Interference Tag Filtering Method for Automatic In-and-Out System of Goods Based on RFID Channel Gates

Abstract

The present invention belongs to the technical field of goods transportation. Specifically, it relates to a method for filtering interference tags in an automatic goods in-out system based on an RFID access gate. This method calculates the distance from the antenna to the tag by reading the same tag at two or more frequencies and obtaining the phase information of the returned signals at different frequencies, thereby determining the accurate position of the tag, and filtering out interference tags based on the position information. At the same time, the accuracy of the judgment result is improved by comparing the distance between the goods tag and the antenna and the distance between the tag on the AGV trailer and the antenna. This method also adopts the design of an interference tag database to improve the accuracy and speed of comprehensive judgment.

Description

Technical Field

[0001] The present invention belongs to the technical field of cargo transportation, and specifically relates to a method for filtering interference tags of an automatic cargo in-out system based on an RFID access gate. Background Art

[0002] Ultra-high frequency RFID technology has the characteristics of batch, long-distance, and non-contact reading. For traditional barcodes or two-dimensional codes, each cargo needs to be scanned one by one, with low efficiency and not suitable for batch automatic in-out scenarios. Applying RFID technology to warehousing, RFID electronic tags are pasted on the cargo packaging boxes, and RFID reading devices are installed at the in-out channels of the warehouse. When the cargo passes by, the RFID tags on the cargo are automatically scanned to achieve automatic in-out. Using RFID technology can save manpower and improve efficiency.

[0003] However, in actual use, there are a large number of goods in the warehouse, and the distance between the placement positions of the goods and the RFID devices at the entrances and exits is relatively close, and the cargo transportation is frequent. Due to the long-distance reading characteristic of RFID, when reading the goods for normal in-out, other surrounding goods may also be read. In addition, to improve the reading rate and reduce the missed reading rate, antennas with larger gains and higher output powers are used in reality, resulting in a farther reading distance of the RFID device and making it easier to read the goods around the warehouse entrances and exits. As a result, it is impossible to accurately distinguish between the valid in-out cargo tags and other surrounding interference tags. The usual solution is to reserve a certain area around the RFID antenna where goods are prohibited from being placed, so that the inventory goods are far away from the RFID antenna, or to increase shielding measures around the antenna. However, limited by the site space, in most usage scenarios, it is impossible to set the cargo entrances and exits where the RFID devices are installed in an area far away from other goods, and adding shielding measures will also increase the equipment deployment cost. Summary of the Invention

[0004] Aiming at the above problems existing in the prior art, the purpose of the present invention is to provide a method for filtering interference tags of an automatic cargo in-out system based on an RFID access gate.

[0005] To solve the above problems, the technical solutions adopted by the present invention are as follows:

[0006] A method for filtering interference tags of an automatic cargo in-out system based on an RFID access gate;

[0007] In this method, there are access gates arranged oppositely, and the range that can be read by the two access gates simultaneously is defined as the effective reading area;

[0008] The method includes the following steps:

[0009] S1: Let the distance between the tag and the antenna be d, the phase of the tag signal received by the reader on the access door is ( ), the wavelength is , and the relationship between the phase and the distance is shown in the following formula:

[0010] ;

[0011] Among them, is the phase difference introduced by the reader transmitting circuit, is the phase difference introduced by the reader receiving circuit, is the phase difference introduced by the RFID tag characteristics, is a positive integer;

[0012] During each reading, the tag information is read at two different frequencies, which are and , and the corresponding wavelengths are 1, 2, and the following formula is obtained by combination:

[0013] ;

[0014] ;

[0015] The distance is calculated, where is the speed of light, ;

[0016] S2: During the reading process of goods in and out of storage, there are two situations where the goods tag is read by the access door;

[0017] Sit1: The RFID tag of the goods is read by the antennas on both sides of the access door at the same time. At this time, the distances , from the tag to the antennas on both sides can be calculated according to the phase information, and then it can be calculated whether the position of the goods is within the effective reading area and whether the goods belong to interference tags;

[0018] Sit2: The RFID tag of the goods is read by only one antenna, or is read by multiple antennas on the same side; at this time, the distance information between the tag at different positions and the antenna can be calculated according to the tag information read at different positions;

[0019] If the change trend of the distance information is from large to small and then to large, it is confirmed that the goods do not belong to interference tags;

[0020] If the change trend of the distance information is stationary or does not conform to the movement law of the RFID tag on the AGV trailer, it is confirmed that the goods belong to interference tags;

[0021] S3: If the position of the RFID tag of the goods cannot be accurately calculated, query whether there is an interfering tag in the interfering tag database. If so, temporarily mark the obtained tag as an interfering tag; if not, enter it into the interfering tag database and perform the next reading.

[0022] For the tags calculated in Sit1 that are not in the effective reading area, after being determined as interfering tags, enter these tags into the interfering tag database.

[0023] For the tags calculated in Sit1 that are located in the effective reading area, after being determined as valid tags, retrieve whether there is such a tag in the interfering tag database. If so, delete the tag from the interfering tag database.

[0024] Further, in step S1, the access door uses a narrow beam directional antenna, and the horizontal lobe angle of the antenna is less than 40°, and the formed radiation area is approximately an ellipsoidal area.

[0025] Further, in step S1, a distance correction factor is added , the actual distance is calibrated by the RFID tag on the AGV trailer and the actual position of the AGV trailer;

[0026] By comparing the true position of the tag calculated from the position of the AGV trailer with the position information obtained from the phase information, the value can be obtained.

[0027] Further, in Sit2 of step S2, the RFID tag on the AGV trailer is also read, and the distance between the RFID tag on the AGV trailer and the antenna is calculated, and it is compared with the data calculated from the RFID tag of the goods and judged synchronously;

[0028] Let the distance vector from the RFID tag of the goods to the antenna be , the distance vector from the RFID tag on the AGV trailer to the antenna be , calculate the correlation coefficient of the two vectors , if is greater than or equal to the pre-set correlation coefficient threshold , it is determined that the variation laws of the two are the same and it is a valid tag, otherwise it is an interfering tag.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] (1) This method calculates the distance from the antenna to the tag by reading the same tag at two or more frequencies and obtaining the phase information of the returned signals at different frequencies, thereby determining the accurate position of the tag, and filtering out interfering tags based on the position information;

[0031] (2) In this method, the accuracy of the judgment result is improved by comparing the distance between the goods tag and the antenna and the distance between the tag on the AGV trailer and the antenna;

[0032] (3) In this method, the design of the interfering tag database is adopted to improve the accuracy and speed of the comprehensive judgment. Description of the Drawings

[0033] Figure 1 It is a schematic diagram of the structure design of the goods inbound and outbound channel corresponding to this method;

[0034] Figure 2 It is a schematic diagram of the distribution of the effective reading area in this method;

[0035] Figure 3 It is a schematic diagram of the change in the relative position distance between the goods position and the antenna in this method;

[0036] Figure 4 It is a schematic diagram of the step flow in this method;

[0037] In the figure: 1 - RFID antenna; 2 - infrared sensor; 3 - main channel door; 4 - RFID antenna; 5 - RFID reader; 6 - AGV; 7 - AGV trailer; 8 - RFID electronic tag; 9 - sub-channel door; 10 - goods outer box; 11 - RFID tag. Specific Embodiments

[0038] The following further describes the present invention in combination with specific embodiments.

[0039] The method for filtering interfering tags of the automatic goods inbound and outbound system based on RFID channel gates according to the present invention first adopts the corresponding structure design of the goods inbound and outbound channel, as Figure 1 shown, specifically including channel gates arranged oppositely on the left and right sides, namely the main channel door 3 and the sub-channel door 9. Among them, an RFID reader 5 and at least two RFID antennas 1 / 4, as well as an infrared sensor 2, are provided on the main channel door 3. Correspondingly, the same number of RFID antennas as those on the main channel door 3 are provided on the sub-channel door 9.

[0040] It can also be seen from the figure that an RFID tag 11 is pasted on the goods outer box 10, the goods are stacked on the AGV trailer 7, and an RFID electronic tag 8 is also pasted on the AGV trailer 7. The AGV 6 transports the AGV trailer 7 through the channel gate to realize the inbound and outbound of the goods.

[0041] When the RFID reader 5 reads a tag, it can obtain information such as the signal strength (RSSI value) of the tag's reflected signal, the phase information of the returned signal, and the antenna number that reads the tag. The RSSI value is related to the distance of the tag. In theory, under the same reading power and environment, the farther the tag is from the reader antenna, the smaller the RSSI value. However, the RSSI value is greatly affected by the environment and cannot accurately calculate the distance to the tag.

[0042] Although the phase information can also reflect the tag distance, due to the periodicity of the phase, the accurate tag distance cannot be calculated through a single phase information. Since the ultra-high frequency RFID technology uses a frequency-hopping communication method, we can use two or more frequencies to read the same tag respectively, obtain the phase information of the returned signal at different frequencies, and then calculate the distance from the antenna to the tag according to the phase. The RFID channel gate usually consists of multiple antennas. If a tag is read by the antennas on different sides of the channel gate at the same time, the accurate position of the tag can be determined by combining the distances between the tag and different antennas. According to the position information, it can be judged whether the tag belongs to the surrounding goods or the goods that are entering or leaving the warehouse, so as to filter out the interfering tags.

[0043] As Figure 2 shown, we first define the range that can be read by two channel gates at the same time as the effective reading area, and the tags outside the effective reading area are regarded as interfering tags. When the AGV transports goods into the reading area, or when the goods trigger the infrared sensor on the channel gate, the channel gate starts to read the goods tags. When the AGV transports goods out of the reading area, or triggers the infrared sensor on the other side of the channel gate, the reading stops. In order to improve the speed of inbound and outbound, the AGV passes through the channel gate at a constant speed during the whole reading process, which is also beneficial to judging the position of the goods and distinguishing the interfering tags.

[0044] In addition, we need the moving direction of the AGV to be parallel to the inbound and outbound direction, that is, to be parallel to the antenna.

[0045] In order to reduce the radiation range of the antenna, in this embodiment, the RFID channel gate uses a narrow-beam directional antenna, whose horizontal lobe angle is less than 40°, and the radiation area is approximately an ellipsoidal area.

[0046] On this basis, as Figure 4 shown, the method described in the present invention includes the following steps:

[0047] S1: Let the distance between the tag and the antenna be d , the phase of the tag signal received by the reader on the channel gate be ([[]] ), and the wavelength be , the relationship between the phase and the distance is shown in the following formula:

[0048] ;

[0049] Among them, is the phase difference introduced by the reader transmitting circuit, is the phase difference introduced by the reader receiving circuit, is the phase difference introduced by the RFID tag characteristics, is a positive integer.

[0050] Due to the periodicity of the phase and the frequency hopping communication characteristics based on RFID, each time a tag is read, two different frequencies are used to read the tag information, which are and , and the corresponding wavelengths are 1, 2, and the following formula is obtained by combination:

[0051] ;

[0052] ;

[0053] The distance is calculated, where is the speed of light, .

[0054] Considering factors such as environmental interference and antenna phase center, a distance correction factor is added. The actual distance is calibrated through the RFID tag on the AGV trailer and the actual position of the AGV trailer to improve the accuracy of tag position calculation. When the AGV transports goods through the access door, the tag on the AGV trailer will be read by the RFID antenna at the same time. According to the obtained phase information, the distance from the electronic tag on the AGV trailer to the antenna is calculated. Since the real-time position of the AGV is known and the tag pasting position is fixed, the real position of the tag can be accurately calculated based on the position of the AGV and compared with the position information obtained through the phase information, so as to obtain value.

[0055] For example, the n distance information calculated through the tag signal phase on the AGV trailer is , and the corresponding real position is , then . In different environments, the interference received by the tag is also different. In order to accurately calculate the tag position information, the correction factor can be calibrated regularly.

[0056] S2: During the reading process of goods in and out of the warehouse, there are two situations where the goods tag is read by the access door;

[0057] Sit1: The RFID tag of the goods is simultaneously read by the antennas on both sides of the access gate. At this time, the distances between the tag and the antennas on both sides can be calculated according to the phase information. 、 , taking the two antennas as the centers, 、 as the radii to draw circles, and the tag is located near the intersection of the two circles. As shown in Figure 3 , the positions of the antennas on both sides are known. According to the antenna positions and 、 , it can be calculated whether the position of the goods is within the effective reading area, that is, the goods may be located at one of the two intersection areas, and it is judged whether the goods belong to interference tags;

[0058] Sit2: Due to the mutual occlusion of the goods, some tags may only be read by one of the antennas or only by multiple antennas on the same side. Since the antennas on the same side are vertically installed, that is, the horizontal positions are the same, the horizontal position of the tag cannot be judged either. During the entire reading process, the AGV is always in a moving state, and the tag can be read by the antennas on the same side or the same antenna at different positions. Furthermore, the distance information between the tag at different positions and the antenna can be calculated according to the tag information read at different positions. At the same time, combined with the RFID tag on the AGV trailer, this tag is also read multiple times, and thus the distance data between the RFID tag on the AGV trailer and the antenna at different positions can be calculated. Further, since the moving direction of the AGV is parallel to the antenna, the moving trajectory of the tag also moves parallel with the AGV. Therefore, when the goods pass through the access and exit channels, the distance change trend between the RFID tag on the goods and the antenna of the access gate is from large to small, and then from small to large (the distance is the smallest when the tag is directly in front of the antenna), similar to the shape of a parabola. And since the goods are transported by the AGV, the change area of the distance between the goods tag and the antenna of a certain side access gate is the same as the change trend of the distance between the tag on the AGV trailer and the antenna of that side.

[0059] For some interference tags, they may be in a stationary state. For example, the goods stacked around the access gate have a constant distance to the antenna. For the interference tags in a moving state, such as the tags passing by near the access gate, the distance to the antenna may exceed the effective range, or the distance change rule is different from the distance change rule of the RFID tag on the AGV trailer to the antenna. Therefore, it can be analyzed whether the tag is a valid tag by comparing whether the change trends of the distances between the goods tag and the antenna and between the AGV trailer and the antenna are consistent.

[0060] In this embodiment, it is set that the antenna number of the main access gate is Ant_1, Ant_2, the sub-channel door antennas are Ant_3 and Ant_4, and the main channel door coordinates are P1(X a1 ，Y a1 ） , the sub-channel door coordinates are P2(X a2 , Y a2 ). The X-axis is perpendicular to the antenna, and the Y-axis is parallel to the antenna.

[0061] During the movement, the information of five tags was obtained, which are respectively:

[0062]

TagId_1, RSSI_1, Phase_1, Ant_1

[0063]

TagId_1, RSSI_2, Phase_2, Ant_1

[0064]

TagId_1, RSSI_3, Phase_3, Ant_1

[0065]

TagId_1, RSSI_4, Phase_4, Ant_1

[0066]

TagId_1, RSSI_5, Phase_5, Ant_1

[0067] That is, the same tag ( TagId_1 ) was read five times by antenna 1 ( Ant_1 ). Five distance information was calculated from the phase data in these five tag information. In the same way, the distance between the RFID tag on the AGV trailer and the channel door antenna at the same moment can be calculated .

[0068] Calculate the correlation coefficient of two vectors , if is greater than or equal to the preset correlation coefficient threshold , it is determined that the variation laws of the two are the same, and it is a valid tag; otherwise, it is an interference tag. is the preset correlation coefficient threshold, which needs to be determined according to factors such as the on-site environment and tag performance.

[0069] S3: If the position of the RFID tag of the goods cannot be accurately calculated, query whether there is an interference tag in the interference tag database. If it exists, temporarily mark the obtained tag as an interference tag; if it does not exist, enter it into the interference tag database and perform the next reading;

[0070] For the tags calculated in Sit1 that are not in the effective reading area, after being determined as interference tags, enter these tags into the interference tag database;

[0071] For the tags calculated in Sit1 and located in the valid reading area, after being determined as valid tags, check whether the tags exist in the interference tag database. If they exist, delete the tags from the interference tag database.

Claims

1. Interference label filtering method for an automatic goods in-out system based on an RFID channel gate, characterized in that in this method, there are channel gates arranged oppositely, and the range that can be read by the two channel gates simultaneously is defined as the effective reading area; the method includes the following steps: S1: Set the distance between the tag and the antenna as d , the phase of the tag signal received by the reader on the access door is , the wavelength is , and the relationship between the phase and the distance is shown in the following formula: ； Among them, is the phase difference introduced by the reader transmitter circuit, is the phase difference introduced by the reader receiver circuit, is the phase difference introduced by the RFID tag characteristics, is a positive integer, ; At each reading, the tag information is read at two different frequencies, namely and , and the corresponding wavelengths are 1, 2, and combining them gives the following equation: ； ； Calculated distance , where is the speed of light ; S2: During the reading process of goods in and out, there are two situations where the goods label is read by the channel gate; Sit1: The RFID tag of the goods is simultaneously read by the antennas on both sides of the access gate. At this time, the distances between the tag and the antennas on both sides can be calculated according to the phase information, and , and then calculate whether the position of the goods is within the effective reading area to determine whether the goods are interference tags; Sit2: The RFID label of the goods is only read by one of the antennas, or only read by multiple antennas on the same side; at this time, the distance information between the label at different positions and the antenna can be calculated based on the label information read at different positions; if the change trend of this distance information is from large to small and then to large, it is confirmed that the goods do not belong to interference labels; if the change trend of this distance information is stationary or does not conform to the movement law of the RFID label on the AGV trailer, it is confirmed that the goods belong to interference labels; S3: If the position of the RFID label of the goods cannot be accurately calculated, query whether the label exists in the interference label database. If it exists, the obtained label is temporarily marked as an interference label; if it does not exist, it is entered into the interference label database and the next reading is performed; For the label calculated in Sit1 that is not in the effective reading area, after being determined as an interference label, this label is entered into the interference label database; For the label calculated in Sit1 that is in the effective reading area, after being determined as a valid label, check whether this label exists in the interference label database. If it exists, this label is deleted from the interference label database.

2. The interference tag filtering method for the automatic goods in-out system based on RFID channel gates according to claim 1, characterized in that In step S1, the channel gate uses a narrow-beam directional antenna, and the horizontal lobe angle of the antenna is less than 40°, and the formed radiation area is approximately an ellipsoidal area.

3. The interference tag filtering method of the automatic goods in-out system based on RFID channel gates according to claim 1, characterized in that In step S1, a distance correction factor is added , the actual distance is calibrated by the RFID tag on the AGV trailer and the actual position of the AGV trailer; The value can be obtained by comparing the true position of the tag calculated from the position of the AGV trailer with the position information obtained from the phase information. value 4. The interference tag filtering method of the automatic goods in-out system based on RFID channel gates according to claim 3, characterized in that, In Sit2 of step S2, the RFID label on the AGV trailer is also read, and the distance between the RFID label on the AGV trailer and the antenna is calculated, and it is compared and judged synchronously with the data calculated by the RFID label of the goods; Let the distance vector between the RFID tag of the goods and the antenna and the distance vector between the RFID tag on the AGV trailer and the antenna Calculate the correlation coefficient of the two vectors If is greater than or equal to a pre-set correlation coefficient threshold then it is determined that the variation laws of the two are the same, and it is a valid tag; otherwise, it is an interference tag.

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