Pressure%20Sensor%20Findings%20and%20Thoughts%20on%20Future%20Work

1
Pressure Sensor Findings and Thoughts on Future
Work

• Miguel Piedrahita
• BDML
• 5/13/04

2
Pressure Sensor Motivation

• Normal force information will be useful for
  climbing
• May be able to get dynamic signals related to
  slipping
• Pressure approach could integrate nicely with dry
  adhesive pads

3
Chamber Fabrication
Mold 1 Mold for Cavity Insert
Cavity Insert placed in Mold 2, leaving gap for
membrane
Completed Cavity Insert (wax or hard urethane)
Mold 2 Mold for Membrane Exterior
Membrane sealed with layer of hard urethane
Membrane cast from soft urethane
Mold 3 Mold for sealing off membrane
Finished Chamber
4
Testing
Mass

• Applied normal force from 0g to 1000g back down
  to 0g, in 50g increments.
• Several trials conducted on two different days.

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Results
Day 2
Day 1
6
Sensor Performance (Day 2)
Sensitivity 1.06 kPa/N, (1.06 V/N) Accuracy -
0.33 N, or - 0.35 kPa
7
Observations

• Drawbacks to practical implementation
• Difficult to fully bleed air from system
  affects repeatability
• Size of system limited by rather large sensor
• Likely not effective for adhesion forces (front
  feet)
• Other technologies may be better for normal force
  measurement
• Strain gage
• Piezoelectric

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Thoughts on Future WorkWhat do we want from
RiSE sensors?

• Climbing-related information
• Foot impact events
• Slip events
• Tangential normal forces on each foot
• Measure of penetration of claws/engagement of dry
  adhesives (i.e. a way to predict likelihood of
  slip)
• Surface-related information
• Information about climbing surface would be
  useful! We could then tailor aggressiveness and
  climbing strategy (claws vs. dry adhesives)
  accordingly
• Inclination
• Surface hardness
• Roughness

9
Array of Instrumented Lamellar Fingers
Embedded PVDF or strain gage

• Force distribution throughout foot in tension
  compression. Useful for evaluating foot design
  performance.
• Surface roughness by comparing deflections

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Why Lamellar Fingers? Good Question!

• Examine advantage of lamellar structures
• Work on optimizing geometry for front feet and
  rear feet
• Front feet Maximize surface contact, minimize
  stress at edges Poisson shrinkage
• Rear feet Maximize shear force
• Solid mechanics, FEA, experiments (RoboToe)