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High-Speed Sorting of Color-Coated Parts with the GEFRA OptiSort®-N System

Fig. 1: GEFRA OPTISORT control
and sorting system

Fig 2: Color coated parts: a) and
b) good parts (IO), c)…f) less
or non-coated parts(NIO)

Fig 3: Complementary color
illumination: dark part (a) in
order, light gray parts (c,d,e)
not in order.

Fig. 4: Color sorting station with
background (a), illumination (b),
camera (c) and glass table
with parts (d).

Fig. 5: Machine setup with
360°-surround view
camera system.

Since many years, the German GEFRA Company offers different product lines of sorting machines for measuring and control applications in the field of fasteners. Machines for dishes, nuts, bolts, screws and many of other parts and applications are available.

Following the demands of booth, the market and special customers, a new type of control application was realized: high-speed sorting of color-coated parts.

GEFRA - the OptiSort® company

Since more than 15 years, the GEFRA Company, situated in the contemplative Westerwald in the middle of Western Germany, is developing and manufacturing complete solutions for measuring, checking, and sorting applications in the field of industrial mass production of fasteners and other production parts made of metal and plastics.

The first business goal of the GEFRA Company is to ensure an efficient 100 percent automatic quality control at neuralgic points within or at the end of the process chain of their customers and where a cost efficient and zero ppm error quote is needed.

For this, different product lines of the optical  control systems OptiSort® are available. Measuring applications as well as surface inspection tasks can be solved with OptiSort® W for washers and dishes-like parts, N for nuts and ST for screws and comparable parts. Modifications in mechanics and optics enlarge the possible applications of the OptiSort® systems. Options for plastic part inspections are available.

The GEFRA product portfolio is complemented by a wide spectrum of offers in the fields of service, maintenance and training.

The strength of the GEFRA Company shows itself especially about intensive consulting activities, delivery reliability, and fast reactions 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 favor.

Color Sorting

Surface coatings can be found on a lot of fastener products and other contraction parts. The coatings realize both, optical and technical properties of the part during the further processes and for the build-in state. Missing or wrong coatings can strongly influence the further steps in production and application of these parts.

To avoid the subsequent processing of such error parts, a reliable control and sorting process for this kind of product properties has to be established.

Based on the demands of the market, inquires and the continuous development of the own portfolio of technologies, the GEFAR Company developed a color sorting system.

First in the GEFRA Lab the problem was analyzed for a lot of coatings and material combinations. Main goal was to develop a universal equipment for a wide range of applications in this field. This system should follow the overall concept of OptiSort®: stable, only few parts, compatible with the well established GEFRA AUTOCONTROL software and a simple integration also in existent systems.

The key result was a special combination of illumination and background together with a gray level camera.

All analyzed coatings show the effect of light refection dependent on the applied wavelength.

Using a tunable light source, the wavelength can be adjusted exactly to the complementary color of the coating. For the optimum wavelength, the light reflection of the part is minimized. In this case the amount of reflected light depends also roughly from the thickness of the coating.  Figur 2 shows an example batch of acceptable coated parts and parts with less coating then demanded or without any coating.

Using a wavelength in the range of blue, the response was maximized: good parts appear from dark gray to black; bad parts appear from light gray to white. Figure 3 shows the light response in this case for good and bad parts from the batch shown in Fig. 2.

In this way, the presence of a color coating can be detected. Further the thickness of a color coating can be roughly inspected. Using the GEFRA AUTOCONTROL software, the control parameter of a surface error inspection can be tuned to distinguish safely between good and bad coated parts.

Figure 4 shows the color sorting equipment integrated in a OptiSort® N system. This system can inspect more than 400 parts per minute.

With one camera the inspection result is limited on its field of view. Using 4 cameras, a 360° surround view can be realized like known from the OptiSort® 360° surface and thread inspection like shown in Fig. 5.

In certain circumstances depending on booth, the color and the coating type, other coating errors can be detected in this way on the surface seen by the camera(s).

Color sorting applications not only for coated metal parts can be realized. Also plastic parts can be checked for the right color and intensity.

The new color sorting equipment can be integrated in new ordered systems as well as in already delivered Windows based units.


With the new high-speed color inspection system the GEFRA Company offers their costumers a additional opportunity for a wider range of quality control and sorting processes.

Colored and color coated parts made of different material can be inspected with the same accuracy and speed known for GEFRA OptiSort® systems.

The color sorting can be combined with all other optical inspection types on new and existing WINDOWS based GEFRA systems.