Tape transport system

A capstan driven web system having a take-up reel and a supply reel, the tape being drawn from the supply reel by a tape driven capstan arrangement. The drawn tape is collected on the take-up reel which is mechanically coupled to the supply reel by a mechanism having variable transfer ratio. In one embodiment, the variable ratio transport system is formed of a belt drive system having variable diameter pulleys coupled to each of the tape reels. The transfer ratio of the variable diameter pulley system is controlled by a servo mechanism which selects an appropriate transfer ratio in response to the position of a servo arm which senses the tension of the tape.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates generally to a tape transport system, and more 
particularly, to a tape tensioning system which controls the relative rate 
of rotation of tape take-up and supply reels over a predetermined range of 
speed ratios, the speed ratios being selected by a servo-control system in 
response to tape tension. 
2. Prior Art 
In known web or tape transport systems, there exists a need for improved 
precision in the control of tape tension at the recording and playback 
head. Servo-control motors have been used to drive each tape reel in an 
effort to more precisely control the speed and tension of the tape; while 
a third motor arrangement is used in a capstan system to drive the tape. 
Although such three-motor systems have performed well, they are very 
inefficient in terms of electrical energy utilization. In fact, 90 percent 
of the overall electrical input energy is wasted as heat. In addition to 
such inefficiency, motor driven systems are complex, expensive, heavy, and 
cause thermal problems in certain applications. 
In capstan driven systems, negator springs have been used to provide for 
the differential motion between supply and take-up reels. A good example 
of a negator spring tension apparatus is described in my previous U.S. 
Pat. No. 4,145,016 issued on Mar. 20, 1979 and assigned to the assignee 
hereof. Negator spring transports are useful to help achieve the precise 
control required with high-density recordings, however, such systems are 
heavy, and tape tension must be equalized by the use of complicated and 
expensive magnetic brakes or their equivalents. 
The foregoing problems are particularly acute in aircraft and space 
applications where reliability and weight are important considerations. 
Moreover, such highly demanding applications require large diameter tape 
reels to be used with relatively large tape widths to permit substantial 
data to be accumulated, but only small amounts of electrical power are 
available. 
It is, therefore, an object of this invention to provide a system which 
precisely controls the tension of a tape or web between a capstan tape 
drive arrangement and a take-up reel. 
It is another object of this invention to provide a tape control system 
which operates at substantially reduced power consumption levels over 
conventional reel drive arrangements. 
It is a still further object of the invention to provide a light-weight, 
affordable system which can handle large reels, of the type which can hold 
up to 12,000 feet of tape at a width of up to 2 inches, such reels being 
readily exchangeable. 
It is yet another object of this invention to provide a tape tension 
control system wherein the tension is not dependent upon the speed of the 
tape, and total electrical input power is reduced by eliminating the need 
for brakes at the reel hubs. 
SUMMARY OF THE INVENTION 
The foregoing and other objects are achieved by this invention which 
provides a tension control system for a tape transport arrangement. A 
first reel with tape wound thereon supplies tape to a tape drive 
mechanism. Drawing of the tape from the first reel by the tape drive 
mechanism causes the first reel to rotate, while the tape which is 
expelled by the tape drive mechanism is collected on a take-up reel. Each 
of the tape reels is mechanically coupled to a respective shaft so that 
the shafts rotate in synchronism with their respective tape reels. In a 
preferred embodiment, tension in the tape between the tape drive mechanism 
and the take-up reel is monitored by a tension sensor which produces a 
tape tension signal in response to deviations from a predetermined tape 
tension force. The shafts from the reels are coupled to one another by a 
variable ratio coupling system whereby the rotation of one shaft is 
coupled to the other. The shafts rotate at respective relative speeds, 
such speeds having a relationship which corresponds to the radius of tape 
wound on the respective reels. Thus, the speeds of the shafts are 
selectable over a predetermined range of speed ratios, the speed ratio 
varying continuously as tape is transferred between the reels. The 
appropriate instantaneous speed ratio is selected by a servo mechanism in 
response to the tension of the tape between the tape drive mechanism and 
the take-up reel. 
In one embodiment of the invention, the tension of the tape between the 
tape drive mechanism and the take-up reel is monitored by a servo arm 
which is displaced in response to the tension of the tape. Circuitry is 
provided for converting the tension-responsive displacement of the servo 
arm to a corresponding electrical signal. 
Each of the shafts is provided with a variable diameter pulley, each formed 
of a pair of pulley halves. The first and second pulley halves on each 
shaft are arranged coaxially, in a manner which permits them to be 
separated by an advantageously adjustable coaxial distance. A drive belt, 
of the type having first and second friction surfaces for simultaneously 
engaging with the pulley halves on each shaft, is provided as a coupling 
member. The advantageous variation in the coaxial distance between the 
pulley halves causes corresponding changes in the effective diameter of 
each pulley. In a preferred embodiment, the pulleys are arranged so that 
their respective pulley operates inversely to the other. Thus, as the 
pulley halves in one pulley are separated, so as to permit the drive belt 
to be located at a shorter radius, the pulley halves in the other pulley 
are brought closer together so as to cause the belt to be located at a 
larger radius on that pulley. The distances between the pulley halves are 
controlled by a servo mechanism which is responsive to the signal produced 
by the tape tension sensor.

DETAILED DESCRIPTION 
FIG. 1 shows a cross-sectional view of an illustrative embodiment of the 
inventive web transport system. A supply reel 11 and a take-up reel 12 are 
stacked coaxially, as shown. Reels 11 and 12 are provided with respective 
hub portions 13 and 14 which are coupled to respective shafts 16 and 17. 
As shown, shaft 16 may be substantially in the form of a cylindrical solid, 
and provided with a spline portion 20. A pair of pulley halves, 21 and 22, 
are mounted on spline portion 20 of shaft 16 so as to rotate with the 
shaft as reel 11 is rotated in response to the drawing of the tape by a 
capstan tape drive mechanism (not shown in this figure). 
Shaft 17, which is coupled to reel 12, is provided with a coaxial, central 
opening 30 through which shaft 16 is arranged. A gear 31 is coaxially 
affixed to shaft 17, so as to rotate with reel 12. Gear 31 is enmeshed 
with a further gear 32 which is concentrically coupled to a shaft 33. 
Gears 31 and 32 may be of the helical type, and, in this embodiment, may 
provide a -1:1 gear ratio. Thus, shaft 33 rotates at the same rotational 
speed as take-up reel 12, but in the opposite rotational direction. 
Shaft 33 is mechanically coupled to a housing of a servo motor 40. Servo 
motor 40 is provided with a screw threaded armature shaft 42, which 
rotates with respect to the housing of servo motor 40 in response to the 
application of electrical signals at slip rings 43 and 44 which are in 
electrical communication with respective electrical contact members 46 and 
47. 
Screw threaded armature shaft 42 is provided with a pair of coaxially 
arranged pulley halves 51 and 52. Pulley halves 51 and 52 are constrained 
to rotate with the housing of servo motor 40 by a key 53 which permits 
pulley halves 51 and 52 to move with respect to one another on the 
longitudinal axis of screw threaded armature shaft 42, but locks the 
pulley halves so as to rotate synchronously with the servo motor housing, 
and consequently with tape reel 12. The application of electrical signals, 
the nature and origin of which will be described hereinbelow, to contact 
members 46 and 47 causes screw threaded armature shaft 42 to rotate so as 
to responsively vary the amount of separation between pulley halves 51 and 
52. 
The pulley halves on screw threaded shaft 42 are coupled to the pulley 
halves on shaft 16 by a belt 55 having a fixed loop length. Belt 55 
transfers rotational motion between respective pairs of pulley halves in 
accordance with a variable transfer ratio. The application of an 
appropriate signal at electrical contact members 46 and 47 rotates shaft 
42 in a direction which causes pulley halves 51 and 52 to separate 
coaxially, as shown. This separation permits belt 55 to be moved radially 
inward towards screw threaded shaft 42, so as to effectively reduce the 
diameter of pulley halves 51 and 52. A spring 23, which urges pulley 
halves 21 and 22 axially toward each other, causes the slack in belt 55, 
which results from the inward motion of the belt along pulley halves 51 
and 52, to be taken up by pulley halves 21 and 22. Thus, as the effective 
diameter of pulley halves 51 and 52 is reduced, the effective diameter of 
pulley halves 21 and 22 is increased. 
If the electrical signals at contact members 46 and 47 are reversed in 
polarity, screw threaded armature shaft 42 will rotate in an opposite 
direction so as to cause pulley halves 51 and 52 to move axially closer to 
one another. This causes belt 55 to be moved radially outward from screw 
threaded shaft 42, thereby increasing the effective radius of pulley 
halves 51 and 52, with respect to the axis of rotation of screw threaded 
armature shaft 42. As belt 55 is urged outward along pulley halves 21 and 
22, by the bringing together of the pulley halves, the belt is caused to 
be moved radially inward on pulley halves 21 and 22, so as to be disposed 
at a shorter radius with respect to the longitudinal axis of shaft 16. 
It becomes apparent, therefore, that the ratio of effective diameters 
between the diameter of pulley halves 51 and 52 and pulley halves 21 and 
22, may be advantageously adjusted by the application of appropriate 
electrical signals at contact members 46 and 47 so as to rotate screw 
threaded armature shaft 42 in a predetermined direction, and thereby 
adjust the distance between pulley halves 51 and 52. It should be noted, 
therefore, that in this embodiment of the invention, the ratio of pulley 
diameters varies exponentially with the distance between pulley halves 51 
and 52. This results from the fact that the axial motion between pulley 
halves 51 and 52 causes variation in the effective diameters of all of the 
pulley halves. As the effective diameter of one pair of pulley halves is 
increased, the effective diameter of the other pair is decreased, and vice 
versa. Thus, in an embodiment of the invention wherein the pulley halves 
have frictional surfaces which slope linearly with respect to pulley 
radius, in the form of truncated cones which are arranged coaxially 
inverted with respect to one another so as to produce two predetermined 
frictional surface angles therebetween, the variations in the ratio of 
pulley diameters varies exponentially with variation in the coaxial 
distance between pulley halves 51 and 52. 
FIG. 2 shows an embodiment of the invention which is particularly suited 
for aeronautic and space applications. Illustratively, tape reels 11 and 
12 (not shown in this figure) may be mounted in an hermetically sealed 
cartridge 60 which mates with an electronics module 62 via innerface 
connector 63. Such modularization permits simple and fool-proof 
replacement of the tape reels, without necessarily replacing the 
electronic circuitry (not shown) which is contained in electronics module 
62. In addition, the use of sealed tape transport module 60 and sealed 
electronics module 62 reduces the size and weight of the tape recorder 
system and facilitates the retrieval of stored data. The sealed cartridge 
also prevents contamination of the tape and inadvertent incorrect assembly 
of the tape reels in the recorder. 
Referring to FIG. 3, single-wrap capstan 70, which is rotated by a motor 
drive mechanism (not shown), provides drive to tape 71. Tape 71 is drawn 
from supply reel 11 by capstan 70 along a path which includes a plurality 
of guide rollers 80 to 89. In a preferred embodiment, tape 71 is one inch 
wide, contains 42 information tracks, and is over 5,000 feet long. 
Although the inventive system can be used with tape which is less than one 
inch in width, the system is better suited for applications utilizing 
large scale tape, wherein light-weight, low-power draw, and reliability, 
are desirable. 
In a further embodiment, capstan 70 provides sufficient torque to drive 
tape 71 having tape width up to two inches. A two inch diameter capstan 
can provide tape speeds of up to 100 inches per second (I.P.S.) with a 
relatively low-power motor. The system can, however, operate at speeds 
between 1 I.P.S. to 480 I.P.S. without a separate reel drive arrangement. 
Furthermore, power consumption at 60 I.P.S. is approximately 10 Watts. 
Tape tensioning system 10 operates to control the relative speeds of supply 
reel 11 and take-up reel 12. Initially, take-up reel 12 is rotating at a 
higher velocity than supply reel 11. The speed differential between the 
reels, however, is continually varying in accordance with the relative 
amounts of tape wound on each. For this reason, tape tension sensing arms, 
90 and 91, are located in the tape path between capstan 70 and reels 11 
and 12. In a first direction of operation, tape 71 is drawn from supply 
reel 11 to take-up reel 12, the servo motor 40 adjusts the diameter ratios 
of pulley halves 21 and 22, and 51 and 52, so as to match the ratio of the 
tape diameters on respective reels 11 and 12. When such correspondence 
between the pulley diameters and the tape diameter on the reels is 
achieved, reel 12 takes up the tape which is drawn by capstan 70 from the 
reel 11 at precisely the same speed at which capstan 70 is operating so as 
to cause tension servo arm 90, which is movable over an arc defined by the 
arcuate arrow 93 over guide roller 82, to remain in a predetermined null 
position, as shown. 
Servo arm 90, as noted, moves in an arcuate path 93, the servo arm being 
rotatable about a stationary hinge point 94. The servo arm is urged 
upwardly by a spring mechanism (not shown), so that if tape 71 were not 
arranged around guide roller 82, the servo arm 90 would be maintained in a 
position whereby guide roller 82 is moved away from guide rollers 81 and 
83. In situations where take-up reel 12 is rotating at a relatively slow 
speed so that slack is being created in tape 71 between capstan 70 and 
reel 12, such slack would cause servo arm 90 to move upward by action of 
the above mentioned spring mechanism. Servo arm 90 is coupled to an 
electric servo circuit (not shown) which conducts a corresponding 
electrical signal to contact members 46 and 47 of FIG. 1. In this 
embodiment, such a signal which is produced by the upper movement of servo 
arm 90 will cause pulley halves 51 and 52 to be coaxially more separated 
from one another so that belt 55 moves inward closer to screw threaded 
shaft 42. This inward motion of belt 55 along pulley halves 51 and 52 is 
accompanied by a corresponding outward motion of belt 55 along pulley 
halves 21 and 22, resulting in reel 12 being rotated slightly faster. Such 
an increase in the rotation speed of reel 12 causes the slack in tape 71 
to be taken up, thereby causing servo arm 90 to be moved downward along 
arcuate path 93 by the increasing tape tension. If reel 12 now moves too 
rapidly so that an excessive tension force is produced in tape 71, 
resulting in servo arm 90 being moved downward beyond its predetermined 
null position, the polarity of the signals at contact points 46 and 47 is 
reversed, thereby causing servo motor 40 to bring pulley halves 51 and 52 
closer together. This causes take-up reel 12 to be slowed somewhat thereby 
relieving some of the tension on tape 71, and permitting servo arm 90 to 
be moved towards its null position. In this manner, the tension on tape 71 
is carefully controlled so that servo arm 90 is maintained at a null 
position. 
In a reversible embodiment of the inventive tape transport system, a 
reverse-forward switch 95 is provided which controls the direction of tape 
motion. Reversal of the tape direction by actuation of switch 95 causes 
reel 11 to become the take-up reel, and reel 12 to become the feed reel. 
In addition, the control of the tension on tape 71 is transferred to a 
servo arm 91 which operates in the manner described above with respect to 
servo arm 90. 
It is to be understood that the above-described arrangement is merely 
illustrative of the many possible specific embodiments which can be 
devised to represent application of the principles of the invention. 
Numerous and varied other arrangement can be devised in accordance with 
these principles by those skilled in the art without departing from the 
spirit and scope of the invention. In particular, it should be noted that 
the servo circuitry associated with the servo arms could be configured in 
the form of a microswitch, or it could be designed as an optical system, 
by persons skilled in the art, in light of this teaching. Furthermore, the 
tensioning apparatus can be adapted for smaller scale devices, and the 
tape transport system need not be fabricated as a modular system as shown 
in FIG. 3. Also, the tape transport arrangement may be arranged with the 
tape reels in a conventional side-by-side arrangement, rather than the 
stacked arrangement described herein.