Patent Publication Number: US-7712716-B2

Title: Adjustable height scaffold combination

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 11/507,944 filed on Aug. 22, 2006 now abandoned which is a continuation-in-part of U.S. patent application Ser. No. 09/955,467, filed Sep. 17, 2001 now U.S. Pat. No. 7,152,835 and titled IMPROVED BRACKET ASSEMBLY LOCK, which is a continuation-in-part of U.S. patent application Ser. No. 09/477,660 filed Jan. 5, 2000, now abandoned all of which are hereby incorporated by reference. 

   TECHNICAL FIELD 
   The present invention relates to scaffolds and more particularly, relates to scaffold bracket assemblies. 
   BACKGROUND INFORMATION 
   Adjustable height scaffolds are well known in the art and typically comprise four main elements: an upright, a bracket assembly for supporting a work platform on the upright, a jack or block and tackle for raising and lowering the bracket assembly on the upright, and a cage for holding the upper end of the upright in place. 
   Two types of adjustable height scaffolds, which are designed with uprights, constructed of wood or rubber-backed aluminum are well known and widely used. The load bearing surfaces of these uprights are elastically deformable and hence, when loaded, have cross sections that change, i.e., the jaws of the clamp of these scaffolds indent said surfaces temporarily. 
   An example of an adjustable height scaffold, which is designed for use with a wooden upright is U.S. Pat. No. 2,216,912 to Hoitsma. The Hoitsma patent discloses an angle bracket to which a jack is coupled, and is commonly referred to as a “pumpjack”. Another example of an adjustable height scaffold that is designed for use on an upright constructed of wood is U.S. Pat. No. 2,342,427 to Riblet. The Riblet patent discloses a bracket assembly which is raised and lowered by block and tackle This adjustable height scaffold has been referred to as the “painter&#39;s pole”. 
   Examples of adjustable height scaffolds, designed for use with aluminum uprights to which a rubber strap has been riveted, include U.S. Pat. No. 4,597,471 to Anderson and U.S. Pat. No. 5,259,478 to Berish et al. It should be noted that the Anderson patent and the Berish patent both use the jaws of the pumpjack mechanism disclosed in the Hoitsma patent. It should also be noted that the jaws of the painter&#39;s pole bracket disclosed in Riblet &#39;427 have been adapted for use on rubber-backed aluminum uprights. 
   U.S. Pat. No. 878,455 to Carter, U.S. Pat. No. 2,801,851 to Meek and U.S. Pat. No. 4,308,934 to Jackson disclose related bracket assemblies. The bracket assemblies disclosed in Carter, Meek and Jackson differ from the bracket assemblies noted above in that the inner jaw of their locks is formed from an extended surface of the associated angle bracket, i.e., they do not pivot with respect to the associated angle bracket. The contact points of said jaws with the upright depend on the straightness of the upright and may be too far apart to provide sufficient friction to support the vertical load. Consequently, they require an outer jaw, in order to supply the vertical force needed to support the load, which indents in some way the upright and so changes, temporarily at least, its cross section. 
   All of the prior art patents use uprights whose cross sections are altered locally when loaded. The present invention, in contrast, teaches how the molecular, friction force between the jaws of the clamp and the upright may safely support a load without temporarily altering the upright&#39;s cross section. 
   In the Pump Jack, a spring is required to initiate contact of the jaws of the clamp with the upright. In the painter&#39;s pole, however, the clamp is coupled to the angle bracket in such a manner that a load placed on the angle bracket exerts a turning moment on the clamp which initiates and maintains contact of the jaws of the clamp with the upright so long as the width of the upright exceeds the design width. A clamp with this property is called a “load activated clamp”. 
   The outer, load supporting jaw of the pumpjack has a square cross section and is fixed in position in the side members of the clamp to insure that the corner of the square jaw bites into the wooden or rubber surface of the upright when the clamp is supporting a load. When the load is being lowered, however, the clamp is rotated to a horizontal position by the worker. Rotating the clamp to a horizontal position moves a face of the square jaw of the pumpjack so that it is more parallel to the upright. This reduces the vertical, supporting force on the jaw and permits the lowering of the scaffold. With the clamp in a horizontal position, so that a face of the jaw is nearly parallel to the upright, the bracket assembly is lowered. 
   The jaws of the lock of a painter&#39;s pole have smooth, cylindrical surfaces that indent the surface of a wooden upright along the points of a shallow cylinder. As we have seen, the outer jaw of a pumpjack has an edge which bites into the surface of an upright along the corner of a square. Because of the elastically, deformable nature of the wood or rubber used in these uprights, the jaws used in the clamps of said adjustable height scaffolds do not damage the uprights. They do, however, alter the cross section of the upright temporarily. Jaws of this type will be referred to as “edged” jaws because they would contact a hard, flat surface on a single line. 
   SUMMARY 
   In this application, the word “pivot” is used in a more general sense than its use in prior art adjustable height scaffolds as typical rotation about an axis that is, the term “pivot” does not mean rotation about a single axis but rather, the ability of one part to move relative or vis-à-vis another part. In order that a jaw of the clamp grip the upright on an extended area firmly, the clamp must pivot approximately horizontally in going from an unlocked position to a locked position. Then, if the contacting surfaces of the upright and at least one of the jaws are portions of cylinders, said jaw pivots approximately about a horizontal axis, and, depending on the accuracy with which the parts are made, slides approximately horizontally and twists about an axis approximately perpendicular to the axis of the upright so that said jaw contacts the upright on an extended area. In this specification and in the claims, the parts which are pivoting with respect to each other may be connected by means which permit relative motion of the clamp jaws with respect to the side members of the clamp with the sufficient number of degrees of freedom needed, to permit the jaws of the clamp to properly contact a cylindrical surface of the upright. 
   According to one embodiment, the present invention features a load activated clamp for use in mounting an angle bracket on an upright. The load activated clamp features at least one side member, a fulcrum bar coupled to the side member and to the angle bracket such that the side member pivots relative to the angle bracket about the fulcrum bar, and an outer jaw and an inner jaw coupled to the side member. One of the jaws pivots relative to the side member and includes a surface, for contacting an extended area of the upright, which extends over a portion of a circular cylinder whose axis parallels the axis of the upright. Alternatively, both the inner and the outer jaws pivot relative to the side member and include surfaces, for contacting extended areas of the upright, which extend over portions of circular cylinders whose axes parallel the axis of the upright. 
   According to another embodiment, the present invention features a bracket kit. The bracket kit includes an upright and a bracket assembly. The upright features at least a contact surface having the surface of a portion of a cylinder whose axis runs along the longitudinal axis of the upright and whose cross-section may be linear, circular or any one of many possible curves. The bracket assembly features an angle bracket, a lower bracket arm, and a load activated clamp. The lower bracket arm is adapted to be secured to the angle bracket and is sized and shaped to mate with at least one surface of the upright. The load activated clamp includes at least one side member, a fulcrum bar coupled to the side member and to the angle bracket such that the side member is adapted to pivot relative to the angle bracket about the fulcrum bar, and an outer jaw and an inner jaw coupled to the side member. At least one of the inner and outer jaws pivots relative to the side member and includes a surface, for contacting the upright, which extends over a portion of a cylinder whose axis parallels the axis of the upright. 
   According to another embodiment, the pivoting of the side member relative to the outer jaw does not employ a cross bar to define a pivot axis, fixed in position, in both the side member and the outer jaw. In this case, a well defined pivot axis exits when no cross bar defining it is present, but for the pivoting of the inner jaw with respect to the side member and the pivoting of the side member with respect to the angle bracket, no well defined pivot axis exists. 
   According to yet another embodiment, the present invention features a clamp for mounting an angle bracket on an upright. The clamp includes a frame having means for pivoting and a jaw coupled to the frame. The jaw includes a contact surface which may be planar or cylindrical in shape depending on the nature of the upright surface that it must contact over an extended area. 
   It is important to note that the present invention is not intended to be limited to a system or method which must satisfy one or more of any stated objects or features of the invention. It is also important to note that the present invention is not limited to the preferred, exemplary, or primary embodiment(s) described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the following claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages of the present invention will be better understood by reading the following detailed description, taken together with the drawings wherein: 
       FIG. 1  is a perspective view of an embodiment of a combination of bracket assembly and an upright according to one embodiment of the teachings of the present invention; 
       FIG. 2  is an enlarged side view of the load activated clamp shown in  FIG. 1 , the clamp being shown in a clamped position on a circular cylindrical upright of width slightly wider than the design width; 
       FIG. 3  is an enlarged side view of the load activated clamp shown in  FIG. 1 , the clamp being shown rotated in the clockwise direction so that the clamp is disposed in an unclamped position on the upright; 
       FIG. 4  is a cross section side view of the clamp and upright of  FIG. 2  in which the pivot axis relating the outer jaw to the side member of the clamp is not defined by a cross bar while the cross bar, supporting the inner jaw, pivots about a pivot axis relative to the side member but neither slides nor twists relative to the side member, and the side member of the clamp pivots relative to the angle bracket without a defined pivot axis; 
       FIG. 5  is a top view of the clamp and upright of  FIG. 1  the inner and outer jaws of the clamp contacting the inner and outer circular cylindrical surfaces of the upright; 
       FIG. 6  is a top view of the clamp and upright of  FIG. 1  showing the inner jaw of the clamp contacting the inner, circular cylindrical surface of the upright while the outer, planar jaw of the clamp contacts the outer surface of the upright on the surface of a plane; 
       FIG. 7  is a direct view of a planar EAC jaw pivotally mounted in a frame that is pivotally mounted in the side members of the clamp; and 
       FIG. 8  is an enlarged side view of the load activated clamp shown in  FIG. 2 , showing the forces acting on the jaws of said clamp resulting from a vertical load placed on the angle bracket. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to  FIG. 1 , there is shown a perspective view of an embodiment of the combination  4  of bracket assembly  7  and upright  13  constructed according to one embodiment of the present invention. Bracket assembly  7  is shown mounted on upright  13 , which may be constructed of a non-elastically, deformable material, such as aluminum or plastic, and has a constant cross section which is dimensioned so that combination  4  will support a heavy load. 
   Bracket assembly  7  comprises an angle bracket  15 , a lower bracket arm  17  and a load activated clamp  18 , pivotally attached to angle bracket  15  by fulcrum bar  60 . Bracket arm  17  and load activated clamp  18  cooperate to mount angle bracket  15  onto upright  13 . In this manner, a pair of bracket assemblies  7  in combination with uprights  13  can be used to create a scaffold. Specifically, with a pair of bracket assemblies  7  each mounted onto its upright  13 , a scaffold is created by placing a plank across each angle bracket of the pair of bracket assemblies  7 . 
   It is to be understood that angle bracket  15 , which comprises a vertical leg  27 , diagonal leg  25  and a horizontal leg  23 , does not serve as a principle feature of the present invention. Accordingly, angle bracket  15  could be replaced with alternative types of angle brackets without departing from the spirit of the present invention. As an example, angle bracket  15  could be modified in such a manner that the inner end of horizontal leg  23  and the vertical leg  27  are welded together, without a need for diagonal leg  25 . 
   Lower bracket arm  17  comprises a U-shaped band  37  having a closed end  31  and an open end  33 . Lower bracket arm  17  is coupled to angle bracket  15  by welding closed end  31  of band  37  onto lower end  24  of vertical leg  27 . Positioned as such, the placement of a vertical load on horizontal leg  23  of angle bracket  15  will force cross bar  35  against inner, load bearing surface  14 - 1  of upright  13 . 
   It is to be understood that neither the particular construction of lower bracket arm  17  nor the means of its attachment to vertical leg  27  is a principal feature of the present invention. 
   Vertical leg  27  includes a pair of apertures  21 . A conventional block and tackle or a jacking device (neither shown) can be attached to angle bracket  15  through apertures  21  to enable bracket assembly  7  to be raised and lowered on upright  13 . 
   Load activated clamp  18  comprises a generally U-shaped band  38  having a pair of spaced apart, parallel side members  39 , with a closed end  41  and a pair of free ends  43  and inner jaw  63  and outer jaw  65 . Said inner and outer jaws and said side members enclose upright  13 . 
   Side members  39  of load activated clamp  18  are coupled to angle bracket  15  near upper region  29  of vertical leg  27  by generally cylindrical fulcrum bar  60 . Specifically, fulcrum bar  60  extends through apertures in side members  39  and vertical leg  27  and provides a fixed axis  60   a  about which load activated clamp  18  can pivot relative to angle bracket  15 . As shown in  FIG. 1 , side members  39  include a first pair of openings  11  and a second pair of openings  12 , shaped to accept cross bars  68  and  70  on which jaws  63  and  65  are mounted to permit the independent pivoting of jaws  63  and  65  about pivot axes  67   a  and  69   a . Since pivot axis  67   a  is disposed beneath the plane defined by fulcrum pivot axis  60   a  and pivot axis  69   a , clamp  18  is load activated. 
   It should be noted that fulcrum bar  60  could be replaced with any means which attaches clamp  18  directly to angle bracket  15  and permits clamp  18  to pivot with respect to angle bracket  15  about fulcrum axis  60   a.    
   The clamp in accordance with the present invention which is connected to the angle bracket by link  50  as shown in  FIG. 4  ‘pivots’ with respect to the angle bracket without the existence of a pivot axis, that is fixed in position in either structures. Any, useful, relative motion between the clamp and the angle bracket will be referred to herein as ‘pivoting’. The clamp in the pumpjack pivots with respect to the angle bracket. The word “pivot” will include this broader meaning in describing the relative motions of the side members with the jaws of the clamp. The jaws may “pivot” relative to the side members whether or not a single “pivot axis” exists. 
   It should be noted that side members  39  are not limited to the particular size and shape shown in  FIG. 1 . Rather, side members  39  could be replaced with a different sized and shaped structure that permits the pivoting of said structure with respect to angle bracket  15 . 
   It should also be noted that the particular shape and construction of inner jaw  63  and outer jaw  65 , which may differ from each other, in combination with a suitable upright  13 , create functional advantages and accordingly serve as a principal feature of the present invention. In particular, as will be described further in detail below, outer jaw  65  and inner jaw  63 , individually or as a pair, function as Extended Area Contacting (EAC) jaws. An EAC jaw, as pictured in  FIG. 1 , is distinguished from the edged jaws of the prior art in that it has a cylindrical surface which, when placed in the proper orientation on an upright  13  with a cylindrical, outer surface of the same shape, will contact said outer surface at points randomly distributed over an extended area. The minimum, cylindrical rectangle, which includes the random points of contact between said EAC jaw and the cylindrical, non-elastically deformable surface of a suitable upright against which it is pressed, has a width, W, and a height, H, with H greater than zero. 
   In order to permit clamp  18  to move from a position where the clamp grips upright  13  to a position where the clamp does not grip the upright  13 , the clamp pivots with respect to angle bracket  15  about fulcrum pivot axis  60   a . Moreover, inner EAC jaw  63  and outer EAC jaw  65  both pivot independently in order to permit said EAC jaws to contact said upright on extended areas. 
   Inner EAC jaw  63  is provided with pins  67  that project through openings  11 ,  12  in side member  39 . The pins are sized and shaped to fit within suitably, dimensioned openings  11 ,  12  in such a manner as to enable inner jaw  63  to pivot independently about inner jaw pivot axis  67   a  relative to side members  39  to slide horizontally relative to side members  39  and to twist independently about an axis perpendicular to the axis of the upright  13  relative to side members  39  and so permit the axis of the contacting cylindrical surface of said jaw to coincide with the axis of the contacting cylindrical surface of the upright  13 . Like means are provided for mounting similar, outer EAC jaw  65 , with three degrees of freedom, in side members  39 . There are many structures that would provide the degrees of freedom achieved in  FIG. 2 . Pins  69  could be the ends of crossbars, passing through elongated holes  12  in outer EAC jaw  65 . 
   Because the principle feature of the present invention pertains to load activated clamp  18  and more particularly, to inner, EAC jaw  63  and outer, EAC jaw  65  in combination with upright  13 , it is to be understood that bracket assembly  7  could be modified without departing from the spirit of the present invention. For example, angle bracket clamp  18  need not be load activated: pivot axes,  60   a ,  67   a  and  69   a  could coplanar. The location of bracket clamp  18  and bracket arm  17  could be interchanged and bracket clamp  18  could be attached by means of a link to angle bracket  15  at a point between upper and lower bracket arms as in Hoitsma &#39;912 and Anderson &#39;471. Only one EAC jaw  65  may be required if the coefficient of friction between the EAC jaw  65  and the upright  13  and the horizontal force exerted on said upright  13  by said jaw  65 , in combination, are sufficient to support the load. This would be the situation for a clamp in the bracket assembly of Anderson &#39;471, where the horizontal force on the outer jaw is much greater than that on the inner jaw. 
   Referring now to  FIGS. 2 and 3 , outer EAC jaw  65  is an elongated member which may be rectangular in the lateral cross-section. Outer EAC jaw  65  comprises a surface  73  that contacts outer, circular cylindrical surface  14 - 2  of upright  13  on an extended area of height, Ho. Similarly inner EAC jaw  63  contacts inner circular cylindrical surface  14 - 1  on an extended area of height, Hi. Axis space, Di, is defined as the distance from inner jaw pivot axis  67   a  to inner jaw contact surface  71 . Axis space Do is defined similarly for pivot axis  69   a  and outer jaw contact surface  73 . 
   Inner and outer EAC jaws  63 ,  65  comprise longitudinal holes (not shown) running throughout their length in which crossbars are fixed, whose terminals,  67  and  69  project through vertically elongated apertures  11 ,  12 . Said jaws  63 ,  65  and said apertures  11 ,  12  are dimensioned so that said jaws  63 ,  65  may, independently, slide horizontally and twist vertically with respect to side members  39  of clamp  18 . 
   Since inner EAC jaw  63  and outer EAC jaw  65  pivot independently with respect to side members  39  about respective pivot axes  67   a  and  69   a  and may move laterally as well as twist vertically within said side members and since side members  39  pivot about fulcrum pivot axis  60   a , inner EAC jaw  63  and outer EAC jaw  65  will, when angle bracket  15  is loaded, contact circular, cylindrical shaped inner surface  14 - 1  and circular, cylindrical shaped outer surface  14 - 2 , respectively, of upright  13  on extended areas. Thus, if the horizontal forces which jaws  63  and  65  exert on upright  13 , when angle bracket  15  is loaded, provide sufficient, vertical force, which depends only on the friction between said jaws and said upright, to support bracket assembly  7 , they can be distributed over sufficient area of upright  13 , to prevent damage to said upright. 
   Providing this extended area of contact between said jaws and said upright is a principal object of the present invention. As can be appreciated, the edged jaws of prior art locks would contact a metal or plastic upright on a one-dimensional line and not on a two-dimensional area. 
   It should be noted that any configuration which permits EAC jaws  63 ,  65  to pivot independently about their respective pivot axes  67   a ,  69   a  in side members  39  and contact upright  13  over an extended area would be in the spirit of the present invention. 
     FIG. 2  shows a side view of load activated clamp  18  mounted on upright  13 . It should be noted that load activated clamp  18  and upright  13  are dimensioned so that outer jaw pivot axis  69   a  lies below a horizontal plane passing through fulcrum pivot axis  60   a . The minimum width of the upright, in combination with the bracket assembly, which satisfies this condition will be referred to as the design width. In addition, clamp  18  is dimensioned so that inner jaw pivot axis  67   a  lies below the plane containing fulcrum pivot axis  60   a  and outer jaw pivot axis  69   a  and accordingly is load activated. 
   As shown in  FIG. 3 , when load activated clamp  18  is rotated clockwise, the horizontal distance between inner jaw pivot axis  67   a  and outer jaw pivot axis  69   a  increases. As a result, as load activated clamp  18  is rotated clockwise, the horizontal force on the fulcrum axis  60   a  resulting from a vertical load on the angle bracket  15  moves contact surface  71  of inner jaw  63  so that said contact surface no longer contacts inner surface  14 - 1  of upright  13  over an extended area. In fact, there may be no contact. It is also clear that the ratio between Hi, and Di, must be large enough so that the upper and lower edges of inner EAC jaw  63 , even if provided with radii  81 ,  83 , as shown in  FIGS. 2 and 3 , do not gall or mar inner surface  14 - 1  of said upright  13  or even jam and prevent the desired up or down movement of the bracket assembly on the upright  13 . Clearly then, an extended area of contact between inner EAC jaw  63  and inner surface  14 - 1  of said upright  13  serves two essential purposes in minimizing damage to said upright  13 . 
     FIG. 4  helps illustrate the defined “pivot means” and illustrates how the pivot axes of  FIGS. 2 and 3  are not essential to this invention. In  FIG. 4 , crossbar  69  passing through outer jaw  65  is replaced by two cross bars  69   a  and  69   b , passing through longitudinal holes (not shown) in said jaw  65 , projecting through two arcuate slots  70   a  and  70   b . If said arcuate slots have a common center, this center then serves as the pivot axis of outer jaw  65 . Outer jaw  65  pivots with respect to side members  39  without the existence of a pivot member, i.e., without a fixed pivot means. The inner jaw  63  includes cross bar  93  having pins, projecting through circular openings  68 , on each end of the rectangular section  98  whose planar surface  94  contacts the wider base of the rectangular groove  95 , in the EAC jaw  63 . A groove centrally located in the base of rectangular groove  95  is dimensioned so that a circular pin  96  on the center of planar surface  94  permits inner jaw  63  to twist and slide relative to cross bar  93 . Strap  50  in  FIG. 4  pivotally connects load activated lock  18  to an angle bracket (not shown) by means of cross bar  55  and fulcrum bar  60  with no defined pivot axis. 
     FIG. 5  illustrates the important role that the inner and outer walls,  14 - 1  and  14 - 2 , of tubular upright  13  in combination with the EAC jaws of inner and outer EAC jaws  63 ,  65  play in this invention when cross bars,  64  and  66  are mounted in side members so that said jaws  63 ,  65  may pivot, slide and twist independently therein as shown in  FIG. 4  and described above. If cross bars  64 ,  66  are neither precisely parallel nor exactly coplanar, the contacting, circular, cylindrical surface of outer wall  14 - 2  will contact the circular, cylindrical surface of outer EAC jaw  65  over a extended area if and only if the axes of the two contacting, circular, cylindrical surfaces coincide. This is made possible by allowing the axis of the contacting, circular, cylindrical surface of outer EAC jaw  65  to slide laterally with respect to side members  39 , twist about an axis perpendicular to the upright  13 , and pivot about pivot axis  69   a  when clasp  18  rotates about pivot axis  60   a  into the clamped position. Then the circular, cylindrical surface of outer EAC jaw  65  will contact the circular, cylindrical surface of outer wall  14 - 2  on an extended area. The same situation holds for inner EAC jaw  63 . 
   The sidewalls  13 - 1 ,  13 - 2  which support the inner and outer surfaces  14 - 1 ,  14 - 2  of upright  13  are not features of this invention. If the circular, cylindrical surfaces of the inner and outer walls were equally dimensioned and properly supported by sidewalls having the same outer circular cylindrical surfaces, the outer surface of the upright could be that of a circular cylinder. 
     FIG. 6  shows another misalignment, of the many possible, between upright  13  and EAC jaws  63  and  65  of clamp  18 . In this case, the contacting surface of EAC jaw  65  and the contacting surface of outer wall  14 - 2  of upright  13  are portions of a plane whose perpendicular is not parallel to side walls  13 - 1  and  13 - 2  of upright  13 . If outer EAC jaw  65  rotates about pivot axis  69   a  and rotates about an axis parallel to that of the upright  13 , both independently, a horizontal force on the clamp will bring EAC jaw  65  into contact with outer wall  14 - 2  on the portion of a plane of extended area. In  FIG. 6 , it is the rotation of upright  13  with respect to clamp  39  together with the pivoting of outer EAC jaw  65  which assures that the contact between the structures will cover an extended area. Rotating the upright does not effect the extent of the area of contact of EAC jaw  63  with the inner surface  14 - 1  of upright  13 . Its three degrees of freedom, pivoting, sliding and twisting, permit the circular, cylindrical surface of EAC jaw  63  to contact the circular, cylindrical, inner surface  14 - 1  of said upright  13  on an extended area when clamp  18  is clamped on the upright  13 . 
     FIG. 7  shows EAC jaw  63  mounted so as to pivot about pivot axis  73   a  in frame  71 , which, in turn, is mounted so as to pivot about pivot axis  67   a  in the side members  39  of clamp  18 . Since EAC jaw  63  pivots independently about vertical pivot axis  73   a  and pivots independently about horizontal pivot axis  67   a , it will contact inner surface  14 - 1  of upright  13  on an extended area when clamp  18  is clamped on said upright  13  if both of the contacting surfaces are sections of planes. 
   Although  FIGS. 1-7  and their detailed description show that EAC jaws, with either cylindrical or planar contacting surfaces, when suitably mounted in the clamp of a bracket assembly of an adjustable height scaffold will contact the matching upright on an extended area, it is not clear that the resulting friction between the jaws of the clamp and the upright will support a loaded angle bracket in the situation of greatest interest namely, steel jaws on an aluminum upright. 
     FIG. 8  shows a horizontal force H and a vertical force V acting on the fulcrum pivot axis  60   a  of load activated clamp  18 . The inwardly directed, horizontal force applied onto inner jaw pivot axis  67   a  is denoted by arrow I, and the upwardly directed, frictional force applied onto inner jaw pivot axis  67   a  is denoted by arrow μI. The outwardly directed, horizontal force applied onto outer jaw pivot axis  69   a  is denoted by arrow, O and the upwardly directed frictional force applied onto outer jaw pivot axis  69   a  is denoted by μO, wherein μ represents the minimum coefficient of friction between jaws  63  and  65  and upright  13  which will prevent slipping of clamp  18 . Distances, A and B represent the horizontal and vertical distances, respectively, between fulcrum pivot axis  60   a  and inner jaw pivot axis  67   a . Distances X and Y represent the horizontal and vertical distances, respectively, between the outer jaw pivot axis  69   a  and the inner jaw—pivot axis  67   a.    
   Accordingly, the horizontal forces represented by arrows I and 0 and the minimum value of μ can be found from the following equations, given the values of H, V:
 
 O=I+H  because the horizontal forces add to zero,  Equation 1
 
and
 
 V =μ×( O+I ) because the vertical forces add to zero.  Equation 2
 
μ= V /( O+I )=( O×Y−V×A−H×B )/( O×X ) because the moment about the pivot axis  67   a  is zero.  Equation 3
 
or
 
 V× 0× X =(2×0− H ) x (0× Y−V×A−H×B )  Equation 4
 
   Given the values of V, H, A, B, X and Y, the value of 0 can be found from quadratic equation (4). The value of I can be determined from (1) and then p, the minimum value of the coefficient of friction which will prevent slipping, can be found from (2). 
   In an experimental model, built to confirm these calculations, X=4.0″, Y=1.15″, A=1.65″ and B=1.15″. For V=1001b and H=501b, it was found by these equations that 0=379.651b, I=329.651b and μ=0.141. As can be appreciated, a bracket assembly with a load activated clamp having stainless steel, EAC jaws can be used on aluminum uprights with a safety factor of 2, since the coefficient of friction of stainless steel on aluminum has value approximating 0.3. The need for the EAC jaws to minimize the damage to an aluminum upright is clear from the fact that a  5001   b  vertical load placed on the horizontal leg of the bracket assembly at a location so that H=2501b will result in an inward force onto the outer wall, of the upright which approximates one ton. As can be appreciated, subjected to these large forces, the edged jaws of prior art locks will significantly damage an aluminum or plastic upright. 
   A model built to these dimensions supported the load even when the aluminum upright was greased. Of course, the safety factor can be increased by lining the inner surface of the EAC jaws with material having a high coefficient of friction: brake lining for example. 
   By using EAC jaws, mounted in the side members with sufficient freedom of motion, instead of edged jaws, the horizontal forces, which the jaws exert on the upright, can be distributed over a sufficiently large area so that the upright suffers minimum damage from a loaded angle bracket. 
   Although a primary application for the use of EAC jaws, in the clamps of bracket assemblies depends on friction between the jaws of the clamps and the uprights to support the load, the same clamp will support a load, with little or no friction, if the distance between the inner and outer surfaces of the upright diminishes with height. 
   Although the clamp must pivot with respect to the angle bracket and each EAC jaw must pivot with respect to the at least one side member if the load supporting bracket assembly is to be adjusted, in height on an upright, safely, it may not be needed that the contacting surface of an EAC jaw have a circular cross section and be slidably and twistably mounted on said side member if the parts involved are fabricated with sufficient accuracy. The accuracy required will be less if the contacting material of an EAC jaw is pliable, brake lining, for example. 
   As mentioned above, the present invention is not intended to be limited to a system or method which must satisfy one or more of any stated or implied object or feature of the invention and should not be limited to the preferred, exemplary, or primary embodiment(s) described herein. The foregoing description of preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiment were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as is suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled and their legal equivalents.