Method and arrangement for tightening a screw connection

Abstract

A method and an arrangement for tightening a screw connection (10) between a first component (12) and a second component (14) which are equipped with cooperating threads (20, 40), comprise the following steps or means for carrying them out: turning one of the threads (20, 40) to tighten the screw connection (10), successively detecting the angle of rotation by means of an angle sensor (50) and the torque by means of a torque sensor (52) when tightening the screw connection (10), and evaluating the signals of the angle sensor (50) and the torque sensor (52) by an electronic processing device (56) to determine one or more characteristic features of the signals and comparing the feature(s) with one or more target values, wherein the electronic processing device (56) recognizes from the comparison whether an intermediate element is inserted between the first and second components (12, 14),which is clamped between the first and second components (12, 14) as intended when the screw connection is tightened, and if the comparison shows that the intermediate element is missing or not correctly inserted, to issue an error message.

Description

[0001] The invention relates to a method and an arrangement for tightening a screw connection between a first component and a second component which are equipped with cooperating threads. State of the art

[0002] In the manufacture or repair of components, assemblies and entire machines or vehicles, screw connections are usually provided to connect two elements, in particular detachably, to one another. The screw connection comprises a first component (nut, sleeve, etc.) with an internal thread and a second component (screw, bolt, etc.) with an external thread complementary to the internal thread. In most cases, intermediate elements are provided in the axial direction between the first and second components, which serve to provide a defined contact surface for the components (e.g. washers) and / or to seal the connection (sealing rings) when the thread is tightened. When the screw connection is tightened, the intermediate element therefore rests against both the first and the second component and is axially (i.e.the direction in which the first or second component moves linearly relative to the other component when the screw connection is tightened) is clamped between the components with a force that depends on the tightening torque.

[0003] To tighten screw connections, so-called torque wrenches are used to ensure defined and reproducible tightening torques. In the simplest case, these comprise a mechanical element (overload clutch) that, when an adjustable torque is reached, breaks the frictional connection between a drive and the output, which is releasably coupled to the rotated component. The drive can be a manually operated lever or power-operated (motor), and the output can be an internal or external hexagon wrench or an open-end wrench as the interface to the rotated component. In advanced torque wrenches, a sensor is used to record the torque. This sensor detects, for example, the torque-dependent deformation of a mechanical element connected to the frictional connection between the drive and output. An evaluation electronics emits a signal that alerts the operator when a predefined target torque is reached.

[0004] Even more advanced torque wrenches measure not only the transmitted torque but also the corresponding angle of rotation. This can be done using an inertial sensor or by measuring the angle between the input and output shafts.

[0005] In this regard, reference is made, for example, to the state of the art according to JP S 591172 A. There, it is proposed to first tighten the screw connection until an initial torque is reached at which the components already come into contact, and then to turn it further by a defined angle by issuing a corresponding warning signal to an operator so that he or she stops tightening in order to ensure the defined screw connection.

[0006] Furthermore, US 2022 / 0214240 A1 proposes equipping a torque wrench equipped with an angle and torque sensor and an electronic evaluation and display unit with a wireless data transmission device to specify the maximum torque and angle of rotation for the screw connection to be tightened using a separate input and output device. When the specified torque or angle has been reached, the operator receives a corresponding signal from the torque wrench's display unit. These values ​​are also fed back to the separate input and output device, where they can be recorded and optionally displayed or used to check whether the correct torque profile was used.

[0007] An optical detection of whether a sealing ring is in the desired position during an assembly process is described in DE 11 2017 005 961 T5. Task

[0008] As mentioned at the beginning, in most cases intermediate elements (washers, sealing rings, etc.) are used between the components. Cases are conceivable, particularly in manufacturing processes (assembly line) or during repair work, in which the intermediate element is missing (e.g. was forgotten or dropped) or has not been positioned correctly, so that it is not in the desired position, for example in a groove, and is crushed when the screw connection is tightened. In these cases, conventional torque wrenches would not detect the problem but would still tighten the connection with the specified torque and angle. The problem is only noticed later, for example when fluids leak out or the desired tightness of the fixation is not achieved. The state of the art cites optical detection of the intermediate element as a solution to this problem.

[0009] The object underlying the invention is to avoid at least some of the disadvantages mentioned. Solution

[0010] This object is achieved according to the invention by the teaching of patent claims 1 and 7, wherein the further patent claims list features which advantageously further develop the solution.

[0011] A method and arrangement for tightening a screw connection between a first component and a second component equipped with cooperating threads, comprising the following steps or means for carrying them out: Turning one of the threads in order to tighten the screw connection, successively detecting the angle of rotation by means of an angle sensor and the torque by means of a torque sensor during tightening of the screw connection, and evaluating the signals of the angle sensor and the torque sensor by an electronic processing device to determine one or more characteristic features of the signals and comparing the feature(s) with one or more target values, wherein the electronic processing device recognizes from the comparison whether an intermediate element is inserted between the first and second components which is clamped as intended between the first and second components when the screw connection is tightened, and if the comparison shows that the intermediate element is missing or not inserted correctly, it issues an error message.

[0012] In other words, it is proposed to record the angle and torque over time when tightening or tightening the screw connection, i.e. the measured values ​​for angle and torque are recorded at specific time intervals. Based on the measured values, one or more characteristic features of the signals are calculated, such as the curve shape (course) and / or curve height and / or curve gradient of the torque plotted as a function of the angle, and by comparing the feature(s) with one or more target values, which can, for example, represent correctly or incorrectly installed intermediate elements, an electronic processing device can detect whether the intermediate element is present or missing. It can optionally also detect if the intermediate element is not installed correctly, e.g. if it is tilted or should not be in a groove.If the intermediate element is missing or incorrectly positioned, the processing device emits an error signal. The latter can be displayed to an operator or used by an automated system to correct the error.

[0013] Various approaches are conceivable for determining the target values. On the one hand, the torque can be measured as a function of the angle on one or more comparable or similar screw connections that are not faulty. This yields a target curve from which characteristic features can be derived, which are then compared with the characteristic features of the tightened screw connection under investigation. On the other hand, it is also possible to determine the target curve and / or target values ​​based on theoretical considerations, simulations, or calculations. For example, finite element calculations can be used to calculate a target curve for expected torques as a function of the angle based on data about the screw connection, such as thread dimensions, pitches, flank angles, materials, friction and elasticity coefficients, etc. Example

[0014] An embodiment of the invention is explained with reference to the figures. They show: Fig. 1 a schematic cross-sectional drawing of a screw connection, Fig. 2 a schematic representation of a torque wrench, Fig. 3 a diagram of absorbed torques as a function of the angle of rotation when tightening screw connections, Fig. 4 a diagram of the angle dependence of the torque when tightening the screw connection, Fig. 5 a histogram for torque gradients in different situations, and Fig. 6 a flow chart for the procedure when tightening the screw connection.

[0015] The Figure 1shows an example of a screw connection 10 between a first component 12 and a second component 14 in a non-assembled state. The first component 12 comprises a tube 16 through which a liquid or a gas can be conducted, and a first hollow part 18 with an external thread 20, which is firmly attached to the tube 16. The first hollow part 18 is provided with a groove 24 on its outer end face 22. The second component 14 also comprises a tube 26 to which a second hollow part 28 is fastened. The second hollow part 28 also comprises a groove 32 on its outer end face 30. A union nut 36 with a rear collar 38, which rests on the rear surface 42 of the second hollow part 28 (spaced apart from the end face 30), is equipped with an internal thread 40.

[0016] The Figure 1shows the screw connection 10 in the disassembled state. It can be seen that between the end faces 22, 30 of the hollow parts 20, 28, a sealing ring 34 can be positioned within the grooves 24, 30, which provides a seal when the union nut 36 is tightened. The hollow parts 20, 28 are also coupled to the pipes 16 and 26 in such a way (e.g., welded, glued, or crimped) that no liquid or gas can escape. The threads 20 and 40 interact in such a way that when the union nut 36 is tightened, the sealing ring 34 is held at a certain, definable axial (in Figure 1 in the horizontal direction) is compressed.

[0017] The Figure 2shows a torque wrench 44 in a schematic representation. It comprises an interface 46 for establishing a torque-locking connection with the union nut 36, a lever arm 48 with a handle 51 as well as an angle sensor 50, a torque sensor 52 and an electronic unit 54 with an electronic processing device 56 and a display device 58. Between the interface 46 and the lever arm 48, an adjustable connection 60 can be arranged, which, among other things for ergonomic reasons, allows the lever 48 to pivot relative to the interface 46 in the plane of the drawing. Figure 2and / or a resetting of the lever 48 (e.g. by means of a ratchet) relative to the interface 46 is enabled after the screw connection has been rotated by a certain angle using the union nut 36. The angle sensor 50 and the torque sensor 52 are connected to the processing device 56 and the display device 58 in a signal-transmitting manner (by cable or wirelessly). The processing device 56 and, if applicable, the display device 58 could also be arranged at a distance from the torque wrench 44. For the basic mechanical and electronic structure of the torque wrench 44, reference is also made to the prior art according to JP S 591172 A and US 2022 / 0214240 A1, the disclosures of which are incorporated by reference into the present documents.

[0018] The Figure 3shows examples of torques M (Y-axis) recorded in practice as a function of the angle theta (X-axis). Two groups of curves can essentially be distinguished, namely those in the left-hand area (below the vertical line 68) and those in the right-hand area beyond line 68. The curves that can only be seen in the left-hand area have a relatively large gradient. They are essentially parabolic or exponential at first and later more or less linear. Those curves that can also be found beyond line 68 are initially relatively flat (here the sealing ring 34 is compressed) and include a point where the gradient increases sharply. This point can be identified as joining point 66, at which two metal surfaces (in the example the Figure 1(ie, the end faces 22, 30) come into contact with one another. The gradient beyond the joining point 66 corresponds approximately to the gradient of the curves shown in the left-hand area, where the sealing ring 34 is missing.

[0019] In the Figure 4is a schematic representation of the torques M (Y-axis) to be expected depending on the angle theta (X-axis) when the screw connection is tightened. Starting from the angle and zero torque, the result (if the sealing ring 34 is correctly fitted) is initially a relatively small gradient m of the torque approximated by a straight line, which is caused by the friction of the threads 20, 40 and the elasticity of the sealing ring 34, until the joining torque MF is reached at a point 66, at which the outer end faces 22, 30 come into direct mechanical contact with one another. From there, the torque M increases approximately linearly with the angle theta, with an approximately constant gradient m lin . At angle theta A (A stands for the tightening angle at which tightening is terminated), the tightening process is terminated because the screw connection is then sufficiently tightened.If, however, the sealing ring 34 is missing or not correctly fitted, the curve 70 shown on the left results with considerably higher gradients in the initial area (the area of ​​flat gradient which, in the case of the curve shown on the right in . Figure 4 drawn curve caused by the deformation of the sealing ring 34 is missing) and later approximately the same gradient as the right curve beyond point 66, at which the joining torque is reached (these gradients result primarily from the restoring forces built up by the tension of the threads 20, 40), but larger absolute values.

[0020] The Figure 5shows a histogram in which the gradient m, i.e. the torque measured by the torque sensor 52 and divided by the angle detected by the angle sensor 50 before the joining torque MF is reached, is represented on the X-axis, while the corresponding frequency is shown on the Y-axis. If the sealing ring 34 has been installed correctly, the gradient m is relatively small, which is due to the fact that the sealing ring 34, which is made of elastomer material, lies in the grooves 24, 32 and is gradually compressed. The corresponding distribution can be approximated by a first (bell-shaped) curve 62. However, there are also cases in which the sealing ring 34 has not been installed correctly and is crushed when the screw connection is tightened, or in which it is missing completely. In these cases, the gradient m is considerably greater because the end faces 22, 32 come into contact with each other sooner than with the sealing ring 34 correctly installed or directly.The corresponding distribution can be approximated by a second curve 64, the maximum of which lies at significantly higher gradients m than the first curve 62.

[0021] It is therefore proposed that the processing device 56 of the torque wrench 44 of the Figure 2 according to the flow chart of Figure 6 works.

[0022] The process begins with an initialization in step 100, in which the processing device 56, for example, takes information about the screw connection to be produced from a database that is stored in the processing device 56 and can be retrieved using an identification that is automatically recognized, e.g., by a computer-aided (production) process control system by means of a remote data transmission such as Bluetooth or WLAN, or an RFID chip of the screw connection or by means of a camera, or can be entered manually.

[0023] In the subsequent step 102, the screw connection is now tightened as described above, and the torque M and the angle theta are recorded over time by means of the sensors 50, 52 and fed to the processing device 56.

[0024] In the following step 104, an evaluation takes place. One or more of the data acquired in step 102 can be evaluated. First, preprocessing takes place, in which implausible data is discarded and only data above a certain minimum torque is used. In addition, known procedures can be used to remove outliers and noise and, for example, to determine mean values ​​for gradients using linear regression.

[0025] The preprocessed angle and torque measurements recorded over time are evaluated to determine characteristic features of the torque angle dependence curves. These features are then compared with target values ​​to determine whether the tightening process of the screw connection is proceeding correctly or incorrectly.

[0026] In a simple case, a comparison can be made between the slope m until the joining moment MF is reached (i.e. before reaching point 66 of the Figures 3 and 4 ) with stored target values ​​taken from the database. Alternatively or additionally, the reaching of the joining moment MF (ie reaching point 66 of the Figures 3 and 4) can be detected by the changing gradient there and compared with stored target values ​​for the joining torque MF taken from the database. Alternatively or additionally, the gradient m lin can be measured beyond the reaching of the joining torque MF (ie after reaching point 66 of the Figure 3 or 4 ) and compared with stored target values ​​taken from the database.

[0027] Based on characteristic features of the measured torque and angle curve, the processing device 56 can thus determine whether the tightening of the screw connection is proceeding correctly or not. This could also involve relying on the learned knowledge of an artificial intelligence that is fed with a sufficient amount of comparison data or that initially only collects data for learning purposes and, after a learning phase, is able to recognize correct tightening of the screw connection. Alternatively, series of measurements or theoretical calculations can be used to calculate the target values ​​of the characteristic features.

[0028] If, in step 106 following step 104, it is determined that the torque curve corresponds to a correctly installed sealing ring 34, step 108 follows, in which it is checked whether the angle thetaA to be set has been reached, and if this is not the case, step 102 follows again. The torque and the angle, as well as the characteristic features derived from them (here: in particular the gradient m), are thus recorded quasi-continuously (or at regular intervals) and compared with target values.

[0029] If it turns out in step 108 that the angle thetaA to be set has been reached, step 112 follows, in which an indication is given by means of the display device 58 (and / or acoustically) that the operator can terminate the process, followed again by step 102 in which another screw connection is tightened.

[0030] However, if step 106 reveals that the torque curve is not as expected for a correctly installed sealing ring 34, step 110 provides an indication via the display device 58 (and / or acoustically) that the screwing process is not proceeding correctly and the sealing ring is missing or has not been inserted correctly. The operator can then disassemble the screw connection and insert or replace the sealing ring 34.

[0031] In the described embodiment, the screwing process is checked continuously throughout the entire screwing process. Alternatively, steps 104 and 106 can be Figure 6 even after reaching thetaA (step 108) on the basis of the complete measurement data of the screw joint.

[0032] It should also be noted that the screw connection according to Figure 1represents only one example. The screw connection 10 could also be designed as a normal screw that extends through openings in two components 12, 14 to be fixed and is secured by means of a washer and a nut attached thereto. In this case, the processing device 56 would be able to detect a missing or incorrectly installed washer. Any other embodiments of the screw connection are conceivable.

[0033] Furthermore, the torque wrench 44 is only one example of an arrangement for tightening a screw connection with a defined torque. Instead of the lever 48 and handle 50, a power-operated drive could be used, which rotates the interface 46 with a torque and angle measurable by sensors 50, 52. This drive could be held by the arm of an operator or robot. In this case, the processing device 56 would be able to automatically stop the drive or reverse its direction of rotation in step 110.

Claims

1. A method for tightening a screw connection (10) between a first component (12) and a second component (14) which are equipped with cooperating threads (20, 40), comprising the following steps: rotating one of the threads (20, 40) to tighten the screw connection (10), successively detecting the angle of rotation by means of an angle sensor (50) and the torque by means of a torque sensor (52) when tightening the screw connection (10), and evaluating the signals of the angle sensor (50) and the torque sensor (52) by an electronic processing device (56) to determine one or more characteristic features of the signals and comparing the feature(s) with one or more target values, characterized in thatthe electronic processing device (56) uses the comparison to detect whether an intermediate element is inserted between the first and second components (12, 14) which is clamped between the first and second components (12, 14) as intended when the screw connection is tightened, and to issue an error message if the comparison shows that the intermediate element is missing or not inserted correctly.

2. The method according to claim 1, wherein the intermediate element is a sealing ring (34) or a washer.

3. Method according to claim 1 or 2, wherein the error message is displayed on a display device (58).

4. Method according to one of claims 1 to 3, wherein the processing device (56) detects the missing or incorrectly inserted intermediate element based on one or more or all of the following characteristic features calculated from the signals of the angle sensor (50) and the torque sensor (52) in comparison with one or more associated target values: gradient (m) of the torque depending on the angle until a joining torque is reached, at which the gradient (m) changes due to a resulting direct mechanical contact between the two components (12, 14) gradient (m lin ) of the torque depending on the angle after reaching the joining torque, and / or value of the joining torque.

5. The method according to any one of claims 1 to 4, wherein the angle sensor (50), the torque sensor (52) and the processing device (56) are incorporated in a torque wrench (44).

6. Method according to one of claims 1 to 5, wherein information regarding the screw connection (10) can be supplied to the processing device (56) and the processing device (56) takes the desired values required for the comparison from a database on the basis of the information.

7. Method according to one of claims 1 to 6, wherein the target values used by the processing device are based on measurements and / or calculations.

8. An arrangement for tightening a screw connection (10) between a first component (12) and a second component (14) which are equipped with cooperating threads (20, 40), comprising: means for rotating one of the threads (20, 40) in the sense of tightening the screw connection (10), an angle sensor (50) and a torque sensor (52) for successively detecting the angle of rotation and the torque when tightening the screw connection (10), and an electronic processing device (56) for evaluating the time-dependent signals of the angle sensor (50) and the torque sensor (52) to determine one or more characteristic features of the signals and comparing the feature(s) with one or more target values, characterized in thatthe electronic processing device (56) is configured to detect, based on the comparison, whether an intermediate element is inserted between the first and second components (12, 14) which is clamped between the first and second components (12, 14) as intended when the screw connection is tightened, and to issue an error message if the comparison shows that the intermediate element is missing or not inserted correctly.

9. Arrangement according to claim 8, wherein the angle sensor (50), the torque sensor (52) and the processing device (56) are installed in a torque wrench (44).

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