ITMI20081360A1 - PNEUMATIC GRIPPING HEAD FOR BAGS CONTAINING BULK MATERIAL - Google Patents

Description

DESCRIPTION

â € œPNEUMATIC GRIP HEAD FOR BAGS CONTAINING BULK MATERIALâ € œ

BACKGROUND OF THE INVENTION

The present invention relates to a pneumatically actuated head for gripping bags containing bulk material, which is for example particularly suitable for gripping and holding bags containing bulk material in a safe and reliable manner in the context of depalletizing operations of the bags themselves.

STATE OF THE ART

In general, the use of pneumatic heads for gripping loads or pieces of various kinds to be handled is known, for example from US 6,065,789 and FR-A-2724644, which conventionally comprise a body or base plate, suitable for being connected to a robot or other handling device, as well as comprising one or more pneumatically operated gripping members, such as vacuum suckers which can be connected to a vacuum or suction source.

In the field of depalletizing systems for bags for bulk material, such as grains, pellets, powders, liquids and the like, an example of which is illustrated in JP-A-7165223, there is a need to have a pneumatic gripping head that is able to pick up the bags from a pallet and hold them safely during the handling operations carried out by the robot, thus preventing dangerous and counterproductive fallout of the bags themselves.

In particular, the major problems that arise in the gripping of bags are linked to the extreme variability in the conformation and arrangement of the surface of the bags on which the gripping head comes into contact; in fact, depending on the type of material contained in the bag, the type of material with which the bag is made, and other uncontrollable variables such as, for example, the manner in which the bags are filled and palletized, as well as the subsequent transport and / or handling of the pallet, the surface of the bags to be depalletised may be variously irregular and / or inclined, leading to imperfect contact between the gripping organ and the surface of the bag which can affect the picking and retention operations of the sack itself.

As regards the problem of the inclination of the contact surface of a generic load with respect to a pneumatic gripping member, it has been variously proposed, for example in EP-A-1256421, to support the gripping member in a freely orientable way in space through a ball joint or the like; however, this solution is not suitable for handling loads having a significant weight, such as bags weighing more than 20 kg, since, due to the high inertia involved, uncontrolled oscillations of the organ would occur during the handling operations. and of the load retained by the body itself, which could give rise to a load disconnection.

Furthermore, in the specific case of bag picking, such a solution would be even less suitable, as the risk of load detachment would be further increased due to the uncertainties in picking linked to the irregularity of the contact surface of the bags.

PURPOSE OF THE INVENTION

The aim of the present invention is therefore to provide a pneumatically operated head for gripping bags for bulk material which is constructively simple, and which allows the bags to be picked up and held reliably and safely, regardless of their conformation and / or the arrangement of the surface of the bags on which the pneumatic head gripping member comes into contact, as well as regardless of the type of loose material contained in the bags or the material with which they are made.

BRIEF DESCRIPTION OF THE INVENTION

The above can be achieved by means of a pneumatic gripping head for bags containing loose material, comprising:

- a base body connectable to a handling device;

- at least one gripping member of a bag, which can be operated pneumatically, said at least one gripping member having a longitudinal axis and being supported in an orientable way in space by the base body, and being connectable to a vacuum or suction source,

characterized in that said at least one gripping member is fixed to the base body by means of an elastomeric joint comprising an elastomeric material to allow a controlled angular orientation of the gripping member, preventing its rotation along said longitudinal axis, and

from understanding:

- means for detecting a sealed contact condition of the gripping member against a bag to be picked up; And

- means for detecting a vacuum condition fluidically connected to the gripping member,

said contact detection means and said vacuum detection means being shaped and arranged to generate consent and / or control signals for a command of said movement device.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further characteristics according to the present invention will become clearer from the following description with reference to the attached drawings, in which:

- Fig. 1 is a front view of the pneumatic head for gripping bags according to a first embodiment of the invention;

- Fig. 2 is an enlarged detail of Fig. 1, in which the elastic joint connecting the gripping member is in an angularly oriented condition;

- Fig. 3 illustrates a variant of the gripping head of Fig. 1, in which different means for detecting the contact between the gripping member and the surface of the bag are shown;

- Figs. 4 to 6 illustrate alternative embodiments of the resiliently compliant joint of the pneumatic bag gripping head according to the present invention;

- Fig. 7 is a front view of the pneumatic head for gripping bags according to a further embodiment of the invention, in which two pneumatic gripping members are provided;

- Fig. 8 is a front view of the pneumatic head for gripping the bags according to a further embodiment of the invention, in which mechanical needle means for retaining the bags are provided; And

- Fig. 9 is a further embodiment of the present invention, for the simultaneous gripping of two bags.

DETAILED DESCRIPTION OF THE INVENTION

The general characteristics of the present invention will be illustrated hereinafter through some embodiment examples.

A first embodiment of the pneumatic head for gripping bags for bulk material, according to the present invention, is illustrated in Figures 1 to 3, which is suitable for example for picking up bags 10 positioned on a pallet or pallet of support, not shown.

The gripping head, indicated as a whole by the numerical reference 11, comprises a base body 12, preferentially in the form of a fixing plate, which can be connected by means of suitable screws to a movement device, such as for example an anthropomorphic robotic arm 13, of to which only the terminal part is shown which comprises an articulation 14 capable of imposing angular movements on the gripping head 11; however, it is not excluded that the movement device may be configured in another way, for example in the form of a Cartesian robot provided in any case with a similar articulation, in such a way as to present similar functions, or in the form of a movement device of the type manual.

The gripping head 11 also comprises a pneumatically actuated gripping member 15 for the bags 10, which, as better illustrated in Figure 2, is preferably in the form of a box-like body, defining a vacuum chamber open downwards, having a contact gasket 16 intended to be pressed and to form a seal against an upward-facing gripping surface of a bag 10.

According to the present invention, the gripping member 15 is connected to the joint 14 of the robotic arm 13 by means of an elastically yielding connection joint 17 comprising an elastomeric material to allow the gripping member 15 to orient itself in a controlled manner, thanks to the elastic reaction provided by the material of the joint itself, and to assume any angular position in space, while preventing a torsional or rotational movement of the member 15 itself around its own longitudinal axis.

In this way, the gripping member 15, when it is supported and pushed with a controlled force against a bag 10 to be picked up, can assume any inclination in space, automatically adapting to the inclination and / or possible deformation or irregularity. of the bag gripping surface 10.

In the embodiment illustrated in Figures 1 to 3, the elastic joint 17 comprises an elastically yielding body 18, which is preferably constituted by a block of elastomeric material, such as rubber, synthetic resin or other suitable material or combination of several materials ; on an upper side, the elastically yielding body 18 is fixed integrally to the fixing plate 12, while at the bottom it is suitably fixed to an axial type force sensor or transducer 21, arranged coaxially to the elastically yielding joint 17, to for example, providing, below the elastically yielding body 18, a metal plate 19 having a central threaded shank 20 which screws into a threaded hole of the force transducer 21.

The force translator 21 in turn is fixed to the upper part 15 'of the pneumatic organ 15 for gripping the bags, by means of suitable screws, not illustrated, or in any other suitable way.

The force transducer 21 can be of any type, for example in the form of a load cell or the like, as long as it is suitable for providing a control signal indicative of a condition of sealed contact of the pneumatic gripping member 15 against a bag 10, and more particularly to provide a signal proportional to the force with which the gripping member 15 is pushed against the bag 10, in order to increase the seal of the gasket 16 or the degree of vacuum or suction necessary for gripping of the sack.

The gripping head 11 also comprises at least one flexible duct 22 for connecting the pneumatic gripping member 15 to a vacuum or suction source, for the creation of a predetermined degree of vacuum which allows a bag to be picked up and retained by means of the gripping member 15 itself, as explained below; in order to ensure greater suction flow rates, the flexible duct 22 is connected directly to the intake member 15, avoiding solutions that provide for the passage of the suction flow through the elastic joint 17.

As illustrated in Fig. 3, in replacement of the force transducer 21, or in combination with it, the gripping member 15 can be provided with two or more sensors or contact detection devices 23, able to supply signals indicative of a condition of having made contact with a bag 10, along the peripheral edge of the gripping member 15.

Returning to Figure 1, the duct 22 can be connected to a source of vacuum, for example to the suction side of a pump 24, by means of a filter 25 and an exchange solenoid valve 26; in turn, the pump 24 can be selectively connected to the atmosphere 27 through the same exchange valve 26, as shown.

The gripping force of the bags depends on the vacuum, i.e. on the depression generated in the pneumatic gripping member 15, which in turn depends on multiple factors such as, for example, the nature and degree of permeability of the bag material, such as plastic material , paper, fabric or their combination, by the nature and / or type of the loose material contained therein, by the weight and / or by the density of the material itself; the determination of the gripping force and / or the degree of vacuum required must be determined from time to time on the basis of specific tests. The vacuum or depression value can be detected directly in the gripping member 15 itself or in the duct 22 for connection to the vacuum source constituted by the air suction pump 24.

According to the embodiment schematized in Figure 1, this is made possible for example by providing a vacuum sensor 28 in a duct 29 derived from the duct 22 for connection to the pump 24; in any case, according to the present invention, it is necessary to provide a sensor or suitable vacuum detection means 28 capable of providing a signal indicative of the achievement and permanence of a predetermined degree of vacuum in the gripping member 15, suitable to allow the collection and retention of a bag in a reliable and safe way.

The vacuum sensor 28 and the force transducer 21 and / or the contact sensors 23 provided according to the present invention therefore generate consent and / or control signals which allow to carry out a lifting command of the handling device only in the case of that the necessary vacuum and sealed contact conditions for gripping the bag are achieved.

In particular, the signals of the vacuum sensor 28 and of the force transducer 21 and / or of the contact sensors 23 can for example be supplied to an external electronic control unit 30, shaped and programmed to manage the operation of the robotic arm 13. to which the gripping head 11 is connected.

In order to perform an effective removal of a bag 10, as mentioned, the gripping head 11 is brought into contact with the bag 10, and subsequently the pneumatic gripping member 15 is progressively pressed against the bag 10 itself, by actuating the robotic arm 13, until the vacuum sensor 28 detects the required vacuum condition.

If the force transducer 21 is provided, it is advantageously used to directly detect the thrust value exerted by the gripping member 15 against the bag 10, so as to be able to verify that it is equal to or greater than a minimum value thrust pre-set prior to withdrawal, according to variables such as the type and density of the material contained in the bag and the material with which the bag is made.

This thrust of the pneumatic gripping member 15 against the bag 10 first of all allows the necessary vacuum seal to be formed by means of the gasket 16 of the gripping member 15 itself; moreover, if the contact surface of the bag 10 to be picked up is inclined and / or deformed with respect to the pneumatic gripping member 15, the aforementioned controlled thrust allows the elastic joint 17 to flex appropriately to allow the gripping member 15 to orient themselves automatically and to position themselves in a manner that conforms to the surface of the bag 10.

In this way, the gasket 16 of the gripping member 15 is always brought into contact and pushed against the bag 10 in an effective manner, allowing to achieve a seal such as to be able to reach in the gripping member 15 the degree of vacuum necessary for gripping. and bag retention.

In the event that the aforementioned vacuum and contact conditions are not verified, it is instead possible to provide corrective maneuvers, such as for example a further increase in the thrust exerted by the gripping member 15 on the bag 10 to be picked up, by activating the robotic arm. 13, to achieve a more effective sealing contact of the gripping member 15 itself, or an increase in the suction flow generated by the pump 24.

In this way, the collection and retention of the bag 10 is always possible, regardless of the conformation and / or arrangement of the surface of the bag on which the pneumatic head gripping member comes into contact, as well as regardless of the type of material. loose contained in the bag or from the material with which it is made.

As illustrated in Fig. 1, the gripping head 11 preferentially also comprises at least one distance sensor 31 arranged peripherally to the pneumatic gripping member 15 for measuring and supplying the aforementioned electronic control unit 30 with a signal indicative of the distance of the gripping member 15 itself from a bag 10 to be withdrawn; the distance sensor 31 can be of any type, for example a photocell or a sonar, and in particular it can be suitable for providing a continuous measurement of the distance, by means of which it is possible to control and gradually reduce the speed of descent or approach to the bag of the gripping member 15, or alternatively it can be suitable for providing a distance signal or pulse when a predetermined threshold value is reached, starting from which the approach speed to the bag of the gripping member 15 is reduced same.

Therefore, thanks to this distance sensor 31, the gripping head 11 can be moved and brought close to a bag 10 to be picked up at different speeds, until the gripping member 15 is brought into contact with the bag 10 itself, in order to then detecting, as mentioned, the contact condition between the gripping member 15 and the bag 10, by means of the force transducer 21 or by means of the contact sensors 23, and the necessary vacuum condition by means of the vacuum sensor 28.

In order to ensure optimal control of the orientation movement of the pneumatic gripping member 15 with respect to the robotic arm 13, the elastic joint 17 is preferably made with a cylindrical block filled with elastomeric material having a Shore A hardness value between 20 and 100, as a function of the weight of the bags to be lifted and the nature of the material contained, and a ratio between diameter and axial height comprised between 0.5 and 3; in this way, the elastic joint provides a sufficient elastic reaction for the control of the gripping member 15, and at the same time has a high resistance to axial compression and torsion around the axis of the joint itself.

As said with reference to Figure 3, the pneumatic gripping head 11 can comprise one or more contact detection devices 23, such as for example feelers, arranged laterally to the gripping member 15 to detect the contact between the gripping member 15 itself and bag 10.

By way of example, each feeler 23 can comprise an axially sliding rod 32, having a contact tip 33 at one front end facing the bag, and an activation element 34 of a sensor 35, for example of the inductive or electromechanical type, at a rear end of the probe itself.

Preferably, the gripping head 11 has a plurality of feelers 23, for example from two to four, arranged peripherally spaced apart around the gripping member 15, in such a way as to also be able to detect the inclination and / or the shape of the bag 10 by means of the signals or the sequence of contact signals provided by the feelers 23.

Thanks to this detection of the configuration of the bag, it is possible to impose on the gripping head 11 a preliminary movement of angular orientation by rotating the articulation 14 of the robotic arm 13, in such a way as to be able to carry out the gripping even in conditions of strong inclination of the sack, in which the elastic yielding of the joint 17 would not allow sufficient orientation of the gripping member 15.

Further embodiments of the invention will now be illustrated hereinafter, in which, although not schematized, the vacuum sensor 28 suitable for detecting the aforementioned vacuum condition, according to the present invention, is intended.

Figure 4 illustrates a second embodiment of the pneumatic gripping head 11 according to the present invention, in which the same numerical references have been used to indicate parts similar or equivalent to the previous embodiment.

In this embodiment, the pneumatic gripping member 15 is fixed to the robotic arm 13 by means of an elastically yielding connection joint 36 which has a different configuration from that of the joint of the previous embodiment.

In particular, the connection joint 36 comprises a body formed by a first and a second tubular element 37, 38 with circular section arranged and fixed orthogonally to each other, in correspondence with a median area of one of their external lateral surfaces; coaxially inside each tubular element 37, 38 there is a respective stress rod 39, 40 which extends axially to the ends of the tubular element 37, 38 itself to be fixed in a rotational way, by means of screws 41, to the lateral arms 42 of a fork fastening member 43 provided for each tubular element 37, 38.

Between each tubular element 37, 38 and the respective biasing rod 39, 40 there is an annular space in which an elastic reaction bush 44 in elastomeric material is provided, which is vulcanized to the tubular element 37, 38 and 'solicitation rod 39, 40 themselves; in this way, a relative rotation around their longitudinal axis can occur between a tubular element 37, 38 and the respective biasing rod 39, 40, which however is opposed by an elastic torsional reaction generated by the elastic bush 44.

The fork members 43 connected to the stress rods 39, 40 of the joint 36 have relative base plates which are respectively fixed to the axial force sensing transducer 21 and to the robotic arm 13 by means of suitable screws.

Similarly to the previous embodiment, the force transducer 21 is therefore in turn connected to the pneumatic member 15 for gripping the bags 10.

The elastically yielding joint 36 thus configured allows controlled rotation and therefore a controlled orientation of the gripping member 15 according to a first and a second rotation axis orthogonal to each other defined by the stress rods 39, 40 of the joint 36 itself, which axes they are horizontal, or substantially horizontal, as they are preferably allowed to rotate between 0 ° and 40 °.

In the elastic joint 36 thus configured, it is not excluded that the tubular elements 37, 38 and the stress rods 39, 40 may alternatively have a polygonal section or other suitable shape; moreover, it is not excluded that, as an alternative to the reaction bush, the joint 36 may comprise a plurality of elongated elastic reaction bodies, arranged angularly spaced apart, longitudinally in the annular space defined between each tubular element 37, 38 and the respective rod of stress 39, 40, and shaped in such a way as to provide the elastic torsion reaction necessary for the operation of the joint 36 by reacting elastically to compression actions.

Figure 5 illustrates another embodiment of the pneumatic gripping head 11 according to the present invention, in which the same numerical references have been used to indicate parts similar or equivalent to the previous embodiment.

In this embodiment, the pneumatic gripping member 15 is fixed to the robotic arm 13 by means of an elastically yielding connection joint 45 differently configured with respect to the joints of the previous embodiments.

In particular, the joint 45 comprises a cup-shaped body 46 having a peripheral flange 47 for fixing, for example by means of suitable screws, to the base body 12 of the gripping head 11.

Inside the cup-shaped body 46, which is open on the side facing the base body 12 of the head 11, there is an elastomeric annular sleeve 48 made of elastomeric material, a lower end of which is fixed, for example by vulcanization, to the bottom wall of the cup-shaped body 46, peripherally around a central hole 49 in the wall itself.

To an upper end of the annular sleeve 48, still inside the cup-shaped body 46, is fixed, for example again by vulcanization, a plate 50 supporting the gripping member 15, which has a threaded shank 51 which extends through the central hole 49 provided in the bottom wall of the cup-shaped body 46 for fixing the gripping member 15.

Thanks to the elastic yielding of the tubular sleeve 48 which supports the plate 50 and to the fact that the central hole 49 has a diameter greater than the threaded shank 51, the gripping member 15 can also in this case orient itself angularly in the space in order to adapt to the inclination and / or the configuration of the surface of the bag 10 to be picked up.

The advantage of this joint 45 lies mainly in the fact that, in the event of the elastic sleeve 48 breaking, the gripping member 15 and any bag 10 held by it cannot fall, since the support plate 50 would in any case be supported. from the bottom wall of the cup-shaped body 46, thus achieving greater safety of use of the gripping head 11.

Figure 6 illustrates a further embodiment of the pneumatic gripping head 11 according to the present invention, in which the same numerical references have been used to indicate parts similar or equivalent to the previous embodiment.

In this embodiment, the pneumatic gripping member 15 is fixed to the robotic arm 13 by means of an elastically yielding connection joint 52 having a still different configuration with respect to the joints of the previous embodiments.

In particular, the joint 52 comprises a hollow sleeve 53 made of elastomeric material sealed between an upper plate 54 and a lower plate 55 for fixing respectively to the base body 12 of the head 11 and to the force transducer 21.

The hollow sleeve 53 thus defines an air chamber 56 which is suitably filled with a pressurized fluid, such as air or a gas, for example through a supply duct 57 which opens into the chamber 56 through the lower plate 55, in in such a way as to exhibit a behavior similar to that of the previously described joints, resulting in a controlled elastically yielding manner.

Fig. 7 illustrates another embodiment of the pneumatic gripping head 11 according to the present invention, in which the same numerical references have been used to indicate similar or equivalent parts.

In this embodiment, suitable for example for picking up particularly extended and / or elongated or heavy bags, the gripping head 11 comprises a first and a second gripping member 15A, 15B arranged side by side, which are connected to the opposite ends of a rocker arm support element 58 by means of respective elastic joints 59 ', 59' 'which allow the independent angular orientation of the gripping members 15A, 15B.

The support element 58, centrally on a rear side, is fixed to a force transducer 21 which, similarly to the previous embodiments, allows to detect the contact thrust exerted by the head 11 against the bag 10; in turn, the force transducer 21 is connected to the robotic arm 13 by means of a further elastic joint 17, which allows an overall orientation of the gripping members 15A, 15B.

Fig. 8 illustrates yet another embodiment of the pneumatic gripping head 11 according to the present invention, in which the same numerical references have been used to indicate parts similar or equivalent to the previous embodiment.

In this embodiment, the gripping head 11 comprises a plurality of movable needle-shaped elements 60, for example a first and a second needle element, which are arranged peripherally to the gripping member 15 for mechanical retention of the bag, for example during an emptying operation.

These movable needle-like retaining elements 60 are particularly essential in the case in which the gripping head 11 is used for the retention and emptying of stratified bags, for example consisting of an outer envelope or bag made of paper, plastic, or jute, and an inner plastic bag; in this case, the needle elements 60 allow to retain the inner plastic bag, which otherwise, after cutting the outer bag, could slip off and fall into an underlying emptying hopper.

Preferably, each needle retaining element 60 is fixed to the movable rod of a linear actuator 61, for example a pneumatic cylinder or an electric type actuator, which is supported on a respective side of the gripping member 15 in in such a way as to be inclined and turned towards the area below the gripping member 15 itself.

In this way, the needle elements 60, once the gripping member 15 has picked up a bag 10, can be moved jointly or sequentially from a retracted rest position to an advanced position for retaining the bag 10, in which they penetrate into the bag itself to retain the inner plastic bag.

Preferably, each actuator 61 for actuating the needle elements 60 is supported elastically in a movable way in the direction of the longitudinal axis of the gripping member 15, for example by means of a rod 62 which slides axially in a guide sleeve 63 suitably fixed to the gripping member 15, in which the support rod 62 is subjected to the elastic reaction of a biasing spring 64 adapted to allow an adaptation of the axial position of the needle retaining elements 60 according to the geometry of the bag.

Advantageously, the axial stroke of the rods 62 supporting the actuators 61 can be conveniently detected by a sensor, not shown, in such a way as to provide a signal indicative of the aforementioned condition of contact between the gripping member 15 and the bag 10.

Finally, Fig. 9 illustrates a still further embodiment of the pneumatic gripping head 11 according to the present invention, in which the same numerical references have been used to indicate parts similar or equivalent to the previous embodiment.

In this embodiment, the gripping head 11 comprises a plurality of gripping members 15, which are supported by a first main rocker element 65 by means of suitable elastically yielding joints, as explained below, in which the rocker element main 65 It can be connected to the robotic arm 13.

The particularity of this embodiment lies in the fact that each gripping member 15, or each pair or group of gripping members 15, can be connected to a separate vacuum source, so as to be able to simultaneously manage the several bags, for example by providing that each gripping member 15 picks up a respective bag or that each pair or group of gripping members 15 picks up a bag.

In the illustrated embodiment, for example, four gripping members 15 are provided, supported in pairs at the ends of the first main rocker element 65; in particular, the gripping members 15 of each pair, arranged side by side, are connected to the opposite ends of a second rocker arm support element 66 by means of respective elastic joints 67 which allow the independent angular orientation of the gripping members 15 of each couple.

The second rocker arm support element 66, centrally on its own rear side, is fixed to a force transducer 21 which, similarly to the previous embodiments, allows to detect the contact thrust exerted by the head 11 against the bag 10; in turn, the force transducer 21 is connected to one end of the first main rocker support element 65 by means of a further elastic joint 68, which allows an overall orientation of the relative pair of gripping members 15.

In this embodiment, each pair of gripping members 15 can be connected to a respective vacuum source, as well as to a respective vacuum sensor, not shown, by means of corresponding flexible connection ducts 22 ', 22' '.

What has been said and shown with reference to the attached drawings has been given purely by way of example and illustrating the general characteristics of the invention, as well as some of its preferential embodiments; therefore other modifications and variations to the pneumatic gripping head for bags for bulk material are possible, without thereby departing from the scope of the claims.

Claims (15)

Claims 1. Pneumatic gripping head for bags containing loose material, comprising: - a base body connectable to a handling device; - at least one gripping member of a bag, which can be operated pneumatically, said at least one gripping member having a longitudinal axis and being supported in an orientable way in space by the base body, and being connectable to a vacuum or suction source, characterized in that said at least one gripping member is fixed to the base body by means of an elastomeric joint comprising an elastomeric material to allow a controlled angular orientation of the gripping member, preventing its rotation along said longitudinal axis, and from understanding: - means for detecting a sealed contact condition of the gripping member against a bag to be picked up; And - means for detecting a vacuum condition fluidically connected to the gripping member, said contact detection means and said vacuum detection means being shaped and arranged to generate consent and / or control signals for a command of said movement device. 2. Pneumatic gripping head according to claim 1, characterized in that said means for detecting a vacuum condition comprise at least one vacuum sensor shaped and arranged to provide a signal indicative of the achievement and permanence of a predetermined vacuum level in said at least one gripping member. 3. Pneumatic gripping head according to claim 1 or 2, characterized in that said contact sensing means comprise an axial force sensing transducer positioned between the elastically yielding joint and the pneumatic gripping member, said force transducer being shaped to detect the contact of the gripping member against the bag, as well as to provide a control signal of the thrust exerted by the gripping member against the bag. 4. Pneumatic gripping head according to any one of the preceding claims, characterized in that said elastomeric connection joint comprises a body made of elastomeric material arranged between said base body of the gripping head and said transducer for detecting axial force, said body in elastomeric material having a Shore A hardness value between 20 and 100. 5. Pneumatic gripping head according to claims 4, wherein the elastomeric material body of the elastic joint is in the form of a solid cylindrical block, characterized in that said cylindrical block made of elastomeric material has a ratio between diameter and axial height including between 0.5 and 3. 6. Pneumatic gripping head according to claim 1, characterized in that said contact detection means comprise one or more contact detection devices arranged laterally to the gripping member. 7. Pneumatic gripping head according to any one of the preceding claims, characterized in that the bag gripping member is in the form of a box-like body, open downwards, said box-like body having a seal for contact with the bag. 8. Pneumatic gripping head according to claim 1, characterized in that it comprises at least one flexible duct for connecting the pneumatic gripping member to a suction source, said flexible duct being directly connected to the pneumatic gripping member. 9. Pneumatic gripping head according to claim 1, characterized in that it comprises at least one distance sensor disposed peripherally to the pneumatic gripping member, said distance sensor being shaped to provide a signal or a continuous measurement indicative of the distance of the member from a bag to be picked up. 10. Pneumatic gripping head according to claim 1, characterized in that the elastically yielding connection joint comprises: - a body formed by a first and a second tubular element arranged and fixed orthogonally to each other; - a first and a second biasing rod, arranged coaxially inside said first and second tubular elements respectively, each biasing rod extending axially to be fixed integrally in rotation to the lateral arms of a relative fork member for fixing to said automatic movement device, respectively to said force sensing transducer; and - an elastic reaction bush made of elastomeric material, interposed and fixed between each tubular element and the respective biasing rod. 11. Pneumatic gripping head according to claim 1, characterized in that it comprises first and second gripping members arranged side by side, said first and second gripping members being connected to the ends of a rocker arm support element by means of respective joints elastic, said support element being fixed to an axial force sensing transducer which is in turn connected to said automatic movement device by means of a further elastic joint. 12. Pneumatic gripping head according to claim 1, characterized in that said elastically yielding joint comprises: - a cup-shaped body fixed to said base body of the gripping head, - an elastomeric resilient annular sleeve made of elastomeric material, arranged inside the cup-shaped body, said annular sleeve having a lower end fixed to a bottom wall of the cup-shaped body, peripherally around a central hole provided therein, and - a support plate of the gripping member, fixed to an upper end of said annular sleeve, said support plate having a stem which extends through said central hole of the bottom wall of the cup-shaped body for fixing said gripping organ. 13. Pneumatic gripping head according to claim 1, characterized in that said elastomeric joint comprises a hollow sleeve made of elastomeric material sealed between an upper plate and a lower plate for fixing respectively to the base body of the head and to the transducer force, said hollow sleeve defining an air chamber filled with pressurized fluid. 14. Pneumatic gripping head according to claim 1, characterized in that it comprises a plurality of needle-shaped retaining elements arranged peripherally to the gripping member, said needle elements being movable between a retracted position and an advanced position for a mechanical bag retention. 15. Pneumatic gripping head according to claim 1, characterized in that it comprises a plurality of gripping members, supported by a main rocker element which can be connected to said movement device, each gripping member, or each pair or group of gripping members of said plurality of gripping members being connectable to a respective and separate vacuum source, for the simultaneous management of the gripping of several bags.