Pivoting lever cam guide tape head positioner

A fine lateral head positioner for a tape drive includes a frame mounted to a base of a tape transport. A tape head slides laterally along a head guide. A guide beam actuated by a fine position actuator applies limited transverse adjustments to the tape head relative to a tape transport path via a cam and cam-follower arrangement. A coarse positioner between the frame and the base provides coarse position adjustment of the tape head laterally among multiple sets of parallel tracks defined along a longitudinal direction of a magnetic tape moving along the tape transport path, and the guide beam provides fine position adjustment of the tape head enabling it to follow in real time a particular set of parallel tracks of the tape during each data writing or reading operation.

SUMMARY OF THE INVENTION 
The present invention relates to tape recording and playback devices and 
subassemblies thereof. More particularly, the present invention relates to 
a tape head positioner subassembly having a pivoting lever cam guide for 
fine positioning a tape head transversely to a magnetic tape carrying 
multiple longitudinal recording tracks and head servo information. 
BACKGROUND OF THE INVENTION 
Tape recording systems employing multiple parallel longitudinal tracks 
recorded on e.g. one half inch tape are known. Each track typically 
extends for the entire useful length of the tape, which may be 1800 feet 
or longer. A head structure contains multiple read/write head elements. 
When user data is being recorded, a first set of tracks is recorded as the 
tape moves in a first or forward direction across the heads. When the end 
of the tape is reached, the head structure is repositioned, and a second 
set of tracks is recorded as the tape moves in a second or reverse 
direction across the heads. This back-and-forth recording process 
continues until the tape is completely filled up with user data, or until 
a host computer stops sending user data to the tape recording system. 
A known coarse positioner mechanism is described in commonly assigned U.S. 
Pat. No. 5,105,322 to Steltzer, entitled: "Transverse Positioner for Read 
Write Head", the disclosure thereof being incorporated herein by 
reference. In this prior patent a moveable head carriage supported the 
tape head structure. The head carriage carried one or more read-write head 
pairs of the head structure. Eight write heads, and four read heads, were 
typically carried by the head structure, in a four-channel tape transport. 
The head carriage engaged a lead screw which was rotated by a stepper 
motor mounted to a base of the tape transport mechanism. The lead screw, 
and a parallel guidepost, enabled the head carriage to be movably 
positioned transversely relative to a direction of travel of the tape. 
Thus, by energizing the stepper motor, the head carriage was stepped 
across the track recording positions of the tape, as the tape streamed 
back and forth from end to end across the head structure during 
writing/reading operations. 
The known coarse positioner operated in a quasi-open loop fashion in the 
sense that servo patterns were recorded at each end of the tape and were 
read and used for precisely positioning the head structure at nominal 
track centerline of the tracks being followed during an ensuing passage of 
the tape across the heads. However, while the known coarse positioner 
worked satisfactorily for tape track densities on the order of 256 tracks 
per inch, instantaneous lateral tape motion disturbances effectively 
limited the number of tracks that could be defined on the tape storage 
medium. 
Some later improvement was obtained by the use of azimuth recording 
techniques, such that the head structure confronted the lineal tracks at a 
first azimuth angle during a pass from beginning of tape to end of tape, 
and at a second azimuth angle differing from the first during a reverse 
direction pass from end of tape to beginning of tape. The resultant data 
track recording patterns defined herringbone geometry and achieved a 
linear track density of e.g. 416 tracks per inch. An example of an azimuth 
recording system is given in commonly assigned U.S. Pat. No. 5,523,904 to 
the present inventor, entitled: "Linear Tape Write Servo Using Embedded 
Azimuth Blocks", the disclosure thereof being incorporated herein by 
reference. A first example of an azimuth head positioning mechanism is 
given in commonly assigned copending U.S. patent application Ser. No. 
08/918,477 filed by Kasetty on Aug. 26, 1997, entitled: "Tape Head 
Positioning Device for Adjusting Head Tilt", and a second example of an 
azimuth head positioning mechanism is given in commonly assigned U.S. Pat. 
No. 5,680,278 to Sawtelle, Jr., entitled: "Apparatus for Combining Linear 
and Rotational Motion of an Azimuth Read-Write Head". The disclosures of 
the pending application of Kasetty and the patent of Sawtelle, Jr., are 
incorporated herein by reference. 
While these prior approaches have worked to enable increases in track 
densities, a limitation with open loop or quasi closed loop positioning 
remained, due to lateral tape motion caused by a number of vibration 
excitation sources, including the supply reel and motor, take-up reel and 
motor, and guide rollers which guide the tape along a predetermined tape 
path across the head structure. These sources may separately or additively 
contribute to cause lateral tape motion. While prior efforts to reduce 
causes of lateral tape motion have been successful, as track densities 
increase (meaning that track widths are decreased) these prior efforts 
have reached practical limits, and have necessitated use of closed loop 
fine positioning servo mechanisms to provide relatively instantaneous 
adjustment of the tape head. 
It has been proposed to combine a stepper motor as a coarse positioner with 
a linear voice coil motor acting as a fine track positioner to realize a 
head support structure capable of being positioned in closed loop during 
track following operations of the tape transport mechanism. One example of 
a dual actuator is provided by U.S. Pat. No. 5,280,402 to Anderson et al., 
entitled: "Combined Stepper Motor and Voice Coil Head Positioning 
Apparatus". In this prior approach, dual cantilever springs extended from 
a threaded nut structure to a head support structure. A lead screw rotated 
by a stepper motor engaged the threaded nut structure and thereby moved 
the head support structure coarsely across the tape during coarse head 
positioning operations. A linear voice coil motor was directly coupled to 
the head support structure and overcame a restorative bias spring force 
applied to the head by the dual cantilever springs. One drawback of this 
approach is that the springs were not stiff, but were flexible and 
susceptible to unwanted vibrations, requiring dampening structures or 
treatments. 
A further prior art closed loop fine positioner for a tape head is 
disclosed in U.S. Pat. No. 5,379,170 to Schwarz, entitled: "Dynamically 
Adjustable Head Positioning Mechanism". This patent describes head 
carriage or stage which is coarsely positioned by a stepper motor lead 
screw relative to a tape transport base. The stage forms a lever which 
secures the tape head at one end and is pivotally mounted to a lead screw 
follower by a leaf spring which allows for longitudinal displacement of 
the head as well as pivotal displacement. An actuator attached to the 
stage rotates and thereby imparts limited rotational displacement of the 
head relative to the tape path to provide for fine position adjustments in 
real time. One drawback with this prior approach is lack of stiffness in 
that the leaf spring fails to isolate the head from vibrations which may 
be induced as the tape passes over the head. Another drawback with this 
prior approach is that the tape head does not remain perpendicular 
relative to the tape over the range of limited lateral displacement, 
thereby causing the tape to stretch and some of the reader-writer elements 
of the head to fail to register with previously-recorded tape tracks, 
particularly when the tape has been written by another tape transport not 
imparting identical rotational displacement to its head. 
Thus, a hitherto unsolved need has remained for a coarse/fine dual actuator 
positioner which is much stiffer and less susceptible to unwanted 
vibrations than heretofore, and which avoids tape distortions otherwise 
resulting from rotating the tape head relative to the tape to provide fine 
position adjustments. 
SUMMARY OF THE INVENTION WITH OBJECTS 
A general object of the present invention is to provide a coarse/fine dual 
actuator positioner for lateral positioning of a tape head structure 
relative to a tape path which overcomes limitations and drawbacks of the 
prior art. 
Another object of the present invention is to provide a dual actuator 
positioner for a tape drive which manifests a high level of mechanical 
rigidity and resistance to vibration in a manner overcoming limitations 
and drawbacks of the prior art. 
Yet another object of the present invention is to provide a dual actuator 
positioner for a tape drive which is simplified over prior designs, which 
may be realized at a lower prime cost in manufacturing, and which operates 
reliably over the useful life of a tape transport with which the 
positioner is combined. 
A still further object of the present invention is to provide a fine 
positioner for a tape head which employs a cam and follower arrangement in 
order to impart fine position adjustment to the tape head without rotating 
the tape head relative to the tape path. 
In accordance with one aspect of the present invention a tape head actuator 
assembly includes a frame disposed relative to a tape path, a tape head 
guide extending from the frame transversely relative to the tape path, and 
a tape head engaging the tape head guide such that the tape head freely 
moves transversely and lineally relative to the tape path along the head 
guide. A lever is pivotally mounted to the frame at a fulcrum thereof. The 
lever defines a head guiding cam region for guiding the tape head. A cam 
follower region of the tape head is engaged by and follows the head 
guiding cam region. An actuator motor has a stator portion secured to the 
frame and an armature portion for moving the lever about the fulcrum over 
a limited displacement range. The actuator motor is responsive to fine 
head position control signals and thereby imparts fine position adjustment 
of the tape head along the head guide relative to the tape path without 
rotating the head relative to the tape. 
In accordance with another aspect of the present invention a coarse and 
fine lateral head positioner is described for positioning a magnetic 
read/write head structure within a tape drive. The tape drive includes a 
base and defines a predetermined tape transport path relative to the base 
which leads a magnetic recording tape across the head structure. The 
coarse and fine lateral head positioner includes a coarse positioner, such 
as a stepper motor, mounted to the base. The stepper motor directly or 
indirectly rotates a threaded lead screw which extends generally 
perpendicular to the tape path. A head carriage assembly includes a 
threaded follower nut which engages the lead screw. A pivoting beam 
structure is pivotally mounted to the head carriage at a fulcrum for 
limited rotational displacement transversely relative to the tape 
transport path and displaces the head structure along a guide post so as 
to be in in confronting relation to a tape moving along the tape transport 
path. A camming arrangement between the pivoting beam structure and the 
head structure enables rotational motion to be translated into lineal 
motion of the head transverse to the tape path. A fine positioner prime 
mover, such as a voice coil actuator, has a fixed part mounted to the head 
carriage assembly and a moving part coupled to rotate the pivoting beam 
structure. In the particular arrangement being described the stepper motor 
provides lateral coarse head position control, and the voice coil motor 
provides lateral fine position control, of the head structure relative to 
the tape path. Accordingly, the head structure is coarsely positionable 
laterally among multiple sets of parallel tracks defined along a 
longitudinal direction of a magnetic tape moving along the tape transport 
path, and finely positionable to follow precisely a particular set of 
parallel tracks of the tape during a data writing or reading operation. 
In this aspect of the invention the rigid beam structure may be mass 
balanced about a pivot axis relative to the head carriage assembly, and 
may further be mass balanced about the threaded lead screw. The rigid beam 
structure may preferably comprise two generally parallel beam sections 
joined at one end by a cam engaging a cam follower of the head structure 
and at another end by the moving part of the voice coil actuator. 
In accordance with another aspect of the present invention a tape drive is 
provided for recording data onto a magnetic recording tape, and for 
reading data from the tape, by use of a magnetic head structure across 
which the tape is moving along a tape path. In this tape drive the 
magnetic head structure is positionable transversely relative to the 
direction of tape travel along the tape path in order to register with a 
multiplicity of lineal tape track positions. Further, the magnetic tape 
provides head structure fine position servo information which is sensible 
by a servo sensing function included within the magnetic head structure. 
Accordingly, the tape drive includes a support base, and a head carriage 
positionable relative to the support base and laterally relative to the 
tape path. A coarse positioning mechanism, such as a stepper motor and 
threaded lead screw, is mounted to the support base for moving the head 
carriage laterally relative to the tape path to position the head carriage 
at a selected one of multiple tape track positions. A rigid head support 
pivot structure including at least one rigid beam is rotationally 
journalled to the head carriage at a rotational pivot point and directly 
supports the magnetic head structure. A fine position servo control loop 
of the drive includes functional circuitry for receiving and processing 
sensed head structure fine position servo information into a fine position 
correction signal. A fine position voice coil actuator motor is mounted to 
the head carriage and is responsive to the fine position correction signal 
for rotating the rigid beam along a locus of limited rotational 
displacement which results in applying incremental lineal head structure 
displacement via a cam and follower mechanism in a direction generally 
lateral relative to the tape path. 
In this aspect of the present invention, fine position servo information 
comprises optically sensible lineal servo tracks formed on a non-magnetic 
side of the magnetic recording tape, and the magnetic head structure 
includes an optical servo head for sensing one of the lineal servo tracks 
which corresponds to a group or set of magnetic recording tracks being 
followed by the head during a particular write or read operation.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
With reference to FIGS. 1 and 2 a tape transport 10 incorporating 
principles of the present invention includes a base 60 which supports and 
registers various structural and functional elements needed for effective 
tape transport, recording and playback. These elements typically include a 
supply tape reel holding a coil or pancake of magnetic recording tape, a 
small segment of which is marked by reference numeral 12 in FIG. 1, and a 
take-up tape reel, and associated reel motors (not shown in FIGS. 1 and 2 
but present in a practical embodiment of the invention). The supply tape 
reel most preferably is contained within a single-reel tape cartridge and 
holds a supply, e.g. 1800 feet or more, of one half-inch magnetic 
recording tape. The single-reel tape cartridge is most preferably of the 
type marketed by the assignee of the present invention under the DLTtape 
(tm) brand of single reel linear streaming tape cartridges. Accordingly, 
the tape transport 10 includes a mechanism for receiving and engaging the 
single reel linear streaming tape cartridge, and causes tape 12 spooled on 
the supply reel to be drawn into the tape mechanism and across a head 
structure 18 along a tape path defined e.g. by tape guide rollers 14 and 
16. These conventional mechanical elements and features are well 
understood by those skilled in the art and, except for the fact that the 
head structure 18, and guide rollers 14 and 16 may induce or amplify tape 
lateral motions which must be followed for proper tape recording and 
playback, are not particularly relevant to the present invention and are 
therefore not further described herein in substantial detail. 
In accordance with principles of the present invention a pivoting lever cam 
guide tape head positioner subassembly is provided for positioning the 
multi-channel head structure 18 in a coarse, lateral direction relative to 
tape travel and in a fine, lateral direction perpendicular to tape travel. 
The head structure 18 is slidably mounted upon a head guide, such as 
cylindrical guide post 22 extending perpendicularly relative to the frame 
20 and the travel path of tape 12. The head structure 18 may include a 
plastic bushing or bushings for facilitating relative sliding motion along 
the guide post 22 without stiction. The plastic bushings 23 may be formed 
of a suitable plastic material, such as Delrin.TM.. A lever 26 is 
rotatably attached to the frame 20 at a dual leg fork-shaped fulcrum 
structure 24 as via a pin axle 25 extending through the fulcrum structure 
24 and through a journal of the lever 26. An armature 28 formed at one end 
of the lever 26 cooperates with a stator assembly 30 fixed to the frame 20 
to form a fine position voice coil actuator motor. This voice coil 
actuator motor translates electrical driving currents into rotary driving 
force which imparts rotational motion to the lever 26 relative to the 
frame 20 about the axis of limited rotation about pin axle 25. In 
practice, the amount of rotation is limited to a lateral head position 
correction typically in the range of a hundredth of an inch, or less, in 
order to compensate for lateral tape motion and flutter. 
A cam 32 is formed at an end of the lever 26 to guide the head structure 18 
laterally along the guidepost 22 as the lever 26 is rotated. The cam 32 
engages e.g. a recessed cam follower surface 34 formed in a back wall of 
the head structure 18. A compression spring 36 applies a bias force to the 
cam 32 in order to maintain it in proper mechanical driving arrangement 
with the head 18. As the lever 26 is rotated about the fulcrum pin 25 by 
the voice coil actuator, rotational motion of the lever is translated into 
lineal motion of the head structure 18 along guide post 22 via the cam 32 
and follower 34. As the lever 26 is rotated the head structure 18 is 
displaced laterally along the guide post 22 thereby to follow lateral tape 
motion and other lateral disturbances to proper tape positioning in 
accordance with a fine position error signal developed by a servo loop 
within the tape transport 10. This arrangement has resulted in a head fine 
positioner mechanism which is considerably stiffer than prior approaches, 
which manifests a very high natural resonant frequency, and which resists 
vibrations and other unwanted exciting forces in a superior manner. 
In the embodiment of FIGS. 1 and 2, the cam pin 32 has an elongated 
engagement surface generally parallel to the direction of tape travel. 
This engagement surface with the follower surface 34 of the head structure 
18 is made sufficiently long in order to stabilize and fix the head 
structure 18 in a desired tape-confrontation position, i.e., so that the 
head structure 18 is not free to rotate relative to the tape 12 about the 
guide post 22. 
The head positioner also preferably includes a coarse positioner mechanism 
and function. The coarse positioner mechanism operates under electrical 
control, such as an incremental rotational motion stepper motor 48 which 
rotationally drives a lead screw 24. The motor 48 may be secured via a 
mounting bracket 50 to a base plate 58 of the head positioner subassembly. 
While a stepper motor is a presently preferred implementation of the 
coarse positioner, other incremental-motion-providing devices are clearly 
within contemplation for use as a coarse positioner. For example, a linear 
motor and shaft encoder providing angular position feedback could also be 
employed in lieu of the stepper motor 48 in a manner known to those 
skilled in the art. The motor 48 may drive the lead screw 24 directly, or 
a gearing arrangement such as a large spur gear 44 driven by a small 
pinion gear 46 rotated by the motor 48, may be employed, depending upon 
particular design and space considerations. In the embodiment shown in 
FIGS. 1 and 2 the lead screw 42 is driven by the large diameter spur gear 
44 which in turn is driven by the pinion gear 44 mounted on the drive 
shaft of the motor 48. The lead screw 42 engages a threaded nut portion 40 
of a carriage frame or platform 20. The threaded nut portion 40 may 
include a backlash-resisting feature to remove any unwanted mechanical 
hysteresis between the lead screw and the threaded nut portion. The lead 
screw 42 engages an upper bearing 52 secured to a top plate 56 of the head 
subassembly, and engages a lower bearing 54 of a base plate 58 of the head 
subassembly. A thrust bearing 55 may also be used between the lead screw 
42 and a base plate 60 in order to maintain precise position of the lead 
screw 42 relative to the base 60 and the frame 20 and nut 40. 
A structural guide feature of the base plate 58, such as guidepost 62, 
extends from the base plate 58 in parallelism with an axis of rotation of 
the lead screw 42. This feature or guidepost 62 is followed the frame 20 
during coarse lateral displacements of the frame 20 in response to lead 
screw rotation. The post 62 may be formed of a suitable polished metal and 
a cylindrical bushing 64 extending through the platform 20 may be formed 
of a suitable self-lubricating plastic material, such as Delrin(tm). The 
guide post 62 and the bushing 64 maintain the frame 20 and head structure 
18 at a desired confrontational orientation angle relative to the tape 12 
while permitting the platform 20 and head structure 18 to be moved 
laterally relative to the tape path. 
In addition to a multi-channel array of magnetic read/write heads 
confronting a storage medium surface of the tape 12, the tape head 
structure 18 may also include an optical servo head 35 supported on an 
integrally formed bracket 37. The optical servo head 35 senses e.g. lineal 
optical servo tracks 37 printed, etched, embossed or otherwise formed on a 
nonmagnetic back surface of the tape 12, most preferably during tape 
manufacturing. Since the optical tracks are always present, a closed loop 
fine position servo can obtain instantaneous lateral tape displacement 
information and use that information to provide fine adjustment of the 
head structure 34 into a proper registration with a track set being 
followed during tape streaming data writing/reading operations of the tape 
transport 10. 
A fine positioner mechanism preferably may be implemented as a rotary voice 
coil motor, although other implementations including piezoelectric effect 
devices, etc., may be used in a particular design. In the FIGS. 1 and 2 
embodiment, the mechanism includes, for example, an armature 28 comprising 
a voice coil wound on a suitable bobbin fixed to a distal end of the 
pivoting lever structure 26. A stator 30 comprises a magnetic core 
structure preferably formed as a laminar structure of soft magnetic core 
material and includes a bar-shaped permanent. A central opening of the 
voice coil 46 is oversized relative to a cross-section of a leg of the 
stator such that the voice coil is free to rotate and be displaced along 
the leg in response to a torque resulting from a directional current 
flowing through the voice coil. Alternatively, as shown in the FIGS. 6 and 
7 embodiment, the positioner may comprise a moving permanent magnet 29 
affixed to the distal end of the pivoting lever structure 26, and a stator 
coil 31 affixed to the platform or frame 20. 
A bidirectionally-sourced driving current is caused to flow through the 
voice coil at all times in order to stabilize the pivoting lever 26 and 
thereby the head structure 18 at the desired position relative to the tape 
12. Optionally, or alternatively a suitable spring such as a hair spring, 
leaf spring or coil spring, may be used to apply a static bias force to 
the pivoting lever 26 in order to bias it to a nominal position, such that 
a unidirectional driving current through the voice coil may be used to 
overcome the bias force and thereby incrementally fine position the head 
structure 18. If a spring bias force is employed, a solenoid actuator 
operated by a unidirectional fine position driving current may be employed 
as a fine positioner mechanism which operates to overcome the static bias 
force. 
In the embodiment of FIGS. 1 and 2, the pivoting lever structure is 
approximately one-half inch long on each side of the pivot axis 25 and 
provides the head structure 18 with a limited transverse displacement 
range on the order of plus/minus 1-2 millinches relative to the tape 12. 
The roller guides 14 and 16 are located in close proximity to the head 
structure 18, such as within about one inch of an adjacent transverse edge 
of the head structure 18. The head structure 18 is arranged such that a 
track-to-track pitch of ten microns or less may be defined and followed. 
This track pitch enables track densities on the order of 2000 tracks per 
inch, or greater. 
FIG. 3 illustrates certain modifications which may be made to the FIGS. 1 
and 2 embodiment. Where elements functionally remain unchanged from the 
FIGS. 1 and 2 embodiment such elements carry the same reference numerals 
previously assigned and are not further described in any particular 
detail. In FIG. 3, a head structure 118 includes lateral pin extensions 
120 and 122 on opposite sidewalls. The pins 120 and 122 are aligned along 
an axis generally parallel with a direction of tape travel across the head 
118. A pivoting lever 126 includes a forked portion having tines 128 and 
130. Tine 128 engages pin 120, and tine 130 engages pin 122. When the 
lever 126 is rotated, the tines impart translational force to the pins and 
cause the head structure 118 to move up and down along the guide shaft 22. 
In the FIG. 3 example, a variant voice coil motor is also shown. In this 
variation, a flat coil 132 extends from a distal end of the arm 126 and 
includes two legs which pass through intense magnetic fields created by 
close proximity of permanent magnets 134 and 136. One of the legs passes 
through a north-south permanent magnet field, while the other leg passes 
through a south-north permanent magnet field. Driving current passing 
through the voice coil causes the arm 126 to pivot about the fulcrum axis 
25 in a direction dependent upon driving current direction. 
In the FIG. 4 example, a head guide structure, such as guide post 222 
incorporates a keying feature such as a longitudinal key 224 formed of a 
suitable material, such as polished metal. A key seat 226 is formed in a 
head structure 218 and follows the key 224 as the head 218 is displaced 
along the guidepost 222. A hemispherical surface of a cam 232 drivingly 
engages a hemispherical cam follower feature 234 formed on a back wall of 
the head structure 218 in order to translate rotational motion of the 
lever arm 26 to lineal motion of the head structure 218 along the guide 
post 222. A helical spring 236 is provided to spring-load the cam 232 
against the cam follower 234. Alternatively, the key 224 may be spring 
biased against the key seat 226 in order to apply a suitable bias force 
between the cam follower 234 and the cam 232. 
In the FIG. 5 example, a lever arm 326 has a fulcrum at an end thereof 
distal to the head structure 18 and pivots about a pivot axis pin 325. A 
piezoelectric device 348 is coupled between the frame or platform 20 and 
the arm 326 adjacent to the head 18. As electrical current is applied to 
the device 348, it expands or contracts, and thereby imparts rotational 
driving force to the arm 326 which is translated into lateral linear 
displacement of the head 18 as previously described. 
In the FIGS. 6 and 7 embodiment, the pivoting lever 26 is formed of two 
parallel beam sections which span the lead screw nut 40 and which also 
span the head 18 as in the FIG. 3 embodiment. By following the arrangement 
of FIGS. 6 and 7, mass balance of the pivoting lever structure 26, moving 
magnet 28 and head 18 about a center of gravity (coincident with an axis 
of rotation of the lead screw 42) is achieved. With such mass balance, the 
actuator achieves a desired immunity to external shock forces. In order to 
achieve mass balance, a location of the fulcrum 24 is chosen so that half 
of the effective mass of the head-pivot lever structure is on one side, 
and half of the effective mass is on the other side thereof. The pivot 
lever structure 26 may be spring biased toward the head 18 at the lead 
screw nut 40, or the head 18 may be spring biased away from the head guide 
post 22. Alternative biasing arrangements may also be employed. 
Further details of the tape transport 10 are provided by the FIG. 8 
diagrammatic example. Therein, a supply reel 15 supplies the tape 12. The 
reel 15 is preferably a part of a single-reel tape cartridge which 
includes a suitable buckling mechanism. The cartridge and buckling 
mechanism are conventional and are not described further. The reel 15 is 
rotationally engaged by a supply reel drive motor 17. A take-up reel 19 
within the transport 10 is controlled by a take-up reel drive motor 21. 
The motors 17 and 21 are controlled independently by a motors control 
servo loop 76 in order to provide an appropriate amount of tension on the 
tape 12 irrespective of the relative diameters of the tape spools formed 
on the reels 15 and 19 at any particular time. The tape guide roller 16A 
is shown coupled to a tape speed-sensing device, such as tachometer 27. 
The tachometer 27 is used conventionally by the motors control loop 76 in 
controlling relative torque's applied by the motors 17 and 21. 
A transport electronics circuit 70 includes a data and command interface 
bus 72 enabling the transport 10 to be connected to a computing 
environment. An interface command decode and user data processing unit 74 
provides conventional tape command decode and status functions, and user 
data compression and expansion functions as well as error correction 
processes. It also supervises the motors loop 76, a coarse head position 
control loop 78 and a fine head position control loop 80. The coarse head 
position control loop is used to control the stepper motor 48 to position 
the head structure 18 at each nominal track set location. It should be 
understood that the transport 10 includes a plurality of parallel user 
data channels, such as 6-12 channels, and that each nominal coarse head 
position locates the head structure 18 at approximately each set of 6-12 
tracks. 
The fine head position control loop 80 responds to instantaneous tape 
position information sensed by e.g. the optical pickup head 35 from one of 
the optical servo track patterns 39 which corresponds to the set or group 
of lineal magnetic tracks presently being followed. Any positional offset 
or position error sensed by the optical head 3 will result in a corrective 
driving current passing through the voice coil of a fine position actuator 
45. This current will apply a torque force to the arm 26, and the head 
structure 18, following the cam 32 of arm 26, will be displaced along 
guide post 22 and thereby be returned to a correct alignment with the 
optical tape tracks being followed (and in turn be returned to alignment 
with the magnetic tracks being written to, or being read from). 
The optical servo track patterns 39 may provide continuous or discrete 
position error signals. Each track may be encoded with a unique value or 
code which enables the optical head 35 and main control module 74 to 
determine the nominal servo track being followed. Advantageously, the 
servo track patterns may be formed as a part of the tape manufacturing 
process, with the result that there need be no separate magnetic servo 
track writing operation as part of tape manufacturing. Conventional laser 
inscribing, embossing or patterning techniques may be used in real time 
during tape manufacture to provide the optical servo tracks 39. 
While an optical-based fine position servo is presently most preferred, 
those skilled in the art will appreciate that the balanced coarse-fine 
pivoting lever tape head positioner of the present invention will work 
advantageously with conventional magnetic servo track patterns 
interspersed among data tracks. A magnetic servo track head and channel 
would be used in lieu of the optical tracks 37, optical head 36 and 
optical servo channel presently preferred. 
Having thus described embodiments of the invention, it will now be 
appreciated that the objects of the invention have been fully achieved, 
and it will be understood by those skilled in the art that many changes in 
construction and widely differing embodiments and applications of the 
invention will suggest themselves without departing from the spirit and 
scope of the invention. The disclosure and the description herein are 
purely illustrative and are not intended to be in any sense limiting.