| Author: | Cheung, Hiu Ching |
| Title: | Design and control of a soft aerial vehicle for conducting aerial grasping |
| Advisors: | Wen, Chih-yung (AAE) Chu, Kar Hang Henry (ME) |
| Degree: | M.Phil. |
| Year: | 2025 |
| Department: | Department of Aeronautical and Aviation Engineering |
| Pages: | xvii, 90 pages : color illustrations |
| Language: | English |
| Abstract: | Unmanned aerial vehicles (UAVs) have gained significant attention because of their potential applications across various industries, including search and rescue, harvesting, and drone delivery. The practical grasping and landing abilities of these aerial robots can guarantee a high success rate in their missions. To improve the grasping performance of UAVs, this thesis introduces a novel modular pneumatic soft gripper design tailored explicitly for aerial grasping of various target objects. Compared to the traditional rigid gripper, the proposed soft gripper aims to act as a shock absorber that can dampen the impact force induced during aerial grasping. The soft gripper can grasp and release the target items through inflation and deflation. The flexibility of the pneumatic soft gripper allows deflation to reach its opening, providing higher grasping tolerance than the traditional rigid gripper. Moreover, the softness of the soft gripper makes it capable of grasping objects without any damage through inflation. Modular connectors of the soft fingers offer two configurations for this 4-tip soft gripper, H-base (cylindrical) and X-base (spherical), allowing adaptability to different target objects. The airflow of the soft gripper is controlled by its two solenoid valves, while a feed-forward proportional controller of an air pump manages the pressure regulation. In addition to the above, a soft aerial vehicle (SAV) with a quadrotor and the proposed soft gripper is proposed. An onboard computer of the SAV can commend the soft gripper's airflow control system and pressure regulation directly to ensure aerial grasping efficiency. The soft gripper is installed under the centre of gravity of the SAV to serve as a soft landing gear when deflated, eliminating the requirement for additional landing gear. Hence, this soft landing design reduces the net weight of the SAV and simplifies aerial manipulation control by removing the extra landing gear control. Nevertheless, controlling the dynamics of UAVs during their aerial grasping mission is challenging. The increased mass from the payload adversely impacts their thrust prediction, while unpredictable environmental disturbances further complicate control efforts. Thus, this thesis aims to enhance the control of the SAV during aerial grasping by integrating a disturbance observer into a Nonlinear Model Predictive Control (NMPC). This incorporation compensates for dynamic model idealization and uncertainties arising from the additional payloads and unpredictable disturbances. Hence, the Disturbance Observer-based Nonlinear Model Predictive Control (DOMPC) can effectively minimize tracking errors and enable precise aerial grasping along all three axes. The proposed disturbance observer utilises an Extended Kalman Filter (EKF) to estimate the linear acceleration disturbances of the SAV. The suggested SAV equipped with DOMPC demonstrates remarkable performance in carrying both static and non-static payloads, leading to the successful grasping of different objects with various mass distributions. Notably, the SAV also achieves an impressive payload-to-weight ratio in its payload test in mid-air, surpassing previous investigations in soft grasping. |
| Rights: | All rights reserved |
| Access: | open access |
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