EP2016013A1

EP2016013A1 - Method and apparatus for pneumatically gripping porous sheet material.

Info

Publication number: EP2016013A1
Application number: EP07724455A
Authority: EP
Inventors: Gabriele Binda; Loredano Sbrana; Davide Mariani; Maurizio Castiglioni; Maurizio Crivelli
Original assignee: Tecnos SpA
Current assignee: Tecnos SpA
Priority date: 2006-05-03
Filing date: 2007-04-23
Publication date: 2009-01-21
Also published as: WO2007128398A1; ITMI20060862A1

Abstract

A sheet of material (13) permeable to air, for example plastic material, fabric, felt, porous material or the like, if necessary impregnated with a resin, is positioned on a supporting surface (12) permeable to air, and picked up by means of a pneumatic gripping device to be retained, conveyed and/or positioned along a processing line. The pneumatic gripping device (16) comprises a frame made with one or more frontally open slots, connectable to a source (17) of air-suction; the pneumatic gripping frame is brought into contact with a lateral face of the sheet of permeable material by activating an air-suction system so as to cause the passage of a sufficient stream of air through the sheet of material, as to create a loss of pressure astride the sheet itself and its partial penetration into the slots of the pneumatic gripping device, for the length of time necessary to retain it.

Description

METHOD AND APPARATUS FOR PNEUMATICALLY GRIPPING POROUS

SHEET MATERIAL.

FIELD OF THE INVENTION

This invention refers to the pneumatic gripping of porous sheets material, and in particular it relates to a method and an apparatus appropriately provided for pneumatically gripping sheet material permeable to air, for retaining, conveying, and/or positioning the sheet material along a processing line.

As known, in conveying sheet material for example in foaming or thermo- forming installations or systems, a need exists of gripping sheets of either rigid or flexible material to retain, convey and/or for positioning them in one or more work stations, or zones.

Picking up sheet material by clamps or mechanical gripping devices has proved to be somewhat unsuitable, giving rise to certain drawbacks in that a mechanical gripping system involves the need to use sheet material having dimen- sions considerably larger than the required ones, with a consequent greater waste of useful and sometimes costly material; moreover, whenever the sheet of material must be heated, a mechanical gripping system gives rise to uneven heating along the peripheral edges, involving a possible negative influence during a subsequent processing step. Moreover, a mechanical gripping restricts the use of sheets to those having simple geometrical shapes, for example square or rectangular shapes.

The stretching by mechanical gripping means may also cause a damage of the material in that they are liable to create localised stresses on the material which in the case of delicate structures, such as for example in carbon fabrics, may damage the fabric itself locally modifying the weft and/or the warp.

Mechanical gripping may also make it difficult to convey the sheets along a processing line, or position them in correspondence with a work station where the sheet material must be correctly positioned, preventing it from coming into contact with obstacles or protruding parts of an installation.

In the past, the use of vacuum systems has been variously proposed for picking up air-impermeable materials, in particular plastic films designed to be positioned inside a mould, in the manufacture of foamed panels, or for other similar applications. Vacuum-operated systems for picking up plastic films are described for example in US-A-5,449,429, EP-A-0.838.320 and DE-A-2630021.

Although the use of vacuum-operated gripping systems proves to be suitable in the case of plastic films, due to the natural impermeableness and flexibility of the film itself, as well as due to its ability to adhere to any peripheral outline of a frame or a mould under the simple action of vacuum, in the case of porous material or air-permeable material, such as fabric, felt or the like, or in the case of layered material, vacuum-operated gripping systems have proved to be impossible or difficult to use due to the variability of physical characteristics of the same material, in particular due to the impossibility to maintain a vacuum condi- tion for gripping and holding the sheets.

The use of vacuum-operated gripping systems for sheets materials was generically mentioned for example in WO-A-2004/062889, WO-A-2005/014262, and DE-A-2630021.

Within the sphere of certain applications, for example in the foaming of carpets or moulded articles in the automotive manufacture, it has also been suggested to retain, pneumatically or by vacuum, a plastic sheet or a sheet of air- permeable material, inside a mould; examples are found in US-A-4,529,693 and EP-A-0.281.724. Nevertheless, there is a need to improve the currently existing gripping systems, or to find new solutions capable of providing a firm pneumatic grip on sheets of material permeable to air, in place of mechanical gripping, and for which it is not possible to make use of vacuum-operated gripping devices. For the purposes of this specification, the expression "air-permeable sheet material", is understood to mean either sheets of material having a single layer, or comprising two or more superimposed layers of air-permeable or in any case porous materials. OBJECTS OF THE INVENTION

The main object of this invention is to provide a method and an apparatus for pneumatically gripping air-permeable sheet material, capable of obviating the limits and drawbacks of the currently known gripping systems.

Another object of the invention is to provide a method and a pneumatic gripping apparatus capable of firmly retaining sheets of single-layered or multiple layered material, also of considerable weight and/or thickness, which are ex- tremely versatile and wholly unaffected by the geometrical shapes and sizes of the sheets and/or by the air-permeability of the materials to be retained.

A still further object is to provide a method and a pneumatic gripping apparatus, as mentioned above, which are also capable of exerting a mechanical retaining action, in addition to the pneumatic retaining action, thereby contribut- ing to provide a high degree of reliability in the event of the air-suction being limited or accidentally cut off.

A still further object is to allow, under certain situations, the sheet material to be pneumatically gripped in different positions on one side, or on opposite sides in correspondence with the same peripheral areas, regardless of the geometrical shapes of the sheets, thereby achieving a significant saving of material and a greater processing facility. BRIEF DESCRIPTION OF THE INVENTION

These and further objects of the invention can be achieved by means of a method for pneumatically gripping air-permeable sheet material according to claim 1 , and by means of an apparatus according to claim 10.

In particular, according to a first solution of the invention, a method has been provided for pneumatically gripping air-permeable sheet material, comprising the steps of: providing air-permeable sheet resting means conformed to allow the passage of an air flux; providing a first pneumatic gripping device having a sheet-contact surface provided with at least one air-suction slot connectable to an air-suction source; arranging a sheet material in a spread out or laid down condition on said sheet resting means; positioning the pneumatic gripping device with the suction slot in contact with at least one edge of a side face of the sheet material; pneumatically gripping the sheet material against the contact surface of the gripping device, causing air-suction through the sheet resting means and the sheet material; and holding the sheet material by maintaining air-suction through the porous material of the sheet.

According to the invention, a gripping apparatus has been provided for pneumatically gripping air-permeable sheet material, comprising: air-permeable sheet resting means for supporting a sheet material, said sheet resting means being conformed to allow a passage of an air flux; a pneumatic gripping device having a sheet-contact surface provided with at least one air-suction slot connectable to an air-suction source; means for positioning the pneumatic gripping device with air-suction slot against a side face of a sheet material on said sheet resting means; and air flow control means to connect the air-suction slot of the pneumatic gripping device to the air-suction source.

According to still further feature of the invention, in the event of sheet ma- terial comprising or being impregnated with a resin substance, capable of being brought to a softening temperature, it is possible to provide an initial heating step and the use of heating means suitable for such purpose. BRIEF DESCRIPTION OF THE DRAWINGS

These and further features of the method and the apparatus according to this invention, as well as several exemplificative embodiments, will be more clearly evident from the following description with reference to the drawings, in which:

Fig. 1 shows a first embodiment of an apparatus according to the invention; Fig. 2 shows an enlarged cross-sectional view along the line 2-2 of figure

1 ;

Fig. 3 shows an enlarged cross-sectional view similar to that of figure 2, for a second embodiment; Fig. 4 shows an enlarged cross-sectional view similar to that of the preceding figures, for a third embodiment;

Fig. 5 shows a graph illustrating the variation in the air flow rate in respect to the suction pressure for different materials, or under different conditions for a same material. DETAILED DESCRIPTION OF THE INVENTION

With reference to the various figures, a description will be now given of the general characteristics of the method and the pneumatic gripping apparatus according to the invention, and of several preferential embodiments.

As shown in figure 1 , the apparatus comprises sheet resting means for supporting a sheet material 13, indicated as a whole by the reference number

14, consisting for example of an air-permeable conveyor belt 10 having an upper branch 1OA sliding over a perforated plate 11 to provide a sheet resting surface

12 conformed to allow the passage of an air flux, on which it is possible to rest a sheet 13 of air-permeable material, which must be pneumatically gripped by air- suction, retained, conveyed and/or positioned along a processing line.

In the case of figure 1 the sheet resting surface 12 is in the form of a flat surface defined by the upper branch 10A of the conveyor belt 10; however, the sheet resting surface 12 may be differently made and/or shaped, provided it is suitable for supporting the sheet 13 and allowing an initial air-suction through the surface 12 and the sheet 13, maintaining the latter in a spread out or laid down condition to enable it to be efficiently gripped by suction. Preferably, the resting surface 12 for supporting the sheet 13 must have no-stick properties, if necessary providing for the application of a no-sticking material, such as polytetra- fluoroethylene material, more commonly known by the trade name "Teflon", or other material suitable for such purpose.

The sheet resting means 14 for the sheet material 13 may be shaped in any way whatsoever, provided they are capable of allowing the passage of a sufficient flux of sucked air through the sheet 13 to pneumatically retain the same sheet 13 with a holding force sufficient to sustain, convey and/or position it along a processing line, or for the contemplated use.

For example, in the case of figures 1 and 2, the conveyor belt 10 may comprise a belt of fabric permeable to air, a net, a mesh belt, a perforated belt, or a belt provided with slight longitudinal and/or cross ribbing, to allow the pas- sage of air.

Wherever so required, the apparatus may comprise a heating device 15 conformed and arranged to heat the sheet 13 to a suitable softening temperature for the material of which the sheet is composed, or of a resin with which the sheet 13 may be impregnated. The heating device 15 may be of any suitable type; for example it may consist of radiating elements, disposed in any way whatsoever with respect to the sheet 13; whenever the sheet supporting means 14 are made of material transparent to infrared radiations, the heating device 15 may be positioned beneath such surface, as shown in figure 1. The apparatus also comprises a pneumatically actuable gripping device, to grip the sheet 13 by air-suction; for example the gripping device may comprise a frame 16 movable in the directions of the arrows shown; the frame 16 may have any geometrical shape or configuration, with one or more linear and/or dif- ferently shaped sides to follow both the outline of one or more peripheral edges of the sheet 13, and a flat or three-dimensional configuration of the sheet resting surface 12. Moreover, the frame 16 may be shaped and disposed in such a way as to pick up the sheet material 13 along a single peripheral edge, or along two or more consecutive edges, or on the entire peripheral edge according to need. The frame 16 may be secured to appropriate support means, not shown, for example to a powered articulated arm, to a carriage or other suitable support system enabling it to be moved in the directions of the arrows in figure 1 , either vertically and or horizontally, or in any other suitable direction.

The pneumatic gripping frame 16 may have on a front sheet contact face, one or more air-suction slots 20 connectable to an air-suction source 17, for example a suction fan, by a manually and/or automatically operable flow control valve 18 to control and adjust the air-suction degree in the slot 20, or the flow rate of the sucked air stream, consequently to vary the gripping force on the sheet 13, maintaining it at a required value. A first embodiment and the working mode of a pneumatic gripping device are schematically shown in the example of figure 2.

As can be seen, one side or each side of the gripping frame 16 consists of a metal bar 19, for example of aluminium or other suitable material having a high degree of thermal conductivity in the event of heating being required. The bar 19, on the downwardly facing front side, designed to come into contact with an edge of a side face of the sheet 13, in the case of figure 2 is provided with a single front-open longitudinal slot 20 or sheet gripping or holding channel appropriately shaped to allow an air-suction or pneumatical gripping due to a partial penetration of the sheet 13, as indicated by reference 13A, as soon as the slot 20 is connected to the air-suction source 17.

After the frame 16 has been brought into contact with the sheet 13, air is sucked in the slot 20 through a plurality of holes 22, only one of which is shown in figure 2, aligned in the longitudinal direction of the bar 19. The holes 22 open out both towards the suction slot 20, and towards a first longitudinal duct 23 positioned close to the slot 20, appropriately connect- able to the air-suction source 17 by the valve 18 as mentioned previously.

Lastly, in figure 2, reference 24 has been used to indicate, with broken lines, a second longitudinal duct for circulation of a thermostatically-controlled fluid for heating the bar 19, while reference 25 has been used to indicate two layers of thermally insulating material, disposed on the two sides of the metal bar

19.

A second embodiment is shown in figure 3 where the same reference numbers of figure 2 have been used to indicate similar or equivalent parts. The solution of figure 3 differs from the solution of figure 2 in that on both sides of the slot 20, the bar 19 is provided with a wing 26 to improve the grip of the sheet 13. The wings 26 may be oriented in any direction; preferably the wings 26 are inwardly slanted, so as to form undercut surfaces which allow a mechanical grip on the ribbing 13A of the sheet 13, due to the air-suction into the slot 20; this proves to be advantageous in the case of sheets 13 of considerable weight, thickness or of large dimensions, in that it helps to support the sheet 13 in the event the air-suction being reduced or cut off, due to accidental causes.

The internal surfaces of the slot 20 and of the wings 26 may be lined with a layer 27 of a no-sticking material, such as "Teflon".

In many cases, depending upon the characteristics of the sheets 13 and the nature of the material, it may prove useful to heat and maintain the metal bar 19, or the entire pneumatic gripping frame 16, at a controlled temperature suitable for allowing a localised softening in the contact area or areas with the sheet, or of a resin with which the sheet 13 may be impregnated, in order to prevent uneven heating and stretching conditions on the edges of the sheet during a thermoforming or foaming operation into a mould; the heating and the thermosetting of the pneumatic gripping frame 16 may be achieved in any suitable way, either electrically, or by circulation of a thermal fluid, for example water or air, maintained at an appropriate temperature.

As shown in the example of figures 2 and 3, the heating and the control of the temperature of the bar or bars 19 of the gripping frame 16, can be obtained by circulation of a thermal fluid along a second duct 24 connected to a supply system. Figure 4 of the drawings shows, also by way of example, a third embodiment of the frame 16 of the pneumatic gripping device. In figure 4 the same numerical reference numbers of figures 2 and 3 have been used to indicate similar or equivalent parts.

The solution of figure 4 differs from that of figure 3 in that the bar or each bar 19 which forms the frame 16, is provided with two parallel slots or channel 20 which open out frontally on the contact surface with the sheet material 13; also in this case, the two slots 20 have undercut internal surfaces, and communicate with the air-suction duct 23 by respective holes 22. The solution of figure 4 also differs in that the disposition of the ducts 23 and 24 has been reversed with respect to figure 3.

With reference to figure 7, a more detailed illustration will now be given of the characteristics and advantages of the method and the pneumatic gripping apparatus for air-suction or pneumatically gripping sheets of porous or air- permeable material, according to this invention.

Figure 7 shows a graph illustrating the variation in the negative pressure difference ΔP, in relation to the flow rate Q of suctioned air, depending upon the permeability of the sheet material 13 and the total suction surface of the slot or slots 20. In particular, from figure 7 it can be seen that in relation to the type and characteristics of the air-suction device, and the characteristics of the pneumatic gripping device, in order to have a certain gripping force it is necessary to have a flow rate Q1 of sucked air, operating with a vacuum ΔP1 ; by varying the characteristics or the permeability of the sheet material 13, for example as its perme- ability decreases it will be possible to operate with a flow rate Q2 of sucked air lower than the previous one, which corresponds to a higher suction pressure value ΔP2, so as to generate the same or a greater gripping force.

In any case, unlike the known vacuum-operated gripping systems which are operated with a flow rate Q equal to zero, and for which it is possible to switch off the suction pump once a high vacuum is created, in the case of the pneumatic gripping system according to the invention it is necessary to maintain the air-suction and a certain flow rate Q of the sucked air, in order to maintain or vary the gripping force on the sheet 13. From what has been described and shown in the accompanying drawings, it will be evident that a method and an apparatus have been provided for pneumatically gripping single-layered and/or multi-lagered sheets of porous or air- permeable, capable of achieving a firm and reliable grip, applicable to different manufacturing processes. By way of example and in no way limitative, the pneumatic gripping method and apparatus could be used in thermoforming and/or vacuum moulding processes, in processes for automatic shaping and foaming carpets in the car manufacturing industry, or for other similar applications. The method and the apparatus according to the invention could also be used for carrying out simple operations for conveying and/or positioning sheets, wherever necessary.

The method and the apparatus according to the invention are therefore characterised by their exceptional stability and versatility in pneumatically gripping, conveying and/or positioning, in that they do not call for any substantial modification upon changes in the dimensions and geometrical shape of the sheets, except for the shape and dimensions of the gripping frame 16. The frame 16 may be of the rigid or articulated type, as mentioned previously, to assume a flat and/or three-dimensional shape once the pneumatic gripping has taken place, or to adapt to different working requirements; the internal profile of the air-suction and gripping slots may also vary with respect to the profile shown; therefore other modifications or variations may be made both to the method, and to the apparatus, without thereby departing from the claims.

Claims

1. A method for pneumatically gripping sheets (13) of porous or air- permeable material, comprising the steps of: providing an air-permeable sheet resting means (14) conformed to allow the passage of an air flux; providing a first pneumatic gripping device (16) having a sheet contact surface provided with at least one air-suction slot (29) connectable to an air- suction source (17); arranging a sheet material (13) in a spread out condition on said sheet- resting means (14); positioning the pneumatic gripping device (16) with the suction slot (20) in contact with at least one edge of a side face of the sheet material (13) arranged on the sheet resting means (14); pneumatically gripping the sheet material (13) against the contact surface of the gripping device (16), causing air-suction through the sheet resting means (14) and the sheet material (13); and holding the sheet material (13) by maintaining air-suction through the porous material of the sheet (13).

2. The method according to claim 1 , comprising the step of retaining the sheet material (13) causing penetration of the sheet material (13) into the suction slot (20) of the pneumatic gripping device (16), by the sucked air.

3. The method according to claim 1 , comprising the step of compressing at gripping areas, the sheet material (13) arranged on the sheet resting means (14), by the pneumatic gripping device (16).

4. The method according to claim 1 , comprising the step of heating the sheet material (13) before gripping.

5. The method according to claim 4, further characterised by the step of heating the pneumatic gripping device (15) to a temperature close to the heating temperature of the sheet material (13).

6. The method according to claim 4, characterised by the step of heating the pneumatic gripping device (16) to a temperature within a range comprising the heating temperature of the sheet material (13).

7. The method according to claim 1 , comprising the step of providing the air-suction slot (20) of the pneumatic gripping device (16), with undercut surfaces

(26) and causing the sheet material (13) to adhere to said undercut surfaces (26) by air-suction.

8. A gripping apparatus for pneumatically gripping sheets (13) of porous air-permeable material, comprising: air-permeable sheet resting means (14) for supporting a sheet material

(13), said sheet resting means (14) being conformed to allow a passage of an air flux; a pneumatic gripping device (16) having a sheet-contact surface provided with at least one front-open air-suction slot (20) connectable to an air-suction source (17); means (29) for positioning the pneumatic gripping device (16) with the air- suction slot (20) against a side face of a sheet material (13) on said resting means (14); and air-flow control means (13) to connect the air-suction slot (20) of the pneu- matic gripping device (16) to the air-suction source (17).

9. The gripping apparatus according to claim 8, characterised in that the air-suction (20) slot comprises a lining no-sticking material.

10. The gripping apparatus according to claim 8, characterised by com- prising heating means (15) for heating the sheet material (13).

11. The gripping apparatus according to claims 8, characterised in that said sheet resting means (14) comprises infrared radiations transparent material, and in that the heating means (15) are positioned beneath said sheet resting means (14).

12. The gripping apparatus according to claim 8, characterised in that the pneumatic gripping device (16) is movably supported along a processing line, for holding, conveying and/or positioning the sheet material (13).

13. The gripping apparatus according to claim 8, characterised in that the air-suction slot is provided with undercut internal surfaces (26).

14. The gripping apparatus according to claim 8, characterised in that the pneumatic gripping device (16) comprises heating means (15).

15. The gripping apparatus according to claim 14, characterised in that the gripping device (16) comprises heat control means for controlling the heating temperature.

16. The gripping apparatus according to claim 14, characterised in that said heating means (15) comprise a thermal fluid circulation duct (24).

17. The gripping apparatus according to claim 16, characterised in that the thermal fluid circulation duct (24) comprises thermo regulating means.

18. The gripping apparatus according to claim 8, characterised in that the gripping device (16) comprises at least one frame member consisting of a metal bar (19) having a first longitudinally extending air-suction duct (23), said air- suction duct (23) being in fluid communication with the air-suction slot (20).

19. The gripping apparatus as claimed in claim 19, characterised by com- prising a second duct (24) for the circulation of a thermal fluid.

20. The gripping apparatus according to claim 19, characterised in that the second duct (24) for circulation of the thermal fluid is positioned between the air-suction slot (20) and the air-suction duct (23).

21. The gripping apparatus according to claim 19, characterised in that the air-suction duct (23) is positioned between the air-suction slot (20) and the duct (24) for circulation of the thermal fluid.

22. The gripping apparatus according to claim 18, characterised in that the air-suction slot (20) comprises a lining of no-sticking material.

23. The gripping apparatus according to claim 8, characterised in that the pneumatic gripping device (16) comprises a rigid frame having at least one air- suction slot (20) extending along at least one side.

24. The gripping apparatus according to claim 8, characterised in that the gripping device (16) comprises an articulated frame conformed to change from a flat and a three-dimensional configuration.