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This paper introduces an indirect adaptive fuzzy sliding mode controller as a power system stabilizer for damping local and inter-area modes of oscillations of multi-machine power systems. This controller is designed based on the combination of sliding mode controller and the fuzzy logic systems. The fuzzy systems are used to approximate the unknown functions of power system model. Generator speed deviation and accelerator power are selected as fuzzy logic system inputs. A new sliding mode control law achieved by changing the sliding condition and the undesirable chattering has been removed by using of a continuous function. Based on the Lyapunov synthesis, adaptation laws are developed. Performance of the proposed stabilizer is studied for a two-area four-machine power system. Simulation results show the effectiveness of the proposed controller in comparison with multi-band power system stabilizer (MB-PSS), classical adaptive fuzzy sliding mode stabilizer and adaptive fuzzy sliding mode stabilizer with a proportional integral function (PI).

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Chatter vibration is one of the limiting factors in increasing the material removing rate in machining operations. In this paper, the integrated mechatronic modeling of a lathe machine equipped with MR damper, and design of a fuzzy semi-active controller are presented. To suppress chatter, the structural dynamic characteristics (i.e., real and imaginary part of the frequency response function), which are the main parameters in drawing the stability lobes, are varied semi-actively using magnetorheological damper . Modified Bouc-Wen model is employed for MR damper modeling, which enables us to account for the input voltage to the damper as the control input of the system. Since the structure becomes nonlinear in the presence of MR damper, a time-domain approach for generation of stability lobes is presented. In controller design and as a feedback of the chatter level, a novel chatter detection index (CDI) is developed, which can also be employed for experimental chatter detection. The obtained results show that the proposed system has been successful in enhancing the stability of the lathe machine.

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Chatter or self-excited violent relative dynamic motion between the cutting tool and the workpiece is an undesirable phenomenon in machining due to its destructive effects on the product surface quality, machining accuracy, cutting tool life and machine tool life. Because of these reason, there is a need for in-process detection methods to predict and avoid chatter vibration during machining processes. In this work, Chatter detection in turning process is performed based on analysis of feed marks in surface texture of work piece using image processing techniques. In order to validate the proposed vision based method an accelerometer was attached to the shank of cutting tool for measuring vibrations.

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A new 3-D nonlinear model of chatter vibration in turning process is presented in this paper. Workpiece and cutting tool are modeled as rotational shaft and cantilever beam, respectively which are excited by cutting forces. Equations of motion of workpiece are derived using Hamilton’s principal. Also, Timoshenko beam theory is used to simulate tool’s vibration. Then π-Buckingham theory is used to extract dimensionless equations of motion for transverse and torsional vibrations of workpiece and transverse and longitudinal vibrations of cutting tool. Using the mode summation method, a numerical solution is presented for this nonlinear problem. Effect of cutting parameters such as longitudinal cutting position, cutting width, cutting depth and radius of workpiece for machining with and without tailstock are investigated. Using these results turning velocity intervals for stable and unstable cuts are determined. Simulation results show that using tailstock in turning process for machining near the end of the workpiece increases process stability. Also in the case of using tailstock, machining near the end of the workpiece is more stable than the machining in the middle region of the workpiece.

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In most of the researches that have been done in the position control of robot manipulator, the assumption is that robot manipulator kinematic or robot Jacobian matrix turns out from the joint-space to the task-space. Despite the fact that none of the existing physical parameters in the equations of the robot manipulator cannot be calculated with high precision. In addition, when the robot manipulator picks up an object, uncertainties occur in length, direction and contact point of the end-effector with it. So, it follows that the robot manipulator kinematic is also has the uncertainty and for the various operations that the robot manipulator is responsible, its kinematics be changed too, certainly. To overcome these uncertainties, in this paper, a simple adaptive fuzzy sliding mode control has been presented for tracking the position of the robot manipulator end-effector, in the presence of uncertainties in dynamics, kinematics and Jacobian matrix of robot manipulator. In the proposed control, bound of existing uncertainties is set online using an adaptive fuzzy approximator and in the end, controller performance happens in a way that the tracking error of the robot manipulator will converge to zero. In the proposed approximator design, unlike conventional methods, single input-single output fuzzy rules have been used. Thus, in the practical implementation of the proposed control, the need for additional sensors is eliminated and calculations volume of control input decreases too. Mathematical proofs show that the proposed control, is global asymptotic stability. To evaluate the performance of the proposed control, in a few steps, simulations are implemented on a two-link elbow robot manipulator. The simulation results show the favorable performance of the proposed control.

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One of the most common problems that occur during machining is Machine tool chatter, which adversely affects surface finish, dimensional accuracy, tool life and machine life. Machine tool chatter can be modeled as a linear time invariant differential equation with time delay or delay differential equation. Infinite dimensional nature of delay differential equations is apparent in the study of time delay systems. The analytical stability methods are thus more difficult for these differential equations and approximate methods do not give accurate results. In this paper, a new method is developed to determine the exact stable region(s) in the parameter space of machine tool chatter. In this method, first, the bifurcation points are determined. Then, the Lambert function is used to decide on the stability characteristics of each particular region. The advantages of this method are simple implementation and applicability to high order linear time delay systems. By resulting stability regions from this method, we can choose an optimal spindle speed to suppress the chatter. The new approach is the most acceptable method with comparison to traditional graphical, computational and approximate methods due to excellent accuracy and other advantages.

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In this paper, a new approach has been presented for dynamic control of active suspension vehicle system subject to the road disturbances. The active suspension system (ASS) which has been considered in this paper is operated by a hydraulic actuator. The input of this hydraulic actuator is a servo valve. In the other word, both mechanical equation of system (related to hydraulic actuator) and its electrical equation (related to servo valve) are considered. Therefore, the equations are complicated and only the input current of servo valve is accessible as the input control signal. The proposed approach is based on dynamic sliding mode control (DSMC).In DSMC chattering is removed due to the integrator which is placed before the input control signal of the plant. However, in DSMC the augmented system (the system plus the integrator) is one dimension bigger than the actual system and then, control of the plant is more complicated. But, its advantage is that the input control signal is obtained from a dynamic system or a low pass filter, while the robust performance (invariance property) of the system is reserved even in the presence of disturbance. Another advantage of proposed approach is that the desired output force of the hydraulic actuator is obtained by the controller.

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Chattering, being the focus of this study is a kind of self-excited vibration that is encountered in different machining processes such as milling and turning. This type of self-excited vibration rapidly develops after commencement and destabilizes the whole process. This phenomenon leads to, among others, increased noise, wavy surface finishes, discontinuous chips, and failure in the tool or machine parts. The depth of cut is the main parameter in the occurrence of chattering in machining processes. Avoiding the critical depth of cut ensures the stability of the process. Process modeling is a way to obtain the critical depth of cut. The vibration assisted turning process, having many advantages, is of a different nature than the conventional machining. In this paper, the vibration assisted turning process is modeled and numerically solved and the critical depth of cut is obtained. Validation of the results is performed using experimental data and comparison with conventional machining. In the vibration assisted turning process, higher stability is obtained with lower ratios of cutting duration to the total vibration period. This ratio is directly proportional to vibration frequency and amplitude and is inversely proportional to the cutting speed.

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Quadrotors are types of Unmanned Aerial Vehicles (UAVs) which have unique features compared to conventional aircrafts because of its vertical take-off and landing capability, flying in small areas and its high maneuverability. Also the relatively simple, economical and easy flight system of quadrotors, makes it to widely used as a good platform for development, implementation and testing a variety of control methods. One of the robust control methods is sliding mode control. In spite of the high capabilities of this approach, it has a main problem which is high frequency switching of the control signal witch is known the chattering phenomenon. In the past several decades, fractional order differential equations have been implemented in engineering application field, including controllers design and provided the possibility of using controllers for improving the performance of system. In this paper, a fractional order sliding surface has been employed for designing sliding mode control rule for quadrotors. The main objective of this study is to improve the performance and reduce the chattering phenomenon in sliding mode method. In this regard, by introducing sliding 〖PD〗^α surface, the control rule is designed in two different modes of 0

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Boring operations due to the large length to diameter ratio and the high flexibility of tool are prone to self-excited (chatter) vibration. This vibration may cause poor surface quality, low dimensional accuracy and tool breakage. In practice, chatter is the main limitation on production rate. The main reason of chatter phenomenon is the dynamic interaction between cutting process and structure of machine tool. By increasing the length of the cutting tool, the vibration tendency in the tool’s structure increases. Improving dynamic stiffness of the tool is the most effective solution for decreasing vibration and increasing chatter stability. For increasing the stability of the tool in long overhang boring operations, passive and active vibration control has been proposed and implemented. In active control methods, vibrations can be effectively damped over a various cutting conditions. The aim of this research is to enhance chatter stability of an industrial boring bar by increasing the dynamic stiffness. A VCA actuator is used for active vibration control. The designed setup can effectively suppress undesirable vibrations in the radial direction. First, modal parameters of the boring bar are determined by experimental modal analysis. Then, the transfer function of the actuator-tool setup is identified with the sweep frequency excitation. In the following, the direct velocity feedback is successfully implemented in the vibration control loop. The results of cutting tests indicate that the actuator has a great performance in suppressing vibrations and increasing the dynamic stiffness. Hence, the developed method can significantly increase chatter stability of boring operations.

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