GB2087626A

GB2087626A - A tape transport mechanism

Info

Publication number: GB2087626A
Application number: GB8130933A
Authority: GB
Original assignee: S Davall and Sons Ltd
Current assignee: S Davall and Sons Ltd
Priority date: 1980-10-29
Filing date: 1981-10-14
Publication date: 1982-05-26
Also published as: GB2087626B

Abstract

A mechanism for transporting an audio or video tape 10 consists of two spaced capstans 3, 7 of which main capstan 3, belt-driven 2 from motor 1, differentially drives slave capstan 7 through a belt 6 to tension the tape. The capstans 3, 7 carry respective pulleys 5, 8 one of which is frusto- conical. An idler pulley 9 located intermediate the drive pulleys determines the position of the belt 6 on the frusto-conical surface, and is arranged to adjust the relative rotational speeds of the capstans to ensure that during tape transport, the tape tension between the capstans is maintained at a predetermined level irrespective of the direction of tape transport. The position of the pulley 9 may be preset or automatically variable in the direction parallel to the drive axes. <IMAGE>

Description

SPECIFICATION Tape transport drive apparatus This invention relates to a tape transport apparatus having two spaced tape drive capstans each adapted to transport the tape. Although particularly applicable to the transport of magnetic tape for audio or visual recording or playback purposes, it is envisaged that the apparatus may be used for transporting other tapes such as computer tape where accuracy of transport is important.

The tape in a video or audio recorder is usually driven at a constant speed during recording and/or playback by a rotatable capstan which contacts the tape. Frequently, the tape is pinched between the capstan and a pressure or pinch roller to reduce the possibility of slip occurring between the rotatable capstan and the tape.

Under certain conditions, it can be advantageous to have two drive capstans, spaced apart, since this can reduce the effects of, for example, reel inertia of the tape supply and tape take-up reels. In such cases, the rotational speeds of the two capstans must be very closely controlled to prevent excessive tension or slack developing in the length of tape between the two capstans.

According to the present invention there is provided a tape transport mechanism including first and second tape drive capstans mounted on rotatable drive shafts arranged in spaced parallel relationship, each capstan being adapted to transport the tape, the first capstan being adapted to be driven by a drive motor selectively in the two directions of rotation and being drivingly connected to the second capstan through a belt drive arrangement, the belt drive arrangement having a belt drivingly connecting the capstan drive shafts, at least one of the drive shafts carrying a frusto-conical surface with which the belt is in driving engagement, the belt drive arrangement also having means to determine the diameter at which the belt runs on the frustoconical surface to thereby adjust the relative rotational speed of the capstans to ensure that, during tape transport, the tape tension for the tape between the capstans is maintained at a predetermined value irrespective of the direction of tape transport.

Preferably, said means comprises an idler pulley arranged to engage the belt at a point on the belt path between the drive shafts to thereby control the diameter at which the belt engages the frusto-conical surface. Preferably, the position of the idler pulley is adjustable in a direction parallel to the axes of rotation of the capstan drive shafts.

The position of the idler roller may be preset, for example during assembly of the recorder apparatus, to give a predetermined differential speed between the capstans but alternatively, the position of the idler roller may be adjustable automatically, in use, by control means responsive to, for example, tape tension, capstan speed, or the difference in speed between the two capstans.

A preferred embodiment of the present invention will now be described by way of example with reference to the accompanying drawings in which:~ Figure 1 shows, in schematic form a side view of a tape transport system with tape moving in a first direction, Figure 2 shows the apparatus of Figure 1 with the tape moving in the opposite direction and, Figure 3 shows a plan view of the apparatus shown in Figures 1 and 2.

Referring now to Figure 1 , there is shown an electric drive motor 1 which drives, through a motor drive belt 2, a shaft 3 carrying a main capstan. The capstan may take the form of a wheel located on the capstan drive shaft 3 but alternatively, the shaft itself may comprise the capstan. The shaft is rotatably mounted in bearings 3a and carries a cylindrical pulley 5 secured to the shaft 3 for rotation therewith. The pulley 5 thus has a constant diameter throughout its length.

The apparatus also includes a second or slave capstan on a shaft 7 spaced from the drive shaft 3.

The axes of the shafts 3 and 7 are in spaced parallel relationship. The drive shaft 7 has secured thereto a belt drive pulley 8 having a frustoconical surface. The drive shaft 7 is driven by a narrow flat belt 6 running around the pulleys 5 and 8.

A Vee pulley 9 engages with one run of the belt between the two pulleys and acts as a belt tensioner in a known manner for which purpose it is movable substantially normal to the path of the belt, and also controls the position of the belt, in the direction of the axes of the shafts, at that point and hence the position of the belt on the two pulleys. In use, the belt 6 tends to ride up the pulley 8 towards the largest diameter of the frusto-conical surface and the pulley 9 controls the extent of this movement. The belt 6 is allowed to run upto a larger diameter of the pulley 8 when the belt 6 feeds direct to the pulley 8 from the cylindrical pulley 5, which is a longer run, than when the direction of the rotation of the capstans is reversed (to that shown in Figure 2).In the direction of rotation shown in Figure 2, the belt 6 has a relatively short run from the pulley 9 to the surface of the pulley 8 and therefore runs on a smaller diameter.

The position of the V pulley 9 can be #adjusted in a direction parallel to the axes of the shafts 3 and 7 and fixed so that the peripheral speed of the two capstans is substantially the same in both the forward and reverse directions of tape transport.

This adjustment may be performed when the apparatus is first assembled and then fixed by, for example, a screw adjustment, but alternatively.

automatic adjusting means may be provided to alter the position in response to changes in, for example, tape tension, capstan speed, or the difference in rotational speed of the two capstans.

By appropriately selecting the dimensions and the cone angle of the belt drive pulleys and the frusto-conical surface, speed difference of small fractions of one per cent can be obtained between the two capstans and these differences are small enough to generate only a few grams tension in the tape and, by maintaining the position of the pulley 9, this speed difference can be maintained to provide constant tape tension.

With this arrangement it is possible to modify the normal means of tape tensioning so that the tape tension can be reduced in controlled stages, the first stage being from the supply reel to the first capstan, the second stage from the first capstan to the second capstan and the third from the second capstan to the take-up reel. Thus, the tape tension between the two capstans always lies between the high tension in the first stage and the low tension in the third stage. This arrangement ensures good tape guidance and accurate control of tape transportation speed.

It will be appreciated that many modifications may be made to the apparatus described without departing from the scope of the invention. For example, it is not essential for the pulley 5 to be uniform diameter since this could also have a frusto-conical. The pulleys 8 and 5 could be reversed so that pulley 8 is cylindrical or both pulleys could have frusto-conical surfaces. The essential feature is the provision of the required difference in effective diameters of the two pulleys. Also, the present invention can be used with any type of tape supply and take-up reel drive arrangement but is preferably used with the apparatus disclosed in our co-pending application No. 8124458.

Claims

1. A tape transport mechanism including first and second tape drive capstans mounted on rotatable drive shafts arranged in spaced parallel relationship, each capstan being adapted to transport the tape, the first capstan being adapted to be driven by a drive motor selectively in the two directions of rotation and being drivingly connected to the second capstan through a belt drive arrangement having a belt drivingly connecting the capstan drive shafts, at least one of the drive shafts carrying a frusto-conical surface with which the belt is in driving engagement, the belt drive arrangement also having means to determine the diameter at which the belt runs on the frusto-conical surface to thereby adjust the relative rotational speed of the capstans to ensure that, during tape transport, the tape tension for the tape between the capstans is maintained at a predetermined value irrespective of the direction of tape transport.

2. A mechanism as claimed in claim 1 wherein said belt runs round respective drive pulleys on the capstan drive shafts, one of said drive pulleys having said frusto-conical surface.

3. A mechanism as claimed in claim 1 or 2 wherein said means comprises an idler pulley arranged to engage the belt at a point on the belt path between the drive shafts to thereby control the diameter at which the belt engages the frustoconical surface.

4. A mechanism as claimed in claim 3 wherein the position of the idler pulley is adjustable in a direction parallel to the axes of rotation of the capstan drive shafts.

5. A mechanism as claimed in claim 3 or 4 wherein the position of the idler pulley is adjustable automatically by control means responsive to at least one of a plurality of operating parameters.

6. A mechanism according to claim 5 wherein said operating parameters include tape tension, capstan speed, or the speed difference between the two capstans.

7. A mechanism according to any one of claims 3 to 6 wherein the idler pulley is movable in a direction substantially normal to the belt path to adjust the belt tension.

8. A tape transport mechanism substantially as described herein with reference to, and as illustrated in Figures 1 and 2 of the accompanying drawings.