EP0612679B1 - Apparatus for delivering semi-rigid sheets, particularly cardboard, from a stack - Google Patents

Description

The present invention relates to the distribution one by one of semi-rigid sheets, in particular of cardboard and particularly of corrugated cardboard, from a stack of sheets substantially of the same format. It relates more precisely to a device allowing such a distribution and which comprises rotary feed members capable of driving, by friction, the sheet with which they are in contact below or above a stop, which locks in position all other sheets in the stack.

Such dispensers are well known in the cardboard industry and more precisely corrugated cardboard, sometimes under the term feeders. They are intended to precisely feed a sheet to introduce it synchronously into a receiving machine such as a printer, a cutter ...

The front edge of the stack is supported on one (or more) vertical stop, called margin stop, which is adjustable in height. In the case of removal of the sheets from below the stack, the free space between the lower edge of the stopper and the part of the feeder, opposite this lower edge, on which the stack rests be slightly more than the thickness of one sheet and less than the thickness of two sheets. In the case of removal of the sheets from above a stack mounted on a lifting system, the free space in question will be delimited by the upper edge of the stop. Thus, during the driving of the sheet by the rotary members, only the sheet in contact with said members is driven by friction, while the other sheets of the stack are held in position against the stop.

In document EP-A-0183 361, a device of this type has been proposed in which the driving of the sheet is carried out using rotary rollers, while the sheet is pressed by depression on said rollers. These rollers are arranged in the form of several parallel sets, arranged towards the front part of the stack, located near the margin stop, and are driven by a movement oscillating.

The feeder, according to document EP-A-0183 361 comprises extractor rollers, located behind the margin stop, and capable of ensuring the total extraction of the sheet and its introduction into the following machine. It also includes vertical pushers which are arranged between the sets of rollers and which lift the stack as soon as the sheet is driven by the extractor rollers. These vertical pushers prevent the rollers from entraining the sheet which follows, in the stack, the sheet to be dispensed. The presence of the extractor rollers is made necessary due to the frictional forces brought into play between the sheet to be dispensed and the fixed parts, on which said sheet is supported during its movement, whether the supply surface, being immediately under the lower edge of the stop, either the pushers or the surfaces on which the rear parts of the stack rest.

Being a sheet of corrugated cardboard, the extraction of the sheet being dispensed by these extractor rollers has two types of drawbacks. On the one hand the pinching of the sheet between the two rollers can lead to a deterioration of the corrugated cardboard, and on the other hand it is necessary to carry out a precise adjustment of the spacing between the two rollers according to the thickness cardboard.

These difficulties have been resolved, in particular in document EP-A-379 306 by replacing these two extractor rollers by the combination of two elements, namely drive belts and a suction system, ensuring the plating of the sheet in progress. distribution on said belts.

In this document EP-A-379 306, the machine has also been simplified by eliminating the vertical pushers. To do this, the device comprising at least two sets of rotary transfer members, each set is driven by an independent motor with variable speed, and the device comprises a control system which is adjusted so as to start and accelerate the motors and therefore the rotary transport members at a predetermined speed for advancing of the sheet to be dispensed and to decelerate or stop each motor and the corresponding transport member after the sheet has moved and before the next sheet has come into contact with a rotary transport member.

Thanks to this particular kinematics of the different sets of rotary members, there is no longer any need to lift the stack between said rotary members, since after the passage of the rear edge of the sheet to be distributed at the margin stop the members that come into contact with the penultimate sheet are stopped.

This last device marks a significant progress compared to the previous device. However, the aim which the applicants have set themselves is to propose a device for the distribution one by one of semi-rigid sheets, in particular of cardboard, from a stack which has additional advantages, namely the outright elimination of sheet extraction means, located in front of the margin stop, and even better precision in the placement of the sheet to be dispensed on the next station.

This object is perfectly achieved by the device of the invention. It is a device for dispensing one to one of the semi-rigid sheets, in particular of cardboard and more particularly of corrugated cardboard, below or above a stop, behind which said sheets are stacked. In known manner, this device comprises rotary supply members, mounted in a suction chamber, and capable of driving by friction, below or above the stop, the sheet with which they are in contact, said members supply being controlled in rotation by motor means.

Typically, the device being free of sheet extraction system in front of the stop and of fixed surface in contact with the stack near said stop, the rotary feed members consist of at least three cylinders, l the axis of the outlet cylinder being vertical to the stop; in addition, the device comprises means for synchronizing the cylinders so that, during the distribution of a sheet given, on the one hand each of the cylinders upstream of the output cylinder is decelerated after said sheet has left contact with it and on the other hand the output cylinder is decelerated after the rear edge of said sheet has exceeded the vertical of the stop, the upstream cylinders already being in the stopped position, and therefore after the next sheet has come into contact with it.

According to the very specific kinematics of the cylinders of the device of the invention, and contrary to what is provided in the document EP-A-0379 306, when the rear edge of the sheet being dispensed leaves, in accordance with the explanations which will be given below in the embodiment, a given cylinder, the next sheet, in the stack, comes into contact with said cylinder while the latter is still rotating, in its phase of constant speed, the phase cylinder deceleration starting only slightly after this step.

Therefore, there is a forward drive of the next sheet which, during the distribution of a given sheet, causes the setting in position of said next sheet. Indeed, the slight entrainment caused by the contact of the next sheet with the cylinders upstream of the output cylinder, in its phase at constant speed then during deceleration, achieves perfect alignment of the front edge of said next sheet along of the stop.

One would have thought that this light training would have negative repercussions. In fact, when the sheet to be dispensed passes under the stop, the next sheet is no longer held in height and descends to the level of the space between the stop and the outlet cylinder.

At this precise moment, the output cylinder is still rotating, at constant speed and will start the deceleration phase. One would therefore have thought that contact between this next sheet and the rotating output cylinder would cause the next sheet to move forward. This is not the case, thanks to the combination of two elements used in the device of the invention, namely on the one hand the fact that the cylinders upstream of the outlet cylinder are stopped at this precise moment and on the other hand the aspiration, as will be explained more clearly in the description of the exemplary embodiment which will be given below.

Preferably, the device of the invention comprises rotary support members, free to rotate, arranged so that they support the rear part of the stack while the supply cylinders support the front part. These will in particular be rollers mounted on at least one shaft, parallel to the axis of rotation of the supply cylinders.

The sheet being dispensed is therefore not supported on any fixed part of the machine.

This particular provision aims to reduce as much as possible the frictional forces capable of slowing the movement of a sheet during the distribution thereof.

Advantageously, the front stop is a continuous plate.

Advantageously, in this case, the device of the invention comprises two shafts, roller supports, the ends of which are mounted on longitudinal arms, as well as a rear wedging stop, which moves on the end of said arms; in addition, a drive system makes it possible to move the rear stopper and correspondingly the two roller support shafts as a function of the length of the stacked sheets.

• a) deux plaques de calage latérales de l'empilement, munies de moyens de déplacement transversal, et,
• b) deux organes de recouvrement, s'étendant de part et d'autre des plaques de calage jusqu'aux bords extérieurs de la chambre d'aspiration.

Preferably, the device also includes means for adapting to the width of the stack, said means comprising:

• a) two lateral wedging plates of the stack, provided with means for transverse displacement, and,
• b) two covering members, extending on either side of the wedging plates to the outer edges of the suction chamber.

• La figure 1 est une vue de côté et en coupe du distributeur de l'invention,
• Les figures 2 et 3 illustrent les étapes de fonctionnement du distributeur de la figure 1,
• La figure 4 est une vue partielle détaillée de la figure 2,
• La figure 5 est une vue de face de ce même distributeur, et
• La figure 6 est une vue de côté montrant la disposition d'un soufflet latéral.

The present invention will be better understood on reading the description which will be given of the preferred embodiment of the dispensing device, one by one, of corrugated cardboard sheets from a stack, system-free. extraction of the sheet during distribution, illustrated by the appended drawing in which:

• FIG. 1 is a side view in section of the dispenser of the invention,
• Figures 2 and 3 illustrate the operating steps of the dispenser of Figure 1,
• FIG. 4 is a detailed partial view of FIG. 2,
• FIG. 5 is a front view of this same dispenser, and
• Figure 6 is a side view showing the arrangement of a side bellows.

The dispenser 1 of the invention is intended to supply sheets 2 of corrugated cardboard, for example to a cutting or printing station. There is shown in Figure 1 an element of this station 3, ensuring the movement of the sheet distributed inside said station.

In the dispenser 1, the sheets 2 of corrugated cardboard are arranged in the form of a stack 4, substantially regular, which rests in its front part on three supply cylinders 5, 6 and 7 and in its rear part in two sets rollers 8 and 9 respectively;

The stack 4 is approximately locked in position thanks to a front stop 10 which is a continuous plate, a rear stop 11 and two side plates 12 and 13 also forming stops. Thus the front 10 and rear 11 stops and the two side plates 12 and 13 define a receptacle for the stack 4.

The three supply cylinders 5, 6 and 7 are rotated in a synchronized manner as will be explained below, while the rollers 8 and 9 are mounted free in rotation on shafts 14,15.

The first cylinder 5, which is located furthest forward of the stack 4, in the direction of evacuation illustrated by the arrow F, has its axis 16 of rotation which is positioned directly above the front stop 10. More precisely, the plane 17, formed by the face 18 of the stop 10 which is turned towards the inside of the receptacle passes through the axis 16 of rotation of this first cylinder 5, which we will call below. outlet cylinder.

A suction chamber 19 is provided under the three supply cylinders 5, 6 and 7. The front 20 and rear 21 transverse uprights of this chamber 19 come, in their upper part, in the immediate vicinity of the exterior surface of the outlet cylinder 5 for the front upright and of the third cylinder 7 for the rear upright 21. The suction 19 includes a pipe 22 for connection to known means for placing under vacuum.

The outer surface of each cylinder 5, 6, 7 must have a high coefficient of friction to carry out the friction drive of a sheet of corrugated cardboard. This surface with a high coefficient of friction can optionally be obtained using a sleeve 23 which is directly fitted onto the body of the cylinder 5, 6, 7. In this way it is possible to replace the sleeve 23 in the event of wear of it.

The rotational drive of the three supply cylinders 5, 6, 7 is synchronized in order to comply with the following two conditions. According to the first condition, during the distribution of a given sheet 2 a , which is the last sheet of the stack 4, each of the three cylinders 7, 6, 5 is braked, one after the other, only after said sheet 2 has left the corresponding cylinder. According to the second condition, the two cylinders 6, 7, located upstream of the output cylinder 5, must be stopped when the sheet 2 has left the output cylinder 5.

dans laquelle e est l'épaisseur de la feuille 2a au niveau de son bord arrière 2c et R est le rayon du cylindre 7. En effet la feuille 2'a ne vient en contact avec la génératrice 27 que lorsque le bord arrière 2c de la feuille 2a s'est déplacé d'une distance suffisante pour que ledit bord 2c se soit décalé en hauteur de son épaisseur e sous l'effet de l'aspiration. Par contre, s'agissant du cylindre de sortie 5 on considère que la feuille distribuée 2a quitte le cylindre de sortie 5 dès qu'elle passe sous la butée 10, au-delà du plan 17.The expression "leaves the cylinder" covers different realities depending on whether it is the cylinders 7, 6 upstream of the outlet cylinder or the outlet cylinder itself. Regarding the cylinders 7, 6 upstream of the outlet cylinder 5 (FIG. 4), it is considered that the sheet 2 has left the corresponding cylinder 7 or 6, when the rear edge 2 c of said sheet 2 a has no longer effective contact with the surface of said cylinder, for example 7 and that the next sheet 2 ' a comes into contact with the surface of said cylinder 7, tangentially to the latter according to the generatrix 27. When the next sheet 2' a comes to rest on the cylinder 7, according to the generator 27, the cylinder 7 has already rotated by an angle α which is such that Cos. α is equal at

in which e is the thickness of the sheet 2 a at its rear edge 2 c and R is the radius of the cylinder 7. Indeed the sheet 2 ' a comes into contact with the generator 27 only when the rear edge 2 c of the sheet 2 a has moved a sufficient distance so that said edge 2 c has shifted in height by its thickness e under the effect of the suction. On the other hand, with regard to the outlet cylinder 5, it is considered that the distributed sheet 2 has left the outlet cylinder 5 as soon as it passes under the stop 10, beyond the plane 17.

Consequently, the operation of the dispenser 1 according to the invention is as follows. The sheets of corrugated cardboard were placed according to the stack 4 inside the receptacle formed by the front stops 10 and rear 11 and the side plates 12 and 13. The first sheet to be dispensed 2 a is therefore supported, rear to front, only on the two sets of rollers 9, 8 then on the three feed rollers 7, 6 and 5 respectively, without any contact with fixed surfaces of the machine.

Since the stop 10 is perpendicular to the axis 16 of rotation of the output cylinder 5, the sheet 2a is supported on said output cylinder 5 with a weaker force than it does on both other cylinders 6 and 7.

To ensure the distribution of the sheet 2 a , the vacuum means are started continuously, which has the effect of pressing the sheet 2 a on the surface of the three cylinders 5, 6, 7. This is to all the more important that most sheets of corrugated cardboard can present deformations of the bending type and that it is therefore necessary to ensure the flattening of said cardboard so that the front edge 2 b of the sheet 2 a is presented so straight at the free space 24 located between the front stop 10 and the outlet cylinder 5.

The distribution of the sheet 2 a is carried out by rotating, simultaneously, the three feed rollers 5, 6, 7, in synchronism with the operating cycle of the downstream station 3, until it reaches a desired speed for the introduction of the sheet 2 is in this position. The supply cylinders 5, 6, 7 are then driven at a constant speed.

The friction forces brought into play, due to the suction and the weight exerted by the stack on the rollers 5, 6 and 7, cause the displacement along the arrow F of the sheet 2 a under the stop 10. During this displacement, the upper face of the sheet 2 a enters into friction with the lower face of the following sheet 2 'a; however, the forces brought into play between the two sheets 2 a and 2 ′ a are low with regard to the friction forces at the level of the supply cylinders 5, 6, 7.

When the rear edge 2 c of the sheet 2 a leaves the surface of the cylinder 7 most upstream, the next sheet 2 ′ a is already in contact with the surface of said cylinder 7.

. Dans laquelle F est la force en Newton appliquée à un corps de masse m et γ l'accélération. Avec une telle accélération, le temps que mettra la feuille pour parcourir une distance correspondant à son épaisseur, soit 4 mm , sera de l'ordre du millième de seconde, en application de la loi de mouvement uniformément accélérée à savoir $\text{x = 1/2 γ t²}$

dans laquelle x est le déplacement et t le temps correspondant.It should be known in fact that the suction necessary to press the sheets on the drive rollers in order to obtain sufficient friction forces to prevent the sliding of said sheets on said rolls corresponds to depressions of the order of 5000 Pa For example, being a sheet of corrugated cardboard of 500 g / m², having a thickness of 4 mm, the effect of the vacuum produces a vertical acceleration of the order of 10,000 m / s.² in application. of the law $\text{F = mγ}$

. In which F is the force in Newton applied to a body of mass m and γ the acceleration. With such an acceleration, the time that the sheet will take to travel a distance corresponding to its thickness, namely 4 mm, will be of the order of a thousandth of a second, in application of the law of motion uniformly accelerated, namely $\text{x = 1/2 γ t²}$

in which x is the displacement and t the corresponding time.

In a specific embodiment, with a cylinder 7 having a diameter of 80 mm, the distance existing between the rear edge 2 c of the sheet 2 a and the point of tangency 27 of the next sheet 2 ' a , in accordance with the representation of Figure 4, is of the order of 17.4 mm. If we take into account a rate of 10,000 sheets per hour and a format for each sheet of 1 meter, the speed of movement of a sheet will be at least of the order of 3 meters / second. Under these conditions the time that the rear edge will take 2 c traveling the aforementioned distance of 17.4 mm will be 5.8 thousandths of a second, that is to say a time much greater than that which is necessary for the sheet 2 ′ a to come to be pressed against the cylinder 7. This explains that when the sheet 2a is in the position shown in Figure 4, the next sheet 2 ' a is already in contact with the cylinder 7. It is from this position that we can start the deceleration of the cylinder 7 without brake sheet 2 a . In practice, according to the invention, to counter possible differences in length, positioning and possible slippage of the sheet 2 a during its transport, the deceleration of the cylinder 7 is started when the rear edge 2 c of the sheet 2 has exceeded the position shown in Figure 4 by about 10 mm. Consequently, the next sheet 2 ′ a comes into contact with the cylinder 7 while the latter is still in its constant speed phase.

It is understood that this kinematics is fundamentally different from that which is provided in the device of document EP-A-0379 306. In fact in this document it is provided that each drive cylinder is decelerated before the next sheet is in contact with said cylinder. In other words, according to the kinematics of document EP-A-0 379 306 the cylinders are decelerated before the sheet is in the position of FIG. 4 while in the feeder of the present invention the cylinder 7 does not start its deceleration that when the rear edge 2 c of the sheet 2 has exceeded the position shown in Figure 4, for example of the order of 10 mm.

The fact that the deceleration, according to document EP-A-0 379 306, begins while the sheet is in contact with a cylinder, causes said sheet to have braking forces. This is what requires in this feeder extraction means downstream of the margin stop. On the contrary, in the feeder of the present invention, the aforementioned particular kinematics, combined with the arrangement of the cylinders, in particular that of the outlet cylinder 5, and the absence of friction of the sheet 2 a on all or part fixed, allows completely discharging the sheet 2a of the stack without the need to implement an extraction system downstream of the margin stop 13, as is the case in the feeder of document EP-A-0 379 306.

After the rear edge 2 c of the sheet 2a has left the surface of the cylinder 7, the most upstream, said cylinder 7 is braked, so that it is completely stopped when the rear edge 2 c leaves the output cylinder 5 and preferably as quickly as possible in order to limit the wear of the lining of this cylinder.

When the same rear edge 2 c leaves the intermediate cylinder 6, and therefore that the next sheet 2 ′ a is in contact with the surface of said intermediate cylinder 6, the latter will be braked under the same conditions as those of cylinder 7 so that 'it is completely stopped when said edge 2 c leaves the output cylinder 5.

Since the next sheet 2 ′ a comes gradually into contact with the two cylinders, first 7 then 6, located upstream of the output cylinder, while the sheet to be fed 2 a is still in the free space 24 , the rotation of these two upstream cylinders, 6, 7 causes a slight displacement of said next sheet 2 ' a . This slight movement sets the next sheet 2 ′ a along the inner face 18 of the stop 10. This setting makes it possible to correct any deviations that may occur during the approximate constitution of the stack 4. Because the front edge 2 ′ b of the next sheet 2 ′ a bears over its entire length against the stop 10, there is no risk of deterioration of said front edge 2 ′ b .

When the rear edge 2 c of the sheet 2 a to be dispensed leaves the outlet cylinder 5, the front edge 2 ' b of the next sheet 2' a is then pressed against the surface of the cylinder under the effect of the suction. output 5 very quickly, as we saw previously, in a time of the order of 1/1000 of a second. At this precise moment, the output cylinder 5 is still at constant speed and begins its deceleration phase after the edge 2 c has exceeded the plane 17 by approximately 1 cm. However, as imposed by the second condition of the synchronization of the three cylinders, the two most upstream cylinders 6, 7 are kept in the off position. The displacement of the next sheet 2 ' a , under the effect of the rotation of the output cylinder 5, is thwarted by the frictional forces at the level of the contact zones between the underside of the sheet 2' a and the two cylinders the most upstream 6 and 7. Due to the arrangement of the cylinders, the support forces of the stack and the forces due to the depression of the chamber 19 are greater on the rollers 6 and 7 than on the roller 5 , so that the sheet is held in position. It is this condition which imposes for this type of feeder, the existence of at least three drive cylinders.

Therefore, the position of the front edge 2 ' b of the sheet 2' a is not affected by the fact that the outlet cylinder 5 is still in rotation when said edge 2 ' b is pressed against the surface of said output cylinder 5.

As has been observed, the distribution of the sheet 2 a was achieved without having to implement an external extraction system, compensating for the frictional forces of the sheet 2 has on fixed parts, or cylinders in the process of deceleration as is the case for already known machines. The conveyor system at the next station 3 can thus be a system without suction or pinch roller, but simply a system allowing the sheet 2 a to be conveyed in synchronization with the output cylinder 5.

According to a preferred embodiment, the dispenser 1 is provided to adapt to the different sheet formats 2, both in length and in width.

As regards the length adjustment, the two shafts 14 and 15 as well as the rear stop 11 move on two longitudinal arms which are mounted on the distributor frame. A drive system moves the rear stop 11 and correlatively drives the shafts 14 and 15. This system is adjusted so that the displacement travel of the shaft 14 is approximately 2/3 of that of the shaft 15 and the stop 11.

As regards the width adjustment, it is provided, as illustrated in Figures 5 and 6 that the two side plates 12, 13 are equipped with means 25 for transverse movement relative to the external upright 26 of the dispenser. In addition, two extensible or sliding members 28 are provided, presenting themselves as bellows or plates, which cover in a sealed manner, for each of them, the zone extending on the one hand between the side plate 12 and the external upright 26 and on the other hand between the stop 10 and the rear upright 21 of the suction chamber 19.

This particular arrangement makes it possible to obtain suction, between the three supply cylinders, only in the space situated between the two side plates 12 and 13, that is to say only where the stack 4 is located.

The present invention is not limited to the embodiment which has just been described by way of non-exhaustive example. In particular, it would be possible to use more than three supply cylinders. It is understood that a number less than three cylinders would not allow to obtain the precise positioning of the sheet to be dispensed, because in this case, we would have a drive of the next sheet during its descent on the output cylinder , not yet arrested.

The particular synchronization between the supply cylinders is obtained by any suitable means, whether it be purely mechanical means as is customary in the field of sheet-by-sheet cardboard printing, or even by equipping each of the cylinders. for supplying an independent motor, in particular an electronic servo motor of the brushless type, controlled by an electronic circuit which is connected to the motors for driving the supply cylinders and possibly to the system for driving the sheet in the station next. In the event that there is only one motor directly driving the output cylinder and the other supply cylinders, for example by means of pinions, clutch-brakes would be mounted on said pinions. The deceleration and stopping sequence would be obtained by actuating the clutch-brakes successively and then the engine.

The embodiment which has just been described relates to a dispenser with driving the sheets from below the stack. The invention also applies to destackers in which the removal of the sheets is carried out from above the stack, the latter being held against the feed rollers by an elevating system. In this case, the sheet to be dispensed passes over the stop behind which the sheets are stacked.

Claims (9)

1. Device for distributing semi-rigid sheets one by one below or above a stop, behind which said sheets are stacked, comprising rotary supply members, mounted in a suction chamber and adapted to entrain by friction the sheet with which they are in contact, characterized in that, said device having no sheet-extraction system in front of the stop (10) and no fixed surface in contact with the stack in the vicinity of said stop (10), the rotary supply members consist of at least three cylinders (5, 6, 7), the axis of the outlet cylinder (5) being vertical with respect to the stop (10), and in that it comprises means for synchronizing said cylinders (5, 6, 7) so that, during distribution of a given sheet (2a), on the one hand, each of the cylinders (6, 7) upstream of the outlet cylinder (5) is decelerated after said sheet (2a) has left contact therewith and therefore after the following sheet has come into contact therewith and, on the other hand, the outlet cylinder (5) is decelerated after the rear edge (2c) of said sheet (2a) has passed to a position vertical with respect to the stop (10), and therefore after the following sheet has come into contact therewith, the cylinders (6, 7) upstream already being in stopped position.
2. Device according to Claim 1, characterized in that the synchronization means are adjusted so as to decelerate the outlet cylinder (5) after the rear edge (2c) of the sheet (2a) has passed beyond the vertical (17) with respect to the stop (10) by a distance of the order of 10 mm.
3. Device according to Claim 1 or 2, characterized in that the synchronization means are adjusted so as to decelerate each cylinder (7, 6) upstream of the outlet cylinder (5) after the rear edge (2c) of the sheet (2a) left contact with said cylinder (7, 6) by a distance of the order of 10 mm.
4. Device according to one of Claims 1 to 3, characterized in that the synchronization means comprise an independent, electronically servo-controlled motor for each supply cylinder (5, 6, 7) and an electronic circuit for controlling said motors.
5. Device according to one of Claims 1 to 3, characterized in that the synchronization means comprise a motor for driving the outlet cylinder (5), gears provided with clutch-brakes mounted on the shafts of the other cylinders and an electronic circuit for controlling the clutch-brakes and the motor.
6. Device according to one of Claims 1 to 5, characterized in that the front stop (10) is a continuous plate.
7. Device according to one of Claims 1 to 6, characterized in that it comprises rotary bearing members (8, 9), free to rotate, disposed so that they support the rear part of the stack (4), whilst the supply cylinders (5, 6, 7) support the front part thereof.
8. Device according to Claim 7, characterized in that it comprises two shafts (14, 15) supporting the rotary bearing members (8, 9) and a rear blocking stop (11), the ends of the shafts (14, 15) and said stop (11) being adapted to be displaced on longitudinal arms as a function of the length of the stacked sheets (2), so that the stroke of displacement of the shaft (14) closest to the supply cylinders is approximately 2/3 that of the other shaft (15) and of the stop (11).
9. Device according to one of Claims 1 to 8, characterized in that it comprises means for adaptation to the width of the stack, comprising:

   a) two lateral plates (12, 13) for blocking the stack (4), provided with transverse displacement means (25), and

   b) two extensible or sliding covering members (28) in the form of gussets or plates and which tightly cover, for each of them, the zone extending, on the one hand, between the lateral plate (12) and the outer upright (26) and, on the other hand, between the stop (10) and the rear upright (21) of the suction chamber (19).

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