Method and measuring device for detecting at least one object based on ultrasound signals reflected from it.

Abstract

A method for detecting at least one object based on ultrasound signals (U(t)) reflected from it, wherein echo signals generated by reflection of ultrasound signals (U(t)) emitted by the ultrasound sensor are received by means of an ultrasound sensor, wherein a corresponding received signal (e(t)) is generated from each received echo signal by means of the ultrasound sensor, and a corresponding time-dependent measurement signal (s(t)) is generated by means of each received signal (e(t)), which is correlated with a corresponding response signal (F(τ)) of a correlation filter dependent on a variable τ to generate a corresponding correlation signal (X(t)), characterized in that for each measurement signal (s(t)) a corresponding time-dependent correlation factor (R(t)) is determined as a function of the corresponding correlation signal (X(t)).a positively defined norm Ns of the corresponding measurement signal (s(t)) and a positively defined norm NF of the corresponding response signal (F(τ)) is determined and evaluated for the detection of at least one object, where , each measurement signal s(t) is the corresponding received signal e(t) and each emitted ultrasound signal (U(t)) comprises a first ultrasound signal part that is not correlated with the correlation filter and a second ultrasound signal part that is correlated with the correlation filter, wherein the first ultrasound signal part of each ultrasound signal to be emitted is emitted before or after the corresponding second ultrasound signal part, or Each emitted ultrasound signal comprises a first ultrasound signal part that is not correlated with the correlation filter, a second ultrasound signal part that is correlated with the correlation filter, and a third ultrasound signal part that is not correlated with the correlation filter, wherein the second ultrasound signal part of each ultrasound signal to be emitted is emitted after the corresponding first ultrasound signal part and before the corresponding third ultrasound signal part.

Description

[0001] The present invention relates to a method and a measuring device for detecting at least one object based on ultrasonic signals reflected therefrom. State of the art

[0002] In the field of environmental detection using ultrasound, an ultrasonic measuring system for detecting an obstacle is known, for example, from document DE 10 2011 075 484 A1. The ultrasonic measuring system comprises an ultrasonic sensor with a resonant transducer element for emitting ultrasonic pulses and for generating received signals from the emitted ultrasonic pulses and those reflected by the obstacle. The ultrasonic pulses emitted and reflected by the obstacle are referred to as echo pulses. After each ultrasonic pulse has been emitted, the resonant transducer element further generates a decay signal at its resonant frequency. The ultrasonic measuring system also comprises an evaluation unit with a control device configured to control the resonant transducer element to emit each ultrasonic pulse using a transmission signal generated by the control device.Furthermore, the control unit of the ultrasonic measuring system is designed to generate each transmission signal using a modulation signal in the form of a frequency-modulated transmission signal such that the signature of each transmitted ultrasonic pulse differs from that of the corresponding decay signal. The evaluation unit has at least one correlation filter, wherein the at least one correlation filter is designed to correlate each signal generated by the resonant transducer with the corresponding transmission signal and to generate a correlation signal. The evaluation unit is further designed to detect the presence of an echo pulse originating from reflection from the obstacle when the correlation signal has a maximum. The same document further describes a corresponding method for detecting an obstacle using ultrasound.

[0003] The document DE 10 2012 211 293 A1 discloses a method for operating an environment detection system of a vehicle and environment detection system.

[0004] The present invention is based on the object of improving such methods according to the known prior art. Disclosure of the invention

[0005] The present object is achieved according to the invention according to independent claims 1 and 6.

[0006] According to the invention, a method is provided for detecting at least one object based on ultrasonic signals reflected therefrom, in which echo signals generated by the reflection of ultrasonic signals emitted by the ultrasonic sensor are received by means of an ultrasonic sensor. From each received echo signal, a corresponding received signal is generated by the ultrasonic sensor, and from each received signal, a corresponding measurement signal s(t) dependent on a time t is generated. Furthermore, each measurement signal s(t) is correlated with a corresponding response signal F(τ) of a correlation filter dependent on a variable τ to generate a corresponding correlation signal X(t).Also, for each measurement signal s(t), a corresponding correlation factor R(t) dependent on time t is determined as a function of the corresponding correlation signal X(t), a positively defined norm Ns of the corresponding measurement signal s(t) and a positively defined norm NF of the corresponding response signal F(τ) and evaluated for the detection of at least one object.

[0007] According to the invention, a measuring device for detecting at least one object by means of ultrasonic signals reflected therefrom is further provided. The measuring device comprises an ultrasonic sensor configured to emit ultrasonic signals, receive echo signals resulting from the reflection of the emitted ultrasonic signals, and generate a corresponding received signal from each received echo signal. The measuring device is configured to generate a measurement signal s(t) dependent on a time t using each received signal and to correlate this measurement signal with a corresponding response signal F(τ) of a correlation filter arranged in the measuring device, dependent on a variable τ, to generate a corresponding correlation signal X(t).Furthermore, the measuring device is designed to determine for each measurement signal s(t) a corresponding correlation factor R(t) dependent on the time t as a function of the corresponding correlation signal X(t), a positively defined norm Ns of the corresponding measurement signal s(t) and a positively defined norm NF of the corresponding response signal F(τ) and to evaluate it for the detection of the at least one object.

[0008] The subclaims show preferred developments of the invention.

[0009] Preferably, each correlation factor R (t) is chosen according to the relation R(t)=X(t)Ns⋅NF=∫0Ts(t+τ)⋅F*(τ)dτ∫0Ts2(t+τ)dτ⋅∫0TF2(τ)dτ where T is a length of the correlation filter and F*(τ) is the corresponding complex conjugate response signal of the correlation filter.

[0010] In the invention, a correlation factor R(t) is calculated for each measurement 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.

[0011] Preferably, each measurement signal s(t) corresponds to the corresponding received signal e(t). To detect the at least one object, an amplitude of each correlation factor R(t) is compared with a predefined limit. Further preferably, if each received signal e(t) whose correlation factor R(t) has a maximum that exceeds the predefined limit, it is recognized that the received signal e(t) originates from an echo signal generated by reflection from the at least one object.

[0012] Preferably, the correlation signal X(t) according to the invention is calculated according to the relation X(t)=∫0Ts(t+τ)⋅F*(τ)dτ determined and evaluated to detect at least one object.

[0013] In the invention, a correlation signal X(t) can be calculated for each measurement 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.

[0014] Further preferably, each emitted ultrasonic signal is an ultrasonic pulse.

[0015] Preferably, frequency-modulated ultrasonic signals, also referred to as chirps, are emitted by an ultrasonic sensor according to the invention. For example, chirps can be emitted whose frequency changes linearly during the duration of their transmission, which is typically approximately 1.0 ms. For example, the frequency of such chirps is 54 kHz at the beginning of their transmission and 45 kHz at the end of their transmission.

[0016] An ultrasonic sensor according to the invention preferably comprises digital signal processing in the form of a correlation module, particularly designed as a cross-correlation module. By means of the correlation module, received ultrasonic signals are correlated with the response signal F(τ) of a correlation filter, particularly designed as a cross-correlation filter, which is optimally matched to the reception of an echo signal generated by the reflection of a transmitted ultrasonic signal from the at least one object.

[0017] The correlation module according to the invention preferably calculates a correlation signal X(t) in the form of a cross-correlation signal and / or a correlation factor R(t), each according to a corresponding one of the two previously specified relations. Further preferably, both the correlation signal X(t) and the correlation factor R(t) are used during echo signal acquisition to detect the at least one object. It should be noted here 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 degree of correlation between the received echo signal and the corresponding response signal F(τ) of the correlation filter.

[0018] Preferably, the correlation factor R(t) is scaled such that its value lies between 0 and 1, i.e., the correlation factor R(t) satisfies the inequality 0 ≤ R(t) ≤ 1.

[0019] In this context, this means that if at a time t0 the value of the correlation factor R(t) is equal to 1, for example, an optimal echo signal was received at time t0, i.e., an echo signal that is fully correlated with the correlation filter. The relation R(t0) = 1 applies here. If, for example, the relation R(t0) = 0.9 holds, this means that at time t0 a quasi-optimal echo signal was received, i.e., an echo signal that is almost fully correlated with the correlation filter. If, for example, the relation R(t0) = 0.1 holds, this means that at time t0 an echo signal that is not comparable to an optimal echo signal, i.e., an echo signal that is not correlated with the correlation filter, was received.

[0020] Preferably, the ultrasonic sensor according to the invention calculates both the corresponding correlation signal X(t) and the corresponding correlation factor R(t) for each received echo signal. Further preferably, an algorithm is used for echo signal detection in which, for each received echo signal, both the corresponding correlation signal X(t) and thus the corresponding echo signal amplitude as well as the corresponding correlation factor R(t) and thus the corresponding echo signal quality are taken into account.

[0021] A major advantage of using an ultrasonic sensor according to the invention for emitting ultrasonic signals, particularly in the form of chirps, is that such an ultrasonic sensor exhibits relatively good robustness against noise and interference. This is very advantageous because, in the aforementioned correlation calculation, noise signals originating from noise sources are suppressed that have a frequency that does not overlap with the frequency spectrum of the correlation filter.

[0022] One difficulty that arises when using an ultrasonic sensor according to the invention is that its functionality can be impaired by more than just the reception of noise signals. When an ultrasonic signal is emitted using the ultrasonic sensor according to the invention, this ultrasonic sensor also receives echo signals that result from the reflection of the emitted ultrasonic signal by many small particles on a subsurface, such as a soil surface. This mixture of echo signals with small amplitudes AB, which result from reflection from the subsurface, is also referred to as the subsurface echo signal.The size of the surrounding area of ​​the ultrasonic sensor from which subsurface echo signals can originate depends on the positioning of the ultrasonic sensor relative to the subsurface, such as the positioning height and the positioning angle of the ultrasonic sensor relative to the subsurface. This surrounding area extends at a distance from the ultrasonic sensor or within the range of the ultrasonic sensor, which is typically between 0.5 m and 3.5 m.

[0023] The occurrence of background echo signals is the most important factor limiting the quality of the echo signal acquisition carried out by such an ultrasonic sensor for a range between 0.5 m and 3.5 m for the detection of at least one object located within this range, since the ultrasonic sensor receives a mixture of echo signals that includes both background echo signals and echo signals originating from the at least one object, which are also referred to as object echo signals. For each received echo signal, the corresponding correlation signal X(t) and the corresponding correlation factor R(t) are calculated. It should be noted that for both a received echo signal that is a background echo signal and a received echo signal that is an object echo signal, the corresponding correlation factor R(t) can often have a maximum with a value 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(τ) of the correlation filter. Consequently, for the ambient area in which background echo signals can arise, differentiating between background echo signals and object echo signals based on an evaluation of the correlation factor R(t) calculated for each of the received echo signals is difficult. Since the amplitude AB of background echo signals is generally smaller than the amplitude AO of the object echo signals, the aforementioned differentiation can preferably continue to be performed based on an evaluation of the corresponding correlation signal X(t).

[0024] A further difficulty that arises when using an ultrasonic sensor according to the invention is that the functionality of such an ultrasonic sensor can also be impaired by the reception of interference signals. It can happen that the interference signals have a frequency that lies in a frequency spectrum similar to the frequency spectrum of the correlation filter. In such a case, an ultrasonic sensor according to the invention receives an interference signal that is similar to the corresponding response signal F(τ) of the correlation filter, i.e., the received interference signal is correlated with the correlation filter. Due to the reception of such interference signals, the amplitude of the correlation factor R(t) calculated for such interference signals has a value within an elevated range, which can often be close to 1.As a result, the error rate in an echo signal acquisition 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 the quality of the functionality of an ultrasonic sensor according to the invention is also reduced.

[0025] The aforementioned interference signals often have an amplitude AS that is much lower than the amplitude AE ​​of object echo signals, thus satisfying the inequality AS << AO. This usually applies to an environmental area extending from the ultrasonic sensor to a distance of 3 m, since echo signals with a large amplitude AO are to be expected in this environmental area. Due to the smaller amplitude AS of the interference signals, differentiation between interference signals and object echo signals can preferably still be performed based on an evaluation of the corresponding correlation signal X(t).However, 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(τ) of the correlation filter, the differentiation between interference signals and object echo signals based on the correlation factor R(t) calculated for the received echo signals is difficult to perform.

[0026] Preferably, in a case where interference signals are received that are correlated with the correlation filter used, a simple solution is proposed in which the correlation filter used is replaced with another correlation filter that has a narrower frequency spectrum. An ultrasonic sensor according to the invention emits ultrasonic signals, particularly in the form of chirps, that have a frequency that lies within a frequency spectrum similar to the narrower frequency spectrum of the additional correlation filter. In this case, there is a high probability that the narrower frequency spectrum of the additional correlation filter is not comparable with the frequency spectrum of the received interference 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, the correlation filter used cannot be replaced, so that in such cases the solution just mentioned is not applicable. This is particularly true for an environmental area located very close to an ultrasonic sensor according to the invention, which extends from the ultrasonic sensor to a distance of approximately 60 cm and for which the differentiation between object echo signals and those originating from low-energy sources is particularly important. Examples of such signals originating from low-energy sources are noise signals and echo signals resulting from weak reflections on license plates or other parts of a vehicle with an ultrasonic sensor according to the invention.A correlation factor R(t) calculated for these signals originating from low-energy sources usually has a high amplitude, which impairs the object detection described above.

[0027] According to the invention, each measurement signal s(t) is the corresponding received signal e(t). According to the invention, each transmitted ultrasonic signal comprises a first ultrasonic signal portion that is not correlated with the correlation filter and a second ultrasonic signal portion that is correlated with the correlation filter. The first ultrasonic signal portion of each ultrasonic signal to be transmitted is transmitted before or after the corresponding second ultrasonic signal portion. Alternatively, according to the invention, each transmitted ultrasonic signal comprises a first ultrasonic signal portion that is not correlated with the correlation filter, a second ultrasonic signal portion that is correlated with the correlation filter, and a third ultrasonic signal portion that is not correlated with the correlation filter.The second ultrasonic signal part of each ultrasonic signal to be transmitted is transmitted after the corresponding first ultrasonic signal part and before the corresponding third ultrasonic signal part.

[0028] Preferably, in the presence of each received signal e(t) whose correlation factor R(t) falls below a first limit value for a first period of time and has a maximum which is immediately after the expiration of the first period of time or before the beginning of the first period of time and which exceeds a second limit value which is greater than the first limit value, it is recognized that the corresponding received signal e(t) originates from an echo signal created by reflection on the at least one object.Further preferably, in the presence of each received signal e(t) whose correlation factor R(t) falls below a first limit value for a first period and also for a second period lying after the expiration of the first period and has a maximum which lies immediately after the expiration of the first period and before a start of the second period and exceeds a second limit value which is greater than the first limit value, it is recognized that the corresponding received signal e(t) originates from an echo signal created by reflection on the at least one object.

[0029] Preferably, a length of the first period is determined as a function of a signal duration of the first ultrasonic signal part of each emitted ultrasonic signal and / or a length of the second period is determined as a function of a signal duration of the third ultrasonic signal part of each ultrasonic signal.

[0030] If an ultrasonic signal is emitted which comprises a first ultrasonic signal part not correlated with the correlation filter and a second ultrasonic signal part correlated with the correlation filter, an echo signal is generated by reflection of this ultrasonic signal which, in accordance with the emitted ultrasonic signal, comprises a first echo signal part not correlated with the correlation filter and a second echo signal part correlated with the correlation filter.

[0031] If an object echo signal is received by the ultrasonic sensor, the first object echo signal component is uncorrelated with the correlation filter, and the second object echo signal component is correlated with the correlation filter. Since the first object echo signal component is correlated with the correlation filter, the correlation factor R(t) calculated for the corresponding measurement signal s(t), which corresponds to 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 component and in which the amplitude of the corresponding correlation factor R(t) has a relatively low first value.Since the second object echo signal component is correlated with the correlation filter, the corresponding correlation factor R(t) has a range, also referred to as a peak, which corresponds to a reception of the second object echo signal component and in which the corresponding correlation factor R(t) has a maximum with a second value that is significantly higher than the first value. Depending on the quality of the corresponding object echo signal, the second value can be close to 1. It should be noted here that the amplitude AO of object echo signals is generally significantly higher than the amplitude AB of background echo signals. Since the first object echo signal component is not correlated with the correlation filter, the amplitude of this correlation signal X(t) occurring in a range of a correlation signal X(t) calculated for the corresponding measurement signal s(t) corresponding to the reception of the first object echo signal component is small.This small 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 measurement signal s(t). This is the reason why such a correlation factor R(t) has an amplitude in its range corresponding to the reception of the first part of the object echo signal that assumes a first value that is significantly lower than a second value, which is the maximum value assumed by the correlation factor R(t) in its range corresponding to the reception of the second part of the object echo signal. Each correlation factor R(t) has a gap and a peak, with the gap lying before or after the peak.

[0032] In a case where the transmitted ultrasonic signal further comprises a third ultrasonic signal part that is not correlated with the correlation filter, and where the second ultrasonic signal part is transmitted 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, with one gap being before the peak and another gap being after the peak.

[0033] Consequently, according to the invention, an ultrasonic signal transmission method and an echo signal detection algorithm are provided by which object echo signals and background echo signals can be differentiated from one another on the basis of an evaluation of the correlation factor R(t) calculated for each of them, even if an amplitude of a correlation factor R(t) calculated for the resulting background echo signals and a correlation factor R(t) calculated for the resulting object echo signals, occurring during the transmission of ultrasonic signals correlated with the correlation filter, each assumes such a high value that no differentiation can be carried out between these two amplitudes.

[0034] In a particular embodiment of the invention, each transmitted ultrasonic signal is correlated with the correlation filter. For each received signal, a corresponding further signal h(t) is used which is dependent on the time t and is in particular a corresponding harmonic signal. Furthermore, each further signal h(t) is not correlated with the correlation filter and has an amplitude AAh which is on the order of magnitude of an amplitude AAS of each received signal which originates from a corresponding echo signal of the received echo signals which did not arise from reflection from the at least one object and is in particular an interference signal. Preferably, each received signal e(t) is mixed with the corresponding further signal h(t) to generate a corresponding mixed signal s(t). Each measured signal s(t) is the mixed signal s(t) generated using the corresponding received signal e(t).Further preferably, each measurement signal s(t) is the corresponding received signal e(t). The correlation factor R(t) to be determined for each received signal e(t) is determined according to the modified relation. R(t) = where Ne is a positively defined norm of the corresponding received signal e(t) and Nh is a positively defined norm of the further signal h(t).

[0035] In the invention, the norm Ne of the received signal e(t) is / are preferably determined according to the relation Ne=∫0Te2(t+τ)dτ and / or the norm Ns of the measurement signal s(t) preferably according to the relation Ns=∫0Ts2(t+τ)dτ and / or the norm Nh of the further signal h(t) preferably according to the relation Nh=∫0Th2(t+τ)dτ and / or the norm NF of the response signal F(τ) of the correlation filter preferably according to the relation NF=∫0TF2(τ)dτ calculated.

[0036] Preferably, if each mixed signal s(t) whose correlation factor R(t) has a maximum that exceeds a predefined limit is present, it is recognized that the received signal e(t) by means of which the corresponding mixed signal s(t) was generated originates from an echo signal generated by reflection from the at least one object. Further preferably, if each received signal e(t) whose modified, determined correlation factor R(t) has a maximum that exceeds a predefined limit is present, it is recognized that the corresponding received signal e(t) originates from an echo signal generated by reflection from the at least one object.

[0037] By receiving interference signals or echo signals to be suppressed, which have a small amplitude AS and are caused by reflection of emitted ultrasonic pulses on objects with a known position, such as by reflection of emitted ultrasonic pulses on a license plate or bumper of a vehicle with an ultrasonic sensor according to the invention, the global value level of the amplitude of a correlation coefficient K(t) calculated for the received signals e(t) generated directly from the received echo signals increases.The effect of the interference signals or the echo signals to be suppressed on a correlation coefficient K(t) calculated for each of the received signals e(t) can be suppressed by mixing, in particular by means of hardware elements, 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 this case, neither the frequency of the ultrasonic signals emitted by an ultrasonic sensor according to the invention needs to be changed nor the correlation filter needs to be replaced. For this purpose, the corresponding measurement signal s(t) generated by mixing a further signal h(t) with the corresponding received signal e(t) is used to calculate each correlation factor K(t), and not the corresponding unchanged received signal e(t).The frequency of the additional signal h(t), generated in particular in the form of a harmonic signal, should be selected such that it is contained in a frequency spectrum that is far removed from the frequency spectrum of the correlation filter but still within the bandwidth of the corresponding measuring device. The additional signal h(t) must have an amplitude AAh that is comparable to the amplitude AAS of a received signal e(t) generated directly from an interference signal or an echo signal to be suppressed, but much lower than the minimum amplitude AAO of a received signal e(t) generated directly from an object echo signal, which is to be reliably detected by the measuring device according to the invention. This means that the amplitude of the additional signal h(t) should, in particular, satisfy the inequality AAh < AAS << AAO.

[0038] This limits or reduces the amplitude value of the correlation factor K(t) calculated for the mixed signals s(t) generated by interference signals or echo signals to be suppressed. At the same time, the amplitude value of the correlation factor K(t) calculated for the mixed signals s(t) generated by object echo signals remains virtually unchanged, allowing optimal detection of high-amplitude echo signals. This significantly reduces the error rate of object detection according to the invention. Here, each measurement signal s(t) corresponds to the corresponding mixed signal s(t).

[0039] The effect of mixing another signal h(t) with each received signal e(t) generated directly from a received echo signal by the ultrasonic sensor can also be achieved by changing the relationship for determining each correlation factor K(t) calculated for the corresponding measurement signal s(t), which in this case corresponds to the received signal e(t) generated directly from the corresponding echo signal. To do so, in the expression of the corresponding correlation factor K(t), the norm Ns of the measurement signal s(t) is replaced with the norm Ne of a corresponding received signal e(t), increased by the Pythagorean addition of the norm Nh of another signal h(t) as described above.

[0040] In a case where an interference signal correlated with the correlation filter is received by an ultrasonic sensor according to the invention, and where the corresponding measurement signal s(t) matches the received signal e(t) generated directly from an interference signal, the effect of the interference signal will be reflected both in the correlation signal X(t) calculated for this measurement signal s(t) and in the norm Ns of this measurement signal s(t). The relation X(t) ≈ Ns*NF applies to the correlation signal X(t) calculated for the received signal e(t) generated directly from the interference signal, whereby for each norm Ns and NF, a corresponding relation of the three previously specified relations is used to calculate norms. Furthermore, the relation R(t) = X(t) / (Ns*NF) ≈ 1 applies to the corresponding correlation factor R(t).This means that the correlation factor K(t) calculated for received signals e(t) generated directly from interference signals assumes a high value close to 1.

[0041] In a further case in which an interference signal correlated with the correlation filter is received by means of an ultrasonic sensor according to the invention, and in which the measurement signal s(t) is generated by mixing 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 interference signal, the correlation signal X(t) calculated for the measurement signal s(t) generated upon reception of the interference 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 measurement signal s(t) is increased by the norm Nh of the further signal h(t) compared to the norm of the corresponding received signal e(t).For clarification, in the following relation and in the following two inequalities, the parameters calculated for the measurement signal s(t) generated upon receipt of the interference signal and containing the further signal h(t) are supplemented with the index "m", and the corresponding parameters calculated for the reception signal e(t) generated directly from the interference signal are supplemented with the index "nm". Here, the correlation signal Xm(t) calculated for this measurement signal s(t) and the correlation signal Xnm(t) calculated for the corresponding reception signal e(t) satisfy the relation Xm(t) ≈ Xnm(t), and the norm Nsm calculated for this measurement signal s(t) and the norm Nenm calculated for the corresponding reception signal e(t) satisfy the inequality Nsm > Nenm. Here, the correspondingly calculated correlation factors Km(t) and Knm(t) therefore also satisfy the inequality Km(t) < Knm(t).This means that the amplitude of the correlation factor Km(t) calculated for the measurement signal s(t) generated upon reception of the interference signal and containing the further signal h(t) is limited to a value which depends on the amplitude AS of the corresponding interference signal and on the amplitude AAh of the further signal h(t).

[0042] Furthermore, another case is considered in which an object echo signal correlated with the correlation filter is received by means of an ultrasonic sensor according to the invention, and in which the corresponding measurement signal s(t) is generated by mixing 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 interference 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 measurement signal s(t) generated upon 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 additional signal h(t) is significantly smaller 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 measurement signal s(t) and the norm Ns of this measurement signal s(t) depend primarily on the amplitude AAO of the received signal e(t) generated directly from the object echo signal. In the following three relations, the parameters calculated for the measurement signal s(t) containing the additional signal h(t) and generated upon reception of the object echo signal are supplemented with the index "m," and the corresponding parameters 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 measurement 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 measurement signal and the norm Nenm calculated for the corresponding received signal e(t) satisfy the relation Nsm ≈ Nenm. Consequently, the corresponding correlation factors Km(t) and Knm(t) also 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 measurement signal s(t) remains almost unchanged compared to the correlation factor Knm(t) calculated for the received signal e(t) generated directly from the object echo signal.

[0043] Preferably, a corresponding output signal s(t) of an additive mixer is used for each mixed signal s(t), wherein to generate the corresponding output signal s(t) the corresponding received signal e(t) is provided as an input signal to the mixer and the corresponding further signal h(t) is provided as a further input signal to the mixer.

[0044] Preferably, for each mixed signal s(t) a corresponding digital output signal s(t) of an analog-to-digital converter is used, wherein to generate the corresponding digital output signal s(t) the corresponding received signal e(t) is applied as input signal to the

[0045] Analog-to-digital converter is provided and for the corresponding further signal h(t) 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-to-digital converter.

[0046] Further preferably, a corresponding digital output signal s(t) of an analog-to-digital converter is used for each mixed signal s(t), wherein, to generate the corresponding digital output signal s(t), the corresponding received signal e(t) is transmitted via a line of two capacitively coupled lines and is provided as an input signal to the analog-to-digital converter, and the corresponding further signal h(t) is transmitted via a further line of the two lines and is provided as a further input signal to the analog-to-digital converter.

[0047] Preferably, each further signal h(t) is generated in the form of a harmonic signal by means of an oscillator. Short description of the drawings

[0048] Embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawings: Fig. 1 shows a curve of a signal strength s't of a composite measurement signal s'(t) as a function of a time t, a curve of a value X't of a correlation signal X(t) calculated for this measurement signal s'(t) as a function of time t, and a curve of a value R't of a correlation factor R'(t) calculated for this measurement signal s'(t) as a function of time t, wherein the composite measurement signal s'(t) is generated during an object detection carried out according to a first embodiment of the invention, Fig. 2 and Fig. 3 shows a curve of a value R'd of a correlation factor R'(d) calculated for a composite measurement signal s'(t) as a function of a distance d measured by an ultrasonic sensor used, wherein the composite measurement signal s'(t) is generated during an object detection carried out according to a first embodiment of the invention, Fig. 4 shows a curve of a signal strength U of an ultrasonic signal U(t) emitted during the object detection carried out according to a second embodiment of the invention as a function of a time t, Fig. 5 to 8 each show a curve of a value R'd of a correlation factor R'(d) calculated for a composite measurement signal s'(t) as a function of a distance d measured by an ultrasonic sensor used, wherein the composite measurement signal s'(t) is generated during an object detection carried out according to the second embodiment of the invention, Fig. 9 shows a curve of a signal strength et of a composite received signal e'(t) as a function of time t, a curve of a value X't of a correlation signal X'(t) calculated for a composite measurement signal s'(t) as a function of time t, a curve of a value h't of a composite further signal h'(t) as a function of time t, and a curve of a value R't of a correlation factor R'(t) calculated for the composite measurement signal s'(t) as a function of time t, wherein the composite received signal e'(t), the composite measurement signal s'(t), and the composite further signal h'(t) are generated during an object detection carried out according to a third embodiment of the invention, Fig. 10-14 each show a configuration for realizing an object detection carried out according to the third embodiment of the invention, and, Fig. 15 shows a curve of a value R'd of a correlation factor R'(d) calculated for a composite measurement signal s'(t) as a function of a distance d measured by an ultrasonic sensor used, wherein the composite measurement signal s'(t) is generated during an object detection carried out according to the third embodiment of the invention. Embodiments of the invention

[0049] In principle, an ultrasonic sensor can transmit ultrasonic signals, each of which is correlated with a correlation filter of a correlation module. Furthermore, the ultrasonic sensor generates a received signal e(t) from each echo signal generated by reflections of the transmitted ultrasonic signals and received by the ultrasonic sensor. This received signal corresponds to a corresponding measurement signal s(t). Each measurement signal s(t) is correlated with a corresponding response signal F(τ) of the correlation filter, which depends on a variable τ, to generate a corresponding correlation signal X(t).

[0050] The correlation module calculates the corresponding correlation signal X(t) for each measurement signal s(t) and consequently also for each received echo signal according to relation (1) already given in the general description. In relation (1), T is a length of the correlation filter and F*(τ) is the corresponding complex conjugate response signal of the correlation filter. X(t)=∫0Ts(t+τ)⋅F*(τ)dτ

[0051] Furthermore, the correlation module calculates a correlation factor R(t) for each measurement signal s(t) and consequently also for each received echo signal according to the relation (2) already given in the general description. R(t)=X(t)Ns⋅NF=∫0Ts(t+τ)⋅F*(τ)dτ∫0Ts2(t+τ)dτ⋅∫0TF2(τ)dτ

[0052] In relation (2), Ns is a positively defined norm of the measurement signal s(t) and NF is a positively defined norm of the response signal F(τ) of the correlation filter. From relation (2), it is clear how the correlation module calculates these norms Ns and NF.

[0053] In order to detect at least one object located in the vicinity of the ultrasonic sensor, reception of object echo signals, which are generated by reflection of the emitted ultrasonic pulses on at least one object located in the vicinity of the ultrasonic sensor, is detected by means of an evaluation of the correlation signal X(t) calculated for received echo signals and / or the correlation factor R(t) calculated for received echo signals.

[0054] It should be noted that in addition to the object echo signals, the ultrasonic sensor can also receive background echo signals, which are created by reflection of the emitted ultrasonic signals from many small particles of a ground or subsurface surface in the vicinity of the ultrasonic sensor, and / or interference signals that are correlated with the correlation filter.

[0055] Since the amplitude AB of background echo signals and the amplitude AS of interference signals are generally each substantially smaller 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 interference signals and object echo signals can be optimally carried out based on an evaluation of the correlation signal X(t) calculated for each received echo signal.

[0056] Since both the background echo signals and the interference signals are correlated with the correlation filter, both the correlation factor R(t) calculated for the background echo signals or interference signals and the correlation factor R(t) calculated for the object echo signals have an amplitude with a high value, which can also be close to 1. As a result, in an object detection carried out according to the first embodiment of the invention, it becomes difficult to differentiate between background echo signals or interference signals and object echo signals based on an evaluation of the correlation factor R(t) calculated for each received echo signal.

[0057] For example, if an ultrasonic sensor is installed in a vehicle, it can often happen during fine adjustment of this ultrasonic sensor that the corresponding measuring device detects an interference signal caused by the reflection of an emitted ultrasonic signal from parts of the vehicle or a vehicle bumper that are located at a fixed distance from the ultrasonic sensor. Since such an interference signal is correlated with the correlation filter, the amplitude of the correlation factor R(t) calculated for such an interference signal has a high value, which can be close to 1. If the correlation factor R(t) calculated for each received echo signal is evaluated for object detection, such objects located at a fixed distance from the ultrasonic sensor are continuously detected.Therefore, a threshold value used in the evaluation of a correlation factor R(t) calculated for each received echo signal for detecting object echo signals is preferably selected in such a way that detection of interference signals is suppressed in such an evaluation.

[0058] Fig. Figure 1 shows a signal strength curve s't of a measurement signal s'(t) composed of two measurement signals s(t) that, during an object detection, each correspond to the received signal e(t) generated directly from a corresponding echo signal of two received echo signals, as a function of time t. This shows that the ultrasonic sensor first received an unwanted echo signal, which may be a background echo signal or an interference signal, and then an object echo signal. A portion of the composite measurement signal s'(t) corresponding to reception of the unwanted echo signal is labeled UE, and a portion of the composite measurement signal s'(t) corresponding to reception of the object echo signal is labeled OE.

[0059] Fig. 1 also shows a curve of a value X't of the Fig. 1 shows the correlation signal X'(t) calculated from the composite measurement signal s'(t) as a function of time t. It can be seen that an amplitude that this correlation signal X'(t) has in a range XtU corresponding to the reception of the unwanted echo signal is significantly smaller than an amplitude that this correlation signal X'(t) has in a range XtO corresponding to the reception of the object echo signal.

[0060] Fig. 1 also shows a history of a value R'T of a for the Fig. 1, calculated from the composite measurement signal s'(t) as a function of time t. It can be seen that an amplitude of this correlation factor R'(t) in a range RtU corresponding to the reception of the unwanted echo signal is close to 1 and is therefore comparable to an amplitude of this correlation factor R'(t) in a range RtO corresponding to the reception of the object echo signal.

[0061] Fig. Figure 2 shows a curve of a value R'd of a further correlation factor K'(d) plotted as a function of a distance d measured by the ultrasonic sensor in meters. This value is obtained by plotting a correlation factor R'(t) calculated for a measurement signal s'(t) composed of the measurement signals s'(t) generated upon reception of background echo signals and two object echo signals as a function of this distance d and is therefore equivalent to this correlation factor R'(t). It should be noted here that the distance d measured by the ultrasonic sensor is traversed by a corresponding echo signal from its point of origin to the ultrasonic sensor at the speed of sound and can therefore be calculated as the product of the speed of sound and the elapsed time t. Fig. 2, each range of this further correlation factor R'(d) corresponding to the reception of background echo signals is labelled RdB and each range of this further correlation factor R'(d) corresponding to the reception of an object echo signal is labelled RdO.

[0062] Fig. Figure 3 shows a curve of a value R'd of a further correlation factor K'(d) obtained for a measurement signal s'(t) composed of the measurement signals s(t) generated upon reception of interference signals and an object echo signal, as a function of a distance d measured in centimeters by the ultrasonic sensor. Fig. 3, each range of this further correlation factor K'(d) corresponding to the reception of interference signals is labelled KdS and a range of this further correlation factor K'(d) corresponding to the reception of the object echo signal is labelled RdO. In the representation based on an actual measurement from the Fig. 3, interference signals were received by means of an ultrasonic sensor according to the invention with a dynamic range between 1.5 V and +1.5 V, from which a reception signal with an amplitude of 20 mV was generated by means of the ultrasonic sensor.

[0063] From the Fig. 2 and Fig. 3 it is evident that the further correlation factor R'(d) shown in each range RdB or RdS, which corresponds to a reception of background echo signals or of interference signals, has a very large number of maxima, each of which assumes a high value and in some cases is close to 1. From the Fig. 2 and Fig. 3 it is further evident that each further correlation factor R'(d) shown has a maximum in each range RdO, which corresponds to the reception of an object echo signal, which also assumes a high value close to 1. Consequently, for these in the Fig. 2 and Fig. 3, object detection is difficult to carry out on the basis of an evaluation of the further correlation factor R(d) obtained for the measurement signals s(t) generated upon reception of the background echo signals or interference signals and the at least one object signal, and consequently also on the basis of an evaluation of the further correlation factor R'(d) obtained for the measurement signal s'(t) composed of these measurement signals s(t).

[0064] Ultrasonic signals are emitted by an ultrasonic sensor according to the invention, each comprising a first ultrasonic signal portion that is not correlated with the correlation filter and is also referred to as a gap signal portion or gap pulse, and a second ultrasonic signal portion that is correlated with the correlation filter and is also referred to as a peak signal portion or peak pulse. The first ultrasonic signal portion of each ultrasonic signal to be emitted is emitted before the second ultrasonic signal portion.

[0065] Fig. Figure 4 shows a curve of the signal strength Ut of the ultrasonic signal U(t) emitted by an ultrasonic sensor according to the invention as a function of the time t measured in milliseconds. Fig. 4, a region of the ultrasonic signal U(t) corresponding to a transmission of the first ultrasonic signal portion is labeled U1, and a region of the ultrasonic signal U(t) corresponding to a transmission of the second ultrasonic signal portion is labeled U2. If an ultrasonic signal U(t) is transmitted that includes a first ultrasonic signal portion uncorrelated with the correlation filter and a second ultrasonic signal portion correlated with the correlation filter, reflection of this ultrasonic signal produces an echo signal that, corresponding to the transmitted ultrasonic signal, includes a first echo signal portion uncorrelated with the correlation filter and a second echo signal portion correlated with the correlation filter. In the second embodiment of the invention, each received signal e(t) generated directly from the corresponding echo signal also matches the corresponding measurement signal s(t).

[0066] A received echo signal can be an object echo signal or a background echo signal. If an object echo signal is received by the ultrasonic sensor, the first object echo signal component is uncorrelated with the correlation filter, and the second object echo signal component is correlated with the correlation filter. Since the first object echo signal component is uncorrelated with the correlation filter, the correlation factor R(t) calculated for the corresponding measurement signal s(t) has an amplitude with a relatively low first value in a region, also referred to as a gap, which corresponds to the reception of the first object echo signal component.Since the second object echo signal portion of a transmitted ultrasonic pulse is correlated with the correlation filter, the corresponding correlation factor R(t) exhibits a maximum in a region known as the peak, which corresponds to the reception of the second object echo signal portion, with a second value that is significantly higher than the first value. Depending on the quality of the corresponding object echo signal, the second value can be close to 1.

[0067] The Fig. 5, Fig. 6, Fig. 7 and Fig. 8 each show a curve of a value R'd of a further correlation factor R'(d) obtained for a measurement signal s'(t) composed of the measurement signals s(t) generated upon reception of background echo signals and of at least one object echo signal as a function of the previously introduced distance d. In the representation from the Fig. 5 the distance d is given in meters and in the representation from each of the Fig. 6 to 8 measured in centimeters. In each of the Fig. 5 to 8, each peak of the corresponding further correlation signal R(d) and consequently also of the further correlation signal R'(t) occurring upon reception of an object echo signal is designated RdPO, and each gap of the corresponding further correlation factor R(d) and consequently of the further correlation factor R'(d) occurring upon reception of an object echo signal is designated RdLO. All other areas of each Fig. The further correlation factor R'(d) shown in Figures 5 to 8 correspond to the reception of background echo signals and are calculated from the Fig. 5 to 8 not marked.

[0068] Unlike the Fig. 2 is from the Fig. 5 it is easy to see that two object echo signals were received. Furthermore, from each of the Fig. 6 to 8, it is very easy to recognize that an object echo signal was received in each case. Since the presence of a gap-peak combination in the curve of the value R'd of the further correlation factor R'(d) causes a signature of the further correlation factor R'(d), based on which the reception of an object echo signal is clearly recognizable, a predetermined algorithm is preferably used in the object detection carried out. In this algorithm, a maximum of the further correlation signal R'(d) is assigned to a reception of an object echo signal if the value of this maximum exceeds a higher threshold value SWh and, at the same time, the amplitude of a predetermined number of maxima of the further correlation signal R'(d) occurring immediately before the maximum exceeding the higher threshold value SWh each remains below a threshold value SWn that is lower than the higher threshold value SWh.This number of maxima depends on the length of the aforementioned gap signal portion or gap pulse of a transmitted ultrasonic signal U(t). The higher threshold value SWh and the lower threshold value SWn are each specified in the . Fig. 5 is shown.

[0069] In the object detection performed, in which the emitted ultrasonic signals each have a gap signal component and a pulse signal component, and in which the aforementioned algorithm is used, the false detection rate of objects is significantly lower than in the object detection performed 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 receiving a background echo signal in the curve of the value R'd of the further correlation factor R'(d) is much lower than the probability with which only a single high maximum or peak occurs as a result of receiving a background echo signal in the aforementioned curve.

[0070] The representations from the Fig. 6 to 8 are based on actual measurements. From each of the Fig. 6 to 8, the gap-pulse combination observed in the corresponding measurement and occurring in the corresponding course of the value R'd of the corresponding further correlation factor R'(d) is easily visible. From each of the Fig. 6 to 8 it is also easily apparent that the gap signal part or gap pulse of the emitted ultrasonic signal or ultrasonic pulse causes an "open area" in the course of the value R'd of the corresponding further correlation factor R'(d), which is located immediately before the maximum or peak of this further correlation factor R'(d) that occurred upon reception of the corresponding object echo signal, and that the corresponding object echo signal originates in each case from the surrounding area of ​​the ultrasonic sensor in which background echo signals can arise.

[0071] It can be provided that for each received signal e(t) generated directly from a corresponding echo signal, a corresponding further signal h(t) dependent on time t, which is in particular a corresponding harmonic signal, is used. Each further signal h(t) is not correlated with the correlation filter and has an amplitude that is on the order of magnitude of an amplitude AAS of each received signal e(t) generated directly from a corresponding interference signal and is therefore significantly smaller than an amplitude AAO of each received signal e(t) generated directly from a corresponding object echo signal.

[0072] The emitted ultrasonic signal can be correlated with the correlation filter.

[0073] Each received signal e(t) can be additively mixed with the corresponding further signal h(t) to generate a corresponding mixed signal s(t). Each mixed signal s(t) corresponds to the corresponding measured signal s(t). Furthermore, each measured signal s(t) is correlated with the corresponding response signal F(τ) of the correlation filter used to generate a corresponding correlation signal X(t). Each correlation signal X(t) is also calculated according to relation (1) and / or each correlation factor R(t) is calculated according to relation (2).

[0074] The effect of mixing a further signal h(t) with each received signal e(t) generated directly from a received echo signal by the ultrasonic sensor can preferably also be achieved by using the corresponding received signal e(t) for each measurement signal s(t) and using a modified relation to determine each correlation factor K(t) to be calculated for the corresponding measurement signal s(t). Each correlation factor R(t) is calculated according to the modified relation (3) already given in the general description, where Ne is a positively defined norm of the corresponding received signal e(t) and Nh is a positively defined norm of the further signal h(t). From relation (3) it is easily apparent how the norm Nh of the further signal h(t) is calculated. R(t) =

[0075] In a case where 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 adding the small harmonic signal h(t) to the received signal e(t) and thus determined according to relation (4). s(t)=e(t)+h(t)

[0076] If the expression s(t) in relation (2) used to determine the correlation factor R(t) is replaced with the sum between the received signal e(t) and the harmonic signal h(t) given in relation (4), the result is relation (5) for calculating the correlation factor R(t). R(t)=∫0T(e(t+τ)+h(t+τ))⋅F*(τ)dτ∫0T(e2(t+τ)+2e(t+τ)h(t+τ)+h2(t+τ))dτ⋅∫0TF2(τ)dτ

[0077] It was assumed that the harmonic signal h(t) is not correlated with the response signal F(τ) of the correlation filter. Therefore, in the numerator of the fraction occurring in relation (5), the value of the function h(t) vanishes according to the expression ∫0Th(t+τ)⋅F*(τ)dτ calculated term, so that in the mentioned numerator only the term according to the expression ∫0Te(t+τ)⋅F*(τ)dτ Since the harmonic signal h(t) is mean-free and not correlated with e(t), the fraction calculated according to the expression ∫0T2e(t+τ)h(t+τ)dτ calculated term, which directly results in the modified relation (3) for determining the correlation factor R(t).

[0078] More preferably, the aforementioned effect can also be achieved by using the corresponding received signal e(t) for each measured signal s(t) and using relation (3) to determine each correlation factor K(t) to be calculated for the corresponding measured signal s(t), wherein a positive, in particular constant, factor Fh is used instead of the norm Nh of the further signal h(t). In this case, the norm Ns occurring in the expression of the corresponding correlation factor R(t) calculated according to relation (2) for each measured signal s(t) corresponding to the corresponding received signal e(t) is increased by Pythagorean addition of said factor Fh.

[0079] A received echo signal can be an object echo signal or an interference signal.

[0080] During the object detection process, a time window is preferably defined during which each received signal e(t) is preferably mixed with a corresponding further signal h(t), which is in particular a corresponding harmonic signal, to generate a corresponding mixed signal s(t). Each correlation signal R(t) is calculated according to relation (2) for each measurement signal s(t) that matches the corresponding mixed signal s(t).

[0081] Alternatively, during the specified time window, the correlation factor R(t) is calculated for each received signal e(t) matching the corresponding measurement signal s(t) according to relation (3). This reduces the amplitude of the correlation factor R(t) calculated for received interference signals with a small amplitude AS. Preferably, the amplitude of each additional signal h(t) or each additive factor Fh is increased such that the effect of the received interference signals on a correlation factor R'(t) calculated for a measurement signal s'(t) composed of the measurement signals s(t) generated upon reception of echo signals is suppressed.Consequently, by evaluating the correlation factor R(t) calculated for each of the received echo signals and consequently also the correlation factor R'(t) calculated for the measurement signal s'(t) composed of the measurement signals s(t) generated upon reception of echo signals, echo signals each having a large amplitude can continue to be detected.

[0082] In a case in which the ultrasonic sensor or a corresponding control unit or a corresponding microcontroller (ECU) detects interference signals, that is to say in a case in which, based on an evaluation of the correlation factor R(t) calculated for received echo signals, too many received echo signals are detected, for which the distance d extending between a respective location of origin of these signals and the ultrasonic sensor changes from measuring cycle to measuring cycle, an increase in the amplitude of the further signal h(t) or of the aforementioned additive factor Fh is preferably initiated by means of the ultrasonic sensor and carried out until the detection of the received echo signals carried out based on the evaluation of the correlation factor R(t) calculated for received echo signals again reaches the desired quality.

[0083] Fig. Figure 9 shows a signal strength curve e't of a received signal e'(t) composed of two received signals e(t), each generated directly from a corresponding echo signal from two received echo signals, as a function of time t. This shows that the ultrasonic sensor first received an interference signal and then an object echo signal. A region of the composite received signal e'(t) corresponding to reception of the interference signal is labeled SE, and a region of the composite received signal e'(t) corresponding to reception of the object echo signal is labeled OE.

[0084] Fig. 9 further shows a curve 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 by means of a corresponding one of the two received signals e(t) generated during the reception of the interference signal and the object echo signal, as a function of time t. Each received signal e(t) is mixed with a corresponding one of two further signals h(t) used to generate a corresponding one of the two mixed signals s(t). Here, each of the two mixed signals s(t) corresponds to the corresponding measurement signal s(t). As can be seen from the Fig. 1, is also from the Fig. 9 that an amplitude that this correlation signal X'(t) has in a range XtS corresponding to the reception of the interference signal is significantly smaller than an amplitude that this correlation signal X'(t) has in a range XtO corresponding to the reception of the object echo signal.

[0085] Fig. 9 also shows a curve of a value h't of a further signal h'(t) composed of the two used further signals h(t) as a function of time t. A portion of the composite further signal h'(t) used for the received signal generated directly from the interference signal is designated htS, and a portion of the composite further signal h'(t) used for the received signal generated directly from the object echo signal is designated htO.

[0086] Fig. Figure 9 further shows a curve of a value R't of a correlation factor R'(t) calculated for the composite measurement signal s'(t) just mentioned as a function of time t. Unlike from the Fig. 1, is from the Fig. 9 that an amplitude having this correlation factor R'(t) in a range RtS corresponding to the reception of the interference signal is significantly smaller than an amplitude having this correlation factor R'(t) in a range RtO corresponding to the reception of the object echo signal.

[0087] Each of the Fig. 10 to 14 show a different configuration for the realization of an object detection.

[0088] Fig. Figure 10 shows a general configuration in which the corresponding received signal e(t) and the corresponding further signal h(t) are additively mixed to generate each mixed signal s(t).

[0089] Fig. Figure 11 shows a hardware-based configuration in which, to generate each mixed signal s(t), the corresponding received signal e(t) is provided as an input signal and the corresponding additional signal h(t) is provided as a further input signal to an additive mixer 10. Each mixed signal s(t) is the corresponding output signal s(t) of the mixer 10. The amplitude of the mixed signal s(t) can be varied using the mixer 10.

[0090] Fig. 12 shows a further hardware-based configuration in which, to generate each mixed signal s(t), the corresponding received signal e(t) is provided to an analog-to-digital converter 20 as an 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-to-digital converter 20. Each mixed signal s(t) here is the corresponding output signal s(t) of the analog-to-digital converter 20.

[0091] Fig. 13 shows another hardware-based configuration in which, to generate each mixed signal s(t), the corresponding received signal e(t) is transmitted via a line 30 of two capacitively coupled lines 30, 35 and provided as an input signal to an analog-to-digital 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 provided as a further input signal to the analog-to-digital converter 20. Each mixed signal s(t) is here the corresponding output signal s(t) of the analog-to-digital converter 20. The strength of the capacitive coupling between the two lines 30, 35 can be controlled here via a value of an amplitude AAh of the corresponding further signal h(t).

[0092] For each in one of the Fig. In the implementation shown in Figures 10 to 13, each mixed signal s(t) corresponds to the corresponding measurement signal s(t) and is correlated with the corresponding response signal F(τ) of a correlation filter to generate a corresponding correlation signal X(t). Also, by means of a correlation module 40, each correlation signal X(t) is calculated according to relation (1) and each correlation factor R(t) is calculated according to relation (2).

[0093] Furthermore, each in one of the Fig. 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 a frequency of each harmonic signal can preferably be adjusted.

[0094] Fig. 14 shows a software-based configuration in which the corresponding received signal e(t) is used for each mixed signal s(t), and each mixed signal s(t) is correlated with the corresponding response signal F(τ) of a correlation filter to generate a corresponding correlation signal X(t). The effect of mixing each received signal e(t) with a corresponding further signal h(t) is achieved by using a correlation module 40 to calculate each correlation signal X(t) according to relation (1) and each correlation factor R(t) according to relation (3), in which the norm Nh of a corresponding further signal h(t) is replaced with a corresponding positively defined constant factor Fh. Here, each mixed signal s(t) corresponds to the corresponding measurement signal s(t).

[0095] Fig. Figure 15 shows a curve of a value R'd of a further correlation factor K'(d) obtained for a measurement signal s'(t) composed of the measurement signals s(t) generated upon reception of interference signals and an object echo signal, plotted as a function of a distance d measured in centimeters by the ultrasonic sensor. An actual measurement on which the representation from the Fig. 15 is based, differs from the actual measurement on which the illustration from the Fig. 3, simply because it took 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. Fig. 15 it is easy to see that the further correlation factor R'(d) shown here has an amplitude in each range RdS corresponding to a reception of an interference signal, which has a value that is significantly smaller than a value of a maximum that this further correlation factor R'(d) has in a range RdO corresponding to a reception of the object echo signal. Fig. 15 clearly shows that, during object detection, the effect of the received interference signals on the additional correlation factor R'(d) shown here is suppressed. Thus, the reception of object echo signals can be easily detected based on an evaluation of this additional correlation factor R'(t).

[0096] For example, during an object detection, the correlation factor R(t), which is calculated for background echo signals or for an echo signal generated by reflection from an object located near the ultrasonic sensor, has a high amplitude, which can also be close to 1. Here, the received background echo signals originate from an environmental area that extends from a distance d of 50 cm measured by the ultrasonic sensor to a distance d of 350 cm measured by the ultrasonic sensor. The object in question is located at a distance d of 150 cm measured by the ultrasonic sensor.

[0097] In addition to the above written disclosure, reference is hereby made to the presentation in the Fig. 1 to 15 are referred to.

Claims

[1] Method for detecting at least one object based on ultrasonic signals (U(t)) reflected therefrom, in which echo signals which are produced by reflection of ultrasonic signals (U(t)) emitted by the ultrasonic sensor are received by means of an ultrasonic sensor, wherein from each received echo signal a corresponding received signal (e(t)) is generated by means of the ultrasonic sensor and a corresponding measurement signal (s(t)) which is dependent on a time (t) is generated by means of each received signal (e(t)), which is correlated with a corresponding response signal (F(τ)) of a correlation filter which is dependent on a variable τ in order to generate a corresponding correlation signal (X(t)), characterized bythat for each measurement signal (s(t)) a corresponding correlation factor (R(t)) dependent on the time (t) is determined as a function of the corresponding correlation signal (X(t)), a positively defined norm Ns of the corresponding measurement signal (s(t)) and a positively defined norm NF of the corresponding response signal (F(τ)) and is evaluated for the detection of the at least one object, wherein each measurement signal s(t) is the corresponding received signal e(t) and each transmitted ultrasonic signal (U(t)) comprises a first ultrasonic signal part that is not correlated with the correlation filter and a second ultrasonic signal part that is correlated with the correlation filter, wherein the first ultrasonic signal part of each ultrasonic signal to be transmitted is transmitted before or after the corresponding second ultrasonic signal part, or each transmitted ultrasonic signal comprises a first ultrasonic signal part that is not correlated with the correlation filter, a second ultrasonic signal part that is correlated with the correlation filter, and a third ultrasonic signal part that is not correlated with the correlation filter, wherein the second ultrasonic signal part of each ultrasonic signal to be transmitted is transmitted after the corresponding first ultrasonic signal part and before the corresponding third ultrasonic signal part. [2] Method according to claim 1, wherein each correlation factor (R(t)) is calculated according to the relation R(t)=X(t)Ns⋅NF=∫0Ts(t+τ)⋅F*(τ)dτ∫0Ts2(t+τ)dτ⋅∫0TF2(τ)dτ where T is a length of the correlation filter and F*(τ) is the corresponding complex conjugate response signal of the correlation filter. [3] Method according to one of the preceding claims, wherein in the presence of each received signal e(t) whose correlation factor R(t) falls below a first limit value for a first period of time and has a maximum which is immediately after the expiration of the first period of time or before the beginning of the first period of time and exceeds a second limit value which is greater than the first limit value, it is recognized that the corresponding received signal e(t) originates from an echo signal produced by reflection from the at least one object, or in the presence of each received signal e(t) whose correlation factor R(t) falls below a first limit value for a first period of time and also for a second period of time which is after the expiration of the first period of time and has a maximum,which occurs immediately after the expiration of the first period and before the beginning of the second period and exceeds a second limit value which is greater than the first limit value, it is recognized that the corresponding received signal e(t) originates from an echo signal created by reflection from the at least one object. [4] Method according to claim 3, wherein a length of the first period is determined as a function of a signal duration of the first ultrasonic signal part of each emitted ultrasonic signal (U(t)) and / or a length of the second period is determined as a function of a signal duration of the third ultrasonic signal part of each ultrasonic signal. [5] Method according to claim 4, wherein, in the presence of each mixed signal (s(t)) whose correlation factor (R(t)) has a maximum which exceeds a predefined limit value, it is recognized that the received signal (e(t)) by means of which the corresponding mixed signal (s(t)) was generated originates from an echo signal produced by reflection from the at least one object, or wherein, in the presence of each received signal (e(t)) whose modified correlation factor (R(t)) has a maximum which exceeds a predefined limit value, it is recognized that the corresponding received signal (e(t)) originates from an echo signal produced by reflection from the at least one object. [6] A measuring device for detecting at least one object by means of ultrasonic signals (U(t)) reflected therefrom, wherein the measuring device comprises an ultrasonic sensor which is designed to emit ultrasonic signals (U(t)), to receive echo signals which are produced by reflection of the emitted ultrasonic signals and to generate a corresponding received signal (e(t)) from each received echo signal, wherein the measuring device is designed to generate a measuring signal (s(t)) which is dependent on a time (t) by means of each received signal (e(t)) and to correlate this with a corresponding response signal (F(τ)) which is dependent on a variable τ, of a correlation filter arranged in the measuring device, characterized bythat the measuring device is designed to determine for each measurement signal (s(t)) a corresponding correlation factor (R(t)) which is dependent on time (t) as a function of the corresponding correlation signal (X(t)), a positively defined norm Ns of the corresponding measurement signal (s(t)) and a positively defined norm NF of the corresponding response signal (F(τ)) and to evaluate it for the detection of the at least one object, wherein the measuring device is designed to use the corresponding received signal e(t) for each measurement signal s(t), wherein the ultrasonic sensor is designed to receive ultrasonic signals (U(t)) which each 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,to transmit the first ultrasonic signal part of each ultrasonic signal to be transmitted (U(t)) before or after the corresponding second ultrasonic signal part, or to transmit ultrasonic signals each comprising a first ultrasonic signal part that is not correlated with the correlation filter, a second ultrasonic signal part that is correlated with the correlation filter, and a third ultrasonic signal part that is not correlated with the correlation filter, and to transmit the second ultrasonic signal part of each ultrasonic signal to be transmitted after the corresponding first ultrasonic signal part and before the corresponding third ultrasonic signal part. [7] Measuring device according to claim 6, which is designed to calculate each correlation factor (R(t)) according to the relation R(t)=X(t)Ns⋅NF=∫0Ts(t+τ)⋅F*(τ)dτ∫0Ts2(t+τ)dτ⋅∫0TF2(τ)dτ where T is a length of the correlation filter and F*(τ) is the corresponding complex conjugate response signal of the correlation filter. [8] Measuring device according to claim 6 or 7, which is designed to detect, in the presence of each received signal e(t) whose correlation factor R(t) falls below a first limit value for a first period of time and has a maximum which is immediately after the expiration of the first period of time or before the beginning of the first period of time and exceeds a second limit value which is greater than the first limit value, that the corresponding received signal e(t) originates from an echo signal produced by reflection from the at least one object, or in the presence of each received signal e(t) whose correlation factor R(t) falls below a first limit value for a first period of time and also for a second period of time which is after the expiration of the first period of time and has a maximum,which occurs immediately after the expiration of the first period and before the beginning of the second period and exceeds a second limit value which is greater than the first limit value, to recognize that the corresponding received signal e(t) originates from an echo signal created by reflection from the at least one object. [9] Measuring device according to claim 8, which is designed to determine a length of the first period of time as a function of a signal duration of the first ultrasonic signal part of each emitted ultrasonic signal (U(t)) and / or a length of the second period of time as a function of a signal duration of the third ultrasonic signal part of each emitted ultrasonic signal.

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