Method, evaluation unit and system for detecting interference in a strain wave gear mechanism by means of strain sensors

Abstract

The invention relates to a method, an evaluation unit and a system for detecting interference in a strain wave gear mechanism, wherein: the strain wave gear mechanism has an elastic transmission element with an outer toothing, a wave generator and a rigid outer ring with an inner toothing; the elastic transmission element has an elastic transmission element with a strain sensor arrangement having a first strain sensor and a second strain sensor; the strain sensor arrangement in the undistorted elastic transmission element is formed substantially in the circumferential direction of a first circle having a first diameter; the first strain sensor is arranged on the first circle substantially diametrically opposite the second strain sensor; the first strain sensor generates a first sensor signal and the second strain sensor generates a second sensor signal; a temporal derivation of the first sensor signal and a temporal derivation of the second sensor signal is formed; interference is detected when first a dedoidal state of the transmission element is detected and then a non-dedoidal state of the transmission element is detected.

Description

[0001] Method, evaluation unit and system for detecting interference faults in a tension wave gear using strain sensors

[0002] The invention relates to a method for detecting engagement faults in a tension wave drive. The invention further relates to an evaluation unit configured to perform the method for detecting engagement faults in the tension wave drive. The invention also relates to a system comprising an elastic transmission element of the tension wave drive and the evaluation unit.

[0003] Background of the invention

[0004] Strain wave gearing (also known as wave gearing or sliding wedge gearing) enables virtually backlash-free power transmission with a high gear ratio and is therefore particularly suitable for applications requiring precise movements and minimal space. Because the high gear ratio allows for the generation of high torques with relatively small motors, strain wave gearing enables the creation of very compact drive mechanisms, which are used, for example, in robotics.

[0005] The main components of a stress wave drive are a wave generator, a rigid outer ring (circular spline) with internal teeth, and an elastic transmission element (flexspline) with external teeth positioned between them. The transmission of torque between the wave generator and the outer ring is based on the elastic deformation of the transmission element. The wave generator deforms the elastic transmission element into an ellipse, so that the elastic transmission element engages with the outer ring on two opposite sides of its circumference. As the wave generator rotates, the elastic transmission element rolls on the outer ring, and the interlocking teeth between the elastic transmission element and the outer ring transmit torque between them.The gear ratio is determined by the difference in the number of teeth between the transmission ring and the outer ring.

[0006] During operation, excessively high torque can occur, for example, when the gearbox is operating under heavy load. This can lead to a misalignment between the transmission element and the outer ring, causing the teeth of the transmission element to skip over the teeth of the outer ring (ratcheting). Under normal operating conditions, the transmission element rotates with a constant tooth feed. However, a misalignment results in a temporary, uncontrolled relative rotation between the outer ring and the transmission element. This leads to an unknown angular offset relative to the input side, making precise control of the angular position impossible. The gearbox's condition does not reveal whether such a misalignment has occurred, thus complicating the search for the cause of the fault.

[0007] In this context, a method is known from publication JP7394551 B2, in which an arrangement of strain gauges is used to measure the torque acting on the output side of a tension wave gear. This makes it possible to detect engagement faults and the occurrence of a dedoidal state, in which the flexible transmission element is not arranged concentrically to the rigid outer ring. However, the method described therein requires an additional sensor and a more complex detection process, which leads to downtime of the tension wave gear. Furthermore, the aforementioned publication does not describe a method for counting recurring tooth jumps caused by engagement faults.

[0008] German patent DE 102022 101 977 A1 describes a method for detecting a malfunction in a voltage wave drive, whereby a decrease in the measured torque over time is determined and compared with a decrease threshold. An exceedance of the decrease threshold is detected, thereby triggering a warning signal.

[0009] DE 102022 128423 B3 also describes a method for detecting an interference fault in a voltage wave drive and includes the steps

[0010] The process involves measuring the torque profile over time on the deformable transmission ring, detecting a meshing fault based on the measured torque profile, determining the number of teeth skipped during the detected meshing fault based on the torque measurement, and calculating an angular offset between the transmission ring and the outer ring. This angular offset corresponds to the determined number of skipped teeth.

[0011] US 2022 / 0273378A1 describes a robot manipulator with a

[0012] Isolation mechanism for a force / torque sensor. The isolation mechanism is coupled to the output of the gearbox driving a robot joint. The sensor has a stationary part and a coupled, movable part relative to it. This stationary part is coupled to the isolation mechanism, which deforms in response to forces induced by the gearbox to mechanically isolate the force / torque sensor from these forces.

[0013] Disclosure of the invention

[0014] Against this background, the task is to provide a method, an evaluation unit for executing the method and a system consisting of the evaluation unit and an elastic transmission element, thereby enabling the detection of interference faults and dedoidal states, as well as the counting of repeatedly occurring tooth jumps in the stress wave drive with less effort.

[0015] The problem is solved by a method for detecting interferences in a stress wave gear, wherein the stress wave gear comprises an elastic transmission element with external teeth, a shaft generator, and a rigid outer ring with internal teeth, wherein the elastic transmission element is an elastic transmission element with a strain sensor arrangement comprising a first strain sensor and a second strain sensor, wherein the strain sensor arrangement is formed in the undeformed elastic transmission element substantially circumferentially along a first circle with a first diameter, wherein the first strain sensor is arranged on the first circle substantially diametrically opposite to the second strain sensor, wherein the first strain sensor receives a first sensor signal and the second

[0016] A strain sensor generates a second sensor signal, whereby a time derivative of the first sensor signal and a time derivative of the second sensor signal are calculated. A malfunction is detected when a dedoidal state of the elastic transmission element is first detected, followed by a non-dedoidal state. The task is further accomplished by an evaluation unit configured to execute the malfunction detection procedure, and by a system comprising the evaluation unit and the elastic transmission element.

[0017] A dedoidal state is defined as a state in which the flexible transmission element is not arranged concentrically to the rigid outer ring. Conversely, a non-dedoidal state is defined as a state in which the flexible transmission element is arranged concentrically to the rigid outer ring.

[0018] According to the invention, the method for detecting interferences in a voltage wave gear is characterized in that the dedoidal state is detected when a test shows that – at a first time point – the magnitude of a first instantaneous value of the time derivative of the first sensor signal and the magnitude of a second instantaneous value of the time derivative of the second sensor signal are greater than a predetermined threshold value and that the product of the first instantaneous value and the second instantaneous value is negative, and that the non-dedoidal state is detected when a test shows that – at a time point following the first time point,second time point - the magnitude of a third instantaneous value of the time derivative of the first sensor signal and the magnitude of a fourth instantaneous value of the time derivative of the second sensor signal is greater than the specified threshold, and that a product of the third instantaneous value and the fourth instantaneous value is negative, and that a product of the first instantaneous value and the third instantaneous value or a product of the second instantaneous value and the fourth instantaneous value is negative.

[0019] This results in the advantage of the inventive method, the inventive evaluation unit configured for carrying out the inventive method and the inventive system that, by comparing the magnitudes of instantaneous values ​​of the derivatives of the sensor signals with a threshold value and by considering the signs of products of the instantaneous values, the operating states associated with intervention disturbances - the dedoidal state and the non-dedoidal state - can be detected with less effort.

[0020] According to an advantageous embodiment of the invention, the strain sensor arrangement comprises a third strain sensor and a fourth strain sensor, wherein the third strain sensor is arranged on the first circuit substantially diametrically opposite to the fourth strain sensor, wherein the third strain sensor generates a third sensor signal and the fourth strain sensor generates a fourth sensor signal, wherein a time derivative of the third sensor signal and a time derivative of the fourth sensor signal are calculated, wherein the dedoidal state is detected if a test additionally shows that – at the first time point – the magnitude of a fifth instantaneous value of the time derivative of the third sensor signal and the magnitude of a sixth instantaneous value of the time derivative of the fourth sensor signal are greater than the predetermined threshold, wherein the non-dedoidal state is detected if a test additionally shows thatthat – at the second time point – the magnitude of the fifth instantaneous value of the time derivative of the third sensor signal and the magnitude of the sixth instantaneous value of the time derivative of the fourth sensor signal are greater than the specified threshold. Such a design can increase the precision of the detection of the dedoidal state and the non-dedoidal state.

[0021] According to a further advantageous embodiment of the invention, the first sensor signal is low-pass filtered before its time derivative is calculated, and / or the second sensor signal is low-pass filtered before its time derivative is calculated, and / or the third sensor signal is low-pass filtered before its time derivative is calculated, and / or the fourth sensor signal is low-pass filtered before its time derivative is calculated. Low-pass filtering suppresses high-frequency interference, thus reducing the risk of misinterpreting the sensor signals due to high-frequency interference.

[0022] According to a further advantageous embodiment of the invention, the number of detected engagement faults is counted. This makes it possible to better estimate the relative positions of the elements of the tension wave drive. For example, if it is assumed that with each engagement fault the flexible transmission element jumps by exactly one tooth relative to the rigid outer ring, the tooth position of the tension wave drive can be corrected by one tooth with each detected engagement fault.

[0023] According to a further advantageous embodiment of the invention, it is provided that the number of detected interference disturbances is displayed in a display device or transmitted to a control unit.

[0024] A further aspect of the invention is an evaluation unit configured to execute the methods according to the invention. The evaluation unit according to the invention can achieve the same technical effects, advantages, and configurations as already described in connection with the methods according to the invention.

[0025] Furthermore, another object of the invention is a system comprising the evaluation unit and an elastic transmission element with external teeth, wherein the elastic transmission element comprises a strain sensor arrangement having a first strain sensor and a second strain sensor, wherein the first strain sensor arrangement is formed in the undeformed elastic transmission element essentially in the circumferential direction of a first circle with a first diameter, wherein the first strain sensor is arranged on the first circle essentially diametrically opposite to the second strain sensor, wherein the first strain sensor generates a first sensor signal, and wherein the second strain sensor generates a second sensor signal.The system according to the invention can achieve the same technical effects, advantages and configurations as have already been described in connection with the method according to the invention.

[0026] Further details and advantages of the invention will be explained below with reference to the exemplary embodiments shown in the drawings. These show:

[0027] Fig. 1 shows an elastic transmission element with a strain sensor arrangement with four strain sensors in a schematic sectional view;

[0028] Fig. 2 shows the dedoidal state resulting from a failure of engagement, as occurs in elastic transmission elements, in a schematic sectional view;

[0029] Fig. 3 shows an outer ring, an elastic transmission element and a wave generator in a schematic sectional view, as well as an enlarged section of an area of ​​the tooth engagement to illustrate engagement disturbances;

[0030] Fig. 4 photographic illustrations (first row) and corresponding schematic representations (second row) of the three phases of an interventional disorder

[0031] Fig. 5 experimentally determined signal profiles of sensor signals and their time derivative from four strain sensors and pairs of two successive instantaneous values ​​of the time derivative of the sensor signals, as used in the method according to the invention.

[0032] Fig. 6 enlarged view of a section of the experimentally determined signal profiles of sensor signals and their time derivative from four strain sensors and pairs of two successive instantaneous values ​​of the time derivative of the sensor signals, as used in the method according to the invention.

[0033] Fig. 7 shows a first embodiment of the method according to the invention in program-based form, represented by a flowchart.

[0034] In the various figures, identical parts are always marked with the same reference symbols and are therefore usually only named or mentioned once.

[0035] Fig. 1 shows a schematic sectional view of an elastic transmission element 1 with a strain sensor arrangement 2 comprising four strain sensors 2.1, 2.2, 2.3, and 2.4. Such elastic transmission elements 1 are used on the drive side of tension wave drives 10 (see Fig. 3) for torque transmission. The strain sensor arrangement 2 has a first strain sensor 2.1, a second strain sensor 2.2, a third strain sensor 2.3, and a fourth strain sensor 2.4, wherein the first strain sensor 2.1 is arranged diametrically opposite to the second strain sensor 2.2, and the third strain sensor 2.3 is arranged diametrically opposite to the fourth strain sensor 2.4. Such strain sensors can be designed as strain gauges, which change their electrical resistance under tensile or compressive deformation.Strain gauges can be attached to elastic transmission elements using adhesive bonds. Alternatively, conductive traces of the strain gauge can be applied to a base body of the flexible transmission element. Bridge circuits of strain gauges in the form of a quarter, half, and / or full bridge are preferably used for measurement.

[0036] Fig. 2 shows a first schematic representation of a ratcheting error between the external teeth 1.1 of an elastic transmission element 1 and the internal teeth 6.1 of a rigid outer ring 6 of a tension wave drive 10 (see Fig. 3). One of the contact points along the main axis of a wave generator 5 (see Fig. 3) has shifted by one tooth in the direction of the shorter axis. This condition is also known as the dedoidal state D (see Fig. 7). During operation of the tension wave drive, after a dedoidal state D, the non-dedoidal state N (see Fig. 7) with normal tooth engagement can occur again, in which case a jump of one tooth is retained. Fig. 3 shows a second schematic representation of a ratcheting error between the external teeth 1.1 of an elastic transmission element 1 and the internal teeth 6.Figure 1 shows a rigid outer ring 6 of a tension wave gear 10, as well as an enlarged section of a tooth engagement area to illustrate the engagement disturbances. The enlarged section shows the result of engagement disturbances P occurring in the tension wave gear. After a single engagement disturbance P.1, there is a jump of one tooth, while after the three engagement disturbances shown here as examples, there is a jump of three teeth.

[0037] Fig. 4 shows photographic images (first row) and, below each, a corresponding schematic representation (second row) of the three phases of a meshing failure. The first image in the second row (second row, left) shows how – for example, due to an excessively high input torque – the outer teeth of an elastic transmission element begin to separate from the inner teeth of a rigid outer ring, the pre-ratcheting phase. The second image in the second row (second row, center) shows how a displacement of one tooth occurs as a result of the continuing rotation of the shaft generator 5, the mid-ratcheting phase (first slip). At this moment, the flexible transmission element is in a dedoidal state. The third image in the second row (second row, right) shows how the previous offset of the shaft generator is reversed by a jump back one tooth, the mid-ratcheting phase (second slip).At this moment, the flexible transmission element is in a non-dedoidal state.

[0038] Fig. 5 shows four experimentally determined signal waveforms of four sensor signals ST1, ST2, ST3, and ST4, and their time derivatives DST1, DST2, DST3, and DST4, respectively, which are generated by the four strain sensors 2.1, 2.2, 2.3, and 2.4 during operation of the strain wave drive 10 as a function of time t. A uniform rotation of the wave generator 5 between the start of the recording and time 138 causes a cyclically increasing and decreasing strain of the strain sensors 2.1, 2.2, 2.3, and 2.4 due to the oval cross-section of the wave generator 5. The uniform rotation of the wave generator 5, i.e., at a constant angular velocity, initially leads to sinusoidal sensor signals (harmonic oscillations) during the period between the start of the recording and time 138.The sensor signals from each pair of diametrically opposite strain sensors (ST1 and ST2, and ST3 and ST4) are in phase, since the main axis (the longer axis) of the oval cross-section of the wave generator 5 stretches the strain sensors simultaneously and equally. The occurrence of an engagement fault in the tension wave drive 10 manifests itself as discontinuities in the sensor signals ST1, ST2, ST3, and ST4, and as signal peaks in the time derivatives of the sensor signals DST1, DST2, DST3, and DST4, such as those that occur between times 139 and 140. During a transition from a non-dedoidal state N (see Fig. 7) to a dedoidal state D (see Fig. 7), the elastic transmission element 1 shifts along the secondary axis (the shorter axis) of the oval cross-section. This rapidly occurring movement, depending on the positions of the strain sensors 2.1, 2.2, 2.3 and 2.4. At the time of the occurrence of the intervention fault, a rapid increase or decrease in the sensor signals ST1, ST2, ST3, and ST4 of the strain sensors 2.1, 2.2, 2.3, and 2.4 is observed, wherein two diametrically opposed strain sensors 2.1 and 2.2 or 2.3 and 2.4 exhibit opposite signs of the signal peaks in their time derivatives DST1 and DST2 or DST3 and DST4, respectively. If the elastic transmission element 1 shifts again at a later time such that a non-dedoidal state N exists, this shift is accompanied by signal peaks of the time derivatives DST1 and DST2 or DST3 and DST4 of the opposite sign. The presence of the dedoidal state D or the non-dedoidal state N, as well as the number of intervention faults that have occurred, can therefore be detected by identifying these signal peaks.A threshold value G serves to distinguish the relevant signal peaks from those signal peaks that occur, for example, as a result of unavoidable noise, which is generally superimposed on the sensor signals ST1, ST2, ST3 and ST4.

[0039] Fig. 6 shows an enlarged section of the experimentally determined signal waveforms from Fig. 5 of sensor signals ST1, ST2, ST3, and ST4 and their time derivatives DST1, DST2, DST3, and DST4 during a period between time 139 and time 140, during which a first intervention disturbance occurs. Also shown are the signs of a first instantaneous value DST1.1 of the time derivative DST1 of the first sensor signal ST1 and a second instantaneous value DST2.1 of the time derivative DST2 of the second sensor signal ST2 at a first time t1. Furthermore, the signs of a third instantaneous value DST1.2 of the time derivative DST1 of the first sensor signal ST1 and a fourth instantaneous value DST2.2 of the time derivative DST2 of the second sensor signal ST2 at a second time t2 are shown.As can be seen in the diagram, the signs of the first pair of values ​​occurring at the first time t1, consisting of the first and second instantaneous values ​​DST1.1 and DST2.1, are opposite to the signs of the second pair of values ​​occurring at the second time t2, consisting of the third and fourth instantaneous values ​​DST1.2 and DST2.2.

[0040] Fig. 7 shows an embodiment of the method according to the invention in program-based form, represented by a flowchart. At the beginning of the program execution, a state variable n and a counter variable m are set to zero. The program execution also includes a loop within which the occurrence of signal peaks exceeding a threshold value G in the derivatives DST1, DST2, DST3, and DST4 of sensor signals ST1, ST2, ST3, and ST4, filtered by low-pass filters T1, T2, T3, and T4, is detected. The derivatives DST1, DST2, DST3, and DST4 are formed by differentiators D1, D2, D3, and D4. Instantaneous values ​​of the derivatives DST1, DST2, DST3, and DST4 thus formed are checked in a first query to see if their magnitudes exceed a threshold value G. If the instantaneous values ​​do not exceed the threshold value G, the query is repeated.If the instantaneous values ​​exceed the threshold, the system checks whether any of the products of two instantaneous values ​​from the derivatives of opposing strain gauges 2.1 and 2.2 or 2.3 and 2.4 are negative. If the product is non-negative, the check is repeated after the magnitudes of new instantaneous values ​​exceed the threshold. If the product is negative, the state variable is incremented by one. If the state variable n then has a value of one, the last queried instantaneous values ​​are stored as the first instantaneous value DST1.1, the second instantaneous value DST2.1, the fifth instantaneous value DST3.1, and the sixth instantaneous value DST4.1. If, however, a value of the state variable n of Zwei is available, the last queried instantaneous values ​​are stored as the third instantaneous value DST1.2, as the fourth instantaneous value DST2.2, as the seventh instantaneous value DST3.2 and as the eighth instantaneous value DST4.2.If the state variable n has a value less than two, a dedoidal state D exists. A display of the current state Z is then generated, and the check for exceeding the threshold G by the magnitudes of new instantaneous values ​​is repeated at a later time. If the state variable n has a value greater than or equal to two, it is checked whether the product of the first instantaneous value DST1.1 and the third instantaneous value DST1.2, or the product of the second instantaneous value DST2.1 and the fourth instantaneous value DST2.2, or the product of the fifth instantaneous value DST3.1 and the seventh instantaneous value DST3.2, or the product of the sixth instantaneous value DST4.1 and the eighth instantaneous value DST4.2 is negative or not.If the product is negative, the transition from the dedoidal state D to the non-dedoidal state N is detected, the state variable n is set to zero, and the counter variable m is incremented by 1, so that the number of tooth jumps that have occurred so far is stored in the counter variable m. The number of tooth jumps that have occurred so far, E, is then displayed, and a current state Z is shown. If, however, the product described above is non-negative, a faulty state F is detected, and a current state Z is shown. Subsequently, the query is repeated at a later time after the threshold value G has been exceeded by the magnitudes of new instantaneous values.

[0041] In the described embodiment of the method, an interference fault is thus detected when first a dedoidal state D of the transmission element 1 is detected and subsequently a non-dedoidal state N of the transmission element 1 is detected. The dedoidal state D is detected when a test reveals that

[0042] — that - at a first time t1 - the magnitude of the first instantaneous value DST1.1 of the time derivative DST 1 of the first sensor signal ST 1 and the magnitude of the second instantaneous value DST2.1 of the time derivative DST2 of the second sensor signal ST2 is greater than the specified threshold G and

[0043] — that the product of the first instantaneous value DST1.1 and the second instantaneous value DST2.1 is negative.

[0044] The non-dedoidal condition is detected when an examination reveals

[0045] — that - at a second time t2 following the first time t1 - the magnitude of the third instantaneous value DST 1.2 of the time derivative DST 1 of the first sensor signal ST 1 and the magnitude of the fourth instantaneous value DST2.2 of the time derivative DST2 of the second sensor signal ST2 is greater than the specified threshold G and

[0046] — that the product of the third instantaneous value DST1.2 and the fourth instantaneous value DST2.2 is negative, and

[0047] — that the product of the first instantaneous value DST1.1 and the third instantaneous value DST1.2, or a product of the second instantaneous value DST2.1 and the fourth instantaneous value DST2.2, is negative. Reference symbol list

[0048] 1 elastic transmission element

[0049] 1.1 External gearing

[0050] 2 Strain gauge sensor arrangement

[0051] 2.1 First strain sensor

[0052] 2.2 Second strain sensor

[0053] 2.3 Third strain sensor

[0054] 2.4 fourth strain sensor

[0055] ST 1 first sensor signal

[0056] ST2 second sensor signal

[0057] ST3 third sensor signal

[0058] ST4 fourth sensor signal

[0059] DST 1 time derivative of the first sensor signal

[0060] DST2 time derivative of the second sensor signal

[0061] DST3 time derivative of the third sensor signal

[0062] DST4 time derivative of the fourth sensor signal

[0063] 5-wave generator

[0064] 6 rigid outer ring

[0065] 6.1 Internal gearing

[0066] T1 first low-pass filter for the first sensor signal

[0067] T2 second low-pass filter for the second sensor signal

[0068] T3 third low-pass filter for the third sensor signal

[0069] T4 fourth low-pass filter for the fourth sensor signal

[0070] D1 first differentiator for the first sensor signal

[0071] D2 second differentiator for the second sensor signal

[0072] D3 third differentiator for the third sensor signal

[0073] D4 fourth differentiator for the fourth sensor signal

[0074] D Dedoidal condition

[0075] E Number of previous tooth jumps

[0076] F Faulty condition

[0077] N Non-dedoidal condition

[0078] Z Display of a current state

[0079] U circumferential direction

[0080] G threshold value n state variable m counter variable t time t1 first time point t2 second time point

[0081] P Interventional disorders

[0082] P.1 Shift by one tooth after a procedure error. P.2 Shift by three teeth after three procedure errors.

Claims

Patent claims 1. Method for detecting interference faults in a tension wave transmission, wherein the tension wave transmission comprises an elastic transmission element (1) with external teeth (1.1) and a shaft generator (5) and a rigid outer ring (6) with internal teeth (6.1), wherein the elastic transmission element (1) comprises a strain sensor arrangement (2) comprising a first strain sensor (2.1) and a second strain sensor (2.2), wherein the strain sensor arrangement (2) is formed in the undeformed elastic transmission element (1) substantially in the circumferential direction (U) of a first circle with a first diameter, wherein the first strain sensor (2.1) is arranged on the first circle substantially diametrically opposite to the second strain sensor (2.2), wherein the first strain sensor (2.1) a first sensor signal (ST1) and the second strain sensor generates a second sensor signal (ST2), wherein a time derivative (DST1) of the first sensor signal (ST1) and a time derivative (DST2) of the second sensor signal (ST2) are formed, wherein an intervention fault is detected when first a dedoidal state (D) of the transmission element (1) is detected and subsequently a non-dedoidal state (N) of the transmission element (1) is detected, wherein the dedoidal state (D) is detected when a test reveals,. — that - at a first time point (t1) - the magnitude of a first instantaneous value (DST1.1) of the time derivative (DST1) of the first sensor signal (ST1) and the magnitude of a second instantaneous value (DST2.1) of the time derivative (DST2) of the second sensor signal (ST2) is greater than a predetermined threshold (G) and — that the product of the first instantaneous value (DST1.1) and the second instantaneous value (DST2.1) is negative, with the non-dedoidal state (N) being detected if an examination reveals, — that - at a second time point (t2) following the first time point (t1) - the magnitude of a third instantaneous value (DST1.2) of the time derivative (DST1) of the first sensor signal (ST1) and the magnitude of a fourth instantaneous value (DST2.2) of the time derivative (DST2) of the second sensor signal (ST2) is greater than the specified threshold (G) and — that the product of the third instantaneous value (DST1.2) and the fourth instantaneous value (DST2.2) is negative, and — that a product of the first instantaneous value (DST1.1) and the third instantaneous value (DST1.2) or a product of the second instantaneous value (DST2.1) and the fourth instantaneous value (DST2.2) is negative.

2. Method according to claim 1, characterized in that the strain sensor arrangement (2) comprises a third strain sensor (2.3) and a fourth strain sensor (2.4), wherein the third strain sensor (2.3) is arranged on the first circuit substantially diametrically opposite to the fourth strain sensor (2.4), wherein the third strain sensor (2.3) generates a third sensor signal (ST3) and the fourth strain sensor generates a fourth sensor signal (ST4), wherein a time derivative (DST3) of the third sensor signal (ST3) and a time derivative (DST4) of the fourth sensor signal (ST4) are formed, wherein the dedoidal state (D) is detected if a test additionally shows that - at the first time point (t1) - the magnitude of a fifth instantaneous value (DST3.1) of the time derivative of the third sensor signal (ST3) and the magnitude of a sixth instantaneous value (DST4.1) the time derivative of the fourth sensor signal (ST4) is greater than the specified threshold (G), whereby the non-dedoidal state (N) is detected if a test additionally shows that - at the second time point (t2) - the magnitude of the fifth instantaneous value (DST3.1) of the time derivative of the third sensor signal (ST3) and the magnitude of the sixth instantaneous value (DST4.1) of the time derivative of the fourth sensor signal (ST4) is greater than the specified threshold (G).

3. Method according to one of the preceding claims, characterized in that the first sensor signal (ST1) is low-pass filtered before the formation of the time derivative (DST1) of the first sensor signal (ST1) and / or that the second sensor signal (ST2) is low-pass filtered before the formation of the time derivative (DST2) of the second sensor signal (ST2) and / or that the third sensor signal (ST3) is low-pass filtered before the formation of the time derivative (DST3) of the third sensor signal (ST3) and / or that the fourth sensor signal (ST4) is low-pass filtered before the formation of the time derivative (DST4) of the fourth sensor signal (ST4).

4. Method according to one of the preceding claims, characterized in that the number of detected interference disturbances is counted. 16 5. Method according to claim 4, characterized in that the number of detected interference disturbances is displayed in a display device or transmitted to a control unit.

6. Method according to one of the preceding claims, characterized in that a currently detected dedoidal state (D) or non-dedoidal state (N) is displayed in a display device or transmitted to a control unit.

7. Evaluation unit configured to execute a method according to any one of claims 1 to 6.

8. System comprising an evaluation unit according to claim 7 and an elastic transmission element (1) with external teeth (1.1), wherein the elastic transmission element (1) is an elastic transmission element (1) with a strain sensor arrangement (2) comprising a first strain sensor (2.1) and a second strain sensor (2.2), wherein the first strain sensor arrangement (2) is formed in the undeformed elastic transmission element (1) substantially in the circumferential direction (U) of a first circle with a first diameter, wherein the first strain sensor (2.1) is arranged on the first circle substantially diametrically opposite to the second strain sensor (2.2), wherein the first strain sensor (2.1) generates a first sensor signal (ST1), and wherein the second strain sensor generates a second sensor signal (ST2).

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