Motion sickness and motion characteristics of vessels at sea

Measurements of vessel motion and consequent seasickness amongst passengers have been made on six ships, two hovercraft and a hydrofoil. Data are presented for 20 029 passengers surveyed on 114 voyages involving 370?hours of motion recordings. Vomiting incidence and illness rating were found to be linearly related to the root-mean-square magnitude of the vertical z-axis acceleration. Sickness increased with increasing duration of exposure and a measure of motion ‘dose’ is examined as a convenient way of combining the variables of stimulus magnitude and duration. High frequency motion in hovercraft at about 0·6?Hz was found to be less provoking of sickness than similar magnitudes at lower frequencies. Motion in axes other than the vertical correlated less highly with sickness, although there was some intercorrelation between axes. The results presented enable predictions to be made of seasickness occurrence in marine vessels and other forms of transport where low frequency vertical oscillations are encountered.     

Surface slope effects on shingling frequency and postural balance in a simulated roofing task

The purpose of this study was to investigate the influence of surface slopes (18 degrees , 26 degrees , 34 degrees ) on the maximum acceptable roof shingling frequency for males performing a simulated roof-shingling task. The psychophysical roof shingling frequency was also compared to the postural sway and trunk motion values. The maximum acceptable roof shingling frequency and selected trunk motion decreased significantly with an increase in slope. Postural sway however increased significantly with an increase in slope. The study also revealed that workers were experiencing a greater postural sway at the earlier phase of task on the steeper surface. This suggests that there might be an adaptation period associated with working on a slope and the body's ability to compensate for a loss of balance. Therefore, more emphasis should be given to the workers in this adaptation period, with additional monitoring and cautionary measures. Collectively, the findings of the study could be utilized for improving work practices on roofs, while reducing the potential risks of falls in roofing construction.     

针对机车低频晃车问题的频变阻尼减振器仿真分析研究

针对某型高速机车车体横向低频晃动问题,提出一种将传统抗蛇行减振器替换为频变阻尼减振器(FSD)的抑制方法.首先,应用Simpack建立该机车动力学模型,从车体振动频域分布对车体横向低频晃动特性进行分析,分析表明车体横向晃动频率在1-2Hz之间;然后,建立频率阀的CFD计算模型和FSD减振器数值简化模型;最后,对比应用传...     

减摇水舱试验台架横荡系统研究

船舶减摇水舱试验台架是研究和设计减摇水舱的重要实验设备,准确模拟船舶在海浪中的运动是设计试验台架的关键。目前试验台架研究的仅是单纯横摇,如果考虑了横荡的基本轨圆运动,以及相应的横摇与水舱内液体加速度的耦合,则船的横摇运动更符合实际情况．本文对横荡运动进行了理论分析,并将PID控制方法应用于模拟横荡运动的电液位置伺服控制系统中,仿真结果表明系统具有良好的跟踪性能．符合设计要求．     

On human response to prolonged repeated whole-body vibration

The experiment was aimed at investigating human response to different doses of whole-body vibration (WBV), at checking adaptation to repeated exposures, at further evaluating the frequency weighting, and at examining the effect of a distinct interruption of prolonged exposure. Eight male seated subjects were exposed for 3 h to sinusoidal WBV in the z-axis with the frequencies 4 Hz and 8 Hz, at a constant acceleration level of 1·0ms^-2 rms,each frequency being repeated 4 times on consecutive days. Transmissibility, impedance, bioelectrical activity of trunk muscles, postural sway, performance in vigilance tasks, and the subjectively assessed psychological state, efforts, and stress experienced in performing the tasks were investigated. The transmissibility decreased during exposure time at 4 Hz and increased at 8 Hz when a controlled posture was maintained. The power-spectral density distribution and amplitude of postural sway were affected by WBV, depending on both duration and frequency. Performance data and rating data exhibited decrements and adverse effects, being greater beyond the ‘fatigue-decreased proficiency’ boundary (FDPB); adaptation and habituation were more pronounced at the FDPB dose. Generally, there were no cumulative effects. A pause for 20min did not essentially affect the reactions investigated.     

Generation and Analyses of the Reinforced Wave Gait for a Mammal-Like Quadruped Robot

The statically stable gait control of a mammal-like quadruped robot that provides an adequate or stable manner of traversing over irregular terrain was addressed. The reinforced wave gait which integrates new parameters of the lateral offset and displacements of the center of gravity (COG) based on the profiles of standard wave gait was investigated. The continuous and discontinuous motion trajectory of a robot’s COG in the periodic reinforced wave gait could be realized. The longitudinal and lateral stability margins of a reinforced wave gait were formulated for the gait generation and control of a quadruped robot. Moreover, the effects of the lateral offset on the stability, velocity and the energy efficiency were studied in details. The reinforced wave gait with lateral sway motion adequately improved the stability, and two particular gait patterns that involve the lateral sway motion for a maximal velocity and maximum achievable stability were described. With consideration of a quadruped robot with asymmetric carrying loads on its body, a scheme that relates to the gait parameters of the displacement of a robot’s COG to avoid losing stability was proposed. The simulation and experimental results about the effects of lateral offset added in the reinforced wave gait on the minimum power consumption during a quadruped robot walking on a flat terrain indicated that the reinforced wave gait with a larger lateral offset would generate a better wave gait with a higher velocity and energy efficiency.     

Auditory and visual interactions in postural stabilization

Abstract

The interaction and subsequent interpretation of sensory feedback from different modalities are important determinants in the regulation of balance. The importance of sound in this respect is not, as yet, fully understood. The aim of the present study was to determine the interaction of specific auditory frequencies and vision on postural sway behaviour. The frequencies employed represent the geometrical mean of 23 of the 25 critical bandwidths of sound, each presented at two loudness levels (70 and 90 phones). Postural sway was recorded using a biomechanical measuring platform. As expected vision had a highly significant stabilizing effect on most sway parameters. The frequency of the sound, however, appeared to influence the regulation of anteroposterior sway, while increasing loudness tended to increase mediolateral sway. At some frequencies the sound appeared to compensate for the lack of visual feedback. The interaction of sound and vision, particularly in combinations that lead to increased sway behaviour, may have implications in the occurrence, and possible prevention, of industrial accidents.     

Features of the Postural Sway Signal as Indicators to Estimate and Predict Visually Induced Motion Sickness in Virtual Reality

Navigation in a 3D immersive virtual environment is known to be prone to visually induced motion sickness (VIMS). Several psychophysiological and behavioral methods have been used to measure the level of sickness of a user, among which is postural instability. This study investigates all the features that can be extracted from the body postural sway: area of the projection of the center of gravity (mainly considered in past studies) and its shape and the frequency components of the signal’s spectrum, in order to estimate and predict the occurrence of sickness in a typical virtual reality (VR) application.

After modeling and simulation of the body postural sway, an experiment on 17 subjects identified a relation between the level of sickness and the variation both in the time and frequency domains of the body sway signal. The results support and go further into detail of findings of past studies using postural instability as an efficient indicator of sickness, giving insight to better monitor VIMS in a VR application.     

The influence of moving auditory stimuli on standing balance in healthy young adults and the elderly

The maintenance of postural balance depends on effective and efficient feedback from various sensory inputs. The importance of auditory inputs in this respect is not, as yet, fully understood. The purpose of this study was to analyse how the moving auditory stimuli could affect the standing balance in healthy adults of different ages. The participants of the study were 12 healthy volunteers, who were divided into two age categories: the young group (mean = 21.9 years) and the elderly group (mean = 68.9 years). The instrument used for evaluation of standing balance was a force plate for measuring body sway parameters. The toe pressure was measured using the F-scan Tactile Sensor System. The moving auditory stimulus produced a white-noise sound and binaural cue using the Beachtron Affordable 3D Audio system. The moving auditory stimulus conditions were employed by having the sound come from the right to left or vice versa at the height of the participant's ears. Participants were asked to stand on the force plate in the Romberg position for 20 s with either eyes opened or eyes closed for analysing the effect of visual input. Simultaneously, all participants tried to remain in the standing position with and without auditory stimulation that the participants heard from the headphone. In addition, the variables of body sway were measured under four conditions for analysing the effect of decreased tactile sensation of toes and feet soles: standing on the normal surface (NS) or soft surface (SS) with and without auditory stimulation. The participants were asked to stand in a total of eight conditions. The results showed that the lateral body sway of the elderly group was more influenced than that of the young group by the lateral moving auditory stimulation. The analysis of toe pressure indicated that all participants used their left feet more than their right feet to maintain balance. Moreover, the elderly had the tendency to be stabilized mainly by use of their heels. The young group were mainly stabilized by the toes of their feet. The results suggest that the elderly may need a more appropriate stimulus of tactile and auditory sense as a feedback system than the young for maintaining and control of their standing postures.     

The influence of moving auditory stimuli on standing balance in healthy young adults and the elderly

The maintenance of postural balance depends on effective and efficient feedback from various sensory inputs. The importance of auditory inputs in this respect is not, as yet, fully understood. The purpose of this study was to analyse how the moving auditory stimuli could affect the standing balance in healthy adults of different ages. The participants of the study were 12 healthy volunteers, who were divided into two age categories: the young group (mean = 21.9 years) and the elderly group (mean = 68.9 years). The instrument used for evaluation of standing balance was a force plate for measuring body sway parameters. The toe pressure was measured using the F-scan Tactile Sensor System. The moving auditory stimulus produced a white-noise sound and binaural cue using the Beachtron Affordable 3D Audio system. The moving auditory stimulus conditions were employed by having the sound come from the right to left or vice versa at the height of the participant's ears. Participants were asked to stand on the force plate in the Romberg position for 20 s with either eyes opened or eyes closed for analysing the effect of visual input. Simultaneously, all participants tried to remain in the standing position with and without auditory stimulation that the participants heard from the headphone. In addition, the variables of body sway were measured under four conditions for analysing the effect of decreased tactile sensation of toes and feet soles: standing on the normal surface (NS) or soft surface (SS) with and without auditory stimulation. The participants were asked to stand in a total of eight conditions. The results showed that the lateral body sway of the elderly group was more influenced than that of the young group by the lateral moving auditory stimulation. The analysis of toe pressure indicated that all participants used their left feet more than their right feet to maintain balance. Moreover, the elderly had the tendency to be stabilized mainly by use of their heels. The young group were mainly stabilized by the toes of their feet. The results suggest that the elderly may need a more appropriate stimulus of tactile and auditory sense as a feedback system than the young for maintaining and control of their standing postures.     

Effects of BMI and task parameters on postural sway during simulated small parts assembly

Postural stability is critical for ensuring a safe workplace. Employees with poor stability are more prone to falls and injuries while at work. In this study, postural sway of participants in different obesity categories was evaluated while performing an assembly workstation task. The study included three workstations: those designed for the 5th, 50th and 95th percentile workers based on anthropometric data tables. Force plates were used to study the differences in postural sway in both the medial–lateral and anterior–posterior directions. The results revealed that the obese class 1 and obese class 2 groups’ anterior–posterior sway was significantly larger than that of the normal weight groups while performing assembly work tasks. Also, pace type (self-paced or time-paced) and workstation (5th, 50th and 95th percentile) significantly affected the postural sway. The postural sway was not affected by gender differences. Workstations should be designed to accommodate the increased postural sway of obese workers.     

侧向推搡下的四足机器人复合抗扰控制策略

针对四足机器人侧向推搡下的平衡恢复问题,提出了一种复合抗扰反应式鲁棒控制策略.该策略由摆动相的自适应侧摆规划策略和支撑相的关节抗扰控制构成.摆动相自适应侧摆规划策略通过四足机器人足端落地点的力平衡条件进行主动式步态规划以保证机器人在侧向推搡下的姿态稳定,并基于关节输出力矩给出了侧摆的启动条件.支撑相关节抗扰控制通过带扰动项的四足机器人完整动力学模型设计了基于干扰观测器的鲁棒滑模控制器,实现对侧向推搡扰动的补偿.最后,通过Matlab与ADAMS联合仿真验证了提出的控制策略的有效性.     

小车吊重系统摆振动力学模型及仿真

认识和掌握吊重摆振的动力学特性,是研究起重机防摇控制方案的前提条件.为了准确分析吊重摆振的动力学规律和影响因素,采用理论分析和动态仿真的方式对吊重摆振特性进行了研究.文中根据起重机小车-吊重系统的三维动力学模型建立了吊重摆振的二自由度摆角动力学模型,通过线性简化从模型中找出了影响摆角大小的主要因素--吊重绳长和运行加(减)速度,并以此动力学模型进行了起重机在多种工况下的动态仿真.通过仿真分析得到了小车加速度和吊重绳长对吊重摆振角度、频率和摆角速度的影响规律.     

Driver-Vehicle Behaviour in Restricted-Path Turns

Abstract

An experiment was conducted in which drivers negotiated a test course containing thirteen low-speed curves with well-defined lateral boundaries (restricted-path turns), but were free to select their speed of travel. No evidence is found that the ‘ preforrcd yaw rato ’ beliuviour exhibited in free-path turns is relevant to restricted-path driving. The results indicate that the maximum lateral acceleration developed was the major determinant of speed selection on a given radius curve, the level adopted decreasing with increased curve radius. The deviations of the vehicle paths from the set-out curves are examined in detail. The effect of experimental instructions designed to elicit ‘ normal ’ and ‘ stressed ’ driving strategies is also investigated. The data obtained appear to provide the first comprehensive collection of detailed information on driver-vehicle behaviour over a range of curve geometries.     

基于Frenet坐标系的自动驾驶轨迹规划与优化算法

针对公路场景下作速度保持的自动驾驶汽车实时轨迹规划问题,提出一种基于Frenet坐标系的优化轨迹规划算法.首先,利用Frenet坐标系将车辆运动解耦,构建无约束横向/纵向独立积分系统;然后,根据初始配置和可内嵌到行为层的目标配置,通过采样生成有限的4次、5次多项式候选轨迹集合;最后,利用以高斯卷积、加速度变化率为核心的安全性和舒适性评价指标构建损失函数,评价轨迹成本,并结合曲率、加速度检查,选择能够最小化损失的最优解.结果表明,该算法能满足公路型场景的规划需求,车辆运动轨迹平滑、舒适、安全性更高.     

Mining free-structured information based on hidden Markov models

The potentials of hidden Markov models (HMM) in mining free-structured information are investigated in this study. The samples under test are relating to C4ISR information derived from the contents of ‘Forecast International’, which is a web-based database containing free-structured archive of forecast reports about aerospace systems, weapon systems, and military industries. This study focuses on three C4ISR relating target terms, namely, ‘Company’, ‘System types’, and ‘cost’, for information mining analysis. The experiments are performed in two stages. In the first stage, each HMM being built is exclusively serving for one target term information extraction so as to test the HMM fundamental information extraction capability. While in the second stage, the experiment is then extended to resolve a more complex, multiple term extraction issue. The results reveal that, by using HMMs as a basis, the accuracies can all achieve more than 80% for single target term extraction, and 76% in average for multi-term extraction case.     

Actively-controlled beds for ambulances

During transportation by ambulance, a patient is exposed to inertial acceleration when an ambulance decelerates or turns a corner. Such acceleration often gives a patient physical stress such as blood pressure variation or body sway, which causes strong pain, feeling of discomfort or sometimes critical damage for seriously injured persons. To reduce this undesirable effect of the acceleration, the authors developed the actively-controlled bed （ACB） which controls the posture of a stretcher in real time to reduce foot-to-head and lateral acceleration acting on a supine person. This paper describes development of the ACB, including control system design and performance evaluation. The control system is designed by Zakian＇s framework, which comprises the principle of matching and the method of inequalities, so that the design specifications on the tracking error and the motor torque are satisfied. From the results of driving experiments and simulation, it is estimated that the ACB can reduce the acceleration acting on a patient by 65% in the foot-to-head direction and by 75% in the lateral direction.     

Animating with style: defining expressive semantics of motion

Actions performed by a virtual character can be controlled with verbal commands such as ‘walk five steps forward’. Similar control of the motion style, meaning how the actions are performed, is complicated by the ambiguity of describing individual motions with phrases such as ‘aggressive walking’. In this paper, we present a method for controlling motion style with relative commands such as ‘do the same, but more sadly’. Based on acted example motions, comparative annotations, and a set of calculated motion features, relative styles can be defined as vectors in the feature space. We present a new method for creating these style vectors by finding out which features are essential for a style to be perceived and eliminating those that show only incidental correlations with the style. We show with a user study that our feature selection procedure is more accurate than earlier methods for creating style vectors, and that the style definitions generalize across different actors and annotators. We also present a tool enabling interactive control of parametric motion synthesis by verbal commands. As the control method is independent from the generation of motion, it can be applied to virtually any parametric synthesis method.     

A study of tipping stability for omnidirectional mobile robot with active dual-wheel caster assemblies

A holonomic omnidirectional mobile robot with active dual-wheel caster assemblies is proposed as a robotic transport vehicle. With concern to the existence of sudden acceleration and other dynamical effects during maneuver, the tip-over instability monitoring is very important to prevent any unexpected injuries and property damage. This work presents the preventive method of the tip-over occurrence by estimating the tipping direction and stability metrics. The dynamical model of the omnidirectional mobile robot is derived to estimate the net force from the supporting reaction force at each wheel which is caused by the inertial and external forces. The direction of tipping and stability metric is estimated using moments stability measure. The performance of the tip-over prediction for an omnidirectional mobile robot with active dual-wheel assemblies is shown by the conducted simulations.     

Effect of passengers’ active head tilt and opening/closure of eyes on motion sickness in lateral acceleration environment of cars

This study examined the effect of passengers’ active head-tilt and eyes-open/eyes-closed conditions on the severity of motion sickness in the lateral acceleration environment of cars. In the centrifugal head-tilt condition, participants intentionally tilted their heads towards the centrifugal force, whereas in the centripetal head-tilt condition, the participants tilted their heads against the centrifugal acceleration. The eyes-open and eyes-closed cases were investigated for each head-tilt condition. In the experimental runs, the sickness rating in the centripetal head-tilt condition was significantly lower than that in the centrifugal head-tilt condition. Moreover, the sickness rating in the eyes-open condition was significantly lower than that in the eyes-closed condition. The results suggest that an active head-tilt motion against the centrifugal acceleration reduces the severity of motion sickness both in the eyes-open and eyes-closed conditions. They also demonstrate that the eyes-open condition significantly reduces the motion sickness even when the head-tilt strategy is used.

Practitioner Summary: Little is known about the effect of head-tilt strategies on motion sickness. This study investigated the effects of head-tilt direction and eyes-open/eyes-closed conditions on motion sickness during slalom automobile driving. Passengers’ active head tilt towards the centripetal direction and the eyes-open condition greatly reduce the severity of motion sickness.