Automatic position detecting system - using position markers on moving tape, light source, photodetector and two optical fibres

摘要

The positioning system provides lateral guidance and longitudinal positioning for a tape as it unwinds. A light beam (from eg a xenon lamp) is projected onto the tape and reflected to a photodetector that responds to changes in intensity produced by markers on the tape. Two optical fibres (6,7) connect the light source (3) and the photodetector (4) to a shared point (9) facing the tape (2). The shared point has a lens (5) that focusses the light onto the tape. The photodetector has a resistance that changes with light intensity. An optical filter (8) is located in front of the photodetector. A screen (10) is situated between the light source and the photodetector.