Simple Active Control Research Articles

Active vibration control in robotic grinding using six-axis acceleration feedback

Industrial robots endure severe vibrations in the grinding process due to factors such as joint flexibility, low damping, and contact force fluctuations. Additionally, the motion control of the robot primarily relies on feedback signals from the motor-side encoders, while lacking motion state feedback from the load side. This exacerbates the robot vibrations, severely compromising the surface quality of the workpieces. To address this problem, an active damping control method for robotic grinding using six-axis acceleration feedback is proposed. This method realizes a simple, reliable, and efficient active vibration control without altering the robot body. A multi-sensor fusion Cartesian space six-axis accelerometer is designed and integrated into the robot end effector, achieving accurate feedback on the robot load side vibration state. The strategy of six-axis acceleration decoupling and principle of the vibration suppression with the acceleration feedback are explained. Compared with conventional sensing schemes, this reduces joint acceleration approximation errors and end vibrations. The robotic grinding experiments are carried out on aeronautic structural parts. Extensive case studies demonstrate that the proposed approach can effectively control the vibration caused by joint flexibility in the robot grinding process, and greatly improve the surface quality of workpieces. This method has great potential application in vibration suppression during robotic grinding and polishing.

A simple active adaptive control method for mitigating and isolating mechanical vibrations of the pyramid-core lattice sandwich structures

In this paper, we propose a simple active adaptive feedback (AAF) control strategy to enhance the vibration mitigation and isolation properties of the conventional pyramid-core lattice sandwich structures (PSSs) and the modified chessboard-designed pyramid-core lattice sandwich structures (CPSSs) via the lead zirconate titanate (PZT) ceramic patches. The proposed simple AAF control strategy is based on the active feedback (AF) control by relating the AF control parameters to the frequency. Firstly, the effects of the AF control parameters on the band structures are analyzed. Subsequently, the mathematical expressions of the frequency-dependent AAF control parameters are derived by the curve fitting technique. The results show that the proposed simple AAF control strategy is sufficiently accurate, highly efficient and can significantly expand the band-gaps compared to the conventional AF control, hence leading to improved vibration mitigation and isolation properties of the PSSs and CPSSs. The proposed simple AAF control strategy provides a simplified and generalized method to enhance the vibration mitigation and isolation properties of the lightweight lattice sandwich structures (LSSs) while maintaining their high stiffness-to-density ratio, which may offer various potential applications in engineering sciences.

Beating of a Spherical Liquid Crystal Elastomer Balloon under Periodic Illumination.

Periodic excitation is a relatively simple and common active control mode. Owing to the advantages of direct access to environmental energy and controllability under periodic illumination, it enjoys broad prospects for application in soft robotics and opto-mechanical energy conversion systems. More new oscillating systems need to be excavated to meet the various application requirements. A spherical liquid crystal elastomer (LCE) balloon model driven by periodic illumination is proposed and its periodic beating is studied theoretically. Based on the existing dynamic LCE model and the ideal gas model, the governing equation of motion for the LCE balloon is established. The numerical calculations show that periodic illumination can cause periodic beating of the LCE balloon, and the beating period of the LCE balloon depends on the illumination period. For the maximum steady-state amplitude of the beating, there exists an optimum illumination period and illumination time rate. The optimal illumination period is proved to be equivalent to the natural period of balloon oscillation. The effect of system parameters on beating amplitude are also studied. The amplitude is mainly affected by light intensity, contraction coefficient, amount of gaseous substance, volume of LCE balloon, mass density, external pressure, and damping coefficient, but not the initial velocity. It is expected that the beating LCE balloon will be suitable for the design of light-powered machines including engines, prosthetic blood pumps, aircraft, and swimmers.

CaF2: A novel electrolyte for all solid-state electrochromic devices

The energy consumption in building ventilation, air, and heating conditioning systems, accounts for about 25% of the overall energy consumption in modern society. Therefore, cutting carbon emissions and reducing energy consumption is a growing priority in building construction. Electrochromic devices (ECDs) are considered to be a highly promising energy-saving technology, due to their simple structure, active control, and low energy input characteristics. At present, H+, OH- and Li+ are the main electrolyte ions used for ECDs. However, H+ and OH- based electrolytes have a high erosive effect on the material surface and have a relatively short lifetime. Li+-based electrolytes are limited due to their high cost and safety concerns. In this study, inspired by prior research on Ca2+ batteries and supercapacitors, CaF2 films were prepared by electron beam evaporation as a Ca2+-based electrolyte layer to construct ECDs. The structure, morphology, and optical properties of CaF2 films were characterized. ECDs with the structure of ITO (indium tin oxide) glass/WO3/CaF2/NiO/ITO show short switching times (22.8 s for the coloring process, 2.8 s for the bleaching process). Additionally, optical modulation of the ECDs is about 38.8% at 750 nm. These findings indicate that Ca2+ based ECDs have the potential to become a competitive and attractive choice for large-scale commercial smart windows.

Yaw compensation and yaw relaxation controls for active steering of railway wheelsets via electromechanical actuators

It is known that good curving performance and stability often have conflicting requirements given a passive yaw stiffness of the wheelset. Using an active steering system, however, has the potential to realize improved curving performance with a satisfactory running stability. Relatively simple active control solutions of yaw relaxation and yaw compensation are illustrated and compared in this paper. In both control solutions, only low-cost electromechanical actuators and load cells are adopted for low-frequency actuations. Associated with a prototype of the two-axle vehicle, the dynamic performances of yaw relaxation and yaw compensation controls for different yaw stiffness configurations are simulated. The homogenous simulation results demonstrate excellent dynamic performance in curve negotiation and stability with the active steering strategies adopted.

Robust and Intelligent Control for Single-stage Grid-Connected Modular Multilevel Converter in PV Applications

Renewable Energy Resources (RESs) are frequently interfaced to the loads/grid via the standard two/three-level inverters. These inverter circuits to comply with the utility regulations must use volumetric and cumbersome filtering arrangements. Therefore, this article advises the application of Modular Multilevel Converter (MMC) for interfacing RESs in stand-alone and/or grid-connected operating modes. The MMC offers high quality voltage/current/power waveforms without additional filtering requirements, which possibly reduce the size/cost of the interfacing circuits. A simple and innovative active and reactive power control is proposed to drive the proposed MMC such that PV arrays operate at Maximum Power Point (MPP) under different climatological operating conditions. The proposed active-reactive control is implemented via Proportional Integral (PI) controllers; their parameters are defined via constraint optimization. Genetic Algorithm (GA) is used in this research to configure the PIs of the main controller. The objective function was designed to increase the stability margins of the system while reducing the overshoot. The proposed MMC has an extra freedom degree of generating/absorbing reactive power. The static and dynamic performances of MMC are analyzed via MATLAB and its dynamic platform, Simulink. The results showed that the proposed MMC produced significantly lower Total Harmonic Distortion (THD) than the three-level inverters. The static performance of the MMC showed that the THD decreases significantly with the increase of the converter level/sub-module number. The results raveled the robustness and effectiveness of the proposed controller, such that the PV generator operates at MPP while introducing high quality power/voltage to the loads/grid.

Active Control of A Piston-Type Absorbing Wavemaker with Fully Reflective Structure

Multiple reflections of the waves between structure and wavemaker in hydraulic flumes could change the frequency content of the desired incident wave or result in resonance. A prominent approach to avoid multiple reflections is active control of the wavemaker. This paper proposes a simple and practical active control algorithm for piston-type wavemaker. The block diagram of the control system is presented in real time domain. It is shown that there is no need to use any transfer function or filter in the feedback and feed forward loops and the use of constant gains can yield acceptable results. In the operating frequency range (0.25–2 Hz), it is revealed that the proposed system is very effective at suppressing the excitation of resonant sloshing for regular wave. In the case of irregular waves, it is depicted that the experimental waves agree quite well with the desired wave elevation in frequency domain. In addition, comparison of the results obtained both with and without absorption discloses the good characteristics in time domain.

Solar Radiation Pressure Enabled Femtosatellite-Based Earth Remote Sensing

Recent developments in electronics have pushed miniaturized satellites to the femto-scale, with masses between 10 and 100 g. Although femtosatellites have been proven as a feasible concept, most designs are limited in mission capacity and lifetime due to the lack of environmental protection and onboard propellant. In this article, a novel concept for femtosatellites for earth remote sensing is proposed. In particular, a swarm of femtosatellites are used as elements of a sparse array in orbit to receive radar echoes. They also feature active orbit control enabled by solar radiation pressure to extend their lifetime. A simple active orbit control algorithm has been demonstrated. A mission concept based on a sun-synchronous circular orbit is proposed to maximize the benefit for both earth remote sensing and active orbit control. A synthetic aperture radar mission has been used to characterize their performance.

Magnetic Levitation Control Based on Flux Density and Current Measurement

This paper presents an active magnetic levitation application that exploits the measurement of coil current and flux density to determine the displacement of the mover. To this end, the nonlinear behavior of the plant and the physical sensing principle are modeled with a finite element approach at different air gap lengths and coil currents. A linear dynamic model is then obtained at the operating point as well as a linear relation for the displacement estimates. The effectiveness of the modeling approach and the performance of the sensing and control techniques are validated experimentally on an active magnetic levitation system. The results demonstrate that the solution is able to estimate the displacement of the mover with a relative error below 3% with respect to the nominal air gap. Additionally, this approach can be exploited for academic purposes and may serve as a reference to implement simple but accurate active magnetic levitation control using low-cost, off-the-shelf sensors.

A Simple Active Power Control for a High-Power Wireless Power Transmission System Considering Coil Misalignment and Its Design Method

A series–series compensated capacitors topology of the wireless power transmission (WPT) system has a characteristic of increasing active power at coil misalignment when controlled using the conventional secondary dc-link voltage control. This results in a larger total capacity of the primary and secondary sides’ converters. To cope with these problems, this paper proposes a simple constant secondary active power control method, where the secondary dc-link voltage is regulated according to the onboard active power rating and secondary current. The effectiveness of the control method is verified by 100 W experimental systems. The numerical simulation that considers the harmonic components is established to be compared and justified by the experimental results, which is then used to design the capacity of a 300 kW WPT system assuming actual railway vehicle application. By the proposed method, the design criteria of the rating voltage and current of the primary and secondary sides’ components can be determined.

A Simple Active and Reactive Power Control for Applications of Single-Phase Electric Springs

Aiming at effective power management in microgrids with high penetration of renewable energy sources (RESs), this paper proposes a simple power control for the so-called second-generation, single-phase electric springs (ES-2), which overcomes the shortcomings of the existing ES control methods. By the proposed control, the unpredictable power generated from RESs is divided into two parts, i.e., the one absorbed by the ES-2 that still varies and the other injected into the grid that is controllable by a simple and accurate signal manipulation that works both at steady-state and during RES transients. It is believed that such a control is suitable for the distributed power generation, especially at domestic homes. In this paper, the proposed control is supported by a theoretical background. Its effectiveness is at first validated by simulations and then by experiments. To this purpose, a typical RES application is considered, and an experimental setup is arranged, built up around an ES-2 implementing the proposed control. Testing of the setup is carried out in three steps and proves not only the smooth operation of the ES-2 itself, but also its capability in running the application properly.

Design, analysis, and control of a variable electromotive-force generator with an adjustable overlap between the rotor and the stator

A variable electromotive-force generator (VEG), which is a modified generator with an adjustable overlap between the rotor and the stator, is proposed to expand the operational range of a regular generator through a simple and robust active control strategy. It has a broad range of applications in hybrid vehicles, wind turbines, water turbines, and similar technologies. A mathematical model of the VEG is developed, and a novel prototype is designed and fabricated. The performance of the VEG with an active control system, which adjusts the overlap ratio based on the desired output power at different rotor speeds for a specific application, is theoretically and experimentally studied. The results show that reducing the overlap between the rotor and the stator of the generator results in reduced torque loss of the generator and an increased rotational speed of the generator rotor. A VEG can improve the fuel efficiency of hybrid vehicles; it can also expand operational ranges of wind turbines and water turbines and harness more power.

Hydrological Storage Length Scales Represented by Remote Sensing Estimates of Soil Moisture and Precipitation

AbstractThe soil water content profile is often well correlated with the soil moisture state near the surface. They share mutual information such that analysis of surface‐only soil moisture is, at times and in conjunction with precipitation information, reflective of deeper soil fluxes and dynamics. This study examines the characteristic length scale, or effective depth Δz, of a simple active hydrological control volume. The volume is described only by precipitation inputs and soil water dynamics evident in surface‐only soil moisture observations. To proceed, first an observation‐based technique is presented to estimate the soil moisture loss function based on analysis of soil moisture dry‐downs and its successive negative increments. Then, the length scale Δz is obtained via an optimization process wherein the root‐mean‐squared (RMS) differences between surface soil moisture observations and its predictions based on water balance are minimized. The process is entirely observation‐driven. The surface soil moisture estimates are obtained from the NASA Soil Moisture Active Passive (SMAP) mission and precipitation from the gauge‐corrected Climate Prediction Center daily global precipitation product. The length scale Δz exhibits a clear east‐west gradient across the contiguous United States (CONUS), such that large Δz depths (>200 mm) are estimated in wetter regions with larger mean precipitation. The median Δz across CONUS is 135 mm. The spatial variance of Δz is predominantly explained and influenced by precipitation characteristics. Soil properties, especially texture in the form of sand fraction, as well as the mean soil moisture state have a lesser influence on the length scale.

Active vibration control using mechanical and electrical analogies

Mechanical-electrical analogous circuit models are widely used in electromechanical system design as they represent the function of a coupled electrical and mechanical system using an equivalent electrical system. This research uses electrical circuits to establish a discussion of simple active vibration control principles using two scenarios: an active vibration isolation system and an active dynamic vibration absorber (DVA) using a voice coil motor (VCM) actuator. Active control laws such as gain scheduling are intuitively explained using circuit analysis techniques. Active vibration control approaches are typically constraint by electrical power requirements. The electrical analogous is a fast approach for specifying power requirements on the experimental test platform which is based on a vibration shaker that provides the based excitation required for the single Degree- of-Freedom (1DoF) vibration model under study.

Comparison of Advanced Control Techniques for Grid Side Converter of Doubly-Fed Induction Generator Back-to-Back Converters to Improve Power Quality Performance During Unbalanced Voltage Dips

A doubly-fed induction generator grid side converter is studied under voltage disturbances. During voltage dips, conventional current control techniques involving the decoupling of d – q axis in the synchronous reference frame (SRF) exhibits oscillations in the stiff dc link voltage, as well as in the active and reactive power outputs of the voltage source converter (VSC). To mitigate the oscillations, an advanced control technique called the sequence domain control (SDC) is evaluated. This approach implements individual controllers in the positive and negative sequence domains and demonstrates stabilization of the dc link voltage to a greater extent during a disturbance, but is more sluggish than the conventional control. An innovative control technique called direct power control (DPC) is also investigated. This control achieves active and reactive power stability with simple active and reactive power control variables replacing the traditional current control loops. The DPC technique is verified using a prototype in the laboratory. A modified DPC algorithm combining the benefits of DPC and SDC to eliminate the current harmonics created by DPC during system disturbances is introduced. The benefits of the proposed controllers are compared using a simulation of voltage dip on a VSC based on the IEC-61400-21 standard.

Active vibration control of structures using a semi-active dynamic absorber

This study is concerned with the theory and application of a tuneable dynamic absorber. The dynamic characteristics of the tuneable dynamic absorber are discussed in terms of the mass ratio, natural frequency of the main structure, natural frequency of a dynamic absorber and excitation frequency. We proposed a semi-active dynamic absorber with a natural frequency that can change through the use of repulsive forces produced by permanent magnets and electromagnetic forces induced by current flowing through a coil. A simple active control algorithm is implemented in the LabView software and the experimental results showed that when the proposed semi-active dynamic absorber is used with the active control algorithm, the vibrations of a structure can be more effectively suppressed than when a passive dynamic absorber with a fixed natural frequency is used.

Modifying the Resonances of a Xylophone Bar Using Active Control

A simple active control method is described which extends the possibilities of a xylophone bar. It allows the performer to modify the vibration of its structure, unlike post-processing effects involving loudspeakers. These variations change the characteristics of the partials radiated by the bar. The xylophone bar, made of composite material, is equipped with two actuators and one sensor in PVDF (polyvinylidene fluoride), the mass and stiffness of which do not modify the mechanical characteristics. A controller in a feedback loop is executed on a midrange digital signal processor. It is composed of a sum of second order band-pass filters. The selection of the controller coefficients relies on the measured transfer function between the input of the controller and the output of the sensor. First the active control method is designed to modify the resonance peaks of a simple model of a xylophone bar, whose transfer function is a superposition of three eigenmodes. Then it is applied to the real system. It is illustrated by increasing and reducing the amplitudes and/or frequencies of the first resonances, and by modifying the tuning of the xylophone bar.

Dynamics and Control of Lateral Tower Vibrations in Offshore Wind Turbines by Means of Active Generator Torque

Lateral tower vibrations of offshore wind turbines are normally lightly damped, and large amplitude vibrations induced by wind and wave loads in this direction may significantly shorten the fatigue life of the tower. This paper proposes the modeling and control of lateral tower vibrations in offshore wind turbines using active generator torque. To implement the active control algorithm, both the mechanical and power electronic aspects have been taken into consideration. A 13-degrees-of-freedom aeroelastic wind turbine model with generator and pitch controllers is derived using the Euler–Lagrangian approach. The model displays important features of wind turbines, such as mixed moving frame and fixed frame-defined degrees-of-freedom, couplings of the tower-blade-drivetrain vibrations, as well as aerodynamic damping present in different modes of motions. The load transfer mechanisms from the drivetrain and the generator to the nacelle are derived, and the interaction between the generator torque and the lateral tower vibration are presented in a generalized manner. A three-dimensional rotational sampled turbulence field is generated and applied to the rotor, and the tower is excited by a first order wave load in the lateral direction. Next, a simple active control algorithm is proposed based on active generator torques with feedback from the measured lateral tower vibrations. A full-scale power converter configuration with a cascaded loop control structure is also introduced to produce the feedback control torque in real time. Numerical simulations have been carried out using data calibrated to the referential 5-MW NREL (National Renewable Energy Laboratory) offshore wind turbine. Cases of drivetrains with a gearbox and direct drive to the generator are considered using the same time series for the wave and turbulence loadings. Results show that by using active generator torque control, lateral tower vibrations can be significantly mitigated for both gear-driven and direct-driven wind turbines, with modest influence on the smoothness of the power output from the generator.

Improving power-extraction efficiency of a flapping plate: From passive deformation to active control

A flapping plate flow energy harvester in a viscous uniform flow is simulated using a two-dimensional numerical approach. Our focus is to study the effects of flexibility and active control on the power-extraction capability of the flapping plate, and consequently to find a strategy to increase its power-extraction efficiency. Four typical cases with optimal kinematics predicted by previous studies are presented and discussed: a rigid plate, a flexible plate, a plate with a flexible leading segment and a rigid trailing segment, and a rigid plate with a simple active control on the leading segment. Our simulations show that with the kinematic parameters considered, the plate flexibility cannot significantly improve the power-extraction capability of the plate while the active control on the leading segment of the rigid plate increases the power coefficient by 11.3%. The analysis of flow fields shows that the changes in the power coefficient and drag force are related to the vortex structures and pressure distributions near the plate, as well as the projection area of the plate in the direction of the translational movement.

Modal Sensitivity and Selectivity of Small, Rectangle-Shaped Piezoelectric Transducers Used as Sensors and Actuators in Active Vibroacoustic Control Systems

The paper focuses on some issues regarding the utilization of small rectangle-shaped piezoelectric transducers as both sensors and actuators in active vibration and vibroacoustic control systems of beam, plate and panelled structures with arbitrary (non-homogeneous) boundary conditions. A new form of description of a simple proportional active control system with multiple independent feedback loops is proposed. The modal sensitivity functions of sensors and the modal selectivity functions of actuators are introduced to describe their ability for sensing and exciting specific structural modes of the structures. Basing on the assumed form of cost function and the derived equations of control system the influence of the modal characteristics of transducers on the stability of the system and on the performance of the active control is analyzed. The results of analytical solutions and numerical simulations are compared with the results of the experiments carried out on various beam and plate structures made up of aluminium or composite materials including the actual materials used in aviation, proving usefulness of the presented approach.