WO2018033422A1

WO2018033422A1 - Autonomous shading system based on coupled bilayer elements

Info

Publication number: WO2018033422A1
Application number: PCT/EP2017/069946
Authority: WO
Inventors: Ingo BURGERT; Chiara VAILATI; Markus RÜGGEBERG
Original assignee: Eth Zurich; Empa, Eidgenössische Materialprüfungs- Und Forschungsanstalt
Priority date: 2016-08-18
Filing date: 2017-08-07
Publication date: 2018-02-22
Also published as: EP3284876A1

Abstract

The invention relates to a shading device. This device comprises a pivot mounted shading element and an actuator element for turning the shading element in a rotary movement. The actuator element comprises a first and a second end and is fixed to a base with the first end. The actuator element is able to reversibly bend its shape in response to environmental parameters, wherein the second end bends towards the shading element in a bending movement. The shading element and the actuator element are arranged in such a way that the bending movement results in an interaction of the elements, achieving the rotary movement of the shading element.

Description

Autonomous shading system based on coupled bilayer elements Field of the invention

The present invention relates to a shading device that adopt in an autonomous fashion to environmental conditions in a repeatable and reversible manner. Background of the invention

Energy efficiency is an important topic in the building industry. A total final energy consumption of 37% is caused in Europe by the building sector, out of which a maximum share of 68% can be attributed to the HVAC (heating, ventilation and air conditioning) systems of the buildings. Considering the lifespan of a building, a minor fault in design or in the choice of architectural solutions can have a severe effect on life-time energy balance.

One factor to be considered is the energy gain of buildings due to sun-radiation. Therefore, efficient shading systems have a profound effect on overall energy balance of buildings. The most functional shading systems, available on the market, are external ones (Brise Soleil). They reduce the heat gain into the building by deflecting the sun rays.

The external shading systems existing in the prior art can be grouped into two categories, depending on the mounting of the shading sheets. One category uses fixed sheets, whereas the other category makes use of moveable elements.

Fixed shading systems cannot adapt to the change of the direction of light incidence and hence, they are used preferably on the south facade of a building.

In the latter category, the sheets are usually motor-driven in order to follow the movement of the sun and thereby adapt the shading according to the need. In some of these shading systems, the angle-inclination of the sheets varies due to the change of the azimuth angle of the sun. These motorized systems are more adaptable, but they are less eco-friendly due to the energy requirements and consumption. Furthermore, they are more expensive due to the complex electronic configuration. The anchorage or rotation systems of the motorized models are also sensible to weather conditions like wind or heavy showers. Furthermore, the anchorage and the rail system need a continuous maintenance in order to keep it functioning.

The use of renewable functional materials with intrinsically implemented stimuli- responsiveness and with an autonomous actuation, that can be predicted and programmed, could offer an innovative solution for smart architectural applications. One possibility is to utilize the deformation principle of bilayer elements in a shading system. Here the inventors provide a shading system based on mechanically coupled bending elements, particular bending bilayer elements.

The problem underlying the present invention is to provide the means for a shading system that can adapt the degree of shading to changing environmental conditions without the use of expensive components such as sensors or motor-driven units.

This problem is solved by the subject-matter of the independent claims. Description of the invention

The finding was made that the combination of materials with different directional elongation properties in response to changes in environmental parameters, particularly within a bilayer element, can be used for an autonomous and adaptive shading system.

The main teaching provided by the present invention is the mechanical coupling of such adaptive bilayer elements with shading elements. Each bilayer element needs a certain thickness to withstand weather conditions such as snow load and wind forces. This is a limiting factor as the thickness of a bilayer element is inversely proportional to its curvature during the change of environmental conditions. Hence, the required thickness for a single bilayer element results in a longer duration to reach the bending needed for the function as a sun shelter. The combination of such bilayer elements with an additional shading element in a way that a lever arm configuration is achieved, allows for a sufficient thickness of the layers and to increase the speed and to amplify the movement of the shading element.

The term autonomous refers to the actuation as not motor driven by an extrinsic system of control (based on sensor, processor and actuator). The actuation is intrinsic, due to the materials response and interaction to the change of the environmental factors, and it is predictable.

The terms repeatable and reversible refer to the mechanism and mechanical behaviour of the lever coupled bilayer elements. Possible effects of delamination could occur due to internal mechanical stresses along the interface glue-wood of the wooden bilayer elements. Furthermore, for the mechanical coupling of the wooden bilayers, the possible relaxation of the actuator element, due to the repeatedly applied load of the shading element, has to be considered.

In the context of the present specification, the term wood material refers to any material comprising wood as an essential part, in particular solid wood products, wood-containing base materials or wood-based materials.

In the context of the present specification, the term solid wood product refers to timber products, which consist basically of solid wood or solid wood parts. Solid wood describes wood-containing base materials, whose profiles are carved out from a tree trunk and are potentially processed further by cutting/machining, without changing the texture of the wood. Solid wood products can be used to produce components, semi-finished products or products.

In the context of the present specification, the term wood-containing base materials refers to all wood-containing materials, which can be used as base materials for the production of wood-based material, components, semi-finished products, products or solid wood products. Wood-containing base materials can include wooden particles or wood pieces, for instance, which are used in the production of chipboards, oriented strand boards or other wood-based materials. Wood-containing base materials are especially used in the production of wood- based materials.

In the context of the present specification, the term wood-based materials refers to a material, which is re-assembled and consists of fibres, particles, or layers of wood of different shape, size and thicknesses. The particles can for example comprise wood strips, wood chips or wood fibers of the same or of different types of wood, of a certain size or of different sizes.

According to a first aspect of the invention, a shading device is provided. The shading device comprises a pivot mounted shading element and an actuator element for turning the shading element in a rotary movement. The actuator element comprises a first and a second end and is fixed to a base with the first end to avoid movement of this first end. Furthermore, the actuator element of the present invention is able to reversibly and repeatedly bend its shape in response to environmental parameters. This bending movement bends the second end of the actuator element towards the shading element and back again in the reverse action. The actuator is arranged in such a way that the bending movement results in an interaction with the shading element and this interaction is achieving the rotary movement of the shading element. In particular the actuator element is bending towards the shading element and the force generated by the bending is transferred onto the shading element that is pushed by the actuator element. Since the shading element is pivot mounted, the force transferred by the actuator element results in the rotary movement of the shading element.

The bending movement of the actuator element correlates closely with the environmental parameter that drives the bending movement. The environmental parameter influences the material of the actuator element in such a way that forces within the material, caused for example by swelling or shrinking, bend the material in one predominant direction. The predominant direction for the bending of the actuator element is towards the shading element. The types of material suitable for such an actuator element would for example include bimetals, thermosensitive synthetic polymers or materials made up of multiple layers with different swelling or shrinking characteristics, such as two different layers of wood. A change of the environmental parameter back to the original value would also result in the actuator element returning to the original shape. Therefore, the bending movement is reversible.

In certain embodiments, the actuator element and/or the shading element (including the first and the second layer of the bilayer element) are of an essentially rectangular shape (including a square shape) having four sides. The first and the second end of such an essentially rectangular shape is defined for the actuator element as the first end being fixed to a base and the second element is the side being parallel to the side of the first end.

The axis running from the first to the second end of the rectangular shape is also referred to as the longitudinal dimension (interaction length).

In certain embodiments, the actuator element comprises a bilayer element. This bilayer element comprises a first (active) and a second (passive) layer, wherein the layers differ in their shrinking and swelling properties in the longitudinal direction of the element (interaction length). The predominant direction of swelling and shrinking of the active layer, runs along the interaction length (Figure 1 A). The swelling and shrinking of the bilayer element is in response to environmental parameters and results in the reversible bending movement of the actuator element.

In certain embodiments, the shading element is a non-bending element.

In certain embodiments, the shading element is able to reversibly bend its shape in response to environmental parameters. The shading element, having a first and a second end, comprises a bilayer element. This bilayer element comprises a first and a second layer, wherein the layers differ in their shrinking and swelling properties in the longitudinal direction of the element (interaction length), The swelling and shrinking of the bilayer element is in response to environmental parameters and results in the reversible bending movement of the shading element. The advantage of shading elements able to reversibly bend their shape is an enhancement of the rotary movement by different interaction with the actuator element. Furthermore, a bent shape can also be beneficial to shed rainwater or snow and to withstand snow load and wind forces.

In certain embodiments, the first layer (active layer) of the bilayer element has a variable thickness along the axis of the interaction length (longitudinal dimension). The bending movement of the bilayer element is inversely proportional to the overall thickness of the bilayer. Different thickness in different sections of the bilayer element would result in a higher velocity of bending. The first layer can increase or decrease continuously over the longitudinal dimension resulting in a wedge-shaped layer. The first layer could also increase and decrease multiple times along the longitudinal dimension resulting in a roughly wave shaped layer or saw tooth profile. A saw tooth profile could also result by a first layer that consists of diagonal stripes of the material.

In certain embodiments, the first layer (active layer) of the bilayer element has a variable thickness along the width (for definition see Fig. 1 A). The bending movement of the bilayer element is inversely proportional to the overall thickness of the bilayer. Different thickness in different sections of the bilayer element would result in a different velocity of bending and different maximal bending achieved in this section. A variable thickness of the layer can result in different shapes. The first layer can increase or decrease continuously over the longitudinal dimension resulting in a wedge-shaped layer. The first layer could also increase and decrease multiple times along the longitudinal dimension resulting in a roughly wave shaped layer or saw tooth profile. A saw tooth profile could also result by a first layer that consists of diagonal stripes of the material.

In certain embodiments, the bending movement of the bilayer element has a minimal and a maximal bending state within the below defined parameters. The slope angle of an axis running from said first end to said second end of said bilayer element in the minimal bending state and such an axis in the maximal bending state differs by up to 90°, particularly by up to 45°, more particular by up to 25° from the other axis. One factor that determines the maximal bending state is the material the bilayer element is made of and the length of the bilayer element. The maximal bending state of the bilayer in the coupled configuration (actuator and shading element) is also dependent on the weight of the shading element. The heavier the shading element is the more force is resisting the bending movement of the actuator element thereby decreasing the angle of the maximal bending state.

In certain embodiments, the predominant shrinking and swelling properties (length change) of the element in response to the environmental parameters of the first layer (active layer) is up to 9%, particularly 6% to 3% more particularly 5% to 4%, of its longitudinal dimension.

In certain embodiments, the predominant shrinking and swelling properties in response to the environmental parameters of the said second layer (passive layer) is less than 1 %, particularly 0% to 1 %, more particularly 0% to 0,5% of its longitudinal dimension.

In certain embodiments, the difference between the predominant shrinking and swelling properties in response to the environmental parameters along the axis running from the first to the second end (interaction length) of the layers in the bilayer element is at least 3%, particularly 9% to 3%, more particularly 5.5% to 4.5%. In certain embodiments, the difference between the predominant shrinking and swelling properties in response to the environmental parameters is around 5%. The bending movement of the bilayer element is dependent on several factors. The different shrinking and swelling properties of the layers in the bilayer element have a profound effect. Thereby the difference in the shrinking and swelling properties of the layer is more important in determining the curvature of the maximal bending state than the absolute value of the properties of the single layers.

In certain embodiments, the first layer and the second layer consists each of a flexible material.

In certain embodiments, the optimum ratio of the elastic moduli of the first and the second layer of the bilayer element depends on the parameter setting.

The interplay of the thickness ratio of the first layer and the second layer and the stiffness ratio of the first and the second layer determine the amplitude of bending. For each stiffness ratio, there exists an optimum thickness ratio to achieve the same maximum bending (Timoshenko, Analysis of Bimetal thermostat, 1925).

In certain embodiments, the shading element has a stiffness and a breaking strength suitable to withstand snow load and wind load. The shading element has to have the required strength to avoid any break or suffer from deformation by the snow or wind load. The required strength strongly depends on the location the shading device is used. The person skilled in the art finds the required strength for example in national or regional guidelines such as NTC2008 for Italy or Eurocode 1 : Actions on structures (EN 1991 ) on the European level.

In certain embodiments, at least one of the layers of the bilayer element comprises a fibre containing material. The fibres of each layer are essentially parallel to each other in the same layer, but have a different orientation in respect to the fibres of other layer. The shrinking and swelling direction of fibre containing material, in particular wood, is perpendicular to the orientation of the fibres. As mentioned above the difference in shrinking and swelling properties between the layers is the major determinant of the bending movement. Therefore layers with a different fibre orientation have a higher difference in their swelling and shrinking properties.

In certain embodiments, the fibre containing material is a hygroscopic material. An increase in moisture content results in swelling of the material along an axis perpendicular to the fibre orientation (or perpendicular to the cellulose fibril orientation at the cell wall level). Conversely, a decrease in moisture content results in shrinking along the axis perpendicular to the fibre orientation.

In certain embodiments, the fibre containing material is a wood material and the environmental parameter resulting in the bending movement is humidity.

Wood material is naturally prone to swelling and shrinking depending on changes in the moisture content of the wood material. The direction of the swelling and shrinking is mainly dependent on the orientation of the wood fibres, which run in an essentially parallel direction. The directions perpendicular to the orientation of the wood fibres experience high degrees of swelling and shrinking, whereas the direction parallel to the wood fibre orientation experiences the least degree of swelling and shrinking.

Changes in the moisture content of the wood material, which is the primary cause of swelling and shrinking is dependent on several parameters. Changes in humidity have a strong effect on moisture content and therefore swelling and shrinking. Relative humidity drops from approx. 90% to approx. 40% on a sunny day from the last part of the morning, especially around noon, until the first part of the afternoon, when the shading function is required most. But other environmental parameters such as temperature, sun light exposure or wind can also affect evaporation or resorption of moisture into the wood material.

In certain embodiments, the actuator element and/or the shading element is comprising a first layer of wood cut tangentially, with the fibre orientation perpendicular to the interaction length (Fig. 1 A), and a second layer of wood cut radially, with the fibre orientation parallel to the interaction length, is provided. Such an element would exhibit a strong bending movement in response to changes in the moisture content of the wood material. Such a change in moisture content can be caused for example by a change in humidity.

In certain embodiments, the first and the second layer of the bilayer element are glued together. Any adhesive that provides the necessary adhesion is suitable. Non-limiting examples of suitable adhesives are polyurethane adhesive, melamine urea formaldehyde (MUF) adhesive, epoxy adhesive and phenol-resorcinol-formaldehyde (PRF) adhesive.

In certain embodiments, the actuator element is comprised of at least two different sections, wherein the sections are selected from a non-bending element and a bilayer element. The non-bending element would not show a reversible and repeatable bending movement in response to a change in environmental parameters, such as the bilayer element. A non- bending element would essentially keep its shape. Such an actuator element can for example be comprised of a bilayer element and a non-bending element or two different bilayer elements. Other actuator elements comprise three or more elements. By including sections with a different curvature in their maximal bending state or even sections with no bending at all the response of the actuator element can be adjusted to the required amount of rotary movement of the shading element. An adjustment of the degree of rotary movement for the shading element can be necessary in different geographical locations or different climates to guarantee optimal shading at the times required most.

In certain embodiments, the shading element is comprised of at least two different sections, wherein the sections are selected from a non-bending element and a bilayer element. The non-bending element would not show a reversible and repeatable bending movement in response to a change in environmental parameters, such as the bilayer element. A non- bending element would essentially keep its shape. Such a shading element is for example comprised of a bilayer element and a non-bending element or of two different bilayer elements.

In certain embodiments, the layers of the additional bilayer element are arranged in such a way that the predominant swelling and shrinking properties have the same direction as the other bilayer element.

In certain embodiments, the layers of the additional bilayer element are arranged in such a way that the predominant swelling and shrinking properties have the opposite direction as the other bilayer element.

In certain embodiments, the bending movement of the additional bilayer element in the additional section has the opposite bending direction as the other bilayer element. This would result in a bilayer element that has an S-shape in its maximal bending state. In the context of the present invention, an S-shape refers to a shape that is characterized by a concave and a convex part. These parts do not have to be of the same size or same curvature as they would have in a perfect S-shape. The advantage of a bilayer element, particularly a shading element, is to avoid overturning of the bilayer element. The center of mass is closer to the fulcrum in a shading element of a S-shape as compared to a shading element of a straight shape or a C-shape. This resists an overturning motion of the shading element (in particular this is of relevance when the bilayers are fixed with a horizontal orientation into a vertical frame structure).

In certain embodiments, the shading element can also comprise or consist of elements such as photovoltaic modules. The shading element of the invention is changing its position in response to changes in environmental parameters. Environmental parameters that are directly or indirectly affected by the sun (sunlight, temperature, humidity etc.) could be advantageous to change the position of a shading element comprising a photovoltaic module. This would align the photovoltaic module in a favourable orientation in respect to the sun rays and increase the efficiency of the module.

In certain embodiments, the actuator element and the shading element are arranged in such a way that the shading element is a class 2 or class 3 lever and said actuator element provides the effort force.

Levers are classified by the relative positions of the fulcrum (pivot), the effort (input force) and the resistance (weight force of the lever arm). This allows the identification of three classes of levers by the relative locations of the fulcrum, the resistance and the effort (Davidovits, Paul (2008). "Physics in Biology and Medicine"). For a class 1 lever the effort is applied on one side of the fulcrum and the resistance on the other side. The relative positions are effort, fulcrum and resistance or vice versa.

For a class 2 lever the effort is applied on one side of the resistance and the fulcrum is located on the other side. The relative positions are effort, resistance and fulcrum or vice versa.

For a class 3 lever the resistance is on one side of the effort and the fulcrum is located on the other side. The relative positions are resistance, effort and fulcrum or vice versa.

By changing the location where the effort force (supplied by the actuator element) is applied, the location of the pivot (fulcrum) in the shading element or the shape and weight of the shading element (resistance), the person skilled in the art is able to arrange the actuator element and the shading element in a configuration corresponding to a class 1 , class 2 or class 3 lever.

In certain embodiments, the shading element is a lever. The bending movement of the actuator element provides the effort or input force for turning the shading element in a rotary movement. The pivot of the shading element represents the fulcrum and the weight force of the shading element is the resistance.

In certain embodiments, the shading element is arranged as a class 3 lever. Therefore the pivot (fulcrum) is mounted on one end of the shading element and the actuator element is arranged in such a way that the effort force is applied in a position between the pivot and the weight force (resistance) of the shading element.

In certain embodiments, the shading element is arranged as a class 2 lever. Therefore, the pivot (fulcrum) is mounted in a position between one end and the middle of the shading element. The actuator element is arranged in such a way that the weight force (resistance) of the shading element is located between the pivot and the position where the effort force is applied.

In certain embodiments, the shading element is arranged as a class 2 lever. Therefore the pivot (fulcrum) is mounted in a position of 1/3 of the length (longitudinal dimension) of the shading element from the first end of the shading element. The actuator element (and thereby the effort force) is arranged in such a way that the weight force (resistance) of the shading element is located between the pivot and the position where the effort force is applied.

In certain embodiments, a weight is attached to the second end of the shading element. This weight increases the resistance (weight force) of the shading element lever arm to assist the bending movement from the bent state into the essentially unbent state. In certain embodiments, the actuator element and the shading element are arranged in an essentially parallel orientation in a minimal bending state.

In certain embodiments, while in a minimal bending state the actuator and the shading element (being essentially parallel to each other) overlap with each other for at least 30% of their longitudinal dimension, particularly for at least 50% of their longitudinal dimension, more particularly for at least 80% of their longitudinal dimension.

In certain embodiments, the actuator element and the shading element are arranged in typologies 1 to 5 as detailed in figure 2A.

The typologies of the coupled bilayers that could be used are presented in figure 2A. They are defined as typologies 1 , 2, 3, 4 and 5. The bending of the actuator element and the effort which is applied by that on the shading element can be varied. This variation is due to the momentum produced by the resistance (the weight force) of the shading element. Also this momentum varies by the different length of the resistance-arm (in respect to the fulcrum).

The typology 1 is disadvantageous in respect to the other typologies, because the effort force is between the fulcrum and the resistance.

The lever typologies 2, 3, 4 and 5 are more advantageous than typology 1 , because the resistance is between the fulcrum and the effort generated by the actuator element.

The typologies 2 and 3 and the typologies 4 and 5 are similar to each other. Typology 2 and 5 bend into a concave shape that avoid the overturning of the shading element (in case that the active layer loses a lot of moisture content (MC) for instance at a very sunny day). The shading element will need lower effort, due to the smaller momentum. The arm of the, resistance, here the center of mass of the shading element, is in fact shorter in comparison to the typologies 2 and 5.

According to a second aspect of the invention a shading system is provided. This shading system comprises a multitude of shading devices according to the first aspect of the invention. These shading devices are arranged within a frame.

In certain embodiments, the shading devices are arranged vertically within the frame of the shading system. The vertical arrangement of the shading devices into a frame is beneficial for coping with snow loads, which are a general challenge for shading systems during the winter season.

In certain embodiments, the shading system is configured to be mounted on the facade of a building. The invention is further illustrated by the following examples and figures, from which further embodiments and advantages can be drawn. These examples are meant to illustrate the invention, but not to limit its scope.

Short description of the figures

Fig. 1 shows a bilayer element in its general configuration A) and its B) bending in response to changes in relative humidity (RH).

Fig. 2 shows A) the arrangement of the shading element (1 ; 10) and the actuator element (2; 20) in a straight unbend configuration (dashed lines) and in the bend state (solid lines). The shading element is mounted on a pivot (3), whereas the actuator element is fixed with its first end to a base (4). The reference numbers shown for typology 1 are also valid for the other typologies. B) shows the forces that result in the rotary movement of the shading element in the different typologies and assign a lever class to the different typologies.

Fig. 3 shows A) changes in the shape of the actuator element and the shading element in response to changes in the relative humidity. B) Graphical definition of the angles a and b.

Fig. 4 shows in the upper graph the changes in relative humidity in percent (continuous black line) and temperature in °C (dashed grey line) in a climate chamber. In the lower graph the response to this change in humidity on the angle a of the shading element (black dashed line) and angle b of the actuator element (continuous grey line) is plotted.

Fig. 5 shows a shading system using the shading devices of the present invention. The upper picture shows an example of how such a shading system is mounted on the facade of a building, with the configuration of the shading devices shown in the lower picture.

Fig. 6 shows an embodiment of a shading system using the shading devices of the present invention in A) a closed configuration, B) an open configuration and C) as 3-dimensional model in a normal view and in an exploded mode of the rotation mechanism and the constrains chosen for the actuators and shading elements.

Fig. 7 shows an embodiment of a shading system according to the present invention. The vertical frame of this embodiment is mounted parallel to the facade of a building, with the actuator element and the shading element being arranged horizontally in the unbend state. The four shading system configurations shown have the typologies 1 , 2, 4 and 5 as indicated in the picture. The shading devices are shown in different states of bending. 8 shows actuator elements with varying shapes of the first layer (active layer) in response to changes in relative humidity from 85% to 35%. The active layer was made by beech with a transverse section (along the width) in some case milled with a milling machine and in some case not milled. The milling operation was done in order to have some strips with a horizontal shape or a diagonal (45°) one. The beech layer has therefore a thickness along the width that varies from 4 mm to 1 mm. The shapes tested are on the left side from top to bottom homogeneous (not milled), a diagonal, a horizontal and a homogeneous again. The shapes on the right side are from top to bottom a diagonal, a horizontal, a homogeneous (not milled), a diagonal and a horizontal again.

9 shows a schematic view of the different shapes of the first layer (active layer). The shapes are of three typologies (homogeneous, with horizontal and diagonal (45°) orientation), as described above. The drawings represent the test-geometries in a flat configuration (left picture; for relative humidity around 85%) and in a bending configuration (right picture; for relative humidity around 35%)

Examples

The present invention provides an autonomous shading system based on coupled bilayer elements.

The invention makes use of the responsiveness of bilayer elements to changes in environmental parameters and by utilizing a mechanical interaction of these elements, the movement of the shading element is enhanced.

Proof of principle model using wooden bilayer elements

The wooden bilayer elements of the invention can be used as lamellae with a function of sun shelters. The lamellae can reduce the thermal load on a building or any other structure. This is achieved by intercepting the sun radiation before they can reach the building envelope.

Due to the daily and yearly movement of the sun, the lamellae have to rotate and to be adaptable to reduce the energy gain caused by sun radiation. The adaptability is also important due to the possible different geographically settlements of the building (and the variation of the azimuth angle of the sun).

The materials used and the bending movement can be seen in Fig. 1

One material especially suitable to exercise the teaching of the invention is wood. The hygroscopic sensitivity of wood to the change of the relative humidity, the temperature and the exposure to the solar radiation is used in a bilayer element. Thereby the natural ability of wood to shrink and swell is used to provide a directed bending movement. This is especially useful since the necessary movement of a shading element is only provided when shading is required.

Wood material is naturally prone to swelling and shrinking depending on changes in the moisture content of the wood material. The direction of the swelling and shrinking is dependent on the orientation of the wood fibres, which run in an essentially parallel direction. The directions perpendicular to the orientation of the wood fibres experience high degrees of swelling and shrinking, whereas the direction of the wood fibre orientation experiences the least degree of swelling and shrinking. The actual degree of swelling is dependent on the type of wood specimen used.

The wooden bilayer elements are made of a spruce layer (0.8 mm) and a beech layer (4 mm) glued together with polyurethane adhesive. Any adhesive that provides the necessary adhesion while still being flexible enough to allow for bending is suitable. Non-limiting examples of suitable adhesives are polyurethane adhesive, melamine urea formaldehyde (MUF) adhesive, epoxy adhesive and phenol-resorcinol-formaldehyde (PRF) adhesive.

The beech layer is cut tangentially, with the fibre orientation perpendicular to the longitudinal axis of the element (interaction length) (Fig. 1 A). The spruce layer is cut radially, with the fibre orientation parallel to the longitudinal axis of the element (Fig. 1 A). By using a different fibre orientation of the wood layers and the wood hygro-responsiveness, a bending is achieved.

The dimensions of the wooden bilayers used are 130 mm width and 430 mm length.

The actuation, due to the lever configuration, and the intrinsic bending of the wooden bilayers are dependent on the difference of swelling parallel and perpendicular to the fibre direction and to the change of the wood moisture content.

The bilayers have a straight unbent configuration for high values of relative humidity (>85%) and a curved configuration for lower values of relative humidity (<40%) (Fig. 1 B). The bending occurs along the interaction length direction whereas there is almost no bending along the width direction (Fig. 1 A).

A decrease of the relative humidity (RH) from 85% to 35% results in shrinking of the respective layers in a direction perpendicular to the fibre orientation of the active layer (identical to interaction length) resulting in the bending movement of the bilayer element (Fig.

1 B).

The actuation is inversely proportional to the overall thickness of the wooden bilayer and shows a pronounced maximum for an optimum thickness ratio of the first and second layer depending on the stiffness ratio of the two layers. For wood this thickness ratio is in the range of 0.2-0.3.

Figure 2 describes the mechanical interaction of elements.

The two wooden bilayers are arranged in a lever arm configuration in order to speed up the movement of the shading device.

The actuator element is fixed with one end to a base, through a built-in or fixed support, (Fig 2A, 4) to prevent movement of this end. The actuator element provides the input force or effort force (Fig. 2B).

A second wooden bilayer, the shading element (Fig. 2A; 1 ), is mounted on a hinge or pin support (Fig 2A; 3). The invention can also be exercised if the shading element is not a bilayer element capable of bending. An element that remains in a straight configuration can also be used.

The different typologies for shading devices, which could be used as configurations are shown in Fig. 2A. They are referred to as Typology 1 , 2, 3, 4 and 5. The typologies differ mainly in the placement of the pivot of the shading element, which is either be placed on one end of the shading element or between the two ends of the shading element. The forces that are involved in the rotary movement of the shading element in the different typologies are shown in figure 2B. A lever class is also assigned to the different typologies.

The classes of levers (Fig. 2B) are differentiated by the distribution of the effort, the resistance and the fulcrum of the level.

An advantageous configuration for the shading system is typology 5 (Fig. 2A). In this configuration, the shading element has both a concave and a convex bending with regard to the hinge. The fulcrum is settled at 2/3 of the length of the upper bilayer with the resistance (due to the weight of the overall sample) kept in the middle between the fulcrum and the effort.

The position of the resistance of the shading element (Fig. 2B), due to the weight of the overall sample is settled with a certain arm-distance, compared to the hinge.

The placement of the center of mass, as the convex bending of the upper layer in the typology 5, compared to the placement of the hinge have a specific purpose. With decreasing of the relative humidity, the effort force of the actuator element could overturn the shading element if its center of mass would correspond to the hinge constrain. This would be a problem in particular if the typologies are used in the horizontal configuration settled in a vertical frame. The movement of the system comprises two separate movements. On one side, there is the pure bending of the actuator element and shading element, if a bilayer is used, due to the change of the relative humidity. This movement generally occurs also in a not-combined configuration.

Further, there is the rotation of the shading element due to the effort force of the actuator element and the interaction of the elements. In the closed configuration (Fig. 2A, dashed lines), the shading element is parallel to the actuator element. This means that the shading element does not constantly put weight on the actuator element. The effort force, from the actuator element to the shading element, is only due to the pure bending of the actuator element. The rotation in this configuration of the shading device is counter-clockwise (arrow in Fig. 2A and 2B). The bending of the actuator element and the effort force which is applied by that on the shading element can be varied. This variation is based on the momentum produced by the resistance (the weight force) of the shading element. This momentum can also be varied by the lengths of the resistance-arm (in respect to the fulcrum).

The typology implemented for this embodiment of the invention is the number 5. Conceptually this is similar to typology 2, but they differ in the value of the momentum and in the arm length of the resistance. In an horizontal configuration, upon decreasing relative humidity, the force effort of the actuator element could overturn the shading element if its center of mass would correspond to the hinge constrain.

The autonomous, repeatable and reversible nature of the shading device is described in Figure 3 and 4.

In order to provide experimental proof that the amplitude of the rotation of the upper bilayer can be kept constant in repeated cycles, four samples of coupled bilayer elements were fixed in a steel frame into a climate chamber (Fig. 3A).

The experiment consisted of 15 cycles of 12 hours absorption and 12 hours desorption (Fig. 4). The relative humidity was varying from a maximum of 95% to a minimum of 20%. For each shading device, the angle a and b of the wooden bilayers were analysed through a computer script.

The angle a is defined by a first axis running from the pivot of the shading element to the lower end (Fig. 3B; point L) of the shading element in the unbent state (RH>85%) and a second axis running from the pivot of the shading element to the lower end (Fig. 3B; point L) of the shading element in the bent state (RH<40%). Similarly the angle b is defined by an axis running from the fixed first end of the actuator element to the second end (Fig. 3A; point A) in the unbent state (RH>85%) and a second axis running from the fixed first end of the actuator element to the second end (Fig. 3A; point A) in the end state (RH<40%). An invariance of the amplitude occurred after an initial adjustment of the configuration after 4 cycles (probably due to the adjustment of the climate chamber settings).

The maximum value for angle a of the shading element is around 28° (Fig. 4 angle a). The maximum value for angle b of the actuator element is around 24° (Fig. 4 angle b). The angular change of both the shading element and the actuator element is around 23° after the fourth cycle. Despite the similar am plitude, the angular speed of the shading element (rate of change of angle b) is higher. (Fig. 4).

The angular velocity was calculated for each cycle through the derivative of the two functions (Fig. 4) for the same input time-point. The slope of the tangent line to the graph of the functions at the same time-point, which is the derivative, is higher for the shading element than the actuator element, both during the first absorption and final desorption time phase.

Furthermore, the data confirmed for the given experiment that there is no relaxation of the actuator element under the applied cyclic load. The minimum and maximum angle values reached by the actuator element are constant after the fourth cycle.

Thus, the actuation is defined as repeatable by the fact that the coupled wooden bilayers movement could be cyclically repeated and reproduced while retaining the amplitude of the rotation. The actuation is defined reversible in the way that the shading device comes back to the original position, in the close configuration, after each cycle.

The upscaling of the shading device to a shading system is described in Figure 5.

The shading system comprising a multitude of shading devices can be fitted horizontally, with a direction perpendicular to a facade, above windows or glass walls.

In certain embodiments, the shading system is composed of a modular steel frame supported by steel tierods. The upscaling of the system is made through the repetition of these modules. In this steel frame, the lamellae are made by shading devices of the present invention.

The shading devices are fixed and constrained in the frame with an interaxle-spacing (center to center distance/ wheel base) of the couple of sheets of 180 mm along the cross section in accordance to the market needs (Fig.5).

The shading devices are in a closed configuration when the relative humidity is high (>85%). Relative humidity is high during the morning and the night, when there is no need for a shading function. The shading devices are converted into an open configuration when the relative humidity is low (<40%). The drop in relative humidity, from 85% to approx. 40%, occurs on a sunny day from the last part of the morning, and especially around noon, until the first part of the afternoon, when the shading function is required most. It therefore represents an adaptive shading system without the use of technical sensors and/or motor devices.

The vertical configuration for fixing the coupled system is advantageous to minimize dynamic loading such as caused by wind and snow. Otherwise, the shading element and the actuator element in an open configuration would need to cover a permanent load in case of snow. This permanent load could lead to plastic deformation of the material, which would affect the functionality of the mechanism.

Configuration of shading devices within a shading system can be seen in Figure 6.

In certain embodiments, the shading devices are mounted within a frame and are arranged in a regular fashion with identical space between the shading devices (Fig. 6). The rotation of the shading element and therefore the shading ability, in respect to the sun rays, are mainly defined by the overlapping length as shown in figure 6. The higher the overlapping length is, the higher is the rotation of the shading system.

In a closed configuration (Fig. 6A) the actuator elements and shading elements are in a straight configuration and would only produce minimal shading. In an open configuration (Fig. 6B) the actuator elements and the shading elements are in a bent state, providing increased shading.

Different shapes for the first layer (active layer)

In certain embodiments, the active layer could have a variance in the thickness along the longitudinal (defined "interaction length " in according to Fig.1 , A) and transverse section (defined "width" in according to Fig. 1 , A).

Samples made by beech (4 mm) and spruce (0.8 mm) were manufactured in accordance with the procedure described above. The beech layer, the active one, in same samples, was milled into a strips configuration by using a milling machine. The strips were milled with a horizontal direction, parallel to the interaction length of the bilayers, or with a 45° diagonal orientation. They had a width of 20 mm and a different length (depending if in the horizontal or the diagonal orientation). The final thickness of the beech layer was toothed for some samples, varying between 4 and 1 mm.

For the experiment, the samples were carried from one climate chamber (with a constant relative humidity of 85%) to another one (with a constant relative humidity of 35%).

The moisture content loss and the change of curvature was evaluated within 24 hours. The homogenous (the sample were the beech was not milled) had a MC loss of 31 % and a change of curvature of 0.00818 mm^"1. The horizontal strips milled samples had a MC loss of 53% and a change in curvature of 0.00971 mm^"1. The diagonal strips milled samples had a MC loss of 55% and a change in curvature of 0.0101 1 mm^"1. The different values of MC and change of curvature are due to the different values of the surface area of the active (beech) layer. This is increased by the milling operation of around 1 .15 times the area of the not milled beech layer.

Claims

Claims:

1 . A shading device comprising a pivot mounted shading element and an actuator element, comprising a first and a second end, for turning said shading element in a rotary movement, wherein said actuator element is

fixed to a base with said first end,

- able to reversibly bend its shape in response to environmental parameters, wherein said second end bends towards said shading element in a bending movement, and

arranged in such a way that said bending movement results in an interaction with said shading element, achieving said rotary movement.

2. The shading device according to claim 1 , wherein

- said actuator element and/or

- said shading element

comprise at least one bilayer element comprising a first and a second layer, wherein said layers differ in their predominant shrinking and swelling properties along an axis running from said first to said second end in response to said environmental parameters resulting in said reversible bending movement.

3. The shading device according to any one of claims 1 or 2, wherein said predominant shrinking and swelling properties are

- for said first layer up to 9%, particularly 3% to 6%, more particularly 4% to 5%, of its dimension and/or

- for said second layer less than 1 %, particularly 0% to 1 %, more particularly 0% to 0,5% of its dimension.

4. The shading device according to any one of claims 2 to 3, wherein the difference between said predominant shrinking and swelling properties is at least 3%, particularly 9% to 3%, more particularly 5.5% to 4.5%.

5. The shading device according to any one of claims 2 to 4, wherein said first layer and said second layer consists each of a flexible material.

6. The shading device according to any one of claims 2 to 5, wherein at least one of said layers comprises a fibre containing material, wherein said fibres have an essentially parallel fibre orientation and said fibre orientation is different between said layers, in particular the fibre orientation is shifted by 40° to 90°, particularly 90°, between said layers.

7. The shading device according to claim 5, wherein said fibre containing material is a hygroscopic material, particularly a wood material, wherein an increase in moisture content results in swelling along an axis perpendicular to the fibre orientation and a decrease in moisture content, wherein particularly the change in moisture content is in response to changes in humidity, results in shrinking along said axis perpendicular to the fibre orientation.

8. The shading device according to any one of claims 2 to 7, wherein said first and said second layer of said bilayer element are glued together, particularly with an adhesive selected from polyurethane adhesive, melamine urea formaldehyde (MUF) adhesive, epoxy adhesive and phenol-resorcinol-formaldehyde (PRF) adhesive.

9. The shading device according to any one of the preceding claims, wherein said actuator element comprises at least one additional section comprising a bilayer element or a non-bending element.

10. The shading device according to any one of the preceding claims, wherein said first layer and/or said second layer of said bilayer element has a variable thickness along said axis running from said first to said second end and/or along an axis of the width.

1 1 . The shading device according to any one of the preceding claims, wherein said shading element comprises an additional section selected from a bilayer element or a non-bending element.

12. The shading device according to any one of claims 9 to 1 1 , wherein the layers of said additional bilayer element are arranged in such a way that the predominant swelling and shrinking properties,

- have the same direction as the other bilayer element or

- have the opposite direction as the other bilayer element.

13. The shading device according to any one of the preceding claims, wherein said actuator element and said shading element are arranged in a way that said shading element is a class 2 or class 3 lever and said actuator element provides the effort force.

14. The shading device according to any one of the preceding claims, wherein said actuator element and said shading element are arranged in an essentially parallel orientation in a minimal bending state and wherein said actuator and said shading element overlap with each other for at least 30% of their longitudinal dimension, particularly for at least 50% of their longitudinal dimension, more particularly for at least 80% of their longitudinal dimension.

15. A shading system comprising a multitude of shading devices according to any one of the claims 1 to 14, wherein said shading devices are arranged within a frame.