WO2003035336A1

WO2003035336A1 - Device for gripping a part, and method for making same

Info

Publication number: WO2003035336A1
Application number: PCT/FR2002/003615
Authority: WO
Inventors: Dominique Moule; Laurent Berthellemy; Francesco Di Mino
Original assignee: Bema Ingenierie
Priority date: 2001-10-22
Filing date: 2002-10-22
Publication date: 2003-05-01
Also published as: FR2831087A1; FR2831087B1; EP1438162A1

Abstract

The invention concerns a gripper device comprising a frame (12) having an interface (22) capable of being fixed to a displacement member (14) and supporting at least a gripping member (16) for maintaining a part (P) in a geometric position defined relative to the frame. The frame (12) comprises at least a shaped element (18, 20) produced in a sintered material obtained by locally melting a powder material by heat input. The inventive gripper device is particularly useful on motor vehicle assembly lines..

Description

Device for gripping a part, and method for manufacturing it

The invention relates to the field of gripping devices used for handling parts.

It relates more particularly to a gripping device of the type comprising a frame which has an interface suitable for being fixed to a displacement member and which supports at least one gripping member suitable for holding the part in a geometrical position defined with respect to the frame.

Such gripping devices, also called grippers, are used mainly on industrial assembly lines to move a part from a first location, for example a storage location, to a second location, for example a final mounting location.

This is how these devices find a preferential application in the assembly lines of motor vehicles to set up a part on a vehicle during assembly.

The frame of such a device is generally fixed, via its interface, to a robot arm or to a similar displacement member to move the frame and the part that it supports between the two locations mentioned.

The frame supports one or more gripping members, such as clamps or clamps, suction cups, etc., which serve to grip the workpiece and hold it in a geometrical position defined precisely with respect to the frame, during all displacement.

One of the essential requirements is to ensure precision when the part is removed and especially when it is put in place, so that it can be placed in a specific location, especially when it comes to positioning a part on a vehicle during assembly. This therefore supposes to ensure jointly a precision of the displacement member and a precision of the gripping device. By way of example, on a motor vehicle assembly line, the precision required is generally of the order of tenths of a millimeter.

In known gripping devices, the frame is produced by different means, for example from mechanically welded metal elements, steel or aluminum, produced specifically according to the given definition plane.

It is also known to produce the frame by assembling standard modules managed from stock and by making specific parts.

In addition, it is known to produce the frame by assembling various profiles (extruded tubes, cylindrical tubes cut to length) using standard junction elements by screwing, pinching or other means, and by making specific parts of the frame. interface and fixing for the holding elements.

Indeed, each gripping device constitutes a specific element, the frame of which is also produced in a specific way to allow the gripping member (s) to be supported in well-defined geometric positions relative to the frame, and therefore relative to the gripping member. displacement (robot or the like).

This traditional design of gripping devices requires managing a certain number of parts in stock, then assembling these parts, possibly with specific elements, to produce a frame of good geometric profile. defined.

This therefore requires a significant time for production and assembly.

In addition, it may happen, accidentally, that the frame is distorted in service.

This then requires dismantling the frame to either repair it or replace it with another identical or similar frame.

This results in significant downtime, during which the assembly line is not operational.

The object of the invention is in particular to overcome the aforementioned drawbacks.

To this end, it proposes a gripping device of the type defined in the introduction, in which the frame comprises at least one shaped element made of a sintered material obtained by localized melting of a powdered material by the addition of heat.

Thus, the frame of the device of the invention is radically different from the traditional frames made by assembling mechanical elements.

The frame of the invention is made from at least one shaped element, that is to say made to the shape, by a sintering technique using a powder material capable of being sintered thermally.

As such, preference is given to a material sintered by a laser beam.

Until now, these sintered materials have been used essentially for rapid prototyping, that is to say for the production of prototypes, which can have very complex, by a thermal sintering technique, and very particularly a laser sintering technique.

It will be recalled that such a sintering technique consists in depositing a first thin layer of a polymerizable powder material, sintering the material of this first layer along a defined surface by means of a laser beam which comes to sweep this first layer, depending of data stored in a computer. Next, a second layer is deposited which is sintered under the same conditions, and according to another defined surface, and so on.

In this way, a part can be produced in three dimensions, possibly with hollow parts, the shape of which exactly corresponds to a shape whose characteristics have been digitized, recorded and stored in a computer. Such a technique makes it possible to produce parts of complex shape which are difficult, if not impossible, to be produced by traditional techniques.

However, this technique has so far not been used to produce industrial parts in large series, because it lends itself essentially to the production of prototypes.

However, in a gripping device, of the type defined above, each frame constitutes a very specific specific element which is generally produced in one copy, or in a very small number of copies.

The Applicant has found that such a prototyping technique could be used to make a frame from one or more shaped elements, that is to say made with very specific shapes, in sintered material, without compromising the mechanical properties of the frame.

Advantageously, the sintered material is chosen from polyamides, sinterable metallic materials, aluminum and polymerizable carbon.

Consideration is particularly given to a fine polyamide, optionally charged, in particular by glass beads.

In one embodiment of the invention, the frame comprises at least one arm connected to the interface and supporting at least one gripping member. The arm can be connected to the interface by fixing means, for example mechanical means and / or bonding means. These bonding means in this case use an adhesive adapted to the sintered material used.

It is also conceivable that the arm is formed in one piece with the interface, the latter then also being made of sintered material. The arm can be completely full. It is advantageous, however, to reduce the weight of the arm, to make it hollow, possibly with internal spacers. This makes it possible to save material, while designing an arm of sufficient mechanical strength.

This does not prevent the arm itself from being made in one piece, or possibly in several pieces.

Therefore, all combinations are possible. One can, for example, have two arms fixed to the interface, one arm fixed to the interface and another made in one piece with it, two arms made in one piece with the interface, etc.

It is advantageous that the frame is surrounded by a protective coating, for example a metallized coating, or even by an added coating, to allow the device to resist an aggressive environment (for example oil splashes, sparks, etc.).

According to another characteristic of the invention, the frame comprises at least one passage accessible from the outside made in an element shaped to receive a cable or a conduit Power. The sintering technique makes it possible to produce selected shapes, and this is the case for a passage accessible from the outside.

In one embodiment of the invention, each gripping member is produced in the form of a clamp comprising a fixed part connected to the frame and a mobile part capable of displacement relative to the fixed part.

In such a case, the fixed part of the clamp can be fixed to the frame or it can also be made in one piece with the frame.

The interface of the device of the invention is susceptible of numerous variants. It may especially be an open box with several faces, at least one of which is provided with cable passage means.

This interface is arranged to be fixed to the end of a robot arm or the like.

In another aspect, the invention relates to a method of manufacturing a gripping device as defined above, this method comprising the operations consisting in:

a) establish a three-dimensional digital model of the device, in particular of the frame, to constitute a data file; and b) making the frame, from the data in this file, by a sintering technique using a powder material capable of being sintered thermally.

Preferably, this sintering technique is a laser technique. The laser used is advantageously a C0 ₂ laser or a YAG laser. In the description which follows, given by way of example, reference is made to the appended drawings, in which:

- Figure 1 is a simplified perspective view showing a gripping device according to the invention fixed on a robot arm and used to move a part;

- Figure 2 is a perspective view of the gripping device, without its holding members; - Figure 3 is a plan view of the gripping device of Figure 2;

- Figure 4 is a side view of the gripping device of Figures 2 and 3;

- Figure 5 is another side view of the gripping device of Figures 2 and 3;

- Figure 6 is a sectional view along line VI-VI of the

Figure 3; and

- Figure 7 shows the detail VII of Figure VI, on an enlarged scale.

First, reference is made to FIG. 1 which shows a gripping device 10 according to the invention, comprising a frame 12 fixed to a displacement member 14, here a robot (shown diagrammatically). The device 10 comprises, in the example, two gripping members 16 for supporting a workpiece P. The gripping members 16 each consist of any suitable member, for example a clamp or clamp, a suction cup , etc. In the example, each of the gripping members is produced in the form of a clamping clamp comprising a fixed part 16a and a movable part 16b capable of being moved relative to the fixed part.

The function of the gripping device is to take a part P from a first location, for example a storage location, in order to move it to a second location, for example a mounting location. By way of example, the part P can be a component of a motor vehicle which is taken from a storage reserve and is then precisely positioned on a vehicle during assembly.

Reference is now made to Figures 2 to 6 to describe the structure of the frame 12 of the aforementioned device 10. In the embodiment shown, the frame 12 comprises two shaped elements 18 and 20 (also called arms) which are connected to an interface 22 intended to be fixed, in a specific location, to the end of the robot 14. In the example shown, the interface 22 is produced in the form of an open box, of generally parallelepipedal shape, comprising a bottom face 24 on which four lateral faces depend, namely two large faces 26 and 28 and two small faces 30 and 32. The bottom face 24 is designed to be fixed to the end of the robot arm 14 and for this purpose it comprises suitable fixing means, in particular holes 31 and positioning grooves 33 (Figure 3). This allows the interface 22 to be locked in a precise position on a mounting interface (not shown) carried by the robot 14.

The faces 26 and 28 are used for fixing the arms 18 and 20 respectively. In the embodiment, the frame is formed exclusively from shaped elements made of sintered material by a rapid prototyping technique, by a laser technique . The sintered material is advantageously chosen from polyamides, sinterable metallic materials, aluminum and polymerizable carbon.

In the example, it is advantageous to use a fine polyamide, optionally charged, in particular with glass beads. As such, polyamide 6-6 is essentially considered. In the example shown, all the elements, including the interface 22, are made of sintered material. However, it is also conceivable to produce the interface in the traditional way by molding or machining of an appropriate metallic material.

In the example shown, the arm 18 first comprises two branches 34 and 36, the ends of which are connected to the large face 26. These two branches 34 and 36 are produced in a single piece with the interface. As can be seen in Figure 2, the branches 34 and 36 are hollow and are provided with internal braces 38 which extend over their entire length to impart better rigidity. The branches 34 and 36 thus have two respective ends 40 and 42 which are attached to the large face 26. They also have two bent ends 44 and 46 on which is stuck an attached element 48 which is advantageously produced by laser sintering, but which could also be produced in a part molded from another material, for example aluminum. Bonding is carried out with an adhesive suitable for the sintered material used. In the case of a material of the polyamide type, an acrylic adhesive is advantageously used.

This insert 48 is formed by two half-shells 48a and 48b and it comprises two cylindrical ends 50 and 52 in which the bent ends 44 and 46 are fitted respectively, and another cylindrical end 54 which receives an end arm 56 having an evolutive shape and ending with an interface 58 on which one of the gripping members 16 can be fixed. To this end, this interface is made flat and has a certain number of holes 60 for screws or the like, which serve, in the example to the fixing of the fixed part 16a of a gripping member.

In an alternative embodiment, the interface 58 could itself constitute a part of the holding member. Thus, in the case where the holding member is a collet having a fixed part 16a and a movable part 16b, this fixed part 16a can be made in one piece with the arm 18, that is to say here with the end arm 56.

The arm 20 is also produced by a laser sintering technique using a sintered material. The arm 20 comprises two branches 62 and 64, generally parallel, each terminated by a base 66, respectively 68, of generally square shape. Each of these bases is intended to be fixed on the large face 28, for example by mechanical fixing and / or bonding. Each of these bases includes four holes which allow the installation of screwed elements. Of course, it is conceivable to produce the two branches 62 and 64 in one piece with the face 28.

The branches 62 and 64 are reinforced by internal braces 65 (Figures 6 and 7) and are extended by an end arm 70 which is made in one piece with these branches. This end arm is reinforced by internal braces and it has an end 72 in which is fitted an elbow element 74 having internal braces 75 (Figures 5 and 6) and terminated by an interface 76. The elbow element 74 and l 'interface 76 are made in one piece by laser sintering.

The interface 76 includes a number of holes 78 to allow the fixing of the fixed part 16a of the other gripping member. As already indicated, the interface 78 could constitute a part of a gripping member, in particular in the case where this comprises a fixed part 16a and a mobile part 16b.

The elbow element 74 and the interface 76 are made in one piece, while the element 74 is attached and glued to the end 72 of the end arm 70. It is conceivable that the elbow element 74 and the arm end 70 have complementary nesting shapes which allow, during assembly, precise positioning of the element 74 relative to the arm 20. The bonding is carried out with a suitable adhesive, here an acrylic adhesive.

Furthermore, as can be seen in Figure 3, the side faces of the interface have different openings 80 forming cable passage to allow power electric and / or pneumatic of the gripping members.

The frame shown in Figures 2 to 6 is one example among others of a frame capable of being produced according to the invention. The basic principle is to produce the frame from at least one shaped element, that is to say having a precise shape, made of a sintered material. For a space-saving frame, it is possible to make the whole frame in one piece. However, depending on the size of the frame and the possibilities of the prototyping machine, it will often be necessary to make the frame in several elements. Thus, the interface can, depending on the case, either be made of sintered material, or be made of a traditional material. The rest of the frame may, in some cases, be made in one piece with this interface for reasons of simplification.

To manufacture a gripping device as defined above, a three-dimensional (3D) digital model of the device and in particular of the frame is established. This makes it possible to form a shape which connects the interface used for fixing to the robot or the like, to the gripping members which are necessary to hold the part. These gripping members can be constituted, for example, by clamping members, pliers, multifunction pilots, linear pilots, pivoting flanges, suction cups, etc. The shape of the elements is chosen to have sufficient rigidity to ensure the grip of the part to be handled, without deformation, ensuring repeatability.

The shape is defined using finite element calculation software to optimize its inertia, its weight and its mechanical strength. The profile of this link does not take into account a conventional embodiment on a machine but allows impossible embodiments according to traditional techniques. It allows in particular to produce elements with hollow bodies ribs of progressive shape having, for example, a cylindrical shape at one end and a parallelepiped section at another.

The realization of the elements is possible after 3D digitization in CAD (computer aided design) of the model and by direct exploitation of the data file thus obtained, in a prototyping machine, and this without carrying out a definition plan. This eliminates the risk of dimensional errors on plans, during machining or assembly.

The frame is then produced by sintering a sinterable material according to a rapid prototyping technique from the data in this file. Sintering is carried out layer by layer by providing thermal energy each time on a precisely defined surface. Various types of prototyping machines operating by laser sintering are commercially available which may be suitable for implementing the invention. These known machines most often operate with a C0 ₂ laser or with a YAG laser. They use a sinterable powder material which is spread out to form a first thin layer on which a laser beam is swept along a defined surface whose characteristics are stored in a computer, and then we proceed in the same way, layer by layer to make the desired piece.

These machines have limited capacities in terms of dimensions of the parts to be produced. This is the reason why, for large frames, it will be necessary to make them in several parts and then to assemble them by mechanical assembly and / or gluing techniques.

The shape made allows, among other things, to include the passage of cables or conduits protected by the shape itself. Figures 6 and 7 show the section of an arm, here the arm 64, made hollow and having a groove 82 accessible from the outside to form a passage for a cable or a conduit 84 extending along the arm. It is also possible to form projecting elements to ensure the maintenance of such a cable or conduit in a defined position. The cable or conduit can be for example an electric cable, a compressed air conduit, etc.

The materials used for the different elements are variable depending on the desired mechanics. Polyamide, for example polyamide 6-6, preferably loaded, will be used very particularly.

After completion of the frame, it is conceivable to protect it with an appropriate coating, in order to limit the risks entailed by projections of material of any kind, for example oil projections or sparks projections. As coatings, consideration is given in particular to a metallized coating, for example a chrome plating, or else an added coating forming a protective sheath.

The advantage of the invention is the total absence of stock. A single digitization allows the identical production of an infinite number of gripping devices. A possible modification of an assembly produced can be integrated by gluing on the existing elements.

In the event of damage to the frame, for example following an impact, it is conceivable to replace this frame purely and simply with a new frame, or even a part of the frame with a new piece of sintered material. The advantage is that we have a digital file of the characteristics of the frame which allows to realize a new frame strictly identical to the initial frame.

The invention finds particular application in the field of gripping devices used in the automotive industry.

Claims

claims

1. Device for gripping a part, of the type comprising a frame (12) which has an interface (22) suitable for being fixed to a displacement member (14) and which supports at least one gripping member (16) to keep the part (P) in a defined geometrical position relative to the frame,

characterized in that the frame (12) comprises at least one shaped element (18, 20) made of a sintered material obtained by localized melting of a powdered material by adding heat.

2. Device according to claim 1, characterized in that the material is sintered by a laser beam.

3. Device according to one of claims 1 and 2, characterized in that the sintered material is chosen from polyamides, sinterable metallic materials, aluminum and polymerizable carbon.

4. Device according to one of claims 1 to 3, characterized in that the sintered material is a fine polyamide, optionally charged, in particular by glass beads.

5. Device according to one of claims 1 to 4, characterized in that the frame comprises at least one arm (18, 20) connected to the interface (22) and supporting at least one gripping member (16).

6. Device according to claim 5, characterized in that an arm (20) is connected to the interface (22) by fixing means (66, 68).

7. Device according to claim 6, characterized in that the fixing means comprise mechanical means and / or bonding means.

8. Device according to claim 5, characterized in that an arm (18) is formed in one piece with the interface (22).

9. Device according to one of claims 5 to 8, characterized in that the arm (18, 20) is hollow.

10. Device according to one of claims 5 to 9, characterized in that the frame (12) comprises two arms (18, 20) connected to the interface (22) and two gripping members (16) carried respectively by the two arms.

11. Device according to one of claims 1 to 10, characterized in that the frame (12) is surrounded by a protective coating.

12. Device according to one of claims 1 to 11, characterized in that the frame (12) comprises at least one passage (82) accessible from the outside produced in an element shaped to receive a cable or a supply conduit .

13. Device according to one of claims 1 to 12, characterized in that each gripping member (16) is produced in the form of a clamp comprising a fixed part (16a) connected to the frame and a mobile part (16a) capable of moving relative to the fixed part.

14. Device according to claim 13, characterized in that the fixed part (16a) of the clamp is fixed to the frame (12).

15. Device according to claim 13, characterized in that the fixed part (16a) of the clamp is made in one piece with the frame (12).

16. Device according to one of claims 1 to 15, characterized in that the interface (22) is an open box with several faces (26, 28, 30, 32), at least one of which is provided with means for cable passage (82).

17. Device according to one of claims 1 to 16, characterized in that the interface (22) is arranged to be fixed to the end of a robot arm (14) or the like.

18. A method of manufacturing a gripping device according to one of claims l to 17, characterized in that it comprises the operations consisting in:

a) establish a three-dimensional digital model of the device, in particular of the frame, to constitute a data file; and b) making the frame by sintering a sinterable material according to a rapid prototyping technique, from the data in this file.

19. The method of claim 18, characterized in that the sintering of operation b) is a laser sintering.