Autofocus module for multilaser print heads

Polaroid's Optical Engineering Department has developed an autofocus module designed for use with Polaroid's multi-laser print head. The print head and focus module are now being manufactured and sold as part of a high-quality laser printer for 14' X 17' medical diagnostic images. The focus module is mated and aligned to a cylinder that is clamped into a V on the print head to utilize the semi-kinematic methodology of the print head. The printer clamps the film onto an external drum that is spun at 3300 RPM. While being spun, the profile of the film is 350 μm peak to valley. The print head's focus tolerance is ± 5μm, which is a consequence of using binary film, laser diodes, and the required gray scale. A moving objective lens that tracks the film based on real-time focus information is needed. Polaroid has developed a new focus sensor and assembly process that is economical, reliable and simple. The new sensor can be assembled in 15 minutes and replaces a more complicated design.