Self-adapting oscillating tenter for softening and stretching flexible sheet-like products

Abstract

An adaptive oscillating softening machine (1) for softening and stretching flexible sheet products such as leather and hides includes a base (2) defining a longitudinal axis (L) and having an inlet area (3) for the product to be processed and an outlet area (4) for the processed product, wherein at least one pair of oscillating plates (6, 7) facing each other and configured to act on opposite surfaces of the product to be processed are mounted on the base, wherein at least one of the oscillating plates (6) is fixed and the other oscillating plate (7) is movable. Associated with a drive mechanism; and a feeding device (5) for advancing the product, the feeding device comprising at least one upper elastic band (8) and at least one lower elastic band (9), the upper elastic band (8) and the lower elastic band (9) being arranged facing each other and sandwiched between the pair of vibrating plates (6, 7), each of the elastic bands (8, 9) having an annular extension and being wound around at least one pair of upper end rollers (10, 11) and a pair of lower end rollers (12, 13), the axes of the upper end rollers and the lower end rollers being perpendicular to the longitudinal direction. The machine includes an automatic adaptive adjustment system (16, 17) for adjusting the tension (T) of each elastic band (8, 9), the automatic adaptive adjustment system being configured to compensate for the elongation of each elastic band over time and to keep the sheet product sandwiched therebetween completely flat, stretched, and free of wrinkles and unevenness during the advance and processing of the sheet product.

Description

Technical Field

[0001] This invention relates generally to the technical field of machinery for the leather industry, and more particularly to an adaptive oscillating softening machine for softening and stretching flexible sheet products such as leather and hides. Background Technology

[0002] In the leather industry, the use of machines known as vibratory softening machines has long been known, which are designed to soften and stretch flexible sheet products such as industrial leather and similar products.

[0003] These machines are used in processes following tanning and / or drying operations to restore the product to its natural softness while increasing its stretch, known as the "perforation pitch".

[0004] These machines include one or more pairs of oscillating plates arranged facing each other and configured to act on opposing surfaces of a product to be processed, wherein at least one oscillating plate is fixed and at least one oscillating plate is movable and associated with a drive mechanism for giving the oscillating plate a reciprocating approach and away motion.

[0005] Typically, each oscillating plate is provided with a tool or crossbar adapted to interact with a corresponding cavity or recess arranged on the opposite oscillating plate and having a complementary shape.

[0006] At least one pair of elastic bands, namely an upper elastic band and a lower elastic band, are provided between the paired oscillating plates, which are arranged facing each other to hold the sheet product therebetween and allow the sheet product to advance along a predetermined longitudinal plane.

[0007] Each elastic band extends in a ring and is wound around multiple rollers, with two rollers located at the front and rear ends of the machine, and the other rollers arranged along the ring extension path.

[0008] The elastic band is used not only to drive the sheet product as it moves between the oscillating plates, but also to keep the product being processed fully stretched across its entire surface area, thereby minimizing wrinkles and curling.

[0009] Therefore, in terms of processing, it is crucial to ensure that the elastic bands are evenly tensioned, especially in areas where they face each other. Furthermore, the tension state also affects the pressure acting on the product being processed, which inevitably has a tendency to slip; thus, areas where the product does not move evenly will experience greater stress.

[0010] Over time, and due to the lateral stress generated by the oscillating plate, the elastic band will partially lose its initial elastic properties, thus tending to relax and no longer providing the initial tension state.

[0011] Therefore, the conveying efficiency of sheet products will be reduced to some extent, and in extreme cases, the products will be fed into the machine in an uneven manner, which can easily lead to processing wrinkles and defects, or even make the finished product unusable.

[0012] Chinese utility model CN209555260U discloses an oscillating stretching machine having an upper belt and a lower belt, each driven by a corresponding motor. The lower belt is wound around an end roller. One of the end rollers is mounted on a support member movable along a horizontal guide rail. The movable support member is associated with a longitudinal screw, which can be rotated by a handwheel. Rotating the handwheel allows the support member to be manually translated, thereby changing the tension of the belt. This manual mechanism does not allow for the determination of the tension of the lower belt.

[0013] Chinese utility model CN202152345U discloses an oscillating stretching machine that also has an upper belt and a lower belt. The lower belt is wound around several rollers. One end roller is mounted on an arm that can be driven to rotate by an actuator to change the tension of the belt. In this case, the actual tension of the belt cannot be known.

[0014] One drawback of these existing vibratory stretching machines is that they can only adjust the tension of one of the conveyor belts, so the surfaces of the two conveyor belts facing each other cannot have the same tension.

[0015] Therefore, in these machines, sheet-like products sandwiched between the upper and lower belts may still curl or wrinkle and cannot remain fully stretched, thus making it impossible to avoid damage to the products being processed. Furthermore, because both belts cannot be tensioned equally, the leather cannot be effectively driven, which may cause the sheet-like products to slip during forward movement.

[0016] Technical issues

[0017] In view of the prior art, the purpose of the present invention is to solve the following technical problem: to provide an oscillating stretching machine that can automatically and effectively tension two elastic conveyor belts and adapt the tension to the processing requirements of the product to be processed, thereby avoiding processing wrinkles and defects. Summary of the Invention

[0018] The purpose of this invention is to solve the above problems by providing an efficient and economical adaptive oscillating stretching machine for softening and stretching flexible sheet products.

[0019] A specific objective of this invention is to provide an oscillating stretching machine that can automatically and accurately adjust the tension of two elastic bands according to the requirements of a specific type of product.

[0020] Another object of the present invention is to give the elastic band such a tension state that it can prevent slippage of flexible sheet products and ensure their uniform processing.

[0021] The above objectives, as well as other objectives that will become more apparent below, are achieved by an adaptive oscillating stretching machine as described in claim 1 for softening and stretching flexible sheet products such as leather and hides.

[0022] The machine includes a base defining a longitudinal axis, the base having an inlet area for a product to be processed and an outlet area for processed products, and mounted on the base: at least one pair of oscillating plates arranged facing each other to act on opposing surfaces of the product to be processed, at least one of the oscillating plates in each pair being fixed and the other oscillating plate being movable and associated with a drive mechanism for imparting reciprocating approach and departure motion to it; and a feeding device for advancing the product, the feeding device including at least one upper elastic band and at least one lower elastic band, the upper elastic band and the lower elastic band being arranged facing each other and sandwiched between the at least one pair of oscillating plates to hold the product and advance the product in the longitudinal direction, each elastic band having an annular extension and being wound around a pair of upper end rollers and a pair of lower end rollers having transverse and parallel axes of rotation.

[0023] According to the present invention, an automatic adaptive adjustment system is provided for adjusting the tension of each elastic band, the automatic adaptive adjustment system being configured to compensate for the elongation of each elastic band over time and to keep the sheet product sandwiched therein completely flat, stretched, and free of wrinkles and unevenness during the advance and processing of the sheet product.

[0024] In one embodiment, the automatic adjustment system includes a first adaptive mechanism associated with the upper elastic band and a second adaptive mechanism associated with the lower elastic band.

[0025] Specifically, a first adaptive mechanism associated with the upper elastic band is arranged above one or more fixed oscillating plates, while a second adaptive mechanism for the lower elastic band is arranged below one or more movable oscillating plates.

[0026] In one embodiment, the first adaptive mechanism includes a first upper tensioning roller with its rotation axis parallel to the end roller, and an upper elastic band wound around the first upper tensioning roller to change its tension, with a first series of return rollers sandwiched between the upper end roller and upstream and downstream of the tensioning roller.

[0027] In one embodiment, the first upper tensioning roller is rotatably mounted on a pair of end supports, which are fixed to corresponding first slides, which are slidably mounted on a first pair of generally horizontal upper guide rails.

[0028] Each of the first slides is associated with a first actuation mechanism configured to move the upper tension roller along the pair of upper guide rails.

[0029] In one embodiment, the first actuation mechanism is a screw-nut type helical motion pair, and the nut is connected to a corresponding geared motor.

[0030] Each geared motor of the first actuation mechanism is equipped with a corresponding encoder, which is configured to generate a first electrical signal and a second electrical signal to synchronize the movement of the corresponding nut.

[0031] The first upper tensioning roller is mounted on the pair of supports by clamping a pair of first force sensors, which are configured to convert the instantaneous tension acting on the first upper tensioning roller into a third electrical signal.

[0032] In one embodiment, the second adaptive mechanism includes a first pair of lower arms and a second pair of lower arms, the first pair of lower arms being configured to support a first lower end roller located at the inlet of the product to be processed, and the second pair of lower arms being configured to support a second lower end roller located at the outlet of the processed product.

[0033] In another embodiment, the second adaptive mechanism includes a first pair of lower arms and a second pair of lower arms, the first pair of lower arms being configured to support a first lower end roller located at the inlet of the product to be processed, and the second pair of lower arms being configured to support a second lower end roller located at the outlet of the processed product.

[0034] The first pair of lower arms and the second pair of lower arms are slidably mounted on corresponding first and second lower guide rails. The first and second lower guide rails are approximately horizontal and are provided with a first actuation mechanism and a second actuation mechanism that act on the first pair of arms and the second pair of arms respectively to make them translate horizontally, thereby changing the tension of the lower elastic band.

[0035] In one embodiment, the second adaptive mechanism is arranged below and close to the first lower end roller, and includes a lower tension roller having a horizontal axis of rotation parallel to the end roller of the lower elastic band.

[0036] The lower elastic band is wound around the lower tension roller, and the lower elastic band is wound around it by clamping the second series of guide rollers.

[0037] The lower tensioning roller is mounted on the second pair of support members, which are fixed on corresponding second slide blocks. The second slide blocks are slidably mounted on the second pair of generally vertical lower guide rails.

[0038] Each of the second slides is associated with a fourth actuation mechanism configured to move the lower tension roller along the pair of generally vertical lower guide rails.

[0039] In one embodiment, the fourth actuation mechanism is a screw-nut type helical motion pair, wherein the nut is connected to a corresponding geared motor, and wherein each geared motor of the fourth actuation mechanism is provided with a corresponding encoder, the encoder being configured to generate a fourth electrical signal to synchronize the movement of the corresponding nut.

[0040] Advantageous embodiments of the invention are implemented according to the dependent claims. Attached Figure Description

[0041] Other features and advantages of the invention will become more apparent from the following detailed description, with reference to the accompanying drawings, of a preferred but not exclusive embodiment of an adaptive oscillating softening machine for softening and stretching flexible sheet products, in which: Figure 1 This is a top axonometric view of one embodiment of the oscillating stretching machine according to the present invention; Figure 2 yes Figure 1 A partially cut-away side view of the machine shown. Figure 3 yes Figure 2 A magnified side view of the details; Figure 4 yes Figure 3 A top view showing the details; Figure 5 yes Figure 3 and Figure 4 Axonometric view showing details; Figure 6 yes Figure 1 A partially cut-away side view of a variant of the machine shown. Figure 7 yes Figure 6 The front view of the machine shown, partially cut along line VII-VII in the vertical plane; Figure 8 yes Figure 1 Side view of the machine shown in several operating steps; Figure 9 This is a side view of another embodiment of the machine according to the present invention; Figure 10 yes Figure 9Details are shown in the side view. Figure 11 yes Figure 10 The details shown are viewed from the opposite side in a side view to better highlight them; Figure 12 This is a flowchart of the machine control system according to the present invention. Detailed Implementation

[0042] Referring to the above figures, an oscillating softening machine, generally indicated by reference numeral 1, is shown. It is used to soften and stretch flexible sheet products with opposite sides, such as industrial leather, which are not shown in the figures.

[0043] The vibrating stretching machine 1 includes a base 2 adapted to define an inlet region 3 and a region 4 for sheet products, and also includes a motor-driven feeding device 5 for conveying the sheet products from the inlet region 3 to the outlet region 4 along a predetermined longitudinal direction L.

[0044] The machine 1 also includes one or more pairs of vibrating plates 6 and 7 arranged facing each other and substantially parallel to the feed device 5, the vibrating plates 6 and 7 acting on opposite sides of the product being processed.

[0045] In one embodiment, the upper oscillating plate 6 is fixed, and the lower oscillating plate 7 is movable and connected to a drive mechanism (not shown in the figures). The drive mechanism imparts a reciprocating approaching and moving away motion of the movable oscillating plate 7 relative to the fixed oscillating plate 6 with a predetermined number of oscillations.

[0046] The fixed upper oscillating plate 6 may include a plurality of horizontal bar-shaped tools not shown in the figures, while the movable lower oscillating plate 7 may include a plurality of cavities or holes, also not shown in the figures, having complementary shapes and aligned with the horizontal bars.

[0047] The oscillating plates 6 and 7 interact during oscillation to apply a predetermined pressure to the advancing sheet product via the crossbars and the holes.

[0048] Obviously, without departing from the scope of protection of this invention, the tools may be different, or their arrangement order may be different. For example, the hole may be formed on the fixed oscillating plate 6, and the crossbar may be formed on the movable oscillating plate 7.

[0049] The feeding device 5 includes at least one upper elastic band 8 and at least one lower elastic band 9, which are arranged facing each other and in contact with each other, and sandwiched between the pair of oscillating plates 6 and 7 to hold the product and move the product forward in the longitudinal direction L.

[0050] The upper elastic band 8 has an annular extension and is wound around a pair of upper rollers 10, 11, which have transverse and parallel axes of rotation.

[0051] Similarly, the lower elastic band 9 has an annular extension and is wound around a pair of lower end rollers 12, 13, which also have a rotation axis that is transverse and parallel to each other and parallel to the upper end rollers 10, 11.

[0052] According to the present invention, the oscillating stretching machine 1 includes an automatic adaptive adjustment system for adjusting the tension of each elastic band 8, 9, the automatic adaptive adjustment system being configured to compensate for the elongation of each elastic band over time and to keep the sheet product sandwiched therein completely flat, stretched and free of wrinkles and unevenness during the advance and processing of the sheet product.

[0053] In one embodiment, the automatic adaptive adjustment system includes a first adaptive mechanism 16 associated with the upper elastic band 8 and a second adaptive mechanism 17 associated with the lower elastic band 9.

[0054] The first adaptive mechanism 16 is arranged above the fixed oscillating plate 6, while the second adaptive mechanism 17 is arranged below the movable oscillating plate 7.

[0055] In one embodiment, the first adaptive mechanism 16 includes an upper tensioning roller 18 substantially parallel to the end rollers 10, 11. The upper elastic band 8 is wound around the upper tensioning roller 18 and also around a first series of return rollers 19, 20 and 21 located between the upper end rollers 10, 11.

[0056] In one implementation, such as Figure 4 As shown, the upper tensioning roller 18 is rotatably mounted on the end support 22, which is fixed on a corresponding slide 23. The slide 23 is capable of sliding along a pair of generally horizontal and parallel upper guide rails 24, which are anchored to the upper part of the base 2 by a bracket.

[0057] The first adaptive mechanism 16 includes a first actuation mechanism 25 connected to the slide 23 to cause the slide 23 to translate along the upper guide rail 24, thereby causing the upper tension roller 18 to move horizontally, thus changing the tension acting on the upper elastic band 8.

[0058] In one embodiment, each actuation mechanism 25 is a screw-nut type helical motion pair, and includes a screw 26 connected to the output shaft of the geared motor 27 and a nut 28 connected to the screw 26 and integrally connected to the slide 23.

[0059] Each geared motor 27 has a corresponding encoder 29 mounted on its drive shaft, the encoder 29 being configured to generate a first position and speed electrical signal E1.

[0060] The electrical signal E1 is sent to the frequency converter of the machine's PLC to synchronize the movement of the corresponding screws 26 arranged at opposite ends of the tension roller 18, thereby controlling the tension roller 18 to maintain its parallel longitudinal movement.

[0061] According to the present invention, the automatic adaptive adjustment system includes a first pair of radial force sensors 30, such as radial force sensors, each of which is disposed on the end support of one of the return rollers in the first series of return rollers, such as return roller 19, to detect the tension of the upper elastic band 8 and emit a second electrical signal E2 proportional to the detected tension of the upper elastic band 8.

[0062] These electrical signals E2 are sent to the frequency converter of the PLC and processed to automatically control the longitudinal movement of the tension roller 18, thereby automatically adjusting the tension of the upper elastic belt 8 to maintain it equal to the value preset by the operator on the machine's accessible interface I.

[0063] In one embodiment, the second adaptive adjustment mechanism 17 includes a pair of front arms 31 and a pair of rear arms 32, the front arms 31 extending cantileveredly from the base 2 toward the inlet region 3, and the rear arms 32 extending cantileveredly from the base 2 toward the outlet region 4.

[0064] The end rollers 12 and 13, which are wound around the lower elastic band 9, are supported at the ends of the two pairs of arms 31 and 32.

[0065] In one embodiment, the arms 31 and 32 are movable, i.e., they slide toward and away from each other in the longitudinal direction L, thereby changing the distance between the end rollers 12 and 13, and thus changing the tension of the lower elastic belt 9.

[0066] For this purpose, the arms 31 and 32 are mounted on corresponding second front slides 33 and second rear slides 34, which slide on corresponding generally horizontal front guide rails 35 and rear guide rails 36 integrally connected to the base 2.

[0067] In order to drive the movement of the arms 31 and 32, a second front actuation mechanism and a second rear actuation mechanism, respectively indicated by 37 and 38, are provided. The second front actuation mechanism and the second rear actuation mechanism act on the corresponding front slide 33 and rear slide 34 to increase the distance between the end rollers 12 and 13, thereby increasing the tension of the lower elastic belt 9.

[0068] In one implementation, such as Figure 2As shown, the second actuation mechanisms 37 and 38 are screw-nut type kinematic pairs. In particular, each actuation mechanism 37 and 38 includes nuts 39 and 40 integrally connected to the corresponding front slide 33 and rear slide 34. The nuts 39 and 40 are kinematically connected to, for example, trapezoidal front screws 41 and rear screws 42, which are connected to corresponding geared motors 43 and 44.

[0069] In this case, encoders 45 and 46 are also installed on the output shaft of each geared motor 43 and 44. The encoders 45 and 46 are configured to generate an electrical signal E3, which is sent to the frequency converter of the PLC to detect the position and translation speed of the arms 31 and 32.

[0070] According to the present invention, the automatic adaptive adjustment system includes a second pair of radial force sensors 47, which are arranged at the end support of the lower elastic belt 9, located at a lower return roller, and configured to detect the tension of the lower elastic belt 9 and generate an electrical signal E4.

[0071] The electrical signal E4 generated by the radial force sensor 47 is sent to the frequency converter of the machine's PLC and processed to automatically control the longitudinal translation of the end rollers 12 and 13, thereby automatically adjusting the tension of the lower elastic belt 9 to keep it equal to the value preset by the operator on the machine's accessible interface I.

[0072] Figure 6 and Figure 7 A third actuation mechanism 25', a variant of actuation mechanism 25, is shown. It controls the longitudinal translation of the telescopic arms 31, 32, and thereby controls the relative positions of the end rollers 12, 13, thereby adjusting the tension of the lower elastic belt 9.

[0073] In this variant, instead of using four geared motors to make the two pairs of arms 31 and 32 translate horizontally, the actuation mechanism 25' is equipped with only one geared motor.

[0074] Specifically, the actuation mechanism 25' includes a geared motor 48 with a geared ring 49 and a chain 50 wound around the geared ring 49 and redirected to one side of the base 2 via two fixed guide pinions 51. The chain 50 simultaneously drives a pair of end pinions 52 located at both ends of the chain 50. Similarly, in this case, an encoder 70 is mounted on the geared motor 48 via a key to detect the number of revolutions and thereby detect the position of the arm.

[0075] Each end pinion 52 is connected to a trapezoidal screw having a right-handed portion 53 and a left-handed portion 54, which engage with corresponding nuts (not shown in the figures) and are integrally connected to corresponding carriages 55 and 56. Arms 31 and 32 are fixed to the carriages 55 and 56 so that the arms extend and retract uniformly and symmetrically, while the end rollers 12 and 13 of the lower elastic band 9 move relative to each other accordingly.

[0076] Similarly, in this case, an encoder 57 is mounted on the trapezoidal screw integrally connected to the pinion 52 via a key to detect the rotational speed of each lower end roller and generate an electrical signal E5, which is adapted to synchronize and coordinate the rotation of the end rollers of the lower elastic belt 9.

[0077] This modification of the actuation mechanism for arms 31 and 32, which uses a single geared motor, can significantly reduce the cost of mechanical components, encoders, wiring, and software. Furthermore, it can reduce the risk of alarms occurring over time during machine operation.

[0078] The second pair of radial force sensors 47 remain unchanged. The second pair of radial force sensors 47 are arranged at the end support of the lower elastic belt 9, located at the lower return roller, and are configured to detect the tension of the lower elastic belt 9 and generate an electrical signal E6.

[0079] Figure 8 Machine 1 is shown, wherein the lower movable arm is in both extended positions 31 and 32 and retracted positions 31' and 32, in which the lower elastic band 9 is in the maximum tension state and the minimum tension state, respectively.

[0080] Reference Figures 9 to 11 This illustrates another embodiment of the second adaptive tension adjustment mechanism 17 according to the present invention.

[0081] In this embodiment, the arms 31 and 32 supporting the lower end rollers 12 and 13 are fixed, and the lower elastic band 9 is wound around the lower tension roller 60, which is substantially parallel to the end rollers 12 and 13. The lower tension roller 60 is arranged below the movable vibrating plate 7 and close to the product inlet area 3.

[0082] The lower tensioning roller 60 is rotatably mounted on the second pair of lower supports 61, which are integrally connected to the second slide block 62. The second slide block 62 is capable of sliding along the second pair of generally vertical lower supports 63.

[0083] The lower elastic band 9 is wound around the fixed rollers 64, 65, and 66 fixed to the base 2 in this region.

[0084] The movement of the lower tension roller 60 is provided by a pair of fourth actuation mechanisms 65, each of which includes a helical screw 66 connected to a geared motor 67 and kinetically coupled to a nut (not shown in the figures), thereby driving the lower tension roller 60 to move vertically.

[0085] An encoder 68 is mounted on the shaft of the geared motor 67. The encoder 68 is configured to generate electrical signals E3 and E4 to synchronize the movement of the nut.

[0086] In this case, due to the overall size, a pair of radial force sensors 47 are provided. The radial force sensors 47 are arranged near the end support of the lower elastic belt 9, located at the lower return roller, and are configured to detect the tension of the lower elastic belt 9 and generate electrical signals E5, E5'.

[0087] When in use, the operator presets the tension value T1 of the upper elastic band 8 and the tension value T2 of the lower elastic band 9 on the PLC interface I. The tension values ​​T1 and T2 must usually be the same or very close, and they correspond to the corresponding "set point + deformation hysteresis" electrical signals.

[0088] As time progresses, the stress caused by the oscillating plates 6 and 7, and the gradual loss of elasticity in the elastic bands 8 and 9, may cause changes in the values ​​T1 and T2. At this time, the PLC of the machine with an appropriate control program detects the electrical signals E2, E4, and E6 generated by the force sensors and automatically supplies power to the geared motors of the actuation mechanisms 25, 25', and 65, thereby adapting the tension values ​​of the elastic bands 8 and 9 to the initially preset T1 and T2.

[0089] Meanwhile, the electrical signals E1, E3, and E5 generated by encoders 45, 46, 57, and 70 are sent to the PLC and processed by the PLC to control the position of the actuation mechanism and cause the actuation mechanism to coordinate actuation.

[0090] Figure 12 The overall operation flowchart of the PLC for the machine according to the present invention is shown.

[0091] The oscillating puller according to the present invention can be modified and varied in many ways, all of which fall within the inventive concept defined by the appended claims. For example, other types of actuation mechanisms can be used instead of the screw-nut type helical motion pair actuation mechanism, and the actuation mechanism is not limited to mechanical actuation mechanisms; for example, a rack-pinion linear actuation mechanism, as well as hydraulic and electromagnetic actuation mechanisms, can be used.

[0092] Although the machine has been described with reference to the accompanying drawings, the reference numerals used in the specification and claims are intended to improve the understanding of the invention and therefore do not limit the scope of the claimed protection in any way.

[0093] Industrial applicability

[0094] This invention can be applied industrially because it can be manufactured on an industrial scale by industrial enterprises belonging to the field of machinery for processing flexible sheet products such as leather and hides.

Claims

1. An adaptive oscillating stretching machine (1) for softening and stretching flexible sheet products such as leather and hides, comprising: A base (2) defining a longitudinal axis (L) and having an inlet area (3) for products to be processed and an outlet area (4) for processed products, wherein the base (2) is equipped with: At least one pair of oscillating plates (6, 7) facing each other, the oscillating plates being configured to act on opposite surfaces of the product to be processed, wherein at least one of the oscillating plates (6) is fixed and the other oscillating plate (7) is movable and associated with a drive mechanism. A feeding device (5) for advancing the product includes at least one upper elastic band (8) and at least one lower elastic band (9) facing each other and disposed between the at least one pair of vibrating plates (6, 7), the elastic bands (8, 9) extending in annular shape and respectively wound around at least one pair of upper end rollers (10, 11) and a pair of lower end rollers (12, 13), the axis of the end rollers being perpendicular to the longitudinal direction; The oscillating stretching machine is characterized by comprising an automatic adaptive adjustment system (16, 17) for adjusting the tension (T) of each of the elastic bands (8, 9), the automatic adaptive adjustment system being configured to compensate for the elongation of each band over time and to keep the sheet product sandwiched between the elastic bands completely flat, stretched and free of wrinkles and unevenness during the advance and processing of the sheet product.

2. The oscillating softener of claim 1, wherein, The automatic adjustment system includes a first adaptive mechanism (16) associated with the upper elastic band (8) and a second adaptive mechanism (17) associated with the lower elastic band (9).

3. The oscillating stretching machine according to claim 2, characterized in that, The first adaptive mechanism (16) includes an upper tensioning roller (18) disposed between the upper rollers (10, 11), and a portion of the upper elastic belt (8) is wound around the upper tensioning roller (18) via a first set of return rollers (19, 20, 21).

4. The oscillating stretching machine according to claim 3, characterized in that, The upper tensioning roller (18) is rotatably mounted on a pair of supports (22), which are fixed on corresponding first slides (23), which are slidably mounted on a pair of substantially horizontal upper guide rails (24) integrally formed with the base (2).

5. The oscillating stretching machine according to claim 4, characterized in that, Each of the slides (23) is connected to a first actuation mechanism (25), which is configured to move the upper tension roller (18) along the pair of upper guide rails (24) to change the tension of the upper elastic band (8).

6. The oscillating stretching machine according to claim 5, characterized in that, A plurality of first geared motors (27) are provided, each of which is equipped with a corresponding encoder (29), the encoder being configured to generate a first position electrical signal (E1).

7. The oscillating stretching machine according to claim 2, characterized in that, The first adaptive mechanism (16) includes a first pair of force sensors (30) arranged in contact with the upper elastic band (8), the first pair of force sensors being configured to output a second electrical signal (E2) proportional to the tension of the upper elastic band (8).

8. The oscillating stretching machine according to claim 2, characterized in that, The second adaptive mechanism (17) includes a first pair of lower arms (31, 32) and a second pair of lower arms (13), the first pair of lower arms being configured to support a first lower end roller (12) located in the inlet region (3), and the second pair of lower arms being configured to support a second lower end roller located in the outlet region (4).

9. The oscillating stretching machine according to claim 8, characterized in that, The first pair of lower arms (31) and the second pair of lower arms (32) are movable and are slidably mounted on the first basic horizontal lower guide rail (35) and the second basic horizontal lower guide rail (36), respectively.

10. The oscillating stretching machine according to claim 9, characterized in that, A second actuation mechanism (37, 38) is provided to act on the first pair of lower arms (31) and the second pair of lower arms (32) to change the relative position of the first pair of lower arms and the second pair of lower arms in the horizontal direction, thereby adjusting the tension of the lower elastic band (9).

11. The oscillating stretching machine according to any one of claims 5 and 9, characterized in that, The first actuation mechanism (25) and the second actuation mechanism (37, 38) are both screw-nut type helical motion pairs, and are respectively connected to the corresponding geared motors (27, 43, 44), and the geared motors are equipped with encoders (29, 45, 46).

12. The oscillating stretching machine according to claim 11, characterized in that, The first pair of lower arms and the second pair of lower arms (31, 32) are respectively associated with a corresponding pair of force sensors (30), which are used to detect the tension acting on each of the lower end rollers and generate a second electrical signal (E2).

13. The oscillating stretching machine according to claim 2, characterized in that, The second adaptive mechanism (17) includes a third actuation mechanism (25') for controlling the longitudinal translation of the movable arms (31, 32), the third actuation mechanism having a single central geared motor (48) having a gear ring (49) with a chain (50) wound around the gear ring (49) and configured to simultaneously drive a pair of end pinions (52), and a corresponding encoder (70) is keyed to the central geared motor (48).

14. The oscillating stretching machine according to claim 2, characterized in that, The second adaptive mechanism (17) includes a lower tension roller (60) rotatably mounted on a second pair of lower supports (61), which are fixed to corresponding second sliding seats (62), which are in turn slidably mounted on a second pair of substantially vertical lower guide rails (63).

15. The oscillating stretching machine according to claim 14, characterized in that, Each of the second sliding blocks (62) is associated with a fourth actuation mechanism (65) configured to move the lower tension roller (60) along the second pair of substantially vertical lower guide rails (63).

16. The oscillating stretching machine according to claim 15, characterized in that, The fourth actuation mechanism (65) is a screw-nut type helical motion pair. Each nut screw (66) is connected to a corresponding geared motor (67). The geared motor is equipped with a corresponding encoder (68). The encoder is configured to generate a fifth electrical signal (E5) for controlling the position of the lower tension roller (60).

17. The oscillating stretching machine according to any one of the preceding claims, characterized in that, A microcontroller electronic unit (PLC) is provided, which is configured to receive the electrical signals (E1, E3, E5) generated by the encoder and the electrical signals (E2, E4, E6) generated by the force sensor. The microcontroller electronic unit (PLC) is equipped with a computer program, which is used to process the electrical signals and automatically adjust the tension of the upper elastic band (8) and the lower elastic band (9) so that the tension is continuously maintained equal to the tension value (T1, T2) preset by the operator on the interface (I) of the microcontroller electronic unit (PLC).

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