Patent Application
20200025228
This application relates to straps that fasten to a human. More specifically, it relates to a system for alleviating the tension on an expanding human body part, produced by wearing a strap, by the use of a flat, nearly flat or degressive spring rate to control the tension.
Most objects or devices that are meant to be carried or worn use elastic straps in order to be coupled with the body, which may be a human, animal or robot body. One challenge raised using this type of strap is that the elastic nature of the strap causes the displacement of the object or device over time. A functional device, which is required to be held in an optimum position on the body, gradually moves away from its initial position as the strap loses its ability to provide an efficient coupling.
Braces, prosthetics and other devices are required to couple tightly to the human, animal, or robot overlay body, for example to the legs, waist, arms, torso or feet. To function efficiently, displacement of the device must be minimized and the coupling should be stiff.
Current devices use elastic straps. Normally, an elastic strap exhibits a linear spring rate behavior, wherein the extension of the strap is proportional to the applied force or tension, or progressive, where the spring rate increases with extension. For example, the inner rubber of an elastic strap is linear but the webbing is somewhat rigid. The combination of these two makes for a combined spring rate curve, albeit mostly linear.
In some applications, such as energy harvesting devices strapped around a user's leg, it is required that the straps be reasonably tight in order to achieve good coupling of the harvester to the leg. During normal walking, an elastic strap is comfortable. However, when the user bends beyond the normal walking range of motion, for example when squatting, the leg circumference grows. The strap is then forced to extend, and as an elastic strap has a linear or progressive spring rate, the strap tension increases, creating additional pressure on the user resulting in discomfort. This problem is common for medical devices, backpacks, harnesses, clothing, braces, utility belts or any medical device that should be attached with a strap. Additionally, there are safety implications: if the strap or device becomes snagged, the stress on the strap may rise until something breaks, which may also occur when, for example, a movement causes the maximum extension of the strap to be exceeded.
Applications where non-linear spring rates are used include Belleville washers, for example. Other applications include leaf springs where a force is applied at an acute angle to the leaf. Lever linkages that have progressive ratios are found in bicycles. Nautilus or other non-circular gears have changing ratios that can be degressive or progressive. Compound bows use cams with a changing pulley arm to achieve a degressive spring rate, meaning that it is initially hard to pull the bow but when it is fully drawn it requires a small holding force to hold it.
This background is not intended, nor should be construed, to constitute prior art against the present invention.
The present invention is directed to a strap that incorporates an inelastic component and a stretchable component. The stretchable component is a mechanism with a semi-flat spring rate (flat, nearly flat or degressive) for the majority of its operating range of extension. The semi-flat spring rate may be the result of a combination of several mechanisms that exhibit various different spring rate profiles such as flat, degressive, constant or linear spring rates. The operating range accommodates the expansion and contraction of a body part to which the strap is to be attached, such that the tension applied to the body part by the strap varies minimally as the body part expands and contracts.
Different embodiments of the invention are presented here in order to illustrate the practicality of the incorporation of a semi-flat spring rate profile into a strap. Embodiments include straps with a cam mechanism and inelastic band; a stretchable band and inelastic buckle; and a flat coil spring mechanism and inelastic band.
For the reasons of comfort, the coupling must be able to allow for expansion of the body as the wearer moves, without imparting significant extra tension. The advantages of each embodiment of the present invention include one or more of: helping to mitigate excessive pressure applied to a person who is wearing the strap; improving coupling of a device to a person; and improving power transmission between a device and the human body.
A practical use of the strap is to connect a genuflective energy harvester to a person. Such an energy harvester is connected between a shin brace and a thigh brace attached to a person's leg. The braces change angle relative to each other as the person locomotes, generating electricity in the harvester. It is important for the braces to be connected firmly yet comfortably to the person for maximum efficiency and effectiveness of the energy harvester. Straps are either used to attach through holes or slots in the braces, or they are incorporated as components of the braces.
As disclosed, an aspect of the present invention is a strap for tightening around an expandable object comprising: a first portion that is inelastic; and a second portion connected to the first portion and having a spring rate profile that is semi-flat in an operating range spanning a first extension of the second portion and a second extension of the second portion; wherein, when the strap is tightened around the expandable object, the second portion remains within the operating range as the expandable object expands and contracts.
The following drawings illustrate embodiments of the invention and should not be construed as restricting the scope of the invention in any way.
The term “degressive” in relation to a spring means that it has a spring rate that is declining as the extension of the spring is increasing. The force to maintain the spring extended further from a given point may be greater or lower than that at the given point, but if it is greater it is not as high as to be proportional to the additional extension of the spring (e.g. curve 79,
The terms “inelastic” and “non-elastic” refer to the non-stretchable property of materials that are not normally considered to be elastic, such as the leather in a belt. While such materials may scientifically exhibit a very small and negligible amount of elasticity, they are still considered to be inelastic. Generally, leather or polymer is multiple orders of magnitude stiffer than an elastic component.
The term “spring rate” of a linear spring refers to the spring constant k given by Hooke's law F=kx, where F is the applied force and x is the extension of the spring.
The term “spring rate profile” refers to a graph of force (or tension) on the y-axis against extension along the x-axis for springs that do not obey Hooke's law, and therefore are not linear springs.
The term “semi-flat” refers to a spring rate profile that is typically flat, approximately flat or degressive over a particular extension range of interest of the spring. In some cases, the spring rate profile may even be slightly progressive, but the minimum requirement for the spring rate profile to be semi-flat is that the percentage variation in extension force is smaller, by at least 10%, than the percentage variation in extension over a range of extension of interest, such as an operating range.
Referring to
In one embodiment the band 14 exhibits an inelastic behavior while the central piece 12 has a semi-flat spring rate over a major portion of its operating range, i.e. a spring rate that is flat, degressive or otherwise allows for a relatively wide range of extension with a relatively small variation in force. Using a semi-flat spring rate helps to prevent an increased force to human body parts such as legs, waist, arms or torso as those body parts expand.
In another embodiment the central piece 12 exhibits an inelastic behavior while the band 14 has a semi-flat spring rate over a major portion of its operating range.
Thus, the present invention can be represented as a strap 10 having a combination of at least two portions, a first portion that has non-elastic behavior and a second portion that has a semi-flat spring rate. As a consequence, when the strap 10 is coupled to a human leg and a movement, such as a squat, calls for an increased extension of the strap, the additional pressure on the leg due to the strap extension is minimized, preventing excessive discomfort to the wearer.
The strap also has an initial extension range 20 for pre-tensioning the strap. In the initial range 20, the spring rate profile 21 is linear, progressive, degressive or a combination of these, and is steep compared to the profile 17 in the operating range of interest 16. Force Fs is needed to set the spring into its working range. Dotted lines 22, 23 show exemplary extents of other spring rate profiles in the initial range 20. The result of using such a spring rate profile 15 is that a relatively large force is needed to prime or preload the strap 10, by stretching it beyond a certain minimum extension E1 but then not much additional force, if any, is needed to continue to extend the strap over its full operating range 16 up to extension point E2. In contrast, if a linear spring rate spring rate 26 were used for the operating range, the force would increase excessively in comparison, causing considerable discomfort to the user.
In most embodiments, the semi-flat spring rate profile is such that the variation in extension force ±ΔF/Favg is smaller, by at least 25%, than the corresponding variation in extension ±ΔE/EM within the operating range.
Range 28 represents an extra-tight force region in the initial range 21 of the spring rate profile 23, which must be overcome for the strap to be properly pre-tensioned. This provides a physical indication or a feel to the user that the strap is set correctly for use. The range 28 can be changed in relative height depending on the embodiment.
In
The cam mechanism 32 has a cam plate 33, a guide 34 defined by the cam plate, two or more followers 36, 38 and a slider 40. The slider 40 is connected non-adjustably to an end region 41 of the band 31 and slides in the guide 34 as the strap 30 is extended, i.e. by pulling the band to the right relative to the cam mechanism 32. The followers 36, 38 each include a wheel 42, 44 mounted thereon, wherein wheel 42 is connected to wheel 44 via a coil spring 46. The followers 36, 38 are biased towards each other by the coil spring 46, or, in other embodiments, another type of spring. The followers 36, 38 are shown behind the cam plate 33, however, duplicate follower plates (not shown) are also present over the cam plate, such that the wheels 42, 44 are each sandwiched between two follower plates. The followers 36, 38 are pivoted at points 45, 47 on the slider 40. Extremities of the coil spring 46 are attached respectively to pivots 50 and 52 located at the center of each wheel 42, 44. Rounded corners 37 and 39 are present in the cam plate 33, between the shoulders 54, 55 and the sides 71, 72 of the cam plate 33. The combination of a shoulder 54, rounded corner 37 and side 71 can be referred to as a profiled edge or cam of the cam plate.
In this view, the strap 30 is not extended, thus the slider 40 is positioned at the left of the guide 34. When the strap 30 is not in extension, the rotating wheel 42 of the follower 36 is located at the inside of the shoulder 54 of the cam plate 33, in contact with the neck 68 of the cam plate 33. Also, the rotating wheel 44 of the follower 38 is located at the inside of the other shoulder 55 of the cam plate 33, also in contact with the neck 68.
The band 31 is attached indirectly to the cam plate 33 via a fixation piece 56 located on the surface of the band. The fixation piece 56 is connected to another fixation piece 58 located on the cam plate 33 by means of a coil spring 60 or other sprung connection. The other end region 65 of the band 31 is connected to a buckle 62 (or other adjustable, disconnectable attachment) at the head of the cam plate 33. The end 66 of the band 31 is narrower than the main part of the band in order to slide inside the holes 64 of the buckle 62.
Instead of the buckle 62, other fixing mechanisms can be used in other embodiments, such as a ratchet strap, Velcro®, a Boa® system, etc.
The coil spring 46, between the wheel 42 located on the follower 36 and wheel 44 of the other follower 38, is at its minimum extension, across a narrow portion or neck 68 of the cam plate 33.
When the strap 30 is partially extended, the band 31 pulls the fixation piece 56 to the right relative to the cam plate 33, in turn extending the coil spring 60 that is attached to the fixation piece 58 located on the cam plate. Therefore, the strap 30 is being extended against the combined resisting forces of both springs 46, 60, and the components of the cam plate mechanism 32 interact with each other to provide an overall non-linear spring force profile to the strap 30.
Referring to
The sides 71, 72 are further apart at the rounded corners 37, 39 than they are at locations in contact with the cam followers 36, 38 when the slider 40 is at its maximum travel, as shown in
In use, the non-elastic band 31 is reasonably tightly wrapped around a leg to hold a device in place, and buckled to the cam plate 33. The strap is tensioned by the cam mechanism 32, which provides a declining spring rate due to the shoulders 54, 55, corners 37, 38 and sides 71, 72 of the cam plate 33. Depending on the embodiment one can achieve a flat spring rate or a decreasing spring rate by altering the shapes and/or sizes of the shoulders 54, 55, corners 37, 38 and sides 71, 72 of the cam plate 33, and by changing the spring rates of the coil springs 46, 60.
Referring to
The spring rate 75 has a linear behavior in that the force applied to the spring is proportional to its extension. The spring rate profile 76 of the cam mechanism 32 has a degressive behavior. In the first part of the spring rate profile 76, the force increases as the cam mechanism 32 is extended until it reaches about 16 mm of extension. Then, in the second part of the profile, between an extension of about 16 mm and 60 mm, the spring rate profile 76 of the cam mechanism 32 becomes semi-flat, which means that the force applied to the cam mechanism changes little when its extension increases, i.e. there is only a relatively little additional force opposing further extension. In the second part, the force applied on the cam mechanism 32 is relatively stable compared to in the first part of the spring rate profile.
The spring rate profile 74 of the strap as a whole can be seen as the summation of the constant spring rate 75 of the coil spring 60 and the degressive spring rate 76 of the cam mechanism 32.
In this embodiment, the strap 30 must be extended by about 16 mm to prime the strap. In other embodiments, the extension to prime the strap can be smaller than that shown here. The range 77 is the target range (for example) in which the strap is to be used during normal walking, i.e. somewhere in the range of 6-10 lbs (2.7-4.5 kg) tension. During a squat, the extension of the strap extends to about 50 mm. It is the operating range 78, in the spring rate profile 74, that can be defined as the portion that is responsible for mitigating the additional pressure applied on the part of the body to which the strap is fastened, during movements that cause the strap to expand. In this particular embodiment, it can be seen that the force exerted by the strap in the operating range is within the range Favg±ΔF, for an extension range of at least EM±ΔE, where ΔF≤0.15Favg and ΔE=0.55EM where Favg is the average force of the strap in its operating range and EM is the midpoint of the operating range.
Referring to
For a strap with spring profile 81, the tension in the strap falls monotonically (i.e. continually without ever rising) as the second portion extends from about 17 mm to the maximum operating extension of 58 mm, which is over the majority of the operating range.
Referring to
Referring to
Referring to
At B, the element is stretched out sideways, by a pulling force applied to the midpoints 109 of the sides 111. The pulling force is applied along, or symmetrically in the region of, the centerline 112 of the band 103, to the side regions 116, 118 of the element 106. The width WB at the middle section of the X-shaped gap 108 is increased at B compared to the width WA of the gap when the element 106 is in its rest state at A. The height of the element has also expanded by D1 at both ends. By applying a force to expand the width of the element 106, the resulting increase in height of the element causes a spring 120, which is connected between opposing end regions 113, 114 of the element, to lengthen.
At C, the element 106 is stretched out sideways further and the element increases in height a little further, by D2 at both ends. While the height has only minimally increased from state of stretch B to state of stretch C, the width WC has increased considerably in comparison to width WB. Therefore, as the side regions 116, 118 are pulled apart, the end regions 113, 114 move apart on a declining basis. This corresponds to a degressive spring rate profile since the additional sideways expansion of element 106 incurs a decreasing additional force on the spring 120. At point C, the height of the element 106 has reached its maximum, and so further sideways expansion of the element will result in a lower force from the spring 120 as the height of the element will start to reduce. As well as the spring 120 providing a restoring force to the element, the material of the element itself provides some springiness in some embodiments. The overall spring rate profile of the strap 101 is a sum of the contributions from the material itself and the incorporated springs 120.
Referring to
In another embodiment, as in
Referring to
While the best presently contemplated mode of carrying out the subject matter disclosed and claimed herein has been presented, other embodiments are possible.
In other embodiments, there is a locking mechanism to lock the cam followers, so that the strap tightening mechanism can be tightened and used as a tourniquet. The cam mechanism has a hard stop that is useful for the tourniquet function.
In some embodiments, the spring rate profile may show hysteresis.
Colored markers may be used in all embodiments to indicate to the wearer that the strap is sufficiently primed. A dial on the cam follower in the first embodiment, which rotates as the strap is extended and aligns with a marker on the housing of the cam, may be used to indicate that the strap is sufficiently primed. In the second embodiment, a hole in the outer layer of the sheath 132 may be positioned to align with a particular coloring on one of the inner elements 106. Other suitable tension indicators may also be employed.
In another embodiment, ΔF≤0.33Favg and ΔE=0.42EM where Favg is the average force of the strap in its operating range and EM is the midpoint of the operating range.
In some embodiments, the strap can be tuned by incorporating adjustment features, such as allowing an initial spring tension to be adjusted by varying its length, or by allowing one spring to be exchanged with another with a different spring rate.
It will be clear to one having skill in the art that further variations to the specific details disclosed herein can be made, resulting in other embodiments that are within the scope of the invention disclosed. All parameters, dimensions, materials, and configurations described herein are examples only and actual values of such depend on the specific embodiment. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.
| Number | Date | Country | |
|---|---|---|---|
| 62699144 | Jul 2018 | US |
