Sticky system modeling -Principle of sticky mechanism-

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Sticky system modeling -Principle of sticky mechanism- Sangbae Kim

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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? - PowerPoint PPT Presentation

Transcript of Sticky system modeling -Principle of sticky mechanism-

Page 1: Sticky system modeling -Principle of sticky mechanism-

Sticky system modeling-Principle of sticky mechanism-

Sangbae Kim

Page 2: Sticky system modeling -Principle of sticky mechanism-

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.

solid

Stiffness

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

Surface roughness

ToesLamellae

BranchedSimple

Nano-bumps

LegsPerformance

Power point slide from POLY-PEDAL

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Sticky system model

Substrate

Sticky element

Sticky structure

An element also has sticky system

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Assumptions1. Sticky structure is linear elastic material.2. Sticky force of each sticky element is constant.

– Which should be determined in smaller scale model3. 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.

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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

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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

Ext

erna

l for

ce

Positive external force

Negative external force

Maximum sticky force

Detaching point

k=5

Plot between External force on sticky system vs distance from substrate

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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

Ext

erna

l for

ce

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

Ext

erna

l for

ce

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

Externa

l force

k=5

Plots in different stiffness in sticky structure

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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 fo

rce

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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 fo

rce

Plot of relationship between Maximum sticky force and sigma(б) of surface height distribution

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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

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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.

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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