Abstract:
A head stack assembly (HAS) of a hard disk drive (HDD) includes a swing arm, a connection plate integral with a terminal end of the swing arm, a head slider including a magnetic head for reading/writing data from/onto a disk, and a suspension that is attached to the connection plate, supports the head slider, and has characteristics which minimize the degree to which the magnetic head will run off-track due to vibrations induced in the HDD. The suspension includes two connecting parts having upper surfaces at which the suspension is attached to the connection plate. In the HDD, the upper surface of the connecting part positioned closest to the center of the disk center lies in a plane beneath the plane in which the upper surface of the other connecting part lies. Also, that half of the suspension which is disposed to one side of the central longitudinal axis of the HSA and is located remotely from the center of the disk in the HDD is stiffer than the other half of the suspension which is proximal the center of the disk. To this end, the suspension includes at least one side-rail that renders the suspension asymmetrical.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hard disk drive (HDD). More particularly, the present invention relates to a head stack assembly (HSA) of an HDD. 
     2. Description of the Related Art 
     A hard disk drive (HDD) is a device used in personal computers (PCs), MP3 players, mobile phones, and the like to store and retrieve data. To this end, an HDD includes a data storage disk, a spindle motor for rotating the disk, and a magnetic head that reads and writes data from and onto the disk. The head is embedded in a head slider, and when the HDD is operating, the head slider floats a predetermined distance above the disk while the disk is rotated by the spindle motor. The head slider is part of a head stack assembly (HSA) which is controlled to move the magnetic head over specified tracks of the disk. The tracks extend along concentric circles, respectively, whose centers coincide with the center of the disk. 
     The HSA also includes a swing arm that moves the head slider to a location over a specified track of the disk, and a suspension to which the head slider is mounted. The suspension supports the head slider during a read/write operation and maintains the spacing between the head slider and the recording surface of the disk. However, the magnetic head may deviate laterally from a specified track due to vibrations in the disk or the HSA. Such vibrations may be created when the HDD is disturbed or when the spindle motor of the HSA is running. This malfunction is referred to as the magnetic head being “off-track”.  FIG. 1  is a conceptual diagram illustrating an off-track state which may arise when the disk of the HDD is vibrating, and  FIG. 2  is a conceptual diagram illustrating an off-track state which may arise when the suspension bends due to vibrations. 
     Referring to  FIG. 1 , a magnetic head h 0  of a head slider  27  and a specific track T of a disk  10  are located at vertically aligned positions h 0 (d 0 ), T(d 0 ), respectively, when a read/write operation begins. Therefore, at this time, the magnitude of the off-track state of the magnetic head h 0  is 0. However, the outer circumference of the disk  10  and the head slider  27  of the HSA vibrate up and down, as illustrated by dotted lines, when the HDD vibrates at a specific frequency. As a result, the magnetic head h 0  becomes misaligned with the track T of the disk  10 , i.e., the magnetic head h 0  runs ‘off-track due to disk vibration’. More specifically, the track T is displaced radially outwardly from position T(d 0 ) to position T(d 1 ) when the disk  10  moves downwards while vibrating. As a result, the suspension undergoes torsion and thereby displaces the magnetic head h 0  radially inwardly from position h 0 (d 0 ) to position h 0 (d 1 ). On the other hand, the track T is displaced radially inwardly from position T(d 0 ) to position T(d 2 ) when the disk  10  move upwards while vibrating. In this case, the twisting of the suspension displaces the magnetic head h 0  radially outwardly from position h 0 (d 0 ) to position h 0 (d 2 ). Therefore, the magnetic head h 0  runs off-track when the head slider  27  moves upwardly or downwardly along with the vertical movement of the outer circumferential portion of the disk  10 . 
     U.S. Pat. Nos. 6,920,018 and 6,958,879 disclose HSAs aimed at reducing the amount by which the magnetic head runs off-track due to disk vibration. To this end, the HSA has a suspension and a connection plate attached at a specific bias angle, or a plurality of members of different thicknesses connecting the suspension and the connection plate. An HSA according to this prior art can reduce the amount by which the magnetic head would otherwise run off-track due to disk vibration because the HSA moves the head slider radially outwardly when the head slider moves downwards and the suspension undergoes torsion, and moves the head slider radially inwardly when the head slider moves upwards and the suspension undergoes torsion. 
     However, the HSAs disclosed in the prior art can not suppress the tendency of the magnetic head to run off-track when vibrations transmitted to the suspension cause the suspension to bend up and down. That is, referring to  FIG. 2 , a suspension  25  of the HSA may vibrate up and down irrespective of the disk. In this case, the head slider  27  connected to the suspension  25  also vibrates up and down, resulting in the magnetic head running ‘off-track due to suspension bending’. More specifically, the bending of the suspension  25  as it vibrates causes the suspension to become alternately convex and concave. The magnetic head of the head slider  27  is displaced towards the center of the disk  10  (from position h 0 (s 0 ) to position h 0 (s 1 )) when the suspension  25  becomes convex. As a result, the magnetic head runs on one side of the desired track T. On the other hand, the magnetic head of the head slider  27  is displaced towards the outer circumference of the disk  10  (from position h 0 (s 0 ) to position h 0 (s 2 )) when the suspension  25  becomes concave. As a result, the magnetic head also runs on the other side of the desired track T. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a head stack assembly (HSA) which minimizes the extent to which the magnetic head runs off-track due to disk vibration and due to suspension bending. 
     Likewise, another object of the present invention is to provide a hard disk drive (HDD) whose magnetic head will hardly run off-track when vibrations are induced in the HDD. 
     Another object of the present invention is to provide a hard disk drive (HDD) that can process data at high speeds. 
     Still another object of the present invention is to provide an HDD that can function well with a disk having a high number of tracks per inch (TPI). 
     According to an aspect of the present invention, there is provided an HSA comprising a swing arm having an axis of rotation, a connection plate integral with the swing arm at a terminal end of the swing arm, a suspension attached to the connection plate, a head slider mounted to a terminal end of the suspension and having a read/write head for reading/writing data from/onto a data storage disk, and wherein the suspension has characteristics which minimize the degree to which the magnetic head will run off-track due to disk vibration and suspension bending. To this end, the suspension includes a main arm, and (at least) first and second connecting parts extending from a rear end of the main arm towards the connection plate. The first and second connecting parts are attached at different heights to the connection plate such that an upper surface of the first connecting part lies in a plane beneath that in which an upper surface of the second connecting part lies. Also, that half of the suspension which includes the second connecting part is stiffer than that half of the suspension which includes the first connecting part. 
     According to another aspect of the present invention, there is provided an HDD comprising a base, a spindle motor mounted to the base, a disk fixed to the spindle motor so as to be rotated by the spindle motor, and a head stack assembly (HSA) supported by the base, wherein the HSA has the features mentioned above. In particular, the first connecting part is disposed closer to the center of the disk than the second connecting part. Thus, the upper surface of the first connecting part lies in a plane beneath that in which the upper surface of the second connecting part lies. Also, the half of the suspension which is remotely from the center of the disk is stiffer than the half of the suspension which is disposed proximal the center of the disk. 
     According to another aspect of the invention, the connection plate may have different thicknesses at respective corners thereof. In this case, the connecting parts of the suspension are directly attached to the corners so as to provide the difference in height at the points of attachment of the connecting parts. Alternatively, a spacer may be interposed between (at least) one of the connecting parts and the connection plate in order to provide the difference in height at the points of attachment of the connecting parts. 
     According to still another aspect of the invention, the suspension may comprise at least one side-rail that accounts for the difference in stiffness between the respective halves of the suspension. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments thereof made with reference to the attached drawings in which: 
         FIG. 1  is a conceptual diagram illustrating an off-track state of a magnetic head caused by vibrations of a data storage disk; 
         FIG. 2  is a conceptual diagram illustrating an off-track state of a magnetic head caused by the bending of a suspension to which the head is attached; 
         FIG. 3  is a plan view of an HDD according to the present invention; 
         FIG. 4  is a perspective partial view of an embodiment of an HSA according to the present invention; 
         FIG. 5  is a perspective partial view of another embodiment of an HSA according to the present invention; 
         FIG. 6  is a perspective partial view of still another embodiment of an HSA according to the present invention; 
         FIG. 7  is a graph illustrating the correlation between frequency of vibrations of an HDD and the magnitude of the off-track state assumed by the magnetic heads of HSAs according to the prior art and the present invention, respectively; 
         FIG. 8  is a conceptual diagram illustrating the effect of the present invention in reducing the off-track state due to disk vibration; and 
         FIG. 9  is a conceptual diagram illustrating the effect of the present invention in reducing the off-track state due to suspension bending. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 3 and 4 , an HDD  100  according to the present invention includes a base  101 , a spindle motor  105 , a data storage disk  107 , and an HSA  110 A. Also, a cover (not shown) is coupled to the base  101  to form a housing in which the spindle motor  105 , disk  107 , and HSA  110 A are enclosed. The spindle motor is fixed to the base  101  within the housing. The data storage disk  107  is mounted to the spindle motor  105  such that the spindle motor  105  rotates the disk  107  at a high speed in the direction of the arrow in  FIG. 3 . The HDD  100  also includes a main printed circuit board (PCB, not shown) disposed below the base  101 , and a flexible printed circuit (FPC)  145  which electrically connects the HSA  110 A to the main PCB. 
     The HSA  110 A includes a head slider  130  having an embedded magnetic head for reading/writing data. The head slider  130  is positioned over a specific track of the disk  107  to read or write data from or onto the disk  107 . To this end, the HSA  110 A also includes a swing arm  113  mounted to the base  101  by a bearing  111  so as to be rotatable about a central (vertical) longitudinal axis of the bearing  111 , a connection plate  117  attached to a terminal end of the swing arm  113 , and a suspension  120 A attached to the connection plate  117 . The head slider  130  is attached to a free end of the suspension  120 A so as to move with the swing arm  113 . Also, the suspension  120 A biases the head slider  130  towards the disk  107 . 
     The swing arm  113  of the HSA  110 A also includes a coil support  134 . A voice coil  135  is wound around the coil support  134 . A respective magnet  137  and yoke  138  supporting the magnet  137  are disposed above and below the coil support  134 . The magnets  137 , the yokes  138 , and the voice coil  135  of the HSA  110 A form a voice coil motor for rotating the swing arm  113  of the HSA  110 A about the central longitudinal axis of the bearing  111 . 
     The high-speed rotation of the disk  107  induces an air flow, in the direction of the arrow in  FIG. 3 , on the surface of the disk  107 . Lift is exerted on the head slider  130  when the air flow passes between the disk  107  and the head slider  130 . As a result, the head slider  130  floats above the disk  107  at a position at which the lift exerted on the head slider  130  is equal to the biasing force exerted on the head slider  130  by the suspension  120 A. The magnetic head of the head slider  130  reads and writes data from and onto the disk  107  while floating in this way above the disk  107 . 
     The HDD  100  also includes a ramp  140  on which the swing arm  130  of the HSA  110 A is parked when a read/write operation is over, i.e., when the HDD  100  is not operating. In this case, the swing arm  113  of the HSA  110 A is rotated clockwise by the voice coil motor. As a result, the head slider  130  is moved off of the disk  107 , and an end-tab  122  of the suspension  120 A is slid along the ramp  140 . The swing arm  130  is stopped once the end-tab  122  is located in a safety zone (not shown) of the ramp  140 . In this parked state, the swing arm  130  of the HSA  110 A is fixed in position and will not rotate even when the HDD is disturbed. 
     The connection plate  117  of the HSA  110 A connects the suspension  120 A to the end of the swing arm  113 . In this respect, the connection plate  117  can be formed by swaging. The suspension  120 A includes a load beam  121 A attached to the connection plate  117 A, and a flexure  129  attached to the load beam  121 A. The flexure  129  supports the head slider  130  such that the head slider  130  faces the disk. The load beam  121 A consists of a plate having a uniform thickness. The end-tab  122  is formed at a terminal distal end of the load beam  121 A. 
     The load beam  121 A includes a pair of connecting parts  126  and  127  attached to the connection plate  117  on opposite sides of the central longitudinal axis B of the HSA ( FIG. 4 ). The central longitudinal axis B lies in a plane coincident with the axis of rotation of the swing arm  113  and bisecting the head slider  130 . Although not shown, the load beam  121 A may also have a third connecting part located between the first connecting part  126  and the second connecting part  127 . The first connecting part  126  is attached directly to the bottom surface of the connection plate  117  at a first corner  119   a  of the connection plate  117 , and the second connecting part  127  is attached directly to the bottom surface of the connection plate  117  at a second corner  119   b  of the connection plate  117  which is further from the center of the disk  107  than the first corner  119   a . Also, as illustrated in  FIG. 4 , the connection plate  117  is thicker at its first corner  119   a  than at its second corner  119   b . Therefore, the first connecting part  126  is lower than the second connecting part  127 . In particular, the upper surface of the first connecting part  126  lies in a plane spaced by a predetermined vertical distance F 1  below the plane in which the upper surface of the second connecting part  127  lies. The distance F 1  is preferably between 0 and 0.5 mm. 
       FIG. 5  illustrates another embodiment of an HSA  110 B according to the present invention. In this embodiment, the connection plate  117  has a uniform thickness. In particular, the thickness of the connection plate  117  at the first corner  119   a  thereof is equal to the thickness of the connection plate  117  at the second corner  119   b . The HSA  110 B of the embodiment of  FIG. 5  also includes a spacer  132  interposed between the first connecting part  126  and the connection plate  117 , in order to situate the first connecting part  126  in a plane beneath that of the second connecting part  127 . More specifically, the spacer  132  is attached to the bottom of the connection plate  117  at the first corner  119   a  thereof, the first connecting part  126  is attached to the bottom surface of the spacer  132 , and the second connecting part  127  is attached to the bottom surface of the connection plate  117  at the second corner  119   b  thereof. As a result, the upper surface of the first connecting part  126  lies in a plane spaced by a predetermined vertical distance F 2  below the plane in which the upper surface of the second connecting part  127  lies. The distance F 2  is equal to the thickness of the spacer  132  and is preferably between 0 and 0.5 mm. 
     Alternatively, the connecting parts  126  and  127  of the suspension  120  may be attached to the top surface of the connection plate  117  in such a way that the upper surface of the first connecting part  126  lies in a plane spaced by a predetermined vertical distance F 1  below the plane in which the upper surface of the second connecting part  127  lies. For instance, a spacer similar to the spacer  132  shown in  FIG. 5  may be interposed between the second connecting part  127  and the connection plate  117 , the second connecting part  127  may be attached to the upper surface of the spacer, and the first connecting part  126  may be attached to the upper surface of the connection plate  117 . 
     Referring back to  FIGS. 3 and 4 , the load beam  121 A of the suspension  120 A also includes a main arm from which the connecting parts  126  and  127  extend rearwards and from which the lift-tab  122  extends forward, and a side-rail  123 A bent upward at an angle from the central portion of the main arm so as to have a height R 1 . The side-rail  123 A extends along only one side of the load beam  121 A, namely, the side of the main arm of the load beam  121 A which is remote from the center of the disk  107 . Similarly, in the embodiment of  FIG. 5 , the suspension  120 B includes a load beam and a flexure  129 . The load beam includes a side-rail  123 B extending along only the side thereof which is remote from the center of the disk  107 . 
     Accordingly, the suspension  120 A ( 120 B) is asymmetrical and thus, the stiffness of the suspension  120 A ( 120 B) varies on opposite sides of the central longitudinal axis B of the HSA  110 A ( 110 B). In particular, the stiffness of the portion of the suspension  120 A ( 120 B) having the side-rail  123 A ( 123 B) and located to one side of the central longitudinal axis B of the HSA  110 A ( 110 B) is greater than the stiffness of the portion of the suspension  120 A ( 110 B) located to the side of the central longitudinal axis B of the HSA  110 A ( 110 B). The asymmetric stiffness of the suspension  120 A ( 120 B) causes the head slider  130  to move towards or away from the center of the disk  107  when the suspension  120 A ( 120 B) bends. 
       FIG. 6  illustrates another embodiment of an HSA  110 C according to the present invention. In this embodiment, the suspension  120 C of the HSA  110 C includes a load beam  121 C having a first side-rail  123 C extending along the side thereof which is remote from the center of the disk  107 , and a second side-rail  124 C extending along the side of the load beam  121 C which is proximal the center of the disk  107 . The second side-rail  124 C is shorter than the first side-rail  123 C. Also, the angle subtended by the first side-rail  123 C and the main arm, as represented by θ 1  in the figure, may differ from the angle (represented by θ 2  )subtended between the second side-rail  124 C and the main arm. On account of the side rails  123 C and  124 C, the stiffness of that longitudinal half of the suspension  120 C which includes the first side-rail  123 C is greater than the stiffness of that longitudinal half of the suspension  120 C which includes the second side-rail  124 C. The asymmetric stiffness of the suspension  120 C causes the head slider  130  to move towards or away from the center of the disk  107  when the suspension  120 C bends. 
     The present inventors conducted computer simulations of HDDs in order to verify the effectiveness of the present invention in minimizing the amount by which a magnetic head will run off-off track when various types of vibrational disturbances occur in an HDD. The HDDs were modeled by the computer simulations so as to each have a 2.5-inch diameter disk. Also, the HDDs were modeled to include, respectively, an HSA having both a first characteristic of the embodiment of  FIG. 4 , namely a load beam in which the first connecting part is lower by 0.1 mm than the second connecting part, and a second characteristic of the embodiment of  FIG. 4 , namely a load beam in which a side-rail extends along only the side of the suspension which is remote from the center of the disk  107  (hereinafter, a first type of HSA); an HSA having only the first characteristic (hereinafter, a second type of HSA); and a conventional HSA having neither the first characteristic nor the second characteristic (hereinafter, a third type of HSA). 
       FIG. 7  is a graph illustrating the correlation, obtained as a result of the computer simulations, between the frequency of vibrations applied to an HDD and the amount by which the magnetic head will run off-track. In  FIG. 7 , peaks formed in zone A 1  indicate the occurrence of the off-track state due to disk vibration, and peak formed in zone A 2  indicate the occurrence of the off-track state due to a bending of the suspension. Table 1 shows results taken from the graph of  FIG. 7 . 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Amount of off-track 
                 Amount of off-track 
               
               
                   
                 due to disk 
                 due to suspension 
               
               
                   
                 vibration [×10 −6  mm] 
                 bending [×10 −6  mm] 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 First type HSA 
                 13.71 
                 6.96 
               
               
                   
                 Second type HSA 
                 12.47 
                 38.93 
               
               
                   
                 Third type HSA 
                 44.29 
               
               
                   
                   
               
             
          
         
       
     
     As can be seen from Table 1, the amounts by which the magnetic heads of the first and second type of HSAs will run off-track are about ⅓ to ¼ the amount by which the third type of HSA will run off-track due to disk vibration. In addition, the amount by which the magnetic head of the first type of HSA will run off-track is about ⅙ the amount by which the second type of HSA will run off-track due to suspension bending. 
       FIG. 8  is a conceptual diagram for use in explaining the effectiveness of the present invention in minimizing the amount by which the magnetic head will run off-track due to disk vibration. In  FIG. 8 , reference character T designates a track of a disk from or onto which data is to be read or written. Reference character h 0  designates the magnetic head of the third type of HSA, i.e., an HSA according to the prior art. Reference character h 1  designates a magnetic head of the first type of HSA, i.e., an HSA according to the present invention, and reference character h 2  designates a magnetic head of the second type of HSA. 
     Referring now to  FIG. 8 , when the outer circumference of a disk moves downwards while vibrating, a track T of the disk is displaced towards the outer circumference of the disk (from T(d 0 ) to T(d 1 )). On the other hand, when the outer circumference of the disk moves upwards while vibrating, the track T is displaced towards the center of the disk (from T(d 0 ) to T(d 2 )). Also, during this time, the magnetic head remains spaced a predetermined distance from the surface of the disk due to the biasing force exerted thereon by the suspension of the HSA. That is, the magnetic head moves upward and downward with the vibrating disk. 
     In the case of the third type of HSA (the HSA of the prior art), when the outer circumference of the disk moves downwards while vibrating, the magnetic head h 0  is displaced towards the center of rotation of the HSA (from h 0 (d 0 ) to h 0 (d 1 )). As a result, the magnetic head h 0  runs off-track by an amount corresponding to the distance between the magnetic head h 0  and the track T (the radial distance between h 0 (d 1 ) and T(d 1 )). Likewise, when the disk moves upwards, the magnetic head h 0  is displaced away from the center of rotation of the HSA (from h 0 (d 0 ) to h 0 (d 2 )). As a result, the magnetic head h 0  runs off-track by an amount corresponding to the distance between the magnetic head h 0  and the track T (the radial distance between h 0 (d 2 ) and T(d 2 )). 
     However, in the first type HSA or the second type HSA, the suspension is distorted when the HSA moves up and down because of the differences in the stiffness of the suspension on opposite sides of the central longitudinal axis of the HSA. Therefore, when the outer circumference of the disk moves downwards, the magnetic head h 1  or h 2  of the HSA is displaced towards the center of rotation of the HSA and is biased towards the outer circumference of the disk (from h 1 (d 0 ) to h 1 (d 1 ) or from h 2 (d 0 ) to h 2 (d 1 )). Similarly, when the outer circumference of the disk moves upwards, the magnetic head h 1  or h 2  moves in the opposite direction (from h 1 (d 0 ) to h 1 (d 2 ) or from h 2 (d 0 ) to h 2 (d 2 )). As can be seen from  FIG. 8 , the distances between the magnetic head and the track (i.e., the radial distances between h 1 (d 1 ) and T(d 1 ), between h 1 (d 2 ) and T(d 2 ), between h 2 (d 1 ) and T(d 1 ), and between h 2 (d 2 ) and T(d 2 )) are shorter than those which occur in the third type of HSA under the same circumstances which give rise to the off-track state. This shows that the present invention is effective in reducing the extent to which the magnetic head will run off-track due to disk vibration. 
       FIG. 9  is a conceptual diagram for use in explaining the effectiveness of the present invention in minimizing the amount by which the magnetic head will run off-track due to the bending of the suspension independently of any vertical fluctuations in the surface of the disk (simply referred to as suspension bending). Referring to  FIG. 9 , if suspension bending occurs in the second type of HSA such that the suspension becomes convex, the suspension distorts due to the differences in the stiffness of the suspension on opposite sides of the central longitudinal axis of the HSA. Accordingly, the magnetic head h 2  is displaced by the suspension towards the center of the disk (from h 2 (s 0 ) to h 2 (s 1 )). Likewise, if suspension bending occurs in the second type of HSA such that the suspension becomes concave, the magnetic head h 2  is displaced by the suspension towards the outer circumference of the disk (from h 2 (s 0 ) to h 2 (s 2 )). Thus, the magnetic head runs off-track by an amount corresponding to the (radial) distance between h 2 (s 1 ) and T or h 2 (s 2 ) and T. 
     However, if suspension bending occurs in the first type of HSA, the magnetic head h 1  is displaced (from h 1 (s 0 ) to h 1 (s 1 ) or from h 1 (s 0 ) to h 1 (s 2 )). In this case, the second characteristic of the first type of HSA offsets the tendency of the magnetic head to be displaced towards the center of the disk due to the first characteristic. Thus, the distances between the magnetic head h 1  of the first type HSA and the track T (i.e., the radial distances between h 1 (s 1 ) and T or between h 1 (s 2 ) and T) are shorter than those (i.e., between h 2 (s 1 ) and T or h 2 (s 2 ) and T) that occur in the second type of HSA under the same circumstances. That is, the amount by which the magnetic head runs off-track due to suspension bending is less in the first type of HSA than in the second type of HSA. 
     As described above, according to the present invention, the amounts by which a magnetic head will run off-track in an HSA due to disk vibration and suspension bending are minimized. Therefore, the present invention provides for improved positioning of the read/write head, minimizes the generation of Positioning Error Signals (PES) and hence, provides for increased data processing speeds. In addition, the present invention allows for data to be read from and written onto a disk having a relative large number of tracks per inch (TPI), i.e., enables an HDD to have a highly integrated disk. 
     Finally, although the present invention has been described in connection with the preferred embodiments thereof, it is to be understood that the scope of the present invention is not so limited. On the contrary, various modifications of and changes to the preferred embodiments will be apparent to those of ordinary skill in the art. Thus, changes to and modifications of the preferred embodiments may fall within the true spirit and scope of the invention as defined by the appended claims.