Environmental Feedback Controller
Center for Limb Loss and Mobility
Project Goal
There is a need for improved and automated experimental methods for mechanically testing biological material for the purposes of mathematical model development. One aspect of these experiments is controlling and maintaining the specimen temperature for multiple consecutive days of testing in order to best mimic biological conditions.
Challenges
Temperature fluctuations could negatively influence the mechanics of the tissue. For instance, increases in temperature result in a decrease in hysteresis, increase in relaxation, and decrease in peak load. There is also some speculation that unregulated temperatures result in contraction/expansion of the mechanical testing apparatus and specimen. Managing temperature over the necessary extended testing period in order to perform a battery of material tests becomes an increasingly challenging problem and an opportunity for an automatic control solution.
My Solution
An environmental testing chamber was designed to house the specimen, retain heat, and not obstruct camera views. Temperatures were monitored using six calibrated thermal sensors mounted around the specimen. Additionally, a ceramic heating element was used to control the temperature of the chamber. A simple feedback controller was programmed on real-time hardware in order to control the heating element based on sensor readings.
Notable Features & Accomplishments
- The controller was implemented on an Arduino Uno and programmed using C++ code.
- Real-time control signals and sampled data readings were sent via an analog/digital BNC breakout board.
- A relay circuit was built to control the heating element based on the automated system's commands.
- A custom LabVIEW program monitored signals between system components and the status of the testing machine.
- Temperature was maintained within ± 1.3 °C of the target temperature.
Skills Used
- Arduino
- C / C++
- LabVIEW
- Embedded Computing
- Embedded Systems
- Automatic Control
- Mechanical Testing
- Material Characterization
- Sensors
- Circuit Prototyping
- Fabrication
- Soldering
- Camera Systems
- Troubleshooting
- Signal Processing
Citation
Images used on this page are adapted from Alexander T. Berardo-Cates' M.S.E. Thesis: "Development of methods for characterizing ankle ligament viscoelastic properties"