Qualification concept for optical multi-scale multi-sensor systems

A Loderer,T Hausotte

doi:10.5194/jsss-5-1-2016

Abstract

Abstract. This article describes a new qualification concept for dimensional measurements on optical measuring systems. Using the example of a prototypical multi-scale multi-sensor fringe projection system for production-related inspections of sheet-bulk metal-formed parts, current measuring procedures of the optical system are introduced. Out of the shown procedures' deficiencies, a new concept is developed for determining the orientations and positions of the sensors' measuring ranges in a common coordinate system. The principle element of the concept is a newly developed flexible reference artefact, adapted to the measuring task of the fringe projection system. Due to its dull surface, the artefact is optimized for optical measuring systems, like the used fringe projection sensors. By measuring the reference artefact with each fringe projection sensor and aligning the resulting data sets on a digital reference model of the artefact, sensor-specific transformation matrices can be calculated which allow transformation of the sensors' data sets into a common coordinate system, without the need for any overlapping areas. This approach is concluded in an automated measuring procedure, using alignment algorithms from commercial available software where necessary. With the automated measuring procedure, geometrical relations between individual measured features can be determined and dimensional measuring beyond the measuring range of a sensor became possible. Due to a series of experiments, the advantages of the new qualification concept in comparison with the current measuring procedures are finally revealed.

Highlights

New production technologies, like sheet-bulk metal forming (Schaper et al, 2011), involve new challenges for dimensional measurements of the manufactured parts
The process of gathering measuring results out of multiscale data sets is divided into four main steps: firstly, measurements were done by all selected fringe projection sensors automatically
The basic principle was proven by a flat-shaped reference artefact using the example of a prototypical multi-scale multi-sensor fringe projection system

Summary

Introduction

Like sheet-bulk metal forming (Schaper et al, 2011), involve new challenges for dimensional measurements of the manufactured parts. Following the recommendation of the golden rule, the measurement uncertainty should be at least less than a fifth, and better less than a tenth, of the tolerance width If this minimum requirement can be met, it ensures that the measurement results are accurate enough (Loderer et al, 2013). To achieve these requirements, a prototype of a multiscale multi-sensor fringe projection system was developed, designed for a production-related environment (see Fig. 1). The process of gathering measuring results out of multiscale data sets is divided into four main steps (see Fig. 2): firstly, measurements were done by all selected fringe projection sensors automatically. Besides the explained four steps, there are other approaches for combining measurement data, e.g. presented in Puente León and Kammel (2003), Komander et al (2014) and Keck et al (2014)

Qualification principle

Flexible qualification concept

Comparison

Application

Result

Conclusion