U.S. patent application number 17/573202 was filed with the patent office on 2022-06-30 for active spacing control for contactless tape recording.
The applicant listed for this patent is L2 DRIVE INC.. Invention is credited to Peter Goglia, Karim Kaddeche, John Wang.
Application Number | 20220208228 17/573202 |
Document ID | / |
Family ID | 1000006200086 |
Filed Date | 2022-06-30 |
United States Patent
Application |
20220208228 |
Kind Code |
A1 |
Kaddeche; Karim ; et
al. |
June 30, 2022 |
ACTIVE SPACING CONTROL FOR CONTACTLESS TAPE RECORDING
Abstract
The present invention relates to the field of tape drives, tape
transport, tape heads and tape head suspension. More particularly,
the present invention is related to magnetic tape data storage and
tape recorders that include components designed to minimize or
eliminate head-to-tape contact to reduce or eliminate wear and
contamination of tape drive heads. Methods and apparatus of the
present invention may dynamically control the head-to-media spacing
by moving locations of magnetic heads relative to a tape. Such
apparatus may include components designed to minimize magnetic
spacing. This may be accomplished using actuators that move the
magnetic heads, that move the tape, or that move both the magnetic
heads and the tape. This may include supporting a back surface of
the tape. Alternatively, or additionally, the movement of the tape
past the magnetic heads may be performed using mechanisms that
contact and drive the back surface of the tape.
Inventors: |
Kaddeche; Karim; (Irvine,
CA) ; Wang; John; (Yorba Linda, CA) ; Goglia;
Peter; (Alamo, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
L2 DRIVE INC. |
Yorba Linda |
CA |
US |
|
|
Family ID: |
1000006200086 |
Appl. No.: |
17/573202 |
Filed: |
January 11, 2022 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
17151021 |
Jan 15, 2021 |
11222663 |
|
|
17573202 |
|
|
|
|
63049085 |
Jul 7, 2020 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11B 5/4893 20130101;
G11B 15/62 20130101; G11B 2220/90 20130101 |
International
Class: |
G11B 15/62 20060101
G11B015/62; G11B 5/48 20060101 G11B005/48 |
Claims
1. An apparatus for controlling magnetic spacing, the apparatus
comprising: a set of magnetic elements; a sensor that senses data
associated with a head-to media-spacing (HMS) between the set of
magnetic elements and a front surface of a tape that stores data
magnetically; a tape guide that contacts a back surface of the
tape; an actuator that moves the set of magnetic elements to
control the HMS between the set of magnetic elements and the front
surface of the tape, wherein the HMS is controlled to correspond to
a desired distance by movement of the actuator; a controller that
controls the movement of the actuator to adjust the HMS to
correspond to the desired distance as the tape moves past the set
of magnetic elements.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation and claims the priority
benefit of U.S. patent application Ser. No. 17/151,021 filed Jan.
15, 2021, now U.S. Pat. No. 11,222,663, which claims the priority
benefit of provisional U. S. patent application 63/049,085 filed
Jul. 7, 2020, the disclosures of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
Field of Invention
[0002] The present disclosure generally relates recording computer
data on tape. More specifically, the present disclosure relates to
controlling the spacing between recording heads in a tape drive and
magnetic tape.
Description of the Related Art
[0003] Magnetic tape has been used for decades to store
information. Early on, magnetic tape was developed and used
primarily for storing audio information, such as voices of people
and music. Later, magnetic tape was adapted to record data for
computers. Over the years, tape recording has been continuously
improved to store more and more information per unit area of tape.
Many different forms of recording heads and recording media have
been developed over decades of development. Still today, tape is
the most cost-effective way to archive computer data for the
future. Companies are also compelled to store data for future by
law. Because of this, there will be a continued demand for magnetic
tape well into the foreseeable future to store data in an
archive.
[0004] Tape drive manufacturers are constantly challenged to
produce tape drives with larger storage capacity to meet market
demands. One way to accomplish this objective is to increase the
storage density by making refinements to the magnetic layer of the
tape. By increasing the storage density, the tape may have more
tracks for a given width and each track may have more bits per unit
length. Refinements in devices referred to as recording
transducers, heads, or magnetic elements have also contributed to
increases in the number of data bits that can be recorded per unit
length and in the number of data tracks per unit width of the
tape.
[0005] An important factor affecting the accuracy of the read/write
processes is magnetic spacing. The distance between the magnetic
layer on the tape where the information is recorded and the
transducer(s) that write data and read data is referred to as
magnetic spacing or head-to-media spacing (HMS). Magnetic spacing
is a critical parameter because the amplitude of a playback signal
decreases exponentially with increasing magnetic spacing. The
decrease in amplitude caused by increased magnetic spacing may be
referred to as Wallace spacing loss. Increased magnetic spacing
increases the width of the read back pulse which leads to reduced
data densities. The quality of recording or writing information
also varies with spacing and decreased magnetic spacing improves
the quality of the write operation. Decreased magnetic spacing
requires the head to be closer to a major surface area of the tape
during operation.
[0006] Magnetic spacing for a tape drive is currently set in the
factory and continually changes during long term operation. After a
sufficient period of time, a steady-state magnetic spacing
develops. Magnetic spacing is generally designed to be in the range
between 20-50 nanometers (nm) today, depending upon product
requirements and materials. Generally, smaller magnetic spacing is
capable of supporting higher data densities for a given read/write
accuracy, while greater magnetic spacing is capable of supporting
lower data densities for a given read/write accuracy. If a system
is designed to run at high data densities, but the magnetic spacing
is too large, an unacceptable drop in read/write accuracy will
occur. Increased magnetic spacing can also result in an increase in
error rates and in a decrease in signal to noise ratio.
[0007] Read and write heads today have features referred to as
"pole tips," and these pole tips commonly wear down when tape media
rubs against them. The wearing of these pole tips is caused by
friction or rubbing of tape media against a read or write head pole
tip. This is commonly referred to as pole tip recession (PTR). PTR
occurs over time and this wearing results in pole tips being worn
down and receding away from the tape. This process also causes
magnetic heads to wear down over time. As such, PTR increases the
magnetic spacing between the magnetic fields in the magnetic layer
of the tape and the transducer in the head. Each transducer in a
tape drive has a unique magnetic spacing. Furthermore, different
transducers wear at different rates. In addition, the location of a
transducer may result in different rates of pole tip recession.
[0008] Ever since the invention of magnetic recording tape, more
than 60 years ago, tape heads operated in full contact with a top
portion of a tape that includes a magnetic material. In fact, in
most tape transport systems, at least parts of the head exert some
pressure on the tape to keep it under a precise tension. Because of
this, head wear and pole tip recession are built into the design of
even modern tape recording systems.
[0009] More sophisticated tape head geometries create a difference
in air pressure between the two sides of the tape as it streams
over the heads. In certain instances, when a tape is streamed over
a surface, an air bearing forms, which prevents the tape from
coming into "close" contact or into a "friction" contact with the
head. Furthermore, modern magnetic heads also use various sorts of
and/or many layers of coatings that increase the spacing between
the recording surface of the tape and the pole tip of a magnetic
head. As a result, minimal tape-to-head distances cannot reach the
nanometer-range.
[0010] One way to help minimize the tape-to-head distance (i.e.
head-to-media spacing) relates to using sharp edges to create a low
pressure near a magnetic head. The phenomena that creates this low
pressure zone near the heads is referred to as skiving and the
sharp edges used to create this low pressure are referred to as
skiving (i.e., sharp) edges to scrape off (skive off) the air. As
mentioned above these shaped edges form a low-pressure region
directly after the skiving edge when a tape moves past that edge.
This low-pressure pulls the tape into intimate contact with the
tape head because of a higher air pressure on the opposite (back)
side of the tape.
[0011] An advantage of this type of skiving solution is that the
tape-head spacing is small and stable over a wide range of tape
speeds. A disadvantage of this skiving is that friction and wear
increase due to the direct contact between head and tape. To
prevent excessive friction, the tape can be intentionally made
rough (i.e. with sporadic bumps on the tape surface) so that only a
fraction of the tape surface is in actual contact with the tape
bearing surface of the head. Effectively, these bumps increase the
tape-to-head spacing.
[0012] Alternatively, to increase the linear recording density, one
can seek to reduce the tape-to-head spacing by using a smoother
tape. This, however, results in an increased friction and/or an
increase in the surface area of a head that rubs against the tape
surface. This friction or rubbing can degrade the recording surface
of the tape and can degrade magnetic heads, which in turn will
degrade read back performance of the tape and the tape drive. In
extreme cases, friction can even cause the tape drive motors to
stall and cause tape breakage, this may occur when surfaces of
magnetic heads stick to the surface of a tape--this sticking
phenomenon is commonly referred to as "stiction."
[0013] Therefore, a tape transport system and a tape head
suspension system that can minimize or eliminate contact between
the tape and the heads, while keeping them in operable proximity,
is highly desirable because they allow for closer head-to-media
spacing without degrading tape media or tape heads.
[0014] For all the reasons above, tape drives are conventionally
designed to accommodate pole tip recession and the resultant
degradation in performance. The need to design for pole tip
recession results in designing for lower data storage densities
than could be supported if the degradation could be prevented.
Conventionally, tape drives must be designed to provide an adequate
margin for differences in transducer wear rates and positions. This
necessitates designing tape drives that have lower data storage
capacity that theoretically possible. One reason for this is
because, tape read and write heads are often manufactured with
numerous coatings that increase head-to-media spacing. As such tape
drives could increase recording densities by reducing spacing
between the pole tips of the transducer and the tape. Greater
storage capacities could also be achieved if there was a reliable
and effective way to eliminate or greatly reduce pole tip wear.
[0015] These and other problems are addressed by Applicant's
invention as summarized below. Furthermore, to maximize an amount
of data that is stored on a tape and to increase reliability, what
are needed are ways to reduce the head-to-media spacing of tape
drives, while minimizing contact between the two.
SUMMARY OF THE CLAIMED INVENTION
[0016] The presently claimed invention relates to an apparatus,
methods, and non-transitory computer readable storage mediums that
control head-to-media spacing in tape drives in novel ways. In one
embodiment, an apparatus includes a set of magnetic elements (e.g.
one or more tape drive read or write heads), a sensor that senses
head-to-media spacing (HMS) data, a tape guide that contacts a back
surface of a tape, and an actuator that moves the set of magnetic
elements when the HMS associated with the magnetic elements is
controlled to a desired distance. This apparatus also includes a
controller that controls the movement of the actuator to adjust the
HMS to correspond to the desired distance as the tape moves past
the set of magnetic elements.
[0017] In another embodiment, a method of the present invention
receives sensor data from a sensor by a controller that monitors
head-to-media spacing (HMS) associated with a tape and a set of
magnetic elements. Here the controller may perform an evaluation of
the data received from the sensor, identify the HMS based on that
evaluation, identify that the HMS should be adjusted to correspond
to a desired distance, and control the movement of the actuator to
adjust the HMS to correspond to the desired distance as the tape
moves past the set of magnetic elements.
[0018] In yet another embodiment, a non-transitory computer
readable storage medium may implement a method of the presently
claimed invention. Here a processor may execute instructions of a
program to control magnetic spacing. This processor when executing
these instructions may receive sensor data from a sensor, perform
an evaluation of the data received from the sensor, identify the
HMS based on that evaluation, identify that the HMS should be
adjusted to correspond to a desired distance, and control the
movement of the actuator to adjust the HMS to correspond to the
desired distance as the tape moves past the set of magnetic
elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 illustrates a tape drive adapted to include magnetic
heads coupled to an actuator to control head-to-media spacing (HMS)
to a degree not previously possible.
[0020] FIG. 2 illustrates a close-up view of several of the
elements illustrated in FIG. 1.
[0021] FIG. 3 illustrates several elements that are similar to the
elements illustrated in FIG. 2
[0022] FIG. 4 illustrates a cross-sectional view of parts included
at or near the surfaces of a tape as data on that tape is read or
written.
[0023] FIG. 5 illustrates an embodiment of the present disclosure
that includes features that change relative pressures of air near a
tape surface.
[0024] FIG. 6 illustrates a series of elements that can include
magnetic reading elements, sensor elements, and writer
elements.
[0025] FIG. 7 illustrates a series of steps that may be performed
during a head-to media-spacing calibration process and when motions
of magnetic heads are controlled when data is read from or written
to a tape.
[0026] FIG. 8 illustrates electronic components that may be used to
communicate with or control the operations of a tape drive.
DETAILED DESCRIPTION
[0027] The present invention relates to the field of tape drives,
tape transport, tape heads and tape head suspension. More
particularly, the present invention is related to magnetic tape
data storage and tape recorders that include components designed to
minimize or eliminate head-to-tape contact to reduce or eliminate
wear and contamination of tape drive heads. Methods and apparatus
of the present invention may dynamically control the head-to-media
spacing by moving locations of magnetic heads relative to a tape.
Apparatus consistent with the present disclosure include components
designed to minimize magnetic spacing. This may be accomplished
using actuators that move the magnetic heads, that move the tape,
or that move both the magnetic heads and the tape. This may include
supporting a back surface of the tape. Alternatively, or
additionally, the movement of the tape past the magnetic heads may
be performed using mechanisms that contact and drive the back
surface of the tape. For example, the back side of the tape could
contact a roller that rotates, as this roller rotates it may force
movement of the tape in either a forward or a reverse direction as
data is read and/or written onto a top portion of the tape. By
reducing, or eliminating, contact between heads and tape, tape
roughness as well as head coating thicknesses can be reduced
allowing for a much lower head to media spacing and higher aerial
densities. In certain instances, particular coatings included on
surfaces of conventional heads may be eliminated based on
head/media contact being reduced or eliminated.
[0028] To write and read at the high areal densities used by modern
tape systems, the magnetic tape must be in close proximity to the
magnetic read/write elements on a tape read/write head. Research
efforts are spent on finding a viable solution to reduce the
distance between the tape's magnetic recording layer and the read
and write elements of the heads. This is commonly referred to as
magnetic spacing or head-to media spacing (HMS). Since reducing
this spacing allows for an increase in the linear recording density
(LD, usually measured in kilobits per inch), reduced HMS increases
recording densities. In fact, the LD of tape recording and reading
system is very sensitive to the magnetic spacing. In the related
field of hard disk drives, it is a well-known fact that the areal
density capability (ADC, measured in kilobits per square inch)
which is the product of the linear density by the track density
(measured in kilo-tracks per square inch) is inversely proportional
to the square of the HMS. So, for example halving the HMS can
potentially quadruple the ADC. Magnetic elements commonly used in
tape recording today include modern forms of magneto-resistive (MR)
heads, commonly referred to as tunneling magneto-resistive (TMR)
heads. Magnetic heads commonly also include inductive elements
capable of generating strong and rapidly changing magnetic fields.
MR heads of various forms including TMR heads include transducers
with enhanced sensitivity by magnetically biasing a read element in
a tape head. Any of the various inductive or magnetoresistive
elements included in a tape write or read heads means that any of
these heads are inherently "magnetic elements" because they are
sensitive to, respond to, receive, or generate electromagnetic
fields.
[0029] Current tape systems have a magnetic spacing of several tens
of nanometers. As the tape drive operates over long periods of
time, this magnetic spacing grows even larger due to deposits on
the heads and differential wear of the read and write elements with
respect to the rest of the tape bearing surface of the heads. Such
deposits may be comprised of media that is scraped off the tape
itself. These deposits may also include contaminates that enter the
tape drive that are then deposited on the heads by landing on
either tape or head surfaces that are then burnished into the
surface of the head by frictional forces associated with the tape
rubbing on the heads.
[0030] A large portion of the spacing in conventional tape drives
is comprised of coatings on the heads and the tape. These coatings
are necessary to protect the read and write elements of the heads
from abrasion by the tape. The art, and science, of magnetic tape
recording systems is in finding a combination of materials with the
right wear resistance properties that will result in a reasonable
head operating life. To further protect the read and write elements
of the heads, these are usually recessed away from the tape to
protect them against protruding defects in the tape. These recessed
elements further contribute to increasing the head-to-media spacing
(HMS).
[0031] Therefore, if a tape drive can eliminate or substantially
reduce contact between the tape and the heads, the coatings on the
heads, the reader and writer recess, and the tape roughness can all
be drastically reduced adding up to an important reduction in
contributions to the HMS. This reduction in coatings, minus the
necessary air gap, would result in a significant reduction is HMS
and a significant increase in LD and ADC. An increase in LD of 50%
or more as the result of lower spacing could be readily
achieved.
[0032] Another way that eliminating head to tape contact can
increase the areal recording density, is by allowing for higher
track densities. Track density refers to the number of parallel
data tracks that can be recorded on a single tape. Higher track
density naturally requires narrower tracks and impose strict track
following capability on the part of the head suspensions. In fact,
as the tape streams by the heads, there is considerable lateral
movement of the tape (movement along the width of the tape). This
lateral tape movement (LTM) is due to misalignments and vibrations
in the tape transport mechanism but is also due to the friction
between the heads and the tape. This friction directly results in
linear tape compression (compression along the tape length), due to
the discontinuity in tape tension at the point of contact between
the tape and the skiving edge of the head. This linear tape
compression results in compression waves that propagate at the
speed of sound along the tape and reflect off the tape rollers.
Resonances modes are thus created and result in high frequency
linear tape compression that couples with the lower frequency LTM
coming from the tape transport. This combination of frequencies
makes the job of track following very hard for the head suspensions
therefore requiring the tracks to be wider and limiting the track
density.
[0033] Eliminating the contact between the tape and the heads,
would eliminate the primary source of the high frequency linear
tape compression (namely the contact with the skiving edge) thus
reducing high frequency components of the LTM making the job of
track following much easier and in turn allowing for narrower
tracks, higher track densities and higher tape storage
capacity.
[0034] Many other advantages arise from limiting or eliminating
head-to-tape contact and friction. Head wear and head contamination
is a principal consequence of contact and friction between heads
and tape. Head contamination currently requires the regular use of
a "cleaning tape" to remove deposits on the heads. Head wear
eventually leads to head failures after only a few thousand hours
of operation. The tape itself is also affected by friction with the
heads resulting in a limited lifetime and occasional catastrophic
tape breakage events.
[0035] Historically, all these disadvantages of tape (head wear,
head cleaning and tape breakages) were considered endemic to the
technology and have become a "fact of life" in the practice of tape
data storage. The present invention of a contactless tape-recording
system aims to change all that.
[0036] As mentioned above, apparatus and methods consistent with
the present invention may apply forces to the back side of a tape
while magnetic heads are carefully positioned above the tape in a
way that mitigates or prevents contact. These back surfaces
typically do not include a magnetic coating and could include rough
surfaces, patterned surfaces, dimpled surfaces, or rollers or
mechanical assemblies that move the back surface of the tape.
Furthermore, surfaces on the back of the tape and surfaces on a
driving mechanism may engage in a manner that prevents slippage,
similar to how gear teeth engage hole or recessions in a chain.
[0037] Pressure gradients derived by a various means may also be
used to maintain relative positions between the back side of a tape
and a mechanical driving mechanism. Such pressure gradients may be
generated by a unique form of skiving design, by pressurized
gasses, or by a vacuum pressure. These pressure gradients could
push, pull, or both push and pull a tape into desired position.
Blunted edges or patterned surfaces could also aid in maintaining a
relative position of a tape to other features of a tape drive or
prevent the formation of a skiving action where it is not
desirable.
[0038] FIG. 1 illustrates a tape drive adapted to include magnetic
heads coupled to an actuator to control head-to-media spacing (HMS)
to a degree not previously possible. Magnetic heads of tape drive
100 of FIG. 1 may be controlled to mitigate or eliminate physical
contact between magnetic heads and magnetic tape 110. FIG. 1
includes magnetic tape 110, tape reels 120A/120B, tape guide
rollers (130A, 130B, 140A, & 140B), tape head roller 150, and
head carrier assembly 160. Tape reels 120A and 120B allow tape to
be rolled in layers around each of the tape reels 120A & 120B,
like a conventional tape drive. Each of these reels may be coupled
to a respective motor that allows tape 110 to be pulled or pushed
onto or off a respective tape reel. As in conventional tape drives,
data may be written as tape 110 moves in different directions
(right to left or left to right) past magnetic heads of the tape
drive. Tape reels 120A/120B may also help maintain a tension in
tape 110. Tape reels 120A/120B may maintain tape tension by being
motor driver, for example by a direct current (DC) brushless
motors. DC brushless motors are commonly used in various forms of
data storage devices, for example, tape drive spindles and media
stacks of disk drives both use DC brushless motors. One of ordinary
skill in the art would understand that DC brushless motors include
coils of wire in close proximity to magnets that are coupled to a
spindle that rotates. The spindle is forced to rotate based on
various different coils of wire being electrically energized in a
series of pulses that generate magnetic fields that in turn
interact with magnetic fields of the rotor magnets. Here the
interaction of magnetic fields (those generated by these pulses of
electricity and those native to the rotor permanent magnets) force
the spindle to rotate. DC brushless motors use magnetic fields to
create motion without requiring any physical contact between the
stator wires and the magnets, because of this, DC brushless motors
do not tend to generate particles from the motions they create,
unlike DC brushed motors that transfer electricity through brushes
as those brushes rub on a surface. While stepper motors are another
form of motors that potentially could be used in tape drives to
move the magnetic tape, DC brushless motors may be preferred
because DC brushless motors tend to rotate more smoothly, without
the cogging associated with stepper motors.
[0039] Tape rollers 130A, 130B, 140A, & 140B help guide tape
110 as it moves, and these tape rollers may also help maintain
tension of tape 110. Tape head roller 150 may also act to guide
tape 110 and may also help move tape 110 (from the right to the
left or left to right direction of FIG. 1) by applying a rotational
force to a backside of tape 110 as a tension of the tape is
maintained. Surfaces on the backside of tape 110 or on an edge
surface of head roller 150 may be patterned or include rough
surfaces the help allow tape head roller 150 to move tape 110. Tape
head roller 150 may be driven by any motor known in the art. For
example, a motor coupled to tape head roller 150 may be a DC
brushless motor or a stepper motor. Relative positioning of tape
head roller 150, tape rollers 140A & 140B may be used to
control a head wrap angle of tape 110 around tape head roller 150.
This may help optimize an amount of physical contact between tape
110 and tape head roller 150. Relative positioning of tape rollers
130A/130B, 140A/140B, and tape reels 120A/120B may help optimize or
control an amount of tension of tape 110. Any of the tape rollers
130A, 130B, 140A, or 140B may include active or passive tensioning
mechanisms, where tape tension is controlled by forces applied to
tape 110. Exemplary wrap angles used include, yet are not limited
to angles that approach 90 degrees. Generally, tape rollers 130A,
130B, 140A, & 140B may freely rotate or allow tape 110 to move
with little to no frictional forces.
[0040] While tape head roller 150 may be coupled to a motor that
may act as a primary driver that moves tape 110, roller 150 may
alternatively not be directly coupled to a motor. When roller 150
is not directly coupled to a motor, motors coupled to tape reels
120A/120B may act to move tape 110 as in conventional tape drives.
In such an instance, tape head roller may freely rotate or allow
tape 110 to move with little to no frictional forces.
[0041] While not illustrated in FIG. 1, tape head roller 150 may be
coupled to one or more actuators (active or passive) that allow
roller 150 to move toward or away (in an up and down direction of
FIG. 1) from magnetic heads of tape drive 100. An actuator that
moves tape head roller 150 may provide a relatively larger or gross
motion that allows a new tape to be fed into tape drive 100. This
relatively larger motion may include a rotational movement or a
liner movement that increased a gap between tape head roller 150
and magnetic head(s) above tape 110 of FIG. 1. Actuators or
actuating systems that move roller 150 may include one actuator
that provides the relatively larger (gross) motion as compared to a
second actuator that may allow roller 150 to be moved by a
relatively smaller (fine) motion. Exemplary larger motions may be
on the order of several millimeters ( 1/10 inch or so) or a
centimeter (1/2 inch or so), where exemplary smaller motions may be
less than a nanometer, several nanometers, to hundreds of
nanometers or so.
[0042] In certain instances, tape head roller 150 may be coupled to
or interlocked with head carrier assembly 160. Such a coupling
mechanism may allow tape head roller 150 when in an operational
position to be within a given tolerance or threshold distance from
a surface of a magnetic head or a relative distance to other
elements of head carrier assembly 160. Once the tape head roller
150 is locked into an operational position the HMS may be adjusted
within a movement capability of a fine positioning actuator. For
example, in an instance when a tape head roller positions a tape
within 1000 nanometers of the surface of a magnetic head, actuators
coupled to that magnetic head may have a stroke of at least 1000 or
2000 nanometers. The actuator could then be used to control a
head-to-media spacing of 1 nanometer or less.
[0043] FIG. 2 illustrates a close-up view of several of the
elements illustrated in FIG. 1. FIG. 2 includes tape 210, tape head
roller 220, and head carrier assembly 230. Roller 220 of FIG. 2 may
be a same type of roller as tape head roller 150 of FIG. 1. Head
carrier assembly 230 of FIG. 2 includes head carrier 240, actuators
250, and head assembly 260. Head carrier 240 itself may include
actuators 250 and head assembly 260. Furthermore, head carrier
assembly 230 or head carrier 240 may also include an actuation
apparatus (passive or active) that grossly adjusts the position of
head carrier 240. Actuators 250 may be used to finely control the
position of head assembly 260. As discussed in respect to in FIG.
1, exemplary gross (or larger) motions and fine (or smaller)
motions. Such large motions may correspond to the order of several
millimeters ( 1/10 inch or so) or a centimeter (1/2 inch, more or
less) and smaller motions may correspond to motions of less than
one nanometer to several hundreds of nanometers or more. Exemplary
fine positioning actuators include piezoelectric actuators and
thermal actuators. In certain instances, piezoelectric actuators
may be used to make very fine position adjustments and thermal
actuators may be used to make a medium-fine position adjustment or
visa-versa. Movement of the actuators may be controlled by applying
a voltage to the actuators and movement of these actuators may be
controlled at frequencies in the range of 30 Hz to 10 Kilohertz
(KHz), for example, to maintain a desired HMS.
[0044] As discussed in respect to tape head roller 150 of FIG. 1,
tape head roller 220 may be motor driven or may be coupled to
actuators or actuation apparatus that provide either of gross (or
larger) motions and fine (or smaller) motions of tape head roller
220.
[0045] FIG. 3 illustrates several elements that are similar to the
elements illustrated in FIG. 2. FIG. 3 includes tape 310, tape head
roller 320, head carrier assembly 330, head carrier 340, head
actuators 350, and head assemblies 360. Here, however, three
different head assemblies 360 that each include a respective head
actuator 350 are illustrated. Note that if a line were drawn
between the different head assemblies 360 of FIG. 3 that line would
have a concave shape much like the concave shape of line 330C of
head carrier assembly 330. This relative positioning of heads
assemblies 360 means that each of a set of different assemblies may
have a similar HMS relative to tape 310C for a given actuation
stroke distance. As such a nominal position for each of the three
different head assemblies of FIG. 3 may be approximately a same
distance away from tape 310 as that tape moves around tape head
roller 320. Here again, exemplary fine positioning actuators
include piezoelectric actuators and/or thermal actuators.
[0046] An edge surface of tape head roller 320 along which tape 310
moves may have a convex shape. The same may be true of an edge
surface of tape head roller 150 of FIG. 1 or tape head roller 220
of FIG. 2. FIG. 3 also includes a cross-sectional side view of tape
head roller 320 (320 Side View). This side view includes a mounting
hole 320H and a convex outer surface 320CV of tape head roller 320.
Each of the head assemblies 360 of FIG. 3 or 260 of FIG. 2 may also
be coupled to an actuator that moves these head assemblies in a
direction perpendicular to tape 310 or 210 (across the width of the
tape) as indicated by the double arrowed line X of FIG. 3. As such,
fine actuators included in tape drives consistent with the present
disclosure may be able to move head assemblies in a first
direction--toward and away from a tape surface--and in a second
direction--along a cross-sectional surface of a tape head
roller--that is perpendicular to the first direction. Hole 320H may
be used to mount tape head roller 320 to a shaft or a set of
bearings.
[0047] Exemplary radius of tape head roller 320 may be about 10
millimeters to about 13 millimeters. This radius may be selected
such to adjust a number of rotations per minute (RPM) that a tape
head roller rotates. Lower values of RPM may produce lower
frequency disturbances to a tape, yet may correspond to a higher
inertia that could make the starting and stopping of tape movement
be slower. While a curvature of the convex portion 320CV of roller
320 in FIG. 3 appears large, this curvature may be very small, for
example, this curvature might only span a few microns. Such a
slightly convex surface could result in offsetting the effects of
concave positioning of head assemblies mounted above or adjacent to
roller 320. This could allow both read and write elements of a
magnetic head assembly to maintain relative positioning more
optimally.
[0048] The positioning of magnetic heads in a tape drive and
compensating for disturbances in tape drive include making various
measurements. Sensors may be used to sends distance between a
head/head assembly and a tape. Sensors associated with measuring
head-to-media spacing (HMS) include, yet are not limited to
capacitive sensors, laser sensors, or laser diode sensors. HMS
values may also be inferred from the strength of a readback signal
calibrated against the Wallace spacing loss equation.
[0049] In instances where HMS is not measured directly, it may be
measured indirectly using a combination of sensors. This process
may include making more than one measurement and by performing a
subtraction. For example, a first sensor could be used to measure
thickness of the tape as it moves over a tape guide and a second
sensor could be used to measure distances from the head to the tape
guide. The HMS could then be calculated by subtracting the tape
thickness from the distances between the head and the tape guide.
The sensor that measures the distance between the head and the tape
guide could also be a capacitive sensor or be another type of
sensor. The sensor that measures the thickness of the tape could
also be a capacitive sensor that includes more than one plate with
a fixed distance between them. A first plate of this capacitive
sensor could be placed at the top surface of the tape and a second
plate of this capacitive sensor could be placed at the bottom
surface of the tape. Any changes in the capacitance of the sensor
could be attributed to changes in the thickness of the tape between
the capacitor plates.
[0050] Once a distance between the tape facing surface and the
roller or tape guide (D1) and the tape thickness (TH) are
identified, the HMS may be calculated by the formula HMS=D1-TH
virtually instantaneously using modern electronic circuits and/or
processing elements as the tape moves. HMS could then be adjusted
to account for changes in the tape thickness.
[0051] While HMS is controlled, reader elements may be used to
sense servo data that are commonly written adjacent to, or inline
with, data tracks on tape. This servo data could be used to
position read and/or write heads precisely over a particular data
track. Digital filtering techniques may be used to help filter out
resonances associated with a tape drive's mechanical parts or may
help filter out the effects of tape flutter or resonances
associated with the tape itself.
[0052] FIG. 4 illustrates a cross-sectional view of parts included
at or near the surfaces of a tape as data on that tape is read or
written. FIG. 4 includes a tape suspension or tape head roller 460
that supports a backside of tape 470. Item 450 is the head-to-media
spacing distances between the surface of tape 470 and the
"tape-facing-surface" 455 of a head or tape head suspension. The
term "tape-facing-surface" refers to surfaces that are more
conventionally referred to as "tape-bearing-surface" because
conventionally this surface bears frictional forces of tape
movement. Since methods and apparatus consistent with the present
disclosure avoid allowing the tape to contact such surfaces, the
term "tape-facing-surface" is used herein. While this term could be
used, it may be used interchangeably with the older term
"tape-bearing-surface" as this "tape-facing-surface" may sometimes
touch the tape, for example during a calibration process. In other
instances, even with precise HMS control a "tape facing surface"
may occasionally accidentally or incidentally touch the tape, for
example as tape speed or direction is changed.
[0053] FIG. 4 also includes head carrier apparatus 410, first stage
actuators 420, second stage actuators 430, and heads or sensors
440. In certain instances, first stage actuators 420 may be
piezoelectric actuators and second stage actuators 430 maybe either
piezoelectric actuators or thermal actuators. Heads or sensors 440
may be magnetic read head elements, magnetic write head elements,
or sensors (e.g. capacitive/other) sensors for measuring distance.
The first stage actuators 420 may act upon an entire head stripe
that includes multiple heads and the second stage actuators 430 may
act on a subset of neighboring heads (e.g. one, two, or some other
number of heads).
[0054] Items 480 and 490 are parts of a structure that may
interlock tape suspension/roller 460 to head carrier apparatus 410
of a tape drive. Items included in FIG. 4, like those of other
figures of this disclosure are not to intended to be to scale.
[0055] FIG. 5 illustrates an embodiment of the present disclosure
that includes features that change relative pressures of air near a
tape surface. FIG. 5 includes head carrier assembly 510, actuators
A1, head assembly 520, read/write or sensing elements 530, and air
channels 540 that are located facing the magnetic surface of tape
550. FIG. 5 also includes tape guide 580, actuators A2, and blocks
570 that are located on or near a back surface of tape 550. This
back surface of tape 550 is a surface that does not record data and
that may not include any magnetic media.
[0056] The edged surfaces 570E on the edges of blocks 570 create a
low pressure area that tends to pull or suck tape 550 to contact
blocks 570. These surfaces 570E may be referred to a skiving edges
located on the back side of tape 550 that create a low pressure at
areas 560. At points 560, low pressure caused by the back surface
of the tape touching or rubbing blocks 570. An angle created by
this low pressure at locations 560 may be on the order of 1 to 5
degrees, for example. The low pressure created by skiving edges
570E pull tape 550 away from read/write elements 530. This is
unlike conventional tape drives that rely on tapes being drug
across or pulled toward the surface of read or write heads.
[0057] Air channels 540 may be used to provide pressurized air or
air at ambient pressure that is higher than air pressures at
locations 560 of FIG. 5. Because of this, the apparatus of FIG. 5
may both pull and push tape 550 in a direction away from elements
530. Actuators A1 and A2 may then be used to control the HMS of
elements 530 of FIG. 5. Air channels 540 may be coupled to the
external environment via filters not illustrated in FIG. 5. Because
of skiving edges 570E and/or because of air channels 540, magnetic
media on a front (or recording) surface of tape 550 may never make
contact when data is written to or read from tape 550.
[0058] FIG. 6 illustrates an assembly of a series of elements that
can include magnetic reading elements, sensor elements, and writer
elements. The element stripes 610 of FIG. 6 include writing
elements 620, sensor elements 630, and reading elements 640. Note
that each of these elements are illustrated with different shapes,
writing elements 620 include two smaller rectangular boxes inside
of a larger rectangular box, sensors 630 include a smaller circle
located inside of a larger circle, and reading elements 640 are
illustrated as a set of lines within a rectangular box (or as 3
equally sized rectangular boxes stacked on top of each other).
[0059] Note that each of the various elements are located at the
tape facing surface in relative positions in proximity to tape 650
as that tape moves in a direction indicated by the upward pointing
arrowed lines of FIG. 6. Note that FIG. 6 identifies sections of
element stripes 610 where two write elements are separated by a
read element--as indicated by text WRW. FIG. 6 also identifies
sensor elements (Sense) that include sensors adjacent to either a
read element, a write element, or both. Note as the tape moves
upward, each set of read/write elements may be used to write
different tracks of data and read back that data immediately after
it is written. These elements may also be able to read track
positioning data that may be used to follow servo data that may
also be written on the tape. FIG. 6 is not intended to be to true
scale.
[0060] The element stripes include one middle read head stripe and
two different write head stripes, on either side of the read head
strip, so that data written as the tape moves in a first direction
(e.g. upward as illustrated in FIG. 6) or as the tape moves in a
second direction (e.g. downward) can be read verified immediately
after it is written. Data from sensors 630 may be used to adjust
head media spacing as discussed in respect to FIGS. 1-5. As
discussed above actuators in a tape drive may also move across the
width of a tape when track following or when seeking from one track
to another. As such element stripes 610 may be moved left to right
when track following or seeking across portions of the width W of
tape 650.
[0061] FIG. 7 illustrates a series of steps that may be performed
during a head-to media-spacing calibration process and when motions
of magnetic heads are controlled when data is read from or written
to a tape. FIG. 7 begins with determination step 705 that
identifies whether a calibration of head-to-media (HMS) spacing
should be performed, when no, program flow moves to step 740 where
a normal or nominal mode of operation may be initiated. When
determination step 705 identifies that HMS spacing should be
calibrated, program flow may move to step 710 where the tape is
positioned to an unused area of the tape and then in step 715 the
tape is moved at a slow speed. Steps 720, 725, 730, and 735 are
steps that may be repeated during the calibration process. These
steps include receiving HMS sensor data (720), evaluating HMS
sensor data (725), and adjusting HMS (730). Determination step 735
identifies whether the calibration process has been completed. This
calibration process may include moving the head carrier assembly of
toward the tape until the head-facing-surface of the carrier
assembly touches the tape when the tape is moved at a slow speed.
Touchdown may be detected based on a change in tape tension, a
detected motion of read elements created by friction, a detection
of an increase in head temperature due to friction with the tape or
the detection of an electrical contact between the head and the
tape, or by other physical attributes associated the
head-facing-surface touching the tape. Once touchdown is detected,
the head carrier assembly may be moved away from tape while sensor
data is received.
[0062] While not illustrated in FIG. 7, the calibration process may
include a rough calibration followed by a fine-tuning calibration.
A fine-tuning calibration may include performing a series of read
and write operations at slightly different altitudes above the
tape. These reads and writes may occur when the tape is moved under
nominal conditions. The data collected during this this fine-tuning
process may identify an optimal HMS and may be used to identify how
much magnetic read/write performance varies given a commanded
change in HMS. As such, the calibration may be tuned based on
optimal magnetic performance decoupled from an absolute knowledge
of actual HMS.
[0063] When determination step 735 identifies that the calibration
is not complete, program flow may move back to step 720. As
mentioned above, steps 720, 725, 730 and 735 may be performed
iteratively until the calibration process is complete. When the
calibration is complete, program flow may move from determination
step 735 to step 740 where normal or nominal operation of the tape
drive may be initiated.
[0064] As long as the tape drive is operating in a normal mode,
program flow may iteratively perform steps 745, 750, 755, 760, 765,
and 770. Step 745 may receive HMS sensor data, step 750 may
evaluate the received HMS sensor data, and step 755 may adjust HMS.
The received HMS sensor data may be evaluated to identify current
HMS spacing such that it can be controlled as tape thickness varies
or to react to observed changes in fly height. As discussed above
HMS may be measured directly or may be calculated from different
measurements (e.g. a distance between the head facing surface to a
tape roller or tape guide minus a tape thickness measurement).
[0065] After step 755, track following (e.g. servo) data may be
received in step 760, this track following data may be evaluated in
step 765, and adjustments to a track following actuator may be
adjusted in step 770. After step 745, program flow may move back to
step 745. While not illustrated in FIG. 7, program flow may end
such that a tape may be removed from a tape drive.
[0066] The steps of FIG. 7 may be performed by any type of
processor or multi-processor known in the art. Such a processor may
be dedicated to the task of moving a head carrier as discussed
above. Alternatively, steps of FIG. 7 may be executed by a
processor that also performs other functions associated with the
operation of a tape drive. In certain instances, program code of
FIG. 7 may be implemented in a low level machine code or firmware.
Certain steps or actions may be performed by any combination of
electronic circuitry or computer logic. Some functions may be
performed using a field programmable gate array, an application
specific integrated circuit, a processor or combination thereof.
While FIG. 7 illustrates a specific sequence of events, embodiments
of the present invention may be performed by changing the order of
these steps or by eliminating certain steps or decoupling certain
sequences of steps.
[0067] FIG. 8 illustrates electronic components that may be used to
communicate with or control the operations of a tape drive. The
Apparatus 800 of FIG. 8 includes one or more processors 810, memory
820, read/write channel 830, inputs 840, outputs 850, and
communication interface 860. Various of the different components
illustrated in FIG. 8 may be communicatively coupled to each other
via bus 870. In operation, processor(s) 810 may execute
instructions out of memory 820 to perform operations of controlling
operation of a tape, controlling read and write operations, and
controlling the motion of actuators as discussed herein.
Processor(s) 810 may be any processor known in the art, yet
typically may be a microcontroller executing instructions out of
memory 820. Memory 820 may be any memory known in the art,
typically memory 820 will be or include a form of random-access
memory (RAM). Memory 820 may also include a non-volatile memory
(e.g. FLASH memory) that stores firmware program code. In operation
instructions stored in FLASH memory may be moved to RAM as part of
an initialization process.
[0068] Read/write channel 830 may include a combination of analog
and digital electronics such as a preamplifier, analog filter
electronics, digitizing circuitry, and a phase-locked-loop/data
separator, for example. Data read from and written to a tape will
pass through circuits of read/write channel 830. Inputs 840 may be
coupled to sensors that sense head-to-media spacing, tape tension,
tape speed, or other parametric data. Inputs 840 may also include
or be coupled to an analog to digital converter that converts
analog sensor data to digital data. In certain instances, inputs
840 may receive digital data directly from a sensor.
[0069] Outputs 850 may include motor driver circuits or actuator
driver circuits. Outputs 850 may control the tape speed or may be
used to drive actuators that affect head-to-media spacing as
discussed herein. As such, outputs 850 may be coupled to DC
brushless motors or to actuators (e.g. piezoelectric or thermal
actuators). Communication interface 860 may be any form of
communication interface known in the art. For example,
communication interface may be compatible with the small computer
system interface (SCSI) or the serial small computer system
interface (SAS). Alternatively, communication interface 860 may be
a network interface such as an Ethernet interface. The apparatus of
FIG. 8 may receive commands and data from other computers and may
provide data to computers via communication interface 820.
[0070] Processor(s) 810 may control operation of a tape drive based
on commands received from other computers. Processor(s) 810 may
receive sensor data from inputs 840, control data that is
transferred through read/write channel 830, and may control the
operation of motors or actuators by sending signals via outputs
850. Processor(s) may also cache data in memory 820 until that data
can be written to tape or provided to other computers.
[0071] While various flow diagrams provided and described above may
show a particular order of operations performed by certain
embodiments of the invention, it should be understood that such
order is exemplary (e.g., alternative embodiments can perform the
operations in a different order, combine certain operations,
overlap certain operations, or decouple other operations,
etc.).
* * * * *