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C D R Design by Composition for Layered Manufacturing

Mark R. Cutkosky

Stanford Center for Design Research

http://cdr.stanford.edu/interface

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C D ROutline

• Layered manufacturing processes: commercial (additive) vs SDM (addition, removal, insertion)

• Design decomposition vs design by composition• Design by composition -- implementation• Application example: biomimetic robotic

mechanisms• Summary & status

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Layered Manufacturing: commercial example

Laser UV curableliquid elevator

Formedobject

Photolithography processschematic Sample prototype (ME310

power mirror for UT Auto)

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C D R

Layered manufacturing processes

Commercial• Photolithography

• Fused deposition

• Laser sintering

• Laminated paper

Research• Selective laser sintering

(UT Austin)

• 3D printing (MIT)

• Shape deposition manufacturing (CMU/Stanford)

“Look and feel” prototypeComplex 3D shapesdirect from CAD model

Engineering materials (metals,ceramics, strong polymers)Graded materialsEmbedded componentsNot quite direct from CAD model...

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Deposit (part)

Shape

EmbedDeposit (support)

Shape

Part

Embedded Component

Support

Shape Deposition Manufacturing (CMU/SU)

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SDM#1: Injection mold tooling (SU RPL)

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C D RSDM #2: Frogman (CMU)

• Example of polymer component with embedded electronics

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Approaches to design with layered shape

manufacturingUsually people think of taking a finished CAD

model and submitting it for decomposition and

manufacture

Example: the slider-crank mechanism, an “integrated assembly” built by SDM

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Decomposition into ‘compacts” and layers

• Several levels of decomposition are required

CompletePart

Compacts Layers Tool Path

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Definitions: Compact [Merz et al 94]

• 3-D volume with no overhanging features• Rays in growth direction enter only once• Compacts correspond to SDM cycles

Build Axis(c) OK(a) no good (b) OK

x y z z z x y z a z z z1 2 1 2, ,

z1

z2

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Layers produced by automatic decomposer for slider crank mechanism

Gray = steel, brown = copper support material

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Layered shape deposition - potential manufacturing problems

How mechanisms are built After support removal

• finite thickness of support material• poor finish on unmachined

surfaces• warping and internal stresses• decomposition depends on geometry, not on intended function

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C D RDesign by Composition (M. Binnard)

Users build designs by combining primitives with Boolean operations– Primitives have high-level manufacturing plans

– Embed components and shapes as needed

Primitivesmerged by designer

Manufacturing plansmerged by algorithm

Primitive = Compact Set + Precedence Graph

• Set of valid compacts• No intersections• Fills the primitive’s projected

volume

Primitive Compact set Compact precedence graph

• Acyclic directed graph• Link for every non-

vertical adjacency

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Merging Algorithm Example

intersection compacts

non-intersecting compacts

A B

+ =

A B C=A B

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Algorithm: intersection compacts

b1

a1

a2

a3

a1 b1

a2b1

b1

b1

A B

C

• Find every compact intersection• Material type depends on operation, f(a,b)

(etc. )

Adda b cP P PP S PS P PS S S

Subtracta b cP P SP S PS P SS S S

Truth tables for result material

a1

a2

a3

b1 b2

C D R

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CPG Simplification algorithm• Combine compacts of the same material• Multiple solutions• Optimum depends on functional and

manufacturing considerations

4

1

3 2

65

7

1

2

65

7

3+4

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Algorithm closure and efficiency demonstrated for multi-material parts and embedded components (Binnard 99)

• Minimal geometric Boolean operations (incremental merging and simplification)

• Worst-case scaling – Compact set merging: O(n2)– CPG link generation: O(n4)– Simplification: O(n3 )

(In practice, 10-20 merged compacts for moderately complex designs)

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Implementation• AutoCAD R14 plug-in (compacts and projected

volumes on hidden layers)• ACIS toolpath planner (extruded shapes, 3D

surfaces underway)

design bycomposition

toolbar

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C D RDecomposed Features

SFF/SDM VLSIBoxes, Circles, Polygons and Wires

SFF/SDM Design Rules Mead-Conway Design Rules

Wc/ >= 2

Minimum gap/rib thickness

d d

d

(top view)a)

Generalized 3D gap/rib

d

(side view)b)

d

Minimum feature thickness

d(m1,m2,m3)

(side view)e)

m1 m2 m3

d(m1,m2,m3,)

m1 m2 m3

Toward a mechanical MOSIS?

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Future Work: Integration with Decomposition

Bold arrows aretransmission ofcompact graphs

Machine Tools

Path Planning

CNC code

solid model

Orientation

Traditional CAD

Analysis

feedbackComposition CAD

Analysis

Compact Splitting

new primitive

feedback

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Application: Small robots with embedded sensors and actuators

Motor

Leg links

Shaft

Shaft coupling

Body frame Lift pot

Knee pot

Hip pot

Abduct pressuresensor

Lift pressuresensor Extend pressure

sensor

Gears

ActuatorsBuilding small robot legs with pre-fabricated components is difficult…Is there a better way?

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Designer composes the design from library of primitives, including embedded components

Steel leaf spring

Piston

Outlet for valve

Valve Primitive

Circuit Primitive

Inlet port primitive

Part Primitive

Robot leg example(http://cdr.stanford.edu/biomimetics)

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Internal components are modeled in the 3D CAD environment.

Steel leaf-spring

Piston

Sensor and circuit

Spacer

Valves

Components are prepared with spacers, etc. to assure accurate placement.

Robot Leg design (cont’d.)

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The output of the software is a sequence of 3D shapes and toolpaths.

Robot Leg: compacts

Support

Part

Embedded components

Robot leg: manufacturingManufacturing takes place in the Stanford Rapid Prototyping Lab

Part material is Urethane. The support is red and blue wax. Cavities inside valves were first filled with soap.

Deposition

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A snapshot just after valves and pistons were inserted.

Steel leaf-spring

Piston

Sensor and circuit

Valves

Robot Leg: embedded parts

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Finished parts ready for testing

Robot Leg: completed

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Summary & statusNew technology provides novel design opportunities

Designers need access to develop an experience base

Making these processes widely used requires:• Ease of use• Flexibility (e.g, decompose geometry or build

from primitives) • Quick feedback

What are we doing?• Creating a design/manufacturing interface for layered processes• Creating design libraries and design rules

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C D RAcknowledgements

Thanks to M. Binnard, S. Rajagopalan, J. Cham, B. Pruitt and Y. Sun fortheir help in generating the results described in this presentation and to the

Stanford Rapid Prototyping Lab for their help in building the parts.

This work has been supported by theNational Science Foundation (MIP-9617994)

and by the Office of Naval Research (N00014-98-1-0669)