RLG DigiNews August 15, 2003, Volume 7, Number 4

As a team of Cornell University librarians and faculty in mathematics and mechanical engineering, we are building a digital library for teaching the principles of kinematics—the geometry of pure motion. The Kinematic Models for Design Digital Library (K-MODDL)[1] project is funded by a two-year collection grant from the National Science Digital Library , a program of the National Science Foundation to build shared digital collections of high-quality materials and services in support of science education at all levels. The project is scheduled for completion in summer 2004. The core of K-MODDL is the Reuleaux Collection of Mechanisms and Machines, an important collection of nineteenth-century model machine elements held by Cornell’s Sibley School of Mechanical and Aerospace Engineering.

Kinematics is central to machine and mechanism design in engineering; it is part of the teaching of basic ideas of dynamics in physics, as well as geometric ideas and the ideas of motion in mathematics. The models in Cornell’s collection were designed for research and teaching by the German engineering professor Franz Reuleaux (1829-1905), the founder of modern kinematics and a forerunner of modern design theory of machines. Reuleaux set out to codify, analyze, and synthesize kinematic mechanisms. He laid the foundation for a systematic study of machines by defining clearly the machine and mechanism, determining the basic mechanical building blocks, and developing a system for classifying known mechanism types. Reuleaux created over eight hundred models of mechanisms to embody his basic machine elements and authorized the manufacture of over three hundred of these for technical schools to use in teaching engineers about machines.[2] Cornell’s collection was acquired in 1882.

A freely accessible, Web-based resource, K-MODDL documents a beautiful and historically significant artifact collection. In addition, the inclusion of navigable moving images and simulations of mathematical principles related to the machines’ movements restores the objects to their intended classroom use as teaching models of geometric and kinematic principles.

The mission of the NSDL is to enhance science, technology, engineering, and mathematics education through a partnership of digital libraries joined by common technical and organizational frameworks. Individually and collectively, these partners engage and inform multiple clienteles, using shared resources to serve many communities of users, each with its own level of knowledge and approach to learning. The NSDL embodies long-standing library traditions of service, longevity, equal access, fair use, and privacy, as well as innovations that foster a spirit of inquiry and the accessibility of science to all.[3]

K-MODDL will exist as an autonomous collection housed at Cornell University Library and will also be searchable through the shared NSDL portal. For a collection such as K-MODDL to participate in the NSDL, it is necessary that the descriptive metadata associated with each item in the collection be shared with the NSDL central metadata repository. The Open Archives Initiative (OAI) Protocol for Metadata Harvesting facilitates this exchange by defining a mechanism for harvesting XML-formatted metadata from repositories.[4] OAI compatibility is thus an essential requirement of the K-MODDL project.

In his article "Developing a 3D Digital Library for Spatial Data," Jeremy Rowe describes topological modeling techniques that permit precise analysis of an artifact’s surface and volume based on its digital representation[5]. The K-MODDL project has taken a different approach to representing three-dimensionality in a two-dimensional medium. For this project the principle spatial quality that must be represented is three-dimensional kinematic motion. We concluded that interactive photographic animations coupled with abstract simulations of the mechanisms suffice to illustrate this factor in most cases.

The K-MODDL team is producing navigable movies that show the kinematic performances of the model machines. A navigable movie is a collection of still images that appear in a sequence determined by the motion of a user interface device, such as a mouse. This allows the display of images in a user-controlled way. For example, if the images depict an object viewed from various viewpoints revolving around the object, then moving the cursor will create the illusion of spinning the object, making the experience three-dimensional. The navigable movies in K-MODDL either depict a machine from various viewpoints, so it appears to spin about its center when the movie is navigated, or they portray various stages in its kinematic motion, so that the machine appears to function when the movie is navigated. This allows the user to go back and forth and examine the kinematic causality in detail.

A sequence of snapshots illustrating the motion of a spiral pump as the user slides the mouse

Still images and movies demonstrate the functionality of the machine but often obscure the pure kinematic motion associated with it. We have therefore developed a number of kinematic simulators to illustrate the geometric motion first hand. Moreover, a simulator allows users to interact with the machine, pushing and pulling in unscripted ways, modifying it and observing the consequences, and even breaking it.

The simulator is written as an applet so that it executes on the user’s computer and is thus fast and responsive. It simulates propagation of forces and motion using a relaxational algorithm. The user interacts with the machine using a "rubber band" that intuitively translates displacement to force. The machine moves, and any overloaded links change colors to red or blue depending on whether they are in tension or compression, respectively. The users can modify link lengths, connect and disconnect bars, and remove or modify grounding points, thereby creating inversions. They can also erase a machine and build a different one from scratch.

Simulator for exploring kinematics in two dimensions: (a)user exploring a sketched 4-bar mechanism, (b) drawing a Peaucellier straight-line mechanism, and (c) testing its performance

What cannot be experienced with a digital collection is the physical handling of the models. Physical models of machines were prevalent in exhibitions and universities in the nineteenth and early twentieth centuries; today their role is largely filled by computer-aided design (CAD) models and simulations. These computational models are more versatile and of lower cost, but they lack the physical embodiment that is essential for an intuitive appreciation of many critical concepts of motion and force.

Members of the K-MODDL team are using current rapid-prototyping technology to reproduce physical models as three-dimensional “prints” from digital files. The replicas are based on CAD drawings of the Reuleaux models, captured in stereolithography (STL) format. STL files can be exported for printing on a rapid-prototyping fabricator. This process creates a sequence of thermoplastic layers from a filament- wound coil that is heated and extruded through a nozzle. In order to create functioning mechanisms, a second, water-soluble release material is placed in the gaps between the movable parts.

STL files for several of the Reuleaux models will be available at the K-MODDL site, allowing users with access to rapid-prototyping equipment to download, 3D-print, and interact with their own fully functional physical replicas. While the audience for this part of the collection is clearly limited to a few large research facilities, the project team expects that as rapid-prototyping becomes more commonly available, such forms of documentation will become increasingly prevalent. Meanwhile, this technology is already reproducing accurate historical kinematic models as tools for both teaching and artifact conservancy.

The team has reproduced several pre-assembled, fully functional mechanisms; a sample of a clock escapement is shown in the figure below.

Along with the machine images and their descriptions, K-MODDL will be a rich source of text materials pertaining to kinematics and the history and theory of mechanisms and machines. The collection will include original scholarship by project team members and others in the form of preprint articles, book chapters, and the like, as well as historical books, digitized in their entirety, and tutorials that model ways of using the collection’s resources in the classroom.

The K-MODDL project has selected fifty books and other print documents for digitization and inclusion in the collection. These stem principally from the nineteenth and early twentieth centuries; some are older, and several are rare titles from Cornell Library’s History of Science Collection. These items will constitute a freely accessible and searchable digital collection of the historical literature of kinematics and the theory of machines. The materials are being scanned in a nondestructive process and stored as 600 dpi TIFF image files backed by searchable OCR’d text. K-MODDL will display PDF versions in a reader similar to the pages in other Cornell retrodigitization projects, such as the Making of America collection.

The project team is developing several tutorials or learning modules that will aid instructors at various educational levels in integrating K-MODDL materials into their students’ curricula. At release in summer 2004, K-MODDL will include tutorials suitable for students in undergraduate, high school, and middle school mathematics and technology classes, as well as for undergraduate education in engineering design and the history of technology. The high school and middle school tutorials are being developed in collaboration with teachers from several school districts in Ithaca, New York, and surrounding areas. This direct contact with members of a key target audience has been crucial in ensuring that the materials developed for the K-MODDL collection are understandable, useful, and usable in as many different ways as possible. It is the aim of the project to encourage other educators to produce tutorials of their own from the K-MODDL source material and submit them for possible inclusion in the collection.

The display of mathematical symbols and equations presents a challenging implementation issue, not only for K-MODDL, but for any Web-based mathematics project. To date, there is no accepted standard for mathematical notation in html. The World Wide Web Consortium (W3C) has issued a recommendation for MathML, an XML application for mathematics, but it is not yet widely implemented. The remaining option is to reproduce the equations and symbols as imbedded graphics files, which in some implementations appear fuzzy or otherwise difficult to read. All of these issues can be avoided using PDF files, but at the sacrifice of the flexibility of html pages. The project team is still wrestling with how best to display mathematics on the K-MODDL site.

The K-MODDL project team includes subject experts—mechanical engineers and mathematicians—who are acting as descriptive catalogers for the objects in the collection. The project team is working with Digital Consulting and Production Services, Cornell University Library’s internal consulting unit, to build a rich, Qualified Dublin Core-based metadata schema to drive collocation and retrieval. The team plans to declare an XML namespace that would establish qualifying element and attribute names for describing mechanical objects.

K-MODDL contains several types of digital object: documents in a variety of formats, bibliographic records, images, and audiovisual formats, as well as multiformat, multipage learning modules, Java-based simulations, etc. Many of these relate in a one-to-one relationship to a specific model, and the concept of the "model" serves as a base element from which the related components inherit certain descriptive metadata.

The project team deliberated at length on the question of a database structure that would be suitable for the K-MODDL collection. Two proprietary solutions for Internet-based image management and delivery already in use at CUL were considered, as was the University of Wisconsin’s open-source Scout Portal Toolkit. The latter has been developed in close association with the NSDL and is promising where a flat database structure and URL aggregation meet a project’s needs. As K-MODDL progressed, it became clear that a relational structure was needed and the decision was made to pursue a homespun solution.

Having established the metadata we will share with other systems via the NSDL Metadata Repository and OAI, we are now mapping metadata requirements to fields and tables in a relational database management system, using a MySQL database server. Our user interfaces for database administration, as well as for searching and browsing the data, are coded in PHP; in a later phase of development, PHP will also be used to develop the OAI interface for metadata harvesting. The K-MODDL Web server is Apache. MySQL, PHP, and Apache are robust, widely used, open source technologies. The use of open source software both technically and philosophically supports our mission to build a repository that is secure, reliable, interoperable, and sustainable over time.

Though a functional prototype of the K-MODDL repository is not yet complete, the project team is working to identify target audiences and their characteristics as Web users (for example, bandwidth limitations, technical ability, system limitations, etc.). K-MODDL is a pedagogical space designed for use by teachers and researchers, as well as students at a range of educational levels, and other young and adult learners in a variety of environments; the project team cannot assume that all our end users possess fast connections to the Internet, up-to-date computers, and advanced computer skills. Special care is being taken to assure that all target audiences will find K-MODDL easy to use and valuable as a learning resource.

K-MODDL will be a resource of lasting value for interdisciplinary teaching and research in machine design, mathematics, the history of science, and other fields. The project breaks new ground in the scholarly application of multimedia techniques on the Web and offers new ways of approaching representations of movement and three-dimensionality in digital libraries. While much work remains to be done, we hope that the project can offer lessons and perhaps even templates that can be applied to digital library work in other areas.

Thanks to Paul White, Susan Peck, Kathryn Gelsone, Jimmy Hai, and Carlo Paventi for assisting in modeling, photographing, and simulating the exhibits and to Javier Lezaun and David Caruso for project research.

[1]The K-MODDL Web site contains project information, news, and pertinent links. Samples and demonstrations from the collection are added and updated periodically. The full collection will debut in summer 2004.(back)

[4]For more information on the NSDL’s prescription and use of metadata, see the NSDL Metadata Primer. The NSDL Communications portal has more information about the architecture of the metadata repository, as well as other technical and social aspects of the NSDL.(back)

[6]On 3D-printing technology and its application in K-MODDL, see Hod Lipson, Francis C. Moon, Jimmy Hai, Carlo Paventi, “3D-Printing the History of Mechanisms,” Cornell University Library Technical Reports and Papers.(back)

RLG DigiNews (ISSN 1093-5371) is a Web-based newsletter conceived by the RLG preservation community and developed to serve a broad readership around the world. It is produced by staff in the Department of Research, Cornell University Library, in consultation with RLG and is published six times a year at www.rlg.org.

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All links in this issue were confirmed accurate as of August 15, 2003.


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