Patent GB-470435-A (GB)
Title: Process and device for the reproduction of designs on printing plates by means of photo-electrically controlled gravers
IPC: B44B3/00
Filed: 1936-07-06
Abstract: 470,435. Copying by scanning. ALICE, F. July 6, 1936, Nos. 18752 and 18753. Convention dates, July 5, 1935 and May 30, 1936. [Class 40 (iii)] In a method of producing printing plates of the kind in which the printing surfaces are reticulated, the design to be copied is arranged upon a surface which is explored by one or more photo-sensitive devices, the currents so generated being applied to one or more electromagnetically operated gravers which are caused to explore a second surface, moved at a speed bearing a suitable relationship to the speed of the first surface, and to remove appropriate parts of a protective coating upon a printing plate arranged upon the second surface, the necessary reticulation being produced with the aid of hatching provided upon the support on which the design to be copied is traced or upon a surface which is explored separately from and simultaneously with the design to be copied. The printing plate is subsequently etched. As shown in Figs. 1 and 2, a sheet of paper bearing the design to be reproduced or a photographic film is wrapped around a roller 1 preferably of adjustable diameter and removably carried in supports 31. A lantern 27 adapted to slide on guides 39, Fig. 5, is fed in the axial direction of the roller 1 by means of a lead screw 30. The lantern contains an electric lamp 33, lens system 34, objective 35, total reflection prism 36 and an adjustable diaphragm or screen 37 through which the light passes on to a photo-electric cell 38. The roller 1 and screw 30 are rotated through gearing from a motor 22, a change-speed gear 23 allowing the rate of displacement of the lantern relative to the speed of rotation of the roller to be varied according to the requirements of the design. The roller 2 which is to be engraved is covered with an acid-proof coating and mounted on a mandrel 44 adapted to be carried by supports 3. The amplified currents from the cell 38 are fed to electromagnetic gravers 4 mounted on rulers 16 which can slide axially of the roller 2 on pivots 42 and are fixed by means of pivots 11 to a carriage 46 which is given by means of a screw 14 a motion of translation corresponding to that of the lantern, a change-speed gear 18, 20 enabling the ratio of displacement between the rulers and the lantern to be varied as desired. The roller 2 is driven from the motor 22 through a change-speed gear 21 and shaft 23<1>. In order to enable the design to be reproduced on the roller 2 at a suitable angle of inclination with respect to the axis of the roller, the rulers 16 can be given an inclination in either sense by means of screws 9 operated by cranks 8. Further screws are also provided which enable the position of the rulers to be adjusted radially with respect to the axis of the roller in order to accommodate rollers of different diameters. If desired, two or more lanterns may be arranged to explore the roller 1 so as to reproduce the design in two or more sections simultaneously. Gravers operating on separate rollers may also be actuated simultaneously and identically. The hatching may be provided on the sheet of paper bearing the design to be reproduced or, alternatively, a sheet of hatched paper may either be placed on the roller 1 separate from the design or on a separate roller. Separate lanterns then explore the hatching and the design respectively and the currents from the photo-cells are combined in such a way that the hatching is introduced automatically into the design produced by the gravers. The hatching may, in some cases, itself constitute the markings of the design, no outlines being provided. Each graver is preferably actuated by a moving coil, Fig. 6 (not shown). In the process according to the present invention, all the lines in the design are reproduced only by points with the exception of those lines which lie in the direction of relative movement of the design and exploring means. In order that these lines shall also be reproduced by points an auxiliary thermionic or mechanical oscillator, Figs. 9-11 (not shown), is provided, this oscillator being controlled by the photoelectric current in such a manner that it is started substantially exactly in correspondence either with the commencement or the cessation of the photo-electric current according to whether the design is to be reproduced in a direct or inverse manner. The Specification as open to inspection under Sect. 91 comprises also particular arrangements of the photo-electric cell. According to one arrangement, the cell, which receives light reflected from the design, is disposed between the design and the source of light with the sensitive part towards the design. The plate of the cell is formed with a perforation through which the beam of light passes in order to be reflected by the design on to the sensitive part of the cell. According to another arrangement in which the design is traced on a transparent film adapted to be wrapped around a transparent roller, the cell is disposed inside the roller. This subject-matter does not appear in the Specification as accepted.