WO2014108300A1

WO2014108300A1 - Device and method for environmental sensing

Info

Publication number: WO2014108300A1
Application number: PCT/EP2013/077595
Authority: WO
Inventors: Matthias Karl
Original assignee: Robert Bosch Gmbh
Priority date: 2013-01-14
Filing date: 2013-12-20
Publication date: 2014-07-17
Also published as: EP2943806A1; DE102013200434A1

Abstract

The invention relates to a device and a method for environmental sensing by means of a signal converter and an evaluating unit, wherein signals received from the environment having a first pulse response length are filtered in dependence on propagation time at a first time during a measurement cycle and signals received from the environment having a second, longer pulse response length are filtered in dependence on propagation time at a second, later time within the same measurement cycle.

Description

description

title

Device and method for environment sensors Field of the invention

The present invention relates to a method and a device for environment sensors. In particular, the present invention relates to methods and apparatus for improved environmental sensor technology based on

Ultrasound signals.

Environment sensors, in particular in the field of automotive technology, is used, for example, the distance between a vehicle and an environment object based on runtime studies on

To detect ambient object of reflected signals. In particular, the

Devices for environmental sensors while units on, are emitted by means of which signals in the vehicle environment, whose echoes are determined by means of receivers and closed on the basis of the running time on the traversed signal path. In this signal evaluation, the received signal is monitored by filters such that upon the arrival of payloads, especially when arriving at

In the case of reflected signals (echoes), the filter output is strongly oriented to a value characteristic of such an event, while upon receipt of other signals (spurious signals) not related to the transmitted signal, the filter output has a different value, which depends on the filter output based on the filter output Nutzsignals strongly different. For example, to identify an echo of a particular frequency, a bandpass filter with a corresponding

Center frequency can be used, so that in particular on the arrival of signals having a frequency which is similar to that of the expected signal, a significant output variable is generated, while caused by frequency-less concentrated interference signals only little energy at the filter output become. Modern systems often use so-called matched filters. These are referred to in the art as matched filters

Filter characteristics are usually derived from the unfiltered echo signal recorded under ideal conditions. In most cases, the filter is realized by means of correlation of this ideal echo signal with the received signal.

Characteristic is that the impulse response of such a receive filter lasts at least as long as the transmission signal of the corresponding

Device for environment sensors continues. The longer such filter durations, the more accurate is the effect of the filter on the transmitted spectrum ("frequency selectivity"). Correspondingly less is the likelihood of randomly distributed signals during long filtering

Produce filter output signal which matches or comes close to incoming echoes. A corresponding length of the impulse response of the filter is thus an essential variable for the successful suppression of noise, with which the effectiveness of the filter with respect to the

Frequency domain can be described and determined. Although currently in the market environment monitoring systems is not always a matched filter realized in the strict sense, but equivalent sizes are already in use today. For example, systems are known which, instead of the filter duration, use a minimum time of exceeding a threshold value in order to make the evaluation of echoes more robust against short-term disturbances. In other words, today's sensors monitor throughout the echo time, i. after the end of the excitation or after the decay of the transmitter diaphragm has subsided until the end of the echo cycle, an incoming signal has at least one predefined filter duration. At a transmission pulse of approx. 0.3 ms (usual value for a

Transmission signal duration), the processed receive signal must exceed a predicted threshold value for at least 0.12 ms before the signal is output as

Echo signal is recognized. At the aforementioned transmit pulse duration of 0.3 ms, a required threshold violation has persisted for a period of at least 60% of the transmit pulse duration, i. for at least 0.2 ms, proved to be particularly effective. However, especially at the beginning of a

Direct echo cycle (that is, the echo cycle of a sensor that had itself sent out the signal at the beginning of the echo cycle) adversely affects such long filter pulse lengths. Finally, the received signal must be present at least during the impulse response of the filter before the evaluation, before a possibly contained and identified echo is also recognized as a valid echo. The longer the Filter impulse response is, the farther away is in principle the upper limit of the rangefinder, the so-called range, since with the time decreasing useful signals can be separated better and longer from noise. However, a longer filter pulse response length also means a longer period of time until the filter responds to the arrival of an echo due to a

Reflex point and has reached its maximum filter output value and then a longer period of time until the filter has finished its response to the arrival of the echo. In filters with a longer impulse response, therefore, the dwell time of received echoes is greater than in filters with a short impulse response. The greater the dwell time of an echo in a filter, the greater must be the time interval between two successive echoes arriving at the sensor, so that the filter can have the different echoes

Echolaufzeiten can still be separated from each other, as the

Measuring method derives the presence of objects from the echo delay. To have a high separation ability of closely running time consecutive

Reflecting points, or echoes reflected from them, which follow closely one after the other or are even partially superimposed by the sensor, can be realized with a filter if the filter has a correspondingly short impulse response.

Document EP 2 251 710 A2 describes a modulation in which short and long pulses are combined in pulse bundles in order to achieve a high measuring rate with high spatial resolution near the sensor. At the same time, high-energy long pulses can be used to achieve a high signal-to-noise ratio in the distance.

WO 2010 063510 A1 describes a modulation with time variant

Transmit signal frequency. It is an object of the present invention to provide a method which allows a small near measurement limit and good noise rejection.

Disclosure of the invention

The above object is achieved by a device having the features of claim 1 and a method having the features of claim 7. Accordingly, the inventive Device for environment sensor on a signal converter and an evaluation unit. By means of the signal converter, the device is set up, from the

Surround the device originating signals into electrical signals. The evaluation unit is set up to evaluate the signals provided by the signal converter, in particular to filter them. Of the

In this case, the signal converter may comprise, for example, a radar sensor, a sound transducer, in particular an ultrasound transducer or another transducer element for conversion to environment sensors of suitable signals. According to the invention, the evaluation unit is set up to carry out a signal delay-dependent filtering of the signals received by the signal converter, wherein a first

When a first-length impulse response is used for the filtering and a second impulse response of a second, longer length of the filter is used at a second time within a same measurement cycle. In other words, in the course of a measurement cycle (the time between emission of a signal into the environment until the time when no echo from the environment is expected due to the emission) the filter is considered to have a duration of an echo pulse in the filter ie, the time that elapses from the first response of the filter output to the arrival of an echo pulse until the last response of the filter output to the arrival of an echo pulse, such that a lower dwell time for early echoes is used, while a longer dwell time for later incoming echoes is provided. The switching can be done differently depending on the filter type. In the scope of the present invention, therefore, both filters are to be understood which use only two different filter lengths as a function of the transit time, as well as multistage or even continuous transit time-dependent filter length adaptations. Because early incoming echoes are generally one over the other

Noise level on the receiving path significantly increased and thus have clearly identifiable levels can by a less accurate, but faster filtering a finer separation of successive incoming echoes and thus a smaller minimum distance for running time adjacent

Environment objects are realized. In contrast, according to the invention for later arriving echoes, which are generally comparatively difficult to identify the noise on the receiving branch, a more accurate filtering estimated, which takes longer, however, ensures an improved detectability for sinking in the noise received signals. Short impulse response filters are generally known to have a higher bandwidth in frequency response than long impulse response filters. The dependent claims show preferred developments and refinements of the present invention.

Preferably, the inventive device for acoustic

Environment sensor, in particular using ultrasound signals, set up. Advantageously, ultrasound signals for humans and technology at a suitable dosage are harmless and the required transducers and evaluation units as a mass-produced comparatively inexpensive available.

More preferably, the device itself can also be set up to emit signals by means of a signal converter. It is both possible to use the same signal converter for transmitting and receiving signals, as well as separate transmitters and receivers in the composite of

Provide device. While pure receivers require a lesser degree of converter robustness, transceivers offer the ability to combine multiple functions within one and the same unit

Use connecting cables several times.

More preferably, the device can be set up, including the

Filter frequency response over time, in particular with respect to a measurement cycle to change. In this way, also over the frequency changeable

Transmission signals are reliably filtered out of the ambient noise. In particular, the emission of frequency-variable signals is synchronized with the filter frequency response in the receiving path of the device, so that a particularly secure detection can be carried out. Likewise, in this way a separation of incoming echoes can be separated from the self-resonant frequency decaying transducer signals.

More preferably, a time-varying threshold can be used to detect possible echoes from the incoming signal. As the echo signal amplitudes also tend to decrease as the echo propagation time increases, the reliability of detection can be compared to the decay signal of a formerly transmitting signal converter as well as the background noise of the echo signal amplitude Systems are increased without that incoming echoes remain below the threshold at a later time in principle.

In general, it will be apparent to those skilled in the art that the present invention has various well-known and well-proven functions and features

Characteristics can be combined, which favor a generic environment sensors, without thereby departing from the scope of the present invention. According to a further aspect of the present invention, a method for environment sensors is proposed, according to which a

signal delay dependent filtering from an environment of received signals is proposed. In this case, an impulse response of a first length of the filter used is used as the basis for a first time within a measurement cycle, and an impulse response of a second and longer length is used for the filtering at a second (later) point in time. In other words, at a first time, a shorter processing time is suggested by means of the filter, while at a later time a longer processing time for realizing a better spectral separation of the useful signal from background noise and other interference signals is accepted. It should be noted in connection with both aspects of the invention that those skilled in signal processing many similar terms are familiar to express the frequency resolution or the associated with the impulse response length of a filter variables, and that depending on the filter used (analog filter, digital Filters, etc.), different terms can be used to describe message-technically identical or equivalent relationships, without thereby departing from the scope of the present invention. For the preferred embodiments of the method according to the invention made in connection with the device according to the invention apply

Embodiments accordingly, so that reference is made to avoid repetition and for clarity on the statements made in connection with the first aspect of the present invention.

For the sake of completeness it should be pointed out that the device according to the invention and the method according to the invention are preferred in the case of Use can be designed in distance measuring systems for automobiles. The required signal transducers can in this case be arranged in particular in the region of bumpers of a vehicle and operated in accordance with the aforementioned aspects of the invention. As an evaluation unit while a built-in anyway in the vehicle microprocessor can be set up by means of software code, so that additional hardware for an evaluation is not required.

Brief description of the figures

Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings. In the drawing are:

Figure 1 is a schematic overview of components according to a

Embodiment of an inventive device;

FIG. 2 is a timing diagram for one shown in FIG

Device recorded ultrasonic signals in a filtering with a shorter impulse response; and

FIG. 3 shows a time diagram for one shown in FIG

Device recorded ultrasonic signals in a filtering with a longer impulse response.

Embodiments of the invention

FIG. 1 shows a schematic overview of components of a device 10 according to an exemplary embodiment of the invention. Therein, an ultrasonic transducer 1, which is designed as a transceiver, connected to a microprocessor 2 as an evaluation unit via a bandpass filter 3. In this case, the microprocessor is set up to control the bandpass filter 3. An object O in the form of a standard cylinder is located in the detection range of the ultrasonic transducer 1. In this case, the device 10 is at least configured to perform the following steps. At the beginning of a measurement cycle, a signal is emitted in the direction of the object O by the illustrated device 10 or an adjacent ultrasound transducer (not shown). To this

At this time, the microprocessor 2 directs the bandpass filter 3 for filtering a short impulse response, although the calculation of the result in the frequency domain is somewhat inaccurate, but can be performed faster and brought to the result. As the time progresses, which coincides with a higher object distance to be expected, the microprocessor 2 alters the filter characteristic of the bandpass filter 3, at least in that it uses a longer impulse response than signals previously received for filtering by means of the ultrasound transducer 1. Because after a long signal delay, the expected echoes due to the increased

Running distance expected to have a lower amplitude, the echoes run increasingly dangerous in the noise of the system and / or in received

"Drowning" interference signals. An increased frequency resolution now helps to be able to extract the often narrow-band ultrasonic echoes from the broadband signal noise and reliably detect them. The effect of the propagation time-dependent impulse response length is illustrated below in connection with FIGS. 2 and 3.

FIG. 2 shows two time signals S1, S2, which were recorded by means of an ultrasonic transducer 1 as a signal converter and measured by a device 10 according to the invention on the basis of impulse responses of different lengths. On the ordinate, the signal voltage of the filter output is plotted in volts logarithmic, while the abscissa represents the distance of the

indicates reflecting object. The output signals of two filters, each of which forms the envelope from the input signal, are shown

different impulse response, and both one and the same

Evaluated input signal. The filter input signal comes from sensor 1, which receives the superposition of multiple echoes that were reflected by closely spaced reflex points. The signal S1 originates from a filter with a short impulse response, while the signal S2 originates from a filter with a longer impulse response. Each of the local maxima of the signal curve S1, marked with black squares, represents the transit time of a reflex point. Thanks to the short

Filter impulse response, each reflex point leads to an independent local maximum in the signal course S1. The signal S2 originates from the filter whose impulse response has been adapted to the length of the emitted acoustic measuring pulse, and whose impulse response is longer than that of the

Waveform S1 leading filter was. A comparison shows that in the waveform S2 no longer all reflections lead to an independent maximum, which based on the signal S2 no longer every reflex point can be detected independently. Thus, the longer the impulse response of the filter, the more the echoes processed in close succession are superimposed by the filter, so that, for example, many small echoes are superimposed by a rough background in the filter, thus producing a disproportionately loud signal at the filter output.

FIG. 3 shows the same signal curves already shown in FIG. 2 in a modified form and over a larger measuring range. Also shown is the course of the echo peak, which will have one and the same reference object at the respective distance. In particular, from the waveform S1 of the filter with a shorter impulse response, it can be seen that the signal values fluctuate the more the signal becomes quieter. This is the result of additive noise. In waveform S2, the variations are compared to

Signal curve S1 is not so great, since the associated filter suppresses the noise more strongly than the filter red with a shorter impulse response because of its impulse response, which is longer by a factor of 3. Since the achievable measuring range is limited by the signal distance to the noise in the signal, the measuring range of the echo evaluated with a shorter impulse response is smaller than that of the signal evaluated with a longer impulse response.

It is a core idea of the present invention to improve the processing by means of an environment sensor of received signals by means of adaptive filtering in such a way that early recorded in the measuring cycle

Signals with higher selectivity are filtered than in the later time range of the same measurement cycle '. The much higher separation between the amplitude peaks of adjacent echoes (useful signal) of other signals at early times in the measurement cycle more than outweighs the disadvantages of the lower signal to noise ratio in the early time range of the measurement cycle. In the later course of the measuring cycle, more time is used according to the invention to filter the sensor signals in order to better separate the anyway low amplitudes expected useful echoes by means of longer impulse responses of the filters used by other signals contained in the sensor signal, such as noise. Although the present invention has been explained in detail with reference to the accompanying figures in the form of embodiments, remain

Modifications and variations of the features shown therein within the skill of the artisans skilled in the art, which are to be understood as being within the purview of the present invention, the scope of which is defined by the appended claims.

Claims

claims

1 . Device for environment sensor comprising

- A signal converter (1), and

an evaluation unit (2),

wherein the evaluation unit (2) is arranged to perform a signal delay-dependent filtering of signals received by the signal converter (1), the filtering having a shorter impulse response at a first time during a measurement cycle than at a second later time within the same measurement cycle.

2. Device according to claim 1, wherein the lengths of the selected

Impulse responses are substantially inversely proportional to each expected average echo amplitude and / or inversely proportional to each expected Echo-to-noise ratio.

3. Apparatus according to claim 1 or 2, wherein the device (10) for

acoustic environment sensor, in particular in the ultrasonic range, is set up.

4. Device according to one of the preceding claims, wherein the length of the impulse response is changed by a modification of the frequency resolution and / or the pulse discrimination time.

5. Device according to one of the preceding claims, wherein additionally the filter frequency response is changed in spectral terms over time.

6. Device according to one of the preceding claims, wherein the

Device (10) is further adapted to emit a transmission signal by means of the signal converter (1).

7. Method for environment sensor system comprising the steps:

Signaling time-dependent filtering from the environment of received signals with a first impulse response length at a first time during a measurement cycle and a second longer impulse response length at a second later time within the same measurement cycle.

8. The method of claim 7, wherein the lengths of the selected

Impulse response are substantially inversely proportional to each expected Echo-to-noise ratio.

9. The method of claim 7 or 8, wherein the signals are acoustic signals, in particular in the frequency range of the ultrasonic range, and / or the method comprises a step of emitting signals into the environment.

10. The method according to any one of claims 7 to 9, wherein additionally the

Filter frequency response over time is changed.