DE102015014853B3 - Device and method for distance determination in ultrasonic sensor systems - Google Patents

Abstract

The invention relates to an ultrasonic sensor system for detecting a spatial distance or the transit time of an ultrasonic signal. It comprises an ultrasound transmitter, an ultrasound sensor that generates an echo signal and / or a received signal, and a subsystem that compares this echo signal and / or received signal with a threshold value and / or threshold signal or the current value of a threshold curve. It is distinguished from the prior art by the fact that the value of the output of a temporal or spatial distance value is determined as a function of a time by the inventive device or the inventive method, also the time derivative of the echo signal and / or received signal for the last time positive second derivative and a first derivative less than or equal to zero before the value of the echo or receive signal (EK) crosses the value of a threshold curve and / or a threshold value.

Description

introduction

The patent application describes a method for determining the distance between an ultrasonic sensor system and an obstacle. In the ultrasonic sensor system, a burst signal is generated, which generates by means of a transducer an ultrasonic signal, typically in the form of an ultrasonic burst. Any obstacle in front of the ultrasonic sensor system reflects the ultrasonic signal. The reflected ultrasound signal is picked up by the transducer and / or another suitable ultrasound sensor and added to the further signal processing in the ultrasound sensor system as a received signal. In a comparator stage within the ultrasound sensor system, the current value of the received signal is compared with a threshold value for a given measuring time from a time-dependent threshold curve. If the value of the received signal rises above the current value of the resulting threshold curve, the start of an echo is identified. If the value of the received signal falls below the value of the threshold curve, the end of an echo is identified. From the time between the emission of the ultrasonic burst and the detection of a start of an echo can be concluded at a known speed of sound on the distance between the ultrasonic sensor system and obstacle. (See also 1 and 2 ).

A method from the prior art therefore comprises, as a first step, the emission of an ultrasound signal. This emission time, typically the beginning of a sequence of ultrasound pulses, called burst for short, forms the reference point for measuring the time of flight of the ultrasound pulse from its emission through the ultrasound transducer (TR) until reentry thereof returns.

In a second step, the ultrasound burst thus emitted is reflected by the obstacle (H). The aim of the method of the prior art is to determine the distance to this obstacle (H).

The ultrasound burst reflected in this way at least partially returns to the ultrasound transducer and is received there by a sensor or the transducer itself in a third method step.

The ultrasonic sensor as sensor system converts the received reflected ultrasonic signal, the ultrasonic burst, back into a received signal and compares the value of this received signal in a fourth step of the method with a threshold value, this threshold typically from the time since the transmission of the ultrasonic burst, the time of flight TOF, depends. The time-dependent threshold is thus a point of a threshold curve (SWK). A sub-device of the ultrasonic sensor system (US) performs this comparison. It may, for example, be a comparator (CMP). This sub-device in the ultrasonic sensor system performs as a comparator, a comparison of the value of the received signal with the associated value from the threshold curve for this measurement time based on the transmission of the ultrasonic burst.

In a fifth step, the exceeding of the current value of the threshold curve is evaluated by the value of the received signal as the beginning of the echo.

In a sixth step, the undershooting of the current value of the threshold curve is evaluated by the value of the received signal as the end of the echo.

It then follows as the seventh step, a calculation of the flight time using the known emission time of the ultrasonic burst as the starting point and the two measured times, the beginning of the echo and the end of the echo. Possibly. the time of transmission can also consist of several data such as the beginning, middle and end of the transmission.

From this data, for example, the time interval in the prior art can then be calculated so that in the simplest case, the time of transmission of the ultrasonic burst is subtracted from the beginning of the echo.

• 1. der Höhe der Schwellwertkurve (SWK) und
• 2. der Steilheit der Signalflanke.

The detection of the flight time in the fifth step has the disadvantage that this value and thus the distance to the obstacle determined in the seventh step depends on two factors:

• 1. the level of the threshold curve (SWK) and
• 2. the steepness of the signal edge.

3 shows in the upper row in the sub-images a to c the unwanted parasitic effect of a falling flight time, ie a falling TOF value, with decreasing thresholds. 3 shows in the lower row in the fields d to f the undesirable parasitic effect of increasing time of flight, ie an increasing TOF value, with falling edge steepness. These parasitic changes in time-of-flight may result from a lower signal level of the receive signal resulting from a lower drive current of the transducer, a shorter burst length, a lower gain in the signal receive path, and an increasing distance between the sensor and Obstacle can come and also is influenced by the shape of the obstacle. The deviation can be significant and, under certain conditions, render the system unusable for safety-related applications.

From the JP 2003-156 561 A a method for accurate ultrasonic distance measurement is known. In this case, the received signal is compared with three threshold values, with reference to the times T1, T2 (reference numerals of the JP 2003-156 561 A ) of exceeding the first two thresholds TH (reference numerals of the JP 2003-156 561 A ) a time t0 (reference number of the JP 2003-156 561 A ) or correspondingly a running time t0 (syllable of the JP 2003-156 561 A ) at which the echo signal increases and this is only evaluated when the signal exceeds the third threshold (summary of JP 2003-156 561 A and their 1 ).

The publication DE 101 46 095 A1 describes a method for distance measurement by means of an echo method, in particular by means of ultrasound waves of an ultrasound measuring device, comprising ultrasound transducers (reference numerals) 3 of the DE 101 46 095 A1 ) on a motor vehicle (summary of DE 101 46 095 A1 , Sp. 3 and Sections [0011] and [0012]). In this case, an overrun of the rectified and low-pass filtered received signal or its envelope is evaluated and compared against a threshold on overshoot or undershoot for maximum detection and additionally checked the first derivative of the envelope threshold below zero crossing detection and by means of the so determined time t3 (reference numerals of DE 101 46 095 A1 ) determines the distance (at maximum) (see also 6 of the DE 101 46 095 A1 , Column 4 section [0018] to column 7 section [0021]).

From the DE 43 01 341 C1 For example, there is known a method of determining the beginning of a pulse signal in which the pulse signal U1 (reference numerals of the DE 43 01 341 C1 ) is compared with a threshold value and its differential quotient dU1 / dt, U2 (reference numerals of DE 43 01 341 C1 ) or whose time derivative is compared with a threshold value (summary of DE 43 01 341 C1 and their 2 ). The received pulse signal can be a pulse signal of an ultrasonic location system for determining the target distance. The aim is to avoid inaccuracies of the measurement by changes in amplitude or slope of the pulse (column 1 line 66 to column 2 line 15 of the DE 43 01 341 C1 ). In this case, an evaluation of the first time derivative U2 (reference numerals of DE 43 01 341 C1 ) of the received signal U1 (reference numerals of DE 43 01 341 C1 ) by means of a threshold value B (reference numerals of the DE 43 01 341 C1 ) to threshold exceeded (see 2 and column 2 lines 16 to 45 of DE 43 01 341 C1 ).

All of these fonts do not solve the problem described above.

Object of the invention

It is the object of the method according to the invention to determine the distance between the sensor and a given obstacle independently of the specific configuration of the sensor. The method according to the invention is therefore not intended to determine the TOF value, ie the time of flight, for the starting point of an echo from the time information of the point of intersection of the received signal with the threshold curve, but to evaluate further signal information which leads to a more precise result.

This object is achieved by a device according to claim 1 and method according to claims 3, 7 and 8.

Description of the invention

The true distance between the sensor and the obstacle is given by the time between the beginning of the transmission of the ultrasonic burst and the beginning of the reception of the associated echo signal at the sensor. This time is referred to below as flight time and thus more precise compared to the prior art. The beginning of the reception can be identified with sufficient accuracy as the time at which an increase in the received ultrasound signal can be detected. The inventive method determines the time of flight, the TOF value, of an echo as the time of the last local minimum before the ultrasonic signal exceeds the threshold curve. However, this tends to measure a TOF value that is a bit too small, ie a too short flight time. In the preparation of the invention but it was recognized that this reduction in the important applications, such as in the use of the ultrasonic sensor as a parking assist sensor, also called "park distance sensor" or short PDC sensor, is irrelevant or negligible, since the TOF Value, ie the measured flight time is influenced to the "safe side". An obstacle appears closer than it actually is, with which the driver stops earlier than necessary, which is therefore not critical for the application. Furthermore, the definition of the echo onset in the manner according to the invention counteracts any possible signal delays in the receiving part of the sensor as the time of the last local minimum.

In case of adverse signal situations, such as a low signal in one Noise signal environment, not a TOF value, ie to obtain a flight time, which is too far in front of the intersection between the signal and threshold curve, a maximum value is preferably introduced, to which the output from the ultrasonic sensor system TOF value, ie the flight time, before this Time of the point of intersection may be. If the maximum value is exceeded, the point in time of the intersection between the signal and the threshold curve reduced by the given maximum value is output as the TOF value, ie as flight time. The maximum value can either be fixedly implemented in the method, or be configurable.

The question remains as to how the time of the last local minimum, before the ultrasonic signal exceeds the threshold curve, is determined.

The method according to the invention therefore comprises the steps which are preferably repeated periodically and / or aperiodically:

Step 1: emitting at least one ultrasonic pulse;

Step 2: Reflection of the emitted ultrasonic pulse on at least one obstacle;

Step 3: Reception of the emitted and reflected ultrasonic pulse by at least one sensor and / or at least one transducer and conversion into a received signal;

Step 4: discreetly sampling the received signal at successive sampling instants and generating a temporally discrete sampled signal from successive samples each representing the value of the received signal at said successive sampling instants;

Step 5: Store the current sample time as a potential echo start time if the current sample at the current sample time is less than or equal to a stored sample of a previous sample time, which is preferably the immediately preceding sample time. As a stored sample, a default value, which may be fixed or may be adjustable or programmable, is preferably used in each case at the beginning of the emission of an ultrasound burst.

Step 6: Storing the current sample for a corresponding evaluation at a subsequent sampling time, which is preferably the immediately following sampling time.

Step 7: Output of a temporal or spatial distance value as a function of the stored potential echo start time, when the value of the received signal (EK) crosses the value of the threshold curve. This point in time is referred to below as crossing time. A typical criterion for crossing the value of the received signal (EK) with the value of the threshold curve would be, for example, the positive result of a check by the device according to the invention, if the current sample value of the received signal is greater than the threshold value of the threshold value curve associated with the current sampling time, and typically immediately preceding sample of the received signal is less than the preceding threshold of the threshold curve associated with that previous sampling instant. An accomplished expert will of course also allow for equality in at least one of these conditions.

In a variant of the invention, the time interval, referred to in the following flow distance, is limited to a predetermined and / or adjustable and / or programmable maximum value of the flow distance as an amount of the difference between the stored potential echo start time and the crossing time. If the flow distance is smaller than the maximum value of the flow distance, then the behavior of the ultrasonic sensor system does not change with respect to the behavior described above. If, however, the lead spacing is greater than the maximum value of the lead gap, then instead of the potential echo start time for the output, the corrected echo start time is used, which is the time difference from the crossing time minus the maximum value of the lead gap. Then, instead of outputting a temporal or spatial distance value as a function of the stored potential echo start time in step 7, the output of a temporal or spatial distance value is effected as a function of the corrected echo start time in step 7.

A system according to the invention is therefore distinguished by the fact that the output of a temporal or spatial distance value takes place as a function of a time, in addition the time derivative of the echo signal or received signal for the last time had a positive second derivative and a negative first derivative, the latter also being almost zero can before the value of the echo or receive signal (EK) crosses the value of a threshold curve and / or a threshold value.

Description of the figures

1 shows a construction for distance measurement with a ultrasonic sensor of the prior art

2 shows the principle of distance measurement with an ultrasonic sensor of the prior art

3 shows the dependence of the TOF value as a function of the threshold level and the steepness of the signal edge of the prior art.

4 shows the independence of the TOF value from the threshold level and the steepness of the signal edge by the method according to the invention

Advantages of the invention

The main economically viable advantage of the invention is the increased precision of the determination of distances to obstacles independent of the threshold curve and the slope of the signal.

LIST OF REFERENCE NUMBERS

• CMP

  Comparator or comparator function performed by a corresponding sub-device of the device.

  EGG

  Echo information stored in a sub-device of the device.

  EK

  Echo curve or course of the received signal

  H

  obstacle

  SWK

  Threshold curve stored as configuration parameter

  TOF

  Time of Flight or Flight Time: This is the time that elapsed between the transmission of the ultrasonic burst, ie an ultrasonic pulse sequence, and its return to the transducer.

  TR

  transducer

  US

  Ultrasonic sensor or ultrasonic sensor system

  USB

  Ultrasonic burst generation

Claims (8)

Ultrasonic sensor system for detecting a spatial distance or the transit time of an ultrasonic signal • with an ultrasonic transmitter and with An ultrasonic sensor that generates an echo signal and / or a received signal, and With a sub-device which compares this echo signal and / or received signal with a threshold and / or threshold signal or the current value of a threshold curve, characterized by a. the value of the output of a temporal or spatial distance value depends on a point in time, in addition to which the time derivative of the echo signal and / or received signal had a positive second derivative last time and a first derivative less than or equal to zero before the value of the echo or received signal (EK) crosses the value of a threshold curve and / or a threshold value. Ultrasonic sensor system according to claim 1, characterized by a. that it is a parking aid sensor system for use in vehicles. A method for operating an ultrasonic sensor system for detecting a spatial distance or the transit time of an ultrasonic signal, the ultrasonic sensor system comprising an ultrasonic transmitter and an ultrasonic sensor which generates a received signal, and a partial device which compares this received signal with a threshold value and / or threshold signal the steps: a. Emitting at least one ultrasonic pulse through the ultrasonic transmitter; b. Reflection of the emitted ultrasonic pulse at at least one obstacle; c. Receiving the emitted and reflected ultrasonic pulse by at least the ultrasonic sensor and / or at least one transducer and conversion into the received signal; d. Continuous discrete-time sampling of the received signal by the ultrasonic sensor system at successive discrete sampling times and generation of a time-discrete sampling signal from consecutive samples each representing the value of the received signal at said successive sampling instants; e. Storing the current sampling instant as a potential echo start timing by the ultrasonic sensor system in a memory of the ultrasonic sensor system when the current sample at the current sampling instant is less than or equal to a sample of a previous sampling instant stored in this or another memory of the ultrasonic sensor system. f. Storing the current sample of the received signal for a corresponding evaluation at a subsequent sampling instant by the ultrasonic sensor system in said memory or other memory of equivalent function; G. Determining a temporal or spatial distance value as a function of the stored potential echo start time, wherein the Determination can also be made at the time of the following issue; H. Determining the time of crossing the course of the value of the received signal (EK) with the curve of the value of the threshold curve at a crossing time; i. Output of the determined temporal or spatial distance value as a function of the stored potential echo start time and the point of intersection. A method according to claim 3, characterized in that a. the time of crossing is the time at which the current sample of the received signal is greater than a threshold value of a threshold curve associated with the current sampling time and the preceding sample of the received signal is less than the preceding threshold value of the threshold curve associated with that previous sampling time. A method according to claim 3 or 4 characterized in that a. the lead time distance is limited to a predetermined and / or adjustable and / or programmable maximum value of the lead gap as the amount of the difference between the stored potential echo start time and the crossing time. A method according to claim 5 and 4, characterized in that a. instead of the potential echo start time for the output, use the corrected echo start time resulting from the time of crossing minus the maximum value of the lead distance if the lead distance is greater than a maximum value of the lead distance, and b. in that case, instead of outputting a temporal or spatial distance value determined in dependence on the stored potential echo start time, the output of a temporal or spatial distance value determined in response to the corrected echo start time is substituted. Method for operating an ultrasound sensor system having an ultrasound transmitter and an ultrasound receiver and / or an ultrasound transducer for detecting a spatial and / or time interval, wherein the ultrasound sensor system comprises at least one reception signal representing the current value of the received ultrasound amplitude, characterized by a. that the detected distance from the temporally last local minimum of the curve of the value of the received signal, the time before exceeding a threshold value and / or exceeding the current value of a threshold signal and / or exceeding the current value of a threshold curve by the current value of the received signal lies, depends. Method for operating an ultrasonic sensor system for detecting a spatial distance or the transit time of an ultrasonic signal • with an ultrasonic transmitter and with An ultrasonic sensor that generates an echo signal and / or a received signal, and With a sub-device which compares this echo signal and / or received signal with a threshold and / or threshold signal or the current value of a threshold curve, comprising the step: a. Output of a value for a temporal or spatial distance value as a function of a time, in addition, the time derivative of the echo signal and / or received signal for the last time a positive second derivative and a first derivative less than or equal to zero, before the value of the echo or receive signal (EK ) crosses the value of a threshold curve and / or a threshold.

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