rails. There is at least one brace leg pivotally connected about an axis adjacent to the platform. A crank arm is journaled onto the rails under the platform and movable into engagement with the brace leg to urge the leg rearwardly. 
     U.S. Pat. No. 3,356,180, issued on Dec. 5, 1967 to R. D. Parry, discloses a tripod stepladder having a pair of side posts, at least two steps to disposed between the side posts a rest bar in a rowwith the side posts and having a substantially inverted U-shaped configuration, a tripod leg pivotally connected at one end to the rest bar, and a standing platform disposed substantially below the rest bar and pivotally connected to the uppermost step at one end. The platform includes a rigid structure defining an aperture at the other end of the platform. The aperture is positioned so that the tripod leg passes there through. 
     U.S. Pat. No. 4,249,637, issued on Feb. 10, 1981 to T. A. Glasgow, teaches a tripod stepladder that includes rigid stiles having steps and a platform secured thereto. A hinge plate is pivoted to the platform and to a pair of legs to permit the legs to pivot as a unit towards and away from the stiles. The legs pivot relative to the hinge plate toward and away from each other to an folded tripod configuration. 
     U.S. Pat. No. 4,600,080, issued on Jul. 15, 1986 the C. R. Forrester, shows a three-legged stepladder in which a brace includes a sleeve or a collar that slides up and down the third or rear leg as the ladder is folded and unfolded. A pail shelf is pivotally attached to the third leg and locks the ladder in the open position. 
     U.S. Pat. No. 4,754,845, issued on Jul. 5, 1988 to W. H. Baker, describes a stepladder having a rigidified step section, a strengthened upper platform, and a pair of independently articulated angled rear legs that are supported by a pair of rigid pivoting supports. The angle of extension of the rear leg creates, in conjunction with the front step section of the stepladder, an essentially equilateral, triangular footprint. 
     U.S. Pat. No. 6,206,139, issued on Mar. 27, 2001 to R. C. Bogart, provides a folding tripod ladder having extendable legs. The ladder includes a top step, a pair of leg assemblies mounted to the top step, and a step assembly mounted to the top step. The leg assembly and the step assembly pivot from a closed position in which the leg assemblies and the step assembly extend vertically downwardly from the top step to an angular position in which the leg assemblies and the step assembly are angularly displaced from vertical and oriented along radial axes positioned 120° from one another in a tripod configuration. Each leg assembly and step assembly are locked in the selected angular position. 
     U.S. Pat. No. 6,874,598, issued on Apr. 5, 2005 to W. H. Baker, teaches a stepladder of a tripod structure with an actuating mechanism that extends the rear legs in the front step assembly in a coordinated manner to assume the tripod footprint. The actuating mechanism includes a vertical center post. A sliding collar journaled on the center post coordinates the extension and retraction of the rear legs and step assembly. An A-brace extends and retracts the step assembly. 
     U.S. Pat. No. 7,255,198, issued on Aug. 14 2007 to J. A. Lo, discloses a tripod extension stepladder having a ladder portion having a pair of ladder side rails, and a support portion that includes a pair of angularly disposed telescoping legs. The telescoping support legs are interconnected to each other and to the ladder side rails by lockable rigid spanner arms. When in use, the spanner arms are locked in an open position to form a tripod formation between the rails while additionally limiting the angle of a spread between the ladder portion and the support legs. 
     U.S. Patent Application Publication No. 2015/0345219, published on Dec. 3, 2015 to Aoi et al., teaches a stepladder provided with a coupling frame in the shape of an equilateral triangle. There is a front support, a rear right support, a rear left support, and spread stoppers for stopping the front support, the rear right support and the rear left support from spreading. 
     It is an object of the present invention provide a tripod stepladder that is very robust. 
     It is another object of the present invention provide a tripod stepladder that is very durable. 
     It is another object of the present invention to provide a tripod stepladder that is easy to assemble. 
     It is another object of the present invention to provide a tripod stepladder that has a minimal number of components. 
     It is a further object of the present invention to provide a tripod stepladder that prevents a twisting motion to the back leg. 
     It is another object of the present invention to provide a tripod stepladder that withstands impact forces. 
     It is another object of the present invention to provide a tripod stepladder that reduces torsional effects to the front section. 
     It is still another object of the present invention to provide a tripod stepladder that distributes loads over a wider area and between the front section and the rear leg. 
     It is still another object of the present invention to provide a tripod stepladder which is relatively inexpensive. 
     It is still further object of the present invention to provide a tripod stepladder which provides enhanced stability while minimizing the weight of the stepladder. 
     These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a stepladder assembly that comprises a front section having of a pair of side rails with a plurality of steps extending between the pair of side rails, a back section having a rail, and a frame pivotally connected or interconnected to the front section. The frame has a collar that receives an upper end of the back section therein. 
     The stepladder assembly of the present invention further includes a ladder top affixed to an upper end of the front section. The frame is pivotally affixed to the ladder top. The ladder top has a top surface extending over the upper end of the front section and over the upper end of the back section. The ladder top has a pair of sides extending downwardly from the top surface. The frame is pivotally mounted to the pair of sides. 
     The rail of the tripod stepladder assembly of the present invention is a square tubular. The collar has a square cross-section. An interior of the collar is in surface-to-surface relation with an exterior of the rail. 
     The frame of the tripod stepladder assembly of the present invention has a horizontal member positioned above the collar, a first side member extending from the collar to one end of the horizontal member, and a second side member extending from the collar to an opposite end of the horizontal member. The first side member has a lower end affixed to one side of the collar at a bottom thereof. The second side member has a lower end affixed to an opposite side of the collar at the bottom thereof. A first cross member has one end affixed to an end of the horizontal member or to an upper end of the first side member and an opposite end affixed to one side of the collar. A second cross member has one end affixed to the opposite end of the horizontal member or to an upper end of the second side member and an opposite end affixed to an opposite side of the collar. A third cross member has one end affixed to the mid-portion of the first side member and an opposite end affixed to an upper end of the collar. A fourth cross member has one end affixed to a mid-portion of the second side member and an opposite end affixed to the upper end of the collar. The opposite end of the first cross member is affixed to a central area of one side of the collar. The opposite end of the second cross member is affixed to a central area of the opposite side of the collar. The collar extends from a bottom of the first and second side members to the horizontal member. A plurality of fasteners are affixed to the collar into the upper end of the rail of the back section. The frame has a first flange extending upwardly from one end of the horizontal member and a second flange extending upwardly from an opposite end of the horizontal member. The first and second flanges are pivotally affixed respectively to the pair of sides of the ladder top. 
     A hinge or brace has one end affixed to a mid-portion of the front section and to a mid-portion of the back section. The hinge or brace limits a pivotal movement of the back section with respect to the front section. 
     In the present invention, the pair of side rails of the front section are angled with respect to each other such that a width of a bottom of the front section is wider than the width of a top of the front section. The frame is integrally formed of a polymeric material. The rail is a single rail. 
     This foregoing Section is intended to describe, with particularity, the preferred embodiments of the present invention. It is understood that modifications to these preferred embodiments can be made within the scope of the present claims. As such, this Section should not to be construed, in any way, as limiting of the broad scope of the present invention. The present invention should only be limited by the following claims and their legal equivalents. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a perspective view of the tripod stepladder in accordance with the preferred embodiment the present invention. 
         FIG. 2  is a perspective close-up view of the upper end of the tripod stepladder of the present invention. 
         FIG. 3  is a rearward view of the upper end of the tripod stepladder assembly of the present invention. 
         FIG. 4  is an upper rearward perspective view of the frame of the tripod stepladder of the present invention. 
         FIG. 5  is a rearward view of the frame of the tripod stepladder assembly of the present invention. 
         FIG. 6  is a cross-sectional view of the frame of the tripod stepladder assembly of the present invention as taken across line  6 - 6  of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , there is shown the tripod stepladder assembly  10  in accordance with the teachings of the present invention. The tripod stepladder assembly has a front section  12 , a back section  14 , a frame  16  and a ladder top  18 . The front section  12  has a first side rail  20  and a second side rail  22 . A plurality of steps  24  extend between the first side rail  20  and the second side rail  22 . The first side rail  20  and the second side rail  20  are angled with respect to each other so such that a width of the front section  12  at the bottom is greater than a width of the front section  12  at the ladder top  18 . As such, each of the plurality of steps  24  will have a decreasing length from the bottom to the top of the front section  12 . Foot  26  is affixed to the bottom of the first side rail  20 . Foot  28  is affixed to the bottom of the second side rail  12 . Feet  26  and  28  are of a polymeric material and provide additional stability to the bottom of the front section  12 . 
     The back section  14  is a single rail. A foot  30  is affixed to the bottom end of the back section  14 . The back section  14  is pivotally mounted so as to be movable into a position generally parallel to the front section  12  and a position angularly disposed away from the front section  12 . A hinge or brace  32  is affixed to the front section  12  and to the back section  14  so as to limit the amount of angular movement between the front section  12  and the back section  14 . Hinge or brace  32  also provides additional structural integrity to the tripod stepladder  10  of the present invention. 
     The frame  16  has a generally V-shaped configuration. In particular, there is a collar  34  (to be described hereinafter) that receives the upper end of the back section  14 . A pair of side members extend upwardly from the collar  34  so as to be pivotally mounted to the ladder top  18 . 
     The ladder top  18  is affixed to the upper end of the front section  12  and receives the upper end of the frame  16  therein. The ladder top  18  has a top surface  36  and a pair of sides  38  and  40  extending downwardly therefrom. The first leg  20  is affixed to the side  38  of the ladder top  18 . Side rail  22  is affixed to the side  40  of the ladder top  18 . Similarly, the upper ends of the frame  16  will be pivotally secured to the sides  38  and  40 . 
     In  FIG. 1 , is important to note that the collar  34  receives a substantial portion of the upper end of the back section  14 . The side members are joined to the collar  34  at the bottom thereof. Any forces imparted to the back section  14  are distributed over a wide area to the ladder top  36 . Similarly, this strong joinder between the frame  16  and the back section  14  serves to reduce torsional effects caused by movement on the front section  12 . The coupling of the collar  34  to the ladder top  18  and to the front section  12  provides strong forces against this torsional movement over the entire area of the front section  12 . Additionally, the wide base of the front section  12  serves to distribute further torsional forces to the side rails  20  and  22  adjacent to the bottom of the front section  12 . The use of the collar  34  on the upper end of the back section  14  provides a secure surface-to-surface contact between the collar  34  and the exterior of the upper end of the back section  14 . This resists any damage to the fasteners that secure the back section  14  to the frame  16 . Over time, the structural connection between the frame  16  and the back section  14  will not weaken or loosen because of this collared configuration. Importantly, since the rail of the back section  14  is a single rail and formed of a square tubular, this serves to further reduce any potential bending of the back section  14 . Since the collar  34  is also of a square cross-section, the engagement between the back section  14  of the collar  34  is very secure. Twisting effects between the collar  34  and the back section  14  are avoided by virtue of this square-in-square relationship. To the extent that the back section  34  receives side forces which would otherwise tend to bend the back section  14 , the substantial portion of the upper end of the back section  14  received within the collar  34  will strongly resist any such bending along the length of the square tubular of the back section  14 . Since the frame  16  can be formed of a polymeric material, the weight of the frame  16  is minimal, the expense for manufacturing the frame  16  is minimal, and the assembly of the frame  16  to the back section  14  is extremely easy. 
       FIG. 2  specifically shows the ladder top  18  as secured to the front section  12  and to the back section  14  through the use of the frame  16 . The frame  16  has the collar  34  receiving the upper end of the back section  14  therein. Fasteners extend through the collar  34  and through the upper end of the back section  14  so as to affix the upper end of the back section  14  permanently within the collar  34 . Side members  42  and  44  extend upwardly from the bottom of the collar  34  at an angle. A horizontal member  46  is formed with or affixed to the upper end of the side members  42  and  44 . Each of the side members  42  and  44  has an either a T-shaped or L-shaped configuration. This L-shaped or T-shaped configuration further enhances the structural strength of the side members  42  and  44  and the horizontal member  46  so as to resist any bending motions associated with the use of the tripod stepladder assembly  10 . 
       FIG. 2  shows that there is a pivot pin  48  which pivotally connects the frame  16  to the ladder top  18  at the side  40 . Another pin will connect the opposite side of the frame  16  to the side  38  of the ladder top  18 . 
       FIG. 3  illustrates how the rail of the back section  14  is received within the interior of the collar  34 . It can be seen that the collar  34  extends all the way from the bottom  50  of the frame  16  to the horizontal member  46  at the top of the frame  16 . As such, substantial portion of the length of the back section  14  is received within the collar  34 . Ultimately, the structural strength of the T-shaped or L-shaped horizontal member  16  will maintain the collar  34  in a fixed and rigid position. The side members  42  and  44  resist deflection of the collar  34  and distribute any forces to the horizontal member  46  and to the sides  38  and  40  of the ladder top  18 . As will be described hereinafter, certain cross members extend within the interior of the frame  16  so as to further distribute forces and resist any bending moment of the collar  34  caused by a shifting of weight on the front section  12  or by an undesired force applied to the rear section  14 . 
       FIG. 4  is a detailed view of the frame  16  in the tripod stepladder assembly  10  of the present invention. In  FIG. 4 , it can be seen that the collar  34  extends from the bottom  50  of the frame  16  all the way to the horizontal member  46 . Side members  42  and  44  extend outwardly from the bottom of the collar  34  at an approximately 45° angle upwardly to the opposite ends, respectively, of the horizontal member  46 . Holes  54  and  56  are formed in the wall of the collar  34  so as to allow fasteners to be received therein so as to secure the square back section  14  within the interior of the square collar  34 . A first flange  58  extends upwardly from one end of the horizontal member  46  and upwardly from an upper end of the side member  42 . Another flange  60  extends upwardly from the opposite end of the horizontal member  46  and from the upper end of the side member  44 . Flanges  58  and  60  are respectively secured to the sides  38  and  40  of the ladder top  18 . The flat outer surfaces of the flanges  58  and  60  against the flat inner surfaces of the sides  38  and  40  of the ladder top  18  further serves to distribute forces over a wider area. A hole  62  is provided on flange  58  and a hole  64  is provided on flange  60 . Holes  62  and  64  are configured to receive pivot pins therethrough so as to allow the frame  16  to pivot with respect to the ladder top  18 . 
     In  FIG. 4 , it can be seen that the side members  42  and  44  each have a T-shaped configuration. As such, there is a center strut that enhances the structural integrity of each of the side members  42  and  44  and further resists deflection. 
       FIG. 5 , in particular, shows the various cross members that are located within the interior of the frame  16  in a location between the side member  42  and the collar  34  and between the side member  44  and the collar  34 . A first cross member  70  has an end  72  that is affixed to an end of the horizontal member  46  or to an upper end of the side member  42 . An opposite end  74  is affixed to the collar  34 . In particular, this opposite end  74  is affixed or formed with a mid-portion of the collar  34 . The end  72  of the first cross member  70  will be structurally enhanced by being located at the intersection of the horizontal member  46  and the first side member  42 , along with the flange  58 . A second cross member  76  has an end  78  affixed to or formed with the opposite end of the horizontal member  46  and/or at an upper end of the second side member  44 . An opposite end  88  is affixed to an opposite side of the collar  34  from that of the first cross member  70 . The end  88  is actually placed at a mid-portion of the collar  34 . The end  78  will be located beneath the flange  60 . 
     A third cross member  80  has one end affixed to a mid-portion of the first side member  42  and an opposite end affixed to an upper end of the collar  34 . A fourth cross member  82  has one end affixed to a mid-portion of the second side member  44  and an opposite end affixed to an upper end of the collar  34 . 
     In  FIG. 5 , it can be seen that each of the side members  42  and  44  and each of the cross members  70  and  76  is of a T-shaped configuration. An L-shaped configuration can be used alternatively. Each of the cross members  80  and  82  is generally of a planar configuration. The intersection of the cross members  80  and  82  with the cross members  70  and  76  further distributes forces from the collar  34  along the side rails  42  or toward the horizontal member  46  in a strong connection area adjacent to the flanges  58  and  60 . 
       FIG. 6  is a cross-sectional view of the frame  16  of  FIG. 5  as taken across line  6 - 6  of  FIG. 5 . In particular, the collar  34  has a generally rectangular or square interior  90 . The side members  42  and  44  extend upwardly from the bottom  50  of the frame  16 . The horizontal member  46  extends entirely across the top of the frame  16 .  FIG. 6  also shows the orientation of the first cross member  70 , the second cross member  76 , the third cross member  80  and the fourth cross member  82 . In the cross-sectional view of  FIG. 6 , each of the cross members is particularly illustrated. As such, the distribution of forces actually crosses a very wide surface area of the frame  16 . The open area shown in  FIG. 6  between the various cross members further enhances the flexibility of the frame  16  while resisting forces applied thereto. 
     The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction can be made within the scope of the appended claims without departing from the true spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents.