The contour error control method based on Iterative Learning Control (ILC) has gained widespread application in multi-axis precision motion systems due to its excellent control accuracy. Fundamentally, ILC works by filtering both repetitive and non-repetitive errors over multiple repetitive control tasks, and iteratively compensating for the repetitive errors to achieve extremely high control precision. In engineering applications, the low-frequency components of errors are typically considered repetitive, while the high-frequency components are regarded as random and non-repetitive. Based on this, ILC often utilizes low-pass filters to filter out repetitive errors. However, the causes of multi-axis contour errors are far more complex than those of single-axis tracking errors. We believe that directly using frequency characteristics to distinguish whether contour errors are repetitive is insufficiently accurate, despite the extensive use of this approach in prior studies. Therefore, this paper proposes a novel ILC method for contour error control based on the selection of repetitive errors. The method determines whether the errors in corresponding frequency bands exhibit repetitive characteristics based on the spectral features of the contour errors, thus enabling more precise filtering of repetitive errors. This approach effectively avoids the issues of convergence speed and precision degradation caused by the introduction of non-repetitive components during the iteration process in traditional ILC. Furthermore, we conducted a series of validation experiments on a multi-axis motion platform, which fully demonstrate that the proposed method outperforms traditional methods under various experimental conditions, effectively addressing the shortcomings of ILC in error filtering.
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