Five laser scanners from the 'Scancontrol 2900-50' series inspect the beverage crates on a conveyor belt from above in the production line. Each scanner measures a row of bottles in the crate.

© Micro-Epsilon

In the production line, the scanners measure from above onto the beverage crates, which are guided on a conveyor belt. Each scanner measures a row of bottles in the crate. The presence check is carried out at throughput speeds of up to 850 mm/s. In contrast to a solution with conventional image processing systems, the laser scanners not only check the presence of the bottles, but also their height. The sensor uses the respective bottle height to determine whether the correct bottle type is in the crate. In this application, the height of the bottles must not deviate by more than 3 mm from the target height of the respective type.

The result of the evaluation as 'OK' or 'not OK' is received by the PLC so that faulty crates can be ejected directly. For the user, the measurement results can also be displayed on an integrated screen on the control unit.

The Slovenian company Tipteh has developed an inspection system with laser line triangulators for the fully automated inspection of empties, which is already being used to inspect incoming crates.

© Micro-Epsilon

With up to 2000 measured values per second, the sensor is suitable for both static and dynamic processes. The main challenge with this measurement task lies in the different reflection properties of the bottles, which vary due to the different glass colors.

The challenge of color and movement

Compared to a solution with conventional image processing systems, the laser scanners not only check the presence of the bottles, but also their height.

© Micro-Epsilon

These are mainly shades of green and brown. To make matters worse, there are bottles with or without lids in the crate at goods inwards. The scanner recognizes this using stored algorithms. Shocks caused by transportation on the conveyor belt also mean that the bottles are exposed to constant vibrations. Thanks to the special measuring principle, the laser scanners are insensitive to these challenges: they use the triangulation principle for two-dimensional profile detection. This means that the scanner emits a laser beam that is expanded into a laser line. This hits the object to be measured. The laser light is reflected by the surface of the measurement object and imaged on a highly sensitive receiver matrix in the sensor.

Christian Kämmerer is Head of Sales 2D/3D Optical Metrology at Micro-Epsilon Messtechnik in Ortenburg.

© Micro-Epsilon

From this matrix image, the controller calculates the position along the laser line (x-axis) in addition to the distance information (z-axis). These measured values are then output in a sensor-fixed, two-dimensional coordinate system . In the case of moving objects or when the sensor is traversed, 3D measurement values can also be determined.

The laser scanners can be positioned at a great distance from the measurement object and record 1280 measurement points per profile via the laser line. The measured values are evaluated directly in the production line. The raw data is integrated into image processing software and evaluated via a GigE Vision connection. The data can also be logged for subsequent statistics, evaluations or process optimization.