Abstract
Method for scanning the surface (O) of metallic workpieces (W), wherein, during a scanning process before a welding process is carried out, a welding torch (1) with a meltable welding wire (2) is moved over the surface (O) of the workpieces (W), and at predefined times (t.sub.i) the welding wire (2) is moved towards the surface (O) of the workpieces (W) until a contact of the welding wire (2) with one of the workpieces (W) is detected, and the position (P.sub.i) of the surface (O) of the workpieces (W) at each time (t.sub.i) is determined and stored in the welding power source (4), wherein an edge (K) is determined if the current position (P.sub.i) of the surface (O) of the workpieces (W) exceeds at least one of the stored previous positions (P.sub.i-n) of the surface (O) of the workpieces (W) by a predefined threshold value (S). To reduce the computing effort and to increase processing speed, the end of the edge (K) is determined if the current position (P.sub.i) of the surface (O) of the workpieces (W) remains the same with respect to at least one of the stored previous positions (P.sub.i-n), and if an edge (K) is determined, an edge detection parameter (KP) is set and output together with the current position value (P.sub.i) and transferred to the manipulator (3).
Claims
1. A method for scanning the surface (O) of metallic workpieces (W), wherein, during a scanning process before a welding process is carried out, a welding torch (1) with a meltable welding wire (2) is moved over the surface (O) of the workpieces (W) using a manipulator (3) along a predefined path (x.sub.A) and at a specified speed (v.sub.A), and at predefined times (t.sub.i) the welding wire (2) is moved towards the surface (O) of the workpieces (W) at a first forward speed (v.sub.SV) until a contact of the welding wire (2) with one of the workpieces (W) is detected by a welding power source (4), and the welding wire (2) is then moved away from the workpieces (W) again at a first reverse speed (v.sub.SR), and the position (P.sub.i) of the surface (O) of the workpieces (W) at each time (t.sub.i) is determined and stored in the welding power source (4), wherein an edge (K) is determined if the current position (P.sub.i) of the surface (O) of the workpieces (W) exceeds at least one of the stored previous positions (P.sub.i-n) of the surface (O) of the workpieces (W) by a predefined threshold value (S), wherein the end of the edge (K) is determined if the current position (P.sub.i) of the surface (O) of the workpieces (W) remains the same with respect to at least one of the stored previous positions (P.sub.i-n), and that if an edge (K) is determined, an edge detection parameter (KP) is set and output together with the current position value (P.sub.i) and transferred to the manipulator (3).
2. The method according to claim 1, wherein an edge (K) is determined if the current position (P.sub.i) of the surface (O) of the workpieces (W) exceeds the mean value of a plurality, preferably 2 to 100, of stored previous positions (P.sub.i-n) of the surface (O) of the workpieces (W) by a predefined threshold value (S).
3. The method according to claim 1, wherein the difference between the position (P.sub.i) of the surface (O) of the workpieces (W) at the end of the determined edge (K) and the last stored position (P.sub.i) before the detection of the edge (K) in a direction perpendicular to the surface (O) of the workpieces (W), or in the direction of the longitudinal extension of the welding wire (2), is determined as the value of the edge height (h.sub.K) and output.
4. The method according to claim 1, wherein from the stored positions (P.sub.i) of the surface (O) of the workpieces (W) between the end of the determined edge (K) and the stored position (P.sub.i) following the detection of the edge (K), the edge inclination (α.sub.K) is determined and output.
5. The method according to claim 1, wherein from the stored positions (P.sub.i) of the surface (O) of the workpieces (W) between the end of the determined edge (K) and the stored position (P.sub.i) following the detection of the edge (K), the radius (R.sub.K) of the edge (K) is determined and output.
6. The method according to claim 3, wherein the edge height (h.sub.K), the edge inclination (α.sub.K) and/or the radius (R.sub.K) of the edge (K) are transferred to the manipulator (3).
7. The method according to claim 1, wherein the welding wire (2) is moved towards the surface (O) of the workpieces (W) at time intervals (at) of 5 ms to 50 ms, preferably of 10 ms.
8. The method according to claim 7, wherein the time intervals (Δt) are adjusted to match the speed (v.sub.A) at which the welding torch (1) is moved over the surface (O) of the workpieces (W) during the scanning process.
9. The method according to claim 1, wherein the welding torch (1) is oriented at an angle (ß) of 60° to 90° to the surface (O) of the workpieces (W), so that the welding wire (2) is moved towards the surface (O) of the workpieces (W) and away from the surface (O) of the workpieces (W) at such an angle (ß) of 60° to 90°.
10. The method according to claim 1, wherein on detecting a longer short-circuit between the welding wire (2) and the workpieces (W), the welding wire (2) is moved away from the surface (O) of the workpieces (W) at a higher reverse speed (v.sub.SR′) than the first reverse speed (v.sub.SR).
11. The method according to claim 10, wherein the welding wire (2) is moved towards the surface (O) of the workpieces (W) at a higher forward speed (v.sub.SV′) than the first forward speed (v.sub.SV) after the welding wire (2) is moved away from the surface (O) of the workpieces (W) at the higher reverse speed (v.sub.SR′) than the first reverse speed (v.sub.SR) and no short-circuit is detected.
12. The method according to claim 1, wherein the welding torch (1) is moved over the surface (O) of the workpieces perpendicular to an expected edge (K) at at least three points.
13. The method for carrying out a welding process using a welding torch (1) with a meltable welding wire (2) on workpieces (W), wherein during the welding process, welding parameters are automatically controlled depending on the edge (K) determined during the method according to claim 1 and if necessary, on the edge parameters determined, such as edge height (h.sub.K), edge inclination (α.sub.K), or edge radius (R.sub.K).
14. The method according to claim 13, wherein during the welding process, the welding current (I) and/or the welding voltage (U) and/or the conveying speed (vs) of the welding wire (2) are controlled depending on the edge (K) determined during the scanning process and if necessary, on the determined edge parameters, such as edge height (h.sub.K), edge inclination (α.sub.K), or edge radius (R.sub.K).
Description
[0023] The present invention will be explained in further detail by reference to the attached drawings. Shown are:
[0024] FIG. 1 a schematic diagram of a welding device for carrying out a welding process and scanning process;
[0025] FIG. 2 a possible path of the welding torch along the surface of metal workpieces during a scanning process;
[0026] FIG. 3 a schematic diagram explaining the present method for scanning the surface of metal workpieces for the purpose of detecting an edge;
[0027] FIG. 4 a schematic diagram for explaining the determination of the height of an edge from the position values of the surface of the workpieces;
[0028] FIG. 5 a schematic diagram for explaining the determination of the edge inclination from the position values of the surface of the workpieces;
[0029] FIG. 6 a schematic diagram for explaining the determination of the edge radius from the position values of the surface of the workpieces; and
[0030] FIG. 7 a variant of the scanning method according to the invention with different conveying speeds of the welding wire depending on the position values of the surface of the workpieces.
[0031] FIG. 1 shows a schematic diagram of a welding device for carrying out a welding process and scanning process. A welding torch 1 with a welding wire 2 is connected to a corresponding manipulator 3, for example a welding robot. A welding power source 4 supplies the welding torch 1 or the welding wire 2 with the welding current I and the welding voltage U. Via a conveying device 5, the welding wire 2 is conveyed from a wire roll 6 to the welding torch 1 with a conveying speed vs. During the scanning process, the welding torch 1 with the welding wire 2 is moved using the manipulator 3 across the surface O of the workpieces W along a predefined path x.sub.A and with a predefined velocity V.sub.A. At specified times t.sub.i, the welding wire 2 is moved towards the surface O of the workpieces W at a first forward speed v.sub.SV until contact of the welding wire 2 with one of the workpieces W is detected by the welding power source 4. This detection is carried out by measuring the breakdown of the voltage upon the short-circuit between welding wire 2 and workpiece W. Thereafter, the welding wire 2 is moved away from the workpieces W again at a first reverse speed v.sub.SR. The position P.sub.i of the surface O of the workpieces W at each of the times t.sub.i is determined and stored in the welding power source 4. In previous scanning methods, these position values P.sub.i were forwarded to the manipulator 3, which meant a high level of data exchange between the welding power source 4 and manipulator 3 and slowed down the scanning process. According to the invention, an edge K on the surface O of the workpieces W is determined if the current position P.sub.i of the surface O of the workpieces W is located above at least one of the stored previous positions P.sub.i-n of the surface O of the workpieces W by a predefined threshold value S. If the specified threshold value S is exceeded, an edge detection parameter KP is set, in the simplest case only one bit is set to “1” and output together with the current position value P.sub.i. In contrast to previous methods, only the value of the edge detection parameter KP together with the current position value P.sub.i now has to be transferred to the manipulator 3, thereby considerably speeding up the method or increasing the accuracy. During the scanning process, the welding torch 1 is preferably oriented at an angle ß of 60° to 90° to the surface O of the workpieces W.
[0032] FIG. 2 shows a possible path of the welding torch 1 along the surface O of metallic workpieces W during a scanning process, looking onto the workpieces W. For a normally straight edge K, for example, a meandering path x.sub.A of the welding torch 1 over the workpieces W is suitable for a unique determination of the position of the edge K. Accordingly, the welding torch 1 is guided from a starting point A in a meandering path around the expected position of the edge K up to an end point E. The scanning method is carried out along the specified path x.sub.A at specified times t.sub.i by the welding wire 2 being moved towards the workpiece W until a physical contact (short-circuit) between welding wire 2 and workpiece W is detected by the power source 4. The welding wire 2 is then moved away from the workpiece W and the values determined via the drive of the conveying device 5 are defined as position P.sub.i of the surface O of the workpieces W. If an edge K is detected (see FIG. 3 of the Description), the edge detection parameter KP is set to 1, for example, and the respective position P.sub.i is stored. In the exemplary embodiment illustrated, the position values P1, P2 and P3 are stored at the 3 points along the edge K where the edge parameter KP=1. Thus, it is no longer necessary to store all the position values P.sub.i that are determined at all times t.sub.i and to forward them to the manipulator 3, but only the edge detection parameter KP, which in the simplest case comprises only one bit, and the corresponding position value P.sub.i. Thus, for the unique definition of the straight edge K, it can be sufficient to transfer three edge parameters KP together with position values P.sub.i. The welding torch 1 can be aligned according to the position of the expected edge K, as a result of which it is possible to take into account whether the welding torch 1 is being moved over the edge K from top to bottom or the other way round, from bottom to top.
[0033] FIG. 3 shows a schematic diagram for explaining the present method for scanning the surface O of metallic workpieces W for the purpose of detecting an edge K. This illustration shows the scanning method according to the invention, in which the positions P.sub.i of the surface O of workpieces W at specified times t.sub.i are detected using the welding wire 2. If the current position P.sub.i of the surface O of the workpieces W is located above at least one of the stored previous positions P.sub.i-n of the surface O of the workpieces W by a predefined threshold value S, an edge detection parameter KP is set and output together with the current position value P.sub.i and the presence of an edge K is indicated. In the present case, this is the case at position P.sub.15, where the threshold value S has been exceeded. For smoothing, mean values of a plurality, preferably 2 to 100, of stored previous positions P.sub.i-n can be used as a comparison value for the current position P.sub.i. By means of an appropriate averaging, in the case of a slowly and continuously rising surface O, an edge K will never be detected nor will the edge detection parameter KP be set. As with the start of the edge K, the end of the edge K can also be determined via the positions P.sub.i if it is detected that the current position P.sub.i of the surface O of the workpieces W remains essentially constant with respect to at least one of the stored previous positions P.sub.i-n. At position P17 according to FIG. 3, the position is essentially the same as the previous value P.sub.16, so that the end of the edge K can be defined.
[0034] FIG. 4 shows a schematic diagram for explaining the determination of the height h.sub.K of an edge K from the position values P.sub.i of the surface O of the workpieces W. From the difference of the positions P.sub.i, surface O of workpieces W at the end of the determined edge K and the last stored position before detection of the edge K, the edge height h.sub.K can be determined. In the present example, the height of the edge h.sub.K would be determined as the difference between position P.sub.16 and P.sub.13.
[0035] FIG. 5 shows a schematic diagram for explaining the determination of the edge inclination α.sub.K from the position values P.sub.i of the surface O of the workpieces W. The edge inclination α.sub.K can be reliably determined from the determined position values P.sub.i and the detection of the start and end of the edge K.
[0036] FIG. 6 shows a schematic diagram for explaining the determination of the edge radius R.sub.K from the position values P.sub.i of the surface O of the workpieces W. From the position values P.sub.i determined from the beginning of the detection of the edge K to the end of the detection of the edge K, the radius R.sub.K of the edge K can be deduced and a corresponding value determined. Deviations of the edge radius R.sub.K from the setpoint can be compensated during a welding process by adjusting the welding parameters, in particular the welding current I, the welding voltage U, or the conveying speed vs of the welding wire 2.
[0037] During the welding process to be carried out, the welding parameters, such as the arc length, the stick-out length, the wire conveying speed or the torch speed, can be adapted to the edge parameters (edge height, edge inclination, edge radius) previously determined during the edge detection process. If a welding process cannot be performed due to the actual edge conditions, for example, because the diameter of the welding wire is too small, an error message can be issued.
[0038] Finally, FIG. 7 shows a variant of the scanning method according to the invention with different conveying speeds Vs of the welding wire 2 depending on the position values P.sub.i of the surface O of the workpieces W. In the upper part of FIG. 7, an edge K between two workpieces W is again shown in cross-section, and the times t.sub.i at which the position P.sub.i of the surface O of the workpieces W is detected, starting with position P.sub.i at time t.sub.i up to position P.sub.8 at time t.sub.8. During the scanning process, the welding wire 2 is moved towards the workpiece W at the times t.sub.i with a predefined first forward velocity v.sub.SV until a short-circuit is detected, and then moved away from the workpiece W with a predefined first reverse velocity v.sub.SR. This is shown for the first five points P.sub.1 to P.sub.5. If a longer short-circuit is detected due to the edge K, which is the case at position P.sub.5 at time t.sub.5, the welding wire 2 can be moved away from the surface O of the workpieces W at a higher reverse speed v.sub.SR′ than the first reverse speed v.sub.SR. This allows the scanning process to be performed even faster and more accurately. After the scanning step with the higher reverse speed V.sub.SR′, the forward speed v.sub.SV is increased to a higher forward speed V.sub.SV′ than the first forward speed v.sub.SV, provided that no further short-circuit is detected. This is the case in the exemplary embodiment illustrated before position P.sub.6 at time t.sub.6.
