Position Control Of Manipulator Research Articles

Adaptive Super-Twisting Sliding Mode Control of Underwater Mechanical Leg with Extended State Observer

Underwater manipulation is one of the most significant functions of the deep-sea crawling and swimming robot (DCSR), which relies on the high-accuracy control of the body posture. As the actuator of body posture control, the position control performance of the underwater mechanical leg (UWML) thus determines the performance of the underwater manipulation. An adaptive super-twisting sliding mode control method based on the extended state observer (ASTSMC-ESO) is proposed to enhance the position control performance of the UWML by taking into account the system’s inherent nonlinear dynamics, uncertainties, and the external disturbances from hydrodynamics, dynamic seal resistance, and compensation oil viscous resistance. This newly designed controller incorporates sliding mode (SMC) feedback control with feedforward compensation of the system uncertainties estimated by the ESO, and the external disturbances of the hydrodynamics by fitting the parameters, the dynamic seal resistance, and the compensation oil viscous resistance to the tested results. Additionally, an adaptive super-twisting algorithm (AST) with integral action is introduced to eliminate the SMC’s chattering phenomenon and reduce the system’s steady-state error. The stability of the proposed controller is proved via the Lyapunov method, and the effectiveness is verified via simulation and comparative experimental studies with SMC and the adaptive fuzzy sliding mode control method (AFSMC).

Conceptual design and control method for a non-contact annular electromagnetic stabilized satellite platform

Disturbance-Free Payload (DFP) spacecraft can meet the requirements of ultra-high attitude pointing accuracy and stability for future space missions. However, as the main control actuators of DFP spacecraft, Linear Non-Contact Lorentz Actuators (LNCLAs) have control output problems with six-degree-of-freedom coupling and nonlinear effects, which will affect the attitude control performance of DFP spacecraft. To solve this problem, a novel concept for Non-Contact Annular Electromagnetic Stabilized Satellite Platform (NCAESSP) is proposed in this study. The concept is centered on replacing the LNCLAs with a non-contact annular electromagnetic actuator to solve the two problems mentioned above. Furthermore, for the different control requirements of the payload module and the support module of the NCAESSP, a high-precision attitude controller based on the robust model matching method and a dual quaternion-based adaptive sliding mode controller are proposed. Additionally, the simulation results verify the feasibility and effectiveness of the proposed approach.

PPO-Based Attitude Controller Design for a Tilt Rotor UAV in Transition Process

The complex aerodynamic changes of the tilt-rotor UAV (TRUAV) in the transition process show strong nonlinearity, which brings a great impact on the stability of the vehicle attitude. This study aims to design a PPO-based RL controller for attitude control in the transition process. A reinforcement-learning PPO approach is used to learn the control strategy by interacting directly with the environment. And the reward function is designed and improved for the transition process. The performance of the proposed controller is tested and compared by simulation. The results show that the PPO algorithm is more suitable for the tilt-rotor transition process control than the A2C algorithm. Our proposed reward function improves the attitude control performance and the designed RL controller has good adaptability to changes in the takeoff weight, the diagonal wheelbase and the tilt rate. This study highlights the effectiveness and potential of reinforcement learning for tilt-rotor UAV transition process attitude control. These findings contribute to the advancement of autonomous flight systems by providing insights into the application of reinforcement learning algorithms. These results have important implications for the development of intelligent flight control systems and could guide future research in this area.

LightSail 2 Solar Sail Control and Orbit Evolution

The propellantless thrust of solar sails makes them capable of entirely new classes of missions compared to conventional or electric engines. Initiated in 2010, the Planetary Society’s LightSail program sought to advance solar sail technology with the flights of LightSail 1 and 2. From launch in 2019 to deorbit in late 2022, LightSail 2 demonstrated the first controlled solar sailing in Earth’s orbit using a CubeSat. By adjusting the orientation of the sail relative to the sun twice per orbit, LightSail 2 controlled solar radiation pressure on the sail to offset losses in orbital energy from atmospheric drag. Previous papers analyzed early mission results to show the effect this had on reducing the spacecraft’s orbital decay rate. Subsequent refinements to the spacecraft’s attitude control made throughout the mission eventually enabled it to achieve sustained net increases in orbital energy. This paper presents an analysis of the orbit changes and attitude control performance over the entire mission. Methods of assessing and improving the sail control are described. Activities and attitude behavior during the final deorbit phase are also analyzed, with results relevant to future drag sails as well as solar sail missions.

Attitude control and on-orbit performance evaluation of spacecraft with variable shape function

The variable shape function enables attitude and orbit control by actively changing the shape of a spacecraft on orbit. In order to demonstrate this function on orbit, we developed the “HIBARI” satellite equipped with drivable solar array paddles and demonstrated the world’s first in-orbit variable shape attitude control in FY2021. The present study first compares the behavior of the paddle drive on the ground and on orbit to evaluate its performance. In addition, attitude change angle data from paddle drive on orbit is used for comparison with analytical values and evaluation control performance.

Stress, COVID-19 related knowledge, attitude, and infection control performance of nurses at long-term care hospitals.

This study aimed to identify the stress level, knowledge, attitude, and infection control performance of nurses at long-term care hospitals (LTCHs) designated for infectious disease management and to investigate factors contributing to infection control performance. A total of 178 nurses who had worked for at least 1 month at seven LTCHs designated for infectious disease management and provided care for patients confirmed with COVID-19 were enrolled in the study. Data were collected from February to March 2022 using written and online self-report questionnaires. COVID-19 infection control performance was higher among married than among single participants (t = -3.71, p < 0.001), among those aged 40-49 versus 30-39 years (F = 4.10, p = 0.003), and those with 1-2, 3-4, or ≥5 sessions versus no prior education (F = 6.41, p < 0.001). COVID-19 infection control performance was negatively correlated with stress (r = 0.26, p < 0.001) and positively correlated with knowledge (r = 0.40, p < 0.001) and attitude toward COVID-19 (r = -0.36, p < 0.001). Stress (β = -0.17, p = 0.012), knowledge of COVID-19 (β = 0.28, p < 0.001), attitude toward COVID-19 (β = 0.20, p = 0.004), and marital status (β = 0.18, p = 0.009) were identified as predictors of COVID-19 infection control performance.

CURER: A Lightweight Cable-Driven Compliant Upper Limb Rehabilitation Exoskeleton Robot

Upper limb exoskeletons show promise for improving functionalities required for stroke patients. Despite recent progress, most of current upper limb rehabilitation devices are still bulky, heavy, and less compliant to be applied. This article presents a cable-driven compliant upper limb rehabilitation exoskeleton robot (CURER) with a lightweight frame and comfortable human–robot interaction. A modular series elastic actuator (SEA) was designed to provide controlled torque for each active robotic joint, and Bowden cables were applied to transfer controlled torque to distal joints. A six-bar double parallelogram mechanism was designed to implement 3 active degrees of freedom (DOFs) of a shoulder. An actuated elbow with 1 DOF and a wrist with a passive DOF were also developed for CURER. The anthropomorphic shoulder, elbow, and wrist joints can minimize misalignment between human upper limbs and the robot. The length of anthropomorphic arm was adjustable for a wide range of users. It can apply up to a 33 N·m torque in shoulder flexion/extension, abduction/adduction, intra/extra rotation, and elbow flexion/extension, with a range of 7.6–8.0 Hz position bandwidth in each actuation. CURER has a large range of motion and can provide accurate torque control for stroke patients’ requirements. Besides, a comprehensive rehabilitation strategy including robot-in-charge mode and human-in-charge mode was developed for different recovery stages. Experiments carried out on CURER actuation units demonstrated good position and impedance control performance. Finally, a virtual reality training system was developed to assist the subjects to accomplish upper limb rehabilitation efficiently.

Finite-time sliding mode attitude control design for a coaxial tilt-rotor UAV

In this article, a finite-time sliding mode controller (FTSMC) is designed with the aim of attitude tracking of the coaxial tilt-rotor UAV (CTRUAV) under external disturbance. The CTRUAV is a multi-input multi-output (MIMO) and highly coupled system, which leads to the complexity of the controller design. Based on the dynamic model of the CTRUAV, an FTSMC is designed to improve the tracking performance of attitude control and robustness under uncertain disturbance, the stability of FTSMC is proved based on Lyapunov theory, and the power distribution is adjusted to solve the control-allocation problem of the CTRUAV. At last, simulation results are provided to show the effectiveness of FTSMC.

Research on force and position control performance of the tendon sheath system with time-varying parameters and flexible robotic arms.

The tendon-sheath-system (TSS) is an excellent medium for remote power transmission, which is widely used in laparoscopic surgery robots. Since the operation process requires the robot to move continuously, this time-varying characteristic further aggravates the force and position transmission loss caused by the nonlinear friction of TSS, which affects the control accuracy of the surgical robot. A time-varying tendon-sheath transmission model (RT model) is proposed. A feedforward control system is designed to improve tendon-sheath transmission accuracy. Furthermore, a tendon-sheath transmission model with velocity characteristics (RV model) is established. Force, position, and velocity experiments were carried out on the platform of TSS with a robotic arm. The results show that the R-square values of force and position compensation are at least 96.57% and 99.16%. The proposed RT and RV models are effective in compensating for the TSS transmission loss during the operation of the surgical robot.

Terminal super-twisting sliding mode based on high order sliding mode observer for two DOFs lower limb system

In this paper, a novel backstepping terminal super-twisting sliding mode (TSTSM) with high order sliding mode observer (HOSMO) is proposed to control the two degrees of freedom (DOFs) Serial Elastic Actuator (SEA), inspired by a lower limb of humanoid robots. First, the dynamic model, extended from our previous study, is presented for developing the control algorithm. Secondly, the backstepping technique is utilized to separate the overall system into two subsystems. One of the challenges of SEA is to deal with the evident oscillations caused by the elastic element, which might lead to the degrading performance of load position control. In order to reduce this adverse effect, a TSTSM is proposed to control the position tracking of two subsystems. The advantages of TSTSM are the finite-time convergence despite the bounded perturbation and the dramatic reduction of the chattering phenomenon. To construct and implement the TSTSM controller, it requires the knowledge of all states, which is not available in the current lower limb system setup. Therefore, a HOSMO is utilized to estimate the unknown states. Finally, experiment results are carried out to assess the effectiveness of the proposed controller and compare it with those of different control schemes.

유압시스템을 사용한 고 하중 양팔 로봇의 모션 추종 성능 향상을 위한 슬라이딩 모드 제어

This paper presents the control implementation of a heavy-duty dual-arm robot, Accident Response Manipulator (ARMstrong), configured as teleoperated control by a master robot. The mater-slave configuration for remote operation in dangerous areas has been implemented. The master robot is an exoskeleton type such that an operator can wear it to control the slave. The slave robot is actuated by the hydraulic system, which generates high power but produces larger motion-tracking errors that suffer from nonlinearity. The dead zone of each joint is identified and compensated to improve motion-following performance after the master. Sliding mode control further improves the positional accuracy under unknown payloads. Experimental studies are conducted to demonstrate the position control performance of the ARMstrong slave robot.

ROBUST CONTROL OF LOW-COST DIRECT DRIVES BASED ON INTERIOR PERMANENT MAGNET SYNCHRONOUS MOTORS

Torque ripple compensation problem is considered for electrical drives, based on low-cost direct drive interior perma-nent magnet synchronous motors. Robustness properties of the speed and position control systems have been studied using time scale separation properties of the current, speed and position control loops. It is shown that system closed-loop dynamics according to new controller design has cascaded properties with speed and position control loops con-nected in series and therefore has potential of high frequency torque ripple compensation by increasing controllers gains. Experimental results are presented for two motors with similar rated data but significantly different level of the torque ripple. It is shown that despite of significand difference in parasitic torque amplitude, the similar position con-trol performance can be achieved. It makes proposed control algorithms suitable for both high dynamic performance and low-cost direct drive applications with medium performance requirements. References 13, figures 7.

Robust Attitude Controller Design for an Uncommon Quadrotor With Big and Small Tilt Rotors

AbstractIn this article, a robust attitude controller design for an uncommon quadrotor aerial vehicle is discussed. This aerial vehicle is designed to have two big rotors on the longitudinal axis to increase the lift capacity and flight endurance, and two small tilt rotors on the lateral axis to stabilize the attitude. Similar to other multirotors, linearization of the full nonlinear model and using an appropriate rotor mixing matrix give the approximate diagonal attitude model of this quadrotor around hover. However, this ideal model lacks sensor delays, uncertain parameters, flexible modes of a structure, and inexact decoupling dynamics. Therefore, using this model in the control design limits the achievable attitude control performance. Unlike most studies, a system identification method is applied to estimate a more accurate model and increase the resulting attitude control performance. The aim of this paper is to obtain a suitable nominal model with accompanying uncertainty using robust control criterion in the system identification. In this way, an uncertain model that gives high performance in the subsequent robust control design is obtained. The experimental results show that this combined identification and robust control procedure improves attitude control performance compared to existing classical controller design methods.

On a Vision-Based Manipulator Simulator

This paper presents a typical grasp–hold–release micromanipulation simulator based on MATLAB and Simulink. Closed-loop force and position control were implemented only based on a camera. The work was mainly focused on control performance improvements and GUI design. Different types of control strategies were investigated in both the position and force control processes. Finally, incremental PID and positional PID were adopted in the gripper position control and force control processes, respectively. The best performance of the gripper position control was the fast response of 0.3 s without overshoot and steady-state errors in the range of 10–40 Hz. The new camera control algorithm kept a big motion range (4.48 × 4.48 mm) and a high position resolution of 0.56 µm, with a high force resolution of 1.56 µN in the force control stage. The maximum error between the measured force and the real force was maintained below 4 µN. The steady-state error and the setting time were less than 1.2% and less than 1.5 s, respectively. A separate app, the Image Generation Simulator app, was developed to assist users in getting suitable initial coordinates, camera parameters, desired position resolutions, and force resolutions, which are packed as a standalone executable file. The main app can run the simulation model, debug, playback, and report simulation results, and calculate the calibration equation. Different initial coordinates, camera parameters, sample frequencies, controller parameters, and even controller types can be adjusted from this app.

CLB-Based Development of BiSS-C Interface Master for Motor Encoders

Encoder interfaces should be operated in real time with high precision and fast processing for industrial motor control systems. The continuous bidirectional serial synchronous (BiSS-C) interface is an open-source serial communication protocol designed for motor encoders and is suitable for industrial purposes because of its fast serial communication speed. In this study, we propose a method for developing a BiSS-C interface master for a motor encoder slave, using only the configurable logic block (CLB) peripheral integrated into TI microcontroller units. By analyzing the detailed operation protocol of the BiSS-C interface, we create the truth and state tables for logic circuits and finite state machines, which are required for the BiSS-C interface master. Then, by programming the CLB based on the created truth and state tables, we implement the master clock, serial peripheral interface (SPI) clock, and operational process for the master. This approach is cost-efficient because additional hardware components, such as a field-programmable gate array or a complex programmable logic device, are not required for the master implementations. The developed method can be immediately applied to developing the masters for other BiSS-C encoders with different specifications, which is certainly necessary for a motor drive development and test. By building an AC motor control system with the developed master and performing various experiments, we verify the performance and practical usefulness of the developed BiSS-C interface master. The maximum master clock frequency without any CRC errors is achieved by 6.25 MHz, which can cope with more than 20 kHz motor control cycle frequency. The usefulness is demonstrated by showing the motor speed and position control performance that are acceptable in real applications.

Model Predictive Control Applied to Different Time-Scale Dynamics of Flexible Joint Robots

Modern Lightweight robots are constructed to be collaborative, which often results in a low structural stiffness compared to conventional rigid robots. Therefore, the controller must be able to handle the dynamic oscillatory effect mainly due to the intrinsic joint elasticity. Singular perturbation theory makes it possible to decompose the flexible joint dynamics into fast and slow subsystems. This model separation provides additional features to incorporate future knowledge of the joint-level dynamical behavior within the controller design using the Model Predictive Control (MPC) technique. In this study, different architectures are considered that combine the method of Singular Perturbation and MPC. For Singular Perturbation, the parameters that influence the validity of using this technique to control a flexible-joint robot are investigated. Furthermore, limits on the input constraints for the future trajectory are considered with MPC. The position control performance and robustness against external forces of each architecture are validated experimentally for a flexible joint robot. The experimental validation shows superior performance in practice for the presented MPC framework, especially respecting the actuator torque limits.

SEMG-based Adaptive Cooperative Multi-mode Control of a Soft Elbow Exoskeleton Using Neural Network Compensation.

Soft rehabilitation exoskeletons have gained much attention in recent years, striving to assist the paralyzed individuals restore motor functions. However, it is a challenge to promote human-robot interaction property and satisfy personalized training requirements. This article proposes a soft elbow rehabilitation exoskeleton for the multi-mode training of disabled patients. An adaptive cooperative admittance backstepping control strategy combined with surface electromyography (sEMG)-based joint torque estimation and neural network compensation is developed, which can induce the active participation of patients and guarantee the accomplishment and safety of training. The proposed control scheme can be transformed into four rehabilitation training modes to optimize the cooperative training performance. Experimental studies involving four healthy subjects and four paralyzed subjects are carried out. The average root mean square error and peak error in trajectory tracking test are 3.18° and 5.68°. The active cooperation level can be adjusted via admittance model, ranging from 4.51 °/Nm to 10.99 °/Nm. In cooperative training test, the average training mode value and effort score of healthy subjects (i.e., 1.58 and 1.50) are lower than those of paralyzed subjects (i.e., 2.42 and 3.38), while the average smoothness score and stability score of healthy subjects (i.e., 3.25 and 3.42) are higher than those of paralyzed subjects (i.e., 1.67 and 1.71). The experimental results verify the superiority of proposed control strategy in improving position control performance and satisfying the training requirements of the patients with different hemiplegia degrees and training objectives.

Controller design for high-speed, ultra-precision positioning of a linear motion stage on a vibrating machine base stage control on a vibrating base

This paper presents a high-speed, ultra-precision point-to-point position control system design. It addresses precision stages with unknown characteristics, affected by machine base vibration and system effectiveness. The design is based on the nominal characteristic trajectory following (NCTF) control method, which can provide ultra-precision position control performance for the precision stages without accurate dynamic models. However, conventional NCTF control systems neither provide sufficient vibration suppression nor exhibit suitable vibration suppression characteristics. The position control performance is deteriorated by the machine base vibration. To overcome this problem, a procedure for incorporating a bandpass filter and derivative compensator in the NCTF control system is proposed and designed. These compensators exhibit high vibration suppression ability when combined, rather than when used individually. Additionally, they can be easily designed without any accurate dynamic model. The effectiveness of the compensator combination was first investigated using a linear model and subsequently experimentally verified. Using the proposed procedure, a control system was designed for the precision stage with friction characteristics on the vibrating machine base. The designed control system suppresses the residual vibration immediately after the target value becomes constant, and the error converges below 50 nm within 80 ms.

Robust Backstepping Control Combined with Fractional-Order Tracking Differentiator and Fractional-Order Nonlinear Disturbance Observer for Unknown Quadrotor UAV Systems

In this paper, we studied a fractional-order robust backstepping control (BSC) combined with a fractional-order tracking differentiator and a fractional-order nonlinear disturbance observer for a quadrotor unmanned aerial vehicle (UAV) system. A fractional-order filtered error and a fractional-order tracking differentiator were utilized in a conventional BSC system to improve the positioning control performance of a highly coupled nonlinear quadrotor UAV system and bypass the differentiation issue of the virtual control and compensation of the transformation error in the conventional BSC design. A new fractional-order disturbance observer with the sine hyperbolic function was then proposed to enhance the estimation performance of the uncertain quadrotor UAV. Sequential comparative simulations were conducted, demonstrating that the proposed positioning controller and observer utilizing fractional-order calculus outperformed those of the conventional controller and observer systems.

Interpretable predictive model for shield attitude control performance based on XGboost and SHAP

The sudden decline in the attitude control performance is a common abnormal situation during shield tunneling. When the problem happens, the shield driver will have difficulty controlling the shield's attitude, which will cause the shield to deviate from its design axis and affect the quality of the tunnel. The causes behind poor control performance are usually complicated, so how to choose appropriate countermeasures is a challenging problem. Based on the above issues, this paper proposes the Interpretable Predictive Model for Shield attitude Control Performance (IPM_SCP). The model first predicts the current shield control performance through the extreme gradient boosting (XGBoost) sub-model and then uses the Shapley additive explanation sub-model to interpret the model output. The model was tested on the left-line tunnel of the Hangzhou–Shaoxing railway project in the Ke-Feng section. The results reveal that the model could effectively predict the control performance of the shield and give the most influential parameter and the direction in adjusting the parameter to improve the shield's attitude control performance when the control performance decreases. Therefore, IPM_SCP gives the correct parameter adjustment instructions when the shield’s attitude control performance declines, and eventually improves tunnel construction quality and efficiency.