ADAPTIVE VARIABLE STRUCTURE CONTROL OF PNEUMATICALLY ACTUATED ROBOT
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Abstract:
To apply a pneumatic robot to not only conventional simple tasks but also more rigorous ones, a servo type control is required. Since it has some high nonlinear properties, some type of adaptive control strategy should be adopted to improve its conrol performance. In this kind of robot, the simplicity of control algorism is also important.In this study, an adaptive variable structure control scheme is developed on the basis of the well-known variable structure system theory. This control scheme confines a phase-plane trajectory on the switching line momentarily rotated adaptively to the phase-state of controlled system. It can suppress the chattering often encountered in the usual sliding mode control with a fixed switching line, to achieve a smooth response. Further, it can automatically generate the specified phase-plane trajectory heading toward the desired position asymptotically.As a result of the application to the PTP type position control of an articulated pneumatic robot, the expected control performance can be well attained. Some advantages of this control method are the simplicity of a control algorism and the flexibility in the decision of control parameter values. Its availability may be verified.Keywords:
Algorism
Nonlinear system control has been widely concern of the research. At present, the nonlinear system decoupling control and static feedback linearization that based on the theory of differential geometry brought the research getting rid of limitation for local linearization and small scale motion. However, differential geometry control must depend on precise mathematical model. As a matter of fact, the control system usually is with parameters uncertainties and output disturbance. In this thesis, nonlinear system of control theory has been studied deeply. Considering sliding mode variable structure control with good robust, which was not sensitive for parameters perturbation and external disturbance, the combination idea of nonlinear system and sliding mode controls was obtained by reference to the large number of documents. Thus, it not only can improve system robustness but solve the difficulties problem of nonlinear sliding mode surface structure. As known to all, traditional sliding mode had a defect that is famous chattering phenomenon. A plenty of research papers focus on elimination/avoidance chattering by using different methods. By comparing, the document is concerned with novel design method for high order sliding mode control, which can eliminate chattering fundamentally. Especially, the approach and realization of nonlinear system high order sliding mode control is presented in this paper. High order sliding mode technique is the latest study. This thesis from the theory analysis to the simulation and experiment deeply study high order sliding mode control principle and its applications. By comparison, the second order sliding mode control law (also known as dynamic sliding mode control, DSM) may be effective to eliminate the chattering phenomenon. But it is still unable to shake off the requirement of system relative degree. Therefore, arbitrary order sliding mode controller is employed, whose relative degree can equal any values instead of one. The robot car model adopted high order sliding mode is taken as an example. The simulation results show that the tracking control is effective. In the control systems design, it is very often to differentiate the variables. Through the derivation of sliding mode, the expression of sliding mode differential value is obtained. The simulation results certificate sliding mode differentiator with robustness and precision. At the same time, the differentiator for arbitrary sliding mode is given to avoiding conventional complex numerical calculation. It not only remains the precision of variables differential value, but also obtains the robustness. A direct application is simplification for high order sliding mode controller. Due to its inherent advantages, the permanent magnet synchronous motor (PMSM) deserves attention and is the most used drive in machine tool servos and modern speed control applications. For improving performance, this paper will applied nonlinear high order sliding mode research achievement to MIMO permanent magnet synchronous motor. It changes the coupling nonlinear PMSM to single input single output (SISO) linear subsystem control problem instead of near equilibrium point linearization. Thereby, the problem of nonlinear and coupling for PMSM has been solved. In addition, Uncertainty nonlinear robust control system has been well-received study of attention. Because the robust control theory is essentially at the expense of certain performance. This kind of robust control strategy often limits bandwidth of closed loop, so that system tracking performance and robustness will be decreased. So, sliding mode control is an effective approach for improving system robust. This thesis first proposed a robust high order sliding mode controller for PMSM. The system has good position servo tracking precision in spite of parameters uncertainties and external torque disturbance. On this basis, According to the principle of high order sliding mode, as well as differentiator, the state variables of PMSM are identified online firstly and successfully. The results of simulation indicate observe value has high precision when sliding mode variable and its differentials are convergent into zero. The same theory is used in external unknown torque disturbance estimation online for PMSM. As if, load torque will no longer be unknown disturbance. System performance can be improved greatly. It establishes theoretical foundation for the future applications. At the end of paper, using advanced half-physical platform controller dSPACE to drive a PMSM, hardware experiment implement is structured completely. The experiment results illustrate that PMSM adopting precious feedback linearization decoupling and high order sliding mode controller can realize system servo tracking control with good dynamic and steady character.
Feedback linearization
Linearization
Robustness
Integral sliding mode
Decoupling (probability)
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The variable structure control(VSC) with sliding mode is an important and interesting topic in modern control of nonlinear systems. However, the discontinuous control law in VSC leads to undesirable chattering in practice. As a method solving this problem, in this paper, we propose a scheme of the VSC with neural network sliding surface. A neural network sliding surface with boundary layer is employed to solve discontinuous control law. The proposed control scheme is verified by simulation results.
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Variable structure system
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Variable structure system
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The developments of sliding mode variable structure control theory at all points in recent years are reviewed.It includes the research of sliding mode surface,the reaching condition of sliding mode,the corresponding studies of controller's nonlinear structure,and a lot of results about its applying in the adaptive control theory.The merits and shortcomings of these methods are introduced.The possible study contents and directions are analyzed.
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Variable structure system
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In this paper, a kind of sliding mode is defined for continuous-time systems. Such sliding mode can be designed using any of linear control methods, like as optimal control, pole assignment, and so on for the overall system, which is different with the general sliding mode designed in the reduced-order system. The designed feedback rule is considered as an equivalent control. For the system without any parameter uncertainty and external disturbance, the trajectories in the state space with the equivalent control for any initial state form the sliding mode, i.e. the proposed sliding mode is a set of trajectories of the system known exactly with the equivalent control for any initial state. Then for a continuous-time system with parameter uncertainty and external disturbance, a chattering-free variable structure (VS) control law is designed to move the state to the sliding mode in a finite time. Such VS control method can be easily extended to servo control, output feedback control, and discrete-time VS control problems. The simulation results show that the proposed VS controller has good control performance without chattering.
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Servomechanism
State variable
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In this paper, a nonlinear control method used to make two different chaotic systems achieve synchronization within finite time is designed based on the sliding mode variable structure control theory and the driving response control method.In this method, the reaching law of the sliding mode variable structure may be adjusted to make the sliding mode become stable at a given moment, and make the state error on the sliding mode surface converge to zero globally and rapidly in the form of terminal sliding mode, so as to achieve speedy and accurate synchronization of the different-structure chaotic system.The theoretical analysis and the simulation result verify the availability of the method together.
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State variable
Terminal sliding mode
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A class of global sliding mode variable structure control (VSC) system is proposed. This VSC permits robustness for the system dynamics over all the response time, but the robustness of the conventional VSC system only resides in its sliding mode. It provides an efficient method for the sliding function design of nonlinear system. The design steps are discussed in detail, and the global variable structure control of inverted pendulum model is also presented to demonstrate its effectiveness.
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Variable structure system
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According to the application and development of sliding mode variable structure control theory, discussed the rapid development of the two different sliding surfaces in recent years, focusing on the development courses, advantages and disadvantages of them. Alleviation of chattering is the most important problem in sliding mode control. This article summarized two kinds of methods: reaching law and continuous methods. Finally, the recent ten years development and further research directions are discussed.
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The paper discusses a class of nonlinear time-varying system that could be replaced by linear time-varying system and present designed method with variable structure control(VSC) by applying nonlinear time-varying(NTV) sliding zone.Firstly,applying Riccati dfferential equation(SDDRE) by depending on state,we give nonlinear time-varying sliding zone which is a subset of state space.Secondly,a variable structure controller is established,which the trajectory of closed-loop system enter sliding zone and Lyapunov function along the trajectory of system is decreased in the nonlinear sliding zone.Finally,we also present a computing method of nonlinear time-varying control and sliding mode control.
Variable structure system
State variable
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