Ergonomic evaluation of standard and alternative pallet jack handless

AimTransportation of materials using a pallet jack pulled behind the operator is common due to the visual advantages while transporting fully loaded pallets. The objective of this laboratory study was to quantify muscle activity, posture, and low back compressive and shear forces while completing typical pallet jack activities using a standard handle that required one handed pulling of a pallet jack compared to an alternative handle that allowed for two handed pushing.MethodsParticipants (n = 14) performed six to ten trials of common pallet jack tasks (straight travel and turning) with each handle. Posture analysis of the trunk and right upper extremity was performed using Motion Analysis (Santa Rosa, CA, USA) and back compressive and shear forces were analyzed using 3D Static Strength Prediction Program (University of Michigan, Ann Arbor, MI). Activity of the upper trapezius (UT), pectoralis major (PM), flexor digitorum superficialis (FDS) and extensor digitorum (ED) muscles were recorded (Telemyo 2400 T, Noraxon, Scottsdale, Arizona) and normalized to percent reference voluntary contraction values. All outcomes were compared using the paired t-test.ResultsPeak and mean muscle activity of the PM (p < 0.001) and ED (p < 0.01) were significantly higher using the alternative push handle during all three tasks. There were larger compressive forces at L4/L5 (p < 0.08) and L5/S1 (p < 0.002) using the alternative handle, and greater shear forces using the standard handle at both L4/L5 (p < 0.0001) and L5/S1 (p < 0.000).DiscussionThe standard handle outperformed the alternative handle with regard to muscle activity. The alternative handle had significantly greater compressive forces at L5/S1 due to the pushing nature of the hand-handle interface, yet the standard handle increased shear forces at both L4/L5 and L5/S1 levels in the low back.ConclusionIn this analysis, there was not a clear benefit to using either handle in terms of trunk strength capacity and varied benefits and drawbacks to each handle when comparing compressive and shear forces in the low back. However, given favorable subjective reports described in a prior publication, and the increased reliance on dynamic versus passive force production, facilitating a workers' ability to push a pallet jack while travelling with large loads is worth further investigation.     

Pushing and pulling: personal mechanics influence spine loads

This study assessed several mechanical issues related to low back loading during pushing and/or pulling tasks. Nine male participants performed two-handed pushing and pulling tasks at two handle heights with three loads, using a cable pulley system. Four of these men were professional firefighters trained in performing pushing and pulling tasks while the other five were graduate students who lacked manual work experience. The more experienced firefighters produced less spinal compression and shearing forces when compared to the less experienced students under the same conditions. The firefighters were able to create less muscle activation as compared to the students, which indicated a more efficient technique. The main contributing factors to the forces produced on the low back were the quantity of the load being pushed or pulled, handle height, experience level and the technique of the participant. Thus, attempts to set load limits for pushing and pulling tasks are difficult, since technique has such a large influence on back loading. In order to create safer working environments, education on proper pushing and pulling techniques is very important – more important than the physical variables in many cases.     

Effects of standardized foot positions during the execution of a submaximal pulling task

This study examined how experimentally controlled foot positions could affect the temporal and spatial parameters of a load (20% of subject mass) during a one-handed repetitive submaximal pulling activity. Foot positions standardized relative to a frontal and sagittal plane defining a pull force vector were derived based on the preferences of 45 volunteer subjects. In general, the subjects assumed asymmetrical foot positions and on average the big toe of the foot contralateral to the hand exerting the pull was located 19% (SD = 4.4) of stature in front of the frontal plane containing the pull origin and 8.6% (SD = 4.5) of stature laterally from the sagittal plane through which the load was displaced. The big toe of the foot ipsilateral to the hand exerting the force was located at a distance of 46.7% (SD = 6.3) of stature in front of the frontal plane containing the pull origin and 0.4% (SD = 3.9) of stature laterally from the sagittal plane through which the load was displaced. The left and right feet were orientated at angles of 56.8° (SD = 20.2°) and 25.9° (SD = 22.7°), respectively, relative to a right horizontal of a frontal plane parallel to the plane containing the origin of pull. These foot positions were subsequently employed in a second experiment to investigate how dictating foot positions would affect the way in which 15 newly recruited subjects exerted a pull force on the same load. Results from this experiment showed that the load velocities and forces were not affected by standardized foot positions when compared to those collected when subjects were free to choose foot orientations. It is suggested that future researchers should consider the benefits of employing standardized foot positions in studies of pull exertions, particularly for methodologies similar to that described in this study.     

修补钢筋混凝土梁新老混凝土界面粘结强度的试验研究

混凝土修补的耐久性问题日益受到关注.本文采用拉拔法对钢筋混凝土修补梁新老混凝土的界面粘结强度进行了为期3年的系统测试.比较了粘结强度随时间的变化规律,分析了不同界面处理剂对耐久性的影响.同时也提出了拉拔法测试界面强度的要点.     

新一代高清电视转播车系统架构及设计思路

新一代高清电视转播车系统的全高清的设计,旨在使转播车具有更好的兼容性、灵活性以及安全性,并从全高清电视技术的优势着手,分别从车体空间结构设计、空调系统容量计算、配电系统安全性设计、转播车整体设计以及视频系统、慢动作系统、VSM控制系统等方面进行了详细的描述,通过引入整体设计使转播车内的工作环境更加的舒适和谐。     

PCB企业拉式生产计划

在ERP系统已经发展30多年的今天,计划排程系统已经发展非常成熟,不论是理论研究还是产品落地都有长足发展,如JIT、APS(先进排程)等先进理论都已经有成功的应用。但遗憾的是印制板这个特殊的行业因为规模较小,并且生产过程复杂到现在还没有成熟的解决方案。本文旨在结合原理、印制板企业手工生产计划思路,希望为印制板企业计划排程提供一个可以操作方案。     

A review and comparison of hybrid and pull-type production control strategies

In order to overcome the disadvantages of Kanban Control Strategy (KCS) in non-repetitive manufacturing environments, two research approaches have been followed in the literature in past two decades. The first approach has been concerned with developing new, or combining existing, pull-type production control strategies in order to maximise the benefits of pull control while increasing the ability of a production system to satisfy demand. The second approach has focused on how best to combine Just-In-Time (JIT) and Material-Requirements-Planning (MRP) philosophies in order to maximise the benefits of pull control in non-repetitive manufacturing environments. This paper provides a review of the research activities in these two approaches, presents a comparison between a Production Control Strategy (PCS) from each approach, and presents a comparison of the performance of several pull-type production control strategies in addressing the Service Level vs. WIP trade-off in an environment with low variability and a light-to-medium demand load. Correspondence to: John Geraghty     

钢筋的局部和整体粘结特性

难以建立精确的钢筋局部粘结应力-滑移关系有两个原因：一是由于钢筋被包在内部，很难用应变仪量化给定钢筋长度的应变变化从而直接测定局部应力-滑移关系。另一方面是钢筋的屈服，它一般发生在剥离之前并显著影响钢筋的性能。为了克服定量测量局部应力-滑移关系的困难，通过纤维增强聚合物包裹钢筋混凝土结构的整体荷载滑移响应来获取理论上的局部粘结应力-滑移关系，研究对钢筋嵌入长度的影响。     

新型小车落纱机性能探讨

探讨细纱机短车配套的新型小车落纱机的性能特点。介绍了第十五届上海国际纺织工业展览会展出的新型小车落纱机的性能特点,并对新型小车落纱机的设计和应用等提出了若干建议。认为:新型小车落纱机已有了长足的进步,尚需不断完善,进一步增强可靠性和稳定性;在设计中对光杆锭子拔纱采用先预松是必要的;应考虑细纱机型,注意解决好预拔纱问题;合理设计新型小车落纱机外形尺寸和重量;与新型细纱机结合进行系列化配套辅机设计;完善安全保护、故障自停、报警和显示等功能;探索开发细纱机短车组与托盘式自动络筒机的柔性细络联,促进细纱短车落纱技术的发展。