Control Chattering Research Articles

Evaluation of Cutting Stability of a Natural-Rubber-Tapping Robot

Natural rubber is a crucial raw material in modern society. However, the process of latex acquisition has long depended on manual cutting operations. The mechanization and automation of rubber-tapping activities is a promising field. Rubber-tapping operations rely on the horizontal cutting of the leading edge and vertical stripping of the secondary edge. Nevertheless, variations in the impact acceleration of the blade can lead to changes in the continuity of the chip, affecting the stability of the cut. In this study, an inertial measurement unit (IMU) and a robotic arm were combined to achieve the real-time sensing of the blade’s posture and position. The accelerations of the blade were measured at 21 interpolated points in the optimized cutting trajectory based on the principle of temporal synchronization. A multiple regression model was used to establish a link between impact acceleration and chip characteristics to evaluate cutting stability. The R-squared value for the regression equation was 0.976, while the correlation analysis for the R-squared and root mean square error (RMSE) values yielded 0.977 and 0.0766 mm, respectively. The correlation coefficient for the Z-axis was the highest among the three axes, at 0.22937. Strict control of blade chatter in the radial direction is necessary to improve the stability of the cut. This study provides theoretical support and operational reference for subsequent work on end-effector improvement and motion control. The optimized robotic system for rubber tapping can contribute to accelerating the mechanization of latex harvesting.

Integral Backstepping Control Algorithm for a Quadrotor Positioning Flight Task: A Design Issue Discussion

For quadrotor control applications, it is necessary to rely on attitude angle changes to indirectly achieve the position trajectory tracking purpose. Several existing literature studies omit the non-negligible attitude transients in the position controller design for this kind of cascade system. The result leads to the position tracking performance not being as good as expected. In fact, the transient behavior of the attitude tracking response cannot be ignored. Therefore, the closed-loop stability of the attitude loop as well as the position tracking should be considered simultaneously. In this study, the flight controller design of the position and attitude control loops is presented based on an integral backstepping control algorithm. This control algorithm relies on the derivatives of the associated virtual control laws for implementation. Examining existing literature, the derivatives of the virtual control law are realized approximated by numerical differentiations. Nevertheless, in practical scenarios, the numerical differentiations will cause the chattering phenomenon of control signals in the presence of unavoidable measurement noise. The noise-induced control signals may further cause damage to the actuators or even diverge the system response. To address this issue, the analytic form for the derivative of the virtual control law is derived. The time derivative virtual control law is analyzed and split into the disturbance-independent compensable and disturbance-dependent non-compensable terms. By utilizing the compensable term, the control chattering due to the differentiation of the noise can be avoided significantly. The simulation results reveal that the proposed control algorithm has a better position tracking performance than the traditional dual-loop control scheme. Meanwhile, a relatively smooth control signal can be obtained for a realistic control algorithm realization. Simulations are provided to illustrate the position tracking issue of a quadrotor and to demonstrate the effectiveness of the proposed compromised control scheme.

An adaptive sliding mode fault‐tolerant control of a quadrotor unmanned aerial vehicle with actuator faults and model uncertainties

AbstractAn adaptive sliding mode fault‐tolerant control strategy is proposed for a quadrotor unmanned aerial vehicle in this article to accommodate actuator faults and model uncertainties. First, a new reaching law is proposed, with which a sliding mode control (SMC) law is constructed. The proposed reaching law is made up of a sliding variable and the distance between it and a designated boundary layer, and it can effectively suppress the unexpected control chattering while preserving the necessary system tracking performance. Then, an adaptive SMC scheme is proposed to further solve the fault and uncertainty compensation problem. The proposed adaptation law helps to prevent overestimation of the adaptive control parameters, as well as avoiding control chattering. Finally, a number of comparative simulation tests are carried out to validate the effectiveness and superiority of the proposed control strategy. The demonstrated quantitative comparison results confirm its advantages.

COMPARISON OF CHATTER CONTROL OF VARIABLE AND REGULAR HELIX TOOLS IN THE ALUMINUM END-MILLING PROCESS

In the chatter, machining operations are undesirable because of the phenomena that affect product results, machining accuracy, tool life, and high operating value. Chatter is a vibration phenomenon that occurs in cutting tools due to the self-excitation of the influence of cutting parameters during the operation process of the machine. Types of chatter in machinery are regenerative and resonant. Because the pitch angles of variable helix tools vary, the helix angles of variable tools produce different tooth passing frequencies on each tool eye next to each other and can be used to prevent and control resonance. This study aimed to compare chatter control from the variable helix and regular-angle tools in the aluminum end milling process. The method is carried out through the end milling process experiment to determine the chatter control of the variable helix and regular-angle tools through the stability loop diagram. The results from this study were obtained by comparing control chatters in the milling process through controlling variable and standard helix angles as a guideline to produce the best surface roughness in the end milling process made from aluminum. The comparison of estimated control charts from variable helix tools is more comprehensive than regular helix tools.

Sliding Mode Control Design for Magnetic Levitation System

This paper presents a control system design for a magnetic levitation system (Maglev) or MLS using sliding mode control (SMC). The MLS problem of levitating the object in the air will be solved using the controller. Inductors used in MLS make the system have nonlinear characteristics. Thus, a nonlinear controller is the most suitable control design for MLS. SMC is one of the nonlinear controllers with good robustness and can handle any model mismatch. Based on simulation results with a step as input reference, MLS provided good system performances: 0.0991s rise time, 0.1712s settling time, and 0.0159 overshoot. Moreover, a prominent tracking control for sine wave reference was also shown. Although the augmented system had a chattering effect on the control signal, the chattering control signal did not affect MLS performances.

Fuel Cell Module Control Based on Switched/Time-Based Adaptive Super-Twisting Algorithm: Design and Experimental Validation

Fuel cells (FCs) have emerged as a sound promising technology for their application in emissions-free generation systems. Their high efficiency, reliability, and clean energy make these electrochemical devices especially suitable for manifold applications such as transportation, stationary generation, and portable devices. In view of the inherent complexity of this technology, the FC control plays a fundamental role to guarantee stability and high performance against system uncertainties and disturbances. Regarding this, sliding mode control has proved to be a powerful technique for the design of robust controllers for generation systems involving FCs. However, its discontinuous control action gives rise to some undesired effects when applied to real nonideal systems, being control chattering is usually the main drawback. In this framework, the brief presents the design and experimental implementation of an FC module control via a switched/time-based adaptive super-twisting algorithm (STA). The designed algorithm is evaluated in an experimental platform of a hybrid generation system based on a commercial 1.2-kW FC. The proposed controller exhibits a low value of chattering and similar robustness features compared to traditional STA.

A Novel Two-Phase Mode Switching Control Strategy for PMSM Position Servo Systems With Fast-Response and High-Precision

In this article, a novel mode switching control (MSC) strategy is proposed containing a fast-response phase and a high-precision settling phase to meet the requirement of high-quality point-to-point permanent magnet synchronous motor servo systems. In the fast-response stage, an adaptive trajectory planning method is developed to program the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current profile online based on the reference for the motor to reach the neighborhood of the reference position in minimum time. The chattering in the conventional time-optimal control is overcome and the idea that skipping speed and position loop with preplanned <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current trajectory is first attempted. After switching, the high-precision settling stage that is responsible for improving the transient performance in terms of reducing the overshoot and settling time is built with the proposed robust composite nonlinear feedback (RCNF) control law. This RCNF method cancels the overall disturbance through an extended state observer. The switching condition for the proposed MSC controller is clarified. Afterward, the whole closed-loop system's stability is strictly proved. Experiments are then conducted based on different scenarios to prove the effectiveness and robustness of the proposed MSC method.

Formation Control of Multiple Mobile Robots Based on Fuzzy Adaptive Sliding Mode Control

In order to solve the problems of slow convergence and chattering in formation control of multiple mobile robots, and to optimize the dynamic characteristics of formation system, a hybrid adaptive controller is proposed by analyzing the characteristics of different sliding mode reaching laws, which can accelerate the convergence speed and effectively suppress the chattering of the system. Firstly, the saturation function is introduced into the double power reaching law to form the saturation double power reaching law; Secondly, the hyperbolic tangent reaching law is used to improve the stability of the system when it approaches the sliding surface; Finally, fuzzy logic rules are used to adjust the coefficients of saturated double-power reaching law to optimize the overall dynamic parameters. Simulation results show that the designed controller can improve the convergence speed of the system, effectively suppress the chattering, and realize the fast and stable following of the follower robot to the pilot robot, which verifies the correctness and availability of the proposed controller.

TOAST: Trajectory Optimization and Simultaneous Tracking Using Shared Neural Network Dynamics

Neural networks have been increasingly employed in Model Predictive Controller (MPC) to control nonlinear dynamic systems. However, MPC still poses a problem that an achievable update rate is insufficient to cope with model uncertainty and external disturbances. In this paper, we present a novel control scheme that can design an optimal tracking controller using the neural network dynamics of the MPC, making it possible to be applied as a plug-and-play extension for any existing model-based feedforward controller. We also describe how our method handles a neural network containing history information, which does not follow a general form of dynamics. The proposed method is evaluated by its performance in classical control benchmarks with external disturbances. We also extend our control framework to be applied in an aggressive autonomous driving task with unknown friction. In all experiments, our method outperformed the compared methods by a large margin. Our controller also showed low control chattering levels, demonstrating that our feedback controller does not interfere with the optimal command of MPC.

Super‐twisting sliding mode trajectory tracking adaptive control of wheeled mobile robots with disturbance observer

AbstractThis article aims at the difficulties of wheeled mobile robots (WMR) system with wheeled slipping and control backlash in trajectory tracking. A novel sliding mode control strategy is proposed. For estimating the lumped disturbance, an adaptive sliding mode disturbance observer is constructed and achieves the finite‐time convergence of estimate error. For the purpose of accelerating the trajectory tracking, a novel arctangent terminal sliding mode surface is designed. To overcome the control chattering, a novel super‐twisting sliding mode controller is constructed which makes the control effect continuous and achieves finite‐time tracking of virtual reference velocities. The asymptotic convergence of trajectory tracking error is guaranteed by the Lyapunov stability theory. The simulation and comparison results of a WMR system demonstrate the validity of the proposed scheme for trajectory tracking.

Terminal time regulator‐based exact‐time sliding mode control for uncertain nonlinear systems

AbstractThis article proposes a sliding mode control scheme with exact convergence time for uncertain nonlinear systems. Terminal time regulator is defined for designing the global exact‐time time‐varying sliding mode. The proposed method has the following advantages: first, the reaching phase is absolutely eliminated from the initial time such that the sliding mode invariance is identically guaranteed on an entire dynamics; second, on the sliding mode, the system state converges to the origin exactly at the predefined settling time instant, rather than at an uncertain time instant with boundedness as obtained by existing methods; third, the control signal of the proposed controller is bounded even when the time approaches to the predefined settling time; and fourth, low‐pass filtering is utilized to suppress the signal chattering in the discontinuous control while maintaining the system transient behaviors by selecting a proper time constant. Lyapunov analysis verifies that for any initial condition the closed‐loop system can terminally converge to zero exactly at the predefined time instant. The proposed control is finally generalized for Euler–Lagrange (EL) systems.

Research on an Improved Sliding Mode Observer for Speed Estimation in Permanent Magnet Synchronous Motor

Aimed at the problems of system chattering and large observation errors in the sensorless control of a permanent magnet synchronous motor (PMSM) based on a traditional sliding mode observer (SMO), a combined reaching law algorithm based on the exponential reaching law and arcsine saturation function reaching law is proposed to improve the sliding mode observer. An appropriate positive real number is taken and compared with the product of controller gain and stator current observation error to judge the system position in sliding mode motion. In the early stage of sliding mode motion, the exponential reaching law is utilized, and then, in the latter and stable stages of sliding mode motion, the arcsine saturation function reaching law is used. The stability of the observer is proved by Lyapunov theory. The simulation and experimental data show that the speed error of the sliding mode observer based on the combined reaching law is reduced by 80% compared with the traditional sliding mode observer, and the chattering problem is also improved.

Adaptive robust finite-time control for active suspension systems via disturbance observation

To improve the ride comfort of vehicles, active suspension control strategy has received widespread attention. Although based on the finite-time and sliding mode control (SMC) technology design scheme, the convergence problem has been solved, the controller chattering and the poor control effect in the face of random interference will definitely limit its application in practice. To address such limitation, considering the variety of driving conditions, based on finite-time and SMC technology, an Adaptive Finite-time High-order SMC Active Suspension control Systems via disturbance observation (AFHASS) is proposed. Firstly, to improve the ride comfort of vehicle, a quarter dynamic model is established for vehicle active suspension; Then, given the advantages of finite-time and SMC technology, an AFHASS method is designed, and based on the Lyapunov analysis function constructed, the stability of the presented AFHASS control strategy has been proved; Finally, the effectiveness of the proposed AFHASS algorithm is validated by performing simulation, and compared with the different methods. Taking the finite-time control algorithm as a benchmark, under the C grade road roughness, the root mean square of vertical displacement has been improved by 29% and the energy consumption has been improved by 8%. The results are presented and discussed to illustrate the advantage and effectiveness of the proposed AFHASS algorithm in terms of energy consumption, vertical performance and controller chattering.

Pattern-based autonomous smooth switching control for constrained flexible joint manipulator

The paper proposes a pattern-based control scheme for a class of flexible joint manipulators with unknown dynamics and position constraints. The scheme consists of two phases: (i) online controller adjustment and task pattern identification; (ii) offline pattern recognition and controller calling. In phase (i), the constraint position vectors are transformed into unconstrained variables by using a transformation function. Subsequently, a set of static neural learning controllers are constructed for different reference patterns by employing experience weights obtained from stable adaptive neural control. Moreover, a dynamic estimator is developed to identify different reference patterns. The identified patterns are stored by constant NNs, thereby constructing a trained pattern library by combining with their corresponding static neural learning controllers. In phase (ii), the dynamic residual system is designed to recognize a tested pattern by comparing the size of residual error between the tested pattern and trained patterns. To avoid misjudgment, a novel recognition strategy is proposed by pre-recognition and recognition phases. When the tested pattern is recognized, the relevant experience-based controller strategy is recalled by an autonomous smooth switching technology. The proposed pattern-based control scheme has some advantages including accurate pattern recognition ability, small controller chattering, and highly autonomous control. Simulation studies on a 2-link flexible joint manipulator are implemented to show these advantages of the proposed scheme.

Displacement difference feedback control of chatter in milling processes

Displacement difference feedback control of chatter in milling processes

Neural network‐based continuous finite‐time tracking control for uncertain robotic systems with actuator saturation

AbstractThis paper proposes a neural network‐based continuous finite‐time tracking controller for the robust high‐precision control of robotic systems under model uncertainty, external disturbance, and actuator saturation. First, a fast nonsingular integral terminal sliding mode (FNITSM) surface is adopted to ensure singularity avoidance and fast finite‐time convergence. Considering the presence of model uncertainties and external disturbance, the fully adaptive radial basis function neural network (ARBFNN) is used to approximate and compensate for the unknown dynamic model. Then, a novel continuous fast fractional‐order power (CFFOP) approach law is explored to increase the convergence rate and eliminate chattering in the FNITSM control. Meanwhile, the approach law relaxes the requirement on the exact information of the upper bound of the disturbances and their time derivatives. Besides, an actuator saturation compensator (ASO) is proposed to compensate for the limited control input. The stability and finite‐time convergence of the proposed controller are analyzed using the Lyapunov theory. Finally, comparative simulations of both the numerical and application examples are conducted to verify the effectiveness of the proposed control schemes, indicating that the CFFOP approach law and ASO can be used effectively for robotic systems.

Analysis of chattering in step down converter via sliding mode reaching law

The reaching law approach is broadly used for chattering repression, minimization of steady state error and reaching pace kept minimsed. The reasons of chattering, in this paper proposes sliding mode reaching law. In one hand, they assurance the scheme arrives at the sliding face swiftly and stay on it, in another way they deteriorate the chattering inefficiently, even matchless certainties and disturbances. This proposed reaching law gives uniqueness of the response. The reaching law is compared with Gao’s reaching law. Sliding mode reaching laws gives the efficacy in reducing the chattering of the variable structure control (VSC). This reaching law also reduces the losses in the switching diplomacy. In turns efficiency of the step-down converter increases. Simulation results give significant decrease of chattering and extremely fewer receptive in supply and load variation.

Nonsingular fast terminal sliding mode control for manipulator based on combinatorial reaching law

Aiming at the problems of external disturbance, modeling errors, tracking speed and chattering in manipulator trajectory tracking control, a nonsingular fast terminal sliding mode control strategy for manipulator based on combinatorial reaching law was proposed. First, the nonlinear disturbance observer was used to observe the system’s external disturbance and modeling errors. Then, on the basis of the nonsingular fast terminal sliding mode surface, an improved nonsingular fast terminal sliding mode surface was proposed, which improves the convergence speed in the sliding motion process of sliding mode control. At the same time, a combinatorial reaching law combining the power reaching law and the variable speed reaching law was proposed, which improved the approach speed of the system under the premise of weakening the chattering. The simulation results verified the effectiveness of this control strategy.

Hardware-in-the-loop simulator for emulation and active control of chatter

Machine tool cutting performance is limited by the onset of regenerative chatter vibrations. Chatter damages the machine tool system and must be avoided. Efficacy of models guiding circumvention of chatter in actual industrial contexts remains restricted due to cutting process nonlinearities and due to uncertainties in dynamics of machine tools. To verify chatter models in the presence of nonlinearities and uncertainties and to explore active control of chatter, a mechatronic hardware-in-the-loop (HiL) simulator is presented in this paper. Hardware layer of the simulator has a flexure approximating a flexible workpiece and two actuators to emulate cutting forces and apply active damping forces. Software layer involves control architecture that is to be emulated on the hardware layer. Since HiL simulators offer a non-destructive, repeatable, and safe platform for emulations and active control of chatter, and because this paper presents the design of a validated simulator with all accompanying source files along with build and operating instructions, the research community can build such simulators to investigate other complex chatter phenomena and can also use it as a pedagogical tool. Learnings from building and using such simulators can also be leveraged to characterize and solve problems across other engineering domains.

Analytical and Experimental Techniques for Chatter Prediction, Suppression and Avoidance in Turning: Literature Survey

Chatter is a self-excited vibration that takes place during turning operations. It is either to be avoided or reduced for its negative impact on the machine-tool, the workpiece surface finish, and the cutting tool life. A lot of research has been carried out in this domain to understand this phenomenon, which leads to finding ways to detect, identify, avoid, reduce, and control chatter in turning processes. In this paper, chatter research related to turning processes is reviewed and summarized. The main goal of this review paper is to compare different chatter prediction, suppression, and avoidance techniques to find out the most effective technique, so a scope of a work related to turning processes chatter is defined.