Mechanism for providing a link with variable stiffness

Abstract

The invention relates to a mechanism (1) with variable stiffness. It comprises a plurality of solid, discrete elements (2) arranged at least in series and at least one connector (3) interconnecting elements. The at least one connector is configured to apply a tensional force (F) of variable size between the series of elements, so that by varying the size of the tensional force, at least the transversal stiffness of the mechanism is varied accordingly. The mechanism constitutes a pivoting system with equilibrium defined by the shape of the elements. The mechanism is configured to adapt to externally applied interaction forces during use by adjusting the tensional form force applied by the connector in response to the applied interaction forces.

Description

[0001] MECHANISM FOR PROVIDING A LINK WITH VARIABLE STIFFNESS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a mechanism for providing a link with variable stiffness. In particular, it relates to a mechanism comprising at least one connector which is configured to apply a tensional force of variable size between a series of elements, so that by varying the size of the tensional force, at least the transversal stiffness of the mechanism is varied accordingly. The invention further relates to a system comprising such a mechanism.

[0004] BACKGROUND OF THE INVENTION

[0005] Robotic systems development has led to various types of robots, designed with functionalities to tackle specific tasks. Rigid robots, soft robots, and most recently variable stiffness robots have emerged as distinct categories due to their different mechanical properties, all of them however having strengths and weaknesses. Rigid robots have a solid and inflexible structure allowing them to excel in tasks requiring precision, strength, and stability which is e.g. important in relation to industrial automation. They do however bear limitations related to safety and adaptability to unknown environments. Soft robots are built using flexible materials, and they are designed to perform physical interaction with delicate or irregular objects. While they are characterized by intrinsic safety, adaptability to physical interaction, and versatility in a wide variety of complex and cluttered environments, they do however lack precision, strength, and often speed. Variable stiffness robots emerge among these two categories for their capability to address both limitations of rigid and soft robots, depending on the task at hand. Variable stiffness robots can in fact show a high degree of adaptability as well as precision, safety as well as load bearing capacity, and a task-dependent high degree of versatility.

[0006] OBJECT OF THE INVENTION

[0007] It is an object of the present invention to provide a mechanism for providing a link with variable stiffness, which mechanism can respond to applied interaction forces with a high degree of precision. It is another object of the present invention to provide a mechanism for providing a link with variable stiffness, which mechanism can quickly respond to different types of applied interaction forces.

[0008] It is another object of the present invention to provide a mechanism for providing a link with variable stiffness, which mechanism can be used in systems designed for navigating in unpredictable environments.

[0009] It is a further object of the present invention to provide an alternative to the prior art.

[0010] SUMMARY OF THE INVENTION

[0011] The above-described object and several other objects are intended to be obtained in a first aspect of the invention by providing a mechanism for providing a link with variable stiffness, the mechanism comprising:

[0012] a plurality of solid, discrete elements arranged at least in series, the elements comprising a first element at a first end of the series of elements, a second element at a second end of the series of elements, and at least one intermediate element arranged between the first and second elements,

[0013] at least one connector extending from the first end to the second end and interconnecting the elements,

[0014] wherein:

[0015] the at least one connector is configured to apply a tensional force of variable size between the first and second elements and thereby between the series of elements, so that by varying the size of the tensional force, at least the transversal stiffness of the mechanism is varied accordingly,

[0016] each of the elements touches at least one, such as each, neighbouring element at least when the tensional force is applied,

[0017] the shape of the rigid elements is so that the mechanism constitutes a pivoting system with equilibrium defined by the shape of the elements, so that there is at least one specific point, and possibly a constant distance, where two neighbouring elements rotate with respect to each other, and

[0018] the mechanism is configured to adapt to externally applied interaction forces during use by adjusting the tensional force applied by the at least one connector in response to the applied interaction forces. The feature that "each of the elements touches at least one, such as each, neighbouring element" means that it touches each element which it is arranged adjacent to. This will be in at least one point, such as a pivoting point or hinge, when present, as will be described in further details below. Neighbouring elements may also touch at multiple points.

[0019] By stating that neighbouring elements touch each other, it is also included that there may be something, such as a layer of rubber, between all or some of them. If the elements comprise an outer layer of e.g. rubber at least on the surfaces where they can get in contact with other elements, such an outer layer will be considered as being a part of the element. An effect of such a layer could be to protect against wear, to increase the friction, or to dampen possible noise.

[0020] However, it should be ensured that such a layer does not reduce the stiffness of the mechanism below a critical value where it could cause a less precise control of the mechanism. In general, all the elements must somehow be physically connected to ensure that there is a pivoting point between neighbouring elements.

[0021] By "providing a link with variable stiffness" is meant that the link has a variable stiffness, and it could therefore also be referred to as "providing a link having variable stiffness". Thus, the intended meaning is not to start with a link without variable stiffness and amending it to have variable stiffness.

[0022] By "transversal stiffness" is meant the bending stiffness causing a certain deflection of the variable stiffness mechanism under transverse force and / or bending moment. Therefore, transversal stiffness is the resistance of a mechanism against bending.

[0023] The feature that "each of the elements touches at least one, such as each, neighbouring element" includes the embodiments having hinges as will be described below, and where the contact is established at least partly via such hinges. By stating that "the mechanism constitutes a pivoting system with equilibrium defined by the shape of the elements" is meant that there is at least one specific point, and possibly a constant distance, where two neighbouring elements rotate with respect to each other. Thus, "rotate" could also be referred to as "pivot". This equilibrium condition preferably applies to all pairs of neighbouring elements. Hereby it is possible to control the stiffness of the mechanism by setting a certain tensional force. In case the pivot point changes, e.g. if the elements are partly spherical or segmented, the pivot point would change depending on the external bending force. An example of such an embodiment will be shown in the figures. The pivoting typically means that at other locations of the mutually facing surfaces than at the pivot point, there is no contact between these facing surfaces. The pivoting typically also means that in the mechanism according to the present invention, the elements move relative to each other in a pivoting movement without any sliding contact. The reference to "equilibrium" preferably also means that when the externally applied interaction forces are removed, the mechanism will assume the equilibrium of the pivoting system. Therefore, this could also be referred to as an equilibrium state or an equilibrium condition.

[0024] In some embodiments of the invention, the elements are or comprise flat parts touching each other. However, the scope of protection also covers embodiments having several flat parts, which can provide multiple equilibrium configurations of the mechanism. Examples of such embodiments will be shown in the figures.

[0025] By "interaction forces" is meant any externally applied mechanical forces and torques. The interaction forces will typically vary in size and orientation, thereby requiring varying stiffness of the mechanism in order to provide a desired response.

[0026] In some embodiments of the invention, the tensional force is variable to assume at least four, such as at least six, such as at least ten different sizes.

[0027] In some embodiments of the invention, the tensional force is incrementally variable, such as continuously variable. The mechanism may comprise at least 4 elements, such as 4-20 elements, such as 10-15 elements.

[0028] In some embodiments of the invention, all the elements are identical. In alternative embodiments, the elements have at least two different sizes and / or shapes. Different sizes and / or shapes can be used to design the mechanism to have a variable stiffness at different parts of the mechanism so that a desired stiffness profile along the mechanism can be obtained. As an example, a mechanism that can bend parabolically can be obtained by using flat circular elements of increasing radius the closer they are to a motor used to control the mechanism. Alternatively, the mechanism can be designed so that bending is achieved only at specific points or regions along the mechanism. A specific design for a given application will typically be determined by use of computer simulation, possibly in combination with tests performed on prototypes.

[0029] Facing surfaces of neighbouring elements may have mutually complementary shaped surfaces so that the elements remain in a desired mutual arrangement with respect to pivot points on the surfaces independent on the size of the applied interaction forces. Hereby it may be easier to control the functioning of the mechanism and thereby avoid any undesired responses.

[0030] The at least one connector may be a single connector. This may allow for a simple and precise control of the stiffness of the mechanism by adjusting the tensional force between the first and second elements. Such a single connector may e.g. be an inextensible wire attached at one end to the first element and at the other end to a variable stiffness spring element. The variable stiffness spring element can be achieved e.g. by a spring element and a motor that constrains the coils of the spring element based on its shaft rotation, so that the number of coils constituting the spring element can be varied. In another embodiment it is achieved by a motor-controlled back-driveable system that can pull a wire in a desired manner and can change the stiffness parameters by adjusting the motor current or the control parameters. However, the scope of protection covers any other variable stiffness mechanism, including a mechanism comprising a nonlinear spring. In some embodiments of the invention, the at least one connector is two wires arranged in a twisted configuration. This type is also referred to as a twist actuator, a twisted actuator, or a twisted string actuator. More details of such an embodiment will be given in relation to the figures.

[0031] The at least one connector may be arranged in a tube extending from the first end to the second end via inner holes in the elements. Hereby the connector will be protected from undesirable interactions with the elements. Such interactions could e.g. be friction, or it could be that a small unevenness of the connector could be caught on an edge of an element. By eliminating such risks, the control of the stiffness of the mechanism may be less prone to unintended disturbances.

[0032] In some embodiments of the invention, the first element is an end cap to which the at least one connector is fastened. When the at least one connector is arranged in a tube, the end cap may surround an end of the tube. An example of such an embodiment will be shown in the figures.

[0033] In some embodiments of the invention, the mechanism comprises:

[0034] - an array of the elements which are arranged and interconnected to form a surface, and

[0035] - a plurality of connectors arranged and interacting with the array of elements, so that the surface can change spatial (i.e. 3D) shape in response to the externally applied interaction forces during use by adjusting the tensional forces applied by the plurality of connectors.

[0036] The surface formed by the array of elements may be plane or non-plane, such as curved. The shape of the surface will depend on the shape of each of the elements and on their mutual arrangement. The shape of the surface will also be influenced by the actual externally applied interaction forces to which the mechanism is configured to adapt during use.

[0037] In some embodiments of the invention, the mechanism comprises:

[0038] - a plurality of the elements which are arranged and interconnected to form a three-dimensional structure, and

[0039] - a plurality of connectors arranged and interacting with the plurality of elements, so that the three-dimensional structure can change spatial shape in response to the externally applied interaction forces during use by adjusting the tensional forces applied by the plurality of connectors.

[0040] In some embodiments of the invention, the mechanism has a storage configuration for storage and transportation and a use configuration. Typically the mechanism is more compact in the storage configuration so that it takes up less space and is easier to handle. Typically the stiffness of the mechanism is higher in the use configuration than in the storage configuration. In the storage configuration, the tensional force may be very low, such as close to zero, and the mechanism may be changed from the storage configuration to the use configuration by applying a tensional force of increasing size. In the use configuration, the tensional force applied to the mechanism by the at least one connector may be varied to allow the mechanism to adapt to varying externally applied interaction forces.

[0041] The mechanism may also comprise further components, such as components used to maintain the mechanism in the storage configuration and / or in the use configuration. Alternatively or in combination therewith, such further components may be for providing additional stiffness and / or strength to the mechanism or to a system comprising the mechanism.

[0042] A mechanism comprising such further components could also be referred to as a system, such as a system to be described in the following.

[0043] In some embodiments of the invention, at least some of the elements are mutually connected via a hinge which applies a constraint to the mechanism by preventing non-rotational movement between the elements that are hingedly connected. Examples of such embodiments are shown in the figures.

[0044] In a second aspect, the invention relates to a system comprising a mechanism according to the first aspect of the invention.

[0045] Such a system may further comprise a controller configured to control the tensional force applied to the series of elements. The system may further comprise at least one motor, piezo electric element, or heating element for applying the tensional force to the at least one connector. In an embodiment in which a motor is used, the motor could be used to twist wires forming a connector connecting the first and second elements of the mechanism and thus changing the tensional force as a function of the motor shaft displacement. Alternatively, a motor could be used to pull a wire connecting the extremities of the mechanism and the tensional force can be changed by changing the motor control parameters.

[0046] In an embodiment where a heating element is implemented, the tensional force applied to the series of elements may be subject to a change of stiffness due to the material properties of the heating element being dependent on the temperature of the element itself. Similarly, in another embodiment, if a piezoelectric material is used, the actuation properties affecting the stiffness of the pulling mechanism may depend on the voltage applied to the piezoelectric element.

[0047] In a system according to the second aspect of the invention, the mechanism may be configured to adapt to externally applied interaction forces mechanically or by using a controller. In embodiments wherein it is done mechanically, an actuator with variable stiffness can be inserted as a pulling system. This can e.g. be in the form of a twisting actuator or a spring with a variable number of coils being engaged. By changing the stiffness and / or the pulling force, it is possible to achieve variable compliance over a certain externally applied interaction force due to the elements being prepacked. In embodiments comprising a controller and a motor, the connector, such as a pulling wire, can be attached to a back-driveable mechanism including a motor. The motor can be controlled to have the system behaving as a spring; thus the stiffness parameters can be set a priori. In embodiments comprising a twisting actuator, both the stiffness and the tensional force change due to the way the twisting actuator is functioning in that it has a variable axial stiffness, but it also shortens by twisting, and therefore it pulls more. In some embodiments of the invention comprising a motor, the current going through the motor can be controlled to be constant. This would achieve a constant tensional force and thus the stiffness of the system would be proportional to the current flowing. None of these two ways would require a sensor on the mechanism, only on the motor side. In yet another embodiment, a load cell may be arranged to measure the tensional force between the elements, and the tensional force can be adjusted through the motor controller based on the data received from the load cell.

[0048] At least for some embodiments of the invention, the system allows for real-time environmental feedback and requirements and provides the system with the ability to handle and adjust to a spectrum of possible scenarios.

[0049] The following is a non-exhaustive list of examples of applications in which the invention may find use:

[0050] - Valve for regulating a flow of fluid therethrough.

[0051] - Scaffolding for supporting another structure, such as a building to be protected against collapse or further collapse.

[0052] - Something having a size that makes it inconvenient to store and transport in the use configuration. This could e.g. be a ladder or an antenna.

[0053] A scaffolding comprising a mechanism according to the invention may e.g. find use in relation to war zones where buildings have been damaged by bombs or in relation to natural disasters, such as earthquakes. In both situations, the mechanism or system may be transported, e.g. by a robot, in a compact configuration into a building that is too dangerous for people to enter. When the mechanism is in place, it can be transformed into the use configuration in which it supports the building to make it safe for rescue workers to enter or at least provides protection to people possibly trapped inside the building.

[0054] In a third aspect, the invention relates to a robot comprising a system according to the second aspect of the invention. As mentioned above, traditional robots often face challenges in navigating unpredictable environments or performing delicate tasks due to a fixed level of stiffness. A robot comprising one or more mechanisms according to the first aspect of the present invention addresses this limitation by offering a dynamic solution that enhances a robot's resilience and adaptability with respect to which applications it can be used for. Alternatively, in a third aspect, the invention relates to an exosuit comprising a system according to the second aspect of the invention. Such an exosuit could e.g. be used for rehabilitation or human performance enhancement.

[0055] The third aspect of the invention could alternatively be formulated as the use of a system according to the second aspect of the invention for a robot or an exosuit. A robot can refer to a large number of applications, including but not limited to soft robotics, robotic structures, and robotic hands. The invention can also be used within other fields, such as haptic interfaces, medical applications, structural components for construction, logistics, security and safety applications, as well as vibration attenuation, just to mention a few potential applications. It may find use within a range of industries, including but not limited to robotic industry, medical industry, computer gaming, space industry, and sex toy industry.

[0056] The first, second and third aspects of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0057] BRIEF DESCRIPTION OF THE FIGURES

[0058] The mechanism according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0059] Figures l.a to l.f schematically show an example of a mechanism according to the first aspect of the invention.

[0060] Figures 2. a to 2.g schematically show another embodiment of the invention with another shape of the elements than in figures l.a to l.f.

[0061] Figures 3. a to 3.c schematically show two neighbouring elements of another embodiment of the invention. Figures 4. a to 4.e schematically show two neighbouring elements having two equilibrium configurations.

[0062] Figures 5. a to 5.c schematically show a series of elements having three equilibrium configurations for each set of neighbouring elements.

[0063] Figures 6. a and 6.b schematically show an embodiment of the invention in which the mechanism comprises an array of elements which are arranged and interconnected to form a surface.

[0064] Figure 7 schematically shows an example of a system according the second aspect of the invention.

[0065] Figures 8.a-8.d schematically show two similar embodiments of the invention, in which the elements are provided with hinges, each hinge interconnecting two neighbouring elements.

[0066] Figures 9.a-9.d schematically show an embodiment of the invention in which the mechanism comprises further components for providing additional stiffness and / or strength to the mechanism or to a system comprising the mechanism.

[0067] Figure lO.a-lO.b schematically show an example of an embodiment of the invention having a storage configuration and a use configuration.

[0068] Figures ll.a-ll.b schematically show an example of an embodiment of the invention in which the mechanism has a storage configuration and a use configuration.

[0069] DETAILED DESCRIPTION OF AN EMBODIMENT

[0070] Figures l.a to l.f schematically show an example of a mechanism 1 according to the first aspect of the invention. The mechanism 1 comprises a plurality of solid, discrete elements 2 arranged in series. Figure l.a shows the mechanism 1 in a fully retracted configuration, figure l.b shows a cross-sectional view along line A-A in figure l.a, and figure l.c shows one of the elements 2. Figure l.d shows the mechanism 1 in an extended and flexible configuration, figure l.e shows a cross- sectional view along line B-B in figure l.d, and figure l.f shows the mechanism 1 in a bent configuration. The configuration with no contact between the elements 2 corresponds to situations in which no tensional force F is applied to the elements 2 by the connector 3. In this configuration, the stiffness of the mechanism 1 is technically zero or the minimum possible stiffness given by the connector 3 itself or the tube 4, when present; see below.

[0071] In other words: The elements 2 are in contact in at least one point if the system has a stiffness >0 or greater than the minimum possible stiffness due to design of a specific embodiment. The reason for this is that if the stiffness is greater than 0, it means that there is one equilibrium configuration which depends on the geometry, and how much the system tries to reach this equilibrium depends on the pulling force.

[0072] However, if a pulling force is applied to the connector 3 from outside, or if a weight is hanging on one side of the mechanism 1, then that external force or weight generates a pull force, but the elements 2 may not be in contact and therefore the system would have zero stiffness.

[0073] The elements 2 comprise a first element 2A at a first end of the series of elements 2, a second element 2B at a second end of the series of elements 2, and intermediate elements 2 arranged between the first and second elements 2A,2B. In this embodiment, the first element 2A and the second element 2B are different from the other elements 2 which are identical. The first element 2A is an end cap to which the connector 3 is fastened. In this embodiment, the connector 3 is in the form of two wires 3 arranged in a twisted configuration and extending from the first end to the second end and interconnecting all the elements 2. Such a connector 3 can also be referred to as a twisted actuator. In the embodiment in figures l.a to l.f, the connector 3 is arranged in a tube 4 extending from the first to the second end via inner holes 5 in the elements 2. Such a tube 4 should preferably not affect the bending stiffness but should introduce a constraint so that if there is a sideward sliding between elements 2, the mechanism 1 gets back to its initial shape. The tube 4 thus has the dual purpose of:

[0074] 1) ensuring that the twisting wire 3 does not get worn out by the contact with the elements, and 2) providing a transversal equilibrium configuration ensuring that the elements get back to have the same axis.

[0075] In embodiments without a tube, at least the second purpose can be fulfilled by designing the elements to be conical in the central part, so that they can mechanically fit into each other and thereby the shape guides the elements towards an equilibrium when an external force is removed.

[0076] The twisting of the two wires is actuated by a motor (not shown), typically integrated in or engaged with the second element 2B. The connector in the form of a twisted actuator 3 has intrinsic compliance properties that change based on how much the actuator 3 twists. The elements 2 will rotate as shown in figure l.f, if an external moment is applied to the mechanism 1, forcing an extension of the twisted wires, thus resulting in a counteracting moment. The moment depends on the stiffness and pulling force of the wires so that the mechanism 1 shows variable stiffness properties. The connector 3 is configured to apply a tensional force of variable size between the first and second elements 2A,2B and thereby between the series of elements 2. This means that when twisting and thereby varying the size of the tensional force, at least the transversal stiffness of the mechanism 1 is varied accordingly. The mechanism 1 is configured to adapt to externally applied interaction forces during use by adjusting the tensional force applied by the connector 3 in response to the applied interaction forces.

[0077] Figures 2. a to 2.g schematically show another embodiment of the invention with another shape of the elements 2 than in figures l.a to l.f. Figures 2. a and 2.b are 3-dimesional and cross-sectional views, respectively, of an element 2. Figure 2.c shows the mechanism 1 in an unloaded state, and figure 2.d shows a cross-sectional view along line C-C in figure 2.c. Figures 2.e to 2.g show the mechanism 1 with an external torque applied thereto resulting in a bending of the mechanism 1. Figure 2.f is a cross-sectional view along line D-D in figure 2.e, and figure 2.g is a sectional view of two elements 2 in figure 2.f. The shape of the rigid elements 2 is so that the mechanism 1 constitutes a pivoting system with equilibrium defined by the shape of the elements 2. Facing surfaces of neighbouring elements have mutually complementary shaped surfaces so that the elements 2 remain in a desired mutual arrangement with respect to pivot points on the surfaces independent of the size of the tensional force. In the illustrated embodiment, the elements 2 are provided with a rim 6 along an upper circumferential edge and a matching groove 7 along a lower circumferential edge; with "upper" and "lower" referring to the orientation in the figures. In the embodiment in figures 2. a to 2.g, the mechanism 1 has a single connector 3 which is arranged in a tube 4 extending from the first to the second end via inner holes 5 in the elements 2. The connector 3 is in the form of twisted wires as described in relation to figures l.a to l.f. The first element 2A is an end cap to which the connector 3 is fastened.

[0078] The rotational stiffness between two consecutive elements 2 is directly proportional to the stiffness of the connector 3 (e.g. a twisting wire) which pulls the elements 2 together. With reference to figures 3. a to 3.c, and considering the embodiment of figures 2.c to 2.f, for an externally applied torque T, it holds r = F-, with F being the force on the connector 3 originated by the displacement among the centres of two adjacent elements 2, and R / 2 being the distance between the connector 3 and the pivoting point of the two adjacent elements 2. The inner force F depends on the stiffness of the connector k and the relative displacement between the centres of two adjacent elements 2, thus being F = kM. Under the assumption of small relative rotations among adjacent elements 2, it is possible to compute the displacement among the centres of two adjacent elements as A / = - 9 , with 9 being the relative rotation between two adjacent elements around the pivoting point. It results that T = k — 9, being the rotational stiffness between two adjacent elements kr= k—, a function of the connector stiffness k. If k can be regulated (e.g. by a motor or a variable stiffness spring element as described above), it results that the bending stiffness of the mechanism 1 can also be consequently regulated.

[0079] Figures 3. a to 3.c schematically show two neighbouring elements 2 of another embodiment of the invention. The rest of the mechanism 1 may e.g. resemble the one in the previous figures. In this embodiment, the elements 2 are not flat but partially round. When the two curved circumferences are in contact, given a rotation there is no elongation of the connector 3, resulting in zero rotational stiffness between two adjacent elements 2. However, when the flat parts enter into contact, the same principle applies as described for the previous figures. If an externally applied force pulls the elements apart as shown in figure 3.b, the pivoting point is at the edge of the rectangular shape and that causes an elongation of the connector, since the two centres get separated from each other. However, if an externally applied force is applied in the opposite direction so that the two elements rotate as in figure 3.c, then no change of distance between the two centres of the circles occurs, and therefore no stiffness is perceived as the two elements can freely rotate. These figures therefore illustrate that in some embodiments of the invention, it is possible to create non-symmetric behaviours by playing with the geometry of the elements.

[0080] With reference to the embodiment of figures 3.a-3.c, considering the embodiment in its rest position as in figure 3. a, with a connector 3 at rest length Is, it is evident that the connector 3 elongates upon an externally applied torque only if the flat part of adjacent elements 2 have a common pivot point located at a distance from the connector 3, resulting in an elongation of the connector 3 equal to 2AI, as in the embodiment of figure 3.b, thus resulting in the adjacent elements 2 experiencing a relative rotational stiffness as in the case of the embodiment of figures 2.a-g. If however, the pivot point coincides with one of the points on the connector 3 (as in the embodiment of figure 3.c) the elongation is either null or does not contribute to the variation of rotational stiffness between the two adjacent elements 2.

[0081] Such a design of the elements 2 may e.g. be used for a knee joint exoskeleton where the knee can be supported e.g. when squatting. Such an exoskeleton can e.g. be a wearable supporting device for elderly people, or it can be an enhancing device for e.g. high impact sports applications, such as parkour and skiing, with the aim of protecting the knee joints and tendons when bending.

[0082] Figures 4. a to 4.e schematically show two neighbouring elements 2 having two equilibrium configurations. Figure 4. a is a side view, figure 4.b is a top view, and figure 4.c is a cross-sectional view along line A-A in figure 4.b. Figures 4.d and 4.e show the two elements 2 in two different equilibrium configurations. The pivot points are marked with black dots.

[0083] Figures 5. a to 5.c schematically show a series of elements 2 having three equilibrium configurations for each set of neighbouring elements 2. A connector 3 passes through and thereby connects the centre points of the elements 2. The pivot points are shown with black dots. Figures 5. a to 5.c show the three equilibrium configurations of the two middle elements, but the mechanism 1 can obtain other shapes when other mutual pivoting of neighbouring elements are allowed to take place.

[0084] Figures 6. a and 6.b schematically show an embodiment of the invention in which the mechanism 1 comprises:

[0085] - an array of elements 2 which are arranged and interconnected to form a surface, and

[0086] - a plurality of connectors 3 arranged and interacting with the array of elements 2,

[0087] so that the surface can change shape in response to the externally applied interaction forces during use by adjusting the tensional forces applied by the plurality of connectors 3. The vertices of the triangles are connected by O-rings 13 which simply keep all the elements in place but do not really give stiffness to the surface. The minor stiffness provided from the O-rings constitutes the minimum stiffness of the surface and allows the different triangular elements not to flip out when the connectors formed by wires are pulled. When the wires are pulled, they have the effect of compressing all the elements together. The elements have a certain thickness, and the wires pass through the centres. This generates an effect similar to the first embodiment against forces acting on the direction orthogonal to the surface.

[0088] Figure 6. a shows a configuration in which the elements 2 bend in response to an externally applied force so that they form a 3D-surface. Figure 6.b shows the same mechanism 1 as in figure 6. a, wherein the bending stiffness of the mechanism has been increased by applying a tensional force F to the two connectors 3. Hereby the shape of the surface formed by the elements will change, such as change to the plane configuration shown in figure 6.b.

[0089] Figure 7 schematically shows an example of a system 8 according the second aspect of the invention. The system comprises first and second members 9,10 mutually interconnected by a mechanism 1 which may e.g. be of one of the types shown on the previous figures. The system 8 comprises a controller 11 configured to control the tensional force applied to the series of elements 2. It further comprises at least one motor 12 for applying the tensional force to the at least one connector of the mechanism 1.

[0090] Figures 8.a-8.d schematically show two almost similar embodiments of the invention, in which the elements 2 are provided with hinges 14, each hinge 14 interconnecting two neighbouring elements 2. In the figures, the hinges 14 are shown at a small distance from the elements 2 for clarity only, but in practise they are connected thereto. In these embodiments, the mechanisms 1 have a storage configuration for storage and transportation and a use configuration. Figure 8. a shows one of the mechanisms 1 in the use configuration, and figure 8.b shows the same mechanism 1 in the storage configuration. In this embodiment, the elements 2 are provided as plates. Figure 8.c shows a side view of the other of the mechanisms 1 in the storage configuration, and figure 8.d shows that mechanism 1 in the use configuration. In this embodiment, the elements 2 are provided as rods. As shown in these figures, the elements 2 are provided with guides 15 used to keep the connector 3 in the desired positions. In figures 8.b-8.d the connector is not shown. In figures 8.c-8.d the guides for the connector are not shown. When the tensional force F applied by the connector 3 is increased, the mechanism 1 can be changed from the storage configuration to the use configuration. Furthermore, when already in the use configuration, the stiffness of the mechanism 1 can still be varied by varying the size of the tensional force F or the stiffness of the connector 3. By arranging the guides 15 e.g. as shown in the figures, it is possible to route the connector 3 in relation thereto in order to maximise / increase the potential torque at the points of rotation, i.e. at the hinges 14, as it is possible to increase the distance d of the connector 3 from the axis of rotation of the hinge joints 14 to the whole element 2 and even outside of that element.

[0091] The following terms are used in the description: wire = connector, F {ext} = externally applied interaction forces, and joint = hinge.

[0092] For example, in the embodiment shown in figure 8. a, the internal wire pull force is, being k the cable stiffness and Al the elongation of the wire due to the external force F {ext}. F = kM

[0093] The equivalent torque experienced at hinges if

[0094] T = Fd = kd

[0095] Being d the distance of the projection between the hinge axis and the pulling wire. While the pulling wire tension F remains the same throughout the wire length, for a given external force F {ext}, the perceived hinge torque due to the external force is dependent on the distance between the hinge position and the orthogonal projection of the external force F {ext}, so that, at joint 1, for example

[0096] T1=Fext^l=kd l

[0097] And given that the total elongation Al is the sum of the elongations due to the individual joint rotations, which we approximate in this configuration as

[0098] A / , = R6tand A / = AZt+ A / 2+ A / 3+ ••• (being R the distance between the hinge joint axis and the wire routing axis) if follows that

[0099] Ti=Fextd-i = kdAl = kdR 61+ d2+ d3+ ••• )

[0100] T2= kdM = kdR 61+ d2+ d3+ ••• )

[0101] And so on.

[0102] Since the stiffness is given by the partial derivative of the joint torque over the joint infinitesimal rotations, it occurs that

[0103] dr /

[0104] — =kl= kdR

[0105]

[0106] Meaning that all joints experience the same stiffness, while every joint will experience a rotation due to the external force that depends on the distance between the external force orthogonal projection and the i-th hinge joint axis.

[0107] Figures 9.a-9.d schematically show an embodiment of the invention in which the mechanism 1 resembles the one in figures 8.c-8.d and further comprises components 16,17 for providing additional stiffness and / or strength to the mechanism 1. Figure 9. a shows the mechanism 1 in the storage configuration, and figure 9.b shows the mechanism 1 in the use configuration into which it has been brought by increasing the tensional force F applied to the connector (not shown in this figure). As shown in figure 9.c, the mechanism 1 is provided with further components in the form of rods 16 connecting an external cable 17 thereby providing structural stiffness in a manner resembling that of a cable-truss system. As schematically shown in figure 9.d, such a mechanism 1 can be used as a temporary bridge that may e.g. be useful at locations where the normal infrastructure has been damaged by bombs or natural disasters.

[0108] Figure lO.a-lO.b shows another example of an embodiment of the invention in which the mechanism 1 can be expanded from a storage configuration as shown in figure 10. a to a use configuration as shown in figure 10. b by applying a tensional force F to the at least one connector 3 and thereby to the elements 2. It will be possible to make such a design with just one connector 3, but it may also be possible to use more than one connector 3 in order to simplify the design or the control thereof.

[0109] Figures ll.a-ll.b schematically show an example of an embodiment of the invention in which the mechanism 1 comprises a plurality of elements 2 which are arranged and interconnected to form a three-dimensional structure, and a plurality of connectors 3 arranged and interacting with the plurality of elements 2, so that the three-dimensional structure can change spatial shape in response to the externally applied interaction forces during use by adjusting the tensional forces F applied by the plurality of connectors 3. Figure 11. a shows the mechanism 1 in a storage configuration, and figure 11. b shows the mechanism 1 in a use configuration. The number and arrangement of the plurality of connectors 3 may differ from what is shown in the figures. In an embodiment as shown in figures ll.a-ll.b, the elements 2 rotate with respect to each other either by approximately 90deg or 180deg, and they may comprise hinges 14 for structural resistance.

[0110] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

CLAIMS1. Mechanism (1) for providing a link with variable stiffness, the mechanism (1) comprising:a plurality of solid, discrete elements (2) arranged at least in series, the elements (2) comprising a first element (2A) at a first end of the series of elements (2), a second element (2B) at a second end of the series of elements (2), and at least one intermediate element (2) arranged between the first and second elements (2A,2B),at least one connector (3) extending from the first end to the second end and interconnecting the elements (2),wherein:the at least one connector (3) is configured to apply a tensional force (F) of variable size between the first and second elements (2A,2B) and thereby between the series of elements (2), so that by varying the size of the tensional force (F), at least the transversal stiffness of the mechanism (1) is varied accordingly, each of the elements (2A,2B) touches at least one, such as each, neighbouring element at least when the tensional force (F) is applied,the shape of the rigid elements (2) is so that the mechanism (1) constitutes a pivoting system with equilibrium defined by the shape of the elements (2), so that there is at least one specific point, and possibly a constant distance, where two neighbouring elements rotate with respect to each other, and the mechanism (1) is configured to adapt to externally applied interaction forces during use by adjusting the tensional force (F) applied by the at least one connector (3) in response to the applied interaction forces.

2. Mechanism (1) according to claim 1, wherein the tensional force (F) is variable to assume at least four, such as at least six, such as at least ten different sizes.

3. Mechanism (1) according to claim 1 or 2, wherein the tensional force (F) is incrementally variable, such as continuously variable.

4. Mechanism (1) according to any of the preceding claims, comprising at least 4 elements (2), such as 4-20 elements, such as 10-15 elements.

5. Mechanism (1) according to any of the preceding claims, wherein all the elements (2) are identical.

6. Mechanism (1) according to any of claims 1 to 4, wherein the elements (2) have at least two different sizes and / or shapes.

7. Mechanism (1) according to any of the preceding claims, wherein facing surfaces of neighbouring elements (2) have mutually complementary shaped surfaces so that the elements (2) remain in a desired mutual arrangement with respect to pivot points on the surfaces independent on the size of the tensional force (F).

8. Mechanism (1) according to any of the preceding claims, wherein the at least one connector (3) is a single connector.

9. Mechanism (1) according to any of the preceding claims, wherein the at least one connector (3) is two wires arranged in a twisted configuration.

10. Mechanism (1) according to any of the preceding claims, wherein the at least one connector (3) is arranged in a tube (4) extending from the first end to the second end via inner holes (5) in the elements (2).

11. Mechanism (1) according to any of the preceding claims, comprising:- an array of the elements (2) which are arranged and interconnected to form a surface, and- a plurality of connectors (3) arranged and interacting with the array of elements (2),so that the surface can change spatial shape in response to the externally applied interaction forces during use by adjusting the tensional forces (F) applied by the plurality of connectors (3).

12. Mechanism (1) according to any of the preceding claims, comprising:- a plurality of the elements (2) which are arranged and interconnected to form a three-dimensional structure, and- a plurality of connectors (3) arranged and interacting with the plurality of elements (2),so that the three-dimensional structure can change spatial shape in response to the externally applied interaction forces during use by adjusting the tensional forces (F) applied by the plurality of connectors (3).

13. Mechanism (1) according to any of the preceding claims, wherein at least some of the elements are mutually connected via a hinge which applies a constraint to the mechanism by preventing non-rotational movement between the elements that are hingedly connected.

14. System (8) comprising a mechanism (1) according to any of the preceding claims.

15. System (8) according to claim 14, further comprising a controller (11) configured to control the tensional force (F) applied to the series of elements (2).

16. System (8) according to claim 14 or 15, further comprising at least one motor (12), piezo electric element, or heating element for applying the tensional force (F) to the at least one connector (3).

17. Robot comprising a system (8) according to any of claims 14-16.

18. Exosuit comprising a system (8) according to any of claims 14-16.

19. Use of a mechanism (1) according to any of claims 1 to 13 for:- haptic interfaces, medical applications, structural components for construction, vibration attenuation, logistics, security and safety applications, or- a system (8) within the robotic industry, medical industry, computer gaming, space industry, or sex toy industry.

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