Servo - December 2013

Predicting the Future

Using fMRI (functional magnetic resonance imaging) to view blood flow in the brain, medical researchers can determine how someone will react to a stimulus before that person is consciously aware of their reaction. That is, our brain pre-computes the necessary neuromuscular signals to, say, avoid a slap to the wrist before we consciously move our hand to avoid that slap. In this way, we subconsciously predict the future. This makes sense, if you think about it. Because the propagation of signals in our biochemical communications network is orders of magnitude slower than electrical signals in a length of copper wire, our movements would be erratic and clumsy without some preparation time.

Long before these discoveries were made about the human brain, roboticists were using various methods of predicting the future so that the movements of their robots could be smooth, precise, and executed in the proper order. Consider the Proportional, Integral, Derivative (PID) controller. The three components of PID control can be combined in various ways, with different emphasis on each component to predict the future speed of a basic carpet roamer or velocity of a military drone.

Depending on the application, the three components of PID control can be combined in various ways and with different emphasis on each component. That is, a Proportional (P) controller might be sufficient for a carpet roamer, while a Proportional-Integral (PI) controller might be best for a quadcopter. Proportional control — when used with the appropriate proportion constant and set point correction — can provide much smoother speed. A major limitation of a P controller is an initial period of instability, where predictions about future speed vary widely.

A PI control addresses the instability of the purely proportional control scheme by adding a term that represents the sum of the difference between desired and actual speed over time. Because the integral term reflects the difference between actual and desired speed over time, proportional integral control predicts future

Mind / Iron

by Bryan Bergeron, Editor ;

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