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附录一：过程在机械设计图纸的重要性计算机与图形,2 号、263 - 274 年,1990 培格曼出版公司。戴维G厄尔曼斯蒂芬伍德，戴维克雷格俄勒冈州立大学机械工程系,科瓦利斯,俄勒冈州 97331 年摘要本文研究图的重要性(起草正式和非正式的草图)在机械设计过程中。五个假设,关注类型的图纸,他们的必要解决机械问题,和他们的关系外部表现媒介,提出和支持。支持是通过引用的研究在其他领域和协议进行研究的结果五个机械设计师。录像带的标记由设计师代表部分详细研究了设计过程的类型和目的。结果数据支持的假设。这些结果也给要求未来的计算机辅助设计工具和图形教育,和目标为进一步研究。一、引言本文的目的是研究图纸(包括正式起草和的重要性非正式的草图)在机械设计的过程。这目标可以扩展国家,我们打算显示绘图在所有的发展的必要性机械设计的阶段。通过本文提供的信息,要求未来的计算机辅助设计工具,图形教育, 进一步研究将会发达。所有的机械工程师都教起草。因此,大多数工程师擅长这些正式的机械图纸制作和解读。这些图纸表示最后一个设计(设计过程的最终产品)和为了归档完成设计和其他设计师和交流生产人员。此外,工程师无法而臭名昭著认为没有“粗略”草图粗糙的想法。有时这些非正式的草图给一位同事沟通的一个概念,但更多通常他们只是帮助的想法成形在纸上。这是在考虑到这些草图帮助一个想法的形式给出了一个暗示图在工程中的作用不仅仅是档案概念或与他人沟通。理解起草和设计草图的使用是很重要的帮助制定未来发展的计算机辅助设计或绘图(CAD)系统。随着 CAD 发展和变得更“聪明”的问题这些系统属性必须变得更加重要。在过去的 CAD 系统主要属性已经被赶出计算机产业的发展。它只有通过理解图纸的重要性在设计过程中,这些系统可以根据设计的需要。此外,CAD 工具的压力开发、教师时间要求和课程费用导致学术机构重新评估他们的“图形”课程的内容。理解图纸的在设计过程中帮助建立什么技能重要性需要教工程师在他们的训练。本文是由第一、二节,澄清图纸中使用的类型机械设计。假设给出了本文需要解决的部分。讨论研究对视觉图像被用作的理解依据参数支持的假设部分 IV,V 是一个节讨论的结果数据的机械工程师如何使用图纸在设计。最后,在第六节,是一个讨论的假设支持我们的发现 CAD 发展的影响, 教育需求和未来的研究方向。二、设计图的类型工程师让许多类型的标志。在研究中所描述的第五部分,我们打破了这些分数分成两个主要团体:支持符号和图形表示。支持符号包括文本笔记、列表维度(包括领导人和箭头)和计算。图形表示对象及其功能,包括图纸和情节和图表。机械设计往往规模图纸用图形表示机械仪器或 CAD 计算机系统。这些图纸,制造的根据被广泛接受的规则集,被定义为起草。草图,另一方面,被定义为“自由的手” 图纸。他们通常不规模和可以使用速记符号来表示对象和它们的功能。必须作出分化之间的行为和图形表示中它发生。中,无论是纸和铅笔,一台电脑笔在平板电脑上,粉笔在黑板上或其他介质可能把接口限制表示。下面讨论关心的是什么被代表,而不是如何表示。然而,表示讨论指出媒介的限制和需要改进的接口。图纸需要考虑的另一个方面是抽象的水平要代表的信息。在设计过程中,设计精致最后一个抽象的概念,详细,起草设计。这在一个清晰可见来自我们的一个示例研究中描述的部分诉在这项研究中设计师是开发一个大会举行三个电池一个时钟/日历电脑。图 1 是一个编译所有草图和图纸的一个主题在开发电池接触的设计。在每个数图形图像的百分比在设计时表示。的组件是一个草图,其中包含精炼出来的主要功能信息提炼,最终形式的比例图。第一个素描图 1 中显示了两个联系人(表示为圆圈)和之间的联系他们的电流(表示为一条线)。这里的象征是清楚功能。图 1 所示。电池接触的进化总协议时间 8 小时,34 岁分钟的演变。即使一个好的工程师图示法的非正式的百分比素描,起草是大多数工程的重点培训和 CAD 的力量系统。另一方面,大多数工程师在草图没有接受正式的培训。它通常认为是一些自然的能力。三种典型文本用于教学综述了本科“机械”图(1、 2、3)。这些介绍只有几页的草图信息。此外,CAD 系统在任何有意义的方式支持草图。出于本文的目的,CAD 的定义是交互式的使用计算机图形学中,帮助解决机械设计问题。目前的 CAD 工具援助机械设计过程在四个方面:作为一种先进的绘图工具,通过协助硬件和数据的可视化,通过改善数据组织和沟通,通过作为前置和后处理器以计算机为基础的分析技术,如有限元分析,重量和质量属性、运动分析等。所有这些用途,“设计”必须精炼,它的比例图。因此,当前系统的“D”CAD 制图方法。三、图纸问题解决的关系最初的减少导致录像数据的设计工程师出版六使用绘图(4、5)的行为:1。存档的几何形式的设计。2。之间的设计师和设计师之间的交流思想和生产人员。3。作为一种分析工具。通常,失踪的计算尺寸和公差图上是发展。4。模拟设计。5。作为完整性检查程序。草图或其他图纸,剩下的细节设计成为设计师明显。实际上,这有帮助建立一个设计任务未完成的议程。6。作为设计师的短期记忆的延伸。设计师通常无意识地使草图,他们可能帮助他们记住的想法忘记。这是意识到这些观察都重叠和不完整的。在基于数据和阅读在认知心理学文献,我们觉得最后一项是潜在的丰富的多。因此这些观察培养了五个假设。下面每一个假设是紧随其后文献的支持。机械设计数据支持这些假设在第五部分。假设 1。绘画是首选的外部数据表示方法通过机械工程设计师。设计师表示数据内部,在他们心目中,和外部在纸上电脑屏幕或其他媒体。这是相当明显的，设计师喜欢画画这些媒介,更喜欢一幅画的书面描述一个对象。这重要的是理解为什么图表示优先于其他形式如文本或命题。为什么一个图是(有时)价值一万字,拉金和西蒙,作者探索利用图解决问题。在这里“图”是一个起草,物理问题示意图表示的对象。摘要句子(文本索引的位置列表-一个句子)和图解(图形)表示,它们对问题解决的影响比较。在比较这些作者得出结论:1。图可以组织一起使用的所有信息,从而避免大大量的搜索需要的元素。文本索引中的下一个元素句子列表(相邻的信息),而图有很多相邻元素。2。图明确保留几何和拓扑信息,而文本只是连续在自然杂志上。这个特性的图允许简单的索引信息来支持计算流程。然而,文本保存时间或逻辑顺序的信息。这是迷失在图。3。图使用位置对单个元素组信息,避免了需要匹配符号标签。大量的图自动支持知觉推理;可以被索引的信息在各种礼仪。它似乎是合理的,这些结论,对图解表示,可以扩展到所有的图形化表示。基于拉金和西蒙的结论很容易理解为什么在机械设计的复杂性,图纸要优于文本。假设 2。素描是一个重要的图形表示形式需要不支持的起草。在本文的后面我们将会分析所有标志由一小群工程设计师。他们的画是将分为自由的手(草图)或起草标志。有一个上面的假设中,素描角色更加正式起草不能填补。丹赫伯特在研究图纸创造l 设计:应用 CAD 系统7认为使用草图(研究图纸)建筑设计问题的解决方案。他定义了“研究图纸”为“非正式私人图纸, 建筑设计师作为媒介图形思维的探索阶段。“架构师经常使这些研究图纸的边界或相邻的正式图纸。在他的纸赫伯特猜测的性质影响设计的草图的过程。这些属性构成他的理论的基础的使用草图设计。在赫伯特的理论中,素描,因为他们提供了一个扩展内存使用视觉图像的设计师。因为草图可以更多快于正式的图纸,他们允许更灵巧的操作理念。此外草图允许信息等各种形式表示不同的观点或抽象级别。因此他把草图图形隐喻实际对象和正式起草对象正在开发。事实上赫伯特称,素描是一个主要外部媒介思维。赫伯特的想法导致第三假说。假设 3。绘画是一个必要的扩展中使用的视觉表象机械设计。这是一个设计师的必要扩展认知能力除了最简单的数据表示,约束传播,心理模拟。这个假说认为,没有媒体外部数据表示设计师没有设计的实质性问题。坊间支持这假设是明显要求设计师设计和观察他/她的东西拿一支铅笔或粉笔。在本文的下一节,我们将讨论的模型信息处理在人类解决问题,提出了一些科学的支持这些轶事观察和假设。在这个模型中,图纸是一个扩展人类的能力有限可视化对象在他们的脑海中。认知能力的局限性导致了假说。假设 4。图纸要求转换从设计师的内存扩展内存中。转型的本质是依赖媒介的特点。人类代表信息的方式在他们的记忆仍然是一个问题的讨论和研究。无论这种内部表示的形式,它是可能不同于表示外部在纸上,在 CAD 系统,或通过其他媒体。这两个媒体之间的转换通信和实现之一。信件是内部和外部的词汇之间的转换。如果设计师可视化三维物体在他/她的思想和希望代表对象外部, 它可以转换成一个等距、正字法或其他二维表示和吗画在纸上或在一个二维 CAD 工具,也可以转换为布尔原语和代表一个坚实的建模工具。此外,根据所选择的媒介,有额外的必要性将图像转换成满足需求的实现。的认知过程用铅笔来画一条线,用于指定不同点的 CAD 表示。拉金和西蒙的研究和赫伯特关注通信。没有文学作者关于实现的认知负荷的影响设计师。尽管人类记忆的确切形式仍然是未知的,这是一般讨论了心理学家的认知单位或者大块的数据，的性质。这些认知单元,这将在下一节中,讨论导致第五和最后的假设。假设 5。图纸利用和认知(设计单位确定功能)用于制定精神形象。因此,设计师的认知绘画的特色信息组织是相互依存的。这一假设是双刃。很明显的内容和结构图纸是依赖于精神形象和它是如何形成的(它的认知块)。它是有争议的心理图像是否受到了影响图纸。将稍后再解决这个问题。四、机械设计的认知模型在早前描述的设计师信息处理器8,我们提出图 2 的环境设计。这个数字是基于该模型开发的纽威尔和西蒙9,称为信息处理系统(IPS)。图可以视为一个“地图”位置信息可能存储设计。它分为一个内部工作空间(在设计师的头脑)和外部工作区(外部设计师的头脑)。在设计师,有两个位置对应于两种不同的记忆:短期记忆(STM)长期记忆(LTM)。还有一个“处理器”,负责应用运营商和控制设计过程。在厄尔曼，梅特涅和斯托福,十个运营商也未发现描述解决问题的机械设计。外部的设计师有很多“设计状态存储位置”包括图形表示媒体如纸片和 CAD 工具,以及其他来源,如文本笔记,手册和同事。因此,设计或设计的一些特性只能在三个代表地点:短期记忆 STM,长期记忆LTM,所谓外部内存。每一个“位置”影响特定的属性,它可以用于设计。以支持假设画的重要性在机械设计过程中,这一点模型需要详细讨论。讨论图的作用在机械设计过程中,的特点 STM,安装,以及它们之间的信息流动和外部环境会发展起来的。这个细节基于纽威尔和西蒙的模型的扩展它视觉表象的柯斯林(10、11、12)和努力将安德森13。它必须意识到此处给出的模型的内容并不完全赞同在认知心理学社区,但他们肯定是足够安全的为讨论提供一个基础的角色在机械设计图纸。4.1 短期记忆短期记忆是非常快速和强大。STM 的内容包括我们知道的信息,我们的意识。所有设计操作(如视觉感知和绘画创作)带进了信息短期记忆。不幸的是,STM 能力有限。研究显示认知仅限于大约七个单位或者“块”的信息9尽管能力有限,STM 是一个快速的处理器与处理时间订的 100 毫秒17。柯斯林认为,短期记忆的一个功能是作为一个视觉缓冲12。在这种能力被认为是天生的,特殊目的,短期缓冲进化的需要处理信息的眼睛。因此,这个缓冲区视为一个坐标空间有限的空间范围,更清晰的中心,图像褪色没有再生的努力。视觉缓冲区支持在感知图像来自眼睛,从眼睛和长词记忆在创意和操纵。4.2 长期记忆长期记忆,另一方面,本质上是无限的容量,但是访问缓慢(从2 到10 秒/块)。进入长期记忆也不是直接。相反,记忆必须由一些线索或基于检索策略短时记忆的信息。在设计、零部件设计的存储状态在长期记忆。这些都是相对容易的线索, 因为在任何时候,目前设计状态的重要部分在短期记忆和可以作为指针长期记忆的知识。的视觉图像,根据柯斯林有两种不同类型的信息存储在长期记忆:事实对象(包括大小对象,它们是如何放在一起,高级的类的名字,它们的功能,等)和编码的文字对象的外观(坐标位置的列表点应放置在视觉缓冲)。谢泼德14认为, 有可能不是是一个具体的或“一级”之间的同构和外部对象相应的表示。他提出了一个“二级”同构的功能之间的关系进行建模和存储对象。很明显,图像包含的信息比文字出现,命题内存必须包括视觉形象的一部分。4.3 认知单元认知的内容单元加工安装和 STM 并不准确明确的。安德森13,在他的努力建立一个计算机模拟的人类信息处理,利用三种类型的数据表示为这些单位:空间图像,文本数据和主张。它将表明,空间表示记忆尤为重要考虑形式面向机械工程设计领域。几乎没有证据的文学的设计师编码信息机械对象的内存。有很多猜想这不过是块的数据,通常被称为工程设计的设计特性,是人类的基本构建块组织设计。因此如果一个设计是最代表的方式从人类设计师容易沟通/,然后应的信息编码的特性,熟悉他。当前 CAD 系统使用功能是由几何基元,如线,弧线,固体和图标。这些都是设计师被教导要使用特性,但目前还不清楚这些的方式信息是最好的组织最容易记忆和索引。这就产生下面的问题。这些特性来自哪里?是设计师有一种天然的特性在头上或模式了吗他们的教育吗?唯一的窗户,存在研究对象的分块设计师的脑袋这些特性通过他/她的代表书面文本、图纸或手势。功能被人类用来代表几何和拓扑通常不是轻松地表示文本或口头,但可以以图形方式表示很容易。例如,新手棋手当被要求召回象棋人的位置董事会在人与人基础上。然而,专家召回模式的男性,比新手更大、更复杂的功能15。这些块没有受过正式的“名字”,可以表示为一个简单的口头或书面的术语,但他们可以图形表示的位置很容易。类似的实验在建筑领域16导致块,虽然很容易图形化表示,只能笨拙地表示文本,的例子,“一连串的外墙”或“两墙段与窗户形成广场的一个外部角落空间”。唯一的这种性质的实验进行机械工程师由沃尔德伦和沃尔德 18。在这个实验中新手(本科学生)、中级(研究生)和专家(练习工程师)显示一个短时间内的装配图。图纸被淹没了受试者要求复制。通过观察视频录音的协议对象执行这个任务很明显,新手想起线段,中间记得对象,如齿轮和专家记忆功能组件包含大量的物理对象。4.4 如何 IPS 模式支持这一假设上面的描述是重要的理解图形的使用表示在机械设计提供洞察的正确性需要第三章提出假设。首先必须指出上执行的所有任务设计要求召回长期记忆的信息或操纵短期 记忆。因为 STM 的信息块的数量可以是有限的和工作机械设计迅速变得复杂,短期记忆形成人类设计师的关键瓶颈。此外,STM 转换信息如此迅速和长期记忆如 此缓慢,只有外部表示通过将图像转换为图形或文本表示可以作为添加内存。由 于文本信息有限界形式,图形表示是唯一合理的内存扩展器机械设计师。这支持 第一个假说。第二个假设,由起草,素描的目的不支持与的速度表示。一个目的一 个图形图像在外部环境中,这样它就可以查看、STM 的编码,以一种新的方式和解析。换句话说,快速的外部图像生成允许设计师“看见”不同于生成方式的信息。 因此,方法生成的外部形象必须快速和灵活的或者它将会放缓认知过程。自从STM 是如此有限的能力和机械设计非常复杂,图纸需要设计视觉表象的扩展能力。因此 IPS 模型支持假说三人。考虑两种假设都两个和三个,画两个延伸 STM 的容 量,给重新解析的能力继续处理的信息。提出假说指出,图示是视觉的一个隐喻图 像和它需要转换依赖于媒介。这将是理想的如果媒介形象表示需求完全匹配的图 像表示在短期记忆。从某种意义上说这场比赛总是发生在,在某种程度上,制定使 用的介质中存储的图像块长期记忆,之后形成一个基础生成和检查图像短期记忆。第五个假说认为,图形表示利用和决定设计功能。我们历来都局限于二维媒体(如。铅笔和纸),这些都在一定程度上,形成我们的交涉。它不是清楚我们编码和存储 三维对象。有一个说法记忆是对象为中心的,作为固体对象可以被操纵模型。这 是内存查看器为中心的反驳的论点和埃弗拉特定的视图存储在安装可用于生成 或检验12。因此,认知研究的当前状态是未精制足以支持这个假设。附录二：The Importance of Drawing in the Mechanical DesignProcessComputer & Graphics Vol.14, No. 2, pp. 263-274, 1990 Pergamon Press plc.David G. Ullman, Stephen Wood, David CraigDepartment of Mechanical Engineering, Oregon State University, Corvallis, Oregon 97331ABSTRACTThis paper is a study on the importance of drawing (both formal drafting and informal sketching) during the process of mechanical design. Five hypotheses, focused on the types of drawings, their necessity in mechanical problem solving, and their relation to the external representatio n medium, are presented and supported. Support is through referenced studies in other domains and the results of protocol studies performed on five mechanical designers. Videotapes of all the marks-on-paper made by designers in representative sections of the design process were studied in detail for their type and purpose. The resulting data is supportive of the hypotheses. These results also give requirements for future computer aided design tools and graphics education, and goals for further studies.INTRODUCTIONThe goal of this paper is to study the importance of drawing (both formal drafting and informal sketching) in the process of mechanical design. This goal can be extended to state that we intend to show the necessity of drawing during all the developmental stages of a mechanical design. Through the information presented here, the requirements for future computer aided design tools, graphics education, and further studies will be developed.All mechanical engineers are taught drafting. Thus, most engineers are skilled at making and interpreting these formal mechanical drawings. These drawings are representations of a final design (the end product of the design process) and they are intended to archive the completed design and communicate it to other designers and manufacturing personnel. Additionally, engineers are notorious for not being able to think without making back-of-the-envelope sketches of rough ideas. Sometimes these informal sketches serve to communicate a concept to a colleague, but more often they just help the idea take shape on paper. It is in considering how these sketches help an idea take form that gives a hint that drawings role in engineering is more than just to archive a concept or to communicate with others.Understanding the use of both drafting and sketching in design is important to help formulate the future development of Computer Aided Design or Drafting (CAD) systems. As CAD evolves and becomes more intelligent, the question of what attributes these systems must have becomes more important. In the past CAD systemattributes have primarily been driven from developments in the computer industry. It is only through understanding drawings importance in the design process that these systems can be based on design needs.(1)Additionally, the pressures of CAD tool development, faculty time demands, and course expenses cause academic institutions to reevaluate the content of their graphics courses. Understanding drawings importance in the design process helps establish what skills need to be taught to engineers during their training.This paper is organized by first, in Section II, clarifying the types of drawings used in mechanical design. The hypotheses to be addressed in this paper are given in Section III. A discussion of research on the understanding of visual imagery to be used as a basis for arguments in support of the hypotheses is in Section IV. In Section V is a discussion of the results of data taken on how mechanical engineers use drawings during design. Lastly, in Section VI, is a discussion of how well the hypotheses have been supported and the implications of our findings on CAD development, educational requirements and future research directions.II. TYPES OF DRAWINGS USED IN DESIGNEngineers make many types of marks-on-paper. In research, to be described in Section V, we have broken down these marks into two main groupings: support notation and graphic representations. Support notation includes textual notes, lists, dimensions (including leaders and arrows) and calculations. Graphic representations include drawings of objects and their functions, and plots and charts.Mechanical design graphic representations are often scale drawings made with mechanical instruments or CAD computer systems. These drawings, made in accordance with a set of widely accepted rules, are defined as having been drafted. Sketches, on the other hand, are defined as free hand drawings. They are usually not to scale and may use shorthand notations to represent both objects and their function. A differentiation must be made between the act of graphic representation and the medium on which it occurs. The medium, whether it be paper and pencil, a computer stylus on a tablet, chalk on a blackboard or other medium may put interface restrictions on the representation. The following discussions are concerned with what is being represented, not with how the representation is made. However, the discussions point to the mediums restriction on representation and the need for improved interfaces.Another aspect of drawings to be considered is the level of abstraction of the information to be represented. During the design process, the design is refined from an abstract concept to a final, detailed, drafted design. This can be clearly seen in an example taken from one of our studies described in Section V. In this study the designer was developing an assembly to hold three batteries for a clock/calendar in a computer. Figure 1 is a compilation of all the sketches and drawings one subject made during the development of a battery contact in this design. The number under each graphic image is the percentage of the way through the design when the representation was made. The component is refined from a sketch that contains primarily functional information to a refined, scale drawing of the final form. The firstsketch in Fig. 1 shows two contacts (represented as circles) and a connection between them for current flow (represented as a line). The symbology here is clearly functional.Figure 1. The evolution of a battery contact - total protocol time of 8 hours and 34 minutes.Even though a good percentage of an engineers graphic representation is informal sketching, drafting is the focus of most engineering training and the strength of CAD systems. On the other hand, most engineers receive no formal training in sketching. I t is often assumed to be some natural ability. Three typical texts used in teaching undergraduate mechanical drawing were reviewed 1, 2, 3. Each of these presented only a few pages of information on sketching. Additionally, CAD systems do not support sketching in any meaningful way.For the purposes of this paper, the term CAD is defined as the use of interactive computer graphics to help solve a mechanical design problem. Current CAD tools aid the mechanical design process in four ways: as an advanced drafting tool; through assisting in the visualization of hardware and data; by improving data organization and communication; and through being used as a pre- and post-processor for computer based analytical techniques such as finite element analysis, weight and mass properties, kinematic analysis, etc. For all these uses, the design must be refined to the point that a scale drawing of it can be made. Thus, for current systems, the D inCAD means drafting.III. THE RELATION OF DRAWING TO PROBLEM SOLVINGThe initial reduction of videotaped data taken of design engineers led to the publication of six uses of the act of drawing 4, 5:1. To archive the geometric form of the design.2. To communicate ideas between designers and between the designers and manufacturing personnel.3. To act as an analysis tool. Often, missing dimensions and tolerances are calculated on the drawing as it is developed.4. To simulate the design.5. To serve as a completeness checker. As sketches or other drawings are being made, the details left to be designed become apparent to the designer. This, in effect, helps establish an agenda of design tasks left to accomplish.6. To act as an extension of the designers short term memory. Designers often unconsciously make sketches to help them remember ideas that they might otherwise forget.It was realized that these observations were both overlapping and incomplete. In particular, based on the data and readings in the cognitive psychology literature, we felt that the last item was potentially much richer than stated. Thus these observations have fostered five hypotheses. Each hypothesis is presented below followed by support from the literature. The mechanical design data in support of these hypotheses is in Section V.Hypothesis 1. Drawing is the preferred method of external data representation by mechanical engineering designers.Designers represent data both internally, in their minds, and externally on paper, a computer screen or other media. It is fairly obvious that designers like to draw in these mediums and prefer a picture to a written description of an object. It is important to understand why drawing representations are preferred over other forms such as text or propositions (if-then rules).In Why a Diagram is (Sometimes) Worth Ten Thousand Words , by Larkin and Simon 6, the authors explore the use of diagrams in problem solving. Here a diagramisadrafted,schematicdrawingrepresentingtheobjectsina physicsproblem. In this paper sentential (textual, indexed by position in a list - a sentence) and diagrammatic (graphical) representations and their effect on problem solvingarecompared.Incomparingthesetheauthorsconcludethat:1. Diagrams can group all information that is used together thus avoiding large amounts of search for needed elements. Text only indexes to the next element in the sentence list (the adjacent piece of information) while diagrams have many adjacent elements.2. Diagrams explicitly preserve information about geometry and topology, whereas text is only serial in nature. This feature of diagrams allows for easy indexing of information to support computation processes. However, text preserves the temporal or logical sequence of information. This is lost in diagrams.3. Diagrams use location to group information about a single element, avoiding theneed to match symbolic labels. Diagrams automatically support a large number of perceptual inferences; the information can be indexed in a variety of manners.It seems reasonable that these conclusions, made about diagrammatic representations, can be extended to all graphical representations. Based on Larkin and Simons conclusions it is easy to see why, in the complexity of mechanical design, drawings are preferred over text.Hypothesis 2. Sketching is an important form of graphical representation serving needs not supported by drafting.Later in this paper we will analyze all the marks-on-paper made by a small group of engineering designers. Their drawing marks will be classified as either free hand (sketching) or drafting marks. The hypothesis above states that the sketches have a role that more formal drafting cannot fill. Dan Herbert in Study Drawings inArchitectural Design: Applications for CAD Systems 7 considers the use of sketches (study drawings) in the solution of architectural design problems. He defines study drawings as informal, private drawings that architectural designers use as a medium for graphic thinking in the exploratory stages of their work. Architects often make these study drawings in the borders of or adjacent to their formal drawings. In his paper Herbert conjectures about the properties of sketches that affect the design process. These properties form the basis for his theory of the use of sketches indesign.In Herberts theory, sketches are used because they provide an extended memory for the visual images in the mind of the designer. Since sketches can be made more rapidly than formal drawings, they allow for more facile manipulation of ideas.Furthermore sketches allow the information to be represented in various forms such as differing views or levels of abstraction. Thus he calls sketches graphic metaphors for both the real object and the formally drafted object under development. In fact Herbert claims that sketches are a principal medium of external thinking. Herberts thoughts lead to the third hypothesis.Hypothesis 3. Drawing is a necessary extension of visual imagery used in mechanical design. It is a necessary extension of a designer cognitive capability for all but the most trivial data representation, constraint propagation, and mental simulation.This hypothesis states that without data representation on media external to the designer there can be no design of substantive problems. Anecdotal support for this hypothesis is evident in asking a designer to design something and observing him/her reach for a pencil or chalk. In the next section of this paper we will discuss a model of information processing in human problem solving that gives some scientific support to these anecdotal observations and to the hypothesis. In this model, drawings are an extension of the humans limited ability to visualize objects in their mind.The limitation of cognitive ability leads to the forth hypothesis.Hypothesis 4. Drawings require transformation from the designers memory to the extended memory medium. The nature of the transformation is dependent on the characteristics of the medium.The manner in which humans represent information in their memory is still asubject of much debate and research. Whatever the form of this internal representa tion, it is potentially different from the representation made externally on paper, in a CAD system, or through some other media. The transformation between these two media is oneofbothcorrespondenceandimplementation.Correspondenceisthe transformation between the internal and the external vocabularies. If the designer hasa visualized 3-D object in his/her mind and wants to represent the object externally, it can be transformed into an isometric, orthographic, or other 2-D representation and drawn on paper or with a 2-D CAD tool, or it can be transformed to boolean primitives and represented on a solid modeling tool.Further, depending on the medium chosen, there is the additional necessity to transform the image to meet the requirements of the implementation. The cognitive process for drawing a line with a pencil is different from that for specifying the end points for a CAD representation of the line. Both the research of Larkin and Simon and of Herbert focus on correspondence. There is no literature known to the authors concerning the effect of implementation on the cognitive load of the designer.Even though the exact form of human memory is still unknown, it is generally discussed by psychologists in terms of cognitive units or chunks of data.The nature of these cognitive units, which will be discussed in the next section, leads to the fifth and final hypothesis.Hypothesis 5. Drawings both utilize and determine the cognitive units (design features) used in mental image formulation. Thus, designers cognitiveinformation organization is interdependent with drawings characteristics. This hypothesis is double edged. It seems obvious that the content and structure of drawings is dependent on the mental image and how it is formed (its cognitive chunks). It is debatable whether or not the mental images are influenced by the drawings. This issue will be addressed again later.IV. A COGNITIVE MODEL OF MECHANICAL DESIGNIn an earlier description of designers as information processors 8, we presented Figure 2 as the environment in which the design takes place.This figure is based on the model developed by Newell and Simon 9 and called the Information Processing System (IPS). The figure can be viewed as a map of thelocations in which information about the design may be stored. It is divided into an internalworkspace(insidethemindofthedesigner)andanexternal workspace(outside the mind of the designer). Within the designer, there are two locations corresponding to the two different kinds of memory: short-term memory (STM) and long-term memory (LTM). There is also a processor that is responsible for applying operators and controlling the design process. In Ullman, Dietterich and Stauffer 8, ten operators were identified that characterize the problem solving in mechanical design. External to the designer there are many design state storage locations including graphical representation media such as pieces of paper and CAD tools, as well as other sources such as textual notes, handbooks and colleagues.Thus, the design or some feature of the design can only be represented in three locations: STM, LTM, and the so-called, external memory. Each location has certain properties that affect how it can be used in design. In order to support the hypotheses about the importance of drawing in the mechanical design process, this model needs to be discussed in more detail.To discuss drawings role in the mechanical design process, the characteristics of the STM, the LTM, and the information flow between them and the external environment will be developed. This detail is based on Newell and Simons model, the extensions of it to visual imagery by Kosslyn 10, 11, 12 and the effort to codify it by Anderson 13. It must be realized that the contents of the model given here are not fully agreed to in the cognitive psychology community, but they are certainly secure enough to provide a basis for discussing the role of drawing in mechanical design.4.1 Short Term MemoryShort-term memory is very fast and powerful. The contents of the STM comprises the information we are aware of, our conscious mind. All design operations (e.g. visual perception and drawing creation) are mad e on information that is brought into short-term memory. Unfortunately, STM has limited capacity. Studies have shown that it is limited to approximately seven cognitive units or chunks of information 9 Although limited in capacity, the STM is a fast processor with processing times on the order of 100 msec 17.In the view of Kosslyn, one function of the short term memory is as a visual buffer 12. In this capacity it is considered a hard-wired, special purpose, short term buffer that evolved from the need to process information from the eyes. Thus, this buffer is viewed as a coordinate space with limited spatial extent, more clarity toward the center, and the image fading without regeneration effort. The visual buffer supports images derived from the eyes during perception, and from both the eyes and the long term memory during idea generation and manipulation.4.2 Long Term MemoryThe long-term memory, on the other hand, has essentially infinite capacity, but access is slow (from 2 to 10 seconds per chunk). Access to long-term memory is also not direct. Instead, memories must be triggered by some cue or retrieval strategy based on information in short-term memory. During design, parts of the design state are stored in long-term memory. These are relatively easy to cue because, at any time, currently important parts of the design state are in short-term memory and can act as pointers for the knowledge in the long-term- memory.In terms of visual imagery, according to Kosslyn there are two different types of information stored in the long term memory: facts about objects (including size of objects, how they are put together, names of superordinate categories, their function, etc.) and encodings of the literal appearance of the object (list of coordinates where points should be placed in the visual buffer). Shepard 14 argues that there may not be a concrete or first order isomorphism between an external object and the corresponding representation. He proposes a second order isomorphism in which functional relations among objects are modeled and stored. It is clear that the information about images contains more than the literal appearance and that a propositional memory must be included as part of the visual image.4.3 Cognitive UnitsThe contents of the cognitive units processed in the LTM and STM are not exactly clear. Anderson 13, in his effort to build a computer simulation of human information processing, utilizes three types of data representations for these units: spatial images, textual data and propositions. It will be shown that the spatial representation viewofmemoryisespeciallyimportantin consideringthe form-oriented field of mechanical engineering design.There is virtually no evidence in the literature about the way in which designers encode information about mechanical objects in their memory. There has been much conjecture about this however as the chunks of data, more commonly referred to in engineering design as the design features, are the basic building blocks of human design organization. Thus if a design is to be represented in a manner that is most easily communicated to/from a human designer, then the information should be encoded in features that are familiar to him. Current CAD systems use features that are made of geometric primitives such as lines, arcs, solids and icons. These are the features designers are taught to use, but it is not clear that these are the way the information is best organized in their memory and most easily indexed. This gives rise to the following questions. Where do these features come from? Is it that designers have a natural set of features in their heads or is the patterning developed through their education?The only windows that exist to study the chunking of objects in a designers head is through his/her representation of these features as written text, words, drawings or gestures. Features used by humans to represent geometry and topology are often not easily represented textually or verbally, but can be graphically represented quite easily.For example, novice chess players when asked to recall the position of chess men on a board did so on a man-by- man basis. However, experts recalled patterns of men, larger, more complex features than the novice 15. These chunks had no formalnames that could be represented as a simple written or spoken term, but they could be graphically represented by the positions on the board quite easily. Similar experiments in the domain of architecture 16 resulted in chunks that, although easily represented graphically, could only be awkwardly represented textually as, for example, A string of exterior walls or Two wall segments with windows forming an exterior corner of a square space.The only experiment of this nature performed on mechanical engineers was performed by Waldron and Waldron 18. In this experiment novice (undergraduate students), intermediate (graduate students) and experts (practicing engineers) were shown an assembly drawing for a short period of time. The drawing was then covered and the subjects asked to reproduce it. By observing the video taped protocols of the subjects performing this task it was evi
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