Experimental derivation of a condition monitoring test cycle for machine tool feed drives

Due to their critical influence on manufacturing accuracy, machine tool feed drives and the monitoring of their condition has been a research field of increasing interest for several years already. Accurate and reliable estimates of the current condition of the machine tool feed drive’s components ball screw drive (BSD) and linear guide shoes (LGSs) are expected to significantly enhance the maintainability of machine tools, which finally leads to economic benefits and smoother production. Therefore, many authors performed extensive experiments with different sensor signals, features and components. Most of those experiments were performed on simplified test benches in order to gain genuine and distinct insights into the correlations between the recorded sensor signals and the investigated fault modes. However, in order to build the bridge between real use cases and scientific findings, those investigations have to be transferred and performed on a more complex test bench, which is close to machine tools in operation. In this paper, a condition monitoring test cycle is developed for such a test bench. The developed test cycle enables the recording of a re-producible data basis, on which models for the condition monitoring of BSDs and LGSs can be based upon.

Minimisation of Pose-Dependent Regenerative Vibrations for 5-Axis Milling Operations

The machining of free-formed surfaces, e.g., dies or moulds, is often affected by tool vibrations, which can affect the quality of the workpiece surface. Furthermore, in 5-axis milling, the dynamic properties of the system consisting of the tool, spindle and machine tool can vary depending on the tool pose. In this paper, a simulation-based methodology for optimising the tool orientation, i.e., tilt and lead angle of simultaneous 5-axis milling processes, is presented. For this purpose, a path finding algorithm was used to identify process configurations, that minimise tool vibrations based on pre-calculated simulation results, which were organised using graph theory. In addition, the acceleration behaviour of the feed drives, which limits the ability of adjusting the tool orientation with a high adaption frequency, as well as potential collisions of the tool, tool chuck and spindle with the workpiece were considered during the optimisation procedure.

A Friction Fluctuation Model of Rolling Guideways

Linear ball guideways are widely employed in machine tool drive systems. Friction fluctuation of linear ball guideways cause the fluctuation of feed rate which results in the contour error in synchronous motions using several feed drives. A model-based systematic methodology to design the raceway profile is demanded to reduce the friction fluctuation of rolling guideways. In this study, a model to estimate the rolling resistance fluctuation of a ball sandwiched by two raceways was proposed. The rolling resistance fluctuation was estimated from the contact angle between the ball and raceways. The contact angle was obtained from the surface profile of the raceway. The estimation accuracy of the proposed model was verified by comparing measured and estimated rolling resistances. The raceway that was finished by face milling with a R-bite was used in the experiment to have rolling resistance fluctuation due to a periodic surface profile. The experimental results showed that the rolling resistance fluctuation could be estimated by the proposed model with 30% amplitude error at maximum. The variation of the rolling resistance was influenced by the phase difference between the upper and lower raceway profiles. The rolling resistance variation could be decreased to 1/3 when the phase difference was 1/2 period of the periodic profile component.

Tracking Control of Single-Axis Feed Drives Based on ADRC and Feedback Linearisation

The accuracy of manufacturing highly characterises the performance of industrial motion control. However, detrimental effects such as nonlinear coupling, model uncertainty and unknown external disturbances severely affect trajectory tracking performance. In this paper, we proposed an ADRC and feedback linearisation-based control algorithm for the high-precision trajectory tracking of feed drives. The controller was rigorously designed to ensure the convergence of observer states and tracking error. The applicability of the proposed approach was successfully demonstrated via high-fidelity simulation, and the numerical results based on different tracking methods were compared.

Störgrößenkompensation für Vorschubantriebe/Disturbance compensation for feed drives

Zahnstange-Ritzel-Antriebe werden überwiegend bei großen Werkzeugmaschinen eingesetzt und häufig mit indirekter Lageregelung betrieben. Hieraus resultiert eine geringe Positioniergenauigkeit und ein unzureichendes dynamisches Nachgiebigkeitsverhalten. Um den hohen Genauigkeitsanforderungen moderner Werkzeugmaschinen gerecht zu werden, wird in diesem Beitrag eine beschleunigungsbasierte Störgrößenkompensation vorgestellt. Experimentelle Ergebnisse belegen eine Verbesserung des Störverhaltens.   Rack-and-pinion drives are mainly used in large machine tools and controlled by indirect position control. This leads to low positioning accuracy as well as an insufficient dynamic compliance. To meet the high accuracy requirements of modern machine tools, this paper presents an acceleration-based disturbance compensation. Experimental results prove a considerable improvement of the disturbance behavior.