Automatic inspection of surface imperfections and dimensions on rotational symmetric mass products.

With the constant increase of product requirements concerning quality, the 100% inspection of outsourced parts becomes more and more important. This is not only restricted to safety-critical components which are not supposed to have any defects at all, but it is also important for all kinds of mass-produced articles. O-rings, other engineered seals and molded parts fall into this category.

The technology is available now for flexible and modular automatic inspection systems which make it possible to inspect rotational symmetric mass-produced articles with high throughput for surface defects and dimensions.

Up to date inspection requirements

Presently, more and more quality assurance tasks can be automated by using optical vision systems. The importance of automatic quality control increases constantly and there are several economic reasons for this:

* If inspected manually, many defects are not detected.

* Human inspection is subjective, and therefore the reproducibility of inspection results is poor.

* Human inspection cannot follow high inspection rates.

* Visual inspection is extremely monotonous for humans.

* Documentation of human manual inspection results is very time-consuming.

As a consequence automatic inspection systems have to fulfill the following requirements:

* An automatic inspection system has to be efficient and productive, i.e., it must be a very exact and reliable system, insensitive to influences of the surroundings.

* In addition, shorter product lifetime and the big range of different products require flexible inspection systems to be adapted easily and economically to different manufacturing conditions.

* An inspection system has to be operator-friendly and easy to use because in general the operating personnel do not know much about computer software.

Inspection systems should allow for the inspection of products in a very reliable and profitable way, satisfying the customer's requirements. This is can be done by combining innovative handling systems and leading image processing technology.

When using state-of-the-art inspection systems, the probability of receiving claims of compensation from demanding customers (e.g., car industry) is reduced. At the same time, the inspection costs can be reduced.

Optical inspection of engineered seals

The handling system of the Basler O3 is able (regardless of the part's material properties, e.g., hardness, coefficient of friction) to quickly and reliably separate and convey round parts of different sizes precisely to the sensor units. Within a few seconds the system can automatically change-over to a new product type. This patented handling design, in comparison to other similar inspection systems, has made it possible to increase the throughput more than three times.

Sensor systems inspect all surfaces of round seals independent of color, geometry and material. These systems are a combination of the leading know-how in the areas of optic, illumination and image processing software.

The optical inspection of engineered seals includes the inspection of geometrical properties like inside diameter, outside diameter, roundness, etc., and the inspection of the complete surface for different defects.

The inspection of geometrical properties can be realized by using a telecentric optical arrangement in combination with transmitted light. The following geometrical defects can be detected:

* Deviations from the outside diameter and inside diameter tolerances;

* non-fills;

* nicks and broken seals;

* double-molded seals;

* off registers and mismatches;

* flashes.

The geometrical inspection of seals is a comparatively simple and well-known technique. The inspection of all surfaces is quite complicated regarding illumination and optical and mechanical components. To be able to inspect the complete surface of an engineered seal sensors with special optical devices and illumination units were designed.

By using the sensors shown in figures 1 and 2, the inspection of the topside, outside and inside surface of a part can be realized. The following defects due to manufacturing processes of o-rings can be detected using the surface sensors of the Basler 03:

* flow marks;

* indentations;

* foreign material;

* dirt;

* nicks.

[Figures 1-2 ILLUSTRATION OMITTED]

To inspect the complete surface of an engineered seal, six different sensor units are required. Five of the sensor units do the surface inspection.

The principle of visual surface inspection consists of the following main steps (figure 5):

[Figures 5 ILLUSTRATION OMITTED]

* image capture;

* transformation and unwinding of the inspected area (image preprocessing);

* detection of defect areas based upon defect thresholds;

* final evaluation of defects (position on the part and sizes).

As the geometry of the parts can vary, a flexible and user-friendly interface with several adaptation possibilities is required. The Basler 03 inspection system allows the user to create several inspection zones for each sensor view. This makes it possible to adapt every inspection zone individually to the part's geometry and to define special inspection sensitivities for different zones. So safety-critical areas of the seal can be inspected with high sensitivity and non-critical areas with a lower sensitivity.