JP2007065976A - Radio tag reader and rfid system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio tag reader and an RFID system allowing response by a radio tag even if communication quality is deteriorated by a peripheral environment. <P>SOLUTION: This radio tag reader transmits an ASK modulation signal and receives a response signal from the radio tag. The radio tag reader is constructed of a modulation means performing ASK modulation of a carrier wave based on a base band signal and generating an ASK modulation signal, a demodulation means demodulating the receipt signal and generating a demodulation signal, a response signal detection part 29b determining receipt of a response signal from the radio tag based on the demodulation signal, a transmission control part 29a generating a response request based on a trigger signal and repeatedly transmitting the response request until the response signal corresponding to the response request transmitted as the ASK modulation signal is received, and a modulation control part 29c switching a modulation degree of the ASK modulation signal based on a determination result by the response signal detection part 29b. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wireless tag reader and an RFID system, and more particularly to an improvement of a wireless tag reader that transmits an ASK modulation signal and receives a response signal from the wireless tag.

  In recent years, wireless tags have attracted attention as a technology for product identification and management that replaces barcodes. This wireless tag is a tag using RFID (Radio Frequency IDentification) technology that can receive an RF signal, read data on a semiconductor memory, and write data in the semiconductor memory. Recently, wireless tags that do not have a battery and can be used semipermanently have emerged due to the development of contactless power transmission technology. A wireless tag reader is used to read / write data from / to such a wireless tag.

  The wireless tag reader is a communication device that modulates and transmits a carrier wave with a digital signal as a baseband signal and receives a response signal from the wireless tag. The modulation based on the baseband signal of the carrier includes ASK (Amplitude Shift Keying) modulation for changing the amplitude of the carrier, FSK (Frequency Shift Keying) modulation for changing the frequency, and PSK (Phase changing the phase). Shift Keying) modulation. Among these, in the ASK modulation used in the wireless tag reader, two communication methods having different modulation degrees are standardized by ISO (International Organization for Standardization).

  The modulation degree is the rate of change of the carrier amplitude in ASK modulation, and the ISO standard defines a communication system with a modulation degree of 100% and a communication system with 10%. In a communication system with a modulation degree of 100%, the signal amplitude becomes zero during the period when the amplitude is reduced by modulation, and power transmission to the wireless tag is interrupted. On the other hand, in a communication system with a modulation degree of 10%, the signal amplitude does not become zero even during the modulation period, and power transmission is not interrupted.

  In general, when a metal exists around the wireless tag or the wireless tag reader, the electromagnetic field of the RF signal transmitted from the wireless tag reader may be canceled, and the communication quality from the wireless tag reader to the wireless tag may deteriorate. Conventionally known. Wireless tags and wireless tag readers are often attached to metal workpieces. For this reason, even when an RF signal modulated with a modulation degree corresponding to the communication method on the tag side is transmitted from the wireless tag reader, the modulation degree of the RF signal at the time of reception decreases due to deterioration of communication quality. There was a problem that I couldn't respond. In particular, in a wireless tag compatible with ASK 10% that specifies a communication method with a modulation degree of 10%, the modulation degree of the RF signal received on the tag side is lower than 10%, and reception processing cannot be performed.

Patent Document 1 describes a wireless tag reading device that switches a communication method and sends a command until a response signal from a wireless tag is received. This wireless tag reader attempts to detect a wireless tag that has entered a communication area by switching a plurality of communication methods with different communication protocols and sending a command. Therefore, even if the modulation degree of the RF signal is reduced due to the deterioration of communication quality, the wireless tag cannot be subjected to reception processing. Patent Document 2 describes a wireless tag reading device that adjusts the modulation degree of ASK modulation based on information read from a wireless tag. This wireless tag reading device reads information related to tag-specific manufacturing conditions from a wireless tag and adjusts the modulation degree based on the read information. In other words, this wireless tag reading device is intended to suppress the influence caused by the change in the degree of modulation when the wireless tag approaches by reducing the influence of the individual difference of the wireless tag on the electrical characteristics on the communication. For this purpose, information on manufacturing conditions is read for each wireless tag. Therefore, when the communication quality of the same wireless tag is deteriorated due to a change in distance or the like, the wireless tag cannot perform reception processing.
JP 2001-312701 A JP 2003-50977 A

  As described above, in the conventional wireless tag reader, even when an RF signal modulated with a modulation degree corresponding to the communication method on the tag side is transmitted from the wireless tag reader, it is received due to deterioration in communication quality. There is a problem in that the modulation degree of the RF signal is reduced and the wireless tag cannot respond.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a wireless tag reading apparatus and an RFID system that enable a wireless tag to respond even if communication quality deteriorates due to the surrounding environment. In particular, it is an object of the present invention to provide a wireless tag reading device that enables a wireless tag to perform reception processing even when the modulation degree of an RF signal received on the tag side is reduced due to deterioration in communication quality.

  A wireless tag reader according to the present invention is a wireless tag reader that transmits an ASK modulated signal and receives a response signal from the wireless tag, and ASK modulates a carrier wave based on a baseband signal to generate an ASK modulated signal A modulation unit that demodulates a received signal and generates a demodulated signal, a response signal detection unit that determines reception of a response signal from the wireless tag based on the demodulated signal, and a response signal detection unit And modulation control means for switching the degree of modulation of the ASK modulation signal based on the determination result.

  Specifically, the modulation means includes two load circuits having different impedances, and a switching element that selects one of these load circuits based on a baseband signal, and the modulation control means performs the ASK modulation. The modulation degree is switched by switching the impedance of the selected load circuit. In this wireless tag reader, reception of a response signal from the wireless tag is determined based on the demodulated signal, and the modulation degree of the ASK modulated signal is switched based on the determination result. That is, when the communication quality deteriorates due to the environment around the wireless tag or the wireless tag reader, and the modulation degree of the RF signal received on the tag side decreases, the wireless tag cannot receive and process the wireless tag reader. Then, even if an ASK modulated signal is transmitted, no response signal is received. In such a case, since the modulation degree of the ASK modulation signal is automatically switched, the wireless tag can receive and process the RF signal even if the modulation degree of the RF signal is reduced due to deterioration of communication quality. Therefore, even if the communication quality deteriorates due to the surrounding environment, the modulation degree is changed to an appropriate modulation degree, so that the wireless tag can respond.

  In addition to the above configuration, the wireless tag reader according to the present invention generates a response request based on a trigger signal, and repeatedly transmits the response request until the response signal for the response request transmitted as the ASK modulation signal is received. Transmission control means is provided, and the modulation control means is configured to set the lowest modulation degree among switchable modulation degrees for the response request transmitted first. According to such a configuration, when the response request is transmitted for the first time, the modulation factor is always the lowest, and when there is no decrease in the modulation factor due to communication quality deterioration, there is no need to switch the modulation factor. Communication in such a case can be simplified.

  In addition to the above configuration, the wireless tag reader according to the present invention switches the modulation degree if the modulation control means does not receive a response signal from the wireless tag within a predetermined time after transmitting the ASK modulated signal. Configured as follows. According to such a configuration, the success or failure of communication with the wireless tag is determined based on whether or not the response signal is received within a predetermined time. If the communication fails, the modulation degree of the ASK modulation signal is switched. It can be detected properly.

  In addition to the above configuration, the wireless tag reader according to the present invention generates a response request based on the trigger signal, and makes a response request until the response signal for the response request transmitted as the ASK modulation signal is received. A transmission control means for repeatedly transmitting; and a modulation degree storage means for storing a modulation degree at the time of reception of the response signal. The modulation control means has a switchable modulation degree for the response request transmitted first. The modulation degree is set to the lowest modulation degree, and when the response signal is received when the response request is generated based on the previous trigger signal, the modulation degree stored in the modulation degree storage unit is used. . According to such a configuration, when a response signal from the wireless tag is received, the modulation degree at the time of reception is stored, and is set as the modulation degree of the response signal transmitted first based on the next trigger signal. The As a result, when a plurality of wireless tags are sequentially processed in an ambient environment where the modulation degree needs to be switched, it is not necessary to switch the modulation degree when the wireless tag is successfully detected by receiving the response signal. It can be simplified.

  In addition to the above configuration, the wireless tag reader according to the present invention has a modulation degree stored in the modulation degree storage means for the response request that the modulation control means first transmits to a new wireless tag. A modulation degree is determined based on the modulation degree.

  In addition to the above configuration, the wireless tag reader according to the present invention generates a response request and repeatedly transmits the response request as the ASK modulation signal until the response signal is received with respect to the same wireless tag. And the modulation control means is configured to switch the degree of modulation within a range in which the same wireless tag can be received. According to such a configuration, since the response request is repeatedly transmitted while switching the modulation degree within the range in which the same wireless tag can be received, the communication quality deteriorates depending on the surrounding environment, and the RF signal cannot be received. A wireless tag can be detected effectively.

  In addition to the above-described configuration, the wireless tag reader according to the present invention further includes transmission control means for starting a series of command transmissions to the wireless tag that has transmitted the response signal after receiving the response signal. However, when the communication with the wireless tag is interrupted, the modulation is switched to a modulation degree different from that before the interruption, and the transmission control means is configured to resume communication with the wireless tag with the modulation degree after the switching. According to such a configuration, even if a series of command transmissions with a certain wireless tag is interrupted due to a decrease in the modulation degree due to deterioration in communication quality, the modulation degree of the ASK modulation signal is switched and communication with the wireless tag is resumed. Therefore, communication with the wireless tag can be effectively performed.

  An RFID system according to the present invention is an RFID system including a wireless tag that generates a response signal and a wireless tag reader that transmits an ASK modulation signal and receives the response signal. Based on the baseband signal to generate an ASK modulated signal, a demodulating means for demodulating the received signal and generating a demodulated signal, and a response signal from the radio tag based on the demodulated signal Response signal detection means for determining reception and modulation control means for switching the modulation degree of the ASK modulation signal based on the determination result by the response signal detection means.

  According to the RFID tag reading apparatus and the RFID system according to the present invention, since the modulation degree of the ASK modulation signal is automatically switched, even if the modulation degree of the RF signal received on the tag side is reduced due to deterioration of communication quality, The wireless tag can receive and process an RF signal. Therefore, even if the communication quality deteriorates due to the surrounding environment, the modulation degree is changed to an appropriate modulation degree, so that the wireless tag can respond.

  FIG. 1 is a perspective view showing an example of a schematic configuration of an RFID system according to an embodiment of the present invention, and shows an overall system including a reader / writer 2 as a wireless tag reader. The RFID system 10 according to the present embodiment writes data to the wireless tag 1 or reads data in the wireless tag 1 using an RF (Radio Frequency) signal modulated by ASK (Amplitude Shift Keying). This is a system for managing the work A1. The RFID system 10 includes a wireless tag 1, a reader / writer 2, a serial bus cable 3, and a control device 4.

  The wireless tag 1 receives an RF signal from the reader / writer 2 and generates electric power necessary for the operation, and writes received data into the memory and reads data from the memory based on the received data. In this memory, UID (Unique ID) assigned at the time of manufacture is stored as identification information for identifying the wireless tag 1. Specifically, a manufacturer code, a product code, a serial number, and the like are stored as a UID. Therefore, the work A1 to which the wireless tag 1 is attached can be identified by reading the UID from the wireless tag 1.

  The reader / writer 2 performs an operation of transmitting an ASK modulation signal and receiving a response signal from the wireless tag 1. The reader / writer 2 is a wireless tag reader based on the ISO (International Organization for Standardization) 15693 standard, and is a so-called proximity reader. Specifically, the distance from the wireless tag 1 suitable for communication is from several centimeters to several tens of centimeters. The reader / writer 2 is connected to the control device 4 via the serial bus cable 3.

  The control device 4 instructs the reader / writer 2 to start communication with the wireless tag 1, and collects, accumulates, or displays data read from the wireless tag 1 by the reader / writer 2. For example, the control device 4 instructs the start of communication at a timing when the work A1 on the transport line is located within the communication area of the reader / writer 2. As such a control device 4, an information processing terminal such as a PLC (Programmable Logic Controller) or a personal computer is used.

  Specifically, a read / write command is output from the control device 4 to the reader / writer 2 as a trigger signal for instructing the start of communication, and the reader / writer 2 issues a response request to the wireless tag 1 based on the read / write command. Transmission starts. This response request is transmitted as an ASK-modulated RF signal, and is repeatedly transmitted until a response signal from the wireless tag is received.

  FIG. 2 is a diagram showing details of the main part of the RFID system of FIG. 1, and shows a card-like wireless tag 1. The wireless tag 1 includes a thin rectangular substrate 11, an antenna coil 12 spirally wired along each side of the substrate 11, and a semiconductor connected to the antenna coil 12 and disposed inside the antenna coil 12. It consists of a chip 13.

  For example, the substrate 11 is made of a resin sheet having a thickness of 0.2 mm, and the antenna coil 12 is formed on the resin sheet by printing or etching. The semiconductor chip 13 includes a capacitor that forms a resonance circuit with the antenna coil 12, a demodulation circuit that demodulates a reception signal, a processing circuit that processes reception data, and a semiconductor memory that stores UID and reception data. The response signal is generated based on a response request from the reader / writer 2. Specifically, it is generated by reading data from the semiconductor memory based on the received data and encoding a subcarrier generated by load modulation of the RF signal.

  FIG. 3 is a block diagram illustrating details of a main part of the RFID system of FIG. 1, and shows a configuration example of the reader / writer 2. The reader / writer 2 includes an oscillation circuit 21, an amplification circuit 22, a modulation circuit 23, an LPF 24, an LC resonance circuit 25, an attenuator 26, a demodulation circuit 27, a binarization circuit 28, a control circuit 29, an external I / F 30 and an encoding. A circuit 31 is formed.

  The oscillation circuit 21 is an RF signal generation circuit that generates an RF (Radio Frequency) signal using a crystal oscillator. For example, a 13.56 MHz RF signal is generated and output as a carrier wave. The carrier wave is amplified by the amplifier circuit 22 and output to the modulation circuit 23.

  The modulation circuit 23 performs ASK (Amplitude Shift Keying) modulation on the carrier wave after power amplification based on the baseband signal from the encoding circuit 31 to generate an ASK modulated signal. The modulation circuit 23 can switch between ASK modulation with a modulation factor of 100% and ASK modulation with a modulation factor of 10% so that communication can be performed even with different types of wireless tags. Furthermore, in the ASK modulation with a modulation degree of 10%, in order to improve the communication performance for an ASK 10% -compatible wireless tag that specifies a communication method with a modulation degree of 10%, the ASK modulation signal is within a range of 10% to 30%. The modulation degree can be switched.

  Generally, in a communication system that specifies a modulation degree of 10%, an allowable range (10% to 30%) is defined for the modulation degree of an RF signal transmitted from a reader / writer. Normally, a wireless tag compatible with ASK 10% can receive and process an RF signal from a reader / writer if the modulation degree at the time of transmission is within this range. That is, at the time of communication with an ASK 10% compatible wireless tag, the modulation degree is switched within a range in which the same type of wireless tag can be received. Designation of the modulation degree in such ASK modulation is performed based on an instruction from the control circuit 29.

  The encoding circuit 31 performs a process of encoding the data input from the control circuit 29 with a pulse position and generating a baseband signal.

  The harmonic component of the ASK modulated signal is removed by an LPF (low-pass filter) 24 and output to the LC resonance circuit 25. The LC resonance circuit 25 is a resonance circuit including an antenna coil and a capacitor. The ASK modulation signal from the modulation circuit 23 is transmitted to the wireless tag via the LC resonance circuit 25, and the response signal from the wireless tag is received by the LC resonance circuit 25. The received signal is attenuated by the attenuator 26 to a level that can be controlled by the demodulation circuit 27 at the subsequent stage.

  The demodulation circuit 27 performs processing for demodulating the received signal after attenuation based on the carrier wave and the sub-carrier wave to generate a demodulated signal. The binarization circuit 28 is a comparator that binarizes the demodulated signal from the demodulation circuit 27 by threshold processing, and generates decoded reception data.

  The control circuit 29 starts communication with the wireless tag based on a trigger signal input from the control device via the external I / F 30, and performs control to switch the modulation degree based on the demodulated signal. Specifically, a response request for the wireless tag is generated based on the read / write command from the control device, and is output to the encoding circuit 31, and the reception of the response signal from the wireless tag is determined based on the demodulated signal, An operation for switching the modulation degree of the ASK modulation signal is performed.

  Here, it is assumed that an operation for automatically setting parameters related to communication with the wireless tag is performed based on a control signal input from the control device. Specifically, the parameter table is read based on the automatic determination command from the control device, and a reception command is generated based on the read parameter table and transmitted to the wireless tag. Communication parameters are set based on a response from the wireless tag by the reception command.

  The parameter table is composed of communication parameters (data) related to communication standards and communication methods, and a plurality of tables are stored in a memory such as an EEPROM according to the type of wireless tag to be communicated. Communication parameters include the degree of modulation in ASK modulation, the radio wave intensity at the time of RF signal transmission, the read size of data read from the wireless tag, the maximum size of received data, and the like. Here, 8 according to the combination of communication parameters, that is, whether the communication system has a modulation degree of 100% or 10%, the strength of the radio wave intensity, and the designation of the read size (either 8 bytes or 4 bytes). It is assumed that a type table is stored as a parameter table.

  One of such parameter tables is read out, and a reception command is transmitted with communication parameters determined based on the read out parameter table. The acceptance command is also called an Inventry command, and consists of data that specifies the manufacturer code or product code of the wireless tag. If there is no response from the wireless tag, this acceptance command is retransmitted after changing the parameter table. If there is a response from the wireless tag to the reception command, the type of the wireless tag is determined based on the received data, and communication parameters are set and registered. That is, an appropriate communication parameter can be automatically set by sending an acceptance command to a wireless tag to be communicated.

  4 (a) and 4 (b) are diagrams showing details of a main part of the reader / writer of FIG. FIG. 4A shows an example of the modulation circuit 23 including the switching element 23a and the two load circuits 23b and 23c, and FIG. 4B shows a configuration example of the load circuit 23b selected at the time of modulation. It is shown. Each of the load circuits 23b and 23c is composed of a DC resistor or a capacitor having different impedance. The switching element 23a is a semiconductor element that selects one of the load circuits 23b and 23c based on the baseband signal and switches the output circuit.

  Here, the impedance of one load circuit 23b (referred to as “load circuit 1”) selected during ASK modulation is set to a predetermined value other than zero, and the impedance of the other load circuit 23c (referred to as “load circuit 2”) is It shall be zero. By switching such load circuits 23b and 23c according to the signal level of the baseband signal, the carrier wave can be ASK modulated.

  The “load circuit 1” (load circuit 23b) includes a plurality of load circuits 102 and 103 having different impedances, and a switching element 101 that selects any one of the load circuits 102 and 103 based on an instruction from the control circuit. It consists of. For example, the load circuit includes two load circuits, a high load circuit 102 having a large impedance and a low load circuit 103 having a small impedance, one of which is selected by the switching element 101 and the output circuit is switched. Thereby, the impedance of the load circuit selected at the time of ASK modulation can be switched, and the high modulation degree mode with a large output impedance and the low modulation degree mode with a small output impedance can be switched. That is, in the high modulation degree mode, ASK modulation is performed using the high load circuit 102, and in the low modulation degree mode, ASK modulation is performed using the low load circuit 103.

  Specifically, when communicating with a wireless tag compatible with ASK 10%, the modulation degree can be changed by switching between a high modulation degree mode with a modulation degree of 30% and a low modulation degree mode with a modulation degree of 10% as necessary. Adjustments are made. It is assumed that “load circuit 1” is switched to a load circuit (not shown) having an infinite impedance when ASK modulation with a modulation degree of 100% is selected.

  FIG. 5 is a block diagram showing the details of the main part of the reader / writer of FIG. 3, in which a configuration example of the control circuit 29 is shown. The control circuit 29 includes a transmission control unit 29a, a response signal detection unit 29b, a modulation control unit 29c, and a modulation degree storage unit 29d. The transmission control unit 29a performs an operation of generating a response request for the wireless tag based on a trigger signal (read / write command) from the control device and outputting the response request to the encoding circuit. The response request is made up of data such as a manufacturer code and a product code specifying a wireless tag to be communicated, encoded by an encoding circuit, modulated as a baseband signal, and transmitted from an LC resonance circuit as an ASK modulation signal. Is done.

  This response request is repeatedly transmitted to the same wireless tag until a response signal for the response request transmitted as the ASK modulation signal is received. The wireless tag as a transmission target when the response request is repeatedly transmitted may have the same modulation degree specified as the communication method.

  The response signal detection unit 29b performs an operation of determining reception of a response signal from the wireless tag based on the demodulated signal. Specifically, it is determined whether or not a response signal from the wireless tag to be communicated has been received based on the received data after decoding. For example, the success or failure of communication is determined by a CRC (Cyclic Redundancy Check) code included in the received data. Alternatively, the success or failure of communication is determined by the waveform or timing of SOF (Start Of Frame) or EOF (End Of Frame).

  The modulation control unit 29c performs an operation of switching the modulation degree of the ASK modulation signal based on the determination result by the response signal detection unit 29b. The modulation degree is switched by outputting an instruction to switch the impedance of the load circuit selected during ASK modulation to the modulation circuit. Specifically, an instruction to switch between a high modulation degree mode with a modulation degree of 30% and a low modulation degree mode with a modulation degree of 10% is output during communication with a wireless tag compatible with ASK 10%.

  Here, when a wireless tag corresponding to ASK 10% is to be communicated, when a response request is first transmitted based on a read / write command from the control device, the mode is switched to the low modulation degree mode. That is, in this case, when transmission of a response request is started, the low modulation degree mode is always set, and a response request modulated with a modulation degree of 10% is transmitted. In addition, if a response signal from the wireless tag is not received within a predetermined time after the response request is transmitted, that is, if communication with the wireless tag fails, the response request is retransmitted by switching the modulation degree mode. To do. If a response signal is received from the wireless tag within a predetermined time, it is assumed that the communication with the wireless tag has succeeded and the modulation degree mode is held.

  When the response signal from the wireless tag is received, the modulation degree at the time of reception is stored in the modulation degree storage unit 29d, and the response signal to be transmitted first based on the next trigger signal (read / write command) is stored. Modulation degree. Specifically, when a response signal is received at the time of generating a response request based on the previous trigger signal, the response request first transmitted to the new wireless tag is stored in the modulation degree storage unit 29d. The modulation degree is determined with the modulation degree as an initial value. On the other hand, when a response signal is not received at the time of generating a response request based on the previous trigger signal, a low modulation degree mode is set for a response request transmitted first to a new wireless tag. As a result, when a plurality of wireless tags are sequentially processed in an ambient environment where the modulation degree needs to be switched, it is not necessary to switch the modulation degree when the wireless tag is successfully detected by receiving the response signal. It can be simplified.

  FIG. 6 is a diagram showing a state of ASK modulation based on the baseband signal. The amplitude of the ASK modulation signal is switched according to a change in the signal level of the baseband signal. Assuming that the amplitude of the signal level in B2 at the time of modulation is a and the amplitude of the signal level in B1 at the time of non-modulation is b (b> a), the modulation degree m of the ASK modulated signal is m = (ba) / It is represented by (b + a).

  In this embodiment, when communicating with a wireless tag whose communication method is ASK modulation with a modulation factor of 10%, a low modulation factor mode with a modulation factor of 10% and a high modulation factor of 30% based on the reception result of the response signal. Control to switch the modulation degree mode is performed.

  FIG. 7 is a diagram showing an example of the modulation degree switching operation in the reader / writer of FIG. 3, and the modulation degree in the wireless tag measured while changing the distance to the wireless tag is shown for each modulation degree mode. ing. Experiments by the inventors of the present invention have revealed that the modulation degree of the RF signal measured on the tag side varies depending on the distance between the reader / writer and the wireless tag. Specifically, the distance decreases monotonously from zero and is minimum at a certain distance. When the distance over which the degree of modulation is minimized is exceeded, the degree of modulation increases monotonously.

  In the interval in which the modulation factor is decreasing, the rate of change of the modulation factor is gradually decreasing, and in the interval in which the modulation factor is increasing, the rate of change is gradually increasing. Since the modulation degree in the wireless tag changes according to the distance in this way, if the modulation degree of the RF signal transmitted from the reader / writer is low, the wireless tag side is below the minimum value m1 of the modulation degree that can be received, A non-communication area that cannot be answered will occur.

  For example, in the low modulation degree mode, the modulation degree in the wireless tag is less than the minimum value m1 due to the surrounding environment such as the presence of a metal around the reader / writer or the wireless tag, and the range from the distance d1 to the distance d2 is the non-communication area. Become. Specifically, m1 = 2.5%, and the degree of modulation measured on the reader / writer side is 10%. In this embodiment, in such a case, control for switching the modulation degree mode to the high modulation degree mode is performed using the fact that a response signal is not received even if a response request is transmitted. As a result, the occurrence of a non-communication area is eliminated, and communication with the wireless tag becomes possible.

  If there is metal around the reader / writer or the wireless tag, if the distance between the reader / writer and the wireless tag is small, the metal will cancel the magnetic field generated by the antenna coil of the reader / writer and the reader / writer will have sufficient power to the wireless tag. Not supplied. For this reason, if the modulation degree of the ASK modulation signal transmitted from the reader / writer is high, the wireless tag side exceeds the maximum value m2 of the modulation degree that can be received, and a non-communication area where the response cannot be made occurs.

  For example, in the high modulation degree mode, due to the presence of metal around the reader / writer or the wireless tag, the modulation degree in the wireless tag becomes the maximum value m2 or more, and a non-communication area occurs. Specifically, m2 = 18%, and the degree of modulation measured on the reader / writer side is 45%. In such a case, control for switching the modulation degree mode to the low modulation degree mode is performed. As a result, the occurrence of a non-communication area is eliminated, and communication with the wireless tag becomes possible.

  FIG. 8 is a cross-sectional view showing an example of a reader / writer and a wireless tag attached to a metal frame. The wireless tag 1 is attached to a metal frame A3 via a resin attachment A2. The metal frame A3 is made of, for example, an iron flat plate, and a concave portion is formed on the side facing the reader / writer (head) 2 with the central portion made thinner than the peripheral portion. An attachment A2 having the same size as the wireless tag 1 is disposed in the recess, and the wireless tag 1 is attached to the attachment A2.

  The attachment A2 and the wireless tag 1 are disposed at a distance d3 from the side wall of the recess, and the wireless tag 1 is disposed at a distance d4 from the head facing surface of the metal frame A3. Specifically, d3 = 10 mm and d4 = 2.8 mm.

  On the other hand, the reader / writer 2 is attached to an iron frame plate B1. Thus, when metal exists around the reader / writer 2 and the wireless tag 1, communication is impossible depending on the distance d between the reader / writer 2 and the wireless tag 1.

  FIG. 9 is a diagram showing an example of communication characteristics between the reader / writer 2 and the wireless tag 1, and the modulation degree measured by changing the distance d is shown for each modulation degree mode. The distance d between the reader / writer 2 and the wireless tag 1 is changed from 5 mm to 65 mm at intervals of 10 mm, and the degree of modulation is measured at each distance. As the modulation degree, a value measured on the wireless tag 1 side and a value measured on the head (reader / writer 2) side are shown.

  In the high modulation degree mode, the modulation degree measured on the head side gradually decreases from 40.9% as the distance d increases, reaches a minimum value of 25.3% at the distance d = 25 mm, and then 28 Increased gradually to 2%. The modulation factor measured on the tag side is gradually proportional to the change on the head side, and gradually decreases from 8.5% as the distance d increases, and reaches a minimum value of 6.2% at the distance d = 25 mm. After that, it gradually increased to 11.2%.

  On the other hand, in the low modulation degree mode, the modulation degree measured on the head side gradually decreases from 17.2% as the distance d increases, and reaches a minimum value of 9.7% at the distance d = 25 mm. It gradually increases to 11.8%. The degree of modulation measured on the tag side gradually decreases from 3.7% as the distance d increases, and becomes a minimum value of 2.3% at the distance d = 35 mm in almost proportion to the change on the head side. After that, it gradually increased to 3.9%.

  In the low modulation degree mode, the modulation degree measured on the tag side is less than the minimum modulation degree m1 = 2.5% that can be received at the distances d = 25 mm and d = 35 mm, and a non-communication area C is generated. . Even in such a case, if the modulation degree mode is switched to the high modulation degree mode, the modulation degree at the distances d = 25 mm and d = 35 mm exceeds m1, and the non-communication area can be eliminated.

  Steps S101 to S110 in FIG. 10 are flowcharts showing an example of an automatic communication parameter setting operation in the reader / writer in FIG. First, when receiving an automatic determination command from the control device (step S101), the control circuit 29 reads a parameter table from the memory (step S102), and temporarily sets communication parameters based on the read parameter table (step S103). .

  Next, a reception command for the wireless tag is generated based on the automatic determination command, and is transmitted according to the temporarily set communication parameter (step S104). If there is a response from the wireless tag within a predetermined time after the reception command is sent, the type of the wireless tag is determined based on the received data, and if necessary, the parameter table is read again (steps S105 and S106). Next, if an appropriate communication parameter is registered in the memory as setting data and a setting completion notification is returned to the control device, the automatic setting process is completed (steps S107 and S108).

  On the other hand, if there is no response from the wireless tag within a predetermined time, the processing procedure from step S102 to step S105 is repeated until all parameter tables have been tried (step S109). If there is no response from the wireless tag even after all parameter tables have been tried, it is determined that the wireless tag is not a communication target, and a communication error notification is returned to the control device (step S110).

  Steps S201 to S209 in FIG. 11 are flowcharts showing an example of the RFID tag reading operation in the reader / writer in FIG. First, the control circuit 29 reads the setting data from the memory and performs the main setting of the communication parameter (step S201).

  Next, if the modulation degree of the set communication parameter is 100%, it waits until a read / write command is received from the control device (steps S202 and S203), and when the read / write command is received, the received read / write command is changed. Based on this, a response request for the wireless tag to be communicated is generated and transmitted with a modulation degree of 100% (step S204).

  If a response signal from the wireless tag is received within a predetermined time after the response request is sent, the received data is returned to the control device (steps S205 and S206), and the process shifts to a read / write command standby state. If the response signal from the wireless tag is not received within a predetermined time, the response request is retransmitted (retry) (step S208), and the response signal from the wireless tag is not received even after a predetermined number of retries. In this case, a communication error notification is returned to the control device as a communication failure with the wireless tag (step S209).

  On the other hand, if the modulation degree of the set communication parameter is 10%, the process proceeds to a reading process related to a wireless tag compatible with ASK 10% (step S207).

  Steps S301 to S310 in FIG. 12 are flowcharts showing an example of a wireless tag reading operation in the reader / writer of FIG. 3, and a reading process regarding a wireless tag compatible with ASK 10% is shown. First, the control circuit 29 stands by until a read / write command is received from the control device (step S301). When the read / write command is received, the control circuit 29 refers to the modulation degree storage unit 29d and acquires the modulation degree (step S301). S302). Next, a response request for the wireless tag to be communicated is generated based on the received read / write command, and transmitted with a modulation factor of 10% (step S303).

  If a response signal from the wireless tag is received within a predetermined time after sending the response request, the modulation degree at the time of reception is stored in the modulation degree storage unit 29d, and the received data is returned to the control device (step S304). To S306).

  On the other hand, if the response signal from the wireless tag is not received within the predetermined time, the response request is retransmitted with the modulation degree switched to 30% (steps S307, S309, and S310). This response request retry is performed while switching the modulation degree until the predetermined number of times is reached. If the response signal from the wireless tag is not received even after the predetermined number of times, the communication request is assumed to have failed to communicate with the wireless tag. An error notification is returned to the control device (step S308).

  According to the present embodiment, since the modulation degree of the ASK modulation signal is automatically switched, the wireless tag can receive and process the RF signal even if the modulation degree of the RF signal is reduced due to deterioration of communication quality. . Therefore, even if the communication quality deteriorates due to the surrounding environment, the modulation degree is changed to an appropriate modulation degree, so that the wireless tag can respond.

  Note that in this embodiment, an example in which the modulation degree of an ASK modulation signal can be switched between 10% and 30% has been described for communication with a wireless tag compatible with ASK 10%. It is not limited to this. For example, within a range from 10% to 30%, it may be possible to switch to any one of three or more different modulation degrees M1 to Mn (n ≧ 3). Furthermore, if the response request transmitted first is the lowest modulation degree among the switchable modulation degrees M1 to Mn, it is not necessary to switch the modulation degree when there is no decrease in the modulation degree due to deterioration of communication quality. Therefore, it is preferable that communication in such a case can be simplified.

  Further, in this embodiment, an example has been described in which a response signal from a wireless tag is not received, and a resending of a response request is performed by switching the modulation degree. However, the present invention is not limited to this. Absent. For example, when communication with a wireless tag is interrupted, the degree of modulation may be switched to resume communication with the wireless tag. Specifically, after receiving the response signal from the wireless tag, a series of command transmission to the wireless tag that transmitted the response signal is started. If reception data cannot be obtained during this series of command transmission, the modulation is switched to a modulation level different from that before the interruption of communication, and data transmission specifying the wireless tag to be communicated is resumed. In other words, the interruption of data reception related to a series of command transmissions is regarded as interruption of communication, and the degree of modulation is switched every time communication is interrupted. In this way, even if communication with a certain wireless tag is interrupted due to deterioration of communication quality, the degree of modulation of the ASK modulation signal is switched and communication with the wireless tag is resumed. Can be done effectively.

  In this embodiment, an example in which the modulation degree is adjusted for communication with a wireless tag compatible with ASK 10% has been described, but the present invention is not limited to this. For example, the modulation degree may be switched within a predetermined range for communication with a wireless tag in which a communication method with a modulation degree of 100% is designated. Specifically, the modulation degree can be switched within a range of 80% to 100%, for example, and the modulation degree is switched based on the reception result of the response signal. According to such a configuration, even when a radio tag for a high modulation degree with a large modulation degree is used, the radio tag can be switched to an appropriate modulation degree, so that the radio tag receives an RF signal with deteriorated communication quality. can do.

1 is a perspective view illustrating an example of a schematic configuration of an RFID system according to an embodiment of the present invention, and illustrates an overall system including a reader / writer 2; FIG. It is the figure which showed the detail in the principal part of the RFID system of FIG. 1, and the card-shaped radio | wireless tag 1 is shown. FIG. 2 is a block diagram showing details of a main part of the RFID system of FIG. 1, and shows a configuration example of a reader / writer 2. It is the figure which showed the detail in the principal part of the reader / writer of FIG. FIG. 4 is a block diagram illustrating details of a main part of the reader / writer of FIG. 3, in which a configuration example of a control circuit 29 is illustrated. It is the figure which showed the mode of ASK modulation based on a baseband signal. It is the figure which showed an example of the switching operation | movement of the modulation degree in the reader / writer of FIG. It is sectional drawing which showed an example of the reader / writer and wireless tag each attached to metal frames. It is the figure which showed an example of the communication characteristic between the reader / writer 2 and the wireless tag 1, and the modulation degree measured by changing the distance d is shown for every modulation degree mode. 4 is a flowchart illustrating an example of an operation for automatically setting communication parameters in the reader / writer of FIG. 3. 4 is a flowchart illustrating an example of a wireless tag reading operation in the reader / writer of FIG. 3. FIG. 4 is a flowchart showing an example of a wireless tag reading operation in the reader / writer of FIG. 3, showing a reading process related to a wireless tag compatible with ASK 10%.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wireless tag 2 Reader / writer 3 Serial bus cable 4 Control apparatus 10 RFID system 11 Board | substrate 12 Antenna coil 13 Semiconductor chip 21 Oscillation circuit 22 Amplification circuit 23 Modulation circuit 24 LPF
25 LC resonance circuit 26 Attenuator 27 Demodulation circuit 28 Binary circuit 29 Control circuit 29a Transmission control unit 29b Response signal detection unit 29c Modulation control unit 29d Modulation degree storage unit 30 External I / F
31 Coding circuit A1 Work A2 Attachment A3 Metal frame B1 Non-modulation B2 Modulation B3 Frame plate

Claims (9)

In the wireless tag reader that transmits the ASK modulation signal and receives the response signal from the wireless tag,
Modulation means for ASK modulating a carrier wave based on a baseband signal and generating an ASK modulated signal;
Demodulation means for demodulating a received signal and generating a demodulated signal;
Response signal detection means for determining reception of a response signal from the wireless tag based on the demodulated signal;
A wireless tag reader, comprising: modulation control means for switching a modulation degree of the ASK modulation signal based on a determination result by the response signal detection means. A transmission control means for generating a response request based on a trigger signal and repeatedly transmitting the response request until the response signal for the response request transmitted as the ASK modulation signal is received;
The RFID tag reading apparatus according to claim 1, wherein the modulation control unit sets the lowest modulation degree among switchable modulation degrees for the response request transmitted first.   2. The wireless tag reader according to claim 1, wherein the modulation control means switches the modulation degree if a response signal from the wireless tag is not received within a predetermined time after the transmission of the ASK modulated signal. A transmission control means for generating a response request based on the trigger signal and repeatedly transmitting the response request until the response signal for the response request transmitted as the ASK modulation signal is received;
Modulation degree storage means for storing the modulation degree at the time of reception of the response signal,
The modulation control means sets the lowest modulation degree among switchable modulation degrees for the response request transmitted first, and when a response signal is received when a response request is generated based on the previous trigger signal. The wireless tag reading device according to claim 1, wherein the modulation degree is stored in the modulation degree storage means.   The modulation control means determines a modulation degree based on a modulation degree stored in the modulation degree storage means for a response request transmitted first to a new wireless tag. The wireless tag reader according to the description. A transmission control unit that generates a response request and repeatedly transmits the response request as the ASK modulation signal until the response signal is received with respect to the same wireless tag;
2. The wireless tag reading device according to claim 1, wherein the modulation control means switches a modulation degree within a range in which the same wireless tag can be received. After receiving the response signal, comprising a transmission control means for starting a series of command transmission to the wireless tag that transmitted the response signal,
When the communication with the wireless tag is interrupted, the modulation control means switches to a modulation degree different from that before the interruption,
2. The wireless tag reading device according to claim 1, wherein the transmission control means resumes communication with the wireless tag with a modulation degree after switching. The modulation means includes two load circuits having different impedances and a switching element that selects one of these load circuits based on a baseband signal,
2. The wireless tag reading device according to claim 1, wherein the modulation control means switches the modulation degree by switching the impedance of the load circuit selected during ASK modulation. In an RFID system comprising a wireless tag that generates a response signal and a wireless tag reader that transmits an ASK modulated signal and receives the response signal,
The wireless tag reader includes a modulation unit that ASK modulates a carrier wave based on a baseband signal to generate an ASK modulated signal;
Demodulation means for demodulating a received signal and generating a demodulated signal;
Response signal detection means for determining reception of a response signal from the wireless tag based on the demodulated signal;
An RFID system comprising: a modulation control unit that switches a modulation degree of the ASK modulation signal based on a determination result by the response signal detection unit.

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