Nanomanipulating systems of macro-stroke has recently attracted significant research attention in various emerging applications like micro-stereolithography. To enhance their precision performance, different control strategies have been adopted.
Despite their compact size and stiffness property, the compliant nano-manipulator poses control challenges due to the existence of cross-axis coupling and loading stiffness effects, which affect the performance of the control systems especially in large strokes tracking. Therefore, a compensation scheme has been proposed to deal with the actuator saturation.
Recently, Mr. Mengjiang Cui and Dr. Zhen Zhang from the Tsinghua University together with Dr. Peng Yan from Shandong University explored a novel nano-manipulator employing 3D printed compliant mechanisms with spatial constraints to achieve a larger stroke without sacrificing its motion accuracy, where an enhanced tracking control architecture was developed for such system capable of tracking desired trajectories and compensating the actuator saturation induced by large range motions. Their work is currently published in, Mechanical Systems and Signal Processing.
Briefly, the integrated control strategy comprised of an internal model principle-based unit tracking controller and a modified anti-windup compensator, for maintaining the tracking performance in the presence of the actuator saturation. Taking advantage of the decoupled feature of the anti-windup compensator, an internal model principle-based control serves as a baseline controller to facilitate the design integration and control implementation.
A nano-manipulator with nonlinear stiffness required saturation compensation to alleviate the nonlinearity impact. For this purpose, it was necessary to enhance the anti-windup compensator with a parallel internal model principle-based control structure. This enabled the authors to schedule mechanism by activating the conventional and anticipatory anti-windup compensators in different operation modes.
It was worth noting that the anti-windup compensator and the tracking controller were designed separately due to its decoupled feature. The authors fabricated a prototype of the compliant manipulaotr, and then experimentally validated the proposed control strategy for different saturation scenarios. In absence of saturation, a tracking error of 62.54 nm (RMS) was achieved. On the other hand, a significant reduction in the tracking error was observed in the presence of saturation thus outperforming the conventional anti-windup compensation scheme.
In summary, the scientists successfully demonstrated a novel 3D printed compliant nano-manipulating system and the associated tracking control architecture achieving millimeter-range high precision tracking with improved anti-windup compensation. The study provides vital technology that offers great potential to various advanced industrial applications such as semiconductor equipment and ultra precision manufacturing.
Cui, M., Zhang, Z., & Yan, P. (2019). Tracking control of a large range 3D printed compliant nano-manipulator with enhanced anti-windup compensation. Mechanical Systems and Signal Processing, 131, 33-48.