Phase Planning
Build & Test Shared Vision
Our vision for week five is to finalize the design and begin building to have an initial prototype completed and demonstrated for our end-of-phase review.Functional Demonstration:
Electrical- The electrical team will demonstrate the following during our phase 2 design review:
- Soldered PCB board
- Data Collection
- Heel strike leading to muscle articulation
Mechanical- The mechanical team will demonstrate the following during our phase 2 design review:
- Working model simulation
- Actuate attached muscle
- Achieve foot lift
- Adequate support provided by upper brace
Additionally, our team plans to complete the following
tests by the time of our end-of-phase review
Tests to be performed:
Electrical:
- Short-circuit test on PCB board
- Regulation test for PCB board
- SD card communication
- To-board-communication
- Boot loader and sketch upload
Mechanical:
- Foot lift
- Integrated strain
- Extended use strain
- Comfort
- Slow-motion deflection video, as required
Engineering Requirements
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Engineering Fruition Plan
Engineering Fruition Plan
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Completed Tests
Dorsiflexion Mobility: Lift Test
OverviewDuring this phase, a lift test was completed to determine the angle range at which the foot is lifted by the actuation of the McKibben Muscle as well as determine the amount of deflection experienced by the upper muscle attachment piece during muscle actuation.
Procedure(s):
Test
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1. Have volunteer sit on table top with their right
foot hanging freely
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2. Place the AFO brace on volunteer’s foot
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3. Attach the McKibben muscle to the brace
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4. Place yellow indicators near user’s heel,
arch, and on brace near upper strap
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5. Set up and start the video recording
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6. Actuate the muscle using the Solenoid- complete this
step 5 times
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7. Stop the video recording
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8. Remove the device from the volunteer’s leg
Data Analysis
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1. Import the recorded video in Tracker (video tracking
software)
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2. Create tracking points using the yellow indicators
on the brace
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3. Use the protractor measure function to find the
ankle angle (foot relative to leg)
- 4. Copy ankle angle data from Tracking Software and put into Excel document
Setup:
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Results:
- Angle Results
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- The foot lift angle range is between -20.9 and -34.5 degrees
- The foot lift angle range during a natural gait cycle is between -8.2 and -38.6 degrees
- DifferenceNaturalGait: 30.4 degrees
- DifferenceDevice: 13.6 degrees
- Deflection Results
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Video:
Foot Lift Test Tracker Video
Conclusion:
- The difference between delta theta of natural gait data and delta theta achieved by our device is 16.8 degrees
- Average vertical displacement experienced by the Upper Muscle Attachment piece is approximately 0.35 inches.
Next Steps:
- Discuss ways to minimize the upper muscle attachment deflection during muscle actuation.
- Implement chosen solution and repeat test.
Extended Use Test Stage 1
OverviewThis test is an extension of the lift foot integrated test. The extended use test was designed to subject the integrated mechanical components of the AFO to extended use testing to determine performance and reliability over time.
Procedure(s):
Test
The procedure for stage one of the extended use test is
essentially the same as that of the lift foot test with
the additional step of actuating the McKibben air muscle
a total of 100 times and noting lift measurements and
changes over time, if any.
Post Test
In addition to the extended use test an experimental post
test was performed to mimic a worst case scenario. In the
post test, the user stretched their toe downward as far
as they could while the muscle was flexed. Following this
worst case situation, the basic foot lift test was
performed again in order to quantify the impact that the
worst case slippage had on AFO performance. Tracker was
again used to mine data from the post test.
Results:
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Extended Use Test S1 Video
Conclusion:
Test: Plots indicate no adverse effects from extended use with the current brace. Post test: Permanent deflection is possible with the current brace resulting in adverse effects on AFO performance.
- Plots from the initial test indicate no adverse effects from extended use given the current brace.
- The post test revealed that permanent deflection is possible with the current brace and the resulting effect on AFO performance is negative.
Next Steps:
- Implement redesign for upper brace strap.
- Complete stage two extended use testing
Extended Use Test Stage 1 Report
Comfort and Application
During this phase, 2 additional team members wore the AFO. Each member was asked to apply the device onto their right foot. Once the device was secure, the McKibben muscle was actuated several times. At the end of the test, both individuals were asked to complete a survey. Their completed surveys are shown below.
Survey
1.) Please rate the comfort of this device by circling
one of the numbers (1-10) on the scale below.
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2.) Are there specific parts/areas of the device that
make it uncomfortable to wear? Please be specific and
feel free to offer suggestions for improvement.
Results
Average Comfort Rating: 1
Problem Tracking
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Failure Modes
Budget Tracking
Our team has made several purchases thus far. Our budget tracking document displays these purchases in an organized manner as well as the total prototype cost thus far.
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Budget Tracking Spreadsheet
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Mechanical Build
Component Housing Redesign
Motivation
After the MSD II, week 2 progress review and more discussion amongst the team, it was determined that the lower component housing, along with the associated parts, needed redesigned to provide better functionality to our design. The old design was not easy to integrate with the PCB board, nor did it provide appropriate ingress protection for our electrical components. The lid for the PCB board cavity was redesigned, and a second lid for the IR sensor cavity was designed. Pictures of the current assembly design are as follows:
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The individual part redesigns and details are as follows:
Lower Component Housing
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In View 1, showing the PCB board cavity:
- Bosses added to base of the cavity so the PCB board is not directly sitting on the base of the cavity, but rather slightly elevated
- Overall depth of the cavity decreased. It is important the wires from the PCB board connector exit the housing at a downward angle, not upward, and the shallow cavity ensures this.
- O-Ring groove removed and added instead to the lid for the cavity.
- Channels for the wires to exit the cavity added. These channels are sized perfectly for the wires to leave the cavity, provided little room for water to enter. Also, these channels are flush with the top of the part, allowing the O-Ring to nearly completely seal these channels.
- Channels for wires flush with top of part for ease of assembly as well; connectors can now be used and placed in the cavity without removing soldering.
- Holes to mate lid to part are sized to fit threaded inserts for plastic to minimize threading into the plastic.
In View 2, showing the PCB board cavity:
- Bosses added inside the cavity to allow lid to seal the cavity around the IR sensor.
- Holes in bosses sized to fit same threaded inserts used for PCB board cavity lid.
PCB Board Cavity Lid
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In View 1, showing the top of the lid:
- Overall thickness of the lid increased significantly, creating a clamshell-like design.
- Countersunk thru holes added to ensure no screws are protruding from the edges of the component housing assembly.
In View 2, showing the mating side of the lid
- O-Ring groove moved to the lid to allow for wire channels on the component housing. Groove is still sized according to specifications for our O-Ring and will provide the same crush seal around the cavity.
- Because the depth of the cavity was decreased, a cavity was added to the lid to provide room for PCB board and connections to fit into the cavity.
IR Sensor Cavity Lid
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- A lid was added to the IR sensor cavity as well. Previously, no lid was present, and the ingress protection code specified in our engineering requirements would not be met. This new lid designs ensures propr protection to meet our requirements while still allowing IR sensor functionality.
In View 1, showing the top of the lid:
- O-Ring groove added to allow for an O-Ring to seal the connection between the inner walls of the cavity and the outer walls of the lid. Calculations are detailed below.
- Countersunk thru holes added to ensure no screws are protruding from the edges of the component housing assembly.
- Countersunk holes also ensure IR sensor functionality, as the screws will not interfere with the signals being input and output from the sensor.
- Two thru holes designed to mate directly to our IR sensor in the correct orientation. The holes are designed for a very tight slip fit to ensure as little gap for damaging matter to enter the cavity as possible.
In View 2, showing the bottom side of the lid
- Groove cut into the base of the lid to sit directly on the upper-most surface on the IR sensor. This will help ensure proper placement.
- Overall depth of lid is designed so, when sitting flush on the bosses on the inside of the cavity, the outside of the lid will be flush with the edge of the component housing, with the IR sensor protruding slightly.
Associated Documents
PCB Lid O-Ring ReportIR Lid O-Ring Report
Slow Motion Deflection
Motivation
The reason for this test is to find the approximate amount of deflection required by an air muscle based on data taken from a slow motion video.Procedure
A camera was placed near a treadmill and video footage (hehe:) was taken while walking slow on a treadmill with the foot rig. The rig is designed to keep tension on the knot in order to take up the slack during the gait cycle to find the deflection required of the air muscle.
Tracker software is available as a free download and was used to mine data from the video footage. Key points were selected on the rig, namely:
- Top of the protractor
- Bottom of the protractor
- Knot
- Back of Heel
- Arch of foot (near toe)
- Back of calf
These points were tracked manually and visually frame by frame during a gait cycle.
Video
Slow Motion Deflection Video
Results
The data from the video required some analysis in order to find useful results. The length and angle between the bottom of the protractor and the knot as well as the length and angle from the top of the protractor and the knot were measured in tracker. After trigonometric manipulation both sets of lengths and angles were resolved into the relative vertical distance between the bottom of the protractor and the knot. The results can be seen in Figure 2. Due to poor resolution in the video, the latter portion of the gait cycle was unreliable.
Conclusions
The strain requirement of 1.0 inche seems to be appropriate for our AFO. This test was based on a level slow terrain and required strain may still possibly be greater on stairs or other terrain. The ankle angle data from our tests is also not dissimilar from scientific data.
More details including the ankle angel data analysis and
comparison to Posture data can be found in the
Slow Motion Deflection Report
Working Model
Motivation
As part of the solution for the problem tracking item "Muscle strain will not provide required displacement" developing a Working Model 2D simulation became a priority for this phase. The potential benefits are twofold: modeling a real gait cycle with accurate foot dimensions could help us determine the amount of deflection required by the muscle and such a model could also be helpful in visualizing the project as a whole. This method involved simulating a virtual kinematic procedure using Working Model. This software can model kinematic processes and measure deflection and rotation.Procedure
Using an adjustable switch, the amount of force provided by the muscle was varied in such a way as to mimic data from a Gait & Posture article [Bovi G., Rabuffetti M., Mazzoleni P., Ferrarin M, 2010, “A multiple-task gait analysis approach: Kinematic, kinetic and EMG reference data for healthy young and adult subjects”, Gait & Posture].With the data mimicked by the switch, it is possible to measure the deflection required by the muscle without using hardware. In order to get accurate measurements, proper foot and leg dimensions must be used. This particular simulation did not use exact measurements, but was successful in visualizing how much flexion occurs during a slow gait cycle.
Video
The actual footage of the working model simulation from which the data above was taken is captured in the video below.Working Model Video
Conclusions
The working model software has a steep learning curve. It has the potential to help determine the amount of deflection required by the muscle but this would require a significant amount of time. Since the integrated prototype is ready for testing and since the slow motion deflection test has already demonstrated low strain requirements, continuing Working Model simulation seems largely inefficient.Recommendations
If this simulation was pursued further, the following recommendations would apply:- make model dimensionally accurate and find accurate foot weight and dimensions for the smallest 5% female to largest 95% male samples
- adjust constraints so that the deflection can be measured where the muscle meets the tether
- model going upstairs and downstairs based off of posture data, the current simulation only models levelground
- add on upper leg simulation to allow visualization to be more realistic
Lower Attachment Strap
Control Diagram
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Upper Brace Design Modifications
Motivation
After assembling our phase 2 prototype for our AFO, it became evident that the upper brace would need to be modified to reduce the additional strain that was being absorbed by the brace. During MSD I testing, the upper brace was tested and it was determined that the brace would not become detached from the leg when the muscle was articulated, but it was not clear until the prototype was assembled that the muscle stretched the brace. Because the brace is elastic, the material stretched when the muscle was articulated. Also, because the strap was not sewn on to the front of the brace, but rather the back, and the top of the brace was slipping downward when the muscle was articulated.Design Modification Proposal
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Design Modifications:
- The strap that is attached to the top of the upper brace will be resewn so the strap is attached directly to the front of the brace above the muscle base, rather than attached in the back of the brace. This will prevent the slippage at the top of the brace.
- Inelastic material will be added between the base of the muscle and the top of the brace. This will prevent the stretching in the elastic material as much as possible.
Conclusions
- These design modifications are proposed to eliminate both sources of additional strain found in the upper brace.
- Once these modifications are made, the muscle will be articulated to see how much the strain in the upper brace has been reduced, as well as how much more strain the muscle gained while lifting the foot.
Associated Documents
Upper Brace Modification PlanIntegrated Prototype
Foot Lift Tests
Motivation
One of the main goals of this phase was to achieve mechanical integration and foot lift using the actual muscle to lift the foot.Video
Preliminary Foot Lift Tests Video
Conclusions
Although formal measurements are yet to be taken, the preliminary foot-lift tests on 2/17/15 achieved comfortable foot-lift despite some apparent slippage in the upper brace. Upper brace design modifications may be necessary to address the apparent slippage.Electrical Build
Schematics
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Tested Systems
- Power Input: Power connection and 5V regulator
- Power LED
- System Clock: 16 MHz microcontroller clock
- TO_AFO Connection
- TO_SOLENOID: Two drive circuits for the Solenoid control as well as a ground connection
- Hardware Low-battery system
- Audio System
Soldered Systems
- SD Card: Level shifter and MicroSD card shield as well as the 3.3V regulator
Unsoldered Systems
- TO_FLOW_SENSOR: Power and ground connections as well as an ADC input to read the flow control as needed.
Board Changes
| Mistake Made | How it effects the system | Actions Taken |
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| Ordered 0402 not 0805 for the 100nF part (C5,C6,C7) | These are decoupling capacitors. They will help long term stability but the system should be fine without them in the short term | Found the right 0805 part in the Makers Space. Corrected the BOM for future use. |
| Incorrectly routed D5 (tied it to 5V) | D5 was an additional digital pin that was being sent to the lower housing for debug. We lose no functionality by losing this pin. | The pin will stay connected for the time being. The trace can be cut later if needed. The schematic should be updated to see this change. |
| Connected wrong LEDs | One of the low batteries alerts is green and the power LED is yellow. | None. Will take action when design is finalized. Not worth the risk of fixing it now. |
| Inconsistent Switch Labeling | Wrong name on jumper. No real effect. | The schematic should be updated to see this change. |
| Number of 12V connections | It would be nice if there was one more connection to 12V. No real effect. | The schematic should be updated to see this change. |
| Programming header | A header to program the microcontroller on the board would be nice. No real effect. | The schematic should be updated to see this change. |
Nazareth Clinic
Pedometer Program
Overview
Our team is working closely with the Physical Therapy Clinic at Nazareth College, also located in Rochester, NY. We are currently setting up a pedometer program in which we will have several Foot Drop clients keep track of the number of steps that they take per day for a total of 3 days. The data collected in this program will be used in a model to calculate the amount of hours that our device will last before needing to refill the air tank.Instructions
Listed below are the instructions that each client will follow to collect data.- At the beginning of the day, put on the pedometer. Note: Please refer to the attached document for instructions on how to properly wear the pedometer.
- Wear pedometer for the duration of the day
- Right before bed, remove the pedometer and complete the questionnaire below for the appropriate day of program (i.e. day 1, 2 or 3)
Questionnaire
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The following document will be given to each participant:
Nazareth Pedometer Program Handout. They will be
required to fill it out and return it when complete.
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Risk List
References
- Information from the The Walking Site was used in order to estimate the distance traveled based on the number of steps taken. For our AFO, the target number of steps is 3,000 (1,500x2). Assuming AFO users walk an average distance of 1.5-2 feet per step, the estimated distance available in one untethered days use is around 1 mile.
- The slow motion deflection test and other documents make used of scientific gait and posture data commonly referred to as "Posture" by the team.
Week 5 Demo
Within the Week 5 Project Progress Demonstration Agenda is an outline for the meeting, an updated list of action items, and additional phase specific documentation.The Phase 2 Review Action Items PDF contains notes and action items taken from the week 5 project progress demo.
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- Node updated 2015-05-11 16:04 by mde5019