CN115657686B - Multi-robot formation control method based on Backstepping - Google Patents

Multi-robot formation control method based on Backstepping Download PDF

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CN115657686B
CN115657686B CN202211594765.3A CN202211594765A CN115657686B CN 115657686 B CN115657686 B CN 115657686B CN 202211594765 A CN202211594765 A CN 202211594765A CN 115657686 B CN115657686 B CN 115657686B
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pilot
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CN115657686A (en
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马小陆
狄敏
姚志强
陆章其
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Jiangsu Province Nanjing University Of Science And Technology Electronic Information Technology Co ltd
Nanjing Aidesheng Software Technology Co ltd
Nanjing Nanda Electronic Wisdom Service Robot Research Institute Co ltd
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Jiangsu Province Nanjing University Of Science And Technology Electronic Information Technology Co ltd
Nanjing Aidesheng Software Technology Co ltd
Nanjing Nanda Electronic Wisdom Service Robot Research Institute Co ltd
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Abstract

The invention discloses a multi-robot formation control method based on Backstepping, which comprises the steps of designing a virtual pilot-following model according to robot kinematics, and converting formation control problems into track tracking problems of a following robot and a virtual pilot; decomposing a nonlinear system of the robot into three subsystems, introducing virtual error variables, and designing a formation controller by combining with a Lyapunov function; according to the invention, a virtual robot is introduced, a virtual pilot-following model is designed, the formation control problem is converted into the track tracking problem of the following robot and a virtual pilot, and the problem that if the pilot robot fails in the actual situation, the whole system is paralyzed is solved; and a stable formation control law is designed, and under the action of the control law, the convergence error of the controller is smaller, and the system error is smaller.

Description

Multi-robot formation control method based on Backstepping
Technical Field
The invention relates to the technical field of automatic control, in particular to a multi-robot formation control method based on Backstepping.
Background
In recent years, with rapid development of robot technology and continuous expansion of task demands, a single mobile robot has been difficult to complete a large number of complex tasks. Inspired by the collaborative behavior of ant foraging, bird colony, fish colony foraging, aggregation, rear-end collision and other populations, researchers have developed exploration for multi-mobile robot formation.
The formation technology has become a hot spot for research in application fields such as daily entertainment, industrial manufacturing, military operations, aerospace and the like at home and abroad. The technology integrates basic knowledge of disciplines such as artificial intelligence, control science, communication technology and the like, and the technical development level represents the state modern automation level. The formation control task is mainly to realize that multiple robots reach target points under the condition of a certain formation. Formation control mainly includes five problems: generating formation, maintaining formation, reconstructing formation, avoiding obstacle and self-adapting. For this reason, researchers have made a great deal of study, and the mainstream formation control methods that have been proposed now are: pilot following method, virtual structure method, behavior-based method, graph theory method, artificial potential field method, etc.
The pilot following method is simple to control, modeling and demonstration are simple, information processing amount is small, a follower does not have formation feedback, the speed of a leader is too high, formation is difficult to stabilize, and in actual conditions, if pilot robots fail, the whole system is paralyzed, the virtual structure method takes formation errors as feedback to control each robot to obtain expected formation more accurately, but the adaptability is insufficient in complex environments; secondly, most methods only consider numerical simulation in MATLAB, and an actual robot needs to carry an ROS platform.
Disclosure of Invention
Aiming at the defects of the background technology, the invention introduces a virtual robot through a multi-robot formation control method based on Backstepping, designs a virtual pilot-following model, converts the formation control problem into a track tracking problem of the following robot and a virtual pilot, and solves the problem that the whole system is paralyzed if the pilot robot fails in the actual situation.
The invention adopts the following technical scheme for solving the technical problems:
the multi-robot formation control method based on Backstepping comprises the following steps:
s1, acquiring coordinates of a pilot robot in a global coordinate system XOY, setting a virtual pilot, acquiring the coordinates of the virtual pilot in the global coordinate system XOY, and acquiring the coordinates of a following robot in the global coordinate system XOY;
s2, obtaining a virtual pose through a robot dynamics model according to a desired distance and a desired angle between a virtual pilot and a pilot robot;
s3, obtaining errors of the virtual robot and the random robot, and obtaining a tracking error kinematic equation, namely an error model;
s4, decomposing the nonlinear system of the robot into three subsystems by adopting a Backstepping method, introducing virtual error variables, and designing a formation controller by combining with a Lyapunov function;
and S5, the controller obtains a control input quantity and inputs the control input quantity into the error model, so that the formation control task is completed.
Further, the step S1 is specifically as follows:
selecting one robot as a pilot of a robot group, wherein the other robots move along with the pilot robot, the pilot robot is equivalent to a brain and is responsible for a pilot, namely, the azimuth trend of a formation, and the other robots are responsible for keeping the relative distance and the relative angle between the robot and the pilot;
setting a virtual pilot for the following robot, and setting the deflection angle, the angular speed, the angular acceleration and the linear speed of the virtual pilot and the pilot robot to be consistent; in addition, the motion trail of the virtual navigator is determined by the relative distance and angle between the virtual navigator and the navigator robot, and the motion trail of the following robot is determined by a set motion control strategy;
order the
Figure 346491DEST_PATH_IMAGE001
Representing coordinates of the piloting robot in the global coordinate system XOY,/for>
Figure 611250DEST_PATH_IMAGE002
Coordinates for virtual navigator, +.>
Figure 833284DEST_PATH_IMAGE003
To follow the coordinates of the robot, < > a->
Figure 153800DEST_PATH_IMAGE004
The angle between the motion direction of the robot and the X axis is represented; />
Figure 119482DEST_PATH_IMAGE005
and />
Figure 238748DEST_PATH_IMAGE006
The desired distance and the desired angle between the pilot robot and the virtual pilot are represented, respectively.
Further, the step S2 specifically includes the following steps:
the dynamics model of the robot is that
Figure 631683DEST_PATH_IMAGE007
(1)
wherein ,v, wrespectively representing the linear speed and the angular speed of the robot;
setting the same direction angle of the virtual navigator and the pilot robot, namely
Figure 702145DEST_PATH_IMAGE008
And according to the expected distance and the expected angle between the robot and the robot, the pose of the virtual robot can be obtained
Figure 940360DEST_PATH_IMAGE009
(2);
Figure 648553DEST_PATH_IMAGE010
、/>
Figure 702135DEST_PATH_IMAGE011
、/>
Figure 26937DEST_PATH_IMAGE012
Is the spatial coordinates of the virtual robot, +.>
Figure 600001DEST_PATH_IMAGE013
、/>
Figure 959438DEST_PATH_IMAGE014
、/>
Figure 694176DEST_PATH_IMAGE015
Space coordinates of the piloting robot;
Figure 4809DEST_PATH_IMAGE016
to pilot the robot and follow the desired angle of the robot.
Further, the step S3, specifically as follows,
virtual robot R V And follower robot R F The error of (2) is
Figure 115985DEST_PATH_IMAGE017
(3);
in the formula :
Figure 329929DEST_PATH_IMAGE018
、/>
Figure 501147DEST_PATH_IMAGE019
、/>
Figure 800541DEST_PATH_IMAGE020
error space coordinates>
Figure 216872DEST_PATH_IMAGE021
、/>
Figure 550902DEST_PATH_IMAGE022
、/>
Figure 893021DEST_PATH_IMAGE023
The space coordinates of the virtual robot are obtained; />
Figure 414133DEST_PATH_IMAGE024
、/>
Figure 132690DEST_PATH_IMAGE025
、/>
Figure 321226DEST_PATH_IMAGE026
The space coordinates of the robot are followed;
from (1), (2) and (3), a tracking error kinematic equation is obtained
Figure 332782DEST_PATH_IMAGE027
(4);
in the formula
Figure 75610DEST_PATH_IMAGE028
、/>
Figure 597858DEST_PATH_IMAGE029
For the linear and angular speed of the virtual robot, < >>
Figure 375321DEST_PATH_IMAGE030
、/>
Figure 59244DEST_PATH_IMAGE031
To follow the linear and angular velocity of the robot.
Further, the specific steps of the step S4 are as follows:
the design idea of the Backstepping method is as follows: firstly, converting the whole nonlinear system into a plurality of different subsystems, wherein the number of the subsystems does not exceed the system order; secondly, setting a virtual feedback variable by a designer, and designing a part of Lyapunov function to enable the set function to be negative; finally, selecting a global Lyapunov function, and designing a controller meeting the negative determination of the Lyapunov function, thereby realizing the stability of a nonlinear system;
based on the Backstepping method, the design steps of the controller are as follows:
s41, decomposing the system, namely decomposing the nonlinear system into three subsystems, wherein the three subsystems are shown as the formula (6)
Figure 56412DEST_PATH_IMAGE032
(6)
Step S42, introducing virtual feedback variable, selectingxTracking error of direction trackx e For the virtual control quantity and introducing virtual feedback variables:
Figure 851192DEST_PATH_IMAGE033
(7)
step S43, designing part Lyapunov functionV 2 Design of
Figure 14321DEST_PATH_IMAGE034
Assume that the system satisfies
Figure 869144DEST_PATH_IMAGE036
,/>
Figure 85100DEST_PATH_IMAGE037
Then
Figure 683571DEST_PATH_IMAGE039
(8)
At the position of
Figure 435626DEST_PATH_IMAGE040
, />
Figure 726930DEST_PATH_IMAGE041
Under the condition of (2) tracking errory e Converging to zero;
step S44, designing a global Lyapunov function, and adding a subsystem Lyapunov function meeting the condition of step S23 in the global Lyapunov function design, wherein the global Lyapunov function is designed as follows
Figure 197226DEST_PATH_IMAGE043
(9)
(9) Deriving and obtaining
Figure 569695DEST_PATH_IMAGE045
(10)
wherein
Figure 176257DEST_PATH_IMAGE046
Deriving from formula (7), obtaining +.>
Figure 372883DEST_PATH_IMAGE048
(11)
Bringing the formulae (7), (8), (11) into (10) to obtain
Figure 64895DEST_PATH_IMAGE049
(12)
Step S45, designing a controller,
Figure 270749DEST_PATH_IMAGE050
stabilize the system, i.e. meet
Figure 495932DEST_PATH_IMAGE051
(13)
Thus, the system controller is designed to be
Figure 597880DEST_PATH_IMAGE052
(14)
wherein ,k 1 >0, k 2 >0,k 1 、k 2 to control gain; if it isw L , v L ,
Figure 777188DEST_PATH_IMAGE053
Is bounded, thenv F , w F Is bounded;
bringing formula (14) into formula (12), and finishing to obtain
Figure 521153DEST_PATH_IMAGE054
Further, the method also comprises the following checking steps:
step S61, controller parametersk 1 ,k 2 The values are obtained through a plurality of experiments, and different values are setk 1 , k 2 Value, comparisonXA shaft(s),YThe convergence speed of the axis and the motion angle tracking error is used for obtaining a relative optimal parameter value;
and step S62, setting different speeds to realize trilateral formation, and carrying out simulation experiments on the system based on the parameter settings.
Compared with the prior art, the technical scheme has the following beneficial effects:
1. according to the multi-robot formation control method based on Backstepping, a virtual robot is introduced, a virtual pilot-following model is designed, the formation control problem is converted into the track tracking problem of the following robot and a virtual pilot, and the problem that if the pilot robot fails in the actual situation, the whole system is paralyzed is solved.
2. The multi-robot formation control method based on Backstepping provided by the invention not only considers MATLAB numerical simulation, but also carries out ROS platform Gazebo experiments, and has more value for practical mobile robot application.
3. The multi-robot formation control method based on Backstepping provided by the invention designs a stable formation control law, and under the action of the control law, the convergence error of a controller is smaller, and the system error is smaller.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a diagram of a Leader-Follower model;
FIG. 3 is a diagram of a trilateral formation trajectory;
FIG. 4 is an X-direction position tracking error map;
FIG. 5 is a graph of Y-direction position tracking error;
FIG. 6 is a diagram of motion angular position tracking error;
FIG. 7 is a diagram of a trilateral formation trajectory after changing the initial linear velocity of a pilot;
FIG. 8 is a graph of X-direction position tracking error after changing the initial linear velocity of the pilot;
FIG. 9 is a graph of Y-direction position tracking error after changing the initial linear velocity of the pilot;
FIG. 10 is a graph of movement angle position tracking error after changing the initial linear velocity of the pilot;
FIG. 11 is a square formation trace plot;
FIG. 12 is an X-direction position tracking error plot for square formations;
FIG. 13 is a graph of Y-direction position tracking error for square formations;
FIG. 14 is a graph of motion angular position tracking error for square formations;
FIG. 15 is a pentagonal formation trace plot;
FIG. 16 is an X-direction position tracking error plot for pentagonal formation;
FIG. 17 is a graph of Y-direction position tracking error for pentagonal formation;
FIG. 18 is a graph of motion angular position tracking error for pentagonal formation;
FIG. 19 is a Gazebo simulation environment;
FIG. 20 is a formation pose diagram;
FIG. 21 is a simulated trilateral formation trajectory graph;
FIG. 22 is a simulated X-direction position tracking error plot;
FIG. 23 is a simulated Y-direction position tracking error plot;
fig. 24 is a simulated motion angular position tracking error plot.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The formation control idea based on the piloting following method is to select one robot as a piloter of a robot group, and the rest robots follow the piloting robots to move. The piloting robot is equivalent to the brain and is responsible for the leader, namely, the azimuth trend of the formation, and the rest robots are responsible for keeping the relative distance and the relative angle between the robot and the leader.
In consideration of the problem that if a pilot robot fails under actual conditions, the whole system is paralyzed, the invention sets a virtual pilot for each following robot, and sets the deflection angle, the angular velocity, the angular acceleration, the linear velocity and the like of the virtual pilot and the pilot robot to be consistent; in addition, the motion trail of the virtual navigator is determined by the relative distance and angle between the virtual navigator and the navigator, and the motion trail of the following robot is determined by the set motion control strategy, so that the complex robot formation problem is converted into the simple tracking error convergence problem of the following robot and the virtual navigator.
As shown in the figure1, the present invention uses a Leader-Follower model of a non-full mobile robot, as shown in fig. 2, wherein,
Figure 615491DEST_PATH_IMAGE055
representing coordinates of the piloting robot in the global coordinate system XOY,/for>
Figure 419499DEST_PATH_IMAGE056
Coordinates for virtual navigator, +.>
Figure 86104DEST_PATH_IMAGE057
To follow the coordinates of the robot, < > a->
Figure 633760DEST_PATH_IMAGE004
The angle between the motion direction of the robot and the X axis is represented;
Figure 69420DEST_PATH_IMAGE005
and />
Figure 309909DEST_PATH_IMAGE006
The desired distance and the desired angle between the pilot robot and the virtual pilot are represented, respectively.
As can be taken from fig. 2, the kinetic model of the robot is
Figure 962345DEST_PATH_IMAGE058
(1)
wherein ,v, wthe linear and angular speeds of the robot are indicated, respectively.
Setting the same direction angle of the virtual navigator and the pilot robot, namely
Figure 782533DEST_PATH_IMAGE059
And according to the expected distance and the expected angle between the robot and the robot, the pose of the virtual robot can be obtained
Figure 338279DEST_PATH_IMAGE060
(2)
Then, the virtual robot R V And follower robot R F The error of (2) is
Figure 484090DEST_PATH_IMAGE061
(3)/>
From (1), (2) and (3), a tracking error kinematic equation is obtained
Figure 125287DEST_PATH_IMAGE062
(4)。
The analysis described above has transformed the formation problem into a tracking error convergence problem, which translates the tracking error
Figure 516210DEST_PATH_IMAGE063
The formation control requirement can be met by converging in a small neighborhood, and further, the proper control input +.>
Figure 926463DEST_PATH_IMAGE064
And (3) obtaining the product. Next, the present invention will be designed by the Backstepping method>
Figure 243175DEST_PATH_IMAGE065
The Backstepping method comprises the following design ideas: firstly, converting the whole nonlinear system into a plurality of different subsystems, wherein the number of the subsystems does not exceed the system order; secondly, setting a virtual feedback variable by a designer, and designing a part of Lyapunov function to enable the set function to be negative; and finally, selecting a global Lyapunov function, and designing a controller meeting the negative setting of the Lyapunov function, thereby realizing the stability of the nonlinear system. The following are design steps and theoretical evidence of the controller of the present invention.
Step S41, system decomposition. Since the robotic system comprises onlyx, y,
Figure 371668DEST_PATH_IMAGE004
Three kinds of error tracking, the system of the inventionOrder 3, thus decomposing the system into three subsystems, as in equation (6)
Figure 799238DEST_PATH_IMAGE066
(6)
Step S42, introducing virtual feedback variables. The virtual control quantity of the invention has three choices, namelyx e ,y e Or (b)
Figure 828112DEST_PATH_IMAGE067
. The invention selectsxTracking error of direction trackx e For virtual control quantity (researchers can choose the other two as virtual control quantity), and introduce virtual feedback variable
Figure 50146DEST_PATH_IMAGE068
(7)
Step S43, designing part Lyapunov functionV 2 . Design of
Figure 665935DEST_PATH_IMAGE069
Assume that the system satisfies
Figure 897196DEST_PATH_IMAGE070
,/>
Figure 282041DEST_PATH_IMAGE071
Then
Figure 940555DEST_PATH_IMAGE072
(8)
As can be seen from the above, in
Figure 279526DEST_PATH_IMAGE073
,/>
Figure 48899DEST_PATH_IMAGE074
Under the condition of (2) tracking errory e Converging to zero.
Step S44, designing a global Lyapunov function. From Step3, the invention can obtain the negative determination of the partial Lyapunov function, so the invention can add the subsystem Lyapunov function meeting the condition of Step S23 in the global Lyapunov function design, and the global Lyapunov function can be designed as follows
Figure 553830DEST_PATH_IMAGE075
(9)
(9) Deriving and obtaining
Figure 383246DEST_PATH_IMAGE076
(10)
wherein
Figure 708048DEST_PATH_IMAGE046
Deriving from (7)
Figure 779647DEST_PATH_IMAGE077
(11)
Bringing the formulae (7), (8), (11) into (10) to obtain
Figure 139084DEST_PATH_IMAGE078
(12)
Step S45, designing a controller. From the above, it can be seen that if the system is to be stabilized
Figure DEST_PATH_IMAGE079
Namely satisfy
Figure 77084DEST_PATH_IMAGE080
(13)
Thus, the system controller is designed to be
Figure DEST_PATH_IMAGE081
(14)
wherein ,k 1 >0, k 2 >0. if it isw L , v L ,
Figure 593909DEST_PATH_IMAGE053
Is bounded, thenv F , w F Is bounded.
Bringing formula (14) into formula (12), and finishing to obtain
Figure 705085DEST_PATH_IMAGE082
(15)
In a summary of the present invention it is known that,Vthe continuous positive determination can be made slightly,
Figure DEST_PATH_IMAGE083
negative semi-definite and continuous consistency. Is obtained by Lasalle invariant set principle
Figure 122291DEST_PATH_IMAGE084
The establishment is realized, so that the controller can realize formation control tasks;
the analysis proves that the proposed controller meets the system requirement through theory, then numerical simulation experiments are carried out in MATLAB 2018a, trilateral, square row and pentagonal formation of the multiple robots are realized, and the system is formedXA shaft(s),YAnalyzing the axis and motion angle tracking errors; to further verify the effectiveness of the proposed algorithm, a platoon simulation experiment was performed with the algorithm transplanted to the Gazebo simulation environment in ROS.
The controller parameters of the inventionk 1 ,k 2 The values are obtained through a plurality of experiments, and different values are setk 1 , k 2 Value, comparisonXA shaft(s),YThe convergence speed of the axis and motion angle tracking error yields the relative optimum parameter values, table 1 being a partial trial and error result.
Figure DEST_PATH_IMAGE085
Above-mentionedx e , y e ,
Figure 729727DEST_PATH_IMAGE086
Is the convergence value of the algorithm inXA shaft(s),YThe recorded value when the axis and motion angle tracking error is less than 0.001m, x represents that the convergence error is more than 0.001m in a prescribed time. Through the experimental comparison, the most suitable is screenedk 1 ,k 2 Values 0.9,0.8, respectively. />
Firstly, setting different speeds to realize trilateral formation so as to prove that the controller can meet formation control tasks under the condition that the online speed and the angular speed of the pilot robot are bounded; and secondly, selecting a certain linear speed and angular speed to realize quadrilateral formation and pentagonal formation, and further verifying the effectiveness of the controller. Based on the parameter settings, simulation experiments are performed on the system, and the experimental effects and analysis are as follows.
Trilateral formation:
three robots, a pilot and two followers are set, and starting from different initial positions, the requirements of trilateral formation are met. Table 2 is a parameter setting of each robot initial information.
Setting the running time of the system to be 50s, and setting the relative distance between two virtual pilots and the pilot robotL 1 =L 2 =1m, relative angle is
Figure DEST_PATH_IMAGE087
,/>
Figure 232384DEST_PATH_IMAGE088
The pilot robot does uniform linear motion. FIG. 3 is a diagram of a trilateral formation trajectory, and FIGS. 4, 5, and 6 are respectivelyxDirection(s),yDirection and motion angle tracking error map.
Figure 881671DEST_PATH_IMAGE089
As can be seen from fig. 3, the formation has been initially formed at about 10s, with the red solid line being the pilot robot motion trajectory and the green dotted line and the blue dot line being the two follower trajectories. It can be seen from fig. 4, 5, and 6 that the system substantially completes formation generation at 19s and the errors converge within a certain range, where the red and green solid lines represent the error convergence variation between the follower robot and the virtual robot.
And (3) keeping the rest parameters unchanged, only changing the initial linear speed of the pilot to realize trilateral formation, and setting the parameters of each robot in table 3.
Figure 684542DEST_PATH_IMAGE090
Fig. 7 is a diagram of a trilateral formation trajectory, and fig. 8, 9, and 10 are respectively a following robot and a virtual pilotXDirection(s),YDirection and motion angle tracking error map.
The simulation result can be used for obtaining that the controller can realize the formation task at different speeds. The initial linear speed of the pilot robot is used as a quantification, and formation is used as a variable, so that square formation and pentagonal formation of the multiple robots are realized.
Square formation
And setting four robots, namely a navigator, three followers and forming a square formation from different initial positions according to the three-side formation setting. Table 4 shows the parameter settings for four robots.
Figure 516408DEST_PATH_IMAGE091
/>
FIG. 11 is a square formation trace diagram, and FIGS. 12, 13 and 14 are respectivelyXDirection(s),YDirection and motion angle tracking error map.
As can be seen from fig. 11-14, as the number of robots increases and the demand for formation increases, the time required for the controller to perform the formation task increases, and the system completes the formation task demand at about 20 s.
Pentagonal formation
The five robots start from different initial positions to form pentagon formation. Table 5 shows the parameter settings for each robot.
Figure 303098DEST_PATH_IMAGE092
FIGS. 15-18 are pentagonal formation trace diagrams and, respectivelyXDirection(s),YDirection and motion angle tracking error map.
In the Gazebo physical simulation environment, three identical robots were selected for the formation experiments, and fig. 19 is a Gazebo simulation environment. In the experiment, three robots are set at different positions, after the pilot robot advances for a certain distance, the following robot starts to follow, finally, triangle formation is realized, and simulation experiment results are shown in fig. 20-24.
Fig. 20 is a pose diagram after formation stabilization, and fig. 20 is a trilateral trajectory diagram, and it can be seen that the following robot and the piloting robot can maintain a desired distance and angle, and no collision or falling phenomenon occurs; fig. 22-24 are graphs of tracking errors of the follower robot and the virtual pilot robot in the X direction, the Y direction and the motion angle, wherein red represents errors of the follower 1 and the virtual robot 1, green represents errors of the follower 2 and the virtual robot 2, and it can be seen that the error tracking curves of the two follower robots eventually gradually converge into a small neighborhood.
From the experimental results, the controller designed by the invention meets various requirements of formation control tasks and has effectiveness and feasibility.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims (3)

1. The multi-robot formation control method based on Backstepping is characterized by comprising the following steps of:
s1, acquiring coordinates of a pilot robot in a global coordinate system XOY, setting a virtual pilot, acquiring the coordinates of the virtual pilot in the global coordinate system XOY, and acquiring the coordinates of a following robot in the global coordinate system XOY;
s2, obtaining a virtual pose through a robot dynamics model according to a desired distance and a desired angle between a virtual pilot and a pilot robot;
s3, obtaining errors of the virtual robot and the random robot, and obtaining a tracking error kinematic equation, namely an error model;
s4, decomposing the nonlinear system of the robot into three subsystems by adopting a Backstepping method, introducing virtual error variables, and designing a formation controller by combining with a Lyapunov function;
s5, the controller obtains a control input quantity and inputs the control input quantity into the error model, so that a formation control task is completed;
the step S2 specifically includes the following steps:
the dynamics model of the robot is that
Figure QLYQS_1
(1)
wherein ,v, wrespectively representing the linear speed and the angular speed of the robot;
setting the same direction angle of the virtual navigator and the pilot robot, namely
Figure QLYQS_2
And can derive a virtual robot according to a desired distance and a desired angle therebetweenPose is
Figure QLYQS_3
(2)
Figure QLYQS_4
Is the spatial coordinates of the virtual robot, +.>
Figure QLYQS_5
Space coordinates of the piloting robot; />
Figure QLYQS_6
The desired angles for the pilot robot and the follower robot;
the step S3, specifically as follows,
virtual robot R V And follower robot R F The error of (2) is
Figure QLYQS_7
(3)
in the formula :
Figure QLYQS_8
error space coordinates>
Figure QLYQS_9
The space coordinates of the virtual robot are obtained; />
Figure QLYQS_10
The space coordinates of the robot are followed;
from (1), (2) and (3), a tracking error kinematic equation is obtained
Figure QLYQS_11
(4)
in the formula
Figure QLYQS_12
For the linear and angular speed of the virtual robot, < >>
Figure QLYQS_13
The linear speed and the angular speed of the following robot;
the specific steps of the step S4 are as follows:
the design idea of the Backstepping method is as follows: firstly, converting the whole nonlinear system into a plurality of different subsystems, wherein the number of the subsystems does not exceed the system order; secondly, setting a virtual feedback variable by a designer, and designing a part of Lyapunov function to enable the set function to be negative; finally, selecting a global Lyapunov function, and designing a controller meeting the negative determination of the Lyapunov function, thereby realizing the stability of a nonlinear system;
based on the Backstepping method, the design steps of the controller are as follows:
s41, decomposing the system, namely decomposing the nonlinear system into three subsystems, wherein the three subsystems are shown as the formula (6)
Figure QLYQS_14
(6)
Step S42, introducing virtual feedback variable, selectingxTracking error of direction trackx e For the virtual control quantity and introducing virtual feedback variables:
Figure QLYQS_15
(7)
step S43, designing part Lyapunov functionV 2 Design of
Figure QLYQS_16
Assume that the system satisfies
Figure QLYQS_17
,/>
Figure QLYQS_18
Then
Figure QLYQS_19
(8)
At the position of
Figure QLYQS_20
Under the condition of (2) tracking errory e Converging to zero;
step S44, designing a global Lyapunov function, and adding a subsystem Lyapunov function meeting the condition of step S23 in the global Lyapunov function design, wherein the global Lyapunov function is designed as follows
Figure QLYQS_21
(9)
(9) Deriving and obtaining
Figure QLYQS_22
(10)
wherein
Figure QLYQS_23
Deriving from formula (7), obtaining +.>
Figure QLYQS_24
(11)
Bringing the formulae (7), (8), (11) into (10) to obtain
Figure QLYQS_25
(12)
Step S45, designing a controller,
Figure QLYQS_26
stabilize the system, i.e. meet
Figure QLYQS_27
(13)
Thus, the system controller is designed to be
Figure QLYQS_28
(14)
wherein ,k 1 >0, k 2 >0,k 1 、k 2 to control the gain, ifw L , v L ,
Figure QLYQS_29
Is bounded, thenv F , w F Is bounded;
bringing formula (14) into formula (12), and finishing to obtain
Figure QLYQS_30
2. The Backstepping-based multi-robot formation control method according to claim 1, wherein step S1 is specifically as follows:
selecting one robot as a pilot of a robot group, wherein the other robots move along with the pilot robot, the pilot robot is equivalent to a brain and is responsible for a pilot, namely, the azimuth trend of a formation, and the other robots are responsible for keeping the relative distance and the relative angle between the robot and the pilot;
setting a virtual pilot for the following robot, and setting the deflection angle, the angular speed, the angular acceleration and the linear speed of the virtual pilot and the pilot robot to be consistent; in addition, the motion trail of the virtual navigator is determined by the relative distance and angle between the virtual navigator and the navigator robot, and the motion trail of the following robot is determined by a set motion control strategy;
order the
Figure QLYQS_31
Representing coordinates of the piloting robot in the global coordinate system XOY,/for>
Figure QLYQS_32
Coordinates for virtual navigator, +.>
Figure QLYQS_33
To follow the coordinates of the robot, < > a->
Figure QLYQS_34
The angle of the robot movement direction to the X-axis is indicated. />
3. The Backstepping-based multi-robot formation control method of claim 1, further comprising a step of checking as follows:
step S61, controller parametersk 1 ,k 2 The values are obtained through a plurality of experiments, and different values are setk 1 , k 2 Value, comparisonXA shaft(s),YThe convergence speed of the axis and the motion angle tracking error is used for obtaining a relative optimal parameter value;
and step S62, setting different speeds to realize trilateral formation, and carrying out simulation experiments on the system based on the parameter settings.
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