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Control rods and elements manage the power distribution in nuclear reactors through the motion of banks of rods distributed throughout the core. These positional changes are achieved through the actuation of fine motion control rod drive (FMCRD) mechanisms. In the BWRX-300 design by GE-Hitachi, this mechanism is electrically driven by a servomotor that allows for high-precision control of power outputs. Under operational transients, such as load-following, accurate and precise operation of these servomotors is necessary over long periods of time, so they are key maintenance targets to maintain availability and operational flexibility. Swiftly and precisely identifying faults in the drive mechanisms will support predictive maintenance and reduced costs. This paper used three different types of simulated faults to test the fault detectability of principal component analysis (PCA) when considering the simulated operations of banks of control rods and their associated servomotors. These faults were stator short-circuit faults, ball screw jam faults, and ball screw wear faults. Torque and position were monitored in the simulation. The position signal was insufficient to detect mechanical faults. Torque signals for each servomotor in the bank of rods undergoing multiple position demand changes were projected to a reduced dimensional space via PCA. Q and T2 statistics were employed for anomaly detection. Using this approach, all faults were detected, and the anomalies were isolated to the faulty FMCRD mechanism. [ABSTRACT FROM AUTHOR]

Abstract Aiming at resolving the parameter uncertainty of the servo system under multi‐working conditions, a flatness‐based switched linear system model is proposed. Firstly, a fifth‐order linear switched discrete‐time system with uncertain parameters is established. The flatness properties of switched system is described and a de Bruijn's graph‐based framework is introduced for graphical description of the switched system. In addition, non‐linear bode diagrams are obtained via sweeping signals with multiple amplitudes. The discrete equations of the electromechanical servo system are established by the bode plots. The unknown parameters of the subsystems in switched model are identified by the simulated annealing algorithm, and compared with the least squares method to verify the accuracy of the identified parameters. Finally, the simulation model and experimental platform are constructed to verify the effectiveness of the proposed method. The switched model is compared with the classical transfer function model and single subsystems. The results indicate that the resolution of parameter uncertainty in servo systems is effective. The accuracy of the established switched model is about 99.5%. The accuracy of the switched linear system model of the electromechanical servo system is verified and the proposed modelling method is validated.

Servomotors have found widespread application in many areas, such as manufacturing, robotics, automation, and others. Thus, the control of servomotors is divided into various principles and methods, leading to a high diversity of control systems. This article provides an overview of types of servomotors and their basic principles and control methods. Principles such as digital signal processing, feedback control principle, field-oriented control, and integration with Industry 4.0 are discussed. Based on these control principles, the article presents popular control methods: PWM control, current control, two-loop control, fuzzy-logic control, and programmable control. The article concludes with a comparison of the presented methods on several criteria, and as an example, it includes the results of modeling a servomotor using the fuzzy-logic control method. [ABSTRACT FROM AUTHOR]

Aiming at resolving the parameter uncertainty of the servo system under multi‐working conditions, a flatness‐based switched linear system model is proposed. Firstly, a fifth‐order linear switched discrete‐time system with uncertain parameters is established. The flatness properties of switched system is described and a de Bruijn's graph‐based framework is introduced for graphical description of the switched system. In addition, non‐linear bode diagrams are obtained via sweeping signals with multiple amplitudes. The discrete equations of the electromechanical servo system are established by the bode plots. The unknown parameters of the subsystems in switched model are identified by the simulated annealing algorithm, and compared with the least squares method to verify the accuracy of the identified parameters. Finally, the simulation model and experimental platform are constructed to verify the effectiveness of the proposed method. The switched model is compared with the classical transfer function model and single subsystems. The results indicate that the resolution of parameter uncertainty in servo systems is effective. The accuracy of the established switched model is about 99.5%. The accuracy of the switched linear system model of the electromechanical servo system is verified and the proposed modelling method is validated. [ABSTRACT FROM AUTHOR]

Abstract Permanent magnet synchronous motors (PMSMs) have expectant low‐speed servo performance. However, complex nonlinear disturbances restrict the performance and lead to speed fluctuations, especially for small inertia PMSMs where the current‐loop cannot be used in special operating conditions. This paper divides complex disturbances into periodic determinable disturbances and other indeterminate disturbances according to their characteristics. A refined anti‐disturbance control (RADC) method is proposed to enable the inner loop to compensate for disturbances in targeted manners. Then ideal low‐speed servo can be achieved using a simple outer loop controller. The proposed RADC consists of two parts. One is a backpropagation neural network based periodic disturbances compensator that is trained using the data from an iterative learning controller. The other is an adaptive sliding‐mode‐assisted disturbance observer that rapidly observes and compensates the residual disturbances. The convergence of the overall algorithm is analyzed. The effectiveness of the proposal is also verified by experiments.

Control rod motion is one of the primary means of regulating the rate of fission in a nuclear reactor core to ensure safe and stable operation. Reactor power distribution and thermal power output can be fine-tuned by adjusting the control rod position. For high-precision control of rod movements, Fine Motion Control Rod Drives (FMCRDs) are often used. The operation of FMCRDs provides a unique opportunity to implement condition monitoring related to the intermittency of motion and the use of control rod banks. This research sets out to detect three types of faults in an electrically driven FMCRD. In addition to detecting faults, this work will attempt to determine both the type of fault and the source of each fault, completing the fault detection and diagnostics (FDD) pipeline on a scarcely researched system. The three types of faults to be investigated are short-circuit faults, ball screw wear faults, and ball screw jam faults. This is a potential advancement to the within-bank FDD of this specific drive system intended for deployment in an advanced nuclear reactor plant. Using encoder-decoder structured convolutional neural networks and autoencoders, the three tested faults were confidently detected and isolated as well as reasonably diagnosed by monitoring the FMCRD servomotor torque.

Servomotors have found widespread application in many areas, such as manufacturing, robotics, automation, and others. Thus, the control of servomotors is divided into various principles and methods, leading to a high diversity of control systems. This article provides an overview of types of servomotors and their basic principles and control methods. Principles such as digital signal processing, feedback control principle, field-oriented control, and integration with Industry 4.0 are discussed. Based on these control principles, the article presents popular control methods: PWM control, current control, two-loop control, fuzzy-logic control, and programmable control. The article concludes with a comparison of the presented methods on several criteria, and as an example, it includes the results of modeling a servomotor using the fuzzy-logic control method.

Permanent magnet synchronous motors (PMSMs) have expectant low‐speed servo performance. However, complex nonlinear disturbances restrict the performance and lead to speed fluctuations, especially for small inertia PMSMs where the current‐loop cannot be used in special operating conditions. This paper divides complex disturbances into periodic determinable disturbances and other indeterminate disturbances according to their characteristics. A refined anti‐disturbance control (RADC) method is proposed to enable the inner loop to compensate for disturbances in targeted manners. Then ideal low‐speed servo can be achieved using a simple outer loop controller. The proposed RADC consists of two parts. One is a backpropagation neural network based periodic disturbances compensator that is trained using the data from an iterative learning controller. The other is an adaptive sliding‐mode‐assisted disturbance observer that rapidly observes and compensates the residual disturbances. The convergence of the overall algorithm is analyzed. The effectiveness of the proposal is also verified by experiments. [ABSTRACT FROM AUTHOR]

Finite control set-model predictive control (FCS–MPC) has a simple and intuitive optimization procedure. Therefore, FCS–MPC is increasingly being applied to control strategies for electrical drive systems. This article presents a method for servo brake control of a permanent magnet synchronous motor (PMSM) based on FCS–MPC. Accordingly, we propose a reference trajectory introduced in a cost function for brake motions and an alternating procedure with speed control. Moreover, this article clarifies the problem peculiar to servo-brake control using FCS–MPC, i.e., the reduction in tracking performance near the brake position because of the low resolution of the output voltage. In addition to the conventional method, a finite number of smoothed voltages were applied as candidate voltages for FCS–MPC to improve the tracking performance near the brake position. The smoothed voltages can effectively increase the resolution of the output voltage, which results in fewer steady-state errors in angular position tracking during servo brake motion. The simulation and experimental results obtained using a PMSM drive system reveal that the proposed strategy exhibited high performance in tracking the reference target during the operation of servobrakes and the ability to seamlessly alternate between servo brake and motor operations. Résumé—La commande prédictive par modèle et ensemble de contrôle fini (FCS-MPC) dispose d’une procédure d’optimisation simple et intuitive. C’est pourquoi la FCS-MPC est de plus en plus appliquée aux stratégies de contrôle des systèmes d’entraînement électriques. Cet article présente une méthode de commande de frein asservi d’un moteur synchrone à aimant permanent (PMSM) basée sur la FCS-MPC. En conséquence, nous proposons une trajectoire de référence introduite dans une fonction de coût pour les mouvements de freinage et une procédure alternée avec le contrôle de la vitesse. En outre, cet article clarifie le problème propre à la commande de servofrein utilisant la FCS-MPC, à savoir la réduction des performances de suivi près de la position de freinage en raison de la faible résolution de la tension de sortie. En plus de la méthode conventionnelle, un nombre fini de tensions lissées ont été appliquées comme tensions candidates pour le FCS-MPC afin d’améliorer les performances de suivi près de la position de freinage. Les tensions lissées peuvent effectivement augmenter la résolution de la tension de sortie, ce qui réduit les erreurs en régime permanent dans le suivi de la position angulaire pendant le mouvement du servofrein. La simulation et les résultats expérimentaux obtenus à l’aide d’un système d’entraînement PMSM révèlent que la stratégie proposée présente des performances élevées en matière de suivi de la cible de référence pendant le fonctionnement des servofreins et la capacité d’alterner de manière transparente entre le fonctionnement des servofreins et celui du moteur. [ABSTRACT FROM AUTHOR]

This article focuses on the fast finite-time tracking consensus for uncertain nonlinear multiagent systems. By gracefully combining the hierarchical decomposition, adding a barrier power integrator and disturbance compensation techniques, a new adaptive fast finite-time controller is proposed. Compared with the existing works, the proposed method has several distinguishing features: 1) It can achieve fast finite-time convergence with full state constraints; 2) it can deal with some fully unknown nonlinearities and state-dependent disturbance. Moreover, the nonlinearities can be related with the states of all the followers; 3) the input of the leader is not required to be zero, meaning a broad class of references signals can be generated; and 4) the controller is computationally simply and ready to be implemented. No fuzzy logic/neural networks are needed. Applications of the proposed method on multiple servo motors are also studied. [ABSTRACT FROM AUTHOR]

A robust output regulation of a control system aims at disturbance rejection and reference tracking in the presence of uncertainties. Technically, the control design contains two mechanisms: the compensation of nontrivial steady states caused by disturbances and/or reference trajectories and the stabilization of an error system relative to steady states. Feedforward compensation and the internal model (including an approximate integrator) are the two main techniques for the former, while the latter is on a case-by-case basis. This article studies an alternative sliding-mode-based approach that can address the two mechanisms simultaneously, thanks to the new concept of sliding-mode-based output zeroing manifold. This concept bridges the two widely studied areas: robust output regulation and sliding-mode control. The approach is also verified by its application in permanent magnet synchronous motor servo systems. [ABSTRACT FROM AUTHOR]

Nanoscale actuators are one of the key technologies in high-precision servo systems. For optical storage systems, the performance of the actuator determines the maximum storage capacity and read/write speed. This article introduces a three-degrees of freedom nanoscale microsuspension actuator. Compared with an actuator from a traditional optical storage system, the proposed actuator can hold dual objective lenses with large apertures, the load capacity of which is increased by 3.14 times. With dual objective lenses operating at the same time, the actuator can achieve a large range of layer jumps. Thanks to the four-sided magnetic circuit and the overall structure, the actuator has an operating bandwidth greater than 10 000 Hz for dynamic performance, can compensate systematic errors in nanoscale, and provides a radial tilt servo direction. We have derived the actuator a unified electromechanical dynamic model, an equivalent stiffness model, an equivalent damping model, and a magnetic circuit analysis model in detail. Compared with other analysis models of microsuspension actuator, the proposed models provide a theoretical guidance for the determination of each key parameter, and can effectively improve design efficiency. The theoretical models and design method of the actuator are also applicable to microactuators design and active vibration isolation design of other high-precision servo systems. The simulation and experimental results verify the good dynamic performance of the actuator and show the effectiveness of the principal analysis and design method. [ABSTRACT FROM AUTHOR]

In this article, a speed control scheme based on an analytically designed fractional-order PID with Bode’s ideal cutoff (FOPID-BICO) filter is proposed. The FOPID controller is designed to track the speed references and the BICO suppress is applied to filter the high-frequency noise. Considering the difficulty of parameters tuning of the FOPID controller, a comprehensive analytical design method based on frequency specifications-defined loop-shaping for the FOPID-BICO controller is first proposed for the permanent magnet synchronous motor speed control. The designed speed servo system satisfies five frequency-domain specifications: gain crossover frequency, phase margin, phase crossover frequency, gain margin, and a “flat phase” constraint. Moreover, the influence of phase crossover frequency on control system is fully exposed through the frequency-domain analysis. The proposed designed method ensures that the control system is robust to loop gain variations and guarantees the optimal performance on rejecting noise in high-frequency and disturbance in low-frequency. The effectiveness of the proposed FOPID-BICO controller has been verified by experimental results. [ABSTRACT FROM AUTHOR]

The dual-motor drive is common in many heavy-duty swinging arm servo systems. A well-tuned dual-motor drive can provide better stability and durability than the regular single motor servo. However, the backlash is usually unavoidable in the heavy transmission chains. In this article, the issues provoked by the backlash are resolved by a virtual average motor model and a simple anti-backlash torsion torque. The transient performance is guaranteed by the dual-motor synchronous drive, and the anti-backlash strategy is only enabled when the load is approaching the reference position. The challenge is that the motion system structure is transforming during this transition. The model predictive control combined with the extended state observer is applied to get adaptive in this scenario. The expected effect is that the servo can track the desired position with high precision and high response. The scheme is comprehensively validated and evaluated in an experimental servo setup with a dual-motor drive. [ABSTRACT FROM AUTHOR]

High-precision position measurement of the gimbal servo system is indispensable to accurate torque output of the control moment gyroscope (CMG). This article addresses the systematic error of the resolver caused by the nonideal output signals of the resolver in the gimbal resolver-to-digital (R/D) conversion system. Due to the limitation of the structure and installation space of the CMG, it is impractical to install additional high-precision sensors to calibrate the raw angular position. Thus, this article proposes a new self-calibration method based on the discrete extended state observer (DESO) to compensate the systematic error of the resolver. The systematic error of the resolver is observed through iterating the resolver systematic estimation error and the compensation table is generated by the output of the DESO. Then, the steady-state error and dynamic performance of the DESO is analyzed and simulated. Finally, the proposed self-calibration method is verified by experiments, which show that the angular position control accuracy is significantly improved, which enhances the speed precision of the gimbal servo system. [ABSTRACT FROM AUTHOR]

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 q-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 q-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. [ABSTRACT FROM AUTHOR]

As the controller parameter adjustment process is simplified significantly by using learning algorithms, the studies about learning-based control attract a lot of interest in recent years. This article focuses on the intelligent servo control problem using learning from desired demonstrations. Compared with the previous studies about the learning-based servo control, a control policy using the broad learning system (BLS) is developed and first applied to a microrobotic system, since the advantages of the BLS, such as simple structure and no-requirement for retraining when new demos’ data is provided. Then, the Lyapunov theory is skillfully combined with the complex learning algorithm to derive the controller parameters’ constraints. Thus, the final control policy not only can obtain the movement skills of the desired demonstrations but also have the strong ability of generalization and error convergence. Finally, simulation and experimental examples verify the effectiveness of the proposed strategy using MATLAB and a microswimmer trajectory tracking system. [ABSTRACT FROM AUTHOR]

Turntable servo systems are affected by working status changing in actual work, thus, bringing some uncertain factors. Having models that have accurate predictive capabilities can be valuable for control and decision-making purposes. This article proposes a deep residual recurrent neural network (DRRNN) model-augmented attention with physical characteristics, which is used to build an accurate speed prediction model for a turntable servo system. Integrating the known physical features into the design of the residual network model can increase the interpretability of the overall model. Meanwhile, the recurrent neural network-augmented attention model is used to represent the unknown nonlinear characteristics. The addition of the attention mechanism can effectively improve the accuracy of the nonlinear model. Finally, this article proposes an iterative identification method based on the linear and nonlinear model error with alternative compensation. Through alternating error compensation, the linear model’s accuracy can be continuously improved, then the overall and the nonlinear part of the model can be established accurately by retraining the whole model. Experimental results show that the DRRNN model designed in this article can predict the rotational speed in single-step or multistep well. Compared with the traditional mechanism modeling method, the modeling accuracy can be greatly improved. [ABSTRACT FROM AUTHOR]

Improving the positioning response is one of the key goals for permanent magnet synchronous motor position servo systems. The sliding mode variable structure controller (SMVSC) is an effective method due to the advantages of strong robustness, fast response, and easy practical implementation. However, the existing SMVSCs have difficulties in optimizing the position tracking response speed and chattering performance at the same time. This article proposes an improved position speed integrated SMVSC (ISMVSC) with a new variable exponential reaching law based on position error and a saturation function, and a speed-limiting method using speed error and trajectory planning. The general design principle is given and various tests are carried out to verify the effectiveness of the proposed method. The experimental results show that compared with traditional methods, the ISMVSC can improve the positioning response speed and reduce chattering problems at the same time; it also exhibits a stronger transient speed-limiting ability. All these advantages make the proposed controller a superior method to achieve high-response positioning control of the servo system that performs point-to-point motion. [ABSTRACT FROM AUTHOR]

A new structure of cross-coupling position command shaping controller using ${H_\infty }$ control scheme for the precise tracking in the multiaxial motion control is proposed in this article, together with its stability analysis.This new structure has the advantage that the controller has a simpler design process and robuster performance than the conventional ones. The proposed controller is evaluated and compared experimentally with an uncoupled controlled and conventional system. The experimental results show that the new structure remarkably reduces contour error. In addition, this new controller can be implemented easily on a majority of motion systems in use today via reprogramming the reference position command subroutine. [ABSTRACT FROM AUTHOR]

This brief presents a speed and acceleration estimation mechanism combining a Luenberger-type observer and a nonlinear second-order disturbance observer (DOB) using servo system angle measurements without system parameters and load information. The resultant observer has the following two contributions: (a) the inclusion of a system parameter information-free nonlinear DOB as a subsystem to ensure improved robustness and (b) the capability of performance assignment by tuning the scalar design factor without involving any matrix calculation processes. An experimental study validates the practical advantage of the proposed solution using a prototype 500 W dynamo system as a speed servo system. [ABSTRACT FROM AUTHOR]

The moving components and servo control systems of computer numerical control (CNC) machine tools spent a substantial energy but received less attention regarding energy saving. This article presents a novel energy saving methodology of feed system using a data-model hybrid driven design optimization approach for the integrated design of moving component structural geometry and control system. Surrogate models are built based on the design of experimental data to avoid time-consuming finite element analysis. The energy consumption mechanism model is constructed via energy flow analysis method. The data-model hybrid modeling method realizes the collaborative optimization of the machine tool feed system structure and controller, while simultaneously accelerating the optimization process. A multi-objective trade-off model with energy consumption and deformation is established. Three different multi-objective optimization approaches are taken to drive the developed multi-objective optimization model. The control performance of the feed system is demonstrated through simulation analysis. Results indicate that the optimized scheme can reduce energy consumption by over 10% and maximum deformation of the tool holder by over 14%. Note to Practitioners—This article is motivated by the problem that a significant energy consumption occurs when the CNC machine tool feed system continuously drives the moving components to move, accelerate or decelerate. The previous studies to cope with this problem broadly are to separately analyze energy-saving characteristics of the structure or control system of the CNC machine tool feed system. This article suggests a novel data-model hybrid approach for energy saving of machine tool feed system, which simultaneously integrates design of moving component structural geometry and servo control system. In this article, we mathematically derive an energy consumption mechanism model of the CNC machine tool feed system. By using surrogate assisted method, a multi-objective trade-off model with energy consumption and deformation is established. Simulation experiments indicate that this approach is feasible and can significantly reduce the energy consumption of CNC machine tool feed system. [ABSTRACT FROM AUTHOR]

Multiple disturbances are the main constraints that hinder the high-performance velocity tracking of the gimbal servo system in control moment gyro. This article presents a non-cascade structured velocity-tracking controller based on a refined disturbance observer for handling multiple disturbances and improve the tracking performance. Specifically, a disturbance observer is designed to estimate the imbalance disturbance, which can be represented by an exogenous system. The disturbances that cannot be modeled a priori are treated as a lumped term and estimated via extended state observer. By resorting to disturbance estimation, a novel sliding mode controller based on the disturbance estimation values is developed to handle the mismatched problem and chattering issue. Finally, experimental tests are conducted to verify the effectiveness of the proposed anti-disturbance control scheme. [ABSTRACT FROM AUTHOR]

This article investigates the trajectory tracking problem of underactuated mechanical systems (UMSs) with companion nonholonomic servo constraints and uncertainties. For such motion tasks, the existing approaches in the literature attempt unrealistically to furnish a reliable closed-form solution, rendering it difficult to have high-quality tracking performance with theoretical support. In addition, the uncertainties typically pose substantial difficulty in the controller synthesis. Here, by invoking the methodology of fuzzy sets, the uncertainties in the UMSs are elegantly represented; and with this, the formulation becomes such that a closer link between the uncertain dynamical model of the UMSs and the real world is established. The reference trajectories are regarded appropriately as servo constraints, and subsequently an adaptive robust controller is designed to accomplish the trajectory tracking task from a specific viewpoint of servo constraint tracking. As supported by rigorous proofs, the closed-form solution to the proposed controller is obtained with guaranteed Lyapunov stability. Leveraging on the closed-form solution, the global optimizer to the controller gain parameter can be determined, which is shown to exhibit several important properties including existence and uniqueness. Finally, a numerical example is presented to demonstrate the effectiveness of the designed method. [ABSTRACT FROM AUTHOR]

The remaining useful life (RUL) prediction of servo motors plays a greatly indispensable role in preventing abnormal and inefficient operation of servo drive system and even major safety accident. In this article, a novel variant of recurrent neural networks, called gated adaptive hierarchical attention unit (GAHAU), is constructed to efficiently predict the RULs of servo motors, which can not only pay attention to the outputs of reset and update gates but also adaptively divide the hierarchy of the sequence information in attention gate. The updating formulas of GAHAU are derived. With the raw vibration signals of servo motors, a quadratic function-based deep convolutional autoencoder is used for automatically generating the health indicator vector. Based on the constructed HI vector, the RULs of servo motors are accurately predicted by GAHAU. The experiments on servo motors demonstrate that the presented GAHAU has remarkable prediction performance especially for the long-term prediction. Compared to the existing typical RUL prediction methods, the proposed methodology has stronger predictive ability according to the comparative results. [ABSTRACT FROM AUTHOR]

This brief introduces a novel bioinspired motor neuron dynamical unit where the neural dynamics, responsible for the generation of the action potentials, is embedded into the actuator dynamics, which here plays the role of, and substitutes, the recovery variable into the classical neuron equations. A recently introduced nullcline-based control strategy, over servomotors embedded into piecewise linearly approximated FitzHugh–Nagumo neuron models, is here applied to the synchronization of two embodied motor-neuron units in the form of either a continuously active proportional gain or an event-driven strategy. In view of the application to such problems as the generation of adaptive control laws for distributed oscillatory networks, at the basis of bioinspired walking machines, the advantages in terms of the reduced-order dynamical equations and ease of synchronization are presented both through simulations and with experiments devoted to control networked Dynamixel MX-28AT servomotors via an microcontroller unit (MCU) board. [ABSTRACT FROM AUTHOR]

This article addresses the hierarchical resilient event triggered sampled-data security control and valve opening management problem for networked hysteretic leaf spring hydro-suspension with asymmetric actuator under false injected deception attack. For the derived Takagi–Sugeno (T–S) fuzzy model employed to tackle hysteresis nonlinearity, a new full-order dynamic output feedback top control with improved error and threshold functions for resilient event triggered mechanism is proposed to generate the target force so as to suppress the body and tire vibration under limited suspension chatter space. For the asymmetric cylinder hydraulic actuator over actuated by multiple servo valves, optimal servo valve openings are dynamic regulated to track the target force with weight adaptive nonlinear model predictive lower control. Benefiting from saved communication resource while more sparsely generating piecewise target force, as well as precise regulation by reasonably allocating over actuated valve openings to produce required force, the obtained results indicating more comfortable ride performance and less tire dynamic loads within smaller suspension chatter space favorably demonstrate the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Gecko-inspired adhesives can allow free-flying space robots to grasp and manipulate large items or anchor themselves on smooth surfaces. In this article, we report on the first tests conducted using gecko-inspired adhesives on a gripper attached to an Astrobee free-flying robot operating inside the International Space Station (ISS). We present results from on-ground testing as well as two on-orbit sessions conducted during early 2021. Recorded data demonstrated that an adhesive gripper for Astrobee could provide 3.15 N of force for manual perching. The adhesives functioned as anticipated, despite a lengthy storage period. The results also highlighted some considerations for future adhesive gripping in space with free-flying robots. We discuss these topics along with system design considerations for successful implementation aboard the ISS, raising the readiness of this technology for a space-grade environment. [ABSTRACT FROM AUTHOR]

The instantaneous large disturbances, which are typically characterized by large amplitudes and short durations, generally force the actual trajectory of a servo motor system to deviate from the desired trajectory dramatically. In view of this, a novel fast trajectory recovery scheme is proposed mainly from the perspective of trajectory planning. To this end, a two-loop constrained trajectory replanning based control framework is developed to recover the deviated trajectory in a minimum-time manner under various modeling uncertainties, kinematic and dynamic constraints. Comparative experiments on a servo motor testbed show superiorities of the proposed approach over other related algorithms. [ABSTRACT FROM AUTHOR]

This article focuses on a robust control scheme for pointing control of the marching tank gun. Both matched and mismatched uncertainties, which may be nonlinear (possibly fast) time varying but bounded, are considered. First, the pointing control system is constructed as a coupled, nonlinear, and uncertain dynamical system with two interconnected (horizontal and vertical) subsystems. Second, for the horizontal pointing control, robust control is proposed to render the horizontal subsystem to be practically stable. Third, for the vertical pointing control, an uncertainty bound-based state transformation is constructed in a similar way of backstepping to convert the original mismatched system (i.e., the vertical subsystem) to be locally matched and then robust control is proposed to render the transformed system to be practically stable. Finally, it is proved that when the transformed system is rendered to be practically stable, the original system renders the same performance; therefore, vertical pointing control is achieved. This work should be among the first ever endeavor to cast all the coupling, nonlinearity, and (both matched and mismatched) uncertainty into the pointing control framework of the marching tank gun. [ABSTRACT FROM AUTHOR]

In this article, we proposed a discrete-time sliding mode load thrust observer to reduce the influence of load thrust mutation on the linear motor and improve the antiinterference ability and speed tracking performance of the system. First, the electrical and dynamic models of linear motor are established, and the limitation of conventional double-closed-loop control based on proportional integral (PI) algorithm is analyzed. Second, the extended state equation of velocity and load thrust is given and an improved sliding mode reaching law is designed to establish the discrete-time load thrust observer. Based on Lyapunov theory, the stability of the observer is proved. The observed load thrust is compensated to the controller in the form of feedforward. Finally, a series of comparative experiments were carried out. The experimental results show that compared with the PI control, the maximum speed fluctuation of this method is reduced by about 18.1% when the load changes between no-load and rated load. This means that the method in this article can effectively improve the antidisturbance ability of the system. [ABSTRACT FROM AUTHOR]

This article presents the design and implementation of an innovative biomimetic underwater vehicle (BUV) and its locomotion controller. Through mimicking a dactylopteridae, the hybrid propulsion BUV is designed with two symmetrical bio-inspired long-fins and a double-joint fishtail. The mechatronic design of the dactylopteridae-inspired BUV with the pectoral long-fins and a double-joint fishtail is first provided. The two flexible long-fins compose the median and/or paired fin (MPF) propulsion, while the fishtail acts as the body and/or caudal fin (BCF) propulsion. Through the coordination of BCF and MPF propulsion modes, the BUV obtains excellent low-speed locomotion stability and also keeps high maneuverability. Moreover, the locomotion control methods based on central pattern generators (CPGs) model and fuzzy adaptive proportion integral differential (PID) are proposed for this BUV. In the end, the experimental results of the multimode motion and closed-loop motion control demonstrate the feasibility and effectiveness of the mechanism and the locomotion control system. Note to Practitioners—The motivation behind this article is the design of a novel biomimetic underwater vehicle (BUV) that possesses low-speed locomotion stability and fast swimming ability, which is suitable for carrying relevant sensors to complete water quality monitoring, biological observation, underwater equipment inspection, underwater structure detection, and other marine tasks. Currently, BUVs are usually designed as only one propulsion mode by caudal fin or paired fins, which makes it difficult to have the advantages of both modes. In order to further study the problem, we designed a dactylopteridae-inspired BUV with the bilateral pectoral long-fins (providing low-speed locomotion stability) and a double-joint fishtail (providing fast swimming ability). A hybrid-driven motion control framework is presented for the BUV based on a central pattern generators (CPGs) model and fuzzy adaptive proportion integral differential (PID). A series of experiments suggests that the mechanism and the locomotion control system are practical and valid. Hopefully, our mechanism and control framework can provide valuable theoretical and technical support guidance to the practicing marine engineer for the codesign of propulsion mode and control. [ABSTRACT FROM AUTHOR]

For pose stabilization task of nonholonomic mobile robots, this article proposes a novel integrated interactive framework, bridging the gap between visual servoing and simultaneous localization and mapping (SLAM). The framework consists of two cooperative components, control module for servoing task and SLAM module for feedback signals estimation. In most visual servoing methods, feedback signals for the servoing controller are estimated by means of multiple-view geometry assuming the target scene being always within the camera field of view (FOV). To handle the challenge that the target scene gets out of view during servoing process, the desired image is associated with the initial map by a two-step strategy, and an incremental map is constructed to guarantee available feedback signals estimation. In addition, on the basis of the kinematic model of the mobile robot and velocities designed by the servo controller, the predicted pose is exploited to discard moving objects in the camera FOV, thus making the proposed framework effective in dynamic scenes. Experimental results operated in different scenes without prior information demonstrate the effectiveness of the proposed approach to handle the FOV problem and dynamic scenes. Note to Practitioners—Traditional visual servoing stabilization approaches usually require that the feature points in the target scene remain within the FOV of the camera for feedback signals calculation, which is often neglected. Motivated by the requirement of continuous feedback signals to the servo controller, the SLAM technique is introduced to relax the FOV constraint during the servoing process. A novel integrated interactive framework is proposed in this article to further increase the applicability of the servoing system in practice, in which the SLAM module is also redesigned for the flexibility in dynamic scenes. The SLAM module provides feedback signals for the servo controller; meanwhile, velocities designed by the servo controller are utilized for the prediction mechanism in the SLAM module to discard features on moving objects. Experiments validate the applicability of the proposed framework in different scenarios. [ABSTRACT FROM AUTHOR]

People who have lost their limbs to amputation and neurological disorders confront this loss every morning. As per the literature review, nearly 30% of the Indian population suffered from upper extremity amputation. As a coping-up measure, a force-controlled prosthetic limb has been developed to improve their self-reliance, quality of lifestyle and mental strength. The current prosthetic limb operation is done by residual muscle contraction, which contributes to the activation of the sensor and the motor. But there are some cons, the amputee does not know how much pressure needs to be exerted for holding various objects. Also, the amputee still has to undergo the surgical procedure. However, this paper proposes a way to predict the force which is needed to regulate the voltage for the servomotors using different Machine Learning (ML) regression approaches. Support Vector Regressor (SVR), Linear Regression and Random Forest models have been used to predict that force requirement. After comparing the results, the Random Forest model gave a highly accurate prediction of the force needed to control the voltage for the DC servomotors [ABSTRACT FROM AUTHOR]

Most recent studies on adaptive hydraulic tracking control focus on the trajectory tracking performance while the parameter convergence property is often unsatisfying. This article proposes a composite learning adaptive position tracking controller with improved parameter convergence for electro-hydraulic servo systems. In the composite learning, a prediction error is formulated to exploit input–output memory data, and parameter estimates are driven simultaneously by tracking and prediction errors. Practical exponential stability of the closed-loop system, which implies the convergence of both the tracking and parameter estimation error, is established by a more realizable interval-excitation condition than the stringent persistent–excitation condition. Therefore, superior trajectory tracking is obtained compared with the classical adaptive hydraulic control. Besides, the initial fluid control volumes of hydraulic systems are assumed to be unknown a priori, which enhances the generality of the proposed control approach. The abovementioned two properties are generally not achievable in prevalent approaches to adaptive hydraulic control. Moreover, noisy acceleration signals and the time derivatives of pressure signals are not needed in the proposed approach, which improves its robustness against measurement noise. Extensive experimental results verify its superiority over currently available ones. [ABSTRACT FROM AUTHOR]

Nowadays, the dual closed loop proportional-integral-lead (PI-Lead) controller is widely used, especially for the servo systems where high performance is required for motion control, like lithography machines and vehicle-used Lidars. Considering complex industrial applications and working conditions, more comprehensive and systematic research about the structure and potential problem of the PI-Lead controller is necessary for enhancing its performance and robustness. In this article, the failure mechanism of the classic antiwindup methods in the PI-Lead controller is analyzed. By adjusting the location of control blocks, a novel reversed structure based PI-Lead controller is proposed as a complement to the traditional antiwindup methods for effective operation and to make the system stable under severe impact disturbances. Then, a self-commissioning strategy is designed based on a fast root mean square error (FRMSE) index and without additional manual tuning factors. Compared with classic indicators, the proposed FRMSE index can achieve faster instability detection and accelerate the tuning process to protect the equipment. [ABSTRACT FROM AUTHOR]

This article proposes a real-time method to control the contour error for industrial five-axis machine tools by combining the generalized predictive control (GPC) and the feedback correction (FBC) with dynamic contour error estimation (CEE). The CEE is developed by well considering the curve’s curvature and torsion based on Taylor series expansion and Frenet frame theory. By utilizing the spherical linear interpolation, the tool orientation and the tool tip position are synchronized with respect to the curve length. A novel dynamic foot point searching procedure is established to weaken the influences of the tracking errors’ magnitude on the CEE precision. To tackle the transmission effect, the GPC is adopted to predict the servo systems’ outputs, and then, the induced tool pose deviations, which are subsequently utilized to counteract the contour errors, are predicted by constructing Jacobian matrixes. Especially, the FBC loops are constructed to suppress the influences of disturbances and further to reduce the magnitudes of contour errors. Simulations and experiments are conducted to verify the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

Gait impairment represented by crouch gait is the main cause of decreases in the quality of lives of children with cerebral palsy. Various robotic rehabilitation interventions have been used to improve gait abnormalities in the sagittal plane of children with cerebral palsy, such as excessive flexion in the hip and knee joints, yet in few studies have postural improvements in the coronal plane been observed. The aim of this study was to design and validate a gait rehabilitation system using a new cable-driven mechanism applying assist in the coronal plane. We developed a mobile cable-tensioning platform that can control the magnitude and direction of the tension vector applied at the knee joints during treadmill walking, while minimizing the inertia of the worn part of the device for less obstructing the natural movement of the lower limbs. To validate the effectiveness of the proposed system, three different treadmill walking conditions were performed by four children with cerebral palsy. The experimental results showed that the system reduced hip adduction angle by an average of $4.57~\pm ~1.79^{\circ }$ compared to unassisted walking. Importantly, we also observed improvements of hip joint kinematics in the sagittal plane, indicating that crouch gait can be improved by postural correction in the coronal plane. The device also improved anterior and lateral pelvic tilts during treadmill walking. The proposed cable-tensioning platform can be used as a rehabilitation system for crouch gait, and more specifically, for correcting gait posture with minimal disturbance to the voluntary movement. [ABSTRACT FROM AUTHOR]

The control bandwidth of the injection-locked system utilizing a DFB fiber laser and fiber ring cavity is analyzed to estimate system stability. Within the bandwidth of the injection lock, an electrical feedback control loop is adopted to better suppress the phase noise of the fiber ring cavity. The entire system operates in low noise conditions of lower than −60 dBc/Hz from 1 Hz to 100 kHz. The output power of the fiber ring cavity is amplified stably to 0.346 W with a polarization extinction ratio of 31 dB based on an all-polarization-maintaining ring structure. The output laser from the single-mode fiber has the near diffraction-limited beam quality for wide applications. [ABSTRACT FROM AUTHOR]

The maneuverability of standard quadrotors with coplanar propellers is limited by their inherent underactuation. To overcome this challenge, in-flight, active propeller tilting has been widely investigated in the literature. However, biaxial propeller tilting that renders extensive thrust vectoring has not been explored much owing to the ensuing mechanical complexities. Therefore, this article presents an innovative design capable of achieving independent biaxial tilting of $\text{100}^\circ$ and $\text{180}^\circ$ about two perpendicular axes while keeping the mechanical complexity relatively low. The developed quadrotor, aptly named QuadPlus, efficiently combines actuator redundancy and propeller rotation in a compact package, compared to its state-of-the-art counterparts. The hyperdynamic QuadPlus with a total of 12 degrees of freedom can control its attitude independent of the position, thus enabling effective maneuvering through narrow spaces. Moreover, a novel cascade approach comprising of a high-level nonlinear model-predictive control algorithm is adopted to obtain the optimal actuator configuration for an underdetermined system while dealing with the physical constraints. In addition, proportional–integral–derivative controllers are employed at low level to track attitude references generated by the navigation algorithm. Finally, with the help of realistic Gazebo simulations, the efficacy of the system is demonstrated by tracking complex 3-D trajectories, which replicate the motion in a constrained environment. Overall, the obtained results manifest QuadPlus's capability of achieving independent position and attitude control even with multiple actuator saturation. The authors envision that the proposed simplistic design would stimulate interest in the community for exploring the benefits offered by biaxial propeller tilting platforms. [ABSTRACT FROM AUTHOR]

This article presents a direct digitizing neural recorder that uses a body-induced offset based DC servo loop to cancel electrode offset (EDO) on-chip. The bulk of the input pair is used to create an offset, counteracting the EDO. The architecture does not require AC coupling capacitors which enables the use of chopping without impedance boosting while maintaining a large input impedance of 238 M $\Omega$ over the whole 10 kHz bandwidth. Implemented in a 180 nm HV-CMOS process, the prototype occupies a silicon area of only 0.02 mm2 while consuming 12.8 μW and achieving 1.82 μV $_{\text{rms}}$ of input-referred noise in the local field potential (LFP) band and a NEF of 5.75. [ABSTRACT FROM AUTHOR]

Inaccurate model, uncertainties, and valve bias are the main challenges for the controller design of high precision electro-hydraulic servo systems. To achieve a satisfactory tracking control performance under such difficulties, a fractional order integral sliding mode controller based on a radial basis function neural network (RBFNN) is proposed and experimentally tested in this article. In this approach, the RBFNN is used to handle the uncertainties in the model; meanwhile, the disturbance and the inaccurate valve zero point are handled by the robustness of the designed controller. The fractional order integral sliding mode is proposed to deal with the possible fractional order fluid dynamics as well as to improve the tracking precision. The stability of the control system is proved by the Lyapunov stability theory. The experimental results prove the effectiveness of the control method. Quantitative comparisons with a number of experiment control methods show that the proposed method results in a higher tracking accuracy. [ABSTRACT FROM AUTHOR]

This article presents a high performance and low-cost design methodology for the servo control of magnetic drive-trains (MDTs) operating in direct drive mode. For the first time, this article considers using sensitivity peaks to analyze the robustness and stability of MDT control systems. Initially, through analysis of a dynamic model, the key spring characteristic parameters with respect to operating points, are developed. It is also shown that a wider dynamic performance envelope can be achieved by linearizing the MDT model at around 60 $\%$ –80 $\%$ of the maximum coupling torque, as opposed to traditional linearization under zero torque conditions. Subsequently, this article exploits the spring characteristics for a design methodology based on the $\text{H}_\infty$ mixed sensitivity approach to determine suitable control parameters. Following this, the maximum exogenous load-torque disturbance and speed reference that will not induce pole-slipping can be determined. Finally, preferential position reference profiles and optimal gains for position controllers are given to prevent demand-induced speed oscillations. The proposed methodologies are validated through simulation and experimental studies. [ABSTRACT FROM AUTHOR]

In order to provide guidance and reference for developing a ball screw drive system of the high-speed machine tool, this article investigates three basic issues with consideration of dynamics, including mechanical characteristics, inertia matching problem, and driving torque characteristics. The axial stiffness and natural frequency of the system are first calculated to verify the correctness of mechanical parts selection, and the stability of the system is ensured by designing an appropriate gain. vvNext, the inertia matching problem between the servo motor and load is analyzed based on the two-inertia-system, and the range of the inertia ratio is determined as an important principle in developing a ball screw drive system. The speed–torque characteristics are further discussed, and a graphical method is proposed to quickly and accurately determine a suitable servo motor. Finally, a complete flow is described, and the ball screw drive systems of a high-speed machine tool for aeroengine casing manufacturing are developed as an application. The actual test results of speed, accuracy, cutting ability, and machining performance indicate that the developed ball screw drive systems have a satisfactory performance, which validate the effectiveness of the comprehensive study. [ABSTRACT FROM AUTHOR]

It is well known that proportional-integral-derivative (PID) controllers are dominant in industrial scenarios. PID with high-order derivative or integral terms named generalized PID is superior to the PID. However, there is little literature investigating how to tune the parameters of the generalized PID to enhance the disturbance rejection ability. Toward that end, this article illustrates that the cascade controllers based on the first-order linear active disturbance rejection controllers (LADRCs) (cascade LADRCs) and high-order LADRCs can be interpreted as the generalized PID with low-pass filters for speed servo systems and position servo systems, which in turn is an alternative method to realize the generalized PID. Moreover, the differences between the high-order LADRC and cascade LADRCs are the generalized integral terms, which can be quantified by integral time multiplied absolute error. The proposed LADRC controllers are verified and compared with the current controllers by simulations in MATLAB/Simulink. Finally, one experimental example of the LADRC controllers is implemented on the position servo dc motor system platform. [ABSTRACT FROM AUTHOR]

The new energy vehicle industry needs a large number of vehicle power batteries, and its production depends on high-speed and high-precision battery pole-piece cutting equipment, which is mainly composed of the electrode material roll uncoiling unit, buffering unit, main drive unit, and cutting unit. Due to the nonlinearity and high-speed intermittent motion mode of a servomotor, the existing control technology is difficult to apply to the cutting system. This article presents a multimotor linear velocity planning approach used to ensure synchronous and cooperative operation of the motors in the cutting system. To achieve fast and accurate positioning control of the main drive motor running in fast acceleration and deceleration, periodic and intermittent mode, an adaptive position controller based on data-driven modeling technique is proposed, which makes the parameters of the controller change with the operation state of the main drive motor so that the controller can obtain good positioning accuracy in a wide working range of the main drive motor. Two linear models are established to represent the relationship between the positioning error and the positioning controller parameters and the main drive motor running conditions. The parameters of the two models are estimated offline and the parameters of the adaptive position controller can be obtained online quickly. Thus, the proposed control method for the main drive motor can be easily realized by general PLC in practical application. Simulation study results show that using the proposed method, the positioning error of the main drive motor is less than 0.1 mm when cutting 89-mm-long battery pole-piece and cutting 1 to 3 pieces/s. This result is much better than that of the position controller with fixed parameters. [ABSTRACT FROM AUTHOR]

In this article, an improved hybrid particle swarm optimization (IHPSO) algorithm is proposed to solve the optimization problem of controller parameters in the design of a permanent magnet synchronous motor (PMSM) servo system. The proposed algorithm presents the directional mutation operation to the particles, which fixes the position of some particular particles so as to enhance the searching ability to some remote regions. In order to cooperate with directional mutation operation, the updating formula of particles velocity is ulteriorly improved. Then, the proposed IHPSO algorithm is adopted to optimize parameters of the designed controller. A simulation and an experimental platform of the PMSM servo system are designed using a biological intelligence controller based on hormone regulation for the speed control and feedforward compensation for the position controller, where IHPSO is applied to the parameter optimization for speed and position controllers, which validate the effectiveness of the IHPSO algorithm and the designed control system. [ABSTRACT FROM AUTHOR]