| 摘要 |
1,201,176. Automatic control for electron beam data recording systems. INTERNATIONAL BUSINESS MACHINES CORP. Nov.27, 1967 [Dec.21, 1966], No.53759/67. Heading G3R. The intensity of an electron beam striking the memory element 9 of a data recording system, is automatically maintained at a predetermined value by detecting the intensity at the element 9 to produce an electrical signal representative thereof, comparing this signal with a reference signal in a differential amplifier 39 and using the error signal to adjust the control current in the coil of an electromagnetic lens 15a, such adjustment altering the beam diameter at an aperture 28a to vary the number of electrons passing therethrough. As shown, a beam detector 37 is placed adjacent the element 9 and comprises a P/N junction having an impedance proportional to the intensity of the beam, which is made to intermittently strike the detector 37 as it scans across the element 9, by providing the latter with a series of opaque lines 41 perpendicular to the scanning direction and forming a series of adjacent and alternately positioned opaque and transparent portions. This produces an A.C. signal superimposed on a constant current through the detector and having a peak value proportional to the beam intensity, the combined signal being fed to a level detector 38 which produces a D.C. output signal representative of the peak value. After comparison of this output with a reference signal 46 representative of desired beam intensity, the error signal from amplifier 39 is fed to an analog storage device 48 which comprises a field effect transistor whose bias voltage is supplied by a large value capacitor charged by the error signal, so that a signal is stored until another is received from the amplifier 39. Thereafter, the signal controls the driver 49 of the coil of lens 15a to vary its magnification and hence the diameter of the beam. To prevent this change in magnification from affecting the overall functioning of the beam generating device 8, the signal from driver 49 is fed to the driver 55 of another lens 15 in such a manner that the magnification of the latter is changed in proportion but oppositely to the change in magnification of the lens 15a. The construction of the electron beam generator 8 is described, Figs.1 and 2 (not shown). Application of the invention to control a laser beam generator is envisaged. |
