JP2000082120A - Article detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a detection sensitivity of a tag without making transmission radio wave power larger or making a distance between transmission/ reception antennas smaller. SOLUTION: A transmitter 1 has a digital signal processor(DSP) 7 that generates many carriers initial phases of which coincide with waveform data written in an EPROM 6 by an operation program, digital/analog(D/A) convert them and transmit them from a transmission antenna 8. A receiver 2 receives many carriers by a reception antenna 9, D/A converts them, compares them with a waveform without a tag 25 stored in advance in the DSP 17 by operation processing, decides that there is the tag when a featured difference is detected, rings a speaker 28 and informs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tag having a resonance circuit incorporated in an article for preventing shoplifting and the like. When the tagged article passes between a transmitting antenna and a receiving antenna, the tag transmits the tag from the transmitting antenna. The present invention relates to an article detection device that detects the passage of an article with a tag by utilizing the characteristic that the resonance circuit resonates and re-emits the radio wave to the transmitted radio wave and receives the re-radiated radio wave with a receiving antenna.

[0002]

2. Description of the Related Art A conventional article detection apparatus sweeps one carrier (radio wave) within a certain frequency band, outputs the same from a transmitter, performs synchronous detection on a receiver side, and transmits a transmission antenna.
The passage of an article is determined by detecting a change in a reception wave that appears when a tag (resonance circuit) exists between the reception antennas.

[0003]

However, in the above detection method, the energy radiated to the resonance circuit is only one carrier, so that the energy re-radiated from the tag is small, the output of synchronous detection is small, and the sensitivity is low. It has become something. As a method of increasing the sensitivity, a method of increasing the output level of the transmitter or a method of bringing the transmitting antenna and the receiving antenna close to each other can be considered. However, the method of increasing the output of the transmitter has a bad influence on other radio wave using devices. In addition, the method of bringing the antenna close to the vehicle means that the passage is narrowed, which gives a discomfort to the passing passengers, which is not preferable.

Accordingly, an object of the present invention is to increase the detection sensitivity of a tag without relying on the above-mentioned improvement method.

[0005]

In order to solve the above-mentioned problems, a first aspect of the present invention is to provide a tag having a resonance circuit incorporated therein, attached to a product, and having a transmitting antenna and a receiving antenna arranged opposite to each other. When the article passes between the antennas, the resonance circuit resonates by the radio wave transmitted from the transmission antenna, and the resonance circuit re-radiates the radio wave, so that the reception antenna receives the re-radiated radio wave, and the article passes. In the article detecting device for detecting the radio wave, the transmitting antenna has a transmitting device that outputs a plurality of radio waves simultaneously, and the receiving antenna has a receiving device that detects all the re-radiated radio waves emitted by the resonance circuit by the radio waves. Is done.

According to a second aspect of the present invention, in the first aspect of the present invention, the transmitting device is configured to output the radio waves transmitted from the transmitting antenna with the same initial phase.

According to a third aspect of the present invention, in the first aspect of the present invention, the transmitting apparatus outputs the radio waves with their phases shifted so that the maximum amplitude obtained by combining a plurality of radio waves output from the transmitting antenna becomes substantially minimum. It is configured as follows.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the receiving apparatus is configured to calculate a phase amount of each radio wave received by the receiving antenna and correct the phase of each radio wave by the phase amount. .

According to a fifth aspect of the present invention, in the first to fourth aspects, the receiving apparatus includes a filter for removing a radio wave having a frequency between the transmission radio waves.

[0010] The invention of claim 6 is the invention of claim 5, wherein the entire transmission frequency can be offset by a predetermined amount. Here, the offset means adding the same frequency to the initial individual transmission frequencies.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram of an article detecting apparatus according to a first embodiment of the present invention. The apparatus comprises a transmitting apparatus 1 and a receiving apparatus 2. The transmitting apparatus 1 includes an EPROM 6 (memory) and a DSP 7 (digital signal). Processing device), DAC 3 (digital / analog conversion device), LPF 4 (filter), amplifier 5, transmission antenna 8 as main parts.
The DSP 7 generates a digital signal and converts the waveform into an analog waveform based on the stored operation program and waveform data such as the wave number of the transmission carrier, the frequency of each carrier, the interval between the carriers, and the phase of each carrier. Then, unnecessary harmonics are removed by the LPF 4 and the transmitting antenna 8
Sent from.

FIG. 2 shows an example of a transmission frequency, in which 194 waves of carriers are simultaneously generated at 10 kHz intervals, and the respective waveforms have the same initial phase as shown in FIG. 2B. In this way, as shown in FIG. 2 (c), a portion where energy concentrates in a cycle of the reciprocal of the frequency interval of each carrier appears, and when the tag 25 passes near the transmitting antenna 8, the tag 25 Since a large number of carriers are radiated, the energy of the majority carrier as shown in FIG.
Re-radiated from

The receiving device 2 comprises a receiving antenna 9, a BPF 1
0 (filter), amplifier 11, LPF12, ADC13
(Analog / digital converter), DSP17, EPO
M19 and a speaker 28 are configured as main parts, and the received wave is converted into digital data after noise removal or the like by the BPF 10 or the LPF 12. DSP17 is EPROM
According to the control program stored in 19, initial calibration is performed at the time of power-on, a reference waveform as shown in FIG. 4A, which does not include a tag signal or a noise component, is averaged and stored in a memory in the DSP 17, Then, at a certain period, the difference between the received waveform and the stored reference waveform is calculated, and if the difference is detected in a characteristic manner in the energy concentrated portion as shown in FIG. Upon determination, a tag detection signal is output and notified by the speaker 28. FIG. 4B shows a reception waveform of the tag 25 having re-radiated radio waves.

As described above, the energy output from the resonance of the tag can be made to have a large characteristic waveform by concentrating the energy of a large number of carriers at one point by adjusting the phase.
Detection performance can be improved. Therefore, it is possible to increase the distance between the transmitting antenna and the receiving antenna. Further, according to this device, since the frequency is not swept, the number of times of detection when the tag passes can be significantly increased, and the S / N is improved by averaging.
Therefore, the detection accuracy can be greatly improved.

FIG. 5 shows a second embodiment, and shows a transmission waveform generated by the transmission device 1. In FIG.
(A) shows the phase characteristics of each transmission wave, and (b) shows the combined waveform. In the first embodiment,
It is possible to greatly improve the detection performance and detection sensitivity.However, since the output is performed by matching the phases of multiple carriers, the maximum amplitude value increases as the number of output carriers increases, and a high-output amplifier is required. Becomes In addition, when the frequency band of the simultaneous output is widened, the influence of the group delay characteristic occurs,
It is difficult for the receiving side to completely match the phases of the carriers. For this reason, in the second embodiment, the phases of the respective carriers to be transmitted are not adjusted to match each other, but the phases of the respective carriers are shifted so that the combined maximum amplitude is minimized. In this case, the entire configuration may be the same as that of FIG.

The operation of the receiving DSP 17 will be described. The operation flow is as shown in FIG. First, when the power is turned on, the DSP 17
Performs initialization, performs boot processing of the program, sets various registers, and the like (processing A). Subsequently, frequency mode detection (process B) and initial calibration (process C) are performed, and a waveform having no tag 25 and little noise is averaged to obtain a reference waveform, and the phase amount of each carrier is calculated and calculated. The data is stored (process D). The number of averaging is, for example, 10,000 and the required time is about 1 second.

Then, a Fourier transform process (FFT process) is performed in processes E and F to rotate the phase of each carrier.
Shift by the amount of phase obtained in the initial calibration. In process G, an inverse Fourier transform process (IFT process) is performed to execute FIG.
A time axis waveform as shown in (a) and (b) is formed by calculation, and a difference component is extracted by comparing with a reference waveform obtained by averaging data of initial calibration stored in process H. Then, in the process I, a determination process is performed at last, and if the obtained waveform of the difference component is a waveform that can be determined as a tag, an operation such as outputting a pulse signal and making the speaker 28 notify the user is performed.

By performing the transmission and reception processes in this manner, the maximum amplitude of the transmission output can be minimized without lowering the tag detection capability. Therefore, the maximum output level of the transmission amplifier can be significantly reduced, and the transmission amplifier can be reduced in size and size. It can be inexpensive. In addition, since the receiving side performs the phase rotation processing of each carrier by calculation and matches the phase of each carrier, tag detection is always performed under optimum conditions without affecting the group delay characteristics of the transmission path etc. Can be.

FIG. 7 is a block diagram of an article detecting apparatus according to a third embodiment, and FIG. 8 is an explanatory diagram of a received waveform operation. In this embodiment, the S / N is further improved. 7, the same components as those in FIG. 1 are denoted by the same reference numerals. Reference numeral 14 denotes an averaging processing circuit formed as an IC, which performs averaging processing on the A / D converted received signal. Upon receiving the control signal 23 from the transmitting DSP 7, the averaging is synchronized and the averaging result is transferred to the receiving DSP 17.
It has a function of receiving a determination result of 17 and controlling an alarm device such as a buzzer or an LED device.

Reference numeral 15 denotes a reference oscillator, and an averaging processing circuit 14 receives the clock signal from the reference oscillator 15 and divides the frequency of the clock signal into ADCs 13, DACs 3, DSPs 7, 17, and clock signals 20, 21, 22, 24. Has been sent out. Reference numeral 27 denotes a frequency mode setting switch for selecting a combination of a transmission frequency and a reception frequency.

The received wave received by the receiving antenna 9 and subjected to the averaging process is Fourier-transformed by the DSP 17. This Fourier transform is performed so that only the frequency of the transmitting carrier or the entire carrier is calculated, and then the frequency range other than the transmission frequency is set to 0. For example, this Fourier transform may be performed as in the following Equation 1.

[0022]

(Equation 1)

In the case where only a specific frequency is calculated, in Equation 1, the frequency index k may be calculated as 0, 1, 2,. By such an arithmetic processing, a signal in a frequency range other than the transmission frequency can be set to 0 by performing the same operation as that performed by filtering as shown in FIG. 8A. Then, by performing the inverse Fourier transform, it is possible to obtain a waveform from which noise is removed and S / N is improved as shown in the time axis waveform of FIG. In FIG. 8, the left waveform is the received waveform before processing, and the right waveform is the processed waveform. Then, a process of comparing the waveform with the improved S / N with the reference waveform may be executed in the same manner as in the first embodiment.

In this way, since only the plurality of carrier parts output on the transmitting side are extracted on the receiving side and the tag detection operation is performed, even if there is interference noise in the band, it is detected unless it matches the transmission carrier. Thus, an article detection device that is resistant to noise and interference waves can be provided.

Further, by configuring as shown in FIG. 7,
Since it is possible to remove received waves other than the transmission frequency, even if an article detection device using a plurality of similar carriers is adjacent to one another, one of the transmission frequencies may be slightly changed so as to come into a gap between the carriers. By offsetting, it is possible to operate well without interference.
FIG. 9 is an explanatory view of this. In the device B, the frequency is offset by Δf so that the transmission wave comes to a gap between the transmission waves. This offset operation can be easily executed only by changing the program of the DSP 7. By offsetting in this manner, both the A and B devices have their signals mixed together immediately after reception, but the Fourier transform operation removes carriers other than the transmission carrier, so that the other carrier can be removed from each other. It is possible to perform the detection operation satisfactorily.

In the above-mentioned embodiment, 194 transmission carriers are generated at regular intervals on the frequency axis. However, the transmission carriers need not be regular intervals, and the number of carriers is not limited to this. In short, considering the variation of the resonance circuit of the tag,
It is preferable to generate a large number of carriers in a resonable frequency range. In particular, it is effective to generate the noise at the center frequency.

[0027]

As described above in detail, according to the first aspect of the present invention, since a plurality of radio waves are simultaneously transmitted to resonate the tag, a plurality of re-radiated radio waves are detected at the same time. Tags can be detected with sensitivity.

According to the second aspect of the present invention, since the initial phases coincide with each other, energy can be concentrated at one point, and the energy of the re-radiated radio wave by the tag can be made to have a characteristic waveform. Detection performance can be improved. Therefore, it is possible to widen the transmission and reception antennas.

According to the third aspect of the present invention, since the maximum amplitude to be transmitted can be minimized, the transmission power can be kept low even when a plurality of carriers are transmitted simultaneously.

According to the fourth aspect of the present invention, since the phase difference of each radio wave is eliminated after reception and converted to the same phase to detect the re-radiated wave of the tag, the same detection effect as that of the second aspect is detected. Sensitivity can be obtained.

According to the fifth aspect of the present invention, it is possible for the receiving device to extract and receive only the frequency output from the transmitting device. Undetected received waves can be deleted, and the detection sensitivity can be improved.

According to the sixth aspect of the present invention, even if two article detection devices are adjacent to each other, by slightly offsetting one of the transmission carriers as a whole, it is possible to remove the radio waves from each other on the receiving side, so that interference can be caused. Operation can be performed satisfactorily.

[Brief description of the drawings]

FIG. 1 is a block diagram of an article detection device showing an example of an embodiment of the present invention.

2A and 2B show the transmission frequency of FIG. 1, wherein FIG. 2A shows a waveform viewed on a frequency axis, FIG. 2B shows a phase characteristic, and FIG. 2C shows a waveform viewed on a time axis.

FIG. 3 is a diagram illustrating frequency characteristics of re-radiated radio waves of a tag with respect to the transmission wave of FIG. 2;

FIGS. 4A and 4B show received waveforms viewed on a time axis, wherein FIG. 4A shows a waveform without a tag, FIG. 4B shows a waveform with a tag, and FIG. 4C shows a difference component between the waveform without a tag and the waveform with a tag. .

FIGS. 5A and 5B are explanatory diagrams of transmission waveforms according to the second embodiment, wherein FIG. 5A shows a phase characteristic and FIG. 5B shows a combined time axis characteristic.

FIG. 6 is a flowchart of a DSP internal process of a receiving apparatus that receives the transmission waveform of FIG. 6;

FIG. 7 is a block diagram of an article detection device according to a third embodiment.

FIG. 8 is an explanatory diagram showing a change in the reception waveform of FIG. 7;
(A) is a frequency axis waveform, and (b) is a time axis waveform.

FIG. 9 shows the fourth embodiment, and is an explanatory diagram in a case where two article detection devices are arranged.

[Explanation of symbols]

1 .... Transmission device, 2 .... Reception device, 8 .... Transmission antenna, 9 ... Reception antenna, 14 .... Averaging processing circuit, 25..Tag

Claims (6)

[Claims] 1. A tag having a resonance circuit incorporated therein is attached to an article, and when the article passes between a transmitting antenna and a receiving antenna arranged opposite to each other, the resonance is generated by a radio wave transmitted from the transmitting antenna. The circuit resonates, and the receiving circuit receives the re-radiated radio wave by the resonance circuit re-radiating the radio wave, and in the article detection device that detects the passage of the article, the transmitting antenna outputs a plurality of radio waves simultaneously. An article detection device, comprising: a receiving device for detecting all of the re-radiated radio waves emitted by the resonance circuit by the radio waves of the receiving antenna. 2. The article detecting apparatus according to claim 1, wherein the transmitting apparatus outputs the radio waves transmitted from the transmitting antenna with the initial phases thereof being matched. 3. The article detection apparatus according to claim 1, wherein the transmitting apparatus outputs the radio waves with their phases shifted so that the maximum amplitude of a plurality of radio waves output from the transmitting antenna is substantially minimized. 4. The article detection device according to claim 3, wherein the receiving device calculates a phase amount of each radio wave received by the receiving antenna and corrects a phase of each radio wave by the phase amount. 5. The article detecting apparatus according to claim 1, wherein the receiving apparatus has a filter for removing a radio wave having a frequency between the transmission radio waves. 6. The article detecting device according to claim 5, wherein the entire transmission frequency can be offset by a predetermined amount.