Ziegler-Nichols Tuning is a practical, model-free method for tuning PID controller gains empirically. Published in 1942, this pioneering method requires only measurement of the system's step response (or closed-loop oscillations), making it applicable to any system without prior identification. Ziegler-Nichols remains widely used in industry because it is simple, fast, and often produces reasonable initial tunings.
Ziegler, J. G., & Nichols, N. B. (1942). Optimum settings for automatic controllers. Transactions of the American Society of Mechanical Engineers, 64(8), 759-768. link ↗
Astrom, K. J., & Hagglund, T. (2006). Advanced PID Control. ISA-The Instrumentation, Systems, and Automation Society. link ↗