GB2081958A - Tape transport apparatus; tape tensioning - Google Patents

Abstract

Belts 7, 8 wrapped round respective tape reels 1, 2 are interconnected 17, so that the supply reel belt drives the take-up reel belt but at increased speed to tension the tape, by means of pulley(s) of tapering, stepped or otherwise variable diameter. The apparatus has tape take-up and supply reels 1, 2 and a capstan 4 for reversibly transporting tape 3 between the reels. Endless belts 7, 8 mounted on a plurality of rollers 9a to 9d are in contact with the peripheries of the tape on the reels 1, 2. The belts are tensioned by a common spring 12 which acts between levers 10, 11 carrying respective rollers 9d over which the belts 7, 8 pass. The rollers 9a are mounted on shafts which carry respective frusto- conical rollers 15, 16 round which a drive belt 17 runs. A freely rotatable shaft 18 lies normal to the plane of the belt 17 and serves to twist the centre region of the belt 17 out of the normal plane of the belt so that one run of the belt runs above the shaft 17 and one below. Thus, for one direction of rotation of the reels, 1, 2 the belt 17 runs on a larger diameter on one shaft and a smaller diameter on the other and vice versa when the direction of transport of the tape is reversed. In this way tape tension is maintained for both directions of transport. Slipping clutches 19 may be incorporated. Recording head 6 presses against slightly resilient capstan 4. <IMAGE>

Description

SPECIFICATION Tape transport apparatus This invention relates to a tape transport apparatus having a tape supply reel and a tape take-up reel and tape drive means for transporting the tape between the reels.

In known transport systems, the tape is usually transported between the two reels by a rotatable capstan, the tape often being urged into contact with the capstan by a pinch roller. Typically, the direction of capstan rotation is reversible to reverse the direction of tape transport and hence the function of the two reels. In order to ensure that the tape is satisfactorily wound onto the two reels, it is necessary for both the reels to be rotated, and also for the take-up reel to be urged to wind up tape slightly faster than the supply to provide a necessary degree of tape tension to ensure accurate and neat winding-on of layers of the tape onto the take-up reel.

One group of tape recorders uses a constant-speed motor driven capstan to pull the tape past the record/playback head(s), and a light friction brake to prevent the supply-reel from letting the supply tape go slack, and a slipping clutch drive to reel up the tape on the wind-on side. Because both the friction brake and the slipping clutch are normally constanttorque devices, tape-tension adjacent to the reel normally changes inversely with the tape reel diameter, resulting in an imbalance which has to be controlled by the capstan and its pinch roller, and other complications.

A second group uses separate motor or motors for controlling the reels; sometimes with sophisticated speed/torque controls so that tape-tension is kept constant. A third group uses a single motor which drives the ever-changing periphery of the tape reels usually through a single semi-resilient drive belt, and these reels then pull the tape past a recording head, at a substantially constant tension. Although this has many advantages, tape stretch and the varying mass of the reels being driven by the semi-resilient belt, can amplify 'stick-slip' of the tape passing over the head resulting in degraded performance, particularly under vibration.

The present invention seeks to provide a new manner of driving and controlling the supply and take-up reels to overcome, or at least reduce, the disadvantages of the known systems.

The present invention also has the advantage that it allows a recording head to be immediately adjacent to the capstan thereby minimising tape stretch and reel resonance effects, and it retains most of the advantages of the single motor peripheral tape reel drive of the third group referred to.

According to its broadest aspect, the present invention provides a tape transport apparatus including first and second reels forming a tape supply reel and a tape take-up reel respectively, tape drive means for transporting the tape between the reels, first rotatable belt means urged into contact with the periphery of the tape on the first reel so as to be driven thereby, second rotatable belt means urged into contact with the periphery of the tape on the second reel, the two belt means each being mounted on a plurality of rollers, the two belt means being drivingly connected through a common shaft having one or more frusto-conical surfaces thereon drivingly engaged by the belts, and means for providing relative axial movement between the frustoconical surface or surfaces and the belt means to thereby alter the drive ratio between the two belt means to thereby urge the periphery of the tape on the take-up reel to a faster speed than the periphery of the tape on the supply reel to maintain tape tension at a predetermined level.

According to a preferred aspect of the present invention there is provided a tape transport apparatus including first and second reels forming a tape supply reel and a tape tnke-up reel respectively, tape drive means for transporting the tape between the reels, first rotatable belt means urged into contact with the periphery of the tape on the first reel so as to be driven thereby, second rotatable belt means urged into contact with the periphery of the tape on the second reel, the two belt means each being mounted on a plurality of rollers, one of the rollers of each belt drive means being drivingly connected to an associated shaft carrying a frusto-conical roller, the frusto-conical rollers having a drive belt extending therebetween with a shaft located intermediate the two frusto-conical rollers and displaced so that its axis is substantially norma to and in a plane parallel to the axes of the frusto-conical rollers to twist the centre region of the drive belt out of plane so that when said first rotatable belt means and its roller are driven by the tape supply reel, the drive belt moves to a smaller diameter portion on the frusto-conical roller associated with the take-up and a larger diameter on the other frusto-conical roller to thereby urge the periphery of the tape on the take-up reel to a faster speed than the periphery of the tape on the supply reel to maintain tape tension at a predetermined level.

Slight variations in speed between the respective belts and the tape is normally accommodated by belt creep but, alternatively a slipping clutch may be provided on one of said shafts. The slipping clutch may comprise a spring wrapping clutch, also referred to as a capstan clutch. This type of slipping clutch provides a resilient energy store and will maintain tape tension even during reversing of the direction of the tape transport.

A preferred embodiment of the invention will now be described by way of example, with reference to the accompanying informal drawing in which: Figure 1 shows in schematic form, a plan view of tape tranport apparatus, Figure 2 shows a side view of a drive belt, and Figure 3 shows a bottom plan view of Fig.

2.

Referring now to Fig. 1 there is shown a schematic plan view of a tape transport apparatus. The apparatus has two reels 1 and 2 which comprise take-up and supply reels for a tape 3. As shown, the tape 3 is driven in the direction of the arrows A and therefore the reel 2 comprises the take-up reel and the reel 1 the supply reel. It will be understood that the direction of movement of the tape is reversible and, when reversed, the reel 1 comprises the take up reel and the reel 2 the supply reel. The tape is driven by a motor (not shown). The tape is urged into contact with the drive capstan 4 by two pinch rollers 5, although in practice, only one such pinch roller need be provided, and in some cases even this can be dispensed with. A recording head 6 presses the tape lightly against the drive capstan 4 which may be constructed of a slightly resilient material.Where the tape is a video tape a number of heads, for sound, vision, sound erase and full width erase, may be required and these are shown in dotted outline. Alternatively the head or heads can touch the tape adjacent to the capstan or pinch roller.

Each of the reels 1 and 2 has an associated rotatable belt 7 and 8 respectively, having one run urged into contact with the tape on the reel. Each of the belts 7, 8 extends around four belt pulleys 9 > 9dwhich are disposed about the axis of the respective reels in such a manner that the run of belt extending between the pulleys 9a9d is wrapped around the respective reel to contact the tape thereon. The amount of wrap around varies in dependence upon the amount of tape wound on to the reel, but is usually greater than an arc of 90 about the axis of the reel. In this way an adequate degree of frictional engagement between the belt and tape is obtained without having an excessively large force urging the belt into contact with the tape.

In each case, the rollers 9b and 9carve freely rotatably mounted on a chassis C of the apparatus. In order to accommodate the varying diameters of the reels 1 and 2, the rollers 9 d of the two belts are each rotatably mounted on the end of an associated arm 10 and 11, respectively, which arms are pivotally mounted adjacent to their other ends to the chassis C of the apparatus. A tension spring 12 biasses the two arms towards each other and hence provides tension in the belts 7 and 8 which is substantially constant and equal for both belts.

The rollers 9a of each belt are each mounted on an associated shaft 13, 14 for rotation therewith, the shafts being rotatably mounted in the chassis C. Each shaft 13, 14 carries a generally frusto-conical roller 15 and 16 respectively, the larger diameters of each being uppermost. Although described as frusto-conical, it will be appreciated that these need not be strictly conical, but could be, for example, part spherical, the requirement being that they have a smaller diameter portion increasing steadily to a larger diameter portion. A drive belt 17 extends between the two rollers 15 and 16 and the centre region of the drive belt 17 is twisted out of the plane determined by the two rollers 15 and 16 by a shaft 18 which may be mounted so as to be freely rotatable about an axis normal to and in a plane parallel to the axes of the shafts 13 and 14.In this way, the centre region of the belt 17 is twisted at 90 compared to the portions passing round the rollers 15 and 16, one run of the belt running above the shaft 18, the other run lying below. With this arrangement, when the reel 2 is the take up reel it rotates clockwise as viewed in Fig. 1 and shaft 14 is consequently rotated anticlockwise. In this condition, referring to Figs.

2 and 3, the lower run of the belt 17 passes under the shaft 18 onto the roller 16 and tends to move to the smaller diameter portion of this roller. Correspondingly, the other run of the belt 17 passes over the shaft 18 and tends to move to the larger diameter portion of the roller 15 because of the belt tension.

Since the linear belt speed is the same for both rollers, it follows that the shaft on the smaller diameter portion, that is the shaft 14, will rotate slightly faster than the other shaft 13. In this way the take-up reel 2 is driven at a slightly faster speed than the supply reel 1.

The varying diameter of the reel 2 which increases as more tape is wound thereon, and the corresponding reduction in diameter of the supply reel 1 is accommodated by the pivoting links 10 and 11 which pivot clockwise as shown in Fig. 1 to accommodate this increased diameter of the reel 2. As mentioned previously the spring 1 extending between the two levers serves to maintain substantially equal belt tension in both belts 7 and 8.

When the functions of the reels 1 and 2 are reversed by reversing the direction of the drive of the capstan 4, the reel 1 becomes the take-up reel and the reel 2 the supply reel. In these circumstances, the bottom run of the drive belt 17 included in Fig. 2 moves to the smaller diameter portion of the roller 15 and the other run, passing across the top of the shaft 18 tends to rise to the larger, top, portion of the roller 16 so that the shaft 13 is rotated at a slightly faster speed than the shaft 14. In this way, the periphery of the tape on the reel 1 is urged to go at a slightly faster speed than that of reel 2 to provide the necessary tape tension.

In this embodiment, the slight difference in speed between the tape and respective belts is accommodated by belt creep. In certain circumstances, however, it may be desirable for one or both of the shafts 13, 14 to be split and provided with a slipping clutch arrangement to provide the necessary accommodation. Such clutch arrangements are shown in outline, reference 19. The slipping clutch may be of the type which provides a resilient energy store, typically using a spring, such as in a spring wrapping clutch otherwise known as a capstan clutch. Such a clutch will maintain tape tension even during reversal of the tape drive.

It will be appreciated that many variations may be made to the details of the apparatus without departing from the scope of the invention. For instance, the drive belt method of providing the speed differential could be replaced by arranging for the two reel belts to drive each other through a common shaft having one or more frusto-conical positions dependent on direction of rotation, thereby altering the ratio. Alternatively both belts could run round a common cylindrical diameter, having a small loose belt or ring which rides in under the driving belt, thus increasing the effective diameter of the cylinder on that side. Upon reversal this belt or ring can be arranged to ride across under the other belt.

Although described with reference to the transport of audio or video magnetic tape, it will be understood that the invention may be used with other forms of tape such as computor tape, or magnetic wire.

Claims (11)

1. Tape transport apparatus including first and second reels forming a tape supply reel and a tape take-up reel respectively, tape drive means for transporting the tape between the reels, first rotatable belt means urged into contact with the periphery of the tape on the first reel so as to be driven thereby, second rotatable belt means urged into contact with the periphery of the tape on the second reel, the two belt means each being mounted on a plurality of rollers, the two belt means being drivingly connected through a common shaft having one or more frusto-conical surfaces thereon drivingly engaged by the belts, and means for providing relative axial movement between the frusto-conical surface or surfaces and the belt means to thereby alter the drive ratio between the two belt means in such a way as to urge the periphery of the tape on the take up reel to a faster speed than the periphery of the tape on the supply reel to maintain tape tension at a predetermined level.

2. Tape transport apparatus including first and second reels forming a tape supply reel and a tape take-up reel respectively, tape drive means for transporting the tape between the reels, first rotatable belt means urged into contact with the periphery of the tape on the first reel so as to be driven thereby, second rotatable belt means urged into contact with the periphery of the tape on the second reel, the two belt means each being mounted on a plurality of rollers, one of the rollers of each belt drive means being drivingly connected to an associated shaft carrying a frusto-conical roller, the frusto-conical rollers having a drive belt extending there-between with a shaft located intermediate the two frusto-conical rollers and displaced so that its axis is substantially normal to and in a plane parallel to the axes of the frusto-conical rollers to twist the centre region of the drive belt out of plane so that when said first rotatable belt means and its roller are driven by the tape supply reel, the drive belt moves to a smaller diameter portion on the frusto-conical roller to thereby urge the periphery of the tape on the take up reel to a faster speed than the periphery of the tape on the supply reel to thereby maintain tape tension at a predetermined level.

3. Tape transport apparatus according to claim 2 wherein said shaft intermediate the two frusto-conical rollers is mounted so as to be freely rotatable.

4. Tape transport apparatus according to claim 2 or 3 wherein a slipping clutch is provided on at least one of said associated shafts to accommodate variations in speed between the respective belts and the tape.

5. Tape transport apparatus according to claim 4 wherein said slipping clutch(s) conprises a spring-wrapping clutch providing a resilient energy store.

6. Tape transport apparatus according to claim 1 wherein the frusto-conical surface(s) are provided on two frusto-conical roller elements carried by said common shaft.

7. Tape transport apparatus according to claim 1 wherein the frusto-conical surface(s) is/are provided on a cylindrical part of said common shaft, said belt on ring being adapted to slide under at least one of said belt means to increase the effective diameter at which the belt means passes round the common shaft.

8. Tape transport apparatus according to any one of claims 1 to 7 wherein said rotatable means are tensioned by common resilient means to maintain equal tension in the two belt means.

9. Tape transport apparatus according to claim 8 wherein one of said rollers of each of said belt means is rotatably mounted on an associated lever, the two levers being movable and inter-connected by said common resilient means which urges the levers in a direction to tension the belt means.

10. Tape transport apparatus according to any one of claims 1 to 9 wherein the belt means wrap round the respective peripheries of the tape over an arc of at least 90.

11. Tape transport apparatus substantially as described herein with reference to and as illustrated in Figs. 1, 2 and 3 of the accompanying drawings.