EP2616842A1

EP2616842A1 - Environment monitoring system for a vehicle

Info

Publication number: EP2616842A1
Application number: EP11749725.5A
Authority: EP
Inventors: Christoph Lücking; Rainer Risse; Udo Ronnenberg; Axel Stender
Original assignee: Wabco GmbH
Current assignee: ZF CV Systems Hannover GmbH
Priority date: 2010-09-17
Filing date: 2011-07-30
Publication date: 2013-07-24
Also published as: WO2012034612A1; DE102010045657A1; CN103119469A; US20130162461A1; US9459347B2

Abstract

The invention relates to an environment monitoring system (3) for a vehicle (1), wherein the environment monitoring system (3) comprises: at least two distance sensors (4-1, 4-2, 4-3) for detecting distance by measuring the propagation time of detection signals, wherein the distance sensors (4-1, 4-2, 4-3) are each designed as a transmitting unit and receiving unit for the detection signal and, in a direct operating mode, emit detection signals, receive reflected components of the detection signals emitted by the distance sensors, and emit active measurement signals according thereto, and a control device (5), which receives the measurement signals of the distance sensors (4-1, 4-2, 4-3) and determines an object distance (s) of detected objects (10). According to the invention, at least one distance sensor (4-1, 4-2, 4-3) additionally can be operated in an indirect operating mode in order to detect a detection signal emitted by another distance sensor (4-2, 4-3, 4-1) and reflected by the object (10) and in order to generate an indirect measurement signal.

Description

Hanover, 17.09.2010

2010P00059DE, Dr. Koschnitzki / Bremen

(EM 2010E00040)

2010P00059DE.rtf

Environment monitoring system for a vehicle

The invention relates to an environment monitoring system for a vehicle and to a method for determining an object distance.

Environment monitoring systems on vehicles are used to determine objects in the environment of the vehicle. In the case of back-room monitoring systems, in particular a possible collision with objects located in the rear space (environment behind the vehicle) during a reverse drive is to be determined.

For this purpose, the environment monitoring systems on distance sensors (distance sensors). In transit time measurements, a distance sensor sends a detection signal into the area to be monitored at a transmission time. When an object is detected by the detection signal, it reflects it back, so that the distance sensor can detect it at a reception time. The transit time of the detection signal can be determined as the difference between the time of reception and the time of transmission, so that the total travel distance, which is twice the distance of the object from the sensor, can be determined by using the signal speed. Such transit time measurements are carried out in particular with ultrasound sensors and radar sensors, in some cases also with light beams (lasers) as detection signals. A direction-dependent or angle-resolved detection can not initially be performed with runtime measurements.

In z. For example, DE 10 2007 052 977 A1 proposes a triangulation in which two ultrasonic sensors in the bumper region of a vehicle are arranged in a horizontal line, and in each case perform a transit time measurement, so that two distance information is determined, which can serve by means of a triangulation for determining the distance of the sensor relative to the vehicle or the environment monitoring system, such a distance in general as minimum distance from the vehicle is determined. DE 10 2006 002 232 B4 also proposes such a triangulation for determining the position of an object by measuring two distances from two different positions.

With triangulations of this type, a triangle can thus be defined with a known sensor spacing (distance between the sensors) and the separately determined individual distances of an object relative to each of the two distance sensors, so that the distance of the object to the monitoring system is defined as height in this triangle. DE 10 2007 042 220 A1 also proposes such a triangulation by means of ultrasonic sensors. From DE 41 37 068 A1 an integrated optical multiple distance sensor is provided, which proposes optical triangulation using position sensitive diodes.

DE 195 07 957 C1 proposes a triangulation using infrared LEDs, wherein a road surface is scanned to detect a lane boundary. From DE 102 51 357 A1 a method for setting or switching off a direction indicator is known, are determined from the determined environment data lane and / or direction change, wherein in addition to a lane detection and a distance measurement as transit time measurement by infrared sensors of a monocamera, and the distance measurement means Triangulation of a stereo camera is described.

Such triangulation methods require that each distance sensor locate the object to be determined at substantially the same location recorded and thus a triangle is formed. For larger objects, however, such triangulation detection may be more complex. Furthermore, if necessary, one of the distance sensors can not detect a measurement signal, if z. B. the object has unfavorable sloping surfaces, since radar and ultrasonic waves undergo a directional reflection, with reflections on unfavorable inclined planes may not lead to an echo at the distance sensor. Another disadvantage is the generally required for conventional rear space monitoring systems high number of distance sensors, usually six to eight distance sensors at a vehicle width of a commercial vehicle of z. B. 2.5 m.

The invention is based on the object to provide an environment monitoring system that enables reliable monitoring of the environment with relatively little effort.

This object is achieved by an environment monitoring system according to claim 1. In addition, a corresponding method is provided for determining distances of objects, in particular using such an environment monitoring system. The dependent claims describe preferred developments.

Thus, according to the invention, an indirect measurement is made in which a first distance sensor emits a detection signal, and another distance sensor detects in a passive operating mode without sending the detection signal of the first distance sensor reflected by an object, i. takes on an indirect echo.

The detection signal output by the first transmitting distance sensor thus passes to the object over a first distance, is reflected thereon and reaches the second distance sensor over a second distance. This indirect measurement can be used for a runtime determining total distance distances are determined, which are the sum of the distances of the transmitting and the received distance sensor to the object.

Preferably, conventional direct measurements in which a distance sensor transmits and receives are combined with the indirect measurements of the invention, thereby forming a combined mode of operation. With this combination, both distance sensors receive, whereby only one sends. Thus, a direct measurement is carried out to determine the first distance and the indirect measurement of the combined total distance, from which the other distance can be determined by using the measured first distance.

Advantageously, such combined modes of operation may be performed alternately so that each distance sensor alternately transmits and receives the others.

According to the invention, some advantages are achieved:

In addition to the direct measurements, indirect measurements can be made without relevant additional hardware expenditure; only supplemental software programming of the distance sensors is required in that they can be operated in the passive operating mode of receiving without their own transmission signal.

By indirect measurement, a triangulation can be done, even if possibly one of the two sensors does not receive direct measurement, which z. B. may be present at unfavorably extending reflection surfaces of the object to be detected. In such cases, the distance between the two distance sensors to the object and, in addition, the lateral position of the object can still be determined by the combined operating mode. In particular, the indirect measurements may be in addition to the direct measurements to allow mutual plausibility or estimation of errors. This is already helpful when using only two distance sensors. In such a case, the distance sensors can be mounted in particular on the lateral areas of the vehicle rear and relatively wide radiation angle, z. B. over 60 degrees, preferably almost 90 degrees, to detect the back space each largely, so that the overlap region of the radiation angle is large. The emission angles are in particular directed inwards, so that they cover the entire rear space as an overlap region towards the rear.

The indirect measurement should in principle result in the same total distance as the sum of the individual distances for two distance sensors in both measuring directions, so that the two reciprocal, indirect measurements can also be used for verification.

According to the invention, additional operating modes or detection methods can be carried out, in particular also for the case that a detection object does not lead to an echo in both sensors. These additional detection methods may include:

a radius estimate, if only a direct echo of a single distance sensor was received,

a combination of direct echoes for conventional triangulation,

- In the case of only indirect measurements, the determination of the object distance on an ellipse. Such ellipse formation may in principle be sufficient to detect a minimum possible distance;

a back-up function or additive power function in which both or all distance sensors transmit and receive at the same time, achievable by superimposing all the radiated detection signals to increase the overall performance. In this case, although the distance of the object can only be estimated, when using a plurality of distance sensors already results in a wavefront, which comes relatively close to the horizontal line of the sensor system. The total power thus achieved enables the detection of objects that may not yet be possible by individual direct measurements.

Thus, a cost-effective system is provided which, in addition to the known direct measurements and direct triangulation method allows additional operating modes and detection methods by which the security and detection accuracy and the plausibility of measurement results is significantly improved without this relevant additional hardware overhead occurs.

The synchronization of the distance sensors for the indirect measurements can be done by the common control device, which is anyway required for data acquisition of conventional triangulation. This synchronization signals can be output via a suitable bus system or via a star connection, so z. B. a LIN bus between the distance sensors and the common control device may be provided. The control device can output the synchronization signals as bus commands, wherein z. B. all distance sensors are addressed, and the indication of each transmitting distance sensor is included as a parameter. The measurement signals are output accordingly from the distance sensors via the bus to the control device. With such a design of the additional software effort is relatively low.

The invention will be explained in more detail below with reference to the accompanying drawings of some embodiments. Show it: 1 shows a vehicle with an inventive environment monitoring system according to a first embodiment with two distance sensors and a schematic representation of the distance measurement.

Fig. 2 is a schematic representation of the invention

Measuring principles and signals;

Fig. 3 is an alternative to Figure 1 embodiment with three distance sensors.

A vehicle 1 may, for. B. be designed as a trailer, or as a single vehicle. In or at its rear region 2, a rear-room monitoring system 3 is mounted, which in the embodiment according to FIG. 1 has two ultrasonic distance sensors 4-1, 4-2 and a control device 5, which are connected to one another via a LIN bus 6 so that the back room monitoring system forms a bus system.

The two ultrasonic distance sensors 4-1 and 4-2 are arranged at the lateral outer portions of the rear portion 2; According to the plan view of Figure 1, the left distance sensor 4-1 is thus the leftmost, and the right distance sensor 4-2 arranged on the rightmost rear of the vehicle 2.

The ultrasonic distance sensors 4-1 and 4-2 have z. B. in a conventional manner, a membrane which serves both to transmit and receive ultrasonic waves. Alternatively, however, the ultrasonic distance sensors 4-1 and 4-2 may also have separate transmitting and receiving devices. In Fig. 1, radiation angle ranges 8-1 and 8-2 of the distance sensors 4-1 and 4-2 which detect a rear space 7 behind the vehicle 1 are shown; These radiation ranges 8-1 and 8-2 can z. B. Abstrahlkegel, but advantageously there is a radiation pattern substantially in the horizontal plane. In FIG. 2, the ultrasonic waves emitted by the first ultrasonic distance sensor 4-1 are denoted by 9-1 and the ultrasonic waves subsequently reflected by an object 10 are denoted by 11-1. Accordingly, the ultrasonic waves emitted by the second ultrasonic distance sensor 4-2 in its emission area 8-2 are designated as 9-2 and the ultrasonic waves subsequently reflected by the object 10 are designated as 1-2. The emission areas 8-1 and 8-2 are respectively directed backwards and inwards, so that the emission areas 8-1 and 8-2 largely overlap. The detection ranges of the ultrasonic distance sensors 4-1 and 4-2, within which they can receive reflected ultrasonic waves, are generally larger than their radiation angle ranges 8-1 and 8-2.

According to the invention, a first direct mode of operation is possible in which - in a manner known per se - each distance sensor 4-1 or 4-2 actively emits ultrasonic waves 9-1 or 9-2 and subsequently detects its reflected ultrasonic waves. Thus, in this first operation mode, the first ultrasonic distance sensor 4-1 transmits ultrasonic waves 9-1 partly reflected by the object 10 as ultrasonic waves 1-1-1, and detects these reflected ultrasonic waves 1-1-1 after a time difference Δθ. A distance L1 of the object 10 from the first distance sensor 4-1 can be subsequently detected according to the principle of transit time measurement: The ultrasound waves 9-1, 11-1 return the distance 2 x L1 with the speed of sound c, so that

2 x L1 = ΔΤ x c,

from which L1 can be determined. The distance sensor 4-1 outputs a direct measurement signal S1 to the control device 5. Accordingly, the second ultrasonic distance sensor 4-2 actively measures its distance L2 to the object 10 in the direct mode of operation by a travel time measurement and outputs a direct measurement signal S2 to the control device 5.

Furthermore, the distance d between the distance sensors 4-1 and 4- 2 is known, so that the triangle 4-1, 10, 4-2 is completely known with its sides L1, L2 and d and an object distance s is thus as height in gives this triangle, the height s is perpendicular to d. The determination of the object distance s thus takes place in the control device 5 by triangulation on the basis of the known triangle 4-1, 10, 4-2.

According to the invention, a second, indirect operating mode is furthermore possible, in which the distance sensors 4-1 and 4-2 receive reflected ultrasonic waves 1 to 1 or 1 to 1, which are emitted by the respective other distance sensor 4 - 2 or 4 - 1 Thus, the first distance sensor 4-1 transmits ultrasonic waves 9-1, and the second distance sensor 4-2 passively detects without transmitting the ultrasonic waves 11-1 reflected from the object 10. The ultrasonic waves have thus covered the total distance L1 + L2 from the first distance sensor 4-1 via the object 10 to the second distance sensor 4-2 in this second operating mode. By the distance sensors 4-1 and 4-2 are synchronized, the time difference between the transmission time at the first distance sensor 4-1 and the reception time at the second distance sensor 4-2 can be determined as transit time and calculated with the speed of sound c corresponding to the total distance L1 + L2 ,

Furthermore, conversely, the second distance sensor 4-2 can actively emit ultrasonic waves 9-2, and accordingly the first distance sensor 4-1 passively transmits the second reflected by the object 10 without transmitting Detecting ultrasonic waves 11-2, so that the same total distance L2 + L1 can be determined by the transit time measurement.

Advantageously, the direct and indirect modes of operation are combined to form a distance sensor, e.g. B. 4-1 sends, and on the one hand receives in the direct mode of operation itself, and the other distance sensor 4-2 receives passively. Thus, in this combined operating mode, the distances L1 and L1 + L2 can be determined simultaneously.

Subsequently, the second distance sensor 4-2 then sends and receives in its direct operating mode, while the first distance sensor 4-1 only receives passively, so that then the distances L2 and L2 + L1 can be measured simultaneously.

The distance sensors 4-1 and 4-2 give indirect measuring signals S3 and S4 to the control device 5. In this combined operating mode, both distances can already be determined from the two measuring signals of each measurement. Thus, in the first measurement in which the first distance sensor 4-1 actively transmits and receives and the second distance sensor 4-2 receives only passively, the distance L1 can be determined directly from the active measurement signal S1 of the first distance sensor 4-1 by halving the distance L1, and this value is subtracted from the total distance L1 + L2 transmitted as the passive measurement signal S4 of the other distance sensor 4-2:

1. the distance sensor 4-1 sends, both distance sensors 4-1 and 4-2 received. Thus, the first distance sensor measures the distance D1 = L1 + L1, the second distance sensor 4-2 measures the distance D2 = L1 + L2;

2. D1 is calculated by halving L1,

3. from D2 and the L1 determined in step 2 is calculated by subtracting L2. Thus, the triangle 4-1, 10, 4-2 is known, so that its height (height of the object 10 on the side d) as object distance s of the object 10 to the sensors 4-1, 4-2 and the vehicle. 1 can be determined. According to FIG. 2, the lateral position p of the object 10 can subsequently be ascertained, eg. As shown in Figure 2 as part of section p between the height projection of the object 10 along the height s and the first distance sensor 4-1, where p ² + S ² = L1. ² Thus, the position of the object 10 to the two distance sensors 4-1 and 4-2, as well as to the vehicle rear 2 (in known position of the distance sensors 4-1, 4-2 at the rear of the vehicle 2) known.

FIG. 3 shows a further embodiment in which, in addition to the embodiment of FIG. 1, the third, middle ultrasonic distance sensor 4-3 is additionally provided. In this embodiment, the Abstrahlwinkelbereiche (emission lobes) 8-1 and 8-2 of the two outer ultrasonic distance sensors 4-1 and 4-2 may possibly be rotated slightly outward, since the central region detected by the complementary provided distance sensor 4-3 becomes. Thus, a lateral rear area can also be detected here.

In the embodiment of FIG. 3, three direct distance measurements can be performed. Furthermore, indirect measurements are possible, alternately each one of the distance sensors 4-1, 4-3, 4-2 sends and all three distance sensors 4-1, 4-2, 4-3 receive, so that there are six indirect measurements, and the distances L1 + L2, L1 + L3, L2 + L3 are again measured twice (in both directions).

Thus, in this embodiment, a more extensive system of equations for determining the object distance s and the lateral width p can be used. In all embodiments, the object 10 may also be located next to the vehicle 1. This lateral position of the object 10 can be recognized according to the invention, in which case the distance p is negative or greater than d. Such objects can be discarded directly by the algorithm or displayed as non-obstructive.

In principle, it may occur that an object 10 does not completely or not symmetrically reflect ultrasonic waves 8-1 or 8-2 in all directions, e.g. B. due to its material properties or in particular the inclination of its surfaces. Thus, z. Example, in Fig. 1, the case that the object 10 does not lead to an echo in both distance sensors 4-1 and 4-2. If z. For example, when the first distance sensor 4-1 transmits, the second distance sensor 4-2 may not receive echo or reflected ultrasonic waves 1-1-1, or conversely, only the second distance sensor 4-2 may receive reflected ultrasonic waves 1-1-1 However, the transmitting distance sensor 4-1 itself. Especially in this last case, the detection of a signal may not be possible in the conventional first operating mode. According to the invention, additional detection methods can be carried out in such and other cases. These are z. B .:

a radius estimate, if only a direct echo, d. H. was received over the distance L1 + L1 or the distance L2 + L2. Thus, the radius of the pitch circle or space ball to the distance sensor is known which receives the direct echo;

- a triangulation of direct measurements if no indirect echoes were received. Thus, the distances L1 + L1 and L2 + L2 are measured, but no mixed heat. In this case, a conventional triangulation of the individually measured distances L1 and L2 and the known sensor distance d is possible. - The determination of the object distance s on an ellipse, if only indirect measurements are possible. The indirect measurements provide the sum L1 + L2 of the two distances L1 and L2. All points with this constant sum lie on an ellipse, at the focal points of which are the distance sensors 4-1 and 4-2. Such an ellipse formation may in principle be sufficient to detect a minimum possible distance.

- as a backup: both distance sensors 4-1 and 4-2 send and receive at the same time to increase the total radiated signal power. Thus, a total power can be achieved, which forms as a superposition of the Abstrahlwinkelbereiche (Abstrahlkegel) 8-1 and 8-2 (in Fig. 3 of the Abstrahlwinkelbereiche 8-1, 8-2, 8-3). This superposition takes the form of a parallel wavefront more strongly towards larger object distances s. In this mode, the object distance s can only be estimated; however, even with larger object distances s, the measurement inaccuracy due to the unknown lateral position is no longer so relevant, especially when s becomes very large towards d. Thus, estimates of larger object distances s are possible.

The synchronization of the distance sensors 4-1 and 4-2 advantageously takes place via the control device 5, which outputs corresponding control signals or commands via the LIN bus 6. Thus, synchronization commands K1 can be output from the control device 5 via the bus 6 to all distance sensors 4-1 and 4-2 of FIGS. 1 and 4-1, 4-2 and 4-3 of FIG. 3, ie all sensors are addressed wherein the synchronization command K1 each contains a parameter for determining the transmitting distance sensor and, and all distance sensors receive, whereupon they output measurement signals S1 and S4 or S2 and S3 to the control device 5. According to the invention, it is also possible to carry out measurements in different levels and measurements over different levels.

Claims

claims

An environment monitoring system (3) for a vehicle (1), the environment monitoring system (3) comprising:

at least two distance sensors (4-1, 4-2, 4-3) for distance detection by transit time measurement of detection signals (9-1, 9-2), wherein the distance sensors (4-1, 4-2, 4-3) each as Transmitter unit and receiver unit are designed for the detection signal (9-1, 9-2, 11-1, 1-2) and output detection signals (9-1, 9-2) in each case in a direct operating mode receive detection signals outputted thereto and output therefrom active measurement signals (S1, S2), and

a control device (5) which receives the measurement signals (S1, S2, S3, S4) of the distance sensors (4-1, 4-2, 4-3) and determines an object distance (s) of detected objects (10),

characterized in that

at least one distance sensor (4-1, 4-2, 4-3) is additionally operable in an indirect operating mode for detecting a signal output from another distance sensor (4-2, 4-3, 4-1) and from the object (10 ) reflected detection signal (11-2, 11-1) and for generating an indirect measurement signal (S3, S4).

Environment monitoring system (3) according to claim 1, characterized in that it is designed as a rear space monitoring system (3) of the vehicle (1) and at the rear (2) or a rear portion of the vehicle (1) is arranged to determine an object distance (s) of a in a rear space (7) behind the vehicle (1) located object (10) to the rear space monitoring system (3) or to the rear (2) of the vehicle (1).

The environmental monitoring system according to claim 1 or 2, characterized in that the detection signals are ultrasonic waves (9-1, 9-2) or radar waves or light rays transmitted from the distance sensors (4-1, 4-2) to a radiation angle region (Fig. 8-1, 8-2) can be output.

4. environmental monitoring system (3) according to claim 3, characterized in that the Abstrahlwinkelbereiche (8-1, 8-2) of the distance sensors (4-1, 4-2) are directed backwards and towards each other, so that they themselves in the rear space (7) behind the vehicle (1) at least largely overlap.

5. environmental monitoring system (3) according to claim 3 or 4, characterized in that the Abstrahlwinkelbereiche (8-1, 8-2) of the distance sensors (4-1, 4-2) lie substantially in a horizontal plane and an angular range greater than 45 degrees, preferably at least 60 degrees in the plane capture.

6. Environment monitoring system according to one of the preceding claims, characterized in that each of the distance sensors (4-1, 4-2, 4-3) are each operable in the following operating modes:

the direct mode of operation in which the distance sensor (4-1, 4-2, 4-3) emits a detection signal (9-1, 9-2) and detects the detection signal (11-1, 11-2) reflected by an object (10) 2) detected to determine a distance (L1, L2) as half the distance traveled in the detection time between transmission time and reception time distance, and

the indirect mode of operation in which the distance sensor (4-2, 4-1) without receiving passively receives the detected signal (11-1) emitted from another distance sensor (4-1) and reflected on an object (10) for detection a total distance (L1 + L2) in an indirect measurement as the sum of the distances (L1, L2) of both level sensors (4-2, 4-1) of the object (10),

wherein in the indirect mode of operation, the transmitting and receiving passive distance sensors (4-1, 4-2, 4-3) are synchronized to equalize the transmission time and reception time, and by the controller (5) subtract a distance obtained in a direct measurement (L1) of a determined in an indirect measurement total distance (L1 + L2), the further distance (L2) can be determined.

7. environment monitoring system according to claim 6, characterized in that a combined operating mode is provided, in which a first distance sensor (4-1) sends and receives in the direct mode of operation and at least a second distance sensor (4-2) in the indirect Operation mode without transmitting passive receives reflections (1 1 -1) of the first distance sensor (4-1) emitted detection signal (9-1).

8. environment monitoring system according to claim 7, characterized in that the combined operating mode is alternately executable such that alternately each distance sensor (4-1, 4-2) sends and receives and the other distance sensors (4-2, 4-1) at the same time receiving only passively.

9. environment monitoring system according to one of the preceding claims, characterized in that one or more of the following further operating modes are feasible:

Radius estimation, if only a single distance sensor (4-1, 4-2) receives a reflected detection signal (1-1, 11-2) in a direct measurement,

- triangulation by direct measurements, in particular in the absence of indirect measurements, by identifying the individual direct measurements Stands (L1, L2) of the distance sensors (4-1, 4-2) to an object (10) using a known sensor distance (d),

Back-up operating mode, in which several, preferably all distance sensors (4-1, 4-2, 4-3) transmit and receive simultaneously, to increase the radiated overall signal power and to estimate the object distance (s) of an object ( 10) from the back room monitoring system (3),

- In the case of only indirect measurements, the determination of the object distance (s) on an ellipse, which forms the set of all points with the same sum of the distances to the distance sensors (4-1, 4-2).

10. Environment monitoring system according to one of the preceding claims, characterized in that the control device (5) for outputting synchronization signals (K1) to all distance sensors (4-1, 4-2, 4-3) for synchronization of the distance sensors (4). 1, 4-2, 4-3) is provided.

11. environment monitoring system according to claim 10 and claim 8 or 9, characterized in that the control device (5) with the distance sensors (4-1, 4-2, 4-3) via a bus, z. B. LIN bus (6), connected and outputs synchronization signals (K1) for the combined operating mode,

wherein the synchronization signals (K1) are addressed to all distance sensors (4-1, 4-2, 4-3) and contain as parameters the indication of the distance sensor (4-1) transmitting in the direct operating mode.

12. environment monitoring system according to any one of the preceding claims, characterized in that exactly two distance sensors (4-1, 4- 2) are provided, which are mounted on the left and the right side rear portion of the vehicle.

13. environment monitoring system according to one of claims 1 to 11, characterized in that three distance sensors (4-1, 4-2, 4-3) are provided, of which a first distance sensor (4-1) on the left side rear area, and a second distance sensor (4-2) is mounted on the right side rear portion and a third distance sensor (4-3) is mounted in the center rear portion of the vehicle.

14. Environment monitoring system according to one of the preceding claims, characterized in that in each case two distance sensors (4-1, 4-2) are provided in a plurality of superimposed planes.

15. A method for determining an object distance (s) of an object (10), in particular using an environment monitoring system (3) according to one of the preceding claims,

in the at least two distance sensors (4-1, 4-2, 4-3)

in direct measurements, output respective detection signals (9-1, 9-2) and receive reflected portions (11-1, 11-2) of the detection signals output by them, and

receive detection signals (11-2, 11-1) reflected in indirect measurements and output from another distance sensor (4-2, 4-3, 4-1) and reflected by the object (10),

wherein the object distance (s) is determined on the basis of at least one indirect measurement.