CN114851198A - Consistent tracking fixed time stability control method for multi-single-link mechanical arm - Google Patents
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Abstract
The invention discloses a consistent tracking fixed time stability control method of a multi-single-link mechanical arm, which comprises the following steps: modeling the single-link mechanical arm to obtain a state equation; defining the consistency tracking error of the ith single-link mechanical arm and designing a first virtual control law alpha i,1 (ii) a Designing a relative threshold event trigger mechanism; design a second virtual law α i,2 And law of adaptationAndestimating unknown system parameters on line; and carrying out simulation experiments on the algorithm based on a Matlab experiment platform. According to the invention, through a relative threshold event trigger mechanism in the controller, on-line dynamic compensation of an input dead zone can be realized on the premise of ensuring the control precision, and meanwhile, the updating frequency of input signals of each mechanical arm is reduced; multiple single connectionThe rod mechanical arm system can realize the convergence of synchronous errors in fixed time under different system initial states, the convergence time is irrelevant to the system initial state, and higher convergence speed and better tracking accuracy are obtained by selecting proper parameters.
Description
Technical Field
The invention relates to the technical field of intelligent control of mechanical arms, in particular to a consistent tracking fixed time stability control method for a multi-single-connecting-rod type mechanical arm.
Background
With the continuous expansion of the application range of the mechanical arm, the mutually independent mechanical arms show more and more limitations, and the multiple mechanical arms can be operated flexibly in a cooperative mode, have strong robustness and can complete complex tasks. The mechanical arms are connected through a topological network, and communication among the mechanical arms is achieved. High-frequency communication is needed among subsystems to ensure the stability of the whole system. However, the communication resources of the system are limited, and the conventional periodic sampling control method may have the problem of network congestion. In addition, there is often an input dead zone in the robotic arm system that affects the stability of the system. Therefore, it is of great importance to study the event-triggered consistency tracking problem for a set of single-link robotic arms with input dead zone constraints.
The convergence speed is an important index of system performance, the existing finite time control method can realize the finite time stabilization of the system, but the convergence time of the system is related to the initial state of the system. In practical applications, the system state is often not measurable. Therefore, this method cannot calculate the settling time in advance. The invention designs the controller based on the fixed time stabilization theory, can realize the rapid finite time stabilization of the system, and the convergence time is irrelevant to the initial state of the system.
Most of the existing technical schemes do not consider that the communication resources of the system are limited, and a large amount of communication resources are occupied to maintain the stability of the system and realize the compensation of the input dead zone. The invention designs an event trigger mechanism, which can reduce the update frequency of control signals, realize the self-adaptive compensation of input dead zones and relieve the communication pressure of a system to a certain extent.
Disclosure of Invention
The invention aims to provide a consistent tracking fixed time stability control method for a plurality of single-link mechanical arms, which solves the problems in the background technology by designing a new relative threshold event trigger mechanism.
In order to achieve the purpose, the invention provides the following technical scheme:
a consistent tracking fixed time stability control method for a multi-single-link mechanical arm comprises the following steps:
s01, modeling the single-link mechanical arm to obtain a state equation;
s02, defining the consistency tracking error of the ith single-link mechanical arm and designing a first virtual control law alpha i,1 ;
S03, designing a relative threshold event trigger mechanism;
s04, designing a second virtual law alpha i,2 And law of adaptationAndestimating unknown system parameters on line;
and S05, carrying out simulation experiments on the algorithm based on the Matlab experiment platform.
Preferably, the step S01 is specifically as follows:
without loss of generality, the mathematical model of the ith single link arm in the follower is set up as follows:
wherein,t represents time, q i (t) is the angle of the joint,is the angular velocity of the joint or joints,is angular acceleration of the joint, J i Is moment of inertia, B i Is the coefficient of friction damping, m i Is the connecting rod mass, g is the gravitational acceleration,/ i Is the length of the connecting rod, u i (t) is an input torque.
Due to the structural characteristics of the mechanical structure, the mechanical arm system often has an input dead zone, which has a great influence on the system performance. The mathematical model for setting the input dead zone is as follows:
D i (u i )=h i u i +g i (2)
wherein ,ui Represents a control input;h i,1 、h i,2 、g i,1 and gi,2 Are all constant, and h i,1 >0、h i,2 >0、g i,1<0 and gi,2 >0。
Coordinate transformation of (1) it can result in:
wherein ,xi,1 =q i (t),Each represents the system state of the i (i ═ 1, 2.., N) th follower;denotes x i,1 A derivative of (a);denotes x i.2 A derivative of (a); y is i A system output representing the i (i ═ 1, 2.., N) th follower;indicating a system uncertainty portion.
In order to facilitate the description of the communication relationship between the mechanical arms in the topological graph, relevant knowledge of algebraic graph theory needs to be introduced. Drawing (A)Directed communication topology diagram representing multi-arm system, wherein each node in the diagram corresponds to one arm, and Ω ═ Ω { Ω [ Ω ] 1 ,Ω 2 ,...,Ω N Denotes the set of N nodes, the set of edges between nodes isThe edge from node i to node j is defined as an ordered pairIndicating that the mechanical arm i can receive the information of the mechanical arm j, and calling the node i to be adjacent to the node j to defineIs the set of adjacent edges of agent i. A ═ a i,j ]∈R N×N Represents a adjacency matrix ifThen a i,j Is greater than 0; otherwise a i,j 0. The degree of entry of the node i isDefinition of Is an in-degree diagonal matrixThen, thenIs a laplacian matrix.
To deal with unknown non-linear functions in the system, radial basis function neural networks are employed. In tight set omega epsilon R n Any continuous function defined aboveCan be approximated by a neural network and can be expressed as:
wherein ,is an ideal unknown weight vector, andq is a positive integer;to representTransposing; Φ (X) is a vector of basis functions, and Φ (X) ═ Φ 1 (X),Φ 2 (X),...,Φ q (X)] T (ii) a q is the node number of the neural network, and q is more than 1; x represents an input vector, and X ═ X 1 ,x 2 ,...,x q ] T ∈R q (ii) a Mu (X) is an approximation error and satisfies and Φi The definition of (X) is as follows:
wherein ,Wi =[W 1 ,W 2 ,...,W q ] T ∈R q Representing a weight vector;andare respectively a Gaussian function phi i The center and width of (X).
Preferably, the step S02 is as follows:
first, the consistency tracking error of the ith robot arm is defined by the knowledge of graph theory:
wherein ,zi,1 For synchronization error, z i,2 Is a virtual control error, α i,1 Is the virtual control law, y d A signal is output for the leader. b i (i ═ 1, 2.., N) denotes the information transmission coefficient from the leader to the i-th follower. b i For positive numbers, if there is a transmission of information between the leader and the ith follower, b i Is greater than 0. Otherwise b i 0. As shown in the formula (7), the synchronization error z i,1 Weighted parameter a ij and bi The influence of (c). Therefore, a directed graphStructural influence of (a) z i,1 . Further according to d i and bi Definition of (d) i +b i Is strictly positive.
Preferably, the step S02 specifically includes:
s021, processing unknown combined parts by adopting radial basis function neural networkIntroducing an unknown positive parameterWherein | · | | represents a two-norm;denotes y d The first derivative of (a); x i,1 Represents an input vector, anx j,1 and xj,2 Represents the system state of the jth (j ═ 1, 2.., N) follower; and the parameter theta i,1 Can pass throughEstimate, i.e.Is a parameter theta i,1 Then the final estimation error can be defined asThus, approximation processingThe expression of (a) is as follows:
wherein ,is an ideal unknown weight vector, and to representTransposing; phi (X) is a vector of basis functions, and phi i,1 (X i,1 )=[Φ 1,1 (X i,1 ),Φ 2,1 (X i,1 ),...,Φ q,1 (X i,1 )] T (ii) a q is the node number of the neural network, and q is more than 1; mu.s i,1 (X i,1 ) Represents an approximation error, satisfiesAnd is
S022, first virtual control law α i,1 The design is as follows:
wherein ,ci,1 、r i,1 、a i,1 and εi,1 Are all constant, and c i,1 >0,r i,1 >0,a i,1 >0,ε i,1 >0。
Preferably, the step S03 is specifically as follows:
in order to save communication resources, a relative threshold event triggering mechanism is designed. Control signal omega i (t) is defined as follows:
only when pre-designed triggeringCondition | e i (t)|≥ρ i |u i (t)|+ο i When true, controls the input signal u i (t) is updated, the expression is as follows:
wherein δi 、ο i 、ρ i 、Are all positive design parameters and satisfy delta i >0,0<ρ i <1,ο>0,k is an integer. inf {. } represents an infimum bound; t is t i,k The kth trigger time of the ith agent; t is t i,k+1 The (k + 1) th trigger time of the ith agent; e.g. of the type i (t) denotes measurement error, and e i (t)=ω i (t)-u i (t)。
Preferably, because the system model has an uncertain part, the uncertain part of the second-order nonlinear system model is approximated through a neural network; designing a virtual control law according to the virtual control error, and determining adaptive parameters, wherein the step S04 specifically includes:
determining uncertain combination parts in system model by radial basis function neural network Denotes y d The second derivative of (a); x i,2 Represents an input vector, anIntroducing an unknown positive parameterWherein | · | | represents a two-norm; and the parameter theta i,2 Can pass throughEstimate, i.e.Is a parameter theta i,2 Then the final estimation error can be defined asThus, approximation processingThe expression of (a) is as follows:
wherein ,is an ideal unknown weight vector, and to representTransposing;is a vector of basis functions, and phi i,2 (X i,2 )=[Φ 1,2 (X i,2 ),Φ 2,2 (X i,2 ),...,Φ q,2 (X i,2 )] T (ii) a q is the node number of the neural network, and q is more than 1; mu.s i,2 (X i,2 ) Represents an approximation error, satisfiesAnd is
S042 according to the second error variable z i,2 In the process, the unknown uncertain part is obtained by solving the radial basis function neural network, and a second virtual control law alpha is designed by utilizing a backstepping design method and the Lyapunov function i,2 While generating adaptive parametersAnd
in which a virtual control law alpha is established i,2 、Law of controlAnd adaptive parameters Satisfies the following calculation formula:
wherein Represents phi i Transpose of (J) i 、ε i,2 、c i,2 、r i,2 、a i,2 、ξ i 、σ i 、l i,2 、η i And ζ i Are all positive design parameters. H i =[1/h i ,-g i /h i ] T ,H i T Represents H i Transpose of (Q) i =[α i,2 ,1] T ,α i,2 Representing a second virtual control law; since in practical cases, H i Are difficult to obtain and designTo estimate H i Defining an estimation errorAnd is wherein Andare respectively estimated asAnd multiplication by multiplication
Compared with the prior art, the invention has the beneficial effects that:
1. according to the consistent tracking fixed time stability control method for the multi-single-link mechanical arm, in order to reduce communication burden among the mechanical arms, a new relative threshold event trigger mechanism is designed in a controller, on-line dynamic compensation of an input dead zone can be achieved on the premise that control precision is guaranteed, and meanwhile the updating frequency of input signals of all the mechanical arms is reduced.
2. According to the consistent tracking fixed time stability control method for the multi-single-link mechanical arm, the multi-single-link mechanical arm system can realize the convergence of synchronous errors in fixed time under different system initial states, the convergence time is irrelevant to the system initial state, and higher convergence speed and better tracking precision can be obtained by selecting proper parameters.
Drawings
FIG. 1 is a communication topology diagram of a control method according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the output of the reference signal and followers of the control method of the embodiment of the invention;
FIG. 3 is a schematic diagram of a synchronization error in an initial state 1 of a control method according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a synchronization error in initial state 2 of the control method according to the embodiment of the present invention;
FIG. 5 is a schematic diagram of a synchronization error in initial state 3 of the control method according to the embodiment of the present invention;
FIG. 6 is a schematic diagram of control signals of follower 1 according to the control method of the embodiment of the present invention;
FIG. 7 is a schematic diagram of control signals of follower 2 according to the control method of the embodiment of the present invention;
FIG. 8 is a schematic diagram of control signals of a follower 3 according to the control method of the embodiment of the present invention;
FIG. 9 is a schematic diagram of control signals of a follower 4 according to the control method of the embodiment of the present invention;
FIG. 10 is a schematic diagram of trigger event time intervals of follower 1 and follower 2 in the control method of the embodiment of the present invention;
fig. 11 is a schematic diagram of trigger event time intervals of the follower 3 and the follower 4 in the control method according to the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Examples
Referring to fig. 1-11, the consistent tracking fixed time stability control method for a multi-single link mechanical arm according to the present invention first models an input dead zone, and establishes a set of single link mechanical arm system models with input dead zone constraints. Then, based on a back-stepping technology, a neural network self-adaptive control technology and a fixed time stability control theory, a new fixed time stability event trigger type controller is designed, and finally, the method is simulated. Simulation results show that each mechanical arm (follower) can well track the set reference signal, the control precision is good, and communication resources are effectively saved.
The method specifically comprises the following steps:
s01, modeling the single-link mechanical arm to obtain a state equation;
s02, defining the consistency tracking error of the ith single-link mechanical arm and designing a first virtual control law alpha i,1 ;
S03, designing a relative threshold event trigger mechanism;
s04, designing a second virtual law alpha i,2 And law of adaptationAndand estimating unknown system parameters on line.
And S05, carrying out simulation experiments on the algorithm based on the Matlab experiment platform.
The further detailed steps are as follows:
s01, without loss of generality, the mathematical model of the ith single link arm in the follower is set as follows:
wherein t represents time, q i (t) is the joint angle (c),is the angular velocity of the joint or joints,is angular acceleration of the joint, J i Is moment of inertia, B i Is the coefficient of friction damping, m i Is the connecting rod mass, g is the gravitational acceleration,/ i Is the length of the connecting rod, u i (t) is an input torque.
Due to the structural characteristics of the mechanical structure, the mechanical arm system often has an input dead zone, which has a great influence on the system performance. The mathematical model for setting the input dead zone is as follows:
D i (u i )=h i u i +g i (2)
wherein ,ui Represents a control input;h i,1 、h i,2 、g i,1 and gi,2 Are all constant, and h i,1 >0、h i,2 >0、g i,1<0 and gi,2 >0。
Coordinate transformation of (1) it can result in:
wherein ,xi,1 =q i (t),Each represents the system state of the i (i ═ 1, 2.., N) th follower;denotes x i,1 A derivative of (a);denotes x i.2 A derivative of (a); y is i A system output representing the i (i ═ 1, 2.., N) th follower;indicating a system uncertainty portion.
In order to facilitate the description of the communication relationship between the mechanical arms in the topological diagram of fig. 2, relevant knowledge of algebraic graph theory needs to be introduced. Drawing (A)Representing a directed communication topological graph of a multi-mechanical arm system, wherein each node in the graph corresponds to one mechanical arm, and omega is { omega ═ omega { (omega) } 1 ,Ω 2 ,...,Ω N Denotes the set of N nodes, the set of edges between nodes isThe edge from node i to node j is defined as an ordered pairIndicating that the mechanical arm i can receive the information of the mechanical arm j, and calling the node i to be adjacent to the node j to defineIs the set of adjacent edges of agent i. A ═ a i,j ]∈R N×N Represents a adjacency matrix ifThen a i,j Is greater than 0; otherwise a i,j 0. The degree of entry of the node i isDefinition of Is an in-degree diagonal matrix, thenIs a laplacian matrix.
To deal with unknown non-linear functions in the system, radial basis function neural networks are employed. In tight set omega ∈ R n Any continuous function defined aboveCan be approximated by a neural network and can be expressed as:
wherein ,is an ideal unknown weight vector, andq is a positive integer;representTransposing; Φ (X) is a vector of basis functions, and Φ (X) ═ Φ 1 (X),Φ 2 (X),...,Φ q (X)] T (ii) a q is the node number of the neural network, and q is more than 1; x represents an input vector, and X ═ X 1 ,x 2 ,...,x q ] T ∈R q (ii) a Mu (X) is an approximation error and satisfies and Φi The definition of (X) is as follows:
wherein ,Wi =[W 1 ,W 2 ,...,W q ] T ∈R q Representing a weight vector;andare respectively a Gaussian function phi i The center and width of (X).
S02, first, defining the consistency tracking error of the ith mechanical arm by using the knowledge of graph theory:
wherein ,zi,1 For synchronization error, z i,2 Is a virtual control error, α i,1 Is the virtual control law, y d To be lost for the leaderAnd (6) outputting a signal. b i (i ═ 1, 2.., N) denotes the information transmission coefficient from the leader to the i-th follower. b i For positive numbers, if there is a transmission of information between the leader and the ith follower, b i Is greater than 0. Otherwise b i 0. As shown in the formula (7), the synchronization error z i,1 Weighted parameter a ij and bi The influence of (c). Therefore, a directed graphStructural influence of (a) z i,1 . Furthermore, according to d i and bi Definition of (d) i +b i Is strictly positive. Further, the step S02 specifically includes:
s021, processing unknown combined parts by adopting radial basis function neural networkIntroducing an unknown positive parameterWherein | | · | | represents a two-norm;denotes y d The first derivative of (a); x i,1 Represents an input vector, anx j,1 and xj,2 Represents the system state of the jth (j ═ 1, 2.., N) follower; and the parameter theta i,1 Can pass throughEstimate, i.e.Is a parameter theta i,1 Then the final estimation error can be defined asThus, approximation processingThe expression of (a) is as follows:
wherein ,is an ideal unknown weight vector, and to representTransposing; phi (X) is a vector of basis functions, and phi i,1 (X i,1 )=[Φ 1,1 (X i,1 ),Φ 2,1 (X i,1 ),...,Φ q,1 (X i,1 )] T (ii) a q is the node number of the neural network, and q is more than 1; mu.s i,1 (X i,1 ) Represents an approximation error, satisfiesAnd is
S022, first virtual control law α i,1 The design is as follows:
wherein ,ci,1 、r i,1 、a i,1 and εi,1 Are all constant, and c i,1 >0,r i,1 >0,a i,1 >0,ε i,1 >0。
S03, in order to save communication resources, a relative threshold event trigger mechanism is designed. Control signal omega i (t) is defined as follows:
only when the pre-designed trigger condition | e i (t)|≥ρ i |u i (t)|+ο i When true, controls the input signal u i (t) is updated, the expression is as follows:
wherein δi 、ο i 、ρ i 、Are all positive design parameters and satisfy delta i >0,0<ρ i <1,ο>0,k is an integer. inf {. } represents an infimum bound; t is t i,k The kth trigger time of the ith agent; t is t i,k+1 The (k + 1) th trigger time of the ith agent; e.g. of the type i (t) denotes measurement error, and e i (t)=ω i (t)-u i (t)。
Because the system model has an uncertain part, the uncertain part of the second-order nonlinear system model is approximated through a neural network; according to the virtual control error z i,2 Design of virtual control law α i,2 And determining adaptive parameters. Further, the step S04 specifically includes:
s041, determining by using radial basis function neural networkUncertain combination parts in fixed system model Denotes y d The second derivative of (a); x i,2 Represents an input vector, anIntroducing an unknown positive parameterWherein | · | | represents a two-norm; and the parameter theta i,2 Can pass throughEstimate, i.e.Is a parameter theta i,2 Then the final estimation error can be defined asThus, approximation processingThe expression of (a) is as follows:
wherein ,is an ideal unknown weight vector, and to representTransposing;is a vector of basis functions, and phi i,2 (X i,2 )=[Φ 1,2 (X i,2 ),Φ 2,2 (X i,2 ),...,Φ q,2 (X i,2 )] T (ii) a q is the number of nodes of the neural network, and q is more than 1; mu.s i,2 (X i,2 ) Represents an approximation error, satisfiesAnd is
S042 according to the second error variable z i,2 In the process, the unknown uncertain part is obtained by solving the radial basis function neural network, and a second virtual control law alpha is designed by utilizing a backstepping design method and the Lyapunov function i,2 While generating adaptive parametersAnd
in which a virtual control law alpha is established i,2 、Law of controlAnd adaptive parameters Satisfies the following calculation formula:
wherein Represents phi i Transpose of (J) i 、ε i,2 、c i,2 、r i,2 、a i,2 、ξ i 、σ i 、l i,2 、η i And ζ i Are all positive design parameters. H i =[1/h i ,-g i /h i ] T ,H i T Represents H i Transpose of (Q) i =[α i,2 ,1] T ,α i,2 Representing a second virtual control law; since in practical cases, H i Are difficult to obtain and designTo estimate H i Defining an estimation errorAnd is wherein Andare respectively estimated asAnd multiplication by multiplication
And S05, simulating the algorithm based on a Matlab experiment platform in order to verify the effectiveness of the method. FIG. 1 depicts a communication topology with one virtual leader and four followers. In this figure, arms 1-4 and arm d represent four followers and a virtual leader, respectively. Without loss of generality, assume that the output signal of the virtual leader (reference signal) is y d Sin (2 t). According to the basic principle of graph theory, an adjacency matrix a and a laplacian matrix L can be obtained:
to deal with the uncertain part, a radial basis function neural network is used, the Gaussian function of which is phi i (X i ) The expression is as follows:
the control objective of the simulation experiment is to make the joint angular velocityTracking the set track signal y d Sin (2 t). The parameters of the relevant system are as follows: moment of inertia J i 0.8, damping coefficient B i =1,m i gl i 10, i is 1,2,3, 4. Unknown part of the systemThe initial state of the system is shown in table 1.
The set values of the relevant parameters are as follows:c 1,1 =r 1,1 =14,c 1,2 =r 1,2 =3,c 2,1 =r 2,1 =25,c 2,2 =r 2,2 =2,c 3,1 =r 3,1 =25,c 3,2 =r 3,2 =1,c 4,1 =r 4,1 =26,c 4,2 =r 4,2 =1,ε i,1 =ε i,2 =0.01,l i,1 =a i,1 =1,ξ i =σ i =0.2,η i =ζ i =0.01,K i =[1,0;0,1],δ i =0.1,ρ i =0.01,ο i =3,and i is 1. The initial estimates are:and i is 1. The simulated sampling period is 0.01 s.
TABLE 1 three initial states of the system
Initial state | x 1,1 (0) | x 1,2 (0) | x 2,1 (0) | x 2,2 (0) | x 3,1 (0) | x 3,2 (0) | x 4,1 (0) | x 4,2 (0) |
|
0.1 | 0 | 0.1 | 0 | 0 | 0 | -0.1 | 0 |
|
0.1 | 0 | 0.1 | 0 | -0.1 | 0 | 0.1 | 0 |
|
0.1 | 0 | 0.1 | 0 | -0.1 | 0 | -0.1 | 0 |
TABLE 2 number of triggers for each follower
The simulation results are shown in fig. 2-9. As can be seen from fig. 2-9, all signals are bounded. FIG. 2 shows the output signals of the leader and follower, indicating good consistency tracking performance. The synchronization error curve of state 1 is shown in fig. 3, and it can be obtained that the synchronization error enters a 5% error band after about 0.05s, which indicates that the convergence rate is fast. In addition, the synchronization errors for the other two initial states (state 2 and state 3 in Table 1) are shown in FIGS. 4-5. Simulation results show that the convergence time of the synchronization errors in the three initial states is about 0.05s, namely the convergence time is not influenced by the initial state of the system. Control input signals for four followers As shown in FIGS. 6-9, the event-triggered control input w (t) is made continuously smooth, while the control input u (t) and the input dead band D i (u i ) Is serrated. Event trigger statistics are shown in table 2, and the event trigger time intervals for each follower are shown in fig. 10-11, respectively. As can be seen from table 2, the total number of triggers based on the conventional Time Trigger Mechanism (TTM) and Event Trigger Mechanism (ETM) is 4000 and 1033 times, respectively. Thus, the event trigger rate is 25.8%, which means a saving of 74.2% of communication resources. From FIGS. 10-11, it can be seen that the minimum trigger interval for all followers is 0.01s, and obviously, noneThere is a Zeno phenomenon.
According to the invention, a new relative threshold event trigger mechanism is designed in the controller, so that on-line dynamic compensation of an input dead zone can be realized on the premise of ensuring the control precision, and the update frequency of input signals of each mechanical arm is reduced; the multi-single-link mechanical arm system can realize the convergence of synchronous errors in fixed time under different system initial states, the convergence time is irrelevant to the system initial state, and higher convergence speed and better tracking accuracy are obtained by selecting proper parameters.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. The term "comprising", without further limitation, means that the element so defined is not excluded from the group consisting of additional identical elements in the process, method, article, or apparatus that comprises the element.
Claims (6)
1. A consistent tracking fixed time stability control method of a multi-single-link mechanical arm is characterized by comprising the following steps:
s01, modeling the single-link mechanical arm to obtain a state equation;
s02, defining the consistency tracking error of the ith single-link mechanical arm and designing a first virtual control law alpha i,1 ;
S03, designing a relative threshold event trigger mechanism;
s04, designing a second virtual law alpha i,2 And law of adaptationAndestimating unknown system parameters on line;
and S05, carrying out simulation experiments on the algorithm based on the Matlab experiment platform.
2. The method for controlling the consistent tracking and fixed time stability of a multi-single link robot arm according to claim 1, wherein the step S01 is as follows:
without loss of generality, the mathematical model of the ith single link arm in the follower is set up as follows:
wherein t represents time, q i (t) is the joint angle (c),is the angular velocity of the joint or joints,is angular acceleration of the joint, J i Is moment of inertia, B i Is the coefficient of friction damping, m i Is the connecting rod mass, g is the gravitational acceleration,/ i Is the length of the connecting rod, u i (t) is input torque;
due to the structural characteristics of the mechanical structure, the mechanical arm system often has an input dead zone, which has great influence on the system performance; the mathematical model for setting the input dead zone is as follows:
D i (u i )=h i u i +g i (2)
wherein ,ui Represents a control input;h i,1 、h i,2 、g i,1 and gi,2 Are all constant, and h i,1 >0、h i,2 >0、g i,1<0 and gi,2 >0;
Coordinate transformation of equation (1) can result in:
wherein ,xi,1 =q i (t),Each represents the system state of the i (i ═ 1, 2.., N) th follower;denotes x i,1 A derivative of (a);denotes x i.2 A derivative of (a); y is i A system output representing the i (i ═ 1, 2.., N) th follower;representing a system uncertainty portion;
in order to facilitate the description of the communication relationship between the mechanical arms in the topological graph, relevant knowledge of algebraic graph theory needs to be introduced. Drawing (A)Representing a directed communication topological graph of a multi-mechanical arm system, wherein each node in the graph corresponds to one mechanical arm, and omega is { omega ═ omega { (omega) } 1 ,Ω 2 ,...,Ω N Denotes the set of N nodes, the set of edges between nodes isEdge from node i to node jIs defined as an ordered pairIndicating that the mechanical arm i can receive the information of the mechanical arm j, and calling the node i to be adjacent to the node j to defineIs the set of adjacent edges of agent i. A ═ a i,j ]∈R N×N Represents a adjacency matrix ifThen a i,j Is greater than 0; otherwise a i,j 0. The degree of entry of the node i isDefinition of Is an in-degree diagonal matrix, thenIs a laplace matrix;
in order to process unknown nonlinear functions in the system, a radial basis function neural network is adopted; in tight set omega ∈ R n Any continuous function defined aboveCan be approximated by a neural network and can be expressed as:
wherein ,is an ideal unknown weight vector, andq is a positive integer;to representTransposing; Φ (X) is a vector of basis functions, and Φ (X) ═ Φ 1 (X),Φ 2 (X),...,Φ q (X)] T (ii) a q is the node number of the neural network, and q is more than 1; x represents an input vector, and X ═ X 1 ,x 2 ,...,x q ] T ∈R q (ii) a Mu (X) is an approximation error and satisfies and Φi The definition of (X) is as follows:
3. The method for controlling consistent tracking and fixed time stability of a multi-single link robot arm according to claim 1, wherein: the step S02 is as follows:
first, the consistency tracking error of the ith robot arm is defined by the knowledge of graph theory:
wherein ,zi,1 For synchronization error, z i,2 Is a virtual control error, α i,1 Is the virtual control law, y d Outputting a signal for the leader. b i (i ═ 1, 2.., N) denotes the information transmission coefficient from the leader to the i-th follower. b i For positive numbers, if there is a transmission of information between the leader and the ith follower, b i Is greater than 0. Otherwise b i 0. As shown in the formula (7), the synchronization error z i,1 Weighted parameter a ij and bi The influence of (c). Therefore, a directed graphStructural influence of (a) z i,1 . Furthermore, according to d i and bi Definition of (d) i +b i Is strictly positive.
4. The method for controlling consistent tracking and fixed time stabilization of a multi-single link robot arm according to claim 3, wherein: the step S02 specifically includes:
s021, processing unknown combined parts by adopting radial basis function neural networkIntroducing an unknown positive parameterWherein | · | | represents a two-norm;denotes y d The first derivative of (a); x i,1 Represents an input vector, anx j,1 and xj,2 Represents the system state of the jth (j ═ 1, 2.., N) follower; and the parameter theta i,1 Can pass throughEstimate, i.e.Is a parameter theta i,1 Then the final estimation error can be defined asThus, approximation processingThe expression of (a) is as follows:
wherein ,is an ideal unknown weight vector, and to representTransposing; phi (X) is a vector of basis functions, and phi i,1 (X i,1 )=[Φ 1,1 (X i,1 ),Φ 2,1 (X i,1 ),...,Φ q,1 (X i,1 )] T (ii) a q is the number of nodes of the neural network, and q is more than 1; mu.s i,1 (X i,1 ) Represents an approximation error, satisfiesAnd is
S022, first virtual control law α i,1 The design is as follows:
wherein ,ci,1 、r i,1 、a i,1 and εi,1 Are all constant, and c i,1 >0,r i,1 >0,a i,1 >0,ε i,1 >0。
5. The method for controlling the consistent tracking and fixed time stability of a multi-single link robot arm according to claim 1, wherein the step S03 is as follows:
in order to save communication resources, a relative threshold event trigger mechanism is designed, and a signal omega is controlled i (t) is defined as follows:
only when the pre-designed trigger condition | e i (t)|≥ρ i |u i (t)|+ο i When true, controls the input signal u i (t) is updated, the expression is as follows:
wherein δi 、ο i 、ρ i 、Are all positive design parameters and satisfy delta i >0,0<ρ i <1,ο>0,k is an integer. inf {. } represents an infimum bound; t is t i,k The kth trigger time of the ith agent; t is t i,k+1 The (k + 1) th trigger time of the ith agent; e.g. of the type i (t) denotes measurement error, and e i (t)=ω i (t)-u i (t)。
6. The method for controlling the consistent tracking and fixed time stability of the multi-single-link mechanical arm according to claim 1, wherein the uncertain part of the second-order nonlinear system model is approximated by a neural network due to the existence of the uncertain part in the system model; designing a virtual control law according to the virtual control error, and determining an adaptive parameter, where step S04 specifically includes:
determining uncertain combination parts in system model by radial basis function neural network Denotes y d The second derivative of (a); x i,2 Represents an input vector, anIntroducing an unknown positive parameterWherein | · | | represents a two-norm; and the parameter theta i,2 Can pass throughEstimate, i.e.Is a parameter theta i,2 Then the final estimation error can be defined asThus, approximation processingThe expression of (a) is as follows:
wherein ,is an ideal unknown weight vector, and to representTransposing;is a vector of basis functions, and phi i,2 (X i,2 )=[Φ 1,2 (X i,2 ),Φ 2,2 (X i,2 ),...,Φ q,2 (X i,2 )] T (ii) a q is the node number of the neural network, and q is more than 1; mu.s i,2 (X i,2 ) Represents an approximation error, satisfiesAnd is
S042 according to the second error variable z i,2 In the process, the unknown uncertain part is obtained by solving the radial basis function neural network, and a second virtual control law alpha is designed by utilizing a backstepping design method and the Lyapunov function i2 While generating adaptive parametersAnd
in which a virtual control law alpha is established i,2 、Law of controlAnd adaptive parametersSatisfies the following calculation formula:
wherein Represents phi i Transpose of (J) i 、ε i,2 、c i,2 、r i,2 、a i,2 、ξ i 、σ i 、l i,2 、η i And ζ i Are all positive design parameters. H i =[1/h i ,-g i /h i ] T ,Represents H i Transpose of (Q) i =[α i,2 ,1] T ,α i,2 Representing a second virtual control law; since in practical cases, H i Are difficult to obtain and designTo estimate H i Defining an estimation errorAnd is wherein Andare respectively estimated asAnd multiplication by multiplication
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