Team Vision for Detailed Design Phase
This phase is dedicated to created the LabVIEW program to run the system as well as developing a prototype for the ventricle heart pump. The LabVIEW program was completed to a satisfactory amount for this phase. The CAD drawings for the prototype are completed and the detailed drawings for the machine shop are being produced. A Laboratory cleanup plan has been developed. As well as a full set of detailed test plans. These were all items that needed to be completed before the end of this phase.
Review of Proposed Design
The adaptation to the design proposed in the preliminary detailed design phase is in regards to recording the ventricle pressure. The pressure is needed to generate a P-v diagram and the pressure waveform with respect to time. Option one requires an additional pressure sensor that is not currently part of the bill of materials. This pressure sensor would be in line with the tubing before the heart pump one-way valve. To avoid having to purchase an additional pressure sensor, one of the three way valves that is surplus from last year’s team could be utilized. Option two illustrates the use of the three-way valve to connect in line with the tubing before the heart pump one-way valve. The three-way valve can be manually turned to control which pressure is being recorded. This limits the system to be able to record either heart pressure or the compliance pressure drop but not simultaneously. Other considerations is the pressure loss in the connecting tubing. This is why option two will be pursued with the understanding that option one may need to be implemented.
Updated Engineering Requirements
Updates to the engineering requirements from the problem definition phase is the addition of S21 the heat requirements for the solenoid and changing the waterproof requirement to a non submersible rating.
Motivation: Analyze the total latency of air driver.
Methods: Use Oscilloscope to measure delay from Computer Signal to Solenoid trigger. Compare various speeds(1Hz, 1.5Hz, 2Hz, 2.5Hz)
Analysis: Results found no statistically relevant variability in latency at various speeds with an average of ~59ms.
Conclusion: Latency will be evaluated for relevance during system testing and used to tune code.
The need for a two-point calibration was observed while generating a LabVIEW program for the compliance pressure drop. The sensors that are currently in use are more accurate at the higher range of the readable pressures. The lower pressure range does not produce accurate enough measurements to not require a calibration before each laboratory use. Calibration of sensors is something that occurs before different Biomedical Engineering Labs and is acceptable to include into the laboratory procedures. The calibration will be a two-point calibration controlled by the LabVIEW program.
The above LabVIEW controls the flowmeter. The raw data is in revolutions per second. The frequency is calculated and then filtered using a running mean filter. Then it is converted using a conversion factor from the sensor specification and then using a general time conversion. The result is the desired output in L/min.
The flow in the system is pulsating flow. This means the sensor is not always running. When the sensor is not running it produces noise at the high end of the sensor limit. This program will have to be adapted to incorporate a filter to account for this noise. Ideally the program will generate zero L/min when the sensor is stationary.
Additional sensors requiring code:
- Capillary pressure sensors, calibration and functionality
- Input pressure controls
All codes will be combined into one document.
Laboratory LayoutThe following diagram shows the expected layout for a laboratory setting.
Laboratory Cleanup Procedure
See live document here: Laboratory Cleanup Procedure
The electrical components will be placed into an enclosure to protect them from water, minimize wire exposure, and to make the system easier to store.
- Reduced risk with emergency stop button and circuit breaker
- Internal solenoid for noise reduction
- Currently using box donated by the construct
- 12’’x12’’x1/2’’ has been machined down into smaller squares
- Drawings are complete, but are being double checked on dimensioning before final drafts
- Accuracy is more important than speed at this point and it needs to be done correctly
- Rob or Jan in Machine Shop will advise/assist when we are ready to make the cuts
- Spoke with machine shop about machining plan
- Ventricle hole will be tricky to machine
- Possible addition of “o-ring’’ slot for sealing
- Week 1 after break – machining center slots and through holes
- Week 2 after break – ventricle hole and drill/tap access holes.
- Week 3 after break – o’ring sealing slot if needed.
See live document here: CAD Drawings
Silicone Ventricle Production
- 2 part silicone mold mix
- 2 piece 3D printed mold with vent holes
- Work Surface covered in butcher paper
- 2 Disposable Cups of known volume
- Disposable stirring sticks (at least 2, 3 preferred)
- Paper Towels
- Spackle Knife, flat head screwdriver
- Exacto Knife
Set-up 1. Lay the butcher paper on the table, tape down if necessary
2. Spray 3D printed mold with a mold release, allowing enough time to set before pouring
3. Acquire the estimate for the volume of your mold, add 15-25% to avoid underfill
4.Estimate the amount each cup will need to be filled based on the volume of the cup and of the ratio for each part of the mold liquid
5.If possible also estimate how full the one part of the mold will be to fill the negative space when the positive top is pressed down
6.In their respective tubs, separately stir the silicone mix parts so they are uniform. Try to avoid stirring up chunks that have solidified at the bottom. Stir until solution is uniform, Stir by “folding” to avoid bubbles
7.Pour the desired amount into separate cups, stir again in a “folding” type manner to avoid making bubbles.
1.Take note of how long you have to work with the mixed parts before it sets (the work time)
2.Combine the two parts. Mix extremely thoroughly, but avoid air bubbles
3.Very slowly drizzle the mix into the mold, the slower you pour the less air bubbles there will be. But be sure to stay within the work time
4.Slowly press down the top of the mold into place
5.Check to be sure a sufficient amount of mixture comes out the vent holes to ensure the mold was filled
6.Check for air bubbles visible from the top
7.Clamp the mold together firmly
8.Allow the required amount of time for the mold to set, use the combined mix cup to gauge readiness
9.Separate mold using Spackle knife or other flat prying tool
10.Trim excess flash
The mold turned out very well. The air bubbles were minimal and largely restricted to the flange; where it will least affect the structural integrity of the ventricle. These air bubbles could have been avoided, but I poured the mix a little too fast and I think it was clamped down a bit quick. Some of the surfaces are a bit uneven as well. This can be solved with some extra sanding of some of the harder to reach places. The ventricle compresses much easier than expected, while still appearing to be very durable. Overall, these are very successful results
Goal: Create several ventricle prototypes that can simulate physiological conditions based on wall thickness and compare to theoretical values predicted using finite element analysis.
Plan: Mold additional ventricle prototypes with Dragon Skin silicone (of varying thicknesses) and compare to current prototype performance.
Outcome: Ventricle chosen best models desired physiological conditions of a human heart.
Bill of Material (BOM)
List of Test Plans
- Solenoid Testing (S1)
- Compliance Testing (S2, S3, and S4)
- Ventricle Pressure Testing (S5, S6, and S20)
- Life Cycle Testing (S7)
- Maintenance Testing (S8)
- Flowmeter Testing (S9)
- Equilibrium Testing (S11 and S15)
- Air Safety Testing (S14)
- Electronic Safety Testing (S16)
- Pressure Input Regulation Testing (S17)
- Ease of Use Testing (S10, S12, S13, and S18)
- Cost Testing (S21)
S1 Solenoid Testing
The goal of this testing is to ensure that the solenoid can provide the needed frequency as well as the system returns an accurate measurement. Solenoid will be activated to determine the functional frequency range. The testing of the solenoid will begin at 1 Hz and increased in increments of 0.5 Hz until it stops functioning. This will not cause damage to the solenoid. It will seize up and stop firing. For each increment the solenoid will be monitored with the LabVIEW program so that it can be ensured that the frequency input is matching the solenoid output.
S2, S3, and S4 Compliance Testing
The goal of this testing is to determine if the system provides proper outputs for compliance and that the method of measurement is user-friendly. The pinch valve will be set to various heights. For each height the pressures will be recorded and the compliance calculated. The system will then be observed to determine of if the compliance reflects the system outputs.
S5, S6, and S20 Ventricle Pressure Testing
The goal of this testing is to ensure accuracy of the system pressure outputs. When they prototype is constructed the system will be hooked up to the software and be used as if it was in a laboratory setting. All sensor must previously be tested for accuracy. The outputs of the system will be recorded and then compared to textbook values. Adjustments will be made to the LabVIEW code and the system where necessary to generate the correct outputs. These adjustments will not be something that a student would have to do in the lab. Compare data to textbook data. Data should be within range of the textbook data.
S7 Life Cycle Testing
The goal of this testing is to determine the fatigue strength of the silicone ventricle and the life cycle of the entire system. A silicone ventricle will have individual life cycle testing done. The ventricle will be stretched and released at the rate of 2.5 Hz for a specified amount of time. The time will be chosen to model the amount of use of the ventricle. Deformation and/or leakage of the durability.
S8 Maintenance Testing
The goal of this testing is to ensure that the maintenance time per part is reasonable. A third party with knowledge of the circulatory system will be given documentation on system maintenance. They will replace parts of the system using the documentation. Each time they are replacing a part they will be timed. The time will be recorded after each part is replaced. The parts being replaced will be the silicone ventricle, the flowmeter, a section of tubing, capillary pressure sensor, and the sphygmomanometer tubing.
S9 Flowmeter Testing
The goal of this testing is to ensure sensor accuracy and test the system for desired flow rate.
Sensor Accuracy: Attach a section of tubing to either side of the flow rate sensor. One side will be placed into a beaker and the other under the faucet. The water from the sink is turned on and sent through the sensor. The amount of water in the beaker is then compared to the reading from the flow meter to ensure accuracy.
System Accuracy: Attach the flow sensor to the system. Run the system as if in a laboratory setting. Collect data from the system for various beats per minute. Determine if changes need to be made to be within the limits required.
S11 and S15 Equilibrium Testing
Ensuring that the system returns to equilibrium in the desired time so that student will be able to take measurements in a timely fashion. Run system as if it was in a laboratory setting. Record data as changes are made to the system. Export the data and determine the time for the system to return to equilibrium.
S14 Air Safety Testing
Fill empty housing chamber with air. Recorded pressure in chamber and when the release valve activates. For safety the housing will also be attached to the vacuum. If the chamber does not activate the emergency release in the specified amount of time then the solenoid will switch to vacuum.
S16 Electronic Safety Testing
To ensure safety of students when using the electronic subsystem and that they system can with stand expected interactions with water. Temporarily seal the enclosure without electronics inside, for safety, Spill water on top of enclosure. Wait a specified amount of time. Clean up spilled water. Then remove enclosure and check for water.
S17 Pressure Input Regulation Testing
To ensure that the input pressure from the shop air is accurate. Hook shop air up to fluid manometer filled with water. The density for the water is known so the pressure can be calculated using density*g*change in height. This can be compared with any of our pressure sensors.
S10, S12, S13, and S18 Ease of Use Testing
To ensure ease of use for students using the system. The system will be weighed and measured. A single person will be timed carrying the equipment two and from storage. The person must be of average strength. Then a group of two will be timed setting up the system as if it was a lab they had to complete. These people will also be timed while making adjustments to the system to determine an estimation of procedure time for the lab. Finally the two group members will disassemble the system while being timed. It is important that all timed activities are done in a leisurely manner to demonstrate real life conditions.
S19 Cost Testing
To ensure that the cost of the system remains in budget, compare the budget to the updated bill of materials.
S21 Solenoid Heat Testing
The goal is to ensure that the solenoid does not heat up to unsafe levels. Skin gets 1st degree burns at around 110 F. The maximum temperature was chosen to be 90F and ideally the temperature would not increase above room temperature. The solenoid will be run for 6 hours, the maximum laboratory time, and the temperature of the solenoid will be recorded. The temperature over time will be plotted to observe peek temperatures. It will then be determined if any heat sink or fins will be needed to keep the heat of the solenoid withing a desirable range.
See live document here: Test Plans
Lab Cleanup Procedure (Bacterial film (biofilm) buildup prevention)
(Also in Lab Cleanup Document)
- Leave a small amount of moisture remaining in the system
- Allow for system to sit without running for multiple days/weeks
- Record Observations per day
- Room Temperature
- Amount of moisture in the system
- Odors from within the system
- Visual cloudiness on inner walls of tubing and tanks
- Swab cloudy region of inner walls of tubing
- Culture bacterial film
- Determine additive to avoid or eliminate biofilm during storage
If the compression seal has any leaks, then the system as a whole will not be functional and it will create a mess. However, it was observed that the compression seal is functional using plastic 3D printed parts. The aluminum plates will be able to create a better compression seal than the 3D printed parts because they can have more pressure applied to them. Increasing the pressure applied to the plates by the bolts and aluminum rods creates a better compression seal between the ventricle and the plates. The expectation for the compression seal to be highly functional makes it a low likelihood of 1, but the severity is a 3 because if it doesn’t seal then the system will not work properly.
Previous Teams Design Does Not Satisfy Requirements
The previous teams design obviously did not satisfy all the requirements since this project is a rev. 2. There have been changes made by the team to move forward to reach all requirements.
- Ventricle instead of a piston
- Changing the resistor to a pinch valve for ease of use
- Using a flowmeter to output flow rate
DAQ Power Up
To prevent the DAQ from turning on the air when it powers up an attempt will be made to reprogram the startup sequence. A pin will also be placed in the emergency release to prevent the chamber from pressurizing. Ideally the DAQ will be reprogrammed, but this may not be viable for all the DAQ used in the lab. It may be more realistic to use the pin method and add a note into the procedure.
See live document here: Detailed Design Risk Assessment
Design Review Materials
See live document here: Detailed Design Presentation
Plans for MSDII
MSDII Three Week Plan
- Before Gate Review
- Update all action items on edge discussed with Charlie post design review
- In MSD II
- Complete LabVIEW Programs
- Update Edge with Documentation
- Flowmeter Sensor Calibration
- Before Gate Review
- Before Gate Review
- Review Lab Maintenance Procedure
- Start Test Plan for cleaning solution prior to MSD II
- In MSD II
- Assist completion of LabView VI’s
- Complete valve engineering design
- Finalize Lab Maintenance Testing & Procedure
- Overall system testing for quantitative physiological outputs
- Before Gate Review
- Pursue safety switch for vacuum
- Work with Kevan to tune solenoid
- Help Henry build new ventricle
- Work on Labview with susan
- Test mock cleaning loop with blake
- Complete all machining of Aluminum
- Cut Arcyllic to size
- Initial Electrical Box fabrication/machining
- Safety pin machining
- Assist in Ventricle production
- Assist in Final Machining
- Fabricate Final Ventricle
- Test current and new ventricle
- Optimize as needed
- Do safety testing