CN1292390C - Digital electronic label detector and its detection method - Google Patents

Abstract

The invention relates to a detection method of a digital electronic label used in an Electronic Article Surveillance (EAS) system, which uses digital signal processing technology to analyze and identify the detected signal to replace the traditional analog label The detection circuit increases the detection distance of the EAS system and reduces the false alarm rate of the EAS system.

Description

Detection method of digital electronic label

technical field

The invention relates to an electronic detection method, in particular to a digital electronic label detection method used in an Electronic Article Surveillance (EAS) system.

technical background

With the rise of large commodity sales centers such as supermarkets, the open-shelf sales model has gradually become the mainstream model of commodity sales. Compared with the traditional over-the-counter sales model, open-shelf sales allow customers to freely choose their favorite products without going through the waiters, which not only provides customers with a free and relaxed shopping environment, but also reduces the required staff and reduces operating costs. the cost of. But on the other hand, open-shelf sales also greatly increase the possibility of merchandise theft.

Electronic Article Surveillance (EAS) system is an electronic detection system widely used in shopping malls to prevent theft. It is usually installed at the exit of shopping malls. By detecting the electronic tags on unpaid goods, it can effectively prevent loss of merchandise. But in the traditional EAS system, the detection of the electronic tag is completed by using an analog circuit. Due to the limitations of the analog method, it is difficult for the tag detection circuit of the traditional EAS system to accurately analyze and identify the detected signal. In the case of interference, metal objects knocking on the antenna, or touching the antenna with hands, the traditional analog EAS system may generate an alarm, which may easily cause disputes between shopping malls and customers.

Contents of the invention

The purpose of the present invention is to provide a digital electronic label detection method for Electronic Article Surveillance (EAS) system in view of the shortcomings of the traditional analog EAS system, such as small detection range and high false alarm rate, using digital signal processing Technology to analyze and identify the detected signal to replace the traditional analog tag detection circuit, increase the detection distance of the EAS system, and reduce the false alarm rate of the EAS system.

In order to clearly describe the method of the present invention, the devices used in the method of the present invention are firstly introduced here.

The connection relationship between the digital electronic label detection device adopted by the present invention and other parts of the EAS system is shown in Figure 1, where the dotted line part is the device of the present invention. The device is installed between the receiving antenna and the alarm circuit, its input end is connected with the signal output end of the receiving antenna, and its output end is connected with the input end of the alarm circuit. The function of the device is to detect the signal output by the antenna, and if the tag signal is detected, an alarm signal will be sent to the alarm circuit.

The structure of the digital electronic label detection device of the present invention is shown in the dotted line in Figure 2, and is mainly composed of a digital signal processor, a filter, an A/D converter, a switch array, and a drive circuit, and its connection relationship is: filter The output terminal of the A/D converter is connected with the signal of the input terminal of the A/D converter; the output terminal of the A/D converter is connected with the signal of the digital signal processor; the switch array is connected with the signal of the digital signal processor; the input of the digital signal processor and the driving circuit Terminal signal connection;

The output end of the drive circuit is externally connected to the alarm circuit through the signal line; the input end of the filter is externally connected to the receiving antenna through the signal line.

An A/D converter is an analog/digital converter.

The digital signal processor is the core of the whole system. Its main function is to analyze the antenna output signal after filtering, sampling and quantization to determine whether it is a tag signal. If a tag signal is detected, an alarm signal will be sent. In addition, digital signal processing The filter also sets the operating frequency of the system, soft/hard tag selection and other parameters according to the switch settings; the function of the filter is to filter out frequency components and anti-aliasing in the antenna output signal that are not related to tag detection; A/D conversion The function of the device is to convert the input analog signal into a digital signal; the function of the switch array is that different switch settings represent different system working parameter settings; the function of the driving circuit is to provide a drive for the alarm signal output by the digital signal processor.

As shown in Figure 3, the method that the device provided by the present invention is used to detect digital electronic tags comprises the following steps:

(1) Use a filter to filter the antenna output signal, filter out frequency components and anti-aliasing that are not related to label detection, and use an A/D converter to convert the filtered signal into a digital signal and input it to a digital signal processor;

(2) In the digital signal processor, the input signal after filtering, sampling and quantization is divided into frames, and the setting of the frame length should ensure that one frame can contain several modulation signal cycles;

(3) Periodic detection and period estimation are performed on the input signal of the current frame. If the input signal is not periodic or the period is not the same as the modulation period set by the switch array, the current frame is judged to be a non-label signal and transferred to Step (5);

(4) Extract the characteristics of the input signal, load the corresponding label template according to the label type set by the switch array, and compare it with the characteristics of the input signal, if there is a significant difference, then judge that the current frame is a non-label signal, otherwise judge the current frame The frame is a tag signal;

(5) Carry out joint judgment according to the judgment results of the current frame and the previous several frames, if the judgment result of most frames is a tag signal, then output an alarm signal to the drive circuit;

(6) Update the stored past frame parameters, and go to step (1) to continue.

Wherein, the periodicity detection and periodical estimation of the input signal in step (3) may adopt an autocorrelation method, an average amplitude difference method or a combination of the two.

The input signal characteristics described in step (4) can use adaptive filter coefficients, second-order moments, high-order statistics or their combination.

Compared with the prior art, the present invention has the following advantages:

1. Using digital signal processing technology to analyze and identify the detected signals can effectively increase the detection distance of the EAS system and significantly reduce the false alarm rate of the system.

2. By modifying the setting of program parameters in the digital signal processor, the working parameters such as modulation frequency and label type can be adjusted, which has good compatibility.

3. The upgrade of the system can be realized by replacing the label detection program with better performance, no need to redesign the circuit, easy to operate, and save the cost of system upgrade.

Description of drawings

Fig. 1 is the connection diagram of the digital electronic tag detection device provided by the present invention and other components of the EAS system;

Fig. 2 is a circuit block diagram of the digital electronic label detection device of the present invention;

Fig. 3 is the flow chart that the digital electronic label detection device of the present invention is used for label detection;

Fig. 4 is the schematic circuit diagram of embodiment;

Fig. 5 is a flow chart of the main program of the embodiment.

5. Specific implementation

A specific embodiment of the present invention is as follows:

(1) Hardware: The schematic circuit diagram of the embodiment is shown in FIG. 4 , wherein IC1 is a digital signal processor chip, and IC2 is an A/D conversion chip. Digital signal processing chip is the key part of label detection, there are many choices, such as TI's 16-bit DSP chip TMS320C5409, AD's ADSP2181, etc.; A/D chip can use 320AC36; filter can be realized by Butterworth filter ; The driving circuit can be realized by using an operational amplifier circuit; the switch array can be realized by using a micro switch array.

(2) Software: the software of the present invention mainly refers to the label detection program running in the digital signal processor, and the program flow chart of the embodiment is as shown in Figure 5.

After starting up and powering on, first perform initialization work, including setting the modulation frequency, label type and other parameters in the detection program according to the switch setting, setting the input buffer of the signal (the buffer size is the length of one frame of data), etc. After completing the above work, enter the main program loop.

In the main program loop, the buffer full flag is continuously detected. When the buffer full flag is detected, it means that a frame of input data has been received, and the label detection process is entered.

During the tag detection process, firstly, the current frame data is periodically detected and estimated. This embodiment adopts the autocorrelation method, and the average amplitude difference method or a combination of the two methods can also achieve the same function. When the periodicity and period of the signal do not meet the requirements of the tag signal, it is judged that the current frame is a non-tag signal, and enters the joint judgment stage. When the periodicity and period of the signal meet the requirements of the label signal, the characteristics of the signal are extracted and compared with the set label template to obtain the judgment result of this frame. In this embodiment, the characteristic of the signal adopts adaptive filter coefficients, and second-order moments, high-order statistics or their combination can also realize the same function. Joint judgment is performed according to the judgment results of the current frame and the previous several frames. If the judgment results of most frames are tag signals, an alarm signal is output to the driving circuit.

After completing the label detection process, update the data saved in the past, and return to the beginning of the main program loop, waiting for the input of new data.

(3) Installation: After making the circuit board, writing and storing the software program, the present invention can be connected to the EAS system as shown in Figure 1, and its installation position can be similar to that of the label detection circuit in the traditional analog EAS system The way is to install it on the base of the antenna and add a metal casing for protection. The output end of the antenna and the input end of the alarm circuit are respectively connected to the input end and the output end of the present invention.

Claims (3)

1, a kind of detection method of digital electric subtab is characterized in that may further comprise the steps:

(1) use wave filter that antenna output signal is carried out filtering, filtering and label detect irrelevant frequency component and anti-aliasing, and filtered signal is converted to digital signal supplied with digital signal processor with A/D converter;

(2) in the digital signal processor, the input signal after filtering, sampling and quantification is carried out the branch frame handle, the setting of frame length should guarantee that a frame can comprise several modulation signal cycles;

(3) input signal of present frame is carried out periodicity detects and the cycle is estimated, inequality if input signal does not have the modulation period that periodicity or cycle and switch arrays sets, then adjudicating present frame is non-label signal, and forwards step (5) to;

(4) feature of extraction input signal, the tag types that sets according to switch arrays loads corresponding tag template, and compares with the feature of input signal, if marked difference is arranged, then adjudicating present frame is non-label signal, otherwise the judgement present frame is a label signal;

(5) court verdict of counting frame according to present frame and front carries out cascading judgement, is label signal as the court verdict of most frames, and then output alarm signal is to driving circuit;

(6) upgrade the past frame parameter of being deposited, forward step (1) to and proceed;

Realize that the digital electronic tag detection device that described method adopts is is mainly connected and composed jointly by digital signal processor, wave filter, A/D converter, switch arrays, driving circuit, its annexation is: the output terminal of wave filter is connected with the input end signal of A/D converter; The output terminal of A/D converter is connected with the digital signal processor signal; Switch arrays are connected with the digital signal processor signal; Digital signal processor is connected with the input end signal of driving circuit;

The output terminal of driving circuit is by the external warning circuit of signal wire; The input end of wave filter is by the external receiving antenna of signal wire.

2, method according to claim 1 is characterized in that input signal cycle detection and cycle estimation employing correlation method, average amplitude difference method or both combinations in the step (3).

3, method according to claim 1 and 2 is characterized in that the input signal feature described in the step (4) adopts adaptive filter coefficient, second moment, high-order statistic or their combination.

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