US3567145A

US3567145A - Method and apparatus for winding up successive segments of a continuously delivered strip

Info

Publication number: US3567145A
Application number: US760631A
Authority: US
Inventors: Michel Ernoult; Pierre Pennel
Original assignee: PLASTIQUES DE ROUBAIX AND ANCI
Current assignee: LES PLASTIQUES DE ROUBAIX AND ANCIENS REPIQUET Ets; PLASTIQUES DE ROUBAIX AND ANCI
Priority date: 1967-09-19
Filing date: 1968-09-18
Publication date: 1971-03-02
Anticipated expiration: 1988-03-02
Also published as: DE1774847C3; GB1233211A; FR1544124A; BE720394A; LU56884A1; DE1774847B2; DE1774847A1; NL6813445A

Abstract

A strip-winding machine for winding on mandrels segments cut from a continuously delivered strip of material, the strip being cut at the end of the winding on a given mandrel by means of a blade carried by a movable blade carrier, which is applied onto a rotating empty mandrel into the surface of which the blade can penetrate, so that at the end of the cutting the transverse leading edge of the strip is automatically pressed by the blade against the surface layer of the mandrel, ensuring the initiation of the winding on the empty mandrel by maintaining for a short time the strip clamped between the mandrel and the movable blade carrier.

Description

' United ttee attend SUCCESSIVE SEGMENTS 01" A CONTINUOUSILY DELIVERED STRIP l1 filaims, 9 Drawing Pigs.

US. Cl 242/56 B6511 35/04 [50] Field of Search 242/56 (A), 56

Primary ExaminerNathan L. Mintz Attorney-Wenderoth, Lind & Ponack ABSTRACT: A strip-winding machine for winding on mandrels segments cut from a continuously delivered strip of material, the strip being cut at the end of the winding on a given mandrel by means of a blade carried by a movable blade carrier, which is applied onto a rotating empty mandrel into the surface of which the blade can penetrate, so that at the end of the cutting the transverse leading edge of the strip is automatically pressed by the blade against the surface layer of the mandrel, ensuring the initiation of the winding on the empty mandrel by maintaining for a short time the strip clamped between the mandrel and the movable blade carrier.

PATENTEUHAR 2mm v 3,567,145

sum 1 OF 4 MICHEL ERNUULI PIERRE PENNE L PATENTEU m 21% 3.557.145

SHEET 2 OF 4 METHOD AND APPARATUS FOR WINDING UlP SUCCESSIVIE SEGMENTS OF A CONTINUOUSLY DELIVERED STlRlIlP The present invention relates to methods and machines for winding on mandrels successive segments of continuously unwound materials having the form of strips, foils or films, which may be constituted of paper, woven or nonwoven fabrics or diverse other materials.

In the known machines, thecutting of the strip is effected by means of a double-blade device. A cutting device of this type operates in the manner of a pair of scissors.

Although a device of this kind cuts the material perfectly, independently of its hardness, rigidity; elasticity thickness, etc., it involves the operation of a number of movable arms carrying the cutting blades and the deflecting cylinders, which arrangement leads to perturbations in the transport circuit of the material to be wound up. These perturbations are manifested as variations of the tension of the wound-up strip and limit the use of the machines employing a cutting device of this kind to the winding-up of relatively strong materials of low elasticity which are capable of withstanding the variations of the winding tension.

Moreover, the movements of the cutting arm and the rotation of the winding machine demand a certain time, which limits either the winding speed or the length of material wound which is propelled against the strip to be cut.

These devices tear the strip rather than cutting it, and their use is limited to materials of low tear strength and low elasticity. v

In the known machines, the engagement of the strip to be wound up on an empty mandrel is effected by enveloping or adhesion.

The engagement by enveloping can be carried out correctly only if the speed of the empty mandrel is synchronized with the transport velocity of the material.

Moreover, the engagement provided in this manner is not reliable; in particular, the strip may have to be folded back on itself, and the portion of increased thickness thus formed at the beginning of the winding operation may mark the woundup material over a great number of turns.

The engagement on the empty mandrel by adhesion, although very reliable, can also lead to the formation of folds within the material.

The object of the invention is to remedy the various shortcomings mentioned above, and relates in particular to an improved method winding on mandrels segments cut from a continuously delivered strip of material. The invention is more especially characterized in that at the end of the winding on a given mandrel, the strip is cut with the aid of a blade carried by a movable blade carrier, which blade is applied to an empty mandrel, of which at least the superficial layer is such as to allow said blade to penetrate thereinto, so that at the end of the cutting the transverse leading edge of the strip is automatically applied by the blade against said surface layer of the mandrel and an initial winding is effected on the empty rotating mandrel by maintaining the strip for a short time clamped between the mandrel and the movable blade carrier.

In this manner, an automatic engagement can be achieved, i.e., a perfect initial winding of the strip on the empty mandrel.

The invention also has for an object a machine for carrying out the method defined above, by winding up materials in strip form.

The invention will now be described with reference to the accompanying drawings, which illustrate the invention but in no restrictive sense.

FIG. 1 is a general view, in side elevation, if the machine according to the invention;

FIGS. 24 show the three positions occupied by the mechanism displacing the blade-carrier roller during an operational cycle of the machine;

FIG. 5 is a top plan view of the mechanism initiating the movement of this roller and the device effecting the lateral displacement of the blade;

FIG. 6 is a more detailed view of the device effecting the lateral displacement of the blade;

FIG. 7 is a diagram of the synchronizing unit of the machine;

FIG. 8 is a graph, showing the time charts of the three operating cycles of the machine; and

FIG. 9 is another embodiment of the invention, showing a helical blade mounted on the blade-carrier roller.

In the example of embodiment here illustrated, the machine essentially comprises a frame 1 (FIG. 1), in which the elements for transporting, cutting, engaging and winding up the strip are mounted, together with the devices for distributing the empty mandrels and for removing the finished rolls.

The strip-transporting device comprises a first roller 2 located at the input of the machine and supporting the strip 3 to be conveyed, followed by a travelling roller 4, suspended by an assembly of cables, chains, belts or levers here not illustrated, to control, by means of a rheostat, the speed of the winding motor here not shown and to maintain constant the tension of the wound-up strip.

l The strip then passes over deflecting rollers 5 and a roller 6, which may be a smoothing roller, a curved roller, a smoothing bar or simply a deflecting roller. Following this, the strip passes about a cutting and engaging roller 7 and winds on to a mandrel 8a carried by a revolving winding frame 9 driven by motors M M and 9, adapted to carry at all times the mandrel 8a in winding position, a second mandrel 8b initially in the rest and cutting position and then in the winding position after removal of mandrel 8a, as well as a third mandrel 8c in waiting position.

The

rollers

4, 5, 6 and 7 are driven by the strip to be wound up, while the winding mandrel 8a and the mandrels 8b and 8c are driven by an electrical, electronic, hydraulic, mechanical or other per se known change speed gear, here not shown, whose speed is controlled by the traveling roller 4.

This mandrel can also be driven by a constant-speed motor, coupled with a hydraulic, electric, magnetic or other type of clutch.

The mandrels 8a, 8b, 8c are connected with their drive motors by means of removable cones here not shown.

The device for cutting and engaging the strip essentially consists of the hollow blade-carrier roller 7, formed by a metal tube 10 surrounded by a sleeve 11 made of a soft elastic material in which a blade 12 is imbedded. This blade is mounted on an internal axle 13 of roller 7 by means of pins 14, the purpose of this arrangement being to impart to the blade 12 a reciprocating motion.

The device effecting the lateral displacement of the blade 12, shown in the bottom portion of FIGS. 5 and 6, comprises a jack 15 at the extremity of which a rod 16 is mounted. This rod carries a roller 17 bearing on a bell-shaped cam 18 fast with the axle 13 of the blade-carrier roller 7.

This axle is provided with a return spring 19 which is supported on the bottom of roller 7.

The roller 7 is loosely mounted on one end of a supporting arm 20, which is itself mounted on a fixed axle 21 and is movable about this axle by means of two

jacks

22, 23 operating in opposing directions. The jack 22, one end of which is pivotally connected to the frame of the machine, its second end being connected to the arm 20 by means of a pin 37 which is engaged in a guide 39 provided in the supporting arm 30 (FIG. 2) is adapted for pulling the supporting arm 20"into engagement with a stop 38 integral with the machine frame, when the roller 7 is to be engaged with the mandrel 8b. The jack 23, the two ends of which are respectively pivotally connected to the frame of the machine and to the end of the supporting arm remote from the roller 7 is adapted for rotating the arm when disengaging the roller 7 from the mandrel 8b.

The support arm 20 can be maintained in three different positions corresponding to the three positions occupied by the roller 7 during an operating cycle of the machine. These three positions are illustrated in FIGS. 2, 3 and 4.

To this end, the support arm 20 is equipped with a locking device (FIG. 2), consisting of a cam 23 mounted on the axle of the blade-carrier roller for cooperation with a roller 24 carried by a lever 25 which is freely articulated by means of a pin 26 on a support 27 fast with the arm 20.

The lever 25 can be made fast with the support arm 20 by means of two

rods

29 and 30, whose joint is connected with a jack 31 pressing these rods against a stop 32 integral with the support 27. The rod 29 is moreover connected to the extremity of lever 25 which does not carry the roller 24 and the rod is connected to the extremity of a locking member 33 movable about the axle 21 of supporting arm 20. A return spring 34 is mounted between the locking member 33 and the support arm 20.

At its opposite end the locking member 33 is provided with a hook comprising two

grooves

35 and 36 for cooperation with a pin 37 fast with the jack 22 and with a stop 38 integral with the machine frame.

The pin 37 is engaged in a guide 39 provided in the supporting arm 20.

The cutting and engaging device is completed by the empty mandrel 8b mounted on the revolving winding frame 9 and set off by 120 relative to the winding mandrel 8a and is driven by a motor here not shown.

At the instant of cutting and engagement, the empty mandrel 8b serves as support for the blade-carrier roller 7 when the latter comes into the cutting position. The empty mandrel 8b, as well as the mandrels 8a and 8c, has at least its superficial layer adapted to allow the blade 12 to penetrate thereinto. It is conveniently made of cardboard, wood, plastic or other material which allows the edge of the blade 12 to penetrate thereinto, but it may also be constituted by a metal cylinder coated with any one of the aforementioned materials. It also serves in cooperation with the blade-carrier roller 7 to initiate the winding thereon and to replace the mandrel 8a when the winding on the latter is terminated.

A hollow glue-applying cylinder 41, having small perforations on its lateral surface and covered with spongy material 42 is mounted so as to apply the adhesive to the empty mandrel 8b.

The term adhesive" as employed in the present context is intended to designate any substance having an adhesive power by itself or a diluting effect on the surface of the material of the mandrel or of the material to be wound up.

The device for introducing the empty mandrels 8c comprises a feed channel 44 acting as magazine, a distributor 45 whose operation is synchronized with the removal of the finished roll carried by the mandrel 8a and the revolving winding frame 9 whose positioning is effected by a mechanical precision-locking means.

A ramp 46 is provided for evacuating the finished rolls b.

The movements and the various positions of the diverse components of the machine are signalled by electrical contact connected to a synchronizing device 47.

The principal electrical contacts are shown in FIG. 1.

The three contacts referenced C serve to indicate the three positions of an arm of the winding frame.

The contact C cooperating with a cam 43 fast with the roller 6 emits impulses in a number proportional to the length of the wound-up strip.

The contact C serves to signal the instant when the bladecarrier roller 7 is in the high or retracted position.

The contacts C C arranged on the discharge ramp 46 serve to indicate the evacuation of a finished roll.

The contact C serves to signal the presence of the mandrels on the winding frame.

C is an end-of-course contact and safety contact which is actuated when the roll being wound has reached a certain diameter.

C is a safety contact actuated by the winding frame 9 and capable of stopping the machine as a whole in the case of a disturbance in the provisioning of the winding frame with empty mandrels.

The synchronizing device of the machine, shown in FIG. 7, essentially comprises a counting element 48 for counting the impulses transmitted by the electrical contact C which cooperates with the cam 43 fastened to the axle of roller 6.

This counting element serves to initiate the cutting of the strip. To this end, it is connected with a cutting control circuit 49 which serves to control the movements of support arm 20 of the blade-carrier roller 7, by acting on the

jacks

15, 22, 23 and 31 the functions of which have been disclosed heretofore. However, since the cutting can only take place when the revolving winding frame 9 is stopped, the circuit 49 is additionally connected with the stopping unit A of a start-stop" circuit 50 of the revolving winding frame 9. A circuit adapted to supply a signal only after receipt of the counting signal during the stoppage of the revolving winding frame is inserted into the assembly.

The start-stop circuit 50 of the revolving winding frame serves to control the drive of the winding frame 9 after execution of a cut. The starting unit M of this circuit comprises an input connected to an output of the cutting control circuit 50 supplying an end-of-cut signal through a circuit 52. In view of the fact that the winding frame can only be driven after evacuation of the finished 'roll from the winding station, followed by the unlocking of the frame, the circuit 52 has two

supplementary inputs

53, 54 serving to transmit respectively a signal indicating the evacuation of the finished roll and a signal for unlocking the winding frame.

An output of the starting unit M of control circuit 50 of the revolving winding frame 9 is connected to a circuit 55 controlling the distribution of empty mandrels and to a circuit 56 controlling the adhesive feed of the applicator cylinder 41.

The stopping unit A of circuit 50 comprises an input 57 controlled by a signal emitted when the empty mandrel arrives in the rest position and an output 58 connected to the starting units M of three start-stop circuits such as 59 of the strip-winding motors. For the sake of simplicity of the diagram only one of these circuits is shown in FIG. 7.

The stopping unit A of the control circuit 59 of a winding motor comprises an input connected via a circuit 60 to the output of the cutting control circuit which emits an end-of-cut signal. The circuit 60 further comprises an input 61 for receiving the starting signal of the next motor.

The output of the stopping unit A of circuit 59 is connected to the input of a circuit 62 which controls the withdrawal of the locking cones of the mandrel, the advance of these cones being controlled by the stopping signal of the next motor received on the input 63 of circuit 62.

The starting unit M of control circuit 59 of the winding motor comprises an input connected to an output of the stopping unit A of the start-stop circuit 50 of the revolving frame.

The speed of the winding motor 64 is controlled by an automatic control unit 65 itself controlled by the travelling roller 4 of the machine.

Manual control elements and numerous safety elements not shown in the drawing ensure the operational reliability of the machine.

The counter 48 is constituted by two counters with preselection and electrical zero reset, which operate alternately, the switching of the pulses to one or the other of these counters being effected by means of electromechanical relays.

The cutting-control circuit 49 comprises electrical valves controlling the

jacks

15, 22, 23 and 31 as well as a certain number of relays with or without time lag, all these elements being ofa conventional type.

The circuit 59 controlling the winding motors likewise comprises conventional contacts and relays, the motors being protected against overloads by magneto-thermic cutouts.

The device 62 for advancing and retracting the coupling cones of the mandrels is also a relay circuit of a conventional type, and comprises in addition electrical valves for actuating the cone-driving jacks.

The

circuits

50, 55, 56 and 65 are constituted by relays and electrical contacts of a conventional type.

The winding motors, such as 64, are driven by the intermediary of speed-change gears known per se, subordinated to tachogenerators driven by the machine which supplies the material to be wound up.

In the form of embodiment according to the invention, the various circuits composing the synchronizing device 47 essentially comprise electromechanical elements, but it is obvious that an assembly of this kind could also be composed of counting circuits, gates and logical circuits with transistors or valves. 1

The time chart shown in FIG, 8 will facilitate the understanding of the operating sequence of the machine.

This chart comprises ll curves AK, which represent respectively the adhesive feed, the rotation of the revolving winding frame 9, the movements of the blade-carrier roller 7, the rotation of the motors driving the mandrels 8a, 8b and 8c, the movement of the blade 12, the operation of the mandrel distributor 45 and the advance and withdrawal of the coupling cones of mandrels 8a, 8b and 8c.

The chart illustrates three operating cycles. The origin of the curves being at an instant preceeding a cutting operation, the roller 7 (curve C), actuated by the

jacks

22 and 23, passes from the intermediate position (FIG. 2) into the low position (FIG. 3) and comes to bear on a mandrel 8b. Simultaneously, the motor of mandrel 8b (curve D) passes from a constant speed to a decreasing speed and maintains a constant tension in the wound-up material. The roller 7 being applied to the empty mandrel 8b, the blade 12 (curve G) is set in reciprocating motion by the assembly constituted bythe jack 15, the rod l6, the roller 17, the cam 18, the axle 13 and the pins 14, and projects from the lateral surface of the roller 7 owing'to the I crushing of the soft elastic material which covers said roller, to

cut the strip 3.

After the cut, the roller 7 remains in contact with the mandrel 8b during a time sufficiently long to ensure that the strip clamped between these two elements is cut, and executes a fractional turn about the empty roller ensure the engagement.

This engagement is further facilitated by the application of an adhesive on the empty roller 8b. The cutting roller 7 then retracts into the high position (FIG. 4) and simultaneously the motor of mandrel 8a stops (curve B). Almost immediately the coupling cones of the third mandrel 8c (curve K) take up an empty mandrel. Following this, the coupling cones of mandrel 3a open (curve J) and discharge the finished roll b on the inclined discharging plane 46. The revolving winding frame then starts to rotate (curve B); in the course of this rotation the distributor 45 admits an empty mandrel (curve H). The motor of mandrel be then starts to operate at a constant speed (curve F), while a certain quantity of adhesive is admitted into the applicator cylinder 41 (curve A). Shortly before the revolving winding frame stops, the blade-carrier roller 7 descends into an intermediate position, called ready position (curve C).

The revolving winding frame stops after executing a onethird revolution.

When a certain length of material has been wound up, a new cut is initiated and the cycle recommences. The mandrel 8b which served as cutting support takes the place of mandrel 8a on which the material has been wound.

The cutting operation proper can be explained with reference to FIGS. 2, 3 and 4.

When the supporting arm is in the intermediate position (FIG. 2), the jack 23 pulls the arm 20 and tends to urge it upwards; however, the jack 22, whose thrust is greater, opposes this action and maintains the assembly in the position shown in FIG. 2. The arm 20 remains blocked in this position by'the pressure of pin 37 against a stop 38 integral with the machine frame.

The cam 23', fast with the blade-carrier roller 7, rotates in the direction indicated by the arrow.

The roller 24 carried by the lever 25 is constantly returned by the

rods

29 and 30.

To effect the cut, the jack 3], of very low power, passes the

rods

29 and 30 from the position shown in FIG. 2 into the position indicated in FIG. 3. The assembly of the two pins is caused to bear against the stop 32 of the support 27 fast with the arm 20, thereby constituting a rigid assembly.

When the cam 23 in the course of its rotation lifts the roller 24, the lever 25 bears via the

rods

29 and 30 on the locking member 33, allowing the pin 37 to escape the stop 38 by sliding laterally in the track 39. The thrust of the jack 22 overcoming that of the jack 23, the supporting arm 20 of the bladecarrier roller tilts and applies the blade to the empty mandrel 8b to effect the cutting. Y

The blade-carrier roller is then in the position shown in FIG. 3, the cam 23 continues to turn and raises again the roller 24, whereby the locking member 33 passes into the position shown in FIG. 4. The pin 37 is completely freed, but since the jack 22 is practically at the end of its course the pull of the jack 23 overcomes it and the support arm 20 entrains the blade-carrier roller into the high position shown in FIG. 4. The jack 31 then dislodges the

rods

29 and 30 from the stop 32, the jack 22 again becomes thrusting and the arm returns into the median position so that a new cut may be executed.

The reciprocating motion is imparted to the blade by the device shown at the bottom of FIGS. 5 and 6.

Shortly before the cut the jack l5 pulls the pin 16 which assumes the position shown in FIG. 6. With each revolution of the blade-carrier roller 7 the internal axle l3 executes a reciprocating movement under the action of the bell cam 18 hearing on the roller 17 and of the spring 19, and entrains the blade 12 by means of the rods 14.

The cam 18 is fixed at an angle so that the movement is generated when the blade passes in front of the empty mandrel 8b.

The invention is of course not limited to the form of embodiment herein described and illustrated by way of example.

Thus, the blade may have a smooth or serrated cutting edge the teeth of which may be triangular or rounded. It may be mounted in the blade-carrier roller along a generatrix of the latter (see FIG. 6) or as shown in FIG. 9, sunk in a helical groove 12 provided in the lateral wall of the blade-carrier roller 7. It may also be doubled over the whole of its length by a second blade executing an oppositely directed alternating movement.

I claim:

1. In a method for winding up on mandrels segments cut from a continuously delivered strip of material, said strip being cut at the end of the winding on a given mandrel by means of a blade carried by a movable blade carrier, the improvement that said cutting is carried out be applying said movable blade carrier onto a rotating empty mandrel having at least a surface layer which has the quality of allowing the cutting edge of said blade to penetrate thereinto so that, at the end of the cutting, the transverse leading edge of the strip is automatically pressed by said blade against said surface layer of the mandrel, ensuring the initiation of the winding on the empty mandrel by maintaining the strip clamped for a short time between said mandrel and said movable blade carrier,

2. A machine for winding up strip materials for carrying out the method according to claim 1, comprising a revolving winding frame adapted to receive a first rotary mandrel on which the material is to be wound, a second empty rotary mandrel to occupy initially a rest position and to take subsequently the place of the first mandrel by rotation of the winding frame, and a rotating blade-carrier roller over which the strip driven by the first mandrel passes, wherein said blade is sunk into the lateral surface of said roller and can project from said surface, a mechanism carrying said roller and adapted to displace said roller relative to said rest position of said empty mandrel which has at least a surface layer which allows the penetration of the edge of said blade thereinto so that, during application of said blade-carrier roller onto said empty mandrel, the projection of said blade from the surface of said blade-carrier roller and its penetration into said surface layer of said empty mandrel bring about the cutting of the strip which is then kept clamped between said blade-carrier roller and said empty mandrel to ensure the engagement of the strip on said empty mandrel.

3. A machine as claimed in claim 2, wherein said blade-carrier roller is covered with a sleeve of a soft elastic material into which said blade is sunk.

4. A machine as claimed in claim 2, wherein said blade mounted on an internal axle by means of pins, said pins being arranged in the interior of said roller and said internal axle being connected to a device comprising a jack at the extremity of which is mounted a rod, said rod carrying a roller which bears on a cam fast with said axle of said blade-carrier roller, and return spring means mounted on said axle, said device being adapted for imparting to said blade a lateral reciprocating motion relative to the lateral surface of said blade-carrier roller.

5. A machine as claimed in claim 2, wherein said blade is sunk in the lateral surface of said blade-carrier roller along a generatrix of said blade-carrier roller.

6. A machine as claimed in claim 2, wherein said blade is sunk in a helical groove provided in the lateral wall of said blade-carrier roller.

7. A machine as claimed in claim 2, wherein said empty mandrel is of a material which allows the edge of said blade to penetrate thereinto.

8. A machine as claimed in claim 2, wherein said empty mandrel is a metal cylinder coated with a material which allows the edge of said blade to penetrate thereinto.

9. A machine as claimed in claim 2, wherein said mechanism comprises an arm mounted to pivot about an axle fast with the machine frame, said arm carrying said blade-carrier roller at one of its ends and being connected at the other end with two oppositely-acting jacks, and a locking device for maintaining said blade-carrier roller in any of three positions, namely respectively a cutting, waiting and retracted position.

10. A machine as claimed in claim 9, wherein said locking device comprises a locking member displaceable by rotation about said axle, said locking member having at one end a hook having two grooves for cooperation with a pin engaged in a slot of the arm fast with one of the jacks for driving said arm and with a stop integral with the machine frame, and being connected at its other end to a control device for operating said locking member with the aid of a cam mounted on the axle of said blade-carrier roller.

11. A machine as claimed in claim 10, wherein said lockoperating device comprises a first link pivoted to said locking member and connected to a second link which carries an oscillating lever on a pin fast with said support arm, said lever having a roller cooperable with the cam keyed on the axle of said blade-carrier roller, the pivot of said two links being connected to a low-power jack mounted on said support arm which, in combination with a fixed stop on said support arm renders said links integral with said arm for transmitting the movements of said roller to said locking member.

Claims

1. In a method for winding up on mandrels segments cut from a continuously delivered strip of material, said strip being cut at the end of the winding on a given mandrel by means of a blade carried by a movable blade carrier, the improvement that said cutting is carried out be applying said movable blade carrier onto a rotating empty mandrel having at least a surface layer which has the quality of allowing the cutting edge of said blade to penetrate thereinto so that, at the end of the cutting, the transverse leading edge of the strip is automatically pressed by said blade against said surface layer of the mandrel, ensuring the initiation of the winding on the empty mandrel by maintaining the strip clamped for a short time between said mandrel and said movable blade carrier.

11. A machine as claimed in claim 10, wherein said lock-operating device comprises a first link pivoted to said locking member and connected to a second link which carries an oscillating lever on a pin fast with said support arm, said lever having a roller cooperable with the cam keyed on the axle of said blade-carrier roller, the pivot of said two links being connected to a low-power jack mounted on said support arm which, in combination with a fixed stop on said support arm renders said links integral with said arm for transmitting the movements of said roller to said locking member.