The Experts below are selected from a list of 15363 Experts worldwide ranked by ideXlab platform
Farhad Aghili - One of the best experts on this subject based on the ideXlab platform.
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adaptive control of manipulators forming closed kinematic chain with inaccurate kinematic model
IEEE-ASME Transactions on Mechatronics, 2013Co-Authors: Farhad AghiliAbstract:The problem of self-tuning control of cooperative manipulators forming closed kinematic chain in the presence of inaccurate kinematics model is addressed in this paper. The kinematic parameters pertaining to the relative position/orientation uncertainties of the interconnected manipulators are updated online by two cascaded estimators in order to tune a cooperative controller for achieving accurate motion tracking with minimum-norm Actuation Force. This technique permits accurate calibration of the relative kinematics of the involved manipulators without needing high precision end-point sensing or Force measurements, and hence, it is economically justified. Investigating the stability of the entire real-time estimator/controller system reveals that the convergence and stability of the adaptive control process can be ensured if 1) the direction of angular velocity vector does not remain constant over time, and 2) the initial kinematic parameter error is upper bounded by a scaler function of some known parameters. The adaptive controller is proved to be singularity-free even though the control law involves inverting the approximation of a matrix computed at the estimated parameters. Experimental results demonstrate the sensitivity of the tracking performance of the conventional inverse dynamic control scheme to kinematic inaccuracies, while the tracking error is significantly reduced by the self-tuning cooperative controller.
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control of redundant mechanical systems under equality and inequality constraints on both input and constraint Forces
Journal of Computational and Nonlinear Dynamics, 2011Co-Authors: Farhad AghiliAbstract:The equality and inequality constraints on constraint Force and/or the actuator Force/ torque arise in several robotic applications, for which different controllers have been specifically developed. This paper presents a unified approach to control a rather general class of robotic systems with closed loops under a set of linear equality and inequality constraints using the notion of projection operator. The controller does not require the kinematic constraints to be independent, i.e., systems with time-varying topology can be dealt with, while demanding minimum-norm Actuation Force or torque in the case that the system becomes redundant. The orthogonal decomposition of the control input Force yields the null-space component and its orthogonal complement. The null-space component is obtained using the projected inverse dynamics control law, while the orthogonal complement component is found through solving a quadratic programming problem, in which the equality and inequality constraints are derived to be equivalent to the originally specified ones. Finally, a case study is presented to demonstrate how the control technique can be applied to multi-arms manipulation of an object. DOI: 10.1115/1.4002689
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a unified approach for inverse and direct dynamics of constrained multibody systems based on linear projection operator applications to control and simulation
IEEE Transactions on Robotics, 2005Co-Authors: Farhad AghiliAbstract:This paper presents a unified approach for inverse and direct dynamics of constrained multibody systems that can serve as a basis for analysis, simulation, and control. The main advantage of the dynamics formulation is that it does not require the constraint equations to be linearly independent. Thus, a simulation may proceed even in the presence of redundant constraints or singular configurations, and a controller does not need to change its structure whenever the mechanical system changes its topology or number of degrees of freedom. A motion-control scheme is proposed based on a projected inverse-dynamics scheme which proves to be stable and minimizes the weighted Euclidean norm of the Actuation Force. The projection-based control scheme is further developed for constrained systems, e.g., parallel manipulators, which have some joints with no actuators (passive joints). This is complemented by the development of constraint Force control. A condition on the inertia matrix resulting in a decoupled mechanical system is analytically derived that simplifies the implementation of the Force control. Finally, numerical and experimental results obtained from dynamic simulation and control of constrained mechanical systems, based on the proposed inverse and direct dynamics formulations, are documented.
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inverse and direct dynamics of constrained multibody systems based on orthogonal decomposition of generalized Force
International Conference on Robotics and Automation, 2003Co-Authors: Farhad AghiliAbstract:This paper presents a unified approach for inverse and direct dynamics of constrained multibody systems that can be served as a basis for analysis, simulation, and control. The compactness of the dynamics formulation can result in computational efficiency. Furthermore, the acceleration is explicitly related to the generalized Force by an introduced "constraint inertia matrix" which is proved to be always invertible. Thus a simulation may proceed even with the presence of redundant constraints or singular configurations. The generalized Forces are decomposed onto two orthogonal subspaces which are considered as control inputs for controlling position and constraint Force. The motion controller scheme, remarkably, requires no Force feedback, proves to be stable, and minimizes Actuation Force. Finally, numerical and experimental results obtained from dynamic simulation and control of constrained mechanical systems, based on the proposed inverse and direct dynamics formulations, are documented.
Thomas Würtz - One of the best experts on this subject based on the ideXlab platform.
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Modeling and Control of the Twisted String Actuation System
IEEE-ASME Transactions on Mechatronics, 2013Co-Authors: Gianluca Palli, Ciro Natale, Claudio Melchiorri, Thomas WürtzAbstract:The innovative Actuation concept presented in this paper allows the implementation of powerful, simple, compact, and light-weight tendon-based driving systems, using as actuators small-size dc motors characterized by high speed and low torque. Due to its properties, this Actuation system is very well suited for implementation in highly integrated robotic devices. The basic working principle of this novel Actuation system is introduced, and the constitutive equations of the system are given, together with their experimental validation. Driven by the necessity of controlling the Actuation Force in the robotic hand, the problem of tracking a desired Force profile is tackled. With the aim of guaranteeing a high level of robustness against disturbances, a control algorithm based on a second-order sliding manifold has first been evaluated by means of simulations and then validated by experiments. The results obtained with this simple and compact Actuation system demonstrate its suitability for use in robotic devices such as robotic hands.
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The twisted string Actuation system: Modeling and control
2010 IEEE ASME International Conference on Advanced Intelligent Mechatronics, 2010Co-Authors: Thomas Würtz, Ciro Natale, Benedikt Holz, Gianluca Palli, Claudio MelchiorriAbstract:This paper describes a novel Actuation system for very compact and light-weight robotic devices, like artificial hands. The Actuation concept presented here allows the implementation of powerful tendon-based driving systems, using as actuators small-size DC motors characterized by high speed and low torque. After the presentation of the basic concept of this novel Actuation system, the constitutive equations of the system are given, validated by means of laboratory tests. Moreover, the problem of tracking a desired Actuation Force profile is taken into account, considering as load a mass-spring-damper system. A control algorithm based on a second-order sliding manifold has been firstly evaluated by means of simulations, and then validated by experiments. This output-feedback controller has been chosen to guarantee a high level of robustness against disturbances, parameter variations and uncertainties while maintaining a low computational burden.
Armano M. - One of the best experts on this subject based on the ideXlab platform.
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Analysis of the accuracy of Actuation electronics in the laser interferometer space antenna pathfinder
'AIP Publishing', 2020Co-Authors: Armano M., Audley H., Baird J., Born M., Bortoluzzi D., Cardines N., Castelli E., Cavalleri A., Cesarini A., Cruise A.m.Abstract:International audienceThe Laser Interferometer Space Antenna Pathfinder (LPF) main observable, labeled Δg, is the differential Force per unit mass acting on the two test masses under free fall conditions after the contribution of all non-gravitational Forces has been compensated. At low frequencies, the differential Force is compensated by an applied electrostatic Actuation Force, which then must be subtracted from the measured acceleration to obtain Δg. Any inaccuracy in the Actuation Force contaminates the residual acceleration. This study investigates the accuracy of the electrostatic Actuation system and its impact on the LPF main observable. It is shown that the inaccuracy is mainly caused by the rounding errors in the waveform processing and also by the random error caused by the analog to digital converter random noise in the control loop. Both errors are one order of magnitude smaller than the resolution of the commanded voltages. We developed a simulator based on the LPF design to compute the close-to-reality Actuation voltages and, consequently, the resulting Actuation Forces. The simulator is applied during post-processing the LPF data
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Analysis of the accuracy of Actuation electronics in the laser interferometer space antenna pathfinder
'AIP Publishing', 2020Co-Authors: Armano M., Audley H., Baird J., Ramos Castro, Juan JoséAbstract:This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Armano, Michele, et al. "Analysis of the accuracy of Actuation electronics in the laser interferometer space antenna pathfinder." Review of Scientific Instruments 91.4 (2020): 045003. and may be found at https://aip.scitation.org/doi/10.1063/1.5140406The Laser Interferometer Space Antenna Pathfinder (LPF) main observable, labeled ¿g, is the differential Force per unit mass acting on the two test masses under free fall conditions after the contribution of all non-gravitational Forces has been compensated. At low frequencies, the differential Force is compensated by an applied electrostatic Actuation Force, which then must be subtracted from the measured acceleration to obtain ¿g. Any inaccuracy in the Actuation Force contaminates the residual acceleration. This study investigates the accuracy of the electrostatic Actuation system and its impact on the LPF main observable. It is shown that the inaccuracy is mainly caused by the rounding errors in the waveform processing and also by the random error caused by the analog to digital converter random noise in the control loop. Both errors are one order of magnitude smaller than the resolution of the commanded voltages. We developed a simulator based on the LPF design to compute the close-to-reality Actuation voltages and, consequently, the resulting Actuation Forces. The simulator is applied during post-processing the LPF data.The Spanish contribution has been supported by contracts AYA2010-15709 (MICINN), ESP2013-47637-P, and ESP2015-67234-P (MINECO). M. Nofrarias acknowledges support from Fundacion General CSIC (Programa ComFuturo). F. Rivas acknowledges an FPI contract (MINECO).Peer ReviewedPostprint (author's final draft
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LISA pathfinder performance confirmed in an open-loop configuration: results from the free-fall Actuation mode
'American Physical Society (APS)', 2019Co-Authors: Armano M., Audley H., Baird J., Born M., Bortoluzzi D., Binetruy P., Ramos Castro, Juan JoséAbstract:We report on the results of the LISA Pathfinder (LPF) free-fall mode experiment, in which the control Force needed to compensate the quasistatic differential Force acting on two test masses is applied intermittently as a series of "impulse" Forces lasting a few seconds and separated by roughly 350 s periods of true free fall. This represents an alternative to the normal LPF mode of operation in which this balancing Force is applied continuously, with the advantage that the acceleration noise during free fall is measured in the absence of the Actuation Force, thus eliminating associated noise and Force calibration errors. The differential acceleration noise measurement presented here with the free-fall mode agrees with noise measured with the continuous Actuation scheme, representing an important and independent confirmation of the LPF result. An additional measurement with larger Actuation Forces also shows that the technique can be used to eliminate Actuation noise when this is a dominant factor.Peer Reviewe
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LISA Pathfinder Performance Confirmed in an Open-Loop Configuration: Results from the Free-Fall Actuation Mode
'American Physical Society (APS)', 2019Co-Authors: Armano M., Audley H., Baird J., Born M., Bortoluzzi D., Castelli E., Cavalleri A., Cesarini A., Binetruy P., Cruise A. M.Abstract:We report on the results of the LISA Pathfinder (LPF) free-fall mode experiment, in which the control Force needed to compensate the quasistatic differential Force acting on two test masses is applied intermittently as a series of "impulse" Forces lasting a few seconds and separated by roughly 350 s periods of true free fall. This represents an alternative to the normal LPF mode of operation in which this balancing Force is applied continuously, with the advantage that the acceleration noise during free fall is measured in the absence of the Actuation Force, thus eliminating associated noise and Force calibration errors. The differential acceleration noise measurement presented here with the free-fall mode agrees with noise measured with the continuous Actuation scheme, representing an important and independent confirmation of the LPF result. An additional measurement with larger Actuation Forces also shows that the technique can be used to eliminate Actuation noise when this is a dominant factor
Ramos Castro, Juan José - One of the best experts on this subject based on the ideXlab platform.
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Analysis of the accuracy of Actuation electronics in the laser interferometer space antenna pathfinder
'AIP Publishing', 2020Co-Authors: Armano M., Audley H., Baird J., Ramos Castro, Juan JoséAbstract:This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Armano, Michele, et al. "Analysis of the accuracy of Actuation electronics in the laser interferometer space antenna pathfinder." Review of Scientific Instruments 91.4 (2020): 045003. and may be found at https://aip.scitation.org/doi/10.1063/1.5140406The Laser Interferometer Space Antenna Pathfinder (LPF) main observable, labeled ¿g, is the differential Force per unit mass acting on the two test masses under free fall conditions after the contribution of all non-gravitational Forces has been compensated. At low frequencies, the differential Force is compensated by an applied electrostatic Actuation Force, which then must be subtracted from the measured acceleration to obtain ¿g. Any inaccuracy in the Actuation Force contaminates the residual acceleration. This study investigates the accuracy of the electrostatic Actuation system and its impact on the LPF main observable. It is shown that the inaccuracy is mainly caused by the rounding errors in the waveform processing and also by the random error caused by the analog to digital converter random noise in the control loop. Both errors are one order of magnitude smaller than the resolution of the commanded voltages. We developed a simulator based on the LPF design to compute the close-to-reality Actuation voltages and, consequently, the resulting Actuation Forces. The simulator is applied during post-processing the LPF data.The Spanish contribution has been supported by contracts AYA2010-15709 (MICINN), ESP2013-47637-P, and ESP2015-67234-P (MINECO). M. Nofrarias acknowledges support from Fundacion General CSIC (Programa ComFuturo). F. Rivas acknowledges an FPI contract (MINECO).Peer ReviewedPostprint (author's final draft
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LISA pathfinder performance confirmed in an open-loop configuration: results from the free-fall Actuation mode
'American Physical Society (APS)', 2019Co-Authors: Armano M., Audley H., Baird J., Born M., Bortoluzzi D., Binetruy P., Ramos Castro, Juan JoséAbstract:We report on the results of the LISA Pathfinder (LPF) free-fall mode experiment, in which the control Force needed to compensate the quasistatic differential Force acting on two test masses is applied intermittently as a series of "impulse" Forces lasting a few seconds and separated by roughly 350 s periods of true free fall. This represents an alternative to the normal LPF mode of operation in which this balancing Force is applied continuously, with the advantage that the acceleration noise during free fall is measured in the absence of the Actuation Force, thus eliminating associated noise and Force calibration errors. The differential acceleration noise measurement presented here with the free-fall mode agrees with noise measured with the continuous Actuation scheme, representing an important and independent confirmation of the LPF result. An additional measurement with larger Actuation Forces also shows that the technique can be used to eliminate Actuation noise when this is a dominant factor.Peer Reviewe
A.m. Cruise - One of the best experts on this subject based on the ideXlab platform.
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Analysis of the accuracy of Actuation electronics in the laser interferometer space antenna pathfinder
Rev.Sci.Instrum., 2020Co-Authors: M. Armano, H. Audley, J. Baird, M. Born, D. Bortoluzzi, N. Cardines, E. Castelli, A. Cavalleri, A. Cesarini, A.m. CruiseAbstract:The Laser Interferometer Space Antenna Pathfinder (LPF) main observable, labeled Δg, is the differential Force per unit mass acting on the two test masses under free fall conditions after the contribution of all non-gravitational Forces has been compensated. At low frequencies, the differential Force is compensated by an applied electrostatic Actuation Force, which then must be subtracted from the measured acceleration to obtain Δg. Any inaccuracy in the Actuation Force contaminates the residual acceleration. This study investigates the accuracy of the electrostatic Actuation system and its impact on the LPF main observable. It is shown that the inaccuracy is mainly caused by the rounding errors in the waveform processing and also by the random error caused by the analog to digital converter random noise in the control loop. Both errors are one order of magnitude smaller than the resolution of the commanded voltages. We developed a simulator based on the LPF design to compute the close-to-reality Actuation voltages and, consequently, the resulting Actuation Forces. The simulator is applied during post-processing the LPF data.
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LISA Pathfinder Performance Confirmed in an Open-Loop Configuration: Results from the Free-Fall Actuation Mode
Phys.Rev.Lett., 2019Co-Authors: M. Armano, H. Audley, J. Baird, M. Born, D. Bortoluzzi, E. Castelli, A. Cavalleri, A. Cesarini, P. Binetruy, A.m. CruiseAbstract:We report on the results of the LISA Pathfinder (LPF) free-fall mode experiment, in which the control Force needed to compensate the quasistatic differential Force acting on two test masses is applied intermittently as a series of “impulse” Forces lasting a few seconds and separated by roughly 350 s periods of true free fall. This represents an alternative to the normal LPF mode of operation in which this balancing Force is applied continuously, with the advantage that the acceleration noise during free fall is measured in the absence of the Actuation Force, thus eliminating associated noise and Force calibration errors. The differential acceleration noise measurement presented here with the free-fall mode agrees with noise measured with the continuous Actuation scheme, representing an important and independent confirmation of the LPF result. An additional measurement with larger Actuation Forces also shows that the technique can be used to eliminate Actuation noise when this is a dominant factor.
