NON-CONTACT, OPTICAL SENSOR FOR SYNCHRONIZING TO FREE ROTATING SAMPLE PLATENS WITH ASYMMETRY

摘要

A method and apparatus for determining the synchronicity of a rotary platen (22) in a vacuum deposition chamber (24). A light source (64) projects a highly collimated light beam (66) onto the rotating platen (22), thereby tracing a circular swept path (67). The swept path (67) passes alternately through samples (20) on the platen (22) and intervening webs (58, 60). The samples (20) are significantly more reflective than the webs (58, 60). The platen (22) includes an asymmetry feature (60) along the swept path (67). A detector (62) measures light signals reflected from the platen (22) along the swept path (67), and generates a unique signal upon encountering the asymmetry feature (60). A microcontroller generates a trigger pulse synchronized to the unique signal.