Development of a multi-rotor aerial vehicle with top mounted counter balanced robotic manipulator

Abstract

Aerial manipulation has been a growing research area within the past few years. This research area was associated with various application ideas and industries. Researchers implemented different aerial vehicle designs and manipulation techniques to accomplish these tasks in complex environmental conditions. Majority of conducted aerial manipulation research was composed of aerial vehicle bottom-mounted manipulators. These kind of aerial manipulation systems were not generally capable of achieving manipulator movements in an environment above the propeller disc plane. A few research projects were carried out by researchers to identify the performance of aerial vehicle top-mounted manipulators. Therefore, the manipulator mechanical designing step plays a challenging role in keeping the dynamic stability within the proper tolerances for manipulation systems. Center of Mass (COM) position and inertia of an aerial manipulation system become variables with respect to an inertial coordinate frame when a manipulator is attached to a multirotor. The manipulator, environmental reaction forces and torques are transferred on to the aerial vehicle as the system interacts with the external environment. Researchers had conducted a limited number of aerial manipulator system related projects with top-mounted manipulators which were capable of inspecting both vertical and overhead structures. The set of aerial manipulator systems capable of inspecting overhead structures are a small subset of the universal set of multirotor mounted manipulator projects. The literature suggests COM of an aerial manipulator system need to be placed in the propeller disc plane and closer to the central axis of a multirotor to achieve a better dynamic performance of that system. If a designer attaches manipulator on the top or bottom surface of a multirotor, the COM position moves vertically up or down from the propeller disc plane respectively. Generally, aerial vehicle top-mounted manipulators have generated more dynamic instabilities compared to manipulators mounted on the underside of multirotors. This thesis introduces a 2 Degrees of Freedom (DOF) serial link planar manipulator which has been mounted on top of a hexacopter by the rigid manipulator base. The research focused on inspection purposes of tall structures that human reach may be costly or vulnerable to physical injuries. The developed system included a novel serial link manipulator design and a force sensor as the end effector of the manipulator. This end-effector sensor would be able to identify the contact with surfaces of high-rise buildings or structures. The manipulator consisted of a separate controller apart from the flight controller. When this manipulator achieved different poses in its planar workspace, COM position of the system varied as a result. Therefore, a novel controller strategy was developed by the author in the research to compensate for the system attitude variations. Variation of the COM position caused attitude fluctuations. The thesis proposes a specifically designed manipulator mechanical design configuration to reduce the inherent COM position variation. Another concept was introduced by the author to counterbalance the COM position variation by synchronizing the motions of the system battery. A variable gain Proportional (P) controller, followed by a Proportional Integral Derivative (PID) controller was presented in the research to maintain the aerial manipulator system attitude. This research introduces novel concepts of designing, disturbance compensation and controlling of the aerial vehicle top-mounted manipulation systems. Theoretical simulations showed the COM, inertia, joint torque, disturbance torque variations of the manipulator. Experiments were carried out by the author considering the manipulator separately and the overall system in-flight to identify the performance of the developed system.