Особливості кінематики багатокоординатних верстатів паралельної структури з надлишковими приводами

У роботі проаналізовано кінематичні залежності багатокоординатного верстата паралельної структури на основі механізму «пентапод» з надлишковою приводною ланкою

Theoretical and practical development of control approaches for redundantly actuated parallel kinematic machines

Die konsequente Weiterentwicklung parallelkinematischer Maschinen (PKM) führt auf eine strukturelle Erweiterung in Form einer Antriebsredundanz. Die wesentlichen Vorteile der Antriebsredundanz sind beispielsweise die Kompensation von Singularitäten im Arbeitsraum, eine erhöhte Endeffektor-Steifigkeit und eine optimale Verteilung der Antriebskräfte. Redundant angetriebene PKM (RA-PKM) sind darum prädestiniert für hochdynamische Pick-and-Place-Bewegungsaufgaben und neue Maschinenkonzepte. Die vorliegende Arbeit befasst sich mit der Frage, welche Konzepte und Verfahren für die Regelung der RA-PKM geeignet sind. Dabei zeigt sich, dass die Beschreibung in Endeffektor-Koordinaten, die Verwendung eines Störgrößenbeobachters auf der Basis des generalisierten Impulses sowie eine modellprädiktive Regelung sehr gute Ergebnisse hinsichtlich der Genauigkeit und des Implementierungs- und Rechenaufwandes ergeben. Dies gilt insbesondere, wenn große Reibkräfte z. B. in den Antrieben zu berücksichtigen sind. Deshalb ist dieses Verfahren für die industrielle Anwendung besonders geeignet. Da für alle hier betrachteten Regelungsverfahren ein mathematisches Modell erforderlich ist, nimmt die Beschreibung der Bewegungsgleichungen in unterschiedlichen Koordinaten einen breiten Raum der Arbeit ein. Es werden die Vor- und Nachteile der verschiedenen Beschreibungsformen wie z. B. die verschiedenen Arten der Singularitäten und die Eliminierung der Zwangskräfte mit Hilfe von Orthogonalprojektionen ausführlich dargestellt. Dabei wurde ein neuartiger Zugang für die Projektion der Bewegungsgleichungen in Endeffektor-Koordinaten hergeleitet. Als erstes Regelungskonzept wird die dezentrale Regelung betrachtet. Es wird gezeigt, wie die hier üblicherweise auftretenden antagonistischen Kräfte mit Hilfe eines Filters kompensiert werden können. Im Anschluss daran wird die große Klasse der modellbasierten Regelungen in den unterschiedlichen Koordinaten untersucht, wobei ein sogenannter Computed Torque Regler (CTC), d. h. die Verwendung einer Vorsteuerung in Form der inversen Dynamik, und ein Augmented PD-Regler (APD) zum Einsatz kommen. Die Gelenkgeschwindigkeiten werden mit Hilfe eines High-Gain-Beobachters und die Störgrößen mit Hilfe eines Störgrößenbeobachters rekonstruiert. Zum Schluss wird die schon erwähnte nichtlineare modellprädiktive Regelung in Endeffektor-Koordinaten beschrieben, wobei der zukünftige Trajektorienfehler durch eine optimale Stellgröße minimiert wird. Die resultierende Reglerstruktur hat die Form eines klassischen APD-Reglers mit variablen Verstärkungen. Die Reglereinstellung erfolgt durch die Prädiktion vollkommen automatisch. Die entwickelten Regler und Methoden wurden anhand eines ebenen Mechanismus mit zwei Freiheitsgraden unter Verwendung industrieller Torque-Motoren erprobt.The consistent further development of parallel kinematics machines (PKM) lead to a structural extension in terms of actuation redundancy. The major advantages of redundant actuation are for example the compensation of singularities in workspace, an increased end-effector stiffness and an optimal distribution of the control forces. Therefore redundantly actuated PKM (RA-PKM) are intended for high speed pick-and-place tasks and new machine concepts. This research work addresses the question which concepts and methods are qualified for the control of RA-PKM. It has been found that a formulation of motion equations in end-effector coordinates, the use of a disturbance observer based on the general momentum as well as a model predictive controller lead to very well results in terms of accuracy, implementation and computing time. This applies particularly, if large friction losses as they occur in drives, have to be taken into account. Therefore this method is particularly suitable for industrial applications. Since a mathematical model is needed for all proposed control schemes, the determination of motion equations in terms of different coordinate formulations makes up a large part of this report. The advantages and disadvantages, such as the different types of singularities and the elimination of constraint forces by means of orthogonal projections are elaborated. Although a novel approach for the projection of motion equations in terms of end effector coordinates is derived. At first, the decentralized control scheme is considered. It will be shown that antagonistic Forces which are inherent to the control-scheme can be compensated by means of a filter. Afterwards, the large class of model-based control schemes is reviewed in which a so called computed torque controller (CTC), i.e. the use of a feed-forward control in the form of the inverse dynamics, and an augmented PD (APD) controller are used. The joint velocities where observed by means of a high gain observer and the disturbances by means of a disturbance observer. Finally, the already mentioned nonlinear model predictive control scheme in terms of end-effector coordinates which minimizes the future trajectory error due to an optimal actuating variable is described. The resulting approach can be structurally incorporated into an APD controller with variable gains. The controller setup is an automated process due to the prediction. The proposed control schemes and methods where experimentally validated by means of a two degree of freedom planar mechanism with industrial torque motors

Recent Advances in Robust Control

Robust control has been a topic of active research in the last three decades culminating in H_2/H_\infty and \mu design methods followed by research on parametric robustness, initially motivated by Kharitonov's theorem, the extension to non-linear time delay systems, and other more recent methods. The two volumes of Recent Advances in Robust Control give a selective overview of recent theoretical developments and present selected application examples. The volumes comprise 39 contributions covering various theoretical aspects as well as different application areas. The first volume covers selected problems in the theory of robust control and its application to robotic and electromechanical systems. The second volume is dedicated to special topics in robust control and problem specific solutions. Recent Advances in Robust Control will be a valuable reference for those interested in the recent theoretical advances and for researchers working in the broad field of robotics and mechatronics

Cinemàtica i Control en entorns multi-robot

Un dels camps de la robòtica que estan despertant gran interès per part de la comunitat científica és el dels entorns multirobot. Aquest nom genèric inclou diferents tipus de sistemes amb característiques i problemàtiques força diferenciades. En aquest treball s'utilitza aquest terme per fer referència a cel·les robotitzades composades per més d'un robot treballant coordinadament, entès robot com braç manipulador. En aquesta tesis s'han abordat diferents aspectes relacionats amb la cinemàtica i el control de sistemes multirobot. Dins de la cinemàtica s'han estudiat en detall les característiques de l'espai del treball i les mesures de manipulabilitat dels sistemes multirobot. En aquesta línia s'ha proposat una nova metodologia per estudiar l'espai de treball del sistemes multirobot basada en els conceptes de figura destra i figura realitzable. Aquestes dues figures geomètriques generades a partir dels espais de treball individuals, permeten descriure l'espai de treball com la intersecció de figures geomètriques. Aquest interpretació permet dissenyar de forma intuïtiva cel·les multirobot en les que hi ha manipulació conjunta. La metodologia s'ha implementat en el cas de dos tipus de robots, SCARA, i PUMA.Dins els aspectes de dinàmica i control tractats en la tesi, cal diferenciar els referents a la dinàmica dels sistemes multirobot i els referents als sistemes en els que cadascun dels robots té un control de posició.En l'àmbit de la dinàmica pròpiament dita s'ha analitzat en detall la formulació en equacions algebraic diferencials (DAE) dels sistemes mecànics amb restriccions holònomes, cas genèric dins el que s'engloben els sistemes multirobot amb manipulació rígida d'objectes rígids. Aquesta formulació permet obtenir el comportament del sistema a partir de les equacions que descriuen el comportament individual de cadascun dels robots i dels conjunt de restriccions cinemàtiques que actuen sobre el sistema.En el cas dels robots amb control de posició, el comportament i el control presenten unes característiques totalment diferents. Per aquest tipus d'entorns s'han proposat, dos enfocs de control diferents: un basat en el control híbrid, i un altre basat en control d'impedància. En l'enfoc de control híbrid es descompossa el sistema en eixos sobre els que s'aplica control de posició i eixos en els que s'aplica control de força, aquests darrers corresponen a les forces internes. Aquest plantejament és totalment centralitzat, es a dir, hi ha un element central encarregat de controlar el comportament del sistema. Com a principal aportació dins aquesta línia, s'ha proposat una metodologia per identificar el comportament de les forces internes que actuen sobre el sistema.Com alternativa, al control híbrid s'ha desenvolupat un esquema de control basat en la imposició d'un comportament d'impedància en cadascun dels robots. Aquest plantejament és totalment desacoblat, és a dir cadascun dels controladors realitza la seva funció sense necessitat d'un intercanvi d'informació amb la resta de controladors. La principal aportació dins aquesta línia és que el comportament d'impedància s'ha plantejat sobre SE(3), el que fa que els comportaments obtinguts estiguin d'acord amb la topologia de l'espai de treball.La tesi finalitza amb una presentació de les principals conclusions i línies de treball obertes per treballs futurs.One field in today robotics in which a lot of people are working is the one concerning multirobot systems. This generic name includes different kinds of systems, each one with its own characteristics and problems. In this work "multirobot system" refers to work cells composed by several robots working in a coordinated way. In this thesis several aspects related with kinematics and control of multirobot systems has been studied. Inside cinematic the workspace and manipulability measures for multirobots systems have been studied in detail. A new methodology to study multirobot systems workspace has been proposed, this approach is based on the dexterous figure and the reachable figure concepts. These two geometric figures are obtained from the individual workspace. A key issue in this new approach is the fact the multirobot workspace can be described as the intersection of several geometric figures, this introduces a new understanding which can be of great interest in the geometric design of multirobot workcell. This methodology has been used in the analysis and design of workcells composed by SCARA and PUMA robots.Inside dynamics and control aspects, the dissertation includes two different problems, one related with multirobot dynamics modeling and control and another related with control of multirobot systems where the different robots are position controlled.In the dynamic related aspects, a new formulation based on the formulation of robotic system with holonomic constraints as Diferential Algebraic Equation Systems (DAE). One particular case of this generic kind of systems is multirobot systems which rigidly manipulate a rigid object. This approach allows obtaining the system behavior from the dynamic equations describing the individual behavior and the set of equations describing the holonomic constrains over the systems.For the multirobot systems formed by position controlled robots, two different strategies have been proposed and tested in a real workcell. The first one is based on the hybrid control approach and the second one is based on the impedance control approach.The hybrid control approach decomposes the space in several axes, some of them are controlled in position and the others are force controlled. These force controlled axes are the ones related with internal force control. Hybrid control follows a centralized approach, so a central coordination element is needed. Inside this area a new methodology to identify and control the internal forces dynamics has been proposed.A different approach has been proposed, impedance control is based on defining an individual behaviour for each robot. This approach is decoupled by definition, in other works each robot do not need information from the other robots. Most important contributions inside this area, is the fact that the individual behaviour is defined over SE(3), this means that obtained movements are topologicaly coherent.The dissertation concludes with some conclusions and future works

Parallel Manipulators

In recent years, parallel kinematics mechanisms have attracted a lot of attention from the academic and industrial communities due to potential applications not only as robot manipulators but also as machine tools. Generally, the criteria used to compare the performance of traditional serial robots and parallel robots are the workspace, the ratio between the payload and the robot mass, accuracy, and dynamic behaviour. In addition to the reduced coupling effect between joints, parallel robots bring the benefits of much higher payload-robot mass ratios, superior accuracy and greater stiffness; qualities which lead to better dynamic performance. The main drawback with parallel robots is the relatively small workspace. A great deal of research on parallel robots has been carried out worldwide, and a large number of parallel mechanism systems have been built for various applications, such as remote handling, machine tools, medical robots, simulators, micro-robots, and humanoid robots. This book opens a window to exceptional research and development work on parallel mechanisms contributed by authors from around the world. Through this window the reader can get a good view of current parallel robot research and applications

Application of ”ART SIMULATOR” for Manufacturing Similarity Identification in Group Technology Design - Chapter 10

This chapter 10 carried out the exceptional implementation of ART-1 neural network in the analysis of the manufacturing similarity of the cylindrical parts within the group technology design. Established concept of the group technology design begins from the complex part of the group or the group representative. Group representative has all the geometrical elements of the parts in group, and manufacturing procedure may be applied to the machining of any part in the group. The complex part may be realistic or a hypothetical one. The ART-1 artificial neural network provided manufacturing classification according to the geometrical similarities of work-pieces for the group of cylindrical parts. For the manufacturing similarity identification within the group technology design, software package "ART Simulator" is developed and presented in this chapter