Sascha Weikert

Testing the Contouring Performance in 6 Degrees of Freedom

Abstract The performance of linear axes is often tested on the basis of one set-up per one or two directions of deviations from a NC path. With the application of multi-axes machining the contouring performance in more than two degrees of freedom is of interest. The paper describes a measuring instrument to check the contouring performance of a machine tool in the six degrees of freedom. The three translations and the three rotations of the relative movement between tool side and workpiece side are measured simultaneously. Results of first measurements are presented and discussed.

State Control of Servo Drives with Flexible Structural Components

This paper is concerned with the state control of servo axes for robots and machine tools. Special consideration is given to the additional damping of elastic structural components. Their effect on the feedback-controlled system is described by a simplified but suitable dynamic model that allows the state observation as well as online parameter identification for all relevant cases of structural flexibility. This leads to an extension of standard servo drives by a robust state space controller. The practical benefit of this method and its implementation on standard control hardware is illustrated for a newly developed machine tool axis

Thermally Caused Location Errors of Rotary Axes of 5-Axis Machine Tools

This paper presents the results of detailed thermal analysis of a 5-axis machine tool with focus on the rotaryaxes. The rotaryaxesare characterizedregarding their position and orientation errors as a function of the underlying thermal load, contributing significantly to the overall accuracy. A physical model is presented, which allows the simulation of the thermal behavior of the rotary axes based on the power input to the drives of the rotary axes and the heat conduction in a swiveling rotary table unit and convection into environment. This enables an external online-compensation of thermal errors. The compensation model is verified and validated.

Comparison of denture models by means of micro computed tomography

The production of dental inlays and crowns requires precise information on patients’ teeth morphology. The conventional method is the preparation of impressions using mold materials, e.g. a silicone impression material. The disadvantage of this technique is the human choke impulse and the flavor of the material. These discomforts can be avoided by methods where a three-dimensional scanner is used for recording the teeth morphology. The present study reveals the accuracy of three model types, namely conventional impression, rapid prototyping using an oral scanner C.O.S., 3M (Schweiz) AG and milling from a proprietary resin using the oral scanner iTero, Straumann Holding AG. For each method five models were fabricated from a steel reference (standard). Using a nanotom m (phoenixǀx-ray, GE Sensing and Inspection Technologies GmbH), three-dimensional micro computed tomography data sets of the standard and the 15 models were recorded and landmark distances within the data sets were measured with sub-pixel accuracy. To verify these results a coordinate measuring machine (Leitz PMM 864, Hexagon Metrology GmbH) based on tactile detection was used for the measurement of the landmark distances, and a correction of the distances measured by the nanotom m was arranged. The nanotom data sets of the 15 models were also compared to the standard by means of a non-rigid registration algorithm. The calculated deformation field exhibited mean pixel displacement values of (0.19 ± 0.09) mm for the C.O.S. models, (0.12 ± 0.07) mm for the gypsum models and (0.19 ± 0.12) mm for the i-Tero models.

Synchronisation of Feed Axes with Differing Bandwidths Using Set Point Delay

This paper presents an effective method for the synchronisation of multiple feed axes with differing controller bandwidths by delaying the set point trajectories of those axes with higher bandwidths. First, a simplified model of a cascade-controlled feed axis is defined, which allows the problem to be treated analytically. The problem of synchronisation of the feed axes is then analysed mathematically, leading to the hypothesis of synchronisation through a delay of the set points of the more dynamic axes. Subsequently, the dynamic error behaviour and boundaries of a feed axis are calculated. The optimal damping factor for a feed axis is shown to be 1/ √ 2 and the dynamic error can be formulated in terms of the bandwidth and acceleration or jerk limit. The proposed method is proven through a simulation and verified based on experimental results. In addition, the stated error bounds are verified, and the limits of the applicability are determined.

CORRELATION OF CUTTING FORCE AND POWER CONSUMPTION FOR ULTRASONIC-VIBRATION-ASSISTED CUTTING OF LABEL PAPER STACKS

Experiments comparing conventional and ultrasonic vibration assisted guillotine cutting of paper stacks have been performed on plain and aluminum coated label paper. It is shown that ultrasonic vibration assisted cutting reduces the cutting force for both paper species. Reduction of the cutting force allows the down holder force to be decreased and lowers the compression of the paper stack necessary to prevent pull-out of the top sheets of paper. Using a higher amplitude setting on the ultrasonic generator further decreases the cutting force for the paper stack. For three different cutting speeds, it is shown that ultrasonic vibration assisted cutting force reduction depends on the average speed of the tool for both paper species. A linear regression with present experimental data is done to obtain an equation for the relation between input generator power and resulting cutting force. Finally, the quality of the cutting edge is examined, quality parameters are defined, and according to these