Paweł Dworak

Linear adaptive structure for control of a nonlinear MIMO dynamic plant

In the paper an adaptive linear control system structure with modal controllers for a MIMO nonlinear dynamic process is presented and various methods for synthesis of those controllers are analyzed. The problems under study are exemplified by the synthesis of a position and yaw angle control system for a drillship described by a 3DOF nonlinear mathematical model of low-frequency motions made by the drillship over the drilling point. In the proposed control system, use is made of a set of (stable) linear modal controllers that create a linear adaptive controller with variable parameters tuned appropriately to operation conditions chosen on the basis of two measured auxiliary signals. These are the ship’s current forward speed measured in reference to the water and the systematically calculated difference between the course angle and the sea current (yaw angle). The system synthesis is carried out by means of four different methods for system pole placement after having linearized the model of low-frequency motions made by the vessel at its nominal “operating points” in steady states that are dependent on the specified yaw angle and the sea current velocity. The final part of the paper includes simulation results of system operation with an adaptive controller of (stepwise) varying parameters along with conclusions and final remarks.

Switched-structure of linear MIMO controllers for positioning of a drillship on a sea surface

In the paper a multicontroller-based switchable control system structure is proposed to control nonlinear MIMO plants. The considered structure contains a set of linear feedback controllers operating together with an additional, statically decoupled loop of the control system. The nonlinear model of a drilling vessel in three degrees of freedom (3DOF) on the sea surface is used as a MIMO plant to be controlled. The system synthesis is carried out by linearization of the adopted nonlinear plant model at its nominal “operating points” that depend on the preset ship yaw angle and the velocity of the see current. Performance of the proposed control systems is illustrated by examples of simulation results carried out in MATLAB/Simulink using the nonlinear model of low-frequency (LF) motions of WIMPEY SEALAB drilling vessel.

Hybrid model-following control algorithm within the motion control system

The goal of this paper is to present a new robust hybrid method that ensures stiffness of the mechanical characteristic of the direct current motor servo drive, which means lack of influence of the varying load torque on quality of the velocity control, what extends the concept of the MFC-V (Model-Following Velocity Control) system that allows one to shape the servo drive transient response, ensuring, among other things, an overshoot free step response in the velocity control loop. The proposed multi-loop-controller solution exemplifies a possible approach to designing a motor servo drive within the motion control system of a CNC (Computer Numerical Control) machines.

Design of a multivariable neural controller for control of a nonlinear MIMO plant

Abstract The paper presents the training problem of a set of neural nets to obtain a (gain-scheduling, adaptive) multivariable neural controller for control of a nonlinear MIMO dynamic process represented by a mathematical model of Low-Frequency (LF) motions of a drillship over the drilling point at the sea bottom. The designed neural controller contains a set of neural nets that determine values of its parameters chosen on the basis of two measured auxiliary signals. These are the ship’s current forward speed measured with respect to water and the systematically calculated difference between the course angle and the sea current (yaw angle). Four different methods for synthesis of multivariable modal controllers are used to obtain source data for training the neural controller with parameters reproduced by neural networks. Neural networks are designed on the basis of 3650 modal controllers obtained with the use of the pole placement technique after having linearized the model of LF motions made by the vessel at its nominal operating points in steady states that are dependent on the specified yaw angle and the sea current velocity. The final part of the paper includes simulation results of system operation with a neural controller along with conclusions and final remarks.

Calibration of Cameras and Fringe Pattern Projectors in the Vision System for Positioning of Workpieces on the CNC Machines

Application of machine vision in automation, robotics and mechatronic systems is one of the most rapidly developing areas of industrial and applied computer science. The vision system presented in the paper can be used for automatic positioning of the workpieces on the numerically controlled machines. The idea of the system is based on the 3D scanning using the fringe patterns approach [ but its accuracy strongly depends on the lighting conditions and the proper calibration of the whole vision system. The most crucial elements for the calibration are both cameras and structural light projectors, as well as the overall geometrical configuration (external parameters in the common coordinate system) and the compensation of the brightness nonlinearities introduced by the structural light sources. In the paper some methods used for the calibration of the experimental system and obtained results are presented.

Improving stability and regulation quality of nonlinear MIMO processes

Abstract The paper presents results of comparative analysis of the control system introducing dynamic decoupling and the robust two-degrees of freedom control system with the use of the decoupled nominal model of the linearized MIMO process. First the design method of the control system with dynamic decoupling of MIMO processes has been replayed. Next, basic advantages of the model following control structure for MIMO systems, its stability and robustness properties are presented. Finally, a MFC-MIMO robust control system has been proposed. The presented control structure has been tested for its performance on the tracking processes of yaw angle and position of the drillship. Results of simulation tests lend support to the view that the proposed MIMO-MFC control method may find wide application to robust control of nonlinear plants with time-varying or perturbed parameters.

About dynamic decoupling of a nonlinear MIMO dynamic plant

The paper presents a method of synthesis and implementation of the multi-controller control structure for a dynamic decoupling of the multi-input multi-output (MIMO) nonlinear dynamic plant. The proposed structure uses some known techniques in order to reduce effects of coupling of the nonlinear plants inputs and outputs. A multi-controller structure is created after linearization of the adopted nonlinear plant model at its operating points and synthesis of the linear controller that dynamically decouple the local linear plant model. Such an adaptive controller varies its parameters depending on the current plant operating point. The presented simulation results confirm applicability of the proposed method.

Adaptive multi-controller TSK Fuzzy Structure for Control of Nonlinear MIMO Dynamic Plant

Abstract In the paper an adaptive multi-controller control system utilizing a TSK fuzzy rules for a MIMO nonlinear dynamic plant is presented. The problems under study are exemplified by synthesis of a position and yaw angle control system for a drillship described by a 3DOF nonlinear mathematical model of low-frequency motions made by the drillship over the drilling point. In the proposed control system use is made of a set of linear modal controllers that create a multi-controller structure from which a group of controllers appropriate to given operation conditions is chosen and used to calculate, by using TSK fuzzy rules, control signals. The final part of the paper includes simulation results of system operation with an adaptive controller of (stepwise) varying parameters along with conclusions and final remarks.

A reduction of a controller set of switched controller for positioning of a drillship on a sea surface

In the paper a multicontroller-based switchable control system for nonlinear MIMO plants is presented. The control system synthesis is carried out by linearization of the adopted nonlinear plant model at its operating “points”. Thus the considered structure contains a collection of linear feedback controllers. In the first stage of the adopted method a great number of controllers is synthesized. The paper discuss problems with reduction of such controller set to make it smaller and possible to implement the system in e.g. constrained memory of programmable automation devices. As an example a nonlinear model of a drilling vessel in three degrees of freedom (3DOF) on a sea surface is used as a MIMO plant to be controlled. Here the controller set depends on the preset ship yaw angle and the velocity of the sea current. The methods of reduction and their possible results are compared and discussed.

PI controller design for indirect vector controlled induction motor: A decoupling approach

Decoupling of the stator currents is important for smoother torque response of indirect vector controlled induction motors. Typically, feedforward decoupling is used to take care of current coupling that requires exact knowledge of motor parameters, additional circuitry and signal processing. In this paper, a method is proposed to design the regulating proportional-integral gains that minimize coupling without any requirement of the additional decoupler. The variation of the coupling terms for change in load torque is considered as the performance measure. An iterative linear matrix inequality based H∞ control design approach is used to obtain the controller gains. A comparison between the feedforward and the proposed decoupling schemes is presented through simulation and experimental results. The results show that the proposed scheme is simple yet effective even without additional block or burden on signal processing.