Patent Publication Number: US-11037590-B2

Title: In-pivot hybrid stepper motor for ball screw cam elevator mechanism for reduced-head hard disk drive

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of and claims the benefit of priority to U.S. patent application Ser. No. 16/513,585, filed Jul. 16, 2019, which claims the benefit of priority to U.S. Provisional Patent Application No. 62/700,777, filed Jul. 19, 2018; to U.S. Provisional Patent Application No. 62/700,780, filed Jul. 19, 2018; to U.S. Provisional Patent Application No. 62/702,163, filed Jul. 23, 2018; to U.S. Provisional Patent Application No. 62/702,154, filed Jul. 23, 2018; and to U.S. Provisional Patent Application Ser. No. 62/747,623, filed Oct. 18, 2018; the entire content of all of which is incorporated by reference for all purposes as if fully set forth herein. 
    
    
     FIELD OF EMBODIMENTS 
     Embodiments of the invention may relate generally to a reduced-head hard disk drive having an actuator elevator mechanism and particularly to approaches to driving a low-profile ball screw cam actuator elevator mechanism. 
     BACKGROUND 
     There is an increasing need for archival storage. Tape is a traditional solution for data back-up, but is very slow to access data. Current archives are increasingly “active” archives, meaning some level of continuing random read data access is required. Traditional hard disk drives (HDDs) can be used but cost may be considered undesirably high. Other approaches considered may include HDDs with extra large diameter disks and HDDs having an extra tall form factor, with both requiring large capital investment due to unique components and assembly processes, low value proposition in the context of cost savings, and barriers to adoption in the marketplace due to uniquely large form factors, for example. 
     Any approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG. 1  is a plan view illustrating a hard disk drive, according to an embodiment; 
         FIG. 2A  is a perspective view illustrating an actuator subsystem in a reduced-head hard disk drive, according to an embodiment; 
         FIG. 2B  is an isolated perspective view illustrating the actuator subsystem of  FIG. 2A , according to an embodiment; 
         FIG. 2C  is an isolated plan view illustrating the actuator subsystem of  FIG. 2A , according to an embodiment; 
         FIG. 3  is a cross-sectional side view illustrating an actuator elevator assembly, according to an embodiment; 
         FIG. 4A  is an exploded view illustrating a low-profile ball screw cam assembly, according to an embodiment; 
         FIG. 4B  is a partial cross-sectional view illustrating a portion of the cam assembly of  FIG. 4A , according to an embodiment; 
         FIG. 4C  is a partial cross-sectional view illustrating a portion of an alternative cam assembly, according to an embodiment; 
         FIG. 5A  is a perspective view illustrating an actuator-elevator assembly, according to an embodiment; 
         FIG. 5B  is a plan view illustrating the actuator-elevator assembly of  FIG. 5A , according to an embodiment; 
         FIG. 5C  is a perspective view illustrating the actuator-elevator assembly of  FIG. 5A  in a reduced-head data storage device, according to an embodiment; 
         FIG. 6A  is an isolated perspective view illustrating an actuator position sensor and flexible cable assembly, according to an embodiment; 
         FIG. 6B  is a perspective view illustrating the assembly of  FIG. 6A  assembled with the actuator elevator assembly of  FIG. 3 , according to an embodiment; 
         FIG. 7A  is a cross-sectional side view illustrating an actuator elevator assembly with an in-pivot hybrid stepper motor, according to an embodiment; 
         FIG. 7B  is a cross-sectional top view illustrating the actuator elevator assembly and in-pivot hybrid stepper motor of  FIG. 7A , according to an embodiment; 
         FIG. 8A  is a top view illustrating a stator laminate for the in-pivot hybrid stepper motor of  FIG. 7A , according to an embodiment; 
         FIG. 8B  is a perspective view illustrating the stator laminate assembly for the in-pivot hybrid stepper motor of  FIG. 7A , according to an embodiment; and 
         FIG. 9  is a flow diagram illustrating a method for vertically translating a head-stack assembly (HSA) in a hard disk drive (HDD) to access multiple magnetic-recording disks, according to an embodiment. 
     
    
    
     DESCRIPTION 
     Approaches to a multi-disk hard disk drive having an actuator elevator mechanism are described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention described herein. It will be apparent, however, that the embodiments of the invention described herein may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention described herein. 
     Physical Description of an Illustrative Operating Context 
     Embodiments may be used in the context of a multi-disk, reduced read-write head, digital data storage device (DSD) such as a hard disk drive (HDD). Thus, in accordance with an embodiment, a plan view illustrating a conventional HDD  100  is shown in  FIG. 1  to aid in describing how a conventional HDD typically operates. 
       FIG. 1  illustrates the functional arrangement of components of the HDD  100  including a slider  110   b  that includes a magnetic read-write head  110   a . Collectively, slider  110   b  and head  110   a  may be referred to as a head slider. The HDD  100  includes at least one head gimbal assembly (HGA)  110  including the head slider, a lead suspension  110   c  attached to the head slider typically via a flexure, and a load beam  110   d  attached to the lead suspension  110   c . The HDD  100  also includes at least one recording medium  120  rotatably mounted on a spindle  124  and a drive motor (not visible) attached to the spindle  124  for rotating the medium  120 . The read-write head  110   a , which may also be referred to as a transducer, includes a write element and a read element for respectively writing and reading information stored on the medium  120  of the HDD  100 . The medium  120  or a plurality of disk media may be affixed to the spindle  124  with a disk clamp  128 . 
     The HDD  100  further includes an arm  132  attached to the HGA  110 , a carriage  134 , a voice-coil motor (VCM) that includes an armature  136  including a voice coil  140  attached to the carriage  134  and a stator  144  including a voice-coil magnet (not visible). The armature  136  of the VCM is attached to the carriage  134  and is configured to move the arm  132  and the HGA  110  to access portions of the medium  120 , all collectively mounted on a pivot shaft  148  with an interposed pivot bearing assembly  152 . In the case of an HDD having multiple disks, the carriage  134  may be referred to as an “E-block,” or comb, because the carriage is arranged to carry a ganged array of arms that gives it the appearance of a comb. 
     An assembly comprising a head gimbal assembly (e.g., HGA  110 ) including a flexure to which the head slider is coupled, an actuator arm (e.g., arm  132 ) and/or load beam to which the flexure is coupled, and an actuator (e.g., the VCM) to which the actuator arm is coupled, may be collectively referred to as a head stack assembly (HSA). An HSA may, however, include more or fewer components than those described. For example, an HSA may refer to an assembly that further includes electrical interconnection components. Generally, an HSA is the assembly configured to move the head slider to access portions of the medium  120  for read and write operations. 
     With further reference to  FIG. 1 , electrical signals (e.g., current to the voice coil  140  of the VCM) comprising a write signal to and a read signal from the head  110   a , are transmitted by a flexible cable assembly (FCA)  156  (or “flex cable”). Interconnection between the flex cable  156  and the head  110   a  may include an arm-electronics (AE) module  160 , which may have an on-board pre-amplifier for the read signal, as well as other read-channel and write-channel electronic components. The AE module  160  may be attached to the carriage  134  as shown. The flex cable  156  may be coupled to an electrical-connector block  164 , which provides electrical communication, in some configurations, through an electrical feed-through provided by an HDD housing  168 . The HDD housing  168  (or “enclosure base” or “baseplate” or simply “base”), in conjunction with an HDD cover, provides a semi-sealed (or hermetically sealed, in some configurations) protective enclosure for the information storage components of the HDD  100 . 
     Other electronic components, including a disk controller and servo electronics including a digital-signal processor (DSP), provide electrical signals to the drive motor, the voice coil  140  of the VCM and the head  110   a  of the HGA  110 . The electrical signal provided to the drive motor enables the drive motor to spin providing a torque to the spindle  124  which is in turn transmitted to the medium  120  that is affixed to the spindle  124 . As a result, the medium  120  spins in a direction  172 . The spinning medium  120  creates a cushion of air that acts as an air-bearing on which the air-bearing surface (ABS) of the slider  110   b  rides so that the slider  110   b  flies above the surface of the medium  120  without making contact with a thin magnetic-recording layer in which information is recorded. Similarly in an HDD in which a lighter-than-air gas is utilized, such as helium for a non-limiting example, the spinning medium  120  creates a cushion of gas that acts as a gas or fluid bearing on which the slider  110   b  rides. 
     The electrical signal provided to the voice coil  140  of the VCM enables the head  110   a  of the HGA  110  to access a track  176  on which information is recorded. Thus, the armature  136  of the VCM swings through an arc  180 , which enables the head  110   a  of the HGA  110  to access various tracks on the medium  120 . Information is stored on the medium  120  in a plurality of radially nested tracks arranged in sectors on the medium  120 , such as sector  184 . Correspondingly, each track is composed of a plurality of sectored track portions (or “track sector”) such as sectored track portion  188 . Each sectored track portion  188  may include recorded information, and a header containing error correction code information and a servo-burst-signal pattern, such as an ABCD-servo-burst-signal pattern, which is information that identifies the track  176 . In accessing the track  176 , the read element of the head  110   a  of the HGA  110  reads the servo-burst-signal pattern, which provides a position-error-signal (PES) to the servo electronics, which controls the electrical signal provided to the voice coil  140  of the VCM, thereby enabling the head  110   a  to follow the track  176 . Upon finding the track  176  and identifying a particular sectored track portion  188 , the head  110   a  either reads information from the track  176  or writes information to the track  176  depending on instructions received by the disk controller from an external agent, for example, a microprocessor of a computer system. 
     An HDD&#39;s electronic architecture comprises numerous electronic components for performing their respective functions for operation of an HDD, such as a hard disk controller (“HDC”), an interface controller, an arm electronics module, a data channel, a motor driver, a servo processor, buffer memory, etc. Two or more of such components may be combined on a single integrated circuit board referred to as a “system on a chip” (“SOC”). Several, if not all, of such electronic components are typically arranged on a printed circuit board that is coupled to the bottom side of an HDD, such as to HDD housing  168 . 
     References herein to a hard disk drive, such as HDD  100  illustrated and described in reference to  FIG. 1 , may encompass an information storage device that is at times referred to as a “hybrid drive”. A hybrid drive refers generally to a storage device having functionality of both a traditional HDD (see, e.g., HDD  100 ) combined with solid-state storage device (SSD) using non-volatile memory, such as flash or other solid-state (e.g., integrated circuits) memory, which is electrically erasable and programmable. As operation, management and control of the different types of storage media typically differ, the solid-state portion of a hybrid drive may include its own corresponding controller functionality, which may be integrated into a single controller along with the HDD functionality. A hybrid drive may be architected and configured to operate and to utilize the solid-state portion in a number of ways, such as, for non-limiting examples, by using the solid-state memory as cache memory, for storing frequently-accessed data, for storing I/O intensive data, and the like. Further, a hybrid drive may be architected and configured essentially as two storage devices in a single enclosure, i.e., a traditional HDD and an SSD, with either one or multiple interfaces for host connection. 
     Introduction 
     References herein to “an embodiment”, “one embodiment”, and the like, are intended to mean that the particular feature, structure, or characteristic being described is included in at least one embodiment of the invention. However, instance of such phrases do not necessarily all refer to the same embodiment, 
     The term “substantially” will be understood to describe a feature that is largely or nearly structured, configured, dimensioned, etc., but with which manufacturing tolerances and the like may in practice result in a situation in which the structure, configuration, dimension, etc. is not always or necessarily precisely as stated. For example, describing a structure as “substantially vertical” would assign that term its plain meaning, such that the sidewall is vertical for all practical purposes but may not be precisely at 90 degrees. 
     While terms such as “optimal”, “optimize”, “minimal”, “minimize”, and the like may not have certain values associated therewith, if such terms are used herein the intent is that one of ordinary skill in the art would understand such terms to include affecting a value, parameter, metric, and the like in a beneficial direction consistent with the totality of this disclosure. For example, describing a value of something as “minimal” does not require that the value actually be equal to some theoretical minimum (e.g., zero), but should be understood in a practical sense in that a corresponding goal would be to move the value in a beneficial direction toward a theoretical minimum. 
     Recall that there is an increasing need for cost effective “active” archival storage (also referred to as “cold storage”), preferably having a conventional form factor and utilizing many standard components. One approach involves a standard HDD form factor (e.g., a 3.5″ form factor) and largely common HDD architecture, with a non-zero finite number of n disks in one rotating disk stack, but containing fewer than 2n read-write heads, according to embodiments. Such a storage device may utilize an articulation mechanism that can move the heads to mate with the different disk surfaces (for a non-limiting example, only 2 heads but 5+ disks for an air drive or 8+ disks for a He drive), where the primary cost savings may come from eliminating the vast majority of the heads in the drive. 
     For a cold storage data storage device, a very thin structure (e.g., the read-write head stack assembly, or “HSA”) needs to be moved while keeping perpendicular to the axis on which it is moving. That structure also needs to maintain sufficient stiffness for structural and resonance control. There may be ball screws on the market that may comply with such requirements, but they are taller than the shaft they ride on and are typically considerably expensive. 
     With other possible approaches, there is a concern that when the actuator arms are unlocked during the time they need to be moved up and down to get to different disks, the interface between the arms and the cam rattles or is relatively loose. This could cause undesirable motion in the suspensions and heads as the arms are raised and lowered. There is also a large range of potential friction between the cam threads, arm threads, and lock nut threads that could over time cause extra wear and bad repeatability in the vertical positioning achieved. 
     Actuator Subsystem for Reduced-Head Hard Disk Drive 
       FIG. 2A  is a perspective view illustrating an actuator subsystem in a reduced-head hard disk drive (HDD),  FIG. 2B  is an isolated perspective view illustrating the actuator subsystem of  FIG. 2A , and  FIG. 2C  is an isolated plan view illustrating the actuator subsystem of  FIG. 2A , all according to embodiments.  FIGS. 2A-2C  collectively illustrate an actuator subsystem comprising a low profile ball screw cam assembly  202  (or “cam  202 ”), which transforms rotary motion into linear motion, with a stepper motor  204  (or “stepping motor”) disposed therein to form an actuator elevator subassembly, which is disposed within the actuator pivot and pivot bearing of the actuator subsystem (e.g., the “pivot cartridge”) and is configured to vertically translate at least one actuator arm  205  (see, e.g., arm  132  of  FIG. 1 ) along with a respective HGA  207  (see, e.g., HGA  110  of  FIG. 1 ). According to an embodiment, the actuator subsystem for a reduced-head HDD consists of two actuator arm  205  assemblies each with a corresponding HGA  207  (e.g., a modified HSA, in which the actuator arm assemblies translate vertically, or elevate, while the VCM coil  209  may be fixed in the vertical direction) housing a corresponding read-write head  207   a  (see, e.g., read-write head  110   a  of  FIG. 1 ). Generally, the term “reduced-head HDD” is used to refer to an HDD in which the number of read-write heads is less than the number of magnetic-recording disk media surfaces. 
     With respect to electrical signal transmission,  FIGS. 2A-2C  further illustrate a flexible cable assembly  208  (“FCA  208 ”), which is configured to comprise a dynamic vertical “loop”  208   a  (“FCA vertical loop  208   a ”) for vertical translation of the end(s) that are coupled to the actuator elevator subassembly and/or another portion of the actuator subsystem. This FCA vertical loop  208   a  is in addition to a typical dynamic horizontal loop for horizontal translation purposes for when the actuator to which one end is connected is rotating. The actuator subsystem further comprises at least one connector housing  210  for housing an electrical connector for transferring electrical signals (e.g., motor power, sensor signals, etc.) between the actuator elevator subassembly and a ramp elevator assembly (described in more detail elsewhere herein). 
     With respect to actuator arm locking,  FIGS. 2A-2C  further illustrate an arm lock subsystem  206 , coupled with or constituent to a coil support assembly  212 , configured to mechanically interact with an outer diameter crash stop  211  (“ODCS  211 ”) to lock and unlock the actuator elevator subassembly, as described in more detail elsewhere herein. 
     Actuator Elevator Assembly 
       FIG. 3  is a cross-sectional side view illustrating an actuator elevator assembly, according to an embodiment. The actuator elevator assembly  300  illustrated in  FIG. 3  is configured for use in an actuator subsystem as illustrated and described in reference to  FIGS. 2A-2C , i.e., configured to vertically translate at least one actuator arm  205  (shown here is a portion of the arm  205  that engages with the pivot; see, e.g.,  FIGS. 2A-2C, 4A-4C ) with a respective HGA  207  ( FIGS. 2B, 2C ) and read-write head  207   a  ( FIGS. 2B, 2C ). 
     Actuator elevator assembly  300  comprises the actuator elevator subassembly comprising the ball screw cam  202 , having the stepper motor  204  coupled to (e.g., with an outer sleeve adhered to the inner surface of the cam  202 ) and disposed therein and interposed between the cam  202  and a pivot shaft  310 , where the pivot shaft  310  bottom is shown positioned within an opening of a bottom support plate  308   b  and the pivot shaft  310  top is shown positioned approaching or within an opening of a top support plate  308   a . In a typical HDD configuration, the inner pivot shaft  310  is further coupled to an HDD enclosure base (see, e.g., housing  168  of  FIG. 1 ) via a screw or other fastener and to an HDD cover (not shown) via another screw or fastener, effectively sandwiching the pivot shaft  310  and the actuator elevator assembly  300  more broadly within the corresponding HDD. 
     Actuator elevator assembly  300  further comprises a first set or pair of HSA pivot bearings  302  (along with upper inner bearing housing  302   a  and lower inner bearing housing  302   b ) interposed between the pivot shaft  310  and the stepper motor  204  (e.g., one bearing assembly near the top and one bearing assembly near the bottom). HSA pivot bearings  302  function to support loads associated at least in part with the rotation of the actuator arms  205  ( FIGS. 2A-2C ), along with the stepper motor  204  and the cam  202  to which it is attached, about the stationary pivot shaft  310 , such as during actuator seek/read/write/load/unload operations. Actuator elevator assembly  300  further comprises a second set or pair of cam bearings  304  interposed between the stepper motor  204  and the cam  202  (e.g., one bearing assembly near the top and one bearing assembly near the bottom). Cam bearings  304  function to support loads associated at least in part with the rotation of the stepper motor  204  and the cam  202  about the stationary pivot shaft  310  (when the actuator elevator subassembly is decoupled from the HSA pivot inner bearing housing  302   a ,  302   b , as described in more detail elsewhere herein with respect to the operation of the arm lock subsystem  206 ), such as during actuator vertical translation operations. 
     Actuator elevator assembly  300  further comprises a third set of ball screw bearings comprising balls  202   c  and retainer  202   b  interposed between a cam screw  202   a  (see, e.g.,  FIGS. 4A-4C ) and the actuator arm  205 . This ball screw bearing assembly functions to support loads associated at least in part with the rotation of the stepper motor  204  and the cam  202  about the stationary pivot shaft  310  and the consequent actuator vertical translation operations. 
     Low Profile Ball Screw Cam 
     According to an embodiment, one approach to an actuator elevator mechanism for a cold storage HDD uses a multi-start threaded shaft (also referred to as a “multi-start ball screw”) with a ball in each start to create a plane perpendicular to the screw/cam. The balls are held equally spaced around the shaft by a bearing retainer. The balls are preloaded to the shaft at all times by compressing the two outer races. This platform is stable and does not rattle or function loosely, thus providing consistent structural integrity. 
       FIG. 4A  is an exploded view illustrating a low-profile ball screw cam assembly, and  FIG. 4B  is a partial cross-sectional view illustrating a portion of the cam assembly of  FIG. 4A , according to an embodiment. The illustrated ball screw cam assembly referred to as cam  202  comprises the hollow threaded shaft or screw  202   a , a bearing retainer  202   b  or retaining ring with a plurality of equally-spaced retained balls  202   c , a bearing half-race  202   d , an O-ring  202   e , and, optionally, a C-clip  202   f , according to an embodiment. Cam  202  is configured for use in the actuator elevator assembly  300  illustrated in  FIG. 3 , which is configured for use in the actuator subsystem illustrated and described in reference to FIGS.  2 A- 2 C, i.e., to vertically translate at least one actuator arm  205  with a respective HGA  207  and read-write head  207   a . However, use of a cam mechanism such as cam  202  in implementations outside of such an actuator subsystem (e.g., in a camera, or in other products requiring a miniature cam/translation mechanism) is contemplated, so the use scenarios for cam  202  are not limited to implementations only within such an actuator subsystem. 
     It is noteworthy that with cam  202 , according to an embodiment, the number of starts equals the number of balls, thereby providing a stable planar “platform” with a single bearing assembly and perpendicular to the axis/translation path. According to an embodiment, three balls  202   c  are held within the bearing retainer  202   b , thereby providing a 3-point planar bearing assembly while facilitating the low-profile aspect of the cam  202 . While three balls are needed to define or construct the plane, the number of balls  202   c  may vary from implementation to implementation. While greater than three balls  202   c  provides a more stable planar platform (e.g., more contact points about the shaft provides more actuator arm stiffness and stability), a greater number of balls  202   c  would also increase the thread pitch and lead corresponding to the screw thread (especially in view of a stepper motor driver), perhaps undesirably in some use scenarios. 
     With reference to  FIG. 4B , one can see that the tapered starts/threads of screw  202   a  function as upper and lower portions of an inner race of the bearing assembly of cam  202 . According to an embodiment, the outer race of the bearing assembly of cam  202  is a split-race, i.e., a 2-part race (whereby the two outer load surfaces are split among two parts), comprising a tapered inner surface  205   a  of the opening in arm  205  as a lower outer race surface, and a tapered lower surface of bearing half-race  202   d  as an upper outer race surface, together forming what may be referred to as a v-notch outer race. The bearing assembly is therefore preloaded radially at four points of contact via the inner and outer races, while the O-ring  202   e  (e.g., elastomeric) functions as a spring to provide a variable compression force applied to the bearing half-race  202   d , in conjunction with the C-clip  202   f  Alternatively to use of an elastomeric O-ring  202   e  (e.g., which can degrade and cause creep over time), according to an embodiment a wavy washer, functioning as a metallic spring, may be implemented to provide the compression force to the outer race. Hence, this arrangement functions to manage or compensate for the possibility of slight changes in the diameter of the inner race/threads at various locations along the length of the screw  202   a , such as those associated with part tolerances and manufacturing variability. 
     Furthermore, one could eliminate use of the C-clip  202   f  and reconfigure the outer race, as illustrated in  FIG. 4C .  FIG. 4C  is a partial cross-sectional view illustrating a portion of an alternative cam assembly, according to an embodiment. As with the embodiment illustrated in  FIG. 4B , the tapered starts/threads of screw  202   a  function as upper and lower portions of an inner race of the bearing assembly of this embodiment of ball screw cam, cam  203 . Here also the outer race of the bearing assembly of cam  203  is a split-race, or 2-part race, comprising a tapered half-race  202   d - 1  as a lower outer race surface and a tapered half-race  202   d - 2  as an upper outer race surface (bonded to an inner surface of the opening in arm  205  after preloading), together forming what may be referred to as a v-notch outer race. Here also the bearing assembly is therefore preloaded radially at four points of contact via the inner and outer races, while the O-ring  202   e  (or wavy washer) functions as a spring to provide a variable compression force applied to the bearing split-race comprising  202   d - 1 ,  201   d - 2 . 
     In-Pivot Claw-Pole Stepper Motor 
     In the context of a cold storage HDD that includes a rotary cam (e.g., cam  202 ) that is rotated with respect to the coil assembly (e.g., VCM coil  209 ), which would vertically move the actuator arms  205  up and down from disk to disk, a means to provide that rotation is needed. According to an embodiment and with reference to  FIGS. 2A-3 , a stepper motor  204  is assembled within the pivot (or, the pivot cartridge) of the actuator subsystem ( FIGS. 2A-2C ), which, in conjunction with the cam  202  ( FIGS. 4A-4B ), forms an actuator elevator assembly  300  ( FIG. 3 ). 
     So-called “claw-pole” designs contain an inner permanent magnet (PM) mounted on a rotary lead-screw shaft. In the context of a multi-disk HDD having an actuator elevator mechanism, the actuator subsystem design comprises a stationary shaft during the translation of the head stack assembly (HSA) to switch between magnetic recording disks. With this, a unique design of a claw-pole stepper motor is needed. The smaller magnet volume of a typical claw-pole motor where the stator circumscribes the PM requires a high number of turns (100 or more) with a very small copper wire (e.g. 0.05 millimeter (mm)) due to the physical limitations. Because electromagnetic torque, T e =kD 2 L, is proportional to the square of the diameter of the magnetic air gap and the stator stack length, it is advantageous to maximize the motor diameter. 
     However, winding with a smaller wire diameter is difficult due to its fragility and is more susceptible to the fluctuation of the winding tension that causes wider distribution of the winding resistance. A high number of turns with a small diameter wire results in a higher copper loss, P copper loss =i 2 R, and subsequent heat that may adversely affect the internal environment of the HDD in terms of the dynamic read-write head gap due to potential ball-bearing oil migration. Thus, in the confined space of the cold storage data storage device rotary cam, it is preferable to implement a compact stepper motor to rotate the cam in order to move the HSA bi-directionally in the vertical direction to access different disks in the stack. 
     A claw-pole motor such as stepper motor  204  comprises, for example, two uni-filar windings in injection-molded-plastic spools for bipolar control and four claw-pole stators made from cold-rolled steel sheet metal, electrical steel sheet metal, SMC (Soft Magnetic Composite), and the like, where use of electrical steel with various levels of silicon content or SMC reduces the eddy current loss. Furthermore, use of SMC can produce a complex geometry through powder metallurgy, unlike stamped and formed electrical steel sheet. Each stator contains p/2 teeth (p=number of poles) (e.g., 5 teeth per claw-pole stator according to an embodiment of stepper motor  204  having a 10-pole PM). The step angle of a stepper motor depends on the number of poles and stator teeth. In a design having 10 poles and 20 teeth, suitable for the intended purpose, the step angle/rotation is 18° or 20 steps/revolution in a full-step control, with both stator assemblies having a pair of claw-pole stators shifted relative to the other by one-half pole width, and where the step angle is inversely proportional to the number of stator teeth. Likewise, a design with 100 teeth yields 360°/100 or 3.6°/step angle, for example. In the case of 4 start-threaded rotary cam, this 3.6° step angle would provide 4 mm/100 steps or 0.04 mm step resolution rather than 4 mm/20 steps or 0.2 mm step resolution, thus providing a more precise and accurate servo control for positioning the HSA between the disks. Stated otherwise, a higher number of the claw (stator) teeth provides for a smaller step resolution. However, the outer diameter (OD) of the system (e.g., cam  202 ) limits the possible number of claw teeth. That is, with a given OD there is a practical limit to the number of teeth implemented because adding more teeth reduces their size and leads to manufacturing difficulty, magnetic saturation, and unstable tooth structures. For example, with an 18 mm OD, the system could be limited to 40 teeth and a step angle of 360°/40 or 9°. To get a higher step resolution, a micro-step may be used, where a typical bi-polar driver provides ½, ¼, ⅛, 1/16, and 1/32 micro-steps. 
     A corresponding rotor of stepper motor  204  comprises a PM (e.g. Nd—Fe—B) attached to the inner diameter of the cam  202  (see, e.g.,  FIG. 3 ), which, according to an embodiment, is constructed of ferritic stainless steel, and where the PM comprises 10 hetero-polar magnets. Hence, when the coils are energized the teeth become north and south poles, and mutual torque is established when the north PM poles align with the south claw poles and the south PM poles align with the north claw poles. Reversing the current polarity in the stator coils reverses the polarity of the electromagnetic claw poles and the resultant torque advances the rotor one full step. 
     Note that the number of coils and corresponding claw-pole stator pairs (i.e., phases), and the number of corresponding teeth on each claw-pole stator, may vary from implementation to implementation based on specific design goals (e.g., torque, phases and rotational degrees/step or steps/revolution) and, therefore, are not limited by the number described in the foregoing example. For example, with a 2-inch form-factor HDD, a four-coil design is feasible, which equates to 9° step angle, i.e., 360°/(number of teeth per claw)*(number of claws)=360°/(4*10)=9°/step. Alternatively, the step angle can be computed from the corresponding number of rotor poles and phases, i.e., 360°/(2 phases*20 rotor poles)=9°/step. 
     With reference back to  FIG. 3 , stepper motor  204  comprises a circular “phase A” coil  320   a  (with or without corresponding bobbin) enveloped by a pair of corresponding circular and mating claw-poles stators  321   a , a circular “phase B” coil  320   b  (with or without corresponding bobbin) enveloped by a pair of corresponding circular and mating claw-pole stators  321   b , disposed within a circular permanent magnet  322  (“PM  322 ”), all positioned around the stationary shaft  310 . Note that when the HSA moves (e.g., actuator arm  205  seeks), the cam  202  and the HSA pivot bearing  302  upper and lower housing  302   a ,  302   b  move synchronously and thus eliminate the differential reluctance or cogging torque that must be overcome in the rotary motion of the HSA. 
     According to an embodiment, it is noteworthy that in-pivot stepper motor  204  is configured with an outer rotor and inner stators. That is, in contrast with typical stepper motors, here the PM  322  is on the outside of the stepper motor  204  assembly and the claw-poles  321   a ,  321   b  and coils  320   a ,  320   b  are on the inside of the PM  322 . Likewise, while a conventional stepper motor typically rotates a central shaft, here the shaft  310  is fixed/stationary and the PM  322  rotor is bonded to the inner diameter of the cam shaft or screw  202   a  such that the stepper motor  204  rotates the outer cam  202  about the fixed inner shaft  310 . In that sense, this embodiment of stepper motor  204  is akin to a conventional stepper motor that is “turned inside-out”. 
     Method of Assembling an Actuator Elevator Subassembly 
     A method of assembling an actuator elevator subassembly, according to an embodiment, is as follows. The described method may be used to assemble an assembly comprising the cam  202  and a 10-pole stepper motor such as in-pivot stepper motor  204 , for example. However, as described elsewhere herein, the number of poles may vary from implementation to implementation and therefore, is not so limited. 
     First, insert the upper HSA pivot bearing  302  into the upper inner bearing housing  302   a  and bond (e.g., glue) the outer race of the upper HSA pivot bearing  302  to the upper inner bearing housing  302   a . Next, insert the upper cam bearing  304  around the inner bearing housing  302   a  and bond the inner race of the upper cam bearing  304  to the upper inner bearing housing  302   a . Once these bearings  302 ,  304  are assembled, the method moves on to the stepper motor  204 , as follows. 
     Insert around, orient, and bond a claw-pole stator  321   a  (a first half of a first pair) to an outer sleeve portion of the upper inner bearing housing  302   a . Next, insert within and bond a first coil  320   a  to the first claw-pole stator  321   a  of the first pair. Next, rotate a claw-pole stator  321   a  (the second half of the first pair) 36° relative to the first claw-pole stator  321   a  of the first pair and bond the second half of the claw-pole stator  321   a  to the outer sleeve portion of the upper inner bearing housing  302   a . Next, rotate a claw-pole stator  321   b  (a first half of a second pair) 18° relative to the second claw-pole stator  321   a  of the first pair and bond the first half of the claw-pole stator  321   b  of the second pair to the outer sleeve portion of the upper inner bearing housing  302   a . Next, insert around and bond a second coil  320   b  to the upper inner bearing housing  302   a . Next, rotate a claw-pole stator  321   b  (the second half of the second pair) 36° relative to the first claw-pole stator  321   b  of the second pair and bond the second half of the claw-pole stator  321   b  to the outer sleeve portion of the upper inner bearing housing  302   a . Insert a magnetized PM  322  (magnetized to produce 10 pole, or 5 pole-pairs) and bond the outer diameter surface of the PM  322  to in the inner diameter surface of the screw  202   a . Once the stepper motor is assembled as above, the method moves on to the lower bearings, as follows. 
     Insert the lower HSA pivot bearing  302  into the lower inner bearing housing  302   b  and bond the outer race of the lower HSA pivot bearing  302  to the lower inner bearing housing  302   b . Next, insert the lower cam bearing  304  around the lower inner bearing housing  302   b  and bond the inner race of the lower cam bearing  304  to the lower inner bearing housing  302   b . Next, bond the outer race of the lower cam bearing  304 , now in assembly form with the lower HSA pivot bearing  302  and the lower inner bearing housing  302   b , into the screw  202   a  subassembly. Next, apply bonding adhesive completely around the outer diameter periphery of the upper inner bearing housing  302   a , and apply bonding adhesive to the outer race of the upper cam bearing  304 , and insert this subassembly into the screw  202   a  subassembly. Next, apply an adhesive bead to the lower inner bearing housing  302   b  and insert that lower bearing assembly into the screw  202   a  subassembly and the upper bearing subassembly. Finally, heat-cure the thermoset adhesive by placement of the assembly in an oven, for example. 
     Locking/Unlocking Mechanism for Vertically Translatable Actuator Assembly 
       FIG. 5A  is a perspective view illustrating an actuator-elevator assembly,  FIG. 5B  is a plan view illustrating the actuator-elevator assembly of  FIG. 5A , and  FIG. 5C  is a perspective view illustrating the actuator-elevator assembly of  FIG. 5A  in a reduced-head data storage device, all according to an embodiment. According to an embodiment and with reference to  FIGS. 2A-4B , the locking/unlocking mechanism is constituent to the actuator subsystem ( FIGS. 2A-2C ) and which operates to vertically lock the actuator arm in place during seek/read/write operations, for example, and to unlock the actuator arm for vertical translation under the control of the cam  202  ( FIGS. 4A-4B ) and the stepper motor  204  ( FIGS. 2A-3 ) constituent to the actuator elevator assembly  300  ( FIG. 3 ). 
       FIGS. 5A-5C  collectively illustrate a locking/unlocking mechanism previously-introduced as arm lock subsystem  206  (hereinafter, “locking mechanism  206 ”), located in the general area labeled as B-B in  FIG. 5A . Locking mechanism  206  comprises a tab  206   d  extending from actuator arm  205  into a slot  206   e  within the structure of coil support assembly  212 , whereby the tab  206   d  is squeezed, held, locked within the slot  206   e  when in a cam locked position and is released, unlocked from the compression of the slot  206   e  and therefore free to travel in the vertical direction when in a cam unlocked position. According to an embodiment, the tab  206   d  and/or the clamping surfaces of the slot  206   e  are coated with a low-wear, high-coefficient of friction material to provide for strong clamping while inhibiting the undesirable particle generation within the drive. Locking mechanism  206  further comprises a spring mechanism  206   b  disposed within a slit  206   c  within the coil support assembly  212 , wherein the slit  206   c  intersects the slot  206   e . According to an embodiment, the spring mechanism  206   b  is a sheet-like piece of material that is relatively thin, and long in the vertical direction in comparison with its width positioned coincident within the slit  206   c . The spring mechanism  206   b  is rigid enough and configured/positioned within the slit  206   c  spanning across the slot  206   e  such that the force produced by the spring mechanism  206   b , in a locked or default position (i.e., slightly bent along a vertical axis to elicit a spring-like force), compresses each side of the slot  206   e  toward each other to squeeze and hold the tab  206   d  in a fixed position within the slot  206   e.    
     The cam is unlocked when the force associated with the spring mechanism  206   b  is overcome, thereby opening wider the slot  206   e , such that the tab  206   d  is released from the hold of the slot  206   e  and thereby enabled to travel vertically within the slot  206   e  so that the actuator arm  205  from which the tab  206   d  extends can be vertically translated by the actuator elevator assembly  300 . The force of spring mechanism  206   b  is overcome when a lock arm  206   a , which is part of or constituent to the coil support assembly  212 , and which is part of or extension of one side of the slot  206   e , mechanically interacts with the previously-introduced ODCS  211 , according to an embodiment. Alternatively, interaction with a mechanical element, feature, or structure other than a crash stop could be used to overcome the holding force of the spring mechanism  206   b . As such, when the actuator arm  205  is driven/rotated far enough past the outer diameter of the disk stack, the lock arm  206   a  “crashes” into the ODCS  211 , which causes the lock arm  206   a  to rotate (e.g., counter-clockwise) which then functions to open the gap corresponding to slot  206   e  (e.g., similarly to how a clothes-pin functions). 
     Flexible Cable Assembly with Vertical Loop 
       FIG. 6A  is an isolated perspective view illustrating an actuator position sensor and flexible cable assembly, and  FIG. 6B  is a perspective view illustrating the assembly of  FIG. 6A  assembled with the actuator elevator assembly of  FIG. 3 , both according to an embodiment. According to an embodiment and with reference to  FIGS. 2A-5C , the illustrated actuator position sensor and flexible cable assembly are constituent to the actuator subsystem ( FIGS. 2A-2C ), which provides for vertical translation of the actuator arm  205  under the control of the cam  202  ( FIGS. 4A-4B ) and the stepper motor  204  ( FIGS. 2A-3 ) constituent to the actuator elevator assembly  300  ( FIG. 3 ). 
     Conventional HDDs typically include a flexible cable assembly (FCA) such as FCA  156  of  FIG. 1 , which require some slack in the horizontal direction (e.g., XY direction) to allow for the distance between its connection points to vary in the horizontal direction in response to actuator rotation, as one connection point is with part of the actuator arm. However, an FCA cable for a rotating and vertically translating actuator connects to an actuator that not only moves in the XY plane for seeking data on the disk, but also moves in the Z direction to move among the disks in the multi-disk stack. Thus, a complete flex may be designed as either a one part solution or designed as two different parts combined together, with the use of a connector to carry electrical signals. With an actuator that is configured to move vertically, such as in the context of the actuator subsystem described in reference to of  FIGS. 2A-5C , according to an embodiment the FCA  208  (see, e.g.,  FIGS. 2A-2C , not shown here), which moves in the XY direction such as during seeking, further comprises or is electronically coupled or spliced with a dynamic vertical loop portion of FCA, referred to as FCA vertical loop  208   a , which moves effectively independently of the FCA  208  portion such as when the actuator is vertically translating. Functionally similar to the FCA  156 , the FCA vertical loop  208   a  provides some slack in the Z direction to allow for the distance between its connection points to vary in the vertical direction in response to actuator vertical translation, as one connection point is with part of the actuator arm  205 . Both the horizontal loop of FCA  208  and the FCA vertical loop  208   a  are configured to move independently of the other. 
     Note that the configuration and shape of the FCA vertical loop  208   a  may vary from implementation to implementation. According to an embodiment, a “U-loop” configuration is implemented for FCA vertical loop  208   a  (the loop generally resembles a letter “U” in various not-fully-extended states), as depicted in  FIGS. 6A-6B . However, other shaped vertical loops may be designed and implemented for use in this context, such as a C-loop shape that resembles the letter “C” when not fully extended and an S-loop shape that resembles the letter “S” when not fully extended, and the like. In the configuration depicted, the FCA vertical loop  208   a  is positioned near a preamp  606  and whereby the XY loop of FCA  208  electrically connects the FCA vertical loop  208   a  to a bracket and/or a connector housing  210  (see, e.g.,  FIGS. 2A-2C ). 
     Further illustrated in  FIGS. 6A-6B  is a pair of proximity or position sensors  602  coupled to the actuator arm  205  and configured to sense the Z position of the actuator arm  205  (e.g., vertical height) relative to a magnetic encoding strip and, ultimately, relative to the disk stack. According to an embodiment, one or more Hall effect sensors mounted in a quadrature configuration are implemented for the position sensor(s)  602 , which function in coordination with a closely-positioned magnetic encoder strip  604 , mounted on a stiffener  605 , to provide sine and cosine signals for sensing the directions and crossing of the waveforms. The stiffener  605  may further function for positioning of the FCA  208  and FCA vertical loop  208   a.    
     Generally, magnetic flux density in the air gap between the Hall sensors and the permanent magnet scale (i.e., magnetic encoding strip  604 ) should be set at an optimum gap range to provide adequate signal strength. A narrow gap causes signal saturation and a wide gap weakens the signal. In either case, detection of the zero-crossing points is uncertain. However, the quadrature configuration of the Hall sensors in conjunction with a 1 mm pole-pitch magnetic scale provides displacement and direction simultaneous by virtue of the leading and lagging nature of the waveforms in the upward and downward translations. For example, one Hall sensor signal leads when the stepper motor moves downward, and another Hall sensor signal leads when the stepper motor moves upward. A leading Hall sensor signal indicates the translational direction and the zero-crossing points of the sine-cosine waveforms provide the amount of the displacement. 
     In-Pivot Hybrid Stepper Motor 
     In the context of a cold storage HDD that includes a rotary cam (e.g., cam  202  of  FIGS. 2A-5C ) that is rotated with respect to an actuator coil assembly (e.g., VCM coil  209  of  FIGS. 2B, 2C, 5A, 5B ), which would vertically move a head-stack assembly (HSA) comprising one or more actuator arms (e.g., actuator arm  205  of  FIGS. 2A-2C, 4A-4C, 5A, 5B ) up and down from disk to disk, a means to provide that rotation is needed. According to an embodiment and with reference to  FIGS. 2A-2C , a hybrid stepper motor  704  is assembled within the pivot (or, the pivot cartridge) of the actuator subsystem ( FIGS. 2A-2C ), which, in conjunction with a cam such as the cam  202  ( FIGS. 4A-4B ), forms an actuator elevator assembly similar to actuator elevator assembly  300  ( FIG. 3 ), however with the hybrid stepper motor  704  substituted for a claw-pole stepper motor embodying stepper motor  204 . 
     In the context of a multi-disk HDD having an actuator elevator mechanism, the actuator subsystem design comprises a stationary shaft during the translation of the head stack assembly (HSA) to switch between magnetic recording disks. Furthermore, in the confined space of the cold storage data storage device rotary cam, it is preferable to implement a compact stepper motor to rotate the cam in order to move the HSA bi-directionally in the vertical direction to access different disks in the stack. With this, a unique design of a stepper motor is needed. 
     The holding torque of a stepper motor reduces precipitously in the micro-stepping mode. For a 40 full steps/rev claw-pole stepper motor to provide the required step resolution to place the read-write heads onto the disk surfaces, it must be driven in a 16 micro-step (μstep) mode. In this case, the holding torque may not always supply enough margin to overcome the variation in the load torque, frictional torque, and detent torque. Consequently, missteps happen often. However, the current manufacturing capability of the progressive dies can only mass-produce a 32 full steps/rev claw pole motor. In this case, the 16 μstep resolution becomes worse and the holding torque in μstep mode still has inadequate margin to overcome the variation of the frictional torque, load torque and the detent torque. Consequently, the μstep displacement profile may deviate from the desirable linearity. 
     A hybrid permanent magnet (PM)-variable reluctance (VR) stepper motor (or simply “hybrid stepper motor”) as described herein can overcome the foregoing issues and provide, for a non-limiting example, 200 full steps/rev for a 3.8 mm translation. Consequently, to meet or surpass the desired step resolution (for a non-limiting example, 6 μm/μstep), a 1.8°/full-step hybrid stepper motor would only need to be operated at 4 micro-steps to surpass the minimum vertical displacement of 0.006 mm/μstep, which enables a smoother motion since the available holding torque at the 4 th  micro-step provides significantly adequate torque margin to overcome the load torque, frictional torque, and detent torque. 
       FIG. 7A  is a cross-sectional side view illustrating an actuator elevator assembly with an in-pivot hybrid stepper motor, and  FIG. 7B  is a cross-sectional top view illustrating the actuator elevator assembly and in-pivot hybrid stepper motor of  FIG. 7A , both according to embodiments. Actuator elevator assembly  700  comprises a permanent magnet (PM)-variable reluctance (VR) hybrid stepper motor  704  (or simply “hybrid stepper motor  704 ”). A hybrid stepper motor refers to a combination of aspects of variable reluctance and permanent magnet type motors, wherein the rotor is axially magnetized, meaning one end is magnetized as a north pole and the other end a south pole, like a permanent magnet stepper motor, and the stator is electromagnetically energized like a variable reluctance stepper motor. Hybrid stepper motor  704  comprises an outer rotor assembly  706  (“rotor  706 ”) and an inner stator assembly  708  (“stator  708 ”) disposed within the rotor  706 , which cooperatively provide an axial magnetic flux path. Hybrid stepper motor  704  is depicted installed around a central pivot shaft  710 , e.g., functionally similar to the inner pivot shaft  310  of  FIG. 3 , and within a low profile ball screw cam assembly  702  (or “cam  702 ”) comprising a screw  702   a , e.g., functionally similar to the cam  202  of  FIGS. 2A-3  and, according to an embodiment, structurally similar to the cam  202  and associated sub-components of  FIGS. 4A-4C . Furthermore, cam  702  may be implemented in an assembly as depicted in  FIGS. 5A-5C . Thus, the cam  702  and the hybrid stepper motor  704  may be substituted for the cam  202  and the stepper motor  204  in each of the aspects and embodiments of cam  202  and stepper motor  204  as described throughout herein. For a non-limiting example, the hybrid stepper motor  704  may be implemented similarly to (e.g., substituted for functionally and operationally) the stepper motor  204  of  FIG. 3 . 
     As with the cam  202 , cam  702  transforms rotary motion into linear motion, with the stepper motor  704  (or “stepping motor”) disposed therein to form an actuator elevator subassembly, which is disposed within the actuator pivot and pivot bearing of the actuator subsystem (e.g., the “pivot cartridge”) and is configured to vertically translate at least one actuator arm  205  (see, e.g., arm  132  of  FIG. 1 ) along with a respective HGA  207  (see, e.g., HGA  110  of  FIG. 1 ). As such, the actuator elevator assembly  300  of  FIG. 3  may comprise the actuator elevator subassembly comprising the ball screw cam  702 , having the hybrid stepper motor  704  coupled to (e.g., with an outer sleeve adhered to the inner surface of the cam  702 ) and disposed therein and interposed between the cam  702  and the pivot shaft  710 . As with a typical HDD configuration, the pivot shaft  710  may be further coupled to an HDD enclosure base (see, e.g., housing  168  of  FIG. 1 ) via a threaded lower end (as depicted in  FIG. 7A ) or a screw or other fastener, and to an HDD cover via another screw or fastener, effectively sandwiching the pivot shaft  710  and the actuator elevator assembly  300  more broadly within the corresponding HDD. 
     According to an embodiment, the outer rotor  706  comprises a plurality of single-pole-axially-magnetized PM rings  712  (for a non-limiting example, 5 pieces×1.5 mm thick) stacked alternatively between stacks of laminations  714  (or “lam stacks  714 ”) (for a non-limiting example, 4 stacks of 24×0.2 mm electrical steel laminations). According to an embodiment, Nd—Fe—B (e.g. Daido NP- 12 L 50 kOes) permanent magnets may be utilized for the PM rings  712 . According to an embodiment found suitable for the intended purpose (see, e.g.,  FIGS. 8A, 8B ), the inner stator  708  is 23 mm long, with either 115×0.2 mm (electrical steel) laminations or 230×0.1 mm (electrical steel) laminations, which may vary from implementation to implementation based on design goals, constraints, etc. 
     According to an embodiment, it is noteworthy that in-pivot hybrid stepper motor  704  is configured with an outer rotor and inner stator. That is, in contrast with typical stepper motors, here the PMs  712  are positioned at the outside of the hybrid stepper motor  704  assembly and the stator  708  and corresponding coils  718  are positioned inside of the PMs  712 . Likewise, while a conventional stepper motor typically rotates a central shaft, here the shaft  710  is fixed/stationary and the rotor  706  is bonded to the inner diameter of the cam screw  702   a  such that the stepper motor  704  rotates the outer cam  702  about the fixed inner shaft  710 . In that sense, this embodiment of hybrid stepper motor  204  is akin to a conventional stepper motor that is “turned inside-out”. 
       FIG. 8A  is a top view illustrating a stator laminate for the in-pivot hybrid stepper motor of  FIG. 7A , and  FIG. 8B  is a perspective view illustrating the stator laminate assembly for the in-pivot hybrid stepper motor of  FIG. 7A , both according to embodiments. According to an embodiment, the stator  708  comprises eight (8) main poles  716  with each pole comprising five (5) teeth  717 , which is found to be suitable for the intended purpose. Hybrid stepper motor  704  further comprises a plurality of coils  718  (not shown here for purposes of clarity; see  FIG. 7B ) wound on each of the main poles  716  of the stator  708  to form phases A and B. For example, and with reference to  FIG. 7B , pole  1  is configured for phase A (South), pole  2  is configured for phase B (North), pole  3  is configured for phase A (North), pole  4  is configured for phase B (South), and so on. 
     According to an embodiment, each of the lam stacks  714  of the rotor  706  comprises fifty (50) inner diameter (ID) teeth  720  having a 7.2° tooth pitch as shown in  FIG. 7B . Two lam stacks  714  are assembled so that its teeth are shifted by one-half (½) tooth pitch angle, or 3.6°. Together, the teeth  720  of the two sets of the rotor  706  lam stacks  714  mutually interact with the teeth  717  on the stator  708  to step 1.8°/full step, based on the midpoint of a tooth  717  on the stator  708  to the midpoint on the nearest tooth  720  on the rotor  706  (i.e., 200 full steps/rev). When the phases A and B are energized, the stator  708  teeth  717  and the rotor  706  teeth  720  become north and south poles. Mutual torque is established due to the attraction between the north rotor poles and the south stator poles. Likewise, the south rotor poles attract the north stator poles. Reversing the current polarity in the stator  708  coils  718  reverses the polarity of the main poles  716  and the resultant torque advances the rotor  706  one full step. According to an embodiment and as depicted in  FIG. 7A , to increase torque two additional (beyond the typical two) sets of lam stacks  714  are implemented for a total of four (4) lam stacks  714  for the rotor  706 . 
     Actuator elevator assembly  700  further comprises a first set or pair of cam bearings  701  (e.g., one bearing assembly near the top and one bearing assembly near the bottom) to support loads associated at least in part with the rotation of the stepper motor  704  and the cam  702  about the stationary pivot shaft  710 , such as during actuator vertical translation operations. Actuator elevator assembly  700  further comprises a second set or pair of HSA pivot bearings  703  (e.g., one bearing assembly near the top and one bearing assembly near the bottom) to support loads associated at least in part with the rotation of the actuator arms  205  ( FIGS. 2A-2C ), along with the hybrid stepper motor  704  and the cam  702  to which it is attached, about the stationary pivot shaft  710 , such as during actuator seek, read, write, load, unload operations. That is, when the cam  702  is locked with the VCM-actuator, the entire assembly behaves like a traditional rotary VCMA (Voice-Coil-Motor Assembly) where the HSA rotates around the pivot shaft  710  via the pivot bearings  703 . 
     A hybrid stepper motor configured as described herein can provide 200 full steps/rev for a 3.8 mm translation. Thus, to meet or surpass a step resolution of 6 μm/μstep or 0.5265°/μstep (i.e., 360°/40 full steps/16 μsteps), the hybrid stepper motor would only need to be operated at 4 micro-step mode in order to achieve a 0.45°/μstep (i.e., 360°/200 full steps/4 μsteps) or 0.00475 mm/μstep (i.e., 3.8 mm/200 full steps/4 μsteps) (as opposed to that of the 40 full steps/rev of the claw-pole motor operated in 16 μsteps (i.e., 9°/16=0.5625°/μstep or 0.0059 mm/μstep)), which enables a smoother motion since the available holding torque at the 4th micro-step provides sufficient torque margin to overcome load torque, frictional torque, and detent torque. 
     Method for Translating a Head-Stack Assembly to Access Multiple Disks 
       FIG. 9  is a flow diagram illustrating a method for vertically translating a head-stack assembly (HSA) in a hard disk drive (HDD) to access multiple magnetic-recording disks, according to an embodiment.  FIG. 9  is described in further reference to components illustrated in  FIGS. 7A-8B  and, as discussed elsewhere herein, hybrid stepper motor  704  may be installed within and operate in conjunction with cam  702 , e.g., functionally similar to the cam  202  of  FIGS. 2A-3  and structurally similar to the cam  202  and associated sub-components of  FIGS. 4A-4C , and may be implemented in an assembly as depicted in  FIGS. 5A-5C . That is, the hybrid stepper motor  704  may be implemented similarly to (e.g., substituted for functionally and operationally) the stepper motor  204  of  FIG. 3  and the corresponding applications, implementations, and installations described in reference thereto. 
     At block  902 , a permanent magnet (PM)-variable reluctance (VR) hybrid stepper motor that is disposed within a ball screw cam assembly comprising a screw is driven, to rotate the screw about a coaxial (e.g., with the hybrid stepper motor) shaft. For example, hybrid stepper motor  704  disposed with cam  702  is driven, e.g., by applying electrical current to the hybrid stepper motor  704 , thereby rotating the screw  702   a  of the cam  702 . 
     At block  904 , a planar multi-ball bearing assembly, which is coupled with a hard disk drive (HDD) head-stack assembly (HSA) is allowed to translate (e.g., vertically) in response to rotation of the screw. For example, driving the rotation of the screw  702   a  via the hybrid stepper motor  704  drives translation of an HSA comprising one or more actuator arms (e.g., actuator arm  205  of  FIGS. 2A-2C, 4A-4C, 5A, 5B , coupled with the bearing balls  202   c  and retainer  202   b  of  FIGS. 4A-4C ) up and down from disk to disk along the length of screw  702   a . Thus, the read-write head(s) of the HSA is enabled to access and perform read operations and write operations on each respective magnetic recording disk (e.g., disk medium  120 ) of a multi-disk stack of a reduced-head HDD. 
     According to an embodiment, translation of the HSA includes translating (e.g., vertically) a multi-ball bearing assembly coupled with the HSA, by each of a particular number of balls of the bearing assembly riding in a corresponding respective start of the same particular number of starts of the multi-start screw. For example, translation of the HSA includes translating (e.g., vertically) actuator arms (e.g., similar to actuator arm  205  of  FIG. 4A ) coupled with the HSA, by each of a particular number of balls (e.g., similar to balls  202   c  of  FIGS. 4A-4C ) of the bearing assembly riding in a corresponding respective start or thread of the same particular number of starts of the multi-start screw  702   a  (e.g., similar to screw  202   a  of  FIGS. 4A-4C ). Thus, as described in reference to  FIGS. 4A-4C , with the number of starts equaling the number of balls a stable planar “platform” is provided with a single bearing assembly perpendicular to the axis/translation path. 
     At block  906 , while the bearing assembly is translating, the vertical position of the HSA is sensed. For example, as illustrated in  FIGS. 6A-6B  a pair of proximity or position sensors  602  may be coupled to the actuator arm  205  and configured to sense the Z position of the actuator arm  205  (e.g., vertical height) relative to a magnetic encoding strip and, ultimately, relative to the disk stack. 
     EXTENSIONS AND ALTERNATIVES 
     In the foregoing description, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Therefore, various modifications and changes may be made thereto without departing from the broader spirit and scope of the embodiments. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Any definitions expressly set forth herein for terms contained in such claims shall govern the meaning of such terms as used in the claims. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. 
     In addition, in this description certain process steps may be set forth in a particular order, and alphabetic and alphanumeric labels may be used to identify certain steps. Unless specifically stated in the description, embodiments are not necessarily limited to any particular order of carrying out such steps. In particular, the labels are used merely for convenient identification of steps, and are not intended to specify or require a particular order of carrying out such steps.