Vibrations transmitted from human hands to upper arm,shoulder, back,neck, and head

Some powered hand tools can generate significant vibration at frequencies below 25 Hz. It is not clear whether such vibration can be effectively transmitted to the upper arm, shoulder, neck, and head and cause adverse effects in these substructures. The objective of this study is to investigate the vibration transmission from the human hands to these substructures. Eight human subjects participated in the experiment, which was conducted on a 1-D vibration test system. Unlike many vibration transmission studies, both the right and left hand-arm systems were simultaneously exposed to the vibration to simulate a working posture in the experiment. A laser vibrometer and three accelerometers were used to measure the vibration transmitted to the substructures. The apparent mass at the palm of each hand was also measured to help in understanding the transmitted vibration and biodynamic response. This study found that the upper arm resonance frequency was 7–12 Hz, the shoulder resonance was 7–9 Hz, and the back and neck resonances were 6–7 Hz. The responses were affected by the hand-arm posture, applied hand force, and vibration magnitude. The transmissibility measured on the upper arm had a trend similar to that of the apparent mass measured at the palm in their major resonant frequency ranges. The implications of the results are discussed.Relevance to industryMusculoskeletal disorders (MSDs) of the shoulder and neck are important issues among many workers. Many of these workers use heavy-duty powered hand tools. The combined mechanical loads and vibration exposures are among the major factors contributing to the development of MSDs. The vibration characteristics of the body segments examined in this study can be used to help understand MSDs and to help develop more effective intervention methods.     

Force control-based vibration suppression in robotic grinding of large thin-wall shells

Vibration suppression is a major difficulty in the grinding of low-stiffness large thin-wall shells. The paper proposes that effective workpiece vibration control can be performed by a novel force-controlled end-effector integrated into a robotic grinding workcell. First, a dynamics model is built to capture the characteristics and vibration suppression mechanism of force control-based robotic grinding, then a novel force control-based vibration suppression method is designed for grinding large thin-wall shells, and three robotic grinding tests are conducted to validate the effects of the new method and the grinding performance of the force control-based robotic grinding workcell. The results are: 75% reduction in the amplitude of workpiece vibration; effective suppression of non-tool passing frequency; stable grinding of large thin-wall shells remarkably enhancing grinding depth up to 0.3 mm per pass, grinding depth error less than ±0.1 mm, and significant improvement of the workpiece surface quality up to Ra=0.762 μm.     

Hand–arm vibration in a group of hand‐operated grinding tools

Vibration acceleration was triaxially and basicentrically measured, and digital‐audio‐tape‐recorded with each axis separately evaluated using both the ANSI S3.34 and ACGIH hand‐arm vibration (HAV) guidelines, for two pairs of pneumatic handheld grinders commonly used in metal fabrication operations including shipyards. Each tool pair consisted of a new and used grinder of the same model, performing the same simulated grinding tasks using new small grinding wheels, carbide burrs, wire brushes, and flap wheels. The results of this limited study showed, primarily, that the HAV standards were not exceeded, but there was a consistent tendency for the acceleration levels to increase between new and used tools, ranging from 11% to 66% on the Z‐axis, 13% to 66% on the Y‐axis, 44% to 58% on the X‐axis, when tasks involved using grinding wheels and carbide burrs (hard implements). The results were mixed when using disposable wire brushes and flap wheels (softer implements). The overall results suggest the need for and implementation of a regular tool vibration monitoring and maintenance program as a primary element to help maintain tool acceleration levels to a minimum. © 2002 Wiley Periodicals, Inc.     

Transmission characteristics of suspension seats in multi-axis vibration environments

The multi-axis vibration transmission characteristics of selected suspension seats were investigated in the laboratory. Subjects were exposed to a flat acceleration spectrum and two low frequency signals extracted from multi-axis acceleration data recorded at the floor of a passenger locomotive. Triaxial accelerations were measured at the floor of the vibration table and at the interfaces between the subject and mounted seat (seat pan and seat back). The transmission ratios between the overall seat pan and seat back accelerations and floor accelerations provided an effective tool for evaluating the effects of measurement site, vibration direction, and posture among the selected seating systems. The results showed that the system transfer matrix, estimated using a multiple-input/single-output model, would be less than ideal for predicting low frequency operational seat vibration when using suspension seats. The Seat Effective Amplitude Transmissibility (SEAT), estimated for the tested locomotive seats, was used to predict the weighted seat pan accelerations and Vibration Total Values for assessing a 1-h operational exposure in accordance with ISO 2631-1: 1997.

Relevance to industry

Multi-axis SEAT values can be estimated for seating systems tested in the laboratory using representative operational exposures. These values can be applied to monitored vehicle floor accelerations to target potentially harmful vibration in accordance with ISO 2631-1: 1997, assuming the operational exposures have similar frequency and magnitude characteristics. The transmission at the seat back should be considered when substantial low frequency multi-axis vibration is present.     

城市有轨电车引发的建筑结构振动响应

为分析城市有轨电车运行引发的建筑结构振动舒适度,基于MATLAB设计结构振动舒适度的计算程序,可结合结构健康监测系统的监测数据对建筑结构的振动舒适度进行分析。采用某有轨电车运行中的实测数据,分析车辆段和行车段电车引发的振动,研究有轨电车的振动响应特性。分析结果表明：有轨电车运行引发的高频振动传至上盖结构几乎已完全消散;上盖结构的振动频率集中在16~20 Hz区间,以有轨电车的低频振动和结构相关附属机器的振动为主。减小有轨电车的行驶速度、增加建筑物与振动源的距离或控制楼内附属机器的振动可明显控制振动。在加速过程中,电车与地面和轨道会产生共振,因此存在振动加速度级的极大值。     

An expert system for hydro/aero-static spindle design used in ultra precision machine tool

A novel expert hydro/aero-static spindle design system strategy is presented in this paper. It is based on the comprehensive principles of machine design, machining dynamics and metal cutting mechanics. The transmission and lubrication types of the spindle are decided by a selection system, which utilize a dedicated logical choice algorithm in the light of the specifications of both workpiece material and desired cutting condition. Hydro/aero-static spindles are designed by this system from its dynamics perspective. The chatter vibration of the spindle is automatically improved by optimizing the structural parameters of the spindle. Meanwhile, the predicted Frequency Response Function (FRF) of the spindle based on the rotor dynamics is integrated to the chatter vibration stability law. Consequently, the expert design system enables the structure of machine tools to be designed efficiently with a higher precision. The proposed system was demonstrated through an aerostatic spindle design for micro-array structures machining.     

Accurate robotic belt grinding of workpieces with complex geometries using relative calibration techniques

Robotic belt grinding operations are performed by mounting a workpiece to the end effector and commanding it to move along a trajectory while maintaining contact with the belt grinding wheel. A constant contact force throughout the grinding process is necessary to provide a smooth finish on the workpiece, but it is difficult to maintain this force due to a multitude of installation, manipulation, and calibration errors. The following describes a novel methodology for robotic belt grinding, which primarily focuses on system calibration and force control to improve grinding performance. The overall theory is described and experimental results of turbine blade grinding for each step of the methodology are shown.     

A new methodology for measuring the vibration transmission from handle to finger whilst gripping

The transmission of vibration from hand-held tools via work gloves and into the operators' hands can be affected by several factors such as glove material properties, tool vibration conditions, grip force, and temperature. The primary aim of this study is to develop a new methodology to measure and evaluate vibration transmissibility for a human finger in contact with different materials, whilst measuring and controlling the grip force. The study presented here used a new bespoke lab-based apparatus for assessing vibration transmissibility that includes a generic handle instrumented for vibration and grip force measurements. The handle is freely suspended and can be excited at a range of real-world vibration conditions whilst being gripped by a human subject. The study conducted a frequency response function (FRF) of the handle using an instrumented hammer to ensure that the handle system was resonance free at the important frequency range for glove research, as outlined in ISO 10819: 1996: 2013, and also investigated how glove material properties and design affect the tool vibration transmission into the index finger (Almagirby et al. 2015). The FRF results obtained at each of six positions shows that the dynamic system of the handle has three resonance frequencies in the low frequency range (2, 11 and 17 Hz) and indicated that no resonances were displayed up to a frequency of about 550 Hz. No significant vibration attenuation was shown at frequencies lower than 150 Hz. The two materials cut from the gloves that were labelled as anti-vibration gloves (AV) indicated resonance at frequencies of 150 and 160 Hz. However, the non-glove material that did not meet the requirements for AV gloves showed resonance at 250 Hz. The attenuation for the three materials was found at frequencies of 315 Hz and 400 Hz. The level and position of the true resonance frequencies were found to vary between samples and individual subjects.     

车削加工中的振动原因分析及消振措施探讨

受机床床身、主轴结构、刀具安装、工件装夹等组成的工艺系统的影响,在机械加工过程中无可避免的会产生受迫振动和自激振动。本文从现有机械加工过程中产生了哪几种振动,这些振动为什么会产生,以及振动产生的影响这三方面人手,提出通过改善机械工艺来解决振动问题。     

The effects of vibration-reducing gloves on finger vibration

Vibration-reducing (VR) gloves have been used to reduce the hand-transmitted vibration exposures from machines and powered hand tools but their effectiveness remains unclear, especially for finger protection. The objectives of this study are to determine whether VR gloves can attenuate the vibration transmitted to the fingers and to enhance the understanding of the mechanisms of how these gloves work. Seven adult male subjects participated in the experiment. The fixed factors evaluated include hand force (four levels), glove condition (gel-filled, air bladder, no gloves), and location of the finger vibration measurement. A 3-D laser vibrometer was used to measure the vibrations on the fingers with and without wearing a glove on a 3-D hand-arm vibration test system. This study finds that the effect of VR gloves on the finger vibration depends on not only the gloves but also their influence on the distribution of the finger contact stiffness and the grip effort. As a result, the gloves increase the vibration in the fingertip area but marginally reduce the vibration in the proximal area at some frequencies below 100 Hz. On average, the gloves reduce the vibration of the entire fingers by less than 3% at frequencies below 80 Hz but increase at frequencies from 80 to 400 Hz. At higher frequencies, the gel-filled glove is more effective at reducing the finger vibration than the air bladder-filled glove. The implications of these findings are discussed.     

The influence of seat backrest angle on human performance during whole-body vibration

This study investigated the effects of reclined backrest angles on cognitive and psycho-motor tasks during exposure to vertical whole-body vibration. Twenty participants were each exposed to three test stimuli of vertical vibration: 2-8 Hz; 8-14 Hz and 14-20 Hz, plus a stationary control condition whilst seated on a vibration platform at five backrest angles: 0° (recumbent, supine) to 90° (upright). The vibration magnitude was 2.0 ms(-2) root-mean-square. The participants were seated at one of the backrest angles and exposed to each of the three vibration stimuli while performing a tracking and choice reaction time tasks; then they completed the NASA-TLX workload scales. Apart from 22.5° seat backrest angle for the tracking task, backrest angle did not adversely affect the performance during vibration. However, participants required increased effort to maintain performance during vibration relative to the stationary condition. These results suggest that undertaking tasks in an environment with vibration could increase workload and risk earlier onset of fatigue. PRACTITIONER SUMMARY: Current vibration standards provide guidance for assessing exposures for seated, standing and recumbent positions, but not for semi-recumbent postures. This paper reports new experimental data systematically investigating the effect of backrest angle on human performance. It demonstrates how workload is elevated with whole-body vibration, without getting affected by backrest angle.     

Development of a new frequency weighting filter for the assessment of grinder exposure to wrist-transmitted vibration

The risk assessment of hand tool workers exposed to hand-arm vibrations is still problematic. It is based, accordingly to ISO 5349, on a frequency-weighted measurement recorded at the handle of the tool. Unfortunately, the frequency-weighted filter recommended by ISO 5349 does not take into account any amplification of the hand-arm system and underestimates the global rms acceleration transmitted to the hand. In this study, the vibration transmitted from the tool handle to the worker's wrist is investigated in an industrial environment for seven commercial grinders, two subjects and three push forces. The results are compared with the ISO-5349 and ACGIH threshold limit values, and a new frequency weighting filter is proposed, by which the amplification close to the natural frequencies of the hand-arm system can be considered in the evaluation of the vibration transmitted to the wrist from vibration measurements at the tool handle in a grinding operation.     

Equivalent comfort contours for fore-and-aft,lateral, and vertical whole-body vibration in the frequency range 1.0 to 10 Hz

Abstract

Standards assume vibration discomfort depends on the frequency and direction of whole-body vibration, with the same weightings for frequency and direction at all magnitudes. This study determined equivalent comfort contours from 1.0 to 10?Hz in each of three directions (fore-and-aft, lateral, vertical) at magnitudes in the range 0.1 to 3.5?ms^?2?r.m.s. Twenty-four subjects sat on a rigid flat seat with and without a beanbag, altering the pressure distribution on the seat but not the transmission of vibration. The rate of growth of vibration discomfort with increasing magnitude of vibration differed between the directions of vibration and varied with the frequency of vibration. The frequency-dependence and direction-dependence of discomfort, therefore, depended on the magnitude of vibration. The beanbag did not affect the frequency-dependence or direction-dependence of vibration discomfort. It is concluded that different weightings for the frequency and direction of vibration are required for low and high magnitude vibration.

Practitioner summary: When evaluating whole-body vibration to predict vibration discomfort, the weightings appropriate to different frequencies and different directions of vibration should depend on the magnitude of vibration. This is overlooked in all current methods of evaluating the severity of whole-body vibration.     

An investigation on major physical hazard exposures and health effects of forestry vehicle operators performing wood logging processes

Forest vehicle operators are occupationally exposed to combined hazards such as noise, whole-body vibration(WBV), adverse microclimate, and carbon monoxide. Such combined exposures may not only increase the risk of accidents but they may also have some synergized effects on the developments of major occupational diseases of the workers, which have been among the major concerns of the occupational safety and health for the forestry sector in Romania. This study investigated the combined exposures through measuring and analyzing the equivalent acoustic level LAeq (dB(A)), whole-body vibration (A(8)-value), working microclimate, and carbon monoxide inside the worker's cabin in the breathable area. The vehicles considered in this study included skidding vehicles dedicated to wood exploitation (type I) and agricultural tractors modified for logging (type II). The cumulative distribution function of each types of exposure was calculated in the analyses. This study found that the noise and WBV exposures had large probabilities of exceeding the permissible limits: for noise, 75% for vehicle type I, and 55% for vehicle type II; for the WBV, 63% for type I vehicles, and 72% for type II vehicles. The measured data suggest that the microclimate and carbon monoxide exposures were within their limits in the process of collecting wood. This study also found that 27% of workers participated in the study were detected with occupational diseases. Based on these findings, some intervention methods were recommended to control the exposures and health effects.     

The design and development of suspended handles for reducing hand-arm vibration in petrol driven grass trimmer

The portable petrol driven grass trimmer is identified as a type of machine whose operator can be subjected to large magnitude of hand-arm vibration. These vibrations can cause complex vascular, neurological and musculoskeletal disorder, collectively named as hand-arm vibration syndrome. The vibration total level on the handle of grass trimmer of 11.30 m/s² was measured, and it has reached the exposure limit value of 5.0 m/s² for daily vibration exposure A(8). New suspended handles were designed to reduce the vibration level. Three different prototype handles with rubber mounts were designed. Handles were made of different materials, and the distance of rubber mounts were varied. From the study, it was observed that not all the handles with rubber mounts were effective in reducing hand-arm vibration. The reduction of vibration depended on the handle material and distance installed between rubber mount and vibration transmissibility of handle-isolation system. Subjective ratings of perception of vibration were measured, and the results indicated that operators were not fully aware of the level of vibration. A prototype handle that is made of heavier material results in the lowest hand-arm vibration of 2.69 m/s². The new handle has significantly reduced the vibration total value by 76% compare with the existing commercial handle.

Relevance to industry

Large numbers of workers are employed to perform grass trimming job in many developing countries. This paper presents the effect of handle types (commercial and prototype) on the commonly used grass trimmer.     

滚动导轨磨削加工尺寸在线测量系统

针对导轨磨削加工尺寸的在线测量问题,本文介绍了一种导轨磨削加工尺寸在线测量系统,该系统以行程开关作工件位置探测器、音圈电机作测头驱动器和电感测头作尺寸检测器,采用相对测量法,配合数据采集卡、工控机和上层处理软件,能对导轨磨削尺寸进行实时检测。     

Perception of fore-and-aft whole-body vibration intensity measured by two methods

This experimental study investigated the perception of fore-and-aft whole-body vibration intensity using cross-modality matching (CM) and magnitude estimation (ME) methods. Thirteen subjects were seated on a rigid seat without a backrest and exposed to sinusoidal stimuli from 0.8 to 12.5 Hz and 0.4 to 1.6 ms^? 2 r.m.s. The Stevens exponents did not significantly depend on vibration frequency or the measurement method. The ME frequency weightings depended significantly on vibration frequency, but the CM weightings did not. Using the CM and ME weightings would result in higher weighted exposures than those calculated using the ISO (2631-1, 1997) W_d. Compared with ISO W_k, the CM and ME-weighted exposures would be greater at 1.6 Hz and lesser above that frequency. The CM and ME frequency weightings based on the median ratings for the reference vibration condition did not differ significantly. The lack of a method effect for weightings and for Stevens exponents suggests that the findings from the two methods are comparable.     

Reliability of physiological and subjective responses to physical and psychosocial exposures during a simulated manufacturing task

Responses to physical and psychosocial exposures can be measured using diverse methods, but their reliability, particularly under multiple exposures, is largely unknown. Five classes of methods were used to assess physiological and subjective responses among 24 participants to four combinations of physical and psychosocial exposures while performing two identical sessions of a simulated overhead manufacturing task. As an exploratory analysis, test–retest reliability was quantified using intraclass correlation coefficients (ICC) and coefficients of variation (CV). Discomfort ratings were reliable under less favorable exposures, and ratings of the psychosocial environment were most reliable under favorable social support. Workload ratings were most reliable with high physical exposure and favorable social support, and task performance was reliable overall. EMG and heart rate had relatively low reliability. Slightly less than half of the variables were considered reliable, but reliability depended on exposure conditions.Relevance to industry: The study provides information on the reliability of commonly used exposure measurement methods. The results can guide the selection of physiological and psychological work outcome measurements in future studies and work evaluations.     

Digital vibration threshold testing and ergonomic stressors in automobile manufacturing workers: a cross-sectional assessment

Upper extremity musculoskeletal disorders (UEMSDs) comprise a large proportion of work-related illnesses in the USA. Physical risk factors including manual force and segmental vibration have been associated with UEMSDs. Reduced sensitivity to vibration in the fingertips (a function of nerve integrity) has been found in those exposed to segmental vibration, to hand force, and in office workers. The objective of this study was to determine whether an association exists between digital vibration thresholds (VTs) and exposure to ergonomic stressors in automobile manufacturing. Interviews and physical examinations were conducted in a cross-sectional survey of workers (n=1174). In multivariable robust regression modelling, associations with workers' estimates of ergonomic stressors stratified on tool use were determined. VTs were separately associated with hand force, vibration as felt through the floor (whole body vibration), and with an index of multiple exposures in both tool users and non-tool users. Additional associations with contact stress and awkward upper extremity postures were found in tool users. Segmental vibration was not associated with VTs. Further epidemiologic and laboratory studies are needed to confirm the associations found. The association with self-reported whole body vibration exposure suggests a possible sympathetic nervous system effect, which remains to be explored.     

The vibration discomfort of standing people: evaluation of multi-axis vibration

Few studies have investigated discomfort caused by multi-axis vibration and none has explored methods of predicting the discomfort of standing people from simultaneous fore-and-aft, lateral and vertical vibration of a floor. Using the method of magnitude estimation, 16 subjects estimated their discomfort caused by dual-axis and tri-axial motions (octave-bands centred on either 1 or 4 Hz with various magnitudes in the fore-and-aft, lateral and vertical directions) and the discomfort caused by single-axis motions. The method of predicting discomfort assumed in current standards (square-root of the sums of squares of the three components weighted according to their individual contributions to discomfort) provided reasonable predictions of the discomfort caused by multi-axis vibration. Improved predictions can be obtained for specific stimuli, but no single simple method will provide accurate predictions for all stimuli because the rate of growth of discomfort with increasing magnitude of vibration depends on the frequency and direction of vibration.