62 research outputs found
On Sensorless Collision Detection and Measurement of External Forces in Presence of Modeling Inaccuracies
The field of human-robot interaction has garnered significant interest in the last decade. Every form of human-robot coexistence must guarantee the safety of the user. Safety in human-robot interaction is being vigorously studied, in areas such as collision avoidance, soft actuators, light-weight robots, computer vision techniques, soft tissue modeling, collision detection, etc. Despite the safety provisions, unwanted collisions can occur in case of system faults. In such cases, before post-collision strategies are triggered, it is imperative to effectively detect the collisions. Implementation of tactile sensors, vision systems, sonar and Lidar sensors, etc., allows for detection of collisions. However, due to the cost of such methods, more practical approaches are being investigated. A general goal remains to develop methods for fast detection of external contacts using minimal sensory information.
Availability of position data and command torques in manipulators permits development of observer-based techniques to measure external forces/torques. The presence of disturbances and inaccuracies in the model of the robot presents challenges in the efficacy of observers in the context of collision detection. The purpose of this thesis is to develop methods that reduce the effects of modeling inaccuracies in external force/torque estimation and increase the efficacy of collision detection. It is comprised of the following four parts:
1. The KUKA Light-Weight Robot IV+ is commonly employed for research purposes. The regressor matrix, minimal inertial parameters and the friction model of this robot are identified and presented in detail. To develop the model, relative weight analysis is employed for identification.
2. Modeling inaccuracies and robot state approximation errors are considered simultaneously to develop model-based time-varying thresholds for collision detection. A metric is formulated to compare trajectories realizing the same task in terms of their collision detection and external force/torque estimation capabilities. A method for determining optimal trajectories with regards to accurate external force/torque estimation is also developed.
3. The effects of velocity on external force/torque estimation errors are studied with and without the use of joint force/torque sensors. Velocity-based thresholds are developed and implemented to improve collision detection. The results are compared with the collision detection module integrated in the KUKA Light-Weight Robot IV+.
4. An alternative joint-by-joint heuristic method is proposed to identify the effects of modeling inaccuracies on external force/torque estimation. Time-varying collision detection thresholds associated with the heuristic method are developed and compared with constant thresholds.
In this work, the KUKA Light-Weight Robot IV+ is used for obtaining the experimental results. This robot is controlled via the Fast Research Interface and Visual C++ 2008. The experimental results confirm the efficacy of the proposed methodologies
Modelling and control of position and velocity drives subject to friction
Performance degradation in most mechanical systems with friction which are not easily eliminated
through design mechanisms can be greatly reduced within acceptable limits through
the process of friction compensation. Generally friction compensators are used to improve
system performance in terms of error reduction, transient response, thereby countering the
effects of friction. Model-based techniques for friction compensation require an accurate
model of the system friction. This is very important for high precision mechanical systems
where excellent positioning and motion tracking, especially in the low velocities, is critical.
This thesis proposes a new integrated friction model structure capable of modelling known
friction dynamics. The new friction model incorporates a pre-sliding friction function with
non-local hysteretic features. Analysis of the model shows the model to possess dissipative,
boundedness, passivity and uniqueness properties. Results of sensitivity and robustness
analysis indicate the new friction model is robust to parameter variations. A friction characterisation
test-bed was designed and constructed for the purposes of friction identification,
compensation and control. A set of experiments were designed and implemented on the
test rig/bed to demonstrate friction dynamics. The input- output results of the experiments
were used for parameter estimation of the proposed new friction model and some other
relevant friction model structures. The performance of the new friction model for position
and velocity control was studied using the experimental friction test-bed and simulations.
The result of such analysis underscores the advantage of integrating a friction observer in the
system control loop. The new friction model provided better position and velocity control of
the experimental friction test-rig when compared with other well known models of friction
Dynamic Friction Parameter Identification Method with LuGre Model for Direct-Drive Rotary Torque Motor
Attainment of high-performance motion/velocity control objectives for the Direct-Drive Rotary (DDR) torque motor should fully consider practical nonlinearities in controller design, such as dynamic friction. The LuGre model has been widely utilized to describe nonlinear friction behavior; however, parameter identification for the LuGre model remains a challenge. A new dynamic friction parameter identification method for LuGre model is proposed in this study. Static parameters are identified through a series of constant velocity experiments, while dynamic parameters are obtained through a presliding process. Novel evolutionary algorithm (NEA) is utilized to increase identification accuracy. Experimental results gathered from the identification experiments conducted in the study for a practical DDR torque motor control system validate the effectiveness of the proposed method
Discrete-Time Series Identification of Sliding Dynamic Friction in Industrial Robotic Joints
Abstract-In this paper, the discrete-time series identification of dynamic friction in actuated robotic joints during the sliding regime is proposed. Considering the friction lag as a firstorder time delay element behind the static friction nonlinearity a reasonable approximation of friction dynamics in sliding is proposed. The regression signal model is derived based on a discrete-time transformation of motion dynamics with nonlinear friction. A robust identification scheme is formulated in the Least-Squares (LS) sense by using an appropriate set of model-related regressors. Further, the related Recursive-LeastSquares (RLS) formulation is provided. The proposed modeling and identification are evaluated experimentally by the offline and online parameter estimation. For these purposes the first vertical rotary joint of the base of a standard industrial robotic manipulator has been used in laboratory environment
Full Vehicle State Estimation Using a Holistic Corner-based Approach
Vehicles' active safety systems use different sensors, vehicle states, and actuators, along with an advanced control algorithm, to assist drivers and to maintain the dynamics of a vehicle within a desired safe range in case of instability in vehicle motion. Therefore, recent developments in such vehicle stability control and autonomous driving systems have led to substantial interest in reliable road angle and vehicle states (tire forces and vehicle velocities) estimation. Advances in applications of sensor technologies, sensor fusion, and cooperative estimation in intelligent transportation systems facilitate reliable and robust estimation of vehicle states and road angles. In this direction, developing a flexible and reliable estimation structure at a reasonable cost to operate the available sensor data for the proper functioning of active safety systems in current vehicles is a preeminent objective of the car manufacturers in dealing with the technological changes in the automotive industry.
This thesis presents a novel generic integrated tire force and velocity estimation system at each corner to monitor tire capacities and slip condition individually and to address road uncertainty issues in the current model-based vehicle state estimators. Tire force estimators are developed using computationally efficient nonlinear and Kalman-based observers and common measurements in production vehicles. The stability and performance of the time-varying estimators are explored and it is shown that the developed integrated structure is robust to model uncertainties including tire properties, inflation pressure, and effective rolling radius, does not need tire parameters and road friction information, and can transfer from one car to another.
The main challenges for velocity estimation are the lack of knowledge of road friction in the model-based methods and accumulated error in kinematic-based approaches. To tackle these issues, the lumped LuGre tire model is integrated with the vehicle kinematics in this research. It is shown that the proposed generic corner-based estimator reduces the number of required tire parameters significantly and does not require knowledge of the road friction. The stability and performance of the time-varying velocity estimators are studied and the sensitivity of the observers' stability to the model parameter changes is discussed. The proposed velocity estimators are validated in simulations and road experiments with two vehicles in several maneuvers with various driveline configurations on roads with different friction conditions. The simulation and experimental results substantiate the accuracy and robustness of the state estimators for even harsh maneuvers on surfaces with varying friction.
A corner-based lateral state estimation is also developed for conventional cars application independent of the wheel torques. This approach utilizes variable weighted axles' estimates and high slip detection modules to deal with uncertainties associated with longitudinal forces in large steering. Therefore, the output of the lateral estimator is not altered by the longitudinal force effect and its performance is not compromised. A method for road classification is also investigated utilizing the vehicle lateral response in diverse maneuvers.
Moreover, the designed estimation structure is shown to work with various driveline configurations such as front, rear, or all-wheel drive and can be easily reconfigured to operate with different vehicles and control systems' actuator configurations such as differential braking, torque vectoring, or their combinations on the front or rear axles. This research has resulted in two US pending patents on vehicle speed estimation and sensor fault diagnosis and successful transfer of these patents to industry
Commande des systèmes sous frottement utilisant le formalisme LMI : application aux systèmes robotiques avec contact et aux actionneurs pneumatiques
Le frottement présente systématiquement un risque accablant dans l'altération des performances de mouvement des systèmes mécaniques. La mise-en-place d'un système de contrôle efficace pour dissiper ce genre d'anomalie constitue encore un sujet d'actualité dans les domaines de la recherche et de l'ingénierie. Les mécaniciens, les tribologues, spécialistes de la théorie de frottement, et les automaticiens oeuvrent pour l'étude de ce phénomène des points de vue: caractérisation, modélisation et compensation. Une revue assez exhaustive de ces travaux est présentée dans le chapitre 1.
Dans le présent travail de thèse, nous proposons un schéma général de contrôle des systèmes sous frottement que nous pouvons utiliser dans plusieurs applications. En respectant les paradigmes standards de stabilité, de robustesse et d'optimisation (de types H2, H∞ , etc.), ce shéma est basé sur l'estimation en boucle fermée du frottement dynamique, selon le modèle de LuGre, et la structure dynamique de contrôle linéaire par retour de sortie. La synthèse de cette commande repose sur les outils numériques des inégalités matricielles linéaires. En plus, pour tenir compte de la variété des structures dynamiques de mouvement et aussi de force dans les différents dispositifs en question, le schéma de la commande que nous proposons peut comprendre des termes d'actions statiques (ou) dynamiques, linéaires (ou) non linéaires et éventuellement robustes. Une illustration simple de la commande de mouvement d'une masse, sur une surface sous frottement, est exposée dans le chapitre 2. Il s'agit d'une généralisation du principe de commande stabilisante par rétroaction statique introduit par Canudas et al.(1995).
Ensuite, nous appliquons notre schéma dans des cas plus complexes (non linéarités, incertitudes et couplages de force/position non négligeables). Pour ce faire, nous proposons dans le chapitre 3 l'étude de la commande hybride de position/force du robot manipulateur dont l'élément final est en contact sous frottement avec une surface donnée. Dans le chapitre 4, nous développons le schéma de contrôle de force (i.e. de pression) de l'actionneur pneumatique. Et dans le chapitre 5, nous présentons le schéma détaillé de contrôle de position de ce type d'installation qui renferme plusieurs points de contact avec frottement. Des résultats expérimentaux sont présentés pour valider notre approche de commande et aussi la comparer à d'autres schémas de commande et/ou de compensation de frottement.
Pour conclure ce travail, nous recommandons, en particulier, l'extension de l'approche proposée en utilisant un modèle de frottement encore plus générale comme celui de glissement généralisé de Maxwell (GMS) dans une suite logique et aussi ambitieuse de ce travail
Learning and Reacting with Inaccurate Prediction: Applications to Autonomous Excavation
Motivated by autonomous excavation, this work investigates solutions to a class of problem where disturbance prediction is critical to overcoming poor performance of a feedback controller, but where the disturbance prediction is intrinsically inaccurate. Poor feedback controller performance is related to a fundamental control problem: there is only a limited amount of disturbance rejection that feedback compensation can provide. It is known, however, that predictive action can improve the disturbance rejection of a control system beyond the limitations of feedback. While prediction is desirable, the problem in excavation is that disturbance predictions are prone to error due to the variability and complexity of soil-tool interaction forces. This work proposes the use of iterative learning control to map the repetitive components of excavation forces into feedforward commands. Although feedforward action shows useful to improve excavation performance, the non-repetitive nature of soil-tool interaction forces is a source of inaccurate predictions. To explicitly address the use of imperfect predictive compensation, a disturbance observer is used to estimate the prediction error. To quantify inaccuracy in prediction, a feedforward model of excavation disturbances is interpreted as a communication channel that transmits corrupted disturbance previews, for which metrics based on the sensitivity function exist. During field trials the proposed method demonstrated the ability to iteratively achieve a desired dig geometry, independent of the initial feasibility of the excavation passes in relation to actuator saturation. Predictive commands adapted to different soil conditions and passes were repeated autonomously until a pre-specified finish quality of the trench was achieved. Evidence of improvement in disturbance rejection is presented as a comparison of sensitivity functions of systems with and without the use of predictive disturbance compensation
Mehatronički pristup pozicioniranju ultravisokih preciznosti i točnosti
Ultra-high precision mechatronics positioning systems are critical devices in current precision engineering and micro- and nano-systems’ technologies, as they allow repeatability and accuracy in the nanometric domain to be achieved. The doctoral thesis deals thoroughly with nonlinear stochastic frictional effects that limit the performances of ultra-high precision devices
based on sliding and rolling elements. The state-of-the-art related to the frictional behavior in the pre-sliding and sliding motion regimes is considered and different friction models are validated. Due to its comprehensiveness and simplicity, the generalized Maxwell-slip (GMS) friction model is adopted to characterize frictional disturbances of a translational axis of an
actual multi-degrees-of-freedom point-to-point mechatronics positioning system aimed at handling and positioning of microparts. The parameters of the GMS model are identified via innovative experimental set-ups, separately for the actuator-gearhead assembly and for the linear guideways, and included in the overall MATLAB/SIMULINK model of the used device.
With the aim of compensating frictional effects, the modeled responses of the system are compared to experimental results when the system is controlled by means of a conventional proportional-integral-derivative (PID) controller, when the PID controller is complemented with an additional feed-forward model-based friction compensator and, finally, when the
system is controlled via a self-tuning adaptive regulator. The adaptive regulator, implemented within the real-time field programmable gate array based control system, is proven to be the most efficient and is hence used in the final repetitive point-to-point positioning tests.
Nanometric-range precision and accuracy (better than 250 nm), both in the case of short-range (micrometric) and long-range (millimeter) travels, are achieved. Different sensors, actuators and other design components, along with other control typologies, are experimentally validated in ultra-high precision positioning applications as well.Mehatronički sustavi ultra-visokih (nanometarskih) preciznosti i točnosti pozicioniranja su u današnje vrijeme vrlo važni u preciznom inženjerstvu i tehnologiji mikro- i nano-sustava. U disertaciji se temeljito analiziraju nelinearni stohastički učinci trenja koji vrlo često ograničavaju radna svojstva sustava za precizno pozicioniranje temeljenih na kliznim i valjnim elementima. Analizira se stanje tehnike za pomake pri silama manjim od sile statičkog trenja, kao i u režimu klizanja, te se vrednuju postojeći matematički modeli trenja. U razmatranom slučaju mehatroničkog sustava ultra-visokih preciznosti i točnosti pozicioniranja, namijenjenog montaži i manipulaciji mikrostruktura, trenje koje se javlja kod linearnih jednoosnih pomaka se, zbog jednostavnosti i sveobuhvatnosti toga pristupa, modelira generaliziranim Maxwell-slip (GMS) modelom trenja. Parametri GMS modela se identificiraju na inovativnim eksperimentalnim postavima, i to posebno za pokretački dio analiziranog sustava, koji se sastoji od istosmjernog motora s reduktorom, te posebno za linearni translator. Rezultirajući modeli trenja se zatim integriraju u cjeloviti model sustava implementiran u MATLAB/SIMULINK okruženju. S ciljem minimizacije utjecaja trenja, modelirani odziv sustava uspoređuje se potom s eksperimentalnim rezultatima dobivenim na sustavu reguliranom pomoću često korištenog proporcionalno-integralno-diferencijalnog (PID) regulatora, kada se sustav regulira po načelu unaprijedne veze, te kada se regulira prilagodljivim upravljačkim algoritmom. Regulator s prilagodljivim vođenjem, implementiran unutar stvarno-vremenskog sustava temeljenog na programibilnim logičkim vratima, pokazao se kao najbolje rješenje te se stoga koristi u uzastopnim eksperimentima pozicioniranja iz točke u točku, koji predstavljaju željenu funkcionalnost razmatranog sustava. Postignute su tako nanometarska preciznost i točnost (bolje od 250 nm) i to kako kod kraćih (mikrometarskih), tako i duljih (milimetarskih) pomaka.
U završnom se dijelu disertacije eksperimentalno analizira i mogućnost korištenja drugih pokretača, osjetnika i strojnih elemenata kao i različitih upravljačkih pristupa pogodnih za ostvarivanje ultra-visokih preciznosti i točnosti pozicioniranja
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