Mobile welding robot with remote motion center

Abstract

The present disclosure relates to a welding robot for performing a welding operation when engaged by a positioning arm, the welding robot comprising a robot arm configured to be connected to the positioning arm at an attachment point and a welding gun connected to the robot arm, at least a first remote center of motion defined by a point on a kinematic chain along the robot arm and the positioning arm, the welding robot configured to continuously monitor at least the first remote center of motion and a tool center point of the welding gun during operation of the welding gun.

Description

[Technical field]

[0001] The present disclosure relates to welding robots, systems and methods for performing welding operations. [Background technology]

[0002] Manufacturers around the world are turning to automation to help alleviate labor shortages, increase productivity, and improve the quality of manufacturing tasks. Therefore, robotic welding systems are becoming more commonly used to provide cost-effective, flexible, and safe automated solutions for a wide range of production tasks.

[0003] One of the challenges in using robotic welding is the supply of welding equipment to the welding site. Furthermore, in some cases, for example when welding large structures, the positioning of the welding equipment can be cumbersome in addition to transportation. Transporting large equipment takes time and effort, and maintenance of the welding equipment is difficult to perform in a cost-effective and efficient manner. Furthermore, due to the structure in which the welding equipment is installed, the movement of the welding equipment to another work site may be limited.

[0004] A further challenge with the use of robotic welding is that the structures on which the welding equipment is installed are generally not stable. Depending on the welding site, the structures may be affected by noise and vibrations in the environment. Noise and vibrations may also be caused by structures provided in association with the welding robot. These structures may be, for example, cranes, lifting devices, levers used to transport and / or position the welding robot. As a result, the welding task cannot be performed accurately. Thus, the quality of the weld is significantly reduced.

[0005] Therefore, there is a need for advanced robotic welding solutions that feature a high degree of automation with enhanced stability and flexibility. This gap in the art extends further to robotic welding solutions for construction sites for welding large structures. Furthermore, flexible robotic welding solutions should be developed that allow manufacturers to fit welding robots into existing worksite flows. Summary of the Invention [Problem to be solved by the invention]

[0006] Accordingly, it is an object of the present disclosure to overcome the above-mentioned challenges in welding fields. [Means for solving the problem]

[0007] The present approach overcomes the above-mentioned shortcomings and provides the first welding robot that can compensate for undesired movements of a positioning device, such as a mobile crane, used to hold and / or transport the welding robot.

[0008] The present disclosure relates in a first aspect to a welding robot for engaging with a positioning arm to perform a welding operation. The welding robot comprises a robot arm connectable at an attachment point to the positioning arm and a welding gun connected to the robot arm. An important aspect of the present disclosure is that at least a first remote center of motion is defined by a point on a kinematic chain along the robot arm and the positioning arm. Furthermore, the welding robot is configured to continuously monitor at least the first remote center of motion during operation of the welding gun, such that, for example, displacements of the positioning arm are compensated for. Preferably, the welding robot is configured to continuously monitor the tool center point. Advantageously, undesired displacements of the welding gun are thereby minimized or even eliminated.

[0009] Thus, the present disclosure contemplates a welding robot for engagement with a positioning device, such as a positioning arm or a device having a positioning arm, which carries and positions the welding robot proximate to an article to be welded. If a welding gun performs a welding operation while the welding robot is engaged with the positioning arm, it may be very difficult to avoid undesirable movements of the positioning arm. Undesirable movements may be, for example, vibrations, noise, or any other environmental factors that affect the stability of the positioning arm. Such undesirable movements may be imposed on the welding robot, thereby adversely affecting the welding operation.

[0010] Therefore, the present disclosure proposes to define a remote center of motion (RCM). At least a first RCM can be defined on the kinematic chain along the robot arm and the positioning arm. Thus, the RCM can be any point along the kinematic chain of the robot arm and the positioning arm, i.e., the RCM point can be freely selected. It should be noted that, in general, the degrees of freedom (DOFs) before the RCM are used to correct undesired displacements of the RCM, and the DOFs after the RCM are used to create the task motion. Thus, in a preferred embodiment of the present disclosure, the robot arm engages with the positioning arm at an attachment point. In a further preferred embodiment, the attachment is the RCM.

[0011] Preferably, the welding robot can be configured to measure the movement and / or vibration of the positioning arm as an RCM control loop. This foresees that the welding robot can be configured to measure an undesired displacement of the RCM. Based on a comparison of the measured RCM at a point in time during the welding operation with at least a first determined RCM, an undesired displacement of the RCM can be calculated. Advantageously, said undesired displacement caused due to the movement or vibration of the positioning arm can be compensated. Thus, a major advantage of the present disclosure is that the welding gun can be controlled to minimize noise and vibration caused by the positioning arm. Thus, the present disclosure can provide a flexible welding robot that can engage with a variety of positioning arms while ensuring high quality welds.

[0012] In a second aspect, the present disclosure relates to a robotic welding system for performing a welding task, the system comprising: a positioning device having a positioning arm; - a welding robot, at least a first robotic arm connected to a positioning arm at an attachment point; and A welding gun connected to a robot arm A welding robot comprising: Equipped with wherein at least a first remote center of motion is defined by a point on a kinematic chain along the robot arm and the positioning arm and / or positioning device, and the system is configured to continuously monitor at least a first remote center of motion during operation of the welding gun such that displacements of the positioning arm and / or positioning device are corrected to minimize undesired displacements of the welding gun. Preferably, the welding robot is configured to continuously monitor the tool center point.

[0013] An important aspect of the present disclosure is that the welding robot and / or welding system is configured to continuously monitor the RCM during the welding operation, for example, by measuring the coordinates of the RCM during the welding operation.

[0014] In a preferred embodiment, the system may be configured to receive sensor inputs from the positioning device and / or the robot arm to calculate the displacement of the RCM from at least a first RCM determined. Thus, undesired displacements of the RCM may be corrected. Advantageously, the system may be configured to solve the inverse kinematics of the entire system such that the RCM is stable at a given time relative to a welding task, such as a welding workpiece.

[0015] Additionally, the welding robot can monitor the tool center point, such as the distance from the welding wire to the workpiece. Thus, a major advantage of the presently disclosed approach is the ability to compensate for both disturbances due to the movement of the positioning arm (and / or positioning device) and deflections that may be caused by the welding process itself.

[0016] The presently disclosed system and method may comprise one or more sensors capable of acquiring data representative of both disturbances. For example, an undesired movement of the welding gun may be detected by an arc sensor. The arc sensor may acquire data on the sum of positioning errors due to external and internal deflections. An external deflection may be any deflection of the positioning arm and / or the robot arm and / or the positioning device that results in an undesired movement of the welding gun, thereby causing the welding gun to deviate from the planned welding path. An internal deflection may be any deflection of the welding task (object) that results in placing the welding gun in an undesired position, such as resulting in a change in the distance between the welding gun and the object. Advantageously, the welding robot may be configured to continuously receive the arc sensor data during the operation of the welding gun so that said sum of positioning errors can be corrected. RCM and / or RCM control, such as calculation of the displacement of the determined at least first RCM, may be used to estimate which part of the error comes from the undesired movement of the positioning device and / or the positioning arm and / or the robot arm and which part comes from the disturbance of the welding path due to the deflection of the welding task. As a result, the approach may ensure an improvement in the welding quality.

[0017] Said compensation of noise and vibration resulting in undesired movement or deflection as described above can be done by moving the RCM to its defined position, such as a predefined position of at least the first RCM. The positioning arm and / or the positioning device can move the RCM to the desired position so that a more stable weld can be achieved. In this way, the system can be configured to keep the RCM stable for the welding task. In this way, any noise and vibration can be counteracted before it affects the welding gun.

[0018] Advantageously, the approach can provide many solutions for providing a stable welding operation. The correction of the undesired displacement of the RCM can be performed by the positioning device, but additionally or alternatively, the undesired displacement of the RCM can also be corrected by the robot arm. The welding robot can be configured to solve an inverse kinematic problem so that the welding robot can calculate the required displacement of the positioning arm and / or the robot arm. The positioning arm and / or the robot arm can then move to correct the calculated displacement of the RCM. However, in some cases, the inverse kinematic problem may not provide a solution to correct the entirety of said undesired movement of the RCM. If the undesired movement is larger than the correction that the robot arm and / or the positioning arm can perform, a maximum possible correction based on inverse kinematics can be performed. This means that the RCM cannot be completely stabilized for the welding task. Therefore, in one embodiment, the system can be configured to calculate at least a second RCM position during the welding operation. Alternatively, the RCM can also be completely corrected at the next time.

[0019] Finally, the present disclosure, in a third aspect, relates to a computer-implemented method for controlling a welding system having a positioning device, a first robotic arm connected to the positioning device at an attachment point, and a welding gun connected to the robotic arm, the method comprising the steps of: - calculating the coordinates of at least a first remote centre of motion defined by a point on a kinematic chain along the robot arm and the positioning device; - measuring the displacement, movement and / or vibration of the positioning device relative to at least a first remote centre of motion or to the welding robot; Includes.

[0020] The method further includes controllably moving the positioner and / or the robot arm such that displacement of the positioner is compensated to minimize undesired displacement of the welding gun.

[0021] In this manner, the disclosed approach can counter vibrations and noises of the positioning device that cause undesired movement of the welding gun, allowing the welding gun to stably operate according to the originally defined welding path.

[0022] Overall, the solution provided by the present disclosure offers several advantages over conventional solutions as the approach offers lower costs, less transportation of large structures, and flexibility to move to different work areas while ensuring accurate and precise welding operations.

[0023] The invention will now be described in more detail with reference to the accompanying drawings. [Brief description of the drawings]

[0024] [Figure 1] 1 illustrates an embodiment of a robotic welding system. [Diagram 2] 1 illustrates one embodiment of a welding robot engaging with a positioning arm. [Diagram 3] 1 illustrates an embodiment of a robotic welding system. [Figure 4] 1 illustrates an embodiment of a robotic welding system with a mobile carriage. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The disclosed welding robot and welding system can counteract undesired movements of the welding gun that may occur due to movement and / or vibration of the positioning arm and / or the positioning device. Advantageously, the present approach provides a solution to improve the precision and accuracy of the welding operation. In general, corrections to minimize undesired displacements of the welding gun can be made by stabilizing the RCM at a given moment.

[0026] In general, an RCM is a point, with or without a physical revolute joint on it, around which a mechanism or part of a mechanism can rotate. Any point or sphere within the angular range of the system can be defined as the pivot point of the end effector or attached tool. The RCM described herein can preferably be a virtual remote center of motion. Thus, from one aspect, the attachment point or point or sphere defined for the RCM may not be mechanically constrained. The RCM may be a virtual point (or sphere) such that the constraint of fixing a point on the robot arm on a mechanically constrained RCM may be removed. Thus, the robot arm can perform RCM operations without having a physically constrained point. As described herein, the RCM may refer to the location of a virtual RCM.

[0027] In some cases, the welding gun may be stable relative to the workpiece. However, when welding large objects, it may be necessary to move the welding gun to reach different areas of the object. Advantageously, the virtual RCM can move along the welding task (workpiece) together with the welding robot. The RCM can thus be a point or an area that moves together with the welding robot according to a predefined welding path of the welding gun. It should therefore be noted that the correction of the displacement of the RCM can be considered as the correction of an undesired displacement of the RCM at a given moment.

[0028] According to the present disclosure, the movement of the positioning arm and / or robot arm and / or RCM and / or tool center point can be monitored during a welding operation. Thus, the displacement of the positioning arm and / or robot arm and / or RCM and / or tool center point with respect to the welding task at a given instant can be detected. As a result, the displacement of the RCM at a given instant can be detected. The instant can be an infinitesimal interval in time, during which the inverse kinematics of the welding robot and / or welding system is solved. The instant can be a predefined time interval.

[0029] In general, the displacement, movement and / or vibration of the positioning device relative to at least a first remote center of motion or the welding robot can be measured. Said measurements can be made by a sensor or a number of sensors. The sensor can be a position sensor embedded in the positioning arm and / or the welding robot and / or provided externally. The sensor can be an encoder. The sensor can also be a combination of a position sensor and an encoder. It is thus envisaged that with this approach the welding robot and / or its system can be configured to receive sensor input from the positioning device and / or from the welding robot.

[0030] In one embodiment, the welding robot may include at least one sensor for measuring the displacement, movement and / or vibration of the positioning arm.

[0031] In one embodiment, the welding robot may be equipped with at least one sensor for measuring the displacement, movement and / or vibration of at least a first remote center of motion.

[0032] In one embodiment, the welding robot may be equipped with at least one sensor for measuring the displacement, movement and / or vibration of the tool center point.

[0033] In one embodiment, the welding system comprises at least one sensor for measuring the displacement, movement and / or vibration of the positioning arm and / or the positioning device.

[0034] The at least one sensor may be, for example, an arc sensor. The arc sensor and a sensor for measuring the displacement, movement and / or vibration of the positioning arm or other part may be provided separately, such that the external sensor is used for the RCM control and the arc sensor is used for the closed-loop control of the task. Advantageously, a combination of the arc sensor and a sensor (such as an external sensor) for measuring the displacement, movement and / or vibration of the positioning arm or other part may be provided.

[0035] In one embodiment, the welding robot and / or the welding system comprises at least one arc sensor for measuring a set of welding process parameters of the welding operation. In a further embodiment, the set of welding process parameters is the welding current and / or the arc voltage. During welding, for example, if the distance between the weld filler and the object changes, the resistance between the weld filler and the object may change. Thus, the measurement of the welding process parameters may be an indication of any changes in the weld path.

[0036] The arc sensor can collect data indicative of the current level of the welding gun. The current level varies as a function of resistance. Therefore, the resistance value can be an indirect measurement of the distance from the welding wire to the item. This means that by using an arc sensor to measure resistance during welding, the welding gun can monitor the tool center point.

[0037] The arc sensor can be any sensor that detects changes in the tool center point or the weld path. These changes can occur due to at least two different sources, such as internal and external. The internal process changes can be any changes caused by the welding process, for example. For example, due to heating of the object, the object being welded can bend, sink or deform relative to its initial shape. Thus, the distance between the weld filler and the object can change due to deflection of the material of the object subjected to high heat from the welding process. These internal changes can be detected by the arc sensor and corrective actions can be calculated.

[0038] External process variations are caused by offsets of the actual weld path relative to the planned path. External process variations are also caused by disturbances from the environment, e.g. vibrations due to the movement of the robot arm and / or an unstable positioning device. Such external variations can be detected by the arc sensor and corrective actions can be calculated. This can be done by combining the arc sensor with RCM control. By combining the sensor data measuring the RCM variations with the sensor data of the arc sensor, the approach can calculate what part of the overall position-orientation error comes from internal process variations and what part comes from external process variations.

[0039] Advantageously, the arc sensor can provide data in such a way that the position of the welding gun can be controlled. In general, the arc sensor data can serve to calculate and correct the distance of the welding gun relative to the object. The disclosed system can be configured to maintain said distance during the welding process. To that end, the welding robot can be configured to receive arc sensor data representing a plurality of measurements of a set of welding process parameters. In one embodiment, the welding robot is configured to continuously monitor the welding process parameters during operation of the welding gun such that the tool center point is maintained along a predefined welding path. This can be performed, for example, by a robot controller that can store correction data that can be used for path planning.

[0040] Generally, the kinematic chain comprises a positioning device and a welding robot. In this combination of chains, the RCM can act as a stable point. The number of degrees of freedom at the point of the RCM may preferably be high enough to handle disturbances that need to be corrected. The arc sensor can be used as an in-process sensor to sense changes in the welding process and / or offsets in the distance between the welding gun and the object. Other disturbance sources can be sensed by other sensors installed in the positioning device. In one embodiment, the approach includes measuring a welding process parameter, such as the welding current. Preferably, the arc sensor can monitor the current level of the welding gun. The positioning device and / or the robot arm can be moved such that the welding process parameter, such as the welding current, is maintained within a predefined range.

[0041] For example, by detecting the current level while pending the welding gun back and forth, calculations and compensation can be made across the groove width. If the current level is higher on one side of the groove compared to the other side, the tool center position is moved to the lower side. Calculations and compensation in the z direction (groove extension direction) can be made as follows: if the average current level across the groove width is below a set threshold, the tool center position can be moved towards the object. If the average current is above a set threshold, the tool center point can be moved away from the object.

[0042] In this manner, the sensor inputs can be used to calculate the displacement of the RCM and the tool center point. As used herein, tool center point refers to a point, sphere, or area used to make necessary adjustments by tracking the welding gun. A tool center point can be defined for each welding gun. The tool center point can be the working point of the welding gun and can be used to determine the position coordinates of the robot arm and / or the welding gun.

[0043] An accurate tool center point is crucial to ensure accurate robot arm movements. An inaccurate tool center point can cause the robot arm to follow a different welding path than originally planned. Inaccuracies can also damage the welding robot or the workpiece. In a preferred embodiment, the welding robot is configured to perform a welding task. Thus, a welding path for performing the welding task can be defined in terms of the coordinates of the tool center point. This means that the tool center point can follow a predefined welding path.

[0044] Advantageously, noise and vibrations arising from at least the positioning device and / or the positioning arm can be compensated at the tool centre point by moving the tool centre point.

[0045] In one embodiment, the welding system can be configured to calculate a relative displacement of the positioning arm and / or the positioning device with respect to the welding robot, e.g., with respect to a tool center point of the welding robot. In a further embodiment, the system can be configured to displace the positioning device and / or the positioning arm and / or the robot arm such that the tool center point of the robot arm is maintained. Similarly, in one embodiment, the welding robot can be configured to calculate a displacement of the tool center point of the welding robot from a predefined tool center point. In a further embodiment, the welding robot can be configured to move the robot arm to compensate for the displacement of the tool center point.

[0046] In a preferred embodiment, the noise and vibrations arising from at least the positioner and / or the positioner arm can be compensated for with the RCM. Thus, the disclosed system can provide a unique solution to the problem of preventing the welding gun from misaligning under the vibrations and noises arising from the positioner arm by monitoring the RCM. The monitoring of the RCM can be monitoring a point of the RCM. In one embodiment, the monitoring point of at least the first remote center of motion is the attachment point of the robot arm relative to the positioner.

[0047] Advantageously, at least the first RCM may be kept stable relative to the tool center point and / or welding task at a given moment during a welding operation. Although the RCM may have a passive coupling such that the RCM may be kept stable in part by damping components, in preferred embodiments of the present disclosure, the inverse kinematic problem is solved.

[0048] General RCM constraints can be formalized to solve the inverse kinematic problem. For general tasks, the approach can derive a constrained kinematic controller for exponential convergence of the task with stable satisfaction of the RCM constraints. This kinematic task controller can provide local convergence even in the presence of parameter uncertainties. Additional stability and robustness analysis specific to the considered application can be applied. In general, the proposed solution of the inverse kinematic problem can take a similar approach in the context of minimally invasive robotic surgery, as disclosed by N. Aghakhani et al. in the Proceedings of the 2013 IEEE International Conference on Robotics and Automation. Thus, the RCM constraints can be formalized for use in combination with other tasks for control design.

[0049] Thus, in one embodiment, the robotic welding system can be configured to calculate a displacement of at least the first RCM. In one embodiment, the system can be configured to correct a displacement of the positioner and / or positioning arm such that the at least the first remote center of motion is maintained. In a further embodiment, the system can be configured to move the positioner and / or positioning arm to correct the calculated displacement of the at least the first remote center of motion. Alternatively or additionally, the welding robot can be configured to allow the robot arm to move to correct the displacement of the at least the first RCM.

[0050] The inverse kinematics of the welding system can be solved to calculate the movement of the RCM required to keep the RCM stable for the welding task at a given moment. The robotic system can be further configured to solve the inverse kinematic problem so that the system determines how to keep the RCM stable. Thus, the system can calculate the degrees of freedom of the robot arm and the positioning arm and analyze how to optimally keep the RCM stable. The analysis to find the optimal solution can be based on various factors such as cost, speed, and operating capacity. As a result, the system can suggest a solution. In some cases, the system can move the robot arm and in some cases, the system can move the positioning arm to correct the displacement of the RCM. In some cases, moving any of the components of the system may not be enough to correct the undesired movement of the RCM. In such cases, a correction can be made to bring the RCM as close as possible to a stable point. Thus, at least the initially defined RCM point, such as the first RCM, can be changed. In one embodiment, the system can be configured to calculate at least a second RCM during the welding operation. This foresees that in one embodiment, the RCM may change for a predefined welding task. The system can be configured to completely correct the undesired displacement during the next moment.

[0051] Therefore, it may be necessary to define (calculate) an updated RCM. In one embodiment, the system may be configured to calculate at least a second remote center of motion. In one embodiment, the welding robot may be configured such that at least a second remote center of motion is defined. In a further embodiment, the welding robot may be configured to continuously monitor at least a second remote center of motion during operation of the welding gun such that displacements of the positioning arm are corrected to minimize undesired displacements of the welding gun. In one embodiment, the robot arm and / or the positioning arm move to correct displacements of the at least a second remote center of motion. Preferably, the system may be configured to calculate multiple remote centers of motion during a welding operation.

[0052] During a welding operation, the corrections can be performed interchangeably by the positioning arm and the robot arm, which foresees that initially the at least first RCM can be stable for a welding task until the at least first RCM is recalculated and replaced by the at least second RCM.

[0053] Additionally, the present disclosure can provide advanced techniques for combining transportation and positioning of welding equipment with operation of the welding equipment.

[0054] In one embodiment, the positioning device is a mobile device, such as a mobile crane. Thus, the welding robot can be transported and positioned with minimal effort. The mobile crane can be, for example, a gantry crane. Advantageously, the dimensions of the gantry, such as the width of the gantry, can be custom-made to meet customer requirements for a specific welding task. The disclosed system set-up with the mobile positioning device allows welding operations to be performed while the welding robot is moved by the mobile crane. In one embodiment, the robotic welding system further comprises a mobile carriage configured to transport and / or position the welding robot. This envisages that the positioning device may comprise a mobile carrier, such as a trolley unit, for transporting and moving the positioning arm.

[0055] Alternatively or additionally, the positioning device may be a device that includes a robotic arm. Thus, in one embodiment, the positioning arm is at least a second robotic arm. As used herein, a robotic arm refers to a mechanical arm or structure that can move linearly and / or rotationally. The robotic arm may be the sum of a mechanism or may be part of a more complex robot.

[0056] In an advantageous embodiment, the welding task has a predetermined frequency, such as 1 Hz or more, preferably 3-10 Hz, more preferably 2-4 Hz. In an embodiment, the sampling frequency of the at least one sensor corresponds to the frequency of the welding task. In an embodiment, the sampling frequency of the at least one sensor and / or the at least one arc sensor is 1000 Hz or more. The advantage of matching the sampling frequency with the frequency of the welding task is to identify undesired movements frequently so that they can be corrected, which may affect the tool center point. Furthermore, with this approach, the inverse kinematics can be solved at a time interval that depends on the sampling frequency. Furthermore, the welding gun vibrates during welding, which can be referred to as weaving during welding. Advantageously, the arc sensor can acquire data according to a weaving frequency, such that at least one data point can be acquired during welding. The weaving frequency can be, for example, 3-10 Hz.

[0057] Advantageously, the present disclosure relates to a computer-implemented method for controlling a welding system including a positioning device, a first robotic arm connected to the positioning device at a mounting location, and a welding gun connected to the robotic arm. The welding gun can be connected to the robotic arm such that the welding gun is responsive to movements of the robotic arm.

[0058] According to the present disclosure, coordinates of at least a first remote center of motion defined by a point on a kinematic chain along the robot arm and the positioning device are calculated. Additionally, the displacement, movement and / or vibration of the positioning device relative to the at least first remote center of motion or the welding robot can be measured. The method can solve an inverse kinematic problem so that movements of the positioning arm and / or the robot arm can be calculated to compensate for undesired movements of the RCM. The positioning device and / or the robot arm can then be controllably moved. As a result, the displacement of the positioning device can be compensated for to minimize undesired displacements of the welding gun and / or the RCM.

[0059] In one embodiment, the present disclosure further includes calculating the displacement of the at least first remote center of motion. In a further embodiment of the present disclosure, the method further includes correcting the displacement of the at least first remote center of motion such that the at least first remote center of motion is stable during operation of the welding gun. This can be done by moving the positioning device and / or the positioning arm.

[0060] Alternatively, in one embodiment, the approach includes moving the robot arm such that the tool center point of the welding gun and / or the RCM is stable during operation of the welding gun.

[0061] In one embodiment, the approach includes moving the positioning device and / or the robot arm such that the undesired displacement of at least a first remote center of motion is corrected.

[0062] In one embodiment, the approach includes moving the positioning device and / or the robot arm such that the undesired displacement of at least a first remote center of motion is partially corrected.

[0063] The distance of the remote center of motion to the tool center point can be maintained constant during operation of the welding gun, which envisions that the present approach can be configured to maintain at least a first remote center of motion during operation of the welding gun.

[0064] Depending on the capabilities of the system, such as the compensation strategy and available degrees of freedom, the compensation may not be fully met. In one embodiment, the method includes calculating at least a second remote center of motion based on the displacement, movement and / or vibration of the positioning device and / or the robot arm.

[0065] In one embodiment of the method, a stable welding operation is provided by a welding robot according to any one of the above-mentioned embodiments.

[0066] In an advantageous embodiment, a robotic welding system, such as any one of the robotic welding systems described above, provides a stable welding operation.

[0067] Detailed Description of the Drawings The present disclosure will now be described more fully with reference to the accompanying exemplary embodiments, as illustrated in the drawings, where appropriate. However, it should be noted that the systems and methods of the present disclosure can be embodied in various forms. The embodiments provided herein are intended to provide a thorough and complete disclosure. Thus, the embodiments described herein should not be construed as limiting, but as a tool to provide those skilled in the art with the scope of the present invention. The same reference numerals refer to the same elements throughout this document.

[0068] Figure 1 illustrates one embodiment of a robotic welding system according to the presently disclosed approach. The robotic welding system includes a positioning device 2 having a positioning arm 22. According to the example shown in Figure 1, the positioning device is a mobile crane 2 having conveyor wheels 3 on which the positioning device is movable. The mobile crane 2 carries and positions a multi-degree-of-freedom welding robot 1 adjacent to a work piece.

[0069] The positioning arm 22 engages the welding robot 1. The welding robot 1 comprises a robot arm 20 connected to the positioning arm 22, with a welding gun 21 connected to the robot arm 20.

[0070] As shown in FIG. 2, the robot arm 20 is connected to the positioning arm 22 at the robot arm base 23. The attachment point of the robot arm base 23 to the positioning arm 22 is defined as a virtual RCM control point. The movements and vibrations of the mobile crane 2 are measured by position sensors and / or cameras (not shown). The system is configured to continuously monitor and control the initially defined virtual RCM during the operation of the welding gun 21. The monitoring and control of the virtual RCM point is based on sensor inputs from the mobile crane 2. The system is configured to calculate the displacement of the virtual RCM point from a desired positioning. Thus, the positioning arm 22 and / or the robot arm 20 can move to compensate for the movements and vibrations of the mobile crane 2. Control of the virtual RCM point to maintain the desired positioning can be performed by moving the positioning arm 22. Alternatively or additionally, the robot arm 20 can move to keep the welding task stable.

[0071] The welding gun 21 may include an arc sensor (not shown) that may measure welding process parameters such as welding current and / or arc voltage. These parameters may change as the distance of the welding gun to the target changes and may change based on internal and external process perturbations. The arc sensor may provide data in such a way that the position of the welding gun 21 may be controlled such that the tool center point is maintained along a predetermined welding path. Combining the sensor data measuring the changes in RCM with the sensor data of the arc sensor may allow different error sources to be identified. The arc sensor may be positioned near the target (weld) area and an external sensor may be configured to measure external displacements.

[0072] 3 shows another embodiment of the robot welding system. According to this embodiment, a positioning device 2' has a stable base 24. The positioning device is provided with a moving arm 22' for moving the welding robot 1 to the vicinity of the welding operation. Thus, the welding operation can be performed while moving the welding robot 1 and / or the moving arm 22'.

[0073] In such a large working space, it may be necessary to provide a mobile platform or a crane for positioning and lifting the necessary equipment. FIG. 4 shows an embodiment of a robotic welding system with a mobile positioning device 2″. The mobile positioning device 2″ comprises a positioning arm 22″ and a mobile carriage base 25. The mobile carriage base 25 is movable on wheels 26 and can be moved with various types of positioning arms mounted thereon. The mobile carriage base 25 comprises a connector link 27 at its upper portion. The connector link 27 is connected to the positioning arm 22″. The positioning arm 22″ engages with the connector link 27 at one end and with the welding robot 1 at the other end. Advantageously, the dimensions of the mobile positioning device 2″ can be tailor-made to the customer's requirements for a particular welding task. The RCM can be freely selected anywhere along the kinematic chain of the robotic welding system with a mobile positioning device. For example, the RCM can be the location where the robot arm 20 is connected to the positioning arm 22″. The RCM can also be the location where the positioning arm 22″ is connected to the connector link 27. The RCM may be where the connector link 27 is connected to the dolly base 25 .

[0074] The proposed welding robot and / or welding system can be used in the energy sector for smart robotic welding of offshore structures, such as crawler-based welding of monopiles. The proposed approach can further be used in the marine sector for hyper-robotic shipbuilding. Furthermore, the present disclosure can also be used in the construction sector. For example, the proposed welding robot and welding system can be provided in robotic construction operations, such as processes around concrete, insulation, cladding. Furthermore, the energy sector can use the present disclosure, for example for robotic nacelle assembly, or robotic composite manufacturing.

Claims

1. 1. A welding robot for performing a welding operation when engaged with a positioning arm, comprising: a robotic arm configured to be connected to the positioning arm at an attachment point; a welding gun connected to the robot arm; Equipped with at least a first remote center of motion is defined by a point on a kinematic chain along the robot arm and the positioning arm; the welding robot is configured to continuously monitor the at least first remote center of motion and a tool center point during operation of the welding gun such that displacements of the positioning arm are corrected to minimize undesired displacements of the welding gun. Welding robot.

2. The welding robot of claim 1 , further comprising at least one sensor for measuring displacement, movement and / or vibration of the positioning arm.

3. The welding robot of claim 1 , further comprising at least one sensor for measuring displacement, movement and / or vibration of the at least first remote center of motion.

4. The welding robot of claim 1 , further comprising at least one sensor for measuring displacement, movement and / or vibration of the tool center point of the welding gun.

5. The welding robot of claim 2 , further comprising at least one arc sensor for measuring a set of welding process parameters of the welding operation.

6. The welding robot of claim 5 , wherein the set of welding process parameters is a welding current and / or an arc voltage.

7. The welding robot according to claim 5 , wherein the sampling frequency of the at least one sensor and / or the at least one arc sensor is 1000 Hz or higher.

8. 6. The welding robot of claim 5, wherein the welding robot is configured to continuously monitor the welding process parameters during operation of the welding gun such that the tool center point is maintained along a predetermined welding path.

9. The welding robot of claim 1 , configured to calculate a displacement of the tool center point of the robot arm from a predetermined tool center point.

10. The welding robot of claim 1 , wherein the robot arm is configured to move to compensate for displacement of the tool center point.

11. The welding robot of claim 1 , wherein the monitoring point of the at least first remote center of motion is the attachment point of the robot arm relative to the positioning device.

12. The welding robot of claim 1 , wherein the robot arm and / or the positioning arm are configured to move to compensate for displacement of the at least first remote center of motion.

13. The welding robot of claim 1 , configured to define at least a second remote center of motion.

14. The welding robot of claim 13 , wherein the robot arm and / or the positioning arm are configured to move to compensate for displacement of the at least second remote center of motion.

15. The welding robot of claim 2 , wherein the welding robot is configured to perform a welding task.

16. The welding robot of claim 15 , wherein the welding task has a predetermined frequency.

17. The welding robot of claim 16 , wherein a sampling frequency of the at least one sensor corresponds to a welding task frequency.

18. 1. A robotic welding system for performing a welding task, comprising: a positioning device having a positioning arm; The welding robot according to any one of claims 1 to 17. Equipped with the system is configured to continuously monitor the at least first remote center of motion and the tool center point during operation of the welding gun such that displacements of the positioning arm and / or the positioning device are corrected to minimize undesired displacements of the welding gun. Robotic welding system.

19. The system of claim 18 , configured to calculate a displacement of the at least first remote center of motion.

20. 20. The system of claim 19, wherein the system is configured to move the positioning device and / or the positioning arm and / or the robot arm to correct the calculated displacement of the at least first remote center of motion.

21. 20. The system of claim 18, further comprising at least one sensor for measuring displacement, movement and / or vibration of the positioning arm and / or the positioning device.

22. 20. The system of claim 18, wherein the system is configured to compensate for displacement of the positioning device and / or the positioning arm such that the at least first remote center of motion is maintained.

23. 20. The system of claim 18, wherein the system is configured to displace the positioning device and / or the positioning arm and / or the robot arm such that a predetermined tool center point of the robot arm is maintained.

24. The system of claim 18 , wherein the system is configured to calculate at least a second remote center of motion.

25. The system of claim 18 configured to calculate a relative displacement of the positioning arm and / or the positioning device with respect to the welding robot.

26. 20. The system of claim 18, wherein the positioning device is a mobile device such as a mobile crane.

27. The system of claim 18 , wherein the positioning arm is at least a second robotic arm.

28. The system of claim 18 , wherein the system further comprises a mobile carriage configured to transport and / or position the welding robot.

29. 1. A computer-implemented method for controlling a welding system having a positioning device, a first robotic arm connected to the positioning device at an attachment point, and a welding gun connected to the first robotic arm, comprising: calculating coordinates of at least a first remote center of motion defined by a point on a kinematic chain along the first robotic arm and the positioning device; measuring displacement, movement and / or vibration of the positioning device relative to the at least first remote center of motion; controllably moving the positioning device and / or the first robotic arm such that displacement of the positioning device is compensated to minimize undesired displacement of the welding gun. A method comprising:

30. 30. The method of claim 29, further comprising the step of calculating the displacement of the at least first remote center of motion.

31. 31. The method of claim 30, further comprising the step of compensating for displacement of the at least first remote center of motion such that the at least first remote center of motion is stable during operation of the welding gun.

32. 30. The method of claim 29, further comprising moving the positioning device and / or the first robotic arm such that undesired displacement of the at least first remote center of motion is fully compensated for.

33. 30. The method of claim 29, further comprising moving the positioning device and / or the first robotic arm such that an undesired displacement of the at least first remote center of motion is partially corrected.

34. 30. The method of claim 29, further comprising calculating at least a second remote center of motion based on displacements, movements and / or vibrations of the positioning device and / or the first robotic arm.

35. 30. The method of claim 29, further comprising measuring a welding process parameter such as a welding current.

36. 36. The method of claim 35, further comprising controllably moving the positioning device and / or the first robotic arm such that the welding process parameters are maintained within predetermined ranges.

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