Clamping method and device for carrying out the same

Abstract

 In order to increase the clamping force on a piece of sheet metal to be machined and the productivity of a press brake that bends it, a method is proposed to lock the piece (L) on a mobile loader suitable for positioning the piece on the press brake, in which a clamping force is applied to the piece having a direction that is substantially parallel to a longer dimension of the piece.

Description

[0001] The invention concerns a method for clamping pieces while they are being manufactured (in particular metal sheets) in a press brake. The invention also concerns a clamping device that achieves the method, in particular a clamp of a robot manipulator used to load the pieces in the press brake.

[0002] Press brakes are formed by a punch that can move vertically and that is forcibly inserted into a corresponding matrix. The metal sheet is grasped with a robotic arm from a loading plane and is transported above the matrix to then be bent by the punch. See for example the presses in GB784981 and EP0476092.

[0003] The arm is able to grasp the metal sheets by means of an end clamp.

[0004] Known types of clamps, see figure 1, are formed by a clamp body 10 with a pneumatic or hydraulic cylinder 12 inside that moves the jaws 14 through inclined planes 16 or racks (not shown). As can be seen, the jaws 14 clamp a metal sheet (L) pressing its thickness.

[0005] These clamps not only are very expensive due to the complexity of the structure, but also have many problems.

[0006] In order to supply a press brake the bulk of the clamp is proportional to that of the piece to be clamped. For small pieces the clamp is miniaturised and is not able to develop sufficient clamping force, especially due to the transmissions in the internal kinematic system and to the smaller pneumatic or hydraulic thrust available. Consequently, on a fast robot, the clamped piece moves losing precision in the bending or extension of the machine cycles for repositioning the piece. In any case, since it is necessary to ensure a minimum clamping force, the dimensions of the clamp are not able to drop below a certain limit. For particularly small pieces the minimum dimensions available for the clamp are still too large, and prevent fast and uninterrupted manipulation of the piece below or near to the punch. Both with these clamps, and when grasping members with suction cups (which have, however, small grasping forces) are used, for the robot, which always operates on the same side of the press, there is always the drawback of having to release the piece below the press and picking it up again in a different point. This occurs especially for pieces to be machined with adjacent bending lines and opposite bending directions. It should be understood that the numerous successive picking up operations of the robot jeopardise the precision of positioning of the piece.

[0007] The invention has the main purpose of solving the problem of the poor clamping force.

[0008] The problem is solved with a method according to claim 1.

[0009] By applying a clamping force to the piece in a direction that is substantially parallel to one of its longer dimensions makes it possible to increase the grasping stability, for example pushing or pulling the piece against an abutment and/or inside a matching seat.

[0010] It is possible to only act upon one edge of the piece, for example hooking and pulling on to an expendable eyelet or a hole, or to clamp it on at least two points of the edge. By edge here, we mean the outline that defines a larger face of the piece or metal sheet.

[0011] Greater steadiness in the press is obtained when on the piece the clamped points are either on opposite sections of edges or on ends of the piece.

[0012] In particular, with the variant of claim 4 it is always ensured that the piece does not rotate since it is kept in contact with an abutment which rotationally constrains it.

[0013] In order to achieve a method a device according to claim 5 can be used.

[0014] The device can have many variants, see figures 2-5. It can be built (figure 2) to pull a piece L towards a groove 20 of a fixed reference 22 and lock it there. The piece is pulled for example by a claw 24 actuated by actuator means containing a main body 26. The pulling or pushing direction in the figures is indicated with arrows.

[0015] Or the device (figure 3) can have:

a body 30,

a segment 34 that extends the body 30 for a certain distance mainly along an axis X,

an abutment 28 for the piece L,

a pushing member 36 that is mounted on the segment 34 and can be moved towards the abutment 28 in a direction that is substantially parallel to the axis X.

[0016] The abutment 28 can be an element present on the main body 30 and/or on the segment 34.

[0017] The pushing member 36 has the function of pressing on an edge of the piece L so as to push one opposite edge against the abutment 28. It should be noted that the member 36 could be made integral with the segment 34, then moving the latter so as to clamp the piece L.

[0018] For all the variants described, the pushing member 36 can be moved in various ways and with actuator means, for example, hydraulically, magnetically or pneumatically. For the sake of simplicity and in order to obtain maximum clamping force, a hydraulic cylinder or piston 38 with controlled movement is placed inside the body 30 and it is connected with the pushing member 36 so as to transfer linear motion to it.

[0019] For all the variants described, preferably the movement direction of the actuator means is substantially parallel to the axis X, or rather to the axis along which said segment projects, and parallel to the direction of linear movement of the pushing member. The fact that they are parallel, which implies the absence of power transmissions or intermediate kinematics, makes it possible to advantageously increase the clamping force.

[0020] In order to simplify the inner construction of the body 30 and eliminate power transmissions, the cylinder 38 can be connected to the pushing member 36 in a point P that is outside with respect to the body 30, and transfers motion to it for example through a rod 40 or an equivalent rigid connection (in order to avoid transmissions and direction changes of the force applied by the cylinder 38). The pushing member 36 can comprise a hook-shaped or grooved portion so as to better engage and/or pull the piece L on its edge against the abutment 28.

[0021] The piece L can be pulled towards an abutment with one (as in figure 4) or more pulling segments, for example two as in figure 5. Here the two segments 34 extend from the body 30 separated and parallel to one another, and their pushing members 36 are actuated by a single cylinder 38 by means of a rigid connection, for example in the shape of a T-junction indicated with 33. It should be noted that this provision eliminates the problem of synchronising many clamping devices, which would move the piece, moving in an uncoordinated manner.

[0022] It can be seen in the examples that it is the larger surface of the piece L that is clamped at the sides and not the thickness. This configuration in general gives greater stability. However, it is also possible to grasp the piece with the device according to the invention by the thickness, in virtue of the strengthened clamping force.

[0023] In order to improve again the stability of the manipulated piece L, one or each segment 34 can comprise a portion, for example flat or shaped in a matching manner, which can rest transversally (i.e. for example from one side to the other, in width) on a larger surface of the piece L.

[0024] Since it is advantageous to construct a single body 30 to actuate the pushing members 36 irrespective of the number or shapes of the pulling segments 34, it is preferable for one or each segment 34 to be removably coupled with the body 30. It is thus sufficient to equip an invariable body 30 with the segment/s 34 necessary for the current machining so as to obtain a manipulator device suitable for the specific piece.

[0025] It is advantageous for a pushing member 36 to be mounted on a relative segment 34 with a certain clearance, so as to automatically adapt to possible tolerances or defects of the piece L. When the member 36 starts to be pulled, the clearance is nullified and the piece is perfectly clamped. Amongst the advantages of the invention we underline:

• the steadiness of the hold of the device makes the positioning of the piece very precise, to the point that the centring systems on the press can be eliminated, especially for small pieces;
• the device has great clamping force but a small bulk, therefore a manipulator robot which is equipped with it is able to work very near to the punch during pressing. This means that both very small pieces can be bent, and the robot no longer needs to release the piece to carry out complicated bending, and therefore the bending precision is increased.

[0026] The advantages of the invention shall be made clearer from the following description of one preferred embodiment of a clamp for robots, with reference to the attached drawings, in which:

• Fig. 1 schematically shows a side view of a known clamp,
• Fig. 2 schematically shows a side view of a device according to the invention,
• Fig. 3 schematically shows a variant for the device of fig.2;
• Fig. 4 schematically shows a plan view of the device of fig. 3,
• Fig. 5 schematically shows a variant for the device of fig.3;
• Fig. 6 shows a section view of a variant for a device according to the invention;
• Fig.7 shows a section view of a second variant for a device according to the invention;
• Fig.8 shows an isolated component of fig.7.

[0027] Fig. 6 shows a clamp 50 for grasping a metal sheet L. It comprises a cylindrical clamp-body 70 to which, through screws, a flat segment 56 can be connected, resting on the piece L.

[0028] A plunger 52 fixedly connected to a stem 54, the free end of which projects from the body 52, is dynamically mobile inside the body 70 and it connects, through for example interlocking coupling or screwing, to a shaft 62 on the end of which a claw or hook 58 is mounted.

[0029] By actuating the plunger 52, the hook 58 can come closer to the body 70, pushing the piece L towards an abutment 60 and clamping it in position.

[0030] Fig. 7 shows another clamp 80 for grasping the metal sheet L. It comprises a cylindrical clamp-body 82 to which a support 84 for a hook 86 can be connected through screws. The hook 86 is slidingly guided above the support 84 and it can move thanks to the force given to it by a shaft 90 that is fixedly attached to a plunger 88 housed inside the body 82 and hit by pressurised fluid or air. The shaft 90 connects to the hook 86 thanks for example to a head, for example T-shaped, which fits inside a seat 92 in the body of the hook 86. Fig 7 shows two positions of the hook 86, one for grasping (minimum distance from the body 82) and one for releasing (maximum distance from the body 82), in a broken line.

[0031] The support 84 has an abutment for the piece L comprising a part or tab 88 that can elastically yield. The purpose is to make the holding seat adaptable for the piece L in the case in which there are burrs or small tolerances.

[0032] At such an abutment there can be one or more recesses with comparable dimensions with a burr of the piece L, again to make the holding seat adaptable.

[0033] The support 84 and the segment 56 for example are about 10 cm long. From experiments carried out with a similar sized piece, no positioning errors were obtained.

Claims

1. Method for locking a piece (L) of sheet metal on a mobile loader suitable for positioning the piece in a press brake so as to bend it, wherein a clamping force is applied to the piece with a direction that is substantially parallel to a longer dimension of the piece.

2. Method according to claim 1, wherein the longer dimension of the piece is defined by an edge and the clamping force is applied on at least two points of the edge.

3. Method according to claim 1 or 2, wherein the clamping force is applied on at least two points that are on opposite sections of the edge that defines the longer dimension, or on ends of the piece.

4. Method according to one of the previous claims, wherein one edge of the piece is pushed or pulled so that the piece comes into abutment against a fixed reference (60) and remains resting there on at least two distinct points or a segment.

5. Clamping device (50; 70) of a loader suitable for locking a piece (L) of sheet metal so as to be able to position it in a press brake to bend it, characterised in that it comprises means (58) suitable for applying a clamping force onto the piece that has a direction (X) that is substantially parallel to a longer dimension of the piece.

6. Clamping device according to claim 5, comprising

- a body (70) with an abutment (60) for the piece,

- a pushing member (58) that is mobile with respect to the body and that can be brought closer to the abutment, the pushing member (58) being suitable for pressing the piece with a clamping force that has a direction (X) that is substantially parallel to a longer dimension of the piece.

7. Clamping device according to claim 5 or 6, comprising

- at least one rigid segment (62) that extends the body for a certain distance mainly along an axis (X),

- an abutment (60) for the piece, the abutment being present on the body (70) and/or on the segment,

- a pushing member (58) that is mounted on the segment and that can be moved towards the abutment in a direction that is substantially parallel to said axis, the pushing member being suitable for pressing on an edge of the piece (L) so as to push an opposite edge thereof against the abutment.

8. Clamping device according to claim 7, comprising two of said segments (62) that extend from the body (70) separately and parallel to one another.

9. Clamping device according to claim 7 or 8, wherein one or each segment (62) comprises a flat portion (56) that can rest transversally on a larger surface of the piece.

10. Clamping device according to one of claims 6 to 9, wherein the body (70) comprises an element with controlled movement (54) that is connected outside the body to the pushing member (58) so as to move it.

11. Clamping device according to claim 10, wherein the element with controlled movement (54) is linearly mobile and is coupled directly with the pushing member (58) so as to transfer linear motion to it.

12. Clamping device according to one of claims 7 to 11, wherein one or each segment (62) is removably fixed to the body (70).

13. Clamping device according to one of claims from 5 to 12, wherein one or each abutment (60) comprises a part (88) that can elastically yield.

14. Clamping device according to one of claims 5 to 13, wherein a pushing member (58) is mounted on the relative segment (62) with a certain clearance.

15. Clamping device according to one of claims 5 to 14, wherein a pushing member comprises a hook-shaped or grooved portion (58) so as to engage and/or pull a piece on one edge.

Drawing