Position Control Scheme Research Articles

Robust UKF Relative Positioning Approach for Tightly Coupled Vehicle Ad Hoc Networks Based on Adaptive M-Estimation

Huber M-estimation, as an estimation method based on mixed norm as cost function, provides an effective method for robust filtering to deal with measurement outliers. Based on statistical linear regression model approximating nonlinear measurement model, M-estimation algorithm is used to realize measurement update of states. However, when the measurement noise pollution rate is high, the filtering performance will be seriously degraded. In order to further improve the actual performance of data fusion under abnormal measurement noise, a vehicle cooperative positioning scheme based on adaptive M-estimation robust unscented Kalman filter (AMRUKF) was proposed. This algorithm combines Huber’s linear regression problem with covariance matching method, and calculates the adaptive matrix through the innovation covariance estimator based on fading memory index weighting to adaptively adjust the measurement noise covariance used in Huber M estimation method. The analytical and experimental results of tightly-coupled vehicle relative positioning show that the proposed AMRUKF method can effectively improve the robustness and accuracy of relative positioning and provide a practical control scheme for vehicle cooperative positioning.

An effective flight attitude and trajectory control scheme for sounding rocket

Existing sounding rocket flight is probably disturbed by external factors, of which attitude is lack of automatic control function and flight trajectory is not stable, thus the project designed a canard adjustable posture scheme based on PID control algorithm, which can effectively solve the sounding rocket flight stability and flight path anti-interference problem with high efficiency.

Hybrid Control of Orientation and Position for Redundant Manipulators Using Neural Network

Position and orientation of the end-effector of redundant manipulators perform a core role in various complex tasks. However, most quadratic programming (QP)-based robot control approaches merely take the position of the end-effector into account, which is relatively inadequate and impractical. Driven by this significant deficiency, this article develops a control method for end-effector orientation representations by analyzing a rotation matrix. Specifically, it is formulated as an equality constraint and applied to control issues of Euler angles and axis-angle representation. On this basis, a QP-based position and orientation control (POC) scheme is proposed for the kinematic control of redundant manipulators. To handle such a POC problem, a dynamic neural network (DNN) is designed with rigorous theoretical analyses. Simulation results show that the POC scheme can accurately control the orientation representations and position of the end-effector. Experimental results and comparisons with state-of-the-art approaches highlight the feasibility and superiority of the proposed method.

Error Analysis and Accuracy Optimization for the Hand-eye Calibration of Line Structured Light

The rapid development of machine vision technology in recent years has resulted in applications in engineering scenarios such as weld tracking, visual measurement, and precision gripping. Focusing on the fundamental steps of applying machine vision technology, the “hand-eye calibration” process is analyzed based on scenarios with a line-structured light camera and calibration ball. We found out that noise and camera pose are the main sources of calibration error. To address these issues, an improved K-medoids noise pre-processing algorithm and a camera shooting attitude control scheme are proposed and applied. The experimental results showed that when the radius of the tangent circle/radius of the calibration sphere approximates 0.618, the root means a square error of the repeatability accuracy of hand-eye calibration could be controlled within 0.23 mm, which fully meets the application requirement. Considering the low cost of line-structured light cameras, the findings of this study contribute to the large-scale diffusion of machine vision technology in engineering practices.

Effects of arm movement strategies on emotional state and balance control during height-induced postural threat in young adults

BackgroundIt is firmly established that postural threat seems to lead to an increased reliance on an ankle control (‘stiffening’) strategy. However, little is known about how postural threat affects performance in challenging tasks that require the use of upper body postural control strategies for stability. It is logical to assume that in such conditions, being able to utilise an upper body strategy may reduce the reliance on such ankle stiffening strategy. Research questionThe objective of this study was to determine how arm movement influences balance control during a challenging balance task performed under conditions of postural threat. MethodsThirty young adults (mean ± SD age; 22.0 ± 4.0 years) balanced in tandem stance whilst standing at both ground-level (no threat) and 0.8 m above ground (threat). In both conditions, participants performed the task under two different arm positions: restricted arm movements and free arm movements. Postural sway amplitude and frequency were calculated to infer postural stiffening response. Self-reported emotional responses were quantified by assessing balance confidence, fear of falling, perceived stability, and conscious balance processing. ResultsIndependent of arm movements, postural threat evoked an increase in fear of falling and conscious balance processing, and reductions in balance confidence and perceived stability. These threat-related changes in emotional state were further amplified when arm movements were restricted. Whilst significant increases in sway frequency during threat were observed in both arm conditions, reductions in sway amplitude were only observed during the restricted arm movement condition. SignificanceWe propose that these responses likely reflect a fear-related cautious strategy intended to reduce the postural destabilisation associated with individuals being unable to use their arms to counter any destabilisation, as would normally be the case in daily life.

Exploring how arm movement moderates the effect of task difficulty on balance performance in young and older adults

Emerging evidence highlights that arm movements exert a substantial and functionally relevant contribution on quiet standing balance control in young adults. Ageing is associated with “non-functional” compensatory postural control strategies (i.e., lower limb co-contraction), which in turn, may increase the reliance on an upper body strategy to control upright stance. Thus, the primary purpose of this study was to compare the effects of free versus restricted arm movements on balance performance in young and older adults, during tasks of different difficulty. Fifteen young (mean ± SD age; 21.3 ± 4.2 years) and fifteen older (mean ± SD age; 73.3 ± 5.0 years) adults performed bipedal, semi-tandem and tandem balance tasks under two arm position conditions: restricted arm movements and free arm movements. Centre of pressure (COP) amplitude and frequency were calculated as indices of postural performance and strategy, respectively. Especially in older adults, restriction of arm movement resulted in increased sway amplitude and frequency, which was primarily observed for the mediolateral direction. Further, increasing balance task difficulty raised the arm restriction cost (ARC; a new measure to quantify free vs. restricted arm movement differences in postural control) that was more prominent in older adults. These findings indicate the ARC provides a measure of reliance on the upper body for balance control and that arm movement is important for postural control in older adults, especially during tasks of greater difficulty.

Center of Pressure Deviation during Posture Transition in Athletes with Chronic Ankle Instability.

Center of pressure (COP) tracking during posture transition is an ideal scale for determining the recurrence of an ankle injury, thereby preventing chronic ankle instability (CAI). However, the same is difficult to determine because the reduced ability of certain patients (who experienced sprain) to control posture at the ankle joint is masked by the chain of hip and ankle joint motion. Thus, we observed the effects of knee joint immobilization/non-immobilization on postural control strategies during the posture transition task and attempted to evaluate the detailed pathophysiology of CAI. Ten athletes with unilateral CAI were selected. To examine differences in COP trajectories in the CAI side and non-CAI legs, patients stood on both legs for 10 s and one leg for 20 s with/without knee braces. COP acceleration during the transition was significantly higher in the CAI group with a knee brace. The COP transition from the double- to single-leg stance phase was significantly longer in the CAI foot. In the CAI group, the fixation of the knee joint increased COP acceleration during postural deviation. This suggests that there is likely an ankle joint dysfunction in the CAI group that is masked by the hip strategy.

Postural Control and Adaptation Strategy of Young Adults on Unstable Surface.

Balance control is essential for postural adjustment in physical activities. This study investigates the behavior of human postural control and the coordination and adaptation strategy of hip, knee, and ankle when standing on an unstable surface. Twenty participants were recruited. Four different conditions were investigated: a quiet bipedal stance with eyes open and eyes closed, and standing on an unstable surface with eyes open and eyes closed. Other than the joint angle, the standard body sway measures, such as sway area and sway velocity, were computed. A nonlinear time series measure, that is,sample entropy, was used to determine the regularity of the time series and body adaptability to change and perturbation. The results show that the body sway increases as the difficulty increases. This study also confirms the coordination of the hip, knee, and ankle to maintain body balance on the unstable surface by decreasing the joint angle and adopting a lower posture. Even though the individual joint has lower sample entropy value and is deemed to be rigid and less adaptive to perturbation, the postural control exhibits higher sample entropy value, particularly in the anterior-posterior direction, and has the ability to stabilize the body by manipulating the joints simultaneously. These outcomes suggest that an unstable surface not only challenges the human postural control, but also reduces the hip, knee, and ankle adaptability to perturbation, thus making it a great tool to train body balance.

Comparison of Dynamic Postural Control in Youth Athletes with and without a History of Lateral Ankle Sprain : A Case-control Study

PURPOSE The purpose of this study was to compare the dynamic postural control of youth athletes with and without a history of lateral ankle sprains. METHODS Twenty-eight youth athletes (14 lateral ankle sprain, 14 healthy control) participated in this study. All participants answered the Foot and Ankle Ability Measure questionnaire and were subject to the Star Excursion Balance Test (SEBT) for dynamic postural control evaluation to collect the joint angles of the lower extremity, a center of pressure (COP) path, and COP velocity. Independent sample t-test or Mann-Whitney U-test were performed to analyze the difference between the groups. RESULTS The lateral ankle sprain group (LAS) was found to have a long experience in participating in sports, and low Foot and Ankle Ability Measure scores were identified when compared to the healthy control (CON; p<0.05). LAS was observed with a short reach distance, less hip flexion, and dorsiflexion angles during the anterior direction of SEBT when compared to CON (p<0.05). Furthermore, LAS showed a slower anteroposterior and mediolateral center of pressure velocities in the posteromedial aspect of SEBT and a slower anteroposterior COP velocity in the posterolateral aspect of SEBT when compared to that of CON (p<0.05). There were no differences between the groups with respect to the other variables (p>0.05). CONCLUSIONS Based on these results, decreased anterior reach distance of SEBT may be affected by changing the dynamic posture control strategy of the lower extremity joint on the sagittal plane in LAS.

Modeling and Analysis of a Reconfigurable Rover for Improved Traversing over Soft Sloped Terrains.

Adjusting the roll angle of a rover's body is a commonly used strategy to improve its traversability over sloped terrains. However, its range of adjustment is often limited, due to constraints imposed by the rover design and geometry factors such as suspension, chassis, size, and suspension travel. In order to improve the rover's traversability under these constraints, this paper proposes a reconfigurable rover design with a two-level (sliding and rolling) mechanism to adjust the body's roll angle. Specifically, the rolling mechanism is a bionic structure, akin to the human ankle joint which can change the contact pose between the wheel and the terrain. This novel adjustment mechanism can modulate the wheel-terrain contact pose, center-of-mass projection over the supporting polygon, wheel load, and the rover driving mode. Combining the wheel-load model and terramechanics-based wheel-terrain interaction model, we develop an integrated model to describe the system dynamics, especially the relationship between rover pose and wheel slippage parameters. Using this model, we develop an associated attitude control strategy to calculate the desired rover pose using particle swarm algorithm while considering the slip rate and angle constraints. We then adjust the sliding and rolling servo angles accordingly for slope traversing operations. To evaluate the proposed design and control strategies, we conduct extensive simulation and experimental studies. The results indicate that our proposed rover design and associated control strategy can double the maximum slope angles that the rover can negotiate, resulting in significantly improved traversability over soft sloped terrains.

Constrained nonlinear high-efficiency model predictive technics for test mass capture

This paper presents a nonlinear high-efficiency model predictive control (NHMPC) with constraints designed for the test mass (TM) capture phase of the drag-free satellite about gravitational wave observatory. To avoid collisions between test mass and satellite cavity, TM capture is the essential technology for drag-free satellite. Test mass is located inside an electrostatic suspension and locked by a clamp mechanism initially. The test masses are released with high initial offsets and velocities when the mechanism is retracted. The purpose of this phase is to guarantee the TM to be positioned at the cage center and attitude aligned with the local cage frame. Due to the low actuation authority of electrostatic suspension along with critical initial offsets and velocities, it is a challenging task to design the attitude and translation control schemes with simultaneous consideration of system performance and energy consumption. For the problem given above, the TM capture can be reformulated into a nonlinear quadratic optimal control problem with the state and input constraints. A nonlinear model predictive control (NMPC) structure is also designed to handle the noises by forming a closed loop. This control framework can realize optimality and robustness in a compromise. To improve the speed of solving high-dimensional nonlinear optimal control online for MPC, the indirect Chebyshev pseudospectral method with constraints is employed. The convergence and stability of the control loop are analyzed. Simulation examples show that the feasibility and performance of the designed control loop are verified compared with the existing methods and computation times in the millisecond range can be achieved.

Six-Dimensional Target Pose Estimation for Robot Autonomous Manipulation: Methodology and Verification

The autonomous and precise grasping operation of robots is considered challenging in situations where there are different objects with different shapes and postures. In this study, we proposed a method of 6-D target pose estimation for robot autonomous manipulation. The proposed method is based on: 1) a fully convolutional neural network for scene semantic segmentation and 2) fast global registration to achieve target pose estimation. To verify the validity of the proposed algorithm, we built a robot grasping operation system and used the point cloud model of the target object and its pose estimation results to generate the robot grasping posture control strategy. Experimental results showed that the proposed method can achieve a six-degree-of-freedom pose estimation for arbitrarily placed target objects and complete the autonomous grasping of the target. Comparative experiments demonstrated that the proposed target pose estimation method achieved a significant improvement in average accuracy and real-time performance compared with traditional methods.

Fault-Tolerant Attitude Control Incorporating Reconfiguration Control Allocation for Supersonic Tailless Aircraft

This paper presents a fault-tolerant attitude control scheme, incorporating reconfiguration control allocation for supersonic tailless aircraft subject to nonlinear characteristics, actuator constraint, uncertainty, and actuator faults. The main idea is to propose an incremental reconfiguration closed-loop control allocation scheme, coupled with a basic backstepping attitude controller, to achieve attitude control. Based on the virtual control input generated by the basic backstepping attitude controller, firstly, the incremental nonlinear control allocation method is adopted to deal with the nonlinear characteristics and actuator constraint. Secondly, a distribution error feedback loop is constructed in the incremental nonlinear control allocation method to enhance the robustness against the uncertainty of the control effectiveness matrix. Thirdly, the control effectiveness matrix is reconstructed by different kinds of fault information to deal with actuator faults, and the proper combination of actuator deflections is generated to achieve accurate command tracking. The stability of the proposed scheme is guaranteed by the Jury stability criterion and the Lyapunov stability analysis. Finally, in comparison with the three existing approaches, the simulation results of two cases are provided to show the effectiveness of the proposed scheme.

A State Observer-Based Fractional-Order Approach for Trajectory Tracking and Attitude Control of A Quadrotor

With the expanding utility base of unmanned aerial vehicles (UAVs), there comes a strong need for dedicated research towards effective control strategies for these aircraft. This paper presents a feedback control scheme for the trajectory tracking and flight control problem for quadrotor-type UAVs. In particular, a robust fractional-order sliding mode control (FOSMC) scheme based on a state observer approach, consisting of position tracking and an attitude control strategy, is proposed. The basic idea behind choosing the state observer technique is to prevent the chattering phenomenon in this highly non-linear and under-actuated dynamic structure, and preserve the robustness and finite time reachability properties of Sliding Mode controllers. The stability of the proposed control law is proved using Lyapunov’s theorem. Furthermore, a detailed performance analysis of the proposed method is presented in comparison to the existing control algorithms from the recent literature. The obtained results are found promising.

Underactuated attitude tracking control of tethered spacecraft for deployment and spin-up

This paper investigates the underactuated attitude tracking control problem of tethered spacecraft during tether deploying and spinning. The attitudes are controlled by the torque inputs along two body axes and perturbed by the tether tension torque. The coupling effect between spacecraft attitudes and flexible tethers can be alleviated by simplifying control inputs. The main contribution is the development of an underactuated tracking controller with an adaptive barrier function that inhibits unknown disturbance. To avoid singularity problems with tether and spacecraft during simulation, the dynamic model of a tethered system is derived using quaternion transformations. The underactuated attitude control strategy is designed by kinematic state coupling relations and dynamic backstepping technique, which is given extensive stability demonstration using Lyapunov’s theory. An adaptive controller gain with barrier function is employed to inhibit the bounded unknown disturbance with no need for the online estimation signal. Finally, numerical simulations demonstrate the effectiveness and robustness of the proposed underactuated strategy in the case of tether deployment and spin-up, respectively.

Reinforcement Learning-Based Adaptive Position Control Scheme for Uncertain Robotic Manipulators with Constrained Angular Position and Angular Velocity

Aiming at robotic manipulators subject to system uncertainty and external disturbance, this paper presents a novel adaptive control scheme that uses the time delay estimation (TED) technique and reinforcement learning (RL) technique to achieve a good tracking performance for each joint of a manipulator. Compared to conventional controllers, the proposed control scheme can not only handle the system parametric uncertainty and external disturbance but also guarantee both the angular positions and angular velocities of each joint without exceeding their preset constraints. Moreover, it has been proved by using Lyapunov theory that the tracking errors are uniformly ultimately bounded (UUB) with a small bound related to the parameters of the controller. Additionally, an innovative RL-based auxiliary term in the proposed controller further minimizes the steady state tracking errors, and thereby the tracking accuracy is not compromised by the lack of asymptotic convergence of tracking errors. Finally, the simulation results validate the effectiveness of the proposed control scheme.

Sensorimotor recalibration of postural control strategies occurs after whole body vibration

Efficient postural control results from an effective interplay between sensory feedbacks integration and muscle modulation and can be affected by ageing and neuromuscular injuries. With this study, we investigated the effect of whole-body vibratory stimulation on postural control strategies employed to maintain an upright posture. We explored both physiological and posturography metrics, through corticomuscular and intramuscular coherence, and muscle networks analyses. The stimulation disrupts balance in the short term, but leads to a greater contribution of cortical activity, necessary to modulate muscle activation via the formation of (new) synergies. We also observed a reconfiguration of muscle recruitment patterns that returned to pre-stimulation levels after few minutes, accompanied by a slight improvement of balance in the anterior–posterior direction. Our results suggest that, in the context of postural control, appropriate mechanical stimulation is capable of triggering a recalibration of the sensorimotor set and might offer new perspectives for motor re-education.

Design and position control of a robotic brace dedicated to the treatment of scoliosis

AbstractThis paper’s content focuses on designing and prototyping a robotic brace dedicated to treating scoliosis. Scoliosis is an abnormal spinal curvature affecting 1–3% of children and constitutes a major therapeutic problem. In moderate cases of deformity, passive brace treatment is performed. However, this approach can lead to important patient discomfort. So, we propose a robotic solution providing greater mobility and the possibility of adapting the procedure to each patient. The robotic brace we built and tested is composed of three specific rings adapted to the patient’s torso. Each independent module of two consecutive rings is movable through a Stewart–Gough platform-type mechanism. As the robotic brace is lightweight, it brings better portability and improves the patient’s comfort.The first part of the paper shows the state of the art of bracing techniques: from passive to active orthoses. Next, the mechatronics of the device is detailed, and the robot’s kinematic models are developed. The motion control principle is given. In the last part, motion tests were administered with a healthy human to validate the brace architecture choice and its position and motion control strategies.

An adaptive robust backstepping improved control scheme for mobile manipulators robot

In this study, an approach with the position control scheme is proposed for the mobile manipulator robot, by applying the adaptive strategies with the backstepping control technique. In the proposed backstepping controller, the fixed problem of main control parameters has been improved by the adaptive self-updating process. In addition, this control method requires no prior knowledge of the control system, such as the unknown dynamics and disturbances. And, to relax uncertainties, an adaptive robust controller is also designed as a compensator for the main backstepping controller. Moreover, all adaptive updating algorithms are designed based on the Lyapunov theorem so that the proposed control system performances are guaranteed. The advantage of the improved control system will be evaluated via simulation results for the 3 - DOF MMR system.

Sliding Mode Control of Active Magnetic Bearings - A Cascaded Architecture

Accurate and robust positioning of rotor axle is essential for efficient and safe operation of high-speed rotational machines with active magnetic bearings. This study presents a cascaded nonlinear control strategy for vertical axial positioning of an active magnetic bearing system. The proposed scheme employs two sliding mode controllers for regulating rotor vertical position and current and an adaptive estimator to invert the nonlinear input mapping. Uniform asymptotic stability is proven for the closed-loop system and the efficacy and performance of the proposed design is evaluated in simulation.