(Image courtesy of Mirko Tobias Schäfer.)
A more complicated, nonlinear robot is more difficult. The rules change when neither the goals nor the variables are understood.
"The knowledge of system dynamics is completely unknown and system states are not available... therefore, it is desirable to design a novel control scheme that does not need the exact knowledge of system dynamics but only the input and output data measured during the operation of the system," said Zhijun Fu, a researcher in the department of mechanical engineering at Zhejiang University, China.
Fu and his research team published a paper describing this novel control scheme in IEEE/CAA Journal of Automatica Sinica (JAS).
The researchers first had to determine the system states in order to figure out how to control them. To that end, they implemented a neural network to observe the system at multiple time scales and to update its information as it studies.
"We cannot apply existing actor-based methods to unknown nonlinear systems directly," Fu said, explaining the appeal of an observer-based method. “An actor must be told what to do, while the observer watches the system to learn the requirements for optimal control.”
"The proposed method may be used [in] industrial systems with 'slow' and 'fast' dynamics, due to the presence of some... parameters, such as small time constants," Fu added.
Such variable dynamics can typically cost a system a lot, in terms of energy and resources. An observer-based method takes into account each type of parameter and makes adjustments accordingly.
This method also accounts for a common system control problem: the overwhelming of actuators. Actuators, the physical sensors in automated machines, can become saturated with information and stop working properly. By accounting for input constraints (since only the input and output data are measured), this control system enables the actuators to avoid oversaturation.
Not all of the system control problems are solved, though.
"[In this paper,] we don't consider the state constraints problem," Fu said, referring to potential limitations that scientists may need to apply to a robotic system in some situations. "[Future] research will be dedicated to solving this problem."
For more robotics news, check out this robot on robot action for up to 12 axes of motion.