POSITION SENSOR FOR LOCALLY RESOLVED DETECTION OF OBJECTS IN A SURVEILLANCE AREA

Description

[0001] The present invention relates to a position sensor for the spatially resolved detection of objects in a surveillance area, which comprises a measuring device for determining respective position signals for detected objects located in the surveillance area, and an RFID reader which is configured to transmit RFID control commands into the surveillance area by generating modulated RFID transmission signals and to receive RFID response signals generated by an RFID transponder arranged on an object in response to received RFID control commands.

[0002] Autonomous or semi-autonomous vehicles are increasingly being used in a variety of technical fields. These vehicles can be land vehicles, aircraft, or watercraft. They can operate in an open system, such as a public road or air transport network. Another area of ​​application is closed systems, such as logistics systems, such as warehouses or storage areas, which often use a large number of industrial trucks such as forklifts or transport vehicles to transport, store, and retrieve goods. Monitoring of traffic areas is necessary, particularly for control and collision avoidance. Monitoring often includes not only vehicles or other movable objects, but also people.Stationary objects such as stationary vehicles or cargo must also be included in the monitoring.

[0003] For this purpose, it is necessary to determine the position of any objects present in the surveillance area. This can be done using suitable measuring devices that can determine the position of a detected object within the surveillance area based on various physical principles. In the context of this disclosure, the term "object" therefore refers to all conceivable objects, vehicles, persons, animals, or the like whose positions can be detected by a measuring device.

[0004] For example, a radar device can be used as a measuring device to determine position signals of a detected object. Radio waves are emitted into the surveillance area and waves reflected from any object present there are detected. To enable localization of a detected object, the determined position signal should include at least one distance coordinate (r or z) and preferably also at least one solid angle coordinate (φ and / or θ) or a Cartesian coordinate (x and / or y). While primary radar can localize a detected object, it cannot identify it. To compensate for this disadvantage, so-called secondary radars are used, particularly in aviation.So-called cooperative targets are equipped with transponders that, upon receiving a corresponding transmission signal from the secondary radar system, actively respond with a response signal, which may, for example, include an identification code. However, such transponders suitable for secondary radar systems are very complex and, in particular, require their own power supply. For additional detection of objects without a transponder, a primary radar is also required.

[0005] Another option for locating targets equipped with transponders is so-called UWB localization. This uses signals from extremely wide frequency ranges, where UWB stands for "ultra-wideband." However, even with this technology, locating targets without transponders is not possible.

[0006] One option for cost-effective object identification is the use of RFID systems. An RFID system (radio frequency identification) is a transmitter-receiver system for the automatic, contactless identification and localization of objects using radio waves. An RFID system consists of an RFID transponder located on or in the object to be identified and containing an identifying code, as well as an RFID reader for reading this identifier. The RFID reader transmits modulated RFID signals into the monitored area. When an RFID transponder present in the monitored area receives such an RFID signal, it transmits an RFID response signal, which can in turn be received by the RFID reader. This RFID response signal includes the identifier stored in the RFID transponder and, if applicable, other signals or information.The RFID transponder contains a microchip. In passive RFID transponders or RFID tags, its power is supplied via the high-frequency energy contained in the high-frequency alternating electromagnetic field generated by the RFID reader and picked up by an antenna of the RFID transponder. Active RFID transponders have a separate power supply, located either within the RFID transponder or externally. The microchip activated in the RFID transponder decodes the RFID control commands sent by the RFID reader and encodes and modulates the RFID response signals into the radiated electromagnetic field by field attenuation in a contactless short circuit or by antiphase reflection of the field emitted by the RFID reader. The RFID transponder therefore generally does not generate a field itself, but rather influences the electromagnetic transmission field of the RFID reader.

[0007] WO 2020 / 053650 A1 discloses a method for improving a vehicle navigation system, in which one or more RFID transponders are arranged on a respective object to be detected, for example, on a road user or a vehicle. In addition to its identifier, the RFID transponder can transmit further information, for example, about its position, speed, or direction of movement. However, to determine the position, a corresponding system, such as a GPS receiver, must be arranged on the object in addition to the RFID transponder. This, however, increases the complexity of the system and thus also the costs. A power supply is also necessary.

[0008] DE 10 2020 206 882 A1 discloses a combination of a radar or lidar system and an RFID system. Linking position signals for objects determined by the measuring device—in this case, a radar (radio detection and ranging) or lidar (light detection and ranging)—to a specific RFID transponder is not possible. In one embodiment, the number of objects determined by radar and / or lidar is compared with the number of objects detected by RFID; if there is no match, emergency braking or the like is performed. Therefore, it is only possible to determine whether all objects marked with RFID transponders within the reading range of the RFID reader were also detected by the environmental sensor. According to a further embodiment, the use of an RFID reader is described, which can additionally provide directional data.

[0009] EP 2 927 838 A1 discloses a device for identifying and locating objects, comprising a laser scanner and an RFID reader. A control and evaluation unit of the device receives from the RFID reader not only an RFID identifier but also an identifier of the RFID signal, which includes, among other things, its phase or propagation time, as well as object positions detected by the laser scanner. This input data is used in a localization device to determine transponder positions. The object positions and the transponder positions are used in an assignment device to assign objects and transponders to one another according to prescribed optimization criteria.

[0010] In the publication by Miesen, R., Kirsch, F., and Vossiek, M.: "Holographic Localization of Passive UHF RFID Transponders." International Conference on RFID, 2011, pp. 32-37. - ISBN 978-1-4244-9606-8, a method for the holographic localization of passive UHF RFID transponders is presented. It demonstrates how people or devices equipped with an RFID reader, moving along a trajectory, can be enabled to reliably localize tagged objects. The localization method is based on phase values ​​sampled by an RFID reader from a synthetic aperture. The calculated holographic image is a spatial probability density function that reveals the actual position of the RFID tag.

[0011] It is the object of the present invention to provide a position sensor which enables position determination and identification of detected objects in a cost-effective manner.

[0012] The object is achieved by a position sensor having the features of claim 1. Advantageous embodiments of the position sensor are specified in the dependent claims.

[0013] A position sensor according to the invention for the spatially resolved detection of objects in a surveillance area comprises a measuring device for determining respective position signals for detected objects located in the surveillance area, an RFID reader arranged adjacent to the measuring device, which is configured to transmit RFID control commands into the surveillance area by generating modulated RFID transmission signals and to receive RFID response signals generated by an RFID transponder arranged on an object in response to received RFID control commands, and to determine a phase shift between the RFID transmission signals and the RFID response signals, and an evaluation unit which is connected to the measuring device and the RFID reader and is configured to assign at least one respectivetemporally corresponding RFID response signal taking into account the determined phase shift of this RFID response signal.,

[0014] In this context, assigning an RFID response signal to a position signal particularly also includes determining that the position signal and an RFID response signal are to be assigned to the same object. The position signal determined by the measuring device comprises at least one distance coordinate and preferably also at least one solid angle coordinate or at least one further Cartesian coordinate.

[0015] The invention is based on the inventors' discovery that, in an RFID system, a determined phase shift between the RFID transmission signals and the RFID response signals can be used to unambiguously assign temporally corresponding RFID response signals to the position signals determined, for example, by radar by taking this phase position into account, even if the solid angle position of the corresponding RFID transponder is unknown. The aforementioned temporal correspondence between a position signal determined by the measuring device and an RFID response signal is to be understood as meaning that the position signal and the RFID response signal are detected at the same time or at least within a defined short period of time.This ensures that both the position signal generated for a given object and the RFID response signal originating from that object are generated at approximately the same position, ensuring that any movement of the object in the time period between the generation of the two signals does not affect the detection result as much as possible. Accordingly, this short time period is preferably adapted to the expected maximum movement speed of the objects to be detected.

[0016] The present invention can also compensate for a disadvantage of conventional measuring devices such as radar devices, which is the limited resolution in determining the distance coordinate. This can result in, for example, two objects that partially obscure each other when viewed in the direction of the radar device and are only a short radial distance apart, possibly not being separated from each other, so that only a single object detection signal is generated for both objects.Since, in the position sensor according to the invention, respective RFID response signals are also available for both objects, for which distance information is also known based on the determined phase position of these signals, the joint position signal determined by the measuring device can be assigned to both the front and rear objects. The initially inaccurately determined distance coordinate can be refined based on the phase shifts for each object. This significantly improves the detection accuracy of the position sensor.

[0017] According to a preferred embodiment, the measuring device comprises a radar device, a lidar device, and / or a distance-measuring camera. With radar and lidar devices, the position of a detected object is determined in a known manner by emitting electromagnetic waves, i.e., radar waves or light waves, into the monitoring area, receiving waves that have been passively remitted by the object, and determining the position of the object based on the received waves. According to this definition, a lidar device can also be synonymous with a 2D or 3D scanning device.With a distance-measuring camera, distance measurement is performed in the usual way using stereoscopy or a so-called TOF (time-of-flight) image sensor, which determines the time of flight of light signals emitted by an illumination unit into the surveillance area and remitted by the object to be detected toward the TOF image sensor. In principle, the measuring device can also be a combination of different distance-measuring devices.

[0018] According to a further preferred embodiment, the evaluation unit is configured to generate an object detection signal for a respective object, wherein the object detection signal contains a position signal determined for this object and an identification code, which is optionally encoded in the associated RFID response signal. The object signal can be transmitted to a higher-level control unit, which, for example, transmits navigation signals to the detected objects or other devices of a higher-level system based on the object detection signals. Thus, the position sensor is configured to additionally identify a detected object based on an identification code, which may be encoded in an RFID response signal.

[0019] According to a further preferred embodiment, the evaluation device is configured to determine the phase shift between the RFID transmission signals and the RFID response signals using a demodulation method, in particular an I&Q demodulation method. The term "I&Q demodulation method" is derived from the English term "in-phase and quadrature." Here, the received signal is split into two paths. One path of demodulation is performed with the original phase position (English: "in-phase") and produces the so-called I data, and the other path is performed with a reference frequency of the RFID transmission signal that is phase-shifted by 90° and produces the Q data. The magnitude of the individual components I and Q can be calculated using an angle function, where: I = A ⋅ cos Φ Q = A ⋅ sin Φ

[0020] Based on this equation, the phase angle Φ can be calculated back, where: Φ = arctan Q I .

[0021] A description of carrier phase measurement in RFID systems and other wireless communication systems is disclosed in the publication R. Miesen, A. Parr, J. Schleu and M. Vossiek, "360° carrier phase measurement for UHF RFID local positioning," 2013 IEEE International Conference on RFID-Technologies and Applications (RFID-TA), Johor Bahru, Malaysia, 2013, pp. 1-6, DOI: 10.1109 / RFID-TA.2013.6694499.

[0022] According to the invention, the evaluation unit is configured to determine an associated division remainder for respective divisions of the distance value by different integer multiples of the wavelength λ by means of an optimization method, starting from a distance value which corresponds to a distance component of the position signal determined by the measuring device, taking into account the wavelength and the respective phase shift of one or more RFID response signals, and to assign a respective RFID response signal to this position signal if, for one of the respective divisions, the difference between the phase shift of this RFID response signal and the division remainder of this division is minimal.

[0023] Within the scope of this optimization process, for example, the distance value, determined using radar, is divided by λ, 2λ, 3λ, etc., and for each of these divisions, the difference between the previously determined phase shift of the RFID response signal under consideration and the respective division remainder is determined. If the "minimal difference" criterion is met for one of these divisions, the corresponding RFID response signal is assigned to the position signal whose distance value was examined. The aforementioned criterion, according to which the difference should be minimal, is to be understood as meaning that the reference value must be equal to zero or less than a specified threshold to meet this criterion. In principle, for each position signal, multiple RFID response signals can be checked for their respective phase position to match the distance value.In this way, as already mentioned above, two or more RFID response signals can be assigned to a position signal determined, for example, by radar. This allows the RFID phase position to be used to separate even objects whose distance is smaller than the resolution of the measuring device.

[0024] In this context, it has proven advantageous if the determination of position signals, the determination of phase shifts of RFID response signals, and the determination of the division remainder are carried out cyclically, wherein the evaluation unit is configured to assign the correspondingly varying RFID response signal to a position signal that does not vary or varies within a predetermined position range during a predetermined number of cycles only if the respective difference is minimal during the predetermined number of cycles. In other words, a moving or stationary object is observed over several cycles, with the assignment only taking place if the assignment criterion is met in each or at least in a majority of these cycles.

[0025] According to a further preferred embodiment, the RFID reader has a transmitting circuit for generating and transmitting the RFID transmit signals and a receiving circuit for receiving the RFID response signals. The transmitting circuit and the receiving circuit are configured such that, in addition to the received RFID response signals, at least a portion of the RFID transmit signals are received directly by the receiving circuit as RFID leak signals. The evaluation unit is configured to determine the phase shift between the RFID leak signals received by the receiving circuit and the RFID response signals. The direct reception of the leak signals by the receiving circuit means that this occurs through crosstalk and, in particular, without any influence from the RFID transponder.The transmitting circuit and the receiving circuit each have at least one antenna, with the RFID leakage signals emitted by the transmitting antenna being directly detected by the receiving antenna. If multiple transmitting or receiving antennas are provided, distance information for the RFID received signals can also be determined in addition to the phase position. This additional distance information can also be taken into account when assigning RFID response signals to the position signals.

[0026] Further advantages of the position sensor according to the invention and advantageous embodiments will become apparent from the following description of the drawings. The drawings illustrate exemplary embodiments of the invention. The drawings, the description, and the claims contain numerous features in combination. Those skilled in the art will expediently consider these features individually and combine them into useful further combinations.

[0027] They show: Fig. 1 is a schematic representation of a position sensor according to an embodiment, and Fig. 2 is a diagram illustrating a determined phase shift between RFID transmission signals and RFID response signals.

[0028] Fig. 1 shows a position sensor 10 according to an embodiment, which is configured for the spatially resolved detection of objects in a monitoring area 12. In Fig. 1Two objects 14.1, 14.2 are shown as examples at different distances from the position sensor 10. The position sensor 10 comprises a measuring device 30 for determining respective position signals for detected objects 14.1, 14.2 located in the monitoring area 12. In the exemplary embodiment, the measuring device is designed as a radar device 30 and can comprise a pivotable transmitting and receiving antenna for scanning the monitoring area 12 or, in addition to a transmitting antenna, an array of receiving antennas for the location-triggered reception of the transmitted signals reflected from an object 14.1, 14.2. Fig. 1 the transmitting and receiving antennas are symbolized by a single antenna 32.

[0029] According to modifications, the measuring device can also be designed as a lidar device or as a distance-measuring camera, in which the distance measurement is carried out by means of stereoscopy or by using a time-of-flight sensor.

[0030] The position sensor 10 further comprises an RFID reader 20 arranged adjacent to the radar device 30, which is configured to transmit RFID control commands into the surveillance area by generating modulated RFID transmission signals and to receive RFID response signals. The RFID reader 20 is advantageously arranged at only a small lateral distance from the radar device 30 in order to minimize any parallax errors.

[0031] Respective RFID transponders 24.1, 24.2 are arranged on or integrated into the objects 14.1, 14.2. The RFID transponders 24.1, 24.2 can be designed as active or passive RFID transponders. An RFID transponder 24.1, 24.2 responds to a received RFID control command by emitting an RFID response signal, which, in addition to an identifier or an identification code that enables unique identification of the respective RFID transponder 24.1, 24.2, can contain further information. The RFID response signals are emitted in a known manner by modulating the radiated electromagnetic transmission field of the RFID reader 20, whereby both field attenuation and antiphase reflection of the field emitted by the RFID reader 20 can occur.The RFID reader 20 is connected to respective antennas and / or antenna arrays for generating the modulated RFID transmission signals and for receiving the RFID response signals, which are shown in . Fig. 1 symbolically represented by antenna 22.

[0032] There is a fixed phase relationship between the RFID transmission signals and the RFID response signals, which depends on a distance r of the respective object 14.1, 14.2 or the RFID transponder 24.1, 24.2 arranged on this object 14.1, 14.2 from the position sensor 10 or the RFID reader 20.

[0033] A phase shift φ between the RFID transmission signals and the RFID response signals can be determined, for example, by a demodulation method, in particular by an I&Q demodulation method.

[0034] In the lower part of Fig. 1Different signals are symbolically drawn as points, with their position on the r-axis depending on the object distance. The radar device 30 has a limited distance resolution A which in Fig. 1 symbolized by a corresponding double arrow. Objects located close to each other or one behind the other, such as objects 14.1, 14.2 in Fig. 1 , can no longer be resolved by the radar device 30. As a result, no separate position signals are generated for the objects 14.1, 14.2, but rather a common position signal 34.

[0035] With the position transmitter 10 according to the invention, it is possible, on the basis of the RFID response signals transmitted by the RFID transponders 24.1, 24.2, to detect and identify the two objects 14.1, 14.2 separately, which would not be possible with the radar device 30 alone.

[0036] This can be done by means of an evaluation unit 40 of the position sensor 10, which is connected to the RFID reader 20 and the radar device 30. The RFID reader 20, the radar device 30 and the evaluation unit 40, including the antennas 22, 32, can be integrated in a common housing, which is indicated by the dashed box in Fig. 1 The evaluation unit 40 is configured to generate corresponding position signals 26.1, 26.2 (in the lower part of Fig. 1 shown).

[0037] Depending on the selected wavelength of the RFID transmission signals, it is only possible to determine the distance of an object 14.1, 14.2 from the position sensor 10 (or its RFID reader 20) based on the phase shift alone to a limited extent, since the unambiguous range is limited to a maximum of one wavelength. However, by taking into account the position signal 34 determined by the radar device 30, it is possible to estimate the corresponding distance of an RFID response signal and assign it to a specific object 14.1, 14.2 in the form of a corrected position signal 26.1, 26.2.

[0038] This relationship is explained below with reference to Fig. 2 explained in more detail. In Fig. 2Different waveforms are symbolically represented for an RFID reader 20 and a single object 14 with an RFID transponder 24 arranged thereon or integrated therein. Depending on the distance r of the object 14 from the RFID reader 20, an RFID response signal has a certain propagation delay compared to the temporally corresponding RFID transmission signal, wherein this propagation delay corresponds to the distance r a certain number n of complete periods and a fraction of a period, taking into account the propagation speed of the radar waves. The fraction of a period results from the determined phase shift φ according to λ ⋅ φ 2 π . The following relationship applies to the distance r: r = λ ⋅ φ 2 π + n ⋅ λ .

[0039] Using an optimization procedure, the distance value r, which corresponds to the distance component of the position signal 34 determined by the radar device 30, taking into account the wavelength λ and the determined phase shift φ the RFID response signals underlying the corrected position signals 26.1, 26.2 for respective divisions of the distance value r by different integer multiples of the wavelength λ associated division remainders are determined. A respective RFID response signal can be assigned to the position signal 34 determined by the radar device 30 if, for a respective division, the difference between the phase shift of this RFID response signal and the division remainder of this division is minimal.

[0040] In other words, the distance value r can be divided by λ, 2λ, 3λ ... within the optimization process, for example, and the difference between the phase shift φof the RFID response signal to be considered and the respective division remainder for each of these divisions. If the difference for one of these divisions becomes minimal, the position signal 34, whose distance value r was investigated, the respective RFID response signal is assigned. This optimization procedure can be mathematically described by the function min λ φ 2 π − modulo r , n i ⋅ λ where the operator no represents the variation over the integer multiples of λ.

[0041] Referring to the schematic embodiment of Fig. 1 This means that for both objects 14.1, 14.2 the division remainder is minimal for the number of periods n = 4 shown there.

[0042] It is understood that the position signals and RFID response signals under consideration must correspond in time, i.e. they should preferably be generated or recorded at the same time or with a very small time difference, so that interim movements of an object do not falsify the assignment result.

[0043] Advantageously, both the position signals and the RFID response signals are determined over several measuring cycles and a corresponding assignment is only made if no or only a slight deviation of the determined distance values ​​was detected over the several measuring cycles.

[0044] An advantage of the position sensor 10 according to the invention is that, in comparison to a position detection system based exclusively on RFID technology, overranges often occurring due to radio technology can be easily and robustly detected and suppressed with the aid of the position determination carried out by the measuring device 30, in particular by means of radar measurement.

[0045] A preferred application area of ​​the position sensor 10 according to the invention is found, for example, in enclosed areas, where at least some of the potentially dangerous objects present there are equipped with RFID transponders, thus enabling identification and tracking. By combining distance measurement using radar, lidar, or a camera with the determination of the phase shift of RFID response signals, resolution problems in complex scenarios can be resolved. As a further advantage over exclusively RFID-based systems, the setup of a surveillance system can be simplified due to the suppression of over-range. List of reference symbols

[0046] 10Position sensor 12Monitoring area 14, 14.1, 14.2Object 20RFID reader 22RFID reader antenna 24, 24.1, 24.2RFID transponder 26.1, 26.2Corrected position signal 30Measuring device, radar device 32Radar device antenna 34Position signal 40Evaluation unit AResolution of the radar device rDistance

Claims

1. A position sensor (10) for the spatially resolved detection of objects (14, 14.1, 14.2) in a monitored zone (12), said position sensor (10) comprising a measurement device (30) for determining respective position signals for detected objects (14, 14.1, 14.2) which are located in the monitored zone (12), an RFID reading device (20) which is arranged adjacent to the measurement device (30) and which is configured to transmit RFID control commands into the monitored zone (12) by generating modulated RFID transmission signals and to receive RFID response signals, which are generated by an RFID transponder (24, 24.1, 24.2) arranged at an object (14, 14.1, 14.2) in response to received RFID control commands, and to determine a phase shift between the RFID transmission signals and the RFID response signals, and an evaluation unit (40) which is connected to the measurement device (30) and the RFID reading device (20) and which is configured to assign at least one respective, temporally corresponding RFID response signal to a respective position signal determined by the measurement device (30), considering the determined phase shift of this RFID response signal, characterized in that the evaluation unit (40) is configured to determine, by means of an optimization method, starting from a distance value which corresponds to a distance component of the position signal determined by the measurement device (30), considering the wavelength and the respective phase shift of one or more RFID response signals, an associated division remainder for respective divisions of the distance value by different integer multiples of the wavelength and to assign a respective RFID response signal to this position signal if the difference amount between the phase shift of this RFID response signal and the division remainder of this division is minimal for one of the respective divisions.

2. A position sensor (10) according to claim 1, characterized in that the measurement device (30) comprises a radar device (30), a lidar device and / or a distance-measuring camera.

3. A position sensor (10) according to claim 1 or 2, characterized in that the evaluation unit (40) is configured to generate an object detection signal for a respective object (14, 14.1, 14.2), with a position signal determined for this object (14, 14.1, 14.2) and an identification code encoded in the associated RFID response signal being contained in the object detection signal.

4. A position sensor (10) according to any one of the preceding claims, characterized in that the evaluation unit (40) is configured to determine the phase shift between the RFID transmission signals and the RFID response signals by a demodulation method, in particular an I&Q demodulation method.

5. A position sensor (10) according to any one of the preceding claims, characterized in that the determination of position signals, the determination of phase shifts of RFID response signals and the determination of the division remainder take place cyclically, with the evaluation unit (40) being configured to assign the correspondingly varying RFID response signal to a position signal which does not vary during a predefined number of cycles, or only varies within a predefined position range, only if the respective difference amount during the predefined number of cycles is minimal.