GB2345692A

GB2345692A - Apparatus to maintain the tension of an elongate flexible feedstock includes a moveable roller linked to a brake

Info

Publication number: GB2345692A
Application number: GB9900862A
Authority: GB
Inventors: Barry John Ward
Original assignee: Thorn Secure Science Ltd
Current assignee: Thorn Secure Science Ltd
Priority date: 1999-01-16
Filing date: 1999-01-16
Publication date: 2000-07-19

Abstract

The apparatus is used to maintain the tension in an elongate flexible feedstock 1, such as cotton thread, recording tape and printer ribbon, supplied, on demand, at varying speeds, from a feedstock reel 2. The transport path includes a loop around a moveable roller 3 which is biassed by spring 9 to provide a tension force. The moveable roller reacts to decrease the transport path length when the supply rate increases, and vice versa. This roller is also linked to a brake band 4 acting on the feedstock reel to reduce the braking force as the supply rate increases. Both mechanisms serve to maintain a uniform tension in the feedstock independent of the rate of its supply.

Description

APPARATUS FOR MAINTAINING THE TENSION OF AN ELONGATE, FLEXIBLE FEEDSTOCK This invention relates to apparatus for maintaining the tension of an elongate, flexible feedstock, such as for example tape, being supplied from a reel at a variable feedstock speed, comprising a rotatable reel for supplying feedstock along a transport path on demand, the transport path being arranged such that said feedstock forms a loop around a moveable roller which is biased to provide a tension force to the feedstock in use.

Apparatus of the above type finds application in many fields, for example unwinding wire or cotton thread from a reel, winding tape from one reel to another in tape recording machines, or providing inked ribbons or embossing foils in the printing industry. A problem with many known systems is that the reel has much greater inertia when it is full than when it is nearly empty, and so if machinery tries to pull the feedstock from the reel with a varying speed (possibly intermittently) the feedstock will experience a wide range of tensions-for example if the reel is heavy and full it cannot accelerate sufficiently quickly when the feedstock is pulled, thus causing unacceptably high tension in the feedstock. A second known problem with such systems is that of overspill, where a heavy reel continues to rotate after the brake has been applied, and the feedstock continues to unwind off the reel although there is nowhere for it to go-this results in zero feedstock tension and jerky operation as the excess feedstock is taken up on the next pull.

According to the present invention there is provided apparatus as defined in the claims. According to a first aspect of the present invention there is provided apparatus as defined in the first paragraph above, characterised in that the moveable roller is coupled to brake means which controls the speed of rotation of the reel in response to changes in feedstock speed, such that when the speed of rotation of the reel is decreasing the roller moves to increase the length of the transport path, and when the speed of rotation of the reel is increasing the roller moves to decrease the length of the transport path, thereby maintaining the tension force on the feedstock substantially independent of feedstock speed.

Preferably, the moveable roller is able to increase the length of the transport path by moving past the point at which maximum braking effect is applied by the brake means, thereby mitigating the problem of overspill of feedstock during rapid braking.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which: Figure 1 shows a plan view of apparatus according to the invention, Figure 2 a)-c) show the apparatus of Figure 1 under different operational conditions.

Figure 1 shows apparatus for maintaining the tension of an elongate flexible feedstock, in the present example an embossing foil, being supplied from a reel at a variable feedstock speed. The apparatus comprises a rotatable reel (2) for supplying said feedstock (1) along a transport path on demand, the transport path being arranged such that said feedstock forms a loop around a moveable roller (3) which is biased to provide a tension force to the feedstock in use. The moveable roller is coupled to brake means (4,5) which controls the speed of rotation of the reel in response to changes in feedstock speed, such that when the speed of rotation of the reel is decreasing the roller moves to increase the length of the transport path, and when the speed of rotation of the reel is increasing the roller moves to decrease the length of the transport path, thereby maintaining the tension force on the feedstock substantially independent of feedstock speed.

The moveable idler roller (3) is mounted at one end (6) of a pivotable tension arm (7), the other end (8) of which is attached to a resilient member (9) which biases the roller to provide said tension force in use. In the present example the resilient member comprises a helical spring, pivotably mounted on a frame (11). The transport path includes further idler rollers or pulleys (15,16) which in the present embodiment are rotatable, but not otherwise moveable in the plane of rotation, unlike roller 3.

The brake means comprises a brake band (4), and a brake drum (5). The brake drum is coaxial with, and attached to, the reel so that stopping rotation of the brake drum stops rotation of the reel. One end of the brake band is coupled to said other end (8) of the tension arm such that the brake band is biased to provide more braking effect to the reel when the roller moves to increase the length of the transport path, and to provide less braking effect to the reel when the roller moves to decrease the length of the transport path. In the present embodiment the brake band is biased by a resilient member (10) such as for example a helical spring, pivotably mounted on a frame (11).

The tension arm (7) in Figure 1 is pivotable about point P, and the end 8 is coupled to both the resilient member 9 and one end of the brake band (4) via a cam roller (20) and a follower member (21) which is pivotable about point 22, the follower being coupled to a rod (23) attached to the brake band and biasing resilient member 10, such that when the rod is pulled away from the resilient member 10 in direction 12 (for example by the tension arm 7 pivoting in an anticlockwise direction) the brake is released.

In use, the tape tensioning arm spring (9) is set to give the required tension in the feedstock at mid travel (i. e. between positions 31 and 32 in Figure 2). The brake band tension arm spring (10) is set to give no slip (just) with a fully weighted reel. There is also provided an operating point adjuster means (25), the position of which can be altered to set the tension arm to be at mid travel during constant speed motion of the feedstock.

Further aspects of the operation of the apparatus of Figure 1 is shown in Figure 2. Figure 2 a) shows the situation under full braking. The tension arm 7 has rotated in a clockwise direction (34) past the point at which full braking has been applied (31), such that the cam roller 20 is no longer contacting the follower surface, and the moveable roller 3 mounted on the end of the tension arm has moved away from the other rollers (15,16), thus increasing the length of the feedstock transport path to take up slack caused by feedstock overspill. Figure 2 b) shows the position of the tension arm at which the brake is fully on (31) and fully off (32). The region of travel 33 between these two points is the region over which the amount of braking effort applied is proportional to the tension arm position. Figure 2 c) shows the situation under maximum acceleration of the reel and/or feedstock. In this position, the tension arm 7 has rotated in an anticlockwise direction (35) past the point at which no braking is applied (32), and the moveable roller 3 mounted on the end of the tension arm has moved towards the other rollers (15,16), thus decreasing the length of the feedstock transport path to minimise feedstock drag.

An important feature of the present invention is to decouple rapid acceleration and deceleration of the feedstock so that it does not result in such rapid acceleration or deceleration of the rotatable reel. To accomplish this the brake band and the tension arm are biased using separate resilient members, and the tension arm is capable of movement over a much larger range than necessary to simply apply or release the brake. For this reason it is important that the pivotable tension arm 3 has a damping inertia which is as low as possible. The present invention provides a passive back tensioner system which is substantially free from the problem of tape bounce on start-up.

Claims

CLAIMS 1. Apparatus for maintaining the tension of an elongate flexible feedstock being supplied from a reel at a variable feedstock speed, comprising a rotatable reel for supplying said feedstock along a transport path on demand, the transport path being arranged such that said feedstock forms a loop around a moveable roller which is biased to provide a tension force to the feedstock in use, characterised in that the moveable roller is coupled to brake means which controls the speed of rotation of the reel in response to changes in feedstock speed, such that when the speed of rotation of the reel is decreasing the roller moves to increase the length of the transport path, and when the speed of rotation of the reel is increasing the roller moves to decrease the length of the transport path, thereby maintaining the tension force on the feedstock substantially independent of feedstock speed.
2. Apparatus as claimed in claim 1 in which the tension force is settable to a plurality of predetermined values.
3. Apparatus as claimed in any preceding claim in which the moveable roller is mounted at one end of a pivotable tension arm, the other end of which is attached to a resilient member which biases the roller to provide said tension force in use.
4. Apparatus as claimed in claim 3 in which the brake means comprises a brake band, one end of the brake band being coupled to said other end of the tension arm such that the brake band is biased to provide more braking effect to the reel when the roller moves to increase the length of the transport path, and to provide less braking effect to the reel when the roller moves to decrease the length of the transport path.
5. Apparatus as claimed in any preceding claim in which the moveable roller is able to increase the length of the transport path by moving past the point at which maximum braking effect is applied by the brake means.
6. Apparatus as claimed in claim 3 in which the resilient member is a spring.
7. Apparatus as claimed in claim 4 in which the brake band is biased by a separate resilient member.
8. Apparatus substantially as described herein with reference to Figure 2 and 3 of the drawings.