Method for operating an inductive proximity sensor and device for operating such a method and aircraft with such a device

Abstract

The invention relates to methods for operating an inductive proximity sensor, comprising the steps of exciting the inductive proximity sensor by applying a voltage signal in the form of a step function to the voltage input of the proximity sensor, in particular by applying a square-wave voltage, Sampling the voltage signal applied to the proximity sensor in order to obtain corresponding voltage values, Sampling the current flowing in the proximity sensor in response to the application of the voltage signal in order to obtain corresponding current values, Summing up the sampled current values ​​of a first time interval of the step response, Calculating an average current value based on at least one current value from a second time interval of the step response following the first time interval, Calculating an average voltage value based on at least one voltage value from the second time interval, Determining a total system resistance (Rtot ) based on the calculated mean current value and the calculated mean voltage value, and determining a normalized current signal (i Σ,norm ) by dividing the summed sampled current values ​​of the first time interval by the calculated current mean value of the second time interval. The invention is characterized by looking up a lookup table or by using a description of a two-dimensional relationship, e.g. by a polynomial, to determine the inductance (L p ), where as input values ​​to look up a corresponding inductance (L p ) in the lookup table the determined total system resistance (R tot ) and the determined standardized current signal (i Σ,norm ) and comparing the determined inductance (L p) with at least one predetermined threshold to infer the presence or absence of a nearby target object.

Description

[0001] The present invention relates to a method for operating an inductive proximity sensor and a device for operating such a method.

[0002] Inductive proximity sensors, also known as inductive sensors or proximity switches, are electronic devices used to detect the proximity of a metallic object without physical contact. These sensors are based on the principle of electromagnetic induction and use magnetic fields to detect metallic objects.

[0003] These sensors detect a change in inductance depending on the presence or absence of a ferromagnetic material or a target object to be detected in the range of the proximity sensor. Proximity sensors are used, for example, in aircraft applications, particularly in determining the weight-on-wheel signal to detect the moment at which the aircraft's wheels touch or leave the ground. This is an important measurement used in aircraft monitoring and control. Another application in the aircraft field is the detection of an aircraft's landing gear position to generate a signal that provides information about whether the landing gear is extended or retracted. In addition, various mechanical conditions can be detected using inductive proximity sensors.

[0004] The operation of passive inductive proximity sensors can be explained as follows: A changing electromagnetic field is generated by the sensor in its surroundings by flowing current through a coil. Metallic objects approaching the sensor influence the magnetic field, so that the presence of this metallic object (also called the target object) changes the inductance of the coil. State-of-the-art technology then tests whether the changed inductance influences the oscillation frequency of the magnetic field. If the frequency is sufficiently influenced, the presence of the target object in the vicinity of the proximity sensor is inferred. Alternatively, the presence of a target object is inferred based on the phase shift between the measured voltage and the measured current.

[0005] Due to their evaluation approach, existing algorithms for evaluating inductive proximity sensors exhibit a significant dependence on ohmic resistance. This means that a conventional system for evaluating passive, inductive proximity sensors, with electronics, a cable, a connector, and a sensor, exhibits various ohmic resistances that are not always precisely known. The algorithm for determining whether the target object is near the sensor or not must then be adapted to the specific total resistance of the proximity sensor with its various components.

[0006] The problem here is that the resistance ratios cannot be clearly assigned due to component tolerances and unknown cable lengths, which means that a corresponding algorithm cannot carry out a clear evaluation of the proximity sensor in a tolerance analysis of the system (taking into account all possible tolerances of the system).

[0007] Furthermore, according to the known implementations from the state of the art, it is not possible to arbitrarily modify the cable lengths of a proximity sensor without adapting the underlying operating algorithm accordingly. This is due to the ohmic resistance of the modified cables, which influences the evaluation algorithm and must be compensated for accordingly in the algorithm.

[0008] DE 10 2017 003 657 A1 discloses a method in which, among other things, a current sum is calculated after a step-like excitation at different time intervals after the excitation. DE 10 2017 212 777 A1 discloses a method for determining system resistances specifically for resistive-inductive loads. Finally, DE 10 2020 214 582 A1 discloses the determination of an inductance directly from measured current and voltage values.

[0009] The invention aims to achieve improved accuracy of the proximity sensor and to make the algorithm resistance-independent. Resistance independence increases the accuracy and tolerance to system deviations compared to previously known approaches. According to the invention, it is possible for proximity sensors, unlike previous algorithms, to be unambiguously evaluated across all resistance tolerances or to be flexibly equipped with cables of different lengths without requiring an adaptation of the sensor's operating algorithm.

[0010] Overcoming or mitigating the disadvantages known from the prior art is achieved with a method or device according to the present invention.

[0011] It is provided that a method according to the invention for operating an inductive proximity sensor, in particular a passive inductive proximity sensor, comprises the steps: Excitation of the inductive proximity sensor by applying a voltage signal in the form of a step function to the voltage input of the proximity sensor, in particular by applying a square-wave voltage, Sampling the voltage signal applied to the proximity sensor to obtain corresponding voltage values, Sampling the current flowing in the proximity sensor in response to the application of the voltage signal to obtain corresponding current values, Summing up the sampled current values ​​of a first time interval of the step response, Calculating an average current value based on at least one current value from a second time interval of the step response following the first time interval, Calculating an average voltage value based on at least one voltage value from the second time interval, Determine the total system resistance based on the calculated mean current and the calculated mean voltage, Determining a standardized current signal by dividing the summed sampled current values ​​of the first time interval by the calculated mean current value of the second time interval, Using any description of the two-dimensional relationship, e.g. by a polynomial or looking up in a lookup table to determine an inductance, whereby the determined total system resistance and the determined standardized current signal are used as input values ​​for looking up a corresponding inductance in the lookup table or for the two-dimensional relationship, and Comparing the measured inductance with a predetermined threshold to determine the presence or absence of a nearby target object.

[0012] The method according to the invention is resistance-independent because a change in the resistance ratios (at constant inductance) simultaneously leads to a change in the normalized current signal, and the operating point then shifts along a level of constant inductance. This inductance calculation also has the advantage that it can be performed relatively resource-efficiently (in terms of computing time) when using lookup tables.

[0013] An exemplary normalized current signal can be represented in an idealized manner in the purely ohmic-inductive case and for a unipolar voltage as follows (where the normalization factor is not shown): i∑,norm=∑n=n1,Startn1,end(1−e−t⋅RtotLp) n 1,start and n1,end , marking the sampled current values ​​in the first time interval. L p stands for the inductance of the proximity sensor and R tot is the total system resistance. This can be calculated from the sampled voltage and current values ​​from the second time interval. As explained above, an average voltage and an average current are first calculated using the sampled values ​​from the second time interval. The total system resistance is then obtained from these two average calculations by dividing the average voltage by the average current.

[0014] The total resistance is therefore calculated on the basis of the second time interval, whereas the current values ​​for the normalized current come from the first time interval, which is earlier in time than the second time interval.

[0015] The normalized current signal can therefore be described as a two-dimensional function of the inductance and the system resistance. This means that the normalized current signal is a function that depends on the inductance and the total system resistance. i∑,norm=f(Lp,Rtot)

[0016] If we now calculate the inverse function of this dependence over L p and assuming that the function thus determined is strictly monotonic in the corresponding direction, the following dependence can be found: Lp=f(i∑,norm,Rtot) the values ​​for L p can be calculated in advance and stored as a lookup table in an alternative form of another two-dimensional description, e.g., by a polynomial. This two-dimensional lookup table or the two-dimensional description is then calculated using the normalized current i Σ,norm and the total system resistance R totused to determine a suitable inductance L p to determine.

[0017] The inductance value supplied by the lookup table or by any description of the two-dimensional relationship is used to detect the target state. Target detection can be achieved using a hysteresis function. Two spaced-apart threshold values ​​can be provided, with a target object near the sensor being detected when a second threshold value is exceeded by the supplied inductance value ("Target Near"). The hysteresis means that even if the value falls below this second threshold value, it is not immediately concluded that the target object is now located far away from the proximity sensor ("Target Far"), but that the first threshold value must first be exceeded.

[0018] According to an optional modification of the present invention, it is provided that the first time interval originates from an ohmic-inductive behavior of the proximity sensor from a range of less than 3 τ or less than 2 τ and preferably greater than 0.5 τ or greater than 1 τ, where τ is a measure of the gradient with which the current builds up in the proximity sensor when a step function is applied to the proximity sensor and is expressed as the ratio of inductance to resistance of the overall system comprising sensor, line and measuring circuit.

[0019] This ensures that current values ​​at the very beginning of the step response are not used for summing, as these are still quite small and the error occurring during digitization would have a significant impact.

[0020] According to a further development of the present invention, the selected first time interval can be provided in a range in which the transient response of the parasitic resonant circuit, which may be caused or influenced by cables or lines of the system, has subsided, but the change in the current rise through the inductance L is still sufficiently large. Therefore, it is also advisable not to use the values ​​at the beginning of the step response.

[0021] Advantageously, it can further be provided that the second time interval originates from an ohmic-inductive behavior of the proximity sensor from a range greater than 3 τ, preferably greater than 4 τ and preferably greater than 5 τ, where τ is a measure of the speed at which the current builds up in the proximity sensor when a step function is applied to the proximity sensor and is expressed as the ratio of inductance to resistance of the overall system comprising sensor, line and measuring circuit.

[0022] The second time interval for forming an average value of the current and the excitation voltage is therefore in a range in which the current flowing in the proximity sensor has reached or almost reached its maximum value and no large signal fluctuations are to be expected.

[0023] According to a further optional development of the present invention, the lookup table, or alternatively any description of the two-dimensional relationship, e.g., by a polynomial, can be generated by generically describing the normalized current as a two-dimensional function of the inductance and the total system resistance, and determining the inverse function of this dependence over the inductance, which then depends on the normalized current and the total system resistance. Thus, a table is determined in which the inductance can be determined as a function dependent on the parameters of the normalized current signal and the total system resistance. This relationship can be represented mathematically as follows: Lp=f(i∑,norm,Rtot)

[0024] Preferably, it can further be provided that the lookup table or alternatively the arbitrary description of the two-dimensional relationship is calculated in advance so that it can be used to determine an inductance on the basis of the total system resistance and the normalized current.

[0025] Calculating the lookup table in advance allows the use of significantly lower-performance and cheaper components during operation of the proximity sensor, since only the pre-calculated values ​​from the table need be accessed. The corresponding inductance value simply needs to be selected from the lookup table based on the two parameters of the normalized current signal and the total system resistance. If parameter values ​​are entered for which no pre-calculated result is available in the table, a corresponding value can be derived using extrapolation and / or interpolation.

[0026] According to an optional development of the present invention, it can be provided that the lookup table is stored in advance in a memory so that it can be accessed by means of a processor.

[0027] Furthermore, according to the invention, it can advantageously be provided that the sampling of the voltage signal applied to the proximity sensor and the sampling of the current flowing in the proximity sensor takes place with an identical sampling frequency and preferably the individual sampling processes of the voltage signal and the current take place simultaneously.

[0028] Sampling both the excitation voltage signal and the current signal generated by the excitation from the proximity sensor at the same frequency and / or at the same sampling times increases the precision of the required calculations. This eliminates a temporal offset between the voltage value and the corresponding current value, which would otherwise distort the results based on them. It is therefore advantageous if the sampled values ​​used for further calculations are not only taken at the same time interval, but also at the same sampling frequency and / or at the same times.

[0029] Furthermore, according to the present invention, it can be provided that the signal for stimulating the proximity sensor is a unipolar or a bipolar voltage signal.

[0030] According to an optional development of the present invention, it can be provided that the determined inductance (Lp) is compared with a first predetermined threshold value and a second predetermined threshold value which is greater than the first predetermined threshold value in order to infer the presence of a nearby target object if the determined inductance is greater than the second predetermined threshold value and to exclude the presence of a nearby target object if the determined inductance is less than the first predetermined threshold value.

[0031] The presence of two threshold values ​​preferably serves to implement hysteresis, whereby after entering a first state, for example, exceeding the second threshold value to infer a "Target Near" state, a subsequent undershoot of the second threshold value does not result in a state change. The state change to the "Target Far" state only occurs when the comparison value also falls below the first threshold value. Conversely, however, it is also true that after entering the "Target Far" state, exceeding the first threshold value does not trigger a state change, since this only occurs when the second threshold value is also exceeded.

[0032] Accordingly, after the finding, it can be provided that an intermediate state is concluded which represents the immediately preceding state if the determined inductance is greater than the first predetermined threshold value and less than the second predetermined threshold value.

[0033] The invention further relates to a device for operating an inductive proximity sensor, comprising: an excitation unit designed to excite the inductive proximity sensor by applying a voltage signal in the form of a step function to the voltage input of the proximity sensor, in particular by applying a square-wave voltage, a sampling unit configured to sample the voltage signal applied to the proximity sensor to obtain corresponding voltage values, wherein the sampling unit is further configured to sample the current flowing in the proximity sensor in response to the application of the voltage signal to obtain corresponding current values, a summation unit designed to sum the sampled current values ​​of a first time interval of the step response, a computing unit designed to calculate an average current value based on current values ​​from a second time interval of the step response following the first time interval, wherein the computing unit is further configured to calculate an average voltage value based on voltage values ​​from the second time interval, wherein the computing unit is further configured to determine the total system resistance based on the calculated average current value and the calculated average voltage value, and wherein the computing unit is further configured to determine a standardized current signal by dividing the summed sampled current values ​​of the first time interval by the calculated mean current value of the second time interval, characterized in that the computing unit is further configured to look up an inductance in a lookup table or alternatively by using any description of the two-dimensional relationship, for example by a polynomial, wherein the determined total system resistance and the determined standardized current signal are used as input values ​​for looking up a corresponding inductance in the lookup table or the description of the two-dimensional relationship, and the computing unit is further designed to compare the determined inductance with a predetermined threshold value in order to conclude whether or not a target object is present in the vicinity.

[0034] It can further be provided that the device is designed to carry out a method according to one of the aspects discussed above.

[0035] The invention further relates to an aircraft having a device according to one of the previously discussed aspects, in particular for detecting an extended or folded landing gear as well as other mechanical states.

[0036] Further features, details, and advantages of the invention will become apparent from the following description of the figures. These show: Fig. 1: a dashed excitation voltage and the corresponding step response for an inductive passive proximity sensor, Fig. 2: a more detailed representation of an exemplary excitation voltage, Fig. 3: an exemplary representation of a sampled current signal of the step response, Fig. 4: a graphical representation of an example of the data stored in a lookup table, and Fig. 5: a flowchart of the method according to the invention.

[0037] Fig. Figure 1 shows a possible dashed excitation voltage U and the corresponding step response I for an inductive passive proximity sensor. It can be seen that, due to its ohmic-inductive nature, the passive proximity sensor provides the corresponding characteristic step response, which is dominated by the coil.

[0038] Fig. Figure 2 shows an example of an excitation voltage, where the voltage level ranges from -5 V to +5 V, thus being bipolar. Those skilled in the art will appreciate that a unipolar excitation voltage also leads to comparable results.

[0039] Fig. 3 shows a current curve as it occurs when the voltage in Fig. 2 is applied to the inductive proximity sensor. The current waveform is shown in sampled form, so that each sampled value represents a discrete current value.

[0040] The time domain of n 1,start to n 1,end defines the first time interval, whereas the time range of n 2,start and n 2,end the second time interval is defined.

[0041] Fig. Figure 4 shows a two-dimensional lookup table that outputs a corresponding inductance based on the parameters of the normalized current signal and the total system resistance.

[0042] Depending on whether the target object is near the proximity sensor or not, a larger or smaller inductance is determined based on the resulting parameter changes. This change is used to compare it with a threshold value to determine whether the target object is near the proximity sensor or not.

[0043] Fig. 5 shows a structural flow diagram of the present invention.

[0044] The process begins by applying a voltage signal in the form of a square wave to the proximity sensor to stimulate the proximity sensor in a step-like manner.

[0045] The voltage applied for excitation, as well as the resulting step response, are then sampled, so that a sum of the sampled current values ​​can be calculated in a first time interval. In a second time interval of the applied step function following the first time interval, an average current value is calculated in the step response and an average voltage value is calculated in the excitation signal.

[0046] Using the current values ​​summed in the first time interval, a standardized current signal is determined by dividing them by the calculated mean current value of the second time interval. Furthermore, the total system resistance is determined, which can be calculated using the mean current and the mean voltage.

[0047] The normalized current signal thus obtained is then used together with the total system resistance to control the pre-generated lookup table or another two-dimensional description, for example a polynomial, and to obtain an inductance value corresponding to the two parameters (normalized current signal and total system resistance).

[0048] The inductance value thus obtained is then subjected to a threshold comparison, which outputs as a result either the presence of a target object near the proximity sensor (“Target Near”) or its absence (“Target Far”).

[0049] The use of the two threshold values ​​of different sizes serves to implement a hysteresis, so that after one of the two detectable states has been entered, the state only changes when the corresponding threshold value is passed.

Claims

[1] A method for operating an inductive proximity sensor, comprising the steps of: Excitation of the inductive proximity sensor by applying a voltage signal in the form of a step function to the voltage input of the proximity sensor, in particular by applying a square-wave voltage, Sampling the voltage signal applied to the proximity sensor to obtain corresponding voltage values, Sampling the current flowing in the proximity sensor in response to the application of the voltage signal to obtain corresponding current values, Summing up the sampled current values ​​of a first time interval of the step response, Calculating an average current value based on at least one current value from a second time interval of the step response following the first time interval, Calculating an average voltage value based on at least one voltage value from the second time interval, Determining a total system resistance (R tot ) based on the calculated mean current and the calculated mean voltage, and Determining a normalized current signal (i Σ,norm ) by dividing the summed sampled current values ​​of the first time interval by the calculated mean current value of the second time interval, characterized by Using a description of a two-dimensional relationship, in particular by a polynomial, or looking up in a lookup table to determine an inductance (L p ), where the input values ​​for looking up the inductance (L p ) in the lookup table the determined total system resistance (R tot ) and the determined standardized current signal (i Σ,norm ) and Compare the determined inductance (L p) with at least one predetermined threshold to infer the presence or absence of a nearby target object. [2] Method according to the preceding claim 1, wherein the first time interval originates from an ohmic-inductive behavior of the proximity sensor from a range of less than 3 τ or less than 2 τ and preferably greater than 0.5 τ or greater than 1 τ, where τ is a measure of the gradient with which the current builds up in the proximity sensor when the step function is applied to the proximity sensor and is defined as the ratio of inductance (L p ) to the total system resistance (R tot ) is expressed. [3] Method according to one of the preceding claims, wherein the second time interval originates from an ohmic-inductive behavior of the proximity sensor from a range greater than 3 τ, preferably greater than 4 τ and preferably greater than 5 τ, where τ is a measure of the gradient with which the current builds up in the proximity sensor when the step function is applied to the proximity sensor and is defined as the ratio of inductance (L p ) to the total system resistance (R tot ) is expressed. [4] A method according to any one of the preceding claims, wherein the lookup table or other two-dimensional description, for example a polynomial, is generated by: the normalized current (i Σ,norm ) generically as a two-dimensional function of the inductance (L p ) and the total system resistance (R tot ) and the inverse function of this dependence over the inductance (L p), which is then subtracted from the normalized current (i Σ,norm ) and the total system resistance (R tot ) depends on. [5] Method according to the preceding claim 4, wherein the lookup table or another two-dimensional description, for example a polynomial, is calculated in advance so that it is suitable for determining an inductance (L p ) based on the total system resistance (R tot ) and the normalized current (i Σ,norm ) can be used. [6] Method according to one of the preceding claims, wherein the lookup table or another two-dimensional description, for example a polynomial, is stored in advance in a memory so that it can be accessed by a processor. [7] Method according to one of the preceding claims, wherein the sampling of the voltage signal applied to the proximity sensor and the sampling of the current flowing in the proximity sensor are carried out with an identical sampling frequency and preferably the individual sampling processes of the voltage signal and the current are carried out simultaneously. [8] Method according to one of the preceding claims, wherein the signal for exciting the proximity sensor is a unipolar or a bipolar voltage signal. [9] Method according to one of the preceding claims, wherein the determined inductance (L p ) is compared with a first predetermined threshold value and a second predetermined threshold value which is greater than the first predetermined threshold value, in order to infer the presence of a nearby target object when the determined inductance (L p) is greater than the second predetermined threshold value and to exclude the presence of a nearby target object if the determined inductance (L p ) is less than the first specified threshold. [10] Method according to the preceding claim 9, wherein an intermediate state is inferred which represents the immediately preceding state when the determined inductance (L p ) is greater than the first predefined threshold and less than the second predefined threshold. [11] Device for operating an inductive proximity sensor, comprising: an excitation unit designed to excite the inductive proximity sensor by applying a voltage signal in the form of a step function to the voltage input of the proximity sensor, in particular by applying a square-wave voltage, a sampling unit configured to sample the voltage signal applied to the proximity sensor to obtain corresponding voltage values, wherein the sampling unit is further configured to sample the current flowing in the proximity sensor in response to the application of the voltage signal to obtain corresponding current values, a summation unit designed to sum the sampled current values ​​of a first time interval of the step response, a computing unit designed to calculate an average current value based on current values ​​from a second time interval of the step response following the first time interval, wherein the computing unit is further configured to calculate an average voltage value based on voltage values ​​from the second time interval, wherein the computing unit is further configured to calculate the total system resistance (R tot) based on the calculated mean current and the calculated mean voltage, and wherein the computing unit is further configured to calculate a normalized current (i Σ,norm ) by dividing the summed sampled current values ​​of the first time interval by the calculated mean current value of the second time interval, characterized by , that the arithmetic unit is further designed to use a lookup table or another two-dimensional description, for example a polynomial, to determine an inductance (L p ), where as input values ​​to look up a corresponding inductance (L p ) in the two-dimensional description or the lookup table, the determined total system resistance (R tot ) and the determined standardized current (i Σ,norm ) and the computing unit is further designed to calculate the determined inductance (L p ) with at least one predetermined threshold value in order to infer the presence or absence of a nearby target object. [12] Device according to the preceding claim 11, which is designed to carry out a method according to one of the preceding claims 1 to 10. [13] Aircraft with a device according to one of the preceding claims 11 or 12, in particular for detecting an extended or a folded landing gear and / or other mechanical states.

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