CN210248880U

CN210248880U - Burden reduction suspension backpack with pre-compression type flexible connection system

Info

Publication number: CN210248880U
Application number: CN201920850886.7U
Authority: CN
Inventors: 苏业旺; 张懋熠; 郭亮; 魏延鹏
Original assignee: Institute of Mechanics of CAS
Current assignee: Zhongke Xingxing (Beijing) Technology Co.,Ltd.
Priority date: 2019-06-06
Filing date: 2019-06-06
Publication date: 2020-04-07
Anticipated expiration: 2029-06-06

Abstract

The utility model discloses a subtract burden suspension knapsack with precompression type flexible connection system, including carrying load's knapsack body, health side device and flexible connection system, flexible connection system is precompression type system, including precompression elastic component, it is the initial power structure of holding that has the pretightning force, and precompression type flexible connection system makes in the finite space, and precompression elastic component can bear bigger load under littleer compression increment. The utility model discloses not only occupation space is little, succinct and pleasing to the eye, and the effect of subtracting burden is obvious moreover.

Description

Burden reduction suspension backpack with pre-compression type flexible connection system

Technical Field

The present invention relates to an ergonomic backpack, and more particularly, to a load-reducing suspension backpack having a pre-compression type flexible connection system.

Background

The individual carrying tool is a harness for carrying weaponry and living goods by an individual, and comprises a knapsack which is equivalent to a knapsack for ordinary people. However, in modern war, the load of individual soldiers is increased continuously, and the rear legs of the fighting power are seriously dragged by the over-high load of the individual soldiers. How to effectively reduce the burden of officers and soldiers on the battlefield has become a key topic of research in various countries.

For a common backpack, when the backpack is stationary, the force exerted on the body by the backpack is only static and is equal to the weight of the backpack. However, when walking or running while wearing the backpack, the peak force exerted on the body can increase significantly to 2-3 times greater than the static force, and this increase in peak force can exert very large forces on the joints, resulting in muscle damage and even joint injury.

Studies have shown that peak forces are related to the rolling motion of the buttocks. The heaving motion of the hips during travel can result in vertical motion of the backpack. If vertical movement of the backpack is desired, the body exerts an acceleration force on the backpack. In turn, the backpack also exerts a downward force on the shoulders and body. This downward force will cause the ground to react more to the foot when the foot is in contact with the ground than at rest, thereby increasing the force on the joint. This also increases the energy consumption of the wearer when walking, greatly increasing the physical burden.

Therefore, the peak force acting on the bearer can be reduced by reducing the vertical displacement amplitude of the backpack, and the energy consumption during walking can be reduced, so that the burden of the bearer is reduced. The carrier can thus bear a greater weight with the same metabolic expenditure during a quick walk, while reducing the stress on the joints and avoiding muscle damage.

The Rome of foreign scholars developed a load-reducing suspension backpack using elastic ropes and pulleys as a flexible connection system using the principle of forced vibration of objects (Rome, l.c., Rubber band reduction the cost of carrying loads. nature,444(7122),1023 + 1024, 2006). The related results have been applied for patent of invention by LIGHTNING PACKS corporation in 2007 (US2008185411A 1). Natural frequency of load-reducing suspension knapsack

Where k is the spring constant of the flexible attachment system and m is the mass of the backpack. And Δ L is mg/k, where Δ L is the amount of expansion and contraction of the elastic element, and g is the acceleration of gravity. Thus is provided with

Therefore, the larger the elastic element expansion amount Δ L is, the smaller the natural frequency f is, the smaller the amplitude of the backpack is, and the better the load reduction effect is. Such pre-stretched flexible connection systems therefore require a relatively large amount of space to accommodate the relatively long lengths of pre-stretched bungee cords and sets of pulleys, as well as sufficient space to allow the bungee cords to be re-stretched, and therefore have a large number of components, long lengths, large volumes, and cumbersome structures.

Foreign scholars HOFMANN and Rome made a suspended backpack with load simulation circuit that could generate Electricity using extension springs (Generation electric wall Walking with loads. science,309(5741), 1725-. The related achievement was patented by LIGHTNING PACKS corporation in 2008 (US2009015022a 1). In this patent, a generator converts mechanical displacement of one part of the suspension system relative to another part of the suspension system into electrical energy, an additional electrical generating device is available for connection to the generator to generate additional power for the backpack at the hip of the wearer, and a rod is included that fits the femur of the wearer to pass through the range.

However, when a user carries a portable electronic device, the electronic device typically requires a secondary battery to supply power. If the only power source from the backpack is generated during walking, it may be that on certain days the user does not have enough walking to generate the necessary power to keep the battery fully charged. Once the power is exhausted, the electronic device cannot operate further because it is not powered. On the other hand, with the recognition of the importance of environmental protection by modern people, it is now a great trend in modern society to reduce the number of batteries or batteries used, and whatever batteries cause environmental pollution.

Moreover, such power plants have a complex structure consisting of a large number of components, which must take purposeful forms of movement or movement, such as swinging, touching and gripping, in order to generate electricity. In the aspect of mechanical structure, only one stretching spring is arranged, and the stretching length of the stretching spring in a limited space is greatly limited because the stretching spring cannot use devices such as pulleys, so that ideal vibration frequency cannot be obtained, and the obtained load reduction effect is not good.

In the country, south China university of marble applied several patents (CN107588312A, CN107594857A, CN107616617A, CN108887863A) for burden-reducing backpacks or apparatus of similar structure, which are basically consistent with the principle adopted by U.S. patent application No. US2008185411A 1. The spring damping mechanism adopted in CN107588312A uses a spring pull rope which needs to be pre-tensioned. If a good load reduction effect is to be achieved, the backpack will fall from the position of the back to the position of the buttocks if the spring is stretched too long at rest, so that the patent has no practical value. Likewise, CN107594857A uses a spring pull cord that requires pretension. It uses a capstan, i.e. a pulley equivalent to the one in US patent invention US20080185411a1, to increase the stretching space by routing in the beam. However, the space in the cross beam is limited and not sufficient to provide a good load-reducing function. The spring cord used in CN107616617A needs to be pretensioned, but the total length of a plurality of spring cords arranged side by side is at most as long as the back plate, so the stretching space is not enough. CN108887863A uses a pulling rope and a spring (i.e. an extension spring) connected with the pulling rope in an extension way, and as in CN107616617A, the total length of the pulling rope and the extension spring after being extended is at most as long as that of the back plate, so that the extension space is limited, and no good load reduction effect is achieved at all.

Aiming at the defect that the prestretched flexible connecting system in the prior art occupies a large space, the invention designs the burden-reducing suspension backpack with the precompressed flexible connecting system, which occupies a small space and has an obvious burden-reducing effect.

Disclosure of Invention

The invention mainly aims to provide a load reduction suspension backpack with a pre-compression flexible connecting system, which adopts the pre-compression flexible connecting system to solve the technical problems of large occupied space and poor load reduction effect of the existing suspension backpack.

To achieve the above object, a load-reducing suspension backpack having a pre-compression type flexible coupling system includes a backpack body carrying a load, a body-side device coupling a body, and a flexible coupling system coupling the backpack body and the body-side device, the backpack body being capable of sliding relative to the body-side device by the flexible coupling system,

the method is characterized in that: the flexible connection system is a pre-compression type system and comprises a pre-compression elastic component which is a force accumulation structure with pre-tightening force initially, and the pre-compression type flexible connection system enables the pre-compression elastic component to bear larger load under smaller compression increment in a limited space; the pre-compressed resilient assembly is further retractable as the backpack body slides relative to the body side device, the pre-compressed flexible coupling system causing the natural frequency of the load-reducing suspension backpack to be less than the walking frequency and the acceleration of the backpack body to be less than the acceleration of the body side device, the amplitude of the backpack body being less than the amplitude of the body side device.

Further, the pre-compressed elastic assembly comprises a plurality of pre-compressed elastic elements connected in parallel to reduce the load borne by a single spring and to adjust the elastic modulus of the pre-compressed elastic assembly, preferably the number of the pre-compressed elastic elements is 2-10, further preferably the pre-compressed elastic elements are pre-compressed compression springs.

Further, the length of the pre-compressed elastic element which can be further stretched after being stressed is at least 5 cm.

Preferably, in order to further ensure that the pre-compressed elastic element is always elastic in the working range, the pre-compressed elastic element is made of metal, and preferably, the pre-compressed elastic element is made of piano wire.

Preferably, the flexible connection system further comprises a support member, a sliding rail assembly and a sliding member, the support member supports the elastic element, the sliding rail assembly is located on the left side and the right side of the elastic assembly, two ends of the sliding member are connected with the sliding rail assembly on the left side and the right side, the sliding member slides back and forth on the support member, and the elastic assembly can be compressed.

Preferably, the support member is a guide rail, a support rod or a sleeve, the support member is inserted into the compression spring or is wrapped outside the compression spring, and preferably, the support member is made of stainless steel and has a solid or hollow structure.

Preferably, the slide rail assembly comprises a slide rail and a ball frame, and two ends of the sliding part are embedded in the ball frame and slide in the slide rail.

Preferably, the slider is connected to the backpack body and the slide rail assembly is connected to the body-side device.

The backpack body comprises a backpack body, a connecting plate and a lining strip, the lining strip is arranged inside the backpack body, the connecting plate is arranged outside the backpack body, the connecting plate and the lining strip clamp the inner surface of the backpack body, and the backpack body is fixed on the connecting plate.

Preferably, the body side device comprises a harness, a support panel and a pad, preferably a waist belt.

Compared with the prior art, the invention has the following advantages and beneficial effects:

first, the flexible joint system of the present invention is a pre-compressed type system comprising a pre-compressed elastic assembly that is initially in a pre-tensioned, force accumulating configuration. The pre-compressed resilient assembly may further flex as the backpack body slides relative to the body side device. The precompression-type flexible attachment system allows the natural frequency of the subtractive suspension backpack to be less than the walking frequency and allows the acceleration of the backpack body to be less than the acceleration of the body side device and the amplitude of the backpack body to be less than the amplitude of the body side device, as can be seen in the experimental data verification of the examples section. The flexible connecting system of the invention obviously reduces the vibration amplitude of the backpack when a user walks or runs, and has obvious burden reduction effect.

Second, the longest working length of the elastic element required for the pre-compression type flexible connection system of the present invention corresponds only to the maximum displacement of the backpack body relative to the body side frame (typically less than 7cm) plus the lowest working length of the elastic element, whereas the prior art pre-stretched elastic systems require the longest working length of the elastic element to be the pre-stretched elongation (at least 24cm) plus the original length of the elastic element plus half the maximum displacement of the backpack body relative to the body side frame (typically less than 7 cm). In addition, the precompression-type flexible connection system allows the precompression spring assembly to carry higher loads at smaller increments of compression in a limited space. Thus, it is apparent that the longest working length of the spring elements employed in the precompressed flexible coupling system of the present invention is significantly shorter, occupies less space, and is more compact and aesthetically pleasing when compared to the prior art.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

FIG. 1 is a schematic diagram of the overall structure and a side view of the load-reducing suspension backpack of the present invention;

FIG. 2 is a schematic illustration of the precompression of the compression spring of the present invention;

FIG. 3 is an exploded view of the load-relieving suspension backpack of the present invention;

FIG. 4 is a graph comparing the results of the tests of the present invention;

FIG. 5 is an isometric view of the flexible connection system of the present invention;

FIG. 6 is a schematic view of an exploded configuration of the flexible connection system of the present invention;

FIG. 7 is an exploded view of the backpack body of the present invention;

fig. 8 is a schematic view of an exploded view of a body side device according to the invention.

In the figure, 101-backpack body; 102-a flexible connection system; 103-a body side device; 1-inclusion; 2-a lining strip; 3-connecting the plates; 4-a slide rail; 5-a ball frame; 6-a slide; 7-a top plate; 8-a back plate; 9-a liner; 10-a harness; 11-a support; 12-rubber pad; 13-a locking switch; 14-a compression spring; 15-clamping piece.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.

It should be noted that in the description of the present invention, the terms "lateral", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

The suspension knapsack is a forced vibration system, and its purpose is to reduce the amplitude of the knapsack during walking. The flexible attachment system is the spring element in the spring damping system and the backpack body is the inertial element in the spring damping system. The body on foot exerts an exciting force on the spring damper system, and the backpack is forced to vibrate. The amplitude of the backpack is related to the ratio of the natural frequency to the excitation frequency. The smaller the ratio of the natural frequency of the load-reducing suspension backpack to the walking frequency of the wearer, the smaller the amplitude of the backpack. When the backpack is static, the larger the stretching amount of the elastic element in the flexible connecting system is designed to be, the smaller the elastic coefficient of the flexible connecting system is, the smaller the natural frequency of the burden reduction suspension backpack is, the smaller the amplitude of the backpack is, and the better the burden reduction effect is. Therefore, the structural design of the flexible connection system is of great importance.

As shown in FIG. 1, the present invention is a load-reducing suspension backpack having a pre-compressed flexible attachment system, pre-compressed meaning that the resilient elements in the flexible attachment system have been compressed when the backpack is initially at rest, as shown in FIG. 2.

As shown in fig. 3, the load-reducing suspension backpack includes a body-side device 103 connected to the body, a backpack body 101 for carrying a weight, and a flexible connection system 102 for connecting the two. The backpack body 101 is slidable relative to the body side device 103 by means of a flexible connection system 102.

As shown in fig. 7, the backpack body 101 includes a backpack body 1, two strips 2 and a connecting plate 3, the connecting plate 3 is disposed outside the backpack body 1, the strips 2 are disposed inside the backpack body 1, the strips 2 can be disposed on two sides, the connecting plate 3 is fixedly connected to the strips 2, and the backpack body 1 is fixed on the connecting plate 3 by clamping the inner surfaces of the backpack body together. Further, the connecting plate 3 is fixedly connected with the sliding member 6 of the flexible connecting system 102 by screws or bolts, so as to realize the connection between the backpack body 101 and the flexible connecting system 102. The connecting plate 3 is a plate after topology optimization, and can be a separate plate with the size similar to that of the slide rail for the convenience of disassembly.

As shown in fig. 8, the body-side device 103 includes a back plate 8, a pad 9, and a shoulder strap 10, and may be provided with a waist belt. The back plate 8 is fixedly connected to the guide rail 4 of the flexible connection system 102 in a manner of screws or bolts, so as to connect the body-side device 103 and the flexible connection system 102. The padding 9 may be skin padding, and the skin padding 9 may be zipped or glued to wrap the flexible attachment system and the back panel 8, exposing only the side of the flexible attachment system that contacts the backpack. The skin pad 9 is an ergonomic skin pad 9, and the shoulder strap 10 is connected to the skin pad 9 or directly connected to the back plate 8. Topology optimization techniques can be used to optimize the structure and reduce the weight of the backplate 8.

As shown in fig. 5 and 6, the flexible connecting system 102 at least includes an elastic component, a support 11, a sliding rail component, and a sliding component 6.

Wherein the elastic assembly comprises a plurality of elastic elements connected in parallel, the number of which may be 2-10, the elastic elements being pre-compressed compression springs 14. In order to further ensure that the compression spring always keeps elasticity in the working range, the compression spring is made of metal materials and can be a piano wire.

In order to avoid excessive bending of the compression spring 14 during compression, a support member 11 slightly smaller than the inner diameter of the compression spring 14 may be disposed inside the compression spring 14, the support member 11 may be in the form of a rail or a support rod or a sleeve, the support member 11 is inserted into the compression spring 14 or is wrapped outside the compression spring 14, and the support member may be made of stainless steel and may be of a solid or hollow structure.

The slide rail assembly comprises two slide rails 4 and two ball frames 5, the two slide rail assemblies are respectively positioned on the left side and the right side of the elastic assembly, one ball frame 5 is arranged in each slide rail 4, and the two ball frames 5 are respectively assembled and connected with the left end portion and the right end portion of the sliding part 6 to help the sliding part 6 to slide up and down in the slide rails 4. One side of the two slide rails 4 is fixedly connected with the back plate 8 of the body-side device 103.

The ball frames 5 on the left side and the right side are connected at two ends of the sliding part 6, and the sliding part can be specifically connected in a clamping fit mode of a groove and a tenon. The slider 6 is provided with a plurality of holes for the support 11 to pass through, while the compression spring 15 cannot pass through. The slider 6 slides back and forth on the support 11 and is able to compress the compression spring 14. The sliding part 6 is connected with the backpack body 101 to drive the backpack body 101 to slide vertically or move vertically.

In addition, to reduce impact and damage caused by the impact, the upper and lower ends of the support 11 may be further equipped with rubber pads 12.

The upper part of a rubber pad 12 on the upper part of a support piece 11 is assembled with the upper top plate 7, the lower part of the rubber pad 12 on the lower part of the support piece 11 is assembled with the lower top plate 7, a plurality of fixing holes are formed in the upper top plate 7 and the lower top plate 7, the support piece 11 is allowed to be inserted into the fixing holes without penetrating out of the fixing holes, and a plurality of fixing grooves are formed in the upper top plate 7 and the lower top plate 7 and are fixedly connected with the rubber pad 12 in a clamping mode, so that the support piece 11 is prevented from.

In order to control the sliding of the sliding plate 6, a locking switch 13 is further disposed on each of the sliding rails 4, so as to lock the sliding rail assembly and prevent the sliding plate 6 from sliding. As for the specific structure of the locking switch 13, it can adopt the form of locking and limiting components commonly and commonly used in the prior art, such as a knob switch or a thread limit stop, etc., which will not be discussed in detail herein.

In order to further increase the strength of the connection of the flexible connection system 102 to the connection plate 3, a detent 15 is provided. One side of the blocking element 15 is connected with the other side wall of the slide rail 4 and can slide along the side wall of the slide rail 4. The other end of the clamping piece 15 and the sliding piece 6 are simultaneously connected and fixed with the connecting plate 3, and the upper end of the connecting plate 3 is fixedly connected with the sliding piece 6. In order to avoid the left-right swing of the lower end of the connecting plate in the actual use process, the lower end of the connecting plate 3 is fixedly connected with the other end of the clamping piece 15 in a screw or screw fixing connection mode.

The experimental situation of the in situ running of the load-reducing suspension backpack of the present invention is shown in fig. 4. The load-reducing suspension backpack in the test uses 6 compression springs connected in parallel. The spring is made of piano steel wires, the outer diameter is 7.3mm, the inner diameter is 5.8mm, the wire diameter is 0.75mm, the total number of turns is 179.46, the effective number of turns is 177.46, the free length is 465mm, and the spring stiffness is 0.0657N/mm. The total load was 8kg, each load was 1.33kg, and each precompression length was 198 mm. The wireless accelerometers are respectively arranged on the backpack and the body side device, the running frequency is measured to be about 3.1Hz, and the natural frequency of the designed backpack is 1Hz and is less than half of the running frequency. In fig. 4, the left side is the acceleration curve of the frame, the right side is the acceleration curve of the backpack, the amplitude of the acceleration curve of the backpack is obviously smaller than that of the body side device, the amplitude of the acceleration of the body side device is about 0.45g, and the amplitude of the acceleration of the backpack is about 0.2g, so that the displacement of the backpack is obviously smaller than that of the body, and the burden of a wearer can be effectively relieved.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. A load-reducing suspension backpack with a pre-compression type flexible connection system, comprising a backpack body (101) carrying a load, a body side device (103) connecting the body, and a flexible connection system (102) connecting the backpack body (101) and the body side device (103), the backpack body (101) being capable of sliding relative to the body side device (103) by means of the flexible connection system (102),

the method is characterized in that: the flexible connection system (102) is a pre-compression type system, comprising a pre-compression elastic component which is a force accumulation structure with pre-tightening force initially, and the pre-compression type flexible connection system enables the pre-compression elastic component to bear larger load under smaller compression increment in a limited space; the pre-compressed resilient assembly is further retractable when the backpack body (101) slides relative to the body side device (103), the pre-compressed flexible coupling system causes the natural frequency of the load-reducing suspension backpack to be less than the walking frequency and causes the acceleration of the backpack body (101) to be less than the acceleration of the body side device (103) and the amplitude of the backpack body (101) to be less than the amplitude of the body side device (103).

2. The backpack of claim 1, wherein the suspension backpack comprises a flexible connection system of the pre-compression type, wherein the flexible connection system comprises: the pre-compressed resilient assembly includes a plurality of pre-compressed resilient elements connected in parallel to reduce the load experienced by a single spring and to adjust the spring rate of the pre-compressed resilient assembly.

3. The backpack of claim 2, wherein the suspension backpack comprises a flexible connection system of the pre-compression type, wherein the flexible connection system comprises: the length of the pre-compressed elastic element which can be further stretched after being stressed is at least 5 cm.

4. The backpack of claim 2, wherein the suspension backpack comprises a flexible connection system of the pre-compression type, wherein the flexible connection system comprises: in order to further ensure the load reducing effect of the load reducing suspension backpack, the pre-compression elastic element is always kept elastic in the working range, and the pre-compression elastic element is made of metal.

5. The backpack of claim 2, wherein the suspension backpack comprises a flexible connection system of the pre-compression type, wherein the flexible connection system comprises: the flexible connecting system (102) further comprises a supporting part (11), a sliding rail assembly and a sliding part (6), wherein the supporting part (11) supports the pre-compressed elastic element, the sliding rail assembly is positioned at the left side and the right side of the pre-compressed elastic element, two ends of the sliding part (6) are connected with the sliding rail assembly at the left side and the right side, the sliding part (6) slides back and forth on the supporting part (11) and can compress the pre-compressed elastic element.

6. The backpack of claim 5, wherein the suspension backpack comprises a flexible connection system of the pre-compression type, wherein the flexible connection system comprises: the supporting piece (11) is a guide rail or a support rod or a sleeve, the pre-compression elastic element is a pre-compression spring (15), and the supporting piece (11) is inserted into the compression spring (15) or coated outside the compression spring (15).

7. The backpack of claim 5, wherein the suspension backpack comprises a flexible connection system of the pre-compression type, wherein the flexible connection system comprises: the sliding rail assembly comprises a sliding rail (4) and a ball frame (5), wherein two ends of the sliding piece (6) are embedded with the ball frame (5) and slide in the sliding rail (4).

8. The backpack of claim 5, wherein the suspension backpack comprises a flexible connection system of the pre-compression type, wherein the flexible connection system comprises: the sliding part (6) is connected with the backpack body (101), and the sliding rail component is connected with the body side device (103).

9. The backpack of any of claims 1-8, wherein the backpack comprises a pre-compressed flexible connection system, wherein the suspension system comprises: the backpack body (101) comprises a backpack body (1), a connecting plate (3) and lining strips (2), wherein the lining strips (2) are arranged inside the backpack body (1), the connecting plate (3) is arranged outside the backpack body (1), the inner surface of the backpack body is clamped by the connecting plate (3) and the lining strips (2), and the backpack body (1) is fixed on the connecting plate (3).

10. The backpack of any of claims 1-8, wherein the backpack comprises a pre-compressed flexible connection system, wherein the suspension system comprises: the body side device (103) includes a harness (10), a backboard (8), and a pad (9).

11. The backpack of claim 10, wherein the suspension backpack comprises a flexible connection system of the pre-compression type, wherein the flexible connection system comprises: the body-side device includes a belt.

12. The backpack of claim 2, wherein the suspension backpack comprises a flexible connection system of the pre-compression type, wherein the flexible connection system comprises: the number of pre-compressed elastic elements is 2-10.

13. The backpack of claim 6, wherein the suspension backpack comprises a flexible connection system of the pre-compression type, wherein the flexible connection system comprises: the supporting piece (11) is made of stainless steel and is of a solid or hollow structure.

14. The backpack of claim 4, wherein the suspension backpack comprises a flexible connection system of the pre-compression type, wherein the flexible connection system comprises: the pre-compressed elastic element is made of piano steel wires.