Patent Application
20100060430
This application claims priority to European Patent Application No. EP08016019.5, filed Sep. 11, 2008, the entire contents of which is incorporated herein by reference.
1. Field of the Invention
The invention relates to a method, a system, and an apparatus for improving the output control of an RFID system. In particular, the present invention relates to a method, system and an apparatus providing improved output control of an RFID system by utilizing a relationship between a carrier enable signal provided to an RFID reader and a data signal comprising the code of a transponder entering the carrier field of the RFID reader.
2. Description of the Related Art
RFID is an acronym for Radio Frequency Identification. RFID is one member in the family of Automatic Identification and Data Capture (AIDC) technologies and is a fast and reliable means of identifying just about any material object. It relies on storing and remotely retrieving data. Primarily, the two main components involved in a radio frequency identification system are the transponder (tags that are attached to the object) and the interrogator (RFID reader). Communication between the RFID reader and tags occurs wirelessly and generally does not require a line of sight between the devices. Some transponders can be read from several meters away.
Most RFID transponders contain at least two parts. One is an integrated circuit (IC) for storing and processing information, modulating and demodulating a radio frequency (RF) signal, and other specialized functions. The second is an antenna for receiving and transmitting a signal. Accordingly, an RFID transponder, which is considered as a next generation barcode, is a miniscule microchip that is attached to an antenna. The transponders come in a wide variety of sizes, shapes, and forms and can be read through most materials with the exception of conductive materials like water and metal. With modifications and positioning, even these obstacles can be overcome.
Tags may be active or passive. Passive tags are generally smaller, lighter, and less expensive than those that are active, they can be applied to objects in harsh environments, they are maintenance free, and they will last for years. These transponders are only activated when within the response range of a reader. The RFID reader emits a low power electromagnetic wave field which is used to power up the tag to facilitate passing on of any information that is contained on the transponder chip.
Active tags differ in that they incorporate their own power source, wherein the tag is a transmitter rather than a reflector of radio frequency signals, which enables a broader range of functionality, like programmable and read/write capabilities.
An RFID reader typically contains a transmitter and receiver module, a control unit, and a coupling element (antenna). Such a typical reader has three main functions: energizing, demodulating, and decoding. In addition, readers can be fitted with an additional interface that converts the radio waves returned from the RFID tag into a form that can then be passed on to another system like a computer, microcontroller unit (MCU), or any programmable logic controller.
In safety engineering, the RFID technology is used, in particular, for non-contact switch devices, e.g., for door monitoring. Here, a predetermined device pair composed of a passive transponder and a reader may be attached to the moveable door and a fixed point of reference. This facilitates monitoring whether a door is closed or open, e.g., in an environment where it is crucial that all doors of the room are closed before safety critical operations are performed inside the room. RFID may also be utilized for access control and general security purposes, providing authentication tags for opening a security door or enabling operation of a specific machine.
In case of a passive transponder, the transponder is only provided with sufficient energy from the RF field of the reader if the transponder is within a certain energy transfer range of the reader. Once enough energy is transferred from the RF field to the transponder and the transponder is within a response range of the reader, the transponder automatically provides a significant response signal comprising its identification code to the RFID reader. Accordingly, once the transponder has entered the response range of the reader and has received enough energy to transmit its code, the reader device will be able to determine the code and facilitate provision of the assigned control signal.
This kind of RFID system suffers from the basic problem that in the border area of the response range of the reader device, transponders may frequently change their state from a state of not being able to transmit a detectable code to a state of providing a meaningful response signal allowing to detect the identification code of the transponder. This frequent change causes an undesired highly volatile switching of the provided control signal. The resulting effect of switching on and off the provided control signal in a high frequency disturbs the normal operation of the apparatus controlled by the RFID system.
Previously, this problem has been solved by averaging a multitude of code readings. These prior solutions suffer, however, from the disadvantage of unwanted high reaction times.
It is one feature of the present invention to provide a method, system, and an apparatus facilitating enhanced RFID output control.
A method of distance determination in an RFID system is provided. The method comprises the steps of first switching on a carrier field of an RFID reader, receiving, at the RFID reader, a response signal from a passive RFID transponder located in the carrier field, said response signal comprising a code related to the RFID transponder, detecting said code, and determining a time difference between the switching on of the carrier field and the detection of the code signal. Said time difference provides a measure for the distance between the RFID transponder and the reader.
According to an aspect of the present invention, the carrier field is switched on and off in response to switching on and off a carrier enable signal provided in or to the RFID reader. According to this aspect, the time difference is determined between the switching on of the carrier enable signal and the detection of the code signal.
According to another aspect of the present invention, the carrier field is switched on and off periodically and the time difference determination is performed with respect to the information pair of the last preceding switching on of the carrier field and the subsequent detection of the code signal.
According to yet another aspect of the present invention, a distance may be calculated from the determined time differences. A provided control signal is switched on if the time difference or the calculated distance is smaller than a first predefined threshold value. Subsequently, other time difference or distance determinations may be performed and the provided control signal may be switched off if a subsequently determined time difference or distance is greater than a second predefined threshold value, wherein the second threshold value is greater than the first threshold value, thereby introducing hysteresis into the output control of the RFID system.
According to yet other aspects of the present invention, the control signal may be a safety control signal or a security control signal. The response signal may correspond to a load modulation of the carrier field or to a load modulation with auxiliary carriers in a configuration utilizing inductive coupling. The response signal may also result from a back scatter modulation.
According to yet another aspect of the present invention, an RFID system for distance determination is provided. The system comprises a microcontroller unit, MCU, for providing a carrier enable signal and receiving a data signal, a passive RFID transponder having a code, for providing a response signal comprising the code when being located in a carrier field, and an RFID reader for generating a carrier field in response to a received carrier enable signal, receiving a response signal comprising a code, and providing a data signal comprising a code signal representing the code to the MCU. The MCU determines a time of detection of the code from the data signal and determines a time difference between the switching on of the carrier enable signal or a corresponding response thereto in the received data signal and said time of detection.
According to yet another aspect of the present invention, an apparatus is provided for distance determination in an RFID system. The apparatus comprises means for generating a carrier enable signal, means for providing the carrier enable signal to an RFID reader, means for receiving a data signal comprising a code signal from the RFID reader, wherein the code signal represents the code of a passive RFID transponder located in the carrier field of the RFID reader, means for determining a time of detection of the code from the data signal, and means for determining a time difference between the time of detection and the preceding switching on of the carrier enable signal or a corresponding response thereto in the received data signal. Said time difference provides a measure for the distance between the RFID transponder and the RFID reader.
According to still another aspect of the present invention the necessary time for powering up the passive RFID transponder is a function of the distance between the transponder and the antenna of the reader device providing the carrier field. Thus, monitoring of a time difference between switching on of a carrier field, for example, accomplished by providing a non-constant carrier enable signal, and receipt of a significant code signal provides information on the distance between both devices. Conventional systems provide either a constant carrier field or switch the carrier field off and on due to external conditions of the system, for example to save power. According to another aspect of the present invention, the carrier field is turned off and on in a controlled and monitored manner allowing to determine the time differences between the start of providing the carrier field and detection of a significant transponder code signal.
Thus, it is a feature of the present invention is to not prolong the reaction time of the controlled system in detecting a transponder while avoiding frequent switching on and off of the provided control signal.
Another feature of the present invention is that a position of a transponder may be determined. A system of reader devices determining the respective distances between each RFID reader and a particular transponder in the inventive manner may be coupled to provide a local positioning system (LPS). Multiple different, or multilevel, control signals may be used depending on the distance between the transponder and the reader device. Contactless multi-level switches and gaming device controllers are within the scope of possible applications of the present invention.
These and other advantages and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.
Various exemplary embodiments of the subject matter disclosed herein are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which:
In describing the various embodiments of the invention which are illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word “connected,” “attached,” or terms similar thereto are often used. They are not limited to direct connection but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art.
Exemplary embodiments of the present invention will now be described in detail with reference to the annexed drawings.
In response to a carrier enable signal 240 provided by MCU 260, the reader 220 generates an electromagnetic carrier field with a typical frequency of 100 to 150 kHz. A frequently employed exemplary frequency of the carrier field is 125 kHz.
The system further comprises an RFID transponder/tag 210 comprising a transponder integrated circuit 212 and a coil antenna module 214. In the illustrated embodiment, if a transponder 210 enters the carrier field generated by RFID reader 220, the transponder 210 is powered up by energy transfer from the carrier field and then inductively couples with the primary coil of the reader, as the distance between both coils is such that the transponder is located in the near field of the antenna module 222 of the reader 220. The resonant transponder 210 extracts energy from the magnetic field of the reader 220. The extracted energy may be measured as a certain voltage drop across an internal resistance of the reader. The switching on and off of a load resistance of the transponder effects specific voltage variations at the antenna module 222 of the reader 220. A binary code signal stored at the transponder 210 controls the switching on and off of this load resistance, thereby transmitting a code signal from the transponder to the reader. This known form of data transmission is called load modulation.
The read channel 236 demodulates an antenna voltage signal of the reader 220 and processes the demodulated signal to generate a data signal 250 comprising the received code signal. The data signal 250 is then provided to MCU 260 for evaluation.
In an embodiment, the identification code is programmed into the transponder integrated circuit 212. Conventionally, the code consists of one bank with four bytes. These bytes are emitted e.g. in Manchester code. In Manchester code, a bit sequence binarily modulates the phasing of a clock signal. Accordingly, Manchester code is one form of digital phase modulation which is also known as phase shift keying (PSK).
In a different embodiment, load modulation with auxiliary carriers may be utilized. In a further possible embodiment, which is not shown in
The MCU 260 provides the carrier enable signal 240 and receives the data signal 250 comprising the code signal. In accordance with an analysis of both the carrier enable signal 240 and the received data signal 250, a control signal 270 is provided, which may be utilized for safety applications or security applications like access control.
In particular, MCU 260 determines a time of detection of the code from the received data signal 250, and determines a time difference between a switching on of the carrier enable signal 240 or a corresponding response thereto in the received data signal 250 and said time of detection. In the embodiment as illustrated in
With further reference to
For this calculation, the applicable carrier field characteristics and the power-up characteristics of the passive RFID transponder may be utilized. However, also a relative calculation may be performed where the carrier field is periodically switched on and off and the distance calculation is then performed relative to a greatest determined time difference compared with the respectively determined time difference. The greatest determined time difference herein represents a range where the transponder has just entered a response range of the carrier field. This response range may be known or determined according to the specifications of the RFID reader. However, as the energy transfer is dependent also on the angle between the two coils, any calculated value will have approximating character only.
According to one embodiment of the present invention, the carrier field is periodically switched on and off, and the time difference is determined between a detection of the code signal and a last preceding switching on of the carrier field. As will be understood by one of ordinary skill in the art, the method according to the present invention may also comprise the conventional steps of identifying a code and validating any identified code. If a code is identified to be valid or, if according to another embodiment, every identifiable code is predefined to be valid, and if a determined time difference is smaller than a first predetermined threshold value, a control signal is switched on.
With further reference to
If it is determined in step 420 that the determined time difference Δt is smaller than the first threshold value T1, control proceeds to step 430 and the control signal is switched on. It will be understood that this procedure may further comprise the steps of code validation. Control proceeds then to step 432, switching the carrier field off and on, which may be performed periodically. While the control signal is in the status of being switched on, another time difference Δt′ is determined in step 434. It is further determined in step 436 whether Δt′ is greater than a second threshold value T2. As long as the result of this determination is negative, control returns back to step 430 and the control signal remains in the switched on status. If the determination, however, is positive, control proceeds to step 440 and the control signal is switched off Control returns then back to step 410 to determine a new time difference Δt.
By means of this control procedure, a hysteresis is introduced into the output control of the RFID system employing a switch on distance and a switch off distance and a corresponding history of distance determinations with regard to the transponder and the reader. For example, a control signal for access control according to this embodiment of the present invention may be switched on only once a small distance between transponder and reader of 15 millimeters is determined, but may afterwards not be switched off before the distance exceeds 20 millimeters.
This will now be explained in detail with further reference to
With further reference to
With further reference to
With further reference to
With further reference to
The inventive method, system, and apparatus facilitates enhanced RFID output control while overcoming the disadvantages of previous systems. While the present invention has been shown as described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail and combinations may be made therein without departing from the scope of the invention as defined by the appended claims. In addition, those areas in which it is believed that those of ordinary skill in the art are familiar have not been described herein in order to not unnecessarily obscure the invention described herein. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrative embodiments, but only by the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08016019.5 | Sep 2008 | EP | regional |
