EP3555662A1

EP3555662A1 - Method for operating an ultrasonic sensor

Info

Publication number: EP3555662A1
Application number: EP17798180.0A
Authority: EP
Inventors: Dirk Schmid; Michael Schumann
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2016-12-14
Filing date: 2017-11-08
Publication date: 2019-10-23
Also published as: CN110073242B; JP2020502500A; DE102016224932A1; JP6840241B2; CN110073242A; US20200072973A1; WO2018108388A1

Abstract

The invention relates to a method for operating an ultrasonic sensor, in which a plurality of measuring cycles are run in succession. In each measuring cycle: - an electroacoustic transducer of said ultrasonic sensor is excited, by means of an exciting pulse, to mechanically vibrate, as a result of which a measurement signal is sent by the transducer; - an echo signal is received by the transducer; and - an item of object information is determined from said echo signal. The frequency response curve of the exciting pulse is differentiated, according to the invention, into measuring cycles run in temporal succession, wherein the frequency response curve of an exciting pulse is selected, in each measuring cycle, from a group of predetermined frequency response curves, either at random or according to a predetermined sequence.

Description

description

title

Method for operating an ultrasonic sensor

The invention relates to a method for operating an ultrasonic sensor, as well as a distance measuring device with at least one ultrasonic sensor, which is operated according to the inventive method.

State of the art

Ultrasonic-based measuring systems are used to measure a distance to an object located in front of an ultrasonic sensor. The sensors used are based on the pulse / echo method. In this operation, an ultrasonic sensor emits an ultrasonic pulse and measures the reflection of the ultrasonic pulse (echo) caused by an object. The distance between the ultrasonic sensor and the object is calculated using the measured echo time and the speed of sound. The ultrasonic sensor acts as transmitter to receiver. Known applications are, for example

Distance warning systems, parking space detectors and parking aids for

Motor vehicles. Usually, several ultrasonic sensors are used in such a measuring system.

In known distance measuring devices on vehicles typically 4 to 6 ultrasonic sensors are used in the front and / or rear bumper. To capture the environment as quickly as possible, it is helpful if all the ultrasonic sensors on the bumper send at the same time and thus the information can be processed in parallel. This can special

Stimulation pattern, so-called codes for sending out for each of

Ultrasonic sensors are chosen that differ. DE 10 2007 029 959 A1 discloses an ultrasound-based measuring system for detecting an environment. It is provided that distance measurements can be made by means of ultrasonic waves. At two

to be able to distinguish successive pulses, these are

frequency modulated.

DE 10 2013 021 845 A1 again discloses a method for measuring a distance by means of ultrasound. It is envisaged that individual

Ultrasonic signals are coded for distinctness.

The processing of the signals in the receive path can be done, for example, by the received signals through a matched filter

(so-called "matched filter") are filtered.

Usually, so-called "ideal codes" are used for the excitation. "Ideal codes" are characterized in that the codes are mutually orthogonal, i. that the matched filters of the codes act in such a way that they largely suppress the foreign codes. In practice, however, complete suppression by the matched filters is hardly possible.

If a particular code is assigned to an ultrasonic sensor of the distance measuring device, then in the case of a foreign vehicle which uses the same coding, the fault is maximum at exactly the time when the parties involved are involved

Opposite ultrasonic sensors.

Disclosure of the invention

The invention is therefore based on the object to provide a method for operating an ultrasonic sensor, in which the influence of disturbances, which can be caused in particular by ultrasonic signals of other vehicles, is reduced.

The invention is based on the idea of receiving signals from one

According to the invention operated ultrasonic sensor are sent to encode. The coding takes place either by means of randomly selected codes or by means of randomly selected code sequences. In addition, it is preferable to stochastically jitter a time of emission of an ultrasonic signal. In this way it can be ensured that interference from adjacent ultrasound systems, such as in particular in the encounter of two vehicles of the case, are largely avoided. In this case, according to the invention, a change of the codes is provided after each measuring cycle. The measuring cycle is a complete run until the next transmission operation of the same sensor.

It is therefore a method for operating an ultrasonic sensor

proposed, wherein a plurality of measuring cycles are performed sequentially. In each measuring cycle is

- An electro-acoustic transducer of the ultrasonic sensor with a

Excitation pulse is excited to mechanical vibrations, whereby a measurement signal is sent through the transducer,

receive an echo signal through the converter, and

- Determined from the echo signal object information.

The frequency response of the excitation pulse differs

According to the invention, measurement cycles executed sequentially in time, wherein the frequency profile of an excitation pulse in each measurement cycle is selected at random or in a predetermined order from a group of predetermined frequency profiles.

In other words, it is accordingly provided according to the invention to operate an ultrasonic sensor for measuring a distance with a special code. Each code corresponds to a specific excitation pattern, it being provided that after each excitation for a temporally following, renewed excitation another excitation pattern, so another code is used. In this case, according to a first variant of the invention, a code from a given group of codes can be randomly selected in each measuring cycle. According to a second variant, the order in which the codes are selected from the given group of codes is fixed. Preferably, the determined object information from at least two measuring cycles are compared with each other and depending on the result of the comparison, a fault is detected. In this case, a malfunction is understood as meaning, in particular, a faulty measurement which may be caused by an ultrasound signal from a foreign ultrasound sensor, which is part of a distance measuring system of a foreign vehicle, for example.

Preferably, the emission time is stochastically jittered within a respective measurement cycle Aussendezeitpunkt. This means that the time at which the respective excitation pulse is applied to the transducer, relative to a

Start time of the measurement cycle is shifted by a randomly selected period. This time period is particularly small in comparison to the total duration of the respective measurement cycle and may be, for example, in the range of 1 to 10 ms, wherein the total duration of the measurement cycle may be, for example, about 40 ms. This embodiment is particularly in the second variant of

Invention is advantageous because in the second variant, although the probability of synchronization is reduced, but it can still interfere with the deterministic order of the selected excitation pattern (codes). This effect can be caused by the stochastic jitter of the

Broadcasting time will be further minimized. Also for the first variant is a

Jitter advantageous.

Furthermore, it is advantageous if the excitation patterns (codes) of the group selected from are designed such that they suppress one another as far as possible. This is achieved, for example, by having the codes of the group orthogonal to each other.

In a preferred embodiment, the duration of a first excitation pulse of a first measurement cycle differs from the duration of a second excitation pulse of a second measurement cycle, wherein the second measurement cycle follows the time of the first measurement cycle. The second measuring cycle can directly follow the first measuring cycle. This means that no further signal is transmitted between the first and the second measuring cycle, but there may be a pause between the first and the second measuring cycle in which no excitation takes place. Alternatively, the second Measuring cycle not immediately follow the first measurement cycle, but between the first and the second measurement cycle, a further excitation.

Alternatively or additionally, the amplitude of a first excitation pulse of a first measurement cycle may differ from the amplitude of a second excitation pulse of a second measurement cycle. This causes the

Sound pressure of the respective emitted signals is different. The second measuring cycle can directly follow the first measuring cycle. This means that no further signal is transmitted between the first and the second measuring cycle, but there may be a pause between the first and the second measuring cycle in which no excitation takes place. Alternatively, the second measurement cycle can not follow directly on the first measurement cycle, but between the first and the second measurement cycle another

Suggestion.

The excitation pulses are preferably designed as frequency-modulated pulses. For the purposes of this invention, a frequency-modulated excitation pulse is to be understood as meaning any excitation pulse whose frequency changes during the pulse duration. In this case, continuous or discontinuous changes in the frequency can be provided. Alternatively or additionally, it is also possible to use pulses with a continuously constant excitation frequency.

In a preferred embodiment of the invention, the respective

Excitation pulses, by a, in particular linear, frequency response, modulated, in particular in a frequency range between 40 kHz and 60 kHz. This means that the frequency of the respective excitation pulse rises steadily and in particular linearly from a starting frequency or drops until an end frequency is reached. Such an excitation is also referred to as "chirp." The start and end frequencies are preferably selected from the frequency range from 40 kHz to 60 kHz.

In a particularly preferred embodiment of the invention, the

received echo signals by means of a matched filter (also referred to as an optimal filter or correlation filter) filtered. This can be done in an advantageous manner the signal-to-noise ratio can be improved by using the known waveform of the excitation pulse in the selection of the filter in a known manner. Depending on the filter result, object information is determined with higher accuracy.

In a particularly preferred embodiment of the invention, depending on the result of the comparison of the object information from at least two

Measuring cycles calculates a probability that a detected object is actually present or that there is a faulty measurement. This can be particularly efficient suppression of interference by ultrasonic signals from other vehicles in the sense of incorrect measurements C.False Positives ") can be achieved.

In a preferred embodiment of the invention are in the operation of the

Ultrasonic sensor provided at least four measuring cycles, wherein in each measuring cycle, the transducer of the ultrasonic sensor is driven with an excitation pulse with a different excitation pattern or frequency response, either randomly an excitation pattern from a group of possible excitation patterns is selected in each measurement cycle, or it is

Excitation pattern selected from a group according to a given order.

According to a second aspect of the invention, a distance measuring device, in particular for a motor vehicle, is provided which comprises at least one ultrasonic sensor which is operated according to one of the methods described above.

In particular, a distance measuring device is provided, which comprises a plurality of ultrasonic sensors, which are operated in accordance with a method as described above, wherein the ultrasonic sensors on a

Body part of a motor vehicle are arranged in a row. In this case, the ultrasonic sensors are operated in such a way that ultrasonic sensors arranged adjacent to one another have measurement cycles which do not overlap in time. Brief description of the drawings

Figure 1 shows schematically a distance measuring device with a plurality of ultrasonic sensors according to an embodiment of the invention.

FIG. 2 shows four diagrams of possible frequency profiles for excitation pulses.

FIG. 3 shows a table with a sequence of measuring cycles for different ultrasonic sensors of a distance measuring device with a plurality of ultrasonic sensors according to an embodiment of the invention.

Embodiments of the invention

In the following description of the embodiments of the invention, the same elements are denoted by the same reference numerals, wherein a repeated description of these elements is optionally omitted. The figures illustrate the subject matter of the invention only schematically.

Figure 1 shows schematically in plan view a motor vehicle 20 with a

Front bumper 27, on the ultrasonic sensors 1 to 6 in a row

are arranged and a rear bumper 28 are arranged on the ultrasonic sensors 7 to 12 in a row. The ultrasonic sensors 1 to 12 are part of a distance measuring device for detecting the environment of the motor vehicle 20. Furthermore, an object 19 to be detected by means of the ultrasonic sensors is shown in the surroundings of the motor vehicle 20. It may be, for example, a traffic obstruction, such as a bucket, a street sign or a lantern as well as another vehicle.

Each of the ultrasonic sensors 1 to 12 has an electroacoustic transducer, which is excited by a frequency-modulated excitation pulse to mechanical vibrations, whereby a measuring signal 30 is emitted through the transducer. The invention is not limited to that

Ultrasonic sensors are arranged at the rear or at the front of a motor vehicle 20. Alternatively or additionally, further ultrasonic sensors For example, in the area of the sides, in particular the doors of the

Motor vehicle 20 may be arranged.

In connection with the ultrasonic sensor 3, a transmission cone of a transmitted measuring signal 30 and a directional arrow 31, which indicates the transmission direction, are shown by way of example. It can be seen that the transmission cone hits the object 19, so that the measurement signal 30 is partially reflected by the object 19 in the direction of the ultrasound sensor 3 in a second transmission cone (echo) 32.

The ultrasonic sensor 3 registers the reflection 32 and determines the elapsed time between transmission of the transmission pulse and reception of the reflection. From the elapsed time can be at a known signal speed, for example, the speed of sound in air of about 343 m / s, calculate the distance of the object 19 of the ultrasonic sensor 3.

The same measuring principle applies to the other ultrasonic sensors.

Now, the ultrasonic sensor 3 can not only receive the measurement signals 32 reflected by the object 19 but also ultrasonic signals 33 emanating from another sound source 21, for example a foreign vehicle. This can lead to erroneous measurement results, or it will be of the

Distance measuring system objects detected, although in reality no object exists C.False Positive ").

In order to counteract these problems, the ultrasound sensor 3 is operated in such a way that several measuring cycles are carried out successively. In each measurement cycle, another excitation pulse is used to excite the

electroacoustic transducer used as in the previous measuring cycle, wherein in successive time measuring cycles, the respective frequency response of the excitation pulses differs. It is the

Frequency response of an excitation pulse in each measurement cycle selected from a group of predetermined frequency curves randomly or in a predetermined order. In particular, frequency modulated excitation pulses (codes) as

This means that the excitation frequency is linearly changed from a start frequency to a target frequency during the excitation pulse, but the invention is not limited to this type of frequency modulation, it is also other excitation patterns Furthermore, for example, constant frequency profiles can be used, at least in sections, for the person skilled in the art, for which a variety of further design possibilities are known.

According to a preferred embodiment of the invention, it is now provided for each of the ultrasonic sensors 1 to 12 to vary the excitation patterns (codes) from shot to shot in such a way that the frequency response of the excitation pulses takes place in successively executed measuring cycles

differs, wherein the frequency response of an excitation pulse in each measurement cycle from a group of predetermined frequency characteristics is selected randomly or in a predetermined order.

Exemplary excitation patterns for the frequency-modulated excitation pulses are shown in the figure in diagrams 41-44. In each case the frequency is plotted against time. These excitation patterns preferably form a group from which an excitation pattern is selected as the excitation pulse for the transducer of an ultrasonic sensor 1 to 12 in each measurement cycle. The selection can be done either by chance or after a predetermined

Sequence. The frequency fo is in this example 48 kHz, the pulse duration T is 1.6 ms.

In the exemplary embodiment illustrated in FIG. 2, it is provided that the group of possible excitation patterns contains the following excitation patterns (codes):

a linear chirp 41 from a start frequency fo = 48.5 kHz to one

Final frequency of fo + Af = 53.5 kHz with a duration of 1.6 ms (= 1600μ5) is executed. This form of an excitation pulse is referred to below with the symbol Cll. - A linear chirp 42 from the start frequency fo = 48 kHz to the final frequency fo - Af = 43 kHz with a duration of 1.6 ms (= 1600μ5) is executed. This form of an excitation pulse is denoted below by the symbol C9.

- A linear chirp 43 from the start frequency of 54 kHz to the final frequency of 45 kHz with a duration of 1.6 ms (= 1600μ5) is executed. This form of excitation pulse is denoted below by the symbol C3.

- A linear chirp 44 from the start frequency of 43.5 kHz to the final frequency of 52.5 kHz with a duration of 1.6 ms (= 1600μ5) is executed. This form of an excitation pulse is denoted below by the symbol C4.

These excitation patterns can now be performed in each of the ultrasonic sensors in a specific or random order, wherein in an ultrasonic sensor each temporally successive measurement cycles preferably differ in their respective excitation pattern.

In addition, a jittering of the starting time to an excitation by one of the excitation pulses C9, Cl1, C3 or C4 may additionally take place.

It should be noted that the representation of the excitation pattern according to FIG. 2 is to be understood as schematic and not true to scale.

A possible example of the timing of the activation of the

Ultrasonic sensors 1 to 12 are shown in tabular form in FIG.

The rows of the table refer to time intervals that are available for a measuring cycle. In such a time interval, both the excitation of the electroacoustic transducer and the reception of reflected ultrasonic signals and the determination of an object information occur. These time intervals can each have the same length, but it can also be provided different lengths. The columns of the table respectively refer to a pair of ultrasonic sensors 1 and 7, 2 and 8, 3 and 9, 4 and 10, 5 and 11 respectively arranged at the front and rear. FIGS. 6 and 12, respectively in this example be driven simultaneously with the same excitation pattern.

In this example, therefore, the ultrasonic sensor 1 and the ultrasonic sensor 7 at the beginning of the operation of the distance measuring device in a first

Time interval la, according to its first measuring cycle with a

Excited pulse of the form C3, the respective electro-acoustic

Transducer of the ultrasonic sensors 1 and 7 is thus charged with a corresponding excitation pulse and each sends a corresponding measurement signal. At the same time, the ultrasonic sensors 3 and 9 are driven with an excitation pulse of the form Cll. Also at the same time, the ultrasonic sensors 5 and 11 are driven with an excitation pulse of the form C9.

Subsequent to the first time interval, the ultrasonic sensor pair 2/8 is then triggered in a second time interval lb with an excitation pulse of the form C9. At the same time, the ultrasonic sensor pair 4/10 is driven with an excitation pulse of the form Cll. At the same time, the ultrasonic sensor pair 6/12 is driven with an excitation pulse of the form C3

In a temporally subsequent third time interval 2a is the

Ultrasonic sensor pair 1/7 with an excitation pulse of the form C4 driven. At the same time, the ultrasonic sensor pair 3/9 is driven with an excitation pulse of the form C9. At the same time, the ultrasonic sensor pair 5/11 is driven by an excitation pulse of the form Cll.

In a temporally subsequent fourth time interval 2b is the

Ultrasonic sensor pair 2/8 with an excitation pulse of the form Cll

driven. At the same time, the pair of ultrasonic sensors 4/10 with a

Excited pulse of the form C9. At the same time it will be

Ultrasonic sensor pair 6/12 with an excitation pulse of the form C4

driven. In a time-subsequent fifth time interval 3a is the

Ultrasonic sensor pair 1/7 driven with an excitation pulse of the form C3. At the same time, the ultrasound sensor pair 3/9 is driven by an excitation pulse of the form Cll. At the same time, the ultrasonic sensor pair 5/11 is driven with an excitation pulse of the form C9.

In a temporally subsequent sixth time interval 3b is the

Ultrasonic sensor pair 2/8 driven with an excitation pulse of the form C9. At the same time, the ultrasonic sensor pair 4/10 is driven with an excitation pulse of the form Cll. Also at the same time the ultrasonic sensor pair

6/12 driven with an excitation pulse of the form C3.

In a time-subsequent seventh time interval 4a is the

Ultrasonic sensor pair 1/7 with an excitation pulse of the form C4 driven. At the same time the ultrasonic sensor pair 3/9 with an excitation pulse of

Form C9 activated. At the same time, the ultrasonic sensor pair 5/11 is driven by an excitation pulse of the form Cll.

In a time subsequent eighth time interval 4b is the

Ultrasonic sensor pair 2/8 with an excitation pulse of the form Cll

driven. At the same time, the pair of ultrasonic sensors 4/10 with a

Excited pulse of the form C9. At the same time it will be

Ultrasonic sensor pair 6/12 with an excitation pulse of the form C4

driven.

Looking at a single ultrasonic sensor or a

Ultrasonic sensor pair, it is clear from the table of FIG. 3 that each ultrasonic sensor or each ultrasonic sensor pair considered individually from shot to shot (ie in successive measuring cycles of the respective sensor or sensor pair) changes its excitation pattern. For example, a measurement is carried out with the ultrasonic sensor 1 in the first time interval. The first time interval thus corresponds to the first measuring cycle of the ultrasonic sensor 1. In this first measuring cycle, the electroacoustic transducer of the ultrasonic sensor 1 is excited to mechanical oscillations with a frequency-modulated excitation pulse having the shape C3. To Completion of the measurement cycle, the ultrasonic sensor 1 remains passive until the second measurement cycle of the ultrasonic sensor 1 is performed in the third time interval. In this second measurement cycle, the electroacoustic transducer of the

Ultrasonic sensor 1 with a frequency-modulated excitation pulse of the form C4 has excited to mechanical vibrations. The third measuring cycle of the ultrasonic sensor 1 takes place in the fifth time interval. The fourth

Measuring cycle of the ultrasonic sensor 1 takes place in the seventh time interval. In each measurement cycle, the frequency response of the

frequency-modulated excitation pulse. This also applies to everyone else

Ultrasonic sensors 2 to 6.

It also becomes clear that adjacently arranged sensors are not operated simultaneously.

Following the transmission of measurement signals 30 by one of

Ultrasonic sensors 1 to 12, the respective ultrasonic sensor 1 to 12 receive a reflected ultrasonic signal 32. By appropriate filtering of the received signals, which is adapted in particular in the form of a "matched filter" to the frequency response of the excitation pulse, actual echo signals can be distinguished from external signals 33 by the

Foreign signals are suppressed by the filter. Due to the embodiment according to the invention, that the respective frequency profile of the excitation pulses differs in measuring cycles executed one after the other in time, wherein the

Frequency response of an excitation pulse in each measurement cycle from a group of predetermined frequency characteristics is selected randomly or in a predetermined order, it is ensured that even with identically designed distance measuring systems on foreign vehicles, there is only a very small chance that the foreign signal 33 exactly the same

Frequency characteristic has, as the own measurement signal 30th

Claims

claims

A method of operating an ultrasonic sensor (1-12), wherein a plurality of measurement cycles are performed sequentially, wherein in each measurement cycle

an electroacoustic transducer of the ultrasonic sensor (1-12) is excited to mechanical vibrations with an excitation pulse, whereby a measurement signal (32) is sent through the transducer,

an echo signal (12) is received by the transducer, an object information is determined from the echo signal, wherein the frequency profile (41, 42, 43, 44) of the excitation pulse differs in two consecutively executed measurement cycles, characterized in that the frequency profile (41, 42, 43, 44) of an excitation pulse in each measuring cycle from a group of predetermined frequency curves at random or after one

predetermined order is selected.

2. The method according to claim 1, characterized in that

Object information from at least two measuring cycles are compared with each other and depending on the result of the comparison, a fault is detected.

3. The method according to claim 1 or 2, characterized in that the excitation pulses have a total duration (T) of ΙΟΟμε to 3000μ5, in particular a total duration (T) of ΙΘΟΟμε have.

4. The method according to any one of claims 1 to 3, characterized in that the duration of a first excitation pulse of a first measurement cycle is different from the duration of a second excitation pulse of a second measurement cycle. Method according to one of claims 1 to 4, characterized in that the amplitude of a first excitation pulse of a first

Measuring cycle is different from the amplitude of a second excitation pulse of a second measurement cycle.

Method according to one of claims 1 to 5, characterized in that at least one excitation pulse as a frequency modulated

Excitation pulse is executed.

7. The method according to claim 6, characterized in that at least one excitation pulse, in particular by a linear frequency characteristic (41, 42, 43, 44) is modulated between a start frequency and a final frequency, wherein the start frequency and the end frequency of a frequency range between 40 kHz to 60 kHz are selected.

8. The method according to any one of claims 1 to 7, characterized in that the echo signals are filtered by means of a matched filter and depending on the filter result, an object information is determined.

9. The method according to any one of claims 1 to 8, characterized in that depending on the result of the comparison of the object information from at least two measuring cycles, a probability is calculated that a detected object (19) is actually present or that a faulty measurement is present.

10. The method according to any one of claims 1 to 9, characterized in that at least two measuring cycles are performed. 11. The method according to claim 10, characterized in that four or more measuring cycles are provided.

12. Distance measuring device, in particular for a motor vehicle (20), comprising at least one ultrasonic sensor (1 - 12), which is operated according to a method according to one of claims 1 to 11. Distance measuring device comprising a plurality of

Ultrasonic sensors (1 - 12), which are operated according to a method according to one of claims 1 to 11, wherein the ultrasonic sensors (1 - 12) on a body part (27, 28) of a motor vehicle (20) are arranged in a row, characterized in that the ultrasonic sensors (1-12) are operated in such a way that ultrasonic sensors (1-12) arranged adjacent to one another have measurement cycles that do not overlap in time.