Dynamically adjustable head positioning mechanism for tape drives

A mechanism for accurately positioning a recording/playback head on the center of a track including a stepper motor and coil assembly in combination controlling coarse and fine transverse head position. The coil is attached to a pivoting actuator arm which provides a mounting member for a recording/playback head. A torsion spring is attached to the actuator arm and to a stage which is driven by a stepper motor lead screw to incrementally position the actuator arm. The coil assembly includes a coil bundle juxtaposed between at least two sets of split magnets. The coil assembly operates to pivot the recording/playback head transversely, thereby providing fine position control.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to magnetic tape recorders and to 
subassemblies utilized therein, particularly with respect to recorders 
adapted for multiple track recording using a multiple track head which is 
responsive to servo signals and transversely movable with respect to the 
recording tape. 
2. Description of the Prior Art 
Data recording cartridges and recorders adapted for their use are disclosed 
and claimed in U.S. Pat. No. 3,692,225 (Von Behren). The cartridge there 
disclosed includes an enclosure together with an endless flexible belt in 
frictional contact with the tape on both reel hubs for bidirectionally 
driving the tape. The cartridge can operate to drive the tape with rapid 
accelerations and decelerations, such as are encountered in digital data 
recording and playback. Recorders adapted to use such data cartridges 
originally employed fixed, multitrack heads which were complex, expensive 
and difficult to maintain in proper alignment. 
To eliminate the multitrack heads, U.S. Pat. No. 4,313,143 (Zarr) disclosed 
a head positioning mechanism by which a single track head could be 
transversely positioned with respect to the width of the recording tape to 
enable recording and playback of any of a plurality of parallel tracks. 
U.S. Pat. No. 4,750,067 (Gerfast) discloses a head positioning mechanism 
for a multitrack data cartridge recorder including a stepper motor, a lead 
screw driven by the stepper motor and a head mounting slide engaged with 
the lead screw by a partial female thread. The Gerfast mechanism moves a 
recording/playback head transverse to the path of a magnetic recording 
tape. 
While the Gerfast mechanism works satisfactorily for some applications, a 
need has recently arisen to provide a mechanism which more accurately 
positions a magnetic recording head on the center of a selected track in 
response to servo signals derived from servo information carried on 
certain tracks on a multitrack tape. This accurate positioning is required 
to allow substantially higher track densities on recording tape. 
The present invention offers a magnetic recording head responsive to such 
servo signals having the advantage of offering an extremely compact head 
mechanism. A further advantage of the head mechanism provided by the 
instant invention is that it is nearly crashproof. The mechanism of the 
present invention also significantly reduces undesirable translational 
reactionary resonances which are typically present in prior art head 
mechanisms. 
SUMMARY OF THE INVENTION 
In contrast to any of the techniques previously employed, the present 
invention provides a voice coil and stepper motor head positioning 
mechanism for a data cartridge recorder which variably positions a 
recording head transversely with respect to the width of the recording 
tape. The mechanism of the invention enables head positioning with very 
close tolerances due to the ability of the voice coil to finely position 
the head very accurately on the center of a track in response to servo 
signals carried by the tape. 
In one embodiment of the invention the voice coil is attached to a rotating 
actuator arm. The actuator arm provides a mounting member for a 
recording/playback head. A torsion spring is attached to the rotating 
actuator arm and a stage which is driven by a stepper motor lead screw to 
initially coarsely position the actuator arm. Following coarse positioning 
by the lead screw, the voice coil then finely positions the head on the 
center of a selected track. The voice coil includes a coil bundle which is 
juxtaposed between at least two sets of split magnets. The voice coil and 
magnets operate together to drive the recording/playback head transversely 
to the direction of movement of the tape by applying a positioning force.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Now referring to FIG. 1 which shows an isometric view of one embodiment of 
the magnetic head assembly of the present invention. As there is seen, the 
magnetic head assembly 10 includes a rotating actuator arm 32 including a 
magnetic recording head assembly 30 rigidly affixed thereto. A stepper 
motor 52, such as is shown in FIGS. 2A and 2B, drives a lead screw 36 
which, in turn moves the stage 44 in a vertical direction perpendicular to 
the surface of a base 5. A coil assembly 60 is attached to one end of the 
rotating actuator arm 32. As best shown in the side cut-away view FIG. 2A, 
the coil assembly 60 comprises a coil frame 61, a coil 62 and a mandrel 
64. The coil 62 comprises an upper portion 62A and a lower portion 62B. A 
recording tape 50 having data contained on a multiplicity of parallel 
tracks moves along a transport path across the head assembly 30. 
The head mounting assembly 10 further includes a stage 44 having a bottom 
surface affixed to a torsion spring 46 which traverses the width of the 
rotating actuator arm 32. Torsion spring 46 is rigidly coupled at its ends 
46A, 46B to opposing sides of the rotating actuator arm 32. The stage 44 
includes apertures 44A and 44B which are sized to receive the lead screw 
36 and an anti-rotation pin 34. Aperture 44A may advantageously be a 
half-nut aperture, slightly larger than necessary to accommodate the lead 
screw 36 so as to allow for movement of the actuating arm 32 in a 
direction normal to the plane of the tape to assure constant loading at 
the tape head interface. The aperture 44A is constructed to also allow 
pivotal movement of the magnetic head assembly. The pin 34 and the lead 
screw 36 are affixed in a well-known manner to a stepper motor 52. The pin 
34 allows movement of the stage 44 in a direction perpendicular to the 
surface of the base 5 but minimizes rotation or movement in other 
directions. The stepper motor 52 turns the lead screw in response to 
control signals applied using well-known techniques. 
Referring to FIGS. 1 and 2A, a magnet housing 38, advantageously in the 
form of a metal U-shaped frame, is rigidly mounted to the fixed base 5. 
The magnet housing 38 is preferably substantially comprised of steel 
material. Magnets 40A and 40B are rigidly affixed to facing sides of the 
magnet housing using epoxy, for example. Magnets 40A and 40B may 
preferably be comprised of split magnets having, for example, a top 
portion being a north pole and a bottom portion being a south pole whose 
heights are equal or greater than the stepper motor translational distance 
plus the width of the coil bundle. The north and south poles of each 
magnet may be advantageously split at the approximate center of the 
vertical height of the magnets as indicated by broken line 70. The magnet 
housing 38 is mounted to the baseplate, as is the stepper motor 52. The 
U-shaped steel housing serves as a return path for the magnetic flux. The 
magnet housing is also used to stiffen the baseplate in the region wherein 
it is mounted. The base 5 is cut out in the region of the assembly to 
allow installation and movement of the assembly. Coil assembly 60 is 
movably juxtaposed between the magnets 40A and 40B so as to allow pivotal 
movement of the frame and, consequently, the entire magnetic head assembly 
transversely to the direction of motion of the magnetic tape as the tape 
moves across the head assembly 30. 
Now referring particularly to FIG. 2A, a cut-away side view of the example 
of the invention illustrated in FIG. 1 is shown wherein the magnetic head 
assembly 10 is in a raised position relative to the tape 50. A load spring 
48 is retained between the housing 16 and the stage 44. The lead screw 36 
may advantageously be positioned within the load spring 48 which may 
advantageously comprise a compliant coil spring having a sufficiently 
large opening in to accommodate the lead screw 36. 
In operation, the stepper motor 52 is used to coarsely position the head 
from track to track and the voice coil responds to a servo signal in a 
track following mode to make extremely small adjustments, as for example, 
within microinches or micrometers, to follow the center of the selected 
track. The torsion spring and voice coil design give the mechanism of the 
invention the ability to dynamically track the servo signal. Higher track 
density data cartridges are now made technically feasible as compared with 
conventional methods found in the prior art. 
The stepper drives the stage 44 through the lead screw 36 which provides 
for substantially zero backlash with slight interference. The stage is 
heavily loaded, the loading approaching the lifting capacity of the 
stepper and lead screw. Loading is achieved by the compression spring 48 
to prevent movement of the stage or lead screw after locking into position 
and to minimize resonance from this portion of the mechanism. The rotating 
actuator arm 32 is attached to the stage 44 by the torsion spring to 
eliminate any translational movement during rotation. In one embodiment of 
the invention, the torsion spring holds the arm several mils above the 
stage. 
For some applications, a stop 66 is advantageously employed. The stop 66 
may advantageously be, for example, an "L-shaped" member which extends 
from a portion of the stage 44 under and in proximity to the cross member 
of arm 32. Stop 66 serves as a crash stop and limits the motion of the arm 
to a few minutes of rotation in a direction substantially transverse to 
the direction of movement of the tape 50. An electrical current of 
sufficient magnitude, herein called a head location signal, may be applied 
in a well known manner to coil 62 in order to drive the cross member of 
arm 32 against the crash stop 66. The head location signal may be applied 
to the coil 62 in order to lock the head assembly 30 against the crash 
stop 66, thereby holding the head assembly 30 in a fixed position relative 
to the stage 44. In this way the position of the head assembly may be 
located in the absence of a servo signal on the tape. Alternatively, if 
the magnetic head assembly of the invention is used in a stepper mode only 
configuration, that is a configuration that does not use track following 
servo signals, the crash stop 66 provides protection against vibration and 
shock. Those skilled in the art will recognize that variations of the 
embodiment shown are readily ascertainable, such as employing multiple 
crash stops extending from the stage, and the invention is not to be 
considered as to be limited by the example discussed herein. 
The forward portion of the arm 32 is a simple rigid box terminated in a 
frame which secures the head. In the implementation shown, the arm height 
is less than its length to allow the moving mechanism to translate about 
150 mils to access all tape tracks, yet allow the entire assembly to fit 
nominally within a 1.0 inch height profile. The rear portion of the arm 32 
holds the coil. The minimum separation of the inner turn of the upper and 
lower portion of the coil is about 250 mils to allow the coil to be 
operated at full power whether the mechanism is at the bottom position or 
the fully extended position. The length of the coil is determined by the 
force required to rotate or pivot the actuator properly at the desired 
frequency and acceleration. The coil is wrapped around and bonded to a 
mandrel 64 which is epoxied into a frame at the rear of the arm, forming a 
rigid body. The mandrel is weighted to balance the rotating arm about its 
axis, reducing translational reactionary forces. 
The invention has been described herein in considerable detail in order to 
comply with the Patent Statutes and to provide those skilled in the art 
with the information needed to apply the novel principles and to construct 
and use such specialized components as are required. However, it is to be 
understood that the invention can be carried out by specifically different 
equipment and devices, and that various modifications, both as to the 
equipment details and operating procedures, can be accomplished without 
departing from the scope of the invention itself.