The invention relates to an identification system, and to a method of determining motion information by means of this system.
As has been described in [1], Klaus Finkenzeller, RFID-Handbook [RFID-Handbuch], 3rd Edition, Carl Hanser Verlag, Munich 2002, page 1, automatic identification methods (auto-ID) have in recent years found wide application in a variety of service sectors, such as in purchasing and distribution logistics, in commerce, in production plants, specifically, material flow systems (see e.g. [2], PHILIPS, TAGSYS, Texas Instruments Inc., White Paper, ITEM-LEVEL VISIBILITY IN THE PHARMACEUTICAL SUPPLY CHAIN, White Paper, July 2004).
Of particular significance among automatic identification systems are transponder systems in which a transponder is attached to the objects to be identified, and interrogated by a reading device using magnetic or electromagnetic fields. Since these systems normally employ radio waves, they are also designated as RFID systems. With these appropriately designed RFID systems, it is also possible to store data issued by the reading device in the transponder.
The reading device typically includes a high-frequency module (transmitter and receiver), a control unit, a coupling element, and normally an interface which enables data to be exchanged with a computer, for example, a central computer of a traffic management system or a decentralized personal computer.
The transponder, functioning as the carrier of the identification data and optionally additional data, is normally composed of a microchip and a coupling element or an antenna. For example, the identification data for a container, as well as data relating to the freight stored in the container, and optionally data relating to the state of this freight, may be stored in a transponder attached to the container (see, e.g. [3], EP 1 408 207 A1).
Outside the response range of the reading device, the transponder, which as a rule does not have its own power supply, is completely passive in function. The transponder becomes active only within the response range of the reading device. The power required to operate the transponder, as well as the clock rate and the data, are transmitted wirelessly to the transponder.
As is described in [1], pages 22-23, the most important differentiation criteria for RFID systems involve the operating frequency of the reading device, or of the reading and writing device (transceiver), the physical coupling method, and the range.
RFID systems having very short ranges of typically 1 cm, called “close coupling systems,” operate using electrical and magnetic fields and frequencies of normally up to 30 MHz.
RFID systems with write/read ranges of up to around 1 m are classified by the designation “remote coupling systems” which employ almost exclusively an inductive (magnetic) coupling of reading device and transponder, and frequencies typically in the ranges 135 kHz, 13.56 MHz, or 27.125 MHz.
RFID systems with ranges above 1 m and operating frequencies in the UHF and microwave range are designated in [1] as “long-range systems.”
The differing properties of the individual systems result in different areas of application. At 100 kHz, the specific absorption rate (attenuation) for water or nonconducting substances is lower by a factor of 100,000 than at 1 GHz. Low-frequency systems are thus utilized primarily due to their better penetration of objects. In transportation-engineering systems, this is a significant factor since transponder housings can often experience metal-containing contaminations or coatings from snow. On the other hand, in the case of electromagnetic systems, electromagnetic interference must be taken into account. With respect to the identification of vehicles, the required range of the RFID system must be designed such that the duration of stay within the response range is sufficient for transmission of the supplied data at the maximum speed of the vehicle.
Specifically in the case of railroad engineering, but also in connection with wider areas of transportation engineering and safety engineering, it is desirable to be able to determine not only identification data but also data relating to the movement of the carrier of a transponder, i.e., of the railroad car.
EP 1 017 577 B1, reference [4], describes a railway vehicle detector in which the direction and speed of a wheel on the railroad car is measured by two wheel-sensor-elements which are spaced relative to each other in the direction of travel and connected to one rail. Based on the field change induced by the wheel, signals are generated sequentially in the inductive wheel-sensor-elements, the evaluation of these signals supplying the desired information.
Determination of travel information by an RFID system can be effected analogously based on two receiving stations, each having one antenna, or one receiving station with two antennas. The sequential coupling of a transponder provided on a railroad car to both antennas in turn produces signals by which the required travel information can be determined. However, the use of two antennas, optionally two receiving stations, has the result that the manufacture and installation of this RFID system is relatively complex/expensive.
U.S. Pat. No. 6,046,683[5] discloses an RFID system classifiable as a “long-range system” by which travel information can be determined. In this system, an interrogator or interrogation unit sends signals to at least one transponder or ID tag which reflects a modulated response signal (backscatter signal). The interrogator then determines the frequency shift of the received signal, produced by the Doppler effect, and the corresponding speed relative to the transponder. Based on multiple measurements, the position of the transponder as well as the direction of motion of the interrogator can be determined. The implementation of this system also entails considerable complexity/expense and is feasible only on a limited basis for certain applications.