High speed, high accuracy 2D/3D profile laser sensor solves tyre inspection problems

A leading manufacturer of 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.

Continental Tyres is now using three scanCONTROL 2800™ 2D/3D laser profile sensors from Micro-Epsilon, on a test rig developed by machine builder/systems integrator MicroStep of the Czech Republic, which 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 2800™ 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.

With laser point or spot sensors, not only would multiple sensors have to be used to acquire the same surface defect data, but the sensors could not cope with the high throughput rates of tyres on the test rig. The sensors also had problems with the reflection properties of newly-produced, black, shiny rubber tyres.


How it Works

The scanCONTROL 2800™ sensor has an integrated, highly-sensitive CMOS array, which enables measurements of almost any shiny, reflective or transparent surface, independent of the reflection from the target. This means excellent accuracy, resolution and reliability are achieved, even at high measurement speeds. Using special software algorithms, logos and symbols on the tyre can be removed from any analyses of the acquired data.

A line optical system projects a laser line onto the surface of the object to be measured. The back scattered light from the laser line is registered on the CMOS matrix by a high quality optical system. Along with distance information (z-axis), the controller also calculates the true position along the laser line (x-axis) from the camera image and outputs both values in the sensor’s 2D coordinate system. A moving target or a traversing sensor generates a 3D representation of the object being measured.
At Continental, MicroStep’s test rig receives tyres automatically from the production line. 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 system consists of three scanCONTROL 2800™ sensors and a controller. The measurement data is output from the controller via a Firewire interface to the manufacturer’s in-house developed analysis/evaluation software.

Potential applications for scanCONTROL 2800™ include contour measurement, robot guidance, door gap alignment, position measurement, rail profile, groove measurement, co-planarity measurement and flatness measurement.