Improvements relating to beamed energy control systems

1, 111, 865. Photo-electric machine control systems. FERRANTI Ltd. Nov. 21, 1966 [Aug. 28, 1965; Oct. 14, 1965], Nos. 37102/65 and 43545/65. Heading G1A. [Also in Divisions B3 and G3] The point of impact of an electron, ion or laser beam on a workpiece in beam cutting or welding apparatus is controlled by a servosystem which maintains the image of the light spot produced by the beam on the workpiece centred upon a photoelectric cell. Means are provided to vary the position of the image on the cell in response to a demand signal whereby the beam is moved in accordance with the demand signal. The light spot is imaged by mirrors 55, 56 on to the photocell system 21 which gives X and Y signals on leads 23, 24 indicative of orthogonal deviations of the image from a reference point on the photocell sensitive surface. The photo-cell system is mounted on a carriage 20, the position of which is indicated by X and Y pick-off signals on leads 33 and 34. The X signals and the Y signals are combined and control the X and Y deflection coils 17, 18 for the beam. The demand signal is arranged to move the carriage, and the signals applied to the deflection coils 17, 18, make the beam 13 follow the movements. If the image of the light spot is not in the sensitive area of the cell system, the summed X and Y signal on lead 25 is below a predetermined level and the unit 41 connects a scan generator 42 to the deflection coils 17, 18 to scan the beam until the image is in the sensitive area. Alternatively, Fig. 2 (not shown) the scan signal may be applied to the carriage 20, in which case, the pick off signals are disconnected from the scanning coils 17, 18. The carriage may be fixed and the demand signal applied to a mirror in the optical system between the workpiece and the photo-cell, Fig. 3 (not shown). Photo-cell circuitry. The photo-cell system 21 may be a four sided reflecting pyramid with pairs of photo-cells differentially connected and viewing opposite faces of the pyramid. Preferably, however, it may comprise a single photo-cell of the type in which an electron image of the spot may be oscillated across an aperture 71, Fig. 4, by coils 73, 74. Circuits produce, under control. of a clock generator 75, alternate positive and negative going triangular waveforms with the result that the electron image makes excursions across the aperture in the +X; -Y; -X; +Y directions in sequence. The pulses generated as the image moves out to the edge of the aperture in each of these d