Ultrasound-based object detection and driver assistance

Abstract

The invention relates to ultrasound-based object detection, for the purpose of which an ultrasonic signal (t) is emitted by means of an ultrasonic sensor (2), wherein an electrical driving signal is applied to the ultrasonic sensor (2) in order for the latter to emit the ultrasonic signal (t). The electrical driving signal corresponds to a specified electrical voltage, and an electrical current caused by the driving signal is determined as the electrical secondary signal, or the electrical driving signal corresponds to a specified electrical current, and an electrical voltage caused by the driving signal is determined as the electrical secondary signal. An object (10) is detected on the basis of an anomaly of the secondary signal.

Description

[0001] Ultrasound-based object detection and driver assistance

[0002] The present invention relates to a method for ultrasound-based object detection, wherein an ultrasound signal is emitted by means of an ultrasound sensor, and to a method for driver assistance in a motor vehicle, wherein such a method for ultrasound-based object detection is carried out. The invention further relates to a corresponding ultrasound sensor system, an electronic vehicle guidance system with such an ultrasound sensor system, and corresponding computer program products.

[0003] Pulse-echo technology is typically used in ultrasonic sensors for object detection, particularly in driver assistance applications in motor vehicles, such as automatic or assisted parking. This often involves the use of piezoelectric bending transducers in resonance mode, which always results in reverberation. For electromechanical energy conversion, a piezoelectrically active element connected to a rigid membrane can be used, for example.

[0004] When the same diaphragm is used for both transmitting and receiving ultrasonic waves, the vibration system typically requires high damping. This can be achieved, for example, by applying a damping material to the diaphragm, such as felt, foam, or other materials with high inherent damping. While high damping is necessary for rapid switching from transmit to receive mode at close range according to the pulse-echo principle, it negatively impacts functionality at long range because less electrical energy is converted into usable ultrasonic energy, and the sensor's receiver sensitivity also decreases.

[0005] Consequently, in order for the same diaphragm to be used for both transmitting and receiving, the time required for the oscillation to decay after transmission results in a practical blind zone of the sensor, extending from the diaphragm to approximately 15 cm from the diaphragm, assuming a sensor range of 3 m, 5 m, or 7 m. Even in special short-range modes where very short pulses and / or low-power pulses are transmitted, this blind zone can only be reduced slightly.

[0006] Document WO 2020 / 064161 A1 proposes analyzing the reverberation signal of a frequency-coded transmit pulse, which can also reduce the blind area, but not below a few centimeters.

[0007] Using independent membranes or sensors for transmitting and receiving, located in close proximity to each other (unlike in current vehicles), could significantly reduce the blind spot, but increases the complexity and size of the overall system and its cost. With sensors positioned further apart, the detection of objects very close to one of the two sensors is also limited or even impossible due to the sensors' directional characteristics.

[0008] It is an object of the present invention to further reduce the blind area of ​​an ultrasonic sensor, wherein the use of a single ultrasonic sensor, in particular a single membrane, can be used for both transmitting and receiving ultrasonic waves.

[0009] This problem is solved by the respective subject matter of the independent claims. Advantageous further developments and preferred embodiments are the subject matter of the dependent claims.

[0010] The invention is based on the idea of ​​analyzing an electrical current or voltage signal, which results from the electrical voltage or current signal used to control an ultrasonic sensor to emit an ultrasonic signal, for an anomaly that indicates the presence of an object in the vicinity of the ultrasonic sensor.

[0011] According to one aspect of the invention, a method for ultrasound-based object detection, particularly in the environment of a motor vehicle, is described. In this method, an ultrasound signal is emitted by means of an ultrasound sensor, particularly one located in the motor vehicle, the frequency of which changes according to a predetermined frequency profile. To emit the ultrasound signal, the ultrasound sensor is supplied with an electrical driver signal, and a secondary electrical signal caused by the driver signal is determined, in particular measured, for example, by means of a measuring circuit. The electrical driver signal corresponds either to a predetermined electrical voltage or a predetermined electrical current. If the driver signal corresponds to the voltage, the secondary signal is determined to be an electrical current caused by the driver signal.If the driver signal corresponds to the current, the secondary signal is determined as an electrical voltage caused by the driver signal. Depending on an anomaly in the secondary signal, an object in the vicinity of the ultrasonic sensor, particularly a motor vehicle, is detected, especially by means of a data processing system.

[0012] The ultrasonic sensor is particularly suitable for emitting the ultrasonic signal. For this purpose, it features, for example, a diaphragm and a piezoelectric element coupled to the diaphragm. Applying the driver signal to the ultrasonic sensor corresponds, for example, to applying the driver signal to the piezoelectric element, which causes the piezoelectric element and consequently the diaphragm to vibrate, thus generating ultrasonic waves, i.e., the ultrasonic signal.

[0013] It is possible that the ultrasonic sensor is designed as an ultrasonic transmitter-receiver, also known as an ultrasonic transducer. In this case, it is also fundamentally suitable for detecting reflected components of the emitted ultrasonic signal or other ultrasonic signals, particularly via the same membrane used to emit the ultrasonic signal. However, this potential functionality is not used in the method according to the invention or in the operating mode described above.

[0014] According to the invention, the ultrasound transmitter is operated not according to the pulse-echo principle, but rather by means of continuous or quasi-continuous emission of the ultrasound signal. Quasi-continuous refers to the fact that the ultrasound signal is not necessarily emitted continuously, but for a period that is significantly longer than the pulse duration in the pulse-echo principle, in particular for at least several milliseconds, for example, 2 ms to 50 ms. However, this does not preclude the possibility that the pulse-echo principle can be used additionally or alternately in some embodiments.

[0015] The driver signal itself can contain a high-frequency oscillating component whose frequency corresponds to the frequency of the ultrasound waves to be generated. However, this high-frequency component is superimposed on a predetermined non-zero, but not necessarily constant, smooth component that does not oscillate. This smooth component can also be referred to as the mean amplitude or envelope. The same principle applies to the secondary signal, where the driver signal is fixed, for example, by a voltage or current source or an oscillator to generate the oscillating component, whereas the secondary signal depends not only on the driver signal but also on the system's impedance or the effective load.

[0016] The invention utilizes the knowledge that the presence of an object in the vicinity of the ultrasonic sensor influences the system's impedance and can therefore lead to an anomaly in the secondary signal. This is due to the fact that reflected components of the emitted ultrasonic signal superimpose with the emitted ultrasonic signal, and the resulting superposition also directly affects the position of the ultrasonic sensor, particularly the membrane.

[0017] The anomaly can be understood, in particular, as a deviation from the reference case in which no object is present in the vicinity of the ultrasound transmitter that can emit the ultrasound signal. The reference case can be quantified by measured or modeled data. However, the anomaly can also be identified without quantitative comparison to reference data. In particular, the secondary signal can be determined as a function of time, and the anomaly can be determined from the temporal evolution of the secondary signal.

[0018] The inventive method requires neither a second membrane nor a second ultrasonic sensor, nor does it require the explicit measurement of the reflected components of the emitted ultrasonic signal. Instead, the effects of these components are measured indirectly, for example, via their influence on the impedance and thus the secondary signal. It has been shown that objects at distances from the ultrasonic sensor ranging from a few centimeters to a few millimeters, and even down to one millimeter, can be detected in this way. The higher the frequency of the emitted ultrasonic signal, the smaller the minimum distance.

[0019] Detecting the object based on the anomaly means, in particular, that the existence of the object within the detection range of the ultrasonic sensor is determined when the anomaly is present. Therefore, the distance of the object from the ultrasonic sensor is not necessarily determined, which is not essential, especially for object detection in the ultra-close range. This can potentially save additional calculations or measurement steps.

[0020] According to at least one embodiment, the ultrasound signal is generated in such a way that its frequency changes according to a predetermined frequency curve.

[0021] In other words, the ultrasound signal of such designs can also be referred to as an ultrasound chirp.

[0022] In particular, the driver signal can be generated in such a way that its oscillating component has a frequency that changes according to the specified frequency curve.

[0023] The frequency response is, in particular, a temporal profile of the frequency. The frequency response can be defined such that one or more successive time intervals are specified, along with a corresponding profile of the frequency during these intervals. For example, exactly one time interval can be specified in which the frequency rises or falls linearly, or two or more time intervals can be specified within which the frequency alternately rises and falls linearly, and so on. The linear profile can also be replaced by a quadratic or other defined profile.

[0024] It has been found that the anomaly is particularly pronounced when the distance between the object and the ultrasonic sensor is such that a standing wave forms between the object and the ultrasonic sensor, especially the membrane. This distance depends on the frequency of the ultrasonic signal; in particular, the following applies to the frequency f at which a standing wave forms: where c denotes the speed of sound, d the distance between the object and the ultrasonic sensor, and N a positive integer. By generating the ultrasonic signal with a variable frequency, the distance at which a standing wave occurs is tuned. In other words, a range of distances is scanned, and if an object is located within this range, the anomaly is particularly pronounced. Consequently, the anomaly, and thus the object, can be detected with increased reliability. Depending on the specific design of the ultrasonic sensor, it may also be possible that the anomaly can only be reliably detected when a standing wave forms. However, this generally also depends on how accurately the secondary signal can be measured, or rather, how precisely deviations of the secondary signal from the reference data can be determined.

[0025] According to at least one embodiment, detecting the object depending on the anomaly involves determining a distance value relating to the distance of the object from the ultrasonic sensor, depending on the anomaly.

[0026] In particular, an anomaly frequency is determined based on the secondary signal, for example using a data processing system, and the distance value is determined based on the anomaly frequency, for example using the same data processing system. This distance value corresponds to the distance of the object from the ultrasonic sensor, to the nearest integer. In such embodiments, the object in the environment can be characterized more precisely by the distance value.

[0027] The distance d is calculated in particular according to the equation above as follows: c N d = — = N d*,

[0028] 2 JA where fA denotes the anomaly frequency, c the speed of sound, N a positive integer as the integer factor, and d* the distance value.

[0029] The anomaly frequency is, in particular, a frequency of the ultrasound signal at which the anomaly is identified. Specifically, the secondary signal can be determined as a function of time, such that the frequency response also gives the secondary signal as a function of frequency. Accordingly, the anomaly frequency can be determined from the time response of the secondary signal or from the secondary signal as a function of frequency. According to at least one embodiment, the frequency response is linear or piecewise linear, particularly as a function of time.

[0030] This makes frequency modulation of the ultrasound signal particularly easy to implement.

[0031] The piecewise linear progression can, for example, be a linearly increasing progression followed by a linearly decreasing progression, or vice versa.

[0032] According to at least one embodiment, the slope of the linear or piecewise linear curve is in the range [1 kHz / ms, 6 kHz / ms] or in the range [2.0 kHz / ms, 2.5 kHz / ms].

[0033] For some ultrasonic sensors used in the automotive sector, such frequency modulation can be easily implemented.

[0034] For example, the frequency response has a minimum frequency in the range [30 kHz, 60 kHz]. Alternatively or additionally, the frequency response has a maximum frequency in the range [40 kHz, 130 kHz].

[0035] Due to the mechanical design of some ultrasonic sensors used in the automotive sector, such frequency ranges can be implemented particularly easily there.

[0036] According to at least one embodiment, the maximum frequency is at least twice as high as the minimum frequency.

[0037] Such embodiments are particularly advantageous because they ensure that a continuous range of distances is sampled without gaps. This results from the spacing of the frequency curves as a function of the spacing for successive values ​​of N in the context described above.

[0038] If we equate the corresponding distances, we obtain or for N=1

[0039] According to at least one embodiment in which the maximum frequency is at least twice as high as the minimum frequency, the minimum frequency is in the range [20 kHz, 60 kHz] and the maximum frequency is in the range [40 kHz, 130 kHz],

[0040] Due to the mechanical design of some ultrasonic sensors used in the automotive sector, such frequency ranges can be implemented particularly easily there.

[0041] According to at least one embodiment, the anomaly includes an amplitude anomaly in the mean amplitude of the secondary signal and / or a phase anomaly in a phase of the secondary signal.

[0042] The phase anomaly of the secondary signal can, in particular, be an anomaly in the phase difference between the phase of the secondary signal and the driver signal.

[0043] The impedance change caused by the object is particularly evident in the mean amplitude and phase of the secondary signal. The mean amplitude, phase, or phase difference can be analyzed as a function of frequency to detect the anomaly and, if necessary, determine the anomaly frequency.

[0044] According to at least one embodiment, the amplitude anomaly is detected as a deviation of the mean amplitude of the secondary signal as a function of the frequency of the emitted ultrasound signal from a predetermined amplitude reference curve, in particular by means of the data processing system.

[0045] The amplitude reference curve corresponds, in particular, to the course of the mean amplitude of the secondary signal as a function of the frequency of the emitted ultrasonic signal when no object is present in the vicinity of the ultrasonic sensor. The amplitude reference curve can be determined by a suitable model of the ultrasonic sensor, for example, an RLC model, or by appropriate reference measurements of the secondary signal. For example, an amplitude anomaly can be considered detected if the deviation is greater than a predefined first threshold value.

[0046] This allows for particularly reliable detection of the amplitude anomaly or determination of the anomaly frequency.

[0047] According to at least one embodiment, the phase anomaly is detected as a deviation of the phase of the secondary signal or the phase difference as a function of the frequency of the emitted ultrasound signal from a predetermined phase reference curve, in particular by means of the data processing system.

[0048] The phase reference curve corresponds, in particular, to the phase of the secondary signal or the phase difference as a function of the frequency of the emitted ultrasonic signal when no object is present in the vicinity of the ultrasonic sensor. The phase reference curve can be determined by a suitable model of the ultrasonic sensor, for example, an RLC model, or by appropriate reference measurements of the secondary signal. For example, a phase anomaly can be considered detected if the deviation is greater than a predefined second threshold value.

[0049] This allows for particularly reliable detection of the phase anomaly or determination of the anomaly frequency.

[0050] According to at least one embodiment, the amplitude anomaly is detected as a jump in the mean amplitude of the secondary signal as a function of frequency, in particular by means of the data processing system.

[0051] This method exploits the fact that the mean amplitude of the secondary signal, when no object is in the vicinity of the ultrasonic sensor, follows a smooth curve as a function of frequency. A jump, i.e., a change in the mean amplitude by more than a predefined third threshold within a predefined frequency interval, therefore indicates an anomaly. Advantageously, it is not necessary to compare the mean amplitude of the secondary signal with a reference curve. According to at least one embodiment, the phase anomaly is detected as a jump in the phase or phase difference of the secondary signal as a function of frequency, particularly by means of the data processing system.

[0052] This method exploits the fact that the phase or phase difference of the secondary signal, as a function of frequency, follows a smooth curve when no object is present in the vicinity of the ultrasonic sensor. A jump, i.e., a change in the phase or phase difference by more than a predefined fourth threshold within a given frequency interval, therefore indicates an anomaly. Advantageously, it is not necessary to compare the phase or phase difference of the secondary signal with a reference curve.

[0053] According to a further aspect of the invention, a method for driver assistance in a motor vehicle is described. This method involves an ultrasound-based object detection method according to the invention, wherein the ultrasound sensor is mounted on the motor vehicle, in particular on the outside of the motor vehicle. Depending on the detection of the object, for example, when the object has been detected, a warning signal is generated for the driver of the motor vehicle and / or at least one control signal is generated to control at least one actuator of the motor vehicle.

[0054] The at least one control signal can be provided to one or more actuators of the motor vehicle, including, for example, one or more brake actuators and / or one or more steering actuators and / or one or more drive motors or other motors or actuators of the motor vehicle. The one or more actuators can influence the longitudinal and / or lateral steering of the motor vehicle in order to steer the motor vehicle at least partially automatically, for example, during a parking maneuver. The one or more actuators can also automatically open a door or hatch of the motor vehicle.

[0055] The warning signal can be output via a vehicle output device, for example a display and / or an audio output system and / or a haptic output system.

[0056] According to a further aspect of the invention, an ultrasonic sensor system is specified, in particular an ultrasonic sensor system for a motor vehicle. The ultrasonic sensor system comprises an ultrasonic sensor and a driver circuit configured to drive the ultrasonic sensor to emit an ultrasonic signal and to supply the ultrasonic sensor with an electrical driver signal for this purpose. The ultrasonic sensor system comprises a measuring circuit configured to determine, in particular to measure, an electrical current caused by the driver signal as a secondary electrical signal, wherein the electrical driver signal corresponds to a predetermined electrical voltage, or to determine, as a secondary electrical signal, an electrical voltage caused by the driver signal, wherein the electrical driver signal corresponds to a predetermined electrical current.The ultrasonic sensor system has a data processing system that is set up to detect an object depending on an anomaly in the secondary signal.

[0057] The measurement circuit can contain the driver circuit, or vice versa. The measurement circuit and the driver circuit can also be designed independently of each other. The data processing system can also be designed separately from the measurement circuit and the driver circuit. However, the data processing system can also include the measurement circuit and / or the driver circuit.

[0058] The terms "data processing system" and "at least one data processing device" may be used interchangeably within the scope of this disclosure. In this disclosure, a data processing device may, for example, be understood as a device with processing circuits for processing data. A data processing device can thus perform arithmetic operations to process data. Indexed access to a data structure, such as a lookup table (LUT) or a database, may also be considered an arithmetic operation. Similarly, data processing that is partially or fully implemented in hardware may be considered an arithmetic operation.

[0059] A data processing device may, in particular, comprise one or more computers, one or more microcontrollers, and / or one or more integrated circuits, for example, one or more application-specific integrated circuits (ASICs), one or more field-programmable gate arrays (FPGAs), and / or one or more systems-on-a-chip (SoCs). A data processing device may also comprise one or more processors, for example, one or more microprocessors, one or more central processing units (CPUs), one or more graphics processing units (GPUs), and / or one or more signal processors, in particular one or more digital signal processors (DSPs). The data processing device may also comprise a physical or virtual cluster of computers or other devices of the aforementioned type.

[0060] A data processing device may also include one or more hardware and / or software interfaces, for example for receiving and / or providing data.

[0061] A data processing device may also include one or more storage devices. A storage device may be implemented as volatile memory, such as dynamic random access memory (DRAM) or static random access memory (SRAM), or as non-volatile data storage, such as read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory or flash EEPROM, ferroelectric random access memory (FRAM), magnetoresistive random access memory (MRAM), or phase-change random access memory (PCRAM).

[0062] According to at least one embodiment, the data processing system is configured to detect the object in a first operating mode depending on the anomaly of the secondary signal and in a second operating mode to detect the object and / or another object based on a pulse-echo method.

[0063] The first and second operating modes can be activated alternately, for example, cyclically. It can also be configured that the first operating mode is only active during system startup and switches to the second operating mode after a certain period. It is also possible for the system to switch from the first to the second operating mode, or vice versa, based on specific trigger events. For example, the system could switch from the second to the first operating mode if the object falls below a minimum distance detectable by the pulse-echo method.

[0064] Further embodiments of the ultrasonic sensor system according to the invention follow directly from the various configurations of the method according to the invention, and vice versa. In particular, individual features and corresponding explanations as well as advantages relating to the various embodiments of the methods according to the invention can be transferred analogously to corresponding embodiments of the ultrasonic sensor system according to the invention. In particular, the ultrasonic sensor system according to the invention is configured to carry out a method according to the invention. In particular, the ultrasonic sensor system according to the invention carries out a method according to the invention.

[0065] According to a further aspect of the invention, an electronic vehicle guidance system for a motor vehicle is provided. The electronic vehicle guidance system comprises an ultrasonic sensor system according to the invention and a control system configured to generate a warning signal for a driver of the motor vehicle, depending on the detection of the object, and / or to generate at least one control signal for controlling at least one actuator of the motor vehicle.

[0066] The control system and the data processing system can be designed separately. The control system can also be part of the data processing system. The control system can also be a separate data processing system.

[0067] Further embodiments of the vehicle guidance system according to the invention follow directly from the various configurations of the method according to the invention, and vice versa. In particular, individual features and corresponding explanations as well as advantages relating to the various embodiments of the methods according to the invention can be transferred analogously to corresponding embodiments of the vehicle guidance system according to the invention. In particular, the vehicle guidance system according to the invention is configured to carry out a method according to the invention. In particular, the vehicle guidance system according to the invention carries out a method according to the invention.

[0068] According to another aspect of the invention, a computer program with commands is provided. When the commands are executed by an ultrasound sensor system according to the invention, for example by the data processing system of the ultrasound sensor system, the commands cause the ultrasound sensor system to carry out a method according to the invention for ultrasound-based object detection.

[0069] The commands can be provided, for example, as program code. This program code can be provided, for example, as binary code or assembler and / or as source code of a programming language, for example, C, and / or as a program script, for example, Python. According to a further aspect of the invention, another computer program with further commands is specified. When the further commands are executed by an electronic vehicle guidance system according to the invention, for example, by the data processing system of the electronic vehicle guidance system, the commands cause the electronic vehicle guidance system to carry out a method according to the invention for driver assistance in a motor vehicle.

[0070] The additional instructions can be provided, for example, as program code. This program code can be provided, for example, as binary code or assembly language, and / or as source code of a programming language, such as C, and / or as a program script, such as Python.

[0071] According to another aspect of the invention, a computer-readable storage medium is specified which stores a computer program according to the invention and / or a further computer program according to the invention.

[0072] The computer program, the further computer program, and the computer-readable storage medium are each computer program products with the commands or the further commands, respectively.

[0073] Further features of the invention are evident from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as those mentioned below in the description of the figures and / or illustrated in the figures, may be encompassed by the invention not only in the combinations specified, but also in other combinations. In particular, embodiments and combinations of features that do not include all the features of an originally formulated claim may also be encompassed by the invention. Furthermore, embodiments and combinations of features that go beyond or deviate from the combinations of features mentioned in the claims may also include the invention.

[0074] The invention is explained in more detail below with reference to specific exemplary embodiments and corresponding schematic drawings. Identical or functionally equivalent elements in the drawings may be provided with the same reference numerals. The description of identical or functionally equivalent elements is not necessarily repeated with respect to the different figures.

[0075] This shows:

[0076] Fig. 1 shows a schematic representation of a motor vehicle with an exemplary embodiment of an electronic vehicle guidance system according to the invention;

[0077] Fig. 2 shows a schematic representation of the relationship between distance and frequency in standing waves;

[0078] Fig. 3 shows a detail from the illustration in Fig. 2.

[0079] Fig. 4 shows a schematic representation of an emitted wave, a reflected wave and a resulting standing wave;

[0080] Fig. 5 shows another schematic representation of an emitted wave, a reflected wave and a resulting standing wave;

[0081] Fig. 6 shows a schematic representation of a mean amplitude and a phase of a secondary signal in an exemplary embodiment of a method according to the invention for ultrasound-based object detection;

[0082] Fig. 7 shows a further schematic representation of a mean amplitude and a phase of a secondary signal in an exemplary embodiment of a method according to the invention for ultrasound-based object detection;

[0083] Fig. 8 shows a further schematic representation of a mean amplitude and a phase of a secondary signal in an exemplary embodiment of a method according to the invention for ultrasound-based object detection; and

[0084] Fig. 9 shows a further schematic representation of a mean amplitude and a phase of a secondary signal in an exemplary embodiment of an inventive method for ultrasound-based object detection. Fig. 1 shows a schematic representation of a motor vehicle 1 with an exemplary embodiment of an inventive electronic vehicle guidance system 9.

[0085] The electronic vehicle guidance system 9 comprises an ultrasonic sensor system 7 according to the invention, with an ultrasonic sensor 2 mounted externally on the motor vehicle 1. The ultrasonic sensor system 7 is configured to detect an object 10 in the vicinity of the motor vehicle 1 and to perform an inventive method for ultrasonic-based object detection. The electronic vehicle guidance system 9 also comprises a control system 8, which is configured to generate a warning signal for a driver of the motor vehicle 1, depending on the detection of the object 10, and / or to generate at least one control signal for controlling at least one actuator of the motor vehicle 1.

[0086] The warning signal can, for example, alert the driver to the existence of object 10 and / or the distance of object 10 from motor vehicle 1.

[0087] The at least one control signal can be transmitted, for example, to one or more actuators of the motor vehicle 1 for longitudinal and / or lateral control of the motor vehicle 1, for example, for parking the motor vehicle 1. This can be the case in particular if the ultrasonic sensor 2 is mounted on a front or rear bumper of the motor vehicle 1 or on a sill of the motor vehicle 1 or the like.

[0088] For example, at least one control signal can be transmitted to one or more actuators of the motor vehicle for the automatic opening of a door, such as a driver's or passenger's door, a rear door, or a tailgate of the motor vehicle 1, or for the automatic opening of a flap, such as a tailgate or trunk lid of the motor vehicle 1. In particular, the automatic opening of the door or flap can be prevented if it is detected that the object 10 is located in the opening area of ​​the door or flap. In such embodiments, the ultrasonic sensor 2 is, for example, mounted on the door or flap or in the immediate vicinity of the door or flap, for example, in a sill or rear bumper of the motor vehicle 1.The ultrasonic sensor system 7 comprises, in addition to the ultrasonic sensor 2, a driver circuit 4 configured to drive the ultrasonic sensor 2 to emit an ultrasonic signal t by applying an electrical driver signal to the ultrasonic sensor 2. The ultrasonic sensor system 7 also comprises a measuring circuit 5 configured to determine a secondary electrical signal generated by the driver signal. The secondary signal is, in particular, an electrical current if the driver signal is a predetermined electrical voltage, and an electrical voltage if the driver signal is a predetermined electrical current. The ultrasonic sensor system 7 also comprises an evaluation unit 6 configured to detect the object 10 based on an anomaly in the secondary signal.

[0089] The driver signal can be configured differently with respect to its mean amplitude, also called envelope, and the shape and / or frequency of its oscillating component. The mean amplitude can be constant or variable, for example, sawtooth, triangular, rectangular, and so on. The oscillating component can be, for example, sinusoidal. The frequency of the oscillating component can be constant or variable, for example, changing linearly or piecewise linearly. This applies accordingly to the ultrasound signal t.

[0090] Figures 4 and 5 show the emitted ultrasonic signal t for two different frequencies. The horizontal axis plots the distance from the ultrasonic sensor 2 in normalized units, where the value 1 corresponds to the distance of object 10 from the ultrasonic sensor 2. Also shown is an ultrasonic signal r reflected from object 10, as well as the resulting superposition s. The vertical axis plots the amplitude of the signals in arbitrary units. For the sake of simplicity, the difference in the maximum amplitude of the emitted ultrasonic signal t and the reflected ultrasonic signal r is not shown.

[0091] The evaluation unit 6 is part of a data processing system 3. The data processing system 3 can, for example, also include the driver circuit 4 and / or the measuring circuit 5 and / or the control system 8. The data processing system 3, or parts thereof, the driver circuit 4 and / or the measuring circuit 5, can also, for example, be integrated into the ultrasonic sensor 2. The ultrasonic sensor system 7 according to the invention can detect the presence of the object 10 even in the ultra-close range of the ultrasonic sensor 2, i.e., in particular in the range of a few centimeters or less. For this purpose, the ultrasonic sensor 2 is not operated in pulse-echo mode, but in a mode that is at least comparable to a continuous transmission mode.If the object 10 is located near the ultrasonic sensor 2, its surface reflects the emitted ultrasonic signal t back to the ultrasonic sensor 2, and the transmitted and reflected waves superimpose, potentially resulting in constructive or destructive interference.

[0092] A particularly relevant point lies directly in front of the membrane of the ultrasonic sensor 2. If the phase angle of the emitted and reflected ultrasonic signals t, r differs by n, a standing wave results as a superposition s. This situation occurs when the frequency f and the distance d between the membrane and the reflection point on object 10 have a specific relationship, namely f = (c / V) / (2 d) , with the speed of sound c and N being a positive integer.

[0093] In other words, a given distance from the reflection point is characterized by a natural frequency f = (c N) / (2 d), since the respective phase velocities are approximately equal to the speed of sound c. In these situations, when the frequency approaches a natural frequency, the impedance of the diaphragm in the air is significantly increased. This increased impedance can be measured as a reduced resulting current as a secondary signal for a given voltage as the driver signal, or conversely, as an increased resulting voltage as a secondary signal for a given current as the driver signal, or, in other words, as a significant anomaly in the secondary signal. This altered impedance is also reflected in the phase relationship between the driver signal and the secondary signal.In general, however, the type of change depends on the specific design of the ultrasonic sensor 2, in particular on its resistive, capacitive and inductive components, so that it is generally an anomaly that occurs and characterizes the presence of the object 10.

[0094] In principle, such an anomaly can also occur if the frequency does not correspond to the stated natural frequency. However, the anomaly is then usually much less pronounced. This means that the described method works particularly reliably for objects 10 at discrete distances d = (cN) / (2f). For f = 50 kHz and at room temperature, this corresponds, for example, to distances d = N*3.43 mm. To achieve this increased reliability at other distances as well, the frequency can be varied in some embodiments. This also eliminates the influence of fluctuating sound speeds or wavelengths.

[0095] For example, the frequency can be varied linearly, which is also known as linear frequency modulation or linear frequency modulation chirp. It is particularly advantageous if the maximum frequency is at least twice as high as the minimum frequency, as this ensures that the entire spacing range is covered without gaps. Figures 2 and 3 illustrate this relationship between the spacing d and the natural frequencies f. In a specific application example, a linearly increasing frequency from the minimum frequency f1 = 30 kHz to the maximum frequency f2 = 60 kHz, or from f1 = 35 kHz to f2 = 70 kHz, could be used.

[0096] However, in some situations it can also be advantageous to tune a slightly smaller frequency range, even if this results in gaps in the spacing. Examples include: a) from f1 = 44 kHz to f2 = 62 kHz in steps of, for example, Hz to 300 Hz over a period of 5 ms to 10 ms; b) from f2 = 62 kHz to f1 = 44 kHz in steps of, for example, Hz to 300 Hz over a period of 5 ms to 10 ms; c) from f1 = 44 kHz to f2 = 62 kHz in steps of, for example, Hz to 300 Hz over a period of 5 ms to 10 ms, and then from f2 = 62 kHz to f1 = 44 kHz in steps of, for example, Hz to 300 Hz over a period of 5 ms to 10 ms.

[0097] The mean amplitude of the driver signal is predetermined, for example, constant, and the resulting secondary signal is measured and analyzed for anomalies that indicate the presence of object 10. For example, the mean amplitude and / or the phase of the secondary signal can be analyzed. Such an analysis can be performed, for example, by comparison with a measured or modeled reference, or by a trend, monotonicity, or step analysis of the respective curve.

[0098] It may be provided that the inventive procedure is only active at system startup to ensure freedom in the ultra-close range, or alternating with a standard pulse-echo mode, or whenever an obstacle leaves the field of view of the standard pulse-echo mode, or even permanently.

[0099] Since the inventive method is particularly advantageous in the ultra-close range, the concealed installation of the ultrasonic sensor 2, especially in moving parts such as flaps or doors of the vehicle 1, is also particularly advantageous. In this case, the ultrasonic sensor 2 is not integrated into the outer skin of the vehicle 1, for example by means of a bore in the corresponding component of the vehicle 1, but is mounted behind the outer skin and transmits its sound through it or uses it as a membrane. In the case of an electrically, for example automatically, driven door or flap, the inventive method can then be used, for example, to move the door or flap very close to a potential obstacle without touching it.

[0100] In Figures 6 to 9, the mean amplitude of the secondary signal, which in this case is primarily a current, is shown in Figure a) (top left) for the case of an object 10 at varying distances from the ultrasonic sensor 2, and the phase difference to the driver signal is shown in Figure b) (top right). A corresponding reference waveform without object 10 is shown in dashed lines. Figure c) (bottom left) shows the difference between the mean amplitude of the secondary signal and the corresponding reference waveform, and Figure d) (bottom right) shows the difference between the phase difference and the corresponding reference waveform. The anomalies are already clearly visible in Figures a) and b) and even more so in Figures c) and d).

Claims

Patent claims 1. Method for ultrasound-based object detection, wherein an ultrasound signal (t) is emitted by means of an ultrasound sensor (2); the ultrasound sensor (2) is supplied with an electrical driver signal to emit the ultrasound signal (t); the electrical driver signal corresponds to a predetermined electrical voltage and an electrical current caused by the driver signal is determined as the electrical secondary signal, or the electrical driver signal corresponds to a predetermined electrical current and an electrical voltage caused by the driver signal is determined as the electrical secondary signal; an object (10) is detected depending on an anomaly of the secondary signal.

2. Method according to claim 1, wherein the detection of the object (10) depending on the anomaly includes determining the existence of the object (10) within a detection range of the ultrasonic sensor (2) when the anomaly is present.

3. Method according to one of the preceding claims, wherein the ultrasound signal is generated such that its frequency changes according to a predetermined frequency profile.

4. Method according to claim 3, wherein the detection of the object (10) depending on the anomaly includes determining an anomaly frequency of the anomaly depending on the secondary signal; and determining a distance value depending on the anomaly frequency which corresponds to a distance of the object (10) from the ultrasonic sensor (2) up to an integer factor.

5. Method according to one of claims 3 or 4, wherein the frequency response is linear or piecewise linear.

6. Method according to claim 5, wherein the slope of the linear or piecewise linear curve is in the range [1 kHz / ms, 6 kHz / ms].

7. Method according to any one of claims 3 to 6, wherein a minimum frequency of the frequency response is in the range [30 kHz, 60 kHz]; and / or a maximum frequency of the frequency response is in the range [40 kHz, 80 kHz].

8. Method according to any one of claims 1 to 6, wherein the frequency profile has a minimum frequency and a maximum frequency which is at least twice as high as the minimum frequency.

9. Method according to any one of claims 3 to 8, wherein the anomaly includes an amplitude anomaly in a mean amplitude of the secondary signal and / or a phase anomaly in a phase of the secondary signal.

10. Method according to claim 9, wherein the amplitude anomaly is detected as a deviation of the mean amplitude of the secondary signal as a function of the frequency of the emitted ultrasound signal (t) from a predetermined amplitude reference curve; and / or the phase anomaly is detected as a deviation of the phase of the secondary signal as a function of the frequency of the emitted ultrasound signal (t) from a predetermined phase reference curve.

11. Method according to claim 9, wherein the amplitude anomaly is detected as a jump in the mean amplitude of the secondary signal as a function of frequency; and / or the phase anomaly is detected as a jump in the phase of the secondary signal as a function of frequency.

12. Method according to one of the preceding claims, wherein the object (10) is detected at a distance from the ultrasonic sensor (2) which is in the range [1 mm, 10 mm].

13. Method for driver assistance in a motor vehicle (1), wherein a method according to one of the preceding claims is carried out, wherein the ultrasonic sensor (2) is mounted on the motor vehicle (1); and depending on the detection of the object (10), a warning signal is generated for a driver of the motor vehicle (1) and / or at least one control signal is generated for controlling at least one actuator of the motor vehicle (1).

14. Method according to claim 13, wherein the at least one control signal corresponds to at least one control signal for longitudinal and / or lateral control of the motor vehicle (1); or corresponds to at least one control signal for automatic opening of a door or flap of the motor vehicle (1 ).

15. Ultrasonic sensor system (7) comprising an ultrasonic sensor (2) and a driver circuit (4) configured to drive the ultrasonic sensor (2) to emit an ultrasonic signal (t) and to supply the ultrasonic sensor (2) with an electrical driver signal; a measuring circuit (5) configured to - to determine an electric current caused by the driver signal as an electrical secondary signal, wherein the electrical driver signal corresponds to a predetermined electrical voltage; or - to determine an electrical voltage caused by the driver signal as an electrical secondary signal, wherein the electrical driver signal corresponds to a predetermined electrical current; and a data processing system (3, 6) that is configured to detect an object (10) depending on an anomaly of the secondary signal.

16. Ultrasonic sensor system according to claim 15, wherein the data processing system (3, 6) is configured to detect the object (10) in a first operating mode depending on the anomaly of the secondary signal and in a second Operating mode to detect the object (10) and / or another object based on a pulse-echo method.

17. Electronic vehicle guidance system (9) for a motor vehicle (1) comprising an ultrasonic sensor system (7) according to claim 15 or claim 16 and a control system (8) configured to generate a warning signal for a driver of the motor vehicle (1) depending on the detection of the object (10) and / or to generate at least one control signal for controlling at least one actuator of the motor vehicle (1).

18. computer program product Commands which, when executed by an ultrasonic sensor system (7) according to one of claims 15 or 16, cause the ultrasonic sensor system (7) to perform a method according to one of claims 1 to 12; and / or further commands which, when executed by an electronic vehicle guidance system (9) according to claim 17, cause the electronic vehicle guidance system (9) to perform a method according to one of claims 13 or 14.

Images