Robust Antiwindup Compensation for High-Precision Tracking of a Piezoelectric Nanostage

Abstract

Ultrahigh-precision tracking in nanomanipulations poses major challenges for mechanical design as well as servo control, due to the general confliction between the precision requirement and large stroke tracking. The situation is further complicated by input saturation, which is almost inevitable for microactuators. This paper presents a novel control architecture combining a parallel internal-model-based tracking design and a robust antiwindup control structure, such that asymptotic tracking can be achieved for nanoservo systems in the presence of saturation nonlinearity and model uncertainties. For the augmented system with internal-model dynamics, an I/Obased equivalent representation from control (free of saturation) to system output is derived by incorporating the dead-zone nonlinearity, saturation compensation blocks, as well internal-model units. The robustness condition on the saturation compensator is also derived based on the sector bound criterion and an H ∞ -optimal design is developed accordingly. The proposed robust antiwindup tracking control architecture is deployed on a customize-designed nanostage driven by a piezoelectric (PZT) actuator, where numerical simulations and real-time experiments demonstrate excellent tracking performance and saturation compensation capability, achieving tracking precision error less than 0.23%.

Actuator Saturation Compensation for Fast Tool Servo Systems With Time Delays

“…Note that the hysteresis effect H(q) is a nonsmooth nonlinear phenomenon with nonlocal memoryless of piezo materials, which results in a multivalued and rate/amplitudedependent behavior of the piezo driving FTS system [26]. Referring to [13], [14], we regard the hysteresis nonlinearity as a bounded uncertainty and derive the dynamical model of the FTS system based on the Laplace transform:…”

“…10(a). Meanwhile, by applying swept sine signals, we experimentally identified the system parameters (listed in Table 1) based on the real-time discrete Fourier transformbased approach in [13]. Accordingly, we obtain the nominal model of the FTS prototype as: P (s) = P 0 (s)e −Ls = 9.13 × 10 6 e −0.0024s s 2 + 394.31s + 1.37 × 10 7 .…”

“…Therefore, a Smith predictorbased control method [11], [12], with successful applications in systems with time delays, was developed to address these challenges. The "predictor" is intended to remove the actual time delay from the closed control loop according to the accurate plant model and delayed times, such that the existing control method (e.g., [13]- [15] and reference therein) can be directly applied to nano servo systems without additional compensations for time delays.…”

“…In this study, we investigate the Smith predictor-based robust anti-windup compensation for FTS systems, which is an extension of the anti-windup concept developed in the previous work [13]. In particular, a Smith predictor controller is first designed for time delay systems to guarantee nominal servo performance in the absence of saturation.…”

Design and trajectory tracking control of a piezoelectric nano-manipulator with actuator saturations

“…However most of the existing results on saturation control are discussed for general control systems without considering the specific properties of tracking control structures, such as internal model based control architecture [14], repetitive control [15] and adaptive backstepping control [16]. With this motivation, our recent work [17] proposed a novel robust anti-windup tracking control architecture by combining a parallel internal-model structure with a robust anti-windup compensator to handle the saturation nonlinearity and the unmodeled dynamics, such that high precision tracking can be achieved.…”