五轴数控渐进成形中挤压工具姿态的确定

在基于STL模型的五轴数控渐进成形中,为了避免三角面片边界处挤压工具的姿态发生突变现象,提出一种挤压工具姿态确定方法。首先,根据挤压工具头中心点与三角面片的位置关系,将工具头中心点分为位于三角面片顶点、三角面片边和三角面片内部3种类型;然后,对不同类型的工具头中心点,分别采用不同的距离加权算法,计算工具头中心点的法向量;最后,根据工具头中心点的法向量和挤压工具轴相对于工具头中心点法向量的引导角和倾斜角,确定挤压工具姿态。采用VC++和OPENGL完成算法的系统实现。算法应用实例表明,所确定的挤压工具姿态变化平缓,在三角面片的边界处,没有发生挤压工具姿态突变现象,软件运行稳定可靠。     

Comparison between low-cost marker-less and high-end marker-based motion capture systems for the computer-aided assessment of working ergonomics

The paper deals with the comparison between a high-end marker-based acquisition system and a low-cost marker-less methodology for the assessment of the human posture during working tasks. The low-cost methodology is based on the use of a single Microsoft Kinect V1 device. The high-end acquisition system is the BTS SMART that requires the use of reflective markers to be placed on the subject's body. Three practical working activities involving object lifting and displacement have been investigated. The operational risk has been evaluated according to the lifting equation proposed by the American National Institute for Occupational Safety and Health. The results of the study show that the risk multipliers computed from the two acquisition methodologies are very close for all the analysed activities. In agreement to this outcome, the marker-less methodology based on the Microsoft Kinect V1 device seems very promising to promote the dissemination of computer-aided assessment of ergonomics while maintaining good accuracy and affordable costs.     

Effects of horizontal whole-body vibration and standing posture on activity interference

Standing people are exposed to whole-body vibration in many environments. This paper investigates the effects of horizontal whole-body vibration and standing posture on task performance. Sixteen participants were exposed to random vibration (up to 4 Hz) whilst performing a timed pegboard task in two standing postures. Objective and subjective indicators of performance were used. Time taken to complete the task increased progressively with increases in vibration magnitude. The fore-and-aft posture generally showed greater performance decrements and postural interruptions (>1.0 ms^?2 root mean square) than the lateral. For both postures, performance was better during y-axis vibration than during x-axis vibration. Subjective ratings showed similar trends to time data. Impairments due to dual axis exposure were well predicted using root sum of squares calculations based on single axis components. These results indicate that best performance for those standing in moving environments will be achieved if individuals adopt a lateral posture with the most severe vibration in the y-axis.

Statement of Relevance: People have a need to work during transportation, either working for the transport provider or as a passenger. All modes of transport result in travellers being exposed to horizontal motion. This study demonstrates that task disturbance is affected by the orientation of the standing person to the vibration and, therefore, vehicle layouts can be optimised.     

碳纤维蜂窝夹层结构二次曲面产品定位加工技术

Ka频段通信卫星天线反射器产品通常是由内面板、蜂窝芯子和外面板胶粘剂固化成型的碳纤维蜂窝夹层结构,内面板形成的反射面为满足一定精度要求的二次曲面。由于反射器本身特征无法作为准确基准进行找正,且在工装上的安装位姿不确定性,因此反射器在固化成型后的数控加工过程中无法直接获取定位基准。针对反射面的三坐标测量机检测数据,采用基于曲面最佳拟合数据调整理论模型位姿的方法,解决了碳纤维蜂窝夹层结构二次曲面产品加工基准的精确获取难题,并在数控程序编制中提出"虚拟理论曲面位姿"方法,对已有的数控程序操作进行重用,大幅提高了反射器产品批量研制的数控编程效率。     

Effects of work surface height on muscle activity and posture of the upper extremity during simulated pipetting

In order to examine the effects of work surface height (WSH) on muscle activity, posture and discomfort during simulated pipetting, an experimental study was conducted using electromyography, electrogoniometry, video techniques and also qualitative data. The experimental design consisted of one independent variable (WSH with six heights) and 13 dependent variables. The levels of muscle strain and discomfort were significantly lower at the shoulder when the WSHs were low but thumb muscle activities and neck flexion levels were markedly higher at these WSHs compared to higher WSHs. To reduce shoulder strain, without raising thumb and neck strain beyond acceptable limits, the findings suggest that the height of a laboratory workbench should be at the level of the pipette tip when held in a standing position with the hand at elbow height. It was also found that pipetting should not be done in a seated posture.

Practitioner Summary: An experimental study was conducted to examine the effects of work surface height on upper extremity muscle activity, posture and discomfort during simulated pipetting. The findings suggest that the laboratory workbench height should be at the pipette-tip level when held in a standing position with the hand at elbow height.     

(De)stabilization of required and spontaneous postural dynamics with learning.

The present research examined how learning a new ankle-hip coordination influenced the preexisting postural repertoire. Standing participants learned a new ankle-hip coordination mode (relative phase of 90'). Before and after practice, postural patterns were evaluated in two different tasks. In the required task, specific ankle-hip patterns were requested (12 relative phases in multiples of 30'). In the spontaneous task, participants performed a tracking task in which no instructions about ankle-hip coordination were given. Learning induced changes in both required and spontaneous coordination dynamics. When ankle-hip patterns were required, learning led to improvement and homogenization in performance over the entire postural repertoire. When ankle-hip patterns emerged spontaneously, in-phase and antiphase preexisting patterns destabilized and changed toward the learned pattern of 90'. These findings demonstrate that learning a new coordination pattern can induce modifications of patterns that have not been practiced. The results also suggest that the consequences of learning do not generalize across different types of tasks, even when similar coordination modes are involved. We discuss implications of these findings for the generality of learning mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A field comparison of neck and shoulder postures in symptomatic and asymptomatic office workers

Poor neck and shoulder postures have been suggested to be a cause of neck and shoulder pain in computer workers. The present study aimed to evaluate and compare the head, neck and shoulder postures of office workers with and without symptoms in these regions, in their actual work environments. The two all female subject groups reported significantly different discomfort scores across five trials repeated in a single working day. The results of repeated video capture and two-dimensional motion analysis showed that there were trends for increased head tilt and neck flexion postures in the symptomatic subjects (n = 8), compared to the asymptomatic subjects (n = 8). Symptomatic subjects also tended to have more protracted acromions compared with asymptomatic subjects and showed greater movement excursions in the head segment and the acromion. All subjects demonstrated an approximately 10% increase in forward head posture from their relaxed sitting postures when working with the computer display, but there were no significant changes in posture as a result of time-at-work.     

Kalman滤波用于舰船运动姿态估计的研究

讨论了 Kalman 滤波用于舰船横摇运动姿态估计的应用方法与应用效果针对海浪干扰及测量噪声均为有色噪声的情况下,提出了如何使用 Kalman 次优滤波器和最优滤波器进行舰船横摇运动姿态的估计和预报的理论基础与方法.在IBM 计算机上进行了数字仿真,并给出了仿真的统计结果与仿真曲线.结果表明,采用本文研究的方法进行舰船横摇运动姿态的估计,可获得令人满意的结果。     

采用单目视觉系统的人体三维姿态恢复

提出了至少存在一个点深度值已知的约束条件下,基于单目视觉系统恢复人体三维姿态的方法.该算法简化了CCD相机的标定过程,实现了人体三维姿态的恢复.避免了多目视觉系统在实际应用中对空间和光照等的限制,以及在对应特征点匹配上的弱点.给出了上述方法的实验过程及计算结果,验证了在上述约束条件下基于单目视觉恢复人体三维姿态算法的可行性.     

几种静态姿势的负荷评价与工作设计

以２５名大学生志愿者为对象，通过实验室模拟生产中常见的几种静态姿势，测定和分析了他们的肺通气量、心率及Ｂｏｒｇ量表分值的变化。结果发现自然坐位和站位情况下，随手臂不同程度地前伸和上举，肺通气量、心率、Ｂｏｒｇ量表分值连续地升高，至双臂９０°上举达到最高值。结果说明，肺通气量、心率及Ｂｏｒｇ量表分值均可在一定程度上反映静态劳动的负荷。手上举及手完全前伸的作业姿势无论从劳动生理还是生物力学的角度看都是不合理的，在工作上应尽量加以避免。