New projection system for television images

摘要

909,401. Television; light modulating. GENERAL ELECTRIC CO. Jan. 5, 1959 [Jan. 13, 1958], No. 339/59. Class 40 (3). In a television receiving system in which deformations produced in a deformable medium by electrostatic charges varying in accordance with the image signals are employed to modulate light from a local source which is then projected on to a viewing screen the deformations produced during each field scan are erased, coincidently with, or just prior to, the setting up of deformations in the next field scan by scanning the medium with an unmodulated electron beam the energy of which, relative to the average potential of the medium for the desired amplitudes of deformation, is equal to that value at which the characteristic relating beam energy and secondary emission ratio for the medium passes through unity for the second time. This point, termed the " second secondary emission cross-over potential " is shown at 49 (Fig. 2) and by arranging the potential of the unmodulated erasing electron beam 13 (Fig. 1) which scans the deformable medium 15 to be less than the required potential of the medium relative to the electrode 19, e.g. - 500 V. medium to electrode and -1900 (from curve) electron gun 11 to medium, giving - 2400 gun to electrode 19, the potential of the medium is brought to - 500 V. (undeformed value) irrespective of its initial condition since a surplus or deficiency of electrons on the medium is neutralized by the change in secondary emission ratio above and below unity due to the effective change in beam energy. With this manner of operation the resistance of the medium 15 may be high enough for the deformation to persist for a complete field period with a consequent improvement in the light efficiency of the system. Molten paraffin or white beeswax or a gelatin are suitable materials. In the embodiment of Fig. 1 the image signals are supplied to the electrode 19 from source 27 so that each point on the medium, after the passage of the beam 13, is left with a charge, relative to electrode 19, and therefore with a deformation appropriate to the image signals appertaining to that point. In a second embodiment (Figs. 3 and 4) the image deformations are produced by a modulated " point-focused " beam 57 and erasure produced by an unmodulated " line-focused," beam 53 which scans the medium 15 in the frame direction a short distance ahead of beam 53. In both embodiments the medium 15 is included in a conventional optical system 29 . . . 39 which projects the image on to a viewing screen 41. Instead of utilizing light transmitted through the deformable medium the optical system may be modified to utilize light reflected from the surface of the medium.