A variable topology multi-stiffness spring structure and adjustment method based on cable constraints

Abstract

This invention proposes a variable topology multi-stiffness spring structure and adjustment method based on flexible cable constraints, belonging to the field of variable stiffness spring technology. The variable topology multi-stiffness spring structure includes a first elastic unit, a second elastic unit, a series flexible cable, and a winch device. The first elastic unit includes a first spring, a first inner connecting plate, and a first outer connecting plate. The second elastic unit includes a second spring, a second inner connecting plate, and a second outer connecting plate. The series flexible cable connects the first inner connecting plate and the second inner connecting plate to adapt to the two elastic units being subjected to series forces under low loads. The winch device is used to adjust the effective access length of the series flexible cable. The first outer connecting plate and the second inner connecting plate are adapted to form a unidirectional rigid constraint through abutment or tension connection, and the second outer connecting plate and the first inner connecting plate are adapted to form a unidirectional rigid constraint through abutment or tension connection to adapt to the two elastic units being subjected to parallel forces under high loads. This invention has a three-stage load stiffness response and an adjustable threshold.

Description

Technical Field

[0001] This invention relates to the field of mechanical variable stiffness technology, and in particular to a variable topology multi-stiffness spring structure and adjustment method based on flexible cable constraints. Background Technology

[0002] Variable stiffness and multi-segment response elastic structures have important applications in robotics, vibration control, and shock absorption. For example, in robotics, the variable stiffness actuator (VSA) adjusts joint stiffness by pre-tensioning a spring with a motor or changing the effective length of the elastic element. However, such solutions are typically complex, costly, require active control and energy supply, and have limitations in passive adaptation and multi-segment response.

[0003] Furthermore, traditional spring combinations can also provide segmented stiffness characteristics to some extent. For example, automotive suspensions use dual-rate springs, connecting two spring segments in series or supplemented with an auxiliary spring to achieve a two-stage response of initial softness and subsequent stiffness. Specifically, this is achieved by having one spring coil compress first, and then having the other spring take over after the travel is halfway complete, thus achieving a jump in stiffness from low to high. However, the stiffness transition point of such structures is determined by the preset spring geometry, making it difficult to easily adjust the threshold. Simultaneously, their force-displacement curves typically only have two segments of change, lacking a clear plateau characteristic (i.e., a buffer zone where displacement increases while force remains essentially constant within a certain load range).

[0004] To achieve a near-constant force plateau response, some cushioning and protective devices in related technologies have introduced special energy absorption mechanisms. For example, the load limiter of a seat belt uses folds sewn into the belt and sets the stitch strength. When the tension exceeds a threshold, the stitches tear, releasing extra belt length and allowing the occupant more displacement cushioning during high impacts. This design is equivalent to creating a controlled "plateau" range under a specific load. However, the stitch-tear type load limiter is irreversible and has a fixed threshold (determined by the stitch design), meaning it can only function once and cannot be repeatedly adjusted or restored under normal operating conditions. Similarly, some seismic isolation devices utilize material yielding or structural impact to generate multilinear stiffness, but these also suffer from the problem of difficult threshold adjustment or structural irreversibility.

[0005] To achieve stiffness transition, related technologies employ tensioned monolithic structures and variable tension members. Tensioned monolithic structures can switch between soft and hard states by changing the relaxation or pretension of the internal cables; for example, adjusting the length of the tension cables can soften or lock the structure, increasing its stiffness. However, tensioned monoliths are typically used for large-scale structures, have a limited range of stiffness variation, and usually only provide two extreme states—relaxation and tension—making it difficult to generate a clear multi-segment mechanical response curve.

[0006] Overall, existing variable stiffness mechanisms and multi-stage stiffness elastic elements still have the following shortcomings: First, some solutions (such as electromechanically driven VSA joints, magnetorheological / shape memory material stiffness adjustment, etc.) have complex structures or rely on external energy, making them unsuitable for purely passive and simple implementation; Second, traditional multi-stage spring or stop designs can usually only provide two-stage stiffness changes, lacking a near-constant force platform transition section; Third, the stiffness switching threshold of most devices is fixed, making it difficult to adjust the load threshold in real time according to requirements once the design is completed. Summary of the Invention

[0007] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, one object of this invention is to propose a variable topology multi-stiffness spring structure based on flexible cable constraints, which aims to solve the problem that existing variable stiffness structures cannot simultaneously achieve structural simplification, adjustable threshold, and multi-segment mechanical response.

[0008] This invention proposes a variable topology multi-stiffness spring structure based on flexible cable constraints. The variable topology multi-stiffness spring structure includes a first elastic unit, a second elastic unit, a series flexible cable, and a winch device. The first elastic unit includes a first spring, a first inner connecting plate, and a first outer connecting plate. The two ends of the first spring are connected to the first inner connecting plate and the first outer connecting plate, respectively. The second elastic unit includes a second spring, a second inner connecting plate, and a second outer connecting plate. The two ends of the second spring are connected to the second inner connecting plate and the second outer connecting plate, respectively. The first inner connecting plate and the second inner connecting plate are connected by a series flexible cable. The winch device is connected to the series flexible cable and is used to adjust the effective connection length of the series flexible cable between the first inner connecting plate and the second inner connecting plate. The first outer connecting plate and the second outer connecting plate are suitable for bearing unidirectional external loads.

[0009] When the external load is less than or equal to the first threshold, the series flexible cable is tensioned, and the first and second elastic units are subjected to series forces. The spacing between the first outer connecting plate and the second inner connecting plate, and the spacing between the second outer connecting plate and the first inner connecting plate, are adaptable to change. When the external load is equal to the first threshold, the spacing between the first outer connecting plate and the second inner connecting plate reaches the first limit value, and the first outer connecting plate and the second inner connecting plate form a unidirectional rigid constraint through abutment or tension connection. The spacing between the second outer connecting plate and the first inner connecting plate reaches the second limit value, and the second outer connecting plate and the first inner connecting plate form a unidirectional rigid constraint through abutment or tension connection. When the external load is greater than the first threshold and less than the second threshold, the first and second elastic units exhibit a mixed series and parallel topology force. When the external load is greater than or equal to the second threshold, the first and second elastic units are subjected to parallel forces.

[0010] The first threshold and the second threshold are associated with the effective access length of the tandem flexible cable.

[0011] According to some embodiments of the present invention, when the unidirectional external load is a tensile load: the first outer connecting plate, the first inner connecting plate, the second inner connecting plate, and the second outer connecting plate are arranged sequentially along the loading axis; a first parallel flexible cable is provided between the first outer connecting plate and the second inner connecting plate, and a second parallel flexible cable is provided between the second outer connecting plate and the first inner connecting plate; wherein, when the external load is less than a first threshold, the first parallel flexible cable and the second parallel flexible cable are relaxed; when the external load is equal to the first threshold, the first parallel flexible cable and the second parallel flexible cable are taut and not under load; when the external load is greater than the first threshold, the first parallel flexible cable and the second parallel flexible cable are tensioned, so as to allow the first outer connecting plate to apply tension to the second inner connecting plate through the first parallel flexible cable, and the second outer connecting plate to apply tension to the first inner connecting plate through the second parallel flexible cable, so as to form a parallel force path of the first elastic unit and the second elastic unit.

[0012] According to some embodiments of the present invention, the initial free length of the first parallel flexible cable is greater than the distance between the first outer connecting plate and the second inner connecting plate when the external load is zero; the initial free length of the second parallel flexible cable is greater than the distance between the second outer connecting plate and the first inner connecting plate when the external load is zero.

[0013] According to some embodiments of the present invention, both the first inner connecting plate and the second inner connecting plate are formed with through holes or notches to allow the first parallel flexible cable to pass through the through holes or notches without interference and connect to the first outer connecting plate and the second inner connecting plate, and the second parallel flexible cable to pass through the through holes or notches without interference and connect to the second outer connecting plate and the first inner connecting plate.

[0014] According to some embodiments of the present invention, when the unidirectional external load is a pressure load: the first outer connecting plate, the second inner connecting plate, and the first inner connecting plate and the second outer connecting plate are arranged sequentially along the loading axis; when the external load is less than a first threshold, there is a gap between the first inner connecting plate and the second outer connecting plate, and a gap between the second inner connecting plate and the first outer connecting plate; when the external load reaches the first threshold, the first inner connecting plate and the second outer connecting plate abut against each other to form a unidirectional rigid constraint, and the second inner connecting plate abuts against the first outer connecting plate to form a unidirectional rigid constraint, so as to form a parallel force path of the first elastic unit and the second elastic unit.

[0015] According to some embodiments of the present invention, the variable topology multi-stiffness spring structure further includes a first guide member and a second guide member; one end of the first guide member is connected to a first inner connecting plate, and the other end is slidably connected to a first outer connecting plate, and the first spring is connected to the first guide member; one end of the second guide member is connected to a second inner connecting plate, and the other end is slidably connected to a second outer connecting plate, and the second spring is connected to the second guide member.

[0016] According to some embodiments of the present invention, both the first inner connecting plate and the second inner connecting plate are formed with through holes or notches to allow the first spring to pass through the through holes or notches without interference and connect the first outer connecting plate and the first inner connecting plate, and the second spring to pass through the through holes or notches without interference and connect the second outer connecting plate and the second inner connecting plate.

[0017] According to some embodiments of the present invention, the variable topology multi-stiffness spring structure further includes a detection unit adapted to detect the effective access length and force of the series flexible cable, and adapted to detect the relative displacement between the first outer connecting plate and the second outer connecting plate.

[0018] According to some embodiments of the present invention, the first spring is constructed in multiple ways, and the multiple first springs are arranged circumferentially around the structural center of the first outer connecting plate; the second spring is constructed in multiple ways, and the multiple second springs are arranged circumferentially around the structural center of the second outer connecting plate.

[0019] This invention also proposes an adjustment method for the above-mentioned variable topology multi-stiffness spring structure, comprising the following steps:

[0020] Based on the application scenario, when the variable topology multi-stiffness spring structure is released from the locking platform stage, the preset relaxation threshold T0 of the tension of the series flexible cable and the preset displacement threshold X0 between the first outer connecting plate and the second outer connecting plate are determined.

[0021] During the process of a variable topology multi-stiffness spring structure bearing an external dynamic load F(t), the tension T(t) of the series flexible cable and the relative displacement X(t) between the first and second outer connecting plates are collected in real time, and the effective length of the series flexible cable is adjusted according to the tension T(t) and relative displacement X(t).

[0022] If T(t) is less than the preset relaxation threshold T0, it is determined that the variable topology multi-stiffness spring structure has left the locking platform stage and entered the high-stiffness parallel buffer zone; at this time, the series flexible cable is shortened to adapt to the adjustment of the variable topology multi-stiffness spring structure to return to the locking platform stage.

[0023] If T(t) is greater than the preset relaxation threshold T0 and X(t) is greater than the preset displacement threshold X0, then the variable topology multi-stiffness spring structure is determined to have left the locking platform stage and entered the low stiffness series action zone; at this time, the series flexible cable is extended to adjust the variable topology multi-stiffness spring structure back to the locking platform stage.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. Three-stage stiffness response: The structure of this invention can passively achieve a three-stage mechanical response of "low stiffness-extremely high stiffness-high stiffness" in a loading / unloading cycle, and has a "locking platform stage" with a clear locking effect;

[0026] 2. Adjustable threshold load: By simply adjusting the length of the series flexible cable, the first and second load thresholds for stiffness switching can be set conveniently and accurately, realizing the "programmability" of the stiffness curve and strong adaptability;

[0027] 3. Simple and reliable structure: The present invention is mainly composed of traditional mechanical components such as springs, end plates and flexible cables. It does not require complex drive mechanisms or rely on special materials. It does not involve material yielding or irreversible deformation of energy-consuming components. The structure is simple, highly reliable and can be repeatedly used.

[0028] 4. Passive adaptive switching: The switching of stiffness state is passively triggered according to the size of external load, without the need for continuous energy input or active control, thus realizing an adaptive mechanical response;

[0029] 5. Wide range of applicable working conditions: This invention is designed with two configurations suitable for tensile and compressive working conditions, which can be widely used in various engineering scenarios such as precise positioning, overload protection, impact buffering, and vibration isolation.

[0030] This invention fully utilizes elastic elements and recoverable flexible cable constraints to achieve stiffness switching, providing a simple, versatile, and highly adaptable variable topology multi-stiffness spring structure. It can automatically switch between a three-stage mechanical response—low stiffness, a locked platform stage, and high stiffness—and possesses advantages such as adjustable threshold, reusability, and simple structure. This meets the requirements for variable compliance and overload protection in applications such as precision positioning, vibration isolation, and impact protection. It provides a new technical solution for the field of mechanical variable stiffness devices and has broad application prospects in precision engineering, robotics, exoskeletons, and safety protection.

[0031] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0033] Figure 1 This is a structural schematic diagram of a tension-type variable topology multi-stiffness spring structure according to some embodiments of the present invention;

[0034] Figure 2 This is a schematic diagram illustrating the topological changes of a tension-type variable topology multi-stiffness spring structure under different loads, according to some embodiments of the present invention.

[0035] Figure 3 This is a structural schematic diagram of a compression-type variable topology multi-stiffness spring structure according to some embodiments of the present invention;

[0036] Figure 4 This is a load-displacement relationship data diagram of a variable topology multi-stiffness spring structure according to some embodiments of the present invention under different series flexible cable length settings.

[0037] Figure label:

[0038] First spring 11; First outer connecting plate 12; First inner connecting plate 13;

[0039] Second spring 21; second outer connecting plate 22; second inner connecting plate 23;

[0040] 31; series flexible cable; 32; winch device;

[0041] First parallel flexible cable 41; Second parallel flexible cable 42;

[0042] First guide member 51; second guide member 52. Detailed Implementation

[0043] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0044] The following is for reference. Figures 1-4 A variable topology multi-stiffness spring structure based on flexible cable constraints according to an embodiment of the present invention is described.

[0045] This invention proposes a variable topology multi-stiffness spring structure based on flexible cable constraints. The variable topology multi-stiffness spring structure includes a first elastic unit, a second elastic unit, a series flexible cable 31, and a hoisting device 32. The first elastic unit includes a first spring 11, a first inner connecting plate 13, and a first outer connecting plate 12. The two ends of the first spring 11 are connected to the first inner connecting plate 13 and the first outer connecting plate 12, respectively. The second elastic unit includes a second spring 21, a second inner connecting plate 23, and a second outer connecting plate 22. The two ends of the second spring 21 are connected to the second inner connecting plate 23 and the second outer connecting plate 22, respectively. The first inner connecting plate 13 and the second inner connecting plate 23 are connected via the series flexible cable 31. The hoisting device 32 is connected to the series flexible cable 31 and is used to adjust the effective connection length of the series flexible cable 31 between the first inner connecting plate 13 and the second inner connecting plate 23. The first outer connecting plate 12 and the second outer connecting plate 22 are adapted to withstand unidirectional external loads.

[0046] When the external load is less than or equal to the first threshold, the series flexible cable 31 is tensioned, and the first elastic unit and the second elastic unit are subjected to series forces. The spacing between the first outer connecting plate 12 and the second inner connecting plate 23, and the spacing between the second outer connecting plate 22 and the first inner connecting plate 13, are adaptable to change. When the external load is equal to the first threshold, the spacing between the first outer connecting plate 12 and the second inner connecting plate 23 reaches the first limit value, and the first outer connecting plate 12 and the second inner connecting plate 23 form a unidirectional rigid constraint through abutment or tension connection. The spacing between the second outer connecting plate 22 and the first inner connecting plate 13 reaches the second limit value, and the second outer connecting plate 22 and the first inner connecting plate 13 form a unidirectional rigid constraint through abutment or tension connection. When the external load is greater than the first threshold and less than the second threshold, the first elastic unit and the second elastic unit exhibit a mixed series and parallel topology force. When the external load is greater than or equal to the second threshold, the first elastic unit and the second elastic unit are subjected to parallel forces. The first threshold and the second threshold are related to the effective access length of the series flexible cable 31.

[0047] According to the variable topology multi-stiffness spring structure of the present invention, in the first elastic unit, the first outer connecting plate 12 bears the external load and transmits the force to the first spring 11. The first spring 11 deforms under the force and simultaneously transmits the force to the first inner connecting plate 13. In the second elastic unit, the second outer connecting plate 22 bears the external load and transmits the force to the second spring 21. The second spring 21 deforms under the force and simultaneously transmits the force to the second inner connecting plate 23. The first inner connecting plate 13 and the second inner connecting plate 23 are connected by a series flexible cable 31, which can transmit the force to the series flexible cable 31 to make it taut. When the external load gradually increases from low load to high load, the force transmission path and the overall structural stiffness of the variable topology multi-stiffness spring structure change.

[0048] Specifically, when the external load F is less than or equal to the first threshold F1, i.e., under low load (when the first outer connecting plate 12 and the second inner connecting plate 23 do not achieve unidirectional rigid constraint, and the second outer connecting plate 22 and the first inner connecting plate 13 do not achieve unidirectional rigid constraint), the series flexible cable 31 is tensioned. The first elastic unit and the second elastic unit form a series force through the series flexible cable 31. The variable topology multi-stiffness spring structure exhibits a lower overall equivalent stiffness, which is suitable for compliant applications requiring large displacement. At the same time, the first spring 11 and the second spring 21 deform under force, changing the distance between the first inner connecting plate 13 and the second outer connecting plate 22, and the distance between the second inner connecting plate 23 and the first outer connecting plate 12.

[0049] When the external load F equals the first threshold F1, the distance between the first inner connecting plate 13 and the second outer connecting plate 22 reaches the first limit value, so as to be suitable for the first outer connecting plate 12 and the second inner connecting plate 23 to form a unidirectional rigid constraint through abutment or tension connection; the distance between the second outer connecting plate 22 and the first inner connecting plate 13 reaches the second limit value, so as to be suitable for the second outer connecting plate 22 and the first inner connecting plate 13 to form a unidirectional rigid constraint through abutment or tension connection.

[0050] When the external load F is greater than the first threshold F1 and less than the second threshold F2, the series flexible cable 31 is tensioned and subjected to force, and forces are generated between the first outer connecting plate 12 and the second inner connecting plate 23, and between the second outer connecting plate 22 and the first inner connecting plate 13. The first outer connecting plate 12 transmits the external load force to the first spring 11 and the second inner connecting plate 23 simultaneously, while the second outer connecting plate 22 transmits the external load force to the second spring 21 and the first inner connecting plate 13 simultaneously. As the external load F increases from F1 to F2, the force transmission path of the variable topology multi-stiffness spring structure is reconstructed, exhibiting a mixed series and parallel topology. The force on the series flexible cable 31 continuously decreases, while the force exerted by the first outer connecting plate 12 on the second inner connecting plate 23 gradually increases, and the force exerted by the second outer connecting plate 22 on the first inner connecting plate 13 gradually increases. During this process, the relative positions of the first outer connecting plate 12, the first inner connecting plate 13, the second outer connecting plate 22, and the second inner connecting plate 23 remain unchanged, the first spring 11 and the second spring 21 do not deform, the deformation of the variable topology multi-stiffness spring structure tends to lock, and the overall structure reaches a locked state. This invention uses the relative displacement of the two outer connecting plates to describe the deformation of the variable topology multi-stiffness spring structure. In the curve showing the relationship between the relative displacement of the two outer connecting plates and the load (hereinafter referred to as the load-displacement curve), this stage is represented by a plateau segment where the load changes but the relative displacement remains basically unchanged. That is, the variable topology multi-stiffness spring structure is in the locked plateau stage, and the whole structure has extremely high stiffness. The equivalent stiffness is mainly dominated by the axial stiffness of the series flexible cable 31.

[0051] When the external load F equals the second threshold F2, the force on the series flexible cable 31 decreases to zero, and it is in a taut and unloaded state. The first elastic unit and the second elastic unit are converted to parallel force.

[0052] When the external load F is greater than the second threshold F2, i.e., under high load, a unidirectional rigid constraint force is generated between the first outer connecting plate 12 and the second inner connecting plate 23, and a unidirectional rigid constraint force is generated between the second outer connecting plate 22 and the first inner connecting plate 13, so that the distance between the first outer connecting plate 12 and the second inner connecting plate 23 remains unchanged, and the distance between the second outer connecting plate 22 and the first inner connecting plate 13 remains unchanged; while the first spring 11 and the second spring 21 continue to deform under high load, which will change the distance between the first inner connecting plate 13 and the second inner connecting plate 23, so that the series flexible cable 31 is relaxed and unloaded, and the first spring 11 and the second spring 21 are connected in parallel. The variable topology multi-stiffness spring structure exhibits high equivalent stiffness as a whole, which is suitable for high stiffness occasions that require small displacement.

[0053] During the process of the external load F changing from low load to high load, the first spring 11 and the second spring 21 change from series force to parallel force, exhibiting a three-stage mechanical response of "low stiffness - extremely high stiffness - high stiffness".

[0054] Furthermore, the effective length of the series flexible cable 31 connected between the first inner connecting plate 13 and the second inner connecting plate 23 is related to the deformation of the first spring 11 and the second spring 21 when the series and parallel forces are converted. The effective connection length of the series flexible cable 31 is related to the first threshold F1 and the second threshold F2. By changing the effective connection length of the series flexible cable 31 through the hoisting device 32, the load threshold during structural topology reconstruction can be set, so that the variable topology multi-stiffness spring structure as a whole can maintain a very high stiffness under certain load conditions.

[0055] The variable topology multi-stiffness spring structure of the present invention is mainly composed of traditional mechanical components such as springs, end plates, and flexible cables. It does not require complex drive mechanisms or rely on special materials, and does not involve material yielding or irreversible deformation of energy-consuming components. The structure is simple, highly reliable, and reusable. The present invention can passively achieve a three-stage mechanical response of "low stiffness - extremely high stiffness - high stiffness" in a loading / unloading cycle, with a "locking platform stage" that has a clear locking effect, which can meet the stiffness requirements of different scenarios. At the same time, the switching of stiffness states is passively triggered according to the size of the external load, without the need for continuous energy input or active control, thus achieving an adaptive mechanical response. In addition, by simply adjusting the length of the series flexible cable 31, the load threshold for stiffness switching can be conveniently and accurately set. The present invention achieves the "programmability" of the stiffness curve and has strong adaptability.

[0056] In some embodiments, the connecting plates (i.e., the first outer connecting plate 12, the first inner connecting plate 13, the second inner connecting plate 23 and the second outer connecting plate 22) are spaced apart along the loading axis of the external load and are aligned with the center line; the series flexible cable 31 is arranged on the center line of each connecting plate.

[0057] Furthermore, the present invention designs two configurations suitable for tensile and compressive conditions, which can be widely used in various engineering scenarios requiring precise positioning, overload protection, impact buffering, vibration isolation, etc., as detailed in the following embodiments.

[0058] According to some embodiments of the present invention, when the unidirectional external load is a tensile load: the first outer connecting plate 12, the first inner connecting plate 13, the second inner connecting plate 23, and the second outer connecting plate 22 are arranged sequentially along the loading axis; a first parallel flexible cable 41 is provided between the first outer connecting plate 12 and the second inner connecting plate 23, and a second parallel flexible cable 42 is provided between the second outer connecting plate 22 and the first inner connecting plate 13; wherein, when the external load is less than a first threshold, the first parallel flexible cable 41 and the second parallel flexible cable 42... Relaxation: When the external load equals the first threshold, the first parallel flexible cable 41 and the second parallel flexible cable 42 are taut and unloaded; when the external load is greater than the first threshold, the first parallel flexible cable 41 and the second parallel flexible cable 42 are tensioned to suit the first outer connecting plate 12 applying tension to the second inner connecting plate 23 through the first parallel flexible cable 41, and the second outer connecting plate 22 applying tension to the first inner connecting plate 13 through the second parallel flexible cable 42, so as to form a parallel force path between the first elastic unit and the second elastic unit.

[0059] like Figure 1 As shown, this embodiment proposes a tension-type variable topology multi-stiffness spring structure suitable for tensile conditions and for bearing tensile loads. In this embodiment, the first outer connecting plate 12 and the second inner connecting plate 23 are connected by a first parallel flexible cable 41. When the first parallel flexible cable 41 is tensioned, the first outer connecting plate 12 and the second inner connecting plate 23 form a unidirectional rigid constraint. The second outer connecting plate 22 and the first inner connecting plate 13 are connected by a second parallel flexible cable 42. When the second parallel flexible cable 42 is tensioned, the second outer connecting plate 22 and the first inner connecting plate 13 form a unidirectional rigid constraint. The first limit value is the tension length of the first parallel flexible cable 41, and the second limit value is the tension length of the second parallel flexible cable 42.

[0060] The force change process of the tension-type variable topology multi-stiffness spring structure in this embodiment is as follows:

[0061] When the external load F is less than the first tensile threshold F 11 At this time, the series flexible cable 31 is taut, while the first parallel flexible cable 41 and the second parallel flexible cable 42 are slack. The first spring 11 and the second spring 21 are connected by a series force through the series flexible cable 31, as shown below. Figure 2 As shown in (a), the variable topology multi-stiffness spring structure exhibits a relatively low overall equivalent stiffness.

[0062] When the external load F equals the first tensile threshold F 11 When the series flexible cable 31 is taut, the first parallel flexible cable 41 and the second parallel flexible cable 42 are just straight and not under tension, and the first spring 11 and the second spring 21 are connected in series and under force.

[0063] When the external load F is greater than the first tensile threshold F 11 And less than the second tensile force threshold F 21 At this time, the series flexible cable 31 is tensioned, the first parallel flexible cable 41 and the second parallel flexible cable 42 are tensioned, and the first spring 11 and the second spring 21 exhibit a mixed series and parallel topology of force, such as Figure 2 As shown in (b) in the diagram; during this change stage, the force transmission path of the variable topology multi-stiffness spring structure is reconstructed. As the external load F increases, the force on the series flexible cable 31 decreases continuously, while the force on the first parallel flexible cable 41 and the second parallel flexible cable 42 gradually increases. The force on the first spring 11 and the second spring 21 remains unchanged, and the overall structure does not deform, exhibiting extremely high stiffness. The equivalent stiffness is mainly dominated by the axial stiffness of the series flexible cable 31 and the parallel flexible cable.

[0064] When the external load F equals the second tensile threshold F 21 When the tension of the series flexible cable 31 drops to zero, it is in a taut and unloaded state, and the first spring 11 and the second spring 21 are connected in parallel.

[0065] When the external load F is greater than the second tensile threshold F 21 When the series flexible cable 31 is not under stress, the first spring 11 and the second spring 21 are under stress in parallel, and the stress increases with the increase of the load, continuing to deform. The distance between the first inner connecting plate 13 and the second inner connecting plate 23 decreases, and the series flexible cable 31 slackens; Figure 2 As shown in (c), the variable topology multi-stiffness spring structure exhibits a high overall equivalent stiffness.

[0066] It should be noted that the deformation of the first spring 11 and the second spring 21 has limits. Under external load, from the second tension threshold F... 21 Increase to the third tensile threshold F 31 At this time, the distance between the first inner connecting plate 13 and the second inner connecting plate 23 decreases to zero, forming an abutment relationship. The first spring 11 is of equal length to the first parallel flexible cable 41, and the second spring 21 is of equal length to the second parallel flexible cable 42 (ignoring the thickness of the connecting plates); constrained by the first parallel flexible cable 41 and the second parallel flexible cable 42, the relative position of the first outer connecting plate 12 and the second outer connecting plate 22 is locked. Therefore, when the external load exceeds the third tensile force threshold F... 31At this time, the first spring 11 and the second spring 21 no longer deform, the overall structure no longer deforms, exhibiting extremely high stiffness, and the equivalent stiffness is mainly dominated by the axial stiffness of the parallel flexible cable.

[0067] In some embodiments, the first parallel flexible cable 41 is coaxially arranged with the second spring 21, and the second parallel flexible cable 42 is coaxially arranged with the first spring 11.

[0068] According to some embodiments of the present invention, the initial free length of the first parallel flexible cable 41 is greater than the distance between the first outer connecting plate 12 and the second inner connecting plate 23 when the external load is zero; the initial free length of the second parallel flexible cable 42 is greater than the distance between the second outer connecting plate 22 and the first inner connecting plate 13 when the external load is zero. For a tension-type variable topology multi-stiffness spring structure, this embodiment can ensure that under low load conditions, when the first spring 11 and the second spring 21 deform, the first parallel flexible cable 41 and the second parallel flexible cable 42 remain in a relaxed state and do not participate in force transmission, so as to be suitable for the first spring 11 and the second spring 21 to be subjected to force in series.

[0069] In some embodiments of the tension-type variable topology multi-stiffness spring structure, the winch device 32 is disposed on an inner connecting plate and on the side close to the adjacent outer connecting plate.

[0070] According to some embodiments of the present invention, both the first inner connecting plate 13 and the second inner connecting plate 23 are formed with through holes or notches to allow the first parallel flexible cable 41 to pass through the through holes or notches without interference and connect to the first outer connecting plate 12 and the second inner connecting plate 23, and the second parallel flexible cable 42 to pass through the through holes or notches without interference and connect to the second outer connecting plate 22 and the first inner connecting plate 13. For a tension-type variable topology multi-stiffness spring structure, in this embodiment, by providing through holes or notches in the inner connecting plates, the two parallel flexible cables pass through the corresponding through holes or notches respectively to connect the non-adjacent outer connecting plate and the inner connecting plate. This avoids interference between the first inner connecting plate 13 and the first parallel flexible cable 41, and between the second inner connecting plate 23 and the second parallel flexible cable 42, ensuring a compact structure and stable force transmission process.

[0071] Furthermore, in some embodiments, the first spring 11 and the first parallel flexible cable 41 are arranged in a staggered manner around the structural center of the first outer connecting plate 12 in the circumferential direction. Specifically, as shown in... Figure 1As shown, there are two first springs 11, with their connection points to the first outer connecting plate 12 located at 0° and 180°, respectively. There are also two first parallel flexible cables 41, with their connection points to the first outer connecting plate 12 located at 90° and 270°, respectively. Simultaneously, the second springs 21 and second parallel flexible cables 42 are arranged circumferentially around the structural center of the second outer connecting plate 22. There are two second springs 21, with their connection points to the second outer connecting plate 22 located at 90° and 270°, respectively; and there are two second parallel flexible cables 42, with their connection points to the second outer connecting plate 22 located at 0° and 180°, respectively. This staggered arrangement ensures that the connection points of the parallel flexible cables and springs are evenly distributed along the circumference, balancing the forces, and preventing the two sets of parallel flexible cables from interfering with each other.

[0072] In some embodiments, guide wheels or guide holes may be provided for the series flexible cable 31 and the two parallel flexible cables to constrain their motion trajectory.

[0073] According to some embodiments of the present invention, when the unidirectional external load is a pressure load: the first outer connecting plate 12, the second inner connecting plate 23, the first inner connecting plate 13, and the second outer connecting plate 22 are arranged sequentially along the loading axis; wherein, when the external load is less than a first threshold, there is a gap between the first inner connecting plate 13 and the second outer connecting plate 22, and there is a gap between the second inner connecting plate 23 and the first outer connecting plate 12; when the external load reaches the first threshold, the first inner connecting plate 13 and the second outer connecting plate 22 abut against each other to form a unidirectional rigid constraint, and the second inner connecting plate 23 and the first outer connecting plate 12 abut against each other to form a unidirectional rigid constraint, so as to form a parallel force path of the first elastic unit and the second elastic unit.

[0074] like Figure 3 As shown, this embodiment proposes a compression-type variable topology multi-stiffness spring structure suitable for compression conditions and for bearing pressure loads. The first limit mentioned above refers to the distance between the second inner connecting plate 23 and the first outer connecting plate 12 being zero, and the second limit refers to the distance between the first inner connecting plate 13 and the second outer connecting plate 22 being zero. The force change process of the compression-type variable topology multi-stiffness spring structure in this embodiment is as follows:

[0075] When the external load F is less than or equal to the first pressure threshold F 12 When the series flexible cable 31 is tensioned, the first spring 11 and the second spring 21 form a series force through the series flexible cable 31, and the variable topology multi-stiffness spring structure as a whole exhibits a low equivalent stiffness.

[0076] When the external load F equals the first pressure threshold F 12At that time, the first inner connecting plate 13 abuts against the second outer connecting plate 22 but does not generate a resisting force, and the second inner connecting plate 23 abuts against the first outer connecting plate 12 but does not generate a resisting force.

[0077] When the external load F is greater than the first pressure threshold F 12 And less than the second pressure threshold F 22 At this time, the series flexible cable 31 is tensioned, the second outer connecting plate 22 exerts a resisting force on the first inner connecting plate 13, and the first outer connecting plate 12 exerts a resisting force on the second inner connecting plate 23; the first spring 11 and the second spring 21 exhibit a mixed series and parallel topology of force; during this change stage, the force transmission path of the variable topology multi-stiffness spring structure is reconstructed, the force on the series flexible cable 31 continuously decreases, the resisting force of the second outer connecting plate 22 on the first inner connecting plate 13 gradually increases, the resisting force of the first outer connecting plate 12 on the second inner connecting plate 23 gradually increases, the force on the first spring 11 and the second spring 21 remains unchanged, the overall structure does not deform, exhibiting extremely high stiffness, and the equivalent stiffness is mainly dominated by the axial stiffness of the series flexible cable 31;

[0078] When the external load F equals the second pressure threshold F 22 When the tension of the series flexible cable 31 drops to zero, it is in a taut and unloaded state, and the first spring 11 and the second spring 21 are connected in parallel.

[0079] When the external load F is greater than the second pressure threshold F 22 When the series flexible cable 31 is not under stress, the first spring 11 and the second spring 21 are under stress in parallel and the stress increases with the load, and they continue to deform. The distance between the first inner connecting plate 13 and the second inner connecting plate 23 decreases, the series flexible cable 31 relaxes, and the variable topology multi-stiffness spring structure as a whole exhibits a high equivalent stiffness.

[0080] It should be noted that the deformation of the first spring 11 and the second spring 21 has limits. Under external load, from the second pressure threshold F... 22 Increase to the third pressure threshold F 32 When the first spring 11 and the second spring 21 reach their minimum compressed length, they cease to deform; constrained by the external load and the first spring 11 and the second spring 21, the relative positions of the first outer connecting plate 12 and the second outer connecting plate 22 are locked. Therefore, when the external load exceeds the third pressure threshold F... 32 When the overall structure is compressed to its limit, it no longer undergoes any deformation and exhibits extremely high stiffness. The equivalent stiffness is mainly dominated by the axial stiffness of the spring when compressed to its limit.

[0081] According to some embodiments of the present invention, the variable topology multi-stiffness spring structure further includes a first guide member 51 and a second guide member 52; one end of the first guide member 51 is connected to the first inner connecting plate 13, and the other end is slidably connected to the first outer connecting plate 12, and the first spring 11 is connected to the first guide member 51; one end of the second guide member 52 is connected to the second inner connecting plate 23, and the other end is slidably connected to the second outer connecting plate 22, and the second spring 21 is connected to the second guide member 52. For the compression-type variable topology multi-stiffness spring structure, in this embodiment, by setting the first guide member 51 and the second guide member 52, the relative displacement of each connecting plate and flexible cable of the elastic unit can be limited to the direction of the preset loading axis, thereby avoiding unexpected movements such as lateral instability, bending, or torsion, and preventing the first spring 11 and the second spring 21 from laterally bending or becoming unstable when subjected to compressive load, thereby improving the stability of the overall structure under stress and force transmission.

[0082] Specifically, such as Figure 3 As shown, the first guide member 51 and the second guide member 52 can be constructed as guide rods. The first guide member 51 and the first outer connecting plate 12 can be slidably connected via a linear bearing, and the first spring 11 is sleeved on the outer periphery of the first guide member 51. Similarly, the second guide member 52 and the second outer connecting plate 22 can be slidably connected via a linear bearing, and the second spring 21 is sleeved on the outer periphery of the second guide member 52. Further, the length of the first guide member 51 is constructed to be greater than the free length of the first spring 11, and the length of the second guide member 52 is constructed to be greater than the free length of the second spring 21, to provide continuous and stable guidance throughout the entire compression stroke. In addition, multiple first guide members 51 are constructed, each corresponding to one of the first springs 11, such as... Figure 3 As shown; the second guide member 52 is constructed in multiple ways, each corresponding to one of the second springs 21, such as... Figure 3 As shown.

[0083] The guide can be implemented in various ways. It can be constructed as a guide rod set inside the elastic unit, or as a guide cylinder covering the outside of the elastic unit structure. The first spring 11 and the second spring 21 are respectively set inside the guide cylinder.

[0084] Furthermore, in the compression-type variable topology multi-stiffness spring structure, for the series flexible cable 31, guide wheels or guide holes can be set to constrain its motion trajectory.

[0085] In some embodiments of the compression-type variable topology multi-stiffness spring structure, the winch device 32 is directly mounted on the series flexible cable 31 to avoid structural interference with the two inner connecting plates during the relative movement of the connecting plates.

[0086] According to some embodiments of the present invention, both the first inner connecting plate 13 and the second inner connecting plate 23 are formed with through holes or notches to allow the first spring 11 to pass through the through holes or notches without interference and connect to the first outer connecting plate 12 and the first inner connecting plate 13, and the second spring 21 to pass through the through holes or notches without interference and connect to the second outer connecting plate 22 and the second inner connecting plate 23. For a compression-type variable topology multi-stiffness spring structure, in this embodiment, by providing through holes or notches, the first spring 11 and the second spring 21 pass through the corresponding through holes or notches respectively, connecting the non-adjacent inner connecting plate and the outer connecting plate. This avoids interference between the first inner connecting plate 13 and the second spring 21, and between the second inner connecting plate 23 and the first spring 11, ensuring a compact structure and stable force transmission process.

[0087] Furthermore, in some embodiments, the structural centers of the first outer connecting plate 12 and the second outer connecting plate 22 are on the same axis; the first spring 11 and the second spring 21 are staggered around the structural centers of the first outer connecting plate 12 and the second outer connecting plate 22. Specifically, as shown... Figure 3 As shown, there are two first springs 11, with the connection points of the two first springs 11 to the first outer connecting plate 12 located at 0° and 180°, respectively; there are also two second springs 21, with the connection points of the two second springs 21 to the second outer connecting plate 22 located at 90° and 270°, respectively. This staggered arrangement ensures that the connection points of each spring are evenly distributed along the circumference, which can balance the force, and the two sets of springs will not interfere with each other.

[0088] In the above embodiments, the geometric shape of each connecting plate can be selected according to the installation space or processing technology; the inner connecting plate may be provided with through holes or notches to allow parallel flexible cables or springs to pass through without interference; each through hole or notch is evenly distributed in the circumference to eliminate off-center load, and the positions of adjacent through holes or notches are staggered to avoid entanglement or interference between parallel flexible cables or springs.

[0089] According to some embodiments of the present invention, the variable topology multi-stiffness spring structure further includes a detection unit. The detection unit is adapted to detect the effective connection length and force of the series flexible cable 31, and to detect the relative displacement between the first outer connecting plate 12 and the second outer connecting plate 22. In this embodiment, by setting the detection unit, the force and shape changes of the compression / tension type variable topology multi-stiffness spring structure can be monitored in real time, so as to determine the stiffness of the variable topology multi-stiffness spring structure. Therefore, the effective connection length of the series flexible cable 31 can be adjusted according to the detection results, so that the variable topology multi-stiffness spring structure is adjusted to the target stiffness condition.

[0090] In some embodiments, the winch 32 and the series flexible cable 31 are connected in a rotatable manner, enabling manual or electric operation. Furthermore, the winch 32 may integrate sensors (such as force sensors or rotary encoders) to collect the tension or winding length of the series flexible cable 31 in real time, and a signal interface is reserved for communication and closed-loop control with an external controller.

[0091] In some embodiments, the winch 32 contains a rotatable drum and is equipped with a pawl self-locking mechanism and a knob for operation, by which the effective length of the tandem flexible cable 31 can be adjusted.

[0092] According to some embodiments of the present invention, multiple first springs 11 are configured, and the multiple first springs 11 are arranged circumferentially around the structural center of the first outer connecting plate 12; multiple second springs 21 are configured, and the multiple second springs 21 are arranged circumferentially around the structural center of the second outer connecting plate 22. In this embodiment, by providing multiple first springs 11 and second springs 21, the load-bearing capacity of the structure can be improved, and by changing the number of springs, the adjustability of the structure can be increased; wherein, the multiple first springs 11 are arranged in parallel between the first outer connecting plate 12 and the first inner connecting plate 13, and the multiple second springs 21 are arranged in parallel between the second outer connecting plate 22 and the second inner connecting plate 23.

[0093] Furthermore, among the multiple first springs 11, some of the first springs 11 have the opposite rotation direction to the rest of the first springs 11; among the multiple second springs 21, some of the second springs 21 have the opposite rotation direction to the rest of the second springs 21; this can balance the torsional torque that the first springs 11 and second springs 21 may generate during deformation, so as to ensure the pure axial movement of the structure and improve the stability of the structure under stress.

[0094] Specifically, such as Figure 1 As shown, in the tension-type variable topology multi-stiffness spring structure, the first spring 11 is constructed as two springs with opposite directions of rotation, namely, an L-shaped first spring 11 and an R-shaped first spring 11; the second spring 21 is constructed as two springs with opposite directions of rotation, namely, an L-shaped second spring 21 and an R-shaped second spring 21. Figure 3 As shown, in the compression-type variable topology multi-stiffness spring structure, the first spring 11 is constructed as two springs with opposite directions of rotation, namely, an L-shaped first spring 11 and an R-shaped first spring 11; the second spring 21 is constructed as two springs with opposite directions of rotation, namely, an L-shaped second spring 21 and an R-shaped second spring 21. The two first springs 11 or the two second springs 21 can mutually balance the torsional moments that may be generated during deformation.

[0095] According to some embodiments of the present invention, the series flexible cable 31 and / or the parallel flexible cable are made of high-strength, low-elongation flexible ropes, such as ultra-high molecular weight polyethylene (UHMWPE / Dyneema) fiber rope or steel wire rope, to ensure that their own deformation is negligible under working load, thereby ensuring the accuracy of stiffness switching.

[0096] According to the variable topology multi-stiffness spring structure of the present invention, the elastic unit has modular characteristics, and multiple elastic units can be combined in series or parallel according to actual needs. The modular design allows for obtaining more stiffness curves by increasing the number of elastic units or adjusting their connection method, thereby improving the flexibility and applicability of the structure.

[0097] In some embodiments, the variable topology multi-stiffness spring structure also includes a housing, and the elastic unit, series flexible cable 31, and hoisting device 32 can be integrated and installed inside a single housing to form a standardized variable stiffness module. This modular design facilitates application, and multiple variable stiffness modules can be combined in series or parallel to obtain more segments and more complex stiffness response curves.

[0098] The variable topology multi-stiffness spring structure of the present invention includes the following specific embodiments:

[0099] Example 1: Tension-type variable topology multi-stiffness spring structure

[0100] The dimensional parameters of each structural component are as follows: The first outer connecting plate 12, the first inner connecting plate 13, the second inner connecting plate 23, and the second outer connecting plate 22 are all made of SUS304 stainless steel with a thickness of 5 mm. Two first springs 11 and two second springs 21 are each provided, with a single spring stiffness k of 0.2 N / mm and a free length of 50 mm. The series flexible cable 31 is made of Dyneema fiber rope, with a reference length (effective access length) set at 50 mm, and its elongation under working load is less than 0.2%. Two first parallel flexible cables 41 and two parallel flexible cables 42 are each provided, made of Dyneema fiber rope, with a reference length (effective access length) set at 155 mm, and its elongation under working load is less than 0.5%. Based on the above parameters, Embodiment 1 has a clear three-segment load-tension relationship. The equivalent stiffness of both the first elastic unit and the second elastic unit is 0.4 N / mm, which is the stiffness of two springs in parallel. When the series flexible cable 31 is straightened and there is no external load, the total initial length of the structure (from the upper surface of the first outer connecting plate 12 to the lower surface of the second outer connecting plate 22) is 170 mm (including: the free length of the springs of the two elastic units is 50 mm + 50 mm, the length of the series flexible cable 31 is 50 mm, and the thickness of the four connecting plates is 5*4=20 mm).

[0101] (1) First stage (F≤F11 (Series low stiffness): When a low load is applied to the external connecting plate, the first parallel flexible cable 41 and the second parallel flexible cable 42 remain relaxed, while the series flexible cable 31 is tensioned, and the tension is transmitted through the series path; the first elastic unit and the second elastic unit form a series configuration, and the equivalent stiffness of the variable topology multi-stiffness spring structure is 0.2 N / mm.

[0102] As the load increases, the first spring 11 and the second spring 21 are stretched. When the total stretch reaches 100 mm (i.e., each elastic unit is stretched by 50 mm), the first parallel flexible cable 41 and the second parallel flexible cable 42 are just taut but not yet under stress. At this time, the load reaches the first tensile threshold F. 11 Its size is 0.2 N / mm × 100 mm = 20 N.

[0103] (2) Second stage (F) 11 <F≤F 21 (Locking Platform Stage): As the load continues to increase from 20 N, the first parallel flexible cable 41 and the second parallel flexible cable 42 begin to bear force and gradually take on more load, while the tension on the series flexible cable 31 decreases accordingly, and the tension transmission path begins to be reconstructed. During this stage, the increase in load mainly affects the redistribution of tension, while the tensile amount of the structure remains unchanged. The structure as a whole exhibits extremely high stiffness (theoretically greater than 200 N / mm), forming the locking platform stage of the load-displacement curve.

[0104] When the load continues to increase, causing the tension in the series flexible cable 31 to decrease to zero, the load reaches the second tension threshold F. 21 At this point, all external loads are transmitted by four parallel flexible cables, which completely transforms the first and second elastic units into a parallel configuration; the external load is 40 N (the two elastic units each bear a tension of 20 N, which is transmitted through the parallel flexible cables), while the tensile strength remains at 100 mm.

[0105] (3) Third stage (F>F) 21 (Parallel High Stiffness): When the load exceeds 40 N, the series flexible cable 31 is fully relaxed, and the two elastic units work in parallel. The equivalent stiffness of the variable topology multi-stiffness spring structure is the sum of the stiffnesses of the two elastic units, i.e., 0.8 N / mm. After this, the structure enters the parallel high stiffness region.

[0106] Furthermore, when the first spring 11 and the second spring 21 are stretched to their maximum working length (the distance between the first inner connecting plate 13 and the second inner connecting plate 23 is reduced to zero), the load reaches the third tensile force threshold F. 31 The size is 80 N, and the total tensile strength is 150 mm.

[0107] By adjusting the length of the series flexible cable 31 using the winch device 32, the parameters of the locking platform stage can be precisely and programmably controlled. The adjustment effect can be seen in Table 1.

[0108] Table 1. Correspondence between the length of the tandem flexible cable and the parameters of the tension-type locking platform stage.

[0109]

[0110] In Table 1, the tension of the locking platform refers to the overall tension of the structure when the tension-type variable topology multi-stiffness spring structure enters the locking platform stage; the minimum load F of the locking platform... 11 This refers to the external load when entering the platform locking phase; the maximum load F of the platform locking phase. 21 This refers to the external load when the platform is no longer locked.

[0111] As can be seen from the data in Table 1 above, the shorter the series flexible cable 31, the greater the amount of tension required to achieve the tensioned state of both the series and parallel flexible cables. Therefore, the amount of tension and the load threshold corresponding to the locking platform stage are also greater. Table 1 confirms the ability of this invention to effectively control its multi-segment stiffness response characteristics by adjusting a single parameter (the length of the series flexible cable 31).

[0112] Example 2: Compression-type variable topology multi-stiffness spring structure

[0113] The dimensional parameters of each structural component are as follows: the first outer connecting plate 12, the second inner connecting plate 23, the first inner connecting plate 13, and the second outer connecting plate 22 are all made of SUS304 stainless steel with a thickness of 5 mm. Two springs are provided for the first spring 11 and the second spring 21, with a single spring stiffness k of 0.2 N / mm, a free length of 105 mm, and a minimum working height (i.e., the height when fully compressed) of 30 mm. The series flexible cable 31 is made of Dyneema fiber rope, with a reference length (effective access length) set at 50 mm, and its elongation under working load is less than 0.2%. The first guide 51 and the second guide 52 are made of SUS304 hardened optical shafts with a length of 120 mm, and are used in conjunction with SCS8UU linear bearings. Based on the above parameters, Embodiment 2 has a clear three-segment load-tension relationship. The equivalent stiffness of both the first and second elastic units is 0.4 N / mm, which is the stiffness of two springs connected in parallel. When the series flexible cable 31 is straightened and there is no external load, the total initial length of the structure (from the upper surface of the first outer connecting plate 12 to the lower surface of the second outer connecting plate 22) is 170 mm.

[0114] (1) First stage (F≤F 12(Series low stiffness): When a low compressive load is applied to the external connecting plate, the series flexible cable 31 is tensioned and becomes the main force transmission channel. The tension is transmitted through the series path; the first elastic unit and the second elastic unit form a series configuration, and the equivalent stiffness of the variable topology multi-stiffness spring structure is 0.2 N / mm.

[0115] As the load increases, the first spring 11 and the second spring 21 are compressed. When the total compression reaches 100 mm (i.e., each elastic unit is compressed by 50 mm), the outer connecting plate will make physical contact with the adjacent inner connecting plate (i.e., the first outer connecting plate 12 contacts the second inner connecting plate 23, and the second outer connecting plate 22 contacts the first inner connecting plate 13). At this time, the load reaches the first pressure threshold F. 12 Its size is 0.2 N / mm × 100 mm = 20 N.

[0116] (2) Second stage (F) 12 <F≤F 22 Locked-up plateau stage): As the load continues to increase from 20 N, the force transmission path begins to be reconfigured due to the rigid contact between the connecting plates. During this stage, the increase in load is mainly used for force redistribution, while the compression of the structure does not change, resulting in extremely high stiffness (theoretically greater than 200 N / mm), thus forming the locked-up plateau stage in the load-displacement curve.

[0117] When the load continues to increase, causing the tension in the series flexible cable 31 to decrease to zero, the load reaches the second pressure threshold F. 22 At this point, the external load is 40 N, while the compression remains at 100 mm, and the first and second elastic units are completely converted into a parallel configuration.

[0118] (3) Third stage (F>F) 22 (Parallel High Stiffness): When the load exceeds 40 N, the series flexible cable 31 is fully relaxed, and the two elastic units work in parallel. The equivalent stiffness of the variable topology multi-stiffness spring structure is the sum of the stiffnesses of the two elastic units, i.e., 0.8 N / mm. After this, the structure enters the parallel high stiffness region.

[0119] Furthermore, when the first spring 11 and the second spring 21 are compressed to their minimum working height, the structure reaches its maximum working length, at which point the load reaches the third pressure threshold F. 32 It has a size of 60 N and a total compression of 125 mm.

[0120] By adjusting the length of the series flexible cable 31 using the winch device 32, the parameters of the locking platform stage can be precisely and programmably controlled. The adjustment effect can be seen in Table 2.

[0121] Table 2. Correspondence between the length of the tandem flexible cable and the parameters of the pressure-type locking platform stage.

[0122]

[0123] In Table 2, the compression of the locking platform refers to the overall compression of the structure when the compression-type variable topology multi-stiffness spring structure enters the locking platform stage; the minimum load F of the locking platform. 12 This refers to the external load when entering the platform locking phase; the maximum load F of the platform locking phase. 22 This refers to the external load when the platform is no longer locked.

[0124] As can be seen from the data in Table 2 above, the shorter the series flexible cable 31, the greater the compression required to achieve the relaxation of the series flexible cable 31 and the contact state of adjacent inner and outer connecting plates. Therefore, the compression and load threshold corresponding to the locking platform stage are also greater. Table 2 confirms the ability of this invention to effectively control its multi-segment stiffness response characteristics by adjusting a single parameter (the length of the series flexible cable 31).

[0125] The three-stage response characteristics of the above-mentioned compression configuration, namely "soft series connection → locking platform stage → high stiffness parallel connection", make it very suitable for use as a high-performance buffer, vibration damping device, or for applications such as robot bases and programmable energy-absorbing structures that require precise force control and impact protection.

[0126] The three-segment force-displacement variation curves of Examples 1 and 2 are as follows: Figure 4 As shown, Figure 4 The three curves in the figure correspond to the lengths of the series flexible cable 31 of 30mm, 50mm and 70mm respectively, showing the changes in the overall structural deformation with the length of the series flexible cable 31 at the first threshold, the second threshold and the locking platform stage.

[0127] Based on the above-mentioned variable topology multi-stiffness spring structure, this invention also proposes an adjustment method for the above-mentioned variable topology multi-stiffness spring structure, comprising the following steps:

[0128] S1. Determine the preset relaxation threshold T0 of the tension of the series flexible cable 31 and the preset displacement threshold X0 between the first outer connecting plate 12 and the second outer connecting plate 22 when the variable topology multi-stiffness spring structure is released from the locking platform stage according to the application scenario.

[0129] S2. During the process of the variable topology multi-stiffness spring structure bearing an external dynamic load F(t), the tension T(t) of the series flexible cable 31 and the relative displacement X(t) between the first outer connecting plate 12 and the second outer connecting plate 22 are collected in real time, and the effective length of the series flexible cable 31 is adjusted according to the tension T(t) and the relative displacement X(t) of the series flexible cable 31.

[0130] If T(t) is less than the preset relaxation threshold T0, it is determined that the variable topology multi-stiffness spring structure has left the locking platform stage and entered the high-stiffness parallel buffer zone; at this time, the series flexible cable 31 is shortened to reduce its length by ΔL, so as to adjust the variable topology multi-stiffness spring structure to return to the locking platform stage.

[0131] If T(t) is greater than the preset relaxation threshold T0 and X(t) is greater than the preset displacement threshold X0, then the variable topology multi-stiffness spring structure is determined to have left the locking platform stage and entered the low stiffness series action zone. At this time, the series flexible cable 31 is extended to increase its length by ΔL, so as to adjust the variable topology multi-stiffness spring structure to return to the locking platform stage and stabilize at the locking platform stage.

[0132] S3. Continuously repeat step S2 to form a closed-loop control, thereby maintaining the load-displacement response of the structure at the desired locking plateau stage as much as possible throughout the entire external load dynamic change cycle.

[0133] The adjustment method of this invention can actively maintain the working state of a variable topology multi-stiffness spring structure within a set locking platform stage under dynamically changing load conditions, thereby giving it extremely high stiffness. The adjustment method of this invention is applicable to both tension-type and compression-type variable topology multi-stiffness spring structures.

[0134] In practical applications, the variable topology multi-stiffness spring structure and adjustment method according to the present invention further includes the following steps before step S1:

[0135] Based on the three-segment stiffness curve required for the application scenario, such as Figure 4 As shown, the first threshold load F1, the second threshold load F2, and the locking displacement S0 corresponding to these two thresholds are determined for the target; based on these target parameters, the effective length Ls required for the series flexible cable 31 is calculated through a mechanical model;

[0136] Operate the winch device 32 to adjust the free length of the series flexible cable 31 by tightening or loosening it, so that it is equal to the calculated target effective length Ls; after adjustment, use the pawl built into the winch device 32, the brake of the servo motor or an equivalent self-locking mechanism to lock the length of the series flexible cable 31.

[0137] The above steps can complete the initial configuration of the variable topology multi-stiffness spring structure according to the requirements of the target scenario.

[0138] In some embodiments, when adjusting the effective length of the series flexible cable 31 using the winch 32, the winding control can be manual or electric servo adjustment. When electric servo adjustment is used, the winch 32 communicates with an external controller (such as a PLC, microcontroller, or industrial computer) through its signal interface. The external controller performs calculations based on the real-time received sensor signals (tension, displacement, etc.) according to a preset control algorithm (such as PID control) and outputs control commands to the servo motor to control the rotation angle of the drum in a closed loop, thereby achieving automatic, precise setting and dynamic adjustment of the length of the series flexible cable 31. This method is also applicable to both tension and compression conditions.

[0139] It should be noted that in the above embodiments, the elastic unit refers to the first elastic unit and the second elastic unit, the inner connecting plate refers to the first inner connecting plate 13 and the second inner connecting plate 23, the outer connecting plate refers to the first outer connecting plate 12 and the second outer connecting plate 22, the spring refers to the first spring 11 and the second spring 21, the parallel flexible cable refers to the first parallel flexible cable 41 and the second parallel flexible cable 42, and the guide member refers to the first guide member 51 and the second guide member 52.

[0140] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0141] In the description of this invention, "first feature" and "second feature" may include one or more of the features.

[0142] In the description of this invention, "a plurality of" means two or more.

[0143] In the description of this invention, the first feature being "above" or "below" the second feature may include the first and second features being in direct contact, or it may include the first and second features not being in direct contact but being in contact through another feature between them.

[0144] In the description of this invention, the terms "above," "over," and "on top" for the first feature and the second feature include the first feature being directly above or diagonally above the second feature, or simply indicate that the first feature is at a higher horizontal level than the second feature.

[0145] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0146] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A variable topology multi-stiffness spring structure based on flexible cable constraints, characterized in that, include: The first elastic unit includes a first spring, a first inner connecting plate, and a first outer connecting plate; the two ends of the first spring are respectively connected to the first inner connecting plate and the first outer connecting plate. The second elastic unit includes a second spring, a second inner connecting plate, and a second outer connecting plate; the two ends of the second spring are respectively connected to the second inner connecting plate and the second outer connecting plate. A series flexible cable is used to connect the first inner connecting plate and the second inner connecting plate. A winch device, which is connected to the series flexible cable, is used to adjust the effective access length of the series flexible cable between the first inner connecting plate and the second inner connecting plate; The first external connecting plate and the second external connecting plate are adapted to withstand unidirectional external loads; wherein, When the external load is less than or equal to the first threshold, the series flexible cable is tensioned, the first elastic unit and the second elastic unit are subjected to force in series, and the distance between the first outer connecting plate and the second inner connecting plate, and the distance between the second outer connecting plate and the first inner connecting plate are adaptable to change; and when the external load is equal to the first threshold, the distance between the first outer connecting plate and the second inner connecting plate reaches the first limit value, the first outer connecting plate and the second inner connecting plate form a unidirectional rigid constraint through abutment or tension connection, the distance between the second outer connecting plate and the first inner connecting plate reaches the second limit value, and the second outer connecting plate and the first inner connecting plate form a unidirectional rigid constraint through abutment or tension connection; When the external load is greater than the first threshold and less than the second threshold, the first elastic unit and the second elastic unit exhibit a mixed series and parallel topology of force. When the external load is greater than or equal to the second threshold, the first elastic unit and the second elastic unit are subjected to forces in parallel. The first threshold and the second threshold are associated with the effective access length of the tandem flexible cable.

2. The variable topology multi-stiffness spring structure based on flexible cable constraints according to claim 1, characterized in that, When the unidirectional external load is a tensile load: The first outer connecting plate, the first inner connecting plate, the second inner connecting plate, and the second outer connecting plate are arranged sequentially along the loading axis. A first parallel flexible cable is provided between the first outer connecting plate and the second inner connecting plate, and a second parallel flexible cable is provided between the second outer connecting plate and the first inner connecting plate; wherein... When the external load is less than a first threshold, the first parallel flexible cable and the second parallel flexible cable relax; When the external load equals the first threshold, the first parallel flexible cable and the second parallel flexible cable are in a taut and unloaded state; When the external load is greater than the first threshold, the first parallel flexible cable and the second parallel flexible cable are tensioned to allow the first outer connecting plate to apply tension to the second inner connecting plate through the first parallel flexible cable, and the second outer connecting plate to apply tension to the first inner connecting plate through the second parallel flexible cable, thereby forming a parallel force path between the first elastic unit and the second elastic unit.

3. The variable topology multi-stiffness spring structure based on flexible cable constraint according to claim 2, characterized in that, The initial free length of the first parallel flexible cable is greater than the distance between the first outer connecting plate and the second inner connecting plate when the external load is zero; the initial free length of the second parallel flexible cable is greater than the distance between the second outer connecting plate and the first inner connecting plate when the external load is zero.

4. The variable topology multi-stiffness spring structure based on flexible cable constraint according to claim 3, characterized in that, Both the first inner connecting plate and the second inner connecting plate are formed with through holes or notches to allow the first parallel flexible cable to pass through the through holes or notches without interference and connect the first outer connecting plate and the second inner connecting plate, and the second parallel flexible cable to pass through the through holes or notches without interference and connect the second outer connecting plate and the first inner connecting plate.

5. The variable topology multi-stiffness spring structure based on flexible cable constraint according to claim 1, characterized in that, When the unidirectional external load is a pressure load: The first outer connecting plate, the second inner connecting plate, and the first inner connecting plate and the second outer connecting plate are arranged sequentially along the loading axis; When the external load is less than a first threshold, there is a gap between the first inner connecting plate and the second outer connecting plate, and there is a gap between the second inner connecting plate and the first outer connecting plate; When the external load reaches the first threshold, the first inner connecting plate and the second outer connecting plate abut against each other to form a unidirectional rigid constraint, and the second inner connecting plate abuts against the first outer connecting plate to form a unidirectional rigid constraint, so as to form a parallel force path of the first elastic unit and the second elastic unit.

6. The variable topology multi-stiffness spring structure based on flexible cable constraint according to claim 5, characterized in that, Also includes: A first guide member, one end of which is connected to the first inner connecting plate, and the other end of which is slidably connected to the first outer connecting plate; a first spring is connected to the first guide member in cooperation. The second guide member has one end connected to the second inner connecting plate and the other end slidably connected to the second outer connecting plate. The second spring is connected to the second guide member.

7. The variable topology multi-stiffness spring structure based on flexible cable constraint according to claim 5, characterized in that, Both the first inner connecting plate and the second inner connecting plate are formed with through holes or notches to allow the first spring to pass through the through holes or notches without interference and connect the first outer connecting plate and the first inner connecting plate, and the second spring to pass through the through holes or notches without interference and connect the second outer connecting plate and the second inner connecting plate.

8. The variable topology multi-stiffness spring structure based on flexible cable constraint according to claim 2 or 5, characterized in that, Also includes: The detection unit is adapted to detect the effective access length and force of the series flexible cable, and is also adapted to detect the relative displacement between the first outer connecting plate and the second outer connecting plate.

9. The variable topology multi-stiffness spring structure based on flexible cable constraint according to claim 2 or 5, characterized in that, The first spring is constructed in multiple ways, and the multiple first springs are arranged circumferentially around the structural center of the first outer connecting plate; the second spring is constructed in multiple ways, and the multiple second springs are arranged circumferentially around the structural center of the second outer connecting plate.

10. A method for adjusting a variable topology multi-stiffness spring structure based on flexible cable constraints as described in any one of claims 1-7, characterized in that, Includes the following steps: Based on the application scenario, when the variable topology multi-stiffness spring structure is released from the locking platform stage, the preset relaxation threshold T0 of the tension of the series flexible cable and the preset displacement threshold X0 between the first outer connecting plate and the second outer connecting plate are determined. During the process of the variable topology multi-stiffness spring structure bearing an external dynamic load F(t), the tension T(t) of the series flexible cable and the relative displacement X(t) between the first outer connecting plate and the second outer connecting plate are collected in real time, and the effective length of the series flexible cable is adjusted according to the tension T(t) of the series flexible cable and the relative displacement X(t). If T(t) is less than the preset relaxation threshold T0, it is determined that the variable topology multi-stiffness spring structure has left the locking platform stage and entered the high-stiffness parallel buffer; at this time, the series flexible cable is shortened to adjust the variable topology multi-stiffness spring structure to return to the locking platform stage. If T(t) is greater than the preset relaxation threshold T0 and X(t) is greater than the preset displacement threshold X0, then it is determined that the variable topology multi-stiffness spring structure has disengaged from the locking platform stage and entered the low stiffness series action zone; at this time, the series flexible cable is extended to adjust the variable topology multi-stiffness spring structure to return to the locking platform stage.

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