Instance Matching for Ontology Population

An electron beam position control for maintaining the position of a beam of charged particles that strikes a workpiece at an impact spot includes an adjustable aperture through which X-rays emanating from the impact spot pass, a rotating cylinder having a plurality of slots formed on its outer surface, a scintillator crystal and photo multiplier located within the rotating cylinder, an electronic circuit for producing an error signal that energizes one or the other of two magnetic coils, which are effective in redirecting the electron beam so that its focal point strikes the workpiece at the target or reference position.