CN110132273B - Mobile robot navigation method based on RFID servo technology - Google Patents
Mobile robot navigation method based on RFID servo technology Download PDFInfo
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- CN110132273B CN110132273B CN201910306967.5A CN201910306967A CN110132273B CN 110132273 B CN110132273 B CN 110132273B CN 201910306967 A CN201910306967 A CN 201910306967A CN 110132273 B CN110132273 B CN 110132273B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C21/00—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00
- G01C21/20—Instruments for performing navigational calculations
- G01C21/206—Instruments for performing navigational calculations specially adapted for indoor navigation
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K17/00—Methods or arrangements for effecting co-operative working between equipments covered by two or more of main groups G06K1/00 - G06K15/00, e.g. automatic card files incorporating conveying and reading operations
- G06K17/0022—Methods or arrangements for effecting co-operative working between equipments covered by two or more of main groups G06K1/00 - G06K15/00, e.g. automatic card files incorporating conveying and reading operations arrangements or provisious for transferring data to distant stations, e.g. from a sensing device
- G06K17/0029—Methods or arrangements for effecting co-operative working between equipments covered by two or more of main groups G06K1/00 - G06K15/00, e.g. automatic card files incorporating conveying and reading operations arrangements or provisious for transferring data to distant stations, e.g. from a sensing device the arrangement being specially adapted for wireless interrogation of grouped or bundled articles tagged with wireless record carriers
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Abstract
The invention belongs to the field of indoor mobile robot navigation and discloses a mobile robot navigation method based on an RFID servo technology. The method comprises the following steps: (a) arranging two RFID antennas on a mobile robot, arranging an RFID tag on a target object, and establishing a direction target function and a target strength function; (b) the mobile robot moves, the two RFID antennas are respectively communicated with the RFID tags to obtain two communication signals, and the two communication signals are respectively analyzed to obtain two phase information and signal strength; (c) and comparing the two communication signals with a preset intensity objective function and a direction objective function so as to adjust the moving direction of the mobile robot and judge whether the mobile robot reaches a target object. By the method, the mobile robot navigation does not need to reference a label and calibrate the position of the antenna, and has the advantages of good real-time performance, small calculated amount and low cost.
Description
Technical Field
The invention belongs to the field of indoor mobile robot navigation, and particularly relates to a mobile robot navigation method based on an RFID servo technology.
Background
The research of the navigation and positioning technology of the mobile robot is the basis for realizing the intellectualization of the mobile robot, and an RFID (radio Frequency identification) system has the unique advantages of unique ID identification, low price, low requirement on computer hardware equipment and the like, and has very outstanding advantages in the functional application of the mobile robot such as positioning and navigation and the like.
Most of the existing navigation methods based on RFID information are based on navigation of reference tags, namely, the current position and direction of a robot are continuously positioned through pose calculation, and then the robot is navigated according to the relative position relationship between the robot and a target object, so that a lot of students research the positions. This method requires placing a set of passive RFID reference tags on a cartesian grid, calibrating the absolute position information of each tag in advance for position identification. During navigation, an RFID reader attached to the mobile robot receives IDs of RFID tags in its vicinity to estimate a current position of the robot, and uses it to solve a minimum cost path from the current position to a target point. In addition to storing the position information in the reference label, the method is to store the distance information from each label to the target label in the reference label, so that a 'navigation map' of the robot can be made into a 'distance map', the robot can calculate the distance to any point, and the optimal path from the robot to the target label is calculated according to the A-line algorithm; the other research method is to store corresponding instructions and actions in the reference label, and the robot executes related control instructions every time the robot reads one label, so as to reach the target label. Although the method has good navigation effect and short path, a large number of reference labels need to be laid, the label arrangement work is very complicated, and the method can only be applied to specific working environments.
Another typical approach to navigation using RFID information is to lay a series of RFID tags on the ceiling and move the robot along a path formed by orthogonal projections of the RFID tags on the ceiling. The method needs to equip 8 antennas to form a circle in the 360-degree range of the top of the robot, estimate the direction in which the robot should move according to the antenna obtaining the maximum RSSI (signal strength), and then control the movement of the robot by continuously updating the movement direction of the robot. The method is different from most RFID-based positioning navigation systems, navigation can be performed without resolving position information, and distance and direction errors generated by continuous accumulation over time are avoided. This method can navigate according to a defined path, but requires 8 RFID antennas, which is costly.
Disclosure of Invention
Aiming at the defects or the improvement requirements of the prior art, the invention provides a mobile robot navigation method based on an RFID servo technology, which ensures that the moving direction of a mobile robot judges whether the mobile robot reaches a target object in real time by arranging an RFID antenna on the mobile robot and arranging an RFID label on the target object and communicating the RFID label through the RFID antenna and moving according to a preset direction target function and a target strength function, realizes navigation under the condition of not positioning the relative position of the robot and the target label, and has the advantages of good real-time performance, small calculation amount, no need of calibrating the relative position of the antenna and the robot, simple system and the like.
In order to achieve the above object, according to the present invention, there is provided a mobile robot navigation method based on RFID servo technology, the method comprising the steps of:
(a) the method comprises the steps that two RFID antennas are arranged on a mobile robot, an RFID tag is arranged on a target object, and a direction objective function and a strength objective function are established, wherein the direction objective function is used for ensuring that the advancing direction of the mobile robot faces the target object, and a target strength threshold value is used for judging whether the mobile robot reaches the target object;
(b) the mobile robot moves, the two RFID antennas are respectively communicated with the RFID tags to obtain two radio frequency signals, and the two radio frequency signals are analyzed to respectively obtain the phase information and the signal intensity of the two radio frequency signals;
(c) comparing the strength of the two communication signals with a preset strength target function, stopping the mobile robot when the preset strength condition is met, otherwise, calculating the direction target function by using the phase information of the two communication signals, keeping the current movement direction of the mobile robot to continuously move when the value of the target function meets the preset direction condition, returning to the step (b), otherwise, adjusting the moving direction of the mobile robot to continuously move, and returning to the step (b) until the preset strength condition is met, thereby realizing the navigation of the mobile robot to the target object.
Further preferably, in step (a), the directional objective function is preferably according to the following expression:
Δg＝g1-g2
wherein, g1And g2Are the phase gradients of the two communication signals, respectively, and Δ g is the phase gradient difference.
Further preferably, in the step (a), when the phase gradient is calculated, the phase information of the communication signal is first unwrapped, and then the phase gradient is calculated according to the following expression:
wherein d phi1And d phi2Respectively the phase variation, s, of two of the communication signals after unwrapping within a sampling time1And s2Respectively the corresponding moving distance of the two RFID antennae acquiring the communication signals in the corresponding sampling time.
Further preferably, in step (c), the preset direction condition is preferably: Δ g ═ 0.
Further preferably, in the step (c), the adjusting the moving direction of the mobile robot to move continuously adjusts the moving speed of the mobile robot preferably by using a PID control algorithm.
Further preferably, the moving speed of the mobile robot is adjusted by using a PID control algorithm, and is preferably calculated according to the following expression:
wherein, KP，KIAnd KDRespectively, proportional, integral and differential term coefficients, j is the jth sampling instant, k is the kth sampling instant, and w is the robot's movement speed.
Further preferably, the preset intensity condition is preferably:
|RSSIleft-RSSI0|＜thresholds1
|RSSIright-RSSI0|＜thresholds1
|RSSIleft-RSSIright|≤thresholds2
wherein the RSSIleft、RSSIrightRespectively signal strength values, RSSI, of two of said communication signals0Is the signal strength, thresholds, corresponding to the set distance of arrival1、thresholds2Respectively, are set acceptable signal strength thresholds.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
1. the method combines the mobile robot with the RFID system, directly carries out navigation control on the robot under the condition of not calculating the relative pose relationship between the robot and the label, has lower requirement on the system, and does not need to calibrate the relative pose relationship between the robot and the antenna;
2. according to the invention, through the designed RFID servo control algorithm, a positioning process is not needed, the situation of navigation failure caused by errors in the positioning process can be avoided, and the calculation load is small;
3. the navigation method provided by the invention does not need a reference label, has good navigation effect, simple system, less required antennas and low cost, and has the advantages of strong anti-interference capability, small calculated amount and the like.
Drawings
FIG. 1 is a schematic diagram of a mobile robot navigation system for implementing an RFID navigation method, constructed in accordance with a preferred embodiment of the present invention;
FIG. 2 is a flow chart of a method for RFID servo technology based mobile robot navigation constructed in accordance with a preferred embodiment of the present invention;
FIG. 3 is a schematic diagram of a servo control system constructed in accordance with a preferred embodiment of the present invention;
fig. 4 is a main flow chart of a servo control process constructed in accordance with a preferred embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Fig. 1 is a schematic diagram of a mobile robot navigation system for implementing an RFID navigation method according to a preferred embodiment of the present invention, as shown in fig. 1, the present invention combines an RFID system with a mobile robot, uses the mobile robot carrying an RFID reader to read an RFID tag mounted on a target object through two left and right antennas mounted on the robot, and the reader can acquire information such as ID information, phase, signal strength, and the like of the RFID tag in real time during communication with the tag through the RFID antenna, and can implement servo control using the information to complete a navigation function.
FIG. 2 is a flow chart of a mobile robot navigation method based on RFID servo technology according to a preferred embodiment of the present invention, as shown in FIG. 2, the present invention is implemented
According to the mobile robot navigation method based on the RFID servo technology, a mobile robot carrying an RFID reader-writer and an RFID antenna senses a target object provided with an RFID label, and a corresponding servo control algorithm is designed according to phase gradient information of the two antennas, so that the robot can directly navigate to the target position provided with the RFID label without referring to the label and positioning the label position, and the method specifically comprises the following steps:
s1 when the RFID reader-writer installed on the mobile robot moves along with the mobile robot, the RFID reader-writer can communicate with the RFID label installed on the target object through two independent RFID antennas installed on the mobile robot, and the RFID reader-writer continuously acquires information such as the phase, the signal intensity and the like of the two groups of RFID labels through the two RFID antennas;
s2, phase unwrapping is carried out on the two sets of acquired phase information, and then phase gradients of the phase information received by the left antenna and the right antenna within a certain time are calculated respectively;
specifically, phase gradients of the left antenna and the right antenna are respectively calculated according to phase information obtained by the left antenna and the right antenna in the communication process of the RFID reader-writer and the tag; order to
The amount of phase change of the left antenna over a sampling period,
is the phase variation quantity, S, of the right antenna in the same sampling time1For the corresponding moving distance, S, of the left antenna in the corresponding sampling time2For the corresponding moving distance of the right antenna in the corresponding sampling time, the phase gradient g of the two antennas can be calculated1，g2Respectively as follows:
s3, according to the phase gradients of the left antenna and the right antenna, constructing an objective function which takes the phase gradients received by the left antenna and the right antenna as a target and ensures that the motion direction of the robot is a direction facing a target label;
according to the difference of the phase gradients of the left and right antennas, g is equal to Δ g1-g2And constructing an objective function of the system. Specifically, the objective function Δ g of the control system is 0, that is, the phase gradients of the left and right antennas are equal during the movement of the robot, and the movement direction of the robot is a direction toward the target tag.
S4, controlling the robot by using a PID control method, adjusting the motion direction of the robot in real time, and keeping the phase gradients received by the left antenna and the right antenna equal in the motion process of the robot, so as to ensure that the robot moves towards the direction of the target label;
fig. 3 is a schematic diagram of a servo control system constructed according to a preferred embodiment of the present invention, as shown in fig. 3, in which a PID control algorithm is used to control the moving direction of a robot, specifically: the setpoint values for the PID control system are 0r (t): g1-g2The output of the system is the rotational speed y (t) of the mobile robot, 0: w, the observed value of the system is
The error value is. error ═ g1-g1。
Fig. 4 is a main flowchart of a servo control process constructed according to a preferred embodiment of the present invention, as shown in fig. 4, according to the control flow of the servo control system, in combination with the control law of the PID algorithm,
the rotation speed (moving speed) of the robot can be obtained according to the control rule of the input and output of the system and the PID control system
The robot then updates its rotational speed in real time, continuing to maintain motion toward the target tag.
S5, according to the corresponding requirements of different application scenes, when the signal strength received by the left antenna and the right antenna on the robot meets the corresponding requirements, the robot is considered to reach the target position with the target label, and the servo process is completed.
Specifically, the RSSI value of the signal strength at the corresponding position can be measured in advance according to the distance between the navigation request and the target object0And if the signal strength value measured by the RFID antenna on the robot meets the following conditions, the robot is considered to have reached the target:
|RSSIleft-RSSI0|＜thresholds1
|RSSIright-RSSI0|＜thresholds1
|RSSIleft-RSSIright|≤thresholds2
wherein the RSSIleft、RSSIrightRespectively representing left and right antenna measurementsSignal strength value of, RSSI0Is the signal strength, thresholds, corresponding to the set distance of arrival1、thresholds2Respectively, corresponding signal strength thresholds.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (6)
1. A mobile robot navigation method based on RFID servo technology is characterized by comprising the following steps:
(a) the method comprises the steps that two RFID antennas are arranged on a mobile robot, an RFID tag is arranged on a target object, and a direction objective function and a strength objective function are established, wherein the direction objective function is used for ensuring that the advancing direction of the mobile robot faces the target object, and a target strength threshold value is used for judging whether the mobile robot reaches the target object;
the directional objective function is expressed as follows:
Δg＝g1-g2
wherein, g1And g2Respectively, the phase gradients of the two communication signals, and Δ g is the phase gradient difference;
(b) the mobile robot moves, the two RFID antennas are respectively communicated with the RFID tags to obtain two radio frequency signals, and the two radio frequency signals are analyzed to respectively obtain the phase information and the signal intensity of the two radio frequency signals;
(c) comparing the strength of the two communication signals with a preset strength target function, stopping the mobile robot when the preset strength condition is met, otherwise, calculating the direction target function by using the phase information of the two communication signals, keeping the current movement direction of the mobile robot to continuously move when the value of the target function meets the preset direction condition, returning to the step (b), otherwise, adjusting the moving direction of the mobile robot to continuously move, and returning to the step (b) until the preset strength condition is met, thereby realizing the navigation of the mobile robot to the target object.
2. The navigation method of a mobile robot based on RFID servo technology as claimed in claim 1, wherein in the step (a), the phase gradient is calculated by first performing unwrapping process on the phase information of the communication signal and then calculating the phase gradient according to the following expression:
wherein d phi1And d phi2Respectively the phase variation, s, of two of the communication signals after unwrapping within a sampling time1And s2Respectively the corresponding moving distance of the two RFID antennae acquiring the communication signals in the corresponding sampling time.
3. The navigation method of a mobile robot based on RFID servo technology as claimed in claim 1 or 2, wherein in step (c), the preset direction condition is: Δ g ═ 0.
4. The navigation method of a mobile robot based on RFID servo technology as claimed in claim 1 or 2, wherein in the step (c), the adjusting the moving direction of the mobile robot continues to move and the moving speed of the mobile robot is adjusted using a PID control algorithm.
5. The navigation method of the mobile robot based on the RFID servo technology as claimed in claim 4, wherein the PID control algorithm is used to adjust the moving speed of the mobile robot, and the moving speed is calculated according to the following expression:
wherein, KP，KIAnd KDRespectively, proportional, integral and differential term coefficients, j is the jth sampling instant, k is the kth sampling instant, and w is the robot's movement speed.
6. The navigation method for a mobile robot based on RFID servo technology as claimed in claim 4, wherein the preset strength condition is:
|RSSIleft-RSSI0|＜thresholds1
|RSSIright-RSSI0|＜thresholds1
|RSSIleft-RSSIright|≤thresholds2
wherein the RSSIleft、RSSIrightRespectively signal strength values, RSSI, of two of said communication signals0Is the signal strength, thresholds, corresponding to the set distance of arrival1、thresholds2Respectively, are set acceptable signal strength thresholds.
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| CN111459192B (en) * | 2020-03-26 | 2021-08-03 | 华中科技大学 | Mobile robot dynamic target tracking method based on RFID |
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