1. Additive Manufacturing File Formats Hod.lipson@cornell.edu Disclaimer: Information in this presentation does not constitute the final standard. Actual specifications is subject to change until finalized by ASTM

2. Overview Background (20m) – Robotics and design automation – Multimaterial analog materials – Digital Materials and rapid assemblers Standards for 3D printing file format (40m) – AMF

4. Lipson & Pollack, Nature 406, 2000

8. Embedded Strain Gages Silver-doped silicon Robot finger sensor

9. Zinc-Air Batteries With Megan Berry

10. Zinc-air Batteries Zinc-Air

11. IPMC Actuators

12. With Evan Malone

16. Fab@home Model 1

17. Fab@home Model 2

18. With Max Lobovsky

20. DIGITAL MATERIALS

21. Neil Gershenfeld (2005): Digital Materials

27. Rob MacCurdy

28. DESIGN

29. Tea. Earl Gray. Hot.

31. PotteryPrint.com

32. . com With Jeff Clune, Jason Yosinski

36. Objet.com

46. Auxetic Materials

47. Complexity is Free Direct (fixed blueprint) Parametric (adjustable) Programed Generative Reactive Dynamic Natural interfaces FabApps Breeding Designs Compilers New Design SpaceNew Designers New ToolsNew Encodings

48. FILE FORMATS

49. Goals Identify needs of new file format Propose new standard Reach consensus  Catalyze adoption

50. Outline of presentation Summarize survey Outline proposed standard Process and timetable for moving forward

51. Prioritized features from survey n=162. Error bars = Standard Error

52. Proposed Format

53. Key considerations Technology independence – Describes target object, not how to make it – Every machine can make it to the best of its ability Simplicity – Easy to understand and implement Scalability – Can handle complex objects, microstructures, repetitions Performance – File size, read/write time, processing, accuracy Backwards compatible – Can covert to/from STL without additional info Forward compatible – Easy to extend new features in the future Adoption path – Takes advantage of existing investments in tools and infrastructure

54. Name AMF – Additive Manufacturing Format – Additive Manufacturing File

55. XML Meta-format: Format of formats – Text based – Easy to read/write/parse – Existing editing tools – Extensible – Highly compressible Mentioned by a number of constituents – E.g. Materialise – Based on work by J. Hiller (Cornell)

56. General Concept Parts (objects) defined by volumes and materials – Volumes defined by triangular mesh – Materials defined by properties/names Color properties can be specified – Color – Texture mapping Materials can be combined – Graded materials – Lattice/Mesostructure Objects can be combined into constellations – Repeated instances, packing, orientation

57. Basic AMF Structure 0 1.32 3.715 0 1.269 2.45354... 0 1 3 1 0 4... Addresses vertex duplication and leaks of STL

58. Compressibility Comparison for 32-bit Floats; need to look at double precision

59. File Size Stored either as text or compressed (zip) Both versions have AMF extension Reader can determine which and decompress during read

60. Read/Write/Parse time Write (seconds) Read + parse + construct data structure (seconds) Still negligible compared to slicing/processing time

61. Increasing Geometric Accuracy Flat triangles do not scale well for complex geometry, esepcially: – Curved surfaces – Microstructures Typical objects require millions of triangles – 10M triangles not uncommon Likely to get worse with increasing printer resolution – 10cm sphere at 10  m requires 20,000 triangles

62. Geometric fidelity is a high priority Must be addressed

63. CURVED PATCH (Curved using vertex normals) PLANNAR PATCH Optionally add normal/tangent vectors to some triangle mesh edges to allow for more accurate geometry. CURVED PATCH (or curved using edge tangents) Curved patches

64. ... 0 0.707... 0 0.577 1 0.707 0 0.707......... Only needed for curved surfaces Only needed for curved edges (rare)

65. Recursive Triangle Subdivision Importer temporarily subdivides each curved triangle into a set of 4 n planar triangles then uses those to calculate slice

68. Icosahedrons (20 Triangles)

69. Flat triangles, error = 10.26% of diameter Error

70. Icosahedrons (still 20 triangles) One subdivision, error = 3.81%

71. Icosahedrons (still 20 triangles) Two-fold subdivisions, error = 1.49%

72. Icosahedrons (20 Triangles) Three-fold subdivisions, error = 0.84%

73. Icosahedrons (still 20 triangles) Four-fold subdivisions, error = 0.67%

74. Icosahedrons (still 20 triangles) Five-fold subdivisions, error = 0.635%

75. Icosahedrons (still 20 triangles) Six-fold subdivisions, error = 0.625%

76. Curving the triangle patches using surface normal reduces error #-fold subdivisions Error on units sphere

77. Double Icosahedrons (n=80)

78. Flat triangles, error = 3.29%

79. Double Icosahedrons (n=80) One subdivision, error = 0.946%

80. Double Icosahedrons (n=80) Two-fold subdivision, error = 0.290%

81. Double Icosahedrons (n=80) Three-fold subdivision, error = 0.121%

82. Double Icosahedrons (n=80) Four-fold subdivision, error = 0.079%

83. Double Icosahedrons (n=80) Five-fold subdivision, error = 0.068%

84. Double Icosahedrons (n=80) Six-fold subdivision, error = 0.065%

85. Curving the triangle patches using surface normal reduces error #-fold subdivisions Error on units sphere

86. Curved Triangles 1001,00010,000100,0001,000,00010 Number of Triangles Error on unit sphere STL AMF curved AMF curved 2-fold AMF curved 3-fold AMF curved 4-fold AMF curved 5-fold AMF curved 6-fold x4 error reduction with every subdivision

87. Curved Triangles 1001,00010,000100,0001,000,00010 Number of Triangles Error on unit sphere STL AMF curved AMF curved 2-fold AMF curved 3-fold AMF curved 4-fold AMF curved 5-fold AMF curved 6-fold Three orders of magnitude improvement in accuracy for same number of triangles

88. Curved Triangles 1001,00010,000100,0001,000,00010 Number of Triangles Error on unit sphere STL AMF curved AMF curved 2-fold AMF curved 3-fold AMF curved 4-fold AMF curved 5-fold AMF curved 6-fold Three orders of magnitude reduction in number of triangles for same accuracy

89. Accuracy

90. Fabricate 10cm diameter sphere with 10μm Precision – STL: 20,480 Flat Triangles 500K Compressed Binary STL – AMF: 320 Curved Triangles 10K Compressed AMF Fabricate 1m Sphere with 1nm precision – AMF: 1M Triangles – STL: !? Examples

91. Simple to implement 1.If tangents t 0 or t 1 not specified, compute tangents from normals 2.Compute center point v 01 = h( 0.5 ) and center tangent t 01 using Hermite curve h(s)=(2s 3 -3s 2 +1)v 0 +(s 3 -2s 2 +s)t 0 +(-2s 3 +3s 2 )v 1 +(s 3 -s 2 )t 1 3.Repeat for three triangle edges, then split triangle into four 4.Recurse 5 levels (1 curved triangle  1024 flat triangles) 5. No ambiguities. Detailed procedure in specification. v0v0 v1v1 d n0n0 t0t0 t1t1 n1n1 n 01 v 01 t 01

92. For each curved triangle 1.Normalize all specified normals to length 1 2.Normalize all specified tangents to length 1 3.If edge tangent not specified and normal is specified, estimate edge tangent from normal as the vector perpendicular to the normal in the direction of the straight edge 4.If edge not specified and normal is not specified, estimate edge tangent along linear edge 5.If a normal is not specified, estimate the normal as perpendicular to two edge tangents 6.Scale each tangent by the length of the corresponding straight-edge chord 7.Split into four sub-triangles as per the instructions in previous page

93. Multiple Materials StiffMaterial FlexibleMaterial MediumMaterial 0.4 0.6 VerticallyGraded z 10-z Checkerboard floor(x+y+z%1)+0.5) 1-floor(x+y+z%1)+0.5).........

94. Graded Materials StiffMaterial FlexibleMaterial MediumMaterial 0.4 0.6 VerticallyGraded z 10-z Checkerboard floor(x+y+z%1)+0.5) 1-floor(x+y+z%1)+0.5).........

95. Microstructure StiffMaterial FlexibleMaterial MediumMaterial 0.4 0.6 VerticallyGraded z 10-z Checkerboard floor(x+y+z%1)+0.5) 1-floor(x+y+z%1)+0.5)......... Can also reference a texture map

96. Periodic functions can be used to describe linear and nonlinear lattice materials

97. Material properties By name – ABS – Nylon 1234 By physical property – 2GPa

98. Color and Graphics Can be assigned to – A material – A volume – A vertex Specified – Fixed RGBA values – By formula – By reference to an image

99. Print Constellation Print orientation Duplicated objects Sets of different objects Efficient packing Hierarchical

100. Metadata John Doe”> SolidX 2.3”> Product 1> 12A”> Part A >

101. Not addressed (for now) Tolerances (critical dimensions) Surface/depth textures Data encryption, copyright External references and subassemblies Process control Non-volumetric support structures Non mesh geometry specification methods – Voxel, FRep

102. Adoption Building Concensus

104. Join The Discussion http://groups.google.com/group/stl2

106. Wikipedia provides an overview of key concepts Refers to ASTM for formal spec

107. STL2.org Repository for sharing code

108. Open-Source AMF Editor BSD License (allows commercialization) Reference implementation of AMF features http://amf.wikispaces.com/AMF+Editor

109. Building consensus Contact hod.lipson@cornell.edu to be added or removedhod.lipson@cornell.edu

110. Required Tools Better Viewers/Slicers – Geometry (with curved triangles) – Alternative platforms Verifier / Analyzers Proposition and testing of new features – Voxel/Frep – IP Management – Digital/Active materials

111. Anticipated adoption stages CAD companies initially only implement AMF geometry export Full-fledged viewers are developed Equipment manufacturers have incentive to implement imports that support their unique capabilities – Companies supporting color implement color – Companies supporting multimaterial implement material parsing (volume, graded) – Companies interested in lattice structures implement lattice materials Small/new CAD programs allow designers to create parts with microstructure, color, graded materials etc. Big CAD follows Other applications emerge: 3D scanning, CNC

112. Conclusion Essential to moving the AM field forward – STL is holding back the field – Machines can do much more than current CAD/STL can support AMF Standard converging – Voice support or suggest improvements – Explore new ideas/concept within the framework