System Design Review

 Team Members: ◦ Pattie Schiotis – Team Manager (ME) ◦ Shane Reardon – Lead Engineer (ME) ◦ Dana Kjolner (EE) ◦ Robert Ellsworth (EE) ◦ Sam Hosig (CE) ◦ John Williams (CE) Faculty Guide: Dr. DeBartolo

 Introduction  Work Breakdown Structure  Customer Needs  Engineering Specifications  Functional Decomposition  Concepts  Component Benchmarking  Risk Assessment  MSD I Project Plan

 Lasting side effect of a stroke: foot drop ◦ Inability to dorsiflex the foot  Ankle Foot Orthotics (AFOs) currently used to aid dorsi-flexion. ◦ Passive devices don’t allow for movement when walking on ramps and stairs  Foot is always pointed upwards

 User will have no ability to either plantar-flex or dorsi-flex their foot  Side to side stability of the foot will be ignored  Worst case will be analyzed: ◦ 95 percentile male having heavy foot. ◦ Fast walker – gait cycle less than 1 second.  Device may not use air muscles as an actuation source

Primary Needs:Secondary Needs:  Safety  Portable ◦ Lasts all day without charging/refueling ◦ Lightweight ◦ Tolerable to wear all day  Reliable  Accommodates Flat Terrain  Accommodates Special Terrain ◦ Stairs ◦ Ramps ◦ Obstacles  Comfortable ◦ Aesthetically Pleasing  Durable ◦ Water Resistant ◦ Corrosion Resistant  Salt & Environment  Biocompatibility  Convenient ◦ Easy to put on and take off

Engineering Specification Number Engineering Specification Description Units of Measure Preferred Direction Nominal Value Method of Validation Stems From Customer Need s1torque on FootN-mUp ≥ ±3.0 TestFT1,2,4,ST1,5 s2 system response time (sensing terrain to actuating device) msdown<400TestST3 s4predicts step downyes/no-yesTestST1,2,4 s5predict flatyes/no-yesTestFT1,ST5 s7predicts ramp downyes/no-yesTestST1,2,4 s10 allowable range of motion between foot and shin degreesrange70 to 135TestFT1,3,CF8,9,ST1 s12untethered usage timehrs/stepsup 8 hrs or 3000 steps P1,2,D1 s17force to secure constraintsNdown< 80TestC4 s18force to remove constraintsNdown< 80TestC3 s23radius of edges/corners on AFOmmup0.5-S4,CF1,2 s24weight of entire devicekgdown ≤3 TestFT6 s28 Operates in environment temperature range °Crange to 37.8 Component Ratings D2 s31Minimum life until failurestepsup 5.5 million testD1

 Mechanical Locking Method Uses a solenoid to unlock the heel which allows the foot to drop.

 Mechanical Locking Method ◦ Mechanically restrict the foot from dorsi/plantar flexing while in the air. ◦ Use gravity to help the foot plantar-flex as needed (stairs/ramps) ◦ Methods: 1.Use a solenoid to unlock the heel which allows the foot to drop. 2.Use a brake to unlock the heel which allows the foot to drop. 3.Ratcheting Device attached to ankle

 Active Actuation ◦ Uses a linear actuator to force the foot into the proper position. ◦ Methods:  Solenoid  Piezoelectric  Power Screw  Hybrid  Power Screw with electric motor

 Hard Stop Two preset distances can be moved back and forth using a servo motor and screw.

42% 0.152H Fw If our actuator is 1.5” (3.3 cm) behind ankle joint: Anthropometric Data for male, 95 percentile: Stature=1.868 m Foot Weight=1.4 kg

θ=20° Dorsi-flexion: Plantar-flexion: Total stroke=3.61 cm In 0.4s, we need 9 cm/s

SolenoidElectro-MechanicalPiezoelectric Actuation Force 30 lbs22 lbs100N Stroke 1.1 cm>4.4 cmmicro-meters Speed <100 ms10 cm/s- Power Consumption 92V, 7.2 A (moving), 0.08 A (holding)12VDC, 5 A100 V

ProsCons Mechanical Locking Low Power Consumption Can hold the foot up in the event of an electrical failure Uses Gravity to position the foot Can only hold the foot in a position that it has been Needs a Large voltage spike to trigger the solenoid Active Actuation Can move the foot to any location needed Can be designed to hold the foot up under failure Large amount of energy required Slow response time Heavy Hard Stop Low Power Consumption Capable of counter-acting large amounts of plantar- flexion force Difficult to create failsafe Slow response time Does not reset it self when the toes need to be pointed up

Concepts ABCD Mechanical Locking Active Actuation Hard Stop Passive Device Selection CriteriaWeightRating Weighted Score Rating Weighted Score Rating Weighted Score Rating Weighted Score Safety20% Portable15% Reliable15% Accommodates Flat Terrain15% Accommodates Special Terrain15% Comfortable8% Durable8% Removability4% Total Score Rank 1432 Continue? YesNo N/A

 Bounces infrared light off terrain to determine distance  10 cm to 80 cm range  Worst case power consumption per sensor is kWhr  Output from -0.3 to +0.3 volts  Highly accurate within operational ranges  Low cost (~$15) 

A FarA NormalA Close B Far Mid Stride, Down Slope/ Stairs Mid Stride, Normal Terrain Mid Stride, Up Slope/ Stairs B Close Foot Planted, Down Slope/ Stairs Foot Planted, Normal Terrain Foot Planted, Up Slope/ Stairs Sensor A Sensor B Terrain

 Nonlinear response  Reflective ratio of materials is mostly irrelevant  Static position  Concerns about irregular terrain types  42

 Predicts what type of terrain we are walking on  Calculates where in the gait cycle we are  Has some modeling that improves performance of predictions NEED TO CHANGE  Need to be able to fully implement in C  Error checking for invalid states  Nothing is done at run-time

 Micro controller needs: ◦ Interface with two IR sensors and possible angle senor  ADC ◦ Control actuation method  PMW or Digital I/O ◦ Other considerations  Must run on battery power for at least 8 hours  Must be able to simulate system in “real time”  Must be able to fit on orthotic  Must be able to export data to sd card if needed

Power From Micro Controller and Sensors Device Time (Hours) Current (A) Voltage (V) Power (mWhr)Total Power (mWhr) IR Sensors Micro C.83.00E Total Power % Efficiency2894 Solenoid Power Usage for Option 1 Watts per stepTime per stepmWhr / step

IDRisk ItemEffectCause Likelihood Severity Importance Action to Minimize RiskOwner 1 Foot failing in down positionUser would trip and fall Sensor unable to detect terrain or send faulty readings 236 Software fail safe, if no data is sensed will fail in natural position Engineering Lead 2 Actuator malfunction 122 System free to move if actuator breaks Engineering Lead 3 Structural failure, orthotic unable to support equipment 133 Large enough factor of safety Engineering Lead 4 Spring Yielding/Buckling 122 Structural modification, mechanical prevented action Engineering Lead 5 Power supply 326 Before system runs out of power, lock in normal state. Warning signal included Electrical Engineers 6 Scheduled deadlines not met Timeline falls behind, other deadlines change Personal conflicts: time management, overloads schedule, illness 326 Communication among members to know each other’s schedules, understand critical path, seek help when needed Team Manager 7 Material acquisition delay Prototype cannot be built and tested Long lead times, parts not ordered on time 122 Contact with vendors, determine parts with long lead times, order by week 7 Team Manager 8 Incorrect material handlingOverload system capabilitiesMisuse of supplies 224 Responsible team members in charge of their components. Understand system capabilities and specifications Engineering Lead 9 Unable to meet customer specifications Project failure, unhappy customer Weight of device too heavy 236 Be cautious of component weights when creating detailed design Engineering Lead 10 Device contains sharp edges, harms the users 133 Ensure all points of contact will not harm user, no pressure points Mechanical Engineers 11 Memory overflowDevice would go into an error state Not enough memory on the micro controller and associated memory systems224 Ensure enough memory is available on micro controller Computer Engineers

ID Task Name Complete (%)Completetion Goal When Completed Issues/Comments 1 Define Project 2 Review customer needs90%10/2/2012 Review after concepts selected 3 Review customer specifcations90%10/2/2012 Review after concepts selected 4 Finalized functional decomposition100%9/21/ Determine work breakdown structure100%10/5/20129/28/2012changes after systems review 6 Observe walking patterns at naz clinic100%9/24/ Concept Generation 8 Create benchmark matrix90%9/28/ Define components100%9/14/20129/28/ Establish system possibilities100%9/14/20129/21/ Create system comparions (Pros and Cons)100%9/28/201210/2/ Develop Proposed Design 13 Assign team member specific jobs100%9/21/2012 Proposed design approval 14 Develop psedeocode100%9/28/ Review previously developed sensor code100%9/28/ Feasibility analysis80%10/2/ Compile Systems Design Review 18 Schedule review100%9/25/20129/28/ Create risk assessment100%10/2/ Create review report out95%9/28/ Develop project schedule90%10/2/ Part Selection 23 Select components40%10/12/ Create budget breakdown0%10/12/2012 Need component specifications 25 Detail component information (specs, vendor)5%10/19/ Purchase parts0%10/26/2012 relient on specs Detailed Design 28 Create BOM0%10/19/ Update risk assessment on going 30 Verify design output0%10/23/ Finalize system architecture0%10/16/ Prepare drawings, schematics, and flow charts0%10/26/ Identify critical design path0%10/12/ Document design changes (if any)0%11/10/ Test Plan 36 Determine component testing0%10/26/ Create testing guide/SOP0%11/3/ Estimate resource requirements0%11/10/ Create data collection sheets0%11/10/ Additional Tasks 41 Update EDGE on going

1. Scope of project is to design a modified AFO that includes:  Energy storage medium  Foot rotation device  Terrain sensing system  Microcontroller 2. We will focus on a detailed design following the “Mechanical Locking Mechanism” concept.