Description

Carousel-type automatic packaging machine of products in bags.

This patent application for industrial invention relates to a carousel- type automatic packaging machine of products in bags, which comprises a series of pairs of grab pliers, each of them being designed to grab a single bag and installed in saddles used to move the bag through the various filling and sealing stations.

Machines of this type are used to fill bags of any shape and size with powder, liquids or tissues, and seal them.

Following is a diagrammatic description of the current constructive layout of the said automatic machines and relevant support means for the pairs of pliers, in order to point out the drawbacks.

In the said packaging machines, each bag to be filled is grabbed by a pair of pliers, designed to support it in vertical position, adjacent to the bag supported by the pair of pliers in immediately preceding or subsequent position. In the case of a standard rectangular bag, it can be said that each bag is grabbed by a pair of pliers in the two upper corners or, more precisely, on top of the vertical right and left side.

As soon as it is grabbed, the bag is transported along a series of stations in order to be first filled and then sealed. The first station opens the bag in order to fill it with the content, which can be either of solid or liquid type.

When the bag is in vertical transportation position, each bag is composed of two sheets with identical size, a front sheet and a back sheet, joined on three sides, and precisely on the opposite pair of vertical sides and on the lower horizontal side.

The two upper horizontal sides of the two sheets that are not joined are first separated in order to fill the bag and then moved close and joined in

order to seal the content that was previously inserted in the bag.

In order to open the bag, starting from the condition in which the two upper sides of the two sheets are aligned and engaged one against the other one, the two grab pliers make an advance travel in order to open the mouth of the bag.

After filling the bag, the pliers make a separation travel until they reach their initial distance, in such a way that the upper sides of the two sheets return in close position before reaching the sealing station, in which the mouth of the bag is sealed. The said pairs of pliers are installed on corresponding support saddles that can support two or more pliers, according to the model of saddle.

In case of saddles that support two pliers only, the pliers can move closer or farther, being evident that each pair of pliers supports only one bag.

Saddles that support four pliers are known, which have the same configuration as the saddles with two pliers, except in that each saddle supports two pairs of pliers in order to support two bags.

Special saddles are known, in which a pair of bags is grabbed by three pliers, of which one is a central fixed pliers, and two are lateral mobile pliers; the only difference of this type compared to the one described above consists in that the central fixed pliers must be provided with two opposite jaws, one rightwards and one leftwards, in order to cooperate with the right-hand mobile pliers and the left-hand mobile pliers, respectively.

For the sake of simplicity, the description of the invention continues with reference to a saddle that supports three pliers, it being understood that the invention may be applied, with the same efficacy and the same advantages, to saddles that support one pair of pliers only or multiple pairs of pliers.

As mentioned above, a saddle for three pliers, of known type, comprises a central fixed pliers and two lateral mobile pliers, designed to translate simultaneously in opposite directions, in order to increase or decrease their distance from the central pliers.

In this way, each saddle can support two bags in adjacent coplanar position, which are supported by the central pliers on the side facing the centre of the saddle, and by the corresponding lateral pliers on the side facing the lateral side of the saddle. More precisely, the central pliers is provided with a pair of opposite jaws, in such a way that the pliers can grab a first bag on the right and a second bag on the left, while the lateral pliers are provided with a pair of jaws that face the central pliers.

The three pliers are in parallel direction and each pair of jaws comprises a mobile jaw and a fixed jaw.

Moreover, the saddle is provided with actuation means of the mobile jaw of each pliers, which are designed to push the mobile jaw forward, moving it away from the fixed one, and bring it back to closing position.

The said machines of known type are also provided with adjustment means designed to adjust the distance between all pairs of mobile pliers from the corresponding fixed pliers since, after choosing the size of the bags to be packaged, all mobile pliers must be separated from the central fixed pliers of a predefined value suitable to the size of the bag to be packaged.

For evident volume reasons, in all automatic packaging machines the said saddles are mounted according to a closed, preferably circular, arrangement to minimise the total volume of the machine, which is consequently identified as "carousel machine".

In the most typical case of machines with carousel structural configuration, each saddle is fixed to a revolving articulated coupling, one next to the other one, in such a way that the rotation of the articulated coupling results in the simultaneous movement of all the saddles.

It must be noted that the pliers are fixed on the saddle with the jaws facing the outside of the carousel, in such a way that the back of the pliers and the back of the saddle face the centre of the carousel. Therefore, the three pliers of each saddle are not in parallel position to the sets of three pliers of the adjacent saddles; in fact, the longitudinal axis of

- A -

each lateral pliers forms, with the longitudinal axis of the adjacent lateral pliers, a convergence angle that varies according to the number of saddles arranged around the circumference of the said articulated coupling.

In view of the above, the longitudinal axes of two adjacent lateral mobile pliers, which belong to two adjacent saddles, converge towards the centre of the carousel, in such a way that the distance between the back end of two adjacent lateral mobile pliers, supported by corresponding adjacent saddles, is by far lower than the distance of the jaws situated in the front ends of the same pliers. This means that the translation travel of the lateral mobile pliers, during their withdrawal travel from the central fixed pliers, is stopped when interference is generated between the back ends of two adjacent lateral mobile pliers, supported by corresponding adjacent saddles.

It appears evident that the maximum distance that can be reached between each pair of jaws of a saddle is determined by the said convergence angle.

This means that the interference condition between the back ends of two adjacent mobile pliers, supported by adjacent saddles, indirectly determines the maximum distance possible, in the same saddle, between the jaws of the fixed pliers and the jaws of the two mobile pliers.

It is understood that the said maximum distance determines the shape of the bags that the can grabbed between a pair of pliers.

A possible solution could be represented by the installation of the lateral mobile pliers in divaricated position in each saddle, in such a way that for each mobile pliers the distance between its jaws and the jaws of the corresponding fixed pliers is higher than the distance between the back ends of the mobile pliers and the back end of the fixed pliers.

However, such a solution would be limited by the fact that the jaws of the mobile pliers would not be able to get close to the jaws of the fixed pliers beyond a certain limit value, due to the stop between the back ends of the mobile pliers and the end of the corresponding fixed pliers.

In fact, the larger the divergence angle between a mobile pliers and a fixed pliers, the larger will be the minimum distance that can be selected between the jaws of the mobile pliers and the jaws of the fixed pliers, with the limitation that the machine is not able to pack bags with width lower than the said minimum distance.

With reference to the current models of carousel machines, additional drawbacks consist in the fact that all the filling devices of the bags are situated in external position to the saddles, and therefore also in external position to the bags grabbed by the pliers. For this reason, it is currently necessary to provide a series of support surfaces under the bags, in order to support the filling devices.

The said surfaces are situated under the filling stations of the bags, with the risk of being easily dirtied because of the inaccurate distribution from the nozzle, and also because of the accidental breakage of the bags during filling.

Another drawback caused by the external position of the said support surfaces with respect to the saddles consists in the increased radial volume of the machine.

Moreover, it must be noted that the current models of carousel packaging machines are provided with two handling devices of the mobile pliers, one being designed to adjust the distance between the pliers according to the width of the bag to be filled, and one being designed to open the bag.

More precisely, the said adjustment means of the distance of the mobile pliers consist in two concentric rings with identical diameter on which the mobile pliers designed to support the bags are mounted.

With each set of three pliers comprising a right-hand mobile pliers and a left-hand mobile pliers, all the right-hand pliers are currently supported by the said first ring, and all the left-hand pliers are supported by the said second ring.

The said rings must be rotated in opposite direction in order to adjust

the distance between each pair of pliers, thus increasing or decreasing the distance between all the pairs of pliers.

The devices designed to open the bag consist in oscillating supports, one for each pliers, which are oscillated by means of a cam system. More precisely, each pliers is supported by a support bracket that oscillates with respect to a vertical axis, which is actuated by a cam system in such a way that when the bag reaches the filling station, the bag is opened by getting the supporting pliers closer; after filling, the bag is brought back to its original position, by oscillating the pliers in opposite direction by the same rotation angle.

The purpose of the present invention consists in devising a carousel- type packaging machine of products in bags, which is provided with a pair of pliers to grab each bag laterally, in which at least one of the said pliers is supported by support means designed to stop it in two different operational position, a parallel position and a divaricated position with respect to the other pliers of the pair.

A further purpose of the invention consists in devising a carousel-type packaging machine of products in bags with the aforementioned characteristics, in which the devices used to open the bags coincide with the devices used to adjust the distance between each pair of pliers.

These and other purposes have been achieved by the packaging machine of the invention, whose main characteristics are illustrated in the first claim.

The machine of the invention provides for the installation of a series of saddles on a revolving articulated coupling, each saddle supporting a fixed pliers in the centre and a pair of mobile pliers on the sides, being designed to make advance and withdrawal travels, sliding along a transversal track that supports them.

The said mobile pliers are actuated by means of a worm-type mechanism, which is actuated by adjustment devices situated on the back of the frame.

The adjustment devices are designed both to adjust the distance and to open the bag inside each pair of pliers.

The peculiarity of the mobile pliers consists in the fact that their position can be varied with respect to the central pliers, passing from a parallel position to a divaricated position, increasing the distance between the jaws of the fixed pliers and the jaws of the mobile pliers, with the same volume on the back of the saddle.

The change from the parallel position to the divaricated position occurs following to 180° overturn of each mobile pliers with respect to the corresponding seat.

Moreover, the said saddle is provided with a flange used to fix it on a revolving articulated coupling situated in external position on an innovative central structure with basket-like configuration, which supports the control devices of the handling devices of the mobile pliers. For major clarity the description of the saddle that supports the pliers according to the present invention continues with reference to the enclosed drawings, which only have an illustrative, not limiting purpose, wherein:

- figures 1A, 1 B and 1 C are views from different angles of an automatic packaging system of products in bags, in which the carousel-type machine of the invention is used;

- figures 2 and 3 are a perspective view and a plan view of the carousel machine of the invention, respectively;

- figure 4 is an axonometric rear view of the saddle used in the carousel machine of the invention to support the pliers used to grab the bag; - figure 5A is an exploded view of the fixed pliers mounted in the centre of the saddle of figure 4, seen from an angle perpendicular to the longitudinal axis;

- figure 5B is an exploded view of one of the two collapsible mobile pliers mounted on the two sides of the saddle of figure 4, seen from an angle perpendicular to the longitudinal axis;

- figure 6 is a diagrammatic view of one of the said collapsible mobile

pliers, of the housing and support sleeve, and of a fixed pliers;

- figures 7A and 7B are a diagrammatic view of a collapsible mobile pliers, respectively in position parallel to the central pliers, diagrammatically illustrated in figure 7c, and in divaricated position with respect to the central pliers; the said mobile pliers is shown in a top view sectioned with a horizontal plane passing through the longitudinal axis;

- figure 8A is a top view of the set of three pliers of the saddle of figure 4, with the collapsible mobile pliers in parallel position with respect to the central pliers; - figure 8B is a top view of the set of three pliers of the saddle of figure

4, with the collapsible mobile pliers in divaricated position with respect to the central pliers;

- figure 9 is a diagrammatic axonometric view of the support sleeve of each collapsible mobile pliers, and the flange of the collapsible mobile pliers that is interfaced with the said support sleeve;

- figures 1 OA and 10B are a side view of the two mutual positions of the support sleeve of each collapsible mobile pliers and the flange of the collapsible mobile pliers that is interfaced with the said support sleeve.

With reference to figures 1A, 1 B and 1 C, the carousel-type packaging machine (M) of the invention is designed to be used in a system (I), of known type, which also includes devices designed to make packaging bags starting from reels (B) of film, in such a way to automatically feed the machine (M) with a series of bags (S) arranged on a vertical plane and designed to be taken by the said machine (M) by a series of pairs of pliers designed to grab each bag (S) at the lateral ends of the upper opening.

More precisely, the said pairs of grab pliers are mounted on a series of identical saddles (1 ) that are moved automatically, with intermittent advance travel, under the filling devices, of known type, of the bags (S).

With reference to figure 4, each saddle (1 ) is provided with a central frame (2) with a lower flange (3) for anchoring above a revolving articulated coupling (4).

The frame (2) supports a coaxial pair of identical transversal threaded bars (5) with horizontal axis that protrude from both sides of the frame (2) and are driven into rotation by means of a mechanism that comprises a worm in orthogonal position to the threaded bars (5), with head (6) protruding on the back of the frame (2).

The frame (2) is centrally provided with a seat for insertion of the body (7) of the fixed central pliers (PF) that must be positioned with axis (D-D) in horizontal position and perpendicular to the axis (F-F) of the said coaxial pair of transversal bars (5). The fixed pliers (PF) is firmly anchored to the frame (2) with suitable means (8) that consist in screws and corresponding threaded holes according to a preferred embodiment.

With reference to figure 2, the body (7) of the central pliers (PF) is provided with an annular flange (9) with holes (9a) that receive screws (10), which engage inside threaded holes obtained directly on the front of the frame (2).

The frame (2) is frontally provided with a transversal bar (1 1 ) in parallel position to the axis (F-F) of the threaded bars (5), having the same length. The transversal bar (1 1 ) acts as guide track for the opening and closing travels of the two lateral mobile pliers (PM), of collapsible type (PM=PR).

With reference to figures 5A and 5B, each collapsible lateral pliers

(PM=PR), as well as each fixed pliers (PF), has an empty body (7, 12), in which a stem (13) is inserted and slides, with the tip (13a) frontally protruding from the body (7, 12), and the head (13b) of the stem (13) protruding on the back.

A return spring (14) is positioned between the head (13b) of the stem (13) and the back of the body (7, 12) and pushes the stem (13) towards the back of the pliers (PM=PR or PF).

Each pliers (PM=PR or PF) is frontally provided with a fixed jaw (15,

15M) composed of a plate fixed on the front of the body (7, 12), which is provided with a central hole in which the stem (13) of the pliers (PM=PR or PF) slides, being provided on the tip (13a) with a mobile jaw (16, 16M) that is interfaced with the corresponding fixed jaw (15, 15M). The stem (13) is laterally provided with a radial pin (13c) designed to slide inside a slot (7a, 12a) internally obtained on the body (7, 12), which acts as cam for the said pin (13c), in such a way that during the advance travel of the stem (13), in addition to translating forward with respect to the body (7, 12), the stem (13) is forced to make a 90° rotation with respect to its axis that coincides with the axis (A-A; D-D) of the pliers (PM=PR or PF).

When the pliers (PM=PR or PF) is actuated to determine the opening of the mobile jaws (16 and 16M), the spring (14) is compressed and the mobile jaw (16, 16M) makes a forward roto-translation, being joined to the tip (13a) of the stem (13). With reference to figure 4, the three pliers (PM=PR or PF), the fixed pliers (PF) and the two collapsible mobile pliers (PM=PR), have the same structural configuration, except for that the fixed pliers (PF) is provided in external position on the body (7) with an annular flange (9) firmly fixed to the frame (2), and the annular flange (17) obtained in external position on the body (12) of the two collapsible mobile pliers (PM=PR) is fixed to a sleeve (18) obtained above a slide (19) that can translate laterally with respect to the central frame (2) and allows the collapsible mobile pliers (PM=PR) to move closer or farther with respect to the fixed pliers (PF).

The slide (19) is provided with a threaded hole in which the threaded bar (5) is engaged; it being evident that, by rotating both threaded bars (5) simultaneously, the two collapsible mobile pliers (PM=PR) slide along the transversal bar (1 1 ), getting closer or farther with respect to the central pliers (PF) according to the rotation direction of the threaded bars (5).

Following is a description of the structural configuration of each collapsible mobile pliers (PM=PR) that, because of the special coupling with the slide (19), has two operational positions, a position in which the axis (A-

A) is parallel to the axis (D-D) of the central pliers (PF), and a position in which the axis (A-A) is divaricated with respect to the axis (D-D).

With reference to figures 5A and 5B, each body (12) of the collapsible mobile pliers (PM=PR) has a longitudinal axis (A-A) that coincides with the axis of the stem (13) that slides inside it and actuates the mobile jaw (16M).

With reference to figure 6, unlike the fixed pliers (PF), the collapsible mobile pliers (PM=PR) are provided in external position on the body (12) with a cylindrical collar (20), with longitudinal axis (B-B) not coinciding with the axis (A-A) of the body (12). When the collapsible mobile pliers (PM=PR) is in one of two operational positions, either the parallel or divaricated position, the two axes (A-A; B-B) lay on the same horizontal plane, forming an angle (α).

The seat of each collapsible mobile pliers (PM=PR) is represented by the said sleeve (18), which is obtained above the slide (19) to exactly receive the said collar (20).

The axis (C-C) of the hole of the sleeve (18) is horizontally coplanar to the longitudinal axis (D-D) of the body (7) of the central fixed pliers (PF).

Moreover, the axis (C-C) intersects an axis (E-E) parallel to the axis (D-D) of the fixed pliers (PF), forming an angle (β) identical to angle (α). When the collapsible mobile pliers (PM=PR) is supported by the slide

(19), and the collar (20) is inserted into the sleeve (18), the collapsible pliers (PM=PR) can have two operational positions.

The first position is the position in which the axis (B-B) of the collar (20) of the pliers (PM=PR) coincides with the axis (C-C), and the axis (A-A) of the mobile pliers (PM=PR) is parallel to the axis (D-D) of the body (12) of the central pliers (PF), as shown in figure 7A.

To position the mobile pliers (PM=PR) in the second operational position, i.e. divaricated position, the body (12) is rotated by 180° inside the sleeve (18). In the second operational position the axis (A-A) of the body (12) is horizontally coplanar with the axis (D-D) of the body (7) of the central pliers

(PF), but in divaricated position.

More precisely, the body (12) rotates around the rotation axis (B-B) of the collar (20) until it is collapsed and arranged in divaricated position, as shown in figure 7B. In the said divaricated position, the axis (A-A) of the body (12) forms an angle (γ) equal to double of angle (α) with the axis (D-D) of the body (7)

(and with the parallel axis E-E)

In order to connect each collapsible mobile pliers (PM=PR) to the slide

(19), an annular flange (17) is obtained from the same piece with the cylindrical collar (20), being designed to interface with the front side (18a) of the sleeve (18).

The said flange (17) is provided with holes (17a) for insertion of screws designed to engage in threaded holes (18b) obtained on the front side of the sleeve (18). With reference to figures 7A and 7B, following is a description of a special embodiment of the said flange (17) and sleeve (18) that allows for fixing the collapsible mobile pliers (PM=PR) either in parallel and divaricated position, using the same holes (18b) obtained on the front side (18a) of the sleeve (18). The aforementioned figures show the transversal axis (F-F) along which each slide (19) supporting the collapsible mobile pliers (PM=PR) slides.

In order to provide the flange (17) and the sleeve (18) with a corresponding series of holes (17a and 18b) that are always coaxial, both when the collapsible pliers (PM=PR) is in parallel position and when the same is in divaricated position, the axis of the holes (17a and 18b) must be parallel to the axis (C-C) of the sleeve and the axis (B-B) of the collar.

Moreover, both the front side (18a) of the sleeve (18) and the back side (17b) of the flange (17) must be arranged along a vertical plane (G-G) inclined by an angle (δ), identical to angle (α), with respect to the vertical plane passing through the transversal axis (F-F).

With reference to figures 5A and 5B, the jaws (15M and 16M) of the collapsible mobile pliers (PM=PR) are asymmetric with respect to the axis (A- A), unlike the jaws (15 and 16) of the central fixed pliers (PF), which are identical and specular. Each pair of jaws (15M and 16M) of a collapsible mobile pliers

(PM=PR) comprises two pairs of grab planes (150a, 160a and 150b, 160b) designed to grab a bag.

The first pair (150a and 160a) is designed to grab the bag when the pliers (PM=PR) is in parallel position, and the second pair (150b and 160b), is designed to grab the bag when the pliers (PM=PR) is in divaricated position.

The two pairs (150a, 160a and 150b, 160b) are situated on the two sides, the right and the left-hand side, with respect to axis (A-A) of the collapsible mobile pliers (PM=PR). More precisely, the pair (150a and 160a) designed to grab the bag (S) when the collapsible mobile pliers (PM=PR) is in parallel position, is situated on the side of the stem (13) opposite the axis (B-B) and the surfaces of both the mobile jaw (160a) and the fixed jaw (150a) are situated along a vertical plane perfectly perpendicular to the axis (A-A) of the collapsible mobile pliers (PM=PR).

Vice versa, the pair (150a and 160a) designed to grab the bag (S) when the collapsible mobile pliers (PM=PR) is in divaricated position, is situated on the side of collapsible mobile pliers (PM=PR) facing the axis (B- B) and the surfaces of the mobile jaw (160b) and the fixed jaw (150b) are situated along a vertical plane inclined by an angle (δ) with respect to the vertical plane passing through the axis (A-A) of the pliers (PM=PR).

Each pair of jaws of a fixed pliers (PF) identifies a single grab plane (Pf), and each pair of jaws of a collapsible mobile pliers (PM=PR) identifies two grab planes (Pa and Pb), the first plane (Pa) being identified by the two surfaces (150a and 160a), and the second surface (Pb) being identified by the two surfaces (150b and 160b).

With reference to figure 8A, the plane (Pf) is aligned with the grab planes (Pa) when the collapsible mobile pliers (PM=PR) are in parallel position.

Following to the divarication of the collapsible mobile pliers (PM=PR), the grab plane (Pb) and the grab plane (Pf) are not aligned along the same vertical plane parallel to axis (F-F).

More precisely, the grab plane (Pb) of the surfaces (150b and 160b) is parallel and in backward position with respect to the grab plane (Pf). The lack of alignment is not illustrated in the enclosed figures. In order to realign the grab planes (Pb and Pf) of the three pliers, as shown in figure 8B, a spacer with suitable thickness must be positioned between the flange (17) and the sleeve (18).

According to a preferred embodiment, in order to avoid using the spacer, the profile of the front side (18a) of the sleeve (18) and the profile of the back side (17b) of the flange (17) are shaped in such a way that when the collapsible mobile pliers (PM=PR) is in parallel position, the grab plane (Pf) is aligned with the grab planes (Pa), and when the collapsible mobile pliers (PM=PR) is in divaricated position, the grab plane (Pf) is aligned with the plane (Pb). With reference to figure 9, the profile of the front side (18a) of the sleeve (18) and the profile of the back side (17b) of the flange (17) are identical, specular and mutually matching, in such a way that they penetrate inside one another, when the collapsible mobile pliers (PM=PR) is in parallel position to the central pliers (PF), and interfere mutually when the collapsible mobile pliers (PM=PR) is in divaricated position.

Because of the said interference the collapsible mobile pliers (PM=PR) is advanced with respect to the sleeve (18) when it is in divaricated position.

With reference to figures 9, 10A and 10B, the front side (18a) of the sleeve (18) and the back side (17b) of the flange (17) have two staggered surfaces joined by a step (17g and 18g) with height (D) equal to the distance

to be recovered when the collapsible mobile pliers (PM=PR) is in divaricated position.

The said staggered surfaces include a section with higher thickness

(17c and 18c) and a section with lower thickness (17d and 18d). In view of the above, when the collapsible mobile pliers (PM=PR) is in parallel position, the two surfaces (17a and 18a) match perfectly, vice versa when the collapsible mobile pliers (PM=PR) is in divaricated position, only the two sections with higher thickness (17c and 18c) adhere and the pliers

(PM=PR) is in advanced position by one length (D) with respect to the sleeve (18) that supports it, but still with the grab planes (Pb) of the collapsible mobile pliers (PM=PR) aligned with the grab plane (Pf) of the fixed central pliers (PF).

With reference to figures 1 OA and 1 OB, it can be noted that the sleeve (18) and the flange (17) can have two alternative positions according to the position of the body (12) of the collapsible mobile pliers (PM=PR) inside the sleeve (18).

In the operational position shown in fig. 1 OB, the body (12) joined to the flange (17) is in advanced position by a distance (D) equal to the height of the step (17g or 18g) with respect to the sleeve (18). With reference to figure 4, a horizontal plate (50) is fixed on the frame

(2), facing the back of the saddle (1 ), under which a track (51 ) is fixed, on which a saddle (52) slides to push forward the stems (13) of the pliers (PM and PF) simultaneously, opening the mobile jaws (16 and 16M).

More precisely, the saddle (52) has an overturned L-shaped section, whose horizontal wing (52a) is provided with means (52d) designed to cooperate with the guide and slide track (51 ), while a revolving roller (53) with vertical axis is provided on the back of the vertical wing (52b).

The length of the vertical wing (52b) is practically identical to the length of the transversal bar (1 1 ) and the front side (52c) is parallel to axis (F-F).

The front side (52c) of saddle (52) is interfaced with the head (13c) of

the stems (13) of the pliers (PM and PF) supported by the saddle (1 ), allowing the stems (13) to move forward as soon as the saddle (52) is actuated and pushed forward.

As mentioned above, when the stem (13) is pushed forward, it makes a roto-translation with respect to its axis (A-A; D-D) and the mobile jaw (16 or 16M) is separated from the fixed jaw (15 or 15M).

Since the head (13b) of the stem (13) is joined to the stem (13) and it makes a roto-translation, a revolving ball (13d) is mounted in idle on the head of each stem (13) to avoid excessive friction. With reference to figures 2 and 3, it can be noted that each saddle (1 ) is fixed on a revolving articulated coupling (4) situated in external position in a central tower (21 ).

As shown in fig. 3, eight saddles (1 ) as the ones illustrated above are anchored with screws on the articulated coupling (4), and the central tower (21 ) has a cage-like structure, composed of a series of eight vertical uprights (22), which are identical and regularly spaced, connected on top by an annular plate (23) with regular octagonal external profile and circular internal profile.

A cover panel (24) with rectangular shape is inserted and screwed between each upright (22).

With reference to fig. 3, two of the cover panels (24) support on the back an electrical motor (26) with shaft in radial direction with respect to the articulated coupling (4) and laying on a horizontal plane.

The shaft drives a screwdriver into clockwise or anti-clockwise rotation, as necessary, whose tip (27) protrudes frontally from the cover (24) and is of flat type.

The flat tip (27) of the said screwdriver, in idle position, is always horizontal, and consequently the shaft of the electrical motor always makes angles equal to an entire multiple of 180°. With reference to fig. 2, when the articulated coupling (4) is stopped, the tip (27) of the screwdriver is inserted into the seat (6a) obtained on the

head (6) of the worm of the adjustment device mounted on the saddle (1 ) that momentarily stands in front of the tip (27) of the screwdriver.

When the articulated coupling (4) is stopped, the electrical motor (26) actuates the tip (27) of the screw, rotating it for a predefined number of times, and always going back to horizontal position before the articulated coupling (4) starts to move again.

Although Fig. 3 shows two electrical motors (26) that correspond to two adjustment stations (SR) of the distance of the mobile pliers (PM), multiple adjustment stations (SR) may be necessary according to the different bags to be filled.

With reference to fig. 3, one of the cover panels (24) supports on the back a jack (28) with stem in radial direction with respect to the articulated coupling (4) and laying on a horizontal plane.

The jack (28) is fixed to the panel (24) in such a way that the tip protrudes frontally from the panel (24), interfering with the roller (53) of the saddle (1 ) that momentarily stands in front of it.

As soon as the articulated coupling (4) stops, one of the saddles (1 ) stops in front of the actuator (28) that corresponds to the jaw opening-closing station (SG). The advantage of a structure with central tower (21 ) and interchangeable cover panels (24) consists in the simplicity and inexpensiveness of changing the number and position of the adjustment stations (SR) as necessary, as well as the number of the jaw opening-closing stations (SG); it being evident that the said change only requires the installation of a new electrical motor (26) or a new jack (28), as illustrated above, in one of the cover panels (24).

In order to guarantee that the distance selected between the pairs of mobile pliers (PM) is not subjected to undesired changes during the movement of each saddle (1 ), between the two adjustment stations (SR), in external position on the structure with central tower (21 ), a guide track for the head (6) of the adjustment screw is fixed.

As shown in fig. 2, the track consists in an annular series of arched segments (29) with maximum thickness identical to the thickness of the tip (27) of the screwdriver; the said annular series of segments (29) is arranged along a circumference concentric to the articulated coupling (4). The track (29) is positioned on a plane that coincides with the plane of the tip (27) of the screwdriver when the articulated coupling (4) is stopped.

Moreover, the track (29) is positioned inside the seat (6a) obtained on the head (6) of the worm for the entire time in which each saddle (1 ) moves between an adjustment station (SR) and the following one, to avoid accidental rotations of the head (6) of the screw, which would correspond to undesired translation travels of the mobile pliers (PM).

Although the above description provides for mobile pliers (PM) of collapsible type (PR), it is understood that in case of a saddle (1 ) that supports only one pair of pliers (PF and PM), of which one is a fixed pliers (PF), then the collapsible pliers (PR) may also coincide with the fixed pliers (PF=PR), while maintaining all the advantages offered by the present invention.