Cycle slip prevention in PLL motion control using multi-state phase detector

PLL, or phase-locked loop, is found in many electronic equipments, and effective in motion control as well, to provide high level of speed and position accuracy. A problem with PLL control is “cycle slip” in cases with rapidly changing speed, leading to large phase error to cause harmful vibrations. We successfully developed a remedy for this problem, with S-shaped drive pattern for smooth acceleration for dual-loop configuration. Here, another method of slip prevention using “multi-state” phase detector is proposed. Larger input range than usual 3-state detector can absorb transient slips. Its effectiveness is confirmed with simulation and experimental results.