A performance evaluation test for laser line scanners on CMMs

Optics and Lasers in Engineering, 2011

Because of its high speed and high detail output, laser line scanning is increasingly included in coordinate metrology applications where its performance can satisfy specified tolerances. Increasing its accuracy will open the possibility to use it in other areas where contact methods are still dominant. Multi-sensor systems allow to select discrete probing or scanning methods to measure part elements. Decision is often based on the principle that tight toleranced elements should be measured by contact methods, while other more loose toleranced elements can be laser scanned. This paper aims to introduce a method for improving the output of a CMM mounted laser line scanner for metrology applications. This improvement is achieved by filtering of the scanner's random error and by combination with widely spread and reliable but slow touch trigger probing. The filtered point cloud is used to estimate the form deviation of the inspected element while few tactile obtained points were used to effectively compensate for errors in the point cloud position.

2011

Non-contact measurement techniques using laser scanning have the advantage of fast acquiring large numbers of points. However, compared to their contact-based counterparts, these techniques are known to be less accurate. The work presented in this paper aims at improving the accuracy of these techniques through an error correction procedure based on an experimental process that concerns mechanical parts. The influence of the three parameters, defining the relative position and the orientation between the sensor and the surface, is studied. The process used to build an experimental global model of error is presented and applied to a typical part composed of planes or skewed surface. The systematic errors have been reduced by half in comparison to the reference values, while the random errors have slightly increased. This phenomenon is due to the fact that the errors correction model does not take into account the local response of the laser sensor. A second model, taking into account the local defect, has been developed. Its application to an example of inspection of a mechanical part shows an improvement of the results of the correction.

This report summarises test results from the National Physical Laboratory’s (NPL, UK) recently launched 3D optical scanner dimensional characterisation facility. This facility comprises a purpose-built environmentally controlled laboratory with test artefacts, test procedures and equipment to assess 3D optical scanner performance. The reported test results include an indication of 3D optical scanner resolution and changes in measured dimensions due to: instrument temperature, artefact illumination, scanner orientation, artefact surface finish and artefact position within a measurement volume. NPL’s 3D optical scanner facility has been developed to assist the rapid take-up of 3D optical scanners on production lines of metre scale precision components manufactured by the aerospace, automotive and power generation industries, by promoting best measurement practice and to support measurement traceability.

DAAAM Proceedings, 2020

Continuous improvement and optimization of products, which is the most often reflected in more complex geometrical and dimensional characteristics of products and increasing market demands for quality, lead to the development of new solutions in quality control. In industry today, the control of geometric characteristics is most often performed by the tactile method of probe stylus, i.e. using 3D coordinate measuring machines (CMM). Coordinate measuring machines have long been the only option in quality control of various products and have become generally accepted in industrial quality. In recent years, the development of digital technologies, i.e. the development of a new generation of hardware and software, has enabled the development of other methods of 3D measurement such as 3D scanner, which has proven to be a good alternative to CMM machines. The aim of this review is to provide insight into the areas of application of both devices as well as their advantages and disadvantages and possible future solutions and application of devices in this area.

2017

The overall quality of a machined component has an important association with the quality of its surface finish. To obtain adequate data for the surface metrology of machined components, areal scanners are often preferred over stylus based profile scanners due to their ability to acquire surface data over a relatively large area. To further improve efficiency, there is a desire to perform on-machine measurement, and recently, high-resolution areal surface scanners have been integrated as an on-machine measurement device. Due to the limited areal coverage, these scanners can require multiple scans to capture data from surfaces produced on machine tools which requires a sufficient amount of time to complete a full surface scan. In addition, since these scanners are very sensitive, scanning delays often cause areal scanners to capture data contaminated with noise which may arise from within the machining environment such as axes vibrations, temperature effects, dust, etc. These factors...

Proceedings of SPIE, 2007

SUMMARY The laser scanning systems are being currently more and more used in a wide spectrum of applications e.g. in documentation of cultural heritage, as-built documentation or for deformation and slide monitoring. Most of those applications require a high quality of the measured data. The measurement and space information processing procedure with a laser scanning system is a black box to a common user so it is necessary to perform the analysis of the data measured in different conditions and to assess their quality on the basis of the analysis. In our experiments we concentrated on observing physical qualities of the laser beam during reflection off the measured object surfaces and assessed accuracy of the measurement on different types of materials under different incidence angles and in different distances. In our next experiment we presumed that distance measurement accuracy determination of the laser scanning systems is easy but angle measurement accuracy determination is mu...

Measurement, 2012

A laser rotary-scanning measurement system was developed for the reverse engineering of 360°objects. The system is constructed by an optical head and a rotary indexing. The optical head is composed of a laser diode strip-light projector and dual CCD cameras. Based on the principle of structured-light triangulation, a laser line is projected onto the object upon which the distorted line is captured by dual CCD cameras from left and right simultaneously. By processing a series of line fittings from the discrete angular positions of an object, the entire 3D profile can be reconstructed. Since the actual space coordinates of the object are computed according to the geometric relationship between the coordinate of optical head system and the coordinate of the rotary indexing systems, if these two coordinate systems are not in good alignment, errors in the computed coordinates will be introduced.

In the last years, the presence of non contact scanning systems has increased continuously in the industry. The main reason is that these systems lead to an important reduction in the inspection time and consequently a reduction in manufacturing costs while maintaining quality levels. The advantages of these systems are well known, such as the high speed data acquisition and the high number of captured points. However there exist some disadvantages, like the poor (undefined) accuracy when comparing with traditional touch trigger probe inspection systems. For this reason, scanning systems are mainly used in Reverse Engineering, heritage conservation or multimedia applications (movies, video games, etc.). In metrological applications, their validity has not been tested, in terms of geometric and dimensional tolerance control and accuracy. This work deals with this problem, performing a comparison between two scanning systems. To carry out this comparison, a laser triangulation sensor ...

Journal of Manufacturing Science and Engineering

The area-based three-dimensional optical inspection of workpiece geometries is the basis for quality control, maintenance tasks, and many other typical applications in mechanical engineering and automation such as adaptive manufacturing. In the context of a cyber–physical approach for semi-autonomous post-processing of additively manufactured parts, this method provides the basis for an iterative manufacturing approach. Commercially available systems for optical inspections often rely on camera-based methods, which are, however, susceptible to reflections. This article describes an approach for developing an optical scanstation that uses blue laser line scanners in combination with a Cartesian three-axis motion system and a turntable. The focus of the work is on the development of a method for the fast extrinsic calibration of the entire scanstation.