Preliminary Detailed Design
Table of Contents
The main goals of preliminary detailed design were:
- finalize & detail subsystem concepts
- continue with engineering analysis
- conduct preliminary testing (when possible)
Ultimately the team hoped to move much closer to finalizing a complete design, from the system level down through details on each individual subsystem. The sections below highlight our team's journey through preliminary detailed design.
To find ALL documents associated with this cycle, please see our Detailed Design Documents directory
Prototyping, Engineering Analysis, Simulation
Critical Design Change
Unexpectedly, the majority of the PDD phase was spent redesigning the pneumatic/hydraulic chamber that will be the driving force behind heart function generation. At phase start, SME's were consulted to gather further insight on the physics behind the chamber's subsystem design (spherical membrane that compresses under applied pneumatic pressure. See Schematics & Flowcharts from the Subsystem Design Phase for more information).
Ultimately, this research led the team to the realization that a flexible membrane design is feasible, however:
- this design is not easily repeatable with consistent results, which would also lead to:
- difficulty & complications when replacing parts (i.e. the membrane)
These 2 points went against two critical Customer Requirements that the team hoped to meet, which were:
- D1: Reliable for consistent usage
- C1: Simplistic design for easy and affordable repair when necessary
Continuing with the chamber design from the subsystem phase would have eventually created a device capable of replicating key heart functions as desired, but, undesirably, would have been built by more of a "guess and check" method. This meant it would have been built by guessing figures, and calibrating the system to fit desired output values once construction of was complete. So, whenever a new membrane would be built, the entire system would have had to be recalibrated. On top of this fact, each pumping motion of the system would include variability in each individual output due to the unknowns of the selected membrane's behavior.
This led to a new diaphragm-like design, integrated with a spring to create a linear reaction to pressure force. This design is much more predictable, as a spring, instead of just a membrane, is now the main factor in the relationship between pneumatic pressure and hydraulic pressure experienced in the working fluid. The new diaphragm design can be fabricated based off of known & desired behaviors of materials, which can be selected based off of desired values of outputs of our system.
The inspiration behind this came from a similar design in industry for air brakes:
Ultimately, our final design will imitate the example photographed above. Below is a 3D model comparison of the up to date chamber design, as compared to the design from the subsystem phase:
|Subsystem Flexible Membrane Chamber Design||PDD Diaphragm Design|
Special thanks to Dr. Debartolo of the RIT mechanical engineering department and Dr. Smith of RIT's Chemistry and Material Science Department for insight on our chamber design.
New Diaphragm Design Theory
To ensure successful construction & correct part selection for the new design, in depth analysis behind a spring driven diaphragm design needs to be conducted. As this design is relatively new, full analysis is not yet complete. Below are pictures highlighting the main concepts behind initial theoretical analysis. Too see up to date progress of the diaphragm analysis, see the PDF document uploaded to EDGE
The most important points gained from initial analysis were:
- This design's theory is simple enough that the team is capable of creating an in depth theoretical model
- The theory can be utilized to find driving parameters for diaphragm & part selection.
By MSD completion, the team will have completed diaphragm analysis to the point of finalizing all part dimensions and system parameters.
Updated 3D model
As mentioned above, this new phase brought with it several design changes. To accommodate these changes, a new 3D model was constructed using Creo.
|Diaphragm Chamber (Rendered)||Hydraulic Side Chamber||One Way Valves|
To see all screen shots of the PDD 3D model (R2), see the Photo Gallery
For access to all CAD files, see the CAD repository of all 3D Models.
Updated Pressure Analysis Spreadsheet
During the PDD phase, a spreadsheet was created that integrated the Subsystem Pressure Analysis equations with our engineering requirements and other system inputs, in order to give us values for desired and/or required system properties.
For example, given our max flow rate, minimum frequency, minimum pressure input, etc, the maximum required pump head can be automatically calculated. Below is a screen shot of the main sheet from this document.
Other values such as head loss and diaphragm volume are also automatically calculated, which can be seen in the live document here
Drawings, Schematics, Flow Charts
Labview Flow Chart
A preliminary flow chart was created for Labview to better map out Data Acquisition and controls. Below are screenshots of each.
See a link to the PDF document here
Bill of Materials (BOM)
Part Benchmarking & Purchasing
During PDD, some parts were benchmarked and eventually purchased. In the example pictured below, a table was created to integrate the engineering requirements with specs on various flow meters that were researched.
This ultimately led to the final selection of a flow meter. Other parts were obtained via donations, such as three way valves. Special thanks to RIT FMS for donations that came from decommissioned parts.
Below is a table of some parts already purchased
|One Way Valve||Three Way Pneumatic Valve||Flow Meter|