NL2015803B1 - Ortho-planar spring and device equipped with such an ortho-planar spring. - Google Patents

Abstract

Ortho-planar spring, comprising a frame and a shuttle that is perpendicularly movable with respect to the frame, wherein flexible members connect the shuttle to the frame, and wherein in an unloaded condition the frame, the flexible mem- bers and the shuttle provide the spring with a flat configuration, wherein the spring is stressed into a non-flat configuration by arranging that at least a first transitional area connecting the frame and a flexible member, and at least a second transitional area connecting a flexible member and the shuttle, are moved out of the flat configuration.

Description

Ortho-planar spring and device equipped with such an ortho-planar spring

The invention relates to an ortho-planar spring, comprising a frame and a shuttle that is perpendicularly movable with respect to the frame, wherein flexible members connect the shuttle to the frame, and wherein in an unloaded condition the frame, the flexible members and the shuttle provide the spring with a flat configuration.

Such an ortho-planar spring is known from US 6,983,924, which document teaches that the spring has a platform or shuttle which is movably coupled to a base or frame, and being linearly movable with respect to said base along at least a portion of an axial direction perpendicular to both a base surface and a platform surface. A resilient and flexible connecting structure is connected to and positioned between the base and the platform. The spring is very compact and does not have rotation between the deflecting ends.

It is an object of the invention to set a condition to an ortho-planar spring in which it will exhibit negative stiffness that is capable to balance a positive stiffness forming part of the same spring, or which positive stiffness is external of the spring so as to enable using this ortho-planar spring to provide a construction which overall will exhibit zero or near to zero stiffness. Such a modified ortho-planar spring is particularly but not exclusively suitable for use in relatively small devices, such as in energy harvesters as will be further disclosed hereinafter.

According to the invention an ortho-planar spring and a device incorporating such an ortho-planar spring are proposed in accordance with one or more of the appended claims.

In a first aspect of the invention the spring is stressed into a non-flat configuration by arranging that at least a first transitional area connecting the frame and a flexible member and/or at least a second transitional area connecting a flexible member and the shuttle, are moved out of the flat configuration and fixated. This provides the possibility that the shuttle will exhibit negative stiffness, which is particularly promoted by arranging that the first and sec ond transitional areas are moved out of the flat configuration by a translation and/or rotation of said areas.

The negative stiffness behaviour is suitably achieved by arranging that the first and second transitional areas are placed and fixated under a predefined angle and/or a predefined displacement with reference to the flat configuration.

The objects of the invention can be realized in many ways, however it is preferable that the spring is clamped between a lower assembly element and an upper assembly element. These elements ensure that said lower assembly element and said upper assembly element can simply clamp and fix the spring at the location of the first and second transitional areas .

Suitably the lower assembly element and the upper assembly element have correspondingly shaped surfaces that engage the ortho-planar spring on opposite sides of said spring to fixate the first and second transitional areas under a predefined angle and/or a predefined displacement with reference to the flat configuration.

It is further preferred that the shuttle is provided in the spring's center and the flexible members are provided to arrange that the spring is rotationally symmetric or mirror s ymme trie.

Advantageously the shuttle is movable perpendicular to the plane of the flat configuration, and is provided with a central connecting means for connecting with an actuation rod or similar. This suitably arranges that the spring of the invention can be applied in a device being provided with such actuation rod.

It is also beneficial that the spring is monolithic, wherein the frame delineates the shuttle and that said frame is along its entire length fixed in position. This arrangement ensures that micro slip of the frame with reference to the shuttle which would otherwise deteriorate the spring's performance, is effectively avoided. A suitable arrangement therefore is that the frame is fixed into position between the lower assembly ele-ment and the upper assembly element.

In another embodiment the shuttle is connected to a neighbouring second shuttle of the spring through a first fur ther flexible element connected to the second shuttle at a first side, wherein at a second side opposite to said first side of the second shuttle a second further flexible element is provided that connects to the frame. This makes possible to integrate in one and the same spring a part that exhibits a positive stiffness and a part that exhibits a negative stiffness. For providing the part with positive stiffness it suffices that the transitional areas of the first and second further flexible elements are moved out of the plane of the flat configuration by translation and/or rotation.

As already mentioned the invention is also embodied in a device incorporating an ortho-planar spring according to the invention. Suitably the device is an energy harvester.

The invention will hereinafter be further elucidated with reference to the drawing of an exemplary embodiment of an apparatus according to the invention that is not limiting as to the appended claims.

In the drawing: - FIGURE 1: represents a top view of an ortho-planar spring of the present invention; - FIGURE 2A: represents a perspective view of a lower assembly element which is used to pre-stress the ortho-planar spring of Figure 1; - FIGURE 2B: represents a perspective view of an upper assembly element which is used to pre-stress the ortho-planar spring of Figure 1; - FIGURE 2C: represents an exploded view of the assembly elements of Figures 2A and 2B prior to their assembly with the ortho-planar spring of Figure 1; - FIGURE 2D: represents a perspective view of the assembly of the assembly elements of Figures 2A and 2B together with the ortho-planar spring of Figure 1; - FIGURE 3A: represents a perspective view of the ortho-planar spring of the present invention in an upward deflected position; - FIGURE 3B: represents a perspective-front view of the ortho-planar spring shown in Figure 3A; - FIGURE 3C: represents a perspective view of the ortho-planar spring of the present invention in a downward de- fleeted position; - FIGURE 3D: represents a perspective-front view of the ortho-planar spring shown in Figure 3C; - FIGURE 4A: represents an exploded view of a vibration energy harvesting device equipped with an ortho planar spring of the invention; - FIGURE 4B: represents a cross-sectional perspective view of an assembled vibration energy harvesting device according to Figure 4A with for clarity purposes fully shown springs; - FIGURE 4C: represents ac Cross-sectional front-view of the assembled vibration energy harvesting device of Figure 4B; - FIGURE 5: represents a top view of a conventional positive stiffness ortho-planar spring which can be used in the device of Figures 4B and 4C; - FIGURE 6: represents a top view of a second embodiment of an ortho-planar spring of the present invention; - FIGURE 7A: represents a schematic top view of a third embodiment of an ortho-planar spring of the present invention which features additional means providing an arbitrary positive stiffness; - FIGURE 7B: represents a top view of a fourth alternative embodiment of an ortho-planar spring according to the present invention with combined stiffness; - FIGURE 8A: represents a perspective view of a lower assembly element which is used to pre-stress the ortho-planar spring of Figure 7B; - FIGURE 8B: represents a perspective view of an upper assembly element which is used to pre-stress the ortho-planar spring of Figure 7B; - FIGURE 8C: represents an exploded view of the assembly elements of Figures 8A and 8B prior to their assembly with the ortho-planar spring of Figure 7B; - FIGURE 8D: represents a perspective view of the assembly of the assembly elements of Figures 8A and 8B together with the ortho-planar spring of Figure 7B; - FIGURE 9A: represents an exploded view of a vibration energy harvesting device provided with the ortho-planar spring of Figure 7B; - FIGURE 9B: represents a cross-sectional perspective view of the assembled vibration energy harvesting device of Figure 9A with fully shown springs; - FIGURE 9C: represents a cross-sectional front-view of the assembled vibration energy harvesting device of Figure 9B; and - FIGURES 10 - 12: represent top views of further embodiments of the ortho-planar spring of the invention.

Whenever in the Figures the same reference numerals are applied, these numerals refer to the same parts.

Referring first to figure 1 the ortho-planar spring 100 is shown to have a frame 10 and a shuttle 20 which are connected directly via an elastic structure 1. The ortho-planar spring 100 is preferably made from a planar and monolithic design. Also it is rotationally symmetric around line A-A and has a shared frame 10 and shared shuttle 20 for elastic structure 1.

The ortho-planar spring 110 shown in figure 6 works similar to the spring 100 of figure 1, but instead of being rotationally symmetric, it is mirror symmetric with respect to line B-B in order to cancel out any created moment to the shuttle .

In order to generate a predetermined negative stiffness behaviour with the ortho-planar spring 100 of figure 1 or figure 6, the elastic structure 1 is pre-stressed by translation and rotation of transitional areas la and lb. This can be done by the assembly as illustrated in Figures 2A to 2D. This pre-stressing is for instance done by means of clamping the full spring device 100 in-between lower assembly element 31 and upper assembly element 32. The pre-stressing may also be done by a fabrication step in which spring device 100 is shaped by (partially) plastic deformations to the contours of the lower and upper assembly elements 31 and 32. The frame 10 is preferably clamped in between lower frame rigid body surface 40 and upper frame rigid body surface 42. The shuttle 20 is at its periphery clamped in between lower shuttle rigid body surface 41 and upper shuttle rigid body surface 43. These clampings can be achieved by bolting the lower assembly ele- ment 31 and the upper assembly element 32 together via holes 11 and 21 or in any other suitable method to join said lower assembly element 31 and upper assembly element 32.

In the assembled system according to figure 2-D, the shuttle 20 is movable in a certain predefined range along axis a-a. Preferably the shuttle 20 is actuated at a center hole 22. The shuttle positions are more clearly shown in Figure 3A and 3B, representing the upwardly deflected position, and Figure 3C and 3D, representing the downwardly deflected position.

In order to preserve the performance of the prestressed spring when actuating at center hole 22, motion directions different from direction a-a must be substantially low.

One application of energy harvesting is shown in Figure 4A - 4D, representing a vibration energy harvesting [VEH] device 70, comprising the ortho-planar spring 100 of the invention, positive stiffness ortho-planar springs 33 and means for transducing energy 34. This VEH 70 is capable of harvesting energy at a low frequency and wide bandwidth. This is due to the overall stiffness at the energy transforming means 50, 51 being at zero with neutral stable behaviour, or at 'near' zero stiffness with slight bi-stable or slight mono-stabile behaviour .

To substantially limit the motion directions other than along axis a-a and to generate the desired stiffness, VEH 70 employs two ortho-planar springs 33 as shown in Figure 5, that are spaced apart at a certain distance, as can be seen in Figures 4A - 4D. The lower assembly element 31 clamps the first ortho-planar spring 33 at its frame 60 to the housing 52 of transducer 34. Further, a bottom plate 35 clamps the frame 60 of the second ortho-planar spring 33 to the housing 52 of the transducer 34. Both positive stiffness ortho-planar springs 33 are coupled at their respective shuttles 61 to a central axle 39 connected to the shuttle 20 of the invention, which substantially limits motions of shuttle 20 in directions different from direction a-a and maintains its intended behaviour. The coupling of ortho-planar spring 100 of the invention with the conventional ortho-planar spring 33 results in the desired combined stiffness characteristics of the VEH 70.

The transduction of vibrational energy is performed by creating movement between magnet 51 and coil 50. The coil 50 is fixed to the housing 52 and the magnet 51 is fixed to the central axle 39. By movement of the central axle 39 along a-a also the magnet 51 is moved and hence motion between magnet 51 and coil 50 is created that provides recoverable energy.

Making now reference to figure 7A it is shown that ortho-planar spring 160 combines the previously mentioned ortho-planar spring of figure 1 with a part 4 having an arbitrary positive stiffness, therewith combining the force deflection behaviour of ortho-planar spring 100 of figure 1 with the behaviour of a conventional positive stiffness second ortho-planar spring 33 as shown in figures 4A - 4C into a single plane .

Figure 7B shows an example of an ortho-planar spring 140, wherein the part having an arbitrary positive stiffness is embodied in a second elastic structure 2-23-3. The ortho-planar spring 140 has a frame 10 and a shuttle 20 which are connected directly via a first elastic structure 1 and via a second elastic structure 2-23-3. The second elastic structure is build up out of two flexible elements 2, 3 in series, wherein the first elastic element 2 is placed between frame 10 and intermediate shuttle 23. The second elastic element 3 is placed between intermediate shuttle 23 and shuttle 20. Also in this embodiment the ortho-planar spring 140 is made from a planar and monolithic design. Further it is rotationally symmetric around line G-G and has a shared frame 10 and shared shuttle 20 for said first elastic structure 1 and second elastic structure 2-23-3.

Figure 8A to 8D depict means to provide the ortho-planar spring 140 of figure 7B with a predetermined stiffness such as a zero stiffness with neutral stable behaviour or 'near' zero stiffness with slight bi-stable or slight monostabile behaviour. The elastic structure 1 is pre-stressed by translation and/or rotation of transitional areas la and lb, and as a consequence of that a negative stiffness behaviour is provided to the ortho-planar spring 140 at its shuttle 20. The second elastic structures 2-23-3 stiffness should therefore be 'near' equal and opposite, or equal to the negative stiffness created in elastic structure 1. The placement in series of elastic elements 2 and 3 and their internal degree of freedom assures that snap-through can be avoided and positive stiffness is maintained in the a-a direction. This is preferably provided by having the clamping points of the second elastic structure 2-23-3 parallel to their fabrication plane and hence transitional areas 2a, 2b, 3a and 3b are translated but not rotated. As the first elastic structure 1 and the second elastic structure 2-23-3 are both coupling frame 10 and shuttle 20 together their stiffness can be added, therewith generating overall zero stiffness behaviour.

As illustrated in Figure 8A to 8D, pre-stressing is done by means of clamping the full spring device 140 in-between lower assembly element 37 and upper assembly element 36. The pre-stressing may also be done by a fabrication step in which spring device 140 is shaped by (partially) plastic deformations to the contours of the lower and upper assembly elements 36 and 37.

The frame 10 of the spring shown in figure 7A is clamped in between lower frame rigid body surface 44 and upper frame rigid body surface 47. The shuttle 20 is clamped in between lower shuttle rigid body 48 and upper shuttle rigid body 45. The shuttle 23 is clamped at its periphery in between lower intermediate shuttle rigid body surface 46 and upper intermediate shuttle rigid body surface 49. The lower and upper assembly element 36 and 37 can be bolted together via holes 11 and 21 or in any other suitable method to join the said lower and upper assembly elements.

The assembled system of figure 8D is movable at its shuttle 20 is movable in a certain predefined range along axis a-a, wherein it is preferably actuated at the center hole 22. When actuating the shuttle the motion directions other than direction a-a must be substantially low to preserve the performance of the pre-stressed spring.

Figure 9 A-D show the application of the spring 140 of the invention in an energy harvesting device VEH 71, comprising said ortho-planar spring 140 and means for transducing energy 34. Compared to the VEH 70 of figures 4A - 4D, the VEH 71 of figures 9A - 9D has an ortho-planar spring 140 with combines positive and negative stiffnesses, which therefore does not need a separate positive stiffness ortho-planar spring.

The device has two springs 140 according to the embodiment shown in figures 8A - 8D that are coupled together having in between them the means for transduction of energy. The respective shuttles of the two ortho-planar springs 140 are coupled by a central connecting axle 39. The house 52 of the transducer 34 is in this embodiment made in one piece with the lower assembly element 37, both at the top and bottom. Also the off axis motions are reduced by applying the two ortho-planar springs 140 at a distance spaced from each other.

The transduction of vibrational energy is performed by creating relative movement between magnet 51 and coil 50. The coil 50 is fixed to the housing 52 and the magnet 51 is fixed to the central axle 39. Since the central axle 39 is movable along a-a in figure 9B, also the magnet 51 is movable in said direction and the resulting relative motion between magnet 51 and coil 50 can be created for the generation of electrical energy.

Although the invention has been discussed in the foregoing with reference to exemplary embodiments of the ortho-planar spring and device of the invention, the invention is not restricted to these particular embodiments which can be varied in many ways without departing from the invention. The discussed exemplary embodiments shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary the embodiments are merely intended to explain the wording of the appended claims without intent to limit the claims to these exemplary embodiments. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using these exemplary embodiment. As an example of the further possible variations, figure 10 shows ortho-planar springs 120 that function similar to the spring 140 of figure 7B, but instead of being rotationally symmetric, this device provides equally spaced rotational symmetry around C-O-C. 0 being the origin (center) .

Further the ortho-planar spring 130 shown in Figure 11 functions similarly with the spring 140 of figure 7B, but a part of D-O-E is mirror symmetric around D-0 and equally spaced rotationally symmetric around E-O-E.

Finally figure 12 shows ortho-planar springs 150 that functions similarly to spring 140 of figure 7B and is symmetric along the line F-F, albeit that the first and second elastic structure are reversed in location.

Claims (15)

An ortho-planar spring (100, 110, 120, 130, 140, 150) comprising a frame (10) and a shuttle (20) that is perpendicular to the frame (10), wherein flexible parts (1) , 2, 3) connect the shuttle (20) to the frame (10), and in an unloaded state the frame (10), the flexible parts (1, 2, 3) and the shuttle (20) provide the spring with a flat provide configuration, characterized in that the spring is loaded until it has an uneven configuration by arranging that at least a first transition area (1a) connecting the frame (10) and a flexible part (1) and / or at least a second transition area (1b) connecting a flexible part (1) and the shuttle (20), have been moved away from the planar configuration and fixed. Ortho-planar spring according to claim 1, characterized in that the first and second transition regions (1a, 1b) are moved out of the planar configuration by a translation and / or rotation of said regions. Ortho-planar spring according to claim 1 or 2, characterized in that the first and second transition area (1a, 1b) are placed at a predetermined angle and / or displacement with respect to the flat configuration. Ortho-planar spring according to one of the preceding claims 1-3, characterized in that said spring is clamped between a lower assembly element (31, 37) and an upper assembly element (32, 36). Ortho-planar spring according to claim 4, characterized in that said lower assembly element (31, 37) and said upper assembly element (32, 36) clamp and fix the spring at the location of the first and second transition area (1a, 1b) ). The ortho-planar spring according to claim 4 or 5, characterized in that the lower assembly element (31, 37) and the upper assembly element (32, 36) are provided with correspondingly shaped surfaces that the ortho-planar spring on opposite sides of enclosing said spring for fixing the first and second transition region (1a, 1b) at a predetermined angle with respect to the planar configuration. Ortho-planar spring according to any one of the preceding claims 1-6, characterized in that the shuttle (20) is provided in the center of the spring and the flexible parts (1) are provided to cause the spring to rotate. symmetrical or mirror-symmetrical. Ortho-planar spring according to one of the preceding claims 1-7, characterized in that the shuttle (20) is movable perpendicularly to the plane of the flat configuration, and is provided with a central connecting means (22) for coupling to a operating rod (39) or the like. Ortho-planar spring according to one of the preceding claims 1-8, characterized in that it is monolithic, the frame (10) bounding the shuttle (20) and said frame (10) being fixed in position along its entire length is. Ortho-planar spring according to one of the preceding claims 4-8, and claim 9, characterized in that the frame (10) is fixed in position between the lower assembly element (31, 37) and the upper assembly element (32, 36). Ortho-planar spring according to one of the preceding claims 1 - 10, characterized in that the shuttle (20) is connected to an adjacent second shuttle (23) of the spring with a first further flexible element connected on a first side with the second shuttle (23), wherein on a second side opposite said first side of the second shuttle (23) a second further flexible element is provided which is connected to the frame (10). Ortho-planar spring according to claim 11, characterized in that the transition regions (2a, 2b, 3a, 3b) of the first and second further flexible elements are moved out of the plane of the flat configuration by translation and / or rotation. Device with at least one ortho-planar spring according to one of the preceding claims 1-12. Device according to claim 13, characterized in that said device is combined with at least one ortho-planar spring, preferably a spiral spring. Device according to claim 13 or 14, characterized in that said device is an energy harvesting device (70, 71).