GB2560113A

GB2560113A - Method and measuring device for detecting at least one object with the aid of ultrasonic signals reflected at this object

Info

Publication number: GB2560113A
Application number: GB1803149.2A
Authority: GB
Inventors: Schumann Michael; Schmid Dirk; Roka Andras
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2014-08-13
Filing date: 2015-08-10
Publication date: 2018-08-29
Anticipated expiration: 2035-08-10
Also published as: DE102014216015A1; GB2560113B; GB201514086D0; GB2530169B; FR3025321A1; GB2530169A; FR3025321B1; GB201803149D0

Abstract

Method for detecting at least one object with the aid of ultrasonic signals reflected at this object, in which, echo signals which arise from reflection of ultrasonic signals emitted by an ultrasonic sensor are received. From each received echo signal, a corresponding received signal e(t) is generated and by means of each received signal e(t) a corresponding measuring signal s(t) is generated. Furthermore, each measuring signal is correlated with a corresponding response signal F(τ) of a correlation filter to determine a correlation signal X(t). Further, for each measuring signal s(t), a corresponding correlation factor R(t) is determined in dependence on the corresponding correlation signal X(t), a positive definite norm Ns of the corresponding measuring signal s(t) and a positive definite norm NF of the corresponding response signal F(τ) and is evaluated in order to detect the at least one object. Each emitted signal is also correlated with the correlation filter and a corresponding harmonic signal h(t) may be used in place of the received signal e(t).

Description

(56) Documents Cited:

WO 2010/013792 A1 US 20090145232 A1 US 20040179428 A1

WO 1994/011753 A US 20080247275 A1 (62) Divided from Application No

1514086.6 under section 15(9) of the Patents Act 1977 (58) Field of Search:

INT CL G01S Other: WPI, EPODOC (71) Applicant(s):

Robert Bosch GmbH

Postfach 30 02 20, 70442 Stuttgart, Germany (72) Inventor(s):

Michael Schumann Dirk Schmid Andras Roka (74) Agent and/or Address for Service:

A.A. Thornton & CO.

Old Bailey, London, EC4M 7NG, United Kingdom (54) Title of the Invention: Method and measuring device for detecting at least one object with the aid of ultrasonic signals reflected at this object

Abstract Title: Object detection using ultrasonic signals and reflected echoes (57) Method for detecting at least one object with the aid of ultrasonic signals reflected at this object, in which, echo signals which arise from reflection of ultrasonic signals emitted by an ultrasonic sensor are received. From each received echo signal, a corresponding received signal e(t) is generated and by means of each received signal e(t) a corresponding measuring signal s(t) is generated. Furthermore, each measuring signal is correlated with a corresponding response signal F(t) of a correlation filter to determine a correlation signal X(t). Further, for each measuring signal s(t), a corresponding correlation factor R(t) is determined in dependence on the corresponding correlation signal X(t), a positive definite norm Ns of the corresponding measuring signal s(t) and a positive definite norm NF of the corresponding response signal F(t) and is evaluated in order to detect the at least one object. Each emitted signal is also correlated with the correlation filter and a corresponding harmonic signal h(t) may be used in place of the received signal e(t).

This print incorporates corrections made under Section 117(1) of the Patents Act 1977.

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Description

Title

Method and measuring device for detecting at least one object with the aid of ultrasonic signals reflected at this obj ect

The present invention relates to a method and a measuring device for detecting at least one object with the aid of ultrasonic signals reflected at this object.

Prior art

In the field of environment detection by means of ultrasound there is known, for example from the document DE 10 2011 075 484 Al, an ultrasonic measuring system for detecting an obstacle, the ultrasonic measuring system comprising an ultrasonic sensor having a resonant transducer element for emitting ultrasonic pulses and for generating received signals comprising the emitted ultrasonic pulses and ultrasonic pulses reflected from the object. The emitted ultrasonic pulses and ultrasonic pulses reflected from the object are referred to echo pulses. The resonant transducer element further generates a decay signal having its resonant frequency after emitting each ultrasonic pulse. Also, the ultrasonic measuring system comprises an evaluation unit having a control device which is designed to activate the resonant transducer element to emit each ultrasonic pulse by means of a transmitted signal generated by the control device. Furthermore, the control unit of the ultrasonic measuring system is designed to generate each transmitted signal by means of a modulation signal in the form of a frequency-modulated transmitted signal in such a way that the signature of each emitted ultrasonic pulse differs from that of the corresponding decay signal. The evaluation unit has at least one correlation filter, the at least one correlation filter being designed to correlate each signal generated by the resonant transducer with the corresponding transmitted signal and to generate a correlation signal. The evaluation unit is furthermore designed to recognise the presence of an echo pulse originating from reflection at the obstacle when the correlation signal has a maximum. The same document further describes a corresponding method for detecting an obstacle by means of ultrasound.

Disclosure of the invention

According to the invention, there is provided a method for detecting at least one object with the aid of ultrasonic signals reflected at this object, in which, by means of an ultrasonic sensor, echo signals which arise from reflection of ultrasonic signals emitted by means of the ultrasonic sensor are received. From each received echo signal, a corresponding received signal is generated by means of the ultrasonic sensor and by means of each received signal a corresponding measuring signal s(t) as a function of a time t is generated. Furthermore, each measuring signal s(t), in order to generate a corresponding correlation signal X(t), is correlated with a corresponding response signal F(t), dependent on a variable τ, of a correlation filter. Also, for each measuring signal s(t), a corresponding correlation factor R(t) as a function of the time t is determined in dependence on the corresponding correlation signal X(t), a positive definite norm Ns of the corresponding measuring signal s(t) and a positive definite norm NF of the corresponding response signal F(t) and is evaluated in order to detect the at least one object.

According to the invention, there is furthermore provided a measuring device for detecting at least one object by means of ultrasonic signals reflected at this object, wherein the measuring device comprises an ultrasonic sensor which is configured to emit ultrasonic signals, to receive echo signals which arise from reflection of the emitted ultrasonic signals, and to generate from each received echo signal a corresponding received signal. The measuring device is configured to generate by means of each received signal a measuring signal s(t) as a function of a time t and to correlate this measuring signal, in order to generate a corresponding correlation signal X(t), with a corresponding response signal F(t), dependent on a variable τ, of a correlation filter arranged in the measuring device. Furthermore, the measuring device is configured to determine, for each measuring signal s(t), a corresponding correlation factor R(t) as a function of the time t in dependence on the corresponding correlation signal X(t), a positive definite norm Ns of the corresponding measuring signal s(t) and a positive definite norm NF of the corresponding response signal F(t), and to evaluate these correlation factors in order to detect the at least one obj ect.

The subclaims show preferred developments of the invention.

Preferably, each correlation factor R(t) is determined according to the relation

J s(t + τ)·Ρ*(τ)ί/τ

W) = ^(0

Ns-NF f s²(t +τ)άτ · J £ F²(r)dT where T is a length of the correlation filter and F*(t) is the corresponding complex conjugate response signal of the correlation filter.

In the invention, for each measuring signal s(t) generated by means of the corresponding received signal, and consequently also for the corresponding echo signal received by means of the ultrasonic sensor, a correlation factor R(t) is calculated.

Preferably, each measuring signal s(t) accords with the corresponding received signal e(t). In this case, for detecting the at least one object, an amplitude of each correlation factor R(t) is compared with a predefined limit value. Further preferably, on the presence of each received signal e(t), the correlation factor R(t) of which has a maximum which exceeds the predefined limit value, it is recognised that the received signal e(t) comes from an echo signal which has arisen from reflection at the at least one obj ect.

Preferably, the correlation signal X(t) according to the invention is determined according to the relation

X(t) = J s(t + τ) and evaluated for detection of the at least one object.

In the invention, for each measuring signal s (t) generated by means of the corresponding received signal, and consequently also for the corresponding echo signal received by means of the ultrasonic sensor, a correlation signal X(t) can be calculated.

Further preferably, each emitted ultrasonic signal is an ultrasonic pulse.

Preferably, frequency-modulated ultrasonic signals, which are also referred to a chirps, are emitted by means of an ultrasonic sensor according to the invention. For example, chirps can be emitted, the frequency of which changes linearly during the period of their emission, which is typically about 1.0 ms. For example, the frequency of such chirps is 54 kHz at the beginning of their emission and 45 kHz at the end of their emission.

Preferably, an ultrasonic sensor according to the invention comprises a digital signal processing in the form of a correlation module configured in particular as a crosscorrelation module. By means of the correlation module, received ultrasonic signals are correlated with the response signal F(t) of a correlation filter configured in particular as a cross-correlation filter which is signalmatched for the reception of an echo signal which has optimally arisen from reflection of an emitted ultrasonic signal at the at least one object.

Preferably, the correlation module according to the invention calculates a correlation signal X(t) in the form of a cross-correlation signal and/or a correlation factor R(t) in each case according to a corresponding one of the two relations given above. Further preferably, both the correlation signal X(t) and the correlation factor R(t) are used in an echo signal detection for detecting the at least one object. Account is to be taken here of the fact that the value of a correlation factor R(t) is independent of the amplitude of the received signal generated directly from the corresponding echo signal and at the same time represents a measure of the similarity or of the degree of correlation between the received echo signal and the corresponding response signal F(t) of the correlation filter .

Preferably, the correlation factor R(t) is scaled in such a way that its value lies between 0 and 1, that is to say that the correlation factor R(t) satisfies the inequality 0 < R(t) < 1.

In this connection, this means that if at an instant tO the value of the correlation factor R(t) is for example equal to 1, at the instant tO an optimal echo signal, that is to say an echo signal completely correlated with the correlation filter, was received. Here the relation R(t0) = 1 holds true. If for example the relation R(t0) = 0.9 holds true, this means that at the instant tO a quasi-optimal echo signal, that is to say an echo signal almost completely correlated with the correlation filter, was received. If for example the relation R(t0) = 0.1 holds true, this means that at the instant tO an echo signal which is not comparable with an optimal echo signal, that is to say an echo signal not correlated with the correlation filter, was received.

Preferably, for each received echo signal, both the corresponding correlation signal X(t) and the corresponding correlation factor R(t) are calculated by means of the ultrasonic sensor according to the invention. Further preferably, an algorithm is preferably used for the echo signal detection, in which algorithm, for each received echo signal, the corresponding correlation signal X(t) and thereby the corresponding echo signal amplitude, as well as the corresponding correlation factor R(t) and thereby the corresponding echo signal quality, are taken into account.

A major advantage in using an ultrasonic sensor according to the invention for emitting ultrasonic signals in particular in the form of chirps is that such an ultrasonic sensor has a relatively good robustness against noise and interference. This is very advantageous since, in the above-mentioned correlation calculation, noise signals coming from noise sources which have a frequency lying in a frequency spectrum not overlapping with the frequency spectrum of the correlation filter are suppressed.

A difficulty which arises in using an ultrasonic sensor according to the invention is that the functionality of such an ultrasonic sensor may be impaired not only by a reception of noise signals. When an ultrasonic signal is emitted by means of the ultrasonic sensor according to the invention, this ultrasonic sensor also receives echo signals which arise from reflection of the emitted ultrasonic signal at many small particles of a background surface, which is for example a ground surface. This mixing of echo signals with low amplitudes AB which arise from reflection at the background surface is also referred to as a background echo signal. The size of a surrounding area of the ultrasonic sensor from which background echo signals originate depends on the positioning of the ultrasonic sensor with respect to the background surface, such as for example on a positioning height and on a positioning angle of the ultrasonic sensor with respect to the background surface. The surrounding area mentioned extends at a distance from the ultrasonic sensor or in a range of the ultrasonic sensor which lies generally between 0.5 m and 3.5 m.

The occurrence of background echo signals is, for a range lying between 0.5 m and 3.5 m, the most important factor which limits the quality of the echo signal detection carried out by means of such an ultrasonic sensor for detecting an object situated in this range, since the ultrasonic sensor receives a mixture of echo signals which comprises both background echo signals and echo signals originating from reflection at the at least one object, which are also referred to as object echo signals. In this regard, for each received echo signal, the corresponding correlation signal X(t) and the corresponding correlation factor R(t) are calculated. Account is to be taken here of the fact that, both for a received echo signal which is a background echo signal and for a received echo signal which is an object echo signal, the corresponding correlation factor R(t) can often have a maximum with a value lying close to 1. The reason for this is that the correlation factor R(t) is independent of the amplitude of a received echo signal and represents a measure of the similarity between the received echo signal and a corresponding response signal F(t) of the correlation filter.

Consequently, for the surrounding area in which background echo signals may arise, a differentiation between background echo signals and object echo signals by an evaluation of the correlation factor R(t) calculated in each case for the received echo signals is difficult to carry out. Since the amplitude AB of background echo signals is generally lower than the amplitude AO of the object echo signals, the differentiation mentioned can preferably still be carried out by an evaluation of the corresponding correlation signal X(t).

A further difficulty arising in the use of an ultrasonic sensor according to the invention is that the functionality of such an ultrasonic sensor may also be impaired by receiving interfering signals. It may happen that the interfering signals have a frequency which lies in a frequency spectrum which is similar to the frequency spectrum of the correlation filter. In such a case, an ultrasonic sensor according to the invention receives an interfering signal which is similar to the corresponding response signal F(t) of the correlation filter, that is to say that the received interfering signal is correlated with the correlation filter. Owing to the reception of such interfering signals, the amplitude of the correlation factor R(t) calculated in each case for such interfering signals has a value lying in an increased value range, which may often lie close to 1. As a result, the error rate in an echo signal detection as described above for detecting the at least one object, that is to say the error rate in an object detection according to the invention, is increased, whereby also the quality of the functionality of an ultrasonic sensor according to the invention is reduced.

Often the above-mentioned interfering signals have an amplitude AS which is much less than an amplitude AE of object echo signals and therefore satisfies the inequality AS << AO. This applies mostly to a surrounding area which extends from the ultrasonic sensor up to a distance of 3 m, since for this surrounding area echo signals with a large amplitude AO are to be expected. Owing to the smaller amplitude AS of the interfering signal, a differentiation between interfering signals and object echo signals can preferably still be carried out by an evaluation of the corresponding correlation signal X(t). Since the correlation factor R(t) is independent of the amplitude of a received signal and represents a measure of the similarity between the received signal and a corresponding response signal F(t) of the correlation filter, the differentiation between interfering signals and object echo signals is, however, difficult to carry out by means of the correlation factor R(t) calculated in each case for the received echo signals.

Preferably, in a case in which interfering signals are received which are correlated with the correlation filter used, a simple solution is proposed, in which the correlation filter used is replaced with a further correlation filter which has a narrower frequency spectrum. Here, by means of an ultrasonic sensor according to the invention, ultrasonic signals, in particular in the form of chirps are emitted, which have a frequency lying in a frequency spectrum which is similar to the narrower frequency spectrum of the further correlation filter. In this case, there exists a high probability that the narrower frequency spectrum of the further correlation filter is not comparable with the frequency spectrum of the received interfering signals. However, there are cases in which an ultrasonic sensor according to the invention with a highly specific transfer function is preferably used and in which in particular also the correlation filter used cannot be exchanged, so that in such cases the solution just mentioned is not applicable. This is true in particular of a surrounding area situated very close around an ultrasonic sensor according to the invention, which extends from the ultrasonic sensor up to a distance of about 60 cm, and for which what is important above all is the differentiation between the object echo signals and signals originating from low-energy sources. Examples of such signals originating from low-energy sources are noise signals and echo signals which arise from weak reflection at number plates or other parts of a vehicle with an ultrasonic sensor according to the invention. A correlation factor R(t) calculated in each case for these signals originating from low-energy sources has generally an amplitude with a high value, with the result that the above-described object detection is impaired.

In a preferred embodiment of the invention, each measuring signal s(t) is the corresponding received signal e(t). Preferably, each emitted ultrasonic signal comprises a first ultrasonic signal part which is not correlated with the correlation filter and a second ultrasonic signal part which is correlated with the correlation filter.

Preferably, the first ultrasonic signal part of each ultrasonic signal to be emitted is emitted before the or after the corresponding second ultrasonic signal part. Preferably, each emitted ultrasonic signal comprises a first ultrasonic signal part which is not correlated with the correlation filter, a second ultrasonic signal part which is correlated with the correlation filter, and a third ultrasonic signal part which is not correlated with the correlation filter. Preferably, the second ultrasonic signal part of each ultrasonic signal to be emitted is emitted after the corresponding first ultrasonic signal part and before the corresponding third ultrasonic signal part.

Preferably, on the presence of each received signal e(t), the correlation factor R(t) of which falls short of a first limit value for a first time period and has a maximum which lies temporally immediately after the first time period has elapsed or before a beginning of the first time period and exceeds a second limit value greater than the first limit value, it is recognised that the corresponding received signal e(t) comes from an echo signal which has arisen from reflection at the at least one object. Further preferably, on the presence of each received signal e(t), the correlation factor R(t) of which falls short of a first limit value for a first time period and also for a second time period lying temporally after the first time period has elapsed, and has a maximum which lies temporally immediately after the first time period has elapsed and before a beginning of the second time period and exceeds a second limit value greater than the first limit value, it is recognised that the corresponding received signal e(t) comes from an echo signal which has arisen from reflection at the at least one object.

Preferably, a length of the first time period is determined in dependence on a signal duration of the first ultrasonic signal part of each emitted ultrasonic signal and/or a length of the second time period is determined in dependence on a signal duration of the third ultrasonic signal part of each ultrasonic signal.

If an ultrasonic signal is emitted which comprises a first ultrasonic signal part which is not correlated with the correlation filter and a second ultrasonic signal part which is correlated with the correlation filter, there results by reflection of this ultrasonic signal an echo signal which comprises, corresponding to the emitted ultrasonic signal, a first echo signal part which is not correlated with the correlation filter and a second echo signal part which is correlated with the correlation filter .

If an object echo signal is received by means of the ultrasonic sensor, the first object echo signal part is not correlated with the correlation filter and the second object echo signal part is correlated with the correlation filter. Since the first object echo signal part is correlated with the correlation filter, the correlation factor R(t), which is calculated for the corresponding measuring signal s(t), which accords with the received signal e(t) generated directly from the object echo signal, has a region, also referred to as a gap, which corresponds to a reception of the first object echo signal part and in which an amplitude of the corresponding correlation factor R(t) has a relatively low first value. Since the second object echo signal part is correlated with the correlation filter, the corresponding correlation factor R(t) has a region, also referred to as a peak, which corresponds to a reception of the second object echo signal part and in which the corresponding correlation factor R(t) has a maximum which has a second value lying markedly higher than the first value. The second value may lie close to 1, depending on the quality of the corresponding object echo signal. Account is to be taken here of the fact that generally the amplitude AO of object echo signals is markedly higher than the amplitude AB of background echo signals. Since the first object echo signal part is not correlated with the correlation filter, the amplitude of a correlation signal X(t), which occurs in a region, corresponding to the reception of the first object echo signal part, of this correlation signal X(t) calculated for the corresponding measuring signal s(t), is low. This low amplitude of the correlation signal X(t) is suppressed in the expression of the corresponding correlation factor R(t) by the high value of the positive norm Ns of the corresponding measuring signal s(t). That is the reason for which such a correlation factor R(t) has, in its region corresponding to the reception of the first object echo signal part, an amplitude which assumes a first value which is markedly lower than a second value assumed by the maximum which the correlation factor R(t) has in its region corresponding to the reception of the second object echo signal part. In this case, each correlation factor R(t) has a gap and a peak, the gap lying in front of or behind the peak.

In a case in which the emitted ultrasonic signal furthermore comprises a third ultrasonic signal part which is not correlated with the correlation filter, and in which the second ultrasonic signal part is emitted after the first ultrasonic signal part and before the third ultrasonic signal part, each corresponding correlation factor R(t) has two gaps and one peak, one gap lying in front of the peak and another gap lying behind the peak.

Consequently, according to the invention, an ultrasonic signal-emitting method and an echo signal-detecting algorithm are provided, by which object echo signals and background echo signals can be differentiated from one another, by an evaluation of the correlation factor R(t) calculated in each case for these signals, even when an amplitude, occurring on an emission of ultrasonic signals correlated with the correlation filter, of a correlation factor R(t) calculated in each case for the background echo signals arising during this and of a correlation factor R(t) calculated in each case for the object echo signals arising during this, assume in each case such a high value that no differentiation between these two amplitudes can be carried out.

In a particular embodiment of the invention, each emitted ultrasonic signal is correlated with the correlation filter. In this case, for each received signal a corresponding further signal h(t) as a function of the time t, which signal is in particular a corresponding harmonic signal, is used. Furthermore, each further signal h(t) is not correlated with the correlation filter and has an amplitude AAh which lies in an order of magnitude of an amplitude AAS of each received signal which comes from a corresponding echo signal of the received echo signals which has not arisen from reflection at the at least one object and in particular is an interfering signal. Preferably, each received signal e(t) is mixed with the corresponding further signal h(t) in order to generate a corresponding mixed signal s(t). Here, each measuring signal s(t) is the mixed signal s(t) generated by means of the corresponding received signal e(t). Further preferably, each measuring signal s(t) is the corresponding received signal e(t). Here, the correlation factor R(t) to be determined for each received signal e(t) is determined according to the changed relation x(0

|θ e(t +τ)· F*(τ)άτ

ο ο where Ne is a positive definite norm of the corresponding received signal e(t) and Nh is a positive definite norm of the further signal h(t).

In the invention, there is/are calculated the norm Ne of the received signal e(t) preferably according to the relation

and/or the norm Ns of the measuring signal s(t) preferably according to the relation 't and/or the norm Nh of the further signal h(t) preferably according to the relation

V o and/or the norm NF of the response signal F(t) of the correlation filter preferably according to the relation

Preferably, on the presence of each mixed signal s (t), the correlation factor R(t) of which has a maximum which exceeds a predefined limit value, it is recognised that the received signal e(t), by means of which the corresponding mixed signal s(t) was generated, comes from an echo signal which has arisen from reflection at the at least one object. Further preferably, on the presence of each received signal e(t), the correlation factor R(t), determined as changed, of which has a maximum which exceeds a predefined limit value, it is recognised that the corresponding received signal e(t) comes from an echo signal which has arisen from reflection at the at least one obj ect.

Through the reception of interfering signals or of echo signals to be suppressed, which have a low amplitude AS and arise from reflection of emitted ultrasonic pulses at objects with known position, such as for example from reflection of emitted ultrasonic pulses at a number plate or bumper of a vehicle with an ultrasonic sensor according to the invention, the overall value level of the amplitude of a correlation coefficient K(t), calculated in each case for the received signals e(t) generated directly from the received echo signals, increases. The effect of the interfering signals or of the echo signals to be suppressed on a correlation coefficient K(t) calculated in each case for the received signals e(t) can be suppressed by a mixing, which can be carried out in particular by means of hardware elements, of a further signal h(t), generated in particular in the form of a respective harmonic signal, with each received signal e(t) generated directly from a received echo signal. In doing so, neither the frequency of the ultrasonic signals to be emitted by means of an ultrasonic sensor according to the invention has to be changed nor does the correlation filter have to be replaced. To this end, for the calculation of each correlation factor K(t), the corresponding measuring signal s(t) generated by the mixing of a further signal h(t) with the corresponding received signal e(t) is used and not the corresponding unchanged received signal e(t). The frequency of the further signal h(t) generated in particular in the form of a harmonic signal should be selected in such a way that this frequency is contained in a frequency spectrum which lies far away from the frequency spectrum of the correlation filter but still in the bandwidth of the corresponding measuring device. The further signal h(t) must have an amplitude AAh which is comparable with the amplitude AAS of a received signal e(t) generated directly from an interfering signal or an echo signal to be suppressed, but is much lower than the minimum amplitude AAO of a received signal e(t) which is generated directly from an object echo signal which is to be reliably detectable by means of the measuring device according to the invention. This means that the amplitude of the further signal h(t) should satisfy in particular the inequality AAh < AAS « AAO.

As a result, the value level of the amplitude of the correlation factor K(t), calculated in each case for the mixed signals s(t) generated by means of interfering signals or echo signal to be suppressed, is limited or reduced. At the same time, the value level of the amplitude of the correlation factor K(t), calculated in each case for the mixed signals s(t) generated by means of object echo signals, remains almost unchanged, so that a detection of echo signals with high amplitude can be optimally carried out. As a result, the error rate of an object detection according to the invention is markedly reduced. Here, each measuring signal s(t) accords with the corresponding mixed signal s(t).

The effect of mixing a further signal h(t) with each received signal e(t) generated by means of the ultrasonic sensor directly from a received echo signal can also be achieved by changing the relation for determining each correlation factor K(t) which is calculated for the corresponding measuring signal s(t) which in this case accords with the received signal e(t) generated directly from the corresponding echo signal. To this end, in the expression of the corresponding correlation factor K(t), the norm Ns of the measuring signal s(t) is replaced with the norm Ne of a corresponding received signal e(t), which norm Ne is increased by Pythagorean addition of the Norm Nh of a further signal h(t) as described above.

In a case in which an interfering signal which is correlated with the correlation filter is received by means of an ultrasonic sensor according to the invention, and in which the corresponding measuring signal s(t) accords with the received signal e(t) generated directly from an interfering signal, the effect of the interfering signal is reflected both in the correlation signal X(t) calculated for this measuring signal s(t) and in the norm Ns of this measuring signal s(t). Here, for the correlation signal X(t) calculated for the received signal e(t) generated directly from the interfering signal, the relation X(t) « Ns*NF holds true, where for each norm Ns and NF a corresponding relation of the three relations given above for the calculation of norms is used. Furthermore, the relation R(t) = X(t)/(Ns*NF « 1 holds true for the corresponding correlation factor R(t). This means that the correlation factor K(t), calculated in each case for received signals e(t) generated directly from interfering signals, assumes a high value which lies close to 1.

In a further case in which an interfering signal which is correlated with the correlation filter is received by means of an ultrasonic sensor according to the invention, and in which the measuring signal s(t) is generated by the mixing of a further signal h(t), generated in particular in the form of a harmonic signal, with the received signal e(t) generated directly from the interfering signal, the correlation signal X(t), calculated for the measuring signal s(t) generated on reception of the interfering signal and containing the further signal h(t), is not influenced by the further signal h(t), since the further signal h(t) is not correlated with the correlation filter. However, the norm Ns of this measuring signal s(t) is increased with respect to the norm of the corresponding received signal e(t) by the norm Nh of the further signal h(t). For clarification, in the following relation and in the following two inequalities, the parameters which are calculated for the measuring signal s(t) generated on reception of the interfering signal and containing the further signal h(t) are supplemented with the index m and the corresponding parameters which are calculated for the received signal e(t) generated directly from the interfering signal are supplemented with the index nm. Here, the correlation signal Xm(t) calculated for this measuring signal s(t) and the correlation signal Xnm(t) calculated for the corresponding received signal e(t) satisfy the relation Xm(t) ~ Xnm(t) and the norm Nsm calculated for this measuring signal s(t) and the norm Nenm calculated for the corresponding received signal e(t) satisfy the inequality Nsm > Nenm. Here, consequently also the correspondingly calculated correlation factors Km(t) and Knm(t) satisfy the inequality Km(t) < Knm(t). This means that the amplitude of the correlation factor Km(t) calculated for the measuring signal s(t) generated on reception of the interfering signal and containing the further signal h(t) is limited to a value which is dependent on the amplitude AS of the corresponding interfering signal and on the amplitude AAh of the further signal h(t).

Furthermore, another case is considered in which an object echo signal which is correlated with the correlation filter is received by means of an ultrasonic sensor according to the invention, and in which the corresponding measuring signal s(t) is generated by the mixing of a further signal h(t), generated in particular in the form of a harmonic signal, with the received signal e(t) generated directly from the object echo signal. If the amplitude AAh of the further signal h(t), the typical amplitude AAS of a received signal e(t) generated directly from an interfering signal and the amplitude AAO of the received signal e(t) generated directly from the corresponding object echo signal satisfy the inequality AAh < AAS << AAO, the correlation signal X(t), calculated for the measuring signal s(t) generated on reception of the object echo signal and containing the further signal h(t), and the corresponding norm Ns are not influenced by the further signal h(t). Since the amplitude AAh of the further signal h(t) is substantially lower than the amplitude AAO of the received signal e(t) generated directly from the object echo signal, both the correlation signal X(t) calculated for the corresponding measuring signal s(t) and the norm Ns of this measuring signal s(t) are dependent mainly on the amplitude AAO of the received signal e(t) generated directly from the object echo signal. In the following three relations, here too the parameters which are calculated for the measuring signal s(t) containing the further signal h(t) and generated on reception of the object echo signal are supplemented with the index m and the corresponding parameters which are calculated for the received signal e(t) generated directly from the object echo signal are supplemented with the index nm. Here, the correlation signal Xm(t) calculated for this measuring signal s(t) and the correlation signal Xnm(t) calculated for the corresponding received signal e(t) satisfy the relation Xm(t) « Xnm(t) and the norm Nsm calculated for this measuring signal and the norm Nenm calculated for the corresponding received signal e(t) satisfy the relation Nsm « Nenm. Here, consequently also the corresponding correlation factors Km(t) and Knm(t) satisfy the relation Km(t) « Knm(t). This means that, in the case considered here, in which an object echo signal is received, the correlation factor Km(t) calculated for the corresponding measuring signal s(t) remains almost unchanged with respect to the correlation factor Knm(t) calculated for the received signal e(t) generated directly from the object echo signal.

Preferably, for each mixed signal s(t) a corresponding output signal s(t) of an additive mixer is used, wherein, in order to generate the corresponding output signal s(t), the mixer is supplied with the corresponding received signal e(t) as input signal and the mixer is supplied with the corresponding further signal h(t) as further input signal.

Preferably, for each mixed signal s(t) a corresponding digital output signal s(t) of an analog-digital converter is used, wherein, in order to generate the corresponding digital output signal s(t), the analog-digital converter is supplied with the corresponding received signal e(t) as input signal and for the corresponding further signal h(t) in each case a further signal h(t) generated in the form of an electrical voltage Vh(t) is additively superimposed on an input-side reference voltage Vr of the analog-digital converter .

Further preferably, for each mixed signal s(t) a corresponding digital output signal s(t) of an analogdigital converter is used, wherein, in order to generate the corresponding digital output signal s(t) , the corresponding received signal e(t) is transmitted via a line of two lines capacitively coupled to one another and is supplied as input signal to the analog-digital converter and the corresponding further signal h(t) is transmitted via a further line of the two lines and is supplied as further input signal to the analog-digital converter.

Preferably, each further signal h(t) is generated in the form of a harmonic signal by means of an oscillator.

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 profile of a signal strength s't of a composite measuring signal s' (t) as a function of a time t, a profile of a value X't of a correlation signal X(t), calculated for this measuring signal s' (t), as a function of the time t and a profile of a value R't of a correlation factor R' (t), calculated for this measuring signal s' (t), as a function of the time t, the composite measuring signal s' (t) being generated in an object detection carried out according to a first embodiment of the invention,

Figures 2 and 3 are each a profile of a value R'd of a correlation factor R'(d), calculated for a composite measuring signal s' (t), as a function of a distance d measured from an ultrasonic sensor used, the composite measuring signal s' (t) being generated in an object detection carried out according to a first embodiment of the invention,

Figure 4 is a profile of a signal strength U of an ultrasonic signal U(t), emitted in the object detection carried out according to a second embodiment of the invention, as a function of a time t,

Figures 5 to 8 are each a profile of a value R'd of a correlation factor R'(d), calculated for a composite measuring signal s' (t) , as a function of a distance d measured from an ultrasonic sensor used, the composite measuring signal s' (t) being generated in an object detection carried out according to the second embodiment of the invention,

Figure 9 is a profile of a signal strength et of a composite received signal e' (t) as a function of a time t, a profile of a value X't of a correlation signal X'(t), calculated for a composite measuring signal s'(t), as a function of the time t, a profile of a value h't of a composite further signal h'(t) as a function of the time t and a profile of a value R't of a correlation factor R'(t), calculated for the composite measuring signal s'(t), as a function of the time t, the composite received signal e' (t), the composite measuring signal s' (t) and the composite further signal h'(t) being generated in an object detection carried out according to a third embodiment of the invention,

Figures 10-14 are each a configuration for realising an object detection carried out according to the third embodiment of the invention, and,

Figure 15 is a profile of a value R'd of a correlation factor R'(d), calculated for a composite measuring signal s' (t) , as a function of a distance d measured by an ultrasonic sensor used, the composite measuring signal s'(t) being generated in an object detection carried out according to the third embodiment of the invention.

Embodiments of the invention

According to a first embodiment of the invention, ultrasonic signals which are each correlated with a correlation filter of a correlation module are emitted by means of an ultrasonic sensor according to the invention.

In the first embodiment of the invention, furthermore a received signal e(t), which here accords with a corresponding measuring signal s(t), is generated by means of the ultrasonic sensor from each echo signal which has arisen from reflections of the emitted ultrasonic signals and is received by means of the ultrasonic sensor. Each measuring signal s(t) is, for the purpose of generating a corresponding correlation signal X(t), correlated with a corresponding response signal F(t), dependent on a variable τ, of the correlation filter.

In this case, the correlation module calculates for each measuring signal s(t), and consequently also for each received echo signal, the corresponding correlation signal X(t) according to the relation (1) already given in the general description. In the relation (1), T is a length of the correlation filter and F*(t) is the corresponding complex conjugate response signal of the correlation filter .

X(f) = J s(t + τ) F* (τ)άτ (1)

Furthermore, the correlation module calculates for each measuring signal s (t), and consequently also for each received echo signal, a correlation factor R(t) according (2) to the relation (2) already given in the general description.

W) = ^(0

Ns-NF

J s(t + τ)· F*(r)(h js²(t+r · J j_o /' ²(τ)άτ

In the relation (2), Ns is a positive definite norm of the measuring signal s(t) and NF is a positive definite norm of the response signal F(t) of the correlation filter. From the relation (2) it can be seen how the correlation module calculates these norms Ns and NF.

For detection of at least one object situated in an environment of the ultrasonic sensor, in the first embodiment of the invention, a reception of object echo signals arising from reflection of the emitted ultrasonic pulses at at least one object situated in the environment of the ultrasonic sensor is recognised by means of an evaluation of the correlation signal X(t) calculated in each case for received echo signals and/or of the correlation factor R(t) calculated in each case for received echo signals.

In this regard, account is to be taken of the fact that the ultrasonic sensor, besides the object echo signals, can also receive background echo signals which arise from reflection of the emitted ultrasonic signals at many small particles of a ground surface or background surface situated in the environment of the ultrasonic sensor, and/or interfering signals which are correlated with the correlation filter.

Since the amplitude AB of background echo signals and the amplitude AS of interfering signals are generally in each case substantially lower than the amplitude AO of an object echo signal, in an object detection carried out according to the first embodiment of the invention, a differentiation between background echo signals or interfering signals and object echo signals can be optimally carried out by an evaluation of the correlation signal X(t) calculated in each case for received echo signals.

Since both the background echo signals and the interfering signals are correlated with the correlation filter, both the correlation factor R(t), calculated in each case for the background echo signals or interfering signals, and the correlation factor R(t) calculated in each case for the object echo signals have an amplitude with a high value, which may lie in each case also close to 1. As a result, in an object detection carried out according to the first embodiment of the invention, a differentiation between background echo signals or interfering signals and object echo signals by an evaluation of the correlation factor R(t) calculated in each case for received echo signals becomes difficult.

If an ultrasonic sensor according to the invention is installed in a vehicle, during a fine adjustment of this ultrasonic sensor it can often happen that the corresponding measuring device detects an interfering signal which has arisen from reflection of an emitted ultrasonic signal at parts of the vehicle or of a bumper of the vehicle which are situated at a fixed distance with respect to the ultrasonic sensor. Since such an interfering signal is correlated with the correlation filter, the amplitude of the correlation factor R(t) calculated for such an interfering signal has a high value, which may lie close to 1. If the correlation factor R(t) calculated in each case for received echo signals is evaluated for object detection, such objects situated in each case at a fixed distance with respect to the ultrasonic sensor are continuously detected. Therefore, a threshold value used for detecting object echo signals in the evaluation of a correlation factor R(t) calculated in each case for received echo signals is preferably selected in such a way that a detection of interfering signals is suppressed in such an evaluation.

Figure 1 shows a profile of a signal strength s't of a measuring signal s' (t) as a function of the time t, which signal is composed of two measuring signals s(t) which, in the object detection carried out according to the first embodiment of the invention, accord in each case with the received signal e(t) generated directly from a corresponding echo signal of two received echo signals.

From this it can be seen that firstly an undesired echo signal, which may be a background echo signal or an interfering signal, and after that an object echo signal were received by means of the ultrasonic sensor. In this case, a region of the composite measuring signal s' (t) which corresponds to a reception of the undesired echo signal is denoted by UE and a region of the composite measuring signal s'(t) which corresponds to a reception of the object echo signal is denoted by OE.

Figure 1 furthermore shows a profile of a value X't of the correlation signal X'(t), calculated for the composite measuring signal s' (t) represented in Figure 1, as a function of the time t. From this it can be seen that an amplitude which this correlation signal X'(t) has in a region XtU corresponding to the reception of the undesired echo signal is markedly lower than an amplitude which this correlation signal X'(t) has in a region XtO corresponding to the reception of the object echo signal.

Figure 1 also shows a profile of a value R'T of a correlation factor R'(t), calculated for the composite measuring signal s' (t) represented in Figure 1, as a function of the time t. From this it can be seen that an amplitude which this correlation factor R'(t) has in a region RtU corresponding to the reception of the undesired echo signal lies close to 1 and is thereby comparable to an amplitude which this correlation factor R'(t) has in a region RtO corresponding to the reception of the object echo signal.

Figure 2 shows a profile, plotted as a function of a distance d measured from the ultrasonic sensor in metres, of a value R'd of a further correlation factor K'(d) which is obtained by a representation of a correlation factor R'(t), calculated for a measuring signal s' (t) composed of the measuring signals s(t) generated on reception of background echo signals and of two object echo signals, as a function of this distance d and consequently is equivalent to this correlation factor R'(t). Account is to be taken here of the fact that the distance d measured from the ultrasonic sensor is travelled in each case by a corresponding echo signal from the place where it arises to the ultrasonic sensor at the speed of sound and can therefore be calculated in each case as a product between the speed of sound and the time t which has elapsed during this. In Figure 2, each region of this further correlation factor R'(d) which corresponds to the reception of background echo signals is denoted by RdB and each region of this further correlation factor R'(d) which corresponds to the reception of an object echo signal is denoted by RdO.

Figure 3 shows a profile, plotted as a function of a distance d measured from the ultrasonic sensor in centimetres, of a value R'd of a further correlation factor K'(d) obtained for a measuring signal s' (t) composed of the measuring signals s (t) generated on reception of interfering signals and of an object echo signal. In Figure 3, each region of this further correlation factor K' (d) which corresponds to the reception of interfering signals is denoted by KdS and each region of this further correlation factor K'(d) which corresponds to the reception of the object echo signal is denoted by RdO. In the representation from Figure 3 based on an actual measurement, interfering signals were received by means of an ultrasonic sensor according to the invention with a dynamic range lying between 1.5 V and +1.5 V, from which signals in each case a received signal with an amplitude of 20 mV was generated by means of the ultrasonic sensor.

From Figure 2 and 3 it can be seen that the further correlation factor R' (d) , represented in each case, has in each region RdB and RdS, respectively, which corresponds to a reception of background echo signals and of interfering signals, respectively, a large number of maxima which each assume a high value and in some cases lying close to 1.

From Figures 2 and 3 it can further be seen that each represented further correlation factor R'(d) has in each region RdO which corresponds to the reception of an object echo signal a maximum which also assumes a high value lying close to 1. Consequently, for these cases represented in Figures 2 and 3, it is difficult to carry out an object detection by an evaluation of the further correlation factor R(d) obtained in each case for the measuring signals s(t) generated on reception of the background echo signals and interfering signals, respectively, and of the at least one object signal, and consequently also by an evaluation of the further correlation factor R'(d) obtained for the measuring signal s' (t) composed of these measuring signals s (t) .

In an object detection carried out according to a second embodiment of the invention, unlike in the object detection carried out according to the first embodiment of the invention, ultrasonic signals are emitted by means of an ultrasonic sensor according to the invention which in each case comprise a first ultrasonic signal part which is not correlated with the correlation filter and is also referred to as a gap part signal or gap pulse, and a second ultrasonic signal part which is correlated with the correlation filter and is also referred to as a peak signal part or peak pulse. In this case, the first ultrasonic signal part of each ultrasonic signal to be emitted is emitted before the second ultrasonic signal part.

Figure 4 shows a profile of the signal strength Ut of an ultrasonic signal U(t), emitted according to a second embodiment of the invention by means of an ultrasonic sensor according to the invention, as a function of the time t measured in milliseconds. In Figure 4, a region of the ultrasonic signal U(t) which corresponds to an emission of the first ultrasonic signal part is denoted by UI and a region of the ultrasonic signal U(t) which corresponds to an emission of the second ultrasonic signal part is denoted by U2. If an ultrasonic signal U(t) is emitted which comprises a first ultrasonic signal part which is not correlated with the correlation filter and a second ultrasonic signal part which is correlated with the correlation filter, there arises from reflection of this ultrasonic signal an echo signal which, corresponding to the emitted ultrasonic signal, comprises a first echo signal part which is not correlated with the correlation filter and a second echo signal part which is correlated with the correlation filter. In the second embodiment of the invention, too, each received signal e(t) generated directly from the corresponding echo signal accords with the corresponding measuring signal s(t).

In the second embodiment of the invention, there is considered a case in which a received echo signal may be an object echo signal or a background echo signal.

If an object echo signal is received by means of the ultrasonic sensor, the first object echo signal part is not correlated with the correlation filter and the second object echo signal part is correlated with the correlation filter. Since the first object echo signal part is not correlated with the correlation filter, the correlation factor R(t) calculated for the corresponding measuring signal s(t) has in a region also referred to as a gap, which corresponds to a reception of the first object echo signal part, an amplitude with a relatively low first value. Since the second object echo signal part of an emitted ultrasonic pulse is correlated with the correlation filter, the corresponding correlation factor R(t) has in a region also referred to as a peak, which corresponds to a reception of the second object echo signal part, a maximum with a second value which lies markedly higher than the first value. The second value may lie close to 1, depending on the quality of the corresponding object echo signal.

Figures 5, 6, 7 and 8 each show a profile of a value R'd of a further correlation factor R'(d), obtained for a measuring signal s' (t) composed of the measuring signals s(t) generated on reception of background echo signals and of at least one object echo signal, as a function of the distance d introduced previously. In the representation from Figure 5, the distance d is measured in metres and in the representation from each of Figures 6 to 8 in centimetres. In each of the Figures 5 to 8, each peak, occurring on reception of an object echo signal, of the corresponding further correlation signal R(d), and consequently also of the further correlation signal R' (t) , is denoted by RdPO and each gap, occurring on reception of an object echo signal, of the corresponding further correlation signal R(d), and consequently also of the further correlation factor R'(d), is denoted by RdLO. All other regions of each further correlation factor R'(d) represented in Figures 5 to 8 correspond to the reception of background echo signals and are not denoted, for simplification of the representation from Figures 5 to 8.

Unlike from Figure 2, from Figure 5 it can very easily be seen that two object echo signals were received. Furthermore, from each of Figures 6 to 8 it can very easily be seen that in each case one object echo signal was received. Since the presence of a gap-peak combination in the profile of the value R'd of the further correlation factor R'(d) causes a signature of the further correlation factor R' (d) by which the reception of an object echo signal can be clearly seen, a predetermined algorithm is preferably used in the object detection carried out according to the second embodiment of the invention. In this algorithm, a maximum of the further correlation signal R'(d) is assigned to a reception of an object echo signal when the value of this maximum exceeds a higher threshold value SWh and simultaneously the amplitude of a predetermined number of maxima, occurring immediately before the maximum exceeding the higher threshold value SWh, of the further correlation signal R'(d) remains in each case below a lower threshold value SWn than the higher threshold value SWh. This number of maxima is in each case dependent on a length of the aforementioned gap signal part or gap pulse of an ultrasonic signal U(t) emitted according to the second embodiment of the invention. The higher threshold value SWh and the lower threshold value SWn are each drawn in in Figure 5.

In the object detection carried out according to the second embodiment of the invention, in which the emitted ultrasonic signals each have a gap signal part and a pulse signal part and in which the algorithm just mentioned is used, an incorrect recognition rate of objects is markedly lower than in the object detection carried out according to the first embodiment of the invention. The reason for this is that the probability with which a gap-peak combination occurs as a result of a reception of a background echo signal in the profile of the value R'd of the further correlation factor R'(d) is very much lower than the probability with which only a single high maximum or peak occurs as a result of a reception of a background echo signal in the profile mentioned.

The representations from Figures 6 to 8 are based on measurements actually carried out. From each of Figures 6 to 8 there can easily be seen the gap-pulse combination observed in the corresponding measurement and occurring in the corresponding profile of the value R'd of the corresponding further correlation factor R'(d). From each of Figures 6 to 8 it can furthermore be easily seen that the gap signal part or gap pulse of the emitted ultrasonic signal or ultrasonic pulse causes an open area in the profile of the value R'd of the corresponding further correlation factor R'(d), which area is situated immediately before the maximum or peak, which has occurred on reception of the corresponding object echo signal, of this further correlation factor R'(d), and that the corresponding object echo signal comes from the surrounding area of the ultrasonic sensor in which the background echo signals may arise.

An object detection carried out according to a third embodiment of the invention differs from the object detection carried out according to the first embodiment of the invention in that, for each received signal e(t) which is generated directly from a corresponding echo signal, a corresponding further signal h(t) as a function of the time t, which is in particular a corresponding harmonic signal, is used. In this case, each further signal h(t) is not correlated with the correlation filter and has an amplitude which lies in an order of magnitude of an amplitude AAS of each received signal e(t) generated directly from a corresponding interfering signal, and is thereby markedly lower than an amplitude AAO of each received signal e(t) generated directly from a corresponding object echo signal. As in the first embodiment of the invention, each ultrasonic signal emitted according to the third embodiment of the invention is correlated with the correlation filter.

According to the third embodiment of the invention, each received signal e(t) is additively mixed with the corresponding further signal h(t) in order to generate a corresponding mixed signal s(t). In this case, each mixed signal s(t) accords with the corresponding measuring signal s(t). Furthermore, each measuring signal s(t) is correlated with the corresponding response signal F(t) of the correlation filter used, in order to generate a corresponding correlation signal X(t). Also, each correlation signal X(t) is calculated according to the relation (1) and/or each correlation factor R(t) is calculated according to the relation (2).

The effect of mixing a further signal h(t) with each received signal e(t) generated by means of the ultrasonic sensor directly from a received echo signal can preferably also be achieved by using for each measuring signal s(t) the corresponding received signal e(t) and by using a changed relation for determining each correlation factor K(t) to be calculated for the corresponding measuring signal s(t). In this case, each correlation factor R(t) is calculated according to the changed relation (3) already given in the general description, where Ne is a positive definite norm of the corresponding received signal e(t) and Nh is a positive definite norm of the further signal h(t).

From the relation (3) it can easily be seen how the norm Nh of the further signal h(t) is calculated.

W) = x(t) ^{Ne² + Nh²)· NF

e(t +τ) · F*(r)dT + ^h²(t + τ)άτ 0

F²(r)dr (3)

In a case in which a received signal e(t) generated directly from a received echo signal is actually mixed with a small harmonic signal h(t), the corresponding signal s(t) is formed by addition of the small harmonic signal h(t) to the received signal e(t) and consequently determined according to the relation (4) .

s(t) = e(t) + h(t) (4)

If, in the relation (2) used for determining the correlation factor R(t), the expression s(t) is replaced with the sum, given in the relation (4), between the received signal e(t) and the harmonic signal h(t), the relation (5) for calculating the correlation factor R(t) is obtained.

W) = f (β(/ + τ) + Α(/+τ))·Ρ*(τ)ί/τ _Jo_ (e²(1 + τ) + 2e(1 +r)h(1 + τ) + h²(1 +r))dr · £ F²(r)dr (5)

It was assumed that the harmonic signal h(t) is not correlated with the response signal F(t) of the correlation filter. Therefore, the term calculated according to the ?t * expression J h(t + τ) · F (τ)άτ vanishes in the numerator of the fraction appearing in the relation (5), so that in the numerator mentioned only the term calculated according to the expression J e(t + T)-F (τ)άτ remains. Since the harmonic signal h(t) is zero-mean and is not correlated with e(t), the term calculated according to the expression h 2e(t+T)h(t+ τ)άτ also vanishes in the denominator of the same fraction appearing in the relation (5), thereby resulting directly in the changed relation (3) for determining the correlation factor R(t).

Further preferably, the aforementioned effect can also be achieved by using for each measuring signal s(t) the corresponding received signal e(t) and by using the relation (3) for determining each correlation factor K(t) to be calculated for the corresponding measuring signal s(t), a positive, in particular constant, factor Fh being used instead of the norm Nh of the further signal h(t). In this case, the norm Ns, appearing in the expression of the corresponding correlation factor R(t) calculated according to the relation (2), of each measuring signal s(t) which accords with the corresponding received signal e(t) is increased by Pythagorean addition of the factor Fh mentioned.

In the third embodiment of the invention, there is considered a case in which a received echo signal may be an object echo signal or an interfering signal. In the object detection carried out according to the third embodiment of the invention, preferably a time window is set, during which for generating a corresponding mixed signal s (t) each received signal e(t) is preferably mixed with a corresponding further signal h(t), which is in particular a corresponding harmonic signal. In this case, each correlation signal R(t) is calculated according to the relation (2) for each measuring signal s(t) which accords with the corresponding mixed signal s(t). Alternatively to this, during the set time window the correlation factor R(t) for each received signal e(t) which accords with the corresponding measuring signal s(t) is calculated according to the relation (3). As a result, the amplitude of the correlation factor R(t) calculated in each case for received interfering signals with low amplitude AS is reduced. Preferably, in this case the amplitude of each further signal h(t) or each additive factor Fh is increased in such a way that the effect of the received interfering signals on a correlation factor R'(t) calculated for a measuring signal s' (t) composed of the measuring signals s(t) generated on reception of echo signals is suppressed. Consequently, echo signals which each have a high amplitude can still be detected by means of an evaluation of the correlation factor R(t) calculated in each case for the received echo signals and consequently also of the correlation factor R'(t) calculated for the measuring signal s' (t) composed of the measuring signals s(t) generated on reception of echo signals.

In a case in which the ultrasonic sensor or a corresponding control unit or a corresponding microcontroller (ECU) detects interfering signals, that is to say in a case in which, by an evaluation of the correlation factor R(t) calculated in each case for received echo signals, too many received echo signals are detected, for which the distance d extending between a respective place where these signals arise and the ultrasonic sensor changes from measuring cycle to measuring cycle, preferably an increase of the amplitude of the further signal h(t) or of the aforementioned additive factor Fh is initiated by means of the ultrasonic sensor and carried out until the detection of the received echo signals carried out by the evaluation of the correlation factor R(t) calculated in each case for received echo signals achieves the desired quality again. Figure 9 shows a profile of a signal strength e't of a received signal e'(t), composed of the two received signals e(t) generated in each case directly from a corresponding echo signal of two received echo signals, as a function of the time t. From this it can be seen that firstly an interfering signal and after that an object echo signal were received by means of the ultrasonic sensor. In this case, a region of the composite measuring signal e'(t) which corresponds to a reception of the interfering signal is denoted by SE and a region of the composite received signal e'(t) which corresponds to a reception of the object echo signal is denoted by OE.

Figure 9 furthermore shows a profile of a value X't of a correlation signal X'(t), calculated for a mixed signal s' (t) composed of two mixed signals s(t) generated in each case by means of a corresponding one of the two received signals e(t) generated on the reception of the interfering signal and the object echo signal, as a function of the time t. In this case, each received signal e(t) is mixed with a corresponding one of two further signals h(t) used, in order to generate a corresponding one of the two mixed signals s(t). Here, each of the two mixed s(t) accords with the corresponding measuring signal s(t). As can be seen from Figure 1, it can also be seen from Figure 9 that an amplitude which this correlation signal X'(t) has in a region XtS corresponding to the reception of the interfering signal is markedly less than an amplitude which this correlation signal X'(t) has in a region XtO corresponding to the reception of the object echo signal.

Figure 9 also shows a profile of a value h't of a further signal h'(t), composed of the two further signals h(t) used, as a function of the time t. In this case, a region of the composite further signal h'(t) which is used for the received signal generated directly from the interfering signal is denoted by htS and a region of the composite further signal h' (t) which is used for the received signal generated directly from the object echo signal is denoted by htO.

Figure 9 further shows a profile of a value R't of a correlation factor R'(t), calculated for the composite measuring signal s' (t) just mentioned, as a function of the time t. Unlike from Figure 1, from Figure 9 it can be seen that an amplitude which this correlation factor R'(t) has in a region RtS corresponding to the reception of the interfering signal is markedly lower than an amplitude which this correlation factor R'(t) has in a region RtO corresponding to the reception of the object echo signal.

Each of the Figures 10 to 14 shows a respectively different configuration for realising an object detection carried out according to the third embodiment of the invention.

Figure 10 shows a general configuration in which, in order to generate each mixed signal s(t) , the corresponding received signal e(t) and the corresponding further signal h(t) are additively mixed.

Figure 11 shows a hardware-based configuration, in which, in order to generate each mixed signal s(t), an additive mixer 10 is supplied with the corresponding received signal e(t) as input signal and the corresponding further signal h(t) as further input signal. Each mixed signal s(t) here is the corresponding output signal s(t) of the mixer 10. In this case, the amplitude of the mixed signal s(t) can be changed by means of the mixer 10.

Figure 12 shows a further hardware-based configuration, in which, in order to generate each mixed signal s(t) , an analog-digital converter 20 is supplied with the corresponding received signal e(t) as input signal and in which the corresponding further signal h(t) generated in the form of an electrical voltage Vh(t) is additively superimposed on an input-side reference voltage Vr of the analog-digital converter 20. Each mixed signal s(t) here is the corresponding output signal s(t) of the analog-digital converter 2 0.

Figure 13 shows another hardware-based configuration, in which, in order to generate each mixed signal s (t), the corresponding received signal e(t) is transmitted via a line 30 of two lines 30, 35 capacitively coupled to one another and is supplied as input signal to an analogdigital converter 20, and in which the corresponding further signal h(t) is transmitted via a further line 35 of the two lines 30, 35 and is supplied as further input signal to the analog-digital converter 20. Each mixed signal s(t) here is the corresponding output signal s(t) of the analog-digital converter 20. The strength of the capacitive coupling between the two lines 30, 35 here can be controlled via a magnitude of an amplitude AAh of the corresponding further signal h(t).

In each realisation represented in Figures 10 to 13, each mixed signal s(t) accords with the corresponding measuring signal s(t) and is correlated with the corresponding response signal F(t) of a correlation filter for generating a corresponding correlation signal X(t). Also, by means of a correlation module 40, each correlation signal X(t) is calculated according to the relation (1) and each correlation factor R(t) is calculated according to the relation (2).

Furthermore, in each realisation represented in one of Figures 11 to 13, the corresponding further signal h(t) is generated in the form of a harmonic signal by means of an oscillator, by means of which preferably a frequency of each harmonic signal is adjustable.

Figure 14 shows a software-based configuration, in which for each mixed signal s(t) the corresponding received signal e(t) is used and each mixed signal s(t) is correlated with the corresponding response signal F(t) of a correlation filter for generating a corresponding correlation signal X(t). In this case, the effect of mixing each received signal e(t) with a corresponding further signal h(t) is achieved by calculating, by means of a correlation module 40, each correlation signal X(t) according to the relation (1) and each correlation factor R(t) according to the relation (3), in which the norm Nh of a corresponding further signal h(t) is replaced with a corresponding positive definite constant factor Fh. Here, each mixed signal s (t) accords with the corresponding measuring signal s(t).

Figure 15 shows a profile, plotted as a function of a distance d measured from the ultrasonic sensor in centimetres, of a value R'd of a further correlation factor K'(d) obtained for a measuring signal s' (t) composed of the measuring signals s(t) generated on reception of interfering signals and of measuring signals s(t) generated by an object echo signal. An actual measurement on which the representation from Figure 15 is based differs from the actual measurement on which the representation from Figure 3 is based, merely in that it has taken place during an object detection carried out according to the third embodiment of the invention, in which each received echo signal was mixed with a corresponding further signal h(t) generated in the form of a harmonic signal with an amplitude of 30 mV and a frequency of 60 kHz. From Figure 15 it can easily be seen that the further correlation factor R'(d), represented here, in each region RdS corresponding to a reception of an interfering signal has an amplitude having a value which is markedly lower than a value of a maximum which this further correlation factor R' (d) has in a region RdO corresponding to a reception of the object echo signal. From Figure 15 it can easily be seen that, in an object detection carried out according to the third embodiment of the invention, the effect of the received interfering signals on the further correlation factor R'(d) represented here is suppressed. As a result, a reception of object echo signals can be very easily recognised by an evaluation of this further correlation factor R' (t) .

In an object detection carried out according to the third embodiment of the invention, the correlation factor R(t), which is calculated in each case for background echo signals and for an echo signal which has arisen from reflection at an object occurring in the vicinity of the ultrasonic sensor, has an amplitude with a respectively high value, which may also lie close to 1. Here, the received background echo signals come from a surrounding area which extends from a distance d of 50 cm measured from the ultrasonic sensor up to a distance d of 350 cm measured from the ultrasonic sensor. The object mentioned is situated here at a distance d of 150 cm measured from the ultrasonic sensor. An object detection carried out according to the third embodiment of the invention does not result in a change of the amplitude just mentioned compared with a corresponding amplitude which occurs in an object detection carried out according to the first embodiment of the invention.

In addition to the aforementioned written disclosure, reference is additionally made to the representation in Figures 1 to 15.

Aspects of the Invention

The invention may be further understood with reference to the following numbered aspects of the invention.

1. Method for detecting at least one object with the aid of ultrasonic signals (U(t)) reflected at this object, in which, by means of an ultrasonic sensor, echo signals which arise from reflection of ultrasonic signals (U(t)) emitted by means of the ultrasonic sensor are received, wherein, from each received echo signal, a corresponding received signal (, e(t)) is generated by means of the ultrasonic sensor and by means of each received signal (, e(t)) a corresponding measuring signal (s(t) ) as a function of a time (t) is generated, which measuring signal, in order to generate a corresponding correlation signal (X(t)), is correlated with a corresponding response signal (F(t)), dependent on a variable τ, of a correlation filter, characterised in that, for each measuring signal (s(t) ) , a corresponding correlation factor (R(t) ) as a function of the time (t) is determined in dependence on the corresponding correlation signal (X(t)), a positive definite norm Ns of the corresponding measuring signal (s(t)) and a positive definite norm NF of the corresponding response signal (F(t)) and is evaluated in order to detect the at least one object.

2. Method according to aspect 1, wherein each correlation factor (R(t)) is determined according to the relation

W) =

Ns · NF(t)

where T is a length of the correlation filter and F*(t) is the corresponding complex conjugate response signal of the correlation filter.

3. Method according to one of aspects 1 or 2, wherein each measuring signal s(t) is the corresponding received signal e(t) and each emitted ultrasonic signal (U(t)) comprises a first ultrasonic signal part which is not correlated with the correlation filter and a second ultrasonic signal part which is correlated with the correlation filter, wherein the first ultrasonic signal part of each ultrasonic signal to be emitted is emitted before the or after the corresponding second ultrasonic signal part, or each emitted ultrasonic signal comprises a first ultrasonic signal part which is not correlated with the correlation filter, a second ultrasonic signal part which is correlated with the correlation filter, and a third ultrasonic signal part which is not correlated with the correlation filter, wherein the second ultrasonic signal part of each ultrasonic signal to be emitted is emitted after the corresponding first ultrasonic signal part and before the corresponding third ultrasonic signal part.

4. Method according to aspect 3, wherein, on the presence of each received signal e(t), the correlation factor R(t) of which falls short of a first limit value for a first time period and has a maximum which lies temporally immediately after the first time period has elapsed or before a beginning of the first time period and exceeds a second limit value greater than the first limit value, it is recognised that the corresponding received signal e(t) comes from an echo signal which has arisen from reflection at the at least one object, or on the presence of each received signal e(t), the correlation factor R(t) of which falls short of a first limit value for a first time period and also for a second time period lying temporally after the first time period has elapsed, and has a maximum which lies temporally immediately after the first time period has elapsed and before a beginning of the second time period and exceeds a second limit value greater than the first limit value, it is recognised that the corresponding received signal e(t) comes from an echo signal which has arisen from reflection at the at least one object.

5. Method according to aspect 4, wherein a length of the first time period is determined in dependence on a signal duration of the first ultrasonic signal part of each emitted ultrasonic signal (U(t)) and/or a length of the second time period is determined in dependence on a signal duration of the third ultrasonic signal part of each ultrasonic signal.

6. Method according to one of aspects 1 or 2, wherein each emitted ultrasonic signal is correlated with the correlation filter, for each received signal (e(t)) a corresponding further signal (h(t)) as a function of the time t, which signal is in particular a corresponding harmonic signal, is used, wherein each further signal (h(t) ) is not correlated with the correlation filter and has an amplitude AAh which lies in an order of magnitude of an amplitude of each received signal AAS which comes from a corresponding echo signal of the received echo signals which has not arisen from reflection at the at least one object, wherein each received signal (e(t)) is mixed with the corresponding further signal (h(t)) in order to generate a corresponding mixed signal (s (t)) and each measuring signal (s (t)) is the mixed signal (s (t)) generated by means of the corresponding received signal or each measuring signal (s(t) ) is the corresponding received signal (e(t)) and the correlation factor (R(t)) to be determined for each received signal (e(t)) is determined according to the changed relation

W) =

A(Z) /(Ne² + Nh²)· NF

J e(t +τ)· F*(r)dT

(t + τ)άτ

T + J/z² (t + τ)άτ

where Ne is a positive definite norm of the corresponding received signal (e(t)) and Nh is a positive definite norm of the further signal (h(t)).

7. Method according to one of aspects 5 or 6, wherein, on the presence of each mixed signal (s (t)), the correlation factor (R(t)) of which has a maximum which exceeds a predefined limit value, it is recognised that the received signal (e(t)), by means of which the corresponding mixed signal (s(t)) was generated, comes from an echo signal which has arisen from reflection at the at least one object, or wherein, on the presence of each received signal (e(t)), the correlation factor (R(t)), determined as changed, of which has a maximum which exceeds a predefined limit value, it is recognised that the corresponding received signal (e(t)) comes from an echo signal which has arisen from reflection at the at least one object.

8. Measuring device for detecting at least one object by means of ultrasonic signals (U(t)) reflected at this object, wherein the measuring device comprises an ultrasonic sensor which is configured to emit ultrasonic signals (U(t)), to receive echo signals which arise from reflection of the emitted ultrasonic signals, and to generate from each received echo signal a corresponding received signal ( e(t)), wherein the measuring device is configured to generate by means of each received signal ( e(t)) a measuring signal (s(t)) as a function of a time (t) and to correlate this measuring signal, in order to generate a corresponding correlation signal (X(t)), with a corresponding response signal (F(t)), dependent on a variable τ, of a correlation filter arranged in the measuring device, characterised in that the measuring device is configured to determine, for each measuring signal (s(t) ) , a corresponding correlation factor (R(t) ) as a function of the time (t) in dependence on the corresponding correlation signal (X(t)), a positive definite norm Ns of the corresponding measuring signal (s(t)) and a positive definite norm NF of the corresponding response signal (F(t)), and to evaluate these correlation factors in order to detect the at least one object.

9. Measuring device according to aspect 8, which is configured to determine each correlation factor (R(t)) according to the relation _R(t) = ₌ Jo + W?

Ns NF K

J s(t + τ') · F\r)dT

10. Measuring device according to one of aspects 8 or 9, which is configured to use for each measuring signal s(t) the corresponding received signal e(t), wherein the ultrasonic sensor is configured to emit ultrasonic signals (U(t)) which in each case comprise a first ultrasonic signal part which is not correlated with the correlation filter and a second ultrasonic signal part which is correlated with the correlation filter, and to emit the first ultrasonic signal part of each ultrasonic signal (U(t)) to be emitted, before the or after the corresponding second ultrasonic signal part, or to emit ultrasonic signals which in each case comprise a first ultrasonic signal part which is not correlated with the correlation filter, a second ultrasonic signal part which is correlated with the correlation filter, and a third ultrasonic signal part which is not correlated with the correlation filter, and to emit the second ultrasonic signal part of each ultrasonic signal to be emitted, after the corresponding first ultrasonic signal part and before the corresponding third ultrasonic signal part.

Measuring device according to aspect 10, which is configured, on the presence of each received signal e(t), the correlation factor R(t) of which falls short of a first limit value for a first time period and has a maximum which lies temporally immediately after the first time period has elapsed or before a beginning of the first time period and exceeds a second limit value greater than the first limit value, to recognise that the corresponding received signal e(t) comes from an echo signal which has arisen from reflection at the at least one object, or on the presence of each received signal e(t), the correlation factor R(t) of which falls short of a first limit value for a first time period and also for a second time period lying temporally after the first time period has elapsed, and has a maximum which lies temporally immediately after the first time period has elapsed or before a beginning of the second time period and exceeds a second limit value greater than the first limit value, to recognise that the corresponding received signal e(t) comes from an echo signal which has arisen from reflection at the at least one object.

Measuring device according to aspect 11, which is configured to determine a length of the first time period in dependence on a signal duration of the first ultrasonic signal part of each emitted ultrasonic signal (U(t)) and/or a length of the second time period .

in dependence on a signal duration of the third ultrasonic signal part of each emitted ultrasonic signal.

13. Measuring device according to one of aspects 8 or 9, wherein the ultrasonic sensor is configured to emit ultrasonic signals which in each case are correlated with the correlation filter, wherein the measuring device is configured to use for each received signal (e(t)) a further signal (h(t)) as a function of the time t, which signal is in particular a corresponding harmonic signal, wherein each further signal (h(t)) is not correlated with the correlation filter and has an amplitude AAh which lies in an order of magnitude of an amplitude AAS of each received signal which comes from an echo signal of the received echo signals which has not arisen from reflection at the at least one object, wherein the measuring device is furthermore configured to mix each received signal (e(t) ) with the corresponding further signal (h(t)) in order to generate a corresponding mixed signal (s (t)) and to use for each measuring signal (s(t)) the mixed signal (s(t) ) generated by means of the corresponding received signal or to use for each measuring signal (s (t)) the corresponding received signal (e(t)) and to determine the correlation factor (R(t)) to be determined for each received signal (e (t)) according to the changed relation x(0

J e(t +τ)· F* (τ)άτ

14. Measuring device according to aspect 13, wherein the measuring device comprises an additive mixer (10) and is configured to use for each mixed signal (s (t)) a corresponding output signal (s(t)) of the mixer (10) and, in order to generate the corresponding output signal s(t), to supply the mixer (10) with the corresponding received signal (e(t)) as input signal and to provide the mixer (10) with the corresponding further signal (h(t) ) as further input signal or wherein the measuring device comprises an analogdigital converter (20) and is configured to use for each mixed signal (s(t)) a corresponding digital output signal (s(t) ) of the analog-digital converter (20) and, in order to generate the corresponding digital output signal (s(t) ) , to supply the analog-digital converter (20) with the corresponding received signal (e(t)) as input signal, to use for the corresponding further signal h(t) in each case a further signal h(t) generated in the form of an electrical voltage Vh(t) and to additively superimpose this further signal on an input-side reference voltage Vr of the analog-digital converter (20) or in order to generate the corresponding digital output signal (s(t) ) , to transmit the corresponding received signal (e(t)) via a line (30) of two lines (30, 35) arranged in the measuring device and capacitively coupled to one another and to supply it as input signal to the analog-digital converter (20), and to transmit the corresponding further signal (h(t)) via a further line (35) of the two lines (30, 35) and to supply it as further input signal to the analog-digital converter (20) .

15. Measuring device according to one of aspects 13 or 14, wherein the measuring device comprises an oscillator which is configured to generate each further signal (h(t)) in the form of a harmonic signal.

16. Measuring device according to one of aspects 13 to 15, which is configured, on the presence of each mixed signal (s(t) ) , the correlation factor (R(t) ) of which has a maximum which exceeds a predefined limit value, to recognise that the received signal (e(t)), by means of which the corresponding mixed signal (s (t)) was generated, comes from an echo signal which has arisen from reflection at the at least one object, or on the presence of each received signal (e (t) ), the correlation factor (R(t)), determined as changed, of which has a maximum which exceeds a predefined limit value, to recognise that the corresponding received signal (e(t)) comes from an echo signal which has arisen from reflection at the at least one object.

Claims

1. Method for detecting at least one object with the aid of ultrasonic signals (U(t)) reflected at this object, in which, an ultrasonic sensor emits ultrasonic signals (U(t)) and receives echo signals which arise from reflection of the emitted ultrasonic signals by an object, wherein, from each received echo signal, a corresponding received signal (, e(t)) is generated by means of the ultrasonic sensor and by means of each received signal (, e(t) ) a corresponding measuring signal (s(t) ) as a function of a time (t) is generated, which measuring signal, in order to generate a corresponding correlation signal (X(t)), is correlated with a corresponding response signal (F(t)), dependent on a variable τ, of a correlation filter, characterised in that, for each measuring signal (s(t)), a corresponding correlation factor (R(t)) as a function of the time (t) is determined in dependence on the corresponding correlation signal (X(t)), a positive definite norm Ns of the corresponding measuring signal (s(t) ) and a positive definite norm NF of the corresponding response signal (F(t)) and is evaluated in order to detect the at least one object wherein each emitted ultrasonic signal is correlated with the correlation filter, for each received signal (e(t)) a corresponding further signal (h(t)) as a function of the time t, which signal is in particular a corresponding harmonic signal, is used, wherein each further signal (h(t)) is not correlated with the correlation filter and has an amplitude AAh which lies in an order of magnitude of an amplitude of each received signal AAS which comes from a corresponding echo signal of the received echo signals which has not arisen from reflection at the at least one object, wherein each received signal (e(t)) is mixed with the corresponding further signal (h(t)) in order to generate a corresponding mixed signal (s (t)) and each measuring signal (s(t)) is the mixed signal (s(t)) generated by means of the corresponding received signal or each measuring signal (s(t)) is the corresponding received signal (e(t)) and the correlation factor (R(t) ) to be determined for each received signal (e(t)) is determined according to the changed relation

J β(/+τ)·Ρ*(τ)ί/τ where Ne is a positive definite norm of the corresponding received signal (e(t)) and Nh is a positive definite norm of the further signal (h(t))..

Method according to Claim 1, wherein each correlation factor (R(t)) is determined according to the relation s(t + T)-F (τ)άτ where T is a length of the correlation filter and F*(t) is the corresponding complex conjugate response signal of the correlation filter.

3. Method according to Claim 1, wherein, on the presence of each mixed signal (s(t)), the correlation factor (R(t)) of which has a maximum which exceeds a predefined limit value, it is recognised that the received signal (e(t)), by means of which the corresponding mixed signal (s(t)) was generated, comes from an echo signal which has arisen from reflection at the at least one object, or wherein, on the presence of each received signal (e(t)), the correlation factor (R(t)), determined as changed, of which has a maximum which exceeds a predefined limit value, it is recognised that the corresponding received signal (e(t)) comes from an echo signal which has arisen from reflection at the at least one object.

4. Measuring device for detecting at least one object by means of ultrasonic signals (U(t)) reflected at this object, wherein the measuring device comprises an ultrasonic sensor which is configured to emit ultrasonic signals (U(t)), to receive echo signals which arise from reflection of the emitted ultrasonic signals, and to generate from each received echo signal a corresponding received signal ( e(t)), wherein the measuring device is configured to generate by means of each received signal ( e(t)) a measuring signal (s (t)) as a function of a time (t) and to correlate this measuring signal, in order to generate a corresponding correlation signal (X(t)), with a corresponding response signal (F(t)), dependent on a variable τ, of a correlation filter arranged in the measuring device, characterised in that the measuring device is configured to determine, for each measuring signal (s(t) ) , a corresponding correlation factor (R(t) ) as a function of the time (t) in dependence on the corresponding correlation signal (X(t)), a positive definite norm Ns of the corresponding measuring signal (s(t)) and a positive definite norm NF of the corresponding response signal (F(t) ) , and to evaluate these correlation factors in order to detect the at least one object wherein the ultrasonic sensor is configured to emit ultrasonic signals which in each case are correlated with the correlation filter, wherein the measuring device is configured to use for each received signal (e(t)) a further signal (h(t)) as a function of the time t, which signal is in particular a corresponding harmonic signal, wherein each further signal (h(t)) is not correlated with the correlation filter and has an amplitude AAh which lies in an order of magnitude of an amplitude AAS of each received signal which comes from an echo signal of the received echo signals which has not arisen from reflection at the at least one object, wherein the measuring device is furthermore configured to mix each received signal (e(t) ) with the corresponding further signal (h(t)) in order to generate a corresponding mixed signal (s (t)) and to use for each measuring signal (s(t)) the mixed signal (s(t) ) generated by means of the corresponding received signal or to use for each measuring signal (s (t)) the corresponding received signal (e(t)) and to determine the correlation factor (R(t)) to be determined for each received signal (e(t)) according to the changed relation x(0

J e(t +τ)· F*(τ)άτ

0 0 where Ne is a positive definite norm of the corresponding received signal (e(t)) and Nh is a positive definite norm of the further signal (h(t)).

5. Measuring device according to Claim 4, which is configured to determine each correlation factor (R(t)) according to the relation R(t) = = Jo +

Ns NF K where T is a length of the correlation filter and F*(t) is the corresponding complex conjugate response signal of the correlation filter.

6. Measuring device according to Claim 4, wherein the measuring device comprises an additive mixer (10) and is configured to use for each mixed signal (s(t)) a corresponding output signal (s(t) ) of the mixer (10) and, in order to generate the corresponding output signal s(t), to supply the mixer (10) with the corresponding received signal (e(t) ) as input signal and to provide the mixer (10) with the corresponding further signal (h(t)) as further input signal or wherein the measuring device comprises an analogdigital converter (20) and is configured to use for each mixed signal (s(t)) a corresponding digital output signal (s(t)) of the analog-digital converter (20) and, in order to generate the corresponding digital output signal (s(t)), to supply the analog-digital converter (20) with the corresponding received signal (e(t)) as input signal, to use for the corresponding further signal h(t) in each case a further signal h(t) generated in the form of an electrical voltage Vh(t) and to additively superimpose this further signal on an input-side reference voltage Vr of the analog-digital converter (20) or in order to generate the corresponding digital output signal (s(t)), to transmit the corresponding received signal (e(t)) via a line (30) of two lines (30, 35) arranged in the measuring device and capacitively coupled to one another and to supply it as input signal to the analog-digital converter (20), and to transmit the corresponding further signal (h(t)) via a further line (35) of the two lines (30, 35) and to supply it as further input signal to the analog-digital converter (20) .

7. Measuring device according to one of Claims 4 or 6, wherein the measuring device comprises an oscillator which is configured to generate each further signal (h(t)) in the form of a harmonic signal.

8. Measuring device according to one of Claims 4 to 7, which is configured, on the presence of each mixed signal (s(t)), the correlation factor (R(t)) of which has a maximum which exceeds a predefined limit value, to recognise that the received signal (e(t)), by means of which the corresponding mixed signal (s(t)) was generated, comes from an echo signal which has arisen from reflection at the at least one object, or on the presence of each received signal (e(t)), the correlation factor (R(t)), determined as changed, of which has a maximum which exceeds a predefined limit value, to recognise that the corresponding received

5 signal (e(t)) comes from an echo signal which has arisen from reflection at the at least one object.

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Application No: GB1803149.2