Interference label filtering method based on RFID access door cargo automatic warehouse-in and warehouse-out system

Abstract

The invention belongs to the technical field of cargo transportation, and particularly relates to an interference label filtering method based on an RFID access door cargo automatic warehouse-in and warehouse-out system. According to the method, the same tag is read by adopting two or more frequencies respectively, the distance from an antenna to the tag is calculated in a mode of obtaining phase information of return signals under different frequencies, then the accurate position of the tag is determined, and interference tags are filtered out according to the position information; meanwhile, the accuracy of the judgment result is improved by comparing the distance between the cargo label and the antenna and the distance between the label on the AGV trailer and the antenna; the method also adopts the design of an interference label database to improve the accuracy and speed of comprehensive judgment.

Description

Technical Field

[0001] The invention belongs to the technical field of cargo transportation, and in particular relates to an interference tag filtering method for an automatic cargo entry and exit system based on an RFID channel door. Background Art

[0002] Ultra-high frequency RFID technology has the characteristics of batch, long-distance, and contactless reading, while traditional barcodes or QR codes need to be scanned one by one, which is inefficient and not suitable for batch automatic entry and exit scenarios. RFID technology is applied to warehousing, and RFID electronic tags are affixed to the cargo packaging boxes. RFID reading equipment is installed in the warehouse entry and exit channels. When the goods pass by, the RFID tags on the goods are automatically scanned to achieve automatic entry and exit. The use of 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 goods are placed close to the RFID equipment at the entrance and exit. The goods are frequently transported. Since RFID has the characteristic of long-distance reading, when reading the normal goods entering and leaving the warehouse, other surrounding goods may also be read. In addition, in order to improve the reading rate and reduce the missed reading rate, antennas with larger gains are used in reality, and higher output powers are set, which leads to a longer reading distance for RFID devices and makes it easier to read goods around the warehouse entrance and exit. As a result, it is impossible to accurately distinguish between the effective goods labels entering and leaving the warehouse and other interference labels around. The usual solution is to reserve a certain prohibited area for goods around the RFID antenna to keep the inventory away from the RFID antenna, or to add shielding measures around the antenna. However, due to the limited space of the site, most usage scenarios cannot set the goods entrance and exit where the RFID equipment is installed in an area away from other goods, and adding shielding measures will also increase the equipment deployment cost. Summary of the invention

[0004] In view of the above problems existing in the prior art, the object of the present invention is to provide an interference tag filtering method for an automatic storage and retrieval system of goods based on an RFID channel door.

[0005] In order to solve the above problems, the technical solution adopted by the present invention is as follows: Interference tag filtering method based on RFID channel door automatic storage and warehousing system; In the method, channel gates are arranged opposite to each other, and a range that can be read simultaneously by two of the channel gates is defined as an effective reading area; The method comprises the following steps: S1: Assume the distance between the tag and the antenna is d , the phase of the tag signal received by the reader on the channel door is ( ), the wavelength is , the relationship between phase and distance is shown as follows: ; in, The phase difference introduced by the reader transmitting circuit, The phase difference introduced by the reader receiving circuit, The phase difference introduced for the RFID tag characteristics, is a positive integer; Each time the tag is read, two different frequencies are used to read the tag information, namely and , and the corresponding wavelengths are 1, 2, combined to get the following formula: ; ; Calculate the distance ,in, is the speed of light, ; S2: During the reading process of goods entering and leaving the warehouse, there are two situations in which the goods label is read by the channel door; Sit1: The RFID tag of the goods is read by the antennas on both sides of the channel door at the same time. At this time, the distance between the tag and the antennas on both sides can be calculated based on the phase information. , , and then calculate whether the location of the goods is within the effective reading area, and determine whether the goods belong to the interference tag; Sit2: The RFID tag of the goods is read by only one of the antennas, or only by multiple antennas located on the same side. In this case, the distance information between the tags and antennas at different locations can be calculated based on the tag information read at different locations. 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 the interference tag; If the change trend of the distance information is stationary or inconsistent with the movement pattern of the RFID tag on the AGV trailer, it is confirmed that the goods belong to the interference tag; S3: If the position of the RFID tag of the goods cannot be accurately calculated, query whether the tag exists in the interference tag database. If so, temporarily mark the acquired tag as an interference tag; if not, enter it into the interference tag database and perform the next reading; For a tag that is not in the effective reading area calculated in Sit1, after being determined as an interference tag, the tag is entered into the interference tag database; For the tag calculated in Sit1 to be located in the effective reading area, after being determined to be a valid tag, the interference tag database is searched to see whether the tag exists. If so, the tag is deleted from the interference tag database.

[0006] Furthermore, in step S1, the channel gate uses a narrow beam directional antenna, the horizontal lobe angle of the antenna is less than 40°, and the radiation area formed is approximately an ellipsoidal area.

[0007] Furthermore, in step S1, the distance correction factor is increased , actual distance Calibrated by RFID tag on AGV trailer and actual position of AGV trailer; By comparing the actual position of the tag calculated from the position of the AGV trailer with the position information obtained from the phase information, it can be obtained The value of .

[0008] Furthermore, in step S2 of Sit2, 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, so as to be compared with the data calculated by the RFID tag of the goods and synchronously judged; Assume that the distance vector between the RFID tag of the goods and the antenna is , the distance vector between the RFID tag on the AGV trailer and the antenna , calculate the correlation coefficient of two vectors ,like Greater than or equal to the preset correlation coefficient threshold , then it is determined that the change rules of the two are the same and they are valid labels, otherwise they are interference labels.

[0009] Compared with the prior art, the present invention has the following beneficial effects: (1) This method uses two or more frequencies to read the same tag and obtain the phase information of the return signal at different frequencies to calculate the distance from the antenna to the tag, thereby determining the exact location of the tag and filtering out interfering tags based on the location information; (2) In this method, the accuracy of the judgment result is improved by comparing the distance between the cargo tag and the antenna and the distance between the tag on the AGV trailer and the antenna; (3) This method uses the design of an interference label database to improve the accuracy and speed of comprehensive judgment. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The schematic diagram of the structural design of the goods in and out passage in this method; Figure 2 Schematic diagram of the distribution of effective reading areas in this method; Figure 3 Schematic diagram of the change of the relative position distance between the cargo position and the antenna in this method; Figure 4 Schematic diagram of the steps of this method; 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-secondary channel door; 10-cargo outer box; 11-RFID tag. DETAILED DESCRIPTION

[0011] The present invention is further described below in conjunction with specific embodiments.

[0012] The interference tag filtering method based on the RFID channel door automatic storage and access system of goods in and out of the warehouse of the present invention first adopts the corresponding goods storage and access channel structure design, such as Figure 1 As shown, it specifically includes channel doors arranged opposite to each other on the left and right sides, namely a main channel door 3 and a secondary channel door 9, wherein the main channel door 3 is provided with an RFID reader 5 and at least two RFID antennas 1 / 4, and an infrared sensor 2. Correspondingly, the secondary channel door 9 is provided with the same number of RFID antennas as that on the main channel door 3.

[0013] It can also be seen from the figure that an RFID tag 11 is attached to the cargo box 10, the cargo is stacked on the AGV trailer 7, and an RFID electronic tag 8 is also attached to the AGV trailer 7. The AGV 6 transports the AGV trailer 7 through the channel door to realize the entry and exit of the cargo.

[0014] When reading a tag, the RFID reader 5 can obtain information such as the signal strength (RSSI value) of the tag's reflected signal, the phase information of the return signal, and the number of the antenna that reads the tag. The RSSI value is related to the tag distance. Theoretically, 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.

[0015] Although 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 UHF RFID technology uses frequency hopping communication, we can use two or more frequencies to read the same tag separately, obtain the phase information of the return signal at different frequencies, and then calculate the distance from the antenna to the tag based on the phase. The RFID channel gate is usually composed of multiple antennas. If a tag is read by the channel gate antennas on different sides at the same time, the exact location of the tag can be determined by combining the distance between the tag and different antennas. Based on the location information, it can be determined whether the tag belongs to surrounding goods or goods that are entering or leaving the warehouse, thereby filtering out interfering tags.

[0016] like Figure 2 As shown in the figure, we first define the range that can be read by the two channel doors at the same time as the effective reading area, and the tags outside the effective reading area are considered interference tags. When the AGV transports the goods into the reading area, or the goods trigger the infrared sensor on the channel door, the channel door starts to read the goods label. When the AGV transports the goods out of the reading area, or triggers the infrared sensor on the other side of the channel door, the reading stops. In order to increase the speed of entering and exiting the warehouse, the AGV passes through the channel door at a uniform speed during the entire reading process, which is also conducive to determining the location of the goods and distinguishing interference tags.

[0017] In addition, we need the AGV's moving direction to be parallel to the direction of entry and exit, that is, to remain parallel to the antenna.

[0018] In order to reduce the radiation range of the antenna, in this embodiment, the RFID channel door adopts a narrow beam directional antenna, whose horizontal lobe angle is less than 40° and the radiation area is approximately an ellipsoidal area.

[0019] On this basis, if Figure 4 As shown, the method of the present invention comprises the following steps: S1: Assume the distance between the tag and the antenna is d , the phase of the tag signal received by the reader on the channel door is ( ), the wavelength is , the relationship between phase and distance is shown as follows: ; in, The phase difference introduced by the reader transmitting circuit, The phase difference introduced by the reader receiving circuit, The phase difference introduced for the RFID tag characteristics, Is a positive integer.

[0020] Due to the periodicity of the phase, based on the frequency hopping communication characteristics of RFID, two different frequencies are used to read the tag information each time, which are and , and the corresponding wavelengths are 1, 2, combined to get the following formula: ; ; Calculate the distance ,in, is the speed of light, .

[0021] Considering environmental interference, antenna phase center and other factors, increase the distance correction factor , actual distance The RFID tag on the AGV trailer is calibrated with the actual position of the AGV trailer to improve the accuracy of tag position calculation. When the AGV transports goods through the channel door, the tag on the AGV trailer will be read by the RFID antenna at the same time. According to the acquired 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 label is fixed, the real position of the label can be accurately calculated based on the position of the AGV and compared with the position information obtained through the phase information to obtain the position information. The value of .

[0022] For example, the phase of the tag signal on the AGV trailer is calculated n The distance information is , the corresponding real position is ,but In different environments, the interference to the tag is different. In order to accurately calculate the tag position information, the correction factor can be calibrated regularly.

[0023] S2: During the reading process of goods entering and leaving the warehouse, there are two situations in which the goods label is read by the channel door; Sit1: The RFID tag of the goods is read by the antennas on both sides of the channel door at the same time. At this time, the distance between the tag and the antennas on both sides can be calculated based on the phase information. , , with the two antennas as the center, , Draw a circle with radius , and place the label near the intersection of the two circles. Figure 3 As shown, the positions of the antennas on both sides are known. , It can calculate whether the cargo is located in the effective reading area, that is, the cargo may be located in one of the two intersection areas, and determine whether the cargo is an interference tag; Sit2: Due to the mutual obstruction of 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 installed vertically, that is, the horizontal position is the same, the horizontal position of the tag cannot be determined. During the entire reading process, the AGV is always in a moving state, and the tag can be read by the same side or the same antenna at different positions. Then, according to the tag information read at different positions, the distance information between the tag and the antenna at different positions can be calculated. At the same time, combined with the RFID tag on the AGV trailer, the tag page is read multiple times at the same time, thereby calculating the distance data between the RFID tag on the AGV trailer and the antenna at different positions. Furthermore, since the moving direction of the AGV is parallel to the antenna, the moving trajectory of the tag also moves parallel to the AGV. Therefore, when the goods pass through the in-and-out channel, the distance between the RFID tag on the goods and the channel door antenna changes from large to small, and then from small to large (when the tag is located directly in front of the antenna, the distance is the smallest), similar to the shape of a parabola. The goods are transported by AGV, so the change area of ​​the distance between the cargo label and the channel door antenna on a certain side is the same as the change trend of the distance between the label on the AGV trailer and the antenna on that side.

[0024] Some interference tags may be stationary, such as goods piled around the passage door, and the distance to the antenna remains unchanged. For interference tags that are in motion, such as tags passing near the passage door, the distance to the antenna may exceed the effective range, or the distance change pattern is different from the distance change pattern from the RFID tag on the AGV trailer to the antenna. Therefore, the distance from the cargo tag to the antenna and the distance from the AGV trailer to the antenna can be compared to see if the change trends are consistent to analyze whether the tag is a valid tag.

[0025] In this embodiment, the antenna number of the main channel door is set to Ant_1, Ant_2 , the secondary channel gate antennas are Ant_3, Ant_4, and the main channel gate coordinates are P1 (X a1 ，Y a1 ） , the coordinates of the secondary channel door are P2 (X a2 , Y a2 ), the X-axis is perpendicular to the antenna and the Y-axis is parallel to the antenna.

[0026] During the movement, information of five tags was obtained, namely: [TagId_1, RSSI_1, Phase_1, Ant_1] ; [TagId_1, RSSI_2, Phase_2, Ant_1]; [TagId_1, RSSI_3, Phase_3, Ant_1] ; [TagId_1, RSSI_4, Phase_4, Ant_1] ; [TagId_1, RSSI_5, Phase_5, Ant_1] ; That is, the same label ( TagId_1 ) is antenna 1( Ant_1 ) is read five times, and five distance information are 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 time can be calculated. .

[0027] Calculates the correlation coefficient between two vectors ,like Greater than or equal to the preset correlation coefficient threshold , then it is determined that the change rules of the two are the same and they are valid labels, otherwise they are interference labels. It is a pre-set correlation coefficient threshold, which needs to be determined based on factors such as the on-site environment and tag performance.

[0028] S3: If the position of the RFID tag of the goods cannot be accurately calculated, query whether the tag exists in the interference tag database. If so, temporarily mark the acquired tag as an interference tag; if not, enter it into the interference tag database and perform the next reading; For the tag that is not in the effective reading area calculated in Sit1, after being determined as an interference tag, the tag is entered into the interference tag database; For the tag calculated in Sit1 to be located in the effective reading area, after being determined to be a valid tag, a search is performed to determine whether the tag exists in the interference tag database. If so, the tag is deleted from the interference tag database.

Claims

1. The interference tag filtering method based on the RFID channel door automatic storage and warehousing system is characterized by: In the method, channel gates are arranged opposite to each other, and a range that can be read simultaneously by two of the channel gates is defined as an effective reading area; The method comprises the following steps: S1: Assume the distance between the tag and the antenna is d , the phase of the tag signal received by the reader on the channel door is , the wavelength is , the relationship between phase and distance is shown as follows: ； in, The phase difference introduced by the reader transmitting circuit, The phase difference introduced by the reader receiving circuit, The phase difference introduced for the RFID tag characteristics, is a positive integer, ; Each time the tag is read, two different frequencies are used to read the tag information, namely and , and the corresponding wavelengths are 1, 2, combined to get the following formula: ； ； Calculate the distance ,in, is the speed of light, ; S2: During the reading process of goods entering and leaving the warehouse, there are two situations in which the goods label is read by the channel door; Sit1: The RFID tag of the goods is read by the antennas on both sides of the channel door at the same time. At this time, the distance between the tag and the antennas on both sides can be calculated based on the phase information. , , and then calculate whether the location of the goods is within the effective reading area, and determine whether the goods belong to the interference tag; Sit2: The RFID tag of the goods is read by only one of the antennas, or only by multiple antennas located on the same side. In this case, the distance information between the tags and antennas at different locations can be calculated based on the tag information read at different locations. 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 the interference tag; If the change trend of the distance information is stationary or inconsistent with the movement pattern of the RFID tag on the AGV trailer, it is confirmed that the goods belong to the interference tag; S3: If the position of the RFID tag of the goods cannot be accurately calculated, query whether the tag exists in the interference tag database. If so, temporarily mark the acquired tag as an interference tag; if not, enter it into the interference tag database and perform the next reading; For a tag that is not in the effective reading area calculated in Sit1, after being determined as an interference tag, the tag is entered into the interference tag database; For the tag calculated in Sit1 to be located in the effective reading area, after being determined to be a valid tag, the interference tag database is searched to see whether the tag exists. If so, the tag is deleted from the interference tag database.

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

3. The interference tag filtering method based on the RFID channel door automatic storage and warehousing system according to claim 1 is characterized in that: In step S1, add the distance correction factor , actual distance Calibrated by RFID tag on AGV trailer and actual position of AGV trailer; By comparing the actual position of the tag calculated from the position of the AGV trailer with the position information obtained from the phase information, it can be obtained The value of .

4. The interference tag filtering method based on the RFID channel door automatic storage and retrieval system according to claim 3 is characterized in that: 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, so as to be compared with the data calculated by the RFID tag of the goods and synchronously judged; Assume that the distance vector between the RFID tag of the goods and the antenna is , the distance vector between the RFID tag on the AGV trailer and the antenna , calculate the correlation coefficient of two vectors ,like Greater than or equal to the preset correlation coefficient threshold , then it is determined that the change rules of the two are the same and they are valid labels, otherwise they are interference labels.

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