Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Invention
This invention pertains generally to transport apparatus and more
particularly to transport apparatus in which a length of pliant material is
fed between supply and take-up rolls in edge driven relationship with a drive
capstan.
In transports of the type described in United States Patents
3,370,803 and 3,370,804, for example, a pliant material such as magnetic
recording tape is wrapped to form supply and take-up rolls, the outer edges
of which are engaged directly by a drive capstan to feed the tape between
the rolls. In order to maintain control of the tape in the region between
the rolls, the take-up roll must be pressed against the capstan with a
greater force than the supply roll. This force differential causes the tape
to pass through the interface between the take-up roll and capstan at a greater
velocity than that with which it passes through the supply roll capstan inter-
face, thereby maintaining a slight tension in the tape and preventing the
formation of undesired tape loops between the rolls. The loose tape can
cause a failure in the handling of the tape, and at high tape speeds the
loss of control can be catastrophic.
To prevent formation of such loops, the proper forces must be
established immediately when tape movement begins, and the force magnitudes
must also be reversed immediately each time that the direction of tape
movement is reversed. This is particularly important when the direction of
tape movement is reversed repeatedly, as, for example, in the recorders
utilized in digital operations, because, under these circumstances, tape
control is more difficult to maintain than in the case of analog recordings
where the tape is fed continuously in one direction.
Force systems heretofore provided are of two basic types - dynamic
and static. In dynamic systems there is a source of power, such as a motor
or other rotating component, which is utilized through various coupling means
to urge t~e take-up roll against the capstan with a force greater than that
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urging the supply roll against the capstan, The ~803 and '804 patents noted
above disclose such systems. In the former, a string wrapped about the
capstan shaft transmits power to the appropriate ~take-up) carriage, and in
the latter, strings wrapped about the roll spindles draw power from these
spindles as they rotate, to respectively urge the take-up roll toward the
capstan and the supply away from the capstan. Also, in United States Patent
3,408,016, it is shown how electric motors may be utilized to urge the roll
carriages toward the capstan with appropriate forces
These dynamic force systems generally meet the requirements for
immediately urging the carriages against the capstan with appropriate force
regardless of direction of tape motion or the rapidity with which this
direction is changed, They are, however, not suitable for all requirements,
in that they may be too expensive, or the power source may be inconvenient
or even impossible to couple to the carriages, or, in some cases, may be
insufficient for the purpose.
To overcome these objections to dynamic force systems, various
static force means have been provided, as for example in United States Patents
3,370,804 and 3,960,342. In such systems, no source of power is utilized to
urge the take-up carriage toward the capstan, but rather, simple static
forces (e.g., friction or spring) are used to yieldably resist the movement
of the take-up roll away from the capstan as roll diameter increases when
tape is wound thereon, In this manner a desired take-up force - even a very
high one - is easily obtained, by merely increasing or decreasing friction
or the strength of a spring, in order to increase or decrease the resistance
to the movement of the take-up carriage away from the capstan
Static forces in general have a serious deficiency, however,
inasmuch as mere reversal of the direction of tape movement will not
immediately and automatically reverse the magnitudes of the static forces
acting to press the tape rolls against the capstan.
In the static friction force systems previously disclosed, such as
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'804, for instance, sliding friction between the carriages and the transport
base is constantly present and resists movement of the carriages in either
direction (toward or away from the capstan), A spring common to both
carriages and of sufficient strength to overcome this frictional force is
coupled between the carriages and acts to draw them toward the capstan so
that the tape rolls are maintained in contact with the capstan at all times.
As a result, the movement of the carriage which has been operating in the
take-up mode (e.g., forced to move away from the caps~an as the roll diameter
increased) has been resisted by the combined forces of friction and that of
the common force spring, and penetration (indentation) of the capstan tire
by the take-up roll is therefore relatively great. On the other hand,
penetration of the supply roll into the capstan tire is relatively little,
inasmuch as it has been urged toward the capstan as its diameter decreased,
by only the force of the common spring minus the resistive force of friction.
ln short, the required force differential is brought about only because the
roll diameters change during winding and unwinding of tape, forcing the
carriages to move against greater static resistive force in one direction
than the other, as a result of which one roll presses against the capstan
with a greater force than does the other.
The problem with such a friction force system derives principally
from the fact that as long as the direction of tape movement remains un- -
changed, the prevailing forces will also remain unchanged, even if tape
movement ceasas altogether or proceeds intermittently. These circumstances
would be desirable for completely unidirectional operation, but act to
defeat rapid force reversals during bi-directional operation, If the forces
are established for a particular direction of tape movement and remain un-
changed when the tape stops in the normal course of a reversal, it will be
evident that when the tape begins to move in the opposite direction, it will
do so with the forces exactly opposite to what they should be: the new take-
up roll will be pressing into the capstan with relatively little force, and
,
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lV72993
the new supply roll will be pressing against the capstan with relatively
high force. This situation will continue to a diminishing extent until
enough tape has been removed from the new supply roll and wound onto the new
take-up roll to force the new take-up carriage to start moving against the
frictional resistance. Until this force reversal is literally complete,
tape control will be compromised, and failure is likely to occur.
Static spring force systems such as described in '342 present
somewhat different problems, particularly in the practical sense. In the
simplest such system, a spring is attached to each of the carriages and is
alternately tensioned so that the carriage acting in the take-up mode (moving
away from the capstan) will always be urged toward the capstan with greater
force than is the other (supply) carriage. In order to prevent the occurrence
of force changes as carriage positions change, low rate springs are generally
used, and because of this considerable movement of the spring anchor points
will be required to tension or untension the springs. With such systems,
there is no automatic reversal of the spring forces upon reversal of the
direction tape movement, and factors such as the strength of the springs and
the amount of movement required to tension or untension them have made it
impractical to utilize electro-mechanical devices for reversing the forces
of the springs.
Summary of the Invention
According to the present invention there is provided in a transport
apparatus for feeding a length of pliant material between supply and take-up
rolls in edge driven relationship with a drive capstan: carriage means
carrying the take~up roll for movement toward and away from the capstan,
static force means for yieldably resisting movement of the take-up roll away
from the capstan with a predetermined force, and means for automatically and
instantaneously coupling the force means to the take-up carriage to press
the take-up roll against the capstan with the predetermined force at the
outset of tape movement toward the take-up roll.
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Brief Description of tlle Drawings
In the accompanying drawings, whi.ch illustrate exemplary embodiments
of the present invention:
Figure 1 is a fragmentary perspective view, partly broken away, of
one embodiment of transport apparatus incorporating the invention.
Figure 2 is a top plan view, partly broken away, of a portion of the
transport apparatus of Figure 1, illustrating the manner in which the take-
up roll is mounted and urged toward the drive capstan.
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~ig. 3 is a cross-sectional view taken along
line 3-3 of Fig. 2.
Fig. 4 is a top plan view similar to Fig. 2,
illustrating a second embodiment of the invention.
S Fig. 5 is a cross-sectional vi~w taken along
line 5-5 of Fig. 4.
Fig, 6 is a top plan view similar to Fig. 2,
illustrating the third embodiment of the invention.
Fig. 7 is a cross-sectional view taken along
line 7-7 of Fig. 6.
Description of the Preferred Embodiments
The transport apparatus illustrated in Figure 1
includes a generally planar deck or base 11 on which a drive
capstan 12 is rotatively mounted. Toward its outer
periphery, the drive capstan is provided with an annular
tire 13 of suitable resilient material, A reversible drive
motor 14 is mounted below the deck, with its output shaft
14a extending through a suitable opening (not shown) in the
deck. A drive roller 16 is mounted on the output shaft
and engages the outer periphery of the capstan for driving
the same about its axis in either a clockwise direction or
a counterclockwise direction, as viewed from above.
A length of pliant magnetic recording tape 19 is
wrapped about hubs 21, 22 to form rolls 23, 24. The
peripheral edges of the rolls engage the peripheral edge
of capstan 12 in a driving relationship, whereby rotation
of the capstan serves to feed the tape from one roll to the
other, depending upon the direction of rotation. Between
rolls 23 and 24, the tape is trained to form a loop
a~
30 B about guide rollers 26, 27. A transduceF head engages
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the tape between the guide rollers for recording and
playback of signals on the tape.
Rolls 23, 24 are mounted on pivot arms 31 and
thereby adapted for movement toward and a~ay from tlle drive
capstan. The pivot arms are mounted below the deck on
stationary posts 32 which are affixed to the deck by suitable
means such as screws 33. Spindles 34 extend upwardly from
the pivot arms and pass through arcuate slots 36 formed in
the deck for receiving hubs 21, 22. Guides 37 are affixed
to the underside of the deck for supporting and guiding the
ends of the pivot arms on which the tape rolls are mounted.
A ~ension spring 38 is connected between the pivot arms
an~ yieldably urges the tape rolls against the capstan.
A force differen~ial system is provided for
increasing the force on the take-up side whenever the
direction of tape movement is reversed and thereafter main-
taining a greater force on the take-up side than the supply
side of the capstan. Since bi-directional tape movement
is contemplated, similar force system elements are mounted
20 ~ on both of the pivot arms, with the elements on the ~ep
arms being arranged as mirror images of each other.
The force system elements associated with hub 22
and tape roll 24 are illustrated in Figures 2 and 3. These
elements include a clutch disk 41 which is rotatively
mounted on post 32. A stationary clutch plate 42 is affixed
to the post on one side of disk 41, and a pressure plate
43 is mounted on the post on the opposite side of the disk.
Plate 43 is movable axially of the post and constrained
. against rotation. Layers of material 44 having a relatively
high coefficient of friction are provided between the
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confronting surfaces of disk 41 and plates 42, 43. A
compression spring urges the disk and plates toget~er, and
a nut 47 mounted on post 32 provides means for adjusting
the force exerted by the spring.
An electrically energizable solenoid 51 is mounted
on pivot arm 31, and a flexible brake band 52 is trained
about the clutch disk 41. One end of the brake band is
connected to a post 53 affixed to the pivot arm, and the other
end of the band is connected to the plunger 51a of the solenoid
O-rings 54 are mounted in peripheral grooves on the clutch
disk, and a brake pad 56 is mounted on the inner surface of
band 52 for f^ictionally e~gaging the O-rings when the
solenoid is energized. As discussed more fully hereinafter,
the solenoid is positioned ~.. the pivot arm in such manner
that the force produced by energization of the solenoid tends
to pivot the arm and urge the roll carried thereby against
the capstan.
Operation and use of the transport apparatus and
differential force system of Figures 1-3 can be described
as follows. Initially, it is assumed that motor 14 is
energized for driving capstan 12 in the clockwise direction,
as viewed from above, which causes the tape te be fed from
roll 23 to roll 24. With the tape moving in t~is direction,
the solenoid associated with supply roll 23 is deenergized,
25~ and the solenoid associated with take-up roll 24 is energized.
With the solenoid on the supply side deenergized, the pivot
arm 31 which supports supply roll 23 is free to pivot about
post 32, subject only to the force of spring 38. On t'ne
take-up side, the pivot arm and clutch disk 41 are locked
~ together by brake band 52. As the diameter of the take-up
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roll increases, the clutch disk is forced to rotate between stationaryplate 42 and pressure plate 43, producing a high force between the take-up
roll and capstan,
When the direction of tape movement is reversed, the solenoid
associated with roll 23 will be energized, and the solenoid associated with
roll 24 will be deenergi~ed. The initial energization of the solenoid
causes arm 31 to pivot in a clockwise direction, as viewed from above,
urging tape roll 23 against the capstan with increased force. This increased
force causes roll 23 to penetrate into the resilient outer portion of the
capstan even before the diameter of roll 23 increases sufficiently for the
frictional force of the clutch to become effective. Deenergization of the
solenoid associated with roll 23 produces an instantaneous decrease in the
force between roll 23 and the capstan.
A second embodiment of a differential force system for use in the
transport apparatus of Figure 1 is illustrated in Figures 4 and 5, In this
embodiment, an idler wheel 61 is rotatively mounted on post 32, and a tension
spring 62 is connected between the deck and a pin 63 affixed to the wheel
for urging the wheel to rotate in a counterclockwise direction, as viewed
in Figure 4. Rotation of the wheel is limited by a stationary pin 60 and
a slot 61a formed in the wheel.
Means is provided for locking the idler wheel to pivot arm 31.
This means includes a solenoid 64 mounted on the pivot arm and a bràke
band 66 trained about the idler wheel One end of the band is connected
to a pin 67 affixed to the pivot arm, and the other end of the band is
connected to the solenoid plunger 64a. O-rings 62 are mounted in peripheral
grooves on the idler wheel, and a brake pad 69 is mounted on band 66 for
engaging the 0-rings when the solenoid is energized.
Means is also provided for retarding the movement
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of idler wheel 61 when solenoid 64 is deenergized. This
means includes a one-way clutch 71 mounted on post 32 and a
brake ring 72 mounted on the clutch, with a layer of frictional
material 73 interposed between the brake ring and clutch.
A spring 74 and an adjusting screw 76 provide means for
adjusting the pressure exerted by the brake ring on the clutch.
For tape roll 24, the one-way clutch is installed for free
rotation in the clockwise direction, as viewed in Figure 4,
and for roll 23 the one-way clutch is installed for free
rotation in the opposite direction. Brake ring 72 is
~ecured to idler wheel 61 by pin 63.
Operation and use of the embodiment of FiguL^es 4
and 5 can now be described. Initially, it is assumed that
t~pe is feeding from roll 23 to roll 24 and that ~he solenoid
associated with roll 24 is energized. With the solenoid
eneryized, pivot arm 31 is locked to idler wheel 61 by band
66, and the en~ire assembly comprising pivot arm 31, idler
wheel 61, clutch 71, and brake ring 72 is free to rotate in
the clockwise direction as the diameter of tape roll 24
increases. As the idler wheel rotates, spring 62 extends,
and tape roll 24 is urged against the capstan with the force
produced by this spring.
When the direction of tape movement is reversed,
solenoid 64 is deenergized, and idler wheel 61 is released.
However, one-way clutch 71 and brake ring 72 prevent the
idler wheel from returning rapidly to its original position,
the rate o~ return being determined by the slippage of the
brake ring on the clutch. Initial energization of the
solenoid on the new take-up side causes that pivot arm
to pivot and move the new take-up roll toward the capstan
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with increased force. Thereafter, the increased force is
maintained by the spring 62 on that side.
A third embodiment of a differential force system
for use in the transport apparatus of Figure l is illustrated
in Figures 6 and 7. In this embodiment, a one-way clutch
81 is mounted on stationary post 32, and a brake ring 82 is
mounted on the clutc~ with a band of frictional material
interposed between the brake ring and clutch. A spring 84
and adjustment screw 86 provide means for adjusting the
pressure of the brake ring on the clutch. The clutch is
oriented to permit free movement of the pivot arm toward
the capstan, e.g. counterclockwise for tape roll 24, as
viewed in Figure 6, and clockwise for roll 23.
~nc7easGJ
~ Means is included for applying an ~dd~tional force
between the take-up roll and capstan when the direction of
tape movement is reversed. This means includes a solenoid
88 mounted on pivot arm 31, with the plunger of the solenoid
being connected to a radially extending arm 82a on brake
ring 82 by means of a pin 89.
Operation and use of the embodiment of Figures 6
and 7 can now be described. Initially, it is assumed that
the tape is feeding from roll 23 to roll 2~. As roll 23
decreases,in diameter, the pivot arm 31 which supports that
roll is drawn toward the capstan by spring 38. The one-way
clutch allows the pivot arm to move freely in this direction.
~n the take-up side, however, the one-way clutch prevents
free rotation, and as the take-up roll increases in diameter,
brake ring 82 is forced to rotate on the clutch, producing
a high force between the take-up roll and the capstan.
When the direction of tape movement is reversed,
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the solenoid on the new take-up side is energized to produce
hc~eas~cl
D an ~a~ional force on the new take-up roll. Thereafter,
the increased force is maintained by the frictional force
developed in the manner described above as the diameter
of the new take-up roll increases.
The invention has a number of important features
and advantages. It provides an improved differential force
system which is particularly suitable for use in recorders
in which the direction of tape travel is reversed repeatedly.
In each embodiment, a solenoid provides an additional force
on the take-up roll at the instant of tape reversal, and
thereafter an increased force is maintained on the take-up
side by springs and/or friction.
It is apparent from the foregoing that a new and
improved differential force system for transport apparatus
has been provided. While only certain presently preferred
embodiments have been described, as will be apparent to those
familiar with the art, certain changes and modifications
can be made without departing from the scope of the invention
as defined by the following claims.
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