Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of Ser. No. 08/659,338 filed Jun. 6, 1996 now U.S. Pat. No. 5,801,899 and claims the benefit of Provisional Application Ser. No. 60/004,924 filed Oct. 6, 1995, hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the field of disc drive data storage devices, and more particularly, but not by way of limitation, to a snubber for protecting a hard disc drive from damage due to non-operational, mechanical shocks. 
     2. Discussion 
     Disc drives are commonly used in workstations, personal computers, portables, and other computer systems to store large amounts of data in a form that can be made readily available to a user. In general, a disc drive comprises one or more magnetic discs that are rotated by a spindle motor at a constant high speed. The surface of each disc is divided into a series of data tracks which are spaced radially from one another across a band having an inner diameter and an outer diameter. The data tracks extend generally circumferentially around the discs and store data in the form of magnetic flux transitions within the radial extent of the tracks on the disc surfaces. Typically, each data track is divided into a number of data sectors that store fixed sized data blocks. 
     A head includes an interactive element such as a magnetic transducer which senses the magnetic transitions on a selected data track to read the data stored on the track, or to transmit an electrical signal that induces magnetic transitions on the selected data track to write data to the track. The head includes a read/write gap that positions the active elements of the head at a position suitable for interaction with the magnetic transitions on the data tracks of a disc as the disc rotates. 
     As is known in the art, each head is mounted to a rotary actuator arm and is selectively positionable by the actuator arm over a preselected data track of the disc to either read data from or write data to the preselected data track. The head includes a slider assembly having an air bearing surface that causes the head to fly over the data tracks of the disc surface due to fluid air currents caused by rotation of the disc. 
     Typically, several discs are stacked on top of each other and the surfaces of the stacked discs are accessed by the heads mounted on a complementary stack of actuator arms which comprise an actuator assembly, or “E-block”. The E-block generally includes head wires which conduct electrical signals from the heads to a flex circuit, which in turn conducts the electrical signals to a flex circuit bracket mounted to a disc drive base deck. For a general discussion of E-block assembly techniques, see U.S. Pat. No. 5,404,636 entitled METHOD OF ASSEMBLING A DISK DRIVE ACTUATOR, issued Apr. 11, 1995 to Stefansky et al., assigned to the assignee of the present invention and incorporated herein by reference. 
     As will be recognized, a continuing trend in the industry is the reduction in size of modern disc drives. As a result, the discs in the disc stacks of modern disc drives are being brought closer together, providing narrower vertical gaps between adjacent discs. Although facilitating greater amounts of storage capacity, such narrow vertical spacing of the discs gives rise to a problem of increased sensitivity of the disc drives to non-operating, mechanical shocks; particularly, predominant failure modes in modern disc drives have been found to include damage to the surfaces of the discs and damage to the actuator arms as a result of mechanical shocks encountered during the shipping and handling of the drives. 
     Computer modeling of particular disc drives has revealed that one primary cause of interference between discs and actuator arms is the first mechanical bending mode of the discs, which has been found to cause over 50% of the motion between the arms and discs in selected disc drive designs. The bending mode is generally dependent upon the material, diameter and thickness of the discs, and these factors are not readily modified in a disc drive design. 
     Thus, there is a need for an improved approach to reducing the susceptibility of damage in disc drives as a result of non-operating, mechanical shocks. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for protecting a disc drive from damage due to mechanical shocks encountered during shipment and handling. 
     The disc drive comprises a disc mounted for rotation at a constant speed about a vertical axis, the disc having an inner radius and an outer radius. A rotary actuator is mounted adjacent the disc, the rotary actuator is controllably rotatable with respect to the disc. A snubber is provided adjacent the disc, the snubber having a body portion rigidly affixed to resist movement in the direction of the vertical axis of the disc. Additionally, snubber arms are connected to and extend from the body portion. 
     The snubber arms extend from the body portion towards the disc and above and below the elevation of the disc, with each snubber arm having a distal end located at a position adjacent the disc between the inner and outer radii of the disc and towards the outer radius of the disc. The vertical height of each snubber arm limits vertical deflection of the disc at the outer radius of the disc as a result of mechanical shock forces supplied to the disc drive assembly. 
     An object of the present invention is to protect components of a disc drive, including discs and actuator assemblies, from damage due to non-operating, mechanical shocks encountered during shipping and handling of the drive. 
     Another object of the present invention is to limit the deflection of the disc of a disc drive as a result of a mechanical shock. 
     Still another object of the present invention is to provide protection from damage due to mechanical shocks in an easily implemented, cost effective manner. 
     Other objects, advantages and features of the present invention will be apparent from the following description when read in conjunction with the drawings and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view of a disc drive in which the present invention is particularly useful. 
     FIG. 2 is a cross-sectional, elevational view of the cylindrical-shaped snubber of FIG.  1 . 
     FIG. 3 is a cross-sectional, elevational view of an L-shaped snubber. 
     FIG. 4 is a top plan view of a disc drive having a shroud-mounted snubber. 
     FIG. 5 is a cross-sectional, elevational view of the shroud-mounted snubber of FIG.  4 . 
     FIG. 6 is an elevational view of a snubber mounted to an E-block. 
     FIG. 7 is a top plan view of the E-block and snubber of FIG.  6 . 
     FIG. 8 is an elevational view of an E-block having an over-molded snubber. 
     FIG. 9 is a top plan view of the E-block and snubber of FIG.  8 . 
     FIG. 10 is a cross-sectional, elevational view of a portion of an E-block and an associated pin snubber. 
     FIG. 11 is a top plan view of the E-block and pin snubber of FIG.  10 . 
     FIG. 12 is an elevational view of a portion of an E-block with a flex circuit assembly having flex extensions which serve as a disc snubber. 
     FIG. 13 is an elevational view of a portion of an E-block with a flex circuit assembly having flex strips adjacent actuator arms and tabs which serve as a disc snubber. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings and more particularly to FIG. 1, shown therein is a top plan view of a disc drive  10  in which the present invention is particularly useful. The disc drive  10  includes a base deck  12  to which various disc drive components are mounted and a top cover  14 , which provides a sealed internal environment for the disc drive  10 . The top cover  14  is shown in a partial cut-away fashion to expose selected components of interest. 
     Mounted to the base deck  12  is a spindle motor (shown generally at  16 ) to which a plurality of discs  18  are mounted for rotation at a constant high speed. Adjacent the discs  18  is an actuator assembly  20  (hereinafter sometimes also referred to as an “E-block”) which pivots about a pivot shaft  22  in a rotary fashion. The E-block  20  includes actuator arms  24  which support gimbal assemblies  26  (hereinafter also sometimes referred to as “load springs”). The load springs  26  in turn support heads  28 , with each of the heads  28  corresponding to a surface of one of the discs  18 . As provided hereinabove, the heads  28  are positionably located over data tracks (not shown) of the discs  18  in order to read data from and write data to the tracks, respectively. At such time that the disc drive  10  is not in use, the heads  28  are moved to landing zones (denoted at broken line  30 ), which are located in FIG. 1 near the inner diameter of the discs  18 . 
     It will be recognized that the E-block  20  is provided with a latching arrangement (shown generally at  32 ) to secure the E-block  20  when the disc drive  10  is not in use. For a general discussion of typical E-block latching arrangements, see U.S. Pat. No. 5,231,556 entitled SELF-HOLDING LATCH ASSEMBLY, issued Jul. 27, 1993 to Blanks, assigned to the assignee of the present invention and incorporated herein by reference. 
     Continuing with FIG. 1, the E-block  20  is controllably positioned by way of a voice coil motor (VCM, shown generally at  34 ), comprising an actuator coil  36  immersed in the magnetic field generated by a permanent magnet  38 . It will be recognized that a magnetically permeable flux path (such as a steel plate) is mounted above the actuator coil  36  to complete the magnetic circuit of the VCM  34 , but for purposes of illustration this flux path has not been shown in FIG.  1 . When controlled DC current is passed through the actuator coil  36 , an electromagnetic field is set up which interacts with the magnetic circuit of the VCM  34  to cause the actuator coil  36  to move relative to the permanent magnet  38  in accordance with the well-known Lorentz relationship. As the actuator coil  36  moves, the E-block  20  pivots about the pivot shaft  22 . causing the heads  28  to move across the surfaces of the discs  18 . 
     To provide the requisite electrical conduction paths between the heads  28  and disc drive read/write circuitry (not shown), head wires (not separately shown) are routed on the E-block  20  from the heads  28 , along the gimbal assemblies  26  and the actuator arms  24 , to a flex circuit assembly  40 . The head wires are secured (by way of a suitable soldering process) to corresponding pads (not separately designated in FIG. 1) of a printed circuit board (PCB)  42  of the flex circuit assembly  40 . In turn, the flex circuit assembly  42  is connected to a flex circuit bracket (shown generally at  44 ) in a conventional manner. Preferably, the head wires are conductive wires having a relatively small diameter and are coated with a thin insulating layer (such as teflon). For purposes of clarity, this thin insulating layer is not separately designated in the drawings; however, it will recognized that this insulating layer is not present at the ends of the head wires where the head wires are soldered to the pads of the PCB  42 . It will further be recognized that the actuator arms  24  and the gimbal assemblies  26  are provided with suitable wire guides (not separately shown) to capture and retain the head wires. 
     Additionally, FIG. 1 shows a snubber  100 , which comprises a cylindrically-shaped assembly adjacent the stack of discs  18 . As will be discussed in more detail below, the snubber  100  protects the disc drive  10  from damage as a result of mechanical shocks provided to the disc drive  10  without otherwise interfering with the normal operation of the drive. Particularly, the snubber  100  is provided with a configuration such that when significant deflection of the discs  18  is induced by a mechanical shock incident, the discs  18  will contact the snubber  100  instead of the E-block  20 , thus minimizing damage to the E-block  20  and the discs  18 . 
     Referring now to FIG. 2, shown therein is a cross-sectional, elevational view of the snubber  100 , in conjunction with outlying portions of the discs  18  and the base deck  12  of FIG.  1 . More particularly, FIG. 2 shows the snubber  100  to comprise a plurality of snubber arms  102  which extend radially away from the center of the snubber  100  and about the circumference of the snubber  100 . The snubber  100  is secured to the base deck  12  by way of a suitable fastener  104 , which as shown in FIG. 2 is provided with a threaded portion  106  which engages with a threaded hole  108  of the base deck  12 . 
     The snubber arms  102  are configured to extend a nominal distance within the radial extent of the discs  18 , as shown. Particularly, the snubber arms  102  are configured to extend sufficiently into the stack of discs  18  to constrain vertical deflection of the discs  18  as a result of mechanical shock. However, the snubber arms  102  preferably do not extend to the recording surfaces (not shown) of the discs  18 , as damage to the surfaces of the discs  18  may occur at locations where the discs  18  contact the snubber arms  102  during deflection of the discs  18 . Thus, the distance the snubber arms  102  extend into the stack of discs  18  is an important consideration and will be dependent upon the design of a particular disc drive. 
     Additionally, the snubber arms  102  are vertically dimensioned to fit between the discs  18  as shown. It is expressly contemplated that the vertical dimensions of the snubber arms  102  will be less than the vertical dimensions of the gaps between adjacent discs  18 , but will be greater than the vertical dimensions of the actuator arms  24  (of FIG.  1 ), to prevent contact between the discs  18  and the actuator arms  24  during deflection of the discs  18 . 
     The snubber  100  is constructed from a suitable material which will provide the desired mechanical strength to constrain deflection of the discs  18 , while at the same time will minimize the potential for damage to the snubber  100  and to the discs  18 . Preferably, the snubber  100  is constructed from a plastic, non-marring material, such as polycarbonate or acetal. As shown in FIG. 1, the snubber  100  is preferably mounted near the E-block  20 , in order to maximize protection of the actuator arms  24  and the discs  18 . It will be recognized, however, that the snubber  100  can be located at positions other than adjacent to the E-block  20 , as desired, further, the use of multiple snubbers  100  at various positions about the circumference of the discs  18  could be found to be advantageous in particular disc drive designs. Additionally, it is contemplated that the snubber arms  102  could extend only about a portion of the circumference of the snubber  100 , the portion being adjacent the discs  18 . 
     Referring now to FIG. 3, shown therein is a cross-sectional, elevational view of a generally L-shaped snubber (designated as  100 A) having a configuration similar to that of the cylindrical snubber  100  of FIGS. 1 and 2. As with the snubber  100 , the snubber  100 A of FIG. 3 includes snubber arms  102 A which extend radially between adjacent discs  18 . Additionally, the snubber  100 A is secured to the base deck  12  with a suitable fastener  104 A by way of a threaded portion  106 A and a corresponding threaded hole  108 A in the base deck  12 . However, the snubber  100 A has an L-shaped, cross-sectional configuration, as shown, including a vertical portion  110 A and a horizontal portion  112 A, which are configured as desired to provide the necessary strength for the snubber  100 A, as well as to conform to internal space requirements of the disc drive  10 . It will be recognized that the snubber  100 A of FIG. 3 will generally require less space and comprise less material than the snubber  100 , which may be important considerations in small form factor or low cost drive designs. 
     Referring now to FIG. 4, shown therein is a disc drive  10 A, which has a configuration similar to the disc drive  10  of FIG. 1 (for purposes of clarity, the same reference numbers for components shown in FIG. 1 have been used in FIG.  4 ). However, the disc drive  10 A includes a disc shroud  46 , which comprises a vertically extending flange adjacent the discs  18 . As will be recognized, the disc shroud  46  is typically used to reduce wind resistance from the spinning discs  18  in order to reduce power requirements of the disc drive  10 A, an important consideration in low power disc drive applications. Typically, the disc shroud  46  is formed as part of the base deck  12  and extends upwardly therefrom. 
     Additionally, FIG. 4 shows a snubber (designated as  100 B) which is mounted to the disc shroud  46  and to the base deck  12 . It will be recognized that the E-block  20  shown in FIG. 4 is at a different rotational position than the E-block  20  shown in FIG. 1 to more fully illustrate the snubber  100 B; however, it will be recognized that a portion of the snubber  100 B will extend under the E-block  20  when the E-block  20  is positioned as shown in FIG.  1 . As with the snubbers  100 ,  100 A discussed hereinabove, the snubber  100 B serves to protect the disc drive  10  from damage due to deflection of the discs  18  as a result of mechanical shock. 
     The snubber  100 B is shown in greater detail in FIG. 5, which provides a cross-sectional, elevational view of the snubber  100 B in conjunction with the disc shroud  46 , the discs  18  and the base deck  12 . Particularly, FIG. 5 shows the snubber  100 B to include snubber arms  102 B, which extend radially between adjacent discs  18 , in a manner similar to that described hereinabove. As shown in FIGS. 4 and 5, the snubber  100 B is provided with a vertically oriented, C-shaped configuration so that the snubber  100 B wraps around the end of the disc shroud  46 , as shown, and is secured to the disc shroud  46  by way of a suitable threaded fastener  114 . Additionally, the snubber  100 B is secured to the base deck  12  by way of a suitable base deck fastener  104 B (by way of threads  106 B which engage with a threaded hole  108 B in the base deck  12 ). Thus, the fasteners  104 B and  114  secure the snubber  100 B relative to the base deck  12  and the disc shroud  46 . The vertical height of the fastener  104 B and a horizontal portion  116  of the snubber  100 B are provided such that mechanical clearance exists between the fastener  104 B and the horizontal portion  116  and the E-block  20  (as shown in FIG.  4 ). 
     Referring now to FIG. 6, shown therein is an elevational view of an E-block  20 A, which is generally similar to the E-block  20  discussed hereinabove, except to the extent that the E-block  20 A includes an E-block mounted snubber  100 C mounted to the “up-wind” side of the E-block  20 . The E-block  20 A is shown in conjunction with the discs  18 , including the extension of the actuator arms  24  between adjacent discs  18 . For purposes of clarity, the load springs  26  and heads  28  have not been shown in FIG. 6, but it will be understood that these elements extend radially from the actuator arms  24 ; particularly, it will be readily understood by those skilled in the art that the top and bottom actuator arms  24  have one load spring  26  and head  28  extending therefrom, respectively, and the rest of the actuator arms  24  have two load springs  26  and heads  28  extending therefrom, respectively. 
     The snubber  100 C is shown mounted to the side of the E-block  20 A, with snubber arms  102 C extending adjacent to the corresponding actuator arms  24  between adjacent discs  18 . The snubber arms  102 C operate in a manner as described hereinabove to protect the actuator arms  24  from damage as a result of deflection of the discs  18 ; by limiting the vertical extent of travel of the outer diameters of the discs  18 . It will be understood that the snubber  100 C is mounted to the side of the E-block  20 A by way of a suitable fastener  118 , which preferably inserts through a hole (not shown) in the snubber  100 C and engages with a corresponding threaded hole (also not shown) in the E-bock  20 A. It will be recognized by those skilled in the art that in actuator designs that use a screw to secure the bearing cartridge (not separately designated, but surrounding the pivot shaft  22 ), this screw can also serve as the fastener  118  shown in FIG. 6 to secure the snubber  100 C to the E-block  20 A. 
     An important advantage of the snubber  100 C is that the protection provided by the snubber arms  102 C is generally maximized by the adjacent placement of the snubber arms  102 C to the actuator arms  24 . Although not shown in the drawings, it will be recognized that the configuration of the snubber arms  102 C can be modified as desired to account for the rotary movement of the E-block  20 A relative to the discs  18  to minimize the radial extent of the snubber arms  102 C into the stack of discs  18  over the range of movement of the E-block  20 A. 
     Referring now to FIG. 7, shown therein, is a top plan view of the E-block  20 A and snubber  100 C of FIG.  6 . For reference, FIG. 7 shows the E-block  20 A to be pivotable about the pivot shaft  22 , as provided above; additionally, the latching arrangement  32  and the flex circuit assembly  40  of FIGS. 1 and 4 are also shown in FIG. 7, for purposes of clarity. 
     As shown in FIG. 7, the snubber  100 C of FIG. 6 is mounted to the side of the E-block  20 A by way the fastener  118 . Further, the snubber arms  102 C extend as shown along the actuator arms  24 . 
     Referring now to FIG. 8, shown therein is an elevational view of an E-block  20 B, similar in configuration and operation to the E-blocks  20  and  20 A discussed hereinabove. The E-block  20 B is also shown in conjunction with the discs  18  and includes the actuator arms  24  extending radially between the discs  18 , in a manner similar to the E-block  20 A of FIG.  6 . 
     However, the E-block  20 B of FIG. 8 includes the use of an over-molded snubber  100 D, formed using a suitable over-molding process wherein an assembled stack of actuator arms  24  is selectively coated with a layer of material, such as plastic. Particularly, it is contemplated that the E-block  20 B of FIG. 7 is subjected to such a process in order to form the over-molded snubber  100 D thereon. Particularly, the snubber  100 D is similar in configuration to the snubber  100 C of FIG. 6, so that snubber arms  102 D extend radially between the discs  18  and adjacent to the actuator arms  24 ; however, instead of providing the snubber arms  102 D just adjacent the sides of the actuator arms  24 , the over-molded snubber  100 D of FIG. 8 includes material along the top and bottom surfaces of the actuator arms  24  as well. Additionally, the over-molding process allows the material comprising the snubber arms  102 D to be “curved” with respect to the actuator arms  24 , in order to maintain minimum extension of the snubber arms  102 D into the stack of discs  18  as the E-block  20 B rotates with respect to the discs  18 . 
     The curved characteristic of the snubber arms  102 D is more fully illustrated in FIG. 9, which shows a top plan view of the E-block  20 B of FIG.  8 . It will be recognized, that the curved characteristic of the snubber arms  102 D of FIG. 9 facilitates nominally constant extension of the snubber arms  102 D into the stack of discs  18 , irrespective of the rotary position of the E-block  20 B. Further, it will be recognized that, depending upon the rotary position of the E-block  20 B with respect to the discs  18  (not shown in FIG.  9 ), different portions of the snubber arms  102 D will extend into the stack of discs  18 . Of course, the curved characteristic of the snubber arms  102 D can be selected as desired, depending upon the design of a particular drive, including the relative position of the pivot shaft  22  with respect to the discs  18  (and the resulting range of motion of the E-block  20 B and the discs  18 ). 
     Referring now to FIG. 10, shown therein is a cross-sectional elevational view of a portion of an E-block  20 C, which is generally similar to the E-blocks ( 20 ,  20 A and  20 B) described hereinabove, but includes a pin snubber  100 E, comprising a plurality of pins  122  extending through each of a plurality of corresponding actuator arms  24 A. The actuator arms  24 A are generally similar in an respects to the actuator arms  24  described hereinabove, except that the actuator arms  24 A are additionally provided with holes  124 , through which the pins  122  are inserted during fabrication of the E-block  20 C. As shown in FIG. 10, the pins  122  are sized and located accordingly with respect to the outer extreme of the discs  18 , so that the pins  122  operate in a fashion as generally described above to limit deflection of the discs  18  as a result of mechanical shocks to the assembly shown therein. The pins  122  are selected from a suitable material that will maximize protection to the E-block  20 C and at the same time minimize damage to the discs  18  in the event of a mechanical shock sufficient to boring the outer extremes of the discs  18  in contact with the pins  122 . In one preferred method of fabrication, the holes  124  are drilled through the actuator arms  24 A during a single operation, a single pin (not shown) in pressed through all of the holes  124  and the single pin is subsequently machined into the pins  122  configured as shown in FIG.  10 . 
     A top plan view of the E-block  20 C of FIG. 10 is shown in FIG. 11, illustrating the relative placement of the pins  122  and the actuator arms  24 A. Although the pins  122  have been shown in FIG. 11 to have generally circular shapes, other shapes may be selected as desired, including shapes having a curved characteristic similar to the snubber arms  102 D of FIG. 9 to maintain the radial extent of the pins  122  into the stack of discs  18  (not shown in FIG.  11 ). 
     Referring now to FIG. 12, shown therein is an elevational view of a portion of an E-block  20 D adjacent the stack of discs  18 , the E-block  20 D including a flex circuit assembly  40 A which is generally similar to the flex circuit assembly  40  described hereinabove, with the addition of flex extensions  132  which extend from the flex circuit assembly  40  into the stack of discs  18 . More particularly, the flex extensions  132  extend from a PCB  42 A of the flex circuit assembly  40 A, as shown. 
     As described hereinabove, electrical signals are transmitted by way of head wires (designated collectively as  134  in FIG. 12) which are routed from the heads  28  (not shown in FIG. 12) and along the actuator arms  24  to the PCB  42 A. The distal ends of the head wires  134  are soldered to corresponding pads (collectively “ 136 ”) on the PCB  42 A as shown. The PCB  42 A is rigidly mounted to the side of the E-block  20 D. The flex extensions  132  extend radially between the discs  18 , and are sufficiently rigid to limit deflection of the discs  18 , in a manner similar to that described hereinabove. It will be recognized that the advantages associated with the flex circuit assembly  40 A of FIG. 12 include the benefit that the snubber features of the flex circuit assembly  40 A can be readily incorporated into the design of the flex circuit assembly  40 A. Thus, the flex circuit assembly  40 A can be implemented into existing drive designs without the need for E-block modifications or additional assembly steps. 
     Referring now to FIG. 13, shown therein is an elevational view of a portion of an E-block  20 E having a flex circuit assembly  40 B, which is similar to the flex circuit assembly  40 A of FIG. 12, with the exception that the flex circuit assembly  40 B includes flex strips  142  which extend along corresponding actuator arms  24 B. 
     The flex strips  142  accommodate connection paths (not shown) from the flex circuit assembly  40 B to the heads  28  (not shown in FIG. 13) and serve as alternatives to the head wires  134  of FIG.  12 . It will be recognized that the actuator arms  24 B include conventional features (not particularly shown) to accommodate the flex strips  142  and such features are generally different from features used to capture and retain the head wires  134  (shown in FIG.  12 ). 
     The flex strips  142  of FIG. 13 include tabs  144 , which are located near the outer extent of the discs  18 . The tabs  144  extend vertically from the flex strips  142  and are configured to limit the deflection of the disc  18 , in the manner described hereinabove. As with the flex circuit assembly  40 A of FIG. 12, the flex circuit assembly  40 B of FIG. 13 can be readily incorporated into existing drive designs that use conventional flex strips instead of wires. 
     It will be clear that the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the invention disclosed and as defined in the appended claims.

Technology Category: g