GB1265362A - - Google Patents

Abstract

1,265,362. Hybrid computers. MULLARD Ltd. 4 Feb., 1969, No. 5833/69. Heading G4G. In a machine in which a beam of charged particles e.g. electrons is accelerated to impinge on a workpiece for etching, welding, cutting or drilling and the beam deflection is controlled from a computer store; correction of deflectional sensitivity is necessary in response to E.H.T. voltage, working distance and focusing field variation and (Fig. 3) a reference voltage R 1 and digital co-ordinate signal L<SP>1</SP> from a control store are fed to a D/A multiplier 21 of the kind incorporating selectively switchable series potentiometric resistors (Figs. 1, 2, not shown) energized from a reference voltage to develop an output analogue signal R1.L which is scale multiplied at 24 by factor A and added at 25 to a further reference voltage R 2 representing the origin co-ordinate of the beam to produce analogue signal R 1 LA + R 2 . This is applied to a further similar D/A multiplier 27 receiving a digital signal M<SP>1</SP> compensating for E.H.T. values from the control store to produce analogue voltage of M. (A.L.R 1 + R 2 ) applicable for electron beam deflection from the R 2 determined origin. The compensating signal M<SP>1</SP> may additionally be made inversely dependent on target distance and corrected for interaction of focusing field and deflection. In a further modification (Fig. 4) a reference signal R is applied to switched potentiometer circuit 33 of a D/A multiplier 31 also receiving from control computer a binary digital deflection sensitivity compensating signal M<SP>1</SP> dependent on E.H.T. voltage and containing correction for focusing field intersection with deflection to produce analogue signal RM applied to D/A switched potentiometer multiplier 41 receiving binary digital deflection sensitivity compensating signal N<SP>1</SP> from control computer inversely proportional to workpiece distance, to produce analogue signal RMN representing deflection sensitivity compensation. This is applied to D/A multipliers 51, 61, 71, 81 receiving binary digital signals L<SP>1</SP> x , P<SP>1</SP>x<SP>,</SP> L<SP>1</SP>y<SP>,</SP> P<SP>1</SP>y' from the control computer representing X co-ordinate displacement of point of impact of beam, X coordinate of origin, Y co-ordinate displacement, and Y co-ordinate of origin which are combined over scaling units 54, 74 and adders 55, 75 to produce X and Y deflectional corrected analogue signals RMN (Px + A.Lx) and RMN (Py + A.Ly).