Patent Application
20090255969
The present invention generally relates to the field of backpacks. More specifically, the invention relates to a backpack that is designed to ease the walking of a wearer while carrying a load in the backpack.
Backpack carrying starts at a very young age for students. As children get older, the frequency of backpack carrying and size of load carried increases, often exceeding a maximum recommended load. The cumulative effects of many years of load carriage can cause many orthopedic and musculoskeletal injuries. People commonly complain about back pain, shoulder pain, and discomfort while wearing a backpack and these negative effects have prompted research on the physical demands of load carriage in attempts to create a physically less demanding product.
Countless adaptations have been made in an attempt to alter attributes such as load placement and size, compression, strap placement, and energy expenditure. A large portion of previous research focused on the load size as the main problem when it comes to the kinematics adjustments of a human body and negative physical effects of load carriage. During investigations, it was found that increased weight in a backpack resulted in significant compressive forces causing the spine, and therefore posture, to be altered. A study conducted in 2006 actually focused on a group of significantly affected college students, found that carrying a load heavier than 15% of their body weight could cause various musculoskeletal injuries. This was reflected in another study which concluded that a load mass corresponding to 10% of a carrier's body weight should be the maximum recommended load carried in a student's backpack. Carrying 15% of the body weight produced an increase in ground reaction forces generated during gait, thereby exerting an increased force to the knee joints, vertebral column and ultimately the shoulders.
Posture is a good measure of physical deviance from carrying a load. Significant postural changes have been found in children when the load was increased from fifteen to twenty percent of their body mass. Carrying a loaded backpack results in the center of mass being farther back than it would be when carrying no load. Due to the fact that the new center of mass is now farther back, the carrier's body has to lean forward to compensate and reposition the new center of mass directly above his feet. Forward body lean is the result of any load on the back, and increases the lean angle in knees, hips, shoulders, and head.
Weight distribution has been determined to influence the effects of carrying a load. When the weight is positioned closer to the center of mass, allowing the body to remain in a more upright position, it not only reduces the energy required to carry the load but also reduces the torques acting on the body. This presents significant indications as to the way the load should be distributed in the backpack. The heavier portion of the load should be positioned in a portion of the backpack that is closest to the body. The vertical placement of the load on the back is also important because in very tall individuals, high placement may further destabilize their posture by causing sway due to rotational inertia. This would require more muscle activity to maintain an upright posture and cause discomfort and an increased energy cost.
There is therefore a need for an improved backpack that does not cause as much strain on a carrier's body as a standard backpack.
It is an object of the present invention to provide a backpack that overcomes or mitigates one or more disadvantages of known backpacks, or at least provides a useful alternative.
The invention provides the advantage of at least partially alleviating the burden of carrying a loaded backpack while walking by suspending the load inside the backpack and allowing it to move up and down in a movement that is out of phase with a gait of a wearer of the backpack.
In accordance with an embodiment of the present invention, there is provided a backpack for carrying a load. The backpack comprises a shoulder strap assembly, an exterior shell and a pouch for storing the load. The exterior shell has an opening and is attached to the shoulder strap. The pouch is located inside the shell and attached to it and comprises a stretchable portion. This stretchable portion is made of a material having an elastic modulus allowing it to stretch and retract when the load is placed inside the pouch so that the pouch moves down and up relative to the shell with a gait of a wearer of the backpack.
These and other features of the present invention will become more apparent from the following description in which reference is made to the appended drawings wherein:
The present invention relates to a backpack that alleviates the burden of carrying the loaded backpack while walking by its construction that suspends the load inside the backpack and allows it to move up and down in a movement that is out of phase with a gait of a wearer of the backpack.
Reference is now made to
Walking velocity also shows minimal, but key adjustments during the various stages of walking kinematics.
As with many activities, walking involves a transfer of energy, namely potential energy into kinetic energy and vice-versa. Potential energy consists of the stored energy of a body in relation to its position. When the body 10 is vertically aligned at a maximal vertical height, the potential energy is also at a maximum. In contrast, the instantaneous kinetic energy is at a minimum. By contrast, kinetic energy reaches a peak when the body 10 reaches its maximum speed, which corresponds to the moment when it is at its lowest height. As a result, both kinetic and potential energy are in constant fluctuation but in opposite phase. This phenomenon is depicted in
Finally, note the arrows in
Turning now to
The backpack 100 further comprises an internal pouch 108 in which carried load items 110 are stored. The pouch 108 is attached to the shell 104 in such a way that its own pouch opening 112 (best viewed in
The pouch 108 has a stretchable portion 114. The stretchable portion 114 may either be located at the top or at a bottom portion of the pouch 108. Alternatively, the whole pouch 108 may be stretchable and thereby define the stretchable portion 114. The purpose of the stretchable portion 114 is to act as a spring and suspend within the shell 104 the load of items 110 located in the pouch 108.
The stretchable portion 114 may be made in many ways: a plurality of rubber bands suspending the lower portion of the pouch 108, a single rubber band that is weaved between the upper portion of the pouch 108 and the shell 104, etc. A person skilled in the art could envision many ways of providing the stretchable effect to the stretchable portion 114. However, it would likely be apparent to this same person skilled in the art that using a stretchable fabric for the stretchable portion 114 is an easy and effective solution. Moreover, completely making the pouch 108 of a stretchable fabric requires even less manipulation during its manufacturing and is effective in performing the task of suspending the load of items 110 inside the pouch 108.
The material making the stretchable portion 114 is a stretchable material having an elasticity modulus that permits the stretchable portion 114 to stretch and retract when the load of items 110 is placed inside the pouch 108. When the wearer of the backpack 100 walks, he moves up and down, as already described. Hence, because of this up and down excitation and because the stretchable portion 114 is loaded with items 110 having a mass, the stretchable portion 114 and the load of items 110 act as a mass-spring system where:
mg+kx=0
and where m is the mass of the load of items 110 inside the pouch 108, g is the gravitational acceleration (9.81 m/s2), k is the spring constant of the stretchable portion 114 and x is the vertical displacement of the shell 104 imposed during walking. Because of this up and down movement of the shell 104 during walking, the stretchable portion 114 of the pouch 108 stretches and retracts, the load of items 110 in the pouch 108 consequently moving down and up relative to the shell 104. Because of this movement of the load of items 110 inside the shell 104, a gap is kept between a bottom of the pouch 108 and a bottom internal wall of the shell 104 to make sure that the pouch 108 does not contact the shell 104. Such gap may be in the order of less than 10 centimeters.
In order to ease as much as possible the burden of carrying the loaded backpack 100 while walking, the mass-spring system constituted by the stretchable portion 114 and the load of items 110 should oscillate at the same frequency as the gait, but out of phase by 180°. The frequency of the system is equal to:
ω=√{square root over (k/m)}
Since the frequency of the gait varies from one person to another and since the load of items 110 (m) varies also, it is not practical to obtain a single exact spring constant k of the stretchable portion 114 that would work optimally in all situations. However, it is possible to select a material for the stretchable portion 114 that has a spring constant k that provides adequate results in most normal situations of walking frequency and load. Effective recoiling abilities and durability are also beneficial properties that are desirable in this material.
The stretchable portion 114 may be made of a material having an elastic modulus allowing a typical load of a few kilograms to oscillate by a few centimeters. The person skilled in the art will understand that the stretchable portion 114 needs to be able to stretch more under the load than if it were made with the material of a typical soft shell backpack, such as a nylon fabric, otherwise the backpack would have no advantage over a conventional backpack. The values of the elastic modulus of the stretchable portion 114 are between those values for rubber and those for nylon and, preferably, closer to the values for rubber than for nylon. For comparison, rubber, for small strain, has an elastic modulus ranging approximately from 0.01 to 0.1 GPa while nylon has an elastic modulus ranging approximately from 3 to 7 GPa. If a heavier load of items 110 needs to be carried, for example in the case of a backpack for military applications where the loads are heavier than for school applications, either the material for the stretchable portion 114 is selected to be stiffer than for typical light loads applications, or more than one layer of stretchable material may be used in the fabrication of the stretchable portion 114.
For example, it was found that making the stretchable portion 114 of the pouch 108 from a material consisting of 86% nylon and 14% spandex (also known as elastane or under the trademark Lycra®) performed adequately when the load of items 110 placed in the pouch 108 consisted of text books weighing approximately 2 kg. Advantageously, the material should be of an adequate thickness to prevent tearing. Other similar types of material may also work as well.
It is somewhat important that the pouch 108 be not too loose inside the shell 104 so that the pouch 104 would not only oscillate vertically, but would also swing as a pendulum. Such movement could be detrimental to the comfort of a user. Hence, it is preferable that the pouch 104 be guided horizontally by a guiding mechanism. The inner walls of the shell 104 may provide this guiding function. By having the pouch 108 and the inner walls of the shell relatively close together (with respect to the height of the backpack 100), such swinging movement gets limited. In the case where it would be desirable to split a cargo space of the backpack 100 between a suspended pouch 108 and a non-suspended portion, or between two suspended pouches 108, it is possible to use an internal divider 116 (shown on
A test was performed where six subjects were asked to walk with a backpack of the present invention loaded with items 110 and a similar backpack loaded with the same items 110, but not having the stretchable portion 114 of the pouch 108. A survey was then conducted to assess which backpack the subjects preferred to use. It should be noted that the test was not conducted on a large scale and under extremely well controlled environment such that it is possible that similar testing conducted a second time would yield somewhat different results. The objective was to obtain a preliminary indication as to whether the backpack of the present invention performed reasonably as intended.
The test was conducted with three females and three males subjects to assess whether there were any sex differences in preferences and walking mechanics. The subjects ranged in age between 20 to 23 years and in height from 5′6″ to 6′2″. The approximate weight of each subject was also recorded and the values ranged from 120 to 205 lbs. It should be noted that the weight, height, and age recorded were not specific criteria for the subjects. The main focus was that all subjects were from a target market for the backpack of the present invention, namely university students.
The testing consisted of three different trial runs. The first trial was the “Conventional backpack without load”. The second trial was the “Conventional backpack with load”. Lastly, the third trial was the “Suspended backpack with load” (backpack of the present invention). Each subject had the “Conventional backpack without load” fitted as a control. Each subject put on the backpack and was allowed to adjust the straps to a comfortable length. At that point, one of the investigators measured the strap length on both the right and left side and the numbers were recorded. This process was done for the purpose of consistency and ruling out variables that could potentially interfere with the data analysis. Throughout all three trials the straps were measured on the backpacks to ensure that the length stayed the same. When fitted and measured, the trials were underway.
Trial one: Each subject wearing the control “Conventional backpack without load” was escorted by one investigator for a 100 meters walk. The purpose of this walk was to allow the subject to normalize his walking speed to a comfortable pace while wearing the backpack. Then, the subject removed his backpack and was lead to a waiting area so as to be blind to which backpack he would be putting on next. While the subject was away, the conventional backpack was loaded with a load of approximately 5 kg. The straps were re-measured to make sure they remained at the consistent length. The subject was brought back and asked to try on the conventional backpack with load, known as bag A. At this point, the subject repeated the 100 meters walk. Then, the subject could remove Bag A and return to the waiting area. Meanwhile, the primary investigators switched the load into the suspended backpack, known as Bag B. The straps were measured to match the length of the initial conventional backpack each subject had been fitted with. Each subject was then allowed to come back and put on Bag B. For the last time they repeated the same procedure. Once the last walk was completed, the subjects were able to remove Bag B.
Each subject was then asked to complete a short survey, an evaluative tool for comparing Bag A (the conventional backpack with load) to Bag B (the suspended backpack with load). The survey included some basic questions such as bag preference and comfort. The survey also provided space for additional comments and explanations as to why they selected one backpack over the other.
Of the eight tested subjects, the results from two subjects were discarded due to the fact that independent variables were not constant in comparison to the other subjects. Such discrepancies included an inconsistent strap length for subject B, and a damaged stretchable portion for subject D.
Among the remaining subjects, four of six individuals preferred the suspended backpack in comparison to the conventional backpack. Furthermore, the written comments of the subjects who preferred the suspended backpack displayed an overall positive feedback. Such comments included that the suspended backpack allowed for a more evenly distributed load, reduced back pressure, stress and discomfort, and was overall more comfortable and enjoyable to wear. By contrast, the two other subjects, subjects F and G, who did not prefer the suspended backpack, commented that it caused the load to feel bunched up, unevenly distributed and created greater pull on their back. In addition, these subjects noted that the weight of the load felt too light, and was positioned abnormally low on their back. Interestingly, both these subjects were males of higher stature (1.85 m and 1.88 m) and also of heavier mass (91 kg and 93 kg). In relation, the subjects who preferred the suspended backpack were of shorter stature, and lighter mass.
The present invention has been described with regard to preferred embodiments. The description as much as the drawings were intended to help the understanding of the invention, rather than to limit its scope. It will be apparent to one skilled in the art that various modifications may be made to the invention without departing from the scope of the invention as described herein, and such modifications are intended to be covered by the present description. The invention is defined by the claims that follow.
