Design, Modeling, and Control of Cable-suspended Aerial Manipulator

Kurzfassung

Aerial manipulation is a modern and prospective field in interaction robotics with many industrial applications in remotely located and dangerous environments. The typical aerial manipulator is a flying system; the manipulation is conducted by utilizing a robotic arm, while the translation of the arm’s base in the space is done by an aerial vehicle. Such systems have found utilization in the inspection of different structures, e.g., bridges, electric lines, and pipelines, assembly/repair of remote constructions, and various operations in conditions hazardous or dangerous for human safety, e.g., decommissioning damaged nuclear power plants. Despite the functional benefits, the manipulator serves as an additional payload, requiring more powerful actuation and, consequently, a bigger flying vehicle. Thus, the high risk of a collision between the aerial vehicle and the obstacles in a complex environment imposes restrictions on aerial manipulation in industry. To overcome this issue and achieve higher safety, a novel approach, a cable-suspended aerial manipulator, is recently proposed. Instead of attaching a robotic manipulator directly to an aerial carrier, it can be mounted on a compact actuated platform, which is suspended by a cable on the external mobile crane and responsible for the system stabilization and non-vertical motion. However, due to the physics of the suspended aerial manipulator, static and dynamics disturbances occur during manipulation that affect the system: pendulum-like cable oscillations due to external perturbation or the platform tilt because of the robotic arm weight. To this end, this thesis brings three major contributions that jointly aim at the development of the control framework and the extensive investigation of the described cable-suspended aerial manipulation concept. We first present an approach for oscillation damping of the critical pendulumlike motion caused by suspension cable. It turns out that the considered concept of the aerial manipulation might be modeled by a double pendulum with a first bob corresponding to the mobile crane’s hook and the second - to the platform itself. The main challenge is the presence of only one onboard Inertial Measurement Unit sensor, which does not provide complete information on the system state, i.e., crane’s chain motion remains unknown. Moreover, common onboard actuation for aerial vehicles, propeller-based actuation, is integrated at the platform, so we cannot affect pendulum joints directly. To cope with these difficulties, we design a controller motivated by a simplified model. The proposed controller is very simple yet robust to uncertainties. Moreover, we propose a gain tuning rule by formulating the proposed controller in the form of output feedback Linear Quadratic Regulator problem. Consequently, it is possible to dampen oscillations with minimal energy consumption quickly. The proposed approach is validated through simulations and experiments aimed at the robustness investigation with respect to the influence of the unmodeled aspects such as wind, robotic arm motion, suspension point motion, and others. Additionally, to achieve smooth manipulation of the aerial system, we introduce a winch-based actuation for the cable-suspended aerial manipulator. Three controllable rigging cables link the suspension point (the crane’s hook) with the platform and allow to change its translational pose. Such an actuation approach reduces the effect of disturbing gravitational torque caused by the robotic arm weigh distribution on the aerial base. In order to coordinate robotic arm and winch dynamics, a Hierarchical impedance-based Whole-Body Controller is elaborated. It resolves two tasks: keeping the robotic arm end effector at the desired pose and shifting the platform Center Of Mass to the location with zero torque due to Gravity. Additionally, in order to pass torque commands to the position-controlled winch motors, the admittance interface is accommodated. The performance of the introduced actuation system under the considered control strategy is validated through experimental studies. Finally, it is worth highlighting that research work in the scope of this thesis was conducted within the H2020 AEROARMS project, which addresses the development of the aerial manipulation technologies for industrial inspection and maintenance. Therefore, the last contribution of this thesis is devoted to the extensive field investigation of the system demonstrator under the developed controllers in industrial-like conditions. It should allow validating the performance, safety, and robustness of the overall framework. The prepared industrial-like environment is complex due to various obstacles in close proximity and challenging due to wind and absence of a direct line of sight. Three industrial scenarios are implemented for investigation of the concept and controllers efficiency: deployment of a mobile inspection robot at the remotely-located pipe, peg-in-hole assembly, and turning a valve. The research results significantly update the state of the art in the aerial manipulation field and facilitate the topic toward the enhanced technology readiness level