Continental Tyres has solved an inline inspection problem by using non-contact laser-based profile measurement sensors, which detect the slightest bulge, recess or other surface defect that may affect the performance of the tyre. The company is using three scanControl 2800 2D/3D laser profile sensors from Micro-Epsilon, on a test rig developed by Czech Republic based machine builder/systems integrator MicroStep. This rig inspects individual tyres in less than one second, enabling Continental to carry out 100% inspection of tyres from its production line.
Rather than using multiple laser-based point sensors or capacitive sensors, the scanControl sensors measure the profile of the tyre using a non-contact laser line, on which multiple measurement points (up to 250 per second) can be acquired and analysed. Previously, Continental used capacitive sensors and laser-based optical point sensors to inspect tyres. Compared to the laser line method, capacitive sensing detects over a relatively large measurement spot and so patterns, symbols or legends on the tyre could not be distinguished from genuine surface defects such as bulges. The sensors also had problems with reflections from the tyre surfaces.
scanControl 2800 features an integral CMOS array, which enables measurements of almost any shiny, reflective or transparent surface, independent of the reflection from the target. Using special software algorithms, logos and symbols on the tyre can be pre-programmed and thus ignored during subsequent data analyses. A line optical system projects the laser onto the surface of the object to be measured, and back-scattered light is registered by the CMOS matrix. Along with distance information (z-axis), the controller also calculates the true position along the laser line (x-axis) from the camera image and both values make up the sensor's 2D co-ordinate system. A moving target or a traversing sensor generates a 3D representation of the object being measured.
MicroStep's test rig receives tyres automatically from the production line, and these are held in place by a fixture or gripper, which rotates the individual tyre through 360° in less than one second. During this time, the three scanControl 2800 sensors inspect the three sides of the tyre walls for defects, taking measurements in real time. The measurement data is transferred from the controller via a Firewire interface to the manufacturer's in-house developed analysis/evaluation software.