Abstract:
A disc slip tester for testing disc slip. The tester including a load actuator and load sensor for supplying and measuring test loads. A processor is coupled to the load sensor and is programmed to determine disc slip. Disc slip data is outputted for quality control and performance analysis. A method for analyzing disc slip including supplying a load to a disc in a disc stack and incrementally measuring load and disc displacement and plotting the relationship between load and displacement during test operations.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Provisional Application Ser. No. 60/126,400, filed Mar. 26, 1999, entitled “UNIVERSAL DISC SLIP TESTER”. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to disc drives. In particular, the present invention relations to a disc slip apparatus for a disc stack of a disc drive. 
     BACKGROUND OF THE INVENTION 
     A disc stack includes a plurality of discs clamped to a hub of a spindle motor. Discs are clamped to the hub with sufficient clamping force to limit slip or movement of the discs during operation and handling of the disc drive. Disc clamps are designed to provide sufficient clamping force to limit disc slip for normal operating loads and shock. 
     Measurement of disc slip force is useful for quality control on an assembly line as well as design analysis. Prior apparatus for simulating loads and measuring disc slip force were not well suited for testing a large sample lot for quality control and “pass-fail” analysis relative to product specifications or disc slip performance standards. Nor were prior test apparatus particularly adaptable for varied testing parameters for design performance evaluation nor establishing standards for clamp force and slip force. The present invention addresses these and other problems, and offers other advantages over the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a disc slip tester for measuring and analyzing disc slip. The tester includes a load actuator and load sensor for supplying and measuring test load. A processor is coupled to the load sensor and is programmed to determine disc slip. Disc slip data is outputted for quality control and performance analysis. The disc slip tester includes a user interface for controlling operating parameters for individual test control for design and performance analysis. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective-view of a disc drive. 
     FIG. 2 is a cross-sectional view of a disc stack. 
     FIG. 3 is schematic illustration of one embodiment of a disc slip tester. 
     FIG. 4 is schematic illustration of another embodiment of a disc slip tester. 
     FIG. 5 is a perspective illustration of an embodiment of a disc slip tester. 
     FIG. 6 is an alternate view of the tester apparatus of FIG.  5 . 
     FIG. 7 is a perspective illustration of an embodiment of a disc stand. 
     FIG. 8 is a perspective illustration of another embodiment of a disc stand. 
     FIG. 9 is a flow chart for operation of an embodiment of a disc slip tester. 
     FIG. 10 is a flow chart of an operation embodiment for measuring and determining disc slip parameters. 
     FIG. 11 is an embodiment of a screen display for displaying disc slip parameters. 
     FIG. 12 is flow chart of a manual operation embodiment for a disc slip tester. 
     FIG. 13 is an embodiment of a control-screen for manual operation of a disc slip tester. 
     FIG. 14 is a flow chart of an embodiment of a set-up mode for inputting operating parameters for a disc slip tester. 
     FIG. 15 is an embodiment of a control screen for inputting operating parameters for a disc slip tester. 
     FIG. 16 is a flow chart of an embodiment of a playback mode for a disc slip tester. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an embodiment of a magnetic disc drive  100  including a disc stack  102  rotationally supported relative to chassis  104  as illustrated by arrow  106 . Disc stack  102  is rotated via a spindle motor (not shown). Actuator block  108  supports heads  110  for reading and writing data to discs  112  in the disc stack  102 . Actuator block  108  moves as illustrated by arrow  114  by operation of voice coil motor  118  for positioning heads  110  for reading and write operations. Operating components of the drive are coupled to drive circuitry  120 . 
     FIG. 2 is a detailed cross sectional view of disc stack  102 . As shown, disc stack  102  includes a plurality of discs  112  separated by spacers  122 . Discs  112  and spacers  122  are assembled on hub  124  of a spindle motor. Discs  112  are stacked on flange  126  and are separated by spacers  122 . A clamp  128  secures discs  112  and spacers  122  on hub  124 . Typically clamp  128  is heated to an elevated temperature and is press fit or forced onto hub  124 . As the clamp cools, clamp  128  shrinks to provide a clamping force to secure the discs for operation. Alternatively hub  124  is screwed in place with required torque or clamping force. Sufficient clamping force is necessary to secure discs against movement or slip for read and write operations. Shock force to the disc drive during operation or transport can cause disc slip or movement degrading operating performance of the disc drive. Testing and analysis of disc slip can enhance drive design and quality control. The present invention relates to a disc slip apparatus for design and evaluation of and quality control for disc slip for a disc stack. 
     FIG. 3 is an illustration of a disc slip apparatus  130  including a disc stand  132  supported by a base  134  and a load actuator  136  supported relative to the disc stand  132  for supplying a test load as illustrated by arrow  138  to a disc  112  in a disc stack. Load actuator  136  is coupled to a controller  142  for operation. For operation, load is supplied to disc  112  via load. pin  144  coupled to load actuator  136 . A load sensor  146  is supported in the load path to measure applied load to the disc  112 . Output from load sensor  146  is coupled to processor  148  for determination of disc slip parameters as will be explained. 
     As shown in FIG. 3, controller  142  includes an automated operation mode  150 , a manual operation mode  152  and a set-up mode  154 . Test operations can be run in automated mode  150  or manual mode  152 . In automated mode, controller  142  operates load actuator  136  to advance load pin  144  at a set velocity to supply a test load to measure disc slip. Operating parameters for the automated mode  150  can be user inputted parameters defined in set up mode  154  or programmed default parameters. Set velocity can be a user set velocity ranging from 0.0001 inches/sec. to 0.01 inches/sec. In the automated mode  150 , test load is automatically supplied over a defined test force range for determination of disc slip parameters. In the manual mode, user manually controls operation and advances the push pin  144  in set increments via operation of position keys  156  illustrated diagrammatically to supply a test load. The manual mode provides desired user control for adjusting testing parameters for detailed design and engineering analysis. 
     As shown in FIG. 3, in the automated mode  150 , the processor  148  is programmed to automatically determine disc slip as illustrated by block  158 . Disc slip is determined based upon a drop in load force. Processor  148  is also programmed to compare the measured disc slip  158  to a nominal or specification slip force for “pass-fail” determination as illustrated by block  160 , which is outputted as illustrated by block  162 . If the tested slip force is equal or more than the nominal slip force, the disc stack meets specification standards and a “pass” notice is displayed. If the tested slip force is below the nominal slip force, then the disc stack does not meet specification standards and a “fail” notice is displayed. 
     In FIG. 4, disc slip apparatus  130 - 1  includes a displacement sensor  170  positioned below disc stand  132 . Thus, as shown in FIG. 4, load pin  144  contacts an upper surface of a supported disc and displacement sensor  170  contacts a lower opposed surface of test disc  112  to measure disc slip displacement. Since displacement is measured on the lower surface opposite from the load pin  144 , the displacement measurement from sensor  170  is a more accurate measurement of disc slip, since indentation of the disc is not included in the measured displacement. Output from load sensor  146  and displacement sensor  170  is downloaded to processor  148 . The processor  148  is programmed to determine disc slip  158 - 1  based upon a drop in load force when dy/dF (where y is the displacement and F is the Force) is negative due to a drop in force. The processor  148  determines disc slip displacement based upon output from displacement sensor  170  as illustrated by block  172 . 
     Data from load sensor  146  and displacement sensor  170  is plotted live in real time during test operations for disc slip analysis as illustrated by block  174 . Load and displacement date is saved to a data file for further use an analysis. The slip force vs. displacement plot can be rescaled or resized upon completion of a test cycle for display. 
     For real time plots, load sensor  146  is a compression load cell having a calibrated measurement scale between 0-10 volts to limit noise and displacement sensor  170  is a linear displacement transducer (LVDT) calibrated for a measurement scale between 0-10 volts to limit noise. In one embodiment, load cell is a Sensortec Compression load cell available from Sensortec of Columbus, Ohio. LVDT preferably includes a vacuum retract and is available from Solitron. Processor  148  is a CIODAS08 computer board available from Computer Board, Inc. of Mansfield, Mass., 02040, for rapid analog signal processing for real time graphic capabilities. Output from load sensor  146  is amplied by in-line amplifier provided by Sensodic. Displacement sensor  170  is amplified for processing via an amplifier available from Lusas Control Systems Products of Hampton, Va. 
     FIGS. 5-6 illustrate test apparatus with a load/unload slide  180 . Slide  180  movably supports a disc stand platform  182  relative to a base plate  184 . Disc stand  132  is coupled to disc stand platform  182  and movable therewith. A slide drive  186  is coupled to slide  180  to move slide  180  between a retracted home position and an operating or test position (shown) as illustrated by arrow  188 . Slide  180  is supported in the retracted home position out of alignment with load actuator  136  and displacement sensor  170  prior to and after testing operations for loading and unloading a disc stack. For operation, slide  180  is moved to the test position as illustrated by arrow  188  by slide drive  186  to position the disc stack in axial alignment with the load pin  144  and a sensor tip- 192  (as shown in FIG. 6) of displacement sensor  170 . 
     Load actuator  136  is supported above stand platform  182  by load platform  202  connected to base plate  184  via post  204 . Load actuator  136  includes a drive motor  206  which operates to move pin  144  from a retracted position (shown in FIG. 5) to test position  160  (shown in FIG.  6 ). For test operations, drive motor  206  moves pin  144  downwardly as illustrated by arrow  138  to supply a test load. Sensor tip  192  is movable between a retracted home position (not shown) and an extended test position by sensor actuator  208  to contact the disc edge for displacement measurements during test operations. In the embodiment shown, drive motor  206  is a linear stepper motor. Operation of drive motor  206 , slide drive  186 , and sensor actuator  208  is coordinated by controller  142   
     As illustrated in FIG. 5, displacement sensor  170  is an LVDT with vacuum retract to operate between the retracted home position and the extended test position. The LVDT is supported by bracket  210  coupled to base plate  184  and in the extended position tip  192  of sensor  170  extends through a platform opening  212  (shown in FIG. 5) to contact an edge surface of a supported disc for displacement measurement. In the retracted home position, tip  192  is retracted from the disc stack for positioning a disc in alignment with load pin  144  and sensor tip  192  for test operation. During operation, a cover  214  is closed as illustrated by arrow  216  for safety. 
     FIGS. 7-8 illustrate alternate embodiment disc stands  132 - 1 ,  132 - 2 . FIG. 7 illustrates a disc stand  132 - 1  for single disc support including base  220 , single disc slot  222 , first and second upright supports  224 ,  226 , and sensor channel  228 . Base  220  is coupleable to stand platform  182  by fastener holes  230 . A test disc is inserted into disc slot  222  and disc stack  102  is supported via spacers on opposed sides of the disc in disc slot  222 . Spacers contact and are supported on “V” shaped seat  232  formed by upright supports  224 ,  226 . Disc slot  222  is opened to sensor channel  228  so that when disc stand  132 - 1  is in the test position, LVDT contacts a lower edge of a supported disc for displacement measurement. For operation, load is supplied to the disc in slot  222  for disc slip measurement relative to spacers. 
     An alternate disc stand  132 - 2  for multidisc support is illustrated in FIG. 8 where similar numbers are used to identify similar parts. Disc stand  132 - 2  includes a disc stack slot  234  opened to sensor channel  228  for contacting a test disc with LVDT or displacement sensor  170  and spaced first and second upright supports  224 - 1 ,  226 - 1 . First upright support  224 - 1  supports a first end of the disc stack and second upright support  226 - 1  supports a second end. In particular, support  224 - 1  engages and supports clamp  128  of disc stack  102  and support  226 - 1  supports flange  126 . Selected discs  112  of the supported disc stack  102  are aligned relative to load pin  144  for test operations as will be explained. Load is supplied to discs in the disc stack for disc slip measurement relative to hub  124 . 
     For test operations for a multi-disc stand  132 - 2  controller  142  is programmed to move the slide  180  to a specified disk position to align a particular disc relative to push pin  144  for testing. For example, a system prompt can request a disk number to be tested and if in response to the prompt, Disc No.  2  is entered, controller  142  operates slide  180  to move the stand  132 - 2  to the align the selected Disc. No.  2  with the push pin  144 . Alternatively, the disc number to be tested can be programmed into the controller  142 . The elevation of tip  192  of LVDT is based upon the disc stack type and size. Prior to operation, a user identifies disc stack type and controller  142  is programmed to raise sensor tip  192  and lower push pin  144  to the proper test elevation (or test position) for commencement of disc slip measurement. 
     FIG. 9 illustrates an operating embodiment for automated operating mode  150 . Controller includes a computer executable operating program with programmed operating instructions and display. As illustrated in FIG. 9, the operating program is initialized as illustrated by block  240 . For initialization the default operating parameters (for example set velocity) are read from a data file. For test operations, slide drive  186  and drive motor  206  are reset to retracted home positions and an operator inserts a disc stack  102  into stand  132  in the retracted position out of alignment with load pin  144  and displacement sensor  170  as illustrated by block  242 . The program prompts a user to input a serial number or product identification code for the disc stack  102  loaded into the disc stand as illustrated by block  244 . 
     In the automated mode  150 , the apparatus of the present invention is adapted for testing disc stack types with different product specifications. As shown in block  246 , the system reads operating parameters for the disc stack type being tested for commencing disc slip test measurements. Program operations can be ended as illustrated by blocks  250 ,  252  or program control can be switched to manual operation mode  152  as illustrated by blocks  254 ,  256  or set up mode as illustrated by blocks  258 ,  260  as will be explained in detail. 
     For operation in the automated mode  150 , the LVDT is retracted, and the slide  180  moves disc stand  132  to the test position as illustrated by block  262 . The pin  144  is actuated (or lowered to) the test position proximate to the disc to be tested by motor  206  as illustrated by block  264 . The LVDT  170  is raised to contact the test disc as illustrated by block  266 . Thereafter, pin  144  is advanced at the set velocity to apply a test load to measure disc slip as illustrated by block  268 . Disc slip parameters are displayed as illustrated by block  270 . Load is supplied to the disc for a test operation until the test operation is complete as illustrated by block  272 . Upon completion of the test, pin  144  and sensor tip  192  are retracted and slide  180  is moved to the retracted home position to unload the tested disc stack as illustrated by blocks  274 . 
     During test operations, processor  148  calculates disc slip parameters (for example, disc slip force and disc slip displacement) as illustrated in FIG.  10 . Operation begins as illustrated by block  280  and the applied load is read from the load sensor as illustrated by block  282 . Once the pre-load force is supplied to the disc as illustrated by block  282 , the position of the LVDT is initialized to calculate net displacement based upon movement of the LVDT pin relative to the initial position of the LVDT pin as illustrated by block  286 . In the embodiment illustrated the pre-load force is 9 lbs. 
     For test operation, force and displacement are measured as illustrated by block  288 . Net displacement is calculated based upon measured displacement minus initial displacement, as illustrated by block  290 . Measured force and displacement values are displayed as illustrated by block  292  during test operation and plotted on a Force vs. Displacement graph as illustrated by block  294 . Measured force and displacement data is saved to a data file as illustrated by block  296 . In a preferred embodiment, processor  148  determines microslip force (preferably at 0.0003 inches slip) which is outputted to a display terminal or saved to a data file for performance analysis as illustrated by block  298 . 
     As previously explained, processor  148  is programmed to determine disc slip as illustrated by block  300 . The processor  148  is programmed to determine disc slip based upon a drop in load force when dy/dF (where y is the displacement and F is the Force) is negative due to a drop in force. The processor  148  totals the number of disc slips (or slip count) as illustrated by block  302 . Test operation and measurement continues as illustrated by line  304  until slip count reaches maximum slip count value  306  or the applied force equals the maximum load as illustrated by block  308  and test operation is ended as illustrated by blocks  310 ,  312 . The maximum slip count or maximum test load can be user defined or a default operation parameter. 
     After test operation is complete, test summary data is displayed. In the embodiment illustrated in FIG. 10, the test summary display includes the number of measurements as illustrated by block  313 . The force vs. displacement graph is rescaled so that the graph data fills the display window as illustrated by block  314 . The measured slip force is compared to the nominal or specification slip force as previously explained and a “pass/fail” notice is displayed as illustrated by block  316 . Summary test data is displayed as illustrated by block  318 . Measured data can be saved to a permanent data file as illustrated by block  320 . 
     FIG. 11 is an embodiment of a program display  322  including Force vs. Displacement graph  324 . Numerical values for force  326 , displacement  328 , slip force  330 , disc slip displacement  332 , nominal disc slip  334 , test velocity  336 , number of measurement cycles  338  and number of disc slips (or disc slip count)  340  are also displayed. A “pass/fail” notice  342  is also displayed as previously explained. 
     As previously explained, test operation can proceed in manual mode  152  as illustrated in FIGS. 12-13. Manual operation begins as illustrated by block  350 . An operating program displays an operating screen as illustrated by blocks  352 ,  354 ,  356 ,  358 . Operating screen displays the position of slide drive  186  and load drive  206 , as illustrated by block  354 . The operating program also displays load cell  146  and displacement sensor  170  output as illustrated by block  356 . Position keys  156  operate slide drive  186  to move slide between a retracted position and a test position in step increments as illustrated by blocks  360 ,  362  and move load motor  206  in step increments to apply a test load to a supported disc as illustrated by blocks  364 ,  366 . FIG. 13 illustrates an embodiment of a program display  370  for manual mode. As shown, program display  370  displays slide drive  186  and load drive  206  position  372 ,  374  and output  376 ,  378  from load cell  146  and displacement sensor  170 . 
     FIGS. 14-15 illustrate an embodiment of set up mode  154  for entering or changing test operation parameters. In the embodiment shown, user inputted operating parameters include motor gain  380  for manual operation of load motor  206 , test-position  382  for slide drive  186 , test position  384  for load motor  206  (to position pin  144  at the edge of the disc), toggle control  386  for displacement sensor between a retracted position and a test position, toggle data save in automated mode  388 , limit slip count  390 , toggle data save-in manual mode  392 , set velocity for push pin  144  in automated mode  394  and toggle for disc stand type  396  for slide  180  control. For automated operation, user exits  398  set up mode  150 . FIG. 15 illustrates an embodiment of a screen display  400  for inputting parameters  402  for set up mode  152 . 
     Test operations can be saved and previous test operations can be replayed by the program upon completion of a test operation without repeating the physical test cycle of the disc stack for later analysis. Test operations can be replayed in a playback mode  420  as illustrated in FIG.  16 . Test operation can be replayed in playback mode  420  by a remote computer without testing equipment. FIG. 16 illustrates an embodiment of playback mode  420 , where like numbers are used to identify like operation steps in FIGS. 9-10. To initiate playback operation  420 , user inputs a saved data file from a previous test operation as illustrated by blocks  422 ,  424 . The program reads the data file as illustrated by block  426  and displays the data as previously explained and illustrated by blocks  292 ,  298 . The program in playback mode  420  also performs disc slip calculations  300  and displays a force vs. displacement graph  294 . Upon completion of the playback of test data as illustrated by block  310 , the program displays test results as illustrated by blocks  313 ,  316 ,  318 . Playback operation continues as illustrated by line  428  until ended as illustrated by blocks  430 ,  432 . 
     Thus as described, the disc slip apparatus of the present invention includes a base  134  and a disc stand  132  supported by the base. A disc is supported by disc stand  132  and a load actuator  136  supplies a load to a disc supported by the disc stand. A load sensor  146  measures applies load and a computer  148  is coupled to the load sensor  146  and is programmed to determine disc slip. 
     It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the particular elements may vary depending on the particular application for a disc stack while maintaining substantially the same functionality without departing from the scope and spirit of the present invention. In addition, although the preferred embodiment described herein is directed to a magnetic disc drive system, it will be appreciated by those skilled in the art that the teachings of the present invention can be applied to other systems, for example, an optical disc drive system, without departing from the scope and spirit of the present invention.