External Disturbance Forces Research Articles

A composite robust reactive control strategy for quadruped robot under external push disturbance

In order to solve the walking stability problem of quadruped robot under lateral disturbance, a robust stabilization reactive control strategy based on capture point stability theory is proposed. This novel control strategy consists of an active adaptive stepping control strategy at the upper planning layer and a joint disturbance rejection controller based on virtual model control at the bottom layer. The adaptive stepping control strategy is based on the capture point stability theory, which determines the stable stepping point of the robot under the action of external disturbance according to the speed and attitude of the body, and the joint disturbance rejection controller at bottom layer realizes the stable torque control of the robot and adjusts the attitude of the body through the virtual model controller. Finally, the effectiveness of the designed composite control strategy is verified by co-simulation of Simulink and ADAMS. Simulation results show that the robot with the proposed composite reactive control strategy is able to cope with large external disturbance and recover to be stable from external force disturbance.

Relative Position Model Predictive Control of Double Cube Test-Masses Drag-Free Satellite with Extended Sliding Mode Observer

The drag-free satellites, being space-borne ultrahigh precise measurement platforms, have played irreplaceable roles in a great number of space science missions such as navigation, earth science, fundamental physics, and astrophysics. Most of these missions have to be performed based on the satellites placed with double cube test-masses, which makes the satellite layout and control strategy be more complex. This paper investigates the orbit keeping control problem of a class of low Earth orbit drag-free satellites with double cube test masses. A disturbance observer-based composite control method is proposed, which consists of an extended sliding mode observer and the tube-based robust model predictive control approach. In this design, the observer is proposed to estimate the relative position and velocity of the satellite and the external space disturbance force. A tube-based robust model predictive control scheme is then developed to stabilize the satellite orbit control systems in the presence of actuator saturation, state constraints, and additive stochastic noises. Finally, a simulation example is presented to demonstrate the efficacy and superiority of the proposed orbit control method.

Vertical–Horizontal Coupling Vibration of Hot Rolling Mill Rolls under Multi-Piecewise Nonlinear Constraints

This study establishes a vertical–horizontal coupling vibration model of hot rolling mill rolls under multi-piecewise nonlinear constraints considering the piecewise nonlinear spring force and piecewise nonlinear friction force constraints of the hydraulic cylinder in the vertical direction of the rolls, the piecewise stiffness constraints in the horizontal direction, and the influence of the nonlinear dynamic rolling force in the rolling process. Using the average method to solve the amplitude–frequency response equation of the coupled vibration system and taking the actual parameters of a 1780 mm hot rolling mill (Chengde Steel Co., Ltd., Chengde, China) as an example, we study the amplitude–frequency characteristics of the mill rolls under different parameter settings. The results show that the amplitude and resonance region can be reduced by appropriately reducing the external disturbance force and the nonlinear spring force of the hydraulic cylinder, appropriately increasing the nonlinear friction force, and eliminating the gap between the bearing seat and the mill housing, to avoid the amplitude jump phenomenon due to piecewise variation. Furthermore, using the singularity theory to study the static bifurcation characteristics of the coupled vibration system, we establish a relationship between the vibration parameters and the topological bifurcation solution of the coupled system. The transition sets and their corresponding bifurcation topological structure in three cases are given, and the steady and unsteady process parameter regions of the rolls are obtained. The dynamic behavior of the coupled vibration system can be controlled by varying the bifurcation parameter. This study provides a theoretical basis for restraining the vibration of hot rolling mill rolls and optimizing the process parameters.

Modeling and Analysis of Suspension Frame of Maglev Train

Based on the acceleration feedback system, the vertical dynamic model of the low-speed maglev train is established. By decoupling the suspension frame module, the author conducted a stress analysis of the single-sided and the entire suspension system, and established a system dynamics model of the suspension frame. The suspension controller is designed using classic PD control and acceleration feedback control methods. Then, the author used Simulink to create a dynamic simulation analysis program to analyze the dynamic performance of the suspension system affected by track misalignment and external disturbance forces, and analyze the impact of the suspension frame’s parameter design on the suspension system performance.

A Human Arm’s Mechanical Impedance Tuning Method for Improving the Stability of Haptic Rendering

SUMMARYRendering of rigid objects with high stiffness while guaranteeing system stability remains a major and challenging issue in haptics. Being a part of the haptic system, the behavior of human operators, represented as the mechanical impedance of arm, has an inevitable influence on system performance. This paper first verified that the human arm impedance can unconsciously be modified through imposing background forces and resist unstable motions arising from external disturbance forces. Then, a reliable impedance tuning (IT) method for improving the stability and performance of haptic systems is proposed, which tunes human arm impedance by superimposing a position-based background force over the traditional haptic workspace. Moreover, an adaptive IT algorithm, adjusting the maximum background force based on the velocity of the human arm, is proposed to achieve a reasonable trade-off between system stability and transparency. Based on a three-degrees-of-freedom haptic device, maximum achievable stiffness and transparency grading experiments are carried out with 12 subjects, which verify the efficacy and advantage of the proposed method.

Robust trajectory tracking of autonomous underwater vehicles using back-stepping control and time delay estimation

In the paper, a robust controller using the back-stepping approach and the time delay estimation(TDE) is proposed for the trajectory tracking of torpedo-shape autonomous underwater vehicles(AUVs). The AUV has several difficult issues to design accurate tracking control: unsatisfaction of matching condition and highly nonlinear dynamics including external disturbances. To overcome the matching condition issues, the proposed controller is designed based on the back-stepping approach, which is a well-known method handling unmatched disturbances effectively and having well-established design procedure. To estimate nonlinear vehicle dynamics including sea currents and external disturbances, the TDE, an efficient estimation method using previous system information, is adopted. Owing simplicity of the TDE, the proposed controller does not need whole vehicle dynamics while requiring only the determination of control gains. The stability analysis of the proposed controller is studied, conducting the guidelines for selection of control gains. Through the simulation results using REMUS model, it is demonstrated that the proposed controller has accurate and robust tracking performance even when a vehicle moves under sea currents and external disturbing forces.

Finite-time formation tracking control with collision avoidance for quadrotor UAVs

In this paper, the distributed finite-time formation tracking control problem with collision avoidance is investigated for multiple quadrotor Unmanned Aerial Vehicles (UAV) subject to external disturbances. Firstly, two finite-time observers are designed to estimate the external disturbance force and torque without upper bound, respectively. Then, utilizing the precisely observed information deriving from the observers, a novel sliding mode surface-like variable based distributed position formation tracking control strategy and a fast terminal sliding mode based attitude tracking control strategy are proposed, respectively. It achieves that the multiple quadrotor UAVs can track the desired trajectory in a specific formation configuration within the safe distance and avoid dynamic obstacles. Meanwhile, the rapid attitude synchronization and tracking is also achieved. The entire multiple UAVs distributed formation tracking closed-loop control system are proved to be globally fast finite-time stable by using Lyapunov-like analysis. Finally, the effective and fine performance of the proposed schemes are demonstrated by a numerical simulation example with a group of quadrotor UAVs.

RETRACTED: Integral backstepping control with RRFNN and MPSO of LPMSM drive system

A linear permanent magnet synchronous motor drive system is existed in many nonlinear effects such as the external load force, the flux saturation, the cogging force, the column friction and Stribeck force, and the parameters variations. Due to the uncertainty effects, the linear permanent magnet synchronous motor drive system is hard to achieve the good control performance by using linear controller. To raise robustness under occurrence of uncertainty, the integral backstepping control system with hitting function is first proposed for controlling the linear permanent magnet synchronous motor drive system. The used integrator can ameliorate the system’s robustness under the parameters uncertainties and external force disturbances. To reduce vibration of control strength, the integral backstepping control system by means of the revised recurrent fuzzy neural network with mended particle swarm optimization is next proposed to operate the linear permanent magnet synchronous motor drive system to raise robustness of system. Furthermore, four variable learning rates in the weights of the revised recurrent fuzzy neural network are adopted by using mended particle swarm optimization to speed up parameter’s convergence. Finally, comparative performances through some experimental upshots are verified that the integral backstepping control system by means of revised recurrent fuzzy neural network with mended particle swarm optimization has better control performances than those of the proposed methods for the linear permanent magnet synchronous motor drive system.

A Theoretical Framework for Stability Regions for Standing Balance of Humanoids Based on Their LIPM Treatment

The aim of this paper is to construct a theoretical framework for stability analysis relevant to standing balance of humanoids on top of the linear inverted pendulum model, in which their dynamics between the center of mass (CoM) and the zero moment point (ZMP) is dealt with. Based on the well-known sufficient condition that the contact between the ground and the support leg is stable if the corresponding ZMP is always inside the supporting region, this paper aims at characterizing three types of the associated stability regions. More precisely, assuming no external force disturbances affecting the motion of the humanoids, the stability region of the initial CoM position and velocity values can be explicitly computed by solving a finite number of linear inequalities. The stability regions of time-invariant force disturbances such as impulsive force and constant force disturbances are also dealt with in this paper, where the former is exactly obtained through a finite number of linear inequalities while the latter is approximately derived by using an idea of truncation. Furthermore, time-varying force disturbances of finite energy and finite amplitude are concerned with, and their maximum admissible ${l} _{2}$ and ${l} _{\infty }$ norms are computed in this paper, where the former can be exactly obtained by solving the discrete-time Lyapunov equation while the latter is approximately derived through an idea of truncation. It is further shown for both the truncation ideas that the approximately obtained stability regions converge to the exact stability regions with an exponential order of ${N}$ , where ${N}$ is the truncation parameter. Finally, the effectiveness of the computation methods proposed in this paper is demonstrated through some simulation results.

Compliant Control of Single Tendon-Sheath Actuators Applied to a Robotic Manipulator

Tendon-sheath actuators (TSAs), similar to Bowden cable-based series elastic actuators (SEAs), have a wide range of applications in robots. However, when applying them to manipulators, force sensors cannot be mounted due to limited space. Therefore, this paper proposes a new method for compliant control based on a dual encoder, and the existing transmission model was improved by considering the joint torque. To validate the proposed method, experimental setups composed of a motor, a tendon-sheath component, a robotic joint, force sensors, and position sensors are established. The transmission processes are interpreted clearly through a position control mode. Parameter identifications without external disturbance force are conducted to acquire the ideal transmission model, and the error value between the experiment data and the fitted curve is measured. The availability of the presented scheme is verified by compliant control experiments, including collision detection and hand guiding, and the frequency characteristics of the actuator are analyzed. The results show that the function can be realized without force and torque sensors during the whole process.

Disturbance Force Self-Sensing and Suppression Method for AMB-Rotor System Based on Disturbance Observer

This paper explores a disturbance force self-sensing and suppression method for active magnetic bearings (AMBs) system. Since the displacement of the AMB-rotor is affected by both the output of the controller and the disturbance force, the mathematical expression of the external disturbance force is deduced based on the inverse model of the controlled plant of the AMB-rotor system. The rotor displacement and output of the controller are both the input of the disturbance self-sensing system. A third-order low-pass filter is added to the self-sensing system so as to avoid the self-sensing system being unstable due to model uncertainty of the controlled plant. Then an adaptive notch filter added to the self-sensing system is used to eliminate the synchronous frequency component in the estimated disturbance. Finally, experiment results validate the proposed self-sensing method can effectively sense the external disturbance force within the range of about 67 Hz, and the AMB-rotor system can well suppress the disturbance force with the sensed value.

Disturbance Rejection Control Using a Novel Velocity Fusion Estimation Method for Levitation Control Systems

Magnetic levitation has been applied to maglev trains and magnetic suspension wind tunnel. However, there are some problems with the existing levitation control. For example, it is difficult to extract smooth velocity signals from the gap sensor with noise. The classical differentiator is susceptible to noise, which makes the levitation system sometimes vibrate. The accuracy and stability of levitation control need to be improved. The velocity fusion estimation method (VFE) is proposed to extract the velocity signal from the gap and acceleration sensor, which is theoretically derived to prove that it reduced the noise of the velocity signal. Then disturbance rejection control(DRC) is proposed that add VFE into classical levitation control. Because of the high-quality velocity signal and accelerometer’s fast responsiveness, it makes DRC have many advantages. The advantages of using the proposed control structure are that it improved the control accuracy of the target gap and resisted disturbance effectively. Air-gap fluctuations in levitation systems can be reduced in transient pulse disturbance test, white noise disturbance test, and external force disturbance test when it applies the proposed control method. The effectiveness and advantages of the proposed control method are verified by the simulation and experiments.

Smart backstepping control using revised recurrent fuzzy neural network and revised ant colony optimization for linear permanent magnet synchronous motor drive system

Because of the uncertainty’s action in a linear permanent magnet synchronous motor drive system such as the external load force, the cogging force, the column friction force and the Stribeck effect force and the parameters variations, it is difficult to reach specific control performances by using the existing linear controller. To raise robustness under occurrence of parameters uncertainties and external force disturbances, the smart backstepping control system with three adaptive laws is proposed for controlling the linear permanent magnet synchronous motor drive system. In accordance with the Lyapunov function, three adaptive laws are derived to ameliorate the system’s robustness. Furthermore, the smart backstepping control system using revised recurrent fuzzy neural network and revised ant colony optimization with the compensated controller is proposed to improve the control performance. The revised recurrent fuzzy neural network acts as the estimator of the uncertainty’s disturbances. In addition, the compensated controller with error estimation law is proposed to compensate the minimum rebuilt error. Moreover, two learning rates of the weights in the revised recurrent fuzzy neural network are derived according to the discrete-type Lyapunov stability to assure convergence of the output tracking error and are adopted by using the revised ant colony optimization to speed-up parameter’s convergence. Finally, some comparative performances are verified through some tentative upshots that the smart backstepping control system by virtue of revised recurrent fuzzy neural network and revised ant colony optimization with the compensated controller results in better control performances for the linear permanent magnet synchronous motor drive system.

ВИЗНАЧЕННЯ ПОТУЖНОСТІ І РОБОТИ ВИМУШЕНИХ КОЛИВАНЬ ПРИ ВІДКЛЮЧЕННІ ЦИЛІНДРІВ В ДВИГУНІ КОЛІСНОЇ МАШИНИ

В даній статті наведені результати по потужності вимушених коливань двигуна та енергетичну діагра-му для вимушених коливань. Отримані залежності накладення вільних і вимушених коливань для різних умов спів падіння відносної частоти на величину потужності. Розглянуті перехідні процеси при вимушених коли-ваннях. Необхідність покращення рівномірності крутного моменту під час відключення циліндрів потребує впливу на показники потужності окремих циліндрів. Щоб знайти загальне рішення, потрібно додати вирази для вільних коливань, тобто загальне рішення однорідного рівняння.В цій роботі також виявляється можливим виділити активну і реактивну складові. Активна робота зро-стає лінійно з часом, в той час як реактивна робота є періодичною функцією часу. Поряд з зовнішньою збу-рюючою силою роботу здійснюють також і внутрішні сили коливальної системи. Робота сили інерції дорівнює кінетичної енергії маси, а робота поновлюючої сили дорівнює потенційної енергії напруженою пружини. При періодичних рухах обидві ці роботи також змінюються періодично і, маючи різні знаки, виключаються із зага-льного балансу енергії системи, якщо їх величина розраховується для одного повного коливання.Отримано відношення додаткових витрат енергії, зумовлених роботою стиснення робочих циліндрів у відключених циліндрах до зміни додаткових витрат енергії двигуна.Поряд з вібрацією двигуна роботу здійснюють також і внутрішні сили коливальної системи. Робота си-ли інерції дорівнює кінетичної енергії маси, а робота оновлюючої сили дорівнює потенційної енергії напруже-ною подушками двигуна. При періодичних рухах обидві ці роботи також змінюються періодично і, маючи різні знаки, виключаються із загального балансу енергії системи, якщо їх величина розраховується для одного повного коливання. Таким чином, обидві роботи є реактивними. Робота, чинена силами демпфування за один повний період, не виключається із загального балансу.Ключові слова: потужність, робота, вимушені коливання, відключення циліндрів, двигун, колісна машина, обурюючи сила.

Experimental study of ergonomic properties of wheeled tractors with units of variable weight

Problem. Nowadays, one of the main tasks that tractor builders solve when creating new machinery is ensuring a comfortable driver's workplace. To ensure this, it is necessary to take into account the complex of ergonomic properties of the wheeled vehicle: comfort, smooth ride, vibration safety and more. Goal. That is why the purpose of this work is to determine the ergonomics of wheeled tractors when performing transportation of liquid cargo by trailer and semi-trailer tanks. According to many scientific papers, the redistribution of fluid in tractor tanks affects the dynamics of the wheeled tractor, especially when the weight of the unit is greater than the weight of the tractor. Therefore, it is advisable to study the effect of the amount of liquid in the tractor tank on the comfort level of the operatordriver. Confirmation of any theoretical studies must be accompanied by a whole series of experimental studies. Methodology. Therefore, in order to determine the ergonomic properties of wheeled tractors with units of variable weight, experimental tests were conducted on the base of a farmland. The measuring equipment consists of a mobile registration complex «VDVMM 4-001» and a radar sensor, which is designed to capture the true speed of the vehicle. Result. Based on the experiment, it was found that the standard acceleration rates, according to ISO 2631 (discomfort levels) for a single tractor and tractor with variable mass units (John Deere with MLT-16 and HTZ-150K with MLT-10), are subject to the level of “uncomfortable”. With the increase of the liquid level, both in the trailer tank and in the semi-trailer tank, it becomes “very uncomfortable”. Originality. The novelty of the work is the determination of ergonomic indicators of wheeled tractors with variable mass units and the dependence of the level of comfort on the height of the filling liquid tanks. Practical value. Therefore, based on the materials of this paper, it can be suggested that the in-depth study of the smooth running of wheeled tractors with variable mass units is feasible. In addition, the task is to reduce the external disturbance forces acting on the driver's seat.

Sliding-Mode Tracking Control of a Walking Quadruped Robot with a Push Recovery Algorithm Using a Nonlinear Disturbance Observer as a Virtual Force Sensor

This paper offers a new push recovery method to stabilize the quadruped robots walking on even terrains in the presence of external disturbance forces exerted on the body and legs of the robot. To avoid force sensors, a class of nonlinear observers is usually used to estimate all the forces that are applied to the leg joints. However, such estimations involve permanent errors in the case of fast varying external forces. A new sliding-mode control method is designed to enable the robot to track a desired gait with high precision despite the persisting estimation error of the original nonlinear disturbance observer. A new push recovery method that uses the estimations of the disturbance observer is proposed to help the robot maintain its balance in the presence of sudden external forces applied to the robot legs and body. To this end, an optimization problem is proposed to calculate the optimized accelerations of the leg joints of the robot. This controller was applied to the TMUBot quadruped robot as a case study to verify the effectiveness of the design. Moreover, unlike other similar works, which use massless model of the legs, the masses of the legs of the quadruped are considered in this work. As such, the dynamic equations of the legs have also been considered throughout the proposed design method.

Control of the Sit-To-Stand Transfer of a Biped Robotic Device for Postural Rehabilitation

This paper deals with the control of the sit-to-stand transfer of a biped robotic device (either an autonomous biped robot or a haptic assistive exoskeleton for postural rehabilitation). The control has been synthesized, instead of considering the physiology, analyzing the basic laws of dynamics. The transfer of a human from sitting on a chair to an erect posture is an interesting case study, because it treats biped balance in a two-phase dynamic setting, with an external force disturbance (the chair–pelvis contact) affecting the center of pressure under the feet. At the beginning, a body is sitting, with a fixed pelvis moving with the hips going toward the supporting feet and, contemporaneously, releasing the load from the chair with ankles and knee torques. Then, after lift-off, it reaches and maintains an erect posture. The paper objectives are threefold: identifying the major dynamical determinants of the exercise; sythesizing an automatic control for an autonomous device; proposing an innovative approach for the rehabilitation process with an exoskeleton. For this last objective, the paper extends the idea of the authors of a haptic exoskeleton for rehabilitation. It is driven to control the joints by electromiographical signals from the patient. The two spaces, cartesian (world) and joint, where, respectively, the automatic control and the patient operate, are considered and a technique to blend the two actions is proposed. The exoskeleton is programed to perform the exercise autonomously. Then, during the evolution of the phases of rehabilitation, we postulated to seamlessly move the control from one space (purely autonomous) to another (completely driven by the patient), choosing and keeping the postural tasks and joints (heaps, knees, or ankles) on which to apply each one of the two actions without interaction.

Estimation and Closed-Loop Control of COG/ZMP in Biped Devices Blending CoP Measures and Kinematic Information

The zero moment point ( Z M P ) and the linearized inverted pendulum model linking the Z M P to the center of gravity ( C O G ) have an important role in the control of the postural equilibrium (balance) of biped robots and lower-limb exoskeletons. A solution for balance real time control, closing the loop from the joint actual values of the C O G and Z M P , has been proposed by Choi. However, this approach cannot be practically implemented: While the Z M P actual value is available from the center of pressure ( C o P ) measured under the feet soles, the C O G is not measurable, but it can only be indirectly assessed from the joint-angle measures, the knowledge of the kinematics, and the usually poorly known weight distribution of the links of the chain. Finally, the possible presence of unknown external disturbance forces and the nonlinear, complex nature of the kinematics perturb the simple relationship between the Z M P and C O G in the linearized model. The aim of this paper is to offer, starting from Choi’s model, a practical implementation of closed-loop balance control fusing C o P and joint-angle measures, eliminating possible inconsistencies. In order to achieve this result, we introduce a model of the linearized inverted pendulum for an extended estimation, not only of C O G and Z M P , but also of external disturbances. This model is then used, instead of Choi’s equations, for estimation and balance control, using H ∞ theory. As the C O G information is recovered from the joint-angle measures, the identification of a statistically equivalent serial chain ( S E S C ) linking the C O G to the joint angles is also discussed.

A Reliable Gravity Compensation Control Strategy for dVRK Robotic Arms With Nonlinear Disturbance Forces

External disturbance forces caused by nonlinear springy electrical cables in the Master Tool Manipulator (MTM) of the da Vinci Research Kit (dVRK) limits the usage of the existing gravity compensation methods. Significant motion drifts at the MTM tip are often observed when the MTM is located far from its identification trajectory, preventing the usage of these methods for the entire workspace reliably. In this paper, we propose a general and systematic framework to address the problems of the gravity compensation for the MTM of the dVRK. Particularly, high order polynomial models were used to capture the highly nonlinear disturbance forces and integrated with the Multi-step Least Square Estimation (MLSE) framework. This method allows us to identify the parameters of both the gravitational and disturbance forces for each link sequentially, preventing residual error passing among the links of the MTM with uneven mass distribution. A corresponding gravity compensation controller was developed to compensate the gravitational and disturbance forces. The method was validated with extensive experiments in the majority of the manipulator's workspace, showing significant performance enhancements over existing methods. Finally, a deliverable software package in MATLAB and C++ was integrated with dVRK and published in the dVRK community for open-source research and development.

Robust Translational Force Control of Multi-Rotor UAV for Precise Acceleration Tracking

In this article, we introduce a translational force control method with disturbance observer (DOB)-based force disturbance cancellation for precise 3-D acceleration control of a multi-rotor unmanned aerial vehicle (UAV). The acceleration control of the multi-rotor requires conversion of the desired acceleration signal to the desired roll, pitch, and total thrust. However, because the attitude dynamics and the thrust dynamics are different, simple kinematic signal conversion without consideration of those difference can cause serious performance degradation in acceleration tracking. Unlike most existing translational force control techniques that are based on such simple inversion, our new method allows controlling the acceleration of the multi-rotor more precisely by considering the dynamics of the multi-rotor during the kinematic inversion. By combining the DOB with the translational force system that includes the improved conversion technique, we achieve robustness with respect to the external force disturbances that hinder the accurate acceleration control. μ-analysis is performed to ensure the robust stability of the overall closed-loop system, considering the combined effect of various possible model uncertainties. Both simulation and experiment are conducted to validate the proposed technique, which confirms the satisfactory performance to track the desired acceleration of the multi-rotor.