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GEFRA OPTISORT® and AUTOCONTROL – Focus on Crack Detection

control and sorting system.

Fig. 2: Screws with cracks
at outer contour.

Fig. 3: Nuts with cracks at
different locations.

Fig. 4: Top view on a cracked
screw head: tool for outer
contour (green) and surface
(yellow) applied, crack (red).

Fig. 5) 360° image acquisition

Fig. 6: Side view on a cracked
screw head: line and rectangle
surface tool applied.

Fig. 7: Top and side view by
a mirror objective.

The quality requirements in the field of fastener products are continuously growing. Besides pure measurements, crack detection on all types of fastener parts gets more and more important. Needed are efficient technologies to guarantee the fast and secure sorting of damaged parts.

The GEFRA Company is actually facing up to this demands for fast crack sorting and offers a new generation of hard- and software for the optical detection, which can be integrated into their approved OPTISORT® product lines.

Sorting technology made in Germany

Since, more than 15 years, the GEFRA Company is developing and manufacturing complete solutions for measuring, checking, sorting and packaging applications in the field of industrial mass produc- tion of fasteners and other production parts made of metal and plastics.

The GEFRA Company ensure with its systems an efficient hundred percent automatic quality control at neuralgic points within or at the end of the process chain of their customers and wherever a cost efficient and zero parts per million error quote is needed.

For this, different product lines of optical control systems OPTISORT are available. Based on both, laser and camera technology, complex measurements and surface inspections are realized. Using a wide spectrum of tools inside the GEFRA-in-house AUTOCONTROL software package, nearly all customer demands can be fulfilled by a GEFRA sorting system. Customer specific solutions can be individually offered.

The GEFRA product portfolio is complemented by a wide spectrum of offers in the fields of service, maintenance, consulting and training. The strength of the GEFRA Company shows itself especially in delivery reliability and short reaction times concerning their products and costumers.

More than 200 systems on the site of many famous national and international fastener manufacturers and also sorting companies are speaking in the GEFRA Company’s favour.

Crack sorting

While in the past some simple dimensions were sufficient, now and in future complex geometric measurements, inspections for damages like scratches, dents, points of impact, errors in colour, surface coatings, impurities, and especially cracks are a daily occurrence.

As a result of various effects inside different production steps and pre-material properties, cracks on screws, nuts, bolts and other cold-formed parts e.g. cannot be avoided hundred per cent.

On the other hand, cracks can constrain especially the automatic application of these parts and, more important, endanger the security of constructions or devices in which these parts are build in without any control.

One of the most common technologies for crack detection is the eddy current method. One of the advantages here is the opportunity to find smallest and hidden cracks also in optical unreachable positions. But to get a complete scan of the interesting regions the part has to be rotated in front of a sensor and this implements a relatively time-consuming clock process for the hole sorting procedure.

In all cases where sorting with a high output rate is needed and cracks with optical visible dimensions have to be found exclusively, an application of camera setups and image processing technologies is implied.

Image Processing for all elevations

Inside the AUTOCONTROL system software project, the GEFRA Company has continuously developed crack detection tools for both, transmitted and reflected light applications.

Whenever a crack or its impact to contour lines of the part is visible under transmitted light, both, tools for measuring and contour control can be applied to detect it. This is possible also for noncircular shapes of the object and can be realized with an accuracy of /-0.02 mm in general.

Not all crack types and localizations can be found by using transmitted light. Especially cracks upside the outer contour and on different part levels need another kind of image acquisition and processing. At this point two imaging methods in combination with several types of part specific illuminations can be applied.

First, the top and if possible the bottom view delivers an image of the outer contour and other contour lines on the part. In principal the same idea for contour control algorithms is applied here on gray level structures. Figure 4 shows a so found crack. This tool is not limited to circular structures like shown in Fig. 2) and 4). Also other shapes like squares and hexagons e.g. like shown in Fig. 3) can be controlled. Further a tool for free shapes is available.

In addition to this contour based method, the surface of the part can be analyzed by special tools for crack detection at this place. Developed in particular for the common characteristics of cracks on different surfaces, various classifications for the quantitative and qualitative properties like shape, dimension, orientation, number etc. can be specified.  Also here from annuli like shown in Fig. 4) up to regions of interest with free form can be defined by the user.

Very often the view from top and bottom to a part is not sufficient to cover all possible cracks and other damages. Here, as the second transmitted light imaging method, a 360° surround view technology can be applied.

Using four cameras in a 90° angle distance like shown in Fig. 5), a complete image set of the part’s side view is generated. On these images all tools for crack detection on surfaces can be used.

As an example, Fig. 6 shows a line and a rectangle as region of interest and the computed result. In this case, the part would be guided to the not in order box.

In certain cases and with nearly fixed part dimension a simultaneous top and side view image can be generated by using a special mirror objective in- stead of five cameras.  Like shown in Fig. 7) tools can be applied in one step on one image by covering nearly the hole part.

In this way both, the number of images to compute and so the data rate per item can be reduced and the number of parts controlled per second can be increased.

At the end, all the mentioned software tools based on reflected light images can be applied more than one time to an image. In this way, different kind of crack types and localizations at one part can be covert.

No end in sight

Driven by every new and unsolved customer problem and also by considering the next and prospective development in both, image processing based quality control and customer sorting tasks, GEFRA Company’s development team will increase the variety of tools and its application opportunities.

The GEFRA Company with its highly qualified and experienced staff members and partners in the field of mechatronics, electro techniques, engineering, informatics and natural sciences is working continuously at the further optimization and development of their products and technologies.

The main focus lies on the further increase of the control performance, on the integration of new concepts for illumination, image acquisition, processing and also on the development of multiple sensor systems. The integration of other imaging media like X-ray and other non-invasive inspections like fast eddy current tests for material hardness will be the next step.

In this field the GEFRA Company will work in collaboration with extern partners and research institutions too.

Also in future the GEFRA Company from Friedewald, Germany, will offer their national and international customers reliable, flexible, and robust state-of-the-art solutions for their quality control applications.