Device for precise connection for a machine for continuous unwinding

Abstract

The present invention relates to a device for precise connection for a continuous unrolling machine, comprising at least a means (3) for unrolling two spools, a strip accumulator (4) and a device for connecting ending strips (1) and new strips (2).

Description

DESCRIPTION

[0001] The present invention relates to the field of machines for continuously unrolling strip material, from spools, to supply continuously printing machines, forwarding machines or the like, and has for its object a device for precise connection for such a continuously unrolling machine.

[0002] The precise connection between ending and new strips of material is necessary in certain fields, so as to ensure a perfect continuity of decorative or informative elements carried on said strips. Such precision, which consists in obtaining a high precision superposed connection, which is to say such that the marks on an ending strip coincide perfectly with those marked on a new strip, is particularly important, for example, in the case of unrolling strips of the material in the form of aluminum films, particularly for closing packages of medications or the like, which bear inscriptions disposed at regular intervals. These inscriptions thus require being perfectly offset relative to each other during connection of two ends of the superposed strips, so as to guarantee perfect agreement of the inscriptions with the contents of the package. The same problems arise in the presence of other strips provided with markings that are to be arranged in a perfectly regular and precise manner.

[0003] At present, there is known from GB 2 148 856, an unrolling machine using independent means for preparation of the end of the new strip and for moving said strip so as to match a junction mark. Such an embodiment however does not permit ensuring a sufficient degree of precision.

[0004] There is also known, from U.S. Pat. No. 4,455,190, an unwinder comprising a device for cutting the ending strip and applying the beginning of the new strip on the end of the cut strip provided with an adhesive, with overlap. The device according to this document does not provide for indexing the strips, nor referencing them, nor detecting position, nor means for moving the strips at reduced speed, it is accordingly impossible to produce a precise superposition and to obtain a sequence of the printing between the two strips.

[0005] These known unwinding machines provide no means for moving the strips at reduced speed under controlled tension, whereby they do not permit producing a high precision connection, in particular because of the inertia of the spool and/or the various changes in strip tension, for example under the influence of motorized strip drive. However, it is very important that the tension in the strip remain constant, and hence that the elongation of the strip be constant, to ensure precision of connecting the markings.

[0006] The present invention has for its object to overcome these drawbacks by providing a precision connecting device for a continuous unwinding machine permitting high precision of superposed connection between two strips, ending and beginning, with complete integrity of the spacing between consecutive markings.

[0007] To this end, the precision connection device for a continuous unrolling machine, comprising at least means for unrolling two spools, a strip accumulator and a connecting device, is characterized in that the connecting device is essentially constituted by a station for joining and indexing the strips and by at least one precise control means for the speed of movement of the strip through the junction and indexing station.

[0008] The invention will be better understood from the following description, which relates to a preferred embodiment, given by way of non-limiting example and explained with reference to the accompanying schematic drawings, in which:

[0009] FIG. 1 is a side elevational view of an unwinding machine provided with a connection device according to the invention;

[0010] FIG. 2 is a fragmentary side elevational and cross-sectional view, on a larger scale, showing the connection device and two precise control means for the speed of movement of the strip;

[0011] FIG. 3 is a fragmentary side elevational view, on a larger scale, of a station for preparing a new strip;

[0012] FIG. 4 is a fragmentary front elevational view of the strip and the drive of the ending strip;

[0013] FIG. 5 is a schematic side elevational view showing the principle of operation of the machine;

[0014] FIGS. 6 and 7 are views on a larger scale analogous to that of FIG. 5, showing two modes for preparation of a new strip;

[0015] FIG. 8 is a view partially in cross-section, on a large scale, showing the junction of two registering strips;

[0016] FIGS. 9a to 9c are partial schematic views showing the operation of the strip accumulator, and

[0017] FIG. 10 is a curve of the speeds of strips during the connection operation.

[0018] FIGS. 1, 2 and 5 of the accompanying drawings show a continuous unrolling machine permitting continuously unrolling with superposed connection between two strips, an ending strip 1 and a new strip 2 and comprising at least one means 3 for unrolling two spools, a strip accumulator 4 and a connection device.

[0019] According to the invention, the connection device is essentially constituted a station for joining and indexing the strips 1 and 2 and by at least one means 6, 37 for precise control of the speed of movement of the strip through the joining and indexing station.

[0020] The unrolling machine according to the invention is essentially adapted for unwinding spools of paper, aluminum or films of other material, so as to obtain a superposed high precision connection as shown in FIG. 8 of the accompanying drawings. To this end, it is a matter of obtaining a perfect coincidence between the marks 7 provided respectively on the ending strip 1 and the new strip 2. Thus, the sections comprised between the markings 7 of the strips 1 and 2 will be joined if it is only a matter of a single and same strip and the supply of the machine disposed downstream will be maintained without interruption and without risk of offset of the sections. The connection of the new strip 2 to the ending strip 1 must be carried out without modification of the speed of supply to the downstream machine.

[0021] This object is achieved by the use of the joining and indexing station 5 for the strips 1 and 2 and at least one means 6, 37 for precise control of the speed of movement of the strip through the joining and indexing station.

[0022] According to a characteristic of the invention, the joining and indexing station 5 of the strips 1 and 2 is constituted by two symmetrical assemblies 8 for preparation and cutting the ending strip 1 and the new strip 2 and by an intermediate bearing crosspiece 9 for cutting the ending strip 1 (FIGS. 2, 4 and 5).

[0023] Each assembly 8 for preparing and cutting the ending strip 1 and the new strip 2 is preferably constituted by a junction block 10 pivotable between a preparatory position, shown at the left in FIGS. 2 and 5 and in FIG. 3, and a connecting position shown at the right of FIGS. 2 and 5 and in FIG. 4, by an indexing device 11 for the new strip 2 and by a means 12 for preparatory cutting of the new strip 2. It is thus possible to position precisely the new strip 2 and to prepare its end adapted to be joined overlappingly with the corresponding end of the ending strip 1.

[0024] Each pivotable junction block 10 is, as shown more particularly in FIGS. 2 and 3 of the accompanying drawings, in the form of a casing which, on the one hand, is connected to a pivoting lever 13 actuated by a jack 14 articulated by its cylinder on the body of the machine and, on the other hand, is provided with suction means 15 and a transverse bearing strip 16 for the new strip 2 during the preparatory cut and the application of an adhesive strip on the end, after said cut. Thus, the new strip 2 can be perfectly maintained on the pivotable block 10 during all the operation of preparation of its beginning and its end can be cut precisely to receive an adhesive strip.

[0025] Moreover, each pivotable junction block 10 is provided with a knife 24 for cutting the ending strip 1, guided in a slot 25 and driven by a jack (not shown).

[0026] Moreover, each pivotable junction block 10 is mounted on the body of the unrolling machine by means of a sliding bearing, not shown, actuated by a jack (not shown) for movement in direction of the intermediate bearing crosspiece 9. Such a mounting permits placing the junction block 10 against the crosspiece 9 during cutting of the ending band 1.

[0027] The suction means 15 consists in holes provided in a surface adjacent to the transverse strip 16 for bearing against the new strip 2, these holes being preferably arranged in groups symmetrical relative to the longitudinal axis of the new strip 2 and with suction chambers controlled pair-wise. In a known manner, each suction chamber is connected to a central suction means by means of manual control valves. As a result, each block 10 can be adapted as a function of the width of the strips to be prepared.

[0028] The preparatory cutting means 12 for the new strip 2 is constituted by a transverse support 17, mounted with the possibility of retractable pivoting in bearings 18 and 19 of the frame of the machine and having a guide slideway 20 for a slider 21 bearing a knife 22 loaded by a spring 23. This cutting means 12 is preferably provided at the free end of the transverse support 17, with a hook or the like, not shown, for holding it in retracted position.

[0029] The device 11 for indexing the new strip 2 is in the form of a return roller 26 and of a gripping roller 27, adapted to exert traction on the new strip 2, and with indexing means 28, such as a magnifying glass or the like, mounted movably transversely to the strip 2 on a support 29, removably fixed in a bearing 19 on the chassis of the machine. This bearing 19 can be released by pivotable retraction of the transverse support 17 constituting the preparatory cutting means 12 for the new strip 2.

[0030] Preferably, the body of the unrolling machine is provided respectively at the level of each indexing device 11 for the new strip 2 and in line with the bearing strip 16 of the new strip 2, in the cutting position of this strip 2, with bearings 18 and 19 for mounting the transverse support 17 constituting the preparatory cutting means 12 for the new strip 2 and for the indexing means 28.

[0031] Thus, these two elements can easily be emplaced and moved as needed.

[0032] According to another characteristic of the invention and as shown in FIG. 3 of the accompanying drawings, the return roller 26 is mounted in a sliding bearing 30 on the body of the machine and is movable in the direction of, or in the opposite direction of, the corresponding gripping roller 27 by means of mechanical or electrical control, such as a jack, a motor reducer assembly or the like. Another embodiment permits, when the reference marks 7 of a new strip 2 are turned toward the center of the spool, moving the return roller 26 relative to the gripping roller 27 by the distance necessary such that a whole number of sections between the reference marks 7 will be located between the indexing means 28 and the position of the cut. As a result, the return roller 26 can be adjusted into different positions relative to the gripping roller 27. Each of these positions corresponds to one format of the strip. These positions are referenced relative to the body of the machine, so as to facilitate preparation.

[0033] The intermediate bearing crosspiece 9 for cutting the end of the strip 1 (FIGS. 2, 4 and 5) is preferably present in the form of an anvil disposed between the pivotable junction blocks 10 of each assembly 8 for preparation and cutting of the ending strips 1 and new strips 2 and is provided with two opposite transverse grooves 9′ adapted to coact with the knife 24 of each pivotable junction block 10.

[0034] According to another characteristic of the invention, and as shown in FIG. 4 of the accompanying drawings, each assembly 8 for preparation and cutting the ending strips 1 and new strips 2 is completed by a punching device 31, mounted on the body of the machine perpendicular to the anvil forming the medial bearing crosspiece 9 and coacting with a matrix 32 provided on said anvil. This punching device 31 is constituted by a punch properly so-called mounted at the end of a piston rod 33 in a guide chamber 34 and provided with means 35 for applying the device against the anvil during the punching operation. This application means 35 of the device against the anvil is preferably constituted by a sleeve movable by the control jack for the punch and provided with a resilient means 36 for compensating the final displacement of the punch, in the form of a spring or the like. Thus, the punch is first moved toward the anvil and the means 35 is applied against this latter, then the punching of the strip is effected during final movement of the control jack.

[0035] The strip accumulator 4 is of known type and is adapted to accumulate a reserve of strip to ensure continuous supply at constant speed to the downstream machine, when the strips 1 and 2 are stopped for connection. The detour rods in the accumulator 4 can move relative to each other thanks to a jack and occupy open positions, working positions and closed positions, as well as any other intermediate positions.

[0036] According to another characteristic of the invention and as shown in FIGS. 1, 2 and 5 of the accompanying drawings, a means 37 for the precise control of the speed of movement of the strip through the joining and indexing station can be constituted by a traction assembly 37 for the ending strip 1, at variable speed, provided between the strip accumulator 4 and the connection device. Such an assembly can be constituted by a return cylinder 38, over which passes the strip 1, which is pressed against this cylinder 38 by means of a pulley drive device 39. Such a pulley drive device 39 is of known type, requiring no further detailed description and permits controlling the speed of movement of the ending strip 1 through the joining and indexing station 5 of the strips 1 and 2.

[0037] The means for precise control of the speed of movement of the strip in the joining and indexing station can also be constituted by a secondary accumulation means 6 for the ending strip 1 disposed upstream the joining and indexing station 5. Such a secondary accumulation means 6 of the ending strip 1 (FIGS. 1, 2, 5 and 9) can be present in the form of two pairs of fixed return cylinders 40 disposed symmetrically relative to the median bearing crosspiece 9, below the assemblies 8 for preparing and cutting the endings strips 1 and the new strips 2, and by two corresponding movable cylinders 41 guided in movement relative to the fixed return cylinders 40 by means of slideways 42 and jacks 43. This secondary accumulation means 6 permits creating a small reserve of strip and delivering it thereafter at low speed and under constant tension, during the connecting operation, such that the connecting position may be predetermined with precision.

[0038] It is also possible, according to another characteristic of the invention, to combine the means 37 and 6 for precise control of the speed of movement of the strip through the joining and indexing station, by arrangement of these latter immediately adjacent the joining and indexing station. Thus, the movement of the ending strip 1 is subject to a double control of its speed of movement, permitting perfect positioning of the connecting reference marks.

[0039] Moreover, there is provided, between the strip accumulator 4 and the joining and indexing station 5, an assembly 44 for detecting reference marks 7 of the ending strip 1, which is disposed at a distance from the knife 24 of the pivotable junction block 10 and from the opposed transverse grooves 9′ of the median bearing crosspiece 9 corresponding to a whole number of sections between reference marks 7. Such a detection assembly 44 can preferably be constituted by a pair of photoelectric cells or the like.

[0040] The unrolling machine according to the present invention operates in the following manner:

[0041] After placing a new spool 2 in replacement on the spindle whose axis of rotation is free, the corresponding junction block 10 is moved such that the transverse bearing strip 16 of the new strip 2 and the suction means 15 will be easily accessible to the operator.

[0042] As a function of the position of the reference marks 7 on the strip, which is to say according to where they are located on the surface oriented toward the center of the spool, as shown in FIG. 6, or toward the exterior of the spool (FIG. 7), the return roller 26 will be moved relative to the gripping roller 27 by the necessary distance, as explained above.

[0043] In the first case, the indexing means 28, for example in the form of a magnifying lens, for the indexing device 11 of the new strip 2, is disposed between the return roller 26 and the gripping roller 27. The operator can then, by looking through the magnifying glass constituting the indexing means 28 and by turning the gripping roller 27, advance the strip 2 until the reference mark 7 coincides perfectly with an index of said magnifying lens 28. In this position, there is a whole number of sections between reference marks 7 between the magnifying glass 28 and the position of the cut, with which exactly and perfectly coincides a reference mark 7. Thus the strip 2 of the new spool is perfectly indexed.

[0044] After the indexing operation, the strip 2 is immobilized against the bearing transverse strip 16 of the junction block 10 by actuating suction means 15. The strip 2 is then cut with the help of the knife 22 and the end of the cut strip is withdrawn. Then a strip of double face adhesive is stuck to the end of the strip 2.

[0045] The junction block 10 is then moved into the connection position, as shown in FIG. 2 at the right, and the strip 2 is tensioned by rotating the spool in the reverse direction to the normal unrolling direction so as to obtain optimum tension in the strip, then the strip is immobilized in known manner on its spindle. As a modification, it is also possible to control the tension of the strip with the help of a tension detector or by subjection to the drive of said spindle.

[0046] When the reference marks 7 are turned outwardly of the spool it is not necessary to move the return roller 26 relative to the format of the sections between the reference marks 7. The strip 2 is threaded in the same manner as when the reference marks 7 are turned toward the center of the spool and the indexing means 28 of the index device 11 of the new strip 2 is placed such that it will be at the level of the means 12 for preparatory cutting of the new strip 2 (see FIG. 7). The movement of the strip 2 is effected in a manner identical to that described above. The same is true as to the other successive operations.

[0047] The connection cycle is explained more particularly with respect to FIGS. 9 and 10. Thus, in fifteen regions Z1 to Z15, there is given:

[0048] VA=linear speed of movement of the ending strip 1 of the first spool, upstream of the secondary accumulation means 6

[0049] VB=linear speed of unwinding of the new strip 2 from the second spool, upstream of the secondary accumulation means 6

[0050] VC=linear velocity of the strip, downstream of the joining and indexing station.

[0051] In the region Z1, the spool A unrolls with a speed VA=V2=nominal speed of operation=speed of the machine to be supplied and the traction assembly 37 for the ending strip 1 also turns at the speed VC=V2. The strip accumulator 4 is in working position, which is to say almost closed and the means 37 and/or 6 for precise control of the speed of movement of the strip are in the rest condition. The new spool is installed and the end of the strip B is prepared.

[0052] In the region Z2, there is detected the next end of the first spool A, whilst the strip accumulator 4 is in the position of FIGS. 9a or 9b.

[0053] In the region Z3, the strip accumulator 4 is filled by spacing, in known manner, the deflecting bars from each other by means of a jack. Simultaneously, the connection cycle is triggered by acceleration of the speed VC, then VA follows VC up to VS.

[0054] In the region Z4, VC and VA are held constant at speed V5 and the strip accumulator 4 is full.

[0055] In the region Z5, the strip accumulator 4 being empty, VC and VA are reduced to V2.

[0056] In the region Z6 the means 37 and/or 6 for precise control of the speed of movement of the strip are actuated. VC remains constant and VA increases to V3.

[0057] In region Z7, after actuation of the means 37 and/or 6 for precise control of the speed of movement of the strip, VA returns to speed V2.

[0058] In region Z8, VC is braked until it stops, VA follows and the ending strip 1 is stopped. The corresponding spool is blocked against rotation. Strip accumulator 4 progressively empties by supplying the downstream machine at nominal speed V2.

[0059] In region Z9, VC is slightly accelerated up to V1, which is a very low speed, the ending strip moves at a very low speed, under the effect of the operation of means 37 and/or 6 for precise control of the speed of movement of the strip and the reference marks 7 are sought on the strip 1 by the detection assembly 44. When the reference mark 7 of the strip 1 coincides with the photoelectric cells or the like of the assembly 44, VC stops. In this position, the reference mark 7 of the strip 1 coincides with the reference mark 7 of the new strip 2, which was previously indexed in region Z1. Thus, to guarantee high precision connection, it is necessary to move the strip 1 at a low speed and under constant tension. This is obtained by the means 37 and/or 6 for precise control of the speed of movement of the strip, operated independently or in combination, which permit delivering the strip 1 at low speed and under constant tension.

[0060] In region Z10, VC=VA=VB=0, the strips are stopped and their respective reference marks 7 are in perfect correspondence. The strip 1 is cut with the knife 24 and the anvil 9 and simultaneously the end of the strip 2 is glued to the end of the strip 1, in superposition, sa shown in FIG. 8.

[0061] In the region Z11, the new spool is freed for rotation. VC is accelerated up to V2 and VD follows.

[0062] In region Z12, VB=VC=the nominal speed of operation.

[0063] In region Z13, the position of the strip accumulator 4 is detected (see FIGS. 9a, b, c). If the latter is too closed, it is opened more by simultaneously accelerating VC to reach the working position of the accumulator; conversely, if it is too open, it is closed and simultaneously VC is slowed.

[0064] In the region Z14 the ending spool is withdrawn.

[0065] In the region Z15, the new spool unrolls to replace the ending spool; the cycle can recommence as in region Z1.

[0066] Thanks to the invention, it is possible to provide an unrolling machine permitting unrolling two spools and their superposed connection with perfect indexing of the new strip relative to the ending strip.

[0067] Of course, the invention is not limited to the embodiment described and shown in the accompanying drawings. Modifications remain possible, particularly as to the construction of the various elements or by substitution of technical equivalents, without thereby departing from the scope of protection of the invention.

Claims

1. Precision connection device for a continuous unrolling machine, comprising at least one means (3) for unrolling two spools, a strip accumulator (4) and a device for connecting an ending strip (1) and a new strip (2), characterized in that the connection device is essentially constituted by adjoining an indexing station for the strips (1 and 2) and by at least one means (6, 37) for precise control of the speed of movement of the strip through the joining and indexing station (5).

2. Device according to claim 1, characterized in that the joining and indexing station (5) for the strips (1 and 2) is constituted by two symmetrical assemblies (8) for preparing and cutting the ending strip (1) and the new strip (2) and by a median bearing crosspiece (9) for cutting the ending strip (1).

3. Device according to claim 2, characterized in that each assembly (8) for preparing and cutting the ending strip (1) and new strip (2) is constituted by a junction block (10) pivotable between a preparatory position and a connecting position, by an indexing device (11) for the new strip (2) and by means (12) for preparatory cutting of said new strip (2).

4. Device according to claim 3, characterized in that each pivotable junction block (10) is in the form of a casing which, on the one hand, is connected to a pivoting lever (13) actuated by a jack (14) articulated by its cylinder on the body of the machine and, on the other hand, is provided with suction means (15) and with a transverse bearing strip (16) for the new strip (2) during preparatory cutting and for application of an adhesive strip on the end, after said cutting.

5. Device according to claim 4, characterized in that each pivotable junction block (10) is provided with a knife (24) for cutting the ending strip (1), guided in a slot (25) and driven by a jack.

6. Device according to claim 4, characterized in that each pivotable junction block (10) is mounted on the body of the machine for movement by means of a sliding bearing actuated by a jack for movement in direction of the median bearing crosspiece (9).

7. Device according to claim 4, characterized in that the suction means (15) consist in holes provided in a surface adjacent to the transverse bearing strip (16) of the new strip (2), these holes being arranged in groups symmetrical relative to the longitudinal axis of the new strip (2) with suction chambers controlled pairwise.

8. Device according to claim 3, characterized in that the preparatory cutting means (12) for the new strip (2) is constituted by a transverse support (17), mounted with the possibility of retractable pivoting in bearings (18 and 19) on the body of the machine and having a guide glideway (20) for a slider (21) bearing a knife (22) loaded by a spring (23).

9. Device according to claim 3, characterized in that the cutting means (12) is provided, at the free end of the transverse support (17), with a hook or the like for holding it in retracted position.

10. Device according to claim 3, characterized in that the device (11) for indexing the new strip (2) is in the form of a return roller (26) and a gripping roller (27), adapted to exert traction on the new strip (2), and by an indexing means (28), such as a magnifying glass or the like, mounted movably transversely to the strip (2) on a support (29) removably fixed in a bearing (19) of the body of the machine.

11. Device according to any one of claims 1 and 10, characterized in that the body of the unrolling machine is provided respectively at each device (11) for indexing the new strip (2) and in line with the transverse bearing strip (16) of the new strip (2), in the cutting position of this strip (2), with bearings (18 and 19) for mounting the transverse support (17) constituting the preparatory cutting means (12) for the new strip (2) and of the indexing means (28).

12. Device according to claim 10, characterized in that the return roller (26) is mounted in a sliding bearing (30) of the body of the machine and is movable in the direction or opposite direction of the corresponding gripping roller (27) by means of a mechanical or electrical control, such as a jack, a motor reducer assembly or the like.

13. Device according to claim 2, characterized in that the median bearing crosspiece (9) for cutting the ending strip (1) is present in the form of an anvil disposed between the pivotable junction blocks (10) of each assembly (8) for preparation and cutting of the ending strips (1) and new strips (2) and is provided with two opposite transverse grooves (9′) adapted to coact with the knife (24) of each pivotable junction block (10).

14. Device according to claim 3, characterized in that each assembly (8) for preparation and cutting of the ending strips (1) and new strips (2) is completed by a punching device (31), mounted on the body of the machine perpendicular to the anvil forming the median bearing crosspiece (9) and coacting with a matrix (32) provided on said anvil.

15. Device according to claim 14, characterized in that the punching device (31) is constituted by a punch properly so-called mounted at the end of a piston rod (33), in a guide chamber (34) and provided with means (35) for application of the device against the anvil during the punching operation.

16. Device according to claim 15, characterized in that the means (35) for application of the device against the anvil is constituted by a sleeve movable by the control jack of the punch and provided with a resilient means (36) for compensating the final displacement of the punch, in the form of a spring or the like.

17. Device according to claim 1, characterized in that the precise control means for the speed of movement of the strip through the joining and indexing station is constituted by a traction assembly (37) for the ending strip (1) of variable speed, provided between the strip accumulator (4) and the connecting device.

18. Device according to claim 17, characterized in that the traction assembly (37) of the ending strip (1) of variable speed is constituted by a return cylinder (38), over which passes the strip (1), which is pressed against this cylinder (38) by means of a pulley drive device (39).

19. Device according to claim 1, characterized in that a precise control means for the speed of movement of the strip through the joining and indexing station is constituted by a secondary accumulation means (6) for the ending strip (1) disposed upstream of the joining and indexing station (5).

20. Device according to claim 19, characterized in that the secondary accumulation means (6) for the ending strip (1) disposed upstream of the joining and indexing station (5) is present in the form of two pairs of fixed return cylinders (40) disposed symmetrically relative to the median bearing crosspiece (9), below the assemblies (8) for preparation and cutting the ending strips (1) and new strips (2), and two corresponding movable cylinders (41) guided in movement relative to the fixed return cylinders (40) by means of slideways (42) and jacks (43).

21. Device according to any one of claims 1, 17 and 19, characterized in that the means (37 and 6) for precise control of the speed of movement of the strip through the joining and indexing station are combined by arrangement of these latter immediately adjacent said joining and indexing station.

22. Device according to any one of claims 1 to 5, characterized in that between the strip accumulator (4) and the joining and indexing station (5) is provided an assembly (44) for detecting reference marks (7) on the ending strip (1), which is disposed at a distance from the knife (24) of the pivotable junction block (10) and transverse opposed grooves (9′) of the median bearing crosspiece (9) corresponding to a whole number of sections between reference marks (7).

23. Device according to claim 22, characterized in that the detection assembly (44) is constituted by a pair of photoelectric cells or the like.