AT515554A4 - Ultrasonic sensor and method for locating objects - Google Patents

Abstract

Ultrasonic sensor (26, 37, 41) and method for locating objects (7, 8, 17) in space with the aid of such an ultrasonic sensor (26, 37, 41), the at least four ultrasonic receivers (27, 28, 29, 30 ), wherein an ultrasonic signal (42 or 9) is radiated from an ultrasonic transmitter (43 or 31) encompassed by the external or ultrasonic sensor (26) and transmitted by the ultrasonic receivers (27, 28, 29, 30) of the ultrasonic sensor (26). each one in at least one associated reflection point (33, 34, 35, 36) reflected ultrasonic signal (11) is received and evaluated to obtain at least one object position, characterized in that at several object positions obtained in parallel these are se lektiert according to a selection criterion, which is defined by the fact that the object position respectively associated at least four reflection points (33, 34, 35, 36) are approximately in a common plane in space.

Description

The invention relates to a method for locating objects in the room with the aid of an ultrasound sensor and a corresponding ultrasound sensor having at least four ultrasound receivers, an ultrasound signal being radiated from an external ultrasound transmitter or from the ultrasound sensor and from the ultrasound receivers each reflected in at least one associated reflection point Received ultrasonic signal and is evaluated to obtain at least one object position in an evaluation unit, which is connected to the Ultraschallemp¬fängern.

In particular, the invention relates to an ultrasonic sensor or method implemented by the ultrasonic sensor for reliably locating three-dimensional object positions (3D localization) relative to the position of the ultrasonic sensor using three-dimensional reflection points in the space by means of ultrasound. The invention particularly targets any non-concave objects. As a reflection point here is a point on a zuortenden object referred to where the ultrasound emitted by the ultrasonic transmitter ultrasonic signal is reflected before it reaches one of the ultrasonic receiver. A reflection point is therefore that point on the surface of the object in which the reflection condition for a particular ultrasound transmitter and a particular, namely the associated ultrasound receiver (i.e. a particular transceiver pair) is met. In general, therefore, the reflection points associated with the receivers are not identical or there are as many reflection points per object as the receiver. The ultrasound sensor is set up for measuring the transit times of an ultrasound signal emitted by the ultrasound transmitter and reflected in the reflection points and received by the ultrasound receivers. From the measured running times, the distance between the ultrasonic sensor and the reflection points or, more precisely, the sum of the distances between ultrasound transmitter and reflection point and reflection point and ultrasound receiver can be derived at a known sound velocity. The ultrasound sensor can basically be embodied as an active sensor device with its own ultrasound transmitter or as a passive sensor device without its own ultrasound transmitter. The ultrasound receivers or the ultrasound transmitters are arranged at distances from one another not only for constructive reasons but also in order to achieve a corresponding spatial resolution. In general, therefore, in the case of several ultrasound transmitters and / or multiple ultrasound receivers, different reflection points exist for the same or the same object. Each reflection point is associated with a particular transceiver pair, and for the sake of simplicity, a single transmitter can be said to have an association with the receivers, and vice versa.

It is well known to use ultrasound sensors to measure the duration of a first reflected ultrasound signal (hereinafter also referred to as echo for short) and, on the assumption that the origin of the echo lies on an acoustic axis of the sensor, this origin, which corresponds to the reflection point of the echo corresponds, to locate. However, such sensors are unsuitable for true three-dimensional positioning since no information about the direction of the echo is obtained. Moreover, these sensors are typically confined to a very narrow field of view (i.e., echoes are received only from a narrow solid angle) to reduce any errors in assuming that the origin of the echo is on an acoustic axis of the sensor.

In addition, sensor devices have already been proposed for the 3D-treatment of objects with several transmitters and / or receivers. To obtain the necessary directional information, at least three transit time measurements are required. Therefore, for example, sensor devices for gesture recognition by means of ultrasound, as proposed for mobile terminals, typically have a plurality of transmitters. For example, WO 2011/048433 A1 shows a system with multiple transmitters and receivers for detecting multiple echoes and for calculating the 3D position information of a hand gesture. Furthermore, Kani-ak et al. (Kaniak, G .; Schweinzer, H., " A 3D Airborne Ultrasound Sensor for High-Precision Location Data Estimation and Conjunction, " Instrumentation and Measurement Technology Conference Proceedings, 2008. IMTC 2008. IEEE, pp.842,847, 12- 15 May 2008, doi: 10.1109 / IMTC.2008.4547154) already a sensor device with four ultrasonic receivers (microphones) for locating the Re¬flexionspunkte described.

The known devices and methods have in common is that they have multiple echoes and / or superimposed echoes, as well as with Si¬tuationen in which the object positions clearly from the two locating, i. in the calculation of the object positions, used models deviate, can not handle in a suitable manner. In particular, difficulties arise when the run-time differences between two echoes on different objects are low. For more than one object, therefore, it often can not be clearly determined which echoes belong together and must be combined to compute the object position. Those objects which are farther apart than the maximum distance between two receivers can still be relatively easily separated because the transit time differences between the echoes of a single object may not be greater than that predefined by the distance between the receivers. However, if the objects are closer together or have a very similar distance from the sensor device, it is difficult to determine which echoes belong together, i. have their origin or reflection point on the same object. To circumvent this problem, elaborate methods have already been proposed in which, for example, an assignment is to be reconstructed on the basis of the phase and amplitude information of the echo. In simpler methods, only those combinations are rejected for which there is no geometric solution for a corresponding object position. However, this does not resolve all ambiguities, in particular if more than three transit time measurements can be present or combined.

As long as the ultrasound receivers are arranged relatively close together and all the reflection points lie on the same object, the object position can be determined relatively accurately on the basis of the reflection points or the error made by the use of different reflection points - depending on the given accuracy requirements and geometry Objects (optimally, objects with flat or convex surfaces, whereas with concave surfaces with comparatively larger errors must be counted) - are neglected. However, if the reflection points are on different objects, this can lead to false object positions. This is because the individual transit time measurements are only distance measurements and do not contain directional information. The Richtungsinforma¬ tion can only be derived from the deviations between the individual run time measurements.

It is an object of the invention to remedy the disadvantages observed in the prior art and to provide an ultrasonic sensor or a method for operating such an ultrasonic sensor, which provides accurate and reliable three-dimensional locating data (in the form of object positions) and thus the processing and ultimately the practical use of gewon¬nenen locating data easier. In particular, it is an object of the invention, with a single ultrasonic sensor, to enable a parallel alignment of a plurality of objects in as wide a space as possible while at the same time largely avoiding object position artifacts (incorrectly recognized object positions), which in particular are attributable to points of discontinuity in the object surfaces.

This object is achieved in a method of the initially mentioned kind according to the invention in that several object positions obtained in parallel are selected according to a selection criterion which is defined by the fact that the at least four reflection points assigned to the object position are approximately in a common plane in space. The approximation is particularly true when the deviations of the reflection points from a common plane are less than 5 mm, preferably less than 1 mm, in particular less than 400 pm, less than 200 μm, or less than 100 μm. While the deviations for plane surfaces are independent of distance, distance-dependent limits can also be used in previously known object geometries (eg in the case of a sphere, the farther the sphere is from the sensor, all the reflection points are closer together since only a very small angle is necessary) at a greater distance the

Distance of the receiver / transmitter to reach; Accordingly, the deviation of the reflection points from a plane increases with increasing distance). It is directly apparent to the person skilled in the art that, depending on the requirements of the particular application and accuracy of the components used and optionally on the distance and on the sensor dimensions, a correspondingly adapted tolerance range for the approximate criterion is selected. The reflection points are in turn assigned to different transmitter-receiver pairs or-in the case of a single transmitter-to different receivers. For selection, the reflection points themselves are not determined as three-dimensional spatial points, but it is only checked whether the measured transit times corresponding to the reflection points are or are not determined. for the corresponding distances and taking into account the reflection condition, a solution exists in which the reflection points characterized by the distances lie in one plane. Since the selection criterion for moving objects (or a moving sensor) is generally satisfied only at one point in time, it is essential, at least in these cases, for the measurements to be taken at a time, i. at the same time and simulataneously, so that the received ultrasonic signals associated with the reconstruction of an object position are due to an ultrasound signal radiated to us the same. The requirement of the minimum number of four measurements arises naturally, since it is always possible to find a plane satisfying the reflection condition for the three corresponding reflection points with only three measurements. The advantage and success of the proposed classification criterion lies in the fact that on the one hand this is not a significant limitation for the recognizable objects since the reflection points on the object are geometrically close to one another due to the sensor size, so that a surface which is approximately even in some sections Meeting the criteria is sufficient. On the other hand, it is at the same time highly unlikely that the reflection points of different objects are located in a common plane. For these reasons, for example, artefacts resulting from an association of reflection points on different objects can be recognized and thus avoided by means of the specified selection criterion. As a result, the positioning method becomes more robust compared to falsifications in the form of false or only apparently plausible object positions.

Accordingly, in the case of an ultrasound sensor of the type mentioned at the outset, the above-stated object is achieved in that the evaluation unit comprises a selection module which is set up to determine those object positions in the case of several object positions obtained in parallel, the at least four reflection points associated with the object position lie approximately in a common plane in the room. The selection module implements the selection criterion detailed above in connection with the method according to the invention. The fact that the evaluation unit is set up to obtain at least one object position from the received ultrasonic signals means, among others, that in addition to the selection module, all elements necessary for the evaluation of the received ultrasound signals, e.g. typically a computing unit, a memory and - in the case of a transit time measurement - a timer, includes. The selection module can be realized as a separate hardware unit or preferably as a software module and, for example, can also subsequently be integrated into a suitable sensor device or its evaluation unit. Any type of device may be used for the ultrasonic transmitter or the ultrasonic receivers. For example, a broadband electrostatic transducer can be used as the ultrasonic transmitter and four or more small non-directional MEMS microphones can be used as the ultrasonic receiver.

In general, the present method does not aim to detect a plane surface, but rather to determine the position of the object or the position of an equivalent reflection point corresponding to the object on the surface of the object. For this reason, the condition that all reflection points lie in one plane must also only be approximately fulfilled, since in practice it applies only to certain object geometries: in the case of a flat surface, it is clearly strict; In the case of a spherical surface, it is generally not exact, but only approximately fulfilled, with the (virtual) plane intersecting the sphere; if the ball converges to a point, the condition is also fulfilled; • in the case of a cylinder, two points may behave as if they were at one level, if aligned accordingly. The two further reflection points behave as with a sphere of corresponding radius; Approximately here too the condition is met again.

In order to further increase the robustness of the present method, it has proven to be advantageous if the ultrasound sensor has at least five ultrasound receivers, the selection criterion correspondingly being defined by the fact that the at least five reflection points respectively associated with the object position lie substantially in a common plane in space , It is only with a fifth sensor that artifacts which are not recognizable in certain symmetries with four sensors (for example, if in each case two reflection points lie on two different objects with parallel surfaces) can be detected and avoided. Accordingly, it is also favorable in the present ultrasonic sensor if it has at least five ultrasonic receivers which are connected to the evaluation unit.

In order to facilitate further processing of the acquired location data or object positions, it is advantageous if object positions for which no common level can be found are recognized as artifacts and discarded. Those object positions in which no common plane can be found for the (hypothetical) reflection points do not satisfy the selection criterion and it is therefore advantageous to do so early, e.g. still in the ultrasonic sensor, and not - like the other location data - e.g. output via a data interface.

A simple, computationally efficient and thus particularly rapid selection can be achieved if an even number of ultrasound receivers are arranged in one plane and in at least two with respect to a common center of mirror-symmetric pairs, the selection criterion being defined by the averaged flight time of the receiver pairs essentially matches. This criterion is of course equivalent to a comparison of the sums of maturities. The selection criterion simplified in this case to a so-called center criterion can therefore be checked by a simple mean value calculation of the transit time for each receiver pair and subsequent comparison of the resulting average values. Accordingly, in connection with the present ultrasonic sensor, it is particularly advantageous if at least a part of the ultrasound receivers is arranged in one plane and at least two mirror-symmetrical pairs with respect to a common center. In contrast, an asymmetrical arrangement of the receivers has the advantage that it is possible to detect artifacts in more situations than in the case of a symmetrical design.

In this context, it has proved to be advantageous if, after checking the selection criterion on the basis of the receiver pairs, a plane is determined on the basis of the transit times measured by the receiver pairs and it is checked for a second part of ultrasound receivers which need not be arranged in mirror-symmetrical pairs Ul¬traschallempfängern associated reflection points lie in the ermit¬telten level, otherwise the Auswahlkriteriumin total is not met. In the event that other receivers are provided in addition to the symmetrically arranged receiver pairs, the selection criterion can thus be evaluated in a two-stage process, wherein in a first step the above-described and efficiently verifiable center criterion is applied and subsequently only those combinations of reflection points are taken into account, which fulfill the middle criteria. The comparatively more computationally intensive examination, although the transit times measured by the non-symmetrically arranged ultrasonic receivers are consistent with the determined plane, takes place only for a comparatively small number of combinations, which have already been preselected. This method can be used in particular when using a fifth ultrasound receiver together with four symmetrically arranged ultrasound receivers.

A particularly efficient method for checking the selection criterion may be used if the receiver pairs have the same distance between the ultrasonic transmitter and the ultrasonic receivers, wherein in particular the receivers are arranged in an n-fold rotational symmetry corresponding to the number n of ultrasound receivers, with an equivalent reflection for all receivers on the basis of the transit times measured by the receiver pairs and for a second part of ultrasound receivers, which need not be arranged symmetrically, it is checked whether the reflection points associated with these ultrasound receivers are consistent with the equivalent reflection point; Otherwise, the selection criterion is not fulfilled. With the distance d zwi¬ the ultrasonic transmitter and the individual

For ultrasonic receivers, the position of the equivalent reflection point can be calculated as follows:

(1) where li is a distance corresponding to a running time measured by the ultrasonic receiver i, respectively. Since the equivalent reflection point is known, the expected running times for the further ultrasonic receiver (s) can be calculated immediately. That the reflection points of the other receivers are consistent if and only if their distance is approximately equal to the distance of the equivalent reflection point.

The present method is particularly suitable for those cases where the object positions of multiple objects are determined based on a single radiated ultrasound signal (e.g., from an ultrasound sensor having only a single ultrasound transmitter). Such scene analyzes are particularly strongly affected by the problem of artifacts, so that the suggested selection criterion makes decisive improvements possible here.

Due to the high significance of the selectivity criterion set forth above, when it is used in receiving more than one reflected ultrasonic signal in a receiver, the object positions can be determined by forming all possible combinations of reflection points, with each reflection point associated with another ultrasonic receiver. As a rule, the reflection points are not known as three-dimensional points, but merely characterized by their (measured) distance from the ultrasound sensor. The naturally large number of combinations - which increases substantially with the number of existing objects - can be reduced to the valid combinations solely by the classification criterion, i. it may be further, much more expensive Selekti¬onsmechanismen such. taking into account the Richtcharak¬teristik or the amplitude and / or phase of the received echoes eliminated.

Quite generally, and in particular in conjunction with the combination of all reflection points, it is favorable if object positions in which the maximum distance between two respectively assigned reflection points exceeds the maximum distance between two ultrasound receivers are rejected before the selection. Since this criterion is even simpler to realize than even the center criterion shown above, it should if necessary be checked before all other selection steps.

The invention will be further elucidated on the basis of particularly preferred embodiments, to which it should not be restricted, and with reference to the drawings. The drawings show in detail:

1A shows an example of an active ultrasonic sensor according to the prior art with only three ultrasonic receivers and FIG. Figure 1B is a timing diagram of the ultrasonic signals detected by the three receivers;

FIG. 2 shows an application of an ultrasonic sensor according to FIG. 1 with objects arranged slightly offset; FIG.

3 shows an active ultrasonic sensor with four ultrasonic receivers in an application according to FIG. 2;

4A shows an active ultrasonic sensor with four ultrasound receivers in an application according to FIG. 1A and FIG. 4B the associated time diagram, comparable to FIG. 1B;

5 shows an active ultrasonic sensor with five ultrasonic receivers in an application according to FIG. 2;

6 schematically shows an application of an active ultrasound sensor with five ultrasound receivers in an environment with retroreflectors;

7 schematically shows an application of a passive ultrasound sensor with five ultrasound receivers in an environment provided with external ultrasound transmitters;

FIG. 8 is a schematic plan view of an active ultrasound sensor according to FIG. 5; FIG. and

9 is a schematic block diagram of an ultrasonic sensor.

FIGS. 1A and 1B illustrate the basic difficulty of assigning the echoes of two different objects. FIG. 1A schematically shows an active ultrasonic sensor 1 with three ultrasonic receivers 2, 3, 4 and with an ultrasonic transmitter 5, wherein the ultrasonic receivers 2, 3, 4 and the ultrasonic transmitter 5 are arranged in a common plane 6. The ultrasonic transmitter 5 provides a short broadband ultrasonic signal 9 for locating the objects 7, 8, for example a linearly frequency-modulated signal with a length of a few hundred microseconds and a band width tuned to the transmitter, e.g. 30 kHz, from. The emitted ultrasonic signal 9 is reflected on objects 7, 8 in the vicinity of the ultrasonic sensor 1. Those points of an object surface which fulfill the reflection condition for a transmitter-receiver pair of the ultrasonic sensor 1 are referred to as reflection points. D.h.das emitted or emitted by the ultrasonic transmitter 5 Ultra¬ sound signal 9 is reflected in the reflection points on each einender ultrasonic receiver 2, 3, 4. The objects 7, 8 arranged here in the vicinity of the ultrasound sensor 1 and at a similar distance from the ultrasound sensor 1 are spherical or approximately punctiform, so that the three reflection points in this case substantially coincide in one point and therefore are not shown separately. An ultrasound signal 9 emitted by the ultrasound transmitter 5 is reflected on the two objects 7, 8 in each case essentially into the entire half space facing the ultrasound transmitter 5. Thus, each ultrasound receiver 2, 3, 4 receives both an ultrasound signal 10 reflected by the first object 7 and an ultrasound signal 11 reflected by the second object 8. The time diagram 12 in FIG. 1B has three separate time axes 13, 14, 15 for each ultrasonic receiver 2, 3, 4, which correspond to the three receiver channels. The two time points ti, t2, t3 of the reception of the two reflected ultrasonic signals 10, 11 are plotted on the time axes 13, 14, 15, wherein the ultrasound signal 10 reflected by the first object 7 is shown as a solid vertical line and the ultrasonic signal reflected by the second object 8 11 are drawn as a gestri¬chelte vertical line. The time-related information of the individual ultrasonic receivers 2, 3, 4 or the corresponding distance information is obtained by correlation of the individual receiver channels on the basis of predicted or learned correlation patterns. In this case, the measured ultrasonic signals are grouped, each group 16 consisting of a respective transit time measurement ti from each receiver channel. In the case of n ultrasound receivers or microphones, a group 16 consists of exactly n transit time measurements ti, with tieine transit time measurement of the channel i representing. In this case, only valid groups 16 are preferably formed, a group 16 being valid if and only if the condition (ti-tj-c <V 1 <i, j <n (2) is fulfilled, where c is the speed of sound in The range of the ultrasound sensor 1 and the physical distance between the ultrasound receivers i and j can in principle include a selected transit time measurements t.sub.i.sup.2.This can be selected, for example, by a group 16 used for locating an object. This allocation is basically based on the assumption that different objects are arranged at different distances from the ultrasonic sensor 1. However, since this is not the case in the case shown (see Fig. 1A), the assignment to the group 16 Therefore, false object positions and object positions reconstructed from the signals assigned to one another are also erroneous The objects 7, 8 can not be recognized in such an assignment.

FIG. 2 shows a further potential error case which can only be detected or solved with the aid of the measured transit times with only three ultrasound receivers 2, 3, 4. An object 17 has a point of discontinuity 18 in the form of a step. The transition at the point of discontinuity 18, i.e. in this case the height of the step, is smaller than the distance between the ultrasonic receivers 2, 3, 4, so that the condition (2) is fulfilled. The reflection points 19, 20, 21 associated with the individual ultrasonic receivers 2, 3, 4 lie on both sides of the point of discontinuity 18 and therefore in different sections 22, 23 of the surface of the object 17. In the case shown, a reflection point 21 is wider The ultrasound sensor 1 is removed from the other two reflection points 19, 20. It is assumed that only the transit times measured in accordance with the three reflection points 19, 20, 21 are available for locating the object 17. From the three running times, the point in space can be calculated by trilateration, for which the distance from the three transmitter-receiver pairs formed with the ultrasonic transmitter 5 and in each case one of the ultrasonic receivers 2, 3, 4 corresponds to the measured transit times ( See, for example, Manolakis, DE, &quot; Efficient solution and performance analysis of 3-D position estimation by trilateration, &quot; Aerospace and Electronic Systems, IEEE Transactions on, vol.32, no.4, pp.1239,1248, Oct, 1996 doi: 10.1109 / 7.543845).

Geometrically, this calculation can be illustrated by the fact that a common tangential plane (not shown) is determined for three imaginary spheres whose radii are the distances measured in each case by the measured transit times, and that the point in the tangent Tialbene is assumed, which is the ultrasound transmitter 5 next. Basically, this reconstruction method would be sufficient for a 3D location, but it is not robust to measurement errors and to errors due to the implicit assumptions concerning the object geometry. In particular, this calculation implies that all reflection points lie on the same object and that the form or type of the object can be neglected. In the situation shown in FIG. 2, however, this assumption fails: owing to the different distances of the three reflection points 19, 20, 21 in FIG. 2, the assumed tangential plane has an inclination which does not correspond to the real conditions and which has been determined Object position25 is faulty. More particularly, the present invention relates to the detection and elimination of this problem by the use of at least a fourth ultrasonic receiver in combination with a location method specially tailored to ultrasonic sensors having four or more receivers.

In Fig. 3, an ultrasonic sensor 26 with four Ultraschallemp¬fängern 27, 28, 29, 30 in a similar situation as in FIG. 2, i. an attempt is made to locate the object 17 with the point of discontinuity 18. Again, the result will be erroneous if one tries to determine an object position from the measured running times with the known methods. In order to avoid such errors, therefore, the present invention proposes to first check the assumption that the reflection points lie on the same object. This check can be carried out in particular by ascertaining whether the (hypothetical) reflection points which correspond to the measured transit times lie in one plane. On the basis of this criterion those groups of transit time measurements ti which withstand the check can be selected and the remaining groups can be discarded. In the case shown in FIG. 3, the ultrasonic receivers 27, 28, 29, 30 are in FIG

Pairs 27, 28 and 29, 30 and mirror-symmetrical with respect to a point of intersection of the connecting lines of the individual pairs 27, 28bzw. 29, 30 arranged. The connecting lines therefore intersect exactly in their respective center. The ultrasound transmitter 31 is also in the center of the receivers, i. arranged exactly in the common intersection of the connecting lines. In this construction of the ultrasonic sensor 26, it can be shown that the transit time measurements ti for the pairs of ultrasonic receivers 27, 28, 29, 30 must fulfill the following condition:

(3)

The inaccuracy of an ultrasonic sensor with a receiver distance of 80 mm to a distance of 1 m is less than 1 mm, so that all groups which do not fulfill the condition (3) can be recognized as invalid and discarded. According to this method, the measurement shown in FIG. 3 can be recognized as invalid, so that at least no faulty object position is detected.

Moreover, the principle described above can also be used in the assignment of the transit time measurements, as will be explained with reference to FIGS. 4A and 4B. As in FIGS. 1A and 1B, two objects 7, 8 are shown here, which are responsible for respectively two reflected ultrasound signals 10, 11 and the corresponding running time measurements ti and ti 'of the here four receiver channels. By checking condition (3) for all combinatorially possible groups, the two correct assignments which correspond to the average transit times t == (ti + t2) / 2 «= (t3 + t4) / 2 or t '== (ti '+ t2') / 2 »= (t3 '+ t4') / 2, determined and calculated on the basis of the grouped measurements the two corresponding object positions.

However, there are special cases in which even an ultrasound sensor with four symmetrically arranged ultrasonic receivers can not detect a discontinuity 18, as shown in FIG. 5. In this case, the ultrasonic sensor 37 is randomly arranged symmetrically with respect to the unsaturation 18 of the object 17, so that for each receiver pair 27, 28 or 29, 30 there is a respective reflection point on each side of the discontinuity 18 and thus the condition ( 3), although each object position determined from the four transit time measurements of the two receiver pairs 27, 28 and 29, 30 would be erroneous for the same reason, as already explained in detail with reference to FIGS. 2 and 3. To cover this special case as well, the ultrasound sensor 37 has a fifth ultrasound receiver 38, so that the distance between the ultrasound sensor 37 and a fifth reflection point 39 on the object 17 can be measured ultrasonically. Thus, the error can be recognized as follows: first, a provisional object position is determined on the basis of the transit time measurements of the four ultrasound receivers 27, 28, 29 and 30 and in a second step it is checked whether the runtime measurement of the fifth ultrasound receiver 38, i. a distance from the ultrasonic transmitter 31 to the reflection point 39 and back to the ultrasonic receiver 38 is consistent with this provisional object position, e.g. the distance corresponding to the provisional object position is compared with the separately measured distance from the fifth ultrasonic receiver 38.

From Figs. 6 to 8 further advantages associated with the use of the ultrasonic sensor 37 for locating are apparent. On the basis of the additional location information, which from the Messun¬gen the fourth and - optionally - the fifth

Ultrasonic receiver can be obtained, it is possible with the aid of corresponding reference points 40 in space to determine not only the position of the ultrasonic sensor 37 but also its orientation. This can be done, for example, by means of passive landmarks, preferably in the form of retroreflectors 40 (see Fig. 6). It can be demonstrated that the selection criteria described above are also valid for retro-reflected reflectors 40 (multiply) reflected ultrasound signals. If there are three such orientation points whose positions in space are known, the position and orientation of the ultrasonic sensor 37 in a global coordinate system can be calculated on the basis of corresponding transit time measurements. The advantage of a retroreflector 40 as a point of orientation is that the "visible" for the ultrasonic sensor 37 ". Position of the retroreflector 40 is independent of the Ein¬fallswinkel the ultrasonic signal 9 and the distance from the ultrasonic sensor 37.

In addition, the present invention can be applied not only to active ultrasound sensors 26 and 37 with their own ultrasound transmitter 31, but also to passive ultrasound sensors 41 (see FIG. In such passive ultrasonic sensors 41, the ultrasonic signals 42 are emitted by external signal transmitters 43, which are arranged at known positions in space and can therefore - as described above - at the same time be used as orientation points. The object positions of possible objects 44 in space can be reconstructed on the basis of the measured running times of the ultrasonic signals 42 and of the known positions of the signal transmitters 43. In this case, the described selection criterion can additionally be used for the assignment of several transit time measurements to an ultrasound transmitter, i.e. in this example a signal generator 43.

Compared with passive sensors 41, an active ultrasonic sensor 37 has the advantage that the fixed distance d between the ultrasound transmitter 31 and the ultrasound receivers 27, 28, 29, 30, 38, for example. can be used for temperature compensation (see Fig.8). In this case, the sound velocity c at the current ambient conditions is preferably measured on the basis of several transit time measurements t and the known distance d, and the ultrasound sensor 37 is calibrated in this way. The accuracy of the measurement is limited only by the time resolution of the Laufzeitmes¬sung and the distance between transmitter 31 and receivers 27, 28,29, 30, 38. At a distance of 4 cm between the transmitter 31 and the receivers 27, 28, 29, 30, 38, the sound velocity could be determined, for example, to an accuracy of approximately ± 2 m / s.

FIG. 9 shows diagrammatically an ultrasonic sensor 45 with an ultrasound transmitter 46 and two (or more) ultrasound receivers 47. The ultrasound transmitter 46 receives an ultrasound signal to be transmitted from a drive unit 48, wherein the signal in an amplifier 49 is adapted to the requirements of the ultrasound transmitter 46. The ultrasonic receivers 47 are adapted to receive the reflected ultrasonic signals and connected to correlator units 50 which can correlate a received reflected ultrasonic signal with the transmitted ultrasonic signal. In order to determine the correct temporal correlation, the correlator units 50 are connected and synchronized with the drive unit 48 via synchronizing connections 51 (dashed lines). Starting from the transit times determined on the basis of the correlations, these are converted in a preselection module 52 to the condition (2), i. based on the sensor dimensions, preselected and verworkfen those combinations which can be physically excluded due to the sensor geometry. Subsequently, in a further selection module 53, the middle criterion (3) is applied to the measured and preselected transit times and thus the majority of artifacts are removed. Finally, in a location module 54, which is connected to the selection module 53, the object location is performed on the basis of the adjusted transit times, checked for plausibility with any additional receiver, and output in the positive case. That after object location, the criterion, if any, is applied to the additional (e.g., fifth) receiver and output after a positive check; the object location is based on the measured by the remaining receivers runtimes. Together, the ultrasound receivers 47 with the correlator units 50, the preselection module 52, the selection module 53 and the locating module 54 have an evaluation unit 55. In this case, the preselecting module 52, the selection module 53 and the locating module 54 can in practice be used as software modules on a common, in the Ultrasonic sensor 45 integrated microprocessor platform (not shown) to be implemented.

Claims (13)

Claims 1. Method for locating objects (7, 8, 17) in space with the aid of an ultrasound sensor (26) comprising at least four ultrasound receivers (27, 28, 29, 30), one of exter- nal or of the Ultrasonic sensor (26) comprising ultrasonic transmitter (43 or 31) an ultrasonic signal (42 or 9) is emitted and from the ultrasonic receivers (27, 28, 29, 30) of the ultrasonic sensor (26) in each case at at least one associated reflection point (33, 34, 35, 36) and evaluated to obtain at least one object position, characterized in that, in the case of several object positions obtained in parallel, these are selected according to a selection criterion which is defined by at least the object positions assigned to each four reflection points (33, 34, 35, 36) are approximately in a common plane in space. 2. The method according to claim 1, characterized in that the ultrasound sensor (37) has at least five ultrasound receivers (27, 28, 29, 30, 38), wherein the selection criterion is accordingly defined by the fact that each of the object positions assigned at least five reflection points (33, 34, 35, 36, 39) lie approximately in a common plane in space. 3. The method according to claim 1 or 2, characterized in that object positions for which no common plane can be found gefun¬den as artifacts and discarded. 4. Method according to one of claims 1 to 3, characterized in that an even number of ultrasonic receivers (27, 28, 29, 30) are arranged in one plane and in at least two mirror-symmetrical pairs (27, 28 and 29, respectively) with respect to a common center. 30), wherein the selection criterion is defined by the fact that the averaged transit times of the receiver pairs (27, 28 or 29, 30) substantially coincide. 5. The method according to claim 4, characterized in that after checking the selection criterion based on the Empfänger¬paare (27, 28 or 29, 30) a plane based on the of the Emp¬fängerpaaren (27, 28 and 29, 30 ) and for a second part of ultrasonic receivers (38) which need not be arranged in mirror-symmetrical pairs, it is checked whether the reflection points (39) associated with these ultrasonic receivers (38) lie in the determined plane, otherwise the selection criterion as a whole is not fulfilled. 6. The method according to claim 4, characterized in that the receiver pairs (27, 28 and 29, 30) have the same distance zwi¬ ultrasonic transmitter (31) and ultrasonic receivers (27, 28,29, 30), in particular the ultrasonic receiver ( 27, 28, 29, 30) are arranged in one of the number n of the ultrasonic receivers (27, 28, 29, 30) corresponding n-fold rotational symmetry, wherein an equivalent reflection point for all Ul¬traschallempfänger (27, 28, 29, 30) is determined on the basis of the transit times measured by the receiver pairs (27, 28 or 29, 30) and checked for a second part of ultrasound receivers (38), which need not be arranged symmetrically, if these ultrasound receivers (38) associated reflection points (39) are consistent with the equivalent reflection point, whereby otherwise the selection criterion is not met in its entirety. 7. The method according to any one of claims 1 to 6, characterized gekenn¬zeichnet that the object positions of a plurality of objects (7, 8) aus¬gehend determined by a single radiated ultrasound signal (9). 8. The method according to any one of claims 1 to 7, characterized gekenn¬zeichnet that when receiving more than one reflected Ul¬traschallsignal (10, 11) in a receiver (27, 28, 29, 30), the object positions by forming all possible combinations of reflection points (33, 34, 35, 36), each reflection point (33, 34, 35, 36) being assigned to another ultrasound receiver (27, 28, 29, 30). 9. The method according to any one of claims 1 to 8, characterized gekenn¬zeichnet that object positions in which the maximum distance between two respectively associated reflection points (33, 34, 35, 36) the maximum distance between two Ultraschallempfän¬gern (27, 28, 29, 30) are discarded prior to selection. 10. An ultrasonic sensor (26, 37, 41, 45) for locating objects (7, 8, 17, 44) in space with at least four ultrasonic receivers (27, 28, 29, 30; 47) arranged one from an external one or ultrasound signal (9, 42 or 10; 11) emitted and reflected in at least one reflection point (33, 34, 35, 36), and the ultrasound sensor (26, 37, 45) assigned to the ultrasound sensor (26, 37, 45), and with an evaluation unit (55) which is connected to the ultrasound receivers (27, 28, 29, 30, 47) and arranged to acquire at least one object position from the received ultrasound signals (10, 11), characterized in that the evaluation unit (55) Selection module (53) which, in the case of several object positions obtained in parallel, is set up for determining those object positions in which the at least four reflection points (33, 34, 35, 36) associated with the object position lie approximately in a common plane in space gen. 11. Ultrasonic sensor (37, 41) according to claim 10, characterized gekenn¬zeichnet that at least five ultrasonic receiver (27, 28, 29, 30, 38, 47) are connected to the evaluation unit (55). 12. Ultrasonic sensor (26, 37, 41) according to claim 10 or 11, da¬durch characterized in that at least a part of the Ultraschall¬ receiver (27, 28, 29, 30) in a plane and in at least zwei a common center mirror-symmetric pairs ( 27, 28 and 29, 30) is arranged. 13. Ultrasonic sensor (26, 37, 41) according to claim 12, characterized in that the receiver pairs (27, 28 or 29, 30) the same distance between the ultrasonic transmitter (31) and Ultra¬schallempfängern (27, 28, 29, 30), wherein in particular the ultrasonic receivers (27, 28, 29, 30) in one of the number nder ultrasonic receiver (27, 28, 29, 30) corresponding n-zäh-ligen rotational symmetry are arranged.