Christoph Budde

Self-calibration of the HEXA-parallel-structure

In order to enhance absolute accuracy of the HEXA-parallel-robot this paper presents a technique to calibrate the structure by means of redundant angular sensors added to its passive joints. Compared to traditional calibration strategies which are based on pose-measurement by external measurement devices the so-called self calibration approach possesses several advantages. Besides a derivation of the kinematic transformation equations of the system under consideration it is shown how to formulate an appropriate residual function that has to be minimized in order to identify the geometric parameters of the robot manipulator. An important difference to previous work on the topic of calibration is the fact, that only angular measurements are available from both the actuator encoders as well as passive joint sensors, making HEXA-self-calibration more elaborate. Simulation studies finally indicate efficiency of the proposed strategy. In order to consider the effect of measurement inaccuracies, noise has been taken into account.

Development of a Triglide-Robot with Enlarged Workspace

Despite of a promising potential robots based on parallel kinematic structures have not yet found their way into industry on a large scale. One of the main reasons for that is a workspace to installation-space ratio, which usually is inferior to that of their serial counterparts. In this paper development and design issues of a triglide-robot based on the linear delta are presented. Using a workspace enlargement approach based on the use of several workspaces going along with different assembly modes of the structures the workspace to installation-space ratio of this robot can be enhanced significantly. Additionally this paper is part of a joint effort of several authors to benchmark different kinematic structures using based-fixed linear drives against each other. Thus, the presented structure is characterized using standardized benchmark criteria.

Parallel Kinematic Structures of the SFB 562

The objective of the Collaborative Research Center (SFB) 562 ”Robot Systems for Handling and Assembly - Highly Dynamic Parallel Structures with Adaptronic Components” is the research of fundamental methods and components for the development of parallel robot systems with regard to high operating speeds, accelerations and accuracy. Eight institutes in the field of mechanical and electrical engineering as well as computer science at the Technische Universitat Braunschweig and the German Aerospace Center (DLR) are cooperating to investigate theoretical results as well as the exploration of new concepts on real robots. These robots which have been developed since the formation of the SFB 562 ten years ago are the topic of this paper.

Configuration Switching for Workspace Enlargement

In order to facilitate a wider use of parallel robots and to make use of their inherent advantages, the drawbacks to these structures, such as singularities in the workspace or the small ratio of workspace to installation space, need to be diminished. The latter can be tackled using an approach presented in this article. An overall workspace, which is substantially larger than the original one, can be obtained by using several robot-configurations corresponding to different working and assembly modes (different solutions of the inverse and direct kinematic problem). The general procedure to change between the configurations requires the passing through singularities and is described exemplarily first for a simple planar manipulator and subsequently for a more complex spatial parallel structure.

Smart structures technologies for parallel kinematics in handling and assembly

Parallel kinematics offer a high potential for increasing performance of machines for handling and assembly. Due to greater stiffness and reduced moving masses compared to typical serial kinematics, higher accelerations and thus lower cycle times can be achieved, which is an essential benchmark for high performance in handling and assembly. However, there are some challenges left to be able to fully exploit the potential of such machines. Some of these challenges are inherent to parallel kinematics, like a low ratio between work and installation space or a considerably changing structural elasticity as a function of the position in work space. Other difficulties arise from high accelerations, which lead to high dynamic loads inducing significant vibrations. While it is essential to cope with the challenges of parallel kinematics in the design-process, smart structures technologies lend themselves as means to face some of these challenges. In this paper a 4-degree of freedom parallel mechanism based on a triglide structure is presented. This machine was designed in a way to overcome the problem of low ratio between work and installation space, by allowing for a change of the structures configuration with the purpose of increasing the work space. Furthermore, an active vibration suppression was designed and incorporated using rods with embedded piezoceramic actuators. The design of these smart structural parts is discussed and experimental results regarding the vibration suppression are shown. Adaptive joints are another smart structures technology, which can be used to increase the performance of parallel kinematics. The adaptiveness of such joints is reflected in their ability to change their friction attributes, whereas they can be used on one hand to suppress vibrations and on the other hand to change the degrees of freedom (DOF). The vibration suppression is achieved by increasing structural damping at the end of a trajectory and by maintaining low friction conditions otherwise. The additional feature to alter the DOF is realized by increasing friction to the point where clamping happens. This can be used to support the change in the machines configuration of parallel kinematics. Two kinds of adaptive joints are presented, both utilizing piezoceramic actuators. The first kind features an adjustable clearance of the slide bearing that provides low friction for high clearance conditions and great friction for reduced clearance. The second kind offers the possibility to reduce the friction by moving the rubbing surfaces dynamically. For both joints experimental results are shown. The paper closes with an outlook on ongoing research in the field of parallel robots for handling and assembly with an emphasis on smart structures technologies.

Parallel Robot Calibration by Working Mode Change

The positioning accuracy of robotic manipulators can be enhanced by identification and correction of the geometry parameters of the controller model in a way that it best matches the real physical robot. This procedure, denoted as kinematic calibration, is performed by analyzing the difference between conflicting information gained by the kinematic model and corresponding redundant measurement information. Most traditional robot calibration approaches require extra sensors or special constraint fixtures in order to obtain redundancy. This paper proposes a new calibration method that does not require any special calibration equipment, thus being very economical. The presented technique which is designed to be applied to parallel robots is based on a working mode change and incorporates special knowledge about serial singularities. Exemplarily the approach is verified by means of simulation studies on a 3-RRR-structure.

Improvement of parallel robots for handling and assembly tasks

Purpose – This paper seeks to establish parallel robots with strong performance characteristics in handling and assembly processes.Design/methodology/approach – The presented work introduces concepts and solutions related to the improvement of parallel kinematic mechanisms. Structural design topics and modeling approaches are as well considered as control schemes and new machine components particularly designed for high‐dynamic parallel robots. The results have been achieved by a unique interdisciplinary research group linking knowledge from mechanical engineering, electrical engineering and computer science.Findings – The paper found numerous individually applicable methods leading to an improved efficiency of parallel robots. Several of the developments have been already implemented and validated by various self‐built machine prototypes and a new control system.Originality/value – Owing to higher stiffness, accuracy and improved dynamic behavior parallel robots proved to be an efficient and suitable sup...

Hochgeschwindigkeitshandhabung und Montage

Kurzfassung Die Entwicklung leistungsstarker Roboter trägt dazu bei, ökonomische Fortschritte in Produktionssystemen zu erzielen. Neue Maschinenkonzepte, basierend auf hybriden kinematischen Strukturen, ermöglichen es, hohe Genauigkeit mit guten dynamischen Fähigkeiten zu kombinieren. Der Entwicklungsprozess eines Roborters für Handhabungs- und Montageaufgaben mit hohen Anforderungen an Genauigkeit und Geschwindigkeit wird von der Aufgabendefinition bis zum Aufbau eines Prototypen beschrieben. Die strukturellen Eigenschaften, die konstruktive Umsetzung und angepasste Steuerungsalgorithmen führen zu einem Roboter mit vorteilhaften Eigenschaften zu angemessenen Kosten.