Abstract:
A hinge and locking assembly includes first and second hinge members that, when locked, are prevented from rotating about an axis and that, when unlocked, are permitted to rotate about the axis and a lock indicator member movable between a retracted position when the hinge members are locked and an extended position when the hinge members are unlocked. A user is able to determine whether the hinge members are locked or unlocked by observing whether the lock indicator member is in the retracted position or the extended position.

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.  
           [0007]    The assembly includes first and second hinge members that, when locked, are prevented from rotating about an axis and that, when unlocked, are permitted to rotate about the axis and a lock indicator member movable between a retracted position when the hinge members are locked and an extended position when the hinge members are unlocked. A user is able to determine whether the hinge members are locked or unlocked by observing whether the lock indicator member is in the retracted position or the extended position.  
           [0008]    A lock is movable between a locking position in which the hinge members are locked to prevent the hinge members from rotating about the axis and a releasing position in which the hinge members are unlocked to permit the hinge members to rotate about the axis. A knob is rotatable about the axis and movable along the axis. A cam is configured to move the lock from the locking position to the releasing position in response to movement of the knob axially toward the hinge members and then rotation of the knob about the axis. The hinge members are rotatably mounted on a drive shaft. The knob and the cam are mounted on the drive shaft for rotation therewith. The lock is coupled to the drive shaft for axial movement toward and away from the hinge members.  
           [0009]    The drive shaft includes a bore for receiving the lock indicator member for axial movement. The lock indicator member has a first end configured to engage the knob when the knob is moved axially toward the hinge members and a second end. The lock is mounted on the lock indicator member near the second end for axial movement therewith. The second end of the lock indicator member extends through an opening in a cover when the hinge members are unlocked. The second end of the lock indicator member retracts into the cover when the hinge members are locked.  
           [0010]    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  
       [0011]    The detailed description particularly refers to the accompanying figures in which:  
         [0012]    [0012]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,  
         [0013]    [0013]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),  
         [0014]    [0014]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,  
         [0015]    [0015]FIG. 8 is an exploded perspective view of a first embodiment of a hinge and locking assembly, 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, spring clip, knob spring, winged hex drive, lock washer, rear outer covers, and knob,  
         [0016]    [0016]FIG. 9 is an exploded perspective view, similar to FIG. 8, of a second embodiment of a hinge and locking assembly having knob rotation limiter and hinge lock indicator features, and showing, from left to right, front outer covers, locking bar support pin, locking bar, snap spring, drive shaft, lifting cam, front support plate, spacer, rear support plate, locking plate, detent plate, spring clip, knob spring, knob assembly, and rear outer covers,  
         [0017]    [0017]FIG. 10 is an exploded perspective view of the knob assembly of FIG. 9, and showing, from left to right, lock washer, slip disc, slip disc rotation spring and knob,  
         [0018]    [0018]FIG. 11 is a perspective view of the knob of FIG. 10 showing a pair of forwardly-extending radial ribs,  
         [0019]    [0019]FIG. 12 is a perspective view of the locking plate of FIG. 9,  
         [0020]    [0020]FIG. 13 is an elevation view of the locking plate of FIG. 12 as viewed from the end of the FIG. 9 hinge and locking assembly having the knob assembly, and  
         [0021]    [0021]FIG. 14 shows details of the locking plate. 
     
    
     DETAILED DESCRIPTION  
       [0022]    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. Hinge and locking assembly  30  at each end permits 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 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 hinge and locking assemblies  30  and legs  22  are then spread apart. The rotated position of knob  68  is shown by the dotted lines in FIG. 2. When legs  22  move to the step ladder configuration shown in FIG. 3, hinge and locking assemblies  30  automatically latch to lock legs  22  securely in the step ladder configuration. Hinge and locking assembly  30  is sometimes referred to herein as a “lockable joint.” 
         [0023]    To move 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 hinge and locking assemblies  30  and legs  22  are then moved to the fully open position. The rotated position of knob  68  is shown by the dotted lines in FIG. 3. When legs  22  move to the extension ladder configuration shown in FIG. 4, the hinge and locking assemblies  30  automatically latch to lock legs  22  securely in the extension ladder configuration.  
         [0024]    To move 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 hinge and locking assemblies  30  and legs  22  are brought together as shown in FIGS. 6 and 7. The rotated position of knob  68  is shown by the dotted lines in FIG. 5, and the direction of rotation is shown therein by numeral  296 . When legs  22  move to the collapsed configuration shown in FIG. 7, hinge and locking assemblies  30  automatically latch to lock legs  22  securely in the collapsed configuration. Hinge and locking assemblies  30  do not lock the ladder as 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. The two hinge and locking assemblies  30  on the opposite sides of center-folding ladder  20  are identical.  
         [0025]    An exploded perspective view of a first embodiment of hinge and locking assembly  30  is shown in FIG. 8. Hinge and locking assembly  30  does not include two features included in the second embodiment of hinge and locking assembly  330  shown in FIGS.  9 - 14 —i.e., the knob rotation limiter feature and the hinge lock indicator feature. As shown in FIG. 8, 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 . Front and rear support plates  50 ,  52  are also sometimes referred to herein as the hinge members, and locking bar  38  is sometimes referred to herein as the lock.  
         [0026]    In this disclosure, the terms “front”, “raised”, “advanced”, “upward”, “forward” and “head end” all mean toward end  24  of hinge and locking assembly  30  having locking bar  38  and lifting cam  46 . On the other hand, the terms “back”, “lowered”, “retracted”, “backward”, “downward”, “rear” and “foot end” mean toward end  26  of hinge and locking assembly  30  having knob  68 . Unless specified otherwise, all rotational directions (clockwise or anticlockwise) are referenced from end  26  of hinge and locking assembly  30  having knob  68 . Also, the terms “slot”, “hole”, “opening”, “aperture”, etc. are synonymous in this disclosure.  
         [0027]    Hinge and locking assembly  30  is described in detail in a U.S. patent application Ser. No. ______ (Attorney Docket No. 20341-73011), filed on Serial No., and entitled “Hinge and Locking Assembly For Center-Folding Ladder”, which is hereby incorporated by reference in its entirety. The operation of hinge and locking assembly  30  is, however, summarized briefly below.  
         [0028]    To move ladder  20  from the collapsed configuration shown in FIG. 2 to the step ladder configuration shown in FIG. 3, knob  68  is first pushed inward against knob spring  58  in a direction  298  to cause hex drive  60  to engage a hex drive portion of drive shaft  44  so that knob  68  can be rotated about 60° in a clockwise direction  300  to, in turn, rotate drive shaft  44  and lifting cam  46  also about 60° in clockwise direction  300 . As lifting cam  46  rotates, the inclined leading edges of lifting cam  46  engage the corresponding leading edges of locking bar  38  to lift locking bar  38  away from support plates  48 ,  50  against the force of snap spring  40 . Lifting locking bar  38  away from support plates  48 ,  50  withdraws locking tabs  108 ,  110  out of locking slots  78  in rear support plate  50  to unlock hinge and locking assembly  30  to, in turn, permit relative movement of support plates  48 ,  50  relative to each other. Legs  22  of ladder  20  are then spread apart. When ladder  20  arrives at the step ladder configuration shown in FIG. 3, locking tabs  108 ,  110  are driven through slots  80  in rear support plate  50  to lock hinge and locking assembly  30 .  
         [0029]    To move ladder  20  from the step ladder configuration shown in FIG. 3 to the extension ladder configuration shown in FIG. 4, hinge and locking assembly  30  is again unlocked by pushing knob  68  inward and turning it through about 60° in clockwise direction  300 . As previously indicated, clockwise rotation of knob  68  through about 60° causes clockwise rotation of drive shaft  44  and lifting cam  46  also through about 60° in clockwise direction  300 . As lifting cam  46  rotates, locking bar  38  is lifted away from support plates  48 ,  50  against the force of snap spring  40 . Lifting locking bar  38  away from support plates  48 ,  50  withdraws locking tabs  108 ,  110  out of locking slots  80  in rear support plate  50  to unlock hinge and locking assembly  30  to, in turn, permit relative movement of support plates  48 ,  50  relative to each other. Legs  22  of ladder  20  are then spread apart. When ladder  20  arrives at the extension ladder configuration shown in FIG. 4, locking tabs  108 ,  110  are driven through slots  78  in rear support plate  50  to lock hinge and locking assembly  30  in the extension ladder configuration.  
         [0030]    To move ladder  20  back to the collapsed configuration shown in FIG. 2, hinge and locking assembly  30  is unlocked by pushing knob  68  inward and turning it through about 60° in clockwise direction  300 . Rotation of knob  68  causes locking bar  38  to move away from support plates  48 ,  50  to permit relative movement of support plates  48 ,  50  relative to each other. Legs  22  of ladder  20  are then brought together. When legs  22  again arrive at the collapsed configuration in FIG. 2, locking tabs  108 ,  110  are driven through slots  78  in rear support plate  50  to lock the assembly  30  in the collapsed configuration. It is noted that while tabs  108 ,  110  are withdrawn from slots  78  or  80  in rear support plate  50  when locking bar  38  is lifted, tabs  108 ,  110  remain extended into slots  76  in front support plate  48 . As previously indicated, the assembly and operation of hinge and locking assembly  30  is described in detail in the afore-mentioned U.S. patent application Ser. No. ______ (Attorney Docket No. 20341-73011), Serial No.  
         [0031]    An exploded perspective view, similar to FIG. 8, of the second embodiment of hinge and locking assembly  330  is shown in FIG. 9. As previously indicated, hinge and locking assembly  330  includes two features not included in the first embodiment of hinge and locking assembly  30 —i.e., the knob rotation limiter feature and the hinge lock indicator feature. Like elements in the two embodiments  30 ,  330  generally bear the same reference numerals, except that the reference numerals in second embodiment  330  are preceded by a numeral “3”. Thus, hinge and locking assembly  330  includes, from left to right, front outer covers  332 ,  334 , a locking bar support pin  336 , a locking bar  338 , a snap spring  340 , a drive shaft  344 , a lifting cam  346 , a front support plate  348 , a spacer  349 , a rear support plate  350 , a locking plate  352 , a detent plate  354 , a spring clip  356 , a knob spring  358 , a knob assembly  368 , and rear outer covers  364 ,  366 . In FIG. 9, numerals  324 ,  326 , and  382  refer to the front end, the back end and the common axis of hinge and locking assembly  330 . As shown in FIG. 10, knob assembly  368  includes, from left to right, a lock washer  400 , a slip disc  402 , a slip disc rotation spring  404 , and a knob  406 . As indicated above, all rotational directions (clockwise or counter-clockwise) are referenced from end  326  of assembly  330  having knob assembly  368 .  
         [0032]    Slip disc  402  cooperates with locking plate  352  to provide the knob rotation limiter feature which limits the rotation of knob  406  to about 60° to 70° each time knob  406  is pushed inward in direction  408  against the bias of knob spring  358  and turned in a clockwise direction  410  to unlock the hinge and locking assembly  330 . Each time knob  406  is pushed in and turned clockwise to unlock hinge and locking assembly  330 , knob  406  must be first released so that slip disc  402  resets itself before knob  406  can be operated again to unlock hinge and locking assembly  330  a second time. This ensures that the user does not overshoot the rotation of knob  406  beyond 60° to 70° required to unlock hinge and locking assembly  330  to maintain the integrity of the operation of hinge and locking assembly  330 .  
         [0033]    Unlike the first embodiment  30 , hinge and locking assembly  330  does not include a knob support pin, such as knob support pin  42  in FIG. 8. Instead, knob  406  is slidably supported on a rearwardly extending portion  414  of drive shaft  344 . Drive shaft  344  includes a bore for receiving locking bar support pin  336  for axial movement therein. A first end of locking bar support pin  336  extends through drive shaft  344  near knob  406  and engages a forwardly-extending boss  415  on inside wall  416  (FIG. 11) of knob  406  so that, when knob  406  is pushed inward in direction  408 , a second end  418  of locking bar support pin  336  extends through a window  420  in front cover  332  to provide visual indication that knob  406  is pushed in. Thus, when knob  406  is pushed in and turned clockwise to unlock hinge and locking assembly  330 , second end  418  of the locking bar support pin  336  extends through window  420  in front cover  332  to provide visual indication that hinge and locking assembly  330  is unlocked. Second end  418  of locking bar support pin  336  may be painted with a suitable color, such as red, to warn the user when assembly  330  is unlocked. Locking bar  338  is mounted on locking bar support pin  336  near second end  418  for axial movement therewith. Thus, locking bar support pin  336  supports locking bar  338 , and also serves as the “lock indicator member.” 
         [0034]    Referring to FIGS. 10 and 11, knob  406  includes a triangular-shaped hub portion  422  extending forwardly from inside wall  416  of knob  406 . Triangular-shaped hub portion  422  has a triangular-shaped bore  424 . The walls defining triangular-shaped hub portion  422  are generally congruent with the walls of triangular-shaped bore  424 . Triangular-shaped rearwardly-extending portion  414  of drive shaft  344  is slidably received in triangular-shaped bore  424  in knob  406  to rotationally couple knob  406  to drive shaft  344 . Triangular-shaped portion  414  of drive shaft  344  is sized for a close-fit sliding reception in triangular-shaped bore  424  so that knob  406  can freely slide back-and-forth relative to drive shaft  344  while transmitting the rotation of knob  406  to drive shaft  344 . As in the first embodiment  30 , knob  406  and drive shaft  344  can only rotate in the clockwise direction  410 . Locking plate  352  and detent plate  354  cooperate to prevent knob  406  and drive shaft  344  from rotating in counterclockwise direction  412 .  
         [0035]    Slip disc  402  includes an annular portion  426  having a central bore  428  configured to rotatably receive triangular-shaped hub portion  422  of knob  406 . Triangular-shaped hub portion  422  has rounded corner portions  430  to facilitate rotation of slip disc  402  relative to knob  406  about common axis  382  of hinge and locking assembly  330 . Central bore  428  in slip disc  402  and hub portion  422  of knob  406  are so sized that that slip disc  402  is free to rotate and slide back-and-forth relative to hub portion  422 . Each rounded corner portion  430  of knob  406  is formed include an outwardly-extending step portion  432 . Slip disc  402  and slip disc rotation spring  404  are positioned on hub portion  422  of knob  406  between step portions  432  and lock washer  400 .  
         [0036]    Lock washer  400  includes inwardly-extending teeth  434  along its inner periphery which are configured to engage rounded corner portions  430  of hub portion  422  to secure lock washer  400  to hub portion  422 . The inside diameter of inwardly-extending teeth  434  and the outside diameter of hub portion  422  are dimensioned to provide a friction or interference fit. Slip disc rotation spring  404  biases slip disc  402  in clockwise direction  410  relative to knob  406  to transmit the rotation of knob  406  to slip disc  402 .  
         [0037]    Slip disc  402  has three radially-extending tabs  436  which extend forwardly toward locking plate  352  secured to rear support plate  350 . Slip disc  402  has one radially-extending tab  438  which extends rearwardly toward inside wall  416  of knob  406 . Forwardly and rearwardly-extending tabs  436 ,  438  are generally perpendicular to the plane of slip disc  402 . Rearwardly-extending tab  438  is positioned between two radial ribs  440 ,  442  (shown in FIG. 11) extending forwardly from inside wall  416  of knob  406 . Radial ribs  440 ,  442  subtend an angle of about 35° at the common axis  382 .  
         [0038]    Reception of rearwardly-extending tab  438  of slip disc  402  between two forwardly-extending radial ribs  440 ,  442  in knob  406  limits rotation of slip disc  402  relative to knob  406  to about 35°, the angle between ribs  440 ,  442 . A forwardly-extending end  444  of slip disc rotation spring  404  is inserted through a hole (not shown) in slip disc  402  to secure forwardly-extending end  444  of slip disc rotation spring  404  to slip disc  402 . A rearwardly-extending end  446  of slip disc rotation spring  404  is inserted through a hole  448  in a boss  450  extending forwardly from inside wall  416  of knob  406  to secure rearwardly-extending end  446  of slip disc rotation spring  404  to knob  406 . Thus, slip disc rotation spring  404  biases slip disc  402  in clockwise direction  410  relative to knob  406  to, in turn, bias rearwardly-extending tab  438  of slip disc  402  against forwardly-extending radial rib  440  (FIG. 11) of knob  406 .  
         [0039]    Locking plate  352  serves two functions. As in first embodiment  30 , locking plate  352  cooperates with detent plate  354  to allow only clockwise rotation of knob  406  and drive shaft  344  in direction  410 , while preventing anticlockwise rotation of knob  406  and drive shaft  344  in direction  412 . Also, locking plate  352  cooperates with slip disc  402  to provide a knob rotation limiter feature so that each time knob  406  is pushed in and turned clockwise to unlock hinge and locking assembly  330 , knob  406  must be first released before knob  406  can be operated again to unlock hinge and locking assembly  330  a second time. Detent plates  54 ,  354  in two embodiments  30 ,  330  are generally similar.  
         [0040]    Referring to FIGS. 12-14, locking plate  352  includes an annular portion  3200  having a central bore  3202  and six segments  3204  which extend radially outwardly from annular portion  3200 . Drive shaft  344  is configured to be rotatably received in central bore  3202 , and is freely rotatable therein. The six segments  3204  are separated by six cutouts  3206 . Each of six cutouts  3206  forms a 20° angle at the common axis  382 . One of segments  3204  is formed to include a positioning tab  3208  at one end thereof which extends perpendicularly from the plane of locking plate  352 . As in the first embodiment, positioning tab  3208  is received in a positioning hole (not shown) in rear support plate  350  to maintain the orientation of locking plate  352  relative to rear support plate  350 . As shown in FIG. 14, each of six segments  3204  has a stub portion  3214  that forms a 40° angle and an extended portion  3216  that forms a 25° angle at common axis  382 . Each stub portion  3214  and the associated extended portion  3216  form a step portion  3218  that forms a 15° angle at common axis  382 .  
         [0041]    Each stub portion  3214  has a leading edge  3210  and a trailing edge  3212 . As in the first embodiment, leading and trailing edges  3210 ,  3212  of the stub portions  3214  of locking plate  352  cooperate with the respective detent portions  3224  (FIG. 9) of detent plate  354  to block counter-clockwise rotation of drive shaft  344  in direction  412 , while allowing clockwise rotation thereof in direction  410 . Each extended portion  3216  of locking plate  352  has a leading edge  3220  and a trailing edge  3222 . Leading and trailing edges  3220 ,  3222  of extended portions  3216  of locking plate  352  cooperate with three forwardly-extending tabs  436  of slip disc  402  to provide the knob rotation limiter feature. Forwardly-extending tabs  436  of slip disc  402  are dimensioned to engage leading and trailing edges  3220 ,  3222  of extended portions  3216  of locking plate  352  when knob  406  is pushed in to unlock hinge and locking assembly  330 . However, it is noted that forwardly-extending tabs  436  of slip disc  402  are sufficiently spaced apart to provide radial clearance for detent plate  354  so that detent plate  354  can rotate with drive shaft  344  when knob  406  is pushed in and rotated without any hindrance from forwardly-extending tabs  436  of the slip disc  402 .  
         [0042]    The assembly and operation of hinge and locking assembly  330  is similar to the operation of hinge and locking assembly  30  except that hinge and locking assembly  330  has knob rotation limiter and the hinge lock indicator features. As previously indicated, the knob rotation limiter feature limits the rotation of knob  406  to about 60° to 70° each time knob  406  is pushed inward and turned clockwise in direction  410  to unlock hinge and locking assembly  330 . Knob  406  must be first released so that slip disc  402  resets itself before knob  406  can be operated again to unlock hinge and locking assembly  330  a second time. The hinge lock indicator feature provides visual indication to the user when hinge and locking assembly  330  is locked.  
         [0043]    As indicated above, locking plate  352  cooperates with detent plate  354  to block counter-clockwise rotation of knob  406 , drive shaft  344  and lifting cam  346  in direction  412 . When knob  406  is not pushed in, locking bar  338  blocks rotation of lifting cam  346  in the clockwise direction  410  to, in turn, block the rotation of drive shaft  344  and knob  406  in clockwise direction  410 . When knob  406  is pushed in, knob  406 , drive shaft  344  and lifting cam  346  can be rotated in the clockwise direction  410 . When knob  406  is pushed in, (1) locking bar support pin  336  is pushed in because locking bar support pin  336  extends through drive shaft  344  and engages boss  415  on inside wall  416  of knob  406 , (2) locking bar  338  is pushed in against the bias of snap spring  340  because locking bar  338  is fixed to locking bar support pin  336 , (3) locking tabs  3108  (FIG. 9) partially retract out of tab-receiving slots  378  or  380  in rear support plate  350 , but not enough to free support plates  348 ,  350  to rotate relative to each other, and (4) locking bar  338  no longer blocks rotation of lifting cam  346  in the clockwise direction  410  to, in turn, free drive shaft  344  and knob  406  to rotate in clockwise direction  410 .  
         [0044]    At this point, with knob  406  pushed in, knob assembly  368  is at a starting position of a new unlocking cycle or sequence. At the starting position, (1) forwardly-extending tabs  436  of slip disc  402  are just past respective trailing edges  3222  (FIG. 14) of locking plate  352  secured to rear support plate  350 , and (2) rearwardly-extending tab  438  of slip disc  402  is positioned between first and second radial ribs  440 ,  442  (FIG. 11) extending forwardly from inside wall  416  of knob  406 . Rearwardly-extending tab  438  of slip disc  402  is normally in engagement with first radial rib  440  of knob  406  under the bias of slip disc rotation spring  404 .  
         [0045]    With knob  406  pushed in, knob  406  is rotated in clockwise direction  410 . Slip disc  402  rotates with knob  406  in clockwise direction  410  under the bias of slip disc rotation spring  404 . Knob  406  is rotated clockwise until forwardly-extending tabs  436  of slip disc  402  engage respective leading edges  3220  (FIG. 14) of locking plate  352  (i.e., about 35°). The engagement of forwardly-extending tabs  436  of slip disc  402  with respective leading edges  3220  of locking plate  352  block further rotation of slip disc  402 . The 35° angle corresponds to the angle between trailing edge  3222  of a segment  3204  of locking plate  352  and leading edge  3220  of the next segment  3204  of locking plate  352  (as viewed from end  326  of assembly  330 ). While the rotation of slip disc  402  is blocked at this point by locking plate  352 , knob  406  is allowed to rotate further in clockwise direction  410  against the bias of slip disc rotation spring  404  until rearwardly-extending tab  438  of slip disc  402  moves away from the first radial rib  440  (FIG. 11) of knob  406  and engages second radial rib  442  (FIG. 11) of knob  406  (i.e., about 35°), at which point knob  406  is blocked from continued clockwise rotation in direction  410 . The 35° angle corresponds to the angle between first and second radial ribs  440 ,  442  of knob  406 .  
         [0046]    The clockwise rotation of knob  406  in direction  410  by about 70°, causes clockwise rotation of drive shaft  344  and lifting cam  346 , also through about 70°. The clockwise rotation of lifting cam  346  by about 70° causes locking bar  338  to move away from support plates  348 ,  350  and, in turn, causes locking tabs  3108  (FIG. 9) of locking bar  338  to retract from the tab-receiving slots  378 ,  380  in rear support plate  350  to free support plates  348 ,  350  to rotate relative to each other. Support plates  348 ,  350  may then be rotated to a step ladder configuration, to an extension ladder configuration or to a collapsed configuration as the case may be, at which point locking tabs  3108  of locking bar  338  snap back into tab-receiving slots  378 ,  380  in rear support plate  350  under the bias of snap spring  340  to again lock support plates  348 ,  350  in place. Knob  406  is then released.  
         [0047]    When knob  406  is released (1) knob  406  moves away from rear support plate  350  under the bias of knob spring  358 , and (2) slip disc  402  moves with knob  406  away from locking plate  352  so that forwardly-extending tabs  436  of slip disc  402  disengage from respective leading edges  3220  of locking plate  352  to free slip disc  402  to rotate clockwise under the bias of slip disc rotation spring  404  until rearwardly-extending tab  438  of slip disc  402  re-engages first radial rib  440  of knob  406  (i.e., about 35°). Thus, slip disc  402  is reset or advanced to the starting position of a next unlocking cycle, where knob  406  is again ready to be pushed in and rotated in clockwise direction  410  to unlock hinge and locking assembly  330 .