Abstract:
Method for controlling installation of a head stack assembly in a disc drive. The head stack assembly is aligned in a head stack installation tool. A base deck assembly is advanced to the head stack installation tool, the base deck assembly having a post supporting a tolerance ring. A robotic assembly is dispatched to pick and press the head stack assembly onto the tolerance ring and post while mechanical resistance and distance traveled parameters by the head stack assembly are measured. The installation is aborted or completed in relation to the mechanical resistance encountered and the distance traveled, thus allowing use of minimum and maximum force thresholds with respect to insertion distance and assuring correct installation of the head stack assembly.

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 60/150,138 filed Aug. 20, 1999. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of disc drive data storage devices, and more particularly, but not by way of limitation, to an automated assembly of a head-disc assembly of a disc drive, which includes a head stack assembly installation system. 
     BACKGROUND 
     Modern hard disc drives are commonly used in a multitude of computer environments, ranging from super computers through notebook computers, to store large amounts of data in a form that can be made readily available to a user. Typically, a disc drive comprises one or more magnetic discs that are rotated by a spindle motor at a constant high speed. The surface of each disc is a data recording surface divided into a series of generally concentric recording tracks radially spaced across a band having an inner diameter and an outer diameter. The data tracks extend around the disc and store data within the tracks on the disc surfaces in the form of magnetic flux transitions. The flux transitions are induced by an array of transducers, otherwise commonly called read/write heads. Typically, each data track is divided into a number of data sectors that store fixed sized data blocks. 
     The read/write head includes an interactive element such as a magnetic transducer, which senses the magnetic transitions on a selected data track to read the data stored on the track. Alternatively, the read/write head transmits an electrical signal that induces magnetic transitions on the selected data track to write data to the track. 
     As is known in the art, each read/write head is mounted to a rotary actuator arm and is selectively positionable by the actuator arm over a selected data track of the disc to either read data from or write data to the selected data track. The read/write head includes a slider assembly having an air-bearing surface that causes the read/write head to fly above the disc surface. The air bearing is developed as a result of load forces applied to the read/write head by a load arm interacting with air currents that are produced by rotation of the disc. 
     Typically, a plurality of open-center discs and open-centered spacer rings are alternately stacked on the hub of a spindle motor, followed by the attachment of a clampring to form a disc pack or disc stack. The hub, defining the core of the stack. serves to align the discs and spacer rings around a common centerline. Movement of the discs and spacer rings is typically constrained by a compressive load maintained by the clampring. The read/write heads mounted on a complementary stack of actuator arms, which compose an actuator assembly, commonly called an E-block, accesses the surfaces of the stacked discs of the disc pack. The E-block also generally includes read/write head wires which conduct electrical signals from the read/write heads to a flex circuit which, in turn, conducts the electrical signals to a printed circuit board assembly (PCB). When the E-block is merged with the disc pack into a base deck and a cover is attached to the base deck a head-disc assembly (HDA) is formed. For a general discussion of E-block assembly techniques, see U.S. Pat. No. 5,404,636 entitled METHOD OF ASSEMBLING A DISC DRIVE ACTUATOR issued Apr. 11, 1995 to Stefansky et al., assigned to the assignee of the present invention. 
     The head-disc assembly (HDA) of a disc drive is typically assembled in a clean room environment. The need for maintaining a clean room environment (free of contaminants of about 0.3 micron and larger) is to ensure the head-disc interface remains unencumbered and damage free. The slightest damage to the surface of a disc or read/write head can result in a catastrophic failure of the disc drive. The primary causes of catastrophic failure, particularly read/write head crashes (a non-recoverable, catastrophic failure of the disc drive), are generally characterized as contamination, exposure to mechanically induced shock, and non-shock induced damage. The source of non-shock induced damage is typically traced to the assembly process, and generally stems from handling damage sustained by the disc drive during the assembly process. 
     Several factors that bear particularly on the problem of assembly process induced damage are the physical size of the disc drive, the spacing of the components, the recording densities sought to be achieved and the level of precision to be maintained during the assembly process. The high levels of precision required by the assembly process are necessary to attain the operational tolerances required by the disc drive. The rigorous operational tolerances are in response to market demands that have driven the need to decrease the physical size of disc drive while simultaneously increasing disc drive storage capacity and performance characteristics. 
     Demands on disc drive mechanical components and assembly procedures have become increasingly more critical in order to support capability and size in the face of these new market demands. Part-to-part variation in critical functional attributes in the magnitude of a micro-inch can result in disc drive failures. Additionally, as disc drive designs continue to decrease in size, smaller read/write heads, thinner substrates, longer and thinner actuator arms, and thinner gimbal assemblies will continue to be incorporated into the drives. This trend significantly increases the need to improve the assembly processes to protect the read/write heads and discs from damage resulting from incidental contact between mating components. The aforementioned factors resultantly increase the difficulty of assembling disc drives. As the assembly process becomes more difficult, the need to invent new tools, methods and control systems to deal with the emerging complexities presents unique problems in need of solutions. 
     Coupled with the size and performance improvement demands is the factor of further market driven requirements for ever increasing fault free performance. 
     The progression of continually decreasing disc thickness and disc spacing, together with increasing track density and increasing numbers of discs in the disc pack, has resulted in a demand for tools, methods and control systems of ever increasing sophistication. A result of the growth in demand for sophisticated assembling equipment has been a decreasing number of assembly tasks involving direct operator intervention. Many of the tasks involved in modem assembly methods are beyond the capability of operators to reliably and repeatedly perform, further driving the need for automation equipment and tools. 
     In addition to the difficulties faced in assembling modem disc drives of high capacity and complex, physical product performance requirements have dictated the need to develop new process technologies to ensure compliance with operating specifications. The primary factors driving more stringent demands on the mechanical components and the assembly process are the continually increasing areal densities and data transfer rates of the disc drives. 
     The continuing trend in the disc drive industry is to develop products with ever increasing areal densities, decreasing access times and increasing rotational speeds. The combination of these factors, place greater demands on the ability of modern servo systems to control the position of read/write heads relative to data tracks. The ability to assemble HDAs nominally free from the effects caused by unequal load forces on the read/write heads, disc pack imbalance or one of the components of runout, velocity and acceleration (commonly referred to as RVA) possess a significant challenge as track densities increase. The components of RVA are: disc runout (a measure of the motion of the disc along the longitudinal axis of the motor as it rotates); velocity (a measure of variations in linear speed of the disc pack across the surface of the disc); and acceleration (a measure of the relative flatness of the discs in the disc pack). 
     One cause of unequal load forces on the read/write heads stems from misalignment of the head stack assembly during assembly of the HDA. Misalignment of the head stack assembly causes the fly-height of the individual read/write heads to deviate from optimum, causing an increase in the distance between the disc the head for some surfaces and decreasing the distance for others the deviation is substantial, head/disc contact occurs that can lead to head crashes. For less severe deviations in fly heights, soft read errors often develop. If the soft errors are detected in the test process, the HDA is returned to the clean room for rework, exposing the HDA to handling damage. If the soft errors go undetected during the test process and develop during operation in the field, disc drive performance denigrates, write faults may be reported and reliability of the disc drive suffers. The ability to control the alignment of the head stack assembly derives from the ability to precisely control the installation of the head stack assembly into the HDA. 
     By design, a disc drive typically has a discreet threshold level of resistance to withstand rotationally induced noise and instability, below which the servo system is not impaired. Also, a fixed range of load forces must be maintained on the read/write head to ensure proper fly height for data exchange. The operating performance of the disc drive servo system is affected by mechanical factors beyond the effects of mechanically induced read/write head oscillation from disc surface anomalies. Errors are traceable to disc pack imbalance and RVA noise sources. Even with improved approaches to the generation of position error signals in the disc drive servo system, the ability of the system to deal with such issues is finite. The limits of the servo system capability to reliably control the position of the read/write head relative to the data track must not be consumed by the noise present in the HDA resulting from the assembly process. Consumption of the available margin by the assembly process leaves no margin in the system to accommodate changes in the disc drive attributes over the life of the product. An inability to accommodate changes in the disc drive attributes leads to field failures and an overall loss in product reliability, a detrimental impact to product market position. 
     Thus, in general, there is a need for an improved approach to disc drive-assembling technology to minimize the potential of damage during assembly, to produce product that is design compliant and reliable, and to minimize mechanically induced system noise. More particularly, there is a need for a head stack assembly installation system controlling the installation of the head stack assembly into an HDA of a disc drive. 
     SUMMARY OF THE INVENTION 
     The present invention provides a head stack assembly installation system with a head stack installation tool electronically communicating with a computer that has an active installation software program directing and controlling process steps enacted by the head stack installation tool to install a head stack assembly into a head disc assembly of a disc drive. The head stack installation tool provides a nesting position for aligning and staging the head stack assembly prior to installation into the head disc assembly, an installation position for locating in securing the head disc assembly while awaiting installation of the head stack assembly, a robotic assembly and a measurement assembly. The robotic assembly picks and places the head stack assembly into the head disc and the measurement assembly collects and communicates process position and force parameters to the computer for use by the computer in calculating distance and force data. The active installation software program directs and controls enactment of process steps followed by the head stack installation tool by directing the computer to execute installation software program steps based on the position and force data calculated by the computer. 
    
    
     
       These and other features and advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings. 
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partially cutaway top view of a disc drive of the type assembled by the head stack assembly installation system of the present invention. 
         FIG. 2  is a partially cutaway top view of a basedeck assembly for the disc drive of FIG.  1 . 
         FIG. 3  is an elevational view of the flex connector body with attached flex circuit and actuator assembly serial number for the disc drive of FIG.  1 . 
         FIG. 4  is a partial cutaway elevational and partial cross-sectional view of the disc drive of FIG.  1 . 
         FIG. 5  is a plan view of the actuator assembly of the disc drive of FIG.  1 . 
         FIG. 6  is a partial cutaway elevational view of the actuator assembly of the disc drive of FIG.  1 . 
         FIG. 7  is a partial cutaway perspective view of the head stack assembly installation system of the present invention. 
         FIG. 8  is a perspective view of an end effector assembly of the head stack assembly installation system of FIG.  7 . 
         FIG. 9  is a cross-sectional, partial cutaway view of radially disposed positionable gripper sections of the end effector of FIG.  8 . 
         FIG. 10  is a flow chart of system hardware communication for the head stack assembly installation system of FIG.  7 . 
         FIG. 11  is a flow chart for logic of main process steps of an installation software program of the head stack assembly installation system of FIG.  7 . 
         FIG. 12  is a flow chart for logic of head stack assembly installation process steps of the installation software program of the head stack assembly installation system of FIG.  7 . 
         FIG. 13  is a flow chart for logic of head stack assembly installation analysis process steps of the installation software program of the head stack assembly installation system of FIG.  7 . 
         FIG. 14  is a diagram showing an a family of empirically derived mechanical resistance thresholds. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings in general, and more particularly to  FIG. 1 , shown therein is a top view of a disc drive  100  constructed in accordance with the present invention. The disc drive  100  includes a basedeck  102  that has several fastener receptacles  104 , the basedeck  102  supporting various disc drive components, and a top cover  106  (shown in part), with several mounting apertures (not separately shown), secured to the basedeck  102  by top cover fasteners  108 . The installed top cover  106  together with the basedeck  102  provides a sealed internal environment for the disc drive  100 . Numerous details of and variations for the construction of the disc drive  100  are not included in the following description as such are well known to those skilled in the art and are believed to be unnecessary for the purpose of describing the present invention. 
     Mounted to the basedeck  102  is a ramp load snubber assembly  110  secured to the basedeck  102  by a fastener  112 , and a spindle motor  114  with a top cover attachment aperture  116 . The spindle motor  114  supports several discs  118  for rotation at a constant high speed, the discs  118  mounted on a spindle motor hub  120  that are secured by a clampring  122  with clampring fasteners  124 . In addition to providing support for the stacked discs  118 , the spindle motor hub  120  also provides a timing mark  126  used during the assembly process to reference the angular location of a source of rotational imbalance. Adjacent the discs  118  is an actuator assembly  128  (also referred to as an “E-block” or a head stack assembly (HSA)) which pivots about a bearing assembly  130  in a rotary fashion. The bearing assembly supports a beveled pick and place member  132  that serves as a tooling grip during assembly operations. The HSA  128  includes actuator arms  134  (only one shown) that support load arms  136 . Each load arm  136  in turn supports read/write heads  138 , with each of the read/write heads  138  corresponding to a surface of one of the discs  118 . As mentioned, each of the discs  118  has a data recording surface divided into concentric circular data tracks  140  (only one shown), and the read/write heads  138  are positionably located over data tracks to read data from, or write data to, the tracks. 
     The HSA  128  is controllably positioned by a voice coil motor assembly (VCM)  142 , comprising an actuator coil  144  immersed in the magnetic field generated by a magnet assembly  146 . A magnetically permeable flux path is provided by a steel plate  148  (also called a top pole piece) mounted above the actuator coil  144  to complete the magnetic circuit of the VCM  142 . 
     When controlled DC current is passed through the actuator coil  144 , an electromagnetic field is setup, which interacts with the magnetic circuit of the VCM  142  to cause the actuator coil  144  to move relative to the magnet assembly  146  in accordance with the well-known Lorentz relationship. As the actuator coil  144  moves, the HSA  128  pivots about the bearing assembly  130 , causing the heads  138  to move over the surfaces of the discs  118  thereby allowing the heads  138  to interact with the data tracks  140  of the discs  118 . When the disc drive  100  is turned off, the VCM  142  parks the HSA  128  on the ramp load snubber assembly  110  to avoid shock induced contact between the read/write heads  138  and the discs  118 . 
     To provide the requisite electrical conduction paths between the read/write heads  138  and disc drive read/write circuitry (not shown), read/write head wires (not shown) are affixed to a read/write flex circuit  150 . Next the read/write flex  150  is routed from the load arms  136  along the actuator arms  134  and into a flex circuit containment channel  152  and on to a flex connector body  154 . The flex connector body  154  supports the flex circuit  150  during passage of the read/write flex circuit  150  through the basedeck  102  and into electrical communication a disc drive printed circuit board assembly (PCBA) (not shown) mounted to the underside of the basedeck  102 . The flex circuit containment channel  152  also supports read/write signal circuitry  156  used to condition read/write signals passed between the read/write circuitry (not shown) and the read/write heads  138 . The disc drive PC BA provides the disc drive read/write circuitry, which controls the operation of the heads  138 , as well as other interface and control circuitry for the disc drive  100 . 
     To maintain the sealed internal environment for the disc drive  100 , a seal gasket  158  is molded on to the top cover  106 . Top cover  106  has a multitude of gasket attachment apertures  160  through, which gasket material flows during the gasket molding process. A continuum of symmetrically formed gasket material is disposed on both the top and bottom surfaces of the top cover  106  and injected through the apertures  160 . During the cure process, the gasket material injected into the gasket attachment apertures  160  bonds the portion of the seal gasket adjacent the top surface of the top cover  106  to the portion of the seal gasket adjacent the bottom portion of the top cover  106 , thereby sealing the gasket attachment apertures  160  and forming the seal gasket  158 . A gasket material found to be useful for this application is “Fluorel” by the 3M Company, and more specifically, 3M “Fluorel”, FE-5621Q. 
     The disc drive  100  has two primary assemblies, the PCBA (not shown) and a head disc assembly (HDA)  162  attached to the PCBA. The HDA  162  typically contains the mechanically active assemblies and components of the disc drive  100 . Typically included within the HDA  162  are the HSA  128 , the VCM  142  and a disc stack  164  sustained within the sealed environment created when the top cover  106  supporting the seal gasket  158  is secured to the basedeck  102  by fasteners  108 . The disc stack  164  is formed by stacking discs  118 , interleaved with spacer rings (not shown), on the spindle hub  120  of the spindle motor  114  and securing the stack with the clampring  122  and fasteners  124 . 
     During operation of the disc drive  100 , spinning discs  118  generate airflow consistent with the direction of rotation of the spinning discs  118 . To reduce chances of a catastrophic failure of the disc drive  100  caused by particulate contamination internal to the HDA  162 , an air filter  166  is provided internal to the HDA  162  to trap airborne particulate either present following assembly or generated during operation of the disc drive  100 . 
       FIG. 2  shows a basedeck assembly  168  to include the basedeck  102 , the disc pack assembly  168 , the air filter  166 , a bottom pole piece  170  supporting a rare earth magnet  172  and a head stack assembly post  174  supporting a removably attached tolerance ring  176 . The bottom pole piece  170 , with the rare earth magnet  172 , together with the top pole pieces  148 , supporting a second rare earth magnet (not shown), form the magnet assembly  146  and the actuator coil  144  collectively form the VCM  142 . The basedeck assembly  168  together with an installed HSA  128 , magnet assembly  146  and top cover  106  combined to form the HDA  162  of FIG.  1 . 
       FIG. 3  shows the flex connector body  154  with the attached flex circuit  150  supporting a machine-readable head stack assembly serial number  178 . In a preferred embodiment machine-readable head stack assembly serial number  178  is a barcode but could also be characters capable of being optically recognized using optical character recognition software (OCR) or other comparable coding methodologies. The serial number  178  represents the physical characteristics for a particular HSA  128  that includes information such as the number and type of read/write heads  138  the HSA  128  contains, the type of bearing assembly  130  or the type of actuator coil  144  supported by the HSA  128 . 
       FIG. 4  shows the disc drive  100  with a machine-readable head disc assembly serial number  180 . Also shown by  FIG. 4  is the mechanical interface between the bearing assembly  130  of the HSA  128  and the tolerance ring  176  removably attached to the head stack assembly post  172 . The bearing assembly  130  includes the beveled pick and place member  132 , and an inner race  182  separated by a bearing  184  from an outer race  186 . During installation of the HSA  128  into the basedeck assembly  168  the inner race  182  of the bearing assembly  130  forcefully engages the tolerance ring  176  as the HSA  128  is pressed onto the tolerance ring  176  through application of a compressive load on the HSA  128 . 
       FIG. 5  shows a tooling hole  188  provided in the actuator arms  134  to supporting the load arms  136 . Typically, the load arms  136  are affixed to the actuator arms  134  through a process referred to as swaging. The swaging process normally involves alignment of the load arms  136  with the actuator arms  134  and passage of a swage tool through the tooling hole  188 . A tooling hole  190  is provided to facilitate alignment and containment of an actuator body  192  during assembly of the HSA  128 , including the swaging process. 
     Actuator coil support arms  194  support the actuator coil  144  of the HSA  128  and serve as reference surfaces, along with tooling hole  190 , for alignment of the HSA  128  in preparation for installation of the HSA  128  into head disc assembly  162 . Additionally,  FIG. 5  shows actuator coil leads  196  electrically communicating with the read/write flex circuit  150 , the actuator coil leads  196  conduct current from the read/write flex circuit  150  to the actuator coil  144 , facilitating operation of the VCM  142 . 
     To initiate the process of installing the HSA  128  onto the tolerance ring  176 , an operator completes a series of inspection and preparation steps. The operator first checks the flex connections (not separately shown) and the bearing assembly  130  to assure the HSA  128  is intact. Next the operator manually removes a shipping constraint (not shown), used to protect the HSA  128  during shipment, and adjusts the head stack assembly installation comb  198  to complete the preparation and inspection steps. 
       FIG. 6  shows the relationship between the various members and components of the HSA  128 . The majority of mass of the HSA  128  is concentrated around the axis of rotation of the bearing assembly  130  and is made up by the actuator body  192  and the bearing assembly  130 . The actuator body  192  supports the actuator coil support arms  194 , the actuator arms  134  and bearing assembly  130 . The beveled pick and place member  132  is supported by the bearing assembly  130  and protrudes about the top plain of the actuator body  192 . The beveled pick and place member  132  provides a grip for handling the HSA  128  during installation of the HSA  128  into the basedeck assembly  168  of the HDA  162  of the disc drive  100 . 
       FIG. 7  shows a head stack assembly installation system  200  with a frame  202  supporting a head stack assembly installation tool  204  and a computer  206 . For a preferred embodiment, the computer  206  is shown adjacent the head stack assembly installation tool  204  and supported by the frame  202 . However, the head stack assembly installation tool  204  and the computer  206  need not be proximately located, one to the other. Electronic communication between the head stack assembly installation tool  204  and the computer  206  is sufficient to operate the head stack assembly installation tool  204  during installation of the HSA  128  into the HDA  162 . 
     The computer  206  is a host for an installation software program (not shown) that has installation software program steps. The computer  206  is used to calculate position and force data from position and force parameter measurements gathered by the head stack assembly installation tool  204  during the process of installing the actuator assembly  128  into the basedeck assembly  168  of the HDA  162 . The installation software program directs and controls process steps executed by the head stack assembly installation tool  204 , based on the position and force data calculated by the computer  206  from the position and force parameter measurements gathered by the head stack assembly installation tool  204 . 
     The head stack installation tool  204  has a main plate  208  that provides a nesting position  210 , an installation position  212  and a robotic assembly  214 . The nesting position  210  provides a tooling pin  216  that communicates with the tooling hole  190  of the HSA  128 ; a connector nest  218 , which cradles and aligns the flex connector body  154  of the HSA  128  with the actuator body  192  for installation of the HSA  128  into the HDA  162 ; and head stack assembly alignment pins  220  that interface with the actuator coil support arms  194  to maintain the HSA  128  in a predetermined position prior to installation of the HSA  128  into the basedeck assembly  168 . The installation position  212  aligns the basedeck assembly  168  of the HDA  162  for installation of the HSA  128  into the basedeck assembly  168 . Adjacent the installation position  212  is a lift and locate assembly  222  that lifts the basedeck assembly  168  from a conveyor (not shown) and locates the basedeck assembly  168  within the installation position  212 . Additionally, the main plate  208  supports a head stack assembly scanner head  224  adjacent the nesting position  210  to read the machine readable head stack assembly serial number  178 ; a head disc assembly scanner head  226  adjacent the installation position  212  to read the machine readable head disc assembly serial number  180 ; a head stack assembly present sensor  228  adjacent the head stack assembly alignment pins  220  to detect the presence of HSA  128  in the nesting position  210 ; and a head disc assembly present sensor  230  adjacent the installation position  212  to detect the presence of the basedeck assembly  168  within the installation position  212 . 
     The robotic assembly  214  has an end effector assembly  232  supported by a vertical slide assembly  234 , which in turn is supported by a horizontal slide assembly  236  that is directly supported by the main plate  208 . The position of the vertical slide assembly  234  during the operation of the head stack assembly installation system  200  is reported to the computer  206  by a vertical slide digital sensor  238  located adjacent the vertical slide  234 . The position of the horizontal slide assembly  236 , during the operation of the head stack assembly installation system  200 , is reported to the computer  206  by a horizontal slide digital sensor  240  positioned adjacent the horizontal slide  236 . The end effector assembly  232  uses the beveled pick and place member  132  of the HSA  128  to grip the HSA  128  for installation onto the tolerance ring  176 . The end effector assembly  232  also has a pair of opposing positionable flex connector grippers  242  configured to communicate with the flex connector body  154 . A pair of opposing positionable flex connector grippers  242  maintain alignment of the flex connector body  154  in relation to the actuator body  192  while the robotic assembly  214  is pressing the HSA  128  onto the tolerance ring  176  during the process of installing the HSA  128  into the basedeck assembly  168  of the HDA  162 . A pneumatic cylinder housing  244  supports the pair of opposing positionable flex connector grippers  242  as well as supporting a pneumatic cylinder (not shown) used to operate the pair of opposing positionable flex connector grippers  242 . 
     As shown in  FIG. 7 , a communication interface electronics assembly  246  is mounted internal to the computer to  206 . However, like the computer  206  itself, the communication interface electronics assembly  246  need not be proximately located to the computer  206 , but rather, electronic communication between the communication interface electronics assembly  246  and the computer  206  is sufficient to operate the head stack assembly installation tool  204  during installation of the HSA  128  into the HDA  162 . The communication interface electronics assembly  246  cooperates with a measurement assembly  247  that includes a radial displacement potentiometer  248 , a linear variable differential transformer  250  (LVDT), and a load cell  252 . The radial displacement potentiometer  248  is supported by the end effector assembly  232  and electronically communicates with the communication interface electronics assembly  246  during the process of installing the HSA  128  into the basedeck assembly  168 . The radial displacement potentiometer  248  measures position parameters of the gripping action of the end effector assembly  232  during installation process, and reports the measurements to the computer  206  through the communications interface electronics assembly  246 . The LVDT  250  is supported by the vertical slide assembly  234  and electronically communicates with the communication interface electronics assembly  246  during the installation process. The LVDT  250  measures parameters of vertical distance traveled by the vertical slide  234  relative to the head stack assembly post  174  and reports the measured parameters to the computer  206 . The load cell  252  is supported by the end effector assembly  232  and electronically communicates with the communication interface electronics assembly  246  during the HSA  128  to HDA  162  installation process. The load cell  252  measures parameters of mechanical resistance between the tolerance ring  176  and HSA  128 , while the HSA  128  is being pressed onto the tolerance ring  176  to install the HSA  128  into the HDA  162 . 
       FIG. 8  shows a gripper  254  of the end effector  232 . Included in the gripper  254  is a radially disposed positionable gripper sections  258  linked to operate in unison and attached to a gripper housing  260 . Each gripper section  258  supports a gripper finger  262  that is shaped to conform to the slope of the external surface of the beveled pick and place member  132 . Each of the radially disposed positionable gripper sections  258  is coupled to the potentiometer  248  by a potentiometer coupling arm  264 . 
     A push pad (also referred to as a “centering post”)  266  is attached to the gripper housing  260  and circumvented by the radially disposed positionable gripper sections  258 . The radially disposed positionable gripper sections  258  move toward the push pad  266  contacting beveled pick and place member  132  to align the HSA  128  to the end effector assembly  232 . Alignment of the HSA  128  to the end effector assembly  232  includes alignment of the top inner race  182  to the push pad  266 . During the installation process the gripper fingers  262  remain in contact with the beveled pick and place member  132  until contact is established between the HSA  128  and the head stack assembly post  174 . Upon measurement of initial contact between the HSA  128  and the HDA  162 , and reporting of that measured contact to the computer  206  by the load cell  252 , the radially disposed positionable gripper sections  258  disengage contact with the beveled pick and place member  132 . The push pad  266  remains in contact with the inner race of the bearing assembly  130  to transfer the compressive load delivered by the end effector assembly  232  to the HSA  128  during the process of pressing the HSA  128  onto the tolerance ring  176  of the HDA  162 . Retracting the radially disposed positionable gripper sections  958  front contact with the beveled pick and place member  132  during the process of pressing the HSA  128  into position reduces the chances of the bearing  184  being damaged during installation process. 
       FIG. 9  shows the interaction between the gripper fingers  262 , the push pad  266  and the beveled pick and place member  132 . The gripper fingers  262  provide a slope surface  268  that conforms to the slope of the outer surface of the beveled pick and place member  132  while the push pad  266  provides a shouldered outer diameter  270  that is inserted into the inner race of the pick and place member  132 . When activated to engage the HSA  128 , the radially disposed positionable gripper sections  258  contact the outer surface of the bevel pick and place member  132  and align the HSA  128  to the end effector assembly  232  by positioning the inner surface of the pick and place member  132  into contact with the outer diameter  270  of the push pad  266 . 
       FIG. 10  shows a central processing unit  272  (CPU) electronically communicating with recordable media  274 . The recordable media  274  holds an installation software program (not separately shown) that has installation software program steps to carry out the assembly herein described. The term electronically communicating or in electronic communication does not necessarily mean that the two devices engaging in the communication are physically connected. The term includes devices that are physically connected and devices that are electronically connected via networking links such as infrared communication, radio-frequency communication or through the internet via satellite communication. For example, the recordable media  274  may located in one country, for example the United States, and the CPU  272  could be located in a different country, for example Ireland. The two devices, the CPU  272  and the recordable media  274 , are each elements of the head stack assembly installation system  200 , dependent on each other for the functioning of the head stack assembly installation system  200 , but neither is in direct physical contact with the other. They are however, linked, one to the other, electronically as portions of the head stack assembly installation station  200 . FIG. also shows the central processing unit  272  in electronic communication with a volatile memory  276  (also referred to herewithin as random access memory or RAM), a head stack assembly serial number data base  278  and a head disc assembly serial number data base  280 . 
     The central processing unit  272  electronically communicates with the recordable media  274  to upload the installation software program into the RAM  276  prior to execution of the installation process. During the installation process the installation software operates out of the RAM  276 . In addition to containing an active version of the installation software program the RAM  276  also temporarily stores information communicated to the computer  206  from the communication interface electronics assembly  246 . The stored information includes a head stack present signal (not shown), detected by the head stack digital sensor  228 , a head disc present signal (not shown), detected by the head disc assembly present digital sensor  230 , a value (not shown) representing the head stack assembly serial number  178 , provided by the head stack assembly scanner head  224  and a value (not shown) presenting the head disc assembly serial number  180 , provided by the head disc assembly scanner head  226 . During operation of the head stack assembly installation system  200  additional data regarding position and force parameters encountered by the HSA  128  during the installation process as well as position data for the radially disposed positionable gripper sections  258 , the vertical slide assembly  234  and the horizontal slide assembly  236  are gathered and written to the RAM  276  on a real-time basis. The position of the horizontal slide assembly  236  is monitored and reported to the communication interface electronics  246  by the linear horizontal slide digital sensor  240 , the position of the vertical slide assembly  234  is monitored and reported to the communication interface electronics  246  by the linear vertical slide digital sensor  238 , while position data for the gripper sections  258  is continually monitored by the radial displacement potentiometer  248 . The position and force parameter measurements encountered by the HSA  128  while being pressed onto the tolerance ring  176  are made and supplied to the RAM  267  by the linear variable differential transformer  250  and the load cell  252  respectively. 
     Two additional elements of the head stack installation system  200  are shown by FIG.  10 . In electronic communication with the CPU  272  are the HSA serial number data base  278  and the HDA serial number data base  280 , the HSA serial number data base  278  containing the physical characteristics of each HSA  128  available for installation into each HDA  164 , while the HDA serial number data base  280  contains the physical characteristics of each HDA  164  available for receipt of the HSA  128 . Prior to joining each available HSA  128  with each available HDA  164 , the installation software program instructs the CPU  272  to read the serial number  178  of the HSA  128  from RAM  276 , query the HSA serial number data base  278  and retrieve the physical characteristics information contained within the HSA serial number data base  278  for the HSA  128  serial number read from the RAM  276 . The installation software program then instructs the CPU  272  to read the serial number  180  from RAM  276 , query the HDA serial number data base  280  and retrieve the physical characteristics information contained within the HDA serial number data base  280  for the HDA  164  serial number read from the RAM  276 . The software installation program then instructs the CPU  272  to compare the physical characteristics of the HDA  164  and the HSA  128  to one another, to ensure compatibility prior to proceeding with the installation of the HSA  128  into the HDA  164 . 
       FIG. 11  shows a main process decision flow  300  utilized by the installation software program to grip the HSA  128  in preparation for installation of the HSA  128  into the HDA  164  of the disc drive  100 . Once a start step  302 , of the installation software program steps is initialized, three decision steps follow. The first decision step, HDA in position  304 , verify the presence of the HDA  164  within the installation position  212  of the main plate  208 . The second decision step, HSA positioned in the nest  306 , verifies the presence of HSA  128  in the nesting position  212  of the main plate  208  and the third decision step, HSA serial number entered  308 , verifies the presence of the serial number  178  within the RAM  276 . 
     The main process decision flow  300  shows the installation software program instructs the robotic assembly  214  to grip the HSA  128  and proceed to predefined process steps install HSA decision flow  320  (of FIG.  12 ), provided responses of the three decision steps are affirmative along with an affirmative response from a decision step HSA and HDA compatible  310 . In addition to the specifically identified decision steps, the main process decision flow  300  shows the decision loops entered into by the installation software program if a non affirmative response is encountered from one of the specifically identified decision steps. The software installation program remains in the decision loop until the installation software program, from that decision loop, receives an affirmative response. 
       FIG. 12  shows the install HSA decision flow  320  of the installation software program utilized by the installation software program to engage the tolerance ring  176  with the HSA  128 . A start step  322  is the first installation software program step of the install HSA decision flow  320 . There are two primary decision steps involved in the install HSA decision flow  320 . The first, a HSA engaged post  324 , initiates step  326  upon successful engagement of the head stack assembly post  174  with the HSA  128 . Installation software program step  326  directs the actions of; releasing the radially disposed positionable gripper sections  258  from contact with the beveled pick and place member  132 , applying a compressive load on the HSA  128  with the robotic assembly  214 , and collecting force and distance parameters from the load cell  252  and the LVDT  250  respectively. Upon successful completion of the second decision step, slide stopped moving  328 , the installation software program initiates step  330 , an action of raising the vertical slide  234  to discontinue application of the compressive load on the HSA  128  and to proceed to an analyze force and position data—decision flow  340  (of FIG.  13 ), another predefined sequence of process steps of the installation software program. 
     The install HSA decision flow  320  shows the decision loops entered into by the installation software program should a non affirmative response be a result of one of the decision steps. The software installation program remains in a decision loop until the installation software program receives, from either of the decision steps  324  or  328 , an affirmative response. However, should the software installation program receive an affirmative response from a slide not moving  332  decision step, the installation software program directs the robotic assembly  214  to return the HSA  128  to the nest position  210  and displays a message on a display  334  for the operator to resolve the conflict and restart the process at main decision flow  300 . 
       FIG. 13  shows the analyze force and position data—decision flow  340  of the installation software program utilized by the installation software program to measure and analyze forces and positions encountered by the HSA  128  while engaging the tolerance ring  176 , as the robotic assembly presses the HSA  128  into the basedeck assembly  168 . A start step  342  is the first installation software program step of the analyze force and position data—decision flow  340 . The software installation program incorporates a force to distance ratio equation  344  to monitor installation of the HSA  128  onto the tolerance ring. During the installation process, process parameter measurements representing force and distance are gathered by the head stack installation tool  204  (of  FIG. 7 ) and electronically communicated to the computer  206  (of FIG.  7 ). The computer  206  manipulates the measurements by converting the measurements into values and substituting those values into equation  344 . The resulting calculated value, a slope, is compared to predetermined value dynamic slope V of decision step  348 . 
     Turning to  FIG. 14 , the predetermined value V is empirically derived for forces typically encountered by the HSA  128  while being pressed onto the tolerance ring  176  at specific increments of distance encountered by the HSA  128  while traveled along the tolerance ring  176  and found to have a maximum value of 600,  358 . The software also monitors mechanical resistance encounter during the process at time intervals of about every 50 milliseconds over the distance traveled by the HSA  128  while traveled along the tolerance ring  176 . Empirically gathered mechanical resistance data yielded a mechanical resistance as a function of position (f(p)) curve  360 . The mechanical resistance as a function of position curve  360  was arrived at through normal curve fitting techniques, relating the mechanical resistance encountered by the HSA  128  while being pressed onto the tolerance ring  176  to a point representing the distance covered by the head stack assembly at the point in time the mechanical resistance was encountered. A tolerance of about plus and minus 5% of the mechanical resistance encountered by the HSA  128  in any region of the tolerance ring  176  was elected and applied to the force curve resulting in a family of values representing dynamic force thresholds  362  against which actual measured process data can be dynamically compared. Forces encountered that fall outside the dynamic, either insufficient or excessive, trigger the head stack assembly installation station to abort the process. 
     Returning to  FIG. 13 , the equation (F=f(p) +/−x) and slop&lt;V of 348 is interpreted to mean; should the force (F) measured as encountered by the HSA  128  at a position (p) while being pressed onto the tolerance ring  176  fall outside the empirically derived force as a function of position (f(p)) curve, plus or minus (x), about 5% of the force empirically found to be encountered at position (p) along the tolerance ring  176  during the mating process, the process will be aborted. And, should the force (F) measured as encountered by the HSA  128  at a position (p) while being pressed onto the tolerance ring  176  fall within the empirically derived mechanical resistance as a function of position (f(p)) curve  360  (of FIG.  14 ), plus or minus (x), about 5% of the mechanical resistance empirically found to be encountered at position (p) along the tolerance ring  176  during the mating process, but the slop exceeds a predetermined value, empirically found to be about 600 the process will be aborted. Or, if the resultant calculated value falls outside the predetermined value V, the installation software program instructs the head stack installation tool  204  to abort the process, return the HSA  128  to the nest position  210  (of FIG.  7 ), and display a message on the display  334  reporting the status of the process and instructing the operator to remove the HSA  128  from the nest position  112 , place the next HSA  128  into the nest position  112  and restart the process at process step  300 . However, typically the software installation program remains in decision loops until the installation software program receives, from either of the installation software program steps  346  or  348 , an affirmative response. 
     Upon receipt of an affirmative response from either installation software program steps  346  or  348 , the installation software program proceeds to evaluate a course of action to be followed by the head stack installation tool  204 , based on decision steps represented by installation software program steps  350 ,  352 ,  354  and  356 . In each of the four installation software program steps  350 ,  352 ,  354  and  356  the installation software program checks process end points for specific values of force or distance encountered by the HSA  128  during the installation process. If the process end point values for the amount of force encountered by the HSA  128  is less than 11.34 kilograms, but greater than 0.363 kilograms, and the distance traveled by the HSA  128  after encountering the head stack assembly post  174  (of  FIG. 4 ) is greater than Z minus 0.0254 centimeters, but less than Z plus 0.0254 centimeters (where Z is typically between 1.203 centimeters and 3.094 centimeters), the head stack installation tool  204  has successfully installed the HSA  128  into the HDA  162  (of FIG.  1 ). If the process end point values for the amount of force encountered by the HSA  128  or the distance traveled by the HSA  128  after encountering the head stack assembly post  174  falls outside those parameters, the installation software program instructs the head stack installation tool  204  to abort the installation process attempt, directs the robotic assembly  214  to return the HSA  128  to the nest position  210  and displays a message on a display  334  for the operator to resolve the conflict and restart the process at main decision flow  300 . 
     The present invention provides a head stack assembly installation system (such as  200 ) with a head stack installation tool (such as  204 ) electronically communicating with a computer (such as  206 ) that has an active installation software program directing and controlling process steps enacted by head stack installation tool to install a head stack assembly (such as  128 ) into a head disc assembly of a disc drive (such as  100 ). The head stack installation tool provides a nesting position (such as  210 ) for aligning in staging head stack assembly prior to installation into the head disc assembly, an installation position (such as  212 ) for locating in securing the head disc assembly while awaiting installation of the head stack assembly, a robotic assembly (such as  214 ) the robotic assembly includes an end effector assembly (such as  232 ) supported by a vertical slide assembly (such as  234 ), which is in turn supported by a horizontal slide assembly (such as  236 ) that attaches to a main plate (such as  208 ). A measurement assembly made up of a communications interface electronics assembly (such as  246 ) electronically communicating with a radial displacement potentiometer (such as  248 ), a linear variable differential transformer (such as  250 ), and a load cell (such as  252 ). The robotic assembly picks and places the head stack assembly into the head disc and the measurement assembly collects and communicates process position and force parameters to the computer for use by the computer in calculating distance and force data. The active installation software program directs and controls enactment of process steps followed by the head stack installation tool by directing the computer to execute installation software program steps based on the position and force data calculated by the computer. 
     It is clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While a presently preferred embodiment of the invention has been described for purposes of the disclosure, it will be understood that numerous changes can be made which will readily suggest themselves to those skilled in the art. Such changes are encompassed within the spirit of the invention disclosed and as defined in the appended claims.