Image processing aims for 0ppm defect rate

For Brehm Prazisionsteile industrial image processing is an important "link" in the chain of effective processing procedures.

In Germany you are only as good as your precision, quality, timely performance and price in the manufacture of precision components.

For Brehm Prazisionsteile industrial image processing is an important "link" in the chain of effective processing procedures.

With over 300 employees and an annual sales volume of about Eur 40 million, the enterprise from Ulm is one of the leaders in its line of business.

Symmetrical parts, subassemblies and structural components are produced from steel and aluminium for the automotive industry, its suppliers and for mechanical engineering.

"The need for sophisticated precision lathe-work parts is still great, and this year we are expecting a two-digit growth rate".

"Efficient automation and maximum flexibility is our daily bread and butter", says Thomas Brehm, Managing Director of Brehm.

The in-house construction of operating materials, devices and tool manufacture are important factors in designing and connecting the individual process steps as effectively as possible.

In this sector, industrial image processing is becoming an increasingly significant part of production with strategic importance.

The demanding requirements of the customers must be reliably fulfilled.

Only 100% flawless goods may be delivered to the customer, and the goal is a rejection rate of 0ppm (parts by million).

Ludwig Zeller, Head of the Tool and Device Construction Department comments: "Image processing is an important means to achieve our goal".

"For this we need system-solutions with maximum reliability".

At the Brehm facilities, the main goal of industrial image processing in applications is to exclude faulty parts.

It's also important to substitute manual work stages in the handling processes, which is an important contribution to rationalisation.

Even if you have vast vision experience within your production, it is essential to work with reliable partners who have distinctive vision knowhow.

It's the best way to adhere to rigid customer specifications and adapt to their processing systems.

To date Brehm has installed 10 image processing systems at its site.

Having complete system solutions from one local supplier that is reactive is a competitive advantage for Brehm; the company chose Hema as its electronic integrator who proposed Cognex vision technology.

A compact solution was installed for a pick-and-place robot application, which faultlessly feeds parts to subsequent processing stages by means of a transfer gripper.

The positions of aluminium lathe-work parts stored in a transport pallet are exactly determined.

This collection of parts consists of a variety of different components.

Varying measurements of the parts means that they are loosely packed in the transport pallets.

The transport pallets used may contain up to 64 parts.

The test-parts, mostly anodised black, can be placed and orientated differently, they may touch each other, or they may vary in number.

Other part variants can also be included in the pallet.

The system will determine the position-data and direct the articulated arm of the robot and its gripper.

Hema's approach to the solution was convincing, and the co-operation with this partner had already been very fruitful in the past.

The extensive functional specifications submitted by Brehm and the further detailed elaboration of the project in collaboration with Hema brought about the fast and focused planning and realisation of the assignment.

In accordance with the Cognex motto "global leader-local expert", the regional proximity of Hema was also an advantage.

Project planning began in December 2004, and the complete installation was already up and running in February 2005; it has been functioning effectively and smoothly on three-shift operations ever since.

A high-resolution vision sensor was employed: the In-Sight 5401 is one of the most powerful and efficient vision sensors made by Cognex.

The extremely compact, splash-proof and rugged aluminium housing is equipped with round, sealed M12 Ethernet connector jacks, it has a safety classification of IP67 and it is therefore protected against oil or cooling lubricant mists.

The completely autonomous image processing system can determine the positions of all test-parts in the pallet within only 2.5 seconds.

The vision sensor was installed in the ceiling of the test-cell in the centre of an illumination arrangement covering the whole area with light, thus creating favourable lighting conditions.

The impressive performance of In-Sight 5401 permits clock frequencies from 0.5 to 2.5 seconds, depending on the loading condition of the pallet.

The vision sensor will also recognise other kinds of parts not belonging there which have been placed in the pallet by mistake.

Until now, such complex tasks could only be performed by PC-based systems.

Ludwig Zeller states: "For more than half a year, this vision solution has proven its efficiency in three shift operation mode by its high precision, its reliability, availability, its simple construction and processing speed".

Another prominent favourable assessment is that the testing-cell is expected to return on investment within one year maximum.

The very reliable recognition of the parts in the x- and y-axes, as well as the orientation of their angle of rotation was of central importance.

The testing-parts have diameters from 3 to 24mm and they are between 33 and 80mm long.

In the grooves of the pallet, the parts may touch each other or they may even cover each other partially.

This may not impair functional safety.

This functional safety is attained thanks to the reliable performance of the PatMax software package from Cognex, and its precise vision algorithms.

Until now, image processing systems were based on the so-called grey-scale/half-tone correlation in the localisation of objects or edges.

In this analysis method, the grey levels of the image pixels are compared with the reference object and the position calculated from there.

This method will reach the limits of its applicability very fast, if utmost precision is the issue and lighting conditions are to be coped with.

Unlike the gray scale/half-tone correlation, the patented method of PatMax uses the basic geometric structures of objects in a three-step procedure.

First the most important individual characteristics of the object image are identified, such as edges, measurements, shapes, angles, bends and shades.

The spatial relations between these central characteristics of the trained sample are compared with the real-time image.

The position of the object and its composition or quality are then precisely determined from the analysis of the geometric information of the features and of their spatial relation.

Characteristics such as contours with low contrast can be recognised more reliably and at greater speed.

By means of a partial contour, PatMax will also immediately recognise where to find further features, despite distortion, displacement/shifting or coverage.

The location of characteristics is simplified greatly because it is not necessary to first conduct a linear analysis of the complete image.

PatMax can also handle very high resolutions down to the subpixel range, and determination of angles on objects down to 0.02 degrees.

The vision tool is invariant with regard to positioning, orientation and varying scales of an object.

The simultaneous examination of contour and structure of the object image can also compensate changing environmental conditions.

This reliable vision tool is also available for the high-powered In-Sight 5400 vision sensor family.

A comfortable development environment allows for simple and fast integration into the flow of production and into the communication system of the production site; this also facilitates linking with documentation assignments or functions.

The parametric mode of operation with the ergonomic user interface has also proven its worth because Brehm's employees can train new test parts without problems.

The reference points of the test parts can be randomly selected and the complete evaluation is carried out in the vision sensor with data transmission by Ethernet or via RS232.

This handling system with its integrated high-performance image processing provides a smooth production process and is paramount in rationalisation.

The positive experiences have resulted in another three vision systems being installed this year to reinforce Brehm's quality and automation standards.

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