The present invention is related to a method of detecting a position of at least one bolt end of at least one bolt of a series of bolts arranged in a linear or curved flanged connection, wherein the bolt ends of the bolts arranged in the flanged connection are protruding beyond the flanged connection, with a camera which is movable along the flanged connection.

The invention is furthermore related to a tightening device for tightening a series of nuts prescrewed on bolts, which bolts are arranged in a linear or in a curved flanged connection, comprising a camera, and a computing unit connected to the camera.

In the field of modern energy production, wind turbines play an essential part to provide renewable, sustainable, and clean energy for the energy market. Wind turbines comprise a tower, on which a rotor is mounted, which is connected to an electric generator. The tower can reach a height of 100 meters, 150 meters, or even more depending on the specific requirements resulting from, among others, the location of the wind turbine. The tower consists of several tube segments with a length of for instance 20 meters or 30 meters. These segments are connected by circular flanged connections on each side of the tube segments. During erection of the wind turbine on site, the tube segments are fitted together and connected with the joint circular flanged connections with bolts and nuts. Large quantities of bolts, typically in the hundreds, of large size are necessary to establish the required stiffness and strength of the connections. In order to achieve the appropriate defined stiffness and strength in the joints, all the bolts have to be bolted down with a predefined preload or torque, and according to a specific bolt tightening pattern.

Previously, this operation was performed manually, using torque wrenches or similar tools. Therefore, the construction of wind turbine towers was very labor intensive. In order to speed up the construction, robots were developed which performed the bolt tightening sequence automatically. Document EP 2 607 685 Al discloses a robot to bolt down a series of nut bolts in a joint circular flanged connection of a wind turbine. This robot comprises at least two wheels and a drive to transport the robot along the series of nut bolts and a tool to bolt down a nut bolt with a predefined torque. This drive used in this robot is a belt drive, which interacts with a side wall of the tower in order to propel itself forward. In order to achieve enough friction with the side wall, several electromagnets are provided, to press the belt drive against the side wall. Using the side wall as a means to propel the robot forward is beneficial, because no obstacles like metal filings, other tools, or further obstructions can be encountered on the side wall.

However, in order for such robots to achieve their desired function of automatically torquing the different bolts of the flanged connection to a specific torque, and therefore achieve a defined clamping force in the flanged connection, the robot has to automatically grip and manipulate the different bolts of the bolt connection. The bolts have therefore to be prearranged in the flanged connection in a specific position. In detail, the upper bolt ends of the different bolts have to be aligned within a certain tolerance range at a level above the flanged connection in order for the robot to function properly.

This alignment of bolts has previously been checked manually, for example by manually measuring the height of the bolts protruding above the flanged connection. This process however is very labor intensive and time consuming, as well as prone to measurement errors. If for example one bolt is not placed properly, the process of tightening the bolts with the robot may not be performed adequately or at all, requiring further user interaction in the bolt tightening process. Furthermore, for purposes of quality control, it is desirable to document the different steps of the tightening process, including the proper bolt alignment.

Furthermore, in order to check and preferably also to document the process of bolt tightening according to specifications, it is necessary to determine if the bolts have been correctly tightened, in order to achieve a predetermined amount of clamping force. The simple measurement of the torque value applied to each bolt during tightening is prone to errors resulting from excessive, or the lack of lubrication of the threads of the bolt or the nut and may also be influenced by dirt and contamination of the bolt threads as well as deviations in the dimensions of the threads.

The technical problem of the present invention is therefore to provide a method of detecting a position of at least one bolt end of at least one bolt of a series of bolts arranged in a linear or curved flanged connection, wherein the bolt ends are protruding beyond the flanged connection, with a camera which is movable along the flanged connection, which enables the automatic detection of the correct placement of the bolts, to tighten the bolts to achieve the correct clamping force, and to determine if the bolts have been correctly tightened.

This problem is solved by the provision of a method according to the subject matter of claim 1, and a tightening device for tightening a series of nuts pre-screwed on bolts according to the subject matter of claim 5.

The method of detecting a position of at least one bolt end of at least one bolt of a series of bolts arranged in a linear or curved flanged connection, wherein the bolt ends of the bolts arranged in the flanged connection are protruding beyond the flanged connection, with a camera which is movable along the flanged connection according to the invention comprises a series of steps. These steps include defining a first bolt end level at a first distance from the flanged connection and defining a first tolerance range surrounding the first bolt end level. Additionally, the method according to the invention includes detecting the position of the bolt end of the at least one bolt arranged in the flanged connection with the camera and determining whether the position of the bolt end of the at least one bolt is located within the first tolerance range surrounding the first bolt end level. By implementing the method according to the invention, a position of at least one bolt within the flanged connection is verified using the camera. It is checked if the bold protrudes by a predefined distance over the flanged connection by comparing the position of the bolt end of the bolt with a predefined first bolt end level. An advantage of the method according to the invention consists therein, that the position of the bolt can be verified and saved for quality control purposes. Furthermore, it is therefore guaranteed, that a bolt tightening device, be it manually operated or automatically operated, can grip the bolt and perform a desired bolt tensioning operation after the position of the bolt has been verified with the method according to the invention.

According to a preferred embodiment of the method according to the invention, the camera is moved along the flanged connection, and the position of the bolt end of each bolt of the flanged connection is detected with the camera, and for each bolt of the flanged connection it is determined, whether the position of the bolt end of the respective bolt is located within the first tolerance range surrounding the first bolt end level. This leads to the advantage, that the bolts arranged in the flanged connection can be tightened in series and rapidly, for example by employing a bolt tightening robot.

The method according to the invention also includes elongating at least one bolt of the flanged connection by applying a force on the bolt in an axial direction of the bolt, and tightening a lock nut threaded onto the bolt while applying the force on the bolt and releasing the force on the bolt. This constitutes the bolt tightening procedure using a bolt elongation process. In order to verify the results of the bolt tightening procedure, the method according to the invention also includes defining a second bolt end level at a second distance from the flanged connection, wherein the second distance is greater than the first distance, defining a second tolerance range surrounding the second bolt end level and after elongating the bolt, tightening the lock nut and releasing the force on the bolt, detecting the position of the bolt end of the bolt with the camera. Additionally, the method includes determining whether the position of the bolt end is located within the second tolerance range surrounding the second bolt end level. By verifying the result of the bolt elongation process in this manner, a dependable documentation of the bolt elongation and tightening procedure can be generated.

Preferably, each bolt of the flanged connection is elongated by applying a force on each bolt in an axial direction of the bolts. This is preferably followed by tightening a lock nut threaded onto each bolt while applying the force on the respective bolt and releasing the force on the respective bolt. Therefore, each bolt of the flanged connection is tightened, ensuring a rigid connection and an equal distribution of clamping force along the flanged connection.

According to the preferred embodiment of the method according to the invention, the camera is moved along the flanged connection, and it is determined with the camera if the position of the bolt ends of each of the bolts is located within the second tolerance range surrounding the second bolt end level, after the respective bolt has been elongated, the lock nut tightened, and the force acting on the bolt released. Therefore, the result of the elongation and tightening process can be verified using the method according to the invention for each of the bolts of the flanged connection.

The technical problem of the invention is also solved by the provision of a tightening device for tightening a series of lock nuts pre-screwed on bolts, which bolts are arranged in a linear or in a curved flanged connection, comprising a camera, and a computing unit connected to the camera. The computing unit is configured to execute the method according to the invention.

According to a preferred embodiment of the tightening device according to the invention, the tightening device comprises a propulsion unit for moving the tightening device along the flanged connection. This enables the tightening device to automatically verify the positioning of each of the bolts prior to the tightening operation, and to verify the result of the tightening operation for each of the bolts.

The tightening device preferably also comprises a lock nut tightening unit for tightening the lock nuts screwed onto the bolts, and two propulsion units disposed on essentially opposite sides of the lock nut tightening unit.

The method and the tightening device according to the invention as well as preferred and alternative embodiments will be described hereinbelow with reference to the figures.

Figure 1 shows a series of three bolts with lock nuts, wherein the bolts comprise bolt ends arranged at different heights.

Figure 2a shows a bolt with a lock nut.

Figure 2b shows the bolt of figure la after it has been elongated, and the lock nut tightened.

Figure 3 shows a perspective view of a tightening device according to the invention Figure 4 shows a cross-section of the tightening device according to figure 3.

The method of detecting a position of at least one bolt end 1 of at least one bolt 2 of a series of bolts 2 arranged in a linear or curved flanged connection 3 is hereinbelow described using Figures 1, 2a and 2b. The three bolts 2 depicted in figure 1 each comprise a bolt end 1, and a lock nut 4 is screwed on each bolt 2. The bolts 2 are arranged in the linear or curved flanged connection 3, which is not shown in figure 1, but can be seen in figure 3. The lock nuts 4 in figure 1 have not been tightened, and the bolt ends 1 rest at different heights, which leads to different thread lengths which are protruding above the lock nuts 4 and therefore the flanged connection 3, against which the lock nuts 4 abut. The method according to the invention utilizes a camera 5, which is moveable along the flanged connection 3, and which is also not shown in figure 1, but can be seen in figure 3. The method according to the invention comprises the steps of defining a first bolt end level 6 at a first distance di from the flanged connection 3 and defining a first tolerance range ti surrounding the first bolt end level 6. The first bolt end level 6 and the first tolerance range ti surrounding the first bolt end level 6 are shown in figure 1, as well as the first distance di. As can be seen, in figure 1, the bolt end 1 of the bolt 2 in the middle is correctly positioned within the tolerance range ti surrounding the first bolt end level 6, whereas the bolt end 1 of the left bolt 2 is positioned too low, and the bolt end 1 of the right bolt 2 is positioned too high. The position of the bolt end 1 of the at least one bolt 2 arranged in the flanged connection 3 is detected with the camera 5 in the method according to the invention. At last, it is determined, whether the position of the bolt end 1 of the at least one bolt 2 is located within the first tolerance range ti surrounding the first bolt end level 6. In figure 1 only the center bolt 2 is positioned correctly. By employing this method, an easy and simple automated validation of the positions of the bolts 3 can be provided. The image generated by the camera 5, or data about the correct or incorrect placement of the bolts 2 can for example be saved in a memory unit connected to the camera 5. The analysis and determination whether the position of the bolt end 1 of the at least one bolt 2 is located within the first tolerance range ti surrounding the first bolt end level 6 can be performed by a computing unit connected to the camera 5, which may also comprise the memory unit, by employing image analysis methods like contrast analysis. The data about the correct placement of the bolt 2 can be stored for example for quality control purposes. Also, if the method according to the invention leads to the determination, that at least one bolt 2 within the flanged connection 3 is placed incorrectly, actions to correct the bolt 2 placement can be taken. Preferably, in the method according to the invention the camera 5 is moved along the flanged connection 3, and the position of the bolt end 1 of each bolt 2 of the flanged connection 3 is detected with the camera 5, and for each bolt 2 of the flanged connection 3 it is determined, whether the position of the bolt end 1 of the respective bolt 2 is located within the first tolerance range ti surrounding the first bolt end level 6. An advantage of the method according to the invention consists therein, that a time-consuming manual measurement of the length of the bolts 2 protruding from the flanged connection 3 is not necessary.

After the position of the bolt 2 has been validated as described above, the method according to the invention includes elongating at least one bolt 2 of the flanged connection 3 by applying a force on the bolt 2 in an axial direction of the bolt 2 and tightening the lock nut 4 threaded onto the bolt 2 while applying the force on the bolt 2. Finally, the method according to the invention includes the step of releasing the force acting on the bolt 2. Figure 2a shows a bolt 2 with its lock nut 4 before the elongation and tightening process as described above. Figure 2b shows the bolt 2 after the lock nut 4 has been tightened, and the force acting on the bolt 2 has been released. This leads to a clearly defined torque by which the lock nut 4 is fastened and a precisely defined clamping force acting on the flanged connection 3.

The method according to the invention also comprises the steps of defining a second bolt end level 7 at a second distance d? from the flanged connection 3, wherein the second distance d? is greater than the first distance di and defining a second tolerance range t2 surrounding the second bolt end level 7. After elongating the bolt 2, the lock nut 4 is tightened, the force acting on the bolt 2 is released, and the position of the bolt end 1 of the bolt 2 is detected with the camera 5. Typically, the difference between the first distance di and the second distance d? is about 1mm, but is generally dependent on bolt material and dimensions. Finally, according to the invention it is determined whether the position of the bolt end 1 is located within the second tolerance range t2 surrounding the second bolt end level 7. In Figure 2b it can be seen, that the bolt end 1 of the bolt 2 is located within the second tolerance range t2. As described above with regards to the positioning of the bolt 2 before the elongation and tightening process, the final result of the elongation and tightening process can be recorded and validated using the method according to the invention preferably by employing a computing unit connected to the camera 5, which is programmed to execute the method according to the invention. The results may be recorded on a memory device, which is connected to or part of the computing unit. Typically, the camera 5 records images at a resolution of 4000 x 4000 pixels, with a picture height of about 15 cm. One pixel may correspond to 0.0375 mm, meaning that 1 mm bolt elongation corresponds to 26-27 pixels.

Preferably, each bolt 2 of the flanged connection 3 is elongated by applying a force on each bolt 2 in an axial direction of the bolts 2, and the lock nut 4 threaded onto each bolt 2 is tightened while applying the force on the respective bolt 2 before releasing the force on the respective bolt 2. Hereby all lock nuts 4 of the bolts 2 of the flanged connection 3 are tightened with the correct torque value. Furthermore, according to the preferred embodiment of the method according to the invention, the camera 5 is moved along the flanged connection 3 and it is determined with the camera 5 if the position of the bolt ends 1 of each of the bolts 2 is located within the second tolerance range t2 surrounding the second bolt end level 7, after the respective bolt 2 has been elongated, the lock nut 4 tightened, and the force acting on the bolt 2 released. The tightening device 10 according to the invention for tightening a series of lock nuts 4 prescrewed on bolts 2, which bolts 2 are arranged in a linear or in a curved flanged connection 3 is shown in figure 3 and figure 4, and comprises the camera 5, and the computing unit connected to the camera 5, which computing unit is configured to execute the method according to the invention. As described with regards to the method, the computing unit may comprise or be connected to a memory unit. The tightening device 10 according to the invention may also comprise, according to a preferred embodiment, a propulsion unit 11 for moving the tightening device 10 along the flanged connection 3. This enables the tightening device 10 to automatically verify the positioning of each of the bolts 2 prior to the tightening operation, and to verify the result of the tightening operation for each of the bolts 2. Preferably, the tightening device 10 according to the invention also comprises a lock nut tightening unit 12 for tightening the lock nuts 4 screwed onto the bolts 2, and two propulsion units 11 disposed on essentially opposite sides of the lock nut tightening unit 12. Furthermore, the tightening device 10 may also comprise a bolt elongation unit 13 for applying a force on the bolts 2 in the axial direction of the bolts 2.