GB898516A - Adjustable offset scanning device - Google Patents

Abstract

898,516. Photo-electric line followers. BRITISH OXYGEN CO. Ltd. Sept. 28, 1960 [Sept. 30, 1959], No. 33361/60. Class 40(3). The invention relates to a photo-electric scanning device for automatically following a path denoted by a line of contrasting reflection on the surface of a drawing for the purpose of controlling a machine implement, for example the torch in a flame-cutting machine, to follow a similar path on a workpiece, and is concerned with means for introducing an adjustable amount of off-set in the implement path so as to allow for such factors as the cross-section of the cutting flame whereby the contour of the finished workpiece may be made identical in size with the original drawing. In Fig. 2 a photoelectric scanning device comprising an oscillating photo-electric cell assembly 40 is moved along a line 27 on a drawing by a constant speed driving wheel 26, the wheel supports 32 being mounted for rotation about a vertical axis by a motor 34 which is controlled by information obtained from the photo-electric cell so as to steer the wheel to cause the device to follow the line. The housing 45 of the photo-electric cell assembly is also mounted for rotation about a vertical axis and is coupled to support 32 by gearing 47, 48, 49. The arrangement is such that the path of oscillation of the cell remains transverse the line or at a constant angle thereto. The scanning device is coupled mechanically to a carriage for the torch of a flame-cutter, Fig. 1 (not shown), and causes the torch to trace out a path on a workpiece similar to line 27. In the photo-electric cell assembly a lens 56 forms an image of the line and the photo-electric cell is supported so that it may be oscillated laterally of the image under the control of coils 43 energized by alternating current, for example the mains supply. The signals from the photo-electric cell are fed to an amplifier circuit 35 incorporating a synchronized gating circuit, and the signals produced by a scan of one side of the line are separated from the signals produced by a scan of the other side of the line. The two groups of signals are then subtracted from each other and any remainder employed to operate motor 34 to steer wheel 26 to centralize line 27 under lens 56. In accordance with the invention, the support 55 for lens 56 is carried by a pair of trunions 58, Fig. 3, so that the support axis may be inclined to the vertical in a direction laterally of line 27. The extent of inclination is determined by an adjustable screw stop 61 carrying a calibrated dial 61a against which the support is urged by a spring 62. Since the scanner functions to centralise line 27 under lens 56, any inclination imparted to support 55 results in the scanner being off-set from the line and a corresponding off-set being given to the flame-cutting torch.