基于AutoLISP的AutoCAD二次开发_任利东_3110644239_刘羽.doc
基于AutoLISP的AutoCAD二次开发（桂理工）
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本科毕业设计(论文)工 作 总 结 学 院： 机械与控制工程学院 课题名称： 基于AutoLISP的AutoCAD二次开发 专业(方向)： 机械设计制造及其自动化 （模具设计与制造） 班 级： 机械11-2班 学 生： 任 利 东 指导教师： 刘 羽 日 期： 2015年5月27日 工作总结本次毕业设计的题目是基于AutoLISP的AutoCAD二次开发。随着时间的推移，在刘老师的悉心指导下，毕业设计的工作已基本接近尾声。本次毕业设计主要是利用AutoLISP对AutoCAD进行二次开发和创建Access关系数据库。二次开发部分主要完成零件的设计和掌握简单的AutoLISP编程语言。在编写AutoLISP编程语言的过程中，一个细小的错误就会导致整段程序失灵，而且它的检查需要使用“逐一排查”法进行检查，过程及其繁琐复杂。因此，经过多段程序的编写、检查，我做事变得更加仔细，不再像以往那样大大咧咧。另外，由于此前并没有接触过AutoLISP编程语言，编程语言的学习也比较费力，在翻阅了大量的二次开发书籍及相关文献之后，终于有所突破，完成了所需要的编程，同时也拓宽了自己的知识面。Access关系数据库的引入主要是为了简化文件管理过程。但是，由于时间的限制，Access关系数据库并没有完成与AutoCAD的链接，只是完成了Access关系数据库的简单应用，如：表、查询、窗体，这是本次毕设的不足之处，也是以后学习需要进一步加强的方面。通过本次毕业设计，我明白了“时间是检验真理的唯一标准”这句话的含义。所学的理论知识不管多丰富，若不与实践相结合，终究只能是纸上谈兵，没有任何实际意义。只有亲身实践理论知识，把理论知识与实践相结合，才能将知识真正学到手。当然了，也不是说，理论知识没有用，理论知识是实践的基础，扎实的掌握理论知识是实践的必要前提。毕业设计不仅仅是对大学四年所学知识的检验，更是一种提高自己能力的方式。通过本次毕业设计，我明白了学无止境，学习是一个长期积累的过程的道理，不再像以前那样自以为自己掌握的知识已经足够多了。在本次毕设中，我学到了很多的知识，也接触到了以前没接触到领域，自己视野也进一步打开了，我相信，通过本次毕设所学到的东西会对我以后的学习、工作，乃至生活产生很大的影响。桂 林 理 工 大 学本科学生毕业设计（论文）任 务 书系( 院 )： 机械与控制工程学院 课题名称： 基于AutoLISP的AutoCAD二次开发 专业(方向)： 机械设计制造及其自动化 （模具设计与制造 ） 班 级： 机械11-2班 学生姓名： 任利东 学号： 3110644239 指导教师： 刘 羽 职称： 教授 下发日期： 2015年1月10日 桂林理工大学教务处制课题名称基于AutoLISP的AutoCAD二次开发主要内容(包括设计参数)与要求一、本设计的主要内容：综合运用所学知识，进行CAD二次开发。基本内容包括：软件应在AutoCAD2010或以上版本上使用，利用AutoCAD的强大的AutoLISP二次开发功能，设一定的零件标准件，要求具有参数化的设计功能，调用程序时输入要求的零件主要参数后能够自动生成零件图形，并且要符合国家标准件的技术要求。要求操作方便、快捷，软件设计符合AutoCAD的界面风格，能实现无缝联接。并且操作简单，运行可靠，管理、维护方便。二、论文基本要求：1）毕业论文应符合我校本科毕业论文格式，内容规范，包括选题的研究或者开发意义，技术理论综述，设计结果展示以及分析评价等。2） 提供CAD设计图和设计程序。3） 完成时间严格按照学院要求执行；4） 设计文件在答辩完成后进行装订；5） 设计文件电子文稿和打印文稿一并上交；6） 设计文档严禁雇人代做、抄袭，一旦发现，无毕业设计成绩；7） 时间要求在2015年5月底前完成。 工 作 进 程 及 需 完 成 工 作 量工 作 进 程 及 工 作 量：1、第1周第3周：结合毕业论文（设计）题目，初步了解相关知识，查找相关文献资料10篇以上，并有综合读书笔记（其中一篇10000个以上印刷符号的外文译文），完成开题；2、第4周第12周：系统详细设计与开发，完成测试；3、第13周第15周：撰写毕业论文（设计），要求完成10000字左右的毕业论文一份；4、第16-17周：毕业答辩，实习总结。应 遵 守 的 法 纪 法 规1、遵守学院及实习单位的有关规定；2、本科毕业设计指导书等规范要求。毕业设计(论文)完成日期： 2015 年 5 月 31 日指导教师： (签字)教研室主任： (签字)桂林理工大学毕业设计（论文）独创性声明本人声明所呈交的设计（论文）是我个人在指导教师指导下进行的研究工作及取得的研究成果。尽我所知，除了设计（论文）中特别加以标注和致谢的地方外，设计（论文）中不包含其他人或集体已经发表或撰写的研究成果，也不包含为获得桂林理工大学或其它教育机构的学位或证书而使用过的材料。对设计（论文）的研究成果做出贡献的个人和集体，均已作了明确的标明。本人完全意识到本声明的法律后果由本人承担。设计（论文）作者签名： 日期： 年 月 日桂林理工大学设计（论文）使用授权声明本设计（论文）作者完全了解学校有关保留、使用设计（论文）的规定，同意学校保留并向国家有关部门或机构送交设计（论文）的复印件和电子版，允许设计（论文）被查阅或借阅。本人授权桂林理工大学可以将本设计（论文）的全部或部分内容编入有关数据库进行检索，可以采用影印、缩印或扫描等复制手段保存和汇编本设计（论文）。设计(论文)作者签名： 日期： 年 月 日指 导 教 师 签 名： 日期： 年 月 日本科毕业设计(论文)外文翻译（附外文原文） 学 院： 机械与控制工程学院 课题名称： 基于AutoLISP的AutoCAD二次开发 专业(方向)： 机械设计制造及其自动化 （模具设计与制造） 班 级： 机械11-2班 学 生： 任 利 东 指导教师： 刘 羽 日 期： 2015年3月10日 计算机辅助人机工程：结合人体工程学为例分析到工作场所设计摘要：一个计算机辅助人机工程的主要目标是开发软件工具，允许在设计的最初阶段访问人机工程学信息。本案例研究讨论了基于PC的软件程序，允许设计者根据拟议的工作场所设计量化工人的生物力学受伤的危险。该计划的夫妇建立的软件工具，用于生物力学分析，三维静强度预测程序（3DSSPP），与广泛使用的计算机辅助设计软件，AutoCAD软件。在汽车装配任务的主动分析利用3DSSPP / AutoCAD的接口描述，其结果与使用执行相同的任务的工人观察的独立评估比较。这两项研究都得到了类似的结论，这表明主动地利用软件，如3DSSPP / AutoCAD的接口可能在评估工作提出设计一个有效的工具。在这种情况下，在有关使用的支撑人体工学工具，假设和姿势的选择工作场所的设计的分析问题进行了讨论。关键词：人体工程学;计算机辅助设计（CAD）;工作场所设计一、背景工作场所的设计师和产品有三大任务：一，关于整合流程，工具，机器，零件，任务和操作人员的信息;二，满足设计约束，往往发生冲突;三，生成接受各方的设计。然而，当完成这些任务，设计者往往难以结合人体工程学关于人类操作员在他们的设计信息。虽然这样的信息存在于在作业设计方法中使用，其中一个原因为在使用该信息的困难是，它是由设计者（劳斯和1998经常呈现为使用差;森特等人，1998;伯恩斯等人，1997年1997; Evans和1986年）。为了克服这一缺陷的一种方法是使用计算机辅助技术来评估在一个工作场所设计人工操作的性能。在一般情况下，这些技术都集中在对人类操作性能奇异的方面，如生物力学强度预测，代谢率预测，达到评估，和时间预测。然而，这需要设计者进行使用几种不同的工具，其中有许多是不容易应用于除非原型或物理实体模型建议的工作区的已构建独立的分析。这样一来，一些研究人员把他们的重点转向集成开发工具，允许从多个来源的信息人体工程学的实际作业前要检查实施*积极的一个，而不是反应的方法。通过结合使用，从计算机辅助设计（CAD）软件的多个来源的信息，设计人员能够使用单一的分析工具，以评估间隙，到达，视觉要求，并在设计的最初阶段，体位舒适。这使设计师能够将功能整合到设计中，最大限度地减少受伤的风险之前，一个人曾经遇到物理产品或工作场所。期望中的功能包括工作场所和设备的三维建模，三维人形模型能够代表各种姿势，评价技术来评估范围，愿景，“T，和姿势，以及交互式界面，使设计人员能够操纵两个人形和工作场所的设计（Porter等，1995）。一种方法是开发具有内置的人体工程学设计评估功能的三维CAD软件。几个这样人体工学的CAD一个系统已经在包含上述一些或全部功能，以不同程度的文献，其中SAMMIE（Porter等，1995）可能是最好的系统已经描述包括APOLIN，畜牧业协会。在一般情况下，对于许多这样的系统，用户必须学习术语，命令结构和建模技术从没有在商业上可用的CAD系统不同。此外，这些系统进行建模和操纵姿势的能力相差很大，也只有少数的系统评估的静态强度的能力或回压缩力的建模的姿势和负荷的基础上，损伤的危险。另一种方法是开发出同时使用市售的CAD系统来提供三维建模要求提供的评价方面和接口互补软件。沿着这条线，人形建模和分析方案已被开发成在用户首选CAD系统创建的工作场所或产品图纸可以导入。 SAFEWORK（福廷等人，1990）是本常用的一个例子中，人的形式的模型和分析工具已经设计用于从CAD内访问系统利用设计师的熟悉程度的术语，技术，和市售的CAD命令结构包括MINTAC，人（森古普塔和达斯，1997），RAMSIS（塞德尔，1997），以及商用系统，例如ANYBODY和人体模型（波特等人，1995）。球蛋白等。对于主动的方式来实现对人体工程学的影响最大，信息，因为它涉及到对未来的员工工作场所的作用应在可能的布局设计的初步评估提供给设计师。通常情况下，上面列出的系统满足此要求在一定程度上，特别是在达到，间隙和视觉需要的评价。然而，评估体位时的舒适度，最系统的功能出现仅限于设计师的关于不良姿势*即使被处理负载时合理姿势往往是无法接受的是沉重的主观判断。此外，许多上面列出的系统都不能访问大多数设计者或分析，因为它们不是已经开发了专门的应用程序（例如，军用飞机或汽车应用），是成本过高，否则不能在个人计算机上运行。这些问题表明，为了符合人体工程学的CAD系统被广泛应用在积极主动的方式，几个额外的标准，应满足。首先，一个系统必须能方便地为设计师和工程学家一般行业。这意味着，该系统可以用来分析广泛的作业，是可用于在合理的成本，并且可以在标准的个人计算机上运行。接下来，用户应迅速，准确地能够操纵利用技术通过几个设计options.Finally，工作的正确分析迭代尤其是当涉及到手动起重，推，或拉应包括生物力学强度评估设计任务兼容姿势。因此，有效的生物力学模型应该被合并到系统中，使得它们可以容易地与精确的结果迅速被计算并显示访问的方式。为了满足这些附加条件，研究人员在密歇根州的中心人机工程学的设计大学的接口程序，它与广泛使用的AutoCAD软件。3DSSPP软件集成了其三维静强度预测程序（3DSSPP），市售自1989年以来，结合功能这让设计人员能够快速，轻松地操纵从大约3000健康在校大学生和工人静态强度数据，年龄介于17至65岁派生评价算法三维人形模型的姿势。这些算法考虑的姿态，选择了人体测量学，性别和部队的手中，以确定脊髓压迫力，联合静强度的能力，平衡和足部滑移考虑（见（1997年），为纳入3DSSPP审查生物力学模型）。所述3DSSPP的验证研究表明，该程序可以预测与相关大于0.85（1992）的静态强度的能力。该3DSSPP / AutoCAD的界面产生在Microsoft Windows 95环境，让设计师来量化风险的生物力学和工作场所设计任务的框架内评估范围，通关和视觉要求符合人体工学的CAD系统。接口本身被集成到3DSSPP菜单系统，并提供控制的3DSSPP人形模型的AutoCAD内的位置和位置图（图1）。一旦人的形式模型被定位的图中，从3DSSPP算法结果可以显示（图2）或设计者可以使用AutoCAD功能执行间隙的粗略检查，到达和人形模型和之间视力工作场所项目。在133使用Windows 95。图.1在左侧，由第95百分位男性（身高和体重）拟议的起重设备安装液力变矩器是用来插入人形到AutoCAD绘图从内显示modeled.The主要3DSSPP/ AutoCAD的界面菜单3DSSPP右侧。兆赫微处理器与奔腾处理器和现有的工作图纸，一个新手用户界面熟悉AutoCAD和3DSSPP可以模拟一个姿势，检查视力，达到和间隙要求，并在不到10分钟的生物力学评估风险。为了说明3DSSPP/ AutoCAD的界面的操作，更详细地说明其功能，汽车装配任务为例进行。案例研究的目的是双重的。的“第一个目的是证明如何接口可能被预先用在设计环境来分析工作场所的设计。第二个目标是向3DSSPP/ AutoCAD的分析的结果与一个独立进行人体工学评估，其中经营者的结果比较观察到在现有的工作站执行的任务。二、任务介绍2.1、手工组装任务要求工人检索齿条变换器在四个级别中的一个（图2），在腰部高度携带到一个输送机，其安装到位于一个装置.工人一个变速器壳体会然后转动转换器与排队起来在输出轴花键和推转换器进入壳体。2.2、大会采用升降援助由于转换器的重量，姿势使用，并且难以安装转换器，一个提升装置中进行作为1990年。援助的一部分的用户试用的评价是，利用一个真空杯保持在天花板上的平衡葫芦转换器。在用户试用，工人对准真空杯与变矩器的中心，致动真空，并从机架解除该转换器。工人回踩清除架，转向臂1803，并与变速器壳（图1）对齐的转换器。在这一点上，平衡臂被推向前，直到变换器接触在输出轴上的花键上，然后绕所述纵轴并同时按压接合的花键的转换器。图2.第95百分位男性检索从最低机架变矩器是仿照左侧。结果显示在显示L5 / S1椎间盘压缩力（右下）的权利和谁具有的接合强度的能力，以保持该姿势中给出的手负载男性的百分比。三、评价方法：使用3DSSPP / AutoCAD的接口3.1、在AutoCAD绘图工作使用明确的研究建立了一个三维CAD图纸分析进行。由于任务是已经存在的研究，工作场所和零件的尺寸进行了审议。这不同于典型的设计阶段分析中，虽然部分的尺寸可以是，工作场所的尺寸很少约束在设计阶段。然而，请注意，在设计阶段一个工作场所的每次迭代中，一组尺寸必须分析。在这种情况下研究中，仅在设计的设置进行的现有工作场所的同时分析，而且与升降援助的任务和可被视为在设计阶段中的初始迭代评估。3.2、在3DSSPP数据录入该3DSSPP / AutoCAD的接口依赖于3DSSPP程序来预测等项目的联合力量的能力和背部压缩力对于一个给定的工人。预测这些，3DSSPP需要手力的方向和大小的输入，工人人体测量和性别，以及工人的负载在手动任务由所述转换器的重量。为材料装卸设备，两个独立的手的力量被使用：一个用于升降机相从零件架和另一个用于操纵平衡。为了比较与独立进行评价，5th百分身高和体重的阴结果和第95百分位身高和体重的男性被用来代表了劳动人口的合理极端。然而，任何性别和身高和体重的百分可以输入到3DSSPP。该3DSSPP别人的姿势造型的三种方法：关节角度进入，直接操作，而反向运动算法。当模拟已知姿势，所述关节角的方法是最精确的和优选的比其他两种方法。在该方法中，通过执行任务的工人特定的关节角度被测量的平面和直接输入到程序中。通过这种方式，分析并不需要依靠由程序向姿势建模生成的人形上，虽然人的形式模型可提供一个粗略的检查数据条目的准确度。在某些情况下，虽然，具体加入缠结不能从源（即，照片或视频静止图像）精确地确定。在这种情况下，3DSSPP结合了相机的比喻的斜视图，使得由人形3DSSPP产生的视图可以被调整到的照片图像的观看距离，仰角，和视角匹配仍然。一旦这些参数都匹配，直接操作，可以使用通过允许设计者点逼近源姿势，并通过鼠标单击一个改变关节或连结位置上。简笔画形式是优选的这种类型的模型作为介晶体类型的3DSSPP人形可偏压由分析感知的关节角度，如果另一个体型被建模的。在设计的设置，然而，工人姿势鲜为人知。相反，设计人员必须选择判断是合理的，并有可能对任务是在此选择一个姿势，一个3DSSP基于行为上反向运动的算法来预测一个姿势一个工人会采取给手的位置相对到脚，工人的人体测量学，和负载在手中。该算法依赖于从美国特种作战部队的平民姿势行为的研究得出回归方程产生的平均姿势的人会采取作为手位置的功能和其他任务参数。虽然该姿势是通常用于分析合理，如果分析判断，否则直接操作可用于进一步调整姿态。3.3、3DSSPP / AutoCAD的接口在3DSSPP / AutoCAD的接口的关键功能使用反向运动算法与职场结合图纸，帮助职场图形中的模型，设计者定义和名称唯一的AutoCAD用户坐标系统（UCS）的位置，其中工人可能是位置和在该手的灵敏度独立沙脚可能被放置。接下来，在3DSSPP，设计师定义区域的，允许人形移动和预定量对任何给定的UCS旋转。要定位图形中的人形模型，设计者选择身体（臀部，眼睛，胸部，或脚中心），一个UCS位置和区域内的点。接口传递相关数据从3DSSPP到AutoCAD，生成三维人的形式以所需的身体点处从由选择的区域中描述的UCS位置的距离。一旦该图是在图中，设计人员可以选择所需的UCS在每个手应位于。的手的位置被传递回3DSSPP，逆运动学算法预测的姿态和由此产生的数据被发送回的AutoCAD到新的姿势。在这一点上，设计者可以决定使用直接操作从内3DSSPP修改预测姿势，或进行分析步骤。3.4、分析能力一旦人形模型位于图纸和确定的姿势中，下列项目可以考虑：视觉要求，到达，清关，和生物力学因素。视觉要求可以通过使用AutoCAD的动态视图特征。在图中指定的目标位置要观看和定位靠近眼中心的观点出发来确定，所看到的工人视图可以通过AutoCAD的近似。如果相关功能是不可见的工人，视点可以移动，直到它们是可见的。在这一点上，姿势或整个“古尔移动时所需的视点来定位眼中心，具体范围的能力可以通过定位在绘图中的工人和指定所需的手的位置来确定。3DSSPP使用联合范围与链路长度数据，以确定运动约束如果手的位置即可到达，要么更新姿势或显示一条消息，姿势是用3DSSPP / AutoCAD的界面无法实现的。间隙检查通常是通过目测AutoCAD环境内完成通过指定不同的观点进行绘图。一旦视觉，到达，和间隙要求得到满足，生物力学因素所得姿势可以计算出来。这些因素包括工人与必须克服的任务，背面的压缩和剪切力在L5 / S1椎间盘突出，工人的平衡，和滑移风险的力要求所需的接合强度的人体测量学的百分比。 3DSSPP计算这些因素为主要关节（见（1997年），为生物力学模型进行全面审查列入3DSSPP），结果与接头强度的能力和回压限制NIOSH准则进行比较。对于接合强度的功能时，NIOSH强度设计限制（SDL）被超过时具有足够的强度的人口在给定的关节的百分比低于99为男性，75为女性。该NIOSH强度上限（SUL）被超过时的百分比低于男性25，女性1。对于回压缩时，NIOSH返回压缩设计限制（BCDL）被超过时背面压缩力大于3400牛顿（N）和NIOSH回到压缩上限（BCUL）被超过时背面压缩力大于6400 （NIOSH，1981）。这些值与用于开发的1981年和1991年NIOSH升降式标准（Waters等al.1993）一致。报告显示的结果可以在屏幕上进行显示（图2），印刷用于审查，或写入用于在电子表格或数据库程序的其他分析。一个重要的注意的是，3DSSPP结果是基于被研究的任务运动要么静止或很慢的假设;因此，结果被计算忽略加速度和动量的影响。这种高估的工人谁使用快速或挺举运动的迅速加速负载和减速的力量所能力的关节和肌肉处理地方附加力。此外，个人的强度能力与移动的速度（1997年，1992年）减小。目前，这种简化的假设是必要的理由，包括缺乏有关动态强度性能足够的数据和涉及建模的移动速度的可能范围的困难。对于被分析的组装任务，这种假设被认为是合理的，因为变矩器是沉重和难以掌握和保持，劝阻快速移动的因素。四、案例研究方法使用3DSSPP / AutoCAD的界面，上述的评价方法被用来研究手动转换器组件的任务和使用该提升装置的转换器组件的任务。 A 133 MHz的微电脑奔腾处理器采用与Windows 95，AutoCAD中的Windows，版本13和3DSSPP用于Windows，3.06版本。设计者在进行分析，经历了符合人体工程学的执行工作分析和熟悉所使用的软件。设计者提供了用照片和工作站，并在装配任务中使用的零件的工程图纸，但没有给出关于在执行工作，工人利用，不知道，一个单独的评估是独立进行的姿势的任何信息。每个任务中的六个特定姿势被认为是：检索姿态在四个机架高度，承载的姿势，并安装姿势。虽然工人在任务持续移动时，假设有人提出，任务可以被分解成的静态姿势，其中每一个可以被单独分析的序列。该装配任务的人体工程学独立评价于1990年进行的，在福特汽车公司一个更大的评估努力的一部分。分析师手动和安装的起重设备观察到执行任务的工作人员，在执行自己的任务，收集体位数据，并采访了工人。基于所收集的信息，几个项目，包括所要求的强度的功能和从任务*所得的低后压缩力进行了分析。从随后的分析（1990雷斯尼克等人）中的报告中包括结果仅用于第95百分位男性，因此，让这些结果和预测结果从主动3DSSPP / AutoCAD的分析，只为第95百分位的数据之间的比较雄性示于图。 3-6。图.3.百分比的第95百分位男性有足够的肩部力量四个任务元素如在1990年进行的独立评价和3DSSPP / AutoCAD的分析确定。图.4.百分比的第95百分位男性与躯干足够的强度四个任务元素如在1990年进行的独立评价和3DSSPP / AutoCAD的分析确定。图.5.百分比的第95百分位男性与臀部强度四个任务元素如在1990年进行的独立评价和3DSSPP / AutoCAD的分析确定。这两项研究的低机架（手动）任务的元素之间的差异是由于在姿势选择的不同：在1990年的研究的分析中使用的对称脚放置而3DSSPP / AutoCAD的分析师所使用的非对称足放置。图.6.第95百分位男性椎间盘突出压迫力在L5 / S1的联合在1990年进行的独立评价和3DSSPP / AutoCAD的分析，确定四个工作组的元素。误差线代表从人群平均值1标准偏差。五、结果5.1、手动任务设计者没有发现任何明显的问题与视觉，伸手，或任何姿势的间隙要求。在一般情况下，分析结果表明，任务创建相当的生物力学应力超过NIOSH准则和应该重新设计（如图手动任务。3-6）。5.2、建议电梯援助设计者没有发现任何困难，达到对任何姿势。然而，设计者报道，无论是男性和女性将试图对准真空杯与转换器组件时遇到困难，从视觉角度看，在所有四个机架高度在检索阶段，因为电梯救援块工人的图。更成问题的是在安装阶段，其中工人必须居中变换器的变速器组件的前部的图。试图排队两个零件进行组装时，提升装置放置工人从壳体和块多视图的大约四脚。为了清楚地查看部分对齐，工人必须转移你咋中心至少有6至两侧，同时还推动直行。检索部分由机架。最低最没有压力的姿势由工人需要时避免与输送机接触也观察到了第95百分位男性工人和传送带之间的间隙困难依然产生生物力学应力超过NIOSH准则（升降机辅助任务示于图3 6）。总体而言，基于视觉，清除率和生物力学问题确定，设计者建议此装置不能使用，以取代现有的手动任务。5.3、工作场所的学习1990年对于在手动装配任务中观察到的姿势，也没有问题表明与携带。尽管，报告（雷斯尼克等人，1990）表明几个其它生物力学问题（图3 6）。大约从肩关节超出了NIOSH指导和检索大约臀部和躯干以及背部的压缩力超出NIOSH行动限制最低机架产生的瞬间最高机架产生的时刻检索。安装阶段创建的时刻对臀部，躯干，肩膀和NIOSH超过准则。分析师对这一报告的结论是任务需要重新设计，以减轻这些风险的生物力学。为用户试用期间使用的材料处理设备的姿势观察，在约臀部和背部压缩力最低机架高度创建时刻它超过了NIOSH动作限制检索阶段（图5和6）。此外，报告中描述的间隙问题，而使用该设备在较低高度的机架工人了。还指出的是，工人有困难，如果被正确地安装该转换器确定和观察周围安装阶段后的设备正以确保该变换器被正确组装。基于这些发现，分析师的结论是，电梯援助是不适合给定的工作场所。六、讨论虽然上述案例研究演示了如何3DSSPP / AutoCAD的接口采用的是一个设计环境中，问题仍然是分析的有效性：是使用类似于在1990年的研究中获得的3DSSPP / AutoCAD的接口得到的结果？在概括地说，3DSSPP / AutoCAD的分析和独立1990年评价产生了相似结论。首先，手动提升和安装转换成变速器壳体导致了超过NIOSH指引生物力学应力。其次，虽然使用的材料处理设备降低了生物机械应力对工人，NIOSH指导方针仍然超过有关躯干和髋关节的强度以及后面的压缩力为男性。第三，工人的视觉要求通过使用材料处理装置的被阻碍。第四，使用电梯援助工作者较大恐难取回部分从下架没有碰撞到传送带。这两项研究的结论是，手动任务应该改变，以消除受伤的工人的风险，但是，使用在停滞在现场将产生其他问题，并不会是一个很好的选择的材料装卸设备。虽然在上述情况下，研究提议的材料处理设备通过分析使用3DSSPP / AutoCAD的接口在用户试用消除以及，分析使用接口不应取代用户试验。相反，该方案表明仅在现有这个特定设备的不良替代手动任务。此外，由于在3DSSPP人形模型是仅限于单个介晶身型，使用该软件的可视化检查“T，到达，和给定的工作空间中的间隙只能算是一个”第一个近似的其他身体类型可能仍会遇到干扰，在实际的设计。因此，通过3DSSPP / AutoCAD的界面内潜在设计迭代应继续进行，直到一个可行的选择是鉴定“编辑和选定的，在该点，用户试用应进行的一点是，如3DSSPP / AutoCAD的接口系统是不恰当的用作评估工作场所设计的唯一手段，而是其他的人体工程学工作分析工具（例如，NIOSH升降导轨，时间和运动的研究，人的形式）应被结合使用，这些系统以评估潜在的设计和验证选择一个特定设计的过程中的用户。例如，在独立1990评价，用户试验与材料处理设备允许利用时间的研究和能量消耗评价的分析，以进一步比较升力辅助任务与药效手工装配。在任务的独立评估和3DSSPP / AutoCAD的分析之间的结果比较接近，人们可能会认为，在不同情况下，得出的结论可能很容易被不同的，特别是如果其它人体测量学，人口，或姿势已经在使用所述3DSSPP / AutoCAD的接口（图5）。首先，有些人会认为，分析了5的女性和95的男性人体尺寸是值得商榷的。不仅仅这种选择中排除选定的人口的10，但它也使统计上不太假设一个人的存在，其主体尺寸都是相同的百分。在这个案例中，这些值被选择，以保持与1990年进行的评估的一致性，并不意味着百分其设计者应在其工作占的推荐范围。虽然设计师们鼓励发展的产品或工作站，所有的人可以方便地使用，有可能是参与显著的权衡。在一般情况下，由于人口由设计增加收纳的范围内，所以没有执行必要使住宿可行的特征和可调节的成本。另一方面，有可能是法律和营销问题以及不包括人口的区段时要考虑的其他成本。在结束时，百分范围的优选的选择可以设计之间是不同的，基于分析独特的每个设计的情况。作为统计学上是不可能的人的假设，这是该程序的使用蒂尼比例常数来估计链路长度（贝克，1992）的结果。虽然身高和许多其他人体尺寸之间的相关性较弱，假设简化了对强度的预测影响不大设计师的数据输入要求。这是由表明3DSSPP静态强度预测具有大于0.85的实际强度数据的相关性的验证研究的支持。然而，软件应该只作为初始近似范围，清除评估，和“t为弱相关的人形图形功能有限会对他们显著影响更大。其次，underlies的3DSSPP / AutoCAD的接口的研究是基于工作年龄（17-65岁左右）的健康个体。尽管假设是，这个接口将只在工业应用这一人群中使用，最近的法律，如美国残疾人法和残疾人歧视法案可能迫使设计人员尝试使用该软件，老年人或残疾人。在前者的情况下，设计者需要认识到，目前，有足够的数据可在老年个体可以被纳入3DSSPP强度的能力。直到数据变得可用，从3DSSPP结果将在预测老年个体的能力。在后一种情况下，有残疾的知识设计者可以在提供所遇到的障碍不损害周围的人的官能接头的强度或迁移率的工作场所设置应用于该软件。虽然细节超出了这个案例研究的范围，一个例子可能是使用该软件来设计工作站全肩关节和躯干的流动性高位截瘫。最后，关于姿势的选择，从任何人体工学分析和CAD软件程序包的结果可以是尤其当与基于实际使用的工人的姿势结果由设计者在设计设置中选择的姿势，非常敏感。事实上，查$ n和ERIG（1991）指出，一个103错误中最弱的联合对于给定的姿势的角度可以产生高达30的误差所产生的人口强度预测。虽然在3DSSPP使用逆运动学算法允许新手用户已知的姿势快速，准确地模型，贝克警告说，这种算法不一定正确使用本身预测，因为姿势它可以预测不良姿势一些。此外，贝克指出，算法的开发和测试，并不构成验证研究。此外，刘等人。 （1997）指出，已知的姿势的人体工学分析的准确性和有效性被建模从照片受所使用的姿势建模系统的摄影视角，可视化方案，并且该姿势的复杂性。如果这是事实的一个已知的姿势，人们一定会问：如何看待这些及其他因素影响积极的人体工程学分析其中的姿势必须在可视化设计师的头脑和任务视为合理的准确性和有效性。因此，由于设计者仍然必须尝试考虑其他因素，如负荷处理，培训，个体联合限制和经验，行为上基于姿势预测算法，例如上述的逆运动学方法只能是一个“第一个近似朝向准确预测实际工作者的姿势，直到进一步的研究证实了在主动辅助软件的使用姿势预测算法，设计师不应该依赖于一个单一的人体尺寸，并通过预测算法产生的唯一依据初始姿势得出结论关于工作场所设计，而是设计人员应该谨慎考虑几个姿势不同作为其设计的评估援助。七、结论虽然持续的研究是必要的，从设计设置的分析和独立评价1990年的结论之间的相似性表明，3DSSPP / AutoCAD的接口，可能是工作场所设计的前瞻性分析的有效工具。该方案具有局限性，不应被用来作为一个独立的程序，但它可以在一个工人的范围，通关，视力，力量能力方面提供初步指导设计师。在一般情况下，使用人体工程学分析软件与CAD结合具有几个明显的优势：在整个项目时间的减少，在设计过程的早期应用人机工程学信息的能力，既符合人体工程学的关切和设计方案，及成本效益改善沟通。更具体地，3DSSPP软件与AutoCAD整合当前存在提供超过许多其它人体工学CAD系统额外的好处。首先，该接口提供了CAD图纸中的人形模型的简单，快速控制。二，接口使用方法与设计任务相兼容，让生物力学评估，积极主动地在工作场所潜在的设计进行了分析。第三，也许是最重要的，界面访问一般行业。软件如3DSSPP / AutoCAD的接口是朝着提供产品或工作场所的设计过程中得到来自单一来源的人体工程学信息的有效和方便的手段“的第一步。随着生物力学和姿势预测模型改进和被纳入这些类型的软件，工作场所的设计师和分析师会发展得越来越好装备，以防止受伤之前提出的工作就开始存在。外文原文：Computer-aided ergonomics: a case study of incorporating ergonomics analyses into workplace designAbstract：One of the primary goals of computer-aided ergonomics is to develop software tools that allow ergonomics information to be accessed at the earliest stages of design. This case study discusses a PC-based software program that allows a designer to quantify a workers biomechanical risk for injury based on a proposed workplace design. The program couples an established software tool for biomechanical analysis, the Three-Dimensional Static Strength Prediction Program (3DSSPP), with a widely used computer-aided design software package, AutoCAD. The use of this 3DSSPP/AutoCAD interface a in the proactive analysis of an automotive assembly task is described and the results compared with an independent assessment using observations of workers performing the same task. Both studies yield similar conclusions, suggesting that proactive use of software such as the 3DSSPP/AutoCAD interface maybe a valid tool in evaluating proposed workplace designs. In this context, issues in the analysis of workplace designs regarding the use of supporting ergonomic tools, assumptions, and posture selection are discussed. ( 2000 Published by Elsevier Science Ltd. All rights reserved.Keywords: Ergonomics; Computer-aided design (CAD); Workplace design1. BackgroundDesigners of workplaces and products have three major tasks: one, integrating information about processes, tools, machines, parts, tasks, and human operators; two, satisfying design constraints which often conflict; and three, generating a design acceptable to all parties involved. However, while completing these tasks, designers often have difficulty incorporating ergonomics information about the human operator into their designs. Although such information exists for use in the job design process, one reason for the difficulties in using this information is that it is often poorly presented for use by designers (Rouse and Bo, 1998; Vicente etal.,1998;Burns 1997; , 1997; Evans and ,1986). One approach to overcome this deficiency has been to use computer-aided techniques to evaluate the performance of human operators in a workplace design.In general, these techniques have focused on singular aspects of human operator performance such as biomechanical strength prediction, metabolic rate prediction, reach assessment, and time prediction. However, this requires the designer to conduct separate analyses using several different tools, many of which are not easily applied unless a prototype or physical mock-up of the proposed work area has been constructed.As a result, several researchers have shifted their focus towards developing integrated tools that allow ergonomics information from several sources to be examined before an actual job is implemented * a proactive a rather than reactive a approach. By coupling information from multiple sources with computer-aided design (CAD) software, designers are able to use a single analysis tool to assess clearances, reach, visual requirements, and postural comfort at the earliest stages of design. This allows the designer to incorporate features into designs that minimize the risk of injuries before a person ever physically encounters the product or workplace. Desired features include three-dimensional modeling of workplaces and equipment, three-dimensional human form modeling able to represent various anthropometries and postures, evaluative techniques to assess reach, vision, and posture, and an interactive interface that allows designers to manipulate both the human form and the workplace design (Porter et al., 1995).One approach has been to develop three-dimensional CAD programs with built-in ergonomics assessment capabilities. Several such ergonomic CAD a systems have been described in the literature that incorporate some or all of the above features to varying degrees, of which SAMMIE (Porter et al., 1995) may be the best known. Other systems include APOLIN CAAA (Hoekstra, 1993), COMBIMAN and Crew Chief (McDaniel,1990), Deneb/ERGO, ERGOMAN). In general, for many of these systems, users must learn terminology, command structures, and modeling techniques differing from those in the commercially available CAD systems. Also, the ability of these systems to model and manipulate postures varies widely, and only a few systems evaluate injury risk on the basis of static strength capabilities or back compression forces for the modeled postures and loads.Another approach has been to develop complementary software that provides the evaluative aspects and interface while using commercially available CAD systems to provide the three-dimensional modeling requirements. Along this line, human form modeling and analysis programs have been developed into which workplace or product-drawing created in the users preferred CAD system can be imported. SAFEWORK (Fortin et al., 1990) is one example of this technique. More commonly, human form models and analysis tools have been designed for access from within a CAD system. These systems take advantage of the designers familiarity with the terminology, techniques, and command structures of commercially available CAD programs. Examples include MINTAC (Mattila,1990), HUMAN (Das, 1997), RAMSIS, and commercial systems such as ANYBODY describe other examples.For a proactive approach to achieve the greatest impact, information on ergonomics as it pertains to a workplaces effect on future employees should be available to designers during the initial evaluation of potential layout designs. Typically, the systems listed above meet this requirement to some degree, particularly in the evaluation of reach, clearance, and visual needs. However, when assessing postural comfort, the capabilities of most systems appear limited to a designers subjective judgment regarding awkward postures * even though reasonable postures are often unacceptable when the loads being handled are heavy. Also, many of the systems listed above are not accessible to most designers or analysts since they have either been developed for specialized applications (e.g., military aircraft or automotive applications), are cost-prohibitive, or cannot run on a personal computer. These concerns suggest that, in order for an ergonomic CAD system to be used widely in a proactive manner, a few additional criteria should be met. First, a system must be readily accessible to designers and ergonomists in general industry. This implies that the system can be used to analyze a wide range of jobs, is available for use at a reasonable cost, and can run on a standard personal computer. Next, the user should quickly and accurately be able to manipulate postures using techniques compatible with the design task especially when iterating through several design options. Finally, a proper analysis of a job involving manual lifting, pushing, or pulling should include a biomechanical strength assessment. Thus, validated biomechanical models should be incorporated into the system in such a way that they can be easily accessed with accurate results quickly being computed and displayed.To meet these additional criteria, researchers at the University of Michigans Center for Ergonomics designed an interface program which integrates their Three-Dimensional Static Strength Prediction Program (3DSSPP) with the widely available AutoCAD software. The 3DSSPP software, commercially available since 1989, combines features which allow designers to quickly and easily manipulate the posture of a three-dimensional human form model with evaluative algorithms derived from static strength data of approximately 3000 healthy college students and workers, ranging in age from 17 to 65 yr. These algorithms consider the posture, selected anthropometry, gender, and forces on the hands to determine spinal compression forces, joint static strength capabilities, balance, and foot slip considerations (see (1997), for a review of the biomechanical models incorporated into the 3DSSPP). Validation studies of the 3DSSPP indicate that the program can predict static strength capabilities with correlations greater than 0.85 (1992).The 3DSSPP/AutoCAD interface yields an ergonomic CAD system in the Microsoft Windows 95 environment that allows a designer to quantify biomechanical risk and assess reach, clearance, and visual requirements within the framework of the workplace design task. The interface itself is integrated into the 3DSSPP menu system and provides controls for the placement and position of the 3DSSPP human form model within the AutoCAD drawing (Fig. 1). Once the human form model is positioned within a drawing, results from the 3DSSPP algorithms can be displayed (Fig. 2) or the designer can use AutoCAD features to perform a rough check of clearance, reach, and vision between the human form model and the workplace items. Using Windows 95 on a 133.Fig.1. On the left, installation of a torque converter by a 95th percentile male (height and weight) with the proposed lifting aid is modeled. The main 3DSSPP/AutoCAD interface menu used to insert the human form into the AutoCAD drawing is displayed from within 3DSSPP on the right.MHz microcomputer with a Pentium processor and an existing workplace drawing, a novice interface user familiar with both AutoCAD and 3DSSPP can model a posture, check the visual, reach, and clearance requirements, and assess biomechanical risk in less than 10 min. To illustrate the operation of the 3DSSPP/AutoCAD interface and describe its features in more detail, a case study of an automotive assembly task was conducted. The objectives of the case study were twofold. The rst objective was to demonstrate how the interface might be used proactively in a design setting to analyze workplace designs. The second objective was to compare the results of the 3DSSPP/AutoCAD analysis with the results of an independently conducted ergonomic evaluation in which operators were observed performing the task at the existing workstations.2. Task description2.1. Manual assemblyThe task required that a worker retrieve a 16.3 converter from a rack at one of the four levels (Fig. 2), carry it at waist height to a conveyor, and install it into a transmission housing located on a conveyor. The worker would then rotate the converter to line it up with the output shaft and push the converter into the housing.2.2. Assembly using a lift aidDue to the converter weight, postures used, and difficulty in installing the converter, a lifting aid was evaluated in a user trial conducted as part of the 1990 study. The aid was a ceiling-mounted balancing hoist that utilized a vacuum cup to hold the converters. In the user trial, the worker aligned the vacuum cup with the center of the torque converter, actuated the vacuum, and lifted the converter from the rack. The worker stepped back to clear the rack, turned the arm 1803, and aligned the converter with the transmission housing (Fig. 1). At this point, the balance arm was pushed forward until the converter contacted the splines on the output shaft,and was then rotated about the longitudinal axis and pushed simultaneously to engage the converter on the splines.Fig.2. A 95th percentile male retrieving a torque converter from the lowest rack is modeled on the left. Results are displayed on the right showing the L5/S1 disc compression force (bottom right) and the percentage of 95thpercentile males who have the joint strength capability to maintain this posture given the hand loads.3. Evaluation method using the 3DSSPP/AutoCAD interface3.1. Workplace drawing in AutoCADAnalysis was conducted using a three-dimensional CAD drawing created explicitly for the study. Since the task being studied already existed, the workplace and part dimensions were considered. This differs from the typical design stage analysis in that, although part dimensions may be, workplace dimensions are rarely constrained in the design phase. However, note that for each iteration of a workplace in the design phase, a set of dimensions must be analyzed. In this case study, both the analysis of the existing workplace and that of the task with the lifting aid were conducted solely within the design setting and could be considered as evaluations of the initial iterations within the design phase.3.2. Data entry in 3DSSPPThe 3DSSPP/AutoCAD interface relies upon the 3DSSPP program to predict such items as the joint strength capabilities and back compression forces for a given worker. To predict these, 3DSSPP requires the input of hand force direction and magnitude, the worker anthropometry and gender, and the workers posture. Hand loads in the manual task consisted of the converter weight. For the materials-handling device, two separate hand forces were used: one for the lift phase from the parts rack and another for manipulating the balance arm. In order to compare results with the independently conducted evaluation, a female of 5th percentile height and weight and a male of 95th percentile height and weight were used to represent reasonable extremes of the working population. However, any gender and percentile of height and weight can be input into 3DSSPP.The 3DSSPP others three methods of posture modeling: joint angle entry, direct manipulation, and an inverse kinematics algorithm. When modeling a known posture, the joint angle method is most precise and preferred over the other two methods. In this method, specific joint angles adopted by a worker performing the task are measured in planes and entered directly into the program. In this way, the analyst does not need to rely on the human form generated by the program to model the posture, although the human form model can provide a rough check for the accuracy of data entry. In certain situations, though, the specific join tangles cannot be determined accurately from the source (i.e., photographs or video stills). In this case, 3DSSPP incorporates a camera metaphor with the oblique view so that the view generated by 3DSSPP of the human form can be adjusted to match the viewing distance, elevation, and viewing angle of the photo video still. Once these parameters are matched, direct manipulation may be used to approximate the source posture by allowing the designer to point and click a via mouse to change joint or link positions. The stick figure form is preferred for this type of modeling as the body type of the 3DSSPP human form may bias the joint angles perceived by the analyst if another body type is being modeled.In the design setting, however, the worker posture is rarely known. Instead, the designer must select a posture judged to be reasonable and likely for the task being performed. in this selection,3DSSPPincorporates a behaviorally based inverse kinematics algorithm to predict a the posture a worker would adopt given the hand location relative to the feet, the workers anthropometry, and the load at the hands. The algorithm relies on regression equations derived from studies of the postural behavior U.S. civilians (Kilpatrick, al.1972; Park, 1973; Beck, 1992) to produce the average posture a person would take as a function of the hand locations and other task parameters. Although this posture is typically reasonable for analysis, if the analyst judges otherwise, direct manipulation may be used to further adjust the posture.3.4. 3DSSPP/AutoCAD interfaceThe key feature of the 3DSSPP/AutoCAD interface uses the inverse kinematics algorithm in conjunction with the workplace drawing to help model postures. Working within the workplace drawing, the designer defines and names unique AutoCAD User Coordinate Systems (UCS) at locations where the worker might be position and where the in feet might be placed. Next, within 3DSSPP, the designer defines zones that allow the human form to be moved and rotated by predetermined amounts about any given UCS.To position the human form model within the drawing, the designer selects a point within the body (hip, eye, chest, or feet center), an UCS location, and zone. The interface passes the relevant data from 3DSSPP to AutoCAD, generating a three-dimensional human form with the desired body point at the distance from the UCS location specified by the chosen zone. Once the figure is within the drawing, the designer can select the desired UCS at which each hand should be located. The hand locations are passed back to 3DSSPP, the inverse kinematics algorithm predicts the posture and the resulting data are sent back to AutoCAD to reffect the new posture. At this point, the designer may decide to use direct manipulation from within 3DSSPP to modify the predicted posture or proceed to the analysis step.3.5. Analysis capabilitiesOnce the human form model is positioned within the drawing and a posture determined, the following items can be considered: visual requirements, reach, clearance, and biomechanical factors. Visual requirements can be determined by using AutoCADs dynamic view feature. By specifying the target location in the drawing to be viewed and positioning the viewpoint near the eye center, the view as seen by the worker can be approximated by AutoCAD. If relevant features are not visible to the worker, the viewpoint can be moved until they are visible. At this point, the posture can be or the entire moved to position the eye center at the desired viewpoint. Specific reach capabilities can be determined by positioning the worker within the drawing and specifying the desired hand locations. 3DSSPP uses the joint range of motion constraints with the link length data to determine if the hand locations can be reached and either updates the posture or displays a message that the posture is unattainable. Clearance checking using the 3DSSPP/AutoCAD interface is typically done by visual inspection within the AutoCAD environment by specifying different viewpoints for the drawing.Once visual, reach, and clearance requirements are satisfied, the biomechanical factors for the resulting posture can be calculated. These factors include the percentage of workers with the anthropometry that have the joint strength needed to overcome the force requirements of the task, the back compression and shear forces at the L5/S1 disc, worker balance, and slip risk. 3DSSPP calculates these factors for the major joints (see (1997), for a complete review of the biomechanical models included in 3DSSPP) and compares the results with the NIOSH guidelines for joint strength capabilities and back compression limits. For joint strength capabilities, the NIOSH Strength Design Limit (SDL) is exceeded when the percent of the population with sufficient strength at a given joint is below 99% for males or 75% for females. The NIOSH Strength Upper Limit (SUL) is exceeded when the percent is below 25% for males or 1% for females. For back compression, the NIOSH Back Compression Design Limit (BCDL) is exceeded when the back compression force is greater than 3400 Newtons (N) and the NIOSH Back Compression Upper Limit (BCUL) is exceeded when the back compression force is greater than 6400 N (NIOSH, 1981). These values are consistent with the criteria used to develop the 1981 and 1991 NIOSH lifting equations (Waters al.1993). Reports showing the results can be displayed on-screen (Fig. 2), printed for review, or written to for additional analysis in a spreadsheet or database program.An important note is that the 3DSSPP results are based on the assumption that the task movements being studied are either stationary or very slow; thus, results are calculated ignoring the effects of acceleration and momentum. This over estimates the strength capability of a worker who uses fast or jerk movements as the rapid acceleration and deceleration of the load being handled places additional forces on the joints and muscles. In addition, the strength capability of individuals decreases with the speed of movement (1997, 1992). At present, this simplifying assumption is necessary for reasons that include the lack of sufficient data pertaining to dynamic strength capabilities and the difficulties involved in modeling the potential range of movement speeds. For the assembly task being analyzed, this assumption was considered reasonable because the torque converter was heavy and difficult to grasp and hold,factors that discourage fast movements.4. Case study methodologyUsing the 3DSSPP/AutoCAD interface, the evaluation method described above was used to study the manual converter assembly task and the converter assembly task using the lifting aid. A 133 MHz microcomputer with Pentium processor was used with Windows 95, AutoCAD for Windows, Release 13 and 3DSSPP for Windows, version 3.06. The designer conducting the analysis was experienced in performing ergonomic job analyses and was familiar with the software used. The designer was provided with photographs and engineering drawings of the workstation and parts used in the assembly task, but was not given any information about the postures that workers utilized while performing the job and was not aware that a separate evaluation had been conducted independently. Six specific postures within each task were considered the retrieval posture at each of the four rack heights, the carrying posture, and the installation posture. Although the worker continually moves during the tasks, the assumption was made that tasks could be broken down into a sequence of static postures, each of which could be analyzed separately.An independent ergonomic evaluation of this assembly task was conducted in 1990 as part of a larger evaluation effort at Ford Motor Company. The analysts observed the workers performing the task manually and with an installed lifting aid, performed the tasks themselves, collected postural data and interviewed the workers. Based on the gathered information, several items including the required strength capabilities and low back compression forces resulting from the task * were analyzed. The report from the subsequent analysis (Resnick et al., 1990) included only results for a 95th percentile male and therefore, to allow comparison between these results and the predicted results from the proactive 3DSSPP/AutoCAD analysis, only the data for the 95th percentile male are shown in Figs. 3-6.Fig.3. Percentage of 95th percentile males with sufficient shoulder strength for four task elements as determined in the independent evaluation conducted in 1990 and the 3DSSPP/AutoCAD analysis.Fig.4. Percentage of 95th percentile males with sufficient torso strength for four task elements as determined in the independent evaluation conducted in 1990 and the 3DSSPP/AutoCAD analysis.Fig.5. Percentage of 95th percentile males with sufficient hip strength for four task elements as determined in the independent evaluation conducted in 1990 and the 3DSSPP/AutoCAD analysis. The difference between the two studies for the low rack (manual) task element is due to differences in posture selection: the analysts in the 1990 study used a symmetric foot placement whereas the 3DSSPP/AutoCAD analyst used an asymmetric foot placement.Fig.6. 95th percentile male disc compression forces at the L5/S1 joint for four task elements as determined in the independent evaluation conducted in 1990 and the 3DSSPP/AutoCAD analysis. Error bars represent 1 standard deviation from the population mean.5. Results5.1. Manual taskThe designer did not identify any obvious problems with the visual, reach, or clearance requirements for any of the postures. In general, the analysis indicated that the task creates considerable biomechanical stresses exceeding NIOSH guidelines and should be redesigned (manual tasks shown in Figs. 3-6).5.2. Proposed lift aidThe designer did not identify any reach difficulties for any of the postures. However, the designer reported that both the male and female would have difficulty from a visual standpoint at all four rack heights in the retrieval phase since the lift aid blocks the view of the workers when attempting to align the vacuum cup with the converter assemblies. More problematic is the view during the installation phase where the workers must center the converter in front of the transmission assembly. The lifting aid places the workers approximately four feet from the housing and blocks much of the view when attempting to line up the two parts for assembly. In order to view the part alignment clearly, the workers must shift center at least 6 in to either side while still pushing straight ahead. Clearance difficulties between the worker and conveyor were also observed for the 95th percentile male when retrieving parts from the lowest rack height. The least stressful posture required by the worker to avoid contact with the conveyor still generated biomechanical stresses exceeding NIOSH guidelines (lift-aided tasks shown in Figs. 36). Overall, based on the visual, clearance, and biomechanical issues identified, the designer recommended that this device not be used to replace the existing manual task.5.3. 1990 study of workplaceFor the postures observed in the manual assembly task, no problems were indicated with the carrying phase. However, the report (Resnick et al., 1990) indicated several other biomechanical problems (Figs. 36). The retrieval from the highest rack created moments about the shoulder joint that exceeded the NIOSH guidelines and retrieval from the lowest rack created moments about the hip and torso as well as back compression forces that exceeded NIOSH action limits. The installation phase created moments about the hip, torso, and shoulder exceeding NIOSH guidelines. The analysts for this report concluded that the task required a redesign to alleviate these biomechanical risks.For the postures observed using the material-handling device during the user trial, the retrieval phase at the lowest rack height created moments about the hip and back compression forces which exceeded NIOSH action limits (Figs. 5 and 6). In addition, the report described clearance problems the worker had while using the device at the lower rack heights. Also indicated was that the worker had difficulty determining if the converter was correctly installed and was observed walking around the device after the installation phase to ensure that the converter was properly assembled. Based on these findings, the analysts concluded that the lift aid was inappropriate for the given workplace.6. DiscussionAlthough the above case study demonstrates how the 3DSSPP/AutoCAD interface is used in a design setting, the question remains as to the validity of the analysis: are the results obtained using the 3DSSPP/AutoCAD interface similar to those obtained in the 1990 study. In general terms, the 3DSSPP/AutoCAD analysis and the independent 1990 evaluation yielded similar conclusions. First, manually lifting and installing the converters into the transmission housing led to biomechanical stresses that exceeded NIOSH guidelines. Second, although the use of the material-handling device reduced the bio- mechanical stresses on workers, NIOSH guidelines were still exceeded regarding torso and hip joint strength as well as back compression force for the male. Third, the visual requirements of the workers were hindered by the use of the material-handling device. And fourth, larger workers using the lift aid would have difficulty retrieving parts from the lower racks without bumping into the conveyor. Both studies concluded that the manual task should be changed to eliminate the risk of injury to the worker, but that using the materials-handling device at the site would create other problems and would not be a good alternative.Although the proposed material handling device in the above case study was eliminated through analysis using the 3DSSPP/AutoCAD interface as well as in the user trial, analyses using the interface should not replace user trials. Rather, the program indicated only that this particular device in the existing work station would be a poor alternative to the manual task. In addition, since the human form model in the 3DSSPP is limited to a single body type, using the software for visual checks of t, reach, and clearance within a given work space can only be considered approximation as other body types may still encounter interference in the actual design. Thus, iteration through potential designs within the 3DSSPP/AutoCAD interface should continue until a feasible option is identified and selected, at which point a user trial should be conducted. The point is that systems such as the 3DSSPP/AutoCAD interface are not appropriate for use as the sole means of evaluating a workplace design. Instead, other ergonomics job analysis tools (e.g., NIOSH lifting guides, time and motion studies, human form) should be used in conjunction with these systems to evaluate potential designs and to validate the selection of a particular design during user trials. For example, in the independent 1990 evaluation, a user trial with the material-handling device allowed the analysts to utilize time studies and energy expenditure evaluations to further compare the efficacy of the lift-aided task with the manual assembly.Upon close comparison of the results between the independent evaluation of the task and the 3DSSPP/AutoCAD analysis, one might argue that under different circumstances, the conclusions reached could have easily been different, particularly if another posture had been used in the 3DSSPP/AutoCAD interface (Fig. 5). Not only does this choice exclude 10% of the selected population, but it also makes the statistically unlikely assumption that a person exists whose body dimensions are all the same percentile. In this case study, those values were selected to maintain consistency with the evaluation conducted in 1990, not to imply a recommended range of percentiles for which designers should account in their work. Although designers are encouraged to develop products or workstations that all people can use easily, there may be significant involved. In general, as the range of population accommodated by a design increases, so does the cost to implement the features and adjust ability necessary to make the accommodations feasible. On the other hand, there may be legal and marketing issues as well as other costs to consider when excluding a segment of the population. In the end, the preferred selection of percentile ranges may differ between designs, based on an analysis unique to each design situation.As for the assumption of the statistically impossible human, this is a result of the programs use of the Drilli and Contini proportionality constants to estimate link length(Beck,1992). Although there is a weak correlation between height and many other anthropometric dimensions, the assumption simplifies the designers data entry requirements with little impact on the strength predictions. This is supported by validation studies indicating that the 3DSSPP static strength predictions have correlations of greater than 0.85 with actual strength data (1992). However, the software should be used only as an initial approximation for assessments of reach clearance, and as the weak correlations and limited features of the human form graphics will have a significantly greater impact on them.Second, the research that underlies the 3DSSPP/AutoCAD interface is based on healthy individuals of working age (1765 yr old). Although the assumption is that this interface would onl
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