WO2018077879A1

WO2018077879A1 - Reading device for an rfid system, retrofit module for an rfid reading device, and method for reading out an rfid transponder

Info

Publication number: WO2018077879A1
Application number: PCT/EP2017/077166
Authority: WO
Inventors: Stefan Suckrow
Original assignee: Wilhelm Sihn Jr. Gmbh & Co. Kg
Priority date: 2016-10-31
Filing date: 2017-10-24
Publication date: 2018-05-03
Also published as: DE102016120770A1

Abstract

The invention relates to a reading device for an RFID system, in conjunction with a plurality of antennas (3, 4), to which the reading device (2) transmits a sending signal, which the antennas (3, 4) emit as a radio signal. According to the invention, a phase element is provided, which, in the event of a sending signal passing through the phase element, causes a phase rotation by a half period of a carrier frequency at which signals are sent from and to a transponder of the RFID system, and a switchover device (5) is provided, which, in a first switching state, conducts a sending signal produced by the reading device (2) through the phase element to a first antenna (3) and past the phase element to a second antenna (4) such that the first antenna (3) and the second antenna (4) emit the radio signal in phase opposition and, in a second switching state, bypasses or deactivates the phase element such that a sending signal produced by the reading device (2) is conducted uninfluenced to the first antenna (3) and to the second antenna (4) and the first antenna (3) and the second antenna (4) emit the radio signal in the same phase. The invention further relates to a corresponding retrofit module for an RFID system and to a method for reading out RFID transponders.

Description

Reader for an RFID system, retrofit module for an RFID reader and method for reading out an RFID transponder

description

The invention relates to a reader for an RFID system, a retrofit module for an RFID reader and a method for reading an RFID transponder. A reader with the features specified in the preamble of claim 1 is known from DE 10 2006 053 987 A1.

RFID (Radio Frequency Identification) is used for contactless identification of objects. An RFID system consists of a reading device (reader), one or more antenna modules and a readable by the reader disk, which is designed as a transponder. A typical RFID transponder has a coupling antenna, an analog circuit for receiving and transmitting high-frequency signals, a digital circuit and a memory, wherein the analog circuit, the digital circuit and the memory are located on an electronic microchip. Excited by the reader, an antenna generates an electromagnetic field which receives the coupling antenna of the transponder. This creates an induction current in the coupling antenna, which activates the microchip of the transponder. In a passive transponder, a capacitor is charged by the induced current, which supplies the microchip with power. With an active transponder, the microchip is activated by the current induced in the coupling antenna and then supplied with power by a built-in battery.

The range of an RFID system depends on the frequency with which it is operated. Depending on the application and supplier, RFID systems are operated on frequencies between 125 KHz and 5.8 GHz. The range increases with the frequency. In the range of very high frequencies of more than 100 MHz up to the gigahertz range, passive transponders achieve ranges of a few meters to a few tens of meters and, with the use of active transponders, even more. Such long-range systems are referred to as long-range RFID systems. Above all, the present invention is concerned.

The reader of a long-range RFID system contains a high-frequency module with which both high-frequency signals are transmitted and signals reflected at the transponder are received. The energy exchange or signal exchange between the transponder and the reading device takes place via the coupling antenna of the transponder and via a transmitting / receiving antenna connected to the reading device.

A stored in the microchip of the transponder code controls the energy exchange between the coupling antenna and the microchip of the transponder by load modulation. This means that the impedance of the microchip alternates between two electrical states, wherein in one state the energy exchange between the coupling antenna and the microchip is maximized - then as much energy as possible is absorbed in the transponder from the field of the antenna of the reader - whereas in the other state the energy exchange between the coupling antenna and the microchip of the transponder is minimized - then the transponder as little energy from the field of the antenna of the reading instead, the radiation impinging on the transponder is reflected on it. The signal reflected by the transponder is received and evaluated by the reader. The transmission of the information stored digitally in the microchip of the transponder is effected by modulation of the reflected signal resulting from the fact that the code stored in the microchip changes the impedance of the microchip according to a timing scheme determined by the stored code between the states absorption and reflection leaves. The reader reads the information based on the transmitted clock signal with the reflected signal.

RFID systems are used in production for the control and monitoring of production processes, in logistics for the control and monitoring of goods flows, and in warehousing for controlling the inventory and its changes. In the identification of goods that are not isolated, but in the crowd, z. B. be delivered on pallets, it is difficult to capture all objects. Experiments have shown that the detection rate varies greatly when identifying goods on pallets. Under very unfavorable circumstances, it can even happen that no recording is possible at all. A lower coverage rate may be acceptable if it is only a matter of determining the nature of a product on a pallet, not its quantity. Basically, however, the goal is to fully capture items that are delivered in the pulk. You have to deal with the following difficulties:

The energy transfer between the reader and the transponder follows the laws of electromagnetic wave propagation. The radiation and the reception take place via antennas. The information to be received by the reading device lies in the signal reflected on the transponder.

The signal reflected at the transponder is amplitude-modulated due to the clocked load modulation. The modulation frequency is typically 200 kHz. The load modulation produces spectral signal components that are located in the sidebands form next to the frequency band of the transmission signal of the reader. The sideband contains the information which the reader is to receive and read. Naturally, the power transmitted in the sideband is significantly smaller than that of the original unmodulated transmit signal.

Due to the propagation conditions, the signal strength in the vicinity of an antenna decreases very sharply with increasing distance. This applies to the signal sent by the reader as well as to the signal reflected by the transponder. The signal returning to the reader as a result of reflection at the transponder has covered twice the distance between the reader and the transponder. The reader therefore receives only a small portion of the originally transmitted energy with the signal coming back from the transponder. This is called field damping. The coupling antenna on a transponder can only be very small in relation to the wavelength of the useful signal to be transmitted. Accordingly, their effective area is also small, and therefore the part of the energy which the coupling antenna can extract and reflect from the field of the transmitting / receiving antenna is small. This is called the reflection attenuation.

In addition, there is a weakening of the signal received by the reader again in that the transponder is not in the direction of the maximum of the radiation pattern. To counter this, it is known to use a reader in conjunction with multiple antennas, the z. B. are arranged one above the other, which increases the probability that one of the antennas is at a height in which the transponder is moved past the reader. The reader is often arranged stationary. It is known to successively connect the superimposed antennas with the RF transmitter and receiver module of the reader, so that successively each of the antennas has the chance to respond to the transponder. The disadvantages of the various damping contributions, however, also have an effect in this case.

Depending on how the environment of the RFI D reading device is designed, not only is there a direct overlap between the reading device and the transponder. transmission, but also to transmission paths, where unwanted reflections of obstacles that are in the area. The unwanted reflections are superimposed on the directly transmitted useful signal and can mask or weaken it. Disturbances caused by such overlays are termed interference interference.

If the detection rate of an RFID system is insufficient, an increase in the transmission power of the reader usually does not succeed, because the proportion of desired reflections and crosstalk between adjacent detection systems, eg. For example, at cash desks of shopping or at gates, then also increase. In addition, certain statutory transmission power limits may not be exceeded. RFID systems therefore generally work at their sensitivity limit. The present invention has for its object to show a way, as under the described adversities in the use of RFID systems whose detection rate can be increased.

This object is achieved by a reading device with the features specified in claim 1 and by a retrofit module for a reading device according to claim 8. This object is also achieved by a method according to claim 9. Advantageous developments of the invention are the subject of dependent claims. The present invention utilizes two or more antennas connected to a reader to generate radio signals having different radiation patterns. In this way, the influence of interference interference during reading RFI D transponders can be reduced since any interference due to reflections and the like depends on the respective radiation pattern. In the radio signals are generated with different emission characteristics, the chance increases that in at least one case sufficiently favorable conditions for the reception of a response signal of a transponder are present. In conventional RFID systems, radio signals with different emission characteristics and radiation diagrams are generated by several antennas transmitting the radio signals one after the other. Due to the different position of the individual antennas, the radio signals then each have different emission characteristics.

The present invention makes it possible with two or more antennas to produce a greater variation of the emission states, for example radiation patterns and emission characteristics, so that correspondingly greater chances exist of reading out an RFID transponder. According to the invention, this is achieved by connecting antennas successively additively and subtractively via corresponding circuit elements. In an additive combination, two or more antennas receive in the same way a transmission signal generated by a reading device, which they then emit as a radio signal. At the individual antennas, the transmission signal then practically always has the same phase.

On the other hand, in the case of a subtractive link, the transmission signals at the individual antennas are not in phase, so that when interference is superimposed on the radio signals emitted by the individual antennas, a different interference pattern and thus a different radiation pattern results than with an additive combination.

A subtractive connection of a first and a second antenna can be achieved by supplying a transmission signal generated by the reading device to the first antenna via a phase element and feeding it to the second antenna past the phase element. In this case, the phase element causes the first antenna to receive the transmission signal in antiphase relative to the second antenna. Such a phase element can be designed, for example, as a delay line or as a reverse transformer. Both methods cause a phase shift of half a period or 180 °.

For an additive link, the antenna is supplied with the transmission signal generated by the reading device via a power divider. The phase element becomes disabled or bypassed. The transmission signal then reaches the two antennas in the same way, ie in phase.

A reading device according to the invention thus contains a phase element and a switching device which effects an additive connection in a first switching state, ie deactivates or bypasses the phase element, and effects a subtractive connection in a second switching state, ie feeds the transmission signal to the first antenna via the phase element , The present invention is also suitable for retrofitting existing RFID systems by connecting a retrofit module on the one hand to a conventional reader and on the other hand to two or more antennas. The retrofit module contains the phase element and the switching device, so that an additive and a subtractive coupling of a first and a second antenna are possible. An advantageous development of the invention provides that in a read operation additionally at least one of the antennas individually emits the transmission signal as a radio signal. For example, the first antenna singly, the second antenna singly, the first and second antennas additive, and the first and second antennas subtractive can be used to generate four different radiation patterns. It can also be used a larger number of antennas, so that there are an even greater number of ways to addively or subtractively link the antennas or a part of the existing antennas. A further advantageous development of the invention provides that the switching device is controlled by a control circuit which synchronizes the switching device with the readings triggered by the reading device. For this purpose, a feeder or decoupling device can be provided in a line leading from the reading device to the switching device, which decouples a part of the transmitted signal and transmits it to a control circuit which forms a control signal actuating the switching device from the decoupled part of the transmission signal. The control circuit preferably contains a counter, for example a binary counter. The control circuit can then actuate the switching device as a function of the count. To this It can be achieved that the different states of the switching device are taken in succession in a read operation, the switching states are taken, for example cyclically. Advantageously, it is thus possible to ensure that the switching device is in the same state when receiving the response signals emitted by transponders, as in the case of the preceding transmission of the radio signals. Consequently, therefore, the response signals can be supplied to the reading device additively or subtractively linked.

The switching device can be designed, for example, as a switching matrix, which assumes its switching states cyclically.

A further advantageous development of the invention provides that the switching device has a switching state in which a separate antenna is addressed, which may be part of a registration unit, for example a registration card. In this further switching state, the switching device preferably changes only by a special switching pulse. After an initialization process, objects freshly provided with RFID transponders can be detected and corresponding data records stored in a database. Such a registration unit may, for example, be designed so that its antenna detects only objects which are supplied to it, for example, are stored in a registration tray.

The invention described above can work with any antenna, for example patch antennas or strip antennas. The individual antennas can be polarized the same or differently.

Further details and advantages of the invention will be explained with reference to an embodiment with reference to the accompanying drawings. Fig. 1 shows a schematic representation of an RFI D reader with an attached retrofit module and multiple antennas.

In Figure 1, the invention using the example of a retrofit module 1 is explained, between a conventional RFI D reader 2 and a plurality of antennas 3, 4th connected. 1, the antenna output of the RFI D reader 2 is connected to a reader terminal of the retrofit module 1 and the antennas 3, 4 are connected to antenna terminals of the retrofit module 1. The retrofit module 1 can have its own housing. But it is also possible to integrate the below-explained content of the retrofit module 1 in an RFID reader.

The retrofit module 1 includes a switching device 5, which may be formed, for example, as a switching matrix. A switching matrix is sometimes referred to as a switch matrix. The switching device 5 has in the illustrated embodiment, four switching states, but may also have a correspondingly larger number of switching states in a larger number of antennas.

In a first switching state, the switching device 5 transmits a transmission signal generated by the RFID reader 2 only as a signal S1 to the first antenna 3. In a further switching state, which is shown in FIG. 1 as the fourth switching state, the switching device 5 supplies a transmission signal generated by the RFID reading device 2 only to the second antenna 4, which is shown as a signal S2 in FIG. In a further switching state, which is shown in FIG. 1 as the second switching state, the switching device 5 supplies the transmission signal generated by the RFID reader 2 to both the first antenna 3 and the second antenna 4. In this switching state, the two antennas 3 and 4 are thus additively linked. This switching state is shown in FIG. 1 as S1 + S2.

In a further switching state, which is shown in FIG. 1 as the third switching state, the switching device 5 links the two antennas 3, 4 by subtraction, which is shown in FIG. 1 as S1-S2. For a subtractive connection of the two antennas 3, 4, the transmission signal generated by the RFID reader 2 of the second antenna 4 is fed via a not shown phase element, which compared to the signal path of the transmission signal to the first antenna 3, a delay by half a period the carrier frequency with which signals are sent from and to a transponder of the RFID system causes. In a subtractive linkage of the two antennas 3, 4, the transmission signal is at the antennas 3, 4 so in opposite phases. Ideally, the transmission signal at the second antenna 4 is compared to the transmission signal at the first antenna. th antenna 3 phase-delayed by 180 °. In the case of an additive combination of the two antennas 3, 4, the phase element is then deactivated or bypassed, so that it has no influence on the signal propagation times. The switching device 5 is controlled by means of a control circuit 6. In the embodiment shown, the control circuit generates a clock signal for actuating the cyclically operating switching device 5, so that the switching states of the switching device 5 are passed through in succession. The control circuit 6 is supplied via a branch or Auskuppeleinrichtung a part of the transmission signal generated by the RFID reader 2 and the switching device 5 is fed. The control circuit 6 can thus synchronize the switching device 5 with the readings triggered by the RFID reader 2. In other words, therefore, a decoupled part of the transmission signal is used as a synchronization signal for the switching device 5 to be controlled. In this way it can be achieved that the actual switching of the switching device 5 can be made in a transmission pause between two transmission signals. Upon receipt of the response signals from RFID transponders, the response signals received by the individual antennas 3, 4 are thus linked in the same way as in the case of the preceding transmission of the radio signals.

The control circuit 6 may include a trigger 7 and a counter 8, for example a binary counter. The trigger 7 continuously monitors the signal level of the coupled-out portion of the transmit signal and generates a pulse or voltage level in response to the signal level, for example, as soon as the signal level falls below a predetermined threshold. In this way, the control circuit 6 can detect when a reading process triggered by the RFID reader 2 is over. The pulse or signal level then generated by the trigger 7 is detected by the counter 8, which then causes the switching device 5 to change their switching state. In this way, the switching device 5 can change its switching state in each case between read operations, so that in successive read operations, in the example shown four Read operations, each have different emission characteristics and thus different areas are illuminated.

The power supply of the retrofit module 1, in particular the Umschaltein- direction 5, both via an external power supply as well as by phantom power via the coaxial cable of an antenna feeder, for example via a suitably equipped reading device. 2

Refurbishment module

RFI D reader

first antenna

second antenna

switchover

control circuit

trigger

counter

Claims

claims

1. reader for an RFID system in conjunction with a plurality of antennas (3, 4) to which the reading device (2) transmits a transmission signal, which emit the antennas (3, 4) as a radio signal, characterized by

a phase element which, in the case of a transmission signal passing through it, effects a phase rotation by half a period of a carrier frequency with which signals are transmitted from and to a transponder of the RFID system, and

a switching device (5), the

in a first switching state, a transmission signal generated by the reading device (2) passes through the phase element to a first antenna (3) and past the phase element to a second antenna (4), so that the first antenna (3) and the second antenna ( 4) emit the radio signal out of phase, and in a second switching state bridges or deactivates the phase element so that a transmission signal generated by the reading device (2) is conducted by the phase element unaffected to the first antenna (3) and to the second antenna (4) and the first antenna (3) and the second antenna (4) emit the radio signal in phase.

2. Reader according to claim 1, characterized in that the switching device (5) the transmission signal in a further switching state only one of the antennas (3, 4) zuleitet.

3. Reading device according to one of the preceding claims, characterized in that in a to the switching device (5) leading line a tap or a decoupling device is provided which decouples a part of the transmission signal and transmitted to a control circuit (6), which from the decoupled Part of the transmission signal forms a control signal that operates the switching device (5).

4. Reading device according to claim 3, characterized in that the control circuit (6) includes a counter (8), preferably a binary counter.

5. Reading device according to one of the preceding claims, characterized in that the switching device (5) is a switching matrix, which assumes its switching states cyclically.

6. Reader according to one of the preceding claims, characterized in that the switching device (5) between the reader (2) and the antennas (3, 4) is arranged in a separate housing.

7. Reading device according to one of the preceding claims, characterized in that the switching device (5) has an additional switching state, in which a separate antenna is addressed, which is part of a registration unit.

8. Retrofit module for an RFID reader, with

a reader terminal for connection to a reader (2),

a first antenna terminal for connection to a first antenna (3), a second antenna terminal for connection to a second antenna (4),

a switching device (5) having a plurality of switching states in which the reader terminal is connected in different ways to the antenna terminals, wherein

in a first switching state, the reader terminal is connected to the first and the second antenna terminal, wherein in the signal path from the reader terminal to the first antenna terminal, a phase element is included, so that the signal path between the reader terminal and the first antenna terminal compared to the signal path of the Reader terminal to the second antenna terminal causes a phase delay by half a period of a carrier frequency with which signals are sent from and to a transponder of the RFID system causes

in a second switching state, the reader terminal is connected to the first and the second antenna terminal, wherein the phase element in the signal path from the reader terminal to the first antenna terminal is deactivated or bypassed.

9. A method for reading an RFID transponder, wherein with a reader (2) a plurality of antennas (3, 4), a transmission signal is supplied, which is emitted by the antennas (3, 4) as a radio signal, which then from the RFID transponder is received, which then emits a response signal, characterized in that for reading the RFID transponder, the antennas (3, 4) emit the transmission signal successively in different control configurations, wherein in a first Ansteuerungskonfigura- tion a first antenna (3) and a second antenna (4) has the transmission signal phase-shifted, preferably phase-shifted by 180 °, so that the antennas (3, 4) send the radio signal out of phase, and in a second configuration the first antenna (3) and the second antenna (4) receive the transmission signal in phase, so that the antennas (3, 4) emit the radio signal in phase.

10. The method according to claim 9, characterized in that in a further configuration in each case only one of the antennas (3, 4) receives the transmission signal.