Kinematic analysis and optimization of robotic milling

Robotic milling is proposed to be one of the alternatives to respond the demand for flexible and cost-effective manufacturing systems. Serial arm robots offering 6 degrees of freedom (DOF) motion capability which are utilized for robotic 5-axis milling purposes, exhibits several issues such as low accuracy, low structural rigidity and kinematic singularities etc. In 5-axis milling, the tool axis selection and workpiece positioning are still a challenge, where only geometrical issues are considered at the computer-aided-manufacturing (CAM) packages. The inverse kinematic solution of the robot i.e. positions and motion of the axes, strictly depends on the workpiece location with respect to the robot base. Therefore, workpiece placement is crucial for improved robotic milling applications. In this thesis, an approach is proposed to select the tool axis for robotic milling along an already generated 5-axis milling tool path, where the robot kinematics are considered to eliminate or decrease excessive axis rotations. The proposed approach is demonstrated through simulations and benefits are discussed. Also, the effect of workpiece positioning in robotic milling is investigated considering the robot kinematics. The investigation criterion is selected as the movement of the robot axes. It is aimed to minimize the total movement of either all axes or selected the axis responsible of the most accuracy errors. Kinematic simulations are performed on a representative milling tool path and results are discusse

Optimal Robot Placement for Tasks Execution

AbstractAutomotive assembly cells are cluttered environments, including robots, workpieces, and fixtures. Due to high volumes and several product variants assembled in the same cell, robot placement is crucial to increase flexibility and throughput. In this paper, we propose a novel method to optimize the base position of an industrial robot with the objective to reach all predefined tasks and minimize cycle time: robot inverse kinematics and collision avoidance are integrated together with a derivative-free optimization algorithm. This approach is successfully used to find feasible solutions on industrial test cases, showing up to 20% cycle time improvement

Robotic Drilling of Aluminum Alloy: Performance and Hole Quality

This paper presents an experimental approach to evaluate the ability of a six-axis industrial robot to drill aluminum alloy parts. A strategy based on statistical tests has been studied to quantify and predict the relative contribution of cutting parameters on cutting force and shape errors during drilling. This technique is based on the identification of relevant sources of error during high-speed robotic fitting. The machining quality was quantified in terms of dimensional and geometric tolerance, chip formation and evacuation, burr formation, edge build-up, tool wear and surface damage. Statistical analysis of the experimental results reveals a strong dependence between part accuracy and drilling force. An experimental model was developed to represent and predict the cutting force during drilling and an accurate error prediction capability was distinguished. It was found that at high cutting speed and feed rate, the cutting force was the main source of error affecting the accuracy of the machined parts. Verification experiments are performed, and the results reveal that dimensional defects are significantly reduced by a heat treatment effect (90 HRE) and the thrust force decreases with an increase in cutting speed. The recommended cutting speed for robotic drilling is 6000 rpm with a feed rate of 0.15 mm/min. This study provides important technical guidance for improving the robotic drilling of aluminum alloy in practice

Energy-efficient and quality-aware part placement in robotic additive manufacturing

The advancements in autonomous robots for additive manufacturing (AM) are opening new horizons in the manufacturing industry, especially in aerospace and construction applications. The use of multiple robots and collaborative work in AM has rapidly gained attention in the industry and research community. Addressing the process planning challenges for single-robotic AM is foundational in addressing more advanced challenges at the collaborative multi-robotic level for AM. Among these challenges include the part placement problem which explores the optimal positioning of the part within the robot’s reach volume. The majority of the existing part placement algorithms take into account the part accuracy and manufacturing time for decision-making, while neglecting the implications of such decisions on energy efficiency and environmental sustainability. To address this gap, this paper presents a methodology for energy-efficient, high-quality part placement (EEHQPP) in robotic additive manufacturing. An energy-quality map is formulated and established to characterize the energy and quality variations across the robot’s workspace to inform the decision-making process. Two case studies (a container and a spur gear) are considered, and the performance of the proposed approach compared to the benchmark (i.e., default part placement by the 3D printing software) are evaluated. The proposed algorithm reduces both the energy consumption and maximum deviation error of the container (6.5% and 19.4%, respectively) and spur gear (1.4% and 32.7%, respectively) geometries manufactured by the robotic additive manufacturing system

Propuesta de inclusión de esfuerzos en el control de un brazo robot para asegurar el cumplimiento de la rugosidad superficial durante operaciones de lijado en diferentes materiales

Tesis por compendio[ES] El mecanizado con brazos robots ha sido estudiado aproximadamente desde los años 90, durante este tiempo se han llevado a cabo importantes avances y descubrimientos en cuanto a su campo de aplicación. En general, los robots manipuladores tienen muchos beneficios y ventajas al ser usados en operaciones de mecanizado, tales como, flexibilidad, gran área de trabajo y facilidad de programación, entre otras, frente a las Máquinas Herramientas de Control numérico (MHCN) que necesitan de una gran inversión para trabajar piezas muy grandes o incrementar sus grados de libertad. Como desventajas, frente a las MHCN, los brazos robóticos poseen menor rigidez, lo que combinado con las altas fuerzas producidas en los procesos de mecanizado hace que aparezcan errores de precisión, desviaciones en las trayectorias, vibraciones y, por consiguiente, una mala calidad en las piezas fabricadas. Entre los brazos robots, los brazos colaborativos están en auge debido a su programación intuitiva y a sus medidas de seguridad, que les permiten trabajar en el mismo espacio que los operadores sin que estos corran riesgos. Como desventaja añadida de los robots colaborativos se encuentra la mayor flexibilidad que estos tienen en sus articulaciones, debido a que incluyen reductores del tipo Harmonic drive. El uso de un control de fuerza en procesos de mecanizado con brazos robots permite controlar y corregir en tiempo real las desviaciones generadas por la flexibilidad en las articulaciones del robot. Utilizar este método de control es beneficioso en cualquier brazo robot; sin embargo, el control interno que incluyen los robots colaborativos presenta ventajas que permiten que el control de fuerza pueda ser aplicado de una manera más eficiente. En el presente trabajo se desarrolla una propuesta real para la inclusión del control de esfuerzos en el brazo robot, así como también, se evalúa y cuantifica la capacidad de los robots industriales y colaborativos en tareas de mecanizado. La propuesta plantea cómo mejorar la utilización de un control de fuerza por bucle interior/exterior aplicado en un brazo colaborativo cuando se desconocen los pares reales de los motores del robot, así como otros parámetros internos que los fabricantes no dan a conocer. Este bucle de control interior/exterior ha sido utilizado en aplicaciones de pulido y lijado sobre diferentes materiales. Los resultados indican que el robot colaborativo es factible para realizar tales operaciones de mecanizado. Sus mejores resultados se obtienen cuando se utiliza un bucle de control interno por velocidad y un bucle de control externo de fuerza con algoritmos, Proporcional-Integral-Derivativo o Proporcional más Pre-Alimentación de la Fuerza.[CA] El mecanitzat amb braços robots ha estat estudiat aproximadament des dels anys 90, durant aquest temps s'han dut a terme importants avanços i descobriments en el que fa al seu camp d'aplicació. En general, els robots manipuladors tenen molts beneficis i avantatges al ser usats en operacions de mecanitzat, com ara, flexibilitat, gran àrea de treball i facilitat de programació, entre d'altres, davant de Màquines Eines de Control Numèric (MECN) que necessiten d'una gran inversió per treballar peces molt grans o incrementar els seus graus de llibertat. Com a desavantatges, enfront de les MECN, els braços robòtics posseeixen menor rigidesa, el que combinat amb les altes forces produïdes en els processos de mecanitzat fa que apareguin errors de precisió, desviacions en les trajectòries, vibracions i, per tant, una mala qualitat en les peces fabricades. Entre els braços robots, els braços col·laboratius estan en auge a causa de la seva programació intuïtiva i a les seves mesures de seguretat, que els permeten treballar en el mateix espai que els operadors sense que aquests corrin riscos. Com desavantatge afegida als robots col·laboratius es troba la major flexibilitat que aquests tenen en les seves articulacions, a causa de que inclouen reductors del tipus Harmonic drive. L'ús d'un control de força en processos de mecanitzat amb braços robots permet controlar, i corregir, en temps real les desviacions generades per la flexibilitat en les articulacions del robot. Utilitzar aquest mètode de control és beneficiós en qualsevol braç robot, però, el control intern que inclouen els robots col·laboratius presenta avantatges que permeten que el control de força es puga aplicar d'una manera més eficient. En el present treball es desenvolupa una proposta real per a la inclusió del control d'esforços en el braç robot, així com s'avalua i quantifica la capacitat dels robots industrials i col·laboratius en tasques de mecanitzat. La proposta planteja com millorar la utilització d'un control de força per bucle interior/exterior aplicat en un braç col·laboratiu, quan es desconeixen els parells reals dels motors del robot, així com altres paràmetres interns que els fabricants no donen a conèixer. Aquest bucle de control interior/exterior ha estat utilitzat en aplicacions de polit sobre diferents materials. Els resultats indiquen que el robot col·laboratiu és factible de realitzar aquestes operacions de mecanitzat. Els seus millors resultats s'obtenen quan s'utilitza un bucle de control intern per velocitat i un bucle de control extern de força amb els algoritmes Proporcional-Integral-Derivatiu o Proporcional més Pre-alimentació de la Força.[EN] Machining with robot arms has been studied approximately since the 90s; during this time, important advances and discoveries have been made in its field of application. In general, manipulative robots have many benefits and advantages when they are used in machining operations, such as flexibility, large work area, and ease of programming, among others, compared to Numerical Control Machine Tools (NCMT) that need a great investment to work very large pieces or increase their degrees of freedom. As for disadvantages, compared to NCMT, robotic arms have lower rigidity, which, combined with the high forces produced in machining processes, causes precision errors, path deviations, vibrations, and, consequently, poor quality in the manufactured parts. Among robot arms, collaborative arms are on the rise due to their intuitive programming and safety measures, which allow them to work in the same space without risk for the operators. An added disadvantage of collaborative robots is their flexibility in their joints because they include Harmonic drive type reducers. The use of force control in machining processes with robot arms makes possible to control and correct, in real-time, the deviations generated by the flexibility in the robot's joints. The use of this control method is beneficial for any robot arm. However, the internal control included in collaborative robots has advantages that allow the force control to be applied more efficiently. In this work, a real proposal is developed to include effort control in the robot arm. The capacity of industrial and collaborative robots in machining tasks is evaluated and quantified. The proposal recommends how to improve the use of an inner/outer force control loop applied in a collaborative arm, when the real torques of the robot's motors are unknown and other internal parameters that manufacturers do not disclose. This inner/outer control loop has been used in polishing and sanding applications on different materials. The results indicate that the collaborative robot is feasible to perform such machining operations. Best results are obtained using an internal velocity control loop and external force control loop with Proportional-Integral-Derivative or Proportional plus Feed Forward.The authors are grateful for the financial support of the Spanish Ministry of Economy and European Union, grant DPI2016-81002-R (AEI/FEDER, UE). This work was funded by the CONICYT PFCHA/DOCTORADO BECAS CHILE/2017 – 72180157.Pérez Ubeda, RA. (2022). Propuesta de inclusión de esfuerzos en el control de un brazo robot para asegurar el cumplimiento de la rugosidad superficial durante operaciones de lijado en diferentes materiales [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/182000TESISCompendi

Optimizing task placement in robotic cells

The primary objective of this dissertation is to develop novel and practical techniques for optimal task placement in robotic cells. To this end, it is shown how task placement affect the efficiency of the cell, whether the task is automated fiber placement to create composite materials, gluing or inspection. Here, efficiency of the cell is defined by either cycle time of the production or distance to singularity, having collision avoidance as a constraint. Task placement, even for one robotic arm, is an under-constrained problem in nature. This issue drastically grows in case of redundant robotic cells. Actuator redundancy in robotic cells is added by either a positioner or another manipulator. This work is focused on taking advantage of redundancy in robotic cells and optimizing it for better performance. One of the main challenges here is to identify the number of independent placement parameters. Therefore, we ignore ineffective variables and only focus on minimum number of parameters possible. Hence, faster optimization process and more precise results are obtained. Another challenge is in motion planning of redundant cells. Because there can be infinite solutions for such cells, there is room for optimization. In this work, we propose methods to fix the optimal placement of the task and, furthermore, assign the optimal motion planning to all manipulators in the cell, simultaneously. A novel method is proposed to identify the number of independent parameters and applied to a gluing path for a coordinated redundant robotic workcell. The workcell consists of a generic six-DOF serial manipulator and a one-DOF redundancy provider (RP). Two cases of RPs are investigated, namely a rotary table and a linear guide. An innovative method using swept volume is proposed for determining the number of independent parameters for both cases under study. The outcome of this study is an intuitive method to identify the number of independent parameters in redundant cells. The results are compared between using all initial parameters, as contrary to only the independent ones. It is proven that the proposed method improves the optimization efficiency by 32%. Moreover, the performance of the rotary table is compared to the linear guide, for a specific gluing application. Optimization methods in this work are based on Particle Swarm Optimization (PSO). A workcell consisting of a six degrees of freedom (DOF) serial manipulator, a six-DOF parallel manipulator and a rotary table mounted on the parallel manipulator is studies for automated fiber placement task. The solution to motion planning is obtained considering the singularities of the serial manipulator and the workspace boundaries of all manipulators. The algorithm to obtain the optimum path placement is explained through a simple example and the results for a helix path with nearly 2,700 points around the workpiece is represented. The results for motion planning are represented where distance to singularity is maximized, collision avoidance and workspace boundaries are respected. The result is obtained after 10 iterations with 20 particles. This outcome of this study is a reliable and easy to apply motion planning algorithm to be used in redundant cells. Another challenge in this work is combinatorial task placement that arises in robotic inspection cells. The goal is to improve the efficiency of a turbine blade inspection cell through optimizing the placement of the camera and optimizing the sequence of the images. The workcell contains a six-DOF serial manipulator that is holding the blade and shows it to the camera from different angles, whereas the camera takes inspection images. The problem at hand consists of a six-DOF continuous optimization for camera placement and discrete combinatorial optimization of sequence of images (end-effector poses). A novel combined approach is introduced, called Blind Dynamic Particle Swarm Optimization (BD-PSO), to simultaneously obtain the optimal design for both domains. Our objective is to minimize the cycle time, while avoiding any collisions in the workcell during the inspection operation. Even though PSO is vastly used in engineering problems, novelty of the proposed combinatorial optimization method is in its ability to be used efficiently in the traveling salesman problems where the distances between cities are unknown (blind) and the distances are subject to change (dynamic). This highly unpredictable domain is the case of the inspection cell where the cycle time between images will change for different camera placements. The cycle time is calculated based on weighted joint travel time of the robot. All the eight configurations of the robot are taken into the consideration, therefore, robot’s configuration is optimized in the final result as well. The outcome of this study is an innovative hybrid algorithm to simultaneously solve combinatorial and continues problems. Results show fast convergence and reliable motions. The test of benchmarks selected from TSPLIB shows that the results obtained by this algorithm are better and closer to the theoretical optimal values with better robustness than those obtained by other methods. The best placement of camera and best image sequence (for 8 images) is obtained after 11 iterations using 30 particles. In general, the main results of this thesis are three algorithms: an algorithm to obtain minimum number of placement parameters in redundant robotic workcells; an algorithm for motion planning of highly redundant cells; and an algorithm to optimize camera placement and simultaneously obtain the optimal image sequence in an inspection cell

Optimisation du comportement de cellules robotiques par gestion des redondances : application à la découpe de viande et à l’Usinage Grande Vitesse

Industrial robots have evolved fundamentally in recent years to reach the industrial requirements. We now find more suitable anthropomorphic robots leading to the realization of more complex tasks like deformable objects cutting such as meat cutting or constrained to high stresses as machining. The behavior study of anthropomorphic robots, parallel or hybrid one highlights a kinematic and dynamic anisotropy, which impacts the expected accuracy. This thesis studied the integration of the kinematic redundancy that can partially overcome this problem by well setting the task to achieve it in a space compatible with the expected capacity. This work followed a three-step approach: analytical modeling of robotic cells by serial equivalent based on the TCS method, formalizing the constraints of meat cutting process and machining process and a multicriteria optimization.The first originality of this work focuses on the development of a 6 DoFs model to analyze the operator actions who naturally optimizes his arm behavior to ensure the task it performs. The second originality concerns the optimized placement of structural redundancy (9 DoFs robotic cell) where positioning parameters are incorporated as controllable variables (11 DoFs robotic cell). Thus, the thesis makes contributions to : - the definition of criteria adapted to the realization of complex and under high stress task for the management of the kinematic redundancy; - the structural behavior identification, under stress, by metrology tools (Laser tracker ) and the self- adaptation paths by using an industrial force control; - the behavior optimization to improve the cutting process quality (meat cutting and machining).Les robots industriels ont évolué fondamentalement ces dernières années pour répondre aux exigences industrielles de machines et mécanismes toujours plus performants. Ceci se traduit aujourd’hui par de nouveaux robots anthropomorphes plus adaptés laissant entrevoir la réalisation de tâches plus complexes comme la découpe d’objets déformables telle que la découpe de viande ou soumis à de fortes sollicitations comme l’usinage. L’étude du comportement des robots anthropomorphes, à structures parallèles ou hybrides montre une anisotropie aussi bien cinématique, que dynamique, impactant la précision attendue. Ces travaux de thèse étudient l’intégration des redondances cinématiques qui permettent de pallier en partie ce problème en positionnant au mieux la tâche à réaliser dans un espace de travail compatible avec les capacités attendues. Ces travaux ont suivi une démarche en trois étapes : la modélisation analytique de cellules robotiques par équivalent sériel basée sur la méthode TCS, la formalisation des contraintes des processus de découpe de viande et d’usinage et une résolution par optimisation multicritère. Une première originalité de ces travaux réside en le développement d’un modèle à 6 degrés de liberté permettant d’analyser les gestes de l’opérateur qui optimise naturellement le comportement de son bras pour garantir la tâche qu’il réalise. La seconde originalité concerne le placement optimisé des redondances structurales (cellules à 9 ddls) où les paramètres de positionnement sont incorporés comme des variables pilotables (cellule à 11 ddls). Ainsi, ces travaux de thèse apportent des contributions à : - la définition de critères adaptés à la réalisation de tâches complexes et sollicitantes pour la gestion des redondances cinématiques ; - l’identification du comportement des structures sous sollicitations par moyen métrologique (Laser tracker) et l’auto-adaptation des trajectoires par l’utilisation d’une commande en effort industrielle ; - l’optimisation du comportement permettant l’amélioration de la qualité de réalisation des différents processus de coupe (découpe de viande et usinage)

Contributions à la maîtrise de la dynamique des robots parallèles

Ce mémoire traite de mes contributions à la maîtrise de la dynamique des robots parallèles. Le premier chapitre présente une introduction générale de mes travaux de recherche. Le deuxième chapitre présente mon curriculum vitae. Mes activités d'encadrement, les projets de recherche que j'ai montés ainsi que ceux auxquels j'ai participé et une synthèse de mes collaborations nationales et internationales sont mentionnés dans le troisième chapitre. Mon rayonnement au sein de la communauté scientifique, qui se traduit par des activités d'intérêt général, la participation à des comités d'expertise, des activités éditoriales, la participation à l'organisation de colloques et quelques distinctions scientifiques, ainsi que la liste de mes publications ont été décrits dans le quatrième chapitre. Le cinquième chapitre synthétise mes activités d'enseignement. Le sixième chapitre présente plus en détail mes activités de recherche principales qui sont organisées autour des deux thèmes suivants : (i) Maîtrise de la dynamique des robots parallèles ; (ii) Conception et commande de nouveaux robots parallèles aux performances dynamiques améliorées. Enfin, le septième chapitre présente mes conclusions sur les travaux que j’ai pu mener ainsi que mes perspectives de recherche.Les activités de recherche que j'ai menées portent principalement sur la maîtrise de la dynamique des robots parallèles qui sont des architectures mécaniques complexes dont les performances dynamiques sont encore mal maîtrisées. J'ai cherché à mieux maîtriser la dynamique de ces machines à deux niveaux :1.un premier niveau intitulé « maîtrise de la dynamique des robots parallèles » qui se situe en aval de la phase de réalisation du robot : pour une machine donnée, comment mieux maîtriser ses performances dynamiques (par une modélisation plus fine, par la compréhension des phénomènes physiques mis en jeu et leur gestion par planification de trajectoire ou mise en place de contrôleurs avancés, etc.) ?2.un second niveau intitulé « conception et commande de nouveaux robots parallèles aux performances statiques et dynamiques améliorées» qui se situe en amont de la phase de réalisation du robot : pour des performances statiques et/ou dynamiques à atteindre, comment concevoir l'architecture de robot, voire la bonne adéquation {architecture de robot – contrôleur} qui permet de répondre au cahier des charges désiré ?Ces deux approches ne sont pas antagonistes, mais au contraire, elles sont complémentaires.Mes contributions principales autour de la maîtrise de la dynamique des robots parallèles se sont concentrées sur quatre points majeurs :1.L'étude des conditions de dégénérescence du modèle dynamique des robots parallèles 2.L'identification des paramètres du modèle dynamique rigide 3.La modélisation élastodynamique4.La proposition de techniques d'équilibrage permettant de diminuer la complexité de mise en oeuvreMes contributions principales autour de la conception et commande de nouveaux robots parallèles aux performances statiques et dynamiques améliorées se sont concentrées sur deux travaux majeurs :1.La conception de robots pour le déplacement de lourdes charges2.La conception et la commande de robots rapides et précisTous les résultats présentés, exception faite de ceux sur l'équilibrage dynamique, ont été validés expérimentalement.Les travaux présentés en perspectives se concentrent autour de deux grands axes thématiques:1.Maîtrise de la dynamique des systèmes,2.Conception de robots orientée environnements.Les activités que je souhaite mener sur la maîtrise de la dynamique des systèmes ciblent :a)La reconfiguration dynamique des robots,b)La modélisation et l'identification basées perception.Ces activités, qui s'inscrivent dans la continuité de mes travaux de recherche actuels.L'objectif du thème « Conception de robots orientée environnements », qui est un thème en rupture, est de proposer des méthodes génériques pour l'analyse, l'évaluation et la conception de nouvelles architectures de robots et de mécanismes,•en fonction d'un environnement donné (environnement en termes de milieu dans lequel le robot évolue, interagit, etc.) : le robot doit être doté d'un système de perception efficace associé à un contrôleur performant et il faut penser la conception du robot de manière intégrée afin que l'ensemble {architecture mécanique – contrôleur – capteurs –moteurs} soit le plus performant possible.•à faible impact pour l'environnement dans lequel ils évoluent (moins de pollution, moins de consommation énergétique, etc.)Les activités que je souhaite mener en conception orientée environnements ciblent :a)La proposition de méthodologies de conception orientée commande qui vont permettre de faire en sorte que l'ensemble {architecture mécanique – contrôleur – capteurs – moteurs} soit le plus performant possible pour une tâche, un ensemble de tâches, ou un environnement donnés,b)La conception de robots à faibles impacts environnementaux

Workpiece Placement Optimization for Machining Operations with a KUKA KR270-2 Robot

International audience— Roboticists are faced with new challenges in robotic-based manufacturing. Up to now manufacturing operations that require both high stiffness and accuracy have been mainly realized with computer numerical control machine tools. This paper aims to show that manufacturing finishing tasks can be performed with robotic cells knowing the process cutting conditions and the robot stiffness throughout its Cartesian workspace. It makes sense that the finishing task of large parts should be cheaper with robots. However, machining robots have not been adapted for such operations yet. As a consequence, this paper introduces a methodology that aims to determine the best placement of the workpiece to be machined knowing the elastostatic model of the robot and the cutting forces exerted on the tool. Therefore, a machining quality criterion is proposed and an optimization problem is formulated and solved. The KUKA KR270-2 robot is used as an illustrative example throughout the paper