Abstract:
An alignment mechanism that employs two slant disks to adjust alignment between the axes of rotation of a lathe spindle and a wheel hub has a float plate positioned between the slant disks. Rotation of the float plate is limited with respect to a base, which affixes to the lathe spindle, and a cap, which affixes with respect to the wheel hub. Limiting rotation of the float plate prevents transfer of torque from one slant disk to the other when one slant disk is rotated with respect to the base and the cap by an alignment adjustment system to vary the angle and orientation of the misalignment between the two axes. Preventing such transfer of torque allows each of the slant disks to be independently adjusted by the alignment adjustment mechanism without applying a drag force to the slant disk.

Description:
FIELD OF THE INVENTION 
     The present invention relates to alignment mechanisms such as are employed in on-vehicle disk brake lathes to adjust the alignment between a spindle axis of the lathe and a hub axis that is the axis of rotation of a disk to be machined by the lathe. 
     BACKGROUND OF THE INVENTION 
     Axial alignment mechanisms are employed in on-vehicle disk brake lathes to connect between a spindle of the lathe and a hub adapter that mounts to a wheel hub on which a brake disk to be machined is also mounted. The alignment mechanism is adjustable in order to substantially align a spindle axis, which is the axis about which the lathe spindle rotates, with a hub axis, about which the wheel hub and brake disk rotate. Substantially aligning the spindle axis with the hub axis avoids introducing lateral runout in the brake disk when its surfaces are machined in a direction normal to the spindle axis. One mechanism that is well-suited for use with an automatic alignment system uses a pair of opposed slant disks to adjust the magnitude and orientation of the angle of misalignment to compensate for misalignment in the elements interposed between the spindle and the wheel hub. Such an alignment mechanism  10  is shown in  FIGS. 1 and 2 , adjusting the alignment of a lathe spindle  12  and a hub adapter  14  (shown in  FIG. 2 ) to substantially align a spindle axis  16 , about which the lathe spindle  12  rotates, with a hub axis  18 , about which the hub adapter  14  rotates. 
     The alignment mechanism  10  has a base  20  for affixing to the lathe spindle  12  and a cap  22  for mounting against the hub adapter  14 , and the adjustment is made by varying the positions of a first slant disk  24  and a second slant disk  26  that are interposed between the base  20  and the cap  22  and which each have side surfaces that are inclined with respect to each other. A torque transfer post  28  extending from the base  20  engages a post recess (not shown) on the cap  22  to prevent rotation therebetween; this allows the base  20 , which is driven by the lathe spindle  12 , to in turn drive rotation of the cap  22 , while allowing a limited degree of non-rotational motion to accommodate the adjustment of the alignment. The cap  22  in turn has a pair of lug recesses  30 , one of which is engaged by a lug  32  on the hub adapter  14  to allow the cap  22  to drive rotation of the wheel hub to which the hub adapter  14  is attached. 
     Ring bearings are interposed between the elements to allow independent rotation of the two slant disks ( 24  and  26 ). A base ring bearing  34  is interposed between the base  20  and the first slant disk  24 , a central ring bearing  36  is interposed between the first slant disk  24  and the second slant disk  26 , and a cap ring bearing  38  is interposed between the second slant disk  26  and the cap  22 . The ring bearings ( 34 ,  36 ,  38 ) and the slant disks ( 24 ,  26 ) are maintained in axial alignment by a centering cylinder  40  provided on the base  20 . 
     To retain the elements of the alignment mechanism  10  together, a retention ring  42  is provided, which attaches to a sleeve  44  extending from the base  20  and forcibly engages the cap  22  via a wave spring  46 . The wave spring  46  applies pressure to maintain the base  20 , the ring bearings ( 34 ,  36 ,  38 ), the slant disks ( 24 ,  26 ), and the cap ( 22 ) in contact and assures that they remain in proper position relative to each other. 
     When the alignment mechanism  10  is in service, a drawbar assembly  48  (only partially shown) engages the hub adapter  14  and the lathe spindle  12  and operates to force the hub adapter  14  toward the lathe spindle  12 , thereby forcibly engaging together the base  20 , the ring bearings ( 34 ,  36 ,  38 ), the slant disks ( 24 ,  26 ), and the cap ( 22 ). The ring bearings ( 34 ,  36 ,  38 ) allow the slant disks ( 24 ,  26 ) to be rotated even when the elements are forcibly engaged together. 
     The first slant disk  24  and the second slant disk  26  are individually driven by an alignment adjustment system that allows the driven slant disk ( 24  or  26 ) to be incrementally moved with respect to the base  20  and the cap  22 . If the non-driven slant disk ( 26  or  24 ) does not track the motion of the driven disk ( 24  or  26 ), this incremental motion serves to adjust the magnitude of the angle of misalignment between the spindle axis  16  and the hub axis  18  and to adjust the orientation of this angle about the spindle axis  16 . Such adjustment of alignment using slant disks is taught in U.S. Pat. No. 6,101,911, and is typically done incrementally in a trial-and-error method, with each adjustment evaluated as to whether it increases or decreases the misalignment, and further adjustments being made accordingly. 
     The alignment adjustment system for use with the alignment mechanism  10  employs a series of spur gears  50  that are each rotatably mounted with respect to the base  20  and configured to engage peripheral teeth  52  on one of the slant disks ( 24 ,  26 ), as shown in  FIGS. 1 and 2 , to drive the slant disks ( 24 ,  26 ) of the alignment mechanism  10 . Each of the spur gears  50  is operably connected to a star wheel  54  such that rotation of the star wheel  54  causes rotation of the spur gear  50  operatively connected thereto, and in turn rotation of the slant disk ( 24 ,  26 ) engaged by the spur gear  50  either in a first direction, when the spur gear  50  is directly connected to the associated star wheel  54  so as to rotate therewith, or in a second and opposite direction when the spur gear  50  is connected to the associated star wheel  54  through an idler gear  56  so as to rotate in a direction opposite that of the star wheel  54 . The alignment adjustment system employs a solenoid (not shown) such as described in the &#39;911 patent to selectively rotate the star wheels  54  in one direction to adjust the alignment. 
     While the ring bearings ( 34 ,  36 ,  38 ) allow each of the slant disks ( 24 ,  26 ) to be driven independently, independent rotation does not necessarily follow. Coupling of the rotation of the two slant disks ( 24 ,  26 ) has been found to occur, since the compression forces on the stacked elements provided by the drawbar assembly  48  result in frictional forces associated with the central ring bearing  36 . As a result of these frictional forces, as one slant disk ( 24  or  26 ) is rotated, torque is transmitted through the central ring bearing  36  to the other slant disk ( 26  or  24 ), causing it to rotate as well. Such rotation of the other slant disk impairs the ability to individually rotate each of the slant disks ( 24 ,  26 ) to make adjustments in their relative positions. To reduce such coupling of the rotation, a drag force is applied to the slant disk gears by friction disks  58  interposed between each of the star wheels  54  and the base  20 . These friction disks  58  become compressed when the star wheel  54  is mounted to the base  20 , and the compression causes a frictional resistance to rotating the star wheel  54 . While such has been found effective, the drag on the star wheels  54  requires the alignment adjustment system to apply a greater force to rotate the star wheels  54  when making adjustments in the alignment, and thus requires a greater size and weight of the alignment adjustment system. The greater force needed also accelerates wear on the star wheels. 
     SUMMARY 
     The present invention is for an alignment mechanism for use in an on-vehicle disk brake lathe which, in combination with an alignment adjustment system, adjusts the alignment between a spindle axis of a lathe spindle and a hub axis about which a wheel hub rotates, the hub having a brake disk to be machined mounted thereto. The alignment mechanism attaches between the lathe spindle and a hub adapter that in turn is attached to the hub. 
     The alignment mechanism has a base for attachment to the lathe spindle. The base has a base bearing-engaging surface and a base mounting surface for placement against the spindle when the base is mounted thereto. 
     A first slant disk is provided, which is bounded by a first indexable ring for engagement by the alignment adjustment system that forms part of the on-vehicle disk lathe, and is also bounded by a pair of planar first disk side surfaces which are inclined with respect to each other by a first disk angle α 1 . Examples of alignment systems employing such slant disks, and where the indexable ring are formed by peripheral teeth on the slant disks, are further described in U.S. Pat. No. 6,101,911, incorporated herein by reference. The first slant disk is interposed between a pair of first disk ring bearings with each of the first disk ring bearings being in contact with one of the first disk side surfaces. In service, the slant disk is positioned with respect to the base such that one of the first disk ring bearings resides in contact with the base bearing-engaging surface of the base. 
     A float plate is provided, which resides in contact with the one of the first disk ring bearings that is not in contact with the base. 
     A second slant disk is provided that is bounded by a second indexable ring for engagement by the alignment adjustment system, as well as being bounded by a pair of planar second slant disk side surfaces which are inclined with respect to each other by a second disk angle α 2  which should be similar in magnitude to the first disk angle α 1 . The second slant disk is interposed between a pair of second disk ring bearings with each of the second disk ring bearings being in contact with one of the second disk side surfaces. The second slant disk is positioned such that one of the second disk ring bearings contacts the float plate. 
     A cap is provided for attachment to the hub adapter. The cap is provided with a cap bearing-engaging surface and is positioned such that the cap bearing-engaging surface is in contact with the one of the second disk ring bearings that is not in contact with the float plate. The cap also has a cap mounting surface for placement against the hub adapter when the cap is mounted thereto. 
     A centering structure is provided to provide axial alignment of the base, the first slant disk and the associated first disk ring bearings, the float plate, the second slant disk and the associated second disk ring bearings, and the cap. 
     Means for limiting rotational motion between the base, the float plate, and the cap are provided. Since the float plate is positioned between the slant disks, limiting rotation of the float plate relative to the base and the cap blocks transmission of torques from one slant disk to the other, and thus eliminates the need to apply a drag force on each of the slant disks and thereby eliminates the problems associated with providing such drag forces. Limiting rotation between the base and the cap allows the base, which is attached to the lathe spindle, to drive rotation of the cap, which in turn drives the hub adapter and the hub attached thereto so as to rotate the brake disk mounted to the hub during the machining process. 
     To maintain the elements of the alignment mechanism in position, the cap can be provided with a wave spring that bears against a cap plate and against an element which attaches to the base, thereby compressing the wave spring and forcing the cap plate towards the base to apply a compressive load on the elements positioned therebetween. 
     The cap and the base can be configured to form a case which encloses the slant disks and the float plate. The alignment adjustment system can employ spur gears that reside within the case and engage peripheral teeth on the slant disks, these peripheral teeth providing the indexable rings. The spur gears are attached to spur gear shafts which pass through the case and engage star wheels, which in turn are acted upon by additional elements of the alignment adjustment system. The base can be provided with a ledge configured with wells into which the spur gears reside in part, bottoms of the wells serving to support the spur gears so that they align with the peripheral teeth on the slant disks. A spacer that seats against the ledge can be provided to support the spur gears to prevent them from sliding out of engagement during service. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a partially exploded isometric view illustrating a prior art alignment mechanism and portions of an alignment adjustment system that adjusts the relative orientation of two slant disks of the alignment mechanism. Friction disks interposed between a base and a series of star wheels provide a drag force to counteract motion of the non-driven slant disk due to transfer of torque from motion of the driven slant disk currently being moved by the alignment adjustment system, such torque being transferred through a central ring bearing that separates the two slant disks. 
         FIG. 2  is a partially exploded isometric view illustrating the alignment mechanism shown in  FIG. 1  with additional elements of an on-vehicle disk brake lathe. The alignment mechanism attaches between a lathe spindle and a hub adapter and serves to align their respective axes of rotation. 
         FIG. 3  is an exploded isometric view showing one embodiment of the present invention, which employs a float plate positioned between the slant disks, and employs a pair of ring bearings for each slant disk, positioned on either side thereof. The float disk is essentially prevented from rotating relative to the base, and thus blocks any transfer of torque from one slant disk to the other. Rotation of the float plate is limited by an array of cylindrical shafts that engage notches in the float plate. These shafts are also employed to provide the centering structure for the ring bearings and the slant disks to maintain their alignment, and engage recesses in the cap to limit rotation between the cap and the base. 
         FIG. 4  is a partially exploded view of the embodiment shown in  FIG. 3 , better illustrating an arrangement of spur gears that engage peripheral teeth that serve as indexable rings on the slant disks to allow the slant disks to be selectively rotated. The base is configured with wells that support the spur gears, and a spacer also constrains the positions of the spur gears to maintain them engaged with the indexable rings on the slant disks. 
         FIG. 5  is a partially sectioned view of the alignment mechanism shown in  FIGS. 3 and 4 , better showing the structure of the cap. The cap is an assembly which includes a cap plate and a terminating post that threadably engages the base. The terminating post has a head that compresses a wave spring interposed between the head and the cap plate, this compression serving to apply a compressive load between the cap plate and the base to maintain them, as well as the elements interposed therebetween, in their relative positions. 
         FIGS. 6 through 9  illustrate a coupling structure that can be employed for attaching the base to the lathe spindle. This structure provides a jacking mechanism to remove the base from the lathe spindle in the event that it sticks, as well as torque transfer lugs that serve to transfer torque from the lathe spindle to the base so as to reduce the requirement of transferring torque via the bolts that attach the base to the lathe spindle. 
         FIG. 10  is a view of an alignment mechanism similar to that shown in  FIGS. 3-5 , but which is designed for use with an alternative alignment adjustment system. In this embodiment, the alignment adjustment system employs one set of star wheels that provide forward motion of the spur gears attached thereto, as well as idler gears that are connected to another set of star wheels by reverse gears so as to cause reverse motion of the spur gears when those star wheels are rotated. The elimination of any requirement to apply a drag force to the slant disks of the alignment mechanism allows the idler gears and reverse gears to be mounted coaxially with their respective star wheels, since there is no need to accommodate friction disks such as are employed in the prior art device shown in  FIGS. 1 and 2 . 
         FIGS. 11 and 12  are exploded isometric views illustrating an alignment mechanism that forms another embodiment of the present invention; this embodiment shares many of the features of the prior art mechanism shown in  FIGS. 1 and 2 , and differs in that it is provided with a float plate and a pair of ring bearings interposed between the slant disks. This embodiment employs an array of ridges in the wall of the base and corresponding notches on the float plate to limit rotation between these elements, and employs a post extending from the base to limit the rotation between the cap and the base. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 3 and 4  are isometric views of an alignment mechanism  100  that forms one embodiment of the present invention.  FIG. 3  is an exploded view of the alignment mechanism  100  that serves to adjust the alignment between a spindle axis  102  of a lathe spindle  104  of an on-vehicle brake disk lathe and a hub axis  106  of an axle on which a disk brake (not shown) rotates.  FIG. 4  is another isometric view of the same structure, which is partially exploded. As illustrated in  FIG. 3 , the alignment mechanism  100  connects between the spindle  104  of the on-vehicle disk lathe and a hub adaptor  108  which in turn attaches to a hub (not shown) mounted on the axle on which the disk brake is mounted. The axial alignment system  100  illustrated in  FIGS. 3 through 5  is designed to operate in conjunction with an alignment adjustment system such as those further described in U.S. Pat. No. 6,101,911. The alignment mechanism  100  has a base  110  having a base mounting surface  112  which attaches to the lathe spindle  104  and a base bearing-engaging surface  114 . 
     A first slant disk  116  is provided, which is bounded by a first ring gear  118  that provides a first indexable ring, and by a pair of first disk side surfaces  120  which are inclined with respect to each other by an angle α 1 . When assembled for service, the first slant disk  116  is positioned such that one of the first disk side surfaces  120 ′ is in contact with one of two first disk ring bearings  122 ′, which in turn is in contact with the base bearing-engaging surface  114  of the base  110 . The other of the first disk side surfaces  120 ″ is in contact with the other of the first disk ring bearings  122 ″ when the alignment mechanism  100  is assembled, and this other first disk ring bearing  122 ″ in turn contacts a float plate  124 . 
     A second slant disk  126  is provided, which is bounded by a second ring gear  128  that provides a second indexable ring, and by a pair of second disk side surfaces  130  which are inclined with respect to each other by an angle α 2 . The angles α 1  and α 2  should be about equal to each other, and should be selected such as to each be at least equal to the largest expected angle of misalignment between the axes ( 102 ,  106 ); typically, these angles (α 1 , α 2 ) measure a fraction of a degree. When assembled for service, the second slant disk  126  is positioned such that one of the second disk side surfaces  130 ′ is in contact with one of a pair of second disk ring bearings  132 ′ that in turn is in contact with the float plate  124 , while the other of the second disk side surfaces  130 ″ is in contact with the other of the second disk ring bearings  132 ″. 
     A cap assembly  134  is provided for attaching to the hub adaptor  108 . The cap assembly  134  has a cap bearing-engaging surface  136  which engages the one of the second disk ring bearings  132 ″ that is not in contact with the float plate  124 , and a cap mounting surface  138  for mounting against the hub adapter  108 . 
     In order to assure cooperative action between the base  110 , the first slant disk  116 , the pair of first disk ring bearings  122 , the float plate  124 , the second slant disk  126 , the pair of second disk ring bearings  132 , and the cap assembly  134 , an array of shafts  140  are provided to serve as a centering structure. The shafts  140  are tangent to an inscribed circle, the diameter of which is slightly less than the diameter of a central passage  142  through each of the slant disks ( 116 ,  126 ) and the ring bearing pairs ( 122 ,  132 ). The shafts  140  are imbedded in the base  110  and non-rotatably engage a cap plate  144  which forms part of the cap assembly  134 . The cap plate  144  is provided with an array of recesses  146  (shown in hidden lines in  FIG. 4 ) that are positioned and configured to slidably engage the shafts  140  when the cap assembly  134  is in place, thereby providing a transfer of torsional loads between the base  110  and the cap plate  144  to assure that the cap plate  144  and the base  110  rotate as a unit, while allowing adjustment of the inclination of the cap plate  144  with respect to the base  110 . 
     The float plate  124  of the axial alignment mechanism  100  has a plate central passage  148 , slightly smaller than the passage  142 , that has a series of notches  150  configured such that they slidably engage the shafts  140  such that the shafts  140  act as blocking elements that allow limited degree of tilting of the float plate  124  but restrict rotation thereof, thereby isolating the rotational movement between the two slant disks ( 116 ,  126 ). Such is not the case of the axial alignment mechanism  10  or the alignment devices taught in the &#39;911 patent. In fact, the lack of isolation in earlier alignment mechanisms requires a drag mechanism to be introduced to limit any coupling of the motion between the two slant disks. Maintaining the motion of the slant disks ( 116 ,  126 ) separate is critical to providing adjustments to allow the hub axis  106  to be aligned with the spindle axis  102 . It was for this reason that friction pads  58  were imposed between the base  20  and the star wheels  54  in the prior art alignment mechanism  10 . 
     It has been found that in many circumstances the alignment process can be speeded by reducing the adjustments needed in the relative positions of the slant disks ( 116 ,  126 ) if a third angle α 3  is introduced in the stacked elements. The angle α 3  should be similar in magnitude to the angles (α 1 , α 2 ), and can be conveniently provided by forming the base bearing-engaging surface  114  inclined with respect to the associated base mounting surface  112  by the angle α 3  (as illustrated in  FIG. 3 ), or by forming the cap bearing-engaging surface  136  inclined with respect to the cap mounting surface  138  by the angle α 3 . Alternatively, the angle α 3  could be provided by employing a skewed shim having surfaces inclined to each other by the angle α 3 , where the shim is interposed between one of the bearing-engaging surfaces of the cap or the base and the associated ring bearing. 
     In service, the hub adapter  108  and the lathe spindle  104  are forced toward each other by a drawbar assembly such as the drawbar  48  discussed above and partially shown in  FIG. 2 ; this compressive force between the hub adapter  108  and the lathe spindle  104  acts to force together the base  110 , the ring bearings ( 122 ,  132 ), the slant disks ( 116 ,  126 ), the float plate  124 , and the cap assembly  134  to maintain them in contact so as to provide adjustment of the axes ( 102 ,  106 ) as the slant disks ( 116 ,  126 ) rotate. When the alignment mechanism  100  is detached from the hub adapter  108 , the elements should be maintained in forcible contact to retain them in their proper spacial relationships with respect to each other. A compressive load should be maintained between the cap plate  144  and the base  110  in order to keep the base  110 , the ring bearings ( 122 ,  132 ), the slant disks ( 116 ,  126 ), the float plate  124 , and the cap assembly  134  forcibly engaged together. To provide such a compressive load, the cap assembly  134  is provided with a wave spring  152  that resides between the cap plate  144  and a head  154  of a terminating post  156  which in turn attaches the cap assembly  134  to the base  110  by threadably engaging the base  110 , thereby affixing the base  110  with respect to the head  154  of the terminating post  156 , as better shown in  FIG. 5 . Since the intervening elements ( 122 ,  132 ,  116 ,  126 , and  124 ) limit motion of the cap plate  144  towards the base  110 , the wave spring  152  becomes compressed between the head  154  and the cap plate  144  when the terminating post  156  is affixed to the base  110 . 
     The introduction of relative motion between the slant disks ( 116 ,  126 ) so that they rotate with respect to each other will vary depending on the details of the alignment adjustment system used. When a system such as described in the &#39;911 patent is employed, the system adjusts the alignment by selectively impacting an alignment adjustment system fabricated with a series star wheels, shafts, and spur gears, where the spur gears in turn engage the ring gears ( 118 ,  128 ) that form part of the slant disks ( 116 ,  126 ). 
       FIG. 4  shows the ring gears ( 118 ,  128 ) engaging a first pair of spur gears  158  which connect to shafts  160  which in turn connect to forward star wheels  162  which are activated by an impulse activation system such as a solenoid as taught in the &#39;911 patent. A second pair of spur gears  164  engage the ring gears ( 118 ,  128 ), these spur gears  164  being idler gears which in turn engage driven spur gears  166  which are turned by shafts  168  which terminate in reverse star wheels  170 . With the idler spur gears  164  provided, the ring gears ( 118 ,  128 ) turn in the reverse direction when the reverse star wheels  170  are activated by the impulse activation system. 
     Wells  172  are provided in a sidewall  174  of the base  110 . These wells  172  have bottom surfaces  176  which provide support for the spur gears ( 158 ,  164 ,  166 ). This assures that the spur gears ( 158 ,  164 ,  166 ) do not fall below the ring gears ( 118 ,  128 ). To assure that the spur gears ( 158 ,  164 ,  166 ) do not rise above the ring gears ( 118 ,  128 ), either the star wheels ( 162 ,  170 ) can be used to restrain upward movement or, alternatively, an overlaying spacer  178  retained between a ledge  180  and a base rim element  182  can be provided to limit upward motion. 
     To provide a seal between the cap assembly  134  and the base  110 , a ring seal  184  can be provided (as better shown in  FIG. 5 ) and to further seal the cap assembly  134 , a circular seal  186  having an X cross-section be inserted between the cap plate  144  and the head  154  of the terminating post  156 . 
       FIGS. 6  though  9  illustrate a coupling assembly for attaching an axial alignment mechanism such as the mechanism such as that shown in  FIGS. 3-5  to a lathe spindle  200 .  FIGS. 6 and 7  illustrated various stages of assembly and  FIGS. 8 and 9  illustrate various degrees of dis-assembly. In this embodiment, the lathe spindle  200  is coupled to a base  202  of an axial alignment mechanism such as that shown in  FIGS. 3-5 . The coupling is in part formed by providing a central cavity  204  (best illustrated in  FIG. 9 ) in a base mounting surface  206 , where the central cavity  204  is configured to slidably engage the lathe spindle  200 , thereby providing partial support by limiting rocking thereon. To allow the coupling to transmit torsional loads, a series of pins  208  is provided. These pins  208  are configured to fit into base cavities  210  and into spindle cavities  212 . Preferably, one of the sets of cavities ( 210 ,  212 ) provides a press fit, while the other provides a slidably engagable fit. A second series of passages  214  are provided in the base  202 , these passages  214  each having a passage lower portion  216  which is threaded, while a passage upper portion  218  is oversized and provided with a smooth wall, terminating in a ledge  220  which will support a head  222  of a coupling bolt  224 , as shown in  FIG. 7 . These coupling bolts  224  each have a bolt shank  226  which is threaded and sized to pass through the threaded passage lower portions  216  without engaging the threads. The lathe spindle  200  is provided with a series of spindle threaded passages  228  which are configured to be threadably engaged by the bolt shanks  226  of the coupling bolts  224  to allow the coupling bolts  224 , when tightened, to secure the spindle  200  and the base  202  together. 
     A larger set of removal bolts  230  are provided and these have threads which are configured to engage the threads of the passage lower portions  216  of the passages  214 . As the removal bolts  230  engage the threads of the passage lower portions  216 , the removal bolts  230  are advanced in the passages  214  so as to forcibly engage the spindle  200  and dislodge the base  202  therefrom in the event that the spindle  200  and the base  202  bind together in service. 
       FIG. 10  illustrates another embodiment of the present invention, an axial alignment mechanism  300  that shares many of the features of the embodiment shown in  FIGS. 3-5 , but which differs in the structure for individually rotating a first slant disk (not visible) and a second slant disk  302  (shown in phantom), each having a peripheral ring gear  304 . The alignment mechanism  300  is designed for use with an impulse activation system that has both a forward solenoid and a reverse solenoid, rather than a single solenoid. For each ring gear  304 , there is a single spur gear  306  that rotates with a forward star wheel  308  mounted with the spur gear  306  on a first shaft  310 . In this embodiment, an idler gear  312  is also mounted on the first shaft  310 , and is positioned below the forward star wheel  308 . The idler gear  312  in turn is engaged with a reversing gear  314  mounted on a second shaft  316 , the reversing gear rotating with a reverse star wheel  318  that is also mounted on the second shaft  316  and positioned below the reversing gear  314 . When the reversing star wheel  318  is rotated by the impulse activation system, the reversing gear  314  also rotates, which causes the idler gear  312  and the spur gear  306  connected thereto to rotate in the opposite direction from that in which the spur gear  306  is rotated by the forward star wheel  308 . Since the star wheels ( 308 ,  318 ) are positioned at different levels, they can selectively be rotated by solenoids positioned at each level. 
       FIGS. 11 and 12  illustrate another embodiment of the present invention, an axial alignment mechanism  400  which shares many features of the prior art axial alignment mechanism  10  shown in  FIGS. 1 and 2 . The alignment mechanism  400  differs from the mechanism  10  in the details of the structure interposed between a first slant disk  402  and a second slant disk  404 , this structure allowing the elimination of the friction pads  58  employed in the device shown in  FIGS. 1 and 2 . 
     In this embodiment, the elimination of the friction pads is provided by substituting for the central ring bearing  36  of the earlier embodiment a pair of ring bearings  406  and a float plate  408  that is interposed between the ring bearings  406 . The float plate  408  is restrained from rotation by an array of ridges  410  provided on a base  412 , which act as blocking elements that engage peripheral notches  414  in the float plate  408 . The notches  414  are configured to slidably engage the ridges  410  to allow a limited degree of tilting of the float plate  408  relative to the base  412 , while restricting rotation. 
     In this embodiment, the axial alignment of the slant disks ( 402 ,  404 ), the ring bearings  406 , the base  412 , and the float plate  408  is maintained by a cylindrical hub  416  on the base  412 , while a cap  418  is axially aligned by a base collar  420  and rotation between the cap  418  and the base  412  is prevented by a post  422  on the base  412  which mates with a recess (not shown) in the cap  418 . 
     While the novel features of the present invention have been described in terms of particular embodiments and preferred applications, it should be appreciated by one skilled in the art that substitution of materials and modification of details can be made without departing from the spirit of the invention.