Analysys of impact a sampling period of digital position controller’s on positioning quality

The article is focused on the influence of the digital position controller’s discrete nature on the accuracy of rendering the set path by the moving parts of a precision jig boring machine in relation to high-speed grinding and milling operations. An analysis of the logarithmic amplitude-frequency response of the digital position loop has revealed a pattern of variation in the servo drive position error (i.e. the discrepancy between the path set and the path rendered by the servo drive) depending on the sampling period of the digital position controller. Based on the presented theoretical studies, an algorithm has been developed for dynamic variation of the digital position controller subroutine call period as a function of the machined piece surface profile parameters. This algorithm ensures the required machining accuracy while minimizing the computational load on the microprocessor of the numerical control unit (NCU). The efficiency of the developed algorithm is confirmed by experimental testing using an actual precision jig boring machine (2440SF4 model) with an NCU by Balt-System Ltd.