KR102289589B1 - Method for detecting an object in a near field of an ultrasonic sensor - Google Patents

Abstract

The present invention relates to a method for detecting an object in the near sound field of an ultrasonic sensor. The method comprises the steps of exciting an acoustic transducer of an ultrasonic sensor by means of a transmission signal, obtaining an attenuation signal 1 describing the attenuation behavior of the acoustic transducer after excitation of the acoustic transducer, the attenuation signal 1 and a reference attenuation signal (2) determining a deviation between the liver and detecting the presence of an object in the near sound field of the ultrasonic sensor based on the determined deviation. Thereby, the near sound field and the object within the measurement range of the ultrasonic sensor can be reliably detected. The near sound field is a region in front of the acoustic transducer of the ultrasonic sensor that cannot be accurately measured by the pulse echo method because the attenuation signal is superimposed on the echo of the transmitted signal.

Description

Method for detecting an object in the near sound field of an ultrasonic sensor

The present invention relates to a method for detecting an object in the near sound field of an ultrasonic sensor.

To measure the distance to an object in front of the ultrasonic sensor, an ultrasonic-based measuring system is used. The ultrasonic sensor used is based on the pulse echo method. In this method, an ultrasonic sensor sends out ultrasonic pulses and measures the reflection (echo) of the ultrasonic pulses caused by the object. The distance between the ultrasonic sensor and the object is calculated from the measured echo propagation time and sound velocity. In this case, the ultrasonic sensor functions as a transmitter and a receiver.

As an ultrasonic sensor in the automotive field, a so-called resonant transducer having post-pulse oscillation after excitation by a transmission signal is used. Echo detection can be performed only when the post-pulse oscillation of the sensor element does not reach a certain level, and the echo signal is similar in magnitude to the post-pulse oscillation or greater than the post-pulse oscillation. Since the receive signal at the onset of the post-pulse oscillations has a level below 100V, and is thus significantly larger than the receive signal to be detected (approximately 1mV), the receive chain of the amplifier and, if present, the A/D converter are not affected by a high level of attenuation. over-controlled. As a result, the echo cannot be localized within this time range. This is the so-called dead time. This also applies to more expensive filter algorithms that can reduce dead time but cannot eliminate it. In this case, the dead time causes a minimum gap of approximately 10 to 15 cm, below which no measurement can be made. Accordingly, no objects below the minimum distance are found.

An object in front of the ultrasonic transducer generates an echo that acts on the sensor membrane of the ultrasonic transducer. Detection and identification as echoes in the measurement mode is characterized in that in the received signal a signal peak above a certain application-specific threshold is detected. To this end, the received signal is filtered by means of a corresponding filter structure, for example an analog bandpass filter. Now in the near field, the following conditions can occur:

a) If the echo hits the sensor membrane after the echo is completely attenuated, the echo and the attenuation can be well separated, and the echo can be detected smoothly. This applies regardless of filtering.

b) After the echo is almost completely attenuated, if this echo strikes the sensor membrane, and a portion of the echo (i.e. the back flank) can be detected as a post-pulse oscillation that is still further extended to the attenuation waveform, the echo will be detected immediately. can An effective range in which detection of the echo immediately succeeds is defined as the minimum measurement effective range. The minimum measurement effective range depends on the temperature, the part and the object, and is typically 10 to 15 cm. A prerequisite for this type of signal analysis is weak filtering of the received signal and subsequent detection based on the envelope curve of the received signal.

As an alternative to the evaluation of the envelope curve, the filter output of a signal adaptation filter applied to the received signal may also be used for detection. In this case, the filter output is characterized in that the signal peak appears when the degree of correspondence between the transmitted signal and the received signal is high. In this case, an effective echo signal exists when the signal peak of the echo (echo peak) can be distinguished from the signal peak of the post-pulse oscillation (post-pulse oscillation peak) through the absolute peak value. In practice, post-pulse oscillation peaks and echo peaks for objects in the near sound field are fused. At the same time, as the amplitude of the echo peak decreases, the echo peak disappears. The reason is that the attenuation amplitude in the received signal is significantly larger than the attenuation amplitude of the echo, and differentiation by means of a signal-adapted filter is no longer possible. The minimum effective range for this type of signal analysis is likewise approximately 10 to 15 cm.

c) while the echo continues to post-pulse oscillations, if the echo strikes the sensor membrane, whereby the attenuation has a level significantly greater than that of the echo, and the received signal is saturated by the amplifier chain, the echo can be detected does not exist. This echo is extinguished in the so-called post-pulse oscillation.

Accordingly, in the conventional ultrasonic sensor, when an object enters the immobile time zone, the echo disappears while approaching the object. Another critical case exists when starting a vehicle from a narrowly parked situation.

A conventional ultrasound system is described in DE 10103936 A1. In this document, in order to detect an obstacle, an ultrasonic wave reflected by the obstacle is received by an ultrasonic vibrator. At this time, the transmission frequency of the ultrasonic wave is set so that this transmission frequency is different from the frequency of the damping vibration or the post-pulse vibration.

Therefore, a method for detecting the presence of an object in a near sound field below the minimum measurement effective range of an ultrasonic sensor is desirable.

A method according to the invention for detecting an object in the near sound field of an ultrasonic sensor comprises the steps of exciting an acoustic transducer of an ultrasonic sensor by means of a transmission signal, obtaining an attenuation signal describing the damping behavior of the acoustic transducer after excitation of the acoustic transducer determining a deviation between the attenuation signal and the reference attenuation signal, and detecting the presence of an object in the near sound field of the ultrasonic sensor based on the determined deviation.

Thereby, objects within the near sound field of the ultrasonic sensor and below the measuring range of the ultrasonic sensor can be reliably detected. Here, the near sound field refers to a region in front of the acoustic transducer of the ultrasonic sensor that cannot be accurately measured by the pulse echo method because the attenuated signal is superimposed on the echo of the transmitted signal.

The dependent claims are preferred refinements of the invention.

The method is performed several times, it is preferred that the reference attenuation signal corresponds to the preceding attenuation signal obtained in the preceding cycle of the method, especially when the ultrasonic sensor is currently operating. In this way, the effect of temperature fluctuations is minimized, since the reference attenuated signal is automatically adapted to the current temperature of the acoustic transducer. Thus, a very reliable detection of an object becomes possible.

In addition, when there is no object in the near sound field of the ultrasonic sensor, it is also preferable that the reference attenuation signal corresponds to the attenuation signal. Accordingly, a state in which an object moves in the near sound field of the ultrasonic sensor is clearly defined, and deviation from this state can be detected very accurately.

In particular, the operation of the ultrasonic sensor is performed during the excitation of the acoustic transducer and/or during the acquisition of the attenuation signal. By such an operation, the deviation is amplified when there is an object in the near sound field of the ultrasonic sensor, thereby increasing the sensitivity when determining the deviation.

Furthermore, the attenuated signal is preferably a signal filtered by a signal adapted filter, in which case the filter is adapted to the transmitted signal. This situation is desirable because such a signal already exists in a plurality of ultrasonic sensors and allows a very simple and accurate determination of the deviation.

It is also desirable to determine the deviation by taking the integral over the attenuated signal or through the difference between the attenuated signal and the reference attenuated signal. In this way, the deviation is determined over a time span, thereby compensating for inaccuracies in the acquisition of the attenuated signal, thereby improving the accuracy in determining the deviation.

Furthermore, it is desirable to determine the deviation over the time range from when the acoustic transducer is excited until it fully decays. Thereby, the time cost for carrying out the method is minimized. Interference by excitation of the acoustic transducer is excluded.

In particular, when the deviation exceeds a predefined value, the object is detected as being present in the near sound field of the ultrasonic sensor. In this way, the detection of the presence or absence of an object can be solved at very low cost. Furthermore, this allows a simple adaptation of the sensitivity when detecting the presence of an object, thereby avoiding error detection again.

In addition, the method is preferably performed several times, and if the deviation does not correspond to the deviation determined at a preceding time point, it is preferable that the object is detected as being present in the near sound field of the ultrasonic sensor. In this way, undesired influences by ambient factors, such as, for example, temperature fluctuations of the acoustic transducer, which determine the damping frequency, are compensated.

Likewise, if the time-dependent behavior of the determined deviation is not constant, it is advantageous to detect the object as being present in the near sound field of the ultrasonic sensor. What this means is that if there is a fluctuation of the deviation, the object is detected as being present in the near sound field of the ultrasonic sensor. Thereby, it is possible to identify whether the deviation is caused by an ambient factor or by an object in the near sound field of the ultrasonic sensor.

In particular, the steps of exciting the acoustic transducer, obtaining an attenuation signal, and determining a deviation between the attenuation signal and the reference attenuation signal are performed several times, in which case the frequency of the transmission signal is determined by the method steps being performed twice. and when the determined deviations in common indicate a positive deviation or a negative deviation between the reference attenuation signal and the attenuation signal, it is detected that the object is present in the near sound field of the ultrasonic sensor. A common positive deviation exists when the attenuated signal is greater than the reference attenuated signal both before and after the frequency fluctuation. A common negative deviation exists when the attenuated signal is less than the reference attenuated signal both before and after the frequency fluctuation. Thereby, it is possible to detect whether the deviation is caused by an ambient factor or by an object in the near sound field of the ultrasonic sensor.

Furthermore, it is advantageous that the steps of exciting the acoustic transducer, obtaining the attenuation signal and determining the deviation between the attenuation signal and the reference attenuation signal are carried out several times, in which case the modulation of the transmission signal is performed in the method step If they fluctuate between the two times, and the determined deviations differ from the reference attenuation signal to a different extent, it is detected that an object is present in the near sound field of the ultrasonic sensor. Thereby, it is possible to detect whether the deviation is caused by an ambient factor or by an object in the near sound field of the ultrasonic sensor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
1 is a flowchart of a method according to the invention in a first embodiment;
2 is a diagram showing an example of an attenuated signal and an example of a reference attenuated signal according to a second embodiment of the present invention.
3 is a schematic diagram of some examples of signal behaviors for different embodiments of the present invention set in relation to each other in time;

According to the present invention, the phase difference of the attenuation caused by the interference of the echo and the attenuated signal 1 in the absence of an object in the near sound field of the ultrasonic sensor is detected. This difference is obtained very clearly by the filter output of the signal-adapted filter.

1 shows a flowchart of a method according to the invention for detecting an object in the near sound field of an ultrasonic sensor in a first embodiment; The method includes a first method step S1, a second method step S2, a third method step S3 and a fourth method step S4. When the distance measurement by the ultrasonic sensor is required, the method is performed starting from the first method step S1. In order to continuously obtain up-to-date information about objects that may be in the near sound field of the ultrasonic sensor, the method is implemented in one iterative loop.

In the first method step S1, excitation of the acoustic transducer of the ultrasonic sensor is performed by the transmission signal. In this first embodiment, the transmission signal is a high-frequency AC voltage signal having a constant frequency and a constant maximum amplitude swing. The transmission signal is applied to the acoustic transducer of the ultrasonic sensor 1 during the first time interval t1, thereby vibratingly exciting the acoustic transducer, whereby an acoustic signal is emitted from the acoustic transducer. After the lapse of the first time interval t1, the transmission signal is terminated, or the transmission signal is no longer applied to the sound transducer. In alternative embodiments of the present invention, the transmit signal has an alternating frequency and amplitude. Thus, the transmit signal may be, for example, an amplitude modulated sweep sine signal.

)도 사용될 수 있으며, 이 경우

는 필터 계수의 표준이고,

는 입력 신호의 표준이다. 그 대안으로, 전술된 옵션들의 수학적 조합도 사용될 수 있다. 상기 방법의 후행 사이클에서 선행 감쇠 신호로서 이용되도록 하기 위해, 감쇠 신호(1)가 저장된다.The first method step S1 is followed by a second method step S2. In this step, an attenuation signal 1 is obtained which describes the damping behavior of the acoustic transducer after excitation of the acoustic transducer. Since the acoustic transducer is in the vibrating state by the excitation performed in the first method step S1, an output signal caused by the vibration is output from this vibrating state. The oscillation of the output signal is determined substantially by the natural frequency of the transducer. The output signal is likewise affected by the acoustic echo signal, which does not depend solely on the transmitted signal as it is caused by the reflection of the acoustic signal from an object in front of the ultrasonic sensor. The output signal is applied to the input of a signal adapted filter and is filtered by the filter. At this time, the signal-adapted filter is adapted to the transmission signal. At the output of the signal-adapted filter, an attenuated signal (1) is obtained. The attenuation signal 1 is thus a signal which has been filtered by the signal adapted filter and describes the attenuation behavior of the acoustic transducer after excitation of the acoustic transducer. The attenuation signal 1 of the signal-adapted filter may be the pure filter output xcorr , ie the convolution integral (cross-correlation function) of the input signal of the filter with filter coefficients. Alternatively, the correlation coefficient

) can also be used, in this case

is the standard of the filter coefficients,

is the standard of the input signal. Alternatively, a mathematical combination of the options described above may also be used. In order to be used as the preceding attenuation signal in subsequent cycles of the method, the attenuation signal 1 is stored.

Following the second method step S2, a third method step S3 is carried out. In this step the determination of the deviation between the attenuated signal and the reference attenuated signal 2 is carried out. In this case, the reference attenuation signal 2 corresponds to the preceding attenuation signal obtained in the preceding cycle of the method. According to the invention, other desirable signals can also be used as reference attenuation signal 2 . In this case, it is preferable to use the preceding attenuation signal obtained in the preceding cycle of the method, especially when the operation of the ultrasonic sensor is made. Thus, in alternative embodiments, the motion of the vehicle on which the ultrasonic sensor is disposed may be detected, whereby the operation of the ultrasonic sensor may be inferred. When the ultrasonic sensor is operated, the preceding attenuation signal is always used as the reference attenuation signal (2).

In the first embodiment, the deviation is determined by finding the difference between the attenuation signal 1 and the reference attenuation signal 2 . For this purpose, the attenuated signal 1 and the preceding attenuated signal are simultaneously applied to the input of the subtractor. At this time, the output voltage of the subtractor reproduces the time-dependent behavior of the differential voltage between the attenuated signal 1 and the reference attenuated signal 2 . Thus, the time-dependent behavior of the differential voltage is the deviation between the attenuated signal 1 and the reference attenuated signal 2 .

Following the third method step S3, a fourth method step S4 is carried out. In this step, the detection of the presence of an object in the near sound field of the ultrasonic sensor is performed on the basis of the determined deviation and together with the time-dependent behavior of the differential voltage in the first embodiment. In the first embodiment, if the deviation and thus the time-dependent behavior of the differential voltage are not constant, ie fluctuate, an object is detected as being present in the near sound field of the ultrasonic sensor. For this purpose, upper and lower limits are defined, in which case the differential voltage progresses between the upper and lower limits over its entire temporal behavior in the absence of an object in the near sound field of the ultrasonic sensor. The presence of an object within the near sound field of an ultrasonic sensor causes a rise or fall in the time-dependent behavior of the differential voltage, which is caused in particular by the altered echo propagation time, whereby other signal sections of the echo interfere with the attenuated signal. When the differential voltage exceeds the upper limit value or the differential voltage falls below the lower limit value, the differential voltage becomes non-constant, and an object is detected as being present in the near sound field of the ultrasonic sensor. If the vehicle has moved and the deviation fluctuates heavily between cycles, the presence of an object is recognized. In contrast, the deviation fluctuations due to temperature are rather gentle and therefore less severe.

Following the fourth method step S4, the method branches back to the first method step S1 and is performed again.

The second embodiment of the method according to the invention substantially corresponds to the first embodiment. However, when there is no object in the near sound field of the ultrasonic sensor, the determination of the deviation between the reference attenuation signal 2 corresponding to the attenuation signal 1 and the attenuation signal is performed in the third method step S3. Such a reference attenuation signal 2 can be defined, for example, by recording the attenuation signal 1 of the ultrasound sensor after a manual confirmation of the fact that there is no object in the near sound field of the ultrasound sensor.

The deviation is determined in the second embodiment by finding the difference between the attenuation signal 1 and the reference attenuation signal 2 . For this purpose, the attenuated signal 1 and the reference attenuated signal 2 are simultaneously applied to the input of the subtractor. At this time, the output voltage of the subtractor reproduces the time-dependent behavior of the differential voltage between the attenuated signal 1 and the reference attenuated signal 2 . Thus, the time-dependent behavior of the differential voltage becomes the deviation between the attenuated signal 1 and the reference attenuated signal 2 .

2 shows an example of an attenuated signal 1 and an example of a reference attenuated signal 2 according to a second embodiment of the present invention. The solid line shows the reference attenuation signal (2). The dotted line shows the attenuation signal (1) when the object is 4 cm in front of the ultrasonic sensor. Here, the intensity of the attenuated signal 1 and the reference attenuated signal 2 over time over time is shown. At this time, the behavior by time starts at the same time as the transmission signal at 0ms. The signal peak at approximately 1.7 ms is caused by the transmit signal applied to the signal adapted filter as well during excitation of the acoustic transducer. The signal peak at approximately 2.3 ms to 2.5 ms corresponds to the post-pulse oscillation (post-pulse oscillation peak) of the acoustic transducer. It can be seen from this figure that until about 2.3 ms, there is a waveform that is congruent between the attenuation signal 1 and the reference attenuation signal 2 . After that, a larger difference appears in the post-pulse oscillations. Post-pulse oscillation peaks show no echo. For an echo to be detectable, the echo peak must lie approximately 0.24 ms after the signal peak caused by the transmit signal, ie approximately 2.0 ms in the diagram shown.

The third method step S3 is followed by a fourth method step S4. In this step, a detection of the presence of an object in the near sound field of the ultrasonic sensor is made on the basis of the determined deviation and together with the time-dependent behavior of the differential voltage in the first embodiment. In this first embodiment, an object is detected as being present in the near sound field of the ultrasonic sensor when the deviation and thus the time-dependent behavior of the differential voltage exceeds a predefined value. To this end, first, the maximum value of the differential voltage is calculated from the time-dependent behavior of the differential voltage. The maximum value of this differential voltage is compared with a predefined value. In this case, the predefined value is preferably a voltage value selected such that the object is detected as present only when the maximum value of the differential voltage exceeds a value reached also by fluctuations in the differential voltage due to a peripheral factor. Accordingly, the presence of an object in the near sound field of the ultrasonic sensor is detected when the absolute value of the deviation exceeds a predefined threshold.

In the second embodiment, since the reference attenuation signal 2 is a predefined voltage waveform, even in this case, as can be seen from FIG. 2 , the attenuation signal 1 itself is pre-defined within the predefined _{time range t S .} It can be assumed that there is always a deviation when exceeding the signal threshold value (S) specified in , and the magnitude of the deviation can be determined according to how much the attenuation signal (1) exceeds the signal threshold value (S). Thus, if the absolute value of the attenuated signal 1 exceeds a predefined _{signal threshold S} within a predefined time interval t S , i.e. filtering to such an extent that it cannot be caused by temperature fluctuations. If the result is high, the presence of an object in the near sound field of the ultrasonic sensor is detected.

In still further embodiments of the invention other criteria are selected, with reference to which the presence of an object in the near sound field of the ultrasonic sensor is detected. Another criterion is to compare the actual deviation with the deviation determined at any preceding time point, for example in a preceding cycle of the method. In this case, when the currently determined deviation does not correspond to the deviation determined at the preceding time, that is, when there is a difference from the deviation determined at the preceding time by a preset value, an object in the near sound field of the ultrasonic sensor is detected as present. Through the combination of several criteria, the influence of ambient conditions (eg air movement, temperature fluctuations) that prevent a stable signal from appearing is minimized.

In a third embodiment of the present invention substantially corresponding to the first or second embodiment, the deviation by finding an integral through the difference between the attenuation signal 1 and the reference attenuation signal 2 in the third method step S3 is decided For this purpose, the attenuation signal 1 is first integrated. This integration process is achieved by using the attenuated signal 1 for charging the first capacitor. The state of charge of the first capacitor and thus the capacitor voltage between the poles of the first capacitor correspond to the integral for the attenuated signal 1 . In addition, the reference attenuated signal 2 is also integrated. This integration process may be accomplished by charging the second capacitor by the reference attenuation signal (2). However, this process is not essential, since it is sufficient to provide a reference voltage corresponding to the voltage between the poles of such a second capacitor when the second capacitor is charged by the reference attenuated signal (2). Because. In alternative embodiments, the analog signal processing described herein, in particular the integration of the attenuated signal 1 , may also be effected by digital signal processing.

Since the capacitor voltage between the poles of the first capacitor corresponds to the integration through the attenuation signal 1 and the reference voltage corresponds to the integration through the reference attenuation signal 2, the voltage difference between the capacitor voltage and the reference voltage corresponds to the attenuation signal ( Corresponds to the integral through the difference between 1) and the reference attenuated signal (2). Such a differential voltage can be obtained, for example, by a subtractor. In this second embodiment, the output voltage of the subtractor corresponds to the deviation between the attenuated signal 1 and the reference attenuated signal 2 . In the diagram of FIG. 2 , the difference between the integral over the attenuated signal 1 and the integral over the reference attenuated signal 2 described herein is shown as the area 3 between the attenuated signal 1 and the reference attenuated signal 2 . can be

In this third embodiment, the deviation is determined only for the time span after excitation of the acoustic transducer and before full attenuation of the acoustic transducer. This means that the attenuation signal is applied to the first capacitor only after the second time interval t2 during which the transmission signal is no longer applied to the acoustic transducer, and the attenuation signal 1 is applied after the third time interval t3. 1 is achieved by disconnecting from the capacitor. In particular, the second time interval t2 and the third time interval t3 are selected such that the integration is found over a time range near the post-pulse oscillation peak. Since only part of the attenuation signal 1 is thereby integrated, the reference voltage is adapted correspondingly, and we now describe the integration through the reference attenuation signal 2 within the desired measurement interval t4 . Accordingly, in the second embodiment, the integral of one signal at the output of the signal-adapted filter is obtained and tracked within a time range near the post-pulse oscillation peak.

It should be noted that the damping behavior of the acoustic transducer can likewise vary over temperature. The reason is that the intrinsic resonance of the acoustic transducer is shifted over temperature, which may result in a greater deviation between the attenuation signal 1 and the reference attenuation signal 2, which can lead to greater variance . The following examples prove particularly resistant to temperature fluctuations.

The fourth embodiment of the present invention substantially corresponds to the first, second or third embodiment. When the ultrasonic sensor operates with respect to its surroundings, strong fluctuations in the deviation should be considered if there is an object in the near sound field of the ultrasonic sensor. This situation arises due to the typical wavelengths of an ultrasonic sensor already corresponding to about 7 mm, even when the motion of the ultrasonic sensor with respect to its surroundings is only a few millimeters. Therefore, in the third embodiment the ultrasonic sensor moves during the excitation of the acoustic transducer and/or during the acquisition of the attenuation signal. The movement of the ultrasonic sensor can be effected, for example, by moving a vehicle in which the ultrasonic sensor is installed, which is applied, for example, to a vehicle control unit in a vehicle equipped with an automatic longitudinal guidance function (eg, automatic entry/exit). It can be triggered by a control signal. This takes place in particular when the vehicle is stationary, for example after starting the vehicle or in a parked state. The vehicle thus moves intentionally infinitesimal, in order to generate fluctuations of the deviation.

The fifth embodiment of the present invention substantially corresponds to the first to fourth embodiments. However, the first method step S1 , the second method step S2 and the third method step are carried out several times. To this end, the method skips back to the first method step S1 after the first execution of the third method step S3. Then, the second to fourth method steps S2 to S4 are then executed. That is, the first cycle of the first to third method steps S1 to S3 is followed by the second cycle of the first to third method steps S1 to S3 and the fourth method step S4. In this case, the frequency of the transmission signal varies between the two executions of these method steps, ie after the first cycle and before the second cycle of the first to third method steps S1 to S3. A signal adapted filter is adapted to a transmission signal having a changed frequency.

In the fourth method step S4, when the deviation determined in the first cycle and the deviation determined in the second cycle commonly indicate a positive deviation or a negative deviation of the attenuation signal with respect to the reference attenuation signal, the near sound field of the ultrasonic sensor An object is detected as being present in it.

The method according to the invention is implemented as described above, in which case attenuation signals of preferably a plurality of various transmission signals are evaluated. In this case, it is particularly preferable that the final frequencies of the transmission signals are clearly distinguished, since the movement of the natural resonance of the acoustic transducer due to temperature is pronounced only in one frequency direction. For example, when the natural resonance of an acoustic transducer shifts from 48 kHz to 50 kHz, the signal-adapted filter shows an increase in the deviation at 52 kHz, and the signal-adapted filter shows a decrease in the deviation at 42 kHz. When an increase is detected in the two signal-adapted filters, an object in the near sound field of the ultrasonic sensor can be inferred with high confidence.

The sixth embodiment of the present invention substantially corresponds to the fifth embodiment. However, the modulation of the transmit signal varies between the first cycle and the second cycle. At this time, in the fourth method step S4, when the deviation determined in the first cycle and the deviation determined in the second cycle deviate from the reference attenuation signal to different degrees, the presence of an object in the near sound field of the ultrasonic sensor is detected.

Thereby, two transmit signals with the same attenuation signature but with different modulations (phase or amplitude) are selected. If there is no object in the near sound field of the ultrasonic sensor, the same deviations will be calculated. If there is an object in the near sound field of the ultrasonic sensor, the echo signature is changed to the selected transmission shape, so that the different deviation is determined by the interference of the echo signal and the output signal.

In alternative embodiments of the invention, the instantaneous frequency of the output signal is used instead of the attenuated signal generated by the signal adapted filter. This instantaneous frequency can be calculated by different methods, such as, for example, a method using a pass-through measurement or a method of calculating an instantaneous phase.

3 shows examples of several signal waveforms for different embodiments of the invention set relative to each other on a temporal basis. Here, the first diagram 11 shows the temporal behavior of the output signal when there is no object in the near sound field of the ultrasonic sensor, and the second diagram 12 shows 30 mm in front of the ultrasonic sensor and thereby in the near sound field of the ultrasonic sensor. It shows the time-dependent behavior of the output signal in the presence of an object. The output signal applied to the acoustic transducer corresponds to the transmission signal within the first time interval t1. The attenuation of the acoustic transducer is effected within a third time interval t3 comprising a second time interval t2 and a preferred measurement interval t4. That is, no excitation of the acoustic transducer is performed. The output signal is dominated by the attenuation of the acoustic transducer within the second time interval. Echo reception is performed with no or only slight attenuation ratio within the desired measurement interval t4. The third diagram 13 shows the frequency waveform 4 of the output signal when there is no object in the near sound field of the ultrasonic sensor, and the frequency waveform 5 of the output signal when there is an object 30 mm in front of the ultrasonic sensor . The two frequency waveforms 4 and 5 overlap within a first time interval t1. In a particularly preferred measurement interval t4, the two frequency waveforms deviate from each other. The fourth diagram 14 shows the signal at the output of the signal-adapted filter in the absence of an object in the near sound field of the ultrasonic sensor, along with the reference attenuated signal 2 of the first embodiment of the invention. The fourth diagram 14 also shows the signal at the output of the signal-adapted filter when there is an object 30 mm in front of the ultrasonic sensor, along with the attenuated signal 1 of the first embodiment of the invention.

Reference is expressly made to the disclosure of FIGS. 1-3 in addition to the above disclosure.

Claims (13)

A method for detecting an object in a near sound field of an ultrasonic sensor, comprising:
- exciting the acoustic transducer of the ultrasonic sensor by the transmission signal;
- obtaining an attenuation signal (1) of an acoustic transducer after excitation of said transducer,
- determining the deviation between the attenuation signal (1) and the reference attenuation signal (2), and
- detecting the presence of an object in the near sound field of the ultrasonic sensor based on the determined deviation, the method of detecting an object in the near sound field of the ultrasonic sensor. The near sound field of an ultrasonic sensor according to claim 1, characterized in that at least some of the steps are performed several times, and the reference attenuation signal (2) corresponds to the preceding attenuation signal obtained in a preceding cycle of the method. A method of detecting an object. The detection of an object in the near sound field of an ultrasonic sensor according to claim 2, characterized in that the reference attenuation signal (2) corresponds to a preceding attenuation signal obtained in a preceding cycle of the method, when the ultrasound sensor is currently in operation. method. The method according to claim 1, characterized in that when there is no object in the near sound field of the ultrasonic sensor, the reference attenuation signal (2) corresponds to the attenuation signal (1). Method according to one of the preceding claims, characterized in that the operation of the ultrasonic sensor is carried out during excitation of the acoustic transducer or during the acquisition of the attenuation signal (1). . 5. In the near sound field of an ultrasonic sensor according to any one of the preceding claims, characterized in that the attenuated signal (1) is a signal filtered by a signal matched filter, in which case the filter is matched to the transmitted signal. A method of detecting an object. 5. The method according to any one of the preceding claims, characterized in that the deviation is determined by finding the integral over the attenuated signal (1) or over the difference between the attenuated signal (1) and the reference attenuated signal (2). A method of detecting an object in a near sound field of an ultrasonic sensor. Method according to any one of claims 1 to 4, characterized in that the deviation is determined during the time range from excitation of the acoustic transducer until complete attenuation. The near sound field of the ultrasonic sensor according to any one of claims 1 to 4, characterized in that when the deviation exceeds a predefined value, it is detected that an object is present in the near sound field of the ultrasonic sensor. How to detect my object. 5. An object according to any one of claims 1 to 4, wherein at least some of the steps are performed multiple times, and if the deviation is not equal to the deviation determined at a preceding time point, an object within the near sound field of the ultrasonic sensor is A method for detecting an object in the near sound field of an ultrasonic sensor, characterized in that it is detected as being present. 5. An object in the near sound field of an ultrasonic sensor according to any one of claims 1 to 4, characterized in that if the determined deviation is not constant over time, it is detected as an object being present in the near sound field of the ultrasonic sensor. detection method. 5. The method according to any one of claims 1 to 4,
- exciting the acoustic transducer, obtaining the attenuation signal 1 and determining the deviation between the attenuation signal 1 and the reference attenuation signal 2 are carried out several times, in which case the frequency of the transmitted signal is fluctuate after the first cycle of the steps and before the second cycle of the steps;
- characterized in that when the determined deviations in common indicate a positive deviation or a negative deviation between the reference attenuation signal (2) and the attenuation signal (1), an object is detected as being present in the near sound field of the ultrasonic sensor, A method of detecting an object in the near sound field of an ultrasonic sensor. 5. The method according to any one of claims 1 to 4,
- exciting the acoustic transducer, obtaining the attenuation signal 1 and determining the deviation between the attenuation signal 1 and the reference attenuation signal 2 are carried out several times, in which case the modulation of the transmission signal is fluctuate after the first cycle of the steps and before the second cycle of the steps;
- When the determined deviations are different, it is detected that the object exists in the near sound field of the ultrasonic sensor, characterized in that it is detected.

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