ES2554822A1 - Inlet retention device for box stacking machine (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Inlet retention device for box stacking machine. The device comprises a retractable stop (1) disposed between an input conveyor (2) and a lifting cavity (3) in which there is a lifting carriage (5) that moves vertically between a lower position, to receive a box from the input conveyor (2), and an upper position, to transfer the box to a support device. The retractable stop (1) is pushed permanently by a recovery element (7) towards a retention position, in which the advance of a box transported by the input conveyor (2) to the lifting cavity (3) interferes, and when the lifting carriage (5) is moved to the lower position it is pushed by the lifting carriage (5) against the force of the recovery element (7) to a retracted position, in which to allow the free passage of the box from the transport conveyor. Entrance (2) to the lifting cavity (3). (Machine-translation by Google Translate, not legally binding)

Description

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DESCRIPTION

INPUT RETENTION DEVICE FOR BOX STACKING MACHINE Technical field

The present invention concerns an entry retention device for a box stacking machine comprising a movable retractable stop between a retention position and a retracted position in combination with movements of a lifting carriage. The box stacking machine has application in the field of corrugated box forming machines or other similar material from the folding of flat sheets of corrugated cardboard or other similar material and joining parts thereof.

Among the materials similar to corrugated cardboard suitable for the formation of boxes can be mentioned the compact cardboard, the plastic, and the corrugated plastic. The joining of folded parts of the flat die plates can be done by gluing, stapling, adhesive tape, etc.

Background of the invention

Box stacking machines are known that are used to stack boxes, for example empty boxes made of corrugated cardboard or other similar material, at the exit of a box-forming machine from flat die-cut plates. These prior art box stacking machines comprise an input conveyor on which successive boxes to be stacked are placed, an elevation cavity adjacent to a delivery end of the input conveyor, a lifting support fixed to a vertically guided lifting carriage and operated by an actuator to move in the lifting cavity between a lower position, suitable for the lifting support to receive a box from the input conveyor, and an upper position, in which the lifting support transfers the box to a support device. Thus, the successive boxes are added to the stack from below. When the stack includes a predetermined number of boxes, an ejection device transfers the stack of boxes from the holding device, for example to an outgoing conveyor.

Document ES 2343771 A1 discloses a box stacking machine comprising the basic features described above.

It is known to equip this type of box stacking machines with an entry retention device that has a retractable stop located between the delivery end of the

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Inlet conveyor and elevation cavity. In the state-of-the-art input retention devices, the said retractable stop has the form of a skirt fixed to the lifting support so that it is moved together with it between a retention position, in which the retractable stop retains a box on the input conveyor while the lift car is lifting the preceding box, and a retracted position, in which the retractable stop allows the free passage of the box from the input conveyor to the lifting cavity.

A drawback of this type of prior art entry retention device is that the retractable skirt-shaped stop must have a height approximately equal to the lift carriage stroke, such that the minimum height of the input conveyor, and therefore, the exit conveyor, with respect to the ground, is conditioned by the length of the lift carriage stroke.

The total height in a box stacking machine is critical since it depends on the number of stackable boxes in each stack for predetermined available height, and also a high center of gravity makes the box stacking machine more unstable during transport , which is important in those cases in which the box stacking machine is installed, usually together with a box-forming machine, in a trailer.

An objective of the present invention is to provide an input retention device for a box stacking machine that allows a more compact and low height box stacking machine design.

Exposition of the invention

The present invention contributes to achieving the above and other objectives by providing an input retention device for a box stacking machine comprising a retractable stop located between a delivery end of an input conveyor and a lifting cavity in which there is a support of lifting fixed to a vertically guided lifting carriage and operated by an actuator to move between a lower position, suitable for said lifting support to receive a box from said input conveyor, and an upper position, in which the lifting support transfers said box to a support device. The retractable stop is movable between a retention position, in which the retractable stop interferes with the advance of a box transported by the input conveyor towards said lifting cavity, and a retracted position, in which the retractable stop allows free passage from the box from the input conveyor to the lift cavity.

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In accordance with the present invention, the retractable stop is fixed to a guided retention assembly relative to a fixed frame so that it can move between said retention position and said retracted position. In addition, at least one recovery element is arranged so that it pulls or pushes the retention assembly towards the retention position, and the lift carriage, or a pusher attached to the lift carriage, is configured so as to interfere with the retention assembly and it pushes it to the position retracted against the force of said recovery element when the lifting carriage is moved to the lower position.

This arrangement allows the retractable stop to have a reduced vertical dimension, much lower than the lift carriage stroke and only sufficient to interfere with and retain a box moved by the inlet conveyor when the retractable stop is in the retention position, and that consequently the retractable stop does not protrude practically below the input conveyor when it is in the retracted position. Thus, a box stacking machine equipped with the entry retention device of the present invention may be lower and therefore more stable and capable of stacking a larger number of boxes in each stack for the same free height available in comparison with the box stacking machines of the prior art.

In one embodiment, the retention assembly is pivotally connected to said fixed frame by a horizontal axis articulation, and preferably perpendicular to the forward direction of the input conveyor. In this embodiment, the retractable stop is located on a front side of the elevation cavity adjacent to said delivery end of the input conveyor, said articulation is located on a rear side of the lift cavity opposite the delivery end of the conveyor input, and the retention assembly has one arm with one end connected to the retractable stop and another end connected to the joint. Obviously, said arm is located below the lifting support.

The arm of the retaining assembly is connected to a push rod transverse to the direction of advance of the inlet conveyor. This push bar is located at one end of the arm adjacent to the retractable stop and has opposite ends adjacent to lateral structures of the fixed frame. Two of the recovery elements have one of their ends connected to said opposite ends of the push bar and others of their ends connected to anchors secured in the fixed frame so that they pull or push the retaining assembly towards the retention position. The lift carriage has a lower structural part that interferes with the arm of the retaining assembly when the

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Lift truck is moved to the lower position and thereby drags the retention assembly to the retracted position against the force of the two recovery elements.

In another embodiment, the retention assembly is guided linearly by a vertical guide in the fixed frame. More specifically, the retention assembly comprises an elongate member transverse to the forward direction of the input conveyor, located adjacent to said delivery end of the input conveyor. This elongate member has opposite ends adjacent to lateral structures of the fixed frame and both ends are guided by two of said vertical gtias in the fixed frame. Two of the aforementioned recovery elements have one of their ends connected to the opposite ends of the elongated member and others of their ends connected to anchors secured in the fixed frame so that they pull or push the retaining assembly towards the retention position. The elongate member also has two retractable stops and two thrust-receiving appendages located adjacent to opposite sides of the elevation cavity below two corresponding pushers attached to the lifting carriage. Thus, when the lifting carriage is moved to the lower position both appendix thrust receivers are pushed simultaneously by the pushers dragging the retaining assembly and the retractable stops to the retracted position against the force of the two recovery elements.

In yet another embodiment there are two individual retaining assemblies, each provided with a retractable stop and a thrust receiver appendix, guided linearly by vertical guides in the fixed frame and pulled or pushed into the retention position by respective retrieval elements. The lifting carriage has two pushers located above the thrust receiving appendages. Thus, when the lift carriage is moved to the lower position, both thrust-receiving appendages are simultaneously pushed by the pushers by dragging the corresponding retention sets and retractable stops to the retracted position against the force of the two recovery elements.

In any of the embodiments, the recovery elements may be, for example, coil springs, compression coil springs, gas springs, or dynamic fluid cylinders.

Generally, the actuator that moves the lift car acts to raise the lift car from the lower position to the upper position and to lower the lift car from the upper position to the lower position. Optionally, the descent of the lift car from

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the upper position to the lower position can be done by gravity. Accordingly, the coil springs for traction or compression, or the gas springs, or the dynamic fluid cylinders that constitute the recovery elements will be sized in accordance with the weight of the retention set so that the retention stop is raised to the position of retention by action of the recovery elements when the lifting carriage or the pushers fixed thereto does not interfere with the retention assembly.

An expert in box stacking machines will understand that various combinations are possible between the elements that make up the two embodiments described above without departing from the scope of the present invention.

Brief description of the drawings

The foregoing and other features and advantages will be more fully understood from the following detailed description of some examples of realization, which have a merely illustrative and non-limiting character, with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of a box stacking machine equipped with an entry retention device according to an embodiment of the present invention;

Fig. 2 is a top view of the box stacking machine of Fig. 1;

Fig. 3 is a side view of the box stacking machine of Fig. 1 with a retractable stop of the entry retention device in a retention position;

Fig. 4 is a side view similar to Fig. 3, but with the retractable stop of the entry retention device in a retracted position;

Fig. 5 is a rear view of the box stacking machine of Fig. 1 with some parts cut out to better show some of the components of the input retention device;

Fig. 6 is a partial perspective view of an input retention device for box stacking machine according to another embodiment of the present invention, with a retractable stop in a retention position;

Fig. 7 is a partial perspective view similar to Fig. 6, but with the retractable stop in a retracted position;

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Fig. 8 is a partial perspective view of an input retention device for box stacking machine according to yet another embodiment of the present invention, with a retractable stop in a retention position;

Fig. 9 is a partial perspective view similar to Fig. 8, but with the retractable stop in a retracted position;

Detailed description of some examples of realization

Referring firstly to Figs. 1 to 5, there is shown a box stacking machine equipped with an entry retention device according to an embodiment of the present invention. In Figs. 2 to 5 some elements of the non-essential box stacking machine for the description of the entry retention device have been removed for clarity in the drawing.

As shown in Fig. 1, the box stacking machine comprises a fixed frame 10 and an auxiliary frame 19 connected to each other and preferably provided with wheels 20. In the auxiliary frame 19 an input conveyor 2 is installed configured to position itself. below a molding cavity of a box-forming machine (not shown) from which successive newly formed boxes are ejected and deposited on the input conveyor 2. The input conveyor 2 comprises a worm belt driven by a motor 21. Some baffles 22 are fixed to the auxiliary frame 19 to help position the boxes from the box-forming machine on the input conveyor 2.

The fixed frame 10 has lateral structures 32 between which an elevation cavity 3 is provided. In one of the mentioned lateral structures 32 of the fixed frame 10, actuator 6 is installed, such as a linear pneumatic actuator, and vertical guides to the that an elevator car 5 is attached which has a lifting support 4 attached. The actuator 6 is operatively connected to move the carriage 5 from a lower position (Fig. 4), in which a support surface of the lifting support 4 is substantially flush with a transport surface of the input conveyor to receive a box (not shown) from the input conveyor 2, to an upper position (Figs. 3 and 5), in which the lifting support 4 transfers said box to a support device. The return of the lift carriage 5 to the lower position is also carried out by action of the actuator 6, or alternatively by gravity.

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The aforementioned support device includes some retractable 23 that automatically retract when they are pushed by each box when climbing and that recover their support position just below the last box that has been raised to support the box in a higher position when the Lift car 5 returns to the lower position. Thus, successive boxes are added to the stack from below by the lifting carriage 5. In an upper part of the fixed frame 10 an ejector device is installed comprising an actuator 24, such as a linear pneumatic actuator, and horizontal glues to the that an ejector car 25 is attached to which an outlet pusher 26 is attached. When the actuator 24 is activated, the ejector carriage 25 is moved along the horizontal glues and the exit pusher 26 drags the stack of boxes out of the fixed frame 10.

The inlet retention device of the present invention comprises a retractable stop 1 located between a delivery end 2a of the inlet conveyor 2 and the elevation cavity. The retractable stop 1 is fixed to a retaining assembly 9 pivotally connected to said fixed frame 10 by a horizontal axis articulation 11. This horizontal axis of the articulation 11 is perpendicular to a forward direction D of the input conveyor 2. The retractable stop 1 is located on a front side of the lift cavity 3 adjacent to the delivery end 2a of the input conveyor 2, while the articulation 11 is located on a rear side of the lift cavity 3 opposite the delivery end 2a of the inlet conveyor 2. The retaining assembly 9 comprises an arm 12 that connects the retractable stop 1 and the articulation 11 below of the lifting support 4 (better shown in Figs. 3 and 4).

The arm 12 of the retaining assembly 9 is connected to a thrust bar 14 transverse to the forward direction D of the inlet conveyor 2 located at one end of the arm 12 adjacent to the retractable stop 1. The device includes two recovery elements 7, by example in the form of two traction coil springs, which have their lower ends connected to opposite ends of said push bar 14 and their upper ends connected to anchors 15 secured in the fixed frame 10. Thus, the recovery elements 7 pull permanently of the retention assembly 9 towards a retention position (Fig. 3) in which the retractable stop 1 protrudes above the level of the transport surface of the inlet conveyor 2 so that the retractable stop 1 interferes with the advance of a box transported by the input conveyor 2 towards said lift cavity 3.

A person skilled in the art will understand that by varying the relative positions of the opposite ends of the push bar 14 and the anchors 15 secured in the fixed frame 10

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Recovery elements 7 can be used in the form of compression coil springs (not shown) to permanently push the retention assembly 9 towards the retention position with an equivalent result. Alternatively, gas springs or cylinders of dynamic fluid (not shown) may be used instead of traction or compression coil springs.

The lifting carriage 5 has a structural part 13 on which the lifting support 4 is fixed, and this structural part 13 is arranged so as to interfere with said arm 12 of the retaining assembly 9 when the lifting carriage 5 is moved to the position bottom thereby pushing the retaining assembly 9 against the force of the recovery elements 7 to a retracted position (Fig. 4), in which the retractable stop 1 is below the level of the transport surface of the input conveyor 2 and allows the free passage of the box from the input conveyor 2 to the lift cavity 3. When the lift carriage is moved by the actuator 6 back to the upper position, the recovery elements 7 automatically move the retention assembly 9 including the retractable stop 1 towards the retention position.

In this embodiment shown in Figs. 1 to 5, the articulation 11 acts as a glutton for the tilting movement of the retention assembly 9, including the retractable stop 1, with respect to the fixed frame 10 between the retention position (Fig. 3) and the retracted position (Fig. 4 ). Elements of the fixed structure 10 interfere with portions of the push bar 14 close to their opposite ends to provide stops for the movement of the retaining assembly 9 in the retention position.

Figs. 6 and 7 show another embodiment of the inlet retention device of the present invention, in which the retaining assembly 9 is linearly guided by two vertical glues 16 (only one of which is shown in Figs. 6 and 7) provided in the side structures 32 of the fixed frame 10. For this, the retaining assembly 9 comprises an elongate member 17, made for example from a sheet element, transverse to the forward direction D of the inlet conveyor 2, and located adjacent to the delivery end 2a of the inlet conveyor 2.

The elongate member 17 has two retractable stops 1 (only one of which is shown in Figs. 6 and 7) formed in portions adjacent to the inner side of the side structures 32 of the fixed frame 10, and each retractable stop 1 has in its upper end a corresponding thrust receiver appendix 18 folded to a horizontal position. The elongate member 17 also has a pair of engaging lugs 29 (only one of the

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which is shown in Figs. 6 and 7) formed at their ends in positions adjacent to the outer side of the side structures 32 of the fixed frame 10.

The sheet member forming the elongate member 17 of the retention assembly 9 has end portions slidably inserted in the vertical glues 16, so that the retention assembly 9 can move vertically guided between a retention position (Fig. 6), in which the retractable stop 1 protrudes above the level of the transport surface of the input conveyor 2 to interfere with the advance of a box transported by the input conveyor 2 towards the elevation cavity 3, and a position retracted (Fig. 7), in which the retractable stop 1 is below the level of the transport surface of the input conveyor 2 to allow free passage of the box from the input conveyor 2 to the lift cavity 3.

In the illustrated example, the vertical glues 16 are formed by grooves between two pieces of the side structures 32 of the fixed frame 10 connected to each other by means of screws 27 and with interposition of spacers 28. A pair of recovery elements 7 constituted by springs Traction helicals (only one of which is shown in Figs. 6 and 7) have their lower ends connected to the engagement lugs 29 of the elongated member 17 and their upper ends connected to anchors (not shown in Figs. 6 and 7) secured in the fixed frame 10. Thus, the recovery elements 7 permanently pull the elongate member 17, including the retractable stop 1 and the push receiving appendages 18, towards the retention position, and the spacers 28 act as a stop for the movement of the elongate member 17 in the retention position.

One skilled in the art will understand that by varying the relative positions of the hook members of the elongate member 17 and the anchors secured in the fixed frame 10, recovery elements 7 can be used in the form of compression coil springs (not shown) to permanently push the retention set 9 towards the retention position with an equivalent result. Alternatively, gas springs or cylinders of dynamic fluid (not shown) may be used instead of helical springs for traction or compression.

In this embodiment, the driving and driving device of the lifting carriage (not shown in Figs. 6 and 7) is located at the rear end of the fixed frame 10, and the lifting carriage is fitted with two lifting supports 4 (only one of which is shown in Figs. 6 and 7) consisting of horizontal bars located adjacent to the inner side of

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the side structures 32 of the fixed frame 10. Each lifting support 4 has a corresponding pusher 8 located above one of the thrust receiving appendages 18 formed at a free end thereof. Thus, the two thrust receiving appendages 18 are pushed simultaneously by the pushers 8 when the lift carriage 5 is moved to the lower position to move the elongate member 17, including the retractable stops 1 and the thrust receiving appendages 18, towards the position retracted against the force of the recovery elements 7.

Figs. 8 and 9 show yet another embodiment of the input retention device of the present invention, which comprises two independent retention assemblies 9 (only one of which is shown in Figs. 8 and 9) located adjacent to side structures 32 of the fixed frame 10 and adjacent to the delivery end 2a of the inlet conveyor 2. Each retaining assembly 9 is made, for example, from a sheet metal element guided linearly by vertical glues 16, 30 in one of the lateral structures 32 of the fixed frame 10.

In the illustrated example, first vertical glues 16 are formed by grooves between two pieces of the side structures 32 of the fixed frame 10 connected to each other by means of screws 27 and with interposition of spacers 28 and the retaining assemblies 9 are inserted in sliding way in said slots. Second vertical glues 30 comprise elongated holes in the vertical direction formed in the retaining assemblies 9 and stems 31 fixed in the fixed frame 10 and inserted in such elongated holes. Alternatively, other glutton devices may be used to guide the vertical movement of the retaining assemblies 9 with respect to the fixed frame 10 with an equivalent result.

Thus, each retention assembly 9 can move vertically guided between a retention position (Fig. 6), in which the retractable stop 1 protrudes above the level of the transport surface of the input conveyor 2 to interfere with the advance of a box transported by the input conveyor 2 towards the lift cavity 3, and a retracted position (Fig. 7), in which the retractable stop 1 is below the level of the transport surface of the input conveyor 2 for allow free passage of the box from the input conveyor 2 to the lift cavity 3.

Two recovery elements 7 (only one of which is shown in Figs. 8 and 9) constituted by helical traction springs have their lower ends connected to hook lugs 29 of each of the retaining assemblies 9 and

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its upper ends connected to anchors (not shown) secured in the fixed frame 10.

One skilled in the art will understand that by varying the relative positions of the engagement element of each retention assembly and the corresponding anchorage secured in the fixed frame 10, recovery elements 7 can be used in the form of compression coil springs (not shown) to permanently push to the retention assembly 9 towards the retention position with an equivalent result. Alternatively, gas springs or cylinders of dynamic fluid (not shown) may be used instead of helical springs for traction or compression.

In this embodiment, the driving and driving device of the lifting carriage (not shown in Figs. 8 and 9) is located at the rear end of the fixed frame 10, and the lifting carriage is fixed by two lifting supports 4 (only one of which are shown in Figs. 8 and 9) constituted by horizontal bars located adjacent to the inner side of the side structures 32 of the fixed frame 10. Each lifting support 4 has a corresponding pusher 8 located at a free end thereof above one of the thrust receiving appendages 18. Thus, the two thrust receiving appendages 18 are simultaneously pushed by the pushers 8 when the lift carriage 5 is moved to the lower position to move both retaining assemblies 9, including the stops retractable 1 and the thrust receiving appendages 18, towards the position retracted against the force of the recovery elements 7.

It will be apparent to one skilled in the art that some of the characteristics of the embodiment described in relation to Figs. 1 to 5 and some of the characteristics of the embodiments described in relation to Figs. 6-7 and 8-9 are combinable with each other without thereby altering the essentiality of the present invention. Likewise, it should be noted that some of the characteristic elements that are duplicated in either of the two embodiments could be unique elements with an equivalent result.

The scope of the present invention is defined in the appended claims.

Claims (17)

5 10 fifteen twenty 25 30 1. - Entry retention device for box stacking machine, comprising a retractable stop (1) located between a delivery end (2a) of an input conveyor (2) and an elevation cavity (3) in which there are a lifting support (4) fixed to a lifting carriage (5) guided vertically and operated by an actuator (6) to move between a lower position, suitable for said lifting support (4) to receive a box from said input conveyor (2), and an upper position, in which the lifting support (4) transfers said box to a support device, said retractable stop (1) being movable between a retention position, in which the retractable stop (1) ) protrudes above the level of the input conveyor (2) and interferes with the advance of a box transported by the input conveyor (2) towards said lifting cavity (3), and a retracted position, in which the retractable stop ( 1) is below transport level or input (2) and allows the free passage of the box from the input conveyor (2) to the lift cavity (3), characterized in that said retractable stop (1) is fixed to a retaining assembly (9) guided with respect to a fixed frame (10) so that it can move between said retention position and said retracted position, at least one recovery element (7) is connected to the retention assembly (9) and to the fixed frame (10) so which pulls or pushes the retention assembly (9) towards said retention position, and the lifting carriage (5), or at least one pusher (8) attached to the lifting carriage (5), is arranged so as to interfere with the assembly of retention (9) and pushes it to said position retracted against the force of said recovery element (7) when the lift carriage (5) is moved to the lower position. 2. - Entry retention device according to claim 1, characterized in that the retention assembly (9) is pivotally connected to said fixed frame (10) by a horizontal axis articulation (11). 3. - Entry retention device according to claim 2, characterized in that said horizontal axis of said articulation (11) is perpendicular to a forward direction (D) of the input conveyor (2). 4. - Entry retention device according to claim 3, characterized in that the retractable stop (1) is located on a front side of the lift cavity (3) adjacent to said delivery end (2a) of the input conveyor ( 2), said joint (11) is located on a rear side of the lift cavity (3) opposite the delivery end (2a) 5 10 fifteen twenty 25 30 of the input conveyor (2), and the retention assembly (9) has an arm (12) that connects the retractable stop (1) and the articulation (11) below the elevation support (4). 5. - Entry retention device according to claim 2, 3 or 4, characterized in that said arm (12) of the retention assembly (9) is connected to a push bar (14) transverse to the forward direction (D ) of the input conveyor (2) and two of said recovery elements (7) have their ends connected to opposite ends of said push bar (14) and others of their ends connected to anchors (15) secured in the fixed frame (10) 6. - Inlet retention device according to claim 5, characterized in that the recovery elements (7) are selected between traction coil springs, compression compression springs, gas springs, and dynamic fluid cylinders. 7. - Entry retention device according to claim 5 or 6, characterized in that the push bar (14) is located at one end of the arm (12) adjacent to the retractable stop (1). 8. - Entry retention device according to any one of claims 2 to 7, characterized in that the lifting carriage (5) has a structural part (13) that interferes with said arm (12) of the retention assembly (9) when The lift carriage (5) is moved to the lower position. 9. - Entry retention device according to claim 1, characterized in that the retention assembly (9) is linearly guided by a vertical glutton (16) in said fixed frame (10). 10. - Entry retention device according to claim 9, characterized in that the retention assembly (9) comprises an elongate member (17) transverse to a forward direction (D) of the input conveyor (2), located adjacent to said delivery end (2a) of the input conveyor (2) and guided at its ends by two of said vertical glues (16) in the fixed frame (10). 11. - Inlet retention device according to claim 10, characterized in that two of said recovery elements (7) have one of its ends connected to opposite ends of said elongate member (17) and other of its ends connected to secured anchors in the fixed frame (10). 5 10 fifteen twenty 25 12. - Inlet retention device according to claim 10, characterized in that the recovery elements (7) are selected from traction coil springs, compression compression springs, gas springs, and dynamic fluid cylinders. 13. - Entry retention device according to any one of claims 9 to 12, characterized in that said elongate member (17) has at least one thrust receiver appendix (18) located below said pusher (8) attached to the carriage elevator (5) so that said appendix push receiver (18) is pushed by the pusher (8) when the elevator car (5) is moved to the lower position to move the retaining assembly (9) to the position retracted against the strength of the recovery elements (7). 14. - Entry retention device according to claim 1, characterized in that it comprises two retention assemblies (9) adjacent to lateral structures (32) of said fixed frame (10), respectively, each retention assembly (9) being it is linearly guided by at least one vertical glutton (16, 30) in one of said lateral structures (32) of the fixed frame (10). 15. - Entry retention device according to claim 14, characterized in that said two retention assemblies (9) are located adjacent to said delivery end (2a) of the input conveyor (2), and at least two of said elements recuperators (7) have some of their ends connected to each of the retaining assemblies (9) and others of their ends connected to anchors secured in the fixed frame (10). 16. - Inlet retention device according to claim 15, characterized in that the recovery elements (7) are selected from traction coil springs, compression coil springs, gas springs, and dynamic fluid cylinders. 17. - Entry retention device according to claim 14, 15 or 16, characterized in that the lifting carriage (5) has two of said pushers (8) fixed, and each of the retention assemblies (9) has at least a push receiver appendix (18) located below one of the pushers (8) such that the pushers (8) interfere with said push receiver appendages (18) when the lift carriage (5) is moved to the lower position and push the retaining assemblies (9) to the position retracted against the force of the recovery elements (7).