2,037 research outputs found
Robust Cooperative Manipulation without Force/Torque Measurements: Control Design and Experiments
This paper presents two novel control methodologies for the cooperative
manipulation of an object by N robotic agents. Firstly, we design an adaptive
control protocol which employs quaternion feedback for the object orientation
to avoid potential representation singularities. Secondly, we propose a control
protocol that guarantees predefined transient and steady-state performance for
the object trajectory. Both methodologies are decentralized, since the agents
calculate their own signals without communicating with each other, as well as
robust to external disturbances and model uncertainties. Moreover, we consider
that the grasping points are rigid, and avoid the need for force/torque
measurements. Load distribution is also included via a grasp matrix
pseudo-inverse to account for potential differences in the agents' power
capabilities. Finally, simulation and experimental results with two robotic
arms verify the theoretical findings
Adaptive tracking for complex systems using reduced-order models
Reduced-order models are considered in the context of parameter adaptive controllers for tracking workspace trajectories. A dual-arm manipulation task is used to illustrate the methodology and provide simulation results. A parameter adaptive controller is designed to track the desired position trajectory of a payload using a four-parameter model instead of a full-order, nine-parameter model. Several simulations with different payload-to-arm mass ratios are used to illustrate the capabilities of the reduced-order model in tracking the desired trajectory
Comparison of joint space versus task force load distribution optimization for a multiarm manipulator system
It is often proposed that the redundancy in choosing a force distribution for multiple arms grasping a single object should be handled by minimizing a quadratic performance index. The performance index may be formulated in terms of joint torques or in terms of the Cartesian space force/torque applied to the body by the grippers. The former seeks to minimize power consumption while the latter minimizes body stresses. Because the cost functions are related to each other by a joint angle dependent transformation on the weight matrix, it might be argued that either method tends to reduce power consumption, but clearly the joint space minimization is optimal. A comparison of these two options is presented with consideration given to computational cost and power consumption. Simulation results using a two arm robot system are presented to show the savings realized by employing the joint space optimization. These savings are offset by additional complexity, computation time and in some cases processor power consumption
Safety-Aware Human-Robot Collaborative Transportation and Manipulation with Multiple MAVs
Human-robot interaction will play an essential role in various industries and
daily tasks, enabling robots to effectively collaborate with humans and reduce
their physical workload. Most of the existing approaches for physical
human-robot interaction focus on collaboration between a human and a single
ground robot. In recent years, very little progress has been made in this
research area when considering aerial robots, which offer increased versatility
and mobility compared to their grounded counterparts. This paper proposes a
novel approach for safe human-robot collaborative transportation and
manipulation of a cable-suspended payload with multiple aerial robots. We
leverage the proposed method to enable smooth and intuitive interaction between
the transported objects and a human worker while considering safety constraints
during operations by exploiting the redundancy of the internal transportation
system. The key elements of our system are (a) a distributed payload external
wrench estimator that does not rely on any force sensor; (b) a 6D admittance
controller for human-aerial-robot collaborative transportation and
manipulation; (c) a safety-aware controller that exploits the internal system
redundancy to guarantee the execution of additional tasks devoted to preserving
the human or robot safety without affecting the payload trajectory tracking or
quality of interaction. We validate the approach through extensive simulation
and real-world experiments. These include as well the robot team assisting the
human in transporting and manipulating a load or the human helping the robot
team navigate the environment. To the best of our knowledge, this work is the
first to create an interactive and safety-aware approach for quadrotor teams
that physically collaborate with a human operator during transportation and
manipulation tasks.Comment: Guanrui Li and Xinyang Liu contributed equally to this pape
An Omnidirectional Aerial Platform for Multi-Robot Manipulation
The objectives of this work were the modeling, control and prototyping of a new fully-actuated
aerial platform. Commonly, the multirotor aerial platforms are under-actuated vehicles, since the
total propellers thrust can not be directed in every direction without inferring a vehicle body rotation.
The most common fully-actuated aerial platforms have tilted or tilting rotors that amplify
the aerodynamic perturbations between the propellers, reducing the efficiency and the provided
thrust. In order to overcome this limitation a novel platform, the ODQuad (OmniDirectional
Quadrotor), has been proposed, which is composed by three main parts, the platform, the mobile
and rotor frames, that are linked by means of two rotational joints, namely the roll and pitch
joints. The ODQuad is able to orient the total thrust by moving only the propellers frame by
means of the roll and pitch joints.
Kinematic and dynamic models of the proposed multirotor have been derived using the Euler-
Lagrange approach and a model-based controller has been designed. The latter is based on two
control loops: an outer loop for vehicle position control and an inner one for vehicle orientation
and roll-pitch joint control. The effectiveness of the controller has been tested by means of numerical
simulations in the MATLAB
c SimMechanics environment. In particular, tests in free motion
and in object transportation tasks have been carried out. In the transportation task simulation, a
momentum based observer is used to estimate the wrenches exchanged between the vehicle and
the transported object.
The ODQuad concept has been tested also in cooperative manipulation tasks. To this aim, a
simulation model was considered, in which multiple ODQuads perform the manipulation of a
bulky object with unknown inertial parameters which are identified in the first phase of the simulation.
In order to reduce the mechanical stresses due to the manipulation and enhance the system
robustness to the environment interactions, two admittance filters have been implemented: an external
filter on the object motion and an internal one local for each multirotor.
Finally, the prototyping process has been illustrated step by step. In particular, three CAD
models have been designed. The ODQuad.01 has been used in the simulations and in a preliminary
static analysis that investigated the torque values for a rough sizing of the roll-pitch joint
actuators. Since in the ODQuad.01 the components specifications and the related manufacturing
techniques have not been taken into account, a successive model, the ODQuad.02, has been designed.
The ODQuad.02 design can be developed with aluminum or carbon fiber profiles and 3D
printed parts, but each component must be custom manufactured. Finally, in order to shorten the
prototype development time, the ODQuad.03 has been created, which includes some components
of the off-the-shelf quadrotor Holybro X500 into a novel custom-built mechanical frame
Equilibria, Stability, and Sensitivity for the Aerial Suspended Beam Robotic System subject to Parameter Uncertainty
This work studies how parametric uncertainties affect the cooperative
manipulation of a cable-suspended beam-shaped load by means of two aerial
robots not explicitly communicating with each other. In particular, the work
sheds light on the impact of the uncertain knowledge of the model parameters
available to an established communication-less force-based controller. First,
we find the closed-loop equilibrium configurations in the presence of the
aforementioned uncertainties, and then we study their stability. Hence, we show
the fundamental role played in the robustness of the load attitude control by
the internal force induced in the manipulated object by non-vertical cables.
Furthermore, we formally study the sensitivity of the attitude error to such
parametric variations, and we provide a method to act on the load position
error in the presence of the uncertainties. Eventually, we validate the results
through an extensive set of numerical tests in a realistic simulation
environment including underactuated aerial vehicles and sagging-prone cables,
and through hardware experiments
Cooperative aerial manipulation with force control and attitude stabilization
Ranging from autonomous flying cars, fixed wing and rotorcraft UAVs, there has been a tremendous interest in aerial robotics over the last decade. This thesis presents contributions to the state-of-art in cooperative payload transport with force synthesis and dynamic interaction using quadcopter UAVs. In this report, we consider multiple quadcopter aerial robots and develop decentralized force controller for them to manipulate a payload. We use quadcopters with a rigid link attached to it to collaboratively manipulate the payload. We develop a dynamic model of the payload for both point mass and rigid body cases. We model the contact force between the agents and the payload as a mass spring model. This assumption is valid when the vehicles are connected to the payload via elastic cables or when the payload is flexible or surrounded by elastic bumper materials. We also extend our aerial manipulation system to a multi-link arm attached to the quadcopter.We develop an adaptive decentralized control law for transporting a payload of unknown mass without explicit communication between the agents. Our controller ensures that all quadcopters and the payload asymptotically converges to a constant reference velocity. It also ensures that all of the forces applied to the payload converges to desired set-points. Desired thrusts and attitude angles are computed from the control algorithms and a low-level PD controller is implemented to track the desired commands for each quadcopter. The sum of the estimates of the unknown mass from all the agents converge to the true mass. We also employ a consensus algorithm based on connected graphs to ensure that each agent gets an equal share of the payload mass. Furthermore, we develop an orientation control algorithm that guarantees attitude stabilization of the payload. In particular, we develop time varying force set-points to enforce attitude regulation without any moment inputs from the quadcopters
A fault detection and isolation system for cooperative manipulators
The problem of fault detection and isolation (FDI) in cooperative manipulators is addressed in this paper. Four FDI procedures are developed to deal with free-swinging joint faults, locked joint faults, incorrectly measured joint position, and incorrectly measured joint velocity. Free-swinging and locked joint faults are isolated via neural networks. For each arm, a Multilayer Perceptron (MLP) is used to reproduce the dynamics of the fault-free robot. The outputs of each MLP are compared to the actual joint velocities in order to generate a residual vector which is then classified by an RBF network. The remaining faults are isolated based on the kinematic constraints imposed on the cooperative system. Results obtained via simulations and via an actual cooperative manipulator robot are presented
Closed-Loop Behavior of an Autonomous Helicopter Equipped with a Robotic Arm for Aerial Manipulation Tasks
This paper is devoted to the control of aerial robots interacting physically with objects in the environment and
with other aerial robots. The paper presents a controller for the particular case of a small‐scaled autonomous helicopter equipped with a robotic arm for aerial manipulation.
Two
types
of
influences
are
imposed
on
the
helicopter
from
a
manipulator:
coherent
and
non
‐
coherent
influence.
In
the
former
case,
the
forces
and
torques
imposed
on
the
helicopter
by
the
manipulator
change
with
frequencies
close
to
those
of
the
helicopter
movement.
The
paper
shows
that
even
small
interaction
forces
imposed
on
the
fuselage
periodically
in
proper
phase
could
yield
to
low
frequency
instabilities
and
oscillations,
so
called
phase
circle
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