Abstract:
A locking hinge apparatus includes first and second hinge members coupled together for rotation about an axis, a lock movable between a locking position in which the first and second hinge members are prevented from rotating about the axis and a releasing position in which the first and second hinge members are permitted to rotate about the axis, and a knob rotatable about the axis and movable along the axis. The lock moves from the locking position to the releasing position in response to movement of the knob axially toward the first and second hinge members and then rotation of the knob about the axis.

Description:
[0001]    This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application Ser. No. 60/467,220, filed May 1, 2003, which is expressly incorporated by reference herein. 
     
    
     
       BACKGROUND  
         [0002]    The present disclosure relates to a center-folding ladder, and more particularly to a hinge and locking assembly for a center-folding ladder.  
           [0003]    Ladders are commonly used for a variety of applications and are of two general types. One type is a center-folding ladder, commonly called a step ladder, which is self-supporting. Step ladders are typically used for such tasks as pruning, painting ceilings, or other similar tasks where it is difficult or inconvenient to lean the ladder against a structure, such as a wall, for support. The other type of ladder is the straight extension ladder. This type of ladder is simply leaned against the wall or some other structure when standing or climbing on the ladder.  
           [0004]    Ladders which are constructed so that they may be used as both step ladders and as straight extension ladders have been known in the art. Such ladders, commonly referred to as combination step and extension ladders, are very versatile and they combine the desirable features of both types of ladders. Such combination ladders typically include a hinge and locking assembly at each end. The hinge and locking assemblies permit the ladder to be folded into and locked in a step ladder configuration or unfolded into and locked in a straight extension ladder configuration. Examples of combination ladders are U.S. Pat. Nos. 3,912,043; 4,566,150; and 4,770,559 which are incorporated herein by reference.  
         SUMMARY  
         [0005]    One or more of the following features or elements or combinations thereof may be incorporated into a hinge and a locking assembly.  
           [0006]    A hinge and locking assembly is provided. Such an assembly may be used, for example, to couple sections of a center-folding ladder. It will be appreciated that such an assembly may have various uses. Such a hinge and locking assembly permits the ladder to be folded into and locked in a step ladder configuration or unfolded into and locked in an extension ladder configuration. The hinge and locking assembly does not lock the ladder as the ladder passes through the step ladder configuration during movement of the ladder from the extension ladder configuration to the collapsed configuration.  
           [0007]    The assembly comprises a pair of support plates, a locking bar and a lifting cam. The support plates are rotatable relative to each other about a common axis. Each plate has at least one locking slot. The locking bar has at least one locking tab configured to engage the locking slots in the support plates to block relative movement of the support plates relative to each other. The lifting cam is configured to move the locking bar relative to the support plates to selectively disengage the locking tab from the locking slots in the support plates to permit relative movement of the support plates relative to each other.  
           [0008]    The assembly includes a drive shaft rotatable about the common axis and the lifting cam is coupled to drive shaft for rotation therewith. The locking bar is coupled to the drive shaft for axial movement relative to the support plates. The locking bar has a pair of axially-extending locking tabs which are spaced at equal radial distances from the common axis on the opposite sides thereof along a line that extends through the common axis.  
           [0009]    A first one of the support plates has a pair of locking slots. The locking slots may be axially extending. The locking slots may be radially extending. The locking slots may be peripherally or circumferentially-spaced. The locking slots may be spaced at equal radial distances from the common axis on the opposite sides of the common axis along a line that extends through the common axis. Each locking slot may be circular, rectangular, square, or any other suitable shape.  
           [0010]    A second one of the support plates has a first pair of locking slots so that the locking tabs of the locking bar can extend through the pair of locking slots in the first support plate and the first pair of locking slots in the second support plate in a first configuration of the support plates. The first pair of locking slots may be axially extending. The first pair of locking slots may be radially extending. The first pair of locking slots may be peripherally or circumferentially-spaced. The first pair of locking slots may be spaced at equal radial distances from the common axis on the opposite sides of the common axis along a line that extends through the common axis. Each of the first pair of locking slots may be circular, rectangular, square, or any other suitable shape.  
           [0011]    The second support plate has a second pair of locking slots so that the locking tabs of the locking bar can extend through the pair of locking slots in the first support plate and the second pair of locking slots in the second support plate in a second configuration of the support plates. The second pair of locking slots may be axially extending. The second pair of locking slots may be radially extending. The second pair of locking slots may be peripherally or circumferentially-spaced. The second pair of locking slots may be spaced at equal radial distances from the common axis on the opposite sides of the common axis along a line that extends through the common axis. Each of the second pair of locking slots may be circular, rectangular, square, or any other suitable shape.  
           [0012]    The first and second pairs of axially-extending locking slots in the second support plate are arranged to form an acute angle relative to each other. The assembly includes a spring for biasing the locking bar toward the support plates so that the locking tabs extend through the locking slots in the support plates to block relative movement of the support plates relative to each other.  
           [0013]    Features of the present disclosure will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode of carrying out the disclosure as presently perceived. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The detailed description particularly refers to the accompanying figures in which:  
         [0015]    [0015]FIG. 1 is a perspective view of a center-folding ladder having at each end a pair of legs coupled together by a hinge and locking assembly in accordance with this disclosure which permit the ladder to be folded into and locked in a step ladder configuration or unfolded into and locked in a straight extension ladder configuration,  
         [0016]    [0016]FIGS. 2-4 are end views showing the ladder moving from a collapsed configuration in FIG. 2 (also referred to as a 0° configuration), to a step ladder configuration in FIG. 3 (also referred to as a folded or 40° configuration) and then to a straight extension ladder configuration in FIG. 4 (also referred to as a fully open or 180° configuration),  
         [0017]    [0017]FIGS. 5-7 are end views similar to FIGS. 2-4 showing the ladder moving from the extension ladder configuration in FIG. 5 to the collapsed configuration in FIG. 7 through an intermediate configuration in FIG. 6,  
         [0018]    [0018]FIG. 8 is an exploded perspective view of various components that can be assembled to produce the hinge and locking assembly in accordance with this disclosure, and showing, from left to right, front outer covers, locking bar support pin, locking bar, snap spring, knob support pin, drive shaft (also referred to as cam drive shaft), tri-lobe lifting cam, front support plate, rear support plate, locking plate, detent plate (also referred to as unidirectional spring), spring clip, knob spring, winged hex drive, lock washer, rear outer covers, and knob,  
         [0019]    [0019]FIG. 9 is a sectional view of the hinge and locking assembly in the collapsed configuration of the ladder in FIG. 2 (and corresponding to a line  9 - 9  in FIG. 8), and showing the locking bar moved to a lowered locked position (also referred to as advanced locked position) and further showing the knob in a released position, where the tabs of the locking bar pass through a pair of aligned tab-receiving slots in each of the front and rear support plates to lock the ladder in the collapsed configuration,  
         [0020]    [0020]FIG. 10 is a sectional view similar to FIG. 9 showing the knob pushed inward to cause the winged hex drive to engage the cam drive shaft,  
         [0021]    [0021]FIG. 11 is a sectional view similar to FIG. 10 showing the knob pushed inward and rotated 60° (corresponding to the dotted position of the knob in FIG. 2) to cause the lifting cam to move the locking bar to a raised unlocked position (also referred to as retracted unlocked position), where the tabs of the locking bar are retracted from the tab-receiving slots in the rear support plate to allow the ladder to move to either the step ladder configuration shown in FIG. 3 or the extension ladder configuration in FIG. 4,  
         [0022]    [0022]FIG. 12 is a sectional view similar to FIG. 11 showing the knob in the released position causing the winged hex drive to disengage from the drive shaft and showing the ladder moved to the 120° configuration in FIG. 6, where the locking bar is off the lobes of the lifting cam and the tabs of the locking bar ride on the front surface of the rear support plate,  
         [0023]    [0023]FIGS. 13-15 show the relative positions of the locking bar and the lifting cam as the ladder moves from the collapsed configuration to the step ladder configuration,  
         [0024]    [0024]FIGS. 16 and 17 show the relative positions of the locking bar and the lifting cam as the ladder moves back from the step ladder configuration to the collapsed configuration,  
         [0025]    [0025]FIGS. 18-20 show the relative positions of the locking bar and the lifting cam as the ladder moves from the step ladder configuration to the straight extension ladder configuration,  
         [0026]    [0026]FIGS. 21-23 show the relative positions of the locking bar and the lifting cam as the ladder moves back from the straight extension ladder configuration to the collapsed configuration,  
         [0027]    [0027]FIG. 24 is a perspective view of the locking bar,  
         [0028]    [0028]FIG. 25 is a perspective view of the drive hub,  
         [0029]    [0029]FIG. 26 is an end view of the drive hub viewing from the end of the assembly opposite from the locking bar,  
         [0030]    [0030]FIG. 27 is a sectional view of the drive hub along a line  27 - 27  in FIG. 26,  
         [0031]    [0031]FIG. 28 is a perspective view of the lifting cam,  
         [0032]    [0032]FIG. 29 is a perspective view of the locking bar support pin,  
         [0033]    [0033]FIG. 30 is a perspective view of the knob support pin,  
         [0034]    [0034]FIG. 31 is a perspective view of the U-shaped snap spring,  
         [0035]    [0035]FIG. 32 is a side view of the snap spring,  
         [0036]    [0036]FIG. 33 is a perspective view of the locking plate,  
         [0037]    [0037]FIG. 34 is a side view of the locking plate,  
         [0038]    [0038]FIG. 35 is a perspective view of the detent plate,  
         [0039]    [0039]FIG. 36 is an elevational view of the detent plate,  
         [0040]    [0040]FIG. 37 is a perspective view of the knob,  
         [0041]    [0041]FIG. 38 is a side view of the knob, and  
         [0042]    [0042]FIG. 39 is an elevational view of the rear support plate. 
     
    
     DETAILED DESCRIPTION  
       [0043]    A perspective view of a center-folding ladder  20  having at each end a pair of legs  22  coupled together by a hinge and locking assembly  30  is shown in FIG. 1. The hinge and locking assembly  30  at each end permits the ladder  20  to be folded into and locked in a step ladder configuration shown in FIG. 3 or unfolded into and locked in an extension ladder configuration as shown in FIG. 4. To move the ladder  20  from the collapsed configuration in FIG. 2 to the step ladder configuration shown in FIG. 3, each knob  68  is pushed inward and rotated 60° clockwise (identified by numeral  290  in FIG. 2) to unlatch the hinge and locking assemblies  30  and the legs  22  are then spread apart. The rotated position of the knob  68  is shown by the dotted lines in FIG. 2. When the legs  22  move to the step ladder configuration shown in FIG. 3, the hinge and locking assemblies  30  automatically latch to securely lock the legs  22  in the step ladder configuration.  
         [0044]    To move the ladder  20  from the step ladder configuration in FIG. 3 to the extension ladder configuration shown in FIG. 4, each knob  68  is again pushed inward and rotated 60° clockwise (identified by numeral  292  in FIG. 3) to unlatch the hinge and locking assemblies  30  and the legs  22  are then moved to the fully open position. The rotated position of the knob  68  is shown by the dotted lines in FIG. 3. When the legs  22  move to the extension ladder configuration shown in FIG. 4, the hinge and locking assemblies  30  automatically latch to securely lock the legs  22  in the extension ladder configuration.  
         [0045]    To move the ladder  20  from the extension ladder configuration in FIG. 5 to the collapsed configuration shown in FIG. 7, each knob  68  is again pushed inward and rotated 60° clockwise (identified by numeral  294  in FIG. 5) to unlatch the hinge and locking assemblies  30  and the legs  22  are brought together as shown in FIGS. 6 and 7. The rotated position of the knob  68  is shown by the dotted lines in FIG. 5, and the direction of rotation is shown therein by numeral  296 . When the legs  22  move to the collapsed configuration shown in FIG. 7, the hinge and locking assemblies  30  automatically latch to lock the legs  22  securely in the collapsed configuration. The hinge and locking assemblies  30  do not lock the ladder as the ladder  20  passes through the step ladder configuration during movement of the ladder  20  from the extension ladder configuration in FIG. 5 to the collapsed configuration in FIG. 7.  
         [0046]    As shown in FIG. 8, each hinge and locking assembly  30  includes, from left to right, front outer covers  32 ,  34 , a locking bar support pin  36 , a locking bar  38 , a U-shaped snap spring  40  (also referred to as the formed spring), a knob support pin  42 , a drive shaft  44  (also referred to as the cam shaft), a tri-lobe lifting cam  46 , a front support plate  48 , a rear support plate  50 , a locking plate  52 , a detent plate  54 , a spring clip  56 , a knob spring  58 , a winged hex drive  60 , a lock washer  62 , rear outer covers  64 ,  66 , and a lock release knob  68 . In this disclosure, the terms “front”, “raised”, “advanced”, “upward”, “forward” and “head end” all mean toward the end  24  of the assembly  30  having the locking bar  38  and the lifting cam  46 . On the other hand, the terms “back”, “lowered”, “retracted”, “backward”, “downward”, “rear” and “foot end” mean toward the end  26  of the assembly  30  opposite from the locking bar  38  and the lifting cam  46 . Unless specified otherwise, all rotational directions (clockwise or anticlockwise) are referenced from the end  26  of the assembly  30  having the knob  68 . Also, the terms “slot”, “hole”, “opening”, “aperture”, etc. are synonymous in this disclosure.  
         [0047]    Referring to FIG. 39, each support plate  48 ,  50  includes an annular head portion  70  and a leg-engaging portion  72 . The leg-engaging portion  72  may be so oriented with respect to the annular head portion  70  that the outer edge of the leg-engaging portion  72  extends generally tangentially from the annular head portion  70  as shown in FIG. 39. The leg-engaging portions  72  are secured to the respective legs  22  of the ladder  20  by suitable fasteners, such as screws or nuts and bolts. Although each support plate  48 ,  50  comprises a single plate in the illustrative embodiment shown, each support plate  48 ,  50  may very well be made of a plurality of individual plates (for example, 2 or 4) which are joined together as a unit by suitable fasteners.  
         [0048]    The two support plates  48 ,  50  are identical with one exception which is explained below. Each support plate  48 ,  50  has a bore  74  at the center of the annular portion  70  for rotatably receiving the cam drive shaft  44 . The front support plate  48  has one set of locking tab-receiving slots  76 . The rear support plate  50 , on the other hand, has 2 sets of locking tab-receiving slots  78 ,  80  which are 40° apart as shown in FIG. 39. The tab-receiving slots  76 ,  78 ,  80  are spaced at equal radial distances from a longitudinal axis  82  (shown in FIG. 8, and sometimes referred to as the common axis) of the assembly  30  on the opposite sides of the central bore  74  along a line that extends through the longitudinal axis  82 .  
         [0049]    Although the front support plate  48  has one set of locking tab-receiving slots  76  in the illustrative embodiment, the front support plate may very well have two sets of locking tab-receiving slots. Also, although the two sets of tab-receiving slots  78 ,  80  in the rear support plate  50  are 40° apart in the illustrative embodiment, they may very well be arranged to lie at a different angle with respect to each other, for example 35° or 60°. Each support plate  48 ,  50  has a positioning tab-receiving hole  84 , and a plurality of apertures  86  for rigidly securing the hinge assembly  30  to the legs  22  of the ladder  20 .  
         [0050]    As shown in FIG. 24, the locking bar  38  includes a dome-shaped annular portion  100  having a central bore  102  sized to permit slidable movement of the locking bar support pin  36  and a pair of straight portions  104 ,  106  which extends generally outwardly from the annular portion  100  on the opposite sides thereof. The terminal portion of each straight portion  104 ,  106  is formed to include a downwardly-extending locking tab  108 ,  110  which extends perpendicularly from the plane of the lifting bar  38  as shown. The locking bar  38  includes a truncated pie-shaped portion  112  on one side thereof and tab  114  on the other side thereof as shown.  
         [0051]    The locking tabs  108 ,  110  are spaced at equal radial distances from the longitudinal axis  82  (see FIG. 8) of the assembly  30  on the opposite sides of the central bore  102  along a line that extends through the longitudinal axis  82 . As shown in FIG. 24, the straight portions  104 ,  106  extend in a direction that is generally parallel to the line extending through the downwardly-extending locking tabs  108 ,  110 . The locking tabs  108 ,  110  are configured to be received in the tab-receiving slots  76  in the front support plate  48  and the tab-receiving slots  78  in the rear support plate  50  when the ladder  20  is either in the collapsed or 0° configuration shown in FIG. 2 or in the extension ladder or 180° configuration shown in FIG. 4. On the other hand, the locking tabs  108 ,  110  are configured to be received in the tab-receiving slots  76  in the front support plate  48  and the tab-receiving slots  80  in the rear support plate  50  when the ladder  20  is in the step ladder configuration shown in FIG. 3.  
         [0052]    Thus, the locking tabs  108 ,  110  are configured to always extend through the tab-receiving slots  76  in the front support plate  48 . However, the locking tabs  108 ,  110  are configured to extend through the first set of tab-receiving slots  78  in the rear support plate  50  when the ladder  20  is either in the collapsed or 0° configuration shown in FIG. 2 or in the extension ladder or 180° configuration shown in FIG. 4. On the other hand, the locking tabs  108 ,  110  are configured to extend through the second set of tab-receiving slots  80  in the rear support plate  50  when the ladder  20  is in the step ladder configuration shown in FIG. 3.  
         [0053]    Referring to FIGS. 25-27, the drive shaft  44  includes a head portion  120 , a longitudinally-extending cylindrical body portion  122  and an annular portion  124 . The drive shaft  44  includes a first longitudinally-extending bore  126  that extends through the head and body portions  120 ,  122  and a second longitudinally-extending counterbore  128  that extends through the annular portion  124 . The first bore  126  is sized to permit slidable movement of the locking bar support pin  36 . The second counterbore  128  is sized to permit slidable movement of the knob support pin  42 . The first and second bores  126 ,  128  intersect at a shoulder or seat portion  130 . The outer surface of the body portion  122  includes a double-D portion  132  having a locking groove  134  formed therein to receive the spring clip  56  and a hex drive portion  136 .  
         [0054]    As shown in FIG. 28, the lifting cam  46  includes an annular portion  140  having a double-D bore  142  at the center of the annular portion  140  for receiving the double-D portion  132  of the drive shaft  44  so that the drive shaft  44  and the lifting cam  46  are rotatably coupled to each other. The lifting cam  46  includes three upwardly-extending lobes  144  which extend perpendicularly from the plane of the lifting cam  46  and which are spaced 120° apart as shown. Each lobe  144  a leading inclined portion  146 , a trailing perpendicular portion  148 , and a raised locking bar-supporting portion  150  arranged to interconnect the inclined portion  146  with the perpendicular portion  148 .  
         [0055]    Referring to FIG. 29, the locking bar support pin  36  includes a head portion  160  and a longitudinally-extending body portion  162  having a raised portion  164  where the head and body portions  160 ,  162  meet. The raised portion  164  of the locking bar support pin  36  provides an interference fit with the bore  102  in the locking bar  38  to secure the locking bar support pin  36  to the locking bar  38 . Although the locking tabs  108 ,  110  always remain extended into the slots  76  in the front support plate  48  as shown, for example, in FIG. 11, the locking bar support pin  36  provides additional stabilization to the locking bar  38  as the locking bar  38  is lifted and lowered by the lifting cam  46 . As shown in FIG. 30, the knob support pin  36  includes a head portion  170  and a longitudinally-extending body portion  172  having a locking groove  174  adapted to receive the lock washer  62 .  
         [0056]    Referring to FIGS. 31 and 32, the snap spring  40  a first arm portion  180  and a second arm portion  182 , and a mid-section  184  interconnecting the first and second arm portions  180 ,  182  and including an outwardly-extending positioning tab  186 . The positioning tab  186  is received in the positioning hole  84  in the front support plate  48  to maintain the orientation of the snap spring  40  relative to the front support plate  50  during operation of the locking mechanism. The first portion  180  includes an inverted dome-shaped portion  188  adapted to press the locking bar  38  against the lifting cam  46 . The second portion  182  includes a cutout  190  configured to receive the drive shaft  44 .  
         [0057]    Locking plate  52  is mounted on the rear support plate  50  as shown in FIGS. 33 and 34, and detent plate  54  is mounted on the drive shaft  44  for rotation therewith as shown in FIG. 35. The locking plate  52  and the detent plate  54  cooperate to allow only clockwise rotation of the drive shaft  44  and the lifting cam  46  coupled thereto. Again as indicated above, unless specified otherwise, all rotational directions (clockwise or anticlockwise) are referenced from the end  26  of the assembly  30  having the knob  68 . The locking plate  52  and the detent plate  54  also serve to provide an auditory and tactile feedback to the user every time the drive shaft  44  is rotated 60° in the clockwise direction.  
         [0058]    As shown in FIGS. 33 and 34, the locking plate  52  includes an annular portion  200  having a central bore  202  configured to rotatably receive the drive shaft  44  and six segments  204  which extend radially outwardly from the annular portion  200 . The drive shaft  44  is freely rotatable in the bore  202 . The six segments  204  are separated by six cutouts  206 . Each of the six segments and six cutouts  204 ,  206  forms a 30° angle at the center of the annular portion  200 . One of the segments  204  extends radially outwardly and is formed to include a positioning tab  208  at one end thereof which extends perpendicularly from the plane of the locking plate  52  as shown. The positioning tab  208  is received in the positioning hole  84  in the rear support plate  50  to maintain the orientation of the locking plate  52  relative to the rear support plate  50 . Each segment  204  has a leading edge  210  and a trailing edge  212 . The leading edge  210  of each segment is slightly depressed below the plane of the locking plate  52  and the trailing edge  212  is slightly raised above the plane of the locking plate  52  to facilitate clockwise rotation of the drive shaft  44  and to block anticlockwise rotation of the drive shaft  44 .  
         [0059]    Referring to FIGS. 35 and 36, the detent plate  54  has a double-D bore  220  at the center for receiving the double-D portion  132  of the drive shaft  44  so that the drive shaft  44  and the detent plate  54  are rotatably coupled to each other. The detent plate  54  further includes three peripheral arcuate segment  222 . The terminal portion of each segment  222  is formed to include a generally V-shaped detent or catch  224  which has a portion extending below the plane of the detent plate  54 . Each V-shaped detent  224  has an inclined leading edge  226  and a trailing edge  228  arranged to lie perpendicular to the plane of the detent plate  54 . The three perpendicular trailing edges  228  are spaced 120° apart as shown. When the drive shaft  44  is rotated clockwise, the inclined leading edges  226  of the detent plate  54  ride up the depressed leading edges  210  of the locking plate  52  to allow clockwise rotation of the drive shaft  44 . On the other hand, the perpendicular trailing edges  228  of the detent plate  54  are blocked by the raised trailing edges  212  of the locking plate  52  to prevent anticlockwise rotation of the drive shaft  44 .  
         [0060]    The assembly of various components will now be explained with reference to FIGS. 8-12. The drive shaft  44  is inserted into the bore  142  of the lifting cam  46  so that the head portion  120  of the drive shaft  44  engages the annular portion  140  of the lifting cam  46  and the double-D portion  132  of the drive shaft  44  engages the double-D bore  142  in the lifting cam  46  as shown, for example, in FIG. 9. The knob support pin  42  is inserted into the counterbore  128  of the drive shaft  44  so that the head portion  170  of the knob support pin  42  engages the annular seat portion  130  of the drive shaft  44 . The locking bar support pin  36  is inserted through the central bore  102  in the locking bar  38 , and then inserted into the bore  126  in the drive shaft  44 . The snap spring  40  is then installed so that the first and second arm portions  180 ,  182  of the snap spring  40  straddle the locking bar  38  and the lifting cam  46 , and the drive shaft  44  is received in the U-shaped cutout  190  in the snap spring  40  as shown, for example, in FIG. 9. The positioning tab  186  of the snap spring  40  engages the positioning hole  84  in the front support plate  48  to maintain the orientation of the snap spring  40  relative to the front support plate  48  during operation of the locking assembly. The snap spring  40  biases the locking bar  38  against the lifting cam  46 . The snap spring  40  also serves to retain the locking assembly comprising the locking bar  38 , lifting cam  46  and the two support pins  36 ,  42  together as a unit. The snap spring  40  is relatively stiff in order to ensure that the locking tabs  108 ,  110  snap into the locking slots  78  or  80  in the rear support plate  50  (depending on whether the ladder  20  is in the 0° or 180° configuration or in the 40° configuration) when they are aligned with the locking slots  76  in the front support plate  48 . The lifting cam  46  is designed to rotate only in the clockwise direction to alternately raise and lower the locking bar  38  with each 60° rotation of the lifting cam  46  in the clockwise direction.  
         [0061]    The drive shaft  44  is then passed through the central bores  74  in the support plates  48 ,  50  so that the rearwardly facing surface of the lifting cam  46  seats against the forwardly-facing surface of the front support plate  48  and the rearwardly-facing surface of the front support plate  48  seats against the forwardly-facing surface of the rear support plate  50  as shown in FIGS. 9-12. The locking plate  52  is installed so that the drive shaft  44  extends through the central bore  202  in the locking plate  52  and the positioning tab  208  of the locking plate  52  engages the positioning hole  84  in the rear support plate  50  to maintain the orientation of the locking plate  52  relative to the rear support plate  50  during operation of the locking assembly. The drive shaft  44  is then inserted through the double-D bore  220  in the detent plate  54  so that the double-D portion  132  of the drive shaft  44  engages the double-D bore  220  in the detent plate  54  to rotatably couple the detent plate  54  to the drive shaft  44 . The spring clip  56  is then installed in the locking groove  136  in the drive shaft  44  to retain the assembly together as a unit.  
         [0062]    The drive shaft  44  is then passed through the knob spring  58  and the winged hex drive  60  so that the knob support pin  42 , which is inserted through the counterbore  128  in the drive shaft  44  and seated against the annular seat portion  130  in the drive shaft  44 , extends through the knob spring  58  and the winged hex drive  60 . The lock washer  62  is inserted in the locking groove  174  in the knob support pin  42 . The knob  68  is then installed so that the tabs  240  of the hex drive  60  and the lock washer  62  are received in the tab-receiving slot  250  in the knob  68  (see FIGS. 37, 38) to attach the knob  68  to the drive shaft  44  securely. The front and rear outer covers  32 ,  34 ,  64 ,  66  are then installed. The outer covers  32 ,  34 ,  64 ,  66  serve to provide a rotational stop to prevent rotation of the legs  22  beyond the 180° or extension ladder configuration; to shield the assembly  30  from dirt and debris; and to prevent foreign objects from being inadvertently inserted therein.  
         [0063]    As indicated previously, the knob  68  must be first pushed inward against the knob spring  58  in a direction  298  in FIG. 10 to cause the hex drive  60  to engage the hex drive portion  136  of the drive shaft  44  before the knob  68  can be rotated in a clockwise direction  300  to, in turn, rotate the drive shaft  44  and the lifting cam  46  also in the clockwise direction  300  to lift the locking bar  38  away from the support plates  48 ,  50 . The knob spring  58  is relatively weak to reduce the force required to push the knob  68  inward to engage the hex drive portion  136  of the drive shaft  44 . FIGS. 9-11 show the sequence of pushing the knob  68  inward and then turning it through 60° in the clockwise direction  300 . Lifting the locking bar  38  away from the support plates. 48 ,  50  withdraws the locking tabs  108 ,  110  out of the locking slots  78 ,  80  in the rear support plate  50  (as shown, for example, in FIG. 11) to unlock the locking assembly  30  to permit relative movement of the support plates  48 ,  50  relative to each other.  
         [0064]    [0064]FIGS. 13-23 show relative positions of the locking bar  38  and the lifting cam  46  as the ladder  20  is cycled between the collapsed configuration shown in FIG. 2, the step ladder configuration shown in FIG. 3, and the extension ladder configuration shown in FIG. 4. When the ladder  20  is locked in any one of the three configurations shown in FIGS. 2-4, the two straight portions  104 ,  106  and the truncated pie-shaped portion  112  are arranged to lie in the three cutouts  152  between the three lobes  144  of the lifting cam  46  as shown, for example, in FIG. 13 (the collapsed configuration), FIG. 15 (the step ladder configuration) and FIG. 20 (the extension ladder configuration). This allows the snap spring  40  to drive the locking bar  38  against the annular base portion  140  of the lifting cam  46  to, in turn, drive the tabs  108 ,  110  of the locking bar  38  through the aligned slots  76  in the front support plate  48  and the slots  78  or  80  in the rear support plate  50  (depending on whether the ladder  20  is in the 0° or 180° configuration or in the 40° configuration) as shown, for example, in FIG. 9 to lock the assembly  30  to, in turn, block relative movement of the support plates  48 ,  50  relative to each other.  
         [0065]    To unlock, the knob  68  is pushed in as shown in FIG. 10 and rotated 60° in the clockwise direction as shown in FIG. 11. This, in turn, causes the drive shaft  44  and the lifting cam  46  to rotate 60° in the clockwise direction. As the lifting cam  46  rotates, the inclined leading edges  146  of the lifting cam  46  engage the respective leading edges  260 ,  262 ,  264  of the outwardly-extending portions  104 ,  106  and  112  of the locking bar  38  (see FIG. 24) to lift the locking bar  38  away from the support plates  48 ,  50  against the force of the snap spring  40  as shown in FIG. 11. Lifting the locking bar  38  away from the support plates  48 ,  50  withdraws the locking tabs  108 ,  110  out of the locking slots  78  or  80  in the rear support plate  50  (depending on whether the ladder  20  is in the 0° or 180° configuration or in the 40° configuration) to unlock the locking assembly  30  to, in turn, permit relative movement of the support plates  48 ,  50  relative to each other. While the tabs  108 ,  110  are withdrawn from the slots  78  or  80  in the rear support plate  50  when the locking bar  38  is lifted, the tabs  108 ,  110  remain extended into the slots  76  in the front support plate  48 . Thus, the locking tabs  108 ,  110  always remain extended into the slots  76 .  
         [0066]    [0066]FIGS. 13-15 show relative positions of the locking bar  38  and the lifting cam  46  as the ladder  20  moves from the collapsed or 0° configuration shown in FIG. 2 to the step ladder or 40° configuration shown in FIG. 3. In the collapsed configuration of the ladder  20  shown in FIG. 13, the locking tabs  108 ,  110  are driven through the slots  78  in the rear support plate  50  as shown, for example, in FIG. 9. The assembly  30  is first unlocked by pushing the knob  68  inward and turning it through 60° in the clockwise direction as shown in FIG. 14. The legs  22  of the ladder  20  are then spread apart. When the ladder  20  arrives at the step ladder configuration shown in FIG. 15, the locking tabs  108 ,  110  are driven through the slots  80  in the rear support plate  50  to lock the assembly  30 .  
         [0067]    [0067]FIGS. 16, 17 show relative positions of the locking bar  38  and the lifting cam  46  as the ladder  20  moves back to the collapsed configuration shown in FIG. 2. The locking assembly  30  is first unlocked by pushing the knob  68  inward and turning it through 60° in the clockwise direction as shown in FIG. 16. The legs  22  of the ladder  20  are then brought together. When the ladder  20  arrives at the collapsed configuration shown in FIG. 17, the locking tabs  108 ,  110  are driven through the slots  78  in the rear support plate  50  to lock the assembly  30 .  
         [0068]    [0068]FIGS. 15 and 18- 20  show relative positions of the locking bar  38  and the lifting cam  46  as the ladder  20  moves from the step ladder configuration shown in FIG. 3 to the extension ladder configuration shown in FIG. 4. In the step ladder configuration of the ladder  20  shown in FIG. 15, the locking tabs  108 ,  110  extend through the slots  80  in the rear support plate  50 . The assembly  30  is first unlocked by pushing the knob  68  inward and turning it through 60° in the clockwise direction as shown in FIG. 18. The legs  22  of the ladder  20  are then spread apart. When the legs  22  are about 120° apart as shown in FIG. 6, the locking bar  38  moves off the lifting cam  46  as shown in FIG. 12 into the areas occupied by the cutouts  152  in the lifting cam  46  as shown in FIG. 19. This allows the locking bar  38  to drop down a distance  270  in FIG. 11, where the locking tabs  108 ,  110  ride on the forwardly-facing surface of the rear support plate  50  and the trailing edges  280 ,  282 ,  284  of the locking bar  38  (see FIG. 24) engage the perpendicular edges  148  of the lifting cam  46  as shown in FIG. 19. As the legs  22  continue to move to the extension ladder configuration, the locking bar  38  drives the lifting cam  46  through about 60° in the clockwise direction as shown in FIGS. 19, 20 (or in the anticlockwise direction as viewed from the end  24  of the assembly  30  having the lifting cam  46 ). When the ladder  20  arrives at the extension ladder configuration shown in FIG. 20, the locking tabs  108 ,  110  are driven through the slots  78  in the rear support plate  50  to lock the assembly  30 .  
         [0069]    [0069]FIGS. 20-23 show relative positions of the locking bar  38  and the lifting cam  46  as the ladder  20  moves from the extension ladder configuration shown in FIG. 4 to the collapsed configuration shown in FIG. 2. The assembly  30  is first unlocked by pushing the knob  68  inward and turning it through 60° in the clockwise direction as shown in FIGS. 20, 21. The legs  22  of the ladder  20  are then brought together. When the legs  22  are about 40° apart corresponding to the step ladder configuration shown in FIG. 3, the locking bar  38  is on top of the lifting cam  46  as shown in FIG. 22. This prevents the snap spring  40  from driving the locking bar  38  toward the support plates  48 ,  50  to, in turn, lock the assembly  30 . Thus, the ladder  20  passes through the step ladder configuration shown in FIG. 3 without locking the assembly  30 . As the legs  22  arrive at the collapsed configuration in FIG. 23, the locking tabs  108 ,  110  are driven through the slots  78  in the rear support plate  50  to lock the assembly  30 .