US3545694A

US3545694A - Apparatus for winding and unwinding strip material

Info

Publication number: US3545694A
Application number: US723155A
Authority: US
Inventors: Kurt Ehrat
Original assignee: Ciba AG
Current assignee: BASF Schweiz AG
Priority date: 1967-04-28
Filing date: 1968-04-22
Publication date: 1970-12-08
Anticipated expiration: 1987-12-08
Also published as: SE331777B; GB1214855A; FR1561746A; DE1774173A1; NL6805967A; CH473725A

Description

0 United States Patent l 13,545,694

[72] inventor Kurt Ehrat [56] References Cited A I N gg ig UNITED STATES PATENTS PP 3,275,258 9/1966 Perez 242/755 1 PM P 1968 3,398,914 8/1968 Cunningham 242/7543 [45] Patented Dec. 8, 1970 [73] Assignee Clbn Limited Primary Examiner-George F. Mautz Ba el, Switze la d Attorney-Pierce, Scheffler and Parker a company of Switzerland Priority ABSTRACT: Apparatus for winding and unwinding strip [31 1 6107/67 material from a spool includes a belt-driven pulley coupled to [54] APPARATUS FOR WINDING AND UNWlNDlNG STRIP MATERIAL 11 Claims, 12 Drawing Figs.

[50] Field of Search 242/672, 67.1, 67.4, 75.5, 75.1, 67.5, 78.6, 78.1, 67.3, 75.43, 75.44; 28/35, 36

the spool, two pairs of rollers for driving the belt in one direction or the other respectively and a brake for stopping the belt. The pairs of driving rollers and the brake are controlled in an alternative manner by means of a cam arrangement associated with and actuated by a spring-loaded tension lever including a strip tensioning roller around which the strip material passes on its way to or from the spool. As the tension in the strip material varies, the tensioning lever will move in one direction or the other from an intermediate position in which the cam means applies the brake to the belt. Movement of the tensioning lever in one direction puts one pair of driving rollers into operation thus to drive the belt and pulley in one direction, and movement of the lever in the opposite direction puts the other pair of driving rollers into operation to drive the belt and pulley in the opposite direction.

PATENTED an". 819m sum 3 OF 7 PATENTED DEC 8 19m SHEET u M 7 PATENTED DEE 8192B SHEET 7 OF 7 kUrt Ehrafi ,JDRA AQPW WWW APPARATUS FOR WINDING AND uNwINnINc STRIP MATERIAL This invention relates to apparatus for winding and unwinding strip material.

In conventional strip winding apparatus the motors driving the winding bobbins or spools are started, stopped, or reversed L by the position of a lever whose position is governed by the i the tensioning lever. Generally the brake means consist of a band which envelops a brake cylinder and which is tensioned' by a solenoid for generating the braking force.

Theseknown strip winding devices have certain drawbacks which are primarily derived from the combination of several strip winding devices requiring provision of separate drive motors with associated switch means for starting, stopping, and reversing the motor, and so forth for each winding bobbin or spool and that all the components must be designed to handle relatively high loads. This is reflected in relatively high cost. Load incurred by the starting and stopping of the motors, activating and deactivating the brake solenoids, are considerable and interference with neighbouring electronic circuits may result. This can be avoided only by providing suppressor devices which add to the cost of the apparatus.

The speed of the winding bobbin or spool depends, on the one hand, upon the speed of the strip and, on the other hand, upon whether the spool carries a fully wound roll or an empty roll. The required ratio of the rotary speeds of the full and the empty winding spool may be as high as 1:4 or even more, in order to keep the speed of the strip perfectly constant. The motors must therefore be designed to provide the maximum necessary speed for the empty spool and also to generate the maximum torque for rotating the fully wound spool. In other words, the motors must be robust. In conventional strip winding apparatus this means that the. controlled loads are high and add considerably to the moment of inertia of the winding spool and the roll of strip material wound thereon.

It is an object, therefore, of the present invention to provide improved apparatus for winding and unwinding strip material.

In accordance with the present invention, I provide apparatus for winding and unwinding strip material, comprising a belt-driven pulley onto and from which the strip material is wound or unwound, at least one tensioning roller over which the strip material is arranged to be passed, the tensioning roller being mounted on a spring-loaded tensioning lever, a first and second pair of drive rollers, and a brake, the two pairs of drive rollers and the brake being alternatively controlled by a cam movable by the tensioning lever so that in a first position of the tensioning lever the cam activates the first pair of drive rollers to engage the belt to drive it in a first direction, in a second position of the tensioning lever the brake is actuated by the cam to stop movement of the belt and in a third position of the tensioning lever the cam activates the second pair of drive rollers to engage the belt to drive it in a direction opposite to said first direction, the drive rollers and brake when engaged with said belt being arranged to provide a frictional force in excess of that between the belt and pulley.

In apparatus for winding and unwinding a strip material of the afore-described kind, the following preferred embodiments include a belt which travels between first and second pairs of continuously driven rollers and a pair of brakeshoes so alternatively controlled by a cam which is movable by a tensioning lever that in a first end position of the tensioning lever the first pair of drive rollers, in a centre position of the tensioning lever the pair of brakeshoes and in the other end position of the tensioning lever the second pair of drive rollers is pressed into contact with the belt and thus activated, the arrangement being such that the driving and braking forces between the drive rollers and brakeshoes respectively and the belt exceed the force of friction between the belt and the pulley that is driven by the belt.

In order that the nature of the invention may be more readi ly understood, embodiments thereof which are not intended to limit the scope of the invention in any way will be hereinafter more particularly described with reference to the accompanying drawings in which:

FIGS. 1 to 3 are a first embodiment of apparatus according to the invention shown in three different operating states;

FIG. 4 is a simplified representation of the apparatus in FIGS. 1 to 3 illustrating the kinematics of the proposed arrangement;

FIG. 5a is an equivalent diagram of the distribution of forces;

FIG. 5b is a time-speed diagram relating to FIG. 5a;

FIG. 6 is a rewinding apparatus combining two complete systems of the kind illustrated in FIGS. 1 to 3;

FIG. 7 is a modification of the apparatus according to FIGS. 1 to 3 adapted to provide three different winding speeds;

FIG. 8 is a simplified section taken on the line VIII- VIII in FIG. 7;

FIG. 9 is a diagram for further elucidating the functioning of the embodiment according to FIGS. 7 and 8; and

FIGS. 10a and 10b represent a modification of a detail in the embodiments according to FIGS. 1 to 3 and 6 to 7.

With reference to FIGS. 1 to 3 there is provided a pulley 4 coupled to a winding bobbin or spool 2 on a shaft 1 for common rotation therewith. The strip material or tape 3 which can be wound on or drawn off the spool 2 runs over rollers 8, 9, l0, and 11. The two

rollers

10 and 11 are mounted on fixed axles, whereas the two others 8 and 9 are mounted on a tensioning lever 7 which pivots on a fulcrum at 37. An endless belt 5 engages the periphery of the pulley 4 and is kept taut by

tensioning rollers

12 and 13. These tensioning rollers are each mounted on a belt tensioning

swivel arm

14 and 15 fulcrumed on fixed pivots l6 and 17. The tension of the belt is maintained by

springs

18 and 19 which apply a given pull to the

swivel arms

14 and 15. The deflection of the belt tensioning swivel arms is limited by

stops

20 and 21. Cooperating with that portion of the belt which travels between the two

tensioning rollers

12 and 13 are a first pair of forward

drive rollers V

22 and 23 and a second pair of reverse

drive rollers R

24 and 25. Between the two pairs of drive rollers is a brake

B comprising brakeshoes

26 and 27. At least one roller of each pair of

drive rollers

22, 23 and 24, 25 can be driven by a motor in the direction indicated by arrows. The

rollers

22 and 24 run in fixed bearings, whereas the two

rollers

23 and 25 are each rotatably mounted on the end of a

swivel arm

28 and 29. The

swivel arms

28 and 29 are fulcrumed on

pivots

30 and 31. Springs 32 and 33 urge the-arms towards the belt 5 and the cooperating fixed

rollers

22, 24. The brakeshoe 26 is fixed, whereas the other brakeshoe 27 is mounted on a lever 34 which is deflectable about a pivot at 35. A spring 36 which is attached to the lever 34 urges the movable brakeshoe 27 towards the fixed brakeshoe 2.6. The pivoted end of the tensioning lever 7 is modified to form a quadrant 38 which contains a cam slot 39. The track of this cam slot 39 cooperates with follower elements which in the illustrated embodiment take the form of

pins

40, 41, and 42,

pins

40 and 42 being affixed to the

lever arms

28 and 29 of the

drive rollers

23 and 25 and pin 41 being affixed to the lever arm 34 carrying the brakeshoe 27. The

pins

40 and 42 are affixed to the ends of their

respective levers

28 and 29.

The cam slot 39 is so shaped and disposed in relation to the follower elements that only one of the pairs of

drive rollers

22, 23 and 24, 25 or the brake can take effect at any one time. To this end the cam slot is formed with a recess E for the reception of one of the

pins

40, 41, and 42 to activate the element controlled by the pin. The recess E exceeds the maximum possible deflection of the

pins

40, 41, and 42 by an amount d to ensure that the full power of the

springs

32, 33, and 36 associated with the pins can be exerted to press the respective element against the belt when one of the pins has been received into the recess. The maximum possible deflection of the

pins

41 and 42 is determined by the position of the

fixed rollers

22 and 24 and that of the pin 41 by the position of the fixed brakeshoe 26.

When the tensioning lever 7 is in the upper position shown in FIG. 1 the pin 40 on the lever 28 carrying the roller 23 will be received into the recess. Consequently, the pull of the spring 32 causes the belt to be tightly gripped between the two

rollers

23 and 22 and to be driven forward in the direction indicated by arrows on the two rollers. However, when the tensioning lever 7 is in the central position shown in FIG. 2, then the pin 41 associated with the brakeshoe 27 on the swivel arm 34 will be received into the recess E in the cam slot and the pull of the spring 36 will cause the belt to be tightly gripped between the two

brakeshoes

26 and 27. Finally in the bottom end position of the tensioning lever shown in FIG. 3 the pin 42 will be in the recess E and the belt will therefore now be gripped between the two rollers 24 and 2S and driven in the reverse direction indicated by the arrows on these rollers.

In the following description of the manner in which the mechanism illustrated in FIGS. 1 to 3 functions, reference will first be made to FIG. 2 which shows the tensioning lever in its centre position. The belt is therefore gripped between the two brakeshoes 26 and 27 and neither the pulley 4 nor the winding spool 2 can move. However, as soon as the strip material is pulled upwards at PE it will also pull the tensioning arm 7 in the upward direction. The pulley and the winding spool first remain stationary untilthe tensioning lever has been upwardly deflected sufficiently for the swivel arm 34 of the

brake

26, 27 to have been retracted by the cam slot 39 in the quadrant 38 and the brake to have been released. Further upward deflection of the tensioning lever moves the recess E far enough for the pin 40 on the swivel arm 28 to be received into the recess E. Consequently, the belt 5 will now be gripped between the two

rollers

22 and 23 and the belt starts to move. The pulley 4 is engaged by the belt and begins to rotate in the clockwise direction. The continuously revolving cooperating

rollers

22 and 23 engage the belt substantially without delay. However, the pulley and the winding spool which is fixed to the pulley require a short period of time to run up to speed, during which the belt must slip on the pulley 4. The rotation of the winding spool 2 allows the strip to unwind from the spool 2. This situation is illustrated in FIG. 1. So long as the speed of the strip at point PE exceeds the circumferential speed of the roll of strip material on the spool the tensioning lever will continue to be further deflected in the upward direction. When the peripheral speed of the roll equals the speed at point PE of the strip, the tensioning roller will have reached its maximum angle of deflection, and when the peripheral speed of the roll exceeds the speed of the strip at PE the spring 44 will begin to pull the tensioning lever downwards again. As soon as the tensioning lever has swung down sufficiently for the cam slot 39 to withdraw the pin 40 and hence the swivel arm 28 and its roller 23 from contact with the belt and the pin 41 of the swivel lever 34 carrying the brakeshoe 27 is received into the recess, the belt will be practically instantaneously stopped. However, owing to the inertia of the rotating mass the spool 2 will require a given time to come to rest whilst the belt slips on the pulley. The apparatus will then be in the position illustrated in FIG. 2. If in the position according to FIG. 2 the strip at point PE is moved downwards, i.e. if the normal tension of the strip at point PE is relaxed, then the tensioning lever 7 will descend further until the brake is released and the

drive rollers

24 and 25 grip and drive the belt, causing the belt to be engaged by the rollers and to be driven in the counterclockwise direction. This position is illustrated in FIG. 3 and is reached from that shown in FIG. 2 in the same way as the latter position is attained from the position in FIG. I. The transition from FIG. 3 back to FIG. 2 proceeds in analogous manner. Owing to the relatively large moment of inertia of the pulley 4, of the winding spool 2, and of the roll 43 periods of delay in starting and stopping also occur during the transitions between the positions shown in FIGS. 2 and 3 and during these periods the belt will slip on the pulley.

In order to prevent the strip from being subjected to severe stress the tension at point PE should be as small as possible. The tension at PE is determined by the rating of the spring 44 of the tensioning lever and by the resistance to displacement of the control cam in the

quadrant

38, 39 of the tensioning lever. This resistance depends upon the efiort required for deflecting the swivel arms (28, 29 and 34). This effort is numerically defined by the distance H of deflection multiplied by the spring force acting on the swivel am. It is therefore desirable to minimise this distance H and the spring force. The distance H may be reduced to as little as a few tenths of a millimetre. The spring force (springs 32, 33 and 36) which determines the gripping power of the rollers and brake must be so chosen that the friction between the belt and the drive rollers and the belt and the brakeshoes will definitely exceed the friction between the belt and the circumference of the pulley. If this were not the case the belt would not slip on the pulley but it would slip between the drive rollers. Continuous slippage between the drive rollers means excessive wear of the belt. It is therefore desirable that the friction between the belt and the circumference of the pulley should not be very high to permit the gripping force of the drive rollers to be correspondingly reduced and the tension (at PE) to remain fairly small. On the other hand, the friction between the belt and the pulley should not be less than a given minimum to prevent the time required for bringing the spool up to speed to become so long that, in the position as shown in FIG. 2 and at an increasing speed of takeoff of the strip at PE when the roll is at its maximum diameter (i.e. its moment of inertia is a maximum), the tensioning lever and its rollers 8 and 9 would be dragged too far upwards and into contact with the fixed

rollers

10 and 11. This would interfere with the proper functioning of the mechanism. Conversely the friction between the belt and the pulley must be sufiicient to ensure that in the most unfavourable circumstances the time that elapses before the winding spool and the roll come to rest after having been braked will not exceed the time required by the tensioning lever to move through the entire braking sector whilst the brake (27) is engaged.

The pulling force of the belt on the circumference of the pulley should not therefore be less than a given minimum value, but at the same time it should also not be excessive. The pulling force applied by the belt to the pulley should therefore be substantially constant. It is well known that in the absence of special arrangements the frictional forces, which are governed by various external factors (contamination, surface quality, and so forth), are not usually constant. The special arrangements which in the present instance this embodiment provides comprise a mechanical compensating device which stablises the pull which the belt is capable of applying to the circumference of the pulley. This compensating device will now be described by reference to FIG. 4.

FIG. 4 illustrates the proposed system at a time when the pulley is still stationary and the

drive rollers

22 and 23 have just been allowed to move into engagement by the control cam (not shown in FIG. 4, but constructed as illustrated in FIGS. 1 to 3) for driving the belt in the forward direction (arrow V).

The portion 5A of the belt therefore rides onto the pulley,

whereas the portion 58 rides off the pulley. The endless belt thus travels in the direction of the arrow V. According to a known formula the relationship between the loads that are transmitted by the portions of the belt which ride on and off the pulley are defined by where p. is the coefficient of friction between the belt and the pulley and p is the angle subtended by the arc of contact of the belt with the pulley. The pull P transmitted by the portion 58 of the belt which rides off the pulley thus always exceeds the pull exerted by the portion 5A of the belt. Since the forces generated by the two

springs

18 and 19 are equal and P, exceeds P the swivel arm 15 will be pulled away from its stop 21 (clearance 1), whereas the swivel arm 14 will be pulled into contact with its stop 20. Consequently the force of spring 18 will cease to have any effect on the belt; Hence the pull P of the belt will be equal to the pulling force F, exerted by the spring 19. In other words P P In view of the practically loss-less deflection of the belt by the roller 13 P1= P Pp. It follows that P, P,-, P,-= P eup and P PM eup.

The actual peripheral pull P, applied to the pulley by the belt is therefore represented by the following equation: P, P, P P P eupor P, P,.-(l l/ezp).

It will therefore be understood that, provided the angle p and the coefficient of friction p. are large, the pull P, applied to the periphery of the pulley is substantially independent of friction and hence substantially depends only upon the practically constant spring force Pp. For instance, assuming an angle p 180 and a coefficient of friction p.= 0.5, the term e'pp will be about 4.5, l/eup will be about 0.22 and hence P, =0.78 P

,If the coefficient of friction were to increase by 100 percent (say from 0.5 to l then eup would become about and Hey. p would be 0.05 so that P, would be 0.95 PF It will therefore be seen that an increase in the coefficient of friction by 100 percent raises the effective peripheral pull by not more than 20 percent and this fact illustrates the degree of stabilisation that is'achieved.

Analogous conditions naturally apply when the direction of rotationis reversed or whenthe brake is applied.

Another requirement for achieving an optimum performance of the proposed apparatus is that whenever the belt is suddenly started for forward running, i.e. when the'two-rollers 22 and 23lar e. pressed together by the spring 32, the friction between the driving rollersand the belt. should remain low to prevent: the belt from getting hot aridfrom being damaged or destroyed. The relatively low mass of the belt should be more or less instantaneously ac'celerated to maximum, speed V,, i.e. the peripheral speed of the drive rollers. Friction due to slippage will then occur only on the pulley where the specific pressure is low because of the large circumference of the pulley and'where cooling is not a problem; I,

With reference to FIGS. 50 and 5b the further question will now be discussed how much work A,is expended for accelerating abelt ofm'ass m from zero speed to maximum speed V This work is done in the time T (switching time). At the time r== 0 the speed V of the belt is assumed to be zero. When the two

rollers

22 and 23 are pressed together they generate a force offriction P which accelerates the belt to the maximum speed V,. When this has been reached the belt continues to travel without slip at V,,. During this switching time T the speed is V =7 b t, where b is the acceleration of the. belt, or V =.(P P **t/m;where P is the force exerted by the

rollers

22, 23, P, is the braking force of the pulley and m ,is the equivalent mass of the belt. In this time T'the speed V, is reached in accordancewith the equation The switching time T can therefore be calculated from I f and the work performed is Hence P A =(P Pu-%)-m.V 2

This equation indicates that the force P exerted by the drive rollers should substantially exceed the braking force P, if the work of friction is to remain low. If P is, much greater than P,

is the minimum possible work of friction for accelerating the belt. It will be seen that this force of friction diminishes in proportion with the mass m of the belt and that the magnitude of the mass of the winding-on or drawoff spool including the roll does not enter into the result. At a speed of V, cm/sec.

for a belt weighing 30 p the work of friction for starting up the cient of friction between the rollers and the belt and, on theother hand, upon the pressure applied to the belt by the action of the spring 32 (FIG. 4). It again transpires that the peripheral pull P, should be as constant as possible to avoid the need of a spring 32 of unnecessarily high rating, since the spring rating must be overcome by the cam and the tensioning lever and should therefore be as small as possible.

Analogous relationships apply to reverse drive and to the braking action.

In FIG. 6 two mechanisms of the kind shown in FIG. 1, (to 3) are combined to form a single rewinding machine .with asingle driving motor M. In the right-hand system components corresponding to like components in FIG. I bear the same reference numerals as in FiG. 1. Like components in the lefthand system are likewise identified by the same reference numerals but they are distinguishedby a prime. Each of the two systems functions independently from the other as has already been described with reference to FIGS. 1 to 3. However, for cooperation one system is always set to wind on and the other to wind off, or both systems are braked. In the drawing the left-hand system is set to wind on. The strip material travels from point PE to point PE through guide meanswhich are irrelevant to the invention. Treating and/or viewing stations may be provided between PE and PE. 7

' FIGS. 7 to 9 illustrate an embodiment of the invention specially designed for several different speed ranges. This embodiment is therefore in effect fitted with three

pulleys

4,, 4,, and 4 of different diameters. As a matter of practice a single pulley structurehaving three stepped diameters is utilized.

They are all mounted on a common rotatable shaft land each' driven by a

different belt

5,, 5,, and 5,,,. The

fixed drive rollers

22 and 24 operate to drive all three belts. However, each of the three

belts

5,, 5,,, and 5,,, is associated with a deflectably

movable roller

23,, 23,,, and 23,,, and 25,, 25,,,

25, (25,, ,,,)'and each pair of rollers (23,/25,, 2 11/25 23,,,/25m) is in turn associated with a control cam of its own. 'The three cams are provided on three

quadrants

38,, 38,, and 38 affixed to a common strip tensioning lever 7. In principle the arrangement functions in exactly the same way as that described with reference to FIGS. 1 to 3, excepting that the position of the tensioning lever 7 controls three forward and three reverse speeds. The three control cams are so contrived and relatively positioned that the system functions as follows: In the highest position of the tensioning lever 7 the roller 23, is pressed into contact with the belt and the highest forward speed is thus obtained. If the tensioning lever drops towards its centre position, the roller 23, is withdrawn and the roller 23,,

is pressed against the belt, thereby generating a medium speed. Further downward deflection of the tensioning lever the lowest, the medium and the highest reverse speeds. The tensioning lever 7 thus functions like a gear selector lever. The three cams of the three

quadrants

38,, 38 and 38 are naturally again so contrived (cf. FIGS. 1 to 5) that only one of the rollers or the brake can cooperate with one of the belts at the same time.

The diagram in FIG. 9in; graph form represents the functional dependence of the speed of the winding spool upon the position of the tensioning lever.

FIGS. 10a and 10b illustrate a variant of the control cam in which the quadrant 38 formed with a cam track 39 is pivotably mounted and coupled to the tensioning lever 7 by a lost motion mechanism. As illustrated, the control quadrant works on the same shaft as the tensioning lever to which it is coupled by a sliding pin and slot motion 52-51. The pin 52 is fast on the tensioning lever and works in a recess 51 cut into the periphery of the quadrant. Thisarrangement introduces the lost motion into the action of the tensioning lever when the latter reverses its direction of deflection. The delay S introduced by the lost motion-is determined by the length of the recess 51 in the quadrant and the diameter of the pin. When the tensioning lever is deflected upwards (FIG. 10a) the quadrant is engaged as soon as the pin 52 makes contact with the upper end of the recess 51. However, when the tensioning lever is lowered the quadrant is engaged when the pin 52 is intercepted by the bottom end of the recess 51. This hysteresis effect which is thus introduced into the working of the control means prevents the tensioning lever from continuously stopping and starting the belt when the lever oscillates within a small angle. After having started the belt the tensioning lever must therefore be deflected through a distance S before the belt is again stopped.

The transmission from the drive motor M (H6. 6) to the drive rollers may be a belt drive, gearing or the like. Either both rollers of a pair or only thefixed roller may be driven.

lclaim:

1. Apparatus for winding and unwinding strip material comprising a belt, a pulley driven by said belt, a winding spool coupled to said pulley, the strip material being wound onto or drawn off said winding spool dependent upon the direction of rotation of said pulley, first and second pairs of driving'rollers between which said belt passes, a brake mechanism for said belt, a spring-loaded tensioning lever, at least one strip material tensioning roller mounted on said lever and around which the strip material passes, and cam means actuated by movement of said tensioning lever as the tension in said strip material passing around said tensioning roller varies and operatively connected respectively with said first and second pairs of belt-driving rollers and said brake mechanisms for alternative activation dependent upon the position of said tensioning lever, said lever when moved to a first position actuating said cam means to activate said first pair of rollers to engage and drive said belt and pulley in one direction, said lever when moved to a second position actuating said cam means to activate said second pair of rollers to engage and drive said belt and pulley in the opposite direction, and said lever when in a position intermediate said first and second positions actuating said brake mechanism to engage and stop said belt and pulley, said pairs of belt-driving rollers and said brake 1 mechanism when engaged with said belt providing frictional forces in excess of the frictional forces existing between said belt and pulley.

2. Apparatus as defined in claim 1 for winding and unwinding strip material and which further includes a plurality of belt-tensioning pulleys around which said belt passes and which are located intermediate said belt-driving rollers and pulley, swivel arms individual to and mounting said belt-tensioning rollers, spring means individual to and biasing said swivel arms and the belt-tensioning rollers thereon into contact with said belt so as to tension it, and stop means individual to said swivel arms for limiting the movement of said swivel arms in the belt-tensionin direction.

3. Apparatus as define in claim 1 for winding and unwinding strip material wherein said cam means includes a cam track member actuated by said tensioning lever and cam follower means engaged with said track and individual respectively to said first and second. pairs of belbdriving rollers and said brake mechanism for actuating the same alternatively into engagement with said belt.

4. Apparatus as defined in claim 3 for winding and unwinding strip material wherein said cam track is formed with a recess and said cam followers are constituted by pins which when engaged with said recess activate alternatively said pairs of belt-driving rollers and brake mechanism.

5. Apparatus as defined in claim 1 for winding and unwinding strip material wherein each pair of belt-driving rollers includes one power-drivenroller engaging said belt and rotating on a fixed axis and a second roller mounted on a spring-loaded swivel arm which normally biases said second roller into pressing engagement withsaid belt, and said cam means includes a cam track member actuated by said tensioning lever and cam followers engaged with said cam track, said cam track being formed with a'recess and said cam followers being mounted respectively on said swivel arms and serving to shift the corresponding second roller in a direction away from said belt except when the cam follower occupies the recess in said cam track.

6. Apparatus as defined .in claim 5 for winding and unwinding strip material wherein said pulley includes a plurality of different driving surfaces of different diameters, there being a separate belt correlated to each different pulley diameter, each said pair of belt-driving rollers including a common power-driven roller and a plurality of second rollers each alternatively engageable with a different one of said belts, and wherein said cam means when actuated by movement of said tensioning lever towards said first or second positions from said intennediate position causes said second rollers to engage said belts in succession to successively increase the .driving speed of said pulley and winding spool.

7. Apparatus as defined 'n clai 1 for winding and unwinding strip material wherein said cam means includes a cam I track fonned integrally with; said tensioning lever and. earn track follower means operatively-connected with said first and second pairs of driving rollers and said brake mechanism.

8. Apparatus as defined in claim 1 for winding and unwinding strip material and which further includes a lost motion mechanism interposed between said tensioning lever and said cam means for delaying actuation of said cam means until said v tensioning lever has moved a predetermined distance from its intermediate position.

9. Apparatus as defined in claim 1 for winding and unwinding strip material wherein said cam means includes a pivotally mounted cam member provided with a cam track and a plurality of cam track follower means operatively connected with said first and second pairs of driving rollers and said brake mechanism respectively and which further includes a lost motion mechanism interposed between said tensioning lever and said cam member for delaying action of said cam means until said tensioning lever has moved a predetermined distance from its intermediate position.

V 10. Apparatus as defined in claim 9 for winding and unwinding strip material wherein said lost motion mechanism includes a pin movable between two spaced abutrnents, said pin being carried by said tensioning lever and said abutrnents being carried by said pivotally mounted cam member, or vice versa.

11. Apparatus as defined in claim 10 wherein said cam member and said tensioning lever are mounted for pivotal movement about a common shaft.