Mechanisms for a closed loop head positioner for streaming tape drives

Tape head positioning apparatus that includes a head carriage frame and a parallel beam positioning structure supported by the head carriage for supporting the magnetic tape head and for variably positioning the magnetic tape head relative to the carriage along a path generally transverse to the tape travel direction. The parallel beam positioning structure includes parallel support beams secured at their ends to the head carriage. The magnetic tape head is secured between the bender beam at a location generally between their ends. In a particular embodiment of the parallel beam positioning apparatus, the parallel support beams comprise first and second resilient reed beams having their ends secured to the head carriage and configured to be deflectable in a direction transverse to the tape travel direction. A voice coil linear motor deflects the reed beams pursuant to a control signal to move the magnetic tape head along the path transverse to the tape travel direction. In a further embodiment of the parallel beam positioning apparatus, the support beams comprise first and second parallel piezoelectric bender beams having their ends secured to the head carriage and configured to deflect in a direction transverse to the tape travel direction in response to a control signal. Deflection of the bender beams pursuant to the control signal displaces the magnetic tape head along the path transverse to the tape travel direction.

BACKGROUND OF THE INVENTION 
The present invention relates generally to tape drives, and more 
particularly to magnetic tape head positioning apparatus that provides 
fine positioning of a magnetic tape head in a closed loop magnetic tape 
head positioning system. 
Tape drives are commonly utilized as secondary storage devices for back up 
of the primary storage devices such as disk drives utilized in large 
computers such as main frames and in small computers such as personal 
computers. For small computers, tape drives using quarter-inch tape 
cartridges (i.e., the width of the tape is nominally one-quarter inch) are 
widely utilized, since they are relatively small and provide sufficient 
storage capacities. 
An important factor that determines the storage capacity of a tape utilized 
with a non-rotating magnetic tape head is number of parallel, 
longitudinally oriented tracks utilized to record data. In other words, 
all other factors being the same, more tracks provide more storage 
capacity. The writing and reading of parallel tracks is achieved by 
magnetic tape head positioning apparatus for positioning the magnetic tape 
head at different locations in the transverse direction relative to the 
tape and its direction of travel. 
Typically, the magnetic tape head positioning apparatus includes a stepper 
motor, an externally threaded lead screw driven by the stepper motor, and 
a head carriage assembly which supports the magnetic tape head and is 
driven by the lead screw along a path transverse to the tape travel 
direction. For writing, each track is defined by positioning the magnetic 
tape head at a location as determined by the calibration of the particular 
tape drive for unformatted tapes, or as close to the center of a track as 
defined by servo information in a pre-formatted tape. In either event, the 
magnetic tape head would be positioned at one of the incremental locations 
defined by the stepper motor. Due to manufacturing variations in the tape 
drive and the tape cartridge, the magnetic tape head might not be 
positioned at the location that corresponds to the center of a particular 
track. 
The consequences of imprecise magnetic tape head positioning include 
distortion and low signal amplitude upon playback on a drive different 
from the one that wrote a tape, or even the inability to read a tape 
written by another drive. Further, magnetic tape head positioning 
apparatus that is not capable of precise head positioning places 
limitations on track density. 
SUMMARY OF THE INVENTION 
It would therefore be an advantage to provide magnetic tape head 
positioning apparatus that is capable of very precise magnetic tape head 
positioning. 
Another advantage would be to provide magnetic tape head positioning 
apparatus having greater positioning precision than increments of a 
stepper motor. 
The foregoing and other advantages are provided by the invention in a 
magnetic tape head positioning apparatus that includes a head carriage 
frame and a parallel beam positioning structure supported by the head 
carriage for supporting the magnetic tape head and for variably 
positioning the magnetic tape head relative to the carriage along a path 
generally transverse to the tape travel direction. The parallel beam 
positioning structure includes parallel support beams secured at their 
ends to the head carriage. 
In a particular embodiment of the magnetic tape head positioning apparatus, 
the parallel beam positioning apparatus includes first and second parallel 
piezoelectric bender beams having their ends secured to the head carriage 
and configured to deflect in a direction transverse to the tape travel 
direction in response to a control signal. The magnetic tape head is 
secured between the bender beams at a location generally between their 
ends, and deflection of the bender beams pursuant to the control signal 
displaces the magnetic tape head along the path transverse to the tape 
travel direction. 
In a further embodiment of the magnetic tape head positioning apparatus, 
the parallel beam positioning apparatus includes first and second 
resilient reed beams having their ends secured to the head carriage and 
configured to be deflectable in a direction transverse to the tape travel 
direction. The magnetic tape head is secured between the reed beams at a 
location generally between their ends, and a voice coil linear motor 
deflects the reed beams pursuant to a control signal to move the magnetic 
tape head along the path transverse to the tape travel direction.

DETAILED DESCRIPTION OF THE DISCLOSURE 
In the following detailed description and in the several figures of the 
drawing, like elements are identified with like reference numerals. 
FIG. 1 illustrates a tape drive 10 which is utilized to write and read a 
magnetic tape 11 stored in a tape cartridge 13. A magnetic tape head 15 
engages the tape 11 which is moved across the face of the head for writing 
data to the tape and for reading data from the tape. The magnetic tape 
head 15 is supported by a head carriage 17 that is moved transversely 
across the tape by rotation of a lead screw 19. The lead screw 19 is 
rotated by a stepper motor 21 via a pinion gear 25 that is fixed to the 
output shaft of the stepper motor and engaged with an anti-backlash gear 
23 that is fixed to the lead screw 19. 
The lead screw is 19 supported by bearings secured to the drive frame, and 
the stepper motor is also secured to the drive frame, so as to provide for 
a rigid and fixed relation between the lead screw and the stepper motor 
output shaft. 
Referring more particularly to FIGS. 2, 3, and 4, the head carriage 17 
includes a base section 27 which includes an internally threaded aperture 
for engaging the lead screw 19. A laterally extending anti-rotation arm 29 
integral with the base section 27 includes an aperture or slot which 
engages an anti-rotation shaft 31 mounted in the drive frame. The 
engagement of the anti-rotation arm 29 on the anti-rotation shaft 31 
prevents rotation of the head carriage 17 while permitting displacement 
thereof transversely to the tape travel direction pursuant to the rotation 
of the lead screw. For convenience, the direction of tape travel is 
indicated by an X axis, while the transverse direction in which the 
magnetic tape head travels is indicated by a Y axis that is perpendicular 
to the X axis. 
The carriage 17 further includes a laterally extending support arm 33 that 
includes at the ends thereof opposing support blocks 35 spaced from each 
other and generally aligned along the direction of tape travel. 
In accordance with the invention, the magnetic tape head 15 is secured to 
the head carriage 17 with magnetic tape head positioning apparatus that 
moves the magnetic tape head relative to the head carriage transversely to 
the tape travel direction in the Y axis direction. The head positioning 
apparatus includes a first support beam 37 which has its ends secured to 
the top portions of the support blocks 35 of the head carriage, and a 
second support 39 beam parallel to the first support beam 37 and having 
its ends secured to the bottom portions of the support blocks 35 of the 
head carriage. Each support beam has a length that is generally parallel 
to the tape travel direction, a width in the direction of a Z axis normal 
to the plane formed by the X and Y axes, and a thickness in the direction 
of the Y axis. 
The support beams 37, 39 function as a resilient suspension for the 
magnetic tape head 15, and displacement thereof is achieved by forcing the 
magnetic tape head to move against the restoring force of the support 
beams. 
The magnetic tape head 15 is secured between the first and support beams 
37, 39, generally centrally between the ends thereof, with the first and 
second support beams being spaced to accommodate the magnetic tape head 
and mounting components therebetween without bending. 
As shown more particularly in FIG. 6, the top of the magnetic tape head 15 
is secured to the first support beam 37 generally in the center thereof 
with an assembly comprising a bracket 42 and a pin 44. The bracket 42, 
which generally resembles an inverted T in cross section, includes a lower 
panel 42a that is secured to the top of the magnetic tape head 15 with 
adhesive, for example. A raised rib 42b is narrow in the X-direction and 
extends laterally relative to the support beam 37 which is secured thereto 
by adhesive, for example. The bracket 42 further includes upwardly 
extending tabs 42c at the ends of the raised rib 42b. Semi-circular slots 
are formed in the tabs 42c to accept the pin 44 which extends laterally 
across the beam and is secured to the beam and the tabs 42c by adhesive, 
for example. 
The bottom of the magnetic tape head 15 is secured to the second support 
beam 39, generally in the center thereof with an assembly comprising a 
bracket 46 and a pin 48, which are similar to the bracket 42 and pin 44 
utilized to the secure the top of the magnetic tape head 15 to the first 
support beam 37. In particular, the bracket 46 is very similar to the 
bracket 42, but is inverted so as to be secured to the bottom of the 
magnetic tape head 15. As discussed more fully herein, the tabs 46c of the 
bracket 46 are configured for the particular implementation. 
With the bracket and pin assemblies utilized to secure the magnetic tape 
head to the parallel support beams, the attachment regions on the support 
beams are relatively narrow in the X-direction, which allows for more 
accurate deflection in the center area of the support beams. 
Referring now in particular to FIGS. 4, 5, and 6, illustrated therein is an 
illustrative example of a head positioning apparatus in accordance with 
the invention wherein the magnetic tape head support beams comprise first 
and second resilient reed or spring beams 137, 139 configured so that 
their center portions are resiliently deflectable in a direction 
transverse to the tape travel direction. 
For the head positioning apparatus of FIGS. 4, 5, and 6, the head carriage 
17 further includes a linear motor 41 supported below the center of the 
second support reed beam 139 by a motor support member 43 that is integral 
with the carriage base section 27. The linear motor 41 comprises a voice 
coil motor that includes an annular pole piece assembly 45 secured to the 
motor support member 43, and a voice coil 47 secured to the second support 
reed beam 139 beneath the magnetic tape head 15. The pole piece assembly 
45 in particular includes an outer pole piece 45a and an inner pole piece 
45b which are separated from each other by an annular gap. The coil 47 is 
secured to the tabs 46c of the bracket 46 in alignment with the annular 
gap, and is linearly movable therein along the longitudinal axis of the 
annular gap which is aligned with the Y axis. As shown in FIG. 6, the 
inner periphery of the coil 47 is secured, for example by adhesive, to the 
outer peripheries of the tabs 46c which are curved to generally conform to 
the inner periphery of the coil 47. The length of the pin 48 is 
appropriately shorter than the inside diameter of the coil 47. 
A servo control signal based on the detected tracking error and generated 
pursuant to conventional servo techniques is provided to the voice coil 47 
which is configured to move in the appropriate direction that will reduce 
the tracking error. 
In a further embodiment of the invention, the support beams 37, 39 comprise 
piezoelectric bender beams 237, 239, as schematically shown in FIG. 7. As 
is well known, a piezoelectric beam can include first and second 
piezoceramic thin sheets bonded to a thin metal shim sandwiched in the 
middle. In the bender beams 237, 239 the metal shims extend beyond the 
piezoceramic layers so that they can be secured to the support arms 39. 
Application of a control voltage to the bender beams 237, 239 will cause 
their center portions to deflect in the Y axis direction. In FIG. 7, the 
piezoelectric bender beams are connected in parallel wherein the 
piezoceramic layers are commonly connected to one potential of the bias 
voltage and the metal shim is connected to the other potential of the 
control voltage. 
FIG. 8 shows a different configuration of piezoelectric bender beams 337, 
339, which by way of further example are connected in series wherein one 
piezoceramic layer of a beam is connected to one potential of the control 
voltage and the other piezoceramic layer of the beam is connected to the 
other potential of the control voltage. 
A servo control signal based on the detected tracking error and generated 
pursuant to conventional servo techniques is provided to the piezoelectric 
benders which are configured to deflect in the appropriate direction to 
reduce the tracking error. 
Referring now to FIG. 9, shown therein is a further example of a magnetic 
tape head suspension in accordance with the invention. In this embodiment, 
the top support beam comprises a piezoelectric bender beam 437, while the 
lower support beam comprises a reed beam 439. A tracking error signal is 
provided to the piezoelectric beam 437 which is configured to deflect in 
the appropriate direction to reduce tracking error. 
With the above described magnetic tape head positioning apparatus, very 
precise head positioning is achieved which provides for more accurate 
reading of tapes, and which allows for a greater number of tracks on a 
tape. 
Although the foregoing has been a description and illustration of specific 
embodiments of the invention, various modifications and changes thereto 
can be made by persons skilled in the art without departing from the scope 
and spirit of the invention as defined by the following claims.