مجله کنترل
سال چهاردهم شماره 2 (تابستان 1399)

This paper deals with analyzing gyroscope drift error in the position-independent navigation algorithm of a stable platform inertial system. Most of the stable platform navigation algorithms proposed in the literature have drawbacks of estimating position rates for alignment commands. Not only the estimating position rates are the basic source of position errors, but they also make the alignment commands and their implementation more complicated. The major advantage of the proposed design is that the angular velocity commands of gyroscopes are independent of the system position and are proportional to accelerations’ integrals, all of which eliminate, the errors resulted from the estimation of the longitude and latitude rates. In this paper, the stable platform system is modeled, and plate alignment procedure is determined and the initial conditions of navigation phase are calculated. In stationary conditions, the position error propagation for the fixed gyroscope drift is obtained analytically. The position error of the proposed algorithm propagates linearly with time, while in the strapdawn algorithm; this error propagates as the cube of time.

The purpose of this paper is to provide a new algorithm for guidance of an underwater vehicle to reach its target, and demonstrate its effectiveness by simulation with a computer code. The meant of target in here is to chase a ship on the surface of the water. In order to do this, one of the most effective methods is to follow the ship wake which produced behind it. Disadvantages of wake guidance can be mentioned as zigzag motion for rediscovering the wake in its path which according to the decreasing linear speed of approaching the target, sometime it doesn't reach the target and collision fails. Therefore various ideas, with both positive and negative aspects, have been introduced to improve movement in the wake path. In this paper, a new guidance algorithm for running an underwater vehicle at the center of wake, which is named central guidance, is introduced that results an optimal path that by using geometric bases, determining the center of the wake in guidance phase like a central line. Then, using the optimal least effort method, the path to central line is presented.  Also, to test this method, the wake of a ship is modelled and programed and its code is used in the guidance program to simulate the performance of this method.

This paper deals with the issues of sensor fault detection for a class of Lipschitz uncertain nonlinear system. By definition coordinate transformation matrix for system states and output system, at first the original system divided into two subsystems. the first subsystem includes uncertainties but without any sensor faults and the second subsystem has sensor faults but is free of uncertainties. Then sensor faults in second subsystem are formed as actuator faults. For the aim of fault detection (FD) two sliding mode observer is designed for two subsystems. The necessary matrices and parameters to design observers are obtained by solving linear matrix inequality (LMI) problem.  Stability condition of observer’s dynamics are reviewed based on Lyapunov approach. Finally simulation example is given to illustrate the effectiveness proposed approach.

A wheeled mobile robot is one of the most important types of mobile robots. A subcategory of these robots is wheeled robots towing trailer(s). Motion control problem, especially in backward motion is one of the challenging research topics in this field. In this article, a control algorithm for path-following problem of a tractor-trailer system is provided, which at the same time provides the ability to control the backward and forward motions of the tractor-trailer robot. To this end, first the kinematic equations of a wheeled robot with a trailer is extracted and then reference paths for the robot are defined. Path following equations, in addition to the robot mathematical equations, also represent the robot movement with respect to the reference path. Then, by using transformations the system equations are expressed in a new space and subsequently a control algorithm is proposed for the system. The investigated control law make the system asymptotically stable around the reference path. Finally, obtained results have been presented which guarantee the designed controller.

The NGL refinery of the Sirri Island has a major role in the production of high-value products. One of the most important refinery units is the demethanizer unit, comprising of a complex network of distillation towers and heat exchangers. In the first step, using the Aspen Hysys software, a proper steady state model was developed for this unit in which the simulation of the main equipment that is, distillation towers and heat exchangers were carried out. The steady state simulation results are in good agreement with the data gathered from the real plant. Then, the simulation was transferred from steady state to dynamic mode in which the main equipment such as distillation towers and control valves were sized. Here, the available controllers which are currently present in the real plant, were added to the simulation. Using the auto tuning variation (ATV) method and by considering the desired behavior namely, stability, fast response, and absence of oscillation, the overall performance of the controllers were examined under different scenarios. Based on the results, it was identified that with carefully tuning the controllers parameters, much better performance can be achieved.

In this study, a force reflection control structure is developed for the surgery training haptic system. In the surgery training haptic system, the surgical operation is cooperatively performed by a trainer and a trainee. The participation of each surgeon in the operation is established through their own haptic consoles. Although the operation is primarily performed by the trainee, the trainer is able to interfere into the procedure in case of observing any deviation on the part of trainee and correct the probable mistakes. To transform the task authority between the trainer and the trainee, the hand force of the trainer is reflected to the hands of the trainee. Utilizing the haptic system, the position of the trainee is transformed to the hands of the trainer, thus the trainer has necessary information regarding the current position of the surgical operation. Stabilizing controllers are developed for each haptic console. The stability of the closed loop system is analyzed using the Input-to-State Stability (ISS) approach. Our simulation results confirmed the appropriate performance of the proposed structure.

In this paper, the problem of finite-time stability and finite-time stabilization for a specific class of dynamical systems with nonlinear functions in the presence time-varying delay and norm-bounded uncertainty terms is investigated. Nonlinear functions are considered to satisfy the Lipchitz conditions. At first, sufficient conditions to guarantee the finite-time stability for time-delay nonlinear system with uncertainties and based on the Lyapunov approach is presented. In the following, sufficient conditions to ensure finite time stabilization the considered system with state feedback are presented. In the proofs of proposed theorems are used from the appropriate Lyapunov-Krasovskii function and newton-Libniz-formula that can reduce the conservative. Also, all of the obtained conditions in this paper are delay-dependent and presented as linear matrix inequalities .Finally, the numerical examples and simulations exhibit the effectiveness of the proposed methods.

Nowadays, the noticeable growth of fractional order calculus in engineering science has transformed this research field into one of the most popular fields of research in engineering and in particular in control engineering. Accordingly, several controllers have been designed based on fractional order mathematics. Adaptive fuzzy controllers are among the designed fractional order controllers. In the literatures, it has been shown that the uncertain fractional order systems can be well compensated by fractional order adaptive fuzzy controllers in the presence of disturbance. For this reason, in this paper, an indirect adaptive TSK fuzzy controller with fractional order sliding mode control is proposed to control a certain class of nonlinear fractional order systems.The stability of the closed-loop system is investigated and using a fractional order Lyapunov function candidate, the adaptation laws are extracted. A fractional order adaptation law is used to adjust the free parameters in the consequence part of the adaptive TSK system and a robust adaptive law is used to reduce the influence of the approximation error between the output of the system nonlinear model and the output of the fuzzy system. Hence, using the fractional order Lyapunov theorem, the Mittag-Leffler stability of the closed-loop system is guaranteed. Finally, the numerical simulation shows the efficiency of the proposed control strategy for a gyroscope uncertain nonlinear fractional order system in the presence of uncertainty.