GB2506992A

GB2506992A - Method for detecting malfunction of an ultrasound transducer

Info

Publication number: GB2506992A
Application number: GB1316837.2A
Authority: GB
Inventors: Albrecht Klotz; Thomas Treptow; Dirk Schmid; Philipp Mayer; Bjoern Herder; Karl-Heinz Richter; Sandipto Neogi
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2012-09-21
Filing date: 2013-09-20
Publication date: 2014-04-16
Anticipated expiration: 2033-09-20
Also published as: DE102012216968A1; FR2996006A1; FR2996006B1; GB2506992B; GB201316837D0

Abstract

An ultrasound transducer, e.g. in a parking sensor system for a vehicle, is checked for malfunction, damage or degradation by measuring the impedance of the transducer versus frequency for an applied test signal and comparing the response 20, 24 of the transducer to a reference 10. The frequencies of the maxima 11, 13 and minima 12, of the reference frequency response may be compared with the maxima 21, 23 and minima 22 of the transducers frequency response to determine if the transducer is faulty. A quotient of the maximum and minimum impedance, a distance between the normalised centroids of the extreme values for each curve or a determinant of vectors between extreme values may additionally or alternatively be used. The test signal may be an electrical test signal. The output of the transducer may be corrected if it is determined that it is degraded e.g. by soiling.

Description

Description Title

Method for evaluation adaptation and function checking of an ultrasonic sensor, and a corresponding ultrasonic sensor

Prior art -

The present invention relates to a method for evaluation adaptation and function checking of an ultrasonic transducer, and to an ultrasonic transducer, a parking assistance system and a parking robot. In particular, the is present invention relates to evaluation steps for checkipg a signal which originates from an ultrasonic sensor or ultrasonic transducer. -Driver assistance functions based on ultrasonic sensors *have for a long time been known and used in standard production. The classic parking aid, i.e. a distance measurement with corresponding signalling to the driver of a vehicle, is increasingly being supplemented by more complex functions, such as for ecample unparking assistance (semi-autonomous parking with intervention in the longitudinal and transverse guidance of the vehicle, etc.).

In such systems, an ultrasonic sensor o ultrasonic transducer emits a signal into the vehicle surroundings and converts signals reflected by objects in the surroundings into electrical signals whichare evaluated by an evaluating unit with regard to propagation delay, amplitude, etc. Owing to increaped safety relevance of such functions, it is of increasing importance to develop improved methods for detecting sensor degradation compared with the current state of the art. A "sensor degradation" is understood to mean losses of function due to ageing phenomena, soiling, icing, snow covering, mud and insect deposits on the transducer, as well as damage of the same, for example by stone impact, traffic accidents, vandalism; etc. The methods known in the prior art do not offer any satisfactory solutions for checking an ultrasonic transducer for the aforementioned function impairments during operation. Furthermore, a quantification of the * ic function impairment is desirable insofar as an adaptation * of evaluating algorithms pan take place when certain losses of function have been reliably detected and a (conditional) further use of the ultrasonic transducers appears possible even despite losses of function.

It is therefore an object of the present invention to meet the aforementioned needs.

Disclosure of the invention

The-aforementioned object is achieved, according to the invention, by-a method having the features according to Claim 1. Furthermore, the aforementioned object is achieved, according to the invention, by a-device having the features according to Claim 9, as well as a parking assistance system or a parking robot having the features according to Claim 10. Accordingly, there is provided a method for detecting a malfunction of an ultrasonic transducer which comprises the following method steps: Firstly the ultrasonic transducer to be tested is supplied with a signal, preferably an electrical test signal, by means of which an impedance of the ultrasonic transducer in a predetermined frequency range can be determined. Here, the relationship of a complex exciting signal (electric voltage) to a reactions (e.g. electric current) shown by the ultrasonic transducer in response to the signal supplied can be determined as the impedance. Preferably, only the magnitude of the impedance with respect to the frequency is determined here. Subsequently, the impedance is compared with a reference, it being possible for the reference to be a predefined impedance urve which has been picked up by a properly functioning or normal ultrasonic transducer. Likewise, a continuous updating of the reference at predefined (updating) time intervals is possible. Of course, the reference may also be a calculated quantity or a calculated graph (or frequency-dependent "corridor" about the same) which shows the average" of a multiplicity of impedance curves originating from normal ultrasonic transducers. According to the invention, a malfunction is detected when frequencies or amplitudes of characteristic points of the determined impedance, which may for example be extreme values of the impedance, and frequencies or amplitudes of corresponding points of the stored reference are in a predefined relationship to one another. Thus, the relative positions of currently determined curve points of the impedance are compared with associated curve points of the reference and compared with one another with regard to predefined values and/or sets of values. Alternatively or additionally, a quotient of an impedance maximum and of an impedance minimum of the determined impedance can be used, where the quotient can.be reduced by "1". In this way, a normalised single-value Jo identification of the determined impedance is obtained, which can be compared with a corresponding quotient (impedance maximum divided by impedance minimum, reduced by 1) of the reference, In this way also, a predefined 4 H relationship of a determined impedance and of the predefined or stored reference is thus determined.

Alternatively or additionally, a distance between a normalised centroid of a plurality of extreme values of the impedance and a normalised centroid of a plurality of corresponding extreme values of the reference can be checked to see whether they are in a predefined relationshipto one another. Distance" is understood here to mean any mathematically and/or graphically determinable differences of the relative position of two points. If an impedance curve has, for example, two maxima and a minimum lying between the two maxima, the normalised centroid of the triangle defined by the three extreme values can be determined by known mathematical methods. A normalisation is advantageous, inter alia, in order tb obtain a uniform influencing factor of the frequency and amplitude components of the centroids. The same can be carried out for corresponding extreme values of t-he reference, and this enables a determination of the aforementioned distance of both centroids. Alternatively or additionally, a determinant of vectors between the extreme values of the impedance and a determinant of vectors between the extreme values of the reference can be checked to see whether the two are in a predefined relationship to one another. If, for example, an impedance curve has two maxima (maxl and max2) and a minimum (mm) lying between-the two, the vectors between the first maximum (maxl) and the second maximum.(max2) and also between the first maximum (maxl) *and the minimum (mm) can be determined and their determinant can be determined. Such a dependence is described,-by way of example, by the equation Det = abs ( (fninfmaxi) * (Zmax2Zmj) -(ZrinZmaxi) * (fmaxrfrnin) ),.

F F

in which Det is the absolute value of the determinant, Z is the magnitude of a respective impedance point and f is the frequency of a respective impedance point. The same can take place for corresponding curve points of the reference, enabling a determination of the relationship of the two determinants In particular with regard to the reference, it is clear that the aforementioned evaluation steps may have already been performed beforehand and the results additionally stored. In other words, it is not necessary for each method step to be carried out only when using the method according to the invention, so that the required computing power for carrying out the method according to the invention can be reduced. If now an evaluation of one or a multiplicity of the aforementioned criteria, optionally in combinatione for example the sum of -differently weighted criteria, shows that there is a malfunction of an ultrasonic transducer, a verification of the result can be performed by repeated carrying-out of the method according to the invention and/or a signalling to the user of the method can take place, in order to enable the user to initiate corresponding measures. Alternatively or additionally, measures (such as eg. eliminating an ultrasonic transducer classified as "faulty" from the sensor group) can. also be performed automatically: The subclaims show preferred developments of the invention.

Preferably, the predefined relationship can be. defined in dependence on a temperature, in particular an ambient temperature, so that it is possible to use different comparison values for temperatures which prevail in the surroundings of the ultrasonic transducer or within the same when carrying out the method according to the invention. In this way, different sensitivities and impedance curves can be taken into account temperature-dependently, so that a malfunction deteètion of the s ultrasonic transducer can take place without the influence of the respective temperature.

According to a further aspect of the present invention, a detection of a malfunction is not provided, but rather a method for adapting an evaluation of an ultrasonic transducer irrespective of the existence of a malfunction.

In other words, for example parameters and/or threshold values can be changed on evaluating the ultrasonic transducer signals if it has been detected that the functioning of the ultrasonic transducer has changed, but the ultrasonic transducer can still be used. In contrast to the aforementioned aspect of the preent invention, for adapting the evaluation of the ultrasonic transducer it is checked in what relationship frequencies of characteristic points, in particular extreme values, of the determined impedance and frequencies of corresponding points of the (stored) reference are to one anothen Using stored sets of evaluating parameters, the evaluation of the ultrasonic transduer can be adapted in response to a concretely determined comparison result, in order for example to modify a change in the characteristic of the ultrasonic transducer in the course of an icing and/or a covering on the same, for exampleby adapting sensitivity thresholds or, using other propaating-delay/distance value pairs.

Alternatively or additionally, a relationship of a quotient of an impedance maximum and of an impedance minimum, reduced by 1, of the determined impedance and a quotient of an impedance maximum and of an impedance minimum, reduced by 1, of the stored referende are checked and the * -* * evaluation of distance measurement signals of the ultrasonic transducer are modified in response to,a predetermined relationship between the two. Alternatively or additionally, it can be checked in what relationship a distance between a normalised centroid of a plurality of extreme values of the impedance and a normalised centroid of a plurality of corresponding extreme values, of the refernce are to one another, and the adaplation of the *10 evaluation of the ultrasonic transducer can be modified in response to a determined relationship between the two.

Alternatively or additionally, it can be checked in what relationship a determinant of vectors between the extreme values of the impedance and a determinant of vectors between the extreme values of the reference are to one another, and an evaluation of the ultrasonic transducer can be modified in response to a predetermined relationship" between the tws.

Preferably, the evaluation according to both of the above aspects according to the invention can be adapted in dependence on the result of the comparison. Irrespective of a detection of an ultrasonic transducer as "faulty", the results of the comparison can enable an expedient reaction to a current state of an ultrasonic'tran'sducer, whereby the use of the ultrasonic transducer for a respective purpose is made more reliable.

Further preferably, the relationship is a difference and/or 30' a difference amount which exceeds or falls short of a predefined maximum value. Here, a reference determination constitutes a simple mathematical operation, in order to compare the determined impedance with the stored reference.

Subsequently, the difference and/or the difference amount can be used as a threshold value with regard to the predefined maximum value, in order either to perform the adaptation of the evaluation of the ultrasonic sensor or to classify the ultrasonic sensor as "faulty". This affords the advantage thai calculating a difference is possible very simply in terms of circuitry.

Further preferably, the signal which is used to test the impedance of the ultrasonio transducer can comprise a plurality of frequencies, so that function reductions which have an effect merely in a determined frequency range can be reliably detected. For this purpose, the signal, which can be for example an alternating voltage signal, can comprise a "sweep", in which frequencies in a predetermined range are continuously "swept". In this way, a function reduction is detected articularly reliably or an evaluation adaptation is enabled particularly exactly.

Preferably, the reference signal caii be stored in -dependence on a temperature or eyaluated in dependence on the temperature, -in particular a dependence on the ambient temperature and/or the ultrasonic transducer temperature being possible and a temperature-independent fault -25 detection and evaluation adaptation being enabled.

Further preferably, the signal, by means of which the impedance of the ultrasonic transducer to be tested or classified is determined, is itself not used for a distance measurement by means of the ultrasonic transducer. In other words, the test signal is not provided for exciting the ultrasonic transducer to transmit sound signals into its surroundings, the echoes of which are subsequently used for a determination of the distance *of the ultrasonic -transducer from its surrounding objects. For this purpose, the signal according to the invention and the conventional signals for distance measurement can have different s amplitudes, different frequency ranges, different time characteristics and a combination of differences of the aforementioned arameters. In this way, it is possible during operation to carry out a function check of the ultrasonic transducer in parallel with a distance measurement by means of the same, i.e. breaks in operation during the testing are avoided, which enables a continuous assurance of usable measurement results.

According to a further aspect of the present invention, a device for distance measurement is proposed, which comprises an ultrasonic transducer, a processing unit and a storage means for providihg a reference. The ultrasonic transducer serves for distance measur.ement and is, according to the invention, functionally checked by the processing unit. According to a further aspect of the present invention, the evaluation of the signals received by means of the ultrasonic transducer is adapted inside the processing unit. In both cases, the reference stored in the * storage means is provided, according to the methods discussed above, for Use by the processing unit. The advantage.s of the device correspond here to the respective advantages mentioned in connection with the methods.

According to a further aspect of the present invention, a parking assistance system (also park distance control or distance warning system) and a parking robot is proposed, which each comprise a device according to the aforementioned aspect. In other words, the device for distance measurement is used inside a vehicle to provide the uset with feedback on distances of the userts vehidle * with respect to relevant surrounding objects and alternatively or additionally also enable an automatic parking of the vehicle using the device for distance measurement. The parking assistance system according to the invention and the parking robot according to the invention are distinguished here by an increased functional reliability by detecting malfunctions and adapting the evaluation of distance measurement, signals.

Brief description cf the drawings

Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawings, in which: Figure 1 shows a view of components of an exemplary embodiment of a device for distance measurement according to the invention; Figure 2 shows an impedance-frequency diagram illustrating a, determined impedance curve in relation to a -reference curve; * * * Figure 3 showsa view of the ultrasonic sensor illustrated in Figure 1, with an alternative function * reuct ion; Figure 4 shows an impedance-frequency diagram illustrating * a determined impedance curve in relation to a reference curve; * * * Figure 5 shows an illustration of damage of an ultrasonic sensor caused by stone impact; Figure 6 shows an illustration of an impedance curve of an ultrasonic transducer impaired in its function, and of a reference curve.

Embodiments of the invention Figure 1 *shows a general view of components of a device according to the invention. In this device, an ultrasonic transducer 1 having a housing 2 and a transducer membrane 3 is illustrated. The transducer membrane 3 has a modelling material as soiling V11 which simulates a function impairment of the ultrasonic traflsducer 1. The ultrasonic transducer 1 is connected to** a processor 6 asprocessing unit via conhecting lines 4, 5. The processing:nit is configured to perform a distance measurement by means of the ultrasonic transducer 1 and with the aid of the storage 7 as storage means to carry out a method according to the invention for detecting a malfunction of the ultrasonic transducer 1 or for adapting an evaluation of the ultrasonic transducer 1, a reference being fetched from the stcrage 7 for the impedance of the ultrasonic transducer 1.

It is clear to a person skilled in the art that significantly more than one ultrasonic transducer 1 are often used by the processing unit 6 in practical *applications, in order to generate a more comprehensive image of the surroundings.

Figure 2 shows an inpedance-freguency diagram, in which a section of two impedance curves between 38 kIz and 58 kHz for the ultrasonic transducer 1 illustrated in Figure 1 and a reference is illustrated. The reference curve 10 has a first maximum 11 and a second maximum 13, between which a first minimum 12 is situated. Owing to the soiling V1 (see Figure 1) , the illustrated impedance 20 and a smoothed curve 24 determined from the latter deviates from the reference 10. The smoothed curve 24 has a first maximum 21 and a second maximum 23, between which a first minimum 22 i arranged. Owing to the soiling V1, the extreme values of the smoothed curve 24 are displaced in the direction of lower frequencies compared with those of the reference 10.

According to the invention, a comparison of the frequency position of mutually associated extreme values of the reference 10 and the impedance 20 or the smoothed curve 24 can therefore be used to detect a malfunction of an ultrasonic transducer or to adapt an evaluation of the signals of the ultrasonic transducer to a changed.operating -state.

Figure 3 shows an ultrasonic transducer 1 which is more severely impaired in its function by a larger-area soiling V2 on its membrane 3. In contrast to the soiling V1 illustrated in Figure 1 which covers approximately half of the area of the membrane 3, only about a quarter of the area of the membrane 3 remains uncovered by the soiling V2 in Figure 3.

Figure 4 shbws a comparison, illustrated analogously to Figure 2, of impedance-freuency curves as can be determined or used in conjunction with an arrangement illustrated in Figure 3. Owing to the greater soiling V2, the impedance 20 and the corresponding smoothed curve 24 is considerably changed compared with the reference 10 in Figure 4. Compared with the first maximum 11 of the reference 10, the first maximum 21 is more than 3000 Hz lower and the impedance is reduced by a third at this point. The frequency separation of mutually associated maximum values has thus significantly increased due to the soiling V2. The minimum 22 of the smoothed curve 24 is also displaced in the direction of lower frequencies compared with the corresponding minimum 12 of the reference 10.

Moreover, the magnitude of the impedance at the minimUm 22 is significantly higher. Thus, the first maximum 21 and the minimum 22 of the smoothed curve 24 are closer together both in terms of the magnitude of the impedance and in terms of the frequency. The second maximum 23 of the smoothed curve 24 is likewise displaced in the direction of lower frequencies compared with the second maximum 13 of is the reference 10, but the magnitude of the transducer impedance has not changed substantially. From Figure 4 it can also be seenthat not only the telative position of the extreme points of the smoothed curve 24 has been displaced compared with those of the reference 10 due to the soiling V21 but also that the relative position of the impedance extreme values with respect to one another has changed considerably. From this finding, it can be deduced that a comparison of the impedance 20 with a predefined reference is not necessarily required. In the context of practical applications, however, such a omparison will always be advantageous in order to provide a suitable reference quantity as a basis and on the other hand to take account of long-term clianges of the ultrasonic transducers by adapting the reference curves over the service life of the sensors. -Figure 5 shows a plan view of a membrane 3 of an ultrasonic transducer 1 which has dents produced by stone impact.

These dents cause deformations, tears arid a different response characteristic of the ultrasonic transducer, which result in a changed impedance with respect to the frequency, as illustrated in Figure 6.

S H

Figure 6 shows an impedance-frequency diagram in which impedance profiles between a frequency of 38 kHz and a frequency of 58 kflz are plotted for two curves 40, 41.

Curve 40 shows the impedance of an ultrasonic transducer 1 which is not limited in its function. The curve is characterised by to maxima, which are separated from one another by a distinct minimum between the maxima. Curve 41 visualises the impedance of the ultrasonic transducer 1 damaged by stone impact, shown in Figure 5. Compared with the curve 40, a second maximum (at a higher frequency) has "slipped" into *a region of lower frequency, while the magnitude of the irñpedance has increased only a little at this point. The minimum of the transducer impedance influenced by stone impact has been displaced in the direction of lower frequencies, while the magnitude of the impedance has, however, risen significantly in the region of the minimum. It is quite conceivable that not every stone impact Hecessitates a replacement of-the ultrasonic transducers 1. Merely slight function reductions can sothetimes be readily tolerated without impairing driving safety. Greater function reductions or bhanges of the impedance response may, according to the present invention, necessitate an adaptation of the evaluating steps, such as for example a modification of threshold values. Only when the function reductions cannot be handled in the manner according to the invention so that further use of the - ultrasonic transducers without safety reductions is --ensured, is it possible according to the invention for a * 15 measurement of the impedance to be used to classify a fault * of an ultrasonic transducer as being not tolerable for safe* operation. Such a result can either be signalled to the user of a vehicle or of a driving.safety system or automatically taken into account by a system which uses the distance measurement results of a distance measurement system designed according to the invention.

A central idea of the present invention is to detect function reductions of an ultrasonic transducer and/or react to changed function parameters of an ultrasonic transducer by first sending a test signal to the ultrasonic transducer, by means of which the electrical impedance of the ultrasonic transducer with respect to the frequency can be determined. From the position of extreme values, in particular relativeto a reference, it can be determined whether the ultrasonic transducer is operable without function reductions. A displacement of the extreme values of the impedance on the frequency axis and/or with respect to the impedance magnitude can be used to detect function reductions and adapt an evaluation of measurements by means of the ultraonic transducer. The procedures or devices and systems defined in the independent claims enable a particularly reliable detection of function reductions and in particular a quantification of function reductions, to which it is possible to react by means of changed evaluating algorithms and/or modified limit values.

Even though the aspects and advantageous embodiments according to the invention have been described in detail with the aid of the exemplary embodiments explained in conjunction with the appended drawing figures, for a person skilled in the art modifications and combinations of features of the exemplary embodiments set ant are possible without departin.g from the scope pf the present invention, the scope of protection of which is defined by the appended claims.

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Claims

Claims 1. Method for detecting a malfunction of an ultrasonic transducer (1), the method comprising the steps: supplying the ultrasonic transducer (1) with a signal, determining an impedance of the ultrasonic transducer (1) with regard to the signal, and comparing the impedance (20) with a reference (10) , a malfunction being detected when -a) frequencies of characteristic points, in particular extreme values (21, 22, 23), of the impedance (20) and frequencies of corresponding points (11, 12, 13) of the reference (10) are in a predefined relationship to one another, and/or -b) a quotient of an impedance maximum (23) and of an impedance minimum> (22) reduced by 1 of the determined impedance (20) and a quotient of an impedance maximum (13) and of an impedance minimum (12) reduced by 1 of the reference (10) are in a predefined relationship to one another, and/or -c) a distance between a normalised centroid of a plurality of extreme values (21, 22, 23) of the impedance (20) and a normalised centroid of a -plurality of corresponding extreme values (11, 12, 13) of the reference (10) are in a predefined relationship to one another, and/or -d) a determinant of vectors between the extreme values (21, 22, 23) of the impedance and a determinant -30 of vectors between the extreme values (11, 12, 13) of the reference (10) are in a predefined relationship to one another.

* *_ -
2. Method according to Claim 1, the predefined relationship and/or the reference (10) being defined in dependence on a temperature, in particular an ambient temperature.
3. Method for adapting an evaluation of an ultrasonic transducer (1), the method comprising the steps: supplying the ultrasonic transducer (U with a signal, determining an impedance of the ultrasonic transducer (1) with regard to the signal, and comparing the impedance (20) with a reference (10), it being checked: -a) in what relationship frequencies of characteristic points, in particular extreme values (21, 22, 23), of the impedance (20) and frequencies of correspoflding points (l1,12, 13) of the reference (10) àre to one anothe and/or -b) in what relationship a quotient of an impedance maximum (23) and of an impedance minimum (22) reduced by 1 of the determined impedance (20) and a quotient of an impedance maximum (13) and of an impedance minimum (12) reduced by 1 of the reference (10) are to one another, and/or -c) in what relationship a distance between a normalised centroid of a plurality of extreme values (21,22, 23) of the impedance (20) and a normalised centroid of a plurality of corresponding extreme values (11, 12, 13) of the. reference (10) are to one another, and/or - -d) in wha relationship a determinant of vectors between the extreme values (21,22,23) of the impedance (20) and a determinant of vectors between A I. -the extreme values (11, 12, 13) of the reference (10) are to one another.
4. Method according to one of.the preceding claims, the evaluation of the ultrasonic transducer (10) being adapted in dependence on the result of the comparison.
5. Method according toone of the preceding claims, the relationship being a difference and/or a difference amount which exceeds a predefined maximum value.
6. Method according to one of the preceding claims, the signal, in particular an alternating voltage, comprising a plurality of frequencies, in particular a sweep.*
7. Method %ccording to one of the preceding dlaims, the reference (10) having a temperature dependence, in* particular on the ambient temperature.B. Method according to one of the preceding claims, the * --signal not being used itself for a distance measurement with the ultrasonic transducer (1) 9. A method substantially as herein describedwith reference to the accompanying drawings-.10. Device for distance measurement comprising;-. -an ultrasonic transducer (1), -a processing-unit (6), -a storage means (7) for providing a reference * (10), the processing unit (6) being configured to carry out a method accoiding to one of the preceding claims.11. A device substantially as herein described wIth -reference to the accompanying drawings.12. -Parking assistance system or parking robot comprising a device according to Claim 10 or 11.