sticky system modeling -principle of sticky mechanism- sangbae kim
TRANSCRIPT
Sticky system modeling-Principle of sticky mechanism-
Sangbae Kim
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?
Compliance == Sticky?
Chemical, atomic, capillary, electro static… etc… friction?
Sticky ?
• Hypothesis– ‘Stickiness’ depends primarily on compliance
in structure.
solid
Stiffness
Liquid ‘Sticky’
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.
Sticky system• Sticky system class of Gecko feet
• Every branch can be sticky element and sticky system according to interested scale
Surface roughness
Toes
Lamellae
BranchedSimple
Nano-bumps
LegsPerform
ance
Power point slide from POLY-PEDAL
Sticky system model
Substrate
Sticky element
Sticky structure
An element also has sticky system
Assumptions
1. Sticky structure is linear elastic material.2. Sticky force of each sticky element is constant.
– Which should be determined in smaller scale model
3. Elongation of sticky element is negligible.4. There are no interactions between sticky elements
– Discrete structure.
5. Substrate surface height follows Normal distribution.6. Substrate and frame of sticky system (black line) are
rigid.7. Nominal length of sticky structure is long enough to
comply.8. Initial force is strong enough to engage every
element.
Sticky system model
• . 1,3 : compression internal force2 : Detached element ( if Fi < k(Yi – h0) , where Fi is sticky force of sticky element)4: Zero internal force5: Tensile force ( Fi > k(Yi – h0))
F : external forcek : stiffness of structure (modulus)
1 2 3 4 5
F
h0
Yik
Simulation
40 60 80 100 120 140 160 180-2
-1
0
1
2
3
4
5x 10
5 External force on Sticky system vs distance from surface
Distance between sticky system and surface
Exte
rnal fo
rce
Positive external force
Negative external force
Maximum sticky force
Detaching point
k=5
Plot between External force on sticky system vs distance from substrate
Elasticity
40 60 80 100 120 140 160 180-4
-3
-2
-1
0
1
2
3x 10
5 External force on Sticky system vs distance from surface
Distance between sticky system and surface
Exte
rnal
forc
e
40 50 60 70 80 90 100 110 120-16
-14
-12
-10
-8
-6
-4
-2
0
2x 10
5 External force on Sticky system vs distance from surface
Distance between sticky system and surface
Exte
rnal
forc
e
k=20 k=70
40 60 80 100 120 140 160 180-2
-1
0
1
2
3
4
5x 10
5 External force on Sticky system vs distance from surface
Distance between sticky system and surface
Exter
nal fo
rce
k=5
Plots in different stiffness in sticky structure
Maximum sticky force vs elasticity
0 10 20 30 40 50 60 70 800
1
2
3
4
5
6x 10
5 Plot of Maximun sticky force vs elasticity
Stiffness(k)
Stic
ky f
orce
Roughness
100
101
102
-1
0
1
2
3
4
5
6x 10
5 Plot of Maximun sticky force vs surface roughness
Roughness
Stic
ky f
orce
Plot of relationship between Maximum sticky force and sigma(б) of surface height distribution
Engaging force
0 0.5 1 1.5 2 2.5 3 3.5
x 105
0
1
2
3
4
5
6x 10
5 Engaging force vs Maximum sticky force
Engaging force
Max
imum
stic
ky fo
rce
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
Application-claw design
Sticky element
Sticky structure
- Compliance in y direction
- Rigidity in x directionx
y
FSticky force
Driving force
- We can modify sticky model for climbing changing angle of substrate and characteristic of sticky element.
Moment
F
Passive engaging moment
Force acting point
More secure engaging
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