Abstract:
A loudspeaker is provided in which precise alignment is obtained between the frame and motor assembly before they are connected to one another so that a voice coil coupled to the frame may be properly radially and vertically positioned with respect to a magnetic gap in the motor assembly while allowing the motor assembly and frame to be easily and quickly separated from one another to perform repairs or complete replacement of the motor assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of co-pending U.S. application Ser. No. 11/847,448 filed on Aug. 30, 2007, which is incorporated herein by reference in its entirety to form a part of the present disclosure. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to loudspeakers, and, more particularly, to a loudspeaker having a replaceable motor assembly. 
     BACKGROUND OF THE INVENTION 
     Loudspeakers generally comprise a frame, a motor assembly, a voice coil, a diaphragm, a lower suspension or spider and a surround or upper suspension. In one type of speaker, the motor assembly includes a permanent magnet sandwiched between a top plate and a back plate, with a pole piece centrally mounted on the back plate so that both the top plate and magnet are concentrically disposed about the pole piece. A magnetic gap is formed between the pole piece and top plate within which the voice coil is axially movable. Preferably, the voice coil consists of a hollow, cylindrical-shaped former having an inner surface and an outer surface which mounts a winding of wire. 
     Other types of speakers, known as pot-type speakers, employ a motor assembly having a top plate, a pot structure including a pot wall integrally connected to a back plate and a permanent magnet sandwiched between a top plate and the back plate. A magnetic gap is formed between the pot wall and the top plate within which the voice coil is axially movable. 
     The voice coil in speakers of the type described above is mounted within the magnetic gap by the upper and lower suspensions and the diaphragm. One end of the diaphragm is connected to the upper suspension, which, in turn, is mounted to the upper end of the frame. The lower suspension is connected at one end to the frame at a point between its upper and lower ends. The free ends of the diaphragm and lower suspension may be mounted to the outer surface of the former of the voice coil and support it for axial movement within the magnetic gap. In many speaker designs, a dust cap is mounted over a central opening formed in the diaphragm so that contaminants are prevented from entering the interior of the speaker. 
     In the course of operation of speakers of the type described above, electrical energy is supplied to the voice coil causing it to axially move within the magnetic gap. The voice coil, diaphragm, upper suspension, lower suspension, and dust cap, if present, collectively form a “moving assembly” which reciprocates as a unit with the excursion of the voice coil. 
     The method of fabricating traditional loudspeakers such as noted above involves a process which takes place for the most part within the confines of the frame of the speaker. Initially, the frame is secured by screws, glue or other permanent fasteners to the motor assembly. In one type of speaker, the voice coil is then placed over the pole piece of the motor assembly, and a centering gauge is positioned between the voice coil and pole piece. The gap between the voice coil and pole piece, as well as the height of the voice coil within the overall speaker, are set at this stage of the assembly operation with the centering gauge in place. A similar assembly operation is employed with pot-type speakers to accurately position the voice coil in the magnetic gap between the pot wall and top plate. 
     After the voice coil is positioned relative to the pole piece or pot wall, the spider or lower suspension is slid along the outer surface of the voice coil, from the top downwardly, until the outer periphery of the lower suspension rests against a spider plateau or seat formed in the frame. When seated, the lower suspension is glued to both the outer surface of the voice coil and to the spider plateau. 
     Many loudspeaker manufacturers purchase the upper suspension and the diaphragm as a pre-assembled unit from a third party. With the lower suspension in place, the diaphragm of the upper suspension—diaphragm unit is slipped over the voice coil and glued in place on the outer surface of the former. The outer periphery of the upper suspension is then glued to an upper flange of the frame, and a gasket is attached to such upper flange outside of the upper suspension. Once all the glue has cured, the voice coil gauge is removed from between the voice coil and pole piece by pulling it upwardly through the central opening formed in the diaphragm. A dust cap is then glued to the diaphragm over its central opening. 
     Beginning with the pole piece or pot wall of the motor structure, essentially the entire speaker consists of elements which are intended to be oriented in concentric relation to one another. The voice coil is concentric to the pole piece or pot wall, and the upper suspension, lower suspension and diaphragm are concentric to the voice coil. Each of these elements is made within certain tolerances, and the tolerance “stack-up” or combined total from the voice coil radially outwardly to the upper suspension can be significant. Further, no effort is typically made to obtain fine alignment between the frame and motor assembly which can add to tolerance stack-up problems, i.e., the seat or spider plateau in the frame where one end of the lower suspension is mounted, and the upper flange of the frame where the upper suspension is mounted, can be out of concentricity with respect to the pole piece or pot wall of the motor structure. In most speaker designs, the total concentric tolerance stack-up must be absorbed by the upper suspension. Especially during high excursion of the voice coil, the upper suspension can deform if the tolerance stack-up is too high, causing the voice coil to “rock” or pivot within the magnetic gap. This can severely degrade the performance of the speaker. 
     Another problem with prior loudspeakers and their method of manufacture involves repairs and warranty work. As noted above, many of the speaker elements are permanently attached together with glue. In the event of a failure of a speaker element, a great deal of time and effort must be expended to clean the surfaces where glue has been applied before a new part can be installed. Often, it is less expensive and time consuming to simply replace entire portions of the speaker, including the entirety of the motor assembly, rather than to attempt to repair a failed part. 
     SUMMARY OF THE INVENTION 
     The loudspeaker of this invention provides for precise alignment between the frame and motor assembly so that the voice coil is properly positioned both in the radial and vertical directions with respect to the magnetic gap, while permitting the frame and motor assembly to be easily and quickly separated from one another to facilitate the performance of warranty work, other repairs and/or the replacement of the motor assembly in its entirety. 
     The loudspeaker of this invention is preferably a pot-type speaker having a frame with a voice coil, and a motor assembly. The motor assembly of the speaker includes a pot structure comprising a vertically extending pot wall integrally formed with a back plate, which is oriented generally parallel to a top plate, with a permanent magnet located between the back plate and the top plate. A magnetic gap is formed between the pot wall and top plate within which the voice coil is axially movable. 
     In one presently preferred group of embodiments of this invention, the lower end of the frame is formed with a seat having a radial alignment surface and a vertical alignment surface. Similarly, the pot structure is formed with both radial and vertical alignment surfaces. In these embodiments, an element such as a flange or plate protrudes radially outwardly from the pot structure. The upper surface of the flange forms the vertical alignment surface of the pot structure, and the radial alignment surface may be the outer edge of the flange or the exterior surface of the pot wall. When the frame is placed into engagement with the motor assembly, the vertical alignment surface of the frame contacts the upper surface of the flange or plate, and the radial alignment surface of the frame engages the exterior surface of the pot wall or the outer edge of the flange. These aligning surfaces of the frame and pot structure ensure that the voice coil coupled to the frame is accurately positioned, both in a vertical and radial direction, within the magnetic gap of the motor assembly. Fasteners connect the motor assembly to the frame. 
     In another group of preferred embodiments of this invention, the desired radial alignment of the voice coil within the magnetic gap of the motor assembly is achieved by the engagement between a radial alignment surface formed on the lower end of the frame and the exterior surface of the pot wall of the motor assembly. In order to ensure that the voice coil is properly vertically aligned within the magnetic gap, the pot structure is formed with notches which receive projections extending from the lower end of the frame when the frame is fitted over the motor assembly. The projections can take the form of set screws or flexible arms carried by the lower end of the frame. When each projection is seated within a corresponding notch in the pot structure, the voice coil is in the appropriate vertical relationship with respect to the magnetic gap. 
     A still further embodiment of this invention employs a flange extending radially outwardly from the pot structure. The flange has an upper surface and a number of circumferentially spaced holes. The lower end of the frame includes a vertical alignment surface, and a number of circumferentially spaced pins. When the frame is fitted onto the motor assembly, the pins are received within the holes in the flange to provide radial alignment of the voice coil with respect to the magnetic gap. The vertical alignment surface of the frame rests atop the upper surface of the flange to accurately vertically locate the voice coil in the magnetic gap. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The structure, operation and advantages of the presently preferred embodiment of this invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an exploded cross sectional view of one embodiment of the loudspeaker of this invention; 
         FIG. 2  is a view similar to  FIG. 1  except with the loudspeaker assembled; 
         FIG. 2A  is an enlarged view of the encircled portion of  FIG. 2  depicting the alignment and connection between the frame and motor assembly; 
         FIG. 3  is a partial, exploded cross sectional view of another embodiment of the loudspeaker of this invention; 
         FIG. 4  is a view similar to  FIG. 3  except with the loudspeaker assembled; 
         FIG. 4A  is an enlarged view of the encircled portion of  FIG. 2  depicting the alignment and connection between the frame and motor assembly; 
         FIG. 5  is a partial, exploded cross sectional view of a further embodiment of the loudspeaker of this invention; 
         FIG. 6  is a view similar to  FIG. 5  except with the loudspeaker assembled; 
         FIG. 6A  is an enlarged view of the encircled portion of  FIG. 6  depicting the alignment and connection between the frame and motor assembly; 
         FIG. 7  is a partial, exploded cross sectional view of a still further embodiment of the loudspeaker of this invention; 
         FIG. 8  is a view similar to  FIG. 7  except with the loudspeaker assembled; 
         FIG. 8A  is an enlarged view of the encircled portion of  FIG. 8  depicting the alignment and connection between the frame and motor assembly; 
         FIG. 9  is a partial, exploded cross sectional view of still another embodiment of the loudspeaker of this invention; 
         FIG. 10  is a view similar to  FIG. 9  except with the loudspeaker assembled; 
         FIG. 10A  is an enlarged view of the encircled portion of  FIG. 10  depicting the alignment and connection between the frame and motor assembly; 
         FIG. 11  is a partial, exploded cross sectional view of another embodiment of the loudspeaker of this invention; 
         FIG. 12  is a view similar to  FIG. 11  except with the loudspeaker in the process of being assembled; 
         FIG. 12A  is an enlarged view of the encircled portion of  FIG. 12  showing the frame and motor assembly partially connected to one another; 
         FIG. 13  is a view similar to  FIG. 12  except with the loudspeaker fully assembled; 
         FIG. 13A  is an enlarged view of the encircled portion of  FIG. 13  illustrating the alignment and connection between the frame and motor assembly; 
         FIG. 14  is a partial, exploded cross sectional view of still another embodiment of the loudspeaker of this invention; 
         FIG. 15  is a view similar to  FIG. 14  except with the loudspeaker assembled; 
         FIG. 15A  is an enlarged view of the encircled portion on the right-hand side of  FIG. 15  depicting the alignment connection between the frame and motor assembly; and 
         FIG. 15B  is an enlarged view of the encircled portion on the left-hand side of  FIG. 15  illustrating the fasteners which connect the frame and motor assembly together. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, a number of alternative embodiments of a pot-type loudspeaker  10  are illustrated which have a substantial amount of common structure but variations of how the frame  12  of the speaker  10  and its motor assembly  14  may be mounted together so as to permit quick and easy separation of the frame  12  and motor assembly  14  from one another while ensuring that accurate alignment between the two is obtained upon assembly. The common elements of the speaker  10  are initially, described below, followed by a discussion of distinct embodiments of the alignment structure.  FIGS. 1 and 2  depict the entire structure of the loudspeaker  10  associated with the frame  12 . For ease of illustration and discussion, the remaining Figs. illustrate only a cross sectional view of the lower portion of the frame  12  and the motor assembly  14  but it should be understood that the loudspeakers  10  therein have the same structure within frame  12  as in  FIGS. 1 and 2 . For purposes of the present discussion, the terms “upper,” “lower,” “inner,” “outer,” “top,” “bottom,” “vertical” and the like refer to the orientation of the speaker  10  as it appears in the Figs. 
     Common Speaker Elements 
     With reference initially to  FIGS. 1 and 2 , the frame  12  of the speaker  10  has an upper end  16  formed with a circumferentially extending recess  18  and a lower end  20 . The recess  18  mounts one end of a surround  22 , whose opposite end connects to a diaphragm  24 . One end of a lower suspension or spider  26  is mounted to approximately the midpoint of the frame  12 , and its opposite end supports a collar  28  having an, upper end which is mounted to a voice coil  30  and to the underside of the diaphragm  24 . The surround  22 , diaphragm  24 , spider  26  and voice coil  30  form the “moving assembly” of the speaker  10  in that they collectively move in an axial direction with respect to the frame  12  and motor assembly  14  when electrical energy is supplied to the voice coil  30 . 
     The motor assembly  14  comprises a top plate  32 , a pot structure  34  and a permanent magnet  36 . The pot structure  34  consists of a vertically extending pot wall  38  which connected to or integrally formed with a back plate  40 . The top plate  32  and back plate  40  are oriented generally parallel to one another with the magnet  36  located between them. A magnetic gap  42  is formed in the space between the pot wall  38  and top plate  32  within which the voice coil  30  is axially movable. In order for the speaker  10  to operate properly, the voice coil  30  must be accurately aligned within the magnetic gap  42  both radially and vertically. The terms “radial” and “radially” used herein in discussing alignment of the voice coil  30  or the location of different elements of the speaker  10  refer to a direction radially outwardly from the center of the speaker  10 , i.e. generally coincident with the center of the bore  44  in the magnet  36 . The discussion which follows is directed to the structure of the various embodiments of the speaker  10  of this invention for achieving accurate radial and vertical alignment of the voice coil  30  within the magnetic gap  42 , while allowing the motor assembly  14  and frame  12  to be readily separated from one another. 
     Embodiments of  FIGS. 1-8A   
     Although somewhat different from one another, the embodiments of this invention shown in  FIGS. 1-8A  are related in that an element protruding from the pot structure  34  engages corresponding structure on the lower end  20  of the frame  12  to obtain the desired vertical and radial alignment of the voice coil  30  within the magnetic gap  42 . 
     Referring initially to  FIGS. 1-3 , the lower end  20  of frame  12  is formed with a seat  44  having a radial alignment surface  46  and a vertical alignment surface  48  oriented at approximately 90° to one another, The pot wall  38  has an exterior surface  50 , and an annular ring  52 , having an upper surface  54 , protrudes radially outwardly from the pot structure  34 . The underside of the lower end  20  of the frame  12  is formed with a number of circumferentially spaced recesses  56 , and a tapped bore  58  is centered on each recess  56  which extends into the frame  12 . 
     In order to assemble the speaker  10  depicted in  FIGS. 1-3 , the frame  12  is fitted onto the motor assembly  14  such that the radial alignment surface  46  contacts the exterior surface  50  of the pot wall  38 . The frame  12  extends downwardly onto the motor assembly  14  until the vertical alignment surface  48  of its lower end  20  engages the upper surface  54  of the annular ring  52 . The exterior surface  50  of the pot wall  38  and radial alignment surface  46  of the frame  12  are dimensioned such that the voice coil  30  is correctly radially positioned within the magnetic gap  42 . Similarly, the height relationship between the upper surface  54  of the annular ring  52  and the vertical alignment surface  48  of the frame lower end  20  ensures that the voice coil  40  is accurately vertically aligned within the magnetic gap  42 . Once the frame  12  and motor assembly  14  are thus positioned, washers  60  are placed within the recesses  56  on the underside of the lower end  20  of frame  12  such that a portion of the washers  60  engage the bottom surface  62  of the annular ring  52 . Screws  63  are then threaded into the bores  58  to tighten the frame  12  down onto the motor assembly  14 . 
     An alternative embodiment of this invention is shown in  FIGS. 3-4A . An annular flange  64  having an upper surface  66 , a lower surface  68  and an outer edge  70  extends radially outwardly from the pot structure  34 . The flange  64  is formed with a number of spaced bores  72 . The lower end  20  of the frame  12  has a seat  74  in the general shape of an upside-down “L” defining a vertical alignment surface  76  and a radial alignment surface  78 . When the frame  12  and motor assembly  14  are fitted together, the vertical alignment surface  76  of the frame  12  contacts the upper surface  66  of the annular flange  64 , and the radial alignment surface  78  of the frame  12  rests against the outer edge  70  of the flange  64 . The engagement of these surfaces provides vertical and radial alignment, respectively, of the voice coil  30  relative to the magnetic gap  42 . The frame  12  and motor assembly  14  are connected together by inserting screws  63  through the bores  72  in the flange  64  into tapped holes  79  in the lower end  20  of the frame  12 . 
     A similar concept to that described in connection with a discussion of  FIGS. 3-4A  is shown in  FIGS. 5-6A , except instead of a flange  64  an annular motor mounting plate  80  is employed having an outer portion  82  which protrudes radially outwardly from the pot structure  34 . The outer portion  82  of plate  80  has an upper surface  84 , a lower surface  86  and a radial alignment edge  88 . A number of circumferentially spaced bores  90  extend through the outer portion  82  of plate  80 . The lower end  20  of the frame  12  is formed with the same seat  74  as in the embodiment of  FIGS. 3-4A  with the vertical and radial alignment surfaces  76  and  78 . When the frame  12  and motor assembly  14  are fitted together, the vertical alignment surface  76  of the frame  12  contacts the upper surface  84  of the outer portion  82  of plate  80 , and the radial alignment surface  78  of the frame  12  rests against the radial alignment edge  88  of the plate  80 . The engagement of these surfaces provides vertical and radial alignment, respectively, of the voice coil  30  relative to the magnetic gap  42 . The frame  12  and motor assembly  14  are connected together by inserting screws  63  through the bores  90  in the outer portion  82  of the plate  80  into tapped holes  91  in the lower end  20  of the frame  12 . 
     Referring now to  FIGS. 7-8A , a similar concept to that described in connection with a discussion of  FIGS. 3-4A , except different structure is employed to mount the frame  12  to the motor assembly  14 . A flange  92  protrudes radially outwardly from the pot structure  34  having an upper surface  94  and an annular edge  96  formed with first threads  98 . The lower end  20  of the frame  12  is formed with a seat  100  including a vertical alignment surface  102  and a radial alignment surface  104  having second threads  106 . In order to connect the frame  12  to the motor assembly  14 , the annular edge  96  of the flange  92  and the radial alignment surface  104  of the lower end  20  of frame  12  are threaded together by engagement of their respective first and second threads  98 ,  106 . This connection between the lower end  20  of the frame  12  and the flange  92  provides accurate radial alignment of the voice coil  30  within the magnetic gap  42 . The frame  12  and motor assembly  14  are threaded together until the upper surface  94  of the flange  92  engages the vertical alignment surface  102  of the lower end  20  of frame  12 . This seats the motor assembly  14  against the frame  12 , and provides accurate vertical alignment of the voice coil  30  within the magnetic gap  42 . 
     Embodiments of  FIGS. 9-13A   
     Referring now to  FIGS. 9-13A , alternative embodiments of mounting and alignment structure for the frame  12  and motor assembly  14  are provided which do not involve the use of a member protruding radially outwardly from the pot structure  34  as in the previously described embodiments. Instead, radial alignment is achieved by the engagement of frame structure with the exterior surface  50  of the pot wall  38 , and vertical alignment involves the insertion of a set screw or projection from the frame  12  into a notch formed in the pot structure  34 . 
     In the specific embodiment of  FIGS. 9-10A , a number of generally V-shaped notches  108  are formed in the pot structure  34  at the juncture of the pot wall  38  and back plate  40 , one of which is shown in the Figs. Each notch  108  is oriented generally horizontally as depicted in  FIGS. 9-10A , and has a vertical alignment surface  110  along the upper portion thereof. The lower end  20  of the frame  12  has a radial alignment surface  112 , and tapped through bores  114  equal in number to the notches  108  in the pot structure  34 . When the frame  12  is fitted onto the motor assembly  14 , the radial alignment surface  112  of the frame  12  contacts and slides along the exterior surface  50  of the pot wall  38  so that the voice coil  30  is accurately aligned within the magnetic gap  42 . The frame  12  extends downwardly relative to the motor assembly  14  until the through bores  114  in the lower end of the frame  12  align with the notches  108  in the pot structure  34 . A set screw  116  or the like, preferably having an arrowhead-shaped tip  118 , is threaded through each bore  114  until the tip  118  seats within one of the notches  108 . Engagement between the tip  118  of a set screw  116  and the vertical alignment surface  110  of a notch  108  ensures that the voice coil  30  is accurately vertically aligned within the magnetic gap  42 . The set screws  116  also function to connect the frame  12  and motor assembly  14  together. 
     The embodiment of this invention illustrated in  FIGS. 11-13A  is similar to that of  FIGS. 9-10A  in that it employs a notch in the pot structure  34 , but different structure associated with the frame  12  is received within the notch to provide the required vertical alignment. The pot structure  34  is formed with a horizontally oriented V-shaped notch  120  having a vertical alignment surface  121 , but in this embodiment the notch  120  is located near the upper portion of the pot wall  38 . The lower end  20  of the frame  12  is formed with a radial alignment surface  122 , and a number of flexible arms  124  which are circumferentially spaced from one another. Each of the flexible arms  124  extends upwardly from the lower end  20  of the frame  12 , but at a slight inward angle relative to vertical, and terminates at a radially inwardly extending tip  128 . See  FIG. 11 . 
     As shown in  FIGS. 12 and 12A , the frame  12  may be fitted onto the pot structure  34  of the motor assembly  14  such that the radial alignment surface  122  of the lower end  20  contacts and slides along the exterior surface  50  of the pot wall  38 . The tip  128  of each arm  124  engages the pot wall  38  and deflects radially outwardly to some extent from its original angular orientation. It is contemplated that the arms  124  may be formed of plastic, thin metal or other resilient material to permit such deflection without requiring the application of undue force in fitting the frame  12  and motor assembly  14  together. The radial alignment surface  122  of the frame  12  and exterior surface  50  of the pot wall  38  are dimensioned so as to ensure that the voice coil  30  is accurately aligned within the magnetic gap  42 . The frame  12  continues to move downwardly relative to the motor assembly  14 , as viewed in  FIGS. 13 and 13A , until the tip  128  of each arm  124  seats within a notch  120  in the pot wall  38 . Preferably, the tips  128  of the flexible arms  124  are rounded so as to engage the vertical alignment surface  121  of a corresponding notch  120  and thus ensure accurate vertical alignment of the voice coil  30  within the magnetic gap  42 . The flexible arms  124  also function to connect the frame  12  and motor assembly  14  together. 
     Embodiment of  FIGS. 14-15B   
     Referring now to  FIGS. 14-15B , a still further embodiment of this invention is illustrated. The lower end  20  of frame  12  is formed with a number of circumferentially spaced pins  130  which extend downwardly, as shown in the orientation of the frame  12  in the Figs., from a vertical alignment surface  132 . A flange  134  extends radially outwardly from the pot structure  34 , approximately at the juncture of the pot wall  38  and back plate  40 . The flange  134  is formed with a number of circumferentially spaced through bores  136  and an upper surface  138 . When the frame  12  is fitted onto the motor structure  14 , the pins  130  of the lower surface  20  of the frame extend into the through bores  136  in the flange  134 , and the vertical alignment surface  132  rests atop the upper surface  138  of the flange  134 . The location of the pins  130  on the lower surface  20  of the frame and the through bores  136  in the flange, ensure that accurate radial alignment of the voice coil  30  relative to the magnetic gap  42  is obtained. Similarly, the vertical positioning of the upper surface  138  of the flange  134  is such that when the vertical alignment surface  132  of the frame  12  rests thereon, the voice coil  30  is accurately vertically aligned within the magnetic gap  42 . The frame  12  and motor assembly  14  are connected together by inserting screws  63  through the bores  136  in the flange  134  into tapped holes  140  formed in the lower end  20  of frame  12  and tightening down the screws  63 . 
     While the invention has been described with reference to a preferred embodiment, it should be understood by those skilled in the art that various changes may be made and equivalents substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. 
     For example, in the embodiment of  FIGS. 5-6A  a motor mounting plate  80  is shown which is essentially donut-shaped, e.g. a circular element with a hole in the middle corresponding to the central bore  44  in the magnet  36 . In alternative embodiments (not shown), the plate  80  may take the form of an annular ring or a series of circumferentially spaced arc segments affixed to the base of the back plate  40 . In both cases, the annular ring or arc segments extend only part way onto the base of the back plate  40  and protrude radially outwardly in the same way as the motor mounting plate  80  depicted in  FIGS. 5-6A . 
     In still further embodiments of this invention, the motor mounting plate  80 , annular ring and/or arc segments described above in connection with a discussion of alternative embodiments of  FIGS. 5-6A  could take the place of the flange  134  in the embodiment of  FIGS. 14-15B . In those cases, the bores  136  which receive the pins  130  of the lower end  20  of frame  12  are formed in the plate  80 , annular ring or arc segments instead of the flange  134 . 
     Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.