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PAPERS: Novel Applications of Design for AM

The MechProcessor: Helping Novices Design Printable Mechanisms Across Different Printers

[+] Author and Article Information
Mark Fuge

Department of Mechanical Engineering,
University of Maryland,
College Park, MD 20742
e-mail: fuge@umd.edu

Greg Carmean

Department of Mechanical Engineering,
University of Maryland,
College Park, MD 20742
e-mail: gcarmean@umd.edu

Jessica Cornelius

Department of Mechanical Engineering,
University of Maryland,
College Park, MD 20742
e-mail: jcornel1@umd.edu

Ryan Elder

Department of Computer Engineering,
University of Maryland,
College Park, MD 20742
e-mail: relder@umd.edu

1Corresponding author.

Contributed by the Design for Manufacturing Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received February 15, 2015; final manuscript received July 2, 2015; published online October 12, 2015. Assoc. Editor: Carolyn Seepersad.

J. Mech. Des 137(11), 111415 (Oct 12, 2015) (9 pages) Paper No: MD-15-1132; doi: 10.1115/1.4031089 History: Received February 15, 2015; Revised July 02, 2015

Additive manufacturing (AM), or 3D-printing, sits at the heart of the Maker Movement—the growing desire for wider-ranges of people to design physical objects. However, most users that wish to design functional moving devices face a prohibitive barrier-to-entry: they need fluency in a computer-aided design (CAD) package. This limits most people to being merely consumers, rather than designers or makers. To solve this problem, we combine advances in mechanism synthesis, computer languages, and design for AM to create a computational framework, the MechProcessor, which allows novices to produce 3D-printable, moving mechanisms of varying complexity using simple and extendable interfaces. The paper describes how we use hierarchical cascading configuration languages, breadth-first search, and mixed-integer linear programming (MILP) for mechanism synthesis, along with a nested, printable test-case to detect and resolve the AM constraints needed to ensure the devices can be 3D printed. We provide physical case studies and an open-source library of code and mechanisms that enable others to easily extend the MechProcessor framework. This encourages new research, commercial, and educational directions, including new types of customized printable robotics, business models for customer-driven design, and STEM education initiatives that involve nontechnical audiences in mechanical design. By promoting novice interaction in complex design and fabrication of movable components, we can move society closer to the true promise of the Maker Movement: turning consumers into designers.

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References

Figures

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Fig. 1

An overview of MechProcessor framework. The user provides a kinematic graph, along with a set of desired default lengths, radii, etc.; (a) a part library containing parametrized kinematic elements is (b) matched to the input graph and adjusted to account for user-specified geometric constraints and (c) machine capabilities, as captured by a calibration test-case. Our framework resolves these constraints and (d) generates a customized stereolithography file tuned to a particular AM machine's capabilities.

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Fig. 2

Examples of some parametrized parts included in the library, include: rod and bar linkages; cylindrical, revolute, and spherical joints; and involute gear pairs

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Fig. 3

An example of a user-input file for a crank-slider linkage (RRRP). The details inside the boxes indicate details that a user might provide to customize the generated mechanism. Removing these details would cause the algorithm to cascade back to default values. If user-provided values conflict with manufacturability limits from the test in Sec. 3.3., they would be overridden.

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Fig. 4

How we progressively resolve ambiguities in the user input (1): (2) Create an undirected mechanism graph, (3) solve for the ideal 2D positions using a geometric constraint solver [51], (4) substitute in user-selected components from the library, if specified, or appropriate defaults given the AM test (Sec. 3.3), (5) create an interface graph from the selected components and optimize build volume using MILP [53], and (6) locally modify the geometry at the selected interfaces to ensure movement when printed

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Fig. 5

For underconstrained systems, we attempt to reduce the mechanism DOF by adding angle constraints starting breadth-first from a randomly selected ground node

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Fig. 6

Top: Our manufacturing test-case accurately emulates the performance of joints across three printers: a consumer-grade FDM machine (Flashforge Creator Pro), and two professional-grade FDM machines (Stratasys uPrint SE and Dimension 1200es). Across all tests, the joint clearances decrease monotonically from 0.6 mm to 0.2 mm. Middle: Our algorithms modify the user-specified geometry to match those achievable clearances. The right-hand side shows the same mechanisms, but printed on different printers and then manually positioned so that each mechanism is in a different point in its motion path. Bottom: the yaml input file and printed mechanism for a four-bar linkage and Stephenson type-II linkage.

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