Self-calibration Method and Pose Domain Determination of Light-Pen in a 3D Vision Coordinate Measurement System

Light pen 3D vision coordinate measurement systems are increasingly widely used due to their advantages, such as small size, convenient carrying and wide applicability. The posture of the light pen is an important factor affecting accuracy. The pose domain of the pen needs to be given so that the measurement system has a suitable measurement range to obtain more qualified parameters. The advantage of the self-calibration method is that the entire self-calibration process can be completed at the measurement site without any auxiliary equipment. After the system camera calibration is completed, we take several pictures of the same measurement point with different poses to obtain the conversion matrix of the picture, and then use spherical fitting, the generalized inverse method of least squares, and the principle of position invariance within the pose domain range. The combined stylus tip center self-calibration method calculates the actual position of the light pen probe. The experimental results show that the absolute error is stable below 0.0737 mm and that the relative error is stable below 0.0025 mm. The experimental results verify the effectiveness of the method; the measurement accuracy of the system can meet the basic industrial measurement requirements.

Error Analysis of Integrated Six-Light-Screen Array Measurement Model

The light-screen array measurement method is very suitable for measuring the coordinates of rapid-fire weapons, and the measurement error is determined by the measurement model. In this paper, the separated light-screen array is improved to an integrated light-screen array, which reduces the parameters and optimizes the measurement model. Three kinds of factors affecting the coordinate measurement error of the projectile under the integrated measurement model are analysed, and the influence of the factors on the distribution of coordinate measurement errors is simulated and analysed in the selected 1m×1m target area. Then the error distribution of the separated measurement model and the integrated measurement model is simulated and analysed under the same conditions based on the design values and current technology level. The result shows that compared with the separated measurement model under the same simulation conditions, the comprehensive coordinate measurement error is optimized by about 2.1mm within 1m×1m target area. The research can provide reference for the design and optimization of light-screen array and other similar photoelectric measurement systems, and provide new ideas for improving the coordinate measurement precision of therapid-fire weapons.

A Novel Measurement Standard for Surface Roughness on Involute Gears

Although manufacturers of coordinate measurement systems and gear measurement systems already provide instruments that enable an end-of-line-monitoring of the roughness properties of gears, the roughness measurement on gear flanks still lacks traceability with respect to the standardised SI-units. There is still a gap between well standardised roughness measurements on planar surfaces and gear measurements on involutes. This gap is bridged by a novel physical measurement standard (PMS), also referred to as material measure, for roughness measurements on involute gears that has been developed at the Physikalisch-Technische Bundesanstalt (PTB). The necessary transformations between the systems of roughness and gear measurements have been implemented. The measurement standard itself represents calibrated roughness values for the parameters Ra, Rz, Rq, Rk, Rpk and Rvk and Mr1 and Mr2. Furthermore, the PMS can be measured both with classic profilometers as well as gear measurement systems with integrated roughness probes.

A FLEXIBLE AND ROBUST 3D COORDINATE MEASUREMENT SYSTEM BASED ON WHITE LIGHT INTERFEROMETRY FOR DEVIATION MEASUREMENTS ON SWISS-TYPE TURNING MACHINES

The calibration of machine tools or industrial robots needs high precision 3-dimensional coordinate measurements. Common available systems still have the need of ambitious and time extensive processes to fulfill the requested requirements. Therefore there is a strong request for fully automated systems that allow an autonomous and easy to handle procedure for 3D volumetric deviation measurements. This exactly is the intension of the here presented 3D Coordinate Measurement System. The so called µ-GPS System is based on reliable white light interferometer and robust technology. The 3D coordinates are determined via trilateration from three measured distances like it is known from the global GPS. Mainly two parts, the sensor unit (transceiver unit) including the emitter and the reference base (three cat’s-eyes) which includes the three reflectors are mounted in the workspace of the machine. A model to evaluate the signals was developed which allows in combination with a 3-dimensional failure correction a 3D accuracy of more than 5 microns. This application will be the base for an exemplary and fully automated calibration process of Swiss-type turning machines. As these machines are used in high volume manufacturing for precision parts, they need to be assembled and calibrated very accurately. For the long term stability the µ-GPS System can be easily assembled in the Swiss-type turning machine so that thermal deviations and abrasion can be measured and compensated in the control. The robust and easy handling of the µ-GPS System later allows an expansion of the showcase to robots and other machine tools.