P17080: Heart Pump and Circulatory System
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Detailed Design

Table of Contents

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.

Progress Report

Completion of Task and Team Members Responsible

Completion of Task and Team Members Responsible

Decisions and Questions

Decisions and Questions

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.

Design Option 1

Design Option 1

Design Option 2

Design Option 2

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.

Updated Engineering Requirements

Updated Engineering Requirements

Calibration Observations

Signal Delay

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.

Observed Signal Delay

Observed Signal Delay

Pressure Calibration

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.

Flow Chart for Pressure Sensor Calibration

Flow Chart for Pressure Sensor Calibration

LabVIEW Development

Controls for Relay

Controls for Relay

The above LabVIEW program controls the relay. The relay is the input to the system that drives the heart pump. The frequency is the rate one cycle occurs. A cycle is one 'pressure on then vacuum on'. The cycle is a square wave. The duty cycle controls the percentage of time that each are on in the cycle.
Controls for Flowmeter

Controls for Flowmeter

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:

All codes will be combined into one document.

Updated Diagrams

Laboratory Layout

The following diagram shows the expected layout for a laboratory setting.
Laboratory Layout

Laboratory Layout

Laboratory Cleanup Procedure

See live document here: Laboratory Cleanup Procedure

Electrical Diagrams

Overall Wiring Diagram

Overall Wiring Diagram

Solenoid Wiring Diagram

Solenoid Wiring Diagram

OpAmp Wiring Diagram

OpAmp Wiring Diagram

The Op-Amp circuit controls the inlet pressure.

Electrical Layout

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.

Electrical Layout in Enclosure

Electrical Layout in Enclosure

Electrical Layout in Cross-sectioned Enclosure

Electrical Layout in Cross-sectioned Enclosure

Front Panel Layout

Front Panel Layout

Prototyping

Machining Plan

Next Steps:

Ventricle Hydraulic Ring

Ventricle Hydraulic Ring

Ventricle Pneumatic Slot Ring

Ventricle Pneumatic Slot Ring

Ventricle Pneumatic Cap

Ventricle Pneumatic Cap

Drawings

See live document here: CAD Drawings

Silicone Ventricle Production

Equipment required

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

Empty Mold Cavity

Empty Mold Cavity

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.

Components to Make Silicone

Components to Make Silicone

Pouring

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

Mixing of Two Components

Mixing of Two Components

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

Pouring of Silicone into Mold

Pouring of Silicone into Mold

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

Mold Setting

Mold Setting

9.Separate mold using Spackle knife or other flat prying tool

10.Trim excess flash

Raw Ventricle From Mold

Raw Ventricle From Mold

Finished Ventricle Prototype

Finished Ventricle Prototype

Observations

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

Future Prototyping

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)

Current BOM

Current BOM

Test Plans

List of Test Plans

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.

Flowchart for Solenoid Testing

Flowchart for Solenoid Testing

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.

Flowchart for Compliance Testing

Flowchart for Compliance Testing

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.

Flowchart for Ventricle Pressure Testing

Flowchart for Ventricle Pressure Testing

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.

Flowchart for Life Cycle Testing

Flowchart for Life Cycle Testing

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.

Flowchart for Maintenance Testing

Flowchart for Maintenance Testing

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.

Flowchart for Flowmeter Sensor Accuracy Testing

Flowchart for Flowmeter Sensor Accuracy Testing

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.

Flowchart for System Flow Accuracy Testing

Flowchart for System Flow Accuracy Testing

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.

Flowchart for Equilibrium Testing

Flowchart for Equilibrium Testing

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.

Flowchart for Air Safety Testing

Flowchart for Air Safety Testing

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.

Flowchart for Electronic Safety Testing

Flowchart for Electronic Safety Testing

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.

Flowchart for Pressure Input Regulation Testing

Flowchart for Pressure Input Regulation Testing

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.

Flowchart for Ease of Use Testing

Flowchart for Ease of Use Testing

S19 Cost Testing

To ensure that the cost of the system remains in budget, compare the budget to the updated bill of materials.

Flowchart for Cost Testing

Flowchart for Cost Testing

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.

Flowchart for Solenoid Heat Testing

Flowchart for Solenoid Heat Testing

See live document here: Test Plans

Lab Cleanup Procedure (Bacterial film (biofilm) buildup prevention)

(Also in Lab Cleanup Document)

Risk Assessment

Compression Seal

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.

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.

Risk Assessment

Risk Assessment

See live document here: Detailed Design Risk Assessment

Design Review Materials

See live document here: Detailed Design Presentation

Plans for MSDII

MSDII Weeks 1-8

MSDII Weeks 1-8

MSDII Weeks 9-13

MSDII Weeks 9-13

MSDII Three Week Plan


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