Athletic injuries, such as from overstressed musculoskeletal structures, can be traumatic and career ending. ACL (anterior cruciate ligament) injuries are particularly notorious and prone to recurrence. These and other injuries often result from some form of loads (e.g., forces and torques) transferred through the footwear of the athlete to the foot and on to an anatomical member, such as, a bone, ligament, cartilage, tendon or other tissue structure. Mitigation of the transfer of these loads can substantially eliminate or alleviate injury risk to the foot, ankle, lower leg and knee. Because an athlete's footwear defines the ground interface, the footwear defines the focal point of potentially injurious load transfers. Protruding cleats are often used on the bottom of shoes used sports played on fields, grass, turf or dirt. These protrusions increase the load transfer from the athletes to the playing surface and can, unmitigated, raise the loads to those that can cause injury.
A force mitigation approach for a footwear appliance defines an interface between a shoe upper and a shoe sole having a planar sole surface. A force dissipating device in the footwear appliance includes an actuator responsive to a displacement force from the shoe sole surface, and an elastic field of resilient, compressible material. The elastic field is elongated in a direction aligned with the displacement force, and an inclined surface is attached to the actuator and disposed against the elastic field. The actuator is adapted for movement parallel to the elastic field, while the inclined surface is oriented to compress the elastic field in a direction defined by the inclined surface. In response to actuator displacement adjacent to and parallel to the elastic field, the inclined surface is oriented at an angle to compress the elastic field in a direction perpendicular to actuator displacement, thus providing a constant region of opposed, compressive force that is generally constant, rather than increasing with displacement distance.
Configurations herein are based, in part, on the observation that the human foot receives and transfers all forces generated from ambulatory activity, including walking, running as well as higher intensity athletics. Unfortunately, conventional footwear suffers from the shortcoming of little to no capability to temper or disperse the upward forces transferred to the ankle, legs and spine from the downward movement of the foot onto the walking or running surface. Many conventional shoes employ rigid materials including wood and hard rubber, and even running sneakers, promoted as adapted to handle the impact of running, employ only some form of foam or air cushioning. Despite these features, substantial loads are still transferred up the leg, particularly from the heel, which typically has proportionally less cushioning than the toe region based on the magnitude of the loads incurred. Accordingly, configurations herein employ a constant force heel spring which provides a mitigating counterforce to upward heel loads. The constant force distributes the received force over time so that a peak impact is “leveled,” avoiding a sharp peak force that causes orthopedic issues. In contrast, even with cushioning in conventional shoes, the load response is a spring reaction where the counterforce increases with distance, and still imposes a substantial peak force. The use of a constant force spring implemented as an elastic field against a constant displaced area absorbs peak forces with a constant counterforce rather than a variable force leading to a peak counterforce.
The foregoing and other objects, features and advantages of the invention will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
The description below presents an example of a footwear appliance, or shoe, for implementing the disclosed force mitigation device using a constant force, or substantially constant force spring structure for mitigating harmful transmission of downward forces or impact though shoe soles. The assembly including the constant force spring implements an elastic field approach where a counterforce is based on an area of the engaged elastic field, rather than an entire length of an elongated or contracted spring. The disclosed elastic field spring for exerting a constant force response is also applicable in alternate contexts without departing from the claimed approach.
The actuator 110 is adapted for displacement adjacent to and parallel to the elastic field 130. The inclined surface 124 is oriented to compress the elastic field 130 in the direction 126 perpendicular to actuator displacement 120. The displacement force 120 results from a downward force of the shoe sole surface 112 against a ground surface 111, and the elastic field 130 is disposed to exert a counterforce against the inclined surface 124 in response to the displacement force 120 exerted on the actuator 110. A linkage 117 and pedestal 119 may complete the force transmission path to the sole surface 112. On a downward stride resulting from running or walking, as the foot/shoe contacts the ground surface 111, the displacement force 120 transfers to the actuator 110 which travels upward, as the inclined surface 124 at the forward edge 114 of the actuator 110 movement forces and compresses the elastic field 130 based on the angle 152.
The elastic field 130 imposes a resistance to the displacement force 120 in a load region 160 defined by an area of the elastic field opposed from the inclined surface 124. In contrast to conventional approaches where a resilient or spring material is subject to increasing compression, the angle 152 results in a constant compression region 160 based on the area of the inclined surface as the elastic field 130 is attains a compressed depth 130′ or thickness. Accordingly, the compressing elastic field 130 defines a constant force spring as it transitions to the compressed 130′ state so that the counterforce remains substantially constant, rather than increasing tantamount to an impact peak or point as with conventional springs.
Since the area of the inclined surface 124 remains constant, the same volume of the elastic field 130 is being compressed at any given displacement, therefore the return force remains substantially constant. Displacement of the inclined surface 124 across the elastic field 130 therefore defines a constant force.
Referring to
While the system and methods defined herein have been particularly shown and described with references to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
This patent application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent App. No. 62/730,194, filed Sep. 12, 2018, entitled “DOWNWARDS ABSORBING AND UPWARDS ACCOMMODATING FOOTWEAR HEEL,” incorporated herein by reference in entirety.
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