Back pack with flexible frame assembly

A back pack having a frame adapted for limited flexing responsive to relative hip and shoulder movement of a hiker. A generally inverted U-shaped main frame unit has side bars that rotate under torsional resistance in a fore and aft direction about a transverse support bar. A cross bar support assembly is coupled to the side bars by fittings that provide for relative rotational and pivotal movement between members of the cross bar assembly and the side bars, thereby permitting such frame flexing.

BACKGROUND OF THE INVENTION 
This invention relates to a mountaineering back pack and, more 
particularly, to an improved frame assembly for such a pack which is 
adapted for limited flexing. 
Most back pack frame assemblies of the prior art have included frames 
having a pair of spaced vertical side bars and a plurality of cross bars 
extending between them in spaced parallel relation. The side bars and 
cross bars are bolted, fused or clamped together to form relatively rigid 
structures. Nylon or canvas bags are then typically secured to the frame 
assembly for holding at least portions of the load. 
This type of frame assembly is in turn supported on the hiker's back by a 
pair of shoulder straps and also by a hip belt that is cinched tightly 
around the hiker in the region of the hips. Considerable effort has been 
directed in recent years toward the design of back packs that are capable 
of being supported primarily on the hips. It has been determined that such 
an arrangement is desirable in order to maximize load carrying ability and 
comfort. 
In walking, the hips of the hiker rotate fore and aft about a vertical axis 
extending generally through the torso. There is also some 
control-rotational shoulder movement about the same axis, but to a much 
lesser extent. It is desirable from the load carrying and comfort 
standpoints that the frame assembly remain in generally parallel relation 
with the plane of the back during such body movement and closely adjacent 
thereto, yet not inhibit the relatively free fore and aft rotational 
movement of the hips. 
In an effort to achieve these desired ends, some packs in the past have 
equipped relatively rigid pack frames with various types of specially 
designed pivotal and flexible couplings between the pack frames and the 
hip belt assemblies. These devices have suffered from various 
deficiencies. In some instances, they simply do not serve to avoid undue 
restriction of the hips. One approach that does reduce restriction 
involves providing a universal joint type coupling allowing for relatively 
free movement between the frame and hip belt assembly. However, this 
results in a shifting or swaying of the frame and supported load as the 
hiker walks, producing a generally unstable feeling. Efforts to avoid this 
instability have been towards the design of generally complicated and 
inherently expensive devices. 
In prior devices which have frame members welded or screwed together, there 
is some tendency to weaken the structure at the joint. Problems have been 
minimized by resort to high strength or to heavier materials or to complex 
joints that rigidly lock the mating parts together. However, these 
expedients undesirably add to the cost or make the frame heavier, or both. 
Moreover, all such constructions, in effect, have fulcrum points at the 
joints about which destructive bending can occur. Further, such 
constructions are not particularly well suited for absorbing shock loads 
such as occur when the pack is dropped. 
It will be appreciated from the foregoing that there is a need for a back 
pack frame that is strong and durable, yet simple, lightweight and 
relatively inexpensive to build and that allows the shoulders and hips to 
rotate relatively freely and independently, without resulting instability. 
The present invention fulfills this need. 
SUMMARY OF THE INVENTION 
The present invention resides in a back pack frame assembly that is, by 
virtue of its construction, adapted for limited flexing. The flexibility 
of the frame effectively minimizes the constriction of the hiker's body 
and thereby significantly increases his load carrying capability and 
comfort. The flexing capability is achieved by a construction 
incorporating free-flex couplings for joining the various load bearing 
structural elements of the pack frame. These couplings allow certain main 
frame members to move relative to one another in the desired directions. 
The result is that the desired freedom is achieved without instability. 
The frame is inherently strong and durable and the distributed nature of 
the flexing capability provides for improved shock-absorption capability, 
enabling the pack to suffer considerable abuse without damage. 
More particularly, the pack frame includes a pair of main or side bars in 
spaced and generally parallel relation, connected by a transverse support 
bar. Counter rotation of the side bars generally about the axis of the 
support bar is permitted, such movement preferably being yieldably 
resisted to some degree. Disposed between the side bars and coupled 
thereto is cross bar means that serves to enhance structural strength and 
provide for convenient load attachment. Coupling is accomplished by means 
allowing for relative movement between the cross bars means and side bars, 
thereby enabling the side bars to rotate fore and aft and the frame to 
maintain a generally conforming relationship to the hiker's body, 
notwithstanding relative hip and shoulder movement. 
In a more detailed aspect of the invention, the coupling means comprises a 
plurality of fittings, each of which is rotatably mounted on the end of 
one of the plurality of cross bars. An end portion of each such fitting is 
shaped to provide a socket that receives the adjacent portion of the 
respective side bar. As the side bars rotate, the sockets in turn rotate 
around the peripheries of the adjacent side bars and the fittings rotate 
relative to the cross bar. Thus, the fittings serve the intended purpose 
of coupling the frame parts, yet permitting the desired relative movement. 
Positioning of the cross bars vertically along the side bars relative to 
one another, as well as further enhancement of the pack frame's strength, 
is achieved in the preferred embodiment by ribs, including elongated rods 
and spacer sleeves, arranged generally parallel to the side bars and 
secured to the transverse support bar. With a generally inverted U-shaped 
frame including the side bars and the transverse bar, the flexing of the 
frame assembly is progressive over the vertical extent of the main frame 
unit and the transverse support bar functions as a torsion bar. 
Another aspect of the invention involves simple and convenient adjustment 
of cross bar location by means of removable spacer means that can be 
snapped onto the elongated rods, thereby changing the lengths of the rib 
segments between the respective cross bars. This arrangement allows 
adjustment of the pack frame assembly for accommodating hikers of 
different physical size and, more particularly, torso length. 
It will be appreciated from the foregoing that the present invention 
represents an advance by virtue of providing a pack frame assembly that is 
not only more comfortable to the hiker and enhances his load carrying 
ability, but is stronger and capable, without resort to heavy or special 
materials, of withstanding shock loads without incurring damage. At the 
same time, it is inherently simple in construction, easily assembled, and 
capable of being made at relatively low cost. Other aspects and advantages 
of the invention will become apparent from the following detailed 
description taken into conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in the drawings, the present invention is embodied in a 
mountaineering back pack frame assembly 10 that is capable of flexibly 
conforming generally to the changing contour of the hiker's back as his 
hips and shoulders rotate during movement. Referring in particular to FIG. 
1, the frame assembly 10 is used in conjunction with a flexible pack bag 
12 and with back-engaging bands 14 and 16, the lower band 16 being padded 
for added comfort. Carrying of the frame assembly on the hiker's back is 
provided for by means of adjustable shoulder straps 18 and an adjustable 
hip belt assembly 20. 
The frame assembly as shown in FIG. 2, includes a pair of side bars 22 and 
24 and a transverse support bar 26. In functional terms, the purpose of 
the transverse bar 26 is to support the side bars 22 and 24 for 
counter-rotational movement generally about the longitudinal axis of the 
bar 26. The nature of this rotational movement, which is the basis of the 
flexing capability of the frame assembly of the invention, is illustrated 
diagrammatically in FIG. 2a. 
Preferably, as illustrated, the side bars 22 and 24 and the transverse bar 
26 are formed integrally as a main frame and have a generally inverted 
U-shaped configuration. With this arrangement, the transverse bar 26 
provides limited torsional resistance to the rotational movement of the 
side bars 22 and 24. As may be seen in FIG. 2a, the extent of movement 
and, correspondingly, the resistance progressively varies over the 
vertical extent of the side bars 22 and 24. Movement is, of course, 
maximum and at the lower ends and the resistance to applied loads is 
minimum at that location. 
The main frame unit may be conveniently formed of an aluminum alloy tubing. 
Such material is relatively light in weight and has adequate strength, as 
well as being capable of being conveniently formed into the desired shape 
by bending. In order to conform the main frame unit to the contour of the 
human torso, the unit is bowed forwardly in the region of the transverse 
bar 26, and each of the side bars 22 and 24 is bent slightly rearwardly at 
the lower ends to avoid interference with the buttocks area. 
A cross bar support framework 30, coupled to the main frame unit, serves 
advantageously to bear and distribute loads. In the preferred embodiment, 
this grid-like framework 30 is rigid in the sense that it resists collapse 
and undesired bending or movement of the main frame unit. 
As previously noted, an important aspect of the invention resides in the 
manner in which the cross bars of the framework 30 are movably coupled to 
the main frame unit. Four such cross bars, designated by the numerals 32, 
34, 36 and 38, are shown by way of illustration in the drawing, each 
rotatably mounting at each end a fitting 40, illustrated in greater detail 
in FIGS. 4 and 5. The cross bars 32-38 may be made from tubular aluminum 
alloy stock smaller in diameter than that of the main frame unit, and are 
bowed slightly as shown to avoid contact with the hiker's back. 
Each of the fittings 40 has a cylindrical base portion 42 rotatably 
received in close bearing engagement in the tubular end of the associated 
cross bar, e.g., cross bar 32 in FIG. 4. A projecting end portion 44 is 
shaped to provide a generally semi-cylindrical socket 46 shaped to conform 
to the contour of the adjacent side bars 22 and 24 so as to receive them 
in bearing engagement. A shoulder 48 at the juncture of the base portion 
42 and end portion 44 abuts the tubular end of the cross bar 32 to serve 
as a stop. To enhance the bearing engagements, the fittings are preferably 
made of a low friction plastic material such as that sold under the Delrin 
trademark. 
In view of the construction of the fittings 40 and the manner in which they 
are mounted, it will be appreciated that each of the cross bars 32-38 may 
pivot about the longitudinal axis of the side bars 22 and 24. As shown in 
FIG. 4, this results in the socketed end portion of the fitting 40 sliding 
about the periphery of side bar 22. By virtue of the nature of the 
counter-rotational movement of the side bars illustrated in FIG. 2a, 
relative rotational movement occurs between the cross bars 32-38 and the 
side bars 22 and 24, such movement being enabled by the turning of the 
cylindrical base 42 of each fitting within its cross bar. Accordingly, it 
will be appreciated that the fittings 40 provide for both relative pivotal 
and rotational movement between the cross bars and associated side bars. 
The configuration of the main frame unit and its resistance to outward 
spreading of the side bars 22 and 24 in cooperation with the socketed end 
portions of the fittings, aids in holding the main frame unit in assembly 
with the support framework. The possibility of separation during flexing 
of the frame assembly is prevented by the back engaging webbing 14 and 16 
which comprises bands wrapped tautly around the frame unit, as shown in 
FIG. 1. The desired counter-rotation of the side bars can still take 
place, but their separation is maintained essentially constant, thus 
insuring that the side bars 22 and 24 remain in the sockets of the 
respective fittings. 
The framework 30 further includes a pair of ribs 50 oriented at 
substantially right angles and spaced substantially equal distance from 
one another and from the side bars 22 and 24. The ribs 50 serve to suspend 
the frame work from the transverse support bar 26 of the main frame unit 
and to vertically position the cross bars 32-38 and maintain the desired 
spacing between them. 
Referring to FIGS. 2 and 3, each of the ribs 50 includes an elongated rod 
52 that extends over the length of the pack and passes through bores 53 of 
corresponding diameter in the support bar 26 and the cross bars 32-38. The 
rods 52 are maintained in assembly with the main frame unit and cross bars 
by any suitable means as by the machine screws 54 illustrated in FIG. 3. 
The spacing between the cross bars is established and maintained by 
sleeves 55, of appropriate length, that are received on the rods 52. The 
sleeves 55 have an outside diameter larger than the bores 53 through the 
cross bars or the transverse support bar. Preferably, although not 
necessarily, washers 56 as shown in FIG. 3 are provided at the junctures 
between the sleeves and the adjacent cross bars 32-38 and transverse 
support bar 26. These washers are made of a low friction material such as 
Delrin plastic and insure against wear at the contact locations. 
The relatively rigid nature of the support framework 30, that is, its 
inherent resistance to distortion from the substantially right angular 
relationship between the ribs 50 and cross bars 32-38, facilitates the 
distribution of the pack frame load and prevents damage. On the other 
hand, the ribs 50 are constructed and positioned so as to permit the 
desired counter rotation of the side bars 22 and 24. Should the pack be 
dropped so that the end of the side bars 22 or 24 contacts a relatively 
hard surface, the load is distributed over the entire frame assembly by 
the cooperating parts, all of which contribute to the shock-absorption 
capability. 
Because the construction of the pack frame assembly and the fact that no 
special assembly techniques or operations, such as welding, riveting, 
staking or the like, are required, it may be quickly and easily assembled. 
Moreover, any damaged component parts may be readily replaced. 
As previously noted, it is desirable to have the pack frame accommodate 
hikers of various physical size. The relative vertical position of the 
uppermost cross bar 32 can be adjusted, to a limited extent, by means of 
removable rib inserts 58. Effectively, this allows adjustment of the 
relative location of the points at which the shoulder straps 18 are 
attached to the pack frame assembly 10. The adjustment can be performed 
without disassembly of any of the structural members of the pack frame. 
The inserts 58 can be snapped onto the rods 52 either above or below the 
cross bar 32 to change the effective lengths of the sleeves 55 immediately 
adjacent such cross bar 32. In FIG. 1, the rib inserts 58 are positioned 
on the rod segments above the cross bar 32, while in FIG. 2, they are 
positioned below the cross bar 32. 
Each of the rib inserts 58, shown in FIGS. 5 and 6, is in the shape of a 
sleeve having a longitudinal slot extending the length thereof. 
Immediately adjacent both edges of such slot and extending over its entire 
length, are lips 60, for facilitating the manual snap engagement and 
disengagement of the inserts 58 with the rods 52. 
Although the back pack frame assembly has been described with reference to 
one preferred embodiment, it will be understood by one skilled in the art 
that modifications may be made that will still embody the spirit of the 
invention herein described.