Abstract:
A modular ceiling-mounted medical services system including a vertical column supported by an articulating arm assembly. Rotational joints connect the column to the lower arm, the lower arm to the upper arm, and the upper arm to the ceiling mount. Rotational movement at each of the joints is controlled by an electrically-released electromagnetic brake, and all of the brakes may be controlled by a switch panel on the column. Thus, the entire assembly is held in place until the switch is activated. Slight hand pressure is sufficient to operate the switch while simultaneously pushing or pulling the column into the desired position. The service lines that supply the outlets in the column all pass through large central openings in the brakes.

Description:
This application is a continuation of application Ser. No. 12/789,639, entitled “Medical Service System on Articulating Arm with Electromagnetic Brakes,” filed May 28, 2010, which is a, continuation of application Ser. No. 11/534,398, entitled “Medical Service System on Articulating Arm with Electromagnetic Brakes,” filed Sep. 22, 2006, which claims the benefit of the filing date of provisional application Ser. No. 60/597,103, entitled “Ceiling Mounted Medical Services Column,” filed Nov. 10, 2005, and the contents of these applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to devices for providing gas, vacuum, electrical, communication, data and other services to medical care facilities or other settings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a ceiling-mounted medical service system constructed in accordance with a preferred embodiment of the present invention and shown in a hospital room. 
         FIG. 2  is a schematic view of the system showing the path of the multiple service conduits entering the mounting assembly from above the ceiling and passing through the arm assembly into the column. 
         FIG. 3  is an exploded, perspective view of the mounting assembly. 
         FIG. 4  is an exploded, perspective view of the first arm of the arm assembly. 
         FIG. 5  is an exploded, perspective view of the second arm of the arm assembly. 
         FIG. 6  is a fragmented sectional view of the distal end of the second arm showing the brake assembly, the rotor assembly and the saddle, forming a joint. 
         FIG. 7  is a partially sectional perspective view of the bearing or rotor end of the second arm. 
         FIG. 8  is an exploded perspective view of the brake assembly. 
         FIG. 9  is a perspective assembled view of the brake assembly. 
         FIG. 10  is a cross-sectional view of the brake assembly shown in  FIG. 9  taken along line  10 - 10  of  FIG. 9 . 
         FIG. 11  is a perspective view of a custom hex nut used in the brake assembly. 
         FIG. 12  is a fragmented plan view of the spacer. 
         FIG. 13  is a fragmented plan view of the rotor showing the custom hex nut received in an oval opening in the rotor. 
         FIG. 14  is a diagrammatic illustration of a preferred handle with an integrated control panel. 
         FIG. 15  is an end view of the arm housing of the first arm. 
         FIG. 16  is a sectional view of the coupler of the first arm with the pin engaged in the slot. 
         FIGS. 17 and 18  illustrate use of the slide-in latch and lock assembly of the arm housings. 
         FIGS. 19 and 20  illustrate placement of the locking bracket after the entire system has been installed and leveled. 
         FIG. 21  is a perspective view of the conduit tray for use inside the arm housings. 
         FIG. 22  is a partially exploded side view illustrating the placement of the mounting assembly shroud, the leveling screw caps, the housing end caps, and the housing cover plates upon completion of the installation. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Ceiling-mounted medical service columns provide several advantages, especially in the surgical, emergency room and critical care settings. Articulating arm assemblies have greatly improved movability of these columns. However, there is an ongoing need to improve these systems to provide quieter, stronger and more reliable braking systems, to facilitate multi-dimensional leveling of the components during assembly and throughout the life of the system, to make installation simpler and safer using modular components, and to achieve these goals without increasing the weight or the footprint of the overall apparatus. 
     Turning now to the drawings in general and to  FIG. 1  in particular, there is shown therein a medical service system constructed in accordance with the present invention and designated generally by the reference numeral  10 . As is apparent from  FIG. 1 , the system  10  is ideally suited to be supported on the ceiling  12  of a hospital room  14  and is depicted adjacent a hospital bed  16 . However, the system  10  may be installed in any structure and in a variety of settings such as clinics, emergency rooms, operating rooms, nursing home rooms, and virtually any sort of medical treatment facility. In addition, though mounting to a ceiling or other horizontal surface is preferred, the system can be supported from other structures such as walls or other vertical support surfaces. 
     As seen in  FIGS. 1-5 , the system  10  may be provided in modular components for easy shipping and simplified installation. Preferably, these components comprise a mounting assembly  20 , an arm assembly  22 , and a medical service unit  24 . Supported on the service unit  24  are at least one and usually several medical service outlets designated collectively at  30 . Also included in the system  10 , as seen in  FIG. 2 , are conduits designated generally at  34  including a conduit for supplying a service to each of the service outlets  30 . 
     As used herein, “services” refers to all types of gases, liquids, vacuum, power and data lines, including but not limited to oxygen, compressed air, vacuum (suction), electricity, telephone, audio and video signals, and all forms of digital and analog data signals for computer networking and the like. Accordingly, each of the service outlets  30  is adapted to supply a particular service in a well known manner. In most instances, the outlets will include several different types of outlets, gas connections, telephone jacks, coaxial cable connections, electrical outlets, and others to make the different types of services all available from the service unit  24 . Likewise the conduits  34  will be adapted to supply the different types of services and will include gas conduits, electrical wires, coaxial cables, telephone and data lines, and so forth. 
     It will now be apparent that, though the system  10  is particularly suited for a medical environment, it could be adapted easily to other settings that require supply of any or all such services. This might include other technical settings, such as laboratories and manufacturing facilities, or office settings, requiring repositionable connections to service lines. 
     With reference now to  FIG. 3 , a preferred mounting assembly  20  will be described. The mounting assembly  20  comprises a mounting member or structure, such as the mounting plate  40  by which the assembly  20  is connectable to the ceiling  12  or other structure. The plate  40  preferably is circular and flat, but may take other shapes as it will be adapted to conform to the supporting surface. 
     The mounting assembly  20  also includes a first rotor assembly  42  mounted for rotation relative to the mounting plate  40 , which is fixed to the ceiling  12  ( FIG. 1 ). The rotor assembly  42  may vary, it will usually be ring-shaped or annular and will include a central bore  44  therethrough. 
     Also included in the mounting assembly  20  is a first electromagnetic brake assembly  46 , which is adapted to control rotation of the first rotor assembly  42 . In a manner to be described in more detail hereafter, the brake assembly  46  is magnetically engageable with the first rotor assembly  42 . 
     A first coupler  50  is supported on the rotor assembly  42  for rotation with it. As will become apparent, there are several similarly formed rotor assemblies, brake assemblies, and couplers in the system  10 , and one of each these components will be described in more detail hereafter. 
     Turning next to  FIGS. 2 ,  4  and  5 , the arm assembly  22  will be described. As best shown in  FIG. 2 , the arm assembly  22  has a distal end  60  and a proximal end  62 . The proximal end  62  of the arm assembly  22  is engageable with the first coupler  50  of the first mounting assembly  20  in a manner yet to be described. 
     Most preferably, the arm assembly  22  includes a first arm  66  and a second arm  68 , the first arm  66  having a proximal end  70  and a distal end  72 , and the second arm  68  having a proximal end  76  and a distal end  78 . Thus, the proximal end  76  of the second arm  68  forms the proximal end  62  of the arm assembly  22 , and the distal end  72  of the first arm  66  forms the distal end  60  of the arm assembly. 
     The first arm  66  comprises an elongate, hollow housing  80  having a generally rectangular cross section. Mounted for rotation on the distal end  72  of the first arm  66  is a second rotor assembly  82 . Like the other rotor assemblies, the rotor assembly  82  has a central bore  84  therethrough ( FIG. 4 ) continuous with the inside of the housing  80 . Also provided on the distal end  72  of the first arm  66  is a second brake assembly  88 , which is adapted to control rotation of the second rotor assembly  82  by magnetic engagement with the rotor assembly  82 . As second coupler  92  with an opening (not shown) is supported from the second rotor assembly  82 . 
     Again referring to  FIG. 2 , in the preferred embodiment shown and described herein the service unit  24  is a long narrow vertically-oriented multi-sided column, although the shape and orientation of the unit can vary, and the arm assembly  22  is generally horizontal. Thus, the column  24  has a proximal end  106  and distal end  108 . In this embodiment, where the column  24  is suspended from the ceiling  12  ( FIG. 1 ), the distal end  108  floats freely and the proximal end  106  is engageable with the distal end  60  of the arm assembly  22 , that is, the distal end  72  of the first arm  66 , and specifically the second coupler  92  thereof. Thus, the second coupler  92  ( FIG. 4 ) may be formed as a small mounting plate that secures to the top of the column  24 . 
     With continuing reference to  FIGS. 2 and 5 , the second arm  68  comprises an elongate, hollow housing  110  similar to the housing  80  of the first arm  66 . The second arm  68  comprises a third rotor assembly  112  mounted for rotation on the distal end  78  of the second arm  68 . Like the other rotor assemblies, the third rotor assembly  112  has a central bore  114  therethrough ( FIG. 4 ). The second arm  68  comprises a third brake assembly  116 , also having a central bore  118  therethrough. A third coupler  120 , similar to the first coupler  50  on the mounting assembly  20 , is fixed to the rotor assembly  112  for rotation therewith. 
     As illustrated in  FIG. 2 , the preferred system  10  provides a continuous path for the conduits  34 . This path begins at the service sources elsewhere in the facility above the ceiling  12  (junction boxes, gas manifolds, etc.), or beyond whatever support surface that engages the mounting assembly  20 . The path continues through the central bores  44  and  48  of the rotor and brake assemblies  42  and  46  in the mounting assembly  20 , then through the second arm  68  and the central bores  114  and  118  of the rotor and brake assemblies  112  and  116  in the second arm. Finally, the path passes through the first arm  66  and the central bores  84  and  90  of the rotor and brake assemblies  82  and  88  in the in the first arm, and down into the column  24  to connect to the outlets  30 . This configuration allows the profile and footprint of the arms and column to be minimized. 
     From the forgoing, it will be understood that each of the above-described sets of rotor and brake assemblies with the attached couplers forms a joint for rotatably connecting a first member, such as the mounting assembly, the first arm or the second arm, to a second member, such as the first arm, the second arm, or the column. This joint is exemplified by the distal end  78  of the second arm  68  shown in  FIGS. 6 and 7 . 
     Referring now to  FIGS. 6-10 , the preferred design for the brake assembly  116  will be described in more detail. The brake assembly  116  comprises a brake member, such as the permanent magnet  130 . In this embodiment, the magnet is ring-shaped and captured between an inner brake housing  132 , which defines the central bore  118 , and an outer brake housing  134 . These components are secured together with multiple screws  136  surrounding by bushings  138  through aligned openings (not separately numbered). 
     For ease of manufacture, the permanent magnet  130  may be formed of multiple sections that together form a ring, with abutting ends of adjacent sections forming the openings to receive the bushings  138 , as best seen in  FIG. 8 . When the magnet  130  is comprised of such multiple segments, it is convenient to include a marking to indicate polarity and thus correct positioning of the magnets relative to each other and of the assembled magnet to the brake assembly. To that end, in the embodiment shown herein, each segment is provided with an indicator, such as a colored dot  140 , in the same position. Thus, assembly of the magnet ring is guided by correct arrangement of the dots. While the dots  140  are visually perceptible, tactile indicators, such as bumps, ribs or grooves could be employed instead. 
     With continuing reference to  FIGS. 6-10 , the outer brake housing  134  has flanges  142  and  144  on opposite sides for receiving bolts  146  ( FIGS. 6 &amp; 7 ), which secure the brake assembly  116  to the floor of the housing  96 . Captured between the heads of the bolts  146  and the floor of the housing  96  is a bearing collar  150  with an inner annular shelf  152  for supporting the outer race  154  of a bearing assembly  156 . 
     Referring to  FIGS. 6 ,  7  and  10 , the coil  160  is received in a downwardly opening groove  162  formed by the inner and outer brake housings  132  and  134  when assembled. The coil  160  is energized by wires  164  ( FIGS. 7 &amp; 9 ) extending through openings  166  in the outer housing  134 . The coil  160  may be embedded in epoxy filler (not shown). 
     Referring briefly again also to  FIG. 5 , the rotor assembly  112  comprises a rotor  170  and a rotor extension tube  172 . The rotor  170  is continuously urged upwardly toward the bottom of the brake assembly  116  by coil springs  176  supported in a plastic spacer ring  178 . The lower ends of the springs  176  sit on an annular bearing cap  180 , which in turns rest on the upper edge of the extension tube  172 . The extension tube  172  and the bearing cap  180  are secured together by long bolts  184  with hex nuts  186 . An outer circumferential shelf  190  formed near the upper edge of the extension tube  172  supports the inner race  192  of the bearing assembly  156  and is captured between the bearing cap  180  and the tube ( FIG. 6 ). 
     The upper ends of the long bolts  184  extend up through openings  194  and  196  in the spacer  178  and the rotor  170  ( FIGS. 5&amp;12 ). The openings  194  in the spacer  178  are large enough to receive the standard hex nuts  186 . The ends of the bolts  184  extend up through but do not engage the openings in the rotor  170 . 
     When torque is applied to the coupler  120  and the attached rotor extension tube  172 , torque is transferred to the “floating” rotor  170  by means of two custom nuts  198  ( FIGS. 11&amp;13 ) threadedly attached to the upper ends of two of the bolts  184 . This arrangement is seen best in  FIGS. 9 and 10 . Two enlarged and oval shaped holes  200  are provided on opposite sides of the rotor  170 . Two custom hex nuts  198  ( FIG. 11 ) have an upper portion  198   a  and a lower portion  198   b . The upper portion  198   a  is sized to be received in the ovoid holes  200  so that there is some hole “slop” or movement in the direction aligned with the long dimension “D” but so that relatively little movement is permitted in the perpendicular direction “d”. 
     The electrical wires  164  supplying the coil  160  are connected to an electrical circuit (not shown) that is controlled by a control panel  202 , which may be formed in a handle  204  illustrated schematically in  FIG. 14 . The handle  204  may be conveniently placed on the column  24 , as seen in  FIGS. 1 and 2 . As shown in  FIG. 14 , the control panel  202  is place at the top of a vertical bar shaped handle  204  and includes a pressure sensitive toggle switch  206  located for comfortable operation by the thumb or forefinger of the user while the fingers of the user&#39;s hand grip the handle  204 . 
     Preferably, the toggle switch  206  has four positions. In the first or stop position, all the brake assemblies are engaged so that the position of the column  24  is maintained. In the second position, with the toggle switch  206  rocked to one side, preferably the left side as viewed in  FIG. 14 , the brake assemblies at the ceiling  12  (between the ceiling and the second arm) and the column  24  (allowing the column to rotate relative to the first arm) are released, so that the system  10  can be repositioned without bending the joint between the first and second arms  66  and  68 . In the third position, with the toggle switch  206  rocked to the other side, preferably the right side as viewed in  FIG. 14 , the brake assemblies between the arms  66  and  68  and for the column  24  are released, so that the column and the first arm  66  can be repositioned without changing the position of the second arm  68  relative to the ceiling  12 . In the fourth position, with the center of the switch  206  depressed, all the brake assemblies are released, allowing multi-directional movement at all joints of the system  10 . 
     Referring still to  FIG. 14 , the control panel  202  preferably also includes appropriate indicator lights  208 , supplied by LED&#39;s (light emitting diodes), for example. In a preferred arrangement, there are four indicator lights. A power light  208   a  remains lit when the system  10  is energized. This also serves to confirm that the system  20  is connected to power. 
     A first horizontal bar-shaped light  208   b  indicates by lighting up or glowing when the brake assembly between the second arm  68  and the ceiling  12  is released. A second horizontal bar-shaped light  208   c  indicates when the brake assembly between the first and second arms  66  and  68  is released. A third vertical bar-shaped light  208   d  indicates when the brake assembly for the column  24  is released. Now it will be understood that the configuration and arrangement of the three bar-shaped lights  208   b - d  generally mimics the shape and arrangement of the first and second arms  66  and  68  and column  24  of the system  10 , visually communicating to the user function of the switch  206 . 
     Now it will also be seen that in all active switch positions the switch  206  releases the third brake assembly, that is, the brake assembly that controls rotation of the column  24 . This is desirable because it will virtually always be necessary to rotate the column  24  at least slightly regardless of how the other components are being repositioned. 
     When the coil  160  is not energized, the permanent magnet  130  exerts a strong direct force on the rotor  170  to resist rotation so that the column will not be inadvertently moved. The magnet and rotor should be selected to provide resistance up to a predetermined torque, selected to prevent inadvertent movement but to allow the column  24  to move in response to a force greater than the resistance to overcome the power of the magnet. This will reduce the likelihood of serious damage to the system  10  if the column  24  is accidentally hit by a strong force, such as a motorized x-ray machine. When the coil  160  is energized, the coil neutralizes the force of the magnet  130  and allows the rotor  42  assembly to rotate freely. 
     Now it will be apparent that the brake assemblies utilized in this embodiment are electrically released, that is, the brake member (the permanent magnet) continuously engages the rotor until the coil is energized, which neutralizes the braking action of the permanent magnet. It will also now be appreciated that other brake designs could be substituted. For example, while the brake member in the preferred embodiment comprises a permanent magnet, there may be applications where only an electric magnet is required. For example, an electric brake without a permanent magnet could be used in applications where the brake is engaged when energized instead of released. 
     Various modifications in the configuration of the brake member are contemplated as well. For example, the brake member in this embodiment is ring-shaped, similar to the rotor, and the two surfaces are structurally arranged much like a clutch plate and a flywheel, although the engagement mechanism is magnetic attraction instead of mechanical pressure to create a frictional engagement. (Of course, in the present invention, engagement of the permanent magnet with the rotor prevents rotation instead of driving it.) Alternative electromagnetic brake configurations include electrically energized magnetic brake shoes, as in a drum brake, or calipers, as in a disc brake. Most preferably, however, the brake system herein relies on magnetic attraction between the brake and the rotor, rather than a purely mechanical engagement. 
     Now it will be appreciated that the preferred brake assembly employed in this invention not only permits multiple service conduits to pass through its center bore but also combines a strong brake force with a simple design having relatively few parts. This provides a service column that is stable for attaching and removing medical equipment, and yet requires less maintenance than more complex systems. In addition, the only power required by the brake assembly is electricity, avoiding the problems associated with pneumatic braking systems, such as the requirement for separate, dedicated air compressors. 
     The system  10  of the present invention also provides an improved coupling design, depicted in  FIGS. 15-18 . As previously mentioned, first, second and third couplers  50 ,  120  and  92  are attached to the bottoms of the rotor assemblies  42 ,  82 , and  112 . The coupler  92  is simply a plate as has been previously explained. The first and second couplers  50  and  120  are identical and therefore only the second coupler will be described. Similarly, since the proximal ends  70  and  76  of the first and second arms  66  and  68  are identically formed, only the proximal or coupling end of the first arm will be described. 
     As shown in  FIG. 15 , the two inwardly projecting pins  210  and  212  are provided on the inside of the side walls of the arm housing  80 . These may be integrally formed in the housing or incorporated in a rib or brace  214  which is then fixed to the inside of the housing. 
     The preferred coupler  120  is a saddle shaped structure having a top wall  216  and two depending side walls  218  and  220  ( FIG. 5 ). Each side wall  218  and  220  has formed in it a J-shaped slot  224  and  226 , each having a horizontal leg and a vertical leg. Also provided on the inside of the side walls  218  and  220  are latches pivotally mounted on pivot pins for movement between an open position, in which the J-slot is open, and a closed position in which the J-slot is blocked. Preferably, each latch  230  has a foot, such as the foot  234 . The latch  230  is biased in the downward or closed position, shown in  FIG. 14 , by a coil spring  236 . 
     The operation of this “slide and lock” coupling is illustrated in  FIGS. 17 and 18 . With the second arm  68  already installed and its coupler/saddle  120  supported from above, the first arm  66  is lifted and tilted as shown in  FIG. 17 . This allows the saddle  120  to be guided inside the access opening  240  ( FIG. 4 ) in the arm housing  80  so that the pins  210  and  212  move into the horizontal legs of the J-slots  224  and  226 . Next, the arm  66  is brought back to a level position and moved forward so that the pin  212  moves back and up into the vertical leg of the J-slot, as seen in  FIG. 18 . As the pin  212  moves through the slot, it pushes the latch  230  upwardly. Once the pin  212  reaches the vertical leg of the J-slot, the foot  234  of the latch  230  snaps back into its resting position and blocks the escape of the pin  212 . In this way, the coupling of the arm  68  to the saddle  120  is accomplished by a single, sliding movement of the arm. 
     The couplers utilized in this invention also comprise a multi-dimensional leveling assembly also seen in  FIGS. 16-18 , designated generally by the reference numeral  242 . The leveling assembly  242 , in its preferred form, comprises two pairs of leveling bolts, including one upwardly extending pair  244  that engages the top of the housing  80  and one downwardly extending pair  246  that engages the bottom of the housing. The pitch and roll of the arm  68  can be adjusted by independently adjusting the each of the four leveling bolts. 
     Once the joint been assembled and the arm have been leveled, the position of the arm can be locked into place with a locking assembly  250 , illustrated in  FIGS. 19 and 20 . The locking assembly  250  comprises a locking bracket  252  and a pair of locking bolts  254 . The bracket  252  is adapted to engage the arm in some manner and so may be provided with a pair of laterally extending ears  256  that are engageable with notches or slots  258  formed on the sides of the arm  66 . The notches are conveniently formed as part of the brace  214 , as is also shown in  FIGS. 4 ,  5  and  15 . As seen in  FIGS. 19 and 20 , the bolts  254  are receivable in the holes  260  in the top of the saddle  120 . 
     First, the locking bracket  252  is placed between the downwardly extending leveling bolts  246  ( FIG. 19 ) so that the ears  256  are positioned in the slots  258 . Then, the locking bolts  254  are inserted through the holes  260  in the top of the saddle  120  and threaded down through the aligned holes  262  in the locking bracket ( FIG. 20 ). As the locking bolts  254  are threaded in the holes  262 , the bracket  252  is pulled upwardly toward the top of the saddle  120 . At the same time, because the ears  256  are extending through the slots  258 , the brace  214  and attached arm housing  80  are likewise pulled upwardly until a tight engagement between the saddle  120  and arm housing is achieved. 
     In the embodiment shown, the locking engagement between the arm housing and the saddle is performed by the notches fixed inside the arm and the ears on the locking bracket. Those skilled in the art will recognize that various other structures and shapes may be employed for this purpose. 
     Having described the various components and features of the system  10 , a preferred installation procedure will be summarized. First, the mounting assembly  20  is secured to a suitable structure in the ceiling  12 . The locking bolts  254  are removed, and the leveling bolts  244  and  246  are retracted. Next, the second arm  68  is lifted into place and the latch pins  212  are engaged with the latch  230  on the saddle/coupler  120 , as previously described. Then the second arm  68  is leveled using the leveling assembly  240 , and the locking assembly. 
     Once the second arm  68  is connected, the first arm  66  is engaged with the second coupler  120 , and the leveling and locking assemblies  242  and  250  are engaged as before. Now the third coupler, the coupling plate  92 , is accessible. At this point the conduits  34  are fed through the arm assembly  22 . Use of a conduit tray  266 , such as that show in  FIG. 21 , inside each housing  80  and  110  will facilitate the conduit placement. The supply ends of the conduits  34  are connected to their respective outlets  30  inside the column  24 , and then the column may be mounted to the coupling plate  92 . Some additional leveling may be necessary after attachment of the column  24 . 
     Once the locking assemblies  250  all are in place, the installation is completed as shown in  FIG. 22  by attaching the shroud  268  around the first rotor assembly  42  on the mounting assembly  20 . End caps  270  are placed over the open ends of the arm housings  80  and  96 . Cover plates  280  are attached over the access openings  240  and  248  ( FIGS. 4&amp;5 ) in the housings. 
     Now it will be appreciated that the four main components of the system  10 —the mounting assembly, the first arm, the second arm, and the column—can be preassembled as modular units and shipped in four separate packages, which are smaller and lighter to ship and to handle at the site. The smaller, modular components can be easily installed by only two workers. This assembly is made safer and simpler by the “slide and lock” couplings at each joint. The leveling assemblies permit easy access and adjustment for routine maintenance throughout the life of the system, as well as during installation. Finally, the brake assemblies are advantageous because they provide improved strength and stability when the column is at rest, while allowing the column to yield in response to an accidental impact that would otherwise be damaging. The electrically releasable magnetic brakes are incorporated into other annular components of the joints with large central openings that allow all the conduits to pass through eliminating the need for additional space around the joints. 
     Changes can be made in the combination and arrangement of the various parts and steps described herein without departing from the spirit and scope of the invention.