WO2020053820A1

WO2020053820A1 - Device and method for gripping objects

Info

Publication number: WO2020053820A1
Application number: PCT/IB2019/057726
Authority: WO
Inventors: Matteo Zoppi; Giorgio Pietronave; Michal JILICH; Alberto BANDINU
Original assignee: Universita' Degli Studi Di Genova
Priority date: 2018-09-13
Filing date: 2019-09-13
Publication date: 2020-03-19

Abstract

The gripping device (10) comprises: a gripping head (12) with a side wall (16) of elastically deformable material encompassing one single working chamber (18) which is open (20) towards one side of the gripping head (12), and with sealing means (22, 24; 34) arranged to ensure airtight closure of the working chamber (18) against an object (O) to be gripped; and a pneumatic circuit (14) connected (30) to the working chamber (18), wherein the pneumatic circuit (14) is arranged to alternately generate inside the working chamber (18) a vacuum state for applying on the object (O) a pull force (F_T) and a pressure state for applying on the object (O) a push force (F_s).

Description

Device and method for gripping objects

FIELD OF THE INVENTION

The present invention relates in general to a gripping device for gripping objects, in partic ular for use on robots and in automation systems. More specifically, the invention relates to a gripping device comprising a suction gripping head and a pneumatic circuit connected to the gripping head.

BACKGROUND OF THE INVENTION

A gripping device of the type indicated above is known, for example, from DE 3516941 Al . According to this known solution, the gripping device comprises:

a gripping head having a first working chamber, a second working chamber ar ranged around the first working chamber, a radially inner sealing lip which encompasses the first working chamber and a radially outer sealing lip which encompasses, together with the radially inner sealing lip, the second working chamber, wherein the two working chambers are open on a side of the gripping head defining a gripping plane and wherein the distal ends of the two sealing lips lie on said gripping plane,

a pressure pneumatic circuit connected to the first working chamber to generate a pressure state inside that chamber, and

a vacuum pneumatic circuit connected to the second working chamber to generate a vacuum state inside that chamber.

This known gripping device is used, in particular, for gripping sheets of porous material (for example paper sheets) from a pile. By virtue of the vacuum state generated inside the second working chamber, the gripping head applies a pull force on the sheet to be gripped, while by virtue of the pressure state generated inside the first working chamber - at the same time as the vacuum state generated inside the second working chamber - the gripping head applies a push force on the underlying sheets, thereby making separation of the first sheet from the underlying sheets easier. As stated above, this known gripping device is adapted to handle light materials, like paper sheets or other porous materials. Furthermore, this known gripping device is particularly complex and expensive, as it has two separate working chambers and two separate pneu matic circuits, with the relating connection conduits extending through the gripping head to connect each pneumatic circuit with the respective working chamber.

WO 2007/046152 Al discloses a gripping device comprising:

a suction gripping head having a side wall which encompasses a working chamber and has an opening through which the working chamber communicates with the external environment,

a pneumatic circuit connected to the working chamber and arranged to alternately generate a vacuum state inside the working chamber for applying a pull force on the object and blow air from the gripping head towards the object to make separation of the object from the gripping head easier,

a plurality of holding arms adapted to hold the object close to the gripping head, in particular underneath it, when the gripping head is detached from the object,

an actuation system associated to the gripping head to control vertical movement of the gripping head relative to the holding arms, and hence relative to the object when the latter is held by said arms.

According to this known solution, the pneumatic circuit is able not only to generate a vac- uum state inside the working chamber of the gripping head to hold the object against the gripping head, but also to blow air through the gripping head towards the object to make separation of the object from the gripping head easier. When the object is not held in con tact with the gripping head by the vacuum state generated inside the working chamber, it is held close to the gripping head by means of the holding arms only.

The gripping device known from WO 2007/046152 Al is, however, rather complex and expensive, since it requires an actuation system to move the gripping head vertically rela- tive to the holding arms. Furthermore, with such a gripping device it is not possible to pressurize the air inside the gripping head, since otherwise the gripping head would be de tached from the object and vent out, and it is not possible, therefore, to apply on the object a push or repulsive force stronger than the minimum force obtained when blowing through the gripping head.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a gripping device that is not affected by the drawbacks of the prior art discussed above.

This and further objects are fully achieved according to the present invention by virtue of a gripping device having the features set forth in independent claim 1.

The invention also relates to a method for gripping an object as defined in independent claim 10.

Advantageous embodiments of the device according to the invention, as well as advanta- geous modes for carrying out the method according to the invention, are defined in the de pendent claims, the subject-matter of which is to be intended as forming an integral part of the following description.

In short, the invention is based on the idea of providing a gripping device comprising: a gripping head having one single working chamber open towards a side of the gripping head, as well as sealing means adapted to ensure airtight closure of the working chamber against the object to be gripped,

a pneumatic circuit connected to the working chamber and arranged to alternately generate inside the working chamber a vacuum state for applying a pull force (i.e. a force directed from the object towards the working chamber) on the object to be gripped and a pressure state for applying a push force (i.e. a force directed from the working chamber towards the object) on the object to be gripped, and

a plurality of abutment members arranged around the gripping head, wherein each abutment member forms a respective abutment surface, against which the object is brought into abutment when the working chamber is pressurized, and is movable between a disengagement position, in which the abutment surface faces laterally away from the gripping head, and a working position, in which the abutment surface faces laterally towards the gripping head to cooperate with the object,

in such a manner that, when the working chamber is pressurized by means of the pneumat- ic circuit and each abutment member is in the working position, the object is held clamped between the gripping head on one side and the abutment surfaces on the other side by the push force applied on the object by the pressure inside the working chamber.

By virtue of such a configuration, the gripping device is thus able both to grip an object to be moved and' to push the object and hold it in abutment against the abutment surfaces of the abutment members. Furthermore, by virtue of the presence of one single working chamber and of one single connection conduit connecting the working chamber to the pneumatic circuit, the gripping head has a simpler structure than the prior art, thereby en suring easier and cheaper manufacturing and servicing of the gripping device.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will become more apparent from the following detailed description, given purely by way of non-limiting example, with ref- erence to the appended drawings, wherein:

Figure 1 is a section view schematically showing a gripping device according to an embodiment of the present invention;

Figures 2 and 3 are section views of two alternative configurations of the gripping head of the gripping device of Figure 1 ; and

Figures 4 to 6 are section views of a further embodiment of a gripping device ac cording to the present invention, in three different operational steps.

DETAILED DESCRIPTION

With reference first to Figure 1, a gripping device according to an embodiment of the pre- sent invention is generally indicated 10. An object or item that may be gripped and held by means of the gripping device 10 is indicated O. The gripping device 10 basically comprises a gripping head 12 and a pneumatic circuit 14 connected to the gripping head 12. In the illustrated example, the gripping device 10 com- prises one single gripping head 12, but it is also possible to provide more than one gripping head, each one connected to a respective pneumatic circuit or, preferably, to one single pneumatic circuit.

The gripping head 12 is a suction-type gripping head and comprises a side wall 16 of elas tically deformable material (for example, of rubber-based material) which laterally encompasses a working chamber 18.

In the embodiment illustrated in Figure 1 , as well as in the other embodiments herein proposed, the side wall 16 has an essentially axisymmetric configuration relative to an axis of symmetry x (which axis is directed vertically in Figure 1 , but may of course have any other orientation). Nevertheless, such a configuration is not essential for the purposes of the pre sent invention, and therefore the side wall 16 of the gripping head 12 may also have a non- axisymmetric configuration.

Furthermore, in the example of Figure 1 the side wall 16 forms a plurality of loops, which are deformable by compression and extension depending on the pressure inside the working chamber 18. The number and shape of the loops will be conveniently chosen depending on the specific application (for example, as it will be clear from the following descrip tion, depending on the axial movement intended to be obtained at the object-side end of the gripping head when shifting from a vacuum state to a pressure state inside the gripping head).

The gripping head 12 has on one side thereof (namely, on the side that in operation faces towards the object O to be gripped and/or held) an opening 20 through which the working chamber 18 in in communication with the external environment. The opening 20 lies on a surface P, which in the illustrated example is a flat surface and will thus be indicated here- inafter as gripping plane for ease of reference. The surface P may, however, be a non-flat surface. Furthermore, even if in the illustrated embodiment there is provided one single opening 20, more than one opening through which the working chamber 18 is in commu- nication with the external environment may instead be provided.

The gripping head 12 is provided with sealing means arranged around the opening 20 to ensure airtight closure of the working chamber 18 when the gripping head 12 is in contact with the object O. Such sealing means are provided at the free end of the side wall 16, i.e. at the end of the side wall 16 arranged on the same side as the opening 20.

In the embodiment of Figure 1 such sealing means are formed by a pair of sealing lips 22 and 24 radially spaced apart from each other, that is to say, a first radially-inner sealing lip 22 and a second radially-outer sealing lip 24. Preferably, the sealing lips 22 and 24 are made in one piece with the side wall 16. As will be clear from the following part of the description, when the working chamber 18 is pressurized, airtight closure between the working chamber 18 and the object O is ensured by the first sealing lip 22, while, when the working chamber 18 is depressurized, airtight closure between the working chamber 18 and the object O is ensured by the second sealing lip 24. The sealing lips 22 and 24 will be conveniently shaped and sized so as not to collapse either when the working chamber 18 is in a vacuum state or when the working chamber 18 is in a pressure state (for example, up to a differential pressure relative to the external environment equal to 6-8 bar approximate ly)·

Figures 2 and 3 schematically show two possible alternative configurations of the gripping head 12. In the configuration shown in Figure 2 the side wall 16 of the gripping head 12 forms a single loop, instead of a plurality of loops as in the configuration of Figure 1 , while in the configuration shown in Figure 3 the sealing means are formed by a ring 34 made in a different material than the material of the gripping head 12, in particular a foam-based material.

The pneumatic circuit 14 is arranged to alternately generate a pressure state or a vacuum state inside the working chamber 18. To this end, according to the proposed embodiment the pneumatic circuit 14 comprises a vacuum pump 26, a compressed air generator 28, a connection conduit 30 in communication with the working chamber 18, and a flow control valve 32 interposed between the vacuum pump 26, the compressed air generator 28 and the connection conduit 30 and selectively switchable between a first working position, in which it puts the vacuum pump 26 into communication with the connection conduit 30, and thus with the working chamber 18, to generate a vacuum state inside that chamber, and a second working position, in which it puts the compressed air generator 28 into communication with the connection conduit 30, and thus with the working chamber 18, to generate a pressure state inside that chamber. By conveniently controlling the flow control valve 32 it is thus possible to control the pressure inside the working chamber 18, generating either a vacuum state or a pressure state inside the working chamber 18.

As shown in Figures 4 to 6, when the gripping head 12 is in contact with the object O, with the opening 20 of the side wall 16 closed by a first surface Si of the object O facing to wards the gripping head 12, generation of a vacuum state inside the working chamber 1 8 (with the sealing means, in this case the sealing lips 22 and 24, ensuring airtight closure of the working chamber 18) causes the gripping head 12 to apply on the object O a pull force FT perpendicular to the gripping plane P and directed towards the inside of the working chamber 18, so that the object O is gripped by the gripping head 12 and may, for example, be lifted and moved by the latter (Figures 4 and 5). When, on the other hand, pressure is generated inside the working chamber 18, the gripping head 12 applies on the object O a push force Fs (Figure 6) directed in the opposite direction with respect to the pull force FT.

Furthermore, as one can see from Figures 1 to 3, the gripping head 12 is configured in such a way that the mouth, that is to say the bottom end portion, of the gripping head 12 has a surface area equal to or greater than the one of the opposite end portion, that is to say the top end portion, of the gripping head. By virtue of such a configuration, when the working chamber 18 of the gripping head is pressurized, the side wall 16 tends to expand radially, without however detaching from the object O with which the gripping head 12 is in contact. The gripping head 12 is thus kept in contact with the object O even when the air pres sure inside the working chamber 18 is higher than the atmospheric one, thereby applying on the object O a push force having a magnitude that is proportional to the difference between the air pressure inside the working chamber 18 and the atmospheric pressure.

With reference again to Figures 4 to 6, the gripping device 10 further comprises abutment members 36 arranged to cooperate with the gripping head 12 to allow, once the object O has been gripped, to firmly and securely hold the object. The abutment members 36 are ar ranged around the gripping head 12, preferably with a symmetric arrangement relative to the same (for example, three abutment members arranged at 120 degrees to each other).

Each abutment member 36 forms a respective abutment surface 36a (that, in the embodiment shown in Figures 4 to 6, is formed by a disc-shaped portion of the abutment member) against which the object O is brought into abutment by the gripping head 12 to be held in position between the gripping head 12, on one side, and the abutment surfaces 36a of the abutment members 36, on the other one. In this connection, it should be noted that, as shown in Figure 4, the gripping device 10 is configured in such a manner that in the non- deformed condition of the side wall 16 of the gripping head 10 the opening 20 with the associated sealing means (sealing lips 22 and 24) is underneath the abutment members 36, in particular underneath the abutment surfaces 36a.

Each abutment member 36 is movable between a disengagement position (Figures 4 and 5), in which the respective abutment surface 36a faces laterally (i.e. radially) away from the gripping head 12, so as not to prevent the object O from moving in a direction perpen dicular to the gripping plane P and thus allow, for example, the gripping head 12 to grip the object O and move it towards the end (in this case, the top end) of the gripping head 12 opposite to the opening 20, and a working position (Figure 6), in which the respective abutment surface 36a faces laterally (i.e. radially) towards the gripping head 12, in particu- lar towards the opening 20, so as to allow the gripping head 12 to push the object O against such surface. In the embodiment shown in Figures 4 to 6, movement of each of the abutment members 36 between said disengagement and working positions is a rotational movement about a respective axis of rotation parallel to the aforementioned axis x. Con figurations of the abutment members different from the one herein illustrated may however be envisaged.

In an initial phase (Figure 4), with the abutment members 36 in the disengagement posi tion, the gripping head 12 of the gripping device 10 may thus be positioned with the sealing means (in this case, the two lips 22 and 24) in contact with the first surface Si of the object O to be gripped, so as to close the opening 20. With the opening 20 closed by the same object O, a vacuum state may be generated inside the working chamber 18 by con veniently controlling the vacuum pump 26 and the flow control valve 32, so that a pull force FT is applied on the object O such as to ensure that the object be held in contact with the gripping head 12.

By increasing the vacuum state inside the working chamber 18, the pull force FT applied by the gripping head 12 on the object O is correspondingly increased. The object O may thus be further moved along the axis x towards the gripping head 12, with a resulting elas tic deformation of the side wall 16 of the gripping head, until it passes beyond the abut- ment surfaces 36a of the abutment members 36 (Figure 5).

At this point, each abutment member 36 is moved from the disengagement position to the working position and the gripping head 12 may thus urge the object O, with a second surface S₂ opposite to the first surface Si, into abutment against the abutment surfaces 36a of the abutment members 36. To this end, the vacuum pump 26 is deactivated, the com pressed air generator 28 is activated and the flow control valve 32 is moved into said second position to put the compressed air generator 28 into communication with the working chamber 18, through the connection conduit 30, so that the gripping head 12 applies a push force Fs on the object O, thus keeping the object O clamped between the gripping head 12, on one side, and the abutment surfaces 36a of the abutment members 36, on the other one (Figure 6).

As is clear from the above description, by virtue of a gripping device according to the invention it is possible to bring the two functions of gripping and holding of the object to gether into a single gripping head, thereby reducing the complexity of the gripping device accordingly.

Moreover, a gripping device according to the invention allows quicker separation of the object from the gripping head than the prior art. In fact, since in the camped condition the object is pushed against the abutment surfaces of the abutment members by the pressure generated inside the working chamber of the gripping head, as soon as the abutment mem- bers are moved from the working position to the disengagement position, the object is very quickly ejected away from the gripping head as a result of the push force generated on the same by the pressure inside the working chamber. Separation of the object from the grip ping head is therefore substantially instantaneous.

Naturally, the principle of the invention remaining unchanged, the embodiments and con- structional details may vary widely from those described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the appended claims.

Claims

1. Gripping device ( 10) for gripping objects (0), comprising:

a gripping head (12) having a side wall (16) of elastically deformable material, which encompasses one single working chamber (18) and has at least one opening (20) through which the working chamber (18) is in communication with the external environment, and sealing means (22, 24; 34) associated to said at least one opening (20) to ensure airtight closure of the working chamber (18) against the object (O) to be gripped,

a pneumatic circuit (14) connected to the working chamber (18) and arranged to alternately generate inside the working chamber (18) a vacuum state for applying a pull force (FT) on the object (O) and a pressure state for applying a push force (Fs) on the object (O), and

a plurality of abutment members (36) arranged around the gripping head (12), wherein each abutment member (36) forms a respective abutment surface (36a), against which the object (O) is brought into abutment when the working chamber (18) is pressur ized by means of the pneumatic circuit (14), and is movable between a disengagement position, in which the abutment surface (36a) faces laterally away from the gripping head (12), and a working position, in which the abutment surface (36a) faces laterally towards the gripping head (12) to cooperate with the object (O),

the gripping device (10) being configured in such a manner that, as the working chamber (18) is pressurized by means of the pneumatic circuit (14) and each abutment member (36) is arranged in the working position, the object (O) is clamped between the gripping head (12), on one side, and the abutment surfaces (36a), on the other one, as a result of the push force (Fs) applied on the object (O) by the pressure in the working chamber (18).

2. Device according to claim 1 , wherein said sealing means (22, 24; 34) comprise a pair of sealing lips (22, 24), that is to say, a first radially-inner sealing lip (22) and a second radially-outer sealing lip (24), which are formed in one piece with the side wall (16) of the gripping head (12).

3. Device according to claim 1, wherein said sealing means (22, 24; 34) comprise a ring (34) of foam material.

4. Device according to any one of the preceding claims, wherein the pneumatic circuit (14) comprises a vacuum generator (26), a compressed air generator (28), a connection conduit (30) in communication with the working chamber (18) of the gripping head (12) and valve means (32) for selectively connecting the connection conduit (30) each time with either one of said vacuum generator (26) and compressed air generator (28).

5. Device according to any one of the preceding claims, wherein each of the abutment members (36) is rotatable about a respective axis of rotation, in such a manner that move- ment between said disengagement and working positions is a rotational movement about said axis of rotation.

6. Device according to any one of the preceding claims, wherein the side wall (16) of the gripping head (12) has an axisymmetric configuration with respect to an axis of sym metry (x).

7. Device according to claim 6, wherein the axis of rotation of each abutment member (36) is parallel to said axis of symmetry (x).

8. Device according to any one of the preceding claims, wherein said at least one opening (20) of the gripping head (12) lies on a flat surface (P).

9. Device according to claim 8, wherein the axis of rotation of each abutment member (36) is perpendicular to said flat surface (P).

10. Method for gripping an object (O), comprising the steps of:

a) moving the gripping head (12) of a gripping device (10) according to any one of the preceding claims close to a first surface (Si) of the object (O), so as to bring said sealing means (22, 24; 34) of the gripping head (12) into contact with said first surface (Si);

b) generating, by means of the pneumatic circuit (14), a vacuum state inside the work- ing chamber (18) of the gripping head (12) so as to apply a pull force (FT) on the object (O);

c) positioning the abutment members (36) in the working position so as to arrange the abutment surfaces (36a) of the abutment members (36) in front of a second surface (S₂) of the object (O) opposite to said first surface (Si); and

d) generating, by means of the pneumatic circuit (14), a pressure state inside the work ing chamber (18) of the gripping head (12) so as to apply a push force (Fs) on the object (O) such as to urge the object (O) with said second surface (S₂) into abutment against the abutment surfaces (36a) of the abutment members (36), in such a manner that the object (O) is clamped between the gripping head (12), on one side, and the abutment surfaces (36a) of the abutment members (36), on the other one, as a result of said push force (Fs).