Patent Application
20220032392
The present invention relates to a method for operating a welding device for resistance welding, to a welding robot, to a computer program product and to a use of an electromechanical drive of a welding device.
Resistance welding, for example by means of welding robots or robot-guided welding guns, is a joining method that is typically used in automotive body making. The best possible quality and the shortest cycle times are required here. However, the welding electrodes thereby undergo continuous wear, which influences the quality of the joints. In order to be able to respond to this, DE 10 2016 211 684 A1 for example discloses a method for the resistance welding of workpieces of aluminum or aluminum alloys with a welding gun, wherein an assessment variable for characterizing the metal pickup on the electrodes is determined from a force profile of the electrodes during the welding. DE 10 2016 209 640 A1 discloses a method for calibrating a welding gun for resistance welding, wherein at least one measured value of at least one variable characterizing the welding process, such as for example an electrode force, is determined during the implementation of regular welding processes, in order then to decide in dependence on this measured value whether a calibration of the welding gun is possibly necessary. However, the approaches mentioned are relatively inaccurate and, for example, do not allow cleaning, in particular milling, of the electrode caps of the welding device in a way that is specifically selective and carried out as and when required.
Therefore, an object of the present invention is to provide a method for operating a welding device, a welding robot, a computer program product and a use of an electromechanical drive of a welding device that allow in particular electrode caps to be milled in a way that is based on quality, carried out as and when required and conserves resources.
According to the invention, a method for operating a welding device for resistance welding, in particular for resistance spot welding, comprises the steps of:
An exact force measurement in this case advantageously allows an exact distance measurement. By means of the “distance”, a position or a spacing of the electrodes, in particular the electrode caps, in relation to one another can be determined. This spacing may change as a result of dirt, contaminants and/or metal picked up. From this, it can be detected that cleaning or changing of the electrodes or the component parts thereof is possibly necessary, while it is also known as a result of the determination or evaluation of the distance in particular whether for example much material or little material has to be removed in the course of electrode cap milling.
According to a preferred embodiment, the welding device comprises an electromechanical drive, wherein the method comprises the step of:
Advantageously, therefore, no additional sensors or the like, which would first have to be laboriously applied and so on, are used. Instead, the drive of the welding gun itself is used to carry out the verification measurement. Advantageously, the welding device, comprising in particular a or the welding gun, has a servomotor with a, preferably internal, possibly piezoelectric, force transducer. For the distance measurement and positioning of the welding gun, advantageously a suitable resolver is used. A resolver is an electromagnetic measuring transducer for converting the angular position of a rotor into an electrical variable. Advantageously, a multipole resolver is used, in particular for example an eight-pole resolver.
The welding gun typically comprises two electrodes. Each of the electrodes in this case comprises an electrode shank and an electrode cap, which is for example arranged on the end of the electrode shank, or the electrode holder or else the electrode arm, for example is fitted on it.
According to one embodiment, the method comprises the step of:
The method thereby advantageously allows both for example the detection of wear of the electrode shank and the determination and detection of wear of the electrode cap(s). Expediently, a number of comparison values, such as for example the aforementioned base value and the aforementioned reference value, are used for this.
According to one embodiment, the method comprises the step of:
Over time, not only the electrode caps but also the shaft on which the electrode caps are arranged become worn. For example, they become shorter. As a result of the verification measurement after an electrode cap change or as a result of the comparison of successive base values, it can be advantageously determined to what extent for example an electrode shank has become shorter.
According to one embodiment, the method comprises the step of:
The cleaning of the electrode caps comprises in particular a removal, in particular a mechanical removal, of material from the electrode caps, in order to clean them and in particular to free them of metal picked up or contaminants. Advantageously, this is not performed randomly, but as and when required and in a way conserving resources, since it can be monitored by the verification measurements for example how much has been mechanically removed.
Expediently, verification measurements are carried out in specific, predeterminable and possibly changeable time intervals. According to one embodiment, after a welding operation, the welding gun moves into a defined position and the verification measurement is started. The distance thereby ascertained is compared with the last reference value, with the current wear being inferred in this way. If the wear is within a definable, and preferably also adaptable, tolerance window, welding can be continued, otherwise cleaning, in particular milling, is performed.
Expediently, the method comprises the step of:
The aforementioned resolver that is used for the distance measurement and positioning of the welding gun may realize an accuracy of 50 μm in the installed state. Together with the highly accurate force measurement, these boundary conditions allow not only an extremely clean and reliable welding operation, but also the direct and immediate implementation of verification measurements, without the use of further or external measuring equipment.
As already mentioned, the verification measurement is preferably always carried out at or in the same position (of the welding guns), in order as far as possible not to influence the measurement. According to one embodiment, in the verification measurement the electrodes are repeatedly moved together or toward one another. The values thereby determined are advantageously averaged and/or used together for a plausibility check.
Preferably, the method also comprises the step of:
According to one embodiment, the method comprises the steps of:
The monitoring is in this case advantageously performed by means of a verification measurement after the milling operation. This verification measurement can be used to find out whether for example a certain amount of material to be removed by milling, which may for example lie in a range of 500 μm, has actually been removed. If this is not the case, for example, the milling force may be corrected upwardly or downwardly. At this point it should also be mentioned that the milling operation may be conducted in such a way that the welding gun moves with its electrode caps toward a milling tool and/or that a suitable milling tool is moved toward the electrode caps.
According to one embodiment, the method comprises the step of:
Advantageously, a dynamic adaptation of the parameters for the following milling cycle can take place if the amount of material removed by milling is outside a certain tolerance band. The parameters in this case comprise in particular the milling force, the milling time and/or the milling interval, that is to say the time interval between two milling cycles. If tolerance limits are exceeded, a warning, for example that a milling tool of the electrode cap miller must be changed because for example it has become worn, may also be issued.
The invention also relates to a welding robot, comprising a controller, which is designed to carry out the method according to the invention. Furthermore, the invention comprises a computer program product, which contains software with sections of software code that cause a computer to carry out the method according to the invention when the computer program product is run on the computer.
Furthermore, the invention comprises the use of an electromechanical drive of a welding device, in particular a welding gun, for monitoring electrode wear. Expediently, the electromechanical drive comprises a servomotor with an internal, and possibly piezoelectric, force transducer and a suitably formed resolver for distance measurement and positioning of the welding gun. Advantageously, a multipole resolver is used, in particular for example an eight-pole resolver. Alternative angular position encoders or angular encoders that can likewise be used are for example a potentiometric encoder, an incremental encoder and/or an absolute encoder. The aforementioned eight-pole resolver is however preferred in particular, because of the high accuracy that is achievable.
The advantages and features mentioned in connection with the method apply analogously and correspondingly to the welding robot, the computer program product and the use, and vice versa as well as in combination.
The provided method allows the electrodes to be changed and/or cleaned in a way that is based on quality, carried out as and when required and conserves resources, in particular allows the electrode caps to be milled in a way that conserves resources. This is advantageously performed on the basis of the mechanical reference variables force and distance of the welding gun, advantageously on-line or after corresponding presettable (milling) intervals. The reproducibility of the milling cycles and the electrode life within each milling cycle can be increased. Moreover, the electrode caps can be milled more often, since the removal of material is not performed randomly but in a way that is specifically selective and carried out as and when required, in particular also by means of the dynamic adaptation of the aforementioned parameters.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/071713 | 8/13/2019 | WO | 00 |
