Scanning apparatus.

摘要

The invention relates to a scanning device for reading and/or writing using a laser beam. A drum (243) includes a rotatable shaft (102) carrying optical elements (120) which are moved rotationally and translationally to cause a laser beam to scan sheet material lying around the surface of a cylinder coaxial with the shaft. A sheet to be scanned is placed on a flexible transport (150) while flat and then the transport is fed into the drum until a surface of the transport is in intimate contact with a location wall (243) of the drum. A bed (191) supports the flat transport outside the drum and there is a support (211,212) for supporting a transport above the bed together with positioning means (200) for the bed and support either for driving a transport on the bed into the drum or for driving a transport in the drum onto the support. The shaft (102) is rotatable in a housing (101) on air journal bearings (100) and end thrusts are balanced by air thrust bearings defined between a wall (125) of a reaction air turbine for driving the shaft, and a wall (124) of a porous plate through which air for the bearing is supplied through a controllable restriction (1232,1233).