WO2000049616A1

WO2000049616A1 - Selecting optimum disc shroud clearance and recirculation filter placement in a disc drive

Info

Publication number: WO2000049616A1
Application number: PCT/US2000/004584
Authority: WO
Inventors: Srinivas Tadepalli; Roy L. Wood
Original assignee: Seagate Technology Llc
Priority date: 1999-02-22
Filing date: 2000-02-22
Publication date: 2000-08-24

Abstract

Method (200) for selecting an optimal disc drive mechanical configuration. A spindle motor (106) is configured to rotate a disc stack (107) comprising at least one disc (108). A plurality of shroud surfaces (154, 174) are provided which circumferentially extend in an adjacent, clearing relationship to an outermost perimeter of the disc stack so that a nominally uniform shroud clearance is maintained between the shroud surface and a portion of the outermost perimeter of the disc stack. Each of a plurality of disc drive configurations with different shroud clearances are provided (202, 203) and selected in turn (208, 218) for each configuration, current applied to the spindle motor to rotate the disc stack at a desired speed is measured (212). An optimum shroud clearance is thereafter selected (222) in relation to the shroud clearance that required a reduced amount of current to rotate the discs, as well as which provided reduced disc vibration. Recirculation filter location and clearance are also evaluated and optimized.

Description

SELECTING OPTIMUM DISC SHROUD CLEARANCE AND RECIRCULATION FILTER PLACEMENT IN A DISC DRIVE

Field of the Invention

This invention relates generally to the field of magnetic data storage devices, and more particularly, but not by way of limitation, to optimizing the mechanical configuration of a disc drive to improve operational performance.

Background

Disc drives are used as primary data storage devices in modern computer systems and networks. A typical disc drive comprises one or more rigid magnetic storage discs which are journaled about a rotary hub of a spindle motor to form a disc stack. An array of read/write transducing heads are supported adjacent the disc stack by an actuator to transfer data between tracks of the discs and a host computer in which the disc drive is mounted.

High performance disc drives of the present generation rotate the discs at speeds measured in the thousands of revolutions per minute. Increasing the disc rotational speed generally increases data transfer performance, since the latency time required for a given data sector on a track to rotate around and reach the corresponding head is reduced. However, increasing the rotational speed of the discs significantly increases the power consumption of a drive, as greater amounts of current are required by the spindle motor to achieve the desired higher rotational speed. Higher spindle motor currents also undesirably reduce the time that the drive can be operated in a portable application that relies on a battery pack power supply (such as a portable computer or hand-held portable device).

As the discs rotate, air currents are established from the frictional contact between the discs and the adjacent air. The heads are provided with aerodynamic features which interact with these air currents to enable the heads to fly in close proximity to the disc surfaces during operation. A portion of the air currents can also be diverted from the disc stack to the coil of a voice coil motor (VCM) used to control the actuator in order to convectively cool the coil during operation. Increasing the rotational speed of the discs accordingly results in greater volumetric of air flow within the drive. As air flow is increased, however, turbulence effects increasingly impact the operational performance of the drive. Disc drive manufacturers typically shroud the disc stack by providing curvilinear surfaces adjacent the outer perimeter of the disc stack to induce a nominally laminar flow, but openings in the shroud to accommodate the actuator, cooling channels for the NCM and a recirculation filter, as well as the actuator itself (which extends out over the discs to support the heads) create air flow disturbances that increase current consumption and induce undesirable disc vibration. Particularly, air turbulence can undesirably introduce axially directed nonrepeatable runout (ΝRR-O) vibrations in the heads and discs which can be amplified by a closed loop servo system used to control head position. As disc rotational speeds increase, compensation for these vibrations accounts for ever increasing amounts of the total track misregistration (TMR) budget, providing an upper limit on achievable track densities. Thus, disc drive manufacturers are challenged to provide disc drive configurations with higher disc rotational speeds in order to achieve increased levels of disc drive operational performance, and at the same time account for the undesired byproducts of higher rotational speeds which tend to degrade operational performance.

Summary of the Invention

The present invention provides a method for reducing spindle motor power consumption and axially directed vibrations by selecting an optimal disc drive mechanical configuration. In accordance with preferred embodiments, a disc drive has a spindle motor configured to rotate a disc stack comprising at least one disc. A plurality of shroud inserts are provided, with each shroud insert establishing a corresponding shroud surface which circumferentially extends in an adjacent, clearing relationship to an outermost perimeter of the disc stack so that a nominally uniform shroud clearance is maintained between the shroud surface and a portion of the outermost perimeter of the disc stack.

Each of the shroud inserts is installed in turn and current is applied to the spindle motor to rotate the disc stack at a desired speed. Current measurements are obtained and an optimum shroud clearance is thereafter selected in relation to the shroud clearance that requires minimum current to rotate the discs, as well as which provides an acceptably low level of axially directed disc vibration. Optimum locations and clearances of a recirculation filter are also identified.

These and various 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 top plan view of a disc drive with a first type of mechanical configuration optimized in accordance with preferred embodiments of the present invention.

FIG. 2 is a functional block diagram of the disc drive of FIG. 1. FIG. 3 is a top plan view of a disc drive with a second type of mechanical configuration optimized in accordance with preferred embodiments of the present invention. FIG. 4 is a flow chart for a MECHANICAL CONFIGURATION

OPTIMIZATION routine, illustrating steps carried out in accordance with preferred embodiments of the present invention.

FIG. 5 is a cross-sectional, elevational view of the disc drive of FIG. 1, showing the use of shroud inserts in accordance with preferred embodiments of the present invention.

FIG. 6 provides a graphical representation of spindle motor current measurements v. various shroud clearances obtained from the routine of FIG. 4 using the disc drive of FIG. 1.

FIG. 7 provides a graphical representation of spindle motor current measurements v. various shroud clearances obtained from the routine of FIG. 4 using the disc drive of FIG. 2.

FIG. 8 provides a top plan view of a portion of a disc drive having a third type of mechanical configuration similar to the configuration of FIG. 2, in accordance with preferred embodiments of the present invention. FIG. 9 provides a graphical representation of spindle motor current measurements v. various shroud clearances from the routine of FIG. 4 using the disc drive of FIG. 8.

FIG. 10 provides a top plan view of a portion of a disc drive having a fourth type of mechanical configuration similar to the configuration of FIG. 1, in accordance with preferred embodiments of the present invention.

FIG. 11 provides a graphical representation of spindle motor current measurements v. various shroud clearances from the routine of FIG. 4 using the disc drive of FIG. 10.

Detailed Description

It will be helpful to first provide a brief overview of various electrical and mechanical features of two disc drives having alternative mechanical configurations that can then be optimized in accordance with preferred embodiments of the present invention. Preferred implementation of the optimization methodology of the present invention will next be discussed, followed by various examples including optimization involving additional possible drive mechanical configurations.

Disc Drive Overview

Referring to FIG. 1 , shown therein is a top plan view of a disc drive 100 used to store computerized data. The disc drive 100 includes a base deck 102 to which various components of the disc drive 100 are mounted. A top cover 104 (shown in partial cutaway fashion) cooperates with the base deck 102 to form an internal, sealed environment for the disc drive. A spindle motor 106 rotates a disc stack 107 comprising a plurality of magnetic recording discs 108. The disc drive 100 has overall dimensions of about 14 centimeters, cm (5.5 inches, in) by about 10 cm (4 in) by about 2.5 cm (1 in), so as to have what is commonly referred to in the industry as a "three and one-half inch, low profile" form factor. The discs 108 each have a nominal diameter of about 8.4 cm (3.3 in). It will be noted that the foregoing dimensions are provided merely for purposes of illustration and the scope of the claimed invention is not limited to disc drives having these dimensions.

User data are written to and read from tracks (not designated) on the discs 108 through the use of an actuator assembly 110, which rotates about a bearing shaft assembly 112 adjacent the discs 108. The actuator assembly 110 includes a plurality of rigid actuator arms 114 which support flexible suspension assemblies 116 (flexures). A head 118 is supported at the end of each flexure 116, with the heads preferably having a magneto-resistive (MR) construction.

When the disc drive 100 is not in use, the heads 1 18 are parked on landing zones 120 and the actuator assembly 110 is secured using a magnetic latch assembly

122. A voice coil motor (VCM) 124 controls the position of the heads 118 through application of current to a coil 126 which interacts with a magnetic circuit which includes a permanent magnet 128. A flex assembly 130 facilitates electrical communication between the actuator assembly 110 and a disc drive printed circuit board (PCB) mounted to the underside of the base deck 102. The flex assembly 130 includes a preamplifier/driver circuit 132 that interfaces with the heads 118.

FIG. 2 provides a functional block diagram of the disc drive 100 of FIG. 1 in conjunction with a host computer 140. A drive processor 142 provides top level control of the disc drive 100. Data are transferred between the host computer 140 and the discs 108 using an interface (I/F) circuit 144, read/write (R/W) channel 146 and the preamp 132. Head positional control is achieved using a closed-loop servo circuit 148 that incorporates a programmable digital signal processor (DSP) 150. A spindle motor control circuit 152 incorporates driver circuitry to rotate the spindle motor 106 at a desired speed in response to commands from the drive processor 142. The host computer 140 is configured to house conventional data acquisition cards (not separately shown) for use as explained below.

Returning to FIG. 1 , the base deck 102 is configured with a number of curvilinear shroud surfaces (shrouds) 154 which extend adjacent portions of the outermost perimeters of the discs 108 to shroud, or enclose, air currents established by the rotation of the discs 108 in an attempt to create a nominally laminar (uniform) flow of the air currents. These air currents are generally denoted by vectors 156. The mechanical configuration of the disc drive 100 of FIG. 1 includes a recirculation filter 158 and associated support 160 disposed in a corner of the base deck 102, as shown. A portion of the air currents established by the rotation of the discs 108 is diverted (as indicated by vector 162) around the support 160 and through the recirculation filter 158 to remove airborne contaminants from the air inside the disc drive 100 before returning to the disc stack 107 (as indicated by vector 164). The mechanical configuration of the disc drive 100 further includes a generally triangularly shaped VCM support 166 which diverts another portion of the air currents (denoted by vector 168) to convectively cool the actuator coil 126. For additional details concerning the VCM support 166, see U.S. Patent No. 5,907,453 issued to Wood et al., assigned to the assignee of the present invention.

FIG. 3 provides a top plan view of a disc drive 170 having an alternative mechanical configuration to that presented in FIG. 1. It will be understood that the disc drive 170 of FIG. 3 has many of the same components of the disc drive 100 of

FIG. 1, including the same electrical configuration of FIG. 2, and so like reference numerals for similar components have been used in FIGS. 1-3.

The disc drive 170 of FIG. 3 has a base deck 172 that includes a continuously extending shroud surface 174. Unlike the disc drive 100 of FIG. 1, the recirculation filter 158 in FIG. 3 is disposed adjacent the VCM 124 so that a portion of the air currents (denoted by vector 176) are diverted from the disc stack 107, pass through the filter 158, and convectively cool the actuator coil 126. The filter 158 is supported by a support 178 which also shrouds the disc stack 107 along the length of the support. -1-

Mechanical Configuration Optimization

It is contemplated that the mechanical configurations of the disc drives 100, 170 of FIGS. 1, 3 generally represent alternative configurations available to a disc drive manufacturer desiring to introduce a new model of disc drive into the marketplace. The manner in which the manufacturer can advantageously select an appropriate configuration in accordance with the present invention will now be discussed beginning with FIG. 4, which shows a flow chart for a MECHANICAL CONFIGURATION OPTIMIZATION routine 200. The routine 200 generally operates to lead to the identification of optimum shroud clearances and recirculation filter placements and clearances. For purposes of the present discussion, at least one disc drive as set forth at 100 in FIG. 1 and at least one disc drive as set forth at 170 in FIG. 3 will be contemplated as being selected at step 202. It is contemplated that the routine 200 will be carried out during the design phase for the new model of disc drive. At step 202, one or more sample disc drives are provided for the various alternative available design configurations under consideration. Such drives will typically comprise engineering mock-ups or prior-generation drives having substantially the same mechanical configurations as being contemplated for the new model. A variety of shroud inserts are also provided during step 202, with the shroud inserts fabricated to provide different shroud clearances; that is, the inserts provide new shroud surfaces at selected distances from the perimeters of the discs 108. Exemplary shroud inserts 204 are shown in FIG. 5, which provides an elevational cross-sectional representation of the disc drive 100 of FIG. 1. The shroud inserts 204 abut the shroud surfaces 154 of the base deck 102 and are affixed in place to provide insert shroud surfaces 206. For reference, the disc stack 107 includes disc spacers 205 and a disc clamp 207. In alternative step 203, a plurality of nominally identical disc drives are provided with different recirculation filter placements and with base decks (similar to the base decks 102, 172) that have been machined to provide shroud surfaces at a variety of shroud clearances from the discs 108. For purposes of the remaining discussion, reference to "inserts" will be understood to also alternatively cover using different disc drives with corresponding shroud clearances.

The general shapes, widths and spacings of the components in a given disc drive will depend upon the particular requirements for the drive, and these respective factors are not necessarily represented to scale in the figures presented herein. For purposes of the present example, however, it is contemplated that the nominal distance between the original shroud surfaces 154, 174 and the disc stack 107 is about 3.0 millimeters, mm (0.120 in). It is common in the U.S. disc drive industry to express smaller dimensions in mils (thousandths of an inch), so for convenience, the nominal 3.0 mm shroud clearance will also be referred to herein as a clearance of 120 mils. In the present example, step 202 accordingly is contemplated as including the operation of providing shroud inserts with respective widths so that the following nominal shroud clearances can be selectively used with the respective configurations of FIGS. 1 and 3:

Shroud Clearance: Millimeters (mm - Mils (1/1000 in)

0.25 10

0.38 15

0.51 20

0.64 25

0.76 30

0.89 35

1.02 40

1.14 45

1.27 50

1.40 55

1.52 60

1.65 65

1.78 70

1.91 75

2.03 80

2.16 85

2.29 90

2.41 95

2.54 100 Table I. From a review of FIGS. 1 and 3, it will be noted that the inserts for the disc drive 170 in FIG. 3 can advantageously comprise a single, continuous insert that affixes to the continuous shroud surface 174, and a shorter insert for attachment to the recirculation filter support 178. The inserts for the disc drive 100 of FIG. 1 are preferably formed as a plurality of inserts that are individually affixed to each of the discrete shroud surfaces 154. One preferred approach to forming the inserts is through the use of suitable plastic sheets commercially available in various precisely determined thicknesses; another preferred approach is machining the inserts from a suitable material, such as aluminum. It will be noted that each of the inserts contemplated as being used in the present example are formed to fit within the existing distance between the respective shroud surfaces 154, 174 and the disc stacks 107. It is readily contemplated that in yet another alternative embodiment the base decks 102, 172 can be machined or otherwise modified to allow substantially thicker inserts to be precisely fabricated and installed to accomplish the desired range of shroud clearances. Of course, any number of different sized inserts can be used, depending upon the desired resolution.

Continuing with the routine of FIG. 4, once the various disc drive configurations are obtained, the flow passes to step 208 where the first configuration is selected for evaluation. For example, the first pass through the routine of FIG. 4 will use the disc drive configuration of FIG. 1 with a shroud clearance of 0.25 mm (10 mils).

At step 210, the disc drive is instructed by the host computer 140 to initiate rotation of the disc stack 107 up to operational speed (such as 10,200 revolutions per minute). As the discs 108 accelerate, the heads 118 will begin to be aerodynamically supported over the discs, allowing the actuator assembly 110 to move the heads out over the disc surfaces. Preferably, the actuator assembly 110 moves the heads 118 to various diameters of the discs 108 to evaluate the effects of disruption of the air currents 156 by the actuator arms 1 14. The host computer 140 proceeds at step 212 to obtain spindle current measurements from the currents applied to the spindle motor using a suitable current probe (denoted at 214 in FIG. 2) and associated data acquisition card or similar test equipment (not separately shown). The measurements are preferably accumulated and averaged over a suitable period of time, such as one-half hour, to ensure consistent measurements are obtained for each of the different inserts in turn. As desired, disc vibrations can also be measured during step 214 using a suitable measurement device, such as a laser doppler vibrometer (shown at 215 in FIG 2).

Decision step 216 inquires whether additional configurations should be evaluated; if so, the next configuration is selected at step 218 and the routine returns to step 210 to obtain a new set of measurements. In the present example, it is contemplated that each of the corresponding inserts having the shroud clearances of Table I are selected in turn for the disc drive 100 of FIG. 1, and then the corresponding inserts are selected in turn for the disc drive 170 of FIG. 3.

Once all of the desired measurements have been obtained, the routine passes to step 220 where the measurement data are assembled and analyzed, leading to selection of a final mechanical configuration in step 222 for the new drive design. The routine then ends at step 224.

Optimization Examples Various examples will now be presented to illustrate use of the routine of

FIG. 4. Referring now to FIGS. 6 and 7, shown therein are respective spindle motor current measurement curves 230 and 232, plotted against respective x-axes 234 indicative of shroud clearance (in mils) and y-axes 236 indicative of spindle motor current magnitude (in milliamps, mA). It will be recognized that FIGS. 6 and 7 represent the spindle motor current measurement data obtained at step 212 for each shroud insert/disc drive combination evaluated in the routine of FIG. 4.

The curve 230 of FIG. 6 shows various average spindle motor current magnitudes that range from about 264 mA to about 270 mA, using the mechanical configuration of the disc drive 100 of FIG. 1 (recirculation filter 158 disposed away from the VCM 124 and the use of the triangularly shaped VCM support 166). The minimum spindle motor current magnitude of about 264 mA occurs with a shroud clearance of about 1.52 mm (60 mils).

The curve 232 of FIG. 7 provides average spindle motor current magnitudes that range from about 252 mA to about 258 mA, using the mechanical configuration of the disc drive 170 of FIG. 3 (recirculation filter 158 disposed adjacent the VCM

124). The minimum spindle motor current magnitude of about 252 mA achieved with a shroud clearance of about 0.51 mm (20 mils). Achieving minimum spindle motor current is desirable for the reasons discussed above, but other factors should also be included in the identification of the optimum configuration, such as component procurement costs, labor costs, automated assembly requirements, etc.

It will be noted that the configuration of FIG. 3 allows use of conventional cylindrically shaped stand-off support spacers 238 instead of the triangularly shaped VCM support 166. Assuming that automated assembly requirements do not favor one configuration over the other, and that both configurations provide acceptable levels of axial nonrepeatable runout (NRRO) vibrations, in the present example the optimum configuration would be the configuration of FIG. 3 with the shroud surfaces 154 disposed about 0.51 mm (20 mils) from the disc stack 107.

To provide another example of the use of the routine of FIG. 4, reference is made to FIG. 8, which provides a top plan view of a portion of a disc drive (generally denoted at 240) having another mechanical configuration similar to that set forth by the disc drive 170 of FIG. 3. However, the disc drive 240 is configured to allow the recirculation filter 158 to be brought closer to the perimeter of the disc stack 107. In one preferred approach, a support 242 can be precisely advanced across the base deck (such as through the use of a magnet or adhesive) to place the recirculation filter 158 in a desired clearing relation to the disc stack 107.

FIG. 9 provides a general graphical representation of spindle motor current magnitude data obtained from the operation of the routine of FIG. 4, plotted against the same shroud clearance and current magnitude axes 234, 236 used in FIGS. 6 and 7. Curve 248 corresponds to a filter clearance (i.e., distance between the filter 158 and the perimeter of the disc stack 107) of about 4.83 mm (190 mils), and curve 250 corresponds to a filter clearance of about 1.52 mm (60 mils). The 4.83 mm (190 mils) of filter clearance provides a minimum run current of about 222 mA with a shroud clearance of 1.52 mm (60 mils), as shown at point 252. The 1.52 mm (60 mils) of filter clearance provides a minimum run current of about 210 mA when used with a shroud clearance of about 0.64 mm (25 mils).

Accordingly, depending on the factors mentioned above, the optimum mechanical configuration of FIG. 8 would likely be selected using a shroud clearance of about 0.64 mm (25 mils) and configuring the support 242 to support the recirculation filter 158 about 1.52 mm (60 mils) from the edge of the discs 108. FIG. 10 provides yet another mechanical configuration for a disc drive 250, substantially similar to the disc drive 100 of FIG. 1 except that the disc drive 250 does not use the triangularly shaped VCM support 166 (FIG. 1), instead opting for the conventional cylindrically shaped support 238. A rationale for evaluating the mechanical configuration of FIG. 10 might be to determine the efficacy of the VCM support 166 for a particular set of requirements (disc diameter, number of discs, rotational speed), as well as to determine optimum filter placement. Thus, in this example the following respective configurations are evaluated: FIG. 10 (recirculation filter 158 in the corner of the base deck, as shown in FIG. 1, and a cylindrical stand-off support 238), FIG. 8 (recirculation filter 158 placed adjacent the disc stack 107, and use of the cylindrical support 238), and FIG. 1 (triangularly shaped VCM support 166, and placement of the recirculation filter 158 in the corner of the base deck 102).

As before, the routine of FIG. 4 is performed for drives having the foregoing configurations, using a range of shroud clearances. The results are graphically illustrated in FIG. 11. Curve 256 represents the spindle motor current magnitude measurements for the configuration of FIG. 10, and provided a minimum run current (at point 258) of about 266 mA for a shroud clearance of 1.40 mm (55 mils).

Curve 260 represents the spindle motor current magnitude measurements for the configuration of FIG. 8, with a minimum run current (at point 262) of about 252 mA for a shroud clearance of 0.64 mm (25 mils). Curve 264 represents the spindle motor current magnitude measurements for the configuration of FIG. 1, with a minimum run current (at point 266) of about 250 mA for a shroud clearance of 0.64 mm (25 mils). It can be seen from a comparison of curve 264 to curve 256 that use of the VCM support spacer 166 in the configuration of FIG. 1 provides a significant performance improvement over that of the alternative configuration of FIG. 8 that uses the cylindrical support spacer 238. However, the configuration of FIG. 8 (curve 260, with minimum current of 252 mA) is not significantly different from the configuration of FIG. 1 (curve 264, minimum current of 250 mA). Thus, manufacturing factors might lead to the selection of the configuration of FIG. 8 as compared to the configuration of FIG. 1.

Yet another possible configuration alternative is to extend the shroud as shown by extension portion 270 in FIG. 1, which enables a larger percentage of the disc circumference to be shrouded, but may prevent automated head merging operations (increasing manufacturing costs). The cost/benefit tradeoffs of this configuration for various shroud clearances, filter placements and clearances, and axial NRRO can be evaluated as discussed above.

From the foregoing examples, it will now be apparent that the methodology embodied by the routine of FIG. 4 enables disc drive manufacturers to make educated decisions regarding the selection of the mechanical configuration of a new disc drive design. The use of shroud inserts readily enables the respective evaluation of various design alternatives to be directly determined in relation to spindle motor current consumption, with lower current levels indicating less drag, turbulence and flutter vibrations. The individual effects of various components, such as the placement and clearance of recirculation filters and elements with shrouding features such as the VCM support spacer 166, can be readily determined in relation to different shroud clearances.

In view of the foregoing, it will now be recognized that the present invention is directed to a method for reducing power consumption requirements of a spindle motor by selecting an optimal disc drive mechanical configuration. In accordance with preferred embodiments, a disc drive 100, 170, 240, 250 is provided (step 202) with a spindle motor 106 configured to rotate a disc stack 107 comprising at least one disc 108. A plurality of shroud inserts 204 are also provided (step 202), each shroud insert establishing a corresponding shroud surface 206 which circumferentially extends in an adjacent, clearing relationship to an outermost perimeter of the disc stack so that a nominally uniform shroud clearance is maintained between the shroud surface and a portion of the outermost perimeter of the disc stack. Each of the shroud inserts is installed in turn (steps 210, 218) and current is applied to the spindle motor to rotate the disc stack at a desired speed.

Current measurements are obtained (step 212) and an optimum shroud clearance is thereafter selected (step 222) in relation to the shroud clearance that required minimum current to rotate the discs. Optimum locations and clearances of a recirculation filter 158 are also identified. It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the invention disclosed and as defined in the appended claims.

Claims

Claims:

1. A method for selecting an optimum mechanical configuration of a disc drive, comprising steps of: (a) providing a disc drive having a spindle motor configured to rotate a disc stack comprising at least one disc about a disc axis;

(b) establishing a first shroud surface which circumferentially extends in an adjacent, clearing relationship to an outermost perimeter of the disc stack so that a nominally uniform, first shroud clearance is maintained between the shroud surface and at least a portion of the outermost perimeter of the disc stack;

(c) applying current to the spindle motor to rotate the disc stack at a desired rotational speed and obtaining a first current measurement indicative of magnitude of the applied current; (d) establishing a second shroud surface which circumferentially extends in an adjacent, clearing relationship to an outermost perimeter of the disc stack so that a nominally uniform, second shroud clearance is maintained between the shroud surface and at least a portion of the outermost perimeter of the disc stack, the second shroud clearance greater than the first shroud clearance;

(e) applying current to the spindle motor to rotate the disc stack at a desired rotational speed and obtaining a second current measurement indicative of magnitude of the applied current; and

(f) selecting a final shroud clearance for the disc drive in relation to the first and second current measurements.

2. The method of claim 1 , further comprising a step of (g) providing a plurality of shroud inserts affixable to the disc drive, wherein the first and second shroud surfaces of the establishing steps (b) and (d) are established using the shroud inserts.

3. The method of claim 1, further comprising steps of: (g) providing a recirculation filter configured to filter particulates from air currents established by the rotation of the disc stack at a first angular location with respect to the disc axis and performing steps (a) through (e) with the recirculation filter in the first angular location to obtain a first set of current measurements; (h) placing the recirculation filter at a second angular location with respect to the disc axis different from the first angular location in the disc drive and repeating steps (a) through (e) with the recirculation filter in the second angular location to obtain a second set of current measurements; and (i) selecting a final angular location for the recirculation filter in relation to the first and second sets of current measurements.

4. The method of claim 1, further comprising steps of:

(g) providing a recirculation filter configured to filter particulates from air currents established by the rotation of the disc stack at a first radial location with respect to the disc axis to form a first filter clearance between the recirculation filter and the disc stack so that steps (a) through (e) are performed using the first filter clearance to obtain a first set of current measurements; (h) placing the recirculation filter at a second radial location with respect to the disc axis to form a second filter clearance between the recirculation filter and the disc stack different from the first filter clearance and repeating steps (a) through (e) using the second filter clearance to obtain a second set of current measurements; and (i) selecting a final filter clearance for the recirculation filter in relation to the first and second sets of current measurements.

5. The method of claim 1, wherein the final shroud clearance of the selecting step (f) reduces the magnitude of current required to rotate the disc stack at the desired rotational speed as compared to at least a selected one of the first and second current measurements.

6. The method of claim 1, further comprising a step of:

(g) measuring axial disc vibration during the applying steps (b) and (e), and wherein the selecting step (f) further comprises selecting the final shroud clearance in relation to the measured axial disc vibration.