Matko Orsag

Modeling and Control of MM-UAV: Mobile Manipulating Unmanned Aerial Vehicle

Compared to autonomous ground vehicles, UAVs (unmanned aerial vehicles) have significant mobility advantages and the potential to operate in otherwise unreachable locations. Micro UAVs still suffer from one major drawback: they do not have the necessary payload capabilities to support high performance arms. This paper, however, investigates the key challenges in controlling a mobile manipulating UAV using a commercially available aircraft and a light-weight prototype 3-arm manipulator. Because of the overall instability of rotorcraft, we use a motion capture system to build an efficient autopilot. Our results indicate that we can accurately model and control our prototype system given significant disturbances when both moving the manipulators and interacting with the ground.

Dynamic stability of a mobile manipulating unmanned aerial vehicle

This paper presents a control scheme to achieve dynamic stability in an aerial vehicle with dual multi-degree of freedom manipulators. Arm movements assist with stability and recovery for ground robots, in particular humanoids and dynamically balancing vehicles. However, there is little work in aerial robotics where the manipulators themselves facilitate flight stability or the load mass is repositioned in flight for added control. We present recent results in arm motions that achieve increased flight stability without and with different load masses attached to the end-effectors. Our test flight results indicate that we can accurately model and control our aerial vehicle when both moving the manipulators and interacting with target objects.

Hybrid Adaptive Control for Aerial Manipulation

This paper presents a control scheme to achieve dynamic stability in a mobile manipulating unmanned aerial vehicle (MM-UAV) using a combination of Gain scheduling and Lyapunov based model reference adaptive control (MRAC). Our test flight results indicate that we can accurately model and control our aerial vehicle when both moving the manipulators and interacting with target objects. Using the Lyapunov stability theory, the controller is proven to be stable. The simulation results showed how the MRAC is capable of stabilizing the oscillations produced from the unstable PI-D attitude control loop. Finally a high level control system based on a switching automaton is proposed in order to ensure the saftey of the aerial manipulation missions.

Valve turning using a dual-arm aerial manipulator

This paper presents a framework for valve turning using an aerial vehicle endowed with dual multi-degree of freedom manipulators. A tightly integrated control scheme between the aircraft and manipulators is mandated for tasks requiring aircraft to environmental coupling. An analysis of yaw angle dynamics is conducted and implemented into the controller. A human machine interface provides user input to actuate the manipulators, become coupled to the valve, and perform the turning operation. We present recent results validating the valve turning framework using the proposed aircraft-arm system.

Towards Valve Turning using a Dual-Arm Aerial Manipulator

We propose a framework for valve turning using an aerial vehicle endowed with dual multi-degree of freedom manipulators. A tightly integrated control scheme between the aircraft and manipulators is mandated for tasks requiring aircraft to environmental coupling. Feature detection is well-established for both ground and aerial vehicles and facilitates valve detection and arm tracking. Force feedback upon contact with the environment provides compliant motions in the presence of position error and coupling with the valve. We present recent results validating the valve turning framework using the proposed aircraft-arm system during flight tests.

Stability control in aerial manipulation

Aerial manipulation, grasping, and perching in small unmanned aerial vehicles (UAVs) require specific control systems to compensate for changing inertial properties. Grasped objects, external forces from terrain objects, or manipulator movements themselves may destabilize or otherwise alter the flight characteristics of small UAVs during operation resulting in undesirable outcomes. Traditional control methods that assume static mass and inertial properties must be modified to produce stable control of a quadrotor system. This paper presents work towards a control scheme to achieve dynamic stability of an aerial vehicle while under the influence of manipulators and grasped objects. A quadrotor with attached multi-degree of freedom manipulators is implemented in simulation and constructed for testing. Compensation of the inertial changes due to in-flight manipulator movements is investigated. A control scheme is developed and results are presented.

Flight stability in aerial redundant manipulators

Ongoing efforts toward mobile manipulation from an aerial vehicle are presented. Recent tests and results from a prototype rotorcraft have shown that our hybrid structure increases stability during flight and manipulation. Since UAVs require significant setup time, suitable testing locations, and have tendencies to crash, we developed an aerial manipulation test and evaluation environment that provides controllable and repeatable experiments. By using force feedback techniques, we have designed multiple, dexterous, redundant manipulators that can grasp objects such as tools and small objects. These manipulators are controlled in concert with an emulated aerial platform to provide hovering stability. The manipulator and aircraft flight control are tightly coupled to facilitate grasping without large perturbations in the end-effector.

Hybrid control of quadrotor

This paper presents the solution to a quadrotor control problem based on a discrete automaton that, in combination with classical PID controllers, creates a hybrid control system. Some modifications to the known and widely used mathematical model of quadrotor aircrafts are also discussed in this paper. The paper shows an open loop control concept that flies the aircraft into looping. Finally, the performance of the suggested control scheme is tested with simulations.

Lyapunov based model reference adaptive control for aerial manipulation

This paper presents a control scheme to achieve dynamic stability in an aerial vehicle with dual multi-degree of freedom manipulators using a lyapunov based model reference adaptive control. Our test flight results indicate that we can accurately model and control our aerial vehicle when both moving the manipulators and interacting with target objects. Using the Lyapunov stability theory, the controller is proven to be stable. The simulation results showed how the MRAC is capable of stabilizing the oscillations produced from the unstable PI-D attitude control loop. Finally a high level control system based on a switching automaton is proposed in order to ensure the safety of the aerial manipulation missions.

Hardware-in-the-Loop Verification for Mobile Manipulating Unmanned Aerial Vehicles

A hardware-in-the-loop test rig is presented to bridge the gap between basic aerial manipulation research and the ability of flying robots to perform tasks such as bridge repair, agriculture care, container inspection and other applications requiring interaction with the environment. Unmanned aerial vehicles have speed and mobility advantages over ground vehicles and can operate in 3-dimensional workspaces. In particular, the usefulness of these capabilities is highlighted in areas where ground robots cannot reach or terrains they are unable to navigate. However, most UAVs operating in near-earth or indoor environments still do not have the payload capabilities to support multi-degree of freedom manipulators. We present a rotorcraft emulation environment using a 7 degree of freedom manipulator. Since UAVs require significant setup time and to avoid potential crashes, our test and evaluation environment provides repeatable experiments and captures reactionary forces experienced during ground interaction. Recent experiments in insertion tests are presented. The lessons learned from these experiments will be ported onto an actual air vehicle with manipulator.