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In this paper, a novel adaptive dynamic sliding mode control(ADSMC) methodology is developed for space manipulator control systems with external disturbance. The proposed ADSMC approach can make the systems stable and accurately track the desired signals in the presence of external disturbances. Firstly, the simplified dynamic model of the manipulator is introduced. Then, the proposed adaptive dynamic sliding mode(ADSM) controller is given, which is proved to be able to guarantee high tracking accuracy via effectively estimating the disturbance boundary. Finally, experimental results show that the dynamic sliding mode controller proposed in this paper can not only track the desired trajectory, but also present strong robustness for external disturbance, meanwhile effectively reduce the chattering phenomenon generated by switching between different sliding mode surfaces. [ABSTRACT FROM AUTHOR]

The general least squares model for milling process state term is presented. A discrete map for milling stability analysis that is based on the third-order case of the presented general least squares milling state term model is first studied and compared with its third-order counterpart that is based on the interpolation theory. Both numerical rate of convergence and chatter stability results of the two maps are compared using the single degree of freedom (1DOF) milling model. The numerical rate of convergence of the presented third-order model is also studied using the two degree of freedom (2DOF) milling process model. Comparison gave that stability results from the two maps agree closely but the presented map demonstrated reduction in number of needed calculations leading to about 30% savings in computational time (CT). It is seen in earlier works that accuracy of milling stability analysis using the full-discretization method rises from first-order theory to second-order theory and continues to rise to the third-order theory. The present work confirms this trend. In conclusion, the method presented in this work will enable fast and accurate computation of stability diagrams for use by machinists. [ABSTRACT FROM PUBLISHER]

This paper proposes, for a class of uncertain nonlinear systems, an adaptive controller based on adaptive second-order sliding mode control and integral sliding mode control concepts. The adaptation strategy solves the problem of gain tuning and has the advantage of chattering reduction. Moreover, limited information about perturbation and uncertainties has to be known. The control is composed of two parts: an adaptive one whose objective is to reject the perturbation and system uncertainties, whereas the second one is chosen such as the nominal part of the system is stabilised in zero. To illustrate the effectiveness of the proposed approach, an application on an academic example is shown with simulation results. [ABSTRACT FROM AUTHOR]

This paper endows the second-order sliding mode control (2-SMC) approach with additional capabilities of learning and control adaptation. We present a 2-SMC scheme that estimates and compensates for the uncertainties affecting the system dynamics. It also adjusts the discontinuous control effort online, so that it can be reduced to arbitrarily small values. The proposed scheme is particularly useful when the available information regarding the uncertainties is conservative, and the classical `fixed-gain’ SMC would inevitably lead to largely oversized discontinuous control effort. Benefits from the viewpoint of chattering reduction are obtained, as confirmed by computer simulations. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive wavelet network sliding mode control (AWNSMC) scheme to track the maximum power point tracking in photovoltaic (PV) pumping systems. For the best use, the PV-generator must operate at its maximum power point. The proposed approach combines the advantages of the wavelet network (WN) and those of sliding mode control (SMC) to adjust the duty cycle control law in order to satisfy reaching conditions without producing chattering phenomenon. Indeed, due to its ability to approximate non-linear function and its fast convergence, a WN system is used to approximate the system uncertainties that are incorporated in the equivalent control component; as a result, it enables a lower switching gain to be used in the robust SMC term. The effectiveness of the designed AWNSMC is illustrated in simulations by a comparison with both standard SMC and neural network SMC techniques. [ABSTRACT FROM PUBLISHER]

The paper focuses on the stability of chatter vibrations and tool wear prediction. Chatter-free (stable) cutting parameters are obtained analytically for a sharp and a worn tool considerations and stability lobes of an orthogonal turning operation are constructed using simulations. The effects of the tool wear on chatter vibrations have been studied widely, but the study of the effects of chatter vibration on tool life is very limited. Tool wear tests are mainly conducted under stable cutting conditions, which really cannot explain the wear behaviour under vibratory cutting conditions. An attempt is made to predict the wear and life of a turning tool under chatter vibrations. A tool wear equation is derived which investigates the effects of self-excited chatter vibrations on tool wear in order to predict the tool life. This new tool wear equation clearly indicates that the tool wear increases very rapidly in the presence of chatter. The proposed analytical model and the tool wear equation have been validated with the orthogonal turning experimental results. [ABSTRACT FROM AUTHOR]

It has been a widely accepted notion that approximation of discontinuous control by certain continuous function in a boundary layer results in chattering elimination in sliding mode control systems. It is shown through three different types of analysis that in the presence of parasitic dynamics, this approach to chattering elimination would work only if the slope of the continuous nonlinear function within the boundary layer is low enough, which may result in the deterioration of performance of the system. A few examples are provided. An approach to robust stability of linear systems from the consideration of the saturating control is proposed. [ABSTRACT FROM AUTHOR]

The productivity of many industrial cutting processes is limited by high amplitude chatter vibrations. An optimization technique based on the use of the stability lobes helps to increase the productivity of these processes, improving the life of machine elements and reducing the tool wear as well. The best-known lobes correspond to Hopf bifurcations. However, in case of interrupted cutting, additional lobes appear due to period doubling or flip bifurcation. When the system has more than one dominant vibration mode, important variations can appear in stability due to interaction between modes. The basic mathematics for the appearance of these new lobes are shown in this article. The frequency domain study shows that lobes related to flip bifurcation are a special case of the interaction between modes. The results of these interactions are verified by comparison with semi-discretization method and time domain simulations, respectively. [ABSTRACT FROM PUBLISHER]

Motorcycle racing teams occasionally experience speed-limiting vibrations of around 25 Hz frequency in mid-corner. The nature of the vibrations has not been closely defined yet and the mechanics are currently not properly understood. Conventional motorcycle-dynamics models are shown here to reveal the existence of a vibration mode that aligns with the experience being referred to, suggesting some explanations. Root loci for variations in speed or cornering vigour, demonstrating modal characteristics for small perturbations from trim states, are employed to indicate how the mode responds to changes in operation and design. Modal participation is examined for a lightly damped case. Influences on the natural frequency and damping of the mode are found and a way of stabilising the mode is suggested. [ABSTRACT FROM AUTHOR]

This study addresses the design and properties of serial sliding mode control (SMC) systems for an induction servo motor drive to track periodic commands. It contains a SMC, an adaptive SMC (ASMC) and an estimator-based SMC (ESMC). The effectiveness of the proposed control systems is verified by numerical simulations, and the superiority of the ESMC system is indicated in comparison with the SMC and ASMC systems. [ABSTRACT FROM AUTHOR]

In this paper, the trajectory tracking control problem of under-actuated autonomous surface vessels is investigated. Both the parameter uncertainties and environmental disturbances are considered in system dynamics. By combining a trajectory planning method and the non-singular terminal sliding mode control technique, two global finite-time stabilising controllers for position tracking, ie. the surge controller and the lateral motion controller, are proposed. In order to reduce the chattering, the boundary layer method with a novel saturation function is employed to derive two modified continuous controllers. Simulations demonstrate the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Spindle speed variation is a well known technique to suppress regenerative machine tool vibrations, but it is usually considered to be effective only for low spindle speeds. In the current paper, spindle speed variation is applied to the high speed milling process, at the spindle speeds where the constant speed cutting results in period doubling chatter. The stability analysis of triangular and sinusoidal shape variations is made numerically with the semi-discretization method. It is shown that the milling process can be stabilized by increasing the amplitude of the spindle speed variation, while the frequency of the variation has no significant effect on the dynamic behaviour. The results are validated by experiments. Based on the analysis of the machined workpieces, it is shown that the surface roughness can also be decreased by the spindle speed variation technique. [ABSTRACT FROM AUTHOR]

A tool for the design of a periodic motion in an underactuated mechanical system via generating a self-excited oscillation of a desired amplitude and frequency by means of the variable structure control is proposed. First, an approximate approach based on the describing function method is given, which requires that the mechanical plant should be a linear low-pass filter-the hypothesis that usually holds when the oscillations are relatively fast. The method based on the locus of a perturbed relay systems provides an exact model of the oscillations when the plant is linear. Finally, the Poincare map's design provides the value of the controller parameters ensuring the locally orbitally stable periodic motions for an arbitrary mechanical plant. The proposed approach is shown by the controller design and experiments on the Furuta pendulum. [ABSTRACT FROM AUTHOR]

A variable structure controller (VSC) with chattering reduction feature applied to interconnected load frequency control (LFC) problem is presented. Formulating the design of VSC as an optimization problem and utilizing tabu search (TS) algorithm provides a simple and systematic way of arriving at the optimal feedback gains and switching vector values of the controller. In addition, this will cut down the need for nonlinear or coordinate transformation as reported before. The tested interconnected LFC model incorporates nonlinearities in terms of generation rate constraint (GRC) and a limiter on the integral control value. In order to guarantee the enhancement of the system, dynamical performance and chattering reduction of the VSC, different objective functions were investigated in the optimization process. In addition, the complexity of the controller is reduced by using only the accessible states in designing the VSC. Comparison with previous LFC methods reported in literature validates the significance of the proposed VSC design. [ABSTRACT FROM AUTHOR]

The principal features of two mathematical models that can be used to study non-linear oscillations of a work piece -- tool system during a milling operation are presented and explained in this article. These models are non-linear, non-homogeneous, delay-differential systems with time-periodic coefficients. In the treatment presented here, the sources of non-linearities are the multiple regenerative effect and the loss-of-contact effect. The time-delay effect is taken into account, and the dependence of this delay effect on the feed rate is modelled. A variable time delay is introduced lo capture the influence of the feed-rate in one of the models. Two formulations that can be used to carry out stability analysis of periodic solutions are presented. The models presented and the stability-analysis formulations are relevant for predicting and understanding chatter in milling. [ABSTRACT FROM AUTHOR]

Switched position control algorithms are developed to globally stabilize friction mechanical manipulators around a desired position. Both static and dynamic position feedback designs are presented. The controllers constructed, referred to as chattering controllers, do not rely on the generation of sliding motions while providing robustness features similar to those possessed by their sliding mode counterparts. Stability analysis is given within the Lyapunov vector functions framework extended to discontinuous dynamic systems. Performance issues of the chattering controllers are evaluated in an experimental study of a three degrees-of-freedom robot manipulator. [ABSTRACT FROM AUTHOR]

We develop a nonlinear model of chatter in drilling that incorporates friction of the material on the cutting tool and its interaction with the axial-torsional mode of vibration seen in twist drills. Stability criteria are determined for both regenerative and non-regenerative chatter, and the effect of tool parameters and the friction law itself on the results is analysed. Our analysis shows that the exact form of the friction law is not critical in the stability calculation, only the size of the friction coefficient for steady cutting, and the slope of the friction law at the steady cutting state. However, its interaction with the geometry of the vibration is crucial. In the laboratory, drilling vibrational instabilities can occur at frequencies less than the natural frequency of the excited mode of the drill, and we find this result depends critically on the shape of the vibration mode projected onto the cutting edge of the drill. [ABSTRACT FROM AUTHOR]

Conventionally, the discrete variable structure control always suffers from the chattering phenomenon. Therefore, in this paper, we shall show that, for the discrete variable structure control, there always exist a limit cycle if the traditional nonlinearity of the sign function is used. This limit cycle behaviour is just the chattering phenomenon in the variable structure control theory. In particular, the frequency of this limit cycle is identical to the Nyquist frequency in the sampling theorem. In addition, a theorem related to the chattering-free design for the multiple-input multiple-output variable structure control is proposed. If the nonlinear function is memoryless and belongs to the sector [0,2), the chattering phenomenon can be eliminated. If the width of the boundary layer is enough, the reaching condition as well as chattering-free design can be attained; otherwise, it will result in the chattering phenomenon. [ABSTRACT FROM AUTHOR]