Eagle Claw Product Proposal

Ossur Prosthetics

From: Peter Rubin (Senior Mechanical Engineer)
To: David Coe (Product Manager)
Subject: Funding for new prosthetic rock-climbing leg

Foreword

     It has been over a year since Ossur Prosthetics has started a new product line. At your request, our engineering team has looked into a number of possible product ideas. We recommend that Ossur Prosthetics pursue the development of the most promising of these concepts: a prosthetic rock-climbing leg for above-knee amputees. There is a significant need for this product, since many amputee rock climbers have difficulty climbing with their standard prostheses, which are often heavy, bulky, and poorly shaped for rock climbing.

Summary

     After interviewing experts in lower-limb prosthetics, biomechanics, and materials science, and observing amputee rock climbers in action, we generated a preliminary design that addresses its users’ needs. We propose to manufacture a temporary, task-specific replacement prosthetic leg comprised of a rigid, lightweight aluminum pylon connected to an aluminum foot with rubber gripping surfaces oriented to optimize the user’s ability to grip rock ledges. This memo details the need for this product and presents a plan for its initial design, test marketing, and prototyping. In order for us to undertake these preliminary stages, we ask that you authorize the appropriate funds.

Introduction

     The following section describes our most pertinent research on user groups and marketing strategies, and relates a typical use scenario. We then describe the design details and specific prototyping methods.

Users and Marketing Strategies

     Ossur has developed a reputation as a leading innovator in the field of prosthetic devices, but has concentrated mostly on prosthetics for the general user and recreational athlete who needs a multi-purpose prosthetic device to use in a variety of settings. But a prosthetic device with a broad range of functions cannot perform well in some specific activities. Consistent with Ossur’s plans for future growth based on users with specialized needs, as demonstrated by the Ossur Sprint Foot, our team has focused on rock climbing as an activity in which a temporary, specialized prosthetic device would be especially valuable. To our knowledge, this would be the first ever mass-scale manufactured rock climbing leg.

     There would be a receptive audience for this product. Currently, above-knee amputees who want to rock climb are impeded by the size, weight, and flexibility of their prosthetic devices, which are effectively designed for walking, but not for climbing. Some amputees have already attempted to create crude rock-climbing feet by sawing off the front half of their standard carbon fiber prosthetic foot. This solution is crude, but it is similar to our solution in that it provides additional stability by making the foot less flexible and shortens the distance of the lever arm between the toes and the ankle. Many news groups and magazines, such as InMotion magazine, target amputee athletes. These media not only confirm the fast-growing market for sports-specific prosthetic products, but would provide an inexpensive, precisely-targeted venue to advertise our product. Donating our rock-climbing device, entitled the Eagle Claw, to a few well-known skilled rock climbers would also provide a great public relations opportunity. Associating Ossur with high-performance products for athletes will likely enhance the Ossur brand name and benefit all of our prosthetic lines.

Use Scenario

     A typical user of the Eagle Claw device will be someone like Britton Caillouette, a 20-year-old amputee and rock climber. He was an avid rock climber until high school, when he was diagnosed with bone cancer in his left femur and his leg had to be amputated to stop the cancer from spreading. Britton is pleased with the performance his Ossur prosthetic leg with a hydraulic knee and a flexible carbon fiber foot for daily activities. This prosthesis allows him to walk, climb stairs, and even run. But when Britton goes rock climbing, the weight of the hydraulic knee makes his prosthetic leg heavy and cumbersome, without providing any corresponding benefit. Furthermore, his flexible foot, optimized for walking, is poorly-suited for gripping small rock ledges, because it bends upwards and slips off the ledge.

     Our Eagle Claw rock-climbing foot (see appendix A) solves each of these problems. It is lightweight, so it can be manipulated more easily, and it is rigid, so it will not bend and slip off the rock. The device attaches to the user’s upper leg using a small pyramid-shaped adapter that fits precisely into a hole on the outer thigh socket, and can be easily attached and detached. The other end of this adapter clamps onto a strong, lightweight hollow aluminum pylon, which attaches at the bottom to an aluminum foot via another tube clamp and a four-hole plate adapter. This adapter in turn connects to the foot, which we currently plan as having three talons (hence the name “Eagle Claw”) that end in chisel-shaped toes. The tip of each toe is covered with the same rubber used to resole rock-climbing shoes, to ensure maximum gripping action. The claw-shaped foot design enables the climber to grip small ledges to the front as well as diagonally and to the side.

Prototyping

     Perfecting the shape of this foot will be our biggest challenge. We plan to achieve an ideal shape through an iterative process of rapid prototyping, testing, and refining. For our first prototypes, we built a series of small wooden feet, and analyzed their ability to grip real rock ledges. We refined the geometry of most successful of these wooden prototypes, which featured three talons. From this geometry, we created a quasi-functional sheet metal prototype (see appendix B). We plan to manufacture subsequent functional prototypes using a three-stage process.

      First, a template of the foot will be cut out of plate aluminum (see appendix C). A band saw will be used to make the rough cuts and a mill will refine the shape. Second, the template will be bent to shape using aluminum fixturing blocks and a hydraulic press (see appendix D). Third, ribs will be TIG welded on the top and bottom of the bent template to add rigidity and strength. These ribs reduce the pressure on the foot and ensure that the material will not fail while being exposed to heavy and repeated loads (see appendix E).

     Every component of the leg will be made from aluminum because it is inexpensive and has a high strength-to-weight ratio. The foot template will be cut out of ¼”, 5052 aluminum plate. This alloy of aluminum was chosen because it is very ductile, unlike 6061, which is stronger, but would become brittle and crack if bent in the desired shape. The ribs will be made of 6061, since they are not designed to bend, and would benefit from the added strength. The foot and pylon will be hard anodized to provide a colored, satin finish and prevent the surface of the foot from scratching.

Conclusion

     The Eagle Claw rock-climbing leg can fulfill Ossur’s need for an innovative and profitable prosthetics product that will open new markets while reinforcing the company’s current image. The availability of this first prosthetic rock climbing leg would greatly improve the lives of its users. We are confident that we this project will be a success and we hope you choose to grant us funding so we can continue pursuing our research.