Whether Harley or Soccer Mom Wagon - only flawlessly working brakes guarantee the safety of passenger and vehicle. That's why the automotive manufacturer relies on brake discs with a documented and reproducible series-production quality. The quality control does not confine itself on final control only: Already the raw brake discs are inspected for non-conformities with a system integrating both inspection and handling.

The inspection of raw brake discs before continuing with further processes turns out to be profitable. In this production step already non-conformities can occur which can be detected and which prohibit the future usage and therewith the sale of the brake discs. However, up to now this inspection has been done mostly manually. Due to frequently alternating people doing the same inspection, the resulting rating can be no more than a subjective one. This can lead to insufficient inspection and thus to consequential costs up to sales returns and reputation damage. The company ibea located in Hamburg, Germany, has developed an automated system which integrates the inspection and handling of brake discs. One of the main goals has been to replace the manual inspection and to integrate existing machinery, so that a collective overview journal of the brake disc can be generated.

Defect Separation with Dark Field
The raw brake discs are cast parts. 90% of the defects are caused during the casting process, e.g. blowholes, pores, blister, cast appendix and filled ventilation channels. The other 10% are e.g. surface or core defects. A lot of the defects exhibit indentations and therefore usually imply the application of triangular lasers. Since the inspection should do both surface inspection as well as structure analysis, the machine vision system by ibea is equipped with dark field illumination instead, which enables the system to recognize the cavity and to deal with contrast defects separately.

System Design
The self-sufficient inspection system primarily consists of a simple centering device for the well-defined rotation of the brake discs. During the rotation three Dalsa line scan cameras with CameraLink interfaces take images of the upper side, lower side and the cooling channel side. By means of this simple handling a fast processing with different dimensions is possible. Furthermore, the wear of parts is reduced to a minimum. Expensive handling robots are not necessary and the accuracy of the image acquisition can also be used for measurement purposes.
The raw brake disc is usually delivered on a roller conveyor. The inspection system is designed for different diameters (max. 50 cm) and heights (max. 15 cm). The parameters are set and saved job wise and can be started up according to selection. The job data includes the data for comparison with reference values for the vision inspection as well as the data for references of mechanical adjustments for e.g. illumination devices or pre-positions of handling devices. By means of a front end entry pulsing device the discs are run in to the test cell separately. The transport takes place on nonwearing chains, firstly on a separating conveyor followed up by the transfer to the test conveyor belt, which then moves the disc to the centering device. All conveying processes are done by a high-performance servomotor.

From Three Sides
The disc is positioned centrically above the centering device. There the disc is pre-centered and is then picked up for the exact centering. As soon as this has been achieved the disc rotates 360° and images are taken with three line scan cameras. One camera takes an image angular from beneath and one camera takes an image angular from above. The third camera takes an image of the cooling channel. During image acquisition a special laser illumination provides for a sufficient illumination of the parts.
The images taken from above and below are arranged in such a way that all defects can be found with merely one image acquisition and a fixed illumination. This applies especially for casting faults such as cavities and bubbles.

Multitude of Inspection Criteria
Following criteria are tested for on the raw brake disc: Diameter and height, imprint or symbols, blowholes, flash, filled ventilation channels, half fans, bubbles in the fan, cracks, and deformations. Contamination - even if they look like defects - must not be rejected. Therefore the system makes use of the dark field illumination to distinguish between area defects and cavities. The generally used laser-triangulation procedure is not applied by ibea by choice.
The system works almost wear-free at approximately six discs per minute. It consists of an image processing module and a drive module, which is accommodated in a system control cabinet. The operations and also the motor adjustments are controlled by a program. The system is user friendly and already prepared for the interlinking with existing lines. For the separation of good and faulty parts diverters and ejectors are offered. The transfer to a pack-robot is already prepared.

Compact and Economical
The main body of the system is designed as a welded construction. Mounted on this construction are all the motor drive elements. To disconnect the agitation all optical elements such as camera and illumination have been mounted onto shock absorbers. The system consists of infeed and outlet conveyors (rolling bar) for instant integration into existing lines. Respective trigger sensors and counters are already integrated. The system comes in a lightproof cabinet with high pressure connection to take in filtered air and to keep the dust away from the inside. The system requires 6 bar compressed air inlet and a wide range AC input of 110-300 V.
The cost performance ratio is very attractive: the investment will be amortized within 1.5 years.