Patent GB-1172333-A (GB)
Title: Improvements in or relating to Data Recording Systems
IPC: G11C13/04
Filed: 1968-06-11
Abstract: 1,172,333. Digitally controlled recorders; electric digital data-storage. NATIONAL CASH REGISTER CO. 11 June, 1968 [16 June, 1967], No. 27634/68. Headings G4C and G4H. [Also in Division G2] In a data recording system a laser beam is amplitude modulated in response to signals representing data to be recorded, the beam being positioned at a point in a selected area on a record medium, the medium being such that the beam can produce an optically detectable change in it, and raster generating means for causing the beam to perform a localized scanning of repetitive lines in the said selected area so as to record data. The beam 12 from laser 10 passes through a modulator 14 able to vary its intensity. A spot formed by lens 16 is reflected by a rotating polygon mirror 18 into field lens 20. The beam then passes via lens 22 to mirror 24 and is reflected via lenses 26, 28 to a second mirror 30. After passing through lens 32 recording lens 34 directs it on to the recording medium 36. The mirrors 24 and 30 tilt under the control of motors 24a, 30a to deflect the beam horizontally and vertically to a selected one of a number of areas 80 and to a selected co-ordinate position in the area. The rotating mirror 18 produces a short vertical scan covering the height of the characters to be recorded. Movement of the mirror 24 produces a series of parallel strokes and modulator 14 passes or obstructs the beam to cause the desired letter to be formed. The apparatus may be arranged to print characters in lines like a typewriter, the mirror 24 moving the beam steadily across the medium 36 to allow characters to be formed in succession. If it is desired to generate a straight line between two points the polygon mirror is not used, the mirrors 24 and 30 are controlled to produce the required line. In this case the mirror 18 is by-passed by moving mirrors 50, 54 into the path of the beam and reflecting it from mirror 52. The recording medium may be a film which is locally deformed or a coating wnich is optically changed by the laser beam. Recorded characters are projected on to a viewing screen 68 by light from source 60 which passes through filters 62, through beam combiner 66, lens 34, through the medium 36 and lens 67 to screen 68. A stationary reference map or the like may also be projected on to the screen being introduced on a transparency 69. The mirrors 24 and 30 are moved by control systems in which the actual position of the mirror is compared with the desired position. The actual position of each mirror is determined by projecting a slit beam via the mirror on to a coded disc having eight binary tracks, each associated with a light guide and a photocell. The difference between the actual and desired position is reduced by 10%, there being about 10% overshoot to bring the mirror to the desired position. Final positioning is made on the tone difference value. The characters, Fig. 10, have coded bars 84 underneath, so that characters recorded on the medium 36 can be read out. For this purpose they are scanned by a laser beam having insufficient intensity to effect recording. Light passing through the medium is diverted by a beam splitter 86 to photo-tube 90. Suitable coatings for the recording medium are given.