DE102018103893B4 - Object with variable stiffness - Google Patents

Abstract

Object with variable stiffness, with
- two films (14,16) which are arranged one above the other and have inner sides (18) facing each other and outer sides (19) facing away from each other,
- wherein the distance between the two films (14,16) can be changed by generating a negative pressure within an inner volume located between the two films (14,16) and/or by generating an overpressure in an outer volume located outside the films (14,16),
- wherein on the inner side (18) of the first film (14) a first surface structure (22) is arranged and/or formed from a first array of a plurality of raised first projections (12) fixed on the inner side (18) of the first film (14) with first intermediate spaces (20) arranged between them, each of which is surrounded by at least three first projections (12),
- wherein on the inner side (18) of the second film (16) a second surface structure (22) is arranged and/or formed from a second array of a plurality of raised second projections (12) fixed on the inner side (18) of the second film (16) with second intermediate spaces (20) arranged between them, each of which is surrounded by a plurality of second projections (12), and
- wherein a first projection (12) of the first surface structure (22) on the inner side (18) of the first film (14) dips into the opposite second intermediate space (20) of the second surface structure (22) on the inner side (18) of the second film (16) associated with this first projection (12) when the distance between the two films (14, 16) is reduced and thereby rests against at least three of the second projections (12) of the second surface structure (22) on the inner side (18) of the second film (16) delimiting this second intermediate space (20) and
- at least one third foil (36'') between the first and the second foil (14,16) is arranged,
- wherein the at least one third film (36'') has on its two main sides a surface structure (22) consisting of an array of a plurality of raised projections (12) fixed on the relevant main side of the third film (36'') with intermediate spaces (20) arranged between them, each of which is surrounded by a plurality of projections (12), and
- wherein the respective surface structure (22) of the at least one third film (36'') is complementary to the respective surface structure (22) of the inner side (18) of the first or second film (14, 16) opposite the relevant main side of the third film (36'') or the opposite main side of a further third film (36''), characterized in that
- that the first, second and third films (14,16,36'') each have an outer edge, wherein the adjacent films (14,16,36'') are connected in a gas-tight manner along their outer edges (24) to form a bag, and
- that each bag is provided with a closable opening (28) for ventilation of the bag.

Description

The invention relates to an object with variable stiffness, which can be used as a construction element of a device or as a semi-finished product for stiffening a device or a part of a device as required.

The invention particularly relates to a mechanical structure by means of which the rigidity of an object can be changed instantly, reversibly and at will. In a first state, the object is almost infinitely flexible and in a second state it is significantly more rigid. In intermediate states, the object can assume intermediate degrees of flexibility or rigidity. These statements apply to a continuous set of bending axes/bending edges along the object or axes/edges through the object. An example is a cuboid-shaped object with a large base and low height, such as a windshield, which is bent along a horizontal bending axis. The rigidity along such a bend can now be changed between two states, regardless of where the object is bent.

• - hohe Sicherheit und Stabilität. Kollidiert ein Mensch mit diesem Objekt, so verformt sich das Material und entzieht dem Aufprall hierdurch Energie. Der Aufprall wirkt weicher, die Verletzungsgefahr sinkt. Die Kraft wird ebenfalls abgefedert, sodass eine geringere Maximalkraft übertragen wird. Hierdurch werden Bauteile wie Servomotoren, welche über eine Feder mit einem Endeffektor verbunden sind, durch einen Aufprall mechanisch weniger belastet.
• - hohe Flexibilität und Adaption. Das Objekt kann sich seiner Umwelt anpassen. Hierdurch kann es in verschiedenen Umgebungen genutzt werden oder um Hindernisse herum bewegt werden. Zudem kann es die Kontaktfläche mit einem Objekt erhöhen, sodass z.B. elastische Haut eine höhere Reibung und damit eine stärkere Verbindung mit einem gegriffenen Gegenstand aufbauen kann.
• - hohe Energie-Effizienz (Resonanz). Bei einer spontan eintretenden Kraft speichert ein elastisch-nachgiebiges Objekt Energie. Diese kann es nutzen, um sich wieder abzustoßen. Kängurus speichern hierdurch bei Bodenkontakt Energie in ihren Muskeln und Sehnen und setzten sie beim Absprung wieder frei.
• - hohe Maximalkraft. Eine anliegende Kraft kann iterativ das Objekt verformen und so Energie in dem Objekt speichern. Zu einem gegebenen Zeitpunkt wird die Verformung wieder aufgelöst, wodurch kurzzeitig eine hohe Kraft entsteht, welche die ursächliche Kraft weit übersteigen kann.
• - viele Freiheitsgrade. Ein nachgiebiges Objekt kann an vielen Stelle verformt werden, wodurch es viele Bewegungen ermöglicht.

In general, the stiffness of a material determines its deformation in response to an applied force or moment. A stiff material deforms little under a given force, while a material with a low stiffness deforms greatly under the same force. Depending on the application, a stiff or flexible material must be used, as both states have mutually exclusive advantages. A flexible object, for example, allows

• - high level of safety and stability. If a person collides with this object, the material deforms and absorbs energy from the impact. The impact is softer and the risk of injury is reduced. The force is also cushioned so that a lower maximum force is transmitted. This means that components such as servo motors, which are connected to an end effector via a spring, are subjected to less mechanical stress in the event of an impact.
• - high flexibility and adaptation. The object can adapt to its environment. This means it can be used in different environments or moved around obstacles. It can also increase the contact area with an object, so that, for example, elastic skin can build up higher friction and thus a stronger connection with a grasped object.
• - high energy efficiency (resonance). When a force occurs spontaneously, an elastic, flexible object stores energy. It can use this energy to push itself off again. Kangaroos store energy in their muscles and tendons when they come into contact with the ground and release it again when they jump.
• - high maximum force. An applied force can iteratively deform the object and thus store energy in the object. At a given point in time, the deformation is released again, which briefly creates a high force that can far exceed the causal force.
• - many degrees of freedom. A flexible object can be deformed in many places, allowing many movements.

• - effiziente Kraftübertragung. Übt man eine Kraft auf das Objekt aus, so wird diese schneller und ohne bzw. mit geringem Kraftverlust übertragen.
• - hohe Präzision und einfache Modelle. Das Verhalten eines steifen Objekts erfordert deutlich einfachere Modelle, sein Verhalten ist sehr vorhersagbar und damit präzise. Damit ist es einfach, die Bewegungen oder auszuübende Kräfte des Objektes zu steuern.

In contrast, a rigid object allows, for example,

• - efficient force transmission. If a force is applied to the object, it is transmitted faster and with little or no loss of force.
• - high precision and simple models. The behavior of a rigid object requires much simpler models, its behavior is very predictable and therefore precise. This makes it easy to control the movements or forces exerted by the object.

Depending on the situation, the advantages of a flexible or rigid object outweigh the disadvantages (see the application examples). For this reason, it is helpful to be able to greatly increase or decrease the rigidity of an object depending on its intended use. Ideally, this process should be executable at any time, instantaneous, reliable and reversible.

In the following, known previous attempts to solve the above-mentioned problem are described together with their specific problems. Problems that can be overcome by means of the invention are listed.

Magneto- and electrorheological materials

Magneto- and electrorheological (MR, ER) materials change their mechanical properties when a magnetic or electric field is applied. They are usually magnetically polarizable or dielectric particles that are dissolved in a liquid. In the absence of a field, they are distributed randomly in the liquid. If a field is applied, the particles form chains and increase the viscosity of the liquid until they form a viscoelastic solid [1].

MR and ER materials usually require high electromagnetic field strengths. Furthermore, they are primarily viscous and not elastic, meaning that they can only dissipate mechanical energy, but not store it. In addition, the theoretical description of their properties is non-trivial, which makes their control difficult [2]. High stiffness is not achievable [3].

Thermorheological materials

Thermorheological materials exploit the phase transitions between different aggregate states of materials that occur at changing temperatures [4]. The transition between ice and water is an example of this.

Temperature changes and the associated phase transitions usually take place very slowly. In addition, the material must be wrapped or penetrated by relatively large devices that can heat it up and cool it down. Energy must be continuously expended to produce and maintain a desired temperature. It is also extremely difficult to produce a spatially focused temperature. Depending on the temperature range of the phase transition, there is also a significant risk of injury from burns/frostbite, particularly in material-human interaction.

Granular Jamming

Granular jamming describes the behavior of granular particles that are placed in a vacuum-tight bag made of flexible film and exposed to a vacuum. The vacuum creates a pressure difference between the external air pressure and the internal vacuum. This pressure difference presses the particles together, causing them to jam/clump together. The more complete the vacuum created, the more jammed the particles become, which changes the behavior of the bag from that of a flexible liquid to that of a solid body [7], [5]. The shape of the bag is not predetermined in the neutral configuration and can change arbitrarily until the vacuum is applied. The vacuum fixes the final shape.

Granular jamming requires a large volume of granular particles to achieve significant stiffness. In addition, the description of such objects is non-trivial, so that the stiffness resulting from a given vacuum cannot be predicted. Accordingly, granular jamming has not yet been used in applied technical systems [3].

Layer Jamming

Layer jamming also uses a bag in which a vacuum is built up. In the bag, layers of materials with a high coefficient of friction are placed on top of each other or woven together. As long as there is no vacuum, the layers can easily slide past each other. As long as the layers themselves are flexible, the bag is flexible. As soon as a vacuum is applied, the layers are pressed against each other. They can then no longer slide past each other, the bag solidifies in its current shape and has a significantly higher stiffness [3], [8]. This principle is used commercially by Tecnalia for the product Varstiff and is e.g. in WO 2011/ 079 865 A1 and US 2015 / 0 369 325 A1 described.

Layer jamming is susceptible to contamination and liquid inclusions within the bag, as the principle is based on friction. In addition, the layers rub against each other even in the neutral state. This means that the object is very viscous even in the neutral state, because the air bag contains many layers, which by definition have a high coefficient of friction. In addition, layer jamming offers a strong limitation on the maximum stiffness for theoretical reasons. On the one hand, it is limited by the coefficient of friction. On the other hand, even with an ideal connection (i.e. an infinite coefficient of friction), the stiffness of the vacuumed bag would be at most equivalent to that of the layer material. These layers are pressed together and are therefore now identical to a single layer with a higher thickness. In the neutral state, however, the bag can only be deformed if the layers themselves can also be deformed. Therefore, ideally a material must be chosen that is rather flexible itself. If the effective thickness of the object changes due to the vacuum, it becomes stiffer but remains basically flexible.

Tooth-Linked Vacuum Pressure Locking Mechanism

Zou et al. [6], [9] developed a mechanism that also uses the pressure difference between normal air pressure and artificial air pressure within a flexible bag. They use a flexible tube surrounded by grooves. This is in turn surrounded by an airtight film with individual teeth. The tube and film together form the airtight bag. If a vacuum is now created, the outer film presses against the tube and the teeth are pressed into the grooves of the tube. If you now want to bend the tube, you would have to stretch the film. As long as the film is not stretchable, the tube is now rigidly fixed in its current shape.

A disadvantage of the mechanism is that it can only be applied to tubular structures. An extension to flat objects is not described and is non-trivial.

The stability of the object is limited by the fact that the film and tube determine the stiffness in the neutral state as well as in the negative pressure state. The film should therefore be rather thin so that the object can be bent slightly in the neutral state. In the negative pressure state, the film is now pressed tightly against the large surface area of the grooves. When it adjusts to the shape of the grooves, a high pressure is created on the film, which can cause it to tear and destroy the required vacuum. In addition, the film will not be able to fit completely into the grooves. Pressure in these places can also easily cause the film to tear.

In addition, the device will not be completely rigid in the negative pressure state, depending on the degree of bending of the tube. It is assumed that the film is taut when the tube is straight. If the tube is bent, the film will hang slightly slack on the side of the inner radius. If the film and tube are then fixed together at certain points using the teeth, there will be some gaps between two teeth where the film is not taut on one side. These gaps can therefore still be bent.

Other well-known concepts for Vacuum Pressure Locking Mechanism are for example in WO 2016/ 100 174 A1 and WO 2016/ 100 182 A1 described.

Out of US 2017 / 0 360 590 A1 An object with variable stiffness according to the preamble of claim 1 is known.

The object of the invention is to further improve the known concepts for the optional stiffening of an object by means of a new mechanical structure.

To achieve this object, according to the invention, an object with variable stiffness is used which, in the non-stiffened state, is flexible along a plurality of bending axes or bending edges and can be optionally stiffened, wherein the object according to the invention is provided with the features of claim 1.

Individual embodiments of the invention are the subject of the subclaims.

According to the invention, it is provided that the object has at least two flexible films made of, for example, plastic material, on the inner sides of which surface structures made of individual projections or blocks are arranged or formed. The projections of one surface structure form spaces associated with the projections of the other surface structure, which are each enclosed by projections. The projections are formed, for example, as cubes or square cuboids in cross section and are arranged, for example, in a checkerboard pattern or otherwise in an array form. Any other form of projection is also conceivable. The projections are advantageously geometrically identical. The projections of one surface structure can be identical or different from one another. The same can also advantageously apply to the projections of the other surface structure. The geometry of the projections and the spaces can be identical or different for each surface structure. It is also advantageous if a projection of one surface structure is complementary to the shape of the space associated with it in the other surface structure.

According to a further embodiment of the invention, each projection has an n-fold rotational symmetry when viewed from the inside of a film in the extension of the normal on this inside, where n is greater than three or four or greater than six or greater than eight.

The invention is easy to implement when using projection shapes that meet the mathematical conditions of a Platonic tiling. According to this, there are exactly three possible tilings of a plane with regular polygons, namely triangle, square and hexagon. In this respect, each projection has a 3-fold, 4-fold or 6-fold rotational symmetry in the sense mentioned above. The projections for the Platonic tiling should have chamfers on the edges and corners so that the projections of both films can be moved into and apart from one another without snagging.

If the two films are arranged at a distance from each other without the projections of the surface structure of one film being immersed in the gaps in the surface structure of the other film, the object is flexible, whereby this flexibility is ultimately and preferably exclusively determined by the material of the films themselves. The further the films are placed on each other are moved, the further the projections sink into the gaps. This already limits the flexibility of the object within certain limits. The object is completely rigid when the projections are completely immersed in the gaps assigned to them. At the latest when the projections are completely immersed in the gaps, they lie against at least one and preferably all of the projections of the other surface structure that delimit the gap in question. In addition, the top of a projection can also lie against the bottom of the gap, which is preferably formed by the film. The interlocking prevents any bending of the object, which is thereby stiffened, with the stiffness now defined by the material of the projections. This material should be much stiffer, i.e. have a much higher modulus of elasticity than the material of the films, which should also have low extensibility.

The two films can be two separate layers or a single layer that is folded back along a line to form the two films, thus creating two layers of film one on top of the other.

As already mentioned above, the projections can basically have almost any desired geometric shape. The projections should preferably have flat surface sections along their peripheral edges. The projections can have the same width over their height or can taper towards their upper free ends. Chamfers, i.e. "broken" edges on the projections, are advantageous in that they prevent snagging or the like when the projections are inserted into the associated gaps in the corresponding counter foil. In this respect, these "broken edges" act as run-in and insertion aids.

The arrangement and shape of the projections and gaps of the two surface structures are particularly complementary, but this does not necessarily apply to the entire area of the surface structures. For example, at least one gap or a small number of gaps could remain free of projections of the other surface structure or could only be partially filled by projections.

The invention further provides at least one third film which is arranged between the first and the second film, wherein the at least one third film has on its two main sides a surface structure made up of an array of a plurality of raised projections fixed on the relevant main side of the third film with intermediate spaces arranged between them, each of which is surrounded by a plurality of projections, and wherein the respective surface structure of the at least one third film is complementary to the respective surface structure of the inner side of the first or second film opposite the relevant main side of the third film or the opposite main side of another third film.

Each of the at least three films has an outer edge, wherein adjacently arranged films are connected in a gas-tight manner along their outer edges to form a bag, and wherein each bag is provided with a closable opening for ventilation of the bag.

In an advantageous embodiment of the invention, it is provided that the distance between the projections of the surface structure of the inside of each film is at least equal to the height of the projections and that the projections of the surface structure of the inside of each film or per individual film have the same geometry.

In a further advantageous embodiment of the invention, it is provided that the projections of the surface structure of the inner side of each film or of each individual film are arranged regularly.

In an advantageous embodiment of the invention, it is provided that each projection has a circumferential surface which protrudes at an angle of substantially 90° from the inside of the film and that a projection, in the state in which it is immersed in the intermediate space assigned to it, contacts the circumferential surface of a projection delimiting this intermediate space and preferably the circumferential surfaces of all projections delimiting this intermediate space.

In a further advantageous embodiment of the invention, it is provided that each projection has a circumferential surface with several adjacent flat surface sections, wherein two adjacent flat surface sections form an interior angle of less than 180°, and that a projection, in the state in which it is immersed in the intermediate space assigned to it, contacts a surface section of a projection surrounding this intermediate space and preferably a surface section of all projections delimiting this intermediate space.

Furthermore, in an advantageous embodiment of the invention, several pairs of foils each consisting of a first foil and a second Foils are arranged one above the other, wherein the outer side of a foil of a foil pair rests against the outer side of a foil of the adjacent foil pair and both foils are connected to one another, in particular glued.

Description of the invention

As can be seen from the above, the invention is based on the principle of generating a negative pressure, for example within a bag, which presses the upper and lower films together.

The films can also be pressed together using negative pressure from outside a bag. The negative pressure can be provided by, for example, a suction pump or a pneumatic piston/cylinder unit in fluid communication with the inside of the bag to exchange gas from the bag into the unit and vice versa (possibly designed as a closed system). The (possibly repeated back and forth) movement of the piston can be manual or motorized. Depending on the application, it can be advantageous if the "pressing together" takes place quite quickly. It is also conceivable for the air in the bag to be introduced by mouth or sucked out (e.g. in the application of the invention for objects that are used in leisure time or during sport, such as a back protector for winter sports, e.g. skiing or snowboarding).

The invention is described below using this embodiment, but is not limited to this embodiment. The direction information on the film (e.g. vertical/horizontal) is given below as if the two films were lying parallel and flat, i.e. horizontally, on top of each other. The films have any thickness and rigidity, but should not be stretchable. Each film is covered over a large area with glued-on blocks of a second, very rigid material such as aluminum (while the films are made of plastic material, for example, which is flexible and non-stretchable). All blocks are the same height. The two films are connected to each other in an airtight manner at the edges. They thus form an approximately two-dimensional object. The rigidity of this surface (more precisely: plate), i.e. the force required to bend it along an axis, should change instantly between the rigidity of the film and that of the blocks by applying a vacuum.

This should apply to every possible bending axis/edge. An axis can be any possible (not necessarily straight) line that extends from one side of the object to the other.

The idea behind the invention is that without negative pressure/slight positive pressure (neutral state), the distance between the two films is so large that the blocks hardly touch each other or not at all. Ideally, the distance between the films is greater than twice the height of the blocks, so that the blocks do not touch each other. On each film, the blocks are arranged so far apart that the film can be bent without the blocks touching each other. If you bend this air bag, the stiffness is determined by the stiffness of the film. As soon as a negative pressure in the bag and/or positive pressure from the outside presses the films together, the blocks of the two opposing films come to lie directly next to each other (edge to edge). If you bend the object, the blocks now block each other (lock mechanism), and the stiffness of the object is determined by the high stiffness of the blocks. Unlike in the case of layer jamming, the stiffness in the neutral and stiff state is determined by different materials with arbitrarily different properties.

• - Jede Folie ist mit den Blöcken bedeckt.
• - Auf jeder einzelnen Folie berühren sich die Blöcke bei einer Verbiegung der Folie nicht oder erst bei einem hohen Biegewinkel. Um einen maximalen Verbiegewinkel zu erreichen, sind die Blöcke so weit voneinander entfernt wie sie selbst hoch sind. Wenn sie näher aneinander angeordnet sind, funktioniert der hier beschriebene Effekt weiterhin; allerdings kann man die Folie zwischen den beiden Blöcken lediglich um einen kleineren Winkel verbiegen. Es ist anzunehmen, dass ein geringfügig kleinerer Verbiegewinkel in den meisten Anwendungen keinen Nachteil darstellt, da die Folie großflächig mit Blöcken bedeckt ist und sich die Biegewinkel zwischen den einzelnen Blöcken addieren zu einem beliebig großen maximalen Verbiegewinkel des gesamten Objekts. Die in diesem Punkt beschriebene Eigenschaft führt dazu, dass jede Folie deshalb alleine genommen nachgiebig ist. Sind die Folien ausreichend weit voneinander entfernt, so ist die Steifigkeit des gesamten Objekts äquivalent zur Steifigkeit der Folien.
• - Legt man die Folien aufeinander, so passen die Blöcke ineinander, d.h. sie können nebeneinander angeordet werden, ohne dass die Folie gedehnt werden müsste.
• - Sobald die Folien übereinandergelegt werden, besitzt jeder Block nun mit Blöcken der anderen Folie Nachbarkanten, welche direkt anliegen. Verbiegt man das Objekt, so blockieren sich die Blöcke gegenseitig. Die Steifigkeit des Objekts ist äquivalent zur Steifigkeit der Blöcke.
• - Die Blöcke müssen nun einer Verbiegung des Objekts entgegenstehen, unabhängig von der Achse der Verbiegung. Sie stehen einer Verbiegung entgegen, wenn entweder auf einer Achse ein Block liegt, oder aber zwei Blöcke eine gemeinsame Kante besitzen. Auf jeder möglichen Verbiegeachse sollen nun möglichst viele (mindestens ein) Blöcke und Nachbarkanten liegen, die einer Verbiegung entlang dieser Kante entgegenstehen. Da die Folie nicht/schwer dehnbar ist, wird sich der Abstand zwischen zwei Blöcken auch bei einer Verbiegung entlang ihrer gemeinsamen Kante nicht erhöhen.
• - Durch die erfindungsgemäße Anordnung der Vorsprünge bzw. Blöcke hat jede Folie Biegerichtungen, entlang derer keine Blöcke bzw. Vorsprünge angeordnet sind. Diese Biegerichtungen bilden eine 2D-Vektorbasis, so dass man jede der beiden Folien in jede beliebige Richtung, nämlich längs jeder Biegerichtung, verbiegen kann.
• - Im Zustand der Kompression ordnen sich nach der Erfindung die Blöcke bzw. Vorsprünge der beiden gegenüberliegenden Folien derart an, dass sie sich in jede mögliche Biegerichtung blockieren.

The arrangement of the blocks on each of the two slides fundamentally determines the properties of the object. The arrangement of the blocks and the blocks themselves should fulfill several properties. Some properties should be fulfilled. Other properties are not necessary, but provide improved properties of the object. It is necessary that the blocks are arranged on the two slides in such a way that the following properties are fulfilled:

• - Each slide is covered with the blocks.
• - On each individual foil, the blocks do not touch each other when the foil is bent, or only touch each other at a high bending angle. To achieve a maximum bending angle, the blocks are as far apart as they are high. If they are arranged closer together, the effect described here still works; however, the foil between the two blocks can only be bent by a smaller angle. It can be assumed that a slightly smaller bending angle is not a disadvantage in most applications, since the foil is covered with blocks over a large area and the bending angles between the individual blocks add up to an arbitrarily large maximum bending angle of the entire object. The property described in this point means that each foil is therefore flexible on its own. If the foils are sufficiently far apart, the stiffness of the entire object is equivalent to the stiffness of the foils.
• - If you place the foils on top of each other, the blocks fit into each other, meaning they can be placed next to each other without having to stretch the foil.
• - As soon as the foils are placed on top of each other, each block now has neighboring edges that are in direct contact with blocks from the other foil. If the object is bent, the blocks block each other. The rigidity of the object is equivalent to the rigidity of the blocks.
• - The blocks must now resist bending of the object, regardless of the axis of the bending. They resist bending if either a block is on an axis or two blocks have a common edge. On each possible bending axis there should now be as many (at least one) blocks and neighboring edges as possible that resist bending along this edge. Since the film is not/hardly stretchable, the distance between two blocks will not increase even if they are bent along their common edge.
• - Due to the arrangement of the projections or blocks according to the invention, each film has bending directions along which no blocks or projections are arranged. These bending directions form a 2D vector basis, so that each of the two films can be bent in any direction, namely along any bending direction.
• - In the state of compression, according to the invention, the blocks or projections of the two opposing films are arranged in such a way that they block each other in every possible bending direction.

• - Die Blöcke sollten möglichst regelmäßig angeordnet sein und die Größe und Form aller Blöcke auf einer einzelnen Folie gleich sein. Darüber hinaus soll jeder Block von oben betrachtet eine n-fache Rotationssymmetrie mit möglichst großem n besitzen. Dies ermöglicht, dass die Blöcke auch dann noch ineinander passen, wenn das Objekt im neutralen Zustand verformt wurde. Hierdurch kann das Objekt im neutralen Zustand verfort und mit Unterdruck die neue Form fixiert werden.
• - Die Blöcke sollten so angeordnet werden, dass im Zustand des Unterdrucks ein möglichst geringer Anteil der Folienfläche nicht von ihnen bedeckt wird. Hierdurch wird die maximale Steifigkeit ebenso wie die Riss-Stabilität bei punktuellem Druck auf die Folien erhöht.
• - Die Blöcke sollen eine senkrechte Kante bilden, welche möglichst rechtwinklig zur Folie ist. Hierdurch verkanten sie sich, wenn man die Folie verbiegt. Wenn die Blöcke sich nach oben hin leicht verjüngen, gleiten sie bei Erzeugen des Unterdrucks leichter ineinander, verkanten sich aber weniger effektiv.
• - Die Blöcke sollten möglichst hoch sein, wenn das Objekt besonders steif werden soll. Demgegenüber sollten die Blöcke niedrig bleiben, wenn das Objekt sehr flexibel verbiegbar sein soll. Nutzt man höhere Blöcke, so erhöht sich die maximale Steifigkeit des Objekts. Allerdings muss man die Blöcke nun weiter auseinander setzen, damit jede einzelne Folie sich noch verbiegen lässt. Dadurch müssen die Blöcke eine höhere Grundfläche haben, was die Flexibilität des Objekts im neutralen Zustand verringert. Dieses „Dilemma“ kann gelöst werden, indem man mehrere effektiv zweidimensionale Objekte mit jeweils niedrigen Blöcken aufeinander klebt. Die Dicke des entstehenden Objekts ist damit um ein vielfaches größer, und mit ihr die Steifigkeit im Zustand des Unterdrucks.

The described effect of the invention can be improved if the blocks and their arrangements also have certain arrangements and properties. The following advantageous embodiments are possible:

• - The blocks should be arranged as regularly as possible and the size and shape of all blocks on a single sheet should be the same. In addition, each block should have n-fold rotational symmetry with n as large as possible when viewed from above. This allows the blocks to fit together even if the object has been deformed in a neutral state. This allows the object to be moved in a neutral state and the new shape to be fixed using negative pressure.
• - The blocks should be arranged in such a way that as little of the film surface as possible is not covered by them when the pressure is negative. This increases the maximum stiffness as well as the tear resistance when pressure is applied to the film at specific points.
• - The blocks should form a vertical edge that is as perpendicular as possible to the foil. This means that they will jam when the foil is bent. If the blocks taper slightly towards the top, they will slide into each other more easily when the vacuum is created, but they will jam less effectively.
• - The blocks should be as high as possible if the object is to be particularly rigid. On the other hand, the blocks should remain low if the object is to be very flexible. If you use higher blocks, the maximum rigidity of the object increases. However, you now have to place the blocks further apart so that each individual sheet can still be bent. This means that the blocks have to have a larger base area, which reduces the flexibility of the object in the neutral state. This "dilemma" can be solved by gluing several effectively two-dimensional objects, each with low blocks, onto one another. The thickness of the resulting object is then many times greater, and with it the rigidity in the state of negative pressure.

Advantages of the invention

The invention makes it possible to change the stiffness of an object instantly and reversibly. The stiffness in the flexible and stiff states is determined by two completely different materials with arbitrarily different stiffnesses. The stiffness in the neutral and in the negative pressure state are independent of each other. Therefore, a high maximum stiffness can be achieved with a small volume. In addition, both materials can be either elastic or viscous as required. The object according to the invention is insensitive to dirt and moisture, since the high stiffness is not built up by friction. Signs of wear are not to be expected, unlike with principles based on friction. The effect does not require specific electromagnetic field strengths and temperatures.

Example

• 1 schematisch den Aufbau der innenliegenden Oberflächenstrukturen zweier einander zugewandter Folien in perspektivischer und Explosionsansicht,
• 2 und 3 Schnittansichten entlang der Linie II der 1 im geradlinigen Zustand der Folie und im gebogenen Zustand der Folie,
• 4 eine schematische Darstellung des Beutels, bestehend aus zwei Folien im flexiblen Zustand des Beutels,
• 5 eine schematische Darstellung ähnlich der nach 4 jedoch im Zustand des Beutels, in dem dieser nach Art einer Platte geformt und damit versteift ist, und
• 6 und 7 alternative Ausgestaltungen von Objekten mit mehreren Beuteln bzw. mit einem Beutel, der drei Folien und damit sozusagen zwei Kammern aufweist.

The invention is explained in more detail below using an embodiment and with reference to the drawing. In detail:

• 1 schematically the structure of the inner surface structures of two facing films in perspective and exploded view,
• 2 and 3 Sectional views along line II of the 1 in the straight state of the film and in the bent state of the film,
• 4 a schematic representation of the bag, consisting of two films in the flexible state of the bag,
• 5 a schematic representation similar to that shown in 4 but in the state of the bag in which it is shaped like a plate and thus stiffened, and
• 6 and 7 alternative designs of objects with several bags or with a bag that has three films and thus, so to speak, two chambers.

The drawing illustrates the operating principle of an object 10 according to the invention. The projections 12 are made of rigid plastic and, viewed from above, have the shape of an octahedron ( 1 ). This shape is chosen because it has a high rotational symmetry, a large edge length and because several octahedra can be arranged evenly over a large area. Each projection 12 has a width of e.g. 10 mm (distance between opposite edges) and a height of e.g. 5 mm ( 2 ).

The projections 12 are glued onto an upper foil 14 and a lower foil 16 which is separate from it or which is formed as one piece with the upper foil 14 by a fold line and folded back onto it, namely on the inner sides 18 of these foils 14, 16 facing each other and on the outer sides 19 facing away from each other (see 1 ), whereby the films 14,16 have a low stiffness against bending and a low stretchability. The projections 12 are arranged in rows on each film 14,16. Along a row, two adjacent projections 12 have a distance that is equal to the width of a projection. This allows each film 14,16, such as 3 shows, bend. Two adjacent rows of projections 12 are arranged offset by one projection 12, so that even between two adjacent rows two projections 12 of a film 14,16 never touch. This leads to a pattern of projections 12 and gaps 20 on each film 14,16 and thus to a surface structure 22 which has projections and depressions arranged like on a chessboard ( 1 ). No square projections 12 are used so that the projections 12 that are the smallest apart from each other, ie the "nearest neighbors" of the projections 12 of each foil 14, 16, are still at a distance of a maximum of one projection height and the projections 12 do not block each other when the foils 14, 16 are bent along their diagonals.

The upper and lower films 14,16 are welded together at their edges 24 and form an airtight bag (see 4 and 5 ). A hose 30 leads into the bag via an opening 28 so that air can be sucked out of the bag via a pump, for example, and air can also be admitted into the bag.

In the neutral state (air in the bag) the projections 12 do not engage with each other ( 4 ). This allows the films 14,16 to be bent along the edges of the projections 12 with little force. As soon as a negative pressure is generated in the bag, the projections 12 interlock and form a rigid plate with a very high filling (material density), such as 5 shows. Bending is not possible in this state even with high force, since the projections 12, which have high rigidity, block each other.

In the 6 and 7 Two alternative embodiments of an inventive object with variable stiffness are shown. In 6 the object 10' has two or more bags arranged one above the other, which can either be ventilated or deventilated individually or can be ventilated or deventilated together via a distributor 32'.

In 7 an embodiment is shown in which the object 10'' has a bag with two chambers 34''. A ventilation hose leads to each chamber 34'', so that the two chambers 34'' can be ventilated and deventilated either separately or simultaneously via a distributor. The bag has, as shown above with reference to the 1 to 5 described, the two foils 14,16 and additionally a middle foil 36''. The opposing surfaces of the two foil pairs thus formed, consisting of the upper foil and the middle foil as well as the middle foil and the lower foil, are provided with the surface structures 22 formed complementarily to one another, consisting of projections 12 and gaps 20, as described above in connection with the 1 to 6 described.

Finally, it should be noted that several double or multi-chamber bags, as in 7 shown, can be arranged one above the other. The different types of bags of the 6 and 7 combined into one object. When using multiple bags, they are firmly connected to each other along the layers of film that lie on top of each other (e.g. glued).

Areas of application

The invention describes a principle which increases the stiffness of a planar object with respect to Bending can increase or decrease instantaneously, ie change. By deforming the basic planar object, changes in stiffness along other axes are also possible. If you create an object in which the planar surface is folded several times in a zigzag pattern, you have a spring with variable stiffness. The folded object can be compressed from above either easily or with difficulty.

If the two films are formed as a double-walled tube, a negative pressure influences the rigidity when it is bent along a transverse axis of the tube. The tube can be easily or not bent depending on its condition. This could be interesting for surgical robots used for minimally invasive surgery. These usually consist of long rods or tubes. In order to insert them into the body, a high degree of flexibility is required so that the robot can move around internal body structures. As soon as the tissue to be operated on is reached, a high degree of rigidity is required in order to work precisely and to be able to apply high forces and torques.

Another possibility is a windshield for cars that consists of two transparent films and blocks of glass or transparent plastic. The normal state here would be a state of negative pressure, so that the windshield is rigid during operation and the view is clear. As soon as an accident, e.g. involving a pedestrian, is detected, the vacuum would be released. This can happen passively by puncturing the air bag, but also by actively inflating the air bag like an airbag. The windshield would become flexible. This would cushion the impact of the pedestrian or any car occupant who may not be wearing a seatbelt on the windshield. If the car then had to be opened by force, rescue workers could simply cut open the windshield film with little force. Unlike smashing a windshield, this would not create any splinters of glass that could endanger rescue workers or car occupants.

Other areas of application would be objects that need to be stiff when in use but flexible for transport, such as protectors in sports, folding kayaks or camping furniture, protective shields, etc.

BIBLIOGRAPHY

1. [1] M. Yalcintas and H. Dai, “Magnetorheological and electrorheological materials in adaptive structures and their performance comparison,” Smart Materials and Structures, vol. 8, no. 5, p. 560, 1999. [Online]. Available: http://stacks.iop.org/0964-1726/8/i=5/a=306
2. [2] C. Laschi and M. Cianchetti, “Soft robotics: New perspectives for robot bodyware and control,” Frontiers in Bioengineering and Biotechnology, vol. 2, p. 3, 2014. [Online]. Available: http://journal.frontiersin.org/article/10.3389/fbioe.2014.00003
3. [3] YJ Kim, S. Cheng, S. Kim, and K. Iagnemma, “A novel layer jamming mechanism with tunable stiffness capability for minimally invasive surgery,” IEEE Transactions on Robotics, vol. 29, no. 4, pp. 1031-1042, Aug 2013 .
4. [4] N. Cheng, G. Ishigami, S. Hawthorne, H. Chen, M. Hansen, M. Telleria, R. Playter, and K. Iagnemma, "Design and analysis of a soft mobile robot composed of multiple thermally activated joints driven by a single actuator," in 2010 IEEE International Conference on Robotics and Automation, May 2010, pp. 5207-5212 .
5. [5] AJ Loeve, OS van de Ven, JG Vogel, P. Breedveld, and J. Dankelman, “Vacuum packed particles as flexible endoscope guides with controllable rigidity,” Granular Matter, vol. 12, no. 6, pp. 543-554, 2010. [Online]. Available: http://dx.doi.org/10.1007/s10035-010-0193-8
6. [6] S. Zuo, N. Ymanaka, K. Masamune, H. Liao, K. Matsumiya, and T. Dohi, MRI Compatible Rigid-flexible Outer Sheath Device Using Pneumatic Locking Mechanism for Endoscopic Treatment. Berlin, Heidelberg: Springer Berlin Heidelberg, 2008, pp. 741-744. [On-line]. Available: http://dx.doi.org/10.1007/978-3-540-79039-6 183
7. [7] Jamming as an enabling technology for soft robotics, vol. 7642, 2010. [Online]. Available: http://dx.doi.org/10.1117/12.853182
8. [8] J. Ou, L. Yao, D. Tauber, J. Steimle, R. Niiyama, and H. Ishii, “jamsheets: Thin interfaces with tunable stiffness enabled by layer jamming,” in Proceedings of the 8th International Conference on Tangible, Embedded and Embodied Interaction, ser. TEI '14. New York, NY, USA: ACM, 2013, pp. 65-72. [On-line]. Available: http://doi.acm.org/10.1145/2540930.2540971
9. [9] S. Zuo, T. Ohdaira, K. Kuwana, Y. Nagao, S. Ieiri, M. Hashizume, T. Dohi, and K. Masamune, Developing Essential Rigid-Flexible Outer Sheath to Enable Novel Multi-piercing Surgery. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012, pp. 26-33. [On-line]. Available: http://dx.doi.org/10.1007/978-3-642-33415-3 4

LIST OF REFERENCE SYMBOLS

10

object

10'

object

10''

object

12

projection

14

upper slide

16

lower foil

18

inside

19

Outside

20

Spaces

22

Surface structure

24

Margins

28

opening

30

Hose

32'

Distributor

34''

chamber

36''

middle slide

Claims (10)

Object with variable stiffness, with - two films (14, 16) which are arranged one above the other and have inner sides (18) facing one another and outer sides (19) facing away from one another, - wherein the distance between the two films (14, 16) can be changed by generating a negative pressure within an inner volume located between the two films (14, 16) and/or by generating a positive pressure in an outer volume located outside the films (14, 16), - wherein on the inner side (18) of the first film (14) a first surface structure (22) is arranged and/or formed from a first array of a plurality of raised first projections (12) fixed on the inner side (18) of the first film (14) with first intermediate spaces (20) arranged between them, each of which is surrounded by at least three first projections (12), - wherein on the inner side (18) of the second film (16) a second surface structure (22) is arranged and/or formed from a second Array of a plurality of raised second projections (12) fixed on the inner side (18) of the second film (16) with second intermediate spaces (20) arranged between them, each of which is surrounded by a plurality of second projections (12), is arranged and/or formed, and - wherein a first projection (12) of the first surface structure (22) on the inner side (18) of the first film (14) dips into the opposite second intermediate space (20) of the second surface structure (22) on the inner side (18) of the second film (16) associated with this first projection (12) when the distance between the two films (14, 16) is reduced, and in doing so rests against at least three of the second projections (12) of the second surface structure (22) on the inner side (18) of the second film (16) delimiting this second intermediate space (20), and - at least one third film (36'') which is arranged between the first and the second film (14, 16), - wherein the at least one third film (36'') on each of its two main sides a surface structure (22) made of an array of a plurality of raised projections (12) fixed on the relevant main side of the third film (36'') with intermediate spaces (20) arranged between them, each of which is surrounded by a plurality of projections (12), and - wherein the respective surface structure (22) of the at least one third film (36'') is complementary to the respective surface structure (22) of the inner side (18) of the first or second film (14,16) opposite the relevant main side of the third film (36'') or the opposite main side of a further third film (36''), characterized in that - the first, second and third films (14,16,36'') each have an outer edge, wherein the respective adjacently arranged films (14,16,36'') are connected in a gas-tight manner along their outer edges (24) to form a bag, and - that each bag has a closable opening (28) for loading and unloading. The bag is provided with ventilation. Object after Claim 1 , characterized in that the distance between the projections (12) of the surface structure (22) of the inner side (18) of each film (14,16) is at least equal to the height of the projections (12). Object after Claim 1 or 2 , characterized in that the projections (12) of the surface structure (22) of the inner side (18) of each film (14,16) or per individual film (14,16) have the same geometry. Object according to one of the Claims 1 until 3 , characterized in that the projections (12) of the surface structure (22) of the inner side (18) of each film (14,16) or per individual film (14,16) are regularly arranged. Object according to one of the Claims 1 until 4 , characterized in that each projection (12) has an n-fold rotational symmetry when looking at the inner side (18) of a film (14, 16) in the extension of the normal on this inner side (18), where n is greater than three or greater than four or greater than six or greater than eight or where the projections (12) in the plan view on the surface structure is particularly triangular, square or hexagonal. Object according to one of the Claims 1 until 5 , characterized in that each projection (12) has a circumferential surface which projects at an angle of 90° from the inner side (18) of the film (14, 16) and that a projection (12), in the state in which it is immersed in the intermediate space (20) assigned to it, contacts the circumferential surface of a projection (12) delimiting this intermediate space (20) and preferably the circumferential surfaces of all projections (12) delimiting this intermediate space (20). Object according to one of the Claims 1 until 6 , characterized in that each projection (12) has a circumferential surface with a plurality of adjacent flat surface sections, wherein two adjacent flat surface sections form an angle of less than 180°, and that a projection (12), in the state in which it is immersed in the intermediate space (20) assigned to it, contacts a surface section of a projection (12) surrounding this intermediate space (20) and preferably a surface section of all the projections (12) delimiting this intermediate space (20). Object according to one of the Claims 1 until 7 , characterized in that several pairs of films each consisting of a first film (14) and a second film (16) are arranged one above the other, wherein the outer side (19) of a film (14) of a pair of films rests against the outer side (19) of a film (16) of the adjacent pair of films and these two films (14, 16) are connected to one another, in particular glued. Object according to one of the Claims 1 until 8 , characterized in that the first surface structure (22) is complementary to the second surface structure at least in partial areas or over its entire surface area. Object according to one of the Claims 1 until 9 , characterized in that the projections (12) protrude directly from the film (14,16) and that the films (14,16) form the bottoms of the intermediate spaces (20).

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