Circularly Orthogonal Projection-Based Iterative Learning Control for Rejecting Spatially Cyclic Disturbances

Iterative learning control (ILC) is known as an effective technique to deal with reciprocating motion and time-based disturbances. However, the spatially cyclic disturbances in rotary machines are not exactly periodic in the time but periodic in the angular position at varying angular velocity. Besides, traditional ILC is generally based on the premise that system repeats in time domain, without making full use of spatially related information. In this article, a circularly orthogonal projection-based iterative learning control method is proposed to deal with the abovementioned disturbances, which is implemented by data storage. The basis functions are determined based on the repetitive information in spatial domain. The error caused by the spatially cyclic disturbances is extracted effectively by projecting the overall signals onto a circularly orthogonal projection-based subspace. To enhance the learning speed and reduce the calculation complexity of the proposed method, optimized learning matrices with fixed dimension are designed. Experimental results demonstrate the feasibility and effectiveness of the proposed method.