Sticky system modeling -Principle of sticky mechanism-

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Sticky system modeling-Principle of sticky
mechanism-

• Sangbae Kim

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Motivation

• Why duct tape works better than normal tape?
• Why double sided tape with sponge in between two
  sides works better?
• Why smooth surface is better for sticky tape?
• Why rubber pad (tire, outsole of shoes) works
  better in grasping ground than stiffer material
  like steel?
• Why soft polyurethane is sticky?

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Compliance Sticky?
Chemical, atomic, capillary, electro static etc
friction?
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Sticky ?

• Hypothesis
• Stickiness depends primarily on compliance in
  structure.

Stiffness
solid
Liquid
Sticky
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Term definition in Sticky system

• Sticky element
• The smaller sticky element that composes upper
  scale sticky system. The sticky element produces
  force in the opposite direction of the force
  acting on the element (especially detaching
  force) like static friction force
• Sticky structure
• The structure that configures sticky element to
  generate optimized sticky force. In other words,
  the structure that delivers force from the sticky
  element to upper scale structure. There are two
  different type of sticky structure. One is
  discrete structure, the other is continues one.
• Sticky force
• Minimum external force that detaches sticky
  element or system.

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Sticky system

• Sticky system class of Gecko feet
• Every branch can be sticky element and sticky
  system according to interested scale

Power point slide from POLY-PEDAL
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Sticky system model
An element also has sticky system
Substrate Sticky element Sticky structure
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Assumptions

• Sticky structure is linear elastic material.
• Sticky force of each sticky element is constant.
• Which should be determined in smaller scale
  model
• Elongation of sticky element is negligible.
• There are no interactions between sticky elements
• Discrete structure.
• Substrate surface height follows Normal
  distribution.
• Substrate and frame of sticky system (black line)
  are rigid.
• Nominal length of sticky structure is long enough
  to comply.
• Initial force is strong enough to engage every
  element.

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Sticky system model

• .

1,3 compression internal force 2 Detached
element ( if Fi lt k(Yi h0) , where Fi
is sticky force of sticky element) 4 Zero
internal force 5 Tensile force ( Fi gt k(Yi
h0)) F external force k stiffness of
structure (modulus)
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Simulation
Plot between External force on sticky system vs
distance from substrate
Maximum sticky force
k5
Positive external force
Negative external force
Detaching point
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Elasticity
Plots in different stiffness in sticky structure
k20
k70
k5
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Maximum sticky force vs elasticity
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Roughness
Plot of relationship between Maximum sticky force
and sigma(?) of surface height distribution
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Engaging force
In this simulation, we exclude the assumption
No.8 that engaging force is strong enough so that
we can estimate the ratio between engaging force
and maximum sticky force
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Application-claw design
F
Sticky force
Driving force
Sticky structure
y
- Compliance in y direction - Rigidity in x
direction
Sticky element
x
- We can modify sticky model for climbing
changing angle of substrate and characteristic of
sticky element.
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Moment
F
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Passive engaging moment
Force acting point
More secure engaging
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Small claw vs big claw
Small sticky force of element - Less chance to
get dull - Less chance to deform substrate
Larger sticky force of element - More chance to
get dull - More chance to deform substrate