Disturbance Forces Research Articles

Robust Discrete-Time Lateral Control of Racecars by Unknown Input Observers

This brief addresses the robust lateral control problem for self-driving racecars. It proposes a discrete-time estimation and control solution consisting of a delayed unknown input-state observer (UIO) and a robust tracking controller. Based on a nominal vehicle model, describing its motion with respect to a generic desired trajectory and requiring no information about the surrounding environment, the observer reconstructs the total force disturbance signal, resulting from imperfect knowledge of the time-varying tire-road interface characteristics, presence of other vehicles nearby, wind gusts, and other model uncertainty. Then, the controller actively compensates the estimated force and asymptotically steers the tracking error to zero. The brief also presents a closed-loop stability proof of the method, ensuring perfect asymptotic estimation and tracking by the controlled vehicle. The proposed solution advantageously needs no a-priori information about the total disturbance boundedness, additional variables to model uncertainty, or observer parameters to be tuned. Its effectiveness and superiority to existing methods are studied in theory and shown in simulations where a full racecar model, based on the vehicle dynamics blockset, is required to track aggressive maneuvers. Through a faster and more accurate disturbance estimation, the solution robustly ensures better dynamic responses even with measurement noise.

Quasi-static balancing for biped robot to perform extreme postures using ducted-fan propulsion system

Quasi-static balancing is important for enabling humanoid robots to move through extremely rugged terrain, e.g., stepping over a ditch whose width exceeds the robot’s leg length. In this study, to overcome such challenges, an innovative solution was developed, in which external thrust is utilized to maintain the robot’s balance. Initially, a model of the robot’s balance was established for analyzing the factors affecting the balance and the means to maintain it. Subsequently, a new controller combining a thrust controller and a center-of-mass controller was developed to compensate for errors in the thrust output and mass distribution. Finally, a new motion-planning method based on line search regression (LSR) and grid search optimization (GSO) was developed. A series of experiments were conducted using a prototype robot (Jet-HR3), including an error compensation test, an external force disturbance test, a comprehensive motion test, and an active sliding steering test. The results indicated the effectiveness and efficiency of the proposed method. The robot successfully crossed a ditch 695 mm wide, i.e., 147% of the robot’s leg length.

Reducing Oscillations in Suspension of Mine Monorail Track

Purpose: The goal of this work is to reduce the effect of dynamic loads on the mine timbering through the use of the elastic devices contained in the monorail suspension and to justify their parameters. Methods and materials: The article considers the developed mathematical model of vertical oscillations of the monorail track, which allows setting the interconnection between the rolling stock parameters and dynamic loads in the suspension. At vertical oscillations of the monorail and under the effect of harmonic disturbing force caused by the movement of the suspension, the system of the monorail suspension can be represented in the form of a dual-mass system. Results: As a result, the equations for oscillation amplitudes of the monorail elements were obtained and damping coefficient of suspension was defined. The obtained results suggest setting reasonable parameters of the monorail fastening, which offers the possibility to decrease dynamic loads occurring during the operation of the mine suspended monorail tracks. The proposed monorail suspension makes it possible to reduce the dynamic loads formed during the movement of the rolling stock by 30–40% and can be used to modernize existing mine suspended monorails. Discussion: Analysis of the obtained results shows that in order to reduce the vibration amplitudes of a suspended monorail mine, it is appropriate to use suspension systems for rolling stock and a monorail track, consisting of elastic elements. The parameters required for this can be determined using the proposed method, and required rigidity of the monorail track is provided by embedding elastic supports into its suspension system. Conclusions: The obtained results allow setting reasonable parameters of the monorail fastening of the mine suspended monorail tracks. The proposed monorail suspension makes it possible to minimize the dynamic loads formed during the movement of rolling stock and can be used to modernize existing mine suspension monorails.

Disturbance Observer based Backstepping Control for Electro-hydraulic Position Servo System of the Projectile Coordination Arm

Due to the existence of unmodeled friction and unknown load disturbance, the position tracking control of electro-hydraulic position servo system of projectile coordination arm becomes an important problem to be solved urgently. In this paper, a dynamic surface backstepping control strategy is proposed based on the disturbance observer(DOB). To be specific, the disturbance observer is applied to estimate the unknown disturbance force, and the backstepping controller realizes the position tracking control. In order to improve the position tracking performance, The estimated value of the observer output is brought into the backstepping controller to realize the model compensation of the disturbance. Meanwhile, the dynamic surface method is utilized to handle the differential explosion problem in the backstepping method. The global stability of the closed-loop system is verified by Lyapunov stability theory. The co-simulation results show that the proposed method can effectively compensate the unknown disturbance in the electro-hydraulic position servo system, and has better tracking performance and strong robustness.

ASSESSMENT OF THE STABILITY OF MOTION OF A WHEEL SEMI-TRACK UNIT

The paper analyzes the influence of the geometric parameters of the semi-trailer unit on the stability of its movement. A mathematical model of the dynamics of the cultivator unit under the influence of disturbing forces is developed. The analysis of research results shows that in the process of movement, the wheeled semi-trailer unit is subjected to transverse forces, which arise as a result of the unevenness of the traction resistance of the side and rear beams. The main vector and the main moment cause the unit to deviate from the rectilinear movement. The differential equations obtained in the work make it possible to determine the values of the lead angles, their components, and the speed at which the lead of the unit will be the smallest. Based on the dependence of the angle of departure of the unit on the disturbing forces and speed of movement, the optimal location of the side bars of the semi-trailer unit on the tractor frame was found.

Adaptive charge control for the space inertial sensor

Inertial sensors are key components of gravitational wave observations and Earth geodesy missions. An inertial sensor includes an isolated free-floating test mass (TM) surrounded by capacitive electrodes and a housing frame (EH) to perform the relative-position measurement and control the TM in six degrees of freedom. Owing to galactic cosmic rays and solar energetic particles, many additional accelerations are introduced through the Coulomb interaction between charged TMs and their surrounding conducting surfaces. Thus, the TM charge control is critical in space-based missions. A contact-free and ultraviolet light-based charge management system (CMS) was developed to reduce charge-induced noises acting on the TMs and minimize force disturbances that can perturb measurements or interrupt science tasks. However, the operating environment for space charge control is full of uncertainties and disturbances. Physical parameters in the discharging process are rarely measured and will vary owing to changes in solar activity, temperature, and so on. The unpredictability and variability of these parameters affects the CMS performance in long-term space missions and must be evaluated or eliminated. This paper presents a simplified physical model for the discharge process based on electron exchange between the TM and the opposing EH. Subsequently, a model reference adaptive control (MRAC) is proposed for the CMS with parametric uncertainties to maintain the TM charge below a certain level and improve its robustness. The simulation results show that the MRAC can automatically adjust control parameters to eliminate the effect of the variability of the aforementioned physical parameters, and the control precision can reach 0.1 mV under uncertainties, which is superior to that of a classic proportional–integral–derivative controller. This study demonstrated the effects of adaptive charge control and its potential for actual applications.

State Observers and Run-Out Reduction for Magnetically Levitated Motor Systems

Magnetically levitated motor systems create opportunities for new applications of electromechanical power conversion where high-speed and contact-free operation are required. These systems require position sensors and control algorithms for stable levitation which often require filters to reduce feedback noise. Noisy position feedback creates challenges for high-bandwidth estimation of velocity and disturbance force; however, these unmeasured states can be helpful for high-performance control algorithms. This common problem in drives for electric motors has been solved using the Luenberger-style motion state observer. This article investigates the applicability of the observer to digitally-controlled magnetically levitated systems. First, the observer's embedded plant model is derived for discrete-time implementation. Then, it is shown that the most advantageous use-case of the observer is different for magnetically levitated systems versus rotary motor systems. Unlike motor systems, the zero-lag filtering property of observers is minimally useful, while the ability to estimate and reject disturbances yields significant performance improvements for applications that care about run-out. Comprehensive experimental results are provided on a prototype bearingless motor which validate the observer's performance versus frequency and its ability to estimate disturbance forces for use in reducing the rotor run-out. Experimental results achieve over 10× run-out reduction at low-medium speeds while also reducing control current by 50%.

Precise Position Control Based on Resonant Controller and Second-Order Sliding Mode Observer for PMSM-Driven Feed Servo System

Precise position control and smooth feed speed are important research areas for permanent magnet synchronous motor (PMSM) driven computerized numerical control (CNC) servo feed systems, but it suffers from aperiodic disturbances caused by unmodeled dynamics, system parameter perturbations, variable cutting force and periodic disturbances caused by the current sampling error, aperiodic disturbances, and periodic disturbances that reduce the positional accuracy of the CNC feed servo. To address the problem, a control scheme is proposed for the position controller to suppress the disturbances. In the control scheme, the second-order sliding mode disturbance observer (SSMDO) is proposed to estimate and compensate for the aperiodic disturbances, and the resonant controller (RC) with phase adjustable is designed to suppress the periodic disturbances. The stability and antidisturbance capability of the studied scheme are analyzed systematically, and the flow of controller design and parameter tuning is presented considering the overall system. The proposed RC combined with SSMDO (RC-SSMDO) scheme can effectively alleviate the position tracking error and feed steady-state speed ripple, which is suitable for the actual working conditions of the CNC feed servo system. Experiment results confirm the validity of the proposed scheme.

Подход к снижению виброактивности малых космических аппаратов

Flawless spacecraft operation and successful implementtation of their research in orbit mainly depend on technical and operational characteristics of the spacecraft orientation and stabilization control systems in space relative to the base frame of reference axes achieved through stabilizing properties of certain external and internal perturbations. The research was aimed at determining static and dynamic imbalances and analyzed the levels of influence of forces and moments created by non-contact electric motor-flywheel operating at the various rotor speeds. In order to reduce the static and dynamic imbalance of the non-contact electric motor-flywheel obtained as a result of ongoing experimental studies, it was proposed to introduce a vibration isolator with natural frequency significantly lower than that in the conventional systems in order to statically hold the non-contact electric motor-flywheel during ground and flight operation. The vibration isolator should have small mass and rigidity, as well as a wide range of operating temperatures, etc. Depending on the orbit altitude, the moments of external disturbing forces acting on the Iskra-5 spacecraft were determined. Electric DC motor-flywheels of various types were analyzed. It was shown that introduction of the non-contact electric motor-flywheel as the executive element of the orientation and stabilization control systems on small spacecraft improved the orientation accuracy. Ways to reduce the effect of vibration disturbances on the spacecraft structure from the non-contact electric motor-flywheel were considered

Self-Docking Characteristics and Sliding Mode Control on Space Electromagnetic Docking Mechanism

Electromagnetic docking technology can realize the flexible docking and safe separation of spacecraft, and presents broad application prospects. However, an electromagnetic force with nonlinearity and uncertainty properties increases the difficulties of the electromagnetic docking control. In this work, the magnetic dipole far-field model of a single coil has been established by simplifying the electromagnetic docking device. Afterward, the electromagnetic force and electromagnetic torque models were obtained during space electromagnetic docking. The space electromagnetic docking dynamics model was established by analyzing the influences of disturbance force and disturbance torque caused by a geomagnetic field. According to the one-dimensional docking reference trajectory, the sliding mode variable structure controllers based on exponential reaching law were proposed and verified. The quasi-sliding mode control method has been adopted to solve the chattering problem in sliding mode variable structure control. The simulation results show that it is necessary to design and add an electromagnetic controller to achieve flexible docking. The sliding mode variable structure controller based on quasi sliding mode can realize one-dimensional electromagnetic flexible docking, and have made good tracking effect on the reference trajectory. Compared with the control method based on exponential reaching law, it can reduce the chattering phenomenon in the control process. The sliding mode variable structure control strategy based on quasi sliding mode presented good robustness. Therefore, it can provide theoretical guidance and control reference for the flexible docking process between electromagnetic satellites.

A Disturbance Force Compensation Framework for a Magnetic Suspension Balance System

The research on the dynamic characteristics of vehicles requires wind tunnel tests. The natural mass frequency of the support mechanism and the interference of the support mechanism on the flow field will greatly reduce the repeatability and accuracy of the experimental results. The magnetic suspension and balance system (MSBS) uses non-contact electromagnetic force instead of mechanical support to eliminate the support mechanism’s interference with the test results. The MSBS needs to actively adjust the electromagnetic force to control the position of the tested model. At present, its control strategy is PID control. However, when the wind tunnel is opened, there will be large aerodynamic loads, leading to large changes in displacement. We propose a disturbance compensation control algorithm framework that can quickly estimate the external force disturbance and quickly compensate it to the control loop, reduce the influence of the disturbance on the control system, and provide stability and accuracy of displacement control.

UKF-Based Observer Design for the Electric Brake Booster in Situations of Disturbance

The motor-driven electric brake booster (E-Booster) can replace the traditional vacuum booster to realize the braking power assistance and active braking. Independent of extra sensors, this paper proposes a full-state observer for E-Booster based on Unscented Kalman Filter (UKF) in the presence of a driver’s input force disturbance. The electro-hydraulic system is first modeled, which includes a nonlinear hydraulic model and the reaction disk’s rubber model. The pre-compression is designed to produce linear power assistance based on the properties of rubber material. With the existence of the disturbance, the linear quadratic regulator (LQR) algorithm is used to track the pre-compression of the reaction disk so that E-Booster is developed into a closed-loop system to achieve power assistance. The proposed UKF observer can online estimate the states considering the controller input and disturbance input. To reduce the process error, the hydraulic p-V characteristic is fitted using the recursive least squares (RLS) method before observation. Furthermore, the simulation test and vehicle tests are performed to validate the observation effect. In the closed-loop test, UKF decreases residual error by 16% when compared to the typical Extended Kalman Filter (EKF). The simulation results remain consistent with the experimental results, demonstrating the effectiveness of the proposed method.

Autonomous collision avoidance system in a multi-ship environment based on proximal policy optimization method

To address the challenge of local path planning in a complex, dynamic environment with multiple ships, we built an autonomous collision avoidance system based on deep reinforcement learning in open water. The system switches between path-tracking and collision avoidance modes in real time, during which any collision danger is perceived through encounter identification and risk calculation. Subsequently, the proximal policy optimization method is applied to design the state space, action space, and reward functions. Decision-making offers advantages in terms of continuous action space, perception of global navigation information, compliance with the International Regulations for Preventing Collisions at Sea (COLREGs), and smooth maneuverings. Simulations are performed under multi-ship encounter conditions, considering the ship hydrodynamic model, environmental disturbance force model, COLREGs, and good seamanship. The results indicate the effectiveness and ability of the proposed system to take appropriate action when faced with dangerous situations under rule constraints and diverse scenarios.

Системный подход в оценке динамических состояний технических объектов: элементы концепции динамических инвариантов

The scientific and methodological base is being developed within the framework of systems theory and system analysis in application to the tasks of assessment, control and formation of dynamic states of technical objects, the design schemes of which are mechanical oscillatory systems with concentrated parameters. In the context of the fundamental problems of the theory of system studies of forced movements under deterministic disturbances there are considered the problems, whose solutions are aimed at developing a methodological approach to assessing the dynamic states of technical objects operating under coherent vibration loads. The purpose of the study is to develop a method for evaluating, controlling and forming dynamic states of the objects under harmonic force loads. It is assumed that mechanical oscillatory systems formed by a solid body performing small steady-state oscillations relative to the position of the static equilibrium can be used as calculation schemes of the technical objects. To construct mathematical models, Lagrange formalism, Laplace integral transformations taking into account zero conditions and structural methods are used, which make it possible to consider mechanical oscillatory systems as dynamically equivalent structural schemes of automatic control systems. The dynamic state of an object is assessed by using a transfer function, which in the physical sense represents the interpretation of a dynamic compliance. The amplitude-frequency characteristics used to assess the dynamic state of the object present a parametric family, for which the first parameter is the coefficient of connectivity of external force disturbances, and the second parameter is the coordinate of the point for which the dynamic accuracy is defined. An infinite family of amplitude-frequency characteristics is regularized due to the introduction of dynamic invariants, which can be considered as generalized dynamic states of mechanical oscillatory systems. To determine the dynamic invariants of a family of amplitude-frequency characteristics, taking into account two parameters, a map of dynamic invariants is constructed, which divides the plane of parameters into disjoint sets using boundaries. A theorem is proved to determine the explicit analytic expressions of these boundaries.

Markovian-Jump Reinforcement Learning for Autonomous Underwater Vehicles under Disturbances with Abrupt Changes

This paper studies the position regulation problems of an Autonomous Underwater Vehicle (AUV) subject to external disturbances that may have abrupt variations due to some events, e.g., water flow hitting nearby underwater structures. The disturbing forces may frequently exceed the actuator capacities, necessitating a constrained optimization of control inputs over a future time horizon. However, the AUV dynamics and the parameters of the disturbance models are unknown. Estimating the Markovian processes of the disturbances is challenging since it is entangled with uncertainties from AUV dynamics. As opposed to a single-Markovian description, this paper formulates the disturbed AUV as an unknown Markovian-Jump Linear System (MJLS) by augmenting the AUV state with the unknown disturbance state. Based on an observer network and an embedded solver, this paper proposes a reinforcement learning approach, Disturbance-Attenuation-net (MDA–net), for attenuating Markovian-jump disturbances and stabilizing the disturbed AUV. MDA–net is trained based on the sensitivity analysis of the optimality conditions and is able to estimate the disturbance and its transition dynamics based on observations of AUV states and control inputs online. Extensive numerical simulations of position regulation problems and preliminary experiments in a tank testbed have shown that the proposed MDA–net outperforms the existing DOB–net and a classical approach, Robust Integral of Sign of Error (RISE).

From basalt to biosphere: Early non-vent community succession on the erupting Vailulu’u deep seamount

Volcanic eruptions provide rare opportunities to witness the biological recolonization of areas covered by new lava flows by effectively resetting the ecological succession clock to zero. The role of submarine volcanic eruptions as disturbance events and the resulting patterns of ecological succession have mainly been studied in hydrothermal vent ecosystems. However, the effects of submarine volcanic eruptions as disturbance forces have rarely been studied in non-vent ecosystems, particularly on seamounts. Here, we document the early stages of ecological succession of non-vent benthic communities inhabiting the summit caldera of the active Vailulu’u submarine volcano in American Samoa. Sitting above the Samoan volcanic hotspot, Vailulu’u is the youngest volcano of the Samoan chain. Repeated mapping of Vailulu’u in 1999, 2005, 2006, 2012, and 2017 revealed the progressive growth of a new cone named Nafanua. In 18 years, the cone grew >300 meters in height from a starting depth of ~1000 meters below sea level (mbsl). The differential analyses of this time-series bathymetry dataset enabled the assignment of maximum age ranges to different portions of the new cone. High-definition ROV imagery collected in 2017 revealed patterns of community structuring consistent with ecological succession: newly erupted seafloor contained a subset of the benthic species found on older seafloor. Furthermore, individual animal sizes in the younger seafloor zones were smaller than in the older zones. This unusual interdisciplinary combination of geological and biological observations provides constraints on which deep-sea animals recolonize new seafloor after a major disturbance event and how quickly. This knowledge could be applied to identify signs and states of recovery from anthropogenic disturbances by a deep seamount ecosystem.

Passivity‐based control of nonlinear active dynamic vibration absorber

AbstractIn this article, a nonlinear active dynamic vibration absorber based on passivity‐based energy shaping control is proposed. Using the proposed method, the vibrations that are excited by force and velocity disturbances simultaneously can be controlled. The control law only uses the relative displacement and velocity of the vibration system, which can be easily measured by sensors. The numerical solutions to the partial differential equations are not required in our proposed method. The main idea of the controller's parameters design is to convert a plant system with a nonlinear dynamic vibration absorber into a desired system with multiple virtual skyhook dampers. We also derive the parameters' selection guidelines for the proposed controller. The global asymptotical stability is guaranteed through passivity‐based control theory, although the parameter design is based on linearization. We verify the effectiveness of the proposed controller by some simulations on a cart‐pendulum system.

Prediction method of soil horizontal displacement caused by non-uniform distribution of disturbance force in shield construction

Based on the Mindlin solution, this paper considers the influence of factors such as the non-uniform distribution of additional thrust of the cutter head influenced by lateral earth pressure in shield excavation, the non-uniform distribution of friction of shield shell influenced by soil softening and slurry spreading, and the non-uniform distribution of grouting pressure influenced by slurry spreading on the horizontal displacement of soil. The existing prediction formula is revised and verified by engineering examples. It is found that: affected by the shield construction disturbance force, the horizontal displacement behind the excavation surface is larger than that in front of the excavation surface, and the peak value of the horizontal displacement appears around the tunnel axis; through the verification of engineering case, when calculating the horizontal displacement in front of the excavation surface, the calculation results of both the modified formula and the original formula are in good agreement with the measured values, which can reflect the change trend of the measured horizontal displacement; when calculating the horizontal displacement behind the excavation surface, the calculation result of the existing formula has a great error due to the assumption of uniform distribution of disturbance force, which is different from the law of the measured result; the calculation result of the modified prediction formula is obviously in better agreement with the measured deformation value, and the error is smaller, which is more in line with the engineering reality.

Nonlinear tracking differentiator and PD controller for piezoelectric actuators in a robotic hand

This article deals with the modeling and control design for piezoelectric actuators of a micro-robotic system. Piezoelectric actuators generally exhibit complex and nonlinear behavior due to their inherent asymmetric hysteresis phenomenon, creep nonlinearity, and oscillatory characteristics. Moreover, these actuators are subject to an external disturbance force caused by the interaction with the manipulated objects. It has been shown in practice that these characteristics have a negative and significant impact on the performance of piezoelectric actuators, which increases the difficulty of their control. The main objective of this paper is to account simultaneously for all undesired and complex characteristics outlined above. To this end, our main idea is to lump the hysteresis and creep phenomena, as well as the disturbing manipulation force together as one total disturbance term. The total disturbance is first estimated in real-time via a nonlinear tracking differentiator, then feedback control law is designed to compensate for the disturbance and achieve a good transient profile. To validate and demonstrate the efficacy of the proposed approach, experiments are conducted, and results obtained are discussed.

Disturbance of intermolecular forces: eutectics as a new tool for the preparation of vapor-phase deposition precursors.

The volatile bis(tert-butylimido)dichloromolybdenum(VI) compounds, (tBuN)2MoCl2·dad (dad = 1,4-di-tert-butyl-1,3-diazabutadiene) (1) and [(tBuN)2MoCl(μ-Cl)·(tBuNH2)]2 (2), form a eutectic, with a two to one composition (χ2 = 0.33). A decrease of 40 °C in the melting temperature has been observed between the eutectic mixture and the pure compounds. We have isolated a co-crystal of (tBuN)2MoCl2·dme (dme = 1,2-dimethoxyethane) (3) and 2, also in a two to one ratio, which serves as a structural model for such mixtures. The lower melting point of carefully chosen eutectic mixtures can offer more consistent precursor delivery in deposition processes.