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A nonlinear multivariable highly coupled system that is susceptible to both internal and external perturbations is the permanent magnet synchronous motor. A new reaching law‐based control approach that combines a sliding‐mode disturbance observer and an enhanced two‐vector model predictive current control is suggested in order to enhance the dynamic performance of the permanent magnet synchronous motor and its robustness to system disturbances. First, a new reaching law is developed in this paper to resolve the conflict between the traditional reaching law's chattering of the system and the reaching time of the sliding‐mode surface. This new reaching law not only makes the system's response more rapid but also reduces chattering; second, taking into account the possibility of systems with internal parameter uptake and external load disturbance, a sliding‐mode disturbance observer based on t is developed. Finally, the q‐axis current obtained from the speed sliding‐mode control rate is added to the model predictive current control, and an optimal duty cycle model predictive current control based on space vector modulation is designed because the traditional two‐vector model predictive current control is to optimize the duty cycle and voltage vectors separately, and the switching frequency is not fixed. The method suggested in this research may successfully suppress the sliding‐mode control system chattering and increase the resilience and dynamic response performance of the speed control system, according to simulation findings compared to the traditional reaching law and traditional duty cycle. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

To solve the problems of serious buffeting in traditional sliding mode control and difficulty in obtaining the derivative information of the system sliding mode surface, a distributed drive electric vehicles active front steering (AFS) control method based on adaptive super-twisting sliding mode control (ASTSMC) is proposed. Taking the yaw rate deviation as the state quantity, the stable and convergent sliding mode surface is designed to obtain the equivalent control input of the front wheel angle. The sliding mode function information is substituted into the parameters of the super-twisting algorithm; the discontinuous term is kept in the integrand function to keep the control signal continuous and weaken the system chattering; the adaptive control law is added to design the AFS controller. The co-simulation results of Matlab/Simulink and Carsim show that ASTSMC can reduce the yaw rate by 40.59% compared with no control under step steering condition. Compared with the sliding mode controller, ASTSMC has optimized the sideslip angle by 5.41% under the double line shifting condition. [ABSTRACT FROM AUTHOR]

This paper proposes a adaptive reaching law-based sliding mode control (SMC) method for maintaining favorable velocity control performance of permanent magnet synchronous motors (PMSMs) under internal and external perturbations. An adaptive switching power reaching law (ASPRL) is designed, which contains adaptive terms and state variables of the sliding mode surface function. This augmented reaching law decreases the chatter of the control system and increases the rate at which the state variables of the system reach the sliding mode surface. Additionally, a Luenberger observer load torque (LOLT) is designed to observe the external load and provide feedback to the velocity controller, reducing the impact of load disturbances and improving the jamming performance of the controller. Simulation experiments confirm that ASPRL reduces buffeting, decreases overshoot, and shortens response time, demonstrating its advantages in PMSM control. [ABSTRACT FROM AUTHOR]

In order to enhance the speed control performance of the permanent magnet synchronous motor (PMSM) with internal and external disturbances, a new adaptive terminal sliding mode reaching law (ATSMRL) is proposed with continuous fast terminal sliding mode control (CFTSMC). Firstly, the ATSMRL is presented with the aim of reducing the input control efforts, which can dynamically adopt all positive aspects in terms of the finite time convergence, high tracking precision, and reduction of the chattering in the control input of the system. Secondly, an extended sliding mode disturbance observer (ESMDO) is designed to estimate the total disturbances of the system, and then the estimated disturbance has been brought for the feed-forward compensation technique, which would enhance the disturbance rejection ability of the system. Afterwards, the close loop stability is validated by the Lyapunov function. Finally the comprehensive numerical and experimental analyses have been carried out to demonstrate the superiority of the ATSMRL method than those of conventional exponential sliding mode reaching law (ESMRL) and terminal sliding mode reaching law (TSMRL). [ABSTRACT FROM AUTHOR]

To control microelectromechanical systems (MEMS) gyroscope axis, we propose and investigate a new robust sliding mode controller (NRSMC). The sliding surface in the phase space converges to the equilibrium point within a finite period from any initial state. However, the main drawback of this control system is the chattering phenomenon, which is undesirable for the MEMS system. To solve this problem, we suggest a novel hybrid control system which improves trajectory tracking and eliminates the chattering. The dynamic stability of NRSMC against external disturbances is proved by applying the Lyapunov theory. The effectiveness of the proposed control method is verified by numerical simulation with a random noise applied to demonstrate the robustness of the proposed control system. [ABSTRACT FROM AUTHOR]

The design of adaptive chattering-free sliding mode controller (SMC) for chaotic systems with unknown input nonlinearities is studied in this paper. A smooth hyperbolic tangent function is utilized to replace the discontinuous sign function; therefore, the proposed adaptive SMC ensures that not only the chaos phenomenon can be suppressed effectively but also the chattering often appearing in the traditional discontinuous SMC with sign function is eliminated, even when the unknown input nonlinearity is present. A sufficient condition for stability of closed-loop system is acquired by Lyapunov theory. The numerical simulation results are illustrated to verify the proposed adaptive sliding mode control method. [ABSTRACT FROM AUTHOR]

In this paper, an output feedback position tracking control problem relevant for a linear piezoelectric ceramic motor is studied. The main goals of the control design include achieving extremely high resolution, accuracy, stability, and improved transient performance when system uncertainties, unknown dynamics, and external disturbances act on the system. The proposed control approach is designed in such a way that the implementation of the high-precisionmicro/nanopositioningis possible. An adaptive sliding-mode-based scheme is adopted to synthesize a robust controller. Stability analysis of the control approach is performed and it is analytically shown that the position tracking error asymptotically converges to zero. The important advantages of this control approach are: 1) designing a controller without the requirement of prior knowledge about uncertainty/disturbance bounds; 2) having a chattering-free control input; and 3) obtaining a fast response without overshoot. The proposed control strategy was experimentally validated and compared to the existing control approaches. [ABSTRACT FROM AUTHOR]

Summary In this paper, we present a robust adaptive control algorithm for a class of bilateral teleoperation systems with system uncertainties and jittering time delays. The remarkable feature of jittering delays is that time delays change sharply and randomly. Conventional controllers would fail because jittering time delays introduce serious chattering. To address the jittering issue, a novel jittering‐free scheme is developed by relaxing and extending the frequently used constant upper bound. Moreover, an adaptive law was incorporated with the Chebyshev neural network to deal with the system uncertainties. To obtain finite‐time synchronization performance, a fast terminal sliding mode controller is proposed through the technique of "adding a power integrator." With the proposed control scheme, the robust finite‐time convergence performance is guaranteed. The settling time can be further calculated with the controller parameters. The simulation and experiment results have demonstrated the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Summary: In this paper, the problem of finite‐time control for small‐scale unmanned helicopter system with high‐order mismatched disturbance is investigated via continuous nonsingular terminal sliding‐mode control approach. The key idea is to design a novel nonlinear dynamic sliding‐mode surface based on finite‐time disturbance observer. Then, the finite‐time convergence and chattering attenuation capability is guaranteed by the continuous nonsingular terminal sliding‐mode control law. Additionally, rigorous finite‐time stability analysis for the closed‐loop helicopter system is given by means of the Lyapunov theory. Finally, some simulation results demonstrate the effectiveness and predominant properties of the proposed control method for the small‐scale unmanned helicopter even in the presence of high‐order mismatched disturbance. [ABSTRACT FROM AUTHOR]

Summary: The attitude control problem of reusable launch vehicles (RLVs) is investigated based on multivariable supertwisting fixed‐time comprehensive control strategy. A novel multivariable supertwisting fixed‐time approach, which can guarantee that the states converge to zero within a fixed time, is proposed. According to the multiple time scale principle, the RLV attitude control system is divided into attitude angle subsystem and attitude angle rate subsystem. Based on multivariable supertwisting fixed‐time approach, comprehensive design of fixed‐time disturbance observer and controller is proposed to ensure that the attitude angle tracking error converges to zero within a fixed time. The features of the proposed control scheme contain that the settling time is independent of initial conditions and it has the better property of chattering reduction. Finally, the efficiency of the proposed method is verified through numerical simulation. [ABSTRACT FROM AUTHOR]

Abstract This paper presents two sliding mode controllers to address the trajectory tracking problem of unmanned airships in the presence of unknown wind disturbance. The sliding mode controller proposed first is designed by a fast power rate reaching law(FPRRL). The disturbance is compensated by a radial basis function neural network (RBFNN). To avoid the aggressive adaptation, the controller is augmented by a command filter. The controller provides good robustness and tracking performance with no chattering under the hypothesis of ideal wind field. However, serious chattering occurs when simulation is performed under discontinuous wind field. To simulate the wind in practice, the wind field employed in the simulation is generated by the combination of a constant field and white noise. The controller is improved subsequently with an extended model to suppress the chattering induced by the white noise. The enhanced controller manipulates the derivation of system input, thus attenuating the chattering. Stability analysis shows that both controllers drive the tracking error into a controllable small region near zero. Simulations are provided to validate the performance of the proposed controllers under different wind hypothesis. [ABSTRACT FROM AUTHOR]

The solvability and regularity of hybrid differential-algebraic systems (DAEs) is studied, and classical stability estimates are extended to hybrid DAE systems. Different reasons for non-regularity are discussed and appropriate regularization techniques are presented. This includes a generalization of Filippov regularization in the case of so-called chattering. The results are illustrated by several numerical examples. [ABSTRACT FROM AUTHOR]

Summary: In this paper, the trajectory tracking guidance problem is investigated for entry vehicle in the presence of uncertainty. First, a robust nonsingular fast terminal sliding mode control law is designed to guarantee the finite‐time tracking performance under uncertainty. Then, to eliminate the need of prior information about uncertainty and mitigate the chattering, a novel adaptive nonsingular fast terminal sliding mode control is proposed by employing adaptive parameter tuning law. Furthermore, with the help of designed adaptation mechanism, the proposed adaptive nonsingular fast terminal sliding mode control can achieve finite‐time convergence of both tracking errors and parameter estimation errors simultaneously. Finally, numerical simulations are given to demonstrate the effectiveness and high‐precision tracking performance of the proposed controllers. [ABSTRACT FROM AUTHOR]

In this paper, a sensorless control method for joint drive unit driven by BLDC motor of low extremity exoskeleton, cascade feedback observer identification method, is proposed. The cascade feedback observer identification method is based on improved Integral-Switching-Function Sliding-Mode-Observer (ISF-SMO) and adaptive FIR filter. The improved Integral-Switching-Function Sliding-Mode-Observer is used to identify the back-EMF of motor. The sliding mode surface redesigned according to Integral-Switching-Function (ISF) eliminates the inevitable chattering problem in conventional Sliding-Mode-Observer (SMO). The stability condition of Integral-Switching-Function Sliding-Mode-Observer is obtained with Lyapunov function. Meanwhile, considering the estimation error and system instability caused by the mismatch between the actual resistance value (Rs) and the set resistance value, the LMS algorithm is used to estimate the resistance value online according to the structure of adaptive FIR filter. When system is running, the modified Integral-Switching-Function Sliding-Mode-Observer and adaptive FIR filter are used to modify the back-EMF and the resistance value by cascading feedback relation, and the modified back-EMF value is taken as the final output of the system. Because of considering the uncertainty of resistance caused by temperature variation, the robustness and stability of the cascade feedback observer can be improved. Meanwhile, higher estimation accuracy is obtained, and operation range of sensorless control is extended, which is suitable for motor in low speed region. Finally, the correctness and validity of the proposed method are verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

A novel full-order terminal sliding-mode controller (FOTSMC) based on the finite-time disturbance observer (FTDO) is proposed for the “JIAOLONG” manned submersible with lumped disturbances. First, a finite-time disturbance observer (FTDO) is developed to estimate the lumped disturbances including the external disturbances and model uncertainties. Second, a full-order terminal sliding-mode surface is designed for the manned submersible, whose sliding-mode motion behaves as full-order dynamics rather than reduced-order dynamics in conventional sliding-mode control systems. Then, a continuous sliding-mode control law is developed to avoid chattering phenomenon, as well as to drive the system outputs to the desired reference trajectory in finite time. Furthermore, the closed-loop system stability analysis is given by Lyapunov theory. Finally, the simulation results demonstrate the satisfactory tracking performance and excellent disturbance rejection capability of the proposed finite-time disturbance observer based full-order terminal sliding-mode control (FTDO-FOTSMC) method. [ABSTRACT FROM AUTHOR]

The paper presents a sensorless fuzzy sliding-mode speed control (FSMC) decoupled by a vector control applied to a double-star induction motor (DSIM) using a sliding mode observer (SMO) fed by two PWM voltage source inverters. The fuzzy sliding-mode control is a hybrid control technique that links two control strategies, the sliding mode and fuzzy logic, whose sign function of the discontinuous part is replaced by a fuzzy inference system to overcome the drawbacks of the chattering phenomenon. For the control, the major problem is the need for using a mechanical sensor. Which imposes an additional cost and increases the complexity of the assembly. For this reason, we propose a sliding mode observer of a high robustness to few parametric uncertainties by providing considerable correction gains. The control + observer set is simulated by the Matlab / Simulink software and the simulation results show that its performance is robust and the chattering problem is solved. [ABSTRACT FROM AUTHOR]

This article proposes a novel fractional order sliding mode control for a class of fractional order and integer order systems with mismatched disturbances. First, a new fractional order disturbance observer is designed to estimate the fractional order differential of the mismatched disturbance directly. Second, the fractional order sliding surface and controller are proposed based on the designed disturbance observer. Our method can deal with mismatched disturbance and has better control performance with faster response speed, lower overshoot, and less chattering effect. The simulations on Quad–Rotor UAV and Maglev suspension systems demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A sliding-mode grid voltage observer (SMGVO) is proposed and experimentally verified in this paper for voltage-sensorless operation under an unbalanced network. The fundamental positive sequence component (FPSC) and fundamental negative sequence component (FNSC) are inherently separated in the observer without employing any additional filters. Due to embedded filtering effect, high frequency chattering and harmonic ripples can be well suppressed. Additionally, dc components can be completely rejected. As a result, dc offset would not cause fundamental frequency oscillations in magnitude and frequency of the estimated FPSC and FNSC. Owing to the predictive ability of SMGVO, one-step delay can be directly compensated using state variables in the observer. By combining estimation and prediction into one stage, the designed SMGVO turns out to be a compact solution for finite-control-set model predictive power control without voltage sensors. Theoretical proof is derived to verify that FPSC and FNSC can be accurately estimated and separated. Experimental results obtained from a two-level PWM rectifier confirm the effectiveness of the whole control system. [ABSTRACT FROM PUBLISHER]

To deal with the operation performance degradation of permanent magnet synchronous machine (PMSM) drives with uncertainties and unmodeled dynamics, this paper presents a finite-time nonlinear disturbance observer (FTNDO) based discretized integral sliding mode (DISM) composite control scheme. Based on the reaching-law approach, a DISM speed controller featuring a superior dynamic quality and global robustness against disturbances is constructed. This controller can avoid the reaching phase and overlarge control action. In addition, a sliding mode differentiator based FTNDO is devised and extended to the discrete-time domain for disturbance estimation. The attractive features of the FTNDO are that it can provide a finite-time converging estimation and alleviate the chattering effect in conventional sliding mode observers, while retaining robustness to parameter variations. By feeding the estimate forward to the pre-stage DISM controller, both disturbances and chattering can be significantly suppressed. Moreover, considering the estimation error of a FTNDO caused by discrete sampling, a stability analysis of the composite controller is discussed. Experimental results validate the superiority of the presented scheme. [ABSTRACT FROM AUTHOR]

In this paper, a class of mismatched uncertain systems is investigated. And a novel sliding mode control design is presented. During the design process of the proposed control, a transformation scheme is proposed, which can easily transform the mismatched uncertain systems into matched systems. Based on the matched systems, a novel full order sliding mode surface is designed, which can avoid the singular issue of terminal sliding mode control. And a chattering alleviating scheme is also proposed, which can ensure that the sliding mode control is chattering free regardless of whether the conventional sliding mode control or the terminal sliding mode control is used. Compared with the recurrent controller, the complexity of the proposed controller is reduced. It is much simpler and easy to implement. Also, the need of system knowledge is also reduced. The control performance is validated by simulation. [ABSTRACT FROM AUTHOR]

In this paper, coordinated motion control of the pneumatic-cylinder-driven biaxial gantry for precise contour tracking is investigated. An adaptive robust coordinated motion controller is developed by incorporating the task coordinate formulation into the adaptive robust control architecture. Specifically, a task coordinate frame is used to approximately calculate the contour error, which is utilized for controller design to generate coordination between two axes. Furthermore, the proposed controller utilizes online parameter adaptation to estimate some important unknown model parameters, and employs a robust control law to attenuate the effects of parameter estimation errors, unmodelled dynamics and external disturbances. Therefore, certain transient contouring performance and steady-state contour tracking accuracy can be guaranteed. Extensive comparative experimental results obtained verify the effectiveness of the proposed coordinated motion control strategy and its performance robustness to sudden disturbances in practical implementation. [ABSTRACT FROM AUTHOR]

The reaching law is an important part of a sliding-mode controller, which guarantees the existence of slidingmotion in finite time. Fast access to sliding motion with a weak chattering phenomenon in control input is always desired. In this paper, 2 different types of reaching laws are proposed, which guarantee finite-time convergence to the sliding manifold. Moreover, the reaching time is robust to initial conditions and can be designed by the user. Some useful discussions on the design of parameters are also presented to weaken the chattering phenomenon. A careful simulation study is finally provided to verify the effectiveness and efficiency of the proposed methods. [ABSTRACT FROM AUTHOR]

A higher-order sliding approach to control a bioreactor model is proposed by non-commensurate fractional equations. According to existing conditions and chattering reduction, a high-order sliding mode approach has been chosen to design the controller. A mathematical problem is a barrier to use the high-order sliding mode approach for fractional order systems. The contribution of the paper is to choose proper sliding surfaces. High-order sliding mode controllers have been taken in accordance with the structure of integer order system. Thus, in order for the system to apply more precise calculations, fractional systems should somehow turn to integer order. The sliding surfaces have been selected so appropriately that we can benefit from the structure of integer order controllers for fractional order system. The sliding surface in both controllers has also been the same so as to provide conditions for comparison. The model outputs are reached the desired values using two controllers. Finally, the comparison in simulations indicates that the proposed approach has a great impact on chattering reduction. [ABSTRACT FROM AUTHOR]

A sliding mode control (SMC) scheme of doubly fed induction generator (DFIG) wind turbine with a novel exponential reaching law (NERL) is proposed in this paper. The DFIG wind turbine is running under variable wind speed. The NERL based SMC proves to be capable of reducing the system chattering phenomenon as well as accelerating the approaching process. A nonlinear case numerical simulation test is employed to verify the superior performance of the ERL method over traditional power rate reaching strategy. The NERL based SMC is employed to control the DFIG wind turbine generator under variable wind speed subsequently and the simulation results evidence the remarkable performance of the NERL based SMC control scheme. [ABSTRACT FROM AUTHOR]

In this study, a new high order sliding mode controller (HOSMC), based on super twisting algorithm (STA), is proposed for vehicle active suspensions. It is well known that first order sliding mode controller (SMC) is insensitive to parameter variations and external disturbances. On the other hand, it suffers from chattering present in control signal that may harm the mechanical components of the system. Therefore, HOSMC is preferred in this study that attenuates chattering effectively while preserving its robustness. Proposed HOSMC uses an estimation for the equivalent part of the control signal and uses the STA for the discontinuous part of the control law. Additionally, the controller gains are obtained by offline multi-objective genetic algorithm search. Extensive simulations and experimental results are presented to reveal the performance of the proposed controller. First order SMC is also designed and used for comparison. The results indicate the superior performance of the proposed HOSMC. [ABSTRACT FROM AUTHOR]

This paper investigates the finite-time synchronization of complex networks (CNs) with non-identical nodes and impulsive disturbances. By utilizing stability theories, new 1-norm-based analytical techniques and suitable comparison, systems, several sufficient conditions are obtained to realize the synchronization goal in finite time. State feedback controllers with and without the sign function are designed. Results show that the controllers with sign function can reduce the conservativeness of control gains and the controllers without sign function can overcome the chattering phenomenon. Numerical simulations are offered to verify the effectiveness of the theoretical analysis. [ABSTRACT FROM AUTHOR]

In cutting process, chatter is an inevitable phenomenon that greatly affects workpiece surface quality, tool life and machining efficiency. The stiffness variation (SV) method has been proposed and applied in chatter suppression for a long time. However, the early studies focused on boring and turning with one degree of freedom. For milling process with two degrees of freedom, there is no related research about SV. In this paper, SV method is employed through modulating the stiffness around a nominal value in order to suppress milling chatter. The milling dynamic model of SV with two degrees of freedom is constructed. In this model, the classical delay differential equation (DDE), which governs the milling process, is replaced with a DDE with a time-varying stiffness term. The stability analysis with different SV is completed using the semi-discretization method (SDM) and results show that the stable region with SV is larger than that under most of the traditional conditions. The results of stability analysis are verified by time domain simulation. In addition, the influences on stability lobe diagram (SLD), which is caused by different waveforms, amplitudes and frequencies of SV, are also analyzed specifically. The analysis results can provide the optimal parameters combination for milling. Cutting experiments are implemented on a three-axis milling machine to validate the effectiveness of SV. In the experiment, piezoelectric stack actuators are used to modulate the stiffness with time-varying preload. The milling forces signals are acquired by data collecting instrument, whose root-mean-square (RMS) is used as the metric of cutting vibrations. Experiment results are in good agreement with theoretical prediction. [ABSTRACT FROM AUTHOR]

This paper describes the design of an interleaved sliding mode control for a multiphase synchronous buck converter, which inherits the properties of sliding mode control, operates with fixed switching frequency in the steady-state, and ensures current equalization among phases. Moreover, a power management algorithm is added in order to decide the number of active phases as function of the power load demand, thus optimizing the converter efficiency. The system uses a Master–Slave structure where each phase can actuate as the Master one in such a way that the overall system reliability is improved. Experimental results in a 1.5 kW eight-phase synchronous buck converter show that interleaving operation, robust output voltage regulation, phase current equalization, switching frequency regulation, and power management are achieved. [ABSTRACT FROM PUBLISHER]

Most cold rolling mills are prone to chatter problem. Chatter marks are often observed on the strip surface in cold rolling mill leading to downgrade and rejection of rolled material. Chatter impact product quality as well as productivity of mill. In absence of online chatter detection no corrective action can be taken immediately and whole campaign gets affected. Most conventional approach for online chatter detection is by using vibration measurement of mill stands in time & frequency domain. Present work proposes two approaches to detect chatter in cold rolling mill using a statistical technique called Principal Component Analysis (PCA). In this paper two methods are used for chatter detection. First method applies PCA on Fast Fourier Transform (FFT) to differentiate between chatter and non-chatter condition. Second method applies PCA on statistical parameters calculated from raw vibration data to detect chatter. [ABSTRACT FROM AUTHOR]

This paper introduces a new hybrid controller for position and force control of an electrohydraulic car active suspension. In most hybrid controllers, a switching function is normally used in order to take advantage of two separate controllers. Switching between the two controllers produces a chattering in the system, in addition to the chattering that may be inherent to the controller itself, which deteriorates the system performance. In this work, we resolved the switching limitations dilemma by transitioning from one controller to another through two low-pass filters. These filters are used with variable gains to improve the new hybrid position/force controller performance that we developed. The produced control signal is a structured combination, in which the signal coming from the position controller reduces the effect of road perturbations on passengers by bringing the car’s vertical motion to zero. Simultaneously, the signal from the force controller tracks a reference force and thus reduces the force transmitted to passengers. To eliminate the chattering that is inherent to the sliding mode controller, we introduced an exponential reaching law function to the hybrid sliding mode controller. This exponential function also reduced the response time, consequently speeding up the system reaction to suppress perturbations. In addition to that, a recent sliding surface-based controller is applied to vary the filters’ gains and obtain better performance. The frequency analysis is done to verify the controller performance. The proposed hybrid controller is also validated in real time on active suspension workbench and compared with a classical PID controller. [ABSTRACT FROM AUTHOR]

Variable pitch and variable helix (VPVH) milling tools are usually utilized to mitigate regenerative chatter vibrations by destroying the vibration phases between adjacent teeth. But this chatter suppression mechanism may considerably be disturbed by the inevitable tool runout, which could also change the phases, even to a larger extent. Thus the cutting performance of VPVH tools in terms of mechanics and dynamics should be re-evaluated by taking runout into consideration. This paper firstly sets up the mechanistic model for VPVH tools and then presents a combined nonlinear optimization procedure to identify the cutting coefficients and runout parameters. Secondly, the dynamic system of VPVH tools considering runout is modeled by a periodic-coefficient delay differential equation with multiple underdetermined delays. Afterwards, the generalized Runge-Kutta (GRK) method is extended to tackle the runout-induced multi-regenerative effects and thus to analyze the milling process stability. The accuracy and efficiency of the GRK method is validated using published numerical examples. A series of cutting experiments with a commercially available VPVH tool are performed to verify the presented mechanistic and dynamic models. It confirms that runout cannot be neglected when evaluating the cutting performance of VPVH tools. Finally, the joint influences of runout and pitch/helix angles on cutting forces and chatter stability of VPVH tools are discussed in detail based on the proposed approach. [ABSTRACT FROM AUTHOR]

Simultaneous turning with extra cutting edges increases the material removal rate (MRR), and thus the productivity of the process. On one hand, chatter could be a fatal threat to the productivity and part quality in simultaneous turning operations of slender and flexible workpieces. On the other hand, stability of flexible part turning can be increased significantly if the process parameters are selected properly. In practice, however, ensuring a stable parallel turning of a flexible workpiece is approached by the costly process of trial and error. In order to tackle this problem, a multi-dimensional model for chatter stability analysis of parallel turning operation is presented where the effects of components' dynamics, i.e. workpiece and cutters, in addition to insert's geometry are accounted for. The stability model is formulated for two configurations of the parallel turning operation in frequency and time domains, and verified experimentally. Chatter-free and high productivity cutting conditions are determined through optimal parameter selection employing stability maps generated for each configuration. [ABSTRACT FROM AUTHOR]

Synchronisation/cooperation between manipulators is a specified emerging application in the field of robotics. However, most of the synchronisation works are reported using rigid manipulators. Flexible manipulators have their advantages over rigid manipulators and hence, the applications of flexible manipulators are more desirable. This paper takes an attempt for the robust tip trajectory synchronisation between assumed modes method modelled two-link flexible manipulators. The synchronisation is achieved between a controlled master and an identical slave manipulators. A conventional SMC is designed for the tip trajectory tracking control of the master manipulator. A second order PID terminal SMC is proposed for the synchronisation between the controlled master and an identical slave manipulators along with fast suppression of tip deflection. This control technique provides chattering free global stability of the error dynamics. The structure of the proposed controller differs from the available second order terminal SMC by enabling chattering free complete stability having no singularity problem for the synchronisation of the flexible manipulators. This superiority of the proposed technique is validated using MATLAB simulation in the presence of variable payloads and ± 5 % to ± 30 % variation in the nominal value of the parameters. The effectiveness of the proposed control technique is compared with the normal second-order SMC, and is found better in terms of low tracking error and smoother control efforts. [ABSTRACT FROM AUTHOR]

Stabilization of a single rotary inverted pendulum (SRIP) system is a benchmark nonlinear control problem. Inherent instability of SRIP in upright position and the presence of modelling uncertainty pose a challenge for control engineers. Sliding-mode control (SMC) is the most widely accepted robust control technique. Various versions of SMCs to stabilize SRIP have been reported in literature. Advantages of SMC come at the cost of chattering of input, which inhibits its usage in many practical applications. Several works have been done to reduce the chattering in SMC. Application of fuzzy logic in SMC to reduce chattering has been analysed extensively in the literature. Even though implementation of fuzzy SMC (FSMC) in theory/simulations completely eliminates chattering, practical implementation of FSMC does not reduce chattering to zero. In this paper, a filtered FSMC is proposed, which filters the high frequency component in the system input. Experimental results of SMC, FSMC and a fuzzy sliding-mode controller with filter (FSMCF) are given in this paper. Results indicate that filtering the output of FSMCF reduces the chattering effect in the system without affecting the closed loop dynamics. [ABSTRACT FROM AUTHOR]

Taking into account the nonlinear feature of a PV array, a Maximum Power Point Tracking (MPPT) algorithm is required in a PV system leading the operation at the Maximum Power Point (MPP) and as a result maximizing the generated power. In this paper, a robust MPPT technique using second order sliding mode control strategy is presented. A super twisting algorithm is used to design second order sliding mode. This algorithm has been developed, in the case where the relative degree of system is equal to one, to eliminate chattering phenomenon. Second order sliding mode presents an adequate mean for control action of nonlinear systems since it overcomes chattering phenomenon of the classical first order sliding mode controller and ensures higher accuracy even with system imperfections. The stability analysis of the proposed controller is performed using a Lyapunov function. We compare second order sliding mode with classical first order sliding mode controller which are both designed for the same PV system. This comparison proves that the second order gives fast response and less chattering. The robustness and stability of the proposed controller are investigated against weather changes. Simulation results with real data, under MATLAB-SIMULINK, are given to demonstrate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

Environmental disturbances and systematical uncertainties are the main obstacles for ship motion control. This paper devotes to enhancing the control system robustness of underactuated surface ships with model uncertainties and environmental disturbances. A novel nonlinear robust adaptive scheme with sliding mode control is proposed for underactuated ships to track the desired path generated by the logical virtual ship in the presence of unknown plant parameters and environmental disturbances. Compared with the existing results, the proposed controller is designed based on the combination of PI sliding mode control and the upper bound estimation of disturbances. With the proposed design, the control scheme could not only obtain a better performance of the control system, the continuous scheme also reduce the chattering of system by a special construction of the sliding manifolds. Numerical simulations are given to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

To regain mobility, stroke patients need to receive repetitive and intensive therapy. Robot-assisted rehabilitation is an active area of research. Cheap robotic leg rehabilitation devices should be developed to meet the demands and assist most patients. A low cost hip-knee exoskeleton prototype powered by pneumatic muscles was developed. On this basis, Functional Electrical Stimulation (FES) induced paralyzed muscles to realize ankle joint rehabilitation training. These three ankle muscles: the tibialis anterior, the soleus, and the gastrocnemius under electrical stimulation cooperated together to realize optimally coordinated control of dorsiflexion and plantar-flexion movement. As both of pneumatic muscle and FES induced muscle possess highly nonlinear characteristics, a sliding control algorithm called Chattering mitigation Robust Variable Control (CRVC) was applied to leg hybrid rehabilitation. The combination of exoskeleton and FES is a promising way to reduce the cost and the complexity of designing hip-knee-ankle exoskeleton. The proposed hybrid method was verified by treadmill-based gait training experiments. [ABSTRACT FROM AUTHOR]

In this paper, a multiphase sliding mode (MPSM) control method with a master-slave structure is proposed and analyzed in order to suppress ripples at input terminals or output terminals in DC/DC converter applications. With the proposed MPSM, the switching frequency of a multiphase DC/DC converter does not need to be operating such a high switching frequency as adopted in a conventional sliding mode control-based DC/DC converter. As a result, switching power losses could be reduced in this converter. Another advantage of this proposed method is that the master-slave multiphase slide control loop could figure out a proper phase shift between each switching phase of a DC/DC converter instead of precalculated phase shift. The proposed concepts are proven by the PSIM computer simulations and the feasibility of the proposed concepts is validated through the test experiments. [ABSTRACT FROM AUTHOR]

This report presents a tool condition monitoring technique for deep-hole drilling that will ensure the quality of precision large-scale components. To avoid catastrophic tool failure, in-process identification of chatter is essential, as is identification of transient and spontaneous events that are highly non-Gaussian and nonlinear. Therefore, we propose a novel system that combines short-time Fourier transform and spectral kurtosis analysis in the time–frequency domain to determine relevant chatter and transient vibration information from an accelerometer signal. A dynamic model of a long drill was used to provisionally set a target frequency band (TFB) in which chatter is predominant, and then a verification experiment was performed on a drilling process involved in steam turbine rotor manufacturing. In the tests, chatter appeared abruptly near the TFB and rapidly caused tool failure, while transient events were less influential. This paper also presents an energy-based chatter criterion that can be applied throughout long-term manufacturing. The proposed method is not only highly capable of preventing tool failure by detecting the onset of chatter, but also provides comprehensive information about the tool’s state. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to induction motor (IM) speed controller design with indirect field-oriented control structure. The designed discrete-time variable structure (VS) speed controller uses elements of reduced-order and full-order (integral) sliding mode (SM) control, and acts as a nonlinear equivalent of conventional PI control. The controlled plant is approximated by a first-order dynamical model. Therefore, the proposed approach leads to an output feedback-based SM control (SMC) system. To improve its disturbances rejection and tracking capability, the controller is supplied with a first-order disturbance compensator based on the switching function measurement. The proposed VS control structure provides a high-performance chattering-free discrete-time SMC system. Numerous experiments have been carried out to test the proposed control method and to compare its performance with the conventional PI control approach. The experimental results demonstrate high tracking accuracy and robustness of the proposed system. [ABSTRACT FROM AUTHOR]

This paper focuses on the finite-time tracking control with external disturbance for active suspension systems. In order to compensate unknown disturbance efficiently, a disturbance compensator with finite-time convergence property is studied. By analyzing the discontinuous phenomenon of classical disturbance compensation techniques, this study presents a simple approach to construct a continuous compensator satisfying the finite-time disturbance rejection performance. According to the finite-time separation principle, the design procedures of the nominal controller for the suspension system without disturbance and the disturbance compensator can be implemented in a completely independent manner. Therefore, the overall control law for the closed-loop system is continuous, which offers some distinct advantages over the existing discontinuous ones. From the perspective of practical implementation, the continuous controller can avoid effectively the unexpected chattering in active suspension control. Comparative experimental results are presented and discussed to illustrate the advantage and effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

A passive vibration absorber, termed the nonlinear tuned vibration absorber (NLTVA), is designed for the suppression of chatter vibrations. Unlike most passive vibration absorbers proposed in the literature for suppressing machine tool vibrations, the NLTVA comprises both a linear and a nonlinear restoring force. Its linear characteristics are tuned in order to optimize the stability properties of the machining operation, while its nonlinear properties are chosen in order to control the bifurcation behavior of the system and guarantee robustness of stable operation. In this study, the NLTVA is applied to turning machining. [ABSTRACT FROM AUTHOR]

Chattering is a low amplitude and high-frequency undesired signal which typically appears in relay or switched systems as in variable structure controllers. The chattering phenomenon can be treated as a limit cycle and the describing function (DF) method results in an useful tool for predicting its existence allowing the computation of the amplitude and frequency of such oscillations. In this paper, a sliding mode control based on fuzzy logic is proposed as an alternative to reduce chattering where DF method is used to demonstrate its attenuation level at the output of the plant. Analytical results are complemented with numerical simulations made for a pneumatic linear actuator. [ABSTRACT FROM AUTHOR]

The unsteady lubrication is one of the major causes for self-excited vibration in rolling. But it is difficult to build a rolling chatter model which considers the unsteady lubrication state in roll bite. Using the regression exponential function model of rolling friction coefficient, a dynamic rolling process model was built. Coupling the dynamic rolling process model with a mill stand structure model, a chatter model which considers the unsteady lubrication state at roll bite was established. Based on the proposed chatter model, the friction coefficient, rolling force and critical velocity of a rolling mill stand under different working conditions were calculated. The computed results were compared to the test results. And it proves the validity of the proposed model. With the proposed chatter model, the effects of rolling process parameters and emulsion lubricant characteristic parameters on friction coefficient and critical velocity were both analyzed and discussed. The chatter model successfully introduces the unsteady friction model into the rolling mill chatter model. It better explains the negative damping effect of the rolling chatter and reflects the rolling mill dynamic vibration characteristic. [ABSTRACT FROM AUTHOR]

Receptance Coupling Substructure Analysis (RCSA), an effective approach to rapidly predict the tool point frequency response function (FRF), generally requires the response of spindle-machine assembly by experiments. This method is feasible for three-axis machine tool because the spindle and its posture are normally unchangeable. But in terms of five-axis milling, the spindle-machine assembly changes continuously. The purpose of this study is to propose new techniques to solve the constantly-changing assembly response in order that RCSA can be used for bi-rotary head five-axis machine tools. Based on receptance matrix determination in coupling direction and single degree of freedom coupling simplification, the swivel model for holder tip receptances is established for swivel motion. According to the concept of oriented frequency response function, the rotational model is derived to calculate the holder tip receptances with rotary motion. By combining the swivel model and the rotational model, the holder tip receptance of arbitrary posture can be calculated by three orthogonal postures. A five-axis machine tool with bi-rotary head is used to conduct FRF tests on different postures. Experimental results show that the models proposed can accurately predict tool point frequency response of any posture and large difference in FRFs among those postures of bi-rotary head is detected. [ABSTRACT FROM AUTHOR]

This paper addresses non-linear sliding mode controller (SMC) with matched and unmatched uncertainties for load frequency control (LFC) application in three-area interconnected power system. In conventional LFC scheme, as the nominal operating point varies due to system uncertainties, frequency deviations cannot be minimized. These lead to degradation in the dynamic performance or even system instability. In this paper, an effective control law is proposed against matched and unmatched uncertainties.. The proposed controller has ability to vary closed-loop system damping characteristics according to uncertainties and load disturbances present in the system. The frequency deviation converges to zero with minimum undershoot/overshoot, fast settling time, significantly reduced chattering and ensures asymptotic stability. In addition, the controller is robust in the presence of parameter uncertainties and different disturbance patterns. It also guarantees high dynamic performance in the presence of governor dead band (GDB) and generation rate constraint (GRC). Simulations are performed to compare the proposed controller with linear SMC. Using proposed control strategy, undershoot/overshoot and settling time gets reduced by approximately 30% with respect to linear SMC. The computed performance indices and qualitative results establish the superiority as well as applicability of the proposed design for the LFC problem. Further, the proposed controller scheme is validated on IEEE 39 bus large power system. [ABSTRACT FROM AUTHOR]

Chatter happens due to the low rigidity of the machining system, and chatter identification is essential for improving the surface quality and productivity. More understanding on the dynamic characteristics of the machining system would help identify chatter more efficiently. This paper proposes a method for detecting chatter in the milling process of the thin-walled workpiece by monitoring and analyzing the cutting torque. A varying chatter detection threshold based on the workpiece geometries, tool path, and dynamic characteristics is utilized to identify chatter. A high-frequency filter and a median filter are utilized for signal denoising. The method is experimentally validated, which proved that it could predict chatter efficiently at its early infancy. The method could be a supplementary to other chatter identification methods. [ABSTRACT FROM AUTHOR]

Chatter is considered as one of the most important causes of instability in the precision grinding process. Suffering from the influence of nonlinearity and changed machining condition, regenerative chatter signal is nonlinear and non-stationary in nature, which makes the linear representations and stationary assumed methods not appropriate. Wavelet bicoherence is considered as an effective method for these nonlinear signals analysis. However, current wavelet bicoherence is often estimated by integrating over the finite time interval. This procedure may result to the loss of the time information; hence, it is not appropriate for chatter signal that cannot be assumed to be stationary. In this paper, an instantaneous nonlinearity indicator-based method is proposed for regenerative chatter identification in grinding by using the servomotor current signal. Firstly, the nonlinearity of servomotor current affected by regenerative chatter is discussed. After that, a non-stationary wavelet bicoherence is proposed for the quadratic nonlinear coupling detection of these nonlinear and non-stationary signals. On this basis, an instantaneous nonlinearity indicator is further established for regenerative chatter identification. The effectiveness of the proposed method is verified by simulations and experiments, and the results show that, compared with the commonly used wavelet bicoherence and continuous wavelet transform, this method can not only describe the non-stationary chatter signal in time-frequency domain but also extract the true nonlinear coupling component resulted from regenerative chatter. [ABSTRACT FROM AUTHOR]