P15001: Soft Ankle-Foot Orthotic
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Problem Definition

Table of Contents

Project Definition

Foot drop is a neurological disorder which impairs the ability of an individual to dorsiflex the foot (i.e., point the toe upward). This condition is a common side effect of a stroke, ALS, Multiple Sclerosis, or a peroneal nerve injury. Patients who experience Foot Drop utilize an assistive device known as an ankle-foot orthotic (AFO) which provides a stable and comfortable support for their foot and ankle and thus mitigates the condition effects. Current AFO’s are bulky, rigid, and disrupt the user’s natural gait by providing assistance at all times, regardless of need. An active AFO will provide users with assistance only during appropriate times in the gait cycle.

The specific goal of our team is to incorporate previous work done, including using a McKibben muscle and a terrain sensing system into an untethered AFO. It also should have an aesthetically pleasing flexible exoskeleton made from allergy conscious materials which comfortably fits into a user’s existing footwear. The exoskeleton need to be integrated with the actuation device, sensing system, and microcontroller. The AFO must also must be capable of applying torque to and rotating the user’s foot and should be designed to endure an entire day use untethered. The sensors and microcontroller system should incorporate the existing terrain sensing system as well as implementing more suitable heel strike sensing. The resulting design and prototype must follow the safety standards set forth by the Institutional Review Board as well as the ASME Boiler and Pressure Vessel Code.

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Project Summary

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Stakeholders

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Use Scenarios

General Use Scenario

Daily Use Scenarios

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Customer Requirements

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Customer Interviews

Interview Date Interview Subject Interview Questions Interview Notes
August 28, 2014 Dan Higgins August 28 Questions August 28 Notes
September 2, 2014 Dr. Elizabeth DeBartolo September 2 Questions September 2 Notes
September 4, 2014 Dr. Kathleen Lamkin-Kennard September 4 Questions September 4 Notes

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Engineering Requirements

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House of Quality

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Critical Design Challenges

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Constraints

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Concerns and Risks

Team Dynamics • Creating and meeting deadlines • Team’s response to first serious problem or crisis • Team overdesigns the product creating an unfeasible design (e.g. addition of unnecessary functionality) and thus loses focus on the things that are most important

AFO Functionality • Too soft and thus not strong enough to provide the necessary force • AFO doesn't allow usage over obstacles • Creating an AFO that can be put on/taken off with only 2 people, including the patient • Inability to display to an external monitor • Muscles on the front of the leg may sacrifice working life

AFO Fit • Unable to fit orthotic into the user's normal shoe • Accommodation of a wide range of foot sizes • AFO slipping down the leg

AFO Comfort • Overheating of leg • AFO heavier than desired • Ability to provide necessary rigidness without sacrificing comfort

Compressed Air • The amount of air that the prototype will be able to hold will not be enough to last an entire day of use • High level of noise

McKibben Muscle(s) • Unable to attach McKibben muscle to an soft exoskeleton • Ability of air muscles, attached to front of AFO, to provide enough force to raise foot • Range of motion that can be produced by muscle

PCB Board • Not cost effective • Not timely to build • Too large

Arduino Board • Not able to drive the muscles

Battery • Ability to find a light weight and low cost battery that can provide an entire day’s use

Safety • Ensuring AFO does not hurt the patient during downtime • Reliability and safety of manual switch, especially for driving and stopping (and ease of use) • Client gets injured and needs to take off AFO • AFO rusts and corrodes • AFO breaks during usage • Client experiences circulation cutoff • Too many wires hanging off of user

Terrain Sensing System • Unable to identify stairs • Sensors spike • Inability to decrease the size of system • Terrain sensing start up and stopping • Terrain prediction not sensed • Infrared sensor functionality

Heal Strike • Finding a more reliable source for detecting heal strike. • Is the current method of measuring foot-strike the best method and the method we want to use?

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Research and Benchmarking

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References

Past Projects

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Problem Definition Review

The following presentation was given on September 11: Presentation or PDF

The notes that were gathered from this review lead to the following action items.

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Home Planning & Execution Problem Definition Systems Design Subsystems Design Detailed Design Gate Review
MSD I
Build Preparation Build & Test Integrate & Assemble System Validation System Verification Final Review
MSD II