Bernd Kauschinger

Challenges in the Development of a Generalized Approach for the Structure Model Based Correction

This paper gives a description of the challenges in the development of a generalized approach for the structure model based correction of thermoelastic errors of machine tools. The correction approach can be divided in modules. The challenges are described on the requirements of the modules.

Uncertain Parameters in Thermal Machine-Tool Models and Methods to Design their Metrological Adjustment Process

The measures taken to improve the thermal behaviour of machine tools are based on thermal models. The models are applied to support the design process and to correct the machine tool operation in a control-based way. Especially the models for correction purposes include uncertain parameters that cannot be estimated with sufficient accuracy. Thus these parameters have to be adjusted by means of measurements. During the adjustment process, a broad diversity of machine behaviour and model characteristics has to be taken in to account. Therefore, substantial time, effort and expert knowledge are required. To identify the key expenses, a generalized and systematic analysis of the adjustment process was carried out. First, the typical design of the models, the parameters of the sub models and the current adjustment procedure were investigated. Based on the results of the analysis, support requirements were identified. Afterwards first methods and software tools for efficient support were developed. This strategy is demonstrated using the example of a hexapod strut model.

Eccentric universal joints for parallel kinematic machine tools: variants and kinematic transformations

In the 1990’s enhanced capabilities of parallel kinematic machine tools (PKM) regarding stiffness, motion accuracy and dynamics have been announced generously. Extensive research and development has been done in this area to date. Regarding this, the application range of PKMs is still small. Looking for reasons often yields inadequate motion accuracy as well as insufficient workspace. In either case the passive joints of the kinematic chains pose essential weak points. This article is about eccentric universal joints as an alternative approach that can avoid drawbacks of conventional universal joints and finally enhance the application range of PKMs. However, one of the consequences is a more complex and no longer unique kinematic transformation. This is significant in a control context, where iterative calculations should be avoided when possible due to real-time demands and the uniqueness of the solution has to be guaranteed in any case. Though the general inverse kinematic problem of industrial robots is identical, no generic closed-form (non-iterative) solution is known so far. But often closed-form as well as unique solutions are possible yet by considering particular features of the kinematic chain. In this paper after an introduction types of joint eccentricity are discussed and corresponding inverse kinematic transformations are derived with control purposes in mind.

Kinematic calibration of a hexapod of simple design

To benefit from the advantages of parallel kinematic machines (PKM) in industrial applications an efficient kinematic calibration is of particular importance. In this paper a new approach for kinematic calibration of PKM is presented that has been developed and successfully tested on a hexapod at the IWM Dresden. The approach particularly respects the concept of simple design that aims at a cost-effective and economic over-all solution. Aspects of calibration that are in many cases not explicitly accounted for are considered. A simple and robust double-ball-bar (DBB) is used for data acquisition while continuously moving the platform on a specific trajectory in 6 degrees of freedom (dof). The measuring trajectory is optimized to ensure the identifiability of kinematic parameters, respecting their sensitivity and orthogonality in the workspace. Parameter identification is based on Genetic algorithms with customized genetic operators as well as real and simulated measurements. A significant rise of motion accuracy was obtained in the whole workspace.

Innovative Simulation Technology for Real-Time Calculation of the Thermo-Elastic Behaviour of Machine Tools in Motion

Heat resulting from motors, moved contacts as well as cutting processes, causes time-dependent deformation of machine structures that reduces the precision of machine tools. For design optimization and especially for correction of thermal induced displacements, it is necessary to have compact models, which allow fast simulation of the thermo-elastic behaviour of the entire moving machine tool during the process. This paper presents an innovative simulation technology that permits, starting from CAD geometry through FE modelling, to come to a time-saving thermo-elastic calculation model of entire moved machine tools. Thereby, calculated temperature and deformation fields are of high geometrical resolution. Results and potentials of the new approach are demonstrated on example of a Hexapod machine tool.

Increasing the Performance of Processing Machines by Executing Output Rate Dependent Motion Profiles

From the economic point of view, rising the output rate of processing machines is a key requirement. Thereby, particular demands are to be met, i.e., product quality, process stability, energy consumption, impact of surroundings, or safety at work. Rising the output rate is limited, if only one of these demands can not longer be met. In this paper, a novel control approach is presented that allows to change the executed motion profile due to the actual output rate. Increasing the machine’s performance is evaluated on experimental results. Unused potentials of servo drives are opened up to generate highly dynamic multi-axis motions in processing machines.

Effiziente Abarbeitung hochdynamischer Bewegungen: Teil 1: Umsetzung eines Steuerungsansatzes zur effizienten Abarbeitung taktratenabhängiger Bewegungen an Verarbeitungsmaschinen

Kurzfassung Eine Möglichkeit zur Erhöhung der Produktausbringung an Verarbeitungsmaschinen ist die Steigerung der Arbeitstaktrate. Die maximal erreichbare Taktrate ist dabei durch Anforderungen begrenzt, die aus Prozess, Maschine oder Umwelt resultieren. Zur Verschiebung dieser Grenzen bieten moderne Servoantriebe Potenziale, die bisher oftmals ungenutzt sind. Im ersten Teil dieses zweiteiligen Beitrags wird das Problemfeld erörtert und ein Ansatz zur Erschließung dieser Potenziale vorgestellt. Im zweiten Teil werden anhand experimenteller Untersuchungen an repräsentativen Verarbeitungsprozessen Vorteile und Grenzen des Ansatzes dargestellt und diskutiert.

Effiziente Abarbeitung hochdynamischer Bewegungen

Kurzfassung Eine Möglichkeit zur Erhöhung der Produktausbringung an Verarbeitungsmaschinen ist die Steigerung der Arbeitstaktrate. Die maximal erreichbare Taktrate ist dabei durch Anforderungen begrenzt, die aus Prozess, Maschine oder Umwelt resultieren. Zur Verschiebung dieser Grenzen bieten moderne Servoantriebe Potenziale, die bisher oftmals ungenutzt sind. Im ersten Teil des Beitrags wurde ein Lösungsansatz zur Erschließung dieser Potenziale vorgestellt. Im vorliegenden Artikel werden anhand experimenteller Untersuchungen Vorteile und Grenzen des Ansatzes dargestellt und diskutiert.

Adjustment of Uncertain Parameters in Thermal Models of Machine Tools

Thermal models of machine tools contain parameters that represent machine-specific and time-variable properties. In the design process, these parameters cannot be estimated with sufficient accuracy. Thus, they have to be adjusted by measurements. At present, substantial time, effort and expensive measurement equipment are required for adjustment, as well as in-depth expertise. Consequently, the goal is to develop cost efficient methods for rapid and comprehensive adjustment. This is to be achieved using a systematic strategy for the support and automation of adjustment processes. The strategy is demonstrated based on a thermal model of a bearing assembly.

Holistic Ontology-Based Assistance System for Efficient Process Model Parameter Identification

Accurate models of technical systems are the basis for many tasks like system analysis, predictions, or controller design. Usually, the values of several important parameters cannot be determined by theoretical analysis only; instead, process identification is necessary. For several applications, the efficiency of the identification procedure is very important, for example, for the creation of thermal models of machine tools, because of the large time constants and the expensive machine time. The goal of the authors is the support of this task as far as possible by software. This paper contributes to that goal twofold: on the one hand, it provides a collection of influences which have to be considered for supporting the identification procedure. On the other hand, concepts for computer-based support are presented—ontologies and automatic design methods based on evolutionary algorithms.