Optimal behaviour prediction using a primitive-based data-driven model-free iterative learning control approach

• An optimal behaviour prediction mechanism for MIMO control systems is suggested.
• Previously learned solutions to simple tasks called primitives are involved.
• Hierarchical control system includes model-free iterative learning control (MFILC).
• Optimization of reference input primitives is carried out by MFILC at higher level.
• Virtual reference feedback tuning performs lower level feedback controllers’ design.

This paper suggests an optimal behaviour prediction mechanism for Multi Input-Multi Output control systems in a hierarchical control system structure, using previously learned solutions to simple tasks called primitives. The optimality of the behaviour is formulated as a reference trajectory tracking problem. The primitives are stored in a library of pairs of reference input/controlled output signals. The reference input primitives are optimized at the higher hierarchical level in a model-free iterative learning control (MFILC) framework without using knowledge of the controlled process. Learning of the reference input primitives is performed in a reduced subspace using radial basis functions for approximations. The convergence of the MFILC learning scheme is achieved via a Virtual Reference Feedback Tuning design of the feedback controllers in the lower level feedback control loops. The new complex trajectories to be tracked are decomposed into the output primitives regarded as basis functions. Next, the optimal reference input fed to the control system in order to track the desired new trajectory is then recomposed from the reference input primitives. The efficiency of this approach is demonstrated on a case study concerning the control of a two-axis positioning mechanism, and the experimental validation is offered.