METHOD FOR TRIMMING A BENT TUBE

Abstract

A method for trimming a bent tube along an actual cutting contour, wherein a virtual tolerance envelope is calculated for the tube and a laser beam cutting the actual cutting contour is guided along a desired cutting contour related to the tolerance envelope, wherein the actual cutting contour is produced as a projection of the desired cutting contour or the laser beam is guided along the corrected desired cutting contour, which then corresponds to the actual cutting contour.

Claims

1. A method for trimming a bent tube along an actual cutting contour, comprising: calculating for the tube a virtual tolerance envelope with a desired cutting contour and storing the virtual tolerance envelope in relation to a spatially fixed coordinate system, picking up the tube using a gripping arm of a tube feeder with a known spatial position in the coordinate system, recording the contour of the tube using an optical measuring device with a known spatial position in the coordinate system, inserting the tube into the virtual tolerance envelope by moving the gripping arm which holds the tube, thereby confirming compliance with a shape tolerance for the tube lying within the shape tolerance, and the tube assumes a spatial position defined by the spatial position of the tolerance envelope, and the tube is fed relatively to a laser cutting device with an accuracy of the position in the tolerance envelope such that the laser cutting device assumes a predetermined position relative to the tolerance envelope, and cutting the actual cutting contour on the tube with a laser beam emitted by the laser cutting device.

2. The method according to claim 1, wherein the laser beam is guided along the desired cutting contour, cutting the actual cutting contour as a projection of the desired cutting contour on the tube, the projection corresponding to a modification of the desired cutting contour.

3. The method according to claim 1, wherein the contour of the tube and its position in the tolerance envelope are recorded and stored, the desired cutting contour is corrected for the tube and the laser beam is guided along the corrected desired cutting contour, which corresponds to the actual cutting contour.

4. The method according to claim 1, wherein before the tube is picked up from a feed surface by the gripping arm, a position of the tube on the feed surface is recorded by a further optical measuring device.

5. The method according to claim 2, wherein before the tube is picked up from a feed surface by the gripping arm, a position of the tube on the feed surface is recorded by a further optical measuring device.

6. The method according to claim 3, wherein before the tube is picked up from a feed surface by the gripping arm, a position of the tube on the feed surface is recorded by a further optical measuring device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In the drawings:

[0023] FIG. 1a shows an ideal tube, lying ideally within a tolerance envelope, where a desired cutting contour and an actual cutting contour coincide;

[0024] FIG. 1b shows a tube lying tilted in the tolerance envelope;

[0025] FIG. 1c shows another tube lying tilted in the tolerance envelope, and

[0026] FIG. 2 shows a schematic diagram of a device suitable for performing the method.

DETAILED DESCRIPTION

[0027] In a first process step, a tolerance envelope H is calculated for a bent tube R to be trimmed. It envelops the tube R either completely or only partially and is calculated in such a way that the tube R, which can be inserted completely into the tolerance envelope H, lies within a shape tolerance. The tolerance envelope H is stored together with the related desired cutting contours K.sub.DESIRED for the tube R. Advantageously, the desired cutting contours K.sub.DESIRED lie within the tolerance envelope H such that they coincide with the actual cutting contours K.sub.ACTUAL along which the tube R is intended to be trimmed, when an ideal tube R lies ideally within the tolerance envelope H. FIG. 1a shows such a situation in a simplified manner, with reference to a straight tube R. The desired cutting contour K.sub.DESIRED is advantageously defined such, with respect to the tolerance envelope H, that potential deviations in the position of the actual cutting contours K.sub.ACTUAL cut on the tubes R lying differently in the tolerance envelope H can lie in front of and behind the desired cutting contour K.sub.DESIRED in the direction of a laser beam directed at the tube R in order to lie close to the focus position of the laser beam guided along the desired cutting contour K.sub.DESIRED.

[0028] FIG. 1b and FIG. 1c show the tube R tilted in the tolerance envelope H. Generally, the tube R will be inserted into the tolerance envelope H in such a way that its tube axis coincides, if possible, with the axis of the tolerance envelope H, which is always possible in the case of an ideal tube R without shape deviations. In the case of shape deviations, the tube axis and the axis of the tolerance envelope H are tilted with respect to each other at least in sections, which FIG. 1b and FIG. 1c are intended to show in a simplified manner.

[0029] The desired cutting contour K.sub.DESIRED, related to the tolerance envelope H, is projected either onto the tubes R lying differently in the tolerance envelope H, in which case the actual cutting contours K.sub.ACTUAL forming on the shell of the respective tube R exhibit a change in size and/or shape compared to the desired cutting contour K.sub.DESIRED. Or the desired cutting contour K.sub.DESIRED is corrected for to the shell of the respective tube R and the laser beam is guided along the corrected desired cutting contour K.sub.DESIRED/CORR, which then corresponds to the actual cutting contour K.sub.ACTUAL.

[0030] The tolerance envelope H and the desired cutting contours K.sub.DESIRED, or only one desired cutting contour K.sub.DESIRED, are stored with reference to a spatially fixed coordinate system. The spatial position of the technical means necessary for performing the method, such as a feeding device, tube feeder or feeding means 2 with a gripping arm 2.1, an optical measuring device 3, and a laser cutting device 4, within the coordinate system is known.

[0031] The technical means mentioned above are each connected to a storage and control unit 6.

[0032] To trim the tube R, the latter is picked up from a feed surface 1 by the gripping arm 2.1 of the feeding means 2 and transported to the optical measuring device 3, where the contour of the tube R is recorded. Knowing the spatial position of the optical measuring device 3, e.g. a 3D camera, the spatial position of the contour of the tube R is also known and the contour can be transformed into the tolerance envelope H, i.e. the tube R is moved by the gripping arm 2.1 until it fits into the virtual tolerance envelope H, which means that on the one hand compliance with a shape tolerance for the tube R is confirmed and on the other hand the tube R has assumed a spatial position defined by the tolerance envelope H.

[0033] The gripping arm 2.1 feeds the tube R to a laser cutting device 4. This may be done after the tube R has been transformed into the tolerance envelope H or during this process. By feeding the tolerance envelope H to the laser cutting device 4 in a predetermined relative position, the laser cutting device 4 assumes a predetermined position with respect to the tolerance envelope H and a laser beam emitted by the laser cutting device 4 cuts the actual cutting contour K.sub.ACTUAL on the tube R.

[0034] In this case, the actual cutting contour K.sub.ACTUAL may correspond to a reduced, enlarged or otherwise modified projection of the desired cutting contour K.sub.DESIRED onto the shell of the tube R.

[0035] The laser beam is guided along the desired cutting contour K.sub.DESIRED, e.g. at an angle to the perpendicular on the tolerance envelope H. By changing the angle, not only an enlargement or reduction but also a change in shape of the actual cutting contour K.sub.ACTUAL compared to the desired cutting contour K.sub.DESIRED can be achieved.

[0036] The actual cutting contour may also be a corrected desired cutting contour K.sub.DESIRED/CORR. In order to calculate the corrected desired cutting contour K.sub.DESIRED/CORR, not only the contour of the tube R is recorded and stored, but also its position in the tolerance envelope H. Knowing the position of the tube R in the tolerance envelope H, the desired cutting contour K.sub.DESIRED can then be corrected for the tube R and the laser beam is guided along the corrected desired cutting contour K.sub.DESIRED/CORR, which then corresponds to the actual cutting contour K.sub.ACTUAL.

[0037] Advantageously, before the tube R is picked up from the feed surface 1 by the gripping arm 2.1, the position of the tube R on the feed surface 1 is recorded by a further optical measuring device 5. This makes it possible to determine whether an intended number of tubes R lie on the feed surface 1 and how they lie on the feed surface 1 in order to be able to pick them up safely with the gripping arm 2.1, even if they lie in a non-reproducible position.

[0038] FIG. 2 shows a schematic diagram of a device suitable for performing the method. The device includes feeding means 2 with a gripping arm 2.1, an optical measuring device 3, a laser cutting device 4, a storage and control unit 6 and a further optical measuring device 5.

[0039] For machining a tube R, i.e. for cutting a desired cutting contour K.sub.DESIRED on the tube R, the tube R is picked up from a feed surface 1 by the gripping arm 2.1 of the feeding means 2. Preferably, several tubes R lie pre-sorted, pre-positioned and pre-oriented on the feed surface 1, so that the gripping arm 2.1, moving to a predetermined gripping position, picks up the respective tube R, lying pre-oriented to the gripping arm 2.1. It is not necessary to position the tubes R so precisely on the feed surface 1 that they are picked up in a reproducible spatial position to the feeding means 2, which benefits the comparatively large shape tolerance of the individual tubes R.

[0040] The gripping arm 2.1 is preferably a multi-axis gripping arm 2.1, which can freely move a gripped workpiece, in this case the tube R, within a limited working area. Arranged within the working area are the feed surface 1, the optical measuring device 3, e.g. a 3D camera, and the laser cutting device 4.

[0041] By means of the gripping arm 2.1 the tube R is transported in front of the 3D camera, where the contour of the tube R and advantageously its spatial position are recorded and stored. Then the gripping arm 2.1 moves the tube R until the acquired data has been projected into the tolerance envelope H of the tube R, thus confirming that the tube R is in tolerance. The spatial position of the tube R within a coordinate system defined by the feeding means 2, or any other spatially fixed coordinate system, is thus determined by the spatial position of the tolerance envelope H in the coordinate system.

[0042] Thereafter or simultaneously, the gripping arm 2.1 feeds the tube R to the laser cutting device 4 in such a way that the tolerance envelope H is in a predetermined relative position to the laser cutting device 4 and thus to the laser beam serving as a tool. The laser beam then cuts an actual cutting contour K.sub.ACTUAL on the tube R, with the laser beam being guided along a desired cutting contour K.sub.DESIRED related to the tolerance envelope H or along a corrected desired cutting contour K.sub.DESIRED/CORR. The method can be performed using the laser beam because the execution of the cut does not require mechanical contact between a cutting tool and a workpiece and thus a defined position of the machining surface, as is the case with mechanical machining. In laser cutting, the machining surface can assume a different spatial position at least within the focus range.

[0043] The method according to the invention makes it possible to cut the actual cutting contours K.sub.ACTUAL on the only roughly tolerated tubes R, to which other tubes R can be attached and welded. By modifying the actual cutting contours K.sub.ACTUAL, depending on the position of the tubes R within the tolerance envelope H and thus depending on their shape deviations, the rough tolerance of the tubes R is included only to a lesser extent, if at all, in the tolerance chain for connecting the tubes R at the actual cutting contours K.sub.ACTUAL. The method also allows the gripping arm 2.1 to automatically pick up merely pre-oriented tubes R and feed them to the laser cutting device 4.

LIST OF REFERENCE NUMERALS

[0044] R tube [0045] H tolerance envelope [0046] K.sub.DESIRED desired cutting contour [0047] K.sub.ACTUAL actual cutting contour [0048] K.sub.DESIRED/CORR corrected desired cutting contour [0049] 1 feed surface [0050] 2 feeding means [0051] 2.1 gripping arm [0052] 3 optical measuring device [0053] 4 laser cutting device [0054] 5 further optical measuring device [0055] 6 storage and control unit