Search

This paper presents modeling simulation and control of stuart type 6-DOF parallel manipulator. Dynamic equations of the parallel manipulator are derived by using Kane's method, inheriting all the advantages while circumventing all the disadvantages of Newtown- Euler and Euler-Lagrangian formulations. In this modeling procedure at first all the inertial torques due to platform, motor and actuators are calculated and then this is equated with active torque supplied by the DC-motors in the form of electromagnetic torque. By this force-torque balance, calculation of time varying equivalent inertia of the motor is avoided. Normal PID principle based controllers are not very effective in achieving desired accuracy in trajectory tracking as reported in literature. Therefore, a novel control architecture has been proposed which not only has industry standard PID controller but also includes compensator for drastically improving tracking performance. Since, over all system of parallel manipulator is highly non-linear in nature with coupling terms and varying parameters, only PID controller alone could not reduce this resultant tracking error, even after best tuning. One lag compensator for each actuator has been designed in combination with PID controller, which resulted in significant improvement in trajectory tracking in comparison to former control methods (only normal PID based controller) for all the parameters of cartesian trajectory.

Control valve stiction is a common problem experienced by process control loops and is one of the main causes of loop cycling during a control session. This paper proposes a simple effective stickband compensator which was applied to a plant for reducing stickband and limit cycle amplitude within a unity feedback system. The technique is based on a 'stickband-jacket' applied across the input and the output of the actual control valve. The feedback error signal is used to vary the width of the stickband and limit cycle frequency. The compensator adds a single increment to the controller's degree-of-freedom and can be easily added to any existing control loop.

This paper investigates the problem of electromechanical stability related to the dynamic interaction between the turbine-alternators and the network. In particular, this paper refers to a software package, named ALICE and developed by CESI and Terna in MATLAB®, which makes available within an unique environment features for linearized analysis of electromechanical cycle and multivariable optimization of power system stabilizers. By using of ALICE, it is possible to make stability analysis of the linearized system, both in local and inter-area frequency interval, and, above all, to take out, thanks to different automatic optimization techniques, the most appropriate calibration of the gains of additional stabilizing feedbacks in order to achieve an adequate damping of electromechanical oscillations.

The conditions for closed-loop identifiability using routine operating data are largely unknown. In this paper, the closed-loop identifiability conditions for a first-order autoregressive process with exogenous input (ARX) that is regulated using a 3-parameter lead-lag controller and that has no external excitation will be examined using an analytical approach. Despite the convoluted nature of the intermediate results, the final conditions for absolute identification of the stable region can be concisely stated. These results suggest that the class of internal model controllers (IMCs) can, despite their aggressive behaviour, successfully identify an ARX model without any external excitation. As well, Monte Carlo simulations performed using MATLAB confirmed the analytical results that were obtained. Future work in this area can focus on extending the results to other model structures, to other types of controllers, and to higher order processes.

Nonlinear EGR and VGT Control with Integral Action for Diesel Engines - A nonlinear multivariable control design with integral action is proposed and investigated for control of Exhaust Gas Recirculation (EGR) and Variable Geometry Turbine (VGT) in heavy duty Diesel engines. The main control goal is to regulate oxygen/fuel ratio and intake manifold EGR-fraction, and they are specified in an outer loop. These are chosen as main performance variables since they are strongly coupled to the emissions. An existing nonlinear control design based on feedback linearization is extended with integral action. In particular; the control design method utilizes a control Lyapunov function, inverse optimal control, and a nonlinear input transformation. Comparisons between different control structures are performed in simulations showing the following four points. Firstly, integral action is necessary to handle model errors so that the controller can track the performance variables specified in the outer loop. Secondly the proposed control design handles the nonlinear effects in the Diesel engine that results in less control errors compared to a control structure with PID controllers. Thirdly, it is important to use the input transformation and it is sufficient to use a control structure with PID controllers and input transformation to handle the nonlinear effects. Fourthly, the proposed control design is sensitive to model errors in the input transformation while a control structure with PID controllers and input transformation handles these model errors.

In the present paper, a new strategy for robust filtering problem of linear time-invariant (LTI) continuous time system is proposed. The key idea consists in generalizing the structure of a linear state estimator of the Luenberger class. As a matter of fact, the closed loop form of this class of state estimator can be assimilated to a closed loop control problem. Then, the standard correction term can be viewed as a Proportional controller. In this paper, we propose a more general form of controller in order to obtain the robustness. An example shows the efficiency of the proposed approach.

The first control course should be taught through discrete time techniques. The difficulties in following this methodology are discussed with possible solutions. A discrete time performance specification has been used to design a pole placement controller and its use illustrated with a difficult example. A procedure to design lead and lag controllers directly in discrete time domain has been presented.

In this paper, a method for auto-tuning of a fractional order lead-lag compensator using relay feedback tests is proposed. A design method for this kind of compensators is discussed, based on the magnitude and phase measurement of the plant to be controlled from relay feedback tests at a frequency of interest. Simple relationships among the parameters of this fractional controller are established and specifications such as the static error constant (kss), phase margin (φm) and gain crossover frequency (ωc) can be fulfilled, with a robustness argument by inspecting the flatness of phase Bode plot of the compensator. The auto-tuning method proposed can be taken as a first step for a latter generalization of these lead-lag compensators to the fractional PIΛDμ controllers.

This paper presents a high precision positioning mechanism design with dual actuator. In the fields of micro positioning, micromanipulation and micro test instrument, the required motion precision is continuously increasing. Dual servo system consisting of a coarse stage and a fine motion stage with VCM and PZT is proposed. Mechanical mechanism is designed with the leaf spring type of a flexure hinge joint. Lead compensator is applied to this control system, and is designed by PQ method.

This paper presents a comparison of different control methodologies for Autonomous Underwater Vehicles (AUVs). As AUVs operate out of contact of human operators and being untetherered it is paramount that the controllers are both robust and reliable. The three control methodologies that are compared in this paper are PID, Lead Lag and Sliding Mode.

A commercially available servo motor system consisting of a DC motor, optical encoder, power driver/amplifier, and a digital feedback controller is considered. The controller contains a lead compensator and an integrator. A knowledge-based system is developed and implemented for tuning the digital controller so as to meet a set of performance requirements. A reference model is utilized for several purposes. First the parameters of this model are adjusted so as to meet the specifications. This will provide some buffer against unreasonable specifications. Then, during tuning, the deviation of the response of the actual servo system from the reference model, for the same input signal, is used to establish the performance conditions. The knowledge-based tuner uses these conditions to infer the necessary tuning actions for the controller parameters which include the pole and zero locations of the lead compensator and the control gain. A model of the control system may be used to gain knowledge on the nature of the response of the system to various changes in tuning parameters and tuning levels. Additional knowledge and experience is obtained through actual operation of the servo system under different tuning conditions. The knowledge base obtained in this manner is fuzzy in general. Furthermore, the relationships of controller attributes such as the maximum phase lead, the crossover frequency, the compensator gain at the crossover frequency, and the low frequency where this gain equals that of the integral controller, with the actual tuning parameters, have to be established as well. Tuning inferences are determined using the compositional rule of inference. The performance of the digital servo system is evaluated through experimentation.

In this paper, the development of a self-tuning feedforward compensator is discussed. The technique is to witness the uncompensated load response and identify the system transfer functions from it and set the compensator for ideal compensation. The compensator is then tuned by a trial and error method so as to account for the modelling error. The transfer functions corresponding to the manipulated and the load variables are assumed to be modelled by first order dead time systems. The self-tuning technique is verified using simulation on a distributed control system.

In order to minimize the transmission lags associated with the pneumatic instrumentation, the Transmission Lag Compensator (TLC) was developed. The construction and features of the TLC which is based on the phase lead compensation are described. The effects of applying the TLCs are investigated by experiments and simulations. Experiments with practical plants using the TLCs show the improvement of the control performance over the system without the TLC. The effects of applying the TLCs are also obtained quantitatively from the control performance simulations.

The implementation of a discrete feedback compensator using block processing is discussed. In this scheme, a block of L measurements are accumulated before the processing is initiated. A block of L compensation samples are then computed and released serially into the system being compensated. Compensator implementations are developed both for the ARMA and the state-variable representations.

It is highly desirable that any control system is not affected by modeling errors or parameter variations of a controlled object. This paper presents an application of a robust feedback control system to load frequency control of an interconnected power system. In the design of this control system, parameter variations in a controlled object are formulated as disturbances to the system, and then a robust compensator is introduced. This compensator makes the transfer functions between these equivalent disturbances and the controlled output exactly or approximately zero. As a result, the frequency characteristic between the reference input and the controlled output is kept almost unchanged over a specified frequency range, even if some parameters in the controlled object vary widely from their nominal values. The robust compensator is, moreover, effective in real disturbances such as load changes. The effect of the control system is demonstrated by an example applied to a two-area interconnected power system model.