Pneumatic Actuation_AA EmTech Biomimetics seminar

BIOMIMETICS - VENUS FLYTRAP J. KHAYYAT - S. SONG - D. VALDIVIA

Photograph by Helene Schmitz March 2010

BIOMIMETICS I Venus Flytrap

CONTENTS

Abstract 03 Venus Flytrap mechanism 05 Abstraction 09 Material experiments 11 Square Waterbomb pattern 13 Latex cells Experiments 15 One component Experiment 18 System Fabrication 20 Membrane Experiments 22 Global Geometry experiments 24 Conclusions 26 Biblioraphy 28

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BIOMIMETICS I Venus Flytrap

ABSTRACT

Architecture is known to often draw inspiration from nature, as the inner-workings of different plants can be applied to man-made systems in order to ingeniously solve practical problems. The appeal of natural systems owes to their inherent simplicity and perfect adaptation to environmental conditions and function, both desirable in an architectural scenario. This report aims to explore the anatomy, energy flow and behavior of the Venus Fly Trap plant and to exemplify how an abstracted logic of the trap leaves closing mechanism can be applied to an architectural system of pneumatically-actuated airtight membranes. The resulting configuration will be shown to mimic the variations in curvature exhibited by the trap leaves during the initial stages of closure.

Building upon this primary configuration, improvements are added by integrating the airtight membranes within an origami tessellation devised by Ron Resch.

In order to prove the viability of this solution, the group used a two-step approach. First, a series of tests were performed on single components in order to better grasp the relationship between the inner and outer membranes, which was considered crucial for the success of the study and an essential part of system modelling. These were followed by tests performed on a global scale with the aim of revealing the effects of locking or actuating such a component on the global curvature thus proving the effectiveness of the mechanism.

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VENUS FLYTRAP MECHANISM

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VENUS FLYTRAP MECHANISM PLANT BODY

Tynes

lower leaf

part

of

midrib of leaf

NECTARY

The Venus Fly Trap features leaves that incorporate multiple nectary cells; these diffuse smells which are attractive to insects.

TRIGGER HAIR

CLOSE LEAVES

[SENSORY CELL]

ELECTIRC STIMULI

The surface of each lobe is adorned with three trigger hairs which act as sensory cells. When an insect is in the vicinity of the lobe and touches the ends of these hairs, the lobes are immediately closed around the insect.

The fly trap conserves its energy by triggering its closing mechanism only after the hairs have been touched multiple times, thus ensuring that an insect has indeed entered the surface.

[

149mN 41kPa open

DIGESTION [PROTEASE]

450mN

] [ 90kPa ] close

HYDRASTATIC PRESSURES

After the insect was captured, an apt generation and distribution of electrical current by the pituitary gland orders the cells to rapidly constrict, causing the blade to bend inwards.

Last, but not least, the plant releases digestive enzymes to the surface between the lobes, thus completing the process of consuming the insect.

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BIOMIMETICS I Venus Flytrap

INITIAL PHASE

CAPTURE PHASE

APPRESSION PHASE

SEALING PHASE

The closing of the Venus Fly trap is drawn by a 5-second stimulation of the trigger hairs. After this condition is met, the movements that follow can be grouped in three stages: 1) Capture – Immediately after the stimulation of the hairs, the trap margins and tynes begin to flex inwards facing the midrib, which causes the tynes to interlock and capture the insect. This process is the fastest one that occurs in the system.

2) Appression - Occurring half an hour after the stimulation of the hairs was detected, this stage is characterized by the fact that the margins are in contact with each other.

3) Sealing – An hour after triggering, the system enters the final stage in which the plant forms a digestive, watertight enclosure around the insect.

Several tissue dynamics assist the fly trap in creating morphological changes to several of its areas. These processes are also time-varying, as the changes that occur are closely linked to the stages described above.

What is remarkable about this plant is that its leaves undergo a complex change in curvature which turns them from a convex shape into a concave one in a short amount of time. The transition from Synclastic to Anticlastic occurs in an even shorter time, during the snapping instance.

concave

convex

Leaf Geometry Closure

during

During the closing period, the leaf of the Venus Flytrap goes through a convex to a concave shape in a small amount of time.

While the transition from Synclastic to Anticlastic occurs for even a shorter period of time in the snapping Instance.

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BIOMIMETICS I Venus Flytrap

LE - lower epidermis LC - lower cortex M - medullary tissue UC- upper cortex UE - upper epidermis 200 Îźm

Although both epidermis layers are very thin (one cell), they are not identical; the upper one also features a thick periclinal wall and a cuticle that are not found on the lower one.

Despite the remarkable anatomic similarity of the upper and lower cortex, the lower one has more cell layers than the other (3-5 vs. 2-3).

About 35%-57% of the trap volume is represented by medullary tissue, which is comprised of emptylooking cells enclosed by large, thin walls.

p- Low pressure

P-

High pressure

The McGraw-Hill Companies, Inc. (http://www.desertbruchid.net/4_GB1_LearnRes_fa10_f/4_GB1_LearnRes_Web_Ch05.html)

Turgor Pressure Plants are subject to a phenomenon called Turgor Pressure, which links the pressure inside them with their water content. A fly trap experiences turgor pressure exchange when water is transferred from cells in the upper epidermis to those in the lower epidermis, causing the latter to expand.

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BIOMIMETICS I Venus Flytrap

ABSTRACTION

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BIOMIMETICS I Venus Flytrap

ABSTRACTION

Having learned how the plant employs curvature to close its leaves by varying the pressure in its cells, we envisioned a system where an addition or removal of pressure from the flexible components of a surface leads to modifications of shape. Specifically, an increase in the pressure applied to the components on one side induces a convex geometry to that side, while a reduction in pressure leads to the opposite effect.

The mechanism observed in the plant relies on water flow, which can be transmitted easily from one cell to another and is readily available in the cells. However, using liquid flow in a real system is not a trivial task, as this could potentially add unwanted weight. Because of this, we thought about other kinds of pressure that are easily transmittable.

(Actuation systems in plants as prototypes for bioinspired devices - I.Burger and P.Fratzl)

The exchange of pressure between cells inside the plant gives a variation in curvature.

The cells subjected to more turgor pressure are those responsible for ‘pushing’ the walls to get the desired curvature.

Using a geometry that contains local spaces similar to cells, we can recreate the plant’s mechanism by adding or removing pressure from various elements.

Instead of using water or any liquid fluid, as plants do, we thought about other kind of pressure that could be trasnmited as easy as water flows through cells. The problem with liquid fluids is that it could add too much weight into the system.

If the actuation of the components is controlled from the exterior, a specific geometry or surface can be obtained by changing the pressure conditions of the appropriate components.

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MATERIAL EXPERIMENT

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MATERIAL EXPERIMENTS Choice of materials is an important stage in the development of a pneumatic system.

For the task at hand, several materials were tested in the search for one which would change curvature according to the air pressure applied to it. Thus, the required material should be flexible, perfectly airtight and pressure resistant.

BLACK TUBE with folded surface.

Attempts to control the shape of the surface by adding pressure to the sides of the tube revealed that no local control over the geometry is possible.

BLAK PLASTIC BAG Using plastic bags as “cells” that could be inflated to affect curvature was shown to be a poor solution. Separating the cells with tape violated the requirement of an air-tight material. Furthermore, plastic is not expandable, which further hindered the desired behaviour. air input

LATEX BAGS A solution employing latex bags proved to be slightly better than that where plastic bags were used.

The system featured three layers of latex bound together with latex glue such that spaces intended for air flow and inflation were exposed.

The fabrication technique, as well as the bonding agent were not adequate for ensuring perfect air-tightness. Some curvature was obtained, but in the end this particular model was improper for mimicking the plant’s mechanism.

air input air input

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SQUARE WATERBOMB PATTERN

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SQUARE WATER BOMB Having chosen the material, the next step required us to integrate the airtight membranes with a solid structure that would enable us to see different curvatures when actuating different membranes situated in different points within the structure. We opted for folded structures in order to reduce the amount of pressure required to actuate the components, as well as the overall weight of the system.

tessellation pattern 1

1 2 4 3

w z

x y

u A

Veterx Point Path

u B

D

1

4

2 3

O

L

C O

In order to understand the behavior of this tessellation pattern, we mapped the path of displacement of each vertex point inside each component.

Each of these travels in an arc path and they meet towards the center.

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BIOMIMETICS I Venus Flytrap

LATEX CELLS EXPERIMENT

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LATEX CELL EXPERIMENTS

After a series of several tests conducted, we discovered a novel method of integrating two sets of membranes within a folded geometry; one would be placed in the centre of the component and would be actuated pneumatically, while the other would be attached to the top of that component and would cause it to spring back to a “locked� position once the air pressure had been drawn out.

FIRST EXPERIMENT GLOBAL GEOMETRY + 1 LATEX CELL

First we tested the behavior of the folded geometry by actuating one single component and see the relationship between the actuation and the change in geometry of the global shape. As we expected, the whole geometry started to change its flat shape into a Synclastic curvature geometry. Adding more actuated components should then start increasing the double curvature.

100 mm 80 mm 60 mm 40 mm 20 mm 0 mm

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BIOMIMETICS I Venus Flytrap

SECOND EXPERIMENT GLOBAL GEOMETRY + 4 LATEX CELL

ELEVATION

100 mm 80 mm 60 mm 40 mm 20 mm 0 mm

100 mm 80 mm 60 mm 40 mm 20 mm 0 mm

100 mm 80 mm 60 mm 40 mm 20 mm 0 mm

TOP VIEW

An early experiment was conducted in order to examine if the actuation of multiple components would affect the global form of the structure, as well as the extent to which this occurred. We concluded that this approach increases the change in curvature, but that there is an inherent lack of control in the amount of pressure applied to each component. The test also revealed that the distribution of pressure to various elements is not easily achieved.

Conclusions: Increased change in geometry and curvature / Lack of control in amount and distribution of pressure.

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ONE COMPONENT EXPERIMENT

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ONE COMPONENT EXPERIMENT

Another experiment was carried out in order to choose the optimum material configuration of the latex membranes. The aim was to make them elastic enough to allow the expansion of the inner membranes, yet tense enough to allow the component to return to its “locked� position once the air from the inner membrane was released. In order to accommodate this, a few minor slits were included on the sides of the outer latex membranes.

Single component experiment To determine the optimum slit within every component.

Conclusions: By performing the experiment on a single component, the optimum position of the slit was determined. It appears that the cut distance must not exceed 74% of the component square unit size, otherwise the amount of pressure applied would not be controlled accurately.

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BIOMIMETICS I Venus Flytrap

SYSTEM FABRICATION

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SYSTEM FABRICATION

In order to make the folding pattern change its shape, we built our own pneumatic system to ensure that air pressure would lead to a folding of the surface. Using a small electric air compressor to provide the pressure for the system, and an air regulator to drop it below 1 bar, we were able to actuate (open) the individual components. A specialized air tight system consisting of pipes and vaults, equipped by Festo was used to transmit the pressure along the whole system, using a simple closed circuit.

SINGLE COMPONENT Outer Latex Membrane

Inner Latex membrane

Closed

Actuated

The air pressure inflates the inner membrane and pushes the walls apart, opening the component. Simultaneously, the outer membrane keeps the component locked when the system is not actuated, stretching it upon actuation.

GLOBAL GEOMETRY

The components in the global geometry were locked from behind in order to have an initially flat configuration, while also showing the results of applying pressure more evidently. When pressure was applied to the inner membranes, the surface curved into a concave shape.

Component

Locked from behind

+ Outer mebranes

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MEMBRANE EXPERIMENT

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MEMBRANE TESTS

In order to improve and optimize the system fabrication, a reduction in the amount of latex used in the inner and outer membranes was tested.

Determining the optimum thickness required to actuate each component was also necessary to make the system accurate enough. To deliver the exact amount of pressure needed for each thickness, an air pressure regulator was attached to the compressor.

Air Compresor

Air Pressure Regulator

Component

100mm 50mm

50mm

50mm

Inner Membrane Unfolded Component

Outer Membrane Folded component

Inner Membrane - Thick latex (.45mm) Outter Membrane - Thin latex (.22mm)

GRID 25x25 mm

Inner Membrane - Thin latex (.22mm) Outter Membrane - Thin latex (.22mm)

GRID 25x25 mm

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BIOMIMETICS I Venus Flytrap

GLOBAL GEOMETRY EXPERIMENT

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previous tests:

- Maximum cuts on top latex layer 74% of sq - Locate disconnected cells:

BIOMIMETICS I Venus Flytrap

GLOBAL GEOMETRY EXPERIMENTS

Global Geometry w/ 4 cells This final experimented gathered the information obtained from previous tests: - Maximum cuts on top latex layer 74% of square unit size - Locate disconnected cells:

When all components are slightly closed, a slightly concave shape is induced in the system.

By applying pressure to the outer membranes, the concavity further increases from this initial condition.

FUTURE OBJECTIVES By regulating the amount of pressure applied by an actuator, curvature can be controlled by inflating or deflating a different combination of membranes. This helps transform sinclastic curvature to anticlastic curvature when each membrane is subdivided in four inner membranes.

Pressuriz membra

PRESSURIZED MEMBRANCES

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BIOMIMETICS I Venus Flytrap

CONCLUSIONS

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BIOMIMETICS I Venus Flytrap

CONCLUSIONS

As the diagrams show, the system achieved a slight change in curvature mainly be¬cause the Square Waterbomb Pattern naturally tends to form a synclastic shape when the components are unfolded. Fabrication issues and using im¬precise materials to build the pneumatic system where also a factor that affected the final re¬sult of the tests.

The system can be improved by using the correct thickness of the latex in the outer membrane, a tweak which can be explored further in future experiments. The same is true for improving the fabri¬cation methodology by looking for a more efficient way of bonding the membranes to the surfaces and hence, making the whole system as airtight as possible.

Further developments can include, but are not limited to, opting for a new folding pattern which gives more flexibility in terms of curvature than the Square Waterbomb pattern, as it would conveniently allow us to obtain other kinds of curvature as well, which would help produce even more shapes. Currently, the design is limited to synclastic curvature.

For instance, the Triangle Waterbomb (also developed

by R. Resch) could provide a more flexible folding pattern that would suit the existing system perfectly. The main advantage of this tessellation is its capability of switching between synclastic and anticlastic curvature, but its ability of translating movement in oblique directions (rather than orthogonal ones) upon the actuation of a component is also a valuable property.

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BIBLIOGRAPHY

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BIBLIOGRAPHY

Books Alexander,G.(2008)Kinetics and Mechanism of Dionaea muscipula Trap Closing.ed.Tejumade Adesina.American Society of Plant Biologiests,pp.694-702 Ingo,B.(2009)Actuation Systems in Plants as Prototypes for Bioinspired Devices.Potsdam:Philosophical Transactions of the Royal Society.pp.1514-1557.

Wayne,R.(1996)A Quantitative Study of Tissue Dunamics in Venus's Flytrap Dionaea Muscipula,II.Trap Reopening.

In:Douglas,G.American Journal of Botany.Durham:The University of New Hampshire.pp.836-842 Yoel,F.(2005)How the Venus Flytrap Snaps.In:Wayne R.Letters to Nature.

Botanical Society of America, Inc.pp.421-425

Cover Page Image: Helene,S.(2010)The Vegetarian's Dilemma:Carnivorous Plants.[Photography]In:National Geographic.

All other images and diagrams were editing,draw and filmed by author(s).

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