Sign inverting and Delay Scheduling Control concepts with multiple rationally independent delays

In this paper we introduce a novel combination of Sign Inverting Control (SIC) and Delay Scheduling (DS) concepts for systems with multiple rationally independent and large delays. The combined scheme functions with a single premise that, the union of a proper choice of control and its sign inverted version (SIC) would provide a larger stable operating region in the domain of the delays. The outstanding question to properly perform this novel control strategy is the crisp knowledge of the stable operating regions for each of the two control schemes. This question is uniquely answered using the CTCR (Cluster Treatment of Characteristic Roots) paradigm. CTCR declares the stable regions very efficiently and exhaustively with no conservatism. The resulting switched operating mode renders more robust control performance against much larger delay variations vis-à-vis each of the schemes. For unstable delay compositions, a paradoxical scheme called the Delay Scheduling Control (DS) is deployed by increasing the present delays in order to regain stability. The crucial question of 'how much increase in delays?' can also be answered by the CTCR without conservatism. The combination of Sign Inverting Control (SIC) and Delay Scheduling Control (DS) schemes provides previously-unexplored tools to control designers. Experimental validations of these methodologies are provided on a simple setup with a single-axis manipulator.