Postdoctoral Fellow, Vanderbilt University
Joshua B. Gafford
Real-Time Controller for Validation Platform
The controller for the validation platform described here was developed in MATLAB/Simulink xPC. Numerous controllers are implemented in discrete time, and executed depending on user input (via graphical user interface). The implemented controllers are described below:
-
Position Controller: PID with velocity/acceleration feed-forward and gravity compensation
-
Force Controller: PD with gravity feed-forward
-
Velocity Controller: PD controller on velocity (discrete derivative of position, low-passed)
-
SMA Current Controller: PD current controller to analog-to-PWM converter
-
SMA Temperature controller: PID controller based on feedback from infrared temperature sensor
-
Virtual Bias Spring: PID position controller where a static equilibrium equation is solved in real time to make the stage behave like a pre-stretched linear-elastic spring
Block diagram of the validation platform control system, configured in SMA actuator quasi-steady characterization mode. Colored boxes correspond with the model being validated.
(left) video of the validation platform demonstrating position and force control, (middle) position control for a 0.5 Hz sine wave, (right) force control for a 0.2Hz sine wave
Design of a Tactile Teaching Tool for Learning the Basics of PID Control
For the purpose of demonstrating high-level principles of proportional-integral-derivative (PID) control to a multidisciplinary medical device design class (ES227: Medical Device Design at Harvard University), I designed a demonstration platform that allows a user to vary PID gains in real-time and observe the resulting dynamic response on a plant (a DC motor with a laser-cut acrylic inertial mass and hall-effect quadrature encoding for position feedback). Intuition of how a PID works can be gained through touch as the user can apply disturbances to the inertial load and 'feel' the resistance of the controller in terms of a tactile spring and damping force. The document summarizes the basic electromechanical design of the hardware, control theory and digital implementation of the controller, as well as some example step responses for various PID gain combinations.
Course: Teaching fellow for ES227: Medical Device Design (Harvard)
Tactile PID learning tool
Demonstrative PID performance for an input step signal