Study and Development of Mechatronic Devices and Machine Learning Schemes for Industrial Applications

Obiettivo del presente progetto di dottorato è lo studio e sviluppo di sistemi meccatronici e di modelli machine learning per macchine operatrici e celle robotizzate al fine di incrementarne le prestazioni operative e gestionali. Le pressanti esigenze del mercato hanno imposto lavorazioni con livelli di accuratezza sempre più elevati, tempi di risposta e di produzione ridotti e a costi contenuti. In questo contesto nasce il progetto di dottorato, focalizzato su applicazioni di lavorazioni meccaniche (e.g. fresatura), che includono sistemi complessi quali, ad esempio, macchine a 5 assi e, tipicamente, robot industriali, il cui utilizzo varia a seconda dell’impiego. Oltre alle specifiche problematiche delle lavorazioni, si deve anche considerare l’interazione macchina-robot per permettere un’efficiente capacità e gestione dell’intero impianto. La complessità di questo scenario può evidenziare sia specifiche problematiche inerenti alle lavorazioni (e.g. vibrazioni) sia inefficienze più generali che riguardano l’impianto produttivo (e.g. asservimento delle macchine con robot, consumo energetico). Vista la vastità della tematica, il progetto si è suddiviso in due parti, lo studio e sviluppo di due specifici dispositivi meccatronici, basati sull’impiego di attuatori piezoelettrici, che puntano principalmente alla compensazione di vibrazioni indotte dal processo di lavorazione, e l’integrazione di robot per l’asservimento di macchine utensili in celle robotizzate, impiegando modelli di machine learning per definire le traiettorie ed i punti di raggiungibilità del robot, al fine di migliorarne l’accuratezza del posizionamento del pezzo in diverse condizioni. In conclusione, la presente tesi vuole proporre soluzioni meccatroniche e di machine learning per incrementare le prestazioni di macchine e sistemi robotizzati convenzionali. I sistemi studiati possono essere integrati in celle robotizzate, focalizzandosi sia su problematiche specifiche delle lavorazioni in macchine operatrici sia su problematiche a livello di impianto robot-macchina. Le ricerche hanno riguardato un’approfondita valutazione dello stato dell’arte, la definizione dei modelli teorici, la progettazione funzionale e l’identificazione delle criticità del design dei prototipi, la realizzazione delle simulazioni e delle prove sperimentali e l’analisi dei risultati.The aim of this Ph.D. project is the study and development of mechatronic systems and machine learning models for machine tools and robotic applications to improve their performances. The industrial demands have imposed an ever-increasing accuracy and efficiency requirement whilst constraining the cost. In this context, this project focuses on machining processes (e.g. milling) that include complex systems such as 5-axes machine tool and industrial robots, employed for various applications. Beside the issues related to the machining process itself, the interaction between the machining centre and the robot must be considered for the complete industrial plant’s improvement. This scenario´s complexity depicts both specific machining problematics (e.g. vibrations) and more general issues related to the complete plant, such as machine tending with an industrial robot and energy consumption. Regarding the immensity of this area, this project is divided in two parts, the study and development of two mechatronic devices, based on piezoelectric stack actuators, for the active vibration control during the machining process, and the robot machine tending within the robotic cell, employing machine learning schemes for the trajectory definition and robot reachability to improve the corresponding positioning accuracy. In conclusion, this thesis aims to provide a set of solutions, based on mechatronic devices and machine learning schemes, to improve the conventional machining centre and the robotic systems performances. The studied systems can be integrated within a robotic cell, focusing on issues related to the specific machining process and to the interaction between robot-machining centre. This research required a thorough study of the state-of-the-art, the formulation of theoretical models, the functional design development, the identification of the critical aspects in the prototype designs, the simulation and experimental campaigns, and the analysis of the obtained results

Concepts for elastic parallel manipulators for the control of structural vibrations

Im Vordergrund der vorliegenden Arbeit steht die Unterdrückung von Schwingungen in der Roboterstruktur eines elastischen parallelen Manipulators. Um dieses Ziel zu realisieren, soll eine Strukturregelung entwickelt werden, die grundsätzlich über die Kenntnis der Bewegungsgleichungen des zu regelnden Manipulators verfügen muss, da diese Art von Maschinen im Allgemeinen zur Klasse der nichtlinearen Systeme gehört. Deswegen müssen, um die gestellte Aufgabe zu erfüllen, grundsätzlich zwei Hauptprobleme gelöst werden: - Modellierung eines elastischen parallelen Manipulators - Entwurf einer modellbasierten Regelung Parallele Manipulatoren werden in der Literatur und in der Praxis vorwiegend als Starrkörpersysteme behandelt. Die für diese Klasse von Robotern entwickelten Methoden können zumeist nicht ohne arbeitsaufwendige Modifikationen auf die elastischen parallelen Manipulatoren übertragen werden. Aus diesem Grund werden im Rahmen dieser Arbeit, basierend auf den am häufigsten eingesetzten und hier beschriebenen Standardmethoden, neue Verfahren und Lösungsansätze entwickelt und vorgestellt. Zu diesen neuen Lösungen gehören - eine Methode zur Herleitung der direkten Kinematik, - zwei Methoden zur Bestimmung des Arbeitsraumes, - eine Methode zur Herleitung der Jacobimatrix, - eine Methode zur verteilten Berechnung der direkten Dynamik und - ein modellbasiertes nichtlineares Regelungsverfahren. Die neuen Konzepte werden auf Basis des ebenen elastischen parallelen Manipulators Fünfgelenk analysiert und diskutiert. Durch Simulationen und Experimente werden die hier vorgeschlagenen Lösungen anschließend bestätigt. Anhand der gewonnenen Ergebnisse wird das Potential der neuen Verfahren aufgezeigt, wodurch eine gute Basis für ihre aufgabenorientierte roboterbezogene Weiterentwicklung und Optimierung geschaffen wird.The main aim of this study is the damping of vibration within the structure of an elastic parallel robot. In order to achieve this aim, the control of the manipulator's structure needs to be developed. Basically the equations of motion of the elastic manipulator need to be known for the control strategy, as generally this type of machine belongs to non-linear systems. Therefore, in order to complete this task, two main problems need to be solved: - The modelling of an elastic parallel manipulator - The design of a model-based control Parallel manipulators are mainly treated as rigid-body systems both in theory and in practise. Those methods developed for these types of robots mostly cannot be transfered directly to the elastic parallel manipulators. For this reason in the course of this study, based on the most commonly used standard methods as described here, new techniques and approaches are developed and presented. These new techniques include: - A method for the derivation of direct kinematics - Two methods to determine a manipulator's workspace - A method to derive a Jacobian matrix - A method for the distributed/simultaneous calculation of direct dynamics - A model-based controller algorithm These new concepts are analysed and discussed on the basis of a Five-Bar planar elastic parallel manipulator. Through simulations and experiments, the solutions suggested here, can subsequently be confirmed. Based on the acquired results, the potential of the new techniques will be shown, whereby a good basis for further task- and manipulator-orientated development and optimisation will be achieved

Robots in machining

Robotic machining centers offer diverse advantages: large operation reach with large reorientation capability, and a low cost, to name a few. Many challenges have slowed down the adoption or sometimes inhibited the use of robots for machining tasks. This paper deals with the current usage and status of robots in machining, as well as the necessary modelling and identification for enabling optimization, process planning and process control. Recent research addressing deburring, milling, incremental forming, polishing or thin wall machining is presented. We discuss various processes in which robots need to deal with significant process forces while fulfilling their machining task

Hibrit artık robot kolu kullanarak yüksek performanslı taşlama işlemi geliştirmesi.

Automatic grinding using robot manipulators, requires simultaneous control of the robot endpoint and force interaction between the robot and the constraint surface. In robotic grinding, surface quality can be increased by accurate estimation of grinding forces where significant tool and workpiece deflection occurs. Tool deflection during robotic grinding operation causes geometrical errors in the workpiece cross-section. Also, it makes controlling the grinding cutting depth difficult. Moreover small diameter of the tool in robotic grinding causes different behavior in the grinding process in comparison with the tools that are used by universal grinding machines. In this study, a robotic surface grinding force model is developed in order to predict the normal and tangential grinding forces. A physical model is used based on chip formation energy and sliding energy. To improve the model for robotic grinding operations, a refining term is added. In order to include the stiffness of the tool and setup in the force model, penetration tests are implemented and their results are used in refining term of the force model. The model coefficients are estimated using a linear regression technique. The proposed model is validated by comparing model outputs with experimentally obtained data. Evaluation of the test results demonstrates the effectiveness of the proposed model in predicting surface grinding forces. In this thesis, a method is proposed for calculation of the tool deflection in normal and tangential directions based on grinding force feedback in these directions. Based on calculated values, a real-time tool deflection compensation algorithm is developed and implemented. Implementing surface grinding with constant normal force is a well-known approach for improving surface quality. Tool deflection in the robotic grinding causes orientation between the force sensor reference frame and tool reference frame. This means that the measured normal and tangential forces by the sensor are not actual normal and tangential interaction forces between the tool and workpiece. In order to eliminate this problem, a resultant grinding force control strategy is designed and implemented for a parallel hexapod-robotic light abrasive surface grinding operation. Due to the nonlinear nature of the grinding operation, a supervised fuzzy controller is designed where the reference input is identified by the proposed grinding force model. Evaluation of the experimental results demonstrates significant improvement in grinding operation accuracy using the proposed resultant force control strategy in parallel with a real-time tool deflection compensation algorithm. The final aim of this thesis is to develop a posture optimization strategy for robotic grinding operation using 12 DOF hybrid redundant manipulator. The 12 DOF redundant hybrid manipulator of present study is composed of a 6 DOF serial ABB IRB2000 robot and a 6 DOF PI H-824 hexapod where the parallel hexapod is connected to the end of the serial ABB manipulator. Here the fifth joint (wrist) of the ABB serial manipulator is the weakest joint in the robot, so the computed torque of this joint is selected as the cost function. The aim is to minimize this factor by finding the best configuration of the hybrid manipulator using genetic algorithm approach. For such a purpose, a complete kinematic and dynamic model of the 12 DOF manipulator is developed where the output of the grinding force model is fed into the dynamic model as external reaction forces. The computed torque of the wrist joint is given to the optimization module and new configuration is generated by the module and is given to the dynamic model. This process continues until converge to the minimum computed torque value. Then the optimal configuration is chosen for the grinding operation. The evaluation of this posture optimization approach shows its great ability to decrease the necessary actuating torques of the redundant manipulator joints.Ph.D. - Doctoral Progra

The investigation and design of a piezoelectric active vibration control system for vertical machining centres

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