Showing 15 results for Robust Control
Volume 12, Issue 3 (12-2012)
Abstract
In this study, a robust controller is designed for fuzzy network control systems (NCSs) using the static output feedback. Delay and data packet dropout affect on the stability of network control systems, and therefore, the asymptotic stability condition is established considering delay and data packet dropout. Delay is time-varying while the lower and upper bounds for delay is defined, and the number of data packet dropout is unknown. Data drift is also an important phenomena that may occur when data is transmitted from sensors to the controller and from the controller to actuators. This phenomenon is modeled as a stochastic variable with a probabilistic distribution. For stability analyses, Lyapunov–Krasovskii functions, which depend on the limits of delay and data packet dropout, are used. Results of controller design are derived as Linear Matrix Inequalities (LMIs). A numerical example is adopted to show the effectiveness of the proposed approach.
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Volume 13, Issue 15 (3-2014)
Abstract
A robust delayed plant-input mapping methodology is proposed to control of industrial plants through wireless communication networks. In this way, firstly a robust classic controller is designed for original continuous-time system according to a predefined uncertainty bound. Then compensation of the destabilizing effects of a constant delay is then concerned. For this purpose, a digital controller is designed using D-K iteration method. Finally this algorithm is modified to overcome the wireless network effects, e.g. random network delay, packet loss and packet disordering. Simulation studies on two benchmark industrial problems demonstrate the effectiveness of the proposed method for uncertain plants.
Hassan Ghorashi, Behnam Moetakef-Imani,
Volume 14, Issue 15 (3-2015)
Abstract
Because of high accuracy and low weight-to-force ratio, servo hydraulic systems are widely used in various branches of industry. Simultaneous improvement of accuracy and time response are among ever increasing needs for these systems. Rapid movement commands to hydraulic actuator excite attached mechanical components and consequently produce undesired vibrations. Recommended solution to overcome the above mentioned problem is to design and implement advanced controller which takes into consideration the high frequency uncertainties. In this research a two-degree-of–freedom (2DOF) position controller has been design and implemented for undesirable vibration regulation and robust performance achievement on a servo hydraulic table. In this regard various elements of the system are modeled and then the servo hydraulic table nominal system and uncertainty are identified using grey-box method. The 2DOF robust controller is designed using general H∞ framework and analyzed by structured singular value, Mu. The feedback block of controller is used to reduce the effect of uncertainty, measurement noises and reject disturbances, whereas the forward controller shapes the command signals to improve the performance. The designed controller has been implemented on the servo hydraulic test rig in order to track sine and trapezoid position command signals. It has been observed the controller has a more accurate performance and faster time response than the common robust controller with just one feedback block. Extensive experimental results of the developed controller indicate robust performance and acceptable response to disturbance and measurement noise rejection in the defined uncertainty range.
Reza Kazemi, Mohammad Amin Saeedi,
Volume 15, Issue 6 (8-2015)
Abstract
In this paper, to improve the roll stability of an articulated vehicle carrying liquid an active roll control system using a robust nonlinear controller is presented. First, a sixteen-degree-of-freedom nonlinear dynamic model of an articulated vehicle is developed next using TruckSim software in a standard maneuver, the vehicle model is validated. Then, the dynamic interaction between the fluid cargo and the tractor semitrailer vehicle, by integrating a quasi-dynamic slosh model with sixteen-degree-of-freedom of a tractor semitrailer model is investigated. Also, for rollover prevention of an articulated vehicle carrying liquid, a novel nonlinear robust control including combination of sliding mode control and feedback linearization control is proposed. Control system performance for two different fill volumes in J-turn and lane change maneuvers is shown. Next, to investigate the rollover stability of an articulated heavy vehicle carrying liquid, load transfer ratio is considered as an important factor. Moreover, in order to study the performance of the robust control system, a linear controller has been used. The simulation results confirm the excellent performance of the proposed robust control system in critical lane change maneuver due to increase of longitudinal velocity and a reduction of road friction coefficient.
Vahab Khoshdel, Alireza Akbarzadeh Tootoonchi,
Volume 15, Issue 8 (10-2015)
Abstract
In this study, a novel robust impedance control for a lower-limb rehabilitation robotic system using voltage control strategy is used. Most existing control approaches are based on control torque strategy, which require the knowledge of robot dynamics as well as dynamics of patients. This requires the controller to overcome complex problems such as uncertainty and nonlinearity involved in the dynamics of the system, robot and patients. Conversely, the voltage-based control approaches is free from the system dynamics. In addition, it considers the actuator dynamics. The performance of voltage-based approaches is demonstrated by experimental result in robotic applications. Compared with a torque control scheme, it is simpler, less computational and more efficient. Nevertheless, uncertainty of actuator dynamics results in challenges for the voltage control strategy applications. The present paper, presents a novel robust impedance control based on the voltage control strategy. To overcome uncertainties, the adaptive fuzzy estimator is designed based on the voltage-based strategy. The proposed control is verified by a stability analysis. To illustrate the effectiveness of the control approach, a 1-DOF lower-limb rehabilitation robot is designed. Both torque-based impedance control and the voltage-based impedance control are compared through a therapeutic exercise. It is shown that the voltage-based impedance control perform better than the traditional torque-based impedance control. Simulation and experimental results both shows that the proposed voltage-based robust impedance control is superior to voltage-based impedance control in presence of uncertainties.
Behnam Miripour Fard, Pegah Abdollahzadeh,
Volume 16, Issue 2 (4-2016)
Abstract
Stratospheric airships have introduced interesting solutions for challenges in aerospace industries. Buoyant and propulsion forces produced by airships makes them to be capable of long-time flight and efficient operation. In spite of many progresses, there are still many challenges in this interesting field of study. In this paper, first the dynamic model of fully-actuated stratospheric airship with 6-DOF expressed by the generalized coordinates, then desired values of the airship attitude, linear and angular velocities obtained according to desired path and using pseudo inversion of the kinematics and dynamics equations. In view of the unknown inertial parameters first in adaptive inverse dynamic control, inertial parameters estimated online by using linearization parameters and gradient update law. Next control law and nonlinear dynamic equation is deduced by designing control algorithm based on passivity, and according to that, adaptive and robust control based on passivity applied for controlling airship. The stability of the closed loop control system is proved by using the Lyapunov stability theory. Finally, comparison between the results of the all methods are shown.
Mahmoud Mazare, Mostafa Taghizadeh,
Volume 16, Issue 10 (1-2017)
Abstract
In this paper, constraint equations are derived based on the kinematic model of the robot and Lagrange method is applied to derive the dynamic equations. In order to control the robot position on planned reference trajectories, in presence of uncertainties of the dynamic model, an adaptive robust controller with uncertainty estimator is designed which is robust against the uncertainties and induced noises. The proposed controller consists of an approximately known inverse dynamics model output as model-based part of the controller, an estimated uncertainty term to compensate for the un-modeled dynamics, external disturbances, and time-varying parameters, and also a decentralized PID controller as a feedback part to enhance closed-loop stability and account for the estimation error of uncertainties. Performance of the designed controller is simulated and evaluated in different conditions including the presence of noise and parameters variation. In this regard, a comparison has been made between the response of the proposed adaptive robust controller and response of a feedback linearization controller, indicating their capabilities in noise rejection and compensation of parameters variation. Also, the results show that the proposed sliding mode controller has a desirable performance in tracking the reference trajectories in presence of the model uncertainties and noises for this kind of parallel mechanism.
Vahid Aberoomand, Rasul Fesharakifard, Ali Kamal Eigoli,
Volume 16, Issue 12 (2-2017)
Abstract
In electromagnetic motors, increase in output torque leads to increase in rotor inertia. Various robotics applications, especially haptic interfaces, oblige convenient dynamic performances of electromagnetic motors which are strongly in turn influenced by the rotor’s inertia. In the present paper, a robust control method for a viscous hybrid actuator is developed which supplies a desired varying torque while maintaining a constant low inertia. This hybrid actuator includes two dc motors with the shafts coupled through a rotational damper using a viscous non-contact coupler. This coupling method is based on Eddy current to provide the required performances. The large far motor eliminates or reduces the inertial forces and external dynamics effects on the actuator. The small near motor provides the desired output torque. Since the system is essentially linear, the applied robust control method is based on Hꝏ and parametric uncertainties and physical constraints including motors’ voltages saturation, rotary damper’s speed saturation, fastest user’s speed and acceleration applied to the actuator and force sensor noise are considered in its design. Also the robust method of µ-synthesis for the system in presence of parameteric uncertainties and other physical constraints are studied. The implementation of the controller on a 1 dof haptic interface model validate the achievement of the desired performances.
Mohammadamin Aliasgharpour, Karim Salahshoor,
Volume 17, Issue 5 (7-2017)
Abstract
Drilling is one of the most critical mechanical process in oil and gas industry in which its operational parameters should properly be tuned to reduce drilling time and consequently enhance efficiency of the drilling process. The main objective in this paper is to present a new method to regulate and optimize the Rate of Penetration (ROP) of the system with top drive rotary motor torque in drill string. The paper presents a formulation of a robust receding horizon controller to track piecewise constant references. To achieve this, a tube-based Robust Model Predictive Control (RMPC) is introduced in which the tubes are based on reachable sets. A drilling system is assumed as a test bed for evaluating the performance of the proposed control scheme. The assumed drilling system is modeled as a linear system with additive bounded uncertainties by using Bourgoyne and Young model which is known as a complete mathematical drilling model. The most important novelty part of this manuscript corresponds to integration of both tracking and regulatory objectives in one control framework. Simulations demonstrate the effectiveness of the stability and robust characteristics the proposed RMPC scheme in terms of its stability and robust characteristics with respect to the usual control approaches.
Mahmood Mazare, Pegah Ghanbari, M.ghasem Kazemi, Mohammad Rasool Najafi,
Volume 17, Issue 8 (10-2017)
Abstract
In this paper, an optimal adaptive sliding mode controller of an Omni-Directional Mobile Robot (ODMR) is proposed using harmony search algorithm. First, kinematic model of the robot is derived and then, governing equations of dynamic model have been obtained using linear and angular momentum equilibrium. Since the derived model is not an exact definition of the system, it includes some uncertainties. To compensate them, a tracking control method has been offered. The proposed controller consists of an approximately known inverse dynamic model output as the model-based part of the controller, an estimated uncertainty term to compensate for the un-modeled dynamics, external disturbances, and time-varying parameters to enhance closed-loop stability and account for the estimation error of the uncertainties. In order to compare the results of the proposed controller, an optimal feedback linearization and sliding mode controllers are designed and then, a cost function has been defined by combining the variation rate of control signal and the integral error index. This cost function has been minimized using harmony search algorithm, resulting in optimum control parameters. Finally, the performance of the designed controller in different conditions, such as in presence of disturbance and system parameter variation has been simulated and discussed.
Majdeddin Najafi, Shahaboddin Rahmanian, Behzad Shirani,
Volume 17, Issue 11 (1-2018)
Abstract
The design of a robust controller for the automatic landing system is investigated for an unmanned fixed-wing aircraft based on an external navigation system. Since landing is the most difficult phase of flight, the major accidents are occurring in the phase. So, providing a high-precision automatic landing system in presence of environmental disturbances is very important for UAVs landing. The used landing navigation system is founded on a portable land-based laser-optics system which can track the UAV and calculate the altitude and direction of it toward the center of runway. However, the navigation system is external; sending them to the UAV can be done with a delay. In this regard, UAV’s control systems must be designed such that the stability of aircraft is satisfied based on information of navigation system with considering the model uncertainty, noises, disturbance and navigation delay. So in this paper, a new robust stabilizer controller is suggested for UAVs to overcome these challenges with considering some limitation in the structure of the controller. Finally, simulation results based on laboratory software in the loop been presented. The results are indicating the capability of using proposed method for automatically landing of UAVs.
Mohammad Mehdi Kakaei, Hassan Salarieh,
Volume 17, Issue 11 (1-2018)
Abstract
In this study, design of a novel robust control method for three-link underactuated biped robot which can satisfy appropriate constrains on the robot and cause the stability and rhythmic movement of the robot, is presented. Due to the wide use of sensors and actuators in mechanisms and robots, and existence of noise and also uncertainty in the system components or other error stemming from unmolded dynamics in the system or unwanted disturbances acting on them, there is an essential need for employment of robust control methods. In order to apply locomotion’s constrains to the system, the feedback linearization method is used. Additionally this method is combined with the sliding mode method to obtain a robust control method. The other purpose of the study is the complete elimination of chattering phenomenon. To this end, the control method is combined with the backstepping method. Finally, the exponential stability of the method, which is called FLBS, is proved, and the stability of the obtained walking cycle is shown using the Poincare map. In the robot modeling procedure, the contact between the swing leg and the ground is considered to be rigid and instantaneous. The underactuated nature of the robot and the importance of the role of contact in stabilizing the robot movement are taken into account in this study. Finally, simulations based on this control method are performed which show the exponential stability of robot movement, elimination of chattering and robustness against either disturbances or uncertainties.
S.a. Khalilpour Seyedi , R. Khorrambakht, A.r. Bourbour, H.r. Taghirad,
Volume 19, Issue 11 (11-2019)
Abstract
Despite the intense development of cable-driven robot in recent years, they have not yet been vastly utilized in their potential applications because of difficulties in their performing accurate installation and calibration. This paper aims to present a suitable control method, relieving the limitation of accurate calibration and installation requirement in the suspended cable-driven parallel robot. In this paper, kinematics and dynamics uncertainties are investigated and based on their bounds, a robust controller is proposed. The main innovation of this article is providing a new control method to cost reduction by eliminating accurate measurement tools such as a camera in position control of a deployable cable-driven robot. Using this approach, reducing costs in building a robot and increasing the speed of installation and calibration is achieved. Another problem investigated in this paper is the problem of joint space controllers applied to redundant cable-driven parallel robots, namely the loosened redundant cable. To solve this problem, the embedded force sensor and a new sliding surface for the controller is proposed. In fact, in this paper, the conventional joint-space controllers are modified to become applicable to the control of cable-driven robots. Finally, by conducting some experiments using ARAS suspended cable-driven parallel robot, the proposed algorithms are verified and it is shown that there are feasible solutions for stable robot maneuvers.
S.f. Alem, E. Sabooni, F. Sheikholeslam, I. Izadi,
Volume 20, Issue 6 (6-2020)
Abstract
Piezoelectric actuators are the most common choice for position control with ultra-high precision. Despite the significant advantages, the linear and nonlinear dynamics of these actuators, such as hysteresis, could decrease the precision of the control system. In this research, a controller based on the sliding mode method is proposed for position control of piezoelectric actuator. Sliding mode control is a model-based and useful method in nanopositioning systems. In this research, Bouc-Wen model is used for description of the actuator’s behavior. In this model, the linear dynamic is modeled with mass, stiffness and damping terms, and the hysteresis is modeled by its nonlinear dynamics. Usually, there are mismatch and uncertainty between the physical system and mathematical model. For stability analysis of the prevalent sliding mode control, the upper bound of uncertainty must be known. But, in practical systems, this is not possible, simply. On the other hand, selecting the large values for this bound, increases the controller gain and distances it from the optimum value. The proposed adaptive robust control eliminates the dependency to the upper bound of uncertainty. This is done by introducing an online adaptive law for estimating this bound. Proposing this law, asymptotic stability of the closed-loop control system is proven. Implementing the presented method on the laboratory setup and simulator software, its effectiveness is shown by simulation and experimental results.
Volume 21, Issue 4 (10-2021)
Abstract
Successful implementation of active control technology requires an appropriate control algorithm to calculate the adaptive control force required by the actuators. Smart structures represent a new engineering approach that integrates the actions of digital sensors, actuators and control circuit elements into a single control system that can respond adaptively to environmental stochastic changes in a useful manner. The mathematical model of the system is an estimation of its actual dynamic behavior. In general, this difference can have a significant effect on the performance and stability of the control system. One of the important issues in active control algorithms is the evaluation of the control systemchr('39')s robustness to model uncertainties and the actuator saturation. In this paper, a Developed Robust Proportional Integral Derivative controller with uncertainties in the structural stiffness parameter, the sensing noise and saturation windup of the saturation is introduced. the PID control force is obtained in such a way that the infinity norm of the closed loop system transfer function from disturbance inputs to target outputs becomes minimal. By considering the parametric uncertainty in the structural stiffness parameters and multiplicative unstructured uncertainty and the windup phenomenon in the actuator model and existence of noise in the velocity sensor, PID control scheme has been developed in the form of state space. The PID control gains by taking advantage of the Hinfinity mixed sensitivity minimization criterion, are obtained simultaneously by considering the effects of all vibration modes of the building in such a way that the infinity norm of the closed loop transfer function from exogenous inputs to the controlled outputs becomes minimal. To demonstrate the robust performance and stability of the proposed algorithm, the results of numerical simulations on a 4-story structure equipped with an active tuned mass damper are used. The obtained results show the robust performance and stability of the proposed robust PID control scheme in comparison with conventional PID and linear quadratic regulator (LQR) control algorithms, both in time and frequency domains. According to the mean values of performance indices, in average 11 and 7% more reduction in J1 , 7 and 5% in J2 and 10 and 6% in J3 in the proposed robust PID in comparison with the LQR and common PID for three models subjected to far field selected earthquake records. And in average 17 and 10% more reduction in J1 , 12 and 8% in J2 and 11 and 8% in J3 in the proposed robust PID in comparison with the LQR and common PID for three models subjected to near field selected earthquake records. And J4 which related to amount of control effort, for the proposed robust PID, LQR and conventional PID are 1.3e-2, 9.1e-3 and 7.9e-3 in average for the three models subjected to far field and 4e-2, 2.4e-2 and 2.7e-2 subjected to near field selected earthquake records. The obtained results show the robust performance and stability of the proposed controller in the presence of structural stiffness uncertainties, actuator saturation and measurement noise.
