Abstract:
The invention is a wedge-shaped support adapted to be fastened to a user&#39;s lower leg to provide comfort when the user is kneeling on an inclined roof, used in pairs. Each shin wedge comprises a wedge of lightweight material capable of supporting the user&#39;s weight. The acute dihedral angle of each wedge is approximately equal to the pitch angle of the roof on which the wedge kneepads are being used, thereby providing a substantially horizontal upper kneeling surface when the wedge is oriented towards the peak of the roof. The wedge&#39;s lower surface typically comprises a durable pad that prevents premature abrasion of the lightweight material and improves grip onto the inclined surface. Each wedge&#39;s upper surface typically includes a soft layer that serves as an ergonomic kneeling pad for the user. An attachment harness secures the wedge kneepad to the user&#39;s shin and thigh or knee.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to kneepads and shin pads and means for alleviating pressure and discomfort of the knees and legs of workers when they are working on inclined surfaces such as roofs. 
       BACKGROUND TO THE INVENTION 
       [0002]    Kneeling to work on either a sloped surface such as a roof, or a horizontal surface such as a floor, presents an ergonomically challenging task that stresses a worker&#39;s legs and feet. When a worker is kneeling on any surface, either with both knees or partially kneeling on one knee, the front of the worker&#39;s knee makes contact and supports the bulk of the worker&#39;s weight. Contact with the surface is made, through the skin of course, by the upper part of the shin bone, also called the tibia, and sometimes but not necessarily the kneecap, also called the patella. This contact surface has no established name, and will here be called the “kneefront”. However the worker&#39;s toes must typically apply balancing pressure that varies with upper body posture. Each of the worker&#39;s legs forms an open triangle over the work surface comprised of the kneefront and unsupported along the triangle&#39;s top side, the foot and toe oriented roughly at a right angle to the shin and forming its second side, with the floor or roof or other kneeling surface closing the triangle along its bottom side between the toe and kneefront. This unsupported leg geometry continuously strains a kneeling worker&#39;s ankle and toe muscles as they counterbalance fore and aft motions of the upper body, regardless of whether a task is being performed on a flat or inclined surface. It also puts strain on the worker&#39;s back. 
         [0003]    These kneeling strains are considerably exacerbated when working on an inclined surface such as a roof because gravity imposes a relentless shear force onto all points where the worker contacts the sloped surface. The shear force results in an unpleasant feeling, as the worker&#39;s skin, whether through clothing or not, stretches to stop sliding down the roof. The worker&#39;s ankles and toes also experience increased stress due to force exerted by the body&#39;s weight tending to move down the slope, which the feet must be continuously counteracting, regardless of upper body posture. The strain on the back is also worse in this position. 
         [0004]    A wide variety of kneepads exists in the prior art. They could generally be classed as simple “kneefront protectors”. In general, the prior art kneepads do not alleviate the foot muscle strain caused by unsupported shins, and none provide relief from the shear forces experienced when working on an inclined work surface. 
         [0005]    A few more advanced kneepads attempt to exploit the users shin, defined as the front part of the leg below the knee and above the ankle, in order to spread the kneeling forces onto a larger area and thereby improve comfort. U.S. Pat. No. 6,795,974 to Howell discloses a kneepad that extends over the shin, but does not have any significant thickness to raise the feet partly or fully off the kneeling surface. U.S. Pat. No. 6,637,034 to Worden discloses a kneepad that extends along the shin and raises the knee from the kneeling surface, but leaves the foot as the other point of support, so that the main result is that the knee is less bent than it would be without that kneepad. 
         [0006]    U.S. Pat. No. 4,438,754 to Canney discloses a knee protector that does not make contact with the kneefront, but straps to the shin and leaves the kneefront in mid-air. This creates an uncomfortable, or uneasy feeling in the wearer, and undue pressure on the knee joint because there is no support directly under the thigh which is putting downward pressure on the knee joint. 
         [0007]    U.S. Pat. No. 6,845,515 to Sveilich discloses a shin rest that is relatively short, at about 5 to 10 inches, and is intended to be worn low on the leg and used in association with a separate kneepad. Sveilich discloses one embodiment that joins the kneepad to the shin rest, at an articulated joint, which would be altogether quite long and massive and that is undesirable for the wearer when standing up while still wearing the device. 
         [0008]    All of these kneepads and shin rests in the prior art have essentially constant thickness, and are best suited for working on a horizontal surface. The present invention is intended for working on a sloped surface, such as a roof. The present invention comprises a wedge shape that is not found in the prior art. 
       SUMMARY OF THE INVENTION 
       [0009]    It is an object of the present invention to overcome the deficiencies noted in the prior art concerning kneepads, particularly as they pertain to working on an inclined roof. It is another object of the present invention to provide kneepads that reduce or eliminate pressure on its user&#39;s feet. 
         [0010]    It is another object of the present invention to provide shin wedges that reduce or eliminate shear forces on a user&#39;s body when working on an inclined surface. 
         [0011]    It is another object of the present invention to increase the safety of workers on steeply inclined surfaces by increasing their frictional contact onto it. 
         [0012]    These objects are attained by a shin wedge comprising a body that is wedge shaped, having an upper surface that is dimensioned and configured to support a user&#39;s kneefront and to supportingly hold a portion of a user&#39;s shin, and having a lower surface that comprises a substantial area that is substantially flat. The upper surface extends from a user&#39;s kneefront distally to more than one-quarter of the distance along the user&#39;s shin but less than one-half of the distance along the user&#39;s shin. There is a third surface that faces in the direction of a user&#39;s foot. One or more harness straps are connected to that body, and are dimensioned and configured to secure the shin wedge to a user&#39;s leg. 
         [0013]    The dihedral angle included between the upper surface and the lower surface is called here the “wedge angle”. 
         [0014]    The user of the present invention is more comfortable because the effect of the incline is substantially eliminated, and the user feels as if he is kneeling on a nearly horizontal surface. This reduces strain on the back, ankle, and toes. The shearing force on the skin of the user, whether felt through clothing or directly on the skin, is completely eliminated if the wedge angle is the same as the pitch of the roof. More generally, that shearing force is at least substantially reduced in proportion to how closely the wedge angle equals the pitch of the roof. 
         [0015]    Furthermore, the user is safer because the contact with the roof is the entire bottom surface of the shin wedge, which can easily be made much larger than the combined area of a person&#39;s kneefronts and toes, even if the kneefront is supplemented by the sort of kneepad existing in the prior art. 
         [0016]    The force of gravity is vertical and in the customary notation of physics is m*g, where m is the mass (in this case, of the worker plus the shin wedge) and g is the acceleration of gravity. When the mass is resting on an inclined plane (such as a roof) having pitch angle P, measured from horizontal, the force of gravity can be resolved into m*g*sin(P) pointing along the roof, and m*g*cos(P) perpendicular to the roof. The vector m*g*cos(P) is not relevant to the following discussion. It is the force vector m*g*sin(P) that causes the worker to slide down the roof. The frictional force that resists sliding of the shin wedge is a vector pointing along the roof in the opposite direction to m*g*sin(P). Undesired sliding occurs when the force vector m*g*sin(P) exceeds the frictional force. As the value of P increases, sin(P) increases, and more frictional force is needed. The wedge angle does not come into this calculation directly. The only way to increase frictional force is to increase the area of the shin wedge in contact with the roof, or to enhance its frictional properties. A larger wedge angle for a given length of the shin wedge along the user&#39;s shin will result in a longer surface, that being the hypotenuse of the triangle in which the length along the shin is adjacent to the wedge angle. Therefore, the wedge angle comes indirectly into the calculations for resisting sliding, by increasing the area providing the friction. The sine for P=45 degrees is approximately twice the sine for P=20 degrees, so the area of frictional contact, and the frictional force (although that also depends on the friction material) would be approximately double for a shin wedge with wedge angle 45 degrees compared to a shin wedge with wedge angle 20 degrees. No knee or shin protector in the prior art has this beneficial effect that increases safety of the user of the present invention. 
         [0017]    These and other objects, features, and characteristics of the present invention will be more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The preferred embodiments of the invention will now be described in detail with reference to the following drawings, in which: 
           [0019]      FIG. 1  illustrates a shin wedge according to the present invention, in the environment in which it is used. 
           [0020]      FIG. 2  is a large-scale illustration of one of the shin wedges shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Referring to  FIG. 1 , roofer  1  is shown kneeling comfortably on inclined roof surface  3  using a pair of shin wedges  2  configured according to the present invention. The shape of the shin wedges is generally that of a wedge, having two non-parallel plane surfaces meeting at the thin side of the solid figure but not necessarily forming a sharp edge there. This shape could be described as a blunt wedge, but here is simply called “wedge”. The top surface may be not a flat plane, but rather (as will be described below) it may have a lengthwise depression to conform to the shin of the user. Opposite the thin blunt side is a thicker side to complete the solid triangle. The shin wedges are always worn so that the thin end is near the users knee (the proximal end) and the thick end is towards the foot (the distal end). 
         [0022]    The shin wedge also usefully provides leverage, allowing the user to lever a knee up by rotation of the shin wedge about its distal edge. 
         [0023]    In  FIG. 1 , for illustration, the wedge angle, is the same angle as the pitch of the roof, so that the upper plane is horizontal, and therefore the user&#39;s kneefronts and shins rest on a horizontal surface, which is the position of least discomfort. In general, the closer the wedge angle is to the pitch of the roof, the greater the comfort of the roofer, because drag on the skin is reduced. However, the wedge angle and the pitch will not be equal in all cases, and any particular shin wedge can be used on roofs with various pitches. The wedge angle may be greater than the pitch of the roof or less than the pitch of the roof, circumstances called here “over-wedging” and “under-wedging” respectively. 
         [0024]    In a case of over-wedging, the user&#39;s shin will be sloping down towards the kneefront, and this is reasonably comfortable as that is the angle of the shin when a person is kneeling on a horizontal surface without any support other than the kneefronts and feet. The tendency, although small, is to slide forward, and that is less distressing and more easily managed than a tendency to slide backward. 
         [0025]    In a case of under-wedging, the user&#39;s shin will be sloping down towards the foot, and that resembles the situation of working without any support other than the kneefronts and feet on a sloping roof of lesser pitch. The present invention then has the effect of reducing the apparent pitch of the roof, which is beneficial to the comfort and safety of the roofer. In cases of pitches of approximately 30 degrees or more, the user should choose a shin wedge with a wedge angle moderately close to the pitch. For steep pitches, usually thought of as 45 degrees or more, the present invention will still be useful, but should not be relied on without other safety measures such as safety ropes. 
         [0026]    In  FIG. 1 , the roofer&#39;s kneefronts  4  and at least a portion of the roofer&#39;s shins  5  rest upon the shin wedges  2  and are secured in place by means of harness straps  6  and  8 . The roofer&#39;s feet  7  are thereby held at least partly suspended above the roof. If the toes of the feet or the toe of the user&#39;s boot are touching the roof and the roofer does not want that, a small turn of the foot sideways, with either the toes going inward or outward in relation to the body, would lift the toes clear of the roof. In this way, the roofer can relieve muscle stresses that would normally be needed to restrain him from sliding down the roof  3 . Since the upper surface of each shin wedge is approximately horizontal, little or no shear force is applied to the user&#39;s kneefront or shin at any time. All forces between the anatomy of user  1  and the shin wedges  2  are widely spread compressive loads onto the shin bone and kneefront, which is strong and well adapted to bear loads, rather than shearing loads onto skin of the kneefront, thereby minimizing discomfort. 
         [0027]      FIG. 2  shows one of the shin wedges  2  shown in  FIG. 1 . Each shin wedge  2  comprises wedge body  11  having an upper surface  12  for engagement to a user such as a kneeling roofer, a lower surface  13  for engagement to a work surface such as an inclined roof, triangular wedge sides  14  and  15 , and rear face  16 . The wedge angle  17  between upper and lower surfaces  12  and  13  is approximately equal to the pitch of the inclined surface upon which the user will kneel. 
         [0028]    Wedge body  11  is typically made of a lightweight plastic material such as a thermoplastic elastomer or expanded polystyrene, thereby providing sufficient strength to support a user while minimizing weight that would be an encumbrance when the user is walking upright while wearing the shin wedges. The width of each wedge body  11  is typically in the range 4 to 7 inches, with about 5 inches preferred. Its length is in the range 6 to 16 inches, with about 9 inches preferred, and in any case should stop well above the ankle. The longer it would be, the heavier it would be, and since it begins at the kneefront, it typically extends from one-third to one-half of the distance from the kneefront to the ankle. That length gives sufficient support to the shin, and a longer supporting surface is not a good trade-off for the added weight and bulk. Lengths in the stated range give sufficient leverage. That range of width and length gives sufficient contact area with an inclined surface so that a useful coefficient of friction may be obtained with suitable material on the lower surface  13 . The coefficient of friction between two surfaces depends on the nature of both surfaces. The roofs on which this may be used may be of a variety of materials, including asphalt shingles, wood, copper, steel, tile, slate, and waterproofing membrane. The metal roofs contribute little to the friction, so the material on the lower surface  13  must accommodate that fact. 
         [0029]    The height of its rear face  16 , which faces the foot, varies with the angle  17  used to compensate for roof pitch. The angle from a typical user&#39;s kneefront to the toe of a boot is in the range 15 degrees to 20 degrees. For such a user, if the wedge angle is greater than that angle, a toe will not make contact with the roof. That is not the preferred situation, but individual users will decide for themselves on whether they will tolerate that situation, or tolerate significant under-wedging. A small wedge angle of about 10 degrees might be preferred by some users. 
         [0030]    The dimensions stated here are rough approximations and may vary as the general wedge shape is rounded or sculpted for either ergonomic or stylistic reasons. Rounded edges  25 ,  26  and  27  at the lower surface  13  allow the user easier movement when crawling in any direction on the roof, because relatively sharp edges would tend to catch on the roof. 
         [0031]    Each shin wedge  2  includes an attachment harness comprising one or more adjustable straps  6 , each configured for securing the user&#39;s shin against the upper surface  12  of the shin wedge  2 . Optionally, there may be a harness element  8  that can encircle the user&#39;s leg at or above the knee, which would be attached to the front of the wedge body  11  by a garter strap  18 . 
         [0032]    Adjustable straps  6  and  8  may be somewhat elastic to aid in achieving a secure fit. Various well-known length adjustment and strap positioning fixtures may be supplied to insure proper fit.  FIG. 2  shows a hook-and-loop fastener (as sold under the trademark Velcro®) patch  20  affixed to each side of wedge body  11  permits straps  6  having corresponding hook-and-loop fastener patches to be adjusted in both length and location. Buckles and snaps may also be used to provide similar functionality. A strap may be a single unit that is detachable only at one or both sides of the wedge body  11 , or it may be a two-piece unit that is fastened to each side of the wedge body  11  and joined by a buckle or other type of fastener 
         [0033]    To provide a more secure leg fixation, the harness may also comprise a garter strap  18  that is affixed to the front of wedge body  11  and to a leg encircling strap  8  that can be secured above the user&#39;s knee as shown attached to in  FIG. 1 . 
         [0034]    The upper surface  12  of wedge body  11  may include an ergonomic indentation  22  that conforms in a general way to a user&#39;s kneefront and shin. This would be a groove running from the distal end, where it is open, either to all the way to the proximal end where it is open, or to near the proximal end where it is closed and shaped to receive the user&#39;s kneefront in a semi-globular hollow. Since the human leg is rarely a simple cylinder, and since the shin wedge should be usable by persons with a range of leg sizes, the groove should be a portion of an elliptical cylinder, that is, it should be wider than it is deep. 
         [0035]    The wedge body  11  may be made of more than one piece. The upper surface  12  may comprise a layer of material that is different than the bulk of the wedge body  11 . The distal end  28  of the upper surface  12  may extend beyond the rear face  16 , in case longer support of the shin is desired while adequate gripping of the inclined surface can be achieved with a shorter length of the lower surface  13 . 
         [0036]    To further improve comfort, a resilient covering  23  of plastic foam or gel may be formed onto upper surface  12 , either just where the kneefront makes contact, as illustrated, or along the full length of the upper surface. This feature can apply to either a flat upper surface or an upper surface that has an ergonomic indentation. 
         [0037]    In its simplest embodiment, the lower surface  13  of wedge body  11  directly contacts the inclined roof on which it is deployed. More typically though, a somewhat denser plastic bottom pad  24   a  is affixed to the bottom of wedge body  11  to form the lower surface  13 , so as to provide better durability than the lighter material, such as expanded polystyrene or thermoplastic elastomer, that is preferred for wedge body  11 . The bottom pad  24   a  should have a large coefficient of friction to resist sliding. The bottom pad  24   a  may have a flat, convex, or concave shape when not in use, but when the user is kneeling the bottom pad  24   a  should conform to the surface on which the user is working in order to maximize contact with that surface. The surface of the bottom pad  24   a  may have knobs or ridges to enhance its coefficient of friction. 
         [0038]    Bottom pad  24   a  may be permanently bonded to the bottom of wedge body  11 . Alternatively, for added flexibility, bottom pad  24   a  may be made replaceable by providing temporary fixation means such as the hook-and-loop fastener (as sold under the trademark Velcro®) strips  25  shown on replaceable pad  24   b . However, the fastening system must resist sideways motion as much as the coefficient of friction on the bottom pad resists sliding down the roof, for it is pointless for the bottom pad to grip well to the roof if it does not stick well to the wedge body  11 . If the bottom pad is replaceable, worn pads can be replaced with new pads with the economy of retaining the wedge body  11  and its harness. 
         [0039]    The bottom pad may have a constant thickness as shown as  24   a  or else have varying degrees of wedge-shape such as shown by replaceable pads  24   b  and  24   c . If wedge-shaped, the replaceable pads would provide the user with a means of adapting a single shin wedge  2  to work on different roof pitches. 
         [0040]    In normal use, a user will have a pair of matching shin wedges  2 , one on each leg. There is no necessity for the shin wedges to be configured differently for the left and right legs, but in embodiments that have rounded edges  26 , there can be a benefit from having the inside edge (that is nearer the centreline of the body) more rounded than the outside edge. In embodiments that have a resilient covering  23  on the upper surface, that covering may optionally be shaped differently for the left leg and right leg. 
         [0041]    The user must be facing substantially up the slope of the roof while wearing the shin wedges, and can easily crawl up the slope. The user also can easily move sideways while facing up the slope, and can move down the slope by crawling backwards. What the user cannot do is remain kneeling while facing sideways on the roof, or facing down the slope. However, the user can easily move about by standing up and walking on the slope while still wearing the shin wedges. 
         [0042]    If the user wants to ascend or descend by ladder, some caution is required, especially if he is wearing shin wedges having a large wedge angle. The shin wedges will collide with the rungs. One reason why the shin wedges are not as long as the entire shin is to provide better clearance from the rungs of a ladder. Also, the attachment harness in most forms will permit the shin wedges to be swung away from the front of the shin, and so out of the way of the ladder. 
         [0043]    It should be understood that where this description refers to user&#39;s shins and knees and other body parts, it envisages a person within the range of common adult sizes. Many modifications and variations besides those mentioned herein may be made in the techniques and structures described and depicted herein, resulting in other embodiments of the present invention without departing from the concept of the present invention. The foregoing disclosures should not be construed in any limited sense other than the limits of the claims that follow. Thus the scope of the invention should be determined by the appended claims and their legal equivalents rather than by the examples given.