Case Study
Pen Injector Design Study
Challenge
- Pen injector design was outside of specification limits for user push force.
- Several improvements to the design were being contemplated – e.g., lubricant-loaded plastics
- ROI was indeterminant
KDPD Approach
- Created analytical kinetic model for the pen injector
- Verified the analytical model with customized test apparatus and a rigorous, systematic, test plan
- Testing at subsystem level verified low level model inputs
- Characterized critical subsystem values such as coefficients of friction
- Tested pen at a system level
- Analytical and empirical model were well aligned
- Testing at subsystem level verified low level model inputs
- The verified analytical model enabled a sensitivity study on independent variables including the coefficients of friction (COF) for each component
- Allowed us to determine which components will benefit most from more costly lubricant loaded materials
- Analytical model Informed client on impact of future design changes on device performance
Results
Plot above shows good correlation between high level model and experimental results
| Variable | Sensitivity | Units |
|---|---|---|
|
COF Component 1 |
0.018 |
N/σ |
|
COF Component 2 |
0.019 |
N/σ |
|
COF Component 3 |
0.002 |
N/σ |
|
COF Component 4 |
0.001 |
N/σ |
|
COF Component 5 |
0.010 |
N/σ |
|
COF Component 6 |
0.007 |
N/σ |
|
COF Component 7 |
0.113 |
N/σ |
|
COF Component 8 |
0.213 |
N/σ |
|
COF Component 9 |
0.013 |
N/σ |
The results of the sensitivity study clearly show that the coefficient of friction for 2 components in particular have a significantly higher impact on the required user force.
- Motivates higher cost materials where they are most impactful
Key Takeaways
- By performing tests on the various subsystems of the device, FPrin was able to systematically verify the accuracy of the analytical model
- The analytical model created by FPrin gave the client the ability to make informed design decisions for this device
- Specifically, material choices and dimensional tolerances
- The sensitivity study also gave insight into the impact on performance of the device to dimensional variation, thereby informing dimensional tolerance requirements
- Specifically, material choices and dimensional tolerances
- With parametric updates to the model the designer can effectively explore the design space of this architecture without the need for exploratory testing of each of them
