1,721,066 research outputs found
Experimental vibration analysis and development of the dynamic model of a uav for aerial manipulation
No full textIn the near future, aerial manipulators will be employed in important field applications, such as inspection and maintenance of bridges, tall buildings, wind farms, and offshore and nuclear plants, and search and rescue or structure assembly in hazardous environments. Unfortunately, the precision of aerial manipulators is seriously affected by the dynamic interaction between the Unmanned Aerial Vehicle (UAV) and the robot manipulator. Indeed, on the one hand, the manipulator transfers forces and torques to the UAV, which affect the UAV position and attitude. On the other hand, the UAV induces undesired vibrations on the manipulator. In this paper, first, Experimental Modal Analysis (EMA) has been used to find the experimental vibration modes of a heavy payload UAV. Then, simplified Mass-Spring-Damper (MSD) dynamic models of the UAV have been proposed, to model the most relevant experimental modes of vibration. Finally, a simple 3-Degrees-of-Freedom (3-DOFs) MSD model has been proposed to model the whole system, which eigenfrequencies and vibration modes are in good agreement with the experimental data. The developed model has been used to simulate the system response in the real scenario of a sudden variation in the lift force due to turbulence
ZERO REACTION WORKSPACE IN THE OPERATIONS OF MULTI DEGREES OF FREEDOM SPACE MANIPULATORS FOR ORBITAL MAINTENANCE
No full textThe control of the reactions transferred to the spacecraft during a manipulator manoeuvre is an important
issue in order to reduce the energy consumption and extend the operating life of the Attitude Control
System. In this paper the performance of a novel least-squares-based reaction control method recently
introduced by some of the authors is analyzed in the case of multi-degrees-of-freedom 3D space
manipulators. The proposed method locally minimizes the base reactions transferred by the manipulator
to the base spacecraft by exploiting its redundancy, and has some important advantages with respect to
the previous ones presented in the literature: a simple mathematical formulation, the possibility to use
simple least-squares real-time routines for the solution, and the possibility to take into account the joint
limits and the joint velocity and acceleration limits of the manipulator. The methods can be profitably
used for the minimization of the base reaction torques, forces, and weighted combinations of them. The
main objectives of the study presented in this paper are the implementation in a software simulator and
the validation of the aforementioned reaction control solution in the case of 3D space robots, the study of
the Zero Reaction Workspace of a modular 3D space robot, and the analysis of its dependence on the
robot initial configuration and on the number of degrees of freedom of the robot. The minimization of the
base reaction torques, forces, and both of them is considered
TRACKING OF A BASE REACTION PROFILE FOR A SPACE MANIPULATOR
No full textA manipulator that is performing a manoeuvre generates reaction forces and
torques that dynamically load the supporting base. A special interest in the control of the base
reactions arises for robots mounted on a moving base, due to the interaction between the
motion of the manipulator and the motion of the base itself, which in many cases needs to be
controlled at the same time. In this paper the problem of tracking an arbitrary base reaction
profile is considered. The present work gives a contribution to the subject of the kinematic
control of spacecraft mounted manipulators and their dynamical effects in terms of reaction
forces and torques, and can be used for the development of centralized control systems aimed
at controlling multiple robots mounted on the same spacecraft, where a non-operating
manipulator can cooperate to compensate the disturbances generated by a second operating
robot, together with the reaction control system actuators. The solution to the problem is
given in the form of a kinematic law for the joint variables of the manipulator, and the joint
acceleration trajectories related to the desired base reaction profile are obtained.
Furthermore, the influence of the degree of redundancy of the robot is analyzed, with respect
both to the kinematic and the dynamic tasks. The availability of the redundancy can be
exploited in order to prescribe a desired trajectory to the end-effector, and specifically the
problem of realizing a defined base reaction profile and in the meantime achieve the best
approximation of an end-effector trajectory is considered. The proposed solutions are
developed in terms of pseudoinverse formulations, and the reaction control problems are set
in local optimization form, leading to the definition of constrained least squares problems.
The implementation of the proposed kinematic schemes in a robot simulator allowed to test
the capabilities of the proposed concepts
Zero Reaction Torque Trajectory Tracking of an Aerial Manipulator through Extended Generalized Jacobian
Full text linkFeatured Application: Inspection of structures, e.g., offshore/nuclear/eolic plants, bridges, and tall buildings. Placement and retrieval of sensors. Assembly of structures in places not accessible/safe for humans. Aerial manipulators are used in industrial and service robotics tasks such as assembly, inspection, and maintenance. One of the main challenges in aerial manipulation is related to the motion of the UAV base caused by manipulator disturbance torques and forces, which jeopardize the precision of the robot manipulator. In this paper, we propose two novel inverse kinematic control methods used to track a trajectory with an aerial manipulator while also considering resultant UAV base motions. The first method is adapted from the generalized Jacobian formulation used in space robotics and includes the change in system momentum resulting from gravity and UAV control forces in the inverse kinematic control equation. This approach is simulated for a 2 and 3 degree-of-freedom aerial manipulator tracking trajectories with the end-effector. Although the end-effector position error is approximately zero throughout the simulated task, we see significant undesired UAV base motions of several centimeters in magnitude. To ameliorate this by exploiting the kinematic redundancy, we modify the generalized Jacobian by adding an additional task constraint which minimizes the reaction torques from the manipulator, to form the extended generalized Jacobian. While the second approach results in improved precision and reduced base motion by an order of magnitude as compared to the generalized Jacobian, a drawback is the reduction in the available workspace as the solution seeks to minimize the manipulator center of gravity translation. We also demonstrate and compare both approaches in a load picking task. All the algorithms are completed computationally faster than real time in the MATLAB simulations, illustrating their potential for application in real-world experiments
NOVEL REACTION CONTROL OF SPACE MANIPULATORS WITH INCREASED ROBUSTNESS AGAINST SINGULARITIES AND PHYSICAL JOINT LIMITS
No full textRedundant space manipulators can perform robotic operations while minimizing the reactions transferred
to the base spacecraft. In this way the load on the Attitude Control System can be reduced thus increasing
its operating life. In this context, a robust reaction control solution should at least take into account the
robot physical joint limits, the robot joint velocity and acceleration limits, and the avoidance of
algorithmic and dynamic singularities. In this paper, the least squares reaction control solution recently
developed by some of the authors, which can take into account the joint acceleration limits in the realtime
solution, has been modified in order to take into account also the joint and the joint velocity limits.
In this way a robust solution is obtained, which can take into account the physical limits of the
manipulator joints and can be used to avoid the manipulator dynamic and algorithmic singularities, thanks
to the imposed change of the history in the joint space. Then, the possibility of time scaling the desired
end-effector trajectories, which allows to perform the given task with reduced joint velocities and
accelerations has been analyzed. An additional advantage of this method is that reduced joint torques are
necessary and, therefore, the error in the control due to joint flexibility is reduced or, from another point
of view, lighter robot structures can be used. In addition, the time scaling of the desired end-effector
trajectory can be used to perform accelerated tests of the operations of a space robot. Finally, the
proposed robust reaction control solution and the method of time scaling have been combined in order to
enhance their performance. The proposed robust reaction control method, the time scaling method, and
their combination have been analyzed in order to evaluate their pros and cons and have been validated by
means of software simulations
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