TER BRAAK, Hans (p/a Daalseplein 101, XS Utrecht, NL-3511, NL)
| CIAIMS
1. A system for determining the position of an object, a person or the like, comprising at least a transmitter for transmitting electromagnetic waves and at least a receiver for receiving electromagnetic waves, connected to which receiver is a positioning organ for, subject to the electromagnetic waves received by the receiver, determining a position of the object or the person located between the transmitter and the receiver, while the object or the person is not carrying the transmitter and the receiver, character- ised in that the at least one transmitter and the at least one receiver form a first transmitter-receiver combination having a direct radio connection, and in that the positioning organ determines the position of the object or the person between the transmitter and the receiver on the basis of, compared with a predetermined reference level, an attenuation of electromagnetic waves as received by the receiver of the first transmitter-receiver combination.
2. A system according to claim 1, characterised in that the positioning organ determines the position of the object or the person on the basis of the attenuation of the electromagnetic waves caused by a person or object in the Fresnel-zone between the transmitter and the receiver of a transmitter-receiver combination .
3. A system according to claim 1 or 2, characterised in that the transmitter-receiver combination during use is adjusted to a transmission frequency that is selected subject to the distance between the transmitter and the receiver, thereby setting a predetermined width for the Fresnel-zone.
4. A system according to claim 1-3, characterised in that the transmitter and the receiver are effective at a frequency ranging from 850 MHz to 2.5 GHz.
5. A system according to one of the preceding claims, characterised in that the transmitter and/or the receiver of the transmitter-receiver combination is of the type transmitting or receiving omnidirectionally.
6. A system according to one of the claims 1-5 / characterised in that during the determination of a position, the transmitter and the receiver of the transmitter-receiver combination are both designed to function at minimally two frequencies that are different from each other.
7. A system according to one of the preceding claims, characterised in that there are at least two transmitter-receiver combinations, and in that the positioning organ determines the position of the object or the person on the basis of a measured attenuation of the electromagnetic waves as received by the receivers of all the transmitter- receiver combinations .
8. A transport system for persons or goods, provided with a system for determining the position of an object ac- cording to one or several of the preceding claims. |
System for determining the position of an object
The invention relates to a system for determining the position of an object, a person or the like, comprising at least a transmitter for transmitting electromagnetic waves and at least a receiver for receiving electromagnetic waves, connected to which receiver is a positioning organ for, subject to the electromagnetic waves received by the receiver, determining a position of the object or the person located between the transmitter and the receiver, while the object or the person is not carrying the transmitter and the receiver. Thus the object or the person does not form a part of the system, as the transmitter and the receiver are not physically in contact with the person or the object.
Such a system is known from the American patent application 2006/0007001. The system disclosed in the American patent application 2006/0007001 uses polarized electromagnetic waves at radio frequency level, which waves, after reflection by the object to be detected, are received by several receivers . This detection and reflection of electromagnetic waves forms the basis for the detection of the object, or the determination of the position of this object.
α drawback of the system known from the American patent application DS 2006/0007001 is the considerable complexity and the need of accurate adjustment with regard to the direction of transmitters and receivers.
It is the aim of the invention to allow such a system for determining the position of an object to be embodied more simply, while the position of the object is nonetheless determined with sufficient accuracy. The system according to the invention is therefore characterized in that the at least one transmitter and the at least one receiver form a first transmitter-receiver combination having a direct radio connection, and in that the positioning organ determines the position of the object or the person on the basis of, compared with a predetermined reference level, an attenuation of electromagnetic waves as re-
ceived by the receiver of the first transmitter-receiver combination .
An important difference between the system of the invention and the prior art system is that a direct radio connection is sustained between the transmitter and the receiver of the first transmitter-receiver combination. One of the advantages this affords is that the effectiveness of the system can be checked continuously and that if the signal of the receiver fails completely, this is a sign for checking the functionality of the system. In the system known from the American patent application US 2006/0007001, the functionality of the system for determining the position of an object is not easy to ascertain, since the absence of a signal at the receiver does not necessarily mean that the system is failing- Another advantage of the invention is that a standard omnidirectional transmitter and a standard omnidirectional receiver can be used.
Moreover, because the system known from the American patent application 2006/0007001 is based on the reflection of electromagnetic waves transmitted by the transmitter, measures have to be taken to polarize these waves in order to be able to determine a position with sufficient accuracy. In the known system, the transmitter and receiver have to be placed in such a way that they possess a common plane of polarisa- tion. In contrast, the system according to the invention can be embodied more simply, which is partly due to the fact that the wave signal does not need to be polarized.
Another important aspect of the system according to the invention is that it makes it possible to determine the position of the object by influencing the electromagnetic waves within the so-called Fresnel-zone, which zone has a width and length ratio that depends on the frequency of the waves. This aspect can be advantageously used to determine the size of the area of influence. It is further desirable- for the transmitter during use to be adjusted to a transmission frequency that is selected subject to the distance between the transmitter and the receiver, thereby setting a predetermined width for the Fresnel-zone .
It has been shown in the context of the invention that the transmitter and the receiver are suitably effective at a frequency ranging from 850 MHz to 2.5 GHz.
A further aspect of the invention relates to the embodiment of the system in which, during the determination of a position, the transmitter and the receiver are both designed to function at minimally two frequencies that are different from each other. This affords the possibility to recognize and eliminate measuring errors caused by multipath, because multipath produces different results for different frequencies .
The system according to the invention can be used for various purposes, but is especially suitable for determining whether there are any objects or persons present in predetermined spacial areas. By combining several transmitter and receiver combinations it is possible to monitor an area of practically any shape. The position of objects or persons can be determined by monitoring several adjacent areas. The reliability may be enhanced by a redundant embodiment. An example is the application in combination with a transport system for persons or goods. The system according to the invention can then be used for safety purposes, for example, for guarding a level crossing.
Hereinafter the invention will be further elucidated by way of several schematically represented drawings of exemplary embodiments, which pose no limitation with respect to the appended claims.
The drawing shows in:
- Fig. 1, an embodiment of the system for monitoring a predetermined area;
- Fig. 2, a system for determining a position, in which several transmitter-receiver combinations are employed, and
- Fig. 3, an embodiment of the system shown in Fig. 1, to which redundant transmitter-receiver combinations have been added.
With reference first to Fig . 1, a rectangular area 1 is shown, provided with transmitter-receivers A, B, C, D, E
and F along its boundaries. In this configuration, transmitter-receiver combinations are formed by the pairs A-B, B-C, C-F, F-E, E-D and D-A. Each of these transmitter-receiver combinations sustains a direct radio connection, which is characterized by the Fresnel-zones 2-7 of the just mentioned transmitter-receiver combinations.
By applying, for example, the ZigBee protocol, these transmitter-receiver combinations A-B, B-C, C-F, F-E, E-D and D-A can form a self-organizing network, wherein the attenua- tion data measured with each of these transmitter-receiver combinations concerning the radio contacts formed by these combinations, can be transmitted to a transmitter-receiver A that is linked to a position determining organ 8.
The in Fig. 1 represented configuration of the sys- tern not only allows the position of an object or person within one of the Fresnel-zones 2-7 to be determined, but the system in its entirety embodies a monitoring system for the area 1.
Fig. 2 shows a system of cooperating transmitter- receiver combinations similar to the system shown in Fig. 1. However, the system of Fig. 2 is characterized by the fact that each transmitter and/or receiver of a transmitter- receiver combination may also be part of another transmitter- receiver combination. Within the area 1 therefore, several intersecting Fresnel-zones can be distinguished, for example, the Fresnel-zone 9 belonging to the transmitter—receiver combination A-F; the Fresnel-zone 10 belonging to the transmitter-receiver combination D-E and the Fresnel-zone 11 belonging to the transmitter-receiver combination D-C. A person or object being present in the area 1 and thus influencing the electromagnetic waves between said transmitter-receiver combinations B-E, C-D and A-F, allows this system to determine a position of a person or object with greater accuracy, because it is possible to use the attenuation data from these three different radio contacts .
Fig. 3 shows a variant of the system shown in Fig. 1. The difference lies in the fact that near the transmitter- receivers A, C, F and D redundant transmitter-receivers A 1 ,
C, F' and D' are placed. The redundancy in the system thus produced with additional Fresnel-zones 4 ' , 7 ' , 12 and 13 provides the system with increased operational reliability. In the event of a failing Fresnel-zone, for example, Fresnel- zone 7 belonging to transmitter-receiver combination A-D, detection can simply be taken over by Fresnel-zone 7 ' belonging to the transmitter-receiver combination A '-D 1 .
It is worth noting that it is possible to avoid multipath effects that lead to the extinction of the signal received at a receiver by simultaneously using different frequency bands such as, for example, 868 MHz and 2.4 GHz. The second Fresnel-zone (with a phase shift in the range from 90°-270°) pertaining to the 2.4 GHz and the first Fresnel-zone (with a phase shift in the range from 0°-90°) pertaining to 868 MHz are practically equally large, so that in the event of the received signal being extinguished in, for example, the 2.4 GHz band, the signal of the 868 MHz band will not be extinguished such that it is still possible to obtain a useful measuring signal. It is further worth noting that the position determining organ 8 is preferably equipped with a so-called alpha filter with which it is possible to calculate a stabilized value of the measured attenuation value of the received radio signals . Such a filter may be adaptive through having the degree to which new attenuation values are taken into account depend on the extent to which the measured values vary. It is thus possible to filter out any variations in the measured attenuation that are of an infrequent nature and that are associated with a change in the measuring condi- tions, such as effects from the weather.
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