Christopher Korpela

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.

MM-UAV: Mobile Manipulating Unmanned Aerial Vehicle

Given significant mobility advantages, UAVs have access to many locations that would be impossible for an unmanned ground vehicle to reach, but UAV research has historically focused on avoiding interactions with the environment. Recent advances in UAV size to payload and manipulator weight to payload ratios suggest the possibility of integration in the near future, opening the door to UAVs that can interact with their environment by manipulating objects. Therefore, we seek to investigate and develop the tools that will be necessary to perform manipulation tasks when this becomes a reality. We present our progress and results toward a design and physical system to emulate mobile manipulation by an unmanned aerial vehicle with dexterous arms and end effectors. To emulate the UAV, we utilize a six degree-of-freedom miniature gantry crane that provides the complete range of motion of a rotorcraft as well as ground truth information without the risk associated with free flight. Two four degree-of-freedom manipulators attached to the gantry system perform grasping tasks. Computer vision techniques and force feedback servoing provide target object and manipulator position feedback to the control hardware. To test and simulate our system, we leverage the OpenRAVE virtual environment and ROS software architecture. Because rotorcraft are inherently unstable, introduce ground effects, and experience changing flight dynamics under external loads, we seek to address the difficult task of maintaining a stable UAV platform while interacting with objects using multiple, dexterous arms. As a first step toward that goal, this paper describes the design of a system to emulate a flying, dexterous mobile manipulator.

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.

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.

Designing a system for mobile manipulation from an Unmanned Aerial Vehicle

Due to their significant mobility advantages, UAVs have the potential to perform many tasks in locations that would be impossible for an unmanned ground vehicle to reach. However, most commercially available UAVs currently do not have the required lift to support high performance robotic arms. Recent advances in UAV size to payload and manipulator weight to payload ratios suggest the possibility of integration in the near future. Therefore, we seek to investigate and develop the tools that will be necessary to perform tasks when this becomes a reality. To emulate the UAV, we utilize a six degree-of-freedom gantry crane that provides the complete range of motion of a rotorcraft. Two seven degree-of-freedom manipulators attached to the gantry system perform grasping tasks. Computer vision techniques, including visual servoing, provide target object and manipulator position feedback to the control hardware. To test and simulate our system, we leverage the OpenRAVE virtual environment and ROS software architecture. Because rotorcraft are inherently unstable, introduce ground effects, and experience changing flight dynamics under external loads, we seek to address the difficult task of maintaining a stable UAV platform while interacting with objects using multiple, dexterous arms. As a first step toward that goal, this paper describes the design of a system to emulate highly dexterous manipulators on a UAV.