Position control of an industrial robot using an optical measurement system for machining purposes

A series of mechanical properties and disturbances limit the accuracy achievable in robotic applications. External control of the end effector position is commonly known as being an appropriate mean to increase accuracy. This paper presents an approach for position control of industrial robots using the pass-through between an industrial CNC and servomotors. A CNC-controlled robot is used together with an external optical measurement system to close the feedback loop of robot end effector and robot controller in order to improve robot accuracy. For short cycle times and implementation reasons a PLC is used for signal processing and control implementation. The relevance of the approach is outlined in experiments. The robot behaviour in free space motion and in machining application is analysed with the optical measurement system and a CMM

Improving robotic machining accuracy through experimental error investigation and modular compensation

Machining using industrial robots is currently limited to applications with low geometrical accuracies and soft materials. This paper analyzes the sources of errors in robotic machining and characterizes them in amplitude and frequency. Experiments under different conditions represent a typical set of industrial applications and allow a qualified evaluation. Based on this analysis, a modular approach is proposed to overcome these obstacles, applied both during program generation (offline) and execution (online). Predictive offline compensation of machining errors is achieved by means of an innovative programming system, based on kinematic and dynamic robot models. Real-time adaptive machining error compensation is also provided by sensing the real robot positions with an innovative tracking system and corrective feedback to both the robot and an additional high-dynamic compensation mechanism on piezo-actuator basis

Development of a sensor system and a method for the computation of the robot's pose based on structured light projection

Die Genauigkeitssteigerung von Industrierobotern ist eine zentrale Aufgabe, um Robotersysteme auch für Produktionsprozesse mit hohen Genauigkeitsanforderungen, wie Entgraten oder Bohren, einzusetzen. Roboter sind in der Lage, Posen im Arbeitsraum des Roboters wiederholbar anzufahren. Jedoch ist das absolutgenaue Anfahren von Roboterposen bisher für viele Prozesse nicht ausreichend. Eine Möglichkeit, die Absolutgenauigkeit von Robotern zu verbessern, ist die Online-Korrektur der Roboterpose mit den Messwerten eines zusätzlichen optischen Sensorsystems. Allerdings erreichen herkömmliche Sensorsysteme kaum eine Marktdurchdringung aufgrund fehlender gemessener Freiheitsgrade, unzureichender Genauigkeit oder den eingeschränkten Möglichkeiten zur Integration am Robotersystem. Das im Rahmen dieser Dissertation entwickelte Messprinzip für ein gestaltetes Sensorsystem verwendet die Projektion einer Maßverkörperung in den Arbeitsraum des Roboters und benutzt diese als berührungslose, ortsfeste Referenz zur Bestimmung der Roboterpose. Der zentrale Beitrag dieser Arbeit ist die Formulierung einer Gesetzmäßigkeit und das daraus entwickelte Messverfahren zur Auswertung der Messungen durch Bildverarbeitung und zur Berechnung der Roboterpose und damit die Möglichkeit zur Genauigkeitssteigerung in der Robotik. Weiterführend untersucht die vorgestellte Arbeit durch Simulation die Auswirkung von Einflussgrößen, wie die Anzahl gemessener Projektionen oder das Rauschniveau der Messung, auf das Ergebnis. Das in der Simulation erprobte Messverfahren wird nach Umsetzung des Sensorsystems und der Integration am Robotersystem in experimentellen Anwendungen, insbesondere bei der Bewegung entlang von Linien und Kreisen in einem Messquader validiert. Das wesentliche Ergebnis ist die Verbesserung der erreichbaren Genauigkeit des Sensorsystems im Vergleich zum Referenzfall eines monokularen Sensorsystems um etwa 83,2% bei Bestimmung aller Freiheitsgrade der Pose. Zudem wurde experimentell bei translatorischen Bewegungen des Roboters entlang paralleler Prüfbahnen die translatorische Genauigkeit eines definierten Kriteriums von 0,087mm bei einer Unsicherheit von 0,048mm erzielt. Aus dem Beitrag dieser Arbeit entsteht die Möglichkeit, Sensorsysteme als Basis für die Entwicklung absolutgenauer Robotersysteme bereitzustellen und folglich bei komplexen und genauen Bearbeitungsaufgaben einzusetzen.Robots are capable to reach points repeatable in its workspace. However, the exact and therefore absolute approaching of points is for various processes insufficient. As a result, the robotic community tries to overcome limitations of robot’s accuracy by compensating path deflections during the execution of processes such as drilling or deburring. The use of additional sensor systems and the measuring of the pose offer one possibility to control the exact positioning. Conventional sensor systems in robotics hardly achieve a penetration of the market because of missing number of measured degree of freedom, lacking accuracy or limited possibilities for integration in robot cells. The conveived measuring principle of this dissertation applies the projection of a material measure in the workspace of the robot as a contact-free reference for a designed sensor system. The main contribution of the work is the development of a formalism and an algorithm that interpret the measurements of the projected reference structure and compute the pose based on image processing operations. Furthermore, the work deals with the simulation of the sensor system and evaluation of influencing variables. Afterwards a real test bed is presented and the experimental validation of the sensor system based on movements along lines or circles in a cuboid are outlined. One essential result is the achieved accuracy of the developed sensor system compared to a monocular approach which is presented as reference measurement. In case of a 6D pose determination, the sensor systems achieves an improvement about 83,2%. In fact, when evaluating parallel test paths the translational accuracy is 0,087mm with an uncertainity 0,048mm of a defined assessment criteria. This shows the effectiveness of the measurement principle in order to set up robot system for complex and accurate machining tasks

Ausgleichsaktorik für Roboter erhöht Genauigkeit beim Fräsen

Der Einsatz von Robotern in spanenden Prozessen war bislang immer durch die schlechte Genauigkeit unter Prozessbedingungen eingeschränkt. Mit Kompensationen unter Echtzeitbedingungen lässt sich nun eine Genauigkeit von unter 100 µm erreichen. Damit wird die Tür für neue Anwendungen aufgestoßen

Production assistants: The rob@work family

Mobile robots offer a high potential for future manufaturing and assembly. To this day the co-operation and co-action is in these fields hardly applicable, because of safety regulations, insufficient technology and its missing integration. In order to fill the gap this paper presents the hard- and software design of the mobile assistant rob@work 2. This system is the second iteration of the rob@work system. As an exemplary work the conditions of a prototypic industrial application are analyzed and divided into modes of operation which are portable to generic assembly processes. For each mode of operation the safety requirements for human-robot interaction are surveyed taking into account recent regulations. In order to evaluate the performance of the robotic system, repeatability benchmarks and respective measurements are presented

Integrated approach to robotic machining with macro/micro-actuation

A novel integrated approach to high-accuracy machining with industrial robots is presented in this paper. By combining a conventional industrial robot with an external compensation mechanism, a significantly higher bandwidth of the control of the relative position between the tool and the workpiece can be achieved. A model-based feedback controller for the compensation mechanism, as well as a mid-ranging control architecture for the combined system with the robot and the compensation mechanism are developed. The system performance is evaluated in extensive machining experiments, and the workpiece accuracies achieved are quantified and compared to the corresponding results obtained with state-of-the-art approaches to robotic machining. It is shown that the proposed approach to machining offers significantly higher accuracy, up to eight times improvement for milling in steel, where the required process forces, and thus the exhibited position deviations of the robot, are significant

Programming system for efficient use of industrial robots for deburring in SME environments

The use of robots in SME production environments requires programming systems that decrease programming effort and can be used by process experts rather than robotics experts. The core sources of information available to the robot system are human input, sensor data and model data. However most programming systems only connect one or two of these information sources to generate robot programs. The presented programming concept featuring hand-guided robot operation for intuitive robot instruction, use of workpiece CAD-models to retrieve nominal model information and a triangulation sensor for detection of workpiece contours features combination of all three sources of information and promises efficient robot programing for deburring applications in SME production. Finally a kinematic compensation approach is investigated which provides good positioning accuracy which is in particular important when dealing with workpieces of large dimensions

Automatic Programming and Control for Robotic Deburring

In the current industrial scenario, robots are rarely used in contact operations such as machining and finishing as they entail complex programming and control methods. Further, the disparity between accuracy specifications, communication technologies and control methods required for such operations calls for greater efforts in robot programming and control. This paper presents a novel approach to automatically program an industrial robot-based on the CAD model of the product variants and to enable online control to minimize errors during a deburring process. The paper starts with the modeling of the product, process and resource (PPR model) which is used to generate robot motion trajectories taking into account the constraints and the free degrees of freedom (DoFs) of the robotic deburring process. The operator selects the edge of the workpiece to be machined, and an automatic program generation system is designed which programs the robot for the deburring process and enables online compensation. A laser scanner sensor device is used for localizing the workpiece in the robot cell and in the online compensation to perform fine corrections of the robot’s movement during the process. Experimental results are used to validate the robotic program generation and control mechanism for a deburring process, and to outline the future potential of this work