UBC Theses and Dissertations
High-performance real-time motion control for precision systems Smeds, Kristofer S.
Digital motion controllers are used almost exclusively in automated motion control systems today. Their key performance parameters are controller execution speed, timing consistency, and data accuracy. Most commercially available controllers can achieve sampling rates up to 20kHz with several microseconds of timing variation between control cycles. A few state-of-the art control platforms can reach sampling rates of around 100kHz with several hundred nanoseconds of timing variation. There exist a growing number of emerging high-speed high-precision applications, such as diamond turning and scanning probe microscopy, that can benefit from digital controllers capable of faster sampling rates, more consistent timing, and higher data accuracy. This thesis presents two areas of research intended to increase the capabilities of digital motion controllers to meet the needs of these high-speed high-precision applications. First, it presents a new high-performance real-time multiprocessor control platform capable of 1MHz control sampling rates with less than 6ns RMS control cycle timing variation and 16-bit data acquisition accuracy. This platform also includes software libraries to integrate it with Simulink for rapid controller development and LabVIEW for easy graphical user interface development. This thesis covers the design of the control platform and experimentally demonstrates it as a motion controller for a fast-tool servo machine tool. Second, this thesis investigates the effect of control cycle timing variations (sampling jitter and control jitter) on control performance, with an emphasis on precision positioning degradation. A new approximate discrete model is developed to capture the effects of jitter, enabling an intuitive understanding of it's effects on the control system. Based on this model, analyses are carried out to determine the relationship between jitter and positioning error for two scenarios: regulation error from jitter's interaction with measurement noise; and tracking error from jitter's interaction with a deterministic reference command. Further, several practical methods to mitigate the positioning degradation due to jitter are discussed, including a new jitter compensator that can be easily added to an existing controller. Through simulations and experiments performed on a fast-tool servo machine tool, the model and analyses are validated and the positioning degradation arising from jitter is clearly demonstrated.
Item Citations and Data
Attribution-NonCommercial-NoDerivatives 4.0 International