GB2531909A

GB2531909A - Ultrasonic measuring system, ultrasonic sensor and method for investigating an ultrasonic echo

Info

Publication number: GB2531909A
Application number: GB1516608.5A
Authority: GB
Inventors: Schumann Michael; Schneider Marcus; Schmid Dirk; Roka Andras
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2014-09-25
Filing date: 2015-09-18
Publication date: 2016-05-04
Anticipated expiration: 2035-09-18
Also published as: GB2531909B; GB201516608D0; FR3026494B1; DE102014219399A1; FR3026494A1

Abstract

An ultrasonic measuring system, an ultrasonic sensor (1) and a method for investigating an ultrasonic sensor are proposed. The method comprises the steps of transmitting an ultrasonic pulse based on a first signal, converting an ultrasonic echo into an electrical second signal, filtering the second signal using a filter which is matched to the second signal, correlating the first signal and the second signal, comparing a result of the correlation with a predefined reference, and from this determining a length of the ultrasonic echo. The system, comprising an ultrasonic transducer, an evaluation unit (3) for filtering and correlating, a signal output (5), and an electronic control device (4) with a signal input (7) for providing the results of the correlation to a processor (8), may be integrated within the bumper of a vehicle in order to determine a spatial extent of an environmental object.

Description

Description Title

Ultrasonic measuring system, ultrasonic sensor and method for investigating an ultrasonic echo

Prior art

The present invention relates to an ultrasonic measuring system, an ultrasonic sensor and a method for investigating an ultrasonic echo. In particular, the present invention relates to improvements in determining a length of an ultrasonic echo, from which conclusions can be drawn about the spatial extent of a reflecting object.

In environment detection in the automotive sector, for the most part recourse is had to ultrasonics. Environment objects are detected, for example, by emitting measuring signals and evaluating their echoes reflected at environment objects. In order to suppress interfering signals and signal artefacts, measures are required which, for example, investigate the echo breadth (the time which an echo exceeds a predefined signal strength). Here the received echo is firstly compared with a simple, for example propagation-time-dependent, threshold curve. The result of the comparison is a binary signal: either the echo has exceeded the threshold curve or not. By processing using a pulse width discriminator, narrow exceedings of the threshold curve are suppressed. The propagation time of the echo is characterised by a rising edge of the filtered binary signal. A measure of the quality of the received echo signal is the echo width, i.e. the time during which the filtered binary signal has a logical high level. For example, in the case of rugged surfaces of reflecting signals, there may result echo signals in which the reflected portions of different partial surfaces of the reflecting object are superimposed and cancel one another out, so that none of the partial echoes results in a high level in the above-described signal processing.

DE 10 2011 109 915 Al describes a method for determining the origin of a received signal received by an ultrasonic sensor of a motor vehicle, in which ultrasonic transmitted signals are provided with codes (code words) and received signals are investigated for these code words. While correlations for identifying the code between transmitted and received signal are usually carried out, it is proposed to generate from the transmitted signal by frequency shift a reference signal which is shortened or lengthened in its temporal length. Subsequently, a correlation coefficient between the received signal on the one hand and the reference signal on the other hand is evaluated with respect to a predetermined Threshold. In doing so, a difference between a temporal length of the transmitted signal on the one hand and a temporal length of the received signal on the other hand can also be determined and used to ascertain a frequency shift.

DE 10 2012 202 975 Al discloses a method for environment detection, in which pulses with a defined transmission spectrum are emitted by an ultrasonic sensor and, with the aid of an amplitude and phase information of a subsequently received signal, the same is classified as an echo signal or as an interfering signal. The transmitted signal can be modulated with respect to irs frequency, in particular against time, or with respect to its amplitude.

DE 10 2012 211 293 Al discloses a method for operating an environment detection system of a vehicle, according to which frequency-modulated signals are emitted and echo signals reflected from environment objects are received. The echo signal evaluation takes place with the aid of amplitude information in the form of a cross-correlation function and phase information in the form of a cross-correlation coefficient for evaluating the signal quality. Additionally, it is mentioned that the phase information gives information on the quality of the phase of the received signal.

Starting from the aforementioned prior art, it is an object of the present invention to reliably determine the length of an ultrasonic echo.

Disclosure of the invention

The aforementioned object is achieved according to the invention by a method for investigating an ultrasonic echo. The method can be carried out, for example, in an ultrasonic measuring system of a motorcar or another means of transportation for detecting distances from environment objects. In this method, in a first step an ultrasonic pulse based on a first electrical signal is transmitted. An echo of the ultrasonic pulse is subsequently converted into an electrical second signal. This can be effected, for example, by means of the same ultrasonic sensor which has transmitted the ultrasonic pulse. The second electrical signal is subsequently filtered using a matched filter. In other words, a filter which is adjusted to the frequency of the second electrical signal is used. In doing so, interfering signals and other components which are not associated with the emitted ultrasonic pulse are eliminated. In a next step, the first electrical signal is correlated with the second electrical signal and the result of the correlation, which may comprise for example a correlation coefficient, is compared with a predefined reference. From the result of the comparison, the length of the ultrasonic echo is subsequently determined. By using the correlation, the result or the obtained length is largely independent of the surface condition of the reflecting environment object. In other words, rugged signals will also produce such echoes which have a high correlation with the transmitted signal. In this way, the length determination of the ultrasonic echo becomes more robust and more reliable.

The subclaims show preferred developments of the invention.

The ultrasonic pulse can comprise a fixed or a time-variable frequency. A computationally simple implementation can take place with a fixed frequency, so that the hardware required for implementation can be of robust and cost-effective design. In principle, a use of so-called chirps is also possible, while the required filters are thereby to be of somewhat more costly design.

Preferably, the method according to the invention can be developed by emitting a second ultrasonic pulse of a predefined frequency which is based on a third electrical signal, it also being possible for the fundamental frequency of the third signal to be fixed or time-variable. The ultrasonic echo received on the basis of the second ultrasonic pulse is also converted into a fourth electrical signal. This signal too is subsequently filtered using a matched filter. In particular, the filter can be matched to the fundamental frequency of the third electrical signal.

Typically, ultrasonic measuring systems addressed according to the invention are characterised by a plurality of ultrasonic sensors and at least one central evaluation unit. Accordingly, a time signal of the received ultrasonic echo and also a correlation coefficient can be transmitted from an ultrasonic sensor to the central electronic control device. In other words, an acoustic conversion and also a correlation between measuring signal and received signal can take place within the ultrasonic sensor (also referred to as a "remote unit" or "intelligent ultrasonic sensor"). The central electronic control device can subsequently determine the length of the received ultrasonic echoes from the correlation coefficient and other information, from which the quality of the received ultrasonic echo is obtained. Additionally, the determination of the distance of the reflecting surface from the ultrasonic sensor can be determined.

The result of the correlation can comprise in particular a correlation coefficient or be represented by a correlation coefficient. The dependence, realised according to the invention, of the correlation coefficient on the length of the received echo compared with the length of the emitted signal thus enables a particularly robust and therefore reliable determination of an extent of a surface of the reflecting object.

The filter length used for filtering can be greater than or equal to the temporal length of the first electrical signal. In other words, the pulse response of the filter used can have one, two, three or four times the length of the measuring signal. This ensures that even environment objects having more complex surfaces and in particular considerably different partial surfaces can be reliably detected and classified according to the invention. While the suppressing of interfering signals in the echo requires markedly shorter filter lengths, filter lengths up to five times the transmitted signal or longer can be used to perform a length determination, according to the invention, on the basis of the correlaion coefficient.

The reference can be predefined, for example, in dependence on a frequency and/or a parameter of the first, second or third signal. Thus, the reference should take into account the frequency of the emitted measuring signal and optionally via additional algorithms for determining the echo equality. In this way, the length of the ultrasonic echo is defined via different parameters and determined with the aid of the reference while taking into account the parameters.

According to a second aspe= of the present invention, an ultrasonic sensor for environment detection is proposed. The ultrasonic sensor can also be referred to and embodied as a "remote unit" or as an "intelligent ultrasonic sensor". It comprises an ulirasonic transducer which comprises, for example, a piezo-transducer, by means of which electrical alternating signals can be converted into ultrasonic signals (or vice versa). In addition, it comprises an evaluation uniu., by means of which, for example, a digital filtering of received ultrasonic echoes and/or a correlation of the same with emitted measuring signals can be carried out. Finally, there is also provided a signal output for outputting electrical signals, via which for example time signals and correlation coefficients of performed correlations can be transmitted to a central evaluation unit (e.g. an electronic control device). The ultrasonic transducer is adapted, according to the invention, to convert an ultrasonic pulse based on a first signal into an electrical second signal. The ultrasonic transducer thus receives an ultrasonic signal reflected at an environment object. The evaluation unit is adapted to filter the second (received) electrical signal and correlate it with the first electrical signal (measuring signal). The second signal can be transmitted (for example after a corresponding matched filtering) including a result of the correlation (in the form of a correlation coefficient) via the signal output to an electronic control device. In this way, according to the invention an investigation of the length of an ultrasonic echo can take place, as has been described in detail above in connection with the first-mentioned aspect of the invention. In other words, the ultrasonic sensor according to the invention can be used as a remote unit in connection with a central electronic control device for carrying out the method according to the invention.

According to a third aspect of the present invention, there is proposed an electronic control device which is suitable for investigating an ultrasonic echo. This device comprises a signal input for receiving a correlation coefficient and in particular also a time signal from an ultrasonic sensor which is configured, for example, according to the second-mentioned aspect of the invention. An evaluation unit is adapted to determine a length of an ultrasonic pulse received by means of the ultrasonic sensor, with the aid of the received correlation coefficient and a predefined reference. In this regard, The principles and dependences mentioned in connection with the method according to the invention are utilised accordingly, so that reference is made to the above statements to avoid repetition.

According to a fourth aspe= of the present invention, there is proposed an ultrasonic measuring system having an electronic control device according to the third-mentioned aspect of the invention and at least one, preferably a plurality of, ultrasonic sensors according to the second-mentioned aspect of the invention. The ultrasonic measuring system can be adapted, for example, to be arranged and operated on a means of transportation or in a means of transportation. A correspondingly equipped vehicle is also proposed, in which, both for the ultrasonic measuring system and for the entire vehicle configured according to the invention, the features, combinations of features and the advantages resulting therefrom, are obtained in accordance with the above statements.

According to the invention, use is made of the mathematical relationship between the level of the correlation coefficient and the length of the received echo, according to which the correlation coefficient becomes greater with increasing length of the echo. Since the level of the correlation coefficient is usually also dependent on other characteristic quantities (e.g. the echo quality or the presence of any interfering signals), corresponding parameters or characteristic quantities are to be determined separately and taken into account in the evaluation according to the invention. In particular when using time-variable fundamental frequencies of the measuring signals used, also a frequency dependence is to be taken into account or the exclusive correlation of related measuring signal/echo signal combinations is to be ensured.

Brief description of the drawings

Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawings: Figure 1 is a schematic overview of components of an exemplary embodiment of an ultrasonic measuring system according to the invention; Figure 2 is a schematic overview of components of an exemplary embodiment of a means of transportation according to the invention; Figure 3 shows time diagrams illustrating problems of ultrasonic measuring systems operating according to the prior art; Figure 4 shows time signals illustrating the advantages of an ultrasonic measuring system operating according to the present invention; Figure 5 is a simulated, a mathematically created and a metrologically determined illustration of a relationship between the level of the correlation coefficient and the length of the Figure 6 ultrasonic echo with a constant length of the matched filter used; shows time diagrams illustrating disadvantages with the investigation of environment signals having complex surface structures by a method according to the prior art; and Figure 7 is a flow diagram illustrating steps of an exemplary embodiment of a method according to the invention.

Embodiments of the invention Figure 1 shows an ultrasonic measuring system 9 which comprises an ultrasonic sensor 1 and an electronic control device 4 as central evaluation unit. Via a piezo-membrane 2 of an ultrasonic sensor 1, an ultrasonic pulse 6 based on an electrical measuring signal is emitted in the direction of a wall 11 as environment object. The ultrasonic echo 6' reflected from the wall 11 is converted by the same piezomembrane 2 into a second electrical signal and filtered in an evaluation unit 3 of the ultrasonic sensor 1 by means of a matched filter and correlated with the electrical measuring signal. Via a signal output 5 of the ultrasonic sensor 1 and a signal input 7 of the electronic control device 4, the time signal of the received ultrasonic echo 6' and the result of the correlation are provided to a programmable processor 8 of the electronic control device 4. Within the programmable processor 8, the ultrasonic echo 6', the correlation coefficient and additional information describing the quality of the ultrasonic echo are investigated in order to derermine the length of the ultrasonic signal.

Figure 2 shows a passenger car 10 as means of transportation, in which an exemplary embodiment of an ultrasonic measuring system 9 according to the invention, shown in Figure 1, is integrated. The ultrasonic sensor 1 is integrated in the front bumper of the passenger car 10, while a head unit as electronic control device 4 undertakes the central evaluation of the correlation.

Figure 3 shows time diagrams which illustrate the detection of echoes in received environment signals according to the prior art. In these diagrams, x(t) denotes the time signal of received echoes. In three time regions wl, w2, w3, the time signal x(t) exceeds the threshold function TH predefined for echo detection. In a binary evaluation of the exceeding of the threshold function, there results the signal xB(t) which has in the time regions wl, w2, w3 corresponding high levels. To distinguish between short-time interference and actual echoes, the prior art proposes a filtering, the output signal of which is described by the signal xF(t). Owing to its minimal duration of exceeding the threshold function for detecting a proper echo, the mean peak or high level in The time region w2 has been filtered out. If this peak is based on an environment object, this environment object is invisible to the system of the prior art. Accordingly, its users or its downstream signal processing have information deficits or incorrect information.

Figure 4 shows time profiles of an ultrasonic measuring system, configured according to the invention, on the basis of the time signal already presented in Figure 3. The time signal is processed by a digital signal processing unit which outputs a cross-correlation (Xcorr) between the received ultrasonic signal x(t) and the output signal of the matched filter, and also a correlation coefficient (also "R-value") which is defined as a normalised cross-correlation function. The echoes are detected by using different threshold functions (TH1, TH2, TH3), with which the cross-correlation function Xcorr(t) and the correlation coefficient R(t) are compared. Here, the propagation time of the ultrasonic echo corresponds to the position of its peak in the cross-correlation function and in the correlation coefficient. A measure of the echo quality is the amplitude of the correlation coefficient R(t), the correlation coefficient R(t) depending on different signal parameters. If the correlation coefficient R(t) is high, the echo is assumed to be "of high quality", since it is similar to the expected "perfect echo". In Figure 4 the peaks of the cross-correlation function Xcorr(t) and also of the correlation coefficient R(t) are denoted by Tl, T2 and T3. While the correlation coefficient R(t) exceeds the threshold function TH2 at the instants Ti and T3, the third threshold function TH3 is only narrowly exceeded at the instant T2. This is because the temporal extent of the ultrasonic echo at the instant T2 is only very small, while the temporal extents of the ultrasonic echoes at the instants Ti and T3 are subsJantially of equal length. An influence of the amplitude of the time signal x(t) is, however, not detectable in The correlation coefficient R(t). The diagram shown underlines the suitability of the correlation coefficient R(t) for determining the length of an ultrasonic echo signal.

Figure 5 shows in sub-diagram a) a calculated (curve 51) and a simulated (curve 52) for the dependence of the amplitude of the correlation coefficient R(t) against the echo length with a fixed length of the matched filter used of 320 ps. In sub-diagram b) the measured dependence of the amplitude of the correlation coefficient R(t) is plotted as a function of the echo lengkh with a fixed frequency (48 kHz) and length (320 us) of the matched filter used, against the pulse duration in microseconds. For both sub-diagrams a) and b) there result marked dependences of the amplitude of the correlation coefficient R(t) up to echo lengths of approximately 270 and 300 us, respectively. This dependence can be used according to the invention for a detection of a length of a received echo.

Figure 6 shows time diagrams which have been produced during an echo detection using a pulse width discriminator known according to the prior art. The environment object reflecting the received ultrasonic echo x(t) has surface regions which are offset from one another, and are at different distances from the ultrasonic measuring system used, such that four signal regions A1, A2, A3, AL exceed a predefined threshold function TH only over comparatively short durations L1, L2, UF, L4. The resulting binary signal x3(t) thus has four very short high-level regions which lie below the predefined minimum length for detecting an echo from the environment. Accordingly, the filtered binary signal xF(t) does not contain a single echo signal, and this may occasionally have disastrous consequences in the case of collision monitoring.

Figure 7 shows a flow diagram illustrating steps of an exemplary embodiment of a method according to the invention for investigating an ultrasonic echo. In step 100 an ultrasonic pulse based on a first electrical signal is transmitted into the environment of an ultrasonic measuring system used. This may take place, for example, by using a piezo-membrane. In step 200 an ultrasonic echo is received by means of an ultrasonic transducer, for which there is used the same ultrasonic transducer by means of which the ultrasonic pulse in step 100 has been emitted. In step 300 the received ultrasonic echo is converted into an electrical second signal. In step 400 the converted second electrical signal is filtered using a filter which is matched to the second electrical signal. In particular, the fundamental frequency of the second filter and also any time-variable profile of the fundamental frequency and also of the harmonic frequencies are taken into account here by the filter. In step 500 the first signal and the second signal are correlated with one another and in step 600 the time signal of the second electrical signal and the correlation coefficient are transmitted from the ultrasonic sensor used to a central electronic control device which has further ultrasonic sensors according to the invention. In step 700 the correlation coefficient is compared with a predefined reference and from this in step 800 a length of the ultrasonic echo is determined. For this purpose, the reference has a dependence on the frequency of the second signal and also on the quality ("relatedness") of the second signal from the firs: signal. In step 900 the spatial extent of the environment object reflecting the ultrasonic pulse is determined from the length of the ultrasonic echo. In step 1000 a further ultrasonic pulse is emitted, which is based on a third electrical signal of a predefined other frequency Than the first electrical signal. In step 1100 an ultrasonic echo based on the second ultrasonic pulse is converted into a fourth electric signal and in step 1200 filtered using a filter matched to the predefined frequency of the third and fourth signal. According to the invention, the method continues in the manner as described in connection with the first electrical signal and the second electrical signal in connection with the steps 500 to 900.

The present invention presents a technique for matched filtering and correlation coefficient evaluation which can be used, for example, for Side View Assist (SVA) systems (blind-spot assistants) operating with a fixed fundamental frequency. These systems usually operate with ultrasonic pulses which lie in the region around 50 kHz or between 48 kHz and 52 kHz. According to the invention, short echoes are suppressed, the length of the echoes measured and environment objects categorised with respect to their surface condition, for example, as to whether they have a single reflecting surface or a plurality of reflecting partial surfaces. For this purpose, cross-correlations using matched-filtered ultrasonic signals are carried out and the above-mentioned dependence between the echo length and the correlation coefficient or its amplitude is utilised. Provided that the length of the echo is less than or equal to the length of the matched filter used, there results for the amplitude Ramps of the correlation coefficient the following relationship: Rampl -Al(Leclac const. ) Al I-111F Provided that the echo length is greater than the length of the matched filter used, there results a correlation coefficient of the amplitude Ramp' of approximately 1.

The matched filter can be adapted in such a way that the frequency of a transmitted ultrasonic pulse and its duration require for the filter used the same frequency and a length which is greater than or equal to the duration of the ultrasonic pulse. If echoes shorter than a predefined length are to be suppressed, echoes with a correlation coefficient of an amplitude less than Rmim are rejected (not treated as actual environment echoes), in which case the following applies: + const. -VL m

If an echo with an amplitude greater than Rmm has been detected, the effective length of the echo Lecho can be determined according to the following formula: 2 const.

Lech()airpl While simple objects have a simple, reflecting surface and a clear single echo, complex environment objects have a large number of reflecting partial surfaces. The echoes coming from a complex obje= usually contain overlapping echoes which cancel out or intensify one another. The cancelling out may result, according to the prior art, in a plurality of single (smaller) echoes being detected. Occasionally, such echoes are also partially or completely suppressed. The proposed invention can, however, be used to measure how much longer the received echo is, compared with the emitted ultrasonic pulse. For this purpose, the length of the matched filter should be markedly longer than the length of the emitted pulse: LMF 2 D If now the length of the echo is less than or equal to the duration of the emitted ultrasonic pulse, the object is a simple object. If the echo duration is greater than the duration of the emitted ultrasonic pulse, the echo was reflected from a complex object, so that more than one reflection was received. If the length of the echo is much greater than the length of The emitted ultrasonic pulse, the echo was produced by a very complex object with a plurality of reflecting surfaces. It is assumed here that a long echo comes from a complex object, not, however, from two simple objects with the same distance but different location. This assumption is appropriate in particular for the use in side view assist systems.

Claims

Claims 1. Method for investigating an ultrasonic echo comprising the steps: - transmitting (100) an ultrasonic pulse based on a first signal, - converting (300) an ultrasonic echo (6') into an electrical second signal, - filtering (400) the second signal using a filter which is matched to the second signal, - correlating (500) the first signal and the second signal, - comparing (700) a result of the correlation with a predefined reference, and from this - determining (800) a length of the ultrasonic echo.
2. Method according to Claim 1, wherein the ultrasonic pulse (6) has a first fixed frequency.
3. Method according to Claim 1 or 2, further comprising emitting (1000) a second ultrasonic pulse (6) of a predefined frequency based on a third signal, - converting (1100) an ultrasonic echo (6') into a fourth electrical signal, and - filtering (1200) the fourth signal using a filter which is matched to the predefined frequency of the fourth signal.
4. Method according to one of the preceding claims, further comprising the step - receiving (200) the ultrasonic echo (6') by means of an ultrasonic transducer (2).
5. Method according to Claim 4, further comprising - transmitting (600) a time signal and a correlation coefficient from an ultrasonic sensor (1) to a central electronic control device (4).
6. Method according to one of the preceding claims, wherein the result of the correlation comprises a correlation coefficient.
7. Method according to one of the preceding claims, further comprising the step - determining (900) a spatial extent of an environment object (11) from the length of the ultrasonic echo (6').
8. Method according to one of the preceding claims, wherein - the filtering (400) takes place by means of a filter length greater than or equal to, in particular two, three or four times, the temporal length of the first signal.
9. Method according to one of the preceding claims, wherein the reference is predefined in dependence on a frequency and/or a parameter of the second or third signal.
10. Ultrasonic sensor for environment detection comprising - an ultrasonic transducer (2), - an evaluation unit (3) and - a signal output (5), wherein - the ultrasonic transducer (2) is adapted to convert an ultrasonic pulse (6) based on a first signal into an electrical second signal, - the evaluation unit (2) is adapted - to filter the second signal, - to correlate the first signal and the filtered second signal with one another, and - to transmit the second signal, preferably filtered, and also a result of the correlation, in particular a determined correlation coefficient, via the signal output (5) to an electronic control device (4).
11. Electronic control device (4), comprising: - a signal input (7) for receiving a correlation coefficient from an ultrasonic sensor (1), in particular according to Claim 10, and - an evaluation unit (3) which is adapted - to determine a length of an ultrasonic pulse (6) received by means of the ultrasonic sensor (1), with the aid of the correlation coefficient and a predefined reference.
12. Ultrasonic measuring system, comprising: - an electronic control device (4) according to Claim 11 and - at least one ultrasonic sensor (1) according to Claim 10.
13. Vehicle comprising an ultrasonic measuring system (9) according to Claim 12.
14. A method for investigating an ultrasonic echo substantially as herein described with reference to, or as shown in, the accompanying Figures.
15. An ultrasonic sensor for environment detection substantially as herein described with reference to, or as shown in, the accompanying Figures.
16. An electronic control device substantially as herein described with reference to, or as shown in, the accompanying Figures.
17. An ultrasonic measuring system substantially as herein described with reference to, or as shown in, the accompanying Figures.
18. A vehicle comprising an ultrasonic measuring system substantially as herein described with reference to, or as shown in, the accompanying Figures.