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In this study, a double-loop tracking control strategy is investigated to realize trajectory tracking control for a wheeled mobile robot (WMR) with unmodeled dynamics. More specifically, two nonlinear ESOs are designed to estimate disturbances from external disturbances and unmodeled dynamics. Combining with integral sliding mode control and backstepping control, a double-loop tracking controller is designed to enhance tracking accuracy for the WMR along the right angle roads. Based on Lyapunov methods, convergence analysis is given for both the nonlinear ESOs and the double-loop tracking controller. Validity of the double-loop tracking control strategy is demonstrated by experimental results on the WMR along a right angle road. • A double-loop tracking controller is proposed to improve tracking precision on trajectory tracking of the right angle roads for the WMR. • Sufficient conditions of adjustable parameters are given for nonlinear ESOs to estimate internal disturbances from unmodeled dynamics. • A sliding control law with nonlinear functions instead of sign functions is designed to weaken the chattering of sliding mode control system. [ABSTRACT FROM AUTHOR]

Abstract In this study, different controllers for control of fractional-order coronary artery system in the presence of external disturbance are designed. Using sliding mode, the proposed type 1 and type 2 fuzzy methods, the suitable controllers are proposed. In sliding mode control, a fractional sliding surface is presented and the control signal is modified to prevent chattering in the control system. With mathematical analysis, a type of membership function is suggested which has better performance in the fractional order system. Also, a rule-base is presented which leads to better results in type 1 and type 2 fuzzy controllers. The risk of the proposed controllers in different conditions is analyzed. Finally, according to the other analyzing methods, it is shown that this analyzing method has more accurate results. Highlights • The proposed sliding mode controller with fractional sliding surface, improves the performance of controller. • One of the inputs in the proposed fuzzy controllers is the fractional variation of error which is exactly derived from the system differential equation. • All of the designed controllers are robust in presence of external disturbances. • According to the relation between the beta function and definition of fractional order differential equation, we use the beta-shaped membership function in the fuzzy controllers. • The risk analysis of the proposed controllers as a new tool for the performance comparison of the proposed controllers in presence of external disturbance is introduced. [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]

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]

An adaptive-gain super-twisting sliding mode observer is proposed for fault reconstruction in electro-hydraulic servo systems (EHSS) receiving bounded perturbations with unknown bounds. The objective is to address challenging problems in classic sliding mode observers: chattering effect, conservatism of observer gains, strong condition on the distribution of faults and uncertainties. In this paper, the proposed super-twisting sliding mode observer relaxes the condition on the distribution of uncertainties and faults, and the gain adaptation law leads to eliminate observer gain overestimation and attenuate chattering effects. After using the equivalent output-error-injection feature of sliding mode techniques, a fault reconstruction strategy is proposed. The experimental results are presented, confirming the effectiveness of the proposed adaptive super-twisting observer for precise fault reconstruction in electro-hydraulic servo systems. [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]

Chattering alarms are the most found nuisance alarms that will probably reduce the usability and result in a confidence crisis of alarm systems for industrial plants. This paper addresses the chattering alarm reduction using median filters. Two rules are formulated to design the window size of median filters. If the alarm probability is estimated using process data, one rule is based on the probability of alarms to satisfy some requirements on the false alarm rate, or missed alarm rate. If there are only historical alarm data available, the other rule is based on percentage reduction of chattering alarms using alarm duration distribution. Experimental results for industrial cases testify that the proposed method is effective. [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 proposes a new compound fractional order integral terminal sliding mode control (FOITSMC) and proportional-derivative control (PD-FOITSMC) for the control of a MEMS gyroscope. In order to improve the robustness of the conventional integral terminal sliding mode control (ITSMC), a fractional integral terminal sliding mode surface is applied. The chattering problem in FOITSMC, which is usually generated by the excitation of fast un-modelled dynamic is the main drawback. A PD controller is employed in order to eliminate chattering phenomenon. The stability of the PD-FOITSMC is proved by Lyapunov theory. The performance of the proposed control method is compared with two other controllers such as ITSMC and FOITSMC. Numerical simulations clearly verified the effectiveness of the proposed control approach. [ABSTRACT FROM AUTHOR]

This paper studies the leader-follower formation control of underactuated surface vehicles with model uncertainties and environmental disturbances. A parameter estimation and upper bound estimation based sliding mode control scheme is proposed to solve the problem of the unknown plant parameters and environmental disturbances. For each of these leader-follower formation systems, the dynamic equations of position and attitude are analyzed using coordinate transformation with the aid of the backstepping technique. All the variables are guaranteed to be uniformly ultimately bounded stable in the closed-loop system, which is proven by the distribution design Lyapunov function synthesis. The main advantages of this approach are that: first, parameter estimation based sliding mode control can enhance the robustness of the closed-loop system in presence of model uncertainties and environmental disturbances; second, a continuous function is developed to replace the signum function in the design of sliding mode scheme, which devotes to reduce the chattering of the control system. Finally, numerical simulations are given to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this work, an adaptive backstepping sliding mode control approach is applied through the piezoelectric layer in order to control and to stabilize an electrostatic micro-plate. The mathematical model of the system by taking into account the small fluctuations in the gap considered as bounded noise is carried out. The accuracy of the proposed modal equation is proven using the method of lines. By using both approaches, the effects of noise are presented. It is found that they lead to pull-in instability as well as to random chaos. A suitable backstepping approach to improve the tracking performance is integrated to the adaptive sliding mode control in order to eliminate chattering phenomena and reinforce the robustness of the system in presence of uncertainties and external random disturbances. It is proved that all the variables of the closed-loop system are bounded and the system can follow the given reference signals as close as possible. Numerical simulations are provided to show the effectiveness of proposed 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]

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]

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]

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]

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]

Five-axis CNC machine tools are widely used in the manufacturing of the complex parts, and the contour error is the key indicator for the accuracy of the final product. Contour error, by definition, is a geometrical quantity solely dependent on the current actual tool pose and the reference trajectory. Contouring control is the main method to reduce or eliminate it. In this paper, based on the geometrical information of the reference trajectory, a high accuracy contour error estimation method for five-axis machine tools is proposed. Then, to avoid the time-consuming calculation of the inverse and derivative of the Jacobian matrix, to reduce tracking and contour errors simultaneously as well as suppress the chattering in the control signal, a dual sliding mode contouring control method is proposed. The dual sliding surface is selected for each drive separately, which integrates the traditional PD-type tracking sliding surface, a PD-type contouring sliding surface consisting of the axis component of the contour errors, and the input signal together. Experiments are conducted on a tilting-rotary-table type five-axis CNC machine tool. The results demonstrate that the contour errors estimated using the proposed method are very close to the true ones, and compared with the traditional sliding mode controller, the proposed method can reduce the contour error and the chattering behavior effectively. [ABSTRACT FROM AUTHOR]

In this paper, we propose two emulator circuits. Firstly, we present a novel memristor emulator based on operational transconductance amplifier (OTA) which is different from classical TiO 2 memristor. This memristor emulator has a threshold switching mechanism. Secondly, we create a novel neuron circuit using proposed memristor, which is capable of generating spiking and bursting firing behaviors, with a biologically plausible spike shapes. The behavior of this neuron circuit can be adjusted by changing only one external biasing voltage. This neuron circuit mimics the behavior of cortical neurons, such as regular spiking (RS), intrinsic bursting (IB), chattering (CH) and fast spiking (FS). Proposed emulator circuits are compatible with VLSI systems and they can also be implemented by using discrete circuit components for different applications. [ABSTRACT FROM AUTHOR]

To avoid the chattering problem in the reaching-law-based discrete-time sliding mode control (DSMC) and the generation of over-large control action in the equivalent-control-based DSMC, a new DSMC method based on non-smooth control is proposed in this paper. Since there is no use of any switching term in the proposed DSMC, it is a chattering-free SMC method. Meanwhile, it is shown that the newly proposed non-smooth control-based DSMC can guarantee the same level of accuracy for the sliding mode motion as that of an equivalent control-based DSMC. To demonstrate the effectiveness of the proposed approach, a simulation example is presented. [ABSTRACT FROM AUTHOR]

The motion of a windshield wiper blade is modelled by a mass-spring-damper system on a moving frictional surface. The system dynamics is time-varying, since three different regimes of motion, characterized by different degrees of freedom, are possible. Indeed the system, which schematizes a blade cross-section, can experience stick and slip motions when it is in contact with the glass surface, and free-flight motion when it is detached. The contact between the system and the surface is governed by Stribeck׳s friction law and Poisson׳s impact law, which make the dynamics non-smooth. The model is numerically implemented in an event-driven code, and simulations are performed which reproduce the three basic classes of undesired oscillations observed in the motion of real windscreen wipers, i.e., squeal, reversal and chattering noises. Attention is focused on the causes of these vibrations, and remedies for reducing or avoiding them are proposed. [ABSTRACT FROM AUTHOR]

This paper proposes a new robust adaptive controller for LCL filter based shunt active power filters in order to solve the control problems of high overshoot and large settling time in the DC link voltage. To this end, the second order sliding mode with the adaptive gain super-twisting control law and proportional-resonant controllers with active damping are used in the DC bus voltage control loop and d – q axis current control loops respectively. The control objectives are fourfold: (i) driving the DC bus voltage to a reference signal; (ii) forcing the d – q axis current errors to zero; (iii) assuring a satisfactory power factor correction and a high harmonic performance in relation to the AC source; and (iv) eliminating the chattering effect. In the closed loop control system, three phase grid currents, LCL capacitor currents and the DC link voltage are available for feedback. As a result, the proposed controller has the advantages of zero overshoot response and fast acting chattering-free behavior. Results of experimental studies prove that the proposed control system guarantees to track reference signals with a high harmonic performance despite external disturbance uncertainties. [ABSTRACT FROM AUTHOR]

In this study, a MEMS acceleration switch using mechanical hooked latch is designed, fabricated, and measured. A mechanical latching mechanism and switching characteristic are analyzed using FEM simulation. The acceleration switch with a size of 1.8 × 3.2 × 0.55 mm 3 was fabricated using a Silicon-on-Glass (SiOG) process. A resonance frequency of the fabricated switch and an acceleration threshold are measured to be 1.022 kHz and 43.7 g, respectively. The fabricated switch is latched when an applied external acceleration is higher than the threshold value of 43.7 g. After latching “on”, the “on” state of the switch is reliably sustained regardless of the applied external acceleration. [ABSTRACT FROM AUTHOR]

In this paper, we present an implementation of the sliding mode twisting controller on an electropneumatic plant for a tracking control problem. To this end, implicitly and explicitly discretized twisting controllers are considered. We discuss their structure, properties and implementations, as well as the experimental results. The analysis of the performance sustains the theoretical superiority of the implicitly discretized version, as shown in previous works. The main advantages of the implicit method are better tracking performance and drastic reduction in the input and output chattering. This is achieved without modifying the structure of the controller compared to its continuous-time version. The tracking error cannot be used as the sliding variable: it has a relative degree 3 w.r.t. the control input. The tuning of the sliding surface has well as some other parameters in the control loop was instrumental in achieving good performance. We detail the selection procedure of those parameters and their influence on the closed-loop behavior. Finally we also present some results with an implicitly discretized EBC-SMC controller. [ABSTRACT FROM AUTHOR]

Chatter bots are software programs that engage in artificial conversations through a text-based input medium. They are extensively deployed in customer service applications. Existing approaches to artificial conversation generation emphasize grammatical and linguistic modeling techniques. They focus on generation of discrete sentence-level utterances. These approaches perform poorly in conversational situations requiring contextual continuity over a series of utterances. We present an approach that combines pragmatics with content semantics to generate artificial conversations in the customer service domain. A conversation is a process that adheres to well-defined semantic conventions and is contextually grounded in domain-specific knowledge. We model this using stochastic finite state machines, where the parameters of the model are learned from a corpus of human conversations. We present a specific set of criteria which we then use to evaluate the quality of artificial conversations in the customer service domain. We also compare chatter bot generated artificial conversations with human generated natural conversations in this domain. [ABSTRACT FROM AUTHOR]

This paper describes a method to produce analytical radial depth of cut stability lobe diagrams that include process damping. The stability limit was defined using the radial, rather than axial, depth due to the path planning approach for many computer-aided manufacturing (CAM) programs, which remove material layer-by-layer with a varying radial immersion. Experimental validation of the predicted stability limits was performed and the results are presented for both the process damping (low cutting speed) range and higher cutting speeds. [ABSTRACT FROM AUTHOR]

Chatter is one of the most limiting factors in improving machining performances. Stability Lobe Diagram (SLD) is the most used tool to select optimal stable cutting parameters in order to avoid chatter occurrence. Its prediction is affected by reliability of input data such as machine tool dynamics or cutting coefficients that are difficult to be evaluated accurately, especially at high speed. This paper presents a novel approach to experimentally evaluate SLD without requiring specific knowledge of the process; this approach is called here Spindle Speed Ramp-up (SSR) test. During this test spindle speed is ramped up, and chatter occurrence is detected by the Order Analysis technique. As result one single test ensures optimal spindle speed identification at one cutting condition, while if few tests are performed the entire SLD could be obtained. Results of the method applied to slotting operation on aluminum are provided and a comparison between different measurements devices is presented. This quick, easy-to-use and efficient test is suitable for industrial application: no knowledge of the process is required, different sensors can be used such as accelerometer, dynamometer or microphone. [ABSTRACT FROM AUTHOR]

In this paper, a tunable vibration absorber (TVA) is designed to suppress regenerative chatter in milling of cantilever plates. In machining industry, the majority of work-piece materials or the interaction of work-piece/cutting tool causes the cutting forces to demonstrate nonlinear behavior. The application of TVA (as a semi-active controller) is investigated for the process with an extensive nonlinear model of cutting forces. Under regenerative chatter conditions, optimum values of the absorber position and its spring stiffness are found such that the plate vibration is minimized. For this purpose, an optimal algorithm is developed based on mode summation approach. Results are presented and compared for two cases: regenerative chatter under resonance and non-resonance conditions. It is shown that the absorber acts efficiently in chatter suppression of both machining conditions, in a wide range of chatter frequencies. Moreover, using TVA leads to the great improvement in stability limits of the process. Therefore, larger values of depth of cut and consequently more material removal rate can be obtained without moving to the unstable machining conditions. [ABSTRACT FROM AUTHOR]

In this paper an optimal second order sliding mode controller (OSOSMC) is proposed to track a linear uncertain system. The optimal controller based on the linear quadratic regulator method is designed for the nominal system. An integral sliding mode controller is combined with the optimal controller to ensure robustness of the linear system which is affected by parametric uncertainties and external disturbances. To achieve finite time convergence of the sliding mode, a nonsingular terminal sliding surface is added with the integral sliding surface giving rise to a second order sliding mode controller. The main advantage of the proposed OSOSMC is that the control input is substantially reduced and it becomes chattering free. Simulation results confirm superiority of the proposed OSOSMC over some existing. [ABSTRACT FROM AUTHOR]

Highlights: [•] Two new rules are formulated to detect chattering and repeating alarms. [•] Alarm durations and intervals are exploited in the detection of chattering and repeating alarms. [•] An online method is proposed to detect the chattering and repeating alarms and to reduce the number of these nuisance alarms. [•] The m-sample delay timer is used to reduce the number of chattering and repeating alarms. [•] Industrial examples are provided to support the formulated rules and to illustrate the effectiveness of the proposed method. [Copyright &y& Elsevier]

Abstract: The suppression of chatter vibration is required to enhance the machined surface quality and to increase tool life. In this study, a new, conceptually active approach for chatter suppression in machining is proposed. The hybrid control method developed by applying sensorless force control with a disturbance observer enables the simultaneous and independent control of the position trajectory and band-limited forces. The proposed method is introduced to the carriage of a prototype desktop-sized turning machine, and the ability to suppress chatter is evaluated by end-face cutting tests. The results demonstrate that actively controlling a band-limited force leads to the avoidance of chatter. [Copyright &y& Elsevier]

Abstract: In conventional sliding-mode control systems, the sliding-mode motion is of reduced order. Two main problems hindering the application of the sliding-mode control are the singularity in terminal sliding-mode control systems and the chattering in both the conventional linear sliding-mode and the terminal sliding-mode control systems. This paper proposes a chattering-free full-order terminal-sliding-mode control scheme. Since the derivatives of terms with fractional powers do not appear in the control law, the control singularities are avoided. A continuous control strategy is developed to achieve the chattering free sliding-mode control. During the ideal sliding-mode motion, the systems behave as a desirable full-order dynamics rather than a desirable reduced-order dynamics. A systematic design method of full-order sliding-mode control for nonlinear systems is presented, which allows both the chattering and singularity problems to be resolved. Simulations validate the proposed chattering free full-order sliding-mode control. [Copyright &y& Elsevier]

Abstract: In the paper chatter detection in band sawing is considered as a signal processing and classification problem. A multi-sensory experimental setup was established on an industrial band saw including sound, acceleration and cutting force, and measurements. Based on an experimental analysis sound signal is shown to be the most appropriate for chatter detection, therefore a sound-based online chatter detection method is proposed. The method consists of a sound signal pre-processing with Short-Time Fourier Transform, extraction of features in frequency space with optimal threshold and application of Quadratic Discriminant Analysis for chatter detection. The proposed method tested with twofold cross validation yields over 96% success of chatter detection. [Copyright &y& Elsevier]

Abstract: The terminal guidance problem for missiles intercepting maneuvering targets with terminal impact angle constraints is investigated. Regarding the target acceleration as an unknown bounded disturbance, novel guidance laws based on integral sliding mode control (ISMC) method technique are developed. The first one is a linear integral sliding mode (ISM) guidance law, which can guarantee the line-of-sight (LOS) angular rate and the LOS angle asymptotical convergence with infinite time. To further improve the convergence characteristics of guidance system, a nonlinear ISM guidance law is developed, which guarantees the LOS angular rate and LOS angle finite-time convergence characteristics. However, to guarantee the guidance system has a good performance for dealing with target acceleration, the switch gains of both linear and nonlinear ISM guidance laws need to be chosen larger than the bound of the target acceleration. It will lead to chattering problem. To reduce the chattering phenomenon and improve the performance of system, nonlinear disturbance observer (NDOB) is employed to estimate the target acceleration. The estimated acceleration is used to compensate to actual target acceleration. Then, two novel composite guidance laws combining linear and nonlinear ISM guidance laws with feedforward compensation terms based on NDOB are developed. Finally, simulation comparison results are provided to demonstrate the effectiveness of the proposed methods. [Copyright &y& Elsevier]

Highlights: [•] A fuzzy based Variable Structure Control with guaranteed stability is presented. [•] New functions for chattering reduction and error convergence without sacrificing invariant properties are proposed. [•] Global stability of the controlled system is guaranteed. [•] The weighting parameters approach is used to optimize local and global modelling capability of T-S fuzzy model. [ABSTRACT FROM AUTHOR]

This paper proposes an innovative integrated path planning and trajectory tracking control framework for a quadrotor unmanned aerial vehicle (UAV) in the presence of environmental and systematic uncertainties to achieve integrated guidance and control. Firstly, in order to perform real-time path planning, a computationally cost-effective planning algorithm is designed to find an optimal and smooth path while avoiding both static and dynamic obstacles. Then, by employing the pure-pursuit path following approach, the generated geometric path is converted to a trajectory profile related to time, which serves as the reference commands for the low-level trajectory tracking controller. Finally, a novel adaptive sliding mode trajectory tracking controller is proposed to compensate model uncertainties and maintain the desired tracking performance for the studied quadrotor UAV. With the proposed adaptive schemes, overestimation of uncertain parameters can be avoided, which further contributes to avoiding control chattering of the system. The performance of the proposed framework is validated through comparative simulation and experimental tests based on a quadrotor UAV subject to model uncertainties and environmental obstacles, which confirms the effectiveness and superiority of the proposed approach for practical applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] An online method is proposed to detect the chattering alarms due to oscillation and to reduce the amount of chattering alarms. [•] A revised chattering index is proposed to quantify the level of chattering alarms. [•] The discrete cosine transform-based method is used to detect the presence of oscillation. [•] The adjustment of alarm trippoint and a delay timer are exploited to reduce the amount of chattering alarms. [•] An industrial case study is provided to illustrate the effectiveness of the proposed method. [Copyright &y& Elsevier]

Abstract: A nonlinear robust control strategy is developed for Six-Degree-of-Freedom (6DOF) Reusable Launch Vehicles (RLV) which is nonlinear, multivariable, strong coupling, and includes uncertain parameters and external disturbances. Firstly, a reentry guidance law is designed to generate feasible guidance commands which are then tracked by second-order sliding mode attitude controller designed based on quasi-continuous high-order sliding mode theory. Furthermore, in order to reduce control chattering, the virtual control is introduced into the design of third-order sliding mode attitude controller which achieves higher tracking accuracy and less control chattering. Finally, 6DOF integrated guidance and control simulation results for X-33 vehicle are presented to demonstrate the effectiveness of the proposed control strategy in tracking the guidance commands as well as achieving safe and stable reentry flight. [Copyright &y& Elsevier]

Highlights: [•] Using extended model of milling with nonlinear cutting forces & chatter. [•] Development of optimal control for nonlinear delay differential equations. [•] Optimal control strategy for regenerative chatter suppression. [•] Robust performance of the optimal controller against parametric uncertainties. [Copyright &y& Elsevier]