WO2005083464A1

WO2005083464A1 - Method and sensor device for detecting information on the position of an object by means of an ultrasound sensor

Info

Publication number: WO2005083464A1
Application number: PCT/AT2005/000064
Authority: WO
Inventors: Herbert Schweinzer; Hannes Elmer
Original assignee: Technische Universität Wien
Priority date: 2004-02-27
Filing date: 2005-02-25
Publication date: 2005-09-09
Also published as: ATA3152004A; AT413890B

Abstract

In order to detect information on the position of an object (4; 31, 32; 42, 43), an ultrasound transmitter signal (5) is emitted by means of an ultrasound emitter (2) and an ultrasound signal (6) which is reflected by an object (4; 31, 32; 42, 43) is received by means of an ultrasound receiver (3) and valued in order to obtained positional information. The invention is characterised in that a narrow, frequency-dependent directional characteristic of an ultrasound emitter compared to the directional characteristic of the ultrasound receiver (3) is dynamically modified using an emitter signal (5') containing different signal frequencies. When a lobe (15a) is changed in the directional characteristic to an adjacent lobe (16b), phase displacement takes place, and the reflected, received ultrasound signal is compared to a stored reference signal in order to determine a radiation angle area (26) of the ultrasound emitter (2) which is to be used for determine the position.

Description

Method and sensor device for obtaining information about the position of an object with an ultrasonic sensor

The invention relates to a method for obtaining information about the position of an object with the aid of an ultrasound sensor which has an ultrasound transmitter and an ultrasound receiver, the directional characteristics of the ultrasound transmitter and receiver being different, in which method an ultrasound transmitter signal is used with the aid of the ultrasound transmitter is emitted and an ultrasound signal reflected by the object is received with the aid of the ultrasound receiver and evaluated to obtain position information.

Furthermore, the invention relates to a sensor device for obtaining information about the position of an object, with an ultrasound sensor which has an ultrasound transmitter and an ultrasound receiver, the directional characteristics of the ultrasound transmitter and receiver being different, and with an evaluation unit assigned to the ultrasound receiver Evaluation of an ultrasound signal emitted by the ultrasound transmitter, reflected by the object and received with the aid of the ultrasound receiver in order to obtain position information.

The classic ultrasonic sensor typically consists of a combined ultrasonic transducer, which allows a switch between transmit and receive operation. Because of the simple generation, narrow-band signals in the form of short bursts of constant frequency (for example 10-15 periods of a frequency between 50 kHz and 400 kHz) are generally used. This measurement signal is transmitted with an electrostatic or piezoelectric ultrasound transmitter. The signal reflected by an object is z. B. received again with the help of the ultrasound receiver. In the case of a combined transmitter and receiver, there is a "blind" area in the immediate vicinity of the ultrasonic sensor, which is used to measure short distances, due to the length of the transmitted signal and the time required for the switchover from transmitter to receiver to occur The time of reception is usually determined with the aid of a threshold value detector, the evaluates the amplitude of the received signal. With this technique, the accuracy of the detection of the time of reception strongly depends on the signal amplitude of the reflected signal and the bandwidth of the transducer used. A narrow band limitation in some of the available ultrasonic transducers and the frequency-dependent air damping result in the inevitable flattening of the rise in the envelope when transmitting ultrasonic signals, which in the case of a fixed threshold value and different reception amplitudes lead to large measurement uncertainties.

The signal amplitude of a reflected signal depends in particular on the following factors:

1) Distance-dependent air damping in the transmission path - here one tries to compensate for the distance-dependent signal damping with the aid of a delay-dependent gain of the received signal.

2) Reflection properties of the object to which the distance is determined - the reflection properties mainly depend on the shape and orientation of the object. A smooth, flat surface provides a strong reflection signal when the sensor axis is aligned approximately normally, but if the alignment is poor, it can also completely mirror the incoming signal so that no reflection signal is received at all. A corner or edge does not reflect an incoming signal in one direction, but reflects it in several directions, but with a significantly smaller amplitude.

3) Position of the object within the radiation characteristic of the sensor - the radiation characteristic of an ultrasonic transducer can only be described in a rough approximation by a cone. In the case of an electrostatic converter (eg Series 600 from Polaroid), the radiation behavior is essentially described by the model of the piston membrane, which is characterized by a main lobe and a number of smaller and smaller side lobes. The amplitude of a reflected signal depends on the amplitude of the signal arriving at the object and thus on the position of the object within the radiation characteristic: the strongest level is in the middle of the When the main lobe is reached, the signal amplitude decreases with increasing radiation angle up to a zero point, in the direction of which no signal is emitted and which thus causes a blind area, and then rises again to the maximum of the first side lobe, which is about 17 dB smaller to reach the following side lobes via further zeros.

Cases 2) and 3) present problems for the classic ultrasonic sensor particularly when it comes to making statements as to whether an object is within a precisely defined area in front of the sensor: namely, while a well-aligned plane over a large angle is detected because the reflection properties are so good that even signals that are emitted via side lobes can be detected by the threshold value detector, a corner or edge is only recognized in a narrow area within the main lobe. At the edge of this strongly object-dependent directional characteristic, there are also strong measurement uncertainties.

The above disadvantages apply in particular to the ultrasonic sensor systems known from JP 59-120875 A and from DE 3913049 A. JP 59-120875 A discloses an ultrasound sensor system in which an ultrasound sensor and an ultrasound receiver with axes that diverge relative to one another are arranged next to one another, the ultrasound sensor and the ultrasound receiver also being equipped with L-shaped tubes for deflecting the ultrasound, to avoid an adverse influence of dirt, rain or the like, if possible. The actual ultrasonic transducers are located inside these L-shaped tubes. In the ultrasonic sensor system according to DE 3913049 A, a larger number of ultrasonic receivers are provided, the receivers being matched to a predetermined directional range. The transmitter also sends out a narrow-band or monofrequency ultrasound signal, and a calculation is carried out on the receiver side on the basis of time difference. However, this training is obviously complex, but the disadvantages explained above in connection with cases 2) and 3) still exist. It is an object of the invention to remedy this situation and to provide a method or a sensor device as stated at the outset, with which or in a comparatively simple manner improved locating and subsequently distance measurement with the aid of ultrasound, in particular of objects in Air.

To achieve this object, the invention provides a method or a sensor device as defined in the following independent claims. Particularly advantageous embodiments and further developments are specified in the dependent claims.

The present invention is based on the use of separate ultrasonic transmitters and receivers, which differ by different directional characteristics, in particular both in amplitude and in phase, which result in different courses of the phase shifts over the radiation or reception angles of the ultrasonic wave , The control of the ultrasound transmitter with signals of different frequencies allows the evaluation of these phase shifts in such a way that received signals can be assigned to precisely defined reflection areas according to their phase shifts. The control signals are selected so that a range of permissible radiation and reception angles is made possible, in which valid measurements can be carried out. By specifically varying this angular range or by analyzing the phase shifts of the received signal, information about the directions of the reflected ultrasound waves can be obtained.

The runtime of a time-limited signal can be measured for distance measurement.

In view of the fact that a signal of different frequencies, ie a broadband signal, is used, ultrasonic transmitters and receivers with a sufficiently large bandwidth corresponding to the signal are also required. The received signal is evaluated using a correlative method which has high resolution, good interference suppression and good echo separation capability for detection of objects in close proximity. If the ultrasonic transmitter has a narrow, rotationally symmetrical main lobe with adjacent, generally likewise rotationally symmetrical side lobes, the effect of the phase shift of a radiated signal that occurs can be described solely by the radiation angle (angle between the sensor axis and the actual radiation direction).

The phase shift of the received signal is then essentially determined solely by the radiation angle if the ultrasound receiver has a significantly broader directional characteristic than the ultrasound transmitter with a constant phase shift in this area and its main lobe overlaps the main lobe and adjacent side lobes of the transmitter.

An ultrasound receiver that is laterally offset with respect to the ultrasound transmitter causes a certain asymmetry due to the different possible, differently long transmission and reception beams, which leads to a mathematically complex determination of the possible reflection areas. In order to remedy this, a concentric arrangement of ultrasound transmitters and receivers can be provided so that their beam axes overlap and the transmission and reception beams travel the same way. In this case it makes sense to use an internal, e.g. circular, converter part to use, which can also be used as part of the transmitter converter in transmit mode.

The directional characteristic of an ultrasonic transducer is to be described here with the model of a piston membrane, which shows a strong dependence on the frequency of the emitted signal: the higher the signal frequency, the narrower the resulting main and side lobes in the directional characteristic. The piston membrane model further shows that every second side lobe, starting with the first one, causes a phase shift of the transmitted or received signal of 180 °. If this phase shift occurs in parts (frequency components) of the signal, there is a strong decrease in the correlation result achieved in a correlative evaluation, which is used for signal detection - β - will. As long as a signal is emitted within the main lobe that results from the highest frequency occurring in the signal, a large, easily detectable correlation maximum is obtained. However, as soon as parts of the signal are emitted outside the main lobe, i.e. through the first side lobe, the phase shift leads to a rapid deterioration of the correlation maximum and thus to a sharp limitation of the directional characteristic of the sensor. The decrease in the correlation maximum occurs much earlier than a shift in the correlation maximum caused by the deterioration in the correlation, as a result of which measurement errors in the marginal region of the valid measuring range, as can be expected with classic ultrasonic sensors, can be excluded.

Due to the relatively strong temperature dependence of the speed of sound in air, temperature-related changes in the directional characteristics of ultrasonic transducers can occur. As mentioned, the directional characteristic also depends on the signal frequency. With an adaptation of the emitted signal based on measured values of the ambient temperature, it is also possible, if necessary, to compensate for the temperature influence on the defined measuring range of the ultrasonic sensor.

A successive variation of the directional characteristic by changing the emitted signal enables the search for a detection limit outside of which no signal detection takes place. On the basis of its associated directional characteristic, this detection limit supplies a family of possible radiation directions with the same phase shift, which, in conjunction with the distance measured value, give an estimate of possible positions of the reflection point. In the case of a rotationally symmetrical ultrasound transmitter (ie a transmitter with a rotationally symmetrical directional characteristic), these limits are concentric conical shells that can be described using the opening angle, which is now the same as the direction of radiation. When using a chirp with a linearly increasing frequency as the transmission signal, as is particularly preferred, there is a variation in the directional characteristic of the ultra- sound transmitter directly with the course of the signal. The determination of the transmitted beam direction to the reflection point is made possible directly by the signal evaluation of the received ultrasound signal. For this purpose, the correlation process is not carried out over the entire signal, but continuously over part of the signal, starting at low frequencies. The limit of the measuring range is recognized by the fact that the correlation result decreases from that part of the signal from which the signal is transmitted through side lobes. In this case, the emission direction of the transmission signal is located in the transition between the main lobe and a side lobe of the directional characteristic of the highest signal frequency of the signal part currently used for the correlation. The angle of the direction of radiation thus results directly from the signal frequency.

Due to the clear and sharply delimited detection area and the possibility of determining the angle of incidence of echoes, the present technique is ideally suited for determining the position of objects in space by recording and evaluating series of measured values from different sensor positions whose position in the room is known become. In such applications, the use of classic ultrasonic sensors leads to ambiguous solutions that are difficult to control due to the ambiguous detection areas that depend on the object properties. If the position of the reflecting objects in the room is already known, the position of the objects in the room can be checked by evaluating individual measured values, and possible position deviations can also be determined.

As a precaution, it should be mentioned that, even if it is preferred to emit a frequency-modulated transmission signal with a frequency that increases continuously, the frequency can be increased from 30 kHz to 80 kHz, for example, a different form of the ultrasound transmission signal can also be provided, which is broadband, ie contains a corresponding number of frequency components. For example, the frequencies in the ultrasound transmission signal can be increased in steps, but in principle the frequencies can also be reduced (continuously or in steps) from the highest frequency to the lowest frequency. Around If necessary, to be able to define several precisely defined angular ranges for the radiation of the ultrasound signal in the room to be measured, corresponding to several and different positions of objects present in the room, it is also expedient to twist or pivot the actual ultrasound sensor, i.e. the ultrasound transmitter together with the ultrasound receiver to be able, whereby the transmission axis and the reception axis change together in their orientation in space.

The invention is explained in more detail below on the basis of particularly preferred exemplary embodiments, to which, however, it should not be limited, and with reference to the drawing. The drawing shows in detail:

1 schematically shows an arrangement of an ultrasound transmitter and an ultrasound receiver in a reference coordinate system and a reflection point (object) which reflects a signal emitted along a transmission beam back along a reception beam to the ultrasound receiver;

1A schematically, in the manner of a block diagram, a sensor device with an ultrasound transmitter and an ultrasound receiver separated therefrom and associated electronic circuits;

2 shows a schematic view of directional characteristics of a piston membrane for different frequencies, with the help of such a model the directional characteristics of many ultrasonic transducers can be described;

3 in a diagram: signal amplitude A (normalized) over time t (in μs) the influence of the directional characteristics shown in FIG. 2 on a broadband signal, in this case on a linear frequency-modulated signal pulse or chirp with a length of 3 ms and with a frequency range from 30 kHz to 80 kHz, at a beam angle of 17 °;

4 in a diagram: relative correlation maximum K (in%) over the radiation angle β the course of determined correlation maxi a, which are used for the detection of received ultrasound signals, as a function of the radiation angle of the Transmission signal in a rotationally symmetrical ultrasound transmitter, thus the course of the dependence of the correlation maximum on the direction of the position of the reflection point in relation to the ultrasound transmitter;

5 schematically shows an ultrasonic sensor in connection with two reflecting objects, the entire radiation angle range and the defined detection range obtained according to the invention being illustrated schematically;

6 shows the basic structure of a concrete measuring arrangement, with a rotatably mounted ultrasonic sensor in association with two reflection objects, namely a smooth plane and a round rod;

Fig. 7 in a diagram: Distance (in m) over the sensor angle ε the results obtained with the measuring arrangement shown in Fig. 6, the measured distances to the plane and the round bar above the orientation (the Beam angle) of the ultrasonic sensor are illustrated; and

8A and 8B show two embodiments of concentric transducer arrangements in a schematic plan view.

1 schematically shows a plate 1 on which an ultrasound transmitter 2 and an ultrasound receiver 3 are rigidly mounted. Furthermore, a coordinate system with coordinate axes x, y, z is illustrated, whereby the x and y axes are assumed to lie in the plane of the plate 1. A transmission signal 5 emitted by the ultrasound transmitter 2 at angles α and β reaches an object 4, that is to say a reflection point, is reflected back by the latter to the ultrasound receiver 3 in accordance with a signal beam 6 and arrives there at angles γ and δ. The angles α and γ denote the angle between the x-axis and the projection of the emitted beam 5 or the received beam β onto the base plane, ie the plate 1, whereas the angles β and δ show the deviation of these beams 5, 6 from the Specify transmitter axis 12 or receiver axis 13. In the case of a rotationally symmetrical directional characteristic of the ultrasonic transmitter 2, the radiation properties of the Transmitter converter with the same beam angles ß the same.

In the case shown in FIG. 1, arrangements of the reflection point (object) 4 with a constant length of the transmission beam 5, which, although they have the same radiation angle β but different angles α, result in different distance measurements, since the angle also results in the measured distance changes, which is composed of the sum of the distance of the reflection point 4 from the ultrasonic transmitter 2 and the distance from the reflection point back to the receiver 3. A completely rotationally symmetrical ultrasound sensor which avoids this - which may be negligible - effect would require a concentric mounting of the ultrasound transmitter 2 and the ultrasound receiver 3 in such a way that they have a common axis of rotation, i.e. axes 12 and 13 then coincide and the distances to object 4 and back would be the same.

Such a concentric arrangement of transmitter 2 and receiver 3 can be obtained, for example, if the transmitter 2 e.g. surrounds the receiver 3 in a ring shape, as will be explained in more detail below with reference to FIGS. 8A and 8B.

In FIG. 1A, in addition to FIG. 1, a schematic of a structure of an ultrasound sensor device with the ultrasound sensor 2 and the ultrasound receiver 3 and associated control and evaluation units assigned to these transducers is shown. In particular, the ultrasonic transmitter 2 is preceded by a control unit 8, in which the desired broadband transmission signal 5 'is formed with a defined length, as is shown by way of example in FIG. 1A. As can also be seen, the intended transmission signal, i.e. in a control signal 5 'with a predetermined duration, e.g. a duration of 3 ms, the frequency increases continuously, the frequency increasing for example from 30 kHz to 80 kHz.

On the other hand, an ultrasound receiver 3 is followed by an evaluation unit, generally designated 9, which contains a correlator unit 9a and a reference pattern memory 9b. The received ultrasound signal is in the correlator unit 9a 6, after its conversion into an electronic signal in the transducer of the ultrasound receiver 3 and after a sampling or digitization (not illustrated in any more detail), is correlatively compared with a reference signal stored in the reference signal memory 9b, the reference signal stored in the memory 9b being free of phase shifts as caused by the transmission of the transmission signal 5 with the aid of the ultrasound transmitter 2 with predetermined - relatively narrow - directional characteristics are introduced. This correlation method will be explained in more detail below.

Finally, a general control and data processing unit 10 is shown in FIG. 1A. With the help of this unit 10, which also forms part of the evaluation unit 9 with regard to the data processing carried out in it, the transit time of a time-limited transmission signal 5 from the ultrasound transmitter 2 to the object 4 and the received signal 6 from the object 4 back to the ultrasound receiver 3 can also be determined to measure the distance from the ultrasonic sensor 7 to the object 4 after determining the angular orientation to the object 4.

An ultrasonic transducer can usually be described using the model of the piston membrane, the frequency-dependent directional characteristic of which can be seen in FIG. 2. In the case of a constant frequency of the emitted signal (for example 30 kHz), it consists of a main lobe 15a and side lobes 16a, 17a with decreasing amplitude maxima compared to the main lobe 15a, the lobes 15a, 16a, 17a being separated from one another by zeros. Each side lobe 16a, 17a, starting with the first side lobe 16a, also ideally (model case) produces a phase shift of 180 ° of the signal emitted by it. When the emitted frequency is increased (for example to 50 kHz or to 80 kHz according to FIG. 2), both the associated main lobe 15b and 15c and the adjacent side lobes 16b and 16c; 17b and 17c narrower. When a frequency-modulated signal is emitted, the effective directional characteristic of the ultrasound transmitter is dynamically changed in accordance with the frequency of the signal part emitted at the respective time. If one considers a linear frequency-modulated signal (eg the signal 5 'in FIG. 1A) of constant amplitude (signal length 3 ms, Frequency range 30 kHz to 80 kHz), which is to be emitted by an ultrasonic transmitter 2 with a piston-membrane-like directional characteristic at an angle of 17 °, so the radiation characteristics show the changes shown in Fig. 3: Signal components of 20 lower frequencies (~ 30 kHz) are emitted according to their directional characteristic via the main lobe 15a. With the increase in the emitted frequency (for example to ~ 50 kHz), the width of the main lobe 15a (FIG. 2) decreases until it reaches the width of the angle under consideration of 17 °. At this time, a zero point 21a is reached in the signal curve of FIG. 3. The following area or signal component 22 is emitted via the first side lobe 16b, which ends again with a zero point 21b. This part of the signal experiences a phase shift (phase shift) of 180 °. The remaining signal component 23 (~ f = 80 kHz) is finally emitted via the second side lobe 17c.

A correlative method is used to evaluate the received ultrasound signal (6 in FIG. 1), which involves a cross-correlation between the received signal 6 and a stored reference signal (ie a signal which generally corresponds to the control signal 5 ′, that is to say a signal without this influencing the directional characteristic, corresponds). In order to obtain behavior that is independent of the amplitude, only the sign but not the amplitude of the signals is evaluated. The evaluation of the maxima occurring in the cross-correlation allows, on the one hand, an assessment of the quality of the received signal 6 and, on the other hand, the exact determination of the position of the reference signal within the received signal. As long as all signal parts are transmitted through the main lobe 15a of the directional characteristic, a good correlation result will occur regardless of the signal amplitude, ie a large correlation maximum will be obtained. However, as soon as higher-frequency parts of the signal 5 or 6 receive the aforementioned 180 ° phase rotation due to the transmission through the first side lobe 16b, the positive and negative signal amplitudes in this area are exchanged (since the reference signal has not undergone the phase shift mentioned). to an anti-correlation. This means that these signal sections (see signal part 22 in 3) provide the contribution of the same magnitude, but with the opposite sign to the overall correlation result and thus cause a rapid reduction in the correlation maximum. The next zero point, ie the transition to the second side lobe (17c according to FIG. 2), is reached at 21b in FIG. 3, with a new 180 ° phase jump taking place for the signal part 23.

This correlation technique can be exemplified with the help of Table 1 below, in which only the signs of signal values (samples) on the one hand of the reference signal (in the first line of the table) and on the other hand of the signal emitted by transmitter 2 and received by receiver 3 (in the second line of the table). Below, the correlation result is illustrated in the third line, whereby it can be seen that the correlation is excellent initially - before the first phase jump by 180 ° due to the radiation in the side lobe, with increasing frequency - see (,, + ^Λ - Character) . An anti-correlation (cf. the "-" signs) can be found from the dashed line.

Table 1

+++ - - ++ - - + - - + - - ++ - - + - - + - - + - - + - + - + - +++ - - ++ - - + - - + - - ++ - - + - - + - - + - - + + - + - +

_{++++ ++++++++++++++++++++++++ ++++++++++++++++++++}

The amplitudes of the correlation maxima K (in%, based on a maximum value) are then plotted in FIG. 4 as a function of the radiation angle β. A flat area 26 at small angles and a steep drop at the edge 27a or 27b of this area 26 can be seen. The introduction of a detection threshold 25 permits an evaluation of the correlation maxima, so that only the correlation maxima are used for the distance measurement, the amplitude of which corresponds to the defined threshold value 25 exceeds. This procedure results in a clear and lent sharply delimited detection range 26 (radiation angle range) of the ultrasonic sensor (2 in FIG. 1, 1A).

An evaluation of the correlation result with the aid of a detection threshold 25 is functionally equivalent to a determination of the positions of the zeros (corresponding to the positions of the phase jumps) of the directional characteristic. The phase jumps in turn take place in the zeros of the directional characteristic of the ultrasound transmitter 2, the radiation angle Θ _{n of} which can be determined using the following equation:

• VΓ sin (Θ ") = £" -.

Inscribed here

Θ _n the radiation angle of the zero point n (corresponds to the angle of the boundary between the side lobe n-1 and the side lobe n of the directional characteristic, where the side lobe 0 denotes the main lobe),

k _n a constant dependent on the number of the zero n,

T is the absolute temperature and

f the signal frequency.

A change in the temperature leads to a shift in the zero points Θ _n in the directional characteristic and thus, with a given radiation angle Θ, to a shift in the relative positions 21a, 21b of the phase jumps in the received chirp signal (see Table 1 and Fig. 3).

The method for determining the radiation angle Θ is based on the evaluation of the relative positions of the phase jumps, in particular the first, in the received signal 6.

Temperature compensation is thus possible in the form that by adapting the start and end frequency and by adapting the time course of the frequency in the transmission signal 5 (or the Control signal 5 ') is achieved in that the relative positions of the phase jumps, in particular of the first phase jump, remain the same in the received signal 6 at the radiation angles Θ to be determined.

The temperature compensation described by adapting the control signal 5 'offers the advantage of a constant measuring range for the radiation angle, but the frequency range must be changed. An alternative to taking the influence of temperature into account is to mathematically correct the knife events on the receiver side.

The evaluation explained above finally leads to the behavior shown in FIG. 5: the ultrasonic sensor 7, consisting of a combination of an ultrasonic transmitter 2 and receiver 3, is used to measure the distance to two reflecting objects 31 and 32. Both objects 31, 32 are illuminated due to the directional characteristics of the ultrasound transmitter 2 that are sufficiently wide for this purpose and reflect the respective incoming signal back to the ultrasound receiver 3. However, due to the phase shift occurring due to the frequency modulation of the transmission signal 5 at larger radiation angles, only the signal reflected by an object 31 is generated 6 shows a good correlation result, while the signal reflected by the other object 32 is ignored due to its low correlation result regardless of the signal amplitude. A prerequisite for this is a sufficiently broad directional characteristic of the ultrasound receiver 3 of the ultrasound sensor 7 with a constant phase shift.

6 shows a comparable measuring arrangement with an ultrasonic sensor 7 and with two objects 42, 43. The results of a measurement carried out with the arrangement shown in FIG. 6 can then be seen in FIG. 7.

The ultrasonic sensor 7 according to FIG. 6 can be rotated with its axis 12 about an axis running perpendicular to it (and to the plane of the drawing) (cf. also the axis 12 'after pivoting), with a correspondingly changing axis angle ε, on a substructure (not shown in more detail) stored, and it measures the distance to the two objects 42, 43, namely to a round rod 42 and to a smooth plane 43. Because of the exclusive swivel or. Rotational movement of the ultrasonic sensor 7, the reflection point R of the plane 43 always remains in a fixed position. The angle 44 between the two reflection points, namely on the plane 43 and on the round rod 42, is 15 °.

The results obtained can be seen in FIG. 7 insofar as the determined distances 50 (to plane 43) and 51 (to round rod 42) are plotted over the radiation angle or axis angle ε. The similar result is remarkable in relation to the angular range between boundaries 52a-52b or 53a-53b, in which the two objects 43, 42, which differed greatly in their reflection properties, were detected. The detection range is approximately + 10 ° in both cases, and as can be seen, there is no measurement error at any of the range ends 52a, 52b and 53a, 53b as would be expected with a conventional measurement method.

As can be seen from the above, the technique described is essentially based on the frequency dependence of the phase shift of ultrasound signals, and this effect is exploited by the use of a broadband ultrasound signal, the different frequency components of which are exposed to corresponding phase shifts so that they are - within one and the same signal - be moved relative to each other. Furthermore, the phase shift changes at a constant frequency depending on the direction, whereby it typically remains approximately constant in the central region of the main lobe, whereas it changes rapidly in the edge region of the main lobe, or jumps by 180 ° in the piston membrane model in the zero crossing. These effects are used to the extent that, depending on the location, a characteristic and unambiguous course of the phase shift occurs over the frequency, which is used as a sharp limitation of the sound lobe and in this area as angle information. This characteristic course of the phase shift over the frequency is only dependent on the properties of the electro-acoustic transducer of the ultrasound transmitter, and the reflected signal subsequently has the frequency course of the phase shift that corresponds to the local position of the reflection point, that is, the object in space. An optimal prerequisite for determining the location or angle information is, of course, a phase response-free measurement of the reflected ultrasound signal in the ultrasound receiver. However, a meaningful measurement can also be carried out easily with an ultrasound receiver that has a defined, direction-dependent phase response. An ultrasound receiver with a different phase response, which is separate from the transmitter, is in any case advantageous, since when using combined transmit / receive converters, compensation effects regarding phase information often occur.

Since the location or angle information is obtained primarily as a property of the ultrasound transmitter 2, a lateral position of the ultrasound receiver 3 (with a negligible phase response) has no influence on the location information, but only on the measurement value; this influence can be neglected in some cases. But if you want to have a sensor that measures properly, there is a concentric arrangement of transmitter 2 and receiver 3, i.e. avoid lateral offset to be provided.

8A and 8B schematically illustrate two embodiments for such a concentric arrangement of the ultrasonic sensor 2 and the ultrasonic receiver 3, the control of the ultrasonic transmitter 2 with the aid of the control unit 8 and the connection of the ultrasonic receiver 3 with the correlator unit 9a also being shown is; see. see also Fig. 1A.

In detail, FIG. 8A shows an ultrasound receiver 3 (reception transducer) which is circular in plan view and which is arranged within an annular transducer means of the ultrasound transmitter 2. In this exemplary embodiment, the transmitter 2 and the receiver 3, which again have different directional characteristics as set out above, are arranged and operated independently of one another, similar to the above-described side-by-side arrangements of transmitter 2 and receiver 3. In the embodiment of FIG. 8B, which essentially corresponds to that according to FIG. 8A, a switch 55 (an electronic switch) is additionally provided which is controlled by the control unit 10 in order to make an electrical connection of the ultrasound receiver 3 which is located within annular ultrasound transmitters. Transducer means 2 is arranged to selectively switch between the control unit 8 and the correlator unit 9a. In this way, the transducer of the “ultrasound receiver” 3 can be connected to the control unit 8 in transmission mode and thus additionally used as an ultrasound transmitter transducer means (cf. the dashed position of the switch 55 in FIG. 8B), whereas in a receiving mode in which the 8B occupies the position shown in full line in FIG. 8B, the transducer of the ultrasound receiver 3 is connected to the correlator unit 9a and thus acts as a receiver transducer, depending on the distance of the objects to be located and thus the transit time of the ultrasound signal 5-6 the switching takes place in accordance with time intervals in the order of magnitude of, for example, half a ms, a ms or a few ms. The directional characteristic of the combined transmitter / transducer means 2 + 3 can certainly have a comparatively narrow form compared to the directional characteristic of the transducer of the ultrasound receiver 3 itself As a result, the Ef effects can be achieved by using the frequency dependence of the directional characteristic of the ultrasonic transmitter (2 + 3 combined).

It should be mentioned that, in principle, it is not necessary to design the transducers of the ultrasound transmitter 2 and receiver 3 in the form of a circle or a ring; other geometric shapes such as ellipses, rectangles, in particular squares, etc. are also conceivable. For reasons of symmetry, however, a circular shape will generally be preferred.

Claims

Claims:

1. A method for obtaining information about the position of an object (4; 31, 32; 42, 43) with the aid of an ultrasonic sensor (7) which has an ultrasonic transmitter (2) and an ultrasonic receiver (3), the directional characteristics of the ultrasonic transmitter (2) and receiver (3) are different, in which method with the aid of the ultrasound transmitter (2) an ultrasound transmission signal (5) is emitted and an ultrasound signal reflected by the object (4; 31, 32; 42, 43) ( 6) received with the aid of the ultrasound receiver (3) and evaluated to obtain position information, characterized in that the frequency-dependent directional characteristic of the ultrasound transmitter (2), which is narrow in comparison to the directional characteristic of the ultrasound receiver (3), by using a control signal (5 '), which contains different signal frequencies, is changed, the frequency-related change from one lobe (15a) in the directional characteristic to an adjacent one Lobe (16b) a phase shift occurs and that the reflected, received ultrasound signal (6) is compared with a stored reference signal in order to determine a radiation angle range (26) of the ultrasound transmitter (2) to be used for position determination.

2. The method according to claim 1, characterized in that a frequency-modulated transmission signal (5) is emitted.

3. The method according to claim 1 or 2, characterized in that a transmission signal (5) is emitted with increasing frequency.

4. The method according to any one of claims 1 to 3, characterized in that a transmission signal (5) with a continuous, e.g. radiated from 30 kHz to 80 kHz, increasing frequency.

5. The method according to any one of claims 1 to 4, characterized in that the received signal is compared with the reference signal in a cross-correlation method in which only the sign of the signals is evaluated.

6. The method according to any one of claims 1 to 5, characterized in that for measuring the distance from the ultrasonic sensor (2) to the object (4; 31, 32; 42, 43) the transit time of the time-limited transmission signal from the ultrasonic transmitter (2) to the object and determined back to the ultrasonic receiver (3).

7. The method according to any one of claims 1 to 6, characterized in that the ultrasonic transmitter (2) and receiver (3) are pivoted together, in the given case several radiation angle ranges, corresponding to several objects (31, 32; 42, 43) in Space to be determined in advance.

8. The method according to any one of claims 1 to 7, characterized in that the temperature influence on the determined radiation angle range (26), preferably by adapting the control signal (5 '), is compensated for on the basis of the measurement of the ambient temperature.

9. Sensor device for obtaining information about the position of an object (4; 31, 32; 42, 43), with an ultrasonic sensor (7), which has an ultrasonic transmitter (2) and an ultrasonic receiver (3), the directional characteristics of the ultrasonic transmitter and receiver are different, and with an evaluation unit assigned to the ultrasound receiver (3) for evaluating an ultrasound signal (object; 4; 31, 32; 42, 43) emitted by the ultrasound transmitter and reflected by the ultrasound receiver (3). 6) for obtaining position information, characterized in that the ultrasound transmitter (2) has a frequency-dependent directional characteristic which is narrow in comparison to the directional characteristic of the ultrasound receiver (3) and can be controlled for emitting a transmission signal (5) which contains different signal frequencies, so that its directional characteristic is changed, with the frequency-related change from a Keu le (15a) a phase shift occurs in the directional characteristic to an adjacent (16b), and that the evaluation unit (9) is set up to compare the reflected, received ultrasound signal (6) with a stored reference signal in order to determine a radiation angle range to be used for position determination (26) of the ultrasound transmitter (2) to determine.

10. The device according to claim 9, characterized in that the ultrasonic transmitter (2) can be controlled to emit a frequency-modulated transmission signal.

11. The device according to claim 9 or 10, characterized in that the ultrasonic transmitter (2) for emitting a transmission signal with increasing frequency can be controlled.

12. Device according to one of claims 9 to 11, characterized in that the ultrasonic transmitter (2) for emitting a transmission signal with a continuous, e.g. from 30 kHz to 80 kHz, increasing frequency can be controlled.

13. Device according to one of claims 9 to 12, characterized in that the evaluation unit (9) has a correlator unit (9a) for comparing the received signal with the reference signal in a cross-correlation method, in which only the sign of the signals is evaluated.

14. Device according to one of claims 9 to 13, characterized in that the evaluation unit (9) for determining the transit time of the time-limited transmission signal from the ultrasound transmitter (2) to the object (4; 31, 32; 42, 43) and back to the ultrasound receiver (3) is set up to measure the distance from the ultrasound sensor (7) to the object (4; 31, 32; 42, 43).

15. The device according to one of claims 9 to 14, characterized in that the ultrasonic transmitter (2) and receiver (3) are arranged jointly pivotable.

16. Device according to one of claims 9 to 15, characterized in that the ultrasonic transmitter (2) and receiver (3) are arranged concentrically.

17. The device according to one of claims 9 to 16, characterized in that the ultrasonic transmitter (2) has transducer means, a part of which can be switched as an ultrasonic receiver (3).