Construction of a variable friction shoe
View Patent ↗A variable friction shoe sole includes a midsole body, one or more compressible portions made of a compressible material, one or more low-friction portions vertically aligned with the one or more compressible portions, and one or more intermediate layers located between the one or more low-friction portions and the one or more compressible portions. The one or more low-friction portions are prominent of the midsole body when vertical ground reaction forces (GRFs) applied to the variable friction shoe sole are low, and wherein an increase in GRFs compresses the one or more compressible portions and causes the one or more low-friction portions to retract inwards.
1 . A variable friction shoe comprising:
a midsole body having an anterior portion defining an anterior curve, and a midsole bottom surface having a first coefficient of friction, the midsole bottom surface being defined by a first horizontal plane when the variable friction shoe is in a horizontal, resting position, wherein the midsole bottom surface forms a portion of an outsole of the variable friction shoe; and
a low-friction outsole material located at the anterior portion of the midsole body, the low-friction outsole material being shaped to follow the anterior curve and forming a low-friction bottom surface defined by a second horizontal plane, wherein when the variable friction shoe is in the horizontal, resting position and vertical ground reaction forces (GRFs) applied to the variable friction shoe are less than a first value, the second horizontal plane is located below the first horizontal plane as a result of the low-friction bottom surface protruding below the midsole bottom surface, the low-friction outsole material having a second coefficient of friction less than the first coefficient of friction;
wherein the low-friction bottom surface is configured to protrude beyond the midsole bottom surface of the midsole body when the vertical GRFs applied to the variable friction shoe are equal to or less than the first value, and wherein the low-friction bottom surface of the low-friction outsole material is configured to retract inwards towards the midsole body when the vertical GRFs are greater than the first value, wherein the midsole bottom surface is configured to make contact with a ground surface when the low-friction outsole material is retracted inwards in response to the vertical GRFs exceeding the first value.
2 . The variable friction shoe of claim 1 , wherein the midsole body has a midfoot shelf and wherein the anterior curve terminates at a level above a top portion of the midfoot shelf.
3 . The variable friction shoe of claim 1 , wherein the low-fiction outsole material located at the anterior portion of the midsole body is configured to protrude beyond the midsole bottom surface of the midsole body at non-zero approach angles of the anterior portion to the ground surface.
4 . The variable friction shoe of claim 3 , wherein the anterior curve is configured to produce a dominant orthogonal force component between the ground surface and the low-friction outsole material during toe-off.
5 . The variable friction shoe of claim 1 , wherein the low-friction outsole material is located on at least one of an anterior lateral edge and an anterior medial edge of the variable friction shoe.
6 . The variable friction shoe of claim 5 , wherein the low-friction outsole material located on at least one of the anterior lateral edge and the anterior medial edge has a radius of curvature greater than 1 mm.
7 . The variable friction shoe of claim 6 , wherein the radius of curvature of at least one of the anterior lateral edge and the anterior medial edge is configured to prevent tripping in response to a sideways scuff.
8 . The variable friction shoe of claim 1 , further including a rear high-friction patch having a third coefficient of friction greater than the second coefficient of friction, wherein the rear patch is configured to be located above the first horizontal plane defined by the midsole bottom surface of the midsole body.
9 . A variable friction shoe comprising:
a midsole body having an anterior portion that defines an anterior curve; and
a low-friction material located at the anterior portion of the midsole body and having a geometry that follows the anterior portion along the anterior curve, the low-fiction material having a bottom surface defined by a first coefficient of friction;
a high friction material defined by a second coefficient of friction that is greater than the first coefficient of friction, the high friction material defining a bottom surface of a portion of the midsole body, wherein the portion of the midsole body forms a portion of an outsole of the variable friction shoe;
wherein the bottom surface of the low-friction material is configured to protrude beyond the bottom surface of the portion of the midsole body including the high friction material when vertical ground reaction forces (GRFs) applied to the variable friction shoe are less than a first value, and wherein the bottom surface of the low-friction material is configured to retract inwards towards the midsole body when the vertical GRFs are greater than the first value, wherein the bottom surface of the portion of the midsole body including the high friction material is located and configured to make contact with a ground surface in response to the vertical GRFs being greater than the first value.
10 . The variable friction shoe of claim 9 , wherein the midsole body has a midfoot shelf and wherein the anterior curve terminates at a level above a top portion of the midfoot shelf.
11 . The variable friction shoe of claim 9 , wherein the bottom surface of the low-friction material located at the anterior portion of the midsole body is configured to protrude beyond the bottom surface of the portion of the midsole body that includes the high friction material when the vertical GRFs are equal to or less than the first value.
12 . The variable friction shoe of claim 11 , wherein the anterior curve is configured to produce a dominant orthogonal force component between the ground surface and the low-friction material during toe-off.
13 . The variable friction shoe of claim 9 , wherein the low-friction material is located on at least one of an anterior lateral edge and an anterior medial edge of the variable friction shoe.
14 . The variable friction shoe of claim 13 , wherein the low-friction material located on the at least one of the anterior lateral edge and the anterior medial edge has a radius of curvature greater than 1 mm.
15 . The variable friction shoe of claim 14 , wherein the radius of curvature of the at least one of the anterior lateral edge and the anterior medial edge is configured to prevent tripping in response to a sideways scuff.
16 . The variable friction shoe of claim 9 , further including a rear high-friction patch having a third coefficient of friction greater than the second coefficient of friction, wherein the rear high-friction patch is located above a plane defined by the bottom surface of the portion of the midsole body.