US 3809336 A
A magnetic tape is transported by a capstan under constant tension provided by a driving-drag system connected to a pair of spools holding the tape. Constant torque, both drag and drive, is provided to both of the reels by a magnetic coupling. A pair of one-way clutches connected to the driving portion of the magnetic couplings provide braking and uniform tension of the tape when a driving motor is stopped. Another pair of one-way clutches enable selective driving of the two reels by a single reversible motor. The motor also drives the capstan.
Description (OCR text may contain errors)
United States Patent [191 Kollar et al.
[4 1 May 7,1974
[ TAPE TRANSPORT  Inventors: Ernest P. Kollar, Broomfield; Joel M. Levine, Boulder; James M. Tagawa, Boulder; Hui-Li Tiao, Boulder, all of C010.
 Assignee: International Business Machines Corporation, Armonk, NY.
 Filed: Oct. 20, 1970  Appl. No.: 82,396
 U.S. Cl 242/202, 242/75.5, 242/204  Int. Cl. Gllb 15/30, G1 lb 15/43  Field of Search 242/201, 202, 204, 205,
 References Cited UNITED STATES PATENTS 2,217,183 10/1940 Ross 242/179 2,325,885 8/1943 Serrurier.... 242/206 2,718,361 9/1955 Evraets 242/203 2,746,691 5/1956 Hoad 242/207 3,090,573 5/1963 Matovich, .lr..... 2,603,678 Helmer 310/93 X Bancroft 242/155 M 3,197,151 7/1965 Sparks et a1.
3,294,332 12/1966 Miville et al....
3,667,701 6/1972 Blum 3,109,603 11/1963 Berlant 242/202 FOREIGN PATENTS OR APPLICATIONS 971,215 1/1959 Germany 242/202 1,016,458 9/1957 Germany 598,105 9/1959 ltaly 242/202 Primary Examiner-George F. Mautz Attorney, Agent, or Firm-Herbert F. Somermeyer  ABSTRACT A magnetic tape is transported by a capstan under constant tension provided by a driving-drag system connected to a pair of spools holding the tape. Constant torque, both drag and drive, is provided to both of the reels by a magnetic coupling. A pair of one-way clutches connected to the driving portion of the magnetic couplings provide braking and uniform tension of the tape when a driving motor is stopped. Another pair of one-Way clutches enable selective driving of the two reels by a single reversible motor. The motor also drives the capstan.
7 Claims, 5 Drawing Figures MOTOR CONTROL CIRCUITS l \T f 26A 4 25A 25A PATENTEDm 7 I974 SHEET 1 [IF 2 FIG. 1'
ERNEST P. KOLLAR JOEL M. LEVINE JAMES M.TAGAWA HUI-LI 0 MQTOR CONTROL CIRCUITS F l G 2 ATTORNEY FIG. 3
1| a fl [k FIG. 5
Q m OPERATlNG 13 E 'RANGE m m 20 2% FIG. 4
SLIPPAGE AN GLE TAPE TRANSPORT BACKGROUND OF THE INVENTION This invention relatesto magnetic tape transports, particularly to establishing constant capstan-tape and transducer-tape relationship.
In bidirectional reel-to-reel tape transports, it has been common practice for many years to drive the spools of tape by using one-way or overrunning clutches. This arrangement permits a spool to take up the tape and pay-out tape by free rotation through a one-way clutch. ln some instances, friction drags were incorporated with the one-way'clutches such that during pay out, the tape would not run free from the spool and entangle the mechanism. An example of a friction drag is the use of felt rubbing on a metallic surface. Most friction drags do not provide a constant torque drag. Accordingly, the pay-out reel is subjected to varying drags which alter the tension of the tape as the tape is transported toward the take-up reel over a magnetic transducer. This variation in tension alters the critical transducer-tape relationships. It also varies the capstan-tape relationships such that the velocity of the tape may be subjected to variations which, in digital tape systems, may introduce degraded operation.
It has been recognized for many years that it is highly desirable in digital tape transports, as well as audio transports, that the tape should be transported over the capstan, past the transducer at a constant velocity under uniform tension. These highly desirable performance criteria have been attempted to be met by the use of eddy-current clutches interposed betweenthe driving motor and the reels. These eddy-current clutches have the characteristics of providing a drag proportional to the relative rotational velocity of the spools and the driving system. Unfortunately, this arrangement not only varies tape tension but creates variations in inertia caused by the amount of tape spooled on the respective spools. In an intermittently operated tape drive, such as that usually used in digital transports, such variations of inertia have a decided adverse affect upon the starting and stopping characteristics of the transport.
In a digital transport for a high-pulse packing density tape, starting and stopping characteristics are critical. It is desired to have a tape transport not only provide uniform tension at constant velocity of the media during transducing operations, but also having consistent starting and stopping characteristics. In low-cost spoolto-spool tape transports for consistent starting characteristics, the driving motor should handle the same inertia for all starts irrespective of the distrubution of tape between the spools. The braking system also should see a similar relatively-constant inertia. Otherwise, the starting and stopping systems must have complex and expensive servomechanisms to compensate for such inertial variations.
In some tape transports, special motor control circuits are added such that the starting characteristics of the motor match the characteristics-of the tape path. It is desired to provide a tape transport having an inexpensive motor control circuit and a motor coupled to the capstan and the reels of the tape transport which obviates the need for such control circuits and yet provides consistent starting and stopping characteristics.
SUMMARY OF THE INVENTION It is an object of the present invention to provide an inexpensive, simple, and improved tape transport system wherein the mechanical design enables consistent starting and stopping and uniform-tension constanttorque cnstant-velocity transport of a tape.
A tape transport using the present invention is exemplified by having a driving capstan intermediate a pair of tape spools or other forms of tape storage such as bins. A single reversible motor not only drives the capstan but also a pair of tape-engaging means on opposite sides of the capstan by symmetrical driving-drag systems. A-magnetic coupling connects to each of the tape-engaging means providing constant maximum force in both the driving and drag modes of operation.
Each coupling has a driving and driven member, with the driven portions being connected to the tape engaging means, respectively. In a spool-to-spool transport, the tape-engaging means are the spool hubs. First and second one-way or overrunning clutches are connected between a frame on the machine, or other stationary reference, and the driving members of the magnetic couplings. The two clutches are arranged to permit free rotation of the driving portion of the couplings in opposite senses. Third and fourth one-way clutches respectively connect the driving member of the magnetic coupling to the motor for selective driving engagement. The third and fourth one-way clutches are arranged to provide driving engagement between the motor and the respective driving members of the coupling in opposite senses. These opposite senses are also opposite to the locking senses between the stationary reference and the driving members of the first and second clutches, respectively.
In one embodiment of the invention, the first and third one-way clutches are on a shaft common to the driving member of a first magnetic coupling. The second and fourth one-way clutches are on a similar shaft connected to the driving member of a second magnetic coupling.
In another embodiment, the third and fourth one-way clutches on the motor capstan drive shaft are connected to the driving members of the magnetic couplings, respectively. The first and second one-way clutches are mounted on a frame of the machine and connected to the driving member of the respective magnetic coupling for unidirectionally rotationally supporting the magnetic couplings.
During the drag mode, each magnetic coupling provides a constant torque drag to the pay-out tape reel. In tape-engaging means in the driving mode, each magnetic coupling provides a constant driving torque to the reel as a take-up reel. The drag and the drive are equal in magnitude such that the capstan provides all of the tape-transporting energy to the tape with the equal drag and drive providing uniform tape tension..
When the motor is turned off, the first and second one-way clutches cooperate through the magnetic couplings to prevent both tape-engaging means from rotating. Since the force applied to both tape-engaging means are equal, the tape tension is maintained at a desired uniform tension. This uniform tension is somewhat less than the driving tension. This arrangement provides for consistent start-up characteristics of the tape, it being maintained under uniform tension between the two tape-engaging means at all times. Likewise, the constant braking torque provides for consistent stopping action.
During starting, the torque reflected to the motor from both spools in a spool-to-spool transport is always limited to the maximum torque of one magnetic coupling. This is selected to be small such that the inertia of the motor is the major portion of the inertia in the system. In this manner, the motor-starting characteristics are a function of motor design. The effect of various tape loadings in the two spools is limited by the torque transmittability through the two magnetic couplings such that starting and stopping is determined by the constant torque characteristics of the couplings.
THE DRAWING FIG. 1 is a diagrammatic illustration of the operating principles of the invention. 7
FIGS. 2 and 3 are simplified perspective views of two embodiments of the present invention using the principles illustrated in FIG. 1.
FIG. 4 is a plan diagrammatic view of the FIG. 3 illustrated embodiment.
FIG. 5 is a graph illustrating torque transmission characteristics of a constant-torque clutch.
DETAILED DESCRIPTION With more particular reference now to the drawing,
like numerals denote like parts and structural features in the various views. The present invention is illustrated by several tape transports of the spool-to-spool type having capstan disposed between a pair of spools 11 and 12. Capstan 10 is reversibly driven by motor13. Motor control 14 controls reversible DC motor 13 in a known manner. First and second reel drives 15 and 16 couple motor 13 to spools 11 and 12 for selectively driving one spool or the other. The reel drives also provide a drag for the spools during tape pay-out. The invention is described using spool 1 1 as the pay-out spool with capstan l0 rotating clockwise to drive tape 20 toward take-up spool 12. Motor 13 drives spool 12 in a clockwise direction. It is understood that by reversing the direction of motor 13, spool 11 becomes the takeup spooland spool 12 becomes the pay-out spool with the operation being symmetrical.
Spool drives 15 and 16 are identically constructed. Spool drive 15 is described with corresponding parts of spool drive 16 being denoted by the same numeral appended with alphabetical character A". Magnetic coupling 22 has driven member 23 and driving member 24. Driven member 23 is in operative connection with the hub of spool 11. Driving member 24 is connected to a pair of one-way clutches 25 and 26. In a first sense of rotation of spool 11 (spool 11 is pay-out spool), oneway clutch 25 provides a rigid connection between stationary reference (frame) 27 and driving member 24. Magnetic coupling 22, as later more fully explained, provides a constant torque drag on spool 11.
One-way clutch 26 selectively connects driving member 24 to motor 13. When motor 13 is rotating in a sec- 0nd sense, opposite to the above-described first sense An important aspect of the present invention is the constant torque characteristics of couplings 22 and 22A. Such constant torque coupling must be distinguished from the variable torque coupling of eddycurrent couplings, also erroneously commonly referred to as hysteresis couplings. While the two couplings may look alike, the modes of operation are entirely different. In both types of couplings, the driving member 24 may be a permanent magnet polarized with two or more poles around the periphery. Driven member 23, in eddy-current coupling, induces eddy currents to flow therein which in turn provides a magnetic flux coupling between the two members. It is well known that this flux intensity, and hence the coupling, is approximately a function of the square of the frequency of the eddy currents. This means that as the relative velocity between members 23 and 24 increases, the coupling also increases. As a result of this increased coupling, the torque transmittable between the two members increases. Therefore, as spool 11 pays out more and more tape, it tends to rotate faster and faster, creating a greater drag. This increased drag provides increased tensionon tape 20 between capstan 10 and spool 11. A discussion of eddy current and hysteresis couplings is found in Helmer US. Pat. No. 2,603,678, Column 2, lines 46, et seq.
On the other hand, member 23 can be constructed such that eddy currents are not induced therein; rather, member 23 is a permeable magnetic member effecting constant maximum torque magnetic flux coupling. It is believed that in such a member 23, the residual magnetization in member 24 induces virtual poles in member 23. These virtual poles tend to follow the permanent poles of member 24. As the two members tend to relatively rotate, the coupling appears to increase to a predictable maximum irrespective of further increases in relative velocity. It is believed that as the poles in members 23 and 24 become separated by relative rotation, the virtual poles in member 23 move thereby limiting the transmittable torque. That is, the magnetic attraction between members 23 and 24 is constant maximum irrespective of the relative velocities. The I-Ielmer US. Pat. No. 2,603,678 supra, beginning at line 20 of Column 3, discusses'hysteresis coupling, showing distinct operational differences from eddy current'couplings. In Column 6 of Helmer, it is stated that the torque transmitted is inversely proportional to RPM to yield a constant power transfer. The operation of the preferred clutches differs in operation from both of the Helmer-described clutches. With the use of facing cylindrical clutch plates or members with the remanent magnetization along the axis of rotation, as opposed to radial coupling as in Helmers disclosed hysteresis clutches, constant torque is provided.
The tape start-up characteristics, as reflected to motor 13, are always constant. Assume the spools l1 and 12 are stationary. Motor 13 is turned on for transporting tape 20 from spool 11 to spool 12. The torque provided to spool 12 is a maximum irrespective of the inertia. This means the inertia reflected to motor 13 and spool drives 15 and 16 is. a constant. When there is a small amount of tape on spool 12, it should rotate faster than if there is a large amount. With a constant torque applied, a small inertia provided by a small amount of tape more rapidly accelerates spool 12 than when there is a large amount of tape. Therefore, the constant torque applied to spool 12 compensates during start-up operation for different amounts of tape contained therein.
Spool 11 is decoupled from the motor-driving system by one-way clutch 26. Similarly, for spool 11, the drag provided thereto is constant. For a small amount of tape on spool 11, it should accelerate rapidly. This action is permitted by low inertia and constant drag. For a large amount of tape on spool 11, it should accelerate slowly, which is also easily permitted by the constant torque drag.
While tape is being transported past transducer 17, a variation in inertia of the two spools as the tape is unwound from spool 11 and wound on spool 12 is compensated in the same manner as described for the startup operation. A similar set of facts occur when the tape is stopped.
An unusual facet of the tape-drive arrangement is that the torque applied to tape between spools 11 and 12 remains relatively constant during start operation, during stopping, and after the spools have been stopped. All of this is effected by-the combination of the magnetic couplings 22 and 22A and the one-way clutches. After motor 13 is turned off and tape 20 has come to rest, the cooperative relationship between one-way clutches 25 and 25A, couplings 22 and 22A, provide a constant force drag on both spools from rotation in either direction. This coupling provides tension on tape 20 equal to the tape transport tension provided by the same coupling, but when connected to motor 13 via one of the one-way clutches 26 or 26A. Note the tension is not constant, the force applied to the cells is constant. I
A constructed embodiment of the present invention is illustrated in simplified form in FIG. 2. In this arrangement, clutches 25 and 25A are supported on the frame 27 and rotatably support couplings 22 and 22A. One-way clutches 26 and 26A are mounted on the motor 13 drive shaft which also mounts capstan 10. A pair of belts connect the outer periphery of clutches 26 and 26A to spool shafts 28 and 28A, respectively. Shafts 28 and 29 extend through clutches 25 and 25A respectively to driving members 24 and 24A.
' FIGS-3 and 4 show a second embodiment of the present invention using one drive belt 30A as opposed to two drive belts in the FIG. 2 illustrated embodiment.
One-way clutches 26 and 26A are mounted on spool shafts 31 and 32 which rotatably extend through oneway clutches 25 and 25A. Clutches 25 and 25A are mounted on the frame 33 to unidirectionally permit rotation of the spool drive shafts. Operation in both embodiments is as set forth in the FIG. 1 diagrammatic illustration.
It should be remembered that in practicing the present invention,.one-way clutches can be driven from the outer periphery or an inner shaft. Similarly, the oneway clutches can have either the outer periphery of the inner shaft connected to a stationary reference. Other shapes of magnetic couplings 22 and 22A may be used, but this type was shown for simplicity and ease of construction of the illustrated embodiments. It is within the scope of the present invention to use the electrically actuated magnetic clutches, such as those having a DC current-carrying coil. In the latter variation, the magnitude of the DC current determines the torque transmitted; therefore, selectively changed in accordance with desired operating characteristics. For more complex drives, adaptive control circuits may be coupled between the spools and the DC current-controlled couplings for adaptively maintaining a constant torque which best suits the design characteristics of a particular transport.
In the illustrated embodiments, hubs 11A and 12A of spools 1 1 and 12 respectively are tape-engaging portions of the spool-that is, it is the hubs of the spools which enable the tape to be paid out or taken up for transport past transducer 17 by capstan 10. In another version of the invention, hubs 11A and 12A are auxiliary capstans which transport tape in and out of tape storage bins. Such bins may be capable of storing all of the tape in a particular tape transport or, alternatively, may be well-known vacuum storage bins interposed between large spools of tape and a tape-transducing station and capstan.
While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
What is claimed is:
1. A combined drive-drag system for a tape transport with a frame having a pair of tape supply and take-up means each including tape-engaging means, means for selectively transporting the tape in either of two directions,
the improved combination including:
a pair of constant torque permanent magnetic noncontact couplings each having a plate-like circular driven member respectively on said tape-engaging means and a plate-like circular driving member coaxially disposed and facing said driven member in spaced-apart relation and magnetically coupled with said driven member, one of said members in each coupling being permanently magnetized with a plurality of magnetic poles disposed around its periphery and facing another of said members, respectively, said another member in each coupling being magnetically permeable, nonretentive, and not capable of inducing substantial eddy currents,
' and a one-way clutch connected to each driving member, one portion of each said one-way clutch connected to said frame, said one-way clutches being respectively arranged to lock said couplings to said frame in opposing senses and freeing said couplings for the rotation in opposite senses to said opposing senses, respectively.
2. A tape spool driving means for use in a tape transport on a frame and having a tape-driving capstan interposed between a pair of tape spools,
the improved spool driving means including the combination:
a constant torque noncontact magnetic coupling on each spool, each coupling having a plate-like cylindrical spool member and a coaxial facing and matching cylindrical driving-drag member, neither of said members capable of having substantial eddy currents induced therein and one being permanently magnetized and having a plurality of poles spaced around its periphery;
one-way clutches on each driving-drag member and having one portion connected to said frame, said clutches being arranged to lock said coupling to said frame respectively in opposing rotational senses, and being freely rotatable in senses opposite to said locking senses; and
one-way driving means connected to one of said driving-drag portions for rotating same in said one direction corresponding to one of said free-rotational senses such that one of said spools is rotated for taking up tape and said driving means including means coupled to said capstan for causing tapeengaging movement for transporting tapes toward said one spool.
3. The arrangement set forth in claim 1 wherein said first one-way clutch is secured to said shaft at one end thereof and being disposed therearound and further having belt-receiving pulley means disposed on the outer periphery for driving engagement with a belt for imparting rotational motion in said first rotational sense to said spool member.
4. A tape handler having a tape driving capstan, a frame, a pair of rotatable tape storage means each hav ing tape engaging means for selectively supplying and receiving tape to and from said storage means in accordance with capstan direction of rotation, a reversible motor for driving said capstan and effecting tape movement with respect to said storage means,
the improvement including in combination:
two separate constant-torque means each having an input portion and including coupling means contin-- uously coupling said input portion to each said tape engaging means and including a constant magnitude force coupling, said coupling force magnitudes in both said coupling means being substantially equal in magnitude;
said reversible motor being operatively connected to each said input portions for reversibly rotating same;
means in each said separate constant-torque means responsive to direction of said input portion rotation to selectively operatively'connect said input portion to said tape engaging means for driving same, respectively, in accordance with the direction of rotation and further including means responsive to said input portion not rotating as above stated to selectively operatively connect said frame to said tape engaging means by said constant magnitude force coupling for each .tape engaging means not being driven by said reversible motor; and
each said coupling means having two noncontacting facing and circular plate-like magnetic members for establishing said constant magnitude force coupling, one of said members being a permanent magnet with a plurality of poles disposed around the periphery thereof, and a second one of said members being a magnetically permeable member not capable of inducing substantial eddy currents therein whereby said constant magnitude force coupling is effected between said two noncontacting members.
5. The tape handler set forth in claim 4 wherein each said constant-torque means further includes a pair of oppositely poled one-way clutches selectively drivingly engaging said motor to said magnetic coupling in accordance with the direction of rotation, said one-way clutches operatively drivingly connecting said motor to said magnetic coupling for driving same in opposite directions, respectively,-and further having third and fourth one-way clutches, respectively, in said constanttorque means and poled in rotational senses opposite to said driving one-way clutches and interposed between one of said magnetic members in each of said couplings and said frame for permitting rotation in a driving sense and locking engagement in a dragging and opposite rotational sense, said magnetic couplings alternately and continuously providing a maximum constant magnitude force coupling in'either-drive or drag relationships.
6. A tape transport having a tape-engaging capstan interposable between a pair of tape spools and adapted to transport tape to or from either one of the spools, a reversible motor in operative connection with said capstan for driving same in either direction,
the improvement including spool driving means, in
a pair of noncontact magnetic clutches each having a spool member respectively connected to said spools and a driving member and arranged such that a constant torque is bidirectionally transmitted therethrough upon the application of any force equal to or greater than said constant torque and otherwise a constant coupling;
first and second one-way clutches arranged to freely rotate in first and second senses, respectively, and being locked in senses opposite to said second and first senses, respectively;
frame means supporting said tape drive means and connected to said first and second clutches such that said clutches only permit rotation of said driving members in opposite directions, said clutches rotationally supporting said driving members for unidirectional rotation coaxially with 'said spool members, respectively; and
third and fourth one-way clutches having driving and driven portions and arranged to permit free rotation between said portions respectively in said first and second senses, said driven portions of said third and fourth clutches being connected to said driving members respectively connected to said second and first one-way clutches and said driving portions of said third and fourth clutches being in operative engagement with said motor for being reversibly rotated;
each said spool member having a spool-receiving spindle extending upwardly in parallel relationship coaxially with said spool members and rotationally supported on said frame;
said driving members being respectively disposed coaxially for rotation with said spool members;
said first and second one-way clutches being supported on said frame immediately adjacent and coaxial to said driving members and rotationally supporting same;
a shaft on each of said driving members coaxially extending through said first and second one-way clutches and coaxially securing said fourth and third one-way clutches respectively at one end thereof; and
said motor being disposed between said spindles and sense and having stationary reference means for locking engagement to prevent rotation of said driving portion in said opposite sense; and
said magnetic clutch exhibits a constant torque coupling in either direction of rotation between said members and further including a shaft on said driving-drag member rotationally supported in said second one-way clutch and separate means supporting said spool member for free rotation coaxially with said driving-drag member.