Note: Descriptions are shown in the official language in which they were submitted.
18 FIELD OF T~lE I~'~VE2!TION
. .
19 This invention relates to reco~-'ing on
magnetic tape with a rotating magnetic transducer.
21 More particularly, the invention relates to providing
22 an air bearing to support the tape in a stable manner
23 along the path of the rotating head. The stability
24 of the air bearing near the path of the rotating
head becomes more critical when the rotating head
26 is a flying head rather than a contact head. Any
27 fluttering of the tape due to an unstable air bearing
28 makes it almost impossible to control the flying
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1 height or separation between a rotating head and
2 the magnetic tape.
3 HISTORY OF TH~ ART
4 Rotating-head magnetic recording is usually
accomplished by wrapping the tape helically about
6 a mandrel split and separated to accommodate a rotating
7 wheel which carries the magnetic head. In other
8 words, the mandrel consists of two separate cylindrical
9 halves which abut a rotating wheel of the same radius
as the cylindrical halves, and this rotating wheel
11 carries the magnetic head. In many applications
12 the magnetic tape makes contact with both the mandrel
13 surface and the rotating wheel carrying the magnetic
14 head.
Alternatively, to reduce wear, the mandrel
16 halves have been made air bearing to support the
17 tape as it is wrapped helically about the mandrel.
18 The air bearing support has been achieved hydrostatically
19 and hydrodynamically. With a hydrostatic air bearing
the mandrel halves contain holes through which air
21 is forced to provide the air bearing between tape
22 and mandrel. With a hydrodynamic air bearing, the
23 mandrel itself is rotated and the rotating action
24 creates a hydrodynamic air bearing to separate the
tape from the mandrel. To date, in both cases, the
26 magnetic head still makes contact with the tape and
27 does not fly relative to the tape.
28 An example of the-hydrostatic air bearing
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1 mandrel is shown in Shashoua et al, U.S. Patent 3,488,455. In this
patent the air bearing is achieved via holes in the mandrel through
-~ which air is forced. The rotary wheel or rotor upon which the head
is mounted produces its own hydrodynamic air bearing based upon the
availability of air from the mandrel and the speed of rotation of the
wheel. The head itself contacts the tape as the wheel rotates. Thus,
since the head is not flying, the problem of controlling head to tape
separation does not exist.
An example of the hydrodynamic air bearing is shown in the J.H.
~ Streets U.S. Patent 3,333,753. In this patent the air bearing is
created by rotating one-half of the mandrel and mounting the head on the
rotating half of the mandrel. The rotating mandrel half creates an
hydrodynamic air bearing for itself and a "squeeze air bearing" for
the stationary half of the mandrel as discussed in the patent. The
magnetic head in this Streets patent also makes contact with the mag-
netic tape. Therefore, the Streets patent does not have the problem
of careful control of tape support to assist in controlling head to
tape separation while flying a magnetic head relative to the tape.
As can be seen from the above prior art examples, the prior
art has taken the approach of keeping the rotating head in contact
with the magnetic tape. This technique carries enormous tape wear
and head wear problems. These wear problems can be
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1 eliminated by flying the rotating head relative to
2 the tape. One critical problem in flying the rotating
3 head relative to the tape is the necessity of providing
4 stable support for the tape along the path of the
rotating head. As is readily apparent, any distur-
6 bance which causes a variation in the thickness or
7 depth of an air bearing along the path of the rotating
8 head amplifies the problem of trying to control flying
9 height between the rotating head and the tape. Some
sources of perturbations are (1) discontinuity in tape
11 support and (2) lack of concentricity or identical
12 diameter in the two mandrel halves located on each
13 side of the rotor carrying the magnetic head.
14 With regard to concentricity, each air
bearing thickness is in the order of 1-3 mils and
16 the flying height relative to the rotating head is
17 in the order of 50 microinches. Accordingly, a 1
18 mil difference in the surface position between mandrel
19 halves, or bet~een the mandrel and the rotor carrying
the head has a catastrophic effect on flying height.
21 With regard to discontinuity in tape support,
22 a change from air bearing over the mandrel to no
23 air bearing over the rotor can cause instability
24 in the tape along the path of the rotating head.
This discontinuity may even cause the tape to crash
26 onto the mandrel, the rotor, or the head carried by
27 the rotor. Also a change in type of air bearing
28 from mandrel to rotor can cause instability in the
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l tape along the path of the rotating head. Thus,
2 either forcing air out past the rotor in the gap
3 between the rotor and each mandrel half, or relying
4 on a hydrodynamic air bearing for the rotor would
still create a discontinuity in the air bearing between
6 mandrel and rotor. The discontinuity causes the
7 tape to wobble or buckle near the path of the rotating
8 head.
9 SUl~MARY OF THE INV~NTION
. In accordance with this invention a stable
ll platform for supporting the magnetic tape along the
12 path of the rotating head has been achieved by providing
13 a support for the magnetic tape which is substantially
14 the same as the support provided the tape by the
two mandrel halves on each side of the rotor carrying
16 the magnetic head. Preferably, this support is a
17 hydrostatic air bearing for each of the mandrel halves
18 and also for the rotor. Of course, a hydrodynamic
19 effect will also exist with the rotor as the rotor
. is in motion. In addition, the width of the rotor
21 . should be substantially greater than the width of
22 the head carried by the rotor, so as to eliminate
23 any perturbation in tape support caused by slight
24 differences in diameter or concentricity between the
mandrel halves and the rotor. In other words, the
26 rotor should be designed so that it provides a stable
27 p1atform for the magnetic tape along the path of
28 the rotating head. In this way, the wobble or
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fluttering of the tape along the path of the rotating
2 head will be eliminated, and flying height between
3 the head and the tape may be more easily controlled.
4 The foregoing and other features and advan-
tages of the invention will be apparent from the
6 following more particular descrlption of a preferred
7 embodiment of the invention as illustrated in the
8 accompanying drawings.
9 BRIEF DESCRIPTION OF DRAWINGS
FIGURE 1 shows one preferred embodiment
11 of the invention whereln the rotor is much wider
12 than the head, which the rotor carries, and provides
13 an air bearing to the magnetic tape via air forced
14 through holes in the rotor.
FIGURE 2 is a cross-section of the surface
16 of the air bearing rotor bounded by air bearing mandrel
17 halves, and showing the flow of air through the rotor
18 to provide a stable platform for the magnetic tape
19 to ride on along the path of the rotating head.
FIGURE 3 shows a pressurized air-bearing
21 rotor mounted on a shaft with a section cut away
22 to show the construction of the rotor.
23 DESCRIPTION OF PREFERRED EMBODIMENT
24 In FIGURE 1 the pressure rotor 10 is shown
mounted between the two mandrel halves 12 and 14.
26 The rotor carries the magnetic head 16 to scan the
27 tape 18. Tape 18 is guided in an arcuate path about
28 the rotary path of the head by being wrapped helically
:
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1 about the mandrel and rotor assembly. Alternatively,
2 the tape might be wrapped. cylindrically about a
3 portion of the mandrel and moved in the direction of
4 the axis of the mandrel.
Rotor 10 has holes in its surface for permit-
6 ting air under pressure to flow through the surface
7 of the rotor to provide the air bearing between the
8 rotor and the tape 18. The mandrel halves 12 and
9 14 are also air bearing which is achieved by forcing
air through porous material making up the surface
11 of the mandrel. Alternatively, the mandrel halves
12 12 and 14 could have holes in their cylindrical
13 surfaces through which the air could be forced to
14 form the air bearing between the mandrel and the
tape 18.
16 FIGURE 1 graphically displays that the
17 rotor 10 is much wider than the head 16 which it
18 carries. This extra width in the rotor, coupled
19 with the fact that the rotor is pressurized to provide
an air bearing, provides a stable platform upon which
21 the tape 18 can rest as the rotating head scans across
22 the tape. Stated another way, the preferred stable
23 platform is a continuous uniform air bearing along
24 the path of the rotating head.
Discontinuities in the transition region
26 from mandrel half to rotor no longer affect the flying
27 helght between the rotating head and the tape, because
28 they have been isolated from the path of the rotating
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1 head. The isolation is due to the fact that the ajr bearjn~ on the
pressurTzed rotor is substantially the same as the air bearing on the
mandrel halves 12 and 14, and is also due to the width of the rotor
separating the head from the discontinuity in height between rotor
and mandrel halYes.
In FIGURE 2 the manner in which the invention provides
a stable platform for the tape along the rotary path of the head is
clearly shown. The surface of rotor 10 is shown in cross-section
between mandrel halves 12 and 14. Head 16 is shown mounted in the
rotor 10. The position of the tape 18 is shown as it rides on an air
bearing above the pressure rotor 10 and the air bearing mandrel halves
12 and 14. The same elements in FIGURES 1 and 2 have been given the
same reference numeral; however, the rotor identified by reference
numeral 10 in both figures is slightly different. In FIGURE 1 rotor
10 has a nonporous surface with holes to supply air, while in
FIGURE 2 rotor 10 has a porous surface to supply air.
The magnetic head 16 is a flying head which aerodynamically
creates a bulge in the tape 18 as the head 16 moves under the tape.
A description of this magnetic head will be found in U.S. Patent
No. 3,821,813, issued June 28, 1974 and entitled "Wasp-Waist Head
For Flying Flexible Magnetic Storage Medium Over Head".
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1 As indicated in FIG~RE 2, the surface of
2 the mandrel halves 12 and 14 and the surface of the
3 rotor 10 are usually at different levels due to
4 dimensional tolerances of components. The difference
in level between a rotor and a mandrel half is
6 general,y no more than 1 mil. However, the tape
7 18 is flying in the order of 2-3 mils above the surface
8 of the mandrel or the rotor, and consequently, a
9 level shift of 1 mil in the transition from mandrel
to rotor puts a sizable perturbation in the level
- ` 11 of the tape 18 above the mandrel or the rotor. This
12 perturbation has been moved laterally away from the
13 rotary path of the head 16 because of the width of
14 the rotor 10. The width of the rotor 10 is not critical,
except that it should be sufficient such that pertur-
16 bations existing at the discontinuity between mandrel
17 half and rotor will be damped out before they reach
18 the path of the head 16. Stated another way, the
19 rotor 10 has sufficient width so that a stable platform
for the tape 18 exists in the immediate area of the
21 head 16.
22 The air bearing in FIGURE 2 is achieved
23 by use of a porous material to form the outer surface
24 of the mandrels 12 and 14 and the rotor 10. Rotor
10 has nonporous sidewalls 20 and 22 which define
26 a plenum chamber 24 which is pressurized~ The porous
27 surface 26 of the rotor then surrounds the head 16
28 and covers the entire outside cylindrical surface
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1 of the rotor 10. Air under pressure in the plenum
2 chamber 24 is forced into the porous material 26,
3 The air works its way through the porous material
4 and provides a uniform air pressure out the surface
of tne porous material adjacent to the tape 18.
6 The flow of air into and out of the porous
7 material is depicted by the arrows in FIGURE 2. Of
8 particular interest is the fact that the corners
9 of the rotor and of the mandrel halves are rounded
and made of porous material so that the air passing
11 out of these corners will tend to support the tape
12 in the transition region 28 between a mandrel half
13 and the rotor.
14 The surface of the mandrel halves 12 and
14 is substantially the same as the surface 26 of
i 16 the rotor 10. The plenum and sidewalls for the mandrel
17 halves 12 and 14 are not shown in the cut-away of
18 the mandrel halves in FIGURE 2. These do exist and
19 do provide the same type of air bearing out the surface
of t~e mandrel halves 12 and 14 just as the air bearing
21 provides out the surface of the rotor 10. The air
22 bearings from both the rotor and mandrel preferably
23 have the same thickness and stiffness.
24 By provi.ding a hydrostatic air bearing
in both the mandrel halves and in the rotor, a con-
26 tinuity of air bearing or continuity of the support
27 of -~he tape is provided across the mandrel and rotor.
28 This continuity adds substantially to the stability
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1 of the tape 18 in the region of the rotary path of
2 head 16. While the manner in which the hydrostatic
3 bearing is achieved is not critical, it is preferable
4 to use the same type of hydrostatic bearing in a
rotor as exists in the mandrel halves. The hydrostatic
6 bearing might be achieved by forcing air through
7 a porous material or by forcing air through holes
8 in a nonporous material. The important thing is
9 that the strength of the air bearing should be sub-
stantially the same over the rotor as over the mandrel
11 halves, so as to achieve a continuity of air bearing
12 from mandrel half to rotor to other mandrel half.
13 An example of the structure of the pressure
14 rotor is shown in FIGURE 3. The rotor 10 is mounted
on a hollow shaft 30. The rotor has a hub 31 which
16 is tied to the shaft via a threaded bolt 32. Inside
17 the rotor is an annular plenum chamber 34 that goes
18 around the entire rotor except in the region 33 where
19 the head is to be mounted. Chamber 36 is provided
for mounting a head through the hole 38 in the porous
21 surface 40 of the rotor.
22 The rotor has nonporous walls 42 and 44
23 which support the cylindrical porous surface 40 of
24 the rotor. The nonporous w~lls and hub of the rotor
may be constructed of aluminum, for example. Possible
26 choices for the porous surface of the rotor could
27 be sintered bronze or porous ceramics.
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1 Wall 42 is constructed as an integral part
2 of the nonporous hub 31 making up the rotor. Also
3 integrated into this nonporous hub 31 is the chamber
4 36 for mounting the magnetic head.
To provide air to the porous surface 40
6 immediately adjacent the hole 38 for the head,
7 channels 46 and 48 are cut. Channel 46 is cut in
8 the hub 31. Integral with the other wall 44 of the
g pressure rotor is the top of the chamber 36. In
this top section of the chamber 36, the second channel
11 48 is cut to provide air to the porous surface 40
12 adjaeent the head. Thus the channels 46 and 48 are
13 provided to communicate to the plenum chamber 34
14 sinee the plenum ehamber is not placed in the region 33
of the head mount. Of course, an alternate choice
16 would be to leave the plenum ehamber eompletely annular
17 all around the entire pressure rotor and seal the
18 plenum chamber after the magnetic head has been mounted
19 in the rotor.
Air flow to the plenum chamber 34 is provided
21 through the hollow center 50 of the shaft 30. The
22 shaft eenter 50 eommunieates with an annular ehamber
23 52 in the shaft through a holes 54 (one shown). An
24 annular ehamber 52 communieates to the plenum chamber
34 through holes 56 drilled in the hub 31 at regularly
26 spaced intervals around the hub. Holes 54 in the
27 shart between the shaft center 50 and the annular
28 chamber 52 are also regularly spaced around the shaft.
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l Thus air under pressure enters the hollow center
2 50 of the shaft 30, passes throuyh the holes 54 in
3 the shaft, and into the annular chamber 52 of the
4 shaft. From there the air moves into holes 56 (one
shown) in the hub 31, and finally to the plenum charrber
6 34 in the pressure rotor.
7 It t~ill be appreciated by one skillea in
8 the art that there are many configurations that the
9 pressure rotor could assume, and that there is nothing
critical in the structure of the rotor as shown in
11 FIGURE 3. The significance of the invention is that
12 the rotor is much wider than the magnetic head which
13 it carries. An additional feature is that the rotor
14 provides a bearing for the magnetic tape similar to
the bearing provided by the mandrel. As a result,
16 a very stable platform exists to support the magnetic
17 tape all along the entire length of the path of the
18 rotating head.
l9 What is claimed is:
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