Foreign matter analysis and inspection in preform production

Need

A preform is thick and clear; a small black speck inside the wall is hidden from some angles by refraction and reflection. The preform sways and turns on the rail; a short shot shows only as a few millimetres of difference at the body tip.

Solution approach

The backlight turns the preform into a silhouette against a uniform bright field; an opaque speck inside the body appears as a dark blob from any direction and wall reflections are suppressed. A long focal-length lens reduces perspective error; the photo-sensor trigger catches every preform at the same position. Dark regions are counted and sized; body length is taken from neck ring to tip.

Process steps

1. 01

   Infeed

   Preforms travel on the air conveyor hanging from their neck rings; the photo-sensor detects the passage.

2. 02

   Acquire

   The backlight strobes and a silhouette image of the clear body is captured.

3. 03

   Analyse

   Dark regions in the body are counted and sized; the body length is taken from the tip.

4. 04

   Decide

   Speck count, speck size and body length are compared with their limits.