Abstract:
A carriage assembly for carrying read/write heads into engagement with a recording medium is provided. The carriage assembly includes a carriage body that defines a sidewall having a first opening and a second opening with a passage extending therebetween. A coil is securely coupled with the carriage body sidewall. The carriage assembly rides on a central guide track when the carriage assembly is mounted within a disk drive. The carriage assembly is free to rotate about the central guide track. A first in-rigger extends laterally from the carriage body and a second in-rigger extends laterally from the carriage body. Each of the in-riggers has a protrusion extending from an inner surface. If the carriage assembly rotates sufficiently in one direction one of the protrusions will contact a magnet of the disk drive to prevent further rotation of the carriage assembly in that direction. Similarly, if the carriage assembly is rotated in the opposite direction, the other protrusion will contact the magnet to prevent rotation of the carriage assembly in the opposing direction. The in-riggers thereby maintain the carriage assembly centered on the central guide track.

Description:
RELATED APPLICATIONS 
     This Application is a divisional of U.S. provisional Application Ser. No. 08/866,180 filed on May 30, 1997, now U.S. Pat. No. 5,969,908 and hereby incorporates by reference that application. 
     The present application is related to the following patent applications all of which are hereby incorporated by reference in their entirety: 
     Ser. No. 08/866,189, filed on May 30, 1997, entitled “An Improved Operating System For Operating An Eject System And A Head Retraction System Of A Disk Drive”; Ser. No. 08/881,804, filed on May 30, 1997, entitled “Media Capture to Prevent Head Damage In A Removable Cartridge Disk Drive”; Ser. No. 08/0866,225, filed on May 30, 1997, entitled “An Improved Head Retraction System for Retracting The Heads Of A Disk Drive”; Ser. No. 08/881,803, filed on May 30, 1997, entitled “Steering Magnets To Reduce Magnetic Leakage Flux In A Disk Drive”; Ser. No. 08/881,805, filed on May 30, 1997, entitled “Laminated Steel Return Path With Actuator Support Features”; Ser. No. 08/866,190, filed on May 30, 1997, entitled “Dual Loop Flex Circuit For A Linear Actuator”; Ser. No. 08/872,712, filed on May 30, 1997, entitled “Interlocking Carriage Assembly For Linear Actuator”; Ser. No. 08/881,806, filed on May 30, 1997, entitled “Head Gimbal Protection For A Disk Drive”; Ser. No. 08/866,168, filed on May 30, 1997, entitled “Flexured Mounting System For Friction Reduction And Friction Linearization In Linear Actuator For Disk Drive; Ser. No. 08/881,807, filed on May 30, 1997, entitled “Return Path Geometry to Enhance Uniformity Of Force On A Linear Actuator”; Ser. No. 08/866,171, filed on May 30, 1997, entitled “Integral Lift Wing For A Disk Drive Actuator”; Ser. No. 08/866,227, filed on May 30, 1997, entitled “Head Protection In A Disk Drive”; Ser. No. 08/866,167, filed on May 30, 1997, entitled “Self-Positioning Lever For Opening The Shutter Of A Removable Disk Cartridge”; Ser. No. 08/866,177, filed on May 30, 1997, entitled “Motor Loading System For A Disk Drive”; Ser. No. 08/866,226, filed on May 30, 1997, entitled “An Improved Eject System For Ejecting A Disk Cartridge From A Disk Drive”; Ser. No. 08/881,808, filed on May 30, 1997, entitled “Cover For A Disk Drive”. 
    
    
     FIELD OF THE INVENTION 
     The present invention is related to linear actuators for carrying read/write heads into engagement with a recording medium, and, more particularly, to an in rigger for maintaining the desired position of the carriage assembly as the read/write heads engage and disengage from the recording medium. 
     BACKGROUND OF THE INVENTION 
     DESCRIPTION OF THE PRIOR ART 
     Disk drives for storing electronic information are found in a wide variety of computer systems, including workstations, personal computers, and laptop and notebook computers. Such disk drives can be stand-alone units that are connected to a computer system by cable, or they can be internal units that occupy a slot, or bay, in the computer system. Laptop and notebook computers have relatively small bays in which to mount internal disk drives and other peripheral devices, as compared to the much larger bays available in most workstation and personal computer housings. The relatively small size of peripheral bays found in laptop and notebook computers, can place significant constraints on the designer of internal disk drives for use in such computers. Techniques that address and overcome the problems associated with these size constraints are therefore important. 
     Disk drives of the type that accept removable disk cartridges have become increasingly popular. FIG. 1 shows one disk drive product, known as the ZIP™ drive, that has been very successful. This disk drive is designed and manufactured by Iomega Corporation, the assignee of the present invention. ZIP™ drives accept removable disk cartridges that contain a flexible magnetic storage medium upon which information can be written and read. The diskshaped storage medium is mounted on a hub that rotates freely within the cartridge. A spindle motor within the ZIP™ drive engages the cartridge hub when the cartridge is inserted into the drive, in order to rotate the storage medium at relatively high speeds. A shutter on the front edge of the cartridge is moved to the side during insertion into the drive, thereby exposing an opening through which the read/write heads of the drive move to access the recording surfaces of the rotating storage medium. The shutter covers the head access opening when the cartridge is outside of the drive, to prevent dust and other contaminants from entering the cartridge and settling on the recording surfaces of the storage medium. 
     The ZIP™ drive is presently available for workstations and personal computers in both stand-alone and internal configurations. In order to provide a version of the ZIP™ drive for use in laptop and notebook computers, the size constraints of the peripheral bays of such computers must be considered. In particular, for an internal drive to fit in the majority of laptop and notebook peripheral bays, the drive must be no longer than 135 mm. The height of the drive must be in the range of 12 to 15 mm. These dimensions place many constraints on the design of such a drive, and give rise to numerous design problems. 
     FIG. 1 shows a carriage assembly that is employed in the ZIP™ and disclosed in Ser. No. 08/727,128 entitled Actuator For Storage Device, filed on Oct. 8, 1996 and hereby incorporated by reference in its entirety. The ZIP™ drive carriage assembly  10  comprises a main carriage  12 , carriage arms  20 , load beams  24 , write/read heads  26 , voice coil  16 , an outrigger  18  and outrigger guide track  46 . The carriage arms  20  are formed with the main carriage  12 . Each carriage arm  20  is mechanically coupled to a corresponding load beam  24 . Each head  26  is mechanically coupled to a corresponding load beam  24 . 
     The carriage  12  comprises an elongated sidewall  28  that defines two opposing open ends  30  and  32  with a passage  34  extending therebetween. The open ends  30  and  32  are adapted to receive cylindrical bushings  36  and  38 . The passage  34 , open ends  30  and  32 , and bushings  36  and  38  are adapted to slidingly receive a guide track (not shown). 
     The coil  16  is mounted to the carriage  14  by adhesives or bonding methods. The outrigger  18  is mounted to a portion of the coil  16  and travels along the outrigger guide track  46  to prevent rotation of the carriage assembly  10  when the carriage assembly is in operation. Most of the components described above are coupled to one another by individual connecting steps, such as with adhesives and bonding methods. There are several drawbacks with having to attach these components individually. 
     One drawback with an outrigger and outrigger guide track is the require a relatively large amount of space within an electronic environment to operate. It would, therefore, be desirable to provide a means for maintaining the desired position of a carriage assembly that requires less space to perform this function. 
     Another drawback of employing the outrigger and outrigger guide track is that they increase the number of components that must be designed and accounted for. It would therefore be desirable to reduce the number of components that comprise a carriage assembly. 
     Yet another drawback of employing the outrigger and outrigger guide track is that they must be individually attached within close tolerances. This production requires near exact precision which is relatively difficult to obtain. It would therefore be desirable to provide a means of manufacturing the desired carriage assembly more exact and easily. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an in-rigger for maintaining a carriage assembly in the desired position as the carriage arm engages a recording medium is provided. The in-rigger comprises an elongated body having a first end and an opposing second end. The body has a relative outer surface and a relative inner surface. At least one protruding member extends proximate the second end along the inner surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art carriage assembly; 
     FIG. 2 is an enlarged perspective view of an linear actuator incorporating a carriage assembly in accordance with the present invention; 
     FIG. 3 is a perspective view of an exemplary disk drive incorporating the present invention; 
     FIG. 4 is a perspective view of the carriage assembly shown in FIG. 2 without all of the operating components coupled thereto; 
     FIG. 5 is an exploded view of a carriage assembly according to one aspect of the present invention; 
     FIG. 6 is a rear view of a carriage assembly in accordance with one aspect of the present invention; 
     FIG. 7 is a perspective view of a carriage arm employed in the carriage assembly shown in FIG. 3; 
     FIG. 8 is an exploded view of a mold assembly employed to produce at least one embodiment in accordance with one aspect of the present invention; 
     FIG. 8A is a sectional sideview of the mold assembly; and 
     FIG. 9 is a perspective view of an exemplary disk drive in which a carriage assembly in accordance with the present invention may be employed. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2 is an enlarged view of an actuator carriage assembly  52  in accordance with the present invention. The actuator carriage assembly comprises a front bearing  54 , a voice coil  56 , upper carriage arm  58 , lower carriage arm  60 , upper load beam  62 , lower load beam  64 , read/write heads  66 , center rod or guide track  68  having a center axis C-C′, an amplifier chip  70 , traces  72  for the voice coil  56 , and flex circuits  74  which are coupled to the carriage body  78 . 
     The guide track  68  is positioned within a passage  76  defined by the carriage body  78  such that the carriage body  78 , voice coil  56 , carriage arms  58  and  60 , and load beams  62  and  64  are all substantially symmetrically centered around and move along the guide track  68 . Additionally, the guide track  68  is adapted to ride along the front bearing  54  and rear bearing (not shown) to linearly direct the carriage assembly. Such symmetrical spacing is advantageous because it aligns the carriage assembly center of mass and center of force along the guide track. Such alignment also minimizes friction and avoids binding forces and resonance problems. 
     Although the guide track  68  linearly directs the carriage assembly  52 , the carriage assembly  52  remains unrestrained from rotating about the guide track  68 . Such rotation causes the carriage assembly  52  to roll about the center axis, which in turn, adversely affects the accurate pitch of the read/heads  66 . This roll can also cause the coil  56  and other components to make contact with the actuator cover  69  (FIG. 3) which is located directly above the voice coil  56 . The in-riggers  80  and  81  are provided to maintain the desired positioning of the carriage assembly  52  when the assembly is in operation. The in-riggers  80  and  81  and cover  68  are discussed in more detail below. 
     The function and purpose of the traces for the coil  72 , amplifier chip  70 , and flex circuit  74  and how they are coupled to the carriage body  78  are discussed in more detail in the following copending patent application assigned to the assignee of the present case entitled “Dual Loop Flex Circuit For a Linear Actuator, Ser. No. 08/866,190, filed concurrently herewith and hereby incorporated by reference in its entirety. 
     FIG. 4 shows the carriage assembly in accordance with the present invention in more detail. Specifically, the carriage body  78  defines a sidewall  82 . Preferably, the sidewall  82  has an upper surface  84 , bottom surface  86  having a generally triangular portion  87  adapted to be coupled with the flex circuit, relative front surface  88 , relative back surface  90 , and two side surfaces  92  and  94  therebetween. The relative front surface  88  defines a first open end  96  and the relative back surface  90  defines a second open end  98 . A passage  76  extends between the first open end  96  and second open end  98 . Preferably, the carriage body  78  is made from VECTRA© Liquid Crystal Polymer (LCP) a plastic material sold by General Electric, located in Massachusetts. 
     A first or front bearing  54  is coupled with the sidewall  82  proximate the first open end  96  and the rear or a second bearing  55  is coupled with the sidewall proximate the second open end  98 . Preferably the front bearing  54  is interlockingly coupled proximate the first open end with the side wall  82 . Preferably, the first bearing is a sapphire jewel bearing. The preferred rear bearing  55  is described in copending patent application assigned to the assignee of the present case entitled “Elongated Rear Bearing For Linear Actuator”, Ser. No. 08/866,758, filed concurrently herewith and hereby incorporated by reference in its entirety. The rear bearing is press fit, attached with an adhesive or other similar methods. The guide track  68  is adapted to be slidingly mounted within the passage  76  and in sliding cooperation with each of the bearings  54  and  55 . With the front bearing  54  interlockingly coupled with the sidewall, the front bearing  54  is maintained in its desired operating position without the application of adhesives or bonding methods. 
     The carriage assembly  52  comprises at least one carriage arm  58  for coupling a load beam  62  and at least one read/head  66 . Preferably, an upper carriage arm  58  and a lower carriage arm  60  are provided. Each carriage arm has a proximal end  100  and distal  102 . A portion of the proximal end  100  of each arm  58  and  60  is interlockingly coupled with the carriage body sidewall  82 , front surface  88 . The upper carriage arm  58  is interlockingly coupled with the sidewall  82  above the first open end  96  in spaced relationship from the lower carriage arm  60  which is interlockingly coupled within the carriage body sidewall  82  below the first open end  96 . The distal end  102  of each carriage arm  58  and  60  is adapted to be mechanically coupled with a corresponding load beam  62  and  64 . The upper  58  and lower  60  carriage arms  58  and  60  are positioned such that when the load beams  62  and  64  and read/write heads  66  are coupled thereto, the heads  66  engage the recording medium at the desired location. With the carriage arms  58  and  60  interlockingly coupled within the sidewall, the carriage arms are maintained in their desired operating position without the application of adhesives or bonding methods. The preferred shape and other characteristics of each carriage arm are discussed in more detail below. 
     The coil  56  is preferably interlockingly coupled along the upper surface  84  of the carriage body sidewall  82  between the front surface  88  and back surface  90  of the carriage body sidewall  82 . Preferably, the coil  56  has a sidewall  57  having a generally rectangular cross-section with a relative outer surface  57   a  and relative inner surface  57   b . In this position, the coil  56  provides opposite openings  59   a  and  59   b  that are adapted to be in sliding communication with the inner return paths  168   a  and  168   b . With the coil  56  interlockingly coupled with the sidewall, the coil is maintained in its desired operating position with the application of bonding methods or adhesives. Additionally, a subcarriage is not required to couple the coil to the carriage body. 
     At least one in-rigger  80  in accordance with the present invention is coupled with the carriage body sidewall  82  such that the carriage assembly  52  is maintained in operating position as the carriage assembly is manipulated to engage a recording medium. Preferably, two opposing in-riggers  80 ,  81  are integrally formed with the carriage body sidewall  82  and interlockingly coupled with portions of the coil inner surface  57 b. Preferably, the in-riggers are made of the same material as the carriage body. With the in-riggers  80 ,  81  provided in this manner, the need for an out-riggers and out-rigger guide rail is eliminated and, thereby, conserves space in the carriage assembly and reduces the number of components that must be accounted for in the carriage assembly. The in-riggers are discussed in more detail below. 
     The coil  56  is adapted to be in sliding cooperation with the two inner return paths  168   a ,  168   b  on opposite sides of the carriage assembly  52  (see FIG.  7 ). Preferably, the in-riggers  80 ,  81  are adapted to be in sliding communication with only one of the inner return paths. 
     FIG. 5 is an exploded view of the carriage assembly, coil, in-rigger, and upper carriage arm. The lower carriage arm and guide track are removed from this figure for clarity sake. An upper in-rigger  80  and lower in-rigger  81  opposing one another are coupled to the carriage body sidewall  82 . Preferably, each in-rigger  80 ,  81  is integrally formed with the carriage body sidewall  82 . 
     Preferably, each in-rigger comprises an elongated member  300  extending laterally from carriage body  78 . The elongated member  300  has a relative front portion  302 , relative rear portion  304 , first end  306  proximate the carriage body, and an opposing second end  308 . The contacted member also has a relative outer surface  310  and relative inner surface  312 . The length and width of each in-rigger will depend upon the size of the coil and of the electrical component that is employed. 
     A protruding portion  314  extends away from the inner surface  312  proximate the second end  308  and traverses from the relative front portion  302  to the relative rear portion  304  of the elongated member  300 . 
     Referring to FIG. 6, the protruding portion  314  is adapted to pressingly or pushingly cooperate with one of the inner return paths  168   a  when the carriage assembly is in operation to maintain the desired position of the carriage assembly. The outer return paths  166  and rear bearing  55  are also shown. 
     The relative outer surface  310  of each elongated member  300  is adapted to abuttingly cooperate with the inner surface  57   b  of the coil  56  when the coil is interlockingly coupled with the carriage body sidewall. Preferably, the outer surface  310  of each elongated member is substantially flat. 
     It is noted that the in-rigger  80  and  81  can be produced separately from the carriage body and be employed with other carriage assemblies in addition to the specific carriage assembly embodiment discussed herein. Each in-rigger can be attached to the coil with an adhesive or like attaching methods. In this alternative embodiment, the dimensions of the in-rigger will depend upon the actual coil and actuator assembly employed. 
     Preferably, the in-riggers  80  and  81  are adapted to be in sliding communication with only one of the inner return paths. The positioning of the in-riggers  80  and  81  in relationship to the inner return paths  168   a  prevents the coil from rotating and hitting the cover. 
     FIG. 7 shows the carriage arm  58  in more detail. The carriage arm  58  comprises an elongate body  104  having a proximal end  100  and distal end  102 . The body  104  defines a stiffening bead  106  for strengthening the carriage arm. Preferably, the bead  106  is a continuous oblong shaped bead. The bead  106  extends between the distal end and proximal end. The proximal end  100  of the body defines one set of opposing relatively small slots  108  and one set of relatively large slots  110 . The portion of the body extending between these slots is adapted to be securely interlocked with the front surface  88  of the carriage body sidewall  82 . Several holes are formed in the body for different purposes. 
     A through hole  112  is formed in the elongated body proximate the proximal end  100  of the body. Preferably, the through hole  112  has an oblong, oval or other like shape. The purpose of the through hole is discussed below. Four apertures  114  are formed in the body  104  to reduce the weight of the carriage arm. It is desired to reduce the weight to enable the carriage assembly to accelerate faster for operating purposes. An attaching opening  116  is provided proximate the distal end  102  of the carriage arm. The attaching opening adapted to mechanically couple with a load beam. 
     The preferred method of making the interlocking carriage assembly will now be discussed in conjunction with FIGS. 8 and 8A. Preferably the interlocking carriage assembly is produced in a mold assembly  200 . The mold assembly  200  comprises a cavity member  202 , core member  204  and slide member  206  which are adapted to form a whole mold chamber  208  having an inner flow surface  210 . An injection assembly  212  is coupled with the core member  204  and spaced from the inner flow surface  210 . 
     Generally, the carriage arms  58  and  60 , front bearing  54 , and coil  56  are placed within respective mold members and sealed therein. A material, preferably, LCP plastic material is injected through the injection assembly (not shown), and in turn, travels along the inner flow surface  210  to form the desired carriage assembly body  78  and interlockingly couple the carriage arms, front bearing, and coil to the carriage body as the material cools and hardens. 
     Specifically, the cavity member  202  comprises a part of the whole mold chamber having an upper carriage arm slot  214 , and lower carriage arm slot  216 . The upper and lower carriage arm slots are adapted to receive corresponding carriage arms in the relative position that the arms would be in the final carriage assembly. The carriage arm slots are formed and positioned within the cavity member such that the carriage arm proximal ends  100  interlocking couple with the carriage body sidewall within the desired tolerances. The carriage arm slots are spaced from a portion of the inner flow path that the plastic material flows to form a part of the carriage assembly. 
     The core member  204  defines another portion of the whole mold chamber and flow path. The core member  204  is designed to be coupled to an injection nozzle (not shown) at the gate  220 . Ejection pins  222  are coupled to the core member to eject the finished carriage assembly from the mold. The core member  204  defines coil retaining members  224 , a passage pin  226  and bearing stud  218 . The coil retaining member  224 , passage pin, and bearing stud are spaced from a portion of the inner flow path such that the material can flow to form the carriage assembly. 
     The coil retaining members  224  are formed and positioned within the core member  204  such that the coil  56  is interlockingly coupled with the body sidewall within the desired tolerances. The coil retaining members  224  are also adapted to form the cavities for forming the in-riggers when the coil  56  is positioned with the coil retaining members. 
     The passage pin  226  is formed and positioned within the core member and adapted from the passage that the guide track slidingly mounts in. The bearing stud  218  is adapted to receive the front bearing  54 . The bearing stud  218  is formed and positioned such that the front bearing  54  is interlockingly coupled proximate the front open end. Additionally, the passage pin  226  cooperates with the front bearing stud  218  to form the carriage assembly passage such that the front bearing is interlocking coupled proximate the front open end when the plastic material is injected into the mold chamber. 
     The slide block member  206  defines a portion of the whole cavity for forming the relatively triangular portion  228  of the carriage body bottom surface  86  to which a flex circuit  74  is coupled to. The slide block  206  defines a portion of the inner flow path that the injected material fills to form the relatively triangular portion on the carriage body. 
     Referring to FIG. 8A, the interlocking carriage assembly  52  is formed by positioning each component in each respective location. The upper carriage arm  58  and lower carriage arm  60  are positioned within each carriage arm slot. The front bearing is positioned on the bearing stud. The voice coil  56  is positioned in cooperation with the coil retaining members. The cavity member  202 , core member  204 , and slide block  206  are sealed together to form the whole mold. A material, preferably a plastic material such as LCP, is injected through the gate which, in turn, flows along the inner flow path interlocking couple each respective component with the carriage body as the material hardens and cools. 
     The carriage arm through holes are in fluid communication with the inner flow path such that the material flows to the relative location of the front open end to form the first open end. 
     One advantage of employing the mold assembly is that it ensures that each component is interlockingly coupled with the carriage body substantially within the desired tolerances. Another advantage is that the mold eliminates the need to individually attach each of these components to the carriage body. 
     Yet another advantage is that it eliminates the need for a sub-carriage to attach the voice coil to the carriage assembly. 
     The operation of the carriage assembly  52  will now be discussed in-conjunction with FIG.  9 . FIG. 9 illustrates an exemplary disk drive  150  with the cover removed, in which the carriage assembly  52  may be employed. The disk drive  150  comprises a chassis  152  having u-shaped outer edges that form opposed guide rails  154 a,  154 b that guide a removable disk cartridge (not shown) into the disk drive through opening  156 . In the present embodiment, the chassis is metallic. A thin metal top cover (not shown) of the disk drive  150  has been removed so that the internal components of the drive are visible. 
     A cartridge shutter lever  158  and an eject lever  160  are rotatably mounted on the chassis. Both levers  158  and  160  are shown in the positions that they occupy when a disk cartridge is fully inserted into the drive. During cartridge insertion, the shutter lever swings from a forward position to the position. During this movement, an abutment surface on the shutter lever  158  engages a shutter of the disk cartridge and moves the shutter to the side, exposing a head access opening in the front peripheral edge of the cartridge. The eject lever also moves from a forward position to the position shown when the cartridge is inserted. In this position, the eject lever is in a cocked position, under spring tension. When it is desired to eject the disk cartridge from the drive  150 , an eject button  162  is pushed. Among other things, this causes the eject lever  160  to be released from its cocked position, so that it springs forward to force the disk cartridge backwardly out of the disk drive. 
     The disk drive  150  also has a linear actuator  164  disposed at the rear of the chassis  152 . The linear actuator  164  comprises a magnetic motor in electrical communication with the coil  56  mounted on the carriage assembly  52  in accordance with the present invention. The outer magnet return path assembly  166 , and two inner return paths  168   a ,  168   b  on opposite sides of the carriage assembly  52  are in sliding communication with the coil  56  and in-rigger  80  and  81 . After a disk cartridge is inserted into the disk drive  150 , the carriage assembly  52  carries a pair of read/write heads  66  over the recording surfaces of a disk-shaped storage medium within the cartridge. 
     A spindle motor  174  is provided on the floor o f the chassis  152 . During cartridge insertion, the spindle motor  174  is translated vertically into engagement with a hub of the disk cartridge, in order to rotate the disk-shaped storage medium at a relatively high speed. A circuit board  170  is attached to the chassis  152  via a plurality of standoffs (not shown). The circuit board  170  carries the drive circuitry. A gear train mechanism  172  controls movement of the eject lever  160  and movement of a head retract mechanism (not shown) that moves the carriage assembly  52  to a parked position to prevent damage to the read/write heads  66 , when the disk drive is not in use. The in-riggers  80  and  81  maintain the carriage assembly  52  in the desired operating position as the carriage assembly  52  moves from the parked position to the operating position and vice versa by pressing or pushing on the inner return path  168   a , thereby preventing the coil  56  from hitting the cover. 
     It is to be understood that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.