Engraving apparatus and method

#This invention relates to the engraving of cylinders commonly used in the gravure printing process, and specifically to engraving apparatus of the general type disclosed, for example, in U.S. Pat. No. 2,881,246, U.S. Pat. No. 2,874,479, U.S. Pat. No. 3,964,382 and U.S. Pat. No. 4,013,829. The basic principle of electro-mechanical engraving of a gravure cylinder involves rotating a copper plated cylinder while actuating an electrically driven tool which cuts or engraves cells or lines into the copper surface. The engraved cylinder is normally used in a web type gravure printing press for printing paper, plastic, or metallic film material.

#In the gravure printing process, the engraved cylinder is flooded with ink, and a doctor blade wipes off excess ink from the surface so that only the engraved cells contain ink which is transferred to the material being printed. To obtain a high quality print, it is necessary that the cells be very accurately placed or located on the cylinder surface, usually within one to two microns of the desired theoretical location. The depth of the engraved cells must also be accurately controlled since the depth determines the amount of ink transferred which, in turn, determines the shade of gray in a black-white print. In a color print, the amount of ink transferred to the paper or material is even more critical since three colors are mixed to produce various shades of all possible colors. A slight variation in the desired amount of ink effects not only the darkness of the color but, more importantly, the production of the desired color tone.

#In addition to printing newspapers and magazines, the engraved cylinders may also be used for direct or indirect printing of cloth, applying glue, printing of packaging materials for products, and printing of wood grain patterns for making of wall paneling, floor coverings and other surface coverings.

#FIG. 1 is a perspective view of an electro-mechanical engraving head constructed in accordance with the invention and illustrating its engraving position relative to a cylinder positioned to be engraved;

#FIG. 2 is an elevational view of the front face of the engraving head and showing a portion is section to illustrate internal assembly;

#FIG. 3 is a fragmentary section taken generally on the line 3--3 and showing a portion of the electro-magnetic drive system within the printing head;

#FIG. 1 shows an engraving head 20 constructed in accordance with the invention and in position for engraving a gravure printing cylinder 22 having a copper coating forming an outer surface 23. The engraving head 20 preferably includes a cast metal housing 26 which rigidly supports opposite end portions 27 and 28 (FIG. 2) of a shaft 30. The shaft 30 includes an intermediate portion 32 which is integrally connected to the end portions 27 and 28 by torsional spring portions 33 of reduced diameter. The intermediate shaft portion 32 extends through a tubular sleeve 36, and an intermediate liner of resilient material 38, such as silicone rubber, is bonded to the intermediate shaft portion 32 and the sleeve 36 for supporting the shaft 32 to avoid any lateral movement or vibration.

#A notch 41 is formed within the shaft portion 32 and supports an actuator arm 42 which is rigidly secured to the shaft portion 32 by a set of screws. A cylindrical transverse hole 43 (FIG. 5) is formed within the actuator arm 42, and an elongated rod-like holder 44 is disposed within the hole 43. A cutting stylus 45, preferably formed of diamond, is cemented into one end of the holder 44 which has a flat surface 47. The surface 47 is engaged by a screw 49 which is threaded into a hole 51 extending outwardly from the shaft 32 through the actuator arm 42 and intersecting the hole 43. As shown in FIG. 6, the diamond stylus 45 includes angularly related flat surfaces 53 which cooperate with a bottom flat surface to form V-shaped cutting edges 56. The actuator arm 42 has a hole 57 which aids in reducing the mass of the arm and in obtaining a desired air flow across the stylus for removing chips.

#Referring to FIGS. 2 and 3, an armature 58 is rigidly secured to the shaft 32 and projects outwardly between a pair of opposing electro-magnets 61 which are mounted within the base portion of the housing 26 and cooperate with the armature 58 to define air gaps 63. When the magnets 61 are energized by an alternating current, the intermediate shaft portion 32 and actuator arm 42 oscillate through a maximum arc of approximately 0.25 degree and at a frequency preferably between 3,000 and 5,000 cycles per second. This oscillation results in vibrating or moving the cutting stylus 45 by a maximum distance of about 100 microns.