Abstract:
A gram load measurement assembly is configured to measure the gram load of a head stack assembly (HSA) of a disk drive being manufactured using the HSA&#39;s suspension tabs, thereby avoiding contact with the Air Bearing Surface (ABS) of the HSA&#39;s sliders when checking the gram load forces after the installation of the Head Gimbal Assembly (HGA) installation on the actuator assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/901,983 entitled “HSA GRAM LOAD MEASURMENT USING SUSPENSION TAB” filed Nov. 8, 2013, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     A typical hard disk drive includes a head disk assembly (“HDA”) and a printed circuit board assembly (“PCBA”). The HDA includes at least one magnetic disk (“disk”), a spindle motor for rotating the disk, and a head stack assembly (“HSA”) that includes a slider with at least one transducer or read/write element (also called “head”) for reading and writing data. The HSA is controllably positioned by a servo system in order to read or write information from or to particular tracks on the disk. The typical HSA has three primary portions: (1) an actuator arm assembly that moves in response to the servo control system; (2) a head gimbal assembly (“HGA”) that extends from the actuator arm assembly and biases the slider toward the disk; and (3) a flex cable assembly that provides an electrical interconnect with minimal constraint on movement. 
     A typical HGA includes a load beam, a gimbal attached to an end of the load beam, and a slider attached to the gimbal. The load beam has a spring function that provides a “gram load” biasing force and a hinge function that permits the slider to follow the surface contour of the spinning disk. The load beam has an actuator end that connects to the actuator arm and a gimbal end that connects to the gimbal that supports the slider and transmits the gram load biasing force to the slider to “load” the slider against the disk. A rapidly spinning disk develops a laminar airflow above its surface that lifts the slider away from the disk in opposition to the gram load biasing force. In this state, the slider is commonly said to be “flying”, although the sliders do not, in fact, fly or develop an aerodynamic force like lift (as air foils do due to the Bernoulli effect). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a HSA in a HDA, showing a cut-away view of the pivot bearing cartridge and the top and bottom Voice Coil Motor (VCM) plates. 
         FIG. 2  is a cross-sectional view of a head stack in an HDA, with the top VCM plate removed. 
         FIG. 3  is a cross-sectional view of an actuator arm assembly, showing the pivot bearing cartridge in cross-section. 
         FIG. 4  is a side view of a HSA. 
         FIG. 5  is a detail side view of a pair of the HGAs and suspension or lift tabs shown in  FIG. 4 . 
         FIG. 6  shows the gram load spring biasing force imposed upon a slider Air Bearing Surface (ABS) during conventional gram load measurement. 
         FIG. 7  is a diagram of a gram load measurement assembly configured for the measurement of HSA gram load using the suspension tabs of the HSAs, according to one embodiment. 
         FIG. 8  is a diagram of a top tooling assembly of the gram load measurement assembly of  FIG. 7 , according to one embodiment. 
         FIG. 9  is a diagram of a base assembly of the gram load measurement assembly of  FIG. 7 , according to one embodiment. 
         FIG. 10  is a cross-sectional view of the gram load measurement assembly of  FIG. 7 . 
         FIG. 11  is a detail cross-sectional view of the of the gram load measurement assembly of  FIG. 7 , showing the clamped captive HSA, a load cell tower and a load cell disposed in the base assembly, according to one embodiment. 
         FIG. 12  is a perspective view of a captive HSA mounted in a gram load measurement assembly, according to one embodiment. 
         FIG. 13  is a side detail view of the captive HSA mounted in a gram load measurement assembly, according to one embodiment. 
         FIG. 14  is a perspective view of a disk drive actuator clamping assembly and a captive HSA, according to one embodiment. 
         FIG. 15  is a detail view of  FIG. 14 , showing the head spreader tabs disposed between the respective HGAs of the HSA. 
         FIG. 16  is a side view of the HGAs, deflected load beams, and head spreader tabs and a disk simulator assembly, according to one embodiment. 
         FIG. 17  illustrates the manner in which the suspension tab acts upon bearing surfaces of the disk simulator assembly when a head spreader tab is moved away from its associated HGA by a head separator tab actuator. 
         FIG. 18  is a flowchart of a method, according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In a modern hard disk drive, and with reference to  FIGS. 1, 2 and 3 , the HSA  40  is pivotally secured to the base of the drive via a pivot-bearing cartridge  42  so that the read/write transducer(s) of sliders  44  at the distal end of the suspension assembly(ies) may be moved over the recording surface(s) of the disk(s)  46 . The pivot-bearing cartridge  42  enables the HSA  40  to pivot, and includes a bearing cartridge and a pivot shaft that defines an axis  48  about which the actuator rotates when power is applied to the VCM. The “rotary” or “swing-type” actuator assembly rotates on the pivot bearing cartridge  42  between limited positions, and the coil assembly  52  that extends from one side of the body portion  50  of the actuator body of the HSA  40  is disposed between and interacts with a first permanent magnet  54  mounted to a bottom VCM plate  56  and a second permanent magnet  58  mounted to a top VCM plate  60  to form the VCM formed by the bottom VCM plate  56 , the first permanent magnet  54 , the coil assembly  52 , the second permanent magnet  58  and the top VCM plate  60 . In operation, when a driving voltage is applied to the VCM, torque is developed that causes the HSA  40  to pivot about the actuator pivot axis  48  and causes the read/write transducer(s) of the sliders  44  to sweep radially over the disk(s)  46 . Most modern drives use a feedback mechanism so that small changes in applied voltage are operative to position the read/write transducer(s) of the sliders  44  precisely over the disk(s)  46 . 
     The increasing number of disks in the disk pack, in particular, has engendered a corresponding increase in the number of actuator arms (four such actuator arms being shown in  FIGS. 1-3 ) on the HSA  40 . Indeed,  FIG. 4  shows a side view of an HSA having six actuator arms that support fully ten sliders comprising read/write actuators configured to read and write data to and from 5 magnetic disks sandwiched therebetween. 
       FIG. 5  is a detail side view of a pair of the HGAs and suspension or lift tabs shown in  FIG. 4 .  FIG. 5  shows two HGAs  102 . Each HGA  102  may comprise a load beam  402  (best seen in  FIG. 4 ), a gimbal  106  and a slider  108  attached to the gimbal  106 . The free distal end of the HGA may comprise a suspension tab  502 . The suspension tab  502  may be configured, among other functions, to enable the heads to be loaded (parked) onto and unloaded from a ramp  202  (best shown in  FIGS. 1 and 2 ) disposed at the outer diameter (OD) of the disks  46 . The slider  108  comprises a read head for reading and writing data from and to a magnetic disk (e.g. disk  46 ). The read head includes a slider substrate having an ABS (the label  108  points to this surface). The slider substrate may comprise AITiC, although another ceramic or silicon materials may also be used. The slider substrate of the read head  210  also includes a trailing face that includes a read/write transducer (too small to be practically shown in the figures). In certain embodiments, the read/write transducer may comprise an inductive magnetic write transducer merged with a magneto-resistive read transducer. One purpose of the load beam  402  is to provide limited vertical compliance for the read head of the slider  108  to follow the vertical undulations of the surface of a disk (e.g. disk  46  of  FIG. 1 ) as it rotates, and to preload the air bearing surface of the read head against the disk surface by the aforementioned “gram load.” 
       FIG. 6  shows the gram load spring biasing forces  602  that are imposed upon a slider ABS during conventional gram load measurement. As shown, a conventional method of gram load measurement uses the ABS as a reference datum for the measurement of the spring force  602 . That is, the load beam, which may be under compression or tension, is made to move (e.g., released from a previously constrained initial configuration and position) such that the ABS of the slider  108  is made to contact the opposing surface of a load cell  604 . The resulting force imposed upon the load cell  604  by the ABS of the slider  108  is measured and is related to the gram load. Such a system presents two major issues; namely, ABS surface damage and contamination. Indeed, the ABS-to-load cell contact may damage the delicate structures of the ABS and/or the facing surface of the load cell  604  may transfer contaminants onto the ABS of the slider  108 , potentially negatively affecting operation of the slider  108  above the disks  46 . 
     One embodiment comprises a gram load measurement assembly that does not rely upon the ABSs of the sliders-to-load cell contact to accurately measure the gram load.  FIG. 7  is a diagram of such a gram load measurement assembly  700 , configured for the measurement of HSA gram load without physical contact between the load cell and the sliders of the HSAs. As shown, the gram load measurement assembly  700  may comprise, according to one embodiment, a base assembly  702  that supports a top tooling assembly  704 . Characteristics and functionality of each is described hereunder and shown in the figures. 
       FIG. 8  is a diagram of a top tooling assembly  704  of the gram load measurement assembly  700  of  FIG. 7 , according to one embodiment.  FIG. 9  is a diagram of the base assembly  702  of the gram load measurement assembly  700  of  FIG. 7 , according to one embodiment.  FIGS. 8 and 9  are shown at different scales, for clarity of illustration. According to one embodiment, the top tooling assembly  704  may comprise structure configured to clamp and hold captive an actuator assembly and to position the load beams of the HGAs thereof in a manner suitable to enable the measurement of the respective gram loads thereof. The base assembly  702  of  FIG. 9  may be configured, according to one embodiment, to house a user interface and controls configured to enable a human or machine operator to operate the gram load measurement assembly  700 . The base assembly  702  may also house a load cell assembly that is acted upon by structure of the top tooling assembly  704  and that generates a corresponding output signal from which a gram load measurement may be derived. 
       FIG. 10  is a cross-sectional view of the gram load measurement assembly  700 , along cross-sectional line AA′ of  FIG. 7 .  FIG. 11  is a detail cross-sectional view of the base assembly  702  of the gram load measurement assembly  700 .  FIG. 10  shows the HSA  802  mounted in and help captive by the top tooling assembly  704 , a load cell tower  804  and a load cell assembly  806 . The top tooling assembly  704 , according to one embodiment, may be configured to measure the force imparted upon a disk simulator assembly by the HGAs of the captive HSA. The disk simulator assembly may be coupled to a load cell tower  804  such as to mechanically transmit the imparted force onto the load cell tower  804 . The load cell tower  804 , in turn, may be coupled to load cell assembly  806  in the base assembly  702 , which load cell assembly  806  may be configured to generate an output signal that may be proportional or otherwise related to the gram load being measured. 
       FIG. 11  is a detail cross-sectional view of the base assembly  702  of the gram load measurement assembly  700 .  FIG. 11  shows a HSA  802  held captive by the top tooling assembly  704 . In detail, the top tooling assembly  704  may comprise a disk drive actuator clamping assembly comprising a first pivot datum  810  and a second pivot datum  812 . The top tooling assembly  704  may be configured, according to one embodiment, to cause the first pivot datum  810  and the second pivot datum  812  to clamp down on the pivot bearing cartridge  42  (also readily visible in  FIGS. 1, 2 and 3 ) of the HSA (along actuator pivot axis  48 , for example). The top tooling assembly  704 , in this manner, holds the HSA under test captive, to enable accurate measurement of the gram load forces. 
       FIG. 12  is a perspective view of an HSA mounted in a gram load measurement assembly  700  according to one embodiment. Shown in  FIG. 12  is the VCM  801 , the actuator body into which the pivot bearing cartridge  42  is fitted, and actuator arms  813  terminated by the respective HGAs of the HSA. According to one embodiment, the HSA and the disk simulator assembly are disposed within the gram load measurement assembly  700  such that there is no contact between the respective ABSs of the sliders (or the slider in its entirety) and any surface during the gram load measurement. Indeed, according to one embodiment and as shown in  FIG. 12 , during the gram load measurement, it is the distal free ends of the HGAs of the HSA that are made to selectively contact the disk simulator assembly  808  and/or any load cell bearing surface during the gram load measurement procedure, rather than ABSs of the sliders. 
     According to one embodiment and as shown in  FIG. 13 , it is the suspension tabs  502  (also called lift tabs) disposed at the distal free end of the load beams of the HGAs that are positioned to bear against corresponding surfaces of the disk simulator assembly  808 , thereby sparing the more proximally-disposed sliders any potentially damaging contact therewith. As shown, each of the suspension tabs  502  faces a bearing surface of the disk simulator assembly  808  against which the suspension tab will bear during the gram load measurement procedure, thereby exerting a force against that bearing surface, which force may be transmitted to and measured by the load cell assembly  806  within the base assembly  702 . As also shown, the sliders  108  and their respective ABSs are disposed well away from the disk simulator assembly  808 , sparing them from potential contamination and damage. 
     To properly position the suspension tabs of the HSA under test to face the corresponding bearing surfaces of the disk simulator assembly  808 , the load beams thereof (attached to the distal end of the actuator arms of the actuator assembly) may be manipulated so as to separate facing sliders  108  away from one another. Once separated, the suspension tabs  502  are in a configuration in which they may be inserted within the openings or features of the disk simulator assembly  808 . Alternatively, the disk simulator assembly  808  may be moved into position such that the respective suspension tabs of the HGAs fit within openings and face their corresponding bearing surfaces. In this configuration, the suspension tabs  502  face corresponding bearing surfaces if the disk simulator assembly  808 . According to one embodiment, a head spreader assembly is configured to separate the facing sliders  108  from one another.  FIG. 14  shows aspects of such a head spreader assembly  814 . 
     The head spreader assembly  814 , according to one embodiment, may comprise a plurality of head spreader tabs, one for each of the HGAs of the HSA. Some of the head spreader tabs are shown in  FIG. 15 , at reference numeral  828 . In the implementation illustrated in  FIG. 14 , six such head spreader tabs are provided and actuated by a, for example, pneumatic air gripper assembly  816 . The pneumatic air gripper assembly  816  may comprise a plurality of spreader tab actuation elements  818 , each of which may be mechanically coupled to a corresponding one of the head spreader tabs  828 . According to one embodiment, when the gram load of, for example, head 0 (coupled to the top-most HGA in  FIG. 14 ) is to be measured, a corresponding one of the spreader tab actuation elements  818  may be actuated by the pneumatic air gripper assembly  816  to cause the head spreader tab coupled thereto move away from the HGA with which it was in contact, thereby enabling the corresponding suspension tab  502  to come into contact with and bear against a corresponding surface on the disk simulator assembly  808 , which bearing force may then be measured by the load cell assembly  806  within the base assembly  702 . For example, when it comes time to measure the gram load of head 5, the corresponding head spreader tab is moved away from the HGA to which head 5 is coupled, causing the suspension tab  820  thereof to move towards and bear against a facing surface  822 , as suggested by the up-facing arrow. Similarly, when it comes time to measure the gram load of head 6, the corresponding head spreader tab is moved away from the HGA to which head 6 is coupled, causing the suspension tab  824  thereof to move towards and bear against a facing surface  826  of the disk simulator assembly  808 , as suggested by the down arrow. 
       FIG. 16  is a simplified side view of the HGAs, the disk simulator assembly  808  the head spreader tabs  828 , according to one embodiment.  FIG. 16  illustrates an initial state before or between gram load measurements. In this state, the head spreader tabs  828  have been actuated to spread the sliders of the HSA such that the suspension tabs  502  face, but do not contact, their corresponding facing surface on the disk simulator assembly  808 . As shown, pairs of HGAs (according to one embodiment, pairs thereof that comprise sliders configured to read and write data from separate but immediately adjacent disks  46 ) may be suitably deflected by the head spreader tabs  828  such that may be interdigitated within corresponding openings defined within the disk simulator assembly  808 . Other HGAs (such as, for example, those to which the top-most and bottom-most sliders are coupled) may be, as shown in  FIG. 16 , disposed so as to face a top-facing bearing surface and a bottom-facing bearing surface of the disk simulator assembly  808 , respectively. 
       FIG. 17  illustrates the manner in which the suspension tabs acts upon the disk simulator assembly  808  when a head spreader tab  828  is moved away from its associated HGA by a corresponding head separator tab actuator coupled thereto, according to one embodiment. As shown therein, when it is desired to measure the gram load of head 0 (shown as slider  108   0 , coupled to the top-most HGA in  FIG. 17 ), the pneumatic air gripper assembly  816  may act upon the spreader tab actuation element  818  coupled to head spreader tab  828   0 . This releases the HGA to which head 0 (slider  108   0 ) is coupled, which elastically tends to move from its initial, deflected state in the direction indicated at  832  until the suspension tab  502   0  comes into contact with and bear against the facing surface  808   0  of the disk simulator assembly  808 . This force, illustrated in  FIG. 17  at  830 , is transmitted through the load cell tower  804  to the load cell assembly  806  in the base assembly  702 . The load cell assembly  806  may then generate an output related to the exerted force  830 , from which output a quantity representative of the gram load of head 0 may be derived. The gram loads of other sliders may be similarly measured, by moving a corresponding head spreader tab  828  away from the HGA to thereby cause the suspension tab thereof to come into contact and bear against a facing bearing surface ( 808   1 ,  808   2  . . . ) of the disk simulator assembly  808 . The gram load of the sliders may be measured sequentially or in any order. The measured/derived gram loads and/or other intermediate values may be stored in a memory disposed, for example, in the base assembly  702  and/or exterior thereto. As may be seen from  FIG. 17 , at no time do the sliders of the HGAs come into contact with the disk simulator assembly  808  or any other surfaces during the gram load measurement procedure, thereby sparing the ABSs thereof damage or contamination that may otherwise occur had the sliders been the datum against which the gram load was measured. 
     Advantageously, one embodiment may be configured to carry out HGA gram load measurements using the suspension tabs of the HGAs using a top tooling assembly  704  that may comprise individually-actuable head spreader tabs  828 . According to one embodiment, the configuration of the pneumatic air gripper assembly  816  and the number and configuration of the spreader tab actuation elements  818  and that of the head spreader tabs  828  may be modified at will to conform to the structure (e.g., size, shape and number of actuator arms) of different actuator assemblies. Likewise, according to one embodiment, the disk simulator assembly  808  may be modular and may be configured for easy removal and replacement with a different disk simulator assembly configured for other actuator assemblies. 
     The base assembly  702  may also be modular and may be configured to accommodate different top tooling assemblies  704  configured for different actuator assemblies. Indeed, rather than modifying the top tooling assembly  704  to accommodate different actuator assemblies, different top tooling assemblies  704  may be configured for different actuator assemblies and may be configured to be hot swappable onto a same base assembly  702 . Other permutations are possible. For example, the base and top tooling assemblies  702 ,  704  may be integrated into a single device. 
     According to one embodiment, precise control over the displacement imposed by the heads spreader tabs  828  on the HGAs is desired, to prevent stacking up tolerances of displacement variations during gram load testing. For example, according to one embodiment, the displacement imposed upon the HGAs by the head spreader tabs (see, e.g., the displacement imposed on head 0 from its state in  FIG. 16  to its state in  FIG. 17 ) may be controlled such that the stacking up of displacement errors across sliders is kept to less than about 10% or less. 
     According to one embodiment, the head spreader assembly  814 , comprising at least the pneumatic air gripper assembly  816 , the spreader tab actuation elements  818  and the head spreader tabs  828 , may be configured to minimize external forces applied to the constituent load beams of the actuator assembly in order to eliminate distortion and side effects of machine operation that may impact other parameters of the HSA. Toward that end, the head spreader tabs  828  may be configured to have minimal contact with the load beam, with a minimized amount of shock load. 
       FIG. 18  is a flowchart of a method, according to one embodiment. As shown, the method may comprise, as shown at B 181 , clamping and holding captive an actuator assembly of a disk drive, the actuator assembly comprising a plurality of load beams. Block B 182  calls for deflecting the plurality of load beams. As further shown in  FIG. 18 , block B 183  calls for causing suspension tabs coupled to respective free ends of the load beams to face respective bearing surfaces. As shown at B 184 , one of the deflected load beams may then be released such that the suspension tab coupled to the released load beam contacts and bears against a corresponding one of the bearing surfaces. As shown at block B 185 , the biasing force of the suspension tab bearing against the corresponding one of the bearing surfaces may then be measured. 
     While certain embodiments of the disclosure have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel methods, devices and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure. For example, those skilled in the art will appreciate that in various embodiments, the actual physical and logical structures may differ from those shown in the figures. Depending on the embodiment, certain steps described in the example above may be removed, others may be added. Also, the features and attributes of the specific embodiments disclosed above may be combined in different ways to form additional embodiments, all of which fall within the scope of the present disclosure. Although the present disclosure provides certain preferred embodiments and applications, other embodiments that are apparent to those of ordinary skill in the art, including embodiments which do not provide all of the features and advantages set forth herein, are also within the scope of this disclosure.