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.
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.
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 ...
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 ...
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.
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.
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.
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 ...
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 ...
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.
13th Symposium on Advanced Space Technologies in Robotics and Automation, (ASTRA ‘15)
Space debris removal and mitigation using space robots are complex missions, which require extens... more Space debris removal and mitigation using space robots are complex missions, which require extensive analysis prior to launch. An important aspect during such a mission is the capturing task; any unsuccessful attempt may create more problems than solve. In this paper, the modelling of the impact docking between two multibody systems is studied. The effects of mass ratios on the resulting changes of relative velocities are analysed and discussed. An extension of the rigid body impact theory to multibody systems is developed, where the effect of system mass ratios to the change of the relative velocities is quantified, and its significance is discussed. Velocity requirements leading to a successful latching at first impact will be identified. Simulation results are presented that validate the proposed analytical approach. Future work is discussed.
13th Symposium on Advanced Space Technologies in Robotics and Automation, (ASTRA ‘15)
Recent successes of missions such as the MSL and the Rosetta have increased the interest in the r... more Recent successes of missions such as the MSL and the Rosetta have increased the interest in the robotic exploration of other planets and asteroids. Although most of these missions envisage the use of rovers, legged robots have shown the potential to outperform wheeled vehicles on rough terrains in terms of speed and energy efficiency. In this paper, the x-MP controller presented in recent work, is used to evaluate the performance of a monopod robot under the effect of different gravitational fields and terrain types. The performance of the x-MP controller during regulating the robot motion on rough terrains and for the exploration of different types of planetary environments will be examined using simulations. Additionally using the Cost of Transport index, useful conclusions regarding the performance of legged robots for planetary exploration will be extracted.
12th Symposium on Advanced Space Technologies in Robotics and Automation, (ASTRA ‘13)
To validate on-orbit servicing strategies, extensive sim- ulations and terrestrial emulation of r... more To validate on-orbit servicing strategies, extensive sim- ulations and terrestrial emulation of robotic systems are necessary. The NTUA has developed a Space Robot Emulator to emulate the operation of free-flying robotic servicers, as already presented in previous works. Until recently, the emulator consisted of one robot with two manipulators, capable of hovering over a flat granite ta- ble using air bearings, and of planar motion employing CO2 thrusters and a reaction wheel. To extend the capa- bilities of the Emulator, a second robot was developed with similar operational and design principles. In this paper, the mechatronic design of the robotic systems is presented. The limitations of the first robot and the de- velopments to overcome them in the second as well as some preliminary validation tests are presented.
12th Symposium on Advanced Space Technologies in Robotics and Automation, (ASTRA ‘13)
On-Orbit Servicing plays a key role in the exploitation of space. To study related issues, the NT... more On-Orbit Servicing plays a key role in the exploitation of space. To study related issues, the NTUA has devel- oped a Space Robot Emulator for free-flying robotic servicers. In this emulator, the fusion of data from an overhead camera and on-board optical sensors is partic- ularly challenging. This becomes more complex due to the large time delay induced by the camera and image processing. To cope with these challenges, a Discrete Extended Kalman Filter (DEKF) is developed and ana- lyzed. Methods for reducing camera distortion errors and for calibration are discussed and simulation results are presented. Experiments validating the developed methodology are included.
In this paper, the development of an Orbital Robotics educational prototype platform is presented... more In this paper, the development of an Orbital Robotics educational prototype platform is presented, consisting of a hardware-developed physical system and an accompanying set of curriculum-based lessons (IB Physics curriculum) that target upper secondary students (16-18 years old target group). The students interactively use the hardware , consisting of a bespoke space-emulating table and small satellite mockups. During the lessons, this platform allows students to acquire knowledge of the dynamics of space systems, as well as the environmental conditions and physical constraints that characterize on-orbit operations. Students will be able to manipulate the space robot (satellite) mockups performing basic tasks such as docking, and landing or grasping space debris. Additionally, a smartphone application has been implemented to allow the interaction with the platform, via a dedicated User Interface (UI). The lessons are inquiry-based and are structured so that the students are actively engaged in the learning process, according to a learner-centric approach.
Highlights Consideration of the effects of permanent ground deformation and compaction. Developme... more Highlights Consideration of the effects of permanent ground deformation and compaction. Development of a controller immune to terrain compliance. No knowledge requirement of ground parameters. Successful tackle of foot slip effects and hard impacts during touchdown. The methodology can be extended to other legged robots such as quadrupeds. Abstract One of the most intriguing research challenges in legged locomotion is robot performance on compliant terrains. The foot-terrain interaction is usually tackled by disregarding some of the effects of ground deformation, like permanent deformation and compaction; however this approach restricts their application to stiff environments. In this work, the foot-terrain interaction is studied, and used in developing a controller immune to terrain compliance. An impact dynamics model is developed, employing a viscoplastic extension a b b
Development and prototyping of robotic systems requires the involvement of many people and many h... more Development and prototyping of robotic systems requires the involvement of many people and many hours of design, development and cooperation; significant time and effort overhead is required for evaluating conceptual ideas in design, control and technology, and for bringing them fast into reality for testing. Based on the important advances of the last decade in hardware and software, a simple and low cost framework and its underlying ideas are presented, with steps that aim at accelerating robotics research work in academia and industry. The framework’s functionality is validated and illustrated by two application examples concerning the control systems of a single- legged hopping robot and an instrumented treadmill. The software required to conduct the same experiments is provided, with the intention to help the reader reuse it in similar applications.
In this paper, the development of an Orbital Robotics educational prototype platform is presented... more In this paper, the development of an Orbital Robotics educational prototype platform is presented, consisting of a hardware-developed physical system and an accompanying set of curriculum-based lessons (IB Physics curriculum) that target upper secondary students (16–18 years old target group). The platform was the outcome of a joint project between the European Space Agency and the National Technical University of Athens. The students use the hardware interactively, consisting of a bespoke space-emulating table and small satellite mockups. The lessons are inquiry-based and are structured so that the students are actively engaged in the learning process, according to a learner-centric approach. During the lessons, this platform allows students to acquire knowledge of the dynamics of space systems, as well as of the environmental conditions and physical constraints that characterize on-orbit operations. Students are able to manipulate the space robot (satellite) mockups performing basic tasks such as docking and landing, or grasping space debris. Additionally, a smartphone application has been implemented to allow the interaction with the platform, via a dedicated User Interface (UI).
Space is an exciting but fundamentally unfriendly environment for mankind. Space robotic systems ... more Space is an exciting but fundamentally unfriendly environment for mankind. Space robotic systems (robots in orbit, planetary rovers or even satellites) are of great importance to space exploration and perform hazardous or impossible for humans tasks. Using micro/nano technologies in space robotic systems results ei- ther in miniaturized systems in terms of volume and mass, while retaining or in- creasing their capabilities, or in space robots with increased capabilities while re- taining their size due to the nature of their tasks. Examples of miniaturization possibilities for space robots and satellites are given, focusing on the challenges and the enabling technologies. The miniaturization process and the use of ad- vanced micro/technologies in space will have a large beneficial impact in the years to come.
International Conference on Robotics and Automation (ICRA '13)
One of the most demanding tasks for a robotic servicer is capturing a target. During this task, t... more One of the most demanding tasks for a robotic servicer is capturing a target. During this task, the mechanical systems can be subject to large forces for short duration (impacts). In space servicers, these impacts may render the capturing of a target impossible without the use of undesirable fuel-consuming maneuvers. This paper presents an approach for minimizing impact reactions, using the Center of Percussion (CoP), a characteristic of rigid bodies rotating around an axis. This work generalizes and delineates the exact requirements for its use. Application of CoP in multibody systems is demonstrated using the Newton-Euler Algorithm. Implementation guidelines are discussed. Simulations of a planar space robot system, and a three-dimensional PUMA-like manipulator on a satellite base confirm the benefit of using the CoP during tasks that include impacts.
6th International Conference on Robotics in Education (RiE ’15)
As part of its Education Programme, the European Space Agency (ESA) is taking several steps towar... more As part of its Education Programme, the European Space Agency (ESA) is taking several steps towards the devel- opment of Educational activities and platforms that use Space Robotics as a mean to support and reinforce STEM (Science, Technology, Engineering and Mathematics) school education in Europe. In this paper the on-going development of an Orbital Robotics educational prototype platform is presented, consisting of a hardware-developed physical platform and an accompanying set of curriculum-based lessons (IB Physics curriculum) that target upper secondary students (16-18 y/o target group). The hardware, a friction-less air-hockey table (physical platform) engineered for this purpose, will be used by students to interac- tively acquire the necessary experience of the dynamics of space systems, as the environmental conditions and physical constraints that are characteristic of on-orbit systems are emulated. The stu- dents will be able to manipulate space robot (satellite) mockups performing basic tasks such as docking, landing and grasping space debris. Additionally, a smartphone application has been implemented to allow the interaction with the platform, via a dedicated User Interface (UI). The lessons are inquiry-based and are structured so that the students are actively engaged in the learning process according to a learner centered approach. The project is jointly undertaken by the ESA Education Office and the ESA Automation and Robotics Section, with the support of the Control Systems Laboratory of the National Technical University of Athens. The development is taking place at the facilities of the Automation and Robotics Laboratory (ARL) of ESTEC, ESA’s European Space Research and Technology Centre in the Netherlands.
International Conference on Robotics and Automation (ICRA '15)
Terrain compliance is a critical parameter for the performance of legged locomotion. In this work... more Terrain compliance is a critical parameter for the performance of legged locomotion. In this work, a single actuator monopod robot hopping on a rough compliant terrain is considered. Based on our controller for flat compliant terrains, this paper introduces the necessary modifications, which allow the robot to tackle the disturbance of small inclinations. Using the developed method, the robot is examined on its performance to traverse rough terrains, while maintaining the goals of reaching a desired height and forward velocity. As the increased compliance and inclination alter the energy requirements from the controller actuator, the Cost of Transport index for a number of scenarios is studied. The correlation between terrain parameters and the CoT is presented, and useful conclusions, which can aid the understanding of the behavior of legged robots in realistic terrains are extracted.
Int. Conf. on Intelligent Robots and Systems (IROS ’14)
Legged locomotion is a rapidly advancing area in robotics, yet still a large number of open quest... more Legged locomotion is a rapidly advancing area in robotics, yet still a large number of open questions exist. This work focuses on the foot-terrain interaction and its effect on the motion of a one-legged system. This interaction is usually tackled by disregarding some of the effects of ground deformation like permanent deformation and compaction. Inspired by other areas of engineering, an impact dynamics model is developed, allowing a more thorough study of the behavior during fast dynamic walking. This approach can be regarded as a viscoplastic one. The monopod controller presented in previous work is extended to cope with deformable terrains, based on energy dissipation considerations, without requiring the knowledge of the ground parameters. Simulation results prove the validity of the theory presented.
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Papers by Evangelos Papadopoulos