Filter for selective speed xerographic printing in facsimile transceivers and the like

Claim 1

In a facsimile transceiver which is selectively operable in a transmit mode for scanning of subject copy and in a receive mode for printing at any one of several different rates on a xerographic photoreceptor, the combination comprising a laser for supplying a beam of substantially collimated light of a predetermined cross-sectional area, an optical path for said light beam, and a filtering means for adjustably attenuating said light beam to provide a substantially unattenuated light beam for scanning while said transceiver is operating in the transmit mode and an attenuated light beam having a power level per unit area on said photoreceptor within a predetermined range while said transceiver is operating in its receive mode, said filtering means including a rotatable member with a predetermined axis of rotation, a plurality of filter holders mounted on said member at a predetermined radial distance from said axis and at spaced angular intervals about said axis, a plurality of filter elements each having an area of substantially uniform optical density larger than the crosssectional area of said light beam, each of said filter elements having a different optical density and mounted on a respective one of said holders, one of said elements being substantially transparent, and drive means for selectively indexing said member to bring a respective one of said filter elements into alignment with said optical path for each of said printing rates when said transceiver is operating in its receive mode and said substantially transparent filter element into alignment with said optical path when said transceiver is operating in its transmit mode.