Adaptive staking machine for softening and stretching flexible laminar products

Abstract

An adaptive staking machine (1) for softening and stretching flexible laminar products, such as leather and hides, which comprises a base (2) defining a longitudinal axis (L) and having an inlet area (3) for the products to be treated and an outlet area (4) for the treated products, on the base there are mounted at least one pair of beating plates (6, 7) which are mutually facing and configured to act on the opposite faces of the products to be treated, at least one of said plates (6) being fixed and the other (7) movable and associated with drive means, advancement means (5) for the advancement of the products comprising at least one upper elastic belt (8) and at least one lower elastic belt (9), arranged mutually facing and interposed between the pair of beating plates (6, 7), each of said elastic belts (8, 9) having an annular development and being wound on at least one pair of upper end rollers (10, 11) and one pair of lower end rollers (12, 13) with axes perpendicular to the longitudinal direction. The machine comprises an automatic adaptive adjustment system (16, 17) for adjusting the tension (T) of each of the elastic belts (8, 9) and configured to recover the elongation of each individual belt over time and maintain the interposed laminar products perfectly flat, stretched and free from creases and unevenness during advancement and treatment thereof.

Description

ADAPTIVE STAKING MACHINE FOR SOFTENING AND STRETCHING FLEXIBLE LAMINAR PRODUCTSDESCRIPTIONField of the invention

[0001] The present invention generally relates to the technical field of machines for the tanning industry and it particularly relates to an adaptive staking machine for softening and stretching flexible laminar products, such as leather and hides.Background art

[0002] In the tanning industry, there has been long known the use of machines called stacking machines, designed to carry out the softening and the stretching of flexible laminar products such as industrial leathers and similar products.

[0003] These machines are used in operations subsequent to tanning and / or drying operations so as to allow the product to reacquire a natural softness, besides increasing the extension, that is the so-called “perforation pitch”.

[0004] These machines comprise one or more pairs of beating plates which are arranged facing each other and configured to act on the opposite faces of the products to be treated, in which at least one of the plates is fixed and at least one is movable and associated with means for imparting thereto a reciprocating approaching and moving away motion.

[0005] Typically, each plate is provided with tools or rungs adapted to interact with corresponding cavities or recesses having a complementary shape and arranged on the opposite plate.

[0006] Between the pairs of beating plates there is interposed at least one pair of elastic belts, one upper and one lower, arranged facing each other to retain between them and advance the laminar products along a predetermined longitudinal plane.

[0007] Each belt has an annular development and it is subtended by several rollers, two of which are arranged at the front and rear ends of the machine and others along the annular extension.

[0008] The elastic belts are not only used for driving the laminar products as they advance between the beating plates but also to keep the products being processed well stretched throughout their surface extension avoiding creases and curling as much as possible.

[0009] Therefore, for processing purposes, it is very important that the belts are evenly stretched, especially at their mutually facing areas. Furthermore, the tension condition also reflects on the pressure acting on products being processed which inevitably tend to slide and therefore be more stressed in the areas where they do not advance evenly.

[0010] Over time and following the stresses in the transversal direction induced by the beating plates, the belts partly lose their initial elastic features and, as a result, they tend to loosen and they can no longer provide the initial tension conditions.

[0011] As a result, the efficiency for the transportation of the laminar products is partly reduced, and, in borderline cases, the products are introduced into the machine in a non-even manner, facilitating the formation of processing creases and defects such to make the finished product unusable.

[0012] The Chinese utility model CN209555260U discloses a staking machine having an upper belt and a lower belt driven by respective motors. The lower belt is wound on end rollers. One of the end rollers is mounted on supports movable along horizontal guides. The movable support is associated with a longitudinal screw which can be rotated by means of a handwheel. Rotating the handwheel allows to obtain the manual translation of the support which in turn causes a change in the tension of the belt. This manual mechanism does not allow to know the degree of tensioning of the lower belt.

[0013] The Chinese utility model CN202152345U discloses a staking machine also having an upper and a lower belt. The lower belt is wound on some rollers. One of the end rollers is mounted on arms which can be rotated by an actuator, so as to change the tension of the belt. Also in this case, it is not possible to know the actual tension of the belt.

[0014] A drawback of these prior art staking machines lies in the fact that the tension can be adjusted only in one of the conveyor belts, and, as a result, the opposite surfaces of the belts do not have the same degree of tension.

[0015] Therefore, in these machines, the laminar products interposed between the two upper and lower belts can however curl or crease, they do not remain perfectly stretched and it is not possible to avoid damaging the products being processed. Furthermore, the lack of tensioning in both belts prevents an effective driving of the leathers and this could result in slipping in the advancement of the laminar products.Technical problem

[0016] In the light of the prior art, the object of the present invention is to solve the technical problem of providing a staking machine which allows an effective and excellent tensioning of both elastic conveyor belts automatically and adapting it to the processing needs of the products to be treated, so as to avoid processing creases and defects.Summary of the invention

[0017] The object of the present invention is to solve the aforementioned problem by providing an adaptive staking machine for softening and stretching flexible laminar products which is highly efficient and cost-effective.

[0018] A particular object of the present invention is to provide a staking machine which allows to adjust the tension of both belts automatically and accurately as required for the specific type of product.

[0019] A further object is to confer to the belts a tension condition such to avoid the slipping of the laminar products and ensure the even processing thereof.

[0020] The objects mentioned above and others which will be more apparent hereinafter, are attained by an adaptive staking machine for softening and stretching flexible laminar products, such as leather and hides, according to claim 1.

[0021] The machine comprises a base defining a longitudinal axis, with an inlet area for the products to be treated and an outlet area for the treatedproducts, on the base there are mounted at least one pair of beating plates arranged facing each other to act on the opposite faces of the products to be treated, at least one of the plates of each pair being fixed and the other movable and associated with drive means for imparting a reciprocating approaching and moving away motion, advancement means for advancing the products comprising at least one upper elastic belt and at least one lower elastic belt, arranged facing each other and interposed between the at least one pair of beating plates to retain and advance the products along a longitudinal direction, each elastic belt having an annular development and being wound on a pair of upper end rollers and a pair of lower end rollers with transversal and mutually parallel rotation axes.

[0022] According to the invention, there is provided an automatic adaptive adjustment system for adjusting the tension of each of the elastic belts configured to recover the elongation of each individual belt over time and maintain the interposed laminar products perfectly flat, stretched and free from creases and unevenness during advancement and treatment thereof.

[0023] In an embodiment, the automatic adjustment system comprises a first adaptive mechanism associated with the upper belt and a second adaptive mechanism associated with the lower belt.

[0024] In particular, the first adaptive mechanism associated with the upper belt is arranged above the one or more fixed plates, and the second mechanism for the lower elastic belt is arranged below the one or more movable plates.

[0025] In an embodiment, the first adaptive mechanism comprises a first upper tensioning roller with rotation axis parallel to the end rollers and on which there is wound the upper elastic belt to vary the tension thereof, upstream and downstream of the tensioning roller there being provided a first series of return rollers interposed between the upper end rollers.

[0026] In an embodiment, the first upper tensioning roller is rotatably mounted on a pair of end supports fixed on respective first slides slidably mounted on a first pair of substantially horizontal upper guides.

[0027] Each of the first slides is associated with first actuator means configured to move the upper tensioning roller along the pair of upper guides.

[0028] In an embodiment, the first actuator means are of the helical and nut screw type, the nut screw being coupled to a respective gearmotor.

[0029] Each of the gearmotors of the first actuator means is provided with a respective encoder configured to generate a first and a second electrical signal for synchronising the movement of the respective nut screws.

[0030] The first upper tensioning roller is mounted on the pair of supports by interposing a pair of first load cells configured to transduce the instantaneous tension acting on said first upper tensioning roller into a third electrical signal.

[0031] In an embodiment, the second adaptive mechanism comprises a first pair of lower arms configured to support a first lower end roller at the inlet of the products to be treated and a second pair of lower arms for supporting a second lower end roller at the outlet of the treated products.

[0032] In another embodiment, the second adaptive mechanism comprises a first pair of lower arms configured to support a first lower end roller at the inlet of the products to be treated and a second pair of lower arms for supporting a second lower end roller at the outlet of the treated products.

[0033] The first pair of lower arms and the second pair of lower arms are slidably mounted on respective first and second substantially horizontal lower guides, there being provided for first and second actuator means respective acting on the first and on the second pair of arms to translate them horizontally so as to change the tension of the lower belt.

[0034] In an embodiment, the second adaptive mechanism is arranged below and in proximity of the first lower end roller and it comprises a lower tensioning roller with horizontal rotation axis and parallel to said end rollers of the lower elastic belt.

[0035] The lower elastic belt is wound on the lower tensioning roller and on which there is wound the lower elastic belt by interposing a second series of guide rollers.

[0036] The lower tensioning roller is mounted on a second pair of supports fixed on respective second slides slidably mounted on a second pair of substantially vertical lower guides.

[0037] Each of the second slides is associated with fourth actuator means configured to move the lower tensioning roller along said pair of substantially vertical lower guides.

[0038] In an embodiment, the fourth actuator means are of the helical and nut screw type, and wherein the nut screw is coupled to a respective gearmotor, and wherein each gearmotor of the fourth actuator means is provided with a respective encoder configured to generate fourth electrical signals for synchronising the movement of the respective nut screws.

[0039] Advantageous embodiments of the invention are attained according to the dependent claims.Brief description of the drawings

[0040] Further characteristics and advantages of the invention will be more apparent in the light of the detailed description of a preferred but not exclusive embodiment of an adaptive staking machine for softening and stretching flexible laminar products, shown by way of non-limiting example with reference to the drawings below, wherein:FIG. 1 is a top axonometric view of an embodiment of a staking machine according to the invention;FIG. 2 is a partially cross-sectional lateral view of the machine of FIG. 1;FIG. 3 is an enlarged lateral view of a detail of FIG. 2;FIG. 4 is a plan view of the detail of FIG. 3;FIG. 5 is an axonometric view of the detail of FIGS. 3 and 4;FIG. 6 is a partially cross-sectional lateral view of a variant of the of the machine of FIG. 1 ;FIG. 7 is a front view of the machine of FIG. 6 partially sectioned along a vertical plane of line VII-VII;FIG. 8 is a lateral view of the machine of FIG. 1 in some operating steps;FIG. 9 is a lateral view of a further embodiment of the machine according to the invention;FIG. 10 is a lateral view of a detail of FIG. 9 on one side;FIG. 11 is a lateral view of the detail of FIG. 10 on the opposite side to better highlight the details;FIG. 12 is a flow chart of the machine control system according to the invention.Detailed description of a preferred embodiment

[0041] With reference to the figures mentioned above, there is shown a staking machine, indicated in its entirety with reference numeral 1 , for softening and stretching flexible laminar products, not shown in the figures, such as industrial leathers and the like which have opposite sides.

[0042] The staking machine 1 comprises a base 2 adapted to define an inlet area 3 and an area 4 for the laminar products and motor-driven advancement means 5 for conveying the laminar products along a predetermined longitudinal direction L from the inlet area 3 to the outlet area 4.

[0043] The machine 1 further comprises one or more pairs of beating 6, 7 arranged facing each other and substantially parallel to the advancement means 5 and acting on the opposite sides of the products being processed.

[0044] In an embodiment, the upper plate 6 is fixed and the lower plate 7 is movable and is connected to drive means, not shown in the figures. The latter impart to the movable plate 7 a reciprocating approaching and moving away motion with respect to the fixed plate 6 with a predetermined number of beats.

[0045] The fixed upper plate 6 may comprise a plurality of rung-shaped tools, not shown in the figures, while the movable lower plate 7 may comprise a plurality of cavities or holes, also not shown in the figures, that have a complementary shape and aligned with respect to the rungs.

[0046] The beating plates 6, 7 interact at the time of the beating to exert with the rungs and the holes a pressure of a predetermined value on the advancing laminar products.

[0047] Obviously, the tools may also be different or they may have a different order, with the holes formed on the fixed plate 6 and the rungs formed on the movable plate 7, without departing from the scope of protection of the present invention.

[0048] The advancement means 5 comprise at least one upper elastic belt 8 and at least one lower elastic belt 9, which are arranged facing each other and with mutual contact, interposed between the pair of beating plates 6, 7 to retain and advance the products along a longitudinal direction L.

[0049] The upper elastic belt 8 has an annular development and it is wound on a pair of upper end rollers 10, 11 having transversal and parallel rotation axes.

[0050] Similarly, the lower elastic belt 9 has an annular development and it is wound on a pair of lower end rollers 12, 13 also having rotation axes that are transversal and parallel to each other and to the upper end rollers 10, 11.

[0051] According to the invention, the staking machine 1 comprises an automatic adaptive adjustment system for adjusting the tension of each of the elastic belts 8, 9 configured to recover the extension of each individual belt over time and maintain the interposed laminar products perfectly flat, stretched and free from creases and unevenness during advancement and treatment thereof.

[0052] In an embodiment, the automatic adaptive adjustment system comprises a first adaptive mechanism 16 associated with the upper elastic belt 8 and a second adaptive mechanism 17 associated with the lower elastic belt 9

[0053] The first adaptive mechanism 16 is arranged above the fixed beating plates 6, while the second adaptive mechanism 17 is arranged below the movable beating plates 7.

[0054] In an embodiment, the first adaptive mechanism 16 comprises an upper tensioning roller 18 which is substantially parallel to the end rollers 10, 11. The upper elastic belt 8 is wound on the upper tensioning roller 18 as wellon the first series of return rollers 19, 20 and 21 positioned between the upper end rollers 10, 11.

[0055] In an embodiment, the upper tensioning roller 18 is rotatably mounted on end supports 22 fixed on respective slides 23 which may slide along a pair of substantially horizontal and parallel upper guides 24, anchored with brackets on the upper part of the base 2, as shown in FIG. 4.

[0056] The first adaptive mechanism 16 comprises first actuator means 25 coupled to the slides 23 to cause the translation thereof along the upper guides 24 and therefore the horizontal movement of the upper tensioning roller 18 so as to change the tension acting on the upper tensioning roller 8.

[0057] In an embodiment, each actuator 25 is a helical pair of the screw-nut type and it comprises a worm screw 26 connected with the output shaft of a gearmotor 27 and coupled with a nut screw 28 integrally joined with the slide 23

[0058] On the drive axis of each of the gearmotors 27 there is mounted a respective encoder 29 configured to generate first position and speed electrical signals E1.

[0059] The electrical signals E1 are sent to an inverter of the PLC of the machine to synchronise the movement of the respective worm screws 26 arranged on the opposite ends of the tensioning roller 18, and therefore control the longitudinal movement of the latter parallel to itself.

[0060] According to the invention, the automatic adaptive adjustment system comprises a first pair of radial load cells 30, for example of the radial type, each arranged on end supports of one of the rollers of the first series of return rollers, for example the return roller 19, to detect the tension of the upper elastic belt 8 and emit second electrical signals E2 proportional to the tension detected on the upper elastic belt 8.

[0061] These electrical signals E2 are sent to the inverter of the PLC and they are processed to automatically control the longitudinal movement of the tensioning roller 18 and therefore automatically adjust the tension of the upperelastic belt 8 and maintain it equal to the value pre-set on the interface I of the machine accessible by the operator.

[0062] In an embodiment, the second adaptive adjustment mechanism 17 comprises a pair of front arms 31 which extend cantilevered from the base 2 towards the inlet area 3 and a pair of rear arms 32 which extend cantilevered from the base 2 towards the outlet area 4.

[0063] The end rollers 12, 13 on which there is wound the lower elastic belt 9 are supported at the ends of the two arms 31 , 32.

[0064] In an embodiment, the arms 31 , 32 are movable, in the sense that they slide in the longitudinal direction L mutually approaching and moving away, so as to change the distance of the end rollers 12, 13 and therefore the tension of the lower elastic belt 9.

[0065] To this end, the arms 31 , 32 are mounted on respective second front 33 and rear slides 34 which slide on respective substantially horizontal front 35 and rear guides 36, integrally joined with the base 2.

[0066] In order to promote the movement of arms 31 , 32 there are provided second front and rear actuator means, respectively indicated with 37, 38 acting on the respective front and rear slides 33, 34 to promote the mutual distance of the end rollers 12, 13 and therefore the tension of the lower elastic belt 9.

[0067] In an embodiment, the second actuator means 37, 38 are kinematic pairs of the screw and nut screw type, as shown in FIG. 2. In particular, each actuator 37, 38 comprises a nut screw or nut 39, 40 integrally joined with a respective front and rear slide 33, 34 kinematically coupled to a screw for example trapezoidal, front and rear 41, 42 connected to respective gearmotors 43, 44.

[0068] Also in this case, on the output shaft of each gearmotor 43, 44 there is mounted an encoder 45, 46 configured to generate electrical signals E3 which are sent to the inverter of the PLC to detect the position and the translation speed of the arms 31 , 32.

[0069] According to the invention, the automatic adaptive adjustment system comprises a second pair of radial load cells 47, arranged at the end supportsof the lower elastic belt 9 at a lower return roller and configured to detect the tension of the lower belt 9 and generate electrical signals E4.

[0070] The electrical signals E4 generated by the radial load cells 47 are sent to the inverter of the PLC of the machine and they are processed to automatically control the longitudinal translation of the end rollers 12, 13 and therefore automatically adjust the tension of the lower elastic belt 9 and maintain it equal to the value preset on the interface I of the machine accessible to the operator.

[0071] In FIGS. 6 and 7 there is shown a third actuator 25’ as a variant of the actuator 25 for controlling the longitudinal translation of the extensible arms 31 , 32 and therefore the relative position of the end rollers 12, 13 so as to adjust the tension of the lower elastic belt 9.

[0072] In this variant, instead of using four gearmotors to translate both pairs of arms 31 , 32 in the horizontal direction, the actuator 25’ is provided with only one gearmotor.

[0073] In particular, the actuator 25’ comprises a gearmotor 48 with a ring gear 49, a chain 50 wound on the ring gear 49 and redirected on two fixed guide pinions 51 towards a side of the base 2. The chain 50 simultaneously actuates a pair of end pinions 52 placed at the ends of the chain 50. Also in this case, on the gearmotor 48 there is keyed an encoder 70 for detecting the number of revolutions and the position of the arms as a result.

[0074] Each of the end pinions 52 is connected to a trapezoidal screw with a rightward 53 and a leftward portion 54, which engage respective nut screws, not shown in the figures, integrally joined with respective carriages 55, 56 to which there are fixed the arms 31 , 32 to allow the extension thereof identically and symmetrically with corresponding mutual movement of the end rollers 12, 13 of the lower elastic belt 9.

[0075] Also in this case, on the trapezoidal screw integrally joined with the pinions 52 there is keyed an encoder 57 for detecting the rotation speed of each lower end roller and generate electrical signals E5 adapted tosynchronise and coordinate the rotation of the end rollers of the lower elastic belt 9.

[0076] This variant of the actuator means of the arms 31 , 32 which uses a single gearmotor, allows to significantly reduce the costs for the mechanical components, for encoders, for wiring and for software. In addition, it limits the risks of alarms over time while the machine is running.

[0077] The provision of a pair of radial load cells 47, arranged at the end supports of the lower elastic belt 9 at a lower return roller and configured to detect the tension of the lower belt 9 and generate electrical signals E6 remains unvaried.

[0078] FIG. 8 shows the machine 1 with the lower movable arms both in the extended position 31 , 32 and in the retracted position 3T, 32, in which the lower elastic belt 9 is in maximum and minimum tension conditions.

[0079] With reference to the FIGS. 9-11 , there is shown a further embodiment of the second adaptive tension adjustment mechanism 17 according to the invention.

[0080] In this embodiment, the arms 31 , 32 which support the lower end rollers 12, 13 are fixed and the lower elastic belt 9 is wound around a lower tensioning roller 60 substantially parallel to the end rollers 12, 13 and arranged below the movable beating plates 7, in proximity of the inlet area 3 for the products.

[0081] The lower tensioning roller 60 is rotatably mounted on a second pair of lower supports 61 integrally joined with second slides 62 which may slide along a second pair of substantially vertical lower supports 63.

[0082] The lower elastic belt 9 in this area is wound on stationary rollers 64, 65, 66 fixed on the base 2.

[0083] The movement of the lower tensioning roller 60 is provided by a pair of fourth actuator means 65, each of which comprises a helical screw 66 connected to a gearmotor 67 and kinematically coupled to a nut screw not shown in the figures, so as to promote the vertical movement of the lower tensioning roller 60.

[0084] On the shaft of the gearmotor 67 there is mounted an encoder 68 configured to generate electrical signals E3, E4 for synchronising the movement of the nut screws.

[0085] In this case, due to the overall dimensions, there is provided a pair of radial load cells 47, arranged in proximity of the end supports of the lower elastic belt 9 at a lower return roller, the load cells being configured to detect the tension of the lower belt 9 and generate electrical signals E5, E5’.

[0086] In use, the operator presets on the interface I of the PLC a tension value T1 of the upper elastic belt 8 and a value T2 of the lower elastic belt 9, which normally must be identical or very similar and they correspond to corresponding electrical signals of set points + deformation hysteresis.

[0087] Over time, the values T1 and T2 may change due to the stress induced by the beating plates 6, 7 and for the progressive loss of elasticity of the elastic belts 8, 9. At this point, the PLC of the machine, on which there is loaded a suitable control program, detects the electrical signals E2, E4, E6 generated by the load cells and it automatically supplies the gearmotors of the actuator means 25, 25’, 65 so as to adapt the value of the tension of the elastic belts 8, 9 to those T1 and T2 preset initially.

[0088] At the same time, the electrical signals E1 , E3, E5 generated by the encoders 45, 46, 57, 70 are sent to the PLC which processes them so as to control the position of the actuator means and promote a coordinated actuation of the actuator means.

[0089] FIG. 12 generally shows a flow chart of the operation of the PLC of the machine according to the invention.

[0090] The staking machine according to the invention is susceptible to numerous modifications and variants all falling within the inventive concept outlined in the attached claims. For example, instead of the actuator means of a helical kinematic pair of the screw-and-nut type, one can use other types of actuator means and not only mechanical, for example linear with rack and pinion, but also of the hydraulic and electromagnetic type.

[0091] Even though the machine has been described with reference to the attached figures, the reference numbers utilised in the description and in the claims are meant for improving the intelligibility of the invention and thus do not limit the claimed scope of protection in any manner whatsoever. Industrial applicability

[0092] The present invention can be applied at industrial level because it can be manufactured on industrial scale by industries belonging to the field of machines for processing flexible laminar products, such as leathers and hides.

Claims

CLAIMS1. An adaptive staking machine (1) for softening and stretching flexible laminar products, such as leathers and hides, which machine comprises:- a base (2) defining a longitudinal axis (L) and having an inlet area (3) for the products to be treated and an outlet area (4) for the treated products, wherein on the base (2) are mounted:- at least one pair of mutually facing beating plates (6, 7) configured to act on the opposite faces of the products to be treated, at least one of said plates (6) being fixed and the other plate (7) being movable and associated with drive means;- advancement means (5) for the advancement of the products and comprising at least one upper elastic belt (8) and at least one lower elastic belt (9) mutually facing and interposed between said at least one pair of beating plates (6, 7), each of said elastic belts (8, 9) having an annular development and being wound on at least one pair of upper end rollers (10, 11) and one pair of lower end rollers (12, 13) with axes perpendicular to said longitudinal direction; characterised by comprising an automatic adaptive adjustment system (16, 17) for adjusting the tension (T) of each of said elastic belts (8, 9) and configured to recover the elongation of each individual belt over time and maintain the interposed laminar products perfectly flat, stretched and free from creases and unevenness during advancement and treatment thereof.

2. A machine as claimed in claim 1 , wherein said automatic adjustment system comprises a first adaptive mechanism (16) associated with said upper belt (8) and a second adaptive mechanism (17) associated with said lower belt (9).

3. A machine as claimed in claim 2, wherein said first adaptive mechanism (16) comprises an upper tensioning roller (18) interposed between said upper end rollers (10, 11) on which there is wound a portion of said upper elastic belt (8) with the interposition of a first series of return rollers (19, 20,4. A machine as claimed in claim 3, wherein said upper tensioning roller (18) is rotatably mounted on a pair of supports (22) fixed on respective first slides (23) which are slidably mounted on a pair of substantially horizontal upper guides (24) integral with said base (2).

5. A machine as claimed in claim 4, wherein each of said slides (23) is connected to first actuator means (25) configured to move said upper tensioning roller (18) along said pair of upper guides (24) and vary the tension of said upper belt (8).

6. A machine as claimed in claim 5, wherein there are provided first gearmotors (27) each equipped with a respective encoder (29) configured to generate first electrical position signals (E1).

7. A machine as claimed in claim 2, wherein said first adaptive mechanism (16) comprises a first pair of load cells (30) arranged in contact with said upper elastic belt (8) and configured to emit second electrical signals (E2) proportional to the tension of said upper elastic belt (8).

8. A machine as claimed in claim 2, wherein said second adaptive mechanism (17) comprises a first pair of lower arms (31 , 32) configured to support a first lower end roller (12) in said inlet area (3) and a second pair of lower arms (13) to support a second lower end roller in said outlet area (4).

9. A machine as claimed in claim 8, wherein said first pair of lower arms (31 ) and said second pair of lower arms (32) are movable and slidably mounted on respective first and second substantially horizontal lower guides (35, 36).

10. A machine as claimed in claim 9, wherein there are provided second actuator means (37, 38) acting on said first and said second pairs of arms (31 , 32) to change their relative position in the horizontal direction and so as to adjust the tension of said lower elastic belt (9).

11. A machine as claimed in one of claims 5 and 9, wherein said first actuator means (25) and said second actuator means (37, 38) are helical kinematic pairs of the screw-nut type, and they are coupled to a respective gearmotor (27, 43, 44) provided with an encoder (29, 45, 46).

12. A machine as claimed in claim 11 , wherein said first and second pairs of lower arms (31 , 32) are associated with a respective pair of load cells (30) for detecting the tension acting on each of said lower end rollers and generate a second electrical signal (E2).

13. A machine as claimed in claim 2, wherein said second adaptive mechanism (17) comprises third actuator means (25’) to control the longitudinal translation of the movable arms (31 , 32), which have a single central gearmotor (48) with a ring gear (49) on which there is wound a chain (50) configured to simultaneously drive a pair of end pinions (52) and on which a respective encoder (70) is keyed.

14. A machine as claimed in claim 2, wherein said second adaptive mechanism (17) comprises a lower tensioning roller (60) which is rotatably mounted on a second pair of lower supports (61) anchored to respective second lower slides (62) in turn slidably mounted on a second pair of substantially vertical lower guides (63).

15. A machine as claimed in claim 14, wherein each of said second lower slides (62) is associated with fourth actuator means (65) which are configured to move said lower tensioning roller (60) along said pair of substantially vertical lower guides (63).

16. A machine as claimed in claim 15, wherein said fourth actuator means (65) are helical pairs of the screw-nut type, each nut screw (66) being coupled to a respective gearmotor (67) provided with a respective encoder (68) which is configured to generate fifth electrical signals (E5) for controlling the position of said lower tensioning roller (60).

17. A machine as claimed in any preceding claim, wherein there is provided a microcontroller electronic unit (PLC) which is configured to receive said electrical signals (E1 , E3, E5) generated by said encoders and electrical signals (E2, E4, E6) generated by said load cells, a computer program being installed on said microcontroller electronic unit (PLC) for processing said electrical signals and automatically adapting the tension of said upper elastic belt (8) and said lower elastic belt (9) and maintaining the tension constantlyequal to tension values (T1, T2) preset by an operator on an interface (I) of said microcontroller electronic unit (PLC).

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