JP2002003017A - Direction aligning unit for sheet form material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To align directions of sheet form materials without changing of the direction aligned positions by a component for aligning the directions, damage of the surface, or other damage. SOLUTION: A plurality of rotation elements 25 for correcting shifting of the sheet form material 1 in the conveying direction 22 and engaging with the sheet form material 1 are mounted into the direction aligning unit. Of these rotation elements, at least two rotation elements 25 positioning in one plane can slide with respect to the remaining rotation elements.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a directional unit for sheet-type materials, which is used, for example, in the printing press of a printing press for processing sheets, to precisely orient the material to be printed. .

[0002]

2. Description of the Related Art DE 44 16 564 A1 relates to a single-wafer aligner. This device for orienting a moving sheet along a generally flat conveying path corrects the moving sheet in a number of orthogonal directions, for example, transverse to the conveying path, the direction of the conveying path and the tilt position. In the direction you want to. The device has a first roller device with a first pressure roller, which roller is centered on an axis lying in a plane extending parallel to the plane of the transport track. It is mounted so as to be rotatable and extends generally along the transport path at right angles to the direction of sheet transport. The second roller device has a second pressure roller, which is located in a plane extending parallel to the plane of the transport track and which is substantially in the direction of sheet transport. It is mounted so as to be rotatable about an axis extending along the transport track at right angles thereto. A third roller arrangement is provided, which has a third pressure roller, which is located in a plane extending parallel to the plane of the transport track and which is approximately Are supported so as to be rotatable about an axis extending along the transport path at right angles to the direction of sheet transport. A third rotatable centering on an axis extending along the transport trajectory substantially perpendicular to the direction of sheet transport and located in a plane extending parallel to the plane of the transport trajectory; Is movable in a direction extending transversely to the transport track along its axis of rotation. Finally, a control device is provided, which is operatively connected to the first, second or third roller device and selectively controls the rotation of the first and second roller device. By controlling, the leading edge of the sheet moving along the conveying path in the sheet conveying direction is aligned to a position arranged at right angles to the sheet conveying direction. This control device further controls the rotation and the lateral movement of the third roller device, and
The sheet is aligned in a direction extending transversely to the direction of sheet conveyance and in a direction in which the sheet moves along the conveyance path.

The single-wafer aligner known from DE 44 16 564 A1 merely fulfills the required alignment accuracy to a limited extent. In order to achieve the required alignment accuracy, it is necessary to greatly change the prior art single-wafer alignment device, which is not economical.

In a printing press that functions on the offset principle for processing sheets, the sheets are arranged and conveyed in a scale-like manner on a paper feed table, and the horizontal needles and the contact pads provided in the plane of the paper feed table are provided. Orientated by After the sheet-shaped material has been oriented, the sheet-shaped material is accelerated to machine speed and delivered to a cylinder located behind the front gripper.

[0005] This solution requires very expensive control technical and mechanical costs.

[0006]

In view of the shortcomings of the solutions known from the background, the problem underlying the present invention is that the image may be unprinted, already printed or otherwise having an image. The alignment of the sheet-shaped material in such a way that its aligned position is not changed by the aligning component and that its surface is not damaged or otherwise damaged. It is to do.

[0007]

According to the present invention, this object is solved by the features of claim 1.

[0008]

The following advantages can be achieved, inter alia, with the solution according to the invention. In other words, by configuring the rotating element which engages the sheet-shaped material in the deflecting unit as a rotatable rotating element, the abrasion or weakening of the reference force causes a change in the coefficient of friction produced on the surface of the corresponding push roller, as well as the sheet. The change in the coefficient of friction of the segment rollers provided above the transport plane is compensated inside the alignment unit. The reference force required to generate the feed force between the cooperating circumferential surfaces of the segment roller and the corresponding pressing roller can be generated, for example, by an elastic spring element. Returning the corresponding push roller after the transverse movement with respect to the sheet transport direction has taken place in the deflecting unit requires a mechanical cam circle after the correction of the position of the print to be rectified with respect to its running direction. The adjustment can be performed by an adjusting member, whether a plate or an electric or pneumatic adjusting member.

[0009]

In one advantageous embodiment of the idea underlying the invention, the feed acting on the sheet-shaped material, whether driven by a segment roller or by a corresponding push roller, is in one plane. Is applied to another pair of rotating elements located in another plane. For this purpose, it is possible to use a storage element such as a spring element in an advantageous manner.

The generation of a reference force on the sheet-shaped material is achieved by applying a reference force to a segment roller located above the sheet transport plane or to a corresponding push roller located below the sheet transport plane. It can be carried out.

[0011] Advantageously, the rotating element in contact with the sheet-shaped material is configured as a segment roller extending over approximately a 3/4 circle.

In another advantageous embodiment of the idea underlying the invention, the segment rollers are arranged in pairs or groups which are located one behind the other as viewed in the sheet transport direction. The segment rollers mounted in a plane located on the upper side of the sheet conveying plane at intervals of two each are driven by a driving device. The driving device of the segment roller is positioned so as to perform the first directional adjustment and the second directional adjustment with respect to the sheet traveling direction. The driven axis of the driving device that performs the first direction adjustment is perpendicular to the sheet traveling direction, whereas the driven axis of the driving device that performs the second direction correction is parallel to the sheet traveling direction. It is.

In one embodiment of the idea underlying the invention, the corresponding pressing roller, which is arranged below the conveying plane of the sheet-shaped material, is fixedly mounted on the shaft, whereas the corresponding pressing roller is The rotary body, which is configured as a segment roller cooperating with the roller, slides against a correspondingly mounted pushing element. In this embodiment, the width of the corresponding push roller, which is fixedly supported in the lower plane of the sheet-shaped material transport plane, is equal to the width of the segment roller in the upper plane of the sheet-shaped material transport plane. Over. In another embodiment of the invention, the corresponding push rollers are configured as a common unit that can slide relative to the segment rollers. In this case, the width of the circumferential surface of the corresponding push roller is equal to the width of the pair of segment rollers provided in a plane above the conveying plane of the sheet-shaped material. The steering unit proposed according to the invention is for example a machine for processing sheet-shaped material,
It can be used in a feeding device for feeding a sheet-shaped material. The advantage of the printing press for processing sheet-shaped materials with the alignment unit proposed by the present invention is that the sheet is not formed in a scaly shape, and thus the scale formation is impeded. In this case, there is no danger of interrupting the sheet supply.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be specifically described below with reference to embodiments shown in the drawings.

FIG. 1 shows a rectangularly oriented sheet-shaped material, for example, a printed sheet 1. The print sheet 1 has a print image 2 printed on its surface,
This print image is surrounded by a frame-shaped edge 3. Deviation Δx or Δ marked inside printing surface 2 and frame 3
y represents a position error in the x direction and the y direction that may occur on the surface of the sheet when printing the print image 2. Code 4
Or, while the deviation indicated by 5 is a position deviation,
FIG. 2 shows the angular deviation of the print image 2 with respect to its position on the print sheet 1.

In FIG. 2, the angle errors Δφ and Δ
ψ is indicated by reference numeral 6. The printed image 2 may be printed on the surface of the printing material 1 in the position shown, the printing material being fed with its leading edge 23 forward in the sheet running direction. FIG. 3 schematically shows a front-to-back register, wherein reference numeral 7 denotes a printed image 2 on the front and back of the sheet-shaped material 1.
Shows the deviation that occurs between This shift is indicated by reference numeral 7 or Δx and Δy in FIG. Front-to-back registration is especially important for see-through paper and brochure printing.

FIG. 4 is a schematic side view of the connection between the sheet alignment unit and the conveyor belt. The transport belt 10 circulating around the run-up roller 11 or the control roller 12 is provided with a sheet-shaped material on a transport plane 9 on its surface.
The alignment unit 8 is connected in front of the conveyor belt. After passing through the orienting unit 8, which will be explained in more detail later, the orientated sheet-shaped material 1
Reaches above the surface of the conveyor belt 10 within the conveyor plane 9. After passing through the run-up roller 11, the sheet-shaped material 1 is held down by an application flap or an application lip which can be moved in an application direction 13.

The application lip or the application flap can be a plastic component and can be switched from the applied position 13.1 to a position 13.2 which has been pulled away, which is indicated by a substantially solid line or Indicated by broken lines. By means of the application flaps or application lips, the sheet-shaped material 1 is pressed against the surface of the conveyor belt 10 in an aligned state. After passing through this crimping element, the sheet on the surface of the conveyor belt 10 passes through the charging unit 14. In the charging unit 14, an electrode 15 is mounted inside a hood-shaped cover, and this electrode electrostatically charges the sheet-shaped material, and thus adheres the sheet-shaped material to the surface of the transport belt 10.

The charging unit 14 is only schematically shown in FIG. 4, and a leading edge sensor 17 is arranged behind the charging device. The leading edge sensor comprises a radiation source 18 arranged below the sheet transport plane, behind which a lens device 19 is provided. The radiation field 20 emerging from the lens arrangement 19 penetrates the sheet transport plane 9 and strikes an aperture device, which is arranged in the transport plane 9 above the transport path of the sheet-shaped material 1. A receiver 21 is arranged behind the drawing device and records the presence of the leading edge 23 of the sheet-shaped material 1.

FIG. 5 shows a plan view of the steering unit 8, the components of the steering unit being shown schematically here.

Sheet-shaped material 1 reaching the steering unit 8
Is transported in the transport direction 22. The leading edge 23 of the sheet-shaped material 1 is offset with respect to the running direction 22 of the sheet-shaped material, which also results in an inclined course of the side edges 24 of the sheet-shaped material 1. As soon as the leading edge 23 of the seat, which is at a position inclined with respect to the running direction 22, passes through the photoelectric detection system 26, the driving device 2 indicated by M 1 or M 2 drives the rotary element 25 via the individual shaft 32
7 is accelerated to the feed speed. Step motor 28 generated via photoelectric detection system 26
Alternatively, the control of M1 or M2 ensures that each sheet-shaped material 1 comes into contact with the same circumferential section of the rotary element 25, which can be configured, for example, as a segment roller. The difference between the feed movements that should occur due to the size and shape tolerances of both rotating elements 25 driven by the drives M1 and M2 is:
Occurs in the same manner in each of the sheet-shaped materials 1;
It can be easily removed.

After the two rotating elements 25 have been rotated by the passage of the first photoelectric detection system 26, the sheet is fed at a feed rate to another sensor unit 30 arranged behind the first photoelectric detection system 26. .1. As soon as the first of the two sensors of the sensor unit 30.1 detects the sheet leading edge 23 of the sheet-shaped material 1, the counting unit starts counting motor steps. When the second sensor of the sensor unit 30.1 detects the leading edge 23 of the sheet, the counting process is terminated.

From the counts determined in this manner, a correction value is determined, which correction value is used as an additional feed as a later driven segment roller, in other words the drive M1.
Or it is used for additional driving of the segment roller driven by M2. As a result, the rotating element 25
The feed speed is increased, and the detected feed distance difference is completely eliminated. At the end of this correction process, the seat leading edge 23 is oriented exactly perpendicular to the seat running direction 22.

After the correction has been carried out, the sheet-shaped material 1 is continuously transferred in the sheet running direction 22 from a first pair of rotating elements 25 to a rear pair of rotating elements 25, which second pair of rotating elements 25. Are mounted on a common shaft 31. Now, the drive of the rotary element 25 via the drive devices M1, M2 is interrupted, and these rotary elements are stopped.

The sheet whose angular position has now been correctly oriented runs up into the sensor field 30 in which the position of the side edge 24 of the sheet-shaped material 1 is measured. From the measured values, the driving device M4
The position change for the stepper motor 29 whose driven shaft extends parallel to the sheet running direction 22 is checked.
By means of this stepping motor 29, which carries out the second directional correction, a correction change of the sheet-shaped material 1 is made parallel to the sheet running direction 22 (see FIG. 7).

Next, the sheet 1 whose angular position and side position have been appropriately aligned with respect to the conveyor belt 10 in this manner is applied to the contact flap which has been turned to the contact position on the conveyor belt 10. Alternatively, it travels beneath the application lip and thus into the next printing unit in a correctly oriented position.

FIG. 6 shows an embodiment of the rotary element 25 mounted in the alignment unit 8 and located above the transport plane 9 of the sheet-shaped material 1.

The rotary element 25 is designed in this preferred embodiment as a segment roller and has a circumferential surface 33 which is interrupted. The segment roller 25 rotates in a direction 34 indicated by an arrow and extends over a 円 circle with respect to its rotation axis. Each segment roller 2
Below the roller 5, a roller for supporting the sheet-shaped material 1 is only schematically shown here. The segment roller 25 serving as a rotating body is shown in the rest position on the left side of FIG. 6, whereas it engages the sheet-shaped material 1 conveyed in the sheet running direction 22 with its circumferential surface on the right side of FIG. And is conveyed in the rotation direction 34.

FIGS. 7, 8 and 9 show the correction of the angular position and the correction of the lateral position of the sheet-shaped material 1 as it passes through the alignment unit 8.

In the position shown in FIG. 7, the sheet-shaped material 1 has just reached its leading edge 23 at the last sensor of the sensor pair 30.1, and thus now has the stepper motor 28 of the drive M1. By virtue of this, the angular position of the sheet-shaped material 1 with respect to the running direction 22 can be corrected. It should be noted that unlike the drives M3 and M4 which are coupled to each other via a consistent drive shaft 31, the drive M
The segment rollers 25 connected to 1 and M2 are respectively driven via individual shafts 32.

As shown in FIG. 7, after the angular position of the sheet-shaped material 1 has been corrected, the sheet-shaped material 1 undergoes a lateral position correction.

By means of a sensor field 30 which is mounted in the area of the side edges of the transport plane 9 of the sheet-shaped material,
After the position of the side edge 24 of the sheet-shaped material 1 has been measured,
The change in position is calculated from the measured value obtained in each case by the side edge sensor 30 and supplied to the stepping motor 28 of the drive M4 for performing the second positioning, whereby the stepping motor is a sheet-shaped material. The first side edge 24 is aligned with the arrow position indicated by reference numeral 37. In the state shown in FIG. 8, the step motor 28 of the driving device M1 or M2 is shut off, and the segment roller 25 is returned to the rest position. These segment rollers remain in this rest position until the next sheet-shaped material 1, which is to be angularly or laterally aligned, arrives.

In the orientation unit shown in FIG. 9, the sheet-shaped material 1 whose angular position and its lateral position have been corrected has its leading edge 23 applied to the application position 13.1. Being held by an applied flap or lip. As a result, the oriented sheet-shaped material 1 is pressed against the surface of the circulating conveyor belt 10, the side edges 24 of the sheet-shaped material 1 being exactly at the arrow position 37. The transport of the sheet-shaped material 1 in the transport plane 9 is now carried out by means of a circulating transport belt 10 supporting the sheet-shaped material 1, which is applied to the transport belt by an application element. .
The sheet-shaped material 1 includes a running roller 11 and a control roller 1.
After being transferred to the circulating conveyor belt 10 around 2, the correction process ends. The second pair of rotating elements 25, now driven by the drive M3, is also returned to its rest position and is ready to modify the next sheet-shaped material 1. By arranging the rotary element 25 as a segment roller, the feeding of the sheet-shaped material 1 takes place over a limited distance without the need to switch over to a drive roller or a corresponding push roller (see FIGS. 10 and 11). The limited distance over which the sheet-shaped material 1 is transported is
It is determined by the length of the circumferential surface 33 of the segment roller. In the steering unit 8, according to FIGS. 7, 8 and 9, two pairs of segment rollers are respectively mounted.
Both segment rollers 25 of the first pair are driven by a drive M
1 and M2 are separately driven in the feed direction by the step motors 28, while the second segment rollers 25
Are connected by a common shaft 31. These segment rollers are moved in the feed direction or the axial direction by the step motors 28 and 29 of the driving devices M3 and M4.

In FIG. 10, a push roller corresponding to a rotating body configured as a segment roller is assigned in the alignment unit.

As can be seen from FIG. 10, the segment rollers 25 each having a circumferential surface 33 can be slid in the direction of the double arrow 41 (see the alignment process in FIG. 8). Below the transport plane defined by the circumferential surface 44 of the corresponding push roller 38 and the circumferential surface 33 of the segment roller, the corresponding push roller is mounted on the individual shaft 43 and has a width 39; This width is significantly larger than the width of the circumferential surface 33 of the segment roller 25. In order to apply a reference force which causes a feed between the circumferential surface 44 of the corresponding push roller and the circumferential surface 33 of the segment roller 25, the individual shaft 43 on which the corresponding push roller is mounted is, for example, spring-loaded. I can put it. The alignment of the sheet-shaped material 1 according to the structure schematically shown in FIG. 10 is achieved by the frictional force between the segment roller 25 and the sheet-shaped material 1 correspondingly between the push roller 38 and the sheet-shaped material 1. An adjustment greater than the frictional force makes it possible to prevent a slip from occurring between the segment roller 25 and the sheet-shaped material 1.

In the embodiment shown in FIG. 11, a rotating body constituted as a segment roller 25 is mounted on, for example, a common shaft 31 and can be moved in the direction of a double arrow 41. For example, if the corresponding push roller attached to the common shaft 42 is configured as a unit that can be slid in the axial direction, the orienting unit 8 determines the coefficient of friction of the circumferential surface 45 of the corresponding push roller 38. Circumferential surface 33 of the segment roller 25 which is robust against changes and
Robust and insensitive to changes in the coefficient of friction at These resulting changes in the coefficient of friction can be compensated for by adapting the reference force. The reference force can be applied to a common shaft 31 or 42 in the form of a spring element which can be applied to these shafts. However, it is also possible to use other clamping elements, for example clamping screws or clamping rods. Returning the corresponding push roller 38, mounted as a slidable unit on the common shaft 42, to its starting position can be achieved, after a lateral correction of the sheet-shaped material 1 in the running direction 22, by suitable adjusting means, for example. This can be done by means of a mechanical cam disc, an electric or pneumatic adjusting element.

In the above-described solution, the friction coefficient is intentionally adjusted so that the circumferential surface 33 of the segment roller 25, which can be applied to the surface of the sheet-shaped material 1,
So that the generated frictional force is sufficient for alignment and can be adjusted to be greater than the frictional force dominating between the circumferential surface 45 of the corresponding push roller 38 and the lower surface of the sheet-shaped material 1. can do. In this way, at the end of the alignment process, whether unprinted material, one-sided printed material, or a material that has already been printed on both sides, the surface of the sheet-shaped material 1 It is guaranteed that no marks or scratches will be left. In addition, the sheet-shaped material 1 enters the machine for processing sheets, for example a printing press or a digital printing press, in a precisely positioned position, without changing its oriented position. Is guaranteed to get.

[Brief description of the drawings]

FIG. 1 shows a positional deviation of a printed image generated with respect to a sheet surface.

FIG. 2 shows a positional shift caused by a rotational shift of a print image printed on a sheet-shaped material.

FIG. 3 shows a displacement of a printed image printed on the lower surface or the upper surface of a sheet-shaped material.

FIG. 4 shows a schematic side view of a sheet entry area into a sheet processing machine.

FIG. 5 shows a plan view of a steering element, a sensor and a drive of a rotary element for orienting a sheet-shaped material with respect to the sheet running direction.

FIG. 6 shows a rotating element configured as a segment roller above the transport plane of the printed material according to the invention in an active position and a non-active position.

FIG. 7 shows the actuation of the drive necessary for orienting the sheet-shaped material with respect to the sheet running direction 22 of a rotating element configured as a segment roller arranged above the sheet transport plane.

FIG. 8 shows the actuation of the drive of a rotating element configured as a segment roller arranged above the sheet transport plane, which is necessary to orient the sheet-shaped material with respect to the sheet running direction 22.

FIG. 9 shows the drive activity of a rotating element configured as a segment roller arranged above the sheet transport plane, which is necessary to orient the sheet-shaped material with respect to the sheet running direction 22.

FIG. 10 shows a segment roller which can be swiveled in one sliding direction relative to an opposing push roller which is fixedly mounted on an individual shaft.

FIG. 11 shows an opposing push roller which can also slide synchronously with the sliding of the segment rollers.

[Explanation of symbols]

1 Print sheet, 2 Print image, 3 Edge, 4 Deviation, 5 Deviation, 6 Angle error, 7 Deviation, 8
Orientation unit, 9 transport plane, 10 transport belt,
11 Running roller, 12 Control roller, 13 Applied direction, 13.1 Applied position, 13.
2 Separated position, 14 Charging unit, 15
Electrode, 17 leading edge sensor, 18 radiation source, 19
Lens device, 20 radiation field, 21 receiver, 22 transport direction, running direction, 23 transport edge, leading edge, 24 side edge, 25 rotating element, 26
Photoelectric detection system, 27 drive device, 28 step motor, 29 step motor, 30 sensor field, side sensor, 30.1 sensor unit, sensor pair, 31 common axis, 32 individual axis, 33 circumferential surface, 34 direction, 37 arrow position, 38 corresponding push roller, rotating body, 39 width, 41 double arrow, 42
Common axis, 43 Individual axis, 44 Circumferential surface, 45
Circumferential surface, M1 drive, M2 drive, M3
Drive, M4 drive, Δx deviation, Δy
Deviation, Δφ angle error, Δψ angle error

Claims (13)

[Claims] 1. An orienting unit for a sheet-shaped material (1), which is connected in front of a transport plane (9) for the sheet-shaped material (1) and which is a sheet-shaped material. In the type in which the feeding of (1) takes place via a driven surface (33) in contact with at least one side of the sheet-shaped material (1), the sheet-shaped material (1) has a sheet-shaped material (1). A plurality of rotating elements (25, 38) that engage with the sheet-shaped material (1), which correct the displacement of the material (1) with respect to the conveying direction (22), are mounted. Alignment unit for sheet-shaped material, characterized in that at least two rotating elements (25) located in one plane are movable with respect to the remaining rotating elements (38). 2. The feed element acting on the sheet-shaped material (1) is provided with a rotary element (25, 3) lying in one plane.
2. The alignment unit according to claim 1, wherein the pair is generated by applying the pair of (8) to another pair of rotating elements (25, 38) located in another plane. 3. A rotary element (25, 38) whose reference force on a sheet-shaped material (1) lies in one plane.
3. The steering unit according to claim 2, wherein the steering unit is generated by applying a spring force to a pair of the steering units. 4. The alignment unit according to claim 1, wherein the rotary element in contact with the sheet-shaped material is configured as a segment roller. 5. The alignment unit according to claim 1, wherein the segment rollers (25) are arranged in pairs located one behind the other as viewed in the sheet transport direction. 6. The steering unit according to claim 5, wherein the segment rollers are driven by a drive. 7. A driving device (27) for a segment roller (25) is provided in a running direction (22) for a sheet-shaped material (1).
The alignment unit according to claim 6, characterized in that it is positioned so as to perform a first directional alignment and a second directional alignment. 8. A corresponding pressing element (38) provided below the transport plane (9) is fixedly mounted on the shaft (43), while the segment roller (25) is attached to the corresponding pressing element. A steering unit according to claim 1, characterized in that a sliding movement (41) is performed on it. 9. The alignment unit according to claim 1, wherein the width of the corresponding push roller, which is fixedly mounted, exceeds the width of the segment roller. 10. The alignment unit according to claim 1, wherein the corresponding push roller is configured as a common unit that can slide relative to the segment roller. . 11. A circumferential surface (4) of a corresponding pressing roller (38).
The alignment unit according to claim 10, wherein the width of (5) is equal to the width of the segment roller (25). 12. A feed device for feeding a sheet-shaped material (1), comprising a deflecting unit (8), the deflecting unit being a transport plane for the sheet-shaped material (1). Of the type connected to the front of (9) and driven by a driven surface (33) in contact with at least one surface of the sheet-shaped material (1). A plurality of rotating elements (25, 38) engaging with the sheet-shaped material (1) in the steering unit (8) for correcting the deviation of the sheet-shaped material (1) with respect to the conveying direction (22). ) Is mounted, at least two of these rotating elements being located in one plane and being rotatable with respect to the remaining rotating element (38). And the sheet shape Supply device to supply the material. 13. A printing press having a deflecting unit (8) for sheet-shaped material (1), the deflecting unit being in front of a transport plane (9) for sheet-shaped material (1). And the feed of the sheet-shaped material (1) is
In the type performed by the driven surface (33) in contact with at least one surface of the sheet-shaped material (1), the transport direction of the sheet-shaped material (1) in the alignment unit (8) 22) A plurality of rotating elements (25, 38) engaging the sheet-shaped material (1), which correct the displacement with respect to 22), are mounted and at least two of these rotating elements are located in one plane. Printing machine, characterized in that the rotating element (25) which is movable is able to slide with respect to the remaining rotating element (38).