MXPA96004523A - Method and apparatus to verify and place a rayoo a beam for operation on a parts detrab - Google Patents

Abstract

The present invention relates to a method for monitoring and placing a beam or beam to operate on a workpiece, in which at least one of a first sensor above the beam or beam and predetermined values, determines the path that goes to be followed by the beam or beam and a second sensor behind the beam or beam monitors the action of the beam or beam characterized in that the predetermined value or the readings obtained by the first sensor with respect to a required position of the beam or beam is or they are compared with the readings obtained by the second sensor with respect to a current position of the beam or beam, taking into account the relative displacement that depends on the speed between the beam or beam and the workpiece, and the beam or beam is corrected to a basic position, if the current position deviates from the required position

Description

METHOD AND APPARATUS FOR VERIFYING AND PLACING A RAY OR JET FOR OPERATION ON A WORK PIECE DESCRIPTION OF THE INVENTION The invention relates to a method for verifying and placing a beam or jet to operate on a workpiece, wherein a first sensor (eg, a seam detector system in the case of a beam) above the beam or The jet, and / or a predetermined value, determines the trajectory that is going to be followed by the beam or the jet, and a second sensor behind the beam or jet inspects the action of the beam or jet. The invention also relates to an apparatus for carrying out the method. In a large number. of mainly industrial machining procedures, a beam or jet has to be verified and / or placed. This can be seen, for example, in the cutting of by means of laser beams or cutting by water jet. In both cases, the trajectory of the beam or jet is predetermined, usually by means of an electronic system. The beam or jet then has to follow this path. The quality of the cut depends (among other factors), the precise adherence of the beam or jet to the predetermined route.

To a greater degree, the same is found in welding with lightning, and especially in welding by means of lasers. Again, the many advantages of sheet metal parts mass produced by butt welding by the laser method (for example, those known in the motor vehicle industry as "adapted models") can not be fully exploited. unless the exact requirements of this procedure are satisfied, in terms of geometric tolerances of components, quality of cutting edges and characteristics of laser radiation. With a normal focal diameter of 0.2 to 0.4 mm, it is possible to obtain an exact positioning of the laser beam on a joint line between two work pieces that are going to be joined together, this is essential to obtain a high quality welding joint. For a "null" technical gap, the maximum position tolerance must not exceed 0.1 mm. In addition, when the gaps have to be bridged by the molten deposit, this tolerance must be further reduced. The lack of fusion due to poor placement of the beam is particularly critical in welds that have only partial penetration, being consolidated by a wider upper welding stroke. Even in welds with full penetration, a slightly widened seam root can result in an invisible internal fault of fusion. At present, sufficiently high positioning accuracies are obtained by means of optoelectronic sensors or image processing systems, which transmit the actual trajectory of the joining line, that is, the trajectory of the stop edges of the pieces of work, above the beam, directly to the machine control system as a series of correction coordinates. By this, a laser head can be oriented with respect to the seam with accuracies of approximately 0.05 mm. A seam detection system of this type is described, for example, in DE-OS 43122441. A fundamental disadvantage of these methods lies in the fact that the line detection systems have to start from a pre-established laser beam position, fixed. The measured position coordinates can not be referenced to the actual position of the beam. This is partially remedied by carrying out a calibration procedure at periodic intervals, and as a minimum after each adjustment of the optical path, but involves an interruption in production. Changes in the position of the laser beam due to thermal effects in the generation of the beam and the guidance system remain totally decompensated. The result is a reduction in the accuracy of the welding operation. Theoretically, these problems can be solved by incorporating a lightning sensor sensor system in the beam guidance system already present as part of the lightning detector system. However, sensor systems are usually not suitable for online operation and, in the end, their use is likely to incur a considerable additional cost. In addition, it is known that a welded seam can be verified by the back of the beam. However, this is done not to take into account the position of the joint line, but merely to determine the quality of the welded seam. An object, which is found in the present invention, is to provide a method and apparatus of the type preferred above by means of which a beam or jet, in particular a laser beam, can be verified and placed continuously and corrected to a basic position. This object can be achieved by comparing the predetermined value, or the readings obtained by the first sensor with respect to the required position of the beam or jet, with the readings obtained by the second sensor with respect to a real position of the beam or jet, taking into account the relative displacement dependent on the speed between the beam or jet and the work piece, and correcting the beam or jet to a basic position, if the actual position deviates from the required position. This means that the path of a seam, in particular of a welded seam, behind the beam, is determined by the second sensor, and compared to the trajectory, or with a required trajectory, above the beam. Preferably, this is combined with the quality inspection of the welded seam itself. This system according to the invention is not restricted to the production of a welded joint between two workpieces, or to the particular case of welding by means of the laser described here, and can be applied in all the procedures used in rays or jets guided by a trajectory. The first of all these procedures is the cutting procedure using high energy radiation. The solution to the problem can arise mainly by generating a coordinate reference system in relation to an image processing system to detect the position of the junction line. A second image processing system can be related to this coordinate reference system, provided that the image generation sensor systems are fixed relative to a common rigid mounting surface and are calibrated therebetween.

Since in many situations, such as in a laser welding unit, a second sensor system is required located immediately below the welding position to perform an automatic inspection of the geometry of the seam produced, the cost of this Second sensor system is extremely low. The requirements for recording optical images and also the scanning speed of the second sensor system are similar to those of the first system for detecting the bond line, so that an almost identical construction can be easily employed. In this way, since the position of the seam to be welded is continuously computerized by the first image processing system, the subsequent image processing system characterizes the seam, which has already been welded, also with respect to its position within the common coordinate reference system. In order to have a superimposition of images that is accurate and complete, even though the two sensor heads have a fixed common mount, it is necessary to know only the displacement time dependent on the speed required by either the work pieces or the beam to move, example from the origin of the coordinate of the image field of the first sensor to the corresponding location in the image field of the second sensor. This displacement time can be easily recorded with a commercially available measurement system, and can form the basis for the alignment of the images that are going to be superimposed. If the feeding speed of the components for welding or cutting is known, an accurate correspondence between the actual path and the required path can be obtained. Using the superimposition of images, which has been described, the point of impact of the laser beam focused with respect to the actual position of the line of attachment can be determined with great precision by the program of image analysis. Once this reference value is known, first, it becomes possible to make a direct inference of the probability of the internal fault of the fusion occurrence, based on the known values for the focus diameter and the width of the seam. Furthermore, since the change in the position of the beam due to thermal causes is relatively gradual, corrections can easily be made in the position of the beam. Of course, the present invention is not limited to a single dimensional feed. It is also feasible for a beam or jet that is going to be verified and placed in a similar way with two or three dimensional feeds. A large number of techniques for detecting the path of a joint line and / or the weld seam are known in the art. All of these techniques can be used in conjunction with the present invention. Examples of which can be mentioned are the light section technique and the technique that uses a gray level image analysis. A description of the light section technique can be found, for example, in DE-OS 4312241, while a description of the detection of the junction geometry by gray-level image analysis can be found in DVS-Berichte, Volume 94 (1985), page 44ff. Depending on. circumstances, you can operate two sensors by the same technique or by different techniques. Experience shows that qualitative requirements must be imposed on individual techniques. If the method according to the invention is to be used for cutting by means of a beam or jet, the sensor is above-the jet beam can be dispensed, in most cases. The function of the sensor to determine the required position and also to guide the beam or jet consequently, is then assumed by a predetermined value, which can be stored in an electronic memory. Other advantages, aspects and details of the invention will be apparent from the following description of the preferred embodiments, and with reference to the drawings, in which: Figure 1 shows a plan view, partly in a block diagram form , of an apparatus to verify or place a beam to operate on work pieces; Figure 2 shows a plan view of the apparatus of Figure 1 with the detection of the beam position diagrammatically illustrated. As shown in Figure 1, two work pieces 1 and 2 are to be joined together by a beam 3. The region of the junction between the two work pieces 1 and 2 above the beam 3 is referred to as the line of work. junction 4, and the same region behind the spoke 3 is referred to as the weld seam 5. The ray 3 comes from a source (not shown) on a displacement device 6, which may consist, for example, of a transverse slider . In this case, the displacement device 6 is movable in two dimensions x and y. However, it could also be possible to provide a three-dimensional movement. Only the essential point is that of the displacement device 6 which allows the ray 3 to be guided along the junction line 4 and be aligned with the latter. In order that the beam 3 can be guided along the line of attachment 4, a sensor 7 (also referred to as a seam detection system) is provided above the beam 3. This sensor 7 is coupled to a control unit 8 and continuously detects the path of the joint line 4. On the basis of the displacement time that depends on the speed, of the work pieces - or the time of movement of the beam if it is crossed with respect to the work pieces - the course of the connecting line 4 is determined by the control unit 8, which fixes the movement to the displacement device 6 in accordance with the readings obtained by the sensor 7, so that the beam 3 always points accurately to the connecting line 4 and preferably to the center line (not shown) of the connecting line 4. According to the invention, another sensor 9 is provided behind the beam 3 and is also connected to the control unit 8. This second sens or observe the welded seam 5. The mode of operation of the apparatus according to the present invention will now be described with reference to Figure 2, by way of example. The sensor 7, which precedes ray 3, operates by the so-called light section technique. This involves projection onto the region of the connecting line 4, at an angle oblique to the optical axis of the sensor lens system, of a pattern of strips, consisting, at present, of five parallel strips 10. These strips 10 extend essentially through the line of the union that is going to be welded, but they can also be located in a different way. In the region of the junction line 4, the strips are interrupted, or changes may occur which are detected by the sensor. The path of the junction line can then be determined from a number of points corresponding to the number of strips. As illustrated in Figure 2, the second sensor 9 operates on the same principle and the welded seam 5 is illuminated with a similar strip pattern 11. If, during the course, for example, as a result of a thermally induced movement, the beam 3 deviates from its position shown on the uninterrupted external line to the position indicated on the interrupted external line, this can not be detected by the sensor 7, which always assumes that beam 3 is in its basic position. However, the next sensor 9 detects a deviation of the path of the welded seam 5 from the path of the sensor 7, as the readings are fed to the control unit 8, consisting, for example, of position coordinates obtained by the image analysis, which never coincide. This is also indicated schematically in the drawing in broken lines. The displacement device is then changed by means of the control unit 8 according to the correction value obtained, restoring beam 3 to the basic position. Having described the invention as above, property is claimed as contained in the following:

Claims (3)

1. A method for verifying and placing a beam or jet to operate on a workpiece, in which a first sensor (e.g. in the case of a beam, a seam detector system) above the beam or jet, and / or a predetermined value, determines. the trajectory that will be followed by the beam or jet and a second sensor behind the beam or jet verify the action of the beam or jet, characterized in that the predetermined value or the readings obtained by the first sensor with respect to a required position of the ray or jet is or are compared with the readings obtained by the second sensor with respect to a real position of the beam or jet taking into account the relative displacement that depends on the speed between the beam or jet and the workpiece, and the beam or jet is corrected to a basic position, and the actual position deviates from the required position.

2. A method for verifying and placing a beam or jet to operate on a workpiece according to claim 1, characterized in that the required position of the beam or jet is detected by a light section technique or a combination of beam analysis techniques. light section and gray level images and the actual position of the beam or beam is detected by a gray-level image analysis technique or a combination of light section and gray level image analysis techniques and detected positions they are compared among them.

3. An apparatus for checking and placing a beam or jet to operate on a workpiece, in which a first sensor (for example in the case of a beam, a seam detector system) above the beam or jet, and / or a predetermined value determines the path that will be followed by the beam or jet and a second sensor below the beam or jet verify the action of the beam or jet, characterized in that the first and second sensors are connected to a control unit for compare the readings obtained by the two sensors, the control unit being connected to a displacement device for relative displacement between the beam or jet and the work piece.