Abstract:
A pallet for carrying dynamo-electric machine component workpieces of different dimensions is provided with first and second support members, at least one of which is movably mounted on the pallet so that the distance between the support members can be adjusted to accommodate a wide range of differently dimensioned workpieces. The pallet may include an aperture which allows a removal device to pass through and remove a workpiece from, or deposit a workpiece to the pallet. Each movable support member is releasably locked so that a user may unlock and adjust the support members to a desired position.

Description:
This application is divisional of U.S. patent application Ser. No. 08/992,687 filed Dec. 17, 1997 now U.S. Pat. No. 6,089,365 and claims the benefit of U.S. provisional applications No. 60/035,559, filed Jan. 14, 1997, and No. 60/040,784, filed Mar. 14, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to improvements for adjustable pallets used in pallet conveyor production line systems for dynamo-electric machine components, and more particularly to apparatus and methods for adjusting the distance between support members of pallets capable of carrying dynamo-electric machine component workpieces of different dimensions. 
     The apparatus and methods disclosed herein are applicable to pallets having support members such as those shown in U.S. Pat. Nos. 5,060,780, 5,060,781, 5,099,978, 5,115,901, 5,255,778, 5,346,058 and 5,474,166, all assigned to the assignee of the present invention. 
     Pallet conveyor systems are used in production lines where dynamo-electric machine component workpieces (e.g., armatures or stators for electric motors, generators, alternators, etc.) are to be subjected to a sequence of operations at successive workstations. A workpiece that is to be assembled, machined, or operated on is placed on support members that are mounted on a pallet. The pallet is set upon a moving conveyor that will advance the pallet and the workpiece to a series of workstations that perform a sequence of desired operations to complete the production cycle. A plurality of pallets carrying a like plurality of workpieces are typically used. 
     The pallets may be frictionally driven by a conveyor. As a workpiece is brought to a workstation, the pallet is stopped and the work station operation is performed. While stopped, the pallet may continue to rest on the moving conveyor in sliding contact, or may be lifted off the moving conveyor. Depending on the desired operation, the workpiece may be worked upon while resting on the support members of the pallet, or it may be removed from the support members, worked upon, and then returned to the support members. At the conclusion of the operation, the pallet is released or placed back on the conveyor to advance to the next workstation. The pallets thus move asynchronously, i.e., pallets upstream of a stopped pallet will advance until they are stopped behind a stopped pallet while the conveyor continues to advance, individually or in sets or groups, and accumulate in order to wait their turn at the workstation. 
     Pallet conveyor production lines are adapted for performing the same operations on workpieces that belong to the same family of workpieces and require the same machining operations, even though they may differ in certain dimensions. It is known to provide workstations with automatic adjustment devices that can receive workpieces of different dimensions and adjust for the differences in order to properly perform the desired operation. Sometimes support members of pallets in conventional pallet conveyor systems are manually adjusted for the dimensions of particular workpieces for a particular production cycle. 
     One of the problems associated with adjusting support members of conventional pallets is the redundancy of effort involved in locking and unlocking the support members relative to the pallet. Support members having mechanical connecting links or fasteners are manually loosened in order to move the support members, and then manually re-fastened to secure the support members in a desired location. This re-fastening step is a substantial duplication of the effort expended to unlock the support member. Thus, it would be desirable to eliminate the duplicative manual re-fastening step. 
     Another problem associated with adjusting support members of conventional pallets is that manual adjustment procedures typically allow for error in the settings used from one pallet to the next. As a result, workpieces are not always properly supported during the production cycle, which may result in differences in the quality of the finished product. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide more efficient methods and apparatus for adjusting the positions of the dynamo-electric machine component workpiece support members of a pallet to correspond to the dimensions of particular workpieces. 
     It is another object of this invention to provide a pallet with a locking means having a manual release mechanism that can be easily unlocked to permit movement of the support members, and then automatically locked to secure support members in place. 
     It is yet another object of this invention to provide adjustment methods and apparatus for uniformly adjusting the locations of and/or distance between support members of the pallets so that dynamo-electric machine component workpieces having a given set of dimensions are properly supported on the pallet. 
     It is a further object of this invention to provide a pallet with a locking means that impedes accidental or unwanted unlocking of the release mechanism. 
     In accordance with this invention, apparatus and methods are provided for uniformly adjusting the locations of and/or distance between two dynamo-electric machine component workpiece support members of pallets to compensate for the different dimensions of the workpieces to be operated on by a given pallet conveyor production line. Broadly, the invention concerns a modified pallet and an adjustment apparatus that is constructed such that the support members can be manually adjusted to a desired position corresponding to the workpiece and, prior to and subsequent to engagement, the support members are locked in place on the pallet. 
     The adjustment apparatus of the present invention includes a means for engaging the first and second support members of the pallet such that once the support members are moved into the desired position further movement in the direction of adjustment is prevented. 
     The pallet of the present invention includes at least two support members that are slidably mounted relative to the pallet and to each other, and a preferably cylindrical guide bar for controlling the direction of movement of the first and second support members. The guide bar may have an inexpensive cylindrical shape and is preferably mounted on the pallet such that it is easy to replace when worn. The first and second support members may be independently laterally moved toward or away from each other along the guide bar within an extreme range of selectable positions to accommodate a range of workpiece dimensions appropriate for a given production line. The guide bar may also support the weight of the support members in the loaded or unloaded condition. 
     A locking means is provided so that each support member can be tightly secured on the guide bar with no movement relative to the pallet, for example, at times other than when the support members are to be adjusted. The locking means includes a manual release mechanism to unlock the support members so that they can be moved relative to the pallet into a desired position. The manual release mechanism is configured so that when the desired adjustment of the support member is obtained, simply disengaging contact with the release mechanism causes it to automatically lock the support member into place. In the preferred embodiment, each support member has a separate locking means. 
     Further with regard to the locking means, the guide bar preferably has a longitudinal axis and first and second surface portions that are each substantially parallel to the longitudinal axis and that face away from one another. Each workpiece support member is mounted on the pallet for movement substantially parallel to the longitudinal axis. The locking structure for a support member is mounted on that support member. The locking structure has first and second edges that respectively face toward the first and second surface portions and that are spaced from one another by a distance which is slightly greater than an adjacent perpendicular distance between the first and second surface portions. The locking structure is resiliently biased to rotate the first and second edges about a medial axis which is between them so that the first and second edges respectively contact the first and second surface portions and thereby cause the locking structure to resist motion of the support structure parallel to the longitudinal axis. The locking structure releases the support structure for movement parallel to the longitudinal axis when a user of the pallet rotates the first and second edges about the medial axis opposite to the resilient bias, thereby reducing contact between the first and second edges and the first and second surface portions. 
     The pallet of the present invention may also be equipped with a means for lifting the workpiece rapidly, to take it to a workstation for operation, and subsequently return the workpiece to the pallet. This arrangement may reduce the amount of time required to perform the operation at the workstation as compared to the time required for the workstation to perform the operation while the workpiece is held by the pallet. 
     In operation, adjustment of the support members in accordance with one embodiment of the invention is carried out as follows. Optional adjustment apparatus is placed at a convenient location, typically along the pallet conveyor of the production line, and preferably before the workpiece is initially placed on the pallet. The adjustment apparatus includes movable stops which have been set to reflect the desired locations of and spacing between support members for a given workpiece. A pallet is placed under the adjustment apparatus so that it can be raised to a higher position in order to be adjusted. An operator unlocks at least one workpiece support member from the guide bar on the pallet and moves the support member along the guide bar in the desired direction of adjustment to a desired position, which is against one of the stops on the adjustment apparatus. After the desired position is obtained, the user relocks the support member to the guide bar and returns the pallet to the pallet conveyor. Subsequent adjustments of the support members may be made during the remainder of the production cycle to accommodate changing needs of the workpiece. However, this is preferably done while the workpiece has been removed from the pallet and taken to a workstation. 
     In an alternate embodiment of the present invention, the operative elements of the locking structure of a support member are recessed so that they cannot be directly engaged by human hands. In embodiments such as this, contact with the locking structure can be made using a tool specifically designed to engage that structure or by inserting a commonly available tool such as pliers into the recess. Once the recessed locking structure is engaged, the support member may be unlocked and moved as described above. This feature improves the security of the pallet by preventing inadvertent or accidental unlocking and movement of the support members. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference numerals refer to like parts throughout, and in which: 
     FIG. 1 is a top view of an illustrative embodiment of the pallet and support member of the present invention. 
     FIG. 2 is a side view, partly in section, of the embodiment depicted in FIG.  1 . 
     FIG. 3 is a top view of one embodiment of a support member of the pallet in FIG. 1, constructed in accordance with the principles of the present invention. 
     FIG. 4 is a detail view, partly in section, of a portion of FIG.  3 . 
     FIG. 5 is a top view of another embodiment of a support member of the pallet in FIG. 1, constructed in accordance with the principles of the present invention. 
     FIG. 6 is a side view taken along the line  6 — 6  in FIG.  5 . 
     FIG. 7 is a perspective view taken in the direction of arrow  7  in FIG.  5 . 
     FIG. 8 is a simplified perspective view of an illustrative embodiment of a tool in accordance with the invention that can be used for facilitating operation of locking means of this invention. 
     FIG. 9 is a sectional view of the tool shown in FIG.  8 . 
     FIG. 10 is a simplified perspective view of an illustrative embodiment of apparatus in accordance with the invention for facilitating adjustment of pallets in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a plan view of a pallet  10 , according to the principles of this invention, traveling along a manufacturing line in direction  10 ′ by resting on spaced apart moving conveyor belts  9 . The pallet is provided with an aperture  11  over which are suspended support members (e.g., member  12 ) for supporting the end portions (e.g., end portion  13 ) of a dynamo-electric machine component workpiece. The aperture has the same function as that of the aperture belonging to the pallets presented in the patents cited above, which is to allow passage of a load/unload device for the workpiece. Only one support member  12  and workpiece end portion  13  are shown in FIG. 1, although another oppositely facing support member for supporting the other workpiece end portion will typically be present for correctly supporting the workpiece. The support members may be adjusted to support workpieces of different lengths by being positioned at different distances from each other along guide bar  14  fixed to the pallet. Up to this point in the description, the foregoing are principles similar to those which have been described in the patents cited above. 
     In the illustrative embodiment shown herein the workpieces are dynamo-electric machine armatures, each of which has a core and a shaft extending axially through the core. Each end of the shaft is supported by a respective one of two support members  12  on the pallet. In particular, element  13  in FIG. 1 represents one end of an armature shaft in a V-shaped seat in support member  12 . (See also FIG. 2 for additional depiction of the V seat.) It will be noted that the depicted V seat terminates (on the left as viewed in FIG. 1) with an abutment surface which cooperates with a similar, but oppositely facing abutment surface on the other support member on the pallet to maintain an armature at a precise location on the pallet. In order for these abutment surfaces to perform this important function satisfactorily, support members  12  must not shift on the pallet, even when the ends of the armature shaft contact the abutment surfaces. Such contact may be produced by inertia or other forces acting on the armature as it travels along the production line. As will be seen from what follows, the support member locking structures of this invention enable support members  12  to resist shifting due to forces acting on an armature on the pallet. While the invention is thus particularly suited to use on pallets for armatures, the invention can also be used on pallets for other dynamo-electric machine components such as stators. 
     FIGS. 2,  3  and  4  illustrate the principles of the present invention for guiding, releasing and locking the support members to the pallet that are required to adjust the supports members when workpieces of different lengths are presented. 
     In FIG. 3 (which is a magnified fragmentary view of the support member shown in FIG. 1) support member  12  of the pallet is provided with two plate arms  15 ′ and  15 ″ that are seated within recess  16 . The two plate arms are oppositely bent in an outward direction along their length starting from end A out to end B. The plate arms  15 ′ and  15 ″ are fixed to the support member  12  by inserting end A into slit  17  with a close fit. When attaching the plate arms to the support member by inserting their ends A into slit  17 , the original outward bend of the plate arms in direction  24 ′ and  24 ″ (respectively for plate arms  15 ′ and  15 ″) is reduced to cause the plate arms to be elastically preloaded when finally assembled. Consequently, in the finally assembled condition, plate arm  15 ′ will be biased outwardly in direction  24 ′, and plate arm  15 ″ will be biased in direction  24 ″. In FIG. 2 (which is a view taken along the line  2 — 2  of FIG. 3) plate arm  15 ′ is shown in an elevated representation having bore  20 ′ with a bore central axis essentially perpendicular to a plane containing plate arm  15 ′. Although not shown, plate arm  15 ″ has an identical associated bore  20 ″. The diameters of the bores are slightly larger than the diameter of the guide bar. Guide bar  14  passes through both the bores  20 ′ and  20 ″, and is concentric around the bore central axis. The guide bar is also received in bores  19  of the support members  12  and  12 ′ for a reason which will be more fully described in the following. Plate arms  15 ′ and  15 ″ are also provided with respective upward extensions  22 ′ and  22 ″ at end B to allow an easier engagement for reasons which will be more fully described in the following. 
     In the assembled condition, when the plate arms are biased outwardly as described above, the bores  20 ′ and  20 ″ will be oblique with respect to axis  14 ′ of the guide bar and in contact at  16 ′ and  16 ″ with the guide bar (i.e., portions of the sides of the bores will be in direct contact with the guide bar). This condition is obtained with the plate arms in the positions shown in FIGS. 2 and 3. The contact at  16 ′ and  16 ″ for plate arm  15 ′ is shown in FIG. 4 (partial section view from  4 — 4  of FIG.  2 ). The force of this contact will be proportional to the elastic preload of the plate arms, causing a friction reaction between the plate arms and the guide bar at  16 ′ and  16 ″, thus securing the support to the guide bar. Any tendency of the support members to move along the guide bar  14  when they are secured increases the elastic deformation of the plate arms, which in turn increases the force of the securing friction reaction at  16 ′ and  16 ″. 
     Human fingers can easily engage upward extensions  22 ′ and  22 ″ to squeeze the plate arms towards each other in directions  25 ′ and  25 ″. This will reduce the bias on the plate arms and bring bores  20 ′ and  20 ″ to be less oblique with respect to the guide bar, thus reducing the contact force at  16 ′ and  16 ″. The reduction of the contact force causes the support members to become “unlocked,” i.e., movable along the guide bar  14 , so that they may be pushed by a human in directions  27 ′ or  27 ″ of FIG. 3 for adjustment. During this movement, the support members will be guided in bores  19  by guide bar  14  and also by feet  25 , which are in contact with the pallet. The inside of bores  19  that contact with guide bar  14  and feet  25  react to oppose any tendency of the support members to topple in directions  26 ′ and  26 ″ contained in the plane of FIG.  2 . 
     The guide bar  14  is secured to the pallet by clamping it in support block  27 . Support member  12  runs on portion  14   a  of guide bar  14 , while the other oppositely facing support member runs on portion  14   b  of guide bar  14  during adjustment. The single, centrally located support block  27  for guide bar  14  leaves clear a considerably long adjustment distance for the support members along guide bar  14 . 
     Another embodiment in accordance with the principles of the present invention is shown in FIGS. 5-7. This embodiment contains modified components and features which improve the security of the previous embodiment. Specifically, FIG. 5 shows that plate arms  15 ′ and  15 ″ no longer have the upward extensions  22 ′ and  22 ″ as shown in FIGS. 1-3. Rather, plate arms  15 ′ and  15 ″ are configured to be completely enclosed within recess  16  of support member  12 . FIG. 6 shows that support member  12  is provided with rectangular horizontal recesses  50  and  50 ′ which are positioned parallel to axis  14 ′ at approximately half the vertical height of plate arms  15 ′ and  15 ″. The configuration of recesses  50  and  50 ′ can be better seen in FIG. 7 which is a perspective view from arrow  7  shown in FIG.  5 . As shown in FIG. 7, portions of plate arms  15 ′ and  15 ″ protrude from support member  12  between recesses  50  and  50 ′. By inserting a tool (such as pliers) into recesses  50  and  50 ′ at locations  52 ′ and  52 ″ the protruding portions of plate arms  15 ′ and  15 ″ may be engaged and moved toward each other in direction  53 ′, causing plate arms  15 ′ and  15 ″ to also move toward each other. If enough force is applied, plate arms  15 ′ and  15 ″ will be released from contact with guide bar  14 , causing support arm  12  to be unlocked and therefore movable along guide bar  14 . The unlocked support member may then be pushed along guide bar  14  in order to adjust the pallet. However, support member  12  must be kept in the unlocked state by applying sufficient force in direction  53 ′ when pushing it along guide bar  14 . 
     Returning to FIG. 6, it will be noted that recesses  50  and  50 ′ communicate with recess  16  (shown in FIG. 5) of support member  12  to the extent that a tool may come in contact with plate arms  15 ′ and  15 ″. In FIG. 7, the end portions of the plate arms  15 ′ and  15 ″ have been broken away to show more clearly how this communication is configured. When the support member  12  is in the unlocked state and has been moved to the desired adjustment position, the tool responsible for unlocking support member  12  is disengaged from contact with plate arms  15 ′ and  15 ″. The preload force on plate arms  15 ′ and  15 ″ causes them to move in direction  54 ′ until the friction of contact with guide bar  14  stops this movement, effectively locking support arm  12  in a particular position on pallet  10 . Recesses  50 ,  50 ′ and  16  are dimensioned such that human fingers cannot be inserted within them to squeeze plate arms  15 ′ and  15 ″ in order to unlock support arm  12 . 
     By recessing plate arms of the present invention, the likelihood of manual or accidental unlocking and moving of the support member during the production cycle is greatly decreased. As a result, the probability that the workpiece will be properly supported throughout the production increases, thus improving the efficiency and security of the production line. 
     An illustrative embodiment of a tool  100  that is particularly adapted for use in adjusting the position of a support member  12  in embodiments of the type shown in FIGS. 5-7 is shown in FIGS. 8 and 9. Tool  100  includes a main body  110  having two laterally extending, semi-cylindrical, recess-defining yoke portions  112   a  and  112   b . The semi-cylindrical recesses defined by yoke portions  112   a  and  112   b  are sized and spaced to fit easily and removably around guide bar  14  on respective opposite sides of support member  12 . Two slidable bars  120   a  and  120   b  are disposed opposite end portions of a bore which extends through main body  110  parallel to the longitudinal axis  130  along which guide bar  14  can be received in the recesses in yoke portions  112 . Bars  120  are resiliently biased apart by a prestressed compression coil spring  140  which is disposed between them. Each bar  120  has a pin  150   a  or  150   b  extending laterally from the bar out of a slot  114  in the side of main body  110  which faces toward yoke portions  112 . The side walls of pins  150  contact the ends of slot  114  to limit the distance that bars  120  can move apart under the influence of spring  140 . 
     When the semi-cylindrical recesses in the yoke portions  112  of tool  100  are pressed against guide bar  14  on respective opposite sides of a support member  12  of the type shown in FIGS. 5-7, the portions of pins  150  that project from slot  114  extend into recess  50 / 50 ′ on respective opposite sides of plate arms  15 ′/ 15 ″. Bars  120  can then be manually squeezed toward one another between the thumb and fingers of a hand holding tool  100 . This causes pins  150  to squeeze plate arms  15 ′/ 15 ″ together between the pins, thereby unlocking support member  12  from guide bar  14 . With bars  120  still squeezed together with one hand, and with semi-cylindrical recesses still pressed against guide bar  14 , tool  100  can be slid in either direction along the guide bar, and unlocked support member  12  will slide along the guide bar with the tool. When support member  12  reaches the desired new location along guide bar  14 , bars  120  are released. This releases plate arms  15 ′/ 15 ″, thereby locking support member  12  in its new location. Tool  100  can then be pulled away from guide bar  14  and support member  12 . 
     From the foregoing it will be seen that tool  100  facilitates one-handed unlocking and shifting of a support member  12 . If desired, two tools  100 , one in each of an operator&#39;s two hands, can be used to help the operator simultaneously unlock and reposition both support members  12  on a pallet. Note that the spacing between yoke portions  112  is just slightly greater than the width of the portion of a support member  12  received between those yoke portions. In addition, bars  120  and pins  150  are positioned and configured so that when both bars are pushed in by approximately the same amount, plate arms  15 ′/ 15 ″ are deflected toward one another by about the same amount. Thus tool  100  helps to hold plate arms  15 ′/ 15 ″ in a neutral unlocked position as tool  100  is slid along guide bar  14  to adjust the location of support member  12 . 
     An illustrative embodiment of apparatus  200  in accordance with the invention for facilitating precise and repeatable adjustments of the positions of support members on pallets is shown in FIG.  10 . Apparatus  200  includes two parallel, spaced support members  210   a  and  210   b  connected at their upper ends by a horizontal beam structure  220 . Apparatus  200  is designed to be mounted relative to a pallet conveyor system so that beam structure  220  extends transversely across the conveyor system above pallets being conveyed along the system. The guide bar  14  of each pallet passing under beam structure  220  is substantially parallel to the longitudinal axis of that beam structure. 
     Beam structure  220  supports two stop structures  230   a  and  230   b . Each stop structure  230  is movable along the longitudinal axis of beam structure  220  and releasably lockable in any desired position along the beam structure by appropriate rotation of the associated handle  232   a  or  232   b . A rotatable turret  240   a  or  240   b  is mounted on an extreme upper portion of each support member  210 . A plurality of abutment bars  242   a   1 -n or  242   b   1 -n (only one representative bar  242   a   1  or  242   b   1  being shown for each turret  240 ) extends from each turret toward the center of beam structure  220 . The bars  242  on each turret  240  are substantially parallel to one another and spaced from one another in the circumferential direction around that turret. Different length bars  242  may be provided on each turret  240 , and the bars are preferably removably mounted on the associated turret by being threaded into the turret. A portion  234   a  or  234   b  of each stop structure  230  can be brought into contact with the end of any bar  242  on the adjacent turret by rotating the turret to properly position the bar and then sliding the stop structure along beam structure  220  until the stop structure portion  234  contacts the end of the bar  242 . 
     To set apparatus  200  up to adjust pallets for a new workpiece size, turrets  240  are rotated until bars  242  associated with that workpiece size are positioned to engage stop structures  230 . Stop structures  230  are then slid along beam structure  220  until they contact the ends of the operative bars  242 . Handles  232  are then rotated to lock stop structures  230  in place. 
     When a pallet to be adjusted reaches apparatus  200 , the pallet is raised up off the pallet conveyor until the support members  12  on the pallet are at least partly intercepted by a horizontal axis that also intercepts lower portions of stop structures  230 . Each support member  12  is then slid along the guide bar  14  of the pallet (e.g., using a manually operable tool or tools of the type shown in FIGS. 8 and 9) until a predetermined portion of the support member  12  comes in contact with a predetermined portion of an associated one of stop structures  230 . The locking structure  15 ′/ 15 ″ of each support member  12  is then released to lock the support member in place, and the pallet is lowered back down onto the pallet conveyor. 
     It will be appreciated that use of pallet adjustment apparatus of the type shown in FIG. 10 facilitates rapid and precise adjustment of pallets, even though the adjustments are actually made manually. 
     In the especially preferred embodiment shown in FIG. 10 the lower portion of each of stop structures  230  is pivotable about a pivot axis  236   a  or  236   b  which is substantially parallel to the longitudinal axis of beam structure  220 . This allows the lower portions of structures  230  to pivot up out of the way of pallets traveling beneath beam structure  220  when apparatus  200  is not in use for facilitating pallet adjustments. In this way the overall height of apparatus  200  can be somewhat reduced if desired. 
     Although the locking structures  15 ′/ 15 ″ of this invention are especially suitable for manual or manual tool operation, they can alternatively be operated by automatic machinery if desired. For example, automatically operable pincers may be automatically extended and then closed to release a locking structure  15 ′/ 15 ″ on a pallet to be adjusted. Then the pincers may be automatically shifted laterally to shift the support member  12  associated with the locking structure  15 ′/ 15 ″. When the support member is at the desired new position, the pincers may be automatically reopened to release and thereby lock locking structure  15 ′/ 15 ″. Finally, the pincers are automatically retracted from the pallet that has been adjusted. To facilitate access to automatically operable locking structures  15 ′/ 15 ″, it may be preferable to provide those structures with a different orientation than is shown in FIGS. 1-7. For example, if the automatically operable pincers are mounted over the pallet conveyor on an assembly somewhat like the structure shown in FIG. 10, then it may be desirable to rotate locking members  15 ′/ 15 ″ 90° about a horizontal axis so that access to them is from above (e.g., by pincers lowered from an overhead beam structure somewhat like beam structure  220  in FIG.  10 ). 
     One skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which are presented for the purposes of illustration and not limitation. The present invention is to be limited only by the claims which follow.