The vibration discomfort of standing people: relative importance of fore-and-aft, lateral, and vertical vibration

Few studies have compared the discomfort caused by vibration in different directions, and few have investigated the vibration discomfort of standing people. This study was designed to compare the discomfort experienced by standing people exposed to sinusoidal vibration in the fore-and-aft, lateral, and vertical directions. Using the method of magnitude estimation, 12 subjects estimated the discomfort caused by 4-Hz sinusoidal vibration at 10 different magnitudes. At 4 Hz, subjects were less sensitive to lateral vibration than to fore-and-aft vibration (K_y/K_x = 0.71), and more sensitive to vertical vibration than to horizontal vibration (K_z/K_x = 1.95; K_z/K_y = 2.77). Previous findings showing how the discomfort of standing people depends on the frequency of fore-and-aft, lateral, and vertical vibration were used to define frequency weightings that reflect relative sensitivity to vibration in each direction. The frequency weightings differ from those appropriate for seated people, and differ from the weightings for standing people in current standards that were mostly derived from understanding of the discomfort of seated people.     

A test rig for the measurement of vibration in hand-held power tools

The purpose of the present project was to study the possibility of using a test rig for the measurement of vibration and noise from hand-held power tools. A test rig was designed to give the same effect on tool handle vibration as the human hand/arm system. Work was simulated by feeding the material to be processed against the tool, clamped into the rig, with the aid of a co-ordinate table. It was designed for use in studies of impact drills, chain saws, grinders and similar power tools. The report describes a proposal for testing the vibration properties of impact drills. Drilling with the test rig was compared with manual drilling. The difference in the acceleration level between the two methods was about 1 dB for ISO-weighted values in the critical direction. Both methods showed good reproducibility. The possibility of conducting noise level tests of a power tool in the rig was studied and the results are reported separately.     

The effect of occupational whole-body vibration on standing balance: A systematic review

Adverse health effects from exposure to occupational whole-body vibration (WBV) are common among drivers. In particular some researchers consider that there is kinaesthetic and balance disturbance from WBV exposure in the workplace and this might be one of the aetiological factors responsible for occupational low back pain in drivers. The purpose of this study was to undertake a critical review of the literature to determine whether exposure to seated occupational WBV can affect standing balance performance in an actual or simulated occupational environment. Specific keywords and MeSH terms for three major areas included WBV, balance and occupation. These were used to conduct a systematic search of the following databases; PubMed, EMBASE (Ovid), Medline (Ovid), CINAHL (EBSCO), Academic Search Complete (ASC), AMED, Scopus, Web of Science, Science Direct, Proquest, Cochrane library(OVID), IEEExplore and ProQuest Dissertations and thesis, Google Scholar, WorldCat and related conference proceedings. Five articles met the inclusion criteria and were assessed for quality. Two were field studies conducted on actual vehicles (a long haul freight truck and a bulldozer), while the other three were laboratory studies simulating the characteristics of the following vehicles; long-haul-dump vehicle, underground mine shuttle car, and helicopter. The systematic review scored the methodological quality of the included articles with an average and standard deviation of 76 ±12.3% (range 59- 93%) indicative of high quality. Three of the five studies (two field and one laboratory) found evidence for seated WBV decreasing standing balance performance while two laboratory studies did not find such effects. Thus there is modest evidence to suggest there is a decrease in standing balance performance following exposure to seated occupational WBV.

Relevance to industry

This systematic review suggests that balance deficits may exist immediately following exposure to occupational seated WBV and may predispose driver/operator to low back injury during manual material handling tasks immediately post driving.     

The vibration characteristics of chain saws and their influence on vibration white finger disease

The vibration from chain saws can cause vibration-induced white finger disease (VWFD). Measurements of vibration levels on the front and rear handles of different chain saw-types, and on the operator's middle finger were collected at three logging camps on Vancouver Island. Factors effecting the vibration levels on the finger and handles were investigated. The acceleration at the firing frequency was found to be the dominant factor effecting handle and finger vibration. Other factors which were investigated were: grip force; the presence of handle covers; and chain sharpening procedure. Weighted acceleration levels are calculated and this information is used to assess the latency period for fallers to develop VWF disease.     

The effect of posture and vibration magnitude on the vertical vibration transmissibility of tractor suspension system

The efficiency of suspension seat can be influenced by several factors such as the input vibration, the dynamic characteristics of the seat and the dynamic characteristics of the human body. The objective of this paper is to study the effect of sitting postures and vibration magnitude on the vibration transmissibility of a suspension system of an agricultural tractor seat. Eleven (11) healthy male subjects participated in the study. All subjects were asked to sit on the suspension system. Four (4) different sitting postures were investigated – i) “relax”, ii) “slouch”, iii) “tense”, and iv) “with backrest support”. All subjects were exposed to random vertical vibration in the range of 1–20 Hz, at three vibration magnitudes - 0.5, 1.0 and 2.0 m/s² r.m.s for 60 s. The results showed that there were three pronounced peaks in the seat transmissibility, with the primary resonance was found at 1.75–2.5 Hz for every sitting postures. The “backrest” condition had the highest transmissibility resonance (1.46), while the “slouch” posture had the highest Seat Effective Amplitude Transmissibility (SEAT) values (64.7%). Changes in vibration magnitude for “relax” posture from 0.5 to 2.0 m/s² r.m.s resulted in greater reduction in the primary resonance frequency of seat transmissibility. The SEAT values decreased with increased vibration magnitude. It can be suggested that variations in posture and vibration magnitude affected the vibration transmission through the suspension system, indicating the non-linear effect on the interaction between the human body and the suspension system.Relevance to industry: Investigating the posture adopted during agricultural activities, and the effects of various magnitudes of vibration on the suspension system's performance are beneficial to the industry. The findings regarding their influence on the human body may be used to optimize the suspension system's performance.     

The load on the spine during the transport of dustbins

Situations causing high postural stress during the transport of dustbins were determined, and the load on the spine was estimated. Electromyographical analyses revealed workload situations with high muscular activities during the transport over edges. Thus the manipulation of large dustcontainers (1100 l) is rendered difficult by kerbstones. Because smaller dustbins (110 l-240 l) are often kept in basements or backyards, stairs must frequently be climed with a heavy load. To quantify the spinal stress, a biomechanical model was developed in order to calculate the torques and forces effective at the lumbosacral joint. In the computations several parameters and transport conditions, such as kerbstone height, were varied. That entails different working postures by the dustbins men. The influence on the load on the spine was estimated. The calculated results are compared with criteria taken from the literature. Special postures were devised to keep the torques and forces as small as possible, and thereby to decrease the health risk of the skeletal system when handling heavy weights like dustbins. In the case of a container transport, only two persons should manipulate and work in well-timed co-ordination and both in special postures. Finally, all dustbins should be positioned at places guaranteeing an easy transport over flat surfaces.     

一种自适应振动主动控制策略及其在C型三维表面检测系统中的应用

基干广义最小方差和一步超前预报理论,围绕三维型面扫描系统中所存在的周期性徽振动问题,提出了一种新的自适应振动主动控制算法.以C型臂式三维激光扫描系统为应用背景,基于来自于该系统的数据样本建立了系统的振动动态自回归滑动平均模型(ARMA模型).采用所提出的自适应控制算法对该模型进行了振动主动控制仿真研究.仿真结果验证了所提出的方案可以有效地抑制C型臂运动过程中产生的振动,提高系统的整体三维检测精度.     

Strength,endurance and fatigue response of rotator cuff muscles during isometric exertions

Among the shoulder musculoskeletal disorders (MSDs), rotator cuff disorders are prevalent and known to substantially limit an individual's strength and ability to work. Despite the frequency and cost of rotator cuff injuries, very little research has been done on understanding the load response relationship of rotator cuff muscles. Therefore, this study was aimed at evaluating the strength, endurance and fatigue response of rotator cuff muscles. As a first step, strengths of Supraspinatus, Infraspinatus, and Teres Minor were measured for ten healthy male participants using muscle specific Maximum Voluntary Contractions (MVC). Then, endurance time and surface Electromyography (EMG) data were recorded during 15%, 30%, 45%, and 60% MVC exertions. Infraspinatus exhibited the highest strength followed by Teres Minor and Supraspinatus. Despite the strength differences, small variations were observed in the endurance time between the muscles. The effect of %MVC exertions on endurance time, average muscle activity and muscle fatigue were statistically significant. Median frequency decreased and muscle activation increased with an increase in force exertion levels; however, the changes observed for an increase in the exertion level from 15% to 30% MVC were much higher than the changes observed for an increase in the exertion level from 45% to 60% MVC.Relevance to industryResults of this study indicate that the rotator cuff muscles have different strengths but exhibit very similar endurance and fatigue behavior. These findings can assist ergonomic practitioners with the design and/or evaluation of workplace upper extremity exertions to reduce/manage stress on the rotator cuff muscles and shoulder.     

一种调节阀减振降噪方法的探索

流体诱发问振动是常见的现象。根据流体诱发阀振动及频率的随机性,用概率论指导研制的“异径多束流调节阀”,在几种工况下,经多年的运行表明,新阀有效地解决了原使用传统调节阀时未能避免的振动,并且其工作特性优良,而所需成本仅为进口低噪音阀的1／8左右。这对解决流体诱发调节间的振动与噪音具有理论和实际价值。     

An ergonomics evaluation of the vibration backpack harness system in walking

Many studies in backpack design have been focused on reducing trunk muscle activity and improving overall comfort while the wearers (college students and outdoor enthusiasts) were walking. However, little work has done on combining the vibration with harness system design. The purpose of the present study was to evaluate the effect of the vibration backpack harness system on trunk muscle activity and overall comfort in walking. There were four vibrators sewn in the four different positions of our harness system. Subjects were asked to support a load (20% body weight) on their backpack while performing 5-min walking trials on the treadmill (speed = 1.6 m/s) with different frequencies of vibration (0 Hz, 28 Hz, 35 Hz, 42 Hz). The objective measures of trunk muscle activity (electromyography) were obtained during the walking task. Subjects also were asked to complete subjective ratings of comfort. The results of the objective measures in this study had shown that the vibration function had a positive effect on reducing muscle activity for upper trapezius (UT), but not for erector spinae (ES). From the data of the two subjective surveys in our study, the comfort level of no-vibration state (0 Hz) was worse than vibration state (28 Hz, 35 Hz, 42 Hz) for both muscles, and when the frequency was 35 Hz, the comfort of the harness system was higher than the other three frequencies. The findings of the present study support that backpack with low frequency vibration has a positive effect on reducing trunk muscle activity and improving overall comfort level for wearers in walking.Relevance to industryObservations of present study is beneficial in assisting wearers to reduce muscle activity and improve overall comfort in walking according to the vibration backpack harness system. New backpack design criteria for harness systems are discussed to optimize production strategies. The wearers could be students, outdoor enthusiasts and old people.     

Curved muscles in biomechanical models of the spine: a systematic literature review

Abstract

Early biomechanical spine models represented the trunk muscles as straight-line approximations. Later models have endeavoured to accurately represent muscle curvature around the torso. However, only a few studies have systematically examined various techniques and the logic underlying curved muscle models. The objective of this review was to systematically categorise curved muscle representation techniques and compare the underlying logic in biomechanical models of the spine. Thirty-five studies met our selection criteria. The most common technique of curved muscle path was the ‘via-point’ method. Curved muscle geometry was commonly developed from MRI/CT database and cadaveric dissections, and optimisation/inverse dynamics models were typically used to estimate muscle forces. Several models have attempted to validate their results by comparing their approach with previous studies, but it could not validate of specific tasks. For future needs, personalised muscle geometry, and person- or task-specific validation of curved muscle models would be necessary to improve model fidelity.

Practitioner Summary: The logic underlying the curved muscle representations in spine models is still poorly understood. This literature review systematically categorised different approaches and evaluated their underlying logic. The findings could direct future development of curved muscle models to have a better understanding of the biomechanical causal pathways of spine disorders.     

Examining the benefits and challenges of using audience response systems: A review of the literature

Audience response systems (ARSs) permit students to answer electronically displayed multiple choice questions using a remote control device. All responses are instantly presented, in chart form, then reviewed and discussed by the instructor and the class. A brief history of ARSs is offered including a discussion of the 26 labels used to identify this technology. Next a detailed review of 67 peer-reviewed papers from 2000 to 2007 is offered presenting the benefits and challenges associated with the use of an ARS. Key benefits for using ARSs include improvements to the classroom environment (increases in attendance, attention levels, participation and engagement), learning (interaction, discussion, contingent teaching, quality of learning, learning performance), and assessment (feedback, formative, normative). The biggest challenges for teachers in using ARSs are time needed to learn and set up the ARS technology, creating effective ARS questions, adequate coverage of course material, and ability to respond to instantaneous student feedback. Student challenges include adjusting to a new method of learning, increased confusion when multiple perspectives are discussed, and negative reactions to being monitored. It is concluded that more systematic, detailed research is needed in a broader range of contexts.     

New upper bounds for excited vibration systems with applications of the differential calculus of norms

In an earlier paper, the author introduced new upper bounds for free linear and nonlinear vibration systems; to compute the best upper bounds, the differential calculus of norms was applied. In the present paper, this work is continued for the corresponding excited systems. Some new techniques and ideas are involved. The results in the applications cannot be obtained by the methods used so far.     

The effect of office concepts on worker health and performance: a systematic review of the literature

Conventional and innovative office concepts can be described according to three dimensions: (1) the office location (e.g. telework office versus conventional office); (2) the office lay-out (e.g. open lay-out versus cellular office); and (3) the office use (e.g. fixed versus shared workplaces). This review examined how these three office dimensions affect the office worker's job demands, job resources, short- and long-term reactions. Using search terms related to the office concept (dimensions), a systematic literature search starting from 1972 was conducted in seven databases. Subsequently, based on the quality of the studies and the consistency of the findings, the level of evidence for the observed findings was assessed. Out of 1091 hits 49 relevant studies were identified. Results provide strong evidence that working in open workplaces reduces privacy and job satisfaction. Limited evidence is available that working in open workplaces intensifies cognitive workload and worsens interpersonal relations; close distance between workstations intensifies cognitive workload and reduces privacy; and desk-sharing improves communication. Due to a lack of studies no evidence was obtained for an effect of the three office dimensions on long-term reactions. The results suggest that ergonomists involved in office innovation could play a meaningful role in safeguarding the worker's job demands, job resources and well-being. Attention should be paid, in particular, to effects of workplace openness by providing acoustic and visual protection.     

Effect of coating over the handle of a drill machine on vibration transmissibility

This study was to see the effect of different coatings on the handle of hand-held drilling machines. Out of five different handles chosen for this study, including one handle uncoated. Root mean square (rms) values of the vibration levels (acceleration) were recorded at the surface of handle and wrist of the operators. Results showed that maximum vibrations were reduced by coating of handle coated with rubber sheet and Rexene (H4) followed by handle coated with cotton sandwiched between jeans cloth (H5). Equivalent vibrations transmitted through coating of handles coated with sponge and velvet (H2) and jute and cotton (H3) were of almost same magnitude and these two coated handles were able to reduce least vibration transmitted. Transmissibility of vibrations along dominant (Z) direction was analyzed using ANOVA. Results showed that coating on handles significantly affected vibration transmitted in Z direction. Vibration transmissibility ratios were found to be 0.354, 0.571, 0.408, 0.4326, and 0.3555 for handles H1, H2, H3, H4 and H5 respectively.     

Flexion and extension forces generated by wrist-dedicated muscles over the range of motion

An experiment was performed to evaluate the relationships among active range of motion (ROM), gender, wrist position and direction of force exertion in their effects on the magnitude of static force exerted by the wrist-dedicated muscles in wrist flexion and extension. This study employed 60 right-hand-dominant subjects (30 male, 30 female) between 20 and 30 years of age, all reporting no prior wrist injury and good to excellent overall physical condition. The ROM of each subject was used to determine the number of wrist positions evaluated for static maximal voluntary forces generated in wrist flexion and extension while they were instructed to relax their fingers; thus only the six wrist-dedicated muscles were employed in the exertion. The ANOVA procedure showed gender, wrist position, direction of force exertion, and the wrist position interaction with direction to have significant effects upon maximal force exertion. Females averaged 76.3% of the mean male flexion force and 72.4% for extension. On average, extension forces were found to be 83.4% of those generated by flexing the wrist-dedicated muscles.     

The reality of virtual schools: A review of the literature

Virtual schooling was first employed in the mid-1990s and has become a common method of distance education used in K-12 jurisdictions. The most accepted definition of a virtual school is an entity approved by a state or governing body that offers courses through distance delivery – most commonly using the Internet. While virtual schools can be classified in different ways, the three common methods of delivery are by independent, asynchronous or synchronous means. Presently, the vast majority of virtual school students tended to be a select group of academically capable, motivated, independent learners. The benefits associated with virtual schooling are expanding educational access, providing high-quality learning opportunities, improving student outcomes and skills, allowing for educational choice, and achieving administrative efficiency. However, the research to support these conjectures is limited at best. The challenges associated with virtual schooling include the conclusion that the only students typically successful in online learning environments are those who have independent orientations towards learning, highly motivated by intrinsic sources, and have strong time management, literacy, and technology skills. These characteristics are typically associated with adult learners. This stems from the fact that research into and practice of distance education has typically been targeted to adult learners. The problem with this focus is that adults learn differently than younger learners. Researchers are calling for more research into the factors that account for K-12 student success in distance education and virtual school environments and more design research approaches than traditional comparisons of student achievement in traditional and virtual schools.     

Accommodation,cognition, and virtual image displays: A review of the literature

This paper reviews the literature on factors that influence the visual (ocular) accommodation response when using see-through virtual image displays (VIDs) such as head-up and helmet-mounted displays. This review suggests that the overall accommodation response is determined by a complex interaction of many factors, some of which are associated with the visual stimulus (such as blur and chromatic aberration) and some of which are cognitive in nature (such as workload and attention). When using VIDs, the effects of these different influences on the accommodation response may not be congruent, leading to the level of accommodation being inappropriate for the task.     

Modeling,tracking, vibration and balance control of an underactuated mobile manipulator (UMM)

This paper presents an underactuated mobile manipulator (UMM) and focuses on solving modeling, tracking, and vibration- and balance-control problems. Although the study has been directed at warehousing applications, the developed techniques are general and can be applied to other applications. The derivation of equations of motion of the UMM, disturbance analysis, and model validation are investigated to reveal the actual system dynamics. Additionally, a simple but effective strategy is also developed to solve the equilibrium point and balance problem. Based on the dynamic model, two control architectures are proposed: Model Predictive Control (MPC) and MPC+Proportional-Integral (PI) with integral actions, respectively, and they can also be applied to other robotic systems. Compared to other MPC-based control strategies, the proposed controllers require less effort to implement in practice. Finally, simulations, experiments, and robustness verification are conducted and discussed, and the results are satisfactory.