US3147933A

US3147933A - Apparatus for controlling the tension in tapes

Info

Publication number: US3147933A
Application number: US134674A
Authority: US
Inventors: Grieve George Thomas Wilson; Watson Harold William Ritchie
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1960-09-02
Filing date: 1961-08-29
Publication date: 1964-09-08
Anticipated expiration: 1981-09-08
Also published as: SE306460B; GB980634A

Description

p 8, 1964 G. T. w. GRIEVE ETAL 43,147,933

APPARATUS FOR CONTROLLING THE TENSION IN TAPES Filed Aug. 29, 1961 4 Sheets-Sheet l I nvenlor 4 Sheets-Sheet 2 G. T. W. GRIEVE ETAL Sept. 8, 1964 APPARATUS FOR CONTROLLING THE TENSION IN TAPES Filed Aug. 29, 1961 Sept- 8, 1964 G. T. w. GRIEVE ETAL 3,147,933

APPARATUS FOR CONTROLLING THE TENSION IN TAPES pt- 8, 1 G. T. w. GRIEVE ETAL 3,147,933

APPARATUS FOR CONTROLLING THE TENSION IN TAPES Filed Aug. 29, 1961 4 Sheets-Sheet 4 Inventor w M i W MM F Attorney United States Patent 3,147,933 APPARATUS FUR CONTROLLING THE TENSION IN TAPE George Thomas Wilson Grieve and Harold William Ritchie Watson, both of London, England, assignors to British Insulated Callenders Cables Limited, London, England, a British company Filed Aug. 29, 1961, Ser. No. 134,674 Claims priority, application Great Britain, Sept. 2, 1960, 30,356/60 11 Claims. (Cl. 242-7547) This invention relates to a method of and apparatus for controlling the tension in tapes, especially in tapes being drawn off from a roll or pad carried on a rotatably driven lapping head and being lapped helically upon a core, for instance an electric cable conductor.

When drawing off tape from a convolute roll or a spirally wound disc of the material (each hereinafter for convenience referred to as a pad) for application to an elongated body by a lapping process, it is desirable to use a pad of which the initial diameter is as great as practicable. For example, it is common practice for paper cable makers to use pads of 16" diameter. In some cases pads of 25" diameter have been used. To prevent over-running of such pads it is essential to apply a braking load which imposes a tension in the paper being drawn oif from the pad. Especially in the case of supertension paper cable manufacture is it desirable that this tension should remain constant within close limits. As more and more tape is drawn off from the pad the braking torque necessary to prevent over-running naturally diminishes. At the same time the tension imposed on the paper by a given braking torque on the pad increases. Numerous devices have been suggested for effecting a gradual reduction in the braking torque as the pad diameter is gradually reduced, with the object of ensuring that tension in the tape as it runs on to the core on which it is to be helically lapped remains substantially constant.

in practice it has been found that most of these suffer from the disadvantage that the braking force imposed on the pad and hence the tension in the tape being drawn off varies both with the linear speed of draw-off and with the size of the pad due to the effect of centrifugal forces, caused by revolution of the lapping head about the machine axis, acting upon the bearings on which the pad and its carrier are mounted with their axes inclined or normal to the axis of rotation of the head and/or upon the bearings incorporated in the tension regulating device itself. It is an object of this invention to provide an improved form of the tension control device described and claimed in the specification of our copending United States application Serial No. 134,673 that is relatively free from the disadvantage referred to.

In accordance with our invention our improved form of tension control device comprises at least one member incorporating bearings which is rotatable about its own axis and is adapted to be rotatably driven by the pad about its axis at a speed proportional to the linear speed at which tape is drawn off from the pad, means for applying to the pad through the rotatably driven member a controlled braking torque which is derived from the deformation of at least one metal surface and of which the value is substantially unaffected by changes in the speed of rotation of the rotatably driven member, and means for generating by centrifugal action a force of such a value as will reduce the controlled braking torque by an amount approximately equal to the increase in braking torque due to the effect of centrifugal force on the pad carrier bearings and on bearings incorporated in the tension regulating device itself.

We may arrange that the controlled braking torque exerted on the pad at creep speed of revolution of the lapping head in which it is carried is due at least in part to the action of a spring force which is opposed by the centrifugal force exerted on a weight of such a mass that at full speed of revolution of the part of the head the braking torque due to the spring is reduced by an amount approximating to the increase in braking torque due to the effect of centrifugal forces on the pad carrier bearings and on the bearings incorporated in the tension regulating device itself.

To enable the invention to be more fully understood a description will now be given by way of example of how the invention may be incorporated in tension control devices described in our copending application Serial No. 134,673 when these devices are applied to heads of paper tape lapping machines of the kind in which each head is capable of revolution about the axis of the machine and in which each of the pads on a head is mounted with its side walls approximately parallel to a plane containing the machine axis. In the drawings accompanying this specification:

FIGURE 1 is a view partly in section and partly in elevation of one form of tension control device in accordance with the present invention applied to one of a number of pads of paper tape carried on a head of such a lapping machine;

FIGURE 2 is a plan view partly in section of the tension control device shown in FIGURE 1 with the pad removed;

FIGURE 3 is a view partly in section and partly in elevation taken on the line IIIIII in FIGURE 2;

FIGURE 4 is a view partly in section and partly in elevation showing a second form of tension control device in accordance with the present invention applied to one of a number of pads of paper tape carried on a head of such a lapping machine, and

FIGURE 5 is an end view partly in section of the tension control device shown in FIGURE 4.

We prefer to apply a controlled braking torque to the pad in the way described in the aforesaid application by applying a controlled value of thrust between races of an anti-friction thrust bearing which rotate relative to one another at a speed equal to or proportional to the linear speed at which tape is drawn off from the pad. The retarding torque so obtained is due to the work done in elastically deforming the balls or rollers and their races as they roll over them and it varies with the pressure exerted between the races and, providing the bearings and lubricated with a lubricant of low viscosity, i.e. one having a viscosity at 60 C. not substantially greater than Redwood seconds is independent of the speed of relative rotation of the races. This retarding torque is applied to the pad at a radius which always closely approximates to the radius at which tape is being drawn off from the pad. The tension so applied to the tape remains very much more nearly constant than in tension control devices in which braking torque is generated by rubbing friction.

The term anti-friction thrust bearing is used herein to mean a ball or roller thrust bearing comprising a series of balls or rollers running between the neighbouring end faces of a pair of annular discs or a ball thrust bearing comprising a series of balls running between the external circumferential surface of an inner race and the internal circumferential surface of anouter race. We have found that for a given pressure applied between the two races of an anti-friction thrust bearing, the resulting retarding torque remains substantially constant throughout a large range of angular velocities, whereas a retarding torque developed by applying a friction pad or band brake to a rotatably driven member varies very considerably as the speed varies. Though both types of thrust bearing may be used, we prefer to use a thrust bearing employing annular discs as races, for the retarding torque developed is more nearly constant over each revolution of the roller than that obtained from a thrust bearing employing inner and outer races.

In the lapping machine to which the tension control device shown in FIGURES l, 2 and 3 is applied, each of the pads of paper tape is mounted with its side walls approximately parallel to a plane containing the machine axis, on a carrier supported in bearings on a beam extending parallel with the machine axis between front and rear rotatable support plates. FIGURE 1 shows one such pad 1 and its supporting beam 2, the supporting beam forming part of the lapping head. The tension control device for this pad 1 comprises a pair of cylindrical rollers 4 mounted one on each side of the pad 1 and each with its axis approximately radial to that of the machine. Each roller 4 has an outer steel sleeve 7 which is supported on a pair of ball bearings 5 on a stationary spindle 6 inclined at an angle of 1 to the adjacent side face of the pad 1. The spindle 6 projects from the inner end of the roller 4, i.e. the end that is the nearer to the pad carrier axis, and this projecting end is secured to the free end of a tubular arm 8 which extends alongside the beam 2 and is connected at its other end to a stub shaft 10 supported in bearings 12 carried by the rotatably driven head of the machine. The axis of this pivot is at approximately right angles to the axis of the pad carrier and its hearing so that the roller 4 can swing towards and away from the neighbouring face of the pad 1. The stub shaft 10 to which the tubular arm 8 of one of the rollers 4 is pivotally connected is mounted on the beam 2 and is keyed to prevent it from rotating. The stub shaft 10 to which the tubular arm 8 supporting the other roller 4 is pivotally connected is carried in a housing 11 which is attached to a bracket 9 secured to the beam 2 and this stub shaft is locked against rotation by a releasable locking device 13. When it is required to replace the pad 1 by a fresh pad the locking device 13 is released and this stub shaft is rotated on its axis to swing the tubular arm 8 and roller 4 carried by the shaft clear of the neighbouring face of the pad a suflicient distance to allow the pads to be changed. The tubular arm 8 and roller 4 can be swung back to their original position after the pads have been changed and the stub shaft 10 locked against rotation by the releasable locking device 13.

Each tubular arm 8 is spring biased in a direction to maintain the roller 4 which it carries in driving engagement with the rim of the side wall of the pad 1. This is effected by a bar spring 14 projecting radially from the stub shaft It to which the tubular arm 8 is hinged and extending along the bore of that arm. Each stub shaft 10 is locked in such a position as to maintain the bar spring 14 and the tubular arm 8 which it carried in a position in which, in the absence of a pad, the roller 4 carried by the arm makes, contact with the roller 4 carried by the corresponding arm 8 on the other side of the pad 1 in the central plane of the pad. Separation of the rollers 4 causes the arms 3 to pivot on the bearings 12, and by means of studs 15 projecting inwardly from the walls of the arms and engaging the free ends of the bar spring 14, elastically deflects the bar springs thus creating spring forces urging the arms 8 and their rollers 4 towards the pad 1. Adjustment of the spring loading for a given width of pad is obtained by adjustment of the effective lengths of the studs 15 engaging the bar spring 14. It will be appreciated that as the width of the pad 1 increases so will the pressure exerted on it by the rollers 4 automatically increase. This increase may not suffice however for pads of tape above a certain width because it is the practice in cable lapping to relate tape thickness to tape width. In consequence the tension required to be imposed in the tape to secure proper lapping does not increase linearly with tape width but more or less exponentially therewith. We, therefore, prefer to use a single bar spring 14 in each tubular arm 8 to supply the 4 spring force required to urge the roller 4 into driving contact with pads of up to a certain width and to augment the spring 14 by a second bar spring (not shown) to deal with pads of greater width. This second bar spring may be mounted at one end of the same releasably fixed spindle as the first bar spring 14 and extend alongside but spaced from it so that it may be engaged by the outer end of the first spring 14 when that has deflected to a predetermined extent corresponding to a pad of certain width. As the rollers 4 move apart to deal with pads of greater width they are each urged into driving engagement by both springs acting together.

As previously mentioned the steel sleeve 7 of each roller 4 is supported on a pair of ball bearings 5 on a fixed spindle 6. An eye member 18 is adjustably clamped in the free end of the tubular arm 8 by a grub screw 22 passing through the arm wall and engaging the wall of the eye member. One end of the spindle 6 fits in a bore in the eye member and is held by clamping the eye member between a nut 19 screwed on to the extreme end of the spindle 6 and a flanged collar 20 screwed on to an enlarged part 21 of the spindle. The eye member 18 and its spindle 6 are rotatable about the axis of the arm 8 and angularly positioned at the required inclination to the end face of the pad 1 by the grub screw 22.

In the outer part of the steel sleeve 7 of the roller 4 that overhangs the ball bearings 5 by which the sleeve is supported are inserted a pair of single ball thrust washers 25 whose races have an external diameter that is smaller than the internal diameter of the sleeve. The neighbouring races 26 of the two washers 25 bear against the opposite end faces of an abutment ring 33 which has an external diameter that corresponds to the internal diameter of, and which is constrained to rotate with, the steel sleeve 7. The abutment ring 33 is spaced from the outer ball bearing 5 by a spacer sleeve 23 and is held in place by a second spacer sleeve 24 and a ring 28 screwed into the projecting internally screw threaded outer end of the steel sleeve 7. The pair of single ball thrust washers 25 serve as the means for applying the major part of the braking torque to the steel sleeve 7 constituting the roller 4 for engaging the pad 1. The neighbouring races 26 of the two washers which bear against the end faces of the abutment ring 33 are driven in rotation by the steel sleeve 7 and the end races 27 are held against rotation relative to the spindle 6 by being clamped between the flange of a flanged bush 29 slidable on the outer end of the spindle 6 but feather-keyed to it and a nut 32 screwed on to the other end of the bush. By suitably dimensioning the nut 32 and the flange of the bush 2? or, as shown, by insertion of washers 41 of small external diameter, application of pressure to the two end races 27 is preferably confined to their radially innerparts as we have found that unless this is done the braking torque resulting from elastic deformation of the thrust washers races end balls is apt to vary during the course of each complete revolution of the roller 4.

In incorporating the present invention in this tension control device we arrange for each of the pair of ball bearings 5 to be provided with deeply grooved internal and external races. One of the pair of ball bearings 5 is mounted on the enlarged part 21 of the spindle 6, the other being positioned a little more than half way along the spindle. The external races 34 of the two ball bearings 5 are held apart by a separating sleeve 36 and the outer bearing, that is the bearing nearer the free end of the roller 4, is urged towards this sleeve and the inner hearing by a helical spring 37 surrounding the spindle 6 and held under compression between the internal race of the outer bearing and a flanged collar 38 secured to the spindle. The steel sleeve 7 of the roller 4 is a sliding fit over the external races 34 of the bearings 5 and over their separating sleeve 36. The inner end of the steel sleeve 7 extends beyond the inner bearing and is held against movement in an outward axial direction by a collar 40 screwed into the projecting end of the sleeve and abutting the flanged collar 2tl between the eye member 18 and the inner bearing.

Freely slidable on the part of the spindle 6 between the two ball bearings 5 is a metal sleeve 42 serving as a weight for imparting a centrifugal force which, when full speed of revolution of the lapping head about the machine axis has been attained, causes the sleeve 42 to be urged radially outward to counterbalance the force exerted by the coil spring 37 which served initially to impart by elastic deformation of the ball bearings 5 a small part of the total braking torque exerted on the roller 4.

In a lapping head of the kind above described the increase in tape tension due to centrifugal forces acting on the rollers running on the peripheral edges of the side walls of the pad is directly proportional to the square of the angular velocity of the taping head and the masses of the rollers. For example, in a head running at a speed of 200 rpm. with pads each fitted with a single pair of rollers weighing 1 lb. each, the tape tension is about 2.5 ozs. higher than that which is imposed when the head is rotating at a creep speed. The increase in tension between creep and running speeds due to centrifugal action on the bearings supporting a pad carrier weighing 4 lbs. and a pad weighing, together with its center, 8.25 lbs. is about 1.3 ozs. Thus making a total increase of 3.8 ozs. due to centrifugal forces. The initial setting of the coil spring on the roller spindle will be such that its axial pressure on the supporting bearing results in a braking torque at least equal to that required to impose a tension of 3.8 02s. in the tape at creep speed, and the mass of the sliding sleeve on the spindle will be such as to exert at full speed a counter pressure sufiicient to reduce the axial thrust exerted by the spring by an amount which will reduce the braking torque applied by the spring force by an amount approximating to the braking torque resulting from the centrifugal effects referred to.

In the second form of tension control device in accordance with the present invention illustrated in FIGURES 4 and 5, where applicable the same reference numerals will be used for parts of the device which correspond to those of the tension control device described with reference to FIGURES l to 3. In the lapping machine to which this modified form of tension control device is applied, each of the pads of paper tape carried on the head is mounted with its side walls approximately parallel to a plane containing the machine axis on a carrier supported in bearings carried by a rotatably driven hub. FIGURE 4 shows one such pad 1 and its rotatably driven hub 3, the hub forming part of the lapping head. The modified tension control device for this pad 1 comprises a pair of cylindrical rollers 4 mounted one on each side of the pad 1 and each with its axis approximately parallel to that of the machine. Each roller 4 has an outer steel sleeve 7 which is supported on a pair of ball bearings 50 and 51 spaced apart on a stationary spindle 52 inclined at an angle of 1 to the adjacent side face of the pad. The spindle 52 projects from the outer end of the roller 4, i.e. the end that is farther from the pad carrier axis, and this projecting end passes through the bore of an eye member 55 adjustably clamped by a grub screw 73 to the free end of an arm 56 which extends radially with respect to the machine axis and is pivotally attached at its other end by bearings 57 and a stub shaft 58 secured to the rear face plate of the machine. The axis of this pivot is at right angles to the axis of the pad carrier and its bearing so that the roller 4 can swing towards and away from the neighbouring face of the pad 1. Each arm 56 is spring biased in a direction to maintain the roller 4 which it carries in driving engagement with the rim of one side wall of the pad. This is effected by means of a rod 60 one end of which is pivotally mounted in a clevis end 61 of one of the eye members 55 with its axis of rotation parallel to that of the rollers 4. The rod 60 is of reduced cross-section over a part of its length and this part passes through and projects beyond a clevis end 62 of the eye member 55 on the other side of the pad 1. A tubular housing 63 surrounds the projecting part of the rod 60 and is urged against the clevis end 62 by a helical spring 64 carried on the projecting part of the rod and held in compression between a washer 65 hearing against the inwardly flanged end of the tubular housing and a bearing plate 66 and nut 67 screwed on to the extreme end of the rod. Adjustment of the spring loading of the arms 56 for a given width of pad is obtained by tightening or slackening of the nut 67 and so controlling the spring force urging the rollers 4 together. The tubular housing 63 also serves as a handle for the device.

The steel sleeve 7 of each roller 4 is supported on a pair of ball bearings Sit and 51 on the stationary spindle 52. One end of the spindle 52, which is stepped to form a shoulder, fits into a stepped bore in the eye member 55 at the free end of the arm 56 and is held by clamping the eye member between a nut 71 screwed on to the extreme end of the spindle 52 and the shoulder on the spindle abutting the step in the bore of the eye member. The eye member 55 and spindle 52 are rotatable about the axis of the arm 56 and angularly positioned at the required inclination to the end face of the pad 1 by the grub screw 73 passing through the wall of the eye member and engaging the arm.

As in the first example a spacer sleeve 23, a pair of single ball thrust washers 25 separated by an abutment ring 33 and a second spacer sleeve 24 are inserted in the part of the steel sleeve 7 that projects beyond the ball bearing 5t) and these inserted parts are held in place by a ring 28 screwed into the end of the steel sleeve. The pair of single ball thrust washers 25 as the means for applying the major part of the braking torque to the steel sleeve 7 constituting the roller 4, the parts of the thrust washer being assembled in the same manner as in the first example.

The ball bearing Stl is mounted on an enlarged part 75 of the spindle 52 a little more than half way along the spindle from its outer end and this bearing is held apart from the other bearing 51 positioned at the outer end of the spindle by a separating sleeve 76 which bears against the external races 77 of the two ball bearings. The steel sleeve 7 is a sliding fit over the external races 77 and the separating sleeve 76 and the outer end of the steel sleeve extends beyond the bearing 51 and is held against movement in an outward axial direction by a collar 8t) screwed into the projecting end of the sleeve and abutting the hearing. The ball bearing 51 is mounted on a flanged sleeve 81 carried on the spindle 52 and a pressure plate 82 is screwed on to the projecting end of the flanged sleeve 81. A helical spring 84 surrounding the spindle 52 and held under compression between the internal race 78 of the ball bearing 51 and a flanged collar 86 adjustably mounted on the spindle urges the ballbearing 51 against the collar 8%. The spring force urging the bearing 51 towards the collar 30 can be adjusted by arranging for the flange of the flanged collar 36 to bear against a pin 87 whose position relative to the bearing 51 is adjustable. The pin 87 is carried by a core 88 slidable in the bore of the spindle 52 and each of its ends projects through an elongated slot in the wall of the spindle. Adjustment of the position of the pin 87 relative to the spindle 52, and hence adjustment of the spring pressure urging the ball bearing 51 outwardly towards the collar 80, is effected by tightening or slackening of the nuts 90 screwed on to the extreme end of the core 88 projecting through the nut 71.

Pivotally mounted on a lateral extension 93 of the eye member 55 are two forked bell cranks 94, which are located on opposite sides of the eye member. The free end of each of an arm 95 of each bell crank bears against the pressure plate 82 screwed on to the end of the flanged sleeve 31 carrying the ball bearing 51. A metal sleeve 96 is freely slidable on the part of the arm 56 between the eye member 55 and the bearings 57 and, when the lapping head revolves about the machine axis, this sleeve serves as a means of imparting a centrifugal force which causes the sleeve 96 to be urged against the elbow of each of the bell cranks 94 to cause the free end of the arms 95 of the bell cranks to be pressed against the pressure plate 82. At full speed of revolution of the lapping head the centrifugal force so imparted counterbalances the force exerted by the coil spring $4 which served initially to impart by elastic deformation of the ball bearing 51 a small part of the total braking torque exerted on the roller 4.

What we claim as our invention is:

1. For controlling the tension in tape being drawn off from a pad held in a pad carrier supported in bearings in a lapping machine head which revolves around the machine axis and being lapped helically upon a core, a tension control device comprising at least one member incorporating bearings which is rotatable about its own axis, and is adapted to be rotatably driven by the pad about its axis at a speed proportional to the linear speed at which tape is drawn off from the pad, means for applying to the pad through the rotatably driven member a controlled braking torque, said last means comprising two relatively rotatable members urged towards each other to deform elastically successive portions of a surface of at least one of the members, one of said members being driven by said rotatably driven member and being retarded by the force required to deform said surface, and in combination with said means for applying a controlled braking torque, a body which is operatively connected to said means for applying controlled braking torque and which is movable under centrifugal action caused by rotation of the lapping machine head and which is of such mass that upon rotation of the head it generates a centrifugal force which reduces the controlled braking torque by an amount approximately equal to the increase in braking torque due to the effect of centrifugal force on the pad carrier bearings and on bearings incorporated in the tension regulating device itself and means for applying the centrifugal force generated by said body to said means for applying a controlled braking torque.

2. For controlling the tension in tape being drawn off from a pad held in a pad carrier supported in hearings in a lapping machine head which revolves around the machine axis and being lapped helically upon a core, a tension control device comprising at least one member incorporating bearings which is rotatable about its own axis and is adapted to be rotatably driven by the pad, about its axis at a speed proportional to the linear speed at which tape is drawn off from the pad, means for applying to the pad through the rotatably driven member a controlled braking torque of which the value is substantially unaffected by changes in the speed of rotation of the rotatably driven member, the last said means comprising at least one anti-friction thrust bearing having relatively rotatable races, means for rotating said races relative to one another at a speed proportional to that of said rotatably driven member and means for adjusting the value of the axial thrust between the said races, and the device also comprising means for generating by centrifugal action a force of such a value as will reduce the controlled braking torque by an amount approximately equal to the increase in braking torque due to the effect of centrifugal force on the pad carrier bearings and on bearings incorporated in the tension regulating device itself.

3. For controlling the tension in tape being drawn off from a pad held in a pad carrier supported in bearings in a lapping machine head which revolves around the machine axis and being lapped helically upon a core, a tension control device comprising at least one member incorporating bearings which is rotatable about its own axis and is adapted to be rotatably driven by the pad about its axis at a speed proportional to the linear speed at which tape is drawn off from the pad, means for applying to the pad through the rotatably driven member a controlled braking torque which is derived from the elastic deformation of at least one metal surface and of which the value is substantially unaffected by changes in the speed of rotation of the rotatably driven member, means for generating a spring force incorporated in said rotatably driven member and adapted initially to impart by elastic deformation of the bearings of the member a braking torque on the pad, and means incorporated in said rotatably driven member for generating by centrifugal action a force which at normal running speed of the lapping head opposes said spring force to an extent to reduce the said braking torque by an amount approximating to braking torque exerted on the pad due to the effect of centrifugal forces on the pad carrier bearings and on the bearings of the rotatably driven member.

4. For controlling the tension in tape being drawn off from a pad held in a pad carrier supported in bearings in a lapping machine head which revolves around the machine axis and being lapped helically upon a core, a tension control device including a pair of rollers, each rotatably mounted in bearings on a stationary spindle and arranged one on each side of the pad to bear upon a peripheral edge of the neighbouring side wall of the pad and to be rotatably driven by the pad as tape is drawn off, at least one anti-friction thrust bearing having relatively rotatable races, means for constraining one of said races to rotate with the roller, means for restraining the other of said races from rotating about the axis of said spindle, means for adjusting the axial thrust between the two races of the anti-friction thrust bearing whereby to apply to the pad through the roller a braking torque of which the value is substantially unaffected by changes in the speed of rotation of the roller, and means for generating by centrifugal action a force of such a value as will reduce the controlled braking torque by an amount approximately equal to the increase in braking torque due to the effect of centrifugal force on the pad carrier bearings and on bearings incorporated in the tension regulating device itself.

5. A tension control device as claimed in claim 4, in which the anti-friction thrust bearing comprises a series of balls running between the neighbouring end faces of a pair of annular races.

6. A tension control device as claimed in claim 4, in which each roller has its axis inclined at a small angle to the plane containing the neighbouring side wall of the pad and means are provided for urging the roller to move bodily towards the pad in a direction parallel to the axis of the pad whereby to maintain the roller in engagement with the peripheral edge of the neighbouring side wall of the pad.

7. A tension control device as claimed in claim 6, in which the angle of inclination of the roller with respect to the plane containing the neighbouring side wall of the pad is approximately 1.

8. A tension control device for controlling the tension in tape being drawn off from a pad and lapped helically upon a core in a lapping machine of the kind in which a lapping head is rotatably driven around the machine axis and in which the pad is mounted on the rotatably driven lapping head with its side walls approximately parallel to a plane containing the axis of the machine, which device comprises a pair of tubular arms arranged one on each side of pad with each arm approximately parallel to the machine axis, means for pivotally securing one end of each arm to a support so as to be capable of pivoting about an axis at right angles to the arm and at right angles to the axis of the pad, means for urging together the free ends of the two arms, a spindle projecting from the free end of each arm in a direction at right angles to the arm and with its axis substantially intersecting the pad axis and inclined at a small angle towards the adjacent side wall of the pad, a roller supported on each spindle by a pair of bearings and running on the peripheral edge of the adjacent side wall of the pad so as to be rotatably driven by the pad as tape is drawn off, an antifriction thrust bearing housed within each roller having relatively rotatable races, means for constraining one of said races to rotate with the roller, means for restraining the other of said races from rotating about the axis of the spindle and means for adjusting the value of the axial thrust between the said races whereby to apply to the pad through the roller a braking torque of which the value is substantially unaffected by changes in the speed of rotation of the roller, a coil spring surrounding a part of the spindle of each roller and adapted initially to impart by elastic deformation of at least one of the support bearings of said roller a small part of the total braking torque, and a metal sleeve which is freely slidable on each spindle and which, when full speed has been attained, will counterbalance by centrifugal action the force exerted by the coil spring, whereby to reduce the braking torque due to the coil spring by an amount approximately equal to the increase in braking torque due to the eifect of centrifugal force on the pad carrier bearings and on the support bearings incorporated in the roller.

9. A tension control device as claimed in claim 8, in which the means for pivotally securing one end of each tubular arm to the support comprises a stub shaft locked against rotation about its axis and carried by the rotatably driven head of the machine, and in which the means for urging the free ends of one of the two tubular arms towards that of the other comprises at least one bar spring secured at one end to the stub shaft and extending from that end along the bore of the tubular arm secured to said stub shaft and means carried at the free end of said bar spring for laterally adjusting the position of said bar spring in the bore for the purpose of maintaining the roller supported by said arm in driving engagement with the peripheral edge of the adjacent side wall of the pad.

10. A tension control device for controlling the tension in tape being drawn 01f from a pad and lapped helically upon a core in a lapping machine of the kind in which a lapping head is rotatably driven around the machine axis and in which the pad is mounted on the rotatably driven lapping head with its side walls approximately parallel to a plane containing the axis of the machine, which device comprises a pair of supporting arms arranged one on each side of the pad with each arm lying substantially at right angles to the machine axis and substantially parallel to the side walls of the pad, means for pivotally securing one end of each arm to a support so as to be capable of pivoting about an axis parallel to the machine axis, means for urging together the free ends of the two arms, a spindle mounted on the free end of each arm and projecting therefrom in a direction at right angles to the arm and with its axis substantially intersecting the pad axis and inclined at a small angle away from the adjacen't side wall of the pad, a roller supported on each spindle by a pair of bearings and running on the peripheral edge of the adjacent side wall of the pad so as to be rotatably driven by the pad as tape is drawn off, an antifriction thrust bearing housed within each roller having relatively rotatable races, means for constraining one of said races to rotate with the roller, means for restraining the other of said races from rotating about the axis of the spindle and means for adjusting the value of the axial thrust between the said races whereby to apply to the pad through the roller a braking torque of which the value is substantially unaffected by changes in the speed of rotation of the roller, a coil spring surrounding a part of the spindle of each roller and adapted initially to impart by elastic deformation of at least one of the support bearings of said roller a small part of the total braking torque, a pair of hell cranks pivotally connected at one of their ends to, and located one on each side of, each supporting arm, the other end of each of the bell cranks bearing against the end face of one of said support bearings, and a metal sleeve which is freely slidable on the supporting arm of each roller and which, when full speed has been attained, is urged against the elbows of the bell cranks to counterbalance by centrifugal action the force exerted by the coil spring whereby to reduce the braking torque due to the coil spring by an amount approximately equal to the increase in braking torque due to the effect of centrifugal force on the pad carrier bearings and on the support bearings incorporated in the roller.

11. A tension control device as claimed in claim 10, in which the means for pivotally securing one end of each supporting arm to the support comprises a stub shaft locked against rotation about its axis and secured to the rotatably driven head of the machine, and in which the means for urging together the free ends of the two supporting arms comprises a rod pivotally connected at one of its ends to the free end of one supporting arm, an adjustable abutment on the free end of the rod which projects beyond the other supporting arm, and a compression spring between the last said arm and the said abutment.

References Cited in the file of this patent UNITED STATES PATENTS 911,412 Lang Feb. 2, 1909 1,686,530 Morris et al Oct. 9, 1928 1,868,915 Richardson July 26, 1932 1,987,141 Casper Jan. 8, 1935 2,095,307 Ball et a1. Oct. 12, 1937 2,941,853 Bartholomaus June 21, 1960