Papers by Evangelos Papadopoulos
Intelligent Robots and …, 2002
Friction is responsible for several servomechanism problems, and their elimination is always a ch... more Friction is responsible for several servomechanism problems, and their elimination is always a challenge for control engineers. In this paper, feedback model-based compensation of friction is used for servomechanism set point and tracking tasks. Basic friction models are tested and their influence on system response is examined using describing function analysis. Analytical predictions are compared to simulations and experimental results. Various control laws using friction compensation are compared ...
This paper studies the attitude dynamics and the control of quadruped robots using tail-like appe... more This paper studies the attitude dynamics and the control of quadruped robots using tail-like appendages during the flight phases of high speed locomotion. Inspiration and data are first obtained from cheetah’s fast galloping techniques. A two-body template is then used to simply describe the dynamics of a large body whose attitude is controlled by a rotating appendage. The equations of motion for a tail and a reaction wheel are given, while by employing cyclic coordinates, all possible reductions are performed to finally lead to the design of model-based controllers. A main contribution lies on the thorough discussion on the holonomy of the system, which only depends on the system’s geometry and the initial angular momentum. A comparison between a reaction wheel and a tail is also carried out, while basic steps and formulas are proposed for selecting the key parameters concerning the design of such systems. Finally, simulation results are presented in order to validate the methods proposed herein.
In this work we study the attitude dynamics and the control of legged robots using tail-like appe... more In this work we study the attitude dynamics and the control of legged robots using tail-like appendages during the aerial phases of high speed locomotion. A free floating two-body system is used to describe the dynamics of a large body controlling its attitude using a rotating appendage. The equations of motion for a tail and a reaction wheel are given, and the meaning of the generalized coordinates being ignorable or palpable is discussed in detail. A thorough discussion on the holonomy of the system is also included. Analytical expressions are given for a further reduced dynamical model and model-based controllers are then proposed. Finally, we present a series of simulation results, and we derive conclusions that can serve as guidelines when designing such systems.
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Volume 4B: Dynamics, Vibration, and Control, 2014
ABSTRACT Higher-order layerwise piezoelectric laminate mechanics are presented for predicting the... more ABSTRACT Higher-order layerwise piezoelectric laminate mechanics are presented for predicting the low-velocity impact response of pristine composite and sandwich composite plates with piezoelectric transducers. The present formulation enables prediction of the global (temporal variation of impact force, deflection, strain and sensory potential) and local through-thickness (distribution of displacement, stress and strain) impact response of plates with piezoelectric layers or patches. Its enhanced capabilities include efficiency in terms of computational cost, since the system matrices are reduced by means of a Guyan scheme or by using the eigenvectors, thus leading to a plate-impactor system containing a single or two deflection amplitudes per vibration mode, depending on consideration of transverse compressibility. The transfer of the plate-impactor system to state-space enables investigation of the feasibility of real-time active control towards impact force reduction by using output feedback control laws.
In a number of industrial, space, or mobile applications, reaction forces and moments transmitted... more In a number of industrial, space, or mobile applications, reaction forces and moments transmitted by a manipulator to its base are undesirable. In this paper, we analyze the problem of force and torque transmission in robotic systems, and propose design and planning methods that can eliminate it, or reduce it. Based on force and moment transmission analysis, a three DOF redundant manipulator design is selected. Dynamic reaction forces are eliminated by force balancing. Reaction moments are eliminated by following reactionless paths, whose planning is simplified by rendering the dynamics configuration-invariant. Reactionless Workspaces are defined in which any end-effector path can result in zero dynamic reactions. An example is used to demonstrate the usefulness of the proposed methods. An important advantage of these methods is that the manipulator can be used either as a redundant, or as a reduced DOF reactionless system.
The Multiple Impedance Control (MIC) is anew algorithm which enforces a designated impedance onbo... more The Multiple Impedance Control (MIC) is anew algorithm which enforces a designated impedance onboth a manipulated object, and all cooperating manipulators. In this paper, the MIC is applied to a space roboticsystem in which robotic arms, mounted on a free-flyingbase, manipulate an object. The general formulation of theMIC is extended to include the dynamic coupling betweenthe arms and the base. It is shown that under the MIC law, all participating manipulators, the free-flyer base, and themanipulated object exhibit the same ...
This paper focuses on the modeling, parameter estimation, andmodel validation in open and closed-... more This paper focuses on the modeling, parameter estimation, andmodel validation in open and closed-loop of an experimentalforestry machine manipulator. Symbolic Newton-Euler and lineargraph methodologies are used in deriving mathematical models ofthe swing, boom and stick subsystems. Actuation dynamics areintegrated with manipulator dynamics to result in a completemanipulator and actuation model. Identification proceduresemployed in estimating physical parameters are discussed. Modelvalidation studies show good ...
Mobile manipulator systems, comprised of a mobile platformwith one or more manipulators, are of g... more Mobile manipulator systems, comprised of a mobile platformwith one or more manipulators, are of great interest in a numberof applications. This paper presents a planning and controlmethodology for such systems allowing them to followsimultaneously desired end-effector and platform trajectorieswithout violating the nonholonomic constraints. Based on areduction of system dynamics, a model-based controller i sdesigned to eliminate tracking errors without requiring largegains. The sensitivity to parameter errors is examined ...
The Multiple Impedance Control (MIC) is anew algorithm which enforces a designated impedance onbo... more The Multiple Impedance Control (MIC) is anew algorithm which enforces a designated impedance onboth a manipulated object, and all cooperating manipulators. In this paper, the MIC is applied to a space roboticsystem in which robotic arms, mounted on a free-flyingbase, manipulate an object. The general formulation of theMIC is extended to include the dynamic coupling betweenthe arms and the base. It is shown that under the MIC law, all participating manipulators, the free-flyer base, and themanipulated object exhibit the same ...
UK PubMed Central (UKPMC) is an archive of life sciences journal literature.
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International Journal of Fluid Power, 2002
This work focuses on the development of a real-time training simulator engine for a forestry mach... more This work focuses on the development of a real-time training simulator engine for a forestry machine. The rigid body dynamics of the machine's manipulator is integrated with electrohydraulic actuator dynamics and joint controllers. System numerical stiffness introduced by the closing valves, high order hydraulic dynamics, and simulator implementation using an interpreted language were identified as the prime reasons for slowing down the integration. Successive models of lower complexity and switching between models for the open and closed phases of the valves are proposed aiming to achieve a satisfactory simulator engine that can run in real-time. Simulation results demonstrate very good prediction of an actual machine behaviour with execution speeds improved by a factor of 35.
Mobile manipulators operating in field environmentsare susceptible to dangerous and costly rollov... more Mobile manipulators operating in field environmentsare susceptible to dangerous and costly rollover ortipover instabilities, particularly when operating overuneven terrain or when exerting large forces or moments. By monitoring the static and dynamic tipoverstability margins of a mobile manipulator it is possibleto predict such tipovers and take appropriate actionsto prevent the tipover from occurring. This paperdescribes a scheme for automatic tipover prediction, and prevention, which uses the static and dynamicForce--Angle ...
European Journal of Mechanics - A/Solids
Coupled higher-order layerwise piezoelectric laminate mechanics are presented, applicable to shal... more Coupled higher-order layerwise piezoelectric laminate mechanics are presented, applicable to shallow cylindrical composite and sandwich shells subjected to static mechanical loads and/or electric voltages. The current formulation enables efficient prediction of (i) global electromechanical response, (ii) local through-thickness distribution of electromechanical variables and (iii) interlaminar shear stress at the interface between adjacent material layers. Using the developed mechanics, the effects of curvature, thickness and ply angle on the global and local through-thickness response of sandwich composite shells are studied.
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Papers by Evangelos Papadopoulos