JP2000049655A - Automatic frequency identification system for lc resonance tag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the retrieving process speeds of various automatic ID identification devices using an LC resonance tag constituted by combining plural resonance frequencies and to increase the number of identification IDs by preventing misidentification. SOLUTION: In order to detect individual resonance frequencies of the LC resonance tag 30 consisting of plural resonance circuits 31a to 31n, amplitude variation and a phase shift of an electromagnetic wave due to the presence of the resonance tag in an induced electromagnetic field are observed independently. Features of the variation and shift are analyzed to exclude factors causing misrecognition. The total retrieving process speed is increased by using a detection system by frequency sweeping and a detection system by scanning in combination and the center frequency of the resonance frequency can precisely be set high, so the number of frequencies which can be identified in the same retrieval frequency range is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an automatic frequency identification system which operates in various non-contact automatic ID identification devices using an LC resonance tag.

[0002]

2. Description of the Related Art A ringing characteristic is remarkably observed in a resonance circuit having a high Q characteristic (sharpness) using a ceramic resonator or a crystal resonator, but a low-cost LC resonance tag has a low Q characteristic. , It is difficult to identify the ringing based on the ringing characteristics. The conventional method uses a so-called dip meter method, which uses an oscillator that changes its frequency continuously (called a sweep) and detects that an energy change occurs near the resonance frequency of the LC resonance tag. do it,
In the method of specifying the resonance frequency, or the so-called echo wave sensing method, the independent frequency is sequentially changed (called scanning) and the emission is intermittently cut off at the same time. There is a method of receiving and analyzing a radio wave emitted as a reflected wave from a receiver provided separately and specifying a resonance frequency.

[0003]

In the above dip meter system, even when a conductive material such as a metal material having no resonance characteristic exists in an induction electromagnetic field formed by an interrogation wave emitted from an interrogator. , And induces an energy change, resulting in erroneous detection (detection due to factors other than the resonance frequency of the LC resonance tag to be originally detected). Further, the determination of the resonance frequency by this method has a large error, and the frequency identification resolution is very low. In the echo wave sensing method, it is difficult to discriminate it from a noise signal because of the method of detecting the amplitude of a reflected wave, and erroneous detection is likely to occur when used in an environment where external noise is strong. In order to improve the frequency discrimination resolution in this method, it is necessary to perform scanning while minimizing the step change width of the scanning frequency. However, the number of individual scanning frequencies required to detect the resonance center frequency of the LC resonance tag with sufficient accuracy increases dramatically, and it is difficult to obtain a practical processing speed. This will be described later with reference to FIGS. Accordingly, the present invention prevents erroneous detection due to the presence of a conductive substance such as a metal object and erroneous detection in an environment where external noise is strong, so as to speed up the overall processing speed and to provide a highly accurate LC resonance tag. An object of the present invention is to improve the frequency discrimination resolution by enabling detection of the resonance center frequency, and to allow more frequencies to be allocated within the same search frequency range.

[0004]

SUMMARY OF THE INVENTION The present invention achieves the above object, and a factor which induces a change in an induced electromagnetic field due to an interrogation wave (electromagnetic wave) emitted from an interrogator is the LC resonance of the original purpose. There can be various other than the resonance circuit of the tag,
Most of the effects are caused by conductive materials such as metal objects and the effects of external noise. However, the change of the induced electromagnetic field induced by these factors is different from the change induced by the resonance circuit. That is, under the influence of a conductive material such as a metal object, the phase change can easily occur with respect to the instantaneous movement or reflection, but the amplitude change rarely occurs. On the other hand, with respect to the influence of external noise, the amplitude changes, but as long as the amplitude is limited, there is little change in the phase of the electromagnetic wave emitted from the interrogator. This is equivalent to the fact that ordinary FM broadcasting is excellent against external noise. By observing the phase change and the amplitude change independently with a focus on the difference between these changes, and using the characteristics of the mutual change as identification factors, it is possible to eliminate the erroneous detection factors.

[0005] In the detection method using the frequency sweep, the search time required to search the same search frequency range is extremely short, but the accuracy is inferior in determining the resonance center frequency of the resonance circuit. On the other hand, the scanning detection method is excellent in that the resonance center frequency of the resonance circuit is determined, but the search time required to search the same search frequency range is slow. Approximate resonance frequency is detected by the frequency sweep detection method, and fine scanning is detected in small steps around the detected frequency, so that the resonance center frequency can be determined with high accuracy while shortening the search time overall. .

As described above, focusing on the amplitude change and phase change of the induced electromagnetic field, both characteristics are used as factors for detection.
In addition, by using the detection method based on the frequency sweep and the detection method based on the scanning together, in the non-contact automatic ID identification device using the LC resonance tag, reliable and accurate identification, high-speed processing, and an increase in the number of identification IDs are realized. An automatic frequency identification method can be provided.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing an example of an LC resonance tag automatic ID identification device equipped with an automatic frequency identification method according to the present invention.
0 indicates an LC resonance tag automatic ID identification device as an interrogator, 30 indicates an LC resonance tag as a transponder, 31a,
Reference numerals 31b and the like denote each resonance circuit constituting the transponder 30. FIG. 2 is a flowchart showing the overall operation. FIG.
FIGS. 4A and 4B are diagrams illustrating the center frequency detection error when scanning is performed at a coarse frequency step and when scanning is performed at a fine frequency step, respectively. The CPU 11 sets the search mode to the phase change detection means (A), and drives the transmission sweep oscillator 12 to sweep the search frequency range from the lowest sweep frequency to the highest sweep frequency at high speed (B). The swept oscillation wave is amplified by the high-frequency amplifier A13 and the high-frequency amplifier B14 and emitted from the transmission antenna 15 into the search area. The transmission cutoff controller 17 controls the high-frequency amplifier to operate as a normal amplifier. The LC resonance tag 30 is constituted by an arbitrary combination of resonance circuits having different resonance frequencies, 31a, 31b and 31n. Transmission antenna 15
The resonance circuit placed in the induced electromagnetic field formed by the emitted electromagnetic waves gives a change to the induced electromagnetic field, and the resulting change is received by the receiving antenna 25. CPU11
Simultaneously controls the transmitter, limits the amplitude of the signal received from the receiving antenna 25 by the amplitude limiter 20, compares the phase with the sweep oscillation wave of the transmitter by the phase comparator 19, and converts the voltage generated by the change in the phase difference into A. The data is fetched through the / D converter A18. Since the LC resonance tag causes a delay phenomenon near the resonance point, if the phase is compared with the swept oscillating wave, the phase comparator generates a voltage with respect to the change in the phase, and the presence thereof can be detected (C). External noise is not detected as a resonance frequency because the amplitude is limited. If the resonance frequency is not detected even after sweeping to the search maximum sweep frequency, the sweep search is repeated by setting the search minimum sweep frequency again (B).

[0008] The error of the resonance frequency of the LC resonance tag detected by this method is very large, and at the same time, it may be due to the influence of a conductive material such as a metal object. The CPU 11 sets the search mode to the detection means based on the amplitude change by the following procedure (D). That is, the transmission sweep oscillation controller 16 is controlled, and the transmission sweep oscillator 12 oscillates a fixed frequency near the previously detected frequency as the scanning frequency. Further, the high-frequency amplifiers 13 and 14 are controlled via the transmission cutoff controller 17 so that the transmission antenna 15 intermittently emits oscillation waves into the search area (E). The receiver starts the operation immediately after the transmission is cut off to receive the reflected wave emitted from the LC resonance tag, and drives the signal received from the reception antenna 25 and, if necessary, the local oscillator 23 of the receiver. To a desired frequency by the frequency converter 24. The received signal is detected by the amplitude detector 22, and the amplitude value is read by the CPU via the A / D converter B21 (F). Searching the entire setting range while changing the scanning frequency set sequentially,
An accurate resonance center frequency is detected by comparing the detected amplitude values (H). If nothing is detected in the set entire scanning frequency range, it is determined as a conductive material such as a metal object or external noise, error processing is performed (G), and the process is restarted from the first search process (A). In the next search cycle, it is necessary to perform a process such as retry for the error-processed frequency after setting the number of times.

It is checked whether the entire search frequency range has been swept (I). If the maximum sweep frequency has not been reached, the search mode is returned to the detection means based on the phase change (J), and the operation of detecting the resonance tag is continued in the remaining search frequency range for the purpose of searching for a plurality of resonance circuits. The sweep of the entire search frequency range is completed, and the accurate resonance center frequency is determined by fine scanning for all the detected frequencies, and the search cycle is completed. The data required from all detected frequency combinations is composed, created, and collated (K), and functions required by the automatic ID identification device according to the data, such as LED and L
The external function control circuits 26a, 26b, 26c perform display driving of a CD or the like, opening / closing by a switch, driving of a sounding body such as a speaker, or transfer of acquired data to a host computer.
And 26n and the like (L).

Curves (a) represented in FIGS. 3 and 4
Are the amplitude response characteristics to the change in the frequency of the resonance circuit, and the center line (b) represents the center frequency of the resonance circuit. The maximum detection error with respect to the actual center frequency when scanning is performed in a coarse step is f1 in FIG.
The error occurs when scanning is performed as in f2, f3, and f4, and the error is represented by an error (e) from the center frequency from the maximum response value (c) in FIG. On the other hand, the maximum detection error with respect to the actual center frequency when scanning is performed in fine steps similarly occurs when scanning is performed like f1 to f14 in FIG. 4, and the error is the maximum response value (f) in FIG. , And is represented by an error (h) from the center frequency. As is clear from the figure, detection with higher accuracy can be realized when scanning is performed in fine steps, as compared with coarse scanning. It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made within the technical scope of the present invention. The present invention extends to the modified embodiments. Of course.

[0011]

The present invention is configured as described above, and eliminates erroneous detection due to the influence of conductive materials such as metal objects and the influence of external noise while reducing the overall search time. Demonstrate. Further, since the resonance center frequency can be determined with high accuracy, the frequency identification resolution is improved, and the effect of increasing the number of identifiable IDs within the same search frequency range is exhibited.

[Brief description of the drawings]

FIG. 1 is a block diagram of an LC resonance tag automatic ID identification device.

FIG. 2 is a flowchart.

FIG. 3 is an explanation of a center frequency detection error when scanning is performed at a coarse frequency step.

FIG. 4 is an explanation of a center frequency detection error when scanning is performed in fine frequency steps.

[Explanation of symbols]

 Reference Signs List 10 LC resonance tag automatic ID identification device 30 LC resonance tag 31a Resonance circuit A 31b Resonance circuit B 31n Resonance circuit N

Claims (2)

[Claims] An interrogator emits a plurality of interrogation waves, and induces a change in the induced electromagnetic field by a transponder constituted by one or more LC resonance circuits existing in the induced electromagnetic field. In the non-contact automatic ID identification device utilizing the ability to identify the transponder by receiving the change of the response and identifying the frequency configuration or the frequency combination of the LC resonance circuit of the transponder, The change induced in the field is divided into the amplitude change and the phase change of the electromagnetic wave, these changes are observed independently, and the characteristics of the mutual change are configured as identification factors. Identification method. 2. An interrogator emits a plurality of interrogation waves, and induces a change in the induced electromagnetic field by a transponder formed of one or more LC resonance circuits existing in the induced electromagnetic field. In the non-contact automatic ID identification device utilizing the ability to identify the transponder by receiving the change of the response and identifying the frequency configuration or the frequency combination of the LC resonance circuit of the transponder, An LC resonance tag automatic frequency identification method, comprising an oscillator that continuously varies a frequency and an oscillator that varies an independent frequency sequentially to form a field.