GB1278122A - Method of controlling the electromagnetically-driven engraving element of an engraving machine - Google Patents

Abstract

1278122 Engraving WERKSPOOR-AMSTERDAM NV 11 March 1969 [26 March 1968] 12831/69 Heading H4F The depth of penetration of an electromagnetically driven engraving element into the engraving material is determined by generating an alternating current and also a direct current and controlling the electromagnetic driving system therewith, the amplitude of the alternating current and the magnitude of the direct current both being determined in dependence on the measured grey value of an original which is being copied. Preferably the sum of the magnitude of the D.C. and the amplitude of the A.C. is constant as the grey value varies and is such that the driving system is substantially saturated. Thus in Fig. 1, the mechanical zero position of the element at rest is at 2, below the surface 1 of the engraving material. For a black tone, the current is mainly A.C. and the element moves about line 2 in a sine curve 3, while for a white tone the current is mainly D.C. and the element follows line 6. For a grey tone a sine curve 4 about a line 5 is followed. The maximum amplitude of the A.C. gives a displacement substantially equal to the distance between line 2 and surface 1. Preferably the frequency of the A.C. is greater than the resonant frequency f 0 of the engraving element, and equal to where # is the damping factor of the vibrating system. Since there is a 180 degree phase difference between the A.C. and the displacement of the engraving element when operated above resonance, current pulses are supplied at required times to provide the required discontinuity in current e.g. when going from black to white and vice versa, Fig. 4 (not shown).