Effect of local wrist muscle fatigue on multiple assembly‐related psychomotor skills

Human operators are still a vital resource in modern manufacturing systems, especially for fine assembly tasks. Declining muscle strength due to physical tasks can impair psychomotor skills and can cause adverse effects on assembly quality. To understand how local muscle fatigue can influence multiple psychomotor skills, 20 subjects participated in an experiment in which four psychomotor tests were performed to mimic fine assembly tasks, and their performances under nonfatigued wrist and fatigued wrist conditions were compared. Results showed that wrist fatigue caused significant decrements in the dexterity of fingers and fingertips, but there was no significant influence on arm‐hand steadiness. Local muscle fatigue impairs psychomotor skills to different extents but does not necessarily lead to lower performance. Humans are capable of coordinating motion units to compensate for the influence of muscle fatigue, but this is rather limited. It is suggested that in assembly operations, tasks should be arranged according to different task demands on diverse psychomotor skills.     

气动人工肌肉关节的自抗扰控制

气动人工肌肉关节系统是一个强非线性时变自平衡2阶系统,鉴于传统控制方法难以克服控制精度、调节速度和稳定性之间的矛盾,设计了一种2阶自抗扰控制器.采用3阶扩张状态观测器实时估计未建模型部分及外界扰动,对系统进行线性补偿,并利用非线性反馈机制提高控制效率,在保证稳定性的前提下,提高调节速度和控制精度,使得系统的稳态精度小于...     

A METHOD OF HUMAN BIODYNAMIC MEASUREMENT BASED ON VIRTUAL MARKER TECHNOLOGY AND WAVELET ALGORITHM

A new method is reported for human biodynamic measurement, which includes an improved motion measurement system via virtual marker technology and a wavelet algorithm to extract muscle activities from electromyography signals in vivo. Four channels of electromyography signals and twelve virtual markers motion data were collected when the subject did a standard gait experiment. Then, a wavelet algorithm was used to process raw electromyography signals and to extract muscle activity features. The results demonstrated that the proposed method could shorten the motion measurement experiment time and improve the measurement accuracy. The proposed wavelet algorithm could efficiently extract muscle activity features from electromyography signals. The reported method may be potentially used for the human biodynamic research and clinical biomechanics. Possible further improvements for this method are also discussed.     

七自由度气动人工肌肉机械手臂的设计及研究

设计了一种气动肌肉驱动的七自由度仿人机械手臂。肩部采用球绞形式,实现类人肩关节旋内／旋外、屈／伸及内收／外展三个自由度,旋转运动范围为-39．5～39．5°,屈伸运动范围为－44．5～44．5°,收展运动范围为0～35．0°。肘部和腕部均采用虎克铰形式,实现肘关节的屈／伸、旋内／旋外以及腕关节的内收／外展、屈／伸,其中肘关节旋转运动范围为～39．5～39．5°,屈伸运动范围为－60．5～32．5°;腕关节收展运动范围为～70．5～70．5°,抬伸运动范围为-39．5～39．5°。对机构进行了仿真分析,并搭建了手臂实物系统进行测试。实验结果表明,该手臂重量轻,受控性好,能够很好地实现人类关节的柔顺运动。     

Placement of forearm surface EMG electrodes in the assessment of hand loading in manual tasks

Surface electromyography (EMG) is commonly used to study the loading of the forearm. Pro-supination movements cause surface electrodes to move in relation to the underlying muscles. We studied the effects of different electrode locations and forearm postures on the association between the EMG signals and external hand load in a laboratory experiment. Eleven subjects performed simulated work tasks with the forearm in neutral, pronated or supinated postures and with systematic variation of external load. The tasks included isometric gripping, pushing and pulling, and lifting and lowering weights. Surface EMG was recorded by six pairs of electrodes located on the forearm. The associations were studied using multiple regression models. EMG activity varied according to the forearm posture, location of electrodes and type of simulated task. Variation was lowest with a through-forearm setting of electrodes. This setting also showed the highest correlation between external loads and the EMG activity [coefficient of determination (R ²) = 0.25–0.66].

Practitioner Summary: Moving of surface electrodes in relation to the underlying muscles interferes with the assessment of loading in ergonomic settings. This laboratory experiment showed that a through-forearm location of electrodes seems to be an optimal option in the assessment of forearm loading.     

Low mean level sustained and intermittent grip exertions: Influence of age on fatigue and recovery

The goal of this study was to quantify localised muscle fatigue resulting from low mean levels of exertion in younger (< 40 years) and older (>50 years) adults. Fatigue, elicited in the finger flexor muscles by intermittent (10% mean maximum voluntary contraction (MVC)) and sustained (8% MVC) handgrip exercises, was quantified by a muscle twitch force response before, immediately after and during 3 h following exercise. Despite greater mean loads, recovery time was shorter following intermittent than sustained contractions, which suggests that recovery from fatigue is more sensitive to rest within the work cycle than mean work. The more pronounced effects for younger than older individuals following the sustained exertion indicate that changes in muscle fibre type composition might predispose older individuals to be more resistant to fatigue resulting from sustained contractions of low level. Performing hand exertion tasks requiring low mean force levels contributes to similar long-lasting fatigue effects regardless of gender and age. Intermittent periods of complete rest reduce muscle fatigue. Since fatigue was not perceived during recovery from the tested sustained and intermittent contractions, subjective evaluations may not be a reliable indicator of localised muscle fatigue.     

池沼公鱼肌肉中脂肪酸成分的GC-MS分析

目的:分析测定池沼公鱼肌肉中的脂肪酸成分.方法:采用索氏提取法提取池沼公鱼肌肉中的脂溶性成分,经甲酯化处理后用气相色谱-质谱联用技术(GC-MS)分离和鉴定,运用面积归一化法确定各个成分的相对百分含量.结果:从池沼公鱼脂肪油中鉴定出38种脂肪酸,其中不饱和脂肪酸21种,主要种类有:棕榈油酸(8.11%),(E)-9-十八碳烯酸(12.25%),顺式二十碳五烯酸(8.43%),二十二碳六烯酸甲酯(11.85%)等;饱和脂肪酸17种,主要种类有:棕榈酸(8.13%),肉豆蔻酸(2.71%),十八烷酸(4.23%)等.结论:试验结果表明,池沼公鱼的营养价值较高,具有很好的开发利用价值.     

固体氧化物燃料电池阳极的研究

介绍了中温固体氧化物燃料电池(IT-SOFC)阳极材料体系及工作过程,为进一步研究新型的阳极材料奠定了基础.     

自行车骑行过程中脚踏力的分析

本文提出了把在骑行过程中的脚踏力分解为直接由纯关节力矩而产生的肌肉分量和由重量与惯性力的作用产生的非肌肉分量的分析方法．在平面关节运动和关节力矩给定条件下，利用Ｎｅｗｔｏｎ－Ｅｕｌｅｒ系统中的动力学方程求解两个分量．通过在３个不同转速下承受普通载荷的自行车脚踏力的分析为例来说明脚踏力的分解方法．主要的结果是：非肌肉力分量的大小随转速增加而增加，肌肉力分量的大小基本保持相对恒定．     

Light Microscopy 1981: The State of the Art

Melamine-formaldehyde, a universally used technical aminoplast, can be modified into a water-compatible electron microscopic embedding medium. The complete processing of tissues—from fixation to sectioning—is described in this paper. It produces stable sections showing remarkable ultrastructural detail.