CN110907890B - RFID smart shelf item misplacement detection method - Google Patents

Abstract

The invention discloses a method for detecting misplacement of goods on an RFID intelligent goods shelf, and belongs to the technical field of goods shelf detection. According to the invention, a plurality of readers are arranged at fixed positions to acquire tag data, the positions of the readers are optimized to maximize the difference value of the acquired phase data, the acquired phase values are effectively processed by unwrapping and the like, then system errors are estimated to solve the problem of equipment diversity, and finally, the phase measurement value is compared with the theoretically calculated phase value and whether the phase difference value changes or not is observed to detect whether the position of the placed article changes or not, so that the effective supervision of the position of the article on the shelf and the detection of the misplacement of the article are realized. The method is used for monitoring and managing the position of the goods on the goods shelf for placing the goods with the RFID labels, monitors and manages the position of the goods in real time, and is a reliable, efficient and accurate intelligent goods shelf goods misplacement detection method.

Description

RFID smart shelf item misplacement detection method

technical field

The invention belongs to the technical field of shelf item detection, and in particular relates to an RFID intelligent shelf item misplacement detection method.

Background technique

Smart shelves are one of the important applications of RFID indoor location awareness. The use of RFID location awareness technology to build smart shelves has greatly reduced labor costs. Now with the continuous increase of item resources, the need to monitor items makes the demand for smart shelves in various fields continue to increase, especially in the field of warehousing and logistics management. and unmanned supermarkets. In particular, there is a need for a smart shelf that can sense the location information of each item in a timely and accurate manner. Previously, the management of smart shelves was still based on active RFID tags, which was expensive and inconvenient to use. Therefore, most of them can only be used for the perception and monitoring of valuables such as artworks and luxury goods. For shopping malls and large shopping malls. There are many kinds of commodities and the scene with large circulation cannot be satisfied. Therefore, the present invention develops a set of smart shelves for real-time monitoring of items by researching the position sensing technology of indoor objects and utilizing RFID technology.

A huge challenge for smart shelves is to be able to monitor the position of items in real time. Usually, the methods of positioning by absolute position or relative position can be divided into dynamic and static. Dynamic tracking requires the movement of radio frequency tags or antennas to observe changes in time-series RF (Radio Frequency), while static positioning requires pre-collecting the Received Signal Strength (RSS) distribution by arranging a large number of reference tags or using expensive equipment (multi-reader antenna or synthetic aperture radar) to analyze the difference in phase. In addition, there are some limitations when using them in real life to detect misplaced labels on smart shelves. Mobile readers and tags are time-consuming and labor-intensive, because the items on the shelf are mostly static, and the complex and expensive equipment is not suitable for large-scale placement.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for detecting misplacement of RFID smart shelf items in view of the above-mentioned problems. The invention identifies the phase shift caused by the misplacement of the item by matching the phase measurement value between the antenna (tag reader antenna) and the tag and its theoretical value, thereby realizing the detection of misplacement of the item.

The RFID smart shelf article misplacement detection method of the present invention comprises the following steps:

Step 1: Deploy a plurality of tag readers around the shelves where the items with RFID tags are placed to collect the tag data of the RFID tags;

Based on the preset coordinate origin O, determine the position of the antenna of the tag reader and the arrangement position of each RFID tag on the shelf;

Step 2: Set the detection threshold for misdischarge detection:

即天线A_s分别采集到标签T_i和T_j的相位理论值的相位偏移；Arbitrarily select the antenna A _r of a tag reader as the reference antenna, form a tag pair for any two RFID tags T _i and T _j , exchange the arrangement position of the tag pair, and calculate the antenna A for each tag reader after the exchange Phase offset of _s

That is, the phase offset of the theoretical phase values of the tags T _i and T _j collected by the antenna A _s respectively;

in,

表示坐标原点O到标签T_i的向量，

表示坐标原点O到天线A_r的向量，

表示参考天线A_r到天线A_s的向量，

表示坐标原点O到标签T_j的向量；即分别将标签、天线的位置作为一个点所得到的两点之间的向量。λ is the wavelength,

represents the vector from the coordinate origin O to the label T _i ,

represents the _vector from the coordinate origin O to the antenna Ar,

represents the _vector from the reference antenna _Ar to the antenna As,

Represents the vector from the coordinate origin O to the label T _j ; that is, the vector between the two points obtained by respectively taking the position of the label and the antenna as a point.

中的最大者作为当前标签对相对于当前参考天线A_r的相位偏移

For each tag pair, take all phase offsets

The largest of them is used as the phase offset of the current tag pair relative to the current reference antenna _Ar

中的最小相位偏移作为当前参考天线A_r的标签误放最小相位偏移

and offset the phase of all tag pairs under the current reference antenna _Ar

The minimum phase offset in the current reference antenna _Ar is used as the minimum phase offset of tag misplacement

即对应的参考天线位置为最优位置；The antennas of all tag readers are used as reference antennas respectively, and the maximum of the minimum phase offsets of tag misplacement is taken as the detection threshold of misplacement detection, denoted as

That is, the corresponding reference antenna position is the optimal position;

Step 3: Based on the phase measurement value of the RFID tag currently collected by the antenna of the tag reader, the misplacement detection process is performed on the item:

对各相位测量值

进行校正处理，得到相位测量值

的校准值

若

小于

则

否则，

其中，下标i为RFID标签的区分符，上标s为标签阅读器的天线区分符；Estimated value of systematic error based on tag reader _'s antenna As

For each phase measurement

Perform correction processing to obtain phase measurements

calibration value of

like

less than

but

otherwise,

Among them, the subscript i is the identifier of the RFID tag, and the superscript s is the antenna identifier of the tag reader;

并根据公式

得到标签T_i的相位偏移的估计值

For any item to be detected by _misplacement , based on the distribution position of the RFID tag Ti attached to the item, calculate the theoretical phase value of the tag _{Ti collected} by the antenna As of each tag reader.

and according to the formula

get an estimate of the phase offset of the label T _i

大于或等于检测门限

则判定标签T_i对应的物品存在误放；If the estimated value

greater than or equal to the detection threshold

Then it is determined that the item corresponding to the label T _i is misplaced;

为：

λ表示波长，

表示天线A_s与标签T_i之间的距离，K为预置的整数；Among them, the theoretical phase value of any tag T _i collected by any antenna A _s

for:

λ is the wavelength,

Indicates the distance between the antenna _As and the label _Ti , and K is a preset integer;

的设置方式为：An estimate of the systematic error of the tag reader _'s antenna As

is set as:

p为参考标签区分符；Place a certain number of reference labels T _p , and calculate the theoretical phase value of the reference labels T _p collected by each antenna _As

p is the reference label specifier;

确定对应各参考标签的系统误差

若理论相位值

大于相位测量值

则

否则

The phase measurement value of each reference tag T _p collected based on the antenna A _s

Determine the systematic error corresponding to each reference label

If the theoretical phase value

greater than the phase measurement

but

otherwise

的均值作为天线A_s的系统误差的估计值

For the same antenna A _s , take the systematic errors corresponding to all reference labels

The mean value of is used as an estimate of the systematic error of the antenna A _s

其中系数α的取值范围为：

Further, the detection threshold of mis-discharge detection can also be set as

The value range of the coefficient α is:

作为粒子的适应值进行粒子群算法查找参考天线的最优位置，得到最优参考天线；并基于最优参考天线对应的标签误放最小相位偏移

设置误放检测的检测门限为

其中系数α的取值为1或

Further, in order to reduce the calculation amount of the reference antenna for finding the optimal position, the label of the reference antenna _Ar can also be misplaced with a minimum phase offset.

As the fitness value of the particle, the particle swarm algorithm is used to find the optimal position of the reference antenna, and the optimal reference antenna is obtained; and the minimum phase offset of label misplacement corresponding to the optimal reference antenna is obtained.

Set the detection threshold for misdischarge detection as

where the coefficient α takes the value 1 or

To sum up, due to the adoption of the above-mentioned technical solutions, the beneficial effects of the present invention are:

For the scene to be detected, some items may change positions when they are repositioned. The present invention only realizes the detection of misplaced items through the phase, that is, compares the processed measured value with the calculated theoretical value, and observes whether the phase is deviated. Move to detect misplacement of items. Due to the periodicity of the phase, different locations may have the same phase measurement, resulting in ambiguity. In order to solve the possible ambiguity, the present invention solves the problem by optimizing the deployment position of the antenna to maximize the phase discrimination between any two positions; the phase measurement value may contain one or more 2π jumps, in order to ensure that the phase value does not exceed its In the normal range [0, 2π), the present invention eliminates the influence of 2π jumps with an effective standard by comparing the measured value and the theoretical value; since the antenna may have different positions, the initial phase rotation (even the same type of Antenna), the present invention calibrates the measured value by estimating the system error, and detects the abnormal phase shift to identify the misplaced label.

Description of drawings

Figure 1 is a model diagram of the misplacement detection model of RFID smart shelf items;

Figure 2 is a frame diagram of the misplacement detection of RFID smart shelf items;

3 is a schematic diagram of a moving trajectory diagram of an antenna;

FIG. 4 is a schematic diagram of the initial phase distribution of the same type of antenna.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

The present invention monitors and manages the position of the article in real time for the shelf on which the article with the RFID tag is placed. Since the measured value of the phase information collected from the tag does not seem to be related to the theoretical value without special processing, the existing RFID-based object detection processing hardly considers the error of comparing the measured value with the theoretical value. However, the RFID smart shelf article misplacement detection method of the present invention collects the phase information of the label through a high-frequency reader, and detects the misplacement by comparing the measured value with the theoretical calculation value, that is, by comparing the phase measurement value. Processing is performed to make it consistent with the theoretical value, that is, the matching of the measured value and the theoretical value is realized, and then the phase shift caused by the misplacement of the item is identified, so as to realize the detection of the misplacement of the item. The invention solves the problems of position ambiguity, winding and equipment diversity existing in the label, and is a cost-effective and real-time detection method.

The main steps of the misplacement detection process of the present invention are as follows:

By optimizing the deployment position of the reader antenna, maximizing the discrimination between the two positions and solving the ambiguity of the position;

Acquire data and detect and correct phase wrapping on phase measurements;

The measured value is calibrated by estimating the systematic error to solve the problem of initial phase inconsistency caused by equipment diversity;

The processed measurements are compared with the theoretical values, and misplacement is detected by observing whether the phase is shifted.

Referring to Figure 1, the misplacement detection of items can be regarded as a special static positioning, assuming that the tags are placed on a series of fixed points, such as the clothing racks shown in Figure 1, each of which is provided with RFID tags (Tag ), some of the hangers were misplaced (Misplaced Tag shown in Figure 1). In order to realize the detection of misplaced items, the key processing of the present invention lies in: calibrating the measured phase value and detecting the abnormal phase shift caused by the misplacement of the item, instead of tracking the change of the phase, so there is no need to assume that the initial State All labels are placed in the correct position, that is, the initial state of the label is not required to be in its placement position.

Referring to Fig. 2, the article misplacement detection processing process of the present invention includes three parts, input, misplacement detection and output.

Among them, the input includes the tag ID, such as EPCxxx0001~0004 as shown in Figure 2, as well as the phase measurement value (θ) and the distribution of tags, that is, the arrangement position of each tag;

Misplacement detection consists of three stages: ambiguity resolution, phase unwrapping, and outlier detection.

The output then contains the tag ID and the location of the misplaced tag.

Among them, the location ambiguity, phase unwrapping and outlier detection involved in misplacement detection are as follows:

(1) The ambiguity of location.

表示从天线A_s(位置信息为(x^s,y^,s,z^s)，可记为A_s(x^s,y^,s,z^s))采集到的标签T_i(位置信息为(x_i,y_i,z_i)，可记为T_i(x_i,y_i,z_i))的理论相位值，其中i∈[1,n]，s∈[1,m]。Define the number of antennas as m, the number of tags as n, and define

Represents the label T _i collected from the antenna As (the position information is (x ^s , y ^{, s} , z ^s ), which can be recorded as A _s (x _s , y ^{, s ,} z ^s )) _i , y _i , z _i ), can be denoted as the theoretical phase value of T _i (x _i , y _i , z _i )), where i∈[1,n], s∈[1,m].

The calculation formula of the theoretical phase value (or the theoretical phase value) is shown in formula (1):

理论值Θ就变化一个周期。Among them, λ represents the wavelength, d represents the distance between the antenna and the tag, and K is an integer. That is, the theoretical value Θ is a function with a period of 2π, and the distance d between the antenna and the tag changes every time

The theoretical value Θ is changed by one cycle.

And the phase measurement θ contains a systematic error μ, defined as:

Among them, k is an integer, the systematic error μ=(θ _TAG + θ _ANT ) mod 2π, θ _TAG and θ _ANT are the additional phase shifts at the transmitting end and the receiving end of the reader antenna caused by the reflection characteristics of the tag, respectively.

是由A_s和T_i之间的距离

决定的，即

为达到部署的目的，假设天线阵列的拓扑是固定的，如图3所示，定义一个任意的天线A_r(坐标位置为(x^r,y^r,z^r))作为天线阵列的参考点。则向量

可以表示为：From formula (1), it can be known that,

is the distance between A _s and T _i

decided, that is

For the purpose of deployment, it is assumed that the topology of the antenna array is fixed, as shown in Figure 3, an arbitrary antenna _Ar (coordinate position is (x ^r , y ^r , z ^r )) is defined as the reference point of the antenna array. then the vector

It can be expressed as:

与商店(误放检测应用的场景)的布局有关，通常都是不会改变的。

依赖于固定不变的天线的相对位置。因此，

仅与

有关，即意味着

可以被视为

的函数，表示为

Among them, point O represents the origin of coordinates,

Related to the layout of the store (scenario for misplacement detection applications), it usually doesn't change.

Depends on the relative position of the fixed antenna. therefore,

only with

related, means

can be regarded as

function, expressed as

然后可以得到

因为

和

都是不变的，如果

的值已经测出来，那么

As shown in Figure 3, the antennas _Ar and As are translated without _rotation . _Ar and As are treated as rigid bodies, if _{Ar moves} towards position _Ar ', A _s will reach A _s ', such that

then you can get

because

and

are unchanged, if

The value of has been measured, then

考虑到有m个天线，定义由T_i和T_j的交换造成的相位偏移为

表示为：For any two labels T _i and T _j , if their positions are swapped, the magnitude of the phase offset for each of them

Considering that there are m antennas, define the phase shift caused by the exchange of T _i and T _j as

Expressed as:

则结合式(1)的理论相位值的表达式可得：where s∈[1,m]. because

Then combined with the expression of the theoretical phase value of formula (1), we can get:

基于标签T_i和T_j的布置位置获得，向量

基于参考点的天线A_r的位置获得，向量

基于天线A_s与天线A_r的相对位置获得。where the vector

Obtained based on the arrangement positions of the labels T _i and T _j , the vector

The position of the antenna Ar based on the reference point is obtained, the _vector

_{Obtained based on the relative position of the antenna As and the antenna Ar .}

种这样的组合。计算出每一对标签的

定义由标签误放造成的最小的相位偏移为

表示为：In fact, you can choose two different labels and swap their positions, a total of

such a combination. Calculate the value of each pair of labels

The minimum phase shift caused by label misplacement is defined as

Expressed as:

Among them, i∈[1,n), j∈(i,n].

以实现最大最小公平分配并且避免错误结果。then maximize

In order to achieve maximum and minimum fair distribution and avoid false results.

)。具体步骤如下：Further, in order to reduce the amount of computation, the present invention can use the particle swarm algorithm to find the optimal position of Ar ( _ie

). Specific steps are as follows:

(a) Randomly initialize the particle swarm in space.

作为粒子的适应值。(b) Calculate the fitness value of each particle according to formula (5), namely

as the fitness value of the particle.

(c) Update the position of the particle according to the fitness value.

(d) If the maximum number of iterations is reached or the global optimal position satisfies the preset _lowermost limit, the optimal position of Ar has been found, otherwise, go to b) to continue execution.

作为粒子的适应值。That is, the present invention uses the existing particle _swarm algorithm to find the optimal position of Ar, and in the process of searching, the

as the fitness value of the particle.

(2) Phase unwinding.

表示从天线A_s采集到的标签T_i的相位测量值，

表示由标签T_i和天线A_s产生的系统误差。将公式(1)与公式(2)相减可得：The process of phase unwrapping is to bring a wrapped phase into the "correct" form, free from the effects of 2π jumps. use

represents the phase measurement of the tag _{Ti collected} from the antenna As,

represents the systematic _error produced by the tag _Ti and the antenna As. Subtract formula (1) and formula (2) to get:

有

考虑到该差值的符号，会存在以下两种情况：because

Have

Considering the sign of this difference, there are two cases:

即满足

(1)

that is satisfied

即满足

(2)

that is satisfied

Combining formulas (7) to (9), we can get:

解缠绕后的值为

则：definition

The unwrapped value is

but:

的变化与

是一致的，这意味着

和

具有很强的线性关系。由

这个结果表明

是一个相对稳定的值。According to formula (11), it can be known that,

changes with

is consistent, which means

and

has a strong linear relationship. Depend on

This result shows that

is a relatively stable value.

(3) Outlier detection.

的值来校准

对式(11)进行重写计算

Referring to the schematic diagram of the initial phase distribution of the same type of antenna given in FIG. 4 , it can be known that the same type of antenna may have different initial phase deflections. Before detecting misplaced labels, estimate

value to calibrate

Rewrite the formula (11) to calculate

是一个稳定的值，本具体实施方式中，通过放置l个参考标签(参考标签的放置位置可以在标签的n个布置位置上选择)以简化操作，估计系统误差

(系统误差的估计值)，其表达式如下：Because it has been demonstrated,

is a stable value. In this specific embodiment, by placing l reference labels (the placement position of the reference label can be selected from the n placement positions of the labels) to simplify the operation, the systematic error is estimated

(estimated value of systematic error), its expression is as follows:

代替

校准

则

的校准值

可以定义为：Among them, p∈[1,l], l<<n. then use

replace

calibration

but

calibration value of

can be defined as:

是一个真实的值，考虑到两种情况：Assuming that _Ar is in the optimal position,

is a real value, considering two cases:

1) If _Ti is in the correct position, then

2) If T _i is at the position of T _j ', then

为：Define the estimated value of _Ti phase offset

for:

where s∈[1,m], and then the misplacement of T _i is detected by equation (16):

That is, if Equation (16) is satisfied, then there is misplacement in T _i , otherwise, there is no misplacement.

In Equation (16), α represents a coefficient that controls the error rate. In theory, α can be set to 1 in order to cover the worst-case conditions.

In addition, a larger α can also be selected to further reduce the false positive rate, that is, the value range of the coefficient α is set to:

The present invention collects tag data by deploying a plurality of readers (tag readers) in a fixed position, optimizes the position of the readers to maximize the difference value of the collected phase data, unwinds the collected phase value, etc. Process, then estimate the system error to solve the problem of equipment diversity, and finally compare the phase measurement value with the theoretically calculated phase value and observe whether the phase difference value changes to detect whether the position of the item has changed, so as to realize the item on the shelf. Effective supervision of location and detection of misplaced items. It can realize the monitoring of the items with the UHF tags on the shelf in the UHF RFID environment, so that the misplaced items in the scene to be monitored can be detected in real time.

The above descriptions are only specific embodiments of the present invention, and any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or All steps in a method or process, except mutually exclusive features and/or steps, may be combined in any way.

Claims (4)

1. The method for detecting the misplacement of the RFID intelligent goods shelf is characterized by comprising the following steps:

   step 1: a plurality of tag readers are arranged at the periphery of a goods shelf on which goods attached with RFID tags are placed and used for collecting tag data of the RFID tags;

   determining the position of an antenna of a tag reader and the arrangement position of each RFID tag on the shelf based on a preset coordinate origin O;

   and 2, step: setting a detection threshold of misplacement detection:

   antenna A of arbitrarily selected tag reader _r As a reference antenna, for any two RFID tags T _i And T _j Forming tag pairs, exchanging the arrangement positions of the tag pairs, and calculating the antenna A of each tag reader after exchange _s Phase shift of

   

   Namely an antenna A _s Respectively acquire the labels T _i And T _j Phase offset of the phase theoretical value of (a);

   wherein,

   

   the x is a wavelength at which,

   

   representing origin of coordinates O to label T _i The vector of (a) is determined,

   

   representing origin of coordinates O to antenna a _r The vector of (a) is determined,

   

   denotes a reference antenna A _r To antenna A _s Vector of (2)，

   

   Representing origin of coordinates O to label T _j The vector of (a);

   for each pair of labels, all phase offsets are taken

   

   As the current tag pair with respect to the current reference antenna a _r Phase shift of

   

   And will be currently referenced to antenna a _r Phase shift of all tag pairs under

   

   As the current reference antenna a _r Tag misplacement minimum phase offset of

   

   Taking the antennas of all the tag readers as reference antennas respectively, and taking the maximum of the minimum phase offsets of the misplaced tags as a detection threshold of the misplaced detection, and recording the detection threshold as

   

   And step 3: carrying out misplacement detection processing on the article based on the phase measurement value of the RFID label currently acquired by the antenna of the label reader:

   antenna A based on label reader _s Of the system error of

   

   For each phase measurement

   

   Performing correction processing to obtain phase measurement value

   

   Calibration value of

   

   If it is

   

   Is less than

   

   Then

   

   If not, then,

   

   the subscript i is an identifier of the RFID label, and the superscript s is an antenna identifier of the label reader;

   for any one article to be misplaced and detected, based on the RFID label T attached to the article _i The distribution position of each tag reader, and the antenna A of each tag reader _s Respectively collected labels T _i Theoretical phase value of

   

   And according to the formula

   

   Obtain the label T _i Estimate of the phase offset of

   

   If the estimated value is

   

   Greater than or equal to the detection threshold

   

   Then the label T is judged _i Misplacing the corresponding article;

   antenna A of tag reader _s Of the system error of

   

   The setting mode is as follows:

   placing a certain number of reference tags T _p And calculates each antenna A _s Acquired reference tag T _p Theoretical phase value of

   

   Based on an antenna A _s Collected reference labels T _p Measured phase of

   

   Determining systematic errors corresponding to each reference tag

   

   If the theoretical phase value

   

   Greater than the phase measurement

   

   Then

   

   Otherwise

   

   For the same antenna A _s Taking the corresponding systematic error of all reference labels

   

   As the mean value of the antenna A _s Of the system error of

   
2. 2. The method of claim 1, wherein in step 2, the step of converting the signal into a signal comprises converting the signal into a signal

   

   The corresponding antenna is used as the optimal reference antenna, and the detection threshold of the misplacement detection is set as

   

   Wherein the value range of the coefficient alpha is as follows:

   

   

   representing the mean of the phase shifts of all tag pairs relative to the optimal reference antenna.
3. 3. The method of claim 1, wherein in step 2, the detection threshold for the misplacement detection is determined by a particle swarm algorithm:

   will refer to antenna A _r Tag misplacement minimum phase offset of

   

   Performing a particle swarm algorithm to search the optimal position of the reference antenna as the adaptive value of the particle to obtain the optimal reference antenna;

   and based on the minimum phase deviation of the label misplacement corresponding to the optimal reference antenna

   

   Setting a detection threshold for the misplacement detection to

   

   Wherein the coefficient alpha takes the value 1 or

   

   

   Representing the mean of the phase shifts of all tag pairs relative to the optimal reference antenna.
4. 4. The method of claim 1, wherein in step 2, a number of reference tags T are placed at the placement positions of the RFID tags _p 。

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