Vision system measures the stress in glass

Engineers at Seidenader Maschinenbau (Markt Schwaben, Germany) and Ilis (Erlangen, Germany) have developed an inspection station that measures the stress in glass containers, enabling it to identify the initial stages of crack formation.

Cracks or leaks in the glass from which pharmaceutical containers are made can affect the sterility of a packaged product. But by measuring and evaluating the stress in the glass, the inspection station can help manufacturers reduce the likelihood of breakage.

Perfect glass is optically isotropic, which means that the refractive index of the glass is the same in all directions. But mechanical stress causes deformations in the glass that leads to changes in the refractive index within the material.

Since birefringence can be quantified by the difference in refractive index within a material, it can be analyzed with a polarimeter, which determines the angle of rotation of the polarization direction of linearly polarized light as it passes through a sample.

By developing an automated imaging polarimeter, rather than using a time-consuming manual approach, the two companies have demonstrated that their inspection station can measure and evaluate mechanical stress in glass containers in real time.

When integrated into a Seidenader MS inspection machine, the system is capable of inspecting up to 24,000 glass containers per hour.

-- Dave Wilson, Senior Editor, Vision Systems Design