Biomimetics_Movement actuation in high pressure pneumatic structures

Emergent Technologies & Design 2015/2016 Core Studio 1 Movement actuation in high pressure pneumatic structures

Patricia Ojeada Francesco M. Massetti Krzesimir Poplawski Sebastian Lundberg

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INDEX

Abstract pag. 4 Introduction pag. 5 Material tests and analysis #1 pag. 6 Global Aggregation #1 pag. 12 Global Aggregation #2 pag. 14 Material tests and analysis #2 pag. 16 Structural analysis pag. 30 Material test and analysis #3 pag. 31 System Logic pag. 32 System variations pag. 36 System performances pag. 38 System prototype pag. 39 Conclusions pag. 40

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ABSTRACT

Starting from the knowledge gained in “Movement actuation in low pressure pneumatic systems, P. Ojeada, F. M. Massetti, K. Poplawski, S. Lundberg, Emergent Technologies & Design, 2015� the main aim of the paper is to proceed within the category of lightweight pneumatic structures analyzing the potential of high pressure systems and the related differencies in material selection and assembling. Materials involved in the research are latex and fabric. Latex permits to be glued to itself more easily than other materials flexible materials such as PVC. Flexible layers that expand indefinitely do not permit to be stiffened and the research moves on the application of fabric layers over the rubber ones, permitting the pressure to be

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constrained within unflexible boundaries that work in tension, counterbalancing the internal and natural predisposition of the air in expanding.

Research tries to exploit material assemblies in order to create architectural shapes with environmental performances, such as shading and shelter. The objective of the project is to design a system which is able to vary its configuration states from a positional point of view through the inflation of local geometries within the system. The general behaviour achieved follows the possibility of being activated through the application of geometric patterns realized in fabric, controlling the angle of rotation between two linear and complanar elements.

INTRODUCTION

Low pressure systems

Air supported structures have been involved in the architectural discourse just in the last two or three decades.

Conversely, the idea of using membranes stabilized by positive pressure has an ancient tradition in human technology.

From a structural point of view pneumatic systems are load-bearing assemblies whose equilibrium in provided through the creation of a pressure gradient between internal and external space.

Many features can be involved in the design process and combinations of them will provide different behaviours and reaction to the loads applied. Some of them are support medium, addition of stabilizing elements, type of curvature, type of membrane material, degree of flexibility, etc.

Low pressure systems are grouped in single and double membrane structures.

In the first case one membrane defines a space in which the pressure is positive or negative, while in the second the internal space is defined by a a membrane whose component are made of two layers curved in opposite directions to each others. This permits not to have pressure differential between inside and outside. Double membrane structure are also called “cushion structures”.

“One of the earliest consideration to focus on is the difference between low pressure and high pressure systems.

In the case of low pression systems the differential pressure of the media divided by the membrane generally amounts to 10 to 100 mm of water pressure. the membrane is thus stressed by a normal pressure of 10 to 100 kp/m2 . In the case of high pressure systems the differential pressure amounts to 2,000 to 70,000 kp/m2.”* While low pressure systems require significant amount of electrical energy, due to the presence of an air compressor that continuously keeps the structure stiff, in high pressure systems it is requested the utilization of valves or mechanisms to constrain the air flow.

High pressure systems Also called “tube structures”, this typology groups all those pneumatic structures in form of tubular elements that show strong curvature in one direction and are able to transmit forces along their main axis. As a consequence they can constitute beams, arches, grids and lattice shells. High pressure sysyems, compared with other structures able to transmit trasversal forces, are quite unefficient, meaning that they will be mainly considerd when high flexibility, easy fabrication and dismantling, low weight and low transport volumes are important parameters within the design process. In addition, they can be easely used in creating supporting patterns for net and membrane structures involved in * high level of tension.

* Pneumatic Structures. A Handbook of Inflatable Structures. Thomas Herzog. New York, Oxford University Press. 1976.

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MATERIAL TESTS AND ANALYSIS #1

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POLYETHYLENE + LATEX The test presents a predifined triangular latex compartment with a size decreasing sealing pattern.

It is then added non-elastic layer of polyethylene 200 Îźm on one side. As a result the latex compartment was filled but the PE cover constrained it from bulging out as much as on the other side. When the whole compartment was filled, the expansion started in the weakest area of the latex, creating an expanding sphere which lifted up the component.

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ISOTROPIC FABRIC + LATEX Keeping on working with the predifined triangular latex compartment with a size decreasing sealing pattern. In contrast to the previous experiment, it is added a layer of an isotropic fabric that is elastic, not only in one direction.

When inflating the component both sides now bulge out evenly until the expansion of the latex begins, to again form a pressured sphere that pushes up the component.

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ISOTROPIC FABRIC + ISOTROPIC FABRIC Here it is added another layer of the fabric, so that both sides where covered, constraining the whole latex compartment. When inflating the component both sides bulge out evenly, but there is no expansion past the maximum elasticity of the fabric that raises it. Because the latex is totally constrained, the compontant can now contain a higher pressure.

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ISOTROPIC FABRIC + ISOTROPIC FABRIC (Rotated 90째) Since the fabric is elastic in one direction, has been decided to redo the previous experiment with one change, rotating the bottom layer of fabric with 90째. This allowed the expansion to react differently on the different sides, showing a raised componant without having a large expanded latex sphere, and still being able to contain a higher pressure.

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GLOBAL AGGREGATION #1

Moving from material experiments and trying to identify possible aggregation model for the component obtained, the first proposal represents an inflatable dome made of a fixed wireframe as main supports for panels grouped in series of six or five elements.

Triangular shape of the flaps allows to form hexagonal or pentagonal clusters subdivided in regular triangules.

While the structure can be inflated all at once in its final configuration, the components are designed to respond in different ways according to the fabrication process and the patterns involved in it.

This configuration has been rapidly abandoned according to the will of not being limited by a rigid and geometric frame. Even if quite reasonable, the proposal was not pushing the boundaries of the system, not permitting to interconnect frame and panels reciprocal influence in the design process.

Overall geometry proposals

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Initial and final stage of inflation simulation

Opening systems proposals

Inflatable dome 13

GLOBAL AGGREGATION #2

Further exploration in testing how the component worked, led the research towards a sligthly different approach.

Instead of looking at the unit as fixed into a frame of defined geometry, it is now the unit arrangement itself that shape its contours. Inflatable flaps are designed to be scalable and deformable, as well as arches supports., and looking at the relation between one arch and the next one, it is clear that the panels area they share has the only limit of being made of two interlocking rows of components. Changing the shape of the area requires every component to be custom design according to a tessellation logic.

The structure is meant to be built starting from the inflatable ribs, element designed to be flexible and adaptable in different shape. Once the final position of the ribs is set, empty and flat flaps are applied in order to cover the volume. When pressure differential is created through injection of air into the panels, they will start to inflate, curling outwards and creating a mesh of openings along the surface that can be set to gradually respond to environmental parameters. Within this logic not only shape and geometry are variable, but also movement velocity and location. Relying on different inputs it is possible to relate inputs located on the surface with local output or external

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Step 1

Closed shape

Step 2

Panels starting to curl and intersect

Step 3

Panels kepp on curling, creating openings

Step 4

Panels start rolling around the supports

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MATERIAL TESTS AND ANALYSIS #2

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Stage 1

Stage 2

Stage 3

FLAT

FILLED

EARLYÂ EXPANSION

There is no air in the latex compartment

The latex starts to The latex expand, revieling its element is filled with air weaker areas which expand faste

Stage 4

The first experiment was made applying pressure to the latex compartment. The rusult showed the possibility to control the expansion to only one point. Only the weakest area of the latex would expand, making it impossible to expand two areas at once.

The single expanding area would then continue expanding and the compartment would never be able to contain a high pressure.

EXPANSION The pressure constrains itself to the the weakest area of the latex compartment, preventing any other area to expand

Stage 1

Stage 2

FLAT

FILLED

There is no air in the fabric constrained latex compartment

The compartment is filled, and the non-elastic fabric prevents expansion and instead allowes for a higher pressure

In the next experiment has been made a sleave out of non-elastic fabric, which we used as a mold around the latex compartment to constrain it.

Restricting it from expanding futher than the mold.

Through this method it is possible achieve a higher pressure in our componant.

Stage 1

Stage 2

Stage 3

FLAT

FILLED

EARLYÂ EXPANSION

There is no air in the compartment

The compartment is filled

The non-elastic fabric prevents expansion in the covered areas, so the pressure gets directed to the area where the latex is exposed

The third experiment was aimed to explore how we could locally bend our componant.

Through making a cut in the previous fabric sleave and exposing the the latex, weit is possible to control the expansion point and get the componant to bend. The exposed latex would grow as a sphere and the two fabric constrained parts would point out perperndiculary from Stage 4 the latex sphere.

Meaning that when EXPANSION the latex sphere The compartment grows, the bending bends when the angle grows. exposed latex expands. The bending point is where the fabrics meet

Stage 1

Stage 2

FILLED

EXPANSION

The compartment is filled

The pressure constrains itself to the the weakest area of the latex compartment, preventing any other area to expand.

Allowing only one of the planned bending points to bend.

Trial to make a component with two bending points. Using the same tecnique as in test number 3, has been sewed a non-elastic fabric sleave to pull over the latex compartment, but now making two cuts instead of one.

Having two areas of exposed latex, the expectations were that both points would expand, creating two bending points. The result was the same as in the first test.

The latex would only expand at its weakest point, meaning that only one of the latex exposed area would

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Stage 1 FILLED The compartment is filled

A fifth experiment to try to solve the problem of multiple bending points, reusing the fabric sleave from the previous experiment, but sewed in an elastic nylon mesh over the two open areas. The pieces we sewed in were a bit bigger than the openings in order to allow for a larger expansion. Initially it reacted in the same way as the previous test, expanding at its weakest point. Though after a while the new mesh would start giving the latex some restraint allowing the late to start expanding at its second weakest point.

These would the expand simultaniously until it reached its final state, when the mesh was streched to its maxium capability, creating two bending points.

Stage 2 EXPANSION The areas covered by elastic fabric is able to expand to a certain point.

The compartment can hold a higher pressure since there’s no exposed latex, allowing the compartment to bend in multiple locations

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COMPARATIVE ANALYSIS OF JOINT-SYSTEM From the previous experiment observations it could be made conclusions on how the design of the joints affects the achieved angle of the bend. We chose the most relevant examples to make a comparison of components with similar shapes in order to accomplish a valid analysis of our joint-system.

1. COMPARISON - CIRCLE / DIAMOND GEOMETRY top view

GEOMETRY top view

d a t a

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PICTURE inflated tube

12

°

DIFFERENCES BETWEEN

CIRCLE

shape

=

DIAMOND

12,00 cm

length

=

12,00 cm

113,00 cm2 (18,83%)

elastic area

41,00 cm2 6,83 %

72,00 cm2 (12,00%)

51° difference 28 %

163°

112°

angle achieved

78°

bending angle

PICTURE inflated tube 17°

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VARIABLES ANALISED

17°

c o n c l u s i o n s

17°

°

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The following analysis is the comparison of two identical joint-lengths with different shapes -a circle and a small diamond- . The size of the elastic area between them differs in 6,83 % (the circle bigger than the small diamond). That small difference drew up a significant difference in the bending angles achieved. The circle-joint bends 78° while the small diamond bends 17°, a 28% difference . Although, it could be thought that a bigger bending-angle would be better in terms of achieving a bigger curvature in the

bending angle

°

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163° 10 2°

structure, an observation was made that at a certain point of inflation the achieved angle of the tube does not change and the elastic area raises, forming a "bubble" until its collapse. In other words, the circle joint shape can achieve larger bending angles than the small diamond but its weakness is related to the difficulty to control its motion, instead the small diamond which bends less gives more stability to the general structure.

angle achieved

2. COMPARISON - CIRCLE / FLAT BASED CIRCLE GEOMETRY top view

GEOMETRY top view

d a t a

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PICTURE inflated tube

14,5

DIFFERENCES BETWEEN

CIRCLE

shape

=

12,00 cm

length

2,5 cm

14,50 cm

113,00 cm2 (18,83%)

elastic area

44,00 cm2 7,33 %

157,00 cm2 (26,17%)

35° difference 19,44 %

137°

102°

angle achieved

78°

bending angle

FLAT BASED CIRCLE

STRETCHED BENDING POINT

PICTURE inflated tube

43°

°

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VARIABLES ANALISED

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BENDING POINTS

STRETCHED BENDING POINT

43°

c o n c l u s i o n s

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43° ° 78

The following analysis is the comparison of two similar joint-shapes with different length -a circle and a circle with flat bases-. The size of their elastic areas differs in 7,33 % (flat based circle larger than the circle). In contrast to the previous example another variable appears. The bending point was stretched and for that reason the

bending angle

°

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137 ° 10 2°

angle achieved

bending angle in the flat based circle is smaller than the circle. (see the bending points in the images). The circle-joint bends 78° while the flat based circle bends 43°. The percentage of the difference between the bending angles resulted in 19,44%.

3. COMPARISON - STRIPED FLAT BASED CIRCLE / FLAT BASED CIRCLE

14,5 1,5

STRETCHED BENDING-POINT

STRETCHED BENDING-POINT

PICTURE inflated tube

GEOMETRY top view

*the area of the rectangle is 600 cm2 the percentages are related to this area

STRETCHED BENDING-POINT

d a t a

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DIFFERENCES BETWEEN

shape

=

FLAT BASED CIRCLE

7,50 cm

length

2,5 cm

14,50 cm

88,00 cm2 (14,67%)

elastic area

69,00 cm2 11,50 %

157,00 cm2 (26,17%)

2° difference 1,11 %

137°

139°

angle achieved

41°

bending angle

STRETCHED BENDING-POINT

PICTURE inflated tube

43°

41°

VARIABLES ANALISED

STRIPEDFLAT BASED CIRCLE

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GEOMETRY top view

43°

c o n c l u s i o n s flat based circle raises faster than the striped flat based circle, it keeps expanding without affecting the angle.

The striped flat based circle something unexpected occurs, the strips integrate the torsion as a new feature, meaning that as well as bending it incorporates a third angle of direction.

43° 41°

The following analysis is the comparison of two similar joints in terms of shape -a striped circle flat bases and a circle flat bases- . The difference in size of the elastic areas differs in 11,50 % (the flat bending angle based circle bigger than the striped flat based circle). Although, the differences 2° 139 between them do not lead to a ° significant difference in the degrees of 137 ° bending angles, the inflation process is completely different in both. While the

angle achieved

4. COMPARISON - BIG DIAMOND / DIAMOND

WITH

ROUND VERTICES GEOMETRY top view

GEOMETRY top view

d a t a

24,5

PICTURE inflated tube

VARIABLES ANALISED

24,5

DIFFERENCES BETWEEN DIAMOND WITH

shape

=

24,50 cm

length

=

24,50 cm

147,00 cm2 (24,50%)

elastic area

55,00 cm2 9,17 %

92,00 cm2 (15,33%)

38° difference 21,11 %

149°

111°

angle achieved

69°

bending angle

PICTURE inflated tube

31°

°

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DIAMOND

ROUND VERTICES

31°

c o n c l u s i o n s

31°

°

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The following analysis is the comparison of two identical joint-lengths with different shapes -a big diamond and a diamond with round vertices- . The difference in size of the elastic area differs in 9,17 % (the big diamond bigger than the diamond with round vertices). That contrast between them drew up a significant difference in the bending angles achieved. The big diamonds bends 69° while the diamond with round vertices bends 31°.

bending angle

°

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149° 11 1° angle achieved

That difference is due to the round vertices which control the expansion of the elastic area. From that experiment it can be concluded that round vertices are better to control the expansion and sharp angles are not suitable to those areas because they tend to brake at high pressure.

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CATEGORISATION BY JOINT SHAPES 3rd GROUP - GREEN

1st GROUP - PURPLE

length

6,00 cm

angles

166°

x100%

35%

12,00 cm 102° x21%

19%

14,50 cm 137°

3,5

12,00 cm 163°

a09

x105%

7

24,50 cm 111°

a02

=

8,5 a04

2nd GROUP - BEIGE

3,50 cm 6,00 cm

39%

90° 27%

x25%

7,50 cm

25%

24,50 cm 157°

14,5 a03

a11

2

4th GROUP - BLUE

160°

x72%

x29%

7 a08

139°

5 a07

a01

5

12,50 cm 168° 11%

x105%

8,5

24,50 cm 149°

a05

7,5 a10

14,5 a06

GRAPH / relation between JOINTS shape-length and angles achieved 180° 170° 160° 150° 140° 130° 120° 110° 100° 90° 80° 70° 60° 50° 40° 30° 20° 10° 0°

a03

25.00

a06

20.00

a11

a02 a07

a05

a08

a09

28

15.00 a04

10.00

a10

ANGLES

5.00 a01

CM

TESTS AND ANALYSIS INFORMATION *

The joints designed and studied where categorised into 4 groups.

Each group is defined by a colour.

First group - PURPLE: circle and similar shapes.

Second group - BEIGE: circle and similar shapes with the addition of strips.

Third group - GREEN: different types of diamonds Fourth group - BLUE: diamonds with round vertices.

*

The component consists of a latex compartment covered by a sleeve made of two different fabrics. A non elastic cotton fabric, restraining the latex from expansion, and an elastic nylon mesh used in the joints to allow expansion which create the bending angle.

*

The dimensions of the unrolled sleeve is 40 cm x 15 cm, resulting in an area of 600 cm2.

*

The percentage analysis of the elastic areas is in relation to the 600 cm2 of the unrolled sleeve.

*

The percentage analysis of the angles is in relation to the 180째 maximum possible bend.

*

"Bending angle" refers to the amount of degrees it is bent.

*

"Achieved angle" refers is the inner angle achieved as a consequence of the bending angle.

GENERAL JOINT - SYSTEM CONCLUSIONS 1.

Variables such as size , shape, length and the fragmentation of the opening areas affects the angle achieved in the component.

2.

The analysis of the testing process of the joints showed that single angles behave differently in a small tube than in a tube of three joints. It can be infer that the length of the tube influences their behaviour due to that the air has to fill a larger volume.

3.

It was found that in most of the experiments there is a negative relation between the size of the elastic area and the angles achieved, meaning that the bigger the elastic area is the smaller the angle achieved. That is due to that the elastic area expands forming a "bubble" that avoids the bending motion.

ELASTIC AREA difference *11,50 %

ANGLES difference 1,11 %

(comparison 3)

7,33 %

19,44 %

(comparison 2)

9,17 %

21,11 %

(comparison 4)

6,83 %

28,00 %

(comparison 1)

A conclusion can be made that the patterns of the joints are more important in controlling the angles than the amount of exposed elastic area.

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STRUCTURAL ANALYSIS

Segment geometry variation: _length _angle

Supports amount: _certain variation of the geometry require additional supports

min. displ.

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max. displ.

MATERIAL TESTS AND ANALYSIS #3 Time control The next idea was to focus more on the usage of material and pressure, rather than joint patterns. Hypothesis was that by using multiple bending points with the same joint pattern in one componant, would be possible to cover the openings with different fabrics that would have the same final stage of expansion, but take different amounts of time to reach that stage. Though this method it would be possible to control the bending points seperately still using only one pressure sorce.

To test this the box containing a latex compartment from earlier elasticity tests was reused. This time three experiments are made with different amounts of layers of the elastic nylon mesh, in hope that they would reach the same final state, at different times. The same amount of pressure is inserted to all of them and timed it. As a result the three experiments reached approximately the same final state, with very small differences. But the time difference was more extreme.

Test 1, One layer- 16 seconds

Test 2, Two layers - 21 seconds

Test 3, Three layers - 36 seconds

After these experiments the layers of nylon mesh has been attached to the joint openings of a non-elastic fabric sleave, to see if the hypothesis would be correct. Three equally spread bending points are covered cronologically with the nylon mesh, nr.1 with one layer, nr.2 with two layers and nr.3 with three layers. It was hoped that the result would be that nr.1 would bend first, followed by nr.2 and then nr.3. Meaning that you could then control the bend of nr.3 on its own, since nr.1 and 2 would have already been expanded to their maxium capability. The problem was that the the multilayered joints had too much resistance and didn’t allow the expansion to behave as needed. Instead of bending the component, joint nr.3 just created a pressures “bubble” on it.

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SYSTEM LOGIC_segment length = 260 units

Amount of segments

Angle 300

3

4

5

6

7

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500

700

900

1100

SYSTEM LOGIC_angle = 300

Amount of segments

Length 200

260

320

380

440

3

4

5

6

7

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SYSTEM LOGIC_amount of segments = 4

440 200

260

320

380

Length

Angle

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300

500

700

900

1100

l1

l1

α1 l1 α1 l1

l1 α1 l1 l1

var.01 single arch

l2 l2 α2 l1 l2 l2

α2 l1 α2 l1

var.02 two arches l3 α3 l1

l3 l3

α3 l1

l3

α3 l1

var.03 three arches

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SYSTEM VARIATIONS

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SYSTEM PERFORMANCES

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SYSTEM PROTOTYPE

The prototype was meant to explore and show how different components would work together when combined and linked to the same actuator.

Three different components were used. Each component had its own joint pattern on three equally spread bending points. When applying pressure the three components would rise simultaniously until their inner latex compartment would be filled.

Then when the expansion starts they

would start behaving differently. Each component reacted according to its joint pattern, but was also affected by the movement of the adjacent components. The result of this was that while applying pressure we could achieve many different geometries on the way to the structures final state. As each component has its own valve, the structure could also be manipulated by opening and closing them at different time during inflation.

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CONCLUSIONS

The tubes are not stiff until all the expandable area is filled.

The more joints there are, the more flexible and unstable the structure becomes.

Very strong materials and perfect fabrication is required to be able to handle the amount of pressure that is needed to stiffen the structure.

Using one actuator wih different patters in different tubes gives us a many changing geometries during the deployment.

Blocking the airflow in some tubes at different moments enables us to control the geometry of the strucutre.

Using only pneumatics is not enough to raise one end of the tube up in the air.

Variables, such as size, shape, length and the fragmentation of the opening areas, affect the angles achieved in the tubular structure.

The testing of the joints analyses, that single angles behave differently in a tube of three joints.

There is a negative relation between size of the elastic area and the angles achieved.

The angle achieved will depend on the lenghth and shape of the joint.

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