Accurate Position Control Research Articles

Construction and performance analysis of DC servo system based on operational amplifier

Abstract. The motivation for researching modelling the severe motor system is its frequent use in applications that demand accurate control of position, speed, or force. Examples include robots and CNC machines, extensively employed and advanced in modern manufacturing processes. The application field of this technology is expanding significantly due to the increasing demand for automation in modern times. In order to achieve seamless integration of the system, using Op-Amp as the central element for signal processing and control is crucial. This research aims to determine the methodology for utilising an operational amplifier (Op-Amp) to construct a model for a direct current (DC) servo motor. Additionally, the research aims to develop a control system and do circuit board simulations.The outcome of this research is to implement theoretical principles into a design model, identify the most appropriate system for this model and develop the corresponding circuit board. This study aims to incorporate a control system to regulate server motors, effectively enhancing the automation process.

Non-singular sliding mode control-based attitude control analysis of ELITE satellite with flywheel failures

Abstract This paper addresses the challenge of maintaining the attitude control of the ELITE satellite in the event of flywheel failures. Given the critical need for highly stable and precise attitude control during Time-Delay Integration (TDI) Imaging missions, a failure in any flywheels poses a significant threat to the satellite’s attitude control stability and accuracy. To tackle this issue, a Non-singular Sliding Mode Control (NSMC) method was proposed to ensure ELITE’s continued performance under flywheel failure conditions. The research involves a thorough analysis of ELITE’s attitude dynamics, followed by designing an NSMC tailored to its specifications. Theoretical validation of the NSMC’s finite-time stability was achieved using the Lyapunov function. Numerical simulations conducted demonstrate that the proposed NSMC method enables ELITE to maintain its attitude control stability and precision even in the presence of flywheel failures, thereby ensuring mission continuity and reliability.

Research on the Friction Force Characteristics for the Double O-ring Seal of the Cylinder under the Small Displacement Condition

In order to obtain a high-precision pneumatic control system, it is necessary to study the friction force of the cylinder. However, few have considered the cylinder's frictional characteristics at small-displacements. This study investigated the influence of different conditions on the cylinder friction characteristics during the process from static to small-displacement of pneumatic double O-ring seal. A set of experimental apparatuses controlled by an electric actuator perform a seal ring small-displacement friction test to achieve the goals. The working principle of sealing rings in different deformation stages is expounded. According to experiments, the sealing ring's friction force in small-displacement movement can be separated into tilt, elastic deformation, pre-sliding, and sliding friction stages. Furthermore, the clearance characteristics between the sealing ring and the piston groove are verified, which decreases with the sealing ring thickness. Finally, the friction displacement characteristics of sealing rings under different pressures and materials during the elastic deformation stage were verified. It can be concluded that when the displacement is between 0.05-0.25mm, the friction of the sealing ring is almost linear with the displacement; when the displacement reaches 0.25mm, with the increase of the displacement, the friction force changes in a similar parabola manner. This study provides a detailed analysis of the friction characteristics of the seal in different stages of small displacement, which plays an important reference role in overcoming cylinder friction and promotes the development of pneumatic systems in the field of accurate position and speed control.

Dual-Arm Space Robot On-Orbit Operation of Auxiliary Docking Prescribed Performance Impedance Control

The impedance control of a dual-arm space robot in orbit auxiliary docking operation is studied. First, for the closed-chain hybrid system formed by the dual-arm space robot after capture operation, the dynamic equation of position uncontrolled and attitude controlled is established. The second-order linear impedance model and second-order approximate environment model are established for the problem of simultaneous output force/pose control of the end of the manipulator. Then, aiming at the transient performance control requirements of the dual-arm space robot auxiliary docking operation in orbit, a sliding mode controller with equivalent replacement of tracking errors is designed by introducing Prescribed Performance Control (PPC) theory. Next, Radial Basis Function Neural Networks (RBFNN) are used to accurately compensate for the modeling uncertainties of the system. Finally, the stability of the system is verified by Lyapunov stability determination. The simulation results show that the attitude control accuracy is better than 0.5°, the position control accuracy is better than 10−3 m, and the output force control accuracy is better than 0.5 N when it reaches 30 N. It also indicated that the proposed control algorithm can limit the transient performance of the controlled system within the preset range and achieve high-precision force/pose control, which ensures a more stable on-orbit auxiliary docking operation of the dual-arm space robot.

Enhancing quadrotor robustness control using image-based visual servoing (IBVS) with fuzzy logic

Visual servoing is a commonly employed approach in robotics and unmanned aerial vehicles (UAVs) that facilitates accurate object positioning and movement control by utilizing visual feedback. As quadrotors gain popularity, more control methods have been developed. This article presents a method for enhancing quadrotor robustness control using image-based visual servoing (IBVS) with fuzzy logic. Unlike traditional visual servoing, which relies on a fixed gain and often encounters challenges with velocity convergence and maintaining the object in the field of view, this method is designed to enhance the visual servo control of quadrotors by dynamically adjusting the gain of the IBVS system through a fuzzy logic controller. This controller adaptively adjusts the servo gain in response to feature errors and the depth of the object's feature points. MATLAB simulations clearly demonstrate the superior performance of this fuzzy logic integrated method compared to classical approaches, showcasing enhanced control capabilities in challenging environments.

YoMo: Yoshimura Continuum Manipulator for MR Environment.

Origami robots have garnered attention due to their versatile deformation and potential applications, particularly for medical applications. In this article, we propose a Yoshimura continuum manipulator (YoMo) that can achieve accurate control of the tip position for the magnetic resonance (MR) environment. The YoMo made of a single piece of paper is cable-actuated to generate the bending and shortening deformation. The paper-based YoMo attached to an arc frame can readily function under different orientations in the MR environment. The design and fabrication of YoMo were formulated according to the Yoshimura folding pattern. The kinematics model based on constant curvature assumption was derived as a benchmark method to predict the tip position of the YoMo. The Koopman operator theory was applied to describe the relationship between the tip position and the length change under different orientations. The linear quadratic regulator integrated into the Koopman-based model (K-LQR) was adopted to achieve the trajectory tracking. Comprehensive experiments were carried out to examine the proposed YoMo, its modeling and control methods. The performance of the YoMo including stiffness and workspace was characterized via a customized test setup. The Koopman-based method demonstrates the superiority over the constant curvature-based model to predict the tip position. The K-LQR control method was examined with different trajectories, and the impact of the orientation, speed, and different trajectories were taken into consideration. The results demonstrate the YoMo is capable of achieving trajectory tracking with satisfied accuracy, indicating its potential for medical applications in the MR environment.

Motion Trajectory Based Position Control Scheme for Switched Reluctance Machines

Switched reluctance machines (SRMs) are widely used in electric drive areas. However, due to the machine structure, the large stride angle makes it hard to achieve accurate position control for SRMs. In this paper, a position control scheme based on motion trajectory is proposed for SRM position control. In the proposed position control scheme, the SRM control is divided into the accelerating process, the steady operating process and the regenerating process. Development of the proposed position control strategy contains two parts. First, a Fuzzy logic controller is designed for rotor speed control in the accelerating process and steady operating process. Then, an aim speed regulator is proposed for the regenerating process, in which the aim speed is regulated according to the difference between aim position and real‐time rotor position. In the end, both simulation and experimental results are given to show the effectiveness of proposed motion trajectory based position control scheme. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Collaborative attitude stabilization and distributed vibration suppression of satellite with ultra–large flexible antenna

Large flexible radar satellites are widely used in space–based remote sensing for wide–area target observation and high–capacity information transmission. To achieve accurate earth observation and structural stability of an ultra–large flexible satellite in hundred–meter length concurrently, this paper presents two–time–scale collaboration for attitude stabilization and vibration suppression. First, the coupling dynamic model of the satellite with ultra–large flexible antenna is established under space disturbances. Next, singular perturbation with boundary layer correction is employed to decompose attitude and vibration controls in different time scales, respectively. Given the respective decoupling models, the slow subsystem employs an angles–only terminal sliding–mode controller with adaptive switching and input saturation to accomplish high–robustness triaxial attitude stabilization in finite time. For the fast subsystem, distributed piezoelectric actuators with leader–follower consensus and feedback control are applicable to rapid and stable vibration suppression of the ultra–large structure. Finally, simulation results validate the effectiveness and superiority of these control methods on the satellite, where collaborative control effects on multiple key indices including attitude and vibration control accuracy and settling time are significant. This work facilitates high–accuracy and –stability collaborative control of future ultra–large satellites.

Research on Space Operation Control of Air Float Satellite Simulator Based on Constraints Aware Particle Filtering-Nonlinear Model Predictive Control

This paper addresses the challenges of close proximity operations, such as rendezvous, docking, and fly-around maneuvers for micro/nano satellites, which require high control precision under the low power and limited computational capabilities of spacecraft. Firstly, a three-degree-of-freedom air float simulator platform is designed for ground-based experiments. Subsequently, model predictive controllers based on constraints aware of particle filtering (CAPF-NMPC) are developed for executing operations such as approach, fly-around, and docking maneuvers. The results validate the effectiveness of the experimental system, demonstrating position control accuracy less than 0.03 m and attitude control accuracy less than 3°, maintaining lower computational resource consumption. This study offers a practical solution for the onboard deployment of optimized control algorithms, highlighting significant value for further engineering applications.

Design and Validation of a Modular, Backdrivable Ankle Exoskeleton.

Partial-assist ankle exoskeletons have been limited by inherent trade-offs between favorable characteristics including high torque capacity, high control bandwidth, back-drivability, compliance, and low mass. Emerging quasi-direct drive actuators have a rigid transmission with a low gear ratio, enabling inherent backdrivability and compliance with accurate torque and position control. Our existing modular, backdrivable exoskeleton system (M-BLUE) uses quasi-direct drive actuators at the hip and/or knee to deliver high assistive torques alongside low dynamic backdrive torques, enabling natural interaction with users with remnant voluntary motion. This paper extends our modular system with the design and validation of a back-drivable ankle exoskeleton module to assist both plantarflexion and dorsiflexion. The bi-directional torque capabilities enable the study of control methods and gait outcomes for able-bodied users and users with gait impairments. Benchtop tests of the actuator performance and control bandwidth indicate that the position, voltage, and current control modes can provide assistance to the ankle joint across activities of daily living (ADLs). We also implement an optimal task-agnostic energy shaping controller for an experiment with a single human subject to validate the ability of the ankle exoskeleton to provide biomimetic torque assistance across a circuit of ADLs.

Characteristic investigation of digital control four quadrant electro-hydrostatic actuator with separated hydraulic motor.

The asymmetric electro-hydrostatic actuator (EHA) is a promising distributed hydraulic actuation solution for the more-electric aircraft (MEA). However, the flow asymmetry is a common problem causing the poor position control accuracy and dynamics of EHA. To achieve good flow control in all quadrants and save energy in the assistive quadrants, a digital control four quadrant electro-hydrostatic actuator with a separated hydraulic motor using a novel four-quadrant division principle was proposed in this article. The theoretical model of the proposed EHA has been developed in MATLAB/Simulink and validated in the experiments. The theoretical results indicated that the increased external force allows the proposed EHA to have a constantly and partly linearly and varied motion velocity of the cylinder piston in the resistive and assistive quadrants, and the latter is determined by the specific external forces of 0.5 and 2.8kN, respectively, in the extension and retraction quadrants. Compared with EHA without SHM, in the second and fourth quadrants, the energy dissipation is reduced by 104% and 36.7%, respectively, while the motion velocity of the cylinder piston is reduced by 12.9% and 25.6%, respectively. The theoretical and experimental results indicated that the proposed four quadrants division method effectively corrects the misjudgment of quadrants by using the existing four quadrants division method under the lower external force.

Research on positioning control strategy of hydraulic support pushing system based on multistage speed control valve

The precise position control of the hydraulic support pushing system in the coal mining face is a key technical support for intelligent coal mining. At present, the hydraulic support pushing system uses the electro-hydraulic directional valve as the control element. However, the electro-hydraulic directional valve has problems such as discrete input values, low switching frequency, delay, inability to adjust flow, and large flow fluctuations during the switching process, which results in relatively low positioning control accuracy of the hydraulic support pushing system. Therefore, this study introduces a multi-stage speed control valve that is suitable for underground coal mine conditions and can achieve flow regulation. At the same time, a segmented control strategy combining Bang-Bang control and online predictive control is proposed. Bang-bang control is used for fast propulsion with large flow rate, large range, and short time. Online predictive control method is used to achieve precise positioning control with small flow rate and small range, thereby solving the problem of low positioning control accuracy caused by the imperfect characteristics of electro-hydraulic directional valves. Finally, this study verified the effectiveness of the proposed scheme through simulation and experiments. The results showed that compared with existing logic positioning control methods based on electro-hydraulic directional valves, the proposed scheme can improve the accuracy of single cylinder positioning control from 62 mm to within 10 mm.

Attitude collaborative control strategy for space gravitational wave detection

This paper proposes a high-precision attitude cooperative control strategy for three spacecraft in space gravitational wave detection. Firstly, based on the layout of optical components on the spacecraft and factors such as external interference and model uncertainty, a relative attitude model based on the Euler angle is constructed for the characteristics of small angle motion in differential wavefront sensing mode. Secondly, aiming at the cooperative control problem of multi drag-free attitude control system after the laser link capture between two spacecraft is completed, an attitude control method based on consensus mode cooperative control strategy is proposed. It combines local neighbourhood error from star sensing and differential wavefront sensing with an adaptive controller for equilateral triangle configuration control. Additionally, a cooperative control strategy based on laser measurement information is established to improve control accuracy by avoiding star sensors with low accuracy. Simulation results indicate that the control accuracy of the consistency mode and its sub-mode laser measurement mode is superior to the master-slave and cyclic modes, achieving better than 5×10−6 rad. The laser measurement mode demonstrates the highest accuracy, with relative attitude control accuracy reaching 1.5×10−7 rad, meeting the requirements for space gravitational wave detection.

Design and fabrication of a multi-purpose four arm electrothermal microgripper; a novel approach to control maximum gripping force limit

The development of microgrippers requires accurate control of force and position for the grasping mechanisms in micromanipulation. This controllability ensures the safe transfer of sensitive micro-objects, such as living cells. The design of microgrippers is often limited by the dimensions and adaptability of the micro-objects being manipulated. Therefore, microgrippers should be customized for each micro-object. Additionally, complex sensor mechanisms are required to control the gripping force. This study introduces a novel design of a four-arm MEMS electrothermal microgripper intended for versatile micromanipulation purposes. The microgripper design procedure is compatible with a list of constraints, including biological and microfabrication constraints. The jaw form is designed to manipulate micro-objects with a wide range of dimensions (1 to 360 μm). Furthermore, a novel approach is presented here to control the force threshold of gripping without a sensor during manipulation. The proposed solution involves using structure stiffening to control the force and prevent damage to micro-objects. GA and analytical models (transient behaviour of structure) are used to satisfy the long list of constraints. The device is fabricated through UV-LIGA, utilizing nickel and copper as the structural and sacrificial layer. The experimental and simulation results demonstrate that the microgripper can achieve a 60 μm jaw displacement at a voltage of 0.329V. The gripping arms can provide a force of 15 to 450 μN for the handling of micro-objects. The maximum gripper temperature of 98 °C makes it suitable for biological applications. The innovative form and systematic design of the microgripper enable its adaptability for various applications.

Research on Design and Optimization of Micro-Hole Aerostatic Bearing in Vacuum Environment

Micro-hole aerostatic bearings are important components in micro-low-gravity simulation of aerospace equipment, and the accuracy of micro-low-gravity simulation tests is affected by them. In order to eliminate the influence of air resistance on the attitude control accuracy of remote sensing satellites and achieve high fidelity of micro-low-gravity simulation tests, in this study, a design and parameter optimization method was proposed for micro-hole aerostatic bearings for a vacuum environment. Firstly, the theoretical analysis was conducted to investigate the impact of various bearing parameters and external conditions on the bearing load capacity and mass flow. Subsequently, a function model describing the variation in bearing load capacity and mass flow with bearing parameters was obtained utilizing a BP neural network. The parameters of aerostatic bearings in a vacuum environment were optimized using the non-dominated sorting genetic algorithm (NSGA-II) with the objectives of maximizing the load capacity and minimizing the mass flow. Subsequently, experimental tests were conducted on the optimized bearings in both atmospheric and vacuum conditions to evaluate their load capacity and mass flow. The results show that in a vacuum environment, the load capacity and mass flow of aerostatic bearings are increased compared to those in standard atmospheric conditions. Furthermore, it has been determined that the optimal solution for the bearing’s load capacity and mass flow occurs when the bearing has an orifice aperture of 0.1 mm, 36 holes, and an orifice distribution diameter of 38.83 mm. The corresponding load capacity and mass flow are 460.644 N and 11.816 L/min, respectively. The experimental and simulated errors are within 10%; thus, the accuracy of the simulation is verified.

An Output Cooperative Controller for a Hydraulic Support Multi-Cylinder System Based on Neural Network Compensation

The straightness control of a fully mechanized working face is the key technology used in intelligent coal mining, so the position control of a hydraulic support multi-cylinder moving system is of great significance. However, due to the harsh environment of coal mines, complex friction, external disturbances, and the coupling relationship between adjacent cylinders, the accuracy of position control is restricted. Therefore, an output cooperative controller is proposed in this paper for a multi-cylinder system. A high-order sliding mode observer is utilized to estimate the system states with the only available output position signal. A neural network disturbance observer is applied to estimate the lump disturbance of the strict-feedback model, including the system uncertainty, disturbance force and the coupling force between adjacent cylinders. Then, continuous motion position tracking simulation is conducted and the estimation performance of the state observer and neural network is analyzed. Furthermore, a multi-cylinder collaborative control test rig is designed, and experiments based on the actual actions of the hydraulic support are conducted. The results show that the proposed output cooperative controller has an excellent position control performance compared with the traditional proportional–integral controller.

Nanoalignment by critical Casimir torques

The manipulation of microscopic objects requires precise and controllable forces and torques. Recent advances have led to the use of critical Casimir forces as a powerful tool, which can be finely tuned through the temperature of the environment and the chemical properties of the involved objects. For example, these forces have been used to self-organize ensembles of particles and to counteract stiction caused by Casimir-Liftshitz forces. However, until now, the potential of critical Casimir torques has been largely unexplored. Here, we demonstrate that critical Casimir torques can efficiently control the alignment of microscopic objects on nanopatterned substrates. We show experimentally and corroborate with theoretical calculations and Monte Carlo simulations that circular patterns on a substrate can stabilize the position and orientation of microscopic disks. By making the patterns elliptical, such microdisks can be subject to a torque which flips them upright while simultaneously allowing for more accurate control of the microdisk position. More complex patterns can selectively trap 2D-chiral particles and generate particle motion similar to non-equilibrium Brownian ratchets. These findings provide new opportunities for nanotechnological applications requiring precise positioning and orientation of microscopic objects.

A Data-Driven Model with Hysteresis Compensation for I2RIS Robot.

Retinal microsurgery is a high-precision surgery performed on a delicate tissue requiring the skill of highly trained surgeons. Given the restricted range of instrument motion in the confined intraocular space, snake-like robots may prove to be a promising technology to provide surgeons with greater flexibility, dexterity, and positioning accuracy during retinal procedures such as retinal vein cannulation and epiretinal membrane peeling. Kinematics modeling of these robots is an essential step toward accurate position control. Unlike conventional manipulators, modeling these robots does not follow a straightforward method due to their complex mechanical structure and actuation mechanisms. The hysteresis problem can especially impact the positioning accuracy significantly in wire-driven snake-like robots. In this paper, we propose a data-driven kinematics model using a probabilistic Gaussian mixture model (GMM) and Gaussian mixture regression (GMR) approach with a hysteresis compensation algorithm. Experimental results on the two-degree-of-freedom (DOF) integrated robotic intraocular snake (I2RIS) show that the proposed model with the hysteresis compensation can predict the snake tip bending angle for pitch and yaw with 0.45° and 0.39° root mean square error (RMSE), respectively. This results in overall 60% and 70% improvements of accuracy for yaw and pitch over the same model without the hysteresis compensation.

RBF neural network dynamic sliding mode control based on lambert W function for piezoelectric stick-slip actuator.

This paper presents a novel approach for increasing the precision of high-precision positioning control experiments for a piezoelectric stick-slip actuator system. This is achieved through dynamic sliding mode control with a radial basis function neural network (RBFNN) based on the Lambert W function. The proposed control strategy is divided into two parts: scanning mode control and stepping mode control. For scanning control, a dynamic sliding mode controller was designed to solve the jitter problem in traditional sliding mode control. The introduction of the RBFNN avoids the effects of uncertainty terms and unknown disturbances in the model; reduces the controller gain, which must be adjusted; and improves the robustness of the system to disturbances. The stability of the dynamic sliding mode controller based on the RBFNN was verified through a Lyapunov analysis, and the Lambert W function was introduced to optimize the controller parameters responsible for the time lag in the closed-loop control system. This optimization improved the system's robustness against time delays, which can adversely affect its performance. Simulation and experimental results indicated that the proposed control strategy achieved a positioning control accuracy of <40nm during the scanning phase and was robust in the presence of a load. In long-distance positioning control experiments, the control strategy achieved a control target of 40 μm while maintaining the positioning control accuracy and reducing the impact of time lag on the system.

Trajectory compensation based adaptive control (TCAC) for high-precision piezoelectric actuators

Piezoelectric actuator (PEA) has been widely used in micro-systems, due to the advantages of nano-scale precision, rapid response speed, high stiffness, etc. Nevertheless, the intrinsic nonlinearities of PEA, particularly hysteresis, severely deteriorate its positioning and tracking control accuracy. In most existing control algorithms of PEA, the approximate inverse model of hysteresis is developed to compensate for motion error, which requires high modeling accuracy. To avoid the influence of complex modeling procedures and modeling errors on tracking precision, a trajectory compensation-based adaptive control method has been proposed in this paper. Firstly, a simple linear controller is used to establish the closed-loop feedback system and to guarantee the basic tracking performance of the PEA system. And then, the trajectory compensation is designed according to the frequency analysis of the closed-loop control system. Finally, nonlinear adaptive compensation is used to eliminate the residual errors of the above linear frequency domain model. Different from conventional controllers, the proposed method can achieve excellent tracking control performance without any hysteresis model of PEA. The stability and convergence of the proposed method have been theoretically proved. In addition to theoretical guarantees, the proposed method is validated experimentally and demonstrated to achieve the root-mean-square and maximum value of tracking errors to less than 8 nm and 25 nm, respectively, which has a clear accuracy advantage over other methods.