External Disturbance Forces Research Articles

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.

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.

USING HYDRAULIC PARAMETRIC VIBRATION EXCITER IN AGRICULTURAL ENGINEERING

Vibration technology is widely used in mechanical engineering, construction, road building and different sectors of the manufacturing. In agriculture, it is used for dosing feed, cleaning and sorting seeds, digging up root crops, planting potatoes, and transporting bulk materials. Vibrations make the mechanical system more stable in relation to external force disturbances and do not change the technological properties of materials during its movement along the working surfaces. Also, the material passing through the vibration zone is not damaged. A wide range of frequency and amplitude of vibrations provides the possibility of vibration regime varying, and the characteristics of the movement of agricultural plant material on the vibrating working bodies. The analysis of possibility of application of vibrating hydraulic drives as elements of transmission of movement to working bodies of agricultural machines is executed. A historical excursion was conducted and the first mentions of the use of hydraulic drives were pointed out. The estimation of technological processes in agricultural production where it is expedient and possible to use vibration and vibrating drives is made. At the present stage of development of agricultural engineering, using vibrating hydraulic drive is accorded to the basic trends of agriculture machinery development. The stand for conduction of studies of amplitude-frequency characteristics of the vibrating drive with regulated perturbations is offered. A mathematical model is presented, which generally describes the course of the vibration process and estimates the stiffness of the mechanical system. The hydraulic parametric vibration exciter is recommended to use for studying and determination the conditions for the occurrence of parametric vibrations in working body of agricultural machines. Also, using a hydraulic drive makes it possible to simplify the kinematics, reduce metal consumption, increase accuracy, reliability and level of automation of working bodies of agricultural machines.

Adaptive ankle impedance control for bipedal robotic upright balance

AbstractUpright balance control is a fundamental skill of bipedal robots for various tasks that are usually performed by human beings. Conventional robotic control is often realized by developing accurate dynamic models using a series of fixed torque‐ankle states, but their success is subject to accurate physical and kinematic models. This can be particularly challenging when external disturbing forces present, but this is common in unstructured robotic working environments, leading to ineffective robotic control. To address such limitation, this paper presents an adaptive ankle impedance control method with the support of the advances of adaptive fuzzy inference systems, by which the desired ankle torques are generated in real time to adaptively meet the dynamic control requirement. In particular, the control method is initialised with specific external disturbing forces first representing a general situation, which then evolves whilst performing in a real‐world working environment by acting on the feedback from the control system. This is implemented by initialising a rule base for a typical situation, and then allowing the rule base to evolve to specific robotic working environments. This closed loop feedback and action mechanism timely and effectively configures the control system to meet the dynamic control requirements. The proposed control method was applied to a bipedal robot on a moving vehicle for system validation and evaluation, with robotic loads ranging from 0 to 1.65 kg and external disturbances in terms of vehicle acceleration ranging from 0.5 to 1.5 , leading to robotic swing angles up to and anti‐disturbance timespans up to 8.5 s. These experimental results demonstrate the power of the proposed upright balance control method in improving the robustness, and thus applicability, of bipedal robots.

A technology of structural mathematical modelling for engineering objects under vibrational loading: Interaction forms and dynamic invariants

We present a system approach to evaluating dynamic forms of interactions between elements of mechanical oscillatory systems, which can be applied as design diagrams of engineering objects used for transport or technology purposes. The approach of structural mathematical modelling was used, where a mechanical oscillatory system (with the finite number of freedom degrees) is compared to the block diagram of a dynamically equivalent automatic control system. The research object was represented by a family of mechanical oscillatory systems with the finite number of freedom degrees under the action of connected force harmonic disturbances. The main research focus was on a set of dynamic states of an engineering object, which are caused by the application of common-phase external force disturbances at various frequencies and characterised by a connection coefficient. For a family of chain mechanical oscillatory systems with two degrees of freedom, a method for interpreting a set of dynamic states in the form of oriented graphs was developed. A method for constructing a population graph of dynamic states based on the frequency response of system transfer functions was developed. Within the framework of the developed interpretation, the graphs of dynamic states can be considered as peculiar invariants that persist on sets of mechanical oscillatory system parameters. Using the methodology of structural mathematical modelling, a concept of dynamic invariants was developed, according to which the totality of dynamic invariants can be used to provide a general evaluation of the variety of dynamic states and forms of dynamic interactions between the elements of mechanical oscillatory systems. The proposed concept of dynamic invariants extends the methodology of structural mathematical modelling in relation to the problems of system analysis for ensuring the safety of engineering objects for transport and technology purposes under the conditions of connected vibrational loading.

Active vibration damping for manufacturing machines using additional cable mechanisms: conceptual design

Undesired vibration is a common issue when dealing with manufacturing machines, especially when dealing with thin structures. To decrease the external disturbance sensitivity of such systems, represented for example by machine tool quill, the auxiliary cable structure is attached to the system. The auxiliary cable structure increases system damping and decreases undesired structure vibrations by the passive or active way, depending on the deployment and purpose. In this article, cables are attached to the end-effector to suppress undesired vibrations and related experimental stand is prepared. Experimental stand parameters are identified using least square method. The control strategy using pole placement is presented and its suitability is verified using external disturbance force. The frequency analysis shows the promising behaviour of controlled cable structure attached to the original system as well as the experimental results.

Virtual Neuromuscular Control for Robotic Ankle Exoskeleton Standing Balance

The exoskeleton is often regarded as a tool for rehabilitation and assistance of human movement. The control schemes were conventionally implemented by developing accurate physical and kinematic models, which often lack robustness to external variational disturbing forces. This paper presents a virtual neuromuscular control for robotic ankle exoskeleton standing balance. The robustness of the proposed method was improved by applying a specific virtual neuromuscular model to estimate the desired ankle torques for ankle exoskeleton standing balance control. In specialty, the proposed control method has two key components, including musculoskeletal mechanics and neural control. A simple version of the ankle exoskeleton was designed, and three sets of comparative experiments were carried out. The experimentation results demonstrated that the proposed virtual neuromuscular control could effectively reduce the wearer’s lower limb muscle activation, and improve the robustness of the different external disturbances.

Data-driven model-free adaptive sliding mode control for electromagnetic linear actuator

A data-driven model-free adaptive sliding mode control (MFASMC) method is proposed to tackle the problems of inaccurate model and time-varying parameters of a micro electro-magnetic linear actuator system, considering the dependence of existing model-based control methods on the system dynamics model and the impact of unmodeled dynamics on the control performance. Firstly, the pseudo-gradient concept in the model-free adaptive control (MFAC) framework is used to transform the electromagnetic linear actuator dynamics model, which is difficult to obtain parameters accurately, into a full-format dynamic linearized data model, the dependence of the controller on the electromagnetic linear actuator model is reduced. To compensate for the effects of unknown perturbations, an improved discrete sliding mode exponential convergence law is introduced to derive a new composite control algorithm based on the pseudo partial derivative estimator, which improves the robustness of the control system. Then, the convergence of the control error and the stability of the system are demonstrated by theoretical analysis. The results show that the proposed MFASMC reduces the 10 mm step response time of the electromagnetic linear actuator by 46.3% and 25.3% compared with proportional-integral-derivative control (PID) and MFAC. The phase lag time and root-mean-square error of MFASMC under sinusoidal conditions are 0.8 ms, 0.178 mm respectively, and the steady-state error does not exceed 0.05 mm. The experimental and simulation results keep the error within 5%, the proposed control algorithm has good trajectory tracking response speed and control accuracy, and has good robustness to system uncertainty and external force disturbance.

External force estimation and disturbance rejection for Micro Aerial Vehicles

To deploy Micro Aerial Vehicles (MAVs) in real-world applications, there is a need for online methods to cope with uncertainties in localization and external disturbances. In this article, we propose a set of novel real-time embedded Nonlinear Model Predictive Control (NMPC) and Nonlinear Moving Horizon Estimation (NMHE) modules for MAV based external disturbance rejection. The NMPC and NMHE are based on the dynamic model of the MAV, thus, avoiding the need for system identification and creating specific aerodynamic models, a benefit that results in a generic solution capable of being independent of the type of the MAVs. As it will be presented, the NMHE estimates the external forces, while the NMPC generates thrust and attitude commands for the low-level controller to compensate the various disturbances that could occur, such as wind gusts, tethered payload, and varying center of gravity. The proposed method is evaluated extensively in multiple experimental results that include the scenarios of position hold against an actuating wind-wall, adding payload, and changing the MAV’s arm configurations.

Enhancement of structural seismic performance of low-rise buildings using displacement-dependent tuned mass damper

Tuned mass dampers are used to reduce vibrations of high-rise buildings due to wind disturbance. Specifically, the displacement-dependent tuned mass damper (DTMD) is an effective vibration energy absorber that is connected to a primary structure to reduce the vibration response of the structure under harmonic and external force disturbances. Its natural frequency is adjusted to be close to the fundamental vibration frequency of the primary structure; this leads to an antiphase resonance that dissipates the external force-induced disturbance energy. Several studies have proposed different optimization design objective functions and developed active and semi-active tuned mass damping systems to improve control efficiency significantly. Therefore, in this study, a reasonable mass and an objective function were considered using a simplified degree-of-freedom structural model (DTMD and primary structure) to derive an optimized design method and evaluate the feasibility of structural reinforcement through numerical analysis of the tuned mass damper and shaking table tests. The fundamental retrofit design process used in this study can facilitate the development of a specialized tuning mass damper that can be used in practical engineering applications, such as improving the seismic resistance of ancient and low-rise buildings.

Smooth second-order sliding mode control for fully actuated multirotor aerial vehicles

The present paper is concerned with the robust and smooth attitude-position tracking control of fully actuated multirotor aerial vehicles equipped with fixed rotors and subject to matched model uncertainties and disturbances. The vehicle coupled dynamic equations representing the translational and rotational motions are thoroughly derived using the multibody approach, considering the external torque and force disturbances as well as the uncertainties in the inertia parameters of the airframe and the rotors. From this model, it is shown that the overall disturbances and uncertainties can be lumped into an additive-matched plant-model discrepancy. Then, based on a geometrically consistent description of the control error in SE(3), a novel joint geometric attitude-position control law is designed using a multi-input smooth second-order sliding mode strategy. The latter uses a high-order sliding mode disturbance observer to guarantee the overall system robustness. The second-order sliding mode is proved to exist using vector-field homogeneity, and the tracking error is shown to exponentially converge to the origin. The method is extensively evaluated via numerical simulations using a fully actuated hexacopter with tilted rotors, showing advantages with respect to state-of-the-art alternatives.

Online Gain Adaptation of Whole-Body Control for Legged Robots with Unknown Disturbances.

This paper proposes an online gain adaptation approach to enhance the robustness of whole-body control (WBC) framework for legged robots under unknown external force disturbances. Without properly accounting for external forces, the closed-loop control system incorporating WBC may become unstable, and therefore the desired task goals may not be achievable. To study the effects of external disturbances, we analyze the behavior of our current WBC framework via the use of both full-body and centroidal dynamics. In turn, we propose a way to adapt feedback gains for stabilizing the controlled system automatically. Based on model approximations and stability theory, we propose three conditions to ensure that the adjusted gains are suitable for stabilizing a robot under WBC. The proposed approach has four contributions. We make it possible to estimate the unknown disturbances without force/torque sensors. We then compute adaptive gains based on theoretic stability analysis incorporating the unknown forces at the joint actuation level. We demonstrate that the proposed method reduces task tracking errors under the effect of external forces on the robot. In addition, the proposed method is easy-to-use without further modifications of the controllers and task specifications. The resulting gain adaptation process is able to run in real-time. Finally, we verify the effectiveness of our method both in simulations and experiments using the bipedal robot Draco2 and the humanoid robot Valkyrie.

PID Tuning using Cross-Entropy Deep Learning: a Lyapunov Stability Analysis

Underwater Unmanned Vehicles (UUVs) have to constantly compensate for the external disturbing forces acting on their body. Adaptive Control theory is commonly used there to grant the control law some flexibility in its response to process variation. Today, learning-based (LB) adaptive methods are leading the field where model-based control structures are combined with deep model-free learning algorithms. This work proposes experiments and metrics to empirically study the stability of such a controller. We perform this stability analysis on a LB adaptive control system whose adaptive parameters are determined using a Cross-Entropy Deep Learning method.

Dynamic walking characteristics and control of four-wheel mobile robot on ultra-high voltage multi-split transmission line

High-voltage lines are an important channel for power transmission, and multi-split transmission lines are the main strength of power transmission. Compared with double-wheel single-wire maintenance robots, ultra-high-voltage multi-split transmission lines and four-wheel mobile robots have a wider application range and greater demand. The maintenance of multi-split transmission lines relies on the stable walking and control of four-wheel mobile robots on heterogeneous multi-split transmission lines. However, uncertain disturbance factors such as wind load in the complex field environment cause vibration of double-split and quad-split lines. The slight change in the line spacing causes the line contact to the edge of the robot’s walking wheel, which increases the friction during the robot’s walking. It also directly hinder the movement of the robot on the multi-split transmission line, thus restricting the completion of the robot’s maintenance operation. Based on the analysis, this paper establishes a mathematical model of the external force disturbance influence on the spacing of the double-split lines. At the same time, the robot walking mechanics characteristics model under the change of the line space has been established. Three different forms of the robot walking online have been obtained through abstraction processing. A method of side friction identification based on fuzzy control has been proposed, through the online monitoring of the friction between line and edge of the walking wheel, the robot walking wheel motor walking force can be intelligently controlled in real time, and effectively avoids the “wheel-line” jam phenomenon under the external uncertain factors in the field environment. Finally, the feasibility and engineering practicability of the method have been verified through MATLAB/ADAMS simulation and field operation experiments. Therefore, the automation and intelligence level of the operation and the transmission system maintenance management has been improved.

Total Force Analysis and Safety Enhancing for Operating Both Guidewire and Catheter in Endovascular Surgery

In vascular interventional surgery (VIS), the doctors often need to be exposed to X-ray radiation for a long time, operate surgical instruments (Ex. Guidewires and catheters) to perform the operation, which is difficult to ensure the health of surgeons and the safety of operation. In addition, the force between the blood vessel wall and the surgical instrument is complex and variable, the existence of the external disturbance forces easily affects the judgment of the doctors. In this paper, to ensure the health and reduce the fatigue of the doctors, a novel tactile sensing robot-assisted system for VIS was developed to assist the surgeons to complete the operation. Then, the forces between the blood vessel and the surgical instrument during the surgery were analyzed. Besides, a self-developed force sensor was used to confirm the collision force between the tip of the catheter and the blood vessel wall. Finally, combining the haptic force feedback of the system and the developed force sensor, a series of experiments in “Vitro” were completed, and it was indicated by the experiment results that the accuracy of the force feedback can be improved by using the analysis method proposed in this paper, the collision force between the catheter tip and the blood vessel environment can be confirmed by the self-developed force sensor. Based on the results, the developed robot-assisted system for VIS has high safety.

Energy optimal control of mobile manipulators subject to compensation of external disturbance forces

This study proposes a new class of controllers for mobile manipulators subject to both undesirable forces exerted on the end-effector and unknown friction forces coming from joints directly driven by the actuators as well as undesirable forces resulting from the kinematic singularities appearing on the mechanism trajectory. Based on the suitably defined task space non-singular terminal sliding manifold (TSM) and the Lyapunov stability theory, we derive a class of estimated extended transposed Jacobian controllers which seem to be effective in counteracting the unstructured forces. Due to a redundant nature of the tasks to be accomplished, our controllers also a involve useful criterion function (energy consumption) in optimally tracking a desired trajectory. Moreover, in order to eliminate (or to alleviate) undesirable chattering effects the proposed control laws include second order sliding techniques. The numerical computations, which are carried out for a mobile manipulator consisting of a platform of (2, 0) type and a holonomic manipulator of two revolute kinematic pairs, illustrate the performance of the proposed controllers and simultaneously their minimizing properties. Numerical comparison with other control algorithms well-known in the literature is also given.

Anti-swing radial basis neuro-fuzzy linear quadratic regulator control of double link rotary pendulum

In this article, a radial basis neuro-fuzzy linear quadratic regulator controller is developed for the anti-swing control of a double link rotary pendulum system. The objective of this work is to study the radial basis neuro-fuzzy linear quadratic regulator controller and to compare it with a fuzzy linear quadratic regulator and the linear quadratic regulator controllers. In the proposed radial basis neuro-fuzzy linear quadratic regulator controllers, the positions and velocities of state variables multiplied by their linear quadratic regulator gains are trained using two radial basis neural networks architecture. The output of the two radial basis neural networks is used as the input variables of the fuzzy controller. The novel architecture of the radial basis neuro-fuzzy controller is developed in order to obtain better control performance than the classical adaptive neuro-fuzzy controller. To determine the control performance of the anti-swing controllers, different control parameters are computed. According to the comparative results, the anti-swing radial basis neuro-fuzzy linear quadratic regulator controller yields improved results than fuzzy linear quadratic regulator and linear quadratic regulator. Furthermore, the performance of the three controllers developed was compared based on robustness analysis under external force disturbance. The results obtained here indicate that the anti-swing radial basis neuro-fuzzy linear quadratic regulator controller product has better performance than other controllers in terms of vibration suppression ability.

A backstepping disturbance observer control for multirotor UAVs: theory and experiment

This paper presents a backstepping disturbance observer based control (DOBC) for trajectory tracking motion control of multirotor Unmanned Aerial Vehicles (UAVs). Two disturbance observers (DO) estimate external force and torque disturbances acting on the UAV. A nonlinear backstepping dynamic state feedback is proposed which uses the DO estimates to achieve exponential stability for the closed-loop tracking error under constant disturbances. The stability analysis accounts for the entire nonlinear vehicle model which includes translational and rotational dynamics. Software-in-the-loop simulation and experimental results are presented showing the effectiveness of the proposed method using the commonly used PX4/Pixhawk development framework.

Attitude Stabilization of Quadrotor Using Adaptive Fuzzy Proportional Integral Derivative Controller

Quadrotor is an unmanned aerial robot from multi-rotor drones group that has high maneuverability, vertical take-off, and landing and stationary flight capabilities. In the most practical applications, the quadrotor system is subjected to external disturbance forces due to wind and unbalanced weight or inertia of the payload. To maintain balance and hold the position, attitude stabilization of the quadrotor is necessary for the presence of disturbances and unbalanced forces. Using conventional controllers with constant gains is not very efficient to eliminate variable disturbances that affect quadrotor motion in different conditions. In this paper, an adaptive fuzzy proportional integral derivative controller is designed for quadrotor attitude stabilization in which controller gains are regulated continuously based on the adaptive laws and the fuzzy inference system. The performance of the proposed controller is examined in the disturbance rejection test and is compared to the conventional proportional integral derivative controller. Also, the performance of the proposed controller is approved by hardware in the loop experimental tests using a 3 degree of freedom pilot platform. The experimental results will show the effectiveness of the adaptive fuzzy proportional integral derivative controller compared with the conventional proportional integral derivative controller.

A Study of Anti-swing Fuzzy LQR Control of a Double Serial Link Rotary Pendulum

In this work, a Fuzzy Linear Quadratic Regulator (FLQR) is developed for the anti-swing control problem of a Double Serial Link Rotary Pendulum (DSLRP) system. The main objective of this paper is to study the anti-swing FLQR controller and compare it with the classical LQR controller. A dynamic mechanical model of the DLRP was simulated numerically in the SimMechanics toolbox/MATLAB. This model can be defined mathematically as the single input and multiple output non-linear dynamic equations. To verify the performance of both anti-swing controllers, different time-domain control specifications are computed. Moreover, to show the controllers performance, simulation and experiments results are given and compared. According to the comparative results, the FLQR anti-swing controller produces better results than classical LQR in term of time-domain control specifications. Moreover, the controllers’ dynamic responses were compared according to robustness analysis in the presence of external force disturbance. The results obtained here indicate that the FLQR anti-swing controller product better performance than others in term of vibration suppression capability.