Modeling and Control of Micro Robots in Various Environments

微型機器人在不同環境中的建模與控制

Student thesis: Doctoral Thesis

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Award date29 Aug 2019

Abstract

The microfield has attracted increasing attention in recent decades, and research objects have gradually been miniaturized. Micro robots are among the most promising tools for exploring the microworld because of their high precision, effectiveness, reliability and stability. However, due to the size effect, the specific environment presents significant challenges for the function of micro robots, such as fluid resisting force at a water interface or under water and interference from light in the light field. The dynamic modeling and control of micro robots in such complex environments have not been fully explored.

This thesis first discusses a strategy for controlling micro robots in the light field for micro waveguide coupling. In the coupling process, micro waveguides should be matched well so that light is maximized. However, laser inevitably disrupts the recognition of the waveguide’s position. Although micro waveguides can be aligned based on the position, the amount of light may remain insufficient because of fabrication error. To resolve these challenges, we present a micro robotic system with three degrees of freedom (DOFs) and a model-free adaptive control strategy based on hybrid position and light intensity feedback. Simulation and experimental results demonstrate that the proposed system can achieve the coupling of the micro waveguides with 300.41% improvement in sensitivity compared with traditional method with single position feedback.

Secondly, this thesis investigates the 3D micro manufacture based on micro robots. Unlike the flexible motion of cameras in macro scale, the microscope such as the scanning electron microscopy (SEM) cannot rotate accordingly with the sample, which can just provide the 2D information. Hence, the 2D image from vision feedback and the required cooperation of micro robots for complex tasks present enormous challenges to 3D in-situ manufacture. In this part, we build a 6-DOF micro-robotic system with vision feedforward and double feedback to realize high-precision 3D in-situ manufacturing of helices. The experimental results demonstrate that the accuracy in manufacturing can reach up to 2 μm.

Moreover, the modeling and control of the micro robot in an air–liquid interface is studied. Currently, researchers have focused on time-invariant normal environments. Meanwhile, complex motions at time-varying air–liquid interfaces, such as the watch hand manipulation, are rarely studied. In this part, a micro-robotic system with corresponding control strategy is presented while the watch hand movement at a time-varying air–liquid interface is modeled. The experimental results demonstrate that only 2–5 seconds is required for the alignment of a single watch hand, and the final alignment accuracy is ~15 μm.

Aqueous environments are the working conditions for swimming micro robots, which have been widely used in biomedical engineering and industrial applications. The single helical tail model is currently the main swimming model for underwater micro robots. Here, we present a new type of sperm swimming model, named the dual-section helical (DSH) model, by investigating the motions of Ray sperms in solutions with various viscosities. We discover that the sperm contains one soft tail and one rigid helical head connected by a mid-piece, and these parts are involved in the propulsion with adjustable contributions corresponding to the motion and liquid environment. Such model offers Ray sperms a high adaptability to an environment with a wide range of Reynolds number and advantages in linearity, straightness and efficiency, which will inspire the design of mobile micro robots. The results will have a long-term impact on robotics, biomedical engineering and industrial applications.

Overall, we realize the dynamic modeling and control of micro robots for different applications in various environments. This thesis will pave a new path for the implementation of micro robots, including the micro assembly, micro manufacture and micro manipulation, which would have broad impacts on various engineering fields, such as biomedical engineering and robotics.

    Research areas

  • micro robot, hybrid feedback, in-situ manufacture, air–liquid interface, dual helical propulsion