Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
132~7
IMPROVED TAPE TRANSPORT CARTRIDGE
Background of the Invention:
The present invention relates to tape transports and
particularly to apparatus for causing movement of a
`q magnetic recording tape relative to a recording and/or
playback head. More specifically, this invention is
directed to an improved tape drive system in which the
tension imposed on the tape is a lower average tension
and more uniform tension from beginning of tape (BOT) to
end of tape (EOT~.
Tape transport mechanisms are, of course, well known
in the art. Tape transports of the same general type as
that to which the present invention is directed are
e~emplified by the apparatus disclosed in U.S. Patent
Nos. 3,620,473, 3,974,982 and 4,455,001 which are
assigned to the assignee of the present invention. A
tape transport will typically include a tape handling
mechanism, a magnetic tape on which a program may be
stored, a read/write head and a drive motor. One type
of tape drive system employs a peripheral drive belt to
drive the tape packs. The belt is arranged to run in a
path which contacts the tape packs, and the belt is
driven by a capstan. A typical peripheral belt drive
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system may have a spring loaded idler to apply
tension to the drive belt and a brake to establish a
differential rotational velocity of the tape to
establish a necessary tape tension to maintain the
tape in contact with the read/write head and avoid
tape spillage.
A particular problem with the prior art
relates to the absolute levels of tape tension and
the average tape tension from BOT to EOT. However,
in practice, the tape tension increases significantly
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at the beginning of the tape and at the end of the
tape, and the average tape tension is higher than the
desired constant level. The high tension levels at
BOT and EOT cause stresses which, in severe cases,
~;~ 15 can distort the tape. Moreover, the increased
average tape tension results in wear of the tape and
the read/write head, wastes power in that more input
power is required to drive the unit, and generally
results in less than ideal transfer of tape from reel
~, 20 to reel.
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Summary of the Invention:
In accordance with a particular embodiment
of the invention, there is provided a tape transport
including:
a base for mounting tape transport
elements;
first tape transport means rotatably
mounted on said base;
second tape transport means rotatably
mounted on said base;
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maqnetic tape means on forming tape packs
each of said tape transport means and extending
between said tape transport means for the transfer of
tape between said tape transport means;
drive belt means for contacting the
periphery of said tape packs on each of said first
and second tape transport means to transfer tape
between said first and second tape transport means;
drive means for driving said drive belt
s 10 means;
*, first rotary brake means adjacent said
`, first tape transport means and in contact with said
drive belt means adjacent said first tape transport
means;
second rotary brake means adjacent said
.~ second tape transport means and in contact with said
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,; drive belt means adjacent said second tape transport
.:i means;
. said first brake means being positioned
~ 20 relative to said first tape transport means to
:~ establish a first predetermined angular relationship
between said drive belt means and the tape on said
~ first tape transport means; and
h said second brake means being positioned
i 25 relative to said second tape transport means to
establish a second predetermined angular relationship
between said drive belt means and the tape on said
` second tape transport means.
, The above discussed problems of the prior
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., 30 art are overcome or reduced by the present invention,
' wherein a pair of rotary brakes are incorporated in
., the peripheral belt drive system. The dual rotary
brakes are positioned adjacent the tape packs and are
positioned so as to increase the separation between
~: 35 the drive belt and the tape in the vicinity where the
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tape is exiting or joining the tape pack and to
increase the angle of contact between the drive belt
and the tape pack. As a result, contact between the
drive belt and tape is reduced in the vicinity where
the tape is exiting or joining the tape pack, and
contact between the drive belt and the tape pack is
concentrated in the location of maximum interlayer
pressure of the tape. This results in a system
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::. having the significant improvements and advantages of
~ 10 this invention over the prior art.
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Brief Description of the Drawinas:
Referring now the drawings, wherein like elements
are numbered alike in the several FIGURES:
FIGURE 1 is a top plan view of a dual brake tape
transport in accordance with a preferred embodiment of
the present invention.
FIGURE 2 is a schematic representation of the tape
transport of FIGURE 1 at a beginning of tape mode.
- FIGURE 3 is a schematic representation of the tape
~ 10 transport of FIGURE 1 at an end of tape mode.
r'. F~GURES 4 and 5 show schematic representations of
~'7.' the prior art single brake tape transport at beginning
of tape and end of tape modes, respectively.
- FIGURE 6 is a graph illustrating a typical tape
15 tension curve for a typical prior art tape transport
system.
FIGURE 7 is a graph showing an improved typical tape
tension curve for a tape transport system of the present
invention.
~ 7
~-.i 20 DescriDtion of the Preferred Embodiment:
Referring jointly to FIGURES 1, 2 and 3, a tape
transport unit in accordance with a preferred embodiment
of the present invention is shown, FIGURE 2
schematically diagramming the path of the recording tape
25 and the drive belts. In the tape transport of FIGURES
1, 2 and 3, the recording tape is contained in two reels
10 and 12 rotatably mounted on a cartridge base 11.
Depending on the direction of tape motion, one reel will
Y function as a supply reel while the other reel acts as a
30 take-up reel. Each of reels 10 and 12 is affised to a
precision ball bearing mounted shaft which permits reel
- rotation. In accordance with the present invention, no
drive or braking power is transmitted to either of the
reels via the free turning reel shafts.
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The tape transport of FIGURES 1, 2 and 3 includes,
in addition to the reels 10 and 12, a maqnetic tape 14
which is transferred between the reels, a drive motor 16
and a rotatable capstan 18 mounted on cartridge body 11
and a drive belt 20 which couples motor 16 to capstan 18
whereby the motor will drive the capstan. The tape
transport also includes a peripheral belt 22 which
' estends over capstan 18 and about the periphery of the
tape packs on reels 10 and 12 as may best be seen from
FIGURE 2. The tape transport also includes a read/write
head 24 over which tape 14 passes and contacts.
The path for the recording tape 14, assuming that
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reel 10 is functioning as the supply reel and reel 12 is
functioning as the take up reel in the forward direction
`~$ of operation, is from the periphery of reel 10 across a first tape guide 26, then across the working gap of the
~-~ head assembly 24, then through a photoelectric beginning
-~ of tape (BOT) end of tape (EOT) sensor which has been
indicated generally at 28, then across a second tape
guide 30 and into the periphery of the tape pack on
take-up reel 12. It should be noted that the only
transport element which contacts the tape oside surface
outside of the tape packs is the working gap surface of
the read/write head 24. The back side of the tape,
rather than the oxide surface, will contact the tape
guides 26 and 30. The absence of extra transport
elements in contact with the tape oxide surface helps
minimize oxide wear and thus prolongs tape life. It is
also to be noted that the BOT/EOT sensor 28 has been
omitted from FIGURES 2 and 3 in the interest of
facilitating understanding of the present invention.
The tape pack and elements described above are known in
` the art.
Of course, if reel 12 is functioning as the supply
. reel and reel 10 is the take up reel, the path for
recording tape 14 will be the reverse of that described
above.
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The path for the endless peripheral
driving belt 22 (in the forward direction), which
is preferably a seamless plastic film material such
as a polyimide film such as Kapton~ or a polyester
film such as Mylar~, is about part of the
periphery of the tape pack on reel 10 about a first
rotary brake 32(b), around an idler roller 35,
around a belt tensioning idler roller 34, about an
idler 33, about a second rotary brake 32(a), around
a portion of the periphery of the tape pack on reel
` 12, about a capstan 18 and back to its starting
point on the tape pack on reel 10. Brakes 32(a)
and 32(b) are magnetic hystereses brakes known in
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the art, but they could also be friction brakes.
The belt tensioning idler roller 34 is rotatably
~ mounted on a shaft on a first end of a spring-
.~, loaded arm 36, and a counterweight 38 is mounted on
the opposite end of arm 36. Arm 36 is mounted on a
rotatable shaft 37 which is mounted in bearings in
housing 39 in base 11. The spring for tensioning
~' arm 36 is indicated at 40. Spring 40 is a torsion
i spring which has one end grounded at post 42 to
base 11 and the other end of spring 40 attached to
a post 44 on arm 36, and the body of spring 40 is
coiled around housing 39. Spring 40 serves to
maintain a substantially constant tension on belt
22 as the tape 14 travels from beginning of tape to
end of tape by urging arm 36 and idler roller 34 in
the direction to impose a tension load on belt 22.
The counterweight 38 serves to dynamically balance
arm 36 to prevent variations in the tension of belt
22 which would otherwise result from vibration
forces to which the tape transport unit is
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subjected. The direction of travel of belt 22 will
be from whichever tape reel is the supply reel,
: ` across the dual brakes and idler/pulley system, to
the take up reel.
The capstan 18 is driven by motor 16 via
~ drive belt 20. Drive motor speed may be controlled
; in the conventional manner, using feedback from a
tachometer
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mounted on the capstan. The direction of rotation of
the motor and capstan and drive belt will depend on
which reel is to function as the supply reel and which
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the take up reel. Tape driving power is transmitted
- from capstan 18 to the peripheral drive belt 22 and from
belt 22 to the outermost layer of the tape 14 on each of
~- reels 10 and 12. Power transmission is effected through
the normal static frictional forces existing at the
belt-capstan interface and at the belt-tape interfaces.
The peripheral belt 22 is maintained under adequate
tension at all times by means of the spring-loaded belt
` tensioning arm 36 and the roller 34 mounted thereon.
-; The spring-loaded belt tensioning arm and associated
roller also serve to compensate for small changes in the
total linear distance around the belt path which occur
with changing disposition of the total tape footage
between the two reels. The belt-capstan and belt-tape
interfacial friction forces are adequate to drive the
tape without significant slippage, even during rapid
start-stop operation.
- 20 A comparison of FIGURES 1 and 2 hereof with FIGURES
- 1 and 3 of U.S. Patent 4,455,001 shows that this
invention differs from the structure shown in FIGURE 1
of U.S. Patent 4,455,001 by: (1) the inclusion of a pair
of rotary brakes 32(a) and 32(b), rather than the single
rotary brake of the prior patent; (2) the location of
; the rotary brakes 32(a) and 32(b) adjacent the tape
reels at locations to increase the separation of the
drive belt 22 from the tape on reels 10 and 12 and to
increase the angles (a) and (b) at which the drive belt
contacts the tape pack on each reel (as compared to the
prior art angles of U.S. Patent 4,455,001 which are
shown in FIGURES 4 and 5); (3) by the inclusion of idler
35 which serves to establish a desired angle of wrap
around brake 32(b); and (4) by the inclusion of idler 33
~ 35 at the location where the brake was placed in the prior
`~ patent.
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The use of dual rotary brakes, i.e., brakes 32(a)
and 32(b) and their locations relative to the tape reels
10 and 12 are the critical features of the present
invention. The presence and location of the two rotary
brakes 32(a) and 32(b) results in a lower average
tension on the magnetic tape 14 from BOT to EOT, and it
also results in significantly lower tape tension at the
beginning of the tape and at the end of the tape. The
lower average tape tension and the lower tension levels
at the beginning and end of the tape enhance and improve
tape life, because high tension is detrimental to tape
life; and these lower tension levels also lead to
several other important advantages which will be
discussed hereinafter.
It is well known in tape transport systems to set
the torque of a single rotary brake to obtain a desired
tape tension to produce optimum tape/head interface
pressure. In the system of the present invention, the
total torque of the two brakes is equal to or slightly
20 less than the torque required for a single brake, that
brake torque is divided approximately equally between
the two brakes so that the torque level o~ each of the
two brakes is egual to or less than one half that of a
single brake.
Referring to FIGURES 6 and 7, graphs are presented
which show typical tension curves for belt driven tape
transports based, respectively, on the prior art and
this invention, where the transports are used for the
same application, and operated under the same
30 conditions,- and using the same tape and tape reels.
FIGURE 6 shows tape tension T versus tape travel from
BOT to EOT. It is to be noted that tape tension varies
from about 2.4 oz. to 4.5 oz., with significant
increases in tension occurring as the tape approaches
35 the BOT or EOT. FIGURE 6 depicts a tension pattern well
known in the art and which is often referred to as a
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~butterfly~ or "bowtie~ curve or pattern. In the system
which is charted in FIGURE 3, the required tension is
2.4 oz.; and tension above 2.4 oz. for the duration of
time from ~OT to EOT represents both a power drain and
excessive wear on the tape.
Referring to FIGURE 7, tension curves are shown for
a system comparable to that on which FIGURE 6 was based,
: but employing the dual brake configuration of the
present invention. As can be seen, the absolute levels
of tension are much lower, ranging from 1.2 oz. to 2.9
oz.; and the curves are much flatter and closer
together, which means that the average tape tension from
BOT to EOT is lower and approaches the absolute minimum
needed for proper operation of the system.
Because of the lower average and absolute values of
tape tension obtained by the present invention, as
illustrated in FIGURE 7, tape life is increased, and
distortion of tape, particularly at the beginning and
end of the tape travel, is reduced or eliminated. Also,
lower average tape tension results in lower wear of
read/write head 24 and reduces the wearing off of
particles from the head which can contaminate the tape
and/or the transport system; lower power is required to
drive the unit (i.e., the unit is more efficient),
because the prior art power drain is reduced; and tape
transfer from reel to reel is enhanced because of the
more even interface between tape and the read/write head.
The advantages realized from the dual brake system
of the present invention are unexpected and unobvious.
While the operation of the present invention and the
esplanation for achievement of its several important
advantages are not fully understood, a theory has been
developed which may offer an explanation. However, it
is to be understood that this theory is only the best
present understanding, and it may not be correct or
accurate; and the invention is not bound to or limited
1~2~ ~7
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by this theory. The two brakes 32(a) and 32(b) are
positioned to maximize the angles (a) and (b) at which
the drive belt 22 contacts the tape packs. This means
that the separation of the drive belt from the tape is
increased (as compared to the prior art single brake
system of U.S. Patents Nos. 3,620,473, 3,974,982 and
- 4,555,001) where the tape enters or leaves the tape pack
(which is an area where the tape is loosest on the tape
pack and where slippage between the drive belt and the
tape can occur most easily), and the contact between the
drive belt 22 and the tape packs is concentrated at the
rear of the tape pack, i.e., at the area of maximum
interlayer pressure of the tape pack. This results in
a system in which more tape mass is being driven by the
belt, and it generates a more constant instantaneous
linear velocity of the tape packs. This is
distinguished from the prior art systems in which the
drive belt contacts the tape pack at a lower angle which
results in a tendency to drive just the first few layers
; 20 of tape (i.e., driving lower tape mass), which results
in uneven tape tension as the tape is being wound up.
Tape tension is established by establishing a slight
differential instantaneous linear velocity between the
tape esiting the payout reel and the tape entering the
take up reel, with the take-up reel operating at a
slightly greater velocity than the pay-out reel. It is
known in the art to establish this differential
instantaneous velocity by a brake in the path of the
drive belt. The use in the present invention of dual
brakes to establish this differential instantaneous
velocity, and the placement of the dual brakes to
increase the angles (a) and (b) is believed to establish
a symmetrical load on the belt path which, in turn,
results in a more constant differential instantaneous
;~ 35 tape velocity in the system. And, it is believed that
`, the more constant differential instantaneous velocity
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results in a more constant average tape tension, and
lower absolute tape tension, particularly in the BOT and
EOT regions, thus leading to the several unexpected
advantages of this invention.
By way of example, as seen in FIGURES 2 and 3, in
the present invention the angles (a) varies from a
minimum of 30 to a maximum of 33.5 and the angle
(b) varies from a minimum 20 to a maximum of 35 as
- the tape goes from initially being all on reel 12 to
being all on reel 10. By way of contrast, in a prior
art single brake system using the same tape packs, angle
(a) varies from a minimum of 12 to a maximum of 23
and angle (b) varies from a minimum of 10 to a
maximum of 18 as the tape goes from initially being
all on reel 12 to being all on reel 10. It is believed
that the angular relationship of the present invention
wherein both angles (a) and (b) are always at least
20 contributes to the improved results of the present
invention.
While preferred embodiments have been shown and
described, various modifications and substitutions may
be made thereto without departing from the spirit and
scope of the invention. Accordingly, it is to be
understood that the present invention has been described
by way of illustrations and not limitation.
What is claimed is:
