Abstract:
A pack frame for a backpack which includes structure for transferring a substantial portion of the vertical load component to a position at the hip area of a wearer which is well below the load&#39;s center of gravity. The pack frame is comprised of a tubular frame structure which is adapted to support a load on the back of a wearer. A pair of crossed, diagonally extending links connect the upper part of the frame structure to a belt-like support means, e.g. hip saddle, which is adapted to be worn about the hips of the wearer. Each of the links is bent into an arch configuration and is rotatably connected to both the frame structure and the hip saddle by means of bearing-supported ball joints so that the frame fits compactly and comfortably on the wearer and does not substantially interfere with most normal body movements of the wearer. Straps are attached to the upper part of the frame structure and are adapted to extend over the shoulders of the wearer before they are attached to the hip saddle.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a backpack to be carried by a human and more particularly relates to a backpack frame for carrying relatively large loads while providing good stability and allowing substantial freedom of movement for the wearer. 
     Campers, alpinists, military personnel, and the like have long used backpacks to physically transport large loads over long distances and/or rough terrains. Typical of such backpacks are those which include a pack frame for suspending the load on the back of the wearer. Conventional pack frames employ shoulder straps to hold the backpack up in position on the back of the wearer. Such straps, however, also introduce a forward tension which counteracts the overturning moment of the pack and keeps the pack from toppling over backward. This continuous tension from the shoulder straps interferes with blood circulation under the straps, and results in a sustained tension in the shoulder and chest muscles. Accordingly, if only the shoulders and the upper back are used in carrying large loads, the discomfort to a wearer caused by shoulder straps of conventional packs can become excessive. 
     To alleviate this problem, many modern pack frames now include an elongated, board-like member which along with additional structure, straps, and/or padding distribute a part of the vertical component of the load to a belt-like structure worn about the hips of the wearer. This distribution of load appreciably decreases the shoulder tension and produces a lower resultant coupling to the body of the wearer thereby improving the wearer&#39;s dynamic stability and ability to maintain balance under rough conditions. 
     However, known means used in backpacks for distributing the load between the shoulders and hips have tended to interfere with the wearer&#39;s inherent counter-rotative body motions and have had an adverse effect on the wearer&#39;s ability to maintain balance while walking under pack, especially on terrain with a changing contour. This interference with normal body motions can also produce cyclic impulsive loading at the shoulder strap and hip contact points which, in turn, may lead to muscle soreness, cramps or chafing and even bruises under severe circumstances. 
     SUMMARY OF THE INVENTION 
     The present invention provides a pack frame for a backpack which includes structure for transferring a substantial portion of the vertical load component to a position at the hip area of a wearer which is well below the load&#39;s center of gravity. 
     Basically, this load transferring structure, i.e. &#34;crossed-four bar linkage,&#34; closely simulates the crossed-tendons within the torso and back of human body which automatically permits a counterbalancing of the dynamic movements required of the lower limbs in bipedal locomotion, i.e. walking. A horizontal cross member near the upper part of the frame structure simulates the shoulders of a wearer while a belt-like support, e.g. hip saddle, simulates his hip area. Two crossed, diagonally-extending links connect the upper cross member to the hip saddle and provide the primary structure by which a portion of a load mounted on the frame structure is transferred to the hip saddle. Straps are attached to the cross member and are adapted to extend over the shoulder of a wearer before being attached to the hip saddle. 
     To allow the pack frame to fit comfortably and compactly around the body of a wearer, each of the cross links are bent to form an arch which can be adjusted in length to accommodate different sized wearers, as will be explained in more detail below. Further, to allow a wearer to achieve a wide range of movement, both cross links are connected to both the cross member and the belt support by means of free-wheeling ball joints. A restraining means maintains the cross links in their relative positions without substantially interferring with the relative movement therebetween. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The actual construction, operation, and the apparent advantages of the invention will be better understood by referring to the drawings in which like numerals identify like parts and in which: 
     FIG. 1 is an elevation view of the present pack frame in an operable position on the back of a wearer; 
     FIG. 2 is a side view of FIG. 1; 
     FIG. 3 is an elevational view of an embodiment of a link used in the pack frame of FIGS. 1 and 2; 
     FIG. 4 is an exploded view of another embodiment of a link used in the pack frame of FIGS. 1 and 2; 
     FIG. 4A is an enlarged view taken along line A--A of FIG. 4; 
     FIG. 5 is an elevational, assembled view of the link of FIG. 4 in a first condition; 
     FIG. 5A is an enlarged view taken along line A--A of FIG. 5; 
     FIG. 6 is an elevational, assembled view of the link of FIG. 4 in a second condition; 
     FIG. 6A is an enlarged view taken along line A--A of FIG. 6; 
     FIG. 7 is an elevational, assembled view of the link of FIG. 4 in a third condition; 
     FIG. 7A is an enlarged view taken along line A--A of FIG. 7. 
     FIG. 8 is an elevational view, partly in section, of the upper end of a link used in the pack frame of FIGS. 1 and 2; 
     FIG. 9 is an elevational view, partly in section, of the lower end of a link used in the pack frame of FIGS. 1 and 2; 
     FIG. 10 is an elevational view, partly in section, of another embodiment of the lower end of a link used in the pack frame of FIGS. 1 and 2; and 
     FIG. 11 is an elevational view, partly in section, of a ball socket used in the pack frame of FIGS. 1 and 2. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Studies of the normal walking patterns of human beings have revealed that balance during walking is maintained by a continual counter-rotation between hips and shoulders plus a dynamically synchronized swing of the arms. Inherent in the knee joint is a built-in change in leverage which provides the continual changes in power and speed to permit a few muscle sets of the body to perform the required complex sequence of movements in perfectly self-coordinated fashion. Coupled to this variability in leverage within the knee joint, is a hip action which, in combination with the knee action, permits normal walking and permits weight to be shifted from one leg to the other without any appreciable raising and lowering of the body&#39;s center of gravity, hence saving a cyclical energy loss. All this would be for naught however, were it not for the cross-coupled tendons within the torso and back which automatically permit a counter-balancing for the dynamic movements required of the lower limbs for bipedal locomotion. 
     The pack frame of the present invention provides a highly effective structure for transferring a substantial part of the pack load to a position at the hip area of a wearer which is well below the load&#39;s center of gravity while, at the same time, permitting a wide range in freedom of movement by closely simulating this natural cross-coupling of the wearer&#39;s body. 
     Referring more particularly to the drawings, FIGS. 1 and 2 disclose pack frame 10 of the present invention in position on the back of wearer 11. Pack frame 10 is comprised of frame structure 12 which is preferably formed from lightweight tubing (e.g. 0.625 inch O.D., thin-walled 6061-T aluminum tubing), bent into an elongated, rectangular configuration as illustrated in the figures. Frame structure 12 has an upper cross member 13 near the top thereof and an intermediate cross member 14 (preferably formed of the same material as frame structure 12) secured thereto to form an integral part of frame structure 12. 
     Attached to the underside of upper cross member 13 are ball sockets 16a, 16b which are positioned near the relative right and left sides, respectively, of frame structure 12. Link 17a has ball joints 18a, 19a secured to its upper and lower ends, respectively. Ball joint 18a is secured in ball socket 16a to thereby rotatably attach the upper end of link 17a to the relative left side of frame structure 12. Ball joint 19a is secured in ball socket 16c which is mounted on the relative left side of belt-like support means, e.g. adjustable hip saddle 20, to thereby rotatably attach link 17a to said hip saddle. 
     Link 17b has ball joints 18b, 19b secured to its upper and lower ends, respectively. Ball joint 18b is secured in ball socket 16b to thereby rotatably attach the upper end of link 17b to the relative right side of frame structure 12. Ball joint 19b is secured in ball socket 16d which is mounted on the relative left side of hip saddle 20 to thereby rotatably attach link 17b to said hip saddle. 
     Retaining means, e.g. spring 22, is connected at one end 22a to an intermediate position on link 17a and at its other end 22b to an intermediate position on link 17b to maintain links 17a, 17b in their basic crossed relationship without substantially interferring with relative movement between the links. Adjustable straps 24a, 24b are connected to upper cross member 13 and are adapted to extend across the respective shoulders of wearer 11 and to be releasably connected at their respective lower ends to hip saddle 20 by means of hook and eye 25. 
     To allow frame 10 to fit compactly on wearer 11, each of links 17a, 17b (both are identical) is bowed or bent in the form of an arch. Ideally, each link 17a, 17b would be formed exactly to fit the actual dimensions (height, hip size, etc.) of a particular wearer. In the commercial world, however, this is impractical since a supplier normally must stock &#34;one size fits all&#34; merchandise. Based on studies which indicate that all humans are somewhat similarly proportioned, a standardized pack frame in accordance with the present invention can be designed for the average male adult with the differences in the physiques of various wearers and between male and female being readily accommodated therein. Height variations can be accommodated by changing the effective lengths of the links 17a, 17b and, if necessary, the distance between ball sockets 16a and 16b on cross member 13. These studies further revealed that to accommodate approximately 98% of the populace (men and women), links 17a, 17b need to have an adjustable distance d (FIG. 3) of approximately 18 to 25 inches. The maximum bowed distance R 1  (FIG. 3) in links 17a, 17b will vary depending on other factors, e.g. load to be carried, etc., but will normally be between 4 to 5 inches. 
     In the embodiment illustrated in FIG. 3, link 17c is comprised of two tubular sections, 30, 31, with section 30 being telescoped within section 31. A plurality of holes 31 are provided at spaced intervals through both sections 30 and 31 which when aligned in different relative positions, adjust the effective length d of link 17c. A pin, bolt, detent, or the like (not shown) is placed through the aligned holes to lock the sections together at their desired position. 
     In a preferred embodiment shown in FIGS. 4 and 5, link 17d is comprised of a length (24 inches) of tubular material, e.g. 0.375 inch OD, 0.305 inch ID, 6061-T-6 aluminum tubing, which is bent in a continuously curving arch wherein the radius of curvature R c  equal approximately 17 inches. A shaping rod 33, e.g. steel, having a length of approximately 16 inches is formed in a continuously curving arch wherein the radius of curvature equals approximately 8 inches. Shaping rod 33 is forced into link 17d wherein due to the difference in radii of curvatures between rod 33 and link 17d, the height and radius of the arch and incidentally the length of link 17d can be varied by rotating rod 33 within link 17d. FIGS. 5-7, although not necessarily to scale, illustrates this adjustment feature. 
     Rod 33 has an operating means, e.g. lever 33a, at one end as shown in FIG. 4A which cooperate with detent means, e.g. slots 35 in link 17d (FIGS. 5A-7A) by which rod 33 may be rotated within link 17d and held in a desired position. Although only three positions, i.e. slots 35, are shown, it should be recognized that fewer or more than three positions could be provided without departing from the present invention. 
     When lever 33a in the position shown in FIG. 5A, R r  of rod 33 substantially aligns with R c  but being less than R c , link 17d will attain additional curvature and will achieve its minimum effective length d min , which also corresponds with its most springy orientation. When lever 33a is in the position shown in FIG. 6A, R r  of rod 33 is 90° out of alignment with R c   of link 17d and link 17d thereby acquires its average effective length, d av  which also corresponds with its average springiness setting. When lever 33a is in the position shown in FIG. 7A, R r  of rod 33 is fully opposed to R c  of link 17d which &#34;flattens&#34; link 17d to its maximum effective length d max  and minimum curvature which corresponds with its stiffest orientation. 
     In addition to allowing frame 10 to comfortably fit on a wearer&#39;s back as mentioned above, by curving links 17a, 17b a high degree of vertical compliance for the frame 10 is also provided. That is, the curvature of links 17a, 17b will increase when the load being carried is increased. Also, links 17a, 17b can bend resiliently whenever a vertical shock is experienced such as when a wearer jumps or when his heel impacts the ground during walking. This is important, especially when a wearer is descending rapidly under pack since the springiness of the links can readily absorb the excessive shocks normally experienced during such a maneuver. 
     Links 17a, 17b are connected to cross member 13 and to belt-like support means 20 to provide maximum movement with minimum effort. As previously described, this is accomplished by using ball joints on links 17 which cooperate with ball sockets on cross member 13 and belt-like support 20. As illustrated in FIG. 8, upper ball joint 18 (both 18a, 18b) (e.g. 0.375 inch diameter ball) has a shank portion 37 which is positioned into the upper end of link 17 and is held therein by any known means, e.g. crimping of link 17 into groove 38 on shank 37. The nominal axis 39 of upper ball joint 18 is canted off axis 40 of shank 37 at a preferred angle at 61.5°. Lower ball joint 19 (both 19a, 19b) has a shank 41 (FIG. 9) which is positioned in the lower end of link 17 and is held therein by any suitable means, e.g. bolt 42. Nominal axis 43 of lower ball joint 19 is canted off axis 44 of shank 41 at a preferred angle of 17°. FIG. 10 illustrates a bottom ball joint for use with shaping rod 33 of the embodiment shown in FIGS. 4-7. 
     To increase the total relative movements between frame structure 12, belt-like support means 20, and crossed links 17a, 17b, ball sockets 16 (FIG. 11) are provided which allows cyclic, rotational swivelling of the links relative to their respective supports while virtually eliminating the energy loss normally associated therewith. Ball socket 16 (16a-16d) is comprised of a support 50 having a bearing race 51 therein which is preferably formed for a self-lubricating material, e.g, nylon impregnated with graphite. A plurality of bearings 52 (e.g. 9 balls) are positioned on race 51 and are adapted to receive the ball joints 18 or 19, as the case may be. Retainer 53 is threaded onto support 50 to secure ball joint 18 in ball socket 16. 
     To insure a high degree of pivotable mobility, the juncture 55 between ball 18 and shank 37 (FIG. 11) is tapered so angle β 3  equals approximately 60°. Retainer 53 is designed so that angles β 4  each equal approximately 40°. This allows an exceedingly wide range of movement between link 17 and ball sockets 16. To further add to this range of movement, the upper ball sockets 16a, 16b are mounted on cross member 13 so the central axis 56 of ball socket 16 is canted off the vertical at an angle α, (FIG. 1) equal to approximately 55° and off parallel with frame member 12 at an angle α 2  (FIG. 4) equal to approximately 11°. 
     Preferably both of cross links 17a, 17b are coated or covered with a smooth, anti-wear material, e.g. plastic tubing, which reduces friction, wear, and noise caused by sliding contact between the links. One link is preferably covered with a first plastic and the other link covered with a second plastic (e.g. polyethylene having differing hardnesses) since wear is normally less between two dissimilar materials. Further, controlled lengths 60 of nylon cords or the like (only one shown in FIG. 2) are provided between frame structure 12 and belt support 20 to prevent forces created by an otherwise dangling belt support 20 from damaging the ball joints on links 17 when pack frame 10 is not in position on a wearer 11. Likewise guard tubes or limit stops (not shown) may be provided for upper ball sockets 16a, 16b to protect links 17a, 17b against any undue twisting or excessive leverage which otherwise may occur. Also, a formed sheet of Mylar or the like (not shown) can be mounted on frame structure 12 between the actual pack sack or load (not shown) and frame structure 12, shaped to permit the full range of useful link mobility but which will prevent damaging movement of the links when frame is not being carried on wearer&#39;s back and will prevent items in the pack sack from interferring with the links&#39; mobility.