METHOD FOR OPERATING AN ULTRASONIC SENSOR

Abstract

A method for operating an ultrasonic sensor is provided, a plurality of measuring cycles being consecutively carried out. In each measuring cycle, an electroacoustic transducer of the ultrasonic sensor is excited to carry out mechanical oscillations with the aid of an excitation pulse, whereby a measuring signal is transmitted by the transducer, an echo signal is received by the transducer, and a piece of object information is ascertained from the echo signal. The frequency profile of the excitation pulse differs in measuring cycles which are carried out chronologically consecutively, the frequency profile of an excitation pulse being selected in each measuring cycle randomly or according to a predefined sequence from a group of predefined frequency profiles.

Claims

1-13. (canceled)

14. A method for operating an ultrasonic sensor, the method comprising: consecutively carrying out a plurality of measuring cycles, in each of the measuring cycles: exciting an electroacoustic transducer of the ultrasonic sensor via an excitation pulse to carry out mechanical oscillations, whereby a measuring signal is transmitted by the transducer; receiving an echo signal the transducer; and ascertaining a piece of object information from the echo signal; wherein a frequency profile of the excitation pulse being different in two measuring cycles which are carried out chronologically consecutively; wherein the frequency profile of the excitation pulse is selected in each measuring cycle randomly or according to a predefined sequence from a group of predefined frequency profiles.

15. The method as recited in claim 14, wherein the object information from at least two measuring cycles is compared to one another and an interference is detected as a function of a result of the comparison.

16. The method as recited in claim 14, wherein the excitation pulses have a total duration from 100 s to 3000 s.

17. The method as recited in claim 14, wherein the excitation pulses have a total duration of 1600 s.

18. The method as recited in claim 14, wherein a duration of a first excitation pulse of a first measuring cycle of the measuring cycles differs from a duration of a second excitation pulse of a second measuring cycle of the measuring cycles.

19. The method as recited in claim 14, wherein an amplitude of a first excitation pulse of a first measuring cycle of the measuring cycles differs from an amplitude of a second excitation pulse of a second measuring cycle of the measuring cycles.

20. The method as recited in claim 14, wherein at least one excitation pulse is carried out as a frequency modulated excitation pulse.

21. The method as recited in claim 20, wherein at least one excitation pulse is modulated, by a linear frequency profile, between a starting frequency and an end frequency, the starting frequency and the end frequency being selected from a frequency range between 40 kHz and 60 kHz.

22. The method as recited in claim 14, wherein the echo signals are filtered using a matched filter and a piece of object information is ascertained as a function of a filtering result of the filtering.

23. The method as recited in claim 14, wherein a probability that a detected object is indeed present or that the measurement is erroneous is computed as a function of a result of a comparison of the object information from at least two measuring cycles of the measuring cycles.

24. The method as recited in claim 14, wherein the measuring cycles include at least two measuring cycles.

25. The method as recited in claim 24, wherein the measuring cycles include at least four measuring cycles are provided.

26. A distance measuring device for a motor vehicle, comprising: at least one ultrasonic sensor, the at least one ultrasonic sensor being operated by: consecutively carrying out a plurality of measuring cycles, in each of the measuring cycles: exciting the consecutively carrying out a plurality of measuring cycles, in each of the measuring cycles: exciting an electroacoustic transducer of the ultrasonic sensor via an excitation pulse to carry out mechanical oscillations, whereby a measuring signal is transmitted by the transducer; receiving an echo signal the transducer; and ascertaining a piece of object information from the echo signal; wherein a frequency profile of the excitation pulse being different in two measuring cycles which are carried out chronologically consecutively; wherein the frequency profile of the excitation pulse is selected in each measuring cycle randomly or according to a predefined sequence from a group of predefined frequency profiles.

27. The distance measuring device, comprising: a plurality of ultrasonic sensors, the ultrasonic sensors being situated in a line at a chassis part of a motor vehicle, each of the ultrasonic sensors being operated by: consecutively carrying out a plurality of measuring cycles, in each of the measuring cycles: exciting the consecutively carrying out a plurality of measuring cycles, in each of the measuring cycles: exciting an electroacoustic transducer of the ultrasonic sensor via an excitation pulse to carry out mechanical oscillations, whereby a measuring signal is transmitted by the transducer; receiving an echo signal the transducer; and ascertaining a piece of object information from the echo signal; wherein a frequency profile of the excitation pulse being different in two measuring cycles which are carried out chronologically consecutively; wherein the frequency profile of the excitation pulse is selected in each measuring cycle randomly or according to a predefined sequence from a group of predefined frequency profile; wherein the ultrasonic sensors are operated in such a way that the ultrasonic sensors which are situated adjacent to one another do not have chronologically overlapping measuring cycles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 schematically shows a distance measuring device including a plurality of ultrasonic sensors according to one embodiment of the present invention.

[0030] FIG. 2 shows four diagrams of possible frequency profiles for the excitation pulses.

[0031] FIG. 3 shows a table having a sequence of measuring cycles for different ultrasonic sensors of a distance measuring device including a plurality of ultrasonic sensors according to one embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0032] In the following description of the exemplary embodiments of the present invention, identical elements are denoted by the same reference numerals; a repetitive description of these elements is dispensed with. The figures represent the subject matter of the present invention only schematically.

[0033] FIG. 1 schematically shows in a top view a motor vehicle 20 including a front bumper 27 on which ultrasonic sensors 1 through 6 are situated in a line and a rear bumper 28 on which ultrasonic sensors 7 through 12 are situated in a line. Ultrasonic sensors 1 through 12 are part of a distance measuring device for detecting the surroundings of motor vehicle 20. Furthermore, an object 19 to be detected with the aid of the ultrasonic sensors is illustrated in the surroundings of motor vehicle 20. Object 19 may, for example, involve a traffic obstruction, such as a flower tub, a traffic sign, or a street lamp as well as another vehicle.

[0034] Each of ultrasonic sensors 1 through 12 includes an electroacoustic transducer which is excited by a frequency modulated excitation pulse to carry out mechanical oscillations, whereby a measuring signal 30 is transmitted by the transducer. The present invention is not limited to the ultrasonic sensors being situated at the rear end or at the front end of a motor vehicle 20. Alternatively or additionally, further ultrasonic sensors may be situated, for example in the area of the sides, in particular of the doors, of motor vehicle 20.

[0035] In conjunction with ultrasonic sensor 3, a transmitting cone of a transmitted measuring signal 30 as well as a directional arrow 31, which indicates the transmitting direction, is illustrated by way of example. It is apparent that the transmitting cone hits object 19, so that measuring signal 30 is partially reflected from object 19 in the direction toward ultrasonic sensor 3 in a second transmitting cone (echo) 32.

[0036] Ultrasonic sensor 3 registers reflection 32 and the time which elapsed overall between the transmission of the transmitted pulse and the reception of the reflection is determined. The elapsed time is used to compute the distance of object 19 from ultrasonic sensor 3, when the signal speed is known, for example the speed of sound in the air of approximately 343 m/s.

[0037] The same measuring principle applies to the other ultrasonic sensors.

[0038] Now, ultrasonic sensor 3 is not only able to receive measuring signals 32 which are reflected from object 19, but also ultrasonic signals 33 which are emitted by a different sound source 21, for example by another vehicle. This may result in erroneous measuring results or objects being detected by the distance measuring system, even though in reality, there is no object present (false positive).

[0039] In order to address these problems, ultrasonic sensor 3 is operated in such a way that several measuring cycles are carried out consecutively. In each measuring cycle, a different excitation pulse is used to excite the electroacoustic transducer than was used in the preceding measuring cycle, the particular frequency profile of the excitation pulses being different in the measuring cycles which are carried out chronologically consecutively. In this case, the frequency profile of an excitation pulse is selected in each measuring cycle randomly or according to a predefined sequence from a group of predefined frequency profiles.

[0040] Frequency modulated excitation pulses (codes) are in particular selected as those excitation patterns which are designed as so-called linear FM chirps. This means that the excitation frequency linearly changes during the excitation pulse from a starting frequency to a target frequency. The present invention is, however, not limited to this type of frequency modulation; other excitation patterns are also possible, such as rising and then declining frequencies during an excitation pulse. Furthermore, at least sectionally constant frequency profiles may also be used, for example. Those skilled in the art are aware of various other possible implementations related hereto.

[0041] According to one preferred embodiment of the present invention, it is now provided for each of ultrasonic sensors 1 through 12 to vary the excitation patterns (codes) on a shot-to-shot basis in such a way that the particular frequency profile of the excitation pulses differs in measuring cycles which are carried out chronologically consecutively, the frequency profile of an excitation pulse being selected in each measuring cycle randomly or according to a predefined sequence from a group of predefined frequency profiles.

[0042] Exemplary excitation patterns for the frequency modulated excitation pulses are shown in the figure in diagrams 41 through 44. In this case, the frequency is plotted against time in each case. These excitation patterns preferably form a group from which one excitation pattern is selected in each measuring cycle as the excitation pulse for the transducer of an ultrasonic sensor 1 through 12. The selecting process may either take place randomly or according to a predetermined sequence. Frequency f.sub.0 is 48 kHz in this example, pulse duration T is 1.6 ms.

[0043] In the exemplary embodiment illustrated in FIG. 2, it is provided that the group of possible excitation patterns includes the following excitation patterns (codes): [0044] a linear chirp 41 is carried out from a starting frequency f.sub.0=48.5 kHz to an end frequency f.sub.0+f=53.5 kHz at a duration of 1.6 ms (=1600 s). This form of an excitation pulse is denoted in the following with symbol C11. [0045] a linear chirp 42 is carried out from the starting frequency f.sub.0=48 kHz to end frequency f.sub.0f=43 kHz at a duration of 1.6 ms (=1600 s). This form of an excitation pulse is denoted in the following with symbol C9. [0046] a linear chirp 43 is carried out from the starting frequency of 54 kHz to the end frequency of 45 kHz at a duration of 1.6 ms (=1600 s). This form of an excitation pulse is denoted in the following with symbol C3. [0047] a linear chirp 44 is carried out from the starting frequency of 43.5 kHz to the end frequency of 52.5 kHz at a duration of 1.6 ms (=1600 s). This form of an excitation pulse is denoted in the following with symbol C4.

[0048] These excitation patterns may now be carried out in each of the ultrasonic sensors in a determined or random sequence, chronologically consecutive measuring cycles preferably differing from one another in one ultrasonic sensor in terms of their particular excitation patterns.

[0049] Preferably, starting point in time t.sub.0 of an excitation by one of excitation pulses C9, C11, C3, or C4 may be additionally jittered.

[0050] It is to be pointed out that the illustration of the excitation patterns according to FIG. 2 is to be understood to be schematic and not true to scale.

[0051] One possible example of the chronological sequence of the control of ultrasonic sensors 1 through 12 is illustrated tabularly in FIG. 3. Here, the rows of the table refer to the time intervals which are available for a measuring cycle. In such a time interval, the excitation of the electroacoustic transducer as well as the reception of reflected ultrasonic signals and the ascertainment of a piece of object information take place. These time intervals may each have the same length, differing lengths may, however, also be provided.

[0052] The columns of the table refer in each case to a pair of ultrasonic sensors 1 and 7, 2 and 8, 3 and 9, 4 and 10, 5 and 11, and 6 and 12 which are situated at the front end and at the rear end and which are each controlled simultaneously with the aid of the same excitation pattern in this example.

[0053] This means that in this example, ultrasonic sensor 1 and ultrasonic sensor 7 are controlled with the aid of an excitation pulse of form C3 at the beginning of the operation of the distance measuring device in a first time interval 1a according to their first measuring cycles; this means that the particular electroacoustic transducer of ultrasonic sensors 1 and 7 is acted on by a corresponding excitation pulse and transmits a corresponding measuring signal in each case. Ultrasonic sensors 3 and 9 are simultaneously controlled with the aid of an excitation pulse of form C11. Ultrasonic sensors 5 and 11 are also simultaneously controlled with the aid of an excitation pulse of form C9.

[0054] Chronologically following the first time interval, ultrasonic sensor pair 2/8 is controlled in a second time interval 1b with the aid of an excitation pulse of form C9. Ultrasonic sensor pair 4/10 is simultaneously controlled with the aid of an excitation pulse of form C11. Ultrasonic sensor pair 6/12 is also simultaneously controlled with the aid of an excitation pulse of form C3.

[0055] In a chronologically following third time interval 2a, ultrasonic sensor pair 1/7 is controlled with the aid of an excitation pulse of form C4. Ultrasonic sensor pair 3/9 is simultaneously controlled with the aid of an excitation pulse of form C9. Ultrasonic sensor pair 5/11 is also simultaneously controlled with the aid of an excitation pulse of form C11.

[0056] In a chronologically following fourth time interval 2b, ultrasonic sensor pair 2/8 is controlled with the aid of an excitation pulse of form C11. Ultrasonic sensor pair 4/10 is simultaneously controlled with the aid of an excitation pulse of form C9. Ultrasonic sensor pair 6/12 is also simultaneously controlled with the aid of an excitation pulse of form C4.

[0057] In a chronologically following fifth time interval 3a, ultrasonic sensor pair 1/7 is controlled with the aid of an excitation pulse of form C3. Ultrasonic sensor pair 3/9 is simultaneously controlled with the aid of an excitation pulse of form C11. Ultrasonic sensor pair 5/11 is also simultaneously controlled with the aid of an excitation pulse of form C9.

[0058] In a chronologically following sixth time interval 3b, ultrasonic sensor pair 2/8 is controlled with the aid of an excitation pulse of form C9. Ultrasonic sensor pair 4/10 is simultaneously controlled with the aid of an excitation pulse of form C11. Ultrasonic sensor pair 6/12 is also simultaneously controlled with the aid of an excitation pulse of form C3.

[0059] In a chronologically following seventh time interval 4a, ultrasonic sensor pair 1/7 is controlled with the aid of an excitation pulse of form C4. Ultrasonic sensor pair 3/9 is simultaneously controlled with the aid of an excitation pulse of form C9. Ultrasonic sensor pair 5/11 is also simultaneously controlled with the aid of an excitation pulse of form C11.

[0060] In a chronologically following eighth time interval 4b, ultrasonic sensor pair 2/8 is controlled with the aid of an excitation pulse of form C11. Ultrasonic sensor pair 4/10 is simultaneously controlled with the aid of an excitation pulse of form C9. Ultrasonic sensor pair 6/12 is also simultaneously controlled with the aid of an excitation pulse of form C4.

[0061] When contemplating one individual ultrasonic sensor or one ultrasonic sensor pair, it becomes apparent from the table in FIG. 3 that each ultrasonic sensor or each ultrasonic sensor pair, contemplated by itself, changes its excitation pattern on a shot-to-shot basis (i.e., in chronologically consecutive measuring cycles of the particular sensor or sensor pair). Ultrasonic sensor 1 is, for example, used to carry out a measurement in the first time interval. The first time interval thus corresponds to the first measuring cycle of ultrasonic sensor 1. In this first measuring cycle, the electroacoustic transducer of ultrasonic sensor 1 is excited to carry out mechanical oscillations with the aid of a frequency modulated excitation pulse having form C3. Following the termination of the measuring cycle, ultrasonic sensor 1 remains passive until the second measuring cycle of ultrasonic sensor 1 is carried out in the third time interval. In this second measuring cycle, the electroacoustic transducer of ultrasonic sensor 1 is excited to carry out mechanical oscillations with the aid of a frequency modulated excitation pulse having form C4. The third measuring cycle of ultrasonic sensor 1 takes place in the fifth time interval. The fourth measuring cycle of ultrasonic sensor 1 takes place in the seventh time interval. The frequency profile of the frequency modulated excitation pulse thus differs in each measuring cycle. The same also applies to all other ultrasound sensors 2 through 6.

[0062] It also becomes apparent that adjacently situated sensors are not operated simultaneously.

[0063] Following the transmission of measuring signals 30 by one of ultrasonic sensors 1 through 12, particular ultrasonic sensor 1 through 12 may receive a reflected ultrasonic signal 32. By appropriate filtering of the received signals, which is in particular adapted to the frequency profile of the excitation pulse in the form of a matched filter, it is possible to distinguish actual echo signals from external signals 33 in that the external signals are suppressed by the filter. With the aid of the embodiment according to the present invention in which the particular frequency profile of the excitation pulses differs in measuring cycles which are carried out chronologically consecutively, the frequency profile of an excitation pulse being selected in each measuring cycle randomly or according to a predefined sequence from a group of predefined frequency profiles, it is ensured that even in the case of identically designed distance measuring systems in other vehicles, there is only a slight chance that external signal 33 has the exact same frequency profile as one's own measuring signal 30.