Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present inventon is directed to an engineered air inflatable cushion system that includes a safety cushion which can safely absorb the impact of a person at the end of a fall or jump from great heights. A typical application would be as a fire rescue device for permitting the saving of people caught at great heights in a high rise building fire.
It is well known that it is not the velocity in a fall that is injurious to a man but the sudden stop or instant deceleration at the end of the fall that is injurious if not fatal. In fact, the fall itself can give a man a certain uninhibited feeling or a sensation of freshness. This is particularly recognized in the sport of "sky diving."
The air inflated cushion or bag of the present invention is so designed that it can absorb energy with controlled deceleration to such an extent that it can be classified as a life saving device.
2. Prior Art
An effective device for safely absorbing the impact of people falling or jumping from great heights, as for example fire escape devices, has been one of the longest sought for inventions in this country and the need therefor has been long felt.
Attempted solutions to the problem go well back into the 1800s, and typical examples thereof are shown in the patents to Strong et al. (U.S. Pat. No. 157,978 issued Dec. 22, 1874); Wettstein (U.S. Pat. No. 312,683 issued Feb. 24, 1885); Bonner (U.S. Pat. No. 360,082 issued Mar. 29, 1887); and Scheel (U.S. Pat. No. 652,645 issued June 26, 1900); all of which are directed to various forms of net or canvas catching devices.
Pneumatic or air inflated cushion devices which were supposedly and allegedly solutions to this problem of safely absorbing people falling from substantial heights have long been claimed but never heretofore achieved, at least for great heights. A very early example thereof is shown in the patent to Simon (U.S. Pat. No. 396,242 issued Jan. 15, 1889). Other such pneumatic or air cushion patents, most of which described themselves as supposed solutions to the problem, are listed below in chronological order: McDonnell (U.S. Pat. No. 2,390,955 issued Dec. 11, 1945); James (U.S. Pat. No. 2,797,853 issued July 2, 1957); Mapes (U.S. Pat. No. 2,906,366 issued Sept. 29, 1959); Dudek (U.S. Pat. No. 2,975,855 issued Mar. 21, 1961); Beaulaurier (U.S. Pat. No. 3,095,947 issued July 2, 1963); Frost (U.S. Pat. No. 3,250,065 issued May 10, 1966); Fischer (U.S. Pat. No. 3,310,818 issued Mar. 28, 1967); Gordon (U.S. Pat. No. 3,391,414 issued July 9, 1968); Olsen (U.S. Pat. No. 3,399,407 issued Sept. 3, 1968); and Kendall et al. (U.S. Pat. No. 3,603,430 issued Sept. 7, 1971).
It is believed the above listed patents represent a good collection of the best prior art to the present invention, and, insofar as the objects and purposes of the present invention are concerned, represent merely at best claims or allegations of achievements of success but in fact represent failures as to fully providing an air inflated cushion which can safely absorb the impact of the human body falling or jumping from great heights, that is, heights in excess of thirty feet.
In contrast to the paper disclosures and "hopes" of the prior art, the present invention has been reduced to actual and effective practice, and the preferred embodiment thereof has been used in the field to safely absorb without any injury the impact of jumps at greater heights than ever heretofore achieved under even the most controlled conditions. It is believed that, for example, the Frost U.S. Pat. No. 3,250,065 may have suggested the desired goals in their broadest terms, but it was not until the present invention that the reality of a safety cushion for great heights finally has been achieved, taught and disclosed.
GENERAL SUMMARY AND DISCUSSION OF THE INVENTION
The safety cushion of the present invention is designed and manufactured to a strict set of limiting relationships expressed in certain equations, and then for absolute certainty tested for safety under specified operation in stopping a fall by ideal control of decelerations. Technically this means that a body upon falling onto the cushion of the present invention is subject to only a limited number of "G's" (units of gravitational force) within the human endurance range. When the present invention is used in the recommended way and when a person lands on it, the deceleration forces on the body which bring the person to a stop after a few inches or feet of depression are such that the person does not encounter what is considered dangerous forces upon the body.
There are many possible sizes of the air inflated cushion of the present invention, and each one is rated at a maximum limiting height at which it is recommended for use. Falls from any height can be absorbed by a particular design of an air cushion in accordance with the present invention. For practical, economic reasons commercial units can be rated at for example: up to fifty feet or five floors; up to one hundred feet or ten floors; up to two hundred feet or twenty floors; and for free fall. The design of a unit rated at one hundred feet will be discussed below for illustrative purposes.
The air safety cushion of the present invention preferably includes in its preferred embodiment upper and lower sections or compartments connected together, the lower one being relatively closed and at a higher pressure, and the upper one including breathers or air release systems and being at a lower pressure, all the basic dimensions and physical relationships of which follow certain unique equations developed in the present invention.
The equations establish the various dimensions of an air cushion in accordance with the present invention and in turn give the volume of the air cushion and the cross-sectional area that the falling body effectively sees as well as the needed cross-sectional area of the breathers or air release systems. It further establishes the reaction of the upper section as well as the secondary reactions or safety reaction of the lower section as based upon the equations of the present invention. The equations are unique and are based upon physical data and tests and have been proven experimentally by both dummy objects and by humans. The derivation and use of the equations and the equations themselves are discussed in detail below.
Along with the information from the equations, use has been made of the test results showing the limits of human endurance of "G" forces which have been established by various U.S. Government publications and studies.
When it is desired to build an air cushion that will absorb falling bodies from heights of for example fifty, one hundred, two hundred and free fall, an air cushion is manufactured according to the specifications determined by the equations of the present invention discussed below and then tested with a dummy weight and an accelograph. The test results of the accelograph must show a result equal to or less than the limitations of human endurance prior to commercial use. The end result is that a human can fall from these heights and, upon hitting the air cushion of the present invention, will decelerate at such a reduced and controlled rate that it is safe and therefore "life sustaining."
EQUATIONS OF THE PRESENT INVENTION
An air cushion of the present invention is an engineered inflatable bag that is used to absorb the shock at the end of a fall from great heights. It is well known that it is not the velocity in fall that is injurious to man but the sudden stop that is undesirable, if not fatal. The safety air cushion of the present invention is designed and manufactured to a strict set of limiting rules or equations, and then tested for safety.
The below factors are taken into consideration in the present equations of the present invention:
1. the affected area of the cushion due to contact and depression of a falling body;
2. the resulting built-up pressure due to depression;
3. the force due to the pressure being applied over the affected area;
4. the work or energy absorbed due to this force being applied to a body while it moves to a greater depression;
5. the limitations of human endurance;
6. the amount of air release required; and, finally,
7. the location and cross-sectional area of the "breather" system in conjunction with the volume and surface dimensions of the air cushion.
The design criteria in the present invention is based on a number of tests, calculations, and graphs. Because of the many uncontrolled conditions that each separate air cushion will have, as well as the differences occuring from one fall to another fall, most of the equations of the present invention have been rounded off to only one significant number. A typical detailed design calculation for a safety cushion to absorb a body falling from an exemplary hundred foot height is included at the end of this section to enhance the clarity of this disclosure.
EQUATION NO. 1 (AFFECTED AREA)
The illustration of FIG. 8C shows some of the view points which must be considered in determining the relationship between the width of the affected area and the depression of the safety cushion upon impact. There are several equations that can be used to estimate the affected area of a body falling upon a cushion, however, it is sufficient that a representative equation be used among all other equations (which under certain conditions are correct) without incurring a significant error. Such a representative equation is:
Aa = 8 (1 + 3d - 2d 2 /h ) (Eq. 1)
where
Aa is the affected area,
d is depression of the air cushion bag in feet, and
h is the thickness of the upper safety air cushion compartment or section.
It is noted that one compartment or section is on top of the other in the preferred embodiment hereof, and hence separate h's must be considered and the two distinguished.
EQUATION NO. 2 (PRESSURE)
Pressure in the air cushion is dependent on the initial pressure; the loss of volume due to depression; and the loss of air due to leakage through any needle holes (usually insignificant), and through the input neck of the blower system (none of which occurs in the preferred embodiment), and through the air release system. Where the loss in volume exceeds ten percent due to depression (which is the usual case in air cushions), the design of the quick release, weighted flap and lip-type air release systems used in the preferred embodiment and described more fully below is mandatory so that the maximum G's incurred during deceleration will not exceed the human endurance level, and so that the force built up due to the absorbtion of the kinetic energy (1/2 mv 2 ) of the falling body can be dissipated by rapid release of air pressure and not by bouncing the body off, as would occur in a closed, totally airtight cushion.
Again by viewing the illustration of FIG. 8C and realizing that the depression takes on the approximate shape of a cone, the following relationship has been derived in the present invention
Vloss = 8 (d + 0.9d 2 - 0.6 d 3 /h) in cu. ft. (Eq. 2a)
where
Vloss is the volume lost due to depression as determined in the present invention.
Other more complex formula can be derived but again this equation of the present invention is sufficient without incurring a significant error to determine pressure.
Now, from physics and by definition, it can be stated that
Pt = 15 × Vloss/Vi + Pg (Eq. 2b)
where
Vi is the initial volume and is equal to Ai . h , where
Ai is the total surface area of the loser area air cushion, and
h is the thickness of the devinate air cushion,
Pt is the pressure at any particular depression, and
Pg is the initial pressure in psi.
By combining the above equations, it is seen that
Pt = 120/Ai . h × (d + 0.9 d 2 - 0.6 d 3 /h ) + pg (Eq. 2c)
which for short-hand purposes can be simply expressed as
Pt = (120/Ai . h) D p + P i (Eq. 2c ')
EQUATION NO. 3 (RETARDING FORCE)
Now that pressure and affected area have been arrived at, some additional laws of physics for falling bodies can be applied. The laws of importance are
Force = mass × acceleration (F = ma )
Force = pressure × area (F = PA)
Work = force × distance (FD) = potential energy = kinetic energy = wt. × ht. = 1/2mv 2
Velocity (v) = √ 2g ht.
where wt. is the weight of the falling body, ht. is the height from which it fell, and g is the acceleration due to gravity which is usually equal to 32 ft./sec./sec.
For the present invention we refer particularly to
Work = wt. × ht. = force x distance = PA × depression in which all the items on the right hand side are variables.
The equation of the retarding force (F) of the air cushion of the present invention is
F = pa = 150000/ai . h (d + 4d 2 + 2d 3 - 3d 4 /h + d 5 /h 2) + 1000 Pg (1 + 3d - 2d 2 /h ) (Eq.3a )
This equation is un-necessarily complex and can be reduced to
F = 1000 Pt (1 + 3d - 2d 2 /h ) (Eq. 3b)
and has a limiting value of
F max = 1000 k (1 + 3d - 2d 2 /h) (Eq. 3c)
which for short-hand purposes can be simply expressed as
Fmax = 1000 k D w (Eq. 3c ')
where
Fmax is the maximum retarding force to which it is desired to subject the falling body during deceleration and
k is more fully identified below in reference to Eq. No. 4.
EQUATION NO. 4 (WORK)
By intergrating
Work = F D = F(d = 1000 Pavg (1 + 3d - 2d 2 /h ) d (Eq. 4a )
= 1000 k (d + 1.5 d 2 - 0.7 d 3 /h ) - 500 in ft. lbs. (Eq. 4b)
where
Pavg is the average pressure and the
-500 is a constant of intergration derived from many samples, and
k is a fixed value representing Pt and can be assigned a value from the table below:
h (in ft.) 3 5 8 1.1 0.8 0.6 ______________________________________
The above table was calculated by using Eqs. 2c and 3c and inserting the maximum pressures and forces (e.g. 40 G's) desired, three exemplary calculations being made.
Reference is made to sample calculations at the end of this section which outlines the sequence of equations for obtaining values which in turn are plotted for verification of design using exact parameter data for Ai , h , along with the maximum ht (height) from which the subject may fall. The family of curves of velocity, force in G's, and depression vs. time will determine the capability of a particular air cushion.
EQUATION NO. 5 (MAXIMUM PRESSURE AND AIR VELOCITY)
From data obtained it has been established that
Pm = 3.3/1 + d (Eq. 5a)
where
Pm is the maximum desired pressure that the man should create by, and hence meet on, his impact on the safety air cushion of the present invention.
Thus since Pm will be values in agreement with the chart shown in the sub-section above related to Equation No. 4, then it is seen that there is a prime need to control the release of air so that pressure will not build up to give too great of a retarding force. Air moves with a velocity of
Va (ft/sec) = 350 √P (Eq. 5b)
where
Va is air velocity and
P is pressure in psi.
EQUATION NO. 6 (BREATHER LOCATION AND CROSS-SECTIONAL AREA)
SInce the maximum pressure at which the safety air cushion of the present invention is to operate has been determined and since this is to coincide with Pt at any particular depression point, then all that needs to be established is the average distance to a breather and the cross-sectional area of the breather after the velocity of the air movement has been determined (see Equation No. 5b). For a given air cushion construction the maximum allowable Pt (Pm ) can be calculated. Once this is established the value d can be determined for the depression that will create this, and in turn the Vloss can be calculated from Equation No. 2a at this particular depression. Then, by calculating the values of "Vloss" at great depressions, the amount of air that must be released can be determined during the time of deceleration to prevent bounce and to large of a G build up. Since we know Pm, then from Eq. 5b, Va in the air cushion under maximum conditions can be calculated. Next the approximate distance from the center of the cushion to any breather is calculated based on time (T 1 ) necessary to allow build up to pressure Pm. This T 1 is determined by reading the tabulated chart below and noting when an excessive G force is reached. Then:
L B = Va/2 × T 1 + 2 ft. (Eq. 6a)
where L B is the distance from the center of the cushion to the breather structure and the +2 ft. factor makes allowance for the extended size of the falling body.
Next it is necessary to calculate the cross-sectional area of the breather (A b ) so that the air cushion will relase the air at a rate equal to the continued Vloss of the air cushion so that Pt does not exceed Pm and the pressure (P) drops back to zero once all the energy of the fall is absorbed and little or no rebound occurs. Thus the change (Δ) in Vloss divided by the time elapsed from T i to Tt (where Tt is the time of full energy absorption) would establish the CFS (cu. ft./sec.) of air. This occurs over such a short period of time that it has been proven sufficient to use the following equation
A B = Vloss/0.6 Tt ÷ Va (Eq. 6b)
where A B is the needed cross-sectional area of the breather. This feature is the most critical of all construction features, and thus, once an air cushion is manufactured in accordance with the present invention, the operation criteria must not be altered. Thus the length (L) and width (W) of an air cushion must each approximately equal 2 L B from Eq. 6a, and the cross-sectional area of the breather determined by Eq. 6b. The Times and Volumes are thus determined by the set of equations herein by:
1. Keeping the G forces under the maximum allowed, and
2. Absorbing all the energy of the falling body.
It is noted that a detailed analysis of any particular condition would be good for that and only that contour, fixed initial pressure, and external load. Test data and straight forward calculations indicate that, even though on initial contact only a slight pressure change may occur, a large area is affected. On continued decent, less area change is experienced but pressure variations respond rapidly. Test results prove out the above assumption, but it is realized that many variations can be designed into an air inflated cushion to meet specific demands and which will vary according to a different set of initial conditions and related equations.
The importance of these equations is the establishment of a cross-sectional area of the breathers and the delay time in opening of the breathers. Likewise the reaction of the upper section as well as secondary reactions and safety reaction of the lower section are based upon the above equations. The equations are unique and are based upon a new and special application and have been proven experimentally by dummy objects and by humans in the present invention.
Along with the information from the equations, reliance has been placed upon the test results showing the limits of human endurance of G forces which have been established by the U.S. Government.
GENERAL DISCUSSION
From various U.S. Government tests the following information has been established regarding acceptable exposure to G's.
______________________________________ USER MAX. G DESIRED G ______________________________________ Professional diver 30 30 Safety net 50 30 Amusement item 25 16 (Though the above indicated figures are desirable, it is noted that man has endured shocks of up to 200 "G's"). ______________________________________
Since all of the deceleration times are between .05 sec and .2 sec. total time, there is no sustained force and on-set rates do not have to be considered as long as the impact is on a very low pressure (less than .2 psi) bag.
Therefore, when it is desired to build an air cushion that will absorb falling bodies from heights of for example 50, 100, 200, 300, 400+ heights (free fall), an air cushion is manufactured according to the specifications determined by the equations and then tested with an accelograph for absolute certainty and safety. The test results of the accelograph should show a result equal to or less than the limitations of human endurance. Then the end result is that a human can fall from up to these heights and, upon hitting the air cushion, will decelerate at such a rate that it is safe and therefore "life sustaining."
SAMPLE CALCULATIONS
The above discussed equations are summarily restated as follows:
Eq. 1 Aa = 8 (1 + 3d - 2d 2 /h)
Eq. 2a Vloss = 8 (d + 0.9d 2 - 0.6 d 3 /h) in cu. ft
Eq. 2b Pt = 15 × Vloss/Vi + Pg
Eq. 2c Pt = 120/Ai . h × (d + 0.9 d 2 - 0.6 d 3 /h) + Pg
Eq. 3a F = 1000 Pt (1 + 3d - 2d 2 /h)
Eq. 3c Fmax = 1000 k (1 + 3d - 2d 2 /h)
Eq. 4a Work = F D = F ∫ d = 1000 Pavg (1 + 3d - 2d 2 /h)Δd
Eq. 5a Pm = 3.3/1 + d
Eq. 5b Va (ft./sec) = 350 √P
Eq. 6a L B = Va/2 × I 1 + 2 ft.
Eq. 6b A B = Vloss/0.6 Tt ÷ Va
wherein
Aa -- affected area of depression,
Ai -- total surface area of air cushion,
d -- depression,
Δd -- change in depression,
D -- distance cushion surface travels,
F -- upward or retarding force of air cushion on falling object,
h -- height or thickness of air cushion,
Pt -- Pressure at any particular depression,
Pm -- max. pressure allowed in air cushion,
Fmax -- maximum desired retarding force to be applied to the falling body
P -- pressure,
Pg -- initial pressure,
Pavg -- average pressure,
Vloss -- volume lost due to depression,
Va -- air velocity, and
Vi -- initial volume
A b -- total cross-sectional area of breathers,
L b -- ideal location of breather from center of impact, and
T 1 -- time for full energy absorbtion or time allowed to reach Pm.
(all dimensions in ft., lbs., and psi).
By experience and from information obtained from deceleration criteria in various Government publications a set of reasonable dimensions of an air cushion can be assumed, and the maximum G force desired can be selected. For example a typical fan inflation system creates an internal pressure of approximately 0.05 psig. Once these dimensions are assumed the equations of the present invention and ordinary physical laws are applied in the below described sequence to:
A. show that the air cushion will absorb the energy of the falling body, and
B. establish the location and cross-sectional areas of the breathers.
Sequence
1. Pt = 120/Ai . h Dp + Pg (for first foot of depression only)
2. Pavg ≅ Pi + Pt/ 1.8
3. Work = 1000 Pavg Dw Δd and Δd = 1 for 1 ft. intervals
Accumulated Work
4. Retarding Force = 1000 Pt × Dw
5. G = Retarding Force/Wt of person in g's
6. Aavg ≅ Gi + Gt/2 × 32 in ft/sec 2
where A is acceleration in ft./sec. 2 and G is gravitational force.
7. Δd = 1 ft = (Vi - Aavg T/2) T
where T is time required to travel Δd in sequence 3 above.
8. Solve No. 7 for T
9. v = Aavg T
where v is velocity.
10. vt = vi - Δv
Subscript are as follows: i -- initial at each interval being calculated, t -- terminal at each interval being calculated, avg -- average; and g -- gravity, T -- time, Δ -- "change in."
SAMPLE CALCULATIONS
If the size of the bag is assumed to be 25 × 20 × 6 feet deep (upper section only), then L, W, and h of the air cushion are thus known and
Ai = L × W = 25 × 20 = 500 sq. ft.
120/Ai . h = 120/500 × 6 = 1200/3000 = .04
Assuming 1 ft. interval of depressions (Δd = 1 ft)
at each 1 ft interval tot- 1 2 3 4 5 6 depression al d ____________________________________________________________
______________ Dp = (d + 0.9d 2 -0.6d 3 )/h ≅ 2 5 8 12 15 17 Dp Dw = 1 + 3d - 2d 2 /h ≅ 3.5 5.5 7 9 11 12 Dw ____________________________________________________________
______________
Assuming a 10 story building or 100 ft. fall of a 160 lb. man and a maximum desired retarding force of 41 G's,
Energy = wt. × ht. = 160 × 100 = 16,000 ft. lbs.
Vi = √2ght. = √2 . 32 . 100 = 80 ft./sec
Pi due to inflation = .05 psi
At the end of 1 ft depression
1. PtT = .04 × 2 + .05 = .13 2. Pavg ≅ .09 3. Work = 1000 × .09 × 3.5 × 1 = 300 ft. lb. Accum W = 300 ft. lb. 4. Retarding Force = 1000 × .13 × 3.5 = 455 5. G's = 455/160 = 2.84 6 Aavg ≅ 0 + 2.84/2 × 32 = 46 ft. sec. 2 7/8. T ≅ .012 9. Δv = 64 × .012 ≅ 1'ft./sec. 10. v t = 80 - 1 = 79 ft./sec
The above and other sample calculations are tabulated below for illustrative purposes.
________________________________________________________
__________________ depression at 1' 2' 3' 4' 5' 6' ____________________________________________________________
______________ P t .13 .2 .32 .48 .55* .55 Pavg .09 .17 .26 .4 .55 .55 W 300 935 1820 3600 6050 6600 WAccum 300 1235 3055 4655 10705 17305* R. Force 455 1100 2240 4320 6600 6600 G's 2.8 6.8 14 27 41* 41 Aavg 46 160 352 672 1120 1320 T .012 .013 .014 .015 .020 .039 TAccum .012 .025 .039 .054 .074* .113 Δv 1 2 5 10 22 40 vt 79 77 72 62 40 0 ____________________________________________________________
______________ *Excessive condition begins; air escape must have started at an accumulated time of .07 sec or less and the maximum pressure limited to .55 psi.
Velocity of air = 350 √ .55 = 250 ft. per sec.
Average distance (Eq. 6a) to breather (L B ) is .07 sec. × 250/2 ft. per sec. + 2 ft. (Eq. 5b) ≉ 9 ft (Eq. 6a) Vloss = 8 × 17 = 136 cu. ft. (use half total time)
Breather cross-sectional area (A 8 ) = 136/0.6 × 0.1 ÷ 250 ≉ 10 sq. ft.
Because the desired exterior dimensions were stated to be 25 ft. wide by 20 ft. long, both of which dimensions are in excess of the distance (one/half the total) of the ideal breather location of approximately 9 ft., this departure from the theoretical ideal can be compensated for by increasing the breather cross-sectional area. Thus the basic, general relationships of the present invention can be substantially satisfied and the exterior dimensions can conform to whatever other considerations may dictate or make desirable. This illustrates the flexibility and general application of the present invention.
Thus, an air cushion manufactured to the dimensions of 25 ft. wide, 20 ft. long and 6 ft. deep will absorb the entire kinetic energy of 17,300 lbs. which is slightly more than the potential energy of 16,000 ft. lbs. of a person weighing 160 lbs. at a height of 100 ft., and the design proves out.
Common sense design calls for a 3 ft. thick secondary bag or lower compartment of the same length and width which will absorb over twice the energy of the "breathing" bag or upper compartment. Thus the overall air cushion for a hundred foot height would be 9 ft. high and would have breathers built in that give a total 10 sq. ft. + cross-sectional area divided equally on the four sides.
BRIEF DESCRIPTION OF THE DRAWINGS
For a further understanding of the nature and objects of the present invention, reference should be had to the following detailed description, taken in conjunction with the accompanying drawings, in which like parts are given like reference numerals and wherein:
FIGS. 1, 2 and 3 are top, end, and side views, respectively, partially cut away, of the preferred embodiment of the inflated safety cushion of the present invention.
FIGS. 4 and 5 are partial, cross-sectional views, showing the structure of a first form of breather system utilized in the preferred embodiment of the present invention, taken through section lines 4--4 and 5--5, respectively, of FIG. 1.
FIG. 6 is a partial, close-up, perspective view of a second form of breather system used in the preferred embodiment of the present invention; while FIG. 7 is a similar view of that of FIG. 6 of the first form of breather system utilized in the preferred embodiment in the present invention.
FIGS. 8A through 8C are perspective views of the inflated safety cushion of the present invention, showing three stages in the controlled deceleration of a person falling from a great height, FIG. 8A showing the cushion prior to impact, FIG. 8B showing the cushion upon initial impact prior to the opening of the breathers, and FIG. 8C showing the cushion upon full impact with the breathers open, releasing the built up high pressure.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of the safety air cushion of the present invention, as illustrated in FIGS. 1-3, comprises an air inflated bag having two sections or main chambers 1, 2. The upper section 1 is designed and has the capability of absorbing energy and controlling deceleration within the limits (less than fifty G's) for a man falling from the specified limited height of the particular bag -- for example, 50 ft. high jump, 100 ft. high jump, 200 ft. high jump, or free fall. The lower half or section 2 of the bag is relatively air tight and is designed as a safety feature of the safety air cushion in that it has the ability to absorb great energy, whether from rebound or the kinetic energy produced from a free fall. It is estimated that this lower section 2 produces a safety factor double or triple the rating of any other air cushion.
By this dual section construction of upper and lower compartments 1, 2, the safety air cushion of the present invention has the ability to save lives within most any limiting criteria whatsoever. It is this feature inter alia that makes the safety air cushion of the present invention so highly reliable. However it would be possible to design an air safety cushion in accordance with the broader principles of the present invention without a lower section 2 with a fan system feeding directly into the upper section 1, but the dual-section preferred embodiment illustrated is considered to be the best.
The air cushion is manufactured by using properly selected material for structural strength and wearability which is then sewed together to the proper designed dimensions. As known to those skilled in the art, a great deal of experience has provided criteria for establishing types of material and thickness of material for use in air inflated products; also experience dictates where stress is greater and what steps in manufacture must be followed to counter these stresses.
The main compartments 1, 2 of the safety air cushion of the present invention include a multiple number of sub-sections or sub-compartments (three being illustrated) formed by vertical walls 11, 21, respectively of for example netting or webbing material. The material for the outer basic structure of the bag can be for example a coated fabric such as nylon coated with neoprene, vinyl or hypolon, that has sufficient strength and which will absorb the energy of a falling body in a controlled decelerated fashion without splitting or tearing. For further protection during use in a fire, the outer material can further include an exterior layer of asbestos or other fire resistant material. A common auxiliary item is a layer 2 in. to 4 in. thick of foam rubber placed on top of the cushion to prevent a "slap" on the person falling. This foam layer would not alter the deceleration value. It only is a finishing touch or desirable operational feature and has a minimum effect on the design.
The coated nylon material meets normal weathering and fire resistance requirements. The material has a warranty from the supplying company of usually one year, but life expectancy according to the various manufacturers is 3 to 7 years for continuous outdoor use, 15 to 20 years for intermittent use; the most damaging elements being the ultra-violet rays of the sun and abrasion during handling.
The following is a list of the typical characteristics of for example 18 oz. vinyl coated nylon fabric material which can be used in the present invention:
Tension per inch width -- 350 lbs.
Fabric weight -- 16 oz per sq yd.
Coating adhesion -- 20 lbs/inch width
Fire resistance -- slow burning to self-extinguishing.
Tear strength -- 50 lbs.
Hydrostatic -- 600 psi
Cold crack -- 20°F
Elongation -- less than 3 percent
Inactive to oils, grease and most solvents.
Laminated fabric material also have similar characteristics as indicated above except with noticable differences in higher tear strength, lower adhesion ratings, and better fire resistance ratings.
An outstanding feature of the air inflated cushion is that maintenance can usually be performed in the field to keep the cushion structurally sound. Repair kits are supplied with the air inflated cushion so that field maintenance can be carried out by any purchaser.
The safety air cushion of the present invention generally is not limited in minimum size nor maximum size or in thickness, width, or height. The operational principles are all relative to each other, and it is possible to design a cushion of any size so as to be adaptable to the particular use intended or desired. Thus, where a building or other structure may have unique limiting features, it is possible to design and manufacture a safety air cushion in accordance with the present invention as outlined fully herein in the discussion of principles and equations so that it satisfies the physical requirements of that particular location.
The cushion of the present invention is inflated by a fan system 5, which includes an open-ended funnel 51 communicating with the lower compartment 2 and having at its open end a continuously running fan 52. A flap 53, which serves as a uni-directional flow checkvalve is included to prevent any air from backing out of the funnel 51, should the fan 52 stop or the pressure within the compartment 2 greatly increase due to an impact on compartment 1.
The particular, detailed method of inflation, or the type of gas to inflate the air cushion is not particularly important to the present invention. Any appropriate fan can accomplish the job and the initial pressure is not critical. The more important aspects of the present invention, as explained more fully below, is in the dual compartment structure and in the cross-sectional areas of the breathers or air release systems and the delay time of their opening, and the related volumes of the air within the bag section which the breathers are a part of.
In the safety air cushion of the present invention it is necessary for there to be included a breather or air release system to release the compressed air energy generated upon impact. The safety air cushion thus further includes within its upper chamber 1 a breather system for quick but controlled release of built up air pressure.
The present invention includes in its preferred embodiment an opposed, identical pair of a first, built-in, mouth or lip-type breather 3, as shown particularly in FIGS. 3, 4 and 7. The lip-type breathers 3 work as follows. A first, horizontally disposed, generally cylindrical air column 31, at a slightly higher pressure than the internal pressure in compartment 1, presses against a second similar cylindrical column 32, also tightly inflated. The higher pressure in the air columns 31, 32 is due to the fact that they are closed and communicate directly with the higher pressure, lower compartment 2, the first column 31 through funnel 34 and the second column directly through appropriately placed holes. External to the air columns or lips 31, 32 and around their middle placed on center is a stretchable elastic cord 33 of for example rubber that can be adjusted to hold the lips 31, 32 sufficiently biased toward each other to hold the breather 3 tightly closed prior to impact.
When a weight or person falls upon the air cushion, pressure builds up in the air cushion. This pressure becomes sufficiently strong to overcome the biasing of the rubber straps 33, allowing the breathers 3 to open up (note particularly FIGS. 7 and 8A and 8B). The air is exhausted as soon as all the energy is absorbed and the increased pressure drops to relative zero internal to the air cushion. The air columns 31, 32 of the breathers 3 then reseal themselves together due to the construction and tautness of their structure and the pressence of the biasing cords 3.
The inflation fan 5 continues to blow air through lower compartment 2 into the now sealed upper air compartment 1, and the air cushion quickly rises and inflates itself again and is ready to receive another body or weight for energy absorbtion.
The preferred embodiment of the present invention thus utilizes breathers 3 having a matching pair of auxiliary inflated columns 31, 32 which due to the tautness of construction, push themselves together in a closure or seal. The lips 31, 32 and cord 33 are designed to sufficiently press together to overcome or resist the air pressure created by the fan 5, but are at the same time sufficiently weak that when air pressure is built up due to a weight or due to external energy, the external pressure of the air cushion forces the two lips or breather columns 31, 32 to separate and thus release the high air pressure.
A second form 4 of the breather system is also used, as particularly shown in FIG. 6 (in its open air releasing position). The second form 4 (note for example FIG. 2) comprises open holes 41 (three being illustrated) kept closed during low pressure by a weighted flap 42 supplemented by a stretchable biasing cord 43 (similar to biasing cord 33) which affects the rate of air escape. The flap 42 is weighted by means of weights 44 placed along the bottom edge of the flap 42. Normally the weight of the flap 4 and the biasing cord 43 maintain the breather 4 in its closed position. However upon impact and after a short (predesigned) period thereafter, the flap 43 opens, allowing the built-up air pressure to be released through the holes 41.
The breathers 2, 3 on the air inflated bag or cushion are designed to release air at a predetermined rate so that it can control the rate of deceleration of a body falling upon it. The first two breather structures 3, 4 mentioned above have the desirable characteristic of being self closing. Thus, after impact, the cushion or bag of the present invention has the ability to be completely self-closing and is reinflated by the continuously running fan system 5.
A third form (not illustrated) of breather is to have temporarily closed, open necks (not illustrated) that explode open, immediately releasing the air, but this structure requires manually going around closing all the necks after release and reinflating the air cushion. The necks could be temporarily closed by for example "Velcro" type fasteners. However because inter alia of it not being self-closing, such a breather structure is considered not as desirable as the above.
The three described embodiments of the breather system are merely exemplary of the many possible variations possible within the broader principles of the present invention. As with any mechanical device, the variations are practically limitless, and, although the two illustrated embodiments are preferred, it is only necessary that the breather system accomplish the necessary rapid exhaustion of the built-up air pressure in the time frame and sequence dictated by the equations of the present invention.
The particular configuration and general structure of the air bag of course is not the most important point in that any material that can retain air can be sewn in a configuration which forms a cylinder or a sphere when inflated, but what is important in the air cushion of the present invention is that the details and characteristics of the breathing system properly in quantity and timing, release the built up air pressure. The volume and timing requirements are based upon imperical formula calculations which have proven to be extremely accurate. Furthermore air cushions produced according to these equations have been tested and are recognized as being "life saving" from a particular height.
For example an air safety cushion having the particular configuration and general structure illustrated designed for a man of for example two hundred pounds weight falling from maximum height of 100 ft. could have for example the dimensions of 20 × 25 feet in plan view with a total thickness or height of both compartments of 9 ft. The detailed breather specifics of the upper section 1 is calculated from Equations 6a and 6b above, and it is established that the breathers 3, 4 must have 7 sq. ft. of cross-sectional area. Further it is established from the above equations that the weight of the flaps 42 and its biasing force on the breathers 4 and the biasing force on the inflated lip breathers 3 must produce the characteristics that, with a 300 ft. per second air velocity, the breathers 3, 4 will open up completely after .07 seconds. This delay is the time which allows the falling body to come in full contact and contour with the top surface 12 and to change the top surface 12 from a velocity of zero to matching the velocity of the falling body, and to decelerate the falling body within the limits that have been established according to recognized tests as within the endurance limitations of humans.
The first few inches, for example six, of depression absorbs little of the shock, while the next some-odd inches, for example twenty, do the work. The breathers 3, 4 all open up after the first six to twelve inches as the pressure has built up sufficiently. Were it not for the breathers 3, 4, the person would be bounced back up and possibly off the cushion with a pretty severe shock. The time of decelration travel lasts of the order of a tenth of a second.
In summary what happens and what is technically described by the equations discussed above is as follows:
When the body of a person comes into contact with the cushion, the top section 1 of the air cushion decreases (note FIG. 8B). As soon as it decreases into the bag so that the overall volume of this particular section 1 of the bag has decreased approximately six and two-thirds percent, the pressure therein has risen from approximately relative zero psig up to one psig. At one psig the restraining effect upon the body has reached the limit, and the force against a man is approximately 30 to 50 G's. This is usually reached between .06 seconds plus or minus .02 seconds.
Therefore, due to the delay caused by the location of the breathers and secondarily by the mass of the weighted closure flap 42 over the breather 4 and the biasing force on the lip breather 3, the air release has been restrained to this point. It is noted that it is necessary for the pressure after reaching this peak to decrease because, as the body goes deeper, greater surface contact area is restraining the body. Therefore, to keep the person from exceeding the G limitation, the air breathers 3, 4 need actually to open more to let the air rush out faster so that the volume of the first or top compartment 1 is decreasing, thus allowing the deceleration to stay within human endurance limits. The importance of the air release system also is that it prevents a rebounding reaction on the man.
The second or lower compartment 2 is there for a safety factor and, as stated above, has no breather or air release system and is relatively airtight.
This lower compartment 2 with zero or no breathers has a typical air pressure of 3 psi which in the above example, like the upper compartment 1, is 20 × 25 feet or approximately 500 sq. ft. in area. The retarding force it alone would create against a falling person would be (500 × 144 × 3) ft. lbs., which is approximately 22,000 ft. lbs. and therefore traveling through 3 ft. thick (the thickness of the bag), it is apparent that the lower compartment 2 alone has a capability of absorbing 66,000 ft. lb. of energy. This means a 200 lb. man could theoretically fall from a height of 330 ft. upon the lower compartment and sustain 110 G's, which would knock the person out but would be within the "life sustaining" limits. However, the fact that air is not released meanse that once the person's impact energy had been absorbed, this air pressure would still exist and must be released, and it would be released instantly in the form of throwing the person back up in the air. This is of course why the lower compartment 2 is used as a safety back-up or foundation, while the upper compartment 1 is used as the cushion which directly absorbs the impact of the falling body.
Although the dual compartment construction has been found to be suitable and preferred, it is possible to use other means than the lower compartment 2 as a back-up foundation, such as for example a solid, non-inflated backing structure or for that matter a single chamber with breathers with no further backing at all. Additionally the cushion could be mounted on a wheeled platform for mobility, if so desired. Additionally, more than two compartments could be used, and it is contemplated that for very great heights (400 ft.+) a triple (or more) layer or tricompartment structure in the vertical direction with also, a multitude of separate but interconnected compartments (e.g. five, one central with four surrounding it) in the horizontal direction in each of the layers, may be used. In each case of course it is important that the breathers have the proper locations and cross-sectional areas to permit the safe absorbtion of an impact for the height for which it is designed.
Because many varying and different embodiments may be made within the scope of the inventive concept herein taught, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.