CN113128650A - Wire collision detection method - Google Patents
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Abstract
The application provides a wire collision detection method, which is based on an RFID technology to realize wire collision detection. The process of realizing wire collision detection based on the RFID technology is as follows: giving a detection boundary line, and arranging an RFID antenna at least one end of the detection boundary line; reading the phase of a target object RFID tag through an RFID antenna, and acquiring a phase-time diagram of the target object RFID tag in the whole time, wherein the phase value on the phase-time diagram is the sum of the phases of the target object RFID tags read by all the RFID antennas; and identifying the inflection point with the minimum phase value in the phase-time diagram, wherein the time stamp of the inflection point is supposed to correspond to the occurrence of the line collision time of the target object. Compared with the existing common line collision detection methods such as an infrared sensor, a camera and a virtual wall, the method can effectively detect the condition that a plurality of target objects collide simultaneously, and can identify the normal line collision and abnormal conditions of the target objects.
Description
Technical Field
The application relates to the field of intelligent detection systems, in particular to a wire collision detection method.
Background
The wire collision detection is a process of detecting whether an object passes a preset boundary line, and the wire collision detection technology is widely applied to the fields of warehouse management, article transportation, safety alarm and the like.
The existing common wire-strike detection methods include the following methods: infrared sensor, camera and virtual wall. The infrared sensor identifies the object by using infrared light emitted by the object; the camera identifies the object by using an image processing algorithm; virtual walls are formed by plasma laser projection, often used in the robotic field, and are used to identify objects.
Although the existing line collision detection methods have respective advantages, they have some defects, for example, when multiple objects collide simultaneously, because the objects are shielded from each other, the existing line collision detection methods cannot identify the condition, and the detection result is unqualified.
Disclosure of Invention
The application provides a wire collision detection method, which aims to solve the problem that a plurality of objects are difficult to identify when colliding with wires simultaneously in the prior art.
The application provides a wire collision detection method, which is based on an RFID (Radio Frequency Identification) technology to realize wire collision detection.
In one embodiment, the process of implementing wire-strike detection based on RFID technology is as follows:
giving a detection boundary line, and arranging an RFID antenna at least one end of the detection boundary line;
reading the phase of a target object RFID tag through an RFID antenna, and acquiring a phase-time diagram of the target object RFID tag in the whole time, wherein the phase value on the phase-time diagram is the sum of the phases of the target object RFID tags read by all the RFID antennas;
and identifying an inflection point with the minimum phase value in the phase-time diagram, wherein the inflection point corresponds to the occurrence of line collision of a target object.
In one embodiment, the number of the RFID antennas is one and is directed towards the detection boundary.
In one embodiment, the number of the RFID antennas is two, and the two RFID antennas are respectively located at two ends of the detection boundary line.
In one embodiment, one of the RFID antennas is arranged to face a starting direction of the target object and the other RFID antenna is arranged to face an ending direction of the target object.
In one embodiment, normal wire-strike and pre-wire-strike steering of a target object are distinguished by:
in the moving process of the target object, reading the RFID tag of the target object for n times by the RFID antenna facing the starting direction of the target object, and recording the corresponding time sequence as TA＝tA,1,tA,2…,tA,n|ti≤tj(i<j≤n)；
Reading the RFID tag of the target object m times by the RFID antenna facing the terminating direction of the target object, and recording the corresponding time sequence as TB＝tB,1,tB,2…，tB,n|ti≤tj(i<j≤m)；
The time when the RFID tag is read at the beginning is denoted as tstart＝min(tA，1,tB,1) And finally, the time of reading the RFID tag is recorded as tend＝max(tA,n,tB,m)；
If tstartAnd tendThe time sequences read by the two RFID antennas are respectively identified as normal wire collision; if tstartAnd tendAnd if the time sequence read by the same RFID antenna belongs to the time sequence read by the same RFID antenna, the direction is determined to be reversed before the wire collision.
In one embodiment, when the target object is stationary at a detection boundary for a long time, the process of identifying an inflection point in the phase-time diagram where the phase value is smallest is as follows:
constructing a sliding window in the phase-time diagram and calculating the entropy E of the phase value in the sliding window, wherein the entropy E of the phase value is defined as follows:
where M represents the number of phase values in the sliding window, piRepresenting the frequency of each phase value;
and setting a threshold, and if E exceeds the threshold, considering that the phase value is changed violently in the sliding window, wherein the point corresponding to the rightmost end of the sliding window is regarded as the inflection point with the minimum phase value.
In one embodiment, each of the RFID antennas is connected to the same reader.
Has the advantages that: compared with the existing common line collision detection methods such as an infrared sensor, a camera and a virtual wall, the light-weight line collision detection method based on the radio frequency identification technology can effectively detect the line collision condition of a plurality of target objects at the same time, and can identify the normal line collision and abnormal conditions of the target objects. Compared with the traditional radio frequency identification positioning method, the required number of the RFID antennas is less, parameters such as specific positions of the RFID antennas and distances between the RFID antennas do not need to be known, the RFID antennas can be directly used in a new scene without being deployed and calibrated in advance, and the time complexity of an algorithm is lower.
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Certain specific embodiments of the present application will hereinafter be described in detail by way of example and not limitation with reference to the accompanying drawings, in which like reference numerals identify the same or similar parts or features, and it will be appreciated by those skilled in the art that the drawings are not necessarily drawn to scale. In the drawings:
FIG. 1 is a schematic diagram of a wire strike detection using an RFID antenna according to an embodiment of the present disclosure;
FIG. 2 is a phase-time diagram of an RFID tag of a target object acquired over time using one RFID antenna in one embodiment of the present application;
FIG. 3 is a schematic diagram illustrating wire-strike detection when two RFID antennas are used in one embodiment of the present application;
FIG. 4 is a phase-time plot of the RFID tag of the target object acquired over time using two RFID antennas in one embodiment of the present application;
FIG. 5 is a schematic diagram illustrating two RFID antennas tilted in orientation according to an embodiment of the present application;
FIG. 6 is a phase-time diagram of a target object at a detection boundary for a long period of time at rest over time in accordance with one embodiment of the present application.
Detailed Description
In order that the manner in which the above-recited objects, features and advantages of the present application are obtained will be readily apparent, a more particular description of the invention briefly described above will be rendered by reference to specific details that are set forth in the appended description, which are indicative of but are capable of being practiced in a variety of ways other than those specifically described herein, and which are readily apparent to those of ordinary skill in the art, and which are therefore not limited to the specific embodiments disclosed below.
The application provides a wire-strike detection method, which is used for realizing wire-strike detection of a target object based on an RFID technology. The process of realizing wire collision detection based on the RFID technology is as follows: a detection boundary line is given, and an RFID antenna is arranged at least at one end of the detection boundary line; reading the phase of the target object RFID tag through the RFID antenna, and acquiring a phase-time diagram of the target object RFID tag in the whole time, wherein the phase value on the phase-time diagram is the sum of the phases of the target object RFID tags read by the RFID antennas; and identifying the inflection point with the minimum phase value in the phase-time diagram, wherein the inflection point corresponds to the occurrence of the line collision of the target object.
The application provides a very simple method for detecting the line collision of an object based on a radio frequency identification technology, wherein the radio frequency identification technology is an automatic identification technology based on a wireless communication technology, and the basic principle of the method is to automatically identify information carried by the identified object by utilizing the coupling transmission characteristics of a radio frequency signal and space. Because the RFID labels on the target objects are different, and the RFID label signals read by the RFID antenna are different, the problem that the objects are difficult to identify when the lines are collided simultaneously can be solved on the basis; in other words, each target object has a specific RFID tag data, and each specific data corresponds to a phase-time diagram, so that when multiple target objects hit a line at the same time, the multiple target objects can be identified without mutual influence.
In addition, only one or two RFID antennas are needed to be arranged on the detection boundary line, the simultaneous line collision detection of a plurality of objects can be realized, and the equipment is very simple to deploy. The existing RFID technology can locate and track an object through multiple RFID antennas, so as to derive a moving track of an RFID tag, and if such a location-based scheme is adopted to detect a wire collision, the following defects are present: the method has the advantages that a plurality of readers are required to be deployed, the positions of the readers are accurately calibrated, the deployment cost is high, a large amount of calculation cost is required, and particularly when multiple targets are detected, the operation burden is heavier.
It should be noted that, when the RFID antenna reads the data of the RFID tag, it also needs to support components such as a reader and a backend server, for example, the RFID antenna is used for transmitting data between the RFID tag and the reader, and the reader is used for transmitting and receiving radio waves to communicate with the RFID tag, which on one hand reads the information of the RFID tag and on the other hand transmits the read result to the backend software, so as to implement data exchange and system management.
The inventor finds that when the target object starts to move from the starting position, passes through the detection boundary and moves to the ending position, the summation of the phases of the RFID tags of the target objects read by the RFID antennae on the phase-time diagram shows very good regularity, namely when the target object passes through the detection boundary, an inflection point with the minimum recognizable phase value is presented on the phase-time diagram, the inflection point corresponds to the occurrence of the line impact of the target object, and the time stamp corresponding to the inflection point can be determined as the line impact time point of the target object.
When the target object normally passes through the detection boundary, the normal passing means that the target object always advances along the preset detection boundary direction and no abnormal condition such as inversion, stationary for a long time at the detection boundary, etc. occurs in the middle, the "inflection point with the minimum phase value" is identified as follows in this application: the "inflection point where the phase value is smallest" is the vertex of the upward opening curve in the phase-time diagram (the bottom where the phase value is smallest), and in this case there are and only 1 upward opening curve in the phase-time diagram, which is one branch of an upward opening hyperbolic curve when an RFID antenna is deployed and the object is in a uniform linear motion perpendicular to the detection boundary. Furthermore, during normal passage, when the target object is stationary for a long time away from the detection boundary, the phase-time diagram corresponds to a relatively flat area, but does not affect the identification of the "inflection point where the phase value is minimal", in other words, there are also and only 1 upward opening curve in the phase-time diagram.
However, when there is an abnormal situation, there may be no upward opening curve or a plurality of upward opening curves in the phase-time diagram, such as: (1) when the target object has the actions of reversing and re-advancing during the movement, although the target object is also a line collision finally, in the process, disturbed upward shedding curves may appear on a phase-time diagram, and each action of reversing and re-advancing corresponds to one disturbed upward shedding curve, but the vertex phase values of the disturbed upward shedding curves are larger, so that the vertex with the minimum phase value of the 'inflection point with the minimum phase value' is determined as the vertex with the minimum phase value of all the upward shedding curves; (2) when the target object is stationary for a long time at the detection boundary, the lower end of the upward opening curve in the phase-time diagram in (1) is not a groove structure without a vertex, but a relatively flat region, in this case, since the curve does not exist, the method of identifying the "inflection point with the minimum phase value" in the phase-time diagram changes, and the corresponding solution is proposed in the following for the case of (2).
A difficulty with wire strike detection based on radio frequency technology is that the effective read range of the RFID antenna is not a straight line, but rather its shape is irregular and unpredictable because the signal from the RFID antenna is susceptible to a variety of factors, such as the design of the RFID antenna, multipath effects, the material carrying the RFID tag object, the surrounding environment, etc. Therefore, the time when the RFID antenna first reads the RFID tag cannot be roughly considered as the time when the wire strike occurs.
When an object carrying the RFID tag moves, the distance between the RFID antenna and the RFID tag changes continuously, which results in a continuous change of a phase value, the phase value reflects the degree of offset between a receiving signal and a transmitting signal of an electromagnetic wave, ranges from 0 to 2 pi, and is a common parameter supported by COTS readers (such as Impinj R420). Assume that the distance between the RFID tag and the RFID antenna is d. Due to the backscatter communication mechanism of radio frequency technology, the total distance traveled by the signal is 2 d. The phase value θ can be expressed as:
where λ is the wavelength, θTX，θRX，θTAGRespectively, the phase inherent offset caused by the transmitting RFID antenna, the receiving RFID antenna, and the RFID tag backscattering the RFID antenna. These offsets may be different for different hardware but will not change as the distance and transmission environment change.
In the following embodiments, how the method in the present application works is described using one RFID tag, and if a plurality of objects carrying RFID tags hit a line at the same time, the collected data can be classified according to the IDs of the RFID tags and the data of each RFID tag can be processed separately, so that the case of multiple RFID tags can be simplified to the case of a single RFID tag.
When the target object moves linearly and the moving direction is perpendicular to the detection boundary line, an RFID antenna may be disposed at one end of the detection boundary line, and the RFID antenna faces the detection boundary line.
Fig. 1 is a schematic diagram illustrating a wire-strike detection when one RFID antenna is used in an embodiment of the present application. In fig. 1, the detection limit is marked as Y-axis, a line perpendicular to the Y-axis is marked as X-axis, the RFID antenna is located at the intersection of one end of the Y-axis and the X-axis, the orientation of the RFID antenna is consistent with the Y-axis, and the target object RFID tag moves in the direction of the arrow.
As the RFID tag moves along the X-axis, the RFID antenna continues to read the RFID tag signal during this process, collecting the phase value and its corresponding timestamp, and the phase-time plot is denoted as
A phase-time plot of the target object RFID tag over time is obtained when one RFID antenna is used as shown in fig. 2. "Whole time" refers to all time periods during which the RFID antenna can read the RFID tag during the entire wire strike.
In fig. 2, the phase value of the RFID tag is initially decreased from 2 pi to 0 repeatedly until the RFID tag moves to a position closest to the RFID antenna, the phase value does not decrease any more, the phase value is minimum when the RFID tag just hits the line, that is, the phase value corresponds to the vertex (inflection point) of the upward opening curve, and then the phase value starts to increase as the RFID tag continues to move away from the detection limit, and the process of increasing from 0 to 2 pi is periodically repeated. Therefore, the change process generates a turning point in the image, and the turning point exactly corresponds to the occurrence of the line impact of the RFID label, and then the time of the line impact of the RFID label can be easily obtained through the time stamp of the turning point. And in fig. 2, the image of the phase-time diagram is symmetrical as the RFID tag moves because as the RFID tag moves, the distance from the RFID tag to the RFID antenna first decreases and then increases, the distance at the time of wire strike reaches a minimum value, and appears as the apex of a curve open to the upper opening on the phase-time diagram.
The above detection of a target object in a linear motion has many and most common application scenarios, such as in the field of conveyor belt transportation, where the transportation of baggage can be detected by deploying an RFID antenna and using the method, which is very convenient and low-cost.
However, when the moving direction of the target object is not a linear movement perpendicular to the detection boundary, the scheme using one RFID antenna is limited. For example, continuing with the example in fig. 1, when the angle between the moving direction of the target object and the detection boundary is not 90 degrees, the closest distance between the target object and the RFID antenna is not on the detection boundary, so that the line impact corresponding to the inflection point in the phase-time diagram is not the target object.
In order to solve the above problem, the number of the RFID antennas may be set to two, and the two RFID antennas may be located at both ends of the detection boundary, respectively, so that the detection of the line impact in which the target object moves in a diagonal manner may be solved, but the detection of the line impact in which the target object moves in a straight line may be also solved in this case of course.
Fig. 3 is a schematic diagram illustrating a wire-strike detection when two RFID antennas are used in an embodiment of the present application. In the figure, another RFID antenna B is added opposite to the RFID antenna a, the RFID antenna a and the RFID antenna B are respectively located at two ends of the detection boundary, and the two RFID antennas are used to simultaneously collect the phase information of the RFID tag, and the dashed oblique line in the figure is the moving direction of the target object. During the movement of the RFID tag, assuming that the distance from the RFID tag to the RFID antenna A and the distance from the RFID antenna B are respectively d1And d2The phase values read are respectively theta1And theta2. Then adding the phases according to equation (1) yields:
FIG. 4 is a graph of phase versus time for the entire time period for acquiring the RFID tag of the target object using two RFID antennas, and FIG. 4 shows the ordinate phase value as θ1And theta2And (4) adding.
In the process of moving the target object, d is known1+d2D is more than or equal to d, wherein d is the distance from the RFID antenna A to the RFID antenna B, and based on the d when the target object is close to the detection boundary line1+d2Will become smaller and smaller, and when the target object hits the line, it is obvious that d1+d2D when d1+d2Minimum, and when the target object is far away from the detection boundary line, d1+d2Will be larger and larger. The image on the phase-time diagram also following the RFID tagThe movement is symmetrical, since d is the time of wire-strike1+d2Reaching a minimum value, which is represented on the phase-time diagram by the apex of an upwardly open curve.
It should be noted that, when the target object does not move along a straight line, such as a curve, the sum of the phase values of the RFID tags read by the two RFID antennas still corresponds to the case where the RFID tag crosses the Y-axis collision line when the sum of the phase values reaches the minimum value, and therefore, the method is suitable for the case where the target object moves along an arbitrary trajectory.
The use of two RFID antennas provides a line-strike detection that is well suited to situations where the target object is moving in an arbitrary trajectory, but when the target object reverses its motion before moving to the detection limit, the RFID tag does not actually strike the line but returns in the original direction. At this time, the phases of the two RFID antennas and the generated phase are very similar to those of fig. 4, and there is also a turning point, and since there is no line collision occurring in the whole time, the turning point actually corresponds to the turning point of the target object, and at this time, if the previous method is adopted, a false judgment is generated. To solve this problem, two RFID antennas are tilted at an angle in the present application, specifically, one RFID antenna is disposed toward the starting direction of the target object, and the other RFID antenna is disposed toward the ending direction of the target object. As shown in fig. 5, which is a schematic diagram of the two RFID antennas being tilted, in fig. 5, it is assumed that the target object moves from left to right with the ARFID antenna toward the starting direction of the lower left target object and the BRFID antenna toward the ending direction of the upper right target object; of course, it can be assumed that the target object moves from right to left, and the starting direction and the ending direction of the target object are reversed at this time.
Based on the arrangement mode of the two RFID antennas with the inclined orientation, the normal line collision and the steering direction before the line collision of the target object are distinguished through the following processes: in the moving process of the target object, reading the RFID tag of the target object for n times by the RFID antenna facing the starting direction of the target object, and recording the corresponding time sequence as TA＝tA,1,tA,2…,tA,n|ti≤tj(i<j is less than or equal to n); reading the target object m times by the RFID antenna toward the terminating direction of the target objectRFID label, the corresponding time sequence is marked as TB＝tB,1,tB,2…,tB,n|ti≤tj(i<j is less than or equal to m); the time when the RFID tag is read at the beginning is denoted as tstart＝min(tA,1,tB,1) And finally, the time of reading the RFID tag is recorded as tend＝max(tA,n,tB,m) (ii) a If tstartAnd tendThe time sequences read by the two RFID antennas are respectively identified as normal wire collision; if tstartAnd tendAnd if the time sequence read by the same RFID antenna belongs to the time sequence read by the same RFID antenna, the direction is determined to be reversed before the wire collision. By identifying tstartAnd tendThe reason why whether the two situations belong to the same RFID tag or not is that the reading range of the RFID antenna has directivity, the RFID antenna facing the starting direction of the target object reads the information of the RFID tag facing the starting direction of the object first, the RFID antenna facing the ending direction of the target object reads the information of the RFID tag facing the ending direction of the object first, and if the target object normally hits the line, t is the distance between the target object and the RFID tagstartTime series read by the RFID antenna belonging to the direction towards the start of the target object, and tendThe time sequence read by the RFID antenna in the direction towards the end of the target object; otherwise, if the direction is turned before the target object hits the line, tstartAnd tendAll belonging to the time series read by the RFID antenna towards the starting direction of the target object.
That is, when the target object moves in the opposite direction when not passing through the Y axis, at this time, the RFID tag should be read by the same RFID antenna for the first time and the last time, as can be seen from fig. 5, since the ARFID antenna faces the starting direction of the target object, at this time, the reading range of the ARFID antenna is also in the starting direction of the target object, when the ARFID antenna reads the RFID tag for the first time, since the BRFID antenna faces the other side, the BRFID antenna cannot read the RFID tag; if the target object continues to move forward after normally colliding with the line, the BRFID antenna can read the last information of the RFID label, and the ARFID antenna cannot continuously read the RFID label.
As shown in fig. 6, it is a phase-time diagram corresponding to the case where the target object is stationary for a long time at the detection boundary in one embodiment. As can be seen from fig. 6, when the target object is stationary for a long time at the detection boundary, the phase value fluctuates in a small range in the stationary time period, and there is no upward opening curve in the phase-time diagram but a relatively flat area is presented at the bottom, the following method is adopted in the present application to identify the "inflection point with the minimum phase value" in the phase-time diagram in this case, and the process is as follows:
constructing a sliding window in the phase-time diagram (as shown in fig. 6) and calculating the entropy E of the phase values within the sliding window, the entropy E of the phase values being defined as follows:
where M represents the number of phase values in the sliding window, piRepresenting the frequency of each phase value;
and setting a threshold, and if E exceeds the threshold, considering that the phase value is changed violently in the sliding window, wherein the point corresponding to the rightmost end of the sliding window is regarded as the inflection point with the minimum phase value. If the phase value change in the window is small, the entropy value is also small and the time in the window is not considered as the time of the line hit, and the sliding window is shifted to the left. That is, when the target object is stationary at the detection boundary for a long time, a local minimum value needs to be found in the phase-time map so as to determine the inflection point at which the phase value is minimum.
Through the mode, the collision line under different conditions such as when the target object normally passes through the detection boundary, is reversed, is static at the detection boundary for a long time and the like can be effectively identified.
To further illustrate the related aspects of the present application, one specific embodiment is as follows:
a scene is constructed, and the scene mainly comprises two parts, namely a radio frequency identification module and a robot module. The radio frequency identification module comprises a reader, two RFID antennae and a plurality of RFID labels. The reader is used in the model of Impinj Speedway R420, the working frequency is 920 to 924MHz, and the RFID antenna is in the model of Laird S9028 PCL. The two RFID antennas are disposed at a distance of 240cm face to face and at a height of 70cm, and each RFID antenna is connected to the same reader through a data line. The robot module comprises a robot and an RFID label carried on the robot. The robot is model number urtlebot 2. The moving track of the robot is controlled through programming to detect the wire collision, and the actual result is recorded by a camera.
The robot carrying the RFID label is made to move under the following three different scenes: straight lines, oblique lines, and curved lines, which are respectively denoted as example 1, example 2, and example 3, and the phase information of the RFID tag is continuously collected. The error distances of the method of wire strike detection in this application are then compared in these three different cases. The error distance is defined as the difference between the line collision time given by the algorithm and the actual line collision time captured by the camera, and the position of the robot is located. Experimental results show that in the three different scenes, the error distances are respectively 4.47cm, 6.23cm and 7.48cm under the conditions of example 1, example 2 and example 3, the average can reach 6.1cm, and the accuracy is better than that of the current best radio frequency identification positioning algorithm.
Compared with the existing common line collision detection methods such as an infrared sensor, a camera and a virtual wall, the light-weight line collision detection method based on the radio frequency identification technology can effectively detect the line collision condition of a plurality of target objects at the same time, and can identify the normal line collision and abnormal conditions of the target objects. Compared with the traditional radio frequency identification positioning method, the required number of the RFID antennas is less, parameters such as specific positions of the RFID antennas and distances between the RFID antennas do not need to be known, the RFID antennas can be directly used in a new scene without being deployed and calibrated in advance, and the time complexity of an algorithm is lower.
Thus, it should be appreciated by those skilled in the art that while a number of exemplary embodiments of the present application have been illustrated and described in detail herein, many other variations and modifications consistent with the principles of the application may be ascertained or derived directly from the disclosure herein without departing from the spirit and scope of the application. Accordingly, the scope of the present application should be understood and interpreted to cover all such other variations or modifications.
Claims (8)
1. A wire collision detection method is characterized in that wire collision detection is achieved based on an RFID technology.
2. The wire-strike detection method according to claim 1, wherein the RFID-based wire-strike detection is implemented as follows:
giving a detection boundary line, and arranging an RFID antenna at least one end of the detection boundary line;
reading the phase of a target object RFID tag through an RFID antenna, and acquiring a phase-time diagram of the target object RFID tag in the whole time, wherein the phase value on the phase-time diagram is the sum of the phases of the target object RFID tags read by all the RFID antennas;
and identifying an inflection point with the minimum phase value in the phase-time diagram, wherein the inflection point corresponds to the occurrence of line collision of a target object.
3. The wire-strike detection method according to claim 2, wherein the number of the RFID antennas is one and is directed toward the detection boundary.
4. The wire-strike detection method according to claim 2, wherein the number of the RFID antennas is two, and the two RFID antennas are respectively located at both ends of the detection boundary.
5. The wire-strike detection method of claim 4, wherein one of the RFID antennas is disposed toward a starting direction of the target object and the other RFID antenna is disposed toward an ending direction of the target object.
6. The wire-strike detection method according to claim 5, wherein normal wire-strike and pre-wire-strike steering directions of the target object are distinguished by:
during the movement of the target object, towards the target objectReading the RFID label of the target object n times by the RFID antenna in the body starting direction, and recording the corresponding time sequence as TA＝tA，1，tA，2…，tA，n|ti≤tj(i<j≤n)；
Reading the RFID tag of the target object m times by the RFID antenna facing the terminating direction of the target object, and recording the corresponding time sequence as TB＝tB，1，tB，2…，tB，n|ti≤tj(i<j≤m)；
The time when the RFID tag is read at the beginning is denoted as tstart＝min(tA，1,tB,1) And finally, the time of reading the RFID tag is recorded as tend＝max(tA,n,tB,m)；
If tstartAnd tendThe time sequences read by the two RFID antennas are respectively identified as normal wire collision; if tstartAnd tendAnd if the time sequence read by the same RFID antenna belongs to the time sequence read by the same RFID antenna, the direction is determined to be reversed before the wire collision.
7. The wire-strike detection method according to claim 2, wherein when the target object is stationary for a long time at a detection boundary, the process of identifying an inflection point in the phase-time diagram where a phase value is smallest is as follows:
constructing a sliding window in the phase-time diagram and calculating the entropy E of the phase value in the sliding window, wherein the entropy E of the phase value is defined as follows:
where M represents the number of phase values in the sliding window, piRepresenting the frequency of each phase value;
and setting a threshold, and if E exceeds the threshold, considering that the phase value is changed violently in the sliding window, wherein the point corresponding to the rightmost end of the sliding window is regarded as the inflection point with the minimum phase value.
8. The wire-strike detection method of claim 4, wherein each of the RFID antennas is connected to the same reader.
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