building small robot legs with pre-fabricated components is difficult

9/6/98Sept 9-10, 1998 MURI Kick-off meetings, Berkeley/Stanford, CA

FabricationBuilding small robot legs with pre-fabricated components is difficult...

Motor

Leg links

Shaft

Shaft coupling

Body frame Lift pot

Knee pot

Hip pot

Abduct pressuresensor

Lift pressuresensor Extend pressure

sensor

Gears

Actuators

Boadicea leg

Electric motor/link

IV. Fabrication and integration experiments2:00-2:30pm (*Cutkosky, Kenny, Howe)

• Overview of SDM fabrication process, capabilities, challenges

• Autonomous robots: experiments with UCB, SRI, (others?)

• Cooperative robots: experiments with Harvard, Johns Hopkins, UCB


Fabrication Concept design for a biomimetic “Insect-Leg”

A prototype design of the same leg employing three-dimensional plastic “exoskeleton” surrounding with embedded actuators, sensor and cooling system.


Fabrication

Mechanics and muscle activation patterns (R. Full)

Three-dimensional musculo-skeletal model of the leg of B. discoidalis constructed by Full’s lab. Simulations such as these help characterize the role of individual muscles in locomotion.


FabricationShape Deposition Manufacturing(SU/CMU)

• sensors • electronics

Shape

e.g., microcasting

(contouring)

e.g., Shot Peen

Deposit

e.g., CNC machining

(planing)

Embed

Stress Reliefe.g., thermocouple

stainless steel

sacrificial copper

internal copper

• CNC milling • CNC EDM • grinding

• microcast • gelcasting • 2-part mixtures • laser cladding • UV curing • plasma spraying • deposition welding • extrusion

• shot-peening • vibratory • preheating


FabricationSDM allows finished parts to be inserted at any point in the cycle

First layer part & support Second layer part & support

Insert bearings and second link Insert a sub-part

Final part deposition After support removal

Green link and red bearings are added as finished components


FabricationSDM capabilities

• Slides and web pages of parts that would be difficult or impossible to create using conventional manufacturing methods– Topology that would be almost impossible with

conventional machining tilted frame (CMU/Stanford) – Integrated assembly of polymers with embedded

electronics and interconnects (CMU Frog Man)– other example parts from RPL at Stanford

http://www-rpl.stanford.edu/~rmerz/ACORN/sdm.html

http://www.cs.cmu.edu/~SDM/examples.htm

http://www-rpl.stanford.edu/RPL/htmls/showcase.html


FabricationFrogman (CMU)

• Example of polymer component with embedded electronics using shape deposition manufacturing

MicroStructures and Sensors Lab (MSSL)

Research on Fundamental Properties and Applications of MEMS-based MicroMechanical Devices.• Micromechanical Sensors.• Micromechanical Elements for Scientific and Technological Collaboration Partners.• Devices and Instruments for Studies of Fundamental Properties of Micromechanical Structures.Collaborators : IBM, JPL, NRL, SNL, SAIC, Medtronic, Raychem, Lucas, Seagate, Perkin-Elmer...Students from :ME, EE, Appl Phys, A/A

2-Axis AFM Cantilevers for Surface Friction Experiments and Thermomechanical Data Storage

Piezoresistive Lateral Accelerometer

Flow Visualization in Microchannels

Ultrathin Cantilevers for attoNewton Force Detection

Kenny


Fabrication

Epoxyacrylic

Shape Memory Alloy wire withwater cooling channels

Embedded SMA actuators

• Intial experiments with epoxy and urethane polymers and various sacrificial supportmaterials have underscored the need to

build in disposable fixtures for proper alignment.


FabricationEmbedded sensor example: pressure sensor unit for pneumatic actuators

Screen shot from SDM CAD environment: several steps in the “building block” design/fabrication sequence for the embedded pressure sensor package

PC board CAD file for commercial MEMS pressure transducer & instrumentation


FabricationEmbedded sensor example (continued)

Completed pressure sensor unit ready for connection to a pneumatic actuator.

A batch of four parts during the final machining step. Part material is urethane (yellow). Sacrificial support material is wax (red), filling cavities and encasing the circuit leads to protect them.

Fabrication instructions archived at http://cdr.stanford.edu/dml/biomimetics/documents.html

http://cdr.stanford.edu/dml/biomimetics/documents.html












FabricationApproaches 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


FabricationSDM process planning: geometric decomposition for tool access

Cross section of part material (gray) in support material

build

dire

ctio

n

9/6/98Sept 9-10, 1998 MURI Kick-off meetings, Berkeley/Stanford, CA 15

FabricationDecomposition into ‘compacts” and layers

• Several levels of decomposition are required

CompletePart

Compacts Layers Tool Path


FabricationTesting for compactness

Build Axis

OKNot a

compact

~

p

ddZ Z

S S0 0

2

2

There exists no point, p, on S which is an inflection point with an undercut surface above an upward-facing surface.

Z


FabricationLayers produced by automatic decomposer for slider crank mechanism

Gray = steel, brown = copper support material


FabricationLayered shape deposition - potential manufacturing problems

How mechanisms are built After support removal

• finite thickness of support material• poor finish on un-machined surfaces• warping and internal stresses


FabricationSlider crank can be built entirely from two kinds of primitives

Yellow = part material, blue = support material


FabricationMerge algorithm for compacts (Binnard)

12

3

12

3Combine thesetwo compact lists

34

5

3

5

24 4

6To form thisresult list

Source lists after subtraction A B

C list(Intersections)

Source compactsa b

1 1

2

3

1

1324

32

2

33

f (a,b )


FabricationBuilding Designs from Primitives• Here is the result of building slider-crank from

primitives• allows manufacturability analysis at design time


Fabrication

SFF Object made up of Part and Support Compacts

What gets sent to the Manufacturing Service

Primitives + Merging Rules

The Final Geometry

What the Designer works with

Building a robot joint from a library of shapes


Fabrication

Link 1 Link 2

Pneumatic Actuator Magnetic Gear Tooth Sensor

Design for a prototype pneumatic knee joint built from primitives (M. Binnard)


FabricationDecomposed FeaturesSFF-MEMS VLSI

Boxes, Circles, Polygons and Wires

SFF-MEMS 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

Comparison with VLSI approach

building small robot legs with pre-fabricated components is difficult

Documents