Device for applying self-adhesive labels

Abstract

The invention relates to a device for applying self-adhesive labels, comprising a label applicator and a conveyor for parts to be labelled that conveys the parts to be labelled along a path, the applicator being arranged with respect to the conveyor such that the parts to be labelled meet a self-adhesive label at a meeting point belonging to the path, such that the label is glued to the object to be labelled at at least one initial gluing point, wherein, after the meeting point, the device has a mechanism for wrappedly affixing the label, which comprises a pivoting arm comprising, at one end, a contact element intended to press the label against the object to be labelled and an actuator that provides the arm of the mechanism for wrappedly affixing the label with movement according to a curved path, preferably back and forth. The device also comprises a means for coordinating the movements of the conveyor and of the mechanism for wrapped affixation, such that when the device actuates the arm, the arm presses the label against the part to be labelled, preferably along a side substantially opposite the side of the part that makes contact with the label at the meeting point.

Description

[0001] DESCRIPTION

[0002] SELF-ADHESIVE LABEL APPLICATION DEVICE

[0003] The present invention relates to the field of devices for applying wrap-around labels, either partially or completely. More specifically, the present invention relates to a device for applying a self-adhesive label arranged around the perimeter of an object.

[0004] Automatic self-adhesive label application devices are known. Patent ES2265697A1 discloses an example of such a device. This document discloses a label applicator device with a label applicator module comprising a label tape feed roll and an applicator, and a parts-to-label conveyor that transports parts to be labeled along a path. The applicator is arranged so that the parts to be labeled encounter a self-adhesive label at a point along the path. However, known automatic devices apply the self-adhesive label to an approximately flat surface.When applied to other types of surfaces, such as curved surfaces, as is the case with objects with cylindrical or almost cylindrical sections, for example, these applicators only manage to make the label partially adhere to the surface.

[0005] However, there is a demand for the automatic application of labels to non-flat surfaces. In particular, there is a demand for the automatic application of self-adhesive labels around the perimeter of an object, that is, partially or completely wrapping or surrounding it. This is useful for labeling elongated objects, whether they have a generally cylindrical, prismatic, or other cross-section, such as cucumbers, bananas, sausages, hoses, and other similar items, as well as objects that are elongated and / or have an approximately cylindrical or prismatic cross-section (such as bunches of green asparagus, garlic, sausages, and profiles). Automatic wrap-around labeling devices are known in which the object is rolled so that the label wraps around it, applying the label to the object's perimeter.This is achieved, for example, by placing the object between two surfaces with parallel relative motion. These devices, however, have several drawbacks that limit their application. Firstly, rotating the object to be labeled is difficult to integrate into a linear object transport line, making it challenging to incorporate these devices into a product treatment or processing line, and lengthening processing times. Secondly, these devices are not easily applicable to irregular objects that are not approximately cylindrical and very uniformly shaped, or to products where product rotation is not particularly suitable or convenient. For example, it is not possible to roll curved objects, such as bananas, or objects with a prismatic cross-section between two parallel surfaces.

[0006] It is an objective of the present invention to disclose means that allow a solution to the aforementioned limitations.

[0007] More specifically, it is an object of the present invention to disclose a device for applying a wrap-around label, either partially or completely, to the contours of products without requiring product rotation. Since product rotation is unnecessary, the label application can be integrated into a linear product conveyor system, without even needing to stop the product to apply the label. The device of the present invention is for the automatic application of self-adhesive labels around the perimeter of objects and can be used for any type of object cross-section (circular, rectangular, etc.).

[0008] More particularly, the present invention discloses a self-adhesive label application device comprising a label applicator and a parts-to-label conveyor that transports parts to be labeled along a path, the applicator being arranged with respect to the conveyor so that the parts to be labeled meet a self-adhesive label at a meeting point belonging to the said path, such that the label is stuck to the object to be labeled at at least one initial sticking point.According to the present invention, after the meeting point, the device has a wrap-around label placement mechanism, comprising a pivoting arm that has, at one end, a contact element intended to press the label against the object to be labeled and an actuator that gives the arm of the wrap-around placement mechanism a movement, preferably back and forth, along a curved path, the device also having a means of coordinating the movements of the conveyor and the wrap-around placement mechanism, such that when the device actuates the said arm, it presses the label against the piece to be labeled, preferably on a side substantially opposite to the side of the piece that makes contact with the label at the meeting point.

[0009] The present invention solves the problem by applying, after the initial application of the label, a wrap-around application mechanism. This mechanism applies the label to the object being labeled in those areas that, after the first application by the applicator, do not adhere due to the shape of the surface on which the label is to be placed (wrapping a section of the product to be labeled, either partially or completely). To achieve this, an arm is provided that operates in a preferably back-and-forth motion and has a contact element designed to press the label against the object in these areas. These areas preferably comprise a side of the object substantially opposite the side that makes contact with the label at the point of intersection; that is, a rear portion in the direction of the object's movement.The wrap-around placement mechanism must be coordinated with the conveyor by any means to ensure it operates at the precise moment. This coordination mechanism may include presence sensors, time-coordinated programming, or any other method. The arm has a curved path, allowing it to operate from behind the object being labeled, using the conveyor's walking path as a reference. This curved path can be circular or any other shape and can be actuated, for example, by a cam-type mechanism.

[0010] Preferably, the products are arranged on the conveyor so that they present the perimeter on which the label will be placed. In the case of elongated objects, this will correspond to a transverse position of the object with respect to the direction of travel of the conveyor. For correct label placement, it is advantageous for the objects to be fixed on the conveyor. To this end, preferably, the objects may be housed between carrier housings. The carrier housings should preferably be placed consecutively and spaced at least far enough apart to allow the wrap-around placement mechanism to pass between two consecutive products to be labeled.

[0011] According to the present invention, the label applicator can be of any type (labeling head, label printer, or other device). This applicator provides the label to be applied to the product. Preferably, the label adheres to at least one point on the object to be labeled as it passes through the applicator, which is driven by the conveyor. The applicator can be supplemented with any complementary element (roller, brush, spatula, etc., articulated or not, with or without a spring) to provide pressure for transferring the label to the product. The complementary element increases the application surface of the label and is usually positioned immediately after the labeling mechanism. Those parts not adhered after the complementary element, generally one or both ends of the label, will be placed in the wrap-around application mechanism.

[0012] The label is wrapped around the perimeter of the object by the wrapping mechanism, which comprises an automated system, preferably a tilting mechanism, that moves a contact or support element (roller, brush, spatula, or other) along a circular or curved path on the product's surface. This element completes the application of the label to the remaining perimeter. A drive, preferably, provides a rotary motion. The wrapping mechanism can be driven by any type of electric, pneumatic, or hydraulic actuator (e.g., fixed-step motor, servomotor, AC motor, pneumatic motor, rotary piston, lever and cam system, pneumatic cylinder and linkage, etc.).

[0013] The present invention allows the label to be placed with the part to be labeled while it is in motion at all times, without needing to stop or rotate the part to be labeled.

[0014] In preferred embodiments, the arm is curved. The curved arm facilitates the roller's approach to the item to be labeled and contacts it from behind. Preferably, the arm has two articulated parts connected by an elastic means, such that the effective length of the arm can vary during the contact phase with the object to be labeled. This embodiment is particularly suitable for wrapping labels onto objects with a prismatic or highly irregular cross-section, because the arm's articulation with the elastic means allows the arm to vary its effective length as it travels over the surface of the object to be labeled, pressing the label against the object.

[0015] As already mentioned, the actuator can be of any type, whether motor-driven, pneumatically, hydraulically, or mechanically powered, for example, by using the conveyor's motion. It is particularly preferable for the actuator to be a motor that drives the arm, for example, in both its forward and return strokes. The contact element (whether a brush, roller, idler roller that rotates freely around its central axis), spatula, or other type can be made of any material, although for some applications, a flexible material is preferred.

[0016] Preferably, the aforementioned arm is located, with respect to the trajectory, on the side substantially opposite to the side on which the applicator is located.

[0017] In a particularly preferred embodiment, the means for coordinating the movements of the conveyor and the wrap-around placement mechanism comprises a sensor for detecting the part to be labeled, located upstream of the wrap-around placement mechanism, such that the sensor signal is used by control means to actuate said motor. The device may also further comprise a sensor system for detecting the start and / or end of the contact element's travel.

[0018] Preferably, the conveyor comprises two parallel conveyor belts with a gap between them. This gap facilitates the placement of device components below the workpiece path, such as the wrap-around positioning mechanism or parts thereof (e.g., the arm).

[0019] Preferably, both conveyor belts have slots for positioning the part to be labeled, such that the part passes over the slot. These slots facilitate the transverse positioning of the part to be labeled and its secure attachment, as excessive movement during the labeling process must be avoided.

[0020] As previously stated, the device of the present invention may comprise a complementary placement element located between the applicator and the wrap-around placement mechanism. This element has at least one contact element positioned in the path of the part to be labeled, such that, with respect to the point of contact, the part to be labeled displaces the contact element to advance along its path, pressing the label against the contour of the part to be labeled. Preferably, the complementary element comprises two contact elements, more preferably opposed to each other and which, when at rest, may be in contact with each other. The contact element or elements may be of any type, for example, rollers, idler rollers, spatulas, brushes, or paddles.In preferred embodiments, the contact element or elements is an idler roller or rollers that rotate freely around their central axis.

[0021] When the contact element(s) are positioned in the path of the part being labeled, and after the point of contact, the contact elements of the complementary element make contact with the part in the label area. As the part moves, it displaces these elements, so they follow the contour of the part and create pressure between the label and the part being labeled. This pressure causes the label to adhere to the part in areas where it does not adhere to the applicator. When the contact elements are facing each other, the part displaces them in opposite directions with respect to the point of contact, causing the self-adhesive label to adhere to the part being labeled in both directions.

[0022] More preferably, the contact element(s) each have elastic means that exert a restoring force, pushing the contact elements back to their initial position after the part to be labeled has passed over them. This force also ensures pressure from the contact elements against the part to be labeled, which will promote label adhesion.

[0023] In a preferred embodiment, the contact element or elements of the complementary element are connected to an articulated arm capable of rotating about an articulation point. More preferably, the articulation point of one of the contact elements is located on one side of the meeting point, and the articulation point of the other contact element is located on the opposite side of the meeting point.

[0024] Alternatively, the contact elements of the complementary element could be motorized.

[0025] In preferred embodiments, one of the contact elements of the complementary element is located in the aforementioned recess of the conveyor.

[0026] In particularly preferred embodiments, the device comprises a label tape feed reel that feeds an applicator module comprising the applicator, the label being peeled off the label tape in the applicator, and a used label tape collection reel. The device may include a label printer. It may also include a receiving area for labeled parts located at the end of the feed path.

[0027] For a better understanding of the description and characteristics of the invention, drawings of an example embodiment of the present invention are attached as an explanatory but not limiting example.

[0028] Figure 1 shows a front elevation view of an embodiment of a self-adhesive label application device according to the present invention.

[0029] Figure 2 shows a front elevation view of an embodiment of a self-adhesive label application device according to the present invention.

[0030] Figure 3 shows a perspective view of an embodiment of a self-adhesive label application device according to the present invention.

[0031] Figure 4 shows a detailed perspective view of a first zone of the area where the label is applied to the object.

[0032] Figure 5 shows a detailed perspective view of a second zone of the label placement area on the object.

[0033] Figure 6 shows a detailed perspective view, from another point of view, of the second zone of the label placement area to the object.

[0034] Figures 7, 8 and 9 schematically show the passage of an object to be labeled through the first label placement zone.

[0035] Figures 10, 11, 12 and 13 show, schematically, the passage of the object to be labeled through the second label placement zone, after having passed through the first one.

[0036] Figure 14 shows, in a schematic way, a variation of the example shown in figures 1 to 13 that is especially suitable for objects with an irregular cross-section.

[0037] The figures show a self-adhesive label applicator device 1. The example device comprises a conveyor 2 for the objects to be labeled, a printer 3, which in this case also includes a roll 31 of carrier strip for the self-adhesive labels to be applied, an applicator head 4, a module 6 for positioning the label around the object to be labeled, and a collection area 5 for the labeled object. The conveyor 2 in the example consists of two parallel conveyor belts 21, 22 separated by a gap 23. In the example, the gap 23 facilitates the placement of the self-adhesive label around the object. The conveyor belts 21, 22 in the example have parallel slots 211, 221 for securing the object to be labeled.Both conveyor belts run in parallel in a coordinated manner, so that the objects to be labeled are sufficiently fixed, perpendicular to the belts and with the section around which the self-adhesive label will be placed in the gap 23.

[0038] At the end of conveyor 2 is a collection zone 5 for labeled objects. In this case, this zone is a tray located below the pivot point of the conveyor belts. Upon reaching this point, the conveyor belts reverse their trajectory and position, causing the object located in slots 211 and 221 to fall into the collection zone 5 for labeled objects.

[0039] The printer 3 in the example prints self-adhesive labels located on a label tape. The printer 3 in the example has a holder for a roll 31 of label tape comprising labels to be printed and applied. In other embodiments, the printer may not be required, for example, because it is not necessary to print the labels. The holder for the roll 31 might not be part of the printer, or it might not be required either.

[0040] The label carrier tape then passes through a label application head 4. The label application head 4 can be a conventional label applicator, such as those used for applying labels to flat surfaces, so not all of its components will be discussed in detail. The end of the applicator head 4 features three label carrier tape guide rollers 42, 43, and 44 and an applicator 41, which is a pointed piece where the label carrier tape changes direction, and the self-adhesive label peels off the carrier tape. Typically, the applicator head 4 may also include a reel for collecting the used label carrier tape.

[0041] In the example shown, the applicator and the label are positioned perpendicular to the path of the item being labeled. Other arrangements are also possible. Alternatively, the applicator and the label can be positioned vertically, preferably downwards, so that gravity assists in the adhesion and subsequent placement of the label.

[0042] Characteristically for the invention, after the applicator head 4, the device has a placement module 6 that places the label peripherally on the objects that pass through the applicator head 4 transported by the conveyor 2.

[0043] In order to apply the label completely around the object, in this example, the labeling module 6 has two application zones. In the first application zone (application element 61), the object to be labeled and the label come into contact, with the label adhering to the front face(s) of the object in the direction of travel on the conveyor belt. In the second application zone (enveloping application mechanism 62), the label adheres to the areas where it did not adhere in the first application zone (typically the rear areas in the direction of travel). The application element 61 has two roller-shaped contact elements 63 and 64, which are in contact with each other in their normal (rest) position. Both rollers are located downstream of the applicator module.The rollers obstruct the passage of the object to be labeled. Preferably, each of the two rollers 63, 64 can rotate around its own central axis. Furthermore, both rollers are tiltable, located at the end of respective articulated arms, each arm having elastic means for returning to its normal position, such as, for example, a torsion spring. Being connected to articulated arms, both rollers can rotate around the articulation point of the arms. Alternatively, each roller can be connected to a linear spring, for example, via its central axis of rotation, in which case the rollers can move linearly to allow passage of the object to be labeled. However, the rotating arrangement is preferred because it allows for a larger contact surface between the object to be labeled and the rollers.The device in the example shown also has a presence sensor 619, which provides a signal to initiate the operation. In the example shown, sensor 619 is located in the gap 23 between conveyor belts 21 and 22 and detects the object to be labeled upstream of the applicator module. The wrap-around placement mechanism 62 is located downstream of the first placement zone and has, as a contact element, a third roller 65 connected to an articulated, motorized arm 625, located in the gap between conveyor belts 21 and 22. In the example, the arm 625 and the roller 65 are located below the path of the object to be labeled (i.e., on the opposite side from where the applicator head 4 was located). Furthermore, in the example, the articulated arm 625 is driven by a motor 624. The motor 624 can be a continuous-flow motor or any other type.The 625 arm has a curved shape, which facilitates the 65 roller's contact with the object to be labeled and / or the label from the back, completing the label's encirclement. Additionally, the second zone can also be equipped with a sensor system to ensure the 625 arm's initial and final movement with the 65 roller and its return to the starting position.

[0044] Figures 7 to 13 show the label adhesion process carried out by the device in the example shown. Elements identical or similar to those already described have been identified in Figures 7 to 13 with the same numbers and will therefore not be described in detail.

[0045] Figure 7 shows an initial moment. The part to be labeled, 1000, is located in housings 211 and 221 and is transported by conveyor belts 21 and 22 (only housing 211 and conveyor belt 21 are visible in Figure 7). As it passes over sensor 619 (for example, an optical sensor), the sensor detects that a part to be labeled, 1000, is approaching. The device's control system (not shown in the figures) can use the signal from sensor 619, for example, to ensure that a self-adhesive label 1001 is in the path of the part to be labeled, 1000, preferably in the gap between the conveyor belts. In Figure 7, a label can be seen almost detached from the label carrier belt 1002 at the level of applicator 41.Another label, 1001, can be seen fully adhered to the label carrier tape 1002, which has not yet reached the abrupt change in direction that the label carrier tape 1002 undergoes at the end of the applicator 41. The figure also shows both rollers 63 and 64 and their articulated arms 632, 642. In the normal (rest) position, both rollers 63 and 64 are in contact at a level above that of the conveyor belts. This ensures a larger contact surface between the rollers and the part to be labeled, leading to a larger surface area for label adhesion. As already mentioned, both rollers are free-spinning, allowing them to rotate freely around their respective central axes 631 and 641. This allows the rollers to roll in contact with the part to be labeled, ensuring better label adhesion. Additionally, each roller rotates around a pivot axis of its respective articulated arm 632, 642.As it continues its advance, the object to be labeled 1000 encounters label 1001 and pulls it along, finally tearing it off the label carrier tape 1002. Furthermore, the label and object to be labeled assembly comes into contact with rollers 63 and 64, which begin to rotate around the pivot axes of their respective articulated arms 632 and 642. Since the arms are equipped with torsion springs (not shown in the figures), rollers 63 and 64 exert pressure against the label and follow the path traced by the surface of the object to be marked, increasing the contact area between label 1001 and the object to be labeled 1000. The spatial arrangement and length of the articulated arms, as well as the diameter of rollers 63 and 64, can be selected to achieve better contact between the rollers, the label, and the object to be labeled, and a longer contact path.

[0046] Once the item to be labeled passes both rollers, they return to their position by the action of the torsion springs. However, a portion of label 1001 may still remain unattached to the object to be labeled 1000, as shown in Figure 8. This is especially true if label 1000 is long enough to completely encircle the object, following the perimeter of its cross-section. In this case, a portion of label 1001 will remain unattached. As shown in the figure, the arrangement of the rollers and the length of the arms have been selected so that the main area remaining to be attached is located opposite the applicator 41. This unattached portion will be fully adhered in the wrap-around positioning mechanism 62 of the positioning module 6, as illustrated in Figures 10 to 13.

[0047] As shown in Figure 10, when the object to be labeled 1000, transported by the conveyor belts, passes over the sensor 629 in the second zone of the placement module 6, it is detected, which activates the motor 624 that moves the articulated arm 625 of the third roller 65. The motor can be a continuous displacement motor, or any other type of motor or drive (e.g., pneumatic, hydraulic, etc.). Because the third roller 65 is located below the part to be labeled, it has access to the main area of ​​the label to be adhered. The curved shape of the arm 625 allows the third roller 65 to approach the object to be labeled 1000 from behind, making contact with it and pressing the label 1000 against the object to be labeled 1001, thus completing the adhesion of the label 1001 to the object to be labeled 1000, completely encircling it. During this journey, the arm is powered by the 624 motor.When the third roller 65 reaches the end of its travel, it must return. In this case, the return is also driven by motor 624. Figure 11 shows two magnetic sensors 628 and 629 that serve to detect the beginning and end of the travel.

[0048] Figure 14 shows, schematically, a variant of the embodiment shown in Figures 1 to 13. The view corresponds to that of Figure 11. Elements equal to or equivalent to those shown in the previous figures have been identified with identical numbers and, therefore, will not be explained in detail.

[0049] The embodiment shown in Figure 14 may correspond to the embodiment shown in Figures 1 to 13, except for the details shown in Figure 14. The embodiment in Figure 14 differs in the embodiment of the arm of the wrapping placement mechanism. In this case, the arm 625 is divided into two sections. A first section 6241 is driven by the motor via shaft 6248, and a second section 6242 is articulated to the first section 6241 via another shaft 6243. An elastic element (spring 6246) is simultaneously attached to a fixed point 6247 of the first section and to a fixed point 6245 of the second section. Furthermore, the second section has a projection, which in the embodiment shown coincides with the fixed point 6245 and runs along a groove 6244 of the first section.Thus, the arm has a rest position, but the second section 6242 can rotate relative to the first section 6243 if a force is applied, while the spring 6246 ensures that the arm returns to its rest position. In this way, the arm can change its apparent length during its travel in contact with the label and the object to be labeled and is better suited to non-circular cross-sections, such as irregular or even square sections. In the example in Figure 14, a roller 64 is shown, but advantageously, the roller could be replaced by any object that makes contact with the label and the object to be labeled, such as a brush, a shovel, a spatula, or a paddle, made of rigid or, more advantageously, flexible material.

[0050] Although the invention has been described with respect to examples of preferred embodiments, these should not be considered limiting to the invention, which will be defined by the broadest interpretation of the following claims.

Claims

CLAIMS 1. A device for applying self-adhesive labels comprising a label applicator and a conveyor for parts to be labeled that transports parts to be labeled along a path, the applicator being arranged with respect to the conveyor so that the parts to be labeled meet a self-adhesive label at a meeting point belonging to said path, such that the label is affixed to the object to be labeled at at least one initial affixing point, characterized in that, subsequent to the meeting point, the device has a wrap-around label placement mechanism, comprising a pivoting arm having, at one end, a contact element for pressing the label against the object to be labeled and an actuator that imparts to the arm of the wrap-around placement mechanism a movement along a curved path, the device further having,a means of coordinating the movements of the conveyor and the wrapping placement mechanism, such that when the device actuates the aforementioned arm, it presses the label against the part to be labeled.

2. Device, according to the preceding claim, characterized in that the arm presses the label against the part to be labeled on a side substantially opposite to the side of the part that makes contact with the label at the meeting point.

3. Device, according to any of the preceding claims, characterized in that the actuator provides the arm of the enveloping placement mechanism with a movement along a curved path of back and forth.

4. Device, according to any of the preceding claims, characterized in that the arm is a curved arm.

5. Device, according to any of the preceding claims, characterized in that the arm has two articulated parts connected by means of an elastic means, such that the effective length of the arm can vary during the contact phase with the object to be labeled.

6. Device, according to any of the preceding claims, characterized in that the actuator is a motor or a pneumatic or hydraulic actuator.

7. Device, according to the preceding claim, characterized in that it is a motor that drives the arm both in the forward and return strokes.

8. Device, according to any of the preceding claims, characterized in that the contact element comprises a roller, or a spatula, or a paddle or a brush.

9. Device, according to the preceding claim, characterized in that the contact element is made of a flexible material.

10. Device, according to claim 8 or 9, characterized in that the contact element is an idler roller that rotates freely around its central axis.

11. Device, according to any of the preceding claims, characterized in that the said arm is located, with respect to the trajectory, on the opposite side to the side on which the applicator is located.

12. Device, according to any of the preceding claims, characterized in that the means for coordinating the movements of the conveyor and the wrapping placement mechanism comprises a sensor for detecting the part to be labeled located upstream of the wrapping placement mechanism, such that the sensor signal is used by control means to actuate said motor.

13. Device, according to any of the preceding claims, characterized in that the device further comprises a sensor system for detecting the beginning and / or end of travel of the contact element.

14. Device, according to any of the preceding claims, characterized in that the conveyor comprises two conveyor belts located in parallel, there being a gap between said conveyor belts.

15. Device, according to the preceding claim, characterized in that the said arm is arranged in the said recess.

16. Device, according to claim 14 or 15, characterized in that the parallel tapes have housings for placing the piece to be labeled, such that a piece to be labeled can be placed transversely to both tapes, and passing over the aforementioned opening.

17. Device, according to any of the preceding claims, characterized in that it comprises a complementary placement element located between the applicator and the enveloping placement mechanism, which has at least one contact element located in the path of the part to be labeled, such that with respect to the meeting point the part to be labeled displaces said contact element to make its way along its path, the contact element pressing the label against the contour of the part to be labeled.

18. Device, according to the preceding claim, characterized in that the complementary element comprises two contact elements opposed to each other.

19. Device, according to the preceding claim and claim 16, characterized in that one of the contact elements of the complementary element is located in the gap between conveyor belts.

20. Device, according to any of claims 17 to 19, characterized in that the contact element or elements of the complementary element each have elastic means that exert a restoring force that pushes the rollers to their initial position after the passage of the piece to be labeled.

21. Device, according to any of claims 17 to 20, characterized in that the contact element or elements of the complementary element are connected, respectively, to an articulated arm capable of rotating about an articulation point.

22. Device, according to any of claims 18 and 21, characterized in that the articulation point of one of the rollers is located on one side of the meeting point, and the articulation point of the other roller is located on the opposite side of the meeting point.

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