1,721,057 research outputs found
Controlling and Learning Constrained Motions for Manipulation in Contact
Full text linkMany practical tasks in robotic systems involving contact interaction with the environment, such as cleaning windows, writing or grasping, are inherently constrained, in that both the task and the environment impose constraints on the robot’s motion. While constraints from manipulation motions in contact represent a challenge when modelling and controlling such robotic systems, they might also be an opportunity, if exploited for decomposing complex controllers into simpler ones that are easier to design, implement, test and even learn from data.
Modelling such systems requires incorporating these constraints in the robot’s dynamic model. In this thesis, I define the class of Task-based Constraints (TbCs) and prove that the forward dynamic models of a constrained system obtained through the Projected Dynamics (PD) and the Operational Space Formulation (OSF) are equivalent. Establishing such equivalence required: reformulating the PD constraint inertia matrix, generalising all its previous distinct algebraic variations; and generalising the OSF to rank deficient constraint Jacobian matrices. This generalization allows us to numerically handle redundant constraints and singular configurations, without having to use different controllers in the vicinity of such configurations.
Furthermore, I show that we can recover both operational space control with constraints and the hybrid position/force control in the operational space from a multiple Task-based Constraint abstraction. I then propose a control and trajectory tracking approach for wiping the train cab front panels, using a velocity controlled robotic manipulator and a force/torque sensor attached to its end-effector, without using any surface model or vision-based surface detection. The control strategy consists of a hybrid position/force controller, adapted from the Operational Space Formulation, that aligns the cleaning tool with the surface normal, maintaining a set- point normal force, while simultaneously moving along the surface. The trajectory tracking strategy consists of specifying and tracking a two dimensional path that, when projected onto the train surface, corresponds to the desired pattern of motion. An experiment with the Baxter robot to wipe a highly curved surface with both a spiral and a raster scan motion patterns validates the approach. I also implemented the same approach in a scaled robot prototype, specifically designed to wipe a 1/8 scaled version of a train cab front, using a raster scan pattern.
Learning these type of control policies subject to constraints is a challenging problem. This thesis proposes a Constraint-aware Policy Learning (CaPL) method that solves the policy learning problem on redundant robots which execute a policy acting in the null-space of a constraint. This learning approach allows the generalization of learnt control policies across constraints that are unknown during the training phase. The CaPL method splits the combined problem of learning constraints and policies into: first estimating the constraint, and then estimating an unconstrained policy using the remaining degrees of freedom. For a linear parametrization, there
is a closed-form solution for the problem of estimating constraints based on Singular Value Decomposition (SVD). In this thesis, I propose another closed-form solution for constraint estimation for the TbC case, which includes estimating the task component without affecting the norm of the constraint matrix, based on Generalized Singular Value Decomposition (GSVD). I also discuss a metric for comparing the similarity of estimated constraints, which is useful to pre-process the trajectories recorded in the demonstrations. An experiment consisting in: learning a wiping task from human demonstration on flat surfaces; and reproducing it on an unknown curved surface using a force/torque based controller, to achieve tool alignment, validates the CaPL method. Despite the differences between the training and validation scenarios, the learnt policy still provides the desired wiping motion
Robotic Assistance by Impedance Compensation for Hand Movements While Manual Welding
Full text linkIn this paper, we present a robotic assistance scheme which allows for impedance compensation with stiffness, damping, and mass parameters for hand manipulation tasks and we apply it to manual welding. The impedance compensation does not assume a preprogrammed hand trajectory. Rather, the intention of the human for the hand movement is estimated in real time using a smooth Kalman filter. The movement is restricted by compensatory virtual impedance in the directions perpendicular to the estimated direction of movement. With airbrush painting experiments, we test three sets of values for the impedance parameters as inspired from impedance measurements with manual welding. We apply the best of the tested sets for assistance in manual welding and perform welding experiments with professional and novice welders. We contrast three conditions: 1) welding with the robot's assistance; 2) with the robot when the robot is passive; and 3) welding without the robot. We demonstrate the effectiveness of the assistance through quantitative measures of both task performance and perceived user's satisfaction. The performance of both the novice and professional welders improves significantly with robotic assistance compared to welding with a passive robot. The assessment of user satisfaction shows that all novice and most professional welders appreciate the robotic assistance as it suppresses the tremors in the directions perpendicular to the movement for welding.LAS
End-point impedance measurements across dominant and nondominant hands and robotic assistance with directional damping
No full textThe goal of this paper is to perform end-point impedance measurements across dominant and nondominant hands while doing airbrush painting and to use the results for developing a robotic assistance scheme. We study airbrush painting because it resembles in many ways manual welding, a standard industrial task. The experiments are performed with the 7 degrees of freedom KUKA lightweight robot arm. The robot is controlled in admittance using a force sensor attached at the endpoint, so as to act as a free-mass and be passively guided by the human. For impedance measurements, a set of nine subjects perform 12 repetitions of airbrush painting, drawing a straight-line on a cartoon horizontally placed on a table, while passively moving the airbrush mounted on the robot's end-point. We measure hand impedance during the painting task by generating sudden and brief external forces with the robot. The results show that on average the dominant hand displays larger impedance than the nondominant in the directions perpendicular to the painting line. We find the most significant difference in the damping values in these directions. Based on this observation, we develop a "directional damping" scheme for robotic assistance and conduct a pilot study with 12 subjects to contrast airbrush painting with and without robotic assistance. Results show significant improvement in precision with both dominant and nondominant hands when using robotic assistance.</p
Optimal protraction of a biologically inspired robot leg
No full textIn this paper, protraction movement, namely forward stepping, of a biologically inspired three-joint robot leg is optimized for minimum energy consumption. Trajectory optimization is performed for various initial-final tip point positions of protraction. A modified version of gradient descent based optimal control algorithm is used. The objective function is modified in steps to jump over many unfeasible and inefficient local optima. The optimized trajectories are used to construct a radial basis function neural network (RBFNN) to interpolate for the untrained regions. The results of optimization are compared with the observations of protraction of stick insects. It is concluded that a direct biological imitation of protraction is not energy efficient. A sample protraction of a leg of the Robot-EA308 is demonstrated in guidance of the optimized trajectory. Energy optimal protraction of a robot leg necessitates flexion of the leg, rather than extension as observed in the stick insects.</p
Robotic training for hand movements during manual welding with real-time alarm feedback
No full textPurpose - The purpose of this study is to develop a robotic training system for the hand movements during manual welding. The system provides real-time notice-feedback with sound or light alarms, whenever the welding hand vibrates beyond the nominal level observed with professional welders. Design/methodology/approach - The large variations of hand movements are detected by monitoring the deviation of the tool position from a smooth curve estimated in real time by a Kalman filter. An alarm is generated in the form of a flashing light or beep sound whenever the deviations exceed a predetermined threshold. The performance of hand movements is measured in terms of the variations of the position data. Twelve novice and five professional welders took part in the experiments and answered a questionnaire that assessed the usability and work load of the system. Findings - Compared to the sound alarms, the light alarms resulted in a larger and statistically significant decrease in the variation of hand movements of the novice welders and brought the level of variation close to that of the professional welders. The alarms did not result in a significant decrease in the variation of hand movements of the professional welders. The responses to the questionnaire indicated that both professional and novice welders found the system useful and they did not experience any significant work load. Social implications - The system developed in this study can ease the training of novice welders, by speeding up the learning and reducing the need for human tutors. Originality/value - This study is first to provide real-time notice-feedback for training while manual welding, based on a comparison of the performances of novice and professional welders.LAS
Hand impedance measurements during interactive manual welding with a robot
No full textThis paper presents a study of hand impedance measurements comparatively across ten professional and 14 novice manual welders, when they are performing tungsten inert gas (TIG) welding interactively with the KUKA lightweight robot arm (LWR). The results show that hand impedance differs across professional and novice welders. The welding torch is attached to the KUKA LWR, which is admittance controlled via a force sensor to give the feeling of a free floating mass at its end-effector. The subjects perform TIG welding on 1.5-mm-thick stainless steel plates by manipulating the torch. Impedance is measured by introducing external force disturbances and fitting a mass-damper-spring model to human hand reactions. The quality of welding is measured using the variance of the position signals above 0.1 Hz. Professional welders demonstrate less variance and, in general, apply larger hand impedance (larger damping and stiffness) than the novice welders. The variance of position during nominal welding is minimal for both professional and novice welders in the direction perpendicular to the welding line in the plane of the plate, which is the most important direction for the quality of the weld. For both professional and novice welders, the mass and damping values are largest in this direction compared with the other two directions. Professional welders demonstrate larger damping than the novice welders in this direction.</p
Altı bacaklı yürüyen makina : robot-EA308
No full textThe work presented in this thesis aims to make contribution to the understanding and application of six-legged statically stable walking machines in both theoretical and practical levels. In this thesis five pieces of work, performed with and for the three-joint six-legged Robot-EA308, are presented: 1) Standard gaits, which include the well-known wave gaits, are defined and a stability analysis, in the sense of static stable walking, is performed on an analytical level. Various definitions are given; theorems are stated and proved. 2) A free gait generation algorithm with reinforcement learning is developed. Its facilities of stability improvement, smooth speed changes, and adaptation in case of a rear-leg deficiency with learning of five-legged walking are experimented in real-time on the Robot-EA308. 3) Trajectory optimization and controller design is performed for the protraction movement of a three-joint leg. The trajectory generated by the controller is demonstrated with the Robot-EA308. 4) The full kinematic-dynamic formulation of a three-joint six-legged robot is performed with the joint-torques being the primary variables. It is demonstrated that the proposed torque distribution scheme, rather than the conventional force distribution, results in an efficient distribution of required forces and moments to the supporting legs. 5) An analysis of energy efficiency is performed for wave gaits. The established strategies for determination of gait parameters for an efficient walk are justified using the Robot-EA308.Ph.D. - Doctoral Progra
Türkiye ve İran'da vatandaşlık ve etnisite.
No full textThis thesis aims at understanding the citizenship formations in Turkey and Iran by a comparative study of ethnicity, state formation, and nation building in the two lands. The research question is what kind of socio-political and cultural elements caused the two nation states to follow different paths and end up with different citizenship and state formations in the end of the twentieth century. The foci of comparison are the homogenization process of the nation states in ethnic terms, the extent of mass movements, the degree of centrality of the state in shaping the sociopolitical life, and the resistance to the state imposed regulations. In this thesis it is argued that the state tradition inherited from the Ottomans, the ethnic cleansing of the non-Muslim minorities, and the intention to assimilate the Kurdish population were the main determinants of Turkish citizenship. The mass movements emanating from the societal groups, the provincial autonomous movements, and the disruption of the state by external invasions were the main determinants of Iranian citizenship. The national identity in Turkey was more strongly based on the Turkish ethnicity; the Iranian national identity functioned as an umbrella identity over all ethnic identities in Iran. The Turkish citizenship, in comparison to Iranian, was closer to the ethnocentric and exclusionary German model; the Iranian citizenship, in comparison to the Turkish, was closer to the soil based and assimilationist French model.Ph.D. - Doctoral Progra
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