Welding device, robotic welding system and method for conveying a wire electrode with high-precision stickout adjustment

Description

Technical field

[0001] The present invention relates to a welding device with high-precision stickout adjustment, a robotic welding system with high-precision stickout adjustment, and a method for conveying a wire electrode with high-precision stickout adjustment. "Stickout" refers to the free wire electrode length of the wire electrode from the end of a contact tube of a welding torch of the welding device. Technical background

[0002] For many welding devices and welding processes, it is necessary to know or provide the free wire electrode length from the end of the contact tube of a welding torch with a high degree of accuracy. If, for example, the welding torch is robot-guided, the position of the robot and thus of the contact tube end is sometimes known with a high degree of accuracy. Any inaccuracy or lack of knowledge regarding the distance between the end of the wire electrode and a workpiece is therefore essentially caused by the less precisely known free wire electrode length from the end of the contact tube. The distance between the end of the wire electrode and the workpiece is, in turn, important for controlling the welding process, for example when igniting an arc. It can also be important to know such distances precisely for processes upstream or downstream of the actual welding process.Even if the wire feed, i.e., the advancement of the wire electrode, is continuously monitored by a monitoring device, errors in the monitoring process can accumulate, resulting in increasingly inaccurate adjustments of the free wire electrode length. Furthermore, it may happen that a welding machine operator manually cuts off a wire electrode end, thereby altering the free wire electrode length, without the monitoring device being aware of this.

[0003] Typically, the free wire electrode length is measured using a ruler or gauge, which is time-consuming and sometimes impossible, as robot welding cells, for example, can be difficult to access. Often, for example, access to robot welding cells is not available, or automated operation or a safety system is required. Furthermore, personnel must always be available for this task.

[0004] US 2010 / 096375 A1, disclosing the preamble of claims 1 and 11, describes an automatic wire feed system with a detection circuit which can detect a short circuit between the welding wire and a workpiece in order to stop the wire feed at a desired free wire length.

[0005] US 2018 / 304391 A1 describes a teaching system for a welding robot in which the welding wire is advanced until it is detected that the tip end of the welding wire has come into contact with a teaching object.

[0006] JP S59 118276 A describes a method for adjusting the free wire electrode length. Upon detection of a short circuit between the wire electrode and the workpiece, the movement of a robot arm is stopped. Depending on the short circuit, the robot arm is retracted to achieve a desired distance.

[0007] All of these methods require the welding torch to be already positioned on a workpiece, so that a short circuit can be established with the workpiece. Furthermore, they lack accuracy, as the distance to the workpiece is another unknown or at least subject to measurement inaccuracy.

[0008] US 2006 / 138116 A1 describes a method for adjusting the free wire electrode length on a welding robot before contact with the workpiece, for which purpose, for example, a special contact plate is provided. This method therefore requires additional components, which not only increase costs but also place additional demands on the welding cell. Summary of the invention

[0009] It is therefore an object of the present invention to provide an improved welding device by means of which the free wire electrode length can be adjusted particularly precisely. A further object is to provide a robot welding system which comprises such a welding device. A further object is to provide an improved method for conveying a wire electrode in a position with a precisely defined free wire electrode from a contact tube of a welding torch of a welding device. A further object is that a free wire electrode length can be adjusted during manual welding or automatically by a welding system, e.g. a robot welding system.

[0010] These problems are solved by the subject-matter of the independent patent claims.

[0011] Accordingly, a welding device having the features of claim 1 is provided.

[0012] Accordingly, one of the fundamental ideas of the present invention is that an electrical parameter measurement, in particular a voltage measurement (more precisely: a detection of a voltage change) or a current measurement, is used to determine the current position of the wire electrode end. For this purpose, the wire electrode contact device is provided, which electrically contacts the wire electrode. Thus, an electrical parameter, z. B. An electrical voltage can be measured between the wire electrode and a reference electrode. If the electrically conductive, consumable wire electrode is electrically contacted at defined points within the welding device and thus comes into contact with a different electrical potential, the position of the wire electrode can be determined based on knowledge of these positions.

[0013] The wire electrode is in particular a consumable wire electrode.

[0014] It is particularly advantageous if the wire electrode runs in an electrically insulating core and thus only makes electrical contact with the contact tube when the wire electrode enters the contact tube. Since the contact tube is already maintained at a defined electrical potential ("welding positive") so that the welding current flows relative to the potential of the workpiece to be welded (ground or "welding negative"), it is therefore advisable for the electrical parameter measuring device to detect voltage changes or current changes that result from the wire electrode making electrical contact with the contact tube. The reference electrode, which is at a defined reference potential, can preferably be grounded or can be connected or connectable to the contact tube of the welding torch. In this way, existing and developed welding potentials in the welding device can be advantageously used.However, it is also conceivable that the reference electrode is at a further electrical potential, which is different from the welding plus and the welding minus.

[0015] A positioning method is understood, in particular, to be a method by which the wire electrode can be brought into a defined position relative to the welding torch, in particular into a position with a defined free wire electrode length in front of the contact tube end ("stickout"). The positioning method differs particularly from a welding method or welding process because no welding current flows and / or no workpiece is machined or contacted during the positioning method. The positioning method can be carried out from the beginning of threading the wire electrode into the welding device, for example, automatically with threading a new wire electrode (also referred to as welding wire).

[0016] The positioning method particularly reveals its advantages when it is carried out between welding processes, so that the free wire electrode length, and thus often also the distance between the wire electrode end and the workpiece, can be determined with particular precision. As will be explained below, a particular strength of the inventive concept lies in the fact that dead time between two welding processes can be used to reset the desired free wire electrode length, or in other words, to readjust it. Such dead time can occur, for example, when a robot arm of a robotic welding system moves between an end point of a first welding process and a start point of a second welding process. This dead time can therefore also be utilized.

[0017] For manual welding, it can be advantageous to automatically adjust the free wire electrode length before welding begins, indicating to the welder the ideal distance between the contact tip and the workpiece. This can be adjusted automatically based on the welding machine's settings regarding the type of welding process, the type of workpiece, and so on.

[0018] In general, it can be provided that an electrical parameter measuring device for measuring an electrical parameter (e.g. voltage or current and electrical quantities derived therefrom) is set up between the wire electrode contact device and the reference electrode, and that the current position of the wire electrode end of the wire electrode is determined based on at least one measurement in which an electrical parameter change (e.g. voltage change or current change) of the electrical parameter measured by the electrical parameter measuring device is detected while the wire electrode is being conveyed through the conveying device. For example, the measured electrical current could initially be 0 mA and increase to a value in the range of 1 mA to 500 mA upon electrical contact between the wire electrode and the contact tube. The electrical parameter change would therefore be an increase in current.

[0019] In the following, a variant will be used as an example to explain the invention, in which the electrical parameter measuring device is or comprises a voltage measuring device, by means of which a voltage change between the wire electrode (more precisely: wire electrode contact device) and the reference electrode can be or is measured. However, it is understood that alternatively (or additionally), the electrical parameter measuring device can also be or comprise a current measuring device, as described.

[0020] According to some preferred embodiments, variants, or further developments of embodiments, the reference electrode is or can be electrically connected to ground. The electrical parameter measuring device is or comprises a voltage measuring device configured at least to measure a voltage between the wire electrode and ground when the reference electrode is electrically connected to ground. In particular, the reference electrode can also be electrically connected to the workpiece. Such an arrangement is particularly simple since it requires hardly any additional elements compared to a conventional welding device.

[0021] According to some preferred embodiments, variants, or further developments of embodiments, the reference electrode is or can be electrically connected to a contact tube of a welding torch of the welding device. The electrical parameter measuring device is or comprises a voltage measuring device configured at least to measure a voltage between the wire electrode and the contact tube when the reference electrode is electrically connected to the contact tube. As already explained, the wire electrode typically makes electrical contact with the contact tube upon entering the contact tube (short circuit).

[0022] According to the invention, a change in the electrical parameter, in particular a voltage change or current change, can be detected at this time, thus concluding that the wire electrode end is located at the inlet of the contact tube. Using a known wire electrode feed rate (or, in short, wire feed speed) by the conveyor and a known distance between the contact tube start and end (contact tube length), the wire electrode end can thus be conveyed from the known position at the start of the contact tube to the desired end position with the desired, defined free wire electrode length in front of the contact tube end.

[0023] The length of the contact tube can be known in advance and, for example, stored or storable in the control device. It is also conceivable that a storage medium or identification code is connected to the contact tube or the welding torch, by means of which the control device can automatically determine the length of the contact tube (contact tube length). In some variants, if the contact tube length is unknown, a user of the welding device can also be prompted, for example via a display or voice control, to enter the length of the contact tube. The user can then measure the contact tube length, take it from a parts list, or determine it in another way and communicate it to the control device using their input device. The input device can, for example, be a touchscreen on the welding device.If the welding device is equipped with a voice control system, the user can also state the contact tube length to the control device in natural language, or the entire interaction between the control unit and the user can be carried out via natural language input and output.

[0024] According to some preferred embodiments, variants, or further developments of embodiments, the wire electrode contact device has a sliding contact and / or a drive roller for the wire electrode. In this way, the wire electrode can be electrically contacted in a simple and controllable manner. Drive rollers, in particular, are typical components, for example within the conveyor device, for which good mechanical contact with the wire electrode is necessary anyway and can therefore be easily configured to electrically contact the wire electrode. However, it is also conceivable for the wire electrode contact device to electrically contact the wire electrode via a guide roller pressed against the wire electrode, a sliding contact, or at least one ball bearing with conductive lubrication.Since it is sufficient to tap the electrical potential, the electrical connection to the wire electrode does not necessarily need to be low-resistance. For example, the electrical connection to the wire electrode can have an electrical resistance of up to 100 kiloohms, for example, an electrical resistance of between 0.5 kiloohms and 100 kiloohms, or between 10 kiloohms and 50 kiloohms.

[0025] According to some preferred embodiments, variants, or further developments of embodiments, the control device comprises a runtime provision module configured to provide a signal delay value ("runtime error") for components of the control device. The control device can be configured to take into account, in particular to compensate for, the provided signal delay value when determining the current position of the wire electrode end. The runtime provision module can include the signal delay value as a stored variable or be designed and configured to determine a current signal delay value. The signal delay value can be determined at the request of a user, regularly, or automatically after a predefined trigger.The trigger can, for example, be the result of a plausibility check if it turns out that carrying out the positioning method according to the invention with the currently known signal delay value does not result in the desired accuracy of the free wire electrode length.

[0026] It is also conceivable for the control device to calculate the current position of the wire electrode end without using the signal delay value, but to adapt the control signals for controlling the conveyor device to set the defined free wire electrode length, taking into account the signal delay value from the runtime provision module. In particular, the control device will reduce the wire electrode length still to be conveyed by a value equal to the signal delay value multiplied by a conveying speed of the wire electrode.

[0027] According to some preferred embodiments, variants, or further developments of embodiments, the control device is configured to determine the current position of the wire electrode end based on multiple measurements of changes in electrical parameters (e.g., voltage changes). Two or more of these multiple measurements can be performed, in particular, at different positions of the wire electrode end, so that each of these measurements provides further information about a current position of the wire electrode.

[0028] Alternatively or additionally, two or more measurements of changes in the electrical parameter (or multiple electrical parameters) can also be performed at different wire electrode feed speed directions, i.e., at least one measurement during forward conveyance of the wire electrode toward the contact tube end and at least one measurement during reverse conveyance of the wire electrode toward the conveyor. Such measurements at different wire electrode feed speed directions can each be performed at the same and / or different positions of the wire electrode (or at the same and / or different contact points of the welding torch, in particular the contact tube).Since the feed speed as well as the start and end of the wire electrode feed and other parameters of the conveyor are preferably known exactly, additional information about the current position and / or the behavior of the wire electrode end can be collected in this way, which can make the positioning process even more precise.

[0029] According to some preferred embodiments, variants, or further developments of embodiments, the at least one positioning method comprises a precision positioning method. The positioning method can consist of the precision positioning method or, in addition to the precision positioning method, have further options, for example, a simple positioning method. The simple positioning method can differ from the precision positioning method in particular in that the simple positioning method requires less effort (for example, can be carried out more quickly), but has a lower accuracy of positioning the wire electrode end compared to the precision positioning method.

[0030] The control device can be configured to: to detect a first change in an electrical parameter (e.g. first voltage change) by means of the electrical parameter measuring device while the wire electrode is being conveyed forwards towards the contact tube by the conveying device at a first speed; then to control the conveying device to convey the wire electrode backwards at a second speed, at least until a second change in the electrical parameter (e.g. second voltage change) is detected by means of the electrical parameter measuring device; then to control the conveying device to convey the wire electrode forwards at a third speed until a third change in the electrical parameter (e.g. third voltage change) is detected by means of the electrical parameter measuring device; and to determine the current position of the wire electrode at least based on a measurement in which the third change was detected.The third speed is preferably lower than the first speed. By conveying at a lower speed, the conveying and thus also the positioning of the wire electrode can be carried out with greater accuracy. The primary purpose of measuring the first and / or second change in the electrical parameter is to ensure that the wire electrode end only needs to be conveyed as far as possible at the (slower) third speed in order to achieve the defined (i.e. desired) free wire electrode length. It is understood that the most precise setting of the free wire electrode length would be achieved by always conveying the wire electrode at a particularly low speed so that any positioning inaccuracy of the wire electrode end due to overtravel, slipping and signal delay is kept as low as possible.In contrast, however, it is preferred that the positioning process be performed as quickly as possible, so that it can be carried out within existing dead times or, if necessary, requires only very short additional dead times. For example, in the automotive industry, the goal is to keep the dead time as close to zero as possible.

[0031] Particularly preferably, the control device is configured to continue advancing the wire electrode at a fourth speed after determining the current position of the wire electrode until the defined free wire electrode length is present between the wire electrode end and the contact tube end. It is particularly preferred if the conveying of the wire electrode at the third speed transitions steadily and monotonically into the conveying at the fourth speed. The fourth speed is preferably greater than the third speed.If, by measuring the third change in the electrical parameter, the current position of the wire electrode (more precisely: the wire electrode end) is known exactly, the wire electrode itself can be conveyed to the position with the defined free wire electrode length at the (increased) fourth speed so that the end position of the wire electrode is reached more quickly and welding can be continued more quickly, for example.

[0032] The invention further provides a robot welding system comprising a welding device according to the invention. The robot welding system further comprises a robot device (for example, a robot arm) configured to guide the welding torch of the welding device, and a system control device configured to generate and transmit control signals for controlling the robot device as well as to generate and transmit control signals for controlling the welding device. The control device of the welding device is advantageously configured to receive, among the control signals, a positioning method trigger signal from the system control device and, in response thereto, to perform one of the at least one positioning method.The system controller can be integrated into the welding device, integrated into the robot device, or configured and arranged separately from both the welding device and the robot device. For example, the system controller can also be implemented via a remotely located server or a cloud computing platform.

[0033] A particular advantage of the system control unit is that it has information about when welding begins and when a dead time occurs, for example, because the robot device must first be moved or realigned. For example, the system control unit can have a welding sequence plan, which it can use to automatically determine how much dead time is inevitable between the end of the previous welding process and the start of the next welding process according to the welding sequence plan.

[0034] The system control device can also contain a database with information about the time durations or the maximum time durations of each positioning method of the at least one positioning method. Based on the known dead time, the system control device can thus advantageously control the control device of the welding device to carry out the most precise positioning method that can be carried out within the upcoming dead time. In this way, at least one dead time in a welding sequence plan with multiple welding processes (or: welding tasks), particularly preferably multiple dead times and most preferably all dead times, in the welding sequence plan can be used to ensure that a known, in particular defined, free wire electrode length is available as frequently as possible or even always before the start of a welding process.

[0035] According to some preferred embodiments, variants, or further developments of embodiments, the at least one positioning method is performed while the robot device is in transit between two positions at which the welding device is controlled for welding, wherein no welding takes place during the transit. In other words, as already discussed, the positioning method can preferably be performed during a dead time of the welding device, i.e., during a time during which no welding is possible or no welding process is being performed, for example, because the welding torch is not at the correct distance and / or alignment to a workpiece of the next welding process.

[0036] Furthermore, the invention provides a method for conveying a wire electrode in a position with a defined free wire electrode length from a contact tube of a welding torch of a welding device with the features of patent claim 11.

[0037] The desired free wire electrode length of the wire electrode can be defined based on a setpoint for the free wire electrode length stored in a control device of the welding device. Alternatively, the desired free wire electrode length can also be defined depending on a welding process to be performed, for example by user input via an input device and / or by control signals from a system control device, as described above. It is also conceivable that the free wire electrode length is automatically defined by the control device based on parameters of a welding process to be performed, for example, using a database.

[0038] According to some preferred embodiments, variants, or further developments of embodiments, a signal delay value is taken into account when determining the current position of the wire electrode end. This allows the current position to be determined even more precisely.

[0039] According to some preferred embodiments, variants, or further developments of embodiments, the current position of the wire electrode end is determined based on multiple measurements of changes in an electrical parameter (e.g., voltage changes), as described above. When detecting or determining the position of the wire electrode at different contact points, the computing device can also perform an averaging to increase the accuracy of determining the position.

[0040] According to some preferred embodiments, variants, or further developments of embodiments, the reference electrode is electrically connected to ground. The measurement of the electrical parameter, e.g., the voltage, can thus be performed in particular between the wire electrode and ground.

[0041] According to some preferred embodiments, variants, or further developments of embodiments, the reference electrode is electrically connected to a contact tube of the welding torch of the welding device. The measurement of the electrical parameter, e.g., the voltage, can be performed in particular between the wire electrode and the contact tube, more precisely, between an electrical potential of the wire electrode and an electrical potential of the contact tube.

[0042] According to some preferred embodiments, variants or further developments of embodiments, the method according to the invention further comprises the steps: Detecting a first change in the electrical parameter (e.g., first voltage change) while the wire electrode is conveyed forward toward the contact tube at a first speed; conveying the wire electrode backward at a second speed at least until a second change in the electrical parameter (e.g., second voltage change) is detected; conveying the wire electrode forward at a third speed at least until a third change in the electrical parameter (e.g., third voltage change) is detected; and determining the current position of the wire electrode end based at least on a measurement with which the third change was detected.

[0043] The third speed is preferably lower than the first speed. A method with the aforementioned additional method steps can also be referred to as a precision positioning method and can be one of several positioning methods that is carried out as the method according to the invention or as part of the method according to the invention. The first change in the electrical parameter, the second change in the electrical parameter, and the third change in the electrical parameter are detected, in particular, in this order.

[0044] In some preferred embodiments, variants, or refinements of embodiments, after determining the current position of the wire electrode end, the wire electrode is advanced at a fourth speed until the defined free wire electrode length is present between the wire electrode end and the contact tube end. The fourth speed is preferably greater than the third speed. Particularly preferably, the third speed transitions steadily and monotonically into the fourth speed.

[0045] Further preferred embodiments, variants and developments of embodiments emerge from the subclaims and from the description with reference to the figures. Short description of the characters

[0046] The invention is explained in more detail below using exemplary embodiments in the figures of the drawings. The partially schematic representation shows:Fig. 1 is a schematic diagram for explaining a welding device according to an embodiment of the present invention; Fig. 2 a) to d) position and movement states of a wire electrode at different times when performing a simple positioning method; Fig. 3a) a flow chart of a position of the wire electrode in the simple positioning method; Fig. 3b) a flow chart of a speed of the wire electrode in the simple positioning method; Fig. 3c) a flow chart of a voltage difference between the wire electrode and a reference electrode in the simple positioning method; Fig. 4a) to g) position and movement states of a wire electrode at different times when performing a precision positioning method; Fig. 5a) a flow chart of a position of the wire electrode in the precision positioning method; Fig.5b) a flowchart of a speed of the wire electrode in the precision positioning method; Fig. 5c) a flowchart of a voltage difference between the wire electrode and a reference electrode in the precision positioning method; Fig. 6 a schematic illustration for explaining a welding apparatus according to another embodiment of the present invention; Fig. 7 shows a schematic block diagram of a robot welding system according to yet another embodiment of the present invention; and Fig. 8 a schematic flowchart for explaining a method according to another embodiment of the present invention.

[0047] In all figures, identical or functionally equivalent elements and devices are provided with the same reference numerals, unless otherwise indicated. The designation and numbering of the process steps does not necessarily imply a sequence, but rather serves to facilitate differentiation, although in some variants the sequence may also correspond to the numbering sequence. Detailed description of the characters

[0048] Fig. 1 shows a schematic diagram for explaining a welding device 100 according to an embodiment of the present invention. The welding device 100 has a conveyor device 110 for conveying a consumable wire electrode 1 of the welding device 100. The wire electrode 1 can be conveyed, for example, using a drive roller and one or more guide rollers.

[0049] The welding device 100 also has a welding torch 140, which ends in a contact tube 141. The contact tube 141 has a contact tube length L between its beginning at the tube bend of the welding torch 140 and the contact tube end 142. For welding, the wire electrode 1 is usually advanced to a defined free wire electrode length S from the contact tube end 142. During a welding process, it is highly advantageous to know the free wire electrode length S as precisely as possible, particularly if the distance of the contact tube end 142 from a workpiece 170 to be welded is known. In this way, the distance between the wire electrode end 2 and the workpiece 170 is also known. The known distance can also be used for other applications upstream or downstream of the actual welding, such as scanning a workpiece with the wire electrode end 2 for sensing, marking, or the like.

[0050] Fig. 1 also shows that the welding device 100 has a welding power source 190, which is designed to provide electrical power, in particular welding power for welding, for the welding device 100. The welding power source 190 and the conveyor device 110 can be arranged in different housings, as in Fig. 1 shown schematically, can be integrated into one and the same housing and / or the like. The conveyor device 110 can also be arranged entirely in a separate housing or, for example, in the case of a push-pull conveyor device, can be arranged partially near or in the welding power source 190 and partially near or in the welding torch 140, so that the wire electrode 1 is partially pushed forward ("push") and partially pulled ("pull").

[0051] The welding device 100 also has a wire electrode contact device 150, by means of which the wire electrode 1 can be and is electrically contacted. Fig. 1 The case is shown in which the wire electrode contact device 150 contacts the wire electrode 1 by means of a drive roller. In order to ensure the reliable conveyance of the wire electrode 1, it is usually provided that such a drive roller is always in firm contact with the wire electrode 1. For this reason, it is therefore advisable to also use this conveyor roller for electrically contacting the wire electrode 1. Alternatively, the potential of the wire electrode 1 could also be tapped at a push-pull unit. In some embodiments, it can be provided that a rotor shaft of an electric motor is at the electrical potential of the wire electrode 1, for example because the drive roller and clamping adapter are not designed to be electrically insulating. In this case, the potential of the wire electrode 1 can therefore also be tapped at the rotor shaft.

[0052] The welding device 100 also has a reference electrode 160 which is electrically connected to a reference potential. Fig. 1 In the example shown, the reference electrode 160 is connected to ground GND or, in other words, to the welding negative, which is also connected to the workpiece 170. The welding current source 190 is designed and configured to generate an electrical voltage, the welding voltage, between the contact tube 141 and the workpiece 170. For this purpose, the welding current source 190 has a positive electrode 161, which, as in Fig. 1 again shown schematically, is electrically connected to the contact tube 141 via an electrical line 163.

[0053] Between the conveyor device 110 and / or the welding torch 140, the wire electrode 1 normally runs at least partially within a core 3, which in this case is electrically insulating. Alternatively, the core can also be electrically conductive, in which case, however, electrical insulation must be provided between the core 3 and the contact tube 141 as well as the welding potential. The core 3 usually runs within a hose package 4. The electrical lines 163 can also run entirely or partially within the hose package 4, as in Fig. 1 is also shown schematically.

[0054] When, advanced by the conveyor device 110, the wire electrode 1 finally enters the contact tube 141 from the tube bend of the welding torch 140, the wire electrode 1 contacts the contact tube there in an electrically conductive manner and is thereby brought to the same potential. Since the location (or contact point) at which this occurs, namely the beginning of the contact tube 141, is known, information about a change in an electrical parameter, e.g., a current or voltage change, at the wire electrode 1 can be used according to the invention to determine that the wire electrode end 2 is currently located at the stated position, i.e., at the contact point of the contact tube 141.

[0055] At the Fig. 1 In the embodiment shown, a voltage measuring device 120 is provided as the electrical parameter measuring device, which is designed to measure a voltage between the wire electrode contact device 150 (and thus the wire electrode 1 itself) on the one hand and the reference electrode 160 (here to ground GND) on the other hand. The voltage measuring device 120 can, as in Fig. 1 shown, may be part of the welding power source 190, but it may also be arranged in another housing of the welding device 100, for example in the conveyor device 110 or in yet another separate housing.

[0056] Furthermore, the welding device 100 has a control device 130 configured to perform at least one positioning method. The control device 130 can also be integrated into the welding power source 190, into the conveyor device 110, and / or into another housing of the welding device 100.

[0057] The control device may include conventional computing units, such as a microprocessor, a central processing unit (CPU), a graphics processing unit (GPU), an application-specific integrated circuit (ASIC), a field-programmable logic gate (FPGA), and / or the like. Furthermore, the control device 130 may include a non-volatile data storage device, such as a hard disk or a magnetic storage device such as a solid-state drive (SSD). The control device 130 may also include a random access memory (RAM). The control device 130 may also be implemented in whole or in part by a cloud computing platform and / or a remotely connected server.For this purpose, the conveyor device 110 and / or the welding power source 190 can have a corresponding interface, for example an Ethernet interface, which can be wired or wireless (WiFi), a radio interface and / or the like.

[0058] In the following, two different positioning methods will be described, according to which, according to the invention, the wire electrode 1 can be conveyed into a position with a defined free wire electrode length S from the contact tube end 142. First, Fig. 2 und Fig. 3 a simple positioning procedure ("simple positioning procedure") is described. Then, using Fig. 4 and Fig. 5 A precision positioning method is described. One and the same welding device 100 can be designed and configured such that it can perform both a simple positioning method and / or a precision positioning method, or even other positioning methods, between which, for example, a user can freely choose.

[0059] As described above, it is also possible for a higher-level control instance, for example, a so-called system control device, to select one of the positioning methods available on the welding device 100. This can be done, for example, depending on the available time period, so that, in particular, the most precise positioning method that can be carried out within the available time period can be carried out.

[0060] The basic idea of ​​the simple positioning method is Fig. 2 The subfigures a) to d) of Fig. 2 show different times t = t1, t = t2, t = t3, t = t4, where t1 <t2<t3<t4 gilt. Die Unterfiguren a) bis d) von Fig. 2 each show the wire electrode 1 moving forward at a feed rate V0, i.e. in the direction of the contact tube end 142, initially only within the core 3, later partially within the contact tube 141 and finally (t = t4) beyond it, so that a free wire electrode length S ("stickout") is created.

[0061] In Fig. 2a ), at time t = t1, it is shown how the wire electrode 1 moves forward at the conveying speed V0 within the core 3 in the direction of the contact tube end 142.

[0062] Fig. 3 shows in the subfigures a) to c) a characteristic curve to explain the positioning procedure from Fig. 2 , where the times t1, t2, t3 and t4 are also shown. Fig. 3a ) shows a wire position x as a function of time t, where the wire position x is plotted from an arbitrary zero point within the core. Fig. 3b ) shows a conveying speed at which the wire electrode 1 is moved by the conveying device 110 as a function of time t. Fig. 3c ) finally shows a voltage U measured by the voltage measuring device 120 as a function of time t between the wire electrode 1 and the reference electrode 160. In the Fig. 1 In the case shown, the reference electrode 160 is connected to ground GND. It is understood that other reference electrodes 160 may be used, as already described above and as will be explained below with reference to Fig. 6 will be explained further.

[0063] As can be seen from the comparison of Fig. 2 und Fig. 3 As can be seen, at time t1, the wire electrode 1 moves forward at the constant speed V0 and thus with a linear increase in the wire position x, while the voltage U remains at zero. At time t2, the wire electrode 1 touches the electrical contact tube 141 for the first time, which is at the positive potential of the welding power source 190 (welding plus). This electrical potential is therefore also directly applied to the wire electrode 1, which in Fig. 3c ) is evident from the sudden increase in the voltage level at time t2. Theoretically, the position of the wire electrode 1 is already known at this time. The control device 130 can thus determine, using the known contact tube length L, that in order to provide the desired free wire electrode length S, the wire electrode 1 must be conveyed by exactly the length L + S from time t = t2. In a simple case, the control device 130 can now be configured to transmit corresponding instructions in corresponding control signals to the conveying device 110.

[0064] As in Fig. 3 However, as also shown, due to a signal delay Δt, it may happen that the control device 130 only learns about the voltage increase measured by the voltage measuring device 120 at time t2 at time t3, t3=t2+ Δt. This signal delay Δt thus causes the control command to feed the wire electrode 1 by L + S, for example, actually only, as in Fig. 2c ), at time t3, at which the wire electrode 1 has already penetrated a distance Δx into the contact tube 141.

[0065] The aforementioned signal delay Δt between the measurement of the voltage change at t2 and the processing by the control device 130 can also be expanded to consider the signal delay with which the control commands actually arrive at the conveyor device 110. It is evident that the aforementioned signal delays cause a (slight, but nevertheless undesirable) deviation of the actually existing free wire electrode length S from the desired and defined target value. The control device 130 can therefore be configured to take into account the aforementioned signal delay and to take it into account, in particular to compensate, when generating the control signals, in particular when calculating the wire electrode length still to be conveyed.As explained above, a signal delay value indicating the signal delay may be provided by a runtime provision module 131 of the controller.

[0066] The more accurately the signal delay value Δt is predetermined or even determined dynamically or regularly, the more accurately the signal delay can be compensated and thus the defined and desired target value for the free wire electrode length S can be achieved as accurately as possible.

[0067] In the following, Fig. 4 and Fig. 5 a precision positioning method can be described, which, for example, is also carried out by the welding device 110 according to Fig. 1 can be carried out, either as an alternative to or optionally as an alternative to the simple positioning method according to Fig. 2 und Fig. 3 .

[0068] Fig. 4 with subfigures a) to g) schematically represents the same situation as Fig. 2 namely the respective position of the wire electrode 1, which is conveyed from the core 3 towards the contact tube 141 and how the precision positioning process takes place. Fig. 5a ) to c) show, with reference to the precision positioning method, the same graphs as Fig. 3a ) to c) with reference to the simple positioning method.

[0069] The fundamental idea behind the precision positioning method is that the positioning error of the wire electrode 1 that exists in the simple positioning method scales essentially linearly with the speed V0 of the wire electrode 1. While a particularly high speed V of the wire electrode 1 is preferred for positioning the wire electrode 1 so that the positioning process can be carried out and completed as quickly as possible, for particularly precise positioning, it would be advantageous if the feed rate V were particularly low in order to further reduce the position error Δx due to the propagation time error (signal delay Δt). The method described above for compensating this error using the signal delay value can of course also be applied.

[0070] The idea behind the precision positioning method is therefore that, in a first, rough step, which is carried out at a relatively high, positive first conveying speed V1, the position of the wire electrode, in particular of the wire electrode end 2, is roughly determined. This is done by measuring a voltage change using the voltage measuring device 120 between the wire electrode 1 and the reference electrode 160. This is shown in Figures Fig. 4a) und Fig. 4b ) and the times t = t1 and t = t2, which lead to the processes in Fig. 2a) und Fig. 2b ) are analogous.

[0071] Subsequently, again with a certain signal delay, the control device 130 instructs the conveyor device 110 to stop the wire electrode 1 and to move backward at a second speed R2. The backward movement begins at time t = t3 and continues until time t = t4. Since the wire electrode 1 remains in electrical contact with the contact tube 141, the voltage U measured by the voltage measuring device 120 remains different from zero, while the wire position x slowly decreases. This continues until, at a time t5 as in Fig. 4e ), the wire electrode 1 is just electrically released from the contact tube 141, which in turn results in a voltage drop of the voltage U to zero, as shown in Fig. 5c ) at time t5.

[0072] The retraction at the second, negative speed R2 serves to reposition the wire electrode 1 as precisely as possible close to the contact point with the contact tube 141, so that the steps already known from the simple positioning method can be performed again, but with increased precision. Therefore, it is preferred that the second speed R2, which is negative, be selected to be smaller in magnitude than the first speed V1, which is positive, in particular to be less than 50%, particularly preferably less than 10%, particularly preferably less than 5% of the first speed V1.

[0073] At time t5, the conveyor device 110 is again instructed by the control device 130 to convey the wire electrode 1 forward, specifically at a third speed V3, which is positive and smaller in magnitude than the first speed V1. The third speed V3 can be equal in magnitude to the second speed R2 or even smaller than it.

[0074] For example, the first speed can be up to 150 m / min, the second speed up to 100 m / min and / or the third speed up to 75 m / min.

[0075] From time t5 onwards, the same procedure is carried out as with the simple positioning procedure, with the difference that the output speed is now not the original forward conveying speed V1 (or V0 in Fig. 2 und Fig. 3 ), but the lower speed V3. The corresponding runtime error, which of course also occurs when conveying at the second speed R2 and the third speed V3, can therefore in principle be neglected and is in Fig. 5 also not shown in detail. In principle, however, as mentioned, it is possible to additionally take runtime differences into account in the precision positioning method by providing the runtime provision module 131 with a corresponding signal delay value, which the control device 130 then compensates for.

[0076] At time t6, electrical contact is again established between the wire electrode 1 and the contact tube 141, so that the voltage U again rises to the non-zero value Us. Due to the low speed V3, the control device 130 thus knows the current position of the wire electrode end 2 very precisely. The control device 130 can therefore transmit appropriate control signals to the conveyor device 110 to continue conveying the wire electrode 1 forward until the desired free wire electrode length S is set.

[0077] As in Fig. 5b ), this can initially continue at the third (forward) speed V3. This speed can be maintained until the end of the precision positioning process. Alternatively, as shown in Fig. 4b ), the final adjustment can be performed with a fourth positive speed V4 to complete the precision positioning process even more quickly. The fourth speed V4 is therefore preferably greater than the third speed V3.

[0078] The third speed V3 can particularly preferably transition continuously and monotonically into the fourth speed V4. The fourth speed V4 can be selected such that any inaccuracies in the acceleration and deceleration of the wire electrode 1 are of the same order of magnitude as the signal delay error. Therefore, the more precisely the acceleration and deceleration of the wire electrode 1 by the conveyor device 110 is possible, the higher the fourth speed V4 can be selected, for example, up to V4 = V1.

[0079] Fig. 6 shows a schematic representation of another possible embodiment of the present invention. In the Fig. 6 One difference in the embodiment shown is that the voltage measuring device 120 is not designed to measure a voltage between the wire electrode 1 and ground GND. Instead, the voltage measuring device 120 is connected in parallel with a measuring voltage source 121 and in series between the wire electrode 1 (via the wire electrode contact device 150) and a reference electrode 160. The reference electrode 160 is here at the electrical potential of the positive electrode 161 of the welding power source 190. The measuring voltage source 121 can be installed or integrated in the power source 190, but can also be arranged externally or be applied externally. Since a measurement is not constantly necessary (especially not during the welding process), the measuring voltage source 121 can be designed so that it can be switched on and off.For example, it can be provided that the measuring voltage source 121 is switched off (preferably automatically) during a welding process and is automatically switched on again at the end of the welding process (in particular if a repositioning of a welding robot has to take place afterwards).

[0080] As long as the wire electrode 1 is not in electrical contact with the contact tube 141, the voltage measuring device 120 will measure the measurement voltage (or auxiliary voltage) output by the measurement voltage source 121. Suitable values ​​for this measurement voltage are between 3V and 60V. As soon as electrical contact is established between the wire electrode 1 and the contact tube 141, a short circuit occurs instead and is detected by the voltage measuring device 120.

[0081] In this embodiment, a voltage drop to zero (short circuit) can be used to detect the position of the wire electrode end 2. Accordingly, the simple positioning method according to Fig. 2 und Fig. 3 and the precision positioning method according to Fig. 4 and Fig. 5 in the embodiment according to Fig. 6 be applied analogously.

[0082] Instead of a voltage measuring device 120, the variant from Fig. 6 A current measuring device could also be used. Instead of a voltage change, a current change could also be measured, in this case a current increase as soon as the wire electrode 1 touches the contact tube 141.

[0083] Fig. 7 shows a schematic block diagram of a robotic welding system 1000 according to yet another embodiment of the present invention.

[0084] The robot welding system 1000 comprises a welding device 100 according to an embodiment of the present invention, in particular as described in the preceding Fig. 1 bis 6 The robot welding system 1000 also includes a robot device 200 configured to guide the welding torch 140 of the welding device 100. In the present example, the robot device 200 is configured as an approximately man-sized robot arm. The conveyor device 110 of the welding device 100 is arranged, for example, on a drum as a wire dispenser 5 and removes the wire electrode 1 therefrom for conveying.

[0085] The robot welding system 1000 also includes a system controller 300, which is configured to generate and transmit control signals for controlling the robot device 200, as well as to generate and transmit control signals for controlling the control device 130 of the welding device 100. As shown in Fig. 7 As shown, the system control device 300 can be integrated into a housing of the welding power source 190 of the welding device 100 and can, for example, also be integrated into the control device 130 of the welding device 100. Alternatively, the system control device 300 can also be integrated into the robot device 200 or be formed separately, e.g., by an additional computing device such as a cloud computing platform.

[0086] The control device 130 of the welding device 100 is configured to receive, among (ie: together with) the control signals from the system control device 300, a positioning method trigger signal from the system control device 300, in response to which the control device 130 performs one of the at least one positioning method.

[0087] Advantageously, the positioning method is performed while the robot device 200 is in transit between two positions at which the welding device 100 is controlled for welding, with no welding taking place during the transit. The positioning method is thus preferably performed during a dead time of a welding sequence plan, in particular with a positioning method that utilizes the dead time available according to the welding sequence plan to achieve maximum precision when setting the stickout.

[0088] Fig. 8 shows a schematic flow diagram for explaining a method according to another embodiment of the present invention. The Fig. 7 The method explained can be carried out in particular with a welding device or a robot welding system according to an embodiment of the present invention, in particular according to a welding device 100 or a robot welding system 1000 as described in one of the Fig. 1 bis Fig. 8 The method is therefore adaptable according to each described option, variant, or further development of the embodiments of the welding device according to the invention and / or the robot welding system according to the invention, and vice versa.

[0089] In a step S10, a desired free wire electrode length S of the wire electrode 1 is defined, for example by a parameter output of a welding sequence plan, a user input, a presetting and / or the like.

[0090] In a step S20, a voltage between the wire electrode 1 and a reference electrode 160 is measured, in particular continuously monitored. As described above, the reference electrode 160 can, for example, be connected to ground GND or to the welding negative, the welding positive, or even to another defined potential value. What is crucial is that a change in the measured or monitored voltage can be detected upon contact of the wire electrode 1 with an electrical contact point, wherein the distance along the path of the wire electrode 1 between the contact point and the contact tube end 142 is known.

[0091] In a step S30, the wire electrode 1 is conveyed toward a contact tube 141, more precisely: toward the contact tube end 142. If the wire electrode end 2 is already inserted into the contact tube 141, this can be determined from the measured voltage. Before performing the subsequent steps, the wire electrode end 2 can then first be retracted by means of the conveying device 110 until it is again outside the contact tube 141, similar to the precision positioning method described above.

[0092] In a step S40, a current position of the wire electrode end 2 of the wire electrode 1 is determined based on a measured voltage change of the measured voltage while the wire electrode 1 is conveyed, in particular a voltage change from zero to the reference potential of the reference electrode 160 or from the reference potential to zero.

[0093] In a step S50, the wire electrode 1 is conveyed based on the determined current position until the defined free wire electrode length S is present between the wire electrode end 2 and the contact tube end 142.

[0094] The detection S40 of the current position of the wire electrode end 2 can be carried out in particular according to the simple positioning method described above and / or according to the precision positioning method described above.

[0095] The precision positioning process can in particular proceed as described with reference to Fig. 4 and Fig. 5 and may include the following steps: In a step S41, a first voltage change is detected (e.g. from Us to 0 in Fig. 5c ) at time t2), while the wire electrode 1 is conveyed forward at a first speed V1 towards the contact tube end 142.

[0096] In a step S42, the wire electrode 1 is conveyed backwards at a second speed R2 at least until (advantageously slightly beyond) a second voltage change is detected (e.g. from 0 to Us in Fig. 5c ) at time t5).

[0097] In a step S43, the wire electrode 1 is conveyed forward at a third speed V3 at least until a third voltage change is detected (e.g. from 0 to Us as in Fig. 5c ) at time t6).

[0098] The determination S40 of the current position of the wire electrode end 2 is based at least on a measurement with which the third voltage change was detected, wherein the third speed V3 is preferably lower than the first speed V1 (V3 <V1). Insbesondere kann der Zeitpunkt t6 der dritten Spannungsänderung mit der Position des Drahtelektrodenendes 2 an einem definierten elektrischen Kontaktpunkt (z.B. Beginn des Kontaktrohrs 141) assoziiert werden. Zusammen mit einer Information über einen Abstand des Kontaktpunkts zu der gewünschten Position des Drahtelektrodenendes 2 (z.B. Kontaktrohrlänge L plus Stickout S) kann somit in einem Schritt S44 bestimmt werden, wie weit die Drahtelektrode 1 nach dem Zeitpunkt t6 noch zu fördern ist oder war. In dem Schritt S50 kann dann die entsprechende Förderung durch die Fördereinrichtung 110 durchgeführt werden, z.B. mit einer vierten Geschwindigkeit V4, wobei bevorzugt: V 4 > V 3 V 4 < V 1 or V4=V1, and / or V 4 > R 2 applies.

[0099] In connection with a robot welding system 1000, for example as in connection with Fig. 7 As described above, the method can optionally comprise further steps. For example, in a step S60, information about an impending dead time of the welding device 100 can be received. In a step S70, based on the impending dead time (e.g., when moving the robot device 200 to the start of the next welding process), a precision positioning method can be selected, which is then carried out, such as the simple positioning method and / or the precision positioning method. The selection is preferably made according to the criterion that the most precise positioning method that can be fully carried out within the dead time should be selected.

[0100] However, in variants of the method it can also be determined that a positioning process should always be carried out between two welding processes and that the dead time (i.e. the welding-free time) is extended in order to ensure that a desired positioning process can be carried out completely.

[0101] In the foregoing detailed description, various features have been combined into one or more examples for clarity of illustration. It should be understood, however, that the above description is merely illustrative and not restrictive. It is intended to cover all alternatives, modifications, and equivalents of the various features and embodiments. Many other examples will be readily apparent to those skilled in the art based on their skill in the art in light of the above description.

[0102] The embodiments were chosen and described in order to best illustrate the principles underlying the invention and their possible practical applications. This will enable those skilled in the art to optimally modify and utilize the invention and its various embodiments with respect to the intended purpose. It is further understood that units described as separate may be partially integrated with one another.

[0103] The inventive concept can be described as follows: The invention provides a welding device 100 and a method for conveying a wire electrode 1 into a position with a defined free wire electrode length S from a contact tube 141 (in particular contact tube end 142) of a welding torch 140 of a welding device 100. Information about a voltage change between the wire electrode 1, on the one hand, and a reference electrode 160, on the other hand, is used to determine a position of the wire electrode end 2 at the time of the voltage change. The wire electrode can then be precisely conveyed to the desired position. List of reference symbols

[0104] 1 Wire electrode 2 Wire electrode end 3 Core 4 Hose package 5 Wire dispenser 100 Welding device 110 Conveyor device 120 Voltage measuring device 121 Measuring voltage source 130 Control device 140 Welding torch 141 Contact tube 142 Contact tube end 160 Reference electrode 161 Electrode 163 Leads 170 Workpiece 190 Welding power source 200 Robot device 300 System control device 1000 Robot welding system L Contact tube length S Free wire electrode length in front of the contact tube S10..S50 Process steps t1..t6 Times

Claims

1. Welding device (100), comprising: a conveying device (110) for conveying a wire electrode (1) of the welding device (100); a wire electrode contact device (150) for electrically contacting the wire electrode (1); a reference electrode (160) which is or can be electrically connected to a reference potential; an electrical parameter measuring device (120) which is configured to measure an electrical parameter between the wire electrode contact device (150) and the reference electrode (160); a welding torch (140) with a contact tube (141) which is or can be electrically connected to a defined electrical potential; and a control device (130) which is configured to carry out at least one positioning method, characterised in that in the at least one positioning method the wire electrode (1) is conveyed by the conveying device (110) into a position with a defined free wire electrode length (S) from a contact tube end (142) of the contact tube (141), in that, for carrying out the at least one positioning method, the control device (130) is configured: - to determine a current position of a wire electrode end (2) of the wire electrode (1) on the basis of at least one measurement in which a change in the electrical parameter measured by the electrical parameter measuring device (120) is detected upon electrical contact between the wire electrode end (2) and the contact tube (141) while the wire electrode (1) is being conveyed by the conveying device (110), while the contact tube (141) is connected to the defined electrical potential and the reference electrode is connected to the reference potential; and - to control the conveying device (110) using a known contact tube length (L) of the contact tube (141), to convey the wire electrode (1) on the basis of the determined current position until the defined free wire electrode length (S) is present between the wire electrode end (2) and the contact tube end (142).

2. Welding device (100) according to claim 1, wherein the reference electrode (160) is or can be electrically connected to earth (GND), and the electrical parameter measuring device comprises a voltage measuring device (120) which is configured at least to measure a voltage between the wire electrode (1) and earth (GND) when the reference electrode (160) is electrically connected to earth (GND).

3. Welding device (100) according to claim 1, wherein the reference electrode (160) is or can be electrically connected to a contact tube (141) of a welding torch (140) of the welding device (100), and the electrical parameter measuring device comprises a voltage measuring device (120) which is configured at least to measure a voltage between the wire electrode (1) and the contact tube (141) when the reference electrode (160) is electrically connected to the contact tube (141).

4. Welding device (100) according to any of claims 1 to 3, wherein the wire electrode contact device (150) has a sliding contact and / or a drive roller for the wire electrode (1).

5. Welding device (100) according to any of claims 1 to 4, wherein the control device (130) has a runtime provision module (131) which is configured to provide a signal delay value for components of the control device (130), the control device (130) being configured to take the provided signal delay value into account when determining the current position of the wire electrode end (2).

6. Welding device (100) according to any of claims 1 to 5, wherein the control device (130) is configured to determine the current position of the wire electrode end (2) on the basis of a plurality of measurements of changes in the electrical parameter.

7. Welding device (100) according to any of claims 1 to 6, wherein the at least one positioning method comprises a precision positioning method, and in the precision positioning method the control device is configured: - to detect a first change in the electrical parameter by means of the electrical parameter measuring device (120) while the wire electrode is being conveyed forwards towards the contact tube (141) at a first speed (V1) by the conveying device (110); - subsequently to control the conveying device (110) to convey the wire electrode (1) backwards at a second speed (R2) at least until a second change in the electrical parameter is detected by means of the electrical parameter measuring device (120); - subsequently to control the conveying device (110) to convey the wire electrode (1) forwards at a third speed (V3) until a third change in the electrical parameter is detected by means of the electrical parameter measuring device (120); and - to determine the current position of the wire electrode (1) at least on the basis of a measurement with which the third change in the electrical parameter was detected, the third speed (V3) preferably being lower than the first speed (V1).

8. Welding device (100) according to claim 7, wherein, after the current position of the wire electrode (1) has been determined, the control device (130) is configured to continue to convey the wire electrode (1) forwards at a fourth speed (V4) until the defined free wire electrode length is present between the wire electrode end (2) and the contact tube end (142).

9. Robot welding system (1000), comprising a welding device (100) according to any of claims 1 to 7, a robot device (200) configured to guide the welding torch (140) of the welding device (100); and a system control device (300) configured both to generate and transmit control signals for controlling the robot device (200) and to generate and transmit control signals for controlling the welding device (100); wherein the control device (130) of the welding device (100) is configured to receive, among the control signals, a positioning method trigger signal from the system control device (300), in response to which the control device (130) performs one of the at least one positioning methods.

10. Robot welding system (1000) according to claim 9, wherein the positioning method is carried out while the robot device (200) is in transit between two positions at which the welding device (100) is controlled for the welding, no welding taking place during the transit.

11. Method for conveying a wire electrode (1) into a position with a defined free wire electrode length (S) from a contact tube (141) of a welding torch (140) of a welding device (100), comprising: - defining (S10) a desired free wire electrode length (S) of the wire electrode (1); - measuring (S20) an electrical parameter between the wire electrode (1) and a reference electrode (160); - conveying (S30) the wire electrode (1) in the direction of a contact tube (141); characterised by - determining (S40) a current position of a wire electrode end (2) of the wire electrode (1) on the basis of a measured change in the measured electrical parameter upon electrical contact between the wire electrode end (2) and the contact tube (141), which is electrically connected to a defined electrical potential, while the wire electrode (1) is being conveyed; - conveying (S50) the wire electrode (1) on the basis of the determined current position and using a known contact tube length (L) of the contact tube (141) until the defined free wire electrode length (S) is present between the wire electrode end (2) and the contact tube end (142).

12. Method according to claim 11, wherein the reference electrode (160) is electrically connected to earth (GND), and, for measuring the electrical parameter, a measurement (S20) of the voltage between the wire electrode (1) and earth (GND) is carried out.

13. Method according to claim 12, wherein the reference electrode (160) is electrically connected to a contact tube (141) of the welding torch (140) of the welding device (100), and, for measuring the electrical parameter, a measurement (S20) of the voltage between the wire electrode (1) and the contact tube (141) is carried out.

14. Method according to any of claims 11 to 13, comprising: - detecting (S41) a first change in the electrical parameter while the wire electrode (1) is being conveyed forwards towards the contact tube end (142) at a first speed (V1); - conveying (S42) the wire electrode (1) backwards at a second speed (R2) at least until a second change in the electrical parameter is detected; - conveying (S43) the wire electrode (1) forwards at a third speed (V3) at least until a third change in the electrical parameter is detected; and - determining (S40) the current position of the wire electrode end (2) at least on the basis of a measurement with which the third change in the electrical parameter was detected, the third speed (V3) preferably being lower than the first speed (V1).

15. Method according to claim 14, wherein, after the current position of the wire electrode end (2) has been determined (S50), the wire electrode (1) is conveyed forwards (S60) at a fourth speed (V4) until the defined free wire electrode length (S) is present between the wire electrode end (2) and the contact tube end (142).