US3808902A - Radial differential tape drive - Google Patents

Abstract

In a tape transport assembly, the combination comprising A. A PAIR OF CARRIERS FOR TAPE TO BE TRANSPORTED FROM A SUPPLY ROLL ON ONE CARRIER TO A TAKE-UP ROLL ON THE OTHER CARRIER, B. BELT MEANS LOCATED TO PRESSURALLY ENGAGE THE TAPE ROLLS AS THE RESPECTIVE CARRIERS FOR EFFECTING ROTATION OF THE ROLLS ON THE CARRIERS IN ORDER TO ACCOMPLISH SAID TRANSPORT, AND C. ROTARY DRIVE MEANS TO DRIVE THE BELT MEANS AT VELOCITIES PROXIMATE THE LOCI OF ENGAGEMENT WITH THE TAPE ROLLS CHARACTERIZED IN THAT THE TAPE EXTENT UNDERGOING TRANSPORTATION BETWEEN THE SUPPLY ROLL AND THE TAKE-UP ROLL IS MAINTAINED IN TENSION, THE DRIVE MEANS LOCATED TO RECEIVE APPLICATION OF COMPRESSIVE FORCES TRANSMITTED THROUGH THE THICKNESS DIMENSIONS OF THE BELT MEANS FROM THE TAPE ROLLS.

Description

United States Patent 1191 Grant May 7, 1974 RADIAL DIFFERENTIAL TAPE DRIVE [5 7] ABSTRACT 7 inventor; Frederic F Grant, 14505 In a tape transport assembly, the combination com- Eastbrook, Bellflower, Calif. 90706 prising a. a pair of carriers for tape to be transported from [22] Flled: 1972 a supply roll on one carrier to a take-up roll on 211 App]. No.: 301,527 the other carrier, b. belt means located to pressurally engage the tape rolls as the respective carriers for effecting [52] U.S. Cl. 74/227 rotation f the rolls on the carriers in Order to [51] Int. Cl. Fl6h 7/00 accomplish i transport, d [58] Field of Search 74/203, 226, 227 c rotary drive means to drive the be means at velocities proximate the loci of engagement with [56] References the tape rolls characterized in that the tape extent UNITED STATES PATENTS undergoing transportation between the supply roll 3,575,058 4/1971 Kraus 74 227 n h k p l is m n in n n ion, h 3,693,513 9/1972 Borsutzki et a] 74/226 X drive means located to receive application of compressive forces transmitted through the thickness dimensions of the belt means from the tape rolls.

10 Claims, 9 Drawing Figures PATENTEDMAY 7 1914 SHEET 1 [IF 2 PATENTEBMAY 71914 SHEET 2 [IF 2 RADIAL DIFFERENTIAL TAPE DRIVE BACKGROUND OF THE INVENTION This invention relates generally to tape transports, and more particularly concerns improvements in transports wherein a single motor is used to effect tape advancement between rotary supply and take-up rolls or packs.

A recently introduced transport technique involves driving the peripheral surfaces of the supply and takeup tape packs with the capstan or capstans. This method requires that the take-up pack be driven at a slightly faster speed than the supply. An alternative is to tend to drive the take-up pack faster through an elastically compliant system. For either of these approaches the difference in speed or tendency for greater speed difference will result in maintaining the tension in the tape between the two tape packs.

One approach uses the effect of exerting a greater normal force on the capstan by the take-up reel, so that it deforms the capstan tire more and drives faster because the rubber of the tire is forced to go through a restricted area and speeds up locally like a fluid going through a venturi. This requires a reversal of forces when tape direction is changed. A two capstan type device may use a complex belt arrangement to use the elasticity in the belts in such a way as to give'a reversible speed differentialwhen drive direction is changed.

It is also possible to change tape pack pressures or use two motors.

Such prior methods at times caused problems dueto substantial tension changes in the tape, as during vibration or shock loading. Also, the elastic tire on the capstan in prior devices was subject to substantial shear deflection occuring during fast start-ups and stops. Nonuniform accelerations and tape tensions result from these transient conditions, limiting the usefulness of such devices in data storage and retrieval applications.

SUMMARY OF THE INVENTION It is a major object of the invention to provide a solution to the above problem and difficulties. As will appear, the inventive method involves the achievement of a tape speed differential at the tape rolls or packs that automatically changes in effect when the direction of tape drive is reversed. The method may be applied in either single or dual capstan systems, and it may employ either an absolute speed difference at the packs to generate tape tension based on the speed difference and the tensile modulus of the tape, or a tendency for a greater speed difference with employment of a compliantdrive member or members yielding elastically to determine the tape tension.

Basically, the invention is embodied in a transport assembly that comprises a. a pair of carriers for tape to be transported from a supply roll on one carrier to a take-up roll on the other carrier,

b. belt means located to pressurally engage the tape rolls on the respective carriers for effecting rotation of the rolls on the carriers in order to accomplish said transport, and

c. rotary drive means to drive the belt means at velocities proximate the loci of engagement with the tape rolls characterized in that the tape extent undergoing transportation between the supply roll and the take-up roll is maintained in tension, the drive means located to receive application of compressive forces transmitted through the thickness dimensions of the belt means from the tape rolls.

As will appear, the belt means typically has tape engaging surfaces characterized in that the velocity V of the belt surface engaging the take-up roll exceeds the velocity V of the belt surface engaging the supply roll. Also, the rotary drive means may comprise a single capstan located in a zone generally between the two tape roll carriers to receive application of compressive force via the belt means; or, the rotary drive means may comprise a pair of drive capstans and the belt means may comprise two belts, one belt for each capstan.

These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following description and drawings in which:

DRAWING DESCRIPTION FIG. 1 is a schematic plan view of a tape transport assembly incorporating the invention;

FIG. 2 and 3 are schematic plan views showing portions of FIG. 1;

FIG. 4 is a schematic plan view similar to FIG. 3 and showing a modified form of the invention; FIG. 5 is a schematic plan view of another modified form of the invention;

FIG. 6 and 7 are sections taken on lines 6-6 and 77 of FIG. 1;

FIG. 8 is a schematic plan view of a still further modified form; and

FIG. 9 is a section taken on lines 99 of FIG. 8.

DETAILED DESCRIPTION Referring first to FIG. 1, there is shown a capstan 10 which may be directly mounted on a motor shaft or belt driven from a motor indicated at 11. A low friction idler 12 carries a belt 13 of thickness t, and may be crowned or flanged to control the belt alignment and tracking. Tape rolls or packs l4 and 15 press against the belt at the points 14a and 15a where the belt is tangent to the capstan or wrapped slightly on the tape roll. Rotary carriers 14b and 15b carry the tape rolls. The tape roll carriers are mounted on arms 17 and 18 which are previously retained to structure 16 as by pivots 19 and 20, and urged toward each other by tension spring 21. The tape 24 travels around rotary guides or rollers 22 and 23 and contacts the read or write transducer 25 as indicated.

Referring to FIG. 2 wherein parts of FIG. 1 are shown in more detail, capstan 10 is shown rotating counter clockwise at an angular velocity to and carrying the belt 13 with it. Since the belt 13 is approaching the capstan in a straight line, the two belt faces (inner and outer faces 13a and 1312 with respect to the capstan) are traveling at the same velocity V and the surfaces of the capstan l0 and supply tape roll 14 will have the same velocity V, which will equal the capstan radius to the inside of the belt, R multiplied by the capstan angular velocity to, or R co. Now directing attention to the takeup tape roll 15, the belt approaches point 15a, in a curved condition so that its outside surface 13b which contacts the outside surface of the tape roll 15 is traveling at a velocity V which is the outside radius R multiplied by the capstan angular velocity 0) or R m. It is evident that the speed difference as between belt exby tension with sufficient force so that the inside surface of the belt does not slip on the capstan anywhere between the tape rolls, and maintaining constant tension with no elongation or shortening so that all of the relative length change between inside and outside to accommodate the curvature occurs as a lengthening of the belt outside surface. This can be made to occur but even in the event that the pitch line of no length change were at the center, the surface velocity V, of tape roll 15 would still be higher than V, (By half the previously assessed amount). Thus by, choice of design and construction details such as belt tension, belt thickness and belt stiffness as will be described in more detail, it becomes possible to provide a desired tape tension.

Referring to FIG. 3 it can be explained how the compliance in the basic mechanism acts to regulate the tape tension: Capstan l carriers belt 13 which in turn contacts tape rolls 14 and 15. At 26 are shown two lines designating a segment of the belt cross section with uniform stress across the belt. At point 27 there is still uniform tensile stress across the belt plus a shear stress that is added by the tension in'the tape strand 24 which moves the outer surface of the belt (near direction indicated pack 14) forward in the directionindicated by the arrows. As the belt proceeds, the shear force is relieved, as at points 28 and 29 after the belt leaves tape roll 14 and approaches tape roll 15. The belt is, however, subject to a different tensile stress across its cross section; higher on the outside surface due to its elongation to accommodate the curvature. Its tension on the inside may be the same, as in the free length at 13 or lower, depending on whether its tension and coefficient of friction are selected to preclude slipping against the capstan 10. At point 30 the effect of the tape tension in strand 24 is again influential on the local belt cross section and deflects the outer surface in shear as shown. At points 27 and 30 these are standing waves of shear deflection that cause the outer surface of the belt 13 to speed up momentarily as it passes through point 27 and the same moving point on the outer surface of the belt will slow down momentarily as it passes through point 30. In each case the point on the belt recovers to its normal local condition on leaving the standing wave and being freed from the effect of tension in tape strand 24. This phenomenon allows a predetermination by design and manufacture of the tape tension in the system based on the compliance of the belt in shear and the thickness of the belt along with consideration of belt tension and friction.

It should be noted that the drive as affected by the aforementioned parameters is completely symmetrical and will operate identically in either direction, simply by reversing the capstan drive rotation direction.

FIG. 4 shows a variation of the drive which eliminates the compliance in the mechanism and determines tape tension essentially by dimensional control and by control of the cross section and modulus of the tape. The modified capstan 100 includes center portion 31 and an elastically compressible peripheral tire 32 made of an elastomer such as rubber or similar material on which a belt 33 of polyester or similar material runs and contacts tape rolls 14 and to drive them. (In this instance because of the yieldable nature of the capstan surface, the belt will shorten some of the inside surface and elongate on the outside surface to accommodate the curvature.) As before, as the belt approaches tape roll 14, it will have a velocity which is a function of the capstan rotational speed 0), and the radius R, of the capstan, and will have a greater velocity where it drives tape roll 15 which will be a function of selected belt thickness. There is essentially no shear deflection in the belt 33 and very little in the tire 32 because of the longitudinal stiffness of the belt 33 which would tend to distribute the shear load on the tire over a long portion of the belt path where the belt 33 contacts tire 32. Thus the tape rolls l4 and 15are linked dimensionally more rigidly together through the belt 33 with a controlled difference in speed between them. This variation of the tape drive accomplishes several useful purposes such as: a) controlling tape tension by tape longitudinal stiffness so that thinner tapes are automatically subjected to lower tensions, b) locking the two tape rolls into a much closer control relative to each other so that there is less peripheral speed variation between them due to different states of fullness during acceleration, and, c) attainment of a more positive control of the tape strand 24 during start and stop modes both with relation to tension and speed.

Variations in the plan view of the mechanism are possible in numerous arrangements. Referring back to FIG. 1, it is evident that the tape rolls 14 and 15 could be relocated in their angular displacement from each other around capstan 10 by using two or more idlers to replace idler 22 so that belt 13 could enter and leave contact with capstan 10 in a different angular relationship, pivots 19 and 20 also being appropriately relocated. This is true of either the concept described in conjunction with FIG. 3 or that described and illustrated in FIG. 4. It is also possible to place transducer 25 on the opposite side of tape strand 24, in which case the tape rolls would be wound oxide'side out rather than the usual oxide side in. Yet another variation is to continue the tape around the rolls and have the guides and transducer in the area below the illustration shown. Also the tape rolls can be supported by other means such as on rails that let them slide toward the capstan at the proper angular relationship to meet the belt tangent point. These variations apply to both basic methods described for maintaining tape tension, and also to the further variation to be described in conjunction with FIG. 5, and are not intended to be considered limiting or exhausting of the possible variations.

A further variation applicable to both tensioning techniques is shown in FIG. 5. The tape rolls 14 and 15 are supported in arms 34 and 35 respectively which are pivotally mounted to support structure 16a at points 36 and 37 and loaded toward capstans 41 and 42 by compression spring 38. The tape 24a moves to the left with tape rolls 14 and 15 and capstans 41 and 42 rotating in the directions shown. With belt idlers 43 and 44 located as illustrated, belts 45 and 46 act at the tangent points 14a and 15a where tape rolls 14 and 15 are held in respective contact in the same way as was previously described in conjunction with FIGS. 1 and 2, and as may be applied in the methods of either FIG. 3 or FIG. 4. Thus, if capstans 41 and 42 are both turned at the same peripheral speed by belt coupling, servocontrolled motors or other means, then the function of the two capstans 41 and 42 and their belts 45 and 46 is the same as capstan 10 and belt 13 of FIG. 1 (or capstan a and belt 33 in FIG. 4) in generating the speed difference and the tension in strand 24 of the tape. A variation of this configuration suitable for cassette packaging involves relocating the transducer 25 at the opposite side of the tape strand 24 and winding the tape on the rolls 14 and oxide side out. The FIG. 5 modification can be used with differential capstans running at different speeds by relocating the belt idlers 43 and 44 at positions 43a and 44a so that there is no different radius effected by the belts. It is also possible to use one belt in FIG. 5 to encompass both capstans 41 and 42 with the aformentioned results by the use of appropriate intermediate belt guide rollers as required.

This configuration also gives the option of operating the two tape rolls l4 and 15 at different levels i.e., in different planes, with known techniques of shifting levels in the tape strand 24 by angled tape guides and/or twists in the tape. One example of this variation may be exemplified by locating capstans 41 and 42 at different levels (axially displaced) on one shaft with appropriately located belt idlers (corresponding to 43 and 44 or 430 and 44a) depending on the tensioning method desired. It is possible to combine capstan peripheral speed difference with belt geometric relationship difference i.e., one large capstan with the alternate idler position and the other belt idler in the standard position. This approach may be used in either the flat orientation of FIG. 5 or at different elevations to give a tension difference between forward and reverse drive modes.

FIGS. 6 and 7 show examples of unusually advantageous construction details that may be used, but shall not be construed limiting in that various changes might be desired for any of several reasons. For instance, the tape path might be moved closer to the mounting plate 16 and the spring 21, and arm 18 moved below the plate 16 for packaging reasons. Capstan 10 is mounted on its rotatably mounted shaft 60 bearing mounted in spindle 48; the latter may be a motor or a spindle as shown, in which case it will have a drive pulley 49 driven by a belt 50 from a separate motor 51 with its pulley 52, all supported by plate 16. The latter may also carry guides such as 23 shown in FIG. 6 along with belt idler 12 which is rotatably mounted to tension and position belt 13 by means of a crown on the pulley 12. FIG. 7 shows a possible construction of tape carrier 15b and its support including bearings 61 and pivotal mount for arm 18.

In viewing FIGS. 6 and 7 it is evident that the tape rolls may have the form of flanged reels, with the capstan fitting between the reel flanges.

In another variation, guides 22 and 23 in FIG. 1 would be removed and transducer 25 moved into contact with the tape 24 which would remain in contact with belt 13.

From the foregoing, the following advantages are seen to be achieved:

a. A single motor drive means may be used for moving tape from one supply roll to a second, tape-up roll under tension control by means of a capstan, with a belt wrapped on the capstan or capstans driving the tape, and with the tape rolls forcibly in juxtaposition to the capstan or capstans at approximately the belt tangent points;

b. A peripheral speed difference is attained at the two tape rolls by reason of the effect to belt thickness;

c. The tape tension is regulated by choice of belt parameters such as thickness, shear modulus, tension and friction;

d. Any tendency for tape speed differentials is moditied and regulated by shear compliance in an elastic belt;

e. A positive difference in speed is attained by use of an inelastic polyester belt with tape tension dependent on tape tensile modulus and cross section;

f. Correction of tape tension variations when tapes of different thicknesses are used;

g. The belt links the two tape rolls sufficiently to allow rapid acceleration and deceleration without excessive tape tension transients;

h. Optional use of two capstans running at identical speed generating a differential tape speed to induce and regulate tape tension;

i. Provision of a two capstan system with longitudinally stiff belts entrained on the capstans to limit and regulate the shear compliance allowing greater tape acceleration while maintaining speed control unaffected by tape roll size and mass;

j. Limited adverse effects from vibration or shock;

k. Location of the capstans at different levels, or axially displaced on one shaft, to allow one tape roll above the other in compact configurations.

Referring to the shock and vibration resistant embodiment of FIGS. 8 and 9, the capstans 61 and 62 carry elastomer peripheral annuli 61a and 62a which are rotated at the same speed, as by motor means indicated at 59. A read or write magnetic transducer head 63 contacts the information side of the tape 64, which is guided as by rollers 65 carried in a magazine 66, which in turn mounts an internal support 67. The latter supports the carriers or spools 68a and 69a for the respective tape rolls 68 and 69 as by axles 80 and 81, the tape being wound oxide side out.

Support plate structure 67 mounts pins 70 and 72 which respectively project into slots 71 and 73 formed in the magazine wall structure, as shown, so as to restrict the motion of support 67 as the tape is transported. The location of the cam slots in such that the take-up roll is constrained to tend to move away from its associated capstan while the supply-reel is contained to tend to move toward its associated capstan. For this purpose, slot 71 is generally straight whereas slot 73 is arcuate. Idlers and belts 74 and 75 operate as previously described in FIG. 5 to maintain tension on the tape 64.

By loading the tape rolls with a predetermined amount of tape and by careful design of the slots 71 and 72 the movement of support 67 is restricted in such a way that as the tape roll 69 unspools and spindle 81 is able to move toward capstan 62, tape roll 68 fills and spindle is forced to move away from capstan 61. The geometry of pins 70 and 72 and slots 71 and 73 can be designed such that the pressure of capstans 61 and 62 against tape rolls 68 and 69 is constant. Slight discrepancies in the geometry due to manufacturing tolerance are accommodated by the elastic tires 61a and 62a of the capstans. This allows the operation of the unit with no springs maintaining tape roll and capstan contact and greatly enhanced the capability of the unit to withstand the effects of vibration or shock, since most of the acceleration forces are transmitted through pin 70 in transverse acceleration and through pin 72 in the vertical direction as shown in FIG. 8. Slide buttons 82 of a bearing material are provided as shown to take-up forces in the vertical direction as shown in FIG. 9.

It is also possible to construct a geometrically controlled carrier for the tape rolls as illustrated in FIGS. 8 and 9 which maintains the rolls in pressure contact with a capstan in a configuration approximately like FIG. 1.

I claim: I

1. In a tape transport assembly, the combination comprising a. a pair of carriers for tape to be transported from a supply roll on one carrier to a take-up roll on the other carrier,

b. belt means located to pressurally engage the tape rolls on the respective carriers for effecting rotation of the rolls on the carriers in order to accomplish said transport, and

c. rotary drive means to drive the belt means at velocities proximate the loci of engagement with the tape rolls characterized in'that the tape extent undergoing transportation between the supply roll and the take-up roll is maintained in tension, the drive means located to receive application of compressive forces transmitted through the thickness dimensions of the belt means from the tape rolls.

2. The combination of claim 1 wherein the belt means has tape engaging surfaces characterized in that the velocity V of the belt surface engaging the take-up roll exceeds the velocity V of the belt surface engaging the supply roll.

3. The combination of claim 1 wherein the rotary drive means comprises a drive capstan located in a zone between the two carriers to receive application of said compressive forces.

4. The combination of claim I wherein the rotary drive means comprises a pair of drive capstans and the belt means comprises a pair of belts, one for each capstan.

5. The combination of claim 1 wherein the rotary drive means comprises capstan means from which the belt means extends tangentially at loci characterized in that said compressive forces are there locally transmitted through the thickness of the belt means.

6. The combination of claim 5 wherein the capstan means includes a radially resilient peripheral annulus in engagement with the belt means.

7. The combination of claim 1 wherein the major extent of the tape undergoing transport between the tape rolls is openly spaced from the belt means and capstan means.

8. The combination of claim 7 including idler roller means and magnetic head structure engageable with the tape extent undergoing transport between the tape rolls in spaced relation to the belt means and capstan means, and wherein the drive means for the capstan means includes a motor.

9. The combination of claim 1 including means yieldably urging the carriers and belt means in directions effecting said pressural engagement of the belt means and tape rolls.

10. The combination of claim 4 including a common support for the tape roll carriers and mechanism constraining the support for movement carrying the tape take-up roll relatively away from its associated capstan and thetape supply roll relatively toward its associated capstan.

Claims (10)

1. In a tape transport assembly, the combination comprising a. a pair of carriers for tape to be transported from a supply roll on one carrier to a take-up roll on the other carrier, b. belt means located to pressurally engage the tape rolls on the respective carriers for effecting rotation of the rolls on the carriers in order to accomplish said transport, and c. rotary drive means to drive the belt means at velocities proximate the loci of engagement with the tape rolls characterized in that the tape extent undergoing transportation between the supply roll and the take-up roll is maintained in tension, the drive means located to receive application of compressive forces transmitted through the thickness dimensions of the belt means from the tape rolls.

2. The combination of claim 1 wherein the belt means has tape engaging surfaces characterized in that the velocity V2 of the belt surface engaging the take-up roll exceeds the velocity V1 of the belt surface engaging the supply roll.

3. The combination of claim 1 wherein the rotary drive means comprises a drive capstan located in a zone between the two carriers to receive application of said compressive forces.

4. The combination of claim 1 wherein the rotary drive means comprises a pair of drive capstans and the belt means comprises a pair of belts, one for each capstan.

5. The combination of claim 1 wherein the rotary drive means comprises capstan means from which the belt means extends tangentially at loci characterized in that said compressive forces are there locally transmitted through the thickness of the belt means.

6. The combination of cLaim 5 wherein the capstan means includes a radially resilient peripheral annulus in engagement with the belt means.

7. The combination of claim 1 wherein the major extent of the tape undergoing transport between the tape rolls is openly spaced from the belt means and capstan means.

8. The combination of claim 7 including idler roller means and magnetic head structure engageable with the tape extent undergoing transport between the tape rolls in spaced relation to the belt means and capstan means, and wherein the drive means for the capstan means includes a motor.

9. The combination of claim 1 including means yieldably urging the carriers and belt means in directions effecting said pressural engagement of the belt means and tape rolls.

10. The combination of claim 4 including a common support for the tape roll carriers and mechanism constraining the support for movement carrying the tape take-up roll relatively away from its associated capstan and the tape supply roll relatively toward its associated capstan.

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