Glass thickness measurement

Noncontact glass thickness measurement based on the chromatic confocal measuring technique has become well established in glass manufacture as it allows glass thicknesses to be measured with µm accuracy even in difficult ambient conditions.

CHRocodile sensors from Precitec Optronic GmbH form the core of our optical glass thickness measuring systems. Together with our hardware and software, flexible, robust measuring systems have evolved that not only give precise results but are also easy to operate.

Regardless of the application this system is used for, the entire measurement and control hardware is incorporated in a robust control cabinet which is connected to the optical probes with glass fibers. Linear and rotary axes controllers are also integrated next to the sensors, together with the interfaces to the production systems.

Flat glas

Inline measurements of flat glass can be performed with stationary or traversing sensors. The high aperture of the optical probes provides reliably reproducible measurements even with structured surfaces.
Traversing measurement gives a detailed cross-section of the entire width of the glass ribbon, which is why this method is frequently used in quality control systems.
Stationary measurement records the glass thickness of fixed (critical) points, enabling roller settings to be checked and adjusted if necessary, for example. This type of measurement has the advantage that no wear parts are contained in the measuring system – with the exception of the light sources which are replaced at set intervals.

Flyer

Container glass

The high sensor measuring rate of up to 4,000 measurements per second and sensor enables inline measurements of the greatest accuracy to be made. The compact dimension of the optical probes means that they can be easily integrated into existing inspection systems. The control electronics interfaces are versatile in their configuration, making connection to a diverse range of inline controllers a simple affair.
Colored and non-round containers can also be measured with the utmost precision thanks to the large dynamic range of the sensors and the high aperture of the optical probes.

Offline measurements used in the processing of complaints, for instance, can be carried out with the help of the rotary modules attached to the axis interfaces.

Measurement at the hot end

A specially developed cooled housing enables measurements to be made at temperatures of up to 1,000°C, i.e. before passing through the lehr. This drastically reduces the adjustment time for glass thickness configuration.

Measurement principle

Thanks to the large chromatic longitudinal aberration of the optical probes, white light is focused at different distances depending on the wavelength,  i.e. the red focus is further away from the optical probe than the blue focus. Surfaces within this focal line reflect the light back into the optical probe and from here through the glass fiber into the spectrometer, where the distances to the optical probe and thus the glass thickness are determined from the reflected colors.