Device for detecting shock and vibration conditions in a magnetostrictive transducer

Abstract

Device for operating an electromagnetic, in particular magnetostrictive, sensor or transducer (500), in particular a position measuring system (500, 505), characterized by an evaluation unit (515 - 555) for detecting mechanical shock and / or vibration conditions that may occur during operation of the sensor / transducer (500) or a vibration of the sensor / transducer (500) caused thereby by evaluating signal fluctuations in the region of a base or zero line (105) of a measurement signal provided by the sensor / transducer (500).

Description

The invention relates generally to the operation of a magnetostrictively or magnetostrictively acting sensor or transducer concerned here and in particular to a device for detecting states of shock and / or vibration in a magnetostrictive sensor or transducer which can be used, for example, in a magnetostrictive position or speed measuring system or in the field of technical diagnostics.Prior ArtMagnetostrictive sensors or transducers can be used in a position measuring system developed and sold by the applicant in order to determine the position of an object along a sensitive axis of a corresponding sensor device. Such a position measuring system, which usually operates inductively (for example, product no. BTL7-V50D-M0250-B-C003 from Balluff GmbH) is designed as a serial sensor device with a planar coil system manufactured using printed circuit board technology. The coil system comprises an excitation coil and a plurality of structured planar receiving coils. In order to determine the object position with respect to the sensor device, the perpendicular component of the magnetic field of the object acting on the coil plane is utilized and detected by measurement using a magnetostrictive transducer. The amplitude and the phase of the induced voltage in each of the receiving coils is dependent on the object position. The measurement range ranges up to about 130 millimeters (mm).DE 10 2018 129 942 A1 (Balluff GmbH) also discloses providing a vibration sensor in such a sensor device for characterizing the operating conditions of a sensor or transducer concerned here. The controller of the transducer may use the resulting vibration information to determine the reliability of acquired sensor data.Furthermore, DE 10 2017 116 828 A1 (Sick AG) discloses an optoelectronic detector for detecting objects in a monitoring region, which comprises a sensor module having a light transmitter for transmitting a transmitted light signal into the monitoring region, a light receiver for receiving a light signal from the monitoring region and for generating a corresponding received signal. In addition, a sensor evaluation unit is provided for evaluating the received signal and for generating process data (so-called "object detection signal") and for generating sensor module data. A process data channel is used to output the process data. Furthermore, a state monitoring module is provided, which monitors the state.a state evaluation unit for generating state data,a first internal interface between the sensor module and the state monitoring module for transmitting the sensor module data to the state monitoring module, anda ring memory which receives data, consisting of the state data and / or sensor module data, from the state monitoring module via a second interface for temporary storage,has. The state monitoring module is designed to output a first trigger signal via the second interface as a function of the state data and / or the sensor module data, wherein the first trigger signal prevents a further overwriting of the data in the ring memory for a defined period of time, and wherein the data can be output from the ring memory via a state data channel. By means of the state monitoring module, abnormal behavior of the sensor data is detected in order to warn of a reduced reliability of the sensor system.Disclosure of the InventionThe invention is based on the object of specifying a device for the precise and reliable detection of states of shock and / or vibration in a magnetostrictive or magnetostrictively acting transducer concerned here, without requiring cost-intensive and technically complicated modifications or changes to an existing magnetostrictive transducer and / or to a stated sensor device having such a transducer.The invention is based on the concept of detecting fluctuations in a detected, preferably amplified, measurement or sensor signal of such a sensor device caused by a mechanical shock or a vibration resulting therefrom.Since, as is known per se, time measurements based on zero crossings in such sensor devices are relatively inaccurate and lead to measurement errors in the range of a few millimeters in the case of a position measurement, in the present case, in particular the noise floor or a corresponding base / zero line (i.e. "baseline") of the sensor signal is monitored in order to reliably detect said disturbances. In this case, the sensor signal is preferably digitized, so that this monitoring is subsequently added to existing sensor devices in the form of a control program or control software.The present invention is based in particular on the realization that the digitized signal profile or data points of a corresponding signal waveform calculated from a measurement signal supplied by a measurement sensor concerned here has a characteristic profile in the region of the base line in the mechanically undisturbed case in a sensor device concerned here. In this case, measurement data, i.e. data points of a said signal waveform, accumulate close to the zero line, provided that there is no said disruption due to shock and / or vibration. Therefore, data points present in a zero-centered window can be statistically evaluated and monitored accordingly.It is noteworthy that the apparatus described herein may have one or more targets causing a target signal (110) involved herein. The corresponding target signals ( 110) can therefore appear at any desired position, so to speak, depending on the position(s) of the targets underlying the same along the waveguide, e.g. target magnets.According to the invention, measurement data which deviate from the characteristic curve of an undisturbed signal waveform mentioned can therefore be characterized as "unreliable", be skipped during the evaluation of the measurement data or taken with a lower weighting during the further processing or even deleted. Such exclusion or such suppression or such deletion can be made dependent on whether the deviation of indicator variables of a currently measured signal waveform from corresponding indicator variables of a previously stored, undisturbed signal waveform exceeds an empirically predefinable measure or, in the case of a scalar indicator variable, an empirically predefinable threshold value.It should be noted here that the evaluation of the measurement data does not necessarily have to be skipped if a shock event is detected. Thus, a shock / vibration state can only be detected when the entire signal curve is already present and it would therefore already be too late to begin the evaluation of the detected signal or signal curve for calculating the position of the target magnet. Therefore, a corresponding waveform detected under a shock condition does not have to be deleted or completely excluded from the position evaluation.It is also to be noted here that skipping unreliable measurement data when generating position data can be implemented by means of a sensor device concerned here or a corresponding evaluation / control system. However, the present invention relates substantially to the generation of said indicator values for detecting shock / vibration states and to the use thereof during operation of a sensor device or a corresponding position measuring system concerned here.For operating an electromagnetic, in particular magnetostrictive, sensor or transducer, in particular of a position measurement system, it is provided in particular that a mechanical shock and / or vibration state that may occur during the operation of the sensor / transducer or a vibration of the sensor / transducer caused thereby is detected by statistical evaluation of signal fluctuations in the region of a base line or zero line of a measurement signal provided by the sensor / transducer.According to the invention, when evaluating signal fluctuations in the region of the base / zero line, a comparison with a characteristic profile of the measurement signal for the undisturbed case is preferably carried out.It can furthermore be provided that the measurement signal is digitized and data points resulting from this are evaluated in a zero-centered, time-limited section or section of the measurement signal. However, it should be noted here that preferably no such sections or sections are evaluated, but complete waveforms.In addition, it can be provided that the characteristic curve of the measurement signal in the undisturbed case is based on the signal waveform of an undisturbed, electromagnetically active, in particular magnetostrictive material.It can furthermore be provided that measurement signals or measurement data, which deviate from the characteristic curve in the undisturbed case, are excluded from the further processing or are taken with a lower weighting or are deleted.It can furthermore be provided that measurement signals or measurement data are excluded from the further processing or are taken with a lower weighting or are deleted if the deviation of a currently measured measurement signal or corresponding measurement data exceeds an empirically predefinable threshold value.It can furthermore be provided that the deviation of a currently measured measurement signal or corresponding measurement data is quantified in that significantly increased values of at least one determined indicator variable are detected in that the at least one indicator variable exceeds an empirically predefinable threshold value, which was determined in advance in undisturbed measurements.It can furthermore be provided that the evaluation of signal fluctuations in the region of a base or zero line of the measurement signal is carried out by statistical evaluation of data points generated from a measurement signal.It can furthermore be provided that the statistical evaluation is carried out on the basis of one or more of the following mathematical evaluation methods, on the basis of waveform data generated from a measurement signal:"Quantile method", in which the difference between a first and a last quantile (e.g. a quartile) of waveform data is evaluated, which increases under a shock influence;"Histogram method" which is based on the fact that the sides of a histogram of waveform data close to zero increase at the expense of the middle part, i.e. corresponding to the ratio of sides to middle, in the event of a shock influence and are therefore evaluated corresponding to the ratio of sides to middle;"Standard deviation method" which is based on the standard deviation of the waveform data increasing near the zero line under the influence of shock, and thus waveform data near the base / zero line are evaluated;"Data density method" in which the data density of the waveform data near the base / zero line is evaluated.According to the invention, it can furthermore be provided that in the histogram method the number of data points is evaluated as a function of the value of a deviation from the value zero.It can be used in particular for operating a magnetostrictive sensor or transducer of a position measuring system having a magnetostrictively active or magnetostrictively active waveguide, wherein a mechanical rotational or torsional wave packet is generated in the waveguide by an interrogation current pulse, which mechanical rotational or torsional wave packet propagates in both directions along the waveguide, wherein a measuring transducer, i.e. transducer or sensor, arranged close to one end of the waveguide is provided for receiving a said measurement signal in order to convert the rotational / torsional wave packet propagating in the waveguide into an electronic signal, wherein in a first time interval of the measurement signal the interrogation current pulse causes an oscillating interrogation noise in the received measurement signal in the region of the base / zero line and a collective mechanical response of the waveguide caused by the interrogation current pulse, and wherein, in a second time interval of the measurement signal, there is an oscillating noise floor as well as a target signal superimposed on the noise floor in the region of the noise floor / zero line, wherein the target signal is followed by a further, oscillating noise floor, it is further provided that, for at least one time range with oscillating noise in the region of the noise floor / zero line, measurement values of the recorded measurement signal in the at least one time range are compared with corresponding measurement values of a sensor / transducer disturbed by a mechanical shock and / or vibration state and of a non-disturbed sensor / transducer, and a disturbed or non-disturbed state of the sensor / transducer is deduced depending on the result of the comparison.It can furthermore be provided that the statistical evaluation is limited to time segments of the measurement signal which are not influenced by the interrogation noise or the superimposed target signal.Finally, it can also be provided that measured values of a sensor / transducer disturbed by a mechanical shock and / or vibration state recorded in the at least one time range are disturbed by low-frequency noise.The device according to the invention for operating an electromagnetic, in particular magnetostrictive or magnetostrictively acting, sensor or transducer, in particular of a position measurement system, has in particular an evaluation unit for detecting mechanical shock and / or vibration conditions that possibly occur during the operation of the sensor / transducer or a vibration of the sensor / transducer caused thereby by evaluating signal fluctuations in the region of a base line or zero line of a measurement signal provided by the sensor / transducer.The device according to the invention can furthermore have at least one amplifier for amplifying the measurement signal supplied by the sensor / converter, a comparator for comparing at least one time section of the amplified measurement signal in the region of the base / zero line with a characteristic profile of the measurement signal for the undisturbed case, a flight time analysis unit which supplies a position result, an analog / digital converter for converting the measurement signal into corresponding digital measurement data, and a statistics unit for statistical evaluation in order to ascertain or supply a shock indicator variable.The device according to the invention can furthermore have at least one amplifier for amplifying the measurement signal supplied by the sensor / converter, at least one analog / digital converter for converting the measurement signal into corresponding digital measurement data, a digital signal processor for evaluating the measurement data, a flight time analysis unit which supplies a position result, and a statistics unit for statistical evaluation in order to ascertain or supply a shock indicator variable.The measurement data of the comparator preferably originate from magnetostrictive time-of-flight position sensors. Such sensors have a great measurement imprecision due to mechanical impacts and / or vibrations. In the case of relatively large disturbances, a measurement may even be completely impossible due to a lack of zero crossing of data points as a result or due to an invalid precondition with respect to the stated time-of-flight measurement. This is because the application of a cross-correlation technique to a digitized waveform and the determination of the flight time from a cross-correlation waveform cause a reduced influence, i.e. a smaller deviation of a determined position of a target object in the presence of a vibration or a shock.By means of the device, vibrations and / or impacts in a sensor device concerned here, which influence the accuracy or reliability of a position measurement, can be reliably detected or determined. As a result, such sensor devices can also be safely used in mechanically more critical applications.As a result, in position / velocity measurements involved here, the probability of incorrect control interventions or reactions of control systems on the basis of correspondingly acquired position information is effectively reduced or even completely prevented. The device also enables a fast pulse-by-pulse display of shock and vibration influences on, for example, an underlying magnetostrictively operating position measuring system. Furthermore, it can be provided that e.g. a corresponding magnetostrictive sensor can report precisely the precise vibration circumstances during its operation, e.g. in the form of a correspondingly provided state monitoring function.When the device according to the invention is used in conventional, i.e. comparator-based position measuring systems with magnetostrictive position sensors, only an analog-digital converter system or A / D converter with a low or medium operating or clock speed of the converter is required. Such A / D converters are usually already present in conventional microcontrollers, wherein the implementation of the device according to the invention described in detail below causes a relatively low computing load.Brief Description of the DrawingsExemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description.The following are shown: FIGS. 1a-d show exemplary measurement curves of a magnetostrictive position measuring system, specifically for the case not disturbed by a mechanical impact pulse (FIGS. 1a, c) and for the case disturbed by a mechanical impact pulse (FIGS. 1b, d); FIGS. 2 a- d show exemplary waveform data obtained from the measurement curves shown in FIGS. 1 aand 1 bfor evaluation according to the invention on the basis of a "quantile" method; FIGS. 3 a- d show different shock indicator variables according to the evaluation according to the invention, e.g. on the basis of histogram representations; FIGS. 4 a, b show examples of a marking or non-marking of data points that can be carried out according to the invention as "unreliable" on the basis of a detected or non-detected shock influence; and FIGS. 5 a, b show five exemplary embodiments of a device according to the invention on the basis of combined sequence / block diagrams, identical or similar components being provided with corresponding reference symbols in FIGS. 5 aand 5 b.DETAILED DESCRIPTION OF EMBODIMENTSMagnetostrictive position sensor systems typically consist ofa waveguide made of a highly magnetostrictive material;an electronic circuit for applying an interrogation current pulse upon an initialization signal to the waveguide itself or to a conductive wire passed through a longitudinal hole of the tubular waveguide to produce temporary magnetization of the waveguide;a target magnet disposed in the vicinity of the waveguide and generating an initial magnetization of the waveguide, the magnetization being overwritten by the magnetization induced by the interrogation current pulse, thereby generating a torsional wave packet propagating in both directions along the waveguide;a transducer disposed near the proximal end of the waveguide, i.e. near the electronics of the waveguide, for converting the torsion wave of the waveguide into an electronic signal;a damping zone / structure at the other end of the waveguide to prevent (or dampen) the reflection of the torsion wave at this end of the waveguide; andan electronics block for evaluating the electronic signal of the measuring sensor.It should be noted here that instead of a conducting wire for applying an interrogation current pulse, which wire is guided through a longitudinal hole of the tubular waveguide, it can also be provided to guide the excitation current through a (solid) magnetostrictive wire itself and to use a copper wire outside the magnetostrictive wire in order to return the current to the excitation circuit.Due to the technical construction of such a sensor system, the torsion shaft package and thus the corresponding electronic signal pattern have a typical shape. The time interval measured between the initiation of an interrogation current pulse and the time of detection of a corresponding electronic pattern is used to characterize the position of the target magnet via the correlation between distance and time. In this case, the wave propagation speed is used as a proportionality factor between these two points in time. The position detection task is thereby transferred into a time measurement task.The measuring technique known per se in magnetostrictive and also in ultrasonic-based position or distance sensors consists in starting a counter together with the active edge of an "init" signal, a comparator being provided in order to detect a level crossing of the electronic output signal of the pickup. The timer is then stopped upon activation of the comparator output. The output of the comparator can be pre-conditioned by further comparators and sequential logic in order to prevent the counter from being stopped by fluctuations not related to the target, since the micro-electronically integrable and highly accurate time counters mostly used here cannot react only to incorrect stops without loss of valid data.Due to the coupling to the magnetostrictive waveguide, the electronic signal of the measuring pickup (or "pickups") or of the sensor signal generated or supplied by the pickup is exposed to undesired mechanical disturbances such as shocks and vibrations which propagate along the waveguide as far as the pickup zone mentioned.Moreover, position measuring systems have become known which are based on the evaluation of the longitudinal magnetic effect of a torsion shaft and which are more sensitive to such disturbances than those using only rotary shafts. This is because in the last-mentioned systems, said disturbances can be coupled into the waveguide from the mechanical environment with much lower efficiency.In the context of the approach proposed herein, cross-correlation techniques have been found to be particularly effective in suppressing the influence of oscillations and shocks on the accuracy of a magnetostrictive position measurement. Since the signal component with respect to the target in the position measuring systems concerned here represents a wave packet with a relatively narrow band with respect to the frequency response, the cross-correlation generates an efficient filtering of the respectively measured waveform. This is because frequency components in the vicinity of the center frequency of the waveform, on the order of 100 kHz, can be retained and only the low-frequency components, namely a few kHz, for example up to 4 kHz, which are typical of oscillations and shocks, can be suppressed or excluded in the position determination.In test studies, it has been found that the undesirable deviation of position data due to external vibration in the case of digitally determining a zero-cross time of a cross-correlation waveform is three to ten times smaller than the deviation resulting from a determination based on an analog comparator with respect to the zero-cross time of an analog sampling signal, but cannot be completely eliminated. This is because, in addition to the coupling in of mechanical disturbances, electronic disturbances can also cause oscillations of the scanning signal, which can likewise influence the reliability of the position evaluation.The starting point for the approach described herein is to include or provide only information which is relevant to the reliability of the position measurement data generated by the magnetostrictive position sensor under external shock and vibration influences.The basis for this information is the structure of the scanning signal. The structure of the measurement signal without the influence of shock is shown in FIG. 1 a. In the diagram, detected signal values in the unit [LSB] are plotted against time in the unit [μs]. The measurement on which this was based used a radially arranged target magnet and the waveforms were recorded at a sampling frequency of 3.125 MHz with a nominal resolution of 12 bits. The measurement signal shown in FIG. 1 abegins with an oscillating noise 100 which is caused by the interrogation pulse about 4.mu.s long and the subsequent collective mechanical response of the waveguide associated with the interrogation pulse. This disturbance 100, independently of other influences, is essentially constant and decays after approximately 20 μs. This interrogation noise is followed by a section with a noise floor 105 near the zero or baseline and a target signal 110 superimposed on the noise floor 105, which is represented as a short wavelet between approximately 105 and 135 μs. The target signal 110 is again followed by a noise floor 115.It should be noted here that instead of a collective mechanical response of the waveguide associated with the interrogation pulse, electronic crosstalk from the excitation to the measurement pickup is also possible. The exact structure of such an interference signal is not relevant in the present context.It is further noted that in the apparatus described herein one or more targets causing a target signal (110) concerned may be present. The corresponding target signals ( 110) can therefore appear everywhere, depending on the position / s of the targets. The course of the measurement signal shown in FIG. 1 ais therefore only exemplary and comprises any appearance of such an undisturbed measurement signal, which differs substantially by the actual position of the target, in the case of a magnetostrictive position detection system of a corresponding target magnet.The concept of shock detection described herein is evident from the comparison between waveforms recorded with the undisturbed waveguide (Fig. 1a) and those in which the sensor was subject to vibration (Fig. 1b).In FIG. 1 b, a complete waveform shown in FIG. 1 a, i.e. including the interrogation noise and the target signal, is again shown, wherein the sensor has however been disturbed by an underlying low-frequency noise 120, 125. In this case, the 2 msec. half-sinus burst pulses with a maximum value of 150 g, perpendicular to the waveguide, were generated with an electrodynamic vibrator. Whereas in the case of the undisturbed waveforms (FIG. 1 a) the data points 105, 115 there are arranged in the region of the base line close to the value zero, the shock-influenced waveforms 120, 125 deviate considerably from the value zero (FIG. 1 b).This difference also results from the respective histograms 130, 135 of the waveform data shown in FIGS. 1 aand 1 bshown in FIGS. 1 cand 1 d, respectively. In these histograms, the frequency or number of data points (Y axis) is plotted as a function of the value of the respective signal deviation (X axis) from the value zero. The differences in the two distributions of the waveform data 130, 135 within such a limited data range around the value zero are used here to distinguish whether or not the respective underlying measurements were carried out under the influence of mechanical shock. This distinction is accordingly based on such statistics based characterization of the shock influence.While the undisturbed and shock-influenced data can be differentiated well by the distributions 130 and 135, respectively, shown in FIGS. 1 cand 1 d, the evaluation is preferably limited to those sections of the signal waveform that are not influenced by the interrogation noise or the superimposed target signal. Therefore, by limiting the horizontal axis of Figs. 1a and 1b to the time required for a torsional wave to propagate only once through the magnetostrictive waveguide, reflections (or echoes) of the torsional vibration from the ends of the waveguide can be effectively prevented from leading to another induced signal in the pickup which would result in a deleterious broadening of the distribution shown in Fig. 1c. Therefore, in the embodiments described herein, said statistical evaluation of complete waveforms is applied within the transit time over a complete length of the waveguide.In the following, embodiments of the apparatus according to the present invention based on various shock detection methods will be described with reference to examples of a "quantile method", a "histogram method" and a "standard deviation method".It should be noted here that other corresponding or similar recognition methods can also be used. However, the four methods mentioned are particularly suitable for characterizing the reliability of the position measurement data in real time in order to enable a control of a measurement system (e.g. position detection system) concerned here to effectively prevent incorrect control reactions.To characterize the actual effect of mechanical disturbances affected here, the following four evaluation strategies are proposed.Example 1: "Quantile Method"In this method, waveform data items are sorted in ascending order. The sorted data elements of the waveforms shown in FIGS. 1 aand 1 bare shown in FIGS. 2 aand 2 bas solid lines 200, 215 and 220, 235, respectively, of the underlying individual data of the detected signals in the unit LSB (LSB="least significant bit" and "lower value byte", respectively) as a function of time. The vertically enlarged view of the same data (at least the data designated 200, 215) by the factor 100 is shown in FIGS. 2 cand 2 d.This evaluation method is based on the finding that the waveforms contain numerous data points around the value zero in the case of a fault-free measurement signal. Therefore, the statistical number of data points that lie within a narrow range of values or windows around the value zero must correlate with the strength of disturbances affected here.In this evaluation method, data points, preferably only every nth data point, e.g. 100 data points, are sorted and the difference between the third and first quartile is calculated. For a spurious signal, this difference is small, but increases when the baseline of the signal is spurious. The use of said quartiles is only preferred, but has the advantages described herein for different lengths of the waveguide and for a different number of targets, i.e. for a magnetostrictive measurement system of a different number of target magnets.It is also noted that the data items of the waveforms shown in FIGS. 1 aand 1 b, for example, are sorted in ascending order, and the waveform values thus sorted are simply plotted serially, so that the horizontal axis corresponds to the serial number of the sorted waveform data points. The vertical axis is given in the LSB units mentioned. The representation of the waveform data in the unit LSB also corresponds to the resolution of the respective analog-to-digital converter (ADC).Since most data points in the time series of the undisturbed acquisition signal waveform of Figure 1a are located near zero, the slope of the center portion of the sorted data sequence is small, while the substantially larger deviations 200, 215 and 220, 235, respectively, at the two ends of the sorted sequence (Figure 2c) are caused by the mentioned interrogation noise and the target signal. In contrast, in the impact-biased case (FIG. 2 d), the data points have an increased deviation due to the mechanical perturbation. In addition, due to the wider distribution of the data, the slope of the middle part of the sorted sequence is greater.The slope of the middle part is advantageously characterized by the difference between the first 205 or 225 and the last quantile 210 or 230 of the sorted sequence. Consequently, the undisturbed signals are characterized by relatively small value differences and the shock-influenced signals by relatively large value differences. Thus, the differences for the two quantiles marked in FIGS. 2a-2d by the points 205, 210 and 225, 230 have the value 16 LSB in FIG. 2c and the value 600 LSB in FIG. 2d.In the "quantile method", the waveform data points can basically be sorted only if they are available at all. However, using a field programmable gate array (FPGA), a real-time sort algorithm can be implemented for a known total data length. The sorting algorithm corresponds to the construction of a one-LSB-per-bin histogram that consumes a memory area according to the ADC resolution (e.g., 4096 bins for a 12-bit ADC resolution).One can cumulate the bin contents from the smallest corresponding ADC values, and for example, if the fourth of the total number of data points is exceeded, a first "quartile" is found. A "quartile" is statistically a type of quantile that divides the number of data points present into four parts or quarters of more or less equal size. The data is ordered from smallest to largest to calculate such quartiles, i.e., quartiles represent a form of ordering statistics.A similar procedure can be performed to find a third quartile. In an FPGA mentioned, both the cumulation and the determination of the quantile can proceed in parallel in real time by digital comparison. A histogram-based implementation of the quantile method can also be implemented by means of microcontrollers, which enables only very small delays.Example 2: "Histogram Method"This method is based on the realization obtained from the two histograms 130, 135 shown in FIGS. 1 cand 1 d, namely that the part of the distributions 105, 115 near the zero line, which is characteristic of the undisturbed signals (hereinafter "characteristic curve"), has a relatively large number of data points (FIG. 1 c ) compared to the peripheral parts, whereas the data points 120, 125 occurring near the zero line are distributed more uniformly in the case of shock-influenced signals (FIG. 1 d ). Thus, in the present example, the peripheral ratio compared to the mean sum ratio (FIG. 1 c) is 0.250, whereas the corresponding sum ratio in the shock-influenced case (FIG. 1 d) is 1.471.In this evaluation method, data points in the lower and upper parts of a narrow zero-centered window are counted and summed, and the resulting sum is divided by the number of data points in the middle part. The narrow distribution of the data points typically resulting from an undisturbed signal leads to smaller sum ratios, whereas a correspondingly wider distribution of the data points leads to larger sum ratios in the case of disturbed signals.Alternatively, the difference in the total summations within the two distributions can also be used. However, the total sum is less sensitive to relatively small mechanical disturbances than the aforementioned ratio of peripheral to average sum.The "histogram method" requires the construction of a three-bin histogram using digital window comparators and, when the required amount of data has been processed, a logical addition component and a logical division component to generate the respective shock indicator parameter.Example 3: "Standard deviation method" (or "sigma" method)The distribution of the data points near the zero line can also be characterized by their standard deviation. The standard deviation of data points of a signal waveform concerned here is calculated within a narrow, zero-centered window. The narrow distribution of the data points typical of an undisturbed signal results in a small sigma value, whereas with disturbed signals, a broader distribution of the data points results, i.e. corresponding to a larger sigma value.Thus, according to FIGS. 2 cand 2 d, the standard deviation of the data points in the range of LSB values between -36 and +36 is approximately 9.5 for the undisturbed case (FIG. 2 c ) and 19.9 for the impact-influenced case (FIG. 2 d ). It should be noted that the standard deviation of the data points of the overall waveform, without the aforesaid limitation to LSB values between -36 and +36, would be substantially less sensitive to aforesaid shocks due to the large values in the sample noise and target signal portions.The "standard deviation method" requires some logical multiplications and the accumulation of some values until the required amount of data is processed. Since the multiply and accumulate operation can be performed on most relevant microcontrollers in a single clock, these steps can be performed on both microcontrollers and on said FPGA architectures as real-time methods.Example 4: "Density Method"By counting data points of a signal waveform under consideration here in an even narrower window around zero, the density of the data points around zero is calculated. This is highest for a noise free signal and decreases as the data points are removed from near zero due to wave forms of the waveform.Compared to the four methods described, other procedures are also conceivable in which the spectrum of the measurement signal waveform is calculated and the low-frequency component of the spectrum is quantitatively characterized, since the effect of impacts and vibrations on a measurement signal concerned here normally occurs below 5 kHz. However, the calculation of the spectrum, also by means of a fast Fourier transform (FFT) or a discrete Fourier transform (DFT), which is limited to the low-frequency range, is relatively computation-intensive and can only be started when the entire waveform has been acquired. Such procedures are therefore not able in real time to characterize the reliability of actual, i.e. currently present, position measurement data.In the following, with reference to FIGS. 3 a- 3 dand FIGS. 4 aand 4 b, measurement results actually carried out on an aforementioned position measurement system will be described.A shock pulse described above was repeatedly applied to a magnetostrictive sensor 76 cm long while interrogation pulses were outputted at a repetition rate of 500 Hz and the signal waveforms were detected at a sampling frequency of 3.125 MHz. For each detected waveform, the three procedures described above were used to generate different indicator magnitudes for the respective shock response. This procedure was continued for about 40 s, with about 20,000 waveforms being acquired in each case. FIGS. 3 a- 3 c plot the resulting values of the indicator variables "D_quantile", "D_histogram" and "D_stdev" described above in arbitrary units [a.u.] as a function of the time t in the unit [s]. In addition, in FIG. 3 d, the prescribed deviation "D_ & posdev" is plotted over time in [s].It can be seen from FIGS. 3 ato 3 dthat values of a described indicator variable have increased values above the respective base line in the time ranges in which surge pulses were present, wherein the base line has a typical profile or a typical, i.e. predefined, value level in the respectively undisturbed case. Furthermore, impact pulses have a stochastic effect both on the indicator values and on the position deviation. While the indicator values of the disturbed cases are always higher than the values of the undisturbed cases, the position deviation is often even opposite, i.e. negative, but mostly positive.It should also be noted that there is obviously no correlation between two of the indicator values described in each case and also no correlation between an indicator value and the position deviation.From the signal curves thus acquired, the position of the target magnet can be calculated. At first, the cross-correlation between a reference waveform and the detected waveform is calculated, the reference waveform having been previously recorded, by basing a limited time period shown in Figs. 1a-d and 2a-d with target influences of an undisturbed signal waveform. The target position is defined, without reference to an inevitable constant offset value, as the location of the first negative zero crossing of the cross-correlation waveform and is calculated by linear regression to the data about this zero crossing. A corresponding deviation of the position values from the main position calculated for undisturbed measurements is shown in FIG. 3 d.It should be noted here that the effect of the burst continues much longer than the burst pulse itself lasting 2 ms. Furthermore, the deviation of the position data to its undisturbed value relaxes later than the decay of the shock indicator variables, which can be attributed to essentially real target oscillations even despite the attenuation of the oscillation of the sensor waveguide itself.The effects of shock-like vibrations, for example on a position measurement, can be quantified in that values of the indicator parameters mentioned that are significantly increased for this measurement are recognized in that at least one of the shock indicator variables exceeds an empirically predefinable threshold value, which was previously determined in vibration-free measurements. Alternatively or additionally, several such quantities may be analyzed, which were obtained under unknown vibration conditions.FIGS. 4 aand 4 b show an example of an automatically executable marking or labeling or nonmarking or nonmarking of data points as "unreliable" on the basis of a detected shock influence.FIG. 4 ashows a shock indicator variable according to the "standard deviation method" for the time interval of a position measurement, namely in the present case for a time interval of 0.8 s. In the diagram shown, the indicator variable "D_stdev" 405, 410 is plotted, again in arbitrary units [a.u.], over the time t in [s]. Circles 415, 420 plotted in FIG. 4 adisplay those data points that have been classified as unreliable and labeled accordingly using the following method:At a time when the shock indicator value exceeds a predefined threshold value 400 (shown as a dashed line in FIG. 4 a), the corresponding position output data is marked as unreliable. In this case, these characteristics are still maintained for an empirically predefinable time period after the recorded shock indicator values have dropped below predefined level 400 again. During this period of time, further measurement points or corresponding data points are thus marked further, namely ten (10) further measurement points in the present exemplary embodiment. In FIG. 4a, data not marked in the manner mentioned are shown as small points.The corresponding position data 425, 435 are shown in FIG. 4 b. Both the marking / labeling threshold 400 shown in FIG. 4 aand the number of output data for which the marking / labeling is maintained can be determined empirically according to the required dynamics of the overall system. While a relatively low threshold value and a relatively long duration for marking / labeling lead to more reliable output data and thus to a more stable position measurement system, such values also reduce the possible dynamics of the control system.It should be noted here that the shock-induced zero point fluctuations shown in FIG. 4 acontinues longer than the underlying shock event itself. As can be seen from FIG. 4 b, the shock-related fluctuations 430, 440 of the position data resulting from the measurement shown in FIG. 4 aconceed even longer than the detected fluctuations of the indicator variable "D_stdev" shown in FIG. 4 a. It should also be noted that the data points of corresponding signal waveforms derived from the measurement data can also be corrected, i.e. e.g. completely deleted, by the data points identified as unreliable.It should be noted here that the measurement data acquired by sensors themselves are not marked as "unreliable" or are even completely deleted. Only the digital signal waveforms derived from the measurement data or the position data resulting therefrom during the evaluation can be characterized as "unreliable". Unreliable position data can also be suppressed by exclusion by means of adaptive filtering, for example by means of a Kalman filter or by corresponding weighting.Exemplary embodiments of a device for implementing the procedures described above are illustrated in FIGS. 5 aand 5 b using combined sequence / block diagrams.The device for generating shock indicator values is based on the digitalization of the respective sensor signals. However, the device for detecting a target position and for parallel generation of previously described reliability information for detected position data, in particular for generating a previously described shock indicator value, can be realized in different ways.FIG. 5a shows two exemplary embodiments of a device, namely with and without the components additionally drawn in dashed lines.According to the first embodiment of the device, the signals to be evaluated are supplied by a measuring pickup ("pick-up") 500 which is arranged near the proximal end of a magnetostrictive waveguide 505, i.e. near the electronics of the waveguide. These signals are applied via a first line 510 to a first amplifier 515 to raise the signal level to a more processable level. Via a second line 520, the signal thus amplified is fed to a comparator (with integrated TDC in the present case) 525, in which the comparison described above is carried out. The data resulting from this processing step are then fed to a time-of-flight ("time-of-flight") analysis 530, which as a result delivers a position result 535.It should be noted here that the evaluation of waveform data derived from the measurement data does not have to be ended or interrupted if a shock event concerned here is detected. Thus, a shock / vibration state can only be detected when the entire signal curve is already present and it is thus already too late to begin the evaluation of the signal / signal curve for calculating the position of the target magnet only afterwards. Therefore, a corresponding waveform detected under a shock condition does not need to be deleted or completely excluded from the position evaluation.This also applies to a comparator-based runtime measurement shown in FIG. 5 a, in which a comparator and a "time-to-digital" converter have already generated position data. In the lower evaluation paths shown in FIGS. 5 aand 5 b, indicator values are calculated from the signal waveforms and based on the indicator values and their comparison with a threshold value, the position data can be marked as unreliable.Via a third line 540 branching off from the second line 520, the amplified signal is additionally supplied to an ADC 545, the digital output signal of which is supplied to a statistics unit 550 for the above-described statistical evaluation of the mentioned waveform, in order to ascertain or supply a shock indicator variable 555 as a result.In the second exemplary embodiment of the device, which is illustrated by dashed lines, the signal supplied by the measuring sensor 500 is fed via a fourth line 560 to a second amplifier 565 and is only then fed to the ADC 545. In the second exemplary embodiment, the third line 540 is thus arranged in an unsoiled or non-arranged manner. This makes it possible for the amplification factors or corresponding level elevations of the signals supplied by the measuring sensor 500 to be chosen differently for the further processing by the comparator 525 and by the ADC 545 or the subsequent statistical evaluation 550, in order to be able to provide suitable or optimum signal levels for the two separate further processing steps 525- 535 or 550, 555.FIG. 5 bshows three further exemplary embodiments of a device mentioned, namely likewise with and without the components additionally drawn in dashed lines. In these exemplary embodiments as well, the measurement signals supplied by the measuring transducer ("pick-up") 500 arranged at one end of the magnetostrictive waveguide 505 are fed via the first line 510 to a first amplifier 515.In the third embodiment, the amplified signal is fed via a second line 570 to a first ADC 575, in which the amplified signal is first digitized. The digital signal or the corresponding data is or are fed via a third line 580 both to a digital signal processor 585 and via a branching fourth line 600 in turn to a statistics unit 605 for the above-described statistics evaluation of a said waveform.The data supplied by the digital signal processor 585 after evaluation has taken place are fed here to a time-of-flight ("time-of-flight") analysis 590, which in turn supplies a position result 595 as a result.The evaluation results supplied by the statistics unit 605 then in turn supply a shock indicator variable 610 described above.In the fourth embodiment of the device shown in dashed lines in FIG. 5 b, the amplified signal supplied by the first amplifier 515 is supplied via a branching, additional fifth line 630 to a second ADC 635. This allows e.g. the parameters for analog-to-digital conversion for the respective subsequent components, i.e. the digital signal processor 585 and that of the statistics unit 605, to be chosen differently. Via a sixth line 640, the digitized signal or the corresponding digital data is supplied to the statistics unit 605 for the described purpose.In the fifth exemplary embodiment of the device, which is additionally illustrated by dashed lines in FIG. 5 b, the measurement signal supplied by the measurement pickup 500 via the first line 510 is additionally supplied to a second amplifier 620 via a branching, seventh line 615 and only then is the second ADC 635 present according to the fourth exemplary embodiment supplied via an eighth line 625. This in turn makes it possible for the amplification factors or corresponding level elevations of the signals supplied by the measuring sensor 500 to be chosen differently for further processing by the subsequent further processing in the digital signal processor 585 and in the statistics unit 605 connected via the sixth line 640, in order to be able to provide suitable or optimum signal levels for these two separate further processing steps 585- 595 or 605, 610.It is also to be noted that in the fourth embodiment the fourth line 600 is insoluble and in the fifth embodiment even the two lines 600, 630 are insoluble.According to the exemplary embodiments shown in FIGS. 5 aand 5 b, the evaluation 530 of the transit time of the target signal for determining the target position 535 can be carried out both by means of a high-resolution time-digital converter ("time-to-digital converter") 525 and by generating a stop input signal by means of an analog zero comparator for the pre-amplified detection signal. In this case, a digital evaluation of the respectively detected waveform takes place, which is generated by digitizing the detection signal.As can also be seen from FIGS. 5 aand 5 b, for the generation of shock indicator values, the requirements both for the signal amplifier and for the respective analog-to-digital converter (ADC) 545, 575, 635 and also its parameters can deviate from those required for the evaluation of the runtime. Thus, the evaluation can be carried out either by the comparator 525, optionally combined with a "time-to-digital" converter (TDC 525), or by digital signal processing by means of a digital signal processor.Since, on the one hand, only values close to zero are relevant for the shock detection, as described above, it is advantageous to apply higher amplifications-regardless of the saturation of the target-influenced section of the signal. On the other hand, the calculation of the shock indicator values does not require high resolution or precise analog-to-digital converters, in contrast to the case where the propagation time is determined from the digitized signal waveform by digital signal processing. Further, since the surge indicator values are calculated by each approach through statistical methods and the signal bandwidth of the surge and vibration related signal components is small, the sampling frequency of the associated ADC 545, 575, 635 is also not time critical.Finally, it should be noted that the method described above can be implemented in a conventional, comparator-based, magnetostrictive position measuring system or in a purely software-based magnetostrictive position measuring system on the basis of the evaluation of a signal waveform described above.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2018 129 942 A1

[0003] DE 10 2017 116 828 A1

[0004]

Claims

Device for operating an electromagnetic, in particular magnetostrictive, sensor or transducer (500), in particular of a position measurement system (500, 505), characterized byan evaluation unit (515 - 555) for detecting mechanical shock and / or vibration conditions which possibly occur during the operation of the sensor / transducer (500) or a vibration of the sensor / transducer (500) caused thereby by evaluating signal fluctuations in the region of a base line or zero line (105) of a measurement signal provided by the sensor / transducer (500).Device according to claim 1, characterised byat least one amplifier (515, 565) for amplifying the measurement signal supplied by the sensor / converter (500), a comparator (525) for comparing at least one time section of the amplified measurement signal in the region of the base / zero line (105) with a characteristic curve (105, 115) of data points of a signal waveform (100 - 115) for the undisturbed case, a flight time analysis unit (530) which supplies a position result (535), an analog / digital converter (545) for converting the measurement signal into digital data points of a corresponding signal waveform, and a statistics unit (550) for statistical evaluation according to one or more of claims 1 to 13 in order to determine or supply a shock indicator variable (555).Device according to claim 1 or 2, characterised byat least one amplifier (515, 620) for amplifying the measurement signal supplied by the sensor / converter (500), at least one analog / digital converter (575, 635) for converting the measurement signal into data points of a corresponding signal waveform, a digital signal processor (585) for evaluating the measurement data, a flight time analysis unit (590) which supplies a position result (595), and a statistics unit (605) for statistical evaluation in order to determine or supply a shock indicator variable (610).Device according to one of the preceding claims, characterized in that a mechanical shock and / or vibration state which may occur during operation of the sensor / converter (500) or a vibration of the sensor / converter (500) caused thereby can be detected by statistical evaluation of signal fluctuations (120, 125) in the region of a base line or zero line (105) of a measurement signal provided by the sensor / converter (500).Device according to Claim 4, characterized in that, when evaluating signal fluctuations (120, 125) in the region of the base / zero line (105), a comparison with a characteristic profile (130) of the measurement signal can be carried out for the undisturbed case.Device according to claim 5, characterised in that the measurement signal is digitised (545) and data points of a corresponding signal waveform (100 - 105) which result therefrom can be evaluated in a zero-centred, time-limited section (Fig. 1a, b) of the measurement signal.Device according to Claim 5 or 6, characterized in that the characteristic curve (105, 115) of the measurement signal in the undisturbed case is based on the signal waveform of an undisturbed, electromagnetically active, in particular magnetostrictive material.Device according to one of the preceding claims, characterized in that signal waveforms (100 - 115) which deviate from the characteristic curve (105, 115) in the undisturbed case can be characterized as "unreliable" and / or the further processing is excluded or taken with a lower weighting or deleted.Device according to Claim 8, characterized in that signal waveforms (100 - 115) are excluded from the further processing or are taken with a lower weighting or are deleted if the deviation of a currently detected signal waveform (100 - 115) exceeds an empirically predefinable threshold value (400) of at least one determined indicator variable (see Figure 4a).Device according to Claim 9, characterized in that the deviation of a currently measured signal waveform (100 - 115) can be quantised in that significantly increased values of at least one indicator variable determined (see Figure 4a) are detected in that the at least one indicator variable exceeds an empirically predefinable threshold value (400) which was determined in advance in the case of undisturbed measurements.Device according to one of the preceding claims, characterized in that the evaluation of signal fluctuations in the region of a base line or zero line (105) of the signal waveform (100 - 115) can be carried out by statistical evaluation (550, 605) of data points generated from a signal waveform (100 - 115).Device according to claim 11, characterised in that the statistical evaluation can be carried out on the basis of one or more of the following mathematical evaluation methods, on the basis of data points of a corresponding signal waveform generated from a measurement signal: - a quantile method, in which the difference between a first and a last quantile (e.g. a quartile) of data points of the signal waveform is evaluated; - a histogram method, in which the sides of a histogram of the data points of the signal waveform close to the value zero are evaluated according to the ratio sides to the centre; - a standard deviation method, in which the standard deviation of data points of the signal waveform close to the base / zero line are evaluated; "Data density method" in which the data density of data points of the signal waveform near the base / zero line is evaluated.Device according to claim 12, characterised in that in the histogram method (130, 135) the number of data points can be evaluated as a function of the value of a deviation from the value zero.Device according to one of the preceding claims for operating a magnetostrictive sensor or transducer (500) of a position measuring system (500, 505) having a magnetostrictive waveguide (505), it being possible for a interrogation current pulse to generate in the waveguide (505) a mechanical rotation or torsion wave packet which propagates in both directions along the waveguide (505), a measuring transducer (500), arranged close to one end of the waveguide (505), being provided for receiving a said measurement signal in order to convert the rotation / torsion wave packet propagating in the waveguide (505) into an electronic signal, wherein in a first time interval of the measurement signal the interrogation current pulse in the recorded measurement signal in the region of the base / zero line causes an oscillating interrogation noise (100) and a collective mechanical response of the waveguide (505) caused by the interrogation current pulse, and wherein in a second time interval of the measurement signal to the interrogation noise (100) in the region of the base / zero line there is an oscillating base noise (105) and a target signal (110) superimposed on the base noise (105), wherein the target signal (110) is followed by a further, oscillating base noise (115), characterized in that for at least one time range with oscillating noise (105, 115) in the region of the base / zero line (105), measurement values of the recorded measurement signal in the at least one time range can be compared with corresponding measurement values of a sensor / converter (500) disturbed by a mechanical shock and / or vibration state and of a non-disturbed sensor / converter (500), and a disturbed or non-disturbed state of the sensor / converter (500) is deduced as a function of the result of the comparison.Device according to Claim 14, characterized in that the statistical evaluation can be restricted to time segments (see Figures 4a, b) of data points of a signal waveform (100 - 115) which cannot be influenced by the interrogation noise (100) or the superimposed target signal (110).Device according to claim 14 or 15, characterised in that measured values of a sensor / transducer disturbed by a mechanical shock and / or vibration state recorded in the at least one time range are disturbed by low-frequency noise (120, 125).

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