Flexible pack frame

BACKGROUND

00011. Field of the Invention

0002The present invention relates to frames for backpacks.

00032. Description of the Prior Art

0004Typically external frame style load bearing pack frames are made of rigid materials such as steel or aluminum. Fabrication techniques used to manufacture these designs generally include cutting, bending, welding and riveting together the component parts. These designs and materials emphasize strength to support heavy loads and rigidity to stabilize those loads while the wearer moves about.

0005Another approach used more recently is to fabricate external pack frames from molded or formed thermoplastics. These offer the benefits of reduced fabrication costs, yet compromises are made in the strength and rigidity of the frames due to the physical limitations of the polymers used.

0006With prior approaches that rely on steel or aluminum, there is virtually no flexing of the structure to accommodate the desired range of movements of the wearer. Additionally, straining against the rigid frame creates pressure points on the wearer that will become uncomfortable under prolonged, heavily loaded use. Rigid frame structures are not capable of absorbing catastrophic impact, and can be overwhelmed when dropped or struck. Moreover, rivets will pop, welds crack, and metal breaks when, for example, loaded packs are tossed off of trucks or strike the ground during parachute deployments. Steel or aluminum frames are expensive to manufacture.

0007Prior approaches that rely on molded or formed thermoplastics also have limitations. For example, frame designs using polymers are not rigid enough for the wearer to stabilize heavy loads while moving about. Thermoplastic frames can flex in unwanted ways at inopportune times, compromising the balance and therefore the safety of the user. Designs that are shaped in a manner to improve rigidity tend to compromise the desired range of motion, move the load's center-of-gravity further away from the wear's own center-of-gravity, and thus negatively impact balance and carrying comfort, creating fit conflicts with items worn on the back such as body armor plates and heavy clothing.

SUMMARY OF THE INVENTION

0008An objective of the present invention is to provide a lightweight, flexible and sturdy backpack frame that provides sufficient fit and range of motion with varying equipment combinations while maintaining a low cost of manufacture. In one aspect of the present invention, a backpack frame has a varying longitudinal centerline geometry in relationship to the geometry of the outboard longitudinal edges and a re-curving longitudinal contour relative to the wearer's back.

0009The backpack frame of the present invention has side rails defining a first profile. The first profile has a flat first base segment lying on a first reference plane, and a first concave segment spaced a maximum distance from the first reference plane at a first location between the first base segment and the upper end of the frame. An intermediate structure interconnects the side rails. The intermediate structure has a second profile with a second flat base segment lying on a second reference plane parallel to the first reference plane, and a second concave segment leading from the second base segment to the upper end of the frame. The second concave segment is spaced a maximum distance from the second reference plane at a second location between the second base segment and the upper end of the frame. The first and second locations of maximum spacing are offset from one another.

0010These and other features and objectives of the present invention will now be described in greater detail with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

0011<figref idref="DRAWINGS">FIG. 1</figref> is a rear view of a backpack frame in accordance with the present invention;

0012<figref idref="DRAWINGS">FIG. 2</figref> is a sectional view taken along the centerline of the backpack frame; and

0013<figref idref="DRAWINGS">FIG. 3</figref> is a plot of the centerline and outboard edges of the backpack frame.

DETAILED DESCRIPTION

0014Referring initially to <figref idref="DRAWINGS">FIGS. 1 and 2</figref>, a backpack frame in accordance with the present invention is generally depicted at <b>10</b>. The frame is integrally molded of a high strength flexible thermoplastic with side rails <b>12</b> extending in a generally parallel relationship to the frame's centerline CL. The side rails are interconnected by an intermediate structure comprising a lattice network of cross members <b>16</b> and generally longitudinally extending ribs <b>18</b>.

0015With reference to <figref idref="DRAWINGS">FIG. 3</figref>, a first plot line <b>20</b> depicts a first profile of the frame's side rails <b>12</b> in relation to a first reference plane P₁, and a second plot line <b>22</b> depicts a second profile of the intermediate structure at the centerline CL in relation to a second reference plane P₂parallel to the first reference plane P₁.

0016The first profile <b>20</b> has a flat first segment <b>20</b><i>a </i>lying on the first reference plane P₁, and a first concave segment <b>20</b><i>b </i>leading from the first base segment to an upper end of the frame. The first concave segment is spaced a maximum distance from the first reference plane at a first location X₁between the first base segment <b>20</b><i>a </i>and the upper frame end.

0017The second profile <b>22</b> has a second flat base segment <b>22</b><i>a </i>lying on the second reference plane P₂, and a second concave segment <b>22</b><i>b </i>leading from the second base segment to the upper frame end. The second concave segment <b>22</b><i>b </i>is spaced a maximum distance from the second reference plane at a second location X₂between the second base segment <b>22</b><i>a </i>and the upper frame end.

0018The first and second locations X₁, X₂are offset one from the other, with the location X₁being closer to the upper frame end.

0019It will be seen, therefore, that stated in reference to the pack frame carried on a person's back, the profiles at the centerline and the outboard edges draw closer to each other while moving vertically toward the top of the frame. This causes the concavity of the frame relative to the wearer's back to decrease in a specific manner that creates the following benefits: <ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0000"><ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0020"> The frame fits closer to body allowing the center of gravity of the carried load to be closer to the wearer's own center of gravity. This results in improved balance and allows the load-carrying plane of the frame to stay closer to vertical as the frame passes up over the wearer's scapula. </li><li id="ul0002-0002" num="0021"> It becomes progressively more flexible torsionally moving towards the top of the frame; the reduced concavity allows the frame to twist with shoulders and upper torso while walking, running and climbing. </li><li id="ul0002-0003" num="0022"> When the wearer's back is unusually flat/broad or body armor, heavy clothing, floatation devices, etc. are being worn, the frame contour allows clearance at the outboard edges of the pack frame so that the weight of the pack is not loading only where the outboard edges touch the wearer's back, body armor, heavy clothing, etc. </li></ul></li></ul>

0023Progressively reducing the concavity of the pack frame as described above, however, can cause the pack frame to become too flexible in the longitudinal axis for stable load carriage unless another feature is included.

0024Stated in reference to a pack frame carried on a person's back and starting with the frame's flat base segments <b>20</b><i>a</i>, <b>22</b><i>a</i>, the invention overcomes this limitation by progressively curving the frame first away from the plane of the wearer's back and then back toward it again as the concavity defined above is progressively reduced, with the locations X₁, X₂of maximum spacing being offset one from the other, and with location X₁being closer than location X₂to the upper end of the frame.