Download presentation
Presentation is loading. Please wait.
1
Active Ankle-Foot Orthotic
Air Muscle Tethered Team P13001 Nathan Couper, ME Bob Day, ME Patrick Renahan, IE Patrick Streeter, ME This material is based upon work supported by the National Science Foundation under Award No. BES Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.
2
Agenda Project Description Proposed Solution
Assumptions and Project Scope Functional Decomposition Customer Needs/Specifications Proposed Solution Physical Decomposition Concept Generation and Feasibility Morphology Chart Concept Screening Concept Selection Air Muscle Assessment Pneumatic Feasibility Risk Assessment Proposed Schedule Questions and Criticism
3
Description of Problem
Aiming to design a device that mechanically assists patients suffering from foot drop Foot Drop Caused By nerve damage in the lower leg Strokes, ALS, MS, Car Accidents, Other Trauma Loss of muscle control prevents patient from dorsi-flexing the foot while walking, as well as extending the toes AFO’s are current solution Generally rigid support that lifts the foot to a proper angle Elastomer Hinge Does not allow for smooth gait cycle Difficult to go up inclined surfaces, up/down stairs, and on uneven terrain Depending on AFO, Plantar-Flexion is not allowed
4
Assumptions and Project Scope
Patient maintains zero muscle control over dorsi-flexion, plantar-flexion, and toe extension This product is designed to be used on a treadmill in a clinical setting; but can be incorporated into an aquatic setting Tethered System The elastomer can be adjusted on a patient basis so that when the patient’s full weight is applied on the AFO, the foot rests at angle slightly above 90 degrees with respect to the patient’s lower limb Designed patient has the ability to use a dorsi-flex assist AFO without receiving tone-lock spasms For calculations: data is from the 50th percentile man 2D system no resistive forces/friction associated with the joints a normal gait cycle time of 1.2 to 1.5 steps per second is assumed
5
Functional Decomposition
6
Customer Needs Red: Rated 7-9
Directly relates to project purpose or patient safety Yellow: Rated 4-6 Relates to lower priority patient interaction, and periphery project goals Green: Rated 1-3 Not critical to solving primary issue
7
Project Specifications
General Breakdown: Sensory Specifications Movement Specifications Force Specifications Safety Specifications User Equipment
8
Agenda Proposed Solution Project Description
Assumptions and Project Scope Functional Decomposition Customer Needs/Specifications Proposed Solution Physical Decomposition Concept Generation and Feasibility Morphology Chart Concept Screening Concept Selection Air Muscle Assessment Pneumatic Feasibility Risk Assessment Proposed Schedule Questions and Criticism 8
9
Proposed Solution Air muscle powers plantar flexion
Elastomer passively causes dorsi-flexion Easier and slimmer packaging
10
Physical Decomposition
Tethered Ankle-Foot Orthotic AFO (the orthotic itself) Air Regulation System Molded Case Air Muscles Foot Bed Calf Cradle Bladder Sheath Computer Control System Hinge Straps Clamps Tendons Fittings Regulator Air Source Tubes Air Regulation Controls Control Outputs Control Inputs Elastomer Hardware (screws/structure)
11
Agenda Concept Generation and Feasibility Project Description
Assumptions and Project Scope Functional Decomposition Customer Needs/Specifications Proposed Solution Physical Decomposition Concept Generation and Feasibility Morphology Chart Concept Screening Concept Selection Air Muscle Assessment Pneumatic Feasibility Risk Assessment Proposed Schedule Questions and Criticism 11
12
Morphological Design Considerations
AFO actuation Concept What motions are air muscles responsible for? Air Muscle Connection How are air muscles attached to AFO? Tendon Design How does force from Air Muscle actuate AFO? Air Supply How will air muscles be filled and regulated AFO Construction Type What construction style will the AFO have? Traction What will keep the AFO from slipping?
13
A B C D AFO actuation Concept (Reference) Passive Dorsi Assist
A B C D AFO actuation Concept (Reference) Passive Dorsi Assist No Plantar Assist Passive Dorsi Assist Active Plantar Active Dorsi Passive Plantar Air Muscle Connection No Air Muscle Rigid Anchor to AFO Cable Attachment AFO snaps into Air muscle Construct Tendon Design Direct mount Cable and housing Steel leader (see Crab) Air Supply Compressed air tank Compressor Regenerative automatic foot pump Construction Type Hard shell (hinged) Soft shell Fully rigid hinge- Less Hybrid (hard foot bed, soft calf sleeve) Traction Shoe reliant Knurled AFO bottom Rubberized AFO Discuss how AFO actuation concept is the biggest design consideration here, and really drives how this device is going to interact with a person walking. Compressor was thrown out because of noise issues (too loud). Regenerative foot pump was thrown out because this would be a senior design project by itself. Non-hinged AFO designs were thrown out because it defeats the purpose of the project (nothing for air muscles to do).
14
A B C D AFO actuation Concept (Reference) Passive Dorsi Assist
A B C D AFO actuation Concept (Reference) Passive Dorsi Assist No Plantar Assist Passive Dorsi Assist Active Plantar Active Dorsi Passive Plantar Air Muscle Connection No Air Muscle Rigid Anchor to AFO Cable Attachment AFO snaps into Air muscle Construct Tendon Design Direct mount Cable and housing Steel leader (see Crab) Air Supply Compressed air tank Compressor Regenerative automatic foot pump Construction Type Hard shell (hinged) Soft shell Fully rigid hinge- Less Hybrid (hard foot bed, soft calf sleeve) Traction Shoe reliant Knurled AFO bottom Rubberized AFO We feel that the passive dorsi assist device does a really good job solving foot drop as an independent problem. Dr. JJ said it was the best device for solving foot drop, if she could put all her patients in one she would. Because of this we felt that the performance of the passive dorsi assist AFO was sufficient for our reference design.
15
Performance Metrics No sharp protrusions
Hold up foot when stepping forward/resist foot slap Secure foot in orthotic Integration of terrain sensing system Allow for both plantar and dorsi-flexion of the foot Ease of attachment/customization Ease of customizable programming per individual Fit customization to individual Installation/ease of use These are the performance metrics we used to grade our morphological designs. A couple I want to touch on. The No Sharp Protrusions is probably a more specific consideration than is usual for this type of review, but after talking to Dr. JJ we felt it was necessary to include. Dr. JJ informed us that many of those who lose control of the extremities also lose sensation, so they cant feel damage being done by the AFO. This can lead to severe pressure sores that can take months to heal. This is obviously a major setback in the rehabilitation process. Because the patient cannot be used as a safeguard against discomfort in this case we wanted to put this in there as part of our morphological analysis. The other metric I want to mention is the ease of customizable programming per individual. This is in regards to integrating terrain sensing, and individual gait analysis for controlling foot movement. In the analysis this really came down to how many air muscles were going to be in use, and how many movements they were going to control.
16
A B C D AFO actuation Concept (Reference) Passive Dorsi Assist
A B C D AFO actuation Concept (Reference) Passive Dorsi Assist No Plantar Assist Passive Dorsi Assist Active Plantar Active Dorsi Passive Plantar Air Muscle Connection No Air Muscle Rigid Anchor to AFO Cable Attachment AFO snaps into Air muscle Construct Tendon Design Direct mount Cable and housing Steel leader (see Crab) Air Supply Compressed air tank Compressor Regenerative automatic foot pump Construction Type Hard shell (hinged) Soft shell Fully rigid hinge- Less Hybrid (hard foot bed, soft calf sleeve) Traction Shoe reliant Knurled AFO bottom Rubberized AFO As discussed previously we feel that AFO actuation concept is the biggest design decision here. We started off with looking at an active-active design.
17
Passive Dorsi Assist No Plantar Assist
Function/Component Reference 1 2 3 AFO actuation concept Passive Dorsi Assist No Plantar Assist Active Dorsi Assist Active Plantar Assist Air Muscle Anchor No Air Muscles Cable Attachment Rigid Anchor to AFO AFO snaps into air muscle construct Tendon Design Cable and housing Air Supply Compressed air tank AFO Construction Type Hard Shell (hinged) Hard shell (hinged) Traction Shoe reliant No sharp protrusions - + Hold up foot when stepping forward/resist foot slap Secure foot in orthotic Integration of terrain sensing system Allow for both plantar and dorsi-flexion of the foot Ease of attachment/customization Ease of customizable programming per Individual Fit customization to Installation/Ease of use Net -2 -3
18
A B C D AFO actuation Concept (Reference) Passive Dorsi Assist
A B C D AFO actuation Concept (Reference) Passive Dorsi Assist No Plantar Assist Passive Dorsi Assist Active Plantar Active Dorsi Passive Plantar Air Muscle Connection No Air Muscle Rigid Anchor to AFO Cable Attachment AFO snaps into Air muscle Construct Tendon Design Direct mount Cable and housing Steel leader (see Crab) Air Supply Compressed air tank Compressor Regenerative automatic foot pump Construction Type Hard shell (hinged) Soft shell Fully rigid hinge- Less Hybrid (hard foot bed, soft calf sleeve) Traction Shoe reliant Knurled AFO bottom Rubberized AFO Discuss how AFO actuation concept is the biggest design consideration here, and really drives how this device is going to interact with a person walking. Compressor was thrown out because of noise issues (too loud). Regenerative foot pump was thrown out because this would be a senior design project by itself. Non-hinged AFO designs were thrown out because it defeats the purpose of the project (nothing for air muscles to do).
19
Function/Component Reference 4 5 6 AFO actuation concept Passive Dorsi Assist No Plantar Assist Active Plantar Assist Air Muscle Anchor No Air Muscles Cable Attachment Rigid Anchor to AFO AFO snaps into air muscle construct Tendon Design Cable and housing Air Supply Compressed air tank AFO Construction Type Hard Shell (hinged) Hard shell (hinged) Traction Shoe reliant No sharp protrusions - + Hold up foot when stepping forward/resist foot slap Secure foot in orthotic Integration of terrain sensing system Allow for both plantar and dorsi-flexion of the foot Ease of attachment/customization Ease of customizable programming per Individual Fit customization to Installation/Ease of use Net 3 2
20
Function/Component Reference 7 8 9 AFO actuation concept Passive Dorsi Assist No Plantar Assist Active Plantar Assist Air Muscle Anchor No Air Muscles AFO snaps into air muscle construct Cable Attachment Tendon Design Cable and housing Air Supply Compressed air tank AFO Construction Type Hard Shell (hinged) Hard shell (hinged) Soft shell Hybrid Traction Shoe reliant Rubberized AFO bottom No sharp protrusions + Hold up foot when stepping forward/resist foot slap - Secure foot in orthotic Integration of terrain sensing system Allow for both plantar and dorsi-flexion of the foot Ease of attachment/customization Ease of customizable programming per individual Fit customization to Installation/Ease of use Net 3 2
21
Morphological Design Results
AFO actuation Concept Passive dorsi assist, active planter assist Air Muscle Connection Cable attachment Tendon Design Cable and housing Air Supply Compressed air tank AFO Construction Type Rigid construction with dorsi assist hinge Traction Shoe dependent
22
Elastomer Force Variation
Performed to see how resistance of elastomer varies over AFO displacement at the ankle joint To obtain resistance values for the elastomer Case specific, performed using AFO in front of you
23
Ankle Linear Force Comparison
Ankle Free-Body Diagram We developed our model based off of a quasi-static analysis due to the fact that the forces found through the dynamic analysis will not be as great as those found in the quasi-static analysis In the dynamic analysis the foot will limit the effect of the elastomer as the momentum will counteract the force that the elastomer applies on the ankle We will do a complete dynamic analysis of the gait cycle for the systems level design review Comparison of necessary forces/torques at each point in gait cycle Let us compare forces from air muscles to those in normal gait cycle Data from military database Discuss FBD 5th percentile female, 50th percentile male, 95th percentile male
24
Air Muscle Extension Data
Shows muscle size is in correct range May need larger muscles Source: Senior Design Project P12029
25
Air Muscle Force Data Source: Senior Design Project P12029
Not a full sweep of force vs pressure or extension More data will be helpful In correct range Source: Senior Design Project P12029
26
Air Supply Concerns Instantaneous Flow rate Stored Energy
Air muscle filling Stored Energy Size of supply and lines required Tank filling cost/convenience Solenoid orifice restriction Size of Solenoid required
27
Transient Muscle Filling
Main factor is orifice size in the solenoid and muscle size Desire .1s fill time minumum Requires 11.7 in3/sec (0.4 CFM) Max flow through .125” orifice at 60psi is approximately 12.7 in3/sec Near the maximum, may require a slower fill time or larger solenoids. Must be examined in detailed design closely Worst case scenario, will likely desire slower fill time Rough calculations just to show plausibility Regulator capability is a concern Loss from fittings and lines also a concern Testing is in order
28
Continuous supply Low continuous air usage
48ci 3000psi tank = 2050 steps or 3.2km 15 Gal 150psi air compressor = 11.8km Assuming 1 muscle event per 2 steps and .8m per step Requirements are reasonable and do not likely pose an issue Patients not likely to do more walking than this Low air usage = low cost/high convenience
29
Agenda Risk Assessment Project Description Proposed Solution
Assumptions and Project Scope Functional Decomposition Customer Needs/Specifications Proposed Solution Physical Decomposition Concept Generation and Feasibility Morphology Chart Concept Screening Concept Selection Air Muscle Assessment Pneumatic Feasibility Risk Assessment Proposed Schedule Questions and Criticism 29
31
7 Inadequate material durability Failure of selected materials in differing environments Poor material selection/analysis 2 4 Over-engineer the materials used in the AFO device and attachments Nate Couper 8 Completion of work within scheduled times Ladder-effect of other work getting pushed behind, or work-overload at the end of the quarter Poor project planning and management 1 Continually update project schedule, and meet bi-weekly at minimum Pat Renahan 9 Unbalanced distribution of work load Different team members carrying the majority of the workload at different points during the design process Poor distribution of workload and poor project management Discuss workload and time commitments from the previous week at bi-weekly meetings 10 Completing the project within the specified budget Inability to continue to fund the project through completion Poor project management and inadequate budget calculations Develop an in-depth budget, and continually update it as progress continues to be made 12 Over simplifying the analytical model Inadequate supply of power or inadequate material selection due to assuming certain forces negligible Desire to reduce needed calculations and oversimplifying to make calculations easier Work in sub-teams of two or greater to allow for a checks and balances system for calculations 13 Keeping the noise level of the air muscle system below 60 dB Uncomfortable surroundings in the clinical setting Inadequate muffling of the pneumatics system Implement a muffler system for the pneumatics that reduces the noise as much as possible maintaining minimal size and mass, and avoiding negative effects on the pneumatics system Bob Day Likelihood scale Severity scale 1 - This cause is unlikely to happen 1 - The impact on the project is very minor. We will still meet deliverables on time and within budget, but it will cause extra work 2 - This cause could conceivably happen 2 - The impact on the project is noticeable. We will deliver reduced functionality, go over budget, or fail to meet some of our Engineering Specifications. 3 - This cause is very likely to happen 3 - The impact on the project is severe. We will not be able to deliver, or what we deliver will not meet the customer's needs.
32
Plan B Actions (for those with importance rating of 4 or higher)
Failure of the device while air muscles are activated Allow for the air system to be easily disconnected (quick connects) Allow for the air system to be easily shut-off in case of an unexpected design failure Pressure source attachment point failure Allow for the air muscles to be quickly connected to the AFO by a commonly used material (zip ties) Supply the clinic/setting with spare muscle assemblies Popping the pressure-fed air muscles when too little or too much force is applied Supply the clinic/setting using this device with spare air muscle assemblies Inadequate material durability Tendon wire stretching Develop a few separate feasible options for tendon wire materials NOTE: Due to the clinical setting of our patients, these actions are not of much concern as the patient is in a safe environment where the device can be easily manipulated and fixed NOTE: Due to the clinical setting of our patients, these actions are not of much concern as the patient is in a safe environment where the device can be easily manipulated and fixed
33
Agenda Proposed Schedule Project Description Proposed Solution
Assumptions and Project Scope Functional Decomposition Customer Needs/Specifications Proposed Solution Physical Decomposition Concept Generation and Feasibility Morphology Chart Concept Screening Concept Selection Air Muscle Assessment Pneumatic Feasibility Risk Assessment Proposed Schedule Questions and Criticism 33
34
Project Schedule Upcoming priority deadlines:
Fall Quarter Week 9: Detailed Design Review Reference EDGE website for working, detailed project schedule: Planning and Execution – Project Plans and Schedules – “Schedule of Action Items” Next major deliverable = detailed design review in week 9
35
Questions or Comments?
Similar presentations
