Todd W. Danko

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.

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.

Design and Control of a Hyper-Redundant Manipulator for Mobile Manipulating Unmanned Aerial Vehicles

Manipulating objects using arms mounted to unmanned aerial vehicles (UAVs) is attractive because UAVs may access many locations that are otherwise inaccessible to other mobile manipulation platforms such as ground vehicles. Despite recent work, several major challenges remain to be overcome before it will be practical to manipulate objects from UAVs. Among these challenges are: (a) The constantly moving UAV platform and compliance of manipulator arms make it difficult to position the UAV and end-effector relative to an object of interest precisely enough for manipulation, and (b) The motions of the manipulator impact the stability of the host UAV, further complicating positioning. Solving these challenges will bring UAVs one step closer to being able to perform meaningful tasks such as infrastructure repair, disaster response, casualty extraction, and cargo resupply. Toward solutions to these challenges, this paper describes a hyper-redundant manipulator, manipulator control approaches and system design considerations to position the manipulator relative to objects of interest in such a way that impacts on platform stability are minimized.

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.

A parallel manipulator for mobile manipulating UAVs

Manipulating objects using arms mounted to unmanned aerial vehicles (UAVs) is attractive because UAVs may access many locations that are otherwise inaccessible to traditional mobile manipulation platforms such as ground vehicles. Most previous efforts seeking to coordinate the combined manipulator-UAV system have focused on using a manipulator to extend the UAVs reach and assume that both the UAV and manipulator can reliably reach commanded goal poses. This work accepts the reality that state of the art UAV positioning precision is not of a high enough quality to reliably perform simple tasks such as grasping objects. A 6 degree of freedom parallel manipulator is used to robustly maintain precise end-effector positions despite host UAV perturbations. A description of a unique parallel manipulator that allows for very little moving mass, and is easily stowed below a quadrotor UAV is presented along with flight test results and an analytical comparison to a serial manipulator.

A hyper-redundant manipulator for Mobile Manipulating Unmanned Aerial Vehicles

Due to their ability to navigate in 6 degree of freedom space, Unmanned Aerial Vehicles (UAVs) can access many locations that are inaccessible to ground vehicles. While mobile manipulation is an extremely active field of research for ground traveling host platforms, UAVs have historically been used for applications that avoid interaction with their environment at all costs. Recent efforts have been aimed at equipping UAVs with dexterous manipulators in an attempt to allow these Mobile Manipulating UAVs (MM-UAVs) to perform meaningful tasks such as infrastructure repair, disaster response, casualty extraction, and cargo resupply. Among many challenges associated with the successful manipulation of objects from a UAV host platform include: a) the manipulators movements and interaction with objects negatively impact the host platforms stability and b) movements of the host platform, even when using highly accurate motion capture systems for position control, translate to poor end effector position control relative to fixed objects. To address these two problems, we propose the use of a hyper-redundant manipulator for MM-UAV applications. The benefits of such a manipulator are that it: a) can be controlled in such a way that links are moved within the arms free space to help reduce negative impacts on the host platforms stability and b) the redundancy of the arm affords a highly reachable workspace for the end effector, allowing the end effector to track environmental objects smoothly despite host platform motions. This paper describes the design of a hyper-redundant manipulator suitable for studying its applicability to MM-UAV applications and provides preliminary results from its initial testing while mounted on a stationary scaffold.

Robotic rotorcraft and perch-and-stare: sensing landing zones and handling obscurants

Perch and stare is a maneuver where a vehicle flies to an overhead vantage point to provide a user with improved tactical information. This may include landing on rooftops, flying from rooftop to rooftop, or to windowsills all while carrying cameras or other intelligence gathering sensors. Miniature rotorcraft are ideal surveillance platforms, especially for perch and stare maneuvers because of their unique ability to take off and land vertically. Minimal vehicle size and weight also greatly enhance portability. Real world environmental influences such as fog, smoke, wind and cluttered or moving landing areas greatly complicate perch and stare maneuvers. This paper describes the application of optic flow and ultrasonic range finding sensors to increase miniature robotic rotorcraft autonomy for perch and stare maneuvers, especially in degraded environments

Evaluation of visual servoing control of aerial manipulators using test gantry emulation

Unmanned Aerial Vehicles (UAVs) offer a means to vastly expand a manipulators reach. Mounting an arm to a UAV greatly increases the utility of both the arm and the UAV. This paper describes the application of partitioning to control the redundant degrees of freedom of an emulated aerial manipulation system. Visual servoing is used to drive the end-effector pose relative to a target, treating relative motions between the host vehicle and target as perturbations. The position of the host platform, emulated by a gantry, is servoed using kinematic information from the manipulator in such a way that it enables the arm to return to a pose with a high degree of reachability while imposing minimal static torque on the host. A prototype system is implemented and evaluated using a 6-DOF manipulator and a gantry in place of a flying UAV. The partitioning algorithm is exercised as a proof of concept motivating the future use of this approach on a flying platform, though further refinement is required before this goal may be realized.

An Architecture for Human-Guided Autonomy: Team TROOPER at the DARPA Robotics Challenge Finals: An Architecture for Human-Guided Autonomy

Recent robotics efforts have automated simple, repetitive tasks to increase execution speed and lessen an operator’s cognitive load, allowing them to focus on higher-level objectives. However, an autonomous system will eventually encounter something unexpected, and if this exceeds the tolerance of automated solutions, there must be a way to fall back to teleoperation. Our solution is a largely autonomous system with the ability to determine when it is necessary to ask a human operator for guidance. We call this approach human-guided autonomy. Our design emphasizes human-on-the-loop control where an operator expresses a desired highlevel goal for which the reasoning component assembles an appropriate chain of subtasks. We introduce our work in the context of the DARPA Robotics Challenge (DRC) Finals. We describe the software architecture Team TROOPER developed and used to control an Atlas humanoid robot. We employ perception, planning, and control automation for execution of subtasks. If subtasks fail, or if changing environmental conditions invalidate the planned subtasks, the system automatically generates a new task chain. The operator is able to intervene at any stage of execution, to provide input and adjustment to any control layer, enabling operator involvement to increase as confidence in automation decreases. We present our performance at the DRC Finals and a discussion about lessons learned. C

Insertion tasks using an aerial manipulator

This paper demonstrates insertion tasks using an aerial vehicle affixed with a multi-degree of freedom manipulator. Using a combined strategy of visual servoing and force feedback compliance, the aerial manipulator achieves peg-in-hole insertion while attached to a validation test rig. A strongly coupled control scheme between the aircraft and manipulator is mandated for tasks requiring millimeter accuracy. Visual servoing is well-established for both ground and aerial vehicles and facilitates the large aircraft-arm motions. Force feedback upon contact with the environment provides compliant insertion and smaller motions in the presence of position error. We present recent results demonstrating and validating peg-in-hole insertion using the proposed aircraft-arm model and system.