GB1418119A - Apparatus for recording with a light beam - Google Patents

Abstract

1418119 Electric selective signalling G S B STREET 30 Nov 1973 [30 Nov 1972] 55704/73 Addition to 1324241 Heading G1J [Also in Division G4] The invention is a modification of the information recording system of Specification 1324241. Fig. 3 shows schematically a modified version of the mirror control circuit of Fig. 2 of Specification 1324241. X, Y position signals for a pair of steering mirrors are fed to binary rate multipliers 300, 301 and compared at 304-307 with feedback position pulse signals from interference fringe counters, the resulting difference signals being converted to analog form at 308, 309 for use as mirror drive signals see Fig. 1 of Specification 1324241. The outputs from 308, 309 are also fed via summing amplifiers 311, 313 and gates 312, 314 to a fine control circuit for the light beam. The pulse-train outputs from 300, 301 are fed directly to an intensity control circuit Fig. 2 (not shown), where they are used to generate bright-up pulses for application to a light-modulator at intervals corresponding to the completion of equal steps of movement across the recording medium. Means (149-155) are provided for varying the amplitude and length of the bright-up pulses to control the density of the trace on the recording medium and to compensate for changes in light source intensity. Means 320-334 are provided for changing the scale and/or orientation of the recorded signals by converting the outputs, X, Y from 300, 301 to the form a X+bY, cX+dY respectively. A diaphragm with a circular aperture is located in the path of the light beam. During non- recording periods, gates 316, 317 connect an oscillator to the fine control circuit to cause the beam to execute a circular movement of diameter greater than that of the aperture.