Method for monitoring track switch and switch drive

Abstract

The invention relates to a method for monitoring a track switch having a switch drive (1), the switch drive (1) comprising a housing (2), a switch actuating motor arranged in the housing (2), and an actuating lever (3) leading out of the housing (2) for coupling to the track switch, the method comprising: providing a piezoelectric sensor (6) arranged on the housing (2); detecting a measurement signal of the piezoelectric sensor (6) during an adjustment operation of the turnout driver (1), periodic components of the measurement signal being at least partially filtered out in order to obtain a signal component representing a non-periodic change in the strain of the housing (2); and evaluating the temporal progression of the signal component representing the non-periodic variation of the strain in order to identify a deviation from the target state.

Description

Field of the Invention

[0001] The present invention relates to a method for monitoring a railway turnout having a turnout drive, wherein the turnout drive includes a housing, a turnout adjustment motor arranged in the housing, and an adjustment rod extending from the housing for coupling with the railway turnout.

[0002] Furthermore, the present invention relates to a turnout drive for performing the method according to the present invention. Background Art

[0003] Turnout diagnostic systems allow the operator of a railway network to identify in advance impending damage to various components of the turnout, in particular the turnout drive, and thereby avoid turnout failures and optimize the maintenance process. Turnout failures can be caused by mechanical, environmental, hydraulic or electrical problems and often result in long-term failures of the railway section involved.

[0004] For remote monitoring of turnout drives, various methods have been proposed, which aim to monitor the conversion of the turnout and identify the wear state from the time trend of the measured measurement parameters during the adjustment operation and, if necessary, from the comparison of the trend with a target value.

[0005] Other known methods utilize sensors in the adjustment mechanism for this purpose, which sensors monitor the current passing through the turnout adjustment motor of the turnout drive. The current trend curve is measured for each conversion process and sent to an evaluation unit, where the data is analyzed according to parameters set individually for each turnout and user rules. Measuring the passing current has the advantage that monitoring can be implemented starting from the adjustment mechanism, so that there is no need to intervene in the turnout drive. However, the disadvantage is that the current trend curve only allows general conclusions to be drawn about the state of the turnout, including the turnout drive, and remote diagnosis cannot be performed in terms of the cause of the failure.

[0006] A more precise localization of the wear phenomenon or the fault state can be achieved by arranging sensors at various components of the turnout drive itself, such as, for example, strain measurement sensors at the adjustment rod or force measurement bolts as connecting elements between the adjustment rod and the drive rod of the turnout. With these sensors, the adjustment force can be measured. Such sensors require wiring at the external moving parts of the turnout drive and are therefore error-prone and costly in terms of installation.

[0007] To overcome these drawbacks, monitoring systems have been proposed in which the sensing device can be arranged at the stationary housing of the switch drive instead of at the moving parts. For example, WO 2019 / 063263 A1 discloses a method for analyzing the switch drive of a track switch by means of a sensor for measuring sound waves during the adjustment operation of the switch drive, wherein the adjustment force of the adjustment force coupling of the switch drive is obtained based on the detected sound waves. Here, the sensor can be configured as a piezoelectric sensor or as a surface acoustic wave sensor. The drawback when detecting sound waves is that it is difficult to associate the anomalies in the sound signal with a specific fault source. Usually, the interference frequencies that cannot be easily filtered out are responsible for this. The problem also manifests itself in that unforeseen interference frequencies occur, which randomly lie in the signal range associated with a specific fault source or adjustment force or distort this signal range. Obtaining the adjustment force by means of sound waves additionally requires regular calibration, because otherwise the measured values are not stable over a long period of time and are therefore not reliable.

[0008] Another feasible solution is disclosed in EP 3269615 A1, in which a fiber optic sensor is installed at the housing of the switch drive in order to detect parameters indicating the state of the switch drive, such as, for example, strain. However, fiber optic sensors are only suitable to a limited extent for use in the switch drive area under harsh conditions. Fiber optic sensors require a so-called interrogator, which is expensive and cannot be integrated into the switch drive due to its size. Therefore, in practice, the interrogator is installed separately at a central location outside the switch drive housing for multiple measurement sites and is connected to the individual fiber optic sensors via fiber optic conductors. Subsequently, the sensitive fiber optic conductors must be laid in a protected manner over a long distance to prevent mechanical influences, which also represents a significant expense. In particular, with regard to the necessary accuracy and reproducibility of the measurements in this application, the fiber optic conductors and their couplings must be pre-assembled in the required length under workshop conditions. In particular, subsequent retrofitting at an already installed switch drive is thus difficult and expensive.

[0009] Another drawback of fiber optic sensors is their lower sensitivity in detecting deformation amplitudes. So-called "bursts" occur during component failure or tearing, which cannot be adequately resolved by fiber optic sensors. Likewise, there are components of bearing noise (such as "pitting") and friction noise (such as during degreasing), which cannot be covered by fiber optic sensors. Another drawback of fiber optic sensors is that they are adversely affected by the change in strain with temperature. Above a specific calibrated temperature, the offset must be continuously compensated. Since the influence of temperature can easily be in the order of magnitude of the measured values or even exceed this order of magnitude, compensation becomes difficult. Summary of the Invention

[0010] Accordingly, the object of the present invention is to enable improved monitoring of a turnout, by means of which the above-mentioned drawbacks can be overcome. In particular, the object of the present invention is to enable monitoring of a turnout without the need for external components to be installed separately, wherein the degree of structural intervention in the existing components of the turnout should be minimized and easy retrofitting of the existing turnout should also be ensured. In addition, the monitoring should be able to identify the cause of the fault and provide targeted maintenance measures.

[0011] To achieve this object, according to a first aspect of the present invention, there is provided a method for monitoring a railway turnout having a turnout drive, the method comprising: providing a piezoelectric sensor arranged at a housing; preferably detecting a measurement signal of the piezoelectric sensor during an adjustment operation of the turnout drive, wherein at least part of the periodic component of the measurement signal is filtered out in order to obtain a signal component representing an aperiodic change in the strain of the housing; and evaluating the time trend of the measurement signal in order to identify a deviation from a target state.

[0012] Accordingly, the concept underlying the present invention is to use a piezoelectric sensor and detect suitable measured values that can be considered for turnout diagnosis, wherein it has been proven that arranging such a sensor at the housing of the turnout drive is sufficient to obtain relevant results. In particular, it has been found that a piezoelectric sensor can be used to detect an aperiodic change in the strain of the housing, wherein the strain can be considered as the degree of mechanical load on the housing and thus the state of the turnout can be inferred therefrom.

[0013] Herein, the aperiodic change in the strain of the housing particularly includes slow or quasi-static strain changes caused by forces acting on the housing of the turnout drive during the switching process of the turnout. Since the housing serves as a support for the components of the turnout (including the turnout drive) that are loaded during the switching process, the load will cause corresponding stresses and thus cause deformation or strain in specific regions of the housing. Herein, the deformation of the housing particularly occurs in the housing regions that are in the force transmission path. In the case of recognizing the surface strain characteristics of the housing at a certain location based on the load, the jamming condition (Schwergang) of the turnout can be deduced by measuring the strain at that location.

[0014] Accordingly, the piezoelectric sensor is arranged on the housing at a location that is in the force transmission path of the force component that variably acts on the housing in general. In particular, the piezoelectric sensor can be arranged at a location where the strain occurring in the housing due to the acting force is at least 0.1 μeps (μm / m).

[0015] For example, it is possible to arrange the piezoelectric sensor as close as possible to the axially fixed screw bearing of the screw drive for adjusting the adjusting rod driven by an electric motor, and if necessary, as close as possible to the threaded connection between the switch drive housing and the switch. In a hydraulically driven switch, the piezoelectric sensor can be arranged as close as possible to the electro-hydraulic fastening point of the drive module.

[0016] The housing of the switch drive can be composed of a plurality of housing components. Preferably, the housing includes a first housing component that at least partially surrounds the switch adjustment motor and a plate-shaped second housing component that is rigidly connected to the first housing component. The switch drive is fastened to the track switch, such as at a sleeper, using the second housing component. The second housing component can be configured as a fastening plate, such as an assembly plate or an adapter plate, which has suitable through-holes for fastening screws, and the switch drive is screwed to the switch, such as at a sleeper, using these fastening screws.

[0017] Here, the piezoelectric sensor can be arranged at the first housing component or the second housing component. In the case of being arranged at the second housing component, preferably, the sensor can be arranged as close as possible to the threaded connection between the switch drive housing and the switch or, for example, at the insertion height of the adjusting rod.

[0018] Here, preferably, the piezoelectric sensor is oriented along the main extension direction at the part of the housing.

[0019] Preferably, the piezoelectric sensor element or the piezoelectric sensor is coupled to the housing surface in a force-locking and / or material-locking manner, so that the strain of the housing or the housing surface is proportionally transmitted to the piezoelectric sensor. In the case of a material-locking connection, an adhesive connection is particularly advantageous.

[0020] The advantages of using a piezoelectric sensor lie especially in its very high measurement sensitivity. Although the measurement result of the piezoelectric sensor depends on temperature, this is only to a small extent. In contrast to fiber optic sensors, the temperature sensitivity does not cause an offset drift when measuring strain, but rather, for example, causes an increase or decrease in the measured amplitude of vibration. Therefore, at temperatures that fluctuate violently in practice, the piezoelectric sensor can be more easily evaluated and is more reliable in terms of accuracy. The temperature compensation of the measured value is achieved on a software basis based on the temperature characteristic curve of the sensor.

[0021] When the coupling characteristics with the base change, the piezoelectric sensor behaves similarly robustly, which is important for reliable measurement of the sensing device with as few interventions as possible over the years. The varying pre-tightening force generated by the coupling (such as chemical-mechanical changes in the adhesive part) does not have an impact in the form of an offset drift similar to thermal strain.

[0022] The piezoelectric sensor can be arranged on the outside or inside of the housing. Arranging it on the inside of the housing is advantageous because it ensures a protected arrangement against external environmental influences or mechanical or force actions. Due to the small structural design of the piezoelectric sensor, such a sensor can be placed inside without damaging other components. It is possible to inexpensively avoid possible electromagnetic interference from railway operation with low material consumption through a shielding part. This also enables preprocessing or complete evaluation of the measurement signals inside the switch actuator.

[0023] Easy retrofittability is achieved regardless of whether it is arranged on the outside or inside of the housing because it is not coupled to moving components and results in low cabling costs. Similarly, easy replaceability is ensured in the event of sensor damage.

[0024] Compared with fiber optic sensors, piezoelectric sensors do not require cabling to an external evaluation module. Rather, the measurement signals can be evaluated using a small-structured electronic circuit that can be arranged closely to the sensor at or inside the housing of the switch actuator, or the electronic circuit can be integrated with the piezoelectric sensor into an integrated unit.

[0025] The piezoelectric sensor can convert the smallest deformation or strain change into an electrical signal, thus also detecting, for example, strain changes induced by structure-borne sound. Therefore, the signal output by the sensor can in principle have high-frequency and low-frequency components. However, piezoelectric sensors are not very suitable for use in pure static measurements. A static force causes a defined charge quantity at the surface of the piezoelectric material. If, for example, a commercially available voltage device is used to measure this charge, the charge will be continuously lost due to the not infinitely high input impedance, which results in a continuous signal drop. Therefore, very slowly occurring strain changes do not cause an accumulation of charge quantity, so that a signal representing the total change cannot be obtained. This effect is less obvious or secondary when measuring periodic, especially high-frequency, strain changes.

[0026] Now, in order to obtain a signal component representing the non-periodic change of strain within the framework of the present invention, it is achieved that at least part of the periodic component of the measurement signal is filtered out. In this regard, a preferred design provides that a signal component representing the non-periodic change of strain is obtained by low-pass filtering, wherein low-pass filtering is performed at a cut-off frequency at which at least part of the periodic signal component corresponding to structure-borne sound of the piezoelectric sensor, preferably having a frequency > 100 Hz, is removed or attenuated. Low-pass filtering can be achieved by conventional analog and / or digital signal processing methods.

[0027] After filtering out the high-frequency signal components, the following signal component is retained, which represents the quasi-static displacement of the high-frequency signal components and represents the deformation of the housing caused by mechanical, non-vibratory loads acting on the housing during the conversion process of the switch. To counteract the effect that due to rapid charge loss, the piezoelectric sensor cannot output the slowly occurring strain changes as an accumulated signal, a preferred configuration of the present invention provides that the signal component representing the non-periodic change in strain is amplified by means of a charge amplifier.

[0028] According to a particularly preferred embodiment of the present invention, not only the non-periodic quasi-static signal component but also the periodic signal component corresponding to the structure-borne sound are used for monitoring the switch. In this regard, it is preferably provided that the signal component representing the structure-borne sound of the piezoelectric sensor is additionally detected and evaluated. In the framework of the present invention, "structure-borne sound" is understood as mechanical vibrations (e.g. > 100 Hz), which can propagate over longer distances from a sound source through mechanically coupled components to each other and can be tapped through the surface of the housing. Here, the sound source can be located in the housing itself or can be formed by components of the switch outside the housing (such as adjusting rods, turnout tracks, loose fastening elements, rolling equipment, switch locks, switching equipment, etc.), in particular by components acoustically coupled to the housing of the switch drive. Structure-borne sound can be caused by the vibration of components of the switch, and the vibration can in turn be caused by frictional contact between the components. As an alternative, the vibration and deformation can be caused by a train passing over the switch and can also be evaluated. Since other excitations act on the components of the switch or the switch drive here, a fault source can also be excited, which cannot be determined sufficiently in the sole conversion operation of the switch.

[0029] Structure-borne sound with a bandwidth of frequency f (e.g. 20 kHz) can only be detected with a sampling rate of at least frequency 2f (i.e. at least 40 kHz in the example).

[0030] A suitable analysis or evaluation of the signal component representing the structure-borne sound, especially in combination with the non-periodic quasi-static signal component, allows the identification of characteristic features of the vibration or the corresponding structure-borne sound, which in turn allows the possible sources of the vibration to be inferred. Thereby, the fault source can be better located and the fault causes can be better distinguished from each other. In a preferred embodiment, the combined evaluation of the signal component representing the structure-borne sound and the signal component representing the non-periodic quasi-static signal component, especially the signals detected during the conversion operation and during the passing of the train, can identify a fault source that cannot be clearly identified either individually during the conversion operation or individually during the passing.

[0031] In terms of detecting the signal component representing structure-borne sound, what stands out as an advantage of piezoelectric sensors is that such sensors have a measurement sensitivity that is one to two orders of magnitude higher than in the case of fiber optic sensors. This means that piezoelectric sensors can detect vibrations with amplitudes that are 10 to 100 times smaller than those of fiber optic sensors. Therefore, piezoelectric sensors are particularly suitable for measuring structure-borne sound waves. In addition, piezoelectric sensors have a higher bandwidth of up to several MHz. Therefore, overall, signals with significantly higher information content are obtained using piezoelectric sensors.

[0032] Especially if the acoustic coupling between the switch and the switch actuator housing is only relatively weak in the end position of the switch actuator, the high measurement sensitivity is important for a meaningful analysis of the switch or its components to be detected by the switch actuator housing during the passage of a train.

[0033] The high measurement sensitivity is also useful for detecting the so-called "popcorn" formed during component failure or tearing, as well as structure-borne sound in the form of high frequencies in the MHz range, which cannot be resolved sufficiently by fiber optic sensors. This also applies to the frequency components of bearing noise (such as "pitting") and friction noise (such as during degreasing), which can be well covered by the frequency band of piezoelectric sensors.

[0034] The detection and / or recording of the signal component representing the non-periodic change in the strain of the housing and the signal component representing structure-borne sound can be carried out successively, individually, or simultaneously.

[0035] The detection and / or recording of the signal component representing the non-periodic change in the strain of the housing and / or the signal component representing structure-borne sound is preferably carried out during the adjustment operation, that is, during the conversion of the switch. As an alternative, outside the adjustment process, the method according to the invention can also be used to detect the influence of a passing train. For example, in addition to the trend of the mechanical load, the same piezoelectric sensor can be used to detect the passage of the train and classify it based on the vibration signal and / or the switch position.

[0036] An improvement of the present invention provides that, in addition to the piezoelectric sensors mentioned so far, at least one additional piezoelectric sensor is arranged at the housing, and the measurement signal of this additional piezoelectric sensor can be detected and evaluated in the same manner and method as described above for the piezoelectric sensors. Arranging two or more piezoelectric sensors can, on the one hand, enable a redundant configuration in the event of sensor failure, and on the other hand, can take into account the fact that the strain in different regions of the housing behaves differently strongly. Therefore, using multiple sensors can more comprehensively detect the relative (i.e., non-absolute) load state or deformation state of the housing and thus the switch.

[0037] As already mentioned, the condition diagnosis of the switch includes the evaluation of the time trend of the signal components representing the non-periodic changes in strain in order to identify deviations from the target condition. This is based on the recognition that the trend of the deformation signal at a fixed location on the housing is characteristic of the adjustment process during repeated adjustment processes, like a fingerprint. Correspondingly, changes in the adjustment process cause changes in the amplitude and trend of the deformation signal. Such changes in the adjustment process can be caused in particular by fatigue, wear, loosening, degreasing, defects (e.g., in the control electronics), current fluctuations, and / or external influences. Here, only the relative change of the deformation signal with respect to the trend of the reference signal needs to be monitored. Such a reference signal can be recorded and stored, for example, in the initial state or new state of the switch drive. Similarly, the reference signal can be recorded after the first start-up, after an inspection, or after maintenance. Calibration is not required because only the changes or qualitative characteristics with respect to the reference state or reference signal need to be considered.

[0038] Therefore, the deformation signal obtained according to the invention together with the reference measurement contains all the information for evaluating the adjustment characteristics and condition of the switch adjustment drive and the switch assembly.

[0039] In this regard, a preferred configuration of the invention provides for obtaining the amplitude of the time trend of the signal components representing the non-periodic changes in strain and comparing it with a target value, wherein the time trend can be incorporated into sub-ranges typical of the process of the switch conversion in order to be able to better correlate the fault modes.

[0040] According to a preferred configuration, the degree of jamming of the switch is obtained from the signal components representing the non-periodic changes in strain. Here, the jamming situation can be expressed as an absolute degree or a relative degree and represents the resistance of the moving components of the switch against the drive during the conversion process. Therefore, the jamming situation is related to the reaction force acting on the switch drive during the conversion process. Different from the (absolute) reaction force that can only be measured by a calibrated sensing device (which is measured in Newtons and can only be quantified with the mentioned additional effort based on the strain detected by a piezoelectric sensor), the jamming situation can be associated as a relative degree, for example, with the change of the conversion resistance with respect to at least one output value or output curve.

[0041] Another preferred configuration provides for recording the time trend of the signal components representing the non-periodic changes in strain during a plurality of adjustment runs and obtaining the maintenance requirements of the switch, such as the switch drive, from the comparison of the recorded trends.

[0042] As already mentioned, the measured values of the piezoelectric sensor fluctuate depending on the temperature. Therefore, it is preferably provided that the temperature measurement value of the temperature sensor representing the temperature in the region of the piezoelectric sensor is detected, and the temperature measurement value is taken into account for compensating the temperature-dependent change of the measurement signal of the piezoelectric sensor.

[0043] According to a second aspect of the invention, a switch actuator is provided, by means of which the method according to the invention according to the first aspect can be carried out, and the switch actuator comprises a housing, a switch adjustment motor arranged in the housing, an adjustment rod led out of the housing for coupling with a track switch, a piezoelectric sensor arranged at the housing, and an evaluation unit, to which the measurement signal of the piezoelectric sensor is supplied, wherein the evaluation unit is configured to preferably detect and record the measurement signal of the piezoelectric sensor during the adjustment operation of the switch actuator, wherein at least part of the periodic components of the measurement signal are filtered out in order to obtain a signal component representing the aperiodic change of the strain of the housing, and the evaluation unit is configured to evaluate the time course of the signal component representing the aperiodic change of the strain in order to identify a deviation from the target state.

[0044] As already implemented in connection with the method according to the invention, the piezoelectric sensor can be arranged at the inner side of the housing.

[0045] Preferably, a low-pass filter with a cut-off frequency is provided, at which at least part of the periodic signal components corresponding to structure-borne sound of the piezoelectric sensor, preferably having a frequency > 100 Hz, are removed or attenuated in order to obtain a signal component representing the aperiodic change of the strain.

[0046] Preferably, a charge amplifier is provided, which amplifies the signal component representing the aperiodic change of the strain.

[0047] Preferably, the evaluation unit is configured to detect the signal component representing the aperiodic change of the strain by acquiring the quasi-static component of the sensor tap.

[0048] Preferably, the evaluation unit is configured to acquire the amplitude of the time course of the signal component representing the aperiodic change of the strain and compare it with a target value, wherein the time course can be combined into sub-ranges typical for the process of the switch conversion in order to be able to better correlate the fault modes.

[0049] Preferably, the evaluation unit is configured to obtain the degree of jamming of the switch from the signal component representing the aperiodic change of the strain.

[0050] The preferred evaluation unit is configured to record the time course of the signal component representing the aperiodic change of strain during a plurality of adjustment runs and to obtain the maintenance requirements of the switch, such as the switch drive, from the comparison of the recorded courses.

[0051] The preferred evaluation unit is configured to additionally detect and evaluate the signal component representing the solid acoustic wave of the piezoelectric sensor.

[0052] Preferably, a temperature sensor for detecting the temperature in the region of the housing of the piezoelectric sensor is provided, and the temperature measured value of this temperature sensor is supplied to the evaluation unit for compensating the temperature-dependent change of the measurement signal of the piezoelectric sensor. Description of the Drawings

[0053] The present invention will be explained in more detail below based on the embodiments schematically shown in the drawings. Among them: Figure 1 The results of the strain measurement are shown, Figure 2 The first embodiment of a switch drive with a piezoelectric sensor is shown, and Figure 3 The second configuration of a switch drive with a piezoelectric sensor is shown. Detailed Description of the Invention

[0054] Figure 1 A plurality of courses are shown, which correspond to the strain measured at the housing of the switch drive by means of the piezoelectric sensor during the switching process. The shown courses are obtained by filtering out the high-frequency signal components of the piezoelectric sensor, so that only the quasi-static components not induced by solid sound are retained. The courses from a plurality of switching processes are shown superimposed on each other.

[0055] Figure 1 The curve cluster shown on the left in corresponds to the switching process in which the turnout track is pushed in one direction, and Figure 1 The curve cluster shown on the right in corresponds to the switching process in which the turnout track is pushed in the opposite direction. By means of an optional amplitude formation step in the evaluation unit, the sensor signal amplitude is shown as a positive value for better comparability regardless of the direction of the switching process. It can be recognized that typical load courses can be detected using the piezoelectric sensor arranged at the housing of the switch drive, which are particularly prominent in the case of a fault-free switch by the access peak, the horizontal course during switchover, and the steep drop after locking.

[0056] Figure 2A partial view of the switch actuator 1 is shown in a sectional view. The switch actuator 1 includes a housing 2 in which a switch adjustment motor (not shown) is arranged, and the switch adjustment motor drives an adjustment rod 3 extending from the housing 2 for coupling with a track switch in the direction of the double arrow 4. The housing 2 further has a mounting plate 5 by means of which the switch actuator 1 can be screwed to a sleeper (not shown) via a drive support. A piezoelectric sensor 6 is fastened to the inner side of the housing 2, i.e., at the side wall 7 of the housing 2, in order to detect strain changes of the housing 2.

[0057] Figure 3 A partial view of the switch actuator 1 is shown in a top view. The switch actuator 1 includes a housing 2 in which a switch adjustment motor (not shown) is arranged, and the switch adjustment motor drives an adjustment rod 3 extending from the housing 2 for coupling with a track switch in the direction of the double arrow 4. The housing 2 further has a mounting plate 5 by means of which the switch actuator 1 is fastened to a frame-shaped drive support by means of fastening screws 13, and the drive support includes frame members 8, 9, 10, 11 and 12. The drive support is in turn fastened to the sleeper 15 by means of fastening screws 14. In this embodiment, the piezoelectric sensor 6 is mounted at the mounting plate 5, more precisely in the vicinity of the fastening screws 13, in order to detect strain changes of the mounting plate 5 of the housing 2.

Claims

1. A method for monitoring a railway turnout having a turnout drive (1), wherein, The switch actuator (1) includes a housing (2), a switch adjustment motor arranged in the housing (2), and an adjustment rod (3) extending from the housing (2) for coupling with the track switch. Wherein, the method includes: - Providing a piezoelectric sensor (6) arranged at the housing (2), - Preferably detecting the measurement signal of the piezoelectric sensor (6) during the adjustment operation of the switch actuator (1), wherein at least part of the periodic component of the measurement signal is filtered out to obtain a signal component representing the aperiodic change of the strain of the housing (2), and - Evaluating the time trend of the signal component representing the aperiodic change of the strain to identify a deviation from the target state.

2. The method according to claim 1, wherein The piezoelectric sensor (6) is arranged at the inner side of the housing (2).

3. The method according to claim 1 or 2, characterized in that, The housing (2) has a first housing part that at least partially surrounds the switch adjustment motor and a preferably plate-shaped second housing part (5) rigidly connected to the first housing part. The switch actuator is fastened to the track switch by using the second housing part, and the piezoelectric sensor (6) is arranged at the first housing part or the second housing part (5).

4. The method according to claim 1, 2 or 3, characterized in that The signal component representing the aperiodic change of the strain is obtained by low-pass filtering, wherein the low-pass filtering is performed at a cut-off frequency at which at least part of the periodic signal component corresponding to the solid-borne sound of the piezoelectric sensor, preferably having a frequency > 100 Hz, is removed or attenuated.

5. The method according to any one of claims 1 to 4, characterized in that, The signal component representing the aperiodic change of the strain is amplified by means of a charge amplifier.

6. The method according to any one of claims 1 to 5, characterized in that, The detection of the signal component representing the aperiodic change of the strain includes obtaining the quasi-static component of the sensor tap.

7. The method according to any one of claims 1 to 6, characterized in that, Obtaining the amplitude of the time trend of the signal component representing the aperiodic change of the strain and comparing it with a target value.

8. The method according to any one of claims 1 to 7, characterized in that, Obtaining the degree of jamming of the switch from the signal component representing the aperiodic change of the strain.

9. The method according to any one of claims 1 to 8, characterized in that, Recording the time trend of the signal component representing the aperiodic change of the strain during multiple adjustment operations, and obtaining the maintenance requirement of the switch, such as the switch actuator (1), from the comparison of the recorded trends.

10. The method according to any one of claims 1 to 9, characterized in that, Additionally detecting and evaluating the signal component of the piezoelectric sensor (6) representing the solid-borne sound wave.

11. The method according to any one of claims 1 to 10, characterized in that, Detecting the temperature measurement value of a temperature sensor, which represents the temperature of the housing (2) in the region of the piezoelectric sensor (6), and taking the temperature measurement value into account for compensating the temperature-dependent change of the measurement signal of the piezoelectric sensor (6).

12. A switch actuator (1), comprising a housing (2), a switch adjustment motor arranged in the housing, an adjustment rod (3) extending from the housing (2) for coupling with the track switch, a piezoelectric sensor (6) arranged at the housing (2), and an evaluation unit to which the measurement signal of the piezoelectric sensor (6) is supplied, wherein, The evaluation unit is configured to preferably detect and record the measurement signal of the piezoelectric sensor (6) during the adjustment operation of the switch actuator (1), wherein at least part of the periodic component of the measurement signal is filtered out to obtain a signal component representing the aperiodic change of the strain of the housing (2), and the evaluation unit is configured to evaluate the time trend of the signal component representing the aperiodic change of the strain to identify a deviation from the target state.

13. The switch actuator according to claim 12, characterized in that, The piezoelectric sensor (6) is arranged inside the housing (2).

14. The switch actuator according to claim 12 or 13, characterized in that, The housing (2) has a first housing part that at least partially encloses the switch adjustment motor and a plate-shaped second housing part (5) that is rigidly connected to the first housing part. The switch actuator can be fastened to the track switch by means of the second housing part, and the piezoelectric sensor (6) is arranged at the first housing part or the second housing part.

15. The switch actuator according to claim 12, 13 or 14, characterized in that, A low-pass filter with a cut-off frequency is provided, at which at least partially the periodic signal components corresponding to structure-borne sound of the piezoelectric sensor, preferably having a frequency > 100 Hz, are removed or attenuated in order to obtain the aperiodically varying signal components representative of strain.

16. The switch actuator according to any one of claims 12 to 15, characterized in that, A charge amplifier is provided that amplifies the aperiodically varying signal components representative of strain.

17. The switch actuator according to any one of claims 12 to 16, characterized in that, The evaluation unit is configured to detect the aperiodically varying signal components representative of strain by acquiring the quasi-static components of the sensor tap.

18. The switch actuator according to any one of claims 12 to 17, characterized in that, The evaluation unit is configured to acquire the amplitude of the time course of the aperiodically varying signal components representative of strain and compare it with a target value.

19. The switch actuator according to any one of claims 12 to 18, characterized in that, The evaluation unit is configured to obtain the degree of jamming of the switch from the aperiodically varying signal components representative of strain.

20. The switch actuator according to any one of claims 12 to 19, characterized in that The evaluation unit is configured to record the time course of the aperiodically varying signal components representative of strain during a plurality of adjustment runs and to obtain the maintenance requirements of the switch, such as the switch actuator, from a comparison of the recorded courses.

21. The switch actuator according to any one of claims 12 to 20, characterized in that, The evaluation unit is configured to additionally detect and evaluate the signal components representative of structure-borne sound of the piezoelectric sensor (6).

22. The switch actuator according to any one of claims 12 to 21, characterized in that, A temperature sensor for detecting the temperature of the housing (2) in the region of the piezoelectric sensor (6) is provided, and the temperature measurement value of this temperature sensor is supplied to the evaluation unit for compensating the temperature-dependent change of the measurement signal of the piezoelectric sensor (6).

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