Patent GB-1012430-A (GB)
Title: Optical printing apparatus
IPC: B41J2/435
Filed: 1964-10-09
Abstract: 1,012,430. Photographic type-composing. INTERNATIONAL BUSINESS MACHINES CORPORATION. Oct. 9, 1964 [Oct. 21, 1963], No. 41222/64. Heading B6W. [Also in Divisions G2 and H3] Characters formed as transparent areas in an otherwise opaque plate 4, Fig. 1, and arranged in eight columns and eight rows, are selectively projected on to a light-sensitive member 7. A light beam is passed through a lens which collimates it, the collimated beam having a crosssectional area slightly larger than that of each character on the plate 4 and being in alignment with the bottom right-hand character, and then through a device which polarizes it in a horizontal plane. The beam is then passed through a first deflector 2 which displaces it vertically and horizontally into alignment with the selected character, and then through the character, the beam then having a cross-section the same as that of the character. A second deflector 5 then restores the beam to its original alignment. A third deflector 6 displaces the beam into alignment with a selected area of the member 7. For printing lines of characters, the deflector 6 produces only horizontal displacement the member 7 being displaced vertically after each line. At least the first two deflectors each comprise a vertical and a horizontal displacement unit, the vertical unit coming first in the deflector 2 and last in the deflector 5. The vertical unit of the deflector 2 comprises birefringent crystals 24, 25, 26, Fig. 5, each of which pass light through undeflected when polarized in a horizontal plane and deflect it when polarized in a vertical plane. The deflection occurs at the entry face of the crystal and is reversed at the exit face, resulting in a vertical displacement. The unit also comprises three electro-optic devices 27, 28, 29, each consisting of a central electro-optic crystal between a pair of transparent electrodes. When a sufficient electric potential is applied between the electrodes, the crystal rotates the plane of polarization of light passing through through 90 degrees. Potential is applied selectively to the devices 27, 28, 29 by closing switches 36, 37, 38, which may be mechanical switches or electronic devices responsive to coded electric pulses. The amount of displacement by each birefringent crystal is proportional to its thickness, and the thickness of the crystals 24, 25, 26 is arranged in a binary series, so that the light emerging from the unit can be on any of eight levels. The light then passes through the horizontal unit comprising crystals 46, 47, 48, the vertical and horizontal units being viewed in directions at right-angles to each other in Fig. 5. The beam then passes through the selected character in the plate 4 and through the horizontal and vertical units of the deflector 5, which are shown at the lower part of Fig. 5 as comprising respectively crystals 58, 57, 56 and 66, 65, 64. The units of the deflector 5 are viewed in Fig. 5 from the opposite direction as compared with those of the deflector 2, the light actually passing in the same general direction through all four units. In the case of the deflector 5, the light passes through the thickest crystal first in each unit and through each crystal before its associated electro-optic device. Each pair of electro-optic devices, i.e. the first (27) in the vertical unit of the deflector 2 and the last (67) in the vertical unit of the deflector 5 and so on as shown, are connected so as to be activated by a common switch 36, 37, 38, 52, 53, 54. The result of this arrangement is to restore the beam to its original alignment polarized in a horizontal plane as before. The units of the deflector 6 are the same as those described above, except that each may have more than three crystals and electro-optic devices, and that the horizontal unit may be omitted. In another form, Fig. 8 (not shown), the deflector 6 is replaced by a mirror continuously rotating about a vertical axis and co-operating with an electro-optic shutter opened at the appropriate time to project the character at the desired horizontal position on the member 7, the latter being shifted vertically after each line. In another form, Fig. 7, a beam of polarized light 81 from a source 82 is directed on to a beam splitter 83 consisting of a pair of sodium nitrate crystals 84, 85 arranged face to face and at an angle of 45 degrees to a vertical plane, and is deflected as shown as a beam polarized at 45 degrees to a vertical plane to a light rotator 87, from which it emerges polarized in a horizontal plane. Vertical and horizontal displacement units 88, 89 direct it to a selected character formed as a reflecting area on a screen 90, whereby it is reflected back through the units 89, 88 into its original alignment and through the rotator 87, which rotates its plane of polarization 45 degrees so as to be at right-angles to its original plane of polarization. The beam now passes through the beam splitter 83 without deflection to a quartz plate 92 from which it emerges polarized in a hori- ,zontal plane. The beam now passes through a lens 93 which sharpens the outline of the beam and inverts the character, vertical and horizontal displacement units 94, 96, and an inverting and magnifying lens 96 to the medium 7. In another form, Fig. 6, a light beam is produced during a lasing action by reflecting light through a negative temperature unit 72 from a fully reflecting mirror 78 and a partly reflecting mirror 73 at the ends of the unit 72. At one end of the unit 72, the optical cavity includes vertical and horizontal displacement units 76, 77, and the mirror 78 comprises reflecting areas formed in the shape of characters. Light passing through the units 76, 77 is brought into alignment with the selector character and on passing back through the units 77, 76 is restored to its original alignment, then passing as a collimated and plane polarized beam through the mirror 73 and vertical and horizontal displacement units 21, 22 to the medium 7. Specification 992,452 is referred to.