Abstract:
A magnetic disc drive system is disclosed. The disc drive system includes at least one substantially flat magnetic disc, at least one read/write head, at least one head stack assembly, at least one head gimbal assembly, and at least one suspension limiter. The suspension limiter is operatively connected to the head stack assembly. The distal end of the suspension limiter is positioned proximate but normally not in contact with the head gimbal assembly for preventing large head slaps in both operational and nonoperational mode.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of Provisional Application Ser. No. 60/111,229 entitled “Disc Drive Having a Suspension Limiter for Improved Nonoperational and Operational Shock Performance,” filed Dec. 7, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to magnetic disc drives and head gimbal assemblies. Specifically, this invention relates to magnetic disc drives and head gimbal assemblies having a suspension limiter for preventing large head slaps during severe operational and nonoperational shocks. 
     Modern computers require media in which digital data can be quickly stored and retrieved. Magnetizable (hard) layers on discs have proven to be a reliable media for fast and accurate data storage and retrieval. Disc drives that read data from and write data to hard discs have thus become popular components of computer systems. To access memory locations on a disc, a read/write head (also referred to as a “slider”) is positioned slightly above the surface of the disc while the disc rotates beneath the read/write head at an essentially constant velocity. By moving the read/write head radially over the rotating disc, all memory locations on the disc can be accessed. The read/write head is typically referred to as “flying” head because it includes a slider aerodynamically configured to hover above the surface on an air bearing located between the disc and the slider that forms as the disc rotates at high speeds. The air bearing supports the read/write head above the disc surface at a height referred to as the “flying height.” 
     In conventional disc drives, multiple hard discs are coupled to and rotate about a spindle, each disc presenting two substantially flat surfaces for reading and recording. Typically, multiple rotating hard discs are stacked in a parallel relationship with minimal spacing between them. Accordingly, the read/write heads must be designed to move within the narrow space between adjacent discs and fly close to the disc surfaces. To achieve this positional capability, the read/write heads in typical disc drives are coupled to the distal end of thin, arm-like structures called head gimbal assemblies, which are inserted within the narrow space between adjacent discs. These head gimbal assemblies are made of materials and thicknesses as to be somewhat flexible and allow a measure of vertical positioning as the read/write heads hover over the surface of the rotating discs. 
     Each head gimbal assembly is coupled at its proximal end to a rigid actuator arm that horizontally positions the head gimbal assembly and read/write head over the disc surface. In conventional disc drives, actuator arms are stacked, forming a multi-arm head stack assembly which moves as a unit under the influence of a voice coil motor to simultaneously position all head gimbal assemblies and corresponding read/write heads over the disc surfaces. 
     Disc drives have two modes, namely operational and nonoperational. The disc drive is in operational mode when the read/write heads (sliders) are in the data zone and the discs are rotating. Nonoperational mode refers to when the disc drive is not operating (i.e. the discs are not rotating). 
     There are two main types of disc drives: load/unload and contact start/stop disc drives. Load/unload disc drives “park” their read/write heads when the disc drive system is powered down or when the discs temporarily stop spinning so that the read/write heads rest over ramps which are located off the disc (typically outside the outer diameter of the discs). Contact Start/Stop (CSS) disc drives park the read/write heads in a landing zone located on the disc. This landing zone is typically located on the innermost central region of the discs but not over the data portion of the disc. 
     In conventional disc drive systems, including both types discussed above, the discs rotate at high velocities and read/write heads are positioned over the discs with very little air gap separation. Contact between the read/write head and the discs, known as a head slap, can be catastrophic. Head slaps occur when the disc drive is shocked (e.g. bumped, jarred or otherwise vibrated) either during operational mode when the discs are rotating or during nonoperational mode when the discs are not rotating. When the disc drive is shocked, the read/write head may lift off the surface of the disc and then return to the surface of the disc making contact with the surface of the disc. Because of this, data can be permanently lost, or the read/write heads and discs can be damaged such that the entire disc drive system no longer functions properly. For load/unload and CSS drives, a head slap can occur during operational mode. For CSS drives, a head slap can also occur during nonoperational mode when the discs are not rotating yet the head is still positioned over the disc surface. 
     The severity of the head slap will determine the extent of the damage to the disc or head. The shock that causes head slap is characterized by shock pulses that the drive is exposed to, typically half sine shape, with a specific duration (e.g. 0.5 ms to 2.0 ms) and a maximum amplitude in gravitational acceleration or g&#39;s (acceleration due to gravity). At a constant pulse duration, head slaps are typically getting larger with increasing shock amplitude. For a typical 30 series head gimbal assembly, minor head slaps may be occurring around 200 g (0.5 ms) and larger head slaps and multiple slaps at 200-500 g. Note that in the drive, where multiple head gimbal assemblies are mounted on actuator arms and multiple discs are used, head slaps are typically observed at lower g levels. Severe head slaps are of even more concern in low pre-load suspensions because the g&#39;s required to cause a severe head slap are smaller. 
     One solution that has been found to reduce minor head slaps is to round or radius the corners of the slider instead of using the traditional sharper shaped sliders. This solution has been found to be very effective in reducing and eliminating minor head slaps. 
     Mechanical latches or stops have been used to reduce non-operational head slap. These stops are not in-situ (part of the head gimbal assembly or head stack assembly) but rather are large mechanical stops attached external to the head gimbal assembly and head stack assembly. These mechanical stops are positioned only to prevent head slap when the head is positioned on its ramp on a load/unload disc drive. In addition to not solving operational head slap, these mechanical stops are large, expensive and unreliable. 
     Further efforts to reduce media damage caused by head slap have included: decreasing the effective mass of the load beam and slider by decreasing suspension length, width, material thickness, material composition, etc. increasing the pre-load biasing force; and increasing the robustness of the disc surface by using glass substrates, hydrogenated carbon or other tough overcoats, or both. However, under the more stringent requirements of disc drives in more recent times and the desire to build disc drives that can withstand more significant shock, these methods do not prevent head slap from occurring. 
     SUMMARY OF THE INVENTION 
     In accordance with this invention the above and other problems have been solved by a head gimbal assembly having a base plate; a load beam having a proximal end and a distal end. The proximal end is connected to the base plate. A gimbal assembly supports a transducer and the gimbal assembly is operatively coupled to the distal end of the load beam. A suspension limiter has a proximal end operatively coupled to the actuator arm, and the suspension limiter is in proximity to but not normally in contact with the load beam. The suspension limiter limits movement of the load beam and transducer in shocked conditions when the load beam comes into contact with the suspension limiter. 
     In accordance with another aspect of the invention, the suspension limiter is operatively coupled to the actuator arm. 
     In accordance with another aspect of the invention, a magnetic disc drive has a disc, a head stack assembly, and a plurality of head gimbal assemblies. The head gimbal assemblies are operatively coupled to the actuator arm of the head stack assembly. The head gimbal assemblies of the disc drive include suspension limiters which are operatively coupled to the actuator arm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a disc drive. 
     FIG. 2 is a perspective view of a head gimbal assembly according to a preferred embodiment of the invention in which an integral suspension limiter base plate is connected to the same side of the load beam as the transducer. 
     FIG. 3 is a side view of several head gimbal assemblies such as that shown in FIG. 2, connected to actuator arms of a head stack assembly according to preferred embodiments of the invention. 
     FIG. 4 is a side view of another preferred embodiment of the invention including two head gimbal assemblies in which a suspension limiter is a separate component from the base plate. 
     FIG. 5 is a perspective view of a head gimbal assembly according to another preferred embodiment of the invention in which an integral suspension limiter base plate is connected to the opposite side of the load beam as the transducer. 
     FIG. 6 is a side view of two head gimbal assemblies such as that shown in FIG. 5 connected to an actuator arm. 
     FIG. 7 is a side view of a two head gimbal assemblies attached to an actuator arm having an extension that serves as a suspension limiter for both head gimbal assemblies according to a preferred embodiment of the invention. 
     FIG. 8 is a perspective view of the actuator arm shown in FIG.  7 . 
     FIG. 9 is a side view of another preferred embodiment of the invention in which an energy absorbing layer is positioned between adjacent suspension limiters of two head gimbal assemblies. A side enlarged view of an alternative preferred embodiment of the invention in which a suspension limiter has a bump on its end is also shown. 
     FIG. 10 is a side view taken from a photographic image (using a high speed camera) of a head gimbal assembly slider in contact with a disc when a suspension limiter is used according to the invention. 
     FIGS. 11 a-b  is a side view showing the results (taken from a high speed camera) of: (a) a shock on a head gimbal assembly without a suspension limiter; and (b) a shock on a head gimbal assembly incorporating a suspension limiter according to the invention. 
     FIG. 12 is a side view of further results (taken from a high speed camera) of a shock on a head gimbal assembly with a suspension limiter. 
     FIG. 13 is a beam drawing of a simple quasistatic tolerance model for modeling the interaction between a suspension limiter and a load beam. 
    
    
     DETAILED DESCRIPTION 
     In the following description of preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the preferred embodiments of the present invention. 
     FIG. 1 is a top view of a disc drive  100 . Disc drive  100  includes a magnetic disc  102  mounted for rotational movement about an axis defined by spindle  104  within housing  106 . Disc drive  100  also includes a stacked actuator system alternatively referred to as head stack assembly  108  mounted to a base plate  110  of the housing  106  and pivotally movable relative to disc  102  about axis  112 . A cover  114  covers a portion of head stack assembly  108 . Programmable controller  116  is coupled to head stack assembly  108 . In a preferred embodiment, programmable controller  116  is either mountable within disc drive  100  or is located outside of disc drive  100  with suitable connection to head stack assembly  108 . 
     In a preferred embodiment, head stack assembly  108  includes an actuator arm assembly  118 , an actuator arm  120 , and a head gimbal assembly  122 . Head gimbal assembly  122  includes a load beam or flexure arm  124  coupled to actuator arm  120 , and a slider  126  coupled by a gimbal assembly (not shown) to load beam  124 . Slider  126  supports a transducer for reading information from disc  102  and encoding information on disc  102 . When reading and writing data to and from the disc, the head gimbal assembly  122 , its associated load beam  124  and slider  126  are positioned over the disc  102 . In other words the head gimbal assembly  122  and load beam  124  are preferably situated substantially within the outer radius of the disc  102  during read/write operations. 
     During operation, programmable controller  116  receives position information indicating a portion of disc  102  to be accessed. Programmable controller  116  receives the position information from the operator, from a host computer or from another suitable controller. Based on the position information, programmable controller  116  provides a position signal to head stack assembly  108 . The position signal causes head stack assembly  108  to pivot or rotate about axis  112 . This, in turn, causes slider  126  and the transducers mounted on slider  126  to move radially over the surface of the disc  102  in a generally arcuate path as indicated by arrow  128 . Once the transducer is properly positioned, programmable controller  116  then executes a desired read or write operation. 
     FIG. 2 is a perspective view of a head gimbal assembly  122  according to a preferred embodiment of the invention. The head gimbal assembly  122  includes a base plate  132  with an integral suspension limiter  130 . The base plate  132  includes a swaging boss  142  for connection of the head gimbal assembly  122  to an actuator arm such as arm  120  shown in FIG.  1 . of the head stack assembly  108 . The base plate  132  is also connected to a proximal end of a load beam  124 . The distal end of the load beam  124  supports a gimbal assembly  136 . Note that the load beam  124  may include a load beam bent region  125  in which each edge of the load beam  124  is bent to be substantially perpendicular to the rest of the load beam  124 . This bent region  125  provides added stiffness in the load beam  124 . The gimbal assembly  136  supports a slider  126  which supports transducer  138 . Read/write data are transferred between the transducer  138  and the programmable controller  116  via flexible circuit  144 , also referred to as flex-on suspension (FOS)  144 . It is noted that the transducer  138  is a portion of the slider  126 . Preferably the transducer  138  is located near the distal end of the slider  126  (the end furthest from the head stack assembly). 
     The base plate  132  is located on the same side of the load beam  124  as the transducer  138 . It can be seen that the swaging boss  142  of the base plate extends through a hole in the load beam  124  so that the swaging boss  142  can be connected to the actuator arm of the head stack assembly which is located on the side of the load beam  124  opposite the transducer  138 . The suspension limiter  130  of this preferred embodiment is an integral part of the base plate  132  of the head gimbal assembly  122 . 
     By the term “integral” it is meant that the suspension limiter  130  and base plate  132  are formed as one unit. Alternatively, they may not be integral, but rather formed as separate components as will be described with reference to FIG.  4 . 
     The suspension limiter  130  has a proximal end  133  nearest the base plate  132  and a distal end  135  furthest from the base plate  132 . The suspension limiter  130  includes a double elbow  127  between the proximal end  133  and distal end  135  in which the suspension limiter  130  extends through a space between two arms  129  and  131  of the load beam  124  wherein the suspension limiter  130  changes its position from one side of the load beam  124  to the other side of the load beam  124 . There is a slight gap between the suspension limiter  130  and the load beam  124  extending from the double elbow  127  to the distal end  135  of the suspension limiter  130 . This slight gap prevents the suspension limiter from interfering with the dynamics of the load beam in the absence of shock. 
     The suspension limiter  130  may be a variety of dimensions and materials as long as it is less flexible than the load beam  124  itself in the direction perpendicular to and away from the load beam  124 . In the embodiment shown in FIG. 2, the suspension limiter  130  is part of the base plate  132  and it may be a single layer material made of the same material and thickness as the base plate  132 , preferably stainless steel with a thickness of 6 mils. Alternatively, the suspension limiter  130  can be a ceramic or a multi-layer material such as a viscoelastic. These materials provide improved damping. Therefore, if the load beam  124  and transducer  138  begin to move in a direction away from a surface of disc  102 , the suspension limiter  130  minimizes such movement when the load beam  124  makes contact with the suspension limiter  130  at some point or points between the double elbow  127  and the distal end  135 . Stopping the movement of the load beam  124  and therefore stopping the movement of the transducer  130  in a direction away from the surface of the disc  102  results from the physical resistance provided by the suspension limiter  130  when the load beam  124  comes into contact with it. 
     FIG. 3 is a side view of five actuator arms  120   a-e  with three head gimbal assemblies  122   a-c  shown attached to actuator arms  120   a,b . The head gimbal assemblies  122   a-c  shown in FIG. 3 are of the same preferred embodiment as discussed above in relation to FIG.  2 . Preferably, each actuator arm has two head gimbal assemblies attached to it, one on each side of the actuator arm as shown by activator arm  120   b . A magnetic disc (not shown) would be positioned between a pair of head gimbal assemblies  122   a  and  122   b  and other discs would be positioned similarly in relation to other pairs of head gimbal assemblies. 
     The side view shown in FIG. 3 illustrates the positioning and attachment of the suspension limiter  130 . The proximal end of the load beam  124   a  (the end nearest the base plate  132   a ) is sandwiched between the base plate  132   a  and the actuator arm  120   a . The base plate  132   a  and load beam  124   a  are swaged to the actuator arm  120   a  by the swaging boss  142  (not shown in FIG. 3) of the base plate  132   a  which extends through the load beam  124   a  for connection to the actuator arm  120   a.  In this preferred embodiment, the suspension limiter  130   a  is an integral part of the base plate  132   a.  The suspension limiter  130   a  extends past the end  146  of the actuator arm  120   a  and includes the double elbow  127   a.  The portion of the suspension limiter  130   a  extending from the double elbow  127   a  to the distal end  135   a  of the suspension limiter  130   a  is positioned substantially parallel to the load beam  124   a  with a small gap between the suspension limiter  130   a  and the load beam  124   a.  Under normal operating conditions and normal non-operating conditions (i.e. in the absence of shock), the suspension limiter  130   a  is not in contact with the load beam  124   a.  If the disc drive assembly is shocked, and the load beam  124   a  and slider begin to lift away from the disc, the load beam  124   a  comes in contact with the suspension limiter  130   a.  This contact prevents the slider from significantly lifting away from the disc. 
     FIG. 4 is a close up side view of another preferred embodiment of the invention in which the suspension limiter is not an integral part of the base plate, but rather is a separate component apart from the base plate. This embodiment is designed for drives in which tight tolerance is not required. FIG. 4 shows two head gimbal assemblies  152  and  154  attached to opposite sides of the actuator arm  160 . The suspension limiter  156  and load beam  166  are sandwiched between the actuator arm  160  and the base plate  161 . A swaging boss (not shown) is used to connect the base plate  161 , the suspension limiter  156  and the load beam  166  to the actuator arm  160 . Likewise a swaging boss (not shown) is used to connect the base plate  163 , suspension limiter  164  and load beam  168  to the actuator arm  160 . Portions  170  and  172  of the load beams  166  and  168  shown in FIG. 4 are the portion in which the load beams are bent for added stiffness. The gimbal assemblies and transducers are not shown in FIG.  4 . The flex-on suspensions (FOS)  174  and  176  provide for transmission of the read/write data to and from the transducer. There are air gaps  151  and  153  respectively between the load beams  166  and  168  and the respective suspension limiters  156  and  158 . 
     FIG. 5 is a perspective view of another preferred embodiment of the head gimbal assembly  178 . In this preferred embodiment the base plate  180  is positioned on the opposite side of the load beam  184  from the transducer  186 . Preferably the suspension limiter is integrally connected to the base plate  180 , although it may also be a separate component. 
     FIG. 6 is a side view of the preferred embodiment shown in FIG.  5 . The actuator arm  181  is connected to two head gimbal assemblies  183  and  185  (only partially shown). With regard to the discussion here, the head gimbal assemblies  183  and  185  are the same. Therefore, the below discussion regarding head gimbal assembly  183  also applies to head gimbal assembly  185 . 
     Base plate  180  is integrally connected with suspension limiter  182 . The base plate  180  and load beam  184  are connected to the actuator arm  181  by the use of a swaging boss (not shown). In this preferred embodiment, the base plate  180  is on the opposite side of the load beam  184  from the transducer (not shown). The base plate  180  is directly adjacent to the actuator arm  181  without the load beam  184  sandwiched between the base plate  180  and the actuator arm  181 . Load beam  184  includes a load beam bent region  198  in which the edge of the load beam is bent to be substantially perpendicular to the rest of the load beam  184 . The head gimbal assembly  183  includes FOS  188  for transmission of read/write data. There is an air gap  192  between FOS  188  and the suspension limiter  182 . Note that the suspension limiter  182  angles in a direction away from the load beam  184  at location marked  187  so that there is space for the air gap  192 . 
     When the load beam  184  and transducer (attached to load beam but not shown) are shocked, the load beam  184  and transducer will begin to lift away from the surface of the magnetic disc. When the load beam  184  makes contact with the suspension limiter  182  severe head slap is prevented because the transducer is not allowed to move any further away from the magnetic disc. In the case of head gimbal assembly  185 , the load beam is shown at  196 , the base plate is at  200 , the suspension limiter is at  194  and an air gap at  190 . 
     Another preferred embodiment of the invention in which the suspension limiter is an extension of the actuator arm is shown in FIG.  7 . Load beams  202  and  204  of head gimbal assemblies  206  and  208  are connected to the actuator arm  210  via a swaging boss (not shown) and base plates  209  and  211 . The actuator arm is integrally connected to an actuator extension  212  also referred to as suspension limiter  212 . This suspension limiter  212  and actuator arm  210  are integral and manufactured as one piece. Alternatively, the suspension limiter  212  and actuator arm  210  may be manufactured as separate pieces. In this embodiment there is only one suspension limiter  212  per two head gimbal assemblies  206  and  208 . The head gimbal assembly  206  includes a FOS  214  for transmission of read/write data. There is an air gap  218  between the load beam  202  and the suspension limiter  212 . 
     Note that the actuator arm extension  212  (i.e. suspension limiter  212 ) has a smaller cross sectional thickness than the actuator arm  210 . In this way the suspension limiter  212  can fit between the two head gimbal assemblies  206  and  208 . Preferably, the actuator arm extension  212  should be the same or smaller cross sectional thickness as the actuator arm  210 . 
     The suspension limiter  212  operates similarly to the suspension limiters of the other described preferred embodiments. As the load beams  202  and  204  move in a direction toward the suspension limiter  212 , and hence away from the magnetic disc, the physical contact between the load beam  202  and suspension limiter  212  will eventually stop such movement and hence reduce the occurrence of head slap. 
     FIG. 8 is a perspective view of the actuator arm  210  and suspension limiter  212  shown in FIG.  7  and discussed above. As can be seen from FIG. 8, a preferred embodiment includes a suspension limiter  212  which is not as wide (in the direction perpendicular to the thickness discussed above with respect to FIG. 7) as the actuator arm  210 . The purpose for this difference in width between the actuator arm  210  and the suspension limiter  212  is to minimize the inertia of the head stack assembly so that the head stack assembly and connected head gimbal assemblies can be moved quickly during operation for quick access to data on the disc. 
     FIG. 9 is a side view of another preferred embodiment of the invention. In this preferred embodiment, the base plate  220  and suspension limiter  222  of head gimbal assembly  221  are integrally connected. At the point where the base plate  220  is connected to the actuator arm  224 , the base plate  220  is on the same side of the load beam  226  as the transducer (not shown). In this respect this embodiment is similar to the embodiment shown in FIGS. 2-3. However, this preferred embodiment also includes an energy absorbing layer  228  between the suspension limiter  222  of head gimbal assembly  221  and the suspension limiter  230  of the adjacent head gimbal assembly  232 . The purpose of the energy absorbing layer  228  is to absorb the energy imparted from the load beam  226  when it contacts the suspension limiter  222  and likewise when the load beam  234  contacts suspension limiter  230 . 
     The energy absorbing layer  228  can be any material that provides high damping. For example, a polymeric material such as polyemide or parylene may be used for energy absorbing layer  228 . The energy absorbing layer  228  is attached to the two suspension limiters  222  and  230  by a glue or an adhesive. 
     Another preferred embodiment of the invention shown in the side enlarged view of FIG. 9 includes a compliant or noncompliant bump  240  located on the suspension limiter  230  at the contact point with the load beam. The bump is provided to add further shock absorption, change boundary conditions during impact and reduce the amount of wear debris. The bump  240  may be any rounded shape that extends out from the suspension limiter  230  toward the load beam  234 . Despite the inclusion of the bump  240  in the expanded portion of FIG. 9, it is also possible to utilize the energy absorbing layer  228  without the bump  240 . Alternately, it is also possible to use the bump  240  without including the energy absorbing layer  228  in any specific preferred embodiment previously described. 
     It should be noted that different designs and configurations of the suspension limiters of this invention can be made to achieve a desired stiffness and damping. High damping is desired for absorbing and dissipating shock energy. Through elementary modeling it was determined that a suspension limiter (modeled as a simple beam) having a thickness of about 6 mil which is about two orders of magnitude larger than the stiffness of the load beam would limit large load beam vibrations. 
     Some limiters were built with a thickness of 6 mil and attached to single head gimbal assemblies and shocked under nonoperational shocks. The experiments were also repeated with the same head gimbal assemblies but without the limiters attached. FIG. 10 is a side view taken from a photographic image (using a high speed camera) of a head gimbal assembly including a load beam  251  connected to a slider  250  in contact with a disc  252  when a suspension limiter  254  is used. 
     FIGS. 11 a-b  illustrate the results taken with a high speed camera of two identical shock experiments without and with a suspension limiter. In FIG. 11 a  no suspension limiter is used. The slider  260  is lifted off the surface of the disc  262  when a shock is delivered to the disc drive. FIG. 11 b  shows what happens when a shock is delivered to the disc drive when a suspension limiter according to the present invention is used. In FIG. 11 b  the slider  264  has barely started to lift off the surface of the disc  266 . The suspension limiter  268  has prevented further lift off by its contact with the load beam  270 . 
     FIG. 12 illustrates the results of another performed shock experiment. Again, this drawing was generated from a photograph taken by a high-speed camera when a suspension limiter according to the present invention was used. As can be seen from FIG. 12, the load beam  270  contacts suspension limiter  272  and deforms slightly at location  274 . However, the slider  276  did not lift away from the disc  278 . 
     In disc drives where tight tolerances are required (high-end drives), the suspension limiters have to be part of the base plate (same thickness). The thickness of the limiters is preferably between about 2 mil and 8 mil and is more preferably about 6 mil. The typical distance between adjacent load beams connected to the same actuator arm is 19 mil. Therefore, as shown in FIG. 4, with 1 mil tolerance between the suspension limiter and the FOS, there are still 5 mils clearance between the two suspension limiters  156  and  158 . Note that manufacture is therefore feasible because manufacturing tolerances are currently 1 mil. 
     FIG. 13 illustrates a simple linear quasistatic tolerance model, showing that with current manufacturing/assembly tolerances, the suspension limiter prevents severe head slap. A head slap is considered “severe” when the lift off distance (the distance between the disc and the transducer) is more than 5 mils. This model assumes a 1 mil gap between the suspension limiter  300  and the load beam  302 . Furthermore, the model assumes a length “L” from the proximal end of the actuator arm  304  to the transducer  306  and a length “1” from the end of the actuator arm  304  to the distal end of the suspension limiter  300 . The table below shows the calculated head lift off distances needed before the suspension limiter  300  is engaged. 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 1/L 
                 Transducer lift off distance(mils) 
               
               
                   
                   
               
             
             
               
                   
                 0.5 
                 2.0 
               
               
                   
                 0.4 
                 2.5 
               
               
                   
                 0.3 
                 3.3 
               
               
                   
                 0.2 
                 5.0 
               
               
                   
                   
               
             
          
         
       
     
     From the analysis above it is clear that the minimum length of the suspension limiter  300  should be 0.3L. Also, with better manufacturing tolerances, the distance between the suspension limiter  300  and the load beam  302  can be further reduced thus further reducing the head lift off distance before limiter engagement. 
     To summarize exemplary embodiments of the invention there is provided a head gimbal assembly ( 122 ,  178 ,  183 ,  206 ,  221 ) for attachment to an actuator arm ( 120 ,  160 ,  181 ,  210 ,  224 ,  304 ) of a disc drive ( 100 ). The head gimbal assembly includes a load beam ( 124 ,  166 ,  168 ,  184 ,  202 ,  226 ,  234 ,  251 ,  270 ,  302 ), wherein the proximal end of the load beam is operatively coupled to the actuator arm and the distal end of the load beam is operatively coupled to a gimbal assembly ( 136 ) wherein the gimbal assembly supports a transducer head ( 138 ,  186 ). The head gimbal assembly includes a stop means ( 130 ,  156 ,  164 ,  182 ,  212 ,  222 ,  230 ,  254 ,  268 ,  272 ,  300 ) operatively coupled to the actuator arm and adjacent to but not normally in contact with the load beam for limiting the motion of the load beam when the head gimbal assembly is subjected to shock. 
     In another exemplary embodiment of the invention there is provided a head gimbal assembly ( 122 ,  178 ,  183 ,  206 ,  221 ) for attachment to an actuator arm ( 120 ,  160 ,  181 ,  210 ,  224 ,  304 ) of a disc drive ( 100 ) and for supporting a flying head transducer ( 138 ,  186 ). The head gimbal assembly includes a load beam ( 124 ,  166 ,  168 ,  184 ,  202 ,  226 ,  234 ,  251 ,  270 ,  302 ) having a proximal end operatively coupled to the actuator arm and a distal end operatively coupled to a gimbal assembly ( 136 ) which supports the transducer head. The head gimbal assembly includes a suspension limiter ( 130 ,  156 ,  164 ,  182 ,  212 ,  222 ,  230 ,  254 ,  268 ,  272 ,  300 ) having aproximal end operatively coupled to the actuator arm and a distal end located adjacent to the load beam but normally not in contact with the load beam. 
     In another exemplary embodiment of the invention there is provided a magnetic disc drive ( 100 ) which includes a disc ( 102 ,  252 ,  262 ,  278 ) and a head stack assembly ( 108 ), the head stack assembly including a coil, an actuator body, and a plurality of actuator arms ( 120 ,  160 ,  181 ,  210 ,  224 ,  304 ). The magnetic disc drive further includes a plurality of head gimbal assemblies ( 122 ,  178 ,  183 ,  206 ,  221 ) operatively coupled to the plurality of actuator arms, each head gimbal assembly including a load beam ( 124 ,  166 ,  168 ,  184 ,  202 ,  226 ,  234 ,  251 ,  270 ,  302 ), wherein the proximal end of the load beam is operatively coupled to the actuator arm and the distal end is operatively coupled to a gimbal assembly ( 136 ) which supports a transducer head ( 138 ,  186 ). A proximal end of a suspension limiter ( 130 ,  156 ,  164 ,  182 ,  212 ,  222 ,  230 ,  254 ,  268 ,  272 ,  300 ) is operatively coupled to the actuator arm and a distal end is located adjacent to the load beam but normally not in contact with the load beam. 
     The foregoing description of preferred embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.