An indoor forklift global positioning method, device and system based on RFID

Abstract

The present invention discloses an indoor forklift global positioning method, device and system based on RFID, belonging to the technical field of indoor logistics warehousing positioning. The phase information of RFID tags on the forklift is collected by an RFID antenna, and then the RFID tags are located through a distance conversion relationship. Then, according to the relationship between the RFID tag group and the forklift position, the possible poses of the forklift are obtained. Furthermore, the loss function is used to eliminate the poses with larger errors to obtain the credible poses, and finally the pose positioning result is selected from them. The present invention constructs a positioning loss function according to the difference degree between the measured phase and the actual phase of each RFID tag, and eliminates the possible poses corresponding to the larger loss function values, which can improve the positioning accuracy and has a low computational complexity. That is, the present invention can realize the rapid global positioning of the stacker forklift, and has the advantages of high positioning accuracy, good positioning real-time performance, and independent positioning, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of indoor logistics warehousing positioning, and more specifically, relates to a global positioning method, device and system for indoor forklifts based on RFID. Background Art

[0002] The digitization, intelligentization of factories, the interconnection of industrial equipment, products and personnel are important links in the transformation. Stacker forklifts are indispensable transportation tools in many manufacturing factories. How to accurately calibrate the two-dimensional pose of forklifts in factories is the key to realizing factory intelligentization and visualization, and can also facilitate managers' overall management to a certain extent and improve production efficiency.

[0003] Current global navigation positioning systems such as GPS can provide outdoor positioning information relatively accurately. However, indoors, due to the obstruction of buildings and the complexity of the indoor environment itself, satellite positioning systems are difficult to play a role in environments such as factories. Therefore, new methods are needed for indoor positioning.

[0004] Existing indoor forklift positioning methods obtain phase information and signal wavelength information, convert the periodically discontinuous phase information into continuously non-periodic phase information, and construct an unwrapped phase-position model to achieve the positioning of mobile robots, which have the advantages of high positioning accuracy, strong anti-interference ability, small calculation amount, and simple system. However, since this method converts discontinuous phases into continuous phases, the positioning uncertainty will gradually increase over time. That is, the accuracy of existing indoor forklift positioning methods is poor, and the calculation complexity is high and cannot meet the real-time requirements. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement requirements of the prior art, the present invention provides a global positioning method, device and system for indoor forklifts based on RFID, aiming to collect the measured phases of RFID tag groups fixedly arranged on the forklift by using an RFID antenna group to calculate the possible poses of the forklift; construct a positioning loss function, calculate the positioning loss function values corresponding to the possible poses of the forklift to determine the credible poses, and select the pose positioning results therefrom; the present invention can achieve high-real-time and high-precision forklift positioning, thereby solving the technical problems of poor real-time performance and low accuracy of existing indoor forklift positioning.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided a global positioning method for indoor forklifts based on RFID, including:

[0007] S1: Calibrate the relative position relationship between the forklift and the RFID tag group fixedly arranged thereon; calibrate the coordinate positions of the RFID antenna group for collecting the signals of the RFID tag group.

[0008] S2: At each sampling moment, use the RFID antenna group to collect the measured phases of each RFID tag in the RFID tag group;

[0009] S3: Based on the coordinate positions of the RFID antenna group, convert the measured phases of at least two RFID tags at each sampling moment into the coordinate positions of the RFID tag group; based on the relative position relationship between the forklift and the RFID tag group, calculate multiple possible poses of the forklift at each sampling moment according to the coordinate positions of the RFID tag group;

[0010] S4: Construct a positioning loss function according to the difference degree between the measured phases and the actual phases of each RFID tag; calculate the positioning loss function values corresponding to each possible pose of the forklift at each sampling moment, and use multiple possible poses with positioning loss function values lower than the threshold as credible poses;

[0011] S5: Select at least one from the multiple credible poses of the forklift at each sampling moment as the pose positioning result corresponding to that sampling moment.

[0012] In one embodiment, the S4 includes:

[0013] S41: Construct the positioning loss function according to the distances between the coordinate positions of each RFID tag and the coordinate positions of the RFID antenna group, and the measured phases of each RFID tag;

[0014] S42: Calculate the positioning loss function values corresponding to each possible pose of the forklift at each sampling moment, and use multiple possible poses with positioning loss function values lower than the threshold as credible poses.

[0015] In one embodiment, the positioning loss function in the S41 is expressed as:

[0016]

[0017] where p is the pose identifier, M represents the total number of RFID antennas in the RFID antenna group; N represents the total number of RFID tags in the RFID tag group; λ represents the wavelength of the RFID signal, (x i ,y i ) represents the coordinates of the i-th RFID antenna, (x j ,y j ) represents the coordinates of the j-th RFID tag, h ij represents the distance from the j-th RFID tag along the Z-axis direction to the i-th RFID antenna, γ ij represents the measured phase of the j-th RFID tag collected by the i-th RFID antenna, βi The constant error of the i-th RFID antenna.

[0018] In one embodiment, the S5 includes:

[0019] S51: Calculate the degree of difference between each credible pose corresponding to the forklift at the (t - 1)-th sampling moment and each credible pose at the t-th sampling moment;

[0020] S52: If the degree of difference between two adjacent sampling moments is within a preset range, it is regarded as a match; otherwise, it is regarded as a mismatch;

[0021] S53: Delete each of the mismatched credible poses to obtain the pose positioning result of the forklift at each of the sampling moments.

[0022] In one embodiment, the S51 includes:

[0023] Using the formula S(p t , p t-1 ) = (x t - x t-1 ) 2 + (y t - y t-1 ) 2 + (ω t - ω t-1 ) 2 Calculate the degree of difference between any credible pose p t-1 = (x t-1 , y t-1 , ω t-1 ) corresponding to the forklift at the (t - 1)-th sampling moment and any credible pose p t = (x t , y t , ω t ) at the t-th sampling moment.

[0024] In one embodiment, the RFID antenna group includes RFID antenna A and RFID antenna B, the RFID tag group includes four RFID tags forming a rectangle; the planes where the two RFID antennas are located are parallel to the plane where the RFID tag group is located; the S3 includes:

[0025] S31: Given the measured phases of any two RFID tags, calculate the possible coordinates of the any two RFID tags according to the distance conversion relationship :

[0026] S32: According to the possible coordinates of the any two RFID tags and the matrix position relationship of the four RFID tags, obtain the possible pose of the forklift at the current sampling moment;

[0027] where γ Aj and γ Bj are the phase values of the j-th RFID tag measured by the RFID antenna A and the RFID antenna B respectively, λ is the wavelength of the RFID signal, (x j , y j ) is the coordinate of the j-th RFID tag in the two-dimensional plane where it is located, β A represents the constant error of the RFID antenna A, β B represents the constant error of the RFID antenna B, (x A , y A ) is the position of the RFID antenna A, and (x B , y B ) is the position of the RFID antenna B.

[0028] In one embodiment, any two RFID tags are located on the diagonal of the rectangle; the S32 includes:

[0029] Using the formula to calculate multiple possible poses (X p , Y p , Ω p ) of the forklift at each sampling moment;

[0030] where each possible pose is represented as (x p , y p , ω p ), (x p , y p ) represents the possible position information of the forklift, and ω p represents the possible angle information of the forklift; RFID tag 1 and RFID tag 3 are on the same diagonal; (X1, Y1) represents the matrix formed by the X-axis and Y-axis coordinate sets of RFID tag 1, and the elements are (x1, y1); (X3, Y3) represents the matrix formed by the X-axis and Y-axis coordinate sets of RFID tag 3, and the elements are (x3, y3); m and n are the numbers of estimated coordinates of RFID tag 1 and RFID tag 3 respectively, |Z| is the distance matrix between RFID tag 1 and RFID tag 3, Arg(Z) is the angle matrix between RFID tag 1 and RFID tag 3, and b and a are the length and width of the matrix respectively.

[0031] In one embodiment, each RFID tag has a unique identity code to ensure the uniqueness of identification.

[0032] According to another aspect of the present invention, there is provided an indoor forklift global positioning device based on RFID, including:

[0033] A position relationship calibration module is used to calibrate the relative position relationship between the forklift and the RFID tag group fixedly arranged thereon; and calibrate the coordinate positions of the RFID antenna group for collecting the signals of the RFID tag group.

[0034] An RFID tag phase acquisition module is used to collect the measured phases of the respective RFID tags in the RFID tag group at each sampling moment by using the RFID antenna group.

[0035] A possible pose calculation module is used to convert the measured phases of at least two of the RFID tags at each sampling moment into the coordinate positions of the RFID tag group based on the coordinate positions of the RFID antenna group; and calculate multiple possible poses of the forklift at each sampling moment according to the coordinate positions of the RFID tag group based on the relative position relationship between the forklift and the RFID tag group.

[0036] A feasible pose determination module is used to construct a positioning loss function according to the degree of difference between the measured phases and the actual phases of the respective RFID tags; calculate the positioning loss function values corresponding to the respective possible poses of the forklift at each sampling moment, and use the multiple possible poses with positioning loss function values lower than the threshold as credible poses.

[0037] A target pose determination module is used to select at least one from the multiple credible poses of the forklift at each sampling moment as the pose positioning result corresponding to that sampling moment.

[0038] According to another aspect of the present invention, there is provided an indoor forklift global positioning device based on RFID, including a memory and a processor, where the memory stores a computer program, and when the processor executes the computer program, the steps of the indoor forklift global positioning method based on RFID are implemented.

[0039] Generally speaking, compared with the prior art by the above technical solution conceived by the present invention, the following beneficial effects can be achieved:

[0040] (1) The present invention uses an RFID antenna to collect the phase information of RFID tags on a forklift, and then converts the positioning of the RFID tags through a distance conversion relationship. Based on the relationship between the RFID tag group and the forklift position, the possible poses of the forklift are obtained. Then, a loss function is used to eliminate the poses with large errors to obtain reliable poses. Finally, a pose positioning result is selected from them. The use of RFID positioning technology has the advantages of fast positioning speed and low cost. A positioning loss function is constructed according to the difference degree between the measured phase and the actual phase of each RFID tag, and the possible poses corresponding to larger loss function values are eliminated, which can improve the positioning accuracy and has a low computational complexity. That is, the present invention can achieve fast global positioning of a stacking forklift, with advantages such as high positioning accuracy, good positioning real-time performance, and independent positioning. In addition, the same set of RFID antennas and readers can simultaneously position multiple forklifts, and the hardware system structure is simple and easy to build. Moreover, the RFID antenna signal has a wide recognition range, and full-area signal coverage can be achieved with fewer RFID antennas.

[0041] (2) According to the distances between the coordinate positions of each RFID tag and the coordinate positions of the RFID antenna group, and the measured phases of each RFID tag, the positioning loss function is constructed; the constructed loss function combines the relative position relationship between the calibrated forklift and the fixedly arranged RFID tag group, and the distance from the RFID antenna group to the RFID tag group, which can characterize the difference degree between the positioning information corresponding to the measured phase of the RFID tag group and the actual positioning, and has a low computational complexity;

[0042] (3) Calculate the difference degree between each reliable pose corresponding to the forklift at the (t - 1)-th sampling moment and each reliable pose at the t-th sampling moment, and delete the poses with large differences from the feasible poses to finally obtain the target positioning result; the computational complexity is low, but it can better improve the positioning accuracy.

[0043] (4) Each RFID tag has a unique identity code to ensure the uniqueness of identification; such as EPC, it has unique identification, and has advantages such as strong anti-wear and anti-pollution capabilities and low cost, which can better adapt to the factory environment and reduce costs. Description of the Drawings

[0044] Figure 1 is the flowchart of the indoor forklift global positioning method based on RFID provided in Embodiment 1 of the present invention.

[0045] Figure 2 is the schematic diagram of the spatial relative position between the forklift, the RFID antenna group and the RFID tag group in Embodiment 6 of the present invention.

[0046] Figure 3It is a schematic diagram of the relative spatial positions among the wireless electromagnetic interference board, the RFID antenna group, and the RFID tag group on the forklift in Embodiment 6 of the present invention. Detailed implementation manners

[0047] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0048] Embodiment 1

[0049] As Figure 1 shown, the present invention provides an indoor forklift global positioning method based on RFID, including:

[0050] S1: Calibrate the relative position relationship between the forklift and the RFID tag group fixedly arranged thereon; calibrate the coordinate positions of the RFID antenna group for collecting the signals of the RFID tag group;

[0051] S2: Use the RFID antenna group to collect the measured phases of each RFID tag in the RFID tag group at each sampling moment;

[0052] S3: Based on the coordinate positions of the RFID antenna group, convert the measured phases of at least two RFID tags at each sampling moment into the coordinate positions of the RFID tag group; based on the relative position relationship between the forklift and the RFID tag group, calculate multiple possible poses of the forklift at each sampling moment according to the coordinate positions of the RFID tag group;

[0053] S4: Construct a positioning loss function according to the difference degree between the measured phases and the actual phases of each RFID tag; calculate the positioning loss function values corresponding to the various possible poses of the forklift at each sampling moment, and use the multiple possible poses with the positioning loss function values lower than the threshold as the credible poses;

[0054] S5: Select at least one from the multiple credible poses of the forklift at each sampling moment as the pose positioning result corresponding to that sampling moment.

[0055] The indoor warehousing forklift positioning system provided in this embodiment includes: a computing center for operation and data processing, an RFID reader, an RFID antenna group, and an RFID tag group; the RFID reader continuously polls through the RFID antenna to obtain relevant information of the RFID tag group, and the computing center executes steps S1 - S5.

[0056] Specifically, in this embodiment, the RFID antenna array is used to collect the phase information of the RFID tags on the forklift, and then the RFID tags are located through the distance conversion relationship. Then, according to the relationship between the RFID tag group and the forklift position, the possible poses of the forklift are obtained. Furthermore, the loss function is used to eliminate the poses with large errors to obtain the reliable poses, and finally the pose positioning result is selected from them. Using RFID positioning technology has the advantages of fast positioning speed and low cost; according to the difference degree between the measured phase and the actual phase of each RFID tag, a positioning loss function is constructed to eliminate the possible poses corresponding to the larger loss function values, which can improve the positioning accuracy and the calculation complexity is low.

[0057] Beneficial effects: The present invention can realize the fast global positioning of the stacker forklift, and has the advantages of high positioning accuracy, good positioning real-time performance, and independent positioning. In addition, the same set of RFID antennas and readers can be used to position multiple forklifts at the same time, and the hardware system structure is simple and easy to build. And the RFID antenna signal recognition range is relatively wide, and the full-area signal coverage can be realized with fewer RFID antennas.

[0058] Embodiment 2

[0059] Step S4 includes:

[0060] S41: Construct a positioning loss function according to the distance between the coordinate positions of each RFID tag and the coordinate position of the RFID antenna array, and the measured phase of each RFID tag;

[0061] S42: Calculate the positioning loss function values corresponding to each possible pose of the forklift at each sampling moment, and take the multiple possible poses with the positioning loss function values lower than the threshold as the reliable poses.

[0062] Among them, the positioning loss function characterizes the difference degree between the positioning information of the RFID tag group corresponding to the measured phase of the RFID tag group and the actual position of the RFID tag group.

[0063] Embodiment 3

[0064] The positioning loss function in S41 is expressed as:

[0065]

[0066] Among them, p is the pose identifier, P=(x, y, ω), which is the forklift pose. The following x, y, z are the coordinates of the RFID antenna and the RFID tag are different. M represents the total number of RFID antennas in the RFID antenna array; N represents the total number of RFID tags in the RFID tag group; λ represents the wavelength of the RFID signal, (x i , y i ) represents the coordinates of the i-th RFID antenna, (x j , yj ) represents the coordinates of the j-th RFID tag, h ij represents the distance from the j-th RFID tag along the Z-axis direction to the i-th RFID antenna, γ ij represents the measured phase of the j-th RFID tag collected by the i-th RFID antenna, β i represents the constant error of the i-th RFID antenna. In the scenario of this embodiment, it is a two-dimensional pose, and the non-parallel situation is not considered. Here, h is a constant.

[0067] Specifically, the system loss function F(p) can be constructed according to the conversion relationship between phase and distance. The value of the loss function is the sum of the squares of the phase and distance errors between the RFID tag and the RFID antenna. For the sake of simplicity of description, an example of two RFID antennas and four RFID tags is used for description; the RFID antenna group includes RFID antenna A and RFID antenna B, and the RFID tag group includes four RFID tags that form a rectangle; the plane where the two RFID antennas are located is parallel to the plane where the RFID tag group is located:

[0068]

[0069] Secondly, construct the relationship between the positions (x i , y i ) of the four RFID tags and the forklift pose (x p , y p , ω p ), and transform F(p) into a function determined by the estimated pose (x p , y p , ω p ) of the forklift and the measured phase Γ.

[0070] (a, b are the length and width of the rectangle)

[0071]

[0072] Set the loss function threshold JF, retain the estimated poses within the threshold, delete the estimated poses beyond the threshold, and at the same time update the pose estimation matrix P to P′. P′ is the credible pose of the forklift, that is:

[0073] P′ = P(F < JF)

[0074] Embodiment 4

[0075] Step S5 includes:

[0076] S51: Calculate the degree of difference between each credible pose corresponding to the forklift at the (t - 1)-th sampling moment and each credible pose at the t-th sampling moment;

[0077] S52: If the degree of difference between two adjacent sampling times is within a preset range, it is regarded as a match; otherwise, it is regarded as a mismatch.

[0078] S53: Delete each unreliable pose that does not match, and obtain the pose positioning result of the forklift at each sampling time.

[0079] Beneficial effects: Based on the reliable poses of the forklift in the two-dimensional space, this embodiment uses the front and rear reliable pose matching algorithm to exclude the incorrect poses caused by errors and interferences, and realizes the determination of the pose of the forklift during movement. The present invention can quickly realize the calibration of the indoor pose of the stacking forklift, and has the advantages of high positioning accuracy and good real-time performance.

[0080] Embodiment 5

[0081] Step S51 includes: Using the formula S(p t , p t-1 ) = (x t - x t-1 ) 2 + (y t - y t-1 ) 2 + (ω t - ω t-1 ) 2 Calculate the degree of difference between any reliable pose p t-1 = (x t-1 , y t-1 , ω t-1 ) corresponding to the forklift at the (t - 1)-th sampling time and any reliable pose p t = (x t , y t , ω t ) at the t-th sampling time.

[0082] Specifically, first, since the sampling time is short, the speed and displacement of the forklift will not mutate at adjacent sampling times, and the following pose front and back matching function can be constructed. Where p t is a reliable pose at the t-th sampling time, p t ∈ P′ t , p t = (x t , y t , ω t ) T . p t-1 Similarly:

[0083] S(p t , p t-1 ) = (x t - x t-1 ) 2 + (y t - yt-1 ) 2 +(ω t -ω t-1 ) 2 。

[0084] Secondly, set the threshold JS of the pose matching function before and after. When S is less than the threshold JS, p t and p t-1 can be matched. Retain all the poses in P' t and P' t-1 that can complete the matching, delete the poses that cannot be matched. At the same time, update P' t and P' t-1 to P'' t and P'' t-1 :

[0085] P t ″, P t-1 ″ = P t ′(S < JS), P t-1 ′(S < JS).

[0086] P″ is the pose where the forklift finally completes two-dimensional positioning. As the sampling time goes by, P″ will soon only contain a unique set of poses, ensuring the reliability of the positioning.

[0087] Embodiment 6

[0088] As Figure 2 and Figure 3 shown, the RFID antenna group includes RFID antenna A and RFID antenna B, and the RFID tag group includes four RFID tags that form a rectangle; the planes where the two RFID antennas are located are parallel to the plane where the RFID tag group is located;

[0089] Among them, two RFID antennas with a certain spacing can be installed in a certain height area in the indoor storage space to poll and scan the RFID tags in the covered area; according to the discontinuous phase information at the same sampling moment, calculate all possible coordinates of the RFID tags in the two-dimensional plane, and according to the relative geometric relationship of the four RFID tags, retain the possible RFID tag coordinates, and then deduce the possible pose of the forklift at that moment; further, use the positioning loss function to perform credibility discrimination to obtain the credible pose (x, y, ω). This positioning system retains the credible pose of the forklift at each sampling moment and performs the front and rear forklift pose matching algorithm to exclude the wrong credible poses caused by errors, and realizes the two-dimensional positioning of the forklift in the indoor storage space.

[0090] The whole process is described in detail as follows: S1: Calibrate the relative coordinates of RFID antenna A and RFID antenna B offline, and the constant error β A 、βB The length a, width b of the rectangle formed by the RFID tag group, and the distance h between the RFID tag and the RFID antenna in the Z-axis direction; S2: The reader polls and scans the RFID tag information to obtain the phase information Γ of the four RFID tags measured by the two RFID antennas near the sampling moment, where Γ is a 2×4 matrix; S3: According to the phase information of RFID tag 1 and RFID tag 3 obtained, calculate all possible two-dimensional coordinates C1, C3 within a certain area. The number of rows of C1 and C3 is 2, and the number of columns is the number of possible coordinates. Then, according to the geometric relationship between C1, C3 and the layout of the RFID tag group, calculate the possible poses of the forklift. S4: Construct a system loss function according to the phase-distance conversion relationship and the relative position relationship of the RFID tag group, and determine the credible position of the forklift according to the value of the loss function. S5: Retain the credible pose of the forklift at each sampling moment, and perform a front-back matching algorithm on the credible poses at adjacent moments to exclude the wrongly estimated poses and retain the correct poses.

[0091] Preferably, S2 specifically includes: The reader polls and scans the RFID tag information, and performs phase information sampling every

[0092]

[0093] to obtain the phase information Γ of the four RFID tags measured by RFID antenna A and RFID antenna B near the same sampling moment. f is the sampling frequency, and Γ is a 2×4 matrix, and the specific form is as follows:

[0094]

[0095] where γ Aj and γ Bj are the phase values of the jth RFID tag measured by RFID antenna A and RFID antenna B respectively, λ is the wavelength of the RFID signal, (x j , y j ) is the coordinate of the jth RFID tag in the two-dimensional plane it is located in, β A represents the constant error of RFID antenna A, β B represents the constant error of RFID antenna B, (x A , y A ) is the position of RFID antenna A, (x B , y B) is the position of RFID antenna B. β is a constant error in the RFID signal measurement process, which is only related to the RFID antenna. The effective range of the RFID signal is limited, about 10m. According to the distance conversion relationship, all possible coordinates of RFID tag 1 and RFID tag 3 within the effective range of the RFID signal can be estimated - C1 2×m , C3 2×n . m and n are the numbers of estimated coordinates of RFID tag 1 and RFID tag 3 respectively.

[0096] Preferably, step S32 specifically includes: First, use the complex number Z mn to represent the relative position relationship between RFID tag 1 and RFID tag 3. The definition of the matrix is as follows. |Z| is the distance matrix between RFID tag 1 and RFID tag 3, and Arg(Z) is the angle matrix between RFID tag 1 and RFID tag 3.

[0097] Z mn = (X1 T × [1] 1×n - [1] m×1 × X3) + i(Y1 T × [1] 1×n - [1] m×1 × Y3).

[0098] Calculate the possible poses of the forklift from C1, C3 and the relative geometric position relationship of the RFID tags,

[0099]

[0100] Then, judge the validity of the pose estimation by |Z|. When the distance between RFID tag 1 and RFID tag 3 is not within the error tolerance range, the pose estimation is invalid.

[0101]

[0102] Retain the valid pose estimation data in matrices X p , Y p , Ω p and update them to X′ p , Y′ p , Ω′ p . The updated X′ p , Y′ p , Ω′ p are all row vectors. The possible pose P of the forklift is:

[0103] Step S3 includes:

[0104] S31: Given the measured phases of any two RFID tags, calculate the possible coordinates of any two RFID tags according to the distance conversion relationship S32: Obtain the possible pose of the forklift at the current sampling moment according to the possible coordinates of any two RFID tags and the matrix position relationship of the four RFID tags; where γ

[0105] S32: Obtain the possible pose of the forklift at the current sampling moment according to the possible coordinates of any two RFID tags and the matrix position relationship of the four RFID tags; where γ Aj 、γ Bj are the phase values of the jth RFID tag measured by RFID antenna A and RFID antenna B respectively, λ is the wavelength of the RFID signal, (x j , y j ) is the coordinate of the jth RFID tag in the two-dimensional plane where it is located, β A represents the constant error of RFID antenna A, β B represents the constant error of RFID antenna B, (x A , y A ) is the position of RFID antenna A, (x B , y B ) is the position of RFID antenna B.

[0106] Among them, according to the conversion relationship between phase and distance, calculate all possible coordinates of RFID tag 1 and RFID tag 3 in the two-dimensional plane where the electromagnetic interference-free flat is located. The effective range of the RFID signal is about 10m, which can limit the coordinate estimation area of the RFID tag. For any set of RFID tag 1 and RFID tag 3, the pose p of the forklift can be calculated from the geometric position relationship, and the validity of the pose estimation can be judged by the distance 13 between RFID tag 1 and RFID tag 3. When their distance satisfies: the pose estimation is valid, where δ is the error tolerance range.

[0107] Example 7

[0108] Any two RFID tags are on the diagonal of a rectangle; step S32 includes: using the formula to calculate multiple possible poses (X p , Y p , Ω p ) of the forklift at each sampling moment.

[0109] Among them, each possible pose is represented as (x p , y p , ω p ), (x p , y p ) represents the possible position information of the forklift, ω pIndicates the possible angle information of the forklift; RFID tag 1 and RFID tag 3 are on the same diagonal; (X1, Y1) respectively represents the matrix composed of the X-axis and Y-axis coordinate sets of RFID tag 1, and the elements are (x1, y1); (X3, Y3) represents the matrix composed of the X-axis and Y-axis coordinate sets of RFID tag 3, and the elements are (x3, y3); m and n are respectively the number of estimated coordinates of RFID tag 1 and RFID tag 3, |Z| is the distance matrix between RFID tag 1 and RFID tag 3, Arg(Z) is the angle matrix between RFID tag 1 and RFID tag 3, and b and a are respectively the length and width of the matrix.

[0110] This embodiment is based on the RFID phase and distance conversion technology. By arranging an RFID tag group with a specific geometric relationship, the reliable pose of the forklift in the two-dimensional space is calculated; and a front and rear reliable pose matching algorithm is proposed to eliminate the wrong poses caused by errors and interference, so as to realize the pose determination of the forklift during the movement process. The present invention can quickly realize the calibration of the indoor pose of the stacker truck, and has the advantages of high positioning accuracy and good real-time performance.

[0111] Embodiment 8

[0112] Each RFID tag has a unique identity code to ensure the uniqueness of identification.

[0113] Specifically, taking the rectangular setting of four RFID tags as an example for description, a non-electromagnetic interference flat plate can be installed on the top of the forklift, and four RFID tags with known EPC (electronic product code) numbers can be orderly pasted on the flat plate in a rectangular arrangement. Two RFID antennas with a certain distance between them are installed in a certain height area in the indoor storage space, and the covered area is polled and scanned; according to the discontinuous phase information at the same sampling moment, all possible coordinates of the RFID tags in the two-dimensional plane are calculated, and according to the relative geometric relationship of the four RFID tags, the reliable RFID tag coordinates are retained, and then the reliable pose (x, y, ω) of the forklift at this moment is deduced.

[0114] Beneficial effects: RFID tags have unique identification, and have the advantages of strong anti-wear and anti-pollution capabilities and low cost, can better adapt to the factory environment, and reduce costs.

[0115] Embodiment 9

[0116] According to another aspect of the present invention, there is provided an indoor forklift global positioning device based on RFID, including:

[0117] A position relationship calibration module for calibrating the relative position relationship between the forklift and the RFID tag group fixedly arranged thereon; calibrating the coordinate positions of the RFID antenna group for collecting the signals of the RFID tag group;

[0118] The RFID tag phase acquisition module is used to collect the measured phases of each RFID tag in the RFID tag group at each sampling moment by using the RFID antenna group;

[0119] The possible pose calculation module is used to convert the measured phases of at least two RFID tags at each sampling moment into the coordinate positions of the RFID tag group based on the coordinate positions of the RFID antenna group; and calculate multiple possible poses of the forklift at each sampling moment according to the coordinate positions of the RFID tag group based on the relative position relationship between the forklift and the RFID tag group;

[0120] The feasible pose determination module is used to construct a positioning loss function according to the difference degree between the measured phase and the actual phase of each RFID tag; calculate the positioning loss function values corresponding to the possible poses of the forklift at each sampling moment, and take the multiple possible poses with the positioning loss function values lower than the threshold as the credible poses;

[0121] The target pose determination module is used to select at least one from the multiple credible poses of the forklift at each sampling moment as the pose positioning result corresponding to the sampling moment.

[0122] Embodiment 10

[0123] According to another aspect of the present invention, there is provided an indoor forklift global positioning device based on RFID, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, the steps of the indoor forklift global positioning method based on RFID are implemented.

[0124] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An indoor forklift global positioning method based on RFID, characterized in that, Including: S1: Calibrate the relative position relationship between the forklift and the RFID tag group fixedly arranged thereon; Calibrate the coordinate positions of the RFID antenna group for collecting the signals of the RFID tag group; S2: Use the RFID antenna group to collect the measured phases of each RFID tag in the RFID tag group at each sampling moment; S3: Based on the coordinate positions of the RFID antenna group, convert the measured phases of at least two of the RFID tags at each sampling moment into the coordinate positions of the RFID tag group; Based on the relative position relationship between the forklift and the RFID tag group, calculate multiple possible poses of the forklift at each sampling moment according to the coordinate positions of the RFID tag group; S4: Use the formula to construct a positioning loss function; calculate the positioning loss function values corresponding to each of the possible poses of the forklift at each sampling moment, and use multiple possible poses with positioning loss function values lower than the threshold as credible poses; where p is the identifier of the pose, M represents the total number of RFID antennas in the RFID antenna group; N represents the total number of RFID tags in the RFID tag group; represents the wavelength of the RFID signal, represents the coordinates of the i-th RFID antenna, represents the coordinates of the j-th RFID tag, represents the distance from the j-th RFID tag along the Z-axis direction to the i-th RFID antenna, represents the measured phase of the j-th RFID tag collected by the i-th RFID antenna, represents the constant error of the i-th RFID antenna; S5: Select at least one from the multiple credible poses of the forklift at each sampling moment as the pose positioning result corresponding to that sampling moment.

2. The indoor forklift global positioning method based on RFID according to claim 1, characterized in that, The S5 includes: S51: Calculate the degree of difference between each credible pose corresponding to the (t - 1)-th sampling moment of the forklift and each credible pose at the t-th sampling moment; S52: If the degree of difference between two adjacent sampling moments is within a preset range, it is regarded as a match, otherwise it is regarded as a mismatch; S53: Delete each of the mismatched credible poses to obtain the pose positioning result of the forklift at each sampling moment.

3. The indoor forklift global positioning method based on RFID according to claim 2, wherein The S51 includes: Using the formula calculate any credible pose corresponding to the forklift at the (t - 1)-th sampling moment and the degree of difference from any credible pose at the t-th sampling moment .

4. The indoor forklift global positioning method based on RFID according to claim 1, wherein The RFID antenna group includes RFID antenna A and RFID antenna B, and the RFID tag group includes four RFID tags forming a rectangle; The planes where the two RFID antennas are located are parallel to the plane where the RFID tag group is located; The S3 includes: S31: Given the measured phases of any two RFID tags, according to the distance conversion relationship Calculate the possible coordinates of any two of the RFID tags: S32: Based on the possible coordinates of the any two RFID tags and the matrix position relationship of the four RFID tags, obtain the possible pose of the forklift at the current sampling moment; Among them, and are the phase values of the j-th RFID tag measured by RFID antenna A and RFID antenna B respectively, is the wavelength of the RFID signal, is the coordinate of the j-th RFID tag in the two-dimensional plane where it is located, represents the constant error of RFID antenna A, represents the constant error of RFID antenna B, is the position of RFID antenna A, is the position of RFID antenna B.

5. The RFID-based indoor forklift global positioning method according to claim 4, characterized in that, The any two RFID tags are on the diagonal of the rectangle; The S32 includes: Using the formula calculate multiple possible poses of each of the forklifts at each of the sampling times ; Among them, each of the possible poses is represented as , represents the possible position information of the forklift, represents the possible angle information of the forklift; RFID tag 1 and RFID tag 3 are on the same diagonal line; respectively represent the matrix formed by the X-axis and Y-axis coordinate sets of RFID tag 1, and the elements are ; represents the matrix formed by the X-axis and Y-axis coordinate sets of RFID tag 3, and the elements are ; and are respectively the numbers of estimated coordinates of RFID tag 1 and RFID tag 3, is the distance matrix between RFID tag 1 and RFID tag 3, is the angle matrix between RFID tag 1 and RFID tag 3, and b and a are respectively the length and width of the matrix.

6. The indoor forklift global positioning method based on RFID according to claim 1, characterized in that, Each of the RFID tags has a unique identity code to ensure the uniqueness of identification.

7. An indoor forklift global positioning device based on RFID, characterized in that, Including: A position relationship calibration module for calibrating the relative position relationship between the forklift and the RFID tag group fixedly arranged thereon; Calibrate the coordinate positions of the RFID antenna group for collecting the signals of the RFID tag group; An RFID tag phase acquisition module for using the RFID antenna group to collect the measured phases of each RFID tag in the RFID tag group at each sampling moment; A possible pose calculation module for converting the measured phases of at least two of the RFID tags at each sampling moment into the coordinate positions of the RFID tag group based on the coordinate positions of the RFID antenna group; Based on the relative position relationship between the forklift and the RFID tag group, calculate multiple possible poses of the forklift at each sampling moment according to the coordinate positions of the RFID tag group; A feasible pose determination module, which is used to utilize the formula to construct a positioning loss function; calculate the positioning loss function values corresponding to each of the possible poses of the forklift at each sampling moment, and use multiple possible poses with positioning loss function values lower than the threshold as credible poses; where p is the identifier of the pose, M represents the total number of RFID antennas in the RFID antenna group; N represents the total number of RFID tags in the RFID tag group; represents the wavelength of the RFID signal, represents the coordinates of the i-th RFID antenna, represents the coordinates of the j-th RFID tag, represents the distance from the j-th RFID tag to the i-th RFID antenna in the Z-axis direction, represents the measured phase of the j-th RFID tag collected by the i-th RFID antenna, represents the constant error of the i-th RFID antenna; The target pose determination module is used to select at least one from the multiple credible poses at each sampling moment of the forklift as the pose positioning result corresponding to that sampling moment.

8. An indoor forklift global positioning device based on RFID, comprising a memory and a processor, wherein the memory stores a computer program, and is characterized in that, When the processor executes the computer program, it implements the steps of the RFID-based indoor forklift global positioning method according to any one of claims 1 to 6.

Images