Sway Angle Research Articles

How the brain can be trained to achieve an intermittent control strategy for stabilizing quiet stance by means of reinforcement learning

The stabilization of human quiet stance is achieved by a combination of the intrinsic elastic properties of ankle muscles and an active closed-loop activation of the ankle muscles, driven by the delayed feedback of the ongoing sway angle and the corresponding angular velocity in a way of a delayed proportional (P) and derivative (D) feedback controller. It has been shown that the active component of the stabilization process is likely to operate in an intermittent manner rather than as a continuous controller: the switching policy is defined in the phase-plane, which is divided in dangerous and safe regions, separated by appropriate switching boundaries. When the state enters a dangerous region, the delayed PD control is activated, and it is switched off when it enters a safe region, leaving the system to evolve freely. In comparison with continuous feedback control, the intermittent mechanism is more robust and capable to better reproduce postural sway patterns in healthy people. However, the superior performance of the intermittent control paradigm as well as its biological plausibility, suggested by experimental evidence of the intermittent activation of the ankle muscles, leaves open the quest of a feasible learning process, by which the brain can identify the appropriate state-dependent switching policy and tune accordingly the P and D parameters. In this work, it is shown how such a goal can be achieved with a reinforcement motor learning paradigm, building upon the evidence that, in general, the basal ganglia are known to play a central role in reinforcement learning for action selection and, in particular, were found to be specifically involved in postural stabilization.

Numerical study on flow characteristics in the primary side of a once-through steam generator under ocean conditions

The flow characteristics of the primary side of the helical coil once-through steam generator (OTSG) have a significant impact on the safe operation of the reactor. Different from the land-based stationary working conditions, the flow of the primary side of the OTSG is influenced by sea waves and winds under ocean conditions. The rigid body motion model is used to calculate the flow of the primary side under different ocean conditions, including heeling, trimming, rolling, pitching, heaving, and combined conditions. The results show that under heeling and trimming conditions, the static pressure of the primary side is different from that under vertical conditions due to the influence of gravity, but its impact on the flow field is relatively small. Under rolling and pitching conditions, the mean flow velocity and pressure drop change periodically with the movement of the OTSG, and the smaller the sway angle, the smaller the variation amplitude of the mean flow velocity and pressure drop. Under the heaving condition, the variation amplitude of the mean flow velocity is greater than that under rolling and pitching conditions, and reverse flow occurs. Under the combined heaving and rolling condition, the mean flow velocity and pressure drop are influenced by the period and amplitude of both the two motions.

Vibration Analysis and Motion Control Method for an Under-Actuated Tower Crane

In this paper, we developed a solution for controlling a tower crane thought as a no-rigid system, and therefore able to have deformation and, during the motion, vibrations. Particularly, large tower cranes show high structural dynamics. Under external excitations, the payload tends to sway around its vertical position and this motion is coupled to the resulting dynamic vibration of the crane structure. These induced vibrations may cause instability and serious damage to the crane system. Furthermore, the energy stored in the flexible structure of a tower crane causes vibrations in the structure during the acceleration and deceleration of slewing movements. A crane operator perceives these vibrations as an unstable speed of the boom. Such behavior involves the control of the crane, particularly precise positioning and manual control of the crane movement at low pivoting speed. We define an Elastic model of the Slewing crane and analyze the bending and Torsional elasticity of the Tower, and the Jib Elasticity. With an approximated method, we calculate the natural wavelengths of the crane structure in the slewing direction. We consider the tower crane as a nonlinear under-actuated system. The motion equations are obtained considering both the normal vibration modes of the tower crane and the sway of the payload. An elastic model of the Slewing crane is achieved, modeling the crane jib as an Euler-Bernoulli beam. Even the payload dynamic is considered, developing an Anti-sway solution by the equation of the movement. We define an iterative calculation of the sway angles and obtain the corresponding velocity profiles, implementing two kinds of solution: an input-shaping control in open-loop, to be used with automatic positioning, and a “command smoothing” method in open-loop, used for reducing the sway of the payload with the operator control. These solutions lead to a reduction of the vibrations of the crane structure. As a consequence, the tower crane is not subject to the strong horizontal and vertical oscillations during the motion of the elastic structure.

The difference in the relationship of spinal sagittal alignment between individuals with flat lumbar and normal lordosis posture based on global and regional angles.

According to previous studies, the relationship between lumbar lordosis and thoracic kyphosis or that between pelvic parameters and thoracic kyphosis have been inconsistent. The purpose of this study was to investigate spinal sagittal alignment and its relationship to global and regional lumbar and thoracic angles, pelvic and sway angles, and C7-S1 distance measurements, followed by a detailed subgroup analysis using an inertial measurement unit system. A total of 51 asymptomatic volunteers stood in a comfortable posture with inertial measurement units attached to the T1, T7, T12, L3, and S2 vertebrae. T1, T7, T12, L3, and S2 sagittal angles were acquired during standing posture using the Eulerian angle coordinate system. All angles are reported as the mean of three 5-s measurements. Following the measurement of lumbar lordosis angles (T12 relative S2), participants were divided into the flat lumbar and normal lordosis groups. There were different correlation patterns between groups because of spinal sagittal imbalance, which was greater in the flat lumbar group than in the normal lordosis group. In addition, sacral inclination proved the ideal parameter to evaluate reciprocal balance in lumbar lordosis, showing a stronger correlation with lower than with upper lumbar lordosis. T1 was the key element in assessing thoracic kyphosis, which showed a stronger correlation with upper than with lower thoracic kyphosis. We suggest that when assessing posture, it is necessary to identify the global and regional angles and it is useful to classify spinal sagittal alignment into subgroups according to lumbar lordosis and evaluate the groups separately.

Automating RTGC with PID Control: Utilizing Camera-Based Image Processing and Object Detection

The high traffic in the container yard requires effective management, and one method to address this is through automation. The Rubber Tyred Gantry Crane (RTGC) plays a crucial role in container yards. Automating the RTGC involves determining the container’s location and sway angle to provide feedback for the control system. The advancements in computer vision technology offer a unique solution to tackle these challenges. This paper proposes image processing as a means to sense the sway angle and MobileNet SSD to detect the container’s location. The proposed method yields accurate measurement results and is integrated with optimized PID-PD for position and sway angle control in RTGC. The effectiveness of the proposed method is demonstrated through successful performance in both simulation and experiments conducted on a laboratory-scale RTGC prototype.

An improved intermittent control model of postural sway during quiet standing implemented by a data driven approach

This paper proposes a new intermittent control model during human quiet standing, which is consisted of postulated “regular intervention” and “imminent intervention”. The regular intervention is within the main control loop, and its trigger condition is equivalent to the switching frequency of center of pressure (COP) data calculated by wavelet transform. The imminent intervention will only be triggered after the postural sway angle exceeds a certain threshold. In order to prove the effectiveness of the new model, the simulation results of the new model and the model proposed by Asai et al. (2009) are compared with the experimental data. The setting parameters of both models are retrieved by Bayesian regression from the experimental data. The results show that the new model not only could exhibit two power law scaling regimes of power spectral density (PSD) of COP, but also show that indices of the probability density function distance, root mean square (RMS), Total Sway Path, displacement Range, 50% power frequency of center of mass (COP) between the simulation results and the experimental data are closer compared to the existing model. Moreover, the limit cycle oscillations (LCOs) obtained from the simulation results of the new model have a higher degree of matching with those retrieved from the experimental data.

Assessing the effects of sway-back posture on global and regional spinal sagittal angles using inertial measurement units.

Sway-back posture in the sagittal profile is a commonly adopted poor standing posture. Although the terms, definitions, and adverse health problems of sway-back posture are widely used clinically, few studies have quantified sway-back posture. To investigate spinal sagittal alignment in sway-back posture while standing based on global and regional angles using inertial measurement units (IMUs). This cross-sectional study recruited 30 asymptomatic young adults. After measuring the sway angle while standing, the participants were divided into sway-back and non-sway-back groups (normal thoracic group). Each participant stood in a comfortable posture for 5 seconds with IMUs at the T1, T7, T12, L3, and S2 levels. Then, we measured the global and regional lumbar and thoracic angles and sacral inclination in the standing position. Although there was no difference in the global lumbar angle, there was a difference in regional lumbar angles between the two groups. The normal thoracic group had balanced lumbar lordosis between the upper and lower lordotic arcs, whereas the sway back group tended to have a flat upper lumbar angle and increased lower lumbar angle. It is useful to assess the global and regional angles in the spinal sagittal assessment of individuals with sway-back posture.

The Effects of Vibro-Tactile Biofeedback Balance Training on Balance Control and Dizziness in Patients with Persistent Postural-Perceptual Dizziness (PPPD).

Patients with persistent postural-perceptual dizziness (PPPD) frequently report having problems with balance control. Artificial systems providing vibro-tactile feedback (VTfb) of trunk sway to the patient could aid recalibration of "falsely" programmed natural sensory signal gains underlying unstable balance control and dizziness. Thus, the question we examine, retrospectively, is whether such artificial systems improve balance control in PPPD patients and simultaneously reduce the effects of dizziness on their living circumstances. Therefore, we assessed in PPPD patients the effects of VTfb of trunk sway on balance control during stance and gait tests, and on their perceived dizziness. Balance control was assessed in 23 PPPD patients (11 of primary PPPD origin) using peak-to-peak amplitudes of trunk sway measured in the pitch and roll planes with a gyroscope system (SwayStar™) during 14 stance and gait tests. The tests included standing eyes closed on foam, walking tandem steps, and walking over low barriers. The measures of trunk sway were combined into a Balance Control Index (BCI) and used to determine whether the patient had a quantified balance deficit (QBD) or dizziness only (DO). The Dizziness Handicap Inventory (DHI) was used to assess perceived dizziness. The subjects first underwent a standard balance assessment from which the VTfb thresholds in eight directions, separated by 45 deg, were calculated for each assessment test based on the 90% range of the trunk sway angles in the pitch and roll directions for the test. A headband-mounted VTfb system, connected to the SwayStar™, was active in one of the eight directions when the threshold for that direction was exceeded. The subjects trained for 11 of the 14 balance tests with VTfb twice per week for 30 min over a total of 2 consecutive weeks. The BCI and DHI were reassessed each week and the thresholds were reset after the first week of training. On average, the patients showed an improved balance control in the BCI values after 2 weeks of VTfb training (24% p = 0.0001). The improvement was greater for the QBD patients than for the DO patients (26 vs. 21%), and greater for the gait tests than the stance tests. After 2 weeks, the mean BCI values of the DO patients, but not the QBD patients, were significantly less (p = 0.0008) than the upper 95% limit of normal age-matched reference values. A subjective benefit in balance control was spontaneously reported by 11 patients. Lower (36%), but less significant DHI values were also achieved after VTfb training (p = 0.006). The DHI changes were identical for the QBD and DO patients and approximately equal to the minimum clinical important difference. These initial results show, as far as we are aware for the first time, that providing VTfb of trunk sway to PPPD subjects yields a significant improvement in balance control, but a far less significant change in DHI-assessed dizziness. The intervention benefitted the gait trials more than the stance trials and benefited the QBD group of PPPD patients more than the DO group. This study increases our understanding of the pathophysiologic processes underlying PPPD and provides a basis for future interventions.

Analysis of Wind Effect on Drone Relay Communications

In this study, we realized a relay network using drones and analyzed the impact of the sway angle of a drone’s attitude on communication in a windy flight environment. Drones in flight act as radio relay stations and communication among them is performed using radio equipment mounted on board. In a windy environment, a directional antenna is used for relay communication among them to avoid interference caused by the spread of radio waves in space and extend the relay distance. However, when wind occurs during flight, the flying attitude of the drone inclines, which causes the beam of the antenna to sway and the communication link to be disconnected, leading to a decrease in the transmission speed. In this study, we statistically evaluated the pitch, yaw, and roll axes of a drone through wind tunnel experiments. Furthermore, the pattern of the swing angle of the drone with respect to the wind speed was investigated using computer simulations to analyze the fluid dynamics and theoretically analyze the swing of the drone. Based on these results, the transmission speed when using a directional antenna was calculated. When the wind speed was 6.0 m/s, the pitch axis deflection angle of the drone was 13∘ at maximum, and the average transmission speed decreased by 33.3 Mbps. In this study, it was found that in communication between drones due to the wind, the transmission efficiency decreased depending on the sway angle of the aircraft.

Development of Autonomous Driving and Motion Control System for a Patient Transfer Robot

In this study, an autonomous driving system of a patient-transfer robot is developed. The developed autonomous driving system has a path-planning module and a motion-control module. Since the developed autonomous driving system is applied to medical robots, such as patient-transfer robots, the main purpose of this study is to generate an optimal path for the robot’s movement and to ensure the patient on board moves comfortably in the PTR. In particular, for the patient’s comfortable movement, a lower controller is needed to minimize the sway angle of the patient. In this paper, we propose a hybrid path-planning algorithm that combines the A-STAR algorithm as a global path-planning method and the AHP (Analytic Hierarchy Process)-based path-planning algorithm as a local path-planning method. In addition, model-based controllers are designed to move patient-transport robots along planned paths. In particular, the LQR controller with the Kalman filter is designed to be robust to the uncertainty and disturbance of the model including the patient. The optimal path generation and patient shaking angle reduction performance of the proposed autonomous driving system have been demonstrated via a simulation on a map that mimics a hospital environment.

Position-Commanding Anti-Sway Controller for 2-D Overhead Cranes Under Velocity and Acceleration Constraints

This paper proposes an anti-sway controller for two-dimensional overhead cranes. The controller is of the position-commanding type, i.e., it sends position commands to the position-controlled trolley, and it uses the sensor information of the payload sway angle. The position commands are determined so that the trolley tracks the desired position signal sent from an upper-level controller and also so that the payload sway is damped. The sway damping is realized by a leaky integral controller, which employs a high-pass filtered time integral of the sway angle. In addition, arbitrary limits can be imposed on the first and second derivatives of the position command, and thus it is applicable to cases where the desired position signal from the upper-level controller is nonsmooth or discontinuous. Due to these features, the controller is expected to be useful in both human-operated and autonomous systems. The controller was validated with a laboratory setup. This paper also presents an algorithm that can be attached to the proposed controller to prevent the overshoot, which can take place when the desired position signal is discontinuous.

Observer-based Control Design for Overhead Crane Systems

This paper proposes an observer-based control design with Disturbance Feedback Control (DFC) for overhead crane systems. DFC is a technique to improve the disturbance rejection capabilities of existing control loops. The crane system is modelled with 3D dynamics and linearized. Payload sway angles are estimated by a Kalman Filter. A state feedback controller for setpoint tracking and a DFC for disturbance rejection are designed using Linear Matrix Inequalities. Both simulation and experimental results show that the observer-based control with DFC can estimate the sway angle and is able to attenuate disturbance inputs better than the conventional observer-based control. The proposed design can thus achieve practical angle sensor-less control with a retro-fit modification of an existing control.

Model reference input shaped neuro-adaptive sliding mode control of gantry crane

This article proposes a hybrid control strategy that integrates the merits of both zero-vibration double derivative input shaping control and neuro-adaptive sliding mode control. The approximation ability of the radial basis function neural network is utilized to estimate the unknown dynamics of the gantry crane system. The input shaping control is used to shape the trolley position, velocity, and acceleration references. These reference trajectories are generated as the state trajectories of a closed-loop system obtained by controlling a nominal system model with a sliding mode control constructed based on the nominal model. The shaped trajectories are sent to the proposed neuro-adaptive sliding mode control as references to be tracked. In comparison with the conventional sliding mode control, the proposed control has higher tracking accuracy and robustness to external disturbances, and effectively reduces the sway angle without suffering from the chattering phenomenon. Moreover, the proposed control has a very high insensitivity to parameter uncertainties. The adaptation mechanisms of the radial basis function neural networks are established based on the Lyapunov stability theory. The effectiveness of the proposed controller is verified through some numerical simulations.

Exploring the Potential of Machine Learning for the Diagnosis of Balance Disorders Based on Centre of Pressure Analyses

Balance disorders are caused by several factors related to functionality deficits in one or multiple sensory systems such as vision, vestibular, and somatosensory systems. Patients usually have difficulty explaining their dizziness, often using ambiguous words to describe their symptoms. A common practice by clinicians is to objectively evaluate the patient's dizziness by applying the Sensory Organization Test (SOT), which measures the contribution of each sensory system (vestibular, visual, somatosensory). The SOT protocol can record up to 2000 measurements in 20 s to generate the Equilibrium Score (EQS) with its five load sensors. EQS is an indicator that reflects how well a patient can maintain balance. However, its calculation only considers two instances from these 2000 measurements that reflect the maximum anterior and posterior sway angle during the test performance; therefore, there is an opportunity to perform further analysis. This article aims to use the Centre of Pressure (COP) time series generated by the SOT and describes a methodology to pre-process and reduce the dimensionality of this raw data and use it as an input for machine learning algorithms to diagnose patients with balance disorder impairments. After applying this methodology to data from 475 patients, the logistic regression model (LR) produced the highest f1-score with 76.47%, and the support vector machine (SVM) performed almost as well, with an f1-score of 76.19%.

Trajectory Tracking of Swing-Arm Type Omnidirectional Mobile Robot

In order to enhance the omnidirectional maneuverability of outdoor wheeled mobile robots, a mobile robot driven by a common wheel is proposed, which realizes four-wheel steering (4WS), oblique motion mode, and spot turn modes according to different power distribution and angle of leg rotation. A dual-mode hybrid controller is designed based on the oblique and 4WS modes, in which multipoint prescanning trajectory tracking control is used for the oblique mode, and incremental linear time-varying model predictive control (ILTV-MPC) is used for the 4WS mode. The constraints required for the dual-mode controller are obtained by experimenting with the test prototype’s transverse and longitudinal tracking performance. A joint MATLAB/CARSIM simulation platform is used to compare and verify the performance of each mode controller under two operating conditions. In the first condition, the tracking accuracy of the 4WS mode can be achieved by using the oblique motion mode, and the transverse sway angle variation is significantly reduced. In the second working condition, the oblique motion mode is better than the tracking effect of the 4WS mode overall. The results show that the oblique motion mode can be used instead of the 4WS mode for trajectory tracking under a small-curvature reference trajectory.

Upgrading for overhead crane anti-sway method using variable frequency drive

The paper discusses about upgrading the overhead crane anti-sway method base on the induction motor torque control from rotor resistance starter to variable frequency drives (VFDs). The upgrading included two phases. The phase 1 is to identify the performance of the overhead crane operation on anti-sway method base on the induction motor torque control using rotor resistance starter (old existing motor starter). The phase 2 is to identify the performance of the overhead crane operation on anti-sway method base on the induction motor torque control that use a variable of frequency drive (new upgrading motor starter). The primary equations connecting tractive force and load sway angle, which the motor torque control law is based on is designed for 0% load wobble at the end of the journey. The words accelerating and braking have been written. Outcomes of modelling the behaviour of a trolley-load of two masses for the normal overhead crane load ratios, a system is described weight to the length of the rope, which supports the hypothesis concerning the feasibility of direct load anti-sway control ON and OFF for regulation of motor for overhead cranes.

Anti-Sway Control on a Harbor Crane System Using a Command Smoothing Iterative Method

The requests for relatively large-sized mobile harbor cranes are increasing. Typically, harbor cranes are self-traveling but do not require any additional civil works to improve the bearing strength of foundation soil. This work describes a novel method able to reduce the sway of a suspended load during the slewing motion of a Harbor Crane. The proposed method is based on an iterative calculation of the sway angle, and the corresponding applied velocity profiles as input to the crane motors. The 'command smoothing' method is used to reduce the sway: additional damping is introduced into the system to control the sway. The multiple-input and multiple-output (MIMO) mechanical system is modeled by a set of non-linear differential equations in which the mathematical model is divided into two subsystems: the first for actuated outputs and the second for underactuated outputs. After defining the stability of the proposed solution and the kinematics of the hydraulic actuators on the boom, a detailed mathematical model is developed, taking into account the non-linear components of the forces, such as centrifugal and Coriolis forces, on the system. Simulation results show that the proposed anti-sway method can dampen the suspended load's oscillations during the harbor crane's slewing movement.

A Pilot Study Comparing the Effects of Concurrent and Terminal Visual Feedback on Standing Balance in Older Adults.

While balance training with concurrent feedback has been shown to improve real-time balance in older adults, terminal feedback may simplify implementation outside of clinical settings. Similarly, visual feedback is particularly well-suited for use outside the clinic as it is relatively easily understood and accessible via ubiquitous mobile devices (e.g., smartphones) with little additional peripheral equipment. However, differences in the effects of concurrent and terminal visual feedback are not yet well understood. We therefore performed a pilot study that directly compared the immediate effects of concurrent and terminal visual feedback as a first and necessary step in the future design of visual feedback technologies for balance training outside of clinical settings. Nineteen healthy older adults participated in a single balance training session during which they performed 38 trials of a single balance exercise including trials with concurrent, terminal or no visual feedback. Analysis of trunk angular position and velocity features recorded via an inertial measurement unit indicated that sway angles decreased with training regardless of feedback type, but sway velocity increased with concurrent feedback and decreased with terminal feedback. After removing feedback, training with either feedback type yielded decreased mean velocity, but only terminal feedback yielded decreased sway angles. Consequently, this study suggests that, for older adults, terminal visual feedback may be a viable alternative to concurrent visual feedback for short duration single-task balance training. Terminal feedback provided using ubiquitous devices should be further explored for balance training outside of clinical settings.

Precise Motion Control of a Power Line Inspection Robot Using Hybrid Time Delay and State Feedback Control.

Intelligent robotic inspection of power transmission lines has proved to be an excellent alternative to the traditional manual inspection methods, which are often tedious, expensive, and dangerous. However, to achieve effective automation of the robots under different working environments, the dynamic analysis and control of the robots need to be investigated for an efficient inspection process. Nonetheless, the application of control techniques for the position, speed and vibration control of these robots has not been explored in detail by the existing literature. Thus, an approach for precise motion control of the sliding inspection robot is presented in this paper. The main contribution of the study is that the chattering problem associated with the traditional command shaping time delay control (TDC) was minimized by smoothing the chattered input signal. Then, the improved control (iTDC) which is effective for oscillation control is hybridized with a pole placement based feedback control (PPC) to achieve both position and the sway angle control of the robot. The nonlinear and the linearized models of the sliding robot were established for the control design and analysis. Three parameters of the robot, namely, the length of the suspended arm, the mass of the payload, and the friction coefficient of different surfaces, were used to assess the robustness of the controller to model uncertainties. The iTDC + PPC has improved the velocity of TDC by 201% and minimizes the angular oscillation of PPC by 209%. Thus, the results demonstrate that the hybridized iTDC + PPC approach could be effectively applied for precise motion control of the sliding inspection robot.

Fine tuning of a PID controller with inlet derivative filter using Pareto solution for gantry crane systems

Gantry cranes are widely used in transporting heavy loads in construction projects and critical industries such as petrochemical industry and nuclear power stations. Their mission should be accomplished with as high accuracy for the trolley positioning, and minimum values of sway oscillation angles as possible. So, the control strategies aim to achieve high productivity (through transporting the trolley with good precision) while considering safety precautions (through eliminating sway oscillations). One of the linear closed loop control methods is using PD and PID controllers. This research provides a non-linear mathematical model for single-pendulum gantry crane with two stable control schemes that depend on PID and PD controllers equipped with inlet derivative filter for every scheme. The two control schemes utilize a PID controller for positioning the trolley and a PD controller for eliminating undesired sway angles of the payload. In the second scheme, the input voltage control signal is always saturated to be positive to preserve the direction of rotation of the driving DC motor. The controllers include up to five gains and two inlet derivative filter coefficients which are tuned using Multi-Objective Genetic Algorithm (NSGA-II) with four different fitness functions and one weighted function to choose a suitable solution from other Pareto solutions. The simulation results are presented to show the superiority of the second scheme precision in trolley transporting with minimum payload sway oscillations.