Method and apparatus for controlling an extrusion string, such as a glue string, and gluing apparatus

A nozzle (1) with a cylindrical body (3) is supplied with glue by a conduit (4) and deposits a continuous bead (6) from an orifice (5) on to a support (7). An optical head (2) travels with the nozzle and has a light source (9) and mirror (11) which projects light on to the bead. Reflected light is directed to a camera (10) by a second mirror (12). Bead height and section are continuously measured and compared to standards An Independent claim is also included for test equipment which includes an optical head with light projector and camera to take partly transverse images also processing means to measure bead height and section