ROBOTIC MESH STRUCTURE GENERATION FOR CONCRETE FORMWORK AND REINFORCEMENT

Abstract

In one aspect the invention relates to a mobile robotic end-effector tool for generating a mesh structure for use in reinforced concrete building systems. The tool comprises: —at least one robotic end-effector (EE), being movable in six degrees of freedom for applying an endless secondary mesh structure (2 ms) to the provided primary mesh structure (1 ms) continuously by roll spot welding, —wherein the at least one robotic end-effector (EE) further comprises: —a welding unit (W), in particular a resistance welding unit, configured for welding the secondary mesh structure (2 ms) to the primary mesh structure (1 ms) at predefined connection positions to generate cross-wire connections; —contact force sensors, configured for measuring the contact force of the robotic end-effector (EE), being applied to the primary mesh structure (1 ms) during rolling over the primary mesh structure (1 ms); —a processor (P) for closed loop control of the at least one robotic end-effector (EE) by means of control signals, wherein the control signals are generated at least in part in response to the measured contact force.

Claims

1. Method for generating a mesh structure for use in constructional engineering, in particular for use in reinforcement systems, comprising the method steps of: Providing a primary mesh structure (1 ms), Using a robotic end-effector tool with at least one end-effector (EE), being movable in six degrees of freedom for applying an endless secondary mesh structure (2 ms) to the provided primary mesh structure (1 ms) continuously by roll spot welding; and during rolling over (S4) the primary mesh structure (1 ms) for roll spot welding: instructing (S1) a welding unit (W), in particular a resistance welding unit, to initiate a welding process in a sequence of interrupted welding processes for welding the secondary mesh structure (2 ms) to the primary mesh structure (1 ms) at pre-defined connection positions to generate cross weldings; instructing (S2) a set of sensors (S) to measure a contact force at the robotic end-effector (EE), being applied to the primary mesh structure (1 ms) during rolling over (S4) the primary mesh structure (1 ms); controlling (S3) the robotic end-effector in real-time with control signals, generated by a processor (P), wherein the control signals are generated at least in part in response to the measured contact force.

2. Method according to claim 1, wherein the welding unit (W) is a resistance welding unit or a gas metal arc welding unit or a tying gun for providing a tying connection.

3. Method according to any of the preceding claims, wherein the control signals comprise first control signals, being dynamic and indicating a trajectory for movement of the end-effector (EE) and second control signals, indicating welding parameters for executing the welding process in the sequence of interrupted welding processes and/or wherein the second control signals are static.

4. Method according to the directly preceding claim, wherein the first control signals are determined on the basis of the measured contact force and/or wherein the second control signals are determined on the basis of a 3D mesh model.

5. Method according to any of the preceding claims, wherein the secondary mesh structure (2 ms) is or comprises a strand of continuous mesh material, in particular mesh wire.

6. Method according to any of the preceding claims, wherein the secondary mesh structure (2 ms) is bent by means of the end-effector and in particular by means of an anode of the welding unit (W) and/or wherein the secondary mesh structure (2 ms) is bent during rolling over the primary mesh structure (1 ms), in particular according to a curvature of the first mesh structure (1 ms).

7. Method according to any of the preceding claims, wherein the secondary mesh structure (2 ms) is not cut to length while rolling over the primary mesh structure (1 ms) and/or wherein the secondary mesh structure (2 ms) is not cut to length before an outer side of the primary mesh structure (1 ms) has been reached after the process of rolling over the primary mesh structure (1 ms) has started.

8. Method according to any of the preceding claims, wherein the sequence of interrupted welding processes is applied with one and the same endless secondary mesh structure (2 ms).

9. Method according to any of the preceding claims, wherein the robotic end-effector tool comprises at least two separate end-effectors (EE) at two different robotic arms, wherein the two separate end-effectors are used in parallel for applying different items of the secondary mesh structure (2 ms) to the primary mesh structure (1 ms), in particular on the same height and/or in the same longitudinal extension in the Y-axis from opposite sides.

10. Method according to any of the preceding claims, wherein the contact force is measured by means of a force measurement sensor, which is attached at a head of the robotic end-effector (EE), in particular in an area where the contact force is applied.

11. Method according to any of the preceding claims, wherein during the sequence of interrupted welding processes, the secondary mesh structure (2 ms) remains in endless form and is not cut.

12. Method according to any of the preceding claims, wherein the secondary mesh structure (2 ms) is welded to the primary mesh structure (1 ms) horizontally or vertically or in an angle between 0° and 90° with respect to a direction of an element of the primary mesh structure (1 ms).

13. Method according to any of the preceding claims, wherein the at least one end-effector (EE) is adapted: to weld the secondary mesh structure (2 ms) onto the primary mesh structure (1 ms); to weld elements off the primary mesh structure (1 ms); to move and in particular to roll over the primary mesh structure (1 ms), by translatory and/or rotational movements, depending on the curvature of the primary mesh structure (1 ms); to bend the secondary mesh structure (2 ms), in particular in case the primary mesh structure (1 ms) is not planar, and/or to cut the secondary mesh structure (2 ms) after completion of the sequence of interrupted welding processes.

14. Method according to any of the preceding claims, wherein the at least one end-effector (EE) comprises an anode and a cathode, wherein the anode is provided as rotating roller and the cathode is provided as rotating carrier, which hops or skips to a respective next element of the primary mesh structure (1 ms).

15. Method according to any of the preceding claims, wherein the at least one robotic end-effector (EE) is placed on a mobile platform, and/or wherein the mobile platform is transferable by a linear actuator for linear movement, in particular parallel to a plane of the primary mesh structure (1 ms).

16. Method according to any of the preceding claims, wherein the at least one robotic end-effector (EE) is moved along a trajectory over the primary mesh structure (1 ms) according to control instructions which are calculated on the basis of a digital 3D-model.

17. A robotic end-effector tool for generating a mesh structure for use in constructional engineering, in particular for use in reinforcement systems, which is configured to be used in a method according to any of the preceding method claims, comprising: at least one robotic end-effector (EE), being movable in six degrees of freedom for applying an endless secondary mesh structure (2 ms) to the provided primary mesh structure (1 ms) continuously by roll spot welding, wherein the at least one robotic end-effector (EE) further comprises: a welding unit (W), in particular a resistance welding unit, configured for welding the secondary mesh structure (2 ms) to the primary mesh structure (1 ms) at pre-defined connection positions to generate cross-wire connections; contact force sensors, configured for measuring the contact force of the robotic end-effector (EE), being applied to the primary mesh structure (1 ms) during rolling over the primary mesh structure (1 ms); a processor (P) for closed loop control of the at least one robotic end-effector (EE) by means of control signals, wherein the control signals are generated at least in part in response to the measured contact force.

18. The robotic end-effector tool according to the directly preceding claim, wherein the welding unit (W) comprises an anode and a cathode, and wherein the anode is configured for bending the secondary mesh structure (2 ms) during rolling over the primary mesh structure (1 ms).

19. A computer program comprising a computer program code, the computer program code when executed by a processor causing a robotic end-effector tool according to the directly preceding claim to perform the steps of the method of any of the preceding method claims, when the robotic end-effector (EE) is provided with a primary mesh structure (1 ms) and in case an initiation signal is provided.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0217] FIG. 1 shows a schematic representation of an end-effector for connecting of secondary mesh structure 2 ms to a primary mesh structure 1 ms;

[0218] FIG. 2a-FIG. 2e shows a process for welding the secondary mesh structure to the primary mesh structure in different phases;

[0219] FIG. 3 shows the end-effector with its components in more detail;

[0220] FIG. 4 is an overview figure of the process for generating a mesh structure according to a preferred embodiment of the present invention;

[0221] FIG. 5 is a block diagram of digital components and related data or message exchange according to another preferred embodiment;

[0222] FIG. 6 shows by way of example two end-effectors for mesh generation;

[0223] FIG. 7 is an overview figure, representing different coils for providing the secondary mesh structure to be used by the robot for generating the mesh structure;

[0224] FIG. 8 is another perspective of the robotic setting with two end-effectors and is platforms with two linear actuators;

[0225] FIG. 9 is a block diagram of an end-effector tool with two end-effectors and their respective components according to a preferred embodiment of the invention;

[0226] FIG. 10 is a flow chart to a computer-implemented method for instructing steps to be executed on an end-effector;

[0227] FIG. 11 is another schematic representation of a robotic process for generating the mesh structure;

[0228] FIG. 12 is a flow chart, representing functional dependencies;

[0229] FIG. 13 shows the end-effector EE when applying the secondary mesh structure onto the primary mesh structure by rolling over.

DETAILED DESCRIPTIONS OF THE FIGURES AND PREFERRED EMBODIMENTS

[0230] This following description does not limit the invention on the contained embodiments. Same components or parts can be labeled with the same reference signs in different figures. In general, the figures are not for scale.

[0231] It shall be understood that a preferred embodiment of the present invention can also be any combination of the dependent claims or above embodiments with the respective independent claim.

[0232] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0233] In case, complex wall or ceiling systems needed to be manufactured, usually it is necessary to provide the concrete with a reinforcement structure. Typically, the reinforcement structure is provided first, like the mesh structure, which may be later filled with concrete. The present invention now relates to the automatic generation of such a mesh structure, in particular a three-dimensional mesh structure for use in constructional engineering, like for example for building reinforced concrete structures. However, the method for generating a mesh structure and us so generated mesh structure may also be applied in other settings, like for example in furniture construction, in façade construction or the like. Further, it is possible to use the generated mesh structure without later filling with concrete.

[0234] Depending on the complexity of the respective structure to be built, there exist a variety of different static requirements for the generation of the mesh structure. Typically, a three-dimensional model is provided, which represents the static requirements. For example, the model may require to use different types of wires (for instance different dimensions and/or different material) in different regions of the mesh structure to be built. For example, a region with a lot of curvatures needs a denser reinforcement and thus a mesh structure being denser or comprising mesh elements with a higher diameter. So, the specifications for different regions in one and the same mesh structure may vary.

[0235] As mentioned above, the process for finally manufacturing the building structure, comprising the reinforcing mesh structure requires several steps and is time-consuming. Therefore, the present invention aims at a further automation of the mesh generation process.

[0236] For this purpose, a robotic end-effector tool has been developed. The robotic end-effector tool (in the following simply abbreviated as tool) may comprise at least one and preferably two end-effectors EE. These end-effectors EE are implemented on and/or supported by an articulated arm, so that the end-effector EE is able to move in 6 degrees of freedom. Thus, preferably, the end-effector and/or the end-effector tool is mobile.

[0237] Such an end-effector EE is shown in FIG. 1. As can be seen, the end-effector EE comprises a head, which is depicted schematically in FIG. 1. The end-effector EE is configured to connect a secondary mesh structure 2 ms, which preferably may be provided as wire, to a primary mesh structure 1 ms. The primary mesh structure 1 ms may be pre-fabricated and is typically provided as two- or three-dimensional mesh wire structure, as can be seen in FIG. 1.

[0238] The end-effector EE may comprise different modules for via processing, in particular: [0239] A welding unit W, which is configured for welding wire. The welding unit W may be used for welding-off wire from the mesh structure, typically from the primary mesh structure 1 ms. The welding unit W may also be configured to be used to weld the secondary mesh structure 2 ms onto the primary mesh structure 1 ms. In a preferred embodiment, the welding unit W is the resistance or contact welding unit. [0240] A bending unit B, which is configured for bending wire. The bending unit B is typically used for bending the secondary mesh structure 2 ms according to the shape of the primary mesh structure 1 ms. In a preferred embodiment the bending unit B may be provided as anode of the welding unit W. So, one part of the welding unit W additionally serves as bending unit B as well. This is reflected in FIG. 9 with the bracket around the welding unit W and the bending unit B. [0241] A set of sensors S, comprising at least one sensor for detecting a contact force which is applied by end-effector EE onto the primary mesh structure 1 ms. Preferably, one contact force sensor is provided at the head of the end-effector EE. Optionally, further sensors may be provided, including terminal sensors, noise sensors, optical sensors and/or other sensors for detecting signals during rolling over the primary mesh structure 1 ms. [0242] The rebar threader R for providing the secondary mesh structure 2 ms (for instance in the form of a rebar strand) from our supply unit, like a coil. The rebar threader R is a hollow structure with an inlet and an outlet for guiding the secondary mesh structure 2 ms (or rebar) from the supply of oil to the rolling anode. [0243] Optionally, the end-effector EE may comprise a cutter C, which is configured for cutting wire, and in particular for cutting the secondary mesh structure 2 ms after completion of the sequence of welding processes.

[0244] In a preferred embodiment, the anode of the welding unit is configured as bending unit, so that no separate component is necessary for bending. In this case the bending unit B is implemented or integrated in the welding unit W.

[0245] FIG. 9 schematically shows the end-effector tool with two end-effectors EE1, EE2, each comprising the welding unit W, the bending unit B, a cutter C and the set of sensors S with the contact force sensors. Preferably, the welding unit W is a resistance welding unit and comprises an anode which is preferably implemented as rotating roll, as can be seen in FIG. 2a-d and/or might be made from copper. The anode in the form of the rotating roll is configured to be rolled over the primary mesh structure 1 ms with the secondary mesh structure 2 ms. The welding unit W further comprises a cathode which preferably is implemented as dog or carrier.

[0246] The carrier may be provided as rectangular unit and may be attached on a support member at the end-effector EE, so that the cathode may swivel or pivot around an axis, extending perpendicular to the surface of the primary mesh structure 1 ms. Generally, it is key that the cathode touches the respective primary structure that is welded to the secondary structure before sending the weld signal. As can be seen in FIG. 2, the cathode is supported at the end-effector EE to engage with the primary mesh structure 1 ms when the end-effector EE is rolled over the primary mesh structure 1 ms. The cathode is forced to swivel around the above-mentioned axis when the end-effector EE is moved translatory in a Y- and/or Z axis. If the end-effector EE is moved from one wire element (element of the primary mesh structure 1 ms, over which the end-effector EE with the secondary mesh structure 2 ms is rolled) to the next wire element of the primary mesh structure 1 ms, the cathode is forced to hop or jump to the next element. Preferably, the cathode is spring-mounted on a support member of the end-effector EE.

[0247] As represented in FIG. 9 with dotted lines, the processor P may be implemented on the end-effector tool or may be associated thereto. Alternatively, or in addition, the processor P may also be implemented on each or on selected end-effectors locally. Both, of the above-mentioned alternatives may be combined.

[0248] Further, the end-effector EE may comprise a rebar threader R for forwarding the rebar or wire of the secondary mesh structure 2 ms to the end-effector EE from a coil.

[0249] FIGS. 2a to 2e shows a top view of the end-effector EE during rolling over the primary mesh structure 1 ms for welding the secondary mesh structure 2 ms at pre-configured positions. Typically, the welding positions are defined by the three-dimensional model. A welding position is defined by a wire crossing between a wire of the primary mesh structure 1 ms and the wire of the secondary mesh structure 2 ms. Depending on the model, not every wire of the primary mesh structure 1 ms needs to be subject for the welding process. With other words it is possible that only a selection of wire elements of the primary mesh structure 1 ms are subject to the welding process. In FIG. 2a-e the following different states in the course of rolling-over can be seen:

a) End-effector EE approaching welding position;
b) Cathode touching primary structure 1 ms;
c) Welding by means of the welding unit W;
d) Welding finished;
e) Cathode jumping from one primary structure element to the next while the robot is moving along the desired trajectory.

[0250] FIG. 3 shows the head of the end-effector EE in another perspective. The end-effector EE is provided with a transformer, the cuboid component in FIG. 3, for providing the appropriate voltage. The cathode and the anode are electrically connected for voltage supply by a cathode cable and an anode cable. As already described above, the cathode is preferably provided as rectangular bar, which is spring-mounted and rotatable around an axis being perpendicular to the movement direction of the end-effector EE and/or usually parallel to the (e.g., vertically extending) elements of the primary mesh structure 1 ms. In this respect it has to be noted, that the rotation axis for the spring-mounted cathode has a lateral offset to the surface of the primary mesh structure 1 ms.

[0251] In a preferred embodiment and as shown in FIG. 3, the anode is provided as rolling bending unit B. Thus, the anode has two functions: [0252] 1. for welding, besides the cathode, as part of the welding unit W and [0253] 2. for bending; the anode serves as a bending unit B for bending the secondary mesh structure 2 ms in the direction, being parallel to the surface of the primary mesh structure 1 ms along with the movement of the end-effector EE rolling over the primary mesh structure. As can be seen in FIG. 3, the anode may be provided as pulley or roll, being rotatable around a rotation axis, being perpendicular the movement direction the effector EE and/or parallel to the surface of the primary mesh structure 1 ms.

[0254] The end-effector EE itself is movable in 6DOF of freedom. Further, the end-effector EE comprises the rebar threader R for providing the secondary mesh structure 2 ms in the form of wire or rebar as mentioned above (see FIG. 9).

[0255] FIG. 4 shows the whole process for generating the mesh structure in a schematic overview figure. In step 1 a 3D mesh model is generated to be provided in a digital form to several computing entities and processors. A two-dimensional part of the primary mesh structure 1 ms is fabricated in step 2 by means of using robots (step 4) which are configured for bending the appropriate wire into a form which is defined by the 3D mesh model. A set of such two-dimensional parts of the primary mesh structure 1 ms are placed (and non-permanently attached, for instance by welding connections) on a platform (step 5) in order to generate the primary mesh structure 1 ms, which is a three-dimensional mesh structure. This primary mesh structure 1 ms e.g., with curvatures in different axes serves as basis for generating the mesh structure with a method according to the present invention. The primary mesh structure 1 ms is processed by the mobile robotic end-effector tool with an end-effector EE for welding two different types of rebar/wires or secondary mesh structures 2 ms, stocked on two different coils, as can be seen in FIG. 4 on the right-hand side onto the primary mesh structure 1 ms. The robotic end-effector EE is provided on an articulated robotic arm, which itself is articulated attached on a platform. The platform may be moved by linear driver motors. Thus, the platform with the end-effector EE may be moved in lateral direction and mainly in parallel to the surface of the primary mesh structure 1 ms. The end-effector EE is instructed to roll over the primary mesh structure 1 ms in order to weld the secondary mesh structure 2 ms at configurable welding positions. Typically, the rolling over process is reiterated in different heights (Z axis direction), depending on the static requirements. Usually, the secondary mesh structure 2 ms may be welded in a configurable angle onto elements of the primary mesh structure 1 ms. For some applications, a 90° angle between the secondary mesh structure 2 ms and the primary mesh structure 1 ms is favorable. After having completed all roll spot weldings with a plurality of different sequences (preferably a plurality of rows or lines of the secondary mesh structure), the final mesh is generated, as can be seen in FIG. 4 on the right-hand side.

[0256] FIG. 5 shows the general data exchange. A processor P (also referred to herein as processing unit) serves to calculate control instructions for control of the robotic end-effector tool with the at least one end-effector EE. Further, the processor P serves to receive the digital three-dimensional model, representing requirements for the mesh structure to be built. The requirements, inter alia, are defining the type of secondary mesh structure 2 ms (for instance rebar strands from metal or in another material, in a certain diameter, and/or with certain physical—chemical properties etc.). The processor may be configured to generate: [0257] 1. static control instructions, which are fix and static for one process of rolling over (the secondary mesh structure onto the primary mesh structure). The static control instructions may in a preferred embodiment be solely calculated on the basis of the 3D model and may e.g., take into account material properties for defining welding parameters like the welding current, voltage etc. [0258] 2. Dynamic control instructions, which are variable or may change over the process of rolling over. The dynamic control instructions are preferably calculated in response to the measured contact force and/or the target contact force. The target contact force may be determined by the 3D model. The dynamic control instructions may preferably relate to the positioning instructions for the end-effector EE (target trajectory).

[0259] Based on the information in the model, the processor P calculates control instructions with a set of control signals for instructing the set of end-effectors EE1, EE2, EE3. The control signals comprise trajectory signals, defining the desired trajectory, the end-effector EE is required to move along the primary mesh structure 1 ms. Usually, the trajectory signals are predefined by the digital three-dimensional model only approximately or roughly, because the primary mesh structure is compliant and may go to side or move back/side or away, if a force is applied to it in direction of the normal onto the surface of the primary mesh structure. Such a force is applied inevitably when the end-effector is rolled over the primary mesh structure, which prompts the primary mesh structure—at least at that position—to change its position in X direction (bounce back a little). Therefore (because of the moving target namely the primary mesh structure) the trajectory needs to be adapted according to the instantaneous and dynamically measured contact force at that point. Further, the force is physically dependent of the position of the end-effector EE. For example, if the end-effector EE is moved along a desired trajectory over the primary mesh structure and a target force Ft needs to be applied at a particular position, due to the flexibility of the primary mesh structure (bounce backwards) the actually measured force Fa (measured at that position) might be lower than the target force Ft. Then, the end-effector EE may be controlled to reposition (offset in X direction towards the primary mesh structure) so that the target force Ft may be reached. If the actually measured force Fa is too high, the control signals may instruct the end-effector EE to reposition (away from the primary mesh structure) so that the target force Ft may be reached.

[0260] The set of control signals further comprises signals, defining the welding process and may be referred to as welding control signals. The welding control signals serve and are adapted to define the welding process of the welding unit W of the respective end-effector EE. The welding control signals may comprise: the welding current, the welding voltage, the welding power, the welding energy. Typically, the above-mentioned control signals are kept constant, whereas the contact force is controlled dynamically. A control of the electrical variables and, in particular, a control of the contact force is important for ensuring stability of the mesh and its welding connections. The welding control signals are preferably optimized in view of material properties and parameters (e.g., mesh diameter etc.). The static welding control signals (e.g., except the contact force) may be pre-set and may preferably be kept constant during rolling over the primary mesh structure 1 ms (by the end-effector EE).

[0261] The contact force is processed in two different instances: as measured contact force and as instructed contact force. On the one hand, the contact force is measured by sensors at the end-effector EE continuously. On the other hand, the contact force is instructed by a processor P to be applied when performing the welding spots. The measured contact force may differ from the instructed contact force for a number of reasons. Mainly material deformation and/or material twisting and/or distortions and/or other forms of re-positionings of the primary mesh structure may be the reason for the deviations. With this, a closed control loop for controlling the welding parameters for the welding process may be provided.

[0262] One major advantage of the present invention is, that the contact force is dynamically and/or adaptively controlled in a closed loop control. For this purpose, the end-effector EE comprises sensors for measuring the contact force. Generally, the contact force may be influenced by a variety of different parameters, including static parameters, like geometric parameters of the primary mesh structure 1 ms, and dynamic parameters, like e.g., additional forces being applied to the primary mesh structure 1 ms at that timepoint (for instance from another end-effector EE, working in parallel on the primary mesh structure 1 ms and/or other technical parameters). Thus, the measured and instructed contact force may vary from position to position over the primary mesh structure or may vary over time. Further, the correct application of the contact force is essential for the quality of the welding process and needs to be controlled. If, on the one hand, the contact force is applied too low, a sufficient welding connection between the respective wires cannot be assured and quality may be impaired. If, on the other hand, too much contact force is applied, the welding process takes too long and the structure of the respective wires may be impaired. Therefore, a correct and appropriate application of the contact force is essential. Further, the contact force to be applied is dependent on the physical parameters of the respective two rebars (wires of the first and secondary mesh structure) to be connected, like for example the diameter of the rebars. The goal of the control loop is to keep the contact force constant per element, by adjusting the position of the end-effector. A different target force might be defined if the material and/or diameter changes.

[0263] The process of contact welding (resistance welding) may preferably be controlled such as to provide a constant and continuous contact force and/or also other welding parameters over time and in particular during rolling over the primary mesh structure. In contrast to usual process control in resistance spot welding, which has the task of controlling/guiding the welding process in the case of changing influencing variables in such a way that sufficient joint quality of the resulting weld spot is ensured the present suggestion, presented herein serves to adapt the trajectory and/or position over time/movement of the end-effector for indirectly influencing and controlling at least one welding parameter, namely the contact force.

[0264] According to a preferred embodiment of the invention, the contact force, in particular the instructed contact force, is controlled adaptively and in response to the measured contact force during the process of rolling over the primary mesh structure 1 ms. For example, a first secondary mesh structure needs to be applied with a different contact force than a second secondary mesh structure. having e.g., another welding resistance and/or for which another welding voltage and/or current have been measured.

[0265] FIG. 6 shows an end-effector tool, comprising two separate end-effectors EE, working from opposite sides on the same primary mesh structure 1 ms. In a preferred embodiment, the two end-effectors EE are controlled in common so that they are positioned at corresponding positions on opposite sides of the primary mesh structure 1 ms and thus have a corresponding position in the Y- and Z-axis for force balancing. As can be seen the secondary mesh structures 2 ms are provided on two different coils. Each end-effector EE is positioned on a separate platform. Each platform is movable by drive motors. Preferably the platform is movable in one axis (laterally), namely in the Y-axis. In addition, the end-effector EE is provided at an articulated arm and is thus mobile in 6 DOF of freedom to operate on the primary mesh structure 1 ms.

[0266] FIGS. 7 and 8 show a similar setting as FIG. 6 in another perspective with the two coils for providing the secondary mesh structure 2 ms being provided below or besides the platforms.

[0267] FIG. 10 shows in an abstract representation of the process of rolling over the primary mesh structure 1 ms for roll spot welding. The start of the actions of the end-effector EE may be initiated upon an initiation signal, which may be provided on a user interface, e.g., associated to a server computer or to the processor P. The process may be executed in a processor P, which may be implemented on different computing entities. The processor P is configured for control of the end-effector EE. The processor may be implemented on the end-effector EE or a related computing entity, being in data exchange. In step S1 the welding may be instructed by respective control signals. In step S2 the measurement may be instructed by respective control signals. Alternatively, the measurement is executed continuously and the measured signals are processed upon instruction (by the processor P). The steps are to be understood as action to be performed during rolling over—represented in FIG. 10 by reference numeral S4 —; they may be executed in parallel or in another sequence or interleaved. During the process of rolling over, roll spot welding is performed. In parallel, the end-effector EE and in particular the welding process of the welding unit W of the end-effector EE is controlled dynamically, shown with S3. The action roll-over S4 and control S3 are executed in parallel.

[0268] FIG. 11 shows a manufacturing pipeline or robotic process for generating the mesh structure from left to right. The secondary mesh structure 2 ms (wire), represented on the left downward section in FIG. 11 may be used for generating the first mesh structure 1 ms (2D part) by bending robots in a preceding step. The so generated first mesh structure 1 ms (2D part) may be fabricated in sequence, one after the other. In a next process step of the automation pipeline shown in FIG. 11, a set of such 2D-parts are the fixed on a platform and are referred to herein as first mesh structure 1 ms. These separate first mesh structures 1 ms need to be connected to each other to generate the (final mesh structure) by another secondary mesh structure (here: two different wires), shown on the right of FIG. 11. Typically, another instance or element of the secondary mesh structure is used for generating the first mesh structure (as shown on the left) as the secondary mesh structure which is used to connect the set of first mesh structures (to provide the final mesh structure), shown in this figure on the right.

[0269] FIG. 12 shows functional dependencies of involved parameters according to a preferred embodiment of the present invention. A digital blueprint may be stored in a storage and indicates the target or desired force as well es the target or desired trajectory for movement of the end-effector EE, to be applied when welding the secondary mesh structure 2 ms to the primary mesh structure 1 ms. Preferably, two separate controllers are used: one controller for controlling the contact force of the end-effector EE and one controller for controlling the position/movement of the same. At the robotic arm of the end-effector EE, in particular at the head of the same, a contact force sensor is attached, which is configured for continuously measuring the contact force or pressure, which is provided to the processor P (not shown) to compare the measured contact force with the desired contact force and to calculate in response to this comparison an adapted trajectory for the position controller.

[0270] FIG. 13 shows the end-effector EE while rolling over the primary mesh structure 1 ms. Here, the rectangular cathode is referenced with numeral C and the rolling anode with numeral A and the rebar threader with numeral R which provides the secondary mesh structure 2 ms to the robotic end-effector EE. The cathode C engages with the primary mesh structure 1 ms as it hops from wire element to wire element of the primary mesh structure 1 ms while the end-effector EE with its anode A is rolling over the primary mesh structure 1 ms. As indicated in FIG. 13, two of such end-effectors EE may be used from opposite sides, working in parallel on the primary mesh structure 1 ms.

[0271] Wherever not already described explicitly, individual embodiments, or their individual aspects and features, described in relation to the drawings can be combined or exchanged with one another without limiting or widening the scope of the described invention, whenever such a combination or exchange is meaningful and in the sense of this invention. Advantages which are described with respect to a particular embodiment of present invention or with respect to a particular figure are, wherever applicable, also advantages of other embodiments of the present invention.