Abstract: A method of patterning a perforated screen printing screen (9) having a lacquer coating filling its perforations (10), using a laser engraving device, includes the steps of locating the position of the locus of aligned perforations (10), aligning an engraving head (7) of the laser engraving device with the locus of the perforations (10) and then selectively actuating the laser to remove the lacquer individually from those perforations (10) which it is required to unblock.

Abstract: A laser engraving machine for engraving rotary printing screens includes a shaft (1) having one end connected to a rotary drive (3)for rotating the shaft (1), two end ring assemblies (7, 8) at least one (8) of which is movable along the shaft (1) and which are arranged to locate concentrically and fix opposite ends of a rotary printing screen (2) to the shaft (1). The machine also includes a laser engraving device including a head (4) movable backwards and forwards parallel to the axis of rotation of the shaft (1) to engrave a printing screen (2) and a support (9, 13). The support (9, 13) is movable along the screen (2) with the laser engraving head (4) to provide local support for the screen (2) so that the part being engraved is supported at a constant predetermined position with respect to the head (4) of the laser engraving device.

Abstract: A method of, and apparatus for, determining the position of an unknown fixed location, e.g. the end of an underground passage inaccessible to human beings, involves establishing a chain of measuring station of known station spacing between a base and a position at the unknown fixed location. Each station (except, optionally, the foremost one) of the chain is provided with light sources and photodetectors as well as a goniometer for measuring in at least one plane the angle of inclination of the station immediately ahead of it. The stations of the chain are spaced apart by a known distance and arranged so that each station is within the operative range of the immediately preceding station. By transmitting the measurement results from each station to the base, and processing the data, the position of the fixed location from the measurement results.

Abstract: A copying process for producing a seamless copy from an unjointed original mounted on a carrier cylinder utilizes electronic control circuitry to "stretch" the copy of the artwork to exactly 360.degree. on a printing cylinder, to produce matched endless joints. The circumferential length of the original is first determined and then the original is scanned by a "read" scanner, the output of which is digitized and temporarily stored in memory. The contents of the memory are used to modulate a power laser during scanning to "write" on the printing cylinder but readout from the memory is adjusted in accordance with the circumferential length determined to produce the required jointing. The system may be varied to produce flexographic rollers, gravure cylinders or general copying.

Abstract: A copying system has an artwork carrier cylinder and a printing cylinder, and electronic control means "stretches" the copy to exactly 360.degree. on the printing cylinder, to produce matched endless joints. The circumferential length of the original is first determined and then the original is scanned by a "read" scanner, the output of which is digitized and temporarily stored in memory. The contents of the memory are used to modulate a power laser during scanning to "write" on the printing cylinder but readout from the memory is adjusted in accordance with the circumferential length determined to produce the required jointing. The system may be varied to produce flexographic rollers, gravure cylinders or general copying.