Dynamical referencing of coordinate measurement machines and machine tools
Measurement Systems
Final Report Abstract
The project "Dynamic Referencing of Coordinate Measuring and Machining Machines" was carried out jointly by the Institute for Applied Optics and the Institute for System Dynamics at the University of Stuttgart and aimed to measure dynamic errors on coordinate measuring and processing machines with high accuracy and to compensate them with suitable control strate- gies. For this purpose, a novel image-based measurement system was used, which is based on the imaging of several point light sources attached both to the tool center point (TCP) and to the workpiece of a coordinate measuring machine. Each point light source is replicated by a computer-generated hologram to a pattern of multiple individual spots on the camera sensor. By averaging the centers of gravity of all replicated spots per pattern, it thus allows to overcome the limitations of classical camera-based position detection regarding accuracy from a few hundredths of a pixel to a few thousandths of a pixel. In order to use this increased accuracy in a measurement system, different calibration functions and methods were simulatively inves- tigated, a stereo-based camera measurement system was implemented and calibrated using new calibration strategies. The residual calibration error was less than 0.5 µm in all three spa- tial directions for a calibration volume of 100 mm x 74 mm x 24 mm. To achieve a high meas- urement rate necessary to compensate for dynamic errors, two image processing approaches were investigated and implemented. Both approaches achieved a measurement rate of 400 Hz. Furthermore, one goal of the project was the control-based online compensation of dy- namic errors that occur when using highly dynamic reference trajectories and the associated increased acceleration forces. Since camera measurements of the actual TCP are only avail- able to the control system at a lower sampling rate and with significant latency, various ap- proaches to estimate the actual TCP position were investigated. A data augmented approach consisting of a simple error model and a Gaussian process to learn model errors provided the lowest estimation errors. Furthermore, redundant additional axes for dynamic and accurate follow-up control of the TCP position were integrated into the considered experimental setup. This results in additional degrees of freedom for distributing the reference trajectory to the individual axes. To exploit these degrees of freedom, two dual-stage control concepts were developed and implemented. Both allow a significant increase in dynamic positioning accu- racy. Due to the modular approach, the methods are also particularly suitable for retrofitting to existing machines.
Publications
- „Gaussian Process Based Multi-Rate Observer for the Dynamic Positioning Error of a Measuring Machine,“ European Control Conference, pp. 627--632, 2019
M. Ringkowski, O. Sawodny
(See online at https://doi.org/10.23919/ecc.2019.8795963) - „Hochgenaue Kalibrierung eines Multipoint-Positionsmesssystems,“ DGaO Proceedings, 120. Tagung, 2019
S. Hartlieb, T. Haist, M. Tscherpel, F. Guerra, W. Osten
- "Estimating dynamic positioning errors of coordinate measuring machines," Elsevier/Mechatronics, Bd. 68, p. 102383, 2020
M. Ringkowski, O. Sawodny, S. Hartlieb, T. Haist, W. Osten
(See online at https://doi.org/10.1016/j.mechatronics.2020.102383) - “Accurate 3D coordinate measurement using holographic multipoint technique,” SPIE International Society for Optics and Photonics, pp. 1 – 12., 2020
S. Hartlieb, C. Erol, M. Tscherpel, T. Haist, F. Guerra, W. Osten
(See online at https://doi.org/10.1117/12.2555372) - „Hochgenaue Kalibrierung eines holografischen Multi-Punkt-Positionsmesssystems,” tm – Technisches Messen, Bd. 87, pp. 504-513, 2020
S. Hartlieb, T. Haist, M. Tscherpel, F. Guerra, W. Osten
(See online at https://doi.org/10.1515/teme-2019-0153) - „Optimal Reference Allocation of Dual-Stage Measuring Machines,“ IEEE/ASME International Conference on Advanced Intelligent Mechatronics, pp. 1362-1367, 2020
M. Ringkowski, E. Arnold, O. Sawodny
(See online at https://doi.org/10.1109/aim43001.2020.9158919) - "Highly accurate imaging based position measurement using holographic point replication," Elsevier/Measurement, Bd. 172, p. 108852, 2021
S. Hartlieb, T. Haist, M. Tscherpel, F. Guerra, W. Osten
(See online at https://doi.org/10.1016/j.measurement.2020.108852) - “Bildbasierte Vibrationsmessung mittels holografischer Punktvervielfältigung“ DGaO Proceedings, 122. Tagung, 2021
S. Hartlieb et al.
