Laser-mark accuracy test on drinking glasses (bubble method)

Need

The laser mark is a frosted sub-millimetre spot inside the glass and hard to image directly. The bubble column sways in the liquid and the conical glass wall refracts the view; the column axis can only be located reliably from many bubbles at once.

Solution approach

A pallet-presence sensor starts the fill; once the glasses are full they are imaged side-on in one frame against a backlight, and the bubbles separate as dark blobs on the bright background. The symmetry axis is derived from the glass edges and the column axis from the bubble blobs; the offset between the two axes and the bubble count give the verdict.

Process steps

1. 01

   Fill

   The pallet sensor detects the glasses and the nozzles fill them with carbonated test liquid.

2. 02

   Bubbles

   The laser mark acts as a nucleation site; a bubble column rises to the surface.

3. 03

   Acquire

   The backlight strobes and both glasses are captured side-on in one frame.

4. 04

   Measure

   The bubble-column axis is located and its offset from the glass axis is measured.

5. 05

   Decide

   Offset and bubble count are compared with the limits; a glass outside tolerance is moved to the reject container by the gripper.